title: Complex regulation of CDK2 during phorbol ester-induced hematopoietic differentiation.
abstract: Phorbol myristate acetate (PMA) treatment of U937 human leukemic cells results in late G1 cell cycle arrest and terminal monocyte/macrophage-like differentiation. The PMA-induced G1 arrest involves a marked decrease in cdk2 activity, which correlates with total cdk2 dephosphorylation. Here, we show that the levels of cyclin A mRNA and protein markedly decrease during PMA-induced differentiation of U937 cells. In contrast, the level of cyclin E protein remains unchanged and in a complex with cdk2 during the entire course of PMA treatment. During the PMA-induced differentiation, cyclin E-associated cdk2 activity drops markedly. Furthermore, the amount of p27(Kip1) protein associated with cyclin E/cdk2 greatly increases 24 to 72 hours after PMA treatment. The absence of changes in p27(Kip1) mRNA levels by Northern blot suggest that the levels of this protein are controlled by posttranscriptional or posttranslational mechanism(s). These results show that the mechanisms mediating PMA-induced G1 arrest are complex. The inhibition of cdk2 activity is associated with (1) a decrease in cyclin A protein levels, (2) inactivation of cdk2 complexes, and (3) upregulation of p27(Kip1) protein.
authors.affiliation: Division of Immunobiology, University of Alabama, Birmingham, AL, USA.
authors.forename: C
authors.initials: C
authors.lastname: Asiedu
authors.forename: J
authors.initials: J
authors.lastname: Biggs
authors.forename: A S
authors.initials: AS
authors.lastname: Kraft
mesh_terms: D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D016193:G1 Phase; D006410:Hematopoiesis / Q000502:physiology*; D006801:Humans; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D013755:Tetradecanoylphorbol Acetate