Cdk2-dependent phosphorylation of p27 facilitates its Myc-induced release from cyclin E/cdk2 complexes

Oncogene. 1997 Nov 20;15(21):2561-76. doi: 10.1038/sj.onc.1201440.


Activation of Myc triggers a rapid induction of cyclin E/cdk2 kinase activity and degradation of p27. Overt degradation of p27 is preceded by a specific dissociation of p27 from cyclin E/cdk2, but not from cyclin D/cdk4 complexes. We now show that cyclin E/cdk2 phosphorylates p27 at a carboxy-terminal threonine residue (T187) in vitro; mutation of this residue to valine stabilises cyclin E/cdk2 complexes. This reaction is not significantly inhibited by high concentrations of p27, suggesting that cdk2 bound to p27 is catalytically active. In vivo, p27 bound to cyclins E and A, but not to D-type cyclins is phosphorylated. Myc-induced release of p27 from cdk2 requires cdk2 kinase activity and is delayed in a T187V mutant of p27. After induction of Myc, p27 phosphorylated at threonine 187 transiently accumulates in a non cdk2 bound form. Our data suggest a mechanism in which p27 is released from cyclin E/cdk2 upon phosphorylation; in Myc-transformed cells, release is efficient as phosphorylated p27 is transiently bound in a non-cdk2 containing complex and subsequently degraded.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • CDC2-CDC28 Kinases*
  • Cell Cycle Proteins*
  • Cells, Cultured
  • Cyclin E / metabolism*
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinase Inhibitor p27
  • Cyclin-Dependent Kinases / metabolism*
  • Genes, myc / physiology*
  • Mice
  • Microtubule-Associated Proteins / metabolism*
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / metabolism*
  • Rabbits
  • Tumor Suppressor Proteins*


  • Cdkn1b protein, mouse
  • Cell Cycle Proteins
  • Cyclin E
  • Microtubule-Associated Proteins
  • Tumor Suppressor Proteins
  • Cyclin-Dependent Kinase Inhibitor p27
  • Protein-Serine-Threonine Kinases
  • CDC2-CDC28 Kinases
  • Cdk2 protein, mouse
  • Cyclin-Dependent Kinase 2
  • Cyclin-Dependent Kinases