College of Marine Sciences, South China Agricultural Universitygrid.20561.30, Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou, China.
Southern Marine Science and Engineering Guangdong Laboratory, Zhuhai, China.
J Virol. 2022 Oct 26;96(20):e0068222. doi: 10.1128/jvi.00682-22. Epub 2022 Oct 3.
Iridoviruses are large DNA viruses which cause great economic losses to the aquaculture industry and serious threats to ecological diversity worldwide. Singapore grouper iridovirus (SGIV), a novel member of the genus , causes high mortality in grouper aquaculture. Previous work on genome annotation demonstrated that SGIV contained numerous uncharacterized or hypothetical open reading frames (ORFs), whose functions remained largely unknown. Here, we reported that the protein encoded by SGIV ORF131R (VP131) was localized predominantly within the endoplasmic reticulum (ER). Ectopic expression of GFP-VP131 significantly enhanced SGIV replication, while VP131 knockdown decreased viral infection , suggesting that VP131 functioned as a proviral factor during SGIV infection. Overexpression of GFP-VP131 inhibited the interferon (IFN)-1 promoter activity and mRNA level of IFN-related genes induced by poly(I:C), cyclic GMP/AMP synthase (EccGAS)/stimulator of IFN genes (EcSTING), TANK-binding kinase 1 (EcTBK1), or melanoma differentiation-associated gene 5 (EcMDA5), whereas such activation induced by mitochondrial antiviral signaling protein (EcMAVS) was not affected. Moreover, VP131 interacted with EcSTING and degraded EcSTING through both the autophagy-lysosome pathway and ubiquitin-proteasome pathway, and targeted for the K63-linked ubiquitination. Of note, we also found that EcSTING significantly accelerated the formation of GFP-VP131 aggregates in co-transfected cells. Finally, GFP-VP131 inhibited EcSTING- or EcTBK1-induced antiviral activity upon red-spotted grouper nervous necrosis virus (RGNNV) infection. Together, our results demonstrated that the SGIV VP131 negatively regulated the IFN response by inhibiting EcSTING-EcTBK1 signaling for viral evasion. STING has been identified as a critical factor participating in the innate immune response which recruits and phosphorylates TBK1 and IFN regulatory factor 3 (IRF3) to induce IFN production and defend against viral infection. However, viruses also distort the STING-TBK1 pathway to negatively regulate the IFN response and facilitate viral replication. Here, we reported that SGIV VP131 interacted with EcSTING within the ER and degraded EcSTING, leading to the suppression of IFN production and the promotion of SGIV infection. These results for the first time demonstrated that fish iridovirus evaded the host antiviral response via abrogating the STING-TBK1 signaling pathway.
虹彩病毒是一种大型 DNA 病毒，它给水产养殖业造成了巨大的经济损失，对全球的生态多样性构成了严重威胁。新加坡石斑鱼虹彩病毒（SGIV）是属的一个新成员，它会导致石斑鱼养殖业的高死亡率。先前的基因组注释工作表明，SGIV 含有许多未被描述或假设的开放阅读框（ORFs），其功能仍知之甚少。在这里，我们报告称，SGIV ORF131R（VP131）编码的蛋白主要定位于内质网（ER）内。GFP-VP131 的异位表达显著增强了 SGIV 的复制，而 VP131 的敲低则降低了病毒感染，表明 VP131 在 SGIV 感染过程中充当了辅助病毒的因子。GFP-VP131 的过表达抑制了 poly(I:C)、环鸟苷酸/AMP 合酶 (EccGAS)/干扰素基因刺激物 (EcSTING)、TANK 结合激酶 1 (EcTBK1) 或黑色素瘤分化相关基因 5 (EcMDA5) 诱导的 IFN-1 启动子活性和 IFN 相关基因的 mRNA 水平，但线粒体抗病毒信号蛋白 (EcMAVS) 诱导的这种激活不受影响。此外，VP131 与 EcSTING 相互作用，并通过自噬溶酶体途径和泛素-蛋白酶体途径降解 EcSTING，靶向 K63 连接的泛素化。值得注意的是，我们还发现 EcSTING 显著加速了共转染细胞中 GFP-VP131 聚集体的形成。最后，GFP-VP131 抑制了 EcSTING 或 EcTBK1 诱导的抗病毒活性，而 RGNNV 感染。总之，我们的研究结果表明，SGIV VP131 通过抑制 EcSTING-EcTBK1 信号通路来逃避 IFN 反应，从而负调控 IFN 反应。STING 已被确定为参与先天免疫反应的关键因素，它募集并磷酸化 TBK1 和干扰素调节因子 3（IRF3），以诱导 IFN 的产生并抵抗病毒感染。然而，病毒也会扭曲 STING-TBK1 途径，以负调控 IFN 反应并促进病毒复制。在这里，我们报告称，SGIV VP131 在 ER 内与 EcSTING 相互作用并降解 EcSTING，导致 IFN 产生受到抑制和 SGIV 感染的促进。这些结果首次表明，鱼类虹彩病毒通过破坏 STING-TBK1 信号通路来逃避宿主抗病毒反应。
