Rolli Sarah, Langridge Chloe A, Sontag Emily M
Department of Biological Sciences, Marquette University, Milwaukee, WI, United States.
Front Mol Biosci. 2024 Aug 21;11:1427542. doi: 10.3389/fmolb.2024.1427542. eCollection 2024.
Cellular protein homeostasis (proteostasis) plays an essential role in regulating the folding, sequestration, and turnover of misfolded proteins via a network of chaperones and clearance factors. Previous work has shown that misfolded proteins are spatially sequestered into membrane-less compartments in the cell as part of the proteostasis process. Soluble misfolded proteins in the cytoplasm are trafficked into the juxtanuclear quality control compartment (JUNQ), and nuclear proteins are sequestered into the intranuclear quality control compartment (INQ). However, the mechanisms that control the formation, localization, and degradation of these compartments are unknown. Previously, we showed that the JUNQ migrates to the nuclear membrane adjacent to the INQ at nucleus-vacuole junctions (NVJ), and the INQ moves through the NVJ into the vacuole for clearance in an ESCRT-mediated process. Here we have investigated what mechanisms are involved in the formation, migration, and clearance of the JUNQ. We find Hsp70s Ssa1 and Ssa2 are required for JUNQ localization to the NVJ and degradation of cytoplasmic misfolded proteins. We also confirm that sequestrases Btn2 and Hsp42 sort misfolded proteins to the JUNQ or IPOD, respectively. Interestingly, proteins required for piecemeal microautophagy of the nucleus (PMN) (i.e., Nvj1, Vac8, Atg1, and Atg8) drive the formation and clearance of the JUNQ. This suggests that the JUNQ migrates to the NVJ to be cleared via microautophagy.
细胞蛋白质稳态（蛋白质平衡）通过伴侣蛋白和清除因子网络在调节错误折叠蛋白的折叠、隔离和周转方面发挥着至关重要的作用。先前的研究表明，作为蛋白质平衡过程的一部分，错误折叠的蛋白质在空间上被隔离到细胞内的无膜区室中。细胞质中的可溶性错误折叠蛋白被运输到近核质量控制区室（JUNQ），而核蛋白则被隔离到核内质量控制区室（INQ）。然而，控制这些区室形成、定位和降解的机制尚不清楚。此前，我们发现JUNQ在核 - 液泡交界处（NVJ）迁移到与INQ相邻的核膜，并且INQ通过NVJ进入液泡，在ESCRT介导的过程中进行清除。在这里，我们研究了JUNQ的形成、迁移和清除涉及哪些机制。我们发现Hsp70家族的Ssa1和Ssa2是JUNQ定位于NVJ以及细胞质错误折叠蛋白降解所必需的。我们还证实，隔离酶Btn2和Hsp42分别将错误折叠的蛋白质分选到JUNQ或IPOD中。有趣的是，细胞核的逐个微自噬（PMN）所需的蛋白质（即Nvj1、Vac8、Atg1和Atg8）驱动JUNQ的形成和清除。这表明JUNQ迁移到NVJ以通过微自噬进行清除。
