title: Extracellular signal-dependent nuclear import of Stat1 is mediated by nuclear pore-targeting complex formation with NPI-1, but not Rch1.
abstract: In response to interferon-gamma (IFN-gamma), Stat1 is tyrosine phosphorylated and translocates to the nucleus where it activates transcription. In this study, we identified factors which mediate the nuclear import of Stat1. Tyrosine-phosphorylated Stat1 associated with the beta subunit (a 97 kDa component) of the nuclear pore-targeting complex via the NPI-1 family, but not the Rch1 family, of alpha subunit (a 58 kDa component) as a result of IFN-gamma stimulation. Antibodies against NPI-1 or beta subunit consistently inhibited the IFN-gamma-dependent nuclear import of Stat1 in living cells, although antibodies reactive to Rch1 had no effect. Solution binding assays with deletion mutants of NPI-1 showed that the Stat1-binding domain of NPI-1 was located in the carboxy-terminal region, which is clearly distinct from the SV40 large T antigen nuclear localization signal (NLS)-binding region. These results indicate that the extracellular signal-dependent nuclear transport of Stat1 is mediated by NPI-1, but not Rch1, in conjunction with beta subunit, and that these factors participate in, not only constitutive, but also the conditional nuclear import of proteins.
authors.affiliation: Department of Anatomy and Cell Biology, Biomedical Research Center, Osaka University Medical School, 2-2 Yamada-oka, Suita, Osaka 565, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sekimoto
authors.forename: N
authors.initials: N
authors.lastname: Imamoto
authors.forename: K
authors.initials: K
authors.lastname: Nakajima
authors.forename: T
authors.initials: T
authors.lastname: Hirano
authors.forename: Y
authors.initials: Y
authors.lastname: Yoneda
mesh_terms: D001665:Binding Sites; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002451:Cell Compartmentation; D016207:Cytokines / Q000494:pharmacology; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D007371:Interferon-gamma / Q000494:pharmacology; D009685:Nuclear Envelope / Q000378:metabolism*; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011485:Protein Binding; D050794:STAT1 Transcription Factor; D015398:Signal Transduction; D015534:Trans-Activators / Q000378:metabolism*; D028901:alpha Karyopherins
chemical_list: D002352:Carrier Proteins; D016207:Cytokines; D004268:DNA-Binding Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D050794:STAT1 Transcription Factor; D015534:Trans-Activators; D028901:alpha Karyopherins; C087978:karyopherin alpha 2; D019000:Phosphotyrosine; D007371:Interferon-gamma