THE CARDIAC TRANSCRIPTION FACTORS NKX2-5 AND GATA-4 ARE MUTUAL COFACTORS

The tissue-restricted GATA-4 transcription factor and Nkx2-5 homeodoma in protein are two early markers of precardiac cells, Both are essenti al for heart formation, but neither can initiate cardiogenesis. Overex pression of GATA-4 or Nkx2-5 enhances cardiac development in committed precursors, suggesting each interacts with a cardiac cofactor, We tes ted whether GATA-4 and Nkx2-5 are cofactors for each other by using tr anscription and binding assays with the cardiac atrial natriuretic fac tor (ANF) promoter-the only known target for Nkx2-5, Co-expression of GATA-4 and Nkx2-5 resulted in synergistic activation of the ANF promot er in heterologous cells, The synergy involves physical Nkx2-5-GATA-4 interaction, seen in vitro and in vivo, which maps to the C-terminal z inc finger of GATA-4 and a G-terminus extension; similarly, a G-termin ally extended homeodomain of Nkx2-5 is required for GATA-4 binding, St ructure/function studies suggest that binding of GATA-4 to the G-termi nus autorepressive domain of Nkx2-5 may induce a conformational change that unmasks Nkx2-5 activation domains, GATA-6 cannot substitute for GATA-4 for interaction with Nkx2-5. This interaction may impart functi onal specificity to GATA factors and provide cooperative crosstalk bet ween two pathways critical for early cardiogenesis. Given the co-expre ssion of GATA proteins and NK2 class members in other tissues, the GAT A/Nkx partnership may represent a paradigm for transcription factor in teraction during organogenesis.