Inhibition of the NF-κB Pathway by Varicella-Zoster Virus In Vitro and in Human Epidermal Cells In Vivo

Abstract

Varicella-zoster virus (VZV) is an alphaherpesvirus that causes varicella and herpes zoster. Using human cellular DNA microarrays, we found that many nuclear factor kappa B (NF-κB)-responsive genes were down-regulated in VZV-infected fibroblasts, suggesting that VZV infection inhibited the NF-κB pathway. The activation of this pathway causes a cellular antiviral response, including the production of alpha/beta interferon, cytokines, and other proteins that restrict viral infection. In these experiments, we demonstrated that VZV interferes with NF-κB activation in cultured fibroblasts and in differentiated epidermal cells in skin xenografts of SCIDhu mice infected in vivo. VZV infection of fibroblasts caused a transient nuclear translocation of p50 and p65, the canonical NF-κB family members. In a process that was dependent upon the presence of infectious VZV, these proteins rapidly became sequestered in the cytoplasm of VZV-infected cells. Exclusion of NF-κB proteins from nuclei was associated with the continued presence of IκBα, which binds p50 and p65 and prevents their nuclear accumulation. IκBα levels did not diminish even though the protein became phosphorylated and ubiquitinated, as determined based on detection of the characteristic high-molecular-weight form of the protein, and the 26S proteasome remained functional in VZV-infected cells. VZV infection also inhibited the characteristic degradation of IκBα that is induced by exposure of fibroblasts to tumor necrosis factor alpha. As expected, herpes simplex virus 1 caused the persistent nuclear translocation of NF-κB proteins, which has been shown to facilitate its replication, whereas VZV infection progressed without persistent NF-κB nuclear localization. We suggest that VZV has evolved a mechanism to limit host cell antiviral defenses by sequestering NF-κB proteins in the cytoplasm, a strategy that appears to be unique among the herpesviruses.