The Role of Trim Proteins in Regulating Norovirus Replication and Tropism

病毒嗜性，即病毒可以感染的细胞、组织或物种的范围，是理解病毒发病机制和出现新的病毒疾病的重要概念。诺如病毒是全世界腹泻疾病的主要原因，但人们对诺如病毒嗜性的原因知之甚少。填补这一知识空白对于更好地理解诺如病毒的生物学、发病机制和治疗方案至关重要。人类诺如病毒不能在小动物模型中强劲复制，因此小鼠诺如病毒(MNV)已成为发现诺如病毒生物学和嗜性机制的模型系统。在过去的几年里，已经确定MNV株可以感染小鼠体内不同的细胞和组织，尽管接种途径相似。这些取向差异的分子基础在很大程度上是未知的。我们最近证实CD300lf是一种通用的MNV受体。这一发现表明，MNV毒株趋向性多样化的主要机制不是不同的受体利用。这些发现表明，未知的宿主抗病毒蛋白可能作为限制因素，限制某些MNV毒株的组织和细胞复制。然而，任何诺沃克病毒的限制因素都无法进行分子鉴定。在这里，我们建立在我们最初将Trim7和Trim47确定为MNV限制因素的基础上。TRIM蛋白是泛素E3连接酶，尽管目前尚不清楚TRIM7和TRIM47的底物和抗病毒机制。Trim7广泛地抑制MNV毒株的复制，而Trim47选择性地抑制某些MNV毒株。在其他病毒系统中，TRIM蛋白负责塑造病毒的细胞和物种取向。因此，我们推测，Trim7和Trim47组成了一个TRIM限制因子家族，调节包括人诺如病毒在内的诺如病毒的趋向性。在具体目标1中，我们将确定Trim7和Trim47抑制MNV的分子机制。我们还将确定Trim7和Trim47对包括人类诺如病毒在内的相关病毒的抗病毒活性的广度。在特定的目标2中，我们将确定Trim7和Trim47在体内形成允许MNV复制的细胞和组织中的生理作用。我们还将确定对Trim7和Trim47产生抗药性的病毒在体内的适应性权衡。该项目利用MNV模型系统来揭示一对知之甚少的TRIM蛋白对病毒限制的新机制。它将提供对诺沃克病毒嗜性和进化的驱动因素的洞察。

Viral tropism, or the range of cells, tissues, or species that a virus can infect, is an important concept to understand viral pathogenesis and the emergence of new viral diseases. Noroviruses are the leading cause of diarrheal diseases worldwide, yet little is known about what contributes to norovirus tropism. Filling in this knowledge gap is crucial to better comprehend norovirus biology, pathogenesis, and therapeutic options. Human noroviruses do not robustly replicate in small animal models and thus murine norovirus (MNV) has emerged as a model system to discover mechanisms of norovirus biology and tropism. Over the past several years, it has been established that MNV strains can infect different cells and tissues in mice despite similar routes of inoculation. The molecular basis for these tropism differences are largely unknown. We recently demonstrated that CD300lf is a universal MNV receptor. This finding demonstrates that the primary mechanism for diversifying MNV strain tropism is not differential receptor utilization. These findings suggest the possibility that unknown host antiviral proteins function as restriction factors that limit the tissue and cellular replication of certain MNV strains. Yet, restriction factors for any norovirus have defied molecular identification. Here, we build upon our initial identification of Trim7 and Trim47 as MNV restriction factors. TRIM proteins are ubiquitin E3 ligases, although the substrates and antiviral mechanisms of Trim7 and Trim47 are currently unknown. While Trim7 broadly inhibits MNV strains from replicating, Trim47 selectively inhibits certain MNV strains. In other viral systems, TRIM proteins are responsible for shaping the cellular and species tropism of viruses. Therefore, we hypothesize that Trim7 and Trim47 constitute a family of TRIM restriction factors that regulate the tropism of noroviruses, including human norovirus. In Specific Aim 1, we will determine the molecular mechanism of Trim7 and Trim47 inhibition of MNV. We will also determine the breadth of the antiviral activity of Trim7 and Trim47 on related viruses, including human norovirus. In Specific Aim 2, we will define the physiological role of Trim7 and Trim47 in shaping the cells and tissues that are permissive for MNV replication in vivo. We will also determine the in vivo fitness tradeoffs for viruses that acquire resistance to Trim7 and Trim47 .This project leverages the MNV model system to uncover new mechanisms of viral restriction by a pair of poorly understood TRIM proteins. It will provide insight into drivers of norovirus tropism and evolution.