title: Angiotensin II and the ERK pathway mediate the induction of myocardin by hypoxia in cultured rat neonatal cardiomyocytes.
abstract: Hypoxic injury to cardiomyocytes is a stress that causes cardiac pathology through cardiac-restricted gene expression. SRF (serum-response factor) and myocardin are important for cardiomyocyte growth and differentiation in response to myocardial injuries. Previous studies have indicated that AngII (angiotensin II) stimulates both myocardin expression and cardiomyocyte hypertrophy. In the present study, we evaluated the expression of myocardin and AngII after hypoxia in regulating gene transcription in neonatal cardiomyocytes. Cultured rat neonatal cardiomyocytes were subjected to hypoxia, and the expression of myocardin and AngII were evaluated. Different signal transduction pathway inhibitors were used to identify the pathway(s) responsible for myocardin expression. An EMSA (electrophoretic mobility-shift assay) was used to identify myocardin/SRF binding, and a luciferase assay was used to identify transcriptional activity of myocardin/SRF in neonatal cardiomyocytes. Both myocardin and AngII expression increased after hypoxia, with AngII appearing at an earlier time point than myocardin. Myocardin expression was stimulated by AngII and ERK (extracellular-signal-regulated kinase) phosphorylation, but was suppressed by an ARB (AngII type 1 receptor blocker), an ERK pathway inhibitor and myocardin siRNA (small interfering RNA). AngII increased both myocardin expression and transcription in neonatal cardiomyocytes. Binding of myocardin/SRF was identified using an EMSA, and a luciferase assay indicated the transcription of myocardin/SRF in neonatal cardiomyocytes. Increased BNP (B-type natriuretic peptide), MHC (myosin heavy chain) and [(3)H]proline incorporation into cardiomyocytes was identified after hypoxia with the presence of myocardin in hypertrophic cardiomyocytes. In conclusion, hypoxia in cardiomyocytes increased myocardin expression, which is mediated by the induction of AngII and the ERK pathway, to cause cardiomyocyte hypertrophy. Myocardial hypertrophy was identified as an increase in transcriptional activities, elevated hypertrophic and cardiomyocyte phenotype markers, and morphological hypertrophic changes in cardiomyocytes.
authors.affiliation: Graduate Institute of Clinical Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors.forename: Chiung-Zuan
authors.initials: CZ
authors.lastname: Chiu
authors.forename: Bao-Wei
authors.initials: BW
authors.lastname: Wang
authors.forename: Tun-Hui
authors.initials: TH
authors.lastname: Chung
authors.forename: Kou-Gi
authors.initials: KG
authors.lastname: Shyu
mesh_terms: D000804:Angiotensin II / Q000502:physiology*; D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D048049:Extracellular Signal-Regulated MAP Kinases / Q000502:physiology*; D006352:Heart Ventricles / Q000473:pathology; D006984:Hypertrophy; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D009687:Nuclear Proteins / Q000096:biosynthesis* / Q000235:genetics; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D026362:Serum Response Factor / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics; D014158:Transcription, Genetic; D000099251:Myocardin
chemical_list: D000804:Angiotensin II; D048049:Extracellular Signal-Regulated MAP Kinases; D009687:Nuclear Proteins; D012333:RNA, Messenger; D026362:Serum Response Factor; D015534:Trans-Activators; D000099251:Myocardin
references.citation: Cardiovasc Pathol. 2007 Nov-Dec;16(6):329-35
references.pmid: 18005871
references.citation: Genes Dev. 2006 Jun 15;20(12):1545-56
references.pmid: 16778073
references.citation: Circ J. 2006 Jun;70(6):787-92
references.pmid: 16723804
references.citation: Nat Cell Biol. 2004 Jun;6(6):499-506
references.pmid: 15146194
references.citation: J Mol Cell Cardiol. 2003 Jun;35(6):577-93
references.pmid: 12788374
references.citation: Mol Cell. 2001 Jul;8(1):1-2
references.pmid: 11511353
references.citation: Clin Genet. 2008 Jan;73(1):71-8
references.pmid: 18028454
references.citation: Circ Res. 2006 Apr 28;98(8):1089-97
references.pmid: 16556869
references.citation: Circ Res. 2004 Aug 20;95(4):340-2
references.pmid: 15321943
references.citation: Regul Pept. 2004 Aug 15;120(1-3):5-13
references.pmid: 15177915
references.citation: Hypertens Res. 2007 Dec;30(12):1219-30
references.pmid: 18344628
references.citation: Mol Cell Biol. 2005 Apr;25(8):3173-81
references.pmid: 15798203
references.citation: J Biol Chem. 1996 Feb 9;271(6):3213-20
references.pmid: 8621723
references.citation: Am J Cardiol. 1999 Jun 17;83(12A):53H-57H
references.pmid: 10750588
references.citation: Circulation. 2007 Oct 30;116(18):2018-28
references.pmid: 17938287
references.citation: Cell. 2001 Jun 29;105(7):851-62
references.pmid: 11439182
references.citation: Clin Sci (Lond). 2003 Oct;105(4):447-56
references.pmid: 12780343
references.citation: J Appl Physiol (1985). 2004 Feb;96(2):765-73
references.pmid: 14715686
references.citation: FASEB J. 2007 Oct;21(12):3369-79
references.pmid: 17579192
references.citation: J Mol Cell Cardiol. 2002 Oct;34(10):1293-6
references.pmid: 12392987
references.citation: Circ Res. 2004 Apr 30;94(8):1075-82
references.pmid: 15016729
references.citation: J Mol Med (Berl). 2003 Sep;81(9):566-77
references.pmid: 12920479
references.citation: Circ Res. 2006 Apr 28;98(8):985-7
references.pmid: 16645146
references.citation: J Biol Chem. 2004 Dec 31;279(53):55626-32
references.pmid: 15492011
references.citation: Can J Physiol Pharmacol. 2005 Oct;83(10):869-75
references.pmid: 16333359
references.citation: Circ Res. 2007 Mar 16;100(5):633-44
references.pmid: 17363709
references.citation: J Mol Cell Cardiol. 2001 Apr;33(4):691-8
references.pmid: 11273722
references.citation: Circ Res. 2005 Sep 30;97(7):645-54
references.pmid: 16141410
references.citation: Proc Natl Acad Sci U S A. 2002 Nov 12;99(23):14855-60
references.pmid: 12397177
references.citation: J Card Fail. 1996 Dec;2(4 Suppl):S1-6
references.pmid: 8951554
references.citation: Annu Rev Physiol. 1997;59:551-71
references.pmid: 9074777
references.citation: Thromb Haemost. 2007 Nov;98(5):940-3
references.pmid: 18000596
references.citation: Cardiovasc Res. 2005 Aug 1;67(2):245-55
references.pmid: 15907818