Evasion of intrinsic antiviral host cell responses by herpesviruses

描述（由申请人提供）：早幼粒细胞核小体（PML NBs）是一种0.2-1um的核细胞器，介导细胞宿主对病毒感染的内在防御反应。疱疹病毒通过多种策略表达调节PML或PML相关蛋白的蛋白，包括PML降解或PML NB蛋白的重新定位。在体内感染过程中，pml -疱疹病毒相互作用的后果尚未得到详细的研究，这主要是因为许多人类疱疹病毒具有物种特异性。鼠γ疱疹病毒68 (？HV68)正逐渐成为研究病毒与宿主相互作用的基本生物学问题的合适模型，因为它能自然感染小鼠。最近我们发现？HV68通过蛋白酶体依赖机制诱导PML降解，PML的缺失导致小鼠成纤维细胞中更强的病毒复制。令人惊讶的是，我们发现？hv68介导的PML降解是由病毒粒子被覆蛋白ORF75c介导的，该蛋白与细胞甲酰基甘氨酸酰胺核糖酰氨基转移酶（FGARAT）酶具有同源性。此外，我们已经证明ORF75c对感染性病毒的产生至关重要。ORF75同源物在所有的病毒中都是保守的，但到目前为止还没有指定的功能。我们的研究揭示了这种不寻常的蛋白质在横纹肌病毒生物学中的潜在作用，并表明？HV68将成为研究pml -疱疹病毒体内相互作用的有用模型。本研究项目的目标是：1)确定ORF75c介导PML降解的机制；2)确定ORF75c如何参与病毒复制周期；3)确定PML在体内调节急性和慢性疱疹病毒感染的动力学和振幅中的作用。从我们的研究中产生的信息将解决两个基本问题。首先，病毒FGARAT蛋白在γ疱疹病毒生物学中的功能是什么；其次，PML在体内调节急性和/或慢性疱疹病毒感染中起什么作用？？HV68将是一个有益的模型系统，以解决这些问题的方式，特别是人类疱疹病毒和γ疱疹病毒，将更加困难或不可能。这项研究的实际应用可能支持pml缺陷系统可以在实验或诊断工作中提供非常敏感的病毒感染读数的概念。此外，可以想象，可以开发出增强PML活性的抗病毒疗法。最后，针对ORF75开发新的抗γ疱疹病毒疗法可能是一种有益的策略，特别是如果发现它具有内在的酶功能。

DESCRIPTION (provided by applicant): Promyelocytic nuclear bodies (PML NBs) are 0.2-1um nuclear organelles that mediate an intrinsic cellular host defense response against virus infections. Herpesviruses express proteins that modulate PML or PML-associated proteins by a variety of strategies, including degradation of PML or relocalization of PML NB proteins. The consequences of PML-herpesvirus interactions during infection in vivo have yet to be investigated in detail, largely because of the species-specific tropism of many human herpesviruses. Murine gammaherpesvirus 68 (?HV68) is emerging as a suitable model to study basic biological questions of virus host interactions because it naturally infects mice. Recently we have found that ?HV68 induces PML degradation through a proteasome-dependent mechanism and that loss of PML results in more robust virus replication in mouse fibroblasts. Surprisingly, we found that ?HV68-mediated PML degradation is mediated by the virion tegument protein ORF75c, which shares homology with the cellular formylglycinamide ribotide amidotransferase (FGARAT) enzyme. In addition, we have shown that ORF75c is essential for production of infectious virus. ORF75 homologs are conserved in all rhadinoviruses but so far have no assigned functions. Our studies shed light on a potential role for this unusual protein in rhadinovirus biology and suggest that ?HV68 will be a useful model for investigation of PML-herpesvirus interactions in vivo. The goals of this research project are to: 1) determine the mechanism by which ORF75c mediates PML degradation, 2) to determine how ORF75c contributes to the viral replication cycle, and 3) to determine the role of PML in modulating the kinetics and amplitude of acute and chronic herpesvirus infection in vivo. The information generated from our studies will address two fundamental questions. First, what is the function of the viral FGARAT proteins for gammaherpesvirus biology and second, what role does PML have in modulating acute and/or chronic herpesvirus infections in vivo? ?HV68 will be a rewarding model system to address these questions in ways that would be significantly more difficult or impossible with human herpesviruses and gammaherpesviruses in particular. Practical applications from this research might support the notion that PML-deficient systems can offer a very sensitive readout for viral infection in experimental or diagnostic work. In addition, antiviral therapies that enhance PML activities could conceivably be developed. Finally, targeting ORF75 for developing novel anti-gammaherpesvirus therapeutics might be a rewarding strategy, especially if it is found to possess intrinsic enzymatic functions. PUBLIC HEALTH RELEVANCE: Human gammaherpesviruses, exemplified by Epstein-Barr virus and Kaposi's Sarcoma herpesvirus (EBV and KSHV), are significant causes of human disease, including cancer. We will utilize murine gammaherpesvirus 68 (?HV68) to help unravel mechanisms by which gammaherpesviruses evade intrinsic host defenses through the activity of an unusual viral protein ORF75, which is conserved in all gammaherpesviruses. Our studies will yield new insights into virus-host interactions that modulate viral infections and possibly identify new viral targets for development of novel antiviral therapeutics.