Cytomegalovirus Restricts the Innate Immune Response by Nuclear Export of Host Restriction Factor DDX41

The innate immune response is the first line of defense against invading pathogens, including the betaherpesvirus, human cytomegalovirus (CMV). The host’s innate response acts as the first line of defense, and CMV, like other viruses, has consequently evolved multiple mechanisms to manipulate host interferon (IFN) responses. DEAD-box Helicase 41 (DDX41) is an intracellular dsDNA sensor that, upon activation by Bruton’s tyrosine kinase (BTK), triggers type I IFN production through the Stimulator of Interferon Genes (STING) signaling pathway. Here, we show the activation of this signaling pathway during lytic CMV infection, wherein BTK, DDX41, and STING are activated through tyrosine phosphorylation, and both DDX41 and BTK interact with STING. Further, CMV infection re-localizes DDX41 from the nucleus to the cytoplasm, where it localizes to the perinuclear virus assembly compartment (vAC). Here, DDX41 phosphorylation is attenuated, suggesting cytoplasmic redistribution leads to a less active or inactive form. Additionally, DDX41 co-localizes in the vAC with the CMV tegument proteins, pp65 and pp71, each of which interact with DDX41 in immunoprecipitation assays. We further demonstrate the protective role of this signaling pathway, as treatment with the BTK inhibitor, orelabrutinib, attenuates DDX41 phosphorylation/activation and supports increased expression of viral proteins and virus replication. In sum, our work highlights the important role of BTK-DDX41-STING signaling in the innate immune response against CMV, which the virus subverts by attenuating its cytoplasmic activity, thereby diverting it from its typically protective function.