On the mechanism of bile acid inhibition of rat sterol 12alpha-hydroxylase gene (CYP8B1) transcription: roles of alpha-fetoprotein transcription factor and hepatocyte nuclear factor 4alpha.
Animals; Rats; Gene Expression Regulation; Base Sequence; Cattle; Cytochrome P-450 Enzyme System/*genetics; Hepatocyte Nuclear Factor 4; *DNA-Binding Proteins; Bile Acids and Salts/*pharmacology; Steroid Hydroxylases/*genetics; alpha-Fetoproteins/genetics/*physiology; DNA; Phosphoproteins/genetics/*physiology; Steroid 12-alpha-Hydroxylase; Transcription Factors/genetics/*physiology; Sprague-Dawley; RNA; Transcription; Genetic; Promoter Regions; Messenger/genetics; Enzymologic/*drug effects/physiology; Genetic/*drug effects
The sterol 12alpha-hydroxylase (CYP8B1) is a key enzyme of the bile acid biosynthetic pathway. It regulates the composition of bile acids in bile, i.e. ratio between cholic acid (CA) and chenodeoxycholic acid (CDCA). In similarity with cholesterol 7alpha-hydroxylase (CYP7A1), this enzyme is subjected to a negative feedback regulation by bile acids. It has been recently reported that bile acid-activated farnesoid X receptor (FXR) induces the small heterodimer partner (SHP) that interacts with alpha-fetoprotein transcription factor (FTF) and down-regulates CYP7A1 transcription. We studied whether the same mechanism also regulated rat CYP8B1 gene transcription. Feeding rats with CDCA caused a
Yang Yizeng; Zhang Ming; Eggertsen Gosta; Chiang John Y L
Biochimica et biophysica acta
2002
2002-06
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Peroxisome proliferator-activated receptor alpha (PPARalpha) and agonist inhibit cholesterol 7alpha-hydroxylase gene (CYP7A1) transcription.
Humans; Animals; Binding Sites; Protein Binding; Rats; Gene Expression Regulation; Species Specificity; Liver/metabolism; Transcriptional Activation; Hepatocyte Nuclear Factor 4; Response Elements; *DNA-Binding Proteins; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Retinoid X Receptors; Anticholesteremic Agents/pharmacology; Cholesterol 7-alpha-Hydroxylase/biosynthesis/*genetics; Clofibric Acid/pharmacology; Peroxisome Proliferators/pharmacology; Phosphoproteins/metabolism; Pyrimidines/pharmacology; Transcription Factors/*agonists/metabolism; Genes; Receptors; Models; Transcription; Genetic; Enzymologic; Reporter; Retinoic Acid/metabolism; Promoter Regions; Nucleic Acid; Cytoplasmic and Nuclear/*agonists; *Regulatory Sequences
Fibrates are widely used hypolipidemic drugs that regulate the expression of many genes involved in lipid metabolism by activating the peroxisome proliferator-activated receptor alpha (PPARalpha). The objective of this study was to investigate the mechanism of action of peroxisome proliferators and PPARalpha on the transcription of cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the conversion of cholesterol to bile acids in the liver. When cotransfected with the expression vectors for PPARalpha and RXRalpha, Wy14,643 reduced human and rat cholesterol 7alpha-hydroxylase gene (CYP7A1)/luciferase reporter activities by 88% and 43%, respectively, in HepG2 cells, but not in CV-1 or CHO cells. We have mapped the peroxisome proliferator response element (PPRE) to a conserved sequence containing the canonical AGGTCA direct repeats separated by one nucleotide (DR1). This DR1 sequence was mapped previously as a binding site for the hepatocyte nuclear factor 4 (HNF-4) which stimulates CYP7A1 transcription. Electrophoretic mobility shift assay (EMSA) showed no direct binding of in vitro synthesized PPARalpha/RXRalpha heterodimer to the DR1 sequence. PPARalpha and Wy14,643 did not affect HNF-4 binding to the DR1. However, Wy14,643 and PPARalpha/RXRalpha significantly reduced HNF-4 expression in HepG2 cells. These results suggest that PPARalpha and agonist repress cholesterol 7alpha-hydroxylase activity by reducing the availability of
Marrapodi M; Chiang J Y
Journal of lipid research
2000
2000-04
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Regulation of human sterol 27-hydroxylase gene (CYP27A1) by bile acids and hepatocyte nuclear factor 4alpha (HNF4alpha).
Humans; Cell Line; Transfection; Gene Expression Regulation/drug effects; Base Sequence; Binding Sites/genetics; Response Elements/genetics; Molecular Sequence Data; Mutation; Chenodeoxycholic Acid/pharmacology; Transcription Factors/genetics/*metabolism; Hepatocyte Nuclear Factor 4; Mutagenesis; *DNA-Binding Proteins; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Bile Acids and Salts/*pharmacology; Cholestanetriol 26-Monooxygenase; DNA/chemistry/genetics; Luciferases/genetics/metabolism; Phosphoproteins/genetics/*metabolism; Recombinant Fusion Proteins/genetics/metabolism; Steroid Hydroxylases/*genetics; DNA; Dose-Response Relationship; Drug; Cultured; Receptors; Tumor Cells; Cloning; Molecular; Sequence Analysis; Promoter Regions; Genetic/*genetics; Cytoplasmic and Nuclear/genetics/metabolism; Site-Directed
Mitochondrial sterol 27-hydroxylase (CYP27A1) catalyses sterol side-chain oxidation of bile acid synthesis from cholesterol, and the first reaction of the acidic bile acid biosynthetic pathway. Hydrophobic bile acids suppress human CYP27A1 gene reporter activity when assayed in human hepatocellular blastoma HepG2 cells. Bile acids also inhibit CYP27A1 reporter activity in human embryonic kidney 293 cells. A putative bile acid response element (BARE) was mapped to a region downstream of nt -147 of the human CYP27A1 gene, within which a binding site for a liver-specific nuclear receptor, HNF4alpha, is identified. HNF4alpha strongly stimulates CYP27A1 gene transcription and mutation of its binding site markedly reduced promoter activity. Results suggest that human CYP27A1 gene transcription is suppressed by bile acids and HNF4alpha plays a pivotal role in transcriptional regulation of this gene.
Chen Wenling; Chiang John Y L
Gene
2003
2003-08
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
Transcriptional regulation of the human sterol 12alpha-hydroxylase gene (CYP8B1): roles of heaptocyte nuclear factor 4alpha in mediating bile acid repression.
*DNA-Binding Proteins; *Transcription; Base Sequence; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; Bile Acids and Salts/*pharmacology; Binding Sites; Cholesterol 7-alpha-Hydroxylase/genetics; Cultured; Cytochrome P-450 Enzyme System/*genetics; Cytoplasmic and Nuclear/physiology; Genetic; Genetic/physiology; Hepatocyte Nuclear Factor 4; Humans; Molecular Sequence Data; Phosphoproteins/*physiology; Promoter Regions; Receptors; Repressor Proteins/*pharmacology; Steroid 12-alpha-Hydroxylase; Steroid Hydroxylases/*genetics; Transcription Factors/*physiology; Tumor Cells
Sterol 12alpha-hydroxylase catalyzes the synthesis of cholic acid and controls the ratio of cholic acid over chenodeoxycholic acid in the bile. Transcription of CYP8B1 is inhibited by bile acids, cholesterol, and insulin. To study the mechanism of CYP8B1 transcription by bile acids, we have cloned and determined 3389 base pairs of the 5'-upstream nucleotide sequences of the human CYP8B1. Deletion analysis of CYP8B1/luciferase reporter activity in HepG2 cells revealed that the sequences from -57 to +300 were important for basal and liver-specific promoter activities. Hepatocyte nuclear factor 4alpha (HNF4alpha) strongly activated human CYP8B1 promoter activities, whereas cholesterol 7alpha-hydroxylase promoter factor (CPF), an NR5A2 family of nuclear receptors, had much less effect. Electrophoretic mobility shift assay identified an overlapping HNF4alpha- and CPF-binding site in the +198/+227 region. The human CYP8B1 promoter activities were strongly repressed by bile acids, and the bile acid response element was localized between +137 and +220. Site-directed mutagenesis of the HNF4alpha-binding site markedly reduced promoter activity and its response to bile acid repression. On the other hand, mutation of the
Zhang M; Chiang J Y
The Journal of biological chemistry
2001
2001-11
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).
<a href="http://doi.org/10.1074/jbc.M105117200" target="_blank" rel="noreferrer noopener">10.1074/jbc.M105117200</a>