title: Kinesin-14 family proteins HSET/XCTK2 control spindle length by cross-linking and sliding microtubules.
abstract: Kinesin-14 family proteins are minus-end directed motors that cross-link microtubules and play key roles during spindle assembly. We showed previously that the Xenopus Kinesin-14 XCTK2 is regulated by Ran via the association of a bipartite NLS in the tail of XCTK2 with importin alpha/beta, which regulates its ability to cross-link microtubules during spindle formation. Here we show that mutation of the nuclear localization signal (NLS) of human Kinesin-14 HSET caused an accumulation of HSET in the cytoplasm, which resulted in strong microtubule bundling. HSET overexpression in HeLa cells resulted in longer spindles, similar to what was seen with NLS mutants of XCTK2 in extracts, suggesting that Kinesin-14 proteins play similar roles in extracts and in somatic cells. Conversely, HSET knockdown by RNAi resulted in shorter spindles but did not affect pole formation. The change in spindle length was not dependent on K-fibers, as elimination of the K-fiber by Nuf2 RNAi resulted in an increase in spindle length that was partially rescued by co-RNAi of HSET. However, these changes in spindle length did require microtubule sliding, as overexpression of an HSET mutant that had its sliding activity uncoupled from its ATPase activity resulted in cells with spindle lengths shorter than cells overexpressing wild-type HSET. Our results are consistent with a model in which Ran regulates the association of Kinesin-14s with importin alpha/beta to prevent aberrant cross-linking and bundling of microtubules by sequestering Kinesin-14s in the nucleus during interphase. Kinesin-14s act during mitosis to cross-link and slide between parallel microtubules to regulate spindle length.
authors.affiliation: Biochemistry Program, Indiana University, Bloomington, IN 47405, USA.
authors.forename: Shang
authors.initials: S
authors.lastname: Cai
authors.forename: Lesley N
authors.initials: LN
authors.lastname: Weaver
authors.forename: Stephanie C
authors.initials: SC
authors.lastname: Ems-McClung
authors.forename: Claire E
authors.initials: CE
authors.lastname: Walczak
mesh_terms: D000818:Animals; D003593:Cytoplasm / Q000378:metabolism; D049452:Green Fluorescent Proteins / Q000032:analysis; D006367:HeLa Cells; D006801:Humans; D007399:Interphase; D016547:Kinesins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D008870:Microtubules / Q000378:metabolism*; D009154:Mutation; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000502:physiology; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000032:analysis; D008941:Spindle Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D029867:Xenopus Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D014982:Xenopus laevis; D028901:alpha Karyopherins / Q000378:metabolism; D028961:beta Karyopherins / Q000378:metabolism; D020931:ran GTP-Binding Protein / Q000502:physiology
chemical_list: C104595:KIFC1 protein, Xenopus; C486566:KIFC1 protein, human; D019913:Nuclear Localization Signals; C120587:RAN protein, human; D011993:Recombinant Fusion Proteins; D029867:Xenopus Proteins; D028901:alpha Karyopherins; D028961:beta Karyopherins; D049452:Green Fluorescent Proteins; D016547:Kinesins; D020931:ran GTP-Binding Protein