Department of Pathology and Laboratory Medicine, University of British Columbia, The Providence Heart and Lung Institute, St Paul's Hospital, Vancouver, British Columbia, Canada.
J Virol. 2010 Sep;84(17):8446-59. doi: 10.1128/JVI.01416-09. Epub 2010 Jun 16.
Cardiomyocyte apoptosis is a hallmark of coxsackievirus B3 (CVB3)-induced myocarditis. We used cardiomyocytes and HeLa cells to explore the cellular response to CVB3 infection, with a focus on pathways leading to apoptosis. CVB3 infection triggered endoplasmic reticulum (ER) stress and differentially regulated the three arms of the unfolded protein response (UPR) initiated by the proximal ER stress sensors ATF6a (activating transcription factor 6a), IRE1-XBP1 (X box binding protein 1), and PERK (PKR-like ER protein kinase). Upon CVB3 infection, glucose-regulated protein 78 expression was upregulated, and in turn ATF6a and XBP1 were activated via protein cleavage and mRNA splicing, respectively. UPR activity was further confirmed by the enhanced expression of UPR target genes ERdj4 and EDEM1. Surprisingly, another UPR-associated gene, p58(IPK), which often is upregulated during infections with other types of viruses, was downregulated at both mRNA and protein levels after CVB3 infection. These findings were observed similarly for uninfected Tet-On HeLa cells induced to overexpress ATF6a or XBP1. In exploring potential connections between the three UPR pathways, we found that the ATF6a-induced downregulation of p58(IPK) was associated with the activation of PKR (PERK) and the phosphorylation of eIF2alpha, suggesting that p58(IPK), a negative regulator of PERK and PKR, mediates cross-talk between the ATF6a/IRE1-XBP1 and PERK arms. Finally, we found that CVB3 infection eventually produced the induction of the proapoptoic transcription factor CHOP and the activation of SREBP1 and caspase-12. Taken together, these data suggest that CVB3 infection activates UPR pathways and induces ER stress-mediated apoptosis through the suppression of P58(IPK) and induction/activation of CHOP, SREBP1, and caspase-12.
心肌细胞凋亡是柯萨奇病毒 B3 (CVB3) 诱导心肌炎的一个标志。我们使用心肌细胞和 HeLa 细胞来探索细胞对 CVB3 感染的反应,重点是导致细胞凋亡的途径。CVB3 感染触发内质网 (ER) 应激,并通过近端 ER 应激传感器 ATF6a(激活转录因子 6a)、IRE1-XBP1(X 盒结合蛋白 1)和 PERK(PKR 样 ER 蛋白激酶)启动的未折叠蛋白反应 (UPR) 的三个分支进行差异调节。在 CVB3 感染后,葡萄糖调节蛋白 78 的表达上调,反过来 ATF6a 和 XBP1 分别通过蛋白切割和 mRNA 剪接被激活。UPR 活性进一步通过 UPR 靶基因 ERdj4 和 EDEM1 的增强表达得到证实。令人惊讶的是,另一个与 UPR 相关的基因,p58(IPK),在感染其他类型病毒时通常上调,但在 CVB3 感染后,其 mRNA 和蛋白水平均下调。在探索三种 UPR 途径之间的潜在联系时,我们发现 ATF6a 诱导的 p58(IPK)下调与 PKR(PERK)的激活和 eIF2alpha 的磷酸化有关,表明 p58(IPK),PERK 和 PKR 的负调节剂,介导 ATF6a/IRE1-XBP1 和 PERK 臂之间的串扰。最后,我们发现 CVB3 感染最终导致促凋亡转录因子 CHOP 的诱导和 SREBP1 和 caspase-12 的激活。总之,这些数据表明,CVB3 感染通过抑制 P58(IPK)和诱导/激活 CHOP、SREBP1 和 caspase-12,激活 UPR 途径并诱导 ER 应激介导的细胞凋亡。