TRANSCRIPTION FACTOR GATA-4 REGULATES CARDIAC MUSCLE-SPECIFIC EXPRESSION OF THE ALPHA-MYOSIN HEAVY-CHAIN GENE

The alpha-myosin heavy-chain (alpha-MHC) gene is the major structural protein in the adult rodent myocardium. Its expression is restricted t o the heart by a complex interplay of trans-acting factors and their c is-acting sites. However, to date, the factors that have been shown to regulate expression of this gene have also been found in skeletal mus cle cells. Recently, transcription factor GATA-4, which has a tissue d istribution limited to the heart and endodermally derived tissues, was identified. We recently found two putative GATA-binding sites within the proximal enhancer of the alpha-MHC gene, suggesting that GATA-4 mi ght regulate its expression. In this study, we establish that GATA-4 i nteracts with the alpha-MHC GATA sites to stimulate cardiac muscle-spe cific expression. Mutation of GATA-4-binding sites either individually or together decreased activity by 50 and 88% in the adult myocardium, respectively. GATA-4-dependent enhancement of activity from a heterol ogous promoter was mediated through the alpha-MHC GATA sites. Conjecti on of an alpha-MHC promoter construct with a GATA-4 expression vector permitted ectopic expression in skeletal muscle but not in fibroblasts . Thus, the lack of alpha-MHC expression in skeletal muscle correlates with a lack of GATA-4. GATA-4 DNA binding activity was significantly up-regulated in triiodothyronine- or retinoic acid-treated cardiomyocy tes. Putative GATA-4-binding sites are also found in the regulatory re gions of other cardiac muscle-expressed structural genes. This indicat es a mechanism whereby triiodothyronine and retinoic acid can exert co ordinate control of the cardiac phenotype through a trans-acting regul atory factor.