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)

Spontaneous mutations and neocarzinostatin-induced mutations were investigated in the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene in exponentially growing Chinese hamster ovary cells. Neocarzinostatin (NCS) treatment caused an 4.5-fold increase in mutation frequency. Analysis by multiplex polymerase chain reaction and sequencing of hprt cDNA revealed that spontaneous mutations in this system were characterized by a relatively high rate of large deletions and double-base substitutions, and a low rate of splice mutations compared with data reported in fibroblastic cell lines. NCS hardly affected this spectrum of spontaneous mutations, which indicates the rare incidence of NCS-specific change in the exponential growth phase. This is in contrast to aprt gene mutations reported in plateau phase cells in which base substitutions occur preferentially at sites affected by NCS. These results suggest that differences in the loci assayed or in the processes involved in mammalian mutagenesis in the exponential growth phase and the plateau phase may be the source of the different results.
Carcinogenesis 1998 May
PMID:Neocarzinostatin-induced mutations at the hprt locus in exponentially growing CHO cells, compared with spontaneous mutations. 963 64

Genome-wide demethylation has been suggested to be a step in carcinogenesis. Evidence for this notion comes from the frequently observed global DNA hypomethylation in tumour cells, and from a recent study suggesting that defects in DNA methylation might contribute to the genomic instability of some colorectal tumour cell lines. DNA hypomethylation has also been associated with abnormal chromosomal structures, as observed in cells from patients with ICF (Immunodeficiency, Centromeric instability and Facial abnormalities) syndrome and in cells treated with the demethylating agent 5-azadeoxycytidine. Here we report that murine embryonic stem cells nullizygous for the major DNA methyltransferase (Dnmt1) gene exhibited significantly elevated mutation rates at both the endogenous hypoxanthine phosphoribosyltransferase (Hprt) gene and an integrated viral thymidine kinase (tk) transgene. Gene deletions were the predominant mutations at both loci. The major cause of the observed tk deletions was either mitotic recombination or chromosomal loss accompanied by duplication of the remaining chromosome. Our results imply an important role for mammalian DNA methylation in maintaining genome stability.
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PMID:DNA hypomethylation leads to elevated mutation rates. 973 4

To establish a cause-effect relationship between the human mismatch repair pathway deficiency and the observed phenotypes, a hMSH2 deficient HeLa cell line (HeLa-MSH2-) was established by transfecting the HeLa cells with an antisense RNA expression plasmid. The expression plasmid was constructed by inserting an 851 bp fragment of hMSH2 cDNA into the polyclonal site of the vector pREP9 in a reversed orientation. The production of the mismatch binding protein, hMSH2, was inhibited in HeLa-MSH2- cells, as demonstrated by Western blotting and band shift assay of its whole cell extract. The growth rate of this cell line was not different from the parental HeLa cells soon after transfection. However, the rate was faster after 10 subcultures. The spontaneous mutation frequency at the hypoxanthine phosphoribosyltransferase (HPRT) locus increased markedly, but no N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) tolerance appeared in this cell line. Our results clearly demonstrated several molecular events happened after the inhibition of a major mismatch recognition protein, hMSH2, in the mismatch repair pathway, mimicking carcinogenesis processes.
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PMID:Molecular events after antisense inhibition of hMSH2 in a HeLa cell line. 975 96

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.
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PMID:Significance of formaldehyde-induced DNA-protein crosslinks for mutagenesis. 981 41

The spectrum of mutations was determined at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus in the human uterine tumor cell line HEC-1-A which is defective in the mismatch repair gene hPMS2. The mutation frequency at the hprt locus in HEC-1-A was about two orders higher than that in wild type repair-proficient cells. The fifty-eight mutations detected were exclusively point mutations, with frameshifts of one base deletion/addition predominating (66%) the remaining were base substitutions. All the frameshift mutations occurred at sites of monotonous repeating sequences, including six consecutive guanine bases site which was the hot spot for the addition of one G that contributed 60% of the total mutations. Although the observed specificity of mutations in HEC-1-A apparently resembled that of the hMLH1-deficient cell line HCT116 [Ohzeki, S., Tachibana, A., Tatsumi, T., Kato, T., 1997. Spectra of spontaneous mutations at the hprt locus in colorectal carcinoma cell lines defective in mismatch repair. Carcinogenesis, 18, 1127-1133.], the pronounced increase of +/-1 bp frameshifts and the reduced incidence of C-->T transitions at the CpG site suggest that the hPMS2 gene product may have an additional function in the mismatch repair process independent of it's role in the hMutLalpha heterodimer.
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PMID:Specificity of mutations in the PMS2-deficient human tumor cell line HEC-1-A. 983 64

Cocaine is a widely abused drug. Recently, it has been shown to induce teratogenesis in both humans and animals. Cocaine-induced teratogenicity has been associated with reactive oxygen species (ROS), which are generated by cytochrome P450 during cocaine biotransformation. Since ROS have been reported to induce genotoxicity, it is of interest to know whether cocaine and/or its metabolites are also genotoxic. In this study, Chinese hamster ovary K1 cells were employed as a model system to investigate the genetic toxicity of cocaine in the presence or absence of rat liver S9 fraction. Cocaine-induced cytotoxicity was potentiated when S9 was present, indicating the cytochrome P450 metabolism plays a role in cocaine-mediated cytotoxicity. Cocaine treatments per se induced a few chromosome aberrations while treatments of cocaine plus S9 caused a significant increase in chromosome aberrations. In contrast, cocaine induced micronuclei (MN) formation and hypoxanthine-guanine phosphoribosyltransferase mutation only in the presence of S9. Therefore, cocaine itself is at best a weak clastogen, whereas metabolite(s) of cocaine is/are truly inducer(s) of clastogenesis and mutagenesis. Cocaine treatments alone also induced a significant increase in sister chromatid exchange frequency but the addition of S9 did not affect the results. Free radical scavengers, including superoxide dismutase and catalase, efficiently decreased the frequency of cocaine plus S9-induced MN, implying that ROS are indeed important components in cocaine-induced genotoxicity. The observation that non-toxic doses of cocaine can inhibit intercellular metabolic cooperation suggests that cocaine may also be a tumor promoter. Our data supports that cocaine could possess genotoxicity in addition to its well-known neurotoxicity and teratogenicity.
Carcinogenesis 1999 Jul
PMID:Genetic toxicity of cocaine. 1038 89

This paper describes the results of a study designed to assess the effects of a variety of dietary and lifestyle factors on background levels of mutant frequency (MF) at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene locus in humans. Eighty-three healthy and free-living subjects (aged 20-80 yr; 61 males and 22 females; mean age of 63.07 +/- 14.71 yr) were recruited. Background levels of MF were determined for each subject using a cloning assay. The mean MF/10(6) clonable cells (MF) for the study subjects was 4.63 +/- 2.20. An interview-administered questionnaire was completed by each study subject in order to assess details of dietary history, physical activity, health and potential genotoxin exposure history. A 7-day estimated dietary record method with a food frequency questionnaire was used to determine average intakes of energy and macronutrients (including alcohol), and a range of micronutrients (including vitamin and mineral supplement usage). The relationships between individual dietary and lifestyle factors and HPRT MF were investigated by univariate and multivariate analysis (data was adjusted for age, lymphocyte plating efficiency [PE] and energy intake [EI]). Univariate analysis revealed a significant positive correlation between EI and MF and multivariate analysis revealed significant positive correlations between, body mass index (BMI), % energy intake from total carbohydrate, starch, fat and MF. These findings suggest that a reduction in EI may be a useful preventative measure against the onset of carcinogenesis in humans. No correlations were found between alcohol intake and MF or between estimated antioxidant intake and MF. Thus, estimated intakes of antioxidants may not reflect their bioavailability and functional capacity in vivo and it may be more useful to examine actual plasma/cell levels vs. MF to establish if any significant relationship exists.
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PMID:Effect of dietary intake and lifestyle factors on in vivo mutant frequency at the HPRT gene locus in healthy human subjects. 1063 83

Types and frequencies of in vivo mutation in the hypoxanthine-guanine phosphoribosyl-transferase (HPRT) gene was studied in 142 T cell mutants from 78 healthy nonsmoking and smoking adults with a mean of 65 years. The HPRT mutant frequency in the nonsmokers was 18.7 +/- 12.0 x 10(-6), and in the smokers 26.6 +/- 18.5 x 10(-6) (mean +/- S.D., P < 0.01). Among 107 single base pair substitutions (SBS) in the coding region of the HPRT gene, one new mutable site, one novel nonsense mutation and three not previously reported SBS were identified. Transitions accounted for 59% of the SBS and transversions for 41%. GC > AT transitions were the predominant type of mutation, with 50% of all SBS. The mutations showed a nonrandom distribution along the coding sequence, with three significant hotspots at positions 143, 197 and 617 (13, 14 and 7 mutations, respectively). There was no difference between smokers and nonsmokers with regard to the distribution of mutations at these hotspot positions. However, 85% of the mutations at GC base pairs and 88% of the mutations at AT base pairs in smokers occurred at sites with guanine or thymine, respectively, in the nontranscribed DNA strand. Moreover, smokers had a higher frequency of transversions and lower frequency of transitions than nonsmokers did. Particularly, GC > TA transversions were increased in smokers (11%) compared to nonsmokers (2%), which suggests that tobacco-smoke induced adducts at guanine bases in the nontranscribed DNA strand contributes to the increase of HPRT mutation in smokers. Overall, these results were very similar to the mutational spectra in two younger study populations reported previously [K.J. Burkhart-Schultz, C.L. Thompson, I.M. Jones, Spectrum of somatic mutation at the hypoxanthine phosphoribosyltransferase (HPRT) gene of healthy people, Carcinogenesis 17 (1996) 1871-1883; A. Podlutsky, A.-M. Osterholm, S.-M. Hou, A. Hofmaier, B. Lambert, Spectrum of point mutations in the coding region of the hypoxanthine-guanine phosphoribosyltransferase, Carcinogenesis 19 (1998) 557-566]. With the possible exception of an increase of mutations at hotspot position 143, and a decrease of 5-methylcytosine deamination mediated transitions at CpG-sites in the older individuals, there were no differences between the mutational spectra of old and young adults. In conclusion, both smoking and ageing seem to have minor influences on the spectrum of HPRT mutation in T cells.
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PMID:Influence of smoking and donor age on the spectrum of in vivo mutation at the HPRT-locus in T lymphocytes of healthy adults. 1063 98

The endometrial tumor cell line HHUA carries mutations in two mismatch repair (MMR) genes MSH3 and MSH6. We have established an MSH3-deficient HHUA/chr.2 cell line by introducing human chromosome 2, which carries wild-type MSH6 and MSH2 genes, to HHUA cells. Introduction of chromosome 2 to HHUA cells partially restored G:G MMR activity to the cell extract and reduced the frequency of mutation at the hypoxanthine-guanine phosphoribosyltransferase (hprt*) locus to about 3% that of the parental HHUA cells, which is five-fold the frequency in MMR-proficient cells, indicating that the residual mutator activity in HHUA/chr.2 is due to an MSH3-deficiency in these cells. The spectrum of mutations occurring at the HPRT locus of HHUA/chr.2 was determined with 71 spontaneous 6TG(r) clones. Base substitutions and +/-1 bp frameshifts were the major mutational events constituting, respectively, 54% and 42% of the total mutations, and more than 70% of them occurred at A:T sites. A possible explanation for the apparent bias of mutations to A:T sites in HHUA/chr.2 is haploinsufficiency of the MSH6 gene on the transferred chromosome 2. Comparison of the mutation spectra of HHUA/chr.2 with that of the MSH6-deficient HCT-15 cell line [S. Ohzeki, A. Tachibana, K. Tatsumi, T. Kato, Carcinogenesis 18 (1997) 1127-1133.] suggests that in vivo the MutSalpha (MSH2:MSH6) efficiently repairs both mismatch and unpaired extrahelical bases, whereas MutSbeta (MSH2:MSH3) efficiently repairs extrahelical bases and repairs mismatch bases to a limited extent.
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PMID:Mutation spectrum of MSH3-deficient HHUA/chr.2 cells reflects in vivo activity of the MSH3 gene product in mismatch repair. 1075 99

1,3-Butadiene (BD), an important chemical used mainly in the production of synthetic rubber, is a potent carcinogen in mice, a weak carcinogen in rats, and a suspected carcinogen in humans. To provide a better understanding of the mutagenic mechanisms involved in interspecies differences in BD-induced carcinogenesis, studies were conducted in rodents to test two hypotheses: (a) the mutagenic potency of BD at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus of T lymphocytes (T cells) can be used to quantify interspecies differences in BD-induced carcinogenicity in exposed rodents and (b) comparison of the mutagenic potency and specificity of BD and racemic mixtures of two epoxy metabolites, 1,2-epoxy-3-butene (BDO) and 1,2,3,4-diepoxybutane (BDO2), at the hprt locus of T cells can be used to define the relative contribution of each intermediate to observed BD mutagenicity in each species. The first hypothesis was investigated by determining the effects of exposure duration and elapsed time after exposures on hprt mutant frequencies (MFs) in T cells from thymus and spleen of female B6C3F1 mice and F344 rats (4 to 5 weeks old). In this study, rodents were exposed by inhalation to 0 or 1,250 parts per million (ppm) BD for up to 2 weeks, or to 0 or 625 ppm BD for up to 4 weeks (with all exposures 6 hours/day, 5 days/week). The second hypothesis was examined by defining the effects of exposure concentration and elapsed time after exposures on the hprt MFs in splenic T cells from mice and rats exposed by inhalation to BD (0, 20, 62.5, or 625 ppm), BDO (0, 2.5, or 25 ppm), or BDO2 (0, 2, or 4 ppm) for 4 weeks (all exposures 6 hours/day, 5 days/week). The hprt MFs were measured weekly or biweekly using the T cell cloning assay for up to 10 weeks after the last exposure. The mutagenic potency of BD (represented by the difference in the areas under the mutant T cell "manifestation" curves [or the "change in MFs over time"] of exposed versus control animals) was significantly greater in mice (4.4-fold) than in rats following 2 weeks of exposure to 1,250 ppm BD. Mutagenic potency in mice was 8.5-fold greater than that in rats following 4 weeks of exposure to 625 ppm BD. These hprt MF data provide the first evidence that BD is mutagenic in the rat, albeit the mutagenic response was significantly less than that observed in similarly exposed mice. In addition, the MF data from the two exposure-duration studies indicate that both exposure concentration and exposure duration are important in determining the magnitude of the mutagenic response to BD. The relative contribution of BDO versus BDO2 to overall BD mutagenicity was evaluated by exposing mice and rats to carefully chosen concentrations of BD and racemic mixtures of BDO and BDO2 (that is, 62.5, 2.5, and 4.0 ppm, respectively) and comparing the mutagenic potency of each compound when comparable blood levels of metabolites were achieved. The resulting MF data indicate that (+/-)-BDO2 is a major contributor to the mutagenicity of BD in mice at lower BD exposure levels (< or = 62.5 ppm), whereas other metabolites and stereochemical configurations are responsible for mutations in BD-exposed rats and for the incremental mutagenic effects at higher exposure levels in mice. Molecular analysis of hprt cDNA from expanded T cell clones from control and BD-exposed mice demonstrated an increased frequency of large deletions in exposed animals (p = 0.016), presumably associated with in situ formation of (+/-)-BDO2, meso-BDO2, or both. Results of these mutagenicity experiments, along with data from collaborative studies of DNA adducts from the same animals, should provide a better understanding of the interspecies variation in carcinogenic response to BD and improve the extrapolation of rodent data to the estimation of cancer risk in exposed persons.
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PMID:1,3-butadiene: cancer, mutations, and adducts. Part III: In vivo mutation of the endogenous hprt genes of mice and rats by 1,3-butadiene and its metabolites. 1092 40


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