Abstract
We examined transforming growth factor-beta 1 (TGF-beta 1) effects on cell cycle progression of human colon carcinoma FET cells. TGF-beta 1 inhibited DNA synthesis and cyclin-dependent kinase (CDK) activity after release from growth arrest in association with induction of the p21 CDK inhibitor, whereas cyclins, CDKs, and p27 protein levels remained relatively unchanged. The decrease in CDK2 kinase activity was the result of increased p21 association with cyclin A-CDK2 and cyclin E-CDK2. TGF-beta 1 treatment in late G(1) showed reduced induction of p21 protein levels in association with increased DNA synthesis. Consequently, p21 induction in early G(1) is critical for TGF-beta 1 inhibition of CDK2 kinase activity. Although TGF-beta 1 treatments in late G(1) failed to induce p21 protein, p21 mRNA induction was observed in late G(1) and in S phase. Further analysis showed that TGF-beta 1 treatment in early G(1) increases p21 protein stability throughout the G(1) and S phases of the cell cycle. Our results demonstrate that TGF-beta 1 stimulation of p21 is regulated at the posttranscriptional and transcriptional levels. This is a novel mechanism of TGF-beta 1 inhibition requiring early G(1) induction and stabilization of p21 protein, which binds to and inhibits cyclin E-CDK2 and cyclin A-CDK2 kinase activity rather than direct modulation of cyclin or CDK protein levels as seen in other systems.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adenocarcinoma / metabolism
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Adenocarcinoma / pathology*
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CDC2-CDC28 Kinases*
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Colonic Neoplasms / metabolism
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Colonic Neoplasms / pathology*
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Cyclin A / metabolism
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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclin-Dependent Kinases / antagonists & inhibitors*
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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 / drug effects
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Genes, Reporter
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Humans
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Kinetics
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Luciferases / biosynthesis
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Macromolecular Substances
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Neoplasm Proteins / antagonists & inhibitors*
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Neoplasm Proteins / genetics
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Neoplasm Proteins / metabolism
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Promoter Regions, Genetic / drug effects
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Protein Serine-Threonine Kinases / antagonists & inhibitors*
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Protein Serine-Threonine Kinases / metabolism
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RNA, Messenger / biosynthesis
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Recombinant Fusion Proteins / biosynthesis
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S Phase
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Transforming Growth Factor beta / pharmacology*
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Transforming Growth Factor beta1
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Tumor Cells, Cultured / drug effects
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Tumor Cells, Cultured / metabolism
Substances
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CDKN1A protein, human
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Cyclin A
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins
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Macromolecular Substances
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Neoplasm Proteins
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RNA, Messenger
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Recombinant Fusion Proteins
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TGFB1 protein, human
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Transforming Growth Factor beta
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Transforming Growth Factor beta1
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Luciferases
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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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Cyclin-Dependent Kinase 2
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Cyclin-Dependent Kinases