Myocardin and Stat3 act synergistically to inhibit cardiomyocyte apoptosis.

Signal transducer and activator of transcription 3 (Stat3) and Myocardin regulate cardiomyocyte differentiation, proliferation, and apoptosis. We report a novel aspect of the cellular function of Myocardin and Stat3 in the regulation of cardiomyocyte apoptosis. Myocardin and Stat3 showed anti-apoptotic function by increasing the expression of Bcl-2 while reducing expression of the pro-apoptotic genes Bax, Apaf-1, caspase-9, and caspase-3. Moreover, myocardin/Stat3-mediated activation of Bcl-2 and Mcl-1 transcription is contingent on the CArG box. Myocardin and Stat3 synergistically inhibited staurosporine-induced cardiomyocyte apoptosis by up-regulating expression of anti-apoptotic Bcl-2 and Mcl-1 in neonatal rat cardiomyocytes. These results describe a novel anti-apoptotic Myocardin/Stat3 signaling pathway operating during cardiomyocyte apoptosis. This provides a molecular explanation for cardiomyocyte apoptosis inhibition as a critical component of myocardial protection.