Activation of FXR by obeticholic acid induces hepatic gene expression of SR-BI through a novel mechanism of transcriptional synergy with the nuclear receptor LXR

Bin Dong, Amar B. Singh, Grace Guo, Mark Young, Jingwen Liu

Research output: Contribution to journalArticle

Abstract

The farnesoid X receptor (FXR) is known to regulate the gene expression of SR-BI, which mediates plasma high-density lipoprotein (HDL)-cholesterol uptake. Our previous study demonstrated that the activation of FXR by obeticholic acid (OCA) lowered plasma HDL-cholesterol levels and increased the hepatic mRNA and protein expression levels of SR-BI in hypercholesterolemic hamsters, but not in normolipidemic hamsters, suggesting that dietary cholesterol may be involved in the OCA-induced transcription of SR-BI. In the present study, a functional 90-base-pair regulatory region was identified in the first intron of the SR‑BI gene of hamster and mouse that contains a FXR response element (IR-1) and an adjacent liver X receptor (LXR) response element (LXRE). By in vitro DNA binding and luciferase reporter gene assays, it was demonstrated that FXR and LXR bind to their recognition sequences within this intronic region and transactivate the SR-BI reporter gene in a synergistic manner. It was also shown that mutations at either the IR-1 site or the LXRE site eliminated OCA-mediated gene transcription. Utilizing chow-fed hamsters as an in vivo model, it was demonstrated that treating normolipidemic hamsters with OCA or GW3965 alone did not effectively induce levels of SR-BI, whereas their combined treatment significantly increased the mRNA and protein levels of SR-BI in the liver. The study further investigated effects of FXR and LXR coactivation on the gene expression of SR-BI in human liver cells. The intronic FXRE and LXRE regulatory region was not conserved in the human SR-BI genomic sequence, however, higher mRNA expression levels of SR-BI were observed in human primary hepatocytes and HepG2 cells exposed to combined treatments of FXR and LXR agonists, compared with those in cells exposed to individual ligand treatment. Therefore, these results suggest that human SR-BI gene transcription may also be subject to concerted activation by FXR and LXR, mediated via currently unidentified regulatory sequences.

Original languageEnglish (US)
Pages (from-to)1927-1938
Number of pages12
JournalInternational journal of molecular medicine
Volume43
Issue number5
DOIs
StatePublished - May 1 2019

Fingerprint

Cytoplasmic and Nuclear Receptors
Cricetinae
Response Elements
Gene Expression
Liver
Nucleic Acid Regulatory Sequences
Reporter Genes
Messenger RNA
HDL Cholesterol
CD36 Antigens
Genes
Dietary Cholesterol
Hep G2 Cells
Luciferases
Base Pairing
Introns
Hepatocytes
Liver X Receptors
6-ethylchenodeoxycholic acid
Ligands

All Science Journal Classification (ASJC) codes

  • Genetics

Keywords

  • Farnesoid X receptor
  • Liver X receptor
  • Obeticholic acid
  • SR-BI
  • Transcriptional synergy

Cite this

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title = "Activation of FXR by obeticholic acid induces hepatic gene expression of SR-BI through a novel mechanism of transcriptional synergy with the nuclear receptor LXR",
abstract = "The farnesoid X receptor (FXR) is known to regulate the gene expression of SR-BI, which mediates plasma high-density lipoprotein (HDL)-cholesterol uptake. Our previous study demonstrated that the activation of FXR by obeticholic acid (OCA) lowered plasma HDL-cholesterol levels and increased the hepatic mRNA and protein expression levels of SR-BI in hypercholesterolemic hamsters, but not in normolipidemic hamsters, suggesting that dietary cholesterol may be involved in the OCA-induced transcription of SR-BI. In the present study, a functional 90-base-pair regulatory region was identified in the first intron of the SR‑BI gene of hamster and mouse that contains a FXR response element (IR-1) and an adjacent liver X receptor (LXR) response element (LXRE). By in vitro DNA binding and luciferase reporter gene assays, it was demonstrated that FXR and LXR bind to their recognition sequences within this intronic region and transactivate the SR-BI reporter gene in a synergistic manner. It was also shown that mutations at either the IR-1 site or the LXRE site eliminated OCA-mediated gene transcription. Utilizing chow-fed hamsters as an in vivo model, it was demonstrated that treating normolipidemic hamsters with OCA or GW3965 alone did not effectively induce levels of SR-BI, whereas their combined treatment significantly increased the mRNA and protein levels of SR-BI in the liver. The study further investigated effects of FXR and LXR coactivation on the gene expression of SR-BI in human liver cells. The intronic FXRE and LXRE regulatory region was not conserved in the human SR-BI genomic sequence, however, higher mRNA expression levels of SR-BI were observed in human primary hepatocytes and HepG2 cells exposed to combined treatments of FXR and LXR agonists, compared with those in cells exposed to individual ligand treatment. Therefore, these results suggest that human SR-BI gene transcription may also be subject to concerted activation by FXR and LXR, mediated via currently unidentified regulatory sequences.",
keywords = "Farnesoid X receptor, Liver X receptor, Obeticholic acid, SR-BI, Transcriptional synergy",
author = "Bin Dong and Singh, {Amar B.} and Grace Guo and Mark Young and Jingwen Liu",
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Activation of FXR by obeticholic acid induces hepatic gene expression of SR-BI through a novel mechanism of transcriptional synergy with the nuclear receptor LXR. / Dong, Bin; Singh, Amar B.; Guo, Grace; Young, Mark; Liu, Jingwen.

In: International journal of molecular medicine, Vol. 43, No. 5, 01.05.2019, p. 1927-1938.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Activation of FXR by obeticholic acid induces hepatic gene expression of SR-BI through a novel mechanism of transcriptional synergy with the nuclear receptor LXR

AU - Dong, Bin

AU - Singh, Amar B.

AU - Guo, Grace

AU - Young, Mark

AU - Liu, Jingwen

PY - 2019/5/1

Y1 - 2019/5/1

N2 - The farnesoid X receptor (FXR) is known to regulate the gene expression of SR-BI, which mediates plasma high-density lipoprotein (HDL)-cholesterol uptake. Our previous study demonstrated that the activation of FXR by obeticholic acid (OCA) lowered plasma HDL-cholesterol levels and increased the hepatic mRNA and protein expression levels of SR-BI in hypercholesterolemic hamsters, but not in normolipidemic hamsters, suggesting that dietary cholesterol may be involved in the OCA-induced transcription of SR-BI. In the present study, a functional 90-base-pair regulatory region was identified in the first intron of the SR‑BI gene of hamster and mouse that contains a FXR response element (IR-1) and an adjacent liver X receptor (LXR) response element (LXRE). By in vitro DNA binding and luciferase reporter gene assays, it was demonstrated that FXR and LXR bind to their recognition sequences within this intronic region and transactivate the SR-BI reporter gene in a synergistic manner. It was also shown that mutations at either the IR-1 site or the LXRE site eliminated OCA-mediated gene transcription. Utilizing chow-fed hamsters as an in vivo model, it was demonstrated that treating normolipidemic hamsters with OCA or GW3965 alone did not effectively induce levels of SR-BI, whereas their combined treatment significantly increased the mRNA and protein levels of SR-BI in the liver. The study further investigated effects of FXR and LXR coactivation on the gene expression of SR-BI in human liver cells. The intronic FXRE and LXRE regulatory region was not conserved in the human SR-BI genomic sequence, however, higher mRNA expression levels of SR-BI were observed in human primary hepatocytes and HepG2 cells exposed to combined treatments of FXR and LXR agonists, compared with those in cells exposed to individual ligand treatment. Therefore, these results suggest that human SR-BI gene transcription may also be subject to concerted activation by FXR and LXR, mediated via currently unidentified regulatory sequences.

AB - The farnesoid X receptor (FXR) is known to regulate the gene expression of SR-BI, which mediates plasma high-density lipoprotein (HDL)-cholesterol uptake. Our previous study demonstrated that the activation of FXR by obeticholic acid (OCA) lowered plasma HDL-cholesterol levels and increased the hepatic mRNA and protein expression levels of SR-BI in hypercholesterolemic hamsters, but not in normolipidemic hamsters, suggesting that dietary cholesterol may be involved in the OCA-induced transcription of SR-BI. In the present study, a functional 90-base-pair regulatory region was identified in the first intron of the SR‑BI gene of hamster and mouse that contains a FXR response element (IR-1) and an adjacent liver X receptor (LXR) response element (LXRE). By in vitro DNA binding and luciferase reporter gene assays, it was demonstrated that FXR and LXR bind to their recognition sequences within this intronic region and transactivate the SR-BI reporter gene in a synergistic manner. It was also shown that mutations at either the IR-1 site or the LXRE site eliminated OCA-mediated gene transcription. Utilizing chow-fed hamsters as an in vivo model, it was demonstrated that treating normolipidemic hamsters with OCA or GW3965 alone did not effectively induce levels of SR-BI, whereas their combined treatment significantly increased the mRNA and protein levels of SR-BI in the liver. The study further investigated effects of FXR and LXR coactivation on the gene expression of SR-BI in human liver cells. The intronic FXRE and LXRE regulatory region was not conserved in the human SR-BI genomic sequence, however, higher mRNA expression levels of SR-BI were observed in human primary hepatocytes and HepG2 cells exposed to combined treatments of FXR and LXR agonists, compared with those in cells exposed to individual ligand treatment. Therefore, these results suggest that human SR-BI gene transcription may also be subject to concerted activation by FXR and LXR, mediated via currently unidentified regulatory sequences.

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KW - Liver X receptor

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KW - SR-BI

KW - Transcriptional synergy

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