Grass carp reovirus VP35 hijacks DHX15 into phase-separated inclusion bodies to evade host antiviral immunity.

Many viral proteins undergo liquid-liquid phase separation (LLPS) to form biomolecular condensates known as viral inclusion bodies (VIBs), which are utilized for genome replication and virion assembly, thus serving as potential targets for antiviral drugs. However, the role of VIBs in viral immune evasion has rarely been explored. In this study, we demonstrated that VP35 protein of type II grass carp reovirus (GCRV-II) formed VIBs through LLPS in cells and in vitro. Moreover, we identified a host interaction partner of GCRV-II VP35, DEAH (Asp-Glu-Ala-His)-box helicase 15 (DHX15), which promoted expression of GCRV-II- or poly(I: C)-induced interferon (IFN) and interferon-stimulated genes (ISGs) via promoting phosphorylation of TBK1 (TANK-binding kinase 1) and stabilizing TBK1 to prevent it from degradation through autophagy pathway. To evade host anti-viral immunity, GCRV-II VP35 sequesters DHX15 from nucleus to the cytoplasm VIBs and degrades DHX15 via lysosomal pathway. Our findings provide a novel immune evasion strategy of GCRV-II, of which VP35 protein recruits DHX15, a positive regulator of host anti-viral immunity, to VIBs and degrades DHX15 via lysosomal pathway, which provides novel insights for the development of anti-viral drugs against GCRV-II infection.