Groenendyk Jody, Peng Zhenling, Dudek Elzbieta, Fan Xiao, Mizianty Marcin J, Dufey Estefanie, Urra Hery, Sepulveda Denisse, Rojas-Rivera Diego, Lim Yunki, Kim Do Han, Baretta Kayla, Srikanth Sonal, Gwack Yousang, Ahnn Joohong, Kaufman Randal J, Lee Sun-Kyung, Hetz Claudio, Kurgan Lukasz, Michalak Marek
Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2S7, Canada.
Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
Sci Signal. 2014 Jun 10;7(329):ra54. doi: 10.1126/scisignal.2004983.
The disruption of the energy or nutrient balance triggers endoplasmic reticulum (ER) stress, a process that mobilizes various strategies, collectively called the unfolded protein response (UPR), which reestablish homeostasis of the ER and cell. Activation of the UPR stress sensor IRE1α (inositol-requiring enzyme 1α) stimulates its endoribonuclease activity, leading to the generation of the mRNA encoding the transcription factor XBP1 (X-box binding protein 1), which regulates the transcription of genes encoding factors involved in controlling the quality and folding of proteins. We found that the activity of IRE1α was regulated by the ER oxidoreductase PDIA6 (protein disulfide isomerase A6) and the microRNA miR-322 in response to disruption of ER Ca2+ homeostasis. PDIA6 interacted with IRE1α and enhanced IRE1α activity as monitored by phosphorylation of IRE1α and XBP1 mRNA splicing, but PDIA6 did not substantially affect the activity of other pathways that mediate responses to ER stress. ER Ca2+ depletion and activation of store-operated Ca2+ entry reduced the abundance of the microRNA miR-322, which increased PDIA6 mRNA stability and, consequently, IRE1α activity during the ER stress response. In vivo experiments with mice and worms showed that the induction of ER stress correlated with decreased miR-322 abundance, increased PDIA6 mRNA abundance, or both. Together, these findings demonstrated that ER Ca2+, PDIA6, IRE1α, and miR-322 function in a dynamic feedback loop modulating the UPR under conditions of disrupted ER Ca2+ homeostasis.
能量或营养平衡的破坏会引发内质网（ER）应激，这一过程会启动各种策略，统称为未折叠蛋白反应（UPR），该反应可重建内质网和细胞的稳态。UPR应激传感器IRE1α（肌醇需求酶1α）的激活会刺激其核糖核酸内切酶活性，导致编码转录因子XBP1（X盒结合蛋白1）的mRNA生成，XBP1可调节编码参与控制蛋白质质量和折叠的因子的基因转录。我们发现，IRE1α的活性受内质网氧化还原酶PDIA6（蛋白质二硫键异构酶A6）和微小RNA miR-322的调节，以应对内质网Ca2+稳态的破坏。PDIA6与IRE1α相互作用，并通过IRE1α的磷酸化和XBP1 mRNA剪接监测增强IRE1α活性，但PDIA6对介导内质网应激反应的其他途径的活性没有实质性影响。内质网Ca2+耗竭和储存操纵性Ca2+内流的激活会降低微小RNA miR-322的丰度，这会增加PDIA6 mRNA的稳定性，从而在应激反应期间增强IRE1α活性。对小鼠和蠕虫进行的体内实验表明，内质网应激的诱导与miR-322丰度降低、PDIA6 mRNA丰度增加或两者都有关。总之，这些发现表明，在内质网Ca2+稳态破坏的情况下，内质网Ca2+、PDIA6、IRE1α和miR-322在调节UPR的动态反馈回路中发挥作用。
