CCAAT/enhancer-binding protein alpha activation of the rat growth hormone promoter in pituitary progenitor GHFT1-5 cells

• Published in: The Journal of biological chemistry 1996-08, Vol.271 (35), p.21484-21489
• Main Author: Schaufele, F
• Format: Article
• Language: English
• Subjects: Animals; Base Sequence; Binding Sites; CCAAT-Enhancer-Binding Proteins; Cell Line; Colforsin - pharmacology; DNA-Binding Proteins - isolation & purification; DNA-Binding Proteins - metabolism; Growth Hormone - genetics; Humans; Molecular Sequence Data; Nuclear Proteins - isolation & purification; Nuclear Proteins - metabolism; Oligodeoxyribonucleotides; Pituitary Gland - cytology; Pituitary Gland - drug effects; Pituitary Gland - metabolism; Promoter Regions, Genetic; Protein Binding; Rats; Stem Cells - cytology; Stem Cells - drug effects; Stem Cells - metabolism; Tetradecanoylphorbol Acetate - pharmacology
• ISSN: 0021-9258
• DOI: 10.1074/jbc.271.35.21484

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.