Background: Marked alterations in the expression of specific genes oCCur during the development of cardiac hypertrophy in vivo. Little is known, however, about the cis-acting elements that mediate these changes in response to clinically relevant hypertrophic stimuli, such as hemodynamic overload, in intact adult animals. Methods and Results: The left ventricular expression of a directly injected reporter gene driven by 3542 bp of rat β-myosin heavy chain (β-MHC) promoter was increased 3.0-fold by aortic constriction (P<.005), an increment similar to the 3.2-fold increase in the level of the endogenous β-MHC mRNA in the same left ventricles. Subsequent analysis identified a 107-bp β-MHC promoter sequence (-303/-197) sufficient to convert a heterologous neutral promoter to one that is activated by aortic constriction. These sequences contain two M-CAT elements, which have previously been demonstrated to mediate inducible expression during α1- adrenergic stimulated hypertrophy in cultured neonatal cardiac myocytes, and a GATA element. Although simultaneous mutation of both M-CAT elements markedly decreased the basal transcriptional activity of an injected 333-bp β-MHC promoter, it had no effect on aortic constriction-stimulated transcription (3,5-fold increase. P<.005 for both wild type and mutant). In contrast, mutation of the GATA motif markedly attenuated aortic constriction- stimulated transcription (1.6-fold, P=NS), without affecting the basal transcriptional activity. This GATA site can interact with in vitro translated GATA-4 and compete with an established GATA site for GATA-4 binding activity in nuclear extracts from aortic constricted hearts. Conclusions: Basal and aortic constriction-stimulated transcription of the β-MHC gene is mediated, at least in part, through different mechanisms. A GATA element within β-MHC sequences -303/-197, plays a role in the transcriptional activation of this gene by aortic constriction.
- Signal transduction
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)