Marburg Virus VP40 Antagonizes Interferon Signaling in a Species-Specific Manner

Abstract

Marburgviruses are zoonotic pathogens that cause lethal hemorrhagic fever in humans and nonhuman primates. However, they do not cause lethal disease in immunocompetent mice unless they are adapted to this species. The adaptation process can therefore provide insight into the specific virus-host interactions that determine virulence. In primate cells, the Lake Victoria marburgvirus Musoke strain ( Filoviruses, which include the genera Marburgvirus and Ebolavirus (EBOV), are causative agents of severe hemorrhagic fevers in humans and nonhuman primates. Human case fatality rates have reached up to 90% in some outbreaks. The genus Marburgvirus includes a single species, Lake Victoria marburgvirus that is comprised of two lineages; one is represented by a 1987 isolate from Kenya (Marburg Ravn virus [RAVV]), and the other is comprised of multiple strains, including Ozolin, Popp, Musoke (abbreviated as MARV here), and Angola (10,14,33).Filoviruses counteract the innate immune responses of primate hosts, preventing the production of and cellular responses to alpha/beta interferon (IFN-␣/␤) (1,28,29,40). IFN-␣/␤ and IFN-␥ are cytokines that induce in cells an antiviral state and are of particular importance to innate antiviral immunity (3, 36). Binding of IFN-␣/␤ to its receptor results in the tyrosine phosphorylation of the Janus kinases Jak1 and Tyk2, which subsequently phosphorylate the transcription factors STAT1 and STAT2. STAT1 and STAT2 form a heterodimer and associate with the IFN regulatory factor 9 (IRF9), translocate into the nucleus, and activate a set of genes involved in antiviral response (25). The absence of Jak1 leads to lack of STAT activation (11,21,30,44).Filovirus proteins that antagonize IFN responses have been identified. EBOV VP35 inhibits the production of IFN-␣/␤ by antagonizing the RIG-I signaling pathway (1,6,12,17). EBOV VP24 inhibits cellular responses to IFN-␣/␤ and IFN-␥ by interacting with the NPI-1 subfamily of karyopherin ␣ nuclear transport proteins, preventing the nuclear accumulation of tyrosine phosphorylated STAT1 (20,28,29). Surprisingly, given the similar genomic organization of EBOVs and Marburg viruses, MARV was demonstrated to block cellular responses to IFNs by a unique mechanism (40). Specifically, while the MARV VP24 protein did not exhibit binding to karyopherin ␣ proteins and did not block IFN signaling, the MARV major matrix protein VP40, which drives viral budding (8,16,34,39), inhibits Jak1-dependent signaling pathways, including the IFN-␣/␤, IFN-␥, and interleukin-6 pathways (40). For the IFN-␣/␤ pathway, VP40 inhibits activation of Jak1, resulting in the absence of IFN-␣/␤-induced Jak1, Tyk2, STAT1, and STAT2 tyrosine phosphorylation (40).The assembly and budding functions of filovirus VP40 proteins are related to their ability to bud from cells, and expression of VP40 proteins results in the release of virus-like particles (VLPs) from the cell surface (13,15,16,23,32,39). Implicated in the budding process are short amino acid motifs known as late domains. EBOV VP40 ...

The VP40 Protein of Marburg Virus Exhibits Impaired Budding and Increased Sensitivity to Human Tetherin following Mouse Adaptation

“…In Hepa1.6 cells, both RAVV and maRAVV VLPs were detected at comparable levels, consistent with a previous study (Fig. 1B) (29). Interestingly, while RAVV VLPs were detected in supernatant harvested from transfected Huh7 and 293T cells, maRAVV VLP release from Huh7 and 293T cells was significantly impaired, despite similar expression levels of RAVV and maRAVV VP40 in all cell lines examined.…”

“…The restriction in human cells maps in part to residue 57, and change at this residue also alters RAVV VP40 oligomerization. This change at residue 57 was also important for VP40 acquisition of anti-IFN function in mouse cells (29). This suggests a model in which RAVV VP40 undergoes changes in its oligomerization potential as it is adapted to mice, enhancing its IFN antagonist function.…”

“…FLAG-tagged RAVV and viral protein expression plasmids were described previously (14,29). The hemagglutinin (HA)-tagged RAVV VP40 plasmids were constructed by restriction enzyme doubledigestion reactions of FLAG-tagged VP40 plasmid with XhoI (NEB) and NotI (NEB).…”

“…In contrast, mouseadapted RAVV (maRAVV) VP40 had gained the ability to inhibit interferon signaling in mouse cells. This gain of function was mapped to changes at VP40 amino acid residues 57 and 165 (29). These and 5 other amino acid mutations acquired during mouse adaptation did not affect the ability of maRAVV VP40 to inhibit IFN responses in human cells, and both the parental and maRAVV VP40s could efficiently bud from mouse cells (29).…”

Structural basis for Marburg virus VP35–mediated immune evasion mechanisms

“…Despite overall similarities in genome size and organization, virion structure, and disease characteristics (3), EBOV and MARV exhibit important differences, including their strategies for immune evasion (4). For example, although EBOV viral protein (VP) 24 and MARV VP40 counter IFN signaling, neither MARV VP24 nor EBOV VP40 appears to function similarly to its corresponding counterparts with regard to immune evasion (5)(6)(7)(8)(9)(10).…”