Cooperative interaction between GATA-4 and GATA-6 regulates myocardial gene expression

Two members of the GATA family of transcription factors, GATA-4 and GATA-6, are expressed in the developing and postnatal myocardium and are equally p otent transactivators of several cardiac promoters. However, several in vit ro and in vivo lines of evidence suggest distinct roles for the two factors in the heart. Since identification of the endogenous downstream targets of GATA factors would greatly help to elucidate their exact functions, we hav e developed an adenovirus-mediated antisense strategy to specifically inhib it GATA-4 and GATA-6 protein production in postnatal cardiomyocytes. Expres sion of several endogenous cardiac genes was significantly down-regulated i n cells lacking GATA-4 or GATA-6, indicating that these factors are require d for the maintenance of the cardiac genetic program. Interestingly, transc ription of some genes like the alpha- and beta-myosin heavy-chain (alpha- a nd beta-MHC) genes was preferentially regulated by GATA-4 due, in part, to higher affinity of GATA-4 for their promoter GATA element. However, transcr iption of several other genes, including the atrial natriuretic factor and B-type natriuretic peptide (ANF and BNP) genes, was similarly down-regulate d in cardiomyocytes lacking one or both GATA factors, suggesting that GATA- 4 and GATA-6 could act through the same transcriptional pathway, Consistent with this, GATA-4 and GATA-6 were found to colocalize in postnatal cardiom yocytes and to interact functionally and physically to provide cooperative activation of the ANF and BNP promoters, The results identify for the first time bona fide in vivo targets for GATA-4 and GATA-6 in the myocardium. Th e data also show that GATA factors act in concert to regulate distinct subs ets of genes, suggesting that combinatorial interactions among GATA factors may differentially control various cellular processes.