Essentiality of Sis1, a J-domain protein Hsp70 cochaperone, can be overcome by Tti1, a specialized PIKK chaperone.
Essentiality of Sis1, a J-domain protein Hsp70 cochaperone, can be overcome by Tti1, a specialized PIKK chaperone.
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DOI：
10.1091/mbc.e21-10-0493
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发表时间：
2022-03-01
影响因子：
3.3
通讯作者：
Craig, Elizabeth A.
中科院分区：
文献类型：
--
作者：
Schilke, Brenda A.;Craig, Elizabeth A.
J-结构域蛋白辅伴侣驱动了基于Hsp 70的伴侣系统的大部分功能多样性。Sis 1是酿酒酵母细胞质/细胞核中唯一必需的J结构域蛋白。为什么它是细胞生长所必需的还不清楚，也不知道它在调节热休克转录因子1（Hsf 1）中的作用有多重要。我们报告说，Tti 1，一个组件的异源三聚体TTT复合物，一个专门的伴侣系统磷脂酰肌醇3-激酶相关激酶（PIKK）蛋白的单残基取代，允许生长的细胞缺乏Sis 1。在Sis 1耗尽后，细胞变得对雷帕霉素（一种特异性TORC 1激酶抑制剂）过敏。此外，三种必需的PIKK（Mec 1，Tra 1和Tor 2）以及Tor 1的水平在Sis 1耗尽后降低。Tti 1的过表达允许生长而不增加TTT复合物的其他亚基Tel 2和Tti 2，这表明它可以独立于复合物发挥作用。缺乏Sis 1的细胞，由Tti 1抑制剂支持的活力，基本上上调了一些，但不是全部，由Hsf 1激活的热休克元件。总之，我们的研究结果表明，Sis 1需要作为一个cochaperone的热休克蛋白70的折叠/维持的PIKKs，使Sis 1的一个必需的基因，其要求的Hsf 1的调节是更微妙的比一般理解。
J-domain protein cochaperones drive much of the functional diversity of Hsp70-based chaperone systems. Sis1 is the only essential J-domain protein of the cytosol/nucleus of Saccharomyces cerevisiae. Why it is required for cell growth is not understood, nor how critical its role is in regulation of heat shock transcription factor 1 (Hsf1). We report that single-residue substitutions in Tti1, a component of the heterotrimeric TTT complex, a specialized chaperone system for phosphatidylinositol 3-kinase-related kinase (PIKK) proteins, allow growth of cells lacking Sis1. Upon depletion of Sis1, cells become hypersensitive to rapamycin, a specific inhibitor of TORC1 kinase. In addition, levels of the three essential PIKKs (Mec1, Tra1, and Tor2), as well as Tor1, decrease upon Sis1 depletion. Overexpression of Tti1 allows growth without an increase in the other subunits of the TTT complex, Tel2 and Tti2, suggesting that it can function independent of the complex. Cells lacking Sis1, with viability supported by Tti1 suppressor, substantially up-regulate some, but not all, heat shock elements activated by Hsf1. Together, our results suggest that Sis1 is required as a cochaperone of Hsp70 for the folding/maintenance of PIKKs, making Sis1 an essential gene, and its requirement for Hsf1 regulation is more nuanced than generally appreciated.