title: The synergistic effect of dexamethasone and all-trans-retinoic acid on hepatic phosphoenolpyruvate carboxykinase gene expression involves the coactivator p300.
abstract: Activation of phosphoenolpyruvate carboxykinase (PEPCK) gene transcription in response to all-trans-retinoic acid (RA) or a glucocorticoid such as dexamethasone (Dex) requires a distinct arrangement of DNA-response elements and their cognate transcription activators on the gene promoter. Two of the accessory factor-binding elements involved in the Dex response (gAF1 and gAF3) coincide with the DNA-response elements involved in the RA response. We demonstrate here that the combination of Dex/RA has a synergistic effect on endogenous PEPCK gene expression in rat hepatocytes and H4IIE hepatoma cells. Reporter gene studies show that the gAF3 element and one of the two glucocorticoid receptor-binding elements (GR1) are most important for this effect. Chromatin immunoprecipitation assays revealed that when H4IIE cells were treated with Dex/RA, ligand-activated retinoic acid receptors (retinoic acid receptor/retinoid X receptor) and glucocorticoid receptors are recruited to this gene promoter, as are the transcription coregulators p300, CREB-binding protein, p/CIP, and SRC-1. Notably, the recruitment of p300 and RNA polymerase II to the PEPCK promoter is increased by the combined Dex/RA treatment compared with Dex or RA treatment alone. The functional importance of p300 in the Dex/RA response is illustrated by the observation that selective reduction of this coactivator, but not that of CREB-binding protein, abolishes the synergistic effect in H4IIE cells.
authors.affiliation: Department of Molecular Physiology and Biophysics, Vanderbilt University School of Medicine, Nashville, TN 37232-0615, USA.
authors.forename: Xiaohui L
authors.initials: XL
authors.lastname: Wang
authors.forename: Birger
authors.initials: B
authors.lastname: Herzog
authors.forename: Mary
authors.initials: M
authors.lastname: Waltner-Law
authors.forename: Robert K
authors.initials: RK
authors.lastname: Hall
authors.forename: Masakazu
authors.initials: M
authors.lastname: Shiota
authors.forename: Daryl K
authors.initials: DK
authors.lastname: Granner
mesh_terms: D000818:Animals; D018931:Antineoplastic Agents, Hormonal / Q000008:administration & dosage; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D002843:Chromatin / Q000378:metabolism; D003907:Dexamethasone / Q000008:administration & dosage*; D004357:Drug Synergism; D050881:E1A-Associated p300 Protein; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D005938:Glucocorticoids / Q000008:administration & dosage / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008099:Liver / Q000201:enzymology*; D008113:Liver Neoplasms / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism*; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000096:biosynthesis*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic; D017434:Protein Structure, Tertiary; D012319:RNA Polymerase II / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000378:metabolism*; D014162:Transfection; D014212:Tretinoin / Q000008:administration & dosage* / Q000378:metabolism
chemical_list: D018931:Antineoplastic Agents, Hormonal; D002843:Chromatin; D005938:Glucocorticoids; D008024:Ligands; D009687:Nuclear Proteins; D015534:Trans-Activators; D014212:Tretinoin; D003907:Dexamethasone; D008156:Luciferases; D050881:E1A-Associated p300 Protein; C494362:Ep300 protein, rat; D012319:RNA Polymerase II; D019764:Phosphoenolpyruvate Carboxykinase (ATP)