title: Two isoforms of Npap60 (Nup50) differentially regulate nuclear protein import.
abstract: Npap60 (Nup50) is a nucleoporin that binds directly to importin alpha. In humans, there are two Npap60 isoforms: the long (Npap60L) and short (Npap60S) forms. In this study, we provide both in vitro and in vivo evidence that Npap60L and Npap60S function differently in nuclear protein import. In vitro binding assays revealed that Npap60S stabilizes the binding of importin alpha to classical NLS-cargo, whereas Npap60L promotes the release of NLS-cargo from importin alpha. In vivo time-lapse experiments showed that when the Npap60 protein level is controlled, allowing CAS to efficiently promote the dissociation of the Npap60/importin alpha complex, Npap60S and Npap60L suppress and accelerate the nuclear import of NLS-cargo, respectively. These results demonstrate that Npap60L and Npap60S have opposing functions and suggest that Npap60L and Npap60S levels must be carefully controlled for efficient nuclear import of classical NLS-cargo in humans. This study provides novel evidence that nucleoporin expression levels regulate nuclear import efficiency.
authors.affiliation: Department of Frontier Biosciences, Graduate School of Frontier Biosciences, and Department of Biochemistry, Graduate School of Medicine, Osaka University, Suita, Osaka 565-0871, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Munehiro
authors.initials: M
authors.lastname: Asally
authors.forename: Masahiro
authors.initials: M
authors.lastname: Oka
authors.forename: Yoshinari
authors.initials: Y
authors.lastname: Yasuda
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yoneda
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006801:Humans; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000235:genetics / Q000378:metabolism; D028861:Nuclear Pore Complex Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D028901:alpha Karyopherins / Q000235:genetics / Q000378:metabolism
chemical_list: C121702:NUP50 protein, human; D019913:Nuclear Localization Signals; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; D020033:Protein Isoforms; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D028901:alpha Karyopherins