Zebrafish Uba1 Degrades IRF3 through K48-Linked Ubiquitination to Inhibit IFN Production

Fish IFN regulatory factor 3 (IRF3) is a crucial transcription factor in the IFN activation signaling pathway, which leads to IFN production and a positive cycle. Unrestricted IFN expression results in hyperimmune responses and therefore, IFN must be tightly regulated. In the current study, we found that zebrafish Ub-activating enzyme (Ubal) negatively regulated IRF3 via the K-48 ubiquitin proteasome degradation of IRF3. First, ifn expression stimulated by spring viraemia of carp virus infection was blunted by the overexpression of Ubal and enhanced by Ubal knockdown. Afterward, we found that Ubal was localized in the cytoplasm, where it interacted with and degraded IRF3. Functional domains analysis revealed that the C-terminal ubiquitin-fold domain was necessary for IRF3 degradation by Ubal and the N-terminal DNA-binding domain of IRF3 was indispensable for the degradation by Ubal.The degradation of IRF3 was subsequently impaired by treatment with MG132, a ubiquitin proteasome inhibitor. Further mechanism analysis revealed that Ubal induced the K48-linked Ub-proteasomal degradation of IRF3. Finally, the antiviral capacity of IRF3 was significantly attenuated by Ubal. Taken together, our study reveals that zebrafish Ubal interacts with and activates the ubiquitinated degradation of IRF3, providing evidence of the IFN immune balance mechanism in fish.

Automated summary

Zebrafish Ubal negatively regulates IRF3 by inducing K48-linked ub-proteasomal degradation, affecting the IFN immune balance mechanism.