UMLS:C0019204 - FACTA Search

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Query: UMLS:C0019204 (hepatocellular carcinoma)
71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Hypoxia-inducible factor-1 (HIF-1), a DNA-binding complex implicated in the regulation of gene expression by oxygen, has been shown to consist of a heterodimer of two basic helix-loop-helix Per-AHR-ARNT-Sim (PAS) proteins, HIF-1alpha, and HIF-1beta. One partner, HIF-1beta, had been recognized previously as the aryl hydrocarbon receptor nuclear translocator (ARNT), an essential component of the xenobiotic response. In the present work, ARNT-deficient mutant cells, originally derived from the mouse hepatoma line Hepa1c1c7, have been used to analyze the role of ARNT/HIF-1beta in oxygen-regulated gene expression. Two stimuli were examined: hypoxia itself and desferrioxamine, an iron-chelating agent that also activates HIF-1. Induction of the DNA binding and transcriptional activity of HIF-1 was absent in the mutant cells, indicating an essential role for ARNT/HIF-1beta. Analysis of deleted ARNT/HIF-1beta genes indicated that the basic, helix-loop-helix, and PAS domains, but not the amino or carboxyl termini, were necessary for function in the response to hypoxia. Comparison of gene expression in wild type and mutant cells demonstrated the critical importance of ARNT/HIF-1beta in the hypoxic induction of a wide variety of genes. Nevertheless, for some genes a reduced response to hypoxia and desferrioxamine persisted in these mutant cells, clearly distinguishing ARNT/HIF-1beta-dependent and ARNT/HIF-1beta-independent mechanisms of gene activation by both these stimuli.
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PMID:The role of the aryl hydrocarbon receptor nuclear translocator (ARNT) in hypoxic induction of gene expression. Studies in ARNT-deficient cells. 866 57

This study demonstrates that the novel in vitro CALUX (chemical-activated luciferase expression) assay is a rapid, sensitive assay for assessing the toxic potency of (mixtures of) aryl hydrocarbon receptor (AhR)-active compounds in sediments and pore waters. A rat hepatoma (H4IIE) cell line, stably transfected with a construct containing the dioxin-responsive element (DRE) sequence and the luciferase reporter gene, was used to determine the relative potency or the total activities of AhR-active compounds in sediment and pore water extracts. This novel CALUX assay had a detection limit of 0.5 fmol of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The sensitivity and linear working range was slightly better than for the ethoxyresorufin O-deethylase (EROD) assay in H4IIE wild type cells. The primary improvement of the CALUX assay compared to the EROD assay, however, is that the CALUX assay is insensitive to substrate inhibition. The CALUX activity induced by organic extracts from 450-mg aliquots of sediment or 250-microl aliquots of pore water corresponded with the instrumentally analyzed degree of pollution of the sediment. Using pore water, only a simple and rapid extraction procedure was needed, without additional clean-up to prevent cell death. The response from pore water samples in an 8-day early life stage test with zebra fish (Branchydanio rerio) corresponded with the CALUX induction, although the correlation was sometimes disturbed by heavy metals. Two polychlorinated terphenyl mixtures, the PCB-substitute Ugilec 141, polybrominated diphenylethers, and the PCB-mixture Clophen A50 were tested in the CALUX assay and had induction potencies that were 10(-4)-10(-7) compared to TCDD.
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PMID:Chemical-activated luciferase gene expression (CALUX): a novel in vitro bioassay for Ah receptor active compounds in sediments and pore water. 881 60

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) suppresses B lymphocyte proliferation and immunoglobulin production. We previously reported that the aryl hydrocarbon receptor (AhR) complex, composed of the AhR ligand binding subunit and the Ah receptor nuclear translocator (ARNT), was constitutively present in nuclear extracts from two human B lymphocyte cell lines (Biochem. Biophys. Res. Commun. 212, 27-34, 1995). The present study compared the AhR complex in the IM-9 and PJS-91 human B lymphocyte and HepG2 human hepatoma cell lines. AhR mRNA levels in the two lymphocyte cell lines were substantially lower than those in HepG2 cells, as was immunoreactive AhR protein. In contrast, ARNT mRNA and protein were expressed at a high level in all three cell lines. TCDD induction of cytochrome P450 1A1 mRNA and protein was detected in only the PJS-91 lymphocyte cell line, and at a markedly lower level than that in HepG2 cells. In gel shift assays, the cytosolic DNA-binding AhR complex in IM-9 and PJS-91 cells was indistinguishable from that in HepG2 cells. In contrast, the nuclear DNA-binding AhR complex in IM-9 and PJS-91 cells consisted of several closely migrating species, one being recognized by an AhR antibody, while an ARNT antibody reacted with all species. Protein:DNA cross-linking analysis revealed the presence of a novel Mr 100,000 DNA-binding protein in nuclear extracts from IM-9 and PJS-91, but not HepG2, cells that was not recognized by either AhR or ARNT antibodies. These results show that IM-9 and PJS-91 human B cells constitutively express a distinct nuclear DNA-binding form of the AhR complex that may result from the presence of an additional protein or a structural variant of the AhR.
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PMID:Characterization of the aryl hydrocarbon receptor complex in human B lymphocytes: evidence for a distinct nuclear DNA-binding form. 895 78

Rare benzo[a]pyrene-resistant clones were previously isolated from the mouse hepatoma cell line, Hepa-1 (Hepa1c1c7), and shown to be deficient in induction of CYP1A1 mRNA by ligands for the aryl hydrocarbon receptor (AHR). Clones belonging to complementation group B were shown to have reduced levels of ligand binding to AHR. It is shown here that all 15 independently derived B clones analyzed had much reduced levels of AHR mRNA, but in each case, the mRNA was normal in size. Infection of B clones with a retroviral expression vector for AHR restores CYP1A1 inducibility (although viral AHR expression is progressively silenced and CYP1A1 expression progressively diminishes as the cells are maintained in culture). Treatment of the B clones with the histone deacetylase inhibitors sodium butyrate or trichostatin A restores AHR expression and also restores CYP1A1 inducibility to nearly 100% of the cells in the treated cultures. Fusion of a representative B clone with a rat hepatoma cell line restores expression to the mouse AHR gene encoded by the B clone's genome. These results demonstrate that the loss of CYP1A1 inducibility in B clones is probably totally ascribable to their reduced levels of AHR and that the clones are most probably not mutated in the AHR gene but are deficient in its expression. The evidence suggests that the reduction in expression of mRNA encoded by the endogenous AHR gene in the B clones is not due to an epigenetic alteration in chromatin structure but that the clones are probably defective either in a transcription factor for the AHR gene or in a protein required for generating an open chromatin configuration over the gene.
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PMID:Basis for the loss of aryl hydrocarbon receptor gene expression in clones of a mouse hepatoma cell line. 896 65

Drosophila single-minded, which acts as a positive master gene regulator in central nervous system midline formation in Drosophila, its two mouse homologs SIM1 and SIM2, and the mammalian aryl hydrocarbon receptor (AHR) and aryl hydrocarbon receptor nuclear translocator (ARNT) proteins are members of the basic-helix-loop-helix.PAS family of transcription factors. In the yeast two-hybrid system, we demonstrate strong constitutive interaction of ARNT with SIM1 and SIM2 and fully ligand-dependent interaction of ARNT with AHR. Both the helix-loop-helix and the PAS regions of SIM1 and of ARNT are required for efficient heterodimerization. SIM1 and SIM2 do not form homodimers, and they do not interact with AHR. We also failed to detect homodimerization of ARNT. The interaction of ARNT with SIM1 was confirmed with in vitro synthesized proteins. Like AHR, in vitro synthesized SIM1 associates with the 90-kDa heat shock protein. SIM1 inhibits binding of the AHR.ARNT dimer to the xenobiotic response element in vitro. Introduction of SIM1 into hepatoma cells inhibits transcriptional transactivation by the endogenous AHR.ARNT dimer. The mouse SIM1. ARNT dimer binds only weakly to a proposed DNA target for the Drosophila SIM.ARNT dimer. In adult mice mRNA for SIM1 was expressed in lung, skeletal muscle, and kidney, whereas the mRNA for SIM2 was found in the latter two. ARNT is also expressed in these organs. Thus mouse SIM1 and SIM2 are novel heterodimerization partners for ARNT in vitro, and they may function both as positive and negative transcriptional regulators in vivo, during embryogenesis and in the adult organism.
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PMID:Two murine homologs of the Drosophila single-minded protein that interact with the mouse aryl hydrocarbon receptor nuclear translocator protein. 902 Jan 69

Western blot analysis was used to determine the concentration of the aryl hydrocarbon receptor nuclear translocator (ARNT) protein and aryl hydrocarbon receptor (AHR) in 11 mammalian cell culture lines derived from hepatic and nonhepatic tissues. The strategy was to first use Western blot analysis to determine the expression of ARNT or AHR in each cell line relative to its concentration in murine wild-type Hepa-1c1c7 (Hepa-1) cells. Actual ARNT and AHR concentrations in known amounts of total cell lysates were then determined by generating a standard curve with defined amounts of a highly purified ARNT or AHR protein and performing regression analysis. The results show that the level of ARNT expression in each of the cell lines is similar and represents approximately 0.001-0.002% of total cellular protein. The range of expression was only approximately 3-fold with wild-type Hepa-1 cells expressing the highest level of ARNT (33,000/cell) and canine kidney cells (MDCK line) expressing 14,000 ARNT molecules/cell. In contrast, the concentration of AHR varied by 65-fold over the different cell lines with the wild-type Hepa-1 expressing 323,000 AHR/cell and rat hepatoma cells (H4IIE) expressing 4700. The ratio of AHR to ARNT ranged from 0.3 in H4IIE cells to 10 in the Hepa-1 line with the majority of cells expressing 1-5 times more AHR than ARNT protein. Immunocytochemical staining of each cell line showed that ARNT was exclusively localized to the nuclear compartment and that a conserved nuclear localization signal mapped to the NH-terminal portion of the protein.
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PMID:Determination of aryl hydrocarbon receptor nuclear translocator protein concentration and subcellular localization in hepatic and nonhepatic cell culture lines: development of quantitative Western blotting protocols for calculation of aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator protein in total cell lysates. 927 42

2,3,7,8-Tetrachlorodibenzo-p-dioxin and related environmental pollutants exert most of their adverse effects such as immunosuppression, induction of endocrine dysfunction, tumor promotion, and teratogenicity via the aryl hydrocarbon or dioxin receptor. While most potent agonists of the aryl hydrocarbon receptor are of synthetic origin, an increasing number of natural compounds are now recognized as receptor agonists. Our findings demonstrated that some tryptanthrin derivatives biosynthesized in incubations of Candida lipolytica with tryptophan and anthranilic acid or its derivatives were agonists of the aryl hydrocarbon receptor. The biosynthetic products 8-methyltryptanthrin, 8-chlorotryptanthrin, and 8-bromotryptanthrin induced cytochrome P4501A1 mRNA and protein in rat hepatocytes in primary culture, characteristic features of aryl hydrocarbon receptor agonists. Log-probit analysis of the catalytic activity of cytochrome P4501A1, 7-ethoxyresorufin O-deethylase (EROD), revealed EC50 induction values of 1.7, 0.25, and 0.17 microM for 8-methyltryptanthrin, 8-chlorotryptanthrin, and 8-bromotryptanthrin, respectively. Interestingly, the nonsubstituted tryptanthrin molecule, biosynthesized from the common physiological precursors tryptophan and anthranilic acid, was also active as an inducer. The specificity of the inducing effect of tryptanthrins was demonstrated in gel retardation experiments in Hepa-1 mouse hepatoma cells, showing the characteristic interaction of the activated aryl hydrocarbon receptor with an oligonucleotide containing a xenobiotic-responsive element. It is suggested that the receptor may be part of a defense system protecting higher organisms from secondary metabolites formed by the microflora of the host or its environment.
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PMID:Tryptanthrins: a novel class of agonists of the aryl hydrocarbon receptor. 929 63

The estrogen receptor and aryl hydrocarbon receptor (AhR) are coexpressed in several Ah and estrogen-responsive human breast cancer cell lines. However, a recent study reported that 17beta-estradiol (E2) inhibited Ah responsiveness in mouse Hepa 1c1c7 hepatoma cells (Kharat, I., and Saatcioglu, F. (1996) J. Biol. Chem. 271, 10533-10537), and therefore, estrogen receptor-AhR cross-talk was reinvestigated in MCF-7 and mouse Hepa 1c1c7 cells. Treatment of MCF-7 or Hepa 1c1c7 cells with 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD) resulted in induction of CYP1A1-dependent activity and mRNA levels. Treatment of both cell lines with E2 had no effect on basal or TCDD-inducible CYP1A1-dependent activity or mRNA levels. In MCF-7 and Hepa 1c1c7 cells transiently transfected with an Ah-responsive plasmid containing the 5'-regulatory region of the human CYP1A1 gene fused to the chloramphenicol acetyltransferase reporter gene 10 nM TCDD significantly induced chloramphenicol acetyltransferase activity; in cells cotreated with TCDD plus E2 the induced response was not affected by the hormone. Nuclear extracts from cells treated with dimethyl sulfoxide, E2, TCDD, and TCDD plus E2 were incubated with the [32P]dioxin-responsive element and analyzed by gel electrophoretic mobility shift assays. A retarded band associated with formation of a [32P]dioxin-responsive element-AhR complex was observed in nuclear extracts from cells treated with TCDD or TCDD plus E2 (cotreated). Collectively these studies suggest that E2 does not modulate AhR-mediated CYP1A1 gene expression in MCF-7 or Hepa 1c1c7 cells.
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PMID:Estrogen does not inhibit 2,3,7, 8-tetrachlorodibenzo-p-dioxin-mediated effects in MCF-7 and Hepa 1c1c7 cells. 937 12

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a non-genotoxic environmental pollutant that causes multiple adverse effects in experimental animals and in humans. We show here that TCDD treatment of mouse hepatoma cells causes a rapid mobilization of intracellular calcium both in wild type Hepa-1 cells and in its c2 variant, a cell line that has highly reduced levels of functional aromatic hydrocarbon (Ah) receptor (AHR). In wild type cells, but not in the c2 variant, TCDD treatment leads to a sustained elevation of cytosolic free calcium. TCDD also induces elevated levels of cyclooxygenase-2 (COX-2) mRNA in wild type and in c37, a CYP1A1-deficient cell line, but not in c2 cells. Induction of Cox-2 is in fact dependent on the presence of a functional Ah receptor, since it can be blocked by antisense oligonucleotides to Ah receptor mRNA. Most likely as a consequence of Cox-2 induction, we find a significant increase in the level of 12-hydroxyheptadecatrienoic acid (12-HHT) secreted from TCDD-treated Hepa-1 cells. In addition, we observe elevated levels of 6-keto prostaglandin F1alpha in c2 cells and high levels of secreted prostaglandin F2alpha in c2, c37 and c4, the variant cell line lacking aromatic hydrocarbon nuclear translocator protein. These data suggest that Cox-2 activation by TCDD leads to the release of prostaglandins, eicosanoids and other mediators which may have an important role in the biological and toxic effects of TCDD.
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PMID:Sustained increase in intracellular free calcium and activation of cyclooxygenase-2 expression in mouse hepatoma cells treated with dioxin. 939 71

We have investigated mechanisms of omeprazole (OME)-mediated induction of CYP1A1 and CYP3A, using the rat hepatoma H4IIE cell line, in comparison with mechanisms exerted by traditional aryl hydrocarbon receptor (AhR) ligands such as benso(a)pyrene (B(a)P) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). OME did not bind specifically to AhR, and it could not activate the AhR complex in rat cytosol to a xenobiotic-responsive element (XRE)-binding form in vitro. Genistein, a tyrosine kinase inhibitor, and daidzein, an inhibitor of casein kinase II, efficiently inhibited OME-mediated but not B(a)P- or TCDD-mediated induction of CYP1A1, as monitored at the transcriptional, mRNA, and protein levels as well as by analysis of activation of XRE-luciferase reporter constructs transfected into H4IIE cells. The protease inhibitor Nalpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and lavendustin A also had similar OME-specific effects. In addition, insulin pretreatment caused an almost complete inhibition of OME-dependent CYP1A1 induction but only partially affected TCDD and B(a)P-mediated induction of CYP1A1. Staurosporine, an inhibitor of protein kinase C, impaired the induction by both B(a)P and OME. OME caused an approximately 2-fold increase in the level of CYP3A expression, but all inhibitors used were ineffective in preventing this induction. Gel shift analysis with radiolabeled XRE and specific peptide antibodies toward AhR and aryl hydrocarbon receptor nuclear translocator protein (Arnt) revealed an OME-mediated translocation of the AhR.Arnt complex into the nuclei. Genistein inhibited the specific nuclear XRE binding caused by OME, but it potentiated the formation of the TCDD-induced XRE.AhR complex. Although daidzein was able to effectively inhibit the OME-stimulated CYP1A1 gene transcription, it did not influence the OME-dependent AhR.XRE complex formation. The data are consistent with a mechanism for OME-mediated induction of CYP1A1 that involves activation of the AhR complex via intracellular signal transduction systems and that is distinct from induction mediated by AhR ligands.
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PMID:Signal transduction-mediated activation of the aryl hydrocarbon receptor in rat hepatoma H4IIE cells. 939 20

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