Abstract
In this report, we describe the mechanism of TGF-beta receptor type I (RI) repression in the GEO human colon carcinoma cells. Treatment of GEO cells with the DNA methyltransferase inhibitor, 5 azacytidine induced RI expression and restored TGF-beta response. A stably transfected RI promoter-reporter construct (RI-Luc) expressed higher activity in the 5 aza C treated GEO cells, suggesting the activation of a transactivator for RI transcription. Gel shift analysis indicated enhanced binding of proteins from the 5 aza C treated nuclear extracts to radiolabeled Sp1 oligonucleotides specifically contained in the RI promoter. Protein stability studies after cyclohexamide treatment suggested an increase in the Sp1 protein stability from the 5 aza C treated GEO cells. Further, transfection of Sp1 cDNA into untreated GEO control cells increased RI promoter activity and thus induced RI expression. 5 aza C mediated Sp1 expression in Sp1 deficient GEO colon and MCF-7 breast cancer cells also enhanced the activity of several other Sp1 dependent promoters such as TGF-beta receptor type II (RII), Cyclin A and p21/waf1/cip1. These results indicate that restoration of Sp1 in several different types of Sp1 deficient cells leads to enhanced activation of a wide range of Sp1 dependent promoters.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Activin Receptors, Type I*
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Adenocarcinoma / genetics
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Adenocarcinoma / metabolism
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Adenocarcinoma / pathology
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Antimetabolites, Antineoplastic / pharmacology
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Azacitidine / pharmacology
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Breast Neoplasms / genetics
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Breast Neoplasms / metabolism
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Breast Neoplasms / pathology
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Colonic Neoplasms / genetics
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Colonic Neoplasms / metabolism
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Colonic Neoplasms / pathology
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Cyclin A / biosynthesis
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Cyclin A / genetics
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Cyclin-Dependent Kinase Inhibitor p21
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Cyclins / biosynthesis
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Cyclins / genetics
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DNA (Cytosine-5-)-Methyltransferases / antagonists & inhibitors
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DNA Methylation / drug effects
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Enzyme Inhibitors / pharmacology
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Female
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Gene Expression Regulation, Neoplastic* / drug effects
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Humans
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Neoplasm Proteins / biosynthesis
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Neoplasm Proteins / deficiency
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Neoplasm Proteins / genetics*
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Neoplasm Proteins / physiology*
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Promoter Regions, Genetic / genetics*
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Protein Serine-Threonine Kinases / biosynthesis
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Protein Serine-Threonine Kinases / genetics*
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Receptor, Transforming Growth Factor-beta Type I
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Receptor, Transforming Growth Factor-beta Type II
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Receptors, Transforming Growth Factor beta / biosynthesis
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Receptors, Transforming Growth Factor beta / genetics*
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Recombinant Fusion Proteins / physiology
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Sp1 Transcription Factor / deficiency*
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Sp1 Transcription Factor / physiology
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Transcriptional Activation
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Transfection
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Tumor Cells, Cultured / drug effects
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Tumor Cells, Cultured / metabolism
Substances
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Antimetabolites, Antineoplastic
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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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Enzyme Inhibitors
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Neoplasm Proteins
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Receptors, Transforming Growth Factor beta
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Recombinant Fusion Proteins
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Sp1 Transcription Factor
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DNA (Cytosine-5-)-Methyltransferases
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Protein Serine-Threonine Kinases
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Activin Receptors, Type I
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Receptor, Transforming Growth Factor-beta Type I
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Receptor, Transforming Growth Factor-beta Type II
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Azacitidine