Molecular regulation of PPARγ/RXRα signaling by the novel cofactor ZFP407

Abstract

AbstractCofactors interacting with PPARγ can regulate adipogenesis and adipocyte metabolism by modulating the transcriptional activity and selectivity of PPARγ signaling. ZFP407 was previously demonstrated to regulate PPARγ target genes such asGLUT4, and its overexpression improved glucose homeostasis in mice. Here, using a series of molecular assays, including protein-interaction studies, mutagenesis, and ChIP-seq, ZFP407 was found to interact with the PPARγ/RXRα protein complex in the nucleus of adipocytes. Consistent with this observation, ZFP407 DNA binding sites significantly overlapped with PPARγ sites, with more than half of ZFP407 binding sites overlapping with PPARγ DNA binding sites. Transcription factor binding motifs enriched in these overlapping sites included GFY-Staf, ELF1, ETS, ELK1, and ELK4, which regulate key functions within adipocytes. Site-directed mutagenesis of frequent PPARγ phosphorylation or SUMOylation sites did not prevent its regulation by ZFP407, while mutagenesis of ZFP407 regions necessary for RXR and PPARγ binding abrogated any impact of ZFP407 on PPARγ activity. These data suggest that ZFP407 controls the activity of PPARγ, but does so independently of post-translational modifications, likely by direct binding, establishing ZFP407 as a newly identified PPARγ cofactor. In addition, ZFP407 was also found to bind to DNA in regions that did not overlap with PPARγ. These DNA binding sites were more significantly enriched for the transcription factor binding motifs of GFY and ZNF143, which may contribute to the non-PPARγ dependent functions of ZFP407 in adipocytes and other cell types.