Zebrafish NDRG1a Negatively Regulates IFN Induction by Promoting the Degradation of IRF7

Viral infection activates the transcription factor IFN regulatory factor 7 (IRF7), which plays a critical role in the induction of IFNs and innate antiviral immune response. How virus-induced IFN signaling is controlled in fish is not fully understood. In this study, we demonstrate that N-myc downstream-regulated gene 1a (NDRG1a) in zebrafish plays a role as a negative regulator for virus-triggered IFN induction. First, the activation of the IFN promoter stimulated by the polyinosinic-polycytidylic acid or spring viremia of carp virus was decreased by the overexpression of NDRG1a. Second, NDRG1a interacted with IRF7 and blocked the IFN transcription activated by IRF7. Furthermore, NDRG1a was phosphorylated by TANK-binding kinase 1 (TBK1) and promoted the K48-linked ubiquitination and degradation of IRF7. Finally, the overexpression of NDRG1a blunted the transcription of several IFN-stimulated genes, resulting in the host cells becoming susceptible to spring viremia of carp virus infection. Our findings suggest that fish NDRG1a negatively regulates the cellular antiviral response by targeting IRF7 for ubiquitination and degradation, providing insights into the novel role of NDRG1a on the innate antiviral immune response in fish.