The cyclin-dependent kinase inhibitor p21WAF1/Cip1 is an antiestrogen-regulated inhibitor of Cdk4 in human breast cancer cells.
The MCF-7 cell line is a model of estrogen-dependent, antiestrogen-sensitive human breast cancer. Antiestrogen treatment of MCF-7 cells causes dramatic decreases in both Cdk4 and Cdk2 activities, which leads to a G(1) phase cell cycle arrest. In this report, we investigate the mechanism(s) by which Cdk4 activity is regulated in MCF-7 cells. Through time course analysis, we demonstrate that changes in Cdk4 activity in response to estrogen or antiestrogen treatment do not correlate directly with cyclin D1 protein levels or association. In contrast, Cdk4 activity does correlate with changes in the level of the Cdk inhibitor p21(WAF1/Cip1). Furthermore, we show that extracts of antiestrogen-treated cells contain a factor capable of inhibiting the Cdk4 activity present in extracts of estrogen-treated cells, and immunodepletion experiments identify this factor as p21(WAF1/Cip1). These results identify p21(WAF1/Cip1) as an important physiological regulator of Cdk4 complexes in human breast cancer cells.
Skildum
Andrew J
AJ
Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, Michigan 48824, USA.
Mukherjee
Shibani
S
Conrad
Susan E
SE
D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism; D019938:Cyclin D1 / Q000096:biosynthesis; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors*; D016213:Cyclins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D000077267:Fulvestrant; D006801:Humans; D011233:Precipitin Tests; D011485:Protein Binding; D011518:Proto-Oncogene Proteins; D013997:Time Factors; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000378:metabolism
D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000077267:Fulvestrant; D004958:Estradiol; C495900:CDK4 protein, human; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases