title: The 70-kD heat shock cognate protein (hsc70) facilitates the nuclear export of the import receptors.
abstract: Transport receptors of the importin beta family continuously shuttle between the nucleus and cytoplasm. We previously reported that the nuclear export of importin beta involves energy-requiring step(s) in living cells. Here, we show that the in vitro nuclear export of importin beta also requires energy input. Cytosol, depleted of ATP-binding proteins, did not support the sufficient nuclear export of importin beta. Further purification revealed that the active component in the absorbed fraction was a 70-kD heat shock cognate protein (hsc70). The addition of recombinant hsc70, but not an ATPase-deficient hsc70 mutant, to the depleted cytosol restored the export activity. In living cells, depletion of hsc70 caused the significant nuclear accumulation of importin beta. These effects of hsc70 were observed in the nuclear export of importin beta, but also for other import receptors, transportin and importin alpha. These results suggest that hsc70 broadly modulates nucleocytoplasmic transport systems by regulating the nuclear export of receptor proteins.
authors.affiliation: Cellular Dynamics Laboratory, Discovery Research Institute, RIKEN, Wako, Saitama 351-0198, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Kose
authors.forename: Maiko
authors.initials: M
authors.lastname: Furuta
authors.forename: Makiko
authors.initials: M
authors.lastname: Koike
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yoneda
authors.forename: Naoko
authors.initials: N
authors.lastname: Imamoto
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000251:Adenosine Triphosphatases / Q000378:metabolism; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000737:chemistry; D003600:Cytosol / Q000737:chemistry / Q000201:enzymology; D050883:HSC70 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins / Q000502:physiology; D009687:Nuclear Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000032:analysis / Q000235:genetics; D028901:alpha Karyopherins / Q000502:physiology; D028961:beta Karyopherins / Q000502:physiology
chemical_list: D050883:HSC70 Heat-Shock Proteins; D028884:Karyopherins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D028901:alpha Karyopherins; D028961:beta Karyopherins; D000251:Adenosine Triphosphatases