title: Myocardin expression is regulated by Nkx2.5, and its function is required for cardiomyogenesis.
abstract: Nkx2.5 (also known as Csx) is an evolutionarily conserved cardiac transcription factor of the homeobox gene family. Nkx2.5 is required for early heart development, since Nkx2.5-null mice die before completion of cardiac looping. To identify genes regulated by Nkx2.5 in the developing heart, we performed subtractive hybridization by using RNA isolated from wild-type and Nkx2.5-null hearts at embryonic day 8.5. We isolated a mouse cDNA encoding myocardin A, which is an alternative spliced isoform of myocardin and the most abundant isoform in the heart from embryo to adult. The expression of myocardin A and myocardin was markedly downregulated in Nkx2.5-null mouse hearts. Transient-cotransfection analysis showed that Nkx2.5 transactivates the myocardin promoter. Inhibition of myocardin function in the teratocarcinoma cell line P19CL6 prevented differentiation into cardiac myocytes after dimethyl sulfoxide treatment. Myocardin A transactivated the promoter of the atrial natriuretic factor gene through the serum response element, which was augmented by bone morphogenetic protein 2 and transforming growth factor beta-activated kinase 1. These results suggest that myocardin expression is regulated by Nkx2.5 and that its function is required for cardiomyogenesis.
authors.affiliation: Cardiovascular Division, Beth Israel Deaconess Medical Center, and Department of Medicine, Harvard Medical School, Boston, MA 02215, USA.
authors.forename: Tomomi
authors.initials: T
authors.lastname: Ueyama
authors.forename: Hideko
authors.initials: H
authors.lastname: Kasahara
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ishiwata
authors.forename: Qing
authors.initials: Q
authors.lastname: Nie
authors.forename: Seigo
authors.initials: S
authors.lastname: Izumo
mesh_terms: D017398:Alternative Splicing; D000595:Amino Acid Sequence; D000818:Animals; D009320:Atrial Natriuretic Factor / Q000235:genetics; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D015536:Down-Regulation; D005318:Fetal Heart / Q000196:embryology* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000235:genetics*; D011401:Promoter Regions, Genetic; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics*; D014157:Transcription Factors; D015533:Transcriptional Activation; D029867:Xenopus Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D000099251:Myocardin
chemical_list: D009320:Atrial Natriuretic Factor; D018076:DNA, Complementary; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D015534:Trans-Activators; D014157:Transcription Factors; D029867:Xenopus Proteins; D000099251:Myocardin; C095552:NKX2-5 protein, human; C484469:Nkx2-5 protein, mouse