Abstract
The xenobiotic receptors, constitutive androstane receptor (CAR), and pregnane X receptor (PXR) regulate and alter the metabolism of xenobiotic substrates. Among the 19 functional UDP-glucuronosyltransferases (UGTs) in humans, UGT2B7 is involved in the metabolism of many structurally diverse xenobiotics and plays an important role in the clearance and detoxification of many therapeutic drugs. To examine whether this gene is regulated by CAR and PXR in vivo, transgenic mice expressing the entire UGT2B7 gene (TgUGT2B7) were created. Gene expression profiles revealed that UGT2B7 is differentially expressed in liver, kidney, adipocytes, brain, and estrogen-sensitive tissues, such as ovary and uterus. Liver UGT2B7 expression levels were decreased when TgUGT2B7 mice were treated with the CAR ligand 1,4-b-s-[2-(3,5,-dichloropyridyloxy)] (TCPOBOP) but not the PXR ligand pregnenolone 16α-carbonitrile. Although TCPOBOP decreased the levels of UGT2B7 mRNA in TgUGT2B7 mice, it had no affect on Tg(UGT2B7)Car(−/−) mice, adding support for a CAR-dependent mechanism contributing toward UGT2B7 gene suppression. Expression of promoter constructs in HepG2 cells showed the CAR-dependent inhibition was linked to hepatocyte nuclear factor-4α (HNF4α)-mediated transactivation of the UGT2B7 promoter. The inhibitory effect of CAR on UGT2B7 gene expression was validated in chromatin immunoprecipitation assays in which TCPOBOP treatment blocked HNF4α binding to the UGT2B7 promoter. These results suggest that HNF4α plays an important role in the constitutive expression of hepatic UGT2B7, and CAR acts as a negative regulator by interfering with HNF4α binding activity.
Footnotes
This work was supported by the National Institutes of Health National Institute of Environmental Health Sciences [Grant P42-ES010337]; and the National Institutes of Health National Institute of General Medicine [Grant GM086713].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.070649.
-
ABBREVIATIONS:
- UGT
- UDP-glucuronosyltransferase
- TCPOBOP
- 1,4-b-s-[2-(3,5,-dichloropyridyloxy)]
- CAR
- constitute androstane receptors
- PXR
- pregnane X receptor
- HNF
- hepatocyte nuclear factor
- HDCA
- hyodeoxycholic acid
- XenR
- xenobiotic receptor
- CHIP
- chromatin immunoprecipitation
- FXR
- farnesoid X receptor
- kb
- kilobase(s)
- BAC
- bacterial artificial chromosome
- bp
- base pair(s)
- PCR
- polymerase chain reaction
- qPCR
- quantitative polymerase chain reaction
- DMSO
- dimethyl sulfoxide
- RT-PCR
- reverse-transcription polymerase chain reaction
- PCN
- pregnenolone-16α-carbonitrile
- Tg
- transgenic.
- Received December 16, 2010.
- Accepted March 17, 2011.
- Copyright © 2011 The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|