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  • Title: A widely used retinoic acid receptor antagonist induces peroxisome proliferator-activated receptor-gamma activity.
    Author: Schupp M, Curtin JC, Kim RJ, Billin AN, Lazar MA.
    Journal: Mol Pharmacol; 2007 May; 71(5):1251-7. PubMed ID: 17290005.
    Abstract:
    Nuclear receptors (NRs) are transcription factors whose activity is regulated by the binding of small lipophilic ligands, including hormones, vitamins, and metabolites. Pharmacological NR ligands serve as important therapeutic agents; for example, all-trans retinoic acid, an activating ligand for retinoic acid receptor alpha (RARalpha), is used to treat leukemia. Another RARalpha ligand, (E)-S,S-dioxide-4-(2-(7-(heptyloxy)-3,4-dihydro-4,4-dimethyl-2H-1-benzothiopyran-6-yl)-1-propenyl)-benzoic acid (Ro 41-5253), is a potent antagonist that has been a useful and purportedly specific probe of RARalpha function. Here, we report that Ro 41-5253 also activates the peroxisome proliferator-activated receptor gamma (PPARgamma), a master regulator of adipocyte differentiation and target of widely prescribed antidiabetic thiazolidinediones (TZDs). Ro 41-5253 enhanced differentiation of mouse and human preadipocytes and activated PPARgamma target genes in mature adipocytes. Like the TZDs, Ro 41-5253 also down-regulated PPARgamma protein expression in adipocytes. In addition, Ro 41-5253 activated the PPARgamma-ligand binding domain in transiently transfected HEK293T cells. These effects were not prevented by a potent RARalpha agonist or by depleting cells of RARalpha, indicating that PPARgamma activation was not related to RARalpha antagonism. Indeed, Ro 41-5253 was able to compete with TZD ligands for binding to PPARgamma, suggesting that Ro 41-5253 directly affects PPAR activity. These results vividly demonstrate that pharmacological NR ligands may have "off-target" effects on other NRs. Ro 41-5253 is a PPARgamma agonist as well as an RARalpha antagonist whose pleiotropic effects on NRs may signify a unique spectrum of biological responses.
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