Publications

The Ebola virus VP35 protein was previously found to act as an interferon (IFN) antagonist which could complement growth of influenza delNS1 virus, a mutant influenza virus lacking the influenza virus IFN antagonist protein, NS1. The Ebola virus VP35 could also prevent the virus- or double-stranded RNA-mediated transcriptional activation of both the beta IFN (IFN-beta) promoter and the IFN-stimulated ISG54 promoter (C. Basler et al., Proc. Natl. Acad. Sci. USA 97:12289-12294, 2000). We now show that VP35 inhibits virus infection-induced transcriptional activation of IFN regulatory factor 3 (IRF-3)-responsive mammalian promoters and that VP35 does not block signaling from the IFN-alpha/beta receptor. The ability of VP35 to inhibit this virus-induced transcription correlates with its ability to block activation of IRF-3, a cellular transcription factor of central importance in initiating the host cell IFN response. We demonstrate that VP35 blocks the Sendai virus-induced activation of two promoters which can be directly activated by IRF-3, namely, the ISG54 promoter and the ISG56 promoter. Further, expression of VP35 prevents the IRF-3-dependent activation of the IFN-alpha4 promoter in response to viral infection. The inhibition of IRF-3 appears to occur through an inhibition of IRF-3 phosphorylation. VP35 blocks virus-induced IRF-3 phosphorylation and subsequent IRF-3 dimerization and nuclear translocation. Consistent with these observations, Ebola virus infection of Vero cells activated neither transcription from the ISG54 promoter nor nuclear accumulation of IRF-3. These data suggest that in Ebola virus-infected cells, VP35 inhibits the induction of antiviral genes, including the IFN-beta gene, by blocking IRF-3 activation.

The potential threat of another influenza virus pandemic stimulates discussion on how to prepare for such an event. The most reasonable prophylactic approach appears to be the use of effective vaccines. Since influenza and other negative-stranded RNA viruses are amenable to genetic manipulation using transfection by plasmids, it is possible to outline new reverse genetics-based approaches for vaccination against influenza viruses. We suggest three approaches. First, we use a plasmid-only rescue system that allows the rapid generation of high-yield recombinant vaccine strains. Second, we propose developing second-generation live influenza virus vaccines by constructing an attenuated master strain with deletions in the NS1 protein, which acts as an interferon antagonist. Third, we suggest the use of Newcastle disease virus recombinants expressing influenza virus haemagglutinin proteins of pandemic (epizootic) strains as novel vaccine vectors for use in animals and possibly humans.