A dominant-negative peroxisome proliferator-activated receptor gamma (PPARgamma) mutant is a constitutive repressor and inhibits PPAR gamma-mediatedadipogenesis

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) promotes adipocyte differentiation, exerts atherogenic and anti-inf lammatory effects in monocyte/macrophages, and is believed to mediate the i nsulin-sensitizing action of antidiabetic thiazolidinedione ligands. As no complete PPAR gamma antagonists have been described hitherto, we have const ructed a dominant-negative mutant receptor to inhibit wild-type PPAR gamma action. Highly conserved hydrophobic and charged residues (Leu(468) and Glu (471)) in helix 12 of the ligand-binding domain were mutated to alanine. Th is compound PPAR gamma mutant retains ligand and DNA binding, but exhibits markedly reduced transactivation due to impaired coactivator (cAMP-response element-binding protein-binding protein and steroid receptor coactivator-l ) recruitment. Unexpectedly, the mutant receptor silences basal gene transc ription, recruits core pressors (the silencing mediator of retinoid and thy roid receptors and the nuclear corepressor) more avidly than wild-type PPAR gamma, and exhibits delayed ligand-dependent corepressor release, It is a powerful dominant-negative inhibitor of cotransfected wild-type receptor ac tion. Furthermore, when expressed in primary human preadipocytes using a re combinant adenovirus, this PPAR gamma mutant blocks thiazolidinedione-induc ed differentiation, providing direct evidence that PPAR gamma mediates adip ogenesis. Our observations suggest that, as in other mutant nuclear recepto r contexts (acute promyelocytic leukemia, resistance to thyroid hormone), d ominant-negative inhibition by PPAR gamma is linked to aberrant corepressor interaction. Adenoviral expression of this mutant receptor is a valuable m eans to antagonize PPAR gamma signaling.