A dominant-negative peroxisome proliferator-activated receptor γ (PPARγ) mutant is a constitutive repressor and inhibits PPARγ-mediated adipogenesis

The nuclear receptor peroxisome proliferator-activated receptor gamma (PPAR gamma) promotes adipocyte differentiation, exerts atherogenic and anti-inflammatory effects in monocyte/macrophages, and is believed to mediate the insulin-sensitizing action of antidiabetic thiazolidinedione ligands. As no complete PPAR gamma antagonists have been described hitherto, we have constructed 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. This 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 transcription, recruits core pressors (the silencing mediator of retinoid and thyroid 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 action. Furthermore, when expressed in primary human preadipocytes using a recombinant adenovirus, this PPAR gamma mutant blocks thiazolidinedione-induced differentiation, providing direct evidence that PPAR gamma mediates adipogenesis. Our observations suggest that, as in other mutant nuclear receptor contexts (acute promyelocytic leukemia, resistance to thyroid hormone), dominant-negative inhibition by PPAR gamma is linked to aberrant corepressor interaction. Adenoviral expression of this mutant receptor is a valuable means to antagonize PPAR gamma signaling.