title: Phosphorylation and activation of human cdc25-C by cdc2--cyclin B and its involvement in the self-amplification of MPF at mitosis.
abstract: We have investigated the mechanisms responsible for the sudden activation of the cdc2-cyclin B protein kinase before mitosis. It has been found previously that cdc25 is the tyrosine phosphatase responsible for dephosphorylating and activating cdc2-cyclin B. In Xenopus eggs and early embryos a cdc25 homologue undergoes periodic phosphorylation and activation. Here we show that the catalytic activity of human cdc25-C phosphatase is also activated directly by phosphorylation in mitotic cells. Phosphorylation of cdc25-C in mitotic HeLa extracts or by cdc2-cyclin B increases its catalytic activity. cdc25-C is not a substrate of the cyclin A-associated kinases. cdc25-C is able to activate cdc2-cyclin B1 in Xenopus egg extracts and to induce Xenopus oocyte maturation, but only after stable thiophosphorylation. This demonstrates that phosphorylation of cdc25-C is required for the activation of cdc2-cyclin B and entry into M-phase. Together, these studies offer a plausible explanation for the rapid activation of cdc2-cyclin B at the onset of mitosis and the self-amplification of MPF observed in vivo.
authors.affiliation: Differentiation Programme, European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: I
authors.initials: I
authors.lastname: Hoffmann
authors.forename: P R
authors.initials: PR
authors.lastname: Clarke
authors.forename: M J
authors.initials: MJ
authors.lastname: Marcote
authors.forename: E
authors.initials: E
authors.lastname: Karsenti
authors.forename: G
authors.initials: G
authors.lastname: Draetta
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D003001:Cloning, Molecular; D016213:Cyclins / Q000378:metabolism*; D004789:Enzyme Activation; D005982:Glutathione Transferase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D007700:Kinetics; D008938:Mitosis; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D009865:Oocytes / Q000166:cytology / Q000502:physiology; D010449:Peptide Mapping; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D010710:Phosphates / Q000378:metabolism; D010748:Phosphopeptides / Q000302:isolation & purification; D010766:Phosphorylation; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism*; D011506:Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000302:isolation & purification / Q000378:metabolism; D014981:Xenopus; D020687:cdc25 Phosphatases
chemical_list: D016213:Cyclins; D009842:Oligopeptides; D010455:Peptides; D010710:Phosphates; D010748:Phosphopeptides; D011506:Proteins; D011993:Recombinant Fusion Proteins; D005982:Glutathione Transferase; D016203:CDC2 Protein Kinase; D017027:Protein Tyrosine Phosphatases; D020687:cdc25 Phosphatases