A Novel Mechanism for Activation of the Protein Kinase Aurora A

• Published in: Current biology 2003-04, Vol.13 (8), p.691-697
• Main Authors: Eyers, Patrick A., Erikson, Eleanor, Chen, Lin G., Maller, James L.
• Format: Article
• Language: English
• Subjects: Animals; Aurora Kinases; Autoradiography; Cell Cycle Proteins; Chromosome Segregation - physiology; Enzyme Reactivators - metabolism; Microtubule-Associated Proteins - isolation & purification; Microtubule-Associated Proteins - metabolism; Mitosis - physiology; Neoplasm Proteins; Nuclear Proteins; Phosphoproteins; Phosphorylation; Protein Kinases - metabolism; Protein-Serine-Threonine Kinases; Spindle Apparatus - physiology; Xenopus; Xenopus Proteins
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/S0960-9822(03)00166-0

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.