Hunnivirus Structural Protein VP2 Inhibits Beta Interferon Production by Targeting the IRF3 Essential Modulator.

Water buffalo Hunnivirus (BufHuV) belongs to the family Picornaviridae and is a newly discovered member of the Hunnivirus A genus. It causes intestinal diseases in cattle, mainly lead to subclinical infections, thereby seriously threatening the health of cattle herds. In addition, it can also bring about various clinical disease syndromes which results in severe economic losses to the cattle industry. To date, there have been no reports worldwide on the study of Hunnivirus virus infecting host cells and causing innate immune responses. In this study, we found that interferon treatment effectively blocked BufHuV replication and infection with the virus weakened the host antiviral responses. Inhibiting the transcription of IFN-beta and ISGs induced by either Sendai virus (SeV) or poly(I:C) in MDBK and HCT-8 cells, were dependent on the IRF3 or NF-kappa B signaling pathways, and this inhibited the activation of IFN-beta promoter by TBK1 and its upstream molecules, RIGI and MDA5. By constructing and screening five BufHuV proteins, we found that VP2, 2 C, 3 C and 3D inhibited the activation of IFN beta promoter induced by SeV. Subsequently, we showed that VP2 inhibited the activation of IRF3 induced by SeV or poly (I:C), and it inhibited IRF3 activation by inhibiting its phosphorylation and nuclear translocation. In addition, we confirmed that VP2 inhibited the activation of IFN beta induced by signaling molecules, MDA5 and TBKI. In summary, these findings provide new insights into the pathogenesis of Hunnivirus and its mechanisms involved in evading host immune responses.