RBCK1 enhances antiviral response through promoting K63-linked polyubiquitination of IRF7 in Carassius auratus var. Pengze.

Ubiquitination is a widely occurring reversible post-translational modification process in cells. RANBP2-type and C3HC4-type zinc finger-containing 1 (RBCK1) is a kind of E3 ubiquitin ligase. It regulates various biological functions, including protein degradation and kinase signaling pathways in mammals. However, the role of RBCK1 in the virus-induced innate immune response remains largely unknown, particularly in teleost. In this study, we demonstrated that the expression of Carassius auratus var Pengze RBCK1 (CapRBCK1) was induced by grass carp reovirus (GCRV) and poly (I:C) stimulation in tissues and cells. CapRBCK1 suppressed the replication of GCRV in cells. Overexpression of CapRBCK1 activated IFN1 response, whereas knockdown of CapRBCK1 inhibited this response. CapRBCK1 is primarily localized in the cytoplasm, where it directly interacted with IRF7 and thereby increased the phosphorylation and dimerization of IRF7 in GCRV-infected cells. Furthermore, CapRBCK1 catalyzed K63-linked ubiquitination of IRF7 at lysine 106. Finally, the mutant of CapRBCK1 RING domain exhibited a significant impairment to IRF7 ubiquitination. So, the RING domain is essential for CapRBCK1 enhancing IFN1 activation. This study provides, to our knowledge, some novel insights into the role of RBCK1 in innate immune response.