The Role of Trim Proteins in Regulating Norovirus Replication and Tropism

病毒嗜性，或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新病毒疾病出现的重要概念。诺如病毒是世界范围内引起牙周病的主要原因，但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、发病机制和治疗选择至关重要。人诺如病毒在小动物模型中不能稳健地复制，因此鼠诺如病毒（MNV）已经成为发现诺如病毒生物学和嗜性机制的模型系统。在过去的几年中，已经确定MNV毒株可以感染小鼠的不同细胞和组织，尽管接种途径相似。这些向性差异的分子基础在很大程度上是未知的。我们最近证明了CD300lf是一种通用的MNV受体。这一发现表明，多样化的MNV株嗜性的主要机制是没有差异的受体利用。这些发现表明，未知的宿主抗病毒蛋白作为限制因子，限制某些MNV株的组织和细胞复制的可能性。然而，任何诺如病毒的限制因子都无法进行分子鉴定。在这里，我们建立在我们的初步鉴定Trim7和Trim47作为MNV限制因子。TRIM蛋白是泛素E3连接酶，尽管Trim7和Trim47的底物和抗病毒机制目前尚不清楚。虽然Trim7广泛抑制MNV毒株复制，但Trim47选择性抑制某些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嗜性。因此，我们假设Trim7和Trim47构成了一个TRIM限制因子家族，该家族调节诺如病毒（包括人诺如病毒）的嗜性。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对相关病毒（包括人类诺如病毒）的抗病毒活性范围。在具体目标2中，我们将定义Trim7和Trim47在塑造允许MNV体内复制的细胞和组织中的生理作用。我们还将确定获得对Trim7和Trim47的抗性的病毒的体内适应性权衡。该项目利用MNV模型系统来揭示一对知之甚少的TRIM蛋白的病毒限制的新机制。它将提供深入了解诺如病毒的嗜性和进化的驱动因素。

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.