Bile acids and FXR represses cholesterol 7A-hydroxylase (CYP7A1), sterol 12A-hydroxylase (CYP8B1) and sterol 27-hydroxylase (CYP27A1), but not oxysterol 7A-hydroxylase (CYP7B1) gene transcription
Gastroenterology & Hepatology
Chiang J Y; Chen W; Zheng M; Wu Z; Kimmel R; Stroup D
Gastroenterology
2000
2000-04
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1016/s0016-5085(00)86175-2" target="_blank" rel="noreferrer noopener">10.1016/s0016-5085(00)86175-2</a>
Farnesoid X receptor (FXR) is a bile acid receptor that mediates transcriptional regulation of the cholesterol 7 alpha-hydroxylase gene (CYP7A1) by bile acids
Gastroenterology & Hepatology
Chiang J Y; Kimmel R; Weinberger C; Stroup D
Hepatology
1999
1999-10
Journal Article or Conference Abstract Publication
n/a
Farnesoid X receptor responds to bile acids and represses cholesterol 7 alpha-hydroxylase gene (CYP7A1) transcription
orphan nuclear receptor; Biochemistry & Molecular Biology; expression; pathway; activation; identification; promoter; element; metabolites; hepg2 cells; ligands
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.
Chiang J Y L; Kimmel R; Weinberger C; Stroup D
Journal of Biological Chemistry
2000
2000-04
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1074/jbc.275.15.10918" target="_blank" rel="noreferrer noopener">10.1074/jbc.275.15.10918</a>
Farnesoid X receptor responds to bile acids and represses cholesterol 7alpha-hydroxylase gene (CYP7A1) transcription.
Humans; Animals; Cricetinae; Cholesterol 7-alpha-Hydroxylase/*genetics; Response Elements; Bile Acids and Salts/*pharmacology; Transcription Factors/genetics/*physiology; Retinoid X Receptors; DNA-Binding Proteins/*physiology; Repressor Proteins/*physiology; Cultured; Receptors; Genetic; Tumor Cells; Promoter Regions; *Transcription; Cytoplasmic and Nuclear; Retinoic Acid/genetics
Cholesterol 7alpha-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 (RXRalpha)/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 microM) were able to repress CYP7A1/luciferase reporter activity, and only CDCA and DCA further repressed reporter activity when cotransfected with RXRalpha/FXR. The concentration of CDCA required to inhibit 50% of reporter activity (IC(50)) was determined to be approximately 25 microM without FXR and 10 microM with FXR. Deletion analysis revealed that the bile acid response element located between nucleotides -148 and -128 was the FXR response element, but RXRalpha/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.
Chiang J Y; Kimmel R; Weinberger C; Stroup D
The Journal of biological chemistry
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 cholesterol 7 alpha-hydroxylase gene (CYP7A1) transcription by the liver orphan receptor (LXR alpha)
bile acid synthesis; expression; Signaling; dietary-cholesterol; Bile acids; pathway; nuclear receptor; nuclear receptors; promoter; Genetics & Heredity; x-receptor; cytochrome P450; gene regulation; reverse cholesterol transport; hepg2 cells; coup-tfii; ligands
The cholesterol 7 alpha -hydroxylase gene (CYP7A1) plays an important role in regulation of bile acid biosynthesis and cholesterol homeostasis. Oxysterol receptor, LXR, stimulates, whereas the bile acid receptor, FXR, inhibits CYP7A1 transcription. The goal of this study was to investigate the role of LXR alpha on the regulation of rat, human and hamster CYP7A1 transcription in its native promoter and cellular context. Cotransfection with LXR alpha and RXR alpha expression plasmids strongly stimulated rat CYP7A1/luciferase reporter activity in HepG2 cells and oxysterol was not required. However, LXR alpha had much less effect on hamster and no significant effect on human CYP7A1 promoter activity in HepG2 cells. In Chinese hamster ovary cells, cotransfection with LXR alpha stimulated reporter activity by less than 2-fold and addition of 22(R)-hydroxycholesterol caused a small but significant stimulation of rat, human and hamster CYP7A1 promoter activity. At least two direct repeats of AGGTCA-like sequences with 4-base spacing (DR4) and five-base spacing (DR5), in previously identified bile acid response elements of the rat CYP7A1 were able to bind LXR alpha /RXR alpha and confer LXR alpha stimulation. However, LXR alpha did not bind to the corresponding sequences of the human gene and bound weakly to hamster and mouse DR4 sequences. Therefore, rats and mice have the unusual capacity to convert cholesterol to bile acids by LXR alpha -mediated stimulation of CYP7A1 transcription, whereas other species do not respond to cholesterol and develop hypercholesterolemia on a diet high in cholesterol. (C) 2001 Elsevier Science B.V. All rights reserved.
Chiang J Y L; Kimmel R; Stroup D
Gene
2001
2001-01
Journal Article or Conference Abstract Publication
<a href="http://doi.org/10.1016/s0378-1119(00)00518-7" target="_blank" rel="noreferrer noopener">10.1016/s0378-1119(00)00518-7</a>
Regulation of cholesterol 7alpha-hydroxylase gene (CYP7A1) transcription by the liver orphan receptor (LXRalpha).
Humans; Animals; Binding Sites; Rats; Species Specificity; Transfection; Gene Expression Regulation/drug effects; Organ Specificity; Transcription Factors/genetics/metabolism; Cricetinae; Response Elements; Luciferases/genetics/metabolism; Retinoid X Receptors; Cholesterol 7-alpha-Hydroxylase/drug effects/*genetics/metabolism; Hydroxycholesterols; Liver/physiology; Lovastatin/pharmacology; Mevalonic Acid/metabolism/pharmacology; Nicotinic Acids/pharmacology; Polyisoprenyl Phosphates/pharmacology; Tetrahydronaphthalenes/pharmacology; Cells; Cultured; Receptors; Transcription; Genetic; Retinoic Acid/genetics/metabolism; Steroid/genetics/*metabolism
The cholesterol 7alpha-hydroxylase gene (CYP7A1) plays an important role in regulation of bile acid biosynthesis and cholesterol homeostasis. Oxysterol receptor, LXR, stimulates, whereas the bile acid receptor, FXR, inhibits CYP7A1 transcription. The goal of this study was to investigate the role of LXRalpha on the regulation of rat, human and hamster CYP7A1 transcription in its native promoter and cellular context. Cotransfection with LXRalpha and RXRalpha expression plasmids strongly stimulated rat CYP7A1/luciferase reporter activity in HepG2 cells and oxysterol was not required. However, LXRalpha had much less effect on hamster and no significant effect on human CYP7A1 promoter activity in HepG2 cells. In Chinese hamster ovary cells, cotransfection with LXRalpha stimulated reporter activity by less than 2-fold and addition of 22(R)-hydroxycholesterol caused a small but significant stimulation of rat, human and hamster CYP7A1 promoter activity. At least two direct repeats of AGGTCA-like sequences with 4-base spacing (DR4) and five-base spacing (DR5), in previously identified bile acid response elements of the rat CYP7A1 were able to bind LXRalpha/RXRalpha and confer LXRalpha stimulation. However, LXRalpha did not bind to the corresponding sequences of the human gene and bound weakly to hamster and mouse DR4 sequences. Therefore, rats and mice have the unusual capacity to convert cholesterol to bile acids by LXRalpha-mediated stimulation of CYP7A1 transcription, whereas other species do not respond to cholesterol and develop hypercholesterolemia on a diet high in cholesterol.
Chiang J Y; Kimmel R; Stroup D
Gene
2001
2001-01
Article information provided for research and reference use only. All rights are retained by the journal listed under publisher and/or the creator(s).