Abstract
ABSTRACTActivity of AURKA is controlled through multiple mechanisms including phosphorylation, ubiquitin-mediated degradation and allosteric interaction with TPX2. Activity peaks at mitosis, before AURKA is degraded during and after mitotic exit in a process strictly dependent on the APC/C coactivator FZR1. We used FZR1 knockout cells (FZR1KO) and a novel FRET-based AURKA biosensor to investigate how AURKA activity is regulated in the absence of destruction. We found that AURKA activity in FZR1KO cells dropped at mitotic exit as rapidly as in parental cells, despite absence of AURKA destruction. Unexpectedly, TPX2 was degraded normally in FZR1KO cells. Overexpression of an N-terminal TPX2 fragment sufficient for AURKA binding, but that is not degraded at mitotic exit, caused delay in AURKA inactivation. We conclude that inactivation of AURKA at mitotic exit is determined not by AURKA degradation but by degradation of TPX2 and therefore is dependent on CDC20 rather than FZR1. The biosensor revealed that FZR1 instead suppresses AURKA activity in interphase and is critically required for assembly of the interphase mitochondrial network after mitosis.This article has an associated First Person interview with the first authors of the paper.
Highlights
Aurora kinase A (AURKA) is a major mitotic kinase required for multiple steps in mitosis, including centrosome maturation, microtubule nucleation and organisation into a bipolar spindle and mitotic checkpoint function (Barr and Gergely, 2007; Courtheoux et al, 2018)
AURKA activity has been described to peak in M phase there has been no detailed characterization of how AURKA activity varies through mitosis
How can we explain the timing of AURKA inactivation at mitotic exit? We have previously shown that interaction with TPX2 stabilizes AURKA against Anaphase Promoting Complex/Cyclosome (APC/C)-FZR1-mediated degradation (Giubettini et al, 2011), and from this concluded that loss of interaction with TPX2 contributes to the timing of AURKA degradation at mitotic exit
Summary
Aurora kinase A (AURKA) is a major mitotic kinase required for multiple steps in mitosis, including centrosome maturation, microtubule nucleation and organisation into a bipolar spindle and mitotic checkpoint function (Barr and Gergely, 2007; Courtheoux et al, 2018). Recent studies of the effects of acute inhibition of AURKA during mitosis have concluded that it plays an important role during mitotic exit in regulating assembly of the anaphase spindle upon which sister chromatids are segregated (Hegarat et al, 2011; Lioutas and Vernos, 2013; Reboutier et al, 2013). The most prominent of these allosteric activators is TPX2, which controls AURKA localization, activation and stability on the mitotic spindle during mitosis (Bayliss et al, 2003; Giubettini et al, 2011; Kufer et al, 2002). Interaction with TPX2, whilst protecting the AURKA autophosphorylated site (pT288 in hsAURKA) from access by PP1 phosphatase (Bayliss et al, 2003), acts to stabilize the T-loop with or without its phosphorylation. Phosphatase-mediated reversal of T288 phosphorylation may not be sufficient to eliminate activity of AURKA
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