Glucocorticoid receptor-mediated upregulation of human CYP27A1, a potential anti-atherogenic enzyme.
Sterol 27-hydroxylase (CYP27A1) is required for the hepatic conversion of cholesterol into bile acids and for production of 27-hydroxycholesterol which affects cholesterol homeostasis in several ways. Dexamethasone increases hepatic bile acid biosynthesis and CYP27A1-mediated enzyme activity in HepG2 cells. This study examines the mechanism of the dexamethasone-induced effect on the human CYP27A1 promoter. Dexamethasone treatment of HepG2 cells overexpressed with glucocorticoid receptor alpha (GRalpha) increased the CYP27A1 promoter activity more than four-fold as compared with untreated cells. The GR-antagonist mifepristone almost completely abolished the dexamethasone-induced effect on the promoter activity. Progressive deletion analysis of the CYP27A1 promoter indicated that sequences involved in GR-mediated induction by dexamethasone are present in a region between -1094 and -792. Several putative GRE sites could be found in this region and EMSA experiments revealed that two of these could bind GR. Site-directed mutagenesis of GR-binding sequences in the CYP27A1 promoter identified a GRE at -824/-819 important for GR-mediated regulation of the transcriptional activity. Endogenous and pharmacological glucocorticoids may have a strong impact on several aspects of cholesterol homeostasis and other processes related to CYP27A1-mediated metabolism. The glucocorticoid-mediated induction of human CYP27A1 transcription is of particular interest due to the anti-atherogenic properties ascribed to this enzyme.
Tang
Wanjin
W
Department of Pharmaceutical Biosciences, Division of Biochemistry, Box 578, University of Uppsala, SE-751 23 Uppsala, Sweden.
Norlin
Maria
M
Wikvall
Kjell
K
D001483:Base Sequence; D053493:Cholestanetriol 26-Monooxygenase / Q000235:genetics / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology*; D024202:Electrophoretic Mobility Shift Assay; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D005938:Glucocorticoids / Q000494:pharmacology*; D006801:Humans; D008156:Luciferases / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011401:Promoter Regions, Genetic / Q000235:genetics; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D014158:Transcription, Genetic; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000187:drug effects / Q000378:metabolism; D015854:Up-Regulation
D005938:Glucocorticoids; D011965:Receptors, Glucocorticoid; C411470:glucocorticoid receptor alpha; D003907:Dexamethasone; D008156:Luciferases; C506831:CYP27A1 protein, human; D053493:Cholestanetriol 26-Monooxygenase