A pure estrogen antagonist inhibits cyclin E-Cdk2 activity in MCF-7 breast cancer cells and induces accumulation of p130-E2F4 complexes characteristic of quiescence.
Estrogen antagonists inhibit cell cycle progression in estrogen-responsive cells, but the molecular mechanisms are not fully defined. Antiestrogen-mediated G(0)/G(1) arrest is associated with decreased cyclin D1 gene expression, inactivation of cyclin D1-cyclin dependent kinase (Cdk) 4 complexes, and decreased phosphorylation of the retinoblastoma protein (pRb). We now show that treatment of MCF-7 breast cancer cells with the pure estrogen antagonist ICI 182780 results in inhibition of cyclin E-Cdk2 activity prior to a decrease in the G(1) to S phase transition. This decrease was dependent on p21(WAF1/Cip1) since treatment with antisense oligonucleotides to p21 attenuated the effect. Recruitment of p21 to cyclin E-Cdk2 complexes was in turn dependent on decreased cyclin D1 expression since it was apparent following treatment with antisense cyclin D1 oligonucleotides. To define where within the G(0) to S phase continuum antiestrogen-treated cells arrested, we assessed the relative abundance and phosphorylation state of pocket protein-E2F complexes. While both pRb and p107 levels were significantly decreased, p130 was increased 4-fold and was accompanied by the formation of p130.E2F4 complexes and the accumulation of hyperphophorylated E2F4, putative markers of cellular quiescence. Thus, ICI 182780 inhibits both cyclin D1-Cdk4 and cyclin E-Cdk2 activity, resulting in the arrest of MCF-7 cells in a state with characteristics of quiescence (G(0)), as opposed to G(1) arrest.
Carroll
J S
JS
Cancer Research Program, Garvan Institute of Medical Research, St. Vincent's Hospital, Sydney, New South Wales 2010, Australia.
Prall
O W
OW
Musgrove
E A
EA
Sutherland
R L
RL
D001943:Breast Neoplasms; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D002455:Cell Division; D019938:Cyclin D1 / Q000235:genetics / Q000502:physiology; D019927:Cyclin E / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D050704:E2F4 Transcription Factor; D004791:Enzyme Inhibitors / Q000378:metabolism; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology*; D005260:Female; D000077267:Fulvestrant; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D020319:Oligodeoxyribonucleotides, Antisense / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011506:Proteins; D016192:Resting Phase, Cell Cycle / Q000187:drug effects / Q000502:physiology; D050717:Retinoblastoma-Like Protein p130; D014157:Transcription Factors / Q000378:metabolism*; D014407:Tumor Cells, Cultured
C493956:CDKN1A protein, human; D019927:Cyclin E; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004268:DNA-Binding Proteins; D050704:E2F4 Transcription Factor; D004791:Enzyme Inhibitors; D004965:Estrogen Antagonists; D020319:Oligodeoxyribonucleotides, Antisense; D010750:Phosphoproteins; D011506:Proteins; C493837:RBL2 protein, human; D050717:Retinoblastoma-Like Protein p130; D014157:Transcription Factors; D019938:Cyclin D1; D000077267:Fulvestrant; D004958:Estradiol; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases