title: Sumoylation of influenza A virus nucleoprotein is essential for intracellular trafficking and virus growth.
abstract: Viruses take advantage of host posttranslational modifications for their own benefit. It was recently reported that influenza A virus proteins interact extensively with the host sumoylation system. Thereby, several viral proteins, including NS1 and M1, are sumoylated to facilitate viral replication. However, to what extent sumoylation is exploited by influenza A virus is not fully understood. In this study, we found that influenza A virus nucleoprotein (NP) is a bona fide target of sumoylation in both NP-transfected cells and virus-infected cells. We further found that NP is sumoylated at the two most N-terminal residues, lysines 4 and 7, and that sumoylation at lysine 7 of NP is highly conserved across different influenza A virus subtypes and strains, including the recently emerged human H7N9 virus. While NP stability and polymerase activity are little affected by sumoylation, the NP sumoylation-defective WSN-NPK4,7R virus exhibited early cytoplasmic localization of NP. The growth of the WSN-NPK4,7R virus was highly attenuated compared to that of the wild-type WSN virus, and the lysine residue at position 7 is indispensable for the virus's survival, as illustrated by the rapid emergence of revertant viruses. Thus, sumoylation of influenza A virus NP is essential for intracellular trafficking of NP and for virus growth, illustrating sumoylation as a crucial strategy extensively exploited by influenza A virus for survival in its host.
  
  
  OBJECTIVE
  Host posttranslational modifications are heavily targeted by viruses for their own benefit. We and others previously reported that influenza A virus interacts extensively with the host sumoylation system. However, the functional outcomes of viral sumoylation are not fully understood. Here we found that influenza A virus nucleoprotein (NP), an essential component for virus replication, is a new target of SUMO. This is the first study to find that NP from different influenza A viruses, including recently emerged H7N9, is sumoylated at conserved lysine 7. Our data further illustrated that sumoylation of influenza A virus NP is essential for intracellular trafficking of NP and virus growth, indicating that influenza A virus relies deeply on sumoylation to survive in host cells. Strategies to downregulate viral sumoylation could thus be a potential antiviral treatment.
authors.affiliation: Molecular Virology Unit, Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Qinglin
authors.initials: Q
authors.lastname: Han
authors.affiliation: Molecular Virology Unit, Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Chong
authors.initials: C
authors.lastname: Chang
authors.affiliation: Molecular Virology Unit, Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Li
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Biochemistry, University of Zürich, Zürich, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Klenk
authors.affiliation: School of Medicine, Shanghai Jiao-Tong University, Shanghai, China.
authors.forename: Jinke
authors.initials: J
authors.lastname: Cheng
authors.affiliation: National Institute of Diagnostics and Vaccine Development in Infectious Disease, State Key Laboratory of Cellular Stress Biology, School of Life Science, Xiamen University, Xiamen, China.
authors.forename: Yixin
authors.initials: Y
authors.lastname: Chen
authors.affiliation: National Institute of Diagnostics and Vaccine Development in Infectious Disease, State Key Laboratory of Cellular Stress Biology, School of Life Science, Xiamen University, Xiamen, China.
authors.forename: Ningshao
authors.initials: N
authors.lastname: Xia
authors.affiliation: Chinese Center for Disease Control and Prevention, Xuanwu District, Beijing, China.
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
authors.affiliation: Shanghai Institute of Biological Products, Shanghai, China.
authors.forename: Ze
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany.
authors.forename: Gülsah
authors.initials: G
authors.lastname: Gabriel
authors.affiliation: Molecular Virology Unit, Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China State Key Laboratory of Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China kxu@sibs.ac.cn bsun@sibs.ac.cn.
authors.forename: Bing
authors.initials: B
authors.lastname: Sun
authors.affiliation: Molecular Virology Unit, Key Laboratory of Molecular Virology & Immunology, Institut Pasteur of Shanghai, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China kxu@sibs.ac.cn bsun@sibs.ac.cn.
authors.forename: Ke
authors.initials: K
authors.lastname: Xu
mesh_terms: D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D004285:Dogs; D057809:HEK293 Cells; D054884:Host-Pathogen Interactions / Q000235:genetics; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000235:genetics / Q000378:metabolism*; D009980:Influenza A virus / Q000235:genetics / Q000378:metabolism*; D008239:Lysine / Q000235:genetics / Q000378:metabolism; D061985:Madin Darby Canine Kidney Cells; D019590:Nucleocapsid Proteins; D021381:Protein Transport / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D025841:Small Ubiquitin-Related Modifier Proteins / Q000235:genetics / Q000378:metabolism; D058207:Sumoylation / Q000235:genetics*; D014758:Viral Core Proteins / Q000235:genetics / Q000378:metabolism*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication / Q000235:genetics
chemical_list: C048842:NP protein, Influenza A virus; D019590:Nucleocapsid Proteins; D016601:RNA-Binding Proteins; D025841:Small Ubiquitin-Related Modifier Proteins; D014758:Viral Core Proteins; D014764:Viral Proteins; D008239:Lysine