Ran modulates spindle assembly by regulating a subset of TPX2 and Kid activities including Aurora A activation.
Ran, a GTPase in the Ras superfamily, is proposed to be a spatial regulator of microtubule spindle assembly by maintaining key spindle assembly factors in an active state close to chromatin. RanGTP is hypothesized to maintain the spindle assembly factors in the active state by binding to importin beta, part of the nuclear transport receptor complex, thereby preventing the inhibitory binding of the nuclear transport receptors to spindle assembly factors. To directly test this hypothesis, two putative downstream targets of the Ran spindle assembly pathway, TPX2, a protein required for correct spindle assembly and Kid, a chromokinesin involved in chromosome arm orientation on the spindle, were analyzed to determine if their direct binding to nuclear transport receptors inhibited their function. In the amino-terminal domain of TPX2 we identified nuclear targeting information, microtubule-binding and Aurora A binding activities. Nuclear transport receptor binding to TPX2 inhibited Aurora A binding activity but not the microtubule-binding activity of TPX2. Inhibition of the interaction between TPX2 and Aurora A prevented Aurora A activation and recruitment to microtubules. In addition we identified nuclear targeting information in both the amino-terminal microtubule-binding domain and the carboxy-terminal DNA binding domain of Kid. However, the binding of nuclear transport receptors to Kid only inhibited the microtubule-binding activity of Kid. Therefore, by regulating a subset of TPX2 and Kid activities, Ran modulates at least two processes involved in spindle assembly.
Trieselmann
Nadia
N
Department of Medical Genetics and Microbiology, University of Toronto, 1 King's College Circle, Toronto, Ontario, Canada, M5S 1A8.
Armstrong
Sheri
S
Rauw
Jennifer
J
Wilde
Andrew
A
D021581:Active Transport, Cell Nucleus; D064127:Aurora Kinases; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D006367:HeLa Cells; D006801:Humans; D016547:Kinesins / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D009363:Neoplasm Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D011485:Protein Binding; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D008941:Spindle Apparatus / Q000378:metabolism*; D029867:Xenopus Proteins; D020931:ran GTP-Binding Protein / Q000378:metabolism*
D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C098764:KIF22 protein, human; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; C122167:TPX2 protein, human; D029867:Xenopus Proteins; D011494:Protein Kinases; C112134:AURKA protein, Xenopus; D064127:Aurora Kinases; D017346:Protein Serine-Threonine Kinases; D016547:Kinesins; D020931:ran GTP-Binding Protein