Short Communication The N pro product of classical swine fever virus and bovine viral diarrhea virus uses a conserved mechanism to target interferon regulatory factor-3

Classical swine fever virus (CSFV) is a member of the genus Pestivirus in the family Flaviviridae. The N pro product of CSFV targets the host’s innate immune response and can prevent the production of type I interferon (IFN). The mechanism by which CSFV orchestrates this inhibition was investigated and it is shown that, like the related pestivirus bovine viral diarrhea virus (BVDV), this involves the N pro protein targeting interferon regulatory factor-3 (IRF-3) for degradation by proteasomes and thus preventing IRF-3 from activating transcription from the IFN-b promoter. Like BVDV, the steady-state levels of IRF-3 mRNA are not reduced markedly by CSFV infection or N pro overexpression. Moreover, IFN-a stimulation of CSFV-infected cells induces the antiviral