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David Shahnazaryan, Elisa Lazzari, Joan Ni Gabhann, Caroline Jefferies, Conor Murphy; Identifying new targets of viral regulatory protein ICP0 in herpes simplex virus type-1 (HSV-1) keratitis. Invest. Ophthalmol. Vis. Sci. 2014;55(13):855.
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© ARVO (1962-2015); The Authors (2016-present)
Herpes simplex keratitis (HSK) is the most common cause of infective corneal blindness in the western world with an estimated incidence of 24000 new cases in per year in the United States alone. HSV-1 infection induces host antiviral responses, including induction of type I interferons (IFNs). Previous studies have shown that HSV-1 viral protein Infected cell protein 0 (ICP0) is able to block type 1 IFN induction to overcome host antiviral responses, however the exact molecular mechanisms of this are not clearly understood. In this study we wanted to investigate if ICP0 targets key regulatory proteins within TLR3, 7 and 9 pathways to suppress the antiviral responses.
HEK293T cell lines were transiently transfected with a plasmid expressing ICP0 and plasmids expressing key proteins of type 1 IFN pathway (MyD88, RIG-I, TBK1, NFkB, IRF3, IRF5 and IRF7). Luciferase dual reporter gene assays were employed to reveal the effect of ICP0 on type 1 IFN promoter activity. Western Blotting of transfected cell lysates was used to reveal the degradation of possible targets.
Our experiments show significant degradation of MyD88 and IRF7 and inhibition of interferon responses in the presence of ICP0. The expression of RIG-I, TBK1, NFkB and IRF3, however, remains unchanged.
A key element of the innate immune response to HSV-1 infection is the production of type 1 IFNs by infected epithelial cells. In order to initiate such response the HSV-1 needs to be recognized by the cells of the ocular surface. This role is attributed to so-called toll-like receptors (TLRs). TLR7 and 9 in particular are responsible for recognition of HSV-1 and have been shown to be upregulated in corneas of patients with HSK. MyD88 and IRF7 are adaptor molecule required for TLR7 and 9 signaling that leads to production of type 1 IFN. Our results suggest that HSV-1 viral protein ICP0 could limit this antiviral response by targeting MyD88 and IRF7 for degradation.
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