Nencioni Lucia, De Chiara Giovanna, Sgarbanti Rossella, Amatore Donatella, Aquilano Katia, Marcocci Maria E, Serafino Annalucia, Torcia Maria, Cozzolino Federico, Ciriolo Maria R, Garaci Enrico, Palamara Anna T
Department of Public Health Sciences, Sapienza University of Rome, 00185 Rome.
J Biol Chem. 2009 Jun 5;284(23):16004-15. doi: 10.1074/jbc.M900146200. Epub 2009 Mar 31.
Previous reports have shown that various steps in the influenza A virus life cycle are impaired in cells expressing the antiapoptotic protein Bcl-2 (Bcl-2(+) cells). We demonstrated a direct link between Bcl-2 and the reduced nuclear export of viral ribonucleoprotein (vRNP) complexes in these cells. However, despite its negative impact on viral replication, Bcl-2 did not prevent host cells from undergoing virally triggered apoptosis. The protein's reduced antiapoptotic capacity was related to phosphorylation of its threonine 56 and serine 87 residues by virally activated p38MAPK. In infected Bcl-2(+) cells, activated p38MAPK was found predominantly in the cytoplasm, colocalized with Bcl-2, and both Bcl-2 phosphorylation and virally induced apoptosis were diminished by specific inhibition of p38MAPK activity. In contrast, in Bcl-2-negative (Bcl-2(-)) cells, which are fully permissive to viral infection, p38MAPK activity was predominantly nuclear, and its inhibition decreased vRNP traffic, phosphorylation of viral nucleoprotein, and virus titers in cell supernatants, suggesting that this kinase also contributes to the regulation of vRNP export and viral replication. This could explain why in Bcl-2(+) cells, where p38MAPK is active in the cytoplasm, phosphorylating Bcl-2, influenza viral replication is substantially reduced, whereas apoptosis proceeds at rates similar to those observed in Bcl-2(-) cells. Our findings suggest that the impact of p38MAPK on the influenza virus life cycle and the apoptotic response of host cells to infection depends on whether or not the cells express Bcl-2, highlighting the possibility that the pathological effects of the virus are partly determined by the cell type it targets.
先前的报道表明，甲型流感病毒生命周期中的各个步骤在表达抗凋亡蛋白Bcl-2的细胞（Bcl-2(+)细胞）中受到损害。我们证明了在这些细胞中Bcl-2与病毒核糖核蛋白（vRNP）复合物核输出减少之间存在直接联系。然而，尽管Bcl-2对病毒复制有负面影响，但它并不能阻止宿主细胞发生病毒触发的凋亡。该蛋白抗凋亡能力的降低与其苏氨酸56和丝氨酸87残基被病毒激活的p38丝裂原活化蛋白激酶磷酸化有关。在感染的Bcl-2(+)细胞中，活化的p38丝裂原活化蛋白激酶主要存在于细胞质中，与Bcl-2共定位，并且通过特异性抑制p38丝裂原活化蛋白激酶活性，Bcl-2磷酸化和病毒诱导的凋亡均减少。相比之下，在对病毒感染完全允许的Bcl-2阴性（Bcl-2(-)）细胞中，p38丝裂原活化蛋白激酶活性主要存在于细胞核中，其抑制降低了vRNP转运、病毒核蛋白的磷酸化以及细胞上清液中的病毒滴度，这表明该激酶也有助于调节vRNP输出和病毒复制。这可以解释为什么在p38丝裂原活化蛋白激酶在细胞质中活跃并使Bcl-2磷酸化的Bcl-2(+)细胞中，甲型流感病毒复制显著减少，而凋亡以与在Bcl-2(-)细胞中观察到的速率相似的速度进行。我们的研究结果表明，p38丝裂原活化蛋白激酶对甲型流感病毒生命周期以及宿主细胞对感染的凋亡反应的影响取决于细胞是否表达Bcl-2，这突出了病毒的病理效应部分由其靶向的细胞类型决定的可能性。
