Ligand type-specific interactions of peroxisome proliferator-activated receptor gamma with transcriptional coactivators.

The nuclear peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily and acts as a ligand-dependent transcription factor mediating adipocyte differentiation, cell proliferation and inflammatory processes, and modulation of insulin sensitivity. Members of the 160-kDa protein (SRC-1/TIF2/AIB-1) family of coactivators, CBP/p300 and TRAP220/DRIP205, are shown to interact directly with PPARgamma and potentiate nuclear receptor transactivation function in a ligand-dependent fashion. Because PPARgamma ligands exert partially overlapping but distinct subsets of biological action through PPARgamma binding, we wished to examine whether interactions between PPARgamma and known coactivators were induced to the same extent by different classes of PPARgamma ligand. The natural ligand 15-deoxy-Delta12,14-prostaglandin J(2) induced PPARgamma interactions with all coactivators tested (SRC-1, TIF2, AIB-1, p300, TRAP220/DRIP205) in yeast and mammalian two-hybrid assays, as well as in a glutathione S-transferase pull-down assay. However, under the same conditions troglitazone, a synthetic PPARgamma ligand that acts as an antidiabetic agent, did not induce PPARgamma interactions with any of the coactivators. Our findings suggest that ligand binding may alter PPARgamma structure in a ligand type-specific way, resulting in distinct PPARgamma-coactivator interactions.