Identification of RXR antagonists and characterization of potent stimulation of ST 13 preadipocyte differentiation

视黄酸X受体(RXR)配体PA451和PA452为RXR泛拮抗剂，HX531为RXR泛拮抗剂和视黄酸受体(RAR)泛拮抗剂。配体置换实验表明，这些RXR拮抗剂强烈取代了天然配体9-顺式维甲酸。哺乳动物细胞双杂交实验表明，RXR拮抗剂剂量依赖地抑制RXR与辅激活剂SRC-1的结合。这些结果表明这些化合物是RXR的完全竞争性拮抗剂，到目前为止还没有产生理想的拮抗剂。虽然这些RxR拮抗剂对RxR：RAR异源二聚体具有拮抗作用，但对RxR：PPARγ(过氧化物酶体增殖物激活受体)具有激动剂的作用。RXR拮抗剂的这种激活性也表现出对内源性RXR：PPARγ的拮抗作用。联合应用RXR拮抗剂和PPARγ激动剂可通过RXR：PPARγγ反式激活PPAR DNA反应元件，诱导ST13前体脂肪细胞分化。构建了嵌合型PPARγ受体(PPARγ-RARγ)，将PPARγ的配体结合域取代RARγ。这些RXR拮抗剂对RXR：PPAR交换的激活作用与对RXR：PPAR-RAR嵌合体受体的拮抗作用有关。这些结果表明，这些RXR拮抗剂的两亲性活性依赖于异源二聚体配基结合域的结构。这是RXR拮抗剂介导的PPARγ活性激动剂的首次报道。

Retinoid X receptor (RXR) ligands PA451 and PA452 are RXR pan-antagonist and HX531 is RXR pan-antagonist with retinoic acid receptor (RAR) pan-antagonist. Ligand displacement assay elucidate that these RXR antagonist displaced natural ligand 9-cis-retinoic acid from recombinant RXR strongly. Two-hybrid assay in mammalian cells demonstrated that RXR antagonists inhibited ligand dependent RXR binding to coactivator SRC-1 (steroid receptor coactivator) dose dependently. These results indicate the compounds are full competitive antagonists of RXR, and the ideal antagonists are not produced until now. Although these RXR antagonists function as antagonist toward RXR : RAR heterodimer, as agonist toward RXR : PPARγ (peroxisome proliferator activated receptor). This agonism of RXR antagonists also demonstrates against endogenous RXR : PPARγ. Simultaneous treatment with RXR antagonists and PPARγ agonist enhance the transactivation of PPARγ response element (PPRE) via RXR : PPARγ and induction of ST 13 preadipocyte differentiation. A chimera PPARγ receptor (PPARγ-RARγ) was constructed which ligand-binding domain of PPARγ has been replacing RARγ. The agonistic action of these RXR antagonists on RXR : PPAR exchange to antagonistic action on RXR : PPAR-RAR chimera receptor. These results suggest that amphypathic activity appeared in these RXR antagonists is depend on the structure of ligand binding domain of heterodimer partner. This is the first report of RXR antagonist-mediated agonism of PPARγ activity.