Novel Mechanisms Of Innate Immune Control Through RNA-binding Proteins During Viral Infection

I型和III型干扰素是针对病毒感染的先天免疫反应的关键介质。新近发现的III型IFN(IFNL)具有抗病毒保护作用，特别是在呼吸道和胃肠道以及肝脏的上皮表面，它们对于增强免疫反应以抵御丙型肝炎病毒(HCV)、西尼罗河病毒和登革病毒等黄病毒成员的感染至关重要。像IFN这样的免疫基因经历了持续的调节，以适应外部刺激，如细胞应激和危险信号，并调整基因剂量以做出适当的免疫反应，同时避免由于免疫系统过度激活而导致的免疫病理。基因表达受到顺式和反式多层调控元件的严格调控。一个强大的转录后调控机制是调节mRNA3‘非翻译区，它决定了mRNA3’非翻译区翻译成蛋白质的速率。针对3‘UTR的主要调控元件包括microRNAs、RNA结合蛋白和长的非编码RNAs，所有这些都改变了免疫基因的剂量和免疫反应。许多免疫基因，如干扰素和细胞因子，在其3‘UTRs中含有至少一个AUUA五聚体的重复的腺苷尿酸富含元件(ARE)。这些不稳定基序被ARE结合蛋白靶向导致mRNA降解，这一过程被称为ARE介导的衰退(AMD)。几项遗传学研究表明，IFNL基因与自发的丙型肝炎病毒清除和对干扰素治疗的反应有很强的相关性。IFNL3基因3‘端非编码区的单核苷酸多态(SNP)通过影响AMD和miRNA介导的衰变程度来决定IFNL3mRNA的周转。虽然丙型肝炎病毒诱导的miRNAs决定了IFNL3mRNA的不稳定性，但3‘UTRSNP是如何影响IFNL3AMD的，以及这一途径涉及哪些成分仍未确定。本研究旨在鉴定与IFNL3mRNA失稳相关的核糖核酸结合蛋白(S)及其组分。我的初步数据表明，RNA结合蛋白ZAP(锌指抗病毒蛋白)是一种针对病毒RNA的抗病毒因子，在丙型肝炎病毒感染过程中与宿主IFNL3 mRNA结合并降解。对这种转录后调控机制的详细了解(S)对于充分理解宿主IFNL3基因与基因稳定性之间的联系，AMD在黄病毒免疫逃避中的作用以及对感染结局的影响是必要的。重要的是，这种免疫逃避机制可以是普遍的，也可以转化为呼吸道和胃肠道上皮的病毒感染(例如肠道病毒、流感病毒、冠状病毒)，为治疗开辟新的途径。

Type I and type III interferons (IFN) are key mediators of the innate immune response against viral infection. The more recently discovered type III IFNs (IFNL) exert antiviral protection particularly at epithelial surfaces of the respiratory and gastrointestinal tract, as well as in the liver, and they are crucial for mounting immune responses against infection with members of the Flaviviridae, such as hepatitis C virus (HCV), West Nile virus and Dengue virus. Immune genes like IFNs undergo constant regulation in order to adapt to external stimuli such as cellular stress and danger signals, and to adjust gene dosage for proper immune responses while avoiding immune pathology due to an overshooting immune system. Gene expression is tightly regulated by multilayered regulatory elements acting in both cis and trans. A powerful post-transcriptional regulatory mechanism is regulation of the mRNA 3' untranslated region (UTR), which determines the rate of translation from mRNA into protein. Prominent regulatory elements targeting the 3' UTR comprise microRNAs, RNA-binding proteins, and long noncoding RNAs, all of which alter immune gene dosage and immune response. Many immune genes such as IFNs and cytokines harbor repetitive adenylate-uridylate rich elements (AREs) consisting of at least one AUUUA pentamer in their 3' UTRs. These instability motifs are targeted by ARE-binding proteins to cause mRNA degradation, a process called ARE-mediated decay (AMD). Several genetic studies showed a strong association of the IFNL genes with spontaneous HCV clearance and response to IFN therapy. A single nucleotide polymorphism (SNP) within the 3' UTR of IFNL3 has been shown to dictate IFNL3 mRNA turnover by influencing the extent of both AMD and miRNA-mediated decay. While the HCV-induced miRNAs dictating IFNL3 mRNA instability have been identified, how the 3' UTR SNP influences IFNL3 AMD and which components are involved in this pathway is still undefined. This research proposal aims at identifying the RNA-binding protein(s) and components involved in destabilization of IFNL3 mRNA. My preliminary data suggests that the RNA-binding protein ZAP (zinc-finger antiviral protein), known as an antiviral factor targeting viral RNA, binds to and degrades host IFNL3 mRNA during HCV infection. A detailed understanding of such post-transcriptional regulatory mechanism(s) is necessary to fully understand the connection between host IFNL3 genotype and mRNA stability, the role of AMD in flaviviral immune evasion and the implications for outcome of infection. Importantly, this mechanism of immune evasion could be universal and also translate to viral infections at the epithelium of the respiratory and gastrointestinal tract (e.g. enterovirus, influenza virus, coronavirus), opening up new avenues for therapy.