Nuclear and cytosolic J-domain proteins provide synergistic control of Hsf1 at distinct phases of the heat shock response [time course]

The heat shock response (HSR) is the major defense mechanism against proteotoxic stress in the cytosol and nucleus of eukaryotic cells. Initiation and attenuation of the response are mediated by stress-dependent regulation of heat shock transcription factors (HSFs). Saccharomyces cerevisiae encodes a single HSF (Hsf1), facilitating the analysis of HSR regulation. Hsf1 is repressed by Hsp70 chaperones under non-stress conditions, and becomes activated under proteotoxic stress, directly linking protein damage and its repair to the HSR. J-domain proteins (JDPs) are essential for targeting of Hsp70s to their substrates, yet the specific JDP(s) regulating Hsf1 and connecting protein damage to HSR activation remain unclear. Here we show that the yeast nuclear JDP Apj1 primarily controls the attenuation phase of HSR by promoting the Hsf1’s displacement from heat shock elements in target DNA. In apj111 cells, HSR attenuation is significantly impaired. Additionally, yeast cells lacking both Apj1 and the major JDP Ydj1 exhibit increased HSR activation even in non-stress conditions, indicating their distinct regulatory roles. Apj1’s role in both nuclear protein quality control and Hsf1 regulation underscores its role in directly linking nuclear proteostasis to HSR regulation. Together these findings establish the nucleus as key stress-sensing signaling hub.热休克反应（heat shock response, HSR）是真核细胞胞质与细胞核内抵御蛋白毒性应激的核心防御机制。该反应的启动与衰减，通过热休克转录因子（heat shock transcription factors, HSFs）的应激依赖性调控实现。酿酒酵母（Saccharomyces cerevisiae）仅编码单一HSF（Hsf1），为HSR调控机制的解析提供了便利。在非应激条件下，Hsf1会被Hsp70分子伴侣抑制；当遭遇蛋白毒性应激时，Hsf1被激活，直接将蛋白质损伤及其修复过程与HSR通路相偶联。J结构域蛋白（J-domain proteins, JDPs）是将Hsp70靶向至其底物的必需因子，但目前调控Hsf1、并将蛋白质损伤与HSR激活相连接的特异性JDP仍不明确。本研究显示，酿酒酵母核定位J结构域蛋白Apj1主要通过促进Hsf1从靶DNA的热休克元件上解离，调控HSR的衰减阶段。在apj11细胞中，HSR的衰减过程会受到显著损伤。此外，同时缺失Apj1与主要JDP Ydj1的酿酒酵母细胞，即使在非应激条件下也会出现HSR激活增强的表型，这表明二者发挥着截然不同的调控功能。Apj1同时参与核蛋白质质量控制与Hsf1调控的特性，凸显了其将核蛋白质稳态与HSR调控直接偶联的作用。综上，本研究结果确立了细胞核作为关键应激感知信号枢纽的地位。