title: A phosphatase threshold sets the level of Cdk1 activity in early mitosis in budding yeast.
abstract: Entry into mitosis is initiated by synthesis of cyclins, which bind and activate cyclin-dependent kinase 1 (Cdk1). Cyclin synthesis is gradual, yet activation of Cdk1 occurs in a stepwise manner: a low level of Cdk1 activity is initially generated that triggers early mitotic events, which is followed by full activation of Cdk1. Little is known about how stepwise activation of Cdk1 is achieved. A key regulator of Cdk1 is the Wee1 kinase, which phosphorylates and inhibits Cdk1. Wee1 and Cdk1 show mutual regulation: Cdk1 phosphorylates Wee1, which activates Wee1 to inhibit Cdk1. Further phosphorylation events inactivate Wee1. We discovered that a specific form of protein phosphatase 2A (PP2A(Cdc55)) opposes the initial phosphorylation of Wee1 by Cdk1. In vivo analysis, in vitro reconstitution, and mathematical modeling suggest that PP2A(Cdc55) sets a threshold that limits activation of Wee1, thereby allowing a low constant level of Cdk1 activity to escape Wee1 inhibition in early mitosis. These results define a new role for PP2A(Cdc55) and reveal a systems-level mechanism by which dynamically opposed kinase and phosphatase activities can modulate signal strength.
authors.affiliation: Department of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz, Santa Cruz, CA 95064, USA.
authors.forename: Stacy L
authors.initials: SL
authors.lastname: Harvey
authors.forename: Germán
authors.initials: G
authors.lastname: Enciso
authors.forename: Noah
authors.initials: N
authors.lastname: Dephoure
authors.forename: Steven P
authors.initials: SP
authors.lastname: Gygi
authors.forename: Jeremy
authors.initials: J
authors.lastname: Gunawardena
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Kellogg
mesh_terms: D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D008938:Mitosis / Q000235:genetics; D008962:Models, Theoretical; D009154:Mutation; D010744:Phosphoric Monoester Hydrolases; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D015533:Transcriptional Activation
chemical_list: C071246:CDC55 protein, S cerevisiae; D018797:Cell Cycle Proteins; D029701:Saccharomyces cerevisiae Proteins; C099685:SWE1 protein, S cerevisiae; D011505:Protein-Tyrosine Kinases; D016203:CDC2 Protein Kinase; D054648:Protein Phosphatase 2; D010744:Phosphoric Monoester Hydrolases