Biology:Pregnane X receptor

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Short description: Mammalian protein found in Homo sapiens


A representation of the 3D structure of the protein myoglobin showing turquoise α-helices.
Generic protein structure example


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.[1][2][3]

Function

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.[4] PXR belongs to the nuclear receptor superfamily, members of which are transcription factors characterized by a ligand-binding domain and a DNA-binding domain. PXR 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.[3][5]

Ligands

Agonists

PXR is activated by a large number of endogenous and exogenous chemicals[4] 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 St. John's Wort), and other compounds such as meclizine, paclitaxel, cafestol,[6] and forskolin.[7][8]

Antagonists

Ketoconazole is an example of one of the relatively few-known antagonists of the PXR.[9][10] SPA70 (also known as LC-1) was recently identified and characterized as a potent and selective PXR antagonist.[11][12]

Mechanism

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.[4]

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.[2][3] In addition, PXR up regulates the expression of phase II conjugating enzymes such as glutathione S-transferase[13] and phase III transport uptake and efflux proteins such as OATP2[14] and MDR1.[15][16]

See also

References

  1. ↑ Entrez result for NR1I2.
  2. ↑ 2.0 2.1 "The human orphan nuclear receptor PXR is activated by compounds that regulate CYP3A4 gene expression and cause drug interactions". The Journal of Clinical Investigation 102 (5): 1016–23. September 1998. doi:10.1172/JCI3703. PMID 9727070. 
  3. ↑ 3.0 3.1 3.2 "Identification of a human nuclear receptor defines a new signaling pathway for CYP3A induction". Proceedings of the National Academy of Sciences of the United States of America 95 (21): 12208–13. October 1998. doi:10.1073/pnas.95.21.12208. PMID 9770465. Bibcode: 1998PNAS...9512208B. 
  4. ↑ 4.0 4.1 4.2 "The nuclear pregnane X receptor: a key regulator of xenobiotic metabolism". Endocrine Reviews 23 (5): 687–702. October 2002. doi:10.1210/er.2001-0038. PMID 12372848. 
  5. ↑ "Entrez Gene: NR1I2 nuclear receptor subfamily 1, group I, member 2". https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=8856. 
  6. ↑ "The cholesterol-raising factor from coffee beans, cafestol, as an agonist ligand for the farnesoid and pregnane X receptors". Molecular Endocrinology 21 (7): 1603–16. July 2007. doi:10.1210/me.2007-0133. PMID 17456796. 
  7. ↑ "Forskolin convalesces memory in high fat diet-induced dementia in wistar rats-Plausible role of pregnane x receptors". Pharmacological Reports 70 (1): 161–171. February 2018. doi:10.1016/j.pharep.2017.07.009. PMID 29367103. 
  8. ↑ Ding, X. (2004). "Induction of Drug Metabolism by Forskolin: The Role of the Pregnane X Receptor and the Protein Kinase A Signal Transduction Pathway". Journal of Pharmacology and Experimental Therapeutics 312 (2): 849–856. doi:10.1124/jpet.104.076331. ISSN 0022-3565. PMID 15459237. 
  9. ↑ "Reverse yeast two-hybrid system to identify mammalian nuclear receptor residues that interact with ligands and/or antagonists". Journal of Visualized Experiments (81): e51085. November 2013. doi:10.3791/51085. PMID 24300333. 
  10. ↑ "PXR antagonists and implication in drug metabolism". Drug Metabolism Reviews 45 (1): 60–72. February 2013. doi:10.3109/03602532.2012.746363. PMID 23330542. 
  11. ↑ "High-Throughput Screening Identifies 1,4,5-Substituted 1,2,3-Triazole Analogs as Potent and Specific Antagonists of Pregnane X Receptor". Assay and Drug Development Technologies 15 (8): 383–394. December 2017. doi:10.1089/adt.2017.809. PMID 29112465. 
  12. ↑ "SPA70 is a potent antagonist of human pregnane X receptor". Nature Communications 8 (1): 741. September 2017. doi:10.1038/s41467-017-00780-5. PMID 28963450. Bibcode: 2017NatCo...8..741L. 
  13. ↑ "Regulation of the rat glutathione S-transferase A2 gene by glucocorticoids: involvement of both the glucocorticoid and pregnane X receptors". Molecular Pharmacology 60 (3): 611–9. September 2001. PMID 11502894. http://molpharm.aspetjournals.org/cgi/pmidlookup?view=long&pmid=11502894. 
  14. ↑ "The nuclear receptor PXR is a lithocholic acid sensor that protects against liver toxicity". Proceedings of the National Academy of Sciences of the United States of America 98 (6): 3369–74. March 2001. doi:10.1073/pnas.051551698. PMID 11248085. Bibcode: 2001PNAS...98.3369S. 
  15. ↑ "The orphan nuclear receptor SXR coordinately regulates drug metabolism and efflux". Nature Medicine 7 (5): 584–90. May 2001. doi:10.1038/87912. PMID 11329060. 
  16. ↑ "Nuclear receptor response elements mediate induction of intestinal MDR1 by rifampin". The Journal of Biological Chemistry 276 (18): 14581–7. May 2001. doi:10.1074/jbc.M010173200. PMID 11297522. 

Further reading

External links

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



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