CCAAT/enhancer-binding protein alpha activation of the rat growth hormone promoter in pituitary progenitor GHFT1-5 cells.
High level, anterior pituitary-specific expression of the rat growth hormone (rGH) promoter requires cooperative actions of several different transcription factors. Previously, we described a series of multisubunit, tissue-general, transcription factor complexes that bound to the GHF3 activation site and strongly regulated rGH promoter activity. A 43-kDa DNA-binding subunit common to each of the different GHF3 complexes is identified here as the transcription factor, CCAAT/Enhancer-binding Protein alpha (C/EBPalpha). In human monocyte U937 cells, which do not express the endogenous or transfected GH genes, co-expression of C/EBPalpha and Pit-1 synergistically activated the transfected rGH promoter. Full-length C/EBPalpha was present in the GH-secreting GC, and prolactin-secreting 235-1, pituitary cell lines, but not in GHFT1-5 cells, which are transformed at a stage in development immediately prior to GH expression. Transient expression of C/EBPalpha in GHFT1-5 cells strongly activated the co-transfected rGH promoter through the GHF3 binding site; a second activation site mapped to evolutionary conserved GH promoter sequences between -106 and -33. C/EBPalpha activation was synergistic with phorbol 12-myristate 13-acetate and forskolin, activators of protein kinases C and A, respectively. Thus, C/EBPalpha is an important regulator of rGH promoter activity that appears to function in synergy with Pit-1, activators of A and C protein kinases and possibly other factors.
Schaufele
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Metabolic Research Unit, University of California, San Francisco, California 94143-0540, USA.
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D022762:CCAAT-Enhancer-Binding Proteins; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D013006:Growth Hormone / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000302:isolation & purification / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051381:Rats; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D009838:Oligodeoxyribonucleotides; D005576:Colforsin; D013006:Growth Hormone; D013755:Tetradecanoylphorbol Acetate