State Key Laboratory of Agricultural Microbiology, College of Veterinary Medicine, Huazhong Agricultural Universitygrid.35155.37, Wuhan, China.
Key Laboratory of Preventive Veterinary Medicine in Hubei Province, The Cooperative Innovation Center for Sustainable Pig Production, Wuhan, China.
J Virol. 2022 Sep 14;96(17):e0094422. doi: 10.1128/jvi.00944-22. Epub 2022 Aug 16.
African swine fever virus (ASFV) is the etiological agent of a highly lethal hemorrhagic disease in domestic pigs and wild boars that has significant economic consequences for the pig industry. The type I interferon (IFN) signaling pathway is a pivotal component of the innate antiviral response, and ASFV has evolved multiple mechanisms to antagonize this pathway and facilitate infection. Here, we reported a novel function of ASFV pI215L in inhibiting type I IFN signaling. Our results showed that ASFV pI215L inhibited IFN-stimulated response element (ISRE) promoter activity and subsequent transcription of IFN-stimulated genes (ISGs) by triggering interferon regulatory factor 9 (IRF9) degradation. Additionally, we found that catalytically inactive pI215L mutations retained the ability to block type I IFN signaling, indicating that this only known viral E2 ubiquitin-conjugating enzyme mediates IFR9 degradation in a ubiquitin-conjugating activity-independent manner. By coimmunoprecipitation, confocal immunofluorescence, and subcellular fractionation approaches, we demonstrated that pI215L interacted with IRF9 and impaired the formation and nuclear translocation of IFN-stimulated gene factor 3 (ISGF3). Moreover, further mechanism studies supported that pI215L induced IRF9 degradation through the autophagy-lysosome pathway in both pI215L-overexpressed and ASFV-infected cells. These findings reveal a new immune evasion strategy evolved by ASFV in which pI215L acts to degrade host IRF9 via the autophagic pathway, thus inhibiting the type I IFN signaling and counteracting the host innate immune response. African swine fever virus (ASFV) causes a highly contagious and lethal disease in pigs and wild boars that is currently present in many countries, severely affecting the global pig industry. Despite extensive research, effective vaccines and antiviral strategies are still lacking, and many fundamental questions regarding the molecular mechanisms underlying host innate immunity escape remain unclear. In this study, we identified ASFV pI215L, the only known viral E2 ubiquitin-conjugating enzyme, which is involved in antagonizing the type I interferon signaling. Mechanistically, pI215L interacted with interferon regulatory factor 9 for autophagic degradation, and this degradation was independent of its ubiquitin-conjugating activity. These results increase the current knowledge regarding ASFV evasion of innate immunity, which may instruct future research on antiviral strategies and dissection of ASFV pathogenesis.
非洲猪瘟病毒（ASFV）是一种高度致命的家猪和野猪出血性疾病的病原体，对养猪业有重大的经济影响。I 型干扰素（IFN）信号通路是先天抗病毒反应的关键组成部分，而 ASFV 已经进化出多种机制来拮抗这条通路并促进感染。在这里，我们报道了 ASFV pI215L 在抑制 I 型 IFN 信号中的新功能。我们的结果表明，ASFV pI215L 通过触发干扰素调节因子 9（IRF9）降解来抑制 IFN 刺激反应元件（ISRE）启动子活性和随后的 IFN 刺激基因（ISG）转录。此外，我们发现无催化活性的 pI215L 突变保留了阻断 I 型 IFN 信号的能力，表明这唯一已知的病毒 E2 泛素连接酶以泛素连接酶活性非依赖的方式介导 IRF9 降解。通过免疫共沉淀、共聚焦免疫荧光和亚细胞分级分离方法，我们证明 pI215L 与 IRF9 相互作用，并破坏 IFN 刺激基因因子 3（ISGF3）的形成和核转位。此外，进一步的机制研究支持 pI215L 通过自噬-溶酶体途径在 pI215L 过表达和 ASFV 感染的细胞中诱导 IRF9 降解。这些发现揭示了 ASFV 进化出的一种新的免疫逃避策略，其中 pI215L 通过自噬途径降解宿主 IRF9，从而抑制 I 型 IFN 信号并拮抗宿主先天免疫反应。非洲猪瘟病毒（ASFV）在猪和野猪中引起高度传染性和致命性疾病，目前在许多国家存在，严重影响了全球养猪业。尽管进行了广泛的研究，但仍然缺乏有效的疫苗和抗病毒策略，并且许多关于宿主先天免疫逃避的分子机制的基本问题仍然不清楚。在这项研究中，我们鉴定了 ASFV pI215L，它是唯一已知的病毒 E2 泛素连接酶，参与拮抗 I 型干扰素信号。从机制上讲，pI215L 与干扰素调节因子 9 相互作用进行自噬降解，这种降解不依赖于其泛素连接酶活性。这些结果增加了对 ASFV 逃避先天免疫的认识，这可能为未来的抗病毒策略研究和 ASFV 发病机制的剖析提供指导。
