title: RanGTP and CLASP1 cooperate to position the mitotic spindle.
abstract: Accurate positioning of the mitotic spindle is critical to ensure proper distribution of chromosomes during cell division. The small GTPase Ran, which regulates a variety of processes throughout the cell cycle, including interphase nucleocytoplasmic transport and mitotic spindle assembly, was recently shown to also control spindle alignment. Ran is required for the correct cortical localization of LGN and nuclear-mitotic apparatus protein (NuMA), proteins that generate pulling forces on astral microtubules (MTs) through cytoplasmic dynein. Here we use importazole, a small-molecule inhibitor of RanGTP/importin-β function, to study the role of Ran in spindle positioning in human cells. We find that importazole treatment results in defects in astral MT dynamics, as well as in mislocalization of LGN and NuMA, leading to misoriented spindles. Of interest, importazole-induced spindle-centering defects can be rescued by nocodazole treatment, which depolymerizes astral MTs, or by overexpression of CLASP1, which does not restore proper LGN and NuMA localization but stabilizes astral MT interactions with the cortex. Together our data suggest a model for mitotic spindle positioning in which RanGTP and CLASP1 cooperate to align the spindle along the long axis of the dividing cell.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720, USA.
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Bird
authors.forename: Rebecca
authors.initials: R
authors.lastname: Heald
authors.forename: Karsten
authors.initials: K
authors.lastname: Weis
mesh_terms: D021581:Active Transport, Cell Nucleus; D002455:Cell Division / Q000187:drug effects / Q000502:physiology*; D045744:Cell Line, Tumor; D056445:Cytoplasmic Dyneins; D004398:Dyneins / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000187:drug effects / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D008938:Mitosis / Q000187:drug effects / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D034521:Nuclear Matrix-Associated Proteins / Q000187:drug effects / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology; D008941:Spindle Apparatus / Q000187:drug effects / Q000378:metabolism*; D050257:Tubulin Modulators / Q000494:pharmacology; D028961:beta Karyopherins / Q000037:antagonists & inhibitors; D020931:ran GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: C497850:CLASP1 protein, human; C102754:GPSM2 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D008869:Microtubule-Associated Proteins; D034521:Nuclear Matrix-Associated Proteins; D011799:Quinazolines; C120587:RAN protein, human; D050257:Tubulin Modulators; D028961:beta Karyopherins; C568452:importazole; D056445:Cytoplasmic Dyneins; D004398:Dyneins; D020931:ran GTP-Binding Protein; D015739:Nocodazole