Abstract
Transcription factors play important roles in regulating cell growth and differentiation. In this study, treatment of the MTC cell line, TT, with phorbol 12-myristate 13-acetate (PMA) was shown to reduce neurite outgrowth which may be associated with de-differentiation and loss of the transformed phenotype. Northern blotting revealed that PMA transiently induced early growth response gene 1 (Egr-1) expression and decreased RET expression. Transient transfection analyses using 5'-deletion constructs of the basal RET promoter, demonstrated the requirement of a region between -70 and -33 bp for PMA-inducible expression. Gel shift and supershift studies demonstrated that PMA induced Egr-1 formed part of a complex capable of binding to the RET minimal promoter. Overexpression of Egr-1 displaced both sephacryl and phosphocellulose protein 1 (Sp1) and Sp3 from a GC-box element previously found to be important for RET basal expression. Furthermore, use of a raf-1 inducible TT cell line, that has been previously shown to downregulate RET expression, revealed that this downregulation may be linked to the induction of Egr-1. Our data suggest that regulation of RET expression during development and in medullary thyroid carcinoma may be determined, at least in part, by this complex of Sp and Egr-1 proteins.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Cell Size / drug effects
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DNA-Binding Proteins / genetics
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Down-Regulation / drug effects
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Down-Regulation / genetics
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Drosophila Proteins*
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Early Growth Response Protein 1
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Electrophoretic Mobility Shift Assay
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Flavonoids / pharmacology
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Gene Expression Regulation / drug effects
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Humans
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Immediate-Early Proteins*
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Luciferases / genetics
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Luciferases / metabolism
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MAP Kinase Signaling System / drug effects
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MAP Kinase Signaling System / physiology*
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Nuclear Proteins / metabolism
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Oligonucleotides / genetics
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Oligonucleotides / metabolism
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Promoter Regions, Genetic / genetics
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Protein Binding / drug effects
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Proto-Oncogene Mas
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Proto-Oncogene Proteins / genetics*
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Proto-Oncogene Proteins c-ret
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Receptor Protein-Tyrosine Kinases / genetics*
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Response Elements / drug effects
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Response Elements / genetics
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Tetradecanoylphorbol Acetate / pharmacology
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Transcription Factors / genetics
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Transcription, Genetic / drug effects
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Tumor Cells, Cultured
Substances
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DNA-Binding Proteins
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Drosophila Proteins
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EGR1 protein, human
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Early Growth Response Protein 1
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Flavonoids
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Immediate-Early Proteins
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MAS1 protein, human
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Nuclear Proteins
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Oligonucleotides
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Proto-Oncogene Mas
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Proto-Oncogene Proteins
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Recombinant Fusion Proteins
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Transcription Factors
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Luciferases
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Proto-Oncogene Proteins c-ret
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Receptor Protein-Tyrosine Kinases
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Ret protein, Drosophila
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Tetradecanoylphorbol Acetate
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2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one