Human norovirus is the leading cause of sporadic gastroenteritis, which is responsible for more than 90% of all nonbacterial gastroenteritis outbreaks. While norovirus infections typically cause mild and self-limiting symptoms lasting 24-48 h, chronic persistent infections can cause severe symptoms. Although recent advances have been made in understanding the molecular characteristics of norovirus infection, no norovirus-specific antiviral drugs, or vaccines are available. Conventional intervention methods used to inactivate norovirus, such as treatment with disinfecting agents (e.g. ethanol, hypochlorite, and quaternary ammonium formulations), have shown a lack of efficacy against human norovirus when they are applied to foods and in food preparation processes. Therefore, alternative antiviral or inactivating agents such as phytochemicals have received attention as potential norovirus inhibitors due to their relatively low toxicity and lack of side effects, which allows them to be prepared as food-safe formulations. Evidence from studies using viral surrogates suggests that numerous phytochemicals and foods containing flavonoids and polyphenols have anti-norovirus activity, and future studies will be necessary to confirm the effectiveness of such compounds against human norovirus and the molecular mechanisms through which they produce antiviral effects.

Upon viral infection, type I interferons, such as alpha and beta interferon (IFN-␣ and IFN-␤, respectively), are rapidly induced and activate multiple antiviral genes, thereby serving as the first line of host defense. Many DNA and RNA viruses counteract the host interferon system by modulating the production of IFNs. In this study, we report that murine gammaherpesvirus 68 (MHV-68), a double-stranded DNA virus, encodes open reading frame 11 (ORF11), a novel immune modulator, to block IFN-␤ production. ORF11-deficient recombinant viruses induced more IFN-␤ production in fibroblast and macrophage cells than the MHV-68 wild type or a marker rescue virus. MHV-68 ORF11 decreased IFN-␤ promoter activation by various factors, the signaling of which converges on TBK1-IRF3 activation. MHV-68 ORF11 directly interacted with both overexpressed and endogenous TBK1 but not with IRF3. Physical interactions between ORF11 and endogenous TBK1 were further confirmed during virus replication in fibroblasts using a recombinant virus expressing FLAG-ORF11. ORF11 efficiently reduced interaction between TBK1 and IRF3 and subsequently inhibited activation of IRF3, thereby negatively regulating IFN-␤ production. Our domain-mapping study showed that the central domain of ORF11 was responsible for both TBK1 binding and inhibition of IFN-␤ induction, while the kinase domain of TBK1 was sufficient for ORF11 binding. Taken together, these results suggest a mechanism underlying inhibition of IFN-␤ production by a gammaherpesvirus and highlight the importance of TBK1 in DNA virus replication. IMPORTANCEGammaherpesviruses are important human pathogens, as they are associated with various kinds of tumors. Upon virus infection, the type I interferon pathway is activated by a series of signaling molecules and stimulates antiviral gene expression. To subvert such interferon antiviral responses, viruses are equipped with multiple factors that can inhibit its critical steps. In this study, we took an unbiased genomic approach using a mutant library of murine gammaherpesvirus 68 to screen a novel viral immune modulator that negatively regulates the type I interferon pathway and identified ORF11 as a strong candidate. ORF11-deficient virus infection produced more interferon than the wild type in both fibroblasts and macrophages. During virus replication, ORF11 directly bound to TBK1, a key regulatory protein in the interferon pathway, and inhibited TBK1-mediated interferon production. Our results highlight a crucial role of TBK1 in controlling DNA virus infection and a viral strategy to curtail host surveillance.

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