cis-Acting sequences that mediate induction of beta-myosin heavy chain gene expression during left ventricular...

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.

The left ventricular expression of a directly injected reporter gene driven by 3542 bp of rat beta-myosin heavy chain (beta-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 beta-MHC mRNA in the same left ventricles. Subsequent analysis identified a 107-bp beta-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 alpha1-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 beta-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.

Basal and aortic constriction-stimulated transcription of the beta-MHC gene is mediated, at least in part, through different mechanisms. A GATA element within beta-MHC sequences -303/-197 plays a role in the transcriptional activation of this gene by aortic constriction.