G2Cdb::Gene report

Gene id
Gene symbol
Homo sapiens
casein kinase 2, alpha 1 polypeptide
G00000878 (Mus musculus)

Databases (8)

Curated Gene
OTTHUMG00000031636 (Vega human gene)
ENSG00000101266 (Ensembl human gene)
1457 (Entrez Gene)
502 (G2Cdb plasticity & disease)
CSNK2A1 (GeneCards)
115440 (OMIM)
Marker Symbol
HGNC:2457 (HGNC)
Protein Sequence
P68400 (UniProt)

Literature (370)

Pubmed - other

  • Casein-kinase-II-dependent phosphorylation of PPARgamma provokes CRM1-mediated shuttling of PPARgamma from the nucleus to the cytosol.

    von Knethen A, Tzieply N, Jennewein C and Brüne B

    Institute of Biochemistry I-Pathobiochemistry, Faculty of Medicine, Goethe-University Frankfurt, 60590 Frankfurt, Theodor-Stern-Kai 7, Germany. v_knethen@zbc.kgu.de

    PPARgamma exerts significant anti-inflammatory signaling properties in monocytes and macrophages, which are affected by its intracellular localization. Based on our previous report, which showed that cytosolic localization of PPARgamma attenuates PKCalpha signaling in macrophages, we elucidated the molecular mechanisms provoking cytosolic PPARgamma localization. Using the DsRed-tagged PPARgamma deletion constructs PPARgamma1 Delta1-31 and PPARgamma1 Delta407-475, we observed an exclusive nuclear PPARgamma1 Delta1-31 localization in transfected HEK293 cells, whereas PPARgamma1 Delta407-475 did not alter its cytosolic or nuclear localization. The casein kinase II (CK-II) inhibitor 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB) prevented cytosolic PPARgamma localization. Mutation of two possible CK-II phosphorylation sites at serine 16 and serine 21 of PPARgamma into alanine (PPARgamma S16A/S21A) inhibited cytosolic PPARgamma localization. Moreover, a PPARgamma S16E/S21E mutant that mimicks constitutive phosphorylation of residues 16 and 21, predominantly resides in the cytosol. The CRM1 inhibitor leptomycin B abolished cytosolic PPARgamma localization, suggesting that this is a CRM1-dependent export process. CRM1-mediated PPARgamma export requires Ran and phosphorylated RanBP3. Finally, co-immunoprecipitation studies demonstrated that DRB blocks PPARgamma binding to CRM1, whereas PD98059 inhibits RanBP3 binding to CRM1 and concomitant shuttling from nucleus to cytosol, but does not alter PPARgamma binding to CRM1. We conclude that CK-II-dependent PPARgamma phosphorylation at Ser16 and Ser21 is necessary for CRM1/Ran/RanBP3-mediated nucleocytoplasmic translocation of PPARgamma.

    Journal of cell science 2010;123;Pt 2;192-201

  • Differential regulation of mitogen- and stress-activated protein kinase-1 and -2 (MSK1 and MSK2) by CK2 following UV radiation.

    Jacks KA and Koch CA

    Ontario Cancer Institute, Princess Margaret Hospital (University Health Network), Toronto, Ontario M5G2M9, Canada.

    Mitogen- and stress-activated protein kinases, MSK1 and the closely related isoform MSK2, are nuclear kinases that are activated following mitogen stimulation or cellular stress, including UV radiation, by the ERK1/2 and p38 MAPK signaling cascades, respectively. However, factors that differentially regulate MSK1 and MSK2 have not been well characterized. Here we report that the CK2 protein kinase, which contributes to NF-kappaB activation following UV radiation in a p38-dependent manner, physically interacts with MSK2 but not MSK1 and that CK2 inhibition specifically impairs UV-induced MSK2 kinase activation. A putative site of CK2 phosphorylation was mapped to MSK2 residue Ser(324) and when substituted to alanine (S324A) also compromised MSK2 activity. RNA interference-mediated depletion of MSK2 in human MDA-MB-231 cells, but not MSK1 depletion, resulted in impaired UV-induced phosphorylation of NF-kappaB p65 at Ser(276) in vivo, which was restored by the ectopic expression of MSK2 but not by MSK2-S324A. Furthermore, UV radiation led to the activation of NF-kappaB-responsive gene expression in MDA-MB-231 cells and induced p65 transactivation capacity that was dependent on MSK2, MSK2 residue Ser(324), and p65-Ser(276). These results suggest that MSK1 and MSK2 are differentially regulated by CK2 during the UV response and that MSK2 is the major protein kinase responsible for the UV-induced phosphorylation of p65 at Ser(276) that positively regulates NF-kappaB activity in MDA-MB-231 cells.

    The Journal of biological chemistry 2010;285;3;1661-70

  • Phosphorylation of serine 205 by the protein kinase CK2 persists on Pax3-FOXO1, but not Pax3, throughout early myogenic differentiation.

    Dietz KN, Miller PJ and Hollenbach AD

    Department of Genetics, Louisiana State University Health Sciences Center, 533 Bolivar Street, New Orleans, Louisiana 70112, USA.

    The myogenic transcription factor Pax3 plays an essential role in early skeletal muscle development and is a key component in alveolar rhabdomyosarcoma (ARMS), a childhood solid muscle tumor. ARMS is characterized by a t(2;13) chromosomal translocation resulting in the fusion of the 5' Pax3 sequences to the 3' FOXO1 sequences to encode the oncogenic fusion protein, Pax3-FOXO1. Posttranslational modifications such as phosphorylation are common mechanisms by which transcription factors are regulated. Consistent with this fact, we demonstrated in a previous report that Pax3 is phosphorylated on Ser205 in proliferating, but not differentiated, primary myoblasts. However, the kinase that mediates this phosphorylation event has yet to be identified. In addition, it is not known whether Pax3-FOXO1 is phosphorylated at this site or how the phosphorylation of the fusion protein changes during early myogenic differentiation. In this report we identify CK2 (formerly termed "casein kinase II") as the kinase responsible for phosphorylating Pax3 and Pax3-FOXO1 at Ser205 in proliferating mouse primary myoblasts. Furthermore, we demonstrate that, in contrast to wild-type Pax3, phosphorylation at Ser205 persists on Pax3-FOXO1 throughout early myogenic differentiation. Finally, we show that Pax3-FOXO1 is phosphorylated at Ser205 in a variety of translocation-containing ARMS cell lines. The results presented in this report not only suggest a possible mechanism by which the disregulation of Pax3-FOXO1 may contribute to tumorigenesis but also identify a novel target for the development of therapies for the treatment of ARMS.

    Funded by: NCI NIH HHS: 1R01CA138656, R01 CA138656, R01 CA138656-01A1; NCRR NIH HHS: 1P20RR020152, P20 RR020152, P20 RR020152-066702

    Biochemistry 2009;48;49;11786-95

  • EGF-induced ERK activation promotes CK2-mediated disassociation of alpha-Catenin from beta-Catenin and transactivation of beta-Catenin.

    Ji H, Wang J, Nika H, Hawke D, Keezer S, Ge Q, Fang B, Fang X, Fang D, Litchfield DW, Aldape K and Lu Z

    Brain Tumor Center and Department of Neuro-Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, 77030, USA.

    Increased transcriptional activity of beta-catenin resulting from Wnt/Wingless-dependent or -independent signaling has been detected in many types of human cancer, but the underlying mechanism of Wnt-independent regulation remains unclear. We demonstrate here that EGFR activation results in disruption of the complex of beta-catenin and alpha-catenin, thereby abrogating the inhibitory effect of alpha-catenin on beta-catenin transactivation via CK2alpha-dependent phosphorylation of alpha-catenin at S641. ERK2, which is activated by EGFR signaling, directly binds to CK2alpha via the ERK2 docking groove and phosphorylates CK2alpha primarily at T360/S362, subsequently enhancing CK2alpha activity toward alpha-catenin phosphorylation. In addition, levels of alpha-catenin S641 phosphorylation correlate with levels of ERK1/2 activity in human glioblastoma specimens and with grades of glioma malignancy. This EGFR-ERK-CK2-mediated phosphorylation of alpha-catenin promotes beta-catenin transactivation and tumor cell invasion. These findings highlight the importance of the crosstalk between EGFR and Wnt pathways in tumor development.

    Funded by: NCI NIH HHS: 5R01CA109035, R01 CA109035, R01 CA109035-05

    Molecular cell 2009;36;4;547-59

  • Association study of 21 circadian genes with bipolar I disorder, schizoaffective disorder, and schizophrenia.

    Mansour HA, Talkowski ME, Wood J, Chowdari KV, McClain L, Prasad K, Montrose D, Fagiolini A, Friedman ES, Allen MH, Bowden CL, Calabrese J, El-Mallakh RS, Escamilla M, Faraone SV, Fossey MD, Gyulai L, Loftis JM, Hauser P, Ketter TA, Marangell LB, Miklowitz DJ, Nierenberg AA, Patel J, Sachs GS, Sklar P, Smoller JW, Laird N, Keshavan M, Thase ME, Axelson D, Birmaher B, Lewis D, Monk T, Frank E, Kupfer DJ, Devlin B and Nimgaonkar VL

    Department of Psychiatry, University of Pittsburgh School of Medicine, Western Psychiatric Institute and Clinic, Pittsburgh, PA 15213, USA.

    Objective: Published studies suggest associations between circadian gene polymorphisms and bipolar I disorder (BPI), as well as schizoaffective disorder (SZA) and schizophrenia (SZ). The results are plausible, based on prior studies of circadian abnormalities. As replications have not been attempted uniformly, we evaluated representative, common polymorphisms in all three disorders.

    Methods: We assayed 276 publicly available 'tag' single nucleotide polymorphisms (SNPs) at 21 circadian genes among 523 patients with BPI, 527 patients with SZ/SZA, and 477 screened adult controls. Detected associations were evaluated in relation to two published genome-wide association studies (GWAS).

    Results: Using gene-based tests, suggestive associations were noted between EGR3 and BPI (p = 0.017), and between NPAS2 and SZ/SZA (p = 0.034). Three SNPs were associated with both sets of disorders (NPAS2: rs13025524 and rs11123857; RORB: rs10491929; p < 0.05). None of the associations remained significant following corrections for multiple comparisons. Approximately 15% of the analyzed SNPs overlapped with an independent study that conducted GWAS for BPI; suggestive overlap between the GWAS analyses and ours was noted at ARNTL.

    Conclusions: Several suggestive, novel associations were detected with circadian genes and BPI and SZ/SZA, but the present analyses do not support associations with common polymorphisms that confer risk with odds ratios greater than 1.5. Additional analyses using adequately powered samples are warranted to further evaluate these results.

    Funded by: NCATS NIH HHS: UL1 TR000005; NCRR NIH HHS: M01 RR000056, M01 RR00056, UL1 RR024153; NIMH NIH HHS: K23 MH072995, MH30915, MH45156, MH56242, MH63420, P20 MH-66054, P20 MH066054, P30 MH030915, P50 MH045156, R01 MH056242, R01 MH060952, R01 MH063420, R01MH060952-06, R10 MH056242

    Bipolar disorders 2009;11;7;701-10

  • Enhancing the apoptotic potential of insulin-like growth factor-binding protein-3 in prostate cancer by modulation of CK2 phosphorylation.

    Cobb LJ, Mehta H and Cohen P

    Division of Pediatric Endocrinology, Mattel Children's Hospital at University of California, Los Angeles, California, USA.

    IGF-binding protein 3 (IGFBP-3) promotes apoptosis by both IGF-dependent and -independent mechanisms. We have previously reported that phosphorylation of IGFBP-3 (S156) by DNA-dependent protein kinase enhances its nuclear accumulation and is essential for its ability to interact with retinoid X receptor-alpha and induce apoptosis in cultured prostate cancer cells. Using specific chemical inhibitors and small interfering RNA, we demonstrate that preventing casein kinase 2 (CK2) activation enhanced the apoptotic potential of IGFBP-3. We mapped potential CK2 phosphosphorylation sites in IGFBP-3 to S167 and S175 and identified that wild-type IGFBP-3- and IGFBP-3-S175A-induced apoptosis to a comparable extent. In contrast, IGFBP-3-S167A was far more potently apoptosis inducing due to inability to undergo CK2 phosphorylation. Pretreatment of 22RV1 cells with IGFBP-3 small interfering RNA also limits the ability of high doses of CK2 inhibitor to induce apoptosis. These effects can be reversed by the addition of exogenous IGFBP-3 protein, suggesting reciprocal regulation of cell survival and apoptosis by IGFBP-3 and CK2. These studies reveal multisite phosphorylation of IGFBP-3 that both positively and negatively regulate its apoptotic potential. Understanding such intrinsic regulation of IGFBP-3 action may enhance the development of potential cancer therapies.

    Funded by: NCI NIH HHS: P50 CA092131, P50CA92131

    Molecular endocrinology (Baltimore, Md.) 2009;23;10;1624-33

  • Programmed cell death protein 5 (PDCD5) is phosphorylated by CK2 in vitro and in 293T cells.

    Salvi M, Xu D, Chen Y, Cabrelle A, Sarno S and Pinna LA

    Department of Biological Chemistry, University of Padova, Viale G. Colombo 3, Padua, Italy. mauro.salvi@unipd.it

    CK2 is a multifunctional kinase, involved in cell growth, apoptosis, DNA integrity preservation, viral infection, and many other biological processes. Based on an analysis of phosphopeptides database derived from phosphoproteomic studies we previously identified a list of potential new CK2 substrates, including, among others, Programmed Cell Death 5 (PDCD5), a protein involved in cell death and down-regulated in different forms of human tumors. Here we provide experimental evidence that PDCD5 is indeed a bona fide substrate of CK2. PDCD5 is phosphorylated in vitro by both CK2alpha subunit and by the CK2 holoenzyme at a residue, S118, which is found phosphorylated in vivo. We also show that PDCD5 is phosphorylated by CK2 in 293T cells. Transfection of the non-phosphorylatable mutant (S118A) impairs the PDCD5 acceleration of either doxorubimicin- or UV-induced apoptosis in U2OS cells. Our results suggest a functional link between the CK2 phosphorylation and the apoptotic potential of PDCD5.

    Biochemical and biophysical research communications 2009;387;3;606-10

  • CK2-dependent phosphorylation determines cellular localization and stability of ataxin-3.

    Mueller T, Breuer P, Schmitt I, Walter J, Evert BO and Wüllner U

    Department of Neurology, Friedrich-Wilhelms-University Bonn, UKB, 53105 Bonn, Germany.

    The nuclear presence of the expanded disease proteins is of critical importance for the pathogeneses of polyglutamine diseases. Here we show that protein casein kinase 2 (CK2)-dependent phosphorylation controls the nuclear localization, aggregation and stability of ataxin-3 (ATXN3), the disease protein in spinocerebellar ataxia type 3 (SCA3). Serine 340 and 352 within the third ubiquitin-interacting motif of ATXN3 were particularly important for nuclear localization of normal and expanded ATXN3 and mutation of these sites robustly reduced the formation of nuclear inclusions; a putative nuclear leader sequence was not required. ATXN3 associated with CK2alpha and pharmacological inhibition of CK2 decreased nuclear ATXN3 levels and the formation of nuclear inclusions. Moreover, we found that ATXN3 shifted to the nucleus upon thermal stress in a CK2-dependent manner, indicating a key role of CK2-mediated phosphorylation of ATXN3 in SCA3 pathophysiology.

    Human molecular genetics 2009;18;17;3334-43

  • Extracellular protein kinase CK2 is a novel associating protein of neuropilin-1.

    Shintani Y, Takashima S, Kato H, Komamura K and Kitakaze M

    Department of Cardiovascular Medicine, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.

    Neuropilin-1 (NRP1) is a multifunctional transmembrane protein which has a short cytoplasmic region with no particular functional domain, and is considered to act as a co-receptor for both VEGFs and semaphorins. However, the molecular mechanisms by which NRP1 carries out such versatile functions are still poorly understood. Here we identified protein kinase CK2 holoenzyme as a novel NRP1 binding protein by our combined purification strategy using epitope-tag immunoprecipitation followed by reverse-phase column chromatography. Further we showed that CK2 binds to the extracellular domain of NRP1 which is also phosphorylated by CK2 both in vitro and in vivo. Our findings of novel molecular interactions and modification of NRP1 may provide a new clue to understand the diverse functions of NRP1.

    Biochemical and biophysical research communications 2009;385;4;618-23

  • Localization of X-ray cross complementing gene 1 protein in the nuclear matrix is controlled by casein kinase II-dependent phosphorylation in response to oxidative damage.

    Kubota Y, Takanami T, Higashitani A and Horiuchi S

    Department of Biochemistry, School of Medicine, Iwate Medical University, 19-1 Morioka, Iwate 020-8505, Japan. yoshikok@iwate-med.ac.jp

    Base excision repair/single strand break repair (BER/SSBR) of damaged DNA is a highly efficient process. X-ray cross complementing protein 1 (XRCC1) functions as a key scaffold protein for BER/SSBR factors. Recent work has shown that XRCC1 forms dense foci at sites of DNA damage in a manner dependent on casein kinase II (CK2) phosphorylation. To investigate the mechanism underlying foci formation, we analyzed the subnuclear localization and phosphorylation status of XRCC1 during the repair process by biochemical fractionation of HeLa cellular proteins. The localization was also verified by in situ extraction of the fixed cells. In unchallenged cells, XRCC1 was primarily found in the chromatin fraction in a highly phosphorylated form; in addition, a minor population (10-15%) existed in the nuclear matrix (NM) with no or marginal phosphorylation. After hydrogen peroxide treatment, hyperphosphorylated XRCC1 appeared in the NM and accordingly, those in the chromatin fraction decreased. Foci formation and changes in XRCC1 distribution could be abolished by the knockdown of CK2, the expression of a non-phosphorylatable version of XRCC1, or the inhibition of poly-ADP ribosylation at the damage sites. Other BER factors, like DNA polymerase beta, were also found to accumulate in the NM after hydrogen peroxide-induced DNA damage, although its association with the NM seemed relatively weak. Our results suggest that the constitutive phosphorylation of XRCC1 in the chromatin and its DNA damage-induced recruitment to the NM are critical for foci formation, and that the core reactions of BER/SSBR may occur in the NM.

    DNA repair 2009;8;8;953-60

  • [Effect of protein kinase CK2 gene silencing on radiosensitization in human nasopharyngeal carcinoma cells].

    Liu L, Zou JJ, Luo HS and Wu DH

    Department of Health Management, Nanfang Hospital, Southern Medical University, Guangzhou 510515, China. liuli@fimmu.com

    Objective: To investigate the effect of protein kinase CK2 gene silencing on the radiosensitization in human nasopharyngeal carcinoma (NPC) cells and its possible mechanism.

    Methods: RNA interference (RNAi) technique was used to down-regulate the protein kinase CK2alpha expression in 5-8F cells, and clonogenic assay was employed to observe the changes in the radiosensitivity of the cells. DNA double-strand break was assessed by immunofluorescence staining of gamma-H2AX foci, and the cell apoptosis was examined using Annexin V-FITC/PI double-staining flow cytometry.

    Results: CK2alpha protein was successfully silenced by siRNA. CK2alpha knockdown significantly decreased the clonogenic activity and increased the radiosensitivity of the NPC cells. After a 15-min exposure of the cells to 1 Gy radiation, significant difference occurred in the gamma-H2AX foci between CK2alpha knockdown cells and the control cells (P<0.01). CK2alpha silencing significantly increased the cell apoptosis after the exposure (P<0.01).

    Conclusions: Protein kinase CK2 plays an important role in the radiosensitivity of the NPC cells, and suppression of its expression might be a potential therapeutic approach of cancer.

    Nan fang yi ke da xue xue bao = Journal of Southern Medical University 2009;29;8;1551-3

  • Involvement of reactive oxygen species in apoptosis induced by pharmacological inhibition of protein kinase CK2.

    Hanif IM, Ahmad KA, Ahmed K and Pervaiz S

    National University of Singapore Graduate School for Integrative Sciences and Engineering, Singapore.

    It has been reported that inhibition of protein kinase CK2 (CK2) with antisense oligodeoxynucleotides (ODN) is a potent inducer of apoptosis in cancer cells but not in normal cells. In this regard, the apoptotic-inducing effect is attributed to the catalytic activity of the enzyme, which phosphorylates proapoptotic proteins to inhibit their functions. In this study we investigate the role of intracellular redox status in the proapoptotic activity of CK2 inhibition in human leukemia Cem cells. We provide evidence that inhibition of CK2 activity induces apoptotic cell death as evident by activation of caspase 3, DNA fragmentation, and phosphatidylserine externalization. Inhibition of CK2 resulted in a significant increase in intracellular hydrogen peroxide production, which we show as a critical mediator of apoptosis. To that end, apoptotic hallmarks, like DNA fragmentation and phosphatidylserine externalization, were blocked with the specific hydrogen peroxide scavenger catalase. We also show that inhibition of CK2 reduces cytosolic intracellular superoxide, a precursor of hydrogen peroxide. In summary, decreasing CK2 activity increases intracellular hydrogen peroxide, creating an intracellular environment conducive for death execution. Taken together, these data provide information on novel pathways involved in CK2 biology with implications for effective tools against drug-resistant tumors.

    Funded by: BLRD VA: I01 BX001731; NCI NIH HHS: CA-15062, R01 CA015062, U01 CA015062

    Annals of the New York Academy of Sciences 2009;1171;591-9

  • Defining the human deubiquitinating enzyme interaction landscape.

    Sowa ME, Bennett EJ, Gygi SP and Harper JW

    Department of Pathology, Harvard Medical School, Boston, MA 02115, USA.

    Deubiquitinating enzymes (Dubs) function to remove covalently attached ubiquitin from proteins, thereby controlling substrate activity and/or abundance. For most Dubs, their functions, targets, and regulation are poorly understood. To systematically investigate Dub function, we initiated a global proteomic analysis of Dubs and their associated protein complexes. This was accomplished through the development of a software platform called CompPASS, which uses unbiased metrics to assign confidence measurements to interactions from parallel nonreciprocal proteomic data sets. We identified 774 candidate interacting proteins associated with 75 Dubs. Using Gene Ontology, interactome topology classification, subcellular localization, and functional studies, we link Dubs to diverse processes, including protein turnover, transcription, RNA processing, DNA damage, and endoplasmic reticulum-associated degradation. This work provides the first glimpse into the Dub interaction landscape, places previously unstudied Dubs within putative biological pathways, and identifies previously unknown interactions and protein complexes involved in this increasingly important arm of the ubiquitin-proteasome pathway.

    Funded by: NIA NIH HHS: AG085011, R01 AG011085, R01 AG011085-16; NIDDK NIH HHS: K01 DK098285; NIGMS NIH HHS: GM054137, GM67945, R01 GM054137, R01 GM054137-14, R01 GM067945

    Cell 2009;138;2;389-403

  • Sgt1 dimerization is negatively regulated by protein kinase CK2-mediated phosphorylation at Ser361.

    Bansal PK, Mishra A, High AA, Abdulle R and Kitagawa K

    Department of Molecular Pharmacology, Hartwell Center for Bioinformatics and Biotechnology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105-3678, USA.

    The kinetochore, which consists of centromere DNA and structural proteins, is essential for proper chromosome segregation in eukaryotes. In budding yeast, Sgt1 and Hsp90 are required for the binding of Skp1 to Ctf13 (a component of the core kinetochore complex CBF3) and therefore for the assembly of CBF3. We have previously shown that Sgt1 dimerization is important for this kinetochore assembly mechanism. In this study, we report that protein kinase CK2 phosphorylates Ser(361) on Sgt1, and this phosphorylation inhibits Sgt1 dimerization.

    Funded by: NCI NIH HHS: CA21765, P30 CA021765; NIGMS NIH HHS: GM68418, R01 GM068418

    The Journal of biological chemistry 2009;284;28;18692-8

  • Ikaros stability and pericentromeric localization are regulated by protein phosphatase 1.

    Popescu M, Gurel Z, Ronni T, Song C, Hung KY, Payne KJ and Dovat S

    Department of Pediatrics, University of Wisconsin, Madison, Wisconsin 53792-4108, USA.

    Ikaros encodes a zinc finger protein that is involved in gene regulation and chromatin remodeling. The majority of Ikaros localizes at pericentromeric heterochromatin (PC-HC) where it regulates expression of target genes. Ikaros function is controlled by posttranslational modification. Phosphorylation of Ikaros by CK2 kinase determines its ability to bind DNA and exert cell cycle control as well as its subcellular localization. We report that Ikaros interacts with protein phosphatase 1 (PP1) via a conserved PP1 binding motif, RVXF, in the C-terminal end of the Ikaros protein. Point mutations of the RVXF motif abolish Ikaros-PP1 interaction and result in decreased DNA binding, an inability to localize to PC-HC, and rapid degradation of the Ikaros protein. The introduction of alanine mutations at CK2-phosphorylated residues increases the half-life of the PP1-nonbinding Ikaros mutant. This suggests that dephosphorylation of these sites by PP1 stabilizes the Ikaros protein and prevents its degradation. In the nucleus, Ikaros forms complexes with ubiquitin, providing evidence that Ikaros degradation involves the ubiquitin/proteasome pathway. In vivo, Ikaros can target PP1 to the nucleus, and a fraction of PP1 colocalizes with Ikaros at PC-HC. These data suggest a novel function for the Ikaros protein; that is, the targeting of PP1 to PC-HC and other chromatin structures. We propose a model whereby the function of Ikaros is controlled by the CK2 and PP1 pathways and that a balance between these two signal transduction pathways is essential for normal cellular function and for the prevention of malignant transformation.

    Funded by: NCI NIH HHS: K12 CA 087718, K12 CA087718, K22 CA 111392; NCRR NIH HHS: 1UL1RR025011; NHLBI NIH HHS: T32 HL07899; NIDDK NIH HHS: 5K01 DK066163

    The Journal of biological chemistry 2009;284;20;13869-80

  • Prefrontal cortex shotgun proteome analysis reveals altered calcium homeostasis and immune system imbalance in schizophrenia.

    Martins-de-Souza D, Gattaz WF, Schmitt A, Rewerts C, Maccarrone G, Dias-Neto E and Turck CW

    Laboratório de Neurociências, Instituto de Psiquiatria, Universidade de São Paulo, Rua. Dr. Ovidio Pires de Campos, no 785, Consolação, São Paulo, SP 05403-010, Brazil.

    Schizophrenia is a complex disease, likely to be caused by a combination of serial alterations in a number of genes and environmental factors. The dorsolateral prefrontal cortex (Brodmann's Area 46) is involved in schizophrenia and executes high-level functions such as working memory, differentiation of conflicting thoughts, determination of right and wrong concepts and attitudes, correct social behavior and personality expression. Global proteomic analysis of post-mortem dorsolateral prefrontal cortex samples from schizophrenia patients and non-schizophrenic individuals was performed using stable isotope labeling and shotgun proteomics. The analysis resulted in the identification of 1,261 proteins, 84 of which showed statistically significant differential expression, reinforcing previous data supporting the involvement of the immune system, calcium homeostasis, cytoskeleton assembly, and energy metabolism in schizophrenia. In addition a number of new potential markers were found that may contribute to the understanding of the pathogenesis of this complex disease.

    European archives of psychiatry and clinical neuroscience 2009;259;3;151-63

  • First inactive conformation of CK2 alpha, the catalytic subunit of protein kinase CK2.

    Raaf J, Issinger OG and Niefind K

    Universität zu Köln, Institut für Biochemie, Zülpicher Str. 47, D-50674 Köln, Germany.

    The Ser/Thr kinase casein kinase 2 (CK2) is a heterotetrameric enzyme composed of two catalytic chains (CK2alpha, catalytic subunit of CK2) attached to a dimer of two noncatalytic subunits (CK2beta, noncatalytic subunit of CK2). CK2alpha belongs to the superfamily of eukaryotic protein kinases (EPKs). To function as regulatory key components, EPKs normally exist in inactive ground states and are activated only upon specific signals. Typically, this activation is accompanied by large conformational changes in helix alpha C and in the activation segment, leading to a characteristic arrangement of catalytic key elements. For CK2alpha, however, no strict physiological control of activity is known. Accordingly, CK2alpha was found so far exclusively in the characteristic conformation of active EPKs, which is, in this case, additionally stabilized by a unique intramolecular contact between the N-terminal segment on one side, and helix alpha C and the activation segment on the other side. We report here the structure of a C-terminally truncated variant of human CK2alpha in which the enzyme adopts a decidedly inactive conformation for the first time. In this CK2alpha structure, those regulatory key regions still are in their active positions. Yet the glycine-rich ATP-binding loop, which is normally part of the canonical anti-parallel beta-sheet, has collapsed into the ATP-binding site so that ATP is excluded from binding; specifically, the side chain of Arg47 occupies the ribose region of the ATP site and Tyr50, the space required by the triphospho moiety. We discuss some factors that may support or disfavor this inactive conformation, among them coordination of small molecules at a remote cavity at the CK2alpha/CK2beta interaction region and binding of a CK2beta dimer. The latter stabilizes the glycine-rich loop in the extended active conformation known from the majority of CK2alpha structures. Thus, the novel inactive conformation for the first time provides a structural basis for the stimulatory impact of CK2beta on CK2alpha.

    Journal of molecular biology 2009;386;5;1212-21

  • Silencing of the CKII alpha and CKII alpha' genes during cellular senescence is mediated by DNA methylation.

    Kim EK, Kang JY, Rho YH, Kim YS, Kim DS and Bae YS

    Department of Biochemistry, College of Natural Sciences, Kyungpook National University Daegu 702-701, Republic of Korea.

    Previously we reported that down-regulation of CKII activity is tightly associated with cellular senescence and that the mRNA and protein levels of CKII alpha decrease during senescence. The present study demonstrates that the mRNA and protein levels of CKII alpha' also decrease during senescence. Knockdown of CKII alpha' in IMR-90 cells by RNA interference induced the senescent phenotype. Treatment of senescent IMR-90 cells with a demethylating agent 5-aza-2'-deoxycytidine induced CKII alpha and CKII alpha' expression, suggesting that DNA hypermethylation might be involved in the silencing of CKII alpha and CKII alpha' genes in senescent cells. However, bisulfite sequencing analysis revealed that the methylation status of the CpG islands within the reported CKII alpha and CKII alpha' promoters was not associated with senescence. Instead, senescence-dependent hypermethylation was observed in the region ranging from position +1112 to +1128 of the CKII alpha gene and at positions -527 and +829 of the CKII alpha' gene. In addition, this study indicates that DNA methylation-dependent down-regulation of transcription factors Sp1, Ets1 and NF-kappaB might be involved in silencing of the CKII alpha and CKII alpha' genes during cellular senescence.

    Gene 2009;431;1-2;55-60

  • KIF5C: a new binding partner for protein kinase CK2 with a preference for the CK2alpha' subunit.

    Schäfer B, Götz C, Dudek J, Hessenauer A, Matti U and Montenarh M

    Medizinische Biochemie und Molekularbiologie, Universität des Saarlandes, Gebäude 44, 66424, Homburg, Germany.

    Protein kinase CK2 is a highly conserved serine/threonine kinase that is ubiquitously expressed in eukaryotic cells. CK2 is a constitutively active tetrameric enzyme composed of two catalytic alpha and/or alpha'-subunits and two regulatory beta-subunits. There is increasing evidence that the individual subunits may have independent functions and that they are asymmetrically distributed inside the cell. To gain a better understanding of the functions of the individual subunits, we employed a yeast-two-hybrid screen with CK2alpha and CK2alpha'. We identified the motor neuron protein KIF5C as a new binding partner for CK2. The interaction found in the yeast-two-hybrid screen was confirmed by co-sedimentation analysis on a sucrose density gradient and by co-immunoprecipitation analysis. Pull-down experiments and surface plasmon resonance spectrometry revealed a direct binding of KIF5C to CK2alpha'. Co-localization studies with neuroblastoma cells, bone marrow and with primary neurons confirmed the biochemical analysis that KIF5C preferentially bound to CK2alpha'.

    Cellular and molecular life sciences : CMLS 2009;66;2;339-49

  • The interaction of CK2alpha and CK2beta, the subunits of protein kinase CK2, requires CK2beta in a preformed conformation and is enthalpically driven.

    Raaf J, Brunstein E, Issinger OG and Niefind K

    Universität zu Köln, Department für Chemie, Institut fü r Biochemie, D-50674 Köln, Germany.

    The protein kinase CK2 (former name: "casein kinase 2") predominantly occurs as a heterotetrameric holoenzyme composed of two catalytic chains (CK2alpha) and two noncatalytic subunits (CK2beta). The CK2beta subunits form a stable dimer to which the CK2alpha monomers are attached independently. In contrast to the cyclins in the case of the cyclin-dependent kinases CK2beta is no on-switch of CK2alpha; rather the formation of the CK2 holoenzyme is accompanied with an overall change of the enzyme's profile including a modulation of the substrate specificity, an increase of the thermostability, and an allocation of docking sites for membranes and other proteins. In this study we used C-terminal deletion variants of human CK2alpha and CK2beta that were enzymologically fully competent and in particular able to form a heterotetrameric holoenzyme. With differential scanning calorimetry (DSC) we confirmed the strong thermostabilization effect of CK2alpha on CK2beta with an upshift of the CK2alpha melting temperature of more than 9 degrees . Using isothermal titration calorimetry (ITC) we measured a dissociation constant of 12.6 nM. This high affinity between CK2alpha and CK2beta is mainly caused by enthalpic rather than entropic contributions. Finally, we determined a crystal structure of the CK2beta construct to 2.8 A resolution and revealed by structural comparisons with the CK2 holoenzyme structure that the CK2beta conformation is largely conserved upon association with CK2alpha, whereas the latter undergoes significant structural adaptations of its backbone.

    Protein science : a publication of the Protein Society 2008;17;12;2180-6

  • Characterization of the InsP6-dependent interaction between CK2 and Nopp140.

    Lee WK, Lee SY, Kim WI, Rho YH, Bae YS, Lee C, Kim IY and Yu YG

    Division of Life Sciences, Korea Institute of Science and Technology, 39-1, Hawolgok-dong, Songbuk-gu, 136-791, Seoul, Republic of Korea.

    Nopp140, a highly phosphorylated nucleolar protein, negatively regulates CK2, a kinase essential for cell proliferation. We quantitatively analyzed the interaction between two subunits of CK2 and Nopp140 and characterized the mechanism by which InsP(6) inhibits the interaction. Nopp140 specifically binds to the catalytic subunit of CK2 (CK2alpha) with a dissociation constant of (K(d)) of 4nM, which interferes with the catalytic activity of CK2. The C-terminal region of Nopp140 is determined as CK2alpha-binding region by a yeast two-hybrid method as well as a direct measurement of the interaction between CK2alpha and deletion mutants of Nopp140. InsP(6) specifically binds to CK2alpha and disrupts the interaction between CK2alpha and Nopp140 with an IC(50) value of 25 microM, thereby attenuating the Nopp140-mediated repression of CK2 activity.

    Biochemical and biophysical research communications 2008;376;2;439-44

  • Protein kinase CK2 catalyzes tyrosine phosphorylation in mammalian cells.

    Vilk G, Weber JE, Turowec JP, Duncan JS, Wu C, Derksen DR, Zien P, Sarno S, Donella-Deana A, Lajoie G, Pinna LA, Li SS and Litchfield DW

    Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada N6A 5C1.

    Protein kinase CK2 exhibits oncogenic activity in mice and is over-expressed in a number of tumors or leukemic cells. On the basis of its amino acid sequence and a wealth of experimental information, CK2 has traditionally been classified as a protein serine/threonine kinase. In contrast to this traditional view of CK2, recent evidence has shown that CK2 can also phosphorylate tyrosine residues under some circumstances in vitro and in yeast. In this study, we provide definitive evidence demonstrating that CK2 also exhibits tyrosine kinase activity in mammalian cells. Tyrosine phosphorylation of CK2 in cells and in CK2 immunoprecipitates is dependent on CK2 activity and is inhibited by the CK2 selective inhibitor 4,5,6,7-tetrabromobenzotriazole. Examination of phosphotyrosine profiles in cells reveals a number of proteins, including CK2 itself, which exhibit increased tyrosine phosphorylation when CK2 levels are increased. Peptide arrays to evaluate the specificity determinants for tyrosine phosphorylation by CK2 reveal that its specificity for tyrosine phosphorylation is distinct from its specificity for serine/threonine phosphorylation. Of particular note is the requirement for an aspartic acid immediately C-terminal to the phosphorylatable tyrosine residue. Collectively, these data provide conclusive evidence that CK2 catalyzes the phosphorylation of tyrosine residues in mammalian cells, a finding that adds a new level of complexity to the challenge of elucidating its cellular functions. Furthermore, these results raise the possibility that increased CK2 levels that frequently accompany transformation may contribute to the increased tyrosine phosphorylation that occurs in transformed cells.

    Cellular signalling 2008;20;11;1942-51

  • The kinesin I family member KIF5C is a novel substrate for protein kinase CK2.

    Schäfer B, Götz C and Montenarh M

    Medizinische Biochemie und Molekularbiologie, Universität des Saarlandes, Gebäude 44, 66424 Homburg, Germany.

    Protein kinase CK2 is ubiquitously expressed. The holoenzyme is composed of two catalytic alpha- or alpha'-subunits and two regulatory beta-subunits but evidence is accumulating that the subunits can function independently. The composition of the holoenzyme as well as the expression of the individual subunits varies in different tissues, with high expression of CK2alpha' in testis and brain. CK2 phosphorylates a number of different substrates which are implicated in basal cellular processes such as proliferation and survival of cells. Here, we report a new substrate, KIF5C, which is a member of the kinesin 1 family of motor neuron proteins. Phosphorylation of KIF5C was demonstrated in vitro and in vivo. Using deletion mutants, a peptide library, and mutation analysis a phosphorylation site for CK2 was mapped to amino acid 338 which is located in the non-motor domain of KIF5C. Interestingly, KIF5C is phosphorylated by holoenzymes composed of CK2alpha/CK2beta and CK2alpha'/CK2beta as well as by CK2alpha' alone but not by CK2alpha alone.

    Biochemical and biophysical research communications 2008;375;2;179-83

  • Regulation of CD163 associated casein kinase II activity is haptoglobin genotype dependent.

    Strauss M and Levy AP

    Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa, Israel.

    Free hemoglobin is now recognized as a major mediator of a variety of vascular diseases. The abundant serum protein haptoglobin irreversibly binds to hemoglobin and promotes the uptake of hemoglobin via the macrophage CD163 receptor. The haptoglobin gene is polymorphic in man with two common alleles denoted 1 and 2. The haptoglobin genotype specifies the nature of the response of the macrophage to free hemoglobin. Hp 1-Hb complexes stimulate an anti-inflammatory macrophage phenotype while Hp 2-Hb complexes do not. We have previously demonstrated that Hp 1-Hb induced anti-inflammatory cytokine production is critically dependent on casein kinase II. In this study we set out to determine whether the amount or the activity of casein kinase II associated with CD163 was altered by the binding of Hp 1-1-Hb to CD163. Our results indicate that casein kinase II activity is increased by the binding of Hp 1-1-Hb to CD163.

    Molecular and cellular biochemistry 2008;317;1-2;131-5

  • The emerging CK2 interactome: insights into the regulation and functions of CK2.

    Gyenis L and Litchfield DW

    Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, Canada, N6A 5C1.

    Protein kinase CK2 represents a small family of protein serine/threonine kinases implicated in a variety of biological processes including events relating to cell proliferation and survival. Notably, CK2 displays oncogenic activity in mice and exhibits altered expression in several types of cancer. Accordingly, a detailed understanding of the cellular functions of CK2 and elucidation of the mechanisms by which CK2 is regulated in cells is expected to contribute to understanding its role in tumorigenesis with the prospect of novel approaches to therapy. While CK2 has traditionally been viewed as a tetrameric complex composed of two catalytic and two regulatory subunits, mounting evidence suggests that its subunits may have functions independent of tetrameric CK2 complexes. In mammals, as is the case in the budding yeast Saccharomyces cerevisiae, there are two isozymic forms of CK2, adding additional heterogeneity to the CK2 family. Studies in yeast and in human cells demonstrate that the different forms of CK2 interact with a large number of cellular proteins. To reveal new insights regarding the regulation and functions of different forms of CK2, we have examined the emerging interactomes for each of the CK2 subunits. Analysis of these interactomes for both yeast and human CK2 reinforces the view that this family of enzymes participates in a broad spectrum of cellular events. Furthermore, while there is considerable overlap between the interactomes of the individual CK2 subunits, notable differences in each of the individual interactomes provides additional evidence for functional specialization for the individual forms of CK2.

    Molecular and cellular biochemistry 2008;316;1-2;5-14

  • Casein kinase 2 binds to the C terminus of Na+/H+ exchanger 3 (NHE3) and stimulates NHE3 basal activity by phosphorylating a separate site in NHE3.

    Sarker R, Grønborg M, Cha B, Mohan S, Chen Y, Pandey A, Litchfield D, Donowitz M and Li X

    Division of Gastroenterology and Hepatology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.

    Na(+)/H(+) exchanger 3 (NHE3) is the epithelial-brush border isoform responsible for most intestinal and renal Na(+) absorption. Its activity is both up- and down-regulated under normal physiological conditions, and it is inhibited in most diarrheal diseases. NHE3 is phosphorylated under basal conditions and Ser/Thr phosphatase inhibitors stimulate basal exchange activity; however, the kinases involved are unknown. To identify kinases that regulate NHE3 under basal conditions, NHE3 was immunoprecipitated; LC-MS/MS of trypsinized NHE3 identified a novel phosphorylation site at S(719) of the C terminus, which was predicted to be a casein kinase 2 (CK2) phosphorylation site. This was confirmed by an in vitro kinase assay. The NHE3-S719A mutant but not NHE3-S719D had reduced NHE3 activity due to less plasma membrane NHE3. This was due to reduced exocytosis plus decreased plasma membrane delivery of newly synthesized NHE3. Also, NHE3 activity was inhibited by the CK2 inhibitor 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole DMAT when wild-type NHE3 was expressed in fibroblasts and Caco-2 cells, but the NHE3-S(719) mutant was fully resistant to DMAT. CK2 bound to the NHE3 C-terminal domain, between amino acids 590 and 667, a site different from the site it phosphorylates. CK2 binds to the NHE3 C terminus and stimulates basal NHE3 activity by phosphorylating a separate single site on the NHE3 C terminus (S(719)), which affects NHE3 trafficking.

    Funded by: NCRR NIH HHS: U54RR020839; NIDDK NIH HHS: K01-DK62264, P01-DK072084, R01-DK26523, R01-DK61765, R24-DK64388

    Molecular biology of the cell 2008;19;9;3859-70

  • Cell cycle and activation of CK2.

    Homma MK and Homma Y

    Department of Biomolecular Science, Fukushima Medical University School of Medicine, 1-Hikari-gaoka, Fukushima, 960-1295, Japan. mkhomma@fmu.ac.jp

    Casein kinase 2 (CK2) is a highly conserved and ubiquitous eukaryotic Ser/Thr protein kinase. Genetic, biochemical, and cell biological studies have indicated the involvement of this enzyme in the control of cell proliferation and in signal transduction. The regulation of CK2 is not well defined, and it has been considered a constitutively non-regulated protein kinase. However, we show that CK2 activation occurred during the progression of cell cycle in response to FBS stimuli of G0 arrested cells. Importantly, we show that as the downstream target for CK2, the phosphorylation of eukaryotic translation-initiation factor eIF5 by CK2 may play a critical role in cell cycle progression. We find that eIF5 is associated with CK2 when the kinase activity is at the highest level in vivo, and is phosphorylated at Ser389 and Ser390 by CK2. Expression of eIF5 mutants that lack those phosphorylation sites reveals that these mutants have a dominant-negative effect on phosphorylation of endogenous eIF5, as well as a significant reduction in the formation of the mature complex, in the growth rate, and the expression of cell cycle-regulated proteins. Also, a pool of CK2 translocates into the nuclear fraction following its activation during the progression of the cell cycle. Consistent with these findings, we report that CK2 may be involved in the regulation of cell cycle progression through the phosphorylation of a key molecule for translation initiation and of nuclear substrates upon activation of CK2 by itself.

    Molecular and cellular biochemistry 2008;316;1-2;49-55

  • CK2 mediates phosphorylation and ubiquitin-mediated degradation of the PML tumor suppressor.

    Scaglioni PP, Yung TM, Choi S, Choi SC, Baldini C, Konstantinidou G and Pandolfi PP

    Division of Hematology-Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390-8852, USA. pier.scaglioni@utsouthwestern.edu

    The PML tumor suppressor controls growth suppression, induction of apoptosis, and cellular senescence. PML loss occurs frequently in hematopoietic and solid tumors. PML loss often correlates with tumor progression. Casein kinase 2 (CK2) is a stress-activated serine/threonine protein kinase that is oncogenic and frequently overexpressed in human tumor of multiple histological origins. In addition, CK2 overexpression due to gene amplification has been reported to be an adverse prognostic factor in non-small cell lung cancer. At the 5th International Conference on Protein Kinase CK2 in Padova, Italy, we reviewed our recent findings that PML undergoes ubiquitin/proteasome-mediated degradation in immortalized and tumor derived cell lines. PML degradation depends on direct CK2 phosphorylation of PML Ser517. PML mutants that are resistant to CK2 phosphorylation display increased tumor suppressive functions in assays measuring apoptosis, replicative senescence, and in xenograft models. More significantly, CK2 pharmacological inhibition enhances PML tumor suppressive property. These data identify a key post-translational mechanism that controls PML protein levels in cancer cells and suggest that CK2 inhibitors may be beneficial anti-cancer drugs.

    Funded by: NCI NIH HHS: K08 CA112325, R01 CA71692

    Molecular and cellular biochemistry 2008;316;1-2;149-54

  • Comparative analysis of CK2 expression and function in tumor cell lines displaying sensitivity vs. resistance to chemical induced apoptosis.

    Di Maira G, Brustolon F, Tosoni K, Belli S, Krämer SD, Pinna LA and Ruzzene M

    Department of Biological Chemistry and CNR Neuroscience Institute, University of Padova, Viale G. Colombo, 3, 35121, Padova, Italy.

    CK2 is a pleiotropic protein kinase, which phosphorylates many substrates and has a global role in promoting cell survival and preventing apoptosis. In this study, we investigated its involvement in the phenomenon of the drug resistance, by which tumor cells frequently become unresponsive to chemical apoptosis. By comparing the expression of CK2 subunits in four different pairs of sensitive (S) and resistant (R) cancer cell lines, we found that in three cases the resistant phenotype is accompanied by the overexpression of the CK2 catalytic alpha subunit, either alone or in combination with the regulatory beta subunit. The degree of CK2 expression correlates with the CK2 catalytic activity, when measured toward endogenous protein substrates. All the tested R cell lines, including the one with no CK2 overexpression, can be induced to undergo death by treatment with CK2 inhibitors. We therefore conclude that, although CK2 overexpression is not an absolute requirement for the resistant phenotype, its activity is essential for cell survival and contributes to a high degree of resistance. We also found that CK2 inhibition increases the accumulation of cytotoxic drugs inside the R cells, presumably by impairing the functionality of the extrusion pump P-gp. We therefore propose that CK2 should be considered a target to counteract the pharmaco-resistant phenotype.

    Molecular and cellular biochemistry 2008;316;1-2;155-61

  • Evaluating CK2 activity with the antibody specific for the CK2-phosphorylated form of a kinase-targeting cochaperone Cdc37.

    Miyata Y and Nishida E

    Department of Cell and Developmental Biology, Graduate School of Biostudies, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan. ymiyata@lif.kyoto-u.ac.jp

    CK2-dependent phosphorylation of a kinase-specific Hsp90 co-chaperone Cdc37 on a conserved serine residue (Ser13) is essential for the function of Cdc37 [Bandhakavi S. et al. J. Biol. Chem. 278:2829-2836, 2003; Shao J. et al. J. Biol. Chem. 278:38117-38220, 2003; Miyata Y., & Nishida E. Mol. Cell. Biol. 24:4065-4074, 2004]. We have recently produced an anti-[pSer13]-Cdc37 antibody which specifically recognizes Cdc37 that is phosphorylated on Ser 13 [Miyata Y. & Nishida E. FEBS J. 274:5690-5703, 2007]. Here we investigated CK2 activity both in vitro and in cultured cells by using anti-[pSer13]-Cdc37 antibody. Immunoblotting with this antibody showed that heparin and 4,5,6,7-tetrabromobenzotriazole (TBB), known CK2 inhibitors, inhibited in vitro phosphorylation of Cdc37 on Ser13 by CK2 holoenzyme or CK2alpha, confirming the specificity of the antibody to detect CK2 activity. Treatment of cells with TBB resulted in the decrease in the phosphorylation level of endogenous Cdc37 on Ser13, as revealed by anti-[pSer13]-Cdc37, and overexpression of either CK2alpha or CK2beta subunit enhanced the Cdc37 phosphorylation level. While CK2 is suggested to be involved in cell proliferation, mitogenic stimulation of starved cells by fresh serum or insulin-like growth factor-I did not enhance phosphorylation of Cdc37 on Ser13. CK2 inhibitors are known to induce cell apoptosis, suggesting a reverse correlation between cell apoptosis and CK2 activity. However, cellular apoptotic stresses, such as anisomycin treatment and UV irradiation, were found to rather modestly increase phosphorylation of Cdc37 on Ser13. These results show that the anti-[pSer13]-Cdc37 antibody can be a promising new tool to evaluate in vivo CK2 activity.

    Molecular and cellular biochemistry 2008;316;1-2;127-34

  • Examination of transcript amounts and activity of protein kinase CK2 in muscle lysates of different types of human muscle pathologies.

    Heuss D, Klascinski J, Schubert SW, Moriabadi T, Lochmüller H and Hashemolhosseini S

    Neurologische Klinik, Universität Erlangen-Nürnberg, Schwabachanlage 6, 91054, Erlangen, Germany.

    Motoneurons release the heparansulfate proteoglycan agrin and thereby activate the muscle-specific receptor tyrosine kinase (MuSK), which is the main organizer of subsynaptic specializations at the neuromuscular junction. Recently, we showed that (1) the protein kinase CK2 interacts with the intracellular region of MuSK; (2) the CK2 protein is enriched and co-localized with MuSK at postsynaptic specializations; (3) CK2-mediated phosphorylation of serine residues within a specific MuSK epitope, named the kinase insert, regulates acetylcholine receptor (AChR) clustering; (4) muscle-specific CK2beta knockout mice develop a myasthenic phenotype due to impaired muscle endplate structure and function (see Genes Dev 20(13):1800-1816, 2006). Here, we investigated for the first time if CK2 is modulated in biopsies from human patients. To this end, we measured transcript amounts of the subunits CK2alpha and CK2beta and determined holoenzyme CK2 activity in 34 muscle biopsies of human patients with different muscle pathologies.

    Molecular and cellular biochemistry 2008;316;1-2;135-40

  • Impact of protein kinase CK2 on inhibitor of apoptosis proteins in prostate cancer cells.

    Wang G, Ahmad KA, Harris NH and Ahmed K

    Cellular and Molecular Biochemistry Research Laboratory (151), Minneapolis Veterans Affairs Medical Center, University of Minnesota, One Veterans Drive, Minneapolis, MN 55417, USA.

    We have previously demonstrated that protein kinase CK2 is a potent suppressor of apoptosis in cells subjected to diverse mediators of apoptosis. The process of apoptosis involves a complex series of molecules localized in various cellular compartments. Among the various proteins that modulate apoptotic activity are inhibitors of apoptosis proteins (IAPs) which are elevated in cancers and have been proposed to block caspase activity. We have examined the impact of CK2 signal on these proteins in prostate cancer cells. Cellular IAPs demonstrate distinct localization and responsiveness to altered CK2 expression or activity in the cytoplasmic and nuclear matrix fractions. Modulation of cellular CK2 by various approaches impacts on cellular IAPs such that inhibition or downregulation of CK2 results in reduction in these proteins. Further, IAPs are also reduced when cells are treated with sub-optimal concentrations of chemical inhibitors of CK2 combined with low or sub-optimal levels of apoptosis-inducing agents (such as etoposide) suggesting that downregulation of CK2 sensitizes cells to induction of apoptosis which may be related to attenuation of IAPs. Decreased IAP protein levels in response to apoptotic agents such as TNFalpha or TRAIL were potently blocked upon forced overexpression of CK2 in cells. Together, our results suggest that one of the modes of CK2-mediated modulation of apoptotic activity is via its impact on cellular IAPs.

    Funded by: NCI NIH HHS: CA-15062

    Molecular and cellular biochemistry 2008;316;1-2;91-7

  • Insights from soft X-rays: the chlorine and sulfur sub-structures of a CK2alpha/DRB complex.

    Raaf J, Issinger OG and Niefind K

    Universität zu Köln, Institut für Biochemie, Zülpicher Strasse 47, 50674, Köln, Germany.

    The diffraction pattern of a protein crystal is normally a product of the interference of electromagnetic waves scattered by electrons of the crystalline sample. The diffraction pattern undergoes systematic changes in case additionally X-ray absorption occurs, meaning if the wavelength of the primary X-ray beam is relatively close to the absorption edge of selected elements of the sample. The resulting effects are summarized as "anomalous dispersion" and can be always observed with "soft" X-rays (wavelength around 2 A) since they match the absorption edges of sulfur and chlorine. A particularly useful application of this phenomenon is the experimental detection of the sub-structures of the anomalous scatterers in protein crystals. We demonstrate this here with a crystal of a C-terminally truncated variant of human CK2alpha to which two molecules of the inhibitor 5,6-dichloro-1-beta-D-ribo-furanosyl-benzimidazole (DRB) are bound. The structure of this co-crystal has been solved recently. For this study we measured an additional diffraction data set at a wavelength of 2 A which showed strong anomalous dispersion effects. On the basis of these effects we detected all sulfur atoms of the protein, the two liganded DRB molecules and a total of 16 additional chloride ions some of them emerging at positions filled with water molecules in previous structure determinations. A number of chloride ions are bound to structural and functional important locations fitting to the constitutive activity and the acidophilic substrate specificity of the enzyme.

    Molecular and cellular biochemistry 2008;316;1-2;15-23

  • [PrP protein can bind to protein kinase CK2 both in native and recombinant forms in vitro].

    Chen JM, Gao C, Shi Q, Gao YJ, Lei YJ, Shan B, Dong CF, Wang GR, Shi S, Han J and Dong XP

    State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing 100052, China.

    To explore the possible molecular interaction between CK2 and PrP, the full length sequences of human CK2alpha and CK2beta genes were amplified with RT-PCR using the mRNA from cell line SH-SY5Y as the template, and then the fusion proteins HIS-CK2alpha and GST-HIS-CK2beta were expressed in E. coli. The interaction between CK2 and PrP was evaluated with immunoprecipitation and pull-down assays. The results demonstrated that recombinant PrP bound specifically with CK2alpha, but not with CK2beta. The native CK2 and PrP in the hamster brains interacted each other, forming protein complexes. The domain responsible for interacting with CK2alpha was located at the C-terminal segment of PrP (residues 90-231). This study proposed reliable experimental data for the molecular interaction between PrP and CK2alpha, both in recombinant and native categories. These results supply scientific clues for further assessing the potential biological significance of the interaction of PrP with CK2 and possible role of CK2 in the pathogenesis of prion diseases.

    Bing du xue bao = Chinese journal of virology / [bian ji, Bing du xue bao bian ji wei yuan hui] 2008;24;5;335-9

  • Transcription factor TAFII250 phosphorylates the acidic domain of Mdm2 through recruitment of protein kinase CK2.

    Allende-Vega N, McKenzie L and Meek D

    Biomedical Research Centre, Ninewells Hospital, University of Dundee, Level 5, Dundee, DD1 9SY, UK.

    Induction and activation of the p53 tumour suppressor protein occurs in response to a number of cellular stresses, including disruption of RNA polymerase II-mediated transcription. Both p53 itself and its principle negative regulator, the E3 ubiquitin ligase Mdm2, are substrates for phosphorylation by the protein kinase CK2 in vitro. CK2 phosphorylates Mdm2 within its central acidic domain, a region that is critical for making a second point of contact with p53 and mediating p53 ubiquitylation and turnover. Additionally, there is evidence that CK2 interacts with, and regulates, both p53 and Mdm2 within the cell but the molecular mechanisms through which CK2-mediated regulation of the p53 response can occur are only poorly understood. Previously, we showed that the basal transcription factor TAFII250, a critical component of TFIID, can interact with Mdm2 and promote the association of the Mdm2 acidic domain with p53. In the present study, we show that immunoprecipitates of TAFII250, either from mammalian cell extracts or from baculovirus-infected cells expressing elevated levels of HA-tagged TAFII250, can phosphorylate Mdm2 in vitro within its acidic domain. We show that CK2 is tightly associated with TAFII250 and is the principal activity responsible for TAFII250-mediated phosphorylation of Mdm2. Our data fit with recent observations that phosphorylation of the acidic domain of Mdm2 stimulates its association with p53 and are consistent with a model in which recruitment of CK2 by TAFII250 may play a contributory role in the maintenance of Mdm2 phosphorylation and function.

    Molecular and cellular biochemistry 2008;316;1-2;99-106

  • Protease activated receptor 1 activation of platelet is associated with an increase in protein kinase CK2 activity.

    Nakanishi K, Komada Y, Hayashi T, Suzuki K and Ido M

    Journal of thrombosis and haemostasis : JTH 2008;6;6;1046-8

  • Regulation of telomeric repeat binding factor 1 binding to telomeres by casein kinase 2-mediated phosphorylation.

    Kim MK, Kang MR, Nam HW, Bae YS, Kim YS and Chung IK

    Department of Biology and Molecular Aging Research Center, Yonsei University, Seoul, Korea.

    Telomere maintenance is essential for continued cell proliferation and chromosome stability. Telomeres are maintained by telomerase and a collection of associated proteins. The telomeric protein telomeric repeat binding factor 1 (TRF1) negatively regulates telomere length by inhibiting access of telomerase at telomere termini. Here we report that TRF1 interacts with the beta subunit of casein kinase 2 (CK2) and serves as a substrate for CK2. CK2-mediated phosphorylation is required for the efficient telomere binding of TRF1 in vitro and in vivo. Inhibition of CK2 by the CK2 inhibitor 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole decreased the ability of TRF1 to bind telomeric DNA. The resulting telomere-unbound form of TRF1 was then ubiquitinated and degraded by the proteasome. Partial knockdown of CK2 by small interfering RNA resulted in removal of TRF1 from telomeres and subsequent degradation of TRF1. Mapping of the CK2 target site identified threonine 122 as a substrate in TRF1. A threonine to alanine change at this position led to a diminished DNA binding due to reduced dimerization of TRF1. In addition, phosphorylation of threonine 122 seemed critical for TRF1-mediated telomere length control. Our findings suggest that CK2-mediated phosphorylation of TRF1 plays an important role in modulating telomere length homeostasis by determining the levels of TRF1 at telomeres.

    The Journal of biological chemistry 2008;283;20;14144-52

  • The CK2 phosphorylation of catalytic domain of Cdc34 modulates its activity at the G1 to S transition in Saccharomyces cerevisiae.

    Coccetti P, Tripodi F, Tedeschi G, Nonnis S, Marin O, Fantinato S, Cirulli C, Vanoni M and Alberghina L

    Department of Biotechnology and Biosciences, University of Milano-Bicocca, Milano, Italy. paola.coccetti@unimib.it

    The ubiquitin-conjugating enzyme Cdc34 was recently shown to be phosphorylated by CK2 on the C-terminal tail. Here we present novel findings indicating that in budding yeast CK2 phosphorylates Cdc34 within the N-terminal catalytic domain. Specifically, we show, by direct mass spectrometry analysis, that Cdc34 is phosphorylated in vitro and in vivo by CK2 on Ser130 and Ser167, and that the phosphoserines 130 and 167 are not present after CK2 inactivation in a cka1Deltacka2-8(ts) strain. CK2 phosphorylation of Ser130 and Ser167 strongly stimulates Cdc34 ubiquitin charging in vitro. The Cdc34(S130AS167A) mutant shows a basal ubiquitin charging activity which is indistinguishable from that of wild type but is not activated by CK2 phosphorylation and its expression fails to complement a cdc34-2(ts) yeast strain, supporting a model in which activation of Cdc34 involves CK2-mediated phosphorylation of its catalytic domain.

    Cell cycle (Georgetown, Tex.) 2008;7;10;1391-401

  • Protein kinase CK2 interacts with the splicing factor hPrp3p.

    Lehnert S, Götz C, Kartarius S, Schäfer B and Montenarh M

    Universität des Saarlandes, Medizinische Biochemie und Molekularbiologie, Homburg, Germany.

    Numerous signalling pathways in cells are influenced by the ubiquitous Ser/Thr protein kinase CK2. Protein kinase CK2 is composed of two regulatory beta-subunits and two catalytic alpha- or alpha'-subunits. Several of the known CK2 substrates are proteins known to regulate transcriptional events. Here, we describe that protein kinase CK2 interacts with the splicing factor hPrp3p, which is important for the assembly of the spliceosome. In a two-hybrid screen hPrp3p is exclusively bound to the catalytic alpha- or alpha'-subunits of CK2 but not to the regulatory beta-subunit. The interaction was confirmed by coimmunoprecipitation experiments in vitro and in vivo. Moreover, both proteins colocalized in nuclear speckles which is typical for splicing factor compartments within the nucleus. Phosphorylation experiments revealed that hPrp3p is also a substrate of protein kinase CK2. The main phosphorylation site was mapped to C-terminal residues. In vitro and in vivo splicing assays showed that the splicing activity is significantly influenced by the CK2-hPrp3p interaction. Thus, these data showed that CK2 is involved in the regulation of RNA processing.

    Oncogene 2008;27;17;2390-400

  • The catalytic subunit of human protein kinase CK2 structurally deviates from its maize homologue in complex with the nucleotide competitive inhibitor emodin.

    Raaf J, Klopffleisch K, Issinger OG and Niefind K

    Universität zu Köln, Institut für Biochemie, Zülpicher Strasse 47, D-50674 Köln, Germany.

    The Ser/Thr kinase CK2 (former name: casein kinase 2) is a heterotetrameric enzyme composed of two catalytic chains (CK2alpha) attached to a dimer of noncatalytic subunits. Together with the cyclin-dependent kinases and the mitogen-activated protein kinases, CK2alpha belongs to the CMGC family of the eukaryotic protein kinases. CK2 is an important survival and stability factor in eukaryotic cells: its catalytic activity is elevated in a wide variety of tumors while its down-regulation can lead to apoptosis. Thus, CK2 is a valuable target for drug development and for chemical biology approaches of cell biological research, and small organic inhibitors addressing CK2 are of considerable interest. We describe here the complex structure between a C-terminal deletion mutant of human CK2alpha and the ATP-competitive inhibitor emodin (1,3,8-trihydroxy-6-methylanthraquinone, International Union of Pure and Applied Chemistry name: 1,3,8-trihydroxy-6-methylanthracene-9,10-dione) and compare it with a previously published complex structure of emodin and maize CK2alpha. With a resolution of 1.5 A, the human CK2alpha/emodin structure has a much better resolution than its maize counterpart (2.6 A). Even more important, in spite of a sequence identity of more than 77% between human and maize CK2alpha, the two structures deviate significantly in the orientation, in which emodin is trapped by the enzyme, and in the local conformations around the ligand binding site: maize CK2alpha shows its largest adaptations in the ATP-binding loop, whereas human CK2alpha shows its largest adaptations in the hinge region connecting the two main domains of the protein kinase core. These observations emphasize the importance of local plasticity for ligand binding and demonstrate that two orthologues of an enzyme can behave quite different in this respect.

    Journal of molecular biology 2008;377;1;1-8

  • Protein kinase CK2 is a key activator of histone deacetylase in hypoxia-associated tumors.

    Pluemsampant S, Safronova OS, Nakahama K and Morita I

    Department of Cellular Physiological Chemistry, Graduate School, Tokyo Medical and Dental University, Tokyo, Japan.

    Increasing evidence points to a link between histone deacetylases (HDACs) and tumorigenesis. Although several HDAC inhibitors have been tested in clinical trials for cancer therapies, the mechanisms of HDAC activation in tumors remain unknown. In this study, we investigated the pathway of HDAC activation in the context of hypoxia and inflammation, common features of solid tumors. In HeLa cells, hypoxia was a more potent activator of HDAC than IL-1beta. As HDAC protein expression did not change during treatment, we hypothesized that hypoxia regulated HDAC activity through post-translational modification. We observed that hypoxia induced HDAC1 and HDAC2 protein phosphorylation both in the presence and absence of IL-1beta. Using TBB, an inhibitor of protein kinase CK2, we showed that CK2 was required for hypoxia-induced HDAC activation. We also observed that CK2 activity was induced by hypoxia but not by IL-1beta alone. While CK2beta subunits were retained in the cytoplasm upon hypoxic treatment, CK2alpha and CK2alpha' subunits were shuttled to the nucleus, where HDAC1 and HDAC2 are predominantly localized. Knockdown of catalytic and regulatory subunits of CK2 revealed that formation of heterotetramic complex was not required for HDAC phosphorylation. von Hippel-Lindau protein (pVHL) inactivation and hypoxia inducible factor-1alpha (HIF-1alpha) activation are associated with tumor growth and vasculogenesis. Use of Apicidin (an HDAC inhibitor) and TBB revealed that CK2-dependent HDAC activation contributed to pVHL downregulation and HIF-1alpha stabilization under hypoxia. Our findings that CK2 may be a key mediator for HDAC activation under hypoxia support the future application of CK2 inhibitors in cancer therapy.

    International journal of cancer 2008;122;2;333-41

  • The N-terminal region of ABC50 interacts with eukaryotic initiation factor eIF2 and is a target for regulatory phosphorylation by CK2.

    Paytubi S, Morrice NA, Boudeau J and Proud CG

    Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee, DD1 5EH, UK.

    ABC50 is an ABC (ATP-binding cassette) protein which, unlike most ABC proteins, lacks membrane-spanning domains. ABC50 interacts with eIF2 (eukaryotic initiation factor 2), a protein that plays a key role in translation initiation and in its control, and in regulation of ribosomes. Here, we establish that the interaction of ABC50 with eIF2 involves features in the N-terminal domain of ABC50, the region of ABC50 that differs most markedly from other ABC proteins. This region also shows no apparent similarity to the eIF2-binding domains of other partners of eIF2. In contrast, the N-terminus of ABC50 cannot bind to ribosomes by itself, but it can in conjunction with one of the nucleotide-binding domains. We demonstrate that ABC50 is a phosphoprotein and is phosphorylated at two sites by CK2. These sites, Ser-109 and Ser-140, lie in the N-terminal part of ABC50 but are not required for the binding of ABC50 to eIF2. Expression of a mutant of ABC50 in which both sites are mutated to alanine markedly decreased the association of eIF2 with 80S ribosomal and polysomal fractions.

    The Biochemical journal 2008;409;1;223-31

  • Human herpesvirus 6B induces phosphorylation of p53 in its regulatory domain by a CK2- and p38-independent pathway.

    Oster B, Bundgaard B, Hupp TR and Höllsberg P

    Institute of Medical Microbiology and Immunology, University of Aarhus, Aarhus, Denmark.

    Here, we demonstrate that human herpesvirus 6B (HHV-6B) infection upregulates the tumour suppressor p53 and induces phosphorylation of p53 at Ser392. Interestingly, phosphorylation at the equivalent site has previously been shown to correlate with p53 tumour suppression in murine models. Although the signalling pathways leading to Ser392 phosphorylation are poorly understood, they seem to include casein kinase 2 (CK2), double-stranded RNA-activated protein kinase (PKR), p38 or cyclin-dependent kinase 9 (Cdk9). By using column chromatography and in vitro kinase assays, CK2 and p38, but not PKR or Cdk9, eluted in column fractions that phosphorylated p53 at Ser392. However, treatment of cells with neither the CK2 and Cdk9 inhibitor 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole (DRB) nor p38 kinase inhibitors reduced HHV-6B-induced Ser392 phosphorylation significantly. Knockdown of the CK2beta subunit or p38alpha by small interfering RNA had no effect on HHV-6B-induced phosphorylation of p53 at Ser392. Thus, HHV-6B induces p53 Ser392 phosphorylation by an atypical pathway independent of CK2 and p38 kinases, whereas mitogen-activated protein (MAP) kinase signalling pathways are involved in viral replication.

    The Journal of general virology 2008;89;Pt 1;87-96

  • Heterogeneity of CK2 phosphorylation sites in the NS5A protein of different hepatitis C virus genotypes.

    Dal Pero F, Di Maira G, Marin O, Bortoletto G, Pinna LA, Alberti A, Ruzzene M and Gerotto M

    Venetian Institute of Molecular Medicine (VIMM), University of Padova, Via Orus, 2, Padova 35129, Italy. francesca.dalpero@unipd.it

    The hepatitis C virus NS5A protein is phosphorylated by several cellular kinases, including casein kinase 2 (CK2). Little is known about CK2 phosphorylation of NS5A from different HCV genotypes and clinical isolates.

    Methods: NS5A from patients with HCV-1a (24 cases), HCV-1b (9) or HCV-3 (16) was analyzed by direct sequencing and CK2 phosphorylation sites were defined using a well-validated prediction rule. In vitro phosphorylation assays were performed using recombinant CK2 and synthetic peptides or full-length NS5A. In vivo phosphorylation by endogenous CK2 of NS5A expressed in hepatoma cells was also investigated.

    Results: The mean number of CK2 sites within full-length NS5A, was significantly higher in HCV-3 compared to HCV-1a (P<0.01) and HCV-1b (P<0.01). The number of CK2 sites was more homogeneous in HCV-3 variants compared to HCV-1a and HCV-1b variants (P<0.05). The number of predicted CK2 sites correlated with the degree of in vitro and in vivo phosphorylation of NS5A by CK2.

    Conclusions: CK2-dependent phosphorylation of NS5A is heterogeneous among different HCV genotypes and clinical isolates. This might have an influence on virus biology and pathogenicity.

    Journal of hepatology 2007;47;6;768-76

  • Differential distribution of unmodified and phosphorylated histone deacetylase 2 in chromatin.

    Sun JM, Chen HY and Davie JR

    Manitoba Institute of Cell Biology, University of Manitoba, 675 McDermot Avenue, Winnipeg, Manitoba, Canada.

    Histone deacetylase 2 (HDAC2) is one of the histone-modifying enzymes that regulate gene expression by remodeling chromatin structure. Along with HDAC1, HDAC2 is found in the Sin3 and NuRD multiprotein complexes, which are recruited to promoters by DNA-binding proteins. In this study, we show that the majority of HDAC2 in human breast cancer cells is not phosphorylated. However, the minor population of HDAC2, preferentially cross-linked to DNA by cisplatin, is mono-, di-, or tri-phosphorylated. Furthermore, HDAC2 phosphorylation is required for formation of Sin3 and NuRD complexes and recruitment to promoters by transcription factors including p53, Rb, YY1, NF-kappaB, Sp1, and Sp3. Unmodified HDAC2 requires linker DNA to associate with chromatin but is not cross-linked to DNA by formaldehyde. We provide evidence that unmodified HDAC2 is associated with the coding region of transcribed genes, whereas phosphorylated HDAC2 is primarily recruited to promoters.

    The Journal of biological chemistry 2007;282;45;33227-36

  • Protein kinase CK2 phosphorylation of EB2 regulates its function in the production of Epstein-Barr virus infectious viral particles.

    Medina-Palazon C, Gruffat H, Mure F, Filhol O, Vingtdeux-Didier V, Drobecq H, Cochet C, Sergeant N, Sergeant A and Manet E

    INSERM U758, ENS-Lyon, 46 allée d'Italie, 69364 Lyon Cedex 07, France.

    The Epstein-Barr Virus (EBV) early protein EB2 (also called BMLF1, Mta, or SM) promotes the nuclear export of a subset of early and late viral mRNAs and is essential for the production of infectious virions. We show here that in vitro, protein kinase CK2alpha and -beta subunits bind both individually and, more efficiently, as a complex to the EB2 N terminus and that the CK2beta regulatory subunit also interacts with the EB2 C terminus. Immunoprecipitated EB2 has CK2 activity that phosphorylates several sites within the 80 N-terminal amino acids of EB2, including Ser-55, -56, and -57, which are localized next to the nuclear export signal. EB2S3E, the phosphorylation-mimicking mutant of EB2 at these three serines, but not the phosphorylation ablation mutant EB2S3A, efficiently rescued the production of infectious EBV particles by HEK293(BMLF1-KO) cells harboring an EB2-defective EBV genome. The defect of EB2S3A in transcomplementing 293(BMLF1-KO) cells was not due to impaired nucleocytoplasmic shuttling of the mutated protein but was associated with a decrease in the cytoplasmic accumulation of several late viral mRNAs. Thus, EB2-mediated production of infectious EBV virions is regulated by CK2 phosphorylation at one or more of the serine residues Ser-55, -56, and -57.

    Journal of virology 2007;81;21;11850-60

  • Induction of cell death in antiestrogen resistant human breast cancer cells by the protein kinase CK2 inhibitor DMAT.

    Yde CW, Frogne T, Lykkesfeldt AE, Fichtner I, Issinger OG and Stenvang J

    Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense, Denmark.

    Protein kinase CK2 is involved in cell proliferation and survival, and found overexpressed in virtually all types of human cancer, including breast cancer. We demonstrate that inhibition of CK2 with 2-dimethylamino-4,5,6,7-tetrabromo-benzimidazole (DMAT), a potent and specific CK2 inhibitor, results in caspase-mediated killing of human breast cancer cells with acquired resistance to antiestrogens, while DMAT fails to kill parental MCF-7 cells. The antiestrogen resistant breast cancer cells express reduced levels of Bcl-2 compared to MCF-7 cells. Reduced Bcl-2 protein level is also found in a tamoxifen resistant human breast tumor grown as a xenograft. We show that re-expression of Bcl-2 partially rescues antiestrogen resistant MCF-7 sublines from DMAT-induced cell death. In summary, our data suggest a novel role of CK2 in antiestrogen resistance.

    Cancer letters 2007;256;2;229-37

  • The protein kinase CK2 phosphorylates SNAP190 to negatively regulate SNAPC DNA binding and human U6 transcription by RNA polymerase III.

    Gu L, Husain-Ponnampalam R, Hoffmann-Benning S and Henry RW

    Department of Biochemistry & Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA.

    Human U6 small nuclear RNA gene transcription by RNA polymerase III requires the general transcription factor SNAP(C), which binds to human small nuclear RNA core promoter elements and nucleates pre-initiation complex assembly with the Brf2-TFIIIB complex. Multiple components in this pathway are phosphorylated by the protein kinase CK2, including the Bdp1 subunit of the Brf2-TFIIIB complex, and RNA polymerase III, with negative and positive outcomes for U6 transcription, respectively. However, a role for CK2 phosphorylation of SNAP(C) in U6 transcription has not been defined. In this report, we investigated the role of CK2 in modulating the transcriptional properties of SNAP(C) and demonstrate that within SNAP(C), CK2 phosphorylates the N-terminal half of the SNAP190 subunit at two regions (amino acids 20-63 and 514-545) that each contain multiple CK2 consensus sites. SNAP190 phosphorylation by CK2 inhibits both SNAP(C) DNA binding and U6 transcription activity. Mutational analyses of SNAP190 support a model wherein CK2 phosphorylation triggers an allosteric inhibition of the SNAP190 Myb DNA binding domain.

    Funded by: NIGMS NIH HHS: R01-GM59805

    The Journal of biological chemistry 2007;282;38;27887-96

  • Extracellular phosphorylation of collagen XVII by ecto-casein kinase 2 inhibits ectodomain shedding.

    Zimina EP, Fritsch A, Schermer B, Bakulina AY, Bashkurov M, Benzing T and Bruckner-Tuderman L

    Department of Dermatology, Faculty of Biology, University of Freiburg, Hauptstrasse 7, 79104 Freiburg, Germany.

    Ecto-phosphorylation is emerging as an important mechanism to regulate cellular ligand interactions and signal transduction. Here we show that extracellular phosphorylation of the cell surface receptor collagen XVII regulates shedding of its ectodomain. Collagen XVII, a member of the novel family of collagenous transmembrane proteins and component of the hemidesmosomes, mediates adhesion of the epidermis to the dermis in the skin. The ectodomain is constitutively shed from the cell surface by metalloproteinases of the ADAM (a disintegrin and metalloproteinase) family, mainly by tumor necrosis factor-alpha converting enzyme (TACE). We used biochemical, mutagenesis, and structural modeling approaches to delineate mechanisms controlling ectodomain cleavage. A standard assay for extracellular phosphorylation, incubation of intact keratinocytes with cell-impermeable [gamma-(32)P]ATP, led to collagen XVII labeling. This was significantly diminished by both broad-spectrum extracellular kinase inhibitor K252b and a specific casein kinase 2 (CK2) inhibitor. Collagen XVII peptides containing a putative CK2 recognition site were phosphorylated by CK2 in vitro, disclosing Ser(542) and Ser(544) in the ectodomain as phosphate group acceptors. Phosphorylation of Ser(544) in vivo and in vitro was confirmed by immunoblotting of epidermis and HaCaT keratinocyte extracts with phosphoepitope-specific antibodies. Functionally, inhibition of CK2 kinase activity or mutation of the phosphorylation acceptor Ser(544) to Ala significantly increased ectodomain shedding, whereas overexpression of CK2alpha inhibited cleavage of collagen XVII. Structural modeling suggested that the phosphorylation of serine residues prevents binding of TACE to its substrate. Thus, extracellular phosphorylation of collagen XVII by ecto-CK2 inhibits its shedding by TACE and represents novel mechanism to regulate adhesion and motility of epithelial cells.

    The Journal of biological chemistry 2007;282;31;22737-46

  • A viral adaptor protein modulating casein kinase II activity induces cytopathic effects in permissive cells.

    Nüesch JP and Rommelaere J

    Program "Infection and Cancer," Abteilung F010 and Institut National de la Santé et de la Recherche Médicale Unité 701, Deutsches Krebsforschungszentrum, D-69120 Heidelberg, Germany. jpf.nuesch@dkfz.de

    Autonomous parvoviruses induce severe morphological and physiological alterations in permissive host cells, eventually leading to cell lysis and release of progeny virions. Viral cytopathic effects (CPE) result from specific rearrangements and destruction of cytoskeletal micro- and intermediate filaments. We recently reported that inhibition of endogenous casein kinase II (CKII) protects target cells from parvovirus minute virus of mice (MVM)-induced CPE, pointing to this kinase as an effector of MVM toxicity. The present work shows that the parvoviral NS1 protein mediates CKII-dependent cytoskeletal alterations and cell death. NS1 can act as an adaptor molecule, linking the cellular protein kinase CKIIalpha to tropomyosin and thus modulating the substrate specificity of the kinase. This action results in an altered tropomyosin phosphorylation pattern both in vitro and in living cells. The capacity of NS1 to induce CPE was impaired by mutations abolishing binding with either CKIIalpha or tropomyosin. The cytotoxic adaptor function of NS1 was confirmed with fusion peptides, where the tropomyosin-binding domain of NS1 and CKIIalpha are physically linked. These adaptor peptides were able to mimic NS1 in its ability to induce death of transformed MVM-permissive cells.

    Proceedings of the National Academy of Sciences of the United States of America 2007;104;30;12482-7

  • Evolved to be active: sulfate ions define substrate recognition sites of CK2alpha and emphasise its exceptional role within the CMGC family of eukaryotic protein kinases.

    Niefind K, Yde CW, Ermakova I and Issinger OG

    Universität zu Köln, Institut für Biochemie, Zülpicher Strasse 47, D-50674 Köln, Germany. Karsten.Niefind@uni-koeln.de

    CK2alpha is the catalytic subunit of protein kinase CK2 and a member of the CMGC family of eukaryotic protein kinases like the cyclin-dependent kinases, the MAP kinases and glycogen-synthase kinase 3. We present here a 1.6 A resolution crystal structure of a fully active C-terminal deletion mutant of human CK2alpha liganded by two sulfate ions, and we compare this structure systematically with representative structures of related CMGC kinases. The two sulfate anions occupy binding pockets at the activation segment and provide the structural basis of the acidic consensus sequence S/T-D/E-X-D/E that governs substrate recognition by CK2. The anion binding sites are conserved among those CMGC kinases. In most cases they are neutralized by phosphorylation of a neighbouring threonine or tyrosine side-chain, which triggers conformational changes for regulatory purposes. CK2alpha, however, lacks both phosphorylation sites at the activation segment and structural plasticity. Here the anion binding sites are functionally changed from regulation to substrate recognition. These findings underline the exceptional role of CK2alpha as a constitutively active enzyme within a family of strictly controlled protein kinases.

    Journal of molecular biology 2007;370;3;427-38

  • The role of protein kinase CK2 in intestinal epithelial cell inflammatory signaling.

    Parhar K, Morse J and Salh B

    The Jack Bell Research Center, 2660 Oak Street, V6H 3Z6, Vancouver, British Columbia, Canada.

    Background: The transcription factor NF-kappaB is believed to play a key pathophysiological role in chronic intestinal inflammation. Further characterization of its mechanism of regulation, predominantly through cell signaling pathways, may provide clues as to the means of its intervention. One such potential signaling candidate is the protein kinase CK2. Despite its known ability to influence NF-kappaB activation, it has received no attention in this particular setting.

    Aim: To characterize the aspects of its activation in response to IL-1beta in the colonic cell lines Caco2 and HCT116.

    A biochemical analysis of kinase activation was performed using phospho-specific antibodies as well as immune complex kinase assays; transcription factor activity was measured by transient transfection and luciferase-based NF-kappaB reporter assays; pro-inflammatory molecule expression was determined using RT-PCR.

    Results: In this report, we show an enhanced activation of CK2 bound to IKKgamma or the p65 subunit of the NF-kappaB in response to IL-1beta stimulation of intestinal epithelial cells. Using two established NF-kappaB reporters, we demonstrate that CK2 is involved in NF-kappaB regulation through the p65 serine 529 site. Using co-immunoprecipitation studies, we also show that p65 is bound to CK2 predominantly in the nucleus. From a functional perspective, two CK2 specific inhibitors were then shown to attenuate IL-8 reporter activation. Finally, the expression of a series of pro-inflammatory molecules including IL-8, GRO-alpha, MCP-1, TNFalpha and iNOS were variably affected in response to CK2 inhibition.

    Conclusion: CK2 plays an active role in NF-kappaB signaling in intestinal epithelial cell lines and may represent a possible target for intervention.

    International journal of colorectal disease 2007;22;6;601-9

  • Modulation of p300 binding by posttranslational modifications of the C-terminal activation domain of hypoxia-inducible factor-1alpha.

    Cho H, Ahn DR, Park H and Yang EG

    Life Sciences Division, Korea Institute of Science and Technology, Seoul, Republic of Korea.

    Posttranslational modifications of hypoxia-inducible factor-1alpha (HIF-1alpha) influence HIF-mediated transcription, likely by affecting binding to p300/cAMP-response element-binding protein (CBP). To systematically analyze the HIF-1alpha-p300/CBP interaction, we developed a fluorescence polarization-based binding assay, employing fluorescein-labeled peptides derived from the C-terminal transactivation domain (C-TAD) of HIF-1alpha. After optimized for effectively capturing p300/CBP, the assay was utilized for evaluating direct effects of posttranslational modifications of the HIF-1alpha C-TAD on p300 binding. The results demonstrated that asparagine hydroxylation and S-nitrosylation of HIF-1alpha decrease p300 binding, while its phosphorylation does not affect p300 binding, which was reconfirmed by competitive inhibition analyses using mutant peptides.

    FEBS letters 2007;581;8;1542-8

  • Proteomic analysis of SET-binding proteins.

    Vera J, Estanyol JM, Canela N, Llorens F, Agell N, Itarte E, Bachs O and Jaumot M

    Departament de Biologia Cel·lular i Anatomia Patològica, Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain.

    The protein SET is involved in essential cell processes such as chromatin remodeling, apoptosis and cell cycle progression. It also plays a critical role in cell transformation and tumorogenesis. With the aim to study new SET functions we have developed a system to identify SET-binding proteins by combining affinity chromatography, MS, and functional studies. We prepared SET affinity chromatography columns by coupling the protein to activated Sepharose 4B. The proteins from mouse liver lysates that bind to the SET affinity columns were resolved with 2-DE and identified by MS using a MALDI-TOF. This experimental approach allowed the recognition of a number of SET-binding proteins which have been classified in functional clusters. The identification of four of these proteins (CK2, eIF2alpha, glycogen phosphorylase (GP), and TCP1-beta) was confirmed by Western blotting and their in vivo interactions with SET were demonstrated by immunoprecipitation. Functional experiments revealed that SET is a substrate of CK2 in vitro and that SET interacts with the active form of GP but not with its inactive form. These data confirm this proteomic approach as a useful tool for identifying new protein-protein interactions.

    Proteomics 2007;7;4;578-587

  • Phosphorylation of a threonine unique to the short C-terminal isoform of betaII-spectrin links regulation of alpha-beta spectrin interaction to neuritogenesis.

    Bignone PA, King MD, Pinder JC and Baines AJ

    Department of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, Great Britain.

    Spectrin tetramers are cytoskeletal proteins required in the formation of complex animal tissues. Mammalian alphaII- and betaII-spectrin subunits form dimers that associate head to head with high affinity to form tetramers, but it is not known if this interaction is regulated. We show here that the short C-terminal splice variant of betaII-spectrin (betaIISigma2) is a substrate for phosphorylation. In vitro, protein kinase CK2 phosphorylates Ser-2110 and Thr-2159; protein kinase A phosphorylates Thr-2159. Antiphospho-Thr-2159 peptide antibody detected phosphorylated betaIISigma2 in Cos-1 cells. Immunoreactivity was increased in Cos-1 cells by treatment with forskolin, indicating that phosphorylation is promoted by elevated cAMP. The effect of forskolin was counteracted by the cAMP-dependent kinase inhibitor, H89. In vitro, protein kinase A phosphorylation of an active fragment of betaIISigma2 greatly reduced its interaction with alphaII-spectrin at the tetramerization site. Mutation of Thr-2159 to alanine eliminated inhibition by phosphorylation. Among the processes that require spectrin in mammals is the formation of neurites (incipient nerve axons). We tested the relationship of spectrin phosphorylation to neuritogenesis by transfecting the neuronal cell line, PC12, with enhanced green fluorescent protein-coupled fragments of betaIISigma2-spectrin predicted to act as inhibitors of spectrin tetramer formation. Both wild-type and T2159E mutant fragments allowed normal neuritogenesis in PC12 cells in response to nerve growth factor. The mutant T2159A inhibited neuritogenesis. Because the T2159A mutant represents a high affinity inhibitor of tetramer formation, we conclude that tetramers are requisite for neuritogenesis. Furthermore, because both the T2159E mutant and the wild-type allow neuritogenesis, we conclude that the short C-terminal betaII-spectrin is phosphorylated during this process.

    Funded by: Biotechnology and Biological Sciences Research Council: C18062

    The Journal of biological chemistry 2007;282;2;888-96

  • CK2 phosphorylation of SAG at Thr10 regulates SAG stability, but not its E3 ligase activity.

    He H, Tan M, Pamarthy D, Wang G, Ahmed K and Sun Y

    Division of Cancer Biology, Department of Radiation Oncology, University of Michigan Comprehensive Cancer Center, 4304 CCGC, 1500 East Medical Center Drive, Ann Arbor, MI 48109-0936, USA.

    Sensitive to Apoptosis Gene (SAG), a RING component of SCF E3 ubiquitin ligase, was shown to be phosphorylated by protein kinase CK2 at the Thr10 residue. It is, however, unknown whether this phosphorylation is stress-responsive or whether the phosphorylation changes its E3 ubiquitin ligase activity. To address these, we made a specific antibody against the phosphor-SAG(Thr10). Transient transfection experiment showed that SAG was phosphorylated at Thr10 which can be significantly inhibited by TBB, a relatively specific inhibitor of protein kinase CK2. To determine whether this SAG phosphorylation is stress-responsive, we defined a chemical-hypoxia condition in which SAG and CK2 were both induced. Under this condition, we failed to detect SAG phosphorylation at Thr10, which was readily detected, however, in the presence of MG132, a proteasome inhibitor, suggesting that the phosphorylated SAG has undergone a rapid degradation. To further define this, we made two SAG mutants, SAG-T10A which abolishes the SAG phosphorylation and SAG-T10E, which mimics the constitutive SAG phosphorylation. The half-life study revealed that indeed, SAG-T10E has a much shorter protein half-life (2 h), as compared to wild-type SAG (10 h). Again, rapid degradation of SAG-T10E in cells can be blocked by MG132. Thus, it appears that CK2-induced SAG phosphorylation at Thr10 regulates its stability through a proteasome-dependent pathway. Immunocytochemistry study showed that SAG as well as its phosphorylation mutants, was mainly localized in nucleus and lightly in cytoplasm. Hypoxia condition did not change their sub-cellular localization. Finally, an in vitro ubiqutination assay showed that SAG mutation at Thr10 did not change its E3 ligase activity when complexed with cullin-1. These studies suggested that CK2 might regulate SAG-SCF E3 ligase activity through modulating SAG's stability, rather than its enzymatic activity directly.

    Funded by: NCI NIH HHS: CA-15062, R01-CA111554, R21-CA116982

    Molecular and cellular biochemistry 2007;295;1-2;179-88

  • Large-scale mapping of human protein-protein interactions by mass spectrometry.

    Ewing RM, Chu P, Elisma F, Li H, Taylor P, Climie S, McBroom-Cerajewski L, Robinson MD, O'Connor L, Li M, Taylor R, Dharsee M, Ho Y, Heilbut A, Moore L, Zhang S, Ornatsky O, Bukhman YV, Ethier M, Sheng Y, Vasilescu J, Abu-Farha M, Lambert JP, Duewel HS, Stewart II, Kuehl B, Hogue K, Colwill K, Gladwish K, Muskat B, Kinach R, Adams SL, Moran MF, Morin GB, Topaloglou T and Figeys D

    Protana, Toronto, Ontario, Canada.

    Mapping protein-protein interactions is an invaluable tool for understanding protein function. Here, we report the first large-scale study of protein-protein interactions in human cells using a mass spectrometry-based approach. The study maps protein interactions for 338 bait proteins that were selected based on known or suspected disease and functional associations. Large-scale immunoprecipitation of Flag-tagged versions of these proteins followed by LC-ESI-MS/MS analysis resulted in the identification of 24,540 potential protein interactions. False positives and redundant hits were filtered out using empirical criteria and a calculated interaction confidence score, producing a data set of 6463 interactions between 2235 distinct proteins. This data set was further cross-validated using previously published and predicted human protein interactions. In-depth mining of the data set shows that it represents a valuable source of novel protein-protein interactions with relevance to human diseases. In addition, via our preliminary analysis, we report many novel protein interactions and pathway associations.

    Molecular systems biology 2007;3;89

  • p53-dependent inhibition of mammalian cell survival by a genetically selected peptide aptamer that targets the regulatory subunit of protein kinase CK2.

    Martel V, Filhol O, Colas P and Cochet C

    Département Réponse et Dynamique Cellulaire, INSERM EMI0104, CEA, Grenoble Cedex, France.

    Based on the perturbation of its expression in human cancers and on its involvement in transformation and tumorigenesis, protein kinase CK2 has recently attracted attention as a potential therapeutic target. To assess the value of CK2 as a target for antiproliferative strategies, we have initiated a program aiming to develop inhibitors targeting specifically the regulatory CK2beta subunit. Here, we use a two-hybrid approach to isolate from combinatorial libraries, peptide aptamers that specifically interact with CK2beta. One of these (P1), which has significant sequence homology to the cytomegalovirus IE2 protein, binds with high affinity to the N-terminal domain of CK2beta without disrupting the formation of the CK2 holoenzyme. Expression of green fluorescent protein (GFP)-P1 in different mammalian cell lines activates p53 phosphorylation on serine 15, induces an upregulation of p21 and the release of the Cyt-C and apoptosis-inducing factor proapoptotic proteins triggering caspase-dependent and caspase-independent apoptosis. GFP-P1-induced apoptosis is associated with a p53-dependent pathway as cell death was abrogated in p53 knocked out cells. In summary, our data show that genetically selected peptide aptamers that specifically target CK2beta can induce apoptosis in mammalian cells through the recruitment of a p53-dependent apoptosis pathway. They also emphasize the critical role of CK2beta for cell survival and might allow the design of novel proapoptotic agents targeting this protein.

    Oncogene 2006;25;56;7343-53

  • CK2 controls the recruitment of Wnt regulators to target genes in vivo.

    Wang S and Jones KA

    Regulatory Biology Laboratory, The Salk Institute, 10010 N. Torrey Pines Road, La Jolla, California 92037, USA.

    Nuclear beta-catenin is a transcriptional coactivator of LEF-1/TCF DNA-binding proteins in the Wnt/Wg signaling pathway. Casein Kinase 2 (CK2), a positive regulator of Wnt signaling, is present in beta-catenin complexes and activated in Wnt-signaling cells. We show here that CK2 enhances beta-catenin:LEF-1 transactivation in vivo and in vitro and that beta-catenin and CK2 cycle on and off the DNA in an alternating manner with the TLE1 corepressor at Wnt target genes. Interestingly, CK2 phosphorylates hLEF-1 directly and stimulates binding and transactivation of beta-catenin:LEF-1 complexes on chromatin templates in vitro. In vitro, CK2 phosphorylation of hLEF-1 strongly enhances its affinity for beta-catenin and reduces its affinity for TLE1. MALDI-TOF mass spectrometry (MS) identified two CK2 phosphorylation sites (S42, S61) within the amino terminus of hLEF-1, and mutation of these sites reduced binding to beta-catenin in vitro and transactivation in vivo. Remarkably, treatment of cells with TBB, a pharmaceutical inhibitor of CK2, blocked the recruitment and cycling of beta-catenin and TLE1 at Wnt target genes in vivo. Taken together, these data indicate that CK2 is required for the assembly and cycling of Wnt-enhancer complexes in vivo.

    Current biology : CB 2006;16;22;2239-44

  • CK2-site phosphorylation of p53 is induced in DeltaNp63 expressing basal stem cells in UVB irradiated human skin.

    Finlan LE, Nenutil R, Ibbotson SH, Vojtesek B and Hupp TR

    The University of Edinburgh, CRUK p53 Signal Transduction Group, Edinburgh, UK.

    The activity of the tumor suppressor protein p53 is controlled by a balance between E3-ligase mediated p53 protein degradation and protein kinase-mediated assembly of p53:p300 transcription machinery. Genetic studies in mice have shown that mutation of the CK2 phospho-acceptor site in p53 increases UV-induced skin cancer formation,(11) highlighting an unexpected role for p53 phosphorylation in mediating p53-dependent tumor suppression. However, it is not known in which cell types CK2-mediated phosphorylation of p53 occurs. Using human skin as a model to determine whether there is cell-selectivity in modulating p53 phosphorylation, we have found a selective induction of p53 phosphorylation at the CK2-site in the basal cells of UV irradiated human skin. Dual-immunofluorescence also revealed that Ser392 and Ser15 phosphorylation of p53 also occur in the same basal cells, although often within distinct regions of the nucleus. Given that p63alphaDeltaN is required for p53 activation after DNA damage, we examined and found a high proportion of cells co-express p63alphaDeltaN and CK2-phosphorylated p53 after UV-irradiation. As controls, the proliferation marker Ki67 and p63alphaDeltaN generally exhibit mutually exclusive expression. These data identify a physiological model with which to identify signaling pathways that mediate cross-talk between p63alphaDeltaN and activating p53 kinase pathways after DNA damage in basal cell populations.

    Cell cycle (Georgetown, Tex.) 2006;5;21;2489-94

  • Nuclear export of S6K1 II is regulated by protein kinase CK2 phosphorylation at Ser-17.

    Panasyuk G, Nemazanyy I, Zhyvoloup A, Bretner M, Litchfield DW, Filonenko V and Gout IT

    Institute of Molecular Biology and Genetics, National Academy of Sciences of Ukraine, Kyiv 03143, Ukraine.

    Ribosomal S6 kinases (S6Ks) are principal players in the regulation of cell growth and energy metabolism. Signaling via phosphatidylinositol 3-kinase and mammalian target of rapamycin pathways mediates the activation of S6K in response to various mitogenic stimuli. The family of S6Ks consists of two forms, S6K1 and -2, that have cytoplasmic and nuclear splicing variants, S6K1 II and S6K1 I, respectively. Nuclear-cytoplasmic shuttling of both isoforms induced by mitogenic stimuli has been reported recently. Here we present the identification of protein kinase CK2 (CK2) as a novel binding and regulatory partner for S6K1 II. The interaction between S6K1 II and CK2beta regulatory subunit was initially identified in a yeast two-hybrid screen and further confirmed by co-immunoprecipitation of transiently expressed and endogenous proteins. The interaction between S6K1 II and CK2 was found to occur in serum-starved and serum-stimulated cells. In addition, we found that S6K1 II is a substrate for CK2. The localization of the CK2 phosphorylation site was narrowed down to Ser-17 in S6K1 II. Mutational analysis and the use of phosphospecific antibody indicate that Ser-17 is a major in vitro and in vivo phosphorylation site for CK2. Functional studies reveal that, in contrast to the wild type kinase, the phosphorylation-mimicking mutant of S6K1 II (S17E) retains its cytoplasmic localization in serum-stimulated cells. Treatment of cells with the nuclear export inhibitor leptomycin B revealed that the S17E mutant accumulates in the nucleus to the same extent as S6K1 II wild type. These results indicate that nuclear import of the S17E mutant is not affected, although the export is significantly enhanced. We also provide evidence that nuclear export of S6K1 is mediated by a CRM1-dependent mechanism. Taken together, this study establishes a functional link between S6K1 II and CK2 signaling, which involves the regulation of S6K1 II nuclear export by CK2-mediated phosphorylation of Ser-17.

    The Journal of biological chemistry 2006;281;42;31188-201

  • A PACS-1, GGA3 and CK2 complex regulates CI-MPR trafficking.

    Scott GK, Fei H, Thomas L, Medigeshi GR and Thomas G

    Vollum Institute, Oregon Health & Science University, Oregon Health Sciences University, Portland, 97239, USA.

    The cation-independent mannose-6-phosphate receptor (CI-MPR) follows a highly regulated sorting itinerary to deliver hydrolases from the trans-Golgi network (TGN) to lysosomes. Cycling of CI-MPR between the TGN and early endosomes is mediated by GGA3, which directs TGN export, and PACS-1, which directs endosome-to-TGN retrieval. Despite executing opposing sorting steps, GGA3 and PACS-1 bind to an overlapping CI-MPR trafficking motif and their sorting activity is controlled by the CK2 phosphorylation of their respective autoregulatory domains. However, how CK2 coordinates these opposing roles is unknown. We report a CK2-activated phosphorylation cascade controlling PACS-1- and GGA3-mediated CI-MPR sorting. PACS-1 links GGA3 to CK2, forming a multimeric complex required for CI-MPR sorting. PACS-1-bound CK2 stimulates GGA3 phosphorylation, releasing GGA3 from CI-MPR and early endosomes. Bound CK2 also phosphorylates PACS-1Ser(278), promoting binding of PACS-1 to CI-MPR to retrieve the receptor to the TGN. Our results identify a CK2-controlled cascade regulating hydrolase trafficking and sorting of itinerant proteins in the TGN/endosomal system.

    Funded by: NIAID NIH HHS: AI49793; NIDDK NIH HHS: DK37274

    The EMBO journal 2006;25;19;4423-35

  • v-Src-dependent down-regulation of the Ste20-like kinase SLK by casein kinase II.

    Chaar Z, O'reilly P, Gelman I and Sabourin LA

    Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario K1H8L6, Canada.

    We have previously shown that the Ste20-like kinase SLK is a microtubule-associated protein inducing actin stress fiber disassembly. Here, we show that v-Src expression can down-regulate SLK activity. This down-regulation is independent of focal adhesion kinase but requires v-Src kinase activity and membrane translocation. SLK down-regulation by v-Src is indirect and is accompanied by SLK hyperphosphorylation on serine residues. Deletion analysis revealed that casein kinase II (CK2) sites at position 347/348 are critical for v-Src-dependent modulation of SLK activity. Further studies show that CK2 can directly phosphorylate SLK at these positions and that inhibition of CK2 in v-Src-transformed cells results in normal kinase activity. Finally, CK2 and SLK can be co-localized in fibroblasts spreading on fibronectin-coated substrates, suggesting a mechanism whereby SLK may be regulated at sites of actin remodeling, such as membrane lamellipodia and ruffles, through CK2.

    The Journal of biological chemistry 2006;281;38;28193-9

  • Casein kinase 2 associates with initiation-competent RNA polymerase I and has multiple roles in ribosomal DNA transcription.

    Panova TB, Panov KI, Russell J and Zomerdijk JC

    Division of Gene Regulation and Expression, School of Life Sciences, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, United Kingdom.

    Mammalian RNA polymerase I (Pol I) complexes contain a number of associated factors, some with undefined regulatory roles in transcription. We demonstrate that casein kinase 2 (CK2) in human cells is associated specifically only with the initiation-competent Pol Ibeta isoform and not with Pol Ialpha. Chromatin immunoprecipitation analysis places CK2 at the ribosomal DNA (rDNA) promoter in vivo. Pol Ibeta-associated CK2 can phosphorylate topoisomerase IIalpha in Pol Ibeta, activator upstream binding factor (UBF), and selectivity factor 1 (SL1) subunit TAFI110. A potent and selective CK2 inhibitor, 3,8-dibromo-7-hydroxy-4-methylchromen-2-one, limits in vitro transcription to a single round, suggesting a role for CK2 in reinitiation. Phosphorylation of UBF by CK2 increases SL1-dependent stabilization of UBF at the rDNA promoter, providing a molecular mechanism for the stimulatory effect of CK2 on UBF activation of transcription. These positive effects of CK2 in Pol I transcription contrast to that wrought by CK2 phosphorylation of TAFI110, which prevents SL1 binding to rDNA, thereby abrogating the ability of SL1 to nucleate preinitiation complex (PIC) formation. Thus, CK2 has the potential to regulate Pol I transcription at multiple levels, in PIC formation, activation, and reinitiation of transcription.

    Funded by: Wellcome Trust: 045160

    Molecular and cellular biology 2006;26;16;5957-68

  • A CK2-dependent mechanism for degradation of the PML tumor suppressor.

    Scaglioni PP, Yung TM, Cai LF, Erdjument-Bromage H, Kaufman AJ, Singh B, Teruya-Feldstein J, Tempst P and Pandolfi PP

    Cancer Biology and Genetics Program, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.

    The PML tumor suppressor controls key pathways for growth suppression, induction of apoptosis, and cellular senescence. PML loss occurs frequently in human tumors through unknown posttranslational mechanisms. Casein kinase 2 (CK2) is oncogenic and frequently upregulated in human tumors. Here we show that CK2 regulates PML protein levels by promoting its ubiquitin-mediated degradation dependent on direct phosphorylation at Ser517. Consequently, PML mutants that are resistant to CK2 phosphorylation display increased tumor-suppressive functions. In a faithful mouse model of lung cancer, we demonstrate that Pml inactivation leads to increased tumorigenesis. Furthermore, CK2 pharmacological inhibition enhances the PML tumor-suppressive property in vivo. Importantly, we found an inverse correlation between CK2 kinase activity and PML protein levels in human lung cancer-derived cell lines and primary specimens. These data identify a key posttranslational mechanism that controls PML protein levels and provide therapeutic means toward PML restoration through CK2 inhibition.

    Funded by: NCI NIH HHS: K08 CA112325-01, P30 CA08748, R01 CA71692

    Cell 2006;126;2;269-83

  • Discrimination between the activity of protein kinase CK2 holoenzyme and its catalytic subunits.

    Salvi M, Sarno S, Marin O, Meggio F, Itarte E and Pinna LA

    Dipartimento di Chimica Biologica, Università di Padova, viale G. Colombo 3, 35121 Padova, Italy.

    The acronym CK2 denotes a highly pleiotropic Ser/Thr protein kinase whose over-expression correlates with neoplastic growth. A vexed question about the enigmatic regulation of CK2 concerns the actual existence in living cells of the catalytic (alpha and/or alpha') and regulatory beta-subunits of CK2 not assembled into the regular heterotetrameric holoenzyme. Here we take advantage of novel reagents, namely a peptide substrate and an inhibitor which discriminate between the holoenzyme and the catalytic subunits, to show that CK2 activity in CHO cells is entirely accounted for by the holoenzyme. Transfection with individual subunits moreover does not give rise to holoenzyme formation unless the catalytic and regulatory subunits are co-transfected together, arguing against the existence of free subunits in CHO cells.

    FEBS letters 2006;580;16;3948-52

  • Compartmentation of the nucleolar processing proteins in the granular component is a CK2-driven process.

    Louvet E, Junéra HR, Berthuy I and Hernandez-Verdun D

    Institut Jacques Monod, Centre National de la Recherche Scientifique, University Paris VI and Paris VII, 75251 Paris Cedex 05, France.

    To analyze the compartmentation of nucleolar protein complexes, the mechanisms controlling targeting of nucleolar processing proteins onto rRNA transcription sites has been investigated. We studied the reversible disconnection of transcripts and processing proteins using digitonin-permeabilized cells in assays capable of promoting nucleolar reorganization. The assays show that the dynamics of nucleolar reformation is ATP/GTP-dependent, sensitive to temperature, and CK2-driven. We further demonstrate the role of CK2 on the rRNA-processing protein B23. Mutation of the major CK2 site on B23 induces reorganization of nucleolar components that separate from each other. This was confirmed in assays using extracts containing B23 mutated in the CK2-binding sites. We propose that phosphorylation controls the compartmentation of the rRNA-processing proteins and that CK2 is involved in this process.

    Molecular biology of the cell 2006;17;6;2537-46

  • Expression of protein kinase CK2 in astroglial cells of normal and neovascularized retina.

    Kramerov AA, Saghizadeh M, Pan H, Kabosova A, Montenarh M, Ahmed K, Penn JS, Chan CK, Hinton DR, Grant MB and Ljubimov AV

    Ophthalmology Research Laboratories, Cedars-Sinai Medical Center, University of California at Los Angeles School of Medicine, 90048, USA. kramerova@cshs.org

    We previously documented protein kinase CK2 involvement in retinal neovascularization. Here we describe retinal CK2 expression and combined effects of CK2 inhibitors with the somatostatin analog octreotide in a mouse model of oxygen-induced retinopathy (OIR). CK2 expression in human and rodent retinas with and without retinopathy and in astrocytic and endothelial cultures was examined by immunohistochemistry, Western blotting, and reverse transcriptase-polymerase chain reaction. A combination of CK2 inhibitors, emodin or 4,5,6,7-tetrabromobenzotriazole, with octreotide was injected intraperitoneally from postnatal (P) day P11 to P17 to block mouse OIR. All CK2 subunits (alpha, alpha', beta) were expressed in retina, and a novel CK2alpha splice variant was detected by reverse transcriptase-polymerase chain reaction. CK2 antibodies primarily reacted with retinal astrocytes, and staining was increased around new intraretinal vessels in mouse OIR and rat retinopathy of prematurity, whereas preretinal vessels were negative. Cultured astrocytes showed increased perinuclear CK2 staining compared to endothelial cells. In the OIR model, CK2 mRNA expression increased modestly on P13 but not on P17. Octreotide combined with emodin or 4,5,6,7-tetrabromobenzotriazole blocked mouse retinal neovascularization more efficiently than either compound alone. Based on its retinal localization, CK2 may be considered a new immunohistochemical astrocytic marker, and combination of CK2 inhibitors and octreotide may be a promising future treatment for proliferative retinopathies.

    Funded by: NEI NIH HHS: 2R01 EY7709

    The American journal of pathology 2006;168;5;1722-36

  • Variable phosphorylation states of pigment-epithelium-derived factor differentially regulate its function.

    Maik-Rachline G and Seger R

    Department of Biological Regulation, The Weizmann Institute of Science, Rehovot 76100, Israel.

    The pigment epithelium-derived factor (PEDF) belongs to the family of noninhibitory serpins. Although originally identified in the eye, PEDF is widely expressed in other body regions including the plasma. This factor can act either as a neurotrophic or as an antiangiogenic factor, and we previously showed that the 2 effects of PEDF are regulated through phosphorylation by PKA and CK2. Here, we studied the interplay between the PKA and CK2 phosphorylation of PEDF, and found that a PEDF mutant mimicking the CK2-phosphorylated PEDF cannot be phosphorylated by PKA, while the mutant mimicking the PKA-phosphorylated PEDF is a good CK2 substrate. Using triple mutants that mimic the PKA- and CK2-phosphorylated and nonphosphorylated PEDF, we found that PEDF can induce several distinct cellular activities dependent on its phosphorylation. The mutant mimicking the accumulative PKA plus CK2 phosphorylation exhibited the strongest antiangiogenic and neurotrophic activities, while the mutants mimicking the individual phosphorylation site mutants had either a reduced activity or only one of these activities. Thus, differential phosphorylation induces variable effects of PEDF, and therefore contributes to the complexity of PEDF action. It is likely that the triple phosphomimetic mutant can be used to generate effective antiangiogenic or neurotrophic drugs.

    Blood 2006;107;7;2745-52

  • NKX3.1 is regulated by protein kinase CK2 in prostate tumor cells.

    Li X, Guan B, Maghami S and Bieberich CJ

    Department of Biological Sciences, University of Maryland Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250, USA.

    Diminished expression of NKX3.1 is associated with prostate cancer progression in humans, and in mice, loss of nkx3.1 leads to epithelial cell proliferation and altered gene expression patterns. The NKX3.1 amino acid sequence includes multiple potential phosphoacceptor sites for protein kinase CK2. To investigate posttranslational regulation of NKX3.1, phosphorylation of NKX3.1 by CK2 was studied. In vitro kinase assays followed by mass spectrometric analyses demonstrated that CK2 phosphorylated recombinant NKX3.1 on Thr89 and Thr93. Blocking CK2 activity in LNCaP cells with apigenin or 5,6-dichlorobenzimidazole riboside led to a rapid decrease in NKX3.1 accumulation that was rescued by proteasome inhibition. Replacing Thr89 and Thr93 with alanines decreased NKX3.1 stability in vivo. Small interfering RNA knockdown of CK2alpha' but not CK2alpha also led to a decrease in NKX3.1 steady-state level. In-gel kinase assays and Western blot analyses using fractionated extracts of LNCaP cells demonstrated that free CK2alpha' could phosphorylate recombinant human and mouse NKX3.1, whereas CK2alpha' liberated from the holoenzyme could not. These data establish CK2 as a regulator of NKX3.1 in prostate tumor cells and provide evidence for functionally distinct pools of CK2alpha' in LNCaP cells.

    Molecular and cellular biology 2006;26;8;3008-17

  • CK2-dependent C-terminal phosphorylation at T300 directs the nuclear transport of TSPY protein.

    Krick R, Aschrafi A, Hasgün D and Arnemann J

    Institute of Human Genetics, Johann Wolfgang Goethe University Hospital, Frankfurt am Main, Germany.

    TSPY (testis-specific protein, Y-encoded) is a member of the greater SET/NAP family of molecules with various functions, e.g., in chromatin remodeling, regulation of gene expression, and has been implicated to play a role in the malignant development of gonadoblastoma, testicular and prostate cancer. Here we demonstrate that the C-terminus has a functional role for the nucleo-cytoplasmatic shuttling of the TSPY protein. Using various combinations of in vitro mutagenesis and enhanced green fluorescent protein reporter gene-expression experiments we were able to show that while the deletion of C-terminus leads to a decreased stability and enhanced degradation of the protein, the selective mutation of a C-terminal CK2 phosphorylation site (T300) prevents the TSPY protein from entering the nucleus. We conclude that phosphorylation of the (T300) residue is a necessary and functional prerequisite for TSPY's transport into the nucleus reminding of comparable data from a related Drosophila molecule, NAP1.

    Biochemical and biophysical research communications 2006;341;2;343-50

  • The N-terminal domain of the human eIF2beta subunit and the CK2 phosphorylation sites are required for its function.

    Llorens F, Duarri A, Sarró E, Roher N, Plana M and Itarte E

    Departament de Bioquímica i Biologia Molecular, Unitat de Bioquímica de Ciències, Universitat Autònoma de Barcelona, Edifici Cs, Campus de Bellaterra, 08193 Bellaterra, Barcelona, Spain. Franc.llorens@uab.es

    CK2 (protein kinase CK2) is known to phosphorylate eIF2 (eukaryotic translation initiation factor 2) in vitro; however, its implication in this process in living cells has remained to be confirmed. The combined use of chemical inhibitors (emodin and apigenin) of CK2 together with transfection experiments with the wild-type of the K68A kinase-dead mutant form of CK2alpha evidenced the direct involvement of this protein kinase in eIF2beta phosphorylation in cultured HeLa cells. Transfection of HeLa cells with human wild-type eIF2beta or its phosphorylation site mutants showed Ser2 as the main site for constitutive eIF2beta phosphorylation, whereas phosphorylation at Ser67 seems more restricted. In vitro phosphorylation of eIF2beta also pointed to Ser2 as a preferred site for CK2 phosphorylation. Overexpression of the eIF2beta S2/67A mutant slowed down the rate of protein synthesis stimulated by serum, although less markedly than the overexpression of the Delta2-138 N-terminal-truncated form of eIF2beta (eIF2beta-CT). Mutation at Ser2 and Ser67 did not affect eIF2beta integrating into the eIF2 trimer or being able to complex with eIF5 and CK2alpha. The eIF2beta-CT form was also incorporated into the eIF2 trimer but did not bind to eIF5. Overexpression of eIF2beta slightly decreased HeLa cell viability, an effect that was more evident when overexpressing the eIF2beta S2/67A mutant. Cell death was particularly marked when overexpressing the eIF2beta-CT form, being detectable at doses where eIF2beta and eIF2beta S2/67A were ineffective. These results suggest that Ser2 and Ser67 contribute to the important role of the N-terminal region of eIF2beta for its function in mammals.

    The Biochemical journal 2006;394;Pt 1;227-36

  • Phosphorylation on Ser106 modulates the cellular functions of the SHOX homeodomain protein.

    Marchini A, Daeffler L, Marttila T, Schneider KU, Blaschke RJ, Schnölzer M, Rommelaere J and Rappold G

    Institute of Human Genetics, University of Heidelberg, Im Neuenheimer Feld 366, D-69120 Heidelberg, Germany. antonio_marchini@med.uni-heidelberg.de

    Mutations within the homeobox SHOX gene have been associated with short stature and the skeletal deformities found in Léri-Weill, Turner and Langer syndromes implying an involvement of SHOX in growth and bone formation. Despite its clinical significance, the precise role of SHOX and the mechanisms that modulate its functions remain unknown. We reported previously that SHOX is a nuclear protein that specifically binds DNA and acts as a transcriptional activator. We have shown that ectopic expression of SHOX leads to cell-cycle arrest and apoptosis in osteosarcoma and primary cells. To further characterize SHOX, we investigated whether the protein could be a target for phosphorylation. Here, we report that SHOX is phosphorylated exclusively on serine residues in vivo. Two-dimensional phospho-peptide mapping showed that SHOX is phosphorylated to various extents on multiple sites. Site-directed mutagenesis demonstrated that serine 106 is the major SHOX phosphorylation site. We show also that casein kinase II phosphorylates SHOX on serine 106 efficiently in vitro and specific casein kinase II inhibitors reduce SHOX phosphorylation strongly in vivo. Finally, we provide evidence that phosphorylation may play an important role in modulating SHOX biological activities, since a S106A SHOX mutant, defective in phosphorylation, does not activate transcription and fails to induce cell-cycle arrest and apoptosis.

    Journal of molecular biology 2006;355;3;590-603

  • Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes.

    Kimura K, Wakamatsu A, Suzuki Y, Ota T, Nishikawa T, Yamashita R, Yamamoto J, Sekine M, Tsuritani K, Wakaguri H, Ishii S, Sugiyama T, Saito K, Isono Y, Irie R, Kushida N, Yoneyama T, Otsuka R, Kanda K, Yokoi T, Kondo H, Wagatsuma M, Murakawa K, Ishida S, Ishibashi T, Takahashi-Fujii A, Tanase T, Nagai K, Kikuchi H, Nakai K, Isogai T and Sugano S

    Life Science Research Laboratory, Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo, 185-8601, Japan.

    By analyzing 1,780,295 5'-end sequences of human full-length cDNAs derived from 164 kinds of oligo-cap cDNA libraries, we identified 269,774 independent positions of transcriptional start sites (TSSs) for 14,628 human RefSeq genes. These TSSs were clustered into 30,964 clusters that were separated from each other by more than 500 bp and thus are very likely to constitute mutually distinct alternative promoters. To our surprise, at least 7674 (52%) human RefSeq genes were subject to regulation by putative alternative promoters (PAPs). On average, there were 3.1 PAPs per gene, with the composition of one CpG-island-containing promoter per 2.6 CpG-less promoters. In 17% of the PAP-containing loci, tissue-specific use of the PAPs was observed. The richest tissue sources of the tissue-specific PAPs were testis and brain. It was also intriguing that the PAP-containing promoters were enriched in the genes encoding signal transduction-related proteins and were rarer in the genes encoding extracellular proteins, possibly reflecting the varied functional requirement for and the restricted expression of those categories of genes, respectively. The patterns of the first exons were highly diverse as well. On average, there were 7.7 different splicing types of first exons per locus partly produced by the PAPs, suggesting that a wide variety of transcripts can be achieved by this mechanism. Our findings suggest that use of alternate promoters and consequent alternative use of first exons should play a pivotal role in generating the complexity required for the highly elaborated molecular systems in humans.

    Genome research 2006;16;1;55-65

  • Phosphorylation by casein kinase 2 induces PACS-1 binding of nephrocystin and targeting to cilia.

    Schermer B, Höpker K, Omran H, Ghenoiu C, Fliegauf M, Fekete A, Horvath J, Köttgen M, Hackl M, Zschiedrich S, Huber TB, Kramer-Zucker A, Zentgraf H, Blaukat A, Walz G and Benzing T

    Renal Division, University Hospital Freiburg, Freiburg, Germany.

    Mutations in proteins localized to cilia and basal bodies have been implicated in a growing number of human diseases. Access of these proteins to the ciliary compartment requires targeting to the base of the cilia. However, the mechanisms involved in transport of cilia proteins to this transitional zone are elusive. Here we show that nephrocystin, a ciliary protein mutated in the most prevalent form of cystic kidney disease in childhood, is expressed in respiratory epithelial cells and accumulates at the base of cilia, overlapping with markers of the basal body area and the transition zone. Nephrocystin interacts with the phosphofurin acidic cluster sorting protein (PACS)-1. Casein kinase 2 (CK2)-mediated phosphorylation of three critical serine residues within a cluster of acidic amino acids in nephrocystin mediates PACS-1 binding, and is essential for colocalization of nephrocystin with PACS-1 at the base of cilia. Inhibition of CK2 activity abrogates this interaction and results in the loss of correct nephrocystin targeting. These data suggest that CK2-dependent transport processes represent a novel pathway of targeting proteins to the cilia.

    The EMBO journal 2005;24;24;4415-24

  • Phosphorylation inhibits DNA-binding of alternatively spliced aryl hydrocarbon receptor nuclear translocator.

    Kewley RJ and Whitelaw ML

    School of Molecular and Biomedical Science (Biochemistry), Centre for the Molecular Genetics of Development, University of Adelaide, SA 5005, Australia. rkewley@csu.edu.au

    The basic helix-loop-helix/PER-ARNT-SIM homology (bHLH/PAS) transcription factor ARNT (aryl hydrocarbon receptor nuclear translocator) is a key component of various pathways which induce the transcription of cytochrome P450 and hypoxia response genes. ARNT can be alternatively spliced to express Alt ARNT, containing an additional 15 amino acids immediately N-terminal to the DNA-binding basic region. Here, we show that ARNT and Alt ARNT proteins are differentially phosphorylated by protein kinase CKII in vitro. Phosphorylation had an inhibitory effect on DNA-binding to an E-box probe by Alt ARNT, but not ARNT, homodimers. This inhibitory phosphorylation occurs through Ser77. Moreover, a point mutant, Alt ARNT S77A, shows increased activity on an E-box reporter gene, consistent with Ser77 being a regulatory site in vivo. In contrast, DNA binding by an Alt ARNT/dioxin receptor heterodimer to the xenobiotic response element is not inhibited by phosphorylation with CKII, nor does Alt ARNT S77A behave differently from wild type Alt ARNT in the context of a dioxin receptor heterodimer.

    Biochemical and biophysical research communications 2005;338;1;660-7

  • Regulation of CK2 activity by phosphatidylinositol phosphates.

    Korolchuk VI, Cozier G and Banting G

    Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.

    The process of clathrin-coated vesicle (CCV) formation/disassembly involves numerous proteins that act cooperatively. Phosphorylation is an important regulatory mechanism governing protein interactions in CCVs, and many of the core and accessory proteins of the CCV machinery are reversibly phosphorylated in vivo. CK2 is highly enriched in CCVs and is capable of phosphorylating a number of peripheral membrane proteins involved in the process of clathrin-mediated endocytosis. At least some of these phosphorylation events have been shown to be inhibitory for CCV assembly, and CK2 has been shown to be inactive when associated with intact CCVs. Here we show that CCV membranes inhibit CK2 activity even after incubation in trypsin, indicating that a component of the lipid bilayer may be the inhibitory factor. Consistent with this, we showed that liposomes containing phosphatidylinositol phosphates inhibit the activity of CK2 and that CK2 binds to those liposomes. Notably, liposomes containing phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)), a component of CCVs, bind CK2 and inhibit its activity. Furthermore, we showed that the binding of CK2 to PtdIns(4,5)P(2)-containing liposomes is via the active site of CK2, thus providing a molecular explanation for the inhibition of CK2 activity when it is bound to PtdIns(4,5)P(2)-containing liposomes. Thus CK2 is inactive in CCVs because of the fact that it is bound to the CCV membrane via an interaction between PtdIns(4,5)P(2) in the CCV membrane and the active site in CK2.

    The Journal of biological chemistry 2005;280;49;40796-801

  • Two human ACAT2 mRNA variants produced by alternative splicing and coding for novel isoenzymes.

    Yao XM, Wang CH, Song BL, Yang XY, Wang ZZ, Qi W, Lin ZX, Chang CC, Chang TY and Li BL

    State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.

    Acyl coenzyme A:cholesterol acyltransferase 2 (ACAT2) plays an important role in cholesterol absorption. Human ACAT2 is highly expressed in small intestine and fetal liver, but its expression is greatly diminished in adult liver. The full-length human ACAT2 mRNA encodes a protein, designated ACAT2a, with 522 amino acids. We have previously reported the organization of the human ACAT2 gene and the differentiation-dependent promoter activity in intestinal Caco-2 cells. In the current work, two human ACAT2 mRNA variants produced by alternative splicing are cloned and predicted to encode two novel ACAT2 isoforms, named ACAT2b and ACAT2c, with 502 and 379 amino acids, respectively. These mRNA variants differ from ACAT2a mRNA by lack of the exon 4 (ACAT2b mRNA) and exons 4-5 plus 8-9-10 (ACAT2c mRNA). Significantly, comparable amounts of the alternatively spliced ACAT2 mRNA variants were detected by RT-PCR, and Western blot analysis confirmed the presence of their corresponding proteins in human liver and intestinecells. Furthermore, phosphorylation and enzymatic activity analyses demonstrated that the novel isoenzymes ACAT2b and ACAT2c lacked the phosphorylatable site SLLD, and their enzymatic activities reduced to 25%-35% of that of ACAT2a. These evidences indicate that alternative splicing produces two human ACAT2 mRNA variants that encode the novel ACAT2 isoenzymes. Our findings might help to understand the regulation of the ACAT2 gene expression under certain physiological and pathological conditions.

    Funded by: NHLBI NIH HHS: HL60306

    Acta biochimica et biophysica Sinica 2005;37;12;797-806

  • CK2 phosphorylation of eukaryotic translation initiation factor 5 potentiates cell cycle progression.

    Homma MK, Wada I, Suzuki T, Yamaki J, Krebs EG and Homma Y

    Department of Biomolecular Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan. mkhomma@fmu.ac.jp

    Casein kinase 2 (CK2) is a ubiquitous eukaryotic Ser/Thr protein kinase that plays an important role in cell cycle progression. Although its function in this process remains unclear, it is known to be required for the G(1) and G(2)/M phase transitions in yeast. Here, we show that CK2 activity changes notably during cell cycle progression and is increased within 3 h of serum stimulation of quiescent cells. During the time period in which it exhibits high enzymatic activity, CK2 associates with and phosphorylates a key molecule for translation initiation, eukaryotic translation initiation factor (eIF) 5. Using MS, we show that Ser-389 and -390 of eIF5 are major sites of phosphorylation by CK2. This is confirmed using eIF5 mutants that lack CK2 sites; the phosphorylation levels of mutant eIF5 proteins are significantly reduced, relative to WT eIF5, both in vitro and in vivo. Expression of these mutants reveals that they have a dominant-negative effect on phosphorylation of endogenous eIF5, and that they perturb synchronous progression of cells through S to M phase, resulting in a significant reduction in growth rate. Furthermore, the formation of mature eIF5/eIF2/eIF3 complex is reduced in these cells, and, in fact, restricted diffusional motion of WT eIF5 was almost abolished in a GFP-tagged eIF5 mutant lacking CK2 phosphorylation sites, as measured by fluorescence correlation spectroscopy. These results suggest that CK2 may be involved in the regulation of cell cycle progression by associating with and phosphorylating a key molecule for translation initiation.

    Proceedings of the National Academy of Sciences of the United States of America 2005;102;43;15688-93

  • Cooperative phosphorylation of the tumor suppressor phosphatase and tensin homologue (PTEN) by casein kinases and glycogen synthase kinase 3beta.

    Al-Khouri AM, Ma Y, Togo SH, Williams S and Mustelin T

    Inflammatory and Infectious Disease Center, The Burnham Institute, La Jolla, California 92037, USA.

    The phosphatase and tensin homologue (PTEN) tumor suppressor is a phosphatidylinositol D3-phosphatase that counteracts the effects of phosphatidylinositol 3-kinase and negatively regulates cell growth and survival. PTEN is itself regulated by phosphorylation on multiple serine and threonine residues in its C terminus. Previous work has implicated casein kinase 2 (CK2) as the kinase responsible for this phosphorylation. Here we showed that CK2 does not phosphorylate all sites in PTEN and that glycogen synthase kinase 3beta (GSK3beta) also participates in PTEN phosphorylation. Although CK2 mainly phosphorylated PTEN at Ser-370 and Ser-385, GSK3beta phosphorylated Ser-362 and Thr-366. More importantly, prior phosphorylation of PTEN at Ser-370 by CK2 strongly increased its phosphorylation at Thr-366 by GSK3beta, suggesting that the two may synergize. Using RNA interference, we showed that GSK3 phosphorylates PTEN in intact cells. Finally, PTEN phosphorylation was affected by insulin-like growth factor in intact cells. We concluded that multiple kinases, including CK2 and GSK3beta, participate in PTEN phosphorylation and that GSK3beta may provide feedback regulation of PTEN.

    Funded by: NCI NIH HHS: CA96949

    The Journal of biological chemistry 2005;280;42;35195-202

  • Caspase-2 primes cancer cells for TRAIL-mediated apoptosis by processing procaspase-8.

    Shin S, Lee Y, Kim W, Ko H, Choi H and Kim K

    Department of Biochemistry and Molecular Biology, Yonsei University College of Medicine, Brain Korea 21 Project for Medical Science of Yonsei University, Seodaemun-gu, Seoul, Korea.

    Although caspase-2 is believed to be involved in death receptor-mediated apoptosis, the exact function, mode of activation, and regulation of caspase-2 remain unknown. Here we show that protein kinase (PK) CK2 phosphorylates procaspase-2 directly at serine-157. When intracellular PKCK2 activity is low or downregulated by specific inhibitors, procaspase-2 is dephosphorylated, dimerized, and activated in a PIDDosome-independent manner. The activated caspase-2 then processes procaspase-8 monomers between the large and small subunits, thereby priming cancer cells for TNF-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. The processed procaspase-8 that is recruited to death-inducing signaling complex by TRAIL engagement becomes fully activated, and cancer cells undergo apoptosis. PKCK2 activity is low in TRAIL-sensitive cancer cell lines but high in TRAIL-resistant cancer cell lines. Thus, downregulating PKCK2 activity is required for TRAIL-mediated apoptosis to occur in TRAIL-resistant cancer cells. Our data provide novel insights into the regulation, mode of activation, and function of caspase-2 in TRAIL-mediated apoptosis.

    The EMBO journal 2005;24;20;3532-42

  • A human protein-protein interaction network: a resource for annotating the proteome.

    Stelzl U, Worm U, Lalowski M, Haenig C, Brembeck FH, Goehler H, Stroedicke M, Zenkner M, Schoenherr A, Koeppen S, Timm J, Mintzlaff S, Abraham C, Bock N, Kietzmann S, Goedde A, Toksöz E, Droege A, Krobitsch S, Korn B, Birchmeier W, Lehrach H and Wanker EE

    Max Delbrueck Center for Molecular Medicine, 13092 Berlin-Buch, Germany.

    Protein-protein interaction maps provide a valuable framework for a better understanding of the functional organization of the proteome. To detect interacting pairs of human proteins systematically, a protein matrix of 4456 baits and 5632 preys was screened by automated yeast two-hybrid (Y2H) interaction mating. We identified 3186 mostly novel interactions among 1705 proteins, resulting in a large, highly connected network. Independent pull-down and co-immunoprecipitation assays validated the overall quality of the Y2H interactions. Using topological and GO criteria, a scoring system was developed to define 911 high-confidence interactions among 401 proteins. Furthermore, the network was searched for interactions linking uncharacterized gene products and human disease proteins to regulatory cellular pathways. Two novel Axin-1 interactions were validated experimentally, characterizing ANP32A and CRMP1 as modulators of Wnt signaling. Systematic human protein interaction screens can lead to a more comprehensive understanding of protein function and cellular processes.

    Cell 2005;122;6;957-68

  • Cyclin-dependent kinase (CDK) phosphorylation destabilizes somatic Wee1 via multiple pathways.

    Watanabe N, Arai H, Iwasaki J, Shiina M, Ogata K, Hunter T and Osada H

    Antibiotics Laboratory, Discovery Research Institute, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. nwatanab@riken.jp

    At the onset of M phase, the activity of somatic Wee1 (Wee1A), the inhibitory kinase for cyclin-dependent kinase (CDK), is down-regulated primarily through proteasome-dependent degradation after ubiquitination by the E3 ubiquitin ligase SCF(beta-TrCP). The F-box protein beta-TrCP (beta-transducin repeat-containing protein), the substrate recognition component of the ubiquitin ligase, binds to its substrates through a conserved binding motif (phosphodegron) containing two phosphoserines, DpSGXXpS. Although Wee1A lacks this motif, phosphorylation of serines 53 and 123 (S53 and S123) of Wee1A by polo-like kinase 1 (Plk1) and CDK, respectively, are required for binding to beta-TrCP. The sequence surrounding phosphorylated S53 (DpSAFQE) is similar to the conserved beta-TrCP-binding motif; however, the role of S123 phosphorylation (EEGFGSSpSPVK) in beta-TrCP binding was not elucidated. In the present study, we show that phosphorylation of S123 (pS123) by CDK promoted the binding of Wee1A to beta-TrCP through three independent mechanisms. The pS123 not only directly interacted with basic residues in the WD40 repeat domain of beta-TrCP but also primed phosphorylation by two independent protein kinases, Plk1 and CK2 (formerly casein kinase 2), to create two phosphodegrons on Wee1A. In the case of Plk1, S123 phosphorylation created a polo box domain-binding motif (SpSP) on Wee1A to accelerate phosphorylation of S53 by Plk1. CK2 could phosphorylate S121, but only if S123 was phosphorylated first, thereby generating the second beta-TrCP-binding site (EEGFGpS121). Using a specific inhibitor of CK2, we showed that the phosphorylation-dependent degradation of Wee1A is important for the proper onset of mitosis.

    Proceedings of the National Academy of Sciences of the United States of America 2005;102;33;11663-8

  • Validation of protein kinase CK2 as oncological target.

    Seeber S, Issinger OG, Holm T, Kristensen LP and Guerra B

    Roche Diagnostics GmbH, Pharma Research Penzberg, Nonnenwald 2, D-82377 Penzberg, Germany.

    Protein kinase CK2 is a highly conserved enzyme composed of two catalytic subunits alpha and/or alpha' and two regulatory subunits beta whose activity is elevated in diverse tumour types as well as in highly proliferating tissues. Several results suggest that the overexpression of either CK2 catalytic subunits or the CK2 holoenzyme contributes to cellular transformation. In a similar vein, experiments performed compromising the intracellular expression of CK2 has led to somehow contradictory results with respect to the ability of this enzyme to control survival and apoptosis. To better elucidate the role of CK2 in programmed cell death, we have depleted cells of CK2 catalytic subunits by the application of antisense oligodeoxynucleotides and siRNAs techniques, respectively. Our results indicate that protein kinase CK2 is characterized by an extremely high stability that might be due to its association with other intracellular proteins, enhanced half-life or lower vulnerability towards proteolytic degradation. In addition, we show that despite the effectiveness of the methods applied in lowering CK2 kinase activity in all cells investigated, CK2 might not by itself be sufficient to trigger enhanced drug-induced apoptosis in cells.

    Apoptosis : an international journal on programmed cell death 2005;10;4;875-85

  • Cooperation between small nuclear RNA-activating protein complex (SNAPC) and TATA-box-binding protein antagonizes protein kinase CK2 inhibition of DNA binding by SNAPC.

    Gu L, Esselman WJ and Henry RW

    Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824, USA.

    Protein kinase CK2 regulates RNA polymerase III transcription of human U6 small nuclear RNA (snRNA) genes both negatively and positively depending upon whether the general transcription machinery or RNA polymerase III is preferentially phosphorylated. Human U1 snRNA genes share similar promoter architectures as that of U6 genes but are transcribed by RNA polymerase II. Herein, we report that CK2 inhibits U1 snRNA gene transcription by RNA polymerase II. Decreased levels of endogenous CK2 correlates with increased U1 expression, whereas CK2 associates with U1 gene promoters, indicating that it plays a direct role in U1 gene regulation. CK2 phosphorylates the general transcription factor small nuclear RNA-activating protein complex (SNAP(C)) that is required for both RNA polymerase II and III transcription, and SNAP(C) phosphorylation inhibits binding to snRNA gene promoters. However, restricted promoter access by phosphorylated SNAP(C) can be overcome by cooperative interactions with TATA-box-binding protein at a U6 promoter but not at a U1 promoter. Thus, CK2 may have the capacity to differentially regulate U1 and U6 transcription even though SNAP(C) is universally utilized for human snRNA gene transcription.

    Funded by: NIGMS NIH HHS: GM59805

    The Journal of biological chemistry 2005;280;30;27697-704

  • Downregulation of CK2 induces apoptosis in cancer cells--a potential approach to cancer therapy.

    Wang G, Unger G, Ahmad KA, Slaton JW and Ahmed K

    Cellular and Molecular Biochemistry Research Laboratory (151), Minneapolis Veterans Affairs Medical Center, Minneapolis, MN 55417, USA.

    We have previously documented that naked antisense CK2alpha ODN can potently induce apoptosis in cancer cells in culture and in mouse xenograft human prostate cancer. The effects of the antisense CK2alpha are related to downregulation of CK2alpha message and rapid loss of the CK2 from the nuclear compartment. Here we demonstrate that downregulation of CK2 elicited by diverse methods leads to inhibition of cell growth and induction of apoptosis. The various approaches to downregulation of CK2 employed were transfection with kinase-inactive plasmid, use of CK2alpha siRNA, use of inhibitors of CK2 activity, and use of antisense CK2alpha ODN packaged in sub-50 nm nanocapsules made from tenascin. In all cases, the downregulation of CK2 is associated with loss in cell survival. We have also described preliminary observations on an approach to targeting CK2 in cancer cells. For this, sub-50 nm tenascin-based nanocapsules bearing the antisense CK2alpha ODN were employed to test that the antisense is delivered to the cancer cells in vivo. The results provide the first preliminary evidence that such an approach may be feasible for targeting CK2 in cancer cells. Together, our results suggest that CK2 is potentially a highly plausible target for cancer therapy.

    Funded by: PHS HHS: UA-15062

    Molecular and cellular biochemistry 2005;274;1-2;77-84

  • Protein kinase CK2 phosphorylates and upregulates Akt/PKB.

    Di Maira G, Salvi M, Arrigoni G, Marin O, Sarno S, Brustolon F, Pinna LA and Ruzzene M

    Venetian Institute of Molecular Medicine (VIMM), University of Padova, Padova, Italy.

    Treatment of Jurkat cells with specific inhibitors of protein kinase CK2 induces apoptosis. Here we provide evidence that the anti-apoptotic effect of CK2 can be at least partially mediated by upregulation of the Akt/PKB pathway. Such a conclusion is based on the following observations: (1) inhibition of CK2 by cell treatment with two structurally unrelated CK2 inhibitors induces downregulation of Akt/PKB, as judged from decreased phosphorylation of its physiological targets, and immunoprecipitate kinase assay; (2) similar results are observed upon reduction of CK2 catalytic subunit by the RNA-interference technique; (3) Akt/PKB Ser129 is phosphorylated by CK2 in vitro and in vivo; (4) such a phosphorylation of activated Akt/PKB correlates with a further increase in catalytic activity. These data disclose an unanticipated mechanism by which constitutive phosphorylation by CK2 may be required for maximal activation of Akt/PKB.

    Cell death and differentiation 2005;12;6;668-77

  • Targeted proteomic analysis of 14-3-3 sigma, a p53 effector commonly silenced in cancer.

    Benzinger A, Muster N, Koch HB, Yates JR and Hermeking H

    Molecular Oncology, Max-Planck-Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried/Munich, Germany.

    To comprehensively identify proteins interacting with 14-3-3 sigma in vivo, tandem affinity purification and the multidimensional protein identification technology were combined to characterize 117 proteins associated with 14-3-3 sigma in human cells. The majority of identified proteins contained one or several phosphorylatable 14-3-3-binding sites indicating a potential direct interaction with 14-3-3 sigma. 25 proteins were not previously assigned to any function and were named SIP2-26 (for 14-3-3 sigma-interacting protein). Among the 92 interactors with known function were a number of proteins previously implicated in oncogenic signaling (APC, A-RAF, B-RAF, and c-RAF) and cell cycle regulation (AJUBA, c-TAK, PTOV-1, and WEE1). The largest functional classes comprised proteins involved in the regulation of cytoskeletal dynamics, polarity, adhesion, mitogenic signaling, and motility. Accordingly ectopic 14-3-3 sigma expression prevented cellular migration in a wounding assay and enhanced mitogen-activated protein kinase signaling. The functional diversity of the identified proteins indicates that induction of 14-3-3 sigma could allow p53 to affect numerous processes in addition to the previously characterized inhibitory effect on G2/M progression. The data suggest that the cancer-specific loss of 14-3-3 sigma expression by epigenetic silencing or p53 mutations contributes to cancer formation by multiple routes.

    Funded by: NCRR NIH HHS: RR11823-08

    Molecular & cellular proteomics : MCP 2005;4;6;785-95

  • Functional characterization of core promoter elements: DPE-specific transcription requires the protein kinase CK2 and the PC4 coactivator.

    Lewis BA, Sims RJ, Lane WS and Reinberg D

    Division of Nucleic Acids Enzymology, Department of Biochemistry, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, New Jersey 08854, USA.

    Downstream core promoter elements are an expanding class of regulatory sequences that add considerable diversity to the promoter architecture of RNA polymerase II-transcribed genes. We set out to determine the factors necessary for downstream promoter element (DPE)-dependent transcription and find that, against expectations, TFIID and the GTFs are not sufficient. Instead, the protein kinase CK2 and the coactivator PC4 establish DPE-specific transcription in an in vitro transcription system containing TFIID, Mediator, and the GTFs. Chromatin immunoprecipitation analyses using the DPE-dependent IRF-1 and TAF7 promoters demonstrated that CK2, and PC4 are present on these promoters in vivo. In contrast, neither PC4 nor CK2 were detected on the TAF1-dependent cyclin D promoter, which contains a DCE type of downstream element. Our findings also demonstrate that CK2 activity alters TFIID-dependent recognition of DCE sequences. These data establish that CK2 acts as a switch, converting the transcriptional machinery from functioning on one type of downstream element to another.

    Funded by: NIDDK NIH HHS: K01 DK60001; NIGMS NIH HHS: GM-64844, GM-71166

    Molecular cell 2005;18;4;471-81

  • Histone deacetylase 3 (HDAC3) activity is regulated by interaction with protein serine/threonine phosphatase 4.

    Zhang X, Ozawa Y, Lee H, Wen YD, Tan TH, Wadzinski BE and Seto E

    H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, USA.

    Histone deacetylase 3 (HDAC3) is one of four members of the human class I HDACs that regulates gene expression by deacetylation of histones and nonhistone proteins. Early studies have suggested that HDAC3 activity is regulated by association with the corepressors N-CoR and SMRT. Here we demonstrate that, in addition to protein-protein interactions with NCoR/SMRT, the activity of HDAC3 is regulated by both phosphorylation and dephosphorylation. A protein kinase CK2 phosphoacceptor site in the HDAC3 protein was identified at position Ser424, which is a nonconserved residue among the class I HDACs. Mutation of this residue was found to reduce deacetylase activity. Interestingly, unlike other class I HDACs, HDAC3 uniquely copurifies with the catalytic and regulatory subunits of the protein serine/threonine phosphatase 4 complex (PP4c/PP4R1). Furthermore, HDAC3 complexes displayed protein phosphatase activity and a series of subsequent mutational analyses revealed that the N terminus of HDAC3 (residues 1-122) was both necessary and sufficient for HDAC3-PP4c interactions. Significantly, both overexpression and siRNA knock-down approaches, and analysis of cells devoid of PP4c, unequivocally show that HDAC3 activity is inversely proportional to the cellular abundance of PP4(c). These findings therefore further highlight the importance of protein-protein interactions and extend the significance of dephosphorylation in the regulation of HDAC activity, as well as present a novel alternative pathway by which HDAC3 activity is regulated.

    Funded by: NCI NIH HHS: CA109699; NIGMS NIH HHS: GM58486

    Genes & development 2005;19;7;827-39

  • CK2 phosphorylates SSRP1 and inhibits its DNA-binding activity.

    Li Y, Keller DM, Scott JD and Lu H

    Department of Biochemistry and Molecular Biology, Oregon Health and Science University, Portland, Oregon 97239, USA.

    We have previously shown that CK2 associates with the human high-mobility group protein SSRP1 and that this association increases in response to UV irradiation. CK2 also phosphorylates SSRP1 in vitro. Here we extend this work by investigating CK2 regulation of SSRP1 function through phosphorylation. Phosphorylation of SSRP1 by CK2 inhibited the nonspecific DNA-binding activity of SSRP1 and FACT (facilitating chromatin-mediated transcription) complex in vitro. Using a serine/threonine-scanning Auto-spot peptide array coupled with a filter-based kinase assay with synthetic peptides as substrates, we identified serines 510, 657, and 688 as phosphorylation targets of CK2 in vitro. Mutagenesis of the three serines revealed that serine 510 was more important for the regulation of SSRP1 DNA-binding activity. Furthermore, we found that SSRP1 was phosphorylated in cells in response to UV (but not gamma) irradiation. These results suggest that CK2 regulates the DNA-binding ability of SSRP1 and that this regulation may be responsive to specific cell stresses.

    Funded by: NCI NIH HHS: CA079721, CA095441, CA93614; NIGMS NIH HHS: GM48231, R01 GM048231

    The Journal of biological chemistry 2005;280;12;11869-75

  • Inclining the purine base binding plane in protein kinase CK2 by exchanging the flanking side-chains generates a preference for ATP as a cosubstrate.

    Yde CW, Ermakova I, Issinger OG and Niefind K

    Syddansk Universitet, Institut for Biokemi og Molekylaerbiologi, Campusvej 55, DK-5230 Odense, Denmark.

    Protein kinase CK2 (casein kinase 2) is a highly conserved and ubiquitously found eukaryotic serine/threonine kinase that plays a role in various cellular key processes like proliferation, apoptosis and circadian rhythm. One of its prominent biochemical properties is its ability to use GTP as well as ATP as a cosubstrate (dual-cosubstrate specificity). This feature is exceptional among eukaryotic protein kinases, and its biological significance is unknown. We describe here a mutant of the catalytic subunit of protein kinase CK2 (CK2alpha) from Homo sapiens (hsCK2alpha) with a clear and CK2-atypical preference for ATP compared to GTP. This mutant was designed on the basis of several structures of CK2alpha from Zea mays (zmCK2alpha) in complex with various ATP-competitive ligands. A structural overlay revealed the existence of a "purine base binding plane" harbouring the planar moiety of the respective ligand like the purine base of ATP and GTP. This purine base binding plane is sandwiched between the side-chains of Ile66 (Val66 in hsCK2alpha) and Met163, and it adopts a significantly different orientation than in prominent homologues like cAMP-dependent protein kinase (CAPK). By exchanging these two flanking amino acids (Val66Ala, Met163Leu) in hsCK2alpha(1-335), a C-terminally truncated variant of hsCK2alpha, the cosubstrate specificity shifted in the expected direction so that the mutant strongly favours ATP. A structure determination of the mutant in complex with an ATP-analogue confirmed the predicted change of the purine base binding plane orientation. An unexpected but in retrospect plausible consequence of the mutagenesis was, that the helix alpha D region, which is in the direct neighbourhood of the ATP-binding site, has adopted a conformation that is more similar to CAPK and less favourable for binding of GTP. These findings demonstrate that CK2alpha possesses sophisticated structural adaptations in favour of dual-cosubstrate specificity, suggesting that this property could be of biological significance.

    Journal of molecular biology 2005;347;2;399-414

  • Differential regulation of phosphoglucose isomerase/autocrine motility factor activities by protein kinase CK2 phosphorylation.

    Yanagawa T, Funasaka T, Tsutsumi S, Raz T, Tanaka N and Raz A

    Tumor Progression and Metastasis Program, Karmanos Cancer Institute, 110 E. Warren Ave., Detroit, Michigan 48201, USA.

    Phosphoglucose isomerase (PGI; EC is a cytosolic housekeeping enzyme of the sugar metabolism pathways that plays a key role in both glycolysis and gluconeogenesis. PGI is a multifunctional dimeric protein that extracellularly acts as a cytokine with properties that include autocrine motility factor (AMF)-eliciting mitogenic, motogenic, and differentiation functions, and PGI has been implicated in tumor progression and metastasis. Little is known of the biochemical regulation of PGI/AMF activities, although it is known that human PGI/AMF is phosphorylated at Ser(185) by protein kinase CK2 (CK2); however, the physiological significance of this phosphorylation is unknown. Thus, by site-directed mutagenesis, we substituted Ser(185) with aspartic acid (S185D) or glutamic acid (S185E), which introduces a negative charge and conformational changes that mimic phosphorylation. A Ser-to-Ala mutant protein (S185A) was generated to abolish phosphorylation. Biochemical analyses revealed that the phosphorylation mutant proteins of PGI exhibited decreased enzymatic activity, whereas the S185A mutant PGI protein retained full enzymatic activity. PGI phosphorylation by CK2 also led to down-regulation of enzymatic activity. Furthermore, CK2 knockdown by RNA interference was associated with up-regulation of cellular PGI enzymatic activity. The three recombinant mutant proteins exhibited indistinguishable cytokine activity and receptor-binding affinities compared with the wild-type protein. In both in vitro and in vivo assays, the wild-type and S185A mutant proteins underwent active species dimerization, whereas both the S185D and S185E mutant proteins also formed tetramers. These results demonstrate that phosphorylation affects the allosteric kinetic properties of the enzyme, resulting in a less active form of PGI, whereas non-phosphorylated protein species retain cytokine activity. The process by which phosphorylation modulates the enzymatic activity of PGI thus has an important implication for the understanding of the biological regulation of this key glucose metabolism-regulating enzyme.

    Funded by: NCI NIH HHS: CA-51714

    The Journal of biological chemistry 2005;280;11;10419-26

  • Activation of pre-mRNA splicing by human RNPS1 is regulated by CK2 phosphorylation.

    Trembley JH, Tatsumi S, Sakashita E, Loyer P, Slaughter CA, Suzuki H, Endo H, Kidd VJ and Mayeda A

    Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, P.O. Box 016129, Miami, FL 33101-6129, USA.

    Human RNPS1 was originally characterized as a pre-mRNA splicing activator in vitro and was shown to regulate alternative splicing in vivo. RNPS1 was also identified as a protein component of the splicing-dependent mRNP complex, or exon-exon junction complex (EJC), and a role for RNPS1 in postsplicing processes has been proposed. Here we demonstrate that RNPS1 incorporates into active spliceosomes, enhances the formation of the ATP-dependent A complex, and promotes the generation of both intermediate and final spliced products. RNPS1 is phosphorylated in vivo and interacts with the CK2 (casein kinase II) protein kinase. Serine 53 (Ser-53) of RNPS1 was identified as the major phosphorylation site for CK2 in vitro, and the same site is also phosphorylated in vivo. The phosphorylation status of Ser-53 significantly affects splicing activation in vitro, but it does not perturb the nuclear localization of RNPS1. In vivo experiments indicated that the phosphorylation of RNPS1 at Ser-53 influences the efficiencies of both splicing and translation. We propose that RNPS1 is a splicing regulator whose activator function is controlled in part by CK2 phosphorylation.

    Funded by: NCI NIH HHS: P30 CA21765-25; NIGMS NIH HHS: 5R01 GM44088-13

    Molecular and cellular biology 2005;25;4;1446-57

  • Phosphorylation of RanGAP1 stabilizes its interaction with Ran and RanBP1.

    Takeda E, Hieda M, Katahira J and Yoneda Y

    Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.

    Ran is a nuclear Ras-like GTPase that is required for various nuclear events including the bi-directional transport of proteins and ribonucleoproteins through the nuclear pore complex, spindle formation, and reassembly of the nuclear envelope. One of the key regulators of Ran is RanGAP1, a Ran specific GTPase activating protein. The question of whether a mechanism exists for controlling nucleocytoplasmic transport through the regulation of RanGAP1 activity continues to be debated. Here we show that RanGAP1 is phosphorylated in vivo and in vitro. Serine-358 (358S) was identified as the major phosphorylation site, by MALDI-TOF-MS spectrometry. Site directed mutagenesis at this position abolished the phosphorylation. Experiments using purified recombinant kinase and specific inhibitors such as DRB and apigenin strongly suggest that casein kinase II (CK2) is the responsible kinase. Although the phosphorylation of 358S of RanGAP1 did not significantly alter its GAP activity, the phosphorylated wild type RanGAP1, but not a mutant harboring a mutation at the phosphorylation site 358S, efficiently formed a stable ternary complex with Ran and RanBP1 in vivo, suggesting that the 358S phosphorylation of RanGAP1 affects the Ran system.

    Cell structure and function 2005;30;2;69-80

  • Involvement of protein kinase CK2 in angiogenesis and retinal neovascularization.

    Ljubimov AV, Caballero S, Aoki AM, Pinna LA, Grant MB and Castellon R

    Ophthalmology Research Laboratories, Burns and Allen Research Institute, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, D-2025, Los Angeles, CA 90048, USA. ljubimov@cshs.org

    Purpose: The purpose of the study was to characterize signaling intermediates involved in angiogenic responses of retinal endothelial cells (RECs) to the extracellular matrix and growth factors, by using specific inhibitors.

    Methods: Tubelike structure formation and the development of secondary sprouts on a basement membrane (BM) matrix, cell proliferation, and cell migration were studied in cultures of bovine and human RECs. Specific inhibitors were tested for inhibition of retinal neovascularization in a mouse model of oxygen-induced retinopathy (OIR).

    Results: In initial experiments, the broad-spectrum protein kinase inhibitors, H7 and H89, stabilized REC tubes on BM matrix and inhibited secondary sprouting, cell migration, and cell proliferation. Among more specific kinase inhibitors tested, only inhibitors of protein kinase CK2 (formerly, casein kinase II), such as emodin and DRB, were able to duplicate the effects of H7 and H89. Actinomycin D caused only minor changes in angiogenic assays, suggesting that CK2's effects on REC did not involve its known impact on transcription. The extent of retinal neovascularization in a mouse OIR model was reduced >70% (versus untreated or vehicle-treated groups) after treatment with emodin (6 days at 60 mg/kg per day) and by approximately 60% after treatment at the same dose with TBB, the most specific CK2 inhibitor known. In the treated retinas, the main vascular tree had minimal changes, but the neovascular tufts were greatly reduced in number or absent.

    Conclusions: This is the first demonstration of the involvement of ubiquitous protein kinase CK2 in angiogenesis. Naturally derived CK2 inhibitors may be useful for treatment of proliferative retinopathies.

    Funded by: NEI NIH HHS: EY07739, EY12601, EY12605, EY13431, R01 EY012605, R01 EY012605-03, R01 EY013431, R01 EY013431-01, R01 EY013431-02

    Investigative ophthalmology & visual science 2004;45;12;4583-91

  • Protein kinase CK2 is an inhibitor of the neuronal Cdk5 kinase.

    Lim AC, Hou Z, Goh CP and Qi RZ

    Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609.

    The complex of Cdk5 and its neuronal activator p35 is a proline-directed Ser/Thr kinase that plays an important role in various neuronal functions. Deregulation of the Cdk5 enzymatic activity was found to associate with a number of neurodegenerative diseases. To search for regulatory factors of Cdk5-p35 in the brain, we developed biochemical affinity isolation using a recombinant protein comprising the N-terminal 149 amino acids of p35. The catalytic alpha-subunit of protein kinase CK2 (formerly known as casein kinase 2) was identified by mass spectrometry from the isolation. The association of CK2 with p35 and Cdk5 was demonstrated, and the CK2-binding sites were delineated in p35. Furthermore, CK2 displayed strong inhibition toward the Cdk5 activation by p35. The Cdk5 inhibition is dissociated from the kinase function of CK2 because the kinase-dead mutant of CK2 displayed the similar Cdk5 inhibitory activity as the wild-type enzyme. Further characterization showed that CK2 blocks the complex formation of Cdk5 and p35. Together, these findings suggest that CK2 acts as an inhibitor of Cdk5 in the brain.

    The Journal of biological chemistry 2004;279;45;46668-73

  • Phosphoproteomic analysis of the developing mouse brain.

    Ballif BA, Villén J, Beausoleil SA, Schwartz D and Gygi SP

    Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.

    Proper development of the mammalian brain requires the precise integration of numerous temporally and spatially regulated stimuli. Many of these signals transduce their cues via the reversible phosphorylation of downstream effector molecules. Neuronal stimuli acting in concert have the potential of generating enormous arrays of regulatory phosphoproteins. Toward the global profiling of phosphoproteins in the developing brain, we report here the use of a mass spectrometry-based methodology permitting the first proteomic-scale phosphorylation site analysis of primary animal tissue, identifying over 500 protein phosphorylation sites in the developing mouse brain.

    Funded by: NHGRI NIH HHS: HG00041

    Molecular & cellular proteomics : MCP 2004;3;11;1093-101

  • CK2 phosphorylation of Bdp1 executes cell cycle-specific RNA polymerase III transcription repression.

    Hu P, Samudre K, Wu S, Sun Y and Hernandez N

    Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA.

    RNA polymerase III (pol III) transcription from the human U6 snRNA promoter can be reconstituted with the recombinant factors SNAPc and Brf2-TFIIIB combined with purified pol III. In this system, CK2 treatment of the pol III complex is required for transcription, whereas treatment of Brf2-TFIIIB is inhibitory. Here we show that CK2 inhibits Brf2-TFIIIB by specifically phosphorylating its Bdp1 component. Bdp1 is phosphorylated by CK2 during mitosis, and this is accompanied by Bdp1 dissociation from the U6 promoter and from chromatin in general and by transcription repression. Remarkably, whereas inhibition of CK2 in mitotic extracts restores pol III transcription, inhibition of CK2 in active S phase extracts debilitates transcription. Thus, CK2 is directed to phosphorylate different targets within the basal pol III transcription machinery at different times during the cell cycle, with opposite transcriptional effects.

    Funded by: NIGMS NIH HHS: GM38810

    Molecular cell 2004;16;1;81-92

  • Xrcc4 physically links DNA end processing by polynucleotide kinase to DNA ligation by DNA ligase IV.

    Koch CA, Agyei R, Galicia S, Metalnikov P, O'Donnell P, Starostine A, Weinfeld M and Durocher D

    Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, ON, Canada.

    Nonhomologous end joining (NHEJ) is the major DNA double-strand break (DSB) repair pathway in mammalian cells. A critical step in this process is DNA ligation, involving the Xrcc4-DNA ligase IV complex. DNA end processing is often a prerequisite for ligation, but the coordination of these events is poorly understood. We show that polynucleotide kinase (PNK), with its ability to process ionizing radiation-induced 5'-OH and 3'-phosphate DNA termini, functions in NHEJ via an FHA-dependent interaction with CK2-phosphorylated Xrcc4. Analysis of the PNK FHA-Xrcc4 interaction revealed that the PNK FHA domain binds phosphopeptides with a unique selectivity among FHA domains. Disruption of the Xrcc4-PNK interaction in vivo is associated with increased radiosensitivity and slower repair kinetics of DSBs, in conjunction with a diminished efficiency of DNA end joining in vitro. Therefore, these results suggest a new role for Xrcc4 in the coordination of DNA end processing with DNA ligation.

    The EMBO journal 2004;23;19;3874-85

  • The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC).

    Gerhard DS, Wagner L, Feingold EA, Shenmen CM, Grouse LH, Schuler G, Klein SL, Old S, Rasooly R, Good P, Guyer M, Peck AM, Derge JG, Lipman D, Collins FS, Jang W, Sherry S, Feolo M, Misquitta L, Lee E, Rotmistrovsky K, Greenhut SF, Schaefer CF, Buetow K, Bonner TI, Haussler D, Kent J, Kiekhaus M, Furey T, Brent M, Prange C, Schreiber K, Shapiro N, Bhat NK, Hopkins RF, Hsie F, Driscoll T, Soares MB, Casavant TL, Scheetz TE, Brown-stein MJ, Usdin TB, Toshiyuki S, Carninci P, Piao Y, Dudekula DB, Ko MS, Kawakami K, Suzuki Y, Sugano S, Gruber CE, Smith MR, Simmons B, Moore T, Waterman R, Johnson SL, Ruan Y, Wei CL, Mathavan S, Gunaratne PH, Wu J, Garcia AM, Hulyk SW, Fuh E, Yuan Y, Sneed A, Kowis C, Hodgson A, Muzny DM, McPherson J, Gibbs RA, Fahey J, Helton E, Ketteman M, Madan A, Rodrigues S, Sanchez A, Whiting M, Madari A, Young AC, Wetherby KD, Granite SJ, Kwong PN, Brinkley CP, Pearson RL, Bouffard GG, Blakesly RW, Green ED, Dickson MC, Rodriguez AC, Grimwood J, Schmutz J, Myers RM, Butterfield YS, Griffith M, Griffith OL, Krzywinski MI, Liao N, Morin R, Morrin R, Palmquist D, Petrescu AS, Skalska U, Smailus DE, Stott JM, Schnerch A, Schein JE, Jones SJ, Holt RA, Baross A, Marra MA, Clifton S, Makowski KA, Bosak S, Malek J and MGC Project Team

    The National Institutes of Health's Mammalian Gene Collection (MGC) project was designed to generate and sequence a publicly accessible cDNA resource containing a complete open reading frame (ORF) for every human and mouse gene. The project initially used a random strategy to select clones from a large number of cDNA libraries from diverse tissues. Candidate clones were chosen based on 5'-EST sequences, and then fully sequenced to high accuracy and analyzed by algorithms developed for this project. Currently, more than 11,000 human and 10,000 mouse genes are represented in MGC by at least one clone with a full ORF. The random selection approach is now reaching a saturation point, and a transition to protocols targeted at the missing transcripts is now required to complete the mouse and human collections. Comparison of the sequence of the MGC clones to reference genome sequences reveals that most cDNA clones are of very high sequence quality, although it is likely that some cDNAs may carry missense variants as a consequence of experimental artifact, such as PCR, cloning, or reverse transcriptase errors. Recently, a rat cDNA component was added to the project, and ongoing frog (Xenopus) and zebrafish (Danio) cDNA projects were expanded to take advantage of the high-throughput MGC pipeline.

    Funded by: PHS HHS: N01-C0-12400

    Genome research 2004;14;10B;2121-7

  • Phosphorylation by protein kinase CK2 modulates the activity of the ATP binding cassette A1 transporter.

    Roosbeek S, Peelman F, Verhee A, Labeur C, Caster H, Lensink MF, Cirulli C, Grooten J, Cochet C, Vandekerckhove J, Amoresano A, Chimini G, Tavernier J and Rosseneu M

    Department of Biochemistry, Faculty of Medicine and Health Sciences, Ghent University, B-9000 Ghent, Belgium. stein.roosbeek@UGent.be

    In a previous characterization of the ABCA subfamily of the ATP-binding cassette (ABC) transporters, we identified potential protein kinase 2 (CK2) phosphorylation sites, which are conserved in eukaryotic and prokaryotic members of the ABCA transporters. These phosphorylation residues are located in the conserved cytoplamic R1 and R2 domains, downstream of the nucleotide binding domains NBD1 and NBD2. To study the possible regulation of the ABCA1 transporter by CK2, we expressed the recombinant cytoplasmic domains of ABCA1, NBD1+R1 and NBD2+R2. We demonstrated that in vitro ABCA1 NBD1+R1, and not NBD2+R2, is phosphorylated by CK2, and we identified Thr-1242, Thr-1243, and Ser-1255 as the phosphorylated residues in the R1 domain by mass spectrometry. We further investigated the functional significance of the threonine and serine phosphorylation sites in NBD1 by site-directed mutagenesis of the entire ABCA1 followed by transfection into Hek-293 Tet-Off cells. The ABCA1 flippase activity, apolipoprotein AI and AII binding, and cellular phospholipid and cholesterol efflux were enhanced by mutations preventing CK2 phosphorylation of the threonine and serine residues. This was confirmed by the effect of specific protein kinase CK2 inhibitors upon the activity of wild type and mutant ABCA1 in transfected Hek-293 Tet-Off cells. The activities of the mutants mimicking threonine phosphorylation were close to that of wild type ABCA1. Our data, therefore, suggest that besides protein kinase A and C, protein kinase CK2 might play an important role in vivo in regulating the function and transport activity of ABCA1 and possibly of other members of the ABCA subfamily.

    The Journal of biological chemistry 2004;279;36;37779-88

  • Proteomic, functional, and domain-based analysis of in vivo 14-3-3 binding proteins involved in cytoskeletal regulation and cellular organization.

    Jin J, Smith FD, Stark C, Wells CD, Fawcett JP, Kulkarni S, Metalnikov P, O'Donnell P, Taylor P, Taylor L, Zougman A, Woodgett JR, Langeberg LK, Scott JD and Pawson T

    Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Avenue, Toronto, Ontario M5G 1X5, Canada.

    Background: 14-3-3 proteins are abundant and conserved polypeptides that mediate the cellular effects of basophilic protein kinases through their ability to bind specific peptide motifs phosphorylated on serine or threonine.

    Results: We have used mass spectrometry to analyze proteins that associate with 14-3-3 isoforms in HEK293 cells. This identified 170 unique 14-3-3-associated proteins, which show only modest overlap with previous 14-3-3 binding partners isolated by affinity chromatography. To explore this large set of proteins, we developed a domain-based hierarchical clustering technique that distinguishes structurally and functionally related subsets of 14-3-3 target proteins. This analysis revealed a large group of 14-3-3 binding partners that regulate cytoskeletal architecture. Inhibition of 14-3-3 phosphoprotein recognition in vivo indicates the general importance of such interactions in cellular morphology and membrane dynamics. Using tandem proteomic and biochemical approaches, we identify a phospho-dependent 14-3-3 binding site on the A kinase anchoring protein (AKAP)-Lbc, a guanine nucleotide exchange factor (GEF) for the Rho GTPase. 14-3-3 binding to AKAP-Lbc, induced by PKA, suppresses Rho activation in vivo.

    Conclusion: 14-3-3 proteins can potentially engage around 0.6% of the human proteome. Domain-based clustering has identified specific subsets of 14-3-3 targets, including numerous proteins involved in the dynamic control of cell architecture. This notion has been validated by the broad inhibition of 14-3-3 phosphorylation-dependent binding in vivo and by the specific analysis of AKAP-Lbc, a RhoGEF that is controlled by its interaction with 14-3-3.

    Funded by: NIDDK NIH HHS: DK44239

    Current biology : CB 2004;14;16;1436-50

  • Large-scale characterization of HeLa cell nuclear phosphoproteins.

    Beausoleil SA, Jedrychowski M, Schwartz D, Elias JE, Villén J, Li J, Cohn MA, Cantley LC and Gygi SP

    Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.

    Determining the site of a regulatory phosphorylation event is often essential for elucidating specific kinase-substrate relationships, providing a handle for understanding essential signaling pathways and ultimately allowing insights into numerous disease pathologies. Despite intense research efforts to elucidate mechanisms of protein phosphorylation regulation, efficient, large-scale identification and characterization of phosphorylation sites remains an unsolved problem. In this report we describe an application of existing technology for the isolation and identification of phosphorylation sites. By using a strategy based on strong cation exchange chromatography, phosphopeptides were enriched from the nuclear fraction of HeLa cell lysate. From 967 proteins, 2,002 phosphorylation sites were determined by tandem MS. This unprecedented large collection of sites permitted a detailed accounting of known and unknown kinase motifs and substrates.

    Funded by: NHGRI NIH HHS: HG00041, K22 HG000041, T32 HG000041; NIGMS NIH HHS: GM67945, GMS6203, R01 GM056203, R01 GM067945

    Proceedings of the National Academy of Sciences of the United States of America 2004;101;33;12130-5

  • The identification of phosphorylation sites of pp32 and biochemical purification of a cellular pp32-kinase.

    Hong R, Macfarlan T, Kutney SN, Seo SB, Mukai Y, Yelin F, Pasternack GR and Chakravarti D

    Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6160, USA.

    The versatile phosphoprotein pp32 is involved in important physiological processes, including cell proliferation, apoptosis, mRNA transport, and transcription. We have previously reported that pp32, through histone masking, inhibits histone acetylation and transcriptional activation by histone acetyltransferases. However, how pp32 itself is regulated remained largely unknown. Although pp32 is a phosphoprotein, neither the phosphorylation sites nor the cellular kinase has been identified. In this report, utilizing an in vitro kinase assay and a biochemical purification scheme, we identify casein kinase II as a cellular pp32-kinase. Our deletion and site-specific mutagenesis studies identify serines 158 and 204 as the sites of phosphorylation. Generation and utilization of antibodies with higher affinity for phospho-pp32 demonstrate that pp32 is indeed phosphorylated in vivo at these two sites. Mutagenesis studies on pp32 suggest a role for serines 158 and 204 in its function. The identification of the pp32 kinase and the sites of pp32 phosphorylation as well as the generation of antibodies with higher affinity for phospho-pp32 should now provide key information and tools for future studies on pp32 regulation.

    Funded by: NIDDK NIH HHS: DK57079, DK65148, R01 DK057079, R01 DK065148

    Biochemistry 2004;43;31;10157-65

  • Phosphorylation of the regulatory beta-subunit of protein kinase CK2 by checkpoint kinase Chk1: identification of the in vitro CK2beta phosphorylation site.

    Kristensen LP, Larsen MR, Højrup P, Issinger OG and Guerra B

    Department of Biochemistry and Molecular Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark.

    The regulatory beta-subunit of protein kinase CK2 mediates the formation of the CK2 tetrameric form and it has functions independent of CK2 catalytic subunit through interaction with several intracellular proteins. Recently, we have shown that CK2beta associates with the human checkpoint kinase Chk1. In this study, we show that Chk1 specifically phosphorylates in vitro the regulatory beta-subunit of CK2. Chymotryptic peptides and mutational analyses have revealed that CK2beta is phosphorylated at Thr213. Formation of a stable complex between CK2beta and Chk1 is not affected by the modification of Thr213 but it does require the presence of an active Chk1 kinase.

    FEBS letters 2004;569;1-3;217-23

  • Proapoptotic function of protein kinase CK2alpha" is mediated by a JNK signaling cascade.

    Hilgard P, Czaja MJ, Gerken G and Stockert RJ

    Department for Gastroenterology and Hepatology, University-Hospital Essen, 45133 Essen, Germany.

    Protein kinase CK2 (formerly casein kinase II) is a tetrameric enzyme constitutively expressed in all eurakyotic tissues that plays a significant role in the regulation of cell proliferation, malignant transformation, and apoptosis. The catalytic alpha-subunit of the enzyme is known to exist in three isoforms CK2alpha, CK2alpha' and CK2alpha". CK2alpha" is highly expressed in liver compared with other tissues and is required for the normal trafficking of several hepatocellular membrane proteins. Initial studies of dengue virus infection indicated that the CK2alpha"-deficient membrane trafficking mutant cell line (Trf1) was resistant to virus-induced cell death compared with the parental human hepatoma (HuH)-7 hepatoma line. Expression of recombinant CK2alpha" in Trf1 was capable of reverting this resistant phenotype. This study was extended to TNF-alpha in addition to other stimuli of cell death in an attempt to uncover common death pathways that might be modulated by CK2alpha". Evaluation of different pathways involved in death signaling suggest that the regulation of a critical proapoptotic step in HuH-7 cells by CK2alpha" is mediated by a JNK signaling cascade.

    Funded by: NIDDK NIH HHS: DK 17702, DK 41918, DK 44234, R01 DK044234, R01 DK061498

    American journal of physiology. Gastrointestinal and liver physiology 2004;287;1;G192-201

  • C-terminal region of protein kinase CK2 alpha: How the structure can affect function and stability of the catalytic subunit.

    Grasselli E, Tomati V, Bernasconi MV, Nicolini C and Vergani L

    Department of Biophysical Sciences and Technologies M&O, School of Medicine, University of Genova, Genoa, Italy.

    A novel mutant of the catalytic alpha subunit of human protein kinase CK2 (CK2 alpha) was designed in an attempt to clarify the role of the carboxylic-terminal segment characteristic of vertebrates, excluding fish. Starting from the sequence alignments, we constructed a phylogenetic tree of the primary structure of CK2 alpha. On this basis, we substituted two distal prolines with alanines (PA 382-384). Theoretical calculations and spectropolarimetry measurements, performed both on native and mutant subunits, indicate an increased content of alpha-helix after this double amino acidic substitution. In order to clarify the structure/function relationship of the C-terminal region, we verified if the structural change affects the catalytic activity of CK2 alpha. The mutant exhibits slightly increased phosphorylation efficiency, but reduced ability to transfer phosphate in comparison with the native subunit. At last, we compared the thermal stability of the mutant with respect to the native subunit and we tested the proteolytic degradability. The observation that the PA 382-384 mutant exhibits an increased thermal and proteolytic stability suggests that this mutant could be employed to solve the three-dimensional (3D) structure of human CK2 alpha and to overcome difficulties in crystallizing the native form.

    Journal of cellular biochemistry 2004;92;2;270-84

  • CK2 controls multiple protein kinases by phosphorylating a kinase-targeting molecular chaperone, Cdc37.

    Miyata Y and Nishida E

    Department of Cell and Developmental Biology, Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan. ymiyata@Lif.kyoto-u.ac.jp

    Cdc37 is a kinase-associated molecular chaperone whose function in concert with Hsp90 is essential for many signaling protein kinases. Here, we report that mammalian Cdc37 is a pivotal substrate of CK2 (casein kinase II). Purified Cdc37 was phosphorylated in vitro on a conserved serine residue, Ser13, by CK2. Moreover, Ser13 was the unique phosphorylation site of Cdc37 in vivo. Crucially, the CK2 phosphorylation of Cdc37 on Ser13 was essential for the optimal binding activity of Cdc37 toward various kinases examined, including Raf1, Akt, Aurora-B, Cdk4, Src, MOK, MAK, and MRK. In addition, nonphosphorylatable mutants of Cdc37 significantly suppressed the association of Hsp90 with protein kinases, while the Hsp90-binding activity of the mutants was unchanged. The treatment of cells with a specific CK2 inhibitor suppressed the phosphorylation of Cdc37 in vivo and reduced the levels of Cdc37 target kinases. These results unveil a regulatory mechanism of Cdc37, identify a novel molecular link between CK2 and many crucial protein kinases via Cdc37, and reveal the molecular basis for the ability of CK2 to regulate pleiotropic cellular functions.

    Molecular and cellular biology 2004;24;9;4065-74

  • The protein kinase CK2 facilitates repair of chromosomal DNA single-strand breaks.

    Loizou JI, El-Khamisy SF, Zlatanou A, Moore DJ, Chan DW, Qin J, Sarno S, Meggio F, Pinna LA and Caldecott KW

    Genome Damage and Stability Centre, University of Sussex, Science Park Road, Falmer, Brighton BN1 9RQ, United Kingdom.

    CK2 was the first protein kinase identified and is required for the proliferation and survival of mammalian cells. Here, we have identified an unanticipated role for CK2. We show that this essential protein kinase phosphorylates the scaffold protein XRCC1 and thereby enables the assembly and activity of DNA single-strand break repair protein complexes in vitro and at sites of chromosomal breakage. Moreover, we show that inhibiting XRCC1 phosphorylation by mutation of the CK2 phosphorylation sites or preventing CK2 activity using a highly specific inhibitor ablates the rapid repair of cellular DNA single-strand breaks by XRCC1. These data identify a direct role for CK2 in the repair of chromosomal DNA strand breaks and in maintaining genetic integrity.

    Funded by: Medical Research Council: G0001259

    Cell 2004;117;1;17-28

  • Protein kinase CK2: a new view of an old molecular complex.

    Filhol O, Martiel JL and Cochet C

    INSERM EMI 104, Département Réponse et Dynamique Cellulaire, CEA, 38054 Grenoble, France.

    Protein kinase CK2 (formerly known as casein kinase II) has been viewed traditionally as a stable heterotetrameric complex, but new analytical techniques are bringing a different picture into focus. The transient nature of this complex has been highlighted by the elucidation of its structure. Furthermore, analysis of the spatiotemporal organization of individual CK2 subunits in living cells has shown that they are dynamic and that they integrate into different multimolecular assemblies. These new studies give an additional dimension to the challenge of determining the cellular regulation of this protein kinase.

    EMBO reports 2004;5;4;351-5

  • Protein kinase CK2 phosphorylates the cell cycle regulatory protein Geminin.

    Kulartz M, Hiller E, Kappes F, Pinna LA and Knippers R

    Department of Biology, University of Konstanz, D-78457 Konstanz, Germany. monika.kulartz@uni-konstanz.de

    Geminin contributes to cell cycle regulation by a timely inhibition of Cdt1p, the loading factor required for the assembly of pre-replication complexes. Geminin is expressed during S and G2 phase of the HeLa cell cycle and phosphorylated soon after its synthesis. We show here that Geminin is an excellent substrate for protein kinase CK2 in vitro; and that the highly specific CK2 inhibitor tetrabromobenzotriazole (TBB) blocks the phosphorylation of Geminin in HeLa protein extracts and HeLa cells in vivo. The sites of CK2 phosphorylation are located in the carboxyterminal region of Geminin, which carries several consensus sequence motifs for CK2. We also show that a minor phosphorylating activity in protein extracts can be attributed to glycogen synthase kinase 3 (GSK3), which most likely targets a central peptide in Geminin. Treatment of HeLa cells with TBB does not interfere with the ability of Geminin to interact with the loading factor Cdt1.

    Biochemical and biophysical research communications 2004;315;4;1011-7

  • Cellular casein kinase II-mediated phosphorylation of rinderpest virus P protein is a prerequisite for its role in replication/transcription of the genome.

    Kaushik R and Shaila MS

    Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560012, India.

    Phosphoprotein P of rinderpest virus (RPV), when expressed in E. coli, is present in the unphosphorylated form. Bacterially expressed P protein was phosphorylated by a eukaryotic cellular extract, and casein kinase II (CK II) was identified as the cellular kinase involved in phosphorylation. In vitro phosphorylation of P-deletion mutants identified the N terminus as a phosphorylation domain. In vivo phosphorylation of single or multiple serine mutants of P protein identified serine residues at 49, 88 and 151 as phospho-acceptor residues. The role of P protein phosphorylation in virus replication/transcription was evaluated using the RPV minigenome system and replication/transcription of a reporter gene in vivo. P protein phosphorylation was shown to be essential for in vivo replication/transcription since phosphorylation-null mutants do not support expression of a reporter gene. Transfection of increased amounts of phosphorylation-null mutant did not support minigenome replication/transcription in vivo.

    The Journal of general virology 2004;85;Pt 3;687-91

  • Identification of phosphoproteins and their phosphorylation sites in the WEHI-231 B lymphoma cell line.

    Shu H, Chen S, Bi Q, Mumby M and Brekken DL

    Protein Chemistry Laboratory, Alliance for Cellular Signaling, University of Texas Southwestern Medical Center, Dallas, TX 75390-9196, USA.

    A major goal of the Alliance for Cellular Signaling is to elaborate the components of signal transduction networks in model cell systems, including murine B lymphocytes. Due to the importance of protein phosphorylation in many aspects of cell signaling, the initial efforts have focused on the identification of phosphorylated proteins. In order to identify serine- and threonine-phosphorylated proteins on a proteome-wide basis, WEHI-231 cells were treated with calyculin A, a serine/threonine phosphatase inhibitor, to induce high levels of protein phosphorylation. Proteins were extracted from whole-cell lysates and digested with trypsin. Phosphorylated peptides were then enriched using immobilized metal affinity chromatography and identified by liquid chromatography-tandem mass spectrometry. A total of 107 proteins and 193 phosphorylation sites were identified using these methods. Forty-two of these proteins have been reported to be phosphorylated, but only some of them have been detected in B cells. Fifty-four of the identified proteins were not previously known to be phosphorylated. The remaining 11 phosphoproteins have previously only been characterized as novel cDNA or genomic sequences. Many of the identified proteins were phosphorylated at multiple sites. The proteins identified in this study significantly expand the repertoire of proteins known to be phosphorylated in B cells. The number of newly identified phosphoproteins indicates that B cell signaling pathways utilizing protein phosphorylation are likely to be more complex than previously appreciated.

    Funded by: NIGMS NIH HHS: U54 GM062114

    Molecular & cellular proteomics : MCP 2004;3;3;279-86

  • Casein kinase II-mediated phosphorylation regulates alpha-synuclein/synphilin-1 interaction and inclusion body formation.

    Lee G, Tanaka M, Park K, Lee SS, Kim YM, Junn E, Lee SH and Mouradian MM

    Genetic Pharmacology Unit, NINDS, National Institutes of Health, Bethesda, Maryland 20824, USA.

    Alpha-synuclein is a phosphoprotein that accumulates as a major component of Lewy bodies in the brains of patients with Parkinson disease. Synphilin-1, which is also present in Lewy bodies, binds with alpha-synuclein and forms cytoplasmic inclusions in transfected cells. Yet the molecular determinants of this protein-protein interaction are unknown. Here we report that casein kinase II (CKII) phosphorylates synphilin-1 and that the beta subunit of this enzyme complex binds to synphilin-1. Additionally, both CKII alpha and beta subunits are present within cytoplasmic inclusions in cells that overexpress synphilin-1. Notably, the interaction between synphilin-1 and alpha-synuclein is markedly dependent on phosphorylation. Inhibition of CKII activity by 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole blocks the binding between these two proteins and significantly reduces the percentage of cells that contain eosinophilic cytoplasmic inclusions. Mutation of the major CKII phosphorylation site in alpha-synuclein (S129A) has no significant impact on the binding between alpha-synuclein and synphilin-1 or on the formation of synphilin-1/alpha-synuclein-positive inclusions. These data suggest that the CKII-mediated phosphorylation of synphilin-1 rather than that of alpha-synuclein is critical in modulating their tendency to aggregate into inclusions. These observations collectively indicate that a ubiquitous post-translational modification such as phosphorylation can regulate inclusion body formation in the context of alpha-synuclein and synphilin-1 interaction.

    The Journal of biological chemistry 2004;279;8;6834-9

  • Direct regulation of microtubule dynamics by protein kinase CK2.

    Lim AC, Tiu SY, Li Q and Qi RZ

    Institute of Molecular and Cell Biology, 30 Medical Drive, Singapore 117609.

    Microtubule dynamics is essential for many vital cellular processes such as morphogenesis and motility. Protein kinase CK2 is a ubiquitous protein kinase that is involved in diverse cellular functions. CK2 holoenzyme is composed of two catalytic alpha or alpha' subunits and two regulatory beta subunits. We show that the alpha subunit of CK2 binds directly to both microtubules and tubulin heterodimers. CK2 holoenzyme but neither of its individual subunits exhibited a potent effect of inducing microtubule assembly and bundling. Moreover, the polymerized microtubules were strongly stabilized by CK2 against cold-induced depolymerization. Interestingly, the kinase activity of CK2 is not required for its microtubule-assembling and stabilizing function because a kinase-inactive mutant of CK2 displayed the same microtubule-assembling activity as the wild-type protein. Knockdown of CK2alpha/alpha' in cultured cells by RNA interference dramatically destabilized their microtubule networks, and the destabilized microtubules were readily destructed by colchicine at a very low concentration. Further, over-expression of chicken CK2alpha or its kinaseinactive mutant in the endogenous CK2alpha/alpha'-depleted cells fully restored the microtubule resistance to the low dose of colchicine. Taken together, CK2 is a microtubule-associated protein that confers microtubule stability in a phosphorylation-independent manner.

    The Journal of biological chemistry 2004;279;6;4433-9

  • Analysis of a high-throughput yeast two-hybrid system and its use to predict the function of intracellular proteins encoded within the human MHC class III region.

    Lehner B, Semple JI, Brown SE, Counsell D, Campbell RD and Sanderson CM

    Functional Genomics Group, MRC Rosalind Franklin Centre for Genomics Research, Hinxton, Cambridge, United Kingdom.

    High-throughput (HTP) protein-interaction assays, such as the yeast two-hybrid (Y2H) system, are enormously useful in predicting the functions of novel gene-products. HTP-Y2H screens typically do not include all of the reconfirmation and specificity tests used in small-scale studies, but the effects of omitting these steps have not been assessed. We performed HTP-Y2H screens that included all standard controls, using the predicted intracellular proteins expressed from the human MHC class III region, a region of the genome associated with many autoimmune diseases. The 91 novel interactions identified provide insight into the potential functions of many MHC genes, including C6orf47, LSM2, NELF-E (RDBP), DOM3Z, STK19, PBX2, RNF5, UAP56 (BAT1), ATP6G2, LST1/f, BAT2, Scythe (BAT3), CSNK2B, BAT5, and CLIC1. Surprisingly, our results predict that 1/3 of the proteins may have a role in mRNA processing, which suggests clustering of functionally related genes within the human genome. Most importantly, our analysis shows that omitting standard controls in HTP-Y2H screens could significantly compromise data quality.

    Genomics 2004;83;1;153-67

  • Cyclin-dependent kinase 11p110 and casein kinase 2 (CK2) inhibit the interaction between tyrosine hydroxylase and 14-3-3.

    Sachs NA and Vaillancourt RR

    Department of Pharmacology and Toxicology, The University of Arizona, College of Pharmacy, Tucson, Arizona 85721, USA.

    Tyrosine hydroxylase (TH) is regulated by the reversible phosphorylation of serines 8, 19, 31 and 40. Upon initiation of this study, serine 19 was unique due to its requirement of 14-3-3 binding after phosphorylation for optimal enzyme activity, although it has been more recently demonstrated that phosphorylated serine 40 also binds 14-3-3. To identify proteins that interact with TH following phosphorylation of serine 19, this amino acid was mutated to alanine and THS19A was used as bait in a yeast two-hybrid system. From this, mouse-derived cyclin-dependent kinase 11 (CDK11)p110 was identified as an interacting partner with THS19A. The interaction was confirmed using human CDK11p110 cDNA in a mammalian system. Previous research has demonstrated that casein kinase 2 (CK2) interacts with CDK11p110, and both were observed to phosphorylate TH in vitro. In addition, CDK11p110 overexpression was observed to inhibit the interaction between TH and 14-3-3. A mechanism contributing to disruption of the interaction between TH and 14-3-3 may be due to CK2 phosphorylation of specific 14-3-3 isoforms, i.e. 14-3-3 tau. Collectively, these results imply that CDK11p110 and CK2 negatively regulate TH catecholamine biosynthetic activity since phosphoserine 19 of TH requires 14-3-3 binding for optimal enzyme activity and a decreased rate of dephosphorylation.

    Funded by: NIA NIH HHS: AG19710; NIEHS NIH HHS: ES07091, ES12007, P30 ES06694, P42 ES04940

    Journal of neurochemistry 2004;88;1;51-62

  • Mutations of the CK2 phosphorylation site of Sic1 affect cell size and S-Cdk kinase activity in Saccharomyces cerevisiae.

    Coccetti P, Rossi RL, Sternieri F, Porro D, Russo GL, di Fonzo A, Magni F, Vanoni M and Alberghina L

    Dipartimento di Biotecnologie e Bioscienze, Università degli Studi Milano-Bicocca, P. zza della Scienza 2, 20126 Milano, Italy.

    By sequence analysis we found an amino acid stretch centred on Serine201 matching a stringent CK2 consensus site within the C-terminal, inhibitory domain of Sic1. Here we show by direct mass spectrometry analysis that Sic1, but not a mutant protein whose CK2 phospho-acceptor site has been mutated to alanine, Sic1S201A, is actually phosphorylated in vitro by CK2 on Serine 201. Mutation of Serine 201 alters the coordination between growth and cell cycle progression. A significant increase of average protein content and of the average protein content at the onset of DNA synthesis is observed for exponentially growing cells harbouring the Sic1S201A protein. A strong reduction of the same parameters is observed in cells harbouring Sic1S201E. The deregulated coordination between cell size and cell cycle is also apparent at the level of S-Cdk activity.

    Molecular microbiology 2004;51;2;447-60

  • The phosphorylation state of an autoregulatory domain controls PACS-1-directed protein traffic.

    Scott GK, Gu F, Crump CM, Thomas L, Wan L, Xiang Y and Thomas G

    Vollum Institute, L-474, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.

    PACS-1 is a cytosolic sorting protein that directs the localization of membrane proteins in the trans-Golgi network (TGN)/endosomal system. PACS-1 connects the clathrin adaptor AP-1 to acidic cluster sorting motifs contained in the cytoplasmic domain of cargo proteins such as furin, the cation-independent mannose-6-phosphate receptor and in viral proteins such as human immunodeficiency virus type 1 Nef. Here we show that an acidic cluster on PACS-1, which is highly similar to acidic cluster sorting motifs on cargo molecules, acts as an autoregulatory domain that controls PACS-1-directed sorting. Biochemical studies show that Ser278 adjacent to the acidic cluster is phosphorylated by CK2 and dephosphorylated by PP2A. Phosphorylation of Ser278 by CK2 or a Ser278-->Asp mutation increased the interaction between PACS-1 and cargo, whereas a Ser278-->Ala substitution decreased this interaction. Moreover, the Ser278-->Ala mutation yields a dominant-negative PACS-1 molecule that selectively blocks retrieval of PACS-1-regulated cargo molecules to the TGN. These results suggest that coordinated signaling events regulate transport within the TGN/endosomal system through the phosphorylation state of both cargo and the sorting machinery.

    Funded by: NIAID NIH HHS: AI48585, AI49793, R01 AI048585, R01 AI049793; NIDDK NIH HHS: DK37274, R01 DK037274

    The EMBO journal 2003;22;23;6234-44

  • Three-dimensional atomic structure of a catalytic subunit mutant of human protein kinase CK2.

    Pechkova E, Zanotti G and Nicolini C

    Fondazione E.L.B.A., Rome, Italy.

    The three-dimensional crystal structure of the triple-point mutant of the catalytic subunit of human protein kinase CK2alpha has been determined at 2.4 A resolution. Microcrystals of mutant CK2 catalytic subunit were obtained by a protein-crystallization method based on thin-film nanotechnology. These microcrystals (of about 20 micro m in diameter) were used for diffraction data collection by means of the microfocus beamline at the ESRF synchrotron. A comparison between the human protein kinase CK2alpha and the corresponding enzyme from a lower organism (Zea mays) is made.

    Acta crystallographica. Section D, Biological crystallography 2003;59;Pt 12;2133-9

  • AP-1 recruitment to VAMP4 is modulated by phosphorylation-dependent binding of PACS-1.

    Hinners I, Wendler F, Fei H, Thomas L, Thomas G and Tooze SA

    Cancer Research UK, London Research Institute, 44 Lincoln's Inn Fields, London WC2A 3PX, UK.

    The R-SNARE VAMP4, which contains a dileucine motif, binds to the AP-1 (adaptor protein-1) subunit mu 1a, but not mu 1b, or the GGAs (Golgi-associated gamma ear containing ARF binding proteins). Serine 20 and leucines 25,26 are essential for this binding. AP-1 association with VAMP4 is enhanced when serine 30, in an acidic cluster, is phosphorylated by casein kinase 2. This phosphorylation-dependent modulation of AP-1 binding is mediated by PACS-1 (phosphofurin acidic cluster sorting protein). Ablation of both the dileucine motif and serine 30 results in a dramatic mislocalization of VAMP4 in the regulated secretory pathway in AtT20 cells. A dominant-negative PACS-1, which binds acidic clusters but not AP-1, also causes mislocalization of VAMP4. Our data support a model whereby phosphorylation-dependent recruitment of PACS-1 enhances AP-1 association to cargo, and suggest that efficient retrieval depends on the formation of a complex between cargo, such as VAMP4, AP-1 and PACS-1.

    Funded by: NIAID NIH HHS: AI48585, AI49793, R01 AI048585, R01 AI049793; NIDDK NIH HHS: DK37274, R01 DK037274

    EMBO reports 2003;4;12;1182-9

  • Protein kinase CKIIalpha interacts with the Bcr moiety of Bcr/Abl and mediates proliferation of Bcr/Abl-expressing cells.

    Mishra S, Reichert A, Cunnick J, Senadheera D, Hemmeryckx B, Heisterkamp N and Groffen J

    Section of Molecular Carcinogenesis, Division of Hematology/Oncology, Ms#54, Childrens Hospital of Los Angeles Research Institute 4650 Sunset Boulevard, Los Angeles, CA 90027, USA.

    The Bcr protein was originally identified because of its fusion to Abl as a consequence of the Philadelphia chromosome translocation found in chronic myelogenous and acute lymphoblastic leukemias. The Bcr moiety is essential for the transforming activity of the Bcr/Abl oncogene. In search of physiologically relevant Bcr and Bcr/Abl-interacting proteins, we performed an interaction screen in yeast using the entire Bcr protein as bait. We here report that the alpha catalytic subunit of protein kinase CKII strongly and specifically forms a complex with Bcr in yeast in mouse lysates. The region in Bcr responsible for CKIIalpha binding was localized to residues 242-413. CKIIalpha was previously shown to be involved in leukemogenesis and tumorigenesis using different experimental approaches including mouse models. Inhibition of Bcr/Abl P190 in lymphoma cells from Bcr/Abl transgenic mice using imatinib reduced CKIIalpha activity. A highly selective inhibitor of CKIIalpha, 4,5,6,7-tetrabromo-2-benzotriazole, inhibited the growth of murine lymphoid cells with induced P210 Bcr/Abl expression and of P190 lymphoma cells. Our results demonstrate that CKIIalpha plays an important role in the proliferation of Bcr/Abl expressing cells, and suggests that inhibitors of CKIIalpha may have therapeutic potential in the treatment of Bcr/Abl-positive leukemia patients.

    Funded by: NCI NIH HHS: CA 50248, CA 90321

    Oncogene 2003;22;51;8255-62

  • Eukaryotic translation-initiation factor eIF2beta binds to protein kinase CK2: effects on CK2alpha activity.

    Llorens F, Roher N, Miró FA, Sarno S, Ruiz FX, Meggio F, Plana M, Pinna LA and Itarte E

    Departament de Bioquímica i Biologia Molecular, Unitat de Bioquímica de Ciències, Universitat Autònoma de Barcelona, Edifici Cs, Campus de Bellaterra, 08193 Bellaterra, Barcelona, Spain.

    eIF2 (eukaryotic translation-initiation factor 2) is a substrate and an interacting partner for CK2 (protein kinase CK2). Co-immuno-precipitation of CK2 with eIF2beta has now been observed in HeLa cells, overexpressing haemagglutinin-tagged human recombinant eIF2beta. A direct association between His6-tagged human recombinant forms of eIF2beta subunit and both the catalytic (CK2alpha) and the regulatory (CK2beta) subunits of CK2 has also been shown by using different techniques. Surface plasmon resonance analysis indicated a high affinity in the interaction between eIF2beta and CK2alpha, whereas the affinity for the association with CK2beta is much lower. Free CK2alpha is unable to phosphorylate eIF2beta, whereas up to 1.2 mol of phosphate/mol of eIF2beta was incorporated by the reconstituted CK2 holoenzyme. The N-terminal third part of eIF2beta is dispensable for binding to either CK2alpha or CK2beta, although it contains the phosphorylation sites for CK2. The remaining central/C-terminal part of eIF2beta is not phosphorylated by CK2, but is sufficient for binding to both CK2 subunits. The presence of eIF2beta inhibited CK2alpha activity on calmodulin and beta-casein, but it had a minor effect on that of the reconstituted CK2 holoenzyme. The truncated forms corresponding to the N-terminal or central/C-terminal regions of eIF2beta were much less inhibitory than the intact subunit. The results demonstrate that the ability to associate with CK2 subunits and to serve as a CK2 substrate are confined to different regions in eIF2beta and that it may act as an inhibitor on CK2alpha.

    The Biochemical journal 2003;375;Pt 3;623-31

  • Regulation of alternative splicing by SRrp86 and its interacting proteins.

    Li J, Hawkins IC, Harvey CD, Jennings JL, Link AJ and Patton JG

    Department of Biological Sciences, Vanderbilt University, Nashville, Tennessee 37235, USA.

    SRrp86 is a unique member of the SR protein superfamily containing one RNA recognition motif and two serine-arginine (SR)-rich domains separated by an unusual glutamic acid-lysine (EK)-rich region. Previously, we showed that SRrp86 could regulate alternative splicing by both positively and negatively modulating the activity of other SR proteins and that the unique EK domain could inhibit both constitutive and alternative splicing. These functions were most consistent with the model in which SRrp86 functions by interacting with and thereby modulating the activity of target proteins. To identify the specific proteins that interact with SRrp86, we used a yeast two-hybrid library screen and immunoprecipitation coupled to mass spectrometry. We show that SRrp86 interacts with all of the core SR proteins, as well as a subset of other splicing regulatory proteins, including SAF-B, hnRNP G, YB-1, and p72. In contrast to previous results that showed activation of SRp20 by SRrp86, we now show that SAF-B, hnRNP G, and 9G8 all antagonize the activity of SRrp86. Overall, we conclude that not only does SRrp86 regulate SR protein activity but that it is, in turn, regulated by other splicing factors to control alternative splice site selection.

    Funded by: NIGMS NIH HHS: GM62487, R01 GM062487

    Molecular and cellular biology 2003;23;21;7437-47

  • CHOP transcription factor phosphorylation by casein kinase 2 inhibits transcriptional activation.

    Ubeda M and Habener JF

    Laboratory of Molecular Endocrinology, Massachusetts General Hospital and Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02114, USA.

    The CAAT/enhancer binding protein homologous transcription factor CHOP, also known as GADD153, is involved in DNA damage, growth arrest, and the induction of apoptosis after endoplasmic reticulum stress and nutrient deprivation. CHOP dimerizes with and inhibits the binding of C/EBP-related transcription factors to their consensus DNA target sequences and also forms novel complexes with other transcriptional proteins (e.g. c-Jun, c-Fos). The transcriptional activation of these complexes is modified by their phosphorylation. Phosphorylation of CHOP at serine 79 and serine 81 by p38-MAP kinase enhances its transcriptional activity. Here we show that an interactive association between CHOP and casein kinase II (CK2) results in the phosphorylation of its amino-terminal transactivation domain. Mapping of the functional domains of CHOP indicates that the region in CHOP required for association with CK2 differs from that required for its phosphorylation. Th binding of CK2 to CHOP requires only the carboxylterminal bZip domain of CHOP, whereas phosphorylation involves residues located in the amino-terminal domain. The presence of the bZip domain, however, facilitates the phosphorylation of CHOP. Analyses of the effect of point mutations of CHOP on its transcriptional activity and the effect of specific inhibitors of CK2 lead us to conclude that CK2-mediated phosphorylation of CHOP inhibits its transcriptional activity. Our findings suggest that inhibition of the proapoptotic functions of CHOP by CK2 may be a mechanism by which CK2 prevents apoptosis and promotes cellular proliferation.

    The Journal of biological chemistry 2003;278;42;40514-20

  • Phosphorylation of serine 13 is required for the proper function of the Hsp90 co-chaperone, Cdc37.

    Shao J, Prince T, Hartson SD and Matts RL

    Department of Biochemistry and Molecular Biology, Oklahoma State University, Stillwater, Oklahoma 74078-3035, USA.

    The Hsp90 co-chaperone Cdc37 provides an essential function for the biogenesis and support of numerous protein kinases. In this report, we demonstrate that mammalian Cdc37 is phosphorylated on Ser13 in situ in rabbit reticulocyte lysate and in cultured K562 cells and that casein kinase II is capable of quantitatively phosphorylating recombinant Cdc37 at this site. Mutation of Ser13 to either Ala or Glu compromises the recruitment of Cdc37 to Hsp90-kinase complexes but has only modest effects on its basal (client-free) binding to Hsp90. Furthermore, Cdc37 containing the complementing Ser to Glu mutation showed altered interactions with Hsp90-kinase complexes consistent with compromised Cdc37 modulation of the Hsp90 ATP-driven reaction cycle. Thus, the data indicate that phosphorylation of Cdc37 on Ser13 is critical for its ability to coordinate Hsp90 nucleotide-mediated conformational switching and kinase binding.

    The Journal of biological chemistry 2003;278;40;38117-20

  • Hes6 promotes cortical neurogenesis and inhibits Hes1 transcription repression activity by multiple mechanisms.

    Gratton MO, Torban E, Jasmin SB, Theriault FM, German MS and Stifani S

    Center for Neuronal Survival, Montreal Neurological Institute, McGill University, Montreal, Quebec H3A 2B4, Canada.

    Hes1 is a mammalian basic helix-loop-helix transcriptional repressor that inhibits neuronal differentiation together with corepressors of the Groucho (Gro)/Transducin-like Enhancer of split (TLE) family. The interaction of Hes1 with Gro/TLE is mediated by a WRPW tetrapeptide present in all Hairy/Enhancer of split (Hes) family members. In contrast to Hes1, the related protein Hes6 promotes neuronal differentiation. Little is known about the molecular mechanisms that underlie the neurogenic activity of Hes6. It is shown here that Hes6 antagonizes Hes1 function by two mechanisms. Hes6 inhibits the interaction of Hes1 with its transcriptional corepressor Gro/TLE. Moreover, it promotes proteolytic degradation of Hes1. This effect is maximal when both Hes1 and Hes6 contain the WRPW motif and is reduced when Hes6 is mutated to eliminate a conserved site (Ser183) that can be phosphorylated by protein kinase CK2. Consistent with these findings, Hes6 inhibits Hes1-mediated transcriptional repression in cortical neural progenitor cells and promotes the differentiation of cortical neurons, a process that is normally inhibited by Hes1. Mutation of Ser183 impairs the neurogenic ability of Hes6. Taken together, these findings clarify the molecular events underlying the neurogenic function of Hes6 and suggest that this factor can antagonize Hes1 activity by multiple mechanisms.

    Molecular and cellular biology 2003;23;19;6922-35

  • Carbon monoxide neurotransmission activated by CK2 phosphorylation of heme oxygenase-2.

    Boehning D, Moon C, Sharma S, Hurt KJ, Hester LD, Ronnett GV, Shugar D and Snyder SH

    Department of Neuroscience, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205, USA.

    Carbon monoxide (CO) is a putative gaseous neurotransmitter that lacks vesicular storage and must be synthesized rapidly following neuronal depolarization. We show that the biosynthetic enzyme for CO, heme oxygenase-2 (HO2), is activated during neuronal stimulation by phosphorylation by CK2 (formerly casein kinase 2). Phorbol ester treatment of hippocampal cultures results in the phosphorylation and activation of HO2 by CK2, implicating protein kinase C (PKC) in CK2 stimulation. Odorant treatment of olfactory receptor neurons augments HO2 phosphorylation and activity as well as cyclic guanosine monophosphate (cGMP) levels, with all of these effects selectively blocked by CK2 inhibitors. Likewise, CO-mediated nonadrenergic, noncholinergic (NANC) relaxation of the internal anal sphincter requires CK2 activity. Our findings provide a molecular mechanism for the rapid neuronal activation of CO biosynthesis, as required for a gaseous neurotransmitter.

    Funded by: NIDA NIH HHS: DA-000266, DA-00074; NIDCD NIH HHS: DC-02979; NINDS NIH HHS: NS-043850, NS-39657

    Neuron 2003;40;1;129-37

  • A minimal RNA polymerase III transcription system from human cells reveals positive and negative regulatory roles for CK2.

    Hu P, Wu S and Hernandez N

    Howard Hughes Medical Institute, Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA .

    In higher eukaryotes, RNA polymerase (pol) III is known to use different transcription factors to recognize three basic types of promoters, but in no case have these transcription factors been completely defined. We show that a highly purified pol III complex combined with the recombinant transcription factors SNAP(c), TBP, Brf2, and Bdp1 directs multiple rounds of transcription initiation and termination from the human U6 promoter. The pol III complex contains traces of CK2, and CK2 associates with the U6 promoter region in vivo. Transcription requires CK2 phosphorylation of the pol III complex. In contrast, CK2 phosphorylation of TBP, Brf2, and Bdp1 combined is inhibitory. The results define a minimum core machinery, the ultimate target of regulatory mechanisms, capable of directing all steps of the transcription process-initiation, elongation, and termination-by a metazoan RNA polymerase, and suggest positive and negative regulatory roles for CK2 in transcription by pol III.

    Funded by: NIGMS NIH HHS: GM 38810

    Molecular cell 2003;12;3;699-709

  • Modulation of human checkpoint kinase Chk1 by the regulatory beta-subunit of protein kinase CK2.

    Guerra B, Issinger OG and Wang JY

    Division of Biological Sciences 0322, University of California, San Diego, CA 92093-0322, USA. bag@bmb.sdu.dk

    Protein kinase CK2 is a serine/threonine protein kinase involved in various aspects of cellular regulation. The regulatory beta-subunit of CK2 exerts a central role not only in mediating formation of tetrameric CK2 complexes but also as a docking partner for several protein kinases. In this study, CK2beta is found to interact with the human cell cycle checkpoint kinase Chk1. The Chk1-interacting region of CK2beta is localized at the C-terminus and the complex between CK2beta and Chk1 is devoid of the catalytic CK2alpha-subunit. The interaction between CK2beta and Chk1 leads to an increase in the Cdc25C phosphorylation activity of Chk1. The screening of several cell lines has revealed that the association between CK2beta and Chk1 also occurs in vivo at a different degree. Collectively, these studies confirm the implication of the regulatory beta-subunit of protein kinase CK2 in cell cycle regulation and identify a novel mechanism for the activation of Chk1 protein kinase.

    Funded by: NCI NIH HHS: CA43054, R01 CA043054

    Oncogene 2003;22;32;4933-42

  • Phosphorylation of threonine 10 on CKBBP1/SAG/ROC2/Rbx2 by protein kinase CKII promotes the degradation of IkappaBalpha and p27Kip1.

    Kim YS, Lee JY, Son MY, Park W and Bae YS

    Department of Biochemistry, College of Natural Sciences, Kyungpook National University, Daegu 702-701, Korea.

    In eukaryotic cells, protein kinase CKII is required for progression through the cell division cycle. We recently reported that CKBBP1/SAG/ROC2/Rbx2 associates with the beta-subunit of CKII and is phosphorylated by purified CKII in the presence of ATP in vitro. In this report, we demonstrate that CKBBP1 is efficiently phosphorylated in vitro by purified CKII in the presence of GTP and by heparin-sensitive protein kinase in HeLa cell extract. Mutational analysis indicates that CKII phosphorylates threonine at residue 10 within CKBBP1. Furthermore, CKBBP1 is phosphorylated in vivo and threonine to alanine mutation at residue 10 abrogates the phosphorylation of CKBBP1 observed in vivo, indicating that CKII is a major kinase that is responsible for in vivo phosphorylation of CKBBP1. As compared with the wild-type CKBBP1 or CKBBP1T10E (in which threonine 10 is replaced by glutamate), overexpression of nonphosphorylatable CKBBP1 (CKBBP1T10A) results in accumulation of IkappaBalpha and p27Kip1. Experiments using proteasome inhibitor MG132 and CKII inhibitor 5,6-dichloro-1-beta-d-ribofuranosylbenzimidazole suggest that the accumulation of IkappaBalpha and p27Kip1 results primarily from the reduction of proteasomal degradation in cells expressing CKBBP1T10A, and that CKII-mediated CKBBP1 phosphorylation is required for efficient degradation of IkappaBalpha and p27Kip1. Overexpression of CKBBP1T10A in HeLa cells suppresses cell proliferation and causes accumulation of G1/G0 peak of the cell cycle. Taken together, our results indicate that CKII may control IkappaBalpha and p27Kip1 degradation and thereby G1/S phase transition through the phosphorylation of threonine 10 within CKBBP1.

    The Journal of biological chemistry 2003;278;31;28462-9

  • Crystal structure of a C-terminal deletion mutant of human protein kinase CK2 catalytic subunit.

    Ermakova I, Boldyreff B, Issinger OG and Niefind K

    Universität zu Köln, Institut für Biochemie, Zülpicher Strasse 47, D-50674 Köln, Germany.

    Protein kinase CK2 (formerly called: casein kinase 2) is a heterotetrameric enzyme composed of two separate catalytic chains (CK2alpha) and a stable dimer of two non-catalytic subunits (CK2beta). CK2alpha is a highly conserved member of the superfamily of eukaryotic protein kinases. The crystal structure of a C-terminal deletion mutant of human CK2alpha was solved and refined to 2.5A resolution. In the crystal the CK2alpha mutant exists as a monomer in agreement with the organization of the subunits in the CK2 holoenzyme. The refined structure shows the helix alphaC and the activation segment, two main regions of conformational plasticity and regulatory importance in eukaryotic protein kinases, in active conformations stabilized by extensive contacts to the N-terminal segment. This arrangement is in accordance with the constitutive activity of the enzyme. By structural superimposition of human CK2alpha in isolated form and embedded in the human CK2 holoenzyme the loop connecting the strands beta4 and beta5 and the ATP-binding loop were identified as elements of structural variability. This structural comparison suggests that the ATP-binding loop may be the key region by which the non-catalytic CK2beta dimer modulates the activity of CK2alpha. The beta4/beta5 loop was found in a closed conformation in contrast to the open conformation observed for the CK2alpha subunits of the CK2 holoenzyme. CK2alpha monomers with this closed beta4/beta5 loop conformation are unable to bind CK2beta dimers in the common way for sterical reasons, suggesting a mechanism to protect CK2alpha from integration into CK2 holoenzyme complexes. This observation is consistent with the growing evidence that CK2alpha monomers and CK2beta dimers can exist in vivo independently from the CK2 holoenzyme and may possess physiological roles of their own.

    Journal of molecular biology 2003;330;5;925-34

  • Phosphorylation of the N-terminal domain regulates subcellular localization and DNA binding properties of the peptidyl-prolyl cis/trans isomerase hPar14.

    Reimer T, Weiwad M, Schierhorn A, Ruecknagel PK, Rahfeld JU, Bayer P and Fischer G

    Max Planck Research Unit, Enzymology of Protein Folding, Weinbergweg 22, D-06120 Halle, Germany.

    Human parvulin 14 (hPar14) is a folding helper enzyme belonging to the parvulin family of peptidyl-prolyl cis/trans isomerases (PPIases). This enzyme is thought to play a role in cell-cycle and chromatin remodeling. Although hPar14 was nuclearly localized and bound to double-stranded DNA, the molecular basis of the subcellular localization and the functional regulation remained unknown. Here we show that subcellular localization and DNA-binding ability of hPar14 is regulated by posttranslational modification of its N-terminal domain. As proved by MALDI-TOF mass spectrometry and MS/MS fragmentation, hPar14 is phosphorylated at Ser19 in vitro and in vivo. In human HeLa cells the protein is most likely modified by casein kinase 2 (CK2). Phosphorylation of hPar14 is inhibited both in vitro and in vivo by 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB), a specific inhibitor of CK2 activity. Mutation of Ser19 to Ala abolishes phosphorylation and alters the subcellular localization of hPar14 from predominantly nuclear to significantly cytoplasmic. Immunostaining shows that a Glu19 mutant of hPar14, which mimics the phosphorylated state of Ser19, is localized around the nuclear envelope, but does not penetrate into the nucleoplasm. In contrast to wild-type hPar14, the in vitro DNA-binding affinity of the Glu19 mutant is strongly reduced, suggesting that only the dephosphorylated protein is the active DNA-binding form of hPar14 in the nucleus.

    Journal of molecular biology 2003;330;5;955-66

  • CK2 phosphorylation of the armadillo repeat region of beta-catenin potentiates Wnt signaling.

    Song DH, Dominguez I, Mizuno J, Kaut M, Mohr SC and Seldin DC

    Department of Medicine, Boston University Medical Center, Boston University, Boston, Massachusetts 02118, USA.

    Protein kinase CK2 is a ubiquitous serine/threonine kinase involved in many biological processes. It is overexpressed in many malignancies including rodent and human breast cancer, and is up-regulated in Wnt-transfected mammary epithelial cells, where it can be found in a complex with dishevelled and beta-catenin. beta-Catenin is a substrate for CK2 and inhibition of CK2 reduces levels of beta-catenin and dishevelled. Here we report that inhibition of CK2 using pharmacologic agents or expression of kinase inactive subunits reduces beta-catenin-dependent transcription and protein levels in a proteasome-dependent fashion. The major region of phosphorylation of beta-catenin by CK2 is the central armadillo repeat domain, where carrier proteins like axin and the adenomatous polyposis coli gene product APC interact with beta-catenin. The major CK2 phosphorylation site in this domain is Thr393, a solvent-accessible residue in a key hinge region of the molecule. Mutation of this single amino acid reduces beta-catenin phosphorylation, cotranscriptional activity, and stability. Thus, CK2 is a positive regulator of Wnt signaling through phosphorylation of beta-catenin at Thr393, leading to proteasome resistance and increased protein and co-transcriptional activity.

    Funded by: NCI NIH HHS: CA71796; NIEHS NIH HHS: ES11624

    The Journal of biological chemistry 2003;278;26;24018-25

  • Protein kinase CK2 phosphorylates Hsp105 alpha at Ser509 and modulates its function.

    Ishihara K, Yamagishi N and Hatayama T

    Department of Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchi-cho, Misasagi, Yamashina-ku, Kyoto 607-8414, Japan.

    The 105 kDa heat-shock protein (Hsp) Hsp105 alpha is a mammalian stress protein that belongs to the HSP105/HSP110 family. We have shown previously that Hsp105 alpha exists as non-phosphorylated and phosphorylated forms in vivo, and is phosphorylated by protein kinase CK2 (CK2) in vitro. In this study, to elucidate the role of phosphorylation of Hsp105 alpha, we first analysed the site of phosphorylation of Hsp105 alpha by CK2. Peptide mapping analysis of Hsp105 alpha phosphorylated by CK2 and in vitro phosphorylation experiments using various deletion and substitution mutants of Hsp105 alpha revealed that Hsp105 alpha is phosphorylated at Ser(509) in the beta-sheet domain. Furthermore, Ser(509) in Hsp105 alpha was also phosphorylated in mammalian COS-7 cells, although other sites were phosphorylated as well. Next, we examined the effects of phosphorylation of Hsp105 alpha on its functions using CK2-phosphorylated Hsp105 alpha. Interestingly, Hsp105 alpha suppressed 70 kDa heat-shock cognate protein (Hsc70)-mediated protein folding, whereas the phosphorylation of Hsp105 alpha at Ser(509) abolished the inhibitory activity of Hsp105 alpha in vitro. In accordance with these findings, wild-type Hsp105 alpha, which was thought to be phosphorylated in vivo, had no effect on Hsp70-mediated refolding of heat-denatured luciferase, whereas a non-phosphorylatable mutant of Hsp105 alpha suppressed the Hsp70-mediated refolding of heat-denatured luciferase in mammalian cells. Thus it was suggested that CK2 phosphorylates Hsp105 alpha at Ser(509) and modulates the function of Hsp105 alpha. The regulation of Hsp105 alpha function by phosphorylation may play an important role in a variety of cellular events.

    The Biochemical journal 2003;371;Pt 3;917-25

  • Phosphorylation of the WASP-VCA domain increases its affinity for the Arp2/3 complex and enhances actin polymerization by WASP.

    Cory GO, Cramer R, Blanchoin L and Ridley AJ

    Ludwig Institute for Cancer Research, Royal Free and University College Medical School Branch, Courtauld Building, 91 Riding House Street, London W1W 7BS, United Kingdom.

    Wiskott-Aldrich syndrome protein (WASP) and neural (N)-WASP regulate dynamic actin structures through the ability of their VCA domains to bind to and stimulate the actin nucleating activity of the Arp2/3 complex. Here we identify two phosphorylation sites in the VCA domain of WASP at serines 483 and 484. S483 and S484 are substrates for casein kinase 2 in vitro and in vivo. Phosphorylation of these residues increases the affinity of the VCA domain for the Arp2/3 complex 7-fold and is required for efficient in vitro actin polymerization by the full-length WASP molecule. We propose that constitutive VCA domain phosphorylation is required for optimal stimulation of the Arp2/3 complex by WASP.

    Molecular cell 2003;11;5;1229-39

  • Transcriptional activity and DNA binding of heat shock factor-1 involve phosphorylation on threonine 142 by CK2.

    Soncin F, Zhang X, Chu B, Wang X, Asea A, Ann Stevenson M, Sacks DB and Calderwood SK

    Centre National de la Recherche Scientifique EP 560, Institut Pasteur de Lille, 1 Rue Calmette-BP 245, 59021, Lille Cedex, France.

    Heat shock factor-1 (HSF-1) is the regulator of hsp molecular chaperone transcription, although the intracellular mechanisms involved in HSF-1 activation have not been fully elucidated. As HSF1 is activated by heat shock simultaneously with the nuclear translocation of the protein kinase CK2, we have investigated the role of CK2 in HSF1 activation. We demonstrate that HSF-1 is phosphorylated by CK2 on both serine and threonine residues and has characterized a phosphorylation site at threonine 142. Mutation of Thr-142 to alanine (T142A) inhibits trans-activation of the HSP70 gene by HSF1 and in addition inhibits the accumulation of HSF-1 competent to bind heat shock elements in the nucleus. HSF1 activation by heat is correlated with the thermal activation of nuclear CK2 and overexpression of CK2 activates HSF1. Phosphorylation by CK2 on threonine 142 may therefore be an essential step in the thermal activation of latent HSF1 by stresses.

    Biochemical and biophysical research communications 2003;303;2;700-6

  • Protein kinase CK2 and protein kinase D are associated with the COP9 signalosome.

    Uhle S, Medalia O, Waldron R, Dumdey R, Henklein P, Bech-Otschir D, Huang X, Berse M, Sperling J, Schade R and Dubiel W

    Division of Molecular Biology, Department of Surgery, Institute of Toxicology, Medical Faculty Charité, Humboldt University, Monbijoustrasse 2, D-10117 Berlin, Germany.

    The COP9 signalosome (CSN) purified from human erythrocytes possesses kinase activity that phosphoryl ates proteins such as c-Jun and p53 with consequence for their ubiquitin (Ub)-dependent degradation. Here we show that protein kinase CK2 (CK2) and protein kinase D (PKD) co-purify with CSN. Immunoprecipitation and far-western blots reveal that CK2 and PKD are in fact associated with CSN. As indicated by electron microscopy with gold-labeled ATP, at least 10% of CSN particles are associated with kinases. Kinase activity, most likely due to CK2 and PKD, co-immuno precipitates with CSN from HeLa cells. CK2 binds to DeltaCSN3(111-403) and CSN7, whereas PKD interacts with full-length CSN3. CK2 phosphorylates CSN2 and CSN7, and PKD modifies CSN7. Both CK2 and PKD phosphorylate c-Jun as well as p53. CK2 phosphoryl ates Thr155, which targets p53 to degradation by the Ub system. Curcumin, emodin, DRB and resveratrol block CSN-associated kinases and induce degradation of c-Jun in HeLa cells. Curcumin treatment results in elevated amounts of c-Jun-Ub conjugates. We conclude that CK2 and PKD are recruited by CSN in order to regulate Ub conjugate formation.

    Funded by: NIDDK NIH HHS: R21 DK071783

    The EMBO journal 2003;22;6;1302-12

  • Role of protein kinase CK2 phosphorylation in the molecular chaperone activity of nucleolar protein b23.

    Szebeni A, Hingorani K, Negi S and Olson MO

    Department of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA.

    Protein B23 is a multifunctional nucleolar protein whose molecular chaperone activity is proposed to play role in ribosome assembly. Previous studies (Szebeni, A., and Olson, M. O. J. (1999) Protein Sci. 8, 905-912) showed that protein B23 has several characteristics typical of molecular chaperones, including anti-aggregation activity, promoting the renaturation of denatured proteins, and preferential binding to denatured substrates. However, until now there has been no proposed mechanism for release of a bound substrate. Protein B23 can be phosphorylated by protein kinase CK2 (CK2) in a segment required for chaperone activity. The presence of bound substrate enhanced the rate of CK2 phosphorylation of protein B23 by 2-3-fold, and this enhancement was dependent on a nonpolar region in its N-terminal end. Formation of a complex between B23 and chaperone test substrates (rhodanese or citrate synthase) was inhibited by CK2 phosphorylation. Furthermore, CK2 phosphorylation of a previously formed B23-substrate complex promoted its dissociation. The dissociation of complexes between B23 and the human immunodeficiency virus-Rev protein required both CK2 phosphorylation and competition with a Rev nuclear localization signal peptide, suggesting that Rev binds B23 at two separate sites. These studies suggest that unlike many molecular chaperones, which directly hydrolyze ATP, substrate release by protein B23 is dependent on its phosphorylation by CK2.

    The Journal of biological chemistry 2003;278;11;9107-15

  • The C-terminal domain phosphatase and transcription elongation activities of FCP1 are regulated by phosphorylation.

    Friedl EM, Lane WS, Erdjument-Bromage H, Tempst P and Reinberg D

    Howard Hughes Medical Institute, Division of Nucleic Acids Research, Department of Biochemistry, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA.

    The C-terminal domain (CTD) of the largest subunit of RNA polymerase II (RNAPII) is heavily phosphorylated during the transition from transcription initiation to the establishment of an elongation-competent transcription complex. FCP1 is the only phosphatase known to be specific for the CTD of the largest subunit of RNAPII, and its activity is believed to be required to reactivate RNAPII, so that RNAPII can enter another round of transcription. We demonstrate that FCP1 is a phosphoprotein, and that phosphorylation regulates FCP1 activities. FCP1 is phosphorylated at multiple sites in vivo. The CTD phosphatase activity of phosphorylated FCP1 is stimulated by TFIIF, whereas dephosphorylated FCP1 is not. In addition to its role in the recycling of RNAPII, FCP1 also affects transcription elongation. Phosphorylated FCP1 is more active in stimulating transcription elongation than the dephosphorylated form of FCP1. We found that only phosphorylated FCP1 can physically interact with TFIIF. We set out to purify an FCP1 kinase from HeLa cells and identified casein kinase 2, which, surprisingly, displayed a negative effect on FCP1-associated activities.

    Funded by: NCI NIH HHS: P30 CA008748, P30 CA08748; NIGMS NIH HHS: GM 37120, R01 GM037120, R37 GM037120

    Proceedings of the National Academy of Sciences of the United States of America 2003;100;5;2328-33

  • The C terminus of initiation factor 4E-binding protein 1 contains multiple regulatory features that influence its function and phosphorylation.

    Wang X, Li W, Parra JL, Beugnet A and Proud CG

    Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom.

    Eukaryotic initiation factor 4E (eIF4E) binds the mRNA cap structure and forms eIF4F complexes that recruit 40S subunits to the mRNA. Formation of eIF4F is blocked by eIF4E-binding proteins such as 4E-BP1, which interacts with eIF4E via a motif in the center of its 118-residue sequence. 4E-BP1 plays key roles in cell proliferation, growth, and survival. Binding of 4E-BP1 to eIF4E is regulated by hierarchical multisite phosphorylation. Here we demonstrate that three different features in the C terminus of 4E-BP1 play distinct roles in regulating its phosphorylation and function. Firstly, we identify a new phosphorylation site in its C terminus (S101). A serine or glutamate at this position is required for efficient phosphorylation at Ser65. A second C-terminal site, S112, directly affects binding of 4E-BP1 to eIF4E without influencing phosphorylation of other sites. Thirdly, a conserved C-terminal motif influences phosphorylation of multiple residues, including rapamycin-insensitive sites. These relatively long-range effects are surprising given the reportedly unstructured nature of 4E-BP1 and may imply that phosphorylation of 4E-BP1 and/or binding to eIF4E induces a more-ordered structure. 4E-BP2 and -3 lack phosphorylatable residues corresponding to both S101 and S112. However, in 4E-BP3, replacement of the alanine at the position corresponding to S112 by serine or glutamate did not confer the ability to be released from eIF4E in response to insulin.

    Molecular and cellular biology 2003;23;5;1546-57

  • Basal and hydrogen peroxide stimulated sites of phosphorylation in heterogeneous nuclear ribonucleoprotein C1/C2.

    Stone JR, Maki JL and Collins T

    Department of Pathology, Children's Hospital and Brigham & Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115,USA. jrstone@partners.org

    Hydrogen peroxide (H2O2) is a recently recognized second messenger, which regulates mammalian cell proliferation and migration. The biochemical mechanisms by which mammalian cells sense and respond to low concentrations of H2O2 are poorly understood. Recently, heterogeneous nuclear ribonucleoprotein C1/C2 (hnRNP-C1/C2) was found to be rapidly phosphorylated in response to the application of low concentrations of H2O2 to human endothelial cells. Here, using tandem mass spectrometry, four sites of phosphorylation are identified in hnRNP-C1/C2, all of which are in the acidic C-terminal domain of the protein. Under resting conditions, the protein is phosphorylated at S247 and S286. In response to low concentrations of H2O2, there is increased phosphorylation at S240 and at one of the four contiguous serine residues from S225-S228. Studies using a recombinant acidic C-terminal domain of hnRNP-C overexpressed in Escherichia coli demonstrate that protein kinase CK2 phosphorylates hnRNP-C1/C2 at S247, while protein kinase A and several protein kinase C isoforms fail to phosphorylate the isolated domain. These findings demonstrate that the acidic C-terminal domain of hnRNP-C1/C2 serves as the site for both basal and stimulated phosphorylation, indicating that this domain may play an important role in the regulation of mRNA binding by hnRNP-C1/C2.

    Funded by: NHLBI NIH HHS: HL07627, HL35716

    Biochemistry 2003;42;5;1301-8

  • Protein kinase CK2 regulates CDC25B phosphatase activity.

    Theis-Febvre N, Filhol O, Froment C, Cazales M, Cochet C, Monsarrat B, Ducommun B and Baldin V

    LBCMCP-CNRS UMR 5088, Institut d'Exploration Fonctionelle des Génomes-IFR 109, Université Paul Sabatier, Toulouse, France.

    Human dual-specificity phosphatases CDC25 (A, B and C) play an important role in the control of cell cycle progression by activating the cyclin-dependent kinases (CDKs). Regulation of these phosphatases during the cell cycle involves post-translational modifications such as phosphorylation and protein-protein interactions. Given the suspected involvement of the protein kinase CK2 at the G2/M transition, we have investigated its effects on the CDC25B phosphatase. We show that in vitro CK2 phosphorylates CDC25B, but not CDC25C. Mass spectrometry analysis demonstrates that at least two serine residues, Ser-186 and Ser-187, are phosphorylated in vivo. We also report that CDC25B interacts with CK2, and this interaction, mediated by the CK2beta regulatory subunit, involves domains that are located within the first 55 amino acids of CK2beta and between amino acids 122 and 200 on CDC25B. This association was confirmed in vivo, in Sf9 insect cells and in U(2)OS human cells expressing an HA epitope-tagged CDC25B. Finally, we demonstrate that phosphorylation of CDC25B by protein kinase CK2 increases the catalytic activity of the phosphatase in vitro as well as in vivo. We discuss the possibility that CDC25B phosphorylation by CK2 could play a role in the regulation of the activity of CDC25B as a starter of mitosis.

    Oncogene 2003;22;2;220-32

  • p53 serine 392 phosphorylation increases after UV through induction of the assembly of the CK2.hSPT16.SSRP1 complex.

    Keller DM and Lu H

    Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97201, USA.

    Previously, we purified a UV-responsive p53 serine 392 kinase from F9 and HeLa cells and found that its activity is attributed to a high molecular weight protein complex containing the protein kinase CK2, along with the chromatin-associated factors hSPT16 and SSRP1. Here we determine that these proteins interact in vitro and in cells via non-overlapping domains and provide evidence consistent with the idea that hSPT16 and SSRP1 change the conformation of CK2 upon binding such that it specifically targets p53 over other substrates. Also, UV irradiation apparently induces the association of the complex, thereby increasing the specificity of CK2 for p53 at the expense of other cellular CK2 substrates and leading to an overall increase in p53 serine 392 phosphorylation.

    Funded by: NCI NIH HHS: CA 095441, CA 93614

    The Journal of biological chemistry 2002;277;51;50206-13

  • Protein kinase CKII regulates the interaction of beta-catenin with alpha-catenin and its protein stability.

    Bek S and Kemler R

    Department of Molecular Embryology, Max-Planck Institute of Immunobiology, Stuebeweg 51, D-79108 Freiburg, Germany.

    beta-Catenin is a multi-functional cellular component and a substrate for several protein kinases. Here we investigated the interaction of protein kinase CKII (casein kinase II) and beta-catenin. We show that CKII phosphorylates the N-terminal region of beta-catenin and we identified Ser29, Thr102, and Thr112 as substrates for the enzyme. We provide evidence that CKII regulates the cytoplasmic stability of beta-catenin and acts synergistically with GSK-3beta in the multi-protein complex that controls the degradation of beta-catenin. In comparing wild-type and Ser/Thr-mutant beta-catenin, a decreased affinity of the mutant protein to alpha-catenin was observed. Moreover, kinase assays in vitro demonstrate a CKII-dependent increase in the binding of wild-type beta-catenin with alpha-catenin. In line with that, cells expressing Ser/Thr-mutant beta-catenin exhibit an increased migratory potential, which correlates with an enhanced cytosolic localization and a reduced association with the cytoskeleton of the mutant protein. From these results we conclude that CKII regulates the function of beta-catenin in the cadherin adhesion complex as well as its cytoplasmic stability.

    Journal of cell science 2002;115;Pt 24;4743-53

  • Prointerleukin-16 contains a functional CcN motif that regulates nuclear localization.

    Wilson KC, Cruikshank WW, Center DM and Zhang Y

    The Pulmonary Center, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA. KWilson@lung.bumc.bu.edu

    The immunomodulatory cytokine interleukin-16 (IL-16) represents the secreted C-terminus of a larger precursor, pro-IL-16. Following cleavage by caspase 3, the residual N-terminal domain translocates into the nucleus, inducing G(0)/G(1) cell cycle arrest. We have previously identified a classical bipartite nuclear localization sequence (NLS) in the N-terminal domain of pro-IL-16. We now show that N-terminal to the NLS domain of pro-IL-16 are protein kinase CK2 substrate and cdc2 kinase substrate sites which, along with the NLS, constitute a dual phosphorylation-regulated CcN motif which regulates nuclear localization of pro-IL-16. In addition, we demonstrate that mutation of either site is associated with impairment of the N-terminal domain's ability to induce G(0)/G(1) cell cycle arrest. This is the first description of a functional CcN motif in a cytokine precursor.

    Funded by: NHLBI NIH HHS: HL 32802

    Biochemistry 2002;41;48;14306-12

  • Specific localization of the catalytic subunits of protein kinase CK2 at the centrosomes.

    Faust M, Günther J, Morgenstern E, Montenarh M and Götz C

    Universität des Saarlandes, Medizinische Biochemie und Molekularbiologie, Gebäude 44, 66424 Homburg, Germany. bccgoe@uniklinik-saarland.de

    The protein kinase CK2 holoenzyme is composed of two regulatory beta subunits and two catalytic alpha or alpha' subunits. Although experimental evidence for involvement of the enzyme in the regulation of cell proliferation is accumulating, the exact mechanism of its action is still unclear. The subcellular localization of the enzyme may be a key to its function. We have recently shown that the CK2 holoenzyme is tightly associated with the Golgi complex and the endoplasmic reticulum. Centrosomes, which organize spindle formation during the cell cycle and microtubule cytoskeleton formation and, thereby, the location and orientation of different organelles in the cell, are in close vicinity to the Golgi complex. Because several kinases and phosphatases have been described to regulate the functions of the centrosome, we analysed the association of CK2 with these organelles. Using biochemical cell fractionation and coimmunoprecipitation, we never found the holoenzyme but only the catalytic alpha subunits associated with the centrosome. These data were confirmed by immunoelectron microscopy. Thus, the present data point to a particular role of the catalytic alpha and alpha' subunit of protein kinase CK2, which may be different from their roles in the holoenzyme.

    Cellular and molecular life sciences : CMLS 2002;59;12;2155-64

  • Characterization of the phosphorylation status of the hepatitis B virus X-associated protein 2.

    Dull AB, Carlson DB, Petrulis JR and Perdew GH

    Graduate Program in Genetics, The Pennsylvania State University, University Park, PA 16802, USA.

    The cytosolic Ah receptor (AhR) heterocomplex consists of one molecule of the AhR, a 90-kDa heat shock protein (Hsp90) dimer, and one molecule of the hepatitis B virus X-associated protein 2 (XAP2). Serine residues 43,53,131-2, and 329 on XAP2-FLAG were identified as putative phosphorylation sites using site-directed mutagenesis followed by two-dimensional phosphopeptide mapping analysis. Protein kinase CK2 (CK2) was identified as the 45-kDa kinase from COS 1 cell or liver extracts that was responsible for phosphorylation of serine 43 in the XAP2 peptide 39-57. Loss of phosphorylation at any or all of the serine residues did not significantly affect the ability of XAP2-FLAG to bind to the murine AhR in rabbit reticulocyte lysate or Hsp90 in COS-1 cells. Furthermore, all of these serine mutants were able to sequester murine AhR-YFP into the cytoplasm as well as wild-type XAP2. YFP-XAP2 S53A was unable to enter the nucleus, indicating a potential role of phosphorylation in nuclear translocation of XAP2.

    Funded by: NIEHS NIH HHS: ES04869, ES05900

    Archives of biochemistry and biophysics 2002;406;2;209-21

  • The transcriptional repressor Sp3 is associated with CK2-phosphorylated histone deacetylase 2.

    Sun JM, Chen HY, Moniwa M, Litchfield DW, Seto E and Davie JR

    Manitoba Institute of Cell Biology, Winnipeg, Manitoba R3E 0V9, Canada.

    Sp1 and Sp3 are ubiquitously expressed mammalian transcription factors that function as activators or repressors. Although both transcription factors share a common domain involved in forming multimers, we demonstrate that Sp1 and Sp3 form separate complexes in estrogen-dependent human breast cancer cells. Sp1 and Sp3 complexes associate with histone deacetylases (HDACs) 1 and 2. Although most HDAC2 is not phosphorylated in the breast cancer cells, HDAC2 bound to Sp1 and Sp3 and cross-linked to chromatin in situ is highly enriched in a phosphorylated form that has a reduced mobility in SDS-polyacrylamide gels. We show that protein kinase CK2 is associated with and phosphorylates HDAC2. Alkaline phosphatase treatment of HDAC2 and Sp1 and Sp3 complexes reduced the associated HDAC activity. Protein kinase CK2 is up-regulated in several cancers including breast cancer, and Sp1 and Sp3 have key roles in estrogen-induced proliferation and gene expression in estrogen-dependent breast cancer cells. CK2 phosphorylation of HDAC2 recruited by Sp1 or Sp3 could regulate HDAC activity and alter the balance of histone deacetylase and histone acetyltransferase activities and dynamic chromatin remodeling of estrogen-regulated genes.

    The Journal of biological chemistry 2002;277;39;35783-6

  • Direct identification of PTEN phosphorylation sites.

    Miller SJ, Lou DY, Seldin DC, Lane WS and Neel BG

    Cancer Biology Program, Division of Hematology-Oncology, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA.

    The PTEN tumor suppressor gene encodes a phosphatidylinositol 3'-phosphatase that is inactivated in a high percentage of human tumors, particularly glioblastoma, melanoma, and prostate and endometrial carcinoma. Previous studies showed that PTEN is a seryl phosphoprotein and a substrate of protein kinase CK2 (CK2). However, the sites in PTEN that are phosphorylated in vivo have not been identified directly, nor has the effect of phosphorylation on PTEN catalytic activity been reported. We used mass spectrometric methods to identify Ser(370) and Ser(385) as in vivo phosphorylation sites of PTEN. These sites also are phosphorylated by CK2 in vitro, and phosphorylation inhibits PTEN activity towards its substrate, PIP3. We also identify a novel in vivo phosphorylation site, Thr(366). Following transient over-expression, a fraction of CK2 and PTEN co-immunoprecipitate. Moreover, pharmacological inhibition of CK2 activity leads to decreased Akt activation in PTEN+/+ but not PTEN-/- fibroblasts. Our results contrast with previous assignments of PTEN phosphorylation sites based solely on mutagenesis approaches, suggest that CK2 is a physiologically relevant PTEN kinase, and raise the possibility that CK2-mediated inhibition of PTEN plays a role in oncogenesis.

    Funded by: NCI NIH HHS: R01 CA49152, R01 CA71796

    FEBS letters 2002;528;1-3;145-53

  • The germ cell-specific transcription factor ALF. Structural properties and stabilization of the TATA-binding protein (TBP)-DNA complex.

    Upadhyaya AB, Khan M, Mou TC, Junker M, Gray DM and DeJong J

    Department of Molecular and Cell Biology, University of Texas at Dallas, 2601 N. Floyd Road, Richardson, TX 75080, USA.

    The assembly and stability of the RNA polymerase II transcription preinitiation complex on a eukaryotic core promoter involves the effects of TFIIA on the interaction between TATA-binding protein (TBP) and DNA. To extend our understanding of these interactions, we characterized properties of ALF, a germ cell-specific TFIIA-like factor. ALF was able to stabilize the binding of TBP to DNA, but it could not stabilize TBP mutants A184E, N189E, E191R, and R205E nor could it facilitate binding of the TBP-like factor TRF2/TLF to a consensus TATA element. However, phosphorylation of ALF with casein kinase II resulted in the partial restoration of complex formation using mutant TBPs. Studies of ALF-TBP complexes formed on the Adenovirus Major Late (AdML) promoter revealed protection of the TATA box and upstream sequences from -38 to -20 (top strand) and -40 to -22 (bottom strand). The half-life and apparent K(D) of this complex was determined to be 650 min and 4.8 +/- 2.7 nm, respectively. The presence of ALF or TFIIA did not significantly alter the ability of TBP to bind TATA elements from several testis-specific genes. Finally, analysis of the distinct, nonhomologous internal regions of ALF and TFIIAalpha/beta using circular dichroism spectroscopy provided the first evidence to suggest that these domains are unordered, a result consistent with other genetic and biochemical properties. Overall, the results show that while the sequence and regulation of the ALF gene are distinct from its somatic cell counterpart TFIIAalpha/beta, the TFIIAgamma-dependent interactions of these factors with TBP are nearly indistinguishable in vitro. Thus, a role for ALF in the assembly and stabilization of initiation complexes in germ cells is likely to be similar or identical to the role of TFIIA in somatic cells.

    The Journal of biological chemistry 2002;277;37;34208-16

  • Heat-shock protein 90 complexes in resting and thrombin-activated platelets.

    Suttitanamongkol S, Polanowska-Grabowska R and Gear AR

    Department of Biochemistry and Molecular Genetics, University of Virginia, Jordan Hall, Box 440, Charlottesville, VA 22908, USA.

    Heat-shock protein 90 (hsp90) is a chaperone important for the function of many signaling proteins. In this study, we show that hsp90 exists in resting platelets as a complex with the heat-shock cognate protein 70 (hsc70), the alpha- and beta-subunits of protein kinase CK2, and other unidentified phosphoproteins. Platelet activation by thrombin caused the rapid dissociation of hsc70 and CK2alpha from the hsp90 complex, the ex vivo phosphorylation of many protein components, and the stimulation of protein kinase(s) associated with the hsp90 complex. These results suggest that the hsp90 complex, with its associated protein kinase(s), which may include CK2, and their substrates, is involved in thrombin-induced platelet activation.

    Biochemical and biophysical research communications 2002;297;1;129-33

  • Regulation of histone deacetylase 2 by protein kinase CK2.

    Tsai SC and Seto E

    H. Lee Moffitt Cancer Center and Research Institute, University of South Florida, Tampa, Florida 33612, USA.

    Histone deacetylase 2 (HDAC2) is a member of a large family of enzymes that alter gene expression by catalyzing the removal of acetyl groups from core histones. Originally isolated as a transcriptional co-repressor, HDAC2 possesses extensive amino acid sequence homology to HDAC1 (the founding member and most extensively studied HDAC enzyme). Because of this high degree of sequence similarity between HDAC1 and HDAC2, coupled with the fact that the two always co-exist in the same complexes, it is difficult to assess whether different properties exist between these two proteins. We report here that HDAC2 is a phosphoprotein similar to HDAC1. In addition, like HDAC1, the phospho-acceptor sites in HDAC2 are located in the C-terminal portion of the protein. However, unlike HDAC1, which can be phosphorylated by protein kinase CK2, cAMP-dependent protein kinase, and protein kinase G, HDAC2 is phosphorylated uniquely by protein kinase CK2 in vitro. Studies using unfractionated cell extracts with CK2 inhibitors suggest that protein kinase CK2 is the major source of HDAC2 kinase. Finally, and perhaps most interesting, HDAC2 phosphorylation promotes enzymatic activity, selectively regulates complex formation, but has no effect on transcriptional repression. Together, our data indicate that like many HDACs, HDAC2 is regulated by post-translational modification, particularly phosphorylation. Furthermore, we demonstrate for the first time that there are similarities and differences in the regulation of HDAC1 and HDAC2 by phosphorylation.

    Funded by: NIGMS NIH HHS: GM58486

    The Journal of biological chemistry 2002;277;35;31826-33

  • Functional interaction of protein kinase CK2 and c-Myc in lymphomagenesis.

    Channavajhala P and Seldin DC

    Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts, MA 02118, USA.

    Protein kinase CK2 (formerly casein kinase II) is frequently upregulated in human cancers, and transgenic expression of CK2alpha in lymphocytes is oncogenic. Lymphomagenesis is dramatically accelerated by co-expression of a c-myc transgene, suggestive of a synergistic interaction between the kinase and the transcription factor. Since c-myc can be phosphorylated by CK2, we hypothesized that the synergy between CK2 and c-myc might be due to a functional interaction of the two molecules. Pharmacologic inhibition of CK2 activity in cell lines established from CK2alpha transgenic T cell lymphomas reduces their proliferation and concomitantly with this, the steady state levels of c-myc protein decline. This is caused by accelerated c-myc protein turnover, which occurs in a proteasome-dependent manner. Transfection of cells with sense or anti-sense CK2 constructs modulates c-myc protein levels in concert with the alteration in CK2 activity, validating the findings obtained using the kinase inhibitors. Thus, CK2 is a critical regulator of c-myc protein stability and of the proliferation of these T cell lymphomas.

    Funded by: NCI NIH HHS: R01 CA71796; NHLBI NIH HHS: T32 HL07501

    Oncogene 2002;21;34;5280-8

  • Binding of FGF-1 variants to protein kinase CK2 correlates with mitogenicity.

    Skjerpen CS, Nilsen T, Wesche J and Olsnes S

    Department of Biochemistry at The Institute for Cancer Research, The Norwegian Radium Hospital, Montebello, 0310 Oslo, Norway.

    Fibroblast growth factor-1 (FGF-1) has both extra- and intracellular functions. To identify intracellular binding partners for FGF-1, we isolated proteins from U2OS human osteosarcoma cells interacting specifically with FGF-1. One of the isolated proteins was identified as protein kinase CK2 (CK2). We here provide evidence that FGF-1 binds to both the catalytic alpha-subunit and to the regulatory beta-subunit of CK2. The interaction between FGF-1 and CK2 alpha and beta was characterized by surface plasmon resonance, giving K(D) values of 0.4 +/- 0.3 and 1.2 +/- 0.2 microM, respectively. By using a novel assay for intracellular protein interaction, FGF-1 and CK2 alpha are shown to interact in vivo. In vitro, FGF-1 and FGF-2 are phosphorylated by CK2, and the presence of FGF-1 or FGF-2 was found to enhance the autophosphorylation of CK2 beta. A correlation between the mitogenic potential of FGF-1 mutants and their ability to bind to CK2 alpha was observed. The possible involvement of CK2 in the FGF-induced stimulation of DNA synthesis is discussed.

    The EMBO journal 2002;21;15;4058-69

  • Phosphorylation by protein kinase CK2: a signaling switch for the caspase-inhibiting protein ARC.

    Li PF, Li J, Müller EC, Otto A, Dietz R and von Harsdorf R

    Max-Delbrück-Center for Molecular Medicine, 13125 Berlin, Germany.

    Caspases play a central role in apoptosis, but their activity is under the control of caspase-inhibiting proteins. A characteristic of caspase-inhibiting proteins is direct caspase binding. It is yet unknown how the localization of caspase-inhibiting proteins is regulated and whether there are upstream signals controlling their function. Here we report that the function of ARC is regulated by protein kinase CK2. ARC at threonine 149 is phosphorylated by CK2. This phosphorylation targets ARC to mitochondria. ARC is able to bind to caspase-8 only when it is localized to mitochondria but not to the cytoplasm. Our results reveal a molecular mechanism by which a caspase-inhibiting protein requires phosphorylation in order to prevent apoptosis.

    Molecular cell 2002;10;2;247-58

  • Sequencing of full-length cDNA encoding the alpha and beta subunits of human casein kinase II from human platelets and megakaryocytic cells. Expression of the casein kinase IIalpha intronless gene in a megakaryocytic cell line.

    Singh LS and Kalafatis M

    Department of Chemistry, Cleveland State University, Science Building, 2351 Euclid Avenue, Cleveland, OH 44115, USA.

    Casein kinase II (CKII) is a ubiquitous protein kinase composed of two subunits, alpha and beta, that can use both ATP and GTP as phosphoryl donors. Two genes located on two separate chromosomes were identified for CKIIalpha: one on chromosome 20 band 13 with an approximate size of 20 kb and a second on chromosome 11 band 15.5-p15.4 that is the same size as the cDNA of locus 20 kb (1.2 kb) and does not contain any introns. The two genes differ in four amino acids. Recently, it has been demonstrated that a membrane-associated platelet-derived CKII phosphorylates coagulation factor Va. The mRNA encoding the platelet CKII was isolated from fresh human platelets, and the corresponding cDNAs encoding the alpha and beta subunits of human platelet CKII were produced and sequenced. The cDNA for platelet CKIIalpha was found to be 99.7% homologous to the CKIIalpha intronless gene, having the same characteristic amino acid residues at positions 128, 256, 287, and 351. However, the cDNA of platelet CKIIalpha has a different amino acid at position 236 (Arg --> His), which is not found in the intronless gene. The cDNA of the CKIIbeta subunit was completely identical with the sequence of the CKIIbeta subunit isolated from other tissues. Since platelets arise from megakaryocytes, mRNA was isolated from the megakaryocytic cell line MEG-01 and the cDNA for CKIIalpha was cloned and sequenced. The cDNA was found to be identical to the intronless gene found in platelets. We have also investigated the expression of the intronless gene in several other cell lines. Expression of the intronless gene was only found in cell line MEG-01. Our data demonstrate expression of the CKIIalpha intronless gene in megakaryocytes and platelets.

    Biochemistry 2002;41;28;8935-40

  • Interactions between protein kinase CK2 and Pin1. Evidence for phosphorylation-dependent interactions.

    Messenger MM, Saulnier RB, Gilchrist AD, Diamond P, Gorbsky GJ and Litchfield DW

    Department of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada.

    The peptidyl-prolyl isomerase Pin1 interacts in a phosphorylation-dependent manner with several proteins involved in cell cycle events. In this study, we demonstrate that Pin1 interacts with protein kinase CK2, an enzyme that generally exists in tetrameric complexes composed of two catalytic CK2 alpha and/or CK2 alpha' subunits together with two regulatory CK2 beta subunits. Our results indicate that Pin1 can interact with CK2 complexes that contain CK2 alpha. Furthermore, Pin1 can interact directly with the C-terminal domain of CK2 alpha that contains residues that are phosphorylated in vitro by p34(Cdc2) and in mitotic cells. Substitution of the phosphorylation sites of CK2 alpha with alanines resulted in decreased interactions between Pin1 and CK2. The other catalytic isoform of CK2, designated CK2 alpha', is not phosphorylated in mitotic cells and does not interact with Pin1, but a chimeric protein consisting of CK2 alpha' with the C terminus of CK2 alpha was phosphorylated in mitotic cells and interacts with Pin1, further implicating the phosphorylation sites in the interaction. In vitro, Pin1 inhibits the phosphorylation of Thr-1342 on human topoisomerase II alpha by CK2. Topoisomerase II alpha also interacts with Pin1 suggesting that the effect of Pin1 on the phosphorylation of Thr-1342 could result from its interactions with CK2 and/or topoisomerase II alpha. As compared with wild-type Pin1, isomerase-deficient and WW domain-deficient mutants of Pin1 are impaired in their ability to interact with CK2 and to inhibit the CK2-catalyzed phosphorylation of topoisomerase II alpha. Collectively, these results indicate that Pin1 and CK2 alpha interact and suggest a possible role for Pin1 in the regulation of topoisomerase II alpha. Furthermore, these results provide new insights into the functional role of the mitotic phosphorylation of CK2 and provide a new mechanism for selectively regulating the ability of CK2 to phosphorylate one of its mitotic targets.

    The Journal of biological chemistry 2002;277;25;23054-64

  • Unique activation mechanism of protein kinase CK2. The N-terminal segment is essential for constitutive activity of the catalytic subunit but not of the holoenzyme.

    Sarno S, Ghisellini P and Pinna LA

    Department of Biological Chemistry, University of Padua, viale G. Colombo 3, 35121 Padua, Italy.

    CK2 is an essential, ubiquitous, and highly pleiotropic protein kinase whose catalytic subunits (alpha and alpha') and holoenzyme (composed by two catalytic and two regulatory beta-subunits) are both constitutively active, a property that is suspected to contribute to its pathogenic potential. Extensive interactions between the N-terminal segment and the activation loop are suspected to underlie the high constitutive activity of the isolated catalytic subunit. Here we show that a number of point mutations (Tyr(26) --> Phe, Glu(180) --> Ala, Tyr(182) --> Phe) and deletions (Delta 2-6, Delta 2-12, Delta 2-18, Delta 2-24, Delta 2-30) expected to affect these interactions are more or less detrimental to catalytic activity of the alpha-subunit of human CK2, the deleted mutants Delta 2-24 and Delta 2-30 being nearly inactive under normal assay conditions. Kinetic analyses showed that impaired catalytic activity of mutants Delta 2-12, Delta 2-18, Delta 2-24, and Y182F is mainly accounted for by dramatic increases in the K(m) values for ATP, whereas a drop in K(cat) with K(m) values almost unchanged was found with mutants Y26F and E180A. Holoenzyme reconstitution restored the activity of mutants Delta 2-12, Delta 2-18, Y26F, E180A, and Y182F to wild type level and also conferred catalytic activity to the intrinsically inactive mutants, Delta 2-24 and Delta 2-30. These data demonstrate that specific interactions between the N-terminal segment and the activation loop are essential to provide a fully active conformation to the catalytic subunits of CK2; they also show that these interactions become dispensable upon formation of the holoenzyme, whose constitutive activity is conferred by the beta-subunit through a different mechanism.

    The Journal of biological chemistry 2002;277;25;22509-14

  • CK2-dependent phosphorylation of the E2 ubiquitin conjugating enzyme UBC3B induces its interaction with beta-TrCP and enhances beta-catenin degradation.

    Semplici F, Meggio F, Pinna LA and Oliviero S

    Dipartimento di Biologia Molecolare, Università degli Studi di Siena, Italy.

    Protein kinase CK2 is a ubiquitous and pleiotropic Ser/Thr protein kinase involved in cell growth and transformation. Here we report the identification by yeast interaction trap of a CK2 interacting protein, UBC3B, which is highly homologous to the E2 ubiquitin conjugating enzyme UBC3/CDC34. UBC3B complements the yeast cdc34-2 cell cycle arrest mutant in S. cerevisiae and transfers ubiquitin to a target substrate in vitro. UBC3B is specifically phosphorylated by CK2 in vitro and in vivo. We mapped by deletions and site directed mutagenesis the phosphorylation site to a serine residue within the C-terminal domain in position 233 of UBC3B and in the corresponding serine residue of UBC3. Following CK2-dependent phosphorylation both UBC3B and UBC3 bind to the F-box protein beta-TrCP, the substrate recognition subunit of an SCF (Skp1, Cul1, F-box) ubiquitin ligase. Furthermore, we observed that co-transfection of CK2alpha' together with UBC3B, but not with UBC3DeltaC, enhances the degradation of beta-catenin. Taken together these data suggest that CK2-dependent phosphorylation of UBC3 and UBC3B functions by regulating beta-TrCP substrate recognition.

    Oncogene 2002;21;25;3978-87

  • CK2 forms a stable complex with TFIIIB and activates RNA polymerase III transcription in human cells.

    Johnston IM, Allison SJ, Morton JP, Schramm L, Scott PH and White RJ

    Institute of Biomedical and Life Sciences, Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow G12 8QQ, United Kingdom.

    CK2 is a highly conserved protein kinase with growth-promoting and oncogenic properties. It is known to activate RNA polymerase III (PolIII) transcription in Saccharomyces cerevisiae and is shown here to also exert a potent effect on PolIII in mammalian cells. Peptide and chemical inhibitors of CK2 block PolIII transcription in human cell extracts. Furthermore, PolIII transcription in mammalian fibroblasts is decreased significantly when CK2 activity is compromised by chemical inhibitors, antisense oligonucleotides, or kinase-inactive mutants. Coimmunoprecipitation and cofractionation show that endogenous human CK2 associates stably and specifically with the TATA-binding protein-containing factor TFIIIB, which brings PolIII to the initiation site of all class III genes. Serum stimulates TFIIIB phosphorylation in vivo, an effect that is diminished by inhibitors of CK2. Binding to TFIIIC2 recruits TFIIIB to most PolIII promoters; this interaction is compromised specifically by CK2 inhibitors. The data suggest that CK2 stimulates PolIII transcription by binding and phosphorylating TFIIIB and facilitating its recruitment by TFIIIC2. CK2 also activates PolI transcription in mammals and may therefore provide a mechanism to coregulate the output of PolI and PolIII. CK2 provides a rare example of an endogenous activity that operates on the PolIII system in both mammals and yeasts. Such evolutionary conservation suggests that this control may be of fundamental importance.

    Molecular and cellular biology 2002;22;11;3757-68

  • Phosphorylation of the recombinant rho1 GABA receptor.

    Sedelnikova A and Weiss DS

    Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294-0021, USA.

    Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the mammalian brain. While a growing body of literature indicates that postsynaptic GABA receptors are regulated by phosphorylation, there is discrepancy as to the specific effects of phosphorylation on GABA receptor function. Here, we have identified phosphorylation sites on the human rho1 GABA receptor for six protein kinases widely expressed in the brain: protein kinase C (PKC); cAMP-dependent protein kinase (PKA); calmodulin-dependent kinase (CaMKII); casein kinase (CKII); mitogen-activated protein kinase (MAPK); and cGMP-dependent protein kinase (PKG). We demonstrate that in nearly all cases, the consensus sites and actual phosphorylation sites do not agree supporting the risk of relying on a sequence analysis to identify potential phosphorylation sites. In addition, of the six kinases examined, only CKII phosphorylated the human rho2 subunit. Site-directed mutagenesis of the phosphorylation sites, or activation/inhibition of select kinase pathways, did not alter the receptor sensitivity or maximal GABA-activated current of the rho1 GABA receptor expressed in Xenopus laevis oocytes suggesting phosphorylation of rho1 does not directly alter receptor properties. This study is a first and necessary step towards elucidating the regulation of rho1 GABA receptors by phosphorylation.

    Funded by: NICHD NIH HHS: P30HD38985; NINDS NIH HHS: NS 40027

    International journal of developmental neuroscience : the official journal of the International Society for Developmental Neuroscience 2002;20;3-5;237-46

  • Protein kinase CK2 inhibitor 4,5,6,7-tetrabromobenzotriazole (TBB) induces apoptosis and caspase-dependent degradation of haematopoietic lineage cell-specific protein 1 (HS1) in Jurkat cells.

    Ruzzene M, Penzo D and Pinna LA

    Dipartimento di Chimica Biologica, Università di Padova, Viale G. Colombo, 3-35121 Padova, Italy.

    Incubation of Jurkat cells with 4,5,6,7-tetrabromobenzotriazole (TBB), a specific inhibitor of protein kinase CK2, induces dose-and time-dependent apoptosis as judged by several criteria. TBB-promoted apoptosis is preceded by inhibition of Ser/Thr phosphorylation of haematopoietic lineage cell-specific protein 1 (HS1) and is accompanied by caspase-dependent fragmentation of the same protein. Both effects are also observable if apoptosis is promoted by anti-Fas antibodies and by etoposide. Moreover, in vitro experiments show that HS1, once phosphorylated by CK2, becomes refractory to cleavage by caspase-3. These findings, in conjunction with similar data in the literature concerning two other CK2 protein substrates, Bid and Max, suggest that CK2 may play a general anti-apoptotic role through the generation of phosphorylated sites conferring resistance to caspase cleavage.

    The Biochemical journal 2002;364;Pt 1;41-7

  • Regulation of arrestin-3 phosphorylation by casein kinase II.

    Kim YM, Barak LS, Caron MG and Benovic JL

    Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.

    Arrestins play an important role in regulating the function of G protein-coupled receptors including receptor desensitization, internalization, down-regulation, and signaling via nonreceptor tyrosine kinases and mitogen-activated protein kinases. Previous studies have revealed that arrestins themselves are also subject to regulation. In the present study, we focused on identifying potential mechanisms involved in regulating the function of arrestin-3. Using metabolic labeling, phosphoamino acid analysis, and mutagenesis studies, we found that arrestin-3 is constitutively phosphorylated at Thr-382 and becomes dephosphorylated upon beta(2)-adrenergic receptor activation in COS-1 cells. Casein kinase II (CKII) appears to be the major kinase mediating arrestin-3 phosphorylation, since 1) Thr-382 is contained within a canonical consensus sequence for CKII phosphorylation and 2) wild type arrestin-3 but not a T382A mutant is phosphorylated by CKII in vitro. Functional analysis reveals that mutants mimicking the phosphorylated (T382E) and dephosphorylated (T382A or T382V) states of arrestin-3 promote beta(2)-adrenergic receptor internalization and bind clathrin, beta-adaptin, and Src to comparable levels as wild type arrestin-3. This suggests that the phosphorylation of arrestin-3 does not directly regulate interaction with endocytic (clathrin, beta-adaptin) or signaling (Src) components and is in contrast to arrestin-2, where phosphorylation appears to regulate interaction with clathrin and Src. However, additional analysis reveals that arrestin-3 phosphorylation may regulate formation of a large arrestin-3-containing protein complex. Differences between the regulatory roles of arrestin-2 and -3 phosphorylation may contribute to the different cellular functions of these proteins in G protein-coupled receptor signaling and regulation.

    The Journal of biological chemistry 2002;277;19;16837-46

  • Association and regulation of casein kinase 2 activity by adenomatous polyposis coli protein.

    Homma MK, Li D, Krebs EG, Yuasa Y and Homma Y

    Department of Biomolecular Science, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan. mkhomma@fmu.ac.jp

    Mutations in the adenomatous polyposis coli (APC) gene are responsible for familial adenomatous polyposis coli and also sporadic colorectal cancer development. By using antibodies raised against the N-terminal region of APC protein, we have detected the variable masses of endogenous APC proteins in individual cell lines established from human colorectal carcinomas caused by nonsense mutations of the gene. Phosphorylation of immunoprecipitates of full-length and truncated APC were observed in in vitro kinase reaction, indicating association of APC with protein kinase activity. The kinase activity complexed with APC was sensitive to heparin and used GTP as phosphoryl donor, suggesting an involvement of casein kinase 2 (CK2). Both CK2alpha- and beta-subunits were found to associate with APC in immunoprecipitates as well as in pull-down assays, with preferential interaction of APC with tetrameric CK2 holoenzyme. In synchronized cell populations, the association of APC with CK2 was cell cycle dependent, with the highest association in G(2)/M. Unexpectedly, APC immunoprecipitates containing full-length APC protein inhibited CK2 in vitro, whereas immunoprecipitates of truncated APC had little effect. This was confirmed by using recombinant APC, and the inhibitory region was localized to the C terminus of APC between residues 2086 and 2394. Overexpression of this fragment in SW480 cells suppressed cell proliferation rates as well as tumorigenesis. These results demonstrate a previously uncharacterized functional interaction between the tumor suppressor protein APC and CK2 and suggest that growth-inhibitory effects of APC may be regulated by inhibition of CK2.

    Proceedings of the National Academy of Sciences of the United States of America 2002;99;9;5959-64

  • Urokinase-dependent human vascular smooth muscle cell adhesion requires selective vitronectin phosphorylation by ectoprotein kinase CK2.

    Stepanova V, Jerke U, Sagach V, Lindschau C, Dietz R, Haller H and Dumler I

    Medical Faculty of the Charité, Franz Volhard Clinic and Max Delbrück Center for Molecular Medicine, Humboldt University of Berlin, Wiltbergstrasse 50, 13125 Berlin-Buch, Germany.

    Urokinase (uPA)- and urokinase receptor (uPAR)-dependent cell adhesion to the extracellular matrix protein vitronectin (Vn) is an important event in wound healing, tissue remodeling, immune response, and cancer. We recently demonstrated that in human vascular smooth muscle cells (VSMC) uPA/uPAR are functionally associated with the ectoprotein kinase casein kinase-2 (CK2). We now asked whether CK2 regulates uPA-dependent cell adhesion to Vn, since the latter is a natural CK2 substrate. We found that Vn is indeed selectively phosphorylated by CK2 and that this phosphorylation is uPA-regulated in VSMC. Vn induces release of ecto-CK2 from the cell surface via a process termed as "shedding." CK2-mediated Vn phosphorylation was decisive for the uPA-dependent VSMC adhesion. Specific inhibition of CK2 completely abolished the uPA-induced cell adhesion to Vn. This effect was specific for cell adhesion to Vn and required participation of both uPAR and alpha(v)beta(3) integrins as adhesion receptors. CK2 localization at the cell surface was highly dynamic; Vn induced formation of clusters where CK2 colocalized with uPAR and alpha(v)beta(3) integrins. These results indicate that the uPA-dependent VSMC adhesion is a function of selective Vn phosphorylation by the ectoprotein kinase CK2 and suggest a regulatory role for Vn phosphorylation in the uPA-directed adhesive process.

    The Journal of biological chemistry 2002;277;12;10265-72

  • Kinetic properties of p53 phosphorylation by the human vaccinia-related kinase 1.

    Barcia R, López-Borges S, Vega FM and Lazo PA

    Instituto de Biología Molecular y Celular del Cáncer, Universidad de Salamanca, Campus Miguel de Unamuno, Salamanca, E-37007, Spain.

    The vaccinia-related kinase 1 (VRK1) protein is a nuclear Ser-Thr kinase that phosphorylates p53 in Thr18. We have determined the enzyme properties regarding its different substrates. VRK1 has a high affinity for ATP (K(m) 50 microM) and is thus saturated by the intracellular concentration of ATP in vivo. VRK1 uses preferentially magnesium, but is also functional with manganese and zinc. The VRK1 protein is autophosphorylated in multiple residues without effect on its activity. One autophosphorylated residue, T355, is within the VRK1 regulatory carboxy terminus. The kinase phosphorylates p53 with a K(m) of 1 microM and is well suited to respond to the variations of intracellular p53 concentration, which fluctuates as a response to different types of cellular stress.

    Archives of biochemistry and biophysics 2002;399;1;1-5

  • Phosphorylation of mammalian translation initiation factor 5 (eIF5) in vitro and in vivo.

    Majumdar R, Bandyopadhyay A, Deng H and Maitra U

    Department of Developmental and Molecular Biology, Albert Einstein College of Medicine of Yeshiva University, Jack and Pearl Resnick Campus, Bronx, NY 10461, USA.

    Eukaryotic translation initiation factor 5 (eIF5) interacts with the 40S initiation complex (40S*eIF3*AUG*Met-tRNA(f)*eIF2*GTP) and, acting as a GTPase activating protein, promotes the hydrolysis of bound GTP. We isolated a protein kinase from rabbit reticulocyte lysates on the basis of its ability to phosphorylate purified bacterially expressed recombinant rat eIF5. Physical, biochemical and antigenic properties of this kinase identify it as casein kinase II (CK II). Mass spectrometric analysis of maximally in vitro phosphorylated eIF5 localized the major phosphorylation sites at Ser-387 and Ser-388 near the C-terminus of eIF5. These serine residues are embedded within a cluster of acidic amino acid residues and account for nearly 90% of the total in vitro eIF5 phosphorylation. A minor phosphorylation site at Ser-174 was also observed. Alanine substitution mutagenesis at Ser-387 and Ser-388 of eIF5 abolishes phosphorylation by the purified kinase as well as by crude reticulocyte lysates. The same mutations also abolish phosphorylation of eIF5 when transfected into mammalian cells suggesting that CK II phosphorylates eIF5 at these two serine residues in vivo as well.

    Funded by: NCI NIH HHS: P30CA13330; NIGMS NIH HHS: GM15399

    Nucleic acids research 2002;30;5;1154-62

  • The transcriptional factor Tcf-4 contains different binding sites for beta-catenin and plakoglobin.

    Miravet S, Piedra J, Miró F, Itarte E, García de Herreros A and Duñach M

    Unitat de Biofisica, Departament de Bioquimica i Biologia Molecular, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain.

    beta-Catenin and plakoglobin are two related armadillo proteins necessary for the establishment of adhesion junctions and desmosomes. Moreover, beta-catenin can also act as a transcriptional co-activator through its interaction with the members of Tcf/LEF-1 transcriptional factor family. We show here that Tcf-4 can be phosphorylated in vitro by protein kinase CK2 stoichiometrically in amino acids Ser-58-Ser-59-Ser-60. Phosphorylation of these residues does not modify the interaction of Tcf-4 with beta-catenin but reduces its association to plakoglobin. The binding sites of Tcf-4 for these two proteins were compared; whereas beta-catenin requires the N-terminal first 50 amino acids, plakoglobin interacts mainly with residues 51-80. Tcf-4-(51-80) binds plakoglobin in the region of armadillo repeats 1-6. Ternary complexes composed by beta-catenin/Tcf-4/plakoglobin could be detected in vitro, demonstrating that simultaneous binding of the two armadillo proteins to Tcf-4 is possible. Experiments performed using a Tcf-4 mutant with decreased interaction to plakoglobin demonstrated that binding to this protein negatively affected the transcriptional activity of Tcf-4. These results indicate that Tcf-4 contains two different sites for binding of beta-catenin and plakoglobin, and the interaction of the latter hinders the transcriptional activity of the complex.

    The Journal of biological chemistry 2002;277;3;1884-91

  • The DNA sequence and comparative analysis of human chromosome 20.

    Deloukas P, Matthews LH, Ashurst J, Burton J, Gilbert JG, Jones M, Stavrides G, Almeida JP, Babbage AK, Bagguley CL, Bailey J, Barlow KF, Bates KN, Beard LM, Beare DM, Beasley OP, Bird CP, Blakey SE, Bridgeman AM, Brown AJ, Buck D, Burrill W, Butler AP, Carder C, Carter NP, Chapman JC, Clamp M, Clark G, Clark LN, Clark SY, Clee CM, Clegg S, Cobley VE, Collier RE, Connor R, Corby NR, Coulson A, Coville GJ, Deadman R, Dhami P, Dunn M, Ellington AG, Frankland JA, Fraser A, French L, Garner P, Grafham DV, Griffiths C, Griffiths MN, Gwilliam R, Hall RE, Hammond S, Harley JL, Heath PD, Ho S, Holden JL, Howden PJ, Huckle E, Hunt AR, Hunt SE, Jekosch K, Johnson CM, Johnson D, Kay MP, Kimberley AM, King A, Knights A, Laird GK, Lawlor S, Lehvaslaiho MH, Leversha M, Lloyd C, Lloyd DM, Lovell JD, Marsh VL, Martin SL, McConnachie LJ, McLay K, McMurray AA, Milne S, Mistry D, Moore MJ, Mullikin JC, Nickerson T, Oliver K, Parker A, Patel R, Pearce TA, Peck AI, Phillimore BJ, Prathalingam SR, Plumb RW, Ramsay H, Rice CM, Ross MT, Scott CE, Sehra HK, Shownkeen R, Sims S, Skuce CD, Smith ML, Soderlund C, Steward CA, Sulston JE, Swann M, Sycamore N, Taylor R, Tee L, Thomas DW, Thorpe A, Tracey A, Tromans AC, Vaudin M, Wall M, Wallis JM, Whitehead SL, Whittaker P, Willey DL, Williams L, Williams SA, Wilming L, Wray PW, Hubbard T, Durbin RM, Bentley DR, Beck S and Rogers J

    The Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK. panos@sanger.ac.uk

    The finished sequence of human chromosome 20 comprises 59,187,298 base pairs (bp) and represents 99.4% of the euchromatic DNA. A single contig of 26 megabases (Mb) spans the entire short arm, and five contigs separated by gaps totalling 320 kb span the long arm of this metacentric chromosome. An additional 234,339 bp of sequence has been determined within the pericentromeric region of the long arm. We annotated 727 genes and 168 pseudogenes in the sequence. About 64% of these genes have a 5' and a 3' untranslated region and a complete open reading frame. Comparative analysis of the sequence of chromosome 20 to whole-genome shotgun-sequence data of two other vertebrates, the mouse Mus musculus and the puffer fish Tetraodon nigroviridis, provides an independent measure of the efficiency of gene annotation, and indicates that this analysis may account for more than 95% of all coding exons and almost all genes.

    Nature 2001;414;6866;865-71

  • Polarized trafficking and surface expression of the AQP4 water channel are coordinated by serial and regulated interactions with different clathrin-adaptor complexes.

    Madrid R, Le Maout S, Barrault MB, Janvier K, Benichou S and Mérot J

    Service de Biologie Cellulaire, Département de Biologie Cellulaire et Moléculaire, CEA/Saclay, F-91191 Gif-sur-Yvette, Cedex, France.

    Aquaporin 4 (AQP4) is the predominant water channel in the brain. It is targeted to specific membrane domains of astrocytes and plays a crucial role in cerebral water balance in response to brain edema formation. AQP4 is also specifically expressed in the basolateral membranes of epithelial cells. However, the molecular mechanisms involved in its polarized targeting and membrane trafficking remain largely unknown. Here, we show that two independent C-terminal signals determine AQP4 basolateral membrane targeting in epithelial MDCK cells. One signal involves a tyrosine-based motif; the other is encoded by a di-leucine-like motif. We found that the tyrosine-based basolateral sorting signal also determines AQP4 clathrin-dependent endocytosis through direct interaction with the mu subunit of AP2 adaptor complex. Once endocytosed, a regulated switch in mu subunit interaction changes AP2 adaptor association to AP3. We found that the stress-induced kinase casein kinase (CK)II phosphorylates the Ser276 immediately preceding the tyrosine motif, increasing AQP4-mu 3A interaction and enhancing AQP4-lysosomal targeting and degradation. AQP4 phosphorylation by CKII may thus provide a mechanism that regulates AQP4 cell surface expression.

    The EMBO journal 2001;20;24;7008-21

  • Histone deacetylase 1 phosphorylation promotes enzymatic activity and complex formation.

    Pflum MK, Tong JK, Lane WS and Schreiber SL

    Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA 02138, USA.

    Accessibility of the genome to DNA-binding transcription factors is regulated by proteins that control the acetylation of amino-terminal lysine residues on nucleosomal histones. Specifically, histone deacetylase (HDAC) proteins repress transcription by deacetylating histones. To date, the only known regulatory mechanism of HDAC1 function is via interaction with associated proteins. Although the control of HDAC1 function by protein interaction and recruitment is well precedented, we were interested in exploring HDAC1 regulation by post-translational modification. Human HDAC1 protein was analyzed by ion trap mass spectrometry, and two phosphorylated serine residues, Ser(421) and Ser(423), were unambiguously identified. Loss of phosphorylation at Ser(421) and Ser(423) due to mutation to alanine or disruption of the casein kinase 2 consensus sequence directing phosphorylation reduced the enzymatic activity and complex formation of HDAC1. Deletion of the highly charged carboxyl-terminal region of HDAC1 also decreased its deacetylase activity and protein associations, revealing its requirement in maintaining HDAC1 function. Our results reinforce the importance of protein associations in modulating HDAC1 function and provide the first step toward characterizing the role of post-translational modifications in regulating HDAC activity in vivo.

    Funded by: NIGMS NIH HHS: GM 19837, GM 38627

    The Journal of biological chemistry 2001;276;50;47733-41

  • FAS-associated factor 1 interacts with protein kinase CK2 in vivo upon apoptosis induction.

    Guerra B, Boldyreff B and Issinger OG

    University of Southern Denmark, Odense University, Institute for Biochemistry and Molecular Biology, DK-5230 Odense, Denmark.

    We show here that in several different cell lines protein kinase CK2 and Fas-associated factor 1 (FAF1) exist together in a complex which is stable to high monovalent salt concentration. The CK2/FAF1 complex formation is significantly increased after induction of apoptosis with various DNA damaging agents. Interestingly this effect is only seen in cell lines with an embryonic origin and not when cells have entered a differentiated state. It is further shown that the CK2 specific phosphorylation sites in the FAF1 molecule, i.e. serines 289 and 291 influence this complex formation. Mutation of the CK2 phosphorylation sites in the FAF1 molecule to alanine leads to a 1.5 to 2.0-fold higher association between CK2 and FAF1. Since the CK2 activity did not increase concomitantly with the complex formation we conclude that the FAF1 becomes to the CK2 enzyme so that a normal enzyme catalysis does not take place anymore. Subcellular localization experiments involving CK2 subunits and FAF1 show a co-localization of both CK2 subunits and FAF1 in the peri-nuclear cytoplasm. The majority of CK2 subunits is found in the nucleus. FAF1 is also found in the nucleoli. The results obtained further support the view that protein kinase CK2 plays an important role in certain steps of apoptosis.

    International journal of oncology 2001;19;6;1117-26

  • A surface plasmon resonance study of the interactions between the component subunits of protein kinase CK2 and two protein substrates, casein and calmodulin.

    Benítez MJ, Cochet C and Jiménez JS

    Departamento de Química Física Aplicada, y Centro de Biología Molecular Severo Ochoa (UAM-CSIC), Universidad Autónoma de Madrid, Cantoblanco, Spain.

    Surface plasmon resonance has been used to study the interaction between the subunits composing protein kinase CK2 (two catalytic, alpha-subunits, and two regulatory, beta-subunits), as well as the interaction of each subunit with two types of protein substrates, casein, the phosphorylation of which is activated by the regulatory subunit, and calmodulin, which belongs to the kind of substrates on which the catalytic subunit is downregulated by the regulatory subunit. The interaction of casein with the catalytic subunit differs from the interaction with the holoenzyme. Similarly to the interaction with the regulatory subunit, the catalytic subunit interacts with the protein substrate forming a very stable, irreversible complex. The reconstituted holoenzyme, however, binds casein reversibly, displaying a binding mode similar to that displayed by the regulatory subunit. The interaction of calmodulin with the catalytic subunit gives place, like in the case of casein, to an irreversible complex. The interactions with the regulatory subunit and with the holoenzyme were practically negligible, and the interaction with the regulatory subunit disappeared upon increasing the temperature value to close to 30 degrees C. The presence of polylysine induced a high increase in the extent of calmodulin binding to the holoenzyme. The results obtained suggest that CK2beta subunit and protein substrates share a common, or at least an overlapping, site of interaction on the catalytic subunit. The interaction between both subunits would prevent substrates from binding irreversibly to alpha subunit, and, at the same time, it would generate a new and milder site of interaction between the whole holoenzyme and the protein substrate. The main difference between casein and calmodulin would consist in the lower affinity display by the last for the new site generated upon the binding of the regulatory subunit, in the absence of polycations like polylysine.

    Molecular and cellular biochemistry 2001;227;1-2;31-6

  • Characterization of CK2 holoenzyme variants with regard to crystallization.

    Guerra B, Niefind K, Ermakowa I and Issinger OG

    Institut für Biochemie, Universität zu Köln, Germany.

    A search for strategies was conducted in order to obtain a human protein kinase CK2 preparation which would be suitable for crystallization, despite the fact that the recombinant enzyme is abundant and can be readily purified to homogeneity. This seemingly contradiction is based on the fact that the catalytic subunit moiety of the human CK2 holoenzyme is not stable neither as a free subunit nor in the tetrameric complex. All attempts to prevent degradation failed. Hence, alternative approaches were designed in order to avoid this degradation, which was expected to hamper any crystallization efforts severely. One of the approaches chosen was the production of a chimeric holoenzyme made up from a human regulatory subunit and a catalytic subunit from Z. mays. The plant catalytic subunit, in contrast to the human counterpart is very stable and does not undergo this kind of degradation. The second strategy to tackle the problem of instability was to produce the homologous recombinant human CK2 holoenzyme and then, instead of trying to avoid degradation, attempt to accelerate degradation until all catalytic subunit material was converted to the degraded form, i.e. a 40 kDa polypeptide.

    Molecular and cellular biochemistry 2001;227;1-2;3-11

  • Consequences of CK2 signaling to the nuclear matrix.

    Yu S, Wang H, Davis A and Ahmed K

    Department of Laboratory Medicine and Pathology and University of Minnesota Cancer Center, University of Minnesota, Minneapolis, USA.

    Protein kinase CK2 is recognized as one of the key cellular signals for cell growth and proliferation. Its nuclear targeting appears to be critical to its role in these functions. In the nucleus, nuclear matrix (NM) which plays a major role in growth-related activities is a primary locus for CK2 signaling. A variety of growth stimuli evoke a rapid translocation of the CK2 to the NM whereas removal of these factors has the opposite effect. These studies, employing various experimental models of cell growth (involving different growth-stimulatory factors), have suggested that rapid shuttling of CK2 to the NM is a key feature of early growth control. By contrast, removal of growth-stimulatory factors leading to the loss of cell viability is associated with early loss of CK2 from the NM (and chromatin). This indicates that absence of CK2 from the nuclear compartment is contributory to induction of cell death via apoptosis, implying a protective role for CK2 against cell death. Here, we review the evidence that suggests that CK2 signaling in the NM is not only involved in cell growth but also in cell survival.

    Funded by: NCI NIH HHS: CA-15062

    Molecular and cellular biochemistry 2001;227;1-2;67-71

  • Functional specialization of CK2 isoforms and characterization of isoform-specific binding partners.

    Litchfield DW, Bosc DG, Canton DA, Saulnier RB, Vilk G and Zhang C

    Department of Biochemistry, University of Western Ontario, London, Canada. litchfi@uwo.ca

    In mammals, protein kinase CK2 has two isozymic forms of its catalytic subunit, designated CK2alpha and CK2alpha'. CK2alpha and CK2alpha' exhibit extensive similarity within their catalytic domains but have completely unrelated C-terminal sequences. To systematically examine the cellular functions of each CK2 isoform in mammalian cells, we have generated human osteosarcoma U2-OS cell lines with the expression of active or inactive versions of each CK2 isoform under the control of an inducible promoter. Examination of these cell lines provides evidence for functional specialization of CK2 isoforms at the cellular level in mammals with indications that CK2alpha' is involved in the control of proliferation and/or cell survival. To understand the molecular basis for functional differences between CK2alpha and CK2alpha', we have undertaken studies to identify proteins that interact specifically with each isoform of CK2 and could contribute to the regulation of their independent functions. A novel pleckstrin-homology domain containing protein, designated CK2-interacting protein 1 (i.e. CKIP-1) was isolated using the yeast two hybrid system as a protein that interacts with CK2alpha but not CK2alpha'. When expressed in cells as a fusion with green fluorescent protein, CKIP-1 localizes to the cell membrane and to the nucleus. In this study, we present evidence from deletion analysis of CKIP-1 suggesting that a C-terminal region containing a putative leucine zipper has a role in regulating its nuclear localization. Collectively, our data supports a model whereby CKIP-1 is a non-enzymatic regulator of CK2alpha that regulates the cellular functions of CK2alpha by targeting or anchoring CK2alpha to specific cellular localization or by functioning as an adapter to integrate CK2alpha-mediated signaling events with components of other signal transduction pathways.

    Molecular and cellular biochemistry 2001;227;1-2;21-9

  • Generation of mutants of CK2alpha which are dependent on the beta-subunit for catalytic activity.

    Sarno S, Ghisellini P, Cesaro L, Battistutta R and Pinna LA

    Dipartimento di Chimica Biologica and Centro per lo Studio delle Biomembrane del CNR, Universita' di Padova, Italy.

    To shed light on the structural features underlying high constitutive activity of protein kinase CK2 a number of mutants of the human CK2alpha-subunit altered in the interactions between the N-terminal segment and the activation loop have been generated and shown to be defective in catalytic activity. In particular the truncated mutant delta2-12 displays under standard conditions an almost complete loss of catalytic activity accounted for by a dramatic rise in its Km forATP (from 10 to 206 microM) and a reduced Kcat. Such a drop in efficiency is paralleled by conformational disorganization, as judged from Superdex 75 gel filtration profile. Both catalytic properties and gel filtration behaviour similar to those of wild type CK2alpha were restored upon association with the regulatory beta-subunit, suggesting that constitutive activity is conferred to CK2alpha and to CK2 holoenzyme through different molecular mechanisms. In the holoenzyme an assumable release of tension at the backbone of Ala-193 (as seems to be indicated by a comparison of the crystal structures of maize CK2alpha alone vs. a CK2alpha-beta peptide complex) may result in the ability of the activation loop to adopt its proper conformation independently of interactions with the N-terminal segment.

    Molecular and cellular biochemistry 2001;227;1-2;13-9

  • HIV-1 Rev transactivator: a beta-subunit directed substrate and effector of protein kinase CK2.

    Meggio F, Marin O, Boschetti M, Sarno S and Pinna LA

    Dipartimento di Chimica Biologica, Centro di Studio delle Biomembrane del CNR, Padova, Italy. meggio@civ.bio.unipd.it

    The phosphorylation of HIV-1 Rev by protein kinase CK2 is strictly dependent on the regulatory beta subunit of the kinase and is deeply affected by conformational changes of the substrate outside the phosphorylation site. Here we show that Rev modulates a variety of CK2 properties, including autophosphorylation, catalytic activity toward calmodulin, and susceptibility to polycationic effectors, whose common denominator is the involvement of the beta subunit. Rev's two major CK2 sites are located at its N-terminus, immediately adjacent to a helix-loop-helix motif. By comparing the behaviour of full-size Rev with that of synthetic peptides reproducing, with suitable modifications, its N-terminal 26 amino acids including the phosphoacceptor site (Ser 5, Ser 8) and amphipathic helix-1, it appears that the functional interaction of the N-terminal portion of Rev with the N-terminal domain of the beta subunit must rely on both electrostatic and hydrophobic interactions. The former mainly involve Rev's arginine-rich domain (residues 35-50) in helix-2, while the latter are mostly mediated by residues 12-24 of helix-1. These data disclose the possibility that, besides displaying protective, regulatory and targeting properties with respect to the catalytic subunit, the CK2 beta subunit also plays a role as a docking site for a subset of CK2 substrates.

    Molecular and cellular biochemistry 2001;227;1-2;145-51

  • Localization of individual subunits of protein kinase CK2 to the endoplasmic reticulum and to the Golgi apparatus.

    Faust M, Jung M, Günther J, Zimmermann R and Montenarh M

    Medical Biochemistry and Molecular Biology, University of the Saarland, Homburg/Saar, Germany.

    The protein kinase CK2 is composed of two catalytic alpha- or alpha'- and two regulatory beta-subunits. In mammalian cells there is ample evidence for the presence of individual CK2 subunits beside the holoenzyme. By immunofluorescence studies using peptide antibodies which allow us to detect the CK2alpha-, alpha'- and beta-subunits we found all three subunits to be co-localized with a 58 KDa Golgi protein which is specific for the Golgi complex. Subfractionation studies using dog pancreas cells revealed the presence of all three subunits of CK2 at the smooth endoplasmic reticulum (sER)/Golgi fraction whereas the rough endoplasmic reticulum (rER) harboured only the catalytic alpha- and alpha'-subunits. We found that the microsomal preparation from dog pancreas cells contained CK2 which phosphorylated a CK2 specific synthetic peptide and which was heparin sensitive. Furthermore, we could immunoprecipitate the CK2alpha-subunit that exhibited a kinase activity which phosphorylated a CK2 specific substrate and which was heparin sensitive. Protease digestion experiments revealed that the CK2 subunits were located on the cytosolic side of the rER and the sER/Golgi complex. Thus, we could demonstrate an asymmetric distribution of the CK2 subunits at the rER and sER/Golgi complex. Since the CK2alpha- and alpha'-subunits exhibit a substrate specificity which is different from the CK2 holoenzyme one might speculate that the asymmetric distribution of the CK2 holoenzyme and the CK2 catalytic subunits may have regulatory functions.

    Molecular and cellular biochemistry 2001;227;1-2;73-80

  • Protein kinase CK2: signaling and tumorigenesis in the mammary gland.

    Landesman-Bollag E, Song DH, Romieu-Mourez R, Sussman DJ, Cardiff RD, Sonenshein GE and Seldin DC

    Department of Pathology, Boston University School of Medicine, MA 02118, USA.

    Breast cancer is a major cause of cancer death in women, and the genetic abnormalities leading to the common sporadic forms of the disease are still under active investigation. CK2 has been reported to be upregulated in human breast cancer, which these studies confirm; CK2 is also upregulated in rat carcinogen-induced breast tumors. Transgenic mice overexpressing CK2alpha in the mammary gland develop mammary hyperplasia, dysplasia, and eventually adenocarcinomas, demonstrating that dysregulated expression of CK2 can contribute to transformation of the mammary epithelium. These mammary tumors have evidence of activation of the Wnt and NFkappaB pathways and upregulation of c-Myc. CK2 is capable of phosphorylating the key signaling molecule in the Wnt pathway, the transcriptional cofactor beta-catenin, and regulating its turnover. CK2 is known to phosphorylate IkappaB and thereby regulate basal NFkappaB levels; in the mammary cell lines and tumors, CK2 activity correlates with NFkappaB levels and inhibition of CK2 downregulates NFkappaB. Thus, CK2 may promote breast cancer through dysregulation of key pathways of transcriptional control in the mammary epithelium, and inhibition of CK2 has a potential role in the treatment of breast and other cancers.

    Funded by: NCI NIH HHS: R01 CA 82742, R01 CA63929

    Molecular and cellular biochemistry 2001;227;1-2;153-65

  • Response of cancer cells to molecular interruption of the CK2 signal.

    Wang H, Davis A, Yu S and Ahmed K

    Department of Laboratory Medicine and Pathology and University of Minnesota Cancer Center, University of Minnesota, Minneapolis, USA.

    Protein kinase CK2 is one of the key cellular signals for cell survival, growth, and proliferation. It is has been observed to be elevated in various cancers that have been examined. Various observations suggest that moderate dysregulation of CK2 may profoundly influence the cell response. We have examined the effects of interfering with the CK2 signal in various cancer cell lines by employing antisense oligodeoxynucleotides (ODN) against the alpha and beta subunits of CK2. Our results demonstrate that antisense CK2-alpha and antisense CK2-beta ODNs markedly influence cell viability of these cancer cells in a dose and time-dependent manner. Antisense CK2-alpha was slightly more effective than antisense CK2-beta in most of the cells tested. The efficacy of the antisense ODN seemed to vary with the cell type; however, in all cases potent induction of apoptosis was observed. Significantly, the effects of the antisense ODN on the CK2 activity in the nuclear matrix were relatively small compared to the much stronger induction of apoptosis in cells. This suggests that modest downregulation of CK2 can evoke a much greater apoptotic response in cancer cells.

    Funded by: NCI NIH HHS: CA-15062

    Molecular and cellular biochemistry 2001;227;1-2;167-74

  • Transcriptional coordination of the genes encoding catalytic (CK2alpha) and regulatory (CK2beta) subunits of human protein kinase CK2.

    Pyerin W and Ackermann K

    Biochemische Zellphysiologie, Deutsches Krebsforschungszentrum, Heidelberg, Germany. w.pyerin@dkfz-heidelberg.de

    Little is known of how protein kinase CK2 genes are regulated, and it is unclear whether there are mechanisms of transcriptional coordination. Response elements present in the promoter sequences of the human catalytic (CK2alpha) and regulatory (CK2beta) subunit genes have been examined for the significance in transcriptional control using reporter gene assays, electrophoretic mobility shift assays, site-directed mutagenesis, ectopic protein expressions, and transcript assessments. Most strikingly, in both promoters the regions of highest transcriptional activity contain two adjoining, completely identical and conserved Ets1 response elements, and both the mutation of motifs and the overexpression of Ets1 affect significantly transcriptional activity. Also in common are Sp1 response elements that cooperate with Ets1, and Sp1 is phosphorylatable by CK2 holoenzyme but not by individual CK2alpha, the phosphorylation negatively affecting DNA binding. CK2alpha and CK2beta transcript levels and stoichiometries of mRNA species turned out quite constant in cultured cells despite progressing through various stages of proliferation and differentiation. The data seem to indicate transcriptional coordination of the human genes encoding CK2alpha and CK2beta based on an Ets1 double motif common to both genes cooperating with Sp1 motifs and amenable to negative feedback control by the gene products which, following complexation into CK2 holoenzyme, could phosphorylate Sp1 (and Ets1?) and thus downregulate transcription and contribute to the observed constant cellular CK2alpha and CK2beta transcripts situation.

    Molecular and cellular biochemistry 2001;227;1-2;45-57

  • Visualization and molecular analysis of nuclear import of protein kinase CK2 subunits in living cells.

    Martel V, Filhol O, Nueda A, Gerber D, Benitez MJ and Cochet C

    INSERM EMI 0104/BRCE, DBMS, CEA, Grenoble, France.

    We have generated fusion proteins between the subunits of CK2 and GFP and characterized their behaviour in living cells. The expressed fusion proteins were functional and interacted with endogenous CK2. Imaging of NIH3T3 cells expressing low level of GFP-CK2alpha or GFP-CK2beta showed that both proteins were mostly nuclear in interphase. Both CK2 subunits contain nuclear localization domains that target them independently to the nucleus. Once in the nucleus, both subunits diffused rapidly in the nucleoplasm. In mitotic cells, CK2 subunits were dispersed throughout the cytoplasm and were not associated to chromatin. Our data are compatible with the idea that each subunit can translocate individually to the nucleus to interact with each other or with important cellular partners. Understanding the molecular mechanisms which regulate the dynamic localization of CK2 subunits will be of central importance.

    Molecular and cellular biochemistry 2001;227;1-2;81-90

  • Mapping of the interaction domain of the protein kinase CKII beta subunit with target proteins.

    Ahn BH, Kim TH and Bae YS

    Department of Biochemistry, College of Natural Sciences, Kyungpook National University, Taegu, Korea.

    Protein kinase CKII is composed of two catalytic (alpha or alpha') subunits and two regulatory (beta) subunits. The CKIIbeta subunit is thought to mediate the tetramer formation and interact with other target proteins. Previously we have shown that CKIIbeta interacts with ribosomal proteins L5 and L41, DNA topoisomerase IIbeta, and SAG/CKBBP1. In this study, the two-hybrid system was used to define the subregions of CKIIbeta that are involved in the interaction with L5, L41, topoisomerase IIbeta, SAG/CKBBP1, and unknown proteins, CKBBP2 and CKBBP3. The results indicated that the region between residues 1 and 167 of CKIIbeta is common binding site for L5, topoisomerase IIbeta, SAG/CKBBP1, and L41. The region between amino acids 19 and 167 of CKIIbeta is sufficient for the interaction with CKBBP3. The region between residues 67 and 130 of CKIIbeta is a minimal fragment that is required for interaction with CKBBP2. Overlay experiments showed that the region between residues 1 and 167 of CKIIbeta interacts with L5, L41, and SAG/CKBBP1 in vitro. These results suggest that the binding sites of CKIIbeta for these target proteins are not located within a small linear sequence stretch, but rather are created by a three-dimensional structure.

    Molecules and cells 2001;12;2;158-63

  • UV-radiation induces dose-dependent regulation of p53 response and modulates p53-HDM2 interaction in human fibroblasts.

    Latonen L, Taya Y and Laiho M

    Haartman Institute, Department of Virology, University of Helsinki, PO Box 63, FIN-00014 Helsinki, Finland.

    We address here the effects of increasing fluencies of UV-radiation on stability, modifications, activity and HDM2-interactions of endogenous p53 tumor suppressor and on cellular damage response of human diploid fibroblasts. Low amounts of UVB/C-radiation induced a transient cell cycle arrest of the cells which correlated with rapid but transient increase in p53 levels. In contrast, high UV-fluency caused cell apoptosis and a slower but sustained increase in p53. Regulation of p53 target genes was highly dependent on the radiation dose used. Whereas low doses induced p21/Cip1/Waf1 and HDM2, high doses induced only GADD45 and BAX increasing the BAX:BCL-2 ratio. The levels of HDM2, a negative regulator of p53, increased only by the low dose of UVC and p53-HDM2 association was promoted. In the absence of HDM2-induction after the high dose of UV-radiation p53-HDM2-interaction was promoted, but HDM2 failed to downregulate p53. p53 site-specific modifications (Ser15, Ser33, Ser37, Lys382) varied kinetically and were dependent on the fluency of the radiation used. Maximal phosphorylation of p53 on Ser15 and Ser33 correlated with increased levels of HDM2-free p53. The results suggest that regulation of p53 and HDM2 by UV-radiation is highly dose-dependent and contributes to the outcome of the cellular response.

    Oncogene 2001;20;46;6784-93

  • Crystal structure of human protein kinase CK2: insights into basic properties of the CK2 holoenzyme.

    Niefind K, Guerra B, Ermakowa I and Issinger OG

    Universität zu Köln, Institut für Biochemie, Zülpicher Strasse 47, D-50674 Köln, Germany. Karsten.Niefind@uni-koeln.de

    The crystal structure of a fully active form of human protein kinase CK2 (casein kinase 2) consisting of two C-terminally truncated catalytic and two regulatory subunits has been determined at 3.1 A resolution. In the CK2 complex the regulatory subunits form a stable dimer linking the two catalytic subunits, which make no direct contact with one another. Each catalytic subunit interacts with both regulatory chains, predominantly via an extended C-terminal tail of the regulatory subunit. The CK2 structure is consistent with its constitutive activity and with a flexible role of the regulatory subunit as a docking partner for various protein kinases. Furthermore it shows an inter-domain mobility in the catalytic subunit known to be functionally important in protein kinases and detected here for the first time directly within one crystal structure.

    The EMBO journal 2001;20;19;5320-31

  • Phosphorylation of the leucocyte NADPH oxidase subunit p47(phox) by casein kinase 2: conformation-dependent phosphorylation and modulation of oxidase activity.

    Park HS, Lee SM, Lee JH, Kim YS, Bae YS and Park JW

    Department of Biochemistry, College of Natural Sciences, Kyungpook National University, Taegu 702-701, Korea.

    The leucocyte NADPH oxidase of neutrophils is a membrane-bound enzyme that catalyses the reduction of oxygen to O(-)(2) at the expense of NADPH. The enzyme is dormant in resting neutrophils but becomes active when the cells are exposed to the appropriate stimuli. During oxidase activation, the highly basic cytosolic oxidase component p47(phox) becomes phosphorylated on several serines and migrates to the plasma membrane. Protein kinase CK2 is an essential serine/threonine kinase present in all eukaryotic organisms. The leucocyte NADPH oxidase subunit p47(phox) has several putative CK2 phosphorylation sites. In the present study, we report that CK2 is able to catalyse the phosphorylation of p47(phox) in vitro. Phosphoamino acid analysis of phosphorylated p47(phox) by CK2 indicated that the phosphorylation occurs on serine residues. CNBr mapping and phosphorylation of peptides containing the putative site of CK2 indicated that the main phosphorylated residues are Ser-208 and Ser-283 in the Src homology 3 (SH3) domains, and Ser-348 in the C-terminal domain of p47(phox). Dependence of phosphorylation on the conformation of p47(phox) is supported by the finding that p47(phox) undergoes better phosphorylation by CK2 in the presence of arachidonic acid, a known activator of NADPH oxidase which induces conformational changes in p47(phox). In addition, 5,6-dichloro-1-beta-o-ribofuranosyl benzimidazole, a CK2 inhibitor, potentiates formyl-Met-Leu-Phe-induced NADPH oxidase activity in DMSO-differentiated HL-60 cells. Taken together, we propose that CK2 is the p47(phox) kinase, and that phosphorylation of p47(phox) by CK2 regulates the deactivation of NADPH oxidase.

    The Biochemical journal 2001;358;Pt 3;783-90

  • Targeting of the transcription factor Max during apoptosis: phosphorylation-regulated cleavage by caspase-5 at an unusual glutamic acid residue in position P1.

    Krippner-Heidenreich A, Talanian RV, Sekul R, Kraft R, Thole H, Ottleben H and Lüscher B

    Institut für Molekularbiologie, Medizinische Hochschule Hannover, Carl-Neuberg Strasse 1, 30623 Hannover, Germany.

    Max is the central component of the Myc/Max/Mad network of transcription factors that regulate growth, differentiation and apoptosis. Whereas the Myc and Mad genes and proteins are highly regulated, Max expression is constitutive and no post-translational regulation is known. We have found that Max is targeted during Fas-induced apoptosis. Max is first dephosphorylated and subsequently cleaved by caspases. Two specific cleavage sites for caspases in Max were identified, one at IEVE(10) decreasing S and one at SAFD(135) decreasing G near the C-terminus, which are cleaved in vitro by caspase-5 and caspase-7 respectively. Mutational analysis indicates that both sites are also used in vivo. Thus Max represents the first caspase-5 substrate. The unusual cleavage after a glutamic acid residue is observed only with full-length, DNA-binding competent Max protein but not with corresponding peptides, suggesting that structural determinants might be important for this activity. Furthermore, cleavage by caspase-5 is inhibited by the protein kinase CK2-mediated phosphorylation of Max at Ser-11, a previously mapped phosphorylation site in vivo. These findings suggest that Fas-mediated dephosphorylation of Max is required for cleavage by caspase-5. The modifications that occur on Max in response to Fas signalling affect the DNA-binding activity of Max/Max homodimers. Taken together, our findings uncover three distinct processes, namely dephosphorylation and cleavage by caspase-5 and caspase-7, that target Max during Fas-mediated apoptosis, suggesting the regulation of the Myc/Max/Mad network through its central component.

    The Biochemical journal 2001;358;Pt 3;705-15

  • The carboxy-terminal domain of Grp94 binds to protein kinase CK2 alpha but not to CK2 holoenzyme.

    Roher N, Sarno S, Miró F, Ruzzene M, Llorens F, Meggio F, Itarte E, Pinna LA and Plana M

    Department de Bioquímica i Biologia Molcular, Facultat de Ciències, Universitat Autònoma de Barcelona, Spain.

    Surface plasmon resonance analysis shows that the carboxy-terminal domain of Grp94 (Grp94-CT, residues 518-803) physically interacts with the catalytic subunit of protein kinase CK2 (CK2 alpha) under non-stressed conditions. A K(D) of 4 x 10(-7) was determined for this binding. Heparin competed with Grp94-CT for binding to CK2 alpha. CK2 beta also inhibited the binding of Grp94-CT to CK2 alpha, and CK2 holoenzyme reconstituted in vitro was unable to bind Grp94-CT. The use of CK2 alpha mutants made it possible to map the Grp94-CT binding site to the four lysine stretch (residues 74-77) present in helix C of CK2 alpha. Grp94-CT stimulated the activity of CK2 alpha wild-type but was ineffective on the CK2 alpha K74-77A mutant.

    FEBS letters 2001;505;1;42-6

  • TATA binding protein-associated CK2 transduces DNA damage signals to the RNA polymerase III transcriptional machinery.

    Ghavidel A and Schultz MC

    Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.

    Here we report that RNA polymerase (pol) III transcription is repressed in response to DNA damage by downregulation of TFIIIB, the core component of the pol III transcriptional machinery. Protein kinase CK2 transduces this stress signal to TFIIIB. CK2 associates with and normally activates the TATA binding protein (TBP) subunit of TFIIIB. The beta regulatory subunit of CK2 binds to TBP and is required for high TBP-associated CK2 activity and pol III transcription in unstressed cells. Transcriptional repression induced by DNA damage requires CK2 and coincides with downregulation of TBP-associated CK2 and dissociation of catalytic subunits from TBP-CK2 complexes. Therefore, CK2 is the terminal effector in a signaling pathway that represses pol III transcription when genome integrity is compromised.

    Cell 2001;106;5;575-84

  • Phosphorylation of bid by casein kinases I and II regulates its cleavage by caspase 8.

    Desagher S, Osen-Sand A, Montessuit S, Magnenat E, Vilbois F, Hochmann A, Journot L, Antonsson B and Martinou JC

    CNRS UPR 9023, Montpellier, France. desagher@montp.inserm.fr

    Bid plays an essential role in Fas-mediated apoptosis of the so-called type II cells. In these cells, following cleavage by caspase 8, the C-terminal fragment of Bid translocates to mitochondria and triggers the release of apoptogenic factors, thereby inducing cell death. Here we report that Bid is phosphorylated by casein kinase I (CKI) and casein kinase II (CKII). Inhibition of CKI and CKII accelerated Fas-mediated apoptosis and Bid cleavage, whereas hyperactivity of the kinases delayed apoptosis. When phosphorylated, Bid was insensitive to caspase 8 cleavage in vitro. Moreover, a mutant of Bid that cannot be phosphorylated was found to be more toxic than wild-type Bid. Together, these data indicate that phosphorylation of Bid represents a new mechanism whereby cells control apoptosis.

    Molecular cell 2001;8;3;601-11

  • Eukaryotic initiation factor 2B: identification of multiple phosphorylation sites in the epsilon-subunit and their functions in vivo.

    Wang X, Paulin FE, Campbell LE, Gomez E, O'Brien K, Morrice N and Proud CG

    Division of Molecular Physiology, School of Life Sciences and MRC Protein Phosphorylation Unit, MSI/WTB Complex, University of Dundee, Dundee DD1 5EH, UK.

    Eukaryotic initiation factor (eIF) 2B is a heteromeric guanine nucleotide exchange factor that plays an important role in regulating mRNA translation. Here we identify multiple phosphorylation sites in the largest, catalytic, subunit (epsilon) of mammalian eIF2B. These sites are phosphorylated by four different protein kinases. Two conserved sites (Ser712/713) are phosphorylated by casein kinase 2. They lie at the extreme C-terminus and are required for the interaction of eIF2Bepsilon with its substrate, eIF2, in vivo and for eIF2B activity in vitro. Glycogen synthase kinase 3 (GSK3) is responsible for phosphorylating Ser535. This regulatory phosphorylation event requires both the fourth site (Ser539) and a distal region, which acts to recruit GSK3 to eIF2Bepsilon in vivo. The fifth site, which lies outside the catalytic domain of eIF2Bepsilon, can be phosphorylated by casein kinase 1. All five sites are phosphorylated in the eIF2B complex in vivo.

    The EMBO journal 2001;20;16;4349-59

  • HSP22, a new member of the small heat shock protein superfamily, interacts with mimic of phosphorylated HSP27 ((3D)HSP27).

    Benndorf R, Sun X, Gilmont RR, Biederman KJ, Molloy MP, Goodmurphy CW, Cheng H, Andrews PC and Welsh MJ

    Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA. rbenndo@umich.edu

    Most of the members of the superfamily of mammalian small heat shock or stress proteins are abundant in muscles where they play a role in muscle function and maintenance of muscle integrity. One member of this protein superfamily, human HSP27, is rapidly phosphorylated on three serine residues (Ser(15), Ser(78), and Ser(82)) during cellular response to a number of extracellular factors. To understand better the role of HSP27, we performed a yeast two-hybrid screen of a human heart cDNA library for HSP27-interacting proteins. By using the triple aspartate mutant, a mimic of phosphorylated HSP27, as "bait" construct, a protein with a molecular mass of 21.6 kDa was identified as an HSP27-binding protein. Sequence analysis revealed that this new protein shares an overall sequence identity of 33% with human HSP27. This protein also contains the alpha-crystallin domain in its C-terminal half, a hallmark of the superfamily of small stress proteins. Thus, the new protein itself is a member of this protein superfamily, and consequently we designated it HSP22. According to the two-hybrid data, HSP22 interacts preferentially with the triple aspartate form of HSP27 as compared with wild-type HSP27. HSP22 is expressed predominantly in muscles. In vitro, HSP22 is phosphorylated by protein kinase C (at residues Ser(14) and Thr(63)) and by p44 mitogen-activated protein kinase (at residues Ser(27) and Thr(87)) but not by MAPKAPK-2.

    Funded by: NCI NIH HHS: R01CA77078-01; NHGRI NIH HHS: R01HG01709-01; NIEHS NIH HHS: ES06265

    The Journal of biological chemistry 2001;276;29;26753-61

  • Autocatalytic tyrosine-phosphorylation of protein kinase CK2 alpha and alpha' subunits: implication of Tyr182.

    Donella-Deana A, Cesaro L, Sarno S, Brunati AM, Ruzzene M and Pinna LA

    Dipartimento di Chimica Biologica and Centro di Studio delle Biomembrane del C.N.R., University of Padova, Padova, Italy.

    CK2 is a pleiotropic and constitutively active serine/threonine protein kinase composed of two catalytic (alpha and/or alpha') and two regulatory beta-subunits, whose mechanism of modulation is still obscure. Here we show that CK2 alpha/alpha' subunits undergo intermolecular (trans) tyrosine-autophosphorylation, which is dependent on intrinsic catalytic activity and is suppressed by the individual mutation of Tyr182, a crucial residue of the activation loop, to phenylalanine. At variance with serine-autophosphorylation, tyrosine-autophosphorylation of CK2alpha is reversed by ADP and GDP and is counteracted by the beta-subunit and by a peptide reproducing the activation loop of CK2alpha/alpha' (amino acids 175-201). These results disclose new perspectives about the mode of regulation of CK2 catalytic subunits.

    The Biochemical journal 2001;357;Pt 2;563-7

  • Phosphorylation of the Fas associated factor FAF1 by protein kinase CK2 and identification of serines 289 and 291 as the in vitro phosphorylation sites.

    Jensen HH, Hjerrild M, Guerra B, Larsen MR, Højrup P and Boldyreff B

    Institut for Biokemi og Molekylaer Biologi, Syddansk Universitet, Campusvej 55, DK-5230, Odense, Denmark.

    We previously identified the human Fas associated factor (FAF1) as one of the interacting partners of protein kinase CK2 beta subunit. Since FAF1 is a phosphoprotein we investigated whether it is a substrate for CK2. Here, we report the full length human FAF1 cDNA sequence, expression of FAF1 in Escherichia coli and purification and characterization of FAF1 as a substrate for CK2. FAF1 as well as an N-terminal 40 kDa degradation product serve as substrates for both the recombinant CK2 holoenzyme (km 100 microM) and the isolated catalytic alpha subunit (km 200 microM). Despite the high k(m) values, we obtained evidence that CK2 is the major cellular kinase responsible for FAF1 phosphorylation, using tissue extracts as kinase sources. By MALDI-MS we identified the two serine residues at positions 289 and 291 as the major in vitro CK2 phosphorylation sites. These data may help us elucidate the functions of FAF1 and the involvement of CK2 mediated phosphorylation in processes such as apoptotic signaling, ubiquitination, nuclear translocation and embryonic development.

    The international journal of biochemistry & cell biology 2001;33;6;577-89

  • Taf(II) 250 phosphorylates human transcription factor IIA on serine residues important for TBP binding and transcription activity.

    Solow S, Salunek M, Ryan R and Lieberman PM

    Wistar Institute, Philadelphia, Pennsylvania 19104, USA.

    Transcription factor IIA (TFIIA) is a positive acting general factor that contacts the TATA-binding protein (TBP) and mediates an activator-induced conformational change in the transcription factor IID (TFIID) complex. Previously, we have found that phosphorylation of yeast TFIIA stimulates TFIIA.TBP.TATA complex formation and transcription activation in vivo. We now show that human TFIIA is phosphorylated in vivo on serine residues that are partially conserved between yeast and human TFIIA large subunits. Alanine substitution mutation of serine residues 316 and 321 in TFIIA alphabeta reduced TFIIA phosphorylation significantly in vivo. Additional alanine substitutions at serines 280 and 281 reduced phosphorylation to undetectable levels. Mutation of all four serine residues reduced the ability of TFIIA to stimulate transcription in transient transfection assays with various activators and promoters, indicating that TFIIA phosphorylation is required globally for optimal function. In vitro, holo-TFIID and TBP-associated factor 250 (TAF(II)250) phosphorylated TFIIA on the beta subunit. Mutation of the four serines required for in vivo phosphorylation eliminated TFIID and TAF(II)250 phosphorylation in vitro. The NH(2)-terminal kinase domain of TAF(II)250 was sufficient for TFIIA phosphorylation, and this activity was inhibited by full-length retinoblastoma protein but not by a retinoblastoma protein mutant defective for TAF(II)250 interaction or tumor suppressor activity. TFIIA phosphorylation had little effect on the TFIIA.TBP.TATA complex in electrophoretic mobility shift assay. However, phosphorylation of TFIIA containing a gamma subunit Y65A mutation strongly stimulated TFIIA.TBP.TATA complex formation. TFIIA-gammaY65A is defective for binding to the beta-sheet domain of TBP identified in the crystal structure. These results suggest that TFIIA phosphorylation is important for strengthening the TFIIA.TBP contact or creating a second contact between TFIIA and TBP that was not visible in the crystal structure.

    Funded by: NIGMS NIH HHS: GM 54687-04

    The Journal of biological chemistry 2001;276;19;15886-92

  • Identification of novel functional regions important for the activity of HOXB7 in mammalian cells.

    Yaron Y, McAdara JK, Lynch M, Hughes E and Gasson JC

    Division of Hematology-Oncology, Department of Medicine, Jonsson Comprehensive Cancer Center, University of California School of Medicine, Los Angeles, CA 90095, USA.

    Members of the HOX family of homeobox transcription factors play a role in pattern formation in diverse developmental systems. The clearly documented role of HOX genes in the proliferation and differentiation of primary hematopoietic cells and cell lines provides a convenient system to pursue a biochemical analysis of HOX gene function in mammalian cells. To explore the role of HOXB7 in myeloid hematopoiesis, a number of mutations and deletions in the gene were constructed that targeted sequences with known functions or in regions that had not been examined previously. The wild-type and mutant B7 constructs were introduced into the murine myelomonocytic cell line, 32D, and assayed for their effects on G-CSF-induced myeloid differentiation. Wild-type HOXB7 inhibited the differentiation of 32D cells, whereas mutations in the Pbx-binding pentapeptide motif or the DNA-binding homeodomain, as well as internal deletions of the N-terminal unique region, blocked this effect. Interestingly, mutations eliminating two target sites for casein kinase II, the glutamate-rich C terminus, or the first 14 amino acids of HOXB7, led to enhanced 32D differentiation. A model proposing a role for these regions of HOXB7 is presented.

    Funded by: NHLBI NIH HHS: P50 HL54850; NIDCR NIH HHS: T32 DE07296; NIGMS NIH HHS: GM08042

    Journal of immunology (Baltimore, Md. : 1950) 2001;166;8;5058-67

  • Constitutive c-Myb amino-terminal phosphorylation and DNA binding activity uncoupled during entry and passage through the cell cycle.

    Cures A, House C, Kanei-Ishii C, Kemp B and Ramsay RG

    Trescowthick Research Laboratories, Peter MacCallum Cancer Institute, Melbourne, Vic. Australia.

    The c-myb gene encodes a transcription factor that is central to hematopoietic cell growth. Phosphorylation of c-Myb by casein kinase 2 (CK2) at serines 11 and 12 has been variously implicated in the regulation of DNA binding. However, it is unclear when c-Myb phosphorylation at serines 11 and 12 occurs during the cell cycle and how this is regulated. We generated specific antisera that recognize phosphoserines 11 and 12 of c-Myb. C-Myb protein levels, extent of CK2 phosphorylation and DNA binding were then monitored following mitogenic stimulus and passage through the cell cycle in normal peripheral T-cells and the T leukemia cell line CCRF-CEM. We found that endogenous c-Myb is constitutively phosphorylated at serines 11 and 12. The amount of phosphorylated c-Myb correlates with DNA binding activity in cycling CEM cells but not upon entry of T-cells into the cell cycle. Exogenous expression of c-Myb with substitutions of serines 11 and 12 with glutamic acid or alanine had no effect on the transactivation of a c-Myb responsive reporter. These data strongly suggest that c-Myb is constitutively phosphorylated on serines 11 and 12 by CK2 or like activity and is not regulated during the cell cycle.

    Oncogene 2001;20;14;1784-92

  • A DNA damage-induced p53 serine 392 kinase complex contains CK2, hSpt16, and SSRP1.

    Keller DM, Zeng X, Wang Y, Zhang QH, Kapoor M, Shu H, Goodman R, Lozano G, Zhao Y and Lu H

    Department of Biochemistry and Molecular Biology, Oregon Health Sciences University, Portland, OR 97201, USA.

    Phosphorylation of the human p53 protein at Ser-392 has been shown to be responsive to UV but not gamma irradiation. Here we describe identification and purification of a mammalian UV-activated protein kinase complex that phosphorylates Ser-392 of p53 in vitro. This kinase complex contains casein kinase 2 (CK2) and the chromatin transcriptional elongation factor FACT (a heterodimer of hSpt16 and SSRP1). In vitro studies show that FACT alters the specificity of CK2 in the complex such that it selectively phosphorylates p53 over other substrates including casein. In addition, phosphorylation by the kinase complex enhances p53 activity. These results thus provide a potential mechanism for p53 activation by UV irradiation.

    Funded by: NCI NIH HHS: R01 CA115468, R01 CA115468-05

    Molecular cell 2001;7;2;283-92

  • A novel casein kinase 2 alpha-subunit regulates membrane protein traffic in the human hepatoma cell line HuH-7.

    Shi X, Potvin B, Huang T, Hilgard P, Spray DC, Suadicani SO, Wolkoff AW, Stanley P and Stockert RJ

    Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.

    A previously isolated endocytic trafficking mutant (TRF1) isolated from HuH-7 cells is defective in the distribution of subpopulations of cell-surface receptors for asialoorosomucoid (asialoglycoprotein receptor (ASGR)), transferrin, and mannose-terminating glycoproteins. The pleiotropic phenotype of TRF1 also includes an increased sensitivity to Pseudomonas toxin and deficient assembly and function of gap junctions. HuH-7xTRF1 hybrids exhibited a normal subcellular distribution of ASGR, consistent with the TRF1 mutation being recessive. A cDNA expression library derived from HuH-7 mRNA was transfected into TRF1 cells, which were subsequently selected for resistance to Pseudomonas toxin. Sequence analysis of a recovered cDNA revealed a unique isoform of casein kinase 2 (CK2), CK2alpha". Western blot analysis of TRF1 proteins revealed a 60% reduction in total CK2alpha expression. Consistent with this finding, the hybrids HuH-7xHuH-7 and HuH-7xTRF1 expressed equivalent amounts of total CK2alpha. Immunoblots using antibodies against peptides unique to the previously described CK2 isoforms CK2alpha and CK2alpha' and the novel CK2alpha" isoform showed that, although TRF1 and parental HuH-7 cells expressed comparable amounts of CK2alpha and CK2alpha', the mutant did not express CK2alpha". Based on the genomic DNA sequence, RNA transcripts encoding CK2alpha" apparently originate from alternative splicing of a primary transcript. Protein overexpression following transfection of TRF1 cells with cDNAs encoding either CK2alpha or the newly cloned CK2alpha" restored the parental HuH-7 phenotype, including Pseudomonas toxin resistance, cell-surface ASGR binding activity, phosphorylation, and the assembly of gap junctions. This study suggests that HuH-7 cells express at least three CK2alpha isoforms and that the pleiotropic TRF1 phenotype is a consequence of a reduction in total CK2 expression.

    Funded by: NIDDK NIH HHS: DK-32972, DK-41918

    The Journal of biological chemistry 2001;276;3;2075-82

  • Distinct organization of DNA complexes of various HMGI/Y family proteins and their modulation upon mitotic phosphorylation.

    Piekielko A, Drung A, Rogalla P, Schwanbeck R, Heyduk T, Gerharz M, Bullerdiek J and Wiśniewski JR

    III. Zoologisches Institut-Entwicklungsbiologie, Universität Göttingen, D-37073 Göttingen, Germany.

    High mobility group (HMG) proteins HMGI, HMGY, HMGI-C, and Chironomus HMGI are DNA-binding proteins thought to modulate the assembly and the function of transcriptional complexes. Each of these proteins contains three DNA-binding domains (DBD), properties of which appear to be regulated by phosphorylation. High levels of these proteins are characteristic for rapidly dividing cells in embryonic tissues and tumors. On the basis of their occurrence, specific functions for each of these proteins have been postulated. In this study we demonstrate differences in the nature of contacts of these proteins with promoter region of the interferon-beta gene. We show that HMGI and HMGY interact with this DNA via three DBDs, whereas HMGI-C and Chironomus HMGI bind to this DNA using only two domains. Phosphorylation of HMGY protein by Cdc2 kinase leads to impairing of contacts between the N-terminally located DBD and a single promoter element. The perturbations in the architecture of the protein.DNA complexes involve changes in the degree of unbending of the intrinsically bent IFNbeta promoter. Our results provide first insights into the molecular basis of functional specificity of proteins of the HMGI/Y family and their regulation by phosphorylation.

    The Journal of biological chemistry 2001;276;3;1984-92

  • Novel properties of the protein kinase CK2-site-regulated nuclear- localization sequence of the interferon-induced nuclear factor IFI 16.

    Briggs LJ, Johnstone RW, Elliot RM, Xiao CY, Dawson M, Trapani JA and Jans DA

    Nuclear Signalling Laboratory, Division for Biochemistry and Molecular Biology, John Curtin School of Medical Research, Australian National University, P.O. Box 334, Canberra City, A.C.T. 2601, Australia.

    Members of the interferon-induced class of nuclear factors possess a putative CcN motif, comparable with that within proteins such as the simian virus 40 large tumour antigen (T-ag), which confers phosphorylation-mediated regulation of nuclear-localization sequence (NLS)-dependent nuclear import. Here we examine the functionality of the interferon-induced factor 16 (IFI 16) CcN motif, demonstrating its ability to target a heterologous protein to the nucleus, and to be phosphorylated specifically by the CcN-motif-phosphorylating protein kinase CK2 (CK2). The IFI 16 NLS, however, has novel properties, conferring ATP-dependent nuclear import completely independent of cytosolic factors, as well as binding to nuclear components. The IFI 16 NLS is not recognized with high affinity by the NLS-binding importin heterodimer, and transport mediated by it is insensitive to non-hydrolysable GTP analogues. The IFI 16 NLS thus mediates nuclear import through a pathway completely distinct from that of conventional NLSs, such as that of T-ag, but intriguingly resembling that of the NLS of the HIV-1 transactivator protein Tat. Since the IFI 16 CK2 site enhances nuclear import through facilitating binding to nuclear components, this represents a novel mechanism by which the site regulates nuclear-protein import, and constitutes a difference between the IFI 16 and Tat NLSs that may be of importance in the immune response.

    The Biochemical journal 2001;353;Pt 1;69-77

  • Protein p21(WAF1/CIP1) is phosphorylated by protein kinase CK2 in vitro and interacts with the amino terminal end of the CK2 beta subunit.

    Romero-Oliva F and Allende JE

    Programa de Biología Celular y Molecular, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Chile.

    Protein kinase CK2 is a ubiquitous protein that phosphorylates multiple substrates and is composed of catalytic (alpha, alpha') and regulatory (beta) subunits. Abundant evidence relates CK2 to the regulation of cell division. p21(WAF1/CIP1) is a potent inhibitor of cyclin-dependent kinases and of DNA replication and acts as a key inhibitor of cell cycle progression. In this work we examine the relation between these two important proteins. The interaction between the CK2 beta regulatory subunit of CK2 and p21(WAF1/CIP1) has been confirmed. Using a pull-down assay and fusion constructs of glutathione transferase with fragments of CK2 beta and other mutants, it was possible to define that the N-terminal (1-44) portion of CK2 beta contains a p21(WAF1/CIP1) binding site. CK2 reconstituted from recombinant alpha and beta subunits can phosphorylate p21(WAF1/CIP1) in vitro. This phosphorylation is greatly enhanced by histone H1. p21(WAF1/CIP1) can inhibit the phosphorylation of substrate casein by CK2. This inhibition, however, seems to be due to competition by p21(WAF1/CIP1) as an alternate substrate since in order to observe inhibition it is necessary that the concentration of p21 be of the same order of magnitude as the casein substrate concentration. This competition is not related to the binding of p21(WAF1/CIP1) to CK2 beta because it can also be observed when, in the absence of CK beta, CK alpha is used to phosphorylate casein in the presence of the p21.

    Journal of cellular biochemistry 2001;81;3;445-52

  • Erk1/2-dependent phosphorylation of Galpha-interacting protein stimulates its GTPase accelerating activity and autophagy in human colon cancer cells.

    Ogier-Denis E, Pattingre S, El Benna J and Codogno P

    INSERM U504, Glycobiologie et Signalisation Cellulaire, 16, avenue Paul-Vaillant Couturier, 94807 Villejuif cedex, France.

    Galpha-interacting protein (GAIP) is a regulator of G protein signaling (RGS) that accelerates the rate of GTP hydrolysis by the alpha-subunit of the trimeric G(i3) protein. Both proteins are part of a signaling pathway that controls lysosomal-autophagic catabolism in human colon cancer HT-29 cells. Here we show that GAIP is phosphorylated by an extracellular signal-regulated (Erk1/2) MAP kinase-dependent pathway sensitive to amino acids, MEK1/2 (PD098059), and protein kinase C (GF109203X) inhibitors. An in vitro phosphorylation assay demonstrates that Erk2-dependent phosphorylation of GAIP stimulates its GTPase-activating protein activity toward the Galpha(i3) protein (k = 0.187 +/- 0.001 s(-)(1), EC(50) = 1.12 +/- 0.10 microm) when compared with unphosphorylated recombinant GAIP (k = 0.145 +/- 0.003 s(-)(1), EC(50) = 3.16 +/- 0. 12 microm) or to GAIP phosphorylated by other Ser/Thr protein kinases (protein kinase C, casein kinase II). This stimulation and the phosphorylation of GAIP by Erk2 were abrogated when serine at position 151 in the RGS domain was substituted by an alanine residue using site-directed mutagenesis. Furthermore, the lysosomal-autophagic pathway was not stimulated in S151A-GAIP mutant-expressing cells when compared with wild-type GAIP-expressing cells. These results demonstrate that the GTPase-activating protein activity of GAIP is stimulated by Erk2 phosphorylation. They also suggested that Erk1/2 and GAIP are engaged in the signaling control of a major catabolic pathway in intestinal derived cells.

    The Journal of biological chemistry 2000;275;50;39090-5

  • Crystallization and preliminary characterization of crystals of human protein kinase CK2.

    Niefind K, Guerra B, Ermakowa I and Issinger OG

    Universität zu Köln, Institut für Biochemie, Zülpicher Strasse 47, D-50674 Köln, Germany. karsten.niefind@uni-koeln.de

    The heterotetrameric recombinant holoenzyme of human protein kinase CK2 was purified to homogeneity. It degraded spontaneously to a stable and fully active state in which the catalytic subunit was about 5 kDa smaller than the wild type. The degraded enzyme was crystallized using polyethylene glycol 3350 as precipitant. The crystals belong to the hexagonal space group P6(3). They have unit-cell parameters a = b = 176.0, c = 93.6 A and diffract X-rays to at least 3.5 A resolution. The calculated crystal packing parameter is V(M) = 3.22 A(3) Da(-1), suggesting that one CK2 tetramer is contained in the asymmetric unit and that the solvent content of the unit cell is 62%.

    Acta crystallographica. Section D, Biological crystallography 2000;56;Pt 12;1680-4

  • Participation of ATM in insulin signalling through phosphorylation of eIF-4E-binding protein 1.

    Yang DQ and Kastan MB

    Department of Hematology-Oncology, St. Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, Tennessee 38105-2794, USA.

    One of the critical responses to insulin treatment is the stimulation of protein synthesis through induced phosphorylation of the eIF-4E-binding protein 1 (4E-BP1), and the subsequent release of the translation initiation factor, eIF-4E. Here we report that ATM, the protein product of the ATM gene that is mutated in the disease ataxia telangiectasia, phosphorylates 4E-BP1 at Ser 111 in vitro and that insulin treatment induces phosphorylation of 4E-BP1 at Ser 111 in vivo in an ATM-dependent manner. In addition, insulin treatment of cells enhances the specific kinase activity of ATM. Cells lacking ATM kinase activity exhibit a significant decrease in the insulin-induced dissociation of 4E-BP1 from eIF-4E. These results suggest an unexpected role for ATM in an insulin-signalling pathway that controls translation initiation. Through this mechanism, a lack of ATM activity probably contributes to some of the metabolic abnormalities, such as poor growth and insulin resistance, reported in ataxia telangiectasia cells and patients with ataxia telangiectasia.

    Nature cell biology 2000;2;12;893-8

  • Phosphorylation of the beta-galactoside-binding protein galectin-3 modulates binding to its ligands.

    Mazurek N, Conklin J, Byrd JC, Raz A and Bresalier RS

    Gastrointestinal Cancer Research Laboratory, Henry Ford Health Sciences Center, Detroit, Michigan 48202, USA.

    The beta-galactoside-binding protein galectin-3 has pleiotropic biological functions and has been implicated in cell growth, differentiation, adhesion, RNA processing, apoptosis, and malignant transformation. Galectin-3 may be phosphorylated at N-terminal Ser(6), but the role of phosphorylation in determining interactions of this endogenous lectin with its ligands remains to be elucidated. We therefore studied the effect of phosphorylation on binding of galectin-3 to two of its reported ligands, laminin and purified colon cancer mucin. Human recombinant galectin-3 was phosphorylated in vitro by casein kinase I, and separated from the native species by isoelectric focusing for use in solid phase binding assays. Non-phosphorylated galectin-3 bound to laminin and asialomucin in a dose-dependent manner with half-maximal binding at 1.5 microg/ml. Phosphorylation reduced saturation binding to each ligand by >85%. Ligand binding could be fully restored by dephosphorylation with protein phosphatase type 1. Mutation of galectin-3 at Ser(6) (Ser to Glu) did not alter galectin ligand binding. Metabolic labeling or separation by isoelectric focusing confirmed the presence of phosphorylated galectin-3 species in vivo in the cytosol of human colon cancer cells from which ligand mucin was purified. Phosphorylation significantly reduces the interaction of galectin-3 with its ligands. The process by which phosphorylation modulates protein-carbohydrate interactions has important implications for understanding the biological functions of this protein, and may serve as an "on/off" switch for its sugar binding capabilities.

    Funded by: NCI NIH HHS: R01CA 46120, R01CA 69480

    The Journal of biological chemistry 2000;275;46;36311-5

  • Bovine prion protein as a modulator of protein kinase CK2.

    Meggio F, Negro A, Sarno S, Ruzzene M, Bertoli A, Sorgato MC and Pinna LA

    Dipartimento di Chimica Biologica, Università di Padova, Viale G. Colombo 3, 35121 Padova, Italy.

    On the basis of far-Western blot and plasmon resonance (BIAcore) experiments, we show here that recombinant bovine prion protein (bPrP) (25-242) strongly interacts with the catalytic alpha/alpha' subunits of protein kinase CK2 (also termed 'casein kinase 2'). This association leads to increased phosphotransferase activity of CK2alpha, tested on calmodulin or specific peptides as substrate. We also show that bPrP counteracts the inhibition of calmodulin phosphorylation promoted by the regulatory beta subunits of CK2. A truncated form of bPrP encompassing the C-terminal domain (residues 105-242) interacts with CK2 but does not affect its catalytic activity. The opposite is found with the N-terminal fragment of bPrP (residues 25-116), although the stimulation of catalysis is less efficient than with full-size bPrP. These results disclose the potential of the PrP to modulate the activity of CK2, a pleiotropic protein kinase that is particularly abundant in the brain.

    Funded by: Telethon: E.0945

    The Biochemical journal 2000;352 Pt 1;191-6

  • Mitotic phosphorylation of DNA topoisomerase II alpha by protein kinase CK2 creates the MPM-2 phosphoepitope on Ser-1469.

    Escargueil AE, Plisov SY, Filhol O, Cochet C and Larsen AK

    Laboratoire de Biologie et Pharmacologie des Tumeurs, CNRS UMR 8532, Institut Gustave-Roussy PR2, Villejuif 94805 Cedex, France.

    DNA topoisomerase II alpha is required for chromatin condensation during prophase. This process is temporally linked with the appearance of mitosis-specific phosphorylation sites on topoisomerase IIalpha including one recognized by the MPM-2 monoclonal antibody. We now report that the ability of mitotic extracts to create the MPM-2 epitope on human topoisomerase II alpha is abolished by immunodepletion of protein kinase CK2. Furthermore, the MPM-2 phosphoepitope on topoisomerase II alpha can be generated by purified CK2. Phosphorylation of C-truncated topoisomerase II alpha mutant proteins conclusively shows, that the MPM-2 epitope is present in the last 163 amino acids. Use of peptides containing all conserved CK2 consensus sites in this region indicates that only the peptide containing Arg-1466 to Ala-1485 is able to compete with topoisomerase II alpha for binding of the MPM-2 antibody. Replacement of Ser-1469 with Ala abolishes the ability of the phosphorylated peptide to bind to the MPM-2 antibody while a peptide containing phosphorylated Ser-1469 binds tightly. Surprisingly, the MPM-2 phosphoepitope influences neither the catalytic activity of topoisomerase II alpha nor its ability to form molecular complexes with CK2 in vitro. In conclusion, we have identified protein kinase CK2 as a new MPM-2 kinase able to phosphorylate an important mitotic protein, topoisomerase II alpha, on Ser-1469.

    The Journal of biological chemistry 2000;275;44;34710-8

  • Redox regulation of casein kinase II autophosphorylation and its effect on Jun-DNA binding.

    Moussazadeh M and Greene JJ

    Department of Biology and Institute for Biomolecular Studies, The Catholic University of America, Washington, DC 20064-0001.

    In previous studies we showed that an oxido-reductase is involved in the restoration of contact inhibition in fibrosacoma cells, implicating the redox state in growth control. In the present report we demonstrate that autophosphorylation of casein kinase II (CKII) is redox-dependent. We have also shown that phosphorylation of the transcription factor Jun by CKII is regulated by the redox state. In vitro kinase assays revealed that CKII-catalyzed phosphorylation increased the affinity of Jun for the DNA. In conformational analyses, CKII maintained an intact structure only within the redox range permissive to its autophosphorylation. Collectively, these data suggest that the redox state profoundly influences the ability of CKII to phosphorylate its substrate Jun and may do so by affecting the autophosphorylation as well as the structure of CKII. To demonstrate the biological relevance of these observations, redox potentials of fibroblast nuclei from different stages of growth were measured. Results indicated that as cell density increased, the intranuclear environment gradually became less reducing. Redox-dependent behaviors of growth-associated proteins such as Jun and CKII, together with evidence for in vivo changes in the nuclear redox state suggest that a redox mechanism may be involved in the regulation of cell growth.

    Cellular and molecular biology (Noisy-le-Grand, France) 2000;46;7;1265-75

  • Tumor necrosis factor alpha-induced phosphorylation of RelA/p65 on Ser529 is controlled by casein kinase II.

    Wang D, Westerheide SD, Hanson JL and Baldwin AS

    Department of Biology, Curriculum in Genetics and Molecular Biology and Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295, USA.

    Nuclear factor kappaB (NF-kappaB)/Rel transcription factors are key regulators of a variety of genes involved in immune and inflammatory responses, growth, differentiation, apoptosis, and development. In unstimulated cells, NF-kappaB/Rel proteins are sequestered in the cytoplasm by IkappaB inhibitor proteins. Many extracellular stimuli, such as tumor necrosis factor alpha (TNFalpha), cause rapid phosphorylation of IkappaB at N-terminal serine residues leading to ubiquitination and degradation of the inhibitor. Subsequently, NF-kappaB proteins translocate to the nucleus and activate gene expression through kappaB response elements. TNFalpha, as well as certain other stimuli, also induces the phosphorylation of the NF-kappaB proteins. Previously, we have shown that TNFalpha induces RelA/p65 phosphorylation at serine 529 and that this inducible phosphorylation increases NF-kappaB transcriptional activity on an exogenously supplied reporter (). In this report, we demonstrate that casein kinase II (CKII) interacts with p65 in vivo and can phosphorylate p65 at serine 529 in vitro. A CKII inhibitor (PD144795) inhibited TNFalpha-induced p65 phosphorylation in vivo. Furthermore, our results indicate that the association between IkappaBalpha and p65 inhibits p65 phosphorylation by CKII and that degradation of IkappaBalpha allows CKII to phosphorylate p65 to increase NF-kappaB transactivation potential. These data may explain the ability of CKII to modulate cell growth and demonstrate a mechanism whereby CKII can function in an inducible manner.

    Funded by: NCI NIH HHS: CA72771; NIAID NIH HHS: AI35098

    The Journal of biological chemistry 2000;275;42;32592-7

  • Unique features of HIV-1 Rev protein phosphorylation by protein kinase CK2 ('casein kinase-2').

    Marin O, Sarno S, Boschetti M, Pagano MA, Meggio F, Ciminale V, D'Agostino DM and Pinna LA

    Dipartmento di Chimica Biologica and Centro del CNR per lo Studio delle Biomembrane, Università delgi Studi di Padova, Padua, Italy.

    The HIV-1 Rev transactivator is phosphorylated in vitro by protein kinase CK2 at two residues, Ser-5 and Ser-8; these sites are also phosphorylated in vivo. Here we show that the mechanism by which CK2 phosphorylates Rev is unique in several respects, notably: (i) it is fully dependent on the regulatory, beta-subunit of CK2; (ii) it relies on the integrity of an acidic stretch of CK2 beta which down-regulates the phosphorylation of other substrates; (iii) it is inhibited in a dose-dependent manner by polyamines and other polycationic effectors that normally stimulate CK2 activity. In contrast, a peptide corresponding to the amino-terminal 26 amino acids of Rev, including the phosphoacceptor site, is readily phosphorylated by the catalytic subunit of CK2 even in the absence of the beta-subunit. These data, in conjunction with the observation that two functionally inactive derivatives of Rev with mutations in its helix-loop-helix motif are refractory to phosphorylation, indicate the phosphorylation of Rev by CK2 relies on conformational features of distinct regions that are also required for the transactivator's biological activity.

    FEBS letters 2000;481;1;63-7

  • Subcellular localization of protein kinase CK2. A key to its function?

    Faust M and Montenarh M

    Medical Biochemistry and Molecular Biology, University of the Saarland, Homburg, Germany.

    More than 46 years ago, Burnett and Kennedy first described protein kinase CK2 (formerly known as casein kinase 2) in liver extracts. Since then, protein kinase CK2 has been investigated in many organisms from yeast to man. It is now well established that protein kinase CK2 is a pleiotropic and ubiquitous serine or threonine kinase, which is highly conserved during evolution. A great number of studies deal with substrates of CK2, but the fact that over 160 substrates exist is more confusing than elucidatory. The holoenzyme is composed of two regulatory beta-subunits and two catalytic alpha- or alpha'-subunits. There is now increasing evidence for individual functions of the subunits that are different from their functions in the holoenzyme. Furthermore, more and more studies describe interacting partners of the kinase that may be decisive in the regulation of this enzyme. A big step forward has been the determination of the crystal structure of the two subunits of protein kinase CK2. Now the interactions of the catalytic subunit of CK2 with ATP as well as GTP and the interaction between the regulatory subunits can be explained. However, cellular functions of protein kinase CK2 still remain unclear. In the present review we will focus our interest on the subcellular localization of protein kinase CK2. Protein kinase CK2 is found in many organisms and tissues and nearly every subcellular compartment. There is ample evidence that protein kinase CK2 has different functions in these compartments and that the subcellular localization of protein kinase CK2 is tightly regulated. Therefore studying the subcellular localization of protein kinase CK2 may be a key to its function.

    Cell and tissue research 2000;301;3;329-40

  • Biochemical characterization of casein kinase II as a protein kinase responsible for stimulation of HIV-1 protease in vitro.

    Haneda E, Furuya T, Asai S, Morikawa Y and Ohtsuki K

    Laboratory of Genetical Biochemistry, Graduate School of Medical Sciences, Kitasato University, Kitasato 1-15-1, Sagamihara, 228-8555, Japan.

    The physiological significance of casein kinase II (CK-II) on the protease (PR) activity of recombinant HIV-1 PR (rPR) was biochemically investigated in vitro. We found that (i) the purified rPR (p11) functions as a phosphate acceptor of CK-II; (ii) the PR activity of rPR is stimulated approximately 2.9-fold after its full phosphorylation by recombinant human CK-II (rhCK-II) in a manner similar to that observed for recombinant HIV-1 reverse transcriptase (rRT); and (iii) this stimulation is completely inhibited by two polyphenol-containing anti-oxidant compounds [quercetin and epigallo-catechin gallate (EGCG)] at 0.1 microM or a glycyrrhetinic acid derivative (oGA) and catechin at 10 microM without significant effect on the PR activity of rPR. These results suggest that (i) CK-II may be a host mediator responsible for stimulation of PR and RT in HIV-1-infected cells; and (ii) the selective inhibition of the CK-II-mediated stimulation of HIV-1 PR and RT by potent CK-II inhibitors may be involved in their anti-HIV-1 effects at the cellular level.

    Biochemical and biophysical research communications 2000;275;2;434-9

  • Synucleins are a novel class of substrates for G protein-coupled receptor kinases.

    Pronin AN, Morris AJ, Surguchov A and Benovic JL

    Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.

    G protein-coupled receptor kinases (GRKs) specifically recognize and phosphorylate the agonist-occupied form of numerous G protein-coupled receptors (GPCRs), ultimately resulting in desensitization of receptor signaling. Until recently, GPCRs were considered to be the only natural substrates for GRKs. However, the recent discovery that GRKs also phosphorylate tubulin raised the possibility that additional GRK substrates exist and that the cellular role of GRKs may be much broader than just GPCR regulation. Here we report that synucleins are a novel class of GRK substrates. Synucleins (alpha, beta, gamma, and synoretin) are 14-kDa proteins that are highly expressed in brain but also found in numerous other tissues. alpha-Synuclein has been linked to the development of Alzheimer's and Parkinson's diseases. We found that all synucleins are GRK substrates, with GRK2 preferentially phosphorylating the alpha and beta isoforms, whereas GRK5 prefers alpha-synuclein as a substrate. GRK-mediated phosphorylation of synuclein is activated by factors that stimulate receptor phosphorylation, such as lipids (all GRKs) and Gbetagamma subunits (GRK2/3), suggesting that GPCR activation may regulate synuclein phosphorylation. GRKs phosphorylate synucleins at a single serine residue within the C-terminal domain. Although the function of synucleins remains largely unknown, recent studies have demonstrated that these proteins can interact with phospholipids and are potent inhibitors of phospholipase D2 (PLD2) in vitro. PLD2 regulates the breakdown of phosphatidylcholine and has been implicated in vesicular trafficking. We found that GRK-mediated phosphorylation inhibits synuclein's interaction with both phospholipids and PLD2. These findings suggest that GPCRs may be able to indirectly stimulate PLD2 activity via their ability to regulate GRK-promoted phosphorylation of synuclein.

    Funded by: NIGMS NIH HHS: GM44944

    The Journal of biological chemistry 2000;275;34;26515-22

  • Phosphorylation of AZT-resistant human immunodeficiency virus type 1 reverse transcriptase by casein kinase II in vitro: effects on inhibitor sensitivity.

    Lazaro JB, Boretto J, Selmi B, Capony JP and Canard B

    Department BCMP, Harvard Medical School, Boston, Massachusetts, USA.

    Casein kinase II (CKII) phosphorylates wild-type (WT) recombinant reverse transcriptase (RT) mainly in the p66 subunit in vitro. Phosphorylation of T215F RT and D67N/K70R/T215F/K219Q RT (AZT-resistant RT) in vitro increases discrimination against AZTTP 2. 5- and 3.6-fold, respectively. This in vitro resistance can be reversed by treatment of phosphorylated AZT-resistant RT with phosphatase. Phosphorylation has no effect on WT RT. Terminal transferase activity of RT is selectively suppressed on phosphorylated AZT-resistant RT. Resistance to phosphonoformic acid (PFA, foscarnet) increases 3-fold upon phosphorylation of AZT-resistant RT. Although T215, the most important residue for AZT-resistance, is part of a CKII consensus target site, serines are primarily phosphorylated relative to threonines. Mutational analysis shows that phosphorylation can be reduced to 10% that of WT when amino-acid changes are introduced both in the "fingers" subdomain and motif D. These results suggest that phosphorylation of RT might be one factor involved in drug resistance in vivo.

    Biochemical and biophysical research communications 2000;275;1;26-32

  • Endogenous protein kinase CK2 participates in Wnt signaling in mammary epithelial cells.

    Song DH, Sussman DJ and Seldin DC

    Departments of Medicine, Chemistry, and Microbiology, Boston Medical Center and Boston University, Boston, Massachusetts 02118, USA.

    Protein kinase CK2 (formerly casein kinase II) is a serine/threonine kinase overexpressed in many human tumors, transformed cell lines, and rapidly proliferating tissues. Recent data have shown that many cancers involve inappropriate reactivation of Wnt signaling through ectopic expression of Wnts themselves, as has been seen in a number of human breast cancers, or through mutation of intermediates in the Wnt pathway, such as adenomatous polyposis coli or beta-catenin, as described in colon and other cancers. Wnts are secreted factors that are important in embryonic development, but overexpression of certain Wnts, such as Wnt-1, leads to proliferation and transformation of cells. We report that upon stable transfection of Wnt-1 into the mouse mammary epithelial cell line C57MG, morphological changes and increased proliferation are accompanied by increased levels of CK2, as well as of beta-catenin. CK2 and beta-catenin co-precipitate with the Dvl proteins, which are Wnt signaling intermediates. A major phosphoprotein of the size of beta-catenin appears in in vitro kinase reactions performed on the Dvl immunoprecipitates. In vitro translated beta-catenin, Dvl-2, and Dvl-3 are phosphorylated by CK2. The selective CK2 inhibitor apigenin blocks proliferation of Wnt-1-transfected cells, abrogates phosphorylation of beta-catenin, and reduces beta-catenin and Dvl protein levels. These results demonstrate that endogenous CK2 is a positive regulator of Wnt signaling and growth of mammary epithelial cells.

    Funded by: NCI NIH HHS: R01 CA63929, R01 CA71796

    The Journal of biological chemistry 2000;275;31;23790-7

  • The human vaccinia-related kinase 1 (VRK1) phosphorylates threonine-18 within the mdm-2 binding site of the p53 tumour suppressor protein.

    Lopez-Borges S and Lazo PA

    Centro de Investigación del Cáncer, Instituto de Biología Molecular y Celular del Cáncer, Consejo Superior de Investigaciones Científicas, Universidad de Salamanca, Spain.

    The tumour suppressor p53 protein integrates multiple signals regulating cell cycle progression and apoptosis. This regulation is mediated by several kinases that phosphorylate specific residues in the different functional domains of the p53 molecule. The human VRK1 protein is a new kinase related to a poxvirus kinase, and more distantly to the casein kinase 1 family. We have characterized the biochemical properties of human VRK1 from HeLa cells. VRK1 has a strong autophosphorylating activity in several Ser and Thr residues. VRK-1 phosphorylates acidic proteins, such as phosvitin and casein, and basic proteins such as histone 2b and myelin basic protein. Because some transcription factors are regulated by phosphorylation, we tested as substrates the N-transactivation domains of p53 and c-Jun fused to GST. Human c-Jun is not phosphorylated by VRK1. VRK1 phosphorylates murine p53 in threonine 18. This threonine is within the p53 hydrophobic loop (residues 13-23) required for the interaction of p53 with the cleft of its inhibitor mdm-2. The VRK1 C-terminus domain (residues 268-396) that contains a nuclear localization signal targets the protein to the nucleus, as determined by using fusion proteins with the green fluorescent protein. We conclude that VRK1 is an upstream regulator of p53 that belongs to a new signalling pathway.

    Oncogene 2000;19;32;3656-64

  • The C-terminal regulatory domain of p53 contains a functional docking site for cyclin A.

    Luciani MG, Hutchins JR, Zheleva D and Hupp TR

    Department of Molecular and Cellular Pathology, Cancer Research Campaign Laboratories, University of Dundee Medical School, Scotland.

    Radiation injury to cells enhances C-terminal phosphorylation of p53 at both Ser315 and Ser392 in vivo, suggesting the existence of two cooperating DNA damage-responsive pathways that play a role in stimulating p53-dependent gene expression. Our previous data has shown that cyclin A-cdk2 is the major enzyme responsible for modifying p53 at Ser315 in vivo after irradiation damage and in this report we dissect the mechanism of cyclinA-cdk2 binding to and phosphorylation of p53. Although cyclin B(1)-dependent protein kinases can phosphorylate small peptides containing the Ser315 site, cyclin A-cdk2 does not phosphorylate such small peptides suggesting that additional determinants are required for cyclin A-cdk2 interaction with p53. Peptide competition studies have localized a cyclin A interaction site to a Lys381Lys382Leu383Met384Phe385 sequence within C-terminal negative regulatory domain of human p53. An alanine mutation at any one of four key positions abrogates the efficacy of a synthetic peptide containing this motif as an inhibitor of cyclin A-cdk2 phosphorylation of p53 protein. Single amino acid mutations of full-length p53 protein at Lys382, Leu383, or Phe385 decreases cyclin A-cdk2 dependent phosphorylation at Ser315. Cyclin B(1)-cdk2 complexes are not inhibited by KKLMF motif-containing peptides nor is p53 phosphorylation by cyclin B-cdk2 reduced by mutation of the cyclin A interaction site. These data identifying a KKLMF cyclin A docking site on p53 protein highlight a common cyclin A interaction motif that is shared between the tumour suppressor proteins pRb and p53.

    Journal of molecular biology 2000;300;3;503-18

  • Phosphohexose isomerase/autocrine motility factor/neuroleukin/maturation factor is a multifunctional phosphoprotein.

    Haga A, Niinaka Y and Raz A

    Metastasis Research Program, Karmanos Cancer Institute, Detroit, MI 48201, USA.

    Phosphohexose isomerase (PHI) is a member of the ectoenzyme/exoenzyme family and plays a key role in both glycolysis and gluconeogenesis pathways. Upon secretion PHI acts as a cytokine with tumor autocrine motility factor (AMF), neuroleukin (NLK) and maturation factor (MF) functions. Signaling is initiated by its binding to a cell surface 78 kDa glycoprotein (gp78). However, since PHI protein is a 'leaderless' secretory protein, released from cells via a non-classical route(s), we questioned whether the molecule undergoes post-translation modification while retaining proper folding and maintaining intact enzymatic and motogenic activities. To address this, we have generated, expressed and isolated a recombinant human AMF (rhAMF). The rhAMF retained the biological activities of the native AMF, i.e., catalyzes phosphohexose isomerization and stimulated cell motility. Additionally, we show here that human PHI is phosphorylated at serine 185 by casein kinase II (CK II) and we provide experimental evidence suggesting that this phosphorylation is associated with secretion, thus providing insights for elucidating the intracellular signal transmission of cell response to stimulation by AMF/NLK/MF.

    Funded by: NCI NIH HHS: R01-CA51714

    Biochimica et biophysica acta 2000;1480;1-2;235-44

  • Phosphorylated syntaxin 1 is localized to discrete domains along a subset of axons.

    Foletti DL, Lin R, Finley MA and Scheller RH

    Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305-5428, USA.

    Syntaxin 1 is a SNARE protein that plays a central role in synaptic vesicle (SV) exocytosis. We generated an antibody that specifically recognizes a casein kinase II-mediated phosphorylation on serine-14 of syntaxin 1. In this report we show that this phosphorylation occurs in vivo and is developmentally regulated in the rat brain, rising to a level of 40% of the total syntaxin in adult animals. Phosphorylated syntaxin is preferentially associated with SNAP-25 and localizes to discrete domains of the axonal plasma membrane that do not colocalize with pools of synaptic vesicles. These phosphosyntaxin domains may define fusion sites for a novel class of vesicles outside classical active zones.

    The Journal of neuroscience : the official journal of the Society for Neuroscience 2000;20;12;4535-44

  • Stress-induced activation of protein kinase CK2 by direct interaction with p38 mitogen-activated protein kinase.

    Sayed M, Kim SO, Salh BS, Issinger OG and Pelech SL

    Department of Medicine, Koerner Pavilion, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada.

    Protein kinase CK2 has been implicated in the regulation of a wide range of proteins that are important in cell proliferation and differentiation. Here we demonstrate that the stress signaling agents anisomycin, arsenite, and tumor necrosis factor-alpha stimulate the specific enzyme activity of CK2 in the human cervical carcinoma HeLa cells by up to 8-fold, and this could be blocked by the p38 MAP kinase inhibitor SB203580. We show that p38alpha MAP kinase, in a phosphorylation-dependent manner, can directly interact with the alpha and beta subunits of CK2 to activate the holoenzyme through what appears to be an allosteric mechanism. Furthermore, we demonstrate that anisomycin- and tumor necrosis factor-alpha-induced phosphorylation of p53 at Ser-392, which is important for the transcriptional activity of this growth suppressor protein, requires p38 MAP kinase and CK2 activities.

    The Journal of biological chemistry 2000;275;22;16569-73

  • Identification and characterization of CKIP-1, a novel pleckstrin homology domain-containing protein that interacts with protein kinase CK2.

    Bosc DG, Graham KC, Saulnier RB, Zhang C, Prober D, Gietz RD and Litchfield DW

    Department of Biochemistry, University of Western Ontario, London, Ontario N6A 5C1, Canada.

    The catalytic subunits of protein kinase CK2, CK2alpha and CK2alpha', are closely related to each other but exhibit functional specialization. To test the hypothesis that specific functions of CK2alpha and CK2alpha' are mediated by specific interaction partners, we used the yeast two-hybrid system to identify CK2alpha- or CK2alpha'-binding proteins. We report the identification and characterization of a novel CK2-interacting protein, designated CKIP-1, that interacts with CK2alpha, but not CK2alpha', in the yeast two-hybrid system. CKIP-1 also interacts with CK2alpha in vitro and is co-immunoprecipitated from cell extracts with epitope-tagged CK2alpha and an enhanced green fluorescent protein fusion protein encoding CKIP-1 (i.e. EGFP-CKIP-1) when they are co-expressed. CK2 activity is detected in anti-CKIP-1 immunoprecipitates performed with extracts from non-transfected cells indicating that CKIP-1 and CK2 interact under physiological conditions. The CKIP-1 cDNA is broadly expressed and encodes a protein with a predicted molecular weight of 46,000. EGFP-CKIP-1 is localized within the nucleus and at the plasma membrane. The plasma membrane localization is dependent on the presence of an amino-terminal pleckstrin homology domain. We postulate that CKIP-1 is a non-enzymatic regulator of one isoform of CK2 (i.e. CK2alpha) with a potential role in targeting CK2alpha to a particular cellular location.

    The Journal of biological chemistry 2000;275;19;14295-306

  • Ser/Thr phosphorylation of hematopoietic specific protein 1 (HS1): implication of protein kinase CK2.

    Ruzzene M, Brunati AM, Sarno S, Marin O, Donella-Deana A and Pinna LA

    Dipartimento di Chimica Biologica and Centro per lo Studio delle Biomembrane del CNR and CRIBI, University of Padova, Italy.

    Hematopoietic lineage cell-specific protein 1 (HS1), a tyrosine multiphosphorylated protein implicated in receptor-mediated apoptosis and proliferative responses, is shown here to become Ser/Thr phosphorylated upon incubation of platelets with radiolabeled inorganic phosphate. The in vivo Ser/Thr phosphorylation of HS1 is enhanced by okadaic acid and reduced by specific inhibitors of casein kinase (CK)2. In vitro, HS1 is an excellent substrate for either CK2 alpha subunit alone (Km = 47 nM) or CK2 holoenzyme, tested in the presence of polylysine (Km = 400 nM). Phosphorylation reaches a stoichiometry of about 2 mol phosphate per mol HS1 and occurs mainly at threonyl residue(s), mostly located in the N-terminal region, but also at seryl residue(s) residing in the central core of the molecule (208-402), as judged from experiments with deleted forms of HS1. Ser/Thr phosphorylation of HS1, either induced in vivo by okadaic acid or catalysed in vitro by CK2, potentiates subsequent phosphorylation at tyrosyl residues. These data indicate the possibility that regulation of HS1 may also be under the control of Ser/Thr phosphorylation, and suggest that in quiescent cells CK2 could play a role in inducing constitutive Tyr phosphorylation of HS1 in the absence of stimuli that activate the protein tyrosine kinase pathway.

    European journal of biochemistry / FEBS 2000;267;10;3065-72

  • NAP-2: histone chaperone function and phosphorylation state through the cell cycle.

    Rodriguez P, Pelletier J, Price GB and Zannis-Hadjopoulos M

    McGill Cancer Center, Montreal, Quebec, Canada.

    We have recently cloned the human nucleosome assembly protein 2 (NAP-2). Here, we demonstrate that casein kinase 2 (CKII) from HeLa cell nuclear extracts interacts with immobilized NAP-II, and phosphorylates both NAP-2 and nucleosome assembly protein 1 (NAP-1) in vitro. Furthermore, NAP-1 and NAP-2 phosphorylation in crude HeLa cell extracts is abolished by heparin, a specific inhibitor of CKII. Addition of core histones can stimulate phosphorylation of NAP-1 and NAP-2 by CKII. NAP-2 is also a phosphoprotein in vivo. The protein is phosphorylated at the G0/G1 boundary but it is not phosphorylated in S-phase. Here, we show that NAP-2 is a histone chaperone throughout the cell cycle and that its cell-cycle distribution might be governed by its phosphorylation status. Phosphorylated NAP-2 remains in the cytoplasm in a complex with histones during the G0/G1 transition, whereas its dephosphorylation triggers its transport into the nucleus, at the G1/S-boundary, with the histone cargo, suggesting that binding to histones does not depend on phosphorylation status. Finally, indirect immunofluorescence shows that NAP-2 is present during metaphase of HeLa and COS cells, and its localization is distinct from metaphase chromosomes.

    Journal of molecular biology 2000;298;2;225-38

  • Phosphorylation of the 105-kDa heat shock proteins, HSP105alpha and HSP105beta, by casein kinase II.

    Ishihara K, Yasuda K and Hatayama T

    Department of Biochemistry, Kyoto Pharmaceutical University, 5 Nakauchicho, Misasagi, Yamashina-ku, Kyoto, 607-8414, Japan.

    The 105-kDa heat shock protein alpha (HSP105alpha) and HSP105beta are mammalian heat shock proteins that belong to the HSP105/HSP110 family. Both HSP105alpha and HSP105beta consist of acidic and basic isoforms. Here we report that the acidic isoforms are serine phosphorylated HSP105alpha or HSP105beta. Furthermore, using an in-gel kinase assay with HSP105alpha or HSP105beta as the substrate, the protein kinase that phosphorylates HSP105alpha and HSP105beta was identified as casein kinase II. Since phosphorylated HSP105alpha is especially prominent in the brain compared to other tissues of mice and rats, the phosphorylation of HSP105alpha by casein kinase II may be biologically significant.

    Biochemical and biophysical research communications 2000;270;3;927-31

  • Functional expression of O-linked GlcNAc transferase. Domain structure and substrate specificity.

    Lubas WA and Hanover JA

    Laboratory of Cell Biochemistry and Biology, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA.

    O-GlcNAc transferase (OGT) modifies nuclear pore proteins and transcription factors. In Arabidopsis, the OGT homolog participates in the gibberellin signaling pathway. We and others have proposed that mammalian OGT is the terminal step in a glucose-sensitive signal transduction pathway that becomes disregulated in insulin resistance. To facilitate mutational analysis of OGT in the absence of competing endogenous activity, we expressed the 103-kDa human OGT in Escherichia coli. Kinetic parameters for the purified recombinant enzyme (K(m) = 1.2 microM for Nup 62; K(m) = 0.5 microM for UDP-GlcNAc) are nearly identical to purified mammalian OGT. Deletions in the highly conserved C terminus result in a complete loss of activity. The N-terminal tetratricopeptide repeat domain is required for optimal recognition of substrates. Removal of the first three tetratricopeptide repeats greatly reduces the O-GlcNAc addition to macromolecular substrates. However, this altered enzyme retains full activity against appropriate synthetic peptides. Autoglycosylation of OGT is augmented when the first six tetratricopeptide repeats are removed showing that these repeats are not required for catalysis. Given its proposed role in modulating insulin action, OGT may modify kinases involved in this signaling cascade. Among the many kinases tested, OGT glycosylates glycogen synthase kinase-3 and casein kinase II, two enzymes critical in the regulation of glycogen synthesis.

    The Journal of biological chemistry 2000;275;15;10983-8

  • Membrane-associated GAIP is a phosphoprotein and can be phosphorylated by clathrin-coated vesicles.

    Fischer T, Elenko E, Wan L, Thomas G and Farquhar MG

    Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA 92093-0651, USA.

    GAIP (G alpha interacting protein) is a member of the RGS (regulators of G protein signaling) family and accelerates the turnover of GTP bound to Galphai, Galphaq, and Galpha13. There are two pools of GAIP-a soluble and a membrane-anchored pool. The membrane-anchored pool is found on clathrin-coated vesicles (CCVs) and pits in rat liver and AtT-20 pituitary cells. By treatment of a GAIP-enriched rat liver fraction with alkaline phosphatase, we found that membrane-bound GAIP is phosphorylated. By immunoprecipitation carried out on [(32)P]orthophosphate-labeled AtT-20 pituitary cells stably expressing GAIP, (32)P-labeling was associated exclusively with the membrane pool of GAIP. Phosphoamino acid analysis revealed that phosphorylation of GAIP occurred largely on serine residues. Recombinant GAIP could be phosphorylated at its N terminus with purified casein kinase 2 (CK2). It could also be phosphorylated by isolated CCVs in vitro. Phosphorylation was Mn(2+)-dependent, using both purified CK2 and CCVs. Ser-24 was identified as one of the phosphorylation sites. Our results establish that GAIP is phosphorylated and that only the membrane pool is phosphorylated, suggesting that GAIP can be regulated by phosphorylation events taking place at the level of clathrin-coated pits and vesicles.

    Funded by: NCI NIH HHS: CA58689, CA67754, T32 CA067754; NIDDK NIH HHS: DK17780, R01 DK017780

    Proceedings of the National Academy of Sciences of the United States of America 2000;97;8;4040-5

  • Shotgun sequencing of the human transcriptome with ORF expressed sequence tags.

    Dias Neto E, Correa RG, Verjovski-Almeida S, Briones MR, Nagai MA, da Silva W, Zago MA, Bordin S, Costa FF, Goldman GH, Carvalho AF, Matsukuma A, Baia GS, Simpson DH, Brunstein A, de Oliveira PS, Bucher P, Jongeneel CV, O'Hare MJ, Soares F, Brentani RR, Reis LF, de Souza SJ and Simpson AJ

    Ludwig Institute for Cancer Research, São Paulo 01509-010, Brazil.

    Theoretical considerations predict that amplification of expressed gene transcripts by reverse transcription-PCR using arbitrarily chosen primers will result in the preferential amplification of the central portion of the transcript. Systematic, high-throughput sequencing of such products would result in an expressed sequence tag (EST) database consisting of central, generally coding regions of expressed genes. Such a database would add significant value to existing public EST databases, which consist mostly of sequences derived from the extremities of cDNAs, and facilitate the construction of contigs of transcript sequences. We tested our predictions, creating a database of 10,000 sequences from human breast tumors. The data confirmed the central distribution of the sequences, the significant normalization of the sequence population, the frequent extension of contigs composed of existing human ESTs, and the identification of a series of potentially important homologues of known genes. This approach should make a significant contribution to the early identification of important human genes, the deciphering of the draft human genome sequence currently being compiled, and the shotgun sequencing of the human transcriptome.

    Proceedings of the National Academy of Sciences of the United States of America 2000;97;7;3491-6

  • Casein kinase II phosphorylation of E-cadherin increases E-cadherin/beta-catenin interaction and strengthens cell-cell adhesion.

    Lickert H, Bauer A, Kemler R and Stappert J

    Max-Planck Institute of Immunobiology, Department of Molecular Embryology, Stübeweg 51, D-79108 Freiburg, Germany.

    Beta-catenin, a member of the Armadillo repeat protein family, binds directly to the cytoplasmic domain of E-cadherin, linking it via alpha-catenin to the actin cytoskeleton. A 30-amino acid region within the cytoplasmic domain of E-cadherin, conserved among all classical cadherins, has been shown to be essential for beta-catenin binding. This region harbors several putative casein kinase II (CKII) and glycogen synthase kinase-3beta (GSK-3beta) phosphorylation sites and is highly phosphorylated. Here we report that in vitro this region is indeed phosphorylated by CKII and GSK-3beta, which results in an increased binding of beta-catenin to E-cadherin. Additionally, in mouse NIH3T3 fibroblasts expression of E-cadherin with mutations in putative CKII sites resulted in reduced cell-cell contacts. Thus, phosphorylation of the E-cadherin cytoplasmic domain by CKII and GSK-3beta appears to modulate the affinity between beta-catenin and E-cadherin, ultimately modifying the strength of cell-cell adhesion.

    The Journal of biological chemistry 2000;275;7;5090-5

  • The effect of phosphorylation by casein kinase 2 on the activity of insulin-like growth factor-binding protein-3.

    Coverley JA, Martin JL and Baxter RC

    Kolling Institute of Medical Research, University of Sydney, Royal North Shore Hospital, St. Leonards, New South Wales, Australia.

    Insulin-like growth factor (IGF)-binding protein-3 (IGFBP-3) is known to be secreted as a phosphoprotein, constitutively phosphorylated at casein kinase 2 (CK2) sites. To examine the effect of phosphorylation by CK2 on the properties of glycosylated human IGFBP-3, we phosphorylated plasma-derived IGFBP-3, containing less than 1 mol/mol phosphoserine, in vitro. As judged by incorporated 32P, enzymatic deglycosylation did not decrease the phosphate content of phospho-IGFBP-3. Phosphorylation had no effect on IGF-I or IGF-II binding, but was inhibitory to acid-labile subunit binding in the presence of either IGF. Determined in simian virus 40-transformed human fibroblasts, cell association by phospho-IGFBP-3 was inhibited approximately 50% compared with that of the nonphosphorylated preparation. Phospho-IGFBP-3 showed significant resistance to proteolysis by plasmin and a cysteine protease secreted by MCF-7 cells. However, no difference was seen between the two preparations in their inhibition of IGF-I-stimulated DNA synthesis when coincubated with IGF-I in neonatal skin fibroblasts or MCF-7 breast cancer cells, and little difference was found in their ability to potentiate IGF-I-stimulated DNA synthesis when preincubated with fibroblasts. These results indicate that IGFBP-3 interaction with acid-labile subunit and with the cell surface, both of which involve basic carboxyl-terminal residues, may be modulated by phosphorylation. Relative resistance to proteolysis and poor binding to cells suggest that CK2-phospho-IGFBP-3 may be a significant inhibitor of IGF activity in the extracellular environment.

    Endocrinology 2000;141;2;564-70

  • Protein phosphorylation is a regulatory mechanism for O6-alkylguanine-DNA alkyltransferase in human brain tumor cells.

    Srivenugopal KS, Mullapudi SR, Shou J, Hazra TK and Ali-Osman F

    Department of Neurosurgery, The University of Texas M.D. Anderson Cancer Center, Houston 77030, USA. ksrivenu@mdanderson.org

    The biochemical regulation of human O6-alkylguanine-DNA alkyltransferase (AGT), which determines the susceptibility of normal tissues to methylating carcinogens and resistance of tumor cells to many alkylating agents, is poorly understood. We investigated the regulation of AGT by protein phosphorylation in a human medulloblastoma cell line. Incubation of cell extracts with [gamma-32P]ATP resulted in Mg(2+)-dependent phosphorylation of the endogenous AGT. Immunoprecipitation after exposure of the cells to 32P-labeled inorganic phosphate showed that AGT exists as a phosphoprotein under physiological conditions. Western analysis and chemical stability studies showed the AGT protein to be phosphorylated at tyrosine, threonine, and serine residues. Purified protein kinase A (PKA), casein kinase II (CK II), and protein kinase C (PKC) phosphorylated the recombinant AGT protein with a stoichiometry of 0.15, 0.28, and 0.44 (mol phosphate incorporated/mol protein), respectively. Residual phosphorylation of the endogenous AGT by the PKs present in cell homogenates and phosphorylation of the recombinant AGT by purified serine/threonine kinases, PKA, PKC, and CK II reduced AGT activity by 30-65%. Conversely, dephosphorylation of cell extracts by alkaline phosphatases stimulated AGT activity. We also identified consensus phosphorylation motifs for many cellular kinases, including PKA and CK II in the AGT protein. These data provide the first and conclusive evidence of AGT phosphorylation and suggest that reversible phosphorylation may control the activity of this therapeutically important DNA repair protein in human normal and cancer cells.

    Funded by: NCI NIH HHS: CA74321

    Cancer research 2000;60;2;282-7

  • Constitutive phosphorylation of the Parkinson's disease associated alpha-synuclein.

    Okochi M, Walter J, Koyama A, Nakajo S, Baba M, Iwatsubo T, Meijer L, Kahle PJ and Haass C

    Adolf-Butenandt Institute, Department of Biochemistry, Ludwig-Maximilians University, 80336 Munich, Germany.

    alpha-Synuclein has been implicated in the pathogenesis of Parkinson's disease, since rare autosomal dominant mutations are associated with early onset of the disease and alpha-synuclein was found to be a major constituent of Lewy bodies. We have analyzed alpha-synuclein expression in transfected cell lines. In pulse-chase experiments alpha-synuclein appeared to be stable over long periods (t((1)/(2)) 54 h) and no endoproteolytic processing was observed. alpha-Synuclein was constitutively phosphorylated in human kidney 293 cells as well as in rat pheochromocytoma PC12 cells. In both cell lines phosphorylation was highly sensitive to phosphatases, since okadaic acid markedly stabilized phosphate incorporation. Phosphoamino acid analysis revealed that phosphorylation occurred predominantly on serine. Using site-directed mutagenesis we have identified a major phosphorylation site at serine 129 within the C-terminal domain of alpha-synuclein. An additional site, which was phosphorylated less efficiently, was mapped to serine 87. The major phosphorylation site was located within a consensus recognition sequence of casein kinase 1 (CK-1). In vitro experiments and two-dimensional phosphopeptide mapping provided further evidence that serine 129 was phosphorylated by CK-1 and CK-2. Moreover, phosphorylation of serine 129 was reduced in vivo upon inhibition of CK-1 or CK-2. These data demonstrate that alpha-synuclein is constitutively phosphorylated within its C terminus and may indicate that the function of alpha-synuclein is regulated by phosphorylation/dephosphorylation.

    The Journal of biological chemistry 2000;275;1;390-7

  • Identification of a phosphatase activity, toward the phosphopeptide pyroGlu-Asp-Asp-Ser(p)-Asp-Glu-Glu-Asn, in nuclear extract from HL-60 promyelocitic leukaemia cells.

    Cardellini E, Nardicchi V and Macchioni L

    Dipartimento di Biologia Cellulare e Molecolare, Sezione di Fisiologia e Biofisica, Università di Perugia, Via Pascoli, 1-06123 Perugia, Italy.

    Total protein extract from HL-60 cells was found to be able to dephosphorylate the RNA polymerase II octapeptide pyroGlu-Asp-Asp-Ser-Asp-Glu-Glu-Asn previously phosphorylated with protein kinase CKII (pCKII). Fractionation in cytoplasm, nuclear and chromatin extracts shows the phosphatase activity to be localized only in the nucleus, but not to be bound to the chromatin.

    Physiological chemistry and physics and medical NMR 2000;32;1;27-33

  • Phosphorylation of the Spi-B transcription factor reduces its intrinsic stability.

    Ray-Gallet D and Moreau-Gachelin F

    INSERM, Unité 248, Institut Curie, 26 rue díUlm, 75248, Paris, France.

    The Spi-B transcription factor is an Ets protein expressed in B lymphoid cells and closely related to the Spi-1/PU.1 oncoprotein. By mutational analysis, we showed that Spi-B is phosphorylated by casein kinase II in vitro on four serine residues. Mutation of these four serines to alanines prevented the phosphorylation of Spi-B in vivo, increased the ability of Spi-B to transactivate expression of a reporter gene and led to a decrease of Spi-B stability. We propose that the phosphorylation of Spi-B may participate in the modulation of Spi-B functional activity by controlling its intracellular protein level.

    FEBS letters 1999;464;3;164-8

  • HIV-1 reverse transcriptase is phosphorylated in vitro and in a cellular system.

    Idriss H, Kawa S, Damuni Z, Thompson EB and Wilson SH

    Sealy Center for Molecular Science, The University of Texas Medical Branch Galveston, TX 77555-0851, USA. hi@st-and.ac.uk

    Phosphorylation modulates the activity of many proteins that interact with nucleic acids including DNA and RNA polymerases. The HIV-1 reverse transcriptase (RT) is essential during the replicative cycle of the HIV-1 virus. HIV-1 RT has several potential sites for phosphorylation that could regulate its activities. In this work, the phosphorylation of HIV-1 RT is examined in vitro and in vivo, to evaluate any role for this modification in regulating RT metabolism. Recombinant unphosphorylated HIV-1 RT heterodimer expressed in bacteria can be phosphorylated in vitro by several purified mammalian protein kinases. Seven kinases were tested, and five of these enzymes phosphorylated HIV-1 RT. Using an insect baculovirus expression system, the 66 kDa HIV-1 RT was also phosphorylated in vivo. However, HIV-1 RT immunoprecipitated from H9-lymphoma cells infected with HIV-1 showed negligible phosphorylation. Our results indicate that purified HIV-1 RT can be phosphorylated by several mammalian protein kinases in vitro and during expression in baculovirus infected insect cells.

    Funded by: NIDDK NIH HHS: DK41058

    The international journal of biochemistry & cell biology 1999;31;12;1443-52

  • Specific binding of protein kinase CK2 catalytic subunits to tubulin.

    Faust M, Schuster N and Montenarh M

    Medical Biochemistry and Molecular Biology, University of Saarland, Building 44, D-66424, Homburg/Saar, Germany.

    Protein kinase CK2 is composed of two regulatory beta-subunits and two catalytic alpha- or alpha'-subunits. To analyse these subunits individually we generated antibodies against unique peptides derived from the alpha-, alpha'- and beta-subunit. Immunofluorescence studies with these antibodies revealed the presence of all three CK2 subunits in the cytoplasm and weakly in the nucleus with strong signals around the nuclear membrane. Double staining experiments revealed a co-localisation of all three subunits with tubulin. A direct association between the CK2 alpha- and the alpha'-subunit and tubulin was confirmed by co-immunoprecipitation experiments as well as by Far Western analysis. There was no binding of the CK2 beta-subunit to tubulin. Thus, with tubulin we have identified a new binding partner specific for the catalytic subunits of CK2.

    FEBS letters 1999;462;1-2;51-6

  • The kinesin-like motor protein KIF1C occurs in intact cells as a dimer and associates with proteins of the 14-3-3 family.

    Dorner C, Ullrich A, Häring HU and Lammers R

    Medical Clinic IV, University of Tübingen, Tübingen, 72076 Germany.

    Proteins of the kinesin superfamily are regulated in their motor activity as well as in their ability to bind to their cargo by carboxyl-terminal associating proteins and phosphorylation. KIF1C, a recently identified member of the KIF1/Unc104 family, was shown to be involved in the retrograde vesicle transport from the Golgi-apparatus to the endoplasmic reticulum. In a yeast two-hybrid screen using the carboxyl-terminal 350 amino acids of KIF1C as a bait, we identified as binding proteins 14-3-3 beta, gamma, epsilon, and zeta. In addition, a clone encoding the carboxyl-terminal 290 amino acids of KIF1C was found, indicating a potential for KIF1C to dimerize. Subsequent transient overexpression experiments showed that KIF1C can dimerize efficiently. However, in untransfected cells, only a small portion of KIF1C was detected as a dimer. The association of 14-3-3 proteins with KIF1C could be confirmed in transient expression systems and in untransfected cells and was dependent on the phosphorylation of serine 1092 located in a consensus binding sequence for 14-3-3 ligands. Serine 1092 was a substrate for the protein kinase casein kinase II in vitro, and inhibition of casein kinase II in cells diminished the association of KIF1C with 14-3-3gamma. Our data thus suggest that KIF1C can form dimers and is associated with proteins of the 14-3-3 family.

    The Journal of biological chemistry 1999;274;47;33654-60

  • The replication factory targeting sequence/PCNA-binding site is required in G(1) to control the phosphorylation status of DNA ligase I.

    Rossi R, Villa A, Negri C, Scovassi I, Ciarrocchi G, Biamonti G and Montecucco A

    Istituto di Genetica Biochimica ed Evoluzionistica, CNR, Via Abbiategrasso 207, 27100 Pavia, Italy.

    The recruitment of DNA ligase I to replication foci in S phase depends on a replication factory targeting sequence that also mediates the interaction with proliferating cell nuclear antigen (PCNA) in vitro. By exploiting a monoclonal antibody directed at a phospho-epitope, we demonstrate that Ser66 of DNA ligase I, which is part of a strong CKII consensus site, is phosphorylated in a cell cycle-dependent manner. After dephosphorylation in early G(1), the level of Ser66 phosphorylation is minimal in G(1), increases progressively in S and peaks in G(2)/M phase. The analysis of epitope-tagged DNA ligase I mutants demonstrates that dephosphorylation of Ser66 requires both the nuclear localization and the PCNA-binding site of the enzyme. Finally, we show that DNA ligase I and PCNA interact in vivo in G(1) and S phase but not in G(2)/M. We propose that dephosphorylation of Ser66 is part of a novel control mechanism to establish the pre-replicative form of DNA ligase I.

    The EMBO journal 1999;18;20;5745-54

  • LIS1 is a microtubule-associated phosphoprotein.

    Sapir T, Cahana A, Seger R, Nekhai S and Reiner O

    Department of Molecular Genetics, The Weizmann Institute of Science, Rehovot, Israel.

    Lissencephaly, a severe brain malformation, may be caused by mutations in the LIS1 gene. LIS1 encodes a microtubule-associated protein (MAP) that is also part of the enzyme complex, platelet-activating factor acetylhydrolase. LIS1 is also found in a complex with two protein kinases; a T-cell Tat-associated kinase, which contains casein-dependent kinase (CDK) activating kinase (CAK), as well as CAK-inducing activity, and with a spleen protein-tyrosine kinase similar to the catalytic domain of p72syk. As phosphorylation is one of the ways to control cellular localization and protein-protein interactions, we investigated whether LIS1 undergoes this post-translational modification. Our results demonstrate that LIS1 is a developmentally regulated phosphoprotein. Phosphorylated LIS1 is mainly found in the MAP fraction. Phosphoamino acid analysis revealed that LIS1 is phosphorylated on serine residues. Alkaline phosphatase treatment reduced the number of visible LIS1 isoforms. In-gel assays demonstrate a 50-kDa LIS1 kinase that is enriched in microtubule-associated fractions. In vitro, LIS1 was phosphorylated by protein kinase CKII (casein kinase II), but not many other kinases that were tested. We suggest that LIS1 activity may be regulated by phosphorylation.

    Funded by: FIC NIH HHS: TW00793; NIGMS NIH HHS: GM36259

    European journal of biochemistry 1999;265;1;181-8

  • Casein kinase II (CK-II)-mediated stimulation of HIV-1 reverse transcriptase activity and characterization of selective inhibitors in vitro.

    Harada S, Haneda E, Maekawa T, Morikawa Y, Funayama S, Nagata N, Ohtsuki K, Nagata N and Ohtsuki K

    Laboratory of Genetical Biochemistry, School of Allied Health Sciences, Kitasato University, Sagamihara, Japan.

    The physiological significance of the casein kinase II (CK-II)-mediated phosphorylation of human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) on its three enzymatic activities [RNA-dependent DNA polymerase (RDDP), DNA-dependent DNA polymerase (DDDP) and ribonuclease H (RNase H)] was investigated in vitro. It was found that (i) the purified recombinant RT (rRT) functioned as an effective phosphate acceptor for CK-II; (ii) the RDDP, DDDP and RNase H activity of rRT was stimulated about 2.8-, 4.1- and 3.9-fold, respectively, after full phosphorylation by CK-II; and (iii) this stimulation was selectively inhibited by potent CK-II inhibitors, such as neocarzinostatin-chromophore (NCS-chrom) and three polyphenol-containing anti-oxidant compounds [quercetin, epigallocatechin gallate (EGCG) and 8-chloro-3',4',5,7-tetrahydroxyisoflavone (8C-3',4',5,7-THI)]. These results suggest that (i) CK-II may be responsible for activation of RT in HIV-1-infected cells; and (ii) the selective inhibition of CK-II-mediated activation of HIV-1 RT by potent CK-II inhibitors may be involved in the mechanism of their anti-HIV-1 effects at the cellular level.

    Biological & pharmaceutical bulletin 1999;22;10;1122-6

  • Phosphorylation of ribosomal protein L5 by protein kinase CKII decreases its 5S rRNA binding activity.

    Park JW and Bae YS

    College of Natural Sciences, Kyungpook National University, Taegu, 702-701, Korea.

    We have recently reported that ribosomal protein L5 associates with the beta subunit of protein kinase CKII (CKII) (Kim, J.-M., Cha, J. -Y., Marshak, D. R., and Bae, Y.-S. (1996) Biochem. Biophys. Res. Commun. 226, 180-186). In this study, we demonstrate that CKII is able to catalyze the phosphorylation of the human L5 protein in vitro, which results in a decrease in 5S rRNA binding activity. Phosphoamino acid analysis indicated that the phosphorylation occurs on serine residues. Sequence analysis of cyanogen bromide-digested phosphopeptides and analysis of L5 deletion mutants indicates that the main phosphorylated residues are located within two fragments corresponding of residues 142-200 and residues 272-297 of the human L5. Based on our present results, we suggest that the phosphorylation of L5 by CKII is one of the mechanisms that regulates nucleolar targeting of 5S rRNA and/or ribosome assembly in the cell.

    Biochemical and biophysical research communications 1999;263;2;475-81

  • Globozoospermia in mice lacking the casein kinase II alpha' catalytic subunit.

    Xu X, Toselli PA, Russell LD and Seldin DC

    Department of Medicine, Boston Medical Center, Boston University School of Medicine, Boston, Massachusetts 02118, USA.

    Protein kinase casein kinase II (Ck2) is a cyclic-AMP and calcium-independent serine-threonine kinase that is composed of two catalytic subunits (alpha and alpha') and two regulatory beta-subunits. Ck2 is not a casein kinase in vivo, but over 100 substrates are known. The highly conserved amino acid sequences of its subunits and their broad expression suggest that Ck2 may have a fundamental role in cell function. Ck2 has been implicated in DNA replication, regulation of basal and inducible transcription, translation and control of metabolism. The Ck2alpha and Ck2alpha' isoforms (products of the genes Csnk2a1 and Csnk2a2, respectively) are highly homologous, but the reason for their redundancy and evolutionary conservation is unknown. We find here that Csnk2a2 is preferentially expressed in late stages of spermatogenesis, and male mice in which Csnk2a2 has been disrupted are infertile, with oligospermia and globozoospermia ('round-headed' spermatozoa). This is the first demonstration of a unique role for a Ck2 isoform in development. The primary spermatogenic defect in Csnk2a2-/- testis is a specific abnormality of anterior head shaping of elongating spermatids; this is the first defined gene that regulates sperm head morphogenesis. As the germ cells differentiate, they are capable of undergoing chromatin condensation, although many abnormal cells are deleted through apoptosis or Sertoli cell phagocytosis. The few that survive to populate the epididymis exhibit head abnormalities similar to those described in human globozoospermia, thus Csnk2a2 may be a candidate gene for these inherited syndromes.

    Nature genetics 1999;23;1;118-21

  • The DNA-binding and transcriptional activities of MAZ, a myc-associated zinc finger protein, are regulated by casein kinase II.

    Tsutsui H, Geltinger C, Murata T, Itakura K, Wada T, Handa H and Yokoyama KK

    Tsukuba Life Science Center, RIKEN (The Institute of Physical and Chemical Research), 3-1-1 Koyadai, Tsukuba, Ibaraki, 305-0074, Japan.

    Myc-associated zinc finger protein (MAZ) is a transcription factor that contains proline-rich, alanine repeats and six C(2)H(2)-type zinc finger motifs, as well as five putative sites of phosphorylation by casein kinase II (CKII). Site-specific mutagenesis of MAZ revealed that the serine residue at position 480 was the major site of phosphorylation by CKII both in vitro and in vivo. Phosphorylation of MAZ by CKII at this serine residue was required for maximum binding of MAZ to the pyrimidine-rich DNA of the nuclease-hypersensitive element (NHE) in the 5'-end promoter region of the c-myc gene. Mutation of serine at position 480 to alanine eliminated the DNA-binding activity of MAZ to this element. Moreover, the mutated MAZ was unable to enhance the expression of luciferase encoded by a c-myc promoter/luciferase reporter gene in HeLa cells in the presence of CKII. These results suggest that phosphorylation of the serine residue at position 480 of MAZ by CKII can control the function of MAZ by altering its DNA-binding activity.

    Biochemical and biophysical research communications 1999;262;1;198-205

  • Serine 32 and serine 36 of IkappaBalpha are directly phosphorylated by protein kinase CKII in vitro.

    Taylor JA, Bren GD, Pennington KN, Trushin SA, Asin S and Paya CV

    Department of Immunology, Division of Infectious Diseases, Mayo Clinic,Rochester, MN 55905, USA.

    IkappaBalpha is an inherently unstable protein which binds to and retains the ubiquitous transcription factor NFkappaB in the cytoplasm of resting cells. A continuous low level translocation of NFkappaB to the nucleus, secondary to the basal turnover of IkappaBalpha, is hypothesized to be necessary for cellular maturation, survival and, potentially, transformation. In response to cellular stimulation by inflammatory cytokines or mitogens, IkappaBalpha is rapidly degraded allowing larger pools of NFkappaB to translocate to the nucleus. Phosphorylation of IkappaBalpha at serine 32 (S32) and serine 36 (S36) is necessary for this stimuli-induced degradation. IKKalpha/beta kinases and p90(rsk1)are involved in stimuli-induced targeting of one or both of these IkappaBalpha sites. Whether other kinases phosphorylate S32 and S36 directly, and if so, what function they serve in NFkappaB activation remains unknown. Here we present evidence of a direct phosphorylation of IkappaBalpha at both S32 and S36 by purified or immunoprecipitated protein kinase CKII (PK-CKII) and a specific in vivo association between IkappaBalpha and PK-CKII. This PK-CKII-specific kinase activity is not found within the IKKalpha/beta-containing signalsome complex and is biochemically distinct from that of the IKKalpha/beta kinases. The identification of an additional N-terminal IkappaBalpha kinase which is constitutively active and not significantly inducible raises numerous possibilities as to its role in cellular function.

    Journal of molecular biology 1999;290;4;839-50

  • Casein kinase 2 binds to and phosphorylates BRCA1.

    O'Brien KA, Lemke SJ, Cocke KS, Rao RN and Beckmann RP

    Lilly Research Laboratories, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana, 46285-0424, USA.

    The BRCA1 gene encodes a complex protein that appears to be involved in some aspects of DNA repair, transcription, or cell cycle regulation. The phosphorylation of BRCA1 is enhanced following episodes of DNA damage or during cell cycle progression, indicating that phosphorylation may be an important regulatory mechanism. Through a yeast two hybrid assay, we found that the beta-subunit of casein kinase 2 (CK2) associated with a carboxy-terminal region of BRCA1. This association was much weaker with the same fragment bearing a missense mutation (M1775R) that has been identified in breast tumors. The interaction was also evident in Sf9 cells. Subsequent studies showed that BRCA1 was phosphorylated in vitro by CK2. An analysis by site directed mutagenesis of BRCA1 showed that in vitro phosphorylation by CK2 required a serine at aa1572. These data implicate CK2 as a potential mediator of BRCA1 activity.

    Biochemical and biophysical research communications 1999;260;3;658-64

  • Heterogeneous nuclear ribonucleoprotein A2 interacts with protein kinase CK2.

    Pancetti F, Bosser R, Krehan A, Pyerin W, Itarte E and Bachs O

    Facultat de Medicina, Institut d'Investigacions Biomèdiques August Pi Sunyer (IDIBAPS), Barcelona, Spain.

    The catalytic subunit of protein kinase CK2 (CK2alpha) was found associated with heterogeneous nuclear ribonucleoprotein particles (hnRNPs) that contain the core proteins A2 and C1-C2. High levels of CK2 activity were also detected in these complexes. Phosphopeptide patterns of hnRNP A2 phosphorylated in vivo and in vitro by protein kinase CK2 were similar, suggesting that this kinase can phosphorylate hnRNPA2 in vivo. Binding experiments using human recombinant hnRNP A2, free human recombinant CK2alpha or CK2beta subunits, reconstituted CK2 holoenzyme and purified native rat liver CK2 indicated that hnRNP A2 associated with both catalytic and regulatory CK2 subunits, and that the interaction was independent of the presence of RNA. However, the capability of hnRNP A2 to bind to CK2 holoenzyme was lower than its binding to the isolated subunits. These data indicate that the association of CK2alpha with CK2beta interferes with the subsequent binding of hnRNP A2. HnRNP A2 inhibited the autophosphorylation of CK2beta. This effect was stronger with reconstituted human recombinant CK2 than with purified native rat liver CK2.

    Biochemical and biophysical research communications 1999;260;1;17-22

  • Partial nuclear localization of a bovine phosphoprotein, BCNT, that includes a region derived from a LINE repetitive sequence in Ruminantia.

    Iwashita S, Nobukuni T, Tanaka S, Kobayashi M, Iwanaga T, Tamate HB, Masui T, Takahashi I and Hashimoto K

    Mitsubishi Kasei Institute of Life Sciences, 11 Minamiooya, Machida-shi, Tokyo 194, Japan. siwast@libra.ls.m-kagaku.co.jp

    BCNT, named after Bucentaur, is a protein that contains a 324-amino-acid region derived from part of a long interspersed DNA sequence element (LINE) in Ruminantia. However, the unique portion is completely missing in human and mouse BCNTs. Since no significant information on their function has been obtained by homology search, we at first examined cellular localization and biochemical characteristics of bovine BCNT to get a hint on its function. Subcellular fractionation and immunohistochemical analyses using a normal bovine epithelial cell line and bovine brain revealed that a significant amount of bovine BCNT is localized in the nuclei, while the major portion is present in the cytosol. Furthermore, it was shown that bovine BCNT is a phosphoprotein and that both bovine and human BCNTs are phosphorylated by casein kinase II in vitro. These results show that BCNTs consist of a unique family, probably a substrate of casein kinase II, which may contribute further to the understanding of gene evolution.

    Biochimica et biophysica acta 1999;1427;3;408-16

  • The double-stranded RNA activated protein kinase PKR physically associates with the tumor suppressor p53 protein and phosphorylates human p53 on serine 392 in vitro.

    Cuddihy AR, Wong AH, Tam NW, Li S and Koromilas AE

    Department of Oncology, McGill University, Montreal, Quebec, Canada.

    The tumor suppressor p53 is a multifunctional protein that plays a critical role in modulating cellular responses upon DNA damage or other stresses. These functions of p53 are regulated both by protein-protein interactions and phosphorylation. The double-stranded RNA activated protein kinase PKR is a serine/threonine kinase that modulates protein synthesis through the phosphorylation of translation initiation factor eIF-2alpha. PKR is an interferon (IFN)-inducible protein that is thought to mediate the anti-viral and anti-proliferative effects of IFN via its capacity to inhibit protein synthesis. Here we report that PKR physically associates with p53. The interaction of PKR with p53 is enhanced by IFNs and upon conditions that p53 acquires a wild type conformation. PKR/p53 complex formation in vitro requires the N-terminal regulatory domain of PKR and the last 30 amino acids of the C-terminus of human p53. In addition, p53 may function as a substrate of PKR since phosphorylation of human p53 on serine392 is induced by activated PKR in vitro. These novel findings raise the possibility of a functional interaction between PKR and p53 in vivo, which may account, at least in part, for the ability of each protein to regulate gene expression at both the transcriptional and the translational levels.

    Oncogene 1999;18;17;2690-702

  • Phosphorylation of CD45 by casein kinase 2. Modulation of activity and mutational analysis.

    Wang Y, Guo W, Liang L and Esselman WJ

    Department of Microbiology, Michigan State University, East Lansing, Michigan 48824-1101, USA.

    CD45 is a receptor-type protein-tyrosine phosphatase (PTP) that is required for antigen-specific stimulation and proliferation in lymphocytes. This study was designed to determine the nature of specific kinases in lymphocytes that phosphorylate CD45 and to determine the effect of phosphorylation on CD45 PTP activity. A major cytoplasmic lymphocyte kinase that phosphorylated CD45 was identified as casein kinase 2 (CK2) by use of an in-gel kinase assay in combination with immunoprecipitation, immunodepletion, and specific inhibition. Mutational analysis of CK2 consensus sites showed that the target for CK2 was in an acidic insert of 19 amino acids in the D2 domain, and Ser to Ala mutations at amino acids 965, 968, 969, and 973 abrogated CK2 phosphorylation of CD45. CK2 phosphorylation increased CD45 activity 3-fold toward phosphorylated myelin basic protein, and this increase was reversible by PP2A treatment. Mutation of Ser to Glu at the CK2 sites had the same effect as phosphorylation and also tripled the Vmax of CD45. CD45 isolated in vivo was highly phosphorylated and could not be phosphorylated by CK2 without prior dephosphorylation with phosphatase PP2A. We conclude that CK2 is a major lymphocyte kinase that is responsible for in vivo phosphorylation of CD45, and phosphorylation at specific CK2 sites regulates CD45 PTP activity.

    Funded by: NIAID NIH HHS: AI/GM42794

    The Journal of biological chemistry 1999;274;11;7454-61

  • Phosphorylation of presenilin-2 regulates its cleavage by caspases and retards progression of apoptosis.

    Walter J, Schindzielorz A, Grünberg J and Haass C

    Central Institute of Mental Health, Department of Molecular Biology, J5, 68159 Mannheim, Germany.

    Mutations within the Presenilin-2 (PS-2) gene are associated with early onset familial Alzheimer's disease. The gene encodes a polytopic transmembrane protein that undergoes endoproteolytic processing resulting in the generation of N-terminal and C-terminal fragments (CTFs). PS-2 is also cleaved by proteases of the caspase family during apoptotic cell death. CTFs of PS-2 were shown to inhibit apoptosis, suggesting an important role in the regulation of programmed cell death. Recently, we found that the CTF of PS-2 is phosphorylated in vivo. We mapped the in vivo phosphorylation sites of PS-2 to serine residues 327 and 330, which are localized immediately adjacent to the cleavage sites of caspases after aspartate residues 326 and 329. Phosphorylation of PS-2 inhibits its cleavage by caspase-3. This effect can be mimicked by substitutions of serines 327 and 330 by aspartate or glutamate. In addition, the uncleavable form of PS-2 CTF was found to enhance its antiapoptotic properties, leading to a slower progression of apoptosis. These results demonstrate that PS-2 cleavage as well as its function in apoptosis can be regulated by protein phosphorylation. Alterations in the phosphorylation of PS-2 may therefore promote the pathogenesis of AD by affecting the susceptibility of neurons to apoptotic stimuli.

    Proceedings of the National Academy of Sciences of the United States of America 1999;96;4;1391-6

  • Differential phosphorylation of syntaxin and synaptosome-associated protein of 25 kDa (SNAP-25) isoforms.

    Risinger C and Bennett MK

    Department of Molecular and Cell Biology, University of California, Berkeley 94720, USA.

    The synaptic plasma membrane proteins syntaxin and synaptosome-associated protein of 25 kDa (SNAP-25) are central participants in synaptic vesicle trafficking and neurotransmitter release. Together with the synaptic vesicle protein synaptobrevin/vesicle-associated membrane protein (VAMP), they serve as receptors for the general membrane trafficking factors N-ethylmaleimide-sensitive factor (NSF) and soluble NSF attachment protein (alpha-SNAP). Consequently, syntaxin, SNAP-25, and VAMP (and their isoforms in other membrane trafficking pathways) have been termed SNAP receptors (SNAREs). Because protein phosphorylation is a common and important mechanism for regulating a variety of cellular processes, including synaptic transmission, we have investigated the ability of syntaxin and SNAP-25 isoforms to serve as substrates for a variety of serine/threonine protein kinases. Syntaxins 1 A and 4 were phosphorylated by casein kinase II, whereas syntaxin 3 and SNAP-25 were phosphorylated by Ca2+- and calmodulin-dependent protein kinase II and cyclic AMP-dependent protein kinase, respectively. The biochemical consequences of SNARE protein phosphorylation included a reduced interaction between SNAP-25 and phosphorylated syntaxin 4 and an enhanced interaction between phosphorylated syntaxin 1A and the synaptic vesicle protein synaptotagmin I, a potential Ca2+ sensor in triggering synaptic vesicle exocytosis. No other effects on the formation of SNARE complexes (comprised of syntaxin, SNAP-25, and VAMP) or interactions involving n-Sec1 or alpha-SNAP were observed. These findings suggest that although phosphorylation does not directly regulate the assembly of the synaptic SNARE complex, it may serve to modulate SNARE complex function through other proteins, including synaptotagmin I.

    Funded by: NIGMS NIH HHS: GM-51313

    Journal of neurochemistry 1999;72;2;614-24

  • Phosphorylation of the DNA repair protein APE/REF-1 by CKII affects redox regulation of AP-1.

    Fritz G and Kaina B

    Division of Applied Toxicology, Institute of Toxicology, University of Mainz, Germany.

    The DNA repair protein apurinic endonuclease (APE/Ref-1) exerts several physiological functions such as cleavage of apurinic/apyrimidinic sites and redox regulation of the transcription factor AP-1, whose activation is part of the cellular response to DNA damaging treatments. Here we demonstrate that APE/Ref-1 is phosphorylated by casein kinase II (CKII). This was shown for both the recombinant APE/Ref-1 protein (Km=0.55 mM) and for APE/Ref-1 expressed in COS cells. Phosphorylation of APE/Ref-1 did not alter the repair activity of the enzyme, whereas it stimulated its redox capability towards AP-1, thus promoting DNA binding activity of AP-1. Inhibition of CKII mediated phosphorylation of APE/Ref-1 blocked mutagen-stimulated increase in AP-1 binding. It also abrogated the induction of c-Jun protein and rendered cells more sensitive to induced DNA damage. Thus, phosphorylation of APE/Ref-1 appears to be involved in regulating the different physiological activities of the enzyme. CKII mediated phosphorylation of APE/Ref-1 and concomitant increase in AP-1 binding activity appears to be a novel mechanism of cellular stress response, forcing transcription of AP-1 target gene(s) the product(s) of which may exert protective function.

    Oncogene 1999;18;4;1033-40

  • A structural model for elongation factor 1 (EF-1) and phosphorylation by protein kinase CKII.

    Sheu GT and Traugh JA

    Department of Biochemistry and Genetics Graduate Group, University of California, Riverside 92521, USA.

    EF-1alpha binds aminoacyl-tRNA to the ribosome with the hydrolysis of GTP; the betagammadelta complex facilitates the exchange of GDP for GTP to initiate another round of elongation. To examine the subunit structure of EF-1 and phosphorylation by protein kinase CKII, recombinant beta, gamma, and delta subunits from rabbit were expressed in E. coli and the subunits were reconstituted into partial and complete complexes and analyzed by gel filtration. To determine the availability of the beta and delta subunits for phosphorylation by CKII, the subunits and the reconstituted complexes were examined as substrates for CKII. Formation of the nucleotide exchange complex increased the rate of phosphorylation of the beta subunit and reduced the Km, while addition of alpha to beta or the betagammacomplex inhibited phosphorylation by CKII. However, alpha had little effect on phosphorylation of delta. Thus, the beta and delta subunits in EF-1 were differentially phosphorylated by CKII, in that phosphorylation of beta was altered by association with other subunits, while the site on delta was always available for phosphorylation by CKII. From the availability of the subunits for phosphorylation by CKII and the composition of the reconstituted partial and complete complexes, a model for the subunit structure of EF-1 consisting of(alpha2betagamma2delta)2 is proposed and discussed.

    Molecular and cellular biochemistry 1999;191;1-2;181-6

  • Identification of the in vivo casein kinase II phosphorylation site within the homeodomain of the cardiac tisue-specifying homeobox gene product Csx/Nkx2.5.

    Kasahara H and Izumo S

    Cardiovascular Division, Beth Israel Deaconess Medical Center and Department of Medicine, Harvard Medical School, Boston, Massachusetts 02215, USA.

    Csx/Nkx2.5, a member of the homeodomain-containing transcription factors, serves critical developmental functions in heart formation in vertebrates and nonvertebrates. In this study the putative nuclear localization signal (NLS) of Csx/Nkx2.5 was identified by site-directed mutagenesis to the amino terminus of the homeodomain, which is conserved in almost all homeodomain proteins. When the putative NLS of Csx/Nkx2.5 was mutated a significant amount of the cytoplasmically localized Csx/Nkx2.5 was unphosphorylated, in contrast to the nuclearly localized Csx/Nkx2.5, which is serine- and threonine-phosphorylated, suggesting that Csx/Nkx2.5 phosphorylation is regulated, at least in part, by intracellular localization. Tryptic phosphopeptide mapping indicated that Csx/Nkx2.5 has at least five phosphorylation sites. Using in-gel kinase assays, we detected a Csx/Nkx2.5 kinase whose molecular mass is approximately 40 kDa in both cytoplasmic and nuclear extracts. Mutational analysis and in vitro kinase assays suggested that this 40-kDa Csx/Nkx2.5 kinase is a catalytic subunit of casein kinase II (CKII) that phosphorylates the serine residue between the first and second helix of the homeodomain. This CKII site is phosphorylated in vivo. CKII-dependent phosphorylation of the homeodomain increased Csx/Nkx2. 5 DNA binding. Serine-to-alanine mutation at the CKII phosphorylation site reduced transcriptional activity when the carboxyl-terminal repressor domain was deleted. Although the precise biological function of Csx/Nkx2.5 phosphorylation by CKII remains to be determined, it may play an important role, as this CKII phosphorylation site within the homeodomain is fully conserved in all known members of the NK2 family of the homeobox genes.

    Funded by: NHLBI NIH HHS: HL51253

    Molecular and cellular biology 1999;19;1;526-36

  • Interactions of protein kinase CK2beta subunit within the holoenzyme and with other proteins.

    Kusk M, Ahmed R, Thomsen B, Bendixen C, Issinger OG and Boldyreff B

    Biokemisk Institut, Odense Universitet, Denmark.

    Protein kinase CK2 is a ubiquitous, highly conserved protein kinase with a tetrameric alpha2beta2 structure. For the formation of this tetrameric complex a beta-alpha dimer seems to be a prerequisite. Using the two-hybrid system and a series of CK2beta deletion mutants, we mapped domains involved in alpha-beta and beta-beta interactions. We also detected an intramolecular beta interaction within the amino acid stretch 132-165. Using CK2beta as a bait in a two-hybrid library screening several new putative cellular partners have been identified, among them the S6 kinase p90rsk, the putative tumor suppressor protein Doc-1, the Fas-associated protein FAF1, the mitochondrial translational initiation factor 2 and propionyl CoA carboxylase beta subunit.

    Molecular and cellular biochemistry 1999;191;1-2;51-8

  • Molecular cloning and regional distribution of a human proton receptor subunit with biphasic functional properties.

    Babinski K, Lê KT and Séguéla P

    Cell Biology of Excitable Tissue Group, Montreal Neurological Institute, McGill University, Quebec, Canada.

    Small changes of extracellular pH activate depolarizing inward currents in most nociceptive neurons. It has been recently proposed that acid sensitivity of sensory as well as central neurons is mediated by a family of proton-gated cation channels structurally related to Caenorhabditis elegans degenerins and mammalian epithelial sodium channels. We describe here the molecular cloning of a novel human proton receptor, hASIC3, a 531-amino acid-long subunit homologous to rat DRASIC. Expression of homomeric hASIC3 channels in Xenopus oocytes generated biphasic inward currents elicited at pH <5, providing the first functional evidence of a human proton-gated ion channel. Contrary to the DRASIC current phenotype, the fast desensitizing early component and the slow sustained late component differed both by their cationic selectivity and by their response to the antagonist amiloride, but not by their pH sensitivity (pH50 = 3.66 vs. 3.82). Using RT-PCR and mRNA blot hybridization, we detected hASIC3 mRNA in sensory ganglia, brain, and many internal tissues including lung and testis, so hASIC3 gene expression was not restricted to peripheral sensory neurons. These functional and anatomical data strongly suggest that hASIC3 plays a major role in persistent proton-induced currents occurring in physiological and pathological conditions of pH changes, likely through a tissue-specific heteropolymerization with other members of the proton-gated channel family.

    Journal of neurochemistry 1999;72;1;51-7

  • Human CD5 signaling and constitutive phosphorylation of C-terminal serine residues by casein kinase II.

    Calvo J, Vildà JM, Places L, Simarro M, Padilla O, Andreu D, Campbell KS, Aussel C and Lozano F

    Servei d'Immunologia, Institut d'Investigacions Biomédiques August Pii Sunger, Hospital Clínic, Barcelona, Spain.

    CD5 is a lymphocyte surface glycoprotein with a long cytoplasmic domain suitable for phosphorylation and signal transduction, which is involved in the modulation of Ag-specific receptor-mediated activation and differentiation signals. In this study, we use Jurkat T cell transfectants of CD5 cytoplasmic tail mutants to reveal phosphorylation sites relevant to signal transduction. Our results show that casein kinase II (CKII) is responsible for the constitutive phosphorylation of CD5 molecules at a cluster of three serine residues located at the extreme C terminus (S458, S459, and S461). Furthermore, the yeast two-hybrid system demonstrates the specific association between the C-terminal regions of the CD5 cytoplasmic tail and the regulatory beta subunit of CKII. We demonstrate that CKII associates with and phosphorylates the C-terminal region of CD5, a conserved domain known to be relevant for the generation of second lipid messengers, and thereby enables at least one component of its signaling function.

    Journal of immunology (Baltimore, Md. : 1950) 1998;161;11;6022-9

  • Biochemical characterization of recombinant HIV-1 reverse transcriptase (rRT) as a glycyrrhizin-binding protein and the CK-II-mediated stimulation of rRT activity potently inhibited by glycyrrhetinic acid derivative.

    Harada S, Maekawa T, Haneda E, Morikawa Y, Nagata N and Ohtsuki K

    Laboratory of Genetical Biochemistry, Kitasato University School of Allied Health Sciences, Sagamihara, Japan.

    By means of successive Mono Q and glycyrrhizin (GL)-affinity column chromatography (HPLC), recombinant HIV-1 RT (rRT) was purified to apparent homogeneity from the Superdex 200 pg fraction of the crude protein extract of E. coli BL21 transfected with pET 21a(+)/HIV-1 PR-RT. It was found that (i) rRT functioned as an effective phosphate acceptor for recombinant human casein kinase II (rhCK-II) in vitro; (ii) this phosphorylation was inhibited by anti-HIV-1 substances [a glycyrrhetinic acid derivative (oGA) and quercetin] and a high dose (100 microM) of GL; (iii) RNA-dependent DNA polymerase (RDDP) activity was stimulated about 2.5-fold after full phosphorylation of rRT by rhCK-II; and (iv) oGA as well as NCS-chromophore effectively prevented the CK-II-mediated stimulation of RDDP activity. These results suggest that the anti-HIV-1 effect of oGA may be involved in the selective inhibition of the CK-II-mediated stimulation of HIV-1 RT at the cellular level.

    Biological & pharmaceutical bulletin 1998;21;12;1282-5

  • Insulin-stimulated kinase from rat fat cells that phosphorylates initiation factor 4E-binding protein 1 on the rapamycin-insensitive site (serine-111).

    Heesom KJ, Avison MB, Diggle TA and Denton RM

    Department of Biochemistry, University of Bristol, School of Medical Sciences, Bristol, Avon BS81TD, UK.

    The effects of insulin and rapamycin on the phosphorylation of the translation regulator, initiation factor 4E-binding protein 1 (4E-BP1) have been studied in rat fat cells by following changes in the incorporation of 32P from [32P]Pi under steady-state conditions. Both unbound 4E-BP1 and 4E-BP1 bound to eukaryotic initiation factor 4E (eIF4E) were isolated from the cells and then digested with trypsin and other proteases; the radiolabelled phosphopeptides were then separated by two-dimensional thin- layer analysis and HPLC. The results provide confirmation of the conclusion of Fadden, Haystead and Lawrence [J. Biol. Chem. (1997) 272, 10240-10247] that insulin increases the phosphorylation of four sites that fit a Ser/Thr-Pro motif (Thr-36, Thr-45, Ser-64 and Thr-69) and that taken together these phosphorylations result in the dissociation of 4E-BP1 from eIF4E. The effects of insulin on the phosphorylation of these sites, and hence dissociation from eIF4E, are blocked by rapamycin. However, the present study also provides evidence that insulin increases the phosphorylation of 4E-BP1 bound to eIF4E on a further site (Ser-111) and that this is by a rapamycin-insensitive mechanism. Extraction of rat epididymal fat cells followed by chromatography on Mono-S and Superose 12 columns resulted in the separation of both an insulin-stimulated eIF4E kinase and an apparently novel kinase that is highly specific for Ser-111 of 4E-BP1. The 4E-BP1 kinase was activated more than 10-fold by incubation of the cells with insulin and was markedly more active towards 4E-BP1 bound to eIF4E than towards unbound 4E-BP1. The effects of insulin were blocked by wortmannin, but not by rapamycin. A 14-mer peptide based on the sequence surrounding Ser-111 of 4E-BP1 was also a substrate for the kinase, but peptide substrates for other known protein kinases were not. The kinase is quite distinct from casein kinase 2, which also phosphorylates Ser-111 of 4E-BP1. The possible importance of these kinases in the phosphorylation of 4E-BP1 in fat cells is discussed. It is suggested that the phosphorylation of Ser-111 might be a priming event that facilitates the subsequent phosphorylation of Thr-36, Thr-45, Ser-64 and Thr69 by a rapamycin-sensitive process that initiates the dissociation of 4E-BP1 from eIF4E and hence the formation of the eIF4F complex.

    Funded by: Wellcome Trust

    The Biochemical journal 1998;336 ( Pt 1);39-48

  • Casein kinase II catalyzes a mitotic phosphorylation on threonine 1342 of human DNA topoisomerase IIalpha, which is recognized by the 3F3/2 phosphoepitope antibody.

    Daum JR and Gorbsky GJ

    Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA.

    The 3F3/2 antibody recognizes a phosphoepitope that is implicated in the mitotic checkpoint regulating the metaphase-to-anaphase transition. Immunoprecipitation and Western blotting revealed that the 3F3/2 antibody binds to human DNA topoisomerase II alpha (HsTIIalpha) from mitotic but not interphase HeLa cells. Extracts from mitotic cells efficiently catalyzed the formation of the 3F3/2 phosphoepitope on fragments of HsTIIalpha expressed in bacteria. Expression and site-directed mutagenesis of various HsTIIalpha protein fragments mapped the 3F3/2 phosphoepitope to the region of HsTIIalpha containing phosphorylated threonine 1342. This threonine lies within a consensus sequence for phosphorylation by casein kinase II (CKII). CKII is present in cellular extracts and is associated with isolated mitotic chromosomes. The 3F3/2 phosphoepitope kinase present in mitotic cell extracts was able to create the epitope using GTP and was inhibited by heparin. A kinase associated with the isolated chromosomes also generated the 3F3/2 phosphoepitope on HsTIIalpha. Recombinant CKII catalyzed the formation of the 3F3/2 phosphoepitope on fragments of HsTIIalpha containing threonine 1342. These results indicate that the mitotic 3F3/2 phosphoepitope kinase activity is attributable to CKII. We suggest that the 3F3/2 phosphoepitope reflects a CKII-catalyzed phosphorylation of threonine 1342 that may regulate mitotic functions of HsTIIalpha.

    Funded by: NIGMS NIH HHS: R01GM50412

    The Journal of biological chemistry 1998;273;46;30622-9

  • Phosphorylation of vitronectin by casein kinase II. Identification of the sites and their promotion of cell adhesion and spreading.

    Seger D, Gechtman Z and Shaltiel S

    Department of Biological Regulation, Weizmann Institute of Science, IL-76100 Rehovot, Israel.

    The cell adhesion protein vitronectin (Vn) was previously shown to be the major target in human blood for an extracellular protein kinase A, which is released from platelets upon their physiological stimulation with thrombin and also prevails as an ectoenzyme in several other types of blood cells. Because plasma Vn was shown to have only one protein kinase A phosphorylation site (Ser378) but to contain approximately 3 mol of covalently bound phosphate, and because human serum and blood cells were shown to contain also a casein kinase II (CKII) on their surface, we studied the phosphorylation of Vn by CKII attempting to find out whether such phosphorylation modulates Vn function, an acid test for its having a physiological relevance. Here we show (i) that the CKII phosphorylation of Vn has a Km of 0.5-2 microM (lower than the Vn concentration in blood, 3-6 microM), (ii) that it is targeted to Thr50 and Thr57, which are vicinal to the RGD site of Vn, and (iii) that the phosphorylation of Thr57 facilitates the phosphorylation of Thr50. The maximal stoichiometry of the CKII phosphorylation of plasma Vn was found to be low, which, in principle, could be due to its partial prephosphorylation in vivo. However, for the detection of a functional modulation, we needed a comparison between a fully phosphorylated Vn (at Thr57 and Thr50) and a nonphosphorylated Vn. Therefore, we expressed Vn in a baculovirus system and show (i) that the CKII phosphorylation of wt-Vn enhances the adhesion of bovine aorta endothelial cells; (ii) that the double mutant T50E/T57E (in which the neutral Thr residues are replaced by the negatively charged Glu residues considered analogs of Thr-P) has a significantly enhanced capacity to promote cell adhesion and to accelerate cell spreading when compared with either wild-type Vn or to the neutral T50A/T57A mutant; and (iii) that, at least in the case of bovine aorta endothelial cells, the T50E/T57E mutant exhibits an enhanced adhesion, which seems to be due to an increased affinity toward the alphav beta3 Vn receptors.

    The Journal of biological chemistry 1998;273;38;24805-13

  • Regulation of erythroid Krüppel-like factor (EKLF) transcriptional activity by phosphorylation of a protein kinase casein kinase II site within its interaction domain.

    Ouyang L, Chen X and Bieker JJ

    Brookdale Center for Molecular Biology, Mount Sinai School of Medicine, New York, New York 10029, USA.

    Erythroid Krüppel-like factor (EKLF) is a red cell-specific activator whose presence is crucial for establishing high levels of adult beta-globin expression in definitive cells during erythroid ontogeny. However, its simple presence within the erythroid lineage is not sufficient to activate the beta-globin promoter. One explanation that may account for this is that post-translational modification of EKLF differs within erythroid cell populations and regulates its activity. We have therefore addressed whether phosphorylation plays a role in modulating EKLF action. First, in vivo analyses implicate serine/threonine kinases as important players in the terminal differentiation of MEL cells, and demonstrate that EKLF is phosphorylated at serine and threonine residues within its transactivation region. Second, directed disruption of a protein kinase casein kinase (CK) II site, located within the EKLF interaction domain, abolishes EKLF transactivation and in vivo competition activity. Third, in vitro assays demonstrate that CKIIalpha interacts with EKLF, and that the EKLF interaction domain is phosphorylated by CKII only at Thr-41; however, the CKII-site mutant is not phosphorylated. Finally, the transactivation capability of EKLF is augmented by co-transfection of CKIIalpha. We conclude that EKLF is a phosphoprotein whose ability to transcriptionally activate an adjacent promoter is critically dependent on the phosphorylation status of a specific site located within the EKLF interaction domain, and that serine/threonine kinases play an important role in this process.

    Funded by: NIDDK NIH HHS: DK46865

    The Journal of biological chemistry 1998;273;36;23019-25

  • Casein kinase II interacts with the bZIP domains of several transcription factors.

    Yamaguchi Y, Wada T, Suzuki F, Takagi T, Hasegawa J and Handa H

    Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku,Yokohama 226-8501, Japan.

    Casein kinase II (CKII) is thought to regulate a broad range of transcription factors, but its mode of action is not well characterized. We previously showed that CKII is co-purified with the ATF family of transcription factors using DNA-affinity latex beads. Here we report a functional and physical interaction between CKII and transcription factors. We demonstrate that CKII binds through its catalytic alpha and alpha' subunits to the basic leucine zipper (bZIP) DNA-binding domains of many transcription factors, including ATF1. Kinetic analysis using a surface plasmon resonance sensor suggests that CKII loosely associates with ATF1 in vivo . Deletion of the bZIP domain of ATF1 markedly reduces its phosphorylation by CKII, suggesting that the bZIP recruits CKII to the vicinity of the target site. ATF1-CKII complex is also formed on DNA. Using CKIIalpha fusedto a heterologous DNA-binding domain, we also demonstrate that CKII, when bound to DNA, efficiently phosphorylates its substrate, which is bound to the same DNA molecule. Taken together, CKII may regulate transcription (and possibly other events) by phosphorylating proteins on DNA.

    Nucleic acids research 1998;26;16;3854-61

  • Effects of phosphorylation on function of the Rad GTPase.

    Moyers JS, Zhu J and Kahn CR

    Research Division, Joslin Diabetes Center, and Department of Medicine, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA.

    Rad, Gem and Kir possess unique structural features in comparison with other Ras-like GTPases, including a C-terminal 31-residue extension that lacks typical prenylation motifs. We have recently shown that Rad and Gem bind calmodulin in a Ca2+-dependent manner via this C-terminal extension, involving residues 278-297 in human Rad. This domain also contains several consensus sites for serine phosphorylation, and Rad is complexed with calmodulin-dependent protein kinase II (CaMKII) in C2C12 cells. Here we show that Rad serves as a substrate for phosphorylation by CaMKII, cAMP-dependent protein kinase (PKA), protein kinase C (PKC) and casein kinase II (CKII) with stoichiometries in vitro of 0.2-1.3 mol of phosphate/mol of Rad. By deletion and point mutation analysis we show that phosphorylation by CaMKII and PKA occurs on a single serine residue at position 273, whereas PKC and CKII phosphorylate multiple C-terminal serine residues, including Ser214, Ser257, Ser273, Ser290 and Ser299. Incubation of Rad with PKA decreases GTP binding by 60-70%, but this effect seems to be independent of phosphorylation, as it is observed with the Ser273-->Ala mutant of Rad containing a mutation at the site of PKA phosphorylation. The remainder of the serine kinases have no effect on Rad GTP binding, intrinsic GTP hydrolysis or GTP hydrolysis stimulated by the putative tumour metastasis suppressor nm23. However, phosphorylation of Rad by PKC and CKII abolishes the interaction of Rad with calmodulin. These findings suggest that the binding of Rad to calmodulin, as well as its ability to bind GTP, might be regulated by the activation of several serine kinases.

    Funded by: NIDDK NIH HHS: DK 45935, P30 DK36836, T32DK 07260

    The Biochemical journal 1998;333 ( Pt 3);609-14

  • Kell and Kx, two disulfide-linked proteins of the human erythrocyte membrane are phosphorylated in vivo.

    Carbonnet F, Hattab C, Cartron JP and Bertrand O

    INSERM U76, Institut National de la Transfusion Sanguine, Paris, France.

    Kell and Kx are two quantitatively minor proteins from the human erythrocyte membrane which carry blood groups antigens and are thought to be a metalloprotease and a membrane transporter, respectively. In the red cell membrane, these proteins form a complex stabilized by disulfide bond(s). Phosphorylation status of these proteins was studied, in the presence or absence of effectors of several kinases, either on intact cells incubated with [32P]-orthophosphate or on ghosts incubated with [gamma-32P]ATP. Purification of Kell-Kx complex, by immunochromatography on an immobilized human monoclonal antibody of Kell blood group specificity allowed to establish that (i) neither protein is phosphorylated on tyrosine; (ii) the Kell protein is a putative substrate for Casein Kinase II (CKII) and Casein Kinase I (CKI) but not for protein kinase C (PKC), whereas Kx protein is phosphorylated by CKII and PKC but not by CKI; (iii) Protein Kinase A neither phosphorylates the Kell nor the Kx proteins.

    Biochemical and biophysical research communications 1998;247;3;569-75

  • Biochemical characterization of HIV-1 Rev as a potent activator of casein kinase II in vitro.

    Ohtsuki K, Maekawa T, Harada S, Karino A, Morikawa Y and Ito M

    Laboratory of Genetical Biochemistry, Kitasato University School of Allied Health Sciences, Sagamihara, Japan. ken@medcc.kitasato-u.ac.jp

    The stimulatory effects of several DNA-binding basic proteins (histone and protamine) and HIV-1 Rev with arginine (Arg)-rich clusters on the activity of casein kinase II (CK-II) were investigated in vitro. It was found that recombinant Rev (rRev) and the synthetic oligo-fragments corresponding to the amino acid sequences of its Arg-rich cluster stimulate CK-II activity in a dose-dependent manner. The activated CK-II phosphorylates several cellular and viral proteins in HIV-1 infected human MOLT-4 cells, and also phosphorylates HIV-1 structural proteins, including recombinant reverse transcriptase (rRT). These phosphorylations are selectively inhibited by CK-II inhibitors, such as quercetin, oGA (a glycyrrhetinic acid derivative) and NCS-chrom (an enediyne containing antibiotic). The data presented here suggest that HIV-1 Rev acts as an effective potent activator of CK-II, which may be a cellular mediator promoting HIV-1 replication in virus-infected cells.

    FEBS letters 1998;428;3;235-40

  • Multiple phosphorylation of chicken protein tyrosine phosphatase 1 and human protein tyrosine phosphatase 1B by casein kinase II and p60c-src in vitro.

    Jung EJ, Kang YS and Kim CW

    Department of Biochemistry, College of Medicine, Gyeongsang National University, Chinju, Korea.

    We have cloned a soluble chicken protein tyrosine phosphatase, named CPTP1, from the cDNA library of chicken intestine. The CPTP1 showed 92% sequence identity to the corresponding 321 amino acid residues of human PTP1B (HPTP1B). CPTP1 lacked 13 amino acids of the N-terminal region compared with HPTP1B, while the C-terminal 48 amino acid sequence of this protein was distinct from those of other PTPs. In vitro phosphorylation and phosphoamino acid analysis showed that both CPTP1 and HPTP1B were phosphorylated on serine and threonine residues near their N-terminus by casein kinase II (CKII). Furthermore, phosphorylation of CPTP1 by CKII resulted in an inhibition of its phosphatase activity in vitro. Interestingly, both CPTP1 and HPTP1B were also tyrosine-phosphorylated near their N-terminus by p60c-src. When we examined the vanadate effect, in the absence of vanadate, the tyrosine-phosphorylated CPTP1 by p60c-src was autodephosphorylated by its own phosphatase activity. These results suggest that both CPTP1 and HPTP1B might play an important role in CKII- and p60c-src-induced signal transduction cascades.

    Biochemical and biophysical research communications 1998;246;1;238-42

  • Proteolytic fragments of the Alzheimer's disease associated presenilins-1 and -2 are phosphorylated in vivo by distinct cellular mechanisms.

    Walter J, Grünberg J, Schindzielorz A and Haass C

    Department of Molecular Biology, Central Institute of Mental Health, Mannheim, Germany.

    The majority of familial Alzheimer's disease mutations are linked to the recently cloned presenilin (PS) genes, which encode two highly homologous proteins (PS-1 and PS-2). Full-length PS proteins undergo endoproteolytic cleavage within their hydrophilic loop domain resulting in the formation of C-terminal (CTF) and N-terminal fragments (NTF). PS-2 was found to be phosphorylated as a full-length protein within its N-terminal domain. In contrast, PS-1 is phosphorylated selectively after proteolytic processing within its approximately 20 kDa CTF involving protein kinase C (PKC) and/or protein kinase A (PKA). We now have found that the CTF of the highly homologous PS-2 is also phosphorylated. Surprisingly, the PS-2 CTF is not phosphorylated by PKC or PKA. Instead, the PS-2 CTF is constitutively phosphorylated in vivo by serine/threonine protein kinases, which are independent of phorbol ester and intracellular cAMP. In vitro the large hydrophilic loop of PS-2 between transmembrane domains 6 and 7 can be phosphorylated by casein kinase-1 (CK-1) and CK-2, but not by PKA or PKC. Quantitative analysis of in vitro phosphorylation demonstrates the presence of two phosphorylation sites for CK-1 and a single site for CK-2. A deletion analysis revealed that the CTF of PS-2 is phosphorylated in vivo within an acidic sequence containing three potential phosphorylation sites for CKs (serines 327, 330, and 335). These data suggest that CK type protein kinases phosphorylate the CTF of PS-2 within its hydrophilic loop domain in vivo. Interestingly, the potential phosphorylation sites are located directly adjacent to the recently identified caspase cleavage sites.

    Biochemistry 1998;37;17;5961-7

  • Identification and partial characterization of factor Va heavy chain kinase from human platelets.

    Kalafatis M

    Department of Biochemistry, University of Vermont, College of Medicine, Burlington, Vermont 05405-0068, USA. m.kalafatis@csuohio.edu

    Factor Va, the essential cofactor for prothrombinase, is phosphorylated on the acidic COOH terminus of the heavy chain of the cofactor, at Ser692, by a platelet membrane-associated casein kinase II (CKII). Consistent with this observation, phosphorylation of the factor Va heavy chain by the platelet kinase was inhibited by heparin. The membrane-associated platelet CKII kinase was partially purified using heparin-agarose, phosphocellulose, and ion exchange chromatography. CKII antigen was monitored using a polyclonal antibody to the alpha-subunit, and kinase activity in the various fractions was confirmed using human factor Va as a substrate. Immunoblotting experiments using polyclonal antibodies raised against synthetic peptides mimicking a portion of the deduced amino acid sequence of the alpha-, alpha'-, and beta-subunits of human CKII demonstrated the coexistence of both alpha- and alpha'-subunits in platelets and suggested that the platelet CKII kinase may exist in part as an alpha alpha'beta2 complex. It is also possible that there are two distinct populations of CKII in platelets, one that is alphaalpha/betabeta and one that is alpha'alpha'/betabeta. In the presence of the purified platelet-derived CKII, human factor Va incorporates between 0.8 and 1.3 mol of phosphate/mol of factor Va depending on the concentration of the beta-subunit in the kinase preparation. A peptide mimicking the sequence 687-705 of the human factor V molecule incorporates radioactivity in the presence of purified CKII and inhibits factor Va heavy chain phosphorylation by the platelet CKII. In contrast, a peptide with an alanine instead of a serine at position 692 neither incorporates phosphate nor inhibits factor Va phosphorylation by the platelet CKII. Human factor Va is inactivated by activated protein C following three cleavages of the heavy chain at Arg506, Arg306, and Arg679. Cleavage at Arg506 is necessary for efficient exposure of the inactivating cleavage site at Arg306. The phosphorylated cofactor has increased susceptibility to inactivation by activated protein C, since phosphorylated factor Va was found to be inactivated approximately 3-fold faster than its native counterpart. Acceleration of the inactivation process of the phosphorylated cofactor occurs because of acceleration of the rate of cleavage at Arg506. These data suggest a critical role for factor Va phosphorylation on the surface of platelets in regulating cofactor activity.

    The Journal of biological chemistry 1998;273;14;8459-66

  • Characterization of protein interaction among subunits of protein kinase CKII in vivo and in vitro.

    Kim MS, Lee YT, Kim JM, Cha JY and Bae YS

    Department of Biochemistry, College of Natural Sciences, Kyungpook National University, Taegu, Korea.

    Protein kinase CKII (CKII) is a ubiquitous protein serine/threonine kinase. CKII usually exists in tetrameric complexes composed of two catalytic (CKII alpha and/or CKII alpha') and two regulatory (CKII beta) subunits. In the present study, using a combined in vivo and in vitro approach, we have investigated the role of CKII subunits in the formation of the tetrameric structure of CKII and the formation of the polymeric structure of CKII holoenzyme. Our in vivo experiments show that CKII beta interacts with either another CKII beta or CKII alpha and that CKII alpha does not interact with another CKII alpha (or CKII alpha'). Our in vitro experiments also show that CKII beta is able to associate with both CKII alpha and another CKII beta and that CKII alpha exists as a monomeric form in solution. These data indicate that CKII beta mediates the formation of a tetramer by both the dimerization of CKII beta and the interaction of CKII beta with CKII alpha. The results of this study also suggest that CKII beta may be involved in the formation of the polymeric structure of the CKII holoenzyme.

    Molecules and cells 1998;8;1;43-8

  • Genomic organization and promoter identification of the human protein kinase CK2 catalytic subunit alpha (CSNK2A1).

    Wirkner U, Voss H, Ansorge W and Pyerin W

    Deutsches Krebsforschungszentrum, Heidelberg, Germany.

    The isolation and characterization of the complete gene coding for human protein kinase CK2 catalytic subunit alpha is described. The gene spans 70 kb and consists of 13 exons, and the exon/intron boundaries conform to the gt/ag rule. Exons range in size from 51 to 2960 bp, introns from 527 to around 34000 bp. The translation start site is located in Exon 2, the stop codon in Exon 13. Two transcription start sites were identified by primer extension analysis: The further 5'-located site defines position 1 of the gene, the second site is located at position 50. The 5' region of the CK2 alpha gene shows features of a housekeeping promoter, such as lack of a TATA box and presence of a CpG island and GC boxes. The region was analyzed by reporter gene assay, and promoter activity was detected within the region ranging from position -256 to 144. Six potential polyadenylation signals were identified in the 3' noncoding region of the CK2 alpha gene. As indicated by comparison with expressed sequence tags from the EMBL databank and by Northern-blot analysis, the most 3' located, active polyadenylation signal seems to be the fourth signal, defining the end of the gene.

    Genomics 1998;48;1;71-8

  • DNA binding by cut homeodomain proteins is down-modulated by casein kinase II.

    Coqueret O, Martin N, Bérubé G, Rabbat M, Litchfield DW and Nepveu A

    Molecular Oncology Group, McGill University, Royal Victoria Hospital, Montreal, Quebec H3A 1A1, Canada.

    The Drosophila and mammalian Cut homeodomain proteins contain, in addition to the homeodomain, three other DNA binding regions called Cut repeats. Cut-related proteins thus belong to a distinct class of homeodomain proteins with multiple DNA binding domains. Using nuclear extracts from mammalian cells, Cut-specific DNA binding was increased following phosphatase treatment, suggesting that endogenous Cut proteins are phosphorylated in vivo. Sequence analysis of Cut repeats revealed the presence of sequences that match the consensus phosphorylation site for casein kinase II (CKII). Therefore, we investigated whether CKII can modulate the activity of mammalian Cut proteins. In vitro, a purified preparation of CKII efficiently phosphorylated Cut repeats causing an inhibition of DNA binding. In vivo, overexpression of the CKII alpha and beta caused a decrease in DNA binding by Cut. The CKII phosphorylation sites within the murine Cut (mCut) protein were identified by in vitro mutagenesis as residues Ser400, Ser789, and Ser972 within Cut repeat 1, 2, and 3, respectively. Cut homeodomain proteins were previously shown to function as transcriptional repressors. Overexpression of CKII reduced transcriptional repression by mCut, whereas a mutant mCut protein containing alanine substitutions at these sites was not affected. Altogether our results indicate that the transcriptional activity of Cut proteins is modulated by CKII.

    The Journal of biological chemistry 1998;273;5;2561-6

  • Properties and phosphorylation sites of baculovirus-expressed nuclear inhibitor of protein phosphatase-1 (NIPP-1).

    Vulsteke V, Beullens M, Waelkens E, Stalmans W and Bollen M

    Afdeling Biochemie, Faculteit Geneeskunde, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.

    NIPP-1 is the RNA-binding subunit of a major species of protein phosphatase-1 in the nucleus. We have expressed nuclear inhibitor of protein phosphatase-1 (NIPP-1) in Sf9 cells, using the baculovirus-expression system. The purified recombinant protein was a potent (Ki = 9.9 +/- 0.3 pM) and specific inhibitor of protein phosphatase-1 and was stoichiometrically phosphorylated by protein kinases A and CK2. At physiological ionic strength, phosphorylation by these protein kinases drastically decreased the inhibitory potency of free NIPP-1. Phosphorylation of NIPP-1 in a heterodimeric complex with the catalytic subunit of protein phosphatase-1 resulted in an activation of the holoenzyme without a release of NIPP-1. Sequencing and phosphoamino acid analysis of tryptic phosphopeptides enabled us to identify Ser178 and Ser199 as the phosphorylation sites of protein kinase A, whereas Thr161 and Ser204 were phosphorylated by protein kinase CK2. These residues all conform to consensus recognition sites for phosphorylation by protein kinases A or CK2 and are clustered near a RVXF sequence that has been identified as a motif that interacts with the catalytic subunit of protein phosphatase-1.

    The Journal of biological chemistry 1997;272;52;32972-8

  • Phosphorylation of the immunosuppressant FK506-binding protein FKBP52 by casein kinase II: regulation of HSP90-binding activity of FKBP52.

    Miyata Y, Chambraud B, Radanyi C, Leclerc J, Lebeau MC, Renoir JM, Shirai R, Catelli MG, Yahara I and Baulieu EE

    Institut National de la Santé et de la Recherche Médicale Unité 33, 94276 Le Kremlin-Bicêtre Cédex, France. L50951@sakura.dudpc.kyoto-u.ac.jp

    FKBP52 (HSP56, p59, HBI) is the 59-kDa immunosuppressant FK506-binding protein and has peptidyl prolyl isomerase as well as a chaperone-like activity in vitro. FKBP52 associates with the heat shock protein HSP90 and is included in the steroid hormone receptor complexes in vivo. FKBP52 possesses a well conserved phosphorylation site for casein kinase II (CK2) that was previously shown to be associated with HSP90. Here we examined whether FKBP52 is phosphorylated by CK2 both in vivo and in vitro. Recombinant rabbit FKBP52 was phosphorylated by purified CK2. We expressed and purified deletion mutants of FKBP52 to determine the site(s) phosphorylated by CK2. Thr-143 in the hinge I region was identified as the major phosphorylation site for CK2. A synthetic peptide corresponding to this region was phosphorylated by CK2, and the peptide competitively inhibited the phosphorylation of other substrates by CK2. The [32P]phosphate labeling of FKBP52-expressing cells revealed that the same site is also phosphorylated in vivo. FK506 binding to FKBP52 did not affect the phosphorylation by CK2 and, conversely, the FK506-binding activity of FKBP52 was not affected by the phosphorylation. Most importantly, CK2-phosphorylated FKBP52 did not bind to HSP90. These results indicate that CK2 phosphorylates FKBP52 both in vitro and in vivo and thus may regulate the protein composition of chaperone-containing complexes such as those of steroid receptors and certain protein kinases.

    Proceedings of the National Academy of Sciences of the United States of America 1997;94;26;14500-5

  • Two putative protein kinase CK2 phosphorylation sites are important for Myf-5 activity.

    Winter B, Kautzner I, Issinger OG and Arnold HH

    Department of Cell and Molecular Biology, University of Braunschweig, Germany.

    Myf-5, a member of a family of muscle-specific transcription factors, is important for myogenic cell determination and differentiation. Here, we report that Myf-5 protein constitutes a substrate for phosphorylation in vitro by protein kinase CK2. We identified two potential phosphorylation sites at serine49 and serine133, both of which seem to be necessary for Myf-5 activity. Mutants which can no longer be phosphorylated fail to transactivate E-box-dependent reporter genes and act as trans-dominant repressors of wild-type Myf-5. Normal activity can be restored by replacing the serine residues with glutamate suggesting that a negative charge at these sites is obligatory for Myf-5 activity. Although serine133 is part of helix 2 which mediates dimerization, we find no evidence for impaired DNA-binding or heterodimerization of the Ser-Ala133 mutant. Some serine49 mutations exhibit reduced nuclear localization and/or protein stability. Our data suggest that CK2-mediated phosphorylation of Myf-5 is required for Myf-5 activity.

    Biological chemistry 1997;378;12;1445-56

  • Phosphorylation of the oncogenic transcription factor interferon regulatory factor 2 (IRF2) in vitro and in vivo.

    Birnbaum MJ, van Zundert B, Vaughan PS, Whitmarsh AJ, van Wijnen AJ, Davis RJ, Stein GS and Stein JL

    Department of Cell Biology, Cancer Center, University of Massachusetts Medical Center, Worcester 01655, USA.

    IRF2 is a transcription factor, possessing oncogenic potential, responsible for both the repression of growth-inhibiting genes (interferon) and the activation of cell cycle-regulated genes (histone H4). Surprisingly little is known about the post-translational modification of this factor. In this study, we analyze the phosphorylation of IRF2 both in vivo and in vitro. Immunoprecipitation of HA-tagged IRF2 expressed in 32P-phosphate labelled COS-7 cells demonstrates that IRF2 is phosphorylated in vivo. Amino acid sequence analysis reveals that several potential phosphorylation sites exist for a variety of serine/threonine protein kinases, including those of the mitogen activated protein (MAP) kinase family. Using a battery of these protein kinases we show that recombinant IRF2 is a substrate for protein kinase A (PKA), protein kinase C (PKC), and casein kinase II (CK2) in vitro. However, other serine/threonine protein kinases, including the MAP kinases JNK1, p38, and ERK2, do not phosphorylate IRF2. Two-dimensional phosphopeptide mapping of the sites phosphorylated by PKA, PKC, and CKII in vitro demonstrates that these enzymes are capable of phosphorylating IRF2 at multiple distinct sites. Phosphoaminoacid analysis of HA-tagged IRF2 immunoprecipitated from an asynchronous population of proliferating, metabolically phosphate-labelled cells indicates that this protein is phosphorylated exclusively upon serine residues in vivo. These results suggest that the oncogenic protein IRF2 may be regulated via multiple pathways during cellular growth.

    Funded by: NIGMS NIH HHS: GM32010

    Journal of cellular biochemistry 1997;66;2;175-83

  • Physical dissection of the structural elements responsible for regulatory properties and intersubunit interactions of protein kinase CK2 beta-subunit.

    Marin O, Meggio F, Sarno S and Pinna LA

    Dipartimento di Chimica Biologica, CNR, Centro di Studio delle Biomembrane, Universitá degli Studi di Padova, Italy.

    The noncatalytic beta-subunit of protein kinase CK2 has been shown to display various and in some respects antagonistic effects on the catalytic alpha-subunit [Boldyreff et al. (1993) Biochemistry 32, 12672-12677; Meggio et al. (1994) Biochemistry 33, 4336-4342]. We have now examined the ability of peptides encompassing the N- and C-terminal regions of the beta-subunit (beta[1-77] and beta[155-215]) to mimic the functions of the whole-length beta-subunit. Peptide beta[155-215] possesses only the positive features of the beta-subunit in that it prevents thermal inactivation and stimulates basal activity of the alpha-subunit, while it does not inhibit but rather stimulates calmodulin phosphorylation. In sharp contrast, peptide beta[1-77] neither protects the alpha-subunit nor stimulates its basal activity, while acting as a powerful and specific inhibitor of calmodulin phosphorylation. Peptide beta[155-215], but not peptide beta[1-77], stably interacts with alpha-subunit and also displays remarkable self-associating properties. A shorter derivative of beta[155-215], beta[170-215], displaying weaker stimulatory properties fails to stably interact with the alpha-subunit and to give rise to dimeric/multimeric forms. These data show that the elements responsible for the negative regulation are concentrated in the N-terminal moiety of the beta-subunit, whereas the C-terminal region retains the beneficial properties of the beta-subunit and is capable of self-association and binding of the alpha-subunit. Residues between 155 and 170 are necessary for the latter functions.

    Biochemistry 1997;36;23;7192-8

  • The Nef protein of human immunodeficiency virus type 1 enhances serine phosphorylation of the viral matrix.

    Swingler S, Gallay P, Camaur D, Song J, Abo A and Trono D

    Infectious Disease Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA.

    The human immunodeficiency virus type 1 matrix (MA) protein is phosphorylated during virion maturation on its C-terminal tyrosine and on several serine residues. Whereas MA tyrosine phosphorylation facilitates viral nuclear import, the significance of MA serine phosphorylation remains unclear. Here, we report that MA serine but not tyrosine phosphorylation is strongly enhanced by Nef. Mutations that abrogated the membrane association of Nef and its ability to bind a cellular serine/threonine kinase greatly diminished the extent of virion MA serine phosphorylation. Correspondingly, a protein kinase coimmunoprecipitated with Nef could phosphorylate MA on serine in vitro, producing a phosphopeptide pattern reminiscent of that of virion MA. Recombinant p21-activated kinase hPAK65, a recently proposed relative of the Nef-associated kinase, achieved a comparable result. Taken together, these data suggest that MA is a target of the Nef-associated serine kinase.

    Funded by: NIAID NIH HHS: AI34306, R01 AI37510

    Journal of virology 1997;71;6;4372-7

  • Phosphorylation of both phosphoacceptor sites in the HIV-1 Vpu cytoplasmic domain is essential for Vpu-mediated ER degradation of CD4.

    Paul M and Jabbar MA

    Department of Molecular Biology-NC20, Research Institute, The Cleveland Clinic Foundation, Ohio 44195, USA.

    Human immunodeficiency virus type 1 (HIV-1) Vpu is phosphorylated at two serine residues (Ser52 and Ser56) present within the acidic dodecapeptide region of the 54-aa cytoplasmic domain. Previous experiments have shown that Vpu phosphorylation is critical for the degradation of CD4 in the endoplasmic reticulum. In this study, we carried out experiments to elucidate the role of individual phosphoacceptor sites in CD4 proteolysis. We show here that acidic amino acids could not functionally substitute for phosphoserines in Vpu that is capable of inducing the degradation of CD4. Our studies have further revealed that phosphorylation of either of the two phosphoacceptor sites is not sufficient to generate a functional Vpu protein. When tested for functional complementation, inactive phosphorylation-proficient Vpu mutants failed to generate Vpu proteins that had the ability to induce the degradation of Vpu-sensitive glycoproteins. The failure to complement was not due to assembly defects in the Vpu protein as unphosphorylated Vpu formed oligomeric complexes in the cell. We also showed that Vpu expression inhibits protein transport in a phosphorylation-dependent manner. Our studies have thus revealed that both phosphoserines in Vpu are critical participants in a pathway that leads to the proteolysis of CD4 in the ER and that these phosphoserines should be present on the same subunit of the Vpu protein.

    Virology 1997;232;1;207-16

  • Casein kinase II-mediated phosphorylation of the C terminus of Sp1 decreases its DNA binding activity.

    Armstrong SA, Barry DA, Leggett RW and Mueller CR

    Cancer Research Laboratories, Queen's University, Kingston, Ontario K7L 3N6, Canada.

    We have previously observed that Sp1, a ubiquitous zinc finger transcription factor, is phosphorylated during terminal differentiation in the whole animal, and this results in decreased DNA binding activity (Leggett, R. W., Armstrong, S. A., Barry, D., and Mueller, C. R. (1995) J. Biol. Chem. 270, 25879-25884). In this study, we demonstrate that casein kinase II (CKII) is able to phosphorylate the C terminus of Sp1 and results in a decrease in DNA binding activity. This suggests that CKII may be responsible for the observed regulation of Sp1. Mutation of a consensus CKII site at amino acid 579, within the second zinc finger, eliminates phosphorylation of this site and the CKII-mediated inhibition of Sp1 binding. Phosphopeptide analysis confirms the presence of a CKII site at Thr-579 as well as additional sites within the C terminus. No gross changes in CKII subunit levels were seen during de-differentiation associated with liver regeneration. The serine/threonine phosphatase PP1 was identified as the endogenous liver nuclear protein able to dephosphorylate Sp1 but again no gross changes in activity were observed in the regenerating liver. Okadaic acid treatment of K562 cells increases Sp1 phosphorylation and inhibits its DNA binding activity suggesting that steady state levels of Sp1 phosphorylation are established by a balance between kinase and phosphatase activities.

    The Journal of biological chemistry 1997;272;21;13489-95

  • Regulation of protein phosphatase 2A by direct interaction with casein kinase 2alpha.

    Hériché JK, Lebrin F, Rabilloud T, Leroy D, Chambaz EM and Goldberg Y

    Commissariat à l'Energie Atomique, Département de Biologie Moléculaire et Structurale, Laboratoire de Biochimie des Régulations Cellulaires Endocrines, Unité 244, F-38054 Grenoble Cédex 9, France.

    Timely deactivation of kinase cascades is crucial to the normal control of cell signaling and is partly accomplished by protein phosphatase 2A (PP2A). The catalytic (alpha) subunit of the serine-threonine kinase casein kinase 2 (CK2) bound to PP2A in vitro and in mitogen-starved cells; binding required the integrity of a sequence motif common to CK2alpha and SV40 small t antigen. Overexpression of CK2alpha resulted in deactivation of mitogen-activated protein kinase kinase (MEK) and suppression of cell growth. Moreover, CK2alpha inhibited the transforming activity of oncogenic Ras, but not that of constitutively activated MEK. Thus, CK2alpha may regulate the deactivation of the mitogen-activated protein kinase pathway.

    Science (New York, N.Y.) 1997;276;5314;952-5

  • The crystal structure of an intact human Max-DNA complex: new insights into mechanisms of transcriptional control.

    Brownlie P, Ceska T, Lamers M, Romier C, Stier G, Teo H and Suck D

    EMBL Structural Biology Programme, Meyerhofstrasse 1, 69117, Heidelberg, Germany.

    Background: Max belongs to the basic helix-loop-helix leucine zipper (bHLHZ) family of transcription factors. Max is able to form homodimers and heterodimers with other members of this family, which include Mad, Mxi1 and Myc; Myc is an oncoprotein implicated in cell proliferation, differentiation and apoptosis. The homodimers and heterodimers compete for a common DNA target site (the E box) and rearrangement amongst these dimer forms provides a complex system of transcriptional regulation. Max is also regulated by phosphorylation at a site preceding the basic region. We report here the first crystal structure of an intact bHLHZ protein bound to its target site.

    Results: The X-ray crystal structure of the intact human Max protein homodimer in complex with a 13-mer DNA duplex was determined to 2.8 A resolution and refined to an R factor of 0.213. The C-terminal domains in both chains of the Max dimer are disordered. In contrast to the DNA observed in complex with other bHLH and bHLHZ proteins, the DNA in the Max complex is bent by about 25 degrees, directed towards the protein. Intimate contacts with interdigitating sidechains give rise to the formation of tetramers in the crystal.

    Conclusions: The structure confirms the importance of the HLH and leucine zipper motifs in dimerization as well as the mode of E box recognition which was previously analyzed by X-ray crystallography of shortened constructs. The disorder observed in the C-terminal domain suggests that contacts with additional protein components of the transcription machinery are necessary for ordering the secondary structure. The tetramers seen in the crystal are consistent with the tendency of Max and other bHLHZ and HLH proteins to form higher order oligomers in solution and may play a role in DNA looping. The location of the two phosphorylation sites at Ser1 and Ser10 (the latter is the N-cap of the basic helix) suggests how phosphorylation could disrupt DNA binding.

    Structure (London, England : 1993) 1997;5;4;509-20

  • Nucleolar protein B23 stimulates nuclear import of the HIV-1 Rev protein and NLS-conjugated albumin.

    Szebeni A, Mehrotra B, Baumann A, Adam SA, Wingfield PT and Olson MO

    Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216, USA.

    Nucleolar phosphoprotein B23 is a putative ribosome assembly factor with a relatively high affinity for peptides containing sequences of nuclear localization signals (NLSs) of the SV40 T-antigen type [Szebeni, A., Herrera, J. E., & Olson, O. J. (1995) Biochemistry 34, 8037-8042]. The effects of protein B23 on nuclear import were determined by an in vitro assay [Dean, D. A., & Kasamatsu, H. (1994) J. Biol. Chem. 269, 4910-4916] using NLS peptide-conjugated bovine serum albumin (NLS-BSA) or the HIV-1 Rev protein as substrates for import into isolated rat liver nuclei. The import was ATP-dependent and inhibited by wheat germ agglutinin or by an antibody against p97, a component of the nuclear import system. The rate of import of either substrate was increased if protein B23 was added to the incubation medium. Similar enhancements of import were seen with both isoforms (B23.1 and B23.2). The stimulatory effect on Rev protein import was saturable with maximum stimulation (2-3-fold) at a molar ratio of protein B23:Rev of approximately 1:1. Phosphorylation of protein B23.1 by casein kinase II produced an additional doubling of the import rate. This effect was not seen if protein B23.1 was phosphorylated with a cdc2 type protein kinase. Mutant forms of protein B23.1 in which the nuclear localization signal was either deleted or altered did not stimulate import of the substrates. These results suggest that protein B23 plays a role as an accessory factor in the nuclear import of the NLS-containing proteins and that phosphorylation at sites in the highly acidic segments of the protein enhances the stimulatory effect.

    Funded by: NIAID NIH HHS: AI34277; NIGMS NIH HHS: GM00659, GM28349

    Biochemistry 1997;36;13;3941-9

  • Phosphorylation of a vesicular monoamine transporter by casein kinase II.

    Krantz DE, Peter D, Liu Y and Edwards RH

    Department of Neurology, University of California School of Medicine, San Francisco, California 94143-0435, USA.

    The vesicular monoamine transporters (VMATs) package monoamine neurotransmitters into secretory vesicles for regulated exocytotic release. One isoform occurs in the adrenal gland (VMAT1) and another in the brain (VMAT2). To assess their potential for regulation, we have investigated the phosphorylation of the VMATs. Using heterologous expression in Chinese hamster ovary, PC12, and COS cells, we find that rat VMAT2, but not VMAT1, is constitutively phosphorylated. Phosphoamino acid analysis indicates that this phosphorylation occurs on serine residues, and the analysis of VMAT1-VMAT2 chimeras and site-directed mutagenesis localize the phosphorylation sites to serines 512 and 514 at the carboxyl terminus of VMAT2. Since these residues occur in an acidic region, we tested the ability of the acidotropic kinases casein kinase I (CKI) and casein kinase II (CKII) to phosphorylate bacterial fusion proteins containing the carboxyl terminus of VMAT2. Purified CKI and CKII phosphorylate the wild-type carboxyl terminus of VMAT2, but not a double mutant with both serines 512 and 514 replaced by alanine. The protein kinase inhibitor CKI-7 and unlabeled GTP both block in vitro phosphorylation by cell homogenates, indicating a role for CKII and possibly CKI in vivo. Both kinases phosphorylate the VMAT2 fusion protein to a much greater extent than a similar fusion protein containing the carboxyl terminus of VMAT1, consistent with differential phosphorylation of the two transporters observed in intact cells. These results provide the first demonstration of phosphorylation of a vesicular neurotransmitter transporter and a potential mechanism for differential regulation of the two VMATs.

    The Journal of biological chemistry 1997;272;10;6752-9

  • The putative cell cycle gene, enhancer of rudimentary, encodes a highly conserved protein found in plants and animals.

    Gelsthorpe M, Pulumati M, McCallum C, Dang-Vu K and Tsubota SI

    Department of Biology, Saint Louis University, MO 63103, USA.

    The enhancer of rudimentary gene, e(r), in Drosophila melanogaster encodes a protein, ER, whose function has been implicated in pyrimidine biosynthesis and the cell cycle (Wojcik et al. (1994) Genetics 138, 1163-1170). In order to identify conserved regions of the protein and potentially important functional domains, the e(r) gene was cloned and sequenced from two other insects (Drosophila virilis and Aedes aegypti) and three vertebrates (Homo sapiens, Mus musculus, and Brachydanio rerio) and sequenced from a flowering plant (Arabidopsis thaliana). These sequences along with those of a nematode (Caenorhabditis elegans) exhibit a high degree of identity. ER of Drosophila melanogaster is 76% identical to the three vertebrate proteins, 49% identical to the nematode protein, and 40% identical to the plant protein. There is high evolutionary conservation among the vertebrates. The mouse and human proteins are identical and differ from that of the zebrafish by a single conservative amino-acid change (valine for isoleucine). A dramatic sequence conservation is seen in the position of the hydrophobic amino acids. Of the 27 positions occupied by hydrophobic amino acids in ER of Drosophila melanogaster, 25 of the corresponding positions in the human protein, 23 of the positions in Caenorhabditis elegans, and 20 of the positions in Arabidopsis thaliana have hydrophobic amino acids. Most of these residues are present in three conserved amphipathic alpha-helices, which are proposed to function in protein-protein interactions. Two phosphorylation sites for casein kinase II (CKII) have also been conserved within the animal groups. Purified ER from Drosophila melanogaster is phosphorylated in vitro by CKII, arguing that these two sites are functional in vivo. A putative shift in the secondary structure of ER caused by the phosphorylation of these sites suggests that CKII may be regulating the activity of the ER in vivo.

    Gene 1997;186;2;189-95

  • Casein kinase II binds to and phosphorylates cytoplasmic dynein.

    Karki S, Tokito MK and Holzbaur EL

    Cell and Molecular Biology Graduate Group, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA.

    We have isolated a 27-kDa protein that binds to cytoplasmic dynein. Microsequencing of a 17-amino acid peptide of this polypeptide yielded a sequence which completely matched the predicted sequence of the beta subunit of casein kinase II, a highly conserved serine/threonine kinase. Affinity chromatography using a dynein column indicates that both the alpha and beta subunits of casein kinase II are retained by the column from rat brain cytosol. Although dynactin is also bound to the column, casein kinase II is not a dynactin subunit. Casein kinase II does not co-immunoprecipitate with dynactin, and it binds to a dynein intermediate chain column which has been preblocked with excess p150(Glued), a treatment that inhibits the binding of dynactin from cytosol. Bacterially expressed and purified rat dynein intermediate chain can be phosphorylated by casein kinase II in vitro. Further, native cytoplasmic dynein purified from rat brain can also be phosphorylated by casein kinase II in vitro. We propose that CKII may be involved in the regulation of dynein function possibly by altering its cargo specificity or its ability to interact with dynactin.

    Funded by: NIGMS NIH HHS: GM48661

    The Journal of biological chemistry 1997;272;9;5887-91

  • Protein kinase A (PKA)- and protein kinase C-phosphorylated glia maturation factor promotes the catalytic activity of PKA.

    Zaheer A and Lim R

    Department of Neurology, Division of Neurochemistry and Neurobiology, University of Iowa College of Medicine and Veterans Affairs Medical Center, Iowa City, Iowa 52242, USA.

    We observed previously that glia maturation factor (GMF), a 17-kDa brain protein, is rapidly phosphorylated in astrocytes following stimulation by phorbol ester, and that protein kinase A (PKA)-phosphorylated GMF is a potent inhibitor of extracellular signal-regulated kinase (ERK) and enhancer of p38; both are subfamilies of mitogen-activated protein (MAP) kinase, suggesting GMF as a bifunctional regulator of the MAP kinase cascades. In the current report, we present evidence that PKA-phosphorylated GMF also promotes (11-fold) the catalytic activity of PKA itself, resulting in a positive feedback loop. Furthermore, GMF phosphorylated by protein kinase C (PKC), but not by casein kinase II or p90 ribosomal S6 kinase, also activates PKA (7-fold). It appears that the mutual augmentation of GMF and PKA, and the stimulating effect of PKC, both serve to maximize the influence of PKA on the regulation of MAP kinase cascades by GMF. Using synthetic peptide fragments containing putative phosphorylation sites of GMF, we demonstrate that PKA is capable of phosphorylating threonine 26 and serine 82, whereas PKC, p90 ribosomal S6 kinase, and casein kinase II, can phosphorylate serine 71, threonine 26, and serine 52, respectively. The generation of various phospho-isoforms of GMF may explain its modulation of signal transduction at multiple locations.

    Funded by: NIDDK NIH HHS: DK-25295

    The Journal of biological chemistry 1997;272;8;5183-6

  • Casein kinase 2 phosphorylates recombinant human spermidine/spermine N1-acetyltransferase on both serine and threonine residues.

    Bordin L, Vargiu C, Colombatto S, Clari G, Testore G, Toninello A and Grillo MA

    Dipartimento di Chimica Biologica, Universita' di Padova and Centro di Studio delle Biomembrane del CNR, via Trieste 75, Padova, 35121, Italy.

    Casein kinase 2 purified from human erythrocyte cytosol has been found to phosphorylate human spermidine/spermine N1-acetyltransferase (SSAT) expressed as a fusion protein in E. coli and purified to homogeneity with a specific activity similar to that reported for pure human SSAT. The amino acid sequence of the protein revealed not less than four phosphorylable residues, optimal target for protein kinase 2 phosphorylation being flanked by acid residues in position +1 and +3. Our results indicate that most 32P-phosphate is taken up by Ser residues, as evidenced by HCl hydrolysis and electrophoresis and that the phosphorylation extent is modulated by the physiological polyamine concentration. Partial digestion with trypsin at a low concentration for less than one hour preferentially hydrolyzes Lys-Arg-Arg in position 141-143 of the SSAT suggesting that the Ser-phosphorylated residues are located in the C-terminus of the protein, probably Ser 146 and 149.

    Biochemical and biophysical research communications 1996;229;3;845-51

  • CD10/neutral endopeptidase 24.11 is phosphorylated by casein kinase II and coassociates with other phosphoproteins including the lyn src-related kinase.

    Ganju RK, Shpektor RG, Brenner DG and Shipp MA

    Department of Medicine, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA 02115, USA.

    CD10/neutral endopeptidase 24.11 (NEP) regulates peptidemediated proliferation of lymphoid progenitors and certain epithelial cells and is itself regulated by cellular proliferation. To further characterize mechanisms by which cell-surface signaling might regulate CD10/NEP expression, we determined whether CD10/NEP was phosphorylated and whether the enzyme co-associated with additional cellular phosphoproteins. The CD10/NEP cytoplasmic tall contains two consensus recognition sequences for casein kinase II (CKII), a serine and threonine kinase that increases in activity following peptide signaling. In standard in vitro kinase assays, CKII phosphorylated full-length recombinant CD10/NEP but did not phosphorylate a truncated CD10/NEP protein that lacked the transmembrane region and cytoplasmic tail. To determine whether CD10/NEP might interact with additional cellular phosphoproteins, in vitro kinase assays were performed on CD10/NEP immune complexes from Nalm-6 cells. Three additional tyrosine phosphoproteins of approximately 40 kD, approximately 58 kD, and approximately 75 kD were identified in the CD10/NEP immunoprecipitates. The approximately 56-kD CD10/NEP-associated phosphoprotein was immunoprecipitated with an anti-lyn antibody confirming its identity as the lyn src-related kinase. Taken together, these data indicate that CD10/NEP is itself phosphorylated by CKII and that CD10/NEP co-associates with additional tyrosine phosphoproteins including lyn.

    Blood 1996;88;11;4159-65

  • Threonine 1342 in human topoisomerase IIalpha is phosphorylated throughout the cell cycle.

    Ishida R, Iwai M, Marsh KL, Austin CA, Yano T, Shibata M, Nozaki N and Hara A

    Laboratory of Biochemistry, Aichi Cancer Center Research Institute, Chikusa-Ku, Nagoya 464, Japan.

    To investigate the relationship between the modulation of topoisomerase II activity and its phosphorylation state during the cell cycle, a monoclonal antibody against C-terminal peptide (residues 1335-1350) of topoisomerase IIalpha containing a consensus sequence of casein kinase II, TDDE and its phosphorylated threonine were prepared. In an enzyme-linked immunosorbent assay, the antibody, named PT1342, recognized the immunogenic phosphopeptide but not the non-phosphorylated form of the peptide. The PT1342 antibody reacted only with a 170-kDa protein from HeLa cells and recognized anti-topoisomerase IIalpha immunoprecipitants. Furthermore, the antibody did not react with the human topoisomerase IIalpha mutated at codon 1342 from threonine to alanine, showing that PT1342 was directed against the phosphorylated threonine 1342. To examine the level of phosphorylation of threonine 1342 of topoisomerase IIalpha through the cell cycle, HeLa cells were stained simultaneously for phosphorylated topoisomerase IIalpha and DNA and analyzed by flow cytometry. Cells in the G2-M phase contained about double the PT1341-reacted topoisomerase IIalpha than did cells in G1 or S phases. The antibody stained the nuclei in interphase and mitotic chromosomes and its periphery, as seen with anti-topoisomerase IIalpha antibody. Thus, threonine 1342 in topoisomerase IIalpha is phosphorylated throughout the cell cycle.

    The Journal of biological chemistry 1996;271;47;30077-82

  • The Alzheimer's disease-associated presenilins are differentially phosphorylated proteins located predominantly within the endoplasmic reticulum.

    Walter J, Capell A, Grünberg J, Pesold B, Schindzielorz A, Prior R, Podlisny MB, Fraser P, Hyslop PS, Selkoe DJ and Haass C

    Central Institute of Mental Health, Department of Molecular Biology, Mannheim, Germany.

    Background: Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the deposition of extracellular senile plaques composed of amyloid beta-peptide (A beta). Whereas most cases of AD occur sporadically, about 10% of AD cases are inherited as a fully penetrant autosomal dominant trait. Mutations in the recently cloned Presenilin genes (PS-1 and PS-2) are by far the most common cause of early onset familial AD.

    Cellular expression of endogenous and overexpressed PS proteins was analyzed by immunocytochemistry and metabolic labeling followed by immunoprecipitation. In vivo phosphorylation sites of PS proteins were analyzed by extensive mutagenesis.

    Results: PS-1 as well as PS-2 proteins were localized predominantly within the endoplasmic reticulum (ER). However, small amounts of the PS proteins were detected within the Golgi compartment, where they colocalize with the beta-amyloid precursor protein (beta APP). The PS-2 protein was found to be highly phosphorylated, whereas very little phosphorylation was observed for PS-1. The selective phosphorylation of PS-2 occurs exclusively on serine residues. In vivo phosphorylation of PS-2 was mapped to serine residues 7, 9, and 19 within an acidic stretch at the N terminus, which is absent in PS-1. casein kinase (CK)-1 and CK-2 were shown to phosphorylate the N terminus of PS-2 in vitro.

    Conclusions: The majority of PS proteins were detected in the ER where little if any proteolytic processing of beta APP was reported. ER retention of PS proteins might occur by intramolecular aggregation. Small amounts of PS proteins were also detected in the Golgi where they colocalized with beta APP. This might suggest that potential interactions between PS proteins and beta APP could occur within the Golgi. Selective phosphorylation of PS-2 proteins within the acidic domain missing in PS-1 indicates differences in the biological functions and regulation of the two highly homologous proteins.

    Funded by: NIA NIH HHS: AG 06173, AG 12749

    Molecular medicine (Cambridge, Mass.) 1996;2;6;673-91

  • Phosphorylation of HIV-1 Rev protein: implication of protein kinase CK2 and pro-directed kinases.

    Meggio F, D'Agostino DM, Ciminale V, Chieco-Bianchi L and Pinna LA

    Dipartimento di Chimica Biologica, Università di Padova, Italy.

    HIV-1 Rev transactivator is readily phosphorylated at separate regions by protein kinase CK2 and MAP kinase. Protein kinase CK1 cannot replace CK2 as phosphorylating agent and cdc2 only slowly phosphorylates Rev at one of the two sites affected by MAP kinase. Mutational analysis shows that Ser-8 and, to a lesser extent, Ser-5 are phosphorylated by CK2. In contrast, a mutation (R14TV-->EED) which suppresses Rev activity dramatically enhances Rev phosphorylation either in vitro by CK2 or in vivo, suggesting that phosphorylation by CK2 could play a role in Rev down-regulation.

    Biochemical and biophysical research communications 1996;226;2;547-54

  • Phosphorylation of the MADS-Box transcription factor MEF2C enhances its DNA binding activity.

    Molkentin JD, Li L and Olson EN

    Department of Molecular Biology, University of Texas, Southwestern Medical Center at Dallas, 75235-9148, USA.

    Members of the myocyte enhancer factor-2 (MEF2) family of transcription factors activate muscle gene expression by binding an A/T-rich DNA sequence in the control regions of muscle-specific genes. There are four MEF2 factors in vertebrates, MEF2A-D, which share homology in an amino-terminal MADS domain and an adjacent region known as the MEF2 domain, that together mediate DNA binding and dimerization. We show that serine 59 located between the MADS and MEF2 domains of MEF2C is phosphorylated in vivo and can be phosphorylated in vitro by casein kinase-II (CKII). Phosphorylation of this site enhanced the DNA binding and transcriptional activity of MEF2C by increasing its DNA binding activity 5-fold. In vivo 32P labeling experiments showed that serine 59 is the only phosphorylation site in the MADS and MEF2 domains. Mutagenesis of this serine to an aspartic acid resulted in an increase in DNA binding and transcriptional activity of MEF2C comparable to that observed when this site was phosphorylated, suggesting that phosphorylation augments DNA binding activity by introducing negative charge. This phosphorylation site, which corresponds to a CKII recognition site, is conserved in all known MEF2 factors in organisms ranging from flies to humans, consistent with its importance for the functions of MEF2C.

    The Journal of biological chemistry 1996;271;29;17199-204

  • Phosphorylation of purified bovine bone sialoprotein and osteopontin by protein kinases.

    Salih E, Zhou HY and Glimcher MJ

    Department of Orthopaedic Surgery, Harvard Medical School and The Children's Hospital, Boston, Massachusetts 02115, USA.

    The large number of covalently bound phosphates on the extracellular phosphoproteins osteopontin (OPN) and bone sialoprotein (BSP) have been implicated in biological functions such as mineral deposition and osteoclast binding. In the present study the state of phosphorylation of BSP and OPN was evaluated by in vitro 32P labeling using a series of protein kinases and quantification. Both the purified bovine BSP and OPN were radiolabeled by [32P]ATP and factor-independent protein kinase. Quantification of 32P radioactivity incorporated on dephosphorylated BSP and OPN provided 6.6 and 8.9 mol of phosphate incorporated/mol, respectively. Native OPN incorporated 1.07 and BSP 2.46 mol of phosphate/mol by factor-independent protein kinase. These data led to calculations that OPN and BSP, respectively, contain 7.83 and 4.14 mol of phosphate/mol in their natural state. Thrombin digests of 32P-labeled BSP showed radioactivity to be associated with fragment of approximately molecular mass values 30 kDa (N-terminal half), with no observable radioactivity associated with the 40-kDa fragment (C-terminal half). Similar experiments with 32P-labeled OPN provided two radiolabeled thrombin fragments, with molecular mass 30 kDa (N-terminal half) and 20 kDa (C-terminal half), both were radioactive. The major phosphorylation was associated with the N-terminal half containing 7.0 mol of phosphate, and 1.9 mol of phosphate were associated with the C-terminal half. Additional experiments of in vitro phosphorylation of OPN and BSP by several other known protein kinases were carried out. cAMP-dependent protein kinase showed no phosphorylation of OPN or BSP, while protein kinase C and cGMP-dependent protein kinase led to minor phosphorylation, each of the latter introduced about 1 mol of phosphate/mol of OPN and BSP molecule.

    Funded by: NIAMS NIH HHS: AR34078

    The Journal of biological chemistry 1996;271;28;16897-905

  • The physical association of casein kinase 2 with nucleolin.

    Li D, Dobrowolska G and Krebs EG

    Department of Pharmacology, University of Washington, Seattle, Washington 98195, USA.

    CK2 (formerly called casein kinase 2) is a ubiquitous messenger-independent serine/threonine protein kinase implicated in cell growth and proliferation. To investigate the regulation and functions of this enzyme, experiments were carried out to search for CK2-interacting proteins. The methods employed included an overlay technique, co-purification, co-immunoprecipitation, and the use of glutathione S-transferase (GST) CK2 fusion proteins. By the CK2 overlay technique, one protein of 110 kDa was found to bind to CK2 with very high affinity. The binding was inhibited by CK2 effectors such as heparin, polyarginine, and histone H1, but was not affected by the CK2 substrate, casein. Protein p110 was also detected by co-immunoprecipitation using anti-CK2 antiserum, suggesting an in vivo association of this protein with CK2. Co-purification of p110 with CK2 from Sf-9 cells that overexpressed CK2 was also observed through sequential chromatographic steps. Using GST fusion proteins of CK2, the CK2-p110 interaction was investigated further and was found to occur primarily through CK2 alpha or alpha' subunits, but not the beta subunit. Protein p110 was purified from 3T3 L1 mouse fibroblast cell lines using a GST-CK2 affinity resin. Amino acid sequence analysis of peptides obtained from the protein indicated that it is the nuclear protein, nucleolin. Furthermore, p110 was recognized by anti-nucleolin antiserum. At present, the physiological significance of the strong interaction between CK2 and nucleolin, an excellent substrate for the enzyme, is not clear. However, this association may be important for regulating rDNA transcription.

    Funded by: NIDDK NIH HHS: DK42528

    The Journal of biological chemistry 1996;271;26;15662-8

  • Casein kinase II associates with Egr-1 and acts as a negative modulator of its DNA binding and transcription activities in NIH 3T3 cells.

    Jain N, Mahendran R, Philp R, Guy GR, Tan YH and Cao X

    Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, Singapore 119260, Republic of Singapore.

    Although the activation domains within early growth response gene protein 1 (Egr-1) have been mapped, little is known of the kinases which phosphorylate Egr-1 and how phosphorylation correlates with the transcriptional activity of Egr-1. In this study we report that casein kinase II (CKII) co-immunoprecipitates with Egr-1 from NIH 3T3 cell lysates. The association of Egr-1 and CKII requires the C terminus of Egr-1 and CKII phosphorylates Egr-1 in vitro. The in vitro phosphorylation of Egr-1 by CKII and that induced by serum in vivo was compared by examining the CNBr-digested fragments of the phosphorylated Egr-1. CKII strongly phosphorylates fragments 7 and 10 which cover part of the activation/nuclear localization and DNA binding domains of Egr-1. CKII also phosphorylates, albeit weakly, fragments 5 and 8 which cover part of activation domain and the entire repression domain of Egr-1, respectively. Strong phosphorylation on fragment 10 as well as fragment 5 was also observed in Egr-1 immunoprecipitated from serum-induced, 32P-labeled cells. CKII phosphorylation of Egr-1 resulted in a decrease of its DNA binding as well as its transcriptional activities.

    The Journal of biological chemistry 1996;271;23;13530-6

  • The human immunodeficiency virus type 1 Vpu protein tethered to the CD4 extracellular domain is localized to the plasma membrane and is biologically active in the secretory pathway of mammalian cells: implications for the mechanisms of Vpu function.

    Raja NU and Jabbar MA

    Department of Molecular Biology, Cleveland Clinic Foundation, Ohio 44195, USA.

    The HIV-1 Vpu protein induces the proteolysis of CD4 in the endoplasmic reticulum (ER) and enhances the release of virus particles from the plasma membrane. The two biological activities of HIV-1 Vpu appear to be reconstituted in distinct membrane compartments of the mammalian cell. We carried out experiments to understand the role of Vpu sequences in membrane trafficking of the Vpu protein and to gain insights into Vpu-mediated proteolytic reactions. To this end, we generated CD4/Vpu hybrid proteins and analyzed their biochemical and biological properties in HeLa cells. We show here that all hybrid proteins are delivered to the plasma membrane undergoing endo-H-resistant modifications in the Golgi complex. Importantly, a hybrid protein bearing the CD4 extracellular domain and full-length Vpu induced the degradation of HIV envelope glycoproteins bearing the transmembrane and cytoplasmic domains of CD4 (Vpu-responsive elements, VRE). Glycoproteins lacking the VRE are stable under these conditions. In addition, a hybrid protein having the extracellular-transmembrane domains of CD4 and the Vpu cytoplasmic domain was only partially active in inducing the degradation of Vpu-sensitive proteins. These results suggest that the Vpu transmembrane domain is capable of regulating Vpu activity in the cell. Mutational studies have further demonstrated that casein kinase-2 phosphorylation is critically important in the degradation reaction, but does not regulate membrane trafficking of the CD4/Vpu hybrid proteins. We also show that the CD4 extracellular domain appended to the Vpu protein is protected from degradation while existing in a complex with Vpu-sensitive ectodomains. Taken together, these studies have revealed that the Vpu protein does not possess sequences that have the ability to sequester CD4 in the intracellular compartments of mammalian cells and that the Vpu protein tethered to the CD4 extracellular domain was biologically active in inducing the degradation of VRE-bearing glycoproteins in the ER.

    Virology 1996;220;1;141-51

  • Identification of insulin-stimulated phosphorylation sites on calmodulin.

    Joyal JL, Crimmins DL, Thoma RS and Sacks DB

    Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.

    Insulin enhances calmodulin phosphorylation in vivo. To determine the insulin-sensitive phosphorylation sites, phosphocalmodulin was immunoprecipitated from Chinese hamster ovary cells expressing human insulin receptors (CHO/IR). Calmodulin was constitutively phosphorylated on serine, threonine, and tyrosine residues, and insulin enhanced phosphate incorporation on serine and tyrosine residues. Phosphocalmodulin immunoprecipitated from control and insulin-treated CHO/IR cells, and calmodulin phosphorylated in vitro by the insulin receptor kinase and casein kinase II were resolved by two-dimensional phosphopeptide mapping. Several common phosphopeptides were detected. The phosphopeptides from the in vitro maps were eluted and phosphoamino acid analysis, manual sequencing, strong cation exchange chromatography, and additional proteolysis were performed. This strategy demonstrated that Tyr-99 and Tyr-138 were phosphorylated in vitro by the insulin receptor kinase and Thr-79, Ser-81, Ser-101 and Thr-117 were phosphorylated by casein kinase II. In vivo phosphorylation sites were identified by comigration of phosphopeptides on two-dimensional maps with phosphopeptides derived from calmodulin phosphorylated in vitro and by phosphoamino acid analysis. This approach revealed that Tyr-99 and Tyr-138 of calmodulin were phosphorylated in CHO/IR cells in response to insulin. Additional sites remain to be identified. The identification of the insulin-stimulated in vivo tyrosine phosphorylation sites should facilitate the elucidation of the physiological role of phosphocal-modulin.

    Funded by: NIDDK NIH HHS: DK09062, DK43682

    Biochemistry 1996;35;20;6267-75

  • Identification of a cryptic protein kinase CK2 phosphorylation site in human complement protease Clr, and its use to probe intramolecular interaction.

    Pelloux S, Thielens NM, Hudry-Clergeon G, Pétillot Y, Filhol O and Arlaud GJ

    Laboratoire d'Enzymologie Moléculaire, Institut de Biologie Structurale Jean-Pierre Ebel, Grenoble, France.

    Treatment of human (activated)C1r by CK2 resulted in the incorporation of [32P]phosphate into the N-terminal alpha region of its non-catalytic A chain. Fragmentation of 32P-labelled (activated)C1r followed by N-terminal sequence and mass spectrometry analyses allowed identification of Ser189 as the phosphorylation site. Accessibility of Ser189 was low in intact C1r, due in part to the presence of one of the oligosaccharides borne by the alpha region, further reduced in the presence of calcium, and abolished when C1r was incorporated into the C1s-C1r-C1r-C1s tetramer or the C1 complex. In contrast, phosphorylation was enhanced in the isolated alpha fragment and insensitive to calcium. Taken together, these data provide support for the occurrence of a (Ca2+)-dependent interaction between the alpha region and the remainder of the C1r molecule.

    FEBS letters 1996;386;1;15-20

  • Human vitamin D receptor phosphorylation by casein kinase II at Ser-208 potentiates transcriptional activation.

    Jurutka PW, Hsieh JC, Nakajima S, Haussler CA, Whitfield GK and Haussler MR

    Department of Biochemistry, College of Medicine, The University of Arizona, Tucson, 85724, USA.

    The potential functional significance of human 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] receptor (hVDR) phosphorylation at Ser-208 was evaluated by cotransfecting COS-7 kidney cells with hVDR constructs and the catalytic subunit of human casein kinase 11 (CK-11). Under these conditions, hVDR is intensely phosphorylated in a reaction that depends on both CK-II and the presence of Ser-208. The resulting hyperphosphorylated receptor is unaltered in its kinetics for binding the 1,25(OH)2D3 ligand, its partitioning into the nucleus, and its ability to associate with a vitamin D responsive element. Replacement of Ser-208 with glycine or alanine indicates that phosphorylation of hVDR at Ser-208 is not obligatory for 1,25(OH)2D3 action, but coexpression of wild-type hVDR and CK-11 elicits a dose-dependent enhancement of 1,25(OH)2D3-stimulated transcription of a vitamin D responsive element reporter construct. This enhancement by CK-II is abolished by mutating Ser-208 to glycine or alanine and does not occur with glucocorticoid receptor-mediated transcription. Therefore, phosphorylation of hVDR by CK-11 at Ser-208 specifically modulates its transcriptional capacity, suggesting that this covalent modification alters the conformation of VDR to potentiate its interaction with the machinery for DNA transcription.

    Funded by: NIAMS NIH HHS: AR-15781; NIDDK NIH HHS: DK-33351, DK-40372

    Proceedings of the National Academy of Sciences of the United States of America 1996;93;8;3519-24

  • Phosphorylation of C8 and C9 subunits of the multicatalytic proteinase by casein kinase II and identification of the C8 phosphorylation sites by direct mutagenesis.

    Castaño JG, Mahillo E, Arizti P and Arribas J

    Departamento de Bioquímica e Instituto de Investigaciones Biomédicas del Consejo Superior de Investigaciones Científicas, Facultad de Medicine de la UAM, Madrid, Spain.

    Two 29 kDa subunits of the multicatalytic proteinase (proteasome) complex, the C8 and C9 components, are phosphorylated in vivo and can be phosphorylated in vitro by casein kinase II (CKII). The major phosphate acceptor is the C8 subunit being phosphorylated in serine, both in vivo and in vitro. The phosphopeptides generated by Glu-C endoprotease digestion from the in vivo 29 kDa labeled subunit and from the in vitro phosphorylation of the recombinant C8 subunit with CKII are identical, suggesting that CKII is likely responsible for the in vivo phosphorylation of the C8 subunit. The in vitro stoichiometry of phosphorylation of the proteasome complex and the recombinant C9 and C8 subunits by CKII is 2-2.5, 0.2, and 2 mol of phosphate per mole, respectively. Several C8 protein constructs allow the location of the CKII phosphorylation sites to be the COOH terminal portion of the protein, and direct mutational analyses show that Ser-243 and Ser-250 are the residues of the C8 subunit phosphorylated by CKII. The in vitro phosphorylation of the proteasome by CKII does not affect its proteolytic activity (on proteins or fluorogenic synthetic peptides), therefore suggesting its involvement in the interaction of the proteasome with other cellular proteins, i.e. in the formation of the 26S complex and/or in the interaction with the nuclear translocation machinery.

    Biochemistry 1996;35;12;3782-9

  • Casein kinase II phosphorylates I kappa B alpha at S-283, S-289, S-293, and T-291 and is required for its degradation.

    McElhinny JA, Trushin SA, Bren GD, Chester N and Paya CV

    Department of Immunology, Mayo Clinic, Rochester, Minnesota 55905, USA.

    The phosphoprotein I kappa B alpha exists in the cytoplasm of resting cells bound to the ubiquitous transcription factor NF-kappa B (p50-p65). In response to specific cellular stimulation, I kappa B alpha is further phosphorylated and subsequently degraded, allowing NF-kappa B to translocate to the nucleus and transactivate target genes. To identify the kinase(s) involved in I kappa B alpha phosphorylation, we first performed an I kappa B alpha in-gel kinase assay. Two kinase activities of 35 and 42 kDa were identified in cellular extracts from Jurkat T and U937 promonocytic cell lines. Specific inhibitors and immunodepletion studies identified the I kappa B alpha kinase activities as those of the alpha and alpha' subunits of casein kinase II (CKII). Immunoprecipitation studies demonstrated that CKII and I kappa B alpha physically associate in vivo. Moreover, phosphopeptide maps of I kappa B alpha phosphorylated in vitro by cellular extracts and in vivo in resting Jurkat T cells contained the same pattern of phosphopeptides as observed in maps of I kappa B alpha phosphorylated in vitro by purified CKII. Sequence analysis revealed that purified CKII and the kinase activity within cell extracts phosphorylated I kappa B alpha at its C terminus at S-283, S-288, S-293, and T-291. The functional role of CKII was tested in an in vitro I kappa B alpha degradation assay with extracts from uninfected and human immunodeficiency virus (HIV)-infected U937 cells. Immunodepletion of CKII from these extracts abrogated both the basal and enhanced HIV-induced degradation of I kappa B alpha. These studies provide new evidence that the protein kinase CKII physically associates with I kappa B alpha in vivo, induces multisite (serine/threonine) phosphorylation, and is required for the basal and HIV-induced degradation of I kappa B alpha in vitro.

    Funded by: NIAID NIH HHS: R01 AI36076-01

    Molecular and cellular biology 1996;16;3;899-906

  • Differential phosphorylations of Spi-B and Spi-1 transcription factors.

    Mao C, Ray-Gallet D, Tavitian A and Moreau-Gachelin F

    Unité INSERM 248, Faculté de Médecine Lariboisière-Saint Louis, Paris, France.

    Spi-1/PU-1 and Spi-B are hematopoietic transcription factors, which, in vitro, display similar affinities for DNA target sequences containing the consensus binding site 5'-GGAA-3'. While the role of Spi-1 in the transcriptional regulation of B cell and myeloid specific genes has been largely demonstrated, the biological function of Spi-B still remains to be elucidated. Since Spi-B and Spi-1 are very divergent in their transactivator domain, these domains might acquire functional specificity in vivo by interacting with different co-factors and/or by undergoing different phosphorylations. First, we observed that casein kinase II phosphorylates Spi-B as well as Spi-1, in vitro. Then, by affinity chromatographies and in vitro kinase assays with fusion proteins between glutathione-S-transferase and the transactivator domain of Spi-B, two kinases were identified on their ability to interact and phosphorylate this domain; the MAP kinase ERK1 and the stress activated protein kinase JNK1. The Threonine 56 was defined as the ERK1 phosphorylation site by using phosphoamino-acid analyses and a Spi-B mutant version with the substitution T56 to A56. Strikingly, ERK1 failed to phosphorylate Spi-1, in vitro, whereas JNK1, like CK II, phosphorylated Spi-B and Spi-1. In addition, other purified Spi-B-kinase activities, unidentified as yet, display similar specificity than ERK1 for Spi-B versus Spi-1. Furthermore, the evident interaction of pRb protein with the transactivator domain of Spi-B in an unphosphorylated state disappeared when this domain was first phosphorylated in vitro either by ERK1 or by the purified Spi-B-kinase activities. Our data revealed multiple phosphorylation sites within Spi-B whose some of them appeared specific for Spi-B versus Spi-1 and which may account for differential regulation of their activities.

    Oncogene 1996;12;4;863-73

  • Casein kinase II phosphorylates the neural cell adhesion molecule L1.

    Wong EV, Schaefer AW, Landreth G and Lemmon V

    Department of Neurosciences, Case Western Reserve University, Cleveland, OH 44106-4975, USA.

    L1 is an axonal cell adhesion molecule found primarily on projection axons of both the CNS and PNS. It is a phosphorylated membrane-spanning glycoprotein that can be immunoprecipitated from rat brain membranes in association with protein kinase activities. Western blot analysis demonstrates that casein kinase II (CKII), a ubiquitous serine/threonine kinase enriched in brain, is present in these immunoprecipitates. CKII preparations partially purified from PC12 cells are able to phosphorylate recombinant L1 cytoplasmic domain (L1CD), which consists of residues 1,144-1,257. Using these as well as more highly purified kinase preparations, phosphorylation assays of small peptides derived from the L1CD were performed. CKII was able to phosphorylate a peptide encompassing amino acids (aa) 1,173-1,185, as well as a related peptide representing an alternatively spliced nonneuronal L1 isoform that lacks aa 1,177-1,180. Both peptides were phosphorylated with similar kinetic profiles. Serine to alanine substitutions in these peptides indicate that the CKII phosphorylation site is at Ser1,181. This is consistent with experiments in which L1CD was phosphorylated by these kinase preparations, digested, and the radiolabeled fragments sequenced. Furthermore, when L1 immunoprecipitates were used to phosphorylate L1CD, one of the residues phosphorylated is the same residue phosphorylated by CKII. Finally, in vivo radiolabeling indicates that Ser1,181 is phosphorylated in newborn rat brain. These data show that CKII is associated with and able to phosphorylate L1. This phosphorylation may be important in regulating certain aspects of L1 function, such as adhesivity or signal transduction.

    Funded by: NEI NIH HHS: R01 EY005285; NINDS NIH HHS: NS31987; PHS HHS: 5285

    Journal of neurochemistry 1996;66;2;779-86

  • Expression of recombinant elongation factor 1 beta from rabbit in Escherichia coli. Phosphorylation by casein kinase II.

    Chen CJ and Traugh JA

    Department of Biochemistry, University of California, Riverside 92521, USA.

    The beta subunit of eukaryotic elongation factor 1 (EF-1) catalyzes the GDP/GTP exchange activity on EF-1 alpha. In these studies, two cDNAs for the beta subunit of EF-1 from rabbit are cloned and sequenced. The cDNAs consist of 808 and 798 bp and are identical except for the 5' leader sequences of 67 and 57 bp. Both cDNAs code for a protein of 225 amino acids. Using the pT7-7 expression vector, EF-1 beta was expressed in Escherichia coli and purified to apparent homogeneity by chromatography on DEAE-cellulose and FPLC on Superose 12 and Mono Q. EF-1 beta was highly phosphorylated by casein kinase II, with up to 1.3 mol of phosphate incorporated per mol protein. From microsequence analysis and manual Edman degradation, the majority of the phosphate was shown to be present in serine 106 in the peptide DLFGS106DDEEES112EEA. Serine 112 was also phosphorylated by casein kinase II, but to a lesser extent. Previously, little phosphorylation of the beta subunit by casein kinase II was observed in native EF-1 unless GDP was bound to the alpha subunit (Palen, E., Venema, R.C., Chang, Y-W.E. and Traugh, J.A. (1994) Biochemistry, 8515-8520). In contrast, purified recombinant EF-1 beta was highly and specifically phosphorylated by casein kinase II; GDP and polylysine had little effect on the rate of phosphorylation of the purified subunit.

    Funded by: NIGMS NIH HHS: GM21424, GM26738

    Biochimica et biophysica acta 1995;1264;3;303-11

  • The human immunodeficiency virus type 1 Vpu protein: a potential regulator of proteolysis and protein transport in the mammalian secretory pathway.

    Vincent MJ and Abdul Jabbar M

    Department of Molecular Biology, Cleveland Clinic Foundation, Ohio 44195, USA.

    HIV-1 Vpu is a small transmembrane phosphoprotein of 16 kDa which performs critical roles in CD4 proteolysis and virus release. Previous studies have demonstrated that Vpu-induced degradation of CD4 occurs in the endoplasmic reticulum (ER), and that the proteolytic process is sequence specific requiring both the transmembrane and cytoplasmic domains of CD4. In the present study, we investigated the effects of Vpu expression on the intracellular membrane trafficking pathway of mammalian cells. In singly transfected cells, the HIV envelope glycoproteins and vesicular stomatitis virus glycoprotein (VSV G) were properly transported to the cell surface undergoing oligosaccharide modifications characteristic of their movement through the Golgi complex. In contrast, the cell surface delivery of glycoproteins was severely impeded in cells expressing Vpu. Biochemical analyses revealed that Vpu expression blocked the transfer of proteins from the ER-Golgi complex to the plasma membrane in a dose- and protein-dependent manner. Soluble gp120 exhibited extreme transport defects in the presence of Vpu, whereas transmembrane proteins (e.g., gp160, VSV) responded only moderately to wild-type Vpu. To gain insight into Vpu-mediated transport inhibition, we performed mutational analysis of the CK-2 phosphorylation sites (serines at 52 and 56) in the Vpu protein. CK-2 phosphorylation of Vpu has been shown to regulate the activity of the protein in reactions that involve the proteolysis of CD4 in the ER. We demonstrate here that the phosphorylation mutant is defective in both sequence-specific degradation of VRE-containing substrates and the transport inhibition of gp120 and VSV-G in the secretory pathway. Thus, these experiments have revealed that Vpu-mediated proteolysis and transport inhibition are mechanistically coupled requiring the same structural elements of the Vpu protein in both processes. We propose that the primary effect of Vpu expression is to impede the secretion process and then access glycoproteins bearing the VRE for Vpu-mediated proteolysis in the ER of mammalian cells.

    Virology 1995;213;2;639-49

  • Casein kinase II phosphorylation site mutations in c-Myb affect DNA binding and transcriptional cooperativity with NF-M.

    Oelgeschläger M, Krieg J, Lüscher-Firzlaff JM and Lüscher B

    Institut für Molekularbiologie, Medizinische Hochschule Hannover, Germany.

    Phosphorylation of c-Myb has been implicated in the regulation of the binding of c-Myb to DNA. We show that murine c-Myb is phosphorylated at Ser-11 and -12 in vivo and that these sites can be phosphorylated in vitro by casein kinase II (CKII), analogous to chicken c-Myb. An efficient method to study DNA binding properties of full-length c-Myb and Myb mutants under nondenaturing conditions was developed. It was found that a Myb mutant in which Ser-11 and -12 were replaced with Ala (Myb Ala-11/12), wild-type c-Myb, and Myb Asp-11/12 bound to the A site of the mim-1 promoter with decreasing affinities. In agreement with this finding, Myb Ala-11/12 transactivated better than wild-type c-Myb and Myb Asp-11/12 on the mim-1 promoter or a synthetic Myb-responsive promoter. Similar observations were made for the myeloid-specific neutrophil elastase promoter. The presence of NF-M or an NF-M-like activity abolished partially the differences seen with the Ser-11/12 mutants, suggesting that the reduced DNA binding due to negative charge at positions 11 and 12 can be compensated for by NF-M. Since no direct interaction of c-Myb and NF-M was observed, we propose that the cooperativity is mediated by a third factor. Our data offer two possibilities for how casein kinase II phosphorylation can influence c-Myb function: first, by reducing c-Myb DNA binding and thereby influencing transactivation, and second, by enhancing the apparent cooperativity between c-Myb and NF-M or an NF-M-like activity.

    Molecular and cellular biology 1995;15;11;5966-74

  • Phosphorylation of casein kinase II by p34cdc2. Identification of phosphorylation sites using phosphorylation site mutants in vitro.

    Bosc DG, Slominski E, Sichler C and Litchfield DW

    Manitoba Institute of Cell Biology, Manitoba Cancer Treatment and Research Foundation, Winnipeg, Canada.

    The alpha and beta subunits of casein kinase II are dramatically phosphorylated in cells that are arrested in mitosis (Litchfield, D. W., Lüscher, B., Lozeman, F. J., Eisenman, R. N., and Krebs, E.G. (1992) J. Biol. Chem. 267, 13943-13951). Comparative phosphopeptide mapping experiments indicated that the mitotic phosphorylation sites on the alpha subunit of casein kinase II can be phosphorylated in vitro by p34cdc2. In the present study, we have demonstrated that a glutathione S-transferase fusion protein encoding the C-terminal 126 amino acids of the alpha subunit is phosphorylated by p34cdc2 at the same sites as intact casein kinase II, indicating that the mitotic phosphorylation sites are localized within the C-terminal domain of alpha. Four residues within this domain, Thr-344, Thr-360, Ser-362, and Ser-370, conform to the minimal consensus sequence for p34cdc2 phosphorylation. Synthetic peptides corresponding to regions of alpha that contain each of these residues are phosphorylated by p34cdc2 at these sites. Furthermore, alterations in the phosphorylation of the glutathione S-transferase proteins encoding the C-terminal domain of alpha are observed when any of the four residues are mutated to alanine. When all four residues are mutated to alanine, the fusion protein is no longer phosphorylated by p34cdc2 at any of the sites that are phosphorylated in mitotic cells. These results indicate that Thr-344, Thr-360, Ser-362, and Ser-370 are the sites on the alpha subunit of casein kinase II that are phosphorylated in mitotic cells.

    The Journal of biological chemistry 1995;270;43;25872-8

  • Mechanisms of platelet activation by a stimulatory antibody: cross-linking of a novel platelet receptor for monoclonal antibody F11 with the Fc gamma RII receptor.

    Naik UP, Ehrlich YH and Kornecki E

    Department of Anatomy and Cell Biology, SUNY/Health Science Center, Brooklyn 11203, USA.

    The mechanisms by which a stimulatory monoclonal antibody (mAb), called mAb F11, induces granular secretion and aggregation in human platelets have been characterized. Fab fragments of mAb F11, as well as an mAb directed against the platelet Fc gamma RII receptor (mAb IV.3) were found to inhibit mAb F11-induced platelet secretion and aggregation, indicating that the mAb F11 IgG molecule interacts with the Fc gamma RII receptor through its Fc domain and with its own antigen through its Fab domain. The mAb F11 recognized two platelet proteins of 32 and 35 kDa on the platelet membrane surface, as identified by Western blot analysis. We purified both proteins from human platelet membranes using DEAE-Sepharose chromatography followed by mAb F11 affinity chromatography. When added to platelet-rich plasma, the purified proteins dose-dependently inhibited mAb F11-induced platelet aggregation. The purified protein preparation also competitively inhibited the binding of 125I-labelled mAb F11 to intact platelets. The N-terminal 26 amino acid sequences of both the 32 and 35 kDa proteins were identical and contained a single unblocked serine in the N-terminal position. When digested with N-glycanase, the 32 and 35 kDa proteins were converted into a single approximately 29 kDa protein, indicating that these two proteins are derived from the same core protein but differ in their degree of glycosylation. Internal amino acid sequence analysis of the F11 antigen provided information concerning 68 amino acids and suggested two consensus phosphorylation sites for protein kinase C (PKC). The phosphorylation by PKC of the isolated F11 antigen was observed following stimulation by phorbol 12-myristate 13-acetate. Databank analysis of the N-terminal and internal amino acid sequences of the F11 antigen indicated that the N-terminal sequence exhibited the highest degree of similarity to the variable region of the alpha-chain of human T-cell receptors (TCR). In contrast, the F11 internal sequences did not exhibit any similarity to the TCR. Our results demonstrate that the F11 antigen is a novel platelet membrane surface glycoprotein which becomes cross-linked with the Fc gamma RII receptor when platelets are activated by the stimulatory mAb F11. These mechanisms may be relevant to the production of immune thrombocytopenia by platelet-activating antibodies.

    Funded by: NHLBI NIH HHS: HL0241203; NICHD NIH HHS: HD28788

    The Biochemical journal 1995;310 ( Pt 1);155-62

  • Activation of mammalian ribosomal gene transcription requires phosphorylation of the nucleolar transcription factor UBF.

    Voit R, Kuhn A, Sander EE and Grummt I

    Division of Molecular Biology of the Cell II, German Cancer Research Center, Heidelberg.

    The nucleolar factor UBF is phosphorylated by casein kinase II (CKII) at serine residues within the C-terminal acidic domain which is required for transcription activation. To investigate the biological significance of UBF modification, we have compared the trans-activating properties of cellular UBF and recombinant UBF expressed in Escherichia coli. Using a variety of assays we demonstrate that unphosphorylated UBF is transcriptionally inactive and has to be phosphorylated at multiple sites to stimulate transcription. Examination of cDNA mutants in which the serine residues within the C-terminal domain were altered by site-directed mutagenesis demonstrates that CKII-mediated phosphorylations of UBF contribute to, but are not sufficient for, transcriptional activation. Besides CKII, other cellular protein kinases phosphorylate UBF at distinct sites in a growth-dependent manner. The marked differences in the tryptic peptide maps of UBF from growing and serum-starved cells suggest that alterations in the degree of UBF phosphorylation may modulate rRNA synthetic activity in response to extracellular signals.

    Nucleic acids research 1995;23;14;2593-9

  • Interaction between casein kinase II and the 90-kDa stress protein, HSP90.

    Miyata Y and Yahara I

    Department of Cell Biology, Tokyo Metropolitan Institute of Medical Science, Japan.

    Purified casein kinase II (CKII) aggregates and loses activity under physiological salt conditions and within the range of physiological temperatures. In accord with our previous report [Miyata, Y., & Yahara, I. (1992) J. Biol. Chem. 267, 7042-7047], we report here that HSP90 protects CKII from the aggregation and inactivation by forming soluble CKII-HSP90 complexes. Surface plasmon resonance (SPR) measurements revealed that CKII binds to immobilized HSP90 within minutes. The KD of the binding is approximately 10(-7) M. ATP does not influence the interaction. The membrane-overlay method revealed that HSP90 binds to the catalytic CKII alpha subunit. Heparin, which binds to CKII alpha, inhibited the binding of CKII to HSP90-Sepharose. In addition, HSP90 competed with DNA for binding to CKII. Finally, SPR experiments showed that a peptide corresponding to the heparin and DNA binding site of CKII alpha binds to immobilized HSP90. These results indicate that HSP90, DNA, and heparin compete with each other for binding to a common site of CKII alpha. If the binding of CKII to DNA is biologically significant, it could be possibly regulated also by HSP90.

    Biochemistry 1995;34;25;8123-9

  • Interaction of nucleolar protein B23 with peptides related to nuclear localization signals.

    Szebeni A, Herrera JE and Olson MO

    Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216-4505, USA.

    Nucleolar protein B23 is a putative ribosome assembly factor with a high affinity for peptides containing nuclear localization signals (NLSs). The interactions of various NLS-containing peptides with two B23 isoforms (B23.1 and B23.2) were examined using equilibrium dialysis and Scatchard analyses. The KD for protein B23 binding to a peptide containing the SV40 T-antigen NLS sequence was approximately 1 microM with a stoichiometry of 1:1 (peptide:protein). No significant differences were seen between the two B23 isoforms in their affinities for any of the peptides tested. Binding by a reverse sequence SV40 T-NLS peptide showed a nonlinear Scatchard plot: this peptide was unable displace the correct sequence peptide, suggesting that the reverse sequence peptide binds to a different site on the protein. A peptide containing the sequence required for nucleolar localization of the HIV-1 Rev protein had an affinity for B23 approximately 10-fold greater than that of the SV40 T-NLS. However, with a sequence sufficient only for Rev location in the nucleoplasm, the affinity for B23 was diminished to a level between that of the longer Rev sequence and the SV40 T-NLS. In competition binding assays, the Rev NLS peptide was able to displace the SV40 T NLS, indicating that both peptides bind to the same site on protein B23. There was no detectable binding to protein B23 by a peptide containing the bipartite NLS of nucleoplasmin. Phosphorylation of protein B23 by casein kinase II enhanced its affinity for the SV40 T- and Rev-derived peptides approximately 2-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

    Funded by: NIAID NIH HHS: 5RO1 AI 34277; NIGMS NIH HHS: 5 RO1 GM28349

    Biochemistry 1995;34;25;8037-42

  • Phorbol ester stimulates rapid intracellular phosphorylation of glia maturation factor.

    Lim R and Zaheer A

    Department of Neurology (Division of Neurochemistry and Neurobiology), University of Iowa College of Medicine, Iowa City, USA.

    We report that recombinant glia maturation factor (GMF), a 17-kD brain protein, can be phosphorylated in vitro at the serine residue by protein kinase C (PKC), protein kinase A (PKA), and casein kinase II (CKII), and at the threonine residue by p90 ribosomal S6 kinase (RSK). Endogenous GMF in astrocytes is phosphorylated at the serine (major) and threonine (minor) residues within 15 min after stimulation by phorbol 12-myristate 13-acetate (PMA). Phosphorylation gradually subsides over the next 24 h. The increased phosphorylation is not blocked by the protein synthesis inhibitor cycloheximide and is not accompanied by a rise in the mRNA for GMF and is therefore strictly a posttranslational regulatory phenomenon. The rapid and transient phosphorylation of GMF upon cellular activation suggests an intracellular role, possibly with involvement in signal transduction.

    Funded by: NIDDK NIH HHS: DK-25295

    Biochemical and biophysical research communications 1995;211;3;928-34

  • Interactions between the subunits of casein kinase II.

    Gietz RD, Graham KC and Litchfield DW

    Department of Biochemistry and Molecular Biology, University of Manitoba, Winnipeg, Canada.

    Casein kinase II (CKII) is a protein serine/threonine kinase known to control the activity of a variety of regulatory nuclear proteins. This enzyme has a tetrameric structure composed of two catalytic (alpha and/or alpha ') subunits and two beta subunits. We have examined the subunit composition of tetrameric complexes of purified bovine CKII by immunoprecipitation using alpha, alpha ', or beta subunit-specific antibodies. These experiments indicate that the enzyme can exist as homotetramers (i.e., alpha 2 beta 2 or alpha 2' beta 2) as well as heterotetramers (i.e. alpha alpha ' beta 2). To further examine subunit interactions between the alpha, alpha ', or beta subunits of CKII, we have utilized the yeast two-hybrid system (Fields, S. and Song, O. (1989) Nature 340: 245-246). For these studies, each subunit of human CKII was expressed in yeast as a fusion with the DNA binding domain or with the transcriptional activation domain of the yeast GAL4 transcriptional activator. These studies demonstrate that the alpha or alpha ' subunits of CKII can interact with the beta subunits of CKII, but not with other alpha or alpha ' subunits. By comparison, the beta subunits of CKII can interact with alpha, alpha ', or beta subunits. These results indicate that the CKII holoenzyme forms because of the ability of beta subunits to dimerize, bringing two heterodimers (alpha beta or alpha ' beta) into a tetrameric complex.

    The Journal of biological chemistry 1995;270;22;13017-21

  • Cell-cycle-dependent alterations of a highly phosphorylated nucleolar protein p130 are associated with nucleologenesis.

    Pai CY, Chen HK, Sheu HL and Yeh NH

    Institute of Microbiology and Immunology, School of Life Science, National Yang-Ming University, Taipei, Taiwan, Republic of China.

    We identified a novel human nucleolar phosphoprotein p130 (130 kDa) using a strategy for selecting monoclonal antibodies against nuclear proteins which oscillate in the cell cycle. p130 is localized in interphase nucleoli in a dotted manner. Complete extraction of p130 required a high concentration of salt (0.5 M NaCl) indicating that it binds firmly to the nucleolar components via ionic interaction. p130 is heavily phosphorylated, since alkaline phosphatase treatment converted the purified p130 into a 95 kDa product; this was further supported by the in vitro demonstration that cellular phosphatase and casein kinase II activities were responsible for the interchange of these two forms. Extracts of mitotic cells had lower concentrations of p130 compared to those of interphase cells suggesting that a proportion of p130 might be degraded during mitosis. Moreover, all the remaining p130 in mitotic cells was further phosphorylated, likely by a cdc2 kinase, resulting in increase in its solubility, and its dispersion throughout the entire cytoplasm. Thus, p130 in metaphase and anaphase cells was unable to be detected by immunofluorescence microscopy. At telophase, p130 reappeared and aggregated into a granular structure, resembling the prenucleolar bodies. These granules migrated from the nucleoplasm to the nucleoli in early G1-phase. Actinomycin D was able to induce segregation of p130-containing granules into the nucleoplasm, similar to the well-known behavior of the fibrillarin-containing granules, indicating that p130 is localized in the dense fibrillar component, a subnucleolar region for pre-rRNA synthesis and processing. The cDNA sequence of p130 revealed a remarkable feature, that a serine-rich stretch interspersed with acidic residues is repeated ten times. Such a characteristic is shared with a rat nucleolar phosphoprotein Nopp140, which is thought to shuttle between the nucleolus and the cytoplasm. Although p130 shows 74% identity to Nopp140, our observations suggest that during mitosis the functions of p130 are related to nucleologenesis.

    Journal of cell science 1995;108 ( Pt 5);1911-20

  • Characterization of Rad, a new member of Ras/GTPase superfamily, and its regulation by a unique GTPase-activating protein (GAP)-like activity.

    Zhu J, Reynet C, Caldwell JS and Kahn CR

    Research Division, Joslin Diabetes Center, Boston, Massachusetts 02215.

    We have recently identified a new member of the Ras/GTPase superfamily termed Rad which has unique sequence features and is overexpressed in the skeletal muscle of humans with type II diabetes (Reynet, C., and Kahn, C. R. (1993) Science, 262, 1441-1444). When expressed in bacteria as a glutathione S-transferase fusion protein, Rad bound [alpha-32P]GTP quickly and saturably. Binding was specific for guanine nucleotides and displayed unique magnesium dependence such that both GTP and GDP binding were optimal at relatively high Mg2+ concentrations (1-10 mM). Rad had low intrinsic GTPase activity which was greatly enhanced by a GTPase-activating protein (GAP) activity present in various tissues and cell lines. Several known GAPs had no stimulatory effect toward Rad. Conversion of Ser to Asn at position 66 in Rad (equivalent to position 12 in Ras) resulted in a total loss of GTP binding. Mutation of Pro61 (equivalent to Gly12 in Ras) or Gln109 (equivalent to Gln61 in Ras) had no effect on Rad GTPase activity, whereas creation of a double mutation at these positions resulted in exceptionally high intrinsic GTPase activity. In vitro, Rad was phosphorylated by the catalytic subunit of cAMP-dependent protein kinase (PK). Phosphopeptide mapping indicated two PKA phosphorylation sites near the COOH terminus. Rad also co-precipitated a serine/threonine kinase activity from extracts of various tissues and cell lines which catalyzed phosphorylation on Rad but was not inhibited by PKA inhibitor. Thus, Rad is a GTP-binding protein and a GTPase which has some structure/function similarities to Ras, but displays unique features. Rad may also be phosphorylated on serine/threonine residues by PKA and other kinases, as well as regulated by its own GAP which is present in many tissues and cell types.

    Funded by: NIDDK NIH HHS: DK 36836, DK 45935

    The Journal of biological chemistry 1995;270;9;4805-12

  • Protein kinases. 4. Protein kinase CK2: an enzyme with multiple substrates and a puzzling regulation.

    Allende JE and Allende CC

    Departamento de Bioquímica, Facultad de Medicina, Universidad de Chile, Santiago.

    Protein kinase CK2 (also known as casein kinase II) is a ubiquitous eukaryotic ser/thr protein kinase present in the nucleus and cytoplasm. CK2 is known to phosphorylate more than 100 substrates, many of which are involved in the control of cell division and in signal transduction. The review centers on the structure and function of CK2 alpha and beta subunits and on the regulation of its activity, a topic that remains to be elucidated. An analogy is drawn between CK2 and the cyclin-dependent kinases (cdks); both types of protein kinases share many substrates and are activated by regulatory subunits.

    FASEB journal : official publication of the Federation of American Societies for Experimental Biology 1995;9;5;313-23

  • Casein kinase II in theileriosis.

    ole-MoiYoi OK

    International Livestock Research Institute (ILRI), Nairobi, Kenya.

    Science (New York, N.Y.) 1995;267;5199;834-6

  • Functional analysis of the phosphorylation sites on the human immunodeficiency virus type 1 Vpu protein.

    Friborg J, Ladha A, Göttlinger H, Haseltine WA and Cohen EA

    Département de Microbiologie et Immunologie, Faculté de Médecine, Université de Montréal, Québec, Canada.

    The human immunodeficiency virus type 1 (HIV-1)-encoded vpu product is a small class 1 integral membrane protein that is phosphorylated by the ubiquitous casein kinase II (CKII) in HIV-1-infected cells. The Vpu protein facilitates the release of budding virions from the surface of infected cells and delays the rate of syncytium formation. In this study, we investigated the role of phosphorylation in the biological activity of Vpu. Our results show that phosphorylation of Vpu occurs on serine residues at positions 52 and 56 located in a highly conserved dodecapeptide sequence. Mutation of either Ser 56, or both Ser 52 and Ser 56 impaired the ability of Vpu to delay the rate of syncytium formation while retaining virion release activity at levels comparable to vpu+ proviruses. Flow cytometry analysis indicates that the relative amounts of envelope glycoprotein gp120 expressed at the surface of cells transfected with these vpu mutant proviruses was two- to threefold greater than that observed on cells transfected with a vpu+ provirus. This increased expression of gp120 at the cell surface may explain the more rapid onset of syncytium formation observed in cell transfected with vpu mutant proviruses. These results suggest that Vpu-facilitated virion release and delayed cytopathic effect are the consequence of two distinct functional activities of the protein.

    Funded by: NIAID NIH HHS: AI34267

    Journal of acquired immune deficiency syndromes and human retrovirology : official publication of the International Retrovirology Association 1995;8;1;10-22

  • Phosphorylation negatively regulates the function of coactivator PC4.

    Ge H, Zhao Y, Chait BT and Roeder RG

    Laboratory of Biochemistry and Molecular Biology, Rockefeller University, New York, NY 10021.

    Human positive cofactor 4 (PC4) mediates activator-dependent transcription by RNA polymerase II, apparently through interactions with transcriptional activators and the basal transcription machinery. We report here that PC4 function is modulated by in vivo phosphorylation. Protein-protein interaction studies and in vitro transcription assays demonstrate that only the nonphosphorylated form of PC4 is functionally active. Although recombinant PC4 can be phosphorylated by casein kinase II and protein kinase C in vitro, mutational and mass spectrometric analyses suggest that the in vivo hyperphosphorylation of PC4 is mediated mainly by casein kinase II and restricted to an N-terminal serine-rich region. These observations provide one example of a transcriptional cofactor that is negatively regulated by casein kinase II phosphorylation.

    Funded by: NCI NIH HHS: CA42567; NCRR NIH HHS: RR00862

    Proceedings of the National Academy of Sciences of the United States of America 1994;91;26;12691-5

  • Identification of phosphorylation sites unique to the B form of human progesterone receptor. In vitro phosphorylation by casein kinase II.

    Zhang Y, Beck CA, Poletti A, Edwards DP and Weigel NL

    Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030.

    The human progesterone receptor (PR), a member of the steroid/thyroid receptor superfamily of ligand-activated transcription factors, is expressed in most tissues as two forms that exhibit differential transcriptional activation potentials, full-length PR-B and NH2-terminally truncated PR-A. In human breast cancer cells (T47D) both forms of PR are constitutively phosphorylated but phosphorylation is increased in response to hormone treatment, suggesting that this modification has a role in regulating the activation state of the receptor. To more directly define the functional role of phosphorylation in the action of A and B receptors requires knowledge of the phosphorylated amino acid residues and the protein kinase(s) involved. Toward this end we have developed a strategy that combines isolation of PR phosphotryptic peptides by reverse phase high performance liquid chromatography, secondary analytical protease digestion, manual Edman degradation, and release of 32P that resulted in identification of two major phosphorylation sites, Ser81 and Ser162. Both sites are located in the amino-terminal region unique to PR-B, and one of these sites (Ser81) is encompassed in a casein kinase II (CKII) consensus sequence. Although human PR contains 11 potential CKII consensus sequences, CKII in vitro phosphorylated purified PR-B only at Ser81 suggesting that this may be an authentic site for CKII in vivo.

    Funded by: NCI NIH HHS: CA46938, CA57539, P30 CA46934; ...

    The Journal of biological chemistry 1994;269;49;31034-40

  • Serine 1524 is a major site of phosphorylation on human topoisomerase II alpha protein in vivo and is a substrate for casein kinase II in vitro.

    Wells NJ, Addison CM, Fry AM, Ganapathi R and Hickson ID

    Imperial Cancer Research Fund Laboratories, Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, United Kingdom.

    Topoisomerase II protein is essential for cell proliferation and is known to exist as a phosphoprotein in cells from both lower and higher eukaryotic species. In this paper, we have investigated the phosphorylation of the alpha isozyme of human topoisomerase II. The topoisomerase II alpha protein was phosphorylated predominantly on serine residues in the human tumor cell lines HeLa and NSCLC-3. Two-dimensional tryptic phosphopeptide mapping studies revealed several sites of phosphorylation in vivo, including a major site that was common to topoisomerase II alpha protein from both HeLa and NSCLC-3 cells. To identify sites of phosphorylation, the regulatory C-terminal domain of human topoisomerase II alpha protein was overexpressed in Escherichia coli as a hexahistidine-tagged fusion protein and purified by nickel chelate chromatography. Tryptic phosphopeptide mapping revealed that casein kinase II phosphorylated the C-terminal domain primarily on 2 serine residues in vitro, which were shown to be sites of modification in vivo. Site-directed mutagenesis studies identified these casein kinase II-specific phosphorylation sites as serine 1524 and serine 1376.

    Funded by: NCI NIH HHS: R0I CA35531

    The Journal of biological chemistry 1994;269;47;29746-51

  • The phosphorylation of the respiratory burst oxidase component p47phox during neutrophil activation. Phosphorylation of sites recognized by protein kinase C and by proline-directed kinases.

    el Benna J, Faust LP and Babior BM

    Department of Molecular and Experimental Medicine, Scripps Research Institute, La Jolla, California 92037.

    The respiratory burst oxidase catalyzes the production of O2.- from oxygen and NADPH. It is dormant in resting cells but becomes active when the cells are stimulated. Activation is accompanied by the phosphorylation of multiple serines in the cytosolic oxidase component p47phox, which moves from cytosol to the membrane during oxidase activation. Using immunopurified p47phox isolated from 32Pi-loaded neutrophils activated with phorbol myristate acetate, we showed that all the 32P was in the C-terminal CNBr fragment of the protein, and that in that fragment, Ser-303, Ser-304, Ser-320, Ser-328, Ser-345, and Ser-348 and at least one of the three serines, Ser-359, Ser-370, and Ser-379, were phosphorylated, while Ser-282, Ser-287, Ser-381, and Ser-388 were not. Of the phosphorylated serines, Ser-303, Ser-304, Ser-320, and Ser-328 are located in protein kinase C substrate sequences. Ser-345 and Ser-348, however, are located in sequences recognized by mitogen-activated protein (MAP) kinase (-PXSP-). This finding suggests that MAP kinase or a related proline-directed kinase may participate in the regulation of O2.- production by activated neutrophils. The tryptic peptide map of p47phox phosphopeptides from neutrophils activated by N-formyl-methionyl-leucyl-phenylalanine closely resembled that of p47phox phosphopeptides from phorbol-activated cells, suggesting that the same serines were phosphorylated in response to each agent.

    Funded by: NIAID NIH HHS: AI-24227, AI-28479, AI-30742; ...

    The Journal of biological chemistry 1994;269;38;23431-6

  • In vitro phosphorylation of caveolin-rich membrane domains: identification of an associated serine kinase activity as a casein kinase II-like enzyme.

    Sargiacomo M, Scherer PE, Tang ZL, Casanova JE and Lisanti MP

    Whitehead Institute for Biomedical Research, Cambridge, MA 02142-1479.

    Caveolae are flask-shaped micro-invaginations associated with the plasma membrane of a wide variety of cell types. Caveolin, an integral membrane component of caveolae, was first identified as the major phosphoprotein whose phosphorylation was elevated in v-Src transformed cells. As both v-Src transformation and elevated caveolin phosphorylation were dependent on membrane attachment of v-Src, it has been suggested that caveolin is a critical target in v-Src transformation. Although an increase in tyrosine phosphorylation of caveolin was evident, the increase in caveolin phosphorylation was predominantly on serine residues. In accordance with these in vivo observations, isolated caveolin-rich membrane domains undergo phosphorylation in vitro predominantly on serine and contain an unidentified serine kinase activity. Here, we have identified this serine kinase activity as a casein kinase II-like enzyme, since the phosphorylation of caveolin-rich membrane domains is stimulated and inhibited by known effectors of casein kinase II (poly-L-lysine, endogenous polyamines, and a casein kinase II inhibitor peptide), but is unaffected by modulators of other known kinases. In support of these observations, caveolin contains a consensus sequence for casein kinase II phosphorylation in its cytoplasmic N-terminal domain (Ser-88). A peptide containing this sequence inhibits the in vitro phosphorylation of caveolin-rich membrane domains, while many other peptides derived from the N-terminal domain of caveolin do not affect phosphorylation. Caveolin-rich membrane domains were also a substrate for exogenously added purified casein kinase II, but not casein kinase I. Finally, immunoblotting of these domains with an antibody directed against the alpha and alpha' subunits of casein kinase II reveals two bands with apparent molecular weights consistent with the known molecular weights of the alpha and alpha' subunits of casein kinase II. As casein kinase II appears to play a role in mitogenic signalling events and casein kinase II activators (endogenous polyamines) are required for v-Src transformation, our results may have implications for understanding the mechanism of v-Src oncogenesis.

    Funded by: NIDDK NIH HHS: DK-47618; NIGMS NIH HHS: GM-49516, GM-50443; ...

    Oncogene 1994;9;9;2589-95

  • Identification of novel phosphorylation sites in the beta-subunit of translation initiation factor eIF-2.

    Welsh GI, Price NT, Bladergroen BA, Bloomberg G and Proud CG

    Department of Biochemistry, School of Medical Sciences, University of Bristol, United Kingdom.

    Initiation factor eIF-2 (a trimer of subunits alpha, beta and gamma) attaches the initiator Met-tRNA to the ribosome during the initiation of translation in eukaryotic cells. Both the alpha and beta subunits can be phosphorylated although the sites in the beta-subunit have not previously been fully identified. Here we identify the sites at which eIF-2 beta is phosphorylated in vitro by three well-characterised protein kinases, casein kinase-2 (which phosphorylates serine residues-2 and -67), protein kinase C (serine-13) and cAMP-dependent protein kinase (serine-218). This constitutes an essential prerequisite for studying the phosphorylation of eIF-2 beta in vivo. Indeed, we present evidence that at least one of these sites (serine-67) is phosphorylated in reticulocytes. The major kinase activity against eIF-2 beta in reticulocyte lysates appears in CK-2 and protein phosphatase-2A is the principal enzyme responsible for dephosphorylation of eIF-2 beta phosphorylated by this kinase.

    Biochemical and biophysical research communications 1994;201;3;1279-88

  • Isolation of phosphorylated calmodulin from rat liver and identification of the in vivo phosphorylation sites.

    Quadroni M, James P and Carafoli E

    Institute of Biochemistry, Swiss Federal Institute of Technology (ETH), Zürich.

    A procedure is described for the isolation of calmodulin (CaM) from rat liver which produces a fraction containing non-phosphorylated, mono-, di-, and triphosphocalmodulin as determined by mass spectrometric analysis. The distribution of CaM between the various phospho-species varies from preparation to preparation even though the isolation procedure is rigidly defined, suggesting that CaM phosphorylation may be a very labile phenomenon dependent on the state of the liver as it is removed from the animal. Approximately 15% of CaM in the cell is phosphorylated. The in vivo phosphorylation sites were determined by mass spectrometric analysis of a combined CNBr and trypsin digestion of the phosphocalmodulin (phospho-CaM)-containing fractions. Phosphorylated peptides were sequenced using two mass scanning devices linked together for collisionally activated fragmentation studies to determine peptide sequences, and the phosphorylation sites were determined as Thr-79, Ser-81, and Ser-101. These correspond to three of the four in vitro target sites of calmodulin phosphorylation by casein kinase II, which indicates that this may be the enzyme responsible for the phosphorylation in vivo. A preliminary study on the modulatory activity of phosphorylated calmodulin using a sample extensively phosphorylated in vitro with casein kinase II confirmed that phospho-CaM has an altered biological activity, i.e. reduced activation of the erythrocyte plasma membrane Ca2+ pump.

    The Journal of biological chemistry 1994;269;23;16116-22

  • Molecular characterization of human stathmin expressed in Escherichia coli: site-directed mutagenesis of two phosphorylatable serines (Ser-25 and Ser-63).

    Curmi PA, Maucuer A, Asselin S, Lecourtois M, Chaffotte A, Schmitter JM and Sobel A

    INSERM U153, Paris, France.

    Stathmin, a probable relay protein possibly integrating multiple intracellular regulatory signals [reviewed in Sobel (1991) Trends Biochem. Sci. 16, 301-305], was expressed in Escherichia coli at levels as high as 20% of total bacterial protein. Characterization of the purified recombinant protein revealed that it had biochemical properties very similar to those of the native protein. It is a good substrate for both cyclic AMP-dependent protein kinase (PKA) and p34cdc2, on the same four sites as the native eukaryotic protein. As shown by m.s., the difference in isoelectric points from the native protein is probably due to the absence of acetylation of the protein produced in bacteria. C.d. studies indicate that stathmin probably contains about 45% of its sequence in an alpha-helical conformation, as also predicted for the sequence between residues 47 and 124 by computer analysis. Replacement of Ser-63 by alanine by in vitro mutagenesis resulted in a ten times less efficient phosphorylation of stathmin by PKA which occurred solely on Ser-16, confirming that Ser-63 is the major target of this kinase. Replacement of Ser-25, the major site phosphorylated by mitogen-activated protein kinase in vitro and in vivo, by the charged amino acid glutamic acid reproduced, in conjunction with the phosphorylation of Ser-16 by PKA, the mobility shift on SDS/polyacrylamide gels induced by the phosphorylation of Ser-25. This result strongly suggests that glutamic acid in position 25 is able to mimic the putative interactions of phosphoserine-25 with phosphoserine-16, as well as the resulting conformational changes that are probably also related to the functional regulation of stathmin.

    The Biochemical journal 1994;300 ( Pt 2);331-8

  • Differential activities of the human immunodeficiency virus type 1-encoded Vpu protein are regulated by phosphorylation and occur in different cellular compartments.

    Schubert U and Strebel K

    Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, Bethesda, Maryland 20892.

    The human immunodeficiency virus type 1 (HIV-1)-specific Vpu is an 81-amino-acid amphipathic integral membrane protein with at least two different biological functions: (i) enhancement of virus particle release from the plasma membrane of HIV-1-infected cells and (ii) degradation of the virus receptor CD4 in the endoplasmic reticulum (ER). We have previously found that Vpu is phosphorylated in infected cells at two seryl residues in positions 52 and 56 by the ubiquitous casein kinase 2. To study the role of Vpu phosphorylation on its biological activity, a mutant of the vpu gene lacking both phosphoacceptor sites was introduced into the infectious molecular clone of HIV-1, pNL4-3, as well as subgenomic Vpu expression vectors. This mutation did not affect the expression level or the stability of Vpu but had a significant effect on its biological activity in infected T cells as well as transfected HeLa cells. Despite the presence of comparable amounts of wild-type and nonphosphorylated Vpu, decay of CD4 was observed only in the presence of phosphorylated wild-type Vpu. Nonphosphorylated Vpu was unable to induce degradation of CD4 even if the proteins were artificially retained in the ER. In contrast, Vpu-mediated enhancement of virus secretion was only partially dependent on Vpu phosphorylation. Enhancement of particle release by wild-type Vpu was efficiently blocked when Vpu was artificially retained in the ER, suggesting that the two biological functions of Vpu are independent, occur at different sites within a cell, and exhibit different sensitivity to phosphorylation.

    Journal of virology 1994;68;4;2260-71

  • The human immunodeficiency virus type 1 encoded Vpu protein is phosphorylated by casein kinase-2 (CK-2) at positions Ser52 and Ser56 within a predicted alpha-helix-turn-alpha-helix-motif.

    Schubert U, Henklein P, Boldyreff B, Wingender E, Strebel K and Porstmann T

    Institut für Medizinische Immunologie, Medizinische Fakultät (Charité), Humboldt-Universität zu Berlin, Germany.

    The human immunodeficiency virus type 1 (HIV-1) encoded Vpu is a small integral membrane phosphoprotein that functions in the enhancement of viral particle release and has more recently been shown to cause degradation of CD4 at the endoplasmic reticulum. We have demonstrated earlier that Vpu is phosphorylated by the ubiquitous casein kinase-2 (CK-2) in HIV-1 infected cells. The phosphoacceptor sites targeted by CK-2 in Vpu, however, have not been demonstrated and it was unclear whether Vpu was phosphorylated at one or more of its four serine residues. In this study we characterized the CK-2 phosphoacceptor sites in Vpu using recombinant CK-2 for in vitro phosphorylation of recombinant Vpu protein as well as synthetic peptides of Vpu. Phosphorylation of both Ser52 and Ser56 was demonstrated by in vitro phosphorylation using three 54-residue peptides comprising the entire hydrophilic part of Vpu and containing single serine to asparagine transitions in either position 52 or 56. The Km values of CK-2 to these peptides were established, revealing a preferential phosphorylation of Ser56. The Km values are: Ser56 = 31 microM; Ser 52 = 156 microM; wild type = 27 microM. In addition, we studied phosphorylation of Vpu by endogenous CK-2 following in vitro translation in rabbit reticulocyte lysate of wild-type Vpu or a mutant, Vpum2/6, carrying serine to asparagine changes at amino acid positions 52 and 56. The in vivo phosphorylation of Vpu was studied in transiently transfected human embryonic kidney (293) cells. In this system, the mutant Vpum2/6 was not phosphorylated, indicating that the seryl residues of Vpu at amino acid positions 52 and 56, but not those at positions 23 and 61, are phosphorylated by CK-2. The two CK-2 phosphorylation sites are conserved in all known Vpu sequences and represent the consensus Ser52GlyAsn(Glu/Asp)Ser(Glu/Asp)Gly(Glu/Asp)59. Prediction of the secondary structure revealed a conserved alpha-helix-turn-alpha-helix motif for the hydrophilic C-terminal part of Vpu. A structural model for Vpu is proposed in which the membrane anchor precedes a region comprising two amphipathic alpha-helices of opposed polarity, joined by a strongly acidic turn that protrudes into the cytoplasm and contains the CK-2 phosphorylation sites. Possible functional and structural homologies of Vpu to the membrane channel-forming M2 protein of influenza A viruses are discussed.

    Journal of molecular biology 1994;236;1;16-25

  • The human gene (CSNK2A1) coding for the casein kinase II subunit alpha is located on chromosome 20 and contains tandemly arranged Alu repeats.

    Wirkner U, Voss H, Lichter P, Ansorge W and Pyerin W

    German Cancer Research Center, Heidelberg, Germany.

    We have isolated and characterized a 18.9-kb genomic clone representing a central portion of the human casein kinase II (CKII) subunit alpha gene (CSNK2A1). Using the whole clone as a probe, the gene was localized on chromosome 20p13. The clone contains eight exons whose sequences comprise bases 102 to 824 of the coding region of the human CKII alpha. The exon/intron splice junctions conform to the gt/ag rule. Three of the nine introns are located at positions corresponding to those in the CKII alpha gene of the nematode Caenorhabditis elegans. The introns contain eight complete and eight incomplete Alu repeats. Some of the Alu sequences are arranged in tandems of two or three, which seem to originate from insertions of younger Alu sequences into the poly(A) region of previously integrated Alu sequences, as indicated by flanking direct repeats.

    Genomics 1994;19;2;257-65

  • Molecular mechanism of the synergistic phosphorylation of phosphatase inhibitor-2. Cloning, expression, and site-directed mutagenesis of inhibitor-2.

    Park IK, Roach P, Bondor J, Fox SP and DePaoli-Roach AA

    Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis 46202-5122.

    Inhibitor-2 (I-2) is the regulatory subunit of the ATP-Mg-dependent phosphatase, a cytosolic form of type 1 protein phosphatase. Phosphorylation of I-2 at Thr-72 by the protein kinase glycogen synthase kinase-3 (GSK-3) leads to activation of the enzyme. Casein kinase II action was shown to synergistically enhance phosphorylation and activation by GSK-3 (DePaoli-Roach, A.A. (1984) J. Biol. Chem. 259, 12144-12152). Rabbit skeletal muscle and liver I-2 cDNA clones have been isolated. Rabbit skeletal muscle cDNAs could be placed in two subtypes, differing in the length of the 3'-untranslated region. The coding sequence of 612 nucleotides was identical in the two skeletal muscle and the liver cDNAs and predicted a protein of 204 amino acids, consistent with analysis of the purified protein. Northern hybridization analysis indicated that the two mRNAs of 1.7 and 2.7 kilobase pairs were present in all rabbit tissues examined, except in liver, where only the larger transcript was detected, and in testis, where additional transcripts were present. Expression in Escherichia coli of wild-type and phosphorylation site mutants resulted in the production of I-2 polypeptides with apparent M(r) values of approximately 31,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The inhibitory activity of the recombinant proteins was similar to that of native rabbit skeletal muscle I-2 and was unaffected by the substitution of alanine for the GSK-3 site (Thr-72) and for the casein kinase II sites (Ser-86 and Ser-120/121) or by substitution of glutamic acid and aspartic acid for Thr-72 and Ser-86. Recombinant wild-type I-2 and the Ala-120/121 mutant were phosphorylated synergistically by GSK-3 and casein kinase II. The Thr-72 and Ser-86 mutants, however, did not undergo this synergistic phosphorylation. Our studies indicate that Thr-72 is the only GSK-3 site and that Ser-86 is the casein kinase II site required for the potentiation of GSK-3 action. Furthermore, acidic residues cannot substitute for the phosphate group either in enhancing GSK-3 phosphorylation or in activating the phosphatase.

    Funded by: NIDDK NIH HHS: DK36569

    The Journal of biological chemistry 1994;269;2;944-54

  • L-29, a soluble lactose-binding lectin, is phosphorylated on serine 6 and serine 12 in vivo and by casein kinase I.

    Huflejt ME, Turck CW, Lindstedt R, Barondes SH and Leffler H

    Department of Psychiatry, University of California, San Francisco 94143.

    L-29, a mammalian soluble lactose-binding lectin, was previously shown to be phosphorylated in confluent 3T3 fibroblasts (Cowles, E. A., Agrwal, N., Anderson, R. L., and Wang, J. L. (1990) J. Biol. Chem. 265, 17706-17712), which contain a small amount of this protein. We have determined the site of phosphorylation on L-29, taking advantage of the abundance of L-29 (about 1% of total soluble cell protein) in confluent polarized Madin-Darby canine kidney (MDCK) cells. Approximately 15-20% of the L-29 is phosphorylated in these cells. Phosphoamino acid analysis showed phosphate incorporation only at serine. Analysis of chymotryptic and endoproteinase Asp-N-generated NH2-terminal fragments by Edman degradation showed that 90% of the phosphate was at Ser6 and 10% at Ser12. The sequence surrounding Ser6, which is conserved in all known L-29 sequences, indicated that this serine might be phosphorylated by casein kinase I or casein kinase II. Reaction of human recombinant L-29 with [gamma-32P]ATP and each of these casein kinases showed that only casein kinase I catalyzed significant incorporation of 32P into L-29; and, as with the L-29 from the MDCK cell extracts, most of the phosphate was incorporated at Ser6 and a small amount was incorporated at Ser12.

    The Journal of biological chemistry 1993;268;35;26712-8

  • Identification of casein kinase II phosphorylation sites in Max: effects on DNA-binding kinetics of Max homo- and Myc/Max heterodimers.

    Bousset K, Henriksson M, Lüscher-Firzlaff JM, Litchfield DW and Lüscher B

    Institute of Molecular Biology, Hannover Medical School, Germany.

    Myc proteins have been implicated in the regulation of cell growth and differentiation. The identification of Max, a basic region/helix-loop-helix/leucine zipper protein, as a partner for Myc has provided insights into Myc's molecular function as a transcription factor. Recent evidence indicates that the relative abundance of Myc and Max is important to determine the level of specific gene transcription. In this report we have identified two major in vivo phosphorylation sites in Max (Ser-2 and -11) which can be modified in vitro by casein kinase II (CKII). Phosphorylation of these sites modulates DNA-binding by increasing both the on- and off-rates of Max homo- as well as Myc/Max heterodimers. In addition, our data indicate that the steady state binding of the shorter version of Max (p21) to DNA was similar yet its rate of dissociation faster than that of longer version of Max (p22). These data argue that different Max complexes have different kinetic properties and that these can be modified by CKII phosphorylation. We propose this as an important biological mechanism by which different dimeric complexes can exchange with varying efficiencies on DNA, thereby responding to changes in cell growth conditions.

    Oncogene 1993;8;12;3211-20

  • Multiple and cooperative phosphorylation events regulate the CREM activator function.

    de Groot RP, den Hertog J, Vandenheede JR, Goris J and Sassone-Corsi P

    Laboratoire Génétique Moléculaire des Eucaryotes, CNRS, U184 de l'INSERM, Faculté de Médecine, Institut de Chimie Biologique, Strasbourg, France.

    Phosphorylation is one of the major mechanisms by which the activity of transcription factors can be regulated. We have investigated the role of phosphorylation in the regulation of the transcription factor CREM. We show that the CREM tau activator is phosphorylated on multiple serine and threonine residues in vivo. Stimulation of various signal transduction pathways by forskolin, TPA or Ca2+ ionophore leads to enhanced phosphorylation of serine 117, concomitant with an increase in the transactivation potential of CREM tau. We have identified multiple kinases that can also phosphorylate S117 in vitro. Moreover, we show that casein kinase I and II cooperatively phosphorylate CREM tau on multiple residues, eliciting enhanced DNA binding. Cooperative phosphorylation is also observed with other kinases. These results show that the activity of CREM tau is regulated by multiple phosphorylation events, suggesting that CREM could be considered as a nuclear effector where signalling pathways may converge and/or cross-talk.

    The EMBO journal 1993;12;10;3903-11

  • Multiple phosphorylation of stathmin. Identification of four sites phosphorylated in intact cells and in vitro by cyclic AMP-dependent protein kinase and p34cdc2.

    Beretta L, Dobránsky T and Sobel A

    Institut National de la Santé et de la Recherche Médicale Unité 153, Centre National de la Recherche Scientifique Unité de Recherche Associée 614, Paris, France.

    Stathmin is a ubiquitous, highly conserved phosphoprotein which most likely acts as a relay integrating various intracellular pathways regulating cell proliferation, differentiation, and functions. At least 14 molecular forms of stathmin have been identified so far, which migrate as 2 unphosphorylated and 12 increasingly phosphorylated spots (M(r) = 19,000-23,000; pI = 6.2-5.6) on two-dimensional electrophoretic gels, and whose pattern may reflect the state of activation of cells. We found that stathmin could be phosphorylated in vitro by at least three different protein kinases: cAMP-dependent protein kinase, p34cdc2, and casein kinase II, cAMP-dependent protein kinase catalyzed the phosphorylation of stathmin on serines 16 (K-R-A-S) and 63 (R-R-K-S), whereas p34cdc2 induced phosphorylation on serines 25 (I-L-S-P-R) and 38 (P-L-S-P-P-K-K-K). Interestingly, phosphorylation by both kinases together yielded all of the phosphoforms of stathmin identified so far. Two-dimensional phosphopeptide analysis allowed us to demonstrate that the same four sites were exclusively found to be phosphorylated in vivo, in brain tissue as well as in control or nerve growth factor-stimulated PC12 cells. In this latter case, the major site phosphorylated in response to nerve growth factor being serine 25, it is likely that a kinase such as a mitogen-activated protein kinase, known to be activated by growth factors, might directly phosphorylate stathmin. The phosphopeptide map analysis allowed further identification of the specific combinations among the four sites whose phosphorylation is responsible for the characteristic two-dimensional polyacrylamide gel electrophoresis migration of the resulting stathmin forms both in vitro and in vivo and revealed the existence of likely structural interactions between the sites phosphorylated. In conclusion, our results show that phosphorylation of serines 16, 25, 38, and 63 accounts for all of the major functional stathmin forms observed in vivo. The present identification of these sites will foster a better understanding of some intracellular mechanisms involved in the diverse physiological regulation of the proliferation, differentiation, and functions of cells, including the role of stathmin in these processes as a relay integrating diverse signaling pathways.

    The Journal of biological chemistry 1993;268;27;20076-84

  • Identification of rat epidermal profilaggrin phosphatase as a member of the protein phosphatase 2A family.

    Kam E, Resing KA, Lim SK and Dale BA

    Department of Oral Biology, University of Washington, Seattle 98195.

    The aggregation of cellular intermediate filaments is an important step in the terminal differentiation of keratinocytes. It has been shown that epidermal filaggrin can cause intermediate filaments to aggregate in vitro and may also have the same function in vivo. Filaggrin is derived via dephosphorylation and proteolysis from a highly phosphorylated precursor, profilaggrin, which is found in the granular layer of the epidermis. Using casein kinase II phosphorylated filaggrin as substrate, a profilaggrin phosphatase has been partially purified from rat epidermal homogenate by three chromatographic steps (DE52, hydroxylapatite and S200 gel filtration). Profilaggrin phosphatase activity eluted from the last column has a Km of 0.12 mM and a Vmax of 8 nmol/mg/min with respect to phosphofilaggrin. Results obtained by initial rate analysis showed that the enzymatic activity is not affected by phospho-tyrosyl phosphatase inhibitors and the active fractions preferentially dephosphorylate the alpha subunit of phosphorylase kinase which has been phosphorylated by cAMP-dependent kinase. These results suggest that epidermal profilaggrin phosphatase is not a phospho-tyrosyl phosphatase or a type 1 phospho-seryl/phospho-threonyl phosphatase. Dephosphorylation is not affected by EDTA, calcium or magnesium, but is very sensitive to okadaic acid inhibition (IC50 = 80 pM), suggesting that the enzymatic activity is related to that of the protein phosphatase 2A (PP2A).(ABSTRACT TRUNCATED AT 250 WORDS)

    Funded by: NIADDK NIH HHS: AM21557; NIDCR NIH HHS: DE04660

    Journal of cell science 1993;106 ( Pt 1);219-26

  • Phosphorylation of the insulin receptor substrate IRS-1 by casein kinase II.

    Tanasijevic MJ, Myers MG, Thoma RS, Crimmins DL, White MF and Sacks DB

    Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts 02115.

    IRS-1, a principal substrate of the insulin receptor, is phosphorylated on serine, threonine, and tyrosine residues in a variety of tissues during insulin stimulation. Casein kinase II, an insulin-sensitive serine/threonine kinase, catalyzed the in vitro incorporation of 1 to 2 mol of phosphate/mol of recombinant rat IRS-1. Two-dimensional phosphopeptide mapping of IRS-1 phosphorylated by casein kinase II in vitro and IRS-1 immunoprecipitated from intact Chinese hamster ovary cells demonstrated multiple common phosphopeptides, suggesting that overexpressed IRS-1 is a substrate for casein kinase II in these cells. Moreover, the common phosphopeptides that appeared to be insulin-sensitive in intact cells comprised 22% of casein kinase II-catalyzed 32P incorporation into IRS-1 in vitro. These data suggest that casein kinase II mediates a portion of the insulin-stimulated serine/threonine phosphorylation of overexpressed IRS-1 in vivo. By using phosphoamino acid analysis, strong cation exchange analysis, manual Edman degradation, and automated amino acid sequencing, Thr-502 was identified as the major casein kinase II-catalyzed phosphorylation site in rat IRS-1. Furthermore, Ser-99, an additional site labeled at low yield, appeared to be contained in an insulin-sensitive phosphopeptide. Thus, casein kinase II-catalyzed phosphorylation of IRS-1 may be a component of the intracellular insulin signalling cascade.

    Funded by: NIDDK NIH HHS: DK 43682, DK 43808

    The Journal of biological chemistry 1993;268;24;18157-66

  • The 25-kDa FK506-binding protein is localized in the nucleus and associates with casein kinase II and nucleolin.

    Jin YJ and Burakoff SJ

    Division of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA.

    FK506-binding proteins (FKBPs) have been identified as the cellular receptors of the immunosuppressive drugs FK506 and rapamycin. Recently, we cloned a 25-kDa FKBP family member (FKBP25) and found that FKBP25 contains a nuclear localization sequence and several potential casein kinase II phosphorylation sites. It has been previously shown that phosphorylation of proteins by casein kinase II can enhance their nuclear localization. Here we demonstrate that FKBP25 is localized to the nucleus and that a glutathione S-transferase fusion protein of FKBP25 (GST-FKBP25) can be phosphorylated by casein kinase II. Also a stable FKBP25/casein kinase II complex was formed when the GST-FKBP25 fusion protein was incubated either with purified casein kinase II or with cell lysates. Furthermore, when GST-FKBP25 was incubated with nuclear lysates, nucleolin, a major nuclear substrate of casein kinase II, was found associated with the GST-FKBP25/casein kinase II complex. Casein kinase II phosphorylation of several cytosolic and nuclear substrates, including nucleolin, appears to be important for the regulation of cell growth. The interaction of FKBP25 with casein kinase II may regulate these functions.

    Proceedings of the National Academy of Sciences of the United States of America 1993;90;16;7769-73

  • Multi-site phosphorylation of the protein tyrosine phosphatase, PTP1B: identification of cell cycle regulated and phorbol ester stimulated sites of phosphorylation.

    Flint AJ, Gebbink MF, Franza BR, Hill DE and Tonks NK

    Cold Spring Harbor Laboratory, NY 11724.

    The non-transmembrane protein tyrosine phosphatase, PTP1B, comprises 435 amino acids, of which the C-terminal 114 residues have been implicated in controlling both localization and function of this enzyme. Inspection of the sequence of the C-terminal segment reveals a number of potential sites of phosphorylation. We show that PTP1B is phosphorylated on seryl residues in vivo. Increased phosphorylation of PTP1B is seen to accompany the transition from G2 to M phase of the cell cycle. Two major tryptic phosphopeptides appear in two-dimensional maps of PTP1B from mitotic cells. One of these comigrates with the peptide generated following phosphorylation of PTP1B in vitro at Ser386 by the mitotic protein Ser/Thr kinase p34cdc2:cyclin B. The site of phosphorylation that is responsible for the pronounced retardation in the electrophoretic mobility of PTP1B from mitotic cells has been identified by site directed mutagenesis as Ser352. The identify of the kinase responsible for this modification is presently unknown. We also show that stimulation of HeLa cells with the phorbol ester TPA enhances phosphorylation of PTP1B. Two dimensional phosphopeptide mapping reveals that the bulk of the phosphate is in a single tryptic peptide. The site, identified as Ser378, is also the site of phosphorylation by protein kinase C (PKC) in vitro. Thus the TPA-stimulated phosphorylation of PTP1B in vivo appears to result directly from phosphorylation by PKC. The effect of phosphorylation on the activity of PTP1B has been examined in immunoprecipitates from TPA-treated and nocodazole-arrested cells. TPA treatment does not appear to affect activity directly, whereas the activity of PTP1B from nocodazole-arrested cells is only 70% of that from asynchronous populations.

    Funded by: NCI NIH HHS: CA40512, CA53840

    The EMBO journal 1993;12;5;1937-46

  • Structure and sequence of an intronless gene for human casein kinase II-alpha subunit.

    Devilat I and Carvallo P

    Departamento de Bioquimica, Facultad de Medicina, Universidad de Chile, Santiago.

    Using sixteen different primers based on the cDNA sequence of the human casein kinase II-alpha subunit, different fragments of this gene were amplified by PCR from human genomic DNA. The sizes of these fragments were identical to amplified cDNA, which suggests the existence of an intronless genomic gene. The amplification was carried out on whole blood genomic DNA from three different individuals. The total sequence of the amplified casein kinase II-alpha gene showed more than 99% homology to the cDNA. The gene contains a noninterrupted open reading frame, as expected for the homolog cDNA. Although the gene sequence is complete, four point mutations were found. Since there are no interruptions of the open reading frame, this intronless gene might be expressed.

    FEBS letters 1993;316;2;114-8

  • Insulin regulates serine/threonine phosphorylation in activated human B lymphocytes.

    Valentine MA, Licciardi KA, Clark EA, Krebs EG and Meier KE

    Department of Microbiology, University of Washington, Seattle 98195.

    Activation of either dense tonsilar B lymphocytes or the B lymphoblastoid cell line T5-1 with Staphylococcus aureus, Cowan strain I, induced surface expression of insulin receptors. Addition of insulin to these activated cells resulted in subsequent phosphorylation of the B cell surface protein CD20, the functions to regulate B cell activation. The cytoplasmic domains of CD20 contain multiple serine and threonine residues, of which at least two are followed by acidic sequences typical of substrate sites favored by casein kinase II. Tryptic mapping of CD20 isolated from intact cells treated with insulin showed increased phosphorylation on peptides having similar migration to those phosphorylated by casein kinase II in vitro. Treatment of tonsilar B cells or T5-1 cells with phorbol esters or in vitro phosphorylation by purified protein kinase C did not result in phosphorylation of peptides phosphorylated by casein kinase II, suggesting that protein kinase C is not directly involved in CD20 phosphorylation in the response to insulin. Phosphorylation of CD20 cannot be triggered by insulin in resting B cells, as the insulin receptor is expressed only after entry into the G1 phase of the cell cycle. Thus, distinct regulation of activation pathways are available to resting as opposed to activated B lymphocytes.

    Funded by: NIGMS NIH HHS: GM37905, GM42508

    Journal of immunology (Baltimore, Md. : 1950) 1993;150;1;96-105

  • Specific phosphorylation of the acidic central region of the N-myc protein by casein kinase II.

    Hagiwara T, Nakaya K, Nakamura Y, Nakajima H, Nishimura S and Taya Y

    Laboratory of Biological Chemistry, School of Pharmaceutical Sciences, Showa University, Tokyo, Japan.

    The central region of the N-myc protein has a characteristic amino acid sequence EDTLSDSDDEDD, which is very similar to those of particular domains of adenovirus E1A, human papilloma virus E7, Simian virus 40 large T, c-myc and L-myc proteins. Domains of these three viral oncoproteins have recently been shown to be specific binding sites for the tumor-suppressor gene retinoblastoma protein. We have noted that the sequence of serine followed by a cluster of acidic amino acids is exactly the same as that of a typical substrate of casein kinase II (CKII). Therefore, we investigated whether these nuclear oncoproteins are phosphorylated by CKII. For this purpose, we fused the beta-galactosidase and N-myc genes including this domain and expressed it in Escherichia coli cells. Several mutant N-myc genes, containing single amino acid substitutions in this domain, were also used to produce fused proteins. Strong phosphorylation by CKII was detected with the fused protein of wild-type N-myc. However, no phosphorylation of beta-galactosidase itself was observed and the phosphorylations of fused mutant proteins were low. Another fused N-myc protein containing most of the C-terminal region downstream of this acidic region was not phosphorylated by CKII. Analysis of phosphorylation sites in synthetic peptides of this acidic region identified the major sites phosphorylated by CKII as Ser261 and Ser263. On two-dimensional tryptic mapping of phosphorylated N-myc proteins, major spots of in vitro-labeled and in-vivo-labeled N-myc proteins were detected in the same positions. These results suggest that two serine residues of the acidic central region of the N-myc protein are phosphorylated by CKII in vivo as well as in vitro. The functional significance of this acidic domain is discussed.

    European journal of biochemistry 1992;209;3;945-50

  • Casein kinase II phosphorylates p34cdc2 kinase in G1 phase of the HeLa cell division cycle.

    Russo GL, Vandenberg MT, Yu IJ, Bae YS, Franza BR and Marshak DR

    W.M. Keck Structural Biology Laboratory, Arnold and Mabel Beckman Neuroscience Center, Cold Spring Harbor, New York.

    The activity of p34cdc2 kinase is regulated in the phases of vertebrate cell cycle by mechanisms of phosphorylation and dephosphorylation. In this paper, we demonstrate that casein kinase II (CKII) phosphorylates p34cdc2 in vivo and in vitro at Ser39 during the G1 phase of HeLa cell division cycle. Human p34cdc2 shows a typical phosphorylation sequence motif site for CKII at Ser39 (ES39EEE). In our experiments, either p34cdc2 expressed and purified from bacteria or p34cdc2 immunoprecipitated from HeLa cells enriched in G1 by elutriation were substrates for in vitro phosphorylation by CKII. Phosphoamino acid analysis, N-chlorosuccinimide mapping, and two-dimensional tryptic mapping of p34cdc2 phosphorylated in vitro were performed to determine the phosphorylation site. A synthetic peptide spanning residues 33-50 of human p34cdc2, including the CKII site, was used to map the site. In addition, phosphorylation at Ser39 also occurs in vivo, since p34cdc2 is phosphorylated during G1 on serine, and its two-dimensional tryptic map shows two phosphopeptides that comigrate exactly with the synthetic peptides used as standard.

    Funded by: NCI NIH HHS: CA 13106

    The Journal of biological chemistry 1992;267;28;20317-25

  • Casein kinase II is a negative regulator of c-Jun DNA binding and AP-1 activity.

    Lin A, Frost J, Deng T, Smeal T, al-Alawi N, Kikkawa U, Hunter T, Brenner D and Karin M

    Department of Pharmacology, University of California, San Diego School of Medicine, La Jolla 92093-0636.

    c-Jun, a major component of the inducible transcription factor AP-1, is a phosphoprotein. In nonstimulated fibroblasts and epithelial cells, c-Jun is phosphorylated on a cluster of two to three sites abutting its DNA-binding domain. Phosphorylation of these sites inhibits DNA binding, and their dephosphorylation correlates with increased AP-1 activity. We show that two of these sites, Thr-231 and Ser-249, are phosphorylated by casein kinase II (CKII). Substitution of the third site, Ser-243, by Phe interferes with phosphorylation of the inhibitory sites in vivo and by purified CKII in vitro. Microinjection into living cells of synthetic peptides that are specific competitive substrates or inhibitors of CKII results in induction of AP-1 activity and c-Jun expression. Microinjection of CKII suppresses induction of AP-1 by either phorbol ester or an inhibitory peptide. These results suggest that one of the roles of CKII, a major nuclear protein kinase with no known functions, is to attenuate AP-1 activity through phosphorylation of c-Jun.

    Funded by: NCI NIH HHS: CA39811, CA50528; NIEHS NIH HHS: ES04151; ...

    Cell 1992;70;5;777-89

  • Insulin-stimulated phosphorylation of calmodulin.

    Sacks DB, Davis HW, Crimmins DL and McDonald JM

    Department of Pathology, Brigham and Women's Hospital, Boston, MA.

    Calmodulin is phosphorylated in vitro by the insulin-receptor tyrosine kinase and a variety of serine/threonine kinases. Here we report that insulin stimulates the phosphorylation of calmodulin on average 3-fold in intact rat hepatocytes. Although calmodulin is constitutively phosphorylated, insulin increases phosphate incorporation into serine, threonine and tyrosine residues. We demonstrate that casein kinase II, an insulin-sensitive kinase, phosphorylates calmodulin in vitro on serine/thyronine residues (Thr-79, Ser-81, Ser-101 and Thr-117). The ability of the insulin receptor to phosphorylate calmodulin that has been pre-phosphorylated by casein kinase II is enhanced up to 35-fold, and the sites of phosphorylation on calmodulin are shifted from tyrosine to threonine and serine. These observations, obtained with a new specific monoclonal antibody to calmodulin, confirm that insulin stimulates calmodulin phosphorylation in intact cells. The observation that calmodulin is phosphorylated in vivo, coupled with the recent demonstration that phosphocalmodulin exhibits altered biological activity, strongly suggests that phosphorylation of calmodulin is a critical component of intracellular signalling.

    Funded by: NIDDK NIH HHS: DK01680, DK25897

    The Biochemical journal 1992;286 ( Pt 1);211-6

  • Assignment of casein kinase 2 alpha sequences to two different human chromosomes.

    Boldyreff B, Klett C, Göttert E, Geurts van Kessel A, Hameister H and Issinger OG

    Institut für Humangenetik, Universität des Saarlandes, Homburg, Federal Republic of Germany.

    Human casein kinase 2 alpha gene (CK-2-alpha) sequences have been localized within the human genome by in situ hybridization and somatic cell hybrid analysis using a CK-2 alpha cDNA as a probe. By in situ hybridization, the CK-2 alpha cDNA could be assigned to two different loci, one on 11p15.1-ter and one on 20p13. The existence of two separate chromosomal loci suggests that CK-2 alpha is a member of a gene family. Only the locus on chromosome 11 was confirmed by somatic cell hybrid analysis. The analysis was based on the presence of a CK-2-alpha-specific 20-kb fragment. However, the CK-2 alpha cDNA hybridizes to several additional fragments in total human DNA.

    Human genetics 1992;89;1;79-82

  • Human-immunodeficiency-virus-type-1-encoded Vpu protein is phosphorylated by casein kinase II.

    Schubert U, Schneider T, Henklein P, Hoffmann K, Berthold E, Hauser H, Pauli G and Porstmann T

    Institut für Medizinische Immunologie, Medizinische Fakultät (Charité), Humboldt-Universität zu Berlin, Federal Republic of Germany.

    Vpu as a human-immunodeficiency-virus-type-1-encoded 81-amino-acid integral-membrane protein was expressed in Escherichia coli using the inducible ptrc promoter of an ATG fusion vector. Recombinant Vpu is associated with membranes of E. coli and could be partially solubilized by detergents. Recombinant Vpu was phosphorylated in vitro with purified porcine casein kinase II (CKII) as well as with a CKII-related protein kinase found in cytoplasmic extracts of human and hamster cells. Recombinant Vpu associated with E. coli membranes has turned out to be the best substrate for in vitro phosphorylation with CKII. This reaction can be inhibited by heparin and the ATP analogue 5,6-dichloro-1-(beta-D-ribofuranosyl)benzimidazole (DRB), both known to be potent inhibitors of CKII. Radiolabelled gamma ATP and gamma GTP were used as phosphate donors in vitro phosphorylation of recombinant Vpu. In vivo phosphorylation of Vpu in HIV-1-infected H9 cells was also inhibited by DRB. We concluded therefrom that the Vpu protein is phosphorylated by the ubiquitous CKII in HIV-1-infected human host cells. Two seryl residues in the sequence of Vpu (position 52 and 56) correspond to the consensus S/TXXD/E for CKII. These potential phosphorylation sites are located within a well-conserved dodecapeptide of Vpu (residues 47-58), which is found in different HIV-1 strains as well as in a Vpu-like protein of SIVCPZ. Monoclonal and polyclonal antibodies directed against two different epitopes of Vpu were used for immunoprecipitation of Vpu from HIV-1-infected cells and for detection of Vpu in Western blot analyses. Vpu from HIV-1-infected cells as well as recombinant Vpu expressed in E. coli were determined by SDS/PAGE using 6 M urea to be 9 kDa, which corresponds to the calculated molecular mass of Vpu.

    European journal of biochemistry 1992;204;2;875-83

  • Casein kinase II phosphorylation increases the rate of serum response factor-binding site exchange.

    Marais RM, Hsuan JJ, McGuigan C, Wynne J and Treisman R

    Imperial Cancer Research Fund, London, UK.

    Recombinant baculoviruses were used to express wild-type serum response factor (SRF) and a mutant, SRF.CKIIA, which lacks all four serine residues in the major casein kinase II (CKII) site at residues 77-90. Purified recombinant SRF binds DNA with an affinity and specificity indistinguishable from that of HeLa cell SRF, and activates transcription in vitro. Comparative phosphopeptide analysis of the wild-type and mutant proteins demonstrated that the wild-type protein is phosphorylated at the major CKII site in insect cells. Dephosphorylation of recombinant SRF does not affect its affinity for the c-fos SRE, and results in only a 3-fold reduction in binding to the synthetic site ACT.L. However, dephosphorylation does cause a large decrease in the rates of association with and dissociation from either site. These effects are due solely to phosphorylation at the major CKII site: the binding properties of the SRF.CKIIA mutant are identical to those of dephosphorylated wild-type SRF, and CKII phosphorylation in vitro converts dephosphorylated wild-type SRF from a slow-binding to a fast-binding form without significantly changing binding affinity. CKII phosphorylation thus acts to potentiate SRF-DNA exchange rates rather than alter equilibrium binding affinity.

    The EMBO journal 1992;11;1;97-105

  • Mapping of the human casein kinase II catalytic subunit genes: two loci carrying the homologous sequences for the alpha subunit.

    Yang-Feng TL, Zheng K, Kopatz I, Naiman T and Canaani D

    Department of Genetics, Yale University School of Medicine, New Haven, CT 06510.

    The human serine/threonine protein casein kinase II (CK II) contains two distinct catalytic subunits, alpha and alpha 1, which are encoded by different genes. A combination of segregation analysis of rodent-human hybrid cells and chromosomal in situ hybridization have localized the human CK II-alpha DNA sequence to two loci: 11p15.5-p15.4 and 20p13. In contrast, the CK II-alpha' gene has been mapped to chromosome 16 by somatic cell hybrid analysis. Taken together with our previous assignment of the CK II regulatory beta-subunit gene to 6p12-p21, these results indicate that although the products of these genes form a single biological complex, they are encoded on different human chromosomes. Further analysis should determine whether both loci of CK II-alpha are functional, or perhaps one of the two constitutes a pseudogene.

    Nucleic acids research 1991;19;25;7125-9

  • Immunocytochemical localization of casein kinase II during interphase and mitosis.

    Yu IJ, Spector DL, Bae YS and Marshak DR

    Cold Spring Harbor Laboratory, New York 11724.

    We have developed specific antibodies to synthetic peptide antigens that react with the individual subunits of casein kinase II (CKII). Using these antibodies, we studied the localization of CKII in asynchronous HeLa cells by immunofluorescence and immunoelectron microscopy. Further studies were done on HeLa cells arrested at the G1/S transition by hydroxyurea treatment. Our results indicate that the CKII alpha and beta subunits are localized in the cytoplasm during interphase and are distributed throughout the cell during mitosis. Further electron microscopic investigation revealed that CKII alpha subunit is associated with spindle fibers during metaphase and anaphase. In contrast, the CKII alpha' subunit is localized in the nucleus during G1 and in the cytoplasm during S. Taken together, our results suggest that CKII may play significant roles in cell division control by shifting its localization between the cytoplasm and nucleus.

    Funded by: NCI NIH HHS: CA 13106, CA45508-04

    The Journal of cell biology 1991;114;6;1217-32

  • Mutation of serum response factor phosphorylation sites and the mechanism by which its DNA-binding activity is increased by casein kinase II.

    Manak JR and Prywes R

    Department of Biological Sciences, Columbia University, New York, New York 10027.

    Casein kinase II (CKII) phosphorylates the mammalian transcription factor serum response factor (SRF) on a serine residue(s) located within a region of the protein spanning amino acids 70 to 92, thereby enhancing its DNA-binding activity in vitro. We report here that serine 83 appears to be the residue phosphorylated by CKII but that three other serines in this region can also be involved in phosphorylation and the enhancement of DNA-binding activity. A mutant that contained glutamate residues in place of these serines had only low-level binding activity; however, when the serines were replaced with glutamates and further mutations were made that increased the negative charge of the region, the resulting mutant showed a constitutively high level of binding equal to that achieved by phosphorylation of wild-type SRF. We have investigated the mechanism by which phosphorylation of SRF increases its DNA-binding activity. We have ruled out the possibilities that phosphorylation affects SRF dimerization or relieves inhibition due to masking of the DNA-binding domain by an amino-terminal region of the protein. Rather, using partial proteolysis to probe SRF's structure, we find that the conformation of SRF's DNA-binding domain is altered by phosphorylation.

    Funded by: NCI NIH HHS: CA 50329-01

    Molecular and cellular biology 1991;11;7;3652-9

  • Phosphorylation of neuromodulin (GAP-43) by casein kinase II. Identification of phosphorylation sites and regulation by calmodulin.

    Apel ED, Litchfield DW, Clark RH, Krebs EG and Storm DR

    Department of Pharmacology, School of Medicine, University of Washington 98195.

    Neuromodulin (P-57, GAP-43, B-50, F-1) is a neurospecific calmodulin-binding protein believed to play a role in regulation of neurite outgrowth and neuroplasticity. Neuromodulin is phosphorylated by protein kinase C, and this phosphorylation prevents calmodulin from binding to neuromodulin (Alexander, K. A., Cimler, B. M., Meier, K. E. & Storm, D. R. (1987) J. Biol. Chem. 262, 6108-6113). The only other protein kinase known to phosphorylate neuromodulin is casein kinase II (Pisano, M. R., Hegazy, M. G., Reimann, E. M. & Dokas, L. A. (1988) Biochem. Biophys. Res. Commun. 155, 1207-1212). Phosphoamino acid analyses revealed that casein kinase II modified serine and threonine residues in both native bovine and recombinant mouse neuromodulin. Two serines located in the C-terminal end of neuromodulin, Ser-192 and Ser-193, were identified as the major casein kinase II phosphorylation sites. Thr-88, Thr-89, or Thr-95 were identified as minor casein kinase II phosphorylation sites. Phosphorylation by casein kinase II did not affect the ability of neuromodulin to bind to calmodulin-Sepharose. However, calmodulin did inhibit the phosphorylation of neuromodulin by casein kinase II with a Ki of 1-2 microM. Calmodulin inhibition of casein kinase II phosphorylation was due to calmodulin binding to neuromodulin rather than to the protein kinase. These data suggest that the minimal secondary and tertiary structure exhibited by neuromodulin may be sufficient to juxtapose its calmodulin-binding domain, located at the N-terminal end, with the neuromodulin casein kinase II phosphorylation sites at the C-terminal end of the protein. We propose that calmodulin regulates casein kinase II phosphorylation of neuromodulin by binding to neuromodulin and sterically hindering the interaction of casein kinase II with its phosphorylation sites on neuromodulin.

    Funded by: NIDDK NIH HHS: DK42528; NIGMS NIH HHS: GM 07270, GM 33708

    The Journal of biological chemistry 1991;266;16;10544-51

  • Phosphorylation of cardiac and skeletal muscle calsequestrin isoforms by casein kinase II. Demonstration of a cluster of unique rapidly phosphorylated sites in cardiac calsequestrin.

    Cala SE and Jones LR

    Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis 46202.

    Calsequestrin is an acidic Ca2(+)-binding protein of sarcoplasmic reticulum existing as different gene products in cardiac muscle and skeletal muscle. A unique feature of cardiac calsequestrin is a 31-amino acid-long COOH-terminal tail (Scott, B. T., Simmerman, H. K. B., Collins, J. H., Nadal-Ginard, B., and Jones, L. R. (1988) J. Biol. Chem. 263, 8958-8964), which is highly acidic and contains several consensus phosphorylation sites for casein kinase II. In the work described here, we tested whether this cardiac-specific sequence is a substrate for casein kinase II. Both cardiac and skeletal muscle calsequestrins were phosphorylated by casein kinase II, but cardiac calsequestrin was phosphorylated to a higher stoichiometry and at least 50 times more rapidly. The site of rapid phosphorylation of cardiac calsequestrin was localized to the distinct COOH terminus, where a cluster of three closely spaced serine residues are found (S378DEESN-DDSDDDDE-COOH). The slower phosphorylation of skeletal muscle calsequestrin occurred at its truncated COOH terminus, at threonine residue 363 (I351NTEDDDDDE-COOH). The similar sequence in cardiac calsequestrin (I351NTEDDDNEE) was not phosphorylated. Cardiac calsequestrin, as isolated, already contained 1.2 mol of Pi/mol of protein, whereas skeletal muscle calsequestrin contained only trace levels of Pi. The endogenous Pi of cardiac calsequestrin was also localized to the distinct COOH terminus. Our results indicate that the cardiac isoform of calsequestrin is the preferred substrate for casein kinase II both in vivo and in vitro.

    Funded by: NHLBI NIH HHS: HL06308, HL28556

    The Journal of biological chemistry 1991;266;1;391-8

  • Cytoplasmic and nuclear distribution of casein kinase II: characterization of the enzyme uptake by bovine adrenocortical nuclear preparation.

    Filhol O, Cochet C and Chambaz EM

    BRCE, INSERM Unité 244, LBIO, Centre d'Etudes Nucléaires, Grenoble, France.

    Casein kinase II (CK II) is a ubiquitous protein kinase that has been found in both nuclear and soluble subcellular fractions and whose precise cellular functions and mechanisms of control remain to be clarified. Using immunocytochemical localization, it was observed that the intracellular distribution of CK II exhibited a striking shift toward an increased nuclear concentration during active proliferation of bovine adrenocortical cells in primary culture. The interaction of CK II with purified adrenocortical cell nuclear preparation was thus examined in vitro. CK II was found to rapidly associate with nuclei in a temperature-dependent and saturable process, resulting in a tight binding of the kinase to nuclear components, as shown by various extraction procedures. This association resulted in a concentration of the kinase in the nuclear preparation about 100-fold that in the medium and exhibited two types of binding sites with Ka of 10(9) and 10(7) M-1, respectively. The nuclear CK II uptake was dependent upon the presence of ATP and was stimulated by a kinase activator such as spermine, although the enzyme activity did not appear to be required for the process. These observations would be in line with a pore-mediated, energy-dependent nuclear uptake of the kinase. Since a number of potential nuclear CK II targets have been reported, including the oncoprotein myc, it is suggested that the nuclear translocation of the kinase as characterized in vitro may have a biological significance in living cell, especially in the control of nuclear activities related to cell proliferation and the mechanism of action of growth factors.

    Biochemistry 1990;29;42;9928-36

  • Isolation and characterization of human cDNA clones encoding the alpha and the alpha' subunits of casein kinase II.

    Lozeman FJ, Litchfield DW, Piening C, Takio K, Walsh KA and Krebs EG

    Howard Hughes Medical Institute, Department of Pharmacology, University of Washington, Seattle 98195.

    Casein kinase II is a widely distributed protein serine/threonine kinase. The holoenzyme appears to be a tetramer, containing two alpha or alpha' subunits (or one of each) and two beta subunits. Complementary DNA clones encoding the subunits of casein kinase II were isolated from a human T-cell lambda gt10 library using cDNA clones isolated from Drosophila melanogaster [Saxena et al. (1987) Mol. Cell. Biol. 7, 3409-3417]. One of the human cDNA clones (hT4.1) was 2.2 kb long, including a coding region of 1176 bp preceded by 156 bp (5' untranslated region) and followed by 871 bp (3' untranslated region). The hT4.1 clone was nearly identical in size and sequence with a cDNA clone from HepG2 human hepatoma cultured cells [Meisner et al. (1989) Biochemistry 28, 4072-4076]. Another of the human T-cell cDNA clones (hT9.1) was 1.8 kb long, containing a coding region of 1053 bp preceded by 171 bp (5' untranslated region) and followed by 550 bp (3' untranslated region). Amino acid sequences deduced from these two cDNA clones were about 85% identical. Most of the difference between the two encoded polypeptides was in the carboxy-terminal region, but heterogeneity was distributed throughout the molecules. Partial amino acid sequence was determined in a mixture of alpha and alpha' subunits from bovine lung casein kinase II. The bovine sequences aligned with the 2 human cDNA-encoded polypeptides with only 2 discrepancies out of 535 amino acid positions. This confirmed that the two human T-cell cDNA clones encoded the alpha and alpha' subunits of casein kinase II. Microsequence data determined from separated preparations of bovine casein kinase II alpha subunit and alpha' subunit [Litchfield et al. (1990) J. Biol. Chem. 265, 7638-7644] confirmed that hT4.1 encoded the alpha subunit and hT9.1 encoded the alpha' subunit. These studies show that there are two distinct catalytic subunits for casein kinase II (alpha and alpha') and that the sequence of these subunits is largely conserved between the bovine and the human.

    Funded by: NIGMS NIH HHS: GM15731

    Biochemistry 1990;29;36;8436-47

  • Phosphate groups as substrate determinants for casein kinase I action.

    Flotow H, Graves PR, Wang AQ, Fiol CJ, Roeske RW and Roach PJ

    Department of Biochemistry, Indiana University School of Medicine, Indianapolis 46223.

    Phosphorylation of rabbit muscle glycogen synthase by cyclic AMP-dependent protein kinase has been shown to enhance subsequent phosphorylation by casein kinase I (Flotow, H., and Roach, P. J. (1989) J. Biol. Chem. 264, 9126-9128). In the present study, synthetic peptides based on the sequences of the four phosphorylated regions in muscle glycogen synthase were used to probe the role of substrate phosphorylation in casein kinase I action. With all four peptides, prior phosphorylation significantly stimulated phosphorylation by casein kinase I. A series of peptides was synthesized based on the NH2-terminal glycogen synthase sequence PLSRTLS7VSS10LPGL, in which phosphorylation at Ser7 is required for modification of Ser10 by casein kinase I. The spacing between the P-Ser and the acceptor Ser was varied to have 1, 2, or 3 intervening residues. The peptide with a 2-residue spacing (-S(P)-X-X-S-) was by far the best casein kinase I substrate. When the P-Ser residue at Ser7 was replaced with P-Thr, the resulting peptide was still a casein kinase I substrate. However, substitution of Asp or Glu residues at Ser7 led to peptides that were not phosphorylated by casein kinase I. Phosphorylation of one of the other peptides showed that Thr could also be the phosphate acceptor. From these results, we propose that there are substrates for casein kinase I for which prior phosphorylation is a critical determinant of protein kinase action. In these instances, an important recognition motif for casein kinase I appears to be -S(P)/T(P)-Xn-S/T- with n = 2 much more effective than n = 1 or n = 3. Thus, casein kinase I may be involved in hierarchal substrate phosphorylation schemes in which its activity is controlled by the phosphorylation state of its substrates.

    Funded by: NIDDK NIH HHS: DK-20542, DK-27221

    The Journal of biological chemistry 1990;265;24;14264-9

  • Mitosis-specific phosphorylation of nucleolin by p34cdc2 protein kinase.

    Belenguer P, Caizergues-Ferrer M, Labbé JC, Dorée M and Amalric F

    Centre de Recherche de Biochimie et de Génétique Cellulaires, Centre National de la Recherche Scientifique, Toulouse, France.

    Nucleolin is a ubiquitous multifunctional protein involved in preribosome assembly and associated with both nucleolar chromatin in interphase and nucleolar organizer regions on metaphasic chromosomes in mitosis. Extensive nucleolin phosphorylation by a casein kinase (CKII) occurs on serine in growing cells. Here we report that while CKII phosphorylation is achieved in interphase, threonine phosphorylation occurs during mitosis. We provide evidence that this type of in vivo phosphorylation involves a mammalian homolog of the cell cycle control Cdc2 kinase. In vitro M-phase H1 kinase from starfish oocytes phosphorylated threonines in a TPXK motif present nine times in the amino-terminal part of the protein. The same sites which matched the p34cdc2 consensus phosphorylation sequence were used in vivo during mitosis. We propose that successive Cdc2 and CKII phosphorylation could modulate nucleolin function in controlling cell cycle-dependent nucleolar function and organization. Our results, along with previous studies, suggest that while serine phosphorylation is related to nucleolin function in the control of rDNA transcription, threonine phosphorylation is linked to mitotic reorganization of nucleolar chromatin.

    Molecular and cellular biology 1990;10;7;3607-18

  • Phosphorylation of DARPP-32, a dopamine- and cAMP-regulated phosphoprotein, by casein kinase II.

    Girault JA, Hemmings HC, Williams KR, Nairn AC and Greengard P

    Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, New York 10021.

    DARPP-32 (dopamine- and cAMP-regulated phosphorprotein, Mr = 32,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) is an inhibitor of protein phosphatase-1 and is enriched in dopaminoceptive neurons possessing the D1 dopamine receptor. Purified bovine DARPP-32 was phosphorylated in vitro by casein kinase II to a stoichiometry greater than 2 mol of phosphate/mol of protein whereas two structurally and functionally related proteins, protein phosphatase inhibitor-1 and G-substrate, were poor substrates for this enzyme. Sequencing of chymotryptic and thermolytic phosphopeptides from bovine DARPP-32 phosphorylated by casein kinase II suggested that the main phosphorylated residues were Ser45 and Ser102. In the case of rat DARPP-32, the identification of these phosphorylation sites was confirmed by manual Edman degradation. The phosphorylated residues are located NH2-terminal to acidic amino acid residues, a characteristic of casein kinase II phosphorylation sites. Casein kinase II phosphorylated DARPP-32 with an apparent Km value of 3.4 microM and a kcat value of 0.32 s-1. The kcat value for phosphorylation of Ser102 was 5-6 times greater than that for Ser45. Studies employing synthetic peptides encompassing each phosphorylation site confirmed this difference between the kcat values for phosphorylation of the two sites. In slices of rat caudate-putamen prelabeled with [32P]phosphate, DARPP-32 was phosphorylated on seryl residues under basal conditions. Comparison of thermolytic phosphopeptide maps and determination of the phosphorylated residue by manual Edman degradation identified the main phosphorylation site in intact cells as Ser102. In vitro, DARPP-32 phosphorylated by casein kinase II was dephosphorylated by protein phosphatases-1 and -2A. Phosphorylation by casein kinase II did not affect the potency of DARPP-32 as an inhibitor of protein phosphatase-1, which depended only on phosphorylation of Thr34 by cAMP-dependent protein kinase. However, phosphorylation of DARPP-32 by casein kinase II facilitated phosphorylation of Thr34 by cAMP-dependent protein kinase with a 2.2-fold increase in the Vmax and a 1.4-fold increase in the apparent Km. Phosphorylation of DARPP-32 by casein kinase II in intact cells may therefore modulate its phosphorylation in response to increased levels of cAMP.

    Funded by: NIMH NIH HHS: MH-40899

    The Journal of biological chemistry 1989;264;36;21748-59

  • Identification of sites on chromosomal protein HMG-I phosphorylated by casein kinase II.

    Palvimo J and Linnala-Kankkunen A

    Department of Biochemistry, University of Kuopio, Finland.

    The amino acid sequence of a region on chromosomal protein HMG-I from human cells that is phosphorylated by casein kinase II has been determined. The sequence is: Leu-Glu-Lys-Glu-Glu-Glu-Glu-Gly-Ile-Ser-Gln-Glu-Ser(P)-Ser(P)-Glu-Glu-Gl u-Gln. It corresponds to the C-terminal residues 90-107 of HMG-I [(1989) Mol. Cell. Biol. 9, 2114-2123]. Sequence analysis of the native peptide (90-107) after treatment, which specifically converts phosphoserine residues to S-ethylcysteine, revealed that 70-80% of serine residues 102 and 103 were phosphorylated in vivo. Both residues were fully phosphorylated in vitro by incubation with casein kinase II. These results suggest that casein kinase II is involved in the regulation of HMG-I function in the cells.

    FEBS letters 1989;257;1;101-4

  • Molecular cloning of the human casein kinase II alpha subunit.

    Meisner H, Heller-Harrison R, Buxton J and Czech MP

    Department of Biochemistry, University of Massachusetts Medical School, Worcester 01655.

    A human cDNA encoding the alpha subunit of casein kinase II and a partial cDNA encoding the rat homologue were isolated by using a Drosophila casein kinase II cDNA probe. The 2.2-kb human cDNA contains a 1.2-kb open reading frame, 150 nucleotides of 5' leader, and 850 nucleotides of 3' noncoding region. Except for the first 7 deduced amino acids that are missing in the rat cDNA, the 328 amino acids beginning with the amino terminus are identical between human and rat. The Drosophila enzyme sequence is 90% identical with the human casein kinase II sequence, and there is only a single amino acid difference between the published partial bovine sequence and the human sequence. In addition, the C-terminus of the human cDNA has an extra 53 amino acids not present in Drosophila. Northern analysis of rat and human RNA showed predominant bands of 5.5, 3.1, and 1.8 kb. In rat tissues, brain and spleen had the highest levels of casein kinase II alpha subunit specific RNA, while skeletal muscle showed the lowest. Southern analysis of human cultured cell and tissue genomic DNA using the full-length cDNA probe revealed two bands with restriction enzymes that have no recognition sites within the cDNA and three to six bands with enzymes having single internal sites. These results are consistent with the possibility that two genes encode the alpha subunits.

    Funded by: NCI NIH HHS: CA 39240

    Biochemistry 1989;28;9;4072-6

  • Myc oncoproteins are phosphorylated by casein kinase II.

    Lüscher B, Kuenzel EA, Krebs EG and Eisenman RN

    Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98104.

    Casein kinase II (CK-II) is a ubiquitous protein kinase, localized to both nucleus and cytoplasm, with strong specificity for serine residues positioned within clusters of acidic amino acids. We have found that a number of nuclear oncoproteins share a CK-II phosphorylation sequence motif, including Myc, Myb, Fos, E1a and SV40 T antigen. In this paper we show that cellular myc-encoded proteins, derived from avian and human cells, can serve as substrates for phosphorylation by purified CK-II in vitro and that this phosphorylation is reversible. One- and two-dimensional mapping experiments demonstrate that the major phosphopeptides from in vivo phosphorylated Myc correspond to the phosphopeptides produced from Myc phosphorylated in vitro by CK-II. In addition, synthetic peptides with sequences corresponding to putative CK-II phosphorylation sites in Myc are subject to multiple, highly efficient phosphorylations by CK-II, and can act as competitive inhibitors of CK-II phosphorylation of Myc in vitro. We have used such peptides to map the phosphorylated regions in Myc and have located major CK-II phosphorylations within the central highly acidic domain and within a region proximal to the C terminus. Our results, along with previous studies on myc deletion mutants, show that Myc is phosphorylated by CK-II, or a kinase with similar specificity, in regions of functional importance. Since CK-II can be rapidly activated after mitogen treatment we postulate that CK-II mediated phosphorylation of Myc plays a role in signal transduction to the nucleus.

    The EMBO journal 1989;8;4;1111-9

  • Two human 90-kDa heat shock proteins are phosphorylated in vivo at conserved serines that are phosphorylated in vitro by casein kinase II.

    Lees-Miller SP and Anderson CW

    Biology Department, Brookhaven National Laboratory, Upton, New York 11973.

    Amino-terminal protein sequence analysis revealed that exponentially growing human HeLa cells at 37 degrees C express two closely related 90-kDa "heat shock" proteins (hsp 90) in nearly equal amounts. Both hsp 90s begin with proline; the initial methionine residue is removed. The alpha protein contains a 9-amino acid segment, TQTQDQPME, from residues 4 to 12, that is replaced by a 4-amino acid segment, VHHG, in the beta form. The purified hsp 90 mixture contains 2 mol of phosphate/mol of polypeptide. Both hsp 90 proteins are phosphorylated at two homologous sites. For the alpha protein, these sites correspond to serine 231 and serine 263. A 5-amino acid segment, ESEDK, between the two phosphorylation sites is absent from the beta protein. The sequence between phosphorylation sites of both hsp 90s is predicted to have alpha helical structure. Dephosphorylated hsp 90 is phosphorylated at both sites by casein kinase II from HeLa cells, calf thymus, or rabbit reticulocytes; no other hsp 90 residues were phosphorylated by casein kinase II in vitro.

    Funded by: NIGMS NIH HHS: GM35945

    The Journal of biological chemistry 1989;264;5;2431-7

  • Analysis of sites phosphorylated on acetyl-CoA carboxylase in response to insulin in isolated adipocytes. Comparison with sites phosphorylated by casein kinase-2 and the calmodulin-dependent multiprotein kinase.

    Haystead TA, Campbell DG and Hardie DG

    Biochemistry Department, Dundee University, Scotland.

    We have examined the sites phosphorylated on acetyl-CoA carboxylase in response to insulin in isolated adipocytes. Two tryptic peptides derived from the enzyme become more radioactive after treatment of 32P-labelled cells with insulin. One of these (T4a) accounts for a large part of the total increase in phosphate observed after insulin treatment, and comigrates with the peptide containing the sites phosphorylated in vitro by casein kinase-2. The other may correspond to the 'I' site peptide originally described by Brownsey and Denton in 1982: labelling of this peptide is stimulated at least threefold by insulin treatment, but it is a minor phosphopeptide and, even after insulin treatment, accounts for only about 2.5% of the enzyme-bound phosphate (equivalent to less than 0.1 mol phosphate/mol 240-kDa subunit). Two other major tryptic phosphopeptides (T1 and T4b) labelled in adipocytes do not change significantly in response to insulin, and comigrate with peptides containing sites phosphorylated in vitro by cyclic-AMP-dependent protein kinase and calmodulin-dependent multiprotein kinase respectively. We have sequenced peptides T4a and T4b from acetyl-CoA carboxylase derived from control and insulin-treated adipocytes, and also after phosphorylation in vitro with casein kinase-2 and the calmodulin-dependent multiprotein kinase. The results show that T4a and T4b are forms of the same peptide containing phosphate groups on different serine residues: Phe-Ile-Ile-Gly-Ser4-Val-Ser5-Gln-Asp-Asn-Ser6-Glu-Asp -Glu-Ile-Ser-Asn-Leu-. Site 5 was phosphorylated by the calmodulin-dependent protein kinase and site 6 by casein kinase-2. Migration in the T4a position was exclusively associated with phosphorylation in site 6, irrespective of the presence of phosphate in sites 4 and 5. Sites 5 and 6 were partially phosphorylated in control adipocytes, and there were also small amounts of phosphate in site 4. On stimulation with insulin, phosphorylation appeared to occur primarily at site 6, thus accounting for the increase in 32P-labelling of T4a. We were unable to isolate sufficient quantities of the other insulin-sensitive peptide to determine its sequence. Our results are consistent with the idea that insulin activates either casein kinase-2, or a protein kinase which has the same specificity as casein kinase-2. The function of this modification is not clear, since phosphorylation by casein kinase-2 has no direct effect on acetyl-CoA carboxylase activity.

    European journal of biochemistry 1988;175;2;347-54

  • Identification of the phosphorylation sites of clathrin light chain LCb.

    Hill BL, Drickamer K, Brodsky FM and Parham P

    Department of Cell Biology, Stanford University, California 94305.

    Clathrin light chains, LCa and LCb, are products of two closely related genes whose mRNAs undergo differential splicing to result in at least four different light chain isoforms. The physiological significance of clathrin light chain diversity remains unclear. To date, the only evidence for a functional distinction of LCa and LCb is the preferential phosphorylation of LCb, which takes place at serine residues and is mediated by coated vesicle-associated casein kinase II. As a first step toward determining the function of light chain diversity, we have mapped the in vitro phosphorylation sites on LCb. We use [32P]ATP to phosphorylate LCb within coated vesicles, followed by sequencing of 32P-labeled chymotryptic peptides thereof, to identify serine residues at positions 11 and 13 as the phosphorylation sites. We find that phosphorylation of LCb within coated vesicles can be inhibited by four monoclonal antibodies specific for different epitopes of the clathrin light chains.

    The Journal of biological chemistry 1988;263;12;5499-501

  • Clathrin-coated vesicles contain two protein kinase activities. Phosphorylation of clathrin beta-light chain by casein kinase II.

    Bar-Zvi D and Branton D

    Incubation of clathrin-coated vesicles with Mg2+-[gamma-32P]ATP results in the autophosphorylation of a 50-kDa polypeptide (pp50) (Pauloin, A., Bernier, I., and Jollès, P. (1982) Nature 298, 574-576). We describe here a second protein kinase that is associated with calf brain and liver coated vesicles. This kinase, which phosphorylates casein and phosvitin but not histone and protamine using either ATP or GTP, co-fractionates with coated vesicles as assayed by gel filtration, electrophoresis, and sedimentation. The enzyme can be extracted with 0.5 M Tris-HCl or 1 M NaCl, and can be separated from the pp50 kinase as well as the other major coat proteins. We identified this enzyme as casein kinase II based on physical and catalytic properties and by comparative studies with casein kinase II isolated from brain cytosol. It has a Stokes radius of 4.5 nm, a catalytic moiety of approximately 45 kDa, and labels a polypeptide of 26 kDa when the pure enzyme is assayed for autophosphorylation. Its activity is inhibited by heparin and not affected by cAMP, phospholipids, or calmodulin. This protein kinase preferentially phosphorylates clathrin beta-light chain. The phosphorylation is markedly stimulated by polylysine and inhibited by heparin. Isolated beta-light chain as well as beta-light chain in triskelions or in intact coated vesicles is phosphorylated. All of the phosphate (0.86 mol of Pi/mol of clathrin beta-light chain) is incorporated into phosphoserine.

    Funded by: NIGMS NIH HHS: GM-31579

    The Journal of biological chemistry 1986;261;21;9614-21

  • Topoisomerase I phosphorylation in vitro and in rapidly growing Novikoff hepatoma cells.

    Durban E, Goodenough M, Mills J and Busch H

    Changes in phosphorylation modulate the activity of topoisomerase I in vitro. Specifically, enzymatic activity is stimulated by phosphorylation with a purified protein kinase (casein kinase type II). The purpose of this study was to compare the sites that are phosphorylated in vitro by casein kinase type II with the site(s) phosphorylated in vivo in rapidly growing Novikoff hepatoma cells. Topoisomerase I labeled in vitro was characterized by three major tryptic phosphopeptides (I-III). Separation of these peptides by a C18-reverse phase h.p.l.c. column resulted in their elution at fractions 18 (I), 27 (II) and 44 (III) with 17%, 22.5% and 33% acetonitrile, respectively. In contrast, only one major phosphopeptide was identified by h.p.l.c. in topoisomerase I labeled in vivo. This phosphopeptide eluted at fraction 18 corresponding to the elution properties of phosphopeptide I labeled in vitro. It also co-migrated with tryptic phosphopeptide I when subjected to high-voltage electrophoresis on thin-layer cellulose plates. Preliminary experiments suggest that phosphorylation occurs at a serine residue six amino acids from the N-terminus of the peptide. These data indicate that topoisomerase I is phosphorylated in vivo and in vitro within the same tryptic peptide and suggest that topoisomerase I is phosphorylated in vivo by casein kinase II.

    Funded by: NCI NIH HHS: CA 10893

    The EMBO journal 1985;4;11;2921-6

Gene lists (6)

Gene List Source Species Name Description Gene count
L00000009 G2C Homo sapiens Human PSD Human orthologues of mouse PSD adapted from Collins et al (2006) 1080
L00000013 G2C Homo sapiens Human mGluR5 Human orthologues of mouse mGluR5 complex adapted from Collins et al (2006) 52
L00000016 G2C Homo sapiens Human PSP Human orthologues of mouse PSP adapted from Collins et al (2006) 1121
L00000061 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-CONSENSUS Mouse cortex PSD consensus (ortho) 984
L00000069 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-FULL Human cortex biopsy PSD full list 1461
L00000071 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-FULL Mouse cortex PSD full list (ortho) 1556
© G2C 2014. The Genes to Cognition Programme received funding from The Wellcome Trust and the EU FP7 Framework Programmes:
EUROSPIN (FP7-HEALTH-241498), SynSys (FP7-HEALTH-242167) and GENCODYS (FP7-HEALTH-241995).

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