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)

Somatic mutation and neoplastic transformation of diploid Syrian hamster embryo cells were examined concomitantly. Mutations induced by benzo[a]pyrene and N-methyl-N'-nitro-N-nitrosoguanidine were quantitated at the hypoxanthine phosphoribosyltransferase and Na(+)/K(+) ATPase loci and compared to phenotypic transformations measured by changes in cellular morphology and colony formation in agar. Both cellular transformations had characteristics distinct from the somatic mutations observed at the two loci. Morphological transformation was observed after a time comparable to that of somatic mutation but at a frequency that was 25- to 540-fold higher. Transformants capable of colony formation in agar were detected at a frequency of 10(-5)-10(-6), but not until 32-75 population doublings after carcinogen treatment. Although this frequency of transformation is comparable to that of somatic mutation, the detection time required is much longer than the optimal expression time of conventionally studied somatic mutations. Neoplastic transformation of hamster embryo cells has been described as a multistep, progressive process. Various phenotypic transformations of cells after carcinogen treatment may represent different stages in this progressive transformation. The results are discussed in this context and the role of mutagenesis in the transition between various stages is considered. Neoplastic transformation may be initiated by a mutational change, but it cannot be described completely by a single gene mutational event involving a dominant, codominant, or X-linked recessive locus. Neoplastic transformation induced by chemical carcinogens is more complex than a single gene mutational process. Thus, this comparative study does not give experimental support to predictions of the carcinogenic potential of chemicals based on a simple extrapolation of the results obtained from conventional somatic mutation assays.
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PMID:Relationship between somatic mutation and neoplastic transformation. 15 Jun

Mutations in the hprt gene in T-lymphocyte clones isolated from primary cultures treated with the (+)-anti enantiomer of 7,8-dihydroxy-9,10-epoxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE) in vitro, and from untreated control cultures, were characterized using polymerase chain reaction and direct sequencing of hprt cDNA and genomic fragments. The spectrum of BPDE-induced mutations was very specific and clearly different from the background spectrum, which comprised many different types of mutations. Of the BPDE-induced mutations, 20/22 were transversions of GC base pairs and 18/22 were GC greater than TA transversions, which is in agreement with what has been found in other mammalian systems. While no particular 'hotspot' was observed for BPDE in the hprt gene, a sequence context specificity was detected. Ten of the 14 BPDE-induced mutations in the coding region were located in the sequence context AGG, and 2 in AG dinucleotides, which indicates that such sequences are sensitive to BPDE mutagenesis. Nine of the 22 BPDE-induced mutations and 2/12 background point mutations caused mRNA splicing errors. Six of the BPDE-induced splicing errors were caused by GC greater than TA transversions in the AG dinucleotide of different splice acceptor sites, which indicates that these sites may be frequent targets of BPDE mutagenesis. All mutated GC base pairs in the BPDE-induced spectrum were oriented so that the guanine was located on the non-transcribed strand. Assuming that the premutagenic lesion in these cases was covalent binding of BPDE to guanine and that BPDE bound randomly to both strands, the strand specificity of the BPDE-induced mutations indicates that preferential excision repair of BPDE adducts on the transcribed strand occurs in the hprt gene in human T-cells.
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PMID:Strand specificity for mutations induced by (+)-anti BPDE in the hprt gene in human T-lymphocytes. 138 65

The mechanism responsible for the modification of mutagenicity by chlorophyllin has been investigated using mutagenic compounds with different mechanisms of action, including the monofunctional alkylating agents, N-methyl-N'-nitrosourea (MNU) and ethylmethanesulphonate (EMS); nitrosamines related to tobacco products, i.e. dimethyl-nitrosamine (DMN), N-nitrosonornicotine (NNN) and 4-(N-methyl-N-nitrosoamino)-1-(3-pyridinyl)-2-butanone (NNK); the polycyclic aromatic hydrocarbon (PAH) benzo[a]pyrene (B[a]P) and two of its metabolites, i.e. (-)-7 beta,8 alpha-dihydroxy-7,8-dihydrobenzo[a]pyrene (7,8-diol) and (+)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha-oxy-7,8,9,10- tetrahydrobenzo[a]pyrene (BPDE); and a complex mutagenic mixture, an extract and subfractions of Swedish moist oral snuff (SMOS). Mutagenicity was monitored with the Ames Salmonella/microsome assays (STY) and hprt V79 point mutation assay (V79). The effects of chlorophyllin on the mutagenicity of the nitrosamines in the STY assays were found to be complex. In the presence of either NNN or NNK, low concentrations of chlorophyllin actually potentiated the mutagenicity > 2-fold. However, at higher, but still non-toxic concentrations, chlorophyllin decreased the mutagenicity of both compounds. The same type of dose-response relationship for chlorophyllin was indicated in the V79 assay system with DMN, although the effect was much weaker. The results with STY were further confirmed by replacing chlorophyllin with another porphyrin compound, hemin. In contrast, biliverdin, a porphyrin structure without the central metal ion, was unable to potentiate the mutagenicity of NNK in STY.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Chlorophyllin is both a positive and negative modifier of mutagenicity. 147 30

The primary goal of our research consists of developing means sufficiently sensitive to allow assessment of human exposure to environmental carcinogens. We describe here a new approach for analyzing point mutational spectra and a test for its validity and precision using cultured human cells exposed to high doses of environmental carcinogens. The approach in its present form includes a) treatment of independent large cultures of human cells with a carcinogen, b) selection of mutant cells en masse by 6-thioguanine resistance, c) amplification of sequences of interest directly from 6TGR cells using high-fidelity polymerase chain reaction, and d) separation of mutant sequences from nonmutant sequences using denaturing gradient gel electrophoresis. We report use of this protocol to observe induced mutational spectra in exon 3 of the hprt gene in cultured human cells by benzo[a]pyrene-diol epoxide (BPDE), an active form of the widely distributed environmental carcinogen benzo[a]pyrene. BPDE induced predominantly G to T transversions within this target sequence. The variation of the frequency of the mutations among independent cultures is consistent with the interpretation that each of them corresponds to a hotspot.
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PMID:Determination of point mutational spectra of benzo[a]pyrene-diol epoxide in human cells. 148 52

The genotoxicity of the terpene beta-myrcene was evaluated in mammalian cells in vitro. Myrcene is the major constituent of oil of bay and hop which are used in the manufacture of alcoholic beverages. Myrcene is also present in lemon grass (Cymbopogon citratus), a plant widely used in Brazilian folk medicine. Recently, it was shown that myrcene is a very potent analgesic substance and might be an alternative to the already available analgesic drugs. Myrcene was tested up to 1,000 micrograms/ml (limit of solubility) in the presence and absence of S9-mix and did not induce chromosome aberrations and sister chromatid exchanges (SCEs) in human lymphocytes in vitro. Neither the mitotic index nor the proliferation index was influenced by the myrcene treatment. Myrcene did not cause increased mutation frequencies at the hprt-locus in V79-cells. Tests with and without S9-mix revealed negative results. There was no indication for induced cytotoxicity. However, myrcene reduced the SCE-inducing effect of cyclophosphamide in human lymphocytes in a dose dependent manner and also reduced the toxic and mutagenic effect of cyclophosphamide in V79-cells. Under the same test conditions, SCE induction by ethyl methanesulfonate (EMS) and benzo [a]pyrene (BP) was not significantly influenced by simultaneous myrcene treatment. The in vitro results show that myrcene is not mutagenic in mammalian cells, but has antimutagenic properties. The possibility that myrcene exerts its antimutagenic activity by inhibiting certain forms of the cytochrome P-450 isoenzymes required for activation of premutagens and precarcinogenes is discussed.
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PMID:Evaluation of the mutagenicity of beta-myrcene in mammalian cells in vitro. 186 66

Strong evidence points to mutation induction as one mechanism by which changes are introduced into normal cells to convert them into cancer cells. To understand the mechanisms by which mutations are induced in human cells by carcinogens, we are determining the kinds and spectra of mutations induced in the coding region of the hypoxanthine(guanine)phosphoribosyltransferase (hprt) gene. This region, composed of 654 bp, represents nine exons from a 44 kbp gene. To be able to analyze a large number of independent mutants rapidly and economically, we have optimized the conditions for copying mRNA directly from lysates of a small number of cells (e.g., 100) from a 6-thioguanine-resistant clone using reverse transcriptase and oligo(dT)12-18 primers. Then two 20-mer primers, specific for the cDNA of the hprt gene, are used to amplify the first and second strand cDNA 5 x 10(7)-fold during 30 cycles of polymerase chain reaction (PCR). The product (2 to 10 ng) is then purified by ultrafiltration, diluted 1:10, and subjected to an additional 30 cycles of PCR, using two 20-mer primers located just interior to the first set. The amplification product, 5 to 10 ug, is sequenced directly using three other end-labeled primers and Sequenase. To date, we have analyzed 26 mutants induced by (+-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha,epoxy-7,8,9,10-tetrahydrobenzo [a]pyrene and found that 24/26 involved base substitutions. 97% of these involved G.C, predominantly G.C----T.A, distributed over seven exons, with many of the substitutions located in exon 3.
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PMID:Amplification of mRNA of the hprt gene from lysates of mutant human cells and direct DNA sequencing to determine the spectrum of mutations induced by (+/-)-7 beta,8 alpha-dihydroxy-9 alpha,10 alpha, epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene. 211 60

Human T-lymphocytes have been treated with benzo[a]pyrene diolepoxide (BPDE) in vitro and T-cell clones mutated in the hprt gene have been isolated. The mutant frequencies in BPDE-treated T-cell cultures were on average 24-fold higher than those of untreated cultures. Thus, BPDE is a potent inducer of gene mutation in this system. In order to examine which types of mutations are induced by BPDE in human cells, 41 spontaneous and 44 BPDE-induced mutant clones have been characterized using the Southern blot technique. In addition, rearrangements of the T-cell-receptor beta and gamma loci have been used to determine the proportion of isolated clones that are unique, and thus likely to represent independent mutational events. Out of 23 independent spontaneous mutants 4 had large hprt alterations that could be detected on Southern blots. Two of these alterations, deletions of exons 2-6, have been confirmed using PCR of hprt cDNA and direct sequencing of the PCR product. All 33 independent BPDE-induced mutants had normal hprt restriction patterns which indicates that BPDE is mainly a point mutagen in this system.
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PMID:Mutations induced by benzo[a]pyrene diolepoxide at the hprt locus in human T-lymphocytes in vitro. 212 May 84

Ethylmethanesulphonate (EMS), benzidine (BZD) and benzo[a]pyrene (B[a]P) were assayed for ability to induce mutation at the hprt locus of wild-type L5178Y mouse lymphoma cells. EMS was assayed in the absence of metabolic activation, B[a]P in the presence of metabolic activation (S-9 mix) and BZD both in the absence and presence of S-9. Treatment with EMS minus S-9 and B[a]P plus S-9, especially when the S-9 content of the incubation was 2% (v/v), produced strong dose-related increases in mutant frequency. BZD failed to induce mutation at the hprt locus, either in the absence or presence of S-9.
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PMID:The mutagenic activity of ethylmethanesulphonate, benzidine and benzo[a]pyrene at the hprt locus of wild-type L5178Y mouse lymphoma cells. 218 16

As part of the third UKEMS collaborative trial, the induction of mutations in mouse lymphoma L5178Y cells was analysed by an agar cloning method. The method used was based on the published methods of Clive and co-workers and Amacher and co-workers. Mutations at the thymidine kinase (tk) locus were analysed following exposure to ethylmethanesulphonate (EMS) in the absence of S9 mix, benzo[a]pyrene (B[a]P) in the presence of S9 mix and benzidine (BZD) in the absence and presence of S9 mix. Mutations were induced under all these conditions and no difference was found between a 48-h and 72-h expression period. Small and large colonies on trifluorothymidine (TFT) selective plates were expanded and found to be stably resistant to TFT. The effects of varying the S9 level and the composition of the cofactor mix on the mutagenicity of BZD and B[a]P were also analysed. The ability of BZD to induce mutations at the hprt locus was investigated. No mutations were detected either in the presence or absence of S9 mix.
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PMID:Induction of mutations in mouse lymphoma L5178Y cells by ethylmethanesulphonate, benzidine and benzo[a]pyrene. 218 17

As a contribution to the third UKEMS collaborative trial, ethyl methanesulphonate (EMS), benzo[a]pyrene (B[a]P) and benzidine (BZD) were examined for mutagenicity at the hprt locus in Chinese hamster V79 cells, as assessed by 6-thioguanine (6TG) resistance. EMS was examined in the absence of any exogenous metabolic activation system, and the mutagenic dose-response obtained served to calibrate the assay. B[a]P and BZD were examined using three levels of Aroclor 1254-induced rat liver S9 supplemented with standardized concentrations of cofactors for NADPH generation. B[a]P showed S9 mediated cytotoxicity and mutagenicity, with the magnitude of both responses decreasing with increasing amounts of S9. No evidence of mutagenicity was seen for BZD with any of the metabolic activation conditions employed.
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PMID:Mutation assays of ethyl methanesulphonate, benzidine and benzo[a]pyrene using Chinese hamster V79 cells. 218 28


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