Importin-β and the small guanosine triphosphatase Ran mediate chromosome loading of the human chromokinesin Kid

• Published in: The Journal of cell biology Vol. 180; no. 3; pp. 493 - 506
• Main Authors: Tahara, Kiyoshi, Takagi, Masatoshi, Ohsugi, Miho, Sone, Takefumi, Nishiumi, Fumiko, Maeshima, Kazuhiro, Horiuchi, Yasuomi, Tokai-Nishizumi, Noriko, Imamoto, Fumio, Yamamoto, Tadashi, Kose, Shingo, Imamoto, Naoko
• Format: Journal Article
• Language: English
• Published: United States The Rockefeller University Press 11.02.2008; Rockefeller University Press
• Subjects: Active Transport, Cell Nucleus - genetics; alpha Karyopherins - genetics; beta Karyopherins - genetics; beta Karyopherins - physiology; Cell lines; Cell Nucleus - genetics; Cell Nucleus - metabolism; Chromosome Pairing - genetics; Chromosomes; Chromosomes - genetics; Chromosomes - metabolism; Cytoplasm - genetics; Cytoplasm - metabolism; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Energy sources; Freight; Guanosine Triphosphate - metabolism; HeLa Cells; Humans; Karyopherins; Kinesin - genetics; Kinesin - metabolism; Microtubules; Mitosis; Mitosis - genetics; Mitotic spindle apparatus; Nuclear Envelope - genetics; Nuclear Envelope - metabolism; Nuclear Localization Signals - genetics; Phosphorylation; Protein Transport - genetics; ran GTP-Binding Protein - genetics; Somatic cells; Spindle Apparatus - genetics
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.200708003

Nucleocytoplasmic transport factors mediate various cellular processes, including nuclear transport, spindle assembly, and nuclear envelope/pore formation. In this paper, we identify the chromokinesin human kinesin-like DNA binding protein (hKid) as an import cargo of the importin-α/β transport pathway and determine its nuclear localization signals (NLSs). Upon the loss of its functional NLSs, hKid exhibited reduced interactions with the mitotic chromosomes of living cells. In digitonin-permeabilized mitotic cells, hKid was bound only to the spindle and not to the chromosomes themselves. Surprisingly, hKid bound to importin-α/β was efficiently targeted to mitotic chromosomes. The addition of Ran-guanosine diphosphate and an energy source, which generates Ran-guanosine triphosphate (GTP) locally at mitotic chromosomes, enhanced the importin-β-mediated chromosome loading of hKid. Our results indicate that the association of importin-β and -α with hKid triggers the initial targeting of hKid to mitotic chromosomes and that local Ran-GTP-mediated cargo release promotes the accumulation of hKid on chromosomes. Thus, this study demonstrates a novel nucleocytoplasmic transport factor-mediated mechanism for targeting proteins to mitotic chromosomes.