Mutation of influenza A virus PA-X decreases pathogenicity in chicken embryos and can increase the yield of reassortant candidate vaccine viruses

Hussain, S., Turnbull, M. L. , Wise, H. M., Jagger, B. W., Beard, P. M., Kovacikova, K., Taubenberger, J. K., Vervelde, L., Engelhardt, O. G. and Digard, P. (2019) Mutation of influenza A virus PA-X decreases pathogenicity in chicken embryos and can increase the yield of reassortant candidate vaccine viruses. Journal of Virology, 93(2), e01551-18. (doi: 10.1128/JVI.01551-18) (PMID:30381488) (PMCID:PMC6321911)

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Abstract

The PA-X protein of influenza A virus has roles in host cell shutoff and viral pathogenesis. While most strains are predicted to encode PA-X, strain-dependent variations in activity have been noted. We found that PA-X protein from the A/PR/8/34 (PR8) strain had significantly lower repressive activity against cellular gene expression than PA-X proteins from the avian strains A/turkey/England/50-92/91 (H5N1) (T/E) and A/chicken/Rostock/34 (H7N1). Loss of normal PA-X expression, either by mutation of the frameshift site or by truncating the X open reading frame (ORF), had little effect on the infectious virus titer of PR8 or PR8 7:1 reassortants with T/E segment 3 grown in embryonated hens' eggs. However, in both virus backgrounds, mutation of PA-X led to decreased embryo mortality and lower overall pathology, effects that were more pronounced in the PR8 strain than in the T/E reassortant, despite the low shutoff activity of the PR8 PA-X. Purified PA-X mutant virus particles displayed an increased ratio of hemagglutinin (HA) to nucleoprotein (NP) and M1 compared to values for their wild-type (WT) counterparts, suggesting altered virion composition. When the PA-X gene was mutated in the background of poorly growing PR8 6:2 vaccine reassortant analogues containing the HA and neuraminidase (NA) segments from H1N1 2009 pandemic viruses or from an avian H7N3 strain, HA yield increased up to 2-fold. This suggests that the PR8 PA-X protein may harbor a function unrelated to host cell shutoff and that disruption of the PA-X gene has the potential to improve the HA yield of vaccine viruses. Influenza A virus is a widespread pathogen that affects both humans and a variety of animal species, causing regular epidemics and sporadic pandemics, with major public health and economic consequences. A better understanding of virus biology is therefore important. The primary control measure is vaccination, which for humans mostly relies on antigens produced in eggs from PR8-based viruses bearing the glycoprotein genes of interest. However, not all reassortants replicate well enough to supply sufficient virus antigen for demand. The significance of our research lies in identifying that mutation of the PA-X gene in the PR8 strain of virus can improve antigen yield, potentially by decreasing the pathogenicity of the virus in embryonated eggs.

Item Type:Articles
Additional Information:This work was funded in part with Federal funds from the Office of the Assistant Secretary for Preparedness and Response, Biomedical Advanced Research and Development Authority, under contract number HHSO100201300005C (to O.G.E. and P.D.), by a grant from the UK Department of Health’s Policy Research Program (NIBSC Regulatory Science Research Unit), grant number 044/0069 (to O.G.E.), and the Intramural Research Program of the National Institute of Allergy and Infectious Diseases (NIAID) (to J.K.T.), as well as Institute Strategic Program Grants (BB/J01446X/1 and BB/P013740/1) from the Biotechnology and Biological Sciences Research Council (BBSRC) to P.D., P.M.B., L.V., and H.M.W. B.W.J., P.D., and J.K.T. are also grateful for the support of the NIH-Oxford-Cambridge Research Scholars program.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Turnbull, Dr Matthew
Authors: Hussain, S., Turnbull, M. L., Wise, H. M., Jagger, B. W., Beard, P. M., Kovacikova, K., Taubenberger, J. K., Vervelde, L., Engelhardt, O. G., and Digard, P.
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:04 January 2019
Copyright Holders:Copyright © 2019 Hussain et al.
First Published:First published in Journal of Virology 93(2): e01551-18
Publisher Policy:Reproduced under a Creative Commons License

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