Abstract 20281: Friend of GATA-2 (FOG-2) Regulates FOXM1 Expression and Cardiomyocyte Proliferation
Embryos deficient in FOG-2 or carrying a mutation that renders GATA-4 independent of FOG-2 have left ventricular hypoplasia, suggesting an important role for these transcription factors as regulators of cardiomyocyte number. Consistent with this hypothesis we found by microarray and cellular analysis that overexpression of FOG-2 altered the expression of cellular proliferation pathway genes, increased BrdU incorporation, and phospho-histone H3 staining in cultured rat neonatal cardiomyocytes. Among the proliferation pathway genes affected, we found that FoxM1b was stimulated by overexpression of FOG-2 in cultured cardiomyocytes and MHC-FOG-2 transgenic mouse hearts. The FoxM1 transcription factor is required for cardiomyocyte proliferation during mid-gestational heart development. Furthermore, the expression of FoxM1 gene targets important for cardiomyocyte proliferation, including cdc25b and survivin, were increased in FOG-2 over-expressing cultured cardiomyocytes and in Fog-2 transgenic hearts. Knockdown of the zebrafish cardiac FOG (z-FOG-1) resulted in a decreased expression of the heart-specific marker cmlc-2, and a concurrent decrease in FoxM1. Injection of the full-length murine FOG-2 mRNA into zebrafish embryos produced a transient increase in cmlc-2 (p<0.001) and FoxM1 mRNA levels (p=0.013) at 48 hpi. As FOG-2 is not known to bind to DNA directly, but rather binds to DNA binding transcription factors such as GATA-4, we speculated that FOG-2 regulates FoxM1 through GATA-4. We identified multiple putative GATA protein binding sites in the FoxM1 promoter and first intron, and a luciferase reporter plasmid regulated by sequences from the foxm1 first intron was positively regulated by FOG-2 or GATA-4. Finally, three of the predicted GATA protein binding sites in the promoter and first intron were found by chromatin immunoprecipitation to be occupied by GATA-4 in vivo. These results demonstrate that FOG-2 regulation of FoxM1 expression via GATA-4 may contribute to cardiomyocyte proliferation and ventricular heart development.
- © 2010 by American Heart Association, Inc.