Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P00492 (hypoxanthine-guanine phosphoribosyltransferase)
 2,385 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

DNA repair-deficient (xeroderma pigmentosum group A (XPA)) and DNA repair-proficient (normal) human skin fibroblasts were genetically engineered by transformation with a controllable human cytochrome P450 (CYP)1A1 expression vector. Induction of CYP1A1 enabled these cells to metabolize (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol (BPD) into a potent cytotoxicant and mutagen. The XPA cells were more susceptible than the normal cells to the cytotoxic effects of both CYP1A1-metabolized BPD and exogenously supplied (+/-)-anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10- epoxide (BPDE). Furthermore, the differential cytotoxicity between XPA and normal cells induced by CYP1A1-metabolized BPD was 8.4-fold greater than that induced by exogenously supplied BPDE. The two cell lines had similar CYP1A1 activities, suggesting that a difference in metabolic potential was not the cause of the differential response to BPD. At comparable cytotoxicity in both XPA and normal cells, BPD treatment induced more mutants and more DNA adducts than BPDE treatment did. At similar levels of DNA adducts in XPA cells, the levels of cytotoxicity induced by CYP1A1-metabolized BPD and exogenously supplied BPDE were similar, but CYP1A1-metabolized BPD induced a threefold higher hypoxanthine phosphoribosyltransferase mutation frequency. In contrast, at similar levels of adducts in CYP1A1-expressing normal cells, BPD induced less cytotoxicity and a lower mutation frequency. DNA adducts were identified and quantified by 32P-postlabeling analyses. The principal adduct formed by both CYP1A1-metabolized BPD and exogenously supplied BPDE was 10-beta-(deoxyguanosin-N2-yl)-7 beta,8 alpha,9 alpha-trihydroxy-7,8,9,10- tetrahydrobenzo[a]pyrene, indicating that the differential effects of BPD- and BPDE-induced adducts were not due to a difference in the types of adducts formed. The results of these studies suggest that CYP1A1-metabolized BPD may form adducts preferentially in transcriptionally active genes or that the intracellular concentration of BPDE may influence the balance between cytotoxicity and mutagenicity (or both).
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PMID:Differential mutagenicity and cytotoxicity of (+/-)-benzo[a]pyrene-trans-7,8-dihydrodiol and (+/-)-anti-benzo[a]pyrene-trans-7,8-dihydrodiol-9,10-epoxide in genetically engineered human fibroblasts. 766 21

Cyclopenta[cd]pyrene (CPP) is a widely distributed polycyclic aromatic hydrocarbon with potent mutagenic and carcinogenic activity. In order to acquire an understanding of the mutagenic pathways of CPP, we studied mutations induced by this chemical in human cells. Four independent cultures of a human cell line expressing cytochrome P450 CYP1A1 (cell line MCL-5) were treated with CPP, and mutants at the hypoxanthine phosphoribosyltransferase (HPRT) locus were selected en masse by 6-thioguanine (6TG) resistance. The kinds and positions of the mutations were analyzed using the combination of high-fidelity polymerase chain reaction (hifi-PCR) and denaturing gradient gel electrophoresis (DGGE). The third exon of the HPRT gene was amplified from the 6TG-resistant cells using the hifi-PCR and the amplified fragment was subsequently analyzed by DGGE to separate mutant sequences from the wild-type sequence. Mutant bands were excised from the gel, amplified using PCR and sequenced. Sixteen different mutations were identified and consisted mostly of the G to T and A to T transversions. Other mutations identified included G to A and A to G transitions, a G to C transversion, and a single G deletion. Of these mutations, six occurred within a run of six guanines. The predominance of transversions involving a guanine or an adenine observed with CPP is similar to the data previously reported for the racemic mixtures of benzo[a]pyrene (B[a]P), suggesting that the mechanisms of mutation induced by CPP may be similar to those induced by B[a]P.
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PMID:In vitro mutational spectrum of cyclopenta[cd]pyrene in the human HPRT gene. 772 67

Molecular epidemiology is a new and evolving area of research, combining laboratory measurement of internal dose, biologically effective dose, biologic effects, and influence of individual susceptibility with epidemiologic methodologies. Biomarkers evaluated were selected according to basic scheme: biomarkers of exposure--metabolites in urine, DNA adducts, protein adducts, and Comet assay parameters; biomarkers of effect--chromosomal aberrations, sister chromatid exchanges, micronuclei, mutations in the hypoxanthine-guanine phosphoribosyltransferase gene, and the activation of oncogenes coding for p53 or p21 proteins as measured on protein levels; biomarkers of susceptibility--genetic polymorphisms of genes CYP1A1, GSTM1, GSTT1, NAT2. DNA adducts measured by 32P-postlabeling are the biomarker of choice for the evaluation of exposure to polycyclic aromatic hydrocarbons. Protein adducts are useful as a biomarker for exposure to tobacco smoke (4-aminobiphenyl) or to smaller molecules such as acrylonitrile or 1,3-butadiene. Of the biomarkers of effect, the most common are cytogenetic end points. Epidemiologic studies support the use of chromosomal breakage as a relevant biomarker of cancer risk. The use of the Comet assay and methods analyzing oxidative DNA damage needs reliable validation for human biomonitoring. Until now there have not been sufficient data to interpret the relationship between genotypes, biomarkers of exposure, and biomarkers of effect for assessing the risk of human exposure to mutagens and carcinogens.
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PMID:Molecular epidemiology studies on occupational and environmental exposure to mutagens and carcinogens, 1997-1999. 1069 23

Metabolic activation of 17beta-estradiol (E2) to catechols and quinones together with lack of deactivation constitute risk factors in human breast carcinogenesis. E2-catchols are generated by cytochrome P450-dependent monooxygenases (CYPs). Deactivation of E2, E2-catechols, and E2-quinones is mediated by UDP-glucuronosyltransferase (UGT), sulfotransferase (SULT), catechol-O-methyltransferase (COMT), glutathione-S-transferase (GST), and NADPH-quinone-oxidoreductase (QR) isozymes, respectively. The aim of the present study was to quantify mRNA levels of E2-metabolizing isozymes expressed in MCF-7 cells cultured in the presence/absence of steroids by reverse transcription/competitive PCR in relation to the housekeeping gene hypoxanthine-guanine phosphoribosyltransferase and compare them with expression levels in normal human mammary gland (MG) and liver tissue. CYP1A1, 1B1, SULT1A1, 1A2, membrane-bound and soluble COMT, GSTT1, QR1, and UGT2B7 were detected in both tissues and MCF-7 cells; however, most enzymes were expressed at least tenfold higher in liver. Yet, CYP1B1 was expressed as high in breast as in liver and UGTs were not detected in MCF-7 cells cultured with steroids. MCF-7 cells cultured steroid-free additionally expressed CYP1A2 as well as UGT1A4, 1A8, and 1A9. Normal human liver but not MG expressed CYP1A2, 3A4, UGT1A1, 1A3, 1A4, 1A9, and SULT2A1. UGT1A8 was only detected in MCF7 cells but was not found in human liver. Thus, our study provides a comprehensive overview of expression levels of E2-metabolizing enzymes in a popular in vitro model and in human tissues, which will contribute to the interpretation of in vitro studies concerning the activation/deactivation of E2.
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PMID:Gene expression of 17beta-estradiol-metabolizing isozymes: comparison of normal human mammary gland to normal human liver and to cultured human breast adenocarcinoma cells. 1849 89

Sudan-1 and para red are industrial dyes that have been illegally added to some foodstuffs, leading to withdrawal of the adulterated products throughout the UK since 2003. This resulted in international concern that arose because Sudan-1 is classified by International Agency for Research on Cancer as a Category 3 carcinogen. However, little is known about the dose response of this chemical at low, more biologically relevant, doses. The study therefore aimed to characterize the dose response for gene mutation and chromosomal damage induced by two azo dyes, namely Sudan-1 and para red. Gene mutations were analysed using the hypoxanthine phosphoribosyltransferase forward mutation assay and chromosomal damage was measured using the cytokinesis-blocked micronucleus assay. Two cell lines were used in these investigations. These were the AHH-1 cell line, which inducibly expresses CYP1A1, and the MCL-5 cell line derived from a subpopulation of AHH-1 cells that expresses a particularly high level of CYP1A1 activity. The MCL-5 cell line has also been transfected with two plasmids that stably express CYP1A2, CYP2A6 and CYP3A4 and all four of these CYP enzymes are known to metabolically activate Sudan-1. AHH-1 cells were used to investigate the dose response of the azo dyes, and MCL-5 cells were used to see if the dose response changed with increased metabolism. Sudan-1 induced a non-linear dose-response curve for gene mutation and chromosomal damage in AHH-1 cells. The genotoxic activity of Sudan-1 was greatly increased in MCL-5 cells. This indicated that the oxidation metabolites from Sudan-1 were both more mutagenic and more clastogenic than the parent compound. Para red also demonstrated a non-linear dose response for both gene mutation and chromosome damage in AHH-1 cells, and an increase in micronuclei induction was observed after increased oxidative metabolism in MCL-5 cells. Sudan-1 and para red are genotoxic chemicals with non-linear dose responses in AHH-1 but not in MCL-5 cells, and oxidative metabolism increases the genotoxic effect of both compounds.
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PMID:Metabolic influences for mutation induction curves after exposure to Sudan-1 and para red. 2019 15

The hypoxia-inducible factor 1 (HIF-1) pathway is induced in many tumors and associated with poorer outcome. The hypoxia-responsive transcription factor HIF-1alpha dimerizes with the aryl hydrocarbon receptor nuclear translocator (ARNT), which is also an important binding partner for the aryl hydrocarbon receptor (AhR). AhR is an important mediator in the metabolic activation and detoxification of carcinogens, such as the environmental pollutant benzo[a]pyrene (BaP). We hypothesized that HIF-1alpha activation attenuates BaP-induced AhR-mediated gene expression, which may lead to increased genetic instability and malignant progression. Human lung carcinoma cells (A549) were simultaneously stimulated with CoCl(2), which leads to HIF-1alpha stabilization and varying concentrations of BaP. Both quantitative PCR and immunoblot analysis indicated that induction of the hypoxia response pathway significantly reduced the levels of AhR downstream targets CYP1A1 and CYP1B1 and AhR protein binding to ARNT. We further demonstrate that the BaP-induced hypoxanthine-guanine phosphoribosyltransferase mutation frequency and gamma-H2AX foci were markedly amplified when the HIF-1 pathway was induced. BaP-DNA adducts were only marginally increased, and transient strand breaks were diminished by HIF-1 induction, indicating changes in DNA repair. These data indicate that concurrent exposure of tumor cells to hypoxia and exogenous genotoxins can enhance genetic instability.
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PMID:Diminished carcinogen detoxification is a novel mechanism for hypoxia-inducible factor 1-mediated genetic instability. 2022 66

Polycyclic aromatic hydrocarbons (PAHs) are widely distributed in the environment and have potent mutagenic and carcinogenic activities. Studies of mutations induced by these compounds in human cells can help acquire an understanding of their mutagenic pathways. In this chapter, independent cultures of a human cell line expressing cytochrome P450 CYP1A1 (cell line MCL-5) were treated with benzo(a)pyrene (BaP) or dibenzo(a,l)pyrene (DBP), and mutants at the hypoxanthine phosphoribosyltransferase (HPRT) locus were selected en masse by 6-thioguanine resistance (6TGR). The kinds and positions of the mutations occurring in the third exon of the HPRT gene were analyzed in the mixed HPRTR mutant cell populations using a combination of polymerase chain reaction (PCR) and denaturing gradient gel electrophoresis (DGGE). Mutant bands were excised from the gel, amplified using PCR, and sequenced to determine the kinds and positions, or spectrum of mutations.
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PMID:Determination of Mutational Spectra Induced by Environmental Toxicants in Complex Human Cell Populations. 3198 63