Marburg Virus Evades Interferon Responses by a Mechanism Distinct from Ebola Virus

Charalampos Valmas,Elke Mühlberger,Sonja M Best,Verena Krähling,Michael Schümann,Judith Olejnik,Melanie N Grosch,Christopher F Basler,Osvaldo Martinez

doi:10.1371/journal.ppat.1000721

Abstract

Previous studies have demonstrated that Marburg viruses (MARV) and Ebola viruses (EBOV) inhibit interferon (IFN)-α/β signaling but utilize different mechanisms. EBOV inhibits IFN signaling via its VP24 protein which blocks the nuclear accumulation of tyrosine phosphorylated STAT1. In contrast, MARV infection inhibits IFNα/β induced tyrosine phosphorylation of STAT1 and STAT2. MARV infection is now demonstrated to inhibit not only IFNα/β but also IFNγ-induced STAT phosphorylation and to inhibit the IFNα/β and IFNγ-induced tyrosine phosphorylation of upstream Janus (Jak) family kinases. Surprisingly, the MARV matrix protein VP40, not the MARV VP24 protein, has been identified to antagonize Jak and STAT tyrosine phosphorylation, to inhibit IFNα/β or IFNγ-induced gene expression and to inhibit the induction of an antiviral state by IFNα/β. Global loss of STAT and Jak tyrosine phosphorylation in response to both IFNα/β and IFNγ is reminiscent of the phenotype seen in Jak1-null cells. Consistent with this model, MARV infection and MARV VP40 expression also inhibit the Jak1-dependent, IL-6-induced tyrosine phosphorylation of STAT1 and STAT3. Finally, expression of MARV VP40 is able to prevent the tyrosine phosphorylation of Jak1, STAT1, STAT2 or STAT3 which occurs following over-expression of the Jak1 kinase. In contrast, MARV VP40 does not detectably inhibit the tyrosine phosphorylation of STAT2 or Tyk2 when Tyk2 is over-expressed. Mutation of the VP40 late domain, essential for efficient VP40 budding, has no detectable impact on inhibition of IFN signaling. This study shows that MARV inhibits IFN signaling by a mechanism different from that employed by the related EBOV. It identifies a novel function for the MARV VP40 protein and suggests that MARV may globally inhibit Jak1-dependent cytokine signaling.

Highlights

Filoviruses, which include the genera ebolavirus (EBOV) and marburgvirus (MARV), are enveloped negative-strand RNA viruses that cause highly lethal hemorrhagic fever in humans and in nonhuman primates
Previous studies demonstrated that both MARV and EBOV block the type I interferon-induced Jak-STAT signaling pathway
The observed inhibition is not achieved by the MARV VP24 protein, but by the matrix protein VP40 which mediates viral budding

Summary

Introduction

Filoviruses, which include the genera ebolavirus (EBOV) and marburgvirus (MARV), are enveloped negative-strand RNA viruses that cause highly lethal hemorrhagic fever in humans and in nonhuman primates. The ability of filoviruses to counteract innate antiviral responses of the host, the IFNa/b response is thought to promote uncontrolled virus replication in vivo and thereby contribute to development of severe disease [1]. The IFNs, which include IFNa/b and IFNc, are antiviral cytokines. IFNa/b are members of a family of proteins that interact with the same ubiquitous receptor to trigger innate antiviral defense mechanisms and promote adaptive immunity [2]. IFNc triggers expression of antiviral genes, its major function is to modulate adaptive immune responses [3]. IFNa/b signaling results in the tyrosine phosphorylation and activation of the Janus kinases Jak and Tyk. IFNa/b signaling results in the tyrosine phosphorylation and activation of the Janus kinases Jak and Tyk2 These phosphorylate STAT2 and STAT1, which in turn heterodimerize and associate with interferon regulatory factor

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