Red-Spotted Grouper Nervous Necrosis Virus Hijacks Sea Perch (Lateolabrax japonicus) OTUB2 to Suppress RLRs-IFN Signaling by Targeting TBK1/IRF3 Deubiquitination

Nervous necrosis virus (NNV) is a highly pathogenic betanodavirus that causes severe mortality in marine fish. However, the mechanisms by which it evades host antiviral immunity remain incompletely defined. Here, we identify the deubiquitinating enzyme Otubain-2 (OTUB2) from sea perch ( Lateolabrax japonicus ), LJOTUB2, as a key host factor subverted by red-spotted grouper NNV (RGNNV) to suppress the RIG-I-like receptor (RLR)-interferon (IFN) signaling pathway. LJOTUB2 functions as a negative regulator of the RLR-IFN axis, thereby facilitating RGNNV replication. It interacts directly with TBK1 and catalyzes the removal of K27-, K48-, and K63-linked polyubiquitin chains from both TBK1 and IRF3, depending on its catalytic cysteine residue C45. This deubiquitination attenuates TBK1 activation, impairs IRF3 nuclear translocation and phosphorylation, and ultimately inhibits interferon (IFN) and IFN-stimulated gene production. Furthermore, we show that the RGNNV capsid protein (CP) upregulates LJOTUB2 expression and binds directly to it via its S domain, thereby hijacking LJOTUB2 to antagonize the host IFN response. Knockdown of LJOTUB2 rescues CP-mediated suppression of IFN signaling, confirming its essential role in viral immune evasion. Our study unveils a novel strategy whereby NNV exploits a host deubiquitinase to dampen antiviral innate immunity and promotes viral replication, highlighting LJOTUB2 as a potential target for antiviral intervention in aquaculture.