J Biol Chem 2002 Mar 4; [epub ahead of print]
T0070907, A selective ligand for peroxisome proliferator-activated receptor g, functions as an antagonist of biochemical and cellular activities.
Lee G, Elwood F, McNally J, Weiszmann J, Lindstrom M, Amaral K, Miao S, Cao P, Learned M, Chen JL, Li Y.
Department of Biology, Tularik Inc., South San Francisco, CA 94080.
The nuclear hormone receptor peroxisome proliferator-activated receptor g (PPARg [NR1C3]) plays a central role in adipogenesis and is the molecular target for the thiazolidinedione (TZD) class of antidiabetic drugs. In a search for novel non-TZD ligands for PPARg, T0070907 was identified as a potent and selective PPARg antagonist. With an apparent binding affinity (concentration at 50% inhibition of [3H]rosiglitazone binding or IC50) of 1 nM, T0070907 covalently modifies PPARg on cysteine 313 in helix 3 of hPPARg2. T0070907 blocked PPARg function in both cell-based reporter gene and adipocyte differentiation assays. Consistent with its role as an antagonist of PPARg, T0070907 blocked agonist-induced recruitment of coactivator-derived peptides to PPARg in an HTRF-based assay, and promoted recruitment of the transcriptional corepressor NCoR to PPARg in both GST pull-down assays and a PPARg/RXRa dependent gel shift assay. Studies with mutant receptors suggest that T0070907 modulates the interaction of PPARg with these cofactor proteins by affecting the conformation of helix 12 of the PPARg ligand-binding domain. Interestingly, while the T0070907-induced NCoR recruitment to PPARg/RXRa heterodimer can be almost completely reversed by the simultaneous treatment with RXRa agonist LGD1069, T0070907 treatment has only modest effects on LGD1069-induced coactivator recruitment to the PPARg/RXRa heterodimer. These results suggest that the activity of PPARg antagonists can be modulated by the availability and concentration of RXR agonists. T0070907 is a novel tool for the study of PPARg/RXRa heterodimer function. |
