The ORF61 Protein Encoded by Simian Varicella Virus and Varicella-Zoster Virus Inhibits NF-κB Signaling by Interfering with IκBα Degradation

• Published in: Journal of virology 2015-09, Vol.89 (17), p.8687-8700
• Main Authors: Whitmer, Travis, Malouli, Daniel, Uebelhoer, Luke S, DeFilippis, Victor R, Früh, Klaus, Verweij, Marieke C
• Format: Article
• Language: English
• Subjects: Animals; beta-Transducin Repeat-Containing Proteins - metabolism; Cell Line; Chickenpox - immunology; Chickenpox - virology; Disease Models, Animal; Enzyme Activation; Gene Deletion; HEK293 Cells; Herpesvirus 3, Human - genetics; Herpesvirus 3, Human - immunology; Humans; I-kappa B Proteins - metabolism; Immune Evasion - immunology; Immunity, Innate - immunology; Macaca mulatta; NF-kappa B - antagonists & inhibitors; NF-kappa B - metabolism; NF-KappaB Inhibitor alpha; Phosphorylation; SKP Cullin F-Box Protein Ligases - metabolism; Snail Family Transcription Factors; Transcription Factors - metabolism; Tumor Necrosis Factor-alpha - metabolism; Ubiquitination; Viral Load; Viral Proteins - genetics; Viral Proteins - metabolism; Virus Activation - immunology; Virus-Cell Interactions
• ISSN: 0022-538X; 1098-5514
• DOI: 10.1128/JVI.01149-15

Varicella-zoster virus (VZV) causes chickenpox upon primary infection and establishes latency in ganglia. Reactivation from latency causes herpes zoster, which may be complicated by postherpetic neuralgia. Innate immunity mediated by interferon and proinflammatory cytokines represents the first line of immune defense upon infection and reactivation. VZV is known to interfere with multiple innate immune signaling pathways, including the central transcription factor NF-κB. However, the role of these inhibitory mechanisms in vivo is unknown. Simian varicella virus (SVV) infection of rhesus macaques recapitulates key aspects of VZV pathogenesis, and this model thus permits examination of the role of immune evasion mechanisms in vivo. Here, we compare SVV and VZV with respect to interference with NF-κB activation. We demonstrate that both viruses prevent ubiquitination of the NF-κB inhibitor IκBα, whereas SVV additionally prevents IκBα phosphorylation. We show that the ORF61 proteins of VZV and SVV are sufficient to prevent IκBα ubiquitination upon ectopic expression. We further demonstrate that SVV ORF61 interacts with β-TrCP, a subunit of the SCF ubiquitin ligase complex that mediates the degradation of IκBα. This interaction seems to inactivate SCF-mediated protein degradation in general, since the unrelated β-TrCP target Snail is also stabilized by ORF61. In addition to ORF61, SVV seems to encode additional inhibitors of the NF-κB pathway, since SVV with ORF61 deleted still prevented IκBα phosphorylation and degradation. Taken together, our data demonstrate that SVV interferes with tumor necrosis factor alpha (TNF-α)-induced NF-κB activation at multiple levels, which is consistent with the importance of these countermechanisms for varicella virus infection. The role of innate immunity during the establishment of primary infection, latency, and reactivation by varicella-zoster virus (VZV) is incompletely understood. Since infection of rhesus macaques by simian varicella virus (SVV) is used as an animal model of VZV infection, we characterized the molecular mechanism by which SVV interferes with innate immune activation. Specifically, we studied how SVV prevents activation of the transcription factor NF-κB, a central factor in eliciting proinflammatory responses. The identification of molecular mechanisms that counteract innate immunity might ultimately lead to better vaccines and treatments for VZV, since overcoming these mechanisms, either by small-molecule