Disruption of Cellular Messenger RNA Processing Events by the Kaposi's Sarcoma-As

描述(申请人提供)：卡波西肉瘤相关疱疹病毒(KSHV)是未经治疗的艾滋病患者最常见的肿瘤的病原体，也与两种B细胞淋巴增生性疾病有关。先前已经证明，裂解病毒复制周期是KSHV诱导的致病机制的重要组成部分。裂解性KSHV感染的一个显著后果是细胞转录组几乎完全被破坏，被称为“宿主关闭”。这种表型是由病毒SOX蛋白介导的，它促进细胞信使RNA(MRNA)的降解，可能是通过拦截细胞RNA稳定途径来实现的。我们发现了两个与宿主关闭相关的新的SOX活性：SOX诱导细胞质Poly(A)结合蛋白(PABPC)的核重新定位，并触发细胞核内细胞mRNAs的3‘端加工中断，导致其高腺苷化。PABPC是一种细胞蛋白，在细胞质中的mRNA翻译和稳定性中起关键作用，但尚不具有已知的核功能。因此，我们假设它在表达SOX的细胞中的异常定位是细胞质mRNA破坏的一个重要因素。在细胞核内，新生的高腺苷化细胞mRNAs不会输出，我们预测它们会被细胞质量控制机制破坏。有趣的是，我们有初步数据表明，核PABPC是高腺苷化表型的重要驱动因素。因此，KSHV似乎以PABPC为靶标，通过不同的机制消除细胞核和细胞质的细胞信息。这代表了病毒诱导宿主基因表达终止的一种全新的机制，此外，还首次在人类细胞中揭示了聚腺苷酸化刺激的mRNA衰退的机制和PABPC在细胞核中的作用。正常细胞RNA周转途径的中断与人类疾病之间的新联系突显了了解此类事件被解除调控的机制的重要性；在这方面，KSHV Sox是探索致病人类病毒如何与这些关键细胞途径相互作用的优秀工具。这项建议将探索SOX诱导的PABPC导入和mRNA高腺苷化之间的联系，以及细胞质量控制通路对这些信息的最终破坏的贡献。具体地说，我们将首先确认核PABPC驱动高腺苷酸化，然后继续剖析发生这种情况的机制。PABPC是细胞质中无意义介导的mRNA衰退途径的关键拮抗剂，因此我们将探索该途径和其他质量控制途径在KSHV感染过程中潜在的异常激活。最后，我们将在细胞培养和小鼠模型中监测宿主关闭对病毒复制和致病的贡献。

DESCRIPTION (provided by applicant): Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of the most common neoplasm in untreated AIDS patients, and is also affiliated with two B cell lymphoproliferative disorders. The lytic viral replication cycle has previously been shown to be an essential component of KSHV-induced pathogenesis. One prominent consequence of lytic KSHV infection is a near total destruction of the cellular transcriptome, termed 'host shutoff'. This phenotype is mediated by the viral SOX protein which promotes enhanced cellular messenger RNA (mRNA) degradation, likely via interception of cellular RNA stability pathways. We have identified 2 novel SOX activities linked to host shutoff: SOX induces nuclear re-localization of cytoplasmic poly(A) binding protein (PABPC), and triggers disruption of the 3' end processing of cellular mRNAs in the nucleus leading to their hyperadenylation. PABPC is a cellular protein that plays a key role in mRNA translation and stability in the cytoplasm yet has no known nuclear functions. Thus, we hypothesize that its aberrant localization in SOX-expressing cells is a significant contributor to cytoplasmic mRNA destruction. Within the nucleus, the nascent hyperadenylated cellular mRNAs are not exported, and we predict they are destroyed by cellular quality control mechanisms. Interestingly, we have preliminary data indicating that nuclear PABPC is an important driver of the hyperadenylation phenotype. Thus, KSHV appears to target PABPC to eliminate both nuclear and cytoplasmic cellular messages via distinct mechanisms. This represents a completely novel mechanism of virus-induced termination of host gene expression and, additionally, reveals for the first time in human cells a mechanism for polyadenylation-stimulated mRNA decay and a role for PABPC in the nucleus. Emerging connections between disruption of normal cellular RNA turnover pathways and human disease have highlighted the importance of understanding mechanisms by which such events become deregulated; it is in this regard that KSHV SOX represents an excellent tool to probe how pathogenic human viruses may interface with these critical cellular pathways. This proposal will explore the connections between SOX-induced PABPC import and mRNA hyperadenylation, as well as explore the contribution of cellular quality control pathways towards the ultimate destruction of these messages. Specifically, we will begin by confirming that nuclear PABPC drives hyperadenylation then proceed to dissect the mechanisms by which this occurs. PABPC is a key antagonist of the nonsense-mediated mRNA decay pathway in the cytoplasm, and we will therefore explore the potential aberrant activation of this and other quality control pathways during KSHV infection. Finally, we will monitor the contribution of host shutoff towards viral replication and pathogenesis both in cell culture and in murine models.