The virion host shutoff protein of herpes simplex virus 1 blocks the replication-independent activation of NF-κB in dendritic cells in the absence of type I interferon signaling.

Immune evasion is a defining feature of the virus-host relationship. During infection, herpes simplex virus type 1 (HSV-1) utilizes multiple proteins to manipulate the host immune response. In the present study, we investigated the mechanism by which the virion host shutoff (vhs) protein blocks the activation of dendritic cells (DCs). Previously, we found that coinfection of wild-type HSV-1 with a panel of RNA viruses resulted in a block to DC activation that was attributable to vhs. These observations led us to hypothesize that the vhs-mediated inhibition was dependent on signaling through the RIG-I-like receptor (RLR) signaling pathway. By examining DCs generated from MAVS (IPS-1) knockout (KO) mice, we determined that RLR/MAVS signaling is not essential for the DC response to HSV-1. We also evaluated the requirement for the type I interferon (IFN) signaling pathway in DC activation following infection with HSV-1 and found that stimulation of DCs with wild-type HSV-1 required intact type I IFN signaling for the production of cytokines, whereas the vhs deletion (vhs(-)) mutant virus activated DCs without the need for exogenous IFN signaling. Comparisons of transcription factor activation in DCs infected with wild-type HSV and the vhs(-) mutant virus revealed that NF-κB activation was inhibited by vhs in the early phase of the infection. In contrast, IRF3 activation was not influenced by vhs. In these studies, measurement of proinflammatory cytokines and type I IFN release from the infected DCs reflected the activation status of these transcription factors. Taken together, the work presented here (i) describes a novel role for the vhs protein as an inhibitor of the early activation of NF-κB during HSV-1 infection of DCs and (ii) offers a mechanistic explanation of how this protein interferes with DC activation.