title: Peroxisome proliferator-activated receptor alpha (PPARalpha) and agonist inhibit cholesterol 7alpha-hydroxylase gene (CYP7A1) transcription.
abstract: 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 HNF-4 for binding to the DR-1 sequence and therefore attenuates the transactivation of CYP7A1 by HNF-4.
authors.affiliation: Department of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, P.O. Box 95, Rootstown, OH 44272-0095, USA.
authors.forename: M
authors.initials: M
authors.lastname: Marrapodi
authors.forename: J Y
authors.initials: JY
authors.lastname: Chiang
mesh_terms: D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001665:Binding Sites; D002790:Cholesterol 7-alpha-Hydroxylase / Q000096:biosynthesis / Q000235:genetics*; D002995:Clofibric Acid / Q000494:pharmacology; D004268:DNA-Binding Proteins; D015971:Gene Expression Regulation, Enzymologic; D017930:Genes, Reporter; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D008099:Liver / Q000378:metabolism; D008957:Models, Genetic; D020025:Peroxisome Proliferators / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011743:Pyrimidines / Q000494:pharmacology; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists*; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D012045:Regulatory Sequences, Nucleic Acid; D020218:Response Elements; D047488:Retinoid X Receptors; D013045:Species Specificity; D014157:Transcription Factors / Q000819:agonists* / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D000924:Anticholesteremic Agents; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D051557:Hepatocyte Nuclear Factor 4; C403128:MLX protein, human; D020025:Peroxisome Proliferators; D010750:Phosphoproteins; D011743:Pyrimidines; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D014157:Transcription Factors; D002995:Clofibric Acid; C006253:pirinixic acid; D002790:Cholesterol 7-alpha-Hydroxylase