Translation Regulation by Enterovirus Proteinase

描述（由申请人提供）：本研究的长期目标是了解肠病毒（如脊髓灰质炎病毒（PV）和柯萨奇病毒（CVB3））灭活几乎所有细胞mRNA翻译的机制，同时刺激感染细胞中病毒mRNA的有效翻译。我们已经证明，翻译起始因子eIF4G的切割会阻断核糖体上新盖帽mRNA的组装，并且PABP的切割需要与eIF4G一致才能完全阻断翻译。PABP切割影响翻译的后期步骤，目前尚未确定，但可能通过mRNA上的5‘-3’相互作用中断核糖体的再循环。核糖体循环的机制及其生化需求尚不清楚。此外，肠病毒和可能大多数其他正链RNA病毒必须在病毒RNA合成开始之前突然关闭感染病毒基因组的翻译。我们假设papp的切割也是抑制病毒翻译所必需的。涉及PABP的翻译调节机制现在被认为在几个层面上与mRNA衰变机制相连接。此外，与靶向细胞mrna的3' UTR结合的microrna也通过未知机制沉默了mrna的翻译，这种翻译以某种方式导致mrna从多聚体转运到其他称为p体和应激颗粒的细胞室。我们发现，G3BP是胁迫颗粒形成的关键因子，在pv感染的细胞中被3C蛋白酶裂解。因此，病毒在一个新的水平上攻击整个翻译调节机构。本研究的目的是确定pbp切割在病毒翻译到RNA复制的转换过程中的作用，确定核糖体循环在这一转换过程中的作用，并研究G3BP切割在病毒复制周期和microrna翻译沉默中的作用。这些结果将为研究细胞如何在翻译水平调控基因表达，以及翻译起始因子与mRNA沉默/衰减途径之间的相互作用提供新的基础信息，这将有助于研究病毒调控基因表达和癌症和细胞凋亡中的细胞应激反应。

DESCRIPTION (provided by applicant): The long term goal of this research is to understand the mechanism by which enteroviruses such as poliovirus (PV) and Coxsackievirus (CVB3) inactivate translation of nearly all cellular mRNA while stimulating efficient translation of viral mRNA in infected cells. We have shown that cleavage of the translation initiation factor eIF4G will block assembly of new capped mRNA on ribosomes, and that cleavage of PABP is required in concert with eIF4G to completely block translation. PABP cleavage affects late steps in translation that are presently undefined, however likely interrupt ribosome recycling via 5'-3' interactions on mRNA. The mechanism of ribosome recycling and its biochemical requirements are unknown. In addition, enteroviruses and probably most other plus strand RNA viruses must abruptly shut down translation of the infecting viral genome before viral RNA synthesis can begin. We hypothesize that PABP cleavage is also required for inhibition of viral translation. Translation regulation mechanisms involving PABP are now thought to interface with mRNA decay mechanisms on several levels. In addition, microRNAs, which bind to 3' UTR of targeted cellular mRNAs, also silence translation by unknown mechanisms that somehow result in transit of mRNAs from polysomes to other cell compartments called P-bodies and stress granules. We have discovered that G3BP, a key factor that nucleates formation of stress granules, is cleaved in PV-infected cells by 3C protease. Thus, the virus is attacking the overall translation regulatory apparatus at a new level. The aims in this proposal will determine the role of PABP cleavage in the switch from viral translation to RNA replication, will determine the role of ribosome recycling in this switch, and will investigate the function of G3BP cleavage on the viral replication cycle and microRNA-translation silencing. These results will provide new fundamental information on how cells regulate gene expression at the translation level, and the interplay between translation initiation factors and mRNA silencing/decay pathways that will be useful in studies of viral regulation of gene expression and cellular stress responses in cancer and apoptosis. This work investigates new ways that poliovirus, the prototype human picornavirus, interferes with host translation and regulation of gene expression by stress granules and microRNAs. These mechanisms are fundamental for cell gene regulation and are disrupted in cancer and numerous non-viral diseases. These experiments will give us more insight how a large class of human pathogens invade and kill cells (cytopathology) and potentially provide new avenues for disease prevention and we will learn more about gene regulation in human cells.