Cdk2-dependent phosphorylation of p27 facilitates its Myc-induced release from cyclin E/cdk2 complexes.
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.
Müller
D
D
Zentrum für Molekulare Biologie Heidelberg, Germany.
Bouchard
C
C
Rudolph
B
B
Steiner
P
P
Stuckmann
I
I
Saffrich
R
R
Ansorge
W
W
Huttner
W
W
Eilers
M
M
D000818:Animals; D042846:CDC2-CDC28 Kinases; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016259:Genes, myc / Q000502:physiology*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011817:Rabbits; D025521:Tumor Suppressor Proteins
C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D019927:Cyclin E; D008869:Microtubule-Associated Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases