G2Cdb::Gene report

Gene id
Gene symbol
Adrbk1 (MGI)
Mus musculus
adrenergic receptor kinase, beta 1
G00001406 (Homo sapiens)

Databases (16)

ENSMUSG00000024858 (Ensembl mouse gene)
110355 (Entrez Gene)
507 (G2Cdb plasticity & disease)
Gene Expression
NM_130863 (Allen Brain Atlas)
g02314 (BGEM)
110355 (Genepaint)
adrbk1 (gensat)
109635 (OMIM)
Marker Symbol
MGI:87940 (MGI)
Protein Sequence
Q99MK8 (UniProt)

Synonyms (8)

  • Adrbk-1
  • Bark-1
  • GRK2
  • beta ARK
  • beta ARK1
  • beta-AR kinase-1
  • beta-adrenergic receptor kinase-1
  • betaARK1

Literature (83)

Pubmed - other

  • Myeloid-specific GPCR kinase-2 negatively regulates NF-κB1p105-ERK pathway and limits endotoxemic shock in mice.

    Patial S, Saini Y, Parvataneni S, Appledorn DM, Dorn GW, Lapres JJ, Amalfitano A, Senagore P and Parameswaran N

    Department of Physiology and Division of Pathology, Michigan State University, East Lansing, Michigan 48824, USA.

    G-protein-coupled receptor kinase 2 (GRK2) is a member of a kinase family originally discovered for its role in the phosphorylation and desensitization of G-protein-coupled receptors. It is expressed in high levels in myeloid cells and its levels are altered in many inflammatory disorders including sepsis. To address the physiological role of myeloid cell-specific GRK2 in inflammation, we generated mice bearing GRK2 deletion in myeloid cells (GRK2▵mye). GRK2▵mye mice exhibited exaggerated inflammatory cytokine/chemokine production, and organ injury in response to lipopolysaccharide (LPS, a TLR4 ligand) when compared to wild-type littermates (GRK2fl/fl). Consistent with this, peritoneal macrophages from GRK2▵mye mice showed enhanced inflammatory cytokine levels when stimulated with LPS. Our results further identify TLR4-induced NF-κB1p105-ERK pathway to be selectively regulated by GRK2. LPS-induced activation of NF-κB1p105-MEK-ERK pathway is significantly enhanced in the GRK2▵mye macrophages compared to GRK2fl/fl cells and importantly, inhibition of the p105 and ERK pathways in the GRK2▵mye macrophages, limits the enhanced production of LPS-induced cytokines/chemokines. Taken together, our studies reveal previously undescribed negative regulatory role for GRK2 in TLR4-induced p105-ERK pathway as well as in the consequent inflammatory cytokine/chemokine production and endotoxemia in mice.

    Funded by: NHLBI NIH HHS: HL095637, R01 HL087871, R01 HL095637, R01 HL095637-01, R01 HL095637-02; NIAMS NIH HHS: AR055726, AR056680, R01 AR056680, R01 AR056680-01A2, R01 AR056680-02, R21 AR055726, R21 AR055726-01A1, R21 AR055726-02; NIEHS NIH HHS: P42 ES004911

    Journal of cellular physiology 2011;226;3;627-37

  • A high-resolution anatomical atlas of the transcriptome in the mouse embryo.

    Diez-Roux G, Banfi S, Sultan M, Geffers L, Anand S, Rozado D, Magen A, Canidio E, Pagani M, Peluso I, Lin-Marq N, Koch M, Bilio M, Cantiello I, Verde R, De Masi C, Bianchi SA, Cicchini J, Perroud E, Mehmeti S, Dagand E, Schrinner S, Nürnberger A, Schmidt K, Metz K, Zwingmann C, Brieske N, Springer C, Hernandez AM, Herzog S, Grabbe F, Sieverding C, Fischer B, Schrader K, Brockmeyer M, Dettmer S, Helbig C, Alunni V, Battaini MA, Mura C, Henrichsen CN, Garcia-Lopez R, Echevarria D, Puelles E, Garcia-Calero E, Kruse S, Uhr M, Kauck C, Feng G, Milyaev N, Ong CK, Kumar L, Lam M, Semple CA, Gyenesei A, Mundlos S, Radelof U, Lehrach H, Sarmientos P, Reymond A, Davidson DR, Dollé P, Antonarakis SE, Yaspo ML, Martinez S, Baldock RA, Eichele G and Ballabio A

    Telethon Institute of Genetics and Medicine, Naples, Italy.

    Ascertaining when and where genes are expressed is of crucial importance to understanding or predicting the physiological role of genes and proteins and how they interact to form the complex networks that underlie organ development and function. It is, therefore, crucial to determine on a genome-wide level, the spatio-temporal gene expression profiles at cellular resolution. This information is provided by colorimetric RNA in situ hybridization that can elucidate expression of genes in their native context and does so at cellular resolution. We generated what is to our knowledge the first genome-wide transcriptome atlas by RNA in situ hybridization of an entire mammalian organism, the developing mouse at embryonic day 14.5. This digital transcriptome atlas, the Eurexpress atlas (http://www.eurexpress.org), consists of a searchable database of annotated images that can be interactively viewed. We generated anatomy-based expression profiles for over 18,000 coding genes and over 400 microRNAs. We identified 1,002 tissue-specific genes that are a source of novel tissue-specific markers for 37 different anatomical structures. The quality and the resolution of the data revealed novel molecular domains for several developing structures, such as the telencephalon, a novel organization for the hypothalamus, and insight on the Wnt network involved in renal epithelial differentiation during kidney development. The digital transcriptome atlas is a powerful resource to determine co-expression of genes, to identify cell populations and lineages, and to identify functional associations between genes relevant to development and disease.

    Funded by: Medical Research Council: MC_U127527203; Telethon: TGM11S03

    PLoS biology 2011;9;1;e1000582

  • Nonenzymatic rapid control of GIRK channel function by a G protein-coupled receptor kinase.

    Raveh A, Cooper A, Guy-David L and Reuveny E

    Department Biological Chemistry Weizmann Institute of Science, Rehovot, Israel.

    G protein-coupled receptors (GPCRs) respond to agonists to activate downstream enzymatic pathways or to gate ion channel function. Turning off GPCR signaling is known to involve phosphorylation of the GPCR by GPCR kinases (GRKs) to initiate their internalization. The process, however, is relatively slow and cannot account for the faster desensitization responses required to regulate channel gating. Here, we show that GRKs enable rapid desensitization of the G protein-coupled potassium channel (GIRK/Kir3.x) through a mechanism independent of their kinase activity. On GPCR activation, GRKs translocate to the membrane and quench channel activation by competitively binding and titrating G protein βγ subunits away from the channel. Of interest, the ability of GRKs to effect this rapid desensitization depends on the receptor type. The findings thus reveal a stimulus-specific, phosphorylation-independent mechanism for rapidly downregulating GPCR activity at the effector level.

    Cell 2010;143;5;750-60

  • Dopamine D1-D2 receptor Heteromer-mediated calcium release is desensitized by D1 receptor occupancy with or without signal activation: dual functional regulation by G protein-coupled receptor kinase 2.

    Verma V, Hasbi A, O'Dowd BF and George SR

    Centre for Addiction and Mental Health, University of Toronto, Toronto, Ontario M5S 1A8, Canada.

    We identified that activation of the G(q)-linked dopamine D1-D2 receptor hetero-oligomer generates a PLC-dependent intracellular calcium signal. Confocal FRET between endogenous dopamine D1 and D2 receptors in striatal neurons confirmed a physical interaction between them. Pretreatment with SKF 83959, which selectively activates the D1-D2 receptor heteromer, or SKF 83822, which only activates the D1 receptor homo-oligomer, led to rapid desensitization of the D1-D2 receptor heteromer-mediated calcium signal in both heterologous cells and striatal neurons. This desensitization response was mediated through selective occupancy of the D1 receptor binding pocket. Although SKF 83822 was unable to activate the D1-D2 receptor heteromer, it still permitted desensitization of the calcium signal. This suggested that occupancy of the D1 receptor binding pocket by SKF 83822 resulted in conformational changes sufficient for desensitization without heteromer activation. Bioluminescence resonance energy transfer and co-immunoprecipitation studies indicated an agonist-induced physical association between the D1-D2 receptor heteromeric complex and GRK2. Increased expression of GRK2 led to a decrease in the calcium signal with or without prior exposure to either SKF 83959 or SKF 83822. GRK2 knockdown by siRNA led to an increase in the signal after pretreatment with either agonist. Expression of the catalytically inactive and RGS (regulator of G protein signaling)-mutated GRK2 constructs each led to a partial recovery of the GRK2-attenuated calcium signal. These results indicated that desensitization of the dopamine D1-D2 receptor heteromer-mediated signal can occur by agonist occupancy even without activation and is dually regulated by both the catalytic and RGS domains of GRK2.

    Funded by: NIDA NIH HHS: DA007223, R01 DA007223

    The Journal of biological chemistry 2010;285;45;35092-103

  • G protein-coupled receptor kinase 2 plays a relevant role in insulin resistance and obesity.

    Garcia-Guerra L, Nieto-Vazquez I, Vila-Bedmar R, Jurado-Pueyo M, Zalba G, Díez J, Murga C, Fernández-Veledo S, Mayor F and Lorenzo M

    Department of Biochemistry and Molecular Biology II, Faculty of Pharmacy, Complutense University, Madrid, Spain.

    Objective: Insulin resistance is associated with the pathogenesis of metabolic disorders as type 2 diabetes and obesity. Given the emerging role of signal transduction in these syndromes, we set out to explore the possible role that G protein-coupled receptor kinase 2 (GRK2), first identified as a G protein-coupled receptor regulator, could have as a modulator of insulin responses.

    We analyzed the influence of GRK2 levels in insulin signaling in myoblasts and adipocytes with experimentally increased or silenced levels of GRK2, as well as in GRK2 hemizygous animals expressing 50% lower levels of this kinase in three different models of insulin resistance: tumor necrosis factor-α (TNF-α) infusion, aging, and high-fat diet (HFD). Glucose transport, whole-body glucose and insulin tolerance, the activation status of insulin pathway components, and the circulating levels of important mediators were measured. The development of obesity and adipocyte size with age and HFD was analyzed.

    Results: Altering GRK2 levels markedly modifies insulin-mediated signaling in cultured adipocytes and myocytes. GRK2 levels are increased by ∼2-fold in muscle and adipose tissue in the animal models tested, as well as in lymphocytes from metabolic syndrome patients. In contrast, hemizygous GRK2 mice show enhanced insulin sensitivity and do not develop insulin resistance by TNF-α, aging, or HFD. Furthermore, reduced GRK2 levels induce a lean phenotype and decrease age-related adiposity.

    Conclusions: Overall, our data identify GRK2 as an important negative regulator of insulin effects, key to the etiopathogenesis of insulin resistance and obesity, which uncovers this protein as a potential therapeutic target in the treatment of these disorders.

    Diabetes 2010;59;10;2407-17

  • Low nociceptor GRK2 prolongs prostaglandin E2 hyperalgesia via biased cAMP signaling to Epac/Rap1, protein kinase Cepsilon, and MEK/ERK.

    Eijkelkamp N, Wang H, Garza-Carbajal A, Willemen HL, Zwartkruis FJ, Wood JN, Dantzer R, Kelley KW, Heijnen CJ and Kavelaars A

    Laboratory of Neuroimmunology and Developmental Origins of Disease, University Medical Center Utrecht, 3584 EA Utrecht, The Netherlands.

    Hyperexcitability of peripheral nociceptive pathways is often associated with inflammation and is an important mechanism underlying inflammatory pain. Here we describe a completely novel mechanism via which nociceptor G-protein-coupled receptor kinase 2 (GRK2) contributes to regulation of inflammatory hyperalgesia. We show that nociceptor GRK2 is downregulated during inflammation. In addition, we show for the first time that prostaglandin E2 (PGE2)-induced hyperalgesia is prolonged from <6 h in wild-type (WT) mice to 3 d in mice with low GRK2 in Nav1.8+ nociceptors (SNS-GRK2+/- mice). This prolongation of PGE2 hyperalgesia in SNS-GRK2+/- mice does not depend on changes in the sensitivity of the prostaglandin receptors because prolonged hyperalgesia also developed in response to 8-Br-cAMP. PGE2 or cAMP-induced hyperalgesia in WT mice is PKA dependent. However, PKA activity is not required for hyperalgesia in SNS-GRK2+/- mice. SNS-GRK2+/- mice developed prolonged hyperalgesia in response to the Exchange proteins directly activated by cAMP (Epac) activator 8-pCPT-2'-O-Me-cAMP (8-pCPT). Coimmunoprecipitation experiments showed that GRK2 binds to Epac1. In vitro, GRK2 deficiency increased 8-pCPT-induced activation of the downstream effector of Epac, Rap1, and extracellular signal-regulated kinase (ERK). In vivo, inhibition of MEK1 or PKCε prevented prolonged PGE2, 8-Br-cAMP, and 8-pCPT hyperalgesia in SNS-GRK2+/- mice. In conclusion, we discovered GRK2 as a novel Epac1-interacting protein. A reduction in the cellular level of GRK2 enhances activation of the Epac-Rap1 pathway. In vivo, low nociceptor GRK2 leads to prolonged inflammatory hyperalgesia via biased cAMP signaling from PKA to Epac-Rap1, ERK/PKCε pathways.

    Funded by: Medical Research Council: G0901905

    The Journal of neuroscience : the official journal of the Society for Neuroscience 2010;30;38;12806-15

  • Reduction of sympathetic activity via adrenal-targeted GRK2 gene deletion attenuates heart failure progression and improves cardiac function after myocardial infarction.

    Lymperopoulos A, Rengo G, Gao E, Ebert SN, Dorn GW and Koch WJ

    Department of Pharmaceutical Sciences, Nova Southeastern University College of Pharmacy, Ft Lauderdale, Florida 33328, USA. al806@nova.edu

    Chronic heart failure (HF) is characterized by sympathetic overactivity and enhanced circulating catecholamines (CAs), which significantly increase HF morbidity and mortality. We recently reported that adrenal G protein-coupled receptor kinase 2 (GRK2) is up-regulated in chronic HF, leading to enhanced CA release via desensitization/down-regulation of the chromaffin cell alpha(2)-adrenergic receptors that normally inhibit CA secretion. We also showed that adrenal GRK2 inhibition decreases circulating CAs and improves cardiac inotropic reserve and function. Herein, we hypothesized that adrenal-targeted GRK2 gene deletion before the onset of HF might be beneficial by reducing sympathetic activation. To specifically delete GRK2 in the chromaffin cells of the adrenal gland, we crossed PNMTCre mice, expressing Cre recombinase under the chromaffin cell-specific phenylethanolamine N-methyltransferase (PNMT) gene promoter, with floxedGRK2 mice. After confirming a significant ( approximately 50%) reduction of adrenal GRK2 mRNA and protein levels, the PNMT-driven GRK2 knock-out (KO) offspring underwent myocardial infarction (MI) to induce HF. At 4 weeks post-MI, plasma levels of both norepinephrine and epinephrine were reduced in PNMT-driven GRK2 KO, compared with control mice, suggesting markedly reduced post-MI sympathetic activation. This translated in PNMT-driven GRK2 KO mice into improved cardiac function and dimensions as well as amelioration of abnormal cardiac beta-adrenergic receptor signaling at 4 weeks post-MI. Thus, adrenal-targeted GRK2 gene KO decreases circulating CAs, leading to improved cardiac function and beta-adrenergic reserve in post-MI HF. GRK2 inhibition in the adrenal gland might represent a novel sympatholytic strategy that can aid in blocking HF progression.

    Funded by: NHLBI NIH HHS: HL075443, HL085503, HL56205, HL61690, P01 HL075443, P01 HL091799, P01-HL091799, R01 HL056205, R01 HL061690, R01 HL085503, R01 HL087871, R37 HL061690

    The Journal of biological chemistry 2010;285;21;16378-86

  • G alpha(q)-mediated activation of GRK2 by mechanical stretch in cardiac myocytes: the role of protein kinase C.

    Malhotra R, D'Souza KM, Staron ML, Birukov KG, Bodi I and Akhter SA

    Department of Surgery, Section of Cardiac and Thoracic Surgery, University of Chicago Medical Center, Chicago, Illinois 60637, USA.

    G protein-coupled receptor kinase-2 (GRK2) is a critical regulator of beta-adrenergic receptor (beta-AR) signaling and cardiac function. We studied the effects of mechanical stretch, a potent stimulus for cardiac myocyte hypertrophy, on GRK2 activity and beta-AR signaling. To eliminate neurohormonal influences, neonatal rat ventricular myocytes were subjected to cyclical equi-biaxial stretch. A hypertrophic response was confirmed by "fetal" gene up-regulation. GRK2 activity in cardiac myocytes was increased 4.2-fold at 48 h of stretch versus unstretched controls. Adenylyl cyclase activity was blunted in sarcolemmal membranes after stretch, demonstrating beta-AR desensitization. The hypertrophic response to mechanical stretch is mediated primarily through the G alpha(q)-coupled angiotensin II AT(1) receptor leading to activation of protein kinase C (PKC). PKC is known to phosphorylate GRK2 at the N-terminal serine 29 residue, leading to kinase activation. Overexpression of a mini-gene that inhibits receptor-G alpha(q) coupling blunted stretch-induced hypertrophy and GRK2 activation. Short hairpin RNA-mediated knockdown of PKC alpha also significantly attenuated stretch-induced GRK2 activation. Overexpression of a GRK2 mutant (S29A) in cardiac myocytes inhibited phosphorylation of GRK2 by PKC, abolished stretch-induced GRK2 activation, and restored adenylyl cyclase activity. Cardiac-specific activation of PKC alpha in transgenic mice led to impaired beta-agonist-stimulated ventricular function, blunted cyclase activity, and increased GRK2 phosphorylation and activity. Phosphorylation of GRK2 by PKC appears to be the primary mechanism of increased GRK2 activity and impaired beta-AR signaling after mechanical stretch. Cross-talk between hypertrophic signaling at the level of PKC and beta-AR signaling regulated by GRK2 may be an important mechanism in the transition from compensatory ventricular hypertrophy to heart failure.

    Funded by: NHLBI NIH HHS: HL058064, HL081472, HL087823, K08 HL081472, P01 HL058064, R01 HL087823

    The Journal of biological chemistry 2010;285;18;13748-60

  • Cell-specific roles of GRK2 in onset and severity of hypoxic-ischemic brain damage in neonatal mice.

    Nijboer CH, Heijnen CJ, Willemen HL, Groenendaal F, Dorn GW, van Bel F and Kavelaars A

    Laboratory of Psychoneuroimmunology, University Medical Center Utrecht, Utrecht, The Netherlands.

    The ubiquitously expressed kinase GRK2 protects against cellular overstimulation by desensitizing G protein-coupled receptors and regulating intracellular signaling. Recently, we described that hypoxia-ischemia (HI)-induced brain damage was accelerated and increased in GRK2(+/-) neonatal mice. Using Cre-Lox technology we now investigated the role of decreased GRK2 in only microglia/macrophages or forebrain neurons in development of HI brain injury. Low GRK2 in microglia/macrophages (LysM-GRK2(f/+) mice) was sufficient to accelerate onset of HI damage, without affecting the severity of brain injury at 24h post-HI as compared to LysM-GRK2(+/+) littermates. Consistently, the ipsilateral hemisphere of GRK2(+/-) mice contained microglia with a more rounded phenotype compared to WT mice at 3h post-HI. Inhibition of microglial/macrophage activity by minocycline treatment prevented the early onset of HI injury in GRK2(+/-) mice. In vitro, primary GRK2(+/-) microglia stimulated with LPS produced more TNF-alpha than WT microglia via a p38-dependent pathway. In vivo, HI-induced cerebral p38 activation and TNF-alpha production were increased in GRK2(+/-) mice or in LysM-GRK2(f/+) mice. Our findings indicate that low GRK2 in microglia/macrophages accelerates brain damage via a GRK2/p38/TNF-alpha-dependent pathway. Reduced GRK2 only in forebrain neurons (CamKIIalpha-GRK2(f/+) mice) significantly increased severity of HI brain damage without affecting the onset of brain damage. In conclusion, our data indicate that low GRK2 in microglia/macrophages facilitates activation of these cells which may contribute to the earlier onset of cerebral HI injury associated with increased p38 phosphorylation and TNF-alpha production. The level of GRK2 in neurons is crucial for determining the ultimate severity of HI damage in the newborn brain.

    Funded by: NHLBI NIH HHS: R01 HL059888, R01 HL059888-01A1, R01 HL059888-02, R01 HL059888-03, R01 HL059888-04, R01 HL059888-05, R01 HL059888-06, R01 HL059888-07, R01 HL059888-08, R01 HL059888-09A1, R01 HL059888-09A1W1, R01 HL059888-10, R01 HL059888-11, R01 HL059888-12, R01 HL080008, R01 HL080008-01A1, R01 HL080008-02, R01 HL080008-03, R01 HL080008-04, R01 HL080008-05, R01 HL080008-06, R01 HL087871, R01 HL087871-01, R01 HL087871-02, R01 HL087871-03, R01 HL087871-04, R01 HL087871-05, R01 HL087871-06

    Brain, behavior, and immunity 2010;24;3;420-6

  • GRK2: a novel cell-specific regulator of severity and duration of inflammatory pain.

    Eijkelkamp N, Heijnen CJ, Willemen HL, Deumens R, Joosten EA, Kleibeuker W, den Hartog IJ, van Velthoven CT, Nijboer C, Nassar MA, Dorn GW, Wood JN and Kavelaars A

    Laboratory of Psychoneuroimmunology, University Medical Center Utrecht, 3584 EA Utrecht, The Netherlands.

    Chronic pain associated with inflammation is a common clinical problem, and the underlying mechanisms have only begun to be unraveled. GRK2 regulates cellular signaling by promoting G-protein-coupled receptor (GPCR) desensitization and direct interaction with downstream kinases including p38. The aim of this study was to determine the contribution of GRK2 to regulation of inflammatory pain and to unravel the underlying mechanism. GRK2(+/-) mice with an approximately 50% reduction in GRK2 developed increased and markedly prolonged thermal hyperalgesia and mechanical allodynia after carrageenan-induced paw inflammation or after intraplantar injection of the GPCR-binding chemokine CCL3. The effect of reduced GRK2 in specific cells was investigated using Cre-Lox technology. Carrageenan- or CCL3-induced hyperalgesia was increased but not prolonged in mice with decreased GRK2 only in Na(v)1.8 nociceptors. In vitro, reduced neuronal GRK2 enhanced CCL3-induced TRPV1 sensitization. In vivo, CCL3-induced acute hyperalgesia in GRK2(+/-) mice was mediated via TRPV1. Reduced GRK2 in microglia/monocytes only was required and sufficient to transform acute carrageenan- or CCL3-induced hyperalgesia into chronic hyperalgesia. Chronic hyperalgesia in GRK2(+/-) mice was associated with ongoing microglial activation and increased phospho-p38 and tumor necrosis factor alpha (TNF-alpha) in the spinal cord. Inhibition of spinal cord microglial, p38, or TNF-alpha activity by intrathecal administration of specific inhibitors reversed ongoing hyperalgesia in GRK2(+/-) mice. Microglia/macrophage GRK2 expression was reduced in the lumbar ipsilateral spinal cord during neuropathic pain, underlining the pathophysiological relevance of microglial GRK2. Thus, we identified completely novel cell-specific roles of GRK2 in regulating acute and chronic inflammatory hyperalgesia.

    Funded by: Biotechnology and Biological Sciences Research Council: BB/F000227/1; Medical Research Council: G0901905; NHLBI NIH HHS: R01 HL059888, R01 HL059888-01A1, R01 HL059888-02, R01 HL059888-03, R01 HL059888-04, R01 HL059888-05, R01 HL059888-06, R01 HL059888-07, R01 HL059888-08, R01 HL059888-09A1, R01 HL059888-09A1W1, R01 HL059888-10, R01 HL059888-11, R01 HL059888-12, R01 HL080008, R01 HL080008-01A1, R01 HL080008-02, R01 HL080008-03, R01 HL080008-04, R01 HL080008-05, R01 HL080008-06, R01 HL087871, R01 HL087871-01, R01 HL087871-02, R01 HL087871-03, R01 HL087871-04, R01 HL087871-05, R01 HL087871-06

    The Journal of neuroscience : the official journal of the Society for Neuroscience 2010;30;6;2138-49

  • G protein-coupled receptor kinase 2 (GRK2) modulation and cell cycle progression.

    Penela P, Rivas V, Salcedo A and Mayor F

    Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Universidad Autónoma, 28049 Madrid, Spain. ppenela@cbm.uam.es

    Cell cycle progression requires changes in the activity or levels of a variety of key signaling proteins. G protein-coupled receptor kinase 2 (GRK2) plays a central role in G protein-coupled receptor regulation. Recent research is uncovering its involvement in additional cellular functions, but the potential role of GRK2 in the cell cycle has not been addressed. We report that GRK2 protein levels are transiently down-regulated during the G2/M transition by a mechanism involving CDK2-mediated phosphorylation of GRK2 at Serine670, which triggers binding to the prolyl-isomerase Pin1 and subsequent degradation. Prevention of GRK2 phosphorylation at S670 impedes normal GRK2 down-regulation and markedly delays cell cycle progression. Interestingly, we find that endogenous GRK2 down-regulation is prevented on activation of the G2/M checkpoint by doxorubicin and that stabilized GRK2 levels in such conditions inversely correlate with the p53 response and the induction of apoptosis, suggesting that GRK2 participates in the regulatory network controlling cell cycle arrest and survival in such conditions.

    Proceedings of the National Academy of Sciences of the United States of America 2010;107;3;1118-23

  • G-protein-coupled-receptor kinases mediate TNFα-induced NFκB signalling via direct interaction with and phosphorylation of IκBα.

    Patial S, Luo J, Porter KJ, Benovic JL and Parameswaran N

    Department of Physiology and Division of Pathology, Michigan State University, East Lansing, MI 48824, USA.

    Tumor necrosis factor-α (TNFα) is a multifunctional cytokine involved in the pathophysiology of many chronic inflammatory diseases. TNFα activation of the nuclear factor κB (NFκB) signaling pathway particularly in macrophages has been implicated in many diseases. We demonstrate here that G-protein coupled receptor kinase-2 and 5 (GRK2 and 5) regulate TNFα-induced NFκB signaling in Raw264.7 macrophages. RNAi knockdown of GRK2 or 5 in macrophages significantly inhibits TNFα-induced IκBα phosphorylation and degradation, NFκB activation, and expression of the NFκB-regulated gene, macrophage inflammatory protein-1β. Consistent with these results, over-expression of GRK2 or 5 enhances TNFα-induced NFκB activity. In addition,we show that GRK2 and 5 interact with IκBα via the N-terminal domain of IκBα and that IκBα isa substrate for GRK2 and 5 in vitro. Furthermore, we also find that GRK5 but not GRK2 phosphorylates IκBα at the same amino acid residues (Ser32/36) as that of IKKβ. Interestingly,associated with these results, knockdown of IKKβ in Raw264.7 macrophages did not affect TNFα-induced IκBα phosphorylation. Taken together, these results demonstrate that both GRK2 and 5 are important and novel mediators of a non-traditional IκBα-NFκB signaling pathway.

    Funded by: NHLBI NIH HHS: HL095637, R01 HL095637, R01 HL095637-01, R01 HL095637-02; NIAMS NIH HHS: AR055726, R01 AR056680, R21 AR055726, R21 AR055726-01A1, R21 AR055726-02; NIGMS NIH HHS: GM44944, R01 GM044944

    The Biochemical journal 2009;425;1;169-78

  • Phosphorylation-independent regulation of metabotropic glutamate receptor 5 desensitization and internalization by G protein-coupled receptor kinase 2 in neurons.

    Ribeiro FM, Ferreira LT, Paquet M, Cregan T, Ding Q, Gros R and Ferguson SS

    Allyn Taylor Centre for Cell Biology, Molecular Brain Research Group, University of Western Ontario, London, Ontario N6A 5K8, Canada.

    The uncoupling of metabotropic glutamate receptors (mGluRs) from heterotrimeric G proteins represents an essential feedback mechanism that protects neurons against receptor overstimulation that may ultimately result in damage. The desensitization of mGluR signaling is mediated by both second messenger-dependent protein kinases and G protein-coupled receptor kinases (GRKs). Unlike mGluR1, the attenuation of mGluR5 signaling in HEK 293 cells is reported to be mediated by a phosphorylation-dependent mechanism. However, the mechanisms regulating mGluR5 signaling and endocytosis in neurons have not been investigated. Here we show that a 2-fold overexpression of GRK2 leads to the attenuation of endogenous mGluR5-mediated inositol phosphate (InsP) formation in striatal neurons and siRNA knockdown of GRK2 expression leads to enhanced mGluR5-mediated InsP formation. Expression of a catalytically inactive GRK2-K220R mutant also effectively attenuates mGluR5 signaling, but the expression of a GRK2-D110A mutant devoid in Galpha(q/11) binding increases mGluR5 signaling in response to agonist stimulation. Taken together, these results indicate that the attenuation of mGluR5 responses in striatal neurons is phosphorylation-independent. In addition, we find that mGluR5 does not internalize in response to agonist treatment in striatal neuron, but is efficiently internalized in cortical neurons that have higher levels of endogenous GRK2 protein expression. When overexpressed in striatal neurons, GRK2 promotes agonist-stimulated mGluR5 internalization. Moreover, GRK2-mediated promotion of mGluR5 endocytosis does not require GRK2 catalytic activity. Thus, we provide evidence that GRK2 mediates phosphorylation-independent mGluR5 desensitization and internalization in neurons.

    The Journal of biological chemistry 2009;284;35;23444-53

  • Two distinct mechanisms mediate acute mu-opioid receptor desensitization in native neurons.

    Dang VC, Napier IA and Christie MJ

    Pain Management Research Institute and Brain and Mind Research Institute, The University of Sydney, New South Wales 2006, Australia.

    Sustained stimulation of G-protein coupled receptors (GPCRs) leads to rapid loss of receptor function (acute desensitization). For many GPCRs including the mu-opioid receptor (MOR), an accepted mechanism for acute desensitization is through G-protein coupled receptor kinase (GRKs) mediated phosphorylation of the receptor, which facilitates the binding of beta-arrestins (betaarrs) to the receptor and then promotes endocytosis. However, the mechanism(s) that mediate acute desensitization have not yet been well defined in native neurons. This study used whole-cell patch clamp recording of G-protein coupled inward-rectifying potassium (GIRK) currents to assay MOR function and identify mechanisms of acute MOR desensitization in locus ceruleus (LC) neurons. The rate and extent of MOR desensitization were unaffected by beta(arr)-2 knock-out. Disruption of GRK2 function via inhibitory peptide introduced directly into neurons also failed to affect desensitization in wild type or beta(arr)-2 knock-outs. Inhibition of ERK1/2 activation alone had little effect on acute desensitization. However, when both GRK2-beta(arr)-2 and ERK1/2 functions were disrupted simultaneously, desensitization of MOR was nearly abolished. Together, these results suggest that acute desensitization of MOR in native LC neurons is determined by at least two molecular pathways, one involving GRK2 and beta(arr)2, and a parallel pathway mediated by activated ERK1/2.

    The Journal of neuroscience : the official journal of the Society for Neuroscience 2009;29;10;3322-7

  • Granulocyte chemotaxis and disease expression are differentially regulated by GRK subtype in an acute inflammatory arthritis model (K/BxN).

    Tarrant TK, Rampersad RR, Esserman D, Rothlein LR, Liu P, Premont RT, Lefkowitz RJ, Lee DM and Patel DD

    Thurston Arthritis Research Center, Department of Medicine, Division of Rheumatology, Allergy and Immunology, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA. tarra002@med.unc.edu

    Objective: Chemokine receptors are G-protein coupled receptors (GPCRs) phosphorylated by G-protein receptor kinases (GRKs) after ligand-mediated activation. We hypothesized that GRK subtypes differentially regulate granulocyte chemotaxis and clinical disease expression in the K/BxN model.

    Methods: Clinical, histologic, and cytokine responses in GRK6-/-, GRK5-/-, GRK2+/-, and wildtype mice were evaluated using K/BxN serum transfer. Granulocyte chemotaxis was analyzed by transendothelial migration assays.

    Results: Both GRK6-/- and GRK2+/- mice had increased arthritis disease severity (p<0.001); whereas GRK5-/- was not different from controls. Acute weight loss was enhanced in GRK6-/- and GRK2+/- mice (p<0.001, days 3-10). However, GRK6-/- mice uniquely had more weight loss (>10%), elevated serum IL-6, and enhanced migration toward LTB4 and C5a in vitro.

    Conclusions: GRK6 and -2, but not GRK5, are involved in the pathogenesis of acute arthritis in the K/BxN model. In particular, GRK6 may dampen inflammatory responses by regulating granulocyte trafficking toward chemoattractants.

    Funded by: NIAID NIH HHS: K08 AI070684, K08 AI070684-03, P01 AI 065858, P01 AI065858-029001; NICHD NIH HHS: K12 HD001441, K12 HD001441-08, K12 HD01441

    Clinical immunology (Orlando, Fla.) 2008;129;1;115-22

  • Inhibition of vascular smooth muscle G protein-coupled receptor kinase 2 enhances alpha1D-adrenergic receptor constriction.

    Cohn HI, Harris DM, Pesant S, Pfeiffer M, Zhou RH, Koch WJ, Dorn GW and Eckhart AD

    Center for Translational Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.

    G protein-coupled receptor kinase 2 (GRK2) is a serine/theorinine kinase that phosphorylates and desensitizes agonist-bound G protein-coupled receptors. GRK2 is increased in expression and activity in lymphocytes and vascular smooth muscle (VSM) in human hypertension and animal models of the disease. Inhibition of GRK2 using the carboxyl-terminal portion of the protein (GRK2ct) has been an effective tool to restore compromised beta-adrenergic receptor (AR) function in heart failure and improve outcome. A well-characterized dysfunction in hypertension is attenuation of betaAR-mediated vasodilation. Therefore, we tested the role of inhibition of GRK2 using GRK2ct or VSM-selective GRK2 gene ablation in a renal artery stenosis model of elevated blood pressure (BP) [the two-kidney, one-clip (2K1C) model]. Use of the 2K1C model resulted in a 30% increase in conscious BP, a threefold increase in plasma norepinephrine levels, and a 50% increase in VSM GRK2 mRNA levels. BP remained increased despite VSM-specific GRK2 inhibition by either GRK2 knockout (GRK2KO) or peptide inhibition (GRK2ct). Although betaAR-mediated dilation in vivo and in situ was enhanced, alpha(1)AR-mediated vasoconstriction was also increased. Further pharmacological experiments using alpha(1)AR antagonists revealed that GRK2 inhibition of expression (GRK2KO) or activity (GRK2ct) enhanced alpha(1D)AR vasoconstriction. This is the first study to suggest that VSM alpha(1D)ARs are a GRK2 substrate in vivo.

    Funded by: NHLBI NIH HHS: R01 HL087871, R01-HL-069847

    American journal of physiology. Heart and circulatory physiology 2008;295;4;H1695-704

  • G protein-coupled receptor kinase 2 ablation in cardiac myocytes before or after myocardial infarction prevents heart failure.

    Raake PW, Vinge LE, Gao E, Boucher M, Rengo G, Chen X, DeGeorge BR, Matkovich S, Houser SR, Most P, Eckhart AD, Dorn GW and Koch WJ

    Center for Translational Medicine, Department of Medicine, Thomas Jefferson University, 1025 Walnut St, Philadelphia, PA 19107, USA. Philip.Raake@jefferson.edu

    Myocardial G protein-coupled receptor kinase (GRK)2 is a critical regulator of cardiac beta-adrenergic receptor (betaAR) signaling and cardiac function. Its upregulation in heart failure may further depress cardiac function and contribute to mortality in this syndrome. Preventing GRK2 translocation to activated betaAR with a GRK2-derived peptide that binds G(beta)gamma (betaARKct) has benefited some models of heart failure, but the precise mechanism is uncertain, because GRK2 is still present and betaARKct has other potential effects. We generated mice in which cardiac myocyte GRK2 expression was normal during embryonic development but was ablated after birth (alphaMHC-Cre x GRK2 fl/fl) or only after administration of tamoxifen (alphaMHC-MerCreMer x GRK2 fl/fl) and examined the consequences of GRK2 ablation before and after surgical coronary artery ligation on cardiac adaptation after myocardial infarction. Absence of GRK2 before coronary artery ligation prevented maladaptive postinfarction remodeling and preserved betaAR responsiveness. Strikingly, GRK2 ablation initiated 10 days after infarction increased survival, enhanced cardiac contractile performance, and halted ventricular remodeling. These results demonstrate a specific causal role for GRK2 in postinfarction cardiac remodeling and heart failure and support therapeutic approaches of targeting GRK2 or restoring betaAR signaling by other means to improve outcomes in heart failure.

    Funded by: NHLBI NIH HHS: P01 HL075443, P01 HL075443-050002, R01 HL056205, R01 HL056205-08, R01 HL061690, R01 HL061690-09, R01 HL061690-10, R01 HL061690-11, R01 HL087871, R01 HL088243, R01 HL088243-01, R01 HL088243-02, R01 HL56205, R01 HL61690, R01 HL87871

    Circulation research 2008;103;4;413-22

  • G protein-coupled receptor kinase 2 positively regulates epithelial cell migration.

    Penela P, Ribas C, Aymerich I, Eijkelkamp N, Barreiro O, Heijnen CJ, Kavelaars A, Sánchez-Madrid F and Mayor F

    Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa, Universidad Autónoma de Madrid, Madrid, Spain. ppenela@cbm.uam.es

    Cell migration requires integration of signals arising from both the extracellular matrix and messengers acting through G protein-coupled receptors (GPCRs). We find that increased levels of G protein-coupled receptor kinase 2 (GRK2), a key player in GPCR regulation, potentiate migration of epithelial cells towards fibronectin, whereas such process is decreased in embryonic fibroblasts from hemizygous GRK2 mice or upon knockdown of GRK2 expression. Interestingly, the GRK2 effect on fibronectin-mediated cell migration involves the paracrine/autocrine activation of a sphingosine-1-phosphate (S1P) Gi-coupled GPCR. GRK2 positively modulates the activity of the Rac/PAK/MEK/ERK pathway in response to adhesion and S1P by a mechanism involving the phosphorylation-dependent, dynamic interaction of GRK2 with GIT1, a key scaffolding protein in cell migration processes. Furthermore, decreased GRK2 levels in hemizygous mice result in delayed wound healing rate in vivo, consistent with a physiological role of GRK2 as a regulator of coordinated integrin and GPCR-directed epithelial cell migration.

    The EMBO journal 2008;27;8;1206-18

  • Toll-like receptors differentially regulate GPCR kinases and arrestins in primary macrophages.

    Loniewski K, Shi Y, Pestka J and Parameswaran N

    Department of Physiology, Division of Pathology, Michigan State University, East Lansing, MI 48824, USA.

    G-protein coupled receptor kinases (GRKs) and arrestins (ARRs) are ubiquitously distributed crucial signaling proteins that are critical in the regulation of responsiveness of G-protein coupled receptors (GPCRs). Toll-like receptors (TLRs) (class of pattern recognition receptors) play a vital role in macrophage biology and innate immunity. Because GPCR responsiveness is regulated in part by the expression levels of GRKs/ARRs, the focus of this work was to uncover potential cross-talk mechanisms between TLRs and GPCRs via regulation of GRK/ARR expression in primary mouse macrophages. We demonstrate here that activation of TLR2 and 4 (but not TLR3 and 7) significantly decrease ARR2 but not ARR3 protein levels in macrophages. Compared to this, activation of TLR2, 4, and 7 (but not TLR3) significantly decrease GRK5 and 6 protein levels. Surprisingly, GRK2 protein levels are markedly increased by TLR2, 3, 4 and 7. Mechanistically, expression of ARR2 and GRK5 are regulated at transcriptional as well as post-translational levels. Downregulation of GRK6 by LPS is regulated primarily at the post-translational level. TLR4-induced GRK2 level, however, is both transcriptionally and post-transcriptionally regulated. Our results demonstrate previously unknown crucial regulatory mechanisms that alter ARR/GRK expression levels in macrophages that might modify many, if not all, GPCR-mediated innate immune responses.

    Funded by: NIDDK NIH HHS: R01DK 58833; NIEHS NIH HHS: R01ES 3358

    Molecular immunology 2008;45;8;2312-22

  • Low endogenous G-protein-coupled receptor kinase 2 sensitizes the immature brain to hypoxia-ischemia-induced gray and white matter damage.

    Nijboer CH, Kavelaars A, Vroon A, Groenendaal F, van Bel F and Heijnen CJ

    Laboratory of Psychoneuroimmunology, University Medical Center Utrecht, 3584 EA Utrecht, The Netherlands.

    Hypoxic-ischemic brain injury is regulated in part by neurotransmitter and chemokine signaling via G-protein-coupled receptors (GPCRs). GPCR-kinase 2 (GRK2) protects these receptors against overstimulation by inducing desensitization. Neonatal hypoxic-ischemic brain damage is preceded by a reduction in cerebral GRK2 expression. We determined the functional importance of GRK2 in hypoxic-ischemic brain damage. Nine-day-old wild-type and GRK2(+/-) mice with a approximately 50% reduction in GRK2 protein were exposed to unilateral carotid artery occlusion and hypoxia. In GRK2(+/-) animals, gray and white matter damage was aggravated at 3 weeks after hypoxia-ischemia. In addition, cerebral neutrophil infiltration was increased in GRK2(+/-) animals. Neutrophil depletion reduced brain damage, but neuronal loss was still more pronounced in GRK2(+/-) animals. Onset of neuronal loss was advanced in GRK2(+/-) animals regardless of neutrophil depletion. White matter injury was advanced in GRK2(+/-) animals and was not affected by neutrophil depletion. Activation/infiltration of microglia/macrophages was stronger in GRK2(+/-) brains but only occurred 24 h after hypoxia-ischemia and is therefore not the primary cause of increased damage. During hypoxia, cerebral blood flow was reduced to the same extent in both genotypes. In vitro, GRK2(+/-) hippocampal slices and cerebellar granular neurons were more sensitive to glutamate-induced death. We propose the novel concept that the kinase GRK2 regulates onset and magnitude of hypoxic-ischemic brain damage. Increased gray and white matter damage in GRK2(+/-) animals was not dependent on infiltrating neutrophils and occurred before microglia/macrophage activation was detected. Collectively, our data suggest that cerebral GRK2 has an important endogenous neuroprotective role in ischemic cerebral damage.

    The Journal of neuroscience : the official journal of the Society for Neuroscience 2008;28;13;3324-32

  • IL-1 beta signaling is required for mechanical allodynia induced by nerve injury and for the ensuing reduction in spinal cord neuronal GRK2.

    Kleibeuker W, Gabay E, Kavelaars A, Zijlstra J, Wolf G, Ziv N, Yirmiya R, Shavit Y, Tal M and Heijnen CJ

    University Medical Centre Utrecht, Laboratory of Psychoneuroimmunology, Lundlaan 6, 3584 EA Utrecht, The Netherlands.

    Many neurotransmitters involved in pain perception transmit signals via G protein-coupled receptors (GPCRs). GPCR kinase 2 (GRK2) regulates agonist-induced desensitization and signaling of multiple GPCRs and interacts with downstream molecules with consequences for signaling. In general, low GRK2 levels are associated with increased responses to agonist stimulation of GPCRs. Recently, we reported that in mice with reduced GRK2 levels, inflammation-induced mechanical allodynia was increased. In addition, mice with impaired interleukin (IL)-1 beta signaling did not develop mechanical allodynia after L5 spinal nerve transection (SNT). We hypothesized that in the L5 SNT model mechanical allodynia would be associated with reduced neuronal GRK2 levels in the spinal cord dorsal horn and that IL-1 beta signaling would be required to induce both the decrease in GRK2 and mechanical allodynia. We show here that in wild type (WT) mice L5 SNT induces a bilateral decrease in neuronal GRK2 expression in the lumbar spinal cord dorsal horn, 1 and 2 weeks after L5 SNT. No changes in GRK2 were observed in the thoracic segments. Moreover, spinal cord GRK2 expression was not decreased in IL-1R(-/-) mice after L5 SNT. These data show that IL-1 beta signaling is not only required for the development of mechanical allodynia, but also to reduce neuronal GRK2 expression. These results suggest a functional relation between the L5 SNT-induced IL-1 beta-mediated decrease in GRK2 and development of mechanical allodynia.

    Brain, behavior, and immunity 2008;22;2;200-8

  • Physiological changes in GRK2 regulate CCL2-induced signaling to ERK1/2 and Akt but not to MEK1/2 and calcium.

    Kleibeuker W, Jurado-Pueyo M, Murga C, Eijkelkamp N, Mayor F, Heijnen CJ and Kavelaars A

    University Medical Center Utrecht, Laboratory of Psychoneuroimmunology, Utrecht, The Netherlands.

    G protein-coupled receptor (GPCR) kinase 2 (GRK2) regulates G protein-coupled receptor signaling via agonist-induced receptor phosphorylation and desensitization. GRK2 can also modulate cellular activation by interacting with downstream signaling molecules. The intracellular GRK2 level changes during inflammatory conditions. We investigated how IL-1beta-induced changes in endogenous GRK2 expression influence chemokine receptor signaling in primary astrocytes. Culturing astrocytes with IL-1beta for 24 h induced a 2-3-fold increase in GRK2 and decreased C-C chemokine ligand 2 (CCL2)-induced ERK1/2 activation. Conversely, the 45% decrease in GRK2 expression in astrocytes from GRK2+/- animals resulted in a more pronounced CCL2-induced ERK1/2 phosphorylation. Increased GRK2 inhibited CCL2-induced Akt phosphorylation at Thr308 and Ser473 as well as pPDK-1 translocation. In contrast, altered GRK2 levels did not change the CCL2-induced increase in intracellular calcium or MEK1/2 phosphorylation. These data suggest that altered GRK2 expression modulates chemokine signaling downstream of the receptor. We found that GRK2 kinase activity was not required to decrease chemokine-induced ERK1/2 phosphorylation, whereas regulation of CCL2-induced Akt phosphorylation did require an active GRK2 kinase domain. Collectively, these data suggest that changes in endogenous GRK2 expression in primary astrocytes regulate chemokine receptor signaling to ERK1/2 and to PDK-1-Akt downstream of receptor coupling via kinase-dependent and kinase-independent mechanisms, respectively.

    Journal of neurochemistry 2008;104;4;979-92

  • Norepinephrine- and epinephrine-induced distinct beta2-adrenoceptor signaling is dictated by GRK2 phosphorylation in cardiomyocytes.

    Wang Y, De Arcangelis V, Gao X, Ramani B, Jung YS and Xiang Y

    Department of Molecular and Integrative Physiology, University of Illinois at Urbana Champaign, Urbana, Illinois 61822, USA.

    Agonist-dependent activation of G protein-coupled receptors induces diversified receptor cellular and signaling properties. Norepinephrine (NE) and epinephrine (Epi) are two endogenous ligands that activate adrenoceptor (AR) signals in a variety of physiological stress responses in animals. Here we use cardiomyocyte contraction rate response to analyze the endogenous beta(2)AR signaling induced by Epi or NE in cardiac tissue. The Epi-activated beta(2)AR induced a rapid contraction rate increase that peaked at 4 min after stimulation. In contrast, the NE-activated beta(2)AR induced a much slower contraction rate increase that peaked at 10 min after stimulation. Whereas both drugs activated beta(2)AR coupling to G(s) proteins, only Epi-activated receptors were capable of coupling to G(i) proteins. Subsequent studies showed that the Epi-activated beta(2)AR underwent a rapid phosphorylation by G protein-coupled receptor kinase 2 (GRK2) and subsequent dephosphorylation on serine residues 355 and 356, which was critical for sufficient receptor recycling and G(i) coupling. In contrast, the NE-activated beta(2)ARs underwent slow GRK2 phosphorylation, receptor internalization and recycling, and failed to couple to G(i). Moreover, inhibiting beta(2)AR phosphorylation by betaARK C terminus or dephosphorylation by okadaic acid prevented sufficient recycling and G(i) coupling. Together, our data revealed that distinct temporal phosphorylation of beta(2)AR on serine 355 and 356 by GRK2 plays a critical role for dictating receptor cellular events and signaling properties induced by Epi or NE in cardiomyocytes. This study not only helps us understand the endogenous agonist-dependent beta(2)AR signaling in animal heart but also offers an example of how G protein-coupled receptor signaling may be finely regulated by GRK in physiological settings.

    Funded by: NHLBI NIH HHS: R01 HL082846, R01 HL082846-01, R01 HL082846-03

    The Journal of biological chemistry 2008;283;4;1799-807

  • Vascular smooth muscle G(q) signaling is involved in high blood pressure in both induced renal and genetic vascular smooth muscle-derived models of hypertension.

    Harris DM, Cohn HI, Pesant S, Zhou RH and Eckhart AD

    Eugene Feiner Laboratory of Vascular Biology and Thrombosis, Center for Translational Medicine, Thomas Jefferson University, Philadelphia, PA, USA.

    More than 30% of the US population has high blood pressure (BP), and less than a third of people treated for hypertension have it controlled. In addition, the etiology of most high BP is not known. Having a better understanding of the mechanisms underlying hypertension could potentially increase the effectiveness of treatment. Because G(q) signaling mediates vasoconstriction and vascular function can cause BP abnormalities, we were interested in determining the role of vascular smooth muscle (VSM) G(q) signaling in two divergent models of hypertension: a renovascular model of hypertension through renal artery stenosis and a genetic model of hypertension using mice with VSM-derived high BP. Inhibition of VSM G(q) signaling attenuated BP increases induced by renal artery stenosis to a similar extent as losartan, an ANG II receptor blocker and current antihypertensive therapy. Inhibition of G(q) signaling also attenuated high BP in our genetic VSM-derived hypertensive model. In contrast, BP remained elevated 25% following treatment with losartan, and prazosin, an alpha(1)-adrenergic receptor antagonist, only decreased BP by 35%. Inhibition of G(q) signaling attenuated VSM reactivity to ANG II and resulted in a 2.4-fold rightward shift in EC(50). We also determined that inhibition of G(q) signaling was able to reverse VSM hypertrophy in the genetic VSM-derived hypertensive model. These results suggest that G(q) signaling is an important signaling pathway in two divergent models of hypertension and, perhaps, optimization of antihypertensive therapy could occur with the identification of particular G(q)-coupled receptors involved.

    Funded by: NHLBI NIH HHS: R01-HL69847

    American journal of physiology. Heart and circulatory physiology 2007;293;5;H3072-9

  • GRK2 interacts with and phosphorylates Nedd4 and Nedd4-2.

    Sanchez-Perez A, Kumar S and Cook DI

    Bosch Institute, Department of Pathology, University of Sydney, Sydney, NSW 2006, Australia.

    Epithelial Na(+) channels (ENaC) mediate the transport of sodium (Na) across epithelia in the kidney, gut, and lungs and are required for blood pressure regulation. They are inhibited by ubiquitin protein ligases, such as Nedd4 and Nedd4-2, which bind to proline-rich motifs (PY motifs) present in the C-termini of ENaC subunits. Loss of inhibition leads to hypertension. ENaC channels are maintained in the active state by G-protein-coupled receptor kinase 2 (GRK2), an enzyme implicated in the development of essential hypertension. Here, we report that GRK2 interacts not only with ENaC, but also with both Nedd4 and Nedd4-2. Additionally, GRK2 is capable of phosphorylating both Nedd4 and Nedd4-2 at multiple sites. Of possible significance is the phosphorylation of the threonine at position 466 in Nedd4, which is located in the area of the ww3 domain that binds ENaC. These results support and extend the role of GRK2 in sodium transport regulation.

    Biochemical and biophysical research communications 2007;359;3;611-5

  • GRK2 negatively regulates glycogen synthesis in mouse liver FL83B cells.

    Shahid G and Hussain T

    Department of Pharmacological and Pharmaceutical Sciences, University of Houston, 4800 Calhoun, Houston, TX 77204, USA.

    G-protein-coupled receptor (GPCR) kinases (GRKs) are serine/threonine kinases that desensitize agonist-occupied classical GPCRs. Although the insulin receptor (IR) is a tyrosine kinase receptor, the IR also couples to G-proteins and utilizes G-protein signaling components. The present study was designed to test the hypothesis that GRK2 negatively regulates IR signaling. FL83B cells, derived from mouse liver, were treated with insulin and membrane translocation of GRK2 was determined using immunofluoresecence and Western blotting. Insulin caused an increase in the translocation of GRK-2 from cytosol to the plasma membrane. To determine the role of GRK2 in IR signaling, GRK2 was selectively down-regulated ( approximately by 90%) in FL83B cells using a small interfering RNA technique. Basal as well as insulin-induced glycogen synthesis (measured by d-[U-(14)C]glucose incorporation) was increased in GRK2-deficient cells compared with control cells. Similarly, GRK2 deficiency increased the basal and insulin-stimulated phosphorylation of Ser(21) in glycogen synthase kinase-3alpha. Insulin-induced tyrosine phosphorylation of the IR was similar in control and GRK2-deficient cells. Basal and insulin-stimulated phosphorylation of Tyr(612) in insulin receptor subunit 1 was significantly increased while phosphorylation of Ser(307) was decreased in GRK2-deficient FL83B cells compared with control cells. Chronic insulin treatment (24 h) in control cells caused an increase in GRK2 (56%) and a decrease in IR (50%) expression associated with the absence of an increase in glycogen synthesis, suggesting impairment of IR function. However, chronic insulin treatment (24 h) did not decrease IR expression or impair IR effects on glycogen synthesis in GRK2-deficient cells. We conclude that (i) GRK2 negatively regulates basal and insulin-stimulated glycogen synthesis via a post-IR signaling mechanism, and (ii) GRK2 may contribute to reduced IR expression and function during chronic insulin exposure.

    The Journal of biological chemistry 2007;282;28;20612-20

  • The membrane-proximal portion of CD3 epsilon associates with the serine/threonine kinase GRK2.

    DeFord-Watts LM, Young JA, Pitcher LA and van Oers NS

    Department of Immunology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9093, USA.

    The activation of protein kinases is one of the primary mechanisms whereby T cell receptors (TCR) propagate intracellular signals. To date, the majority of kinases known to be involved in the early stages of TCR signaling are protein-tyrosine kinases such as Lck, Fyn, and ZAP-70. Here we report a constitutive association between the TCR and a serine/threonine kinase, which was mediated through the membrane-proximal portion of CD3 epsilon. Mass spectrometry analysis of CD3 epsilon-associated proteins identified G protein-coupled receptor kinase 2 (GRK2) as a candidate Ser/Thr kinase. Transient transfection assays and Western blot analysis verified the ability of GRK2 to interact with the cytoplasmic domain of CD3 epsilon within a cell. These findings are consistent with recent reports demonstrating the ability of certain G protein-coupled receptors (GPCR) and G proteins to physically associate with the alpha/beta TCR. Because GRK2 is primarily involved in arresting GPCR signals, its interaction with CD3 epsilon may provide a novel means whereby the TCR can negatively regulate signals generated through GPCRs.

    Funded by: NIAID NIH HHS: 5T32AI005284

    The Journal of biological chemistry 2007;282;22;16126-34

  • Regulation of beta-adrenergic receptor signaling by S-nitrosylation of G-protein-coupled receptor kinase 2.

    Whalen EJ, Foster MW, Matsumoto A, Ozawa K, Violin JD, Que LG, Nelson CD, Benhar M, Keys JR, Rockman HA, Koch WJ, Daaka Y, Lefkowitz RJ and Stamler JS

    Department of Medicine, Duke University Medical Center, Durham, NC 27710, USA.

    beta-adrenergic receptors (beta-ARs), prototypic G-protein-coupled receptors (GPCRs), play a critical role in regulating numerous physiological processes. The GPCR kinases (GRKs) curtail G-protein signaling and target receptors for internalization. Nitric oxide (NO) and/or S-nitrosothiols (SNOs) can prevent the loss of beta-AR signaling in vivo, but the molecular details are unknown. Here we show in mice that SNOs increase beta-AR expression and prevent agonist-stimulated receptor downregulation; and in cells, SNOs decrease GRK2-mediated beta-AR phosphorylation and subsequent recruitment of beta-arrestin to the receptor, resulting in the attenuation of receptor desensitization and internalization. In both cells and tissues, GRK2 is S-nitrosylated by SNOs as well as by NO synthases, and GRK2 S-nitrosylation increases following stimulation of multiple GPCRs with agonists. Cys340 of GRK2 is identified as a principal locus of inhibition by S-nitrosylation. Our studies thus reveal a central molecular mechanism through which GPCR signaling is regulated.

    Funded by: NHLBI NIH HHS: P01-HL075443, R01 HL16037, R01 HL61690, R01 HL70631; NIEHS NIH HHS: U19-ES012496

    Cell 2007;129;3;511-22

  • A role for G protein-coupled receptor kinase 2 in mechanical allodynia.

    Kleibeuker W, Ledeboer A, Eijkelkamp N, Watkins LR, Maier SF, Zijlstra J, Heijnen CJ and Kavelaars A

    University Medical Center Utrecht, Laboratory of Psychoneuroimmunology, KC03.068.0, Lundlaan 6, 3584 EA, Utrecht, The Netherlands.

    Inflammation and nerve injury can both induce mechanical allodynia via mechanisms involving the production of pro-inflammatory cytokines and increased neuronal activity. Many neurotransmitters involved in pain signal via G protein-coupled receptors (GPCRs). GPCR kinase (GRK)2 is a member of the GRK family that regulates agonist-induced desensitization and signalling of GPCRs. Low intracellular GRK2 levels are associated with increased receptor signalling. The aim of this study was to investigate whether mechanical allodynia is associated with decreased spinal cord GRK2 expression and whether reduced GRK2 increases inflammation-induced mechanical allodynia. Mechanical allodynia was induced in rats by chronic constriction injury of the sciatic nerve. After 2 weeks, neuronal GRK2 expression was decreased bilaterally in the superficial layers of the lumbar spinal cord dorsal horn. Moreover, interleukin-1beta significantly reduced GRK2 expression ex vivo in spinal cord slices. To investigate whether reduced GRK2 potentiates inflammation-induced mechanical allodynia, we used GRK2(+/-) animals expressing decreased GRK2. At baseline, the threshold for mechanical stimulation did not differ between GRK2(+/-) and wild-type mice. However, GRK2(+/-) animals were more sensitive to mechanical stimulation than wild-type animals after intraplantar lambda-carrageenan injection. We propose cytokine-induced down-regulation of spinal cord neuronal GRK2 expression as a novel mechanism that contributes to increased neuronal signalling in mechanical allodynia.

    The European journal of neuroscience 2007;25;6;1696-704

  • Adrenal GRK2 upregulation mediates sympathetic overdrive in heart failure.

    Lymperopoulos A, Rengo G, Funakoshi H, Eckhart AD and Koch WJ

    Center for Translational Medicine, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.

    Cardiac overstimulation by the sympathetic nervous system (SNS) is a salient characteristic of heart failure, reflected by elevated circulating levels of catecholamines. The success of beta-adrenergic receptor (betaAR) antagonists in heart failure argues for SNS hyperactivity being pathogenic; however, sympatholytic agents targeting alpha2AR-mediated catecholamine inhibition have been unsuccessful. By investigating adrenal adrenergic receptor signaling in heart failure models, we found molecular mechanisms to explain the failure of sympatholytic agents and discovered a new strategy to lower SNS activity. During heart failure, there is substantial alpha2AR dysregulation in the adrenal gland, triggered by increased expression and activity of G protein-coupled receptor kinase 2 (GRK2). Adrenal gland-specific GRK2 inhibition reversed alpha2AR dysregulation in heart failure, resulting in lowered plasma catecholamine levels, improved cardiac betaAR signaling and function, and increased sympatholytic efficacy of a alpha2AR agonist. This is the first demonstration, to our knowledge, of a molecular mechanism for SNS hyperactivity in heart failure, and our study identifies adrenal GRK2 activity as a new sympatholytic target.

    Funded by: NHLBI NIH HHS: P01-HL075443, R01 HL56205, R01 HL61690

    Nature medicine 2007;13;3;315-23

  • G protein-coupled receptor (GPCR) kinase 2 regulates agonist-independent Gq/11 signaling from the mouse cytomegalovirus GPCR M33.

    Sherrill JD and Miller WE

    Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524, USA.

    The mouse cytomegalovirus M33 protein is highly homologous to mammalian G protein-coupled receptors (GPCRs) yet functions in an agonist-independent manner to activate a number of classical GPCR signal transduction pathways. M33 is functionally similar to the human cytomegalovirus-encoded US28 GPCR in its ability to induce inositol phosphate accumulation, activate NF-kappaB, and promote smooth muscle cell migration. This ability to promote cellular migration suggests a role for viral GPCRs like M33 in viral dissemination in vivo, and accordingly, M33 is required for efficient murine cytomegalovirus replication in the mouse. Although previous studies have identified several M33-induced signaling pathways, little is known regarding the membrane-proximal events involved in signaling and regulation of this receptor. In this study, we used recombinant retroviruses to express M33 in wild-type and Galpha(q/11)(-/-) mouse embryonic fibroblasts and show that M33 couples directly to the G(q/11) signaling pathway to induce high levels of total inositol phosphates in an agonist-independent manner. Our data also show that GRK2 is a potent regulator of M33-induced G(q/11) signaling through its ability to phosphorylate M33 and sequester Galpha(q/11) proteins. Taken together, the results from this study provide the first genetic evidence of a viral GPCR coupling to a specific G protein signaling pathway as well as identify the first viral GPCR to be regulated specifically by both the catalytic activity of the GRK2 kinase domain and the Galpha(q/11) binding activity of the GRK2 RH domain.

    Funded by: NIAID NIH HHS: R01 AI058159, R01 AI058159-01A2, R01 AI058159-02, R01 AI058159-03, R01 AI058159-04, R01 AI058159-05

    The Journal of biological chemistry 2006;281;52;39796-805

  • Protein kinase A-mediated phosphorylation contributes to enhanced contraction observed in mice that overexpress beta-adrenergic receptor kinase-1.

    Mueller EE, Grandy SA and Howlett SE

    Department of Pharmacology, Dalhousie University, Halifax, Nova Scotia, Canada.

    Transgenic mice with cardiac specific overexpression of beta-adrenergic receptor kinase-1 (betaARK-1) exhibit reduced contractility in the presence of adrenergic stimulation. However, whether contractility is altered in the absence of exogenous agonist is not clear. Effects of betaARK-1 overexpression on contraction were examined in mouse ventricular myocytes, studied at 37 degrees C, in the absence of adrenergic stimulation. In myocytes voltage-clamped with microelectrodes (18-26 MOmega; 2.7 M KCl) to minimize intracellular dialysis, contractions were significantly larger in betaARK-1 cells than in wild-type myocytes. In contrast, when cells were dialyzed with patch pipette solution (1-3 MOmega; 0 mM NaCl, 70 mM KCl, 70 mM potassium aspartate, 4 mM MgATP, 1 mM MgCl(2), 2.5 mM KH(2)PO(4), 0.12 mM CaCl(2), 0.5 mM EGTA, and 10 mM HEPES), the extent of cell shortening was similar in wild-type and betaARK-1 myocytes. Furthermore, when cells were dialyzed with solutions that contained phosphodiesterase-sensitive sodium-cAMP (50 microM), the extent of cell shortening was similar in wild-type and betaARK-1 myocytes. However, when patch solutions were supplemented with phosphodiesterase-resistant 8-bromo-cAMP (50 muM), contractions were larger in betaARK-1 than wild-type cells. This difference was eliminated by the protein kinase A inhibitor N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89). Interestingly, Ca(2+) current amplitudes and inactivation rates were similar in betaARK-1 and wild-type cells in all experiments. These results suggest components of the adenylyl cyclase-protein kinase A pathway are sensitized by chronically increased betaARK-1 activity, which may augment contractile function in the absence of exogenous agonist. Thus, changes in contractile function in myocytes from failing hearts may reflect, in part, effects of chronic up-regulation of betaARK-1 on the cAMP-protein kinase A pathway.

    The Journal of pharmacology and experimental therapeutics 2006;319;3;1307-16

  • Knock-out mice reveal the contributions of P2Y and P2X receptors to nucleotide-induced Ca2+ signaling in macrophages.

    del Rey A, Renigunta V, Dalpke AH, Leipziger J, Matos JE, Robaye B, Zuzarte M, Kavelaars A and Hanley PJ

    Institute of Physiology, Marburg University, Deutschhausstrasse 2, 35037 Marburg, Germany.

    Immune cell function is modulated by changes in extracellular nucleotide levels. Here we used reverse transcription-PCR analyses, single cell Ca2+ imaging, and knock-out mice to define the receptors mediating nucleotide-induced Ca2+ signaling in resident peritoneal macrophages. In Ca2+-free buffer, the potent (K0.5<1 microm) stimulatory effect of UTP (or ATP) on endoplasmic reticulum (ER) Ca2+ release was abolished in cells isolated from P2Y2/P2Y4 double knock-out mice. Moreover, P2Y4(0/-), but not P2Y2-/-, macrophages responded to UTP. In P2Y2-/- macrophages, we could elicit Ca2+ responses to "pure" P2X receptor activation by applying ATP in buffer containing Ca2+. Purified UDP and ADP were ineffective agonists, although modest UDP-induced Ca2+ responses could be elicited in macrophages after "activation" with lipopolysaccharide and interferon-gamma. Notably, in Ca2+-free buffer, UTP-induced Ca2+ transients decayed within 1 min, and there was no response to repeated agonist challenge. Measurements of ER [Ca2+] with mag-fluo-4 showed that ER Ca2+ stores were depleted under these conditions. When extracellular Ca2+ was available, ER Ca2+ stores refilled, but Ca2+ increased to only approximately 40% of the initial value upon repeated UTP challenge. This apparent receptor desensitization persisted in GRK2+/- and GRK6-/- macrophages and after inhibition of candidate kinases protein kinase C and calmodulin-dependent kinase II. Initial challenge with UTP also reduced Ca2+ mobilization by complement component C5a (and vice versa). In conclusion, homologous receptor desensitization is not the major mechanism that rapidly dampens Ca2+ signaling mediated by P2Y2, the sole Gq-coupled receptor for UTP or ATP in macrophages. UDP responsiveness (P2Y6 receptor expression) increases following macrophage activation.

    The Journal of biological chemistry 2006;281;46;35147-55

  • Beta-arrestin2-mediated inotropic effects of the angiotensin II type 1A receptor in isolated cardiac myocytes.

    Rajagopal K, Whalen EJ, Violin JD, Stiber JA, Rosenberg PB, Premont RT, Coffman TM, Rockman HA and Lefkowitz RJ

    Department of Surgery, Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA.

    The G protein-coupled receptor kinases (GRKs) and beta-arrestins, families of molecules essential to the desensitization of G protein-dependent signaling via seven-transmembrane receptors (7TMRs), have been recently shown to also transduce G protein-independent signals from receptors. However, the physiologic consequences of this G protein-independent, GRK/beta-arrestin-dependent signaling are largely unknown. Here, we establish that GRK/beta-arrestin-mediated signal transduction via the angiotensin II (ANG) type 1A receptor (AT(1A)R) results in positive inotropic and lusitropic effects in isolated adult mouse cardiomyocytes. We used the "biased" AT(1A)R agonist [Sar(1), Ile(4), Ile(8)]-angiotensin II (SII), which is unable to stimulate G(alpha)q-mediated signaling, but which has previously been shown to promote beta-arrestin interaction with the AT(1A)R. Cardiomyocytes from WT, but not AT(1A)R-deficient knockout (KO) mice, exhibited positive inotropic and lusitropic responses to both ANG and SII. Responses of WT cardiomyocytes to ANG were dramatically reduced by protein kinase C (PKC) inhibition, whereas those to SII were unaffected. In contrast, cardiomyocytes from beta-arrestin2 KO and GRK6 KO mice failed to respond to SII, but displayed preserved responses to ANG. Cardiomyocytes from GRK2 heterozygous knockout mice (GRK2(+/-)) exhibited augmented responses to SII in comparison to ANG, whereas those from GRK5 KO mice did not differ from those from WT mice. These findings indicate the existence of independent G(alpha)q/PKC- and GRK6/beta-arrestin2-dependent mechanisms by which stimulation of the AT(1A)R can modulate cardiomyocyte function, and which can be differentially activated by selective receptor ligands. Such ligands may have potential as a novel class of therapeutic agents.

    Funded by: NHLBI NIH HHS: HL 075443, HL 16037, HL 70631, P01 HL075443, R01 HL016037, R01 HL070631

    Proceedings of the National Academy of Sciences of the United States of America 2006;103;44;16284-9

  • Cardiac-specific ablation of G-protein receptor kinase 2 redefines its roles in heart development and beta-adrenergic signaling.

    Matkovich SJ, Diwan A, Klanke JL, Hammer DJ, Marreez Y, Odley AM, Brunskill EW, Koch WJ, Schwartz RJ and Dorn GW

    Center for Molecular Cardiovascular Research, University of Cincinnati, Ohio, USA.

    G-protein receptor kinase 2 (GRK2) is 1 of 7 mammalian GRKs that phosphorylate ligand-bound 7-transmembrane receptors, causing receptor uncoupling from G proteins and potentially activating non-G-protein signaling pathways. GRK2 is unique among members of the GRK family in that its genetic ablation causes embryonic lethality. Cardiac abnormalities in GRK2 null embryos implicated GRK2 in cardiac development but prevented studies of the knockout phenotype in adult hearts. Here, we created GRK2-loxP-targeted mice and used Cre recombination to generate germline and cardiac-specific GRK2 knockouts. GRK2 deletion in the preimplantation embryo with EIIa-Cre (germline null) resulted in developmental retardation and embryonic lethality between embryonic day 10.5 (E10.5) and E11.5. At E9.5, cardiac myocyte specification and cardiac looping were normal, but ventricular development was delayed. Cardiomyocyte-specific ablation of GRK2 in the embryo with Nkx2.5-driven Cre (cardiac-specific GRK2 knockout) produced viable mice with normal heart structure, function, and cardiac gene expression. Cardiac-specific GRK2 knockout mice exhibited enhanced inotropic sensitivity to the beta-adrenergic receptor agonist isoproterenol, with impairment of normal inotropic and lusitropic tachyphylaxis, and exhibited accelerated development of catecholamine toxicity with chronic isoproterenol treatment. These findings show that cardiomyocyte autonomous GRK2 is not essential for myocardial development after cardiac specification, suggesting that embryonic developmental abnormalities may be attributable to extracardiac effects of GRK2 ablation. In the adult heart, cardiac GRK2 is a major factor regulating inotropic and lusitropic tachyphylaxis to beta-adrenergic agonist, which likely contributes to its protective effects in catecholamine cardiomyopathy.

    Funded by: NHLBI NIH HHS: HL58010, HL59888, HL69779, HL77101, R01 HL087871

    Circulation research 2006;99;9;996-1003

  • Competitive displacement of phosphoinositide 3-kinase from beta-adrenergic receptor kinase-1 improves postinfarction adverse myocardial remodeling.

    Curcio A, Noma T, Naga Prasad SV, Wolf MJ, Lemaire A, Perrino C, Mao L and Rockman HA

    Dept. of Medicine, Cell Biology, and Molecular Genetics, Duke Univ. Medical Center, DUMC 3104, Durham, NC 27710, USA.

    Adverse remodeling after myocardial infarction (MI) determines the progression of heart failure. Failing hearts are characterized by downregulation of beta-adrenergic receptor (beta-AR) signaling in part because of increased beta-AR kinase 1 activity. Our previous studies have shown that overexpression of the phosphoinositide kinase (PIK) domain of phosphoinositide 3-kinase (PI3K), prevents beta-AR downregulation and enhances adrenergic agonist responsiveness by inhibiting the targeting of PI3K to the beta-AR complex. To investigate whether preventing beta-AR downregulation in the heart ameliorates cardiac function post-MI, transgenic mice with cardiac-specific overexpression of the PIK domain peptide (TgPIK) underwent left coronary artery ligation and were subsequently followed by serial echocardiography at 4, 8, 12, 16, and 20 wk. Despite having similar infarction sizes, TgPIK mice showed better systolic function, less cardiac dilatation, and improved hemodynamic response to dobutamine compared with littermate controls after MI. To test that displacement of PI3K from the beta-AR complex, but not the total loss of PI3K-gamma, is critical for amelioration of cardiac function, mice lacking the PI3K-gamma (PI3K-gamma-KO) underwent MI, and their cardiac function was assessed 20 wk post-MI. Serial echocardiographic measurements showed severe reduction in contractile performance in PI3K-gamma-KO compared with TgPIK mice. Furthermore, significant beta-AR downregulation and desensitization were only seen in infarcted wild-type and PI3K-gamma-KO mice and not in TgPIK mice. Together, these results demonstrate that adverse remodeling of the ventricle after MI can be attenuated by a strategy that prevents recruitment of PI3K to the plasma membrane and restores normal beta-AR function.

    Funded by: NHLBI NIH HHS: P01 HL-75443

    American journal of physiology. Heart and circulatory physiology 2006;291;4;H1754-60

  • Enhancement of the recycling and activation of beta-adrenergic receptor by Rab4 GTPase in cardiac myocytes.

    Filipeanu CM, Zhou F, Lam ML, Kerut KE, Claycomb WC and Wu G

    Department of Pharmacology and Experimental Therapeutics, Louisiana State University Health Sciences Center, New Orleans, Louisiana 70112, USA.

    We investigate the role of Rab4, a Ras-like small GTPase coordinating protein transport from the endosome to the plasma membrane, on the recycling and activation of endogenous beta-adrenergic receptor (beta-AR) in HL-1 cardiac myocytes in vitro and transgenic mouse hearts in vivo. Beta1-AR, the predominant subtype of beta-AR in HL-1 cardiac myocytes, was internalized after stimulation with isoproterenol (ISO) and fully recycled at 4 h upon ISO removal. Transient expression of Rab4 markedly facilitated recycling of internalized beta-AR to the cell surface and enhanced beta-AR signaling as measured by ISO-stimulated cAMP production. Transgenic overexpression of Rab4 in the mouse myocardium significantly increased the number of beta-AR in the plasma membrane and augmented cAMP production at the basal level and in response to ISO stimulation. Rab4 overexpression induced concentric cardiac hypertrophy with a moderate increase in ventricle/body weight ratio and posterior wall thickness and a selective up-regulation of the beta-myosin heavy chain gene. These data provide the first evidence indicating that Rab4 is a rate-limiting factor for the recycling of endogenous beta-AR and augmentation of Rab4-mediated traffic enhances beta-AR function in cardiac myocytes.

    Funded by: NCRR NIH HHS: 1P20RR018766, P20 RR018766; NIGMS NIH HHS: R01 GM076167, R01 GM076167-01

    The Journal of biological chemistry 2006;281;16;11097-103

  • BGEM: an in situ hybridization database of gene expression in the embryonic and adult mouse nervous system.

    Magdaleno S, Jensen P, Brumwell CL, Seal A, Lehman K, Asbury A, Cheung T, Cornelius T, Batten DM, Eden C, Norland SM, Rice DS, Dosooye N, Shakya S, Mehta P and Curran T

    Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee, United States.

    Funded by: NINDS NIH HHS: 5R37NS036558, N01-NS-0-2331, R37 NS036558

    PLoS biology 2006;4;4;e86

  • G protein-coupled receptor kinase 2 negatively regulates chemokine signaling at a level downstream from G protein subunits.

    Jiménez-Sainz MC, Murga C, Kavelaars A, Jurado-Pueyo M, Krakstad BF, Heijnen CJ, Mayor F and Aragay AM

    Departamento de Biología Molecular and Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, 28049 Madrid, Spain.

    The G protein-coupled receptor kinase 2 (GRK2) phosphorylates and desensitizes ligand-activated G protein-coupled-receptors. Here, evidence is shown for a novel role of GRK2 in regulating chemokine-mediated signals. The presence of increased levels of GRK2 in human embryonic kidney (HEK) 293 cells produced a significant reduction of the extracellular signal-regulated kinase (ERK) response to CCL2. This effect is independent of its role in receptor phosphorylation because the kinase-deficient mutant GRK2K220R was able to reduce this response, and ERK activation by CCR2BIX, a phosphorylation-defective receptor mutant, was also inhibited by GRK2. Constructs containing the Galpha(q)-binding RGS-like RH domain of GRK2 or its Gbetagamma-binding domain could not reproduce the inhibition, thus revealing that GRK2 acts downstream of G proteins. Interestingly, chemokine-driven mitogen-activated protein kinase kinase (MEK) stimulation is not affected in cells overexpressing GRK2 or GRK2K220R or in splenocytes from heterozygous GRK2 mice, where reduced kinase levels correlate with enhanced ERK activation by chemokines. We find GRK2 and MEK in the same multimolecular complex, thus suggesting a mechanism for GRK2 regulation of ERK activity that involves a direct or coordinate interaction with MEK. These results suggest an important role for GRK2 in the control of chemokine induction of ERK activation at the level of the MEK-ERK interface.

    Molecular biology of the cell 2006;17;1;25-31

  • Beta-arrestin mediates desensitization and internalization but does not affect dephosphorylation of the thyrotropin-releasing hormone receptor.

    Jones BW and Hinkle PM

    Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, New York 14642, USA.

    The G protein-coupled thyrotropin-releasing hormone (TRH) receptor is phosphorylated and binds to beta-arrestin after agonist exposure. To define the importance of receptor phosphorylation and beta-arrestin binding in desensitization, and to determine whether beta-arrestin binding and receptor endocytosis are required for receptor dephosphorylation, we expressed TRH receptors in fibroblasts from mice lacking beta-arrestin-1 and/or beta-arrestin-2. Apparent affinity for [(3)H]MeTRH was increased 8-fold in cells expressing beta-arrestins, including a beta-arrestin mutant that did not permit receptor internalization. TRH caused extensive receptor endocytosis in the presence of beta-arrestins, but receptors remained primarily on the plasma membrane without beta-arrestin. beta-Arrestins strongly inhibited inositol 1,4,5-trisphosphate production within 10 s. At 30 min, endogenous beta-arrestins reduced TRH-stimulated inositol phosphate production by 48% (beta-arrestin-1), 71% (beta-arrestin-2), and 84% (beta-arrestins-1 and -2). In contrast, receptor phosphorylation, detected by the mobility shift of deglycosylated receptor, was unaffected by beta-arrestins. Receptors were fully phosphorylated within 15 s of TRH addition. Receptor dephosphorylation was identical with or without beta-arrestins and almost complete 20 min after TRH withdrawal. Blocking endocytosis with hypertonic sucrose did not alter the rate of receptor phosphorylation or dephosphorylation. Expressing receptors in cells lacking Galpha(q) and Galpha(11) or inhibiting protein kinase C pharmacologically did not prevent receptor phosphorylation or dephosphorylation. Overexpression of dominant negative G protein-coupled receptor kinase-2 (GRK2), however, retarded receptor phosphorylation. Receptor activation caused translocation of endogenous GRK2 to the plasma membrane. The results show conclusively that receptor dephosphorylation can take place on the plasma membrane and that beta-arrestin binding is critical for desensitization and internalization.

    Funded by: NIDDK NIH HHS: DK19974

    The Journal of biological chemistry 2005;280;46;38346-54

  • Uncoupling and endocytosis of 5-hydroxytryptamine 4 receptors. Distinct molecular events with different GRK2 requirements.

    Barthet G, Gaven F, Framery B, Shinjo K, Nakamura T, Claeysen S, Bockaert J and Dumuis A

    CNRS UMR5203, Montpellier, F-34094, France.

    The 5-hydroxytryptamine type 4 receptors (5-HT4Rs) are involved in memory, cognition, feeding, respiratory control, and gastrointestinal motility through activation of a G(s)/cAMP pathway. We have shown that 5-HT4R undergoes rapid and profound homologous uncoupling in neurons. However, no significant uncoupling was observed in COS-7 or HEK293 cells, which expressed either no or a weak concentration of GRK2, respectively. High expression of GRK2 in neurons is likely to be the reason for this difference because overexpression of GRK2 in COS-7 and HEK293 cells reproduced rapid and profound uncoupling of 5-HT4R. We have also shown, for the first time, that GRK2 requirements for uncoupling and endocytosis were very different. Indeed, beta-arrestin/dynamin-dependent endocytosis was observed in HEK293 cells without any need of GRK2 overexpression. In addition to this difference, uncoupling and beta-arrestin/dynamin-dependent endocytosis were mediated through distinct mechanisms. Neither uncoupling nor beta-arrestin/dynamin-dependent endocytosis required the serine and threonine residues localized within the specific C-terminal domains of the 5-HT4R splice variants. In contrast, a cluster of serines and threonines, common to all variants, was an absolute requirement for beta-arrestin/dynamin-dependent receptor endocytosis, but not for receptor uncoupling. Furthermore, beta-arrestin/dynamin-dependent endocytosis and uncoupling were dependent on and independent of GRK2 kinase activity, respectively. These results clearly demonstrate that the uncoupling and endocytosis of 5-HT4R require different GRK2 concentrations and involve distinct molecular events.

    The Journal of biological chemistry 2005;280;30;27924-34

  • G protein-coupled receptor kinase 2 in multiple sclerosis and experimental autoimmune encephalomyelitis.

    Vroon A, Kavelaars A, Limmroth V, Lombardi MS, Goebel MU, Van Dam AM, Caron MG, Schedlowski M and Heijnen CJ

    Laboratory for Psychoneuroimmunology, University Medical Center Utrecht, Utrecht, The Netherlands.

    Many modulators of inflammation, including chemokines, neuropeptides, and neurotransmitters signal via G protein-coupled receptors (GPCR). GPCR kinases (GRK) can phosphorylate agonist-activated GPCR thereby promoting receptor desensitization. Here we describe that in leukocytes from patients with active relapsing-remitting multiple sclerosis (MS) or with secondary progressive MS, GRK2 levels are significantly reduced. Unexpectedly, cells from patients during remission express even lower levels of GRK2. The level of GRK2 in leukocytes of patients after stroke, a neurological disorder with paralysis but without an autoimmune component, was similar to GRK2 levels in cells from healthy individuals. In addition, we demonstrate that the course of recombinant myelin oligodendrocyte glycoprotein (1-125)-induced experimental autoimmune encephalomyelitis (EAE), an animal model for MS, is markedly different in GRK2(+/-) mice that express 50% of the GRK2 protein in comparison with wild-type mice. Onset of EAE was significantly advanced by 5 days in GRK2(+/-) mice. The earlier onset of EAE was associated with increased early infiltration of the CNS by T cells and macrophages. Although disease scores in the first phase of EAE were similar in both groups, GRK2(+/-) animals did not develop relapses, whereas wild-type animals did. The absence of relapses in GRK2(+/-) mice was associated with a marked reduction in inflammatory infiltrates in the CNS. Recombinant myelin oligodendrocyte glycoprotein-induced T cell proliferation and cytokine production were normal in GRK2(+/-) animals. We conclude that down-regulation of GRK2 expression may have important consequences for the onset and progression of MS.

    Journal of immunology (Baltimore, Md. : 1950) 2005;174;7;4400-6

  • Targeted overexpression of G protein-coupled receptor kinase-2 in osteoblasts promotes bone loss.

    Wang L, Liu S, Quarles LD and Spurney RF

    Division of Nephrology, Department of Medicine, Duke University, Durham, North Carolina, USA.

    To investigate the role of G protein-coupled receptor kinases (GRKs) in regulating bone formation in vivo, we overexpressed the potent G protein-coupled receptor (GPCR) regulator GRK2 in osteoblasts, using the osteocalcin gene-2 promoter to target expression to osteoblastic cells. Using the parathyroid hormone (PTH) receptor as a model system, we found that overexpression of GRK2 in osteoblasts attenuated PTH-induced cAMP generation by mouse calvaria ex vivo. This decrease in GPCR responsiveness was associated with a reduction in bone mineral density (BMD) in transgenic (TG) mice compared with non-TG littermate controls. The decrease in BMD was most prominent in trabecular-rich lumbar spine and was not observed in cortical bone of the femoral shaft. Quantitative computed tomography indicated that the loss of trabecular bone was due to a decrease in trabecular thickness, with little change in trabecular number. Histomorphometric analyses confirmed the decrease in trabecular bone volume and demonstrated reduced bone remodeling, as evidenced by a decrease in osteoblast numbers and osteoblast-mediated bone formation. Osteoclastic activity also appeared to be reduced because urinary excretion of the osteoclastic activity marker deoxypyridinoline was decreased in TG mice compared with control animals. Consistent with reduced coupling of osteoblast-mediated bone formation to osteoclastic bone resorption, mRNA levels of both osteoprotegrin and receptor activator of NF-kappaB ligand were altered in calvaria of TG mice in a pattern that would promote a low rate of bone remodeling. Taken together, these data suggest that enhancing GRK2 activity and consequently reducing GPCR activity in osteoblasts produces a low bone-turnover state that reduces bone mass.

    Funded by: NIAMS NIH HHS: R01-AR-37308, R01-AR-4672

    American journal of physiology. Endocrinology and metabolism 2005;288;4;E826-34

  • Libraries enriched for alternatively spliced exons reveal splicing patterns in melanocytes and melanomas.

    Watahiki A, Waki K, Hayatsu N, Shiraki T, Kondo S, Nakamura M, Sasaki D, Arakawa T, Kawai J, Harbers M, Hayashizaki Y and Carninci P

    Genome Science Laboratory, RIKEN, Wako main campus, 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan.

    It is becoming increasingly clear that alternative splicing enables the complex development and homeostasis of higher organisms. To gain a better understanding of how splicing contributes to regulatory pathways, we have developed an alternative splicing library approach for the identification of alternatively spliced exons and their flanking regions by alternative splicing sequence enriched tags sequencing. Here, we have applied our approach to mouse melan-c melanocyte and B16-F10Y melanoma cell lines, in which 5,401 genes were found to be alternatively spliced. These genes include those encoding important regulatory factors such as cyclin D2, Ilk, MAPK12, MAPK14, RAB4, melastatin 1 and previously unidentified splicing events for 436 genes. Real-time PCR further identified cell line-specific exons for Tmc6, Abi1, Sorbs1, Ndel1 and Snx16. Thus, the ASL approach proved effective in identifying splicing events, which suggest that alternative splicing is important in melanoma development.

    Nature methods 2004;1;3;233-9

  • 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

  • GRK2 is an endogenous protein inhibitor of the insulin signaling pathway for glucose transport stimulation.

    Usui I, Imamura T, Satoh H, Huang J, Babendure JL, Hupfeld CJ and Olefsky JM

    Department of Medicine, Division of Endocrinology and Metabolism, University of California, San Diego, La Jolla, CA 92093-0673, USA.

    G protein-coupled receptor kinases (GRKs) represent a class of proteins that classically phosphorylate agonist-activated G protein-coupled receptors, leading to uncoupling of the receptor from further G protein activation. Recently, we have reported that the heterotrimeric G protein alpha-subunit, Galphaq/11, can mediate insulin-stimulated glucose transport. GRK2 contains a regulator of G protein signaling (RGS) domain with specificity for Galphaq/11. Therefore, we postulated that GRK2 could be an inhibitor of the insulin signaling cascade leading to glucose transport in 3T3-L1 adipocytes. In this study, we demonstrate that microinjection of anti-GRK2 antibody or siRNA against GRK2 increased insulin-stimulated insulin-responsive glucose transporter 4 (GLUT4) translocation, while adenovirus-mediated overexpression of wild-type or kinase-deficient GRK2 inhibited insulin-stimulated GLUT4 translocation as well as 2-deoxyglucose uptake. Importantly, a mutant GRK2 lacking the RGS domain was without effect. Taken together, these results indicate that through its RGS domain endogenous GRK2 functions as a negative regulator of insulin-stimulated glucose transport by interfering with Galphaq/11 signaling to GLUT4 translocation. Furthermore, inhibitors of GRK2 can lead to enhanced insulin sensitivity.

    Funded by: NIDDK NIH HHS: DK 33651, R01 DK033651, R37 DK033651

    The EMBO journal 2004;23;14;2821-9

  • Antidiabetic effect of novel modulating peptides of G-protein-coupled kinase in experimental models of diabetes.

    Anis Y, Leshem O, Reuveni H, Wexler I, Ben Sasson R, Yahalom B, Laster M, Raz I, Ben Sasson S, Shafrir E and Ziv E

    Keryx Biopharmaceuticals, Jerusalem, Israel.

    G-protein-coupled receptor kinases (GRKs) play a key role in agonist-induced desensitisation of G-protein-coupled receptors (GPCRs) that are involved in metabolic regulation and glucose homeostasis. Our aim was to examine whether small peptides derived from the catalytic domain of GRK2 and -3 would ameliorate Type 2 diabetes in three separate animal models of diabetes.

    Methods: Synthetic peptides derived from a kinase-substrate interaction site in GRK2/3 were initially screened for their effect on in vitro melanogenesis, a GRK-mediated process. The most effective peptides were administered intraperitoneally, utilising a variety of dosing regimens, to Psammomys obesus gerbils, Zucker diabetic fatty (ZDF) rats, or db/db mice. The metabolic effects of these peptides were assessed by measuring fasting and fed blood glucose levels and glucose tolerance.

    Results: Two peptides, KRX-683(107) and KRX-683(124), significantly reduced fed-state blood glucose levels in the diabetic Psammomys obesus. In animals treated with KRX-683(124) at a dose of 12.5 mg/kg weekly for 7 weeks, ten of eleven treated animals responded with mean blood glucose significantly lower than controls (4.7+/-0.4 vs 16.8+/-0.8 mmol/l, p</=0.0001). Significant reductions in blood glucose compared with controls were also seen in ZDF rats administered KRX-683(124) and in db/db mice, which had significantly reduced fasting and 2-hour postprandial glucose levels after the treatment.

    Sequence-based peptides derived from GRK2/3 have an antidiabetic effect demonstrated in three different animal models of Type 2 diabetes. By modulating GRK2/3 activity, these peptides enhance GPCR-initiated signal transduction, resulting in improved glucose homeostasis. Sequence-based peptide modulation of GRK could prove useful in the treatment of Type 2 diabetes.

    Diabetologia 2004;47;7;1232-1244

  • Spinophilin blocks arrestin actions in vitro and in vivo at G protein-coupled receptors.

    Wang Q, Zhao J, Brady AE, Feng J, Allen PB, Lefkowitz RJ, Greengard P and Limbird LE

    Department of Pharmacology and Center of Molecular Neuroscience, Vanderbilt University Medical Center, Nashville, TN 37232, USA.

    Arrestin regulates almost all G protein-coupled receptor (GPCR)-mediated signaling and trafficking. We report that the multidomain protein, spinophilin, antagonizes these multiple arrestin functions. Through blocking G protein receptor kinase 2 (GRK2) association with receptor-Gbetagamma complexes, spinophilin reduces arrestin-stabilized receptor phosphorylation, receptor endocytosis, and the acceleration of mitogen-activated protein kinase (MAPK) activity following endocytosis. Spinophilin knockout mice were more sensitive than wild-type mice to sedation elicited by stimulation of alpha2 adrenergic receptors, whereas arrestin 3 knockout mice were more resistant, indicating that the signal-promoting, rather than the signal-terminating, roles of arrestin are more important for certain response pathways. The reciprocal interactions of GPCRs with spinophilin and arrestin represent a regulatory mechanism for fine-tuning complex receptor-orchestrated cell signaling and responses.

    Funded by: NHLBI NIH HHS: HL16037, HL42671; NIDA NIH HHS: DA10044; NIDDK NIH HHS: DK43879; NIMH NIH HHS: MH40899

    Science (New York, N.Y.) 2004;304;5679;1940-4

  • Reduced GRK2 level in T cells potentiates chemotaxis and signaling in response to CCL4.

    Vroon A, Heijnen CJ, Lombardi MS, Cobelens PM, Mayor F, Caron MG and Kavelaars A

    Laboratory for Psychoneuroimmunology, University Medical Center Utrecht, The Netherlands.

    Chemokine receptors belong to the family of G-protein-coupled receptors (GPCR). Phosphorylation of GPCR by GPCR kinases (GRKs) is considered to play an important role in desensitization of these receptors. We have recently shown in patients with rheumatoid arthritis that the level of GRK2 in lymphocytes is reduced by approximately 50%. However, the physiological relevance of reduced GRK2 levels in lymphocytes is not known. Here, we investigated whether reduced GRK2 expression changes the chemotactic response of T cells to the chemokines CCL3, CCL4, and CCL5. Activated T cells from GRK2+/- mice, which have a 50% reduction in GRK2 protein levels, showed a significant 40% increase in chemotaxis toward the CCR5 ligand CCL4. In addition, chemotaxis toward the CCR1 and CCR5 ligands CCL3 and CCL5 was also increased. Binding of CCL4 to activated T cells from GRK2+/- and wild-type (WT) mice was similar, but agonist-induced CCR5 phosphorylation was attenuated in GRK2+/- cells. Moreover, the calcium response and phosphorylation of protein kinase B and extracellular-regulated kinase in response to CCL4 were significantly increased in GRK2+/- T cells, showing that signaling is increased when the level of GRK2 is reduced. GRK2+/- and WT cells do become refractory to restimulation with CCL4. In conclusion, a 50% decrease in T cell GRK2 expression results in increased responsiveness to CCL3, CCL4, and CCL5, suggesting that the 50% reduction in lymphocyte GRK2 level as observed during inflammation can have functional consequences for the response of these cells to chemokines.

    Journal of leukocyte biology 2004;75;5;901-9

  • G-protein-coupled receptor-mediated activation of rap GTPases: characterization of a novel Galphai regulated pathway.

    Weissman JT, Ma JN, Essex A, Gao Y and Burstein ES

    ACADIA Pharmaceuticals Inc., 3911 Sorrento Valley Blvd, San Diego, CA 92121, USA.

    Ras proteins mediate the proliferative effects of G-protein-coupled receptors (GPCRs), but the role of Rap proteins in GPCR signaling is unclear. We have developed a novel cellular proliferation assay for examining signal transduction to Rap utilizing Ras-rap chimeras that respond selectively to Rap-specific exchange factors, but which stimulate cellular proliferation through Ras effectors. Both the D1 dopamine receptor (Gs-coupled) and the 5HT1E serotonin receptor (Gi-coupled) mediated cellular proliferation in a Ras/rap chimera-dependent manner. Responses to both receptors were PKA-independent. Both receptors activated Ras/rap and full-length Rap as measured by activation-specific probes. Pertussis toxin blocked Ras/rap-dependent responses to 5HT1E but not D1. Ras/rap-dependent responses to both receptors were insensitive to beta-gamma scavengers. Responses to 5HT1E, but not D1, were sensitive to inhibition by a dominant-negative C3G fragment, by the Src-like kinase inhibitors PP1 and PP2, and by a dominant-negative mutant of Src. Very similar data were obtained for two other Gi-coupled receptors, the D2 dopamine receptor and the alpha2C adrenergic receptor. A constitutively active mutant of Galphai2 also mediated Ras/rap-dependent responses. These data indicate that GPCRs coupled to pertussis-toxin-sensitive G-proteins activate Rap through a Galpha subunit, C3G, and Src-dependent pathway.

    Oncogene 2004;23;1;241-9

  • Protein kinase C switches the Raf kinase inhibitor from Raf-1 to GRK-2.

    Lorenz K, Lohse MJ and Quitterer U

    Institut für Pharmakologie und Toxikologie, Versbacher Strasse 9, D-97078 Würzburg, Germany.

    Feedback inhibition is a fundamental principle in signal transduction allowing rapid adaptation to different stimuli. In mammalian cells, the major feedback inhibitor for G-protein-coupled receptors (GPCR) is G-protein-coupled receptor kinase 2 (GRK-2), which phosphorylates activated receptors, uncouples them from G proteins and initiates their internalization. The functions of GRK-2 are indispensable and need to be tightly controlled. Dysregulation promotes disorders such as hypertension or heart failure. In our search for a control mechanism for this vital kinase, here we show that the Raf kinase inhibitor protein (RKIP) is a physiological inhibitor of GRK-2. After stimulation of GPCR, RKIP dissociates from its known target, Raf-1 (refs 6-8), to associate with GRK-2 and block its activity. This switch is triggered by protein kinase C (PKC)-dependent phosphorylation of the RKIP on serine 153. The data delineate a new principle in signal transduction: by activating PKC, the incoming receptor signal is enhanced both by removing an inhibitor from Raf-1 and by blocking receptor internalization. A physiological role for this mechanism is shown in cardiomyocytes in which the downregulation of RKIP restrains beta-adrenergic signalling and contractile activity.

    Nature 2003;426;6966;574-9

  • Wnk1 kinase deficiency lowers blood pressure in mice: a gene-trap screen to identify potential targets for therapeutic intervention.

    Zambrowicz BP, Abuin A, Ramirez-Solis R, Richter LJ, Piggott J, BeltrandelRio H, Buxton EC, Edwards J, Finch RA, Friddle CJ, Gupta A, Hansen G, Hu Y, Huang W, Jaing C, Key BW, Kipp P, Kohlhauff B, Ma ZQ, Markesich D, Payne R, Potter DG, Qian N, Shaw J, Schrick J, Shi ZZ, Sparks MJ, Van Sligtenhorst I, Vogel P, Walke W, Xu N, Zhu Q, Person C and Sands AT

    Lexicon Genetics, 8800 Technology Forest Place, The Woodlands, TX 77381, USA. brian@lexgen.com

    The availability of both the mouse and human genome sequences allows for the systematic discovery of human gene function through the use of the mouse as a model system. To accelerate the genetic determination of gene function, we have developed a sequence-tagged gene-trap library of >270,000 mouse embryonic stem cell clones representing mutations in approximately 60% of mammalian genes. Through the generation and phenotypic analysis of knockout mice from this resource, we are undertaking a functional screen to identify genes regulating physiological parameters such as blood pressure. As part of this screen, mice deficient for the Wnk1 kinase gene were generated and analyzed. Genetic studies in humans have shown that large intronic deletions in WNK1 lead to its overexpression and are responsible for pseudohypoaldosteronism type II, an autosomal dominant disorder characterized by hypertension, increased renal salt reabsorption, and impaired K+ and H+ excretion. Consistent with the human genetic studies, Wnk1 heterozygous mice displayed a significant decrease in blood pressure. Mice homozygous for the Wnk1 mutation died during embryonic development before day 13 of gestation. These results demonstrate that Wnk1 is a regulator of blood pressure critical for development and illustrate the utility of a functional screen driven by a sequence-based mutagenesis approach.

    Proceedings of the National Academy of Sciences of the United States of America 2003;100;24;14109-14

  • Cardiac hypertrophy and altered beta-adrenergic signaling in transgenic mice that express the amino terminus of beta-ARK1.

    Keys JR, Greene EA, Cooper CJ, Naga Prasad SV, Rockman HA and Koch WJ

    Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA.

    The G protein-coupled receptor (GPCR) kinase beta-adrenergic receptor (beta-AR) kinase-1 (beta-ARK1) is elevated during heart failure; however, its role is not fully understood. Beta-ARK1 contains several domains that are capable of protein-protein interactions that may play critical roles in the regulation of GPCR signaling. In this study, we developed a novel line of transgenic mice that express an amino-terminal peptide of beta-ARK1 that is comprised of amino acid residues 50-145 (beta-ARKnt) in the heart to determine whether this domain has any functional significance in vivo. Surprisingly, the beta-ARKnt transgenic mice presented with cardiac hypertrophy. Our data suggest that the phenotype was driven via an enhanced beta-AR system, as beta-ARKnt mice had elevated cardiac beta-AR density. Moreover, administration of a beta-AR antagonist reversed hypertrophy in these mice. Interestingly, signaling through the beta-AR in response to agonist stimulation was not enhanced in these mice. Thus the amino terminus of beta-ARK1 appears to be critical for normal beta-AR regulation in vivo, which further supports the hypothesis that beta-ARK1 plays a key role in normal and compromised cardiac GPCR signaling.

    American journal of physiology. Heart and circulatory physiology 2003;285;5;H2201-11

  • Suppression of the morphine-induced rewarding effect and G-protein activation in the lower midbrain following nerve injury in the mouse: involvement of G-protein-coupled receptor kinase 2.

    Ozaki S, Narita M, Narita M, Iino M, Miyoshi K and Suzuki T

    Department of Toxicology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Tokyo 142-8501, Japan.

    The present study was designed to investigate whether a state of neuropathic pain induced by sciatic nerve ligation could alter the rewarding effect, antinociception, and G-protein activation induced by a prototype of mu-opioid receptor agonist morphine in the mouse. The sciatic nerve ligation caused a long-lasting and profound thermal hyperalgesia. Under this neuropathic pain-like state, an i.c.v. morphine-induced place preference was observed in sham-operated mice but not in sciatic nerve-ligated mice. However, no differences in the antinociceptive effect of i.c.v.-administered morphine were noted between the groups. The increases in the binding of guanosine-5'-o-(3-[(35)S]thio)triphosphate induced by morphine in lower midbrain membranes including the ventral tegmental area, which contributes to the expression of the rewarding effect of opioid, were significantly attenuated in sciatic nerve-ligated mice. On the other hand, there were no differences in the stimulation of guanosine-5'-o-(3-[(35)S]thio)triphosphate binding to pons/medulla membranes, which plays an important role in the antinociception of mu-opioid receptor agonists, between the groups. In addition, no changes in levels of guanosine-5'-o-(3-[(35)S]thio)triphosphate binding by either the selective delta- or kappa-opioid receptor agonists were noted in membrane of the lower midbrain and limbic forebrain membranes obtained from sciatic nerve-ligated mice. Reverse transcription-polymerase chain reaction analysis showed that sciatic nerve ligation did not alter the mRNA product of mu-opioid receptors in the lower midbrain, indicating that a decrease in some mu-opioid receptor functions may result from the uncoupling of mu-opioid receptors from G-proteins. We found a significant increase in protein levels of G-protein-coupled receptor kinase 2, which causes receptor phosphorylation in membranes of the lower midbrain but not in the pons/medulla, obtained from mice with nerve injury, whereas there were no changes in the protein level of phosphorylated-protein kinase C in the lower midbrain. These results suggest that the uncoupling of mu-opioid receptors from G-proteins by G-protein-coupled receptor kinase 2 in the lower midbrain may, at least in part, contribute to the suppression of the rewarding effect of morphine under neuropathic pain.

    Neuroscience 2003;116;1;89-97

  • Acute and chronic morphine treatments and morphine withdrawal differentially regulate GRK2 and GRK5 gene expression in rat brain.

    Fan X, Zhang J, Zhang X, Yue W and Ma L

    National Laboratory of Medical Neurobiology, Fudan University Medical Center, 138 Yi Xue Yuan Road, Shanghai 200032, People's Republic of China.

    Opioid agonist stimulates activation of G protein-coupled receptor kinase (GRK) and causes desensitization of opioid signaling, which plays an important role in opioid tolerance. The current study investigated the potential regulatory effects of acute and chronic morphine administration and withdrawal on GRK2 and GRK5 gene expression in rat brain. Our results showed that the initial morphine treatment (10 mg/kg) significantly increased GRK mRNA levels in cerebral cortex, hippocampus, and lateral thalamic nuclei. A significant decrease in GRK5 mRNA levels was observed in periaqueductal gray. In strong contrast, repeated administration of morphine for 9 days failed to cause any significant increase in GRK5 mRNA in any of these brain regions. Chronic morphine treatment resulted in 30-70% down-regulation of GRK2 expression in cerebral cortex, hippocampus, thalamus, and locus coeruleus, opposite to what observed with the single morphine administration. Moreover, spontaneous and naloxone-precipitated morphine withdrawal resulted in aberrant increases in GRK2 and GRK5 mRNA levels in these brain regions. Taken together, our study suggests that opioid not only induces rapid negative feedback regulation on opioid signals through activation of GRK but also exerts its impact, via controlling levels of GRK gene expression, on the regulatory machinery itself over a longer period of time in brain.

    Neuropharmacology 2002;43;5;809-16

  • Molecular characterization of the mouse Tem1/endosialin gene regulated by cell density in vitro and expressed in normal tissues in vivo.

    Opavsky R, Haviernik P, Jurkovicova D, Garin MT, Copeland NG, Gilbert DJ, Jenkins NA, Bies J, Garfield S, Pastorekova S, Oue A and Wolff L

    Laboratory of Cellular Oncology, NCI, National Institutes of Health, Bethesda, Maryland 20892-4255, USA.

    Human tumor endothelial marker 1/endosialin (TEM1/endosialin) was recently identified as a novel tumor endothelial cell surface marker potentially involved in angiogenesis, although no specific function for this novel gene has been assigned so far. It was reported to be expressed in tumor endothelium but not in normal endothelium with the exception of perhaps the corpus luteum. Here we describe the cDNA and genomic sequences for the mouse Tem1/endosialin homolog, the identification and characterization of its promoter region, and an extensive characterization of its expression pattern in murine and human tissues and murine cell lines in vitro. The single copy gene that was mapped to chromosome 19 is intronless and encodes a 92-kDa protein that has 77.5% overall homology to the human protein. The remarkable findings are 1) this gene is ubiquitously expressed in normal human and mouse somatic tissues and during development, and 2) its expression at the mRNA level is density-dependent and up-regulated in serum-starved cells. In vitro, its expression is limited to cells of embryonic, endothelial, and preadipocyte origin, suggesting that the wide distribution of its expression in vivo is due to the presence of vascular endothelial cells in all the tissues. The ubiquitous expression in vivo is in contrast to previously reported expression limited to corpus luteum and highly angiogenic tissues such as tumors and wound tissue.

    The Journal of biological chemistry 2001;276;42;38795-807

  • Cardiac beta ARK1 inhibition prolongs survival and augments beta blocker therapy in a mouse model of severe heart failure.

    Harding VB, Jones LR, Lefkowitz RJ, Koch WJ and Rockman HA

    Department of Medicine, and Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA.

    Chronic human heart failure is characterized by abnormalities in beta-adrenergic receptor (betaAR) signaling, including increased levels of betaAR kinase 1 (betaARK1), which seems critical to the pathogenesis of the disease. To determine whether inhibition of betaARK1 is sufficient to rescue a model of severe heart failure, we mated transgenic mice overexpressing a peptide inhibitor of betaARK1 (betaARKct) with transgenic mice overexpressing the sarcoplasmic reticulum Ca(2+)-binding protein, calsequestrin (CSQ). CSQ mice have a severe cardiomyopathy and markedly shortened survival (9 +/- 1 weeks). In contrast, CSQ/betaARKct mice exhibited a significant increase in mean survival age (15 +/- 1 weeks; P < 0.0001) and showed less cardiac dilation, and cardiac function was significantly improved (CSQ vs. CSQ/betaARKct, left ventricular end diastolic dimension 5.60 +/- 0.17 mm vs. 4.19 +/- 0.09 mm, P < 0.005; % fractional shortening, 15 +/- 2 vs. 36 +/- 2, P < 0.005). The enhancement of the survival rate in CSQ/betaARKct mice was substantially potentiated by chronic treatment with the betaAR antagonist metoprolol (CSQ/betaARKct nontreated vs. CSQ/betaARKct metoprolol treated, 15 +/- 1 weeks vs. 25 +/- 2 weeks, P < 0.0001). Thus, overexpression of the betaARKct resulted in a marked prolongation in survival and improved cardiac function in a mouse model of severe cardiomyopathy that can be potentiated with beta-blocker therapy. These data demonstrate a significant synergy between an established heart-failure treatment and the strategy of betaARK1 inhibition.

    Funded by: NHLBI NIH HHS: HL16037, HL28556, HL61558, HL61690, R01 HL016037, R01 HL028556, R01 HL061690, R37 HL061690

    Proceedings of the National Academy of Sciences of the United States of America 2001;98;10;5809-14

  • Cardiac overexpression of a G(q) inhibitor blocks induction of extracellular signal-regulated kinase and c-Jun NH(2)-terminal kinase activity in in vivo pressure overload.

    Esposito G, Prasad SV, Rapacciuolo A, Mao L, Koch WJ and Rockman HA

    Department of Medicine and Cell Biology, Duke University Medical Center, Durham, NC 27710, USA.

    Background: Understanding the cellular signals that initiate cardiac hypertrophy is of critical importance in identifying the pathways that mediate heart failure. The family of mitogen-activated protein kinases (MAPKs), including the extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminal kinase (JNK), and p38 MAPKs, may play specific roles in myocardial growth and function.

    To determine the mechanism of activation of MAPK pathways during the development of cardiac hypertrophy, we evaluated the induction of MAPK activity after aortic constriction in wild-type and in 2 types of cardiac gene-targeted mice: one overexpressing a carboxyl-terminal peptide of Galpha(q) that inhibits G(q)-mediated signaling (TG GqI mouse) and another overexpressing a carboxyl-terminal peptide of beta-adrenergic receptor kinase-1 that inhibits Gbetagamma signaling (TG betaARKct mouse). Wild-type mice with pressure overload showed an acute induction of JNK, followed by the induction of p38/p38beta at 3 days and ERK at 7 days. Both JNK and p38 activity remained elevated at 7 days after banding. In TG GqI mice, hypertrophy was significantly attenuated, and induction of ERK and JNK activity was abolished, whereas the induction of p38 and p38beta was robust, but delayed. By contrast, all 3 MAPK pathways were activated by aortic constriction in the TG betaARKct hearts, suggesting a role for Galpha(q), but not Gbetagamma.

    Conclusions: Taken together, these data show that the induction of ERK and JNK activity in in vivo pressure-overload hypertrophy is mediated through the stimulation of G(q)-coupled receptors and that non-G(q)-mediated pathways are recruited to activate p38 and p38beta.

    Funded by: NHLBI NIH HHS: HL-56687, HL-61690

    Circulation 2001;103;10;1453-8

  • Cellular and functional defects in a mouse model of heart failure.

    Esposito G, Santana LF, Dilly K, Cruz JD, Mao L, Lederer WJ and Rockman HA

    Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.

    Heart failure and dilated cardiomyopathy develop in mice that lack the muscle LIM protein (MLP) gene (MLP(-/-)). The character and extent of the heart failure that occurs in MLP(-/-) mice were investigated using echocardiography and in vivo pressure-volume (P-V) loop measurements. P-V loop data were obtained with a new method for mice (sonomicrometry) using two pairs of orthogonal piezoelectric crystals implanted in the endocardial wall. Sonomicrometry revealed right-shifted P-V loops in MLP(-/-) mice, depressed systolic contractility, and additional evidence of heart failure. Cellular changes in MLP(-/-) mice were examined in isolated single cells using patch-clamp and confocal Ca(2+) concentration ([Ca(2+)]) imaging techniques. This cellular investigation revealed unchanged Ca(2+) currents and Ca(2+) spark characteristics but decreased intracellular [Ca(2+)] transients and contractile responses and a defect in excitation-contraction coupling. Normal cellular and whole heart function was restored in MLP(-/-) mice that express a cardiac-targeted transgene, which blocks the function of beta-adrenergic receptor (beta-AR) kinase-1 (betaARK1). These data suggest that, despite the persistent stimulus to develop heart failure in MLP(-/-) mice (i.e., loss of the structural protein MLP), downregulation and desensitization of the beta-ARs may play a pivotal role in the pathogenesis. Furthermore, this work suggests that the inhibition of betaARK1 action may prove an effective therapy for heart failure.

    Funded by: NHLBI NIH HHS: HL-36974, HL-61558, HL-61602; ...

    American journal of physiology. Heart and circulatory physiology 2000;279;6;H3101-12

  • Expression of the G protein-coupled receptor kinase 2 during early mouse embryogenesis.

    Sefton M, Blanco MJ, Penela P, Mayor F and Nieto MA

    Instituto Cajal, CSIC., Av. Doctor Arce, 37, E-28002, Madrid, Spain.

    Whilst several G protein-coupled receptors (GPCRs) have been shown to play important roles during development, little study has been carried out on the G protein-coupled receptor kinases (GRKs) that modulate their activity in embryos. Here, we have analyzed the expression of GRK2, the predominant GRK expressed during embryogenesis. We show that at early stages, the expression of GRK2 is restricted to populations of cells that are undifferentiated, multipotent and in many cases, migratory. As such, GRK2 transcripts were found in the early mesoderm and neural crest as they migrate from the primitive streak and the neural tube, respectively. In the limb bud, GRK2 transcripts were observed in cells of the progress zone and in the interdigital areas. At later stages, the expression in the heart is compatible with the phenotype observed in the GRK2 deficient mice.

    Mechanisms of development 2000;98;1-2;127-31

  • Genome-wide expression profiling of mid-gestation placenta and embryo using a 15,000 mouse developmental cDNA microarray.

    Tanaka TS, Jaradat SA, Lim MK, Kargul GJ, Wang X, Grahovac MJ, Pantano S, Sano Y, Piao Y, Nagaraja R, Doi H, Wood WH, Becker KG and Ko MS

    Laboratory of Genetics and DNA Array Unit, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224-6820, USA.

    cDNA microarray technology has been increasingly used to monitor global gene expression patterns in various tissues and cell types. However, applications to mammalian development have been hampered by the lack of appropriate cDNA collections, particularly for early developmental stages. To overcome this problem, a PCR-based cDNA library construction method was used to derive 52,374 expressed sequence tags from pre- and peri-implantation embryos, embryonic day (E) 12.5 female gonad/mesonephros, and newborn ovary. From these cDNA collections, a microarray representing 15,264 unique genes (78% novel and 22% known) was assembled. In initial applications, the divergence of placental and embryonic gene expression profiles was assessed. At stage E12.5 of development, based on triplicate experiments, 720 genes (6.5%) displayed statistically significant differences in expression between placenta and embryo. Among 289 more highly expressed in placenta, 61 placenta-specific genes encoded, for example, a novel prolactin-like protein. The number of genes highly expressed (and frequently specific) for placenta has thereby been increased 5-fold over the total previously reported, illustrating the potential of the microarrays for tissue-specific gene discovery and analysis of mammalian developmental programs.

    Proceedings of the National Academy of Sciences of the United States of America 2000;97;16;9127-32

  • The GRK4 subfamily of G protein-coupled receptor kinases. Alternative splicing, gene organization, and sequence conservation.

    Premont RT, Macrae AD, Aparicio SA, Kendall HE, Welch JE and Lefkowitz RJ

    Department of Medicine, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA.

    G protein-coupled receptor kinases (GRKs) desensitize G protein-coupled receptors by phosphorylating activated receptors. The six known GRKs have been classified into three subfamilies based on sequence and functional similarities. Examination of the mouse GRK4 subfamily (GRKs 4, 5, and 6) suggests that mouse GRK4 is not alternatively spliced in a manner analogous to human or rat GRK4, whereas GRK6 undergoes extensive alternative splicing to generate three variants with distinct carboxyl termini. Characterization of the mouse GRK 5 and 6 genes reveals that all members of the GRK4 subfamily share an identical gene structure, in which 15 introns interrupt the coding sequence at equivalent positions in all three genes. Surprisingly, none of the three GRK subgroups (GRK1, GRK2/3, and GRK4/5/6) shares even a single intron in common, indicating that these three subfamilies are distinct gene lineages that have been maintained since their divergence over 1 billion years ago. Comparison of the amino acid sequences of GRKs from various mammalian species indicates that GRK2, GRK5, and GRK6 exhibit a remarkably high degree of sequence conservation, whereas GRK1 and particularly GRK4 have accumulated amino acid changes at extremely rapid rates over the past 100 million years. The divergence of individual GRKs at vastly different rates reveals that strikingly different evolutionary pressures apply to the function of the individual GRKs.

    Funded by: NHLBI NIH HHS: HL16037

    The Journal of biological chemistry 1999;274;41;29381-9

  • Enhanced contractility and decreased beta-adrenergic receptor kinase-1 in mice lacking endogenous norepinephrine and epinephrine.

    Cho MC, Rao M, Koch WJ, Thomas SA, Palmiter RD and Rockman HA

    Department of Medicine, University of North Carolina at Chapel Hill, 27599-7075, USA.

    Background: Elevated circulating norepinephrine (NE) has been implicated in causing the profound beta-adrenergic receptor (betaAR) downregulation and receptor uncoupling that are characteristic of end-stage human dilated cardiomyopathy, a process mediated in part by increased levels of beta-adrenergic receptor kinase (betaARK1). To explore whether chronic sustained NE stimulation is a primary stimulus that promotes deterioration in cardiac signaling, we characterized a gene-targeted mouse in which activation of the sympathetic nervous system cannot lead to an elevation in plasma NE and epinephrine.

    Gene-targeted mice that lack dopamine beta-hydroxylase (dbh-/-), the enzyme needed to convert dopamine to NE, were created by homologous recombination. In vivo contractile response to the beta1AR agonist dobutamine, measured by a high-fidelity left ventricular micromanometer, was enhanced in mice lacking the dbh gene. In unloaded adult myocytes isolated from dbh-/- mice, basal contractility was significantly increased compared with control cells. Furthermore, the increase in betaAR responsiveness and enhanced cellular contractility were associated with a significant reduction in activity and protein level of betaARK1 and increased high-affinity agonist binding without changes in betaAR density or G-protein levels.

    Conclusions: Mice that lack the ability to generate NE or epinephrine show increased contractility associated primarily with a decrease in the level of betaARK1 protein and kinase activity. This animal model will be valuable in testing whether NE is required for the pathogenesis of heart failure through mating strategies that cross the dbh-/- mouse into genetically engineered models of heart failure.

    Funded by: NHLBI NIH HHS: HL-56687; NICHD NIH HHS: HD-09172

    Circulation 1999;99;20;2702-7

  • Altered airway and cardiac responses in mice lacking G protein-coupled receptor kinase 3.

    Walker JK, Peppel K, Lefkowitz RJ, Caron MG and Fisher JT

    Howard Hughes Medical Institute, Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA.

    Contraction and relaxation of airway smooth muscles is mediated, in part, by G protein-coupled receptors (GPCRs) and dysfunction of these receptors has been implicated in asthma. Phosphorylation of GPCRs, by G protein-coupled receptor kinase (GRK), is an important mechanism involved in the dampening of GPCR signaling. To determine whether this mechanism might play a role in airway smooth muscle physiology, we examined the airway pressure time index and heart rate (HR) responses to intravenous administration of the cholinergic agonist methacholine (MCh) in genetically altered mice lacking one copy of GRK2 (GRK2 +/-), homozygous GRK3 knockout (GRK3 -/-), and wild-type littermates. (GRK2 -/- mice die in utero.) GRK3 -/- mice demonstrated a significant enhancement in the airway response to 100 and 250 microgram/kg doses of MCh compared with wild-type and GRK2 +/- mice. GRK3 -/- mice also displayed an enhanced sensitivity of the airway smooth muscle response to MCh. In addition, GRK3 -/- mice displayed an altered HR recovery from MCh-induced bradycardia. Although direct stimulation of cardiac muscarinic receptors measured as vagal stimulation-induced bradycardia was similar in GRK3 -/- and wild-type mice, the baroreflex increase in HR associated with sodium nitroprusside-induced hypotension was significantly greater in GRK3 -/- than wild-type mice. Therefore, these data demonstrate that in the mouse, GRK3 may be involved in modulating the cholinergic response of airway smooth muscle and in regulating the chronotropic component of the baroreceptor reflex.

    Funded by: NHLBI NIH HHS: HL-16037; NINDS NIH HHS: NS-19576

    The American journal of physiology 1999;276;4 Pt 2;R1214-21

  • Exploring the role of the beta-adrenergic receptor kinase in cardiac disease using gene-targeted mice.

    Koch WJ and Rockman HA

    Department of Surgery, Duke University Medical Center, Durham, North Carolina 27710, USA.

    The beta-adrenergic receptor signaling system plays a fundamental role in heart function. Signaling through beta ARs can be dampened by the actions of the beta AR kinase, a kinase whose expression and activity are elevated in chronic human heart failure. In this review we highlight studies that have used genetically engineered mice to understand how perturbations in myocardial beta AR signaling could adversely impact the pathogenesis of cardiac disease. Interrupting this process may provide novel therapeutic strategies in the treatment of human heart failure.

    Trends in cardiovascular medicine 1999;9;3-4;77-81

  • Structure and mapping of the G protein gamma3 subunit gene and a divergently transcribed novel gene, gng3lg.

    Downes GB, Copeland NG, Jenkins NA and Gautam N

    Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri, 63110, USA.

    The mammalian nervous system is rich in signaling mediated by heterotrimeric (alphabetagamma) G proteins. As an initial step to define the roles that particular gamma subunit types play in signaling, we have begun to clone and characterize those genes that encode gamma subunits enriched within neural tissue. In the present study, we have isolated and characterized the mouse gamma3 subunit gene (Gng3). The gamma3 subunit is expressed abundantly in the brain and at low levels in testes. Gng3 is composed of three exons spanning approximately 1.4 kb. A comparison of Gng3 with the gene structure for five other gamma subtypes indicates that although these proteins are diverse at the amino acid level, their exon-intron boundaries are conserved. Sequence analysis of the 5' flanking region of Gng3 revealed the presence of a novel gene, the gamma3 linked gene (Gng3lg). Gng3 and Gng3lg are organized in a head-to-head fashion with major transcription initiation sites separated by approximately 133 bp. Sequence analysis of a Gng3lg cDNA clone revealed an open reading frame encoding a 410-amino-acid protein of unknown function. Gng3lg transcripts are expressed in a variety of tissues including both brain and testes. Using an interspecific backcross panel, we localized both Gng3 and Gng3lg to the same locus on chromosome 19. The orientation, close proximity, and expression pattern of these two genes raise the distinct possibility that shared regulatory elements are used to control their expression.

    Funded by: NIGMS NIH HHS: GM 17289-04, GM 46963

    Genomics 1998;53;2;220-30

  • Physiological consequences of beta-adrenergic receptor disruption.

    Rohrer DK

    Department of Molecular Pharmacology, Roche Bioscience, Palo Alto, CA 94304, USA.

    Activation of beta-adrenergic receptors (beta-ARs) in vivo is an important means by which animals regulate cardiac performance, vascular tone, lipid and carbohydrate metabolism, and behavior. The advent of targeted gene disruption in mice has led to significant advances in our understanding of the role that beta-AR subtypes play in these processes, and this technique has become an important tool for the study of G protein coupled receptors in general. To date, targeted disruption of both beta1- and beta3-ARs in mice has been reported. Mice lacking beta1-ARs are unresponsive to cardiac beta-AR stimulation, suggesting that neither beta2- nor beta3-ARs couple to inotropic or chronotropic responses in the mouse. Conversely, mice lacking beta3-ARs retain at least some adipose beta-AR responsiveness through remaining beta1- and beta2-ARs, suggesting that all three beta-AR subtypes mediate similar functions in this tissue. While these knockout models have been extremely valuable tools for revealing the roles that individual beta-ARs play in whole animal physiology, it is also useful to integrate the results of experiments derived from either transgenic overexpression of beta-ARs or purely pharmacological approaches to the study of beta-AR function in order to create a comprehensive model of beta-AR function in vivo.

    Journal of molecular medicine (Berlin, Germany) 1998;76;11;764-72

  • Control of myocardial contractile function by the level of beta-adrenergic receptor kinase 1 in gene-targeted mice.

    Rockman HA, Choi DJ, Akhter SA, Jaber M, Giros B, Lefkowitz RJ, Caron MG and Koch WJ

    Department of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599, USA.

    We studied the effect of alterations in the level of myocardial beta-adrenergic receptor kinase betaARK1) in two types of genetically altered mice. The first group is heterozygous for betaARK1 gene ablation, betaARK1(+/-), and the second is not only heterozygous for betaARK1 gene ablation but is also transgenic for cardiac-specific overexpression of a betaARK1 COOH-terminal inhibitor peptide, betaARK1(+/-)betaARKct. In contrast to the embryonic lethal phenotype of the homozygous betaARK1 knockout (Jaber, M., Koch, W. J., Rockman, H. A., Smith, B., Bond, R. A., Sulik, K., Ross, J., Jr., Lefkowitz, R. J., Caron, M. G., and Giros, B. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 12974-12979), betaARK1(+/-) mice develop normally. Cardiac catheterization was performed in mice and showed a stepwise increase in contractile function in the betaARK1(+/-) and betaARK1(+/-)betaARKct mice with the greatest level observed in the betaARK1(+/-)betaARKct animals. Contractile parameters were measured in adult myocytes isolated from both groups of gene-targeted animals. A significantly greater increase in percent cell shortening and rate of cell shortening following isoproterenol stimulation was observed in the betaARK1(+/-) and betaARK1(+/-)betaARKct myocytes compared with wild-type cells, indicating a progressive increase in intrinsic contractility. These data demonstrate that contractile function can be modulated by the level of betaARK1 activity. This has important implications in disease states such as heart failure (in which betaARK1 activity is increased) and suggests that betaARK1 should be considered as a therapeutic target in this situation. Even partial inhibition of betaARK1 activity enhances beta-adrenergic receptor signaling leading to improved functional catecholamine responsiveness.

    Funded by: NHLBI NIH HHS: HL 16037, HL 56687; NINDS NIH HHS: NS 19576

    The Journal of biological chemistry 1998;273;29;18180-4

  • Expression of a beta-adrenergic receptor kinase 1 inhibitor prevents the development of myocardial failure in gene-targeted mice.

    Rockman HA, Chien KR, Choi DJ, Iaccarino G, Hunter JJ, Ross J, Lefkowitz RJ and Koch WJ

    Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. hrockman@med.unc.edu

    Heart failure is accompanied by severely impaired beta-adrenergic receptor (betaAR) function, which includes loss of betaAR density and functional uncoupling of remaining receptors. An important mechanism for the rapid desensitization of betaAR function is agonist-stimulated receptor phosphorylation by the betaAR kinase (betaARK1), an enzyme known to be elevated in failing human heart tissue. To investigate whether alterations in betaAR function contribute to the development of myocardial failure, transgenic mice with cardiac-restricted overexpression of either a peptide inhibitor of betaARK1 or the beta2AR were mated into a genetic model of murine heart failure (MLP-/-). In vivo cardiac function was assessed by echocardiography and cardiac catheterization. Both MLP-/- and MLP-/-/beta2AR mice had enlarged left ventricular (LV) chambers with significantly reduced fractional shortening and mean velocity of circumferential fiber shortening. In contrast, MLP-/-/betaARKct mice had normal LV chamber size and function. Basal LV contractility in the MLP-/-/betaARKct mice, as measured by LV dP/dtmax, was increased significantly compared with the MLP-/- mice but less than controls. Importantly, heightened betaAR desensitization in the MLP-/- mice, measured in vivo (responsiveness to isoproterenol) and in vitro (isoproterenol-stimulated membrane adenylyl cyclase activity), was completely reversed with overexpression of the betaARK1 inhibitor. We report here the striking finding that overexpression of this inhibitor prevents the development of cardiomyopathy in this murine model of heart failure. These findings implicate abnormal betaAR-G protein coupling in the pathogenesis of the failing heart and point the way toward development of agents to inhibit betaARK1 as a novel mode of therapy.

    Funded by: NHLBI NIH HHS: HL16037, HL46345, HL56687, P01 HL046345, P50 HL053773, R01 HL016037, R01 HL056687

    Proceedings of the National Academy of Sciences of the United States of America 1998;95;12;7000-5

  • Genetic mapping of the galanin-GMAP (Galn) gene to mouse chromosome 19.

    Guida LC, Charlton P, Gilbert DJ, Jenkins NA, Copeland NG and Nicholls RD

    Department of Genetics, Case Western Reserve University, Cleveland, Ohio 44106-4955, USA.

    Mammalian genome : official journal of the International Mammalian Genome Society 1998;9;3;240-2

  • Comparative mapping of two adjacent regions of MMU19 with their human counterpart on HSA11q13.

    Fernandes M, Lespinasse F, Rotomondo F, Poirier C, Guenet JL, Gaudray P and Carle GF

    CNRS/UNSA UMR 6549, Faculté de Médecine, Nice, France.

    High resolution physical maps of two adjacent regions of MMU19 were constructed in order to establish a comparative map between the pericentromeric region of MMU19 and its human counterpart on HSA11q13. These two physical maps span 2.5 and 0.5 megabases on MMU19. Long range restriction analysis and YAC contigs have been built, five genes were located on MMU19 and eight new STSs were generated. The 0.5-Mb map which has been positioned close to the centromere of MMU19, based on dual-color FISH experiments and genetic data, includes eight genes (Type I markers), three microsatellites (Type II markers) and five new STSs. The 2.5-Mb map is located more telomeric and contains seven genes, four microsatellites and four new STSs. Gene order and physical distances appear to be similar in human and in mouse in this 2.5-Mb region. Strikingly, the 0.5-Mb region has a similar size in human but gene order is shuffled. The overall comparative map shows that these two regions are inverted on MMU19 when compared with HSA11q13.

    Cytogenetics and cell genetics 1998;81;3-4;237-46

  • Chromosomal mapping of the human and murine orphan receptors ERRalpha (ESRRA) and ERRbeta (ESRRB) and identification of a novel human ERRalpha-related pseudogene.

    Sladek R, Beatty B, Squire J, Copeland NG, Gilbert DJ, Jenkins NA and Giguère V

    Royal Victoria Hospital, Department of Biochemistry, McGill University, 687 Pine Avenue West, Montr-eal, Quebec, H3A 1A1, Canada.

    The estrogen-related receptors ERRalpha and ERRbeta (formerly ERR1 and ERR2) form a subgroup of the steroid/thyroid/retinoid receptor family. ERRalpha and ERRbeta are homologous to the estrogen receptor and bind similar DNA targets; however, they are unable to activate gene transcription in response to estrogens. We have used interspecific backcross analysis to map the murine Estrra locus to chromosome 19 and Estrrb to mouse chromosome 12. Using fluorescence in situ hybridization, we have mapped the human ESRRA gene to chromosome 11q12-q13 and the human ESRRB gene to chromosome 14q24.3. In addition, we report the isolation of a processed human ERRalpha pseudogene mapping to chromosome 13q12.1. To our knowledge, this represents the first report of a pseudogene associated with a member of the nuclear receptor superfamily.

    Genomics 1997;45;2;320-6

  • Mammalian homolog of Drosophila retinal degeneration B rescues the mutant fly phenotype.

    Chang JT, Milligan S, Li Y, Chew CE, Wiggs J, Copeland NG, Jenkins NA, Campochiaro PA, Hyde DR and Zack DJ

    Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287-9289, USA.

    Mutations in the Drosophila rdgB gene, which encodes a transmembrane phosphatidylinositol transfer protein (PITP), cause a light-enhanced retinal degeneration. Cloning of mammalian rdgB orthologs (mrdgB) reveal predicted proteins that are 39% identical to rdgB, with highest homology in the N-terminal PITP domain (62%) and in a region near the C terminus (65%). The human mrdgB gene spans approximately 12 kb and maps to 11q13.1, a locus where several retinal diseases have also been mapped. Murine mrdgB maps to a syntenic region on the proximal region of chromosome 19. MrdgB is specifically expressed in the retina and brain. In the retina, MrdgB protein is localized to photoreceptor inner segments and the outer and inner plexiform layers. Expression of murine mrdgB in mutant flies fully rescues both the rdgB-dependent retinal degeneration and abnormal electroretinogram. These results suggest the existence of similarities between the invertebrate and mammalian retina that were not previously appreciated and also identify mrdgB as a candidate gene for retinal diseases that map to 11q13.1.

    Funded by: NEI NIH HHS: EY05951, EY08058, EY09679

    The Journal of neuroscience : the official journal of the Society for Neuroscience 1997;17;15;5881-90

  • A dominant negative mutant of the G protein-coupled receptor kinase 2 selectively attenuates adenosine A2 receptor desensitization.

    Mundell SJ, Benovic JL and Kelly E

    Department of Pharmacology, School of Medical Sciences, University of Bristol, UK.

    G protein-coupled receptor kinases (GRKs) are thought to be important in mediating the agonist-induced phosphorylation and consequent desensitization of G protein-coupled receptor responses. NG108-15 mouse neuroblastoma X rat glioma cells express a wide range of G protein-coupled receptors and significant levels of GRK2. Therefore, to determine the role of GRK2 in agonist-induced desensitization of various G(s)-coupled receptors in NG108-15 cells, we stably transfected cells with a dominant negative mutant GRK2 construct (Lys220Arg). In homogenates prepared from cells overexpressing the dominant negative mutant GRK2, the acute stimulation of adenylyl cyclase by various receptor and nonreceptor agonists was the same as in control cells stably transfected with plasmid only. NG108-15 cells express both A2a and A2b adenosine receptors, which mediate activation of adenylyl cyclase, with both of these responses being subject to agonist-induced desensitization with a t1/2 of 15-20 min. In dominant negative mutant GRK2 cells, the rates of desensitization of A2a and A2b receptor-stimulated adenylyl cyclase were markedly slower than in plasmid transfected controls, with the latter being similar to wild-type cells. After a 20-min treatment with an adenosine agonist, the desensitization of A2a and A2b receptor-stimulated adenylyl cyclase in dominant negative mutant GRK2 cells was less than half that seen in plasmid transfected control cells. On the other hand, the agonist-induced desensitization of secretin and IP-prostanoid receptor-stimulated adenylyl cyclase was the same in dominant negative mutant GRK2 cells as in plasmid transfected control cells. These results indicate that in intact cells, GRK2 may mediate the desensitization of adenosine A2 receptors. Furthermore, there seems to be selectivity of GRK2 action between G(s)-coupled receptors because the agonist-induced desensitization of secretin and IP-prostanoid receptor-stimulated adenylyl cyclase was not affected by dominant negative mutant GRK2 overexpression.

    Funded by: NIGMS NIH HHS: GM44944

    Molecular pharmacology 1997;51;6;991-8

  • Essential role of beta-adrenergic receptor kinase 1 in cardiac development and function.

    Jaber M, Koch WJ, Rockman H, Smith B, Bond RA, Sulik KK, Ross J, Lefkowitz RJ, Caron MG and Giros B

    Howard Hughes Medical Institute Laboratories, Duke University Medical Center, Durham, NC 27710, USA.

    The beta-adrenergic receptor kinase 1 (beta ARK1) is a member of the G protein-coupled receptor kinase (GRK) family that mediates the agonist-dependent phosphorylation and desensitization of G protein-coupled receptors. We have cloned and disrupted the beta ARK1 gene in mice by homologous recombination. No homozygote beta ARK1-/- embryos survive beyond gestational day 15.5. Prior to gestational day 15.5, beta ARK1-/- embryos display pronounced hypoplasia of the ventricular myocardium essentially identical to the "thin myocardium syndrome" observed upon gene inactivation of several transcription factors (RXR alpha, N-myc, TEF-1, WT-1). Lethality in beta ARK1-/- embryos is likely due to heart failure as they exhibit a > 70% decrease in cardiac ejection fraction determined by direct in utero intravital microscopy. These results along with the virtual absence of endogenous GRK activity in beta ARK1-/- embryos demonstrate that beta ARK1 appears to be the predominant GRK in early embryogenesis and that it plays a fundamental role in cardiac development.

    Funded by: NHLBI NIH HHS: HL 16037, R01 HL016037; NINDS NIH HHS: NS 19576, R01 NS019576

    Proceedings of the National Academy of Sciences of the United States of America 1996;93;23;12974-9

  • Identification by polymerase chain reaction of the G protein-coupled receptor kinases expressed in the mouse gonadotropic alpha T3-1 cell line.

    Neill JD, Musgrove LC, Sellers JC and Duck LW

    Department of Physiology and Biophysics, Schools of Medicine and Dentistry, University of Alabama at Birmingham 35294, USA. Neill@Phybio.bhs.uab.edu

    G protein-coupled receptor kinases (GRK 1-6) stimulate short-term desensitization (< 5 min) by phosphorylating G-protein coupled receptors, and also participate in receptor sequestration, which may relate to intermediate-term desensitization (30-60 min). The existence of such kinases and hence a potential role for them in gonadotrope/GnRH receptor desensitization was investigated using the PCR to identify GRKs in messenger RNA (mRNA) from the mouse alpha T3-1 gonadotrope cell line. The 150-bp complementary DNAs amplified by PCR from the kinase catalytic domain were cloned and sequenced. Seventeen of 42 clones were receptor kinases based on high nucleotide identities of 85-100% and amino acid identities of 97-100% with rat GRK2 and 3, and with human GRK6. Among the eight GRK3 clones was one differing from rat GRK3 by a single nucleotide and seven differing by six; no amino acid difference resulted from the nucleotide differences. Of the five GRK2 clones, one sequence was identical with rat GRK2, but four sequences differed by three nucleotides and one amino acid. Among four GRK6 sequences, one showed 15 nucleotide differences from human GRK6 (with no amino acid differences), and three had 16 nucleotide and one amino acid differences. For each of the three GRKs found, the most closely related isoform is assumed to be the mouse homolog of rat GRK2 and GRK3, and human GRK6, whereas the others are assumed to be previously undescribed isoforms or subtypes of GRK2, 3, and 6. Immunocytochemical staining using antibodies to GRK2, 3, and 6 confirmed their presence in alpha T3-1 cells. The function of these GRKs in alpha T3-1 cells is unknown, but they may be involved in short-term desensitization of the gonadotrope/GnRH receptor or perhaps, more likely, the sequestration of this receptor during intermediate-term desensitization.

    Funded by: NIDDK NIH HHS: DK-45519

    Endocrinology 1996;137;9;3942-7

  • Cloning of GRK2 cDNA from S49 murine lymphoma cells.

    Hughes RJ, Anderson KL, Kiel D and Insel PA

    Department of Pharmacology, University of California at San Diego, La Jolla 92093-0636, USA.

    Beta-adrenergic receptor kinase is a member of the G protein-linked receptor kinase (GRK1) family that elicits receptor desensitization. We have cloned GRK2 from S49 mouse lymphoma cells. The nucleotide sequences of rat GRK2 and GRK3 were aligned and conserved primers chosen for use in reverse transcription-polymerase chain reaction (RT-PCR) of S49 mRNA. Direct sequencing of the PCR fragment provided a rapid means to identify the expression of the GRK2 but not the GRK3 transcript in these cells. Unique expression of GRK2 in S49 cells was confirmed by Western blotting. Three additional pairs of primers were chosen from the rat GRK2 sequence to amplify overlapping regions that together encompassed the entire coding sequence. After attempts to ligate the four fragments of S49 cell GRK2 cDNA by using PCR proved unsuccessful, the intact cDNA was assembled by digesting the PCR products in the region of the overlaps and ligating them in a single step into pBlue-script SK(+).

    Funded by: NIGMS NIH HHS: GM-40781

    The American journal of physiology 1996;270;3 Pt 1;C885-91

  • Cardiac function in mice overexpressing the beta-adrenergic receptor kinase or a beta ARK inhibitor.

    Koch WJ, Rockman HA, Samama P, Hamilton RA, Bond RA, Milano CA and Lefkowitz RJ

    Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA.

    Transgenic mice were created with cardiac-specific overexpression of the beta-adrenergic receptor kinase-1 (beta ARK1) or a beta ARK inhibitor. Animals overexpressing beta ARK1 demonstrated attenuation of isoproterenol-stimulated left ventricular contractility in vivo, dampening of myocardial adenylyl cyclase activity, and reduced functional coupling of beta-adrenergic receptors. Conversely, mice expressing the beta ARK inhibitor displayed enhanced cardiac contractility in vivo with or without isoproterenol. These animals demonstrate the important role of beta ARK in modulating in vivo myocardial function. Because increased amounts of beta ARK1 and diminished cardiac beta-adrenergic responsiveness characterize heart failure, these animals may provide experimental models to study the role of beta ARK in heart disease.

    Funded by: NCI NIH HHS: 5F32-CA09350; NHLBI NIH HHS: HL-16037

    Science (New York, N.Y.) 1995;268;5215;1350-3

  • G protein--coupled receptor kinases.

    Haga T, Haga K and Kameyama K

    Department of Biochemistry, Institute for Brain Research, Faculty of Medicine, University of Tokyo, Japan.

    Journal of neurochemistry 1994;63;2;400-12

  • Beta-adrenergic receptor kinase-2 and beta-arrestin-2 as mediators of odorant-induced desensitization.

    Dawson TM, Arriza JL, Jaworsky DE, Borisy FF, Attramadal H, Lefkowitz RJ and Ronnett GV

    Department of Neuroscience, Johns Hopkins Medical Institutions, Baltimore, MD 21205.

    beta-Adrenergic receptor kinase (beta ARK) and beta-arrestin function in the homologous or agonist-activated desensitization of G protein-coupled receptors. The isoforms beta ARK-2 and beta-arrestin-2 are highly enriched in and localized to the dendritic knobs and cilia of the olfactory receptor neurons where the initial events of olfactory signal transduction occur. Odorants induce a rapid and transient elevation of adenosine 3',5'-monophosphate (cAMP), which activates a nonspecific cation channel and produces membrane depolarization. Preincubation of rat olfactory cilia with antibodies raised against beta ARK-2 and beta-arrestin-2 increased the odorant-induced elevation of cAMP and attenuated desensitization. These results suggest that beta ARK-2 and beta-arrestin-2 mediate agonist-dependent desensitization in olfaction.

    Funded by: NINDS NIH HHS: NS 01578-01, NS-02131

    Science (New York, N.Y.) 1993;259;5096;825-9

  • Evolution of the mammalian G protein alpha subunit multigene family.

    Wilkie TM, Gilbert DJ, Olsen AS, Chen XN, Amatruda TT, Korenberg JR, Trask BJ, de Jong P, Reed RR, Simon MI et al.

    Biology Division, California Institute of Technology, Pasadena 91125.

    Heterotrimeric guanine nucleotide binding proteins (G proteins) transduce extracellular signals received by transmembrane receptors to effector proteins. The multigene family of G protein alpha subunits, which interact with receptors and effectors, exhibit a high level of sequence diversity. In mammals, 15 G alpha subunit genes can be grouped by sequence and functional similarities into four classes. We have determined the murine chromosomal locations of all 15 G alpha subunit genes using an interspecific backcross derived from crosses of C57BL/6J and Mus spretus mice. These data, in combination with mapping studies in humans, have provided insight into the events responsible for generating the genetic diversity found in the mammalian alpha subunit genes and a framework for elucidating the role of the G alpha subunits in disease.

    Nature genetics 1992;1;2;85-91

  • Cloning, expression, and chromosomal localization of beta-adrenergic receptor kinase 2. A new member of the receptor kinase family.

    Benovic JL, Onorato JJ, Arriza JL, Stone WC, Lohse M, Jenkins NA, Gilbert DJ, Copeland NG, Caron MG and Lefkowitz RJ

    Fels Institute for Cancer Research and Molecular Biology, Temple University School of Medicine, Philadelphia, Pennsylvania 19140.

    The beta-adrenergic receptor kinase (beta ARK) specifically phosphorylates the agonist-occupied form of the beta-adrenergic and related G protein-coupled receptors. Structural features of this enzyme have been elucidated recently by the isolation of a cDNA that encodes bovine beta ARK. Utilizing a catalytic domain fragment of the beta ARK cDNA to screen a bovine brain cDNA library we have isolated a clone encoding a beta ARK-related enzyme which we have termed beta ARK2. Overall, this enzyme has 85% amino acid identity with beta ARK, with the protein kinase catalytic domain having 95% identity. The ability of beta ARK2 to phosphorylate various substrates was studied after expression in COS 7 cells. Although beta ARK2 is essentially equiactive with beta ARK in phosphorylating an acid-rich synthetic model peptide it was only approximately 50% as active when the substrate was the agonist-occupied beta 2-adrenergic receptor and only approximately 20% as active toward light-bleached rhodopsin. As with beta ARK, phosphorylation of the receptor substrates by beta ARK2 was completely stimulus dependent. RNA blot analysis with selected bovine tissues reveals an mRNA of 8 kilobases with a distribution similar to that of beta ARK. More detailed RNA analysis using a ribonuclease protection assay in various rat tissues suggests that the beta ARK2 message is present at much lower levels (typically 10-20%) than the beta ARK message. In the rat the beta ARK2 mRNA is localized predominantly in neuronal tissues although low levels are also observed in various peripheral tissues. The beta ARK2 gene has been localized to a region of mouse chromosome 5 whereas the beta ARK gene is localized on mouse chromosome 19. These data suggest the existence of a "family" of receptor kinases which may serve broadly to regulate receptor function.

    Funded by: NCI NIH HHS: N01-CO-74101; NHLBI NIH HHS: HL16037; NIGMS NIH HHS: GM44944

    The Journal of biological chemistry 1991;266;23;14939-46

  • Beta-adrenergic receptor kinase: identification of a novel protein kinase that phosphorylates the agonist-occupied form of the receptor.

    Benovic JL, Strasser RH, Caron MG and Lefkowitz RJ

    Agonist-promoted desensitization of adenylate cyclase is intimately associated with phosphorylation of the beta-adrenergic receptor in mammalian, avian, and amphibian cells. However, the nature of the protein kinase(s) involved in receptor phosphorylation remains largely unknown. We report here the identification and partial purification of a protein kinase capable of phosphorylating the agonist-occupied form of the purified beta-adrenergic receptor. The enzyme is prepared from a supernatant fraction from high-speed centrifugation of lysed kin- cells, a mutant of S49 lymphoma cells that lacks a functional cAMP-dependent protein kinase. The beta-agonist isoproterenol induces a 5- to 10-fold increase in receptor phosphorylation by this kinase, which is blocked by the antagonist alprenolol. Fractionation of the kin- supernatant on molecular-sieve HPLC and DEAE-Sephacel results in a 50- to 100-fold purified beta-adrenergic receptor kinase preparation that is largely devoid of other protein kinase activities. The kinase activity is insensitive to cAMP, cGMP, cAMP-dependent kinase inhibitor, Ca2+-calmodulin, Ca2+-phospholipid, and phorbol esters and does not phosphorylate general kinase substrates such as casein and histones. Phosphate appears to be incorporated solely into serine residues. The existence of this novel cAMP-independent kinase, which preferentially phosphorylates the agonist-occupied form of the beta-adrenergic receptor, suggests a mechanism that may explain the homologous or agonist-specific form of adenylate cyclase desensitization. It also suggests a general mechanism for regulation of receptor function in which only the agonist-occupied or "active" form of the receptor is a substrate for enzymes inducing covalent modification.

    Funded by: NHLBI NIH HHS: HL16037

    Proceedings of the National Academy of Sciences of the United States of America 1986;83;9;2797-801

Gene lists (5)

Gene List Source Species Name Description Gene count
L00000001 G2C Mus musculus Mouse PSD Mouse PSD adapted from Collins et al (2006) 1080
L00000008 G2C Mus musculus Mouse PSP Mouse PSP adapted from Collins et al (2006) 1121
L00000062 G2C Mus musculus BAYES-COLLINS-MOUSE-PSD-CONSENSUS Mouse cortex PSD consensus 984
L00000070 G2C Mus musculus BAYES-COLLINS-HUMAN-PSD-FULL Human cortex biopsy PSD full list (ortho) 1461
L00000072 G2C Mus musculus BAYES-COLLINS-MOUSE-PSD-FULL Mouse cortex PSD full list 1556
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