title: Orphan nuclear receptor pregnane X receptor sensitizes oxidative stress responses in transgenic mice and cancerous cells.
abstract: Efficient handling of oxidative stress is critical for the survival of organisms. The orphan nuclear receptor pregnane X receptor (PXR) is important in xenobiotic detoxification through its regulation of phase I and phase II drug-metabolizing/detoxifying enzymes and transporters. In this study we unexpectedly found that the expression of an activated human PXR in transgenic female mice resulted in a heightened sensitivity to paraquat, an oxidative xenobiotic toxicant. Heightened paraquat sensitivity was also seen in wild-type mice treated with the mouse PXR agonist pregnenolone-16alpha-carbonitrile. The PXR-induced paraquat sensitivity was associated with decreased activities of superoxide dismutase and catalase, enzymes that scavenge superoxide and hydrogen peroxide, respectively. Paradoxically, the general expression and activity of glutathione S-transferases, a family of phase II enzymes that detoxify electrophilic and cytotoxic substrates, was also induced in the transgenic mice. PXR regulates glutathione S-transferase expression in an isozyme-, tissue-, and sex-specific manner, and this regulation is independent of the nuclear factor-erythroid 2 p45-related factor 2/Kelch-like Ech-associated protein 1 pathway. In cell cultures, expression of activated human PXR sensitizes the cancerous colon and liver cells to the cytotoxic effect of paraquat, which is associated with an increased production of the reactive oxygen species. The current study reveals a novel function of PXR in the mammalian oxidative stress response, and this regulatory pathway may be implicated in carcinogenesis by sensitizing normal and cancerous tissues to oxidative cellular damage.
authors.affiliation: Center for Pharmacogenetics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: Haibiao
authors.initials: H
authors.lastname: Gong
authors.forename: Shivendra V
authors.initials: SV
authors.lastname: Singh
authors.forename: Sharda P
authors.initials: SP
authors.lastname: Singh
authors.forename: Ying
authors.initials: Y
authors.lastname: Mu
authors.forename: Jung Hoon
authors.initials: JH
authors.lastname: Lee
authors.forename: Simrat P S
authors.initials: SP
authors.lastname: Saini
authors.forename: David
authors.initials: D
authors.lastname: Toma
authors.forename: Songrong
authors.initials: S
authors.lastname: Ren
authors.forename: Valerian E
authors.initials: VE
authors.lastname: Kagan
authors.forename: Billy W
authors.initials: BW
authors.lastname: Day
authors.forename: Piotr
authors.initials: P
authors.lastname: Zimniak
authors.forename: Wen
authors.initials: W
authors.lastname: Xie
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015500:Chloramphenicol O-Acetyltransferase / Q000378:metabolism; D003110:Colonic Neoplasms / Q000378:metabolism*; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D050556:Fatty Acid-Binding Proteins / Q000235:genetics; D005260:Female; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D000072019:Kelch-Like ECH-Associated Protein 1; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D051267:NF-E2-Related Factor 2 / Q000235:genetics / Q000378:metabolism; D018384:Oxidative Stress; D010269:Paraquat / Q000633:toxicity; D000077297:Pregnane X Receptor; D011401:Promoter Regions, Genetic; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists / Q000378:metabolism*; D011987:Receptors, Steroid / Q000819:agonists / Q000378:metabolism*; D012737:Sex Factors; D013482:Superoxide Dismutase / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; D050556:Fatty Acid-Binding Proteins; D007527:Isoenzymes; C117301:Keap1 protein, mouse; D000072019:Kelch-Like ECH-Associated Protein 1; D051267:NF-E2-Related Factor 2; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D013482:Superoxide Dismutase; D015500:Chloramphenicol O-Acetyltransferase; D005982:Glutathione Transferase; D005978:Glutathione; D010269:Paraquat