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

Abstract

The nuclear receptor peroxisome proliferator-activated receptor γ (PPAR-γ) 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 PPARγ antagonists have been described hitherto, we have constructed a dominant-negative mutant receptor to inhibit wild-type PPAR-γ action. Highly conserved hydrophobic and charged residues (Leu468 and Glu471) in helix 12 of the ligand-binding domain were mutated to alanine. This compound PPARγ 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-1) recruitment. Unexpectedly, the mutant receptor silences basal gene transcription, recruits corepressors (the silencing mediator of retinoid and thyroid receptors and the nuclear corepressor) more avidly than wild-type PPARγ, 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 PPARγ mutant blocks thiazolidinedione-induced differentiation, providing direct evidence that PPARγ mediates adipogenesis. Our observations suggest that, as in other mutant nuclear receptor contexts (acute promyelocytic leukemia, resistance to thyroid hormone), dominant- negative inhibition by PPARγ is linked to aberrant corepressor interaction. Adenoviral expression of this mutant receptor is a valuable means to antagonize PPARγ signaling.