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)

Cytochrome P-450 (CYP) 1B1 expression in mouse hepatoma (Hepa-1) wild-type (WT) cells was compared with responses in Hepa-1 variants LA1 and LA2, which, respectively, exhibit low aryl hydrocarbon receptor (AhR) level and defective AhR nuclear translocator (ARNT) protein. 10T1/2 mouse embryo fibroblasts express predominantly CYP1B1 and at a 100 times higher level than in Hepa-1 cells, whereas they express about 300-fold lower CYP1A1 than Hepa-1 cells. The expression of CYP1B1 in WT and LA1 variant, although at a much lower level, follows that of CYP1A1, reflecting their common regulation through the AhR. The LA2 (ARNT-defective) cells showed a major difference between CYP1B1 and CYP1A1 expression. Although CYP1A1 mRNA levels in LA2 were extremely low and unresponsive to 2,3,7, 8-tetrachlorodibenzo-p-dioxin (TCDD), basal CYP1B1 mRNA and protein were expressed at levels similar to those seen in TCDD-induced WT. The elevated basal CYP1B1 mRNA in LA2 cells decreased by 50% after transient transfection of ARNT cDNA, in parallel with substantial restoration of CYP1A1 induction. This implicates ARNT as a suppressor of CYP1B1 basal expression in Hepa cells. In transient CYP1B1-luciferase constructs in LA2 cells, ARNT shows stimulatory effects in the enhancer region but an inhibitory effect on the proximal promoter. Two CYP1B1 enhancer elements [xenobiotic-responsive element (XRE) 1/2 and XRE4] formed TCDD-unresponsive complexes of similar mobility to TCDD-stimulated AhR-ARNT complex with XRE5. However, because these two complexes were formed to the same extent in LA2 as in WT cells, they cannot be due to ARNT or contribute to ARNT-regulated suppression.
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PMID:Regulation of cytochrome P-450 (CYP) 1B1 in mouse Hepa-1 variant cell lines: A possible role for aryl hydrocarbon receptor nuclear translocator (ARNT) as a suppressor of CYP1B1 gene expression. 1005 45

The effect of several structurally different benzimidazole compounds on CYP1A1 expression at the transcriptional, mRNA and protein levels was investigated in the rat hepatoma H4IIE cell line. Omeprazole, thiabendazole, carbendazim, 2-mercaptobenzimidazole and 2-mercapto-5-methoxybenzimidazole caused a dose-dependent increase in CYP1A1 protein levels that reached maximum effect at 250 microm, as measured by Western blot. In addition, hydroxyomeprazole, 2-aminobenzimidazole and 2-mercapto-5-nitro-benzimidazole caused a notable increase in CYP1A1 protein expression, whereas 5-O-desmethylomeprazole, 2-hydroxybenzimidazole, 2-benzimidazole propionic acid and 5-benzimidazole carboxylic acid were ineffective. Thus, benzimidazole substituted with a thiol or an amino group in the 2-position were active inducers. Northern blot analysis confirmed an extensive increase of CYP1A1 mRNA induced by omeprazole and 2-mercapto-5-methoxybenzimidazole which was 32% and 49% of maximal induction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) respectively, whereas thiabendazole and carbendazim showed approximately 15% increase as compared to TCDD. Transient transfection of H4IIE cells, with a XRE-pGL3 reporter gene construct revealed a 2.3-4.3-fold induction by carbendazim, thiabendazole, and 2-mercapto-5-methoxybenzimidazole as compared to a 3.3- and 23-fold induction by omeprazole and TCDD, respectively. Thus, these data indicate that the benzimidazoles utilize the aryl hydrocarbon receptor-arnt-XRE-mediated signal-transduction pathway for induction of the CYP1A1 gene.
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PMID:Structural and mechanistic aspects of transcriptional induction of cytochrome P450 1A1 by benzimidazole derivatives in rat hepatoma H4IIE cells. 1010 34

: Transcriptional up-regulation of mammalian CYP1A1 genes by dioxin is known to require binding of dioxin to the Ah receptor (AHR), subsequent interaction of this ligand-receptor complex with the AHR nuclear translocator (ARNT), and binding of this heterodimer to aromatic hydrocarbon response elements (AHREs) located in the 5' flanking sequences. From the rainbow trout (Oncorhyncus mykiss), we have isolated and sequenced the CYP1A3 gene-spanning 4.0 kb and containing seven exons and six introns-and 1897 bp of the 5' flanking region. The transcription start site was determined by primer extension analysis. Five putative AHREs were found between -451 and -1820, with an overlap of AHRE3 and AHRE4 sharing 1 bp. The 5' flanking region of the trout CYP1A3 gene was fused to the firefly luciferase (luc) reporter gene and transiently transfected into mouse hepatoma Hepa-1c1c7 wild-type (wt) cell cultures and three benzo[a]pyrene-resistant mutant lines: c2, containing less than 10% levels of functional AHR; c4, defective in ARNT; and c37, deficient in CYP1A1 metabolism. We compared the trout CYP1A3 promoter-luc constructs with mouse and human CYP1A1 promoter-luc constructs. All of our trout CYP1A3 promoter data are consistent with dioxin-inducible luciferase activity being controlled by two or more AHREs via cooperativity with a GC-rich region (-1852)-as has previously been demonstrated for AHREs in mammalian CYP1A1 promoters. The dependence of trout CYP1A3 promoter activity on the AHR and on the ARNT, and the enhancement of CYP1A3 promoter activity in the absence of CYP1A1 metabolic capacity, are all similar to that with mammalian CYP1A promoters. These findings indicate that the DNA motifs in trout, and the mouse liver proteins that bind to these motifs, are evolutionarily conserved elements.
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PMID:Trout CYP1A3 Gene: Recognition of Fish DNA Motifs by Mouse Regulatory Proteins. 1037 24

Some flavonoids are ligands of the aryl hydrocarbon receptor (AHR) and cause cell cycle arrest. The dependency of the cytostatic effects of five flavonoids (flavone, alpha-naphthoflavone, apigenin, 3'-methoxy-4'-nitroflavone and 2'-amino-3'-methoxyflavone) on a functional AHR was examined in AHR-containing rat hepatoma 5L cells and an AHR-deficient cell line (BP8) derived from the 5L line. The potent AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was cytostatic to the 5L line due to the induction of a G(1) arrest and dramatically elevated steady-state levels of CYP1A1 mRNA. TCDD affected neither the proliferation nor CYP1A1 mRNA contents of BP8 cells. With the exception of apigenin, the flavonoids under study induced G(1) arrest in both 5L and BP8 cells when used at concentrations at which they functioned as AHR agonists, but not antagonists. Apigenin-treated 5L and BP8 cultures primarily arrested in G(2)/M. The AHR-containing murine hepatoma cell line 1c1c7 arrested following exposure to AHR agonist concentrations of flavone and alpha-naphthoflavone, but not TCDD. Unlike the G(1) arrest observed in 5L cultures, the latter two flavonoids caused principally G(2)/M arrest in 1c1c7 cells. These studies demonstrate that the cytostatic activities of flavonoids do not require the AHR and the site of checkpoint arrest with a specific flavonoid can vary with cell type.
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PMID:Suppression of cell cycle progression by flavonoids: dependence on the aryl hydrocarbon receptor. 1042 7

We investigated the effect of resveratrol, a constituent of the human diet that has been shown to inhibit aryl hydrocarbon-induced carcinogenesis in animals, on the carcinogen activation pathway regulated by the aryl hydrocarbon receptor. Resveratrol inhibited the metabolism of the environmental aryl hydrocarbon benzo[a]pyrene (B[a]P) catalyzed by microsomes isolated from B[a]P-treated human hepatoma HepG2 cells. Resveratrol competitively inhibited, in a concentration-dependent manner, the activity of the carcinogen activating enzymes cytochrome P-450 (CYP)1A1/CYP1A2 in microsomes and intact HepG2 cells. Resveratrol inhibited the B[a]P-induced expression of the CYP1A1 gene, as measured at the mRNA and transcriptional levels. Resveratrol abolished the binding of B[a]P-activated nuclear aryl hydrocarbon receptor to the xenobiotic-responsive element of the CYP1A1 promoter but did not itself bind to the receptor. Resveratrol was also effective in inhibiting CYP1A1 transcription induced by the aryl hydrocarbon dimethylbenz[a]anthracene in human mammary carcinoma MCF-7 cells. These data demonstrate that resveratrol inhibits aryl hydrocarbon-induced CYP1A activity in vitro by directly inhibiting CYP1A1/1A2 enzyme activity and by inhibiting the signal transduction pathway that up-regulates the expression of carcinogen activating enzymes. These activities may be an important part of the chemopreventive activity of resveratrol in vivo.
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PMID:Inhibition of aryl hydrocarbon-induced cytochrome P-450 1A1 enzyme activity and CYP1A1 expression by resveratrol. 1049 59

The aryl hydrocarbon nuclear translocator (ARNT) protein functions as a transcription factor after dimerization with other basic helix-loop-helix proteins. Thus, dimerization of ARNT within one pathway may limit the availability of this protein to others. To investigate this issue, aryl hydrocarbon receptor (AHR)-mediated signaling was investigated in mouse (Hepa-1), rat (H4IIE), and human (HepG2) hepatoma cell lines undergoing physiologically induced hypoxia (<1% O(2)). Basal levels of ARNT protein were not affected by hypoxia in any cell line, and ARNT remained exclusively nuclear. Furthermore, quantitative Western blotting revealed that the concentration of ARNT sequestered during hypoxia represented a small fraction of the total ARNT protein pool (12 and 15% in Hepa-1 and H4 cells, respectively). When the AHR-mediated signaling pathway was activated during hypoxia by 2,3,7,8-tetrachlorodibenzo-p-dioxin, the induction of P4501A1 protein was reduced by 55% without changes in the level of mRNA in Hepa-1 cells, whereas the levels of induction of both P4501A1 protein and CYP1A1 mRNA were reduced by >80% in the H4 cell line. Importantly, gel mobility shift analysis and Western blotting showed that the same level of AHR/ARNT complexes could be detected in cells treated with 2,3,7,8-tetrachlorodibenzo-p-dioxin during hypoxia and normoxia. These data suggest that the effects of hypoxia on AHR-mediated gene regulation occur distal to the formation of AHR/ARNT complexes and imply that functional interference between hypoxia and AHR-mediated signaling does not occur through competition for ARNT protein.
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PMID:Analysis of aryl hydrocarbon receptor-mediated signaling during physiological hypoxia reveals lack of competition for the aryl hydrocarbon nuclear translocator transcription factor. 1057 39

We have used polycyclic aromatic hydrocarbon (PAH) alkyne metabolism-based inhibitors to test whether CYP1B1 metabolism is linked to aryl hydrocarbon receptor (AhR) activation in mouse embryo fibroblasts (MEF). 1-ethynylpyrene (1EP) selectively inactivated CYP1B1 dimethylbenzanthracene (DMBA) metabolism in C3H10T1/2 MEFs; whereas 1-(1-propynyl)pyrene (1PP) preferentially inhibited CYP1A1 activity in Hepa-1c1c7 mouse hepatoma cells (Hepa). In each cell type >90% inhibition of DMBA metabolism after 1 h treatment with each inhibitor (0.1 microM) was progressively reversed and then increased to levels seen with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induction (fourfold stimulation). It was found that 0.1 microM 1EP and 1PP maximally induce CYP1B1 and CYP1A1 mRNA levels in10T1/2 and Hepa cells, respectively, after 6 h. 1-Ethylpyrene (EtP), which lacks the activatable acetylene moiety, was far less effective as an inhibitor and as an inducer. AhR activation is essential for 1EP induction as evidenced by the use of AhR antagonists and AhR-deficient MEFs and absence of induction following inhibition of DMBA metabolism with carbon monoxide (CO). Inhibition of CYP1B1 was linked to enhanced AhR activation even at early stages prior to significant ligand depletion. 1EP and EtP were similarly effective in stimulating AhR nuclear translocation, though 5-10 times slower compared with TCDD, and produced no significant down-regulation of the AhR. TCDD activated AhR/Arnt complex formation with an oligonucleotide xenobiotic response element far more extensively than 1EP or EtP, even at concentrations of 1EP that increased CYP1B1 mRNA to similar levels. CO did not influence these responses to EtP, event hough CO treatment potentiated EtP induction of CYP1B1 mRNA. These differences suggest a fundamental difference between PAH/AhR and TCDD/AhR complexes where CYP1B1 metabolic activity regulates the potency, rather than the formation of the AhR/Arnt complex.
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PMID:Metabolism-based polycyclic aromatic acetylene inhibition of CYP1B1 in 10T1/2 cells potentiates aryl hydrocarbon receptor activity. 1058 Dec 6

The mouse cytosolic aldehyde dehydrogenase ALDH3A1 (encoded by the Aldh3a1 gene) has previously been shown in cell culture to be markedly inducible by 2,3,7,8,-tetrachlorodibenzo-p-dioxin (TCDD; dioxin), downregulated by the metabolism of functional CYP1A1/1A2 enzymes, and upregulated by a gene on Chr 7 that leads to endogenous oxidative stress. In order to study the regulation of Aldh3a1 gene expression, we isolated two overlapping genomic sequences from a B6/CBA mouse genomic library that included the entire Aldh3a1 gene, along with considerable 5' and 3' flanking sequences. The Aldh3a1 gene was shown to span approximately 10 kb and comprise 11 exons including a noncoding first exon. The sequence of 3.18 kb upstream of exon 1 reveals numerous consensus transcription factor-binding sites, some of which were shown to be important in the positive and negative control of Aldh3a1 gene expression; these include seven aromatic hydrocarbon response elements (AHREs), an electrophile response element (EPRE), and AP-1, C/EBP beta, c/EBP alpha, NF-kappaB, Sp1, and NF-1 putative binding sites. Deletion fusion constructs containing regions of the Aldh3a1 gene 5' flanking sequence, ligated to chloramphenicol experiments suggested that the 5' flanking region of the gene contains a strong promoter, at least four functional AHREs appear to act cooperatively in causing dioxin-mediated upregulation, and a putative negative regulatory element (NRE) controls basal gene expression independent of dioxin inducibility. The dioxin-mediated upregulation of Aldh3a1 expression in mouse hepatoma Hepa-1c1c7 cell cultures was shown to depend exclusively on the aromatic hydrocarbon receptor. acetyltransferase (CAT) or luciferase (LUC) reporter genes, were studied. Transient transfection experiments suggested that the 5' flanking region of the gene contains a strong promoter, at least four functional AHREs appear to act cooperatively in causing dioxin-mediated upregulation, and a putative negative regulatory element (NRE) controls basal gene expression independent of dioxin inducibility. The dioxin-mediated upregulation of Aldh3a1 expression in mouse hepatoma Hepa-1c1c7 cell cultures was shown to depend exclusively on the aromatic hydrocarbon receptor.
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PMID:Mouse cytosolic class 3 aldehyde dehydrogenase (Aldh3a1): gene structure and regulation of constitutive and dioxin-inducible expression. 1059 37

Using the Cre-lox system, we have generated a cytochrome P450 1A1 Cyp1a1(-/-) knockout mouse by deletion of the translated portions of the Cyp1a1 gene. These mice are viable and demonstrate no obvious phenotype, compared with wild-type littermates. As a first step toward characterizing genes that might be expected to compensate for loss of CYP1A1, constitutive expression of [Ah] gene battery members was examined. In a cultured hepatoma CYP1A1 metabolism-deficient mutant line that does not express Cyp1a2, we have previously shown that constitutive transcriptional up-regulation of other [Ah] gene battery members occurs; these results are consistent with the elevation of a putative endogenous ligand (EL) for the Ah receptor that is a substrate for CYP1A1. The [Ah] battery includes Cyp1a2, NAD(P)H:quinone oxidoreductase (Nqo1), and three other Phase II genes. Examining mRNA, protein, and enzyme activity, we demonstrate that the absence of CYP1A1 has no effect on the hepatic constitutive expression of Cyp1a2 or Nqo1. We postulate that CYP1A1 and CYP1A2 might have overlapping substrate specificity for metabolism of the EL, such that basal CYP1A2 in the liver can compensate for the loss of CYP1A1.
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PMID:Targeted knockout of Cyp1a1 gene does not alter hepatic constitutive expression of other genes in the mouse [Ah] battery. 1062 96

Recent studies from this laboratory have demonstrated that L-tryptophan, after oxidation either by UV-irradiation or ozone, induces aryl hydrocarbon receptor (AhR) activation and binding of the liganded AhR complex to its specific DNA recognition site, thereby initiating transcription of the cytochrome P-450 1a1 (Cyp1a1) gene with concomitant increase of CYP1A1 protein and 7-ethoxyresorufin O-deethylase activity in wild-type mouse hepatoma cells, Hepa lclc7 (Hepa-1), in culture. Temporary inhibition of protein synthesis by cycloheximide resulted in superinduction of oxidized tryptophan-inducible CYP1A1 mRNA, protein, and 7-ethoxyresorufin O-deethylase activity in Hepa-1 cells. In the present communication, the results obtained by immunoblot analyses with monoclonal CYP1A1/1A2 antibody (NIH 1-7-1) demonstrate that both UV- or ozone-oxidized tryptophan also induce CYP1A2 protein in Hepa-1 cells. CYP1A2 mRNA, detected by reverse transcription-polymerase chain reaction, was markedly induced in the UV- or ozone-oxidized tryptophan-treated cells. Temporary inhibition of protein synthesis by cycloheximide further induced oxidized tryptophan-inducible CYP1A2 mRNA as well as the protein in Hepa-1 cells. This is the first report demonstrating the induction of CYP1A2 mRNA and protein in Hepa-1 cells.
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PMID:Induction of cytochrome P-450 1A2 by oxidized tryptophan in Hepa lclc7 cells. 1068 17


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