Abstract
Retinoic acid (RA) inhibition of breast cancer cell growth is associated with an accumulation of cells in G1 phase of the cell cycle. We have investigated the effects of RA on the expression and activity of cell cycle-regulatory proteins in MCF-7 human breast cancer cells. Flow cytometry analysis of MCF-7 cells treated with RA revealed a decrease in the percentage of cells in S phase by 48 h, which was maximal by 72 h. Phosphorylation of the retinoblastoma protein (pRb) was partially reduced in RA-treated cells accompanied by a decrease in the level of retinoblastoma protein. Expression of the cyclin D1 transcript was reduced by 48 h and cyclin-dependent kinase 2 (cdk2) mRNA levels declined within 8 h posttreatment followed by a decrease in cyclin D1 and cdk2 protein levels. Message and protein levels of cdk4 and cdc2 were not affected by RA. While cdk4 activity was similar in control and RA-treated cells, cdk2 activity began to decrease within 48 h of exposure to RA and was profoundly reduced after 72 h. This reduced activity was associated with decreased phosphorylation of cdk2. The decrease in cdk2 activity occurred in the absence of RA-mediated increases in the levels of the cdk inhibitors p21 and p27. However, assays of cdk2 from pooled lysates from RA-treated and control cells showed that RA-treated cells contain a cdk2-inhibitory activity. Our results show that RA inhibits cell cycle progression of MCF-7 cells by inhibiting cdk2 mRNA and protein production and by decreasing cdk2 activity.
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 / metabolism*
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CDC2-CDC28 Kinases*
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Cell Cycle / drug effects
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Cell Cycle Proteins*
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Cell Division / drug effects
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Cyclin D1
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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 Kinase-Activating Kinase
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Cyclin-Dependent Kinases / drug effects*
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Cyclin-Dependent Kinases / genetics
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Cyclin-Dependent Kinases / metabolism
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Cyclins / drug effects
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Cyclins / genetics
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Cyclins / metabolism
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G1 Phase / drug effects
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Gene Expression Regulation, Neoplastic
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Humans
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Microtubule-Associated Proteins / drug effects
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Microtubule-Associated Proteins / metabolism
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Oncogene Proteins / drug effects
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Oncogene Proteins / genetics
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Oncogene Proteins / metabolism
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Phosphorylation
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Protein Serine-Threonine Kinases / drug effects*
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Protein Serine-Threonine Kinases / genetics
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Protein Serine-Threonine Kinases / metabolism
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Proto-Oncogene Proteins*
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RNA, Messenger / biosynthesis
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RNA, Messenger / drug effects
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Retinoblastoma Protein / drug effects
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Retinoblastoma Protein / metabolism
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Tretinoin / pharmacology*
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Tumor Cells, Cultured
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Tumor Suppressor Proteins*
Substances
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CDKN1A protein, human
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Cell Cycle Proteins
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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Microtubule-Associated Proteins
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Oncogene Proteins
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Proto-Oncogene Proteins
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RNA, Messenger
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Retinoblastoma Protein
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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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Tretinoin
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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
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Cyclin-Dependent Kinase-Activating Kinase