A study on an immunosuppressant mizoribine-binding renal proteins (esp. molecular chaperones)

1.哺乳动物HSP 60是免疫抑制剂咪唑立宾的主要靶标（参考文献1）从猪肾中分离出60-kDa咪唑立宾结合蛋白。根据其氨基酸序列，该蛋白被鉴定为HSP 60。此外，咪唑立宾干扰HSP 60的伴侣活性。这些发现表明咪唑立宾的治疗作用的一种机制可能是抑制HSP 60.2的伴侣活性。免疫抑制剂咪唑立宾与14-3-3蛋白的功能相互作用（参考文献2）从猪肾中分离出四种30-32 kDa咪唑立宾结合蛋白。根据它们的氨基酸序列，蛋白质被鉴定为14-3-3蛋白质同种型，其最近被认为是分子伴侣。咪唑立宾影响了14 -3-3蛋白的构象，增强了糖皮质激素受体（GR）与14-3-3蛋白的相互作用。咪唑立宾对GR的转录激活也有刺激作用。这些结果表明咪唑立宾的治疗作用的一种机制可能是通过14-3-3蛋白调节GR功能。通过14-3-3依赖性的辅助阻遏物RIP 140的细胞内再定位调节糖皮质激素受体活性（参考文献3）进一步阐明了在参考文献2中鉴定为咪唑立宾结合蛋白的14-3-3蛋白的功能。14-3-3蛋白与核受体辅阻遏物RIP 140相互作用，改变了RIP 140的亚细胞定位。这些结果表明，14-3-3对糖皮质激素受体反式激活的积极作用是由于14-3-3与RIP 140结合并从细胞核中除去负作用的RIP 140。此外，14-3-3蛋白还能与多种核受体和辅因子结合。这表明14-3-3蛋白在信号转导系统中具有更普遍的作用。

1. Mammalian HSP60 is a major target for an immunosuppressant mizoribine (Reference 1)A 60-kDa mizoribine-binding protein was isolated from porcine kidney. Based on its amino acid sequences, the protein was identified as HSP60. Moreover, mizoribine interfered with the chaperone activity of HSP60. These findings suggest the possibility that one mechanism for the therapeutic effect of mizoribine could be to inhibit the chaperone activity of HSP60.2. Functional interaction of the immunosuppressant mizoribine with the 14-3-3 protein (Reference 2)Four 30-32 kDa mizoribine-binding proteins were isolated from porcine kidney. Based on their amino acid sequences, the. proteins were identified as 14-3-3 protein isoforms, which have recently been considered to be molecular chaperones. Mizoribine affected the conformation of 1 4-3-3 proteins and enhanced the glucocorticoid receptor (GR)/14-3-3 protein interaction. Mizoribine also had a stimulatory effect on transcriptional activation by the GR. These results point to the possibility that one mechanism for the therapeutic effect of mizoribine could be to regulate the GR function via 14-3-3 proteins.3. Regulation of glucocorticoid receptor activity by 14-3-3-dependent intracellular relocalization of the corepressor RIP140 (Reference 3)The function of 14-3-3 proteins, which were identified as mizoribine-binding proteins in Reference 2, was further elucidated. 14-3-3 proteins interacted with the nuclear receptor corepressor RIP140 and changed its subcellular localization. These results suggest that the positive effect of 14-3-3 on glucocorticoid receptor transactivation is due to 14-3-3 binding to RIP140 and removing the negatively acting RIP140 from the nucleus. Moreover, 14-3-3 proteins could bind to various other nuclear receptors and co factors. This indicates a more general role for 14-3-3 proteins in the signal transduction systems.