Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: HUMANGGP:028038 (ARNT)
 578 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In an effort to provide a more powerful system to study the Ah receptor (AHR) signaling pathway, we expressed the AHR, its dimerization partner ARNT, and a beta-galactosidase (lacZ) reporter gene, driven by two dioxin-responsive enhancers, in the yeast Saccharomyces cerevisiae. In this system, the agonists beta-naphthoflavone and alpha-naphthoflavone induced transcription of the lacZ gene, with EC50 values of 7.9 x 10(-8) and 3.0 x 10(-7) M, respectively, while the nonagonist dexamethasone was without effect. As a first application of this system, we examined the relationship between the 90-kDa heat shock protein (hsp90) and AHR function. To accomplish this in a manner that was independent of the ARNT protein, we constructed a chimeric receptor in which the DNA binding and primary dimerization domains of the AHR were swapped with analogous domains from the LexA protein. Coexpression of this AHR-LexA chimera and a lacZ reporter gene driven by eight LexA operator sites in a yeast strain with regulatable levels of hsp90, yielded pharmacology that closely mirrored that of the AHR/ARNT/dioxin-responsive enhancer system described above, but only when hsp90 levels were held near their wild type levels. When hsp90 levels were reduced to approximately 5% of normal, AHR signaling in response to agonist was completely blocked despite normal cell growth. These results provide the first genetic evidence for the role of hsp90 in AHR signaling and provide the basis for a powerful new system in which to study this pathway.
J Biol Chem 1994 Dec 02
PMID:The 90-kDa heat shock protein is essential for Ah receptor signaling in a yeast expression system. 798 13

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor through which halogenated aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) cause altered gene expression and toxicity. The AHR belongs to the basic helix-loop-helix/Per-ARNT-Sim (bHLH-PAS) family of transcriptional regulatory proteins, whose members play key roles in development, circadian rhythmicity, and environmental homeostasis; however, the normal cellular function of the AHR is not yet known. As part of a phylogenetic approach to understanding the function and evolutionary origin of the AHR, we sequenced the PAS homology domain of AHRs from several species of early vertebrates and performed phylogenetic analyses of these AHR amino acid sequences in relation to mammalian AHRs and 24 other members of the PAS family. AHR sequences were identified in a teleost (the killifish Fundulus heteroclitus), two elasmobranch species (the skate Raja erinacea and the dogfish Mustelus canis), and a jawless fish (the lamprey Petromyzon marinus). Two putative AHR genes, designated AHR1 and AHR2, were found both in Fundulus and Mustelus. Phylogenetic analyses indicate that the AHR2 genes in these two species are orthologous, suggesting that an AHR gene duplication occurred early in vertebrate evolution and that multiple AHR genes may be present in other vertebrates. Database searches and phylogenetic analyses identified four putative PAS proteins in the nematode Caenorhabditis elegans, including possible AHR and ARNT homologs. Phylogenetic analysis of the PAS gene family reveals distinct clades containing both invertebrate and vertebrate PAS family members; the latter include paralogous sequences that we propose have arisen by gene duplication early in vertebrate evolution. Overall, our analyses indicate that the AHR is a phylogenetically ancient protein present in all living vertebrate groups (with a possible invertebrate homolog), thus providing an evolutionary perspective to the study of dioxin toxicity and AHR function.
Proc Natl Acad Sci U S A 1997 Dec 09
PMID:Molecular evolution of two vertebrate aryl hydrocarbon (dioxin) receptors (AHR1 and AHR2) and the PAS family. 939 Oct 97

Introduction of a retroviral expression vector for the aryl hydrocarbon receptor (AHR) restores CYP1A1 inducibility to a mutant derivative of the Hepa-1 cell line that is defective in induction of CYP1A1 by ligands for the receptor. An AHR protein with normal ligand binding activity is expressed in the mutant but ligand treatment of mutant cell extract fails to induce binding of the AHR. ARNT (aryl hydrocarbon receptor nuclear translocator) dimer to the xenobiotic responsive element (XRE). AHR cDNAs derived from the mutant encode a protein that is unimpaired in ligand-dependent dimerization with ARNT, but the AHR.ARNT dimer so formed is severely impaired in XRE binding activity. The mutant cDNAs contain a C to G mutation at base 648, causing a cysteine to tryptophan alteration at amino acid 216, located between the PER-ARNT-SIM homology region (PAS) A and PAS B repeats. Introduction of the same mutation in the wild-type AHR sequence by site-directed mutagenesis similarity impaired XRE binding activity. Substitution with the conservative amino acid, serine, had no effect on XRE binding. The tryptophan mutation, but not the wild-type allele, was detectable in genomic DNA of the mutant. The implication that an amino acid within the PAS region may be involved in DNA binding indicates that the DNA binding behavior of AHR may be more anomalous than previously suspected.
J Biol Chem 1997 Dec 12
PMID:A mutation in the aryl hydrocarbon receptor (AHR) in a cultured mammalian cell line identifies a novel region of AHR that affects DNA binding. 939 31

The aryl hydrocarbon receptor (AHR) is believed to mediate the toxic effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), polychlorinated biphenyls, and polycyclic aromatic hydrocarbons. AHR is a member of the Per, ARNT, Sim/basic-helix-loop-helix superfamily of ligand-activated transcription factors that also harbors the transcription factors involved in the hypoxia response, development of the central nervous system, and day-night adaptations. To investigate the role of AHR in chemical toxicity and carcinogenesis and to determine any possible function in mammalian development and physiological homeostasis, AHR-null mice were developed. The AHR-null mice were resistant to the acute toxicity of TCDD and had an altered teratogenic response to this compound. These mice were found to have a number of abnormal phenotypes, thus confirming that AHR plays an important developmental and physiological role. Among the most consistent phenotypes was an altered liver pathology that was associated with accelerated rates of apoptosis. Evidence suggests that this may be related to an abnormal accumulation of levels of hepatic retinoic acid that cause an activation of transforming growth factor beta, resulting in stimulation of apoptosis. AHR may directly or indirectly control levels of a cytochrome P450 that is responsible for catabolizing retinoic acid.
Drug Metab Dispos 1998 Dec
PMID:The aryl hydrocarbon receptor: studies using the AHR-null mice. 986 Sep 27

These studies characterized the profile of AhR and ARNT expression in primary splenocytes and purified splenic B cells after cellular activation with lipopolysaccharide (LPS). LPS treatment of mouse splenocytes markedly increased the magnitude of both AhR and ARNT steady state mRNA expression. AhR mRNA expression peaked at 8 hr post-LPS activation and was increased by approximately 5-fold compared with freshly isolated splenocytes (i.e., time 0). ARNT mRNA expression began to increase at 8 hr postactivation, peaked at approximately 48 hr and was increased by approximately 4-fold when compared with nonactivated splenocytes at time 0. Western blotting also demonstrated an increase in the relative magnitude of both the AhR and ARNT proteins in LPS activated splenocytes. Likewise, the presence of the AhR, ARNT and cytochrome P450IA1 (CYP1A1) proteins were also detected in purified primary splenic B cells, and the magnitude of protein expression was enhanced in LPS activated splenic B cells at 12 and 24 hr relative to time matched controls for each of these proteins. In summary, these findings suggest that on LPS activation the magnitude of AhR and ARNT mRNA and protein increases in both splenocytes and purified primary splenic B cells. Moreover, because the increase in the relative magnitude of CYP1A1 protein in response to LPS occurred in the absence of exogenous AhR ligand, these results suggest that B-cell activation is sufficient to induce AhR nuclear translocation and binding to dioxin-responsive elements in the promoter region of AhR-responsive genes.
J Pharmacol Exp Ther 1998 Dec
PMID:Lipopolysaccharide activation of murine splenocytes and splenic B cells increased the expression of aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator. 986

The basic helix-loop-helix/Per-ARNT-Sim homology domain dioxin receptor (DR) translocates to the nucleus upon binding of aromatic hydrocarbon ligands typified by dioxin, whereupon it partners the Ah receptor nuclear translocator and initiates transcription. Concurrently, ligand binding down-regulates receptor levels via an unknown mechanism. In this study we show that receptor levels are dependent upon cellular compartmentalization, with entry into the nucleus leading to the rapid destruction of the DR. Ligand-induced DR translocation was bypassed by adding a heterologous nuclear localization signal to the DR, creating a constitutively nuclear form of the dioxin receptor (DRNLS). The DRNLS protein was shown to be unstable with a half-life of </=1 h whether partnering ARNT or HSP90. Thus, the structural changes induced by ligand binding have no inherent effect on DR stability but are critical in transporting the receptor prior to degradation. The proteolytic pathway that degrades the nuclear receptor is suggested to involve ubiquitination as it was inhibited by the proteasome inhibitor MG132 or co-expression of DRNLS with the ubiquitin mutant UbK48R. Incubation of cells expressing DRNLS with the phosphatase inhibitor calyculin resulted in the rapid phosphorylation and ubiquitination of DRNLS, suggesting that a nuclear kinase is required to trigger receptor proteolysis. Overall, this study demonstrates a novel mechanism of proteolysis whereby the simple relocation of a transcription factor from cytoplasm to nucleus initiates its rapid destruction.
J Biol Chem 1999 Dec 17
PMID:Degradation of the basic helix-loop-helix/Per-ARNT-Sim homology domain dioxin receptor via the ubiquitin/proteasome pathway. 1059 27

Using fluorescence in situ hybridization analysis, breakpoints involving the long arm of chromosome 1 (1q) were localized in 36 patients with various hematopoietic disorders and rearrangements of the proximal part of 1q, as ascertained with banding techniques. The breakpoint was localized within the satellite II (sat II) domain in 14 patients with various abnormalities, between the sat II domain and the BCL9 locus in eight, between the BCL9 and ARNT loci in two, between sat II and ARNT in two others, and distal to ARNT in seven. A dicentric chromosome 1 was present in two patients. A high incidence of heterochromatin heteromorphism of chromosome 1 was present in this series. Two recurrent translocations were identified, t(1;2)(q12;q37) in three patients suffering from three different acute leukemia subtypes, and t(1;16)(q12;q24) in two patients with different diseases. Two patients had jumping translocations. Most of the rearrangements of 1q were secondary abnormalities, included in complex karyotypes. The roles of methylation, interactions with the proteins interfering with heterochromatin and possible gene silencing due to heterochromatin rearrangements are discussed.
Leukemia 1999 Dec
PMID:Fluorescence in situ hybridization analysis of chromosome 1 abnormalities in hematopoietic disorders: rearrangements of DNA satellite II and new recurrent translocations. 1060 18

Placental development is profoundly influenced by oxygen (O(2)) tension. Human cytotrophoblasts proliferate in vitro under low O(2) conditions but differentiate at higher O(2) levels, mimicking the developmental transition they undergo as they invade the placental bed to establish the maternal-fetal circulation in vivo. Hypoxia-inducible factor-1 (HIF-1), consisting of HIF-1alpha and ARNT subunits, activates many genes involved in the cellular and organismal response to O(2) deprivation. Analysis of Arnt(-/-) placentas reveals an aberrant cellular architecture due to altered cell fate determination of Arnt(-/-) trophoblasts. Specifically, Arnt(-/-) placentas show greatly reduced labyrinthine and spongiotrophoblast layers, and increased numbers of giant cells. We further show that hypoxia promotes the in vitro differentiation of trophoblast stem cells into spongiotrophoblasts as opposed to giant cells. Our results clearly establish that O(2) levels regulate cell fate determination in vivo and that HIF is essential for mammalian placentation. The unique placental phenotype of Arnt(-/-) animals also provides an important tool for studying the disease of preeclampsia. Interestingly, aggregation of Arnt(-/-) embryonic stem (ES) cells with tetraploid wild-type embryos rescues their placental defects; however, these embryos still die from yolk sac vascular and cardiac defects.
Genes Dev 2000 Dec 15
PMID:Placental cell fates are regulated in vivo by HIF-mediated hypoxia responses. 1112 10

One possible mechanism by which diet may reduce cancer risk is through enhancement of metabolic systems that prevent activation of carcinogens or accelerate carcinogen inactivation. We studied the effects of diet and 7,12-dimethylbenz-(a)anthracene (DMBA) on hepatic and mammary gland CYP1A1, CYP1A2 and CYP1B1 enzymes in female Sprague-Dawley rats. Diets (AIN-93G) were fed from conception to adulthood, and DMBA was given by oral gavage at age 48-50 d. The protein sources of diets were casein (CAS), soy protein isolate (SPI) or whey protein hydrolysate (WPH). The DMBA-induced hepatic ethoxyresorufin-O-deethylase and methoxyresorufin-O-demethylase activities and CYP1A1 protein and mRNA expression were lower (P < 0.05) in SPI-fed rats compared with those fed casein. Differences in mammary gland CYP1 expression were also observed with decreased DMBA induction (P < 0.05) of all three CYP1 proteins and mRNAs in rats fed either SPI or WPH compared with those fed CAS. Most notable were the decreased constitutive and DMBA-induced mammary gland expression of CYP1B1 protein of 93 and 96%, respectively, in the SPI-fed rats relative to the CAS-fed controls. The diet-induced changes in CYP1 enzyme expression were consistent with changes in the AhR and ARNT transcription factors that regulate them. Decreased (P < 0.05) mammary constitutive AhR and ARNT proteins were measured in SPI-fed rats. There was also a 100% increase in constitutive AhR protein in the WPH-fed rats that paralleled a 100% increase in constitutive CYP1B1 protein in the mammary gland. These results demonstrate the importance of diet in regulation of phase I metabolism in liver and mammary gland, and suggest a potential mechanism by which soy or whey proteins reduce DMBA-induced mammary tumor incidence.
J Nutr 2001 Dec
PMID:Soy and whey proteins downregulate DMBA-induced liver and mammary gland CYP1 expression in female rats. 1173 81

Upon exposing mammalian tissues to hypoxia, expression of a number of physiologically important genes such as erythropoietin and vascular endothelial growth factor (VEGF) increases. The key regulator for this oxygen-dependent gene expression is the hypoxia-inducible factor-1 (HIF-1), a heterodimeric transcription factor consisting of an alpha and a beta subunit. Both HIF-1 subunits are widely expressed in the cells and tissue of vertebrates, flies, fishes, worms and probably most other species. The beta subunit (also termed ARNT, aryl hydrocarbon receptor nuclear translocator) is abundantly expressed in an oxygen-independent manner. On the other hand, HIF-1alpha cannot be detected above a critical partial pressure of oxygen when it is subjected to rapid ubiquitinylation and proteasomal degradation. Hypoxic exposure leads to stabilization of HIF-1alpha protein and subsequent activation of HIF-1-dependent target genes. HIF-1 is not only a master regulator of oxygen homeostasis, it also appears to play a key role in tumor development as well as cardiovascular and ischemic diseases. Genetic modulation of HIF-1alpha activity in vivo may therefore represent a novel therapeutic approach to these disorders. In this overview, we report on the generation of HIF-1alpha overexpressing HeLa cell lines and demonstrate the feasibility of normoxic HIF-1 gene transfer in vitro and in vivo thereby identifying the limiting steps for full activation of HIF-1.
Comp Biochem Physiol C Toxicol Pharmacol 2002 Dec
PMID:Characterization of HIF-1 alpha overexpressing HeLa cells and implications for gene therapy. 1245 76


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