title: Mutations in the Schmallenberg Virus Gc Glycoprotein Facilitate Cellular Protein Synthesis Shutoff and Restore Pathogenicity of NSs Deletion Mutants in Mice.
abstract: Serial passage of viruses in cell culture has been traditionally used to attenuate virulence and identify determinants of viral pathogenesis. In a previous study, we found that a strain of Schmallenberg virus (SBV) serially passaged in tissue culture (termed SBVp32) unexpectedly displayed increased pathogenicity in suckling mice compared to wild-type SBV. In this study, we mapped the determinants of SBVp32 virulence to the viral genome M segment. SBVp32 virulence is associated with the capacity of this virus to reach high titers in the brains of experimentally infected suckling mice. We also found that the Gc glycoprotein, encoded by the M segment of SBVp32, facilitates host cell protein shutoff in vitro Interestingly, while the M segment of SBVp32 is a virulence factor, we found that the S segment of the same virus confers by itself an attenuated phenotype to wild-type SBV, as it has lost the ability to block the innate immune system of the host. Single mutations present in the Gc glycoprotein of SBVp32 are sufficient to compensate for both the attenuated phenotype of the SBVp32 S segment and the attenuated phenotype of NSs deletion mutants. Our data also indicate that the SBVp32 M segment does not act as an interferon (IFN) antagonist. Therefore, SBV mutants can retain pathogenicity even when they are unable to fully control the production of IFN by infected cells. Overall, this study suggests that the viral glycoprotein of orthobunyaviruses can compensate, at least in part, for the function of NSs. In addition, we also provide evidence that the induction of total cellular protein shutoff by SBV is determined by multiple viral proteins, while the ability to control the production of IFN maps to the NSs protein.
  
  
  
  The identification of viral determinants of pathogenesis is key to the development of prophylactic and intervention measures. In this study, we found that the bunyavirus Gc glycoprotein is a virulence factor. Importantly, we show that mutations in the Gc glycoprotein can restore the pathogenicity of attenuated mutants resulting from deletions or mutations in the nonstructural protein NSs. Our findings highlight the fact that careful consideration should be taken when designing live attenuated vaccines based on deletions of nonstructural proteins since single mutations in the viral glycoproteins appear to revert attenuated mutants to virulent phenotypes.
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland Mariana.varela@glasgow.ac.uk Massimo.palmarini@glasgow.ac.uk.
authors.forename: Mariana
authors.initials: M
authors.lastname: Varela
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland.
authors.forename: Rute Maria
authors.initials: RM
authors.lastname: Pinto
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland.|Istituto Zooprofilattico Sperimentale dell'Abruzzo e Molise G. Caporale, Teramo, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Caporale
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland.
authors.forename: Ilaria M
authors.initials: IM
authors.lastname: Piras
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland.
authors.forename: Aislynn
authors.initials: A
authors.lastname: Taggart
authors.affiliation: Department of Pathology and Center of Systems Neuroscience, University of Veterinary Medicine, Hannover, Germany.
authors.forename: Frauke
authors.initials: F
authors.lastname: Seehusen
authors.affiliation: Department of Pathology and Center of Systems Neuroscience, University of Veterinary Medicine, Hannover, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Hahn
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland.
authors.forename: Anna
authors.initials: A
authors.lastname: Janowicz
authors.affiliation: Virology Research Center, Ribeirão Preto School of Medicine, University of São Paulo, Ribeirao Preto, Brazil.
authors.forename: William Marciel
authors.initials: WM
authors.lastname: de Souza
authors.affiliation: Department of Pathology and Center of Systems Neuroscience, University of Veterinary Medicine, Hannover, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Baumgärtner
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Shi
authors.affiliation: MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland Mariana.varela@glasgow.ac.uk Massimo.palmarini@glasgow.ac.uk.
authors.forename: Massimo
authors.initials: M
authors.lastname: Palmarini
mesh_terms: D000818:Animals; D001921:Brain / Q000821:virology; D002044:Bunyaviridae Infections / Q000821:virology*; D002460:Cell Line; D016679:Genome, Viral; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D054884:Host-Pathogen Interactions; D007372:Interferons / Q000037:antagonists & inhibitors / Q000235:genetics; D051379:Mice; D009154:Mutation; D016851:Orthobunyavirus / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity*; D014176:Protein Biosynthesis; D017384:Sequence Deletion; D019562:Viral Load; D017361:Viral Nonstructural Proteins / Q000235:genetics*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D014771:Virion; D037521:Virulence Factors
chemical_list: D006023:Glycoproteins; D017361:Viral Nonstructural Proteins; D014764:Viral Proteins; D037521:Virulence Factors; D007372:Interferons