GATA-4 AND NKX-2.5 COACTIVATE NKX-2 DNA-BINDING TARGETS - ROLE FOR REGULATING EARLY CARDIAC GENE-EXPRESSION

The cardiogenic homeodomain factor Nkx-2.5 and serum response factor ( SRF) provide strong transcriptional coactivation of the cardiac alpha- actin (alpha CA) promoter in fibroblasts (C. Y. Chen and R. J. Schwart z, Mol. Cell. Biol. 16:6372-6384, 1996). We demonstrate here that Nkx- 2.5 also cooperates with GATA-4, a dual C-4 zinc finger transcription factor expressed in early cardiac progenitor cells, to activate the al pha CA promoter and a minimal promoter, containing only multimerized N kx-2.5 DNA binding sites (NKEs), in heterologous CV-1 fibroblasts. Tra nscriptional activity requires the N-terminal activation domain of Nkx -2.5 and Nkx-2.5 binding activity through its homeodomain but does not require GATA-4's activation domain, The minimal interactive regions w ere mapped to the homeodomain of Nkx-2.5 and the second zinc finger of GATA-4. Removal of Nkx-2.5's C-terminal inhibitory domain stimulated robust transcriptional activity, comparable to the effects of GATA-4 o n wild-type Nkx-2.5, which in part facilitated Nkx-2.5 DNA binding act ivity. We postulate the following simple model: GATA-4 induces a confo rmational change in Nkx-2.5 that displaces the C-terminal inhibitory d omain, thus eliciting transcriptional activation of promoters containi ng Nkx-2.5 DNA binding targets. Therefore, alpha Ca promoter activity appears to be regulated through the combinatorial interactions of at l east three cardiac tissue-enriched transcription factors, Nkx-2.5, GAT A-4, and SRF.