Patel Shivani, Kumar Santosh, Baldan Simone, Hesin Arkadi, Yaglom Julia, Sherman Michael Y
Laboratory of Cancer Biology, Department of Molecular Biology, Ariel University, Ariel, 40700, Israel.
iScience. 2022 Apr 22;25(5):104282. doi: 10.1016/j.isci.2022.104282. eCollection 2022 May 20.
The major heat shock protein Hsp70 forms a complex with a scaffold protein Bag3 that links it to components of signaling pathways. Via these interactions, the Hsp70-Bag3 module functions as a proteotoxicity sensor that controls cell signaling. Here, to search for pathways regulated by the complex, we utilized JG-98, an allosteric inhibitor of Hsp70 that blocks its interaction with Bag3. RNAseq followed by the pathway analysis indicated that several signaling pathways including UPR were activated by JG-98. Surprisingly, only the eIF2α-associated branch of the UPR was activated, while other UPR branches were not induced, suggesting that the response was unrelated to the ER proteotoxicity and ER-associated kinase PERK1. Indeed, induction of the UPR genes under these conditions was driven by a distinct eIF2α kinase HRI. Hsp70-Bag3 directly interacted with HRI and regulated eIF2α phosphorylation upon cytoplasmic proteotoxicity. Therefore, cytosolic proteotoxicity can activate certain UPR genes via Hsp70-Bag3-HRI-eIF2α axis.
主要热休克蛋白Hsp70与支架蛋白Bag3形成复合物，将其与信号通路的组分连接起来。通过这些相互作用，Hsp70-Bag3模块作为一种蛋白毒性传感器发挥作用，控制细胞信号传导。在此，为了寻找由该复合物调节的通路，我们使用了JG-98，一种Hsp70的变构抑制剂，它可阻断Hsp70与Bag3的相互作用。RNA测序随后进行的通路分析表明，包括未折叠蛋白反应（UPR）在内的几种信号通路被JG-98激活。令人惊讶的是，只有UPR中与eIF2α相关的分支被激活，而其他UPR分支未被诱导，这表明该反应与内质网蛋白毒性和内质网相关激酶PERK1无关。实际上，在这些条件下UPR基因的诱导是由一种独特的eIF2α激酶HRI驱动的。Hsp70-Bag3直接与HRI相互作用，并在细胞质蛋白毒性时调节eIF2α磷酸化。因此，胞质蛋白毒性可通过Hsp70-Bag3-HRI-eIF2α轴激活某些UPR基因。
