Regulation of peroxisome proliferator-activated receptor gamma expression by adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1: implications for adipocyte differentiation and metabolism
Peroxisome proliferator-activated receptor gamma (PPARgamma) is a nuclear receptor implicated in adipocyte differentiation and insulin sensitivity. We investigated whether PPARgamma expression is dependent on the activity of adipocyte differentiation and determination factor 1/sterol regulatory element binding protein 1 (ADD-1/SREBP-1), another transcription factor associated with both adipocyte differentiation and cholesterol homeostasis. Ectopic expression of ADD-1/SREBP-1 in 3T3-L1 and HepG2 cells induced endogenous PPARgamma mRNA levels. The related transcription factor SREBP-2 likewise induced PPARgamma expression. In addition, cholesterol depletion, a condition known to result in proteolytic activation of transcription factors of the SREBP family, induced PPARgamma expression and improved PPRE-driven transcription. The effect of the SREBPs on PPARgamma expression was mediated through the PPARgamma1 and -3 promoters. Both promoters contain a consensus E-box motif that mediates the regulation of the PPARgamma gene by ADD-1/SREBP-1 and SREBP-2. These results suggest that PPARgamma expression can be controlled by the SREBP family of transcription factors and demonstrate new interactions between transcription factors that can regulate different pathways of lipid metabolism.