Molecular and functional characterization of viperin in golden pompano, Trachinotus ovatus

The radical S-adenosyl methionine domain-containing protein 2 (RSAD2), also known as viperin, plays a momentous and multifaceted role in antiviral immunity. However, the function of viperin is uninvestigated in golden pompano, Trachinotus ovatus. In the present study, a viperin homolog, named To-viperin, was cloned and characterized from golden pompano, and its role in response to grouper iridovirus (SGIV) and nervous necrosis virus (NNV) infection was investigated. The whole open reading frame (ORF) of To-viperin was composed of 1050 bp and encoded a polypeptide of 349 amino acids with 70.66%-83.51% identity with the known viperin homologs from other fish species. A variable N-terminal domain, a highly conserved C-terminal domain, and a conserved middle radical SAM domain (aa 61-271) with the three-cysteine motif CxxCxxC was found in To-viperin sequence. Expression analysis showed that To-viperin was constitutively expressed in all tested organs and was located mainly in the ER of golden pompano cells. Treatments with SGIV, poly I: C, or NNV could induce the up-regulation of viperin to varying degrees. The ectopic expression of To-viperin in vitro significantly reduced the viral titer of SGIV and NNV. Furthermore, To-viperin overexpression enhanced the expression of IFNc, IRF3, and ISG15 genes as well as, to a lesser extent, the IL-6 gene. In summary, our results suggested that the function of viperin is likely to be conserved in fish specise, as observed in other vertebrates, shedding light on the evolutionary conservation of viperin.