West Nile virus versus the host cell: Identification of host factors that modulate infection



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There are two competing aspects of virus-host interactions: (i) those that enhance virus transmission and (ii) those that reduce or prevent viral replication and transmission. Each of these types of interactions is critical and both must be investigated to fully understand viral pathogenesis. Cells encode a variety of molecules which are critical for recognizing viral infections. One such molecule, the dsRNA sensor PKR, has been shown to be important for IFN-beta induction. Therefore, to determine whether PKR was involved in the recognition of WNV infection, cells lacking PKR were infected with WNV and assayed for IFN production. Interestingly, PKR-null cells demonstrated dramatically lower levels of WNV-induced IFN compared to wild type cells. Additionally, chemical inhibition of PKR activity or post-translational gene silencing of PKR expression severely impaired WNV-induced IFN production, suggesting that PKR is critical for the induction of IFN following WNV infection. Further analysis suggested that PKR may be important for the activation of NF-kappaB, suggesting a possible mechanism of IFN-beta induction. Consistent with cell line data, PKR was shown to be critical for WNV-induced IFN production in primary mouse bone marrow-derived dendritic cells.\r\nThe recognition of WNV is an important aspect of controlling infection; however, it is only one side of the story. Host factors which WNV utilizes to facilitate its infection and replication are also key to understanding viral pathogenesis. The presence or absence of specific factors may control the level of viral replication, host tropisms and, ultimately, viral pathogenesis. To identify host co-factors that are essential for WNV infection and/or replication, small interfering RNAs (siRNAs) were used to systematically knockdown host gene products and levels of WNV infection and/or replication was assayed in the absence of these factors. A siRNA library screen identified ten cellular proteins which are essential for WNV infection and/or replication. Two of these genes encoded subunits of the proteasome. Chemical inhibitors of proteasome activity confirmed that the proteasome is critical for efficient WNV replication.



WNV, West Nile virus, proteasome, PKR, interferon, host factors