Herpes Simplex Virus 1-Encoded Tegument Protein VP16 Abrogates the Production of Beta Interferon (IFN) by Inhibiting NF-κB Activation and Blocking IFN Regulatory Factor 3 To Recruit Its Coactivator CBP

Host cells activate innate immune signaling pathways to defend against invading pathogens. To survive within an infected host, viruses have evolved intricate strategies to counteract host immune responses. Herpesviruses, including herpes simplex virus type 1 (HSV-1), have large genomes and therefore have the capacity to encode numerous proteins that modulate host innate immune responses. Here we define the contribution of HSV-1 tegument protein VP16 in the inhibition of beta interferon (IFN-beta) production. VP16 was demonstrated to significantly inhibit Sendai virus (SeV)-induced IFN-beta production, and its transcriptional activation domain was not responsible for this inhibition activity. Additionally, VP16 blocked the activation of the NF-kappa B promoter induced by SeV or tumor necrosis factor alpha treatment and expression of NF-kappa B-dependent genes through interaction with p65. Coexpression analysis revealed that VP16 selectively blocked IFN regulatory factor 3 (IRF-3)-mediated but not IRF-7-mediated transactivation. VP16 was able to bind to IRF-3 but not IRF-7 in vivo, based on coimmunoprecipitation analysis, but it did not affect IRF-3 dimerization, nuclear translocation, or DNA binding activity. Rather, VP16 interacted with the CREB binding protein (CBP) coactivator and efficiently inhibited the formation of the transcriptional complexes IRF-3-CBP in the context of HSV-1 infection. These results illustrate that VP16 is able to block the production of IFN-beta by inhibiting NF-kappa B activation and interfering with IRF-3 to recruit its coactivator CBP, which may be important to the early events leading to HSV-1 infection.