Pregnane X receptor

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"PXR" redirects here. For file format .pxr, see Pixar Image Computer. For SXR, see soft x-ray.
Nuclear receptor subfamily 1, group I, member 2
Protein NR1I2 PDB 1ilg.png
PDB rendering based on PDB 1ilg.[1]
Available structures
PDB Ortholog search: PDBe, RCSB
Symbols NR1I2 ; BXR; ONR1; PAR; PAR1; PAR2; PARq; PRR; PXR; SAR; SXR
External IDs OMIM603065 MGI1337040 HomoloGene40757 IUPHAR: 606 ChEMBL: 3401 GeneCards: NR1I2 Gene
RNA expression pattern
PBB GE NR1I2 207202 s at tn.png
PBB GE NR1I2 207203 s at tn.png
More reference expression data
Species Human Mouse
Entrez 8856 18171
Ensembl ENSG00000144852 ENSMUSG00000022809
UniProt O75469 O54915
RefSeq (mRNA) NM_003889 NM_001098404
RefSeq (protein) NP_003880 NP_001091874
Location (UCSC) Chr 3:
119.78 – 119.82 Mb
Chr 16:
38.25 – 38.29 Mb
PubMed search [1] [2]

In the field of molecular biology, the pregnane X receptor (PXR), also known as the steroid and xenobiotic sensing nuclear receptor (SXR) or nuclear receptor subfamily 1, group I, member 2 (NR1I2) is a protein that in humans is encoded by the NR1I2 (nuclear Receptor subfamily 1, group I, member 2) gene.[2][3][4]


PXR is a nuclear receptor whose primary function is to sense the presence of foreign toxic substances and in response up regulate the expression of proteins involved in the detoxification and clearance of these substances from the body.[5] PXR belongs to the nuclear receptor superfamily, members of which are transcription factors characterized by a ligand-binding domain and a DNA-binding domain. The encoded protein is a transcriptional regulator of the cytochrome P450 gene CYP3A4, binding to the response element of the CYP3A4 promoter as a heterodimer with the 9-cis retinoic acid receptor RXR. It is activated by a range of compounds that induce CYP3A4, including dexamethasone and rifampicin.[4][6]



PXR is activated by a large number of endogenous and exogenous chemicals including steroids (e.g., progesterone, 17α-hydroxyprogesterone, 17α-hydroxypregnenolone, 5α-dihydroprogesterone, 5β-dihydroprogesterone, allopregnanolone, corticosterone, cyproterone acetate, spironolactone, dexamethasone, mifepristone), antibiotics (e.g., rifampicin, rifaximin), antimycotics, bile acids, hyperforin (a constituent of the herbal antidepressant St. John's Wort), and many herbal and other compounds (e.g., meclizine, paclitaxel).[5]


Ketoconazole is an example of one of the relatively few-known antagonists of the PXR.[7]


Like other type II nuclear receptors, when activated, it forms a heterodimer with the retinoid X receptor, and binds to hormone response elements on DNA which elicits expression of gene products.[5]

One of the primary targets of PXR activation is the induction of CYP3A4, an important phase I oxidative enzyme that is responsible for the metabolism of many drugs.[3][4] In addition, PXR up regulates the expression of phase II conjugating enzymes such as glutathione S-transferase[8] and phase III transport uptake and efflux proteins such as OATP2[9] and MDR1.[10][11]

See also[edit]


  1. ^ Liao SK, Axelrad AA (March 1975). "Erythropoietin-independent erythroid colony formation in vitro by hemopoietic cells of mice infected with friend virus". Int. J. Cancer 15 (3): 467–82. doi:10.1002/ijc.2910150313. PMID 1140862. 
  2. ^ Entrez result for NR1I2.
  3. ^ a b Lehmann JM, McKee DD, Watson MA, Willson TM, Moore JT, Kliewer SA (September 1998). "The human orphan nuclear receptor PXR is activated by compounds that regulate CYP3A4 gene expression and cause drug interactions". J. Clin. Invest. 102 (5): 1016–23. doi:10.1172/JCI3703. PMC 508967. PMID 9727070. 
  4. ^ a b c Bertilsson G, Heidrich J, Svensson K, Asman M, Jendeberg L, Sydow-Bäckman M, Ohlsson R, Postlind H, Blomquist P, Berkenstam A (October 1998). "Identification of a human nuclear receptor defines a new signaling pathway for CYP3A induction". Proc. Natl. Acad. Sci. U.S.A. 95 (21): 12208–13. doi:10.1073/pnas.95.21.12208. PMC 22810. PMID 9770465. 
  5. ^ a b c Kliewer S, Goodwin B, Willson T (2002). "The nuclear pregnane X receptor: a key regulator of xenobiotic metabolism". Endocr. Rev. 23 (5): 687–702. doi:10.1210/er.2001-0038. PMID 12372848. 
  6. ^ "Entrez Gene: NR1I2 nuclear receptor subfamily 1, group I, member 2". 
  7. ^ Li H, Dou W, Padikkala E, Mani S (2013). "Reverse yeast two-hybrid system to identify mammalian nuclear receptor residues that interact with ligands and/or antagonists". J Vis Exp (81): e51085. doi:10.3791/51085. PMC 3904218. PMID 24300333. 
  8. ^ Falkner KC, Pinaire JA, Xiao GH, Geoghegan TE, Prough RA (September 2001). "Regulation of the rat glutathione S-transferase A2 gene by glucocorticoids: involvement of both the glucocorticoid and pregnane X receptors". Mol. Pharmacol. 60 (3): 611–9. PMID 11502894. 
  9. ^ Staudinger JL, Goodwin B, Jones SA, Hawkins-Brown D, MacKenzie KI, LaTour A, Liu Y, Klaassen CD, Brown KK, Reinhard J, Willson TM, Koller BH, Kliewer SA (March 2001). "The nuclear receptor PXR is a lithocholic acid sensor that protects against liver toxicity". Proc. Natl. Acad. Sci. U.S.A. 98 (6): 3369–74. doi:10.1073/pnas.051551698. PMC 30660. PMID 11248085. 
  10. ^ Synold TW, Dussault I, Forman BM (May 2001). "The orphan nuclear receptor SXR coordinately regulates drug metabolism and efflux". Nat. Med. 7 (5): 584–90. doi:10.1038/87912. PMID 11329060. 
  11. ^ Geick A, Eichelbaum M, Burk O (May 2001). "Nuclear receptor response elements mediate induction of intestinal MDR1 by rifampin". J. Biol. Chem. 276 (18): 14581–7. doi:10.1074/jbc.M010173200. PMID 11297522. 

Further reading[edit]

External links[edit]

This article incorporates text from the United States National Library of Medicine, which is in the public domain.