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Septins suppress the release of vaccinia virus from infected cells.

ABSTRACT: Septins are conserved components of the cytoskeleton that play important roles in many fundamental cellular processes including division, migration, and membrane trafficking. Septins can also inhibit bacterial infection by forming cage-like structures around pathogens such as Shigella We found that septins are recruited to vaccinia virus immediately after its fusion with the plasma membrane during viral egress. RNA interference-mediated depletion of septins increases virus release and cell-to-cell spread, as well as actin tail formation. Live cell imaging reveals that septins are displaced from the virus when it induces actin polymerization. Septin loss, however, depends on the recruitment of the SH2/SH3 adaptor Nck, but not the activity of the Arp2/3 complex. Moreover, it is the recruitment of dynamin by the third Nck SH3 domain that displaces septins from the virus in a formin-dependent fashion. Our study demonstrates that septins suppress vaccinia release by "entrapping" the virus at the plasma membrane. This antiviral effect is overcome by dynamin together with formin-mediated actin polymerization.

SUBMITTER: Pfanzelter J

PROVIDER: S-EPMC6080921 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Septins suppress the release of vaccinia virus from infected cells.

Pfanzelter Julia J Mostowy Serge S Way Michael M

The Journal of cell biology 20180619 8

Septins are conserved components of the cytoskeleton that play important roles in many fundamental cellular processes including division, migration, and membrane trafficking. Septins can also inhibit bacterial infection by forming cage-like structures around pathogens such as <i>Shigella</i> We found that septins are recruited to vaccinia virus immediately after its fusion with the plasma membrane during viral egress. RNA interference-mediated depletion of septins increases virus release and cel ...[more]

PMID: 29921601

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Project description:Cell-to-cell transmission of vaccinia virus can be mediated by enveloped virions that remain attached to the outer surface of the cell or those released into the medium. During egress, the outer membrane of the double-enveloped virus fuses with the plasma membrane leaving extracellular virus attached to the cell surface via viral envelope proteins. Here we report that F-actin nucleation by the viral protein A36 promotes the disengagement of virus attachment and release of enveloped virus. Cells infected with the A36(YdF) virus, which has mutations at two critical tyrosine residues abrogating localised actin nucleation, displayed a 10-fold reduction in virus release. We examined A36(YdF) infected cells by transmission electron microscopy and observed that during release, virus appeared trapped in small invaginations at the plasma membrane. To further characterise the mechanism by which actin nucleation drives the dissociation of enveloped virus from the cell surface, we examined recombinant viruses by super-resolution microscopy. Fluorescently-tagged A36 was visualised at sub-viral resolution to image cell-virus attachment in mutant and parental backgrounds. We confirmed that A36(YdF) extracellular virus remained closely associated to the plasma membrane in small membrane pits. Virus-induced actin nucleation reduced the extent of association, thereby promoting the untethering of virus from the cell surface. Virus release can be enhanced via a point mutation in the luminal region of B5 (P189S), another virus envelope protein. We found that the B5(P189S) mutation led to reduced contact between extracellular virus and the host membrane during release, even in the absence of virus-induced actin nucleation. Our results posit that during release virus is tightly tethered to the host cell through interactions mediated by viral envelope proteins. Untethering of virus into the surrounding extracellular space requires these interactions be relieved, either through the force of actin nucleation or by mutations in luminal proteins that weaken these interactions.

Project description:BACKGROUND: Animal-borne orthopoxviruses, like monkeypox, vaccinia and the closely related cowpox virus, are all capable of causing zoonotic infections in humans, representing a potential threat to human health. The disease caused by each virus differs in terms of symptoms and severity, but little is yet know about the reasons for these varying phenotypes. They may be explained by the unique repertoire of immune and host cell modulating factors encoded by each virus. In this study, we analysed the specific modulation of the host cell's gene expression profile by cowpox, monkeypox and vaccinia virus infection. We aimed to identify mechanisms that are either common to orthopoxvirus infection or specific to certain orthopoxvirus species, allowing a more detailed description of differences in virus-host cell interactions between individual orthopoxviruses. To this end, we analysed changes in host cell gene expression of HeLa cells in response to infection with cowpox, monkeypox and vaccinia virus, using whole-genome gene expression microarrays, and compared these to each other and to non-infected cells. RESULTS: Despite a dominating non-responsiveness of cellular transcription towards orthopoxvirus infection, we could identify several clusters of infection-modulated genes. These clusters are either commonly regulated by orthopoxvirus infection or are uniquely regulated by infection with a specific orthopoxvirus, with major differences being observed in immune response genes. Most noticeable was an induction of genes involved in leukocyte migration and activation in cowpox and monkeypox virus-infected cells, which was not observed following vaccinia virus infection. CONCLUSION: Despite their close genetic relationship, the expression profiles induced by infection with different orthopoxviruses vary significantly. It may be speculated that these differences at the cellular level contribute to the individual characteristics of cowpox, monkeypox and vaccinia virus infections in certain host species.

Project description:Three experiments, corresponding to the three figures in the article, are represented in this set. Each experiment was an ex vivo treatment time course as described in the paper. For each of the experiments, mRNA was isolated at the indicated time points, cDNA was directly prepared by reverse transcription in the presence of Cy5-labeled dUTP, and the expression profiled using Cy3-labeled cDNA prepared by reverse transcription of Stratagene Universal Human Reference RNA as a control. One experiment, corresponding to Figure 1 in the paper, is a set of infection, or mock-infection time courses, in which each of three cell types: primary human dermal fibroblasts, primary human macrophages, or HELA cells were respectively infected with Monkeypox virus, Vaccinia virus, or Ebola virus, or mock-infected. Infected cells or mock-infected cells were harvested and lysed at the indicated times after infection and mRNA isolated for analysis following the protocol described above. The second experiment, corresponding to Figure 2 in the paper, is a set of treatments of human dermal fibroblasts, each in 24-well plates with either: PBS only (mock), interferon alpha (IFN-alpha) at 0.6 pM final concentration (Sigma, St. Louis, MO), tumor necrosis factor alpha (TNF-alpha) at 0.6 pM final concentration (Sigma), PMA at 25ng/mL final concentration plus ionomycin at 1micromolar final concentration, polyinosinic-polycytidylic acid as potassium salt (poly(I-C)) at 100 microg/mL final concentration (Sigma), Escherichia coli 055:B5 lipopolysaccharide (LPS) at 1microg/mL final concentration (Sigma), or dexamethasone at 1 micromolar final concentration (Sigma). Cells were harvested and lysed at the indicated times and mRNA isolated for analysis following the protocol described above. The third experiment, corresponding to Figure 3 in the paper, is a set of infections or mock-infections of human dermal fibroblasts, or human primary macrophages, with Monkeypox virus or Vaccinia virus, respectively, followed by treatment with either ionomycin + phorbol myristic acid (PMA) or with poly(I-C). The intention of the experiment was to investigate whether prior infection altered the response of the cells to the chemical agents. Cells were harvested and lysed at the indicated times and mRNA isolated for analysis following the protocol described above. Description of sample characteristics: Time: Time after infection or Mock infection Infection: Ebola-Zaire/killed Monkeypox Virus/Mock infection/Monkaypox Virus/None/Pre infection/Vaccinia NY/Vaccinia WR Compound Based Treatment: Dexamethasone/Interferon-alpha/Ionomycin + PMA/LPS/PBS/polyinosinic-polycytidylic acid/TNF-alpha Cell Type: Primary Human Dermal Fibroblast/Primary Human Macrophage/HeLa Figure in article: Numbers group slides that are represented in the same figure of the article.

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Septins suppress the release of vaccinia virus from infected cells.

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Septins suppress the release of vaccinia virus from infected cells.

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