神经坏死病毒(NNV),属于Betanodavirus的水生RNA病毒,感染各种海洋和淡水鱼,导致养殖幼虫和幼体大量死亡,并造成巨大的经济损失。环磷酸鸟苷-磷酸腺苷合酶(cGAS)被广泛认为是对源自不同病原体的胞质DNA的先天免疫应答中的中心成分。然而,对cGAS对水生RNA病毒的反应知之甚少。这项研究发现,石斑鱼cGAS(EccGAS)过表达抑制NNV复制,而EccGAS沉默促进NNV复制。EccGAS的抗NNV活性参与干扰素(IFN)信号激活,包括肿瘤坏死因子受体相关因子家族成员相关的NF-κB激活剂结合激酶1(TBK1)磷酸化,干扰素调节因子3(IRF3)核易位,以及随后诱导的IFNc和ISGs。有趣的是,NNV利用其衣壳蛋白(CP)或蛋白A(ProA)通过同时靶向EccGAS来负或正调节EccGAS介导的IFN信号传导。CP通过arm-P与EccGAS交互,S-P,和SD结构域,并以EcUBE3C(泛素连接酶)依赖性方式促进其聚泛素化与K48和K63连接,最终导致EccGAS降解。相反,ProA与EccGAS结合并抑制其泛素化和降解。在调节EccGAS蛋白含量时,CP的抑制作用比ProA的保护作用更明显,允许成功的NNV复制。这些新发现表明NNVCP和ProA动态调节EccGAS介导的IFN信号通路以促进NNV的免疫逃逸。我们的发现揭示了病毒与宿主相互作用的新机制,并为NNV的预防和控制提供了理论依据。重要的是众所周知的DNA传感器,cGAS是对抗DNA病毒的先天抗病毒免疫中的关键成分。尽管有越来越多的证据表明cGAS在抵抗RNA病毒中的功能,cGAS参与RNA病毒诱导的鱼类免疫反应的机制以及水生病毒如何逃避cGAS介导的免疫监视仍然难以捉摸。这里,我们研究了EccGAS正向调节抗NNV反应的详细机制。此外,NNVCP和ProA与EccGAS相互作用,通过泛素-蛋白酶体途径调节其蛋白质水平,动态调节EccGAS介导的IFN信号通路并促进病毒逃避。值得注意的是,NNVCP被鉴定为通过泛素连接酶EcUBE3C促进EccGAS的泛素化。这些发现揭示了水生RNA病毒逃避cGAS介导的先天免疫的新策略。增强我们对病毒-宿主相互作用的理解。
Nervous necrosis virus (NNV), an aquatic RNA virus belonging to Betanodavirus, infects a variety of marine and freshwater fishes, leading to massive mortality of cultured larvae and juveniles and substantial economic losses. The enzyme cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) is widely recognized as a central component in the innate immune response to cytosolic DNA derived from different pathogens. However, little is known about the response of cGAS to aquatic RNA viruses. This study found that Epinephelus coioides cGAS (EccGAS) overexpression inhibited NNV replication, whereas EccGAS silencing promoted NNV replication. The anti-NNV activity of EccGAS was involved in interferon (IFN) signaling activation including tumor necrosis factor receptor-associated factor family member-associated NF-kappa-B activator-binding kinase 1 (TBK1) phosphorylation, interferon regulatory factor 3 (IRF3) nuclear translocation, and the subsequent induction of IFNc and ISGs. Interestingly, NNV employed its capsid protein (CP) or Protein A (
ProA) to negatively or positively modulate EccGAS-mediated IFN signaling by simultaneously targeting EccGAS. CP interacted with EccGAS via the arm-P, S-P, and SD structural domains and promoted its polyubiquitination with K48 and K63 linkages in an EcUBE3C (the ubiquitin ligase)-dependent manner, ultimately leading to EccGAS degradation. Conversely,
ProA bound to EccGAS and inhibited its ubiquitination and degradation. In regulating EccGAS protein content, CP\'s inhibitory action was more pronounced than
ProA\'s protective effect, allowing successful NNV replication. These novel findings suggest that NNV CP and
ProA dynamically modulate the EccGAS-mediated IFN signaling pathway to facilitate the immune escape of NNV. Our findings shed light on a novel mechanism of virus-host interaction and provide a theoretical basis for the prevention and control of NNV.IMPORTANCEAs a well-known DNA sensor, cGAS is a pivotal component in innate anti-viral immunity to anti-DNA viruses. Although there is growing evidence regarding the function of cGAS in the resistance to RNA viruses, the mechanisms by which cGAS participates in RNA virus-induced immune responses in fish and how aquatic viruses evade cGAS-mediated immune surveillance remain elusive. Here, we investigated the detailed mechanism by which EccGAS positively regulates the anti-NNV response. Furthermore, NNV CP and
ProA interacted with EccGAS, regulating its protein levels through ubiquitin-proteasome pathways, to dynamically modulate the EccGAS-mediated IFN signaling pathway and facilitate viral evasion. Notably, NNV CP was identified to promote the ubiquitination of EccGAS via ubiquitin ligase EcUBE3C. These findings unveil a novel strategy for aquatic RNA viruses to evade cGAS-mediated innate immunity, enhancing our understanding of virus-host interactions.