人巨细胞病毒DNA聚合酶亚基UL44拮抗宿主抗病毒免疫应答的分子机制研究

Innate immunity is the first line of defense against viral invasion. The induction of type I interferons (IFNs) and inflammatory cytokine is essential to host antiviral immune responses，which is also a key target of viral immune evasion. Human cytomegalovirus (HCMV) can establish long-term latent infection in vivo. However, immune escape is the pivotal step to HCMV establish latent infection. Previous research show that UL44 is a HCMV DNA polymerase subunit that promotes virus genome replication. Its roles in the regulation of host antiviral immune responses and HCMV immune evasion remain unknown. In our previous study, we found that overexpression of UL44 markedly inhibited HCMV-triggered production of IFN beta and inflammatory cytokines，and promoted virus replication. Knockdown of UL44 increased HCMV-induced expression of downstream antiviral gene. In this project, we propose to investigate the mechanism of UL44-mediated inhibition of host antiviral immune responses, and to identify its roles in HCMV immune evasion. These efforts will reveal a new molecular mechanism of HCMV immune evasion. Furthermore, it will contribute to the development of vaccines and therapeutic against HCMV infection.

天然免疫是机体抵抗病毒入侵的第一道防线。I型干扰素和炎症因子的诱导表达是机体抗病毒天然免疫反应的关键事件，也是病毒免疫逃逸的重要靶标。人巨细胞病毒（Human cytomegalovirus, HCMV）可在宿主体内建立长期潜伏感染，而免疫逃逸是其建立潜伏感染的关键。已有研究表明UL44是HCMV DNA聚合酶的亚基，它在病毒基因组复制过程中发挥重要作用，但目前对于UL44是否调控宿主抗病毒免疫及参与病毒免疫逃逸尚不清楚。申请人在前期工作中发现过量表达UL44显著抑制HCMV诱导的I型干扰素和炎症因子表达并促进病毒复制，而敲低UL44则增强HCMV诱导的宿主天然免疫应答。本项目拟进一步研究UL44负调控宿主抗病毒免疫应答及介导HCMV免疫逃逸的分子机理。这些研究一方面有望揭示HCMV免疫逃逸新的机制，另一方面将为预防和治疗HCMV感染的药物研发提供潜在的分子靶标。

I型干扰素和炎症因子的诱导表达是机体抗病毒天然免疫反应的关键事件，也是病毒免疫逃逸的重要靶标。人巨细胞病毒（Human cytomegalovirus, HCMV）可在宿主体内建立长期潜伏感染，而免疫逃逸是其建立潜伏感染的关键。我们研究发现UL44（HCMV DNA聚合酶亚基）是一个负调控宿主天然免疫应答的蛋白。UL44抑制IRF3和p65等关键蛋白介导的ISRE，IFN或NF-B报告基因的激活。进一步研究结果表明，UL44主要通过抑制IRF3和p65与相应的抗病毒基因启动子的结合，从而拮抗其介导的抗病毒免疫应答。另外，UL42可以显著抑制HCMV感染以及转染核酸模拟物HSV120诱导的宿主抗病毒天然免疫反应。机制研究显示，UL42抑制cGAS寡聚化及与DNA的结合从而影响cGAMP的合成；另外UL42通过促进p62介导的TRAP经自噬途径讲解从而抑制活化的MITA从ER向核周转移。HCMV晚期蛋白UL94能够拮抗cGAS-MITA介导的信号转导。UL94参与了HCMV的免疫逃逸。作用机制研究发现，UL94靶向MITA发挥拮抗天然免疫应答的功能。一方面，UL94抑制MITA的二聚化，从而阻碍MITA从内质网向细胞核周微小体的转运。另一方面，UL94抑制MITA对TBK1的招募，从而阻碍信号转导过程。这些研究发表在PLOS Pathogens 和Journal of Virology杂志上。