Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

We have isolated a new benzo(a)pyrene-resistant clone, c35, of the mouse hepatoma line, Hepa-1. Cytochrome P1-450 mRNA and P1-450-dependent aryl hydrocarbon hydroxylase (AHH) activity are no longer inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin in c35. The phenotype of c35 is unstable in long-term culture. A subclone, c35-1, having partially restored AHH inducibility, was studied in detail. The concentration of dioxin required to give half-maximal induction of AHH activity was 16-fold greater in c35-1 than in Hepa-1. Scatchard analysis showed that c35-1 contains reduced levels of the Ah (dioxin) receptor, which mediates induction of P1-450, but that the affinity of the receptor for dioxin is unaltered. In vivo assays confirmed that c35-1 possesses reduced levels of receptor but showed that it is even more severely affected in nuclear translocation of the receptor. Somatic cell hybridization experiments demonstrated that c35 is recessive and belongs to a new, third complementation group of mutants defective in Ah receptor activity. We propose that c35 is mutated either in the ligand-binding Ah receptor polypeptide or in another polypeptide required for receptor function and that in c35-1 partial reversion has occurred to generate a polypeptide which is still impaired in its role in promoting nuclear translocation and/or DNA binding.
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PMID:A third genetic locus affecting the Ah (dioxin) receptor. 283 75

Inhibition of protein synthesis superinduces transcription of the cytochrome P1-450 gene in Hepa 1c1c7 mouse hepatoma cells. The superinduced transcription rate is 10-15-fold higher than the maximal rate of transcription induced by the known inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) alone. Superinduction is maximal within 30-40 min and remains maximal for at least 90 min. Cytochrome P1-450 mRNA is the same length in TCDD-induced and superinduced cells. Superinduction does not occur in variant cells in which TCDD-receptor complexes bind weakly to nuclei and which do not transcribe the cytochrome P1-450 gene in response to TCDD. Inhibition of protein synthesis does not alter several properties of TCDD-receptor complexes. The results imply that a second control mechanism modulates the action of the TCDD-receptor complex in regulating cytochrome P1-450 gene transcription.
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PMID:Superinduction of cytochrome P1-450 gene transcription by inhibition of protein synthesis in wild type and variant mouse hepatoma cells. 298 7

We analyzed the function and sequence of a dioxin-responsive genomic element flanking the 5' end of the cytochrome P1-450 gene in high-activity variant mouse hepatoma cells. The element can regulate the mouse mammary tumor virus promoter. The element retains responsiveness to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) when the distance, the 5' or 3' position, and/or the 5' or 3' orientation with respect to the promoter are varied. The function of the element requires TCDD-receptor complexes. The element remains responsive to TCDD when transfected into cells from either a heterologous mouse tissue or a heterologous species (human). The DNA element and TCDD receptors together constitute a dioxin-responsive enhancer system.
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PMID:Control of cytochrome P1-450 gene expression: analysis of a dioxin-responsive enhancer system. 301 Mar 18

In laboratory animals and in mouse hepatoma cells in culture the Ah receptor previously has been shown to mediate induction of aryl hydrocarbon hydroxylase (cytochrome P1-450) by 3-methylcholanthrene, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and related compounds. We examined human lung cytosols to determine whether the Ah receptor was present in human tissues. Cytosol was prepared from grossly normal lung tissue obtained at pulmonary lobectomy for presumed lung cancer from 53 consecutive adult patients including 32 males (42-77 years old) and 21 females (18-81 years old). Ah receptor in the cytosols was identified and quantitated by specific binding of [3H]TCDD after separation by ultracentrifugation on sucrose gradients. Specific binding of [3H]TCDD to a component which met the criteria for Ah receptor was detected in 10 of the 53 specimens. As previously established in tissues from laboratory animals, the specific [3H]TCDD-binding component sedimented approximately 9S. Binding of [3H]TCDD to the 9S component was competitively inhibited by incubation in the presence of 2,3,7,8-tetrachlorodibenzofuran, dibenz(a,h)anthracene, and nonradioactive TCDD, all known to be potent agonists for Ah-receptor-mediated induction of aryl hydrocarbon hydroxylase. Specific Ah receptor also was detected in some specimens by direct binding of [3H]-3-methylcholanthrene. The human population studied exhibited striking heterogeneity in Ah receptor concentrations. Only 10 of the 53 individuals studied had detectable Ah receptor. In specimens with detectable specific binding, the mean concentration of binding sites was 6.9 +/- 1.2 (SE) fmol/mg cytosolic protein. These concentrations are approximately 10-30% of the concentrations of Ah receptor found in lung cytosols from laboratory animals. Our experiments indicate that the Ah receptor can be detected in lung cytosol from some humans and suggest that the regulatory mechanism mediating human cytochrome P1-450 induction may be similar to that in the murine model. Aryl hydrocarbon hydroxylase, the major enzyme induced under control of the Ah receptor, plays an important role in the metabolism of several carcinogens including polycyclic aromatic hydrocarbons such as benzo(a)pyrene. It is possible that differences in the Ah receptor content within the human population may be genetically based and that variation at the Ah receptor level may be an important determinant of individual susceptibility to certain chemically induced cancers.
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PMID:Ah receptor mediating induction of aryl hydrocarbon hydroxylase: detection in human lung by binding of 2,3,7,8-[3H]tetrachlorodibenzo-p-dioxin. 301 Dec 54

A mouse hepatoma cell line, Hepa-1, is highly sensitive to the toxic effects of Aflatoxin B1 (AFB1). Half maximal survival (LD50) of cells occurs at 0.068 ug AFB1/ml. Benzo(a)anthracene, which induces aryl hydrocarbon hydroxylase and cytochrome P1-450 in Hepa-1, causes a slight increase in the toxicity of AFB1 (LD50 = 0.034 ug/ml). An aryl hydrocarbon hydroxylase- and cytochrome P1-450-deficient mutant of Hepa-1 is, however, over 100 times more resistant to AFB1 than Hepa-1. Almost no decline in survival is observed at 5 ug AFB1/ml. Cytochrome P1-450 thus effects strongly on the cytotoxicity of AFB1 in these cells. The basal activity in Hepa-1 is enough to elicit an almost full toxic effect. AFB1, although a substrate for cytochrome P1-450, does not act as an inducer of aryl hydrocarbon hydroxylase.
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PMID:Mechanism of cytotoxicity of aflatoxin B1: role of cytochrome P1-450. 310 20

The lack of aryl hydrocarbon (benzo[a]pyrene) hydroxylase (AHH) (EC 1.14.14.1) induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in a clone of rat hepatoma (HTC cl-1) cells is not caused by the lack of nuclear Ah receptor or by a deficiency in the activity of NADPH-cytochrome c (P-450) reductase. Treatment of HTC cl-1 cell line with TCDD for 18 h in culture resulted in a reproducible 500-600% increase in reductase activity without concomitant expression in AHH activity. These data suggests that TCDD induces cytochrome c reductase activity and that the lack of inducible AHH activity in rat hepatoma cells could reflect a defect in the structural gene (s) encoding for cytochrome P1-450, or an Ah receptor with a faulty DNA binding domain.
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PMID:Evidence that 2,3,7,8-tetrachlorodibenzo-p-dioxin induces NADPH cytochrome c (P-450) reductase in rat hepatoma cells in culture. 339 76

In mouse hepatoma cells, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) stimulates cytochrome P1-450 gene transcription via the formation of TCDD-receptor complexes and the accumulation of the complexes in the nucleus. Here, we show that the DNA that flanks the 5'-end of the cytochrome P1-450 gene contains at least two discrete TCDD-responsive domains. Each domain has properties analogous to those of transcriptional enhancers. Each domain requires TCDD-receptor complexes for its function. There is no significant nucleotide sequence homology between the two TCDD-responsive domains.
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PMID:Control of gene expression by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Multiple dioxin-responsive domains 5'-ward of the cytochrome P1-450 gene. 370 Apr 11

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) may produce its effects by altering gene expression in susceptible cells. In mouse hepatoma cells, TCDD induces the transcription of the cytochrome P1-450 gene, whose product, aryl hydrocarbon hydroxylase, contributes both to the detoxification and to the metabolic activation of carcinogenic polycyclic aromatic hydrocarbons. A DNA fragment containing sequences flanking the 5' end of the cytochrome P1-450 gene was isolated and analyzed. This DNA fragment contains a cis-acting control element with at least three functional domains: a putative promoter, an inhibitory domain upstream from the promoter that blocks its function, and a TCDD-responsive domain still farther (1265 to 1535 base pairs) upstream of the promoter. These findings, together with results from earlier studies, imply that transcription of the cytochrome P1-450 gene is under both positive and negative control by at least two trans-acting regulatory factors.
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PMID:Control of cytochrome P1-450 gene expression by dioxin. 385 21

Aryl hydroxylase activity has been demonstrated to depend on the pattern of tumor cell structural organization. The activity of microsomal monoxygenases in the ascitic forms of sarcoma MC-11, hepatoma 22a and Ehrlich's tumor was much lower than in the corresponding solid tumors. Aryl hydroxylase was activated after the animals received 3-MC, but the magnitude of the activity induced did not correlate with the basic activity in the different tumors. In in vitro experiments, 7,8-benzoflavone inhibited the enzyme in all the tumors, whereas metyrapone did not affect BP-hydroxylation. It is assumed that all the tumors investigated contain hemoprotein that is similar to cytochrome P1-450.
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PMID:[Differing microsomal monoxygenase activity in the cells of ascitic and solid forms of transplantable tumors]. 402 74

Hepa-1c1c7, a mouse hepatoma cell line, was used to study the effect of cytochrome P1-450 inducers on the binding of 125I-epidermal growth factor (EGF), 125I-insulin, or [20-3H]phorbol 12,13-dibutyrate each to its specific cell-surface receptor. After a 24-h exposure to the cultured cells, several polycyclic hydrocarbon P1-450 inducers decrease the binding of EGF to EGF receptors much more than phenobarbital does. There appears to be a selectivity in the inhibitory effects: whereas EGF binding to EGF receptors is blocked, the binding of either phorbol ester or insulin each to its specific cell-surface receptors remains unaffected. The rank order of binding affinities of these chemicals to the cytosolic Ah receptor (2,3,7,8-tetrachlorodibenzo-p-dioxin much greater than benzo[a]pyrene greater than benzo[a]anthracene greater than 6-aminochrysene much greater than phenobarbital) is not correlated with their effects on EGF binding capacity. The effect of polycyclic hydrocarbons on EGF binding takes 24 h at 37 degrees C to be maximal, whereas phorbol 12-myristate 13-acetate, a potent tumor-promoting compound, inhibits EGF binding in less than 30 min. Removal of benzo[a]anthracene from the growth medium after 24 h results in a gradual recovery in EGF binding, indicating that the effect is reversible. Benzo[a]pyrene and benzo[a]anthracene are relatively ineffective at decreasing EGF binding to the EGF receptors in Hepa-1 mutant clones c2 and c4, which lack a normally functioning Ah receptor and inducible aryl hydrocarbon hydroxylase activity (P1-450). The very toxic metabolite (+)-7 beta,8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene, when added directly to the growth medium of c4 cells, however, is effective at decreasing EGF binding. These data suggest that electrophilic metabolites of polycyclic aromatic compounds, formed by P1-450 induced during the exposure of Hepa-1 cells to these chemicals, are important in decreasing EGF binding to the EGF cell-surface receptor. Occupancy of the Ah receptor per se does not affect EGF binding.
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PMID:Effects of cytochrome P1-450 inducers on the cell-surface receptors for epidermal growth factor, phorbol 12,13-dibutyrate, or insulin of cultured mouse hepatoma cells. 630 1


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