The Npro product of classical swine fever virus interacts with IκBα, the NF-κB inhibitor

Classical swine fever virus (CSFV) belongs to the genus Pestivirus and is the causative agent of classical swine fever, a haemorrhagic disease of pigs. The virus replicates in host cells without activating interferon (IFN) production and has been reported to be an antagonist of doublestranded RNA-induced apoptosis. The N-terminal protease (N pro) of CSFV is responsible for this evasion of the host innate immune response. In order to identify cellular proteins that interact with the N pro product of CSFV, a yeast two-hybrid screen of a human library was carried out, which identified li Bj,, the inhibitor of NF-i 13, a transcription factor involved in the control of apoptosis, the immune response and IFN production. The IN pro_, i 13),. interaction was confirmed using yeast two-hybrid analysis and additional co-precipitation assays. It was also shown that N pro localizes to both the cytoplasmic and nuclear compartments in stably transfected cells and in CSFVinfected cells. Following stimulation by tumour necrosis factor alpha, PK-1 5 cell lines expressing Nor' exhibited transient nuclear accumulation of pli,713j., but no effect of CSFV infection on li B:t. localization or Nl`-/ B p65 activation was observed.