Abstract
The proto-oncogene c-myc is up-regulated by estrogen stimulation of hormone-dependent breast cancer cells and is frequently overexpressed in breast and other cancers. Therapeutic interventions that inhibit c-Myc expression have been extensively investigated, including antisense oligonucleotides that have high specificity and potential clinical application. This investigation compared antiestrogen-mediated growth arrest with the molecular events after repression of c-Myc expression in MCF-7 breast cancer cells using an antisense oligonucleotide. We show that the decreased cellular proliferation of MCF-7 cells after direct inhibition of c-Myc is a consequence of inhibition of cyclin D1 expression, subsequent redistribution of p21(WAF1/CIP1) from cyclin D1-Cdk4 to cyclin E-Cdk2 complexes, and a decline in cyclin E-Cdk2 enzymatic activity. Simultaneous repression of p21(WAF1/CIP1) can attenuate the growth-inhibitory effects of reduced c-Myc expression emphasizing the importance of this cyclin-dependent kinase (CDK) inhibitor in growth arrest. These molecular events are similar to the initial changes in cyclin gene expression, CDK complex formation and CDK activity seen after antiestrogen (ICI 182780)-mediated growth inhibition of MCF-7 cells, which suggests that the down-regulation of c-Myc by ICI 182780 is a primary event that culminates in cell cycle arrest.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Breast Neoplasms / drug therapy
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Breast Neoplasms / genetics*
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Breast Neoplasms / pathology*
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CDC2-CDC28 Kinases*
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Cell Cycle Proteins / metabolism
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Cell Division / drug effects
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Cell Division / genetics
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Cyclin D1 / biosynthesis
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Cyclin D1 / genetics
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Cyclin D1 / metabolism
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Cyclin E / biosynthesis
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Cyclin E / genetics
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Cyclin E / metabolism
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase 4
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclin-Dependent Kinase Inhibitor p27
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Cyclin-Dependent Kinases / metabolism
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Cyclins / biosynthesis
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Cyclins / genetics
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Cyclins / metabolism
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Estradiol / analogs & derivatives*
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Estradiol / pharmacology
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Estrogen Receptor Modulators / pharmacology*
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Fulvestrant
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Gene Expression Regulation, Neoplastic
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Genes, myc / drug effects
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Genes, myc / genetics*
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Humans
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Oligonucleotides, Antisense / genetics
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Oligonucleotides, Antisense / pharmacology*
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Protein Serine-Threonine Kinases / metabolism
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Proto-Oncogene Mas
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Proto-Oncogene Proteins c-myc / antagonists & inhibitors*
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Proto-Oncogene Proteins c-myc / biosynthesis
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Proto-Oncogene Proteins c-myc / genetics
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Proto-Oncogene Proteins*
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Tumor Suppressor Proteins / metabolism
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Up-Regulation
Substances
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CDKN1A protein, human
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Cell Cycle Proteins
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Cyclin E
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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Estrogen Receptor Modulators
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MAS1 protein, human
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Oligonucleotides, Antisense
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Proto-Oncogene Mas
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Proto-Oncogene Proteins
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Proto-Oncogene Proteins c-myc
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RNA, Messenger
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Tumor Suppressor Proteins
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Cyclin D1
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Cyclin-Dependent Kinase Inhibitor p27
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Fulvestrant
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Estradiol
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Protein Serine-Threonine Kinases
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CDC2-CDC28 Kinases
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CDK2 protein, human
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CDK4 protein, human
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase 4
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Cyclin-Dependent Kinases