CrmA/SPI2负调控宿主细胞I型干扰素表达的分子机制研究

Innate immune system is the first line of defense against viral invasion. Immune evasion of viruses may lead to diseases. The induction of type I interferons (IFNs) is one of the most fundamental events of host antiviral immune responses. Also, Type I IFNs are target of viral immune evasion. CrmA (Cytokine response modifier A), an early gene of cowpox virus (CPXV), is well known for its anti-apoptotic function and was identified as an inhibitor in the maturation of IL-1beta and IL-18. Vaccinia Virus (VACV) SPI2 (Serine proteinase inhibitor 2, also known as B13R) gene is highly homologous to CrmA. Their identities of both nucleotide and amino acid sequence are more than 90%. And the reported function of SPI2 shares similarity with CrmA. Still, their roles in Type-I-IFN-induction signaling remain unclear. In our pilot study, CrmA inhibits IFN-beta induction in host cells. In this study, we propose to investigate the mechanism of negative regulation of type I IFNs induction by CrmA/SPI2, and to identify their roles in immune evasion of poxviruses. This work may reveal a new molecular mechanism of viral immune evasion. Furthermore, it may provide new insights into the construction of more stable attenuate vaccine virus with lower virulence.

天然免疫系统是人类对抗病毒入侵的第一道防线，病毒免疫逃逸可能引发疾病。I型干扰素诱导表达是宿主细胞抗病毒天然免疫反应的标志事件之一，也是病毒免疫逃逸的重要靶标。牛痘病毒的早期表达基因CrmA基因与痘苗病毒的SPI2基因序列同源性超过90%，功能类似。前人研究表明CrmA和SPI2抑制细胞凋亡并阻断IL-1beta、IL-18等细胞因子的成熟，目前尚无CrmA/SPI2调节宿主细胞I型干扰素表达方面的报道。申请人在前期工作中发现CrmA能抑制宿主细胞beta干扰素的诱导。本项目拟通过研究CrmA/SPI2负调控宿主细胞I型干扰素表达的分子机制，探讨痘病毒免疫逃逸的机理。本项目一方面有望揭示痘病毒免疫逃逸的新机制，另一方面有望为构建稳定的痘苗病毒减毒活疫苗提供直接的理论依据。

在宿主抗病毒天然免疫反应与病毒免疫逃逸的博弈中，宿主细胞I型干扰素表达信号通路是细胞抗病毒天然免疫反应的重要事件，同时也是病毒免疫逃逸的重要靶标。本项目基于前期发现的牛痘病毒CrmA——这一著名的抗细胞凋亡和抗炎症反应的病毒蛋白对宿主细胞beta干扰素诱导表达的抑制作用，进一步挖掘CrmA及其同源基因——痘苗病毒SPI-2对于宿主细胞I型干扰素表达信号通路的作用机理。本项目结果表明，CrmA/SPI-2特异性的负调控病毒诱导细胞I型干扰素表达信号通路。从机理上讲，CrmA/SPI-2调控细胞I型干扰素表达信号通路的蛋白靶标为TBK1/IKKε；CrmA/SPI-2发挥作用的具体机制为通过影响MITA-TBK1/IKK-IRF3复合体的组装负调控细胞beta干扰素的诱导表达。相应的，下调SPI-2的表达能促进痘苗病毒诱导宿主细胞beta干扰素的表达。相关结果项目负责人以第一作者和通讯作者身份发表于Scientific Report期刊。综上，本项目解释了一种全新的痘病毒蛋白负调节细胞抗病毒天然免疫反应的机制，加深了我们对病毒蛋白参与多个信号通路并与宿主基因发生分子交谈的理解，也拓展了我们对病毒免疫逃逸的认识，在基础研究领域具有较强的科学意义。同时，痘苗病毒实基础研究的重要模式病毒和经典活疫苗载体，因此本项研究也对研制痘苗病毒减毒疫苗和研发抗病毒药物提供了理论依据，在应用转化领域有一定的参考意义。