Gata1 Regulates Erythroid Transcription by Cooperating with Chromatin Remodeling Protein Snf2h

Gata1 is transcription factor that regulates erythropoiesis and its direct interaction with chromatin remodeling protein Snf2h may affect chromatin structure (Rodriguez 2005). Snf2h belongs to SWI/SNF2 superfamily of ATPases regulating structure of nuclear chromatin by nucleosome movement and assembly. Snf2h knockout in mice is embryonic lethal and heterozygotes display mild growth retardation (Stopka 2003). We studied nuclear localization of Snf2h and detected its presence in euchromatin and to a lesser extent in heterochromatin. Decreased Snf2h levels in Snf2h heterozygotes and Snf2h-null embryos exhibit significantly decreased heterochromatin size. In addition, histone modifications associated with transcription activation (histone H3K79 dimethylation and H4K16 acetylation) are globally decreased in Snf2h mutants. To test the involvement of Snf2h in hematopoiesis, ectopically expressed Snf2h mutants were tested in Gata1-mediated transcription assay in HeLa cells and demonstrated that Snf2h efficiently repressed Gata1 transactivation. Testing whether the ATPase domain is required for the repression mechanism we found the Snf2h dominant negative mutant (DN) can also repress Gata1-dependent transcription in both HeLa and Snf2h +/− fibroblasts. We next studied the effect of Snf2h DN mutant on histone modifications downstream the Gata1 binding site and found that Snf2h DN further increases H3K79 dimethylation induced by Gata1. In contrast, an occupancy of histone H3 downstream the Gata1 binding site was significantly reduced by Snf2h DN mutant indicated it caused a defect in chromatin remodeling. Collectively, our data demonstrate a cooperative role of Gata1 and Snf2h in erythroid transcription regulation and propose that Snf2h in both ATP-dependent and ATPindependent manner represses transcription by disrupting the regular array of nucleosomes near Gata1 binding sites.