Fish TRIM8 exerts antiviral roles through regulation of the proinflammatory factors and interferon signaling.

The tripartite motif (TRIM)-containing proteins usually exert important regulatory roles during multiple biological processes. TRIM8 has been demonstrated to be a RING domain-containing E3 ubiquitin ligase which plays critical roles in inflammation and cancer. In this study, a TRIM8 homolog from grouper, Epinephelus coioides (EcTRIM8) was cloned, and its effects on fish virus replication were investigated. The full-length EcTRIM8 cDNA encoded a polypeptide of 568 amino acids with 92% identity to TRIM8 homolog from large yellow croaker (Larimichthys crocea). Sequence alignment analysis indicated that EcTRIM8 contained conserved RING finger, B-box and coiled-coil domain. Expression patterns analysis showed that EcTRIM8 was predominant in kidney, gill, fin, liver, spleen and brain. After challenging with Singapore grouper iridovirus (SGIV) or polyinosin-polycytidylic acid (poly I:C), the EcTRIM8 transcript was significantly increased at the early stage of injection. Under fluorescence microscopy, we observed different distribution patterns of EcTRIM8 in grouper spleen (GS) cells, including punctate fluorescence evenly situated throughout the cytoplasm and bright aggregates. The ectopic expression of EcTRIM8 in vitro significantly inhibited the replication of SGIV and red spotted grouper nervous necrosis virus (RGNNV), evidenced by the obvious reduction in the severity of cytopathic effect (CPE) and the significant decrease in viral gene transcription and protein synthesis. Moreover, the transcription of the proinflammatory factors and interferon related immune factors were differently regulated by EcTRIM8 during SGIV or RGNNV infection. In addition, overexpression of EcTRIM8 significantly increased the transcription of interferon regulator factor 3 (IRF3) and IRF7, and enhanced IRF3 or IRF7 induced interferon-stimulated response element (ISRE) promoter activity. Together, our results firstly demonstrated that fish TRIM8 could exert antiviral function through the regulation of the expression of proinflammatory cytokines and interferon related transcription factors in response to fish viruses.