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)

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin induces the microsomal enzyme cytochrome P4501A1 by increasing the transcription rate of the CYP1A1 gene. Induction requires two basic helix-loop-helix proteins, the ligand-binding aromatic hydrocarbon receptor (AhR) and its heterodimerization partner, the AhR nuclear translocator (Arnt). The AhR/Arnt heterodimer induces transcription by binding to dioxin-responsive elements (DREs) within an enhancer upstream of the CYP1A1 gene. The basic regions of AhR and Arnt are crucial for DRE binding. We have mutated these regions in order to analyze the relationship between DRE binding (determined in vitro using an electrophoretic mobility shift assay) and induction of CYP1A1 transcription (determined in vivo by genetic complementation of AhR-defective and Arnt-defective mouse hepatoma cells, using an RNase protection assay to measure mRNA accumulation). Our findings reveal the amino acids in the basic regions of AhR/Arnt that are important for both DRE binding and induction of transcription. This information provides biological background for the interpretation of structural (e.g. crystallographic) studies of the interactions between AhR/Arnt and the DRE. Our findings also indicate that the in vitro behavior of the mutants does not consistently predict their functional activity in vivo. Thus, genetic complementation constitutes an important and stringent test for analyzing the effects of mutations on AhR/Arnt function.
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PMID:DNA binding by the heterodimeric Ah receptor. Relationship to dioxin-induced CYP1A1 transcription in vivo. 862 73

The rat CYP1A1 negative regulatory element (NRE) contains AP-1 and Oct-1 motifs at -808 to -788 bp. The CYP1A1 sequence from -813 to -779 bp and an identical sequence bearing a point mutation in the octamer motif were synthesized. Gel mobility shift assays showed the formation of two complexes with the wild-type CYP1A1 sequence and nuclear extracts from H4IIE and HepG2 hepatoma cells and from rat liver. The formation of the major complex was significantly reduced with the mutant octamer-containing oligomer and was specifically competed by an Oct-1 oligodeoxyribonucleotide. The addition of Oct-1 antibody caused a supershift of the major complex. The presence of the wild-type sequence, but not the mutant octamer sequence, caused a 3-fold decrease in SV40 enhancerless promoter activity in transfected HepG2 cells. Co-transfection of an Oct-1 expression vector with rat CYP1A1 NRE octamer-containing, promoter/reporter gene constructs specifically further decreased promoter activity of the wild-type octamer-containing constructs in HepG2 cells. The results indicate that Oct-1 binds to the rat CYP1A1 promoter NRE and is a negative regulator of rat CYP1A1 expression.
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PMID:Oct-1 transcription factor is a negative regulator of rat CYP1A1 expression via an octamer sequence in its negative regulatory element. 863 66

We have cloned and sequenced the mouse AHD3 cDNA, which codes for the Class 3 microsomal aldehyde dehydrogenase (ALDH3m). The cDNA is 2,997 bp in length excluding the poly(A)+ tail, and has 5' and 3' non-translated regions of 113 bp and 1,429 bp, respectively. The deduced amino acid sequence consists of 484 amino acids, including the first methionine (Mr = 53,942), and contains a hydrophobic segment at the carboxyl terminus which is the putative membrane anchor. The mouse AHD3 protein was found to be: 95% similar to the rat microsomal ALDH3m protein, 65% identical to the mouse, rat and human cytosolic ALDH3c protein, and <28% similar to the rat Class 1 and Class 2 ALDH and methylmalonate-semialdehyde dehydrogenase proteins. Southern hybridization analysis of mouse cDNA probed with the full-length AHD3 cDNA revealed that the Ahd3 gene likely spans less than a total of 25 kb. The mouse Ahd3 gene is very tightly linked to the Ahd4 gene on chromosome 11. Mouse AHD3 mRNA levels are increased by dioxin in mouse Hepa-1c1c7 hepatoma wild-type (wt) cells but not in the Ah receptor nuclear translocator (ARNT)-defective (c4) mutant line, indicating that the induction process is mediated by the Ah (aromatic hydrocarbon) dioxin-binding receptor. AHD3 mRNA levels are also inducible by clofibrate in both the wt and c4 lines. AHD3 mRNA levels are not elevated in the CYP1A1 metabolism-deficient c37 mutant line or as part of the oxidative stress response found in the untreated 14CoS/14CoS mouse cell line. These data indicate that, although inducible by dioxin, the Ahd3 gene does not qualify as a member of the aromatic hydrocarbon [Ah] gene battery.
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PMID:Mouse microsomal Class 3 aldehyde dehydrogenase: AHD3 cDNA sequence, inducibility by dioxin and clofibrate, and genetic mapping. 863 52

The molecular mechanism of induction of cytochromes P4501A1/2 (CYP1A1/2) by a synthetic compound YH439 was studied in rodents as well as in cultured hepatoma cells. CYP1A1-mediated ethoxyresorufin-O-deethylase activity and amounts of its immunoreactive protein were increased in a time- and concentration-dependent manner after a single dose of YH439 (150 mg/kg). Northern blot analyses revealed that YH439 rapidly increased (< or = 2 hr) the levels of CYP1A1/2 mRNAs, resulting in an increase in CYP1A protein level by > 6-fold at 8 hr after injection. After YH439 administration, the levels of CYP1A1 and CYP1A2 mRNAs peaked at 8 hr and 16 hr, respectively, before returning to control levels at 16 and 24 hr. The CYP1A protein level, on the other hand, reached a maximum at 24 hr after YH439 treatment and returned to near-control levels at 72 hr. Nuclear run-on analyses revealed that YH439 induces CYP1A1/2 gene transcription as early as 2 hr after YH439 treatment. Cytosolic electrophoretic mobility shift assays suggested that YH439 activates the CYP1A1/2 genes through the aryl hydrocarbon (Ah) receptor and the xenobiotic response elements. The dependency on the Ah receptor for the induction of CYP1A1/2 by YH439 was confirmed by the lack of CYP1A1/2 induction in the Ah receptor knock-out mice (Ahr-1-) as well as in murine hepatoma cells without a functional Ah receptor. Molecular structural analysis of YH439 and several other compounds indicated that the planarity and size of a molecule are important in its interaction with the Ah receptor and subsequent CYP1A1/2 induction. YH439 is a thiazolium compound with little aromaticity and with a two-dimensional structure different from that of the Ahs. Therefore, it represents a new class of Ah receptor ligand and CYP1A inducer.
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PMID:Transcriptional induction of the cytochrome P4501A1 gene by a thiazolium compound, YH439. 864 58

Polychlorobiphenyls are potent inducers of hepatic cytochrome P450 in various species. Until now, no model based on cultured cells can be considered as a universal surrogate for in vivo metabolism. In this respect, cultured rat hepatocytes, quail hepatocytes, and human hepatoma (HepG2) cells were used to study the effects of 3,3',4,4'-tetrachlorobiphenyl (3,3',4,4'-TCB) and Aroclor 1254 on drug-metabolizing enzymes. The presence of dexamethasone in the culture medium allows the expression and the induction of several cytochrome P450 isoenzymes found in adult cells. Induction of ethoxycoumarin-(ECOD) and ethoxyresorufin-O-deethylase (EROD), activities were measured. Induced P450s were identified by immunoblotting and Northern blotting. Aroclor 1254 induced ECOD activity in all three cell types, but the effect was much stronger in fetal rat hepatocytes than in human or quail cells. Aroclor failed to induce EROD activity in quail cells, had a slight inducer effect in HepG2 cells, and a marked effect in rat hepatocytes. 3,3',4,4'-TCB had no effect in HepG2 cells but significantly increased EROD and ECOD activities, especially the latter, in rat and quail cells. On the immunoblots, specific antibodies revealed essentially CYP1A1 in fetal rat hepatocytes, CYP2B1/2 in quail hepatocytes and CYP3A1 in HepG2 cells. Analysis of Northern blots showed an hybridization with CYP1A1, 2B1 and 3A1 mRNA in fetal rat hepatocytes, CYP3A and 1A mRNA in HepG2 cells, and a form of CYP2 mRNA in fetal quail hepatocytes closely related to homolog rat CYP2E or CYP2C. In quail hepatocytes, induction did not increase proportionally with the concentration of inducer in the culture medium. Instead, the dose-response curves (for EROD activity especially) peaked sharply at 1 muM Aroclor 1254, an effect attributed to changes in membrane fluidity or lipid content. Our results highlight the advantage of using several types of cultured hepatocytes to investigate fundamental aspects of drug-metabolism-linked toxicity, the balance between xenobiotic bioactivation and detoxication being differently affected by PCBs in different animal species.
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PMID:P450 induction by Aroclor 1254 and 3,3',4,4'-tetrachlorobiphenyl in cultured hepatocytes from rat, quail and man: interspecies comparison. 866 1

Cytochromes P450 2B1 and 2B2 (CYP2B1 and CYP2B2) are well-known phenobarbital-inducible genes in rat liver. Potential transcriptional regulatory elements in the proximal promoter regions of rat CYP2B genes were analyzed by transfection in HepG2 hepatoma cells and by binding of nuclear proteins. Deletion of sequences from -1,400 to -110 had modest effects on promoter activity, but further deletion to -57 decreased the transcriptional activity by more than 90%, suggesting the presence of strong cis-acting elements in this region. Sequences similar to a basal transcription element (BTE) in CYP1A1 and a proposed phenobarbital responsive element (Barbie box) are present from -89 to -67. However, no protection was detected in these regions by DNase I footprinting assay. Instead, a region (FP1) from -64 to -45 was protected by liver nuclear extracts. Mutation of either the BTE or FP1 sequences of CYP2B1, or both, reduced transcriptional activity by 70-80% in HepG2 cells. FP1 was identified as a functional C/EBP site by co-transfection of C/EBP expression vectors and supershift assays with C/EBP antisera. Binding of liver nuclear proteins to sequences within the -110 to +1 region was not detectably altered by pretreatment of rats with phenobarbital.
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PMID:The CYP2B1 proximal promoter contains a functional C/EBP regulatory element. 876 71

In the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related chemicals, the Ah receptor nuclear translocator (Arnt) forms a heterodimeric complex with the ligand-bound Ah receptor, leading to recognition of dioxin-responsive elements within the enhancer of the CYP1A1 gene and transcription activation by an unknown mechanism. To understand the role of Arnt in transcription activation by the Ah receptor-Arnt heterodimer, we performed a deletion analysis of Arnt to locate domains that are directly involved in transcription activation. We showed that the C-terminal 34 amino acids of Arnt encode a transcription activation domain (TAD) that functions independently of other sequences in the Ah receptor complex when attached to the heterologous Gal4 DNA binding domain. Deletion of the C-terminal acidic-rich 14 amino acids completely abolishes activity. Sequences important in Arnt TAD function were independent of the glutamine-rich region which is an important structural feature in the TAD of other transcription factors. The strength of the Arnt TAD when compared with the strong TAD from the herpes simplex virus VP16 protein was cell-type specific. Both the Arnt and VP16 TAD were equally strong in COS-1 cells, but the Arnt TAD had weak activity in an Arnt-deficient mouse hepatoma cell line and was not needed for restoration of CYP1A1 activation. These results imply that for CYP1A1 activation the Ah receptor provides the dominant activation function for the heterodimer in hepatoma cells. The potential of the Arnt TAD to contribute to activation by the Ah receptor complex is likely determined by availability or activity of cell-specific factors with which the TAD interacts.
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PMID:Identification of a cell-specific transcription activation domain within the human Ah receptor nuclear translocator. 880 43

Environmental pollutants are classically associated with increased drug metabolism. Cultures of rat hepatocytes, quail hepatocytes, and human hepatoma (Hep G2) cells were used to study the effects of pesticides on drug-metabolizing enzymes. Membrane integrity and mitochondrial activity were evaluated and induction of ethoxycoumarin-O-deethylase and ethoxyresorufin-O-deethylase activities were measured. Induced P450s were identified by immunoblotting. Pentachlorophenol and lindane appeared as the strongest inducers. On the immunoblots, specific antibodies revealed induced CYP1A1 in fetal rat hepatocytes, CYP2B in quail hepatocytes, and CYP3A7 in Hep G2 cells. Pesticide effects on these different activities in each type of cultured cells were compared by cluster analysis. Results obtained under similar conditions with reference inducers phenobarbital (PB) and benzo[a]anthracene and other environmental pollutants (polychlorobiphenyls) were added to previous data prior to multivariate analysis. The tested products fell into four major groups: a first group with pentachlorophenol, identified as a CYP3A inducer; a second group containing the methylcholanthrene-type inducers that increase CYP1A-related activities; a third class represented by dieldrin, a PB-type inducer; a fourth group including inert compounds or weak inducers. Lindane shares the criteria of the second and third groups and seems to induce both CYP1A and CYP2B activities. The current study results highlight the advantage of using several types of cultured hepatocytes to evaluate the short-term toxicity of environmental pollutants in vitro and constitute a useful model for predicting the potential toxicity of pesticides in humans (Hep G2 cells) and wildlife (fetal quail hepatocytes).
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PMID:Hierarchical cluster analysis of environmental pollutants through P450 induction in cultured hepatic cells. 881 89

Three benzimidazole compounds, omeprazole (OP), thiabendazole (TBZ), and lansoprazole (LP), were compared with respect to the induction of CYP1A1-mRNA in human hepatoma cells, HepG2. OP was the most potent inducer among the three compounds, but LP was found to be a weak inducer. Induction by TBZ was at an intermediate level. None of these compounds induced CYP1A1-mRNA in a mouse hepatoma cell line, Hepa-1. The transient expression of mouse Cyp1a1-CAT gene into HepG2 cells showed that OP treatment of the transfectants induced CAT activity to the same degree as 2,3,7,8-tetrachlorodibenzo-p-dioxin treatment. Therefore, the cellular factors in human cells were able to work on the mouse regulatory element. The expression of human aryl hydrocarbon (Ah) receptor in the mouse Hepa-1 mutant cell line cl-19, which is defective in Ah receptor, did not increase the induction level of CYP1A1-mRNA by OP treatment. When the cultured medium of HepG2 cells in the presence of OP was added to the mouse Hepa-1 cell culture medium, CYP1A1-mRNA was not induced in Hepa-1 cells. It is thus concluded that metabolites of OP in human cells are not the ligands for the human Ah receptor. Therefore, in human cells, but not mouse cells, there must be an OP-sensitive activation factor for the human Ah receptor.
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PMID:Differences in inducibility of CYP1A1-mRNA by benzimidazole compounds between human and mouse cells: evidences of a human-specific signal transduction pathway for CYP1A1 induction. 890 Mar 97

Cigarette smoke is known to induce cytochrome P4501A1 expression and activity in a variety of species. Although the elevation of this isozyme is assumed to be associated with the activation of the CYP1A1 gene through a ligand-mediated mechanism involving the Ah-receptor (AhR), this has not been determined. In this study we have examined the mechanism by which an ambient level of aged and diluted sidestream cigarette smoke (ADSS) induces cytochrome P4501A1. Effects of ADSS on C57BL/6N and DBA/ 2N mice were examined. Induction of P4501A1-associated ethoxyresorufin-O-dealkylase (EROD) activity was observed in the lungs of C57BL/6N mice, while there was no induction in DBA/ 2N mice. ADSS also induced EROD in wild-type mouse hepatoma (Hepa1c1c7) cells (hepa1), but not in variant hepa1 cells defective in the AhR nuclear translocator (ARNT) protein. ADSS exposure of recombinant hepa1 cells, stably transfected with a reporter plasmid containing the luciferase gene under control of several dioxin responsive enhancers (DREs), resulted in a time- and exposure-dependent induction of luciferase activity. ADSS-mediated induction of luciferase activity was inhibited by alpha-naphthoflavone (alpha NF), an Ah-receptor antagonist. Gel retardation analysis demonstrated that exposure to ADSS induced transformation and DNA binding of the AhR complex. In summary, our results not only indicate a role for the AhR in mediating the induction of P4501A1 by ADSS, but also demonstrate that environmentally relevant levels of ADSS must contain AhR ligands at sufficient concentrations to activate gene expression in an AhR-dependent manner.
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PMID:Ah-receptor-dependent modulation of gene expression by aged and diluted sidestream cigarette smoke. 891 78

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