title: The vaccinia virus O1 protein is required for sustained activation of extracellular signal-regulated kinase 1/2 and promotes viral virulence.
abstract: Sustained activation of the Raf/MEK/extracellular signal-regulated kinase (ERK) pathway in infected cells has been shown to be crucial for full replication efficiency of orthopoxviruses in cell culture. In infected cells, this pathway is mainly activated by the vaccinia virus growth factor (VGF), an epidermal growth factor (EGF)-like protein. We show here that chorioallantois vaccinia virus Ankara (CVA), but not modified vaccinia virus Ankara (MVA), induced sustained activation of extracellular signal-regulated kinase 1/2 (ERK1/2) in infected human 293 cells, although both viruses direct secretion of functional VGF. A CVA mutant lacking the O1L gene (CVA-ΔO1L) demonstrated that the O1 protein was required for sustained upregulation of the ERK1/2 pathway in 293 cells as well as in other mammalian cell lines. The highly conserved orthopoxvirus O1L gene encodes a predicted 78-kDa protein with a hitherto-unknown function. CVA-ΔO1L showed reduced plaque size and an attenuated cytopathic effect (CPE) in infected cell cultures and reduced virulence and spread from lungs to ovaries in intranasally infected BALB/c mice. Reinsertion of an intact O1L gene into MVA, which in its original form harbors a fragmented O1L open reading frame (ORF), restored ERK1/2 activation in 293 cells but did not increase replication and spread of MVA in human or other mammalian cell lines. Thus, the O1 protein was crucial for sustained ERK1/2 activation in CVA- and MVA-infected human cells, complementing the autocrine function of VGF, and enhanced virulence in vivo.
authors.affiliation: Department of Research, Bavarian Nordic GmbH, Martinsried, Germany.
authors.forename: Marc
authors.initials: M
authors.lastname: Schweneker
authors.forename: Susanne
authors.initials: S
authors.lastname: Lukassen
authors.forename: Michaela
authors.initials: M
authors.lastname: Späth
authors.forename: Michael
authors.initials: M
authors.lastname: Wolferstätter
authors.forename: Eveline
authors.initials: E
authors.lastname: Babel
authors.forename: Kay
authors.initials: K
authors.lastname: Brinkmann
authors.forename: Ursula
authors.initials: U
authors.lastname: Wielert
authors.forename: Paul
authors.initials: P
authors.lastname: Chaplin
authors.forename: Mark
authors.initials: M
authors.lastname: Suter
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hausmann
mesh_terms: D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation; D005260:Female; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D008807:Mice, Inbred BALB C; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000235:genetics / Q000378:metabolism*; D014615:Vaccinia / Q000201:enzymology* / Q000378:metabolism / Q000821:virology; D014616:Vaccinia virus / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D014774:Virulence
chemical_list: D014764:Viral Proteins; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3