title: PA-X is a virulence factor in avian H9N2 influenza virus.
abstract: H9N2 influenza viruses have been circulating worldwide in multiple avian species, and regularly infect pigs and humans. Recently, a novel protein, PA-X, produced from the PA gene by ribosomal frameshifting, was demonstrated to be an antivirulence factor in pandemic 2009 H1N1, highly pathogenic avian H5N1 and 1918 H1N1 viruses. However, a similar role of PA-X in the prevalent H9N2 avian influenza viruses has not been established. In this study, we compared the virulence and cytopathogenicity of H9N2 WT virus and H9N2 PA-X-deficient virus. Loss of PA-X in H9N2 virus reduced apoptosis and had a marginal effect on progeny virus output in human pulmonary adenocarcinoma (A549) cells. Without PA-X, PA was less able to suppress co-expressed GFP in human embryonic kidney 293T cells. Furthermore, absence of PA-X in H9N2 virus attenuated viral pathogenicity in mice, which showed no mortality, reduced progeny virus production, mild-to-normal lung histopathology, and dampened proinflammatory cytokine and chemokine response. Therefore, unlike previously reported H1N1 and H5N1 viruses, we show that PA-X protein in H9N2 virus is a pro-virulence factor in facilitating viral pathogenicity and that the pro- or antivirulence role of PA-X in influenza viruses is virus strain-dependent.
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Huijie
authors: H
authors: Gao
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Guanlong
authors: G
authors: Xu
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Yipeng
authors: Y
authors: Sun
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Lu
authors: L
authors: Qi
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Jinliang
authors: J
authors: Wang
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Weili
authors: W
authors: Kong
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Honglei
authors: H
authors: Sun
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Juan
authors: J
authors: Pu
authors: School of Veterinary Medicine and Science, University of Nottingham, Sutton Bonington Campus, Sutton Bonington, UK.
authors: Kin-Chow
authors: KC
authors: Chang
authors: Key Laboratory of Animal Epidemiology and Zoonosis, Ministry of Agriculture, College of Veterinary Medicine and State Key Laboratory of Agrobiotechnology, China Agricultural University, Beijing, PR China.
authors: Jinhua
authors: J
authors: Liu
mesh_terms: D000818:Animals; D002460:Cell Line; D002645:Chickens; D016207:Cytokines / Q000235:genetics / Q000276:immunology; D005260:Female; D006801:Humans; D053127:Influenza A Virus, H9N2 Subtype / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D005585:Influenza in Birds / Q000235:genetics / Q000276:immunology / Q000821:virology*; D007251:Influenza, Human / Q000235:genetics / Q000276:immunology / Q000821:virology*; D008168:Lung / Q000276:immunology / Q000821:virology; D051379:Mice; D008807:Mice, Inbred BALB C; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*; D037521:Virulence Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D016207:Cytokines; C573926:PA-X protein, influenza A virus; D012097:Repressor Proteins; D017361:Viral Nonstructural Proteins; D037521:Virulence Factors