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Pondugula SR, Brimer-Cline C, Wu J, Schuetz EG, Tyagi RK, Chen T. A phosphomimetic mutation at threonine-57 abolishes transactivation activity and alters nuclear localization pattern of human pregnane x receptor. Drug Metab Dispos 2009; 37:719-30. [PMID: 19171678 DOI: 10.1124/dmd.108.024695] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The pregnane X receptor (PXR) plays crucial roles in multiple physiological processes. However, the signaling mechanisms responsible are not well defined; it is most likely that multiple functions of PXR are modulated by its phosphorylation. Therefore, we sought to determine whether mutation at a highly conserved Thr(57) affects human PXR (hPXR) function. Site-directed mutagenesis was performed to generate phosphorylation-deficient (hPXR(T57A)) and phosphomimetic (hPXR(T57D)) mutants. Gene reporter, Western blotting, immunocytochemistry, mammalian two-hybrid, and electrophoretic mobility shift assays were used to study cytochrome P450 3A4 (CYP3A4) promoter activation, protein levels, localization, cofactor interaction, and CYP3A4 promoter binding of the hPXR mutants, respectively. hPXR(T57D), but not hPXR(T57A), lost its transcriptional activity. Neither mutation altered hPXR's protein levels and interaction with steroid receptor coactivator-1. hPXR and hPXR(T57A) exhibited a homogenous nuclear distribution, whereas hPXR(T57D) exhibited a distinctive punctate nuclear localization pattern similar to that of hPXR mutants with impaired function that colocalize with silencing mediator of retinoid and thyroid receptors (SMRT), although silencing of SMRT did not rescue the altered function of hPXR(T57D). However, hPXR(T57D), but not hPXR(T57A), impaired hPXR's ability to bind to the CYP3A4 promoter, consistent with the mutant's transactivation function. Furthermore, the 70-kDa form of ribosomal protein S6 kinase (p70 S6K) phosphorylated hPXR in vitro and inhibited its transcriptional activity, whereas hPXR(T57A) partially resisted the inhibitory effect of p70 S6K. Our studies identify a functionally significant phosphomimetic mutant (hPXR(T57D)) and show p70 S6K phosphorylation and regulation of hPXR transactivation to support the notion that phosphorylation plays important roles in regulating hPXR function.
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Affiliation(s)
- Satyanarayana R Pondugula
- Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Mail Stop 1000, Memphis, TN 38105, USA
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Zhou C, Verma S, Blumberg B. The steroid and xenobiotic receptor (SXR), beyond xenobiotic metabolism. NUCLEAR RECEPTOR SIGNALING 2009; 7:e001. [PMID: 19240808 PMCID: PMC2646121 DOI: 10.1621/nrs.07001] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/23/2008] [Accepted: 12/12/2008] [Indexed: 12/31/2022]
Abstract
The steroid and xenobiotic receptor (SXR) (also known as pregnane X receptor or PXR) is a nuclear hormone receptor activated by a diverse array of endogenous hormones, dietary steroids, pharmaceutical agents, and xenobiotic compounds. SXR has an enlarged, flexible, hydrophobic ligand binding domain (LBD) which is remarkably divergent across mammalian species and SXR exhibits considerable differences in its pharmacology among mammals. The broad response profile of SXR has led to the development of "the steroid and xenobiotic sensor hypothesis". SXR has been established as a xenobiotic sensor that coordinately regulates xenobiotic clearance in the liver and intestine via induction of genes involved in drug and xenobiotic metabolism. In the past few years, research has revealed new and mostly unsuspected roles for SXR in modulating inflammation, bone homeostasis, vitamin D metabolism, lipid homeostasis, energy homeostasis and cancer. The identification of SXR as a xenobiotic sensor has provided an important tool for studying new mechanisms through which diet, chemical exposure, and environment ultimately impact health and disease. The discovery and pharmacological development of new PXR modulators might represent an interesting and innovative therapeutic approach to combat various diseases.
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Affiliation(s)
- Changcheng Zhou
- Laboratory of Biochemical Genetics and Metabolism, The Rockefeller University, New York, New York, USA.
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Gupta D, Venkatesh M, Wang H, Kim S, Sinz M, Goldberg GL, Whitney K, Longley C, Mani S. Expanding the roles for pregnane X receptor in cancer: proliferation and drug resistance in ovarian cancer. Clin Cancer Res 2008; 14:5332-40. [PMID: 18765524 DOI: 10.1158/1078-0432.ccr-08-1033] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
PURPOSE We examined the presence of the pregnane X receptor (PXR) and its effects on ovarian cancer cells after activation by its cognate ligand. EXPERIMENTAL DESIGN SKOV-3 and OVCAR-8 ovarian carcinoma cells were analyzed for expression of PXR by quantitative reverse transcription-PCR and Western blot. Human ovarian cancer tissue was also analyzed for PXR expression by immunochemistry. Ligand (agonist)-induced PXR target genes were analyzed in SKOV-3 cells by quantitative reverse transcription-PCR. SKOV-3 cell proliferation was assessed by MTT assay. In vivo confirmation of in vitro effects of PXR ligands were done in NOD.SCID mice carrying SKOV-3 xenografts. RESULTS PXR is expressed in ovarian cancer cells. In SKOV-3 cells, PXR is functional and its activation by cognate ligands induces PXR target genes (CYP2B6, CYP3A4, and UGT1A1) but not MDR1 and MRP2. PXR activation in SKOV-3 cells induces cell proliferation and drug resistance. In mice harboring SKOV-3 xenografts, rifampicin (PXR agonist) induces cell proliferation and tumor growth. CONCLUSION PXR activation, regardless of the type of ligand agonist present, promotes the "malignant" phenotype of cancer cells. These data serve as the basis for finding novel nontoxic inhibitors of PXR activation as a method to control cell growth and prevent induction of drug resistance.
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Affiliation(s)
- Divya Gupta
- Division of Gynecologic Oncology, Department of Obstetrics and Gynecology and Women's Health, Albert Einstein College of Medicine and Montefiore Medical Center, Bronx, NY 10461, USA
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Meijerman I, Beijnen JH, Schellens JH. Combined action and regulation of phase II enzymes and multidrug resistance proteins in multidrug resistance in cancer. Cancer Treat Rev 2008; 34:505-20. [DOI: 10.1016/j.ctrv.2008.03.002] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2007] [Revised: 02/11/2008] [Accepted: 03/01/2008] [Indexed: 01/16/2023]
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Ory B, Moriceau G, Trichet V, Blanchard F, Berreur M, Rédini F, Rogers M, Heymann D. Farnesyl diphosphate synthase is involved in the resistance to zoledronic acid of osteosarcoma cells. J Cell Mol Med 2008; 12:928-41. [PMID: 18494934 PMCID: PMC4401135 DOI: 10.1111/j.1582-4934.2008.00141.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
We recently demonstrated original anti-tumor effects of zoledronic acid (Zol) on osteosarcoma cell lines independently of their p53 and Rb status. The present study investigated the potential Zol-resistance acquired by osteosarcoma cells after prolonged treatment. After 12 weeks of culture in the presence of 1 μm Zol, the effects of high doses of Zol (10–100 μm) were compared between the untreated rat (OSRGA, ROS) and human (MG63, SAOS2) osteosarcoma cells and Zol-pretreated cells in terms of cell proliferation, cell cycle analysis, migration assay and cytoskeleton organization. Long-term treatment with 1 μm Zol reduced the sensitivity of osteosarcoma cells to high concentrations of Zol. Furthermore, the Zol-resistant cells were sensitive to conventional anti-cancer agents demonstrating that this resistance process is independent of the multidrug resistance phenotype. However, as similar experiments performed in the presence of clodronate and pamidronate evidenced that this drug resistance was restricted to the nitrogen-containing bisphosphonates, we then hypothesized that this resistance could be associated with a differential expression of farnesyl diphos-phate synthase (FPPS) also observed in human osteosarcoma samples. The transfection of Zol-resistant cells with FPPS siRNA strongly increased their sensitivity to Zol. This study demonstrates for the first time the induction of metabolic resistance after prolonged Zol treatment of osteosarcoma cells confirming the therapeutic potential of Zol for the treatment of bone malignant pathologies, but points out the importance of the treatment regimen may be important in terms of duration and dose to avoid the development of drug metabolic resistance.
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Affiliation(s)
- B Ory
- Institut National de la Santé et de la Recherche Médicale, ERI 7, Nantes, France
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56
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Lin W, Wu J, Dong H, Bouck D, Zeng FY, Chen T. Cyclin-dependent kinase 2 negatively regulates human pregnane X receptor-mediated CYP3A4 gene expression in HepG2 liver carcinoma cells. J Biol Chem 2008; 283:30650-7. [PMID: 18784074 DOI: 10.1074/jbc.m806132200] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The human pregnane X receptor (hPXR) regulates the expression of critical drug metabolism enzymes. One of such enzymes, cytochrome P450 3A4 (CYP3A4), plays critical roles in drug metabolism in hepatocytes that are either quiescent or passing through the cell cycle. It has been well established that the expression of P450, such as CYP3A4, is markedly reduced during liver development or regeneration. Numerous studies have implicated cellular signaling pathways in modulating the functions of nuclear receptors, including hPXR. Here we report that inhibition of cyclin-dependent kinases (Cdks) by kenpaullone and roscovitine (two small molecule inhibitors of Cdks that we identified in a screen for compounds that activate hPXR) leads to activation of hPXR-mediated CYP3A4 gene expression in HepG2 human liver carcinoma cells. Consistent with this finding, activation of Cdk2 attenuates the activation of CYP3A4 gene expression. In vitro kinase assays revealed that Cdk2 directly phosphorylates hPXR. A phosphomimetic mutation of a putative Cdk phosphorylation site, Ser(350), significantly impairs the function of hPXR, whereas a phosphorylation-deficient mutation confers resistance to Cdk2. Using HepG2 that has been stably transfected with hPXR and the CYP3A4-luciferase reporter, enriched in different phases of the cell cycle, we found that hPXR-mediated CYP3A4 expression is greatly reduced in the S phase. Our results indicate for the first time that Cdk2 negatively regulates the activity of hPXR, and suggest an important role for Cdk2 in regulating hPXR activity and CYP3A4 expression in hepatocytes passing through the cell cycle, such as those in fetal or regenerating adult liver.
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Affiliation(s)
- Wenwei Lin
- Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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57
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Chen T. Nuclear receptor drug discovery. Curr Opin Chem Biol 2008; 12:418-26. [PMID: 18662801 DOI: 10.1016/j.cbpa.2008.07.001] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2008] [Revised: 06/30/2008] [Accepted: 07/01/2008] [Indexed: 12/13/2022]
Abstract
Nuclear receptors (NR) are ligand-activated transcription factors that regulate the activation of a variety of important target genes. There are 48 genes that encode NRs in the human genome, and these receptors now represent one of the most important targets for therapeutic drug development. Successful identification of selective NR modulators has transformed the NR drug discovery strategy from the designing of synthetic compounds that mimic the full function of cognate ligands to developing compounds that selectively modulate the functional activity of an NR in a manner that is distinct from the cognate ligands. Current efforts regarding NR drug development continue to focus on improving the function and tissue selectivity of drug candidates to reduce undesirable side effects. This review focuses on modulators of the glucocorticoid receptor (GR), androgen receptor (AR), and pregnane X receptor (PXR).
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MESH Headings
- Androgen Receptor Antagonists
- Androgens
- Animals
- Drug Evaluation, Preclinical/methods
- Humans
- Pharmacology/trends
- Pregnane X Receptor
- Receptors, Androgen/metabolism
- Receptors, Cytoplasmic and Nuclear/agonists
- Receptors, Cytoplasmic and Nuclear/antagonists & inhibitors
- Receptors, Cytoplasmic and Nuclear/metabolism
- Receptors, Glucocorticoid/agonists
- Receptors, Glucocorticoid/antagonists & inhibitors
- Receptors, Glucocorticoid/metabolism
- Receptors, Steroid/agonists
- Receptors, Steroid/antagonists & inhibitors
- Receptors, Steroid/metabolism
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Affiliation(s)
- Taosheng Chen
- Department of Chemical Biology and Therapeutics, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA.
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Goel S, Cohen M, Çömezoglu SN, Perrin L, André F, Jayabalan D, Iacono L, Comprelli A, Ly VT, Zhang D, Xu C, Humphreys WG, McDaid H, Goldberg G, Horwitz SB, Mani S. The Effect of Ketoconazole on the Pharmacokinetics and Pharmacodynamics of Ixabepilone: A First in Class Epothilone B Analogue in Late-Phase Clinical Development. Clin Cancer Res 2008; 14:2701-9. [DOI: 10.1158/1078-0432.ccr-07-4151] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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59
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Mir O, Ropert S, Alexandre J, Goldwasser F, Treluyer JM. CYP3A4/5 and pharmacogenetics in patients with sarcoma. Lancet Oncol 2007; 8:667-8; author reply 668-9. [PMID: 17679078 DOI: 10.1016/s1470-2045(07)70215-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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60
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Masuyama H, Nakatsukasa H, Takamoto N, Hiramatsu Y. Down-Regulation of Pregnane X Receptor Contributes to Cell Growth Inhibition and Apoptosis by Anticancer Agents in Endometrial Cancer Cells. Mol Pharmacol 2007; 72:1045-53. [PMID: 17636047 DOI: 10.1124/mol.107.037937] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Recent studies have revealed that pregnane X receptor (PXR) can function as a master regulator to control the expression of drug-metabolizing enzymes, cytochrome P450 3A (CYP3A) family, and members of the drug transporter family, including multiple drug resistance 1 (MDR1). We demonstrated previously that steroid/xenobiotic metabolism by tumor tissue through the PXR-CYP3A pathway might play an important role in endometrial cancer and that PXR ligands enhance PXR-mediated transcription in a ligand- and promoter-dependent fashion, leading to differential regulation of individual PXR targets, especially CYP3A4 and MDR1. In this study, we investigated the potential contribution of PXR down-regulation by RNA interference toward the augmentation of drug sensitivity and the overcoming of drug resistance. We observed the protein levels of both CYP3A4 and MDR1 in PXR small interfering RNA (siRNA)-transfected cells were not increased in the presence of PXR ligands, paclitaxel, cisplatin, estradiol, or medroxyprogesterone acetate (MPA) compared with control siRNA-transfected cells. There was no PXR-mediated transactivation or augmentation of transcription by coactivators in the presence of these ligands. We then found that PXR down-regulation caused a significant increase in cell growth inhibition and enhancement of apoptosis in the presence of the anticancer agents, paclitaxel, cisplatin, and MPA. Finally, we demonstrated that PXR overexpression caused a significant decrease in cell growth inhibition and inhibited apoptosis in the presence of paclitaxel or cisplatin. These data suggest that PXR down-regulation could be a novel therapeutic approach for the augmentation of sensitivity to anticancer agents, or to overcome resistance to them, in the treatment of endometrial cancer.
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Affiliation(s)
- Hisashi Masuyama
- Department of Obstetrics and Gynecology, Okayama University Graduate School of Medicine, Dentist and Pharmaceutical Science, Shikata, Okayama, 700-8558, Japan.
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