Black carp ubiquitin-conjugating enzyme variant 2 regulates type I IFN production via ubiquitin-mediated degradation of key transcription factors

Ubiquitin-conjugating enzyme variant 2 (UBE2V2) is an E2 ubiquitin-conjugating enzyme involved in diverse cellular processes. However, its role in teleost antiviral immunity remains poorly understood. In this study, we identified black carp ( Mylopharyngodon piceus ) UBE2V2 (bcUBE2V2) as a negative regulator in type I interferon (IFN) production. Sequence and structural analyses revealed that bcUBE2V2 is evolutionarily conserved, particularly in its ubiquitin-conjugating enzyme E2, catalytic (UBCc) domain. Upon viral infection, bcUBE2V2 expression was upregulated in Mylopharyngodon piceus kidney (MPK) cells and immune-related tissues including kidney, liver, and spleen. Silencing bcUBE2V2 enhanced IFN production and restricted viral replication both in vitro and in vivo, while its overexpression suppressed IFN production induced by both viral infection and synthetic RNA. Co-immunoprecipitation assays demonstrated that bcUBE2V2 interacted directly with bcIRF3 and bcIRF7, mediated through the DNA-binding domain of bcIRF3 and the IRF-association domain of bcIRF7. This interaction resulted in the inhibition of IFN-promoter activation and antiviral activity driven by bcIRF3/7. Mechanistically, bcUBE2V2 promoted the proteasomal degradation of bcIRF3 and bcIRF7 by enhancing their ubiquitination. Furthermore, mutational analysis revealed that the conserved residues F30 and S49 were indispensable for bcUBE2V2's suppressive function. Collectively, our findings highlight bcUBE2V2 as a pivotal modulator of the antiviral innate immune response in black carp, offering valuable insights into fish immune regulation and potential strategies to enhance disease resistance. • Black carp UBE2V2 (bcUBE2V2) was identified as a negative regulator of type I interferon production. • bcUBE2V2 interacts with bcIRF3 and bcIRF7 to negatively regulate their activity in antiviral signaling. • bcUBE2V2 promotes ubiquitination-mediated degradation of bcIRF3 and bcIRF7, suppressing type I IFN signaling. • The conserved residues F30 and S49 in bcUBE2V2 are essential for its suppressive function.