title: Cdk2-dependent Inhibition of p21 stability via a C-terminal cyclin-binding motif.
abstract: p21 is a member of the Cip/Kip family of cyclin-dependent kinase (CDK) inhibitors that includes p21, p27, and p57. Recent studies have suggested that Cdk2 activity may promote p21 degradation through a pathway similar to that for p27, although the mechanism by which this occurs has not been clarified. In the current report, co-expression with cyclin E and Cdk2 stabilized p21 in a manner that required the CDK-binding site of p21 and a cyclin-binding site (cy1) located in the p21 N terminus. Strikingly, however, a kinase-dead Cdk2 mutant stabilized p21 to a greater extent than did wild-type Cdk2, consistent with the notion that Cdk2 activity can destabilize p21. The ability of wild-type Cdk2 to destabilize p21 required a potential Cdk2 phosphorylation site in p21 at serine 130 and an intact cyclin-binding motif (cy2) in the p21 C terminus. Finally, p21 was phosphorylated by Cdk2 at Ser-130 in vitro, and this ability of Cdk2 to phosphorylate p21 was dependent, in large part, on the presence of cy2. These results support a model in which active Cdk2 destabilizes p21 via the cy2 cyclin-binding motif and p21 phosphorylation.
authors.affiliation: Department of Radiation and Cellular Oncology, Center for Molecular Oncology, University of Chicago, Chicago, IL 60637, USA.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Zhu
authors.forename: Linghu
authors.initials: L
authors.lastname: Nie
authors.forename: Carl G
authors.initials: CG
authors.lastname: Maki
mesh_terms: D020816:Amino Acid Motifs; D001665:Binding Sites; D042846:CDC2-CDC28 Kinases / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000737:chemistry; D003720:Densitometry; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012694:Serine / Q000737:chemistry; D013997:Time Factors; D014162:Transfection
chemical_list: C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D011500:Protein Synthesis Inhibitors; D012694:Serine; D004247:DNA; D003513:Cycloheximide; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D046988:Proteasome Endopeptidase Complex