Cdc25M2 activation of cyclin-dependent kinases by dephosphorylation of threonine-14 and tyrosine-15.
Recent evidence has suggested that human cyclin-dependent kinase 2 (CDK2) is an essential regulator of cell cycle progression through S phase. CDK2 is known to complex with at least two distinct human cyclins, E and A. The kinase activity of these complexes peaks in G1 and S phase, respectively. The vertebrate CDC2/cyclin B1 complex is an essential regulator of the onset of mitosis and is inhibited by phosphorylation of CDC2 on Thr-14 and Tyr-15. In vitro, CDC2/cyclin B1 is activated by treatment with the members of the Cdc25 family of phosphatases. We found that, like CDC2, CDK2 is also phosphorylated on Thr-14 and Tyr-15 and that treatment of cyclin A or cyclin E immunoprecipitates with bacterially expressed Cdc25M2 (the mouse homolog of human CDC25B) increased the histone H1 kinase activity of these immune complexes 5- to 10-fold. Tryptic peptide mapping demonstrated that Cdc25M2 treatment of cyclin A or cyclin B1 immune complexes resulted in the specific dephosphorylation of Thr-14 and Tyr-15 on CDK2 or CDC2, respectively. Thus, we have confirmed that Cdc25 family members comprise a class of dual-specificity phosphatases. Furthermore, our data suggest that the phosphorylation and dephosphorylation of CDKs on Thr-14 and Tyr-15 may regulate not only the G2/M transition but also other transitions in the cell cycle and that individual cdc25 family members may regulate distinct cell cycle checkpoints.
Sebastian
B
B
Molecular Biology and Virology Laboratory, Salk Institute for Biological Studies, San Diego, CA 92186.
Kakizuka
A
A
Hunter
T
T
D000595:Amino Acid Sequence; D000818:Animals; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D004789:Enzyme Activation; D005982:Glutathione Transferase / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D010449:Peptide Mapping; D010710:Phosphates / Q000378:metabolism; D010748:Phosphopeptides / Q000302:isolation & purification; D010766:Phosphorylation; D011494:Protein Kinases / Q000302:isolation & purification / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases; D011506:Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013912:Threonine; D014357:Trypsin; D014443:Tyrosine; D020687:cdc25 Phosphatases
D010710:Phosphates; D010748:Phosphopeptides; D011506:Proteins; D011993:Recombinant Fusion Proteins; D013912:Threonine; D014443:Tyrosine; D005982:Glutathione Transferase; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D020687:cdc25 Phosphatases; D014357:Trypsin