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

NAD(P)H:Quinone oxidoreductase (QR) is a widely-distributed enzyme that promotes obligatory two-electron reductions of quinones and thereby protects cells against the cytotoxicity of quinones and their metabolic precursors. QR is induced by a wide variety of chemoprotectors in many animal tissues as well as in the Hepa 1c1c7 murine hepatoma cell line. Such inducers fall into two families: dual inducers (e.g. polycyclic aromatics, azo dyes, beta-naphthoflavone) that elevate QR as well as cytochrome P1-450, and selective inducers of QR (e.g. tert-butylhydroquinone and other redox-labile diphenols). Induction by the first family of inducers depends on binding to the Ah (Aryl hydrocarbon) receptor and the associated expression of a functional cytochrome P1-450 enzyme, whereas the induction by redox-labile diphenols does not appear to be receptor-mediated. In order to analyze the possible role of the cytochrome P1-450 system in the induction of QR, we examined this process in the Hepa 1c1c7 cells and in four mutants of this cell line that are defective in the induction or expression of functional cytochrome P1-450. tert-Butylhydroquinone was an effective inducer of QR in all of the cell lines, and this process does not, therefore, depend on a functional cytochrome P1-450 enzyme. In contrast, azo dyes and polycyclic aromatics induce QR in the parent cell line but not in the various types of cytochrome P1-450-defective mutants. We conclude that the Ah receptor and cytochrome P1-450 function are involved in the induction of QR by certain azo dyes and polycyclic aromatics, but not by phenolic antioxidants.
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PMID:Role of cytochrome P1-450 in the induction of NAD(P)H:quinone reductase in a murine hepatoma cell line and its mutants. 282 Jun 4

The induction of cytochrome P 450c mRNA and associated aryl hydrocarbon hydroxylase (AHH) activity is mediated by the Ah receptor in rodent liver and hepatic cells in vitro. In the present study we have investigated the underlying mechanisms responsible for the regulation of AHH activity in differentiated and dedifferentiated variants of the rat hepatoma cell line H4IIEC3. All of the dedifferentiated variants expressed inducible cytochrome P-450c mRNA and AHH activity following treatment with polycyclic aromatic hydrocarbons or the compound 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Most of the differentiated derivatives, however, were not inducible for either of these functions. Somatic cell hybridization studies revealed that the differentiated cells were AHH negative due to a defect that corresponded to the Ah receptor D gene product. 5-Azacytidine and sodium butyrate, but not mutagens, reactivated a functional Ah receptor in the differentiated line Fao, indicating that a requisite gene had been silenced by an epigenetic mechanism in this strain. Since many of the 5-azacytidine-induced revertant clones resembled dedifferentiated derivatives with respect to morphology and/or diminished expression of hepatic traits, our results support a correlation between coexpression of the dedifferentiated phenotype and AHH inducibility in these hepatoma cells.
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PMID:Regulation of cytochrome P-450c in differentiated and dedifferentiated rat hepatoma cells: role of the Ah receptor. 282 31

The induction of cytochrome P-450c, the isozyme most closely associated with aryl hydrocarbon hydroxylase activity in the rat, is mediated through a cytosolic polycyclic aromatic hydrocarbon (PAH)-binding protein(s). We have reported on the purification and characterization of a 4 S protein that interacts in a specific and saturable manner with [3H]benzo[a]pyrene and other PAHs. (W. H. Houser et al. (1985) Biochemistry 24, 7839-7845). We have also reported on the specific and saturable interaction of the 4 S protein with a plasmid containing 1.9 kbp of cloned rat P-450c sequence including exon 1, the 5' half of intron 1, and approximately 882 bp upstream information. Our investigations now show that incubation of this protein with a portion of the rat P-450c gene, followed by digestion with either lambda exonuclease or exonuclease III, tentatively identified two protected regions at -225 and -455 bp 5' from exon 1. To further study the significance of these protected regions, a 3.4-kbp fragment containing cytochrome P-450c promoter and 5'-upstream sequences (-882 to +2545) was fused to the chloramphenicol acetyl transferase (CAT) reporter gene and transfected into either rat epithelial RL-PR-C cells or rat hepatoma H-4-II-E cells. Both cell lines expressed CAT activity in response to induction by 3-methylcholanthrene (3MC), indicating that important regulatory regions responsive to 3MC are present in these constructs. However, neither cell line expressed CAT activity in response to 3MC when transfected with plasmids containing deletions (-95 to -724 or -240 to -720) in the regions shown to be protected by our footprinting studies. These results corroborate previous studies which indicated that the 4 S PAH-binding protein interacts in a specific manner with regions of the rat cytochrome P-450c gene. We conclude that the 4 S protein may play an important role in the regulation of expression of cytochrome P-450c in the rat.
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PMID:Interaction of the 4 S polycyclic aromatic hydrocarbon-binding protein with the cytochrome P-450c gene. 282 98

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) dioxin, produces a diverse set of biological responses which, in some cases, reflects the altered expression of specific genes. An intracellular receptor protein binds TCDD saturably and with high affinity and mediates several of TCDD's biological effects. In mouse hepatoma cells, TCDD induces aryl hydrocarbon hydroxylase activity by activating the transcription of the cytochrome P1-450 gene. Studies of receptor-defective variant cells indicate that the activation of cytochrome P1-450 gene transcription requires functional TCDD receptors. Analysis of the DNA that flanks the 5'-end of the mouse cytochrome P1-450 gene reveals at least three control regions: a promoter, an inhibitory element, and a dioxin-responsive element (DRE). Therefore, expression of the cytochrome P1-450 gene represents a balance between negative and positive control. The DRE contains two discrete, non-overlapping DNA domains that respond to TCDD. Each TCDD-responsive domain acts independently of the other, each requires TCDD receptors for function, and each has the properties of a transcriptional enhancer. For example, the function of the DREs is relatively independent of both their location and their orientation with respect to the promoter. Together, the DREs and the TCDD-receptor complex constitute a dioxin-responsive enhancer system. Exposure of cells to TCDD results in the protection of a specific DNA domain from exonuclease digestion. This protection requires TCDD receptors. The protected domain maps to a DRE. This observation implies that the TCDD-receptor complex interacts with the DRE to activate the transcription of the cytochrome P1-450 gene.
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PMID:2,3,7,8-Tetrachlorodibenzo-p-dioxin receptors regulate transcription of the cytochrome P1-450 gene. 282 85

In addition to being one of the most toxic chemicals known, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most potent inducer of rat liver microsomal cytochrome P-4501A1 (P-450c). Previous studies have demonstrated that a high affinity, low capacity cytosolic receptor (the Ah receptor) mediates the activity of TCDD to induce cytochrome P-4501A1, which catalyzes benzo[a]pyrene hydroxylation [aryl hydrocarbon hydroxylase (AHH]) and 7-ethoxyresorufin O-dealkylation (EROD). The results of the present study indicate that 6-methyl-1,3,8-trichlorodibenzofuran (MCDF) effectively competes with [3H]TCDD for binding to the Ah receptor in rat liver cytosol. The concentration of MCDF effecting 50% displacement of [3H]TCDD was 4.9 X 10(-8) M, which is approximately 50 times greater than the EC50 for unlabeled TCDD (approximately 1 X 10(-9) M). However, in contrast to TCDD, MCDF was only a weak inducer of AHH and EROD activity in rat hepatoma H-4-II cells in culture. When co-incubated, MCDF diminished in a concentration-dependent manner the ability of TCDD to induce AHH and EROD activity in vitro. Treatment of rats with 20-200 mumol/kg MCDF in vivo had little or no effect on liver microsomal AHH and EROD activity, whereas treatment of rats with 16 nmol/kg TCDD caused a 6- and a 70-fold induction of AHH and EROD activity, respectively. When co-administered, MCDF diminished by approximately 50% the ability of TCDD to induce AHH and EROD activity in vivo. The partial antagonism produced by 50 mumol/kg MCDF could be partially overcome by doubling the dosage of TCDD from 16 to 32 nmol/kg. Immunochemical analysis of rat liver microsomes revealed that treatment of rats with 20-200 mumol/kg MCDF caused little or no induction of cytochromes P-4501A1 and P-4501A2 (P-450d), whereas these isozymes were induced 33- and 5-fold, respectively, in rats treated with 16 nmol/kg TCDD. When co-administered, MCDF diminished by approximately 50% the ability of TCDD to induce cytochrome P-4501A1 in vivo, which established that MCDF was not simply acting as an inhibitor of AHH and EROD activity. MCDF also antagonized the ability of TCDD to induce cytochrome P-4501A2, which suggests that the induction of both cytochromes P-4501A1 and P-4501A2 is regulated by the Ah receptor. These results indicate that MCDF binds with high affinity to the Ah receptor in rat liver cytosol and competitively blocks the binding of TCDD.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:6-Methyl-1,3,8-trichlorodibenzofuran as a 2,3,7,8-tetrachlorodibenzo-p-dioxin antagonist: inhibition of the induction of rat cytochrome P-450 isozymes and related monooxygenase activities. 282 16

Certain human cell lines previously have been shown to exhibit substantial induction of aryl hydrocarbon hydroxylase (AHH, cytochrome P450IA1) when treated in culture with aromatic hydrocarbons such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or benz(a)anthracene. Yet the Ah receptor, which is known to mediate the AHH induction process in rodent cells and tissues, has not previously appeared to be present at a significant level in any human cell line. In the human A431 squamous cell carcinoma line we found that cytosolic Ah receptor was present in high concentration (approximately 200 fmol/mg cytosol protein at maximal saturation); this corresponds to approximately 10,000 Ah receptor sites per cell in the human A431 line compared with about 35,000 receptor sites per cell in the mouse Hepa-1 hepatoma cell line in which Ah receptor previously has been extensively characterized. Detection of Ah receptor in A431 cytosol required modification of assay techniques, especially reduction in the amount of charcoal used to adsorb nonspecifically bound radioligand. The specific binding peak from A431 cytosol sedimented approximately 9S on sucrose gradients, the same as the cytosolic receptor from the well-characterized mouse Hepa-1 hepatoma cell line. In addition to [3H]TCDD, specific binding to Ah receptor in A431 cytosol also was detected with [3H]3-methylcholanthrene and with [3H]benzo(a)pyrene as radioligands. A specific [3H]TCDD-Ah receptor complex was extracted from nuclei of A431 cells incubated in culture at 37 degrees C with [3H]TCDD. The nuclear form of Ah receptor sedimented approximately 5S, the same as the nuclear receptor from mouse Hepa-1 cells. AHH activity was induced in A431 cells treated in culture with TCDD or benz(a)anthracene. The maximum level of induced AHH activity that could be achieved in A431 cells was about 20% of the maximally induced level in the mouse Hepa-1 cell line. However, the dose-response curves for AHH induction by TCDD or benz(alpha)anthracene in A431 cells were shifted about one log unit to the right of the curves for Hepa-1 cells. The lower sensitivity of A431 cells to AHH inducers was in proportion to the lower affinity with which cytosolic Ah receptor in A431 cells bound [3H]TCDD. The saturation curve for binding of [3H]TCDD to cytosolic Ah receptor in A431 cells also was shifted about one log unit to the right of the curve for saturation of the cytosolic receptor from mouse Hepa-1 cells.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Characterization of the Ah receptor and aryl hydrocarbon hydroxylase induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin and benz(a)anthracene in the human A431 squamous cell carcinoma line. 283 45

We have identified in mouse hepatoma cells a third cis-acting dioxin-responsive element (DRE) within the 5' flanking region of the cytochrome P1-450 gene, which is transcriptionally activated by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The DRE can activate a heterologous promoter and functions in either orientation; therefore, it has the properties of a transcriptional enhancer. The DRE fails to activate transcription in receptor-defective cells; therefore, it requires TCDD-receptor complexes for its function. By using a gel retardation assay, we show that nuclear extracts contain a protein that binds to the DRE in TCDD-inducible, receptor-dependent, and DNA sequence-specific fashion. The protein-DNA interaction occurs within 10 min of exposure of the cell to TCDD and does not require ongoing protein synthesis. Our results imply that the TCDD-receptor complex interacts specifically with the DRE and demonstrate a relationship between protein-DNA interaction in vitro and function in vivo. Our findings also suggest that the affinity of the TCDD-receptor complex for the DRE may be relatively high in comparison to analogous protein-DNA interactions at other inducible enhancers.
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PMID:Inducible, receptor-dependent protein-DNA interactions at a dioxin-responsive transcriptional enhancer. 283 43

Based on the following 3 points: 1) tumor proliferation is energy-dependent, 2) mitochondrial energy-production system is dominant for cell growth, and 3) liver mitochondria (mt) possess their own DNA and RNA synthesizing some of their own proteins including respiratory enzymes such as cytochrome oxidases, a possible relationship between mutations of mt-DNA and clinical status of cell proliferation was examined in 10 HCC patients who underwent liver resection. Mt-DNA at the cancerous and the noncancerous portions of 1g resected liver specimens were separated from the nuclear DNA, and then digested with Hinf I endonuclease. DNA filters were made of the digested mt-DNA fragments on the agarose and polyacrylamide gel. The filters were hybridized with a nick-translated 32P-labeled DNA fragments. In two cases, abnormal mt-DNA were detected. In the first case, the tumor was the massive type and grew rapidly invading the bile duct. One restriction fragment of 3.0 Kb of the cancerous and non cancerous portion became larger by 60 bp. In the second case, regarded as metachronous multicentric HCC, the second largest band of the 3.4 Kb fragment of the cancerous portion showed a wider range but not of the noncancerous portion. The former change may indicate polymorphism but the latter indicates an occurrence of the mutation of mt-DNA. Further studies are required, including examinations on the rest of mitochondrial fragments.
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PMID:[Analysis of human mitochondrial DNA in hepatocellular carcinomas]. 283 32

In cultured human hepatoma cells phenolphthalein glucuronidation was increased 3-fold by 2 mM phenobarbitone (PB) in the culture medium but not by 25 microM benz(a)anthracene (BA), while 1-naphthol glucuronidation was not increased by either PB or BA. Ethoxyresorufin O-deethylation (EROD) was increased 15-fold by BA but not by PB, while the O-dealkylations of pentoxyresorufin (PROD) and benzyloxyresorufin (BROD) were increased by either PB or BA. The BROD activity increased by BA was sensitive to inhibition by alpha-naphthoflavone whereas that induced by PB was not. This suggests induction of different cytochrome P-450 isoenzymes. Control Hep G2 cells had similar glucuronide conjugation and cytochrome reductase activities to freshly isolated human adult hepatocytes, but had lower O-dealkylation and elevated microsomal epoxide hydrolase activities.
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PMID:Mixed function oxidase and UDP-glucuronyltransferase activities in the human Hep G2 hepatoma cell line. 284 53

Genetic toxicology assays that rely on S9 microsomal mixes are subject to artifacts related to the generation of mutagenic metabolites by acidic pHs, variation in individual isolations of microsomes and the failure of subcellular fractions to faithfully produce metabolites generated in intact cells. We have developed a gene mutation assay utilizing the human hepatoma cell line HepG2, which has been shown to metabolize a broad spectrum of promutagens. Optimal conditions for assaying the induction of 6-thioguanine-resistant mutants in this cell line include: 1) growth of colonies for three weeks on lethally irradiated feeder layers of 10(6) thioguanine-resistant HepG2 cells (average plating efficiency = 60-80%); 2) a thioguanine concentration in selection dishes of 10(-4) M with a maximum seeding density of 2.5 x 10(5) cells per 100 mm culture dish; and 3) a minimum expression time of 6 days. In addition to ultraviolet light C (254 nm), a cytochrome P450 (cyclophosphamide)-dependent and a cytochrome P448 (aflatoxin B1)-dependent promutagen were shown to induce cytotoxicity and mutations in this test system. The present studies, therefore, suggest that the HepG2 cell line may be useful for a variety of assays in genetic toxicology.
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PMID:Use of an established human hepatoma cell line with endogenous bioactivation for gene mutation studies. 285 51


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