MITA的N-聚糖修饰在抗DNA病毒天然免疫中的作用和机制研究

Studies during the past decade have led to considerable advances in the mechanisms of viral RNA-triggered innate immune signaling. However, with the discovery of cGAS and cGAMP, the mechanisms of viral DNA-triggered innate immune signaling are emerging in recent years. MITA, acts as a critical downstream adaptor of cGAS and cGAMP, is essential for the activation of innate immune response to DNA virus. Hence, MITA is rigorously regulated by host immune system. Current studies demonstrate that the activity of MITA is regulated by various modifications such as ubiquitylation and phosphorylation, but little is known about other types of posttranslational modification of MITA. Current works by applicant show that MITA possesses two potential N-glycan modification sites, and mutants of N-glycan modification site lead to significant effect on the expression of downstream antiviral genes induced by DNA virus and intracellular DNA. We will answer two key scientific problems with accomplishment of this project: 1) what is the role of N-glycan modification of MITA in innate immune response to DNA virus; 2) what are the mechanisms of MITA activation and MITA-medicated downstream signal transduction regulated by N-glycan modification. This work may reveal an unknown links between N-glycan modification and MITA-mediated signaling, and provide valuable insights into the dynamic regulatory mechanisms for MITA activation.

过去十年，病毒RNA诱导细胞抗病毒天然免疫分子机制的研究已取得很大进展。然而，随着cGAS和cGAMP的发现，病毒DNA诱导细胞抗病毒天然免疫分子机制才开始被逐步了解。MITA是cGAS和cGAMP下游的关键接头蛋白，它对于抗DNA病毒天然免疫反应的激活至关重要。因此，MITA的活性被宿主免疫系统严格调控。目前的研究表明，MITA的活性能被泛素化、磷酸化等修饰调控，但是MITA其它的翻译后修饰还了解得很少。申请人前期的研究显示MITA具备潜在的N-聚糖修饰位点，且该位点突变能显著的影响DNA病毒和胞内DNA诱导的下游抗病毒基因的表达。通过本项研究，我们将回答两个关键科学问题：1)MITA的N-聚糖修饰在抗DNA病毒天然免疫反应中的作用；2)N-聚糖修饰调控MITA活性及其下游信号转导的分子机制。本研究有望揭示N-聚修饰与MITA介导的天然免疫的关系，并有助于深入理解MITA活化的动态调控。

环鸟甘酸-腺苷酸合成酶cGAS对细胞质DNA的识别在宿主抵御病原感染、细胞损伤等过程中是必需的。结合DNA的cGAS催化合成第二信使cGAMP，cGAMP能够被关键接头蛋白MITA识别激活下游信号。此外，cGAS-MITA信号也在细胞衰老和死亡、抗肿瘤免疫等方面扮演重要作用。然而异常的MITA激活被报道与多种自身免疫症相关，因此MITA的激活必须受到免疫系统的严格控制。目前研究表明MITA的泛素化和磷酸化等翻译后修饰是其激活调控的重要分子机制，但是MITA的糖基化修饰目前还没有报道。本项目拟研究MITA的N聚糖修饰在抗DNA病毒天然免疫反应中的作用以及其调控MITA激活和下游信号转导的潜在分子机制。通过本项目，我们鉴定了MITA 的N聚糖修饰位点，并发现MITA的N聚糖修饰动态调控MITA介导的抗病毒天然免疫应答。在未感染和病毒感染早期，MITA的N聚糖修饰抑制免疫反应。在病毒感染后期，MITA的N聚糖修饰促进DNA诱导的免疫应答。人和鼠的MITA N聚糖修饰调控MITA的活性有不一样的机制。鼠MITA的N聚糖修饰调控内质网-高尔基体转运的稳态，维持未激活的MITA定位在内质网。另一方面，鼠MITA的N聚糖修饰通过调控其泛素化维持其在DNA病毒感染后的稳定性。而人MITA的N聚糖修饰主要通过调控MITA的二聚化及其磷酸化，促进cGAS-MITA信号的激活。本研究揭示了N聚修饰与MITA介导的天然免疫的关系，有助于深入理解MITA活化的动态调控机制。