Control of Aurora-A stability through interaction with TPX2

Abstract

The Aurora-A kinase has well-established roles in spindle assembly and function and is frequently overexpressed in tumours. Its abundance is cell cycle regulated, with a peak in G2 and M phases, followed by regulated proteolysis at the end of mitosis. The microtubule-binding protein TPX2 plays a major role in regulating the activity and localisation of Aurora-A in mitotic cells. Here, we report a novel regulatory role of TPX2 and show that it protects Aurora-A from degradation both in interphase and in mitosis in human cells. Specifically, Aurora-A levels decrease in G2 and prometaphase cells silenced for TPX2, whereas degradation of Aurora-A is impaired in telophase cells overexpressing the Aurora-A-binding region of TPX2. The decrease in Aurora-A in TPX2-silenced prometaphases requires proteasome activity and the Cdh1 activator of the APC/C ubiquitin ligase. Reintroducing either full-length TPX2, or the Aurora-A-binding region of TPX2, but not a truncated TPX2 mutant lacking the Aurora-A-interaction domain, restores Aurora-A levels in TPX2-silenced prometaphases. The control by TPX2 of Aurora-A stability is independent of its ability to activate Aurora-A and to localise it to the spindle. These results highlight a novel regulatory level impinging on Aurora-A and provide further evidence for the central role of TPX2 in regulation of Aurora-A.

Tpx2 Controls Spindle Integrity, Genome Stability, and Tumor Development

“…All these features are also found in Aurora A null primary MEFs (15,31,32), which is consistent with the role of Tpx2 as a critical regulator of the Aurora A kinase (4,6,8,(33)(34)(35). However, some differences are detected between these 2 models suggesting separate functions.…”

Spatial regulation of Aurora A activity during mitotic spindle assembly requires RHAMM to correctly localize TPX2

“…26,40 Chemical inhibition of the proteasome rescued TPX2 and Aurora A abundance but incompletely recovered Aurora A activity in RHAMM-depleted cells. Thus, kinase activity required both abundance and the correct location of TPX2, and RHAMM was a necessary regulator for these 2 interdependent processes.…”

“…To test the possibility that the specific loss of RHAMM altered the stability of TPX2, the abundance of these proteins were determined in lysates from G 2 /M synchronized cell populations, as each gene product is strongly cell cycle regulated. 6,7,26 Synchronized populations of RHAMM-silenced cells showed reduced abundance of RHAMM and TPX2, but not the GTP binding protein Ran (Fig. 3E).…”

Mitotic Stress and Chromosomal Instability in Cancer: The Case for TPX2

“…28,37,38 The mechanisms of activation of Aurora-A are still under deep investigation, although it is clear that TPX2 is a major regulator of its activity at different levels. TPX2 is involved in the localization of Aurora-A at the spindle, 17,31 stabilization of Aurora-A protein levels, 39 and achievement of appropriate levels of kinase activity. 20,21,40 The TPX2-Aurora-A binding occurs between the catalytic C-terminal part of the kinase and the N-terminal part of TPX2 (Fig.…”