Aurora-A-Dependent Control of TACC3 Influences the Rate of Mitotic Spindle Assembly

Abstract

The essential mammalian gene TACC3 is frequently mutated and amplified in cancers and its fusion products exhibit oncogenic activity in glioblastomas. TACC3 functions in mitotic spindle assembly and chromosome segregation. In particular, phosphorylation on S558 by the mitotic kinase, Aurora-A, promotes spindle recruitment of TACC3 and triggers the formation of a complex with ch-TOG-clathrin that crosslinks and stabilises kinetochore microtubules. Here we map the Aurora-A-binding interface in TACC3 and show that TACC3 potently activates Aurora-A through a domain centered on F525. Vertebrate cells carrying homozygous F525A mutation in the endogenous TACC3 loci exhibit defects in TACC3 function, namely perturbed localization, reduced phosphorylation and weakened interaction with clathrin. The most striking feature of the F525A cells however is a marked shortening of mitosis, at least in part due to rapid spindle assembly. F525A cells do not exhibit chromosome missegregation, indicating that they undergo fast yet apparently faithful mitosis. By contrast, mutating the phosphorylation site S558 to alanine in TACC3 causes aneuploidy without a significant change in mitotic duration. Our work has therefore defined a regulatory role for the Aurora-A-TACC3 interaction beyond the act of phosphorylation at S558. We propose that the regulatory relationship between Aurora-A and TACC3 enables the transition from the microtubule-polymerase activity of TACC3-ch-TOG to the microtubule-crosslinking activity of TACC3-ch-TOG-clathrin complexes as mitosis progresses. Aurora-A-dependent control of TACC3 could determine the balance between these activities, thereby influencing not only spindle length and stability but also the speed of spindle formation with vital consequences for chromosome alignment and segregation.

The role of TACC3 in mitotic spindle organization

“…Thus, the model can be further elaborated as follows: first, ch‐TOG binds to TACC3; then the complex is recruited to microtubules after TACC3 phosphorylation by Aurora‐A; third, clathrin is added to the pTACC3 and finally, the TACC3/ch‐TOG/clathrin complex is formed (Figure B). The model is consistent with a recent study that the interaction between Aurora‐A and TACC3 promotes TACC3 to transform TACC3‐ch‐TOG as the microtubule‐polymerase to TACC3‐ch‐TOG‐clathrin complexes to crosslink the k‐fibers (Burgess et al, ).…”

“…Although TACC3 has a well‐characterized role as a substrate of Aurora‐A kinase, a new study reveals that TACC3 also plays a role in the activation of Aurora‐A in vitro (Burgess et al, ), which is consistent with a previous experiment in Xenopus (Pascreau, Delcros, Cremet, Prigent, & Arlot‐Bonnemains, ). TACC3 stimulates Aurora‐A activity through TACC3act (residues 519–563), including S558 (Burgess et al, ). Thus, we do not understand whether this local activation of Aurora‐A serves solely to enhance the phosphorylation of S558 on TACC3, and if not, then, the mechanism remains unknon.…”

“…Furthermore, the TACC3/ch‐TOG/clathrin intermicrotubule bridge stabilizes the k‐fibres by physical crosslinking, and possibly by reducing the rate of microtubules catastrophe. The depletion of clathrin results in k‐fibers that lack the shortest type of intermicrotubule bridges, which is similar to TACC3 depletion (Cheeseman, Booth, Hood, Prior, & Royle, ). Destroying the structure of the TACC3/ch‐TOG/clathrin complex mainly disrupts short intermicrotubule bridges, suggesting that the complex plays a role mainly in the short intermicrotubule bridges to stabilize the spindle (Booth et al, ).…”

“…Although numerous studies have explored the mechanisms of how members of the TACC3/ch‐TOG/clathrin interact with one another and how the complex interacts with microtubules, further studies are required. Furthermore, the links between TACC3/ch‐TOG and TACC3/ch‐TOG/clathrin is still unintelligible, even though some experiments suggest that TACC3/ch‐TOG/clathrin is changed from TACC3/ch‐TOG (Burgess et al, ). Future studies should focus on clearing up the links and differences among the various processes that TACC3 participates in during mitosis.…”

Revisiting protein kinase–substrate interactions: Toward therapeutic development

“…Nuclear magnetic resonance (NMR) has also been used to map kinase-substrate interaction sites (99,100). Improved techniques that can directly determine the structural nature of kinasesubstrate interactions or increasing the affinity between the kinase and the substrate may lead to a better understanding of the structural nature of this interaction and the development of more specific kinase inhibitors.…”