Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Ah (aromatic hydrocarbon) receptor mediates induction of aryl hydrocarbon hydroxylase (AHH; an enzyme activity associated with cytochrome P450IA1) by polycyclic aromatic hydrocarbon carcinogens such as 3-methylcholanthrene (MC) and benzo[a]pyrene (BP) and the halogenated toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Until recently the AhR seemed to be present only at very low levels in human cells and tissue. With a modified assay (the presence of sodium molybdate and a reduction in the amount of charcoal used to adsorb "excess" ligand) we found that cytosol from LS180 cells contains a high concentration of AhR (400-500 fmol/mg cytosolic protein) when detected by [3H]TCDD or [3H]MC. Cytosolic receptor also was detected with [3H]BP but at a level that was 35% of that detected with [3H]TCDD or [3H]MC. These levels are similar to those found in mouse Hepa-1 hepatoma cells in which AhR has been extensively characterized. The apparent binding affinity (Kd) of the cytosolic receptor for [3H]TCDD and for [3H]MC was about 5 nM. As with Hepa-1, the human LS180 cytosolic AhR sedimented at about 9 S on sucrose gradients when detected with [3H]TCDD, [3H]BP or [3H]MC. The nuclear-associated ligand.receptor complex recovered from cells incubated in culture with [3H]TCDD sedimented at about 6.2 S. The 9.8 S cytosolic form corresponds to a multimeric protein of a relative molecular mass (Mr) of about 285,000 whereas the 6.2 S nuclear receptor corresponds to a multimeric protein of Mr 175,000. The smallest specific ligand-binding subunit (detected by sodium dodecyl sulfate-polyacrylamide electrophoresis under denaturing conditions of receptor photoaffinity labeled with [3H]TCDD) was about Mr 110,000. AHH activity was induced in cells exposed in culture to TCDD or benz[a]anthracene (BA). The EC50 was 4 x 10(-10) M for TCDD and 1.5 x 10(-5) M for BA. For both inducers the EC50 in LS180 cells was shifted about one log unit to the right as compared to the EC50 for AHH induction in mouse Hepa-1 cells. The lower sensitivity of the LS180 cells to induction of AHH activity by TCDD or BA is consistent with the lower affinity of TCDD and MC for binding to human AhR. The ligand-binding properties, physicochemical properties, and mode of action of the AhR in this human cell line are therefore very similar to those of the extensively characterized AhR in rodent cells and tissues.
 ...
PMID:Detection and characterization of the Ah receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin in the human colon adenocarcinoma cell line LS180. 165 65

Fish-eating waterbirds from the Great Lakes of North America have shown symptoms of poisoning similar to those observed in laboratory exposures of various avian species to planar halogenated hydrocarbons (PHHs). PHHs, include among others, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs), and have been implicated in some of the reproductive problems of Great Lakes water-birds. The objectives of this study were to assess the overall potencies of PCB-containing extracts from colonial water-bird eggs taken from the Great Lakes and to compare the potencies with the location and spatial distribution of the colonies. The potencies of the extracts were assessed by their ability to induce cytochrome P450IA1-associated ethoxyresorufin O-deethylase (EROD) activity in H4IIE rat hepatoma cells as compared to the standard, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The H4IIE bioassay-derived TCDD-equivalents (TCCD-EQs) in the waterbird eggs concur with residue analyses and biological data from other studies. The greatest concentrations of TCDD-EQs were found in waterbird eggs from historically polluted, industrialized or urbanized areas in which the reproductive impairment of colonial waterbirds was most severe. However, significant concentrations of TCDD-EQs were detected at all sites tested; with a range of 49 to 415 pg TCDD-EQ/g egg, uncorrected for extraction efficiencies. The H4IIE bioassay proved to be a useful biomonitoring tool to assess the overall potency of complex PHH mixtures in environmental samples.
 ...
PMID:H4IIE rat hepatoma cell bioassay-derived 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents in colonial fish-eating waterbird eggs from the Great Lakes. 165 67

alpha-Naphthoflavone (ANF) has previously been shown to compete with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for binding to the Ah receptor under conditions in vitro. However, ANF also prevents TCDD-elicited cytochrome P450lA1 induction, immunosuppression, and down-regulation of the estrogen receptor in vivo and within intact isolated cells. These data suggest that ANF is a TCDD antagonist. This study investigated the ability of ANF to transform the Ah receptor contained in rat hepatic cytosol or mouse hepatoma cells to a form that recognizes the dioxin-responsive enhancer element (DRE) upstream of the cytochrome P450lA1 gene. Gel retardation analysis indicated that TCDD- or beta-naphthoflavone (BNF)-bound receptor was able to bind to the DRE, whereas essentially no receptor-DRE complexes were observed using cytosol incubated with ANF concentrations as high as 1000 nM. Furthermore, an excess of ANF, when added to cytosol just before TCDD, blocked, in a concentration-dependent manner, the ability of TCDD to transform the receptor to a form that bound to the DRE. These studies indicated that ANF binds to the receptor and confers on it a conformation that cannot recognize the DNA recognition sequence contained in the DRE. Although an excess of the agonist 2,3,7,8-tetrachlorodibenzofuran (TCDF) readily reversed the inhibitory actions of ANF, ANF was unable to reverse the effects of TCDD, TCDF, or BNF on the receptor. These studies suggested that TCDD binding, unlike that of ANF, results in a receptor conformation that has higher affinity for the ligand. Treatment of mouse hepatoma Hepa 1c1c7 cells with TCDD or BNF resulted in receptor contained in nuclear extracts that bound to the DRE. Only a very minor ligand-dependent protein-DNA complex was detected when cells were treated with ANF. These data indicated that ANF acts as an antagonist of TCDD by directly binding to the Ah receptor and eliciting a protein conformation that has very low affinity for DNA.
 ...
PMID:Alpha-naphthoflavone acts as an antagonist of 2,3,7, 8-tetrachlorodibenzo-p-dioxin by forming an inactive complex with the Ah receptor. 165 99

Indole-3-carbinol (I3C) is a secondary plant metabolite produced in vegetables of the Brassica genus, including cabbage, cauliflower, and brussels sprouts. I3C is both an anti-initiator and a promoter of carcinogenesis. Consumption of I3C by humans and rodents can lead to marked increases in activities of cytochrome P-450-dependent monooxygenases and in a variety of phase II drug-metabolizing enzymes. We have reported previously that the enzyme-inducing activity of I3C is mediated through a mechanism requiring exposure of the compound to the low-pH environment of the stomach. We report here the aromatic hydrocarbon responsiveness-receptor Kd values (22 nM-90 nM), determined with C57BL/6J mouse liver cytosol and the in vitro- and in vivo-molar yields (0.1-6%) of the major acid condensation products of I3C. We also show that indolo[3,2-b]carbazole (ICZ) is produced from I3C in yields on the order of 0.01% in vitro and, after oral intubation, in vivo. ICZ has a Kd of 190 pM for aromatic hydrocarbon responsiveness-receptor binding and an EC50 of 269 nM for induction of cytochrome P4501A1, as measured by ethoxyresorufin O-deethylase activity in murine hepatoma Hepa 1c1c7 cells. The binding affinity of ICZ is only a factor of 3.7 x 10(-2) lower than that of the highly toxic environmental contaminant and cancer promoter 2,3,7,8-tetrachlorodibenzo-p-dioxin. ICZ and related condensation products appear responsible for the enzyme-inducing effects of dietary I3C.
 ...
PMID:Aromatic hydrocarbon responsiveness-receptor agonists generated from indole-3-carbinol in vitro and in vivo: comparisons with 2,3,7,8-tetrachlorodibenzo-p-dioxin. 165 85

The aromatic hydrocarbon (Ah) receptor behaves as a ligand-dependent transcription factor in the induction of cytochrome P450IA1. In cells exposed to the Ah receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), the Ah receptor undergoes a transformation from a form with low affinity for nucleic acids (cytosolic receptor) into a form that preferentially associates with the cell nucleus (nuclear receptor). We followed the fate of the Ah receptor in mouse hepatoma cells during short-term exposure to [3H]TCDD by analyzing both cytosolic and nuclear fractions for specific binding. Nuclear Ah receptor levels increased over the first 2 h of treatment and then decreased to about 50% of maximal concentrations by 5 h after start of treatment. The decrease in nuclear receptor was not accompanied by a reappearance of detectable Ah receptor in the cytosolic fraction; further incubation with [3H]TCDD in cytosols from lysed cells did not label any additional receptor sites in cytosolic extract. By the 6th h of incubation, the total receptor population in the cell was only about 15-20% of that detected at the start of the incubation. The levels of specific binding detected were unaffected by up to 20 h of incubation with the vehicle DMSO, confirming that the presence of TCDD is required for the observed downregulation to occur. These results indicate that there is a substantial ligand-dependent loss in total Ah receptor during short-term exposure of cells to TCDD in culture.
 ...
PMID:Downregulation of the Ah receptor in mouse hepatoma cells treated in culture with 2,3,7,8-tetrachlorodibenzo-p-dioxin. 166 93

The polymorphism of mammalian aromatic hydrocarbon (Ah) responsiveness appears to be correlated with genetic differences in risk of bronchogenic carcinoma caused by cigarette smoking. The human polymorphism has been uncovered, largely as the result of corresponding genetic differences characterized first in the mouse. The murine Ah locus has been defined as the gene encoding the aromatic hydrocarbon-responsive (Ah) receptor, responsible for the inducibility of a battery of at least six genes, two of which encode P450 enzymes. The high-affinity receptor and, hence, more highly induced levels of P450, can result in greater concentrations of polycyclic aromatic reactive intermediates that form DNA adducts and, ultimately, mutation fixation (tumour initiation). The Ah receptor is also likely to participate in growth and differentiation signal transduction pathways (tumour promotion). Positive and negative control regions flanking the murine Cyp 1a-1 and human CYP1A1 (cytochrome P(1)450) genes have been identified. A DNA motif approximately 1 kb upstream of the transcription start site appears to affect the translatability of the CYP1A1 mRNA and activity of the enzyme. Expression of the CYP1A1 or CYP1A2 enzyme in mouse hepatoma Hepa-1 cells lacking endogenous CYP1A1 activity represses constitutive transcription of not only the endogenous Cyp1a-1 gene but other genes in the dioxin-inducible [Ah] battery. Human polymorphisms involving a Msp I site 450 bp downstream from the last CYP1A1 exon have been described in Japan, the Eastern Mediterranean, Norway and the USA. The '1.9 allele' is associated with an increased incidence of Kreyberg Type I bronchogenic carcinomas in Japan and has recently been correlated with a valine-to-isoleucine substitution at position 462 in the haeme-binding region. This allele is about 3 times more frequent in Japan than in Caucasians of Norway and the USA, in which no correlation has been found between this allele and lung cancer. More work is needed to clarify these findings. Isolation and sequencing of the human Ah receptor cDNA, and the subsequent screening of populations for polymorphisms, hold great promise for predicting interindividual risk of cancer caused by smoking and other environmental pollutants.
 ...
PMID:Human AH locus polymorphism and cancer: inducibility of CYP1A1 and other genes by combustion products and dioxin. 184 73

The 4 S polycyclic aromatic hydrocarbon (PAH)-binding protein had been implicated in regulating the expression of rat cytochrome P450IA1 which is most closely associated with aryl hydrocarbon hydroxylase (AHH). We have now investigated the presence of both the 4 S PAH-binding protein and the 8 S Ah receptor in rat hepatoma H4-II-E cells as well as the induction of P450IA1 upon their exposure to PAH's such as benzo[a]pyrene (BP) and 3-methylcholanthrene (3MC), and halogenated dioxins such as 2,3,7,8-tetrachlordibenzo-p-dioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDBF). Sucrose density gradient analyses and hydroxylapatite assays indicate that, in addition to the 8 S protein, the 4 S PAH binding protein is present in these cells. This protein interacts in a saturable and high affinity manner with BP and 3MC, but not with TCDD or TCDBF. Using a P450IA1 probe, the induction of gene expression was observed by Northern blot analysis of total cellular RNA after exposure of the H4-II-E cells to BP, 3MC, or TCDBF. Since the 4 S protein was observed to interact only with BP and 3MC, these results suggest that this protein may also play a role in the PAH-induced expression of cytochrome P450IA1 gene expression in H4-II-E.
 ...
PMID:Presence of the 4 S polycyclic hydrocarbon-binding protein in H4-II-E cells. 184 70

The Ah receptor is a soluble protein complex that mediates carcinogenesis by a wide range of environmental pollutants, including polycyclic aromatic hydrocarbons, heterocyclic amines, and polychlorinated aromatic compounds. The best understood activity of the receptor concerns its role in the induction of cytochrome P450IA1. We undertook a somatic cell genetic analysis of P450IA1 induction using the mouse hepatoma cell line, Hepa-1. Clones of Hepa-1 were isolated that are defective in induction of P450IA1. Evidence was obtained that the clones are mutational in origin. Cell fusion experiments demonstrated that a few of the mutants are dominant, while the majority are recessive. The dominant mutants were shown to synthesize a repressor of P450IA1 transcription. The recessive mutants were assigned to 4 complementation groups (probably corresponding to 4 different genes). Complementation group A corresponds to the P450IA1 structural gene. Mutations in the B, C and D genes all affect functioning of the Ah receptor. A 'reverse selection procedure', whereby cells that express P450IA1 inducibility can be selected from a majority population of cells lacking inducibility, was developed. The reverse selection procedure was used to isolate transfectants of representative recessive mutants in which the mutational defects are complemented by exogenously applied genomic DNA. A human DNA-derived transfectant of a C- mutant was used to clone the human C gene. The C gene is not the ligand-binding subunit of the Ah receptor but is a protein that is required for translocation of Ah receptor-ligand complexes from cytoplasm to nucleus. In analogous experiments the dominant gene from one of the dominant mutants was transfected into wild-type Hepa-1 cells. Success in transfecting the dominant gene should provide the means for cloning it.
 ...
PMID:Genetic and molecular analysis of the Ah receptor and of Cyp1a1 gene expression. 185 44

Six alkyl ethers of 7-hydroxycoumarin, ranging from methoxy- to hexoxycoumarin, were studied for their NADPH-dependent metabolism by liver microsomes of male rats treated with phenobarbital (PB) or 3-methyl-cholanthrene (MC). The six alkyl ethers were metabolized by both types of microsomes, forming 7-hydroxycoumarin as the major product. Among the test compounds, 7-methoxycoumarin was unusual in that its dealkylation was inducible only by PB and not by MC. PB increased 7-methoxycoumarin-O-demethylase (MOCD) activity about four- to eightfold. Metyrapone strongly inhibited MOCD in PB-treated microsomes but not in MC-treated microsomes. Similarly, monoclonal antibodies directed toward PB-induced cytochrome P450s selectively suppressed MOCD in PB-treated microsomes. MOCD activity was observed in preparations of SD1 cells containing only cytochrome P450IIB1, while it was not found in preparations of XEM1 cells containing only cytochrome P450IA1. Demethylation of 7-methoxycoumarin was also mediated by the constitutive cytochrome P450 form(s) of liver, lung, small intestine, and kidney (in decreasing order). PB increased MOCD activity of small intestine by 40% but was without effect on the dealkylation activity of lung and kidney. MOCD activity was also detectable in differentiated rat hepatoma lines H4IIEC3 and 2sFou. The studies indicate that dealkylation of 7-methoxycoumarin is a highly sensitive, simple, and practical assay for estimating constitutive and PB-inducible cytochrome P450-dependent monooxygenase activities.
 ...
PMID:Dealkylation of 7-methoxycoumarin as assay for measuring constitutive and phenobarbital-inducible cytochrome P450s. 186 30

This study examined the pathophysiological role of parathyroid hormone-related protein (PTHrP) in humoral hypercalcaemia of malignancy (HHM). Seven human tumour xenografts were analysed in nude mice; five tumours (KEsC-2, oesophageal carcinoma; FA-6, pancreatic carcinoma; SEKI, melanoma; Lu-65A and Lu-61, lung carcinomas) were associated with hypercalcaemia and two tumours (MIA PaCa-2, pancreatic carcinoma; PLC/PRF/5, hepatocellular carcinoma) with normocalcaemia. Northern blot analyses, radioimmunoassay and bioassay confirmed the synthesis of PTHrP-like peptides by all five tumours associated with hypercalcaemia, but not by the two associated with normocalcaemia. These observations indicated a very close relationship between the production of PTHrP and the development of HHM. Gel filtration studies of three tumour tissue extracts revealed at least two different molecules with both PTHrP-like immunological and biological activities. One peak eluted at a position between PTHrP (1-141) and cytochrome C and the other at a position identical to cytochrome C. These results suggest that PTHrP molecules with a molecular size equal to or greater than cytochrome C participate as causative agents of HHM. All five tumour xenografts caused hypercalcaemia when grown to a size of 1.5 g in nude mice. Under cell culture conditions, four original cell lines, KEsC-2, FA-6, SEKI and Lu-65A secreted 450.0, 45.0, 3.6 and 3.0 pmol of immunoreactive PTHrP/1.5 x 10(9) cells (approximately equivalent to 1.5 g wet weight) 24 h-1 into their respective culture media. Since a subcutaneous infusion of 100 pmol 24 h-1 of PTHrP (1-34) into nude mice was sufficient to induce significant hypercalcaemia, we speculate that PTHrP alone released from tumour cells could induce hypercalcaemia at least in the case of KEsC-2, and possibly in FA-6. With regard to other tumours associated with hypercalcaemia, further examination of PTHrP and other compounds with bone-resorbing activity in these transplantable tumours is required to obtain a better understanding of this morbidity.
 ...
PMID:Production of parathyroid hormone-related protein in tumour xenografts in nude mice presenting with hypercalcaemia. 199 2


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>