Porcine circovirus type 2 capsid protein induces unfolded protein response with subsequent activation of apoptosis

Abstract

Porcine circovirus type 2 (PCV2) has recently been reported to elicit the unfolded protein response (UPR) via activation of the PERK/eIF2α (RNA-activated protein kinase-like endoplasmic reticulum (ER) kinase/eukaryotic initiation factor 2α) pathway. This study attempted to examine which viral protein might be involved in inducing UPR and whether this cellular event would lead to apoptosis of the cells expressing the viral protein. By transient expression, we found that both replicase (Rep) and capsid (Cap) proteins of PCV2 could induce ER stress as shown by increased phosphorylation of PERK with subsequent activation of the eIF2α-ATF4 (activating transcription factor 4)-CHOP (CCAAT/enhancer-binding protein homologous protein) axis. Cap expression, but not Rep, significantly reduced antiapoptotic B-cell lymphoma-2 (Bcl-2) and increased caspase-3 cleavage, possibly due to increased expression of CHOP. Since knockdown of PERK by RNA interference clearly reduced Cap-induced CHOP expression, caspase-3 cleavage, and apoptotic cell death possibly by partially rescuing Bcl-2 expression, we propose that there is connection between Cap-induced UPR and apoptosis via the PERK/eIF2α/ATF4/CHOP/Bcl-2 pathway. This study, together with our earlier studies, provides insight into the mechanisms underlying PCV2 pathogenesis.

中文概要

题目

猪圆环病毒2 型衣壳蛋白通过未折叠蛋白反应诱导凋亡

目的

确定猪圆环病毒2 型衣壳蛋白(PCV2)感染引起 未折叠蛋白反应的关键病毒蛋白,以及探究 PCV2 感染中未折叠蛋白反应与凋亡之间的联 系。

创新点

本文首次鉴定出PCV2 感染引起未折叠蛋白反应 的关键病毒蛋白。

方法

构建表达病毒蛋白的真核表达载体,通过瞬时转 染PK-15 细胞,采用免疫印迹检测未折叠蛋白反 应通路的关键分子;利用RNA 干扰抑制perk 基 因的表达来验证激活的通路;通过抑制内质网上 游分子PERK 并利用免疫印迹和流式细胞术检测 凋亡,研究内质网应激与凋亡之间的联系。

结论

PCV2 Rep 和Cap 蛋白能激活PERK-eIF2α-ATF4-CHOP 通路,PERK 通路在Cap 诱导的细胞凋亡中起重要作用。