Farnesoid X receptor responds to bile acids and represses cholesterol 7 alpha-hydroxylase gene (CYP7A1) transcription

Farnesoid X receptor responds to bile acids and represses cholesterol 7 alpha-hydroxylase gene (CYP7A1) transcription

Chiang J Y L; Kimmel R; Weinberger C; Stroup D

Journal of Biological Chemistry

2000

2000-04

Cholesterol 7 alpha-hydroxylase gene (CYP7A1) transcription is repressed by bile acids. The goal of this study is to elucidate the mechanism of CYP7A1 transcription by bile acid-activated farnesoid X receptor (FXR) in its native promoter and cellular context and to identify FXR response elements in the gene. In Chinese hamster ovary cells transfected with retinoid X receptor alpha (RXR alpha)/FXR, only chenodeoxycholic acid (CDCA) and deoxycholic acid (DCA) were able to stimulate a heterologous promoter/reporter containing an ecdysone response element. In HepG2 cells, all bile acids (25 mu M) were able to repress CYP7A1/luciferase reporter activity, and only CDCA and DCA further repressed reporter activity when cotransfected with RXR alpha/FXR, The concentration of CDCA required to inhibit 50% of reporter activity (IC(50)) was determined to be approximately 25 mu M without FXR and 10 mu M with FXR. Deletion analysis revealed that the bile acid response element located between nucleotides -148 and -128 was the FXR response element, but RXR alpha/FXR did not bind to this sequence. These results suggest that bile acid-activated FXR exerts its inhibitory effect on CYP7A1 transcription by an indirect mechanism, in contrast to the stimulation and binding of FXR to intestinal bile acid-binding protein gene promoter. Results also reveal that bile acid receptors other than FXR are present in HepG2 cells.

orphan nuclear receptor; Biochemistry & Molecular Biology; expression; pathway; activation; identification; promoter; element; metabolites; hepg2 cells; ligands

Journal Article or Conference Abstract Publication

Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).

10918-10924

15

275