title: Two Bistable Switches Govern M Phase Entry.
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.
authors.affiliation: 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.
authors.forename: Satoru
authors.initials: S
authors.lastname: Mochida
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
authors.forename: Scott
authors.initials: S
authors.lastname: Rata
authors.affiliation: Priority Organization for Innovation and Excellence, Kumamoto University, Kyoyoto-honjo 1, 2-2-1 Honjo, Chuo-ku, Kumamoto 860-0811, Japan.
authors.forename: Hirotsugu
authors.initials: H
authors.lastname: Hino
authors.affiliation: The Institute of Scientific and Industrial Research, Osaka University, Mihogaoka 8-1, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Takeharu
authors.initials: T
authors.lastname: Nagai
authors.affiliation: Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK. Electronic address: bela.novak@bioch.ox.ac.uk.
authors.forename: Béla
authors.initials: B
authors.lastname: Novák
mesh_terms: D000818:Animals; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism*; D059447:Cell Cycle Checkpoints / Q000502:physiology*; D002455:Cell Division / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic; D036341:Intercellular Signaling Peptides and Proteins; D008954:Models, Biological; D010455:Peptides / Q000378:metabolism; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C075663:endosulfine; D016203:CDC2 Protein Kinase; D054648:Protein Phosphatase 2
keywords: Greatwall kinase; PP2A; cyclin-dependent kinase; hysteresis; mitosis; robustness; threshold