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Curr Biol. 2018 Dec 3;28(23):3824-3832.e6. doi: 10.1016/j.cub.2018.09.059. Epub 2018 Nov 15.

Two Interlinked Bistable Switches Govern Mitotic Control in Mammalian Cells.

Author information

1
Department of Biochemistry, University of Oxford, South Park Road, Oxford OX1 3QU, UK.
2
Genome Damage and Stability Centre, University of Sussex, Science Park Road, Brighton BN1 9RQ, UK.
3
Department of Chemical and Process Engineering, University of Surrey, 388 Stag Hill, Guildford GU2 7JP, UK.
4
Department of Mathematics, University of Sussex, Science Park Road, Brighton BN1 9QH, UK.
5
Wellcome Trust Centre for Cell Biology, University of Edinburgh, Max Born Crescent, Edinburgh EH9 3BF, UK.
6
Spanish National Cancer Research Centre, Melchor Fernandez Almagro, Madrid E28029, Spain.
7
Department of Biochemistry, University of Oxford, South Park Road, Oxford OX1 3QU, UK. Electronic address: bela.novak@bioch.ox.ac.uk.
8
Genome Damage and Stability Centre, University of Sussex, Science Park Road, Brighton BN1 9RQ, UK. Electronic address: h.hochegger@sussex.ac.uk.

Abstract

Distinct protein phosphorylation levels in interphase and M phase require tight regulation of Cdk1 activity [1, 2]. A bistable switch, based on positive feedback in the Cdk1 activation loop, has been proposed to generate different thresholds for transitions between these cell-cycle states [3-5]. Recently, the activity of the major Cdk1-counteracting phosphatase, PP2A:B55, has also been found to be bistable due to Greatwall kinase-dependent regulation [6]. However, the interplay of the regulation of Cdk1 and PP2A:B55 in vivo remains unexplored. Here, we combine quantitative cell biology assays with mathematical modeling to explore the interplay of mitotic kinase activation and phosphatase inactivation in human cells. By measuring mitotic entry and exit thresholds using ATP-analog-sensitive Cdk1 mutants, we find evidence that the mitotic switch displays hysteresis and bistability, responding differentially to Cdk1 inhibition in the mitotic and interphase states. Cdk1 activation by Wee1/Cdc25 feedback loops and PP2A:B55 inactivation by Greatwall independently contributes to this hysteretic switch system. However, elimination of both Cdk1 and PP2A:B55 inactivation fully abrogates bistability, suggesting that hysteresis is an emergent property of mutual inhibition between the Cdk1 and PP2A:B55 feedback loops. Our model of the two interlinked feedback systems predicts an intermediate but hidden steady state between interphase and M phase. This could be verified experimentally by Cdk1 inhibition during mitotic entry, supporting the predictive value of our model. Furthermore, we demonstrate that dual inhibition of Wee1 and Gwl kinases causes loss of cell-cycle memory and synthetic lethality, which could be further exploited therapeutically.

KEYWORDS:

Cdk1-Cyclin B; Greatwall-kinase; HeLa Cdk1as cell line; PP2A-B55; bistability; cell cycle; hysteresis; mitosis; mitotic control

PMID:
30449668
PMCID:
PMC6287978
DOI:
10.1016/j.cub.2018.09.059
[Indexed for MEDLINE]
Free PMC Article

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