NS1 protein of avian influenza A virus prevents activation of NF-κB through binding to IKKα and IKKβ

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Background: Highly pathogenic strains of avian influenza A virus H5N1 have caused the deaths of more than 262 people since 2003, corresponding to a death rate of about 60% for known infections (information from WHO website). If these viruses acquire the ability for efficient transmission between humans, the next pandemic will come. Therefore, it is important to study the factors that limit the transmission of avian viruses within humans. Methods: The non-structure protein NS1 of H5N1 influenza virus contributes to virulence during virus infection by allowing the virus to disarm the IFN-based defence system of the host cell. To identify new potential antiviral genes regulated by NS1, we measured the expression pattern of cellular gene using DNA microarray technology. The down-regulation of several NF-κB-mediated downstream genes, IL-6, IL-8, COX-2, CCL-20, etc, was observed in the presence of NS1. Real-time PCR and ELISA were used to further confirm the microarray results. Luciferase activity assay indicated that the NF-κB binding sites were essential for the regulation of IL-6 and IL-8 by NS1 protein. Further studies demonstrated that NS1 protein can suppress NF-κB activity in a dose-dependent manner. Western blot assay suggested that NS1 did not alter the expression level of NF-κB, but prevented the translocation of NF-κB from cytosol to nucleus. This inhibitory property of the NS1 protein was dependent on its ability to bind IKKα and IKKβ, which confirmed by the GST pull down, co-immunoprecipitation and confocal assay. Results: We for the first time demonstrated that NS1 can prevent activation of NF-κB through binding to IKK& and IKK$. Conclusion: NF-κB, an important transcription factor, plays an essential role in the regulation of immune and inflammatory responses. Therefore, NS1-mediated inhibition of the NF-κB pathway may thus play a key role in regulating the host innate and adaptive immune responses during virus infection. Abstracts for SupplementInternational Journal of Infectious DiseasesVol. 14Preview Full-Text PDF Open Archive