Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
 2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Bleomycin is one of the radiomimetic antibiotics which induces DNA double-strand breaks by highly specific free radical attack on deoxyribose moieties in DNA. Earlier, we have shown that bleomycin induces a high proportion of large deletions involving one or more exons in the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in a Chinese hamster ovary (CHO) cell line CHO K1-BH4, in which no spontaneously occurring large deletions were detected by a polymerase chain reaction (PCR)-based deletion screening assay. Here we report the molecular nature of another class of mutants in which we did not observe any abnormal exon pattern. We refer to these mutants as the "nondeletion" type. Since bleomycin is a reactive oxygen species (ROS)-generating agent, we also studied whether the change of intracellular levels of ROS may affect the bleomycin-induced mutation spectra. We therefore also investigated the hprt mutation spectra induced by bleomycin with pretreatment by TRIEN (triethylenetetramine), a superoxide dismutase (SOD) inhibitor, and TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl), a SOD mimic. Analysis of these three bleomycin-induced "nondeletion" mutation spectra revealed that 5'-GTC-3' or 5'-GCC-3' sequences were the hot spots for single basepair deletions. Other types of mutation include abnormal cDNA or no cDNA amplification on the hprt locus. Due to the small sample size, we are unable to draw a definitive conclusion about the effects of TRIEN and TEMPOL on bleomycin-induced spectrum of "nondeletion" type hprt mutations.
Environ Mol Mutagen 1998
PMID:PCR-directed DNA sequencing of "nondeletion" HPRT-mutants induced by bleomycin in CHO K1-BH4 cells. 981 39

Formaldehyde (FA) is a genotoxic substance, induces tumors in the nasal epithelium of rats, and is suspected to be a human carcinogen. As a primary DNA lesion, FA induces DNA-protein crosslinks (DPC) and the formation of DPC has been used as a measure of exposure for risk estimation. However, the significance of DPC for mutagenesis and carcinogenesis is at present poorly understood. We therefore performed comparative investigations on the induction of DPC and other genetic endpoints by FA in V79 Chinese hamster cells. The amount of DPC was comparatively determined with the K-SDS assay and the comet assay. Both tests gave similar results but the comet assay was much foster and easier to perform. Our results show that FA significantly induces DPC, sister-chromatid exchanges, and micronuclei in the same range of concentrations, parallel to the induction of cytotoxicity (relative cloning efficiency). In contrast, treatment of V79 cells with FA did not induce gene mutations in the HPRT test even after variations of the treatment protocol. Our results indicate that FA-induced DPC seem to be related to cytotoxicity and clastogenicity but do not lead to the formation of gene mutations in mammalian cells. It is suggested that FA-induced DPC do not cause gene mutations that are involved in FA-induced carcinogenesis.
Environ Mol Mutagen 1998
PMID:Significance of formaldehyde-induced DNA-protein crosslinks for mutagenesis. 981 41

The alkaline comet assay is a sensitive test for the detection of a variety of DNA lesions. However, crosslinks are not readily detected under standard test conditions. Recently, modifications have been introduced measuring crosslinks by determining the reduction of induced DNA migration. We used the comet assay to comparatively investigate in V79 cells the effect of three different crosslinkers: formaldehyde (FA), which predominantly induces DNA-protein crosslinks, cisplatin (DDP), which mainly produces DNA-DNA-intrastrand crosslinks, and mitomycin C (MMC), which mainly leads to DNA-DNA-interstrand crosslinks. In the standard alkaline comet assay, only MMC induced a slight increase in DNA migration at high toxic concentrations. FA and DDP did not induce any DNA migration under the test conditions used. In the modified comet assay, all three crosslinkers led to a clear reduction of gamma-ray-induced DNA migration. This reduction was seen in the case of FA parallel to the induction of cytotoxicity and SCE, while for MMC and DDP induction of cytotoxicity, SCE and HPRT gene mutations occurred at much lower concentrations than the effects in the comet assay. The DNA-DNA crosslinkers caused a reduction of induced DNA migration only at cytotoxic concentrations. Our results indicate that the modified comet assay protocol is a sensitive test for the detection of DNA-protein crosslinks. However, the results for MMC and DDP suggest that the modified protocol is not well suited for the evaluation of DNA-DNA crosslinkers. Furthermore, the relationship between crosslinking and genotoxicity seems to be very different for the three different types of crosslinking substances.
Environ Mol Mutagen 1999
PMID:Detection of crosslinks with the comet assay in relationship to genotoxicity and cytotoxicity. 1021 71

The cellular response to multiple carcinogen treatment has not been extensively studied, even though the effect of individual carcinogens is, in many cases, well known. We have previously shown that potassium dichromate can protect normal human fibroblasts from the mutagenic effects of benzo[a]pyrene diolepoxide (BPDE), and that this effect may be via an oxidative stress mechanism [Tesfai et al. (1998) Mutat Res 416:159-168]. Here, we extend our previous work by showing that nickel subsulfide can produce the some effect. Normal human fibroblasts, preincubated with nickel subsulfide for 46 hr followed by a coincubation of nickel subsulfide and BPDE for 2 hr, showed a dramatic reduction in the mutant frequency of the hypoxanthine (guanine)phosphoribosyl-transferase (HPRT) gene when compared to cells treated only with BPDE. The preincubation period with nickel subsulfide was necessary to see the antagonistic effect, since it was not observed if the cells were simply incubated with both carcinogens for 2 hr. The extent of the antagonistic effect was nickel subsulfide dose-dependent and also appeared to be species-specific, since the effect was not observed when Chinese hamster fibroblasts were tested. Finally, the antagonistic effect of the nickel subsulfide was eliminated by vitamin E, suggesting that production of reactive oxygen species by the nickel may be required. This data, along with our previous work, suggest that the antagonistic effect we observe is not chromium-specific, and that it could be species-specific.
Environ Mol Mutagen 1999
PMID:Nickel subsulfide is similar to potassium dichromate in protecting normal human fibroblasts from the mutagenic effects of benzo[a]pyrene diolepoxide. 1033 23

The molecular analysis of T-lymphocytes from experienced cosmonauts and seven pairs of unexposed twins was performed [M. Khaidakov, D. Young, H. Erfle, A. Mortimer, Y. Voronkov, B.W. Glickman, Molecular analysis of mutations in T-lymphocytes from experienced soviet cosmonauts, Environ. Mol. Mutagen, 30 (1997) 21-30; J. Curry, G. Bebb, J. Moffat, D. Young, M. Khaidakov, A. Mortimer, B.W. Glickman, Similar mutant frequencies observed between monozygotic twins, Human Mutation, 9 (1997) 445-451]. Hprt mutant frequencies (MF) in both datasets were considerably higher (38.0+/-14.6x10(-6) in cosmonauts, and 18.5+/-8.9x10(-6) in twins) than in the background Western control (8-12x10(-6)), [A.D. Tates, F.J. van Dam, H. van Mossel, H. Shoemaker, J.C.P. Thijssen, V.M. Woldring, A.H. Zwinderman, A.T. Natarajan, Use of the clonal assay for the measurement of frequencies of HPRT mutants in T-lymphocytes from five control populations, Mutation Res., 253 (1991) 199-213; R.F. Branda, L.M. Sullivan, J.P. O'Neill, M.T. Falta, J.A. Nicklas, B. Hirsch, P.M. Vacek, R.J. Albertini, Measurement of HPRT mutant frequencies in T-lymphocytes from healthy human populations, Mutation Res., 285 (1993) 267-279]. The distribution of mutations by class in the twin dataset was essentially similar to the background Western control, whereas cosmonaut samples demonstrated a significant excess of splice errors and complex mutations. The distribution of base substitutions showed similar trends in both the cosmonaut and twin samples, which are quite distinct compared to those seen in the Western control. The differences observed between cosmonaut and twin samples (a 2-fold higher MF and an excess of complex mutations in cosmonaut mutational spectra) could be an indication of possible effects of the space environment. However, these changes could also be age-related because the twin group was, on average, 17 years younger. Moreover, very similar patterns of base substitution distribution in both datasets suggest the involvement of certain region-specific factors reflected in mutational spectra. In order to discriminate between occupation and region-specific factors contributing to mutagenesis, an additional study involving trainees and cosmonauts with recent long-term flight experience is required.
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PMID:Study on genotoxic effects of the space environment: a comparison between experienced cosmonauts and unexposed Russian twins. 1063 49

The genotoxic potential of 1,4-dichlorobenzene (1,4-DCB) has been extensively evaluated in vitro and in vivo. The majority of the studies demonstrated the absence of a genotoxic potential for 1, 4-DCB. At variance are a bone marrow micronucleus test (MNT) after intraperitoneal (i.p.) treatment of NMRI mice [Mohtashamipur et al., Mutagenesis 2 (1987) 111-113] and a gene mutation assay on mouse lymphoma cells [McGregor et al., Environ. Mol. Mutagen. 12 (1988) 85-145]. Therefore, we investigated 1,4-DCB and its main metabolite 2,5-dichlorophenol (2,5-DCP) for both endpoints. In an MNT, male and female NMRI mice were treated orally with single doses of 2500mg/kg 1,4-DCB and 1500mg/kg 2,5-DCP, respectively. Smears were prepared 24, 48 and 72h thereafter. No induction of micronuclei was detected for both compounds. Also under the conditions of Mohtashamipur et al. (1987), intraperitoneal treatments of male and female mice with 2 x 177.5 and 2 x 355mg/kg 1,4-DCB failed to induce micronuclei. In addition, CHO/HPRT-gene mutation tests with 1,4-DCB and 2,5-DCP yielded negative results for both compounds with and without metabolic activation system. Therefore, 1,4-DCB and 2,5-DCP are considered to be non-mutagenic in these test systems.
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PMID:Investigations on the mutagenicity of 1,4-dichlorobenzene and its main metabolite 2,5-dichlorophenol in vivo and in vitro. 1102 71

In the human glutathione S-transferase (GST) mu gene family, homozygous deletion of GSTM1 is the null phenotype (frequency of approximately 50% in Caucasians). In the current study, GSTM1 status was determined in human cell lines using reverse transcriptase, polymerase chain reaction, and immunochemistry. Cell lines were challenged with a range of doses of styrene-7,8-oxide (SO) and then toxicity and genotoxicity were monitored. Toxicity was determined by growth in flasks and genotoxicity by cloning in microplates in the presence/absence of 6-thioguanine, to detect mutations at the hypoxanthine phosphoribosyltransferase (hprt) locus. A SO concentration-dependent decrease in survival was observed for all cell lines, with GSTM1-deficient lines being more sensitive. The IC(50)s of deficient and proficient cell lines were 0.45 and 0.55 mM SO, respectively. The difference between survival of GSTM1-deficient and -proficient cell lines approached statistical significance. The background mutation frequency of GSTM1-deficient cell lines was 2 x 10(-5), and that of GSTM1-proficient cell lines was 3 x 10(-6). GSTM1-deficient cell lines were significantly more sensitive than GSTM1-proficient cell lines to mutation induction for concentrations up to 2.5 mM SO (P < 0.001, regression analysis). These results suggest that cell lines containing metabolically competent GSTM1 are able to efficiently use GSTM1 to conjugate SO and reduce its hazard. This supports the epidemiological evidence that GSTM1 influences sensitivity to chemical carcinogenesis and subsequent risk of cancer induction.
Environ Mol Mutagen 2001
PMID:Role of glutathione S-transferase mu (GSTM1) in styrene-7,8-oxide toxicity and mutagenicity. 1142 77

Rheumatoid arthritis (RA) is an inflammatory disease in which high levels of reactive nitrogen oxygen species (RNOS) may be present in the affected joints. RNOS are known to produce small-scale mutational events (transitions, transversions, small insertions, and small deletions) but the ability of these compounds to cause deletion of large segments of genomic DNA has not been previously determined. To address this question, a human lymphoblastoid cell line (WIL2-NS) was exposed to nitric oxide (NO)-donating drugs and hypoxanthine phosphoribosyltransferase (hprt)-negative clones were selected and analyzed by multiplex-PCR. Large-scale deletions accounted for 60-80% of hprt mutations arising in drug-treated cultures compared to 12% in untreated cultures (P-values of 0.006 and 0.0001, respectively, in two experiments). Deletion mutations in untreated cultures affected exon 9, whereas 75% of drug-induced deletion mutations affected exons 2, 3, and 9, and the remainder were very large, ranging from 26 to 1200 kbp. To compare this spectrum of NO-induced mutations in a lymphoblastoid line to that arising in vivo in arthritis patients, T-cells from RA patients, osteoarthritis (OA) patients, and controls were cloned and similarly analyzed. We previously showed that the overall frequency of Hprt mutant clones from patients is appreciably elevated compared to that of control subjects. Large-scale hprt deletions (0.5 to >26 kb) were detected in mutant T-cell clones from both RA and OA patients and also from control subjects. A total of 54 mutant clones from 16 RA patients and 19 mutant clones from 6 OA patients were studied. Of these, 6 clones (from 3 RA and 1 OA patient) had suffered large-scale deletions. A total of 9 control subjects were studied and 62 mutant clones were obtained. Of these, 19 had suffered large-scale deletions, arising in 7 of 9 control subjects. In conclusion, (1) RNOS are capable of inducing large-scale deletion mutations in a human lymphoblastoid cell line and (2) large-scale deletion mutations were found in 10-30% of T-cell clones from RA and OA patients and controls, which we hypothesize may be induced by RNOS.
Environ Mol Mutagen 2001
PMID:Nitric oxide donors induce large-scale deletion mutations in human lymphoblastoid cells: implications for mutations in T-lymphocytes from arthritis patients. 1177 57

Combinations of antiretroviral drugs that include nucleoside reverse transcriptase inhibitors (NRTIs) are superior to single-agent regimens in treating or preventing HIV infection, but the potential long-term health hazards of these treatments in humans are uncertain. In earlier studies, our group found that coexposure of TK6 human lymphoblastoid cells to 3'-azido-2',3'-dideoxythymidine (AZT) and 2',3'-dideoxyinosine (ddI), the first two NRTIs approved by the FDA as antiretroviral drugs, produced multiplicative synergistic enhancement of DNA incorporation of AZT and mutagenic responses in both the HPRT and TK reporter genes, as compared with single-drug exposures (Meng Q et al. [2000a]: Proc Natl Acad Sci USA 97:12667-12671). The purpose of the current study was to characterize the mutational specificity of equimolar mixtures of 100 microM or 300 microM AZT + ddI at the HPRT and TK loci of exposed cells vs. unexposed control cells, and to compare the resulting mutational spectra data to those previously found in cells exposed to AZT alone (Sussman H et al. [1999]: Mutat Res 429:249-259; Meng Q et al. [2000b]: Toxicol Sci 54:322-329). Molecular analyses of HPRT mutant clones were performed by reverse transcription-mediated production of cDNA, PCR amplification, and cDNA sequencing to define small DNA alterations, followed by multiplex PCR amplification of genomic DNA to define the fractions of deletion events. TK mutants with complete gene deletions were distinguished by Southern blot analysis. The observed HPRT mutational categories included point mutations, microinsertions/microdeletions, splicing-error mutations, and macrodeletions including partial and complete gene deletions. The only significant difference or shift in the mutational spectra for NRTI-treated cells vs. control cells was the increase in the frequency of complete TK gene deletions following exposures (for 3 days) to 300 microM AZT-ddI (P = 0.034, chi-square test of homogeneity); however, statistical analyses comparing the observed mutant fraction values (measured mutant frequency x percent of a class of mutation) between control and NRTI-treated cells for each class of mutation showed that the occurrences of complete gene deletions of both HPRT and TK were significantly elevated over background values (0.34 x 10(-6) in HPRT and 6.0 x 10(-6) in TK) at exposure levels of 100 microM AZT-ddI (i.e., 1.94 x 10(-6) in HPRT and 18.6 x 10(-6) in TK) and 300 microM AZT-ddI (i.e., 5.6 x 10(-6) in HPRT and 34.6 x 10(-6) in TK) (P < 0.05, Mann-Whitney U-statistic). These treatment-related increases in complete gene deletions were consistent with the spectra data for AZT alone (ibid.) and with the known mode of action of AZT and ddI as DNA chain terminators. In addition, cotreatments of ddI with AZT led to substantial absolute increases in the mutant fraction of other classes of mutations, unlike cells exposed solely to AZT [e.g., the frequency of point mutations among HPRT mutants was significantly increased by 130 and 323% over the background value (4.25 x 10(-6)) in cells exposed to 100 and 300 microM AZT-ddI, respectively]. These results indicate that, at the same time that AZT-ddI potentiates therapeutic or prophylactic efficacy, the use of a second NRTI with AZT may confer a greater cancer risk, characterized by a spectrum of mutations that deviates from that produced solely by AZT.
Environ Mol Mutagen 2002
PMID:Molecular analysis of mutations at the HPRT and TK loci of human lymphoblastoid cells after combined treatments with 3'-azido-3'-deoxythymidine and 2',3'-dideoxyinosinedagger. 1211 80

The polycyclic aromatic hydrocarbon dibenzo[a,l]pyrene (DB[a,l]P) is an exceptionally potent carcinogen. Its direct DNA-reactive metabolite, the fjord region (-)-anti-11R,12S-dihydrodiol 13S,14R-epoxide [(-)-anti-DB[a,l]PDE], was used to investigate induction of mutations in the coding region of the hypoxanthine phosphoribosyltransferase (Hprt) gene in Chinese hamster V79 cells. Cells exposed to 1-10 nM (-)-anti-DB[a,l]PDE exhibited a close dose-responsive increase in the frequency of mutant clones resistant to 6-thioguanine. RNA was isolated from mutant clones and cDNAs were prepared by reverse transcription. The coding region of the cDNA of the Hprt gene was amplified by polymerase chain reaction and sequenced. Analysis of the DNA base sequence changes induced by (-)-anti-DB[a,l]PDE indicated that base substitutions were the most prevalent mutations, followed by exon deletions. Among the groups of V79 cells treated with low concentrations of (-)-anti-DB[a,l]PDE, most displayed high selectivity for both A:T-->T:A transversions and A:T-->G:C transitions, while cells exposed to a higher dose (10 nM) formed predominantly G:C-->T:A transversions. Also, the number of base substitutions per mutant clone increased with dose. In general, the mutation profiles induced by (-)-anti-DB[a,l]PDE exhibited a wide spectrum; in addition to base substitutions, deletions, insertions, frameshift mutations, as well as tandem mutations were detected. Analysis of the DNA adduct levels induced by (-)-anti-DB[a,l]PDE revealed that a concentration-dependent increase in the level of adduct formation preceded the concentration-dependent increase in mutational events in these cells and that an increasing proportion of DNA adducts at deoxyadenosine were formed with dose. The results of this study demonstrate a correspondence between the concentration and types of DNA adducts and the frequency and types of mutations induced by (-)-anti-DB[a,l]PDE in V79 cells.
Environ Mol Mutagen 2003
PMID:Mutations induced by (-)-anti-11R,12S-dihydrodiol 13S,14R-epoxide of dibenzo[a,l]pyrene in the coding region of the hypoxanthine phosphoribosyltransferase (Hprt) gene in Chinese hamster V79 cells. 1260 83


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