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. 2002 Oct 15;99(21):13801-6.
doi: 10.1073/pnas.212494599. Epub 2002 Oct 7.

V体育2025版 - Regulation of a xenobiotic sulfonation cascade by nuclear pregnane X receptor (PXR)

Junichiro Sonoda  1 , Wen Xie, John M Rosenfeld, Joyce L Barwick, Philip S Guzelian, Ronald M Evans
Affiliations

Regulation of a xenobiotic sulfonation cascade by nuclear pregnane X receptor (PXR)

Junichiro Sonoda (VSports app下载) et al. Proc Natl Acad Sci U S A. .

Abstract

The nuclear receptor PXR (pregnane X receptor) protects the body from hepatotoxicity of secondary bile acids such as lithocholic acid (LCA) by inducing expression of the hydroxylating cytochrome P450 enzyme CYP3A and promoting detoxification. We found that activation of PXR also increases the activity and gene expression of the phase II conjugating enzyme dehydroepiandrosterone sulfotransferase (STD) known to sulfate LCA to facilitate its elimination VSports手机版. This activation is direct and appears to extend to other xenobiotic sulfotransferases as well as to 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2), an enzyme that generates the donor cofactor for the reaction. Because sulfation plays an important role in the metabolism of many xenobiotics, prescription drugs, and toxins, we propose that PXR serves as a master regulator of the phase I and II responses to facilitate rapid and efficient detoxification and elimination of foreign chemicals. .

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Figures

Figure 1
Figure 1
Activation of PXR induces dehydroepiandrosterone (DHEA) sulfotransferase (STD) activity in rodent livers. (A) Two pathways known to metabolize LCA in the liver. Hydroxylation by CYP3A converts LCA (1) to nontoxic bile acids such as hyodeoxycholic acid or murideoxycholic acid (2), whereas sulfation by STD converts LCA to a less toxic and more water-soluble form (3). (B) Cytosolic liver extracts from transgenic Alb-VP-hPXR male mice or nontransgenic littermates were subjected to enzymatic assays for STD activity on the prototypic substrate DHEA using the cofactor 3′-phosphoadenosine 5′-phospho[35S]sulfate ([35S]PAPS). Shown is the mean ± SD obtained from three pairs of mice. (C) Total liver RNA obtained from transgenic Alb-VP-hPXR mice or nontransgenic littermates of indicated age and sex was subjected to Northern blot analysis using STD and GAPDH (loading control) cDNAs as probes. (D) Northern blot analysis of adult male liver and intestine RNA with ST2B2 cDNA as probe. Note that ST2B2 mRNA is detectable in the intestine, but not in the liver. (E) Total liver RNA from male mice treated with PCN or solvent control was extracted and subjected to Northern blot analysis using STD, OATP2, and GAPDH cDNA as probes. The results show that PCN treatment induces expression of STD mRNA. The film was exposed for 5 times longer than the image shown in C to visualize the relatively lower levels of induction of STD and OATP2 by PCN. OATP2, which encodes Na+-independent organic anion transporter, was previously shown to be a direct target of PXR and thus serves as a positive control for the drug treatment (9). Note that neither STD nor OATP2 is induced by PCN in PXR-null mice. (F) Primary hepatocytes were isolated from rat livers and treated with PCN or solvent control. Total mRNA was isolated and subjected to Northern blot analysis using mouse STD cDNA as a probe.
Figure 2
Figure 2
Regulation of the STD promoter by PXR. (A) HepG2 cells were cotransfected with expression vector for human PXR (hPXR; ▵), human RXRα (hRXRα; ♦), both hPXR and hRXRα (□), or with a control vector (●) together with rSTD-luc, CMX-β-gal. Transfected cells were incubated with media containing increasing concentrations of LCA or solvent control for 24 h before luciferase and β-galactosidase assays. Transcriptional activation was assessed by the relative luciferase activity normalized by β-galactosidase activity. The results are shown as a fold induction over solvent control and represent the average of triplicate experiments. (B) Schematic of the conserved 5′ flanking region from rat and mouse STD genes. Position of the IR0 element is indicated by a filled rectangle. The transcription start site is indicated by the arrow. Also, the sequences of IR0 elements from rat and mouse STDs as well as the mutant IR0 (used in C and D and Fig. 3) are shown with arrows indicating the inverted repeat. The core IR0 sequence is shown in uppercase and flanking nucleotides are shown in lowercase. Nonconserved nucleotides in the mouse IR0 and mutant IR0 are shown in underlined lowercase. (C) HepG2 cells were cotransfected as in A with the indicated receptor expression vectors along with the rSTD-luc vector containing either the wild-type or the mutant IR0 element. Transfected cells were incubated with medium containing rifampicin (Rif; for hPXR), PCN (for mouse PXR, mPXR), or solvent control for 24 h before being assayed. The results are shown as a fold induction over solvent control and represent the mean ± SD from triplicate experiments. (D) A similar experiment in which monkey kidney CV-1 cells were cotransfected with synthetic tk-luc reporters harboring three copies of indicated response elements. A reporter gene harboring the DR3 elements from CYP3A23 was used as a positive control. Similar results were obtained by using LCA or 3-keto-LCA as a ligand (not shown).
Figure 3
Figure 3
PXR/RXR heterodimers bind to IR0 elements. Shown are electrophoretic mobility-shift assays (EMSAs). Each reaction mixture contained reticulocyte lysate programmed to synthesize hPXR and/or hRXRα along with a 32P-labeled oligonucleotide encoding a single copy of the indicated PXR response element. Arrowheads indicate labeled DNA-bound PXR/RXR. Free probes are indicated with asterisks. In B, all reaction mixtures contained 32P-labeled rat STD IR0 probe along with increasing amounts (0.5×, 5×, 50×) of unlabeled oligonucleotide harboring the competitive response element. Note that both IR0 and DR3 competitor probes prevent formation of the slower mobility complex to similar extents, whereas the IR0 mutant competitor does not.
Figure 4
Figure 4
Coordinate regulation of the phase II sulfonation system by PXR. (A) Northern blot analysis of total liver RNA isolated from transgenic Alb-VP-hPXR male mice or nontransgenic littermates of the indicated age. The same blot was reprobed with the indicated labeled cDNAs. Mice encode two isoforms of PAPSS, of which only PAPPS2, not PAPSS1, is induced by the presence of VP-hPXR (not shown). (B) Cytosolic liver extracts from transgenic VP-hPXR male mice or nontransgenic littermates were subjected to enzymatic assay for phenolic SULT activity by using the prototypic substrate p-nitrophenol and the cofactor [35S]PAPS. Shown is the mean ± SD of results obtained from three pairs of mice. (C) Model for PXR as a regulator of sulfonation pathway and drug clearance. Activation of PXR by LCA or xenobiotic compounds (gray oval) results in coordinate up-regulation of drug-metabolizing pathways through transcriptional induction of genes encoding phase I CYP enzymes (1), phase II SULT enzymes (2), a bifunctional enzyme, PAPSS2, that catalyzes conversion of ATP and inorganic sulfate (Si) into the SULT cofactor PAPS (3), and drug transporters such as MDR1 or MRP2 (4).
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"V体育安卓版" References

    1. Fisher M M, Magnusson R, Miyai K. Lab Invest. 1971;25:88–91. - PubMed
    1. Javitt N B. Nature. 1966;210:1262–1263. - PubMed
    1. Owen R W, Dodo M, Thompson M H, Hill M J. Nutr Cancer. 1987;9:73–80. - PubMed
    1. Kishida T, Taguchi F, Feng L, Tatsuguchi A, Sato J, Fujimori S, Tachikawa H, Tamagawa Y, Yoshida Y, Kobayashi M. J Gastroenterol. 1997;32:306–311. - PubMed
    1. Lehmann J M, McKee D D, Watson M A, Willson T M, Moore J T, Kliewer S A. J Clin Invest. 1998;102:1016–1023. - PMC - PubMed

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