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Curr Biol. 2016 Dec 19;26(24):3361-3367. doi: 10.1016/j.cub.2016.10.022. Epub 2016 Nov 23.

Two Bistable Switches Govern M Phase Entry.

Author information

1
Priority Organization for Innovation and Excellence, Kumamoto University, Kyoyoto-honjo 1, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan; Institute for Medical Embryology and Genetics, Kumamoto University, Kyoyoto-honjo 1, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan; International Research Center for Medical Science, Kumamoto University, Kyoyoto-honjo 1, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan; Precursory Research for Embryonic Science and Technology (PRESTO) Program, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan. Electronic address: mochida@kumamoto-u.ac.jp.
2
Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
3
Priority Organization for Innovation and Excellence, Kumamoto University, Kyoyoto-honjo 1, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan.
4
The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
5
Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK. Electronic address: bela.novak@bioch.ox.ac.uk.

Abstract

The abrupt and irreversible transition from interphase to M phase is essential to separate DNA replication from chromosome segregation. This transition requires the switch-like phosphorylation of hundreds of proteins by the cyclin-dependent kinase 1 (Cdk1):cyclin B (CycB) complex. Previous studies have ascribed these switch-like phosphorylations to the auto-activation of Cdk1:CycB through the removal of inhibitory phosphorylations on Cdk1-Tyr15 [1, 2]. The positive feedback in Cdk1 activation creates a bistable switch that makes mitotic commitment irreversible [2-4]. Here, we surprisingly find that Cdk1 auto-activation is dispensable for irreversible, switch-like mitotic entry due to a second mechanism, whereby Cdk1:CycB inhibits its counteracting phosphatase (PP2A:B55). We show that the PP2A:B55-inhibiting Greatwall (Gwl)-endosulfine (ENSA) pathway is both necessary and sufficient for switch-like phosphorylations of mitotic substrates. Using purified components of the Gwl-ENSA pathway in a reconstituted system, we found a sharp Cdk1 threshold for phosphorylation of a luminescent mitotic substrate. The Cdk1 threshold to induce mitotic phosphorylation is distinctly higher than the Cdk1 threshold required to maintain these phosphorylations-evidence for bistability. A combination of mathematical modeling and biochemical reconstitution show that the bistable behavior of the Gwl-ENSA pathway emerges from its mutual antagonism with PP2A:B55. Our results demonstrate that two interlinked bistable mechanisms provide a robust solution for irreversible and switch-like mitotic entry.

KEYWORDS:

Greatwall kinase; PP2A; cyclin-dependent kinase; hysteresis; mitosis; robustness; threshold

PMID:
27889260
PMCID:
PMC5196020
DOI:
10.1016/j.cub.2016.10.022
[Indexed for MEDLINE]
Free PMC Article

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