Nervous necrosis virus (NNV), a highly pathogenic RNA virus, is a major pathogen in the global aquaculture industry. To efficiently infect fish, NNV must evade or subvert the host IFN for their replication; however, the precise mechanisms remain to be elucidated. In this study, we reported that capsid protein (CP) of red-spotted grouper NNV (RGNNV) suppressed the IFN antiviral response to promote RGNNV replication in Lateolabrax japonicus brain cells, which depended on the ARM, S, and P domains of CP. CP showed an indirect or direct association with the key components of retinoic acid–inducible gene-I–like receptors signaling, L. japonicus TNFR-associated factor 3 (LjTRAF3) and IFN regulatory factor (LjIRF3), respectively, and degraded LjTRAF3 and LjIRF3 through the ubiquitin-proteasome pathway in HEK293T cells. Furthermore, we found that CP potentiated LjTRAF3 K48 ubiquitination degradation in a L. japonicus ring finger protein 114–dependent manner. LjIRF3 interacted with CP through the S domain of CP and the transcriptional activation domain or regulatory domain of LjIRF3. CP promoted LjIRF3 K48 ubiquitination degradation, leading to the reduced phosphorylation level and nuclear translocation of LjIRF3. Taken together, we demonstrated that CP inhibited type I IFN response by a dual strategy to potentiate the ubiquitination degradation of LjTRAF3 and LjIRF3. This study reveals a novel mechanism of RGNNV evading host immune response via its CP protein that will provide insights into the complex pathogenesis of NNV.

神经坏死病毒（NNV）是一种高致病性RNA病毒，是全球水产养殖业的主要病原体。为了有效地感染鱼类，NNV 必须逃避或破坏宿主 IFN 的复制；然而，确切的机制仍有待阐明。在这项研究中，我们报道了红斑石斑鱼 NNV (RGNNV) 的衣壳蛋白 (CP) 抑制了 IFN 抗病毒反应以促进日本海参脑细胞中的 RGNNV 复制，这取决于 CP 的 ARM、S 和 P 结构域。CP 显示出与视黄酸诱导基因 I 样受体信号传导的关键成分L. japonicus的间接或直接关联TNFR 相关因子 3 (LjTRAF3) 和 IFN 调节因子 (LjIRF3) 分别通过 HEK293T 细胞中的泛素-蛋白酶体途径降解 LjTRAF3 和 LjIRF3。此外，我们发现 CP 增强了L. japonicus中的 LjTRAF3 K48 泛素化降解环指蛋白 114 依赖的方式。LjIRF3通过CP的S域和LjIRF3的转录激活域或调控域与CP相互作用。CP促进LjIRF3 K48泛素化降解，导致LjIRF3磷酸化水平降低和核转位。总之，我们证明了 CP 通过增强 LjTRAF3 和 LjIRF3 泛素化降解的双重策略来抑制 I 型 IFN 反应。本研究揭示了 RGNNV 通过其 CP 蛋白逃避宿主免疫反应的新机制，这将为深入了解 NNV 的复杂发病机制提供见解。