G2Cdb::Gene report

Gene id
Gene symbol
Homo sapiens
tropomyosin 1 (alpha)
G00000757 (Mus musculus)

Databases (8)

ENSG00000140416 (Ensembl human gene)
7168 (Entrez Gene)
1206 (G2Cdb plasticity & disease)
TPM1 (GeneCards)
191010 (OMIM)
Marker Symbol
HGNC:12010 (HGNC)
Protein Expression
261 (human protein atlas)
Protein Sequence
P09493 (UniProt)

Literature (85)

Pubmed - human_disease

  • Single-gene mutations and increased left ventricular wall thickness in the community: the Framingham Heart Study.

    Morita H, Larson MG, Barr SC, Vasan RS, O'Donnell CJ, Hirschhorn JN, Levy D, Corey D, Seidman CE, Seidman JG and Benjamin EJ

    The Program in Genomics Applications: CardioGenomics Group--Department of Genetics, NRB Room 256, Harvard Medical School, 77 Avenue Louis Pasteur, Boston, Massachusetts 02115, USA.

    Background: Mutations in sarcomere protein, PRKAG2, LAMP2, alpha-galactosidase A (GLA), and several mitochondrial genes can cause rare familial cardiomyopathies, but their contribution to increased left ventricular wall thickness (LVWT) in the community is unknown.

    We studied 1862 unrelated participants (52% women; age, 59+/-9 years) from the community-based Framingham Heart Study who had echocardiograms and provided DNA samples but did not have severe hypertension, aortic prosthesis, or significant aortic stenosis. Eight sarcomere protein genes, 3 storage cardiomyopathy-causing genes, and 27 mitochondrial genes were sequenced in unrelated individuals with increased LVWT (maximum LVWT >13 mm). Fifty eligible participants (9 women) had unexplained increased LVWT. We detected 8 mutations in 9 individuals (2 women); 7 mutations in 5 sarcomere protein genes (MYH7, MYBPC3, TNNT2, TNNI3, MYL3), and 1 GLA mutation. In individuals with increased LVWT, participants with sarcomere protein and storage mutations were clinically indistinguishable from those without mutations.

    Conclusions: In a community-based cohort, about 3% of eligible participants had increased LVWT, of whom 18% had sarcomere protein or lipid storage gene mutations. Increased LVWT in the community is a very heterogeneous condition, which sometimes may arise from single-gene variants in one of a number of genes.

    Funded by: NHLBI NIH HHS: K24-HL04334, N01-HC 25195, U01 HL 66582; NINDS NIH HHS: 5R01-NS 17950

    Circulation 2006;113;23;2697-705

Pubmed - other

  • Molecular and functional characterization of a novel cardiac-specific human tropomyosin isoform.

    Rajan S, Jagatheesan G, Karam CN, Alves ML, Bodi I, Schwartz A, Bulcao CF, D'Souza KM, Akhter SA, Boivin GP, Dube DK, Petrashevskaya N, Herr AB, Hullin R, Liggett SB, Wolska BM, Solaro RJ and Wieczorek DF

    Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati Medical Center, Cincinnati, OH 45267-0524, USA.

    Background: Tropomyosin (TM), an essential actin-binding protein, is central to the control of calcium-regulated striated muscle contraction. Although TPM1alpha (also called alpha-TM) is the predominant TM isoform in human hearts, the precise TM isoform composition remains unclear.

    In this study, we quantified for the first time the levels of striated muscle TM isoforms in human heart, including a novel isoform called TPM1kappa. By developing a TPM1kappa-specific antibody, we found that the TPM1kappa protein is expressed and incorporated into organized myofibrils in hearts and that its level is increased in human dilated cardiomyopathy and heart failure. To investigate the role of TPM1kappa in sarcomeric function, we generated transgenic mice overexpressing cardiac-specific TPM1kappa. Incorporation of increased levels of TPM1kappa protein in myofilaments leads to dilated cardiomyopathy. Physiological alterations include decreased fractional shortening, systolic and diastolic dysfunction, and decreased myofilament calcium sensitivity with no change in maximum developed tension. Additional biophysical studies demonstrate less structural stability and weaker actin-binding affinity of TPM1kappa compared with TPM1alpha.

    Conclusions: This functional analysis of TPM1kappa provides a possible mechanism for the consequences of the TM isoform switch observed in dilated cardiomyopathy and heart failure patients.

    Funded by: NHLBI NIH HHS: HL062426, HL081680, HL22231, HL79032, P01 HL062426, P01 HL062426-09, P01 HL062426-10, R01 HL022231, R01 HL022231-31, R01 HL022231-32, R01 HL079032, R01 HL079032-03, R01 HL079032-04, R01 HL081680, R01 HL081680-01A2, R01 HL081680-02, R01 HL081680-03, R37 HL022231

    Circulation 2010;121;3;410-8

  • A genome-wide meta-analysis identifies 22 loci associated with eight hematological parameters in the HaemGen consortium.

    Soranzo N, Spector TD, Mangino M, Kühnel B, Rendon A, Teumer A, Willenborg C, Wright B, Chen L, Li M, Salo P, Voight BF, Burns P, Laskowski RA, Xue Y, Menzel S, Altshuler D, Bradley JR, Bumpstead S, Burnett MS, Devaney J, Döring A, Elosua R, Epstein SE, Erber W, Falchi M, Garner SF, Ghori MJ, Goodall AH, Gwilliam R, Hakonarson HH, Hall AS, Hammond N, Hengstenberg C, Illig T, König IR, Knouff CW, McPherson R, Melander O, Mooser V, Nauck M, Nieminen MS, O'Donnell CJ, Peltonen L, Potter SC, Prokisch H, Rader DJ, Rice CM, Roberts R, Salomaa V, Sambrook J, Schreiber S, Schunkert H, Schwartz SM, Serbanovic-Canic J, Sinisalo J, Siscovick DS, Stark K, Surakka I, Stephens J, Thompson JR, Völker U, Völzke H, Watkins NA, Wells GA, Wichmann HE, Van Heel DA, Tyler-Smith C, Thein SL, Kathiresan S, Perola M, Reilly MP, Stewart AF, Erdmann J, Samani NJ, Meisinger C, Greinacher A, Deloukas P, Ouwehand WH and Gieger C

    Human Genetics, Wellcome Trust Sanger Institute, Hinxton, UK. ns6@sanger.ac.uk

    The number and volume of cells in the blood affect a wide range of disorders including cancer and cardiovascular, metabolic, infectious and immune conditions. We consider here the genetic variation in eight clinically relevant hematological parameters, including hemoglobin levels, red and white blood cell counts and platelet counts and volume. We describe common variants within 22 genetic loci reproducibly associated with these hematological parameters in 13,943 samples from six European population-based studies, including 6 associated with red blood cell parameters, 15 associated with platelet parameters and 1 associated with total white blood cell count. We further identified a long-range haplotype at 12q24 associated with coronary artery disease and myocardial infarction in 9,479 cases and 10,527 controls. We show that this haplotype demonstrates extensive disease pleiotropy, as it contains known risk loci for type 1 diabetes, hypertension and celiac disease and has been spread by a selective sweep specific to European and geographically nearby populations.

    Funded by: Canadian Institutes of Health Research: MOP77682, MOP82810, NA6650; Medical Research Council: G0000111; NCRR NIH HHS: U54 RR020278, U54 RR020278-01; NHLBI NIH HHS: R01 HL056931-02, R01 HL056931-03, R01 HL056931-04; Wellcome Trust

    Nature genetics 2009;41;11;1182-90

  • The role of Lamin A/C mutations in Danish patients with idiopathic dilated cardiomyopathy.

    Møller DV, Pham TT, Gustafsson F, Hedley P, Ersbøll MK, Bundgaard H, Andersen CB, Torp-Pedersen C, Køber L and Christiansen M

    Department of Cardiology, Rigshospitalet, Copenhagen University Hospital, Blegdamsvej 9, 2100 Copenhagen O, Denmark. dvega@gmx.net

    European journal of heart failure 2009;11;11;1031-5

  • Histologic characterization of hypertrophic cardiomyopathy with and without myofilament mutations.

    McLeod CJ, Bos JM, Theis JL, Edwards WD, Gersh BJ, Ommen SR and Ackerman MJ

    Department of Internal Medicine, Mayo Clinic, Rochester, MN 55905, USA.

    Background: Between 30% and 60% of clinical cases of hypertrophic cardiomyopathy (HC) can be attributed to mutations in the genes encoding cardiac myofilament proteins. Interestingly, it appears that the likelihood of an underlying myofilament mutation can be predicted by echocardiographic assessment of left ventricular morphology. However, it is not known whether genotypically characterized HC exists as a separate entity with discrete phenotypic morphology and histology or to what extent recognized polymorphisms of the renin-angiotensin-aldosterone system (RAAS) influence this relationship. The presence of cardiac myofilament and mutations and RAAS polymorphisms will have a strong association with the severity of histologic features of HC and characteristic septal shape.

    Methods: We conducted a retrospective review of histology specimens, obtained at septal myectomy among 181 patients with medically refractory symptomatic HC. All patients underwent comprehensive genetic analysis for mutations in 8 myofilament-encoding genes; a subset was genotyped for 6 known RAAS-polymorphisms. Patients underwent comprehensive echocardiography by an expert blinded to genotype and microscopic status.

    Results: Microscopically, severity of myocyte hypertrophy appears to be associated with the presence of recognized HC cardiac myofilament mutations (P = .03). Other histologic features characteristic of HC were not consistently associated with myofilament mutation status. A higher burden of pro-LVH RAAS polymorphisms also appeared to predict only myocyte hypertrophy (P = .01). The presence of RAAS polymorphisms was not associated with the development of a specific septal morphology (P = .6).

    Conclusion: Myofilament-positive HC does not appear to represent a distinct clinical phenotypic entity as evidenced by specific histologic characteristics and septal shape.

    Funded by: NCRR NIH HHS: KL2 RR024151, KL2 RR024151-02; NIGMS NIH HHS: T32 GM072474

    American heart journal 2009;158;5;799-805

  • The role of sarcomere gene mutations in patients with idiopathic dilated cardiomyopathy.

    Møller DV, Andersen PS, Hedley P, Ersbøll MK, Bundgaard H, Moolman-Smook J, Christiansen M and Køber L

    Department of Cardiology, Rigshospitalet, University of Copenhagen, Denmark. dvega@gmx.net

    We investigated a Danish cohort of 31 unrelated patients with idiopathic dilated cardiomyopathy (IDC), to assess the role that mutations in sarcomere protein genes play in IDC. Patients were genetically screened by capillary electrophoresis single strand conformation polymorphism and subsequently by bidirectional DNA sequencing of conformers in the coding regions of MYH7, MYBPC3, TPM1, ACTC, MYL2, MYL3, TNNT2, CSRP3 and TNNI3. Eight probands carried disease-associated genetic variants (26%). In MYH7, three novel mutations were found; in MYBPC3, one novel variant and two known mutations were found; and in TNNT2, a known mutation was found. One proband was double heterozygous. We find evidence of phenotypic plasticity: three mutations described earlier as HCM causing were found in four cases of IDC, with no history of a hypertrophic phase. Furthermore, one pedigree presented with several cases of classic DCM as well as one case with left ventricular non-compaction. Disease-causing sarcomere gene mutations were found in about one-quarter of IDC patients, and seem to play an important role in the causation of the disease. The genetics is as complex as seen in HCM. Thus, our data suggest that a genetic work-up should include screening of the most prominent sarcomere genes even in the absence of a family history of the disease.

    European journal of human genetics : EJHG 2009;17;10;1241-9

  • Prevalence of sarcomere protein gene mutations in preadolescent children with hypertrophic cardiomyopathy.

    Kaski JP, Syrris P, Esteban MT, Jenkins S, Pantazis A, Deanfield JE, McKenna WJ and Elliott PM

    Inherited Cardiovascular Diseases Unit, Institute of Child Health, University College London, London, United Kingdom.

    Background: Hypertrophic cardiomyopathy (HCM) in infants and children is thought to be commonly associated with metabolic disorders and malformation syndromes. Familial disease caused by mutations in cardiac sarcomere protein genes, which accounts for most cases in adolescents and adults, is believed to be a very rare cause of HCM.

    Seventy-nine consecutive patients diagnosed with HCM aged 13 years or younger underwent detailed clinical and genetic evaluation. The protein-coding sequences of 9 sarcomere protein genes (MYH7, MYBPC3, TNNI3, TNNT2, TPM1, MYL2, MYL3, ACTC, and TNNC1), the genes encoding desmin (DES), and the gamma-2 subunit of AMP kinase (PRKAG2) were screened for mutations. A family history of HCM was present in 48 patients (60.8%). Forty-seven mutations (15 novel) were identified in 42 (53.2%) patients (5 patients had 2 mutations). The genes most commonly implicated were MYH7 (48.9%) and MYBPC3 (36.2%); mutations in TNNT2, ACTC, MYL3, and TNNI3 accounted for <5% of cases each. A total of 16.7% patients with sarcomeric mutations were diagnosed before 1 year of age. There were no differences in clinical and echocardiographic features between those children with sarcomere protein gene mutations and those without or between patients with 2 mutations and those with 1 or no mutations.

    Conclusions: This study shows that familial disease is common among infants and children with HCM and that, in most cases, disease is caused by mutations in cardiac sarcomere protein genes. The major implication is that all first-degree relatives of any child diagnosed with HCM should be offered screening. Furthermore, the finding that one sixth of patients with sarcomeric disease were diagnosed in infancy suggests that current views on pathogenesis and natural history of familial HCM may have to be revised.

    Funded by: British Heart Foundation: PG/05/135/19913; Department of Health

    Circulation. Cardiovascular genetics 2009;2;5;436-41

  • The effect of the dilated cardiomyopathy-causing mutation Glu54Lys of alpha-tropomyosin on actin-myosin interactions during the ATPase cycle.

    Borovikov YS, Karpicheva OE, Avrova SV, Robinson P and Redwood CS

    Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, St. Petersburg 194064, Russia. boroviko@mail.cytspb.rssi.ru

    In order to understand how the Glu54Lys mutation of alpha-tropomyosin affects actomyosin interactions, we labeled SH1 helix of myosin subfragment-1 (S1) and the actin subdomain-1 with fluorescent probes. These proteins were incorporated into ghost muscle fibers and their conformational states were monitored during the ATPase cycle by measuring polarized fluorescence. The addition of wild-type alpha-tropomyosin to actin filaments increases the amplitude of the SH1 helix and subdomain-1 movements during the ATPase cycle, indicating the enhancement of the efficiency of work of each cross-bridge. The Glu54Lys mutation inhibits this effect. The Glu54Lys mutation also results in the coupling of the weak-binding sub-state of S1 to the strong-binding sub-state of actin thus altering the concerted conformational changes during the ATPase cycle. We suggest that these alterations will result in reduced force production, which is likely to underlie at least in part the contractile deficit observed in human dilated cardiomyopathy.

    Funded by: British Heart Foundation: RG/07/012/24110

    Archives of biochemistry and biophysics 2009;489;1-2;20-4

  • Presence of activating KRAS mutations correlates significantly with expression of tumour suppressor genes DCN and TPM1 in colorectal cancer.

    Mlakar V, Berginc G, Volavsek M, Stor Z, Rems M and Glavac D

    Department of Molecular Genetics, Institute of Pathology, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia. vid.mlakar@mf.uni-lj.si

    Background: Despite identification of the major genes and pathways involved in the development of colorectal cancer (CRC), it has become obvious that several steps in these pathways might be bypassed by other as yet unknown genetic events that lead towards CRC. Therefore we wanted to improve our understanding of the genetic mechanisms of CRC development.

    Methods: We used microarrays to identify novel genes involved in the development of CRC. Real time PCR was used for mRNA expression as well as to search for chromosomal abnormalities within candidate genes. The correlation between the expression obtained by real time PCR and the presence of the KRAS mutation was investigated.

    Results: We detected significant previously undescribed underexpression in CRC for genes SLC26A3, TPM1 and DCN, with a suggested tumour suppressor role. We also describe the correlation between TPM1 and DCN expression and the presence of KRAS mutations in CRC. When searching for chromosomal abnormalities, we found deletion of the TPM1 gene in one case of CRC, but no deletions of DCN and SLC26A3 were found.

    Conclusion: Our study provides further evidence of decreased mRNA expression of three important tumour suppressor genes in cases of CRC, thus implicating them in the development of this type of cancer. Moreover, we found underexpression of the TPM1 gene in a case of CRCs without KRAS mutations, showing that TPM1 might serve as an alternative path of development of CRC. This downregulation could in some cases be mediated by deletion of the TPM1 gene. On the other hand, the correlation of DCN underexpression with the presence of KRAS mutations suggests that DCN expression is affected by the presence of activating KRAS mutations, lowering the amount of the important tumour suppressor protein decorin.

    BMC cancer 2009;9;282

  • MiR-21 indicates poor prognosis in tongue squamous cell carcinomas as an apoptosis inhibitor.

    Li J, Huang H, Sun L, Yang M, Pan C, Chen W, Wu D, Lin Z, Zeng C, Yao Y, Zhang P and Song E

    Oral and Maxillofacial Surgery, and Breast Tumor Center, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, People's Republic of China.

    Purpose: We aim to examine miR-21 expression in tongue squamous cell carcinomas (TSCC) and correlate it with patient clinical status, and to investigate its contribution to TSCC cell growth, apoptosis, and tumorigenesis.

    MicroRNA profiling was done in 10 cases of TSCC with microarray. MiR-21 overexpression was quantitated with quantitative reverse transcription-PCR in 103 patients, and correlated to the pathoclinical status of the patients. Immunohistochemistry was used to examine the expression of TPM1 and PTEN, and terminal deoxynucleotidyl transferase-mediated dUTP labeling to evaluate apoptosis. Moreover, miR-21 antisense oligonucleotide (ASO) was transfected in SCC-15 and CAL27 cell lines, and tumor cell growth was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, adherent colony formation, and soft agar assay, whereas apoptosis was determined by Annexin V assay, cytochrome c release, and caspase 3 assay. Tumorigenesis was evaluated by xenografting SCC-15 cells in nude mice.

    Results: MiR-21 is overexpressed in TSCC relative to adjacent normal tissues. The level of miR-21 is reversely correlated with TPM1 and PTEN expression and apoptosis of cancer cells. Multivariate analysis showed that miR-21 expression is an independent prognostic factor indicating poor survival. Inhibiting miR-21 with ASO in TSCC cell lines reduces survival and anchorage-independent growth, and induces apoptosis in TSCC cell lines. Simultaneous silencing of TPM1 with siRNA only partially recapitulates the effect of miR-21 ASO. Furthermore, repeated injection of miR-21 ASO suppresses tumor formation in nude mice by reducing cell proliferation and inducing apoptosis.

    Conclusions: miR-21 is an independent prognostic indicator for TSCC, and may play a role in TSCC development by inhibiting cancer cell apoptosis partly via TPM1 silencing.

    Clinical cancer research : an official journal of the American Association for Cancer Research 2009;15;12;3998-4008

  • Dilated cardiomyopathy mutations in alpha-tropomyosin inhibit its movement during the ATPase cycle.

    Borovikov YS, Karpicheva OE, Chudakova GA, Robinson P and Redwood CS

    Laboratory of Mechanisms of Cell Motility, Institute of Cytology, Russian Academy of Sciences, 4 Tikhoretsky Avenue, 194064 St. Petersburg, Russia. boroviko@mail.cytspb.rssi.ru

    The Glu40Lys and Glu54Lys mutations in alpha-tropomyosin cause dilated cardiomyopathy (DCM). Functional analysis has demonstrated that both mutations decrease thin filament Ca2+-sensitivity and that Glu40Lys reduces maximum activation. To understand the molecular mechanism underlying these changes, we labeled wild type alpha-tropomyosin and both mutants at Cys190 with 5-iodoacetamide-fluorescein and incorporated the labeled proteins into ghost muscle fibers. Using the polarized fluorimetry, the position of the labeled tropomyosins on the thin filament and their affinity for actin were measured and the change in these parameters at different stages of the ATPase cycle determined. Both DCM mutations were found to shift tropomyosin towards the periphery of thin filament and to change the affinity of tropomyosin for actin; during the ATPase cycle the amplitude of tropomyosin movement was reduced and at some stages of the cycle even reversed. The correlation of these structural changes with the observed function effects is discussed.

    Funded by: British Heart Foundation: RG/07/012/24110

    Biochemical and biophysical research communications 2009;381;3;403-6

  • Diagnostic yield, interpretation, and clinical utility of mutation screening of sarcomere encoding genes in Danish hypertrophic cardiomyopathy patients and relatives.

    Andersen PS, Havndrup O, Hougs L, Sørensen KM, Jensen M, Larsen LA, Hedley P, Thomsen AR, Moolman-Smook J, Christiansen M and Bundgaard H

    Department of Clinical Biochemistry, Statens Serum Institute, Copenhagen, Denmark. psa@ssi.dk

    The American Heart Association (AHA) recommends family screening for hypertrophic cardiomyopathy (HCM). We assessed the outcome of family screening combining clinical evaluation and screening for sarcomere gene mutations in a cohort of 90 Danish HCM patients and their close relatives, in all 451 persons. Index patients were screened for mutations in all coding regions of 10 sarcomere genes (MYH7, MYL3, MYBPC3, TNNI3, TNNT2, TPM1, ACTC, CSRP3, TCAP, and TNNC1) and five exons of TTN. Relatives were screened for presence of minor or major diagnostic criteria for HCM and tracking of DNA variants was performed. In total, 297 adult relatives (>18 years) (51.2%) fulfilled one or more criteria for HCM. A total of 38 HCM-causing mutations were detected in 32 index patients. Six patients carried two disease-associated mutations. Twenty-two mutations have only been identified in the present cohort. The genetic diagnostic yield was almost twice as high in familial HCM (53%) vs. HCM of sporadic or unclear inheritance (19%). The yield was highest in families with an additional history of HCM-related clinical events. In relatives, 29.9% of mutation carriers did not fulfil any clinical diagnostic criterion, and in 37.5% of relatives without a mutation, one or more criteria was fulfilled. A total of 60% of family members had no mutation and could be reassured and further follow-up ceased. Genetic diagnosis may be established in approximately 40% of families with the highest yield in familial HCM with clinical events. Mutation-screening was superior to clinical investigation in identification of individuals not at increased risk, where follow-up is redundant, but should be offered in all families with relatives at risk for developing HCM.

    Human mutation 2009;30;3;363-70

  • [Mutations in sarcomeric genes MYH7, MYBPC3, TNNT2, TNNI3, and TPM1 in patients with hypertrophic cardiomyopathy].

    García-Castro M, Coto E, Reguero JR, Berrazueta JR, Alvarez V, Alonso B, Sainz R, Martín M and Morís C

    Genética Molecular, Instituto de Investigación Nefrológica, Hospital Universitario Central de Asturias, Oviedo, Asturias, Spain.

    Mutation of a sarcomeric gene is the most frequent cause of hypertrophic cardiomyopathy. For each such gene, however, previous studies have reported a range of different mutation frequencies, and clinical manifestations have been highly heterogeneous, both of which limit the use of genetic information in clinical practice. Our aim was to determine the frequency of mutations in the sarcomeric genes MYH7, MYBPC3, TNNT2, TNNI3, and TPM1 in a cohort of Spanish patients with hypertrophic cardiomyopathy.

    Methods: We used sequencing to analyze the coding regions of these five genes in 120 patients (29% with a family history) and investigated how the patient phenotype varied with the gene mutated.

    Results: In total, 32 patients were found to have mutations: 10 in MYH7 (8%), 20 in MYBPC3 (16%), 2 in TNNT2, 1 in TPM1 and none in TNNI3. Overall, 61% of mutations had not been described before. Two patients had two mutations (i.e., double mutants). There was no difference in the mean age at diagnosis or the extent of the hypertrophy between those with MYH7 mutations and those with MYBPC3 mutations.

    Conclusions: Some 26% of patients had a mutation in one of the five sarcomeric genes investigated. More than half of the mutations had not been described before. The MYBPC3 gene was the most frequently mutated, followed by MYH7. No phenotypic differences were observed between carriers of the various mutations, which makes it difficult to use genetic information to stratify risk in these patients.

    Revista espanola de cardiologia 2009;62;1;48-56

  • A tropomyosin 1 induced defect in cytokinesis can be rescued by elevated expression of cofilin.

    Thoms JA, Loch HM, Bamburg JR, Gunning PW and Weinberger RP

    Oncology Research Unit, The Children's Hospital at Westmead, Westmead, New South Wales, Australia. julie.a.thoms@gmail.com

    Cytokinesis in eukaryotic cells is mediated by the contractile ring, an actomyosin-based structure which provides the force required to separate daughter cells. Isoforms of the actin-binding protein tropomyosin are also localised to the contractile ring in both fission yeast and human astrocytes. Although tropomyosin is required for cytokinesis in yeast, its precise role in the contractile ring is unknown. In this study we find that increased expression of a single tropomyosin isoform, tropomyosin 1, in U373MG astrocytoma cells leads to multinucleated cells and mitotic spindle defects. Furthermore, cells expressing increased levels of tropomyosin 1 usually fail to complete cytokinesis and this is accompanied by reduced accumulation of actin depolymerising factor/cofilin in the contractile ring. Adenovirus mediated expression of cofilin is able to relieve the tropomyosin 1 induced effects on cytokinesis. We conclude that tropomyosin 1 and cofilin play antagonistic roles within the contractile ring and that the balance between tropomyosin 1 and cofilin expression is important for cytokinesis.

    Cell motility and the cytoskeleton 2008;65;12;979-90

  • Relationship between sex, shape, and substrate in hypertrophic cardiomyopathy.

    Bos JM, Theis JL, Tajik AJ, Gersh BJ, Ommen SR and Ackerman MJ

    Department of Internal Medicine, Division of Cardiovascular Diseases, Mayo Clinic, Rochester, MN 55905, USA.

    Background: Hypertrophic cardiomyopathy (HCM) is a disease characterized by substantial genetic, morphologic, and prognostic heterogeneity. Recently, sex-related differences in HCM were reported, with women being older at diagnosis and exhibiting greater left ventricular outflow tract obstruction than men. We sought to evaluate the influence of sex on the HCM phenotype in a large cohort of unrelated patients with genetically and morphologically classified HCM.

    Methods: Comprehensive genotyping of 13 HCM-susceptibility genes encoding myofilament and Z-disc proteins of the cardiac sarcomere was performed previously on 382 unrelated patients with HCM. Blinded to the genotype, the septal morphology was graded as reverse-curvature, sigmoidal, apical, or neutral-contour HCM by echocardiography.

    Results: Overall, women (a) were significantly older at diagnosis (45.1 +/- 20 vs 35.8 +/- 17 years, P < .001), (b) had greater left ventricular outflow tract obstruction (53.5 +/- 45 vs 41.7 +/- 42 mm Hg, P = .009), (c) were more likely to have concomitant hypertension (19% vs 11%, P = .02), and (d) had a higher rate of surgical myectomy (49% vs 36%, P = .01) than men. Interestingly, these sex-based differences were apparent only among patients with sigmoidal HCM (P < .001).

    Conclusions: In this largest cohort of comprehensively genotyped and morphologically classified patients with clinically diagnosed HCM, we observed that the striking sex-related differences in the clinical phenotype are confined largely to the subset of mutation-negative sigmoidal HCM. Whereas mutations within the sarcomere appear to dominate the disease process, in their absence, sex has a significant modifying effect, specifically noted in cases of sigmoidal HCM.

    Funded by: NCRR NIH HHS: 1 UL1 RR024150-01, UL1 RR024150; NIGMS NIH HHS: T32 GM072474

    American heart journal 2008;155;6;1128-34

  • Shared genetic causes of cardiac hypertrophy in children and adults.

    Morita H, Rehm HL, Menesses A, McDonough B, Roberts AE, Kucherlapati R, Towbin JA, Seidman JG and Seidman CE

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

    Background: The childhood onset of idiopathic cardiac hypertrophy that occurs without a family history of cardiomyopathy can portend a poor prognosis. Despite morphologic similarities to genetic cardiomyopathies of adulthood, the contribution of genetics to childhood-onset hypertrophy is unknown.

    Methods: We assessed the family and medical histories of 84 children (63 boys and 21 girls) with idiopathic cardiac hypertrophy diagnosed before 15 years of age (mean [+/-SD] age, 6.99+/-6.12 years). We sequenced eight genes: MYH7, MYBPC3, TNNT2, TNNI3, TPM1, MYL3, MYL2, and ACTC. These genes encode sarcomere proteins that, when mutated, cause adult-onset cardiomyopathies. We also sequenced PRKAG2 and LAMP2, which encode metabolic proteins; mutations in these genes can cause early-onset ventricular hypertrophy.

    Results: We identified mutations in 25 of 51 affected children without family histories of cardiomyopathy and in 21 of 33 affected children with familial cardiomyopathy. Among 11 of the 25 children with presumed sporadic disease, 4 carried new mutations and 7 inherited the mutations. Mutations occurred predominantly (in >75% of the children) in MYH7 and MYBPC3; significantly more MYBPC3 missense mutations were detected than occur in adult-onset cardiomyopathy (P<0.005). Neither hypertrophic severity nor contractile function correlated with familial or genetic status. Cardiac transplantation and sudden death were more prevalent among mutation-positive than among mutation-negative children; implantable cardioverter-defibrillators were more frequent (P=0.007) in children with family histories that were positive for the mutation.

    Conclusions: Genetic causes account for about half of presumed sporadic cases and nearly two thirds of familial cases of childhood-onset hypertrophy. Childhood-onset hypertrophy should prompt genetic analyses and family evaluations.

    Funded by: Howard Hughes Medical Institute; NHLBI NIH HHS: R01 HL087000, R01 HL087000-02

    The New England journal of medicine 2008;358;18;1899-908

  • Toward a confocal subcellular atlas of the human proteome.

    Barbe L, Lundberg E, Oksvold P, Stenius A, Lewin E, Björling E, Asplund A, Pontén F, Brismar H, Uhlén M and Andersson-Svahn H

    Department of Biotechnology, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.

    Information on protein localization on the subcellular level is important to map and characterize the proteome and to better understand cellular functions of proteins. Here we report on a pilot study of 466 proteins in three human cell lines aimed to allow large scale confocal microscopy analysis using protein-specific antibodies. Approximately 3000 high resolution images were generated, and more than 80% of the analyzed proteins could be classified in one or multiple subcellular compartment(s). The localizations of the proteins showed, in many cases, good agreement with the Gene Ontology localization prediction model. This is the first large scale antibody-based study to localize proteins into subcellular compartments using antibodies and confocal microscopy. The results suggest that this approach might be a valuable tool in conjunction with predictive models for protein localization.

    Molecular & cellular proteomics : MCP 2008;7;3;499-508

  • Role of high-molecular weight tropomyosins in TGF-beta-mediated control of cell motility.

    Zheng Q, Safina A and Bakin AV

    Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, NY 14263, USA.

    Transforming growth factor beta1 (TGF-beta1) suppresses tumor development at early stages of cancer, but enhances tumor invasion and formation of metastasis. TGF-beta1-mediated tumor invasion is associated with epithelial to mesenchymal transition (EMT) and matrix proteolysis. The mechanisms of these TGF-beta1 responses in normal and tumor cells are not well understood. Recently, we have reported that TGF-beta1 increases expression of high-molecular weight tropomyosins (HMW-tropomyosins) and formation of actin stress fibers in normal epithelial cells. The present study investigated the role of tropomyosin in TGF-beta1-mediated cell motility and invasion. We found that TGF-beta1 restricts motility of normal epithelial cells although it promotes EMT and formation of actin stress fibers and focal adhesions. Cell motility was enhanced by siRNA-mediated suppression of HMW-tropomyosins. TGF-beta1 stimulated migration and matrix proteolysis in breast cancer MDA-MB-231 cells that express low levels of HMW-tropomyosins. Tet-Off-regulated expression of HMW-tropomyosin inhibited cell migration and matrix proteolysis without affecting expression of matrix metalloproteinases. Tropomyosin increased cell adhesion to matrix by enhancing actin fibers and focal adhesions. Finally, tropomyosin impaired the ability of tumor cells to form lung metastases in SCID mice. Thus, these results suggest that HMW-tropomyosins are important for TGF-beta-mediated control of cell motility and acquisition of the metastatic potential.

    Funded by: NCI NIH HHS: CA 16056, R01 CA95263

    International journal of cancer 2008;122;1;78-90

  • Dilated and hypertrophic cardiomyopathy mutations in troponin and alpha-tropomyosin have opposing effects on the calcium affinity of cardiac thin filaments.

    Robinson P, Griffiths PJ, Watkins H and Redwood CS

    Department of Cardiovascular Medicine, University of Oxford, United Kingdom.

    Dilated cardiomyopathy and hypertrophic cardiomyopathy (HCM) can be caused by mutations in thin filament regulatory proteins of the contractile apparatus. In vitro functional assays show that, in general, the presence of dilated cardiomyopathy mutations decreases the Ca(2+) sensitivity of contractility, whereas HCM mutations increase it. To assess whether this functional phenomenon was a direct result of altered Ca(2+) affinity or was caused by altered troponin-tropomyosin switching, we assessed Ca(2+) binding of the regulatory site of cardiac troponin C in wild-type or mutant troponin complex and thin filaments using a fluorescent probe (2-[4'-{iodoacetamido}aniline]-naphthalene-6-sulfonate) attached to Cys35 of cardiac troponin C. The Ca(2+)-binding affinity (pCa(50)=6.57+/-0.03) of reconstituted troponin complex was unaffected by all of the HCM and dilated cardiomyopathy troponin mutants tested, with the exception of the troponin I Arg145Gly HCM mutation, which caused an increase (DeltapCa(50)=+0.31+/-0.05). However, when incorporated into regulated thin filaments, all but 1 of the 10 troponin and alpha-tropomyosin mutants altered Ca(2+)-binding affinity. Both HCM mutations increased Ca(2+) affinity (DeltapCa(50)=+0.41+/-0.02 and +0.51+/-0.01), whereas the dilated cardiomyopathy mutations decreased affinity (DeltapCa(50)=-0.12+/-0.04 to -0.54+/-0.04), which correlates with our previous functional in vitro assays. The exception was the troponin T Asp270Asn mutant, which caused a significant decrease in cooperativity. Because troponin is the major Ca(2+) buffer in the cardiomyocyte sarcoplasm, we suggest that Ca(2+) affinity changes caused by cardiomyopathy mutant proteins may directly affect the Ca(2+) transient and hence Ca(2+)-sensitive disease state remodeling pathways in vivo. This represents a novel mechanism for this class of mutation.

    Circulation research 2007;101;12;1266-73

  • DAP kinase mediates the phosphorylation of tropomyosin-1 downstream of the ERK pathway, which regulates the formation of stress fibers in response to oxidative stress.

    Houle F, Poirier A, Dumaresq J and Huot J

    Le Centre de recherche en cancérologie de l'Université Laval, 9 rue McMahon, Québec G1R 2J6, Canada.

    Endothelial cells are actively involved in regulating the exchanges between blood and tissues. This function is tightly dependent on actin cytoskeleton dynamics and is challenged by a wide variety of stimuli, including oxidative stress. In endothelial cells, oxidative stress quickly activates the extracellular-signal-regulated kinase (ERK) MAP kinase, which results in the phosphorylation of tropomyosin. Here, we investigated further the mechanisms of tropomyosin phosphorylation and its function in actin remodeling. We identified, for the first time, death-associated protein kinase 1 (DAP kinase 1) as the kinase that phosphorylates tropomyosin-1 in response to ERK activation by hydrogen peroxide (H(2)O(2)). We also report that the phosphorylation of tropomyosin-1 mediated by DAP kinase occurs on Ser283. Moreover, the expression of the pseudophosphorylated tropomyosin mutant Ser283Glu triggers by itself the formation of stress fibers in untreated cells, and the effect is maintained in H(2)O(2)-treated cells in which DAP kinase expression is knocked-down by siRNA. By contrast, the expression of the nonphosphorylatable tropomyosin mutant Ser283Ala is not associated with stress fibers and leads to membrane blebbing in response to H(2)O(2). Our finding that tropomyosin-1 is phosphorylated downstream of ERK and DAP kinase and that it helps regulate the formation of stress fibers will aid understanding the role of this protein in regulating the endothelial functions associated with cytoskeletal remodeling.

    Journal of cell science 2007;120;Pt 20;3666-77

  • Dilated cardiomyopathy mutant tropomyosin mice develop cardiac dysfunction with significantly decreased fractional shortening and myofilament calcium sensitivity.

    Rajan S, Ahmed RP, Jagatheesan G, Petrashevskaya N, Boivin GP, Urboniene D, Arteaga GM, Wolska BM, Solaro RJ, Liggett SB and Wieczorek DF

    Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati Medical Center, Cincinnati, OH 45267-0524, USA.

    Mutations in striated muscle alpha-tropomyosin (alpha-TM), an essential thin filament protein, cause both dilated cardiomyopathy (DCM) and familial hypertrophic cardiomyopathy. Two distinct point mutations within alpha-tropomyosin are associated with the development of DCM in humans: Glu40Lys and Glu54Lys. To investigate the functional consequences of alpha-TM mutations associated with DCM, we generated transgenic mice that express mutant alpha-TM (Glu54Lys) in the adult heart. Results showed that an increase in transgenic protein expression led to a reciprocal decrease in endogenous alpha-TM levels, with total myofilament TM protein levels remaining unaltered. Histological and morphological analyses revealed development of DCM with progression to heart failure and frequently death by 6 months. Echocardiographic analyses confirmed the dilated phenotype of the heart with a significant decrease in the left ventricular fractional shortening. Work-performing heart analyses showed significantly impaired systolic, and diastolic functions and the force measurements of cardiac myofibers revealed that the myofilaments had significantly decreased Ca(2+) sensitivity and tension generation. Real-time RT-PCR quantification demonstrated an increased expression of beta-myosin heavy chain, brain natriuretic peptide, and skeletal actin and a decreased expression of the Ca(2+) handling proteins sarcoplasmic reticulum Ca(2+)-ATPase and ryanodine receptor. Furthermore, our study also indicates that the alpha-TM54 mutation decreases tropomyosin flexibility, which may influence actin binding and myofilament Ca(2+) sensitivity. The pathological and physiological phenotypes exhibited by these mice are consistent with those seen in human DCM and heart failure. As such, this is the first mouse model in which a mutation in a sarcomeric thin filament protein, specifically TM, leads to DCM.

    Funded by: NHLBI NIH HHS: HL-062426, HL-22231, HL-71952, HL-79032, K01 HL-67709-4

    Circulation research 2007;101;2;205-14

  • The effect of mutations in alpha-tropomyosin (E40K and E54K) that cause familial dilated cardiomyopathy on the regulatory mechanism of cardiac muscle thin filaments.

    Mirza M, Robinson P, Kremneva E, Copeland O, Nikolaeva O, Watkins H, Levitsky D, Redwood C, El-Mezgueldi M and Marston S

    National Heart and Lung Institute, Imperial College London, London SW3 6LY, United Kingdom.

    E40K and E54K mutations in alpha-tropomyosin cause inherited dilated cardiomyopathy. Previously we showed, using Ala-Ser alpha-tropomyosin (AS-alpha-Tm) expressed in Escherichia coli, that both mutations decrease Ca(2+) sensitivity. E40K also reduces V(max) of actin-Tm-activated S-1 ATPase by 18%. We investigated cooperative allosteric regulation by native Tm, AS-alpha-Tm, and the two dilated cardiomyopathy-causing mutants. AS-alpha-Tm has a lower cooperative unit size (6.5) than native alpha-tropomyosin (10.0). The E40K mutation reduced the size of the cooperative unit to 3.7, whereas E54K increased it to 8.0. For the equilibrium between On and Off states, the K(T) value was the same for all actin-Tm species; however, the K(T) value of actin-Tm-troponin at pCa 5 was 50% less for AS-alpha-Tm E40K than for AS-alpha-Tm and AS-alpha-Tm E54K. K(b), the "closed" to "blocked" equilibrium constant, was the same for all tropomyosin species. The E40K mutation reduced the affinity of tropomyosin for actin by 1.74-fold, but only when in the On state (in the presence of S-1). In contrast the E54K mutation reduced affinity by 3.5-fold only in the Off state. Differential scanning calorimetry measurements of AS-alpha-Tm showed that domain 3, assigned to the N terminus of tropomyosin, was strongly destabilized by both mutations. Additionally with AS-alpha-Tm E54K, we observed a unique new domain at 55 degrees C accounting for 25% of enthalpy indicating stabilization of part of the tropomyosin. The disease-causing mechanism of the E40K mutation may be accounted for by destabilization of the On state of the thin filaments; however, the E54K mutation has a more complex effect on tropomyosin structure and function.

    Funded by: British Heart Foundation: RG/07/012/24110; Wellcome Trust

    The Journal of biological chemistry 2007;282;18;13487-97

  • Myocardial perfusion, oxidative metabolism, and free fatty acid uptake in patients with hypertrophic cardiomyopathy attributable to the Asp175Asn mutation in the alpha-tropomyosin gene: a positron emission tomography study.

    Tuunanen H, Kuusisto J, Toikka J, Jääskeläinen P, Marjamäki P, Peuhkurinen K, Viljanen T, Sipola P, Stolen KQ, Hannukainen J, Nuutila P, Laakso M and Knuuti J

    Turku PET Centre, Turku, Finland.

    Background: The relationship between myocardial metabolic changes and the severity of left ventricular (LV) hypertrophy in patients with hypertrophic cardiomyopathy (HCM) is largely unknown. We characterized metabolic abnormalities in patients with a genetically identical cause for HCM but with variable LV hypertrophy.

    Eight patients with HCM attributable to the Asp175Asn mutation in the alpha-tropomyosin gene underwent myocardial perfusion, oxidative, and free fatty acid (FFA) metabolism measurements via positron emission tomography and oxygen 15-labeled water, carbon 11 acetate, and fluorine 14(R,S)-[18F] Fluoro-6-thia-heptadecanoic acid (18 FTHA). LV mass, work, and efficiency were assessed by echocardiography. Thirty-six healthy volunteers served as control subjects. Compared with control subjects, HCM patients had increased myocardial oxidative metabolism and FFA uptake (P < .05). However, in patients, LV mass was inversely related to global myocardial perfusion, oxidative metabolism, and FFA uptake (all P < .03), and regional wall thickness was inversely related to regional perfusion (P < .01), oxidative metabolism (P < .001), and FFA uptake (P < .01). Therefore patients with mild (LV mass less than median of 177 g) but not advanced LV hypertrophy were characterized by increased perfusion, oxidative metabolism, and LV efficiency as compared with control subjects (P < .05).

    Conclusions: In HCM attributable to the Asp175Asn mutation in the alpha-tropomyosin gene, myocardial oxidative metabolism and FFA metabolism are increased and inversely related to LV hypertrophy at both the whole heart and regional level. Increased metabolism and efficiency characterize patients with mild myocardial hypertrophy. These hypermetabolic alterations regress with advanced hypertrophy.

    Journal of nuclear cardiology : official publication of the American Society of Nuclear Cardiology 2007;14;3;354-65

  • Exon selection in alpha-tropomyosin mRNA is regulated by the antagonistic action of RBM4 and PTB.

    Lin JC and Tarn WY

    Institute of Biomedical Sciences, Academia Sinica, 128 Academy Road Section 2, Nankang, Taipei 11529, Taiwan.

    RNA-binding motif protein 4 (RBM4) has been implicated in the regulation of precursor mRNA splicing. Using differential display analysis, we identified mRNAs that associate with RBM4-containing messenger RNPs in vivo. Among these mRNAs, alpha-tropomyosin (alpha-TM) is known to exhibit a muscle cell type-specific splicing pattern. The level of the skeletal muscle-specific alpha-TM mRNA isoform partially correlated with that of RBM4 in human tissues examined and could be modulated by ectopic overexpression or suppression of RBM4. These results indicated that RBM4 directly influences the expression of the skeletal muscle-specific alpha-TM isoform. Using minigenes, we demonstrated that RBM4 can activate the selection of skeletal muscle-specific exons, possibly via binding to intronic pyrimidine-rich elements. By contrast, the splicing regulator polypyrimidine tract binding protein (PTB) excluded these exons; moreover, RBM4 antagonized this PTB-mediated exon exclusion likely by competing with PTB for binding to a CU-rich element. This study suggests a possible mechanism underlying the regulated alternative splicing of alpha-TM by the antagonistic splicing regulators RBM4 and PTB.

    Molecular and cellular biology 2005;25;22;10111-21

  • Towards a proteome-scale map of the human protein-protein interaction network.

    Rual JF, Venkatesan K, Hao T, Hirozane-Kishikawa T, Dricot A, Li N, Berriz GF, Gibbons FD, Dreze M, Ayivi-Guedehoussou N, Klitgord N, Simon C, Boxem M, Milstein S, Rosenberg J, Goldberg DS, Zhang LV, Wong SL, Franklin G, Li S, Albala JS, Lim J, Fraughton C, Llamosas E, Cevik S, Bex C, Lamesch P, Sikorski RS, Vandenhaute J, Zoghbi HY, Smolyar A, Bosak S, Sequerra R, Doucette-Stamm L, Cusick ME, Hill DE, Roth FP and Vidal M

    Center for Cancer Systems Biology and Department of Cancer Biology, Dana-Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, Massachusetts 02115, USA.

    Systematic mapping of protein-protein interactions, or 'interactome' mapping, was initiated in model organisms, starting with defined biological processes and then expanding to the scale of the proteome. Although far from complete, such maps have revealed global topological and dynamic features of interactome networks that relate to known biological properties, suggesting that a human interactome map will provide insight into development and disease mechanisms at a systems level. Here we describe an initial version of a proteome-scale map of human binary protein-protein interactions. Using a stringent, high-throughput yeast two-hybrid system, we tested pairwise interactions among the products of approximately 8,100 currently available Gateway-cloned open reading frames and detected approximately 2,800 interactions. This data set, called CCSB-HI1, has a verification rate of approximately 78% as revealed by an independent co-affinity purification assay, and correlates significantly with other biological attributes. The CCSB-HI1 data set increases by approximately 70% the set of available binary interactions within the tested space and reveals more than 300 new connections to over 100 disease-associated proteins. This work represents an important step towards a systematic and comprehensive human interactome project.

    Funded by: NCI NIH HHS: R33 CA132073; NHGRI NIH HHS: P50 HG004233, R01 HG001715, RC4 HG006066, U01 HG001715; NHLBI NIH HHS: U01 HL098166

    Nature 2005;437;7062;1173-8

  • Proteomics of human umbilical vein endothelial cells applied to etoposide-induced apoptosis.

    Bruneel A, Labas V, Mailloux A, Sharma S, Royer N, Vinh J, Pernet P, Vaubourdolle M and Baudin B

    Service de Biochimie A, Hôpital Saint-Antoine, AP-HP, Paris, France. arnaud.bruneel@sat.ap-hop-paris.fr

    We have undertaken to continue the proteomic study of human umbilical vein endothelial cells (HUVECs) using the combination of 2-DE, automated trypsin digestion, and PMF analysis after MALDI-TOF MS and peptide sequencing using nano LC-ESI-MS/MS. The overall functional characterization of the 162 identified proteins from primary cultures of HUVECs confirms the metabolic capabilities of endothelium and illustrates various cellular functions more related to cell motility and angiogenesis, protein folding, anti-oxidant defenses, signal transduction, proteasome pathway and resistance to apoptosis. In comparison with controls cells, the differential proteomic analysis of HUVECs treated by the pro-apoptotic topoisomerase inhibitor etoposide further revealed the variation of eight proteins, namely, GRP78, GRP94, valosin-containing protein, proteinase inhibitor 9, cofilin, 37-kDa laminin receptor protein, bovine apolipoprotein, and tropomyosin. These data suggest that etoposide-induced apoptosis of human vascular endothelial cells results from the intricate involvement of multiple apoptosis processes including at least the mitochondrial and the ER stress pathways. The presented 2-D pattern and protein database, as well as the data related to apoptosis of HUVECs, are available at http://www.huvec.com.

    Proteomics 2005;5;15;3876-84

  • Silencing of the Tropomyosin-1 gene by DNA methylation alters tumor suppressor function of TGF-beta.

    Varga AE, Stourman NV, Zheng Q, Safina AF, Quan L, Li X, Sossey-Alaoui K and Bakin AV

    Department of Cancer Genetics, Roswell Park Cancer Institute, Buffalo, NY 14263, USA.

    Loss of actin stress fibers has been associated with cell transformation and metastasis. TGF-beta induction of stress fibers in epithelial cells requires high molecular weight tropomyosins encoded by TPM1 and TPM2 genes. Here, we investigated the mechanism underlying the failure of TGF-beta to induce stress fibers and inhibit cell migration in metastatic cells. RT-PCR analysis in carcinoma cell lines revealed a significant reduction in TPM1 transcripts in metastatic MDA-MB-231, MDA-MB-435 and SW620 cell lines. Treatment of these cells with demethylating agent 5-aza-2'-deoxycytidine (5-aza-dC) increased mRNA levels of TPM1 with no effect on TPM2. Importantly, 5-aza-dC treatment of MDA-MB-231 cells restored TGF-beta induction of TPM1 and formation of stress fibers. Forced expression of TPM1 by using Tet-Off system increased stress fibers in MDA-MB-231 cells and reduced cell migration. A potential CpG island spanning the TPM1 proximal promoter, exon 1, and the beginning of intron 1 was identified. Bisulfite sequencing showed significant cytosine methylation in metastatic cell lines that correlated with a reduced expression of TPM1. Together these results suggest that epigenetic suppression of TPM1 may alter TGF-beta tumor suppressor function and contribute to metastatic properties of tumor cells.

    Funded by: NCI NIH HHS: R01 CA95263

    Oncogene 2005;24;32;5043-52

  • The regulatory effects of tropomyosin and troponin-I on the interaction of myosin loop regions with F-actin.

    Patchell VB, Gallon CE, Evans JS, Gao Y, Perry SV and Levine BA

    Division of Medical Sciences, School of Medicine, University of Birmingham, Birmingham B15 2TT, United Kingdom.

    The N terminus of skeletal myosin light chain 1 and the cardiomyopathy loop of human cardiac myosin have been shown previously to bind to actin in the presence and absence of tropomyosin (Patchell, V. B., Gallon, C. E., Hodgkin, M. A., Fattoum, A., Perry, S. V., and Levine, B. A. (2002) Eur. J. Biochem. 269, 5088-5100). We have extended this work and have shown that segments corresponding to other regions of human cardiac beta-myosin, presumed to be sites of interaction with F-actin (residues 554-584, 622-646, and 633-660), likewise bind independently to actin under similar conditions. The binding to F-actin of a peptide spanning the minimal inhibitory segment of human cardiac troponin I (residues 134-147) resulted in the dissociation from F-actin of all the myosin peptides bound to it either individually or in combination. Troponin C neutralized the effect of the inhibitory peptide on the binding of the myosin peptides to F-actin. We conclude that the binding of the inhibitory region of troponin I to actin, which occurs during relaxation in muscle when the calcium concentration is low, imposes conformational changes that are propagated to different locations on the surface of actin. We suggest that the role of tropomyosin is to facilitate the transmission of structural changes along the F-actin filament so that the monomers within a structural unit are able to interact with myosin.

    The Journal of biological chemistry 2005;280;15;14469-75

  • 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

  • Effects of cardiomyopathic mutations on the biochemical and biophysical properties of the human alpha-tropomyosin.

    Hilario E, da Silva SL, Ramos CH and Bertolini MC

    Instituto de Química, UNESP, Departamento de Bioquímica e Tecnologia Química, Araraquara, São Paulo, Brazil.

    Mutations in the protein alpha-tropomyosin (Tm) can cause a disease known as familial hypertrophic cardiomyopathy. In order to understand how such mutations lead to protein dysfunction, three point mutations were introduced into cDNA encoding the human skeletal tropomyosin, and the recombinant Tms were produced at high levels in the yeast Pichia pastoris. Two mutations (A63V and K70T) were located in the N-terminal region of Tm and one (E180G) was located close to the calcium-dependent troponin T binding domain. The functional and structural properties of the mutant Tms were compared to those of the wild type protein. None of the mutations altered the head-to-tail polymerization, although slightly higher actin binding was observed in the mutant Tm K70T, as demonstrated in a cosedimentation assay. The mutations also did not change the cooperativity of the thin filament activation by increasing the concentrations of Ca2+. However, in the absence of troponin, all mutant Tms were less effective than the wild type in regulating the actomyosin subfragment 1 Mg2+ ATPase activity. Circular dichroism spectroscopy revealed no differences in the secondary structure of the Tms. However, the thermally induced unfolding, as monitored by circular dichroism or differential scanning calorimetry, demonstrated that the mutants were less stable than the wild type. These results indicate that the main effect of the mutations is related to the overall stability of Tm as a whole, and that the mutations have only minor effects on the cooperative interactions among proteins that constitute the thin filament.

    European journal of biochemistry 2004;271;20;4132-40

  • alpha-Tropomyosin mutations Asp(175)Asn and Glu(180)Gly affect cardiac function in transgenic rats in different ways.

    Wernicke D, Thiel C, Duja-Isac CM, Essin KV, Spindler M, Nunez DJ, Plehm R, Wessel N, Hammes A, Edwards RJ, Lippoldt A, Zacharias U, Strömer H, Neubauer S, Davies MJ, Morano I and Thierfelder L

    Max-Delbrück Center for Molecular Medicine, Robert-Roessle-Str. 10, Berlin 13092, Germany. dwernic@mdc-berlin.de

    To study the mechanisms by which missense mutations in alpha-tropomyosin cause familial hypertrophic cardiomyopathy, we generated transgenic rats overexpressing alpha-tropomyosin with one of two disease-causing mutations, Asp(175)Asn or Glu(180)Gly, and analyzed phenotypic changes at molecular, morphological, and physiological levels. The transgenic proteins were stably integrated into the sarcomere, as shown by immunohistochemistry using a human-specific anti-alpha-tropomyosin antibody, ARG1. In transgenic rats with either alpha-tropomyosin mutation, molecular markers of cardiac hypertrophy were induced. Ca(2+) sensitivity of cardiac skinned-fiber preparations from animals with mutation Asp(175)Asn, but not Glu(180)Gly, was decreased. Furthermore, elevated frequency and amplitude of spontaneous Ca(2+) waves were detected only in cardiomyocytes from animals with mutation Asp(175)Asn, suggesting an increase in intracellular Ca(2+) concentration compensating for the reduced Ca(2+) sensitivity of isometric force generation. Accordingly, in Langendorff-perfused heart preparations, myocardial contraction and relaxation were accelerated in animals with mutation Asp(175)Asn. The results allow us to propose a hypothesis of the pathogenetic changes caused by alpha-tropomyosin mutation Asp(175)Asn in familial hypertrophic cardiomyopathy on the basis of changes in Ca(2+) handling as a sensitive mechanism to compensate for alterations in sarcomeric structure.

    American journal of physiology. Regulatory, integrative and comparative physiology 2004;287;3;R685-95

  • Histidine-proline rich glycoprotein (HPRG) binds and transduces anti-angiogenic signals through cell surface tropomyosin on endothelial cells.

    Guan X, Juarez JC, Qi X, Shipulina NV, Shaw DE, Morgan WT, McCrae KR, Mazar AP and Doñate F

    Attenuon, LLC, San Diego, California 92121, USA.

    The anti-angiogenic properties of the histidine-proline-rich (H/P) domain of HPRG have recently been described (Juarez JC, et al. Cancer Research 2002; 62: 5344-50). However, the binding site that mediates these properties is unknown. HPRG is evolutionarily, functionally and structurally related to cleaved high molecular weight kininogen (HKa), an anti-angiogenic polypeptide that stimulates apoptosis of proliferating endothelial cells through binding to cell-surface tropomyosin (Zhang J-C, et al. Proc Natl Acad Sci USA 2002; 99: 12224-9). In this study, we demonstrate that HPRG binds with high affinity to FGF-2-stimulated human umbilical vein endothelial cells (HUVEC) and immobilized tropomyosin in a Zn2+ or pH-dependent manner, and that this interaction is mediated by the H/P domain of HPRG. At least two binding sites for HPRG, tropomyosin and heparan sulfate proteoglycans (HSPs), were identified on the surface of FGF-2-activated endothelial cells. Translocation of tropomyosin to the surface of HUVEC occurred in response to FGF-2, and the anti-angiogenic activity of HPRG in a Matrigel plug model was partially inhibited by soluble tropomyosin. These results suggest that HPRG binds to endothelial cell surface tropomyosin which at least partially mediates the antiangiogenic effects of HPRG.

    Thrombosis and haemostasis 2004;92;2;403-12

  • Alterations in tropomyosin isoform expression in human transitional cell carcinoma of the urinary bladder.

    Pawlak G, McGarvey TW, Nguyen TB, Tomaszewski JE, Puthiyaveettil R, Malkowicz SB and Helfman DM

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

    Previous studies of transformed rodent fibroblasts have suggested that specific isoforms of the actin-binding protein tropomyosin (TM) could function as suppressors of transformation, but an analysis of TM expression in patient tumor tissue is limited. The purpose of our study was to characterize expression of the different TM isoforms in human transitional cell carcinoma of the urinary bladder by immunohistochemistry and Western blot analysis. We found that TM1 and TM2 protein levels were markedly reduced and showed >60% reduction in 61% and 55% of tumor samples, respectively. TM5, which was expressed at very low levels in normal bladder mucosa, exhibited aberrant expression in 91% of tumor specimens. The Western blot findings were confirmed by immunohistochemical analysis in a number of tumors. We then investigated the mechanism underlying TM expression deregulation, in the T24 human bladder cancer cell line. We showed that levels of TM1, TM2 and TM3 are reduced in T24 cells, but significantly upregulated by inhibition of the mitogen-activated protein kinase-signaling pathway. In addition, inhibition of this pathway was accompanied by restoration of stress fibers. Overall, changes in TM expression levels seem to be an early event during bladder carcinogenesis. We conclude that alterations in TM isoform expression may provide further insight into malignant transformation in transitional cell carcinomas of the bladder and may be a useful target for early detection strategies.

    Funded by: NCI NIH HHS: CA83182

    International journal of cancer 2004;110;3;368-73

  • Transcriptome characterization elucidates signaling networks that control human ES cell growth and differentiation.

    Brandenberger R, Wei H, Zhang S, Lei S, Murage J, Fisk GJ, Li Y, Xu C, Fang R, Guegler K, Rao MS, Mandalam R, Lebkowski J and Stanton LW

    Geron Corporation, Menlo Park, California 94025, USA. rbrandenberger@geron.com

    Human embryonic stem (hES) cells hold promise for generating an unlimited supply of cells for replacement therapies. To characterize hES cells at the molecular level, we obtained 148,453 expressed sequence tags (ESTs) from undifferentiated hES cells and three differentiated derivative subpopulations. Over 32,000 different transcripts expressed in hES cells were identified, of which more than 16,000 do not match closely any gene in the UniGene public database. Queries to this EST database revealed 532 significantly upregulated and 140 significantly downregulated genes in undifferentiated hES cells. These data highlight changes in the transcriptional network that occur when hES cells differentiate. Among the differentially regulated genes are several components of signaling pathways and transcriptional regulators that likely play key roles in hES cell growth and differentiation. The genomic data presented here may facilitate the derivation of clinically useful cell types from hES cells.

    Nature biotechnology 2004;22;6;707-16

  • Complete sequencing and characterization of 21,243 full-length human cDNAs.

    Ota T, Suzuki Y, Nishikawa T, Otsuki T, Sugiyama T, Irie R, Wakamatsu A, Hayashi K, Sato H, Nagai K, Kimura K, Makita H, Sekine M, Obayashi M, Nishi T, Shibahara T, Tanaka T, Ishii S, Yamamoto J, Saito K, Kawai Y, Isono Y, Nakamura Y, Nagahari K, Murakami K, Yasuda T, Iwayanagi T, Wagatsuma M, Shiratori A, Sudo H, Hosoiri T, Kaku Y, Kodaira H, Kondo H, Sugawara M, Takahashi M, Kanda K, Yokoi T, Furuya T, Kikkawa E, Omura Y, Abe K, Kamihara K, Katsuta N, Sato K, Tanikawa M, Yamazaki M, Ninomiya K, Ishibashi T, Yamashita H, Murakawa K, Fujimori K, Tanai H, Kimata M, Watanabe M, Hiraoka S, Chiba Y, Ishida S, Ono Y, Takiguchi S, Watanabe S, Yosida M, Hotuta T, Kusano J, Kanehori K, Takahashi-Fujii A, Hara H, Tanase TO, Nomura Y, Togiya S, Komai F, Hara R, Takeuchi K, Arita M, Imose N, Musashino K, Yuuki H, Oshima A, Sasaki N, Aotsuka S, Yoshikawa Y, Matsunawa H, Ichihara T, Shiohata N, Sano S, Moriya S, Momiyama H, Satoh N, Takami S, Terashima Y, Suzuki O, Nakagawa S, Senoh A, Mizoguchi H, Goto Y, Shimizu F, Wakebe H, Hishigaki H, Watanabe T, Sugiyama A, Takemoto M, Kawakami B, Yamazaki M, Watanabe K, Kumagai A, Itakura S, Fukuzumi Y, Fujimori Y, Komiyama M, Tashiro H, Tanigami A, Fujiwara T, Ono T, Yamada K, Fujii Y, Ozaki K, Hirao M, Ohmori Y, Kawabata A, Hikiji T, Kobatake N, Inagaki H, Ikema Y, Okamoto S, Okitani R, Kawakami T, Noguchi S, Itoh T, Shigeta K, Senba T, Matsumura K, Nakajima Y, Mizuno T, Morinaga M, Sasaki M, Togashi T, Oyama M, Hata H, Watanabe M, Komatsu T, Mizushima-Sugano J, Satoh T, Shirai Y, Takahashi Y, Nakagawa K, Okumura K, Nagase T, Nomura N, Kikuchi H, Masuho Y, Yamashita R, Nakai K, Yada T, Nakamura Y, Ohara O, Isogai T and Sugano S

    Helix Research Institute, 1532-3 Yana, Kisarazu, Chiba 292-0812, Japan.

    As a base for human transcriptome and functional genomics, we created the "full-length long Japan" (FLJ) collection of sequenced human cDNAs. We determined the entire sequence of 21,243 selected clones and found that 14,490 cDNAs (10,897 clusters) were unique to the FLJ collection. About half of them (5,416) seemed to be protein-coding. Of those, 1,999 clusters had not been predicted by computational methods. The distribution of GC content of nonpredicted cDNAs had a peak at approximately 58% compared with a peak at approximately 42%for predicted cDNAs. Thus, there seems to be a slight bias against GC-rich transcripts in current gene prediction procedures. The rest of the cDNAs unique to the FLJ collection (5,481) contained no obvious open reading frames (ORFs) and thus are candidate noncoding RNAs. About one-fourth of them (1,378) showed a clear pattern of splicing. The distribution of GC content of noncoding cDNAs was narrow and had a peak at approximately 42%, relatively low compared with that of protein-coding cDNAs.

    Nature genetics 2004;36;1;40-5

  • Genetics of hypertrophic cardiomyopathy in eastern Finland: few founder mutations with benign or intermediary phenotypes.

    Jääskeläinen P, Miettinen R, Kärkkäinen P, Toivonen L, Laakso M and Kuusisto J

    Department of Medicine, University of Kuopio, Kuopio, Finland.

    Hypertrophic cardiomyopathy (HCM) is a genetically and clinically heterogeneous myocardial disease caused by mutations in genes encoding sarcomeric proteins. To assess the genetic background and phenotypic expression of HCM in eastern Finland, we screened 35 unrelated patients with HCM from the Kuopio University Hospital area for variants in 9 genes encoding sarcomeric proteins with the PCR-SSCP method. We herewith describe our previous findings in five sarcomeric genes and also report hitherto unpublished data on four additional sarcomeric genes. Mutations in the cardiac myosin-binding protein C gene (MYBPC3) were most frequent, accounting for 26% of cases. A novel mutation (Gln1061X) in this gene was the most common mutation, found in 6 of 35 families and accounting for 17% of all cases. Other novel mutations in MYBPC3 (IVS5-2A --> C, IVS14-13G --> A, and Ex25deltaLys) were found in one family each. A previously described alpha-tropomyosin (TPM1) mutation (Asp175Asn) was found in 11% of cases. Haplotype analysis suggested that the two most common variants (MYBPC3-Gln1061X and TPM1-Asp175Asn) were founder mutations. Only one mutation (Arg719Trp) in the beta-myosin heavy chain gene (MYH7) was found in one family, and no disease-causing mutations were found in the genes encoding alpha-actin, cardiac troponin I, T, C, or myosin essential and regulatory light chains. Altogether, the aforementioned 6 mutations found in MYBPC3, TPM1, and MYH7 accounted for 61% of familial and 40% of all HCM cases. The mutations were associated mostly with benign or intermediary phenotypes with only few HCM-related deaths. We conclude that the genetic profile of HCM in eastern Finland is unique, characterized by few founder mutations with benign or intermediary phenotypes.

    Annals of medicine 2004;36;1;23-32

  • Smooth muscle contraction and relaxation.

    Webb RC

    Department of Physiology, Medical College of Georgia, Augusta, Georgia 30912, USA. cwebb@mcg.edu

    This brief review serves as a refresher on smooth muscle physiology for those educators who teach in medical and graduate courses of physiology. Additionally, those professionals who are in need of an update on smooth muscle physiology may find this review to be useful. Smooth muscle lacks the striations characteristic of cardiac and skeletal muscle. Layers of smooth muscle cells line the walls of various organs and tubes in the body, and the contractile function of smooth muscle is not under voluntary control. Contractile activity in smooth muscle is initiated by a Ca(2+)-calmodulin interaction to stimulate phosphorylation of the light chain of myosin. Ca(2+) sensitization of the contractile proteins is signaled by the RhoA/Rho kinase pathway to inhibit the dephosphorylation of the light chain by myosin phosphatase, thereby maintaining force generation. Removal of Ca(2+) from the cytosol and stimulation of myosin phosphatase initiate the process of smooth muscle relaxation.

    Funded by: NHLBI NIH HHS: HL-18575, HL-71138

    Advances in physiology education 2003;27;1-4;201-6

  • Mutation spectrum in a large cohort of unrelated consecutive patients with hypertrophic cardiomyopathy.

    Erdmann J, Daehmlow S, Wischke S, Senyuva M, Werner U, Raible J, Tanis N, Dyachenko S, Hummel M, Hetzer R and Regitz-Zagrosek V

    Department of Internal Medicine II/Cardiology, University of Regensburg, Regensburg, Germany. jeanette.erdmann@klinik.uni-regensburg.de

    Defects in nine sarcomeric protein genes are known to cause hypertrophic cardiomyopathy (HCM). Mutation types and frequencies in large cohorts of consecutive and unrelated patients have not yet been determined. We, therefore, screened HCM patients for mutations in six sarcomeric genes: myosin-binding protein C3 (MYBPC3), MYH7, cardiac troponin T (TNNT2), alpha-tropomyosin (TPM1), cardiac troponin I (TNNI3), and cardiac troponin C (TNNC1). HCM was diagnosed in 108 consecutive patients by echocardiography (septum >15 mm, septal/posterior wall >1.3 mm), angiography, or based on a state after myectomy. Single-strand conformation polymorphism analysis was used for mutation screening, followed by DNA-sequencing. A total of 34 different mutations were identified in 108 patients: 18 mutations in MYBPC3 in 20 patients [intervening sequence (intron) 7 + 1G > A and Q1233X were found twice], 13 missense mutations in MYH7 in 14 patients (R807H was found twice), and one amino acid change in TPM1, TNNT2, and TNNI3, respectively. No disease-causing mutation was found in TNNC1. Cosegregation with the HCM phenotype could be demonstrated for 13 mutations (eight mutations in MYBPC3 and five mutations in MYH7). Twenty-eight of the 37 mutation carriers (76%) reported a positive family history with at least one affected first-grade relative; only eight mutations occurred sporadically (22%). MYBPC3 was the gene that most frequently caused HCM in our population. Systematic mutation screening in large samples of HCM patients leads to a genetic diagnosis in about 30% of unrelated index patients and in about 57% of patients with a positive family history.

    Clinical genetics 2003;64;4;339-49

  • Loss of expression of tropomyosin-1, a novel class II tumor suppressor that induces anoikis, in primary breast tumors.

    Raval GN, Bharadwaj S, Levine EA, Willingham MC, Geary RL, Kute T and Prasad GL

    Surgical Oncology and Vascular Surgery Services, Department of General Surgery, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.

    Suppression of tropomyosins (TMs), a family of actin-binding, microfilament-associated proteins, is a prominent feature of many transformed cells. Yet it is unclear whether downregulation of TMs occur in human tumors. We have investigated the expression of tropomyosin-1 (TM1) in human breast carcinoma tissues by in situ hybridization and immunofluorescence. TM1 mRNA and protein are readily detectable in normal mammary tissue. In contrast, TM1 expression is abolished in the primary human breast tumors. Expression of other TM isoforms, however, is variable among the tumors. The consistent and profound downregulation of TM1 suggests that TM1 may be a novel and useful biomarker of mammary neoplasms. These data also support the hypothesis that suppression of TM1 expression during the malignant conversion of mammary epithelium as a contributing factor of breast cancer. In support of this hypothesis, we show that the ability to suppress malignant growth properties of breast cancer cells is specific to TM1 isoform. Investigations into the mechanisms of TM1-induced tumor suppression reveal that TM1 induces anoikis (detachment induced apoptosis) in breast cancer cells. Downregulation of TM1 in breast tumors may destabilize microfilament architecture and confer resistance to anoikis, which facilitates survival of neoplastic cells outside the normal microenvironment and promote malignant growth.

    Oncogene 2003;22;40;6194-203

  • High-molecular-weight tropomyosins localize to the contractile rings of dividing CNS cells but are absent from malignant pediatric and adult CNS tumors.

    Hughes JA, Cooke-Yarborough CM, Chadwick NC, Schevzov G, Arbuckle SM, Gunning P and Weinberger RP

    Oncology Research Unit, Children's Hospital at Westmead, Australia.

    Tropomyosin has been implicated in the control of actin filament dynamics during cell migration, morphogenesis, and cytokinesis. In order to gain insight into the role of tropomyosins in cell division, we examined their expression in developing and neoplastic brain tissue. We found that the high-molecular-weight tropomyosins are downregulated at birth, which correlates with glial cell differentiation and withdrawal of most cells from the cell cycle. Expression of these isoforms was restricted to proliferative areas in the embryonic brain and was absent from the adult, where the majority of cells are quiescent. However, they were induced under conditions where glial cells became proliferative in response to injury. During cytokinesis, these tropomyosin isoforms were associated with the contractile ring. We also investigated tropomyosin expression in neoplastic CNS tissues. Low-grade astrocytic tumors expressed high-molecular-weight tropomyosins, while highly malignant CNS tumors of diverse origin did not (P </= 0.001). Furthermore, high-molecular-weight tropomyosins were absent from the contractile ring in highly malignant astrocytoma cells. Our findings suggest a role for high-molecular-weight tropomyosins in astrocyte cytokinesis, although highly malignant CNS tumors are still able to undergo cell division in their absence. Additionally, the correlation between high-molecular-weight tropomyosin expression and tumor grade suggests that tropomyosins are potentially useful as indicators of CNS tumor grade.

    Glia 2003;42;1;25-35

  • Extracellular signal-regulated kinase mediates phosphorylation of tropomyosin-1 to promote cytoskeleton remodeling in response to oxidative stress: impact on membrane blebbing.

    Houle F, Rousseau S, Morrice N, Luc M, Mongrain S, Turner CE, Tanaka S, Moreau P and Huot J

    Le Centre de Recherche en Cancérologie de l'Université Laval, L'Hôtel-Dieu de Québec, Québec G1R 2J6, Canada.

    Oxidative stress induces in endothelial cells a quick and transient coactivation of both stress-activated protein kinase-2/p38 and extracellular signal-regulated kinase (ERK) mitogen-activated protein kinases. We found that inhibiting the ERK pathway resulted, within 5 min of oxidative stress, in a misassembly of focal adhesions characterized by mislocalization of key proteins such as paxillin. The focal adhesion misassembly that followed ERK inhibition with the mitogen-activated protein kinase kinase (MEK) inhibitor PD098059 (2'-amino-3'-methoxyflavone) or with a kinase negative mutant of ERK in the presence of H(2)O(2) resulted in a quick and intense membrane blebbing that was associated with important damage to the endothelium. We isolated by two-dimensional gel electrophoresis a PD098059-sensitive phosphoprotein of 38 kDa that we identified, by mass spectrometry, as tropomyosin-1. In fact, H(2)O(2) induced a time-dependent phosphorylation of tropomyosin that was sensitive to inhibition by PD098059 and UO126 (1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio]butanediane). Tropomyosin phosphorylation was also induced by expression of a constitutively activated form of MEK1 (MEK(CA)), which confirms that its phosphorylation resulted from the activation of ERK. In unstimulated cells, tropomyosin-1 was found diffuse in the cells, whereas it quickly colocalized with actin and stress fibers upon stimulation of ERK by H(2)O(2) or by expression of MEK(CA). We propose that phosphorylation of tropomyosin-1 downstream of ERK by contributing to formation of actin filaments increases cellular contractility and promotes the formation of focal adhesions. Incidentally, ML-7 (1-[5iodonaphthalene-1-sulfonyl]homopiperazine, HCl), an inhibitor of cell contractility, inhibited phosphorylation of tropomyosin and blocked the formation of stress fibers and focal adhesions, which also led to membrane blebbing in the presence of oxidative stress. Our finding that tropomyosin-1 is phosphorylated downstream of ERK, an event that modulates its interaction with actin, may lead to further understanding of the role of this protein in regulating cellular functions associated with cytoskeletal remodeling.

    Molecular biology of the cell 2003;14;4;1418-32

  • Polycystin-2 associates with tropomyosin-1, an actin microfilament component.

    Li Q, Dai Y, Guo L, Liu Y, Hao C, Wu G, Basora N, Michalak M and Chen XZ

    Membrane Protein Research Group, Department of Physiology, University of Alberta, 7-29 Medical Sciences Building, T6G 2H7, Edmonton, AB, Canada.

    Polycystin-2 (PC2) is the product of the second cloned gene (PKD2) responsible for autosomal dominant polycystic kidney disease and has recently been shown to be a calcium-permeable cation channel. PC2 has been shown to connect indirectly with the actin microfilament. Here, we report a direct association between PC2 and the actin microfilament. Using a yeast two-hybrid screen, we identified a specific interaction between the PC2 cytoplasmic C-terminal domain and tropomyosin-1 (TM-1), a component of the actin microfilament complex. Tropomyosins constitute a protein family of more than 20 isoforms arising mainly from alternative splicing and are present in muscle as well as non-muscle cells. We identified a new TM-1 splicing isoform in kidney and heart (TM-1a) that differs from TM-1 in the C terminus and interacted with PC2. In vitro biochemical methods, including GST pull-down, blot overlay and microtiter binding assays, confirmed the interaction between PC2 and the two TM-1 isoforms. Further experiments targeted the interacting domains to G821-R878 of PC2 and A152-E196, a common segment of TM-1 and TM-1a. Indirect double immunofluorescence experiments showed partial co-localization of PC2 and TM-1 in transfected mouse fibroblast NIH 3T3 cells. Co-immunoprecipitation (co-IP) studies using 3T3 cells and Xenopus oocytes co-expressing PC2 and TM-1 (or TM-1a) revealed in vivo association between the protein pairs. Furthermore, the in vivo interaction between the endogenous PC2 and TM-1 was demonstrated also by reciprocal co-IP using native human embryonic kidney cells and human adult kidney. Considering previous reports that TM-1 acts as a suppressor of neoplastic growth of transformed cells, it is possible that TM-1 contributes to cyst formation/growth when the anchorage of PC2 to the actin microfilament via TM-1 is altered.

    Journal of molecular biology 2003;325;5;949-62

  • What is the role of tropomyosin in the regulation of muscle contraction?

    Perry SV

    Department of Physiology, Medical School, University of Birmingham, Edgbaston, UK.

    Journal of muscle research and cell motility 2003;24;8;593-6

  • Prevalence and severity of "benign" mutations in the beta-myosin heavy chain, cardiac troponin T, and alpha-tropomyosin genes in hypertrophic cardiomyopathy.

    Van Driest SL, Ackerman MJ, Ommen SR, Shakur R, Will ML, Nishimura RA, Tajik AJ and Gersh BJ

    Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Clinic, Rochester, Minn 55905, USA.

    Background: Genotype-phenotype correlative studies have implicated 8 particular mutations that cause hypertrophic cardiomyopathy (HCM) as "benign defects," associated with near-normal survival: N232S, G256E, F513C, V606M, R719Q, and L908V of beta-myosin heavy chain (MYH7); S179F of troponin T (TNNT2); and D175N of alpha-tropomyosin (TPM1). Routine genetic screening of HCM patients for specific mutations is anticipated to provide important diagnostic and prognostic information. The frequency and associated phenotype of these mutations in a large, unselected cohort of HCM is unknown.

    A total of 293 unrelated HCM patients were genotyped for the presence of a benign mutation. DNA was obtained after informed consent; specific MHY7, TNNT2, and TPM1 fragments were amplified by polymerase chain reaction; and the mutations were detected by denaturing high-performance liquid chromatography and automated DNA sequencing. Only 5 (1.7%) of the 293 patients possessed a benign mutation. Moreover, all 5 subjects with an ascribed benign mutation had already manifested clinically severe expression of HCM, with all 5 requiring surgical myectomy, 3 of the 5 having a family history of sudden cardiac death, and 1 adolescent requiring an orthotopic heart transplant.

    Conclusions: These findings demonstrate the rarity of specific mutations in HCM and challenge the notion of mutation-specific clinical outcomes. Fewer than 2% of the subjects harbored a benign mutation, and those patients with a benign mutation experienced a very serious clinical course.

    Funded by: NICHD NIH HHS: HD42569

    Circulation 2002;106;24;3085-90

  • Tropomyosin-1, a novel suppressor of cellular transformation is downregulated by promoter methylation in cancer cells.

    Bharadwaj S and Prasad GL

    Department of General Surgery, Medical Center Boulevard, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.

    Tropomyosins (TMs) are a family of microfilament binding proteins, which are suppressed in the transformed cells. We have investigated the mechanism of suppression of TMs, in particular that of tropomyosin-1 (TM1), in breast cancer cells. Inhibition of DNA methyl transferase with 5-aza-2'-deoxycytidine (AZA) alone did not induce TM1 expression. However, combined treatment of trichostatin A (TSA) and AZA resulted in readily detectable expression of TM1, but not that of other TM isoforms. Upregulation of TM1 expression paralleled with the reemergence of TM1 containing microfilaments, and in abolition of anchorage-independent growth. The synergistic action of AZA and TSA in reactivation of TM1 gene was also evident in ras-transformed fibroblasts. These data, for the first time, show that hypermethylation of TM1 gene and chromatin remodeling are the predominant mechanisms by which TM1 expression is downregulated in breast cancer cells.

    Cancer letters 2002;183;2;205-13

  • Cardiac dysfunction in hypertrophic cardiomyopathy mutant tropomyosin mice is transgene-dependent, hypertrophy-independent, and improved by beta-blockade.

    Michele DE, Gomez CA, Hong KE, Westfall MV and Metzger JM

    Department of Physiology, University of Michigan, Ann Arbor, Mich 48109-0622, USA.

    Familial hypertrophic cardiomyopathy (FHC) has been linked to mutations in proteins of the cardiac contractile apparatus, including alpha-tropomyosin (Tm). Mice expressing alphaTm in the heart were developed to determine the effects of FHC mutant Tm on cardiac structure and function from single cardiac myocytes to whole organ function in vivo. Expression of E180G mutant Tm did not produce cardiac hypertrophy or detectable changes in cardiac muscle morphology. However, E180G mutant Tm expression increased the Ca2+ sensitivity of force production in single cardiac myocytes in a transgene expression-dependent manner. Contractile dysfunction in single myocytes manifested organ level dysfunction, as conductance-micromanometry showed E180G Tm mice had significantly slowed relaxation (diastolic dysfunction) under physiological conditions. The diastolic dysfunction in E180G Tm mice was no longer evident during beta-blockade because propranolol eliminated the effect of E180G Tm to slow myocardial relaxation. Cellular and organ level dysfunction were evident in E180G Tm mice in the absence of significant cardiac structural abnormalities normally associated with FHC. These findings therefore suggest that diastolic dysfunction in FHC may be a direct consequence of FHC mutant protein expression. In addition, because diastolic dysfunction in E180G Tm mice is dependent on inotropic status, cardiovascular stress may play an important role in FHC pathogenesis.

    Circulation research 2002;91;3;255-62

  • Tropomyosin requires an intact N-terminal coiled coil to interact with tropomodulin.

    Greenfield NJ and Fowler VM

    University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway, New Jersey 08854-5635, USA. greenfie@rwja.umdnj.edu

    Tropomodulins (Tmods) are tropomyosin (TM) binding proteins that bind to the pointed end of actin filaments and modulate thin filament dynamics. They bind to the N termini of both "long" TMs (with the N terminus encoded by exon 1a of the alpha-TM gene) and "short" nonmuscle TMs (with the N terminus encoded by exon 1b). In this present study, circular dichroism was used to study the interaction of two designed chimeric proteins, AcTM1aZip and AcTM1bZip, containing the N terminus of a long or a short TM, respectively, with protein fragments containing residues 1 to 130 of erythrocyte or skeletal muscle Tmod. The binding of either TMZip causes similar conformational changes in both Tmod fragments promoting increases in both alpha-helix and beta-structure, although they differ in binding affinity. The circular dichroism changes in the Tmod upon binding and modeling of the Tmod sequences suggest that the interface between TM and Tmod includes a three- or four-stranded coiled coil. An intact coiled coil at the N terminus of the TMs is essential for Tmod binding, as modifications that disrupt the N-terminal helix, such as removal of the N-terminal acetyl group from AcTM1aZip or striated muscle alpha-TM, or introduction of a mutation that causes nemaline myopathy, Met-8-Arg, into AcTM1aZip destroyed Tmod binding.

    Funded by: NHLBI NIH HHS: HL-35726; NIGMS NIH HHS: GM-36326, GM34225

    Biophysical journal 2002;82;5;2580-91

  • Cluster analysis of an extensive human breast cancer cell line protein expression map database.

    Harris RA, Yang A, Stein RC, Lucy K, Brusten L, Herath A, Parekh R, Waterfield MD, O'Hare MJ, Neville MA, Page MJ and Zvelebil MJ

    Ludwig Institute for Cancer Research/University College London Breast Cancer Laboratory, UK.

    In the current study, the protein expression maps (PEMs) of 26 breast cancer cell lines and three cell lines derived from normal breast or benign disease tissue were visualised by high resolution two-dimensional gel electrophoresis. Analysis of this data was performed with ChiClust and ChiMap, two analytical bioinformatics tools that are described here. These tools are designed to facilitate recognition of specific patterns shared by two or more (a series) PEMs. Both tools use PEMs that were matched by an image analysis program and locally written programs to create a match table that is saved in an object relational database. The ChiClust tool uses clustering and subclustering methods to extract statistically significant protein expression patterns from a large series of PEMs. The ChiMap tool calculates a differential value (either as percentage change or a fold change) and represents these graphically. All such differentials or just those identified using ChiClust can be submitted to ChiMap. These methods are not dependent on any particular commercial image analysis program, and the whole software package gives an integrated procedure for the comparison and analysis of a series of PEMs. The ChiClust tool was used here to order the breast cell lines into groups according to biological characteristics including morphology in vitro and tumour forming ability in vivo. ChiMap was then used to highlight eight major protein feature-changes detected between breast cancer cell lines that either do or do not proliferate in nude mice. Mass spectrometry was used to identify the proteins. The possible role of these proteins in cancer is discussed.

    Proteomics 2002;2;2;212-23

  • Deciphering the design of the tropomyosin molecule.

    Brown JH, Kim KH, Jun G, Greenfield NJ, Dominguez R, Volkmann N, Hitchcock-DeGregori SE and Cohen C

    Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02454-9110, USA.

    The crystal structure at 2.0-A resolution of an 81-residue N-terminal fragment of muscle alpha-tropomyosin reveals a parallel two-stranded alpha-helical coiled-coil structure with a remarkable core. The high alanine content of the molecule is clustered into short regions where the local 2-fold symmetry is broken by a small (approximately 1.2-A) axial staggering of the helices. The joining of these regions with neighboring segments, where the helices are in axial register, gives rise to specific bends in the molecular axis. We observe such bends to be widely distributed in two-stranded alpha-helical coiled-coil proteins. This asymmetric design in a dimer of identical (or highly similar) sequences allows the tropomyosin molecule to adopt multiple bent conformations. The seven alanine clusters in the core of the complete molecule (which spans seven monomers of the actin helix) promote the semiflexible winding of the tropomyosin filament necessary for its regulatory role in muscle contraction.

    Funded by: NHLBI NIH HHS: HL35726; NIAMS NIH HHS: 1R01-AR46524-01, AR17346, R01 AR017346, R01 AR046524, R37 AR017346; NIGMS NIH HHS: GM36326, R01 GM036326

    Proceedings of the National Academy of Sciences of the United States of America 2001;98;15;8496-501

  • Mutations that alter the surface charge of alpha-tropomyosin are associated with dilated cardiomyopathy.

    Olson TM, Kishimoto NY, Whitby FG and Michels VV

    Department of Pediatrics, Division of Cardiology and Biochemistry, University of Utah, Salt Lake City, UT 84113, USA. olson.timothy@mayo.edu

    Proteins in cardiac myocytes assemble into contractile units known as sarcomeres. Contractile force is generated by interaction between sarcomeric thick and thin filaments. Thin filaments also transmit force within and between myocytes. Mutations in genes encoding the thin filament proteins actin and tropomyosin cause hypertrophic cardiomyopathy. Mutations affecting functionally distinct domains of actin also cause dilated cardiomyopathy (DCM). We used a non-positional candidate gene approach to test further the hypothesis that dysfunction of sarcomeric thin filaments, due to different mutations in the same gene, can lead to either hypertrophic or dilated cardiomyopathy. Mutational analyses of alpha-tropomyosin 1 were performed in patients with idiopathic DCM. We identified two mutations that alter highly conserved residues and that, unlike hypertrophic cardiomyopathy-associated mutations, cause localized charge reversal on the surface of tropomyosin. Therefore, substitution of different amino acid residues in the same thin filament proteins is associated with the distinct phenotypes of cardiac hypertrophy or congestive heart failure.

    Journal of molecular and cellular cardiology 2001;33;4;723-32

  • Hypertrophic cardiomyopathy caused by a novel alpha-tropomyosin mutation (V95A) is associated with mild cardiac phenotype, abnormal calcium binding to troponin, abnormal myosin cycling, and poor prognosis.

    Karibe A, Tobacman LS, Strand J, Butters C, Back N, Bachinski LL, Arai AE, Ortiz A, Roberts R, Homsher E and Fananapazir L

    Department of Medicine, Baylor College of Medicine, Houston, TX, USA.

    Background: We report hypertrophic cardiomyopathy (HCM) in a Spanish-American family caused by a novel alpha-tropomyosin (TPM1) mutation and examine the pathogenesis of the clinical disease by characterizing functional defects in the purified mutant protein.

    HCM was linked to the TPM1 gene (logarithm of the odds [LOD] score 3.17). Sequencing and restriction digestion analysis demonstrated a TPM1 mutation V95A that cosegregated with HCM. The mutation has been associated with 13 deaths in 26 affected members (11 sudden deaths and 2 related to heart failure), with a cumulative survival rate of 73+/-10% at the age of 40 years. Left ventricular wall thickness (mean 16+/-6 mm) and disease penetrance (53%) were similar to those for the ss-myosin mutations L908V and G256E previously associated with a benign prognosis. Left ventricular hypertrophy was milder than with the ss-myosin mutation R403Q, but the prognosis was similarly poor. With the use of recombinant tropomyosins, we identified several functional alterations at the protein level. The mutation caused a 40% to 50% increase in calcium affinity in regulated thin filament-myosin subfragment-1 (S1) MgATPase assays, a 20% decrease in MgATPase rates in the presence of saturating calcium, a 5% decrease in unloaded shortening velocity in in vitro motility assays, and no change in cooperative myosin S1 binding to regulated thin filaments.

    Conclusions: In contrast to other reported TPM1 mutations, V95A-associated HCM exhibits unusual features of mild phenotype but poor prognosis. Both myosin cycling and calcium binding to troponin are abnormal in the presence of the mutant tropomyosin. The genetic diagnosis afforded by this mutation will be valuable in the management of HCM.

    Funded by: NHLBI NIH HHS: HL-63774; NIAMS NIH HHS: AR-30988

    Circulation 2001;103;1;65-71

  • Vertebrate tropomyosin: distribution, properties and function.

    Perry SV

    Department of Physiology, Medical School, University of Birmingham, Edgbaston.

    Tropomyosin (TM) is widely distributed in all cell types associated with actin as a fibrous molecule composed of two alpha-helical chains arranged as a coiled-coil. It is localised, polymerised end to end, along each of the two grooves of the F-actin filament providing structural stability and modulating the filament function. To accommodate the wide range of functions associated with actin filaments that occur in eucaryote cells TM exists in a large number isoforms, over 20 of which have been identified. These isoforms which are expressed by alternative promoters and alternative RNA processing of four genes, TPM1, 2, 3 and 4, all conform to a general pattern of structure. Their amino acid sequences consist of an integral number, six or seven in vertebrates, of quasiequivalent regions of about 40 residues that are considered to represent the actin-binding regions of the molecule. In addition to the variable regions a large part of the polypeptide chains of the TM isoforms, mainly centrally located and expressed by five exons, is invariant. Many of the isoforms are tissue and filament specific in their distribution implying that the exons expressed in them and the regions of the molecule they represent are of significance for the function of the filament system with which they are associated. In the case of muscle there is clear evidence that the TM moves its position on the F-actin filament during contraction and it is therefore considered to play an important part in the regulation of the process. It is uncertain how the role of TM in muscle compares to that in non-muscle systems and if its function in the former tissue is unique to muscle.

    Journal of muscle research and cell motility 2001;22;1;5-49

  • A nonerythroid isoform of protein 4.1R interacts with components of the contractile apparatus in skeletal myofibers.

    Kontrogianni-Konstantopoulos A, Huang SC and Benz EJ

    Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.

    The approximately 80-kDa erythroid 4.1R protein is a major component of the erythrocyte cytoskeleton, where it links transmembrane proteins to the underlying spectrin/actin complexes. A diverse collection of 4.1R isoforms has been described in nonerythroid cells, ranging from approximately 30 to approximately 210 kDa. In the current study, we identified the number and primary structure of 4.1R isoforms expressed in adult skeletal muscle and characterized the localization patterns of 4.1R message and protein. Skeletal muscle 4.1R appears to originate solely from the upstream translation initiation codon (AUG-1) residing in exon 2'. Combinations of alternatively spliced downstream exons generate an array of distinct 4.1R spliceoforms. Two major isoform classes of approximately 105/110 and approximately 135 kDa are present in muscle homogenates. 4.1R transcripts are distributed in highly ordered signal stripes, whereas 4.1R protein(s) decorate the sarcoplasm in transverse striations that are in register with A-bands. An approximately 105/110-kDa 4.1R isoform appears to occur in vivo in a supramolecular complex with major sarcomeric proteins, including myosin, alpha-actin, and alpha-tropomyosin. In vitro binding assays showed that 4.1R may interact directly with the aforementioned contractile proteins through its 10-kDa domain. All of these observations suggest a topological model whereby 4.1R may play a scaffolding role by anchoring the actomyosin myofilaments and possibly modulating their displacements during contraction/relaxation.

    Funded by: NHLBI NIH HHS: HL 44985, R01 HL044985

    Molecular biology of the cell 2000;11;11;3805-17

  • Refined localization of the human alpha-tropomyosin gene (TPM1) by genetic mapping.

    Mogensen J, Kruse TA and Børglum AD

    Department of Cardiology and Research Unit for Molecular Medicine, Skejby University Hospital, Arhus N, Denmark. skejjm@aau.dk

    Cytogenetics and cell genetics 1999;84;1-2;35-6

  • The cardiac beta-myosin heavy chain gene is not the predominant gene for hypertrophic cardiomyopathy in the Finnish population.

    Jääskeläinen P, Soranta M, Miettinen R, Saarinen L, Pihlajamäki J, Silvennoinen K, Tikanoja T, Laakso M and Kuusisto J

    Department of Medicine, University of Kuopio, Finland.

    Objectives: The aim of the study was to screen 36 unrelated patients with hypertrophic cardiomyopathy (HCM; 16 familial and 20 sporadic cases) from a genetically homogeneous area in eastern Finland for variants in the cardiac beta-myosin heavy chain (beta-MHC) and alpha-tropomyosin (alpha-TM) genes.

    Background: Mutations in the beta-MHC and alpha-TM genes have been reported to be responsible for 30% to 40% and less than 5% of familial HCM cases, respectively. However, most genetic studies have included patients from tertiary care centers and are subject to referral bias.

    Methods: Exons 3-26 and 40 of the beta-MHC gene and the nine exons of the alpha-TM gene were screened with the PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism) method. Linkage analyses between familial HCM locus and two intragenic polymorphic markers (MYO I and MYO II) of the beta-MHC gene were performed in 16 familial HCM kindreds.

    Results: A previously reported Arg719Trp (arginine converted to tryptophan in codon 719) mutation of the beta-MHC gene was found in one proband and two relatives. In addition, a novel Asn696Ser (asparagine converted to serine in codon 696) substitution was found in one HCM patient. No linkage between familial HCM and the beta-MHC gene was observed in 16 familial kindreds. A previously reported Aspl75Asn (aspartic acid converted to asparagine in codon 175) mutation of the alpha-TM gene was found in four probands and 16 relatives. Mutations in the beta-MHC and alpha-TM genes accounted for 6% and 25% familial HCM cases and 3% and 11% of all cases, respectively.

    Conclusions: Our results indicate that the beta-MHC gene is not the predominant gene for HCM in the Finnish population, whereas HCM caused by the Aspl75Asn mutation of the a-TM gene is more common than previously reported.

    Journal of the American College of Cardiology 1998;32;6;1709-16

  • Actin and tropomyosin isoforms in morphogenesis.

    Gunning P, Weinberger R and Jeffrey P

    Cell Biology Unit, Children's Medical Research Institute, Wentworthville, NSW, Australia.

    The major components of the actin microfilament system, actin and tropomyosin (Tm), are encoded by multigene families. There are at least 6 actin and over 20 Tm isoforms in mammals. The observation that isoforms are expressed in a tissue-specific manner has encouraged the hypothesis that they contribute to the formation of cell type-specific structures. Recent studies have indicated that certain specific isoforms do play unique structural roles. One nonmuscle actin isoform, beta, is implicated in the regulation of cell spreading and membrane organisation. The intracellular location of beta-actin mRNA has been shown to be regulated by growth factor stimulation of signal transduction pathways. Actin isoforms have also been shown to differ in their contractile properties in both muscle and non-muscle cells. Tropomyosins have been found to show isoform specific regulation in response to cell transformation. This has correlated with the view that some isoforms of tropomyosin promote filament stability whereas others are associated with more dynamic structures. Neuronal development and maturation are accompanied by dynamic spatial sorting of tropomyosin isoforms into different cellular compartments. It is now apparent that isoforms of these proteins perform different structural tasks. The challenge is now to link the significance of spatial sorting to the different physicochemical properties of these isoforms.

    Anatomy and embryology 1997;195;4;311-5

  • Ca2+-dependent interaction of S100A2 with muscle and nonmuscle tropomyosins.

    Gimona M, Lando Z, Dolginov Y, Vandekerckhove J, Kobayashi R, Sobieszek A and Helfman DM

    Cold Spring Harbor Laboratory, NY 11724, USA.

    Zero-length chemical crosslinking with 1-ethyl-3-[3-(dimethyl amino)propyl]carbodiimide (EDC) indicated an association of the Ca2+-binding protein S100A2 with tropomyosin (TM) in vitro. The mobility of the crosslinked product on SDS-PAGE gels indicated the formation of a 1:1 complex between S100A2 and TM and the interaction was Ca2+ dependent. Monoclonal antibodies were raised against S100A2 and used to determine its cellular localization in the porcine epithelial cell line LLC PK1. It was found that the localization of S100A2 depended on the differentiation state of the cells, being absent from actin stress fibers in sparsely seeded cultures, but present in the actin-containing microvilli characteristic of differentiated cells. Immunoprecipitations of [35S]methionine-labeled extracts using S100A2 as well as TM-specific antibodies failed to co-precipitate TM and S100A2, indicating a transient association between these two molecules in solution. Affinity chromatography of cell extracts on immobilized recombinant TMs, however, confirmed the Ca2+-dependent interaction between S100A2 and both muscle TMs as well as with high and low molecular mass nonmuscle TMs, suggesting that the binding site resides in one of the conserved regions of TM. Our data demonstrate the possible interaction of S100A2 with TM that is not bound to the microfilaments and indicate a differentiation-related function for S100A2 in LLC PK1 cells. The possible functional implications of this interaction are discussed.

    Funded by: NCI NIH HHS: CA45508, CA58607

    Journal of cell science 1997;110 ( Pt 5);611-21

  • Fine mapping of five human skeletal muscle genes: alpha-tropomyosin, beta-tropomyosin, troponin-I slow-twitch, troponin-I fast-twitch, and troponin-C fast.

    Tiso N, Rampoldi L, Pallavicini A, Zimbello R, Pandolfo D, Valle G, Lanfranchi G and Danieli GA

    Biology Department, University of Padova, Italy.

    In this paper the chromosomal localization of the human skeletal muscle genes Troponin-I slow-twitch (TNNI1), Troponin-I fast-twitch (TNNI2), and Troponin-C fast (TNNC2) and the refinement of the position for alpha-Tropomyosin (TPM1) and beta-Tropomyosin (TPM2) are reported. By radiation hybrid mapping, TPM1 was assigned to chromosome 15q22.1, TPM2 to chromosome 9p13.2-p13.1, TNNI1 to chromosome 1q31.3, TNNI2 to chromosome 11p15.5, and TNNC2 to chromosome 20q12-q13.11. The genomic distribution of these genes is discussed, with particular emphasis on the cluster organization of the Troponin genes.

    Biochemical and biophysical research communications 1997;230;2;347-50

  • Interaction of deletion mutants of troponins I and T: COOH-terminal truncation of troponin T abolishes troponin I binding and reduces Ca2+ sensitivity of the reconstituted regulatory system.

    Jha PK, Leavis PC and Sarkar S

    Department of Anatomy and Cellular Biology, Tufts University Health Science Campus, Boston, Massachusetts 02111, USA.

    The interaction between troponin I (TnI) and troponin T (TnT) remains the least understood binary interaction among the regulatory proteins of vertebrate striated muscle. To identify the specific binding domains of TnI and TnT and to evaluate the interactions of TnT with troponin C and tropomyosin (Tm), we generated an NH2-terminal fragment of human fast skeletal beta TnT (TnT1-201; residues 1-201) using site-directed mutagenesis. The mutant protein failed to bind to rabbit skeletal muscle TnI as judged by HPLC, showed reduced TnC binding and reduced ternary troponin (Tn) complex formation, and exhibited a much reduced Ca2+ sensitivity in the reconstituted regulatory system. It is shown that the amount of Tn complex formed by TnT1-201 rather than the activity of the mutant Tn complex affected this Ca2+ sensitivity. Binding of the mutant to Tm was similar to that of intact TnT. These results support the view that the COOH-terminal segment of TnT is necessary for binding to TnI and TnC and Ca2+ sensitivity in the thin filament, whereas its NH2-terminus strongly binds to Tm. To identify the regions of TnI which bind to muscle TnT, we used four recombinant fragments of fast skeletal muscle TnI containing amino acid residues 1-94 (TnI1-94), 1-120 (TnI1-120), 96-181 (TnI96-181), and 122-181 (TnI122-181) and a synthetic peptide, TnI98-114, containing residues 98-114 corresponding to the inhibitory region. Only TnI1-120 showed weak binding to TnT but not to TnT1-201. These results suggest that (i) a region within the NH2-terminal 120 residues of TnI interacts with TnT and (ii) the COOH-terminal residues 202-258 of TnT contain the interaction site of TnI. Overall, our results also imply that residues 159-201 constitute the smallest region of TnT which contributes to the Ca2+ sensitivity of actoS1 ATPase in a reconstituted regulatory system.

    Biochemistry 1996;35;51;16573-80

  • N-tropomodulin: a novel isoform of tropomodulin identified as the major binding protein to brain tropomyosin.

    Watakabe A, Kobayashi R and Helfman DM

    Cold Spring Harbor Laboratory, NY 11724, USA.

    We have identified and characterized two proteins in rat brain that bind to the neuron-specific tropomyosin isoform, TMBr3. The two proteins were identified by blot overlay assay, in which the proteins immobilized on the membrane were probed by epitope-tagged TMBr3, followed by detection with anti-epitope antibody. We have purified these proteins using a TMBr3 affinity column. Peptide sequencing as well as immunoblotting showed that one of the two proteins is identical to tropomodulin, a tropomyosin-binding protein originally identified in erythrocytes. The cDNA for the other protein was cloned from an adult rat brain cDNA library using degenerate oligonucleotides that we designed based on the peptide sequences. Sequence analysis of the cDNA clone revealed this protein to be a novel isoform of tropomodulin which is the product of a distinct gene, and is herein referred to as N-tropomodulin. Recombinant N-tropomodulin bound to TMBr3 as well as to other low molecular mass tropomyosins (TM5a or TM5), but not to high molecular mass tropomyosins (TM2 or TMBr1). Northern blotting and RNase protection assays as well as immunoblotting showed that N-tropomodulin is expressed predominantly in brain. Furthermore, RNase protection assays revealed no alternatively spliced regions within the coding sequence. Developmentally, N-tropomodulin was detected in rat brain as early as embryonic day 14 and reaches the adult level before birth. Immunofluorescence of primary frontal cortex cell cultures showed that N-tropomodulin is specifically expressed in neurons. The neuron-specific expression of N-tropomodulin strongly suggests specialized roles of this TM-binding protein in neurons.

    Funded by: NCI NIH HHS: CA45508, CA58607

    Journal of cell science 1996;109 ( Pt 9);2299-310

  • Specificity of dimer formation in tropomyosins: influence of alternatively spliced exons on homodimer and heterodimer assembly.

    Gimona M, Watakabe A and Helfman DM

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

    Tropomyosins consist of nearly 100% alpha-helix and assemble into parallel and in-register coiled-coil dimers. In vitro it has been established that nonmuscle as well as native muscle tropomyosins can form homodimers. However, a mixture of muscle alpha and beta tropomyosin subunits results in the formation of the thermodynamically more stable alpha/beta heterodimer. Although the assembly preference of the muscle tropomyosin heterodimer can be understood thermodynamically, the presence of multiple tropomyosin isoforms expressed in nonmuscle cells points toward a more complex principle for determining dimer formation. We have investigated the dimerization of rat tropomyosins in living cells by the use of epitope tagging with a 16-aa sequence of the influenza hemagglutinin. Employing transfection and immunoprecipitation techniques, we have analyzed the dimers formed by muscle and nonmuscle tropomyosins in rat fibroblasts. We demonstrate that the information for homo- versus heterodimerization is contained within the tropomyosin molecule itself and that the information for the selectivity is conferred by the alternatively spliced exons. These results have important implications for models of the regulation of cytoskeletal dynamics.

    Funded by: NCI NIH HHS: CA58607

    Proceedings of the National Academy of Sciences of the United States of America 1995;92;21;9776-80

  • Novel missense mutation in alpha-tropomyosin gene found in Japanese patients with hypertrophic cardiomyopathy.

    Nakajima-Taniguchi C, Matsui H, Nagata S, Kishimoto T and Yamauchi-Takihara K

    Department of Medicine III, Osaka University Medical School, Japan.

    We have searched for mutations in alpha-tropomyosin gene in 50 Japanese patients with hypertrophic cardiomyopathy (HCM) by means of polymerase chain reaction (PCR)-single strand conformation polymorphism (SSCP) analysis. Two missense mutations of the alpha-tropomyosin gene were detected in Japanese patients with familial HCM. Sequencing analysis revealed a C to T transition at codon 63 leading to a replacement of Ala with Val residue, and a G to A transition with replacement of Asp by Asn at codon 175. These missense mutations were found at residues which were markedly conserved across the species, and have been reported to interact with troponin T. This is the first report on a mutant alpha-tropomyosin gene in a Japanese population. Familial HCM is a genetically heterogeneous disease in Japanese patients, similar to that reported in Caucasian kindreds.

    Journal of molecular and cellular cardiology 1995;27;9;2053-8

  • Mutations in the genes for cardiac troponin T and alpha-tropomyosin in hypertrophic cardiomyopathy.

    Watkins H, McKenna WJ, Thierfelder L, Suk HJ, Anan R, O'Donoghue A, Spirito P, Matsumori A, Moravec CS, Seidman JG et al.

    Howard Hughes Medical Institute, Boston, MA.

    Background: Familial hypertrophic cardiomyopathy can be caused by mutations in the genes for beta cardiac myosin heavy chain, alpha-tropomyosin, or cardiac troponin T. It is not known how often the disease is caused by mutations in the tropomyosin and troponin genes, and the associated clinical phenotypes have not been carefully studied.

    Methods: Linkage between polymorphisms of the alpha-tropomyosin gene or the cardiac troponin T gene and hypertrophic cardiomyopathy was assessed in 27 families. In addition, 100 probands were screened for mutations in the alpha-tropomyosin gene, and 26 were screened for mutations in the cardiac troponin T gene. Life expectancy, the incidence of sudden death, and the extent of left ventricular hypertrophy were compared in patients with different mutations.

    Results: Genetic analyses identified only one alpha-tropomyosin mutation, identical to one previously described. Five novel mutations in cardiac troponin were identified, as well as a further example of a previously described mutation. The clinical phenotype of four troponin T mutations in seven unrelated families was similar and was characterized by a poor prognosis (life expectancy, approximately 35 years) and a high incidence of sudden death. The mean (+/- SD) maximal thickness of the left ventricular wall in subjects with cardiac troponin T mutations (16.7 +/- 5.5 mm) was significantly less than that in subjects with beta cardiac myosin heavy-chain mutations (23.7 +/- 7.7 mm, P < 0.001).

    Conclusions: Mutations in alpha-tropomyosin are a rare cause of familial hypertrophic cardiomyopathy, accounting for approximately 3 percent of cases. Mutations in cardiac troponin T account for approximately 15 percent of cases of familial hypertrophic cardiomyopathy in this referral-center population. These mutations are characterized by relatively mild and sometimes subclinical hypertrophy but a high incidence of sudden death. Genetic testing may therefore be especially important in this group.

    Funded by: Telethon: 600

    The New England journal of medicine 1995;332;16;1058-64

  • Assignment of the human skeletal muscle alpha-tropomyosin gene (TPM1) to band 15q22 by fluorescence in situ hybridization.

    Eyre H, Akkari PA, Wilton SD, Callen DC, Baker E and Laing NG

    Department of Cytogenetics and Molecular Genetics, Women's and Children's Hospital, North Adelaide, Australia.

    A sequence-tagged site (STS) was developed for the human skeletal muscle alpha-tropomyosin gene (TPM1) and used to isolate a genomic clone, lambda TPM1.1, containing part of the TPM1 gene. Fluorescence in situ hybridization of this clone to metaphase chromosome spreads localised TPM1 to chromosome band 15q22. This localisation in humans is consistent with that recently described for the mouse.

    Cytogenetics and cell genetics 1995;69;1-2;15-7

  • Alpha-tropomyosin and cardiac troponin T mutations cause familial hypertrophic cardiomyopathy: a disease of the sarcomere.

    Thierfelder L, Watkins H, MacRae C, Lamas R, McKenna W, Vosberg HP, Seidman JG and Seidman CE

    Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115.

    We demonstrate that missense mutations (Asp175Asn; Glu180Gly) in the alpha-tropomyosin gene cause familial hypertrophic cardiomyopathy (FHC) linked to chromosome 15q2. These findings implicated components of the troponin complex as candidate genes at other FHC loci, particularly cardiac troponin T, which was mapped in this study to chromosome 1q. Missense mutations (Ile79Asn; Arg92Gln) and a mutation in the splice donor sequence of intron 15 of the cardiac troponin T gene are also shown to cause FHC. Because alpha-tropomyosin and cardiac troponin T as well as beta myosin heavy chain mutations cause the same phenotype, we conclude that FHC is a disease of the sarcomere. Further, because the splice site mutation is predicted to function as a null allele, we suggest that abnormal stoichiometry of sarcomeric proteins can cause cardiac hypertrophy.

    Funded by: NHLBI NIH HHS: HL42467, HL46320; Wellcome Trust

    Cell 1994;77;5;701-12

  • [Analysis of the diversity of tropomyosin isoforms].

    Balvay L and Fiszman MY

    INSERM U 153, Groupe Hospitalier Pitié-Salpêtrière, Paris.

    Tropomyosins are a family of actin filament binding proteins. Like many structural proteins, tropomyosin isoform expression involves the use of multiple genes, but diversity is to a large extent generated by alternative processing of RNA. The tropomyosin family consists of 15 to 20 different protein isoforms which are coded by four genes. Each of these genes code for multiple proteins ranging from two up to as many as nine different isoforms. These genes have been named alpha CTM, alpha FTM, alpha STM and beta TM after to the striated muscle specific subunit of tropomyosin which they code. Their multiple coding potential is based upon the existence of multiple exons associated with initiation of transcription, multiple exons associated with polyadenylation signals and multiple mutually exclusive internal exons which are alternatively spliced. The regulation of this process of alternative splicing have been extensively studied both in the case of exons 2a/2b of the alpha FTM gene and in the case of exons 6a/6b of the beta TM gene. In both cases, one exon is specifically used in one type of muscle tissue, exon 2a is smooth muscle specific and exon 6b is skeletal muscle specific. In both cases, alternative splicing involves a combination of negative regulation, on exon 2b in smooth muscle and on exon 6b in non muscle tissues, and of competition in the alternative situation.

    Comptes rendus des seances de la Societe de biologie et de ses filiales 1994;188;5-6;527-40

  • A familial hypertrophic cardiomyopathy locus maps to chromosome 15q2.

    Thierfelder L, MacRae C, Watkins H, Tomfohrde J, Williams M, McKenna W, Bohm K, Noeske G, Schlepper M, Bowcock A et al.

    Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115.

    We report that a gene responsible for familial hypertrophic cardiomyopathy (FHC) in a kindred with a mild degree of cardiac hypertrophy maps to chromosome 15q2. The gene encoding cardiac actin, located on chromosome 15q, was analyzed and excluded as a candidate for FHC at this locus. Two additional families with typical FHC were studied and the disorder in one also maps to the chromosome 15q2 locus. The maximum combined multipoint logarithm of odds score in the two linked families is 6.02. Although these two kindreds reside in the same country, we believe that their disorder is caused by independent mutations in the 15q2 locus because of the clinical and genotypic differences between affected individuals. Mutations in at least four loci can cause FHC: chromosomes 14q1 (beta cardiac myosin heavy chain gene), 1q3, and 15q2 and another unidentified locus, suggesting substantial genetic heterogeneity.

    Funded by: NHGRI NIH HHS: HG00461; NHLBI NIH HHS: HL41474, HL46320

    Proceedings of the National Academy of Sciences of the United States of America 1993;90;13;6270-4

  • Cleavage of human and mouse cytoskeletal and sarcomeric proteins by human immunodeficiency virus type 1 protease. Actin, desmin, myosin, and tropomyosin.

    Shoeman RL, Sachse C, Höner B, Mothes E, Kaufmann M and Traub P

    Max-Planck-Institut für Zellbiologie, Ladenburg, Federal Republic of Germany.

    HeLa cell actin was cleaved by human immunodeficiency virus type 1 protease when in its soluble, globular form (G-actin). No cleavage of the polymerized, filamentous form of actin (F-actin) was observed when examined by denaturing gel electrophoresis; however, electron microscopy revealed a low level of cleavage of F-actin. Immunoblotting of mouse skeletal and human pectoral muscle myofibrils treated in vitro with human immunodeficiency virus type 1 protease showed that myosin heavy chain, desmin, tropomyosin, and a fraction of the actin were all cleaved. Electron microscopy of these myofibrils demonstrated changes consistent with cleavage of these proteins: Z-lines were rapidly lost, the length of the A bands was shortened, and the thick filaments (myosin filaments) were often laterally frayed such that the structures disintegrated. Nonmuscle myosin heavy chains were also cleaved by this enzyme in vitro. These data demonstrate that this protease can cause alterations in muscle cell ultrastructure in vitro that may be of clinical relevance in infected individuals.

    The American journal of pathology 1993;142;1;221-30

  • Human fibroblast tropomyosin isoforms: characterization of cDNA clones and analysis of tropomyosin isoform expression in human tissues and in normal and transformed cells.

    Novy RE, Lin JL, Lin CS and Lin JJ

    Department of Biological Sciences, University of Iowa, Iowa City 52242-1324.

    A tropomyosin-specific oligonucleotide probe (REN29) designed to hybridize to all known human tropomyosin isoforms was used to study tropomyosin mRNA levels in normal and transformed human cells. At least four different sizes of RNAs were detected in normal human fibroblast KD cells by Northern blot analysis. The major bands of 1.1 kb RNA for hTM1 and 3.0 kb RNA for hTM4 were decreased substantially in various transformed cell lines. One of the minor RNA bands (2.0 kb for hTM2 and hTM3) appeared to be absent in a human pancreatic carcinoma cell line. The level of the other minor RNA band (2.5 kb for hTM5) was found to be unchanged or slightly decreased in transformed cells. This differential expression of tropomyosin isoforms at the RNA level was not totally in agreement with the difference in the protein amounts found in normal and transformed cells, suggesting that translational control may also play an important role in the expression of some tropomyosin isoforms. The REN29 probe was further used to screen lambda gt10 and lambda gt11 cDNA libraries, which were constructed from poly(A)+ RNAs of human fibroblast cell lines HuT-14 and WI-38, respectively. In addition to cDNA clones encoding known isoforms, we obtained three classes of new cDNA clones that encode two low M(r) isoforms (hTM5a and hTM5b), and a high M(r) isoform (hTMsm alpha). Sequence comparison revealed that hTM5a and hTM5b are alternatively spliced products derived from the same gene that encodes hTM2 and hTM3. Northern blot analysis and amino acid sequence comparison suggested that the hTMsm alpha represents a smooth muscle tropomyosin which is also expressed in human fibroblasts. The exon specific for, and common to, hTM5a and hTM5b was found to be highly expressed in small intestine. However, there was no detectable expression of this exon in stomach and skeletal muscle. The difference in tissue-specific expression suggests that different isoforms may perform distinct functions in different tissues.

    Funded by: NICHD NIH HHS: HD18577; NIGMS NIH HHS: GM40580

    Cell motility and the cytoskeleton 1993;25;3;267-81

  • Protein interaction cloning in yeast: identification of mammalian proteins that react with the leucine zipper of Jun.

    Chevray PM and Nathans D

    Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205.

    To identify proteins that interact with Jun or Fos we have used the protein interaction cloning system developed by S. Fields and O.-K. Song [(1989) Nature (London) 340, 245-246] to clone mammalian cDNAs encoding polypeptides that interact with the dimerization and DNA-binding motif (bZIP; basic domain leucine zipper motif) of Jun. For this purpose, yeast cells lacking GAL4 activity but expressing a GAL4 DNA-binding domain-Jun bZIP fusion protein were transformed with a mouse embryo cDNA plasmid library in which the cDNA was joined to a gene segment encoding the GAL4 transcriptional activation domain. Several transformants exhibiting GAL4 activity were identified and shown to harbor plasmids encoding polypeptides predicted to form coiled-coil structures with Jun and/or Fos. One of these is a bZIP protein of the ATF/CREB protein family--probably the murine homolog of TAXREB67. Two others encode polypeptides with predicted potential to form coiled-coil structures, and seven other isolates encode segments of alpha- or beta-tropomyosin, classical coiled-coil proteins. The tropomyosin polypeptides were found to interact in the yeast assay system with the bZIP region of Jun but not with the bZIP region of Fos. Our results illustrate the range of protein interaction cloning for discovering proteins that bind to a given target polypeptide.

    Funded by: NCI NIH HHS: P01 CA16519-16; NIGMS NIH HHS: GM07309

    Proceedings of the National Academy of Sciences of the United States of America 1992;89;13;5789-93

  • Degradation of cytoskeletal proteins by the human immunodeficiency virus type 1 protease.

    Höner B, Shoeman RL and Traub P

    Max-Planck-Institut für Zellbiologie, Ladenburg/Heidelberg, FRG.

    Triton X-100-extracted human skin fibroblasts were exposed to human immunodeficiency virus type 1 protease and analysed by 2D-gel electrophoresis and immunofluorescence microscopy. Vimentin, two of the tropomyosin isoforms, a protein with M(r) approximately 90,000 and a protein with M(r) approximately 200,000 were found to be degraded. Structurally, this was accompanied by the disintegration of the vimentin filament network and the disappearance of the microfilament network. In contrast to our in vivo observations (Höner et al., 1991), prominent stress fibers and chromatin structure seemed to be rather resistant to the action of this protease.

    Cell biology international reports 1992;16;7;603-12

  • The molecular basis for tropomyosin isoform diversity.

    Lees-Miller JP and Helfman DM

    Cold Spring Harbor Laboratory, New York, NY 11724.

    The tropomyosins are a family of actin filament binding proteins. In multicellular animals, they exhibit extensive cell type specific isoform diversity. In this essay we discuss the genetic mechanisms by which this diversity is generated and its possible significance to cellular function.

    BioEssays : news and reviews in molecular, cellular and developmental biology 1991;13;9;429-37

  • Non-viral cellular substrates for human immunodeficiency virus type 1 protease.

    Shoeman RL, Kesselmier C, Mothes E, Höner B and Traub P

    Max-Planck-Institut für Zellbiologie, Ladenburg/Heidelberg, Germany.

    A computer search revealed 10 proteins with homology to the sequence we originally identified in vimentin as the site of cleavage by human immunodeficiency virus type 1 (HIV-1) protease. Of these 10 proteins (actin, alpha-actinin, spectrin, tropomyosins, vinculin, dystrophin, MAP-2, villin, TRK-1 and Ig mu-chain), we show that 4 of the first 5 were cleaved in vitro by this protease, as are MAP-1 and -2 [(1990) J. Gen. Virol. 71, 1985-1991]. In these proteins, cleavage is not restricted to a single motif, but occurs at many sites. However, cleavage is not random, since 9 other proteins including the cytoskeletal proteins filamin and band 4.1 are not cleaved in the in vitro assay. Thus, the ability of HIV-1 protease to cleave specific components of the cytoskeleton may be an important, although as yet unevaluated aspect of the life cycle of this retrovirus and/or may directly contribute to the pathogenesis observed during infection.

    FEBS letters 1991;278;2;199-203

  • Smooth muscle calponin. Inhibition of actomyosin MgATPase and regulation by phosphorylation.

    Winder SJ and Walsh MP

    Department of Medical Biochemistry, University of Calgary, Alberta, Canada.

    Calponin isolated from chicken gizzard smooth muscle inhibits the actin-activated MgATPase activity of smooth muscle myosin in a reconstituted system composed of contractile and regulatory proteins. ATPase inhibition is not due to inhibition of myosin phosphorylation since, at calponin concentrations sufficient to cause maximal ATPase inhibition, myosin phosphorylation was unaffected. Furthermore, calponin inhibited the actin-activated MgATPase of fully phosphorylated or thiophosphorylated myosin. Although calponin is a Ca2(+)-binding protein, inhibition did not require Ca2+. Furthermore, although calponin also binds to tropomyosin, ATPase inhibition was not dependent on the presence of tropomyosin. Calponin was phosphorylated in vitro by protein kinase C and Ca2+/calmodulin-dependent protein kinase II, but not by cAMP- or cGMP-dependent protein kinases, or myosin light chain kinase. Phosphorylation of calponin by either kinase resulted in loss of its ability to inhibit the actomyosin ATPase. The phosphorylated protein retained calmodulin and tropomyosin binding capabilities, but actin binding was greatly reduced. The calponin-actin interaction, therefore, appears to be responsible for inhibition of the actomyosin ATPase. These observations suggest that calponin may be involved in regulating actin-myosin interaction and, therefore, the contractile state of smooth muscle. Calponin function in turn is regulated by Ca2(+)-dependent phosphorylation.

    The Journal of biological chemistry 1990;265;17;10148-55

  • The amino terminus of muscle tropomyosin is a major determinant for function.

    Cho YJ, Liu J and Hitchcock-DeGregori SE

    Department of Anatomy, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, Piscataway.

    The amino-terminal region of muscle tropomyosin is highly conserved among muscle and 284-residue non-muscle tropomyosins. Analysis of fusion and nonfusion striated alpha-tropomyosins and a mutant in which residues 1-9 have been deleted has shown that the amino terminus is crucial for function. The presence of 80 amino acids of a nonstructural influenza virus protein (NS1) on the amino terminus of tropomyosin allows magnesium-independent binding of tropomyosin to actin. The fusion tropomyosin inhibits the actomyosin S1 ATPase at all myosin S1 concentrations tested, indicating that the presence of the fusion peptide prevents myosin S1 from switching the actin filament from the inhibited to the potentiated state. Nonfusion tropomyosin, an unacetylated form, has no effect on the actomyosin S1 ATPase, though it regulates normally with troponin. Deletion of residues 1-9, which are believed to overlap with the carboxyl-terminal end of tropomyosin in the thin filament, results in loss of tropomyosin function. The mutant is unable to bind to actin, in the presence and absence of troponin, and it has no regulatory function. The removal of the first 9 residues of tropomyosin is much more deleterious than removal of the last 11 by carboxypeptidase digestion. We suggest that the structure of the amino-terminal region and acetylation of the initial methionine are crucial for tropomyosin function.

    Funded by: NHLBI NIH HHS: HL35726

    The Journal of biological chemistry 1990;265;1;538-45

  • Cloning and characterization of a cDNA encoding transformation-sensitive tropomyosin isoform 3 from tumorigenic human fibroblasts.

    Lin CS and Leavitt J

    Armand Hammer Cancer Research Center, Linus Pauling Institute of Science and Medicine, Palo Alto, California 94306.

    We isolated a cDNA clone from the tumorigenic human fibroblast cell line HuT-14 that contains the entire protein coding region of tropomyosin isoform 3 (Tm3) and 781 base pairs of 5'- and 3'-untranslated sequences. Tm3, despite its apparent smaller molecular weight than Tm1 in two-dimensional gels, has the same peptide length as Tm1 (284 amino acids) and shares 83% homology with Tm1. Tm3 cDNA hybridized to an abundant mRNA of 1.3 kilobases in fetal muscle and cardiac muscle, suggesting that Tm3 is related to an alpha fast-tropomyosin. The first 188 amino acids of Tm3 are identical to those of rat or rabbit skeletal muscle alpha-tropomyosin, and the last 71 amino acids differ from those of rat smooth muscle alpha-tropomyosin by only 1 residue. Tm3 therefore appears to be encoded by the same gene that encodes the fast skeletal muscle alpha-tropomyosin and the smooth muscle alpha-tropomyosin via an alternative RNA-splicing mechanism. In contrast to Tm4 and Tm5, Tm3 has a small gene family, with, at best, only one pseudogene.

    Funded by: NCI NIH HHS: CA-34763

    Molecular and cellular biology 1988;8;1;160-8

  • Human hTM alpha gene: expression in muscle and nonmuscle tissue.

    MacLeod AR and Gooding C

    Ludwig Institute for Cancer Research, MRC Centre, Cambridge, United Kingdom.

    We have isolated a cDNA clone from a human skeletal muscle library which contains the complete protein-coding sequence of a skeletal muscle alpha-tropomyosin. This cDNA sequence defines a fourth human tropomyosin gene, the hTM alpha gene, which is distinct from the hTMnm gene encoding a closely related isoform of skeletal muscle alpha-tropomyosin. In cultured human fibroblasts, the hTM alpha gene encodes both skeletal-muscle- and smooth-muscle-type alpha-tropomyosins by using an alternative mRNA-splicing mechanism.

    Molecular and cellular biology 1988;8;1;433-40

  • Evolution of tropomyosin functional domains: differential splicing and genomic constraints.

    Colote S, Widada JS, Ferraz C, Bonhomme F, Marti J and Liautard JP

    INSERM U-249, CRBM du CNRS, Université de Montpellier I, France.

    We have cloned and determined the nucleotide sequence of a complementary DNA (cDNA) encoded by a newly isolated human tropomyosin gene and expressed in liver. Using the least-square method of Fitch and Margoliash, we investigated the nucleotide divergences of this sequence and those published in the literature, which allowed us to clarify the classification and evolution of the tropomyosin genes expressed in vertebrates. Tropomyosin undergoes alternative splicing on three of its nine exons. Analysis of the exons not involved in differential splicing showed that the four human tropomyosin genes resulted from a duplication that probably occurred early, at the time of the amphibian radiation. The study of the sequences obtained from rat and chicken allowed a classification of these genes as one of the types identified for humans. The divergence of exons 6 and 9 indicates that functional pressure was exerted on these sequences, probably by an interaction with proteins in skeletal muscle and perhaps also in smooth muscle; such a constraint was not detected in the sequences obtained from nonmuscle cells. These results have led us to postulate the existence of a protein in smooth muscle that may be the counterpart of skeletal muscle troponin. We show that different kinds of functional pressure were exerted on a single gene, resulting in different evolutionary rates and different convergences in some regions of the same molecule. Codon usage analysis indicates that there is no strict relationship between tissue types (and hence the tRNA precursor pool) and codon usage. G + C content is characteristic of a gene and does not change significantly during evolution.(ABSTRACT TRUNCATED AT 250 WORDS)

    Journal of molecular evolution 1988;27;3;228-35

  • The effects of troponin T fragments T1 and T2 on the binding of nonpolymerizable tropomyosin to F-actin in the presence and absence of troponin I and troponin C.

    Heeley DH, Golosinska K and Smillie LB

    Using a nonpolymerizable form of tropomyosin (NPTM) we have investigated the interactions between the T1 (residues 1-158) and T2 (residues 159-259) regions of troponin T and the other components of the thin filament at 50 mM KCl +/- Ca2+. Under these conditions the binding of NPTM to F-actin is fully restored by whole troponin (+/- Ca2+), and in each case, retains a residual degree of cooperativity as demonstrated by Scatchard and Hill plots. Fragment T2 alone had a small inductive effect on the interaction of NPTM with F-actin. In the presence of troponin I, this interaction is increased to a level which exceeds that observed with either component alone. The effects of T2 and troponin I are moderately (-Ca2+) and markedly (+Ca2+) reduced by troponin C. While fragment T1 alone did not promote induction, it accentuated the effects of T2 and troponin I. Since T1 does not interact with T2 or troponin I but does interact weakly with the NH2 terminus of tropomyosin and can be expected to bind weakly at the residual interaction site(s) at the COOH terminus of NPTM, the observed effects of T1 have been ascribed to the linking of neighboring NPTM molecules at their ends.

    The Journal of biological chemistry 1987;262;21;9971-8

  • Relation of streptococcal M protein with human and rabbit tropomyosin: the complete amino acid sequence of human cardiac alpha tropomyosin, a highly conserved contractile protein.

    Mische SM, Manjula BN and Fischetti VA

    Partial sequences of group A streptococcal M proteins exhibit up to 50% sequence identity with segments of rabbit skeletal tropomyosin. It is well recognized that rheumatic fever and rheumatic heart disease in humans are sequelae of group A streptococcal infection. To examine whether the human cardiac tropomyosin would exhibit greater homology with the streptococcal M proteins, we have now determined its complete amino acid sequence. The amino acid sequence of human cardiac tropomyosin was established from sequence analyses of its peptides derived by enzymic and chemical cleavages, and comparison of these sequences to the reported sequence of rabbit skeletal tropomyosin. These studies have revealed that the amino acid sequence of human cardiac alpha tropomyosin is identical to that of the rabbit skeletal alpha tropomyosin, but for a single conservative substitution of Arg/Lys at position 220. This observation increases the significance of the previously observed sequence homology between streptococcal M protein and rabbit skeletal tropomyosin and may have relevance to the pathogenesis of rheumatic fever. Furthermore, these results rank tropomyosin as one of the most highly conserved contractile proteins between vertebrate species reported thus far.

    Funded by: NHLBI NIH HHS: HL25219, HL36025; NIAID NIH HHS: AI11822

    Biochemical and biophysical research communications 1987;142;3;813-8

  • Renaturation of skeletal muscle tropomyosin: implications for in vivo assembly.

    Brown HR and Schachat FH

    The observation that the alpha beta heterodimer is the predominant species of tropomyosin in rabbit skeletal muscles has led to the suggestion that this species assembles preferentially. To understand the molecular basis of this assembly process, we have studied renaturation under conditions that favor heterodimer formation. When skeletal muscle tropomyosin composed of equal amounts of alpha and beta subunits is renatured either by cooling or by dialysis a distribution that favors homodimers is generated. In contrast, rapid renaturation by dilution from urea favors the heterodimer. Further analysis of this latter renaturation procedure with cysteine-cleavage fragments of tropomyosin using circular dichroic measurements shows that as few as 30 residues in the NH2-terminal third of each tropomyosin subunit are involved in the initial interaction that results in heterodimer formation. Based on the density of sequence substitutions between the alpha and beta subunits, that region probably includes residues 36-64.

    Funded by: NINDS NIH HHS: NS 18228

    Proceedings of the National Academy of Sciences of the United States of America 1985;82;8;2359-63

  • Interactions among chymotryptic troponin T subfragments, tropomyosin, troponin I and troponin C.

    Tanokura M and Ohtsuki I

    The binding of various combinations of chymotryptic troponin T subfragments, troponin I and troponin C to tropomyosin, troponin C and troponin I was examined semiquantitatively by using affinity chromatography. The interaction between troponin T2 and troponin I intensified the interaction between troponin T2 (or troponin T) and tropomyosin. When a mixture of troponin T2 and troponin C was applied to a tropomyosin-Sepharose 4B column, neither troponin T2 nor troponin C was retained in the presence of Ca2+ ion, while only troponin T2 was bound in the absence of Ca2+ ion. Such a Ca2+-dependent effect was not observed with troponin T. Troponin T2 subfragments, except troponin T2 beta III, were retained by troponin C-Sepharose 4B in the presence of troponin I, even in the solution containing 1.0 M NaCl, in the presence and absence of Ca2+ ion. On the basis of these findings, the interactions among troponin components and tropomyosin are discussed.

    Journal of biochemistry 1984;95;5;1417-21

  • Effects of troponin-I plus-C on the binding of troponin-T and its fragments to alpha-tropomyosin. Ca2+ sensitivity and cooperativity.

    Pearlstone JR and Smillie LB

    The binding of troponin-I to tropomyosin, as well as its effects on the binding of troponin-T and its fragments T1 (residues 1-158) and T2 (residues 159-259) to tropomyosin, have been studied using immobilized alpha-tropomyosin. When applied alone, troponin-I exhibited weak interaction with tropomyosin and was eluted with a NaCl gradient at 0.12 M. Intact troponin-T was eluted at 0.40 M NaCl, while its fragment T1 was eluted from site 1 (near the COOH terminus of tropomyosin) at 0.32 M, independently from T2, which was eluted from site 2 (near Cys-190) at 0.22 M NaCl. However, the simultaneous presence of troponin-I and T2 resulted in formation of a strong troponin-I/T2/tropomyosin ternary complex at site 2 such that troponin-I/T2 complex was now eluted at 0.45 to 0.5 M NaCl. This binding was Ca2+-sensitive in the presence of troponin-C. An additional effect of troponin-I binding at site 2 was the strengthening of the T1/tropomyosin interaction at site 1, such that T1 was now eluted at the higher value of 0.45 to 0.50 M NaCl. Troponin-I also enhanced the binding of intact troponin-T to tropomyosin. These results suggest that cooperativity exists between the two sites, presumably induced by the binding of troponin-I to tropomyosin and mediated by a conformational change in the latter.

    The Journal of biological chemistry 1983;258;4;2534-42

  • Specific phosphorylation at serine-283 of alpha tropomyosin from frog skeletal and rabbit skeletal and cardiac muscle.

    Mak A, Smillie LB and Bárány M

    Tropomyosin, extracted from the leg muscle of frogs that had been injected with [32P]orthophosphate, was fractionated into two components, alpha and beta, on a CM-cellulose column. Radioactivity was associated only with the alpha component. A single phosphorylation site was located at serine-283 (pentultimate at the COOH-terminal end) of the frog alpha tropomyosin. The same phosphorylated peptide was recovered in low yields from both rabbit skeletal alpha and cardiac tropomyosin. The presence of covalently bound phosphate in alpha tropomyosin and its absence in the beta component of rabbit skeletal muscle was suggested by 31P NMR spectroscopy. The amino acid sequences around the phosphorylation sites of frog and rabbit tropomyosin are identical. Because this sequence is not similar to any other known phosphorylation site in proteins, this indicates the existence of either specific kinase or phosphatase that can distinguish between alpha and beta tropomyosins. In a model proposed for the head-to-tail overlap of alpha tropomyosin molecules, one O-phosphoserine-283 residue could form a salt linkage with lysine-6 on one side of the overlap region and another with lysine-12 on the other side. This would predict a difference in the stability of polymers of phosphorylated and nonphosphorylated alphaalpha and alphabeta dimers of tropomyosin.

    Proceedings of the National Academy of Sciences of the United States of America 1978;75;8;3588-92

Gene lists (6)

Gene List Source Species Name Description Gene count
L00000009 G2C Homo sapiens Human PSD Human orthologues of mouse PSD adapted from Collins et al (2006) 1080
L00000016 G2C Homo sapiens Human PSP Human orthologues of mouse PSP adapted from Collins et al (2006) 1121
L00000059 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-CONSENSUS Human cortex PSD consensus 748
L00000061 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-CONSENSUS Mouse cortex PSD consensus (ortho) 984
L00000069 G2C Homo sapiens BAYES-COLLINS-HUMAN-PSD-FULL Human cortex biopsy PSD full list 1461
L00000071 G2C Homo sapiens BAYES-COLLINS-MOUSE-PSD-FULL Mouse cortex PSD full list (ortho) 1556
© G2C 2014. The Genes to Cognition Programme received funding from The Wellcome Trust and the EU FP7 Framework Programmes:
EUROSPIN (FP7-HEALTH-241498), SynSys (FP7-HEALTH-242167) and GENCODYS (FP7-HEALTH-241995).

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