Relative to wild-type EBOV VP40 or wild-type MARV VP40, M40-AAAA exhibited greatly reduced budding, in the form of virus-like particles (VLPs), from transfected 293T cells, despite comparable expression in the whole cell extracts (Fig. both IFN/ and IFN is usually reminiscent of the phenotype seen in Jak1-null cells. Consistent with this model, MARV contamination 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 usually 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 Lenvatinib mesylate novel function for the MARV VP40 protein and suggests that MARV may globally inhibit Jak1-dependent cytokine signaling. Author Summary The closely related members of the filovirus family, Ebola computer Lenvatinib mesylate virus (EBOV) and Marburg computer virus (MARV), cause severe hemorrhagic disease in humans with high fatality rates. Infected individuals exhibit dysregulated immune responses which appear to result from several factors, including virus-mediated impairment of innate immune responses. Previous studies exhibited that both MARV and EBOV block the type I interferon-induced Jak-STAT signaling pathway. For EBOV, the viral protein VP24 mediates the inhibitory effects by interfering with the nuclear translocation of activated STAT proteins. Here, we show that MARV uses a distinct mechanism to block IFN signaling pathways. Our data revealed that MARV blocks the phosphorylation of Janus kinases and their target STAT proteins in response to type I and type II interferon and interleukin 6. Surprisingly, the observed inhibition is not achieved by the MARV VP24 protein, but by the matrix protein VP40 which also mediates viral budding. Over-expression studies indicate that MARV VP40 globally antagonizes Jak1-dependent signaling. Further, we show that a MARV VP40 mutant defective for budding retains interferon antagonist function. Our results spotlight a basic difference between EBOV and MARV, define a new function for MARV VP40 and reveal new targets for the development of anti-MARV therapies. Introduction Filoviruses, which include the genera (EBOV) and (MARV), are enveloped negative-strand RNA viruses that cause highly lethal hemorrhagic fever in humans and in non-human primates. The ability of filoviruses to counteract innate antiviral responses of the host, particularly the IFN/ response is usually thought to promote uncontrolled computer virus replication and thereby contribute to development of severe disease Lenvatinib mesylate [1]. The IFNs, which include IFN/ and IFN, are antiviral cytokines. IFN/ 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]. IFN also triggers expression of antiviral genes, however, its major function is usually to modulate adaptive immune responses [3]. IFN/ signaling results in the tyrosine phosphorylation and activation of the Janus kinases Jak1 and Tyk2. These phosphorylate STAT2 and STAT1, which in turn heterodimerize and associate with interferon regulatory factor 9 (IRF9) to form a complex that is translocated into the nucleus to activate genes involved in antiviral response (reviewed in [4]). IFN signaling activates Jak1 and Jak2, resulting in tyrosine phosphorylation of STAT1. This induces STAT1 homodimerization and translocation to the nucleus such that IFN dependent gene expression is usually induced (reviewed in [4]). Of note, Jak1, a kinase involved in multiple cytokine signaling pathways, is critical for both IFN/ and IFN signaling. For example, in cells lacking Jak1, IFN/ fails to trigger STAT1 or STAT2 tyrosine phosphorylation and Tyk2 tyrosine phosphorylation is usually greatly reduced or eliminated [5],[6]. Similarly, in cells lacking Jak1, IFN fails to trigger Jak1, Jak2 or STAT1 tyrosine phosphorylation [5],[7],[8]. Filovirus genomes encode seven structural proteins. Four of these proteins, the nucleoprotein (NP), the viral proteins VP35 and VP30, and the L protein are tightly associated with the RNA genome, form the nucleocapsid and mediate replication and transcription (reviewed in [9]). Besides its function Rabbit polyclonal to Sin1 as polymerase cofactor, VP35 acts as an inhibitor of antiviral pathways (see below). Two of the filovirus structural proteins are matrix proteins, VP40, the functional equivalent of the matrix (M) proteins of other non-segmented negative-stand RNA viruses, and the minor matrix protein VP24 that is unique to filoviruses. As a peripheral membrane protein.
