title: Characteristics of nucleocytoplasmic transport of H1N1 influenza A virus nuclear export protein.
abstract: The influenza A virus nuclear export protein (NEP) plays crucial roles in the nuclear export of the viral ribonucleoprotein complex through the chromosome region maintenance 1 (CRM1)-mediated cellular protein transport system. However, the detailed mechanism of NEP nucleocytoplasmic trafficking remains incompletely understood. Here, we investigated the subcellular localization of NEP from two strains of H1N1 influenza A virus and found that 2009 swine-origin H1N1 influenza A virus A/California/04/2009 (CA04) NEP displayed a distinct cellular distribution pattern, forming unique nuclear aggregates, compared to A/WSN/33 (H1N1) (WSN) NEP. Characterization of the nucleocytoplasmic transport pathways of these two NEPs showed that they both enter the nucleus by passive diffusion but are exported through the nuclear export receptor CRM1-mediated pathway with different efficiencies. The two identified nuclear export signals (NESs) on the two NEPs functioned similarly despite differences in their amino acid sequences. Using a two-hybrid assay, we confirmed that the CA04 NEP interacts less efficiently with CRM1 and that a threonine residue at position 48 is responsible for the nuclear aggregation. The present study revealed the dissimilarity in subcellular NEP transport processes between the 2009 pandemic (H1N1) influenza A virus CA04 and the laboratory-adapted H1N1 virus WSN and uncovered the mechanism responsible for this difference.
  
  
  OBJECTIVE
  Because the efficiency of the nucleocytoplasmic transport of viral components is often correlated with the viral RNA polymerase activity, propagation, and host range of influenza viruses, the present study investigated the subcellular localization of NEP from two strains of H1N1 influenza virus. We found that the NEPs of both A/California/04/2009 (H1N1) (CA04) and A/WSN/33 (H1N1) (WSN) enter the nucleus by passive diffusion but are exported with different efficiencies, which were caused by weaker binding activity between the CA04 NEP and CRM1. The results of the present study revealed characteristics of the nuclear import and export pathways of NEP and the mechanism responsible for the differences in the cellular distribution of NEP between two H1N1 strains.
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Shengyan
authors.initials: S
authors.lastname: Gao
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China University of Chinese Academy of Sciences, Beijing, China.
authors.forename: Shanshan
authors.initials: S
authors.lastname: Wang
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Cao
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Sun
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors.forename: Yuhai
authors.initials: Y
authors.lastname: Bi
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.
authors.forename: George F
authors.initials: GF
authors.lastname: Gao
authors.affiliation: CAS Key Laboratory of Pathogenic Microbiology and Immunology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China liuwj@im.ac.cn.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Liu
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000145:classification / Q000502:physiology*; D007251:Influenza, Human / Q000378:metabolism* / Q000821:virology; D028884:Karyopherins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D049790:Nuclear Export Signals / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D013347:Subcellular Fractions; D020798:Two-Hybrid System Techniques; D014779:Virus Replication / Q000502:physiology; D000097606:Exportin 1 Protein
chemical_list: D028884:Karyopherins; D049790:Nuclear Export Signals; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein
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