Hiromori Youhei, Aoki Akira, Nishikawa Jun-ichi, Nagase Hisamitsu, Nakanishi Tsuyoshi
Laboratory of Hygienic Chemistry and Molecular Toxicology, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu, Gifu 501-1196, Japan.
Metallomics. 2015 Jul;7(7):1180-8. doi: 10.1039/c5mt00086f.
Organotins, such as tributyltin (TBT) and triphenyltin (TPT), may disrupt endocrine activity in mammals arising from their ability to act as ligands for the retinoid X receptor (RXR) and the peroxisome proliferator-activated receptor γ (PPARγ). The structure of TBT is completely different from that of 9-cis retinoic acid (9cRA), an endogenous RXR ligand; and X-ray crystallographic studies have revealed that TBT and 9cRA have distinct binding interactions with human RXRα. Therefore, organotins and rexinoids likely activate RXR by different mechanisms. Here, we used human RXRα mutants to investigate which amino acid residues of the receptor are critical for transactivation induced by rexinoids and organotins. We found that 9cRA and a synthetic RXR agonist (LG100268) failed to activate R316A and L326A RXRα mutants. In contrast, all the tested organotins activated the R316A mutant, the L326A mutant, or both but failed to activate a C432A mutant. These results suggest that the importance of L326, which is located in the β-strand, for rexinoid-induced transactivation of RXRα is comparable to that of R316; in contrast, C432 is critical for organotin-induced transactivation, whereas R316 and L326 are not required. We used a PPARγ/RXRα C432A heterodimer to determine whether TBT and TPT could activate the heterodimer by binding to PPARγ. We found that TBT and TPT activated the PPARγ/RXRα C432A heterodimer, which suggests that both compounds can activate the heterodimer through PPARγ. These findings indicate that the amino acid residues that are critical for organotin-induced transactivation of RXRα are distinct from those required for rexinoid-induced transactivation.
有机锡化合物，如三丁基锡（TBT）和三苯基锡（TPT），可能会干扰哺乳动物的内分泌活动，因为它们能够作为视黄酸X受体（RXR）和过氧化物酶体增殖物激活受体γ（PPARγ）的配体。TBT的结构与内源性RXR配体9-顺式视黄酸（9cRA）完全不同；X射线晶体学研究表明，TBT和9cRA与人类RXRα具有不同的结合相互作用。因此，有机锡化合物和视黄酸类药物可能通过不同的机制激活RXR。在此，我们使用人类RXRα突变体来研究受体的哪些氨基酸残基对视黄酸类药物和有机锡化合物诱导的反式激活至关重要。我们发现，9cRA和一种合成的RXR激动剂（LG100268）未能激活R316A和L326A RXRα突变体。相反，所有测试的有机锡化合物都激活了R316A突变体、L326A突变体或两者，但未能激活C432A突变体。这些结果表明，位于β链中的L326对视黄酸类药物诱导的RXRα反式激活的重要性与R316相当；相反，C432对有机锡化合物诱导的反式激活至关重要，而R316和L326则不是必需的。我们使用PPARγ/RXRα C432A异二聚体来确定TBT和TPT是否可以通过与PPARγ结合来激活该异二聚体。我们发现，TBT和TPT激活了PPARγ/RXRα C432A异二聚体，这表明这两种化合物都可以通过PPARγ激活该异二聚体。这些发现表明，对有机锡化合物诱导的RXRα反式激活至关重要的氨基酸残基与视黄酸类药物诱导的反式激活所需的氨基酸残基不同。
