title: A novel mechanism for activation of the protein kinase Aurora A.
abstract: Segregation of chromosomes during mitosis requires interplay between several classes of protein on the spindle, including protein kinases, protein phosphatases, and microtubule binding motor proteins [1-4]. Aurora A is an oncogenic cell cycle-regulated protein kinase that is subject to phosphorylation-dependent activation [5-11]. Aurora A localization to the mitotic spindle depends on the motor binding protein TPX2 (Targeting Protein for Xenopus kinesin-like protein 2), but the protein(s) involved in Aurora A activation are unknown [11-13]. Here, we purify an activator of Aurora A from Xenopus eggs and identify it as TPX2. Remarkably, Aurora A that has been fully deactivated by Protein Phosphatase 2A (PP2A) becomes phosphorylated and reactivated by recombinant TPX2 in an ATP-dependent manner. Increased phosphorylation and activation of Aurora A requires its own kinase activity, suggesting that TPX2 stimulates autophosphorylation and autoactivation of the enzyme. Consistently, wild-type Aurora A, but not a kinase inactive mutant, becomes autophosphorylated on the regulatory T loop residue (Thr 295) after TPX2 treatment. Active Aurora A from bacteria is further activated at least 7-fold by recombinant TPX2, and TPX2 also impairs the ability of protein phosphatases to inactivate Aurora A in vitro. This concerted mechanism of stimulation of activation and inhibition of deactivation implies that TPX2 is the likely regulator of Aurora A activity at the mitotic spindle and may explain why loss of TPX2 in model systems perturbs spindle assembly [14-16]. Our finding that a known binding protein, and not a conventional protein kinase, is the relevant activator for Aurora A suggests a biochemical model in which the dynamic localization of TPX2 on mitotic structures directly modulates the activity of Aurora A for spindle assembly.
authors.affiliation: Howard Hughes Medical Institute and Department of Pharmacology, University of Colorado School of Medicine, Denver, CO 80262, USA.
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Eyers
authors.forename: Eleanor
authors.initials: E
authors.lastname: Erikson
authors.forename: Lin G
authors.initials: LG
authors.lastname: Chen
authors.forename: James L
authors.initials: JL
authors.lastname: Maller
mesh_terms: D000818:Animals; D064127:Aurora Kinases; D001345:Autoradiography; D018797:Cell Cycle Proteins; D020090:Chromosome Segregation / Q000502:physiology; D004793:Enzyme Reactivators / Q000378:metabolism*; D008869:Microtubule-Associated Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008938:Mitosis / Q000502:physiology*; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D008941:Spindle Apparatus / Q000502:physiology*; D014981:Xenopus; D029867:Xenopus Proteins
chemical_list: D018797:Cell Cycle Proteins; D004793:Enzyme Reactivators; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D010750:Phosphoproteins; C486551:TPX2 protein, Xenopus; D029867:Xenopus Proteins; D011494:Protein Kinases; C112134:AURKA protein, Xenopus; D064127:Aurora Kinases; D017346:Protein Serine-Threonine Kinases