The Experts below are selected from a list of 3927 Experts worldwide ranked by ideXlab platform
Timothy M Willson - One of the best experts on this subject based on the ideXlab platform.
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the nuclear Pregnane X Receptor a key regulator of Xenobiotic metabolism
Endocrine Reviews, 2002Co-Authors: Steven A Kliewer, Bryan Goodwin, Timothy M WillsonAbstract:The nuclear Pregnane X Receptor (PXR; NR1I2) is an important component of the body's adaptive defense mechanism against toXic substances including foreign chemicals (Xenobiotics). PXR is activated by a large number of endogenous and eXogenous chemicals including steroids, antibiotics, antimycotics, bile acids, and the herbal antidepressant St. John's wort. Elucidation of the three-dimensional structure of the PXR ligand binding domain revealed that it has a large, spherical ligand binding cavity that allows it to interact with a wide range of hydrophobic chemicals. Thus, unlike other nuclear Receptors that interact selectively with their physiological ligands, PXR serves as a generalized sensor of hydrophobic toXins. PXR binds as a heterodimer with the 9-cis retinoic acid Receptor (NR2B) to DNA response elements in the regulatory regions of cytochrome P450 3A monooXygenase genes and a number of other genes involved in the metabolism and elimination of Xenobiotics from the body. Although PXR evolved to protect the body, its activation by a variety of prescription drugs represents the molecular basis for an important class of harmful drug-drug interactions. Thus, assays that detect PXR activity will be useful in developing safer prescription drugs.
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regulation of Xenobiotic and bile acid metabolism by the nuclear Pregnane X Receptor
Journal of Lipid Research, 2002Co-Authors: Steven A Kliewer, Timothy M WillsonAbstract:The nuclear Pregnane X Receptor (PXR; NR1I2) is an integral component of the body's defense mechanism against chemical insult (chemoprotection). PXR is activated by a diverse array of lipophilic chemicals, including Xeno- biotics and endogenous substances, and regulates the eXpres- sion of cytochromes P450, conjugating enzymes, and trans- porters involved in the metabolism and elimination of these potentially harmful chemicals from the body. Among the chemicals that bind and activate PXR is the toXic bile acid lithocholic acid; activation of PXR, in turn, protects against the severe liver damage caused by this bile acid. Thus, PXR serves as a physiological sensor of lithocholic acid and perhaps other bile acids and coordinately regulates genes involved in their detoXification. Interestingly, both the anti- biotic rifampicin and the herbal antidepressant St. John's wort activate PXR and have anticholestatic properties, which suggests that more potent, selective PXR agonists may be useful in the treatment of biliary cholestasis or other diseases characterized by the accumulation of bile acids or other toXins in the liver. —Kliewer, S. A., and T. M. Willson. Regulation of Xenobiotic and bile acid metabolism by the nuclear Pregnane X Receptor. J. Lipid Res. 2002. 43: 359-364.
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Regulation of Xenobiotic and bile acid metabolism by the nuclear Pregnane X Receptor
Journal of Lipid Research, 2002Co-Authors: Timothy M Willson, Abstract The, X PxrAbstract:The nuclear Pregnane X Receptor (PXR; NR1I2) is an integral component of the body's defense mechanism against chemical insult (chemoprotection). PXR is activated by a diverse array of lipophilic chemicals, including Xenobiotics and endogenous substances, and regulates the eXpression of cytochromes P450, conjugating enzymes, and transporters involved in the metabolism and elimination of these potentially harmful chemicals from the body. Among the chemicals that bind and activate PXR is the toXic bile acid lithocholic acid; activation of PXR, in turn, protects against the severe liver damage caused by this bile acid.Thus, PXR serves as a physiological sensor of lithocholic acid and perhaps other bile acids and coordinately regulates genes involved in their detoXification. Interestingly, both the antibiotic rifampicin and the herbal antidepressant St. John's wort activate PXR and have anticholestatic properties, which suggests that more potent, selective PXR agonists may be useful in the treatment of biliary cholestasis or other diseases characterized by the accumulation of bile acids or other toXins in the liver.
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st john s wort induces hepatic drug metabolism through activation of the Pregnane X Receptor
Proceedings of the National Academy of Sciences of the United States of America, 2000Co-Authors: Linda B Moore, Timothy M Willson, Bryan Goodwin, Stacey A Jones, Bruce Wisely, Jon L Collins, Cosette J Serabjitsingh, Steven A KliewerAbstract:St. John's wort (Hypericum perforatum) is an herbal remedy used widely for the treatment of depression. Recent clinical studies demonstrate that hypericum eXtracts increase the metabolism of various drugs, including combined oral contraceptives, cyclosporin, and indinavir. In this report, we show that hyperforin, a constituent of St. John's wort with antidepressant activity, is a potent ligand (Ki = 27 nM) for the Pregnane X Receptor, an orphan nuclear Receptor that regulates eXpression of the cytochrome P450 (CYP) 3A4 monooXygenase. Treatment of primary human hepatocytes with hypericum eXtracts or hyperforin results in a marked induction of CYP3A4 eXpression. Because CYP3A4 is involved in the oXidative metabolism of >50% of all drugs, our findings provide a molecular mechanism for the interaction of St. John's wort with drugs and suggest that hypericum eXtracts are likely to interact with many more drugs than previously had been realized.
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orphan nuclear Receptors constitutive androstane Receptor and Pregnane X Receptor share Xenobiotic and steroid ligands
Journal of Biological Chemistry, 2000Co-Authors: Timothy M Willson, Bryan Goodwin, Christopher Liddle, Linda B Moore, Derek J Parks, Stacey A Jones, Randy K Bledsoe, Thomas G Consler, Julie B Stimmel, Steven G BlanchardAbstract:Xenobiotics induce the transcription of cytochromes P450 (CYPs) 2B and 3A through the constitutive androstane Receptor (CAR; NR1I3) and Pregnane X Receptor (PXR; NR1I2), respectively. In this report, we have systematically compared a series of Xenobiotics and natural steroids for their effects on mouse and human CAR and PXR. Our results demonstrate dual regulation of PXR and CAR by a subset of compounds that affect CYP eXpression. Moreover, there are marked pharmacological differences between the mouse (m) and human (h) orthologs of both CAR and PXR. For eXample, the planar hydrocarbon 1, 4-bis[2-(3,5-dichloropyridyl-oXy)]benzene activates mCAR and hPXR but has little or no activity on hCAR and mPXR. In contrast, the CAR deactivator androstanol activates both mouse and human PXR. Similarly, the PXR activator clotrimazole is a potent deactivator of hCAR. Using radioligand binding and fluorescence resonance energy transfer assays, we demonstrate that several of the compounds that regulate mouse and human CAR, including natural steroids, bind directly to the Receptors. Our results suggest that CAR, like PXR, is a steroid Receptor that is capable of recognizing structurally diverse compounds. Moreover, our findings underscore the compleXity in the physiologic response to Xenobiotics.
Ronald M Evans - One of the best experts on this subject based on the ideXlab platform.
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Pregnane X Receptor controls hepatic glucuronidation during pregnancy and neonatal development in humanized ugt1 mice
Hepatology, 2012Co-Authors: Shujuan Chen, Ronald M Evans, Meifei Yueh, Robert H TukeyAbstract:In humanized UDP glucuronosyltransferase-1 (hUGT1) mice that eXpress the entire UGT1 locus, the maternal hepatic UGT1A genes are dramatically induced 12-14 days after conception. Steroid induction of the UGT1A1 gene indicates that Xenobiotic sensors, such as the Pregnane X Receptor (PXR) and constitutive androstane Receptor (CAR), may underlie the induction process. In contrast, neonatal hUGT1 mice display severe hyperbilirubinemia, with limited eXpression of the UGT1A genes. This study identifies PXR as both a positive and negative regulator of the UGT1A1 gene. Pregnancy hormones, in particular the glucocorticoids, target PXR as a positive regulator of human glucuronidation. Employing reverse genetics, where PXR has been genetically deleted, hUGT1/PXr−/− mice show limited induction of the liver UGT1A genes during pregnancy, whereas the eXact opposite occurs in newborn mice. Neonatal hUGT1 mice show delayed eXpression of hepatic UGT1A1 and are severely hyperbilirubinemic. However, in hUGT1/PXr−/− mice, hyperbilirubinemia is greatly reduced due to induction of hepatic UGT1A1. Thus, PXR serves to repress UGT1A1 gene eXpression during development. Transcriptional silencing of the UGT1A1 gene was relieved in neonatal hUGT1 hepatocytes through interruption of PXR by small interfering RNA. Conclusion: PXR is a key regulator of pregnancy induced glucuronidation capacity in addition to modulating the severity of neonatal jaundice. (Hepatology 2012;56:658–667)
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Pregnane X Receptor prevents hepatorenal toXicity from cholesterol metabolites
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Junichiro Sonoda, Christopher Liddle, Ling Wa Chong, Michael Downes, Grant D Barish, Sally Coulter, Chihhao Lee, Ronald M EvansAbstract:Efficient detoXification and clearance of cholesterol metabolites such as oXysterols, bile alcohols, and bile acids are critical for survival because they can promote liver and cardiovascular disease. We report here that loss of the nuclear Xenobiotic Receptor PXR (Pregnane X Receptor), a regulator of enterohepatic drug metabolism and clearance, results in an uneXpected acute lethality associated with signs of severe hepatorenal failure when mice are fed with a diet that elicits accumulation of cholesterol and its metabolites. Induction of a distinct drug clearance program by a high-affinity ligand for the related nuclear Receptor, the constitutive androstane Receptor, does not overcome the lethality, indicating the unique requirement of PXR for detoXification. We propose that the PXR signaling pathway protects the body from toXic dietary cholesterol metabolites, and, by eXtension, PXR ligands may ameliorate human diseases such as cholestatic liver diseases and the associating acute renal failure.
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nuclear Receptors constitutive androstane Receptor and Pregnane X Receptor ameliorate cholestatic liver injury
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Catherine A M Stedman, Ronald M Evans, Christopher Liddle, Junichiro Sonoda, Sally Coulter, Jacqueline G A Alvarez, David D Moore, Michael DownesAbstract:Cholestasis is associated with accumulation of bile acids and lipids, and liver injury. The constitutive androstane Receptor (CAR) and Pregnane X Receptor (PXR) are Xenobiotic nuclear Receptors that coordinate protective hepatic responses to potentially toXic stimuli, including bile acids. We investigated the role of these Receptors in the regulation of bile acid and lipid metabolism in a bile duct ligation (BDL) model of cholestasis applied to Receptor knockout mice. Hepatic damage from bile acid accumulation was increased in both CAR knockout (CARKO) and PXR knockout mice, but bile acid concentrations were lower in CARKO mice. High-density lipoprotein (HDL) cholesterol was elevated in CARKO mice, and serum total cholesterol increased less in CARKO or PXR knockout mice than WT mice after BDL. Gene eXpression analysis of the BDL knockout animals demonstrated that, in response to cholestasis, PXR and CAR both repressed and induced the specific hepatic membrane transporters Oatp-c (organic anion transporting polypeptide C) and Oatp2 (Na+-dependent organic anion transporter 2), respectively. Induction of the Xenobiotic transporter multidrug resistance protein 1 in cholestasis was independent of either PXR or CAR, in contrast to the known pattern of induction of multidrug resistance protein 1 by Xenobiotics. These results demonstrate that CAR and PXR influence cholesterol metabolism and bile acid synthesis, as well as multiple detoXification pathways, and suggest their potential role as therapeutic targets for the treatment of cholestasis and lipid disorders.
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genetic profiling defines the Xenobiotic gene network controlled by the nuclear Receptor Pregnane X Receptor
Molecular Endocrinology, 2003Co-Authors: John M Rosenfeld, Wen Xie, Reynaldo Vargas, Ronald M EvansAbstract:The orphan nuclear Receptor Pregnane X Receptor (PXR) is essential for the transcriptional regulation of hepatic Xenobiotic enzymes including the cytochrome 3A isoenzymes. These enzymes are central to the catabolism and clearance of most endogenous sterol metabolites (endobiotics) and a vast diversity of foreign compounds (Xenobiotics) including pharmaceuticals, pesticides, and toXins encountered through diet and environmental eXposure. To eXplore a broader role of PXR in the mammalian Xenobiotic response, we have conducted a unique microarray gene profiling analysis on liver samples derived from PXR knockout mice and mice eXpressing a constitutively active variant, VP-hPXR. This genetically guided eXpression analysis enables targeting and restriction of the PXR response to liver, and is devoid of side effects resulting from drugs and their metabolites. As with pharmacological studies, Receptor-dependent genes include both phase I and phase II metabolic enzymes, as well as certain drug and anion transporters as principal PXR targets. Moreover, comparative analysis of data from both genetic and pharmacological arrays reveals a core network that represents a genetic description of the Xenobiotic response.
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control of steroid heme and carcinogen metabolism by nuclear Pregnane X Receptor and constitutive androstane Receptor
Proceedings of the National Academy of Sciences of the United States of America, 2003Co-Authors: Wen Xie, Meifei Yeuh, Anna Radominskapandya, S P S Saini, Yoichi Negishi, Bobbie Sue Bottroff, Geraldine Y Cabrera, Robert H Tukey, Ronald M EvansAbstract:Through a multipleX promoter spanning 218 kb, the phase II UDP-glucuronosyltransferase 1A (UGT1) gene encodes at least eight differently regulated mRNAs whose protein products function as the principal means to eliminate a vast array of steroids, heme metabolites, environmental toXins, and drugs. The orphan nuclear Receptors Pregnane X Receptor (PXR) and constitutive androstane Receptor (CAR) were originally identified as sensors able to respond to numerous environmentally derived foreign compounds (Xenobiotics) to promote detoXification by phase I cytochrome P450 genes. In this report, we show that both Receptors can induce specific UGT1A isoforms including those involved in estrogen, thyroXin, bilirubin, and carcinogen metabolism. Transgenic mice eXpressing a constitutively active form of human PXR show markedly increased UGT activity toward steroid, heme, and carcinogens, enhanced bilirubin clearance, as well as massively increased steroid clearance. The ability of PXR and constitutive androstane Receptor and their ligands to transduce both the phase I and phase II adaptive hepatic response defines a unique transcriptional interface that bridges the ingestion and metabolism of environmental compounds to body physiology.
Steven A Kliewer - One of the best experts on this subject based on the ideXlab platform.
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crystal structure of the Pregnane X Receptor estradiol compleX provides insights into endobiotic recognition
Molecular Endocrinology, 2007Co-Authors: Linda B Moore, Steven A Kliewer, Jillian Orans, Li Peng, Sompop Bencharit, Matthew R RedinboAbstract:The human nuclear Pregnane X Receptor (PXR) responds to a wide variety of Xenobiotic and endobiotic compounds, including Pregnanes, progesterones, corticosterones, lithocholic acids, and 17β-estradiol. In response to these ligands, the Receptor controls the eXpression of genes central to the metabolism and eXcretion of potentially harmful chemicals from both eXogenous and endogenous sources. Although the structural basis of PXR’s interaction with small and large Xenobiotics has been eXamined, the detailed nature of its binding to endobiotics, including steroid-like ligands, remains unclear. We report the crystal structure of the human PXR ligand-binding domain (LBD) in compleX with 17β-estradiol, a representative steroid ligand, at 2.65 A resolution. Estradiol is found to occupy only one region of PXR’s eXpansive ligand-binding pocket, leaving a notable 1000 A3 of space unoccupied, and to bridge between the key polar residues Ser-247 and Arg-410 in the PXR LBD. Positioning the steroid scaffold in this way...
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structural disorder in the compleX of human Pregnane X Receptor and the macrolide antibiotic rifampicin
Molecular Endocrinology, 2005Co-Authors: Jill E Chrencik, Steven A Kliewer, Linda B Moore, Jillian Orans, Li Peng, Bruce Wisely, Jon L Collins, Millard H Lambert, Matthew R RedinboAbstract:The human nuclear Xenobiotic Receptor, Pregnane X Receptor (PXR), detects a variety of structurally distinct endogenous and Xenobiotic compounds and controls eXpression of genes central to drug and cholesterol metabolism. The macrolide antibiotic rifampicin, a front-line treatment for tuberculosis, is an established PXR agonist and, at 823 Da, is one of the largest known ligands for the Receptor. We present the 2.8 A crystal structure of the ligand-binding domain of human PXR in compleX with rifampicin. We also use structural and mutagenesis data to eXamine the origins of the directed promiscuity eXhibited by the PXRs across species. Three structurally fleXible loops adjacent to the ligand-binding pocket of PXR are disordered in this crystal structure, including the 200–210 region that is part of a sequence insert novel to the promiscuous PXRs relative to other members of the nuclear Receptor superfamily. The 4-methyl-1-piperazinyl ring of rifampicin, which would lie adjacent to the disordered protein reg...
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structural disorder in the compleX of human Pregnane X Receptor and the macrolide antibiotic rifampicin
Molecular Endocrinology, 2005Co-Authors: Jill E Chrencik, Steven A Kliewer, Linda B Moore, Jillian Orans, Li Peng, Bruce Wisely, Jon L Collins, Millard H Lambert, Yu Xue, Matthew R RedinboAbstract:The human nuclear Xenobiotic Receptor, Pregnane X Receptor (PXR), detects a variety of structurally distinct endogenous and Xenobiotic compounds and controls eXpression of genes central to drug and cholesterol metabolism. The macrolide antibiotic rifampicin, a front-line treatment for tuberculosis, is an established PXR agonist and, at 823 Da, is one of the largest known ligands for the Receptor. We present the 2.8 A crystal structure of the ligand-binding domain of human PXR in compleX with rifampicin. We also use structural and mutagenesis data to eXamine the origins of the directed promiscuity eXhibited by the PXRs across species. Three structurally fleXible loops adjacent to the ligand-binding pocket of PXR are disordered in this crystal structure, including the 200-210 region that is part of a sequence insert novel to the promiscuous PXRs relative to other members of the nuclear Receptor superfamily. The 4-methyl-1-piperazinyl ring of rifampicin, which would lie adjacent to the disordered protein regions, is also disordered and not observed in the structure. Taken together, our results indicate that one wall of the PXR ligand-binding cavity can remain fleXible even when the Receptor is in compleX with an activating ligand. These observations highlight the key role that structural fleXibility plays in PXR's promiscuous response to Xenobiotics.
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Pregnane X Receptor predicting and preventing drug interactions
Thrombosis Research, 2005Co-Authors: Steven A KliewerAbstract:The Pregnane X Receptor, PXR, is a member of the nuclear Receptor family of ligand-activated transcription factors [1]. The hormones that act through the nuclear Receptors include the steroid hormones, thyroid hormone, retinoic acid, and vitamin D [2]. They are all small, lipophilic molecules that diffuse into the cell and interact with their cognate Receptors. The Receptors bind to DNA and regulate gene transcription directly. There are 48 nuclear Receptors in the human genome that share structural features, including conserved DNA binding and ligand binding domains. The so-called borphanQ nuclear Receptors contain the DNA and ligand binding domains. However, they are called orphans because at the time they were cloned their physiological ligands were not known [3]. PXR is involved in protecting the body against foreign chemicals or bXenobioticsQ [1]. These chemicals can either be ingested in the diet, inhaled, or absorbed. The liver and the intestine are key tissues for clearing Xenobiotics. Within these tissues, there are sets of proteins that play prominent roles in the detoXification of Xenobiotics. These
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the nuclear Pregnane X Receptor regulates Xenobiotic detoXification
Journal of Nutrition, 2003Co-Authors: Steven A KliewerAbstract:The Pregnane X Receptor (PXR), which is a member of the nuclear Receptor family of ligand-activated transcription factors, is an integral component of the body's defense mechanism against toXic Xenobiotics. PXR is activated by a broad spectrum of lipophilic Xenobiotics including prescription drugs, herbs, pesticides, endocrine disruptors and other environmental contaminants. The promiscuous ligand-binding properties of PXR are facilitated by the large volume and smooth shape of its ligand-binding pocket. PXR binds to DNA as a heterodimer with the 9-cis retinoic acid Receptor (RXR) and regulates a large number of genes involved in the detoXification and eXcretion of toXic substances. Although PXR evolved to protect the body, its activation by various prescription drugs and herbs such as St. John's wort represents the molecular basis for an important class of drug-drug interactions. Assays that detect PXR activation can now be used to predict and prevent these drug-drug interactions.
Linda B Moore - One of the best experts on this subject based on the ideXlab platform.
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the phytoestrogen coumestrol is a naturally occurring antagonist of the human Pregnane X Receptor
Molecular Endocrinology, 2008Co-Authors: Hongwei Wang, Bryan Goodwin, Linda B Moore, Derek J Parks, Michael David Johnson, Jodi M Maglich, Olivia R R Ittoop, Bruce Wisely, Katrina L Creech, Jon L CollinsAbstract:Antagonizing the action of the human nuclear Xenobiotic Receptor Pregnane X Receptor (PXR) may have important clinical implications in preventing drug-drug interactions and improving therapeutic efficacy. We provide evidence that a naturally occurring phytoestrogen, coumestrol, is an antagonist of the nuclear Receptor PXR (NR1I2). In transient transfection assays, coumestrol was able to suppress the agonist effects of SR12813 on human PXR activity. PXR activity was assessed and correlated with effects on the metabolism of the anesthetic tribromoethanol and on gene eXpression in primary human hepatocytes. We found that coumestrol was able to suppress the effects of PXR agonists on the eXpression of the known PXR target genes, CYP3A4 and CYP2B6, in primary human hepatocytes as well as inhibit metabolism of tribromoethanol in humanized PXR mice. Coumestrol at concentrations above 1.0 microm competed in scintillation proXimity assays with a labeled PXR agonist for binding to the ligand-binding cavity. However, mammalian two-hybrid assays and transient transcription data using ligand-binding-cavity mutant forms of PXR show that coumestrol also antagonizes coregulator recruitment. This effect is likely by binding to a surface outside the ligand-binding pocket. Taken together, these data imply that there are antagonist binding site(s) for coumestrol on the surface of PXR. These studies provide the basis for development of novel small molecule inhibitors of PXR with the ultimate goal of clinical applications toward preventing drug-drug interactions.
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the phytoestrogen coumestrol is a naturally occurring antagonist of the human Pregnane X Receptor
Molecular Endocrinology, 2008Co-Authors: Hongwei Wang, Bryan Goodwin, Linda B Moore, Derek J Parks, Michael David Johnson, Jodi M Maglich, Olivia R R Ittoop, Bruce Wisely, Katrina L Creech, Jon L CollinsAbstract:Antagonizing the action of the human nuclear Xenobiotic Receptor Pregnane X Receptor (PXR) may have important clinical implications in preventing drug-drug interactions and improving therapeutic efficacy. We provide evidence that a naturally occurring phytoestrogen, coumestrol, is an antagonist of the nuclear Receptor PXR (NR1I2). In transient transfection assays, coumestrol was able to suppress the agonist effects of SR12813 on human PXR activity. PXR activity was assessed and correlated with effects on the metabolism of the anesthetic tribromoethanol and on gene eXpression in primary human hepatocytes. We found that coumestrol was able to suppress the effects of PXR agonists on the eXpression of the known PXR target genes, CYP3A4 and CYP2B6, in primary human hepatocytes as well as inhibit metabolism of tribromoethanol in humanized PXR mice. Coumestrol at concentrations above 1.0 μm competed in scintillation proXimity assays with a labeled PXR agonist for binding to the ligand-binding cavity. However, ma...
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crystal structure of the Pregnane X Receptor estradiol compleX provides insights into endobiotic recognition
Molecular Endocrinology, 2007Co-Authors: Linda B Moore, Steven A Kliewer, Jillian Orans, Li Peng, Sompop Bencharit, Matthew R RedinboAbstract:The human nuclear Pregnane X Receptor (PXR) responds to a wide variety of Xenobiotic and endobiotic compounds, including Pregnanes, progesterones, corticosterones, lithocholic acids, and 17β-estradiol. In response to these ligands, the Receptor controls the eXpression of genes central to the metabolism and eXcretion of potentially harmful chemicals from both eXogenous and endogenous sources. Although the structural basis of PXR’s interaction with small and large Xenobiotics has been eXamined, the detailed nature of its binding to endobiotics, including steroid-like ligands, remains unclear. We report the crystal structure of the human PXR ligand-binding domain (LBD) in compleX with 17β-estradiol, a representative steroid ligand, at 2.65 A resolution. Estradiol is found to occupy only one region of PXR’s eXpansive ligand-binding pocket, leaving a notable 1000 A3 of space unoccupied, and to bridge between the key polar residues Ser-247 and Arg-410 in the PXR LBD. Positioning the steroid scaffold in this way...
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structural disorder in the compleX of human Pregnane X Receptor and the macrolide antibiotic rifampicin
Molecular Endocrinology, 2005Co-Authors: Jill E Chrencik, Steven A Kliewer, Linda B Moore, Jillian Orans, Li Peng, Bruce Wisely, Jon L Collins, Millard H Lambert, Matthew R RedinboAbstract:The human nuclear Xenobiotic Receptor, Pregnane X Receptor (PXR), detects a variety of structurally distinct endogenous and Xenobiotic compounds and controls eXpression of genes central to drug and cholesterol metabolism. The macrolide antibiotic rifampicin, a front-line treatment for tuberculosis, is an established PXR agonist and, at 823 Da, is one of the largest known ligands for the Receptor. We present the 2.8 A crystal structure of the ligand-binding domain of human PXR in compleX with rifampicin. We also use structural and mutagenesis data to eXamine the origins of the directed promiscuity eXhibited by the PXRs across species. Three structurally fleXible loops adjacent to the ligand-binding pocket of PXR are disordered in this crystal structure, including the 200–210 region that is part of a sequence insert novel to the promiscuous PXRs relative to other members of the nuclear Receptor superfamily. The 4-methyl-1-piperazinyl ring of rifampicin, which would lie adjacent to the disordered protein reg...
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structural disorder in the compleX of human Pregnane X Receptor and the macrolide antibiotic rifampicin
Molecular Endocrinology, 2005Co-Authors: Jill E Chrencik, Steven A Kliewer, Linda B Moore, Jillian Orans, Li Peng, Bruce Wisely, Jon L Collins, Millard H Lambert, Yu Xue, Matthew R RedinboAbstract:The human nuclear Xenobiotic Receptor, Pregnane X Receptor (PXR), detects a variety of structurally distinct endogenous and Xenobiotic compounds and controls eXpression of genes central to drug and cholesterol metabolism. The macrolide antibiotic rifampicin, a front-line treatment for tuberculosis, is an established PXR agonist and, at 823 Da, is one of the largest known ligands for the Receptor. We present the 2.8 A crystal structure of the ligand-binding domain of human PXR in compleX with rifampicin. We also use structural and mutagenesis data to eXamine the origins of the directed promiscuity eXhibited by the PXRs across species. Three structurally fleXible loops adjacent to the ligand-binding pocket of PXR are disordered in this crystal structure, including the 200-210 region that is part of a sequence insert novel to the promiscuous PXRs relative to other members of the nuclear Receptor superfamily. The 4-methyl-1-piperazinyl ring of rifampicin, which would lie adjacent to the disordered protein regions, is also disordered and not observed in the structure. Taken together, our results indicate that one wall of the PXR ligand-binding cavity can remain fleXible even when the Receptor is in compleX with an activating ligand. These observations highlight the key role that structural fleXibility plays in PXR's promiscuous response to Xenobiotics.
Frank J. Gonzalez - One of the best experts on this subject based on the ideXlab platform.
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Pregnane X Receptor activation potentiates ritonavir hepatotoXicity
Journal of Clinical Investigation, 2019Co-Authors: Amina I. Shehu, Wen Xie, Pengcheng Wang, Junjie Zhu, Yue Wang, Da Yang, Deborah Mcmahon, Frank J. GonzalezAbstract:Ritonavir (RTV) is on the World Health Organization's List of Essential Medicines for antiretroviral therapy, but can cause hepatotoXicity by unknown mechanisms. Multiple clinical studies found that hepatotoXicity occurred in 100% of participants who were pretreated with rifampicin or efavirenz followed by RTV-containing regimens. Both rifampicin and efavirenz are activators of the Pregnane X Receptor (PXR), a transcription factor with significant inter-species differences in ligand-dependent activation. Using PXR-humanized mouse models, we recapitulated the RTV hepatotoXicity observed in the clinic. PXR was found to modulate RTV hepatotoXicity through CYP3A4-dependent pathways involved in RTV bioactivation, oXidative stress, and endoplasmic reticulum stress. In summary, the current work demonstrated the essential roles of human PXR and CYP3A4 in RTV hepatotoXicity, which can be applied to guide the safe use of RTV-containing regimens in the clinic.
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Pregnane X Receptor promotes ethanol induced hepatosteatosis in mice
Journal of Biological Chemistry, 2018Co-Authors: Sora Choi, Frank J. Gonzalez, Prince Neequaye, Samuel W French, Maxwell A GyamfiAbstract:The Pregnane X Receptor (PXR, NR1I2) is a Xenobiotic-sensing nuclear Receptor that modulates the metabolic response to drugs and toXic agents. Both PXR activation and deficiency promote hepatic triglyceride accumulation, a hallmark feature of alcoholic liver disease. However, the molecular mechanism of PXR-mediated activation of ethanol (EtOH)-induced steatosis is unclear. Here, using male wildtype (WT) and PXr-null mice, we eXamined PXR-mediated regulation of chronic EtOH-induced hepatic lipid accumulation and hepatotoXicity. EtOH ingestion for 8 weeks significantly (1.8-fold) up-regulated PXr mRNA levels in WT mice. The EtOH eXposure also increased mRNAs encoding hepatic constitutive androstane Receptor (3-fold) and its target, Cyp2b10 (220-fold), in a PXR-dependent manner. Furthermore, WT mice had higher serum EtOH levels and developed hepatic steatosis characterized by micro- and macrovesicular lipid accumulation. Consistent with the development of steatosis, lipogenic gene induction was significantly increased in WT mice, including sterol regulatory element-binding protein 1c target gene fatty-acid synthase (3.0-fold), early growth response-1 (3.2-fold), and TNFα (3.0-fold), whereas the eXpression of peroXisome proliferator-activated Receptor α target genes was suppressed. Of note, PXR deficiency suppressed these changes and steatosis. Protein levels, but not mRNAs levels, of EtOH-metabolizing enzymes, including alcohol dehydrogenase 1, aldehyde dehydrogenase 1A1, and catalase, as well as the microsomal triglyceride transfer protein, involved in regulating lipid output were higher in PXr-null than in WT mice. These findings establish that PXR signaling contributes to ALD development and suggest that PXR antagonists may provide a new approach for ALD therapy.
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skin response to a carcinogen involves the Xenobiotic Receptor Pregnane X Receptor
Experimental Dermatology, 2015Co-Authors: Andreas Elentner, Matthias Schmuth, Frank J. Gonzalez, Daniela Ortner, Bjorn E Clausen, Pedro M Fernandezsalguero, Sandrine DubracAbstract:Skin is in daily contact with potentially harmful molecules from the environment such as cigarette smoke, automobile emissions, industrial soot and groundwater. Pregnane X Receptor (PXR) is a transcription factor eXpressed in liver and intestine that is activated by Xenobiotic chemicals including drugs and environmental pollutants. Topical application of the tumor initiator 7,12-dimethylbenz(a)anthracene (DMBA) enhances PXr, Cyp1a1, Cyp1b1 and Cyp3a11, but not Ahr eXpression in the skin. Surprisingly, DMBA-induced PXr upregulation is largely impaired in Langerin(+) cell-depleted skin, suggesting that DMBA mainly triggers PXr in Langerin(+) cells. Furthermore, PXR deficiency protects from DNA damage in epidermal cells but to a lesser eXtent than aryl hydrocarbon Receptor (AHR) deficiency. Interestingly, skin eXposure to low doses of DMBA induces migration of PXR-deficient but not of wild-type and AHR-deficient Langerhans cells (LCs). PXR-humanized mice show a marked increase in DNA damage to epidermal cells after topical application of DMBA, demonstrating relevance of these findings in human tissue. This is the first report suggesting that carcinogens might trigger PXR in epidermal cells, particularly in LCs, thus leading to DNA damage. Further studies are required to better delineate the role of PXR in cutaneous carcinogenesis.
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activation of intestinal human Pregnane X Receptor protects against azoXymethane deXtran sulfate sodium induced colon cancer
Journal of Pharmacology and Experimental Therapeutics, 2014Co-Authors: Jie Cheng, Zhongze Fang, Kenjiro Nagaoka, Minoru Okamoto, Naoki Tanaka, Shioko Kimura, Frank J. GonzalezAbstract:The role of intestinal human Pregnane X Receptor (PXR) in colon cancer was determined through investigation of the chemopreventive role of rifaXimin, a specific agonist of intestinal human PXR, toward azoXymethane (AOM)/deXtran sulfate sodium (DSS)–induced colon cancer. RifaXimin treatment significantly decreased the number of colon tumors induced by AOM/DSS treatment in PXR-humanized mice, but not wild-type or PXr-null mice. Additionally, rifaXimin treatment markedly increased the survival rate of PXR-humanized mice, but not wild-type or PXr-null mice. These data indicated a human PXR–dependent therapeutic chemoprevention of rifaXimin toward AOM/DSS-induced colon cancer. Nuclear factor κ-light-chain-enhancer of activated B cells–mediated inflammatory signaling was upregulated in AOM/DSS-treated mice, and inhibited by rifaXimin in PXR-humanized mice. Cell proliferation and apoptosis were also modulated by rifaXimin treatment in the AOM/DSS model. In vitro cell-based assays further revealed that rifaXimin regulated cell apoptosis and cell cycle in a human PXR-dependent manner. These results suggested that specific activation of intestinal human PXR eXhibited a chemopreventive role toward AOM/DSS-induced colon cancer by mediating anti-inflammation, antiproliferation, and proapoptotic events.
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bisphenol a increases atherosclerosis in Pregnane X Receptor humanized apoe deficient mice
Journal of the American Heart Association, 2014Co-Authors: Yipeng Sui, Frank J. Gonzalez, Sehyung Park, Robert N Helsley, Manjula Sunkara, Andrew J Morris, Changcheng ZhouAbstract:Background Bisphenol A (BPA) is a base chemical used eXtensively in many consumer products. BPA has recently been associated with increased risk of cardiovascular disease (CVD) in multiple large-scale human population studies, but the underlying mechanisms remain elusive. We previously reported that BPA activates the Pregnane X Receptor (PXR), which acts as a Xenobiotic sensor to regulate Xenobiotic metabolism and has pro-atherogenic effects in animal models upon activation. Interestingly, BPA is a potent agonist of human PXR but does not activate mouse or rat PXR signaling, which confounds the use of rodent models to evaluate mechanisms of BPA-mediated CVD risk. This study aimed to investigate the atherogenic mechanism of BPA using a PXR-humanized mouse model. Methods and Results A PXR-humanized ApoE deficient (huPXR•ApoE−/−) mouse line was generated that respond to human PXR ligands and feeding studies were performed to determine the effects of BPA eXposure on atherosclerosis development. EXposure to BPA significantly increased atherosclerotic lesion area in the aortic root and brachiocephalic artery of huPXR•ApoE−/− mice by 104% ( P <0.001) and 120% ( P <0.05), respectively. By contrast, BPA did not affect atherosclerosis development in the control littermates without human PXR. BPA eXposure did not affect plasma lipid levels but increased CD36 eXpression and lipid accumulation in macrophages of huPXR•ApoE−/− mice. Conclusion These findings identify a molecular mechanism that could link BPA eXposure to increased risk of CVD in eXposed individuals. PXR is therefore a relevant target for future risk assessment of BPA and related environmental chemicals in humans.