A Systematic Analysis of Host Factors Reveals a Med23-Interferon-λ Regulatory Axis against Herpes Simplex Virus Type 1 Replication

Abstract

Herpes simplex virus type 1 (HSV-1) is a neurotropic virus causing vesicular oral or genital skin lesions, meningitis and other diseases particularly harmful in immunocompromised individuals. To comprehensively investigate the complex interaction between HSV-1 and its host we combined two genome-scale screens for host factors (HFs) involved in virus replication. A yeast two-hybrid screen for protein interactions and a RNA interference (RNAi) screen with a druggable genome small interfering RNA (siRNA) library confirmed existing and identified novel HFs which functionally influence HSV-1 infection. Bioinformatic analyses found the 358 HFs were enriched for several pathways and multi-protein complexes. Of particular interest was the identification of Med23 as a strongly anti-viral component of the largely pro-viral Mediator complex, which links specific transcription factors to RNA polymerase II. The anti-viral effect of Med23 on HSV-1 replication was confirmed in gain-of-function gene overexpression experiments, and this inhibitory effect was specific to HSV-1, as a range of other viruses including Vaccinia virus and Semliki Forest virus were unaffected by Med23 depletion. We found Med23 significantly upregulated expression of the type III interferon family (IFN-λ) at the mRNA and protein level by directly interacting with the transcription factor IRF7. The synergistic effect of Med23 and IRF7 on IFN-λ induction suggests this is the major transcription factor for IFN-λ expression. Genotypic analysis of patients suffering recurrent orofacial HSV-1 outbreaks, previously shown to be deficient in IFN-λ secretion, found a significant correlation with a single nucleotide polymorphism in the IFN-λ3 (IL28b) promoter strongly linked to Hepatitis C disease and treatment outcome. This paper describes a link between Med23 and IFN-λ, provides evidence for the crucial role of IFN-λ in HSV-1 immune control, and highlights the power of integrative genome-scale approaches to identify HFs critical for disease progression and outcome.

Interferon-λ restricts West Nile virus neuroinvasion by tightening the blood-brain barrier

“…This results in a tighter BBB, which restricts pathogen entry into the CNS parenchyma. In humans, multiple polymorphisms in the IFN-λ locus are associated with differential clearance of hepatitis B and C viruses (31), as well as the severity of herpesvirus infections (32, 33). Further analysis is warranted to define similar genetic linkages to neuroinvasive infections or CNS autoimmune diseases.…”

Guarding the frontiers: the biology of type III interferons

“…Finally, another group has identified Med23, a subunit of the mediator complex 51 , as a direct interaction partner for IRF7 (ref. 52). Med23 and IRF7 synergistically increase IFNL transcription but have no effect on IFNB1.…”

Interferon Lambda Genetic Polymorphisms and Viral Infection: The Tip of the Iceberg?

“…Using a genome-wide approach to identify host factors that functionally influence HSV-1 infection in vitro, Griffiths et al (2013) identified Med23 as an antiviral factor able to inhibit HSV-1 replication by upregulating the expression of IFN-l. IFN-l is already implicated in the control of herpes labialis (cold sore) in an Italian cohort of patients, where individuals who suffer recurrent herpes labialis were shown to produce lower levels of IFN-l from peripheral blood mononuclear cells, in comparison to HSV-1 sero-positive controls who do not experience recurrent disease (Pica et al, 2010). Genotyping of this same cohort by Griffiths et al for the IFN-l rs12979860 SNP found that the T allele was associated with disease severity in a dose-dependent manner (TT genotype more prevalent with increased disease severity), and there was a significant association between the CT or TT genotype and the most severe category of disease (high recurrence and high clinical severity).…”