cis -Acting Sequences That Mediate Induction of β-Myosin Heavy Chain Gene Expression During Left Ventricular Hypertrophy due to Aortic Constriction

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Abstract
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 α 1 -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.