Fish novel TRIM protein FTR14 negatively regulates interferon response by targeting TBK1-IRF3

Growing evidence highlights that tripartite motif (TRIM) family members exert crucial functions in host defense upon infection with microbial pathogens. Of note, the roles of a subfamily of fish-specific TRIM (FTR, also named as finTRIM) which have no true orthologues in mammals were largely unexplored. In this study, a novel FTR gene from grouper (EcFTR14) was identified, and its effects on fish virus infection and host interferon response were investigated. EcFTR14 contained RING, B-Box, and PRY-SPRY domains, and shared 54.81% identity to zebrafish FTR14. The transcription levels of EcFTR14 were markedly induced upon fish virus infection. EcFTR14 was mainly localized in the cytoplasm as small spots or bright aggregates. The overexpression of EcFTR14 could markedly enhance the replication of RGNNV or SGIV. Moreover, overexpression of EcFTR14 reduced the mRNA level of IFN-associated immune signaling molecules, suggesting that the antiviral action of EcFTR14 was due to the negative regulation on IFN response. EcFTR14 was found to interact with EcTBK1, EcIRF3 and EcIRF7, but not with EcSTING. Overexpression of EcFTR14 markedly suppressed the transcription levels of IFN-signaling related molecules evoked by EcSTING and EcTBK1. In addition, overexpression of EcFTR14 could degrade EcTBK1, EcIRF3 and EcIRF7 in a dose-dependent manner, that resulted in the suppression of antiviral effects induced by EcIRF3 and EcTBK1. Collectively, our findings illuminated that EcFTR14, a novel member of FTR family, acted as a pro-viral factor through negatively regulating targeting TBK1-IRF3 activated antviral action. The present study will for the first time shed light on the regulatory roles of FTR14 in innate immune response upon fish virus infection.