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

J Cell Biol. 2008 Feb 11;180(3):493-506. doi: 10.1083/jcb.200708003.

Abstract

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-alpha/beta 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-alpha/beta 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-beta-mediated chromosome loading of hKid. Our results indicate that the association of importin-beta and -alpha 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Active Transport, Cell Nucleus / genetics
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism
  • Chromosome Pairing / genetics*
  • Chromosomes / genetics
  • Chromosomes / metabolism*
  • Cytoplasm / genetics
  • Cytoplasm / metabolism
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Guanosine Triphosphate / metabolism
  • HeLa Cells
  • Humans
  • Kinesins / genetics
  • Kinesins / metabolism*
  • Mitosis / genetics*
  • Nuclear Envelope / genetics
  • Nuclear Envelope / metabolism
  • Nuclear Localization Signals / genetics
  • Phosphorylation
  • Protein Transport / genetics
  • Spindle Apparatus / genetics
  • alpha Karyopherins / genetics
  • beta Karyopherins / genetics
  • beta Karyopherins / physiology*
  • ran GTP-Binding Protein / genetics*

Substances

  • DNA-Binding Proteins
  • KIF22 protein, human
  • Nuclear Localization Signals
  • alpha Karyopherins
  • beta Karyopherins
  • karyopherin alpha 2
  • Guanosine Triphosphate
  • Kinesins
  • ran GTP-Binding Protein