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

Abstract

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-B. 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-B activation. We demonstrate that both viruses prevent ubiquitination of the NF-B inhibitor IB␣, whereas SVV additionally prevents IB␣ phosphorylation. We show that the ORF61 proteins of VZV and SVV are sufficient to prevent IB␣ ubiquitination upon ectopic expression. We further demonstrate that SVV ORF61 interacts with ␤-TrCP, a subunit of the SCF ubiquitin ligase complex that mediates the degradation of IB␣. This interaction seems to inactivate SCF-mediated protein degradation in general, since the unrelated ␤-TrCP target Snail is also stabilized by ORF61. In addition to ORF61, SVV seems to encode additional inhibitors of the NF-B pathway, since SVV with ORF61 deleted still prevented IB␣ phosphorylation and degradation. Taken together, our data demonstrate that SVV interferes with tumor necrosis factor alpha (TNF-␣)-induced NF-B activation at multiple levels, which is consistent with the importance of these countermechanisms for varicella virus infection. IMPORTANCEThe 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-B, 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 inhibition or by genetic modification of vaccine strains, is expected to reduce the pathogenic potential of VZV. Moreover, using SVV infection of rhesus macaques, it will be possible to study how increasing the vulnerability of varicella viruses to innate immunity will impact viral pathogenesis. V aricella-zoster virus (VZV) is a member of the subfamily Alphaherpesvirinae and is the causative agent of chickenpox and herpes zoster (HZ). Following primary infection, VZV establishes latency in ganglia. Reactivation from latency, which typically occurs late...

Simian varicella virus inhibits the interferon gamma signalling pathway

“…Recently, it was shown that SVV inhibits type I interferon (IFNa/b) signalling by reducing STAT2 and IRF9 protein levels in infected cells [27]. Furthermore, SVV impaired NFkB signalling by preventing the ubiquitination and degradation of the NFkB inhibitor IkBa [28]. Herein, we have extended these findings by demonstrating that SVV also blocks type II IFN (IFNg) signalling in infected cells.…”

Simian varicella virus causes robust transcriptional changes in T cells that support viral replication

“…Interestingly, immune genes that mapped to antigen presentation were downregulated 3 and 10 DPI, but upregulated 7 DPI. This change in FC direction could be due to initial immune evasion strategies employed by SVV (Whitmer et al, 2015;Meysman et al, 2013) 3 DPI, followed by development of host defense 7 DPI, and again downregulation of these pathways as the immune response begins to resolve 10 DPI.…”

Manipulation of the Innate Immune Response by Varicella Zoster Virus

“…Furthermore, the E3 ubiquitin ligase domain of VZV ORF61 was required to modulate this pathway, downstream of triggering receptors TLR3, TLR8, and TLR9 (87). Use of the SVV model indicated that SVV, like VZV, can prevent ubiquitination of IκBα and additionally prevents the phosphorylation of IκBα (134). This study also revealed that in addition to SVV ORF61, SVV is likely to encode additional modulators of NFκB signaling, as an ORF61 deletion virus retained its capacity to prevent IκBα phosphorylation and degradation.…”