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)

To determine the basis for unexpected differences in CYP1A1 inducing potencies and efficacies for the diet-derived indole derivative, indolo[3,2-b]carbazole (ICZ) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), we conducted a systematic analysis of events involved in the induced expression of CYP1A1 in murine hepatoma-derived cell lines (Hepa-1). In contrast to the effects of TCDD, induction kinetics and CYP1A1 mRNA half-life were dependent on ICZ concentration, and the response from low doses of inducer was transient due to rapid clearance of ICZ. TCDD and ICZ produced the same maximum response (i.e. equal efficacies) from a TCDD-responsive CAT reporter construct in Hepa-1 cells. When measured by the immediate responses associated with CYP1A1 expression, including cellular uptake of inducer, receptor transformation and binding to DRE (gel mobility shift assay), initiation of transcription (nuclear run-on assay), and short-term accumulation of mRNA (Northern blot assay), ICZ also exhibited an efficacy equal to that of TCDD and a potency that corresponds to its receptor affinity. ICZ is a potent and selective noncompetitive inhibitor of ethoxyresorufin O-deethylase activity (Ki = 1.5 nM). Taken together these results indicate that ICZ is a bifunctional modulator of CYP1A1 expression with intrinsic efficacy equal to that of TCDD.
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PMID:Regulation of CYP1A1 by indolo[3,2-b]carbazole in murine hepatoma cells. 767 47

Treatment of murine hepatoma 1c1c7 cultures with dibenz[a,c]anthracene (DB[a,c]A)-induced P450 Cyp1a-1, as indicated by analyses of CYP1A1 mRNA and 7-ethoxyresorufin O-deethylase (EROD) activity. Pretreatment of cultures with 12-O-tetradecanoylphorbol-13-acetate (TPA) for as short as 1 h reduced protein kinase C (PKC) activity and resulted in a temporary suppression of EROD induction. The dose-response curves defining the TPA-dependent suppression of EROD induction and PKC down-regulation were very similar, as were the initial kinetics of PKC loss and the times of TPA pretreatment required for suppression of EROD induction. The effects of TPA could not be mimicked by 4 alpha-TPA, an analog incapable of activating and down-regulating PKC. Pretreatment of cultures with the protein kinase inhibitors staurosporine, calphostin C, or H7 resulted in dose-dependent suppressions of EROD induction. However, the suppressive and cytotoxic effects of these agents could be separated from one another in the case of only H7. HA1004, an analog of H7 that inhibits the same spectrum of protein kinases as H7 except for PKC, did not inhibit DB[a,c]A induction of EROD. Pretreatment of cultures with H7, but not HA1004, suppressed the accumulation of CYP1A1 mRNA that normally occurred following treatment with DB[a,c]A. Collectively, these studies suggest that PKC plays a role in the processes involved in the induction of Cyp1a-1.
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PMID:Suppression of cytochrome P450 Cyp1a-1 induction in murine hepatoma 1c1c7 cells by 12-O-tetradecanoylphorbol-13-acetate and inhibitors of protein kinase C. 768 64

Cultured mouse hepatoma cell line Hepa-1c1c7 cells were treated with methoxsalen to assess the role of methoxsalen in the process of Cyp1a-1 induction. Treatment of Hepa-1c1c7 cultures with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced Cyp1a-1, as indicated by analysis of 7-ethoxyresorufin O-deethylation (EROD) activity and P4501A1 protein. When methoxsalen and TCDD were both added to cultures, TCDD-inducible EROD activity was greatly suppressed by methoxsalen in a dose-dependent manner. We find that treatment of Hepa-1c1c7 cells with methoxsalen inhibited CYP1A1 mRNA induction by TCDD as well as the concomitant increase P4501A1 protein. Formation of DNA-protein complexes between the dioxin receptor and its DRE target was inhibited by methoxsalen, as determined by gel mobility shift assays using oligonucleotides corresponding to DRE 3 of the Cyp1a-1 gene. These results suggest that the inhibitory action of methoxsalen on TCDD induction of the Cyp1a-1 gene expression in Hepa-1c1c7 cells might be antagonism of the DNA binding potential of nuclear dioxin receptor.
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PMID:Suppression of cytochrome P450 (Cyp1a-1) induction in mouse hepatoma Hepa-1C1C7 cells by methoxsalen. 770 11

We have cloned and sequenced the mouse NMO1 cDNA, which encodes the NAD(P)H:menadione oxidoreductase [also called NAD(P)H:(quinone acceptor) oxidoreductase; quinone reductase; azo dye reductase; DT diaphorase; EC 1.6.99.2]. The cDNA is 1528 bp in length excluding the poly(A+) tail, and has 5' and 3' nontranslated regions of 108 bp and 595 bp, respectively. The deduced protein contains 274 amino acids, including the first methionine (M(r) = 30,959). The mouse NMO1 protein is: 94% similar to the rat NMO1 and 86.5% to the human NMO1 proteins; 49.3% identical to the human NQO2 protein; and < 20% similar to several dozen other proteins in the quinone oxidoreductase superfamily. Southern hybridization analysis of mouse DNA reveals that the Nmo1 gene is likely to span less than a total of 20 kb. The Nmo1 gene is highly inducible by 2,3,7,8,-tetrachlorodibenzo-p-dioxin (dioxin; TCDD) in mouse liver and mouse cell cultures. TCDD inducibility of NMO1 is detectable at 12 and 18 days of gestation, but markedly elevated at 1-3 weeks post partum as compared with the 6- and 12-week-old mouse. NMO1 mRNA levels are strikingly elevated in the untreated mouse hepatoma Hepa-1c1c7 mutant line c37 lacking CYP1A1 (aryl hydrocarbon hydroxylase) activity, and in the untreated 14CoS/14CoS mouse cell line having an 'oxidative stress response' caused by homozygous deletion of about 3800 kb on chromosome 7. Previous work and the data in this report show that the murine Nmo1 gene is regulated by three distinct mechanisms: CYP1A1 metabolism-dependent repression, Ah receptor-mediated induction by TCDD, and activation by the chromosome 7-mediated oxidative stress response.
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PMID:Mouse dioxin-inducible NAD(P)H: menadione oxidoreductase: NMO1 cDNA sequence and genetic differences in mRNA levels. 770 40

The mouse hepatoma cell line Hepa-1 is inducible by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for both CYP1A1 (aryl hydrocarbon hydroxylase, AHH) and class 3 aldehyde dehydrogenase (ALDH3) enzymes. To test the hypothesis of a common regulatory mechanism, several AHH deficient mutants of Hepa-1 were studied for their ALDH3 activities and specific mRNA levels before and after TCDD treatment. The recessive (with respect to the wild-type Hepa-1) mutants have defects in Cypla-1 structural gene (mutant c1) or in the Ah (aryl hydrocarbon) receptor (mutants c2 and c6 with decreased levels of Ah receptor; mutant c4 defective in the DNA binding of the Ah receptor). The results with these mutants suggested that Ah receptor nuclear translocator protein, ARNT, is needed for ALDH3 expression. Two dominant mutants, one of which is characterized by preventing the binding of the Ah receptor complex to DNA, were also studied. Surprisingly, these mutants possessed elevated levels of ALDH3 mRNA and enzyme activities which were also inducible by TCDD. The binding of Ah receptor-ligand complex to DNA was thus not needed for the expression of ALDH3. A dominant repressor for Cypla-1 gene transcription did not prevent the derepression or induction of ALDH3. The results thus suggest that Aldh-3 gene is regulated by a mechanism independent of the Ah receptor.
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PMID:Comparison of expression of aldehyde dehydrogenase 3 and CYP1A1 in dominant and recessive aryl hydrocarbon hydroxylase-deficient mutant mouse hepatoma cells. 782 19

In previous studies, we identified a 21 bp palindrome (-794 to -774) located within the negative regulatory element of the human CYP1A1 gene consisting of an 8 bp inverted repeat and 5 bp spacer. This element specifically binds protein(s) present in HepG2 nuclear extract preparations and is capable of down-regulating heterologous promoters and enhancers in transient expression assays. Conserved guanine/cytosine-rich regions which flank the palindrome also were implicated in this activity. In the present study, we examined similar regions from the rat (-881 to -746) and mouse (-822 to -683) CYP1A1 genes for their ability to bind nuclear protein and down-regulate heterologous promoters and enhancers. These rodent DNA fragments contain the conserved guanine/cytosine-rich sequences, as well as half-sites similar to those found in the human CYP1A1 palindrome. However, each half-site is separated by approximately 40 bp. DNase I footprint analyses revealed the presence of rat and mouse nuclear proteins which gave a similar protection pattern as that observed with nuclear proteins from the human cell line, HepG2. Electrophoretic mobility shift assays with the human negative regulatory element demonstrated the formation of specific DNA-protein complexes with rat and mouse nuclear protein(s). Interestingly, two specific DNA-protein complexes were observed with rodent extracts as compared to the single specific complex seen with human extract. Specific binding was not observed with either the orthologous rat or mouse fragments using human or rodent extracts. In transient expression assays, the rat and mouse fragments were unable to down-regulate enhancer/promoter activity. This absence of negative regulatory activity occurred whether transfections were performed in human, rat or mouse hepatoma cell lines. The human negative regulatory element, which was previously shown to down-regulate heterologous enhancers/promoters approximately 70% in human cells, did not exhibit this activity in rodent cell lines. UV cross-linking and southwestern blot analyses indicated a high degree of similarity between human and rodent NRE binding proteins, although some differences also were apparent. The possible implications of these findings with regards to species differences in the regulation of CYP1A1 expression are discussed.
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PMID:In vitro binding and functional studies comparing the human CYP1A1 negative regulatory element with the orthologous sequences from rodent genes. 785 71

A genomic clone encoding the hamster CYP1A1 gene was isolated from a hamster EMBL-3 genomic library and characterized. The CYP1A1 gene contained seven exons including the noncoding first exon as determined for CYP1A1 of other species. DNA sequence analysis up to -2307 bp of the CYP1A1 gene revealed the occurrence of five consensus xenobiotic responsive elements (XREs) and one basal transcription element (BTE) in addition to the canonical TATA box. For functional analysis, transfection experiments were performed in human hepatoma HepG2 cells with reporter gene constructs consisting of fragments with various lengths of the 5'-flanking region of the CYP1A1 gene and bacterial chloramphenicol acetyltransferase (CAT) gene. External deletion of the upstream region from the reporter gene resulted in a stepwise decrease of the CAT activity, suggesting that XREs were responsible for inducible expression of CYP1A1 gene by 3-methylcholanthrene (MC). A negative regulatory element (NRE) was also identified in the 5'-flanking region at -833 to -642. Removal of the NRE from the CYP1A1-CAT fusion gene resulted in about 3-fold increase of MC-inducible CAT activity. Using gel retardation assays with HepG2 nuclear extract, we demonstrated the presence of a specific protein which bound to the NRE fragment. Further competition analysis and methylation interference assays revealed that the nuclear protein bound to a 22-base fragment (from -688 to -709) of the NRE region, whose sequences were conserved among hamster, human, and rat CYP1A1 genes.
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PMID:Characterization of hamster CYP1A1 gene: inducible expression and negative regulation. 788 54

The exposure of two hepatoma cell lines, Hep G2 and Hepa-1, to moderate hydrodynamic shear, in microcarrier-attached suspension cultures, resulted in the transient induction of cytochrome P450IA1 (CYP1A1). Both cell lines have been characterized with respect to their Ah receptor (AhR) concentrations and induce CYP1A1 in response to exposure to xenobiotics such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Using an AhR antagonist, alpha-naphthoflavone (alpha-NF) and a protein kinase C (PKC) inhibitor, staurosporine (ST), in the Hep G2 cell line, the induced CYP1A1 activity was modulated in the same manner as when the cells were coexposed to TCDD and either alpha-NF or ST. Exposure of the Hep G2 cell line to TCDD and shear resulted in both enhancement of the induced CYP1A1 activity in addition to a competitive response. Finally, using the wild type and AhR defective Hepa-1 cell lines, it was demonstrated that a functional AhR was required for shear-induced CYP1A1 expression. The data obtained in the three cell lines indicate a role for the AhR in the induction of CYP1A1 by shear in agitated microcarrier cultures.
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PMID:Possible involvement of the Ah receptor in the induction of cytochrome P-450IA1 under conditions of hydrodynamic shear in microcarrier-attached hepatoma cell lines. 788 22

We have recently demonstrated that release of normal human epithelial cells from cell-substratum and/or cell-cell adhesion generates cellular signals that induce the expression of CYP1A1 in the absence of xenobiotic polycyclic aromatic hydrocarbons (Sadek, C. M., and Allen-Hoffmann, B. L. (1994) J. Biol. Chem. 169, 16067-16074). To directly test the involvement of the Ah receptor signal transduction pathway in CYP1A1 induction following suspension of epithelial cells, we analyzed wild-type Hepa 1c1c7 cells, a subclone of the Hepa-1c1 mouse hepatoma line, and two mutant Hepa 1c1c7 lines, Class I and Class II. Suspension of wild-type Hepa 1c1c7 cells for 4 h led to an induction of steady state levels of CYP1A1 mRNA, similar to that obtained following treatment of adherent cells with 10(-9) M 2,3,7,8-tetrachlorodibenzo-p-dioxin. Mutants of the Hepa 1c1c7 cells defective in different aspects of the Ah receptor signal transduction pathway exhibited negligible (Class I) or no (Class II) suspension-mediated induction of CYP1A1 mRNA. Gel mobility shift analysis of nuclear extracts from suspended or 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated wild-type cells showed that both treatments produced identical shifts in the mobility of an XRE-containing probe. Antibody supershift experiments confirmed that the Ah receptor was a component of the DNA-protein complex from suspended wild-type Hepa 1c1c7 cells. These data directly demonstrate that suspension of wild-type Hepa 1c1c7 cells leads to nuclear localization and activation of the Ah receptor to a DNA-binding form.
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PMID:Suspension-mediated induction of Hepa 1c1c7 Cyp1a-1 expression is dependent on the Ah receptor signal transduction pathway. 798 17

The Hepa-1 enzyme induction assay (assay of the induction of CYP1A1 catalytic activities in the Hepa-1 mouse hepatoma cell line by various compounds or mixtures) was evaluated as an in vitro indicator of the CYP1A1-inducing potencies of laboratory rodent diets in vivo. C57BL/6J mice were fed for three weeks four selected commercially available diets (one semisynthetic and three standard natural ingredient diets) exhibiting different enzyme-inducing effects in the Hepa-1 assay. beta-Naphthoflavone mixed in a semisynthetic diet (33 and 330 mg/kg of diet) was used as a model inducer. CYP1A1-dependent enzyme activities (aryl hydrocarbon hydroxylase and 7-ethoxyresorufin O-deethylase) were measured in the small intestinal mucosa and liver. There was good agreement between the induction of CYP1A1 in vitro and in vivo: the rank order of the enzyme activities elicited by the diets was the same in the mice as in the Hepa-1 cells. The standard diets were less effective inducers than beta-naphthoflavone in the Hepa-1 cells and in the mice, especially in the small intestinal mucosa. The Hepa-1 enzyme induction assay thus seems to be a mechanistically sound, reliable and sensitive in vitro indicator of the CYP1A1-inducing potencies of laboratory rodent diets in vivo.
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PMID:Hepa-1 enzyme induction assay as an in vitro indicator of the CYP1A1-inducing potencies of laboratory rodent diets in vivo. 799 Jun 55

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