Abstract

Rhabdovirus nucleoprotein (N) primarily encapsidates the viral RNA, facilitating genome replication and packaging. It also plays a potential role in modulating host antiviral immune responses by interacting with host factors. Hirame novirhabdovirus (HIRRV) is highly infectious and poses a significant threat to the fish farming industry. However, there have been no studies investigating the role of HIRRV nucleoprotein in viral pathogenicity and immune evasion. In this study, a highly specific polyclonal antibody against HIRRV-N protein was generated to examine its expression characteristics following viral infection of target cells. The results showed that the N protein was predominantly localized in the cytoplasm and its gene copies peaked at 48 h post-infection, while the protein expression continued to increase over the course of 96 h. Importantly, temporal analysis during viral infection revealed that host IFNphi 1 transcription peaked at 24 h post-infection and subsequently exhibited a continuous decline as the N protein accumulated. Overexpression of N protein could suppress the transcription of interferon pathway-related genes including IFNphi 1, MX, ISG15 and ISG56. The results of subcellular colocalization assay, BiFC and Co-IP collectively demonstrated that N protein could directly bind with stimulator of interferon genes (STING) to block the interaction between STING and MAVS, hereby inhibiting STING-mediated antiviral immune responses. Overexpression of N protein in the HIRRV infected cells also promoted the transciption of viral genes and led a significant reduction in cell viability. Moreover, it was revealed that N participated in immune escape by degrading STING through autophagy-lysosomal pathway. These findings provide crucial insights into the immune escape strategies of HIRRV, contributing to a more comprehensive understanding of its pathogenic mechanisms.