人巨细胞病毒编码蛋白pUL23抑制γ干扰素抗病毒效应的作用机制

Human cytomegalovirus (HCMV) can profoundly modify the immune response of the host cells in order to establish infection and latency. We have shown previously that HCMV-coding protein pUL23 interferes with interferon-γ（IFN-γ)-dependent JAK/STAT1 signal transduction, and selectively modulates IFN stimulated-genes(ISGs) expression, for example, stimulating UBC9 gene expression; as well as interacts with interferon- induced protein Nmi[N-myc (and STAT) interactor], leading to the alteration of the subcellular localisation of E2 ligase of sumolylation UBC9. The activity of mammalian transcription factor STAT1,whose cellular biology is relatively well characterized, is modulated by sumolation of STAT1 itself and the nuclear receptors LXRα、LXRβ. Based on our finding, we further hypothesize that pUL23 might reduce the IFN-γ-induced immune responsiveness of host cell through the modification of protein sumolylation. In this study, we propose to analyse the alteration on the sumolytion of STAT1, LXα and LXβ, also measure transcriptional profiling of the IFN-γ stimulated-genes (ISGs) by means of RNA-seq after the treatment of IFN-γ in the pUL23-overexpressing cells and HCMV-infected cells, respectively. Identifying and characterizing direct acting antiviral effectors from pUL23-regulating ISGs have the potential to uncover evolutionarily selected mechanisms of pathogen defense. Our study will help to understand the mechanism how pUL23 leads to globally responsiveness of HCMV-infected cells to IFN-γ. The mechanism is complex and fascinating. The study of this mechanism will reveal novel insights on the host–pathogen interaction and introduce new concepts on cell biological and immunological pathology. Importantly, our study might provide useful information for identifying pharmacological drugs which interfere with the IFN-inhibitory capacities of HCMV to reconstitute innate immunity and allow the hosts to help themselves.

人巨细胞病毒（HCMV）在裂解和潜伏感染过程中，能对宿主免疫系统进行深度修饰，实现免疫逃逸。项目组前期研究表明HCMV编码的pUL23蛋白能降低依赖γ干扰素（IFN-γ）的JAK/STAT1信号途径的活性，并发现pUL23调控蛋白SUMO化修饰E2连接酶（UBC9）的细胞定位及表达、调节核蛋白SUMO化修饰，选择性调控干扰素刺激基因ISGs表达。在此基础上，结合干扰素抗病毒机制研究进展，我们提出了pUL23通过影响核蛋白SUMO化修饰，选择性调控干扰素刺激基因表达，从而抵抗IFN-γ抗病毒效应的假说。本项目拟深入研究pUL23对IFN-γ信号通路相关转录因子STAT1、LXRs等蛋白SUMO化修饰的调控作用，探讨pUL23调控的干扰素刺激基因ISGs及其对病毒复制的影响。旨在阐明人巨细胞病毒调控宿主天然免疫、实现免疫逃逸的分子机理，为研发重构机体自身免疫力抵抗病毒感染的药物奠定基础。

人巨细胞病毒(HCMV)可在免疫功能低下的成年患者和新生儿中引起严重病症。本项目研究了HCMV编码的UL23蛋白介导的病毒与干扰素免疫系统相互作用的分子机理。干扰素-γ(IFN-γ)是宿主对抗包括人类疱疹病毒在内的许多病毒感染的最重要的天然免疫反应之一。人N-myc相互作用蛋白(Nmi)，已被证明与信号转导和转录激活因子(STAT)蛋白(包括STAT1)相互作用，在IFN-γ诱导的STAT1依赖转录激活和干扰素刺激基因的表达调控中起重要作用。在本研究中，我们发现UL23 蛋白特异性地与Nmi相互作用。在过表达UL23的细胞中，我们观察到(a)在细胞核中Nmi和STAT1的水平显著降低，这些蛋白在细胞核中起着诱导IFN-γ刺激基因转录的作用；(b)IFN-γ刺激基因转录水平显著降低。在IFN-γ处理细胞中，UL23缺失的HCMV突变病毒诱导了更高水平的IFN-γ刺激基因的转录，并表现出低于表达功能UL23的亲本对照病毒的滴度。因此，UL23与Nmi直接相互作用，抑制Nmi及其相关蛋白STAT1的核易位，导致IFN-γ诱导的反应减少，并增加病毒对IFN-γ的抗性。我们的研究结果进一步证明了UL23-Nmi相互作用在促进病毒免疫逃离IFN-γ反应和增强病毒抵抗IFN抗病毒效应的作用。.I型干扰素(IFN-I)在抗病毒感染中发挥同样重要的作用。在本研究中，UL23也被证实是负向调节I型IFN免疫应答的关键因子。详细分析表明，在HCMV感染期间，病毒UL23蛋白增加了病毒对IFN-I抵抗作用。此外，UL23显著降低了干扰素刺激基因的表达水平和IFN-I依赖的启动子活性。我们进一步发现UL23降低IFN-I依赖的STAT1磷酸化。此外，STAT1核定位水平显著减少，而IFN调节因子9或STAT2的核表达则没有减少。本研究的结果表明，HCMVUL23是一种可以对抗细胞固有免疫的病毒拮抗剂，并揭示了UL23可能对IFN-I信号转导的新作用。