Contribution of the interaction between the rabies virus P protein and I-kappa B kinase ε to the inhibition of type I IFN induction signalling

The P protein of rabies virus (RABV) is known to interfere with the phosphorylation of the host IFN regulatory factor 3 (IRF-3) and to consequently inhibit type I IFN induction. Previous studies, however, have only tested P proteins from laboratory-adapted fixed virus strains, and to the best of our knowledge there is no report about the effect of P proteins from street RABV strains or other lyssaviruses on the IRF-3-mediated type I IFN induction system. In this study, we evaluated the inhibitory effect of P proteins from several RABV strains, including fixed and street virus strains and other lyssaviruses (Lagos bat, Mokola and Duvenhage viruses), on IRF-3 signalling. All P proteins tested inhibited retinoic acid-inducible gene-1 (RIG-I)- and TANK binding kinase 1 (TBK1)-mediated IRF-3-dependent IFN-beta promoter activities. On the other hand, the P proteins from the RABV street strains 1088 and HCM-9, but not from fixed strains Nishigahara (Ni) and CVS-11 and other lyssaviruses tested, significantly inhibited I-kappa B kinase epsilon (IKK epsilon)-inducible IRF-3-dependent IFN-beta promoter activity. Importantly, we revealed that the P proteins from the 1088 and HCM-9 strains, but not from the remaining viruses, interacted with IKK epsilon. By using expression plasmids encoding chimeric P proteins from the 1088 strain and Ni strain, we found that the C-terminal region of the P protein is important for the interaction with IKK epsilon. These findings suggest that the P protein of RABV street strains may contribute to efficient evasion of host innate immunity.