Ebola Zaire virus blocks type I interferon production by exploiting the host SUMO modification machinery.
Ebola Zaire virus is highly pathogenic for humans, with case fatality rates approaching 90% in large outbreaks in Africa. The virus replicates in macrophages and dendritic cells (DCs), suppressing production of type I interferons (IFNs) while inducing the release of large quantities of proinflammatory cytokines. Although the viral VP35 protein has been shown to inhibit IFN responses, the mechanism by which it blocks IFN production has not been fully elucidated. We expressed VP35 from a mouse-adapted variant of Ebola Zaire virus in murine DCs by retroviral gene transfer, and tested for IFN transcription upon Newcastle Disease virus (NDV) infection and toll-like receptor signaling. We found that VP35 inhibited IFN transcription in DCs following these stimuli by disabling the activity of IRF7, a transcription factor required for IFN transcription. By yeast two-hybrid screens and coimmunoprecipitation assays, we found that VP35 interacted with IRF7, Ubc9 and PIAS1. The latter two are the host SUMO E2 enzyme and E3 ligase, respectively. VP35, while not itself a SUMO ligase, increased PIAS1-mediated SUMOylation of IRF7, and repressed Ifn transcription. In contrast, VP35 did not interfere with the activation of NF-kappaB, which is required for induction of many proinflammatory cytokines. Our findings indicate that Ebola Zaire virus exploits the cellular SUMOylation machinery for its advantage and help to explain how the virus overcomes host innate defenses, causing rapidly overwhelming infection to produce a syndrome resembling fulminant septic shock.
Chang
Tsung-Hsien
TH
Program in Genomics of Differentiation, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, United States of America.
Kubota
Toru
T
Matsuoka
Mayumi
M
Jones
Steven
S
Bradfute
Steven B
SB
Bray
Mike
M
Ozato
Keiko
K
D000818:Animals; D003713:Dendritic Cells / Q000378:metabolism / Q000821:virology; D029043:Ebolavirus / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D050839:Interferon Regulatory Factor-7 / Q000378:metabolism; D016898:Interferon-alpha / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D016899:Interferon-beta / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D009521:Newcastle Disease / Q000235:genetics / Q000378:metabolism; D009522:Newcastle disease virus / Q000235:genetics; D011401:Promoter Regions, Genetic; D050828:Protein Inhibitors of Activated STAT / Q000378:metabolism; D015398:Signal Transduction; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics / Q000378:metabolism
D050839:Interferon Regulatory Factor-7; D016898:Interferon-alpha; C494235:Irf7 protein, mouse; D016328:NF-kappa B; C494211:Pias1 protein, mouse; D050828:Protein Inhibitors of Activated STAT; D025841:Small Ubiquitin-Related Modifier Proteins; C080980:VP35 protein, filovirus; D054334:Viral Regulatory and Accessory Proteins; D016899:Interferon-beta