Cardozo Christopher P, Michaud Charlene, Ost Michael C, Fliss Albert E, Yang Emy, Patterson Cam, Hall Simon J, Caplan Avrom J
Department of Medicine, Mount Sinai School of Medicine, Box 1232, One Gustave L. Levy Place, New York, NY 10029, USA.
Arch Biochem Biophys. 2003 Feb 1;410(1):134-40. doi: 10.1016/s0003-9861(02)00680-x.
The androgen receptor (AR) is a member of the nuclear receptor superfamily that requires the action of molecular chaperones for folding and hormone binding. C-terminal Hsp-interacting protein (Chip) is a cochaperone that interacts with Hsp70 and Hsp90 molecular chaperones via a tetratricopeptide domain and inhibits chaperone-dependent protein folding in vitro. Chip also stimulates protein degradation by acting as an E3 ubiquitin ligase via a modified ring finger domain called a U box. We analyzed whether Chip affected AR levels using a transient transfection strategy. Chip overexpression led to a large decrease in AR steady state levels and increased levels of AR ubiquitinylation. However, Chip effects were not fully reversed by proteasome inhibitors, suggesting that mechanisms alternative to or in addition to proteasome-mediated degradation were involved. This hypothesis was supported by the finding that Chip overexpression reduced the rate of AR degradation, consistent with an effect on AR folding, perhaps leading to aggregation. The possibility that Chip affected AR folding was further supported by the finding that the effects of exogenous Chip were reproduced by a mutant lacking the U box. These results are discussed in terms of the role played by molecular chaperones in AR biogenesis.
雄激素受体（AR）是核受体超家族的成员，其折叠和激素结合需要分子伴侣的作用。C末端热休克蛋白相互作用蛋白（Chip）是一种辅助伴侣蛋白，它通过四肽重复结构域与Hsp70和Hsp90分子伴侣相互作用，并在体外抑制伴侣蛋白依赖性蛋白折叠。Chip还通过一个称为U盒的修饰泛素连接酶结构域作为E3泛素连接酶来刺激蛋白质降解。我们使用瞬时转染策略分析了Chip是否影响AR水平。Chip的过表达导致AR稳态水平大幅下降，并增加了AR泛素化水平。然而，蛋白酶体抑制剂并不能完全逆转Chip的作用，这表明除了蛋白酶体介导的降解之外，还涉及其他机制或与之相关的机制。这一假设得到了以下发现的支持：Chip的过表达降低了AR的降解速率，这与对AR折叠的影响一致，可能导致聚集。缺乏U盒的突变体能够重现外源性Chip的作用，这一发现进一步支持了Chip影响AR折叠的可能性。本文将根据分子伴侣在AR生物合成中的作用来讨论这些结果。
