Joachims M, Van Breugel P C, Lloyd R E
Department of Microbiology and Immunology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA.
J Virol. 1999 Jan;73(1):718-27. doi: 10.1128/JVI.73.1.718-727.1999.
Many enteroviruses, members of the family Picornaviridae, cause a rapid and drastic inhibition of host cell protein synthesis during infection, a process referred to as host cell shutoff. Poliovirus, one of the best-studied enteroviruses, causes marked inhibition of host cell translation while preferentially allowing translation of its own genomic mRNA. An abundance of experimental evidence has accumulated to indicate that cleavage of an essential translation initiation factor, eIF4G, during infection is responsible at least in part for this shutoff. However, evidence from inhibitors of viral replication suggests that an additional event is necessary for the complete translational shutoff observed during productive infection. This report examines the effect of poliovirus infection on a recently characterized 3' end translational stimulatory protein, poly(A)-binding protein (PABP). PABP is involved in stimulating translation initiation in lower eukaryotes by its interaction with the poly(A) tail on mRNAs and has been proposed to facilitate 5'-end-3'-end interactions in the context of the closed-loop translational model. Here, we show that PABP is specifically degraded during poliovirus infection and that it is cleaved in vitro by both poliovirus 2A and 3C proteases and coxsackievirus B3 2A protease. Further, PABP cleavage by 2A protease is accompanied by concurrent loss of translational activity in an in vitro-translation assay. Similar loss of translational activity also occurs simultaneously with partial 3C protease-mediated cleavage of PABP in translation assays. Further, PABP is not degraded during infections in the presence of guanidine-HCl, which blocks the complete development of host translation shutoff. These results provide preliminary evidence that cleavage of PABP may contribute to inhibition of host translation in infected HeLa cells, and they are consistent with the hypothesis that PABP plays a role in facilitating translation initiation in higher eukaryotes.
许多肠道病毒属于小核糖核酸病毒科，在感染过程中会迅速且显著地抑制宿主细胞蛋白质合成，这一过程被称为宿主细胞关闭。脊髓灰质炎病毒是研究最为深入的肠道病毒之一，它会显著抑制宿主细胞的翻译，同时优先允许自身基因组mRNA的翻译。大量实验证据表明，感染期间一种关键的翻译起始因子eIF4G的裂解至少部分导致了这种关闭。然而，来自病毒复制抑制剂的证据表明，在有效感染期间观察到的完全翻译关闭还需要另外一个事件。本报告研究了脊髓灰质炎病毒感染对一种最近被鉴定的3'端翻译刺激蛋白——聚腺苷酸结合蛋白（PABP）的影响。PABP通过与mRNA上的聚腺苷酸尾相互作用，参与刺激低等真核生物中的翻译起始，并且在闭环翻译模型的背景下，有人提出它有助于5'端与3'端的相互作用。在这里，我们表明PABP在脊髓灰质炎病毒感染期间会被特异性降解，并且它在体外会被脊髓灰质炎病毒2A和3C蛋白酶以及柯萨奇病毒B3 2A蛋白酶切割。此外，在体外翻译试验中，2A蛋白酶切割PABP会伴随着翻译活性的同时丧失。在翻译试验中，部分3C蛋白酶介导的PABP切割也会同时发生类似的翻译活性丧失。此外，在存在盐酸胍的情况下感染时，PABP不会被降解，盐酸胍会阻止宿主翻译关闭的完全发展。这些结果提供了初步证据，表明PABP的切割可能有助于抑制感染的HeLa细胞中的宿主翻译，并且它们与PABP在促进高等真核生物翻译起始中起作用的假设一致。
