Table_1_Grass Carp Reovirus (GCRV) Giving Its All to Suppress IFN Production by Countering MAVS Signaling Transduction.docx

Viruses typically target host RIG-I-like receptors (RLRs), a group of key factors involved in interferon (IFN) production, to enhance viral infection. To date, though immune evasion methods to contradict IFN production have been characterized for a series of terrestrial viruses, the strategies employed by fish viruses remain unclear. Here, we report that all grass carp reovirus (GCRV) proteins encoded by segments S1 to S11 suppress mitochondrial antiviral signaling protein (MAVS)-mediated IFN expression. First, the GCRV viral proteins blunted the MAVS-induced expression of IFN, and impair MAVS antiviral capacity significantly. Interestingly, subsequent co-immunoprecipitation experiments demonstrated that all GCRV viral proteins interacted with several RLR cascades, especially with TANK-binding kinase 1 (TBK1) which was the downstream factor of MAVS. To further illustrate the mechanisms of these interactions between GCRV viral proteins and host RLRs, two of the viral proteins, NS79 (S4) and VP3 (S3), were selected as representative proteins for two distinguished mechanisms. The obtained data demonstrated that NS79 was phosphorylated by gcTBK1, leading to the reduction of host substrate gcIRF3/7 phosphorylation. On the other hand, VP3 degraded gcMAVS and the degradation was significantly reversed by 3-MA. The biological effects of both NS79 and VP3 were consistently found to be related to the suppression of IFN expression and the promotion of viral evasion. Our findings shed light on the special evasion mechanism utilized by fish virus through IFN regulation, which might differ between fish and mammals.

病毒通常靶向宿主维甲酸诱导基因I样受体 (RIG-I-like receptors)——一类参与干扰素 (interferon, IFN) 生成的关键因子——以增强病毒感染能力。截至目前，尽管一系列陆生病毒的干扰素拮抗免疫逃逸机制已被解析阐明，但鱼类病毒所采用的免疫逃逸策略仍不明晰。本研究发现，由草鱼呼肠孤病毒 (grass carp reovirus, GCRV) S1至S11片段编码的全部病毒蛋白，均可抑制线粒体抗病毒信号蛋白 (mitochondrial antiviral signaling protein, MAVS) 介导的干扰素表达。首先，GCRV病毒蛋白可削弱MAVS诱导的干扰素表达，并显著损伤MAVS的抗病毒活性。有趣的是，后续免疫共沉淀实验证实，所有GCRV病毒蛋白均可与多条RLR信号级联反应因子发生相互作用，尤其与MAVS下游的TANK结合激酶1 (TANK-binding kinase 1, TBK1) 结合。为进一步阐明GCRV病毒蛋白与宿主RLRs相互作用的具体机制，本研究选取两种病毒蛋白NS79 (S4)与VP3 (S3)作为代表，分别阐释两种截然不同的作用机制。实验数据显示，NS79可被草鱼TBK1 (gcTBK1) 磷酸化，进而降低宿主底物gcIRF3/7的磷酸化水平。另一方面，VP3可介导gcMAVS的降解，且该降解过程可被3-甲基腺嘌呤 (3-MA) 显著逆转。研究发现，NS79与VP3的生物学效应均与干扰素表达抑制及病毒免疫逃逸增强相关。本研究揭示了鱼类病毒通过调控干扰素通路实现免疫逃逸的独特机制，该机制或与哺乳动物存在差异。