Structural features, transcriptional profiles, and potential roles in antiviral immunity of interferon-stimulated 20-kDa exonuclease (ISG20) in red-spotted grouper (Epinephelus akaara)

Interferon-stimulated 20-kDa exonuclease (ISG20) is a fundamental antiviral gene that plays a critical role in the vertebrate innate immune system. However, its function in fish remains poorly understood. In this study, we aimed to evaluate the structural and functional features of Epinephelus akaara ISG20 (EAISG20). EAISG20 exhibited the highest degree of association with its orthologs from Epinephelus species and clustered with teleostean ISG20s in the phylogenetic tree. Under normal physiological conditions, EAISG20 mRNA was the most highly expressed in the blood. The temporal expression analysis of EAISG20 indicated significant transcriptional responses following stimulation with lipopolysaccharide, polyinosinic: polycytidylic acid (poly I:C), and nervous necrosis virus (NNV) in the immune challenge experiment. The subcellular localization assay revealed that EAISG20 was predominantly localized in the cell nucleus. To examine its role in antiviral defense, EAISG20 was overexpressed in fish cells, and it resulted in a significant reduction in viral gene transcription and an increased cell survival following infection with viral hemorrhagic septicemia virus (VHSV) and NNV. Additionally, EAISG20 contributed substantially to apoptosis suppression by maintaining mitochondrial membrane potential during poly I:C stimulation. Overall, the present study highlighted the antiviral potential of EAISG20 against various viral stimuli, thereby providing remarkable insight into the innate immune response of ISG20 in teleosts and laying the groundwork for future research on its role in antiviral defense.