Mutations in the Schmallenberg virus Gc glycoprotein facilitate cellular protein synthesis shutoff and restore pathogenicity of NSs deletion mutants in mice

Varela, M. et al. (2016) Mutations in the Schmallenberg virus Gc glycoprotein facilitate cellular protein synthesis shutoff and restore pathogenicity of NSs deletion mutants in mice. Journal of Virology, 90(11), pp. 5440-5450. (doi: 10.1128/JVI.00424-16) (PMID:26984728) (PMCID:PMC4934738)

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 higher 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 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 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 IFN antagonist. Therefore SBV mutants can retain pathogenicity even when they are unable to fully control the production of IFN by the infected cells. Overall, this study suggests that the viral glycoprotein of orthobunyaviruses can compensate, at least in part, 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. Importance The identification of viral determinants of pathogenesis is key to the development of prophylactic and interventions 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 pathogenicity of attenuated mutants resulting from deletions or mutations in the non-structural protein NSs. Our findings highlight the fact that careful consideration should be taken when designing live attenuated vaccines based on deletions of non-structural proteins since single mutations in the viral glycoproteins appear to revert attenuated mutants to virulent phenotypes.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Janowicz, Dr Anna and Palmarini, Professor Massimo and Shi, Dr Xiaohong and Pinto, Dr Rute and Caporale, Dr Marco and Piras, Dr Ilaria and Taggart, Ms Aislynn and Varela, Dr Mariana
• Authors: Varela, M., Pinto, R. M., Caporale, M., Piras, I. M., Taggart, A., Seehusen, F., Hahn, K., Janowicz, A., de Souza, W. M., Baumgärtner, W., Shi, X., and Palmarini, M.
• College/School: College of Medical Veterinary and Life Sciences > School of Infection & Immunity; College of Medical Veterinary and Life Sciences > School of Infection & Immunity > Centre for Virus Research
• Journal Name: Journal of Virology
• Publisher: American Society for Microbiology
• ISSN: 0022-538X
• ISSN (Online): 1098-5514
• Published Online: 16 March 2016
• Copyright Holders: Copyright © 2016 Varela et al.
• First Published: First published in Journal of Virology 90(11):5440-5450
• Publisher Policy: Reproduced under a Creative Commons License