Department of Biochemistry and Molecular Biology, Centre for High-Throughput Biology, University of British Columbia, 2125 East Mall, Vancouver, British Columbia V6T 1Z4, Canada.
Nat Cell Biol. 2011 Oct 9;13(11):1344-52. doi: 10.1038/ncb2343.
Cellular toxicity introduced by protein misfolding threatens cell fitness and viability. Failure to eliminate these polypeptides is associated with numerous aggregation diseases. Several protein quality control mechanisms degrade non-native proteins by the ubiquitin-proteasome system. Here, we use quantitative mass spectrometry to demonstrate that heat-shock triggers a large increase in the level of ubiquitylation associated with misfolding of cytosolic proteins. We discover that the Hul5 HECT ubiquitin ligase participates in this heat-shock stress response. Hul5 is required to maintain cell fitness after heat-shock and to degrade short-lived misfolded proteins. In addition, localization of Hul5 in the cytoplasm is important for its quality control function. We identify potential Hul5 substrates in heat-shock and physiological conditions to reveal that Hul5 is required for ubiquitylation of low-solubility cytosolic proteins including the Pin3 prion-like protein. These findings indicate that Hul5 is involved in a cytosolic protein quality control pathway that targets misfolded proteins for degradation.
蛋白质错误折叠引起的细胞毒性会威胁细胞的适应性和生存能力。如果不能清除这些多肽，就会引发许多聚集性疾病。几种蛋白质质量控制机制通过泛素-蛋白酶体系统降解非天然蛋白质。在这里，我们使用定量质谱分析证明，热休克会导致与胞质蛋白错误折叠相关的泛素化水平大幅增加。我们发现，Hul5 HECT 泛素连接酶参与了这种热休克应激反应。Hul5 是热休克后维持细胞适应性和降解短命错误折叠蛋白所必需的。此外，Hul5 在细胞质中的定位对于其质量控制功能很重要。我们在热休克和生理条件下鉴定了潜在的 Hul5 底物，揭示了 Hul5 是泛素化低可溶性胞质蛋白（包括 Pin3 朊病毒样蛋白）所必需的。这些发现表明，Hul5 参与了一种胞质蛋白质量控制途径，该途径可将错误折叠的蛋白质靶向降解。
