Phosphorylation and activation of human cdc25-C by cdc2--cyclin B and its involvement in the self-amplification of MPF at mitosis

EMBO J. 1993 Jan;12(1):53-63.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • CDC2 Protein Kinase / metabolism*
  • Cloning, Molecular
  • Cyclins / metabolism*
  • Enzyme Activation
  • Glutathione Transferase / genetics
  • Glutathione Transferase / isolation & purification
  • Glutathione Transferase / metabolism
  • HeLa Cells
  • Humans
  • Immunoblotting
  • Kinetics
  • Mitosis
  • Molecular Sequence Data
  • Oligopeptides / pharmacology
  • Oocytes / cytology
  • Oocytes / physiology
  • Peptide Mapping
  • Peptides / chemical synthesis
  • Peptides / immunology
  • Phosphates / metabolism
  • Phosphopeptides / isolation & purification
  • Phosphorylation
  • Protein Tyrosine Phosphatases / metabolism*
  • Proteins / genetics
  • Proteins / isolation & purification
  • Proteins / metabolism*
  • Recombinant Fusion Proteins / isolation & purification
  • Recombinant Fusion Proteins / metabolism
  • Xenopus
  • cdc25 Phosphatases


  • Cyclins
  • Oligopeptides
  • Peptides
  • Phosphates
  • Phosphopeptides
  • Proteins
  • Recombinant Fusion Proteins
  • Glutathione Transferase
  • CDC2 Protein Kinase
  • Protein Tyrosine Phosphatases
  • cdc25 Phosphatases