Marek's disease virus protein kinase US3 inhibits DNA-sensing antiviral innate immunity via abrogating activation of NF-κB.

Marek's disease virus (MDV) is an avian alphaherpesvirus associated with Marek's disease, an immunosuppressive and lymphoproliferative disease in chickens. The DNA sensing pathway mediates innate immune defense against infection by many DNA-containing pathogens, while viruses have evolved multiple strategies to evade the host immune response to survive in host cells. This study found that ectopic expression of MDV protein kinase US3 inhibited beta interferon (IFN-β) and interleukin-6 (IL-6) production induced by interferon-stimulatory and viral DNA. US3 was further shown to abolish the nuclear factor κB (NF-κB) activation. The US3 kinase activity was indispensable for its inhibitory function, as the kinase-dead US3 mutant (US3K220A) did not inhibit NF-κB activation. Further studies showed that US3 interacted with the Rel homology domains of the NF-κB subunits p65 and p50, which phosphorylated these transcription factors and blocked their nuclear translocation. Finally, US3 deficiency promoted IFN-β and IL-6 production, resulting in reduced viral replication and lower MDV-specific lesion incidence during MDV infection in chickens. Altogether, these findings reveal a novel mechanism for MDV to evade host antiviral immunity.IMPORTANCEMarek's disease virus (MDV) is an oncogenic avian alphaherpesvirus that causes an economically important disease affecting the health and welfare of poultry worldwide. Whereas human herpesviruses have been shown to evolve various strategies to inhibit the DNA sensing signaling for the evasion of the host's innate immunity, little is known regarding the mechanism for MDV to regulate this pathway. In this study, MDV US3 protein kinase was demonstrated to inhibit the activation of NF-κB in the DNA sensing pathway via binding to the Rel homology domains of the NF-κB subunits p65 and p50, which hyperphosphorylated these transcription factors and abolished their nuclear translocation. This is an important finding toward a better understanding of the functions of avian alphaherpesviruses encoded US3 protein kinase.