McLean Jeffrey E, Datan Emmanuel, Matassov Demetrius, Zakeri Zahra F
Department of Biology, Queens College and Graduate Center of the City University of New York, Flushing, New York 11367, USA.
J Virol. 2009 Aug;83(16):8233-46. doi: 10.1128/JVI.02672-08. Epub 2009 Jun 3.
The ectopic overexpression of Bcl-2 restricts both influenza A virus-induced apoptosis and influenza A virus replication in MDCK cells, thus suggesting a role for Bcl-2 family members during infection. Here we report that influenza A virus cannot establish an apoptotic response without functional Bax, a downstream target of Bcl-2, and that both Bax and Bak are directly involved in influenza A virus replication and virus-induced cell death. Bak is substantially downregulated during influenza A virus infection in MDCK cells, and the knockout of Bak in mouse embryonic fibroblasts yields a dramatic rise in the rate of apoptotic death and a corresponding increase in levels of virus replication, suggesting that Bak suppresses both apoptosis and the replication of virus and that the virus suppresses Bak. Bax, however, is activated and translocates from the cytosol to the mitochondria; this activation is required for the efficient induction of apoptosis and virus replication. The knockout of Bax in mouse embryonic fibroblasts blocks the induction of apoptosis, restricts the infection-mediated activation of executioner caspases, and inhibits virus propagation. Bax knockout cells still die but by an alternative death pathway displaying characteristics of autophagy, similarly to our previous observation that influenza A virus infection in the presence of a pancaspase inhibitor leads to an increase in levels of autophagy. The knockout of Bax causes a retention of influenza A virus NP within the nucleus. We conclude that the cell and virus struggle to control apoptosis and autophagy, as appropriately timed apoptosis is important for the replication of influenza A virus.
Bcl-2的异位过表达可限制甲型流感病毒诱导的MDCK细胞凋亡及甲型流感病毒复制,从而提示Bcl-2家族成员在感染过程中发挥作用。在此我们报告,甲型流感病毒若没有Bcl-2的下游靶点——具有功能的Bax,就无法建立凋亡反应,且Bax和Bak均直接参与甲型流感病毒复制及病毒诱导的细胞死亡。在MDCK细胞的甲型流感病毒感染过程中,Bak显著下调,而在小鼠胚胎成纤维细胞中敲除Bak会导致凋亡死亡率急剧上升以及病毒复制水平相应增加,这表明Bak可抑制凋亡及病毒复制,且病毒可抑制Bak。然而,Bax被激活并从胞质溶胶转位至线粒体;这种激活对于有效诱导凋亡及病毒复制是必需的。在小鼠胚胎成纤维细胞中敲除Bax可阻断凋亡诱导,限制感染介导的效应半胱天冬酶激活,并抑制病毒传播。Bax敲除细胞仍会死亡,但通过一种显示出自噬特征的替代死亡途径,这与我们之前的观察结果相似,即在存在泛半胱天冬酶抑制剂的情况下甲型流感病毒感染会导致自噬水平增加。Bax的敲除导致甲型流感病毒核蛋白(NP)滞留于细胞核内。我们得出结论,细胞与病毒在控制凋亡和自噬方面相互斗争,因为适时的凋亡对于甲型流感病毒的复制很重要。