title: Phosphatase 2A and polo kinase, two antagonistic regulators of cdc25 activation and MPF auto-amplification.
abstract: The auto-catalytic activation of the cyclin-dependent kinase Cdc2 or MPF (M-phase promoting factor) is an irreversible process responsible for the entry into M phase. In Xenopus oocyte, a positive feed-back loop between Cdc2 kinase and its activating phosphatase Cdc25 allows the abrupt activation of MPF and the entry into the first meiotic division. We have studied the Cdc2/Cdc25 feed-back loop using cell-free systems derived from Xenopus prophase-arrested oocyte. Our findings support the following two-step model for MPF amplification: during the first step, Cdc25 acquires a basal catalytic activity resulting in a linear activation of Cdc2 kinase. In turn Cdc2 partially phosphorylates Cdc25 but no amplification takes place; under this condition Plx1 kinase and its activating kinase, Plkk1 are activated. However, their activity is not required for the partial phosphorylation of Cdc25. This first step occurs independently of PP2A or Suc1/Cks-dependent Cdc25/Cdc2 association. On the contrary, the second step involves the full phosphorylation and activation of Cdc25 and the initiation of the amplification loop. It depends both on PP2A inhibition and Plx1 kinase activity. Suc1-dependent Cdc25/Cdc2 interaction is required for this process.
authors.affiliation: Laboratoire de Physiologie de la Reproduction, ESA 7080-CNRS, INRA, Université Pierre et Marie Curie, Boîte 13, 75252 Paris cédex 05, France.
authors.forename: A
authors.initials: A
authors.lastname: Karaïskou
authors.forename: C
authors.initials: C
authors.lastname: Jessus
authors.forename: T
authors.initials: T
authors.lastname: Brassac
authors.forename: R
authors.initials: R
authors.lastname: Ozon
mesh_terms: D048948:14-3-3 Proteins; D000818:Animals; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D002474:Cell-Free System; D002648:Child; D018844:Cyclin-Dependent Kinases / Q000235:genetics* / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D006801:Humans; D008540:Meiosis / Q000502:physiology*; D009865:Oocytes / Q000201:enzymology*; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism*; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins; D014446:Tyrosine 3-Monooxygenase; D014981:Xenopus / Q000502:physiology*; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D000097869:Polo-Like Kinase 1
chemical_list: D048948:14-3-3 Proteins; D018797:Cell Cycle Proteins; D018844:Cyclin-Dependent Kinases; D005656:Fungal Proteins; D010744:Phosphoric Monoester Hydrolases; D054648:Protein Phosphatase 2; D017346:Protein Serine-Threonine Kinases; D011506:Proteins; D029702:Schizosaccharomyces pombe Proteins; D014446:Tyrosine 3-Monooxygenase; D029867:Xenopus Proteins; D020687:cdc25 Phosphatases; C051655:Suc1 protein, S pombe; C101085:Plk1 protein, Xenopus; D000097869:Polo-Like Kinase 1; C102266:Cdc25A protein, Xenopus