X Receptor (x + receptor)

Distribution by Scientific Domains
Distribution within Medical Sciences

Kinds of X Receptor

  • farnesoid x receptor
  • liver x receptor
  • pregnane x receptor
  • retinoid x receptor

  • Selected Abstracts

    Dose-dependent Induction of Cytochrome P450 (CYP) 3A4 and Activation of Pregnane X Receptor by Topiramate

    EPILEPSIA, Issue 12 2003
    Srikanth C. Nallani
    Summary:,Purpose: In clinical studies, topiramate (TPM) was shown to cause a dose-dependent increase in the clearance of ethinyl estradiol. We hypothesized that this interaction results from induction of hepatic cytochrome P450 (CYP) 3A4 by TPM. Accordingly, we investigated whether TPM induces CYP3A4 in primary human hepatocytes and activates the human pregnane X receptor (hPXR), a nuclear receptor that serves as a regulator of CYP3A4 transcription. Methods: Human hepatocytes were treated for 72 h with TPM (10, 25, 50, 100, 250, and 500 ,M) and known inducers, phenobarbital (PB; 2 mM), and rifampicin (10 ,M). The rate of testosterone 6,-hydroxylation by hepatocytes served as a marker for CYP3A4 activity. The CYP3A4-specific protein and mRNA levels were determined by using Western and Northern blot analyses, respectively. The hPXR activation was assessed with cell-based reporter gene assay. Results: Compared with controls, TPM (50,500 ,M),treated hepatocytes exhibited a considerable increase in the CYP3A4 activity (1. 6- to 8.2-fold), protein levels (4.6- to 17.3-fold), and mRNA levels (1.9- to 13.3-fold). Comparatively, rifampicin (10 ,M) effected 14.5-, 25.3-, and a 20.3-fold increase in CYP3A4 activity, immunoreactive protein levels, and mRNA levels, respectively. TPM (50,500 ,M) caused 1.3- to 3-fold activation of the hPXR, whereas rifampicin (10 ,M) caused a 6-fold activation. Conclusions: The observed induction of CYP3A4 by TPM, especially at the higher concentrations, provides a potential mechanistic explanation of the reported increase in the ethinyl estradiol clearance by TPM. It also is suggestive of other potential interactions when high-dose TPM therapy is used. [source]

    ChemInform Abstract: Pyrrole[2,3-d]azepino Compounds as Agonists of the Farnesoid X Receptor (FXR).

    CHEMINFORM, Issue 5 2010
    John F. Mehlmann
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

    Dose-dependent Induction of Cytochrome P450 (CYP) 3A4 and Activation of Pregnane X Receptor by Topiramate

    EPILEPSIA, Issue 12 2003
    Srikanth C. Nallani
    Summary:,Purpose: In clinical studies, topiramate (TPM) was shown to cause a dose-dependent increase in the clearance of ethinyl estradiol. We hypothesized that this interaction results from induction of hepatic cytochrome P450 (CYP) 3A4 by TPM. Accordingly, we investigated whether TPM induces CYP3A4 in primary human hepatocytes and activates the human pregnane X receptor (hPXR), a nuclear receptor that serves as a regulator of CYP3A4 transcription. Methods: Human hepatocytes were treated for 72 h with TPM (10, 25, 50, 100, 250, and 500 ,M) and known inducers, phenobarbital (PB; 2 mM), and rifampicin (10 ,M). The rate of testosterone 6,-hydroxylation by hepatocytes served as a marker for CYP3A4 activity. The CYP3A4-specific protein and mRNA levels were determined by using Western and Northern blot analyses, respectively. The hPXR activation was assessed with cell-based reporter gene assay. Results: Compared with controls, TPM (50,500 ,M),treated hepatocytes exhibited a considerable increase in the CYP3A4 activity (1. 6- to 8.2-fold), protein levels (4.6- to 17.3-fold), and mRNA levels (1.9- to 13.3-fold). Comparatively, rifampicin (10 ,M) effected 14.5-, 25.3-, and a 20.3-fold increase in CYP3A4 activity, immunoreactive protein levels, and mRNA levels, respectively. TPM (50,500 ,M) caused 1.3- to 3-fold activation of the hPXR, whereas rifampicin (10 ,M) caused a 6-fold activation. Conclusions: The observed induction of CYP3A4 by TPM, especially at the higher concentrations, provides a potential mechanistic explanation of the reported increase in the ethinyl estradiol clearance by TPM. It also is suggestive of other potential interactions when high-dose TPM therapy is used. [source]

    Properties of ecdysteroid receptors from diverse insect species in a heterologous cell culture system , a basis for screening novel insecticidal candidates

    FEBS JOURNAL, Issue 11 2009
    Joshua M. Beatty
    Insect development is driven by the action of ecdysteroids on morphogenetic processes. The classic ecdysteroid receptor is a protein heterodimer composed of two nuclear receptors, the ecdysone receptor (EcR) and Ultraspiracle (USP), the insect ortholog of retinoid X receptor. The functional properties of EcR and USP vary among insect species, and provide a basis for identifying novel and species-specific insecticidal candidates that disrupt this receptor's normal activity. A heterologous mammalian cell culture assay was used to assess the transcriptional activity of the heterodimeric ecdysteroid receptor from species representing two major insect orders: the fruit fly, Drosophila melanogaster (Diptera), and the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera). Several nonsteroidal agonists evoked a strong response with the L. decemlineata heterodimer that was consistent with biochemical and in vivo evidence, whereas the D. melanogaster receptor's response was comparatively modest. Conversely, the phytoecdysteroid muristerone A was more potent with the D. melanogaster heterodimer. The additional presence of juvenile hormone III potentiated the inductive activity of muristerone A in the receptors from both species, but juvenile hormone III was unable to potentiate the inductive activity of the diacylhydrazine methoxyfenozide (RH2485) in the receptor of either species. The effects of USP on ecdysteroid-regulated transcriptional activity also varied between the two species. When it was tested with D. melanogaster EcR isoforms, basal activity was lower and ligand-dependent activity was higher with L. decemlineata USP than with D. melanogaster USP. Generally, the species-based differences validate the use of the cell culture assay screen for novel agonists and potentiators as species-targeted insecticidal candidates. [source]

    Peroxisome proliferator-activated receptor ,,retinoid X receptor agonists induce beta-cell protection against palmitate toxicity

    FEBS JOURNAL, Issue 23 2007
    Karine Hellemans
    Fatty acids can stimulate the secretory activity of insulin-producing beta-cells. At elevated concentrations, they can also be toxic to isolated beta-cells. This toxicity varies inversely with the cellular ability to accumulate neutral lipids in the cytoplasm. To further examine whether cytoprotection can be achieved by decreasing cytoplasmic levels of free acyl moieties, we investigated whether palmitate toxicity is also lowered by stimulating its ,-oxidation. Lower rates of palmitate-induced beta-cell death were measured in the presence of l -carnitine as well as after addition of peroxisome proliferator-activated receptor , (PPAR,) agonists, conditions leading to increased palmitate oxidation. In contrast, inhibition of mitochondrial ,-oxidation by etomoxir increased palmitate toxicity. A combination of PPAR, and retinoid X receptor (RXR) agonists acted synergistically and led to complete protection; this was associated with enhanced expression levels of genes involved in mitochondrial and peroxisomal ,-oxidation, lipid metabolism, and peroxisome proliferation. PPAR,,RXR protection was abolished by the carnitine palmitoyl transferase 1 inhibitor etomoxir. These observations indicate that PPAR, and RXR regulate beta-cell susceptibility to long-chain fatty acid toxicity by increasing the rates of ,-oxidation and by involving peroxisomes in fatty acid metabolism. [source]

    Molecular cloning of the ecdysone receptor and the retinoid X receptor from the scorpion Liocheles australasiae

    FEBS JOURNAL, Issue 23 2007
    Yoshiaki Nakagawa
    cDNAs of the ecdysone receptor and the retinoid X receptor were cloned from the Japanese scorpion Liocheles australasiae, and the amino acid sequences were deduced. The full-length cDNA sequences of the L. australasiae ecdysone receptor and the L. australasiae retinoid X receptor were 2881 and 1977 bp in length, respectively, and the open reading frames encoded proteins of 560 and 414 amino acids. The amino acid sequence of the L. australasiae ecdysone receptor was similar to that of the ecdysone receptor-A of the soft tick, Ornithodoros moubata (68%) and to that of the ecdysone receptor-A1 of the lone star tick, Amblyomma americanum (66%), but showed lower similarity to the ecdysone receptors of Orthoptera and Coleoptera (53,57%). The primary sequence of the ligand-binding region of the L. australasiae ecdysone receptor was highly homologous to that of ticks (85,86%). The amino acid sequence of the L. australasiae retinoid X receptor was also homologous to the amino acid sequence of ultraspiracles of ticks (63%) and insects belonging to the orders Orthoptera and Coleoptera (60,64%). The identity of both the L. australasiae ecdysone receptor and the L. australasiae retinoid X receptor to their lepidopteran and dipteran orthologs was less than 50%. The cDNAs of both the L. australasiae ecdysone receptor (L. australasiae ecdysone receptor-A) and the L. australasiae retinoid X receptor were successfully translated in vitro using a rabbit reticulocyte lysate system. An ecdysone analog, ponasterone A, bound to L. australasiae ecdysone receptor-A (KD = 4.2 nm), but not to L. australasiae retinoid X receptor. The L. australasiae retinoid X receptor did not enhance the binding of ponasterone A to L. australasiae ecdysone receptor-A, although L. australasiae retinoid X receptor was necessary for the binding of L. australasiae ecdysone receptor-A to ecdysone response elements. [source]

    15-Deoxy ,12,14 -prostaglandin J2 suppresses transcription by promoter 3 of the human thromboxane A2 receptor gene through peroxisome proliferator-activated receptor , in human erythroleukemia cells

    FEBS JOURNAL, Issue 18 2005
    Adrian T. Coyle
    In humans, thromboxane (TX) A2 signals through two receptor isoforms, thromboxane receptor (TP), and TP,, which are transcriptionally regulated by distinct promoters, Prm1 and Prm3, respectively, within the single TP gene. The aim of the current study was to investigate the ability of the endogenous peroxisome proliferator-activated receptor (PPAR), ligand 15-deoxy-,12,14 -prostaglandin J2 (15d-PGJ2) to regulate expression of the human TP gene and to ascertain its potential effects on the individual TP, and TP, isoforms. 15d-PGJ2 suppressed Prm3 transcriptional activity and TP, mRNA expression in the platelet progenitor megakaryocytic human erythroleukemia (HEL) 92.1.7 cell line but had no effect on Prm1 or Prm2 activity or on TP, mRNA expression. 15d-PGJ2 also resulted in reductions in the overall level of TP protein expression and TP-mediated intracellular calcium mobilization in HEL cells. 15d-PGJ2 suppression of Prm3 transcriptional activity and TP, mRNA expression was found to occur through a novel mechanism involving direct binding of PPAR,,retinoic acid X receptor (RXR) heterodimers to a PPAR, response element (PPRE) composed of two imperfect hexameric direct repeat (DR) sequences centred at ,159 and ,148, respectively, spaced by five nucleotides (DR5). These data provide direct evidence for the role of PPAR, in the regulation of human TP gene expression within the vasculature and point to further critical differences in the modes of transcriptional regulation of TP, and TP, in humans. Moreover, these data highlight a further link between enhanced risk of cardiovascular disease in diabetes mellitus associated with increased synthesis and action of thromboxane A2 (TXA2). [source]

    Functional analysis of the rat bile salt export pump gene promoter

    FEBS JOURNAL, Issue 14 2002
    Regulation by bile acids, drugs, endogenous compounds
    The 5, flanking region of the bile salt export pump (Bsep) gene was systematically analysed to provide the basis for understanding the mechanisms which regulate Bsep transcription. In addition substrates and drugs were investigated for their ability to alter Bsep promoter activity. Bsep promoter function was restricted to hepatocyte derived HepG2 cells. The 5, deletional analysis revealed a biphasic shape of reporter gene activities, indicating a suppressive element between nucleotides ,800 and ,512. Two consensus sites for the farnesoid X receptor (FXR) were located at nucleotides ,473 and ,64. The latter was characterized as functionally active in bile acid-mediated feed-back regulation of Bsep transcription. Bsep promoter activity was reduced by rifampin and ,-estradiol. The anti-estrogen tamoxifen stimulated promoter activity. Dexamethasone, hydrocortisone and phenobarbital had no effect on Bsep promoter activity. In conclusion, the data suggest that transcriptional regulation of the Bsep gene can be modulated by a number of endogenous compounds and xenobiotics. FXR was a major regulatory factor, mediating bile acid feed-back stimulation of Bsep transcription. [source]

    A role for the pregnane X receptor in flucloxacillin-induced liver injury,

    HEPATOLOGY, Issue 5 2010
    Elise Andrews
    Drug-induced liver injury (DILI) due to flucloxacillin is a rare but serious complication of treatment. There is some evidence that flucloxacillin is a human pregnane X receptor (PXR) agonist. This study was designed to investigate the relevance of PXR to flucloxacillin toxicity and to identify genes changing in expression in response to flucloxacillin. Changes in gene expression in human hepatocytes after treatment with 500 ,M flucloxacillin for 72 hours were examined by expression microarray analysis. The ability of flucloxacillin to act as a PXR agonist was investigated with reporter gene experiments. Flucloxacillin DILI cases (n = 51), drug-exposed controls without toxicity (n = 64), and community controls (n = 90) were genotyped for three common PXR polymorphisms. Luciferase reporter assays were used to assess the significance of a promoter region PXR polymorphism. Seventy-two probe sets representing 50 different genes showed significant changes in expression of 1.2-fold or higher. Most genes showing changes greater than 3-fold were known to be rifampicin-responsive, and this suggested a PXR-dependent mode of regulation. Using a luciferase-everted repeat separated by 6 base pairs element construct, we confirmed that flucloxacillin was a PXR agonist. We found a difference in the distribution of a PXR polymorphism (rs3814055; C-25385T) between flucloxacillin DILI cases and controls with the CC genotype associated with an increased risk of disease (odds ratio = 3.37, 95% confidence interval = 1.55-7.30, P = 0.0023). Reporter gene experiments showed lower promoter activity for the C allele than the T allele. Conclusion: Flucloxacillin is a PXR agonist at pharmacologically relevant concentrations, and a functionally significant upstream PXR polymorphism is a risk factor for flucloxacillin-induced DILI. Hepatology 2010 [source]

    The G protein,coupled receptor G2A: Involvement in hepatic lipid metabolism and gallstone formation in mice,

    HEPATOLOGY, Issue 4 2008
    Laura E. Johnson
    The G2A receptor is a member of the ovarian cancer G protein,coupled receptor 1 family of stress-inducible G protein,coupled receptors. In this study, we examined the hepatobiliary effects of loss of function of G2A in mice fed either a chow or lithogenic diet. G2A-deficient (G2A,/,) mice fed chow had a 25% reduction in biliary phosphatidylcholine content, reduced hepatic gene expression of the phosphatidylcholine transporter adenosine triphosphate,binding cassette B4, and an 8-fold increase in expression of the nuclear receptor liver X receptor (LXR). Despite the increased expression of LXR, transcription of several LXR target genes was reduced. G2A,/, mice fed a lithogenic diet had rapid gallstone formation, an increased cholesterol saturation index, a 2.5-fold increase in farnesoid X receptor expression, a 5-fold increase in LXR expression, and a 90% reduction in cholesterol 7,-hydroxylase expression in comparison with wild-type mice. There were no changes in gallbladder volume. Conclusion: These data demonstrate that the G2A receptor is important for hepatobiliary bile salt, cholesterol, and phospholipid homeostasis and for the pathogenesis of cholesterol gallstone formation. (HEPATOLOGY 2008;48:1138,1148.) [source]

    The nuclear bile acid receptor FXR as a novel therapeutic target in cholestatic liver diseases: Hype or hope?

    HEPATOLOGY, Issue 1 2004
    Michael Trauner M.D.
    Farnesoid X receptor (FXR) is a bile acid,activated transcription factor that is a member of the nuclear hormone receptor superfamily. FXR-null mice exhibit a phenotype similar to Byler disease, an inherited cholestatic liver disorder. In the liver, activation of FXR induces transcription of transporter genes involved in promoting bile acid clearance and represses genes involved in bile acid biosynthesis. We investigated whether the synthetic FXR agonist GW4064 could protect against cholestatic liver damage in rat models of extrahepatic and intrahepatic cholestasis. In the bile duct ligation and alpha-naphthylisothiocyanate models of cholestasis, GW4064 treatment resulted in significant reductions in serum alanine aminotransferase, aspartate aminotransferase, and lactate dehydrogenase, as well as other markers of liver damage. Rats that received GW4064 treatment also had decreased incidence and extent of necrosis, decreased inflammatory cell infiltration, and decreased bile duct proliferation. Analysis of gene expression in livers from GW4064-treated cholestatic rats revealed decreased expression of bile acid biosynthetic genes and increased expression of genes involved in bile acid transport, including the phospholipid flippase MDR2. The hepatoprotection seen in these animal models by the synthetic FXR agonist suggests FXR agonists may be useful in the treatment of cholestatic liver disease. [source]

    Effects of proinflammatory cytokines on rat organic anion transporters during toxic liver injury and cholestasis

    HEPATOLOGY, Issue 2 2003
    Andreas Geier M.D.
    Hepatobiliary transporters are down-regulated in toxic and cholestatic liver injury. Cytokines such as tumor necrosis factor , (TNF-,) and interleukin 1, (IL-1,) are attributed to mediate this regulation, but their particular contribution in vivo is still unknown. Thus, we studied the molecular mechanisms by which Ntcp, Oatp1, Oatp2, and Mrp2 are regulated by proinflammatory cytokines during liver injury. Rats were injected intraperitoneally with either carbon tetrachloride or endotoxin. Inactivation of TNF-, and IL-1, was achieved by repetitive intraperitoneal injection of etanercept and anakinra, respectively. Messenger RNA (mRNA) levels of transporters and binding activities as well as nuclear protein levels of Ntcp, Oatp2, and Mrp2 transactivators were determined 20 to 24 hours later. In contrast to IL-1,, TNF-, inactivation alone fully prevented down-regulation of Ntcp, Oatp1, and Oatp2 mRNA as well as reduced binding activity of hepatocyte nuclear factor 1 (HNF-1) in CCl4 -induced toxic injury. In endotoxemia, down-regulation of Mrp2, and partially in case of Ntcp, could be prevented by IL-1, but not TNF-, blockade. However, inactivation of either cytokine led to preservation of HNF1 and partially of retinoid X receptor/retinoic acid receptor (RXR/RAR) binding activity. No effect of anticytokines was seen on pregnane X receptor (PXR) and constitutive androstane receptor (CAR) binding activity as well as nuclear protein mass. In conclusion, TNF-, represents the master cytokine responsible for HNF1-dependent down-regulation of Ntcp, Oatp1, and Oatp2 in CCl4 -induced toxic liver injury. IL-1, predominates in a complex signaling network of Ntcp and Mrp2 regulation in cholestatic liver injury. In contrast to in vitro studies, HNF1 and RXR/RAR-independent mechanisms appear to be more important in regulation of Mrp2 and Ntcp gene expression in endotoxemia. [source]

    CYP3A4 and pregnane X receptor humanized mice

    Frank J. Gonzalez
    Abstract Marked species differences exist in P450 expression and activities. In order to produce mouse models that can be used to more accurately predict human drug and carcinogen metabolism, P450- and xenobiotic receptor humanized mice are being prepared using bacterial artificial chromosomes (BAC) and P1 phage artificial chromosomes (PAC) genomic clones. In some cases, transgenic mice carrying the human genes are bred with null-mice to produce fully humanized mice. Mice expressing human CYP1A1, CYP1A2, CYP2E1, CYP2D6, CYP3A4, and CYP3A7 were generated and characterized. Studies with the CYP3A4-humanized (hCYP3A4) mouse line revealed new information on the physiological function of this P450 and its role in drug metabolism in vivo. With this mouse line, CYP3A4, under certain circumstances, was found to alter the serum levels of estrogen resulting in deficient lactation and low pup survival as a result of underdeveloped mammary glands. This hCYP3A4 mouse established the importance of intestinal CYP3A4 in the pharmacokinetics of orally administered drugs. The hCYP3A4 mice were also used to establish the mechanisms of potential gender differences in CYP3A4 expression (adult female > adult male) that could account for human gender differences in drug metabolism and response. The pregnane X receptor (PXR) is also involved in induction of drug metabolism through its target genes including CYP3A4. Since species differences exist in ligand specificity between human and mice, a PXR -humanized mouse (hPXR) was produced that responds to human PXR activators such as rifampicin but does not respond to the rodent activator pregnenalone 16,-carbonitrile. © 2007 Wiley Periodicals, Inc. J Biochem Mol Toxicol 21:158,162, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20173 [source]

    Vitamin D Receptor: Key Roles in Bone Mineral Pathophysiology, Molecular Mechanism of Action, and Novel Nutritional Ligands,

    Peter W Jurutka
    Abstract The vitamin D hormone, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], binds with high affinity to the nuclear vitamin D receptor (VDR), which recruits its retinoid X receptor (RXR) heterodimeric partner to recognize vitamin D responsive elements (VDREs) in target genes. 1,25(OH)2D3 is known primarily as a regulator of calcium, but it also controls phosphate (re)absorption at the intestine and kidney. Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone produced in osteoblasts that, like PTH, lowers serum phosphate by inhibiting renal reabsorption through Npt2a/Npt2c. Real-time PCR and reporter gene transfection assays were used to probe VDR-mediated transcriptional control by 1,25(OH)2D3. Reporter gene and mammalian two-hybrid transfections, plus competitive receptor binding assays, were used to discover novel VDR ligands. 1,25(OH)2D3 induces FGF23 78-fold in osteoblasts, and because FGF23 in turn represses 1,25(OH)2D3 synthesis, a reciprocal relationship is established, with FGF23 indirectly curtailing 1,25(OH)2D3 -mediated intestinal absorption and counterbalancing renal reabsorption of phosphate, thereby reversing hyperphosphatemia and preventing ectopic calcification. Therefore, a 1,25(OH)2D3,FGF23 axis regulating phosphate is comparable in importance to the 1,25(OH)2D3,PTH axis that regulates calcium. 1,25(OH)2D3 also elicits regulation of LRP5, Runx2, PHEX, TRPV6, and Npt2c, all anabolic toward bone, and RANKL, which is catabolic. Regulation of mouse RANKL by 1,25(OH)2D3 supports a cloverleaf model, whereby VDR-RXR heterodimers bound to multiple VDREs are juxtapositioned through chromatin looping to form a supercomplex, potentially allowing simultaneous interactions with multiple co-modulators and chromatin remodeling enzymes. VDR also selectively binds certain ,3/,6 polyunsaturated fatty acids (PUFAs) with low affinity, leading to transcriptionally active VDR-RXR complexes. Moreover, the turmeric-derived polyphenol, curcumin, activates transcription of a VDRE reporter construct in human colon cancer cells. Activation of VDR by PUFAs and curcumin may elicit unique, 1,25(OH)2D3 -independent signaling pathways to orchestrate the bioeffects of these lipids in intestine, bone, skin/hair follicle, and other VDR-containing tissues. [source]

    Constitutive activation of the mitogen-activated protein kinase pathway impairs vitamin D signaling in human prostate epithelial cells

    Zhentao Zhang
    We studied the effect of prolonged activation of mitogen-activated protein kinase (MAPK) signaling on 1,25 dihydroxyvitamin D (1,25(OH)2D3) action in the immortalized human prostate epithelial cell line RWPE1 and its Ki-Ras transformed clone RWPE2. 1,25(OH)2D3 -treatment caused growth arrest and induced gene expression in both cell lines but the response was blunted in RWPE2 cells. Vitamin D receptor (VDR) levels were lower in RWPE2 cells but VDR over-expression did not increase vitamin-D-mediated gene transcription in either cell line. In contrast, MAPK inhibition restored normal vitamin D transcriptional responses in RWPE2 cells and MAPK activation with constitutively active MEK1R4F reduced vitamin-D-regulated transcription in RWPE1 cells. 1,25(OH)2D3 -mediated transcription depends upon the VDR and its heterodimeric partner the retinoid X receptor (RXR) so we studied whether changes in the VDR,RXR transcription complex occur in response to MAPK activation. Mutation of putative phosphorylation sites in the activation function 1 (AF-1) domain (S32A, T82A) of RXR, restored 1,25(OH)2D3 -mediated transactivation in RWPE2 cells. Mammalian two-hybrid and co-immunoprecipitation assays revealed a vitamin-D-independent interaction between steroid receptor co-activator-1 (SRC-1) and RXR, that was reduced by MAPK activation and was restored in RWPE2 cells by mutating S32 and T82 in the RXR, AF-1 domain. Our data show that a common contributor to cancer development, prolonged activation of MAPK signaling, impairs 1,25(OH)2D3 -mediated transcription in prostate epithelial cells. This is due in part to the phosphorylation of critical amino acids in the RXR, AF-1 domain and impaired co-activator recruitment. J. Cell. Physiol. 224: 433,442, 2010. © 2010 Wiley-Liss, Inc. [source]

    Nuclear receptors and drug disposition gene regulation

    Rommel G. Tirona
    Abstract In this minireview, the role of various nuclear receptors and transcription factors in the expression of drug disposition genes is summarized. Specifically, the molecular aspects and functional impact of the aryl hydrocarbon receptor (AhR), nuclear factor-E2 p45-related factor 2 (Nrf2), hepatocyte nuclear factor 1, (HNF1,), constitutive androstane receptor (LAR), pregnane X receptor (PXR), farnesoid X receptor (FXR), peroxisome proliferator-activated receptor , (PPAR,), hepatocyte nuclear factor 4, (HNF4,), vitamin D receptor (VDR), liver receptor homolog 1 (LRH1), liver X receptor (LXR,), small heterodimer partner-1 (SHP-1), and glucocorticoid receptor (GR) on gene expression are detailed. Finally, we discuss some current topics and themes in nuclear receptor-mediated regulation of drug metabolizing enzymes and drug transporters. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1169,1186, 2005 [source]

    The influence of common gene variants of the xenobiotic receptor (PXR) in genetic susceptibility to intrahepatic cholestasis of pregnancy

    Aliment Pharmacol Ther,31, 583,592 Summary Background, The xenobiotic nuclear pregnane X receptor is implicated in many physiological pathways and diseases, including bile acid detoxification and cholestasis. Aim, To estimate the contribution of common gene variants of the xenobiotic receptor (pregnane X receptor, PXR) to genetic susceptibility to intrahepatic cholestasis of pregnancy. Methods, A total of 101 intrahepatic cholestasis of pregnancy patients and 171 healthy pregnant women in the third trimester of their pregnancies were included. Four tag single nucleotide polymorphisms (SNPs) (rs12488820 C/T, rs2472671 C/T, rs2461823 A/G, and rs1054191 A/G) encompassing 36 kb in chromosome 3, with a minor allele frequency ,0.10 and representing 33 polymorphic sites were genotyped. Besides these, three additional SNPs (rs3814057, rs6785049, and rs7643645) were included because they showed previous evidence of functionality. Results, Genotypic test for single SNPs showed that rs2461823 genotypes were significantly associated with intrahepatic cholestasis of pregnancy (P < 0.0069), OR per G allele: 1.44, 95% CI: 1.01,2.05, P < 0.042. The Cochran-Armitage test for trend and the allelic test showed a significant association with disease status (P < 0.04 and 0.03 respectively), G being the risk allele. A positive association between rs2461823 and ALT, AST, and bilirubin concentrations was observed. Neonate birth weight adjusted by the Capurro index was significantly associated with rs2461823 (P < 0.05); the proportion of the total variation attributed to rs2461823 genotypes was 7.8%. Conclusion, Common PXR polymorphisms may contribute to the genetic susceptibility to intrahepatic cholestasis of pregnancy. [source]

    Learning from the pregnane X receptor: how to fight one aggressor with two strategies

    Christian Rust
    No abstract is available for this article. [source]

    Retinoic acid signalling induces the differentiation of mouse fetal liver-derived hepatic progenitor cells

    LIVER INTERNATIONAL, Issue 10 2009
    Jiayi Huang
    Abstract Background: Hepatic progenitor cells (HPCs) can be isolated from fetal liver and extrahepatic tissues. Retinoic acid (RA) signalling plays an important role in development, although the role of RA signalling in liver-specific progenitors is poorly understood. Aims: We sought to determine the role of RA in regulating hepatic differentiation. Methods: RNA was isolated from liver tissues of various developmental stages. Liver marker expression was assessed by reverse transcriptase-polymerase chain reaction and immunofluorescence staining. Reversibly immortalized HPCs derived from mouse embryonic day 14.5 (E14.5) liver (aka, HP14.5) were established. Albumin promoter-driven reporter (Alb-GLuc) was used to monitor hepatic differentiation. Glycogen synthesis was assayed as a marker for terminal hepatic differentiation. Results: Retinoic acid receptor (RAR)-,, retinoid X receptor (RXR)-, and RXR-, expressed in E12.5 to postnatal day 28 liver samples. Expression of RAR-, and RXR-, was low perinatally, whereas RAR-, was undetectable in prenatal tissues and increased postnatally. Retinal dehydrogenase 1 and 2 (Raldh1 and Raldh2) were expressed in all tissues, while Raldh3 was weakly expressed in prenatal samples but was readily detected postnatally. Nuclear receptor corepressors were highly expressed in all tissues, while expression of nuclear co-activators decreased in perinatal tissues and increased after birth. HP14.5 cells expressed high levels of early liver stem cell markers. Expression of RA signalling components and coregulators was readily detected in HP14.5. RA was shown to induce Alb-GLuc activity and late hepatocyte markers. RA was further shown to induce glycogen synthesis in HP14.5 cells, an important function of mature hepatocytes. Conclusions: Our results strongly suggest that RA signalling may play an important role in regulating hepatic differentiation. [source]

    Role of insulin-like growth factor binding protein-3 in breast cancer cell growth

    Lynette J. Schedlich
    Abstract The mitogenic effects of insulin-like growth factors (IGFs) are regulated by a family of insulin-like growth factor binding proteins (IGFBPs). One member of this family, IGFBP-3, mediates the growth-inhibitory and apoptosis-inducing effects of a number of growth factors and hormones such as transforming growth factor-,, retinoic acid, and 1,25-dihydroxyvitamin D3. IGFBP-3 may act in an IGF-dependent manner by attenuating the interaction of pericellular IGFs with the type-I IGF receptor. It may also act in an IGF-independent manner by initiating intracellular signaling from a cell surface receptor, or by direct nuclear action, or both. The possibility of a membrane-bound receptor is strengthened by recent studies which have identified members of the transforming growth factor-, receptor family as having a role, either directly or indirectly, in signaling from the cell surface by IGFBP-3. A number of growth factors and hormones stimulate the expression and secretion of cellular IGFBP-3, which then signals from the cell surface to bring about some of the effects attributed to the primary agents. Within the cell, the apoptosis-inducing tumor suppressor, p53, can also induce IGFBP-3 expression and secretion. Since IGFBP-3 upregulates the cell cycle inhibitor, p21Waf1, and increases the ratio of proapoptotic to antiapoptotic members of the Bcl family, it appears to exert the same effects on major downstream targets of cell signaling as p53 does. The nuclear localization of IGFBP-3 has been described in a number of cell types. IGFBP-3 may act to import IGFs or other nuclear localization signal-deficient signaling molecules into the nucleus. It may also act directly in the nucleus by enhancing the activity of retinoid X receptor-, and thereby promote apoptosis. All of the above phenomena will be discussed with particular emphasis on the growth of breast cancer cells. Microsc. Res. Tech. 59:12,22, 2002. © 2002 Wiley-Liss, Inc. [source]

    Type 2 Diabetes Susceptibility Genes on Chromosome 1q21,24

    S. J. Hasstedt
    Summary Type 2 diabetes (T2D) has been linked to chromosome 1q21,24 in multiple samples, including a Utah family sample. Variants in 13 of the numerous candidate genes in the 1q region were tested for association with T2D in a Utah case-control sample. The most promising, 19 variants in 6 candidates, were genotyped on the Utah family sample. Herein, we tested the 19 variants individually and in pairs for an effect on T2D risk in family members using a logistic regression model that accounted for gender, age, and BMI and attributed residual genetic effects to a polygenic component. Seven variants increased risk significantly through 5 pairs of interactions. The significant variant pairs were apolipoprotein A-II (APOA2) rs6413453 interacting with calsequestrin 1 (CASQ1) rs617698, dual specificity phosphatase 12 (DUSP12) rs1503814, and retinoid X receptor , (RXRG) rs10918169, a poly-T insertion-deletion polymorphism in liver pyruvate kinase (PKLR) interacting with APOA2 rs12143180, and DUSP12 rs1027702 interacting with RXRG rs10918169. Genotypes of these 5 variant pairs accounted for 25.8% of the genetic variance in T2D in these pedigrees. [source]

    Liver X receptor is a therapeutic target in collagen-induced arthritis

    ARTHRITIS & RHEUMATISM, Issue 4 2007
    Subba R. Chintalacharuvu PhD
    No abstract is available for this article. [source]

    Gene Induction by Phenobarbital: An Update on an Old Question that Receives Key Novel Answers,

    Laurent Corcos
    The drug is the representative of a myriad of lipophilic molecules able to evoke a pleiotropic response in the liver and also in prokaryotes and flies. A great deal of novel information has been obtained in recent years regarding the mechanism of cytochrome P450 (CYP) gene induction by phenobarbital. Most importantly, a nuclear orphan receptor, the constitutive androstane receptor has been identified as a primary determinant of the transcriptional activation of CYP genes in response to phenobarbital-like inducers in mammals. Another nuclear receptor, the pregnane X receptor can also mediate some of the phenobarbital response, but the functional overlap of the two inductive pathways is only partial. The response of mammalian CYP2B genes to phenobarbital was abolished in the liver of mice carrying a null allele of the constitutive androstane receptor gene, whereas that of CYP3A genes was lost in pregnane X receptor knock-out mice. [source]

    Expression and regulation of the bile acid transporter, OST, -OST, in rat and human intestine and liver

    Ansar A. Khan
    Abstract The regulation of the OST, and OST, expression was studied in the rat jejunum, ileum, colon and liver and in human ileum and liver by ligands for the farnesoid X receptor (FXR), pregnane X receptor (PXR), vitamin D receptor (VDR) and glucocorticoid receptor (GR) using precision cut tissue slices. The gradient of protein and mRNA expression in segments of the intestine for rOST, and rOST, paralleled that of rASBT. OST, and OST, mRNA expression, quantified by qRT-PCR, in rat jejunum, ileum, colon and liver, and in human ileum and liver was positively regulated by FXR and GR ligands. In contrast, the VDR ligand, 1,25(OH)2D3 decreased the expression of rOST, -rOST, in rat intestine, but had no effect on human ileum, and rat and human liver slices. Lithocholic acid (LCA) decreased the expression of rOST, and rOST, in rat ileum but induced OST, -OST, expression in rat liver slices, and human ileum and liver slices. The PXR ligand, pregnenolone-16, carbonitrile (PCN) had no effect. This study suggest that, apart from FXR ligands, the OST, and OST, genes are also regulated by VDR and GR ligands and not by PXR ligands. This study show that VDR ligands exerted different effects on OST, -OST, in the rat and human intestine and liver compared with other nuclear receptors, FXR, PXR, and GR, pointing to species- and organ-specific differences in the regulation of OST, -OST, genes. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Changes in mRNA expression of ABC and SLC transporters in liver and intestines of the adjuvant-induced arthritis rat

    Satoshi Uno
    Abstract In this study, a real-time reverse transcription-polymerase chain reaction was used to determine the effects of adjuvant-induced arthritis (AA) on the amounts of mRNA of 12 types of rat ATP-binding cassette (ABC) and solute carrier (SLC) transporters in the liver and small intestine, 7 (D7) and 21 days (D21) after the injection of adjuvant. There were no significant differences in mRNA levels of ABC and SLC transporters between the livers of AA and control rats on D7, except in the case of Mdr1a. However, levels of Mdr1a, Mrp2 and Oatp SLC transporters were significantly lower in AA than in the control livers on D21. In contrast, the mRNA levels of several ABC and SLC transporters, especially Mrp2, Bcrp, LAT2 and Oatp1a5, were significantly lower in the small intestines of AA rats compared with the controls on D7, though there were no significant differences by D21. The time-dependent alterations in mRNA levels of the pregnane X receptor, but not the constitutive androstane receptor, in the liver and intestine were similar to the changes in mRNA levels of most transporters examined. The present study showed that AA was associated with reduced mRNA expression of several ABC and SLC transporters in the liver and small intestine, but that the time courses of the effects of AA on mRNA expression differed between the liver and small intestine. These results raise the possibility of a functional change of the transporters of liver and intestine in AA rats. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Effects of intrauterine undernutrition on the expression of CYP3A23/3A1, PXR, CAR and HNF4, in neonate rats

    Shaoqing Ni
    Abstract Cytochrome P-450 3A (CYP3A) together with its nuclear receptors plays a critical role in drug metabolism. The present study investigated the effects of undernutrition in utero on hepatic mRNA and protein expression of the enzyme CYP3A23/3A1 and nuclear receptors including pregnane X receptor (PXR; NR1I2), constitutive androstane receptor (CAR; NR1I3) and nuclear factor-4alpha (HNF4,; HNF4A) in neonatal rats. At gestational day 2, pregnant rats were randomly divided into two groups: nourished (fed ad libitum) and undernourished (50% of nourished group). The pups delivered by nourished rats were designated as the normal-birth-weight group (NBW, n=15) and those delivered by undernourished rats were designated as the low-birth-weight group (LBW, n=15). Hepatic mRNA expression was detected by quantitative real-time PCR and the corresponding protein expression was examined by immunohistochemistry (IHC). Compared with NBW pups, LBW pups tended to have lower mRNA expression levels of CYP3A23/3A1, PXR and CAR but higher levels of HNF4,. Only the CAR mRNA expression differences were significant (p<0.05). mRNA expression of CYP3A23/3A1 correlated with that of HNF4, in both the LBW(r=0.808, p=0.007) and NBW (r=0.452, p=0.012) groups. CYP3A23/3A1 and CAR protein expression differed between the two groups (CYP3A23/3A1, ,2=7.87, p=0.005; CAR, ,2=12.069, p=0.001). In conclusion, these findings suggest that undernutrition may influence the mRNA expression of CAR and protein expression of both CYP3A23/3A1 and CAR in neonatal rats. Since CYP3A23/3A1 and CAR are critically involved in drug metabolism, these results may have clinical implications for optimal medication in LBW children. Copyright © 2008 John Wiley & Sons, Ltd. [source]

    A multiparameter flow cytometric analysis of the effect of bexarotene on the epidermis of the psoriatic lesion

    M.E.J. Franssen
    Summary Background A new retinoid, bexarotene (Targretin®), was recently investigated in a large multicentre trial for its efficacy and safety in psoriasis. Bexarotene is a novel retinoid X receptor (RXR)-selective ligand. Objectives The aim was to study the effect of bexarotene in psoriasis by analysing markers for epidermal differentiation, proliferation and inflammation in epidermal single cell suspensions from lesions of patients with psoriasis treated with various doses of bexarotene. Methods Thirty-four patients with moderate to severe plaque psoriasis participated in this study and were assigned in sequence to four different dose regimens: 0·5, 1, 2 and 3 mg kg,1 once daily. Before and after 12 weeks of bexarotene treatment, punch biopsies were taken from lesional skin from which epidermal single cell suspensions were prepared using an optimized thermolysin protocol. A sum of scores was determined for each biopsy site, based on a four-point scale for erythema, induration and desquamation. An improved multiparameter flow cytometric assay was used that enabled simultaneous assessment of epidermal proliferation, various aspects of differentiation and epidermal inflammation. The following variables were measured simultaneously: relative DNA content, relative cell size, keratin (K) 10, K6 and vimentin expression. Results The psoriasis area and severity index (PASI) and sum of scores for the individual psoriatic lesion each showed a statistically significant decrease of 28% after 12 weeks of bexarotene treatment (P < 0·001). However, no significant dose,response effect was found. The total percentage of K10+ cells showed a significant increase of 43% (P < 0·01). The total population of K6 expressing cells did not show significant changes. Regarding the subpopulations of K6 single, K10 single and K6 and 10 co-expressing cells, a significant increase of 77% was seen in the K10+ K6, cells (P < 0·05), a significant decrease of 33% in K10, K6+ cells (P < 0·01), and no significant changes in the remaining population of K10+ K6+ cells. After 12 weeks of treatment with bexarotene no significant changes in epidermal proliferation and inflammation were shown. Conclusions The present study indicates a direct effect of RXR activation by bexarotene on the transition of proliferation-associated keratinization into normal keratinization. Although no direct effect of bexarotene on DNA content in the total K10, cells was shown, further studies on subpopulations within the germinative layer such as stem cells and transit amplifying cells might be worthwhile. [source]

    Strategy and mechanism for the prevention of hepatocellular carcinoma: Phosphorylated retinoid X receptor , is a critical target for hepatocellular carcinoma chemoprevention

    CANCER SCIENCE, Issue 3 2009
    Masahito Shimizu
    Hepatocellular carcinoma (HCC) is a major health care problem worldwide. The prognosis of patients with HCC is poor because even in the early stages when surgical treatment might be expected to be curative, the incidence of recurrence in patients with underlying cirrhosis is very high due to multicentric carcinogenesis. Therefore, strategies to prevent recurrence and second primary HCC are required to improve the prognosis. One of the most practical approaches to prevent the multicentric development of HCC is ,clonal deletion' therapy, which is defined as the removal of latent (i.e. invisible) (pre)malignant clones from the liver in a hypercarcinogenic state. Retinoids, a group of structural and functional analogs of vitamin A, exert their biological function primarily through two distinct nuclear receptors, retinoic acid receptors and retinoid X receptors (RXR), and abnormalities in the expression and function of these receptors are highly associated with the development of various cancers, including HCC. In particular, a malfunction of RXR, due to phosphorylation by the Ras,mitogen-activated protein kinase signaling pathway is profoundly associated with the development of HCC and thus may be a critical target for HCC chemoprevention. Acyclic retinoid, which has been clinically shown to reduce the incidence of a post-therapeutic recurrence of HCC, can inhibit Ras activity and phosphorylation of the extracellular signal-regulated kinase and RXR, proteins. In conclusion, the inhibition of RXR, phosphorylation and the restoration of its physiological function as a master regulator for nuclear receptors may be a potentially effective strategy for HCC chemoprevention and clonal deletion. Acyclic retinoid, which targets phosphorylated RXR,, may thus play a critical role in preventing the development of multicentric HCC. (Cancer Sci 2009; 100: 369,374) [source]

    Effects of retinoids and thiazolidinediones on proliferation, insulin release, insulin mRNA, GLUT 2 transporter protein and mRNA of INS-1 cells

    J. Blumentrath
    Abstract Both 9-cis-retinoic acid (9cRA) and all-trans-retinoic acid (ATRA) are active metabolites of vitamin A (retinol). There exists an interaction between retinoid receptors and peroxisome proliferator-activated receptors (PPAR,). To define their functions in an insulin secreting system the effects of ATRA, 9cRA and the PPAR, agonist rosiglitazone on cell proliferation, insulin release and glucose transporter (GLUT) 2 of INS-1 cells were tested. Retinoic acid receptor (RAR-, and -,) and retinoid X receptor (RXR-, and -,) proteins are present (immunoblots). Both 9cRA and ATRA inhibit INS-1 cell proliferation ([3H]-thymidine assay) in a concentration dependent manner. Both 9cRA and ATRA increased insulin release, but only ATRA ralsed the GLUT 2 mRNA in a bell-shaped concentration response curve after 48,h. The insulinotropic effect of one compound is not significantly superimposed by the other indicating that the same binding sites are used by 9cRA and ATRA. The acute and chronic effects of the PPAR, agonist rosiglitazone on insulin release were additionally determined since glitazones act as transcription factors together with RXR agonists. At high concentrations (100,,m) rosiglitazone inhibited glucose (8.3,mm) stimulated insulin secretion (acute experiment over 60,min). Insulin secretion, however, was increased during a 24,h treatment at a concentration of 10,,m and again inhibited at 100,,m. Changes in preproinsulin mRNA expression were not observed. Rosiglitazone (100,,m) increased GLUT 2 mRNA paralleled by an increase of GLUT 2 protein, but only after 24,h of treatment. This data indicate that RAR and RXR mediate insulin release. The changes in GLUT 2 have no direct impact on insulin release; the inhibition seen at high concentrations of either compound is possibly the result of the observed inhibition of cell proliferation. Effects of rosiglitazone on preproinsulin mRNA and GLUT 2 (mRNA and protein) do not play a role in modulating insulin secretion. With the presence of an RXR receptor agonist the effect of rosiglitazone on insulin release becomes stimulatory. Thus the effects of RAR-, RXR agonists and rosiglitazone depend on their concentrations, the duration of their presence and are due to specific interactions. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Pyrazine Arotinoids with Inverse Agonist Activities on the Retinoid and Rexinoid Receptors

    CHEMBIOCHEM, Issue 7 2009
    José García
    Abstract RAR and RXR agonists: A collection of pyrazine-based RAR/RXR ligands were prepared by a series of palladium catalyzed cross-coupling reactions and characterized. Structure,activity relationships were elucidated. Retinoic acid receptor (RAR) ,/,-subtype-selective and retinoid X receptor (RXR) inverse agonist activities are described for pyrazine acrylic acid arotinoid, 14,d. Heterocyclic arotinoids derived from central-region dihalogenated pyrazine scaffolds have been synthesized by consecutive halogen and/or position-selective palladium-catalyzed cross-coupling reactions. Pyrazines were further functionalized as alkyl ethers or methylamines prior to the last Pd-catalyzed reactions. Transient transactivation studies with the retinoic acid receptor (RAR) ,, ,, and , subtypes and with retinoid X receptor (RXR) , revealed distinct agonist, antagonist, and inverse agonist activities for these compounds. Of interest are the RAR,,,-selective inverse agonists with pyrazine acrylic acid structures, in particular 14,c, which is RAR,-selective, and 14,d, a pan-RAR/RXR inverse agonist with more affinity for the RAR subtypes that enhance the interaction of RAR with cognate corepressors. [source]