title: Mechanisms of cholesterol and sterol regulatory element binding protein regulation of the sterol 12alpha-hydroxylase gene (CYP8B1).
abstract: Sterol 12alpha-hydroxylase (CYP8B1) is an obligatory enzyme for the synthesis of cholic acid and regulation of liver bile acid synthesis and intestine cholesterol absorption. The present study evaluates the roles for sterol regulatory element binding proteins (SREBPs) in the regulation of the CYP8B1 gene. Cholesterol feeding of mice and rats decreased the activity of CYP8B1, contrary to the up-regulation of cholesterol 7alpha-hydroxylase (CYP7A1). Cholesterol feeding also reduced mRNA levels for SREBP-1 but not for SREBP-2 in rat livers. Cholesterol and 25-hydroxycholesterol decreased the CYP8B1/luciferase reporter activity. Co-transfection of SREBP-1a and -1c stimulated CYP8B1 promoter activity, while SREBP-2 did not have any effects. Electrophoretic mobility shift assay and mutagenesis analyses identified several functional sterol regulatory elements (SRE) and E-box motifs in the rat CYP8B1 promoter. Our results indicate that SREBP-1a and -1c enhance transcription of the CYP8B1 gene through binding to SRE. Cholesterol loading reduces SREBP-1 mRNA expression in addition to reducing functional SREBP-1 protein, and results in decreasing CYP8B1 gene transcription.
authors.affiliation: Division of Clinical Chemistry, Karolinska Institute at Huddinge University Hospital, Huddinge S-141 86, Sweden.
authors.forename: Yizeng
authors.initials: Y
authors.lastname: Yang
authors.forename: Gösta
authors.initials: G
authors.lastname: Eggertsen
authors.forename: Mats
authors.initials: M
authors.lastname: Gåfvels
authors.forename: Ulla
authors.initials: U
authors.lastname: Andersson
authors.forename: Curt
authors.initials: C
authors.lastname: Einarsson
authors.forename: Ingemar
authors.initials: I
authors.lastname: Björkhem
authors.forename: John Y L
authors.initials: JY
authors.lastname: Chiang
mesh_terms: D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism*; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006801:Humans; D066298:In Vitro Techniques; D007668:Kidney / Q000196:embryology / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity; D013253:Steroid 12-alpha-Hydroxylase / Q000378:metabolism*; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D013261:Sterols / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; C497387:SREBF1 protein, human; C497390:SREBF2 protein, human; C497389:Srebf1 protein, rat; D051780:Sterol Regulatory Element Binding Protein 1; D051782:Sterol Regulatory Element Binding Protein 2; D013261:Sterols; D014157:Transcription Factors; D002784:Cholesterol; D013253:Steroid 12-alpha-Hydroxylase