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: EC:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Styrene-7,8-oxide (SO) is the major in vivo metabolite of styrene, a widely used plastic monomer. SO has been classified as probably carcinogenic to humans. We studied the genotoxic effects of SO in human peripheral blood lymphocytes (PBL) in vitro. SO-treatment in the range of 0.05-0.6 mM for 24 h resulted in a dose-dependent decrease of cell survival and increase of HPRT mutation, O6-guanine DNA adducts and DNA strand breaks, whereas higher concentrations caused pronounced cell death. SO was a weak mutagen, inducing at most 10-20 mutants per 10(6) clonable cells (approximately 4-fold over the background) after treatment with 0.2-0.4 mM for 24 h or 6 days. The levels of DNA adducts in treated cells correlated with SO-concentrations, but only four adducts per 10(8) nucleotides were detected at the highest treatment concentrations. Yet, adducts were still detectable in cells that had been cultured for 6-8 days after treatment. SO-induced DNA strand breaks, measured with the Comet assay, were detectable after 1 h exposure to 0.05-0.1 mM. Post-treatment incubation for 24 h decreased the level of DNA strand breaks to the control level. There was no correlation between the levels of DNA adducts and frequency of HPRT mutation. The present results indicate that SO is relatively inefficient in inducing HPRT mutation and O6-guanine DNA adducts in human lymphocytes in vitro, which may be related to its pronounced cytotoxicity at concentrations above 0.4 mM. A comparison with previous in vivo data obtained by the same assays in T-lymphocytes of styrene-exposed workers suggests that chronic, low dose exposure to styrene in the work environment may be more efficient in inducing persistent DNA adducts and HPRT mutation than acute, short-term exposure.
Carcinogenesis 1995 Oct
PMID:Styrene oxide-induced HPRT mutations, DNA adducts and DNA strand breaks in cultured human lymphocytes. 758 35

The potent mouse skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) was examined for its mutagenic and recombinagenic activity at the heterozygous thymidine kinase (tk +/-) locus and the hemizygous hypoxanthine phosphoribosyltransferase (hprt +/0) locus in the TK6 human lymphoblastoid cell line. TPA at concentrations of 0.01-1.0 micrograms/ml induced a low frequency of tk mutants showing the slow growth phenotype in a dose-dependent manner, but few normal growth tk mutants or hprt mutants. Concentrations of 1.0-10 micrograms/ml TPA induced all three types of mutants. The molecular structure of tk mutants arising spontaneously or induced by 1.0 and 10 micrograms/ml TPA was investigated by Southern hybridization with a human tk cDNA probe: 86% of all mutants arising after incubation with 10 micrograms/ml TPA lost the entire active tk allele, resulting in loss of heterozygosity (LOH), while 71% of spontaneously arising mutants showed LOH. Densitometric analysis indicated that the majority of LOH mutants induced by TPA were homozygous at the tk locus (retained two copies of the mutant allele), consistent with the occurrence of interchromosomal homologous recombination. These results support the hypothesis that tumor promoters such as TPA may increase the rate of chromosomal mitotic recombination and hence facilitate the segregation of recessive mutations. TPA may thus induce a type of genetic instability during the process of tumor promotion that involves enhanced recombinagenic activity.
Carcinogenesis 1995 Aug
PMID:Recombinagenic activity of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate in human lymphoblastoid cells. 763 95

Recently, we found an elevated frequency of 6-thioguanine-resistant (TGr) mutations at the hyoxanthine-guanine phosphoribosyltransferase (hprt) gene in T cells of peripheral blood from atomic bomb survivors and a slight, but significant, positive correlation between the frequency of mutation and radiation dose. Southern blot analysis of DNA from TGr mutant T cells of atomic bomb survivors, however, failed to show a significant difference between the control and survivor groups. We here report mutational events at the hprt locus of TGr mutant T cell clones from atomic bomb survivors as found by (i) the multiplex polymerase chain reaction (PCR) and (ii) the reverse transcription (RT)-PCR of cDNA and sequencing. The numbers of independent TGr mutant T cell clones examined were 41 from a control group of 18 individuals who had received less than 0.005 Gy and 50 from an exposed group of 24 individuals who had received more than 1.5 Gy (mean dose 2.45 +/- 0.85 Gy). Gross structural alterations, which were detected by multiplex PCR as a loss of or shift in hprt exon-containing fragments of genomic DNA, were found in 10-15% of the clones from both groups, thus indicating that there was no significant difference between them. The altered sequences in the HPRT cDNAs recovered from both groups were of various types. Similar proportions of base substitutions (approximately 45%), deletions or insertions (approximately 25%) and exon skipping (approximately 20%) were found in both groups, indicating that neither the gross structural alterations in the genomic DNA nor sequence alterations in the hprt cDNA of both groups differ significantly. These results confirm our previous observation that A-bomb-induced HRT- mutant T cells have mostly been eliminated from the peripheral blood over the decades that have elapsed since exposure. Some unique features of the mutational sequence alterations found are also described.
Carcinogenesis 1995 Mar
PMID:Spectrum of in vivo hprt mutations in T lymphocytes from atomic bomb survivors. I. Sequence alterations in cDNA. 769 17

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.
Carcinogenesis 1995 Apr
PMID:In vitro mutational spectrum of cyclopenta[cd]pyrene in the human HPRT gene. 772 67

Testosterone, testosterone propionate, 17 beta-trenbolone and progesterone, which represent the main endogenous and synthetic androgens and a progestin, were evaluated for possible cell transformation and genetic effects in Syrian hamster embryo (SHE) cells. Cell growth was reduced by treatment with the steroids at 10-30 micrograms/ml in a dose-related manner. Testosterone and testosterone propionate were less toxic than the other two steroids. Testosterone, testosterone propionate and progesterone induced morphological transformation of SHE cells with similar transformation frequencies. The most potent effects were observed with testosterone propionate, which induced cell transformation at 1-30 micrograms/ml in a dose-related manner. Testosterone and progesterone transformed cells only at the highest dose (30 micrograms/ml). 17 beta-Trenbolone did not induce a statistically significant level of cell transformations at any dose tested (up to 30 micrograms/ml). The transformation frequencies induced by testosterone, testosterone propionate and progesterone were less than one-half that induced by benzo[a]pyrene at 1 microgram/ml. None of these steroids induced significant increases in frequencies of chromosome aberrations or aneuploidy. Gene mutations were not observed for testosterone at the HPRT or Na+/K+ ATPase locus. Because these steroids are also associated with carcinogenic activity in vivo, these in vitro findings provide a model and new insights into the study of the mechanisms of androgen- and progestin-induced cell transformation.
Carcinogenesis 1995 Jun
PMID:Effects of testosterone, testosterone propionate, 17 beta-trenbolone and progesterone on cell transformation and mutagenesis in Syrian hamster embryo cells. 778 50

Mutations induced by ionizing radiation have historically elicited significant public concern. However, only a limited database of ionizing radiation-induced point mutations is available, particularly at endogenous human cell loci. Here, we report the mutational spectrum for 184 X-ray induced TK- mutants derived from TK6 human lymphoblasts. This report represents the first large scale utilization of the tk locus for investigation of mutational specificity at the DNA sequence level. Rapid, single nucleotide sequencing assays at frameshift polymorphism sites in tk exons 4 and 7 were used to partition TK- mutants into two groups: 126 were attributed to either partial gene deletion or to loss of heterozygosity, and DNA sequence alterations were identified for 51. X-ray-induced point mutations included all classes of transitions and transversions, tandem base substitutions, frameshifts, small deletions and a small duplication. The distribution within tk was characterized by clustering at some sites. Twelve TK- point mutations, including five entirely within the coding sequence in exons 3 and 4, resulted in aberrant splicing of the tk transcript. The spectrum of X-ray-induced point mutations was found to be highly reproducible when TK- mutations were compared with HPRT- mutations in TK6. A statistically significant decrease in transitions (P = 0.04) was observed in the combined data set as compared to the spontaneous background. These findings suggest a reproducible pattern which may be utilized in recognizing radiation-induced mutations at other loci of interest.
Carcinogenesis 1995 Feb
PMID:Mutational spectrum of X-ray induced TK- human cell mutants. 785 58

The DNA sequence of 11 in vivo-arising intragenic deletion junctions occurring in the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene of human T-lymphocytes was determined. These deletions ranged in size from 16 bp to 4057 bp. Extensive homology was not found at the deletion breaksites, indicating that non-homologous recombination was responsible for these deletions. Short regions of homology (1-3 nucleotides) at the deletion termini, which may direct the recombination event, were found in seven of the mutations. Only one mutation had an unaccounted for nucleotide at the junction. V(D)J recombinase recognition sequences, previously identified at other hprt deletion breaksites, were not present. Such features are also found at the deletion and translocation junctions of rearranged oncogenes and suppressor oncogenes. The ability to isolate and molecularly analyze deletion mutations occurring in vivo in peripheral human T-lymphocytes allows the assay of DNA breakage/rejoining events. Such a system may serve as a biomarker of exposure to environmental and occupational agents which may be important in the etiology of cancer.
Carcinogenesis 1994 Jul
PMID:Deletion mutations in the hprt gene of T-lymphocytes as a biomarker for genomic rearrangements important in human cancers. 803 26

Earlier studies from our laboratories characterized the mutation profile of the optically active (+)-7R,8S-dihydroxy-9S,10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-BPDE--the ultimate carcinogenic metabolite of benzo[a]pyrene] in the coding region of the hypoxanthine (guanine) phosphoribosyltransferase (HPRT) gene of Chinese hamster V-79 cells. In the present study, we evaluated the mutation profile of (-)-7S,8R-dihydroxy-9R, 10S-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(-)-BPDE-a weakly carcinogenic or inactive enantiomer] and compared its mutation profile with that of (+)-BPDE. In both diol epoxide enantiomers, the benzylic 7-hydroxy group and epoxide oxygen are trans. The mutation frequency for V-79 cells treated with DMSO vehicle or with a low, non-cytotoxic dose (0.5 microM) or a high cytotoxic dose (2.0 microM) of (-)-BPDE was 1, 25 or 185 8-azaguanine-resistant colonies/10(5) survivors, respectively. Independent 8-azaguanine-resistant clones were isolated, and complementary DNAs were prepared by reverse transcription. The coding region of the HPRT gene was amplified by the polymerase chain reaction and sequenced. Altogether, 92 (-)-BPDE-induced mutant clones were examined. At both doses, base substitutions were the most prevalent mutations observed (present in approximately 7% of the mutant clones), followed by exon deletions (present in approximately 22% of the mutant clones) and frame shift mutations (present in approximately 6% of the mutant clones) in the cDNAs analyzed. At the high cytotoxic dose, 5 out of 36 base substitutions occurred at AT base pairs (14%) and 31 at GC base pairs (86%). At the low, non-cytotoxic dose, 7 out of 34 base substitutions were at AT base pairs (21%) and 27 were at GC base pairs (79%). Although there was a trend towards an increase in the proportion of mutations at AT base pairs when the dose of (-)-BPDE was decreased, this trend was not statistically significant. The data also indicated no dose-dependent differences in the kinds of base substitutions or exon deletions in cDNAs induced by (-)-BPDE. Ninety-one per cent of the (-)-BPDE-induced mutations that occurred at guanine were on the non-transcribed strand of DNA and 9% were on the transcribed strand. In contrast to these results, 50% of the (-)-BPDE-induced mutations that occurred at adenine were on the transcribed strand and 50% on the non-transcribed strand.(ABSTRACT TRUNCATED AT 400 WORDS)
Carcinogenesis 1994 Aug
PMID:Mutagenic selectivity at the HPRT locus in V-79 cells: comparison of mutations caused by bay-region benzo[a]pyrene 7,8-diol-9,-10-epoxide enantiomers with high and low carcinogenic activity. 805 56

We have characterized the molecular spectrum of mutations in 116 X-ray-induced and 78 spontaneous, HPRT- mutants derived from the human B lymphoblastoid cell line TK6. Multiplex PCR analysis demonstrated that the overall representation of large deletions was not significantly different in the two spectra. However, highly significant differences were observed for specific deletion types. Total gene deletions represented 41/78 (0.53) X-ray-induced, but only 7/43 (0.16) spontaneous deletions (P < 0.0001). In contrast, 5' terminal deletions were significantly more common among spontaneous (17/43, 0.40) than X-ray-induced (13/78, 0.17) large deletions (P = 0.0079). The types of point mutations induced by X-ray exposure were very diverse including all classes of transitions and transversions, tandem base substitutions, frameshifts, small deletions and a deletion/insertion compound mutation. Compared to spontaneous data, radiation-induced point mutations exhibited a reduced number of transitions and an increased representation of small deletions. Small deletions were uniformly surrounded by direct sequence repeats. The distribution of point mutations was characterized by a cluster within the 5' portion of exon 8. Thirteen HPRT- point mutations exhibited aberrant splicing. Four of these were attributable to coding sequence alterations in exons 4 and 8. These results suggest that it may be possible to identify hallmark mutations associated with X-ray exposure of human cells.
Carcinogenesis 1994 Mar
PMID:Spectrum of X-ray-induced mutations in the human hprt gene. 811 35

6-Nitrochrysene can be activated to genotoxic derivatives by two major metabolic pathways: nitroreduction to N-hydroxy-6-aminochrysene, and a combination of ring-oxidation and nitroreduction that involves the intermediate formation of trans-1,2-dihydro-1,2-dihydroxy-6-aminochrysene (6-AC-1,2-dihydrodiol). The DNA adduct formed from this latter pathway was evaluated by reacting individual deoxynucleoside 5'-monophosphates with 6-AC-1,2-dihydrodiol in the presence of liver microsomal enzymes from 3-methylcholanthrene-pretreated rats. Binding was greatest to deoxyguanosine monophosphate and the major deoxyguanosine (dG) adduct co-chromatographed with the single major adduct formed from the microsome-catalyzed reaction of 6-AC-1,2-dihydrodiol with DNA. In order to characterize the mutational changes associated with the 6-AC-1,2-dihydrodiol pathway, we analyzed the mutational spectrum produced by 6-AC-1,2-dihydrodiol in the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene of CHO-K1 cells. cDNA was synthesized from the RNA of 28 6-thioguanine-resistant mutants, the hprt coding region amplified by the polymerase chain reaction, and the DNA products directly sequenced. Twenty independent primary mutations were found: 12 G:C-->T:A transversions, three G:C-->C:G transversions, one G:C-->A:T transition, one A:T-->T:A transversion, two -1 frameshift mutations in sequences containing consecutive guanines, and one 11 bp deletion. All G:C basepair substitutions had the mutated dG on the non-transcribed strand and 86% of the G:C basepair substitutions had one purine 3' to the mutated dG. The pattern of 6-AC-1,2-dihydrodiol-induced basepair substitutions was distinct from the pattern observed in solvent control mutants. These results are consistent with the formation of a promutagenic dG adduct from a metabolite of 6-AC-1,2-dihydrodiol.
Carcinogenesis 1993 Oct
PMID:Trans-1,2-dihydro-1,2-dihydroxy-6-aminochrysene is metabolized to form a major adduct with deoxyguanosine and produces mutations in the hprt gene of Chinese hamster ovary cells at G:C basepairs. 822 62


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