Friend of GATA 2 physically interacts with chicken ovalbumin upstream promoter-TF2 (COUP-TF2) and COUP-TF3 and represses COUP-TF2-dependent activation of the atrial natriuretic factor promoter

Friend of GATA (FOG)-2 is a multi-zinc finger transcriptional corepressor p rotein that binds specifically to GATA4. Gene targeting studies have demons trated that FOG-2 is required for normal cardiac morphogenesis, including t he development of the coronary vasculature, left ventricular compact zone, and heart valves. To better understand the molecular mechanisms by which FO G-2 regulates these cardiac developmental programs, we screened a mouse day 11 embryo library using a yeast two-hybrid interaction trap with the fifth and sixth zinc fingers of FOG-2 as bait. Using this approach, we isolated clones encoding the orphan nuclear receptors chicken ovalbumin upstream pro moter-transcription factor (COUP-TF) 2 and COUP-TF3. COUP-TF2-null embryos die during embryonic development with defective angiogenesis and cardiac de fects, a pattern that partly resembles the FOG-2-null phenotype. The intera ction between COUP-TF2 and FOG-2 in mammalian cells was confirmed by co-imm unoprecipitation of these proteins from transfected COS-7 cells. The sites of binding interaction between COUP-TF2 and FOG-2 were mapped to zinc finge rs 5 and 6 and fingers 7 and 8 of FOG-2 and to the carboxyl terminus of the COUP-TF proteins. Binding to COUP-TF2 was specific because FOG-2 did not i nteract with the ligand-binding domains of retinoid X receptor alpha, gluco corticoid receptor, and peroxisome proliferating antigen receptor gamma, wh ich are related to the COUP-TF proteins. Full-length FOG-2 markedly enhance d transcriptional repression by GAL4-COUP-TF2(117-414), but not by a COUP-T F2 repression domain mutant. Moreover, FOG-2 repressed COUP-TF2dependent sy nergistic activation of the atrial natriuretic factor promoter by both GATA 4 and the FOG-2-independent mutant GATA4-E215K. Taken together, these findi ngs suggest that FOG-2 functions as a corepressor for both GATA and COUP-TF proteins.