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

The mutagenic 'fingerprint' of the cooked food carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was determined in a Chinese hamster cell line genetically engineered to express human CYP1A2 (XEMh1A2-MZ). The parental Chinese hamster V79 and XEMh1A2-MZ cells were exposed to PhIP at various concentrations for 24h. There was a dose-dependent increase in frequency of mutations at the hypoxanthine-guanine phosphoribosyltransferase (hprt) locus only in the metabolically competent XEMh1A2-MZ cells. The mutant frequency ranged from 25 to 90 X 10(-6) with final concentrations of 2.5 to 100 microM PhIP compared to 8 X 10(-6) in the solvent controls and the V79MZ cells. The molecular nature of the PhIP-induced mutations in XEMh1A2-MZ cells was determined by examining DNA sequence modifications at the hprt locus in forty five 6-thioguanine resistant (6-TGr) mutant clones. Single base substitutions predominantly GC-->TA transversions, were the major class of PhIP-induced mutation. However, a -1 frameshift 'hotspot' in a 5'-GGGA sequence was also observed. With the exception of a compound modification, all of the PhIP-induced mutations involved G.C base pairs. This is consistent with the previously observed PhIP-induced mutations in cultured mammalian cells and 32P-postlabelling experiments that show PhIP adducts to the guanine base and that major adduct is at the C8 position. Furthermore, nearly all of these mutations involved guanine bases on the non-transcribed strand which is possibly indicative of preferential repair of PhIP adducts from the transcribed strand. Nearest neighbor analysis of induced base substitutions indicates a preference for 5' guanine and 3' adenine. These data effectively define a mutation 'fingerprint' for PhIP, which may provide the basis for definitive studies on the role of PhIP in diet associated cancers such as tumours of colon. It is, therefore, intriguing that in their recent report of mutation in tumours of the colon induced by PhIP in male rate Kakiuchi et al. (Proc. Natl Acad. Sci. USA, 92, 910-914) report that four out of eight tumors had identical mutation of the tumour suppressor gene apc which is comprised of a -1 G frameshift in a 5'-GGGA sequence.
Carcinogenesis 1996 Apr
PMID:Mutational spectra of the dietary carcinogen 2-amino-1-methyl-6- phenylimidazo[4,5-b]pyridine(PhIP) at the Chinese hamsters hprt locus. 862 68

Sulfur dioxide, a ubiquitous air pollutant, is a co-carcinogen for benzo[a]pyrene (BP). We have demonstrated previously that the interaction between sulfite, the physiological form of sulfur dioxide, and (+/-) -7r,8t-dihydroxy-9t,10t-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti-BPDE), the ultimate carcinogenic form of BP, results in an enhanced mutagenic effect in Salmonella typhimurium strains TA98 and TA100. We report here that this same co-mutagenic effect of sulfite occurs in a mammalian cell line. Treatment of Chinese hamster V79 cells with 50 nM anti-BPDE, a concentration on the linear portion of the dose-response, resulted in a four-fold increase in mutations at the hprt locus relative to the spontaneous rate. When V79 cells were exposed to 1 or 10 mM sulfite immediately prior to the addition of anti-BPDE, the mutation rate increased by 73% and 210%, respectively, over that elicited by anti-BPDE alone. Sulfite itself was moderately cytotoxic, but caused no increase in mutation over the spontaneous rate. Characterization of the dose- and time-dependance of this enhancement of diol epoxide mutagenicity by sulfite closely resembled the effects seen previously in the bacterial system. In particular, enhancement by sulfite was evident when sulfite was added to the cells between 60 min and 1 min prior to the addition of the diol epoxide. Concurrent addition of sulfite and the diol epoxide attenuated the enhancement, and the effect was lost altogether when sulfite was added 10 min after the diol epoxide. The specificity of this effect of sulfite was shown by comparison with sulfate, which at concentrations of either 1 or 10 mM exhibited modest cytotoxicity, but neither was directly mutagenic nor able to enhance the mutagenic effect of anti-BPDE. Binding studies with labeled anti-BPDE showed that the addition of 10 mM sulfite increased binding of anti-BPDE to DNA by over 43%, corresponding to the observed increase in mutant frequency. Interestingly, this difference in level of DNA modification was not apparent after 30 min to 2 h exposures, but only emerged at the 4 h time point. The 4 h point was routinely used for all mutagenicity studies. Binding of anti-BPDE-derived materials to cellular RNA was not altered by 10 mM sulfite. The emergence of increased DNA modification at the latest time point suggests either a more prolonged period of active DNA binding than would occur with diol epoxide, or a difference in the ability to recognize and clear specific DNA adducts. Both possibilities are discussed in regard to the observed formation of 7r,8t,9t-trihydroxy-7,8,9,10-tetrahydrobenzo[a] pyrene-10c-sulfonate (BPT-10-sulfonate) in those incubations. BPT-10-sulfonate is a relatively stable BP derivative which retains the ability to covalently modify DNA. The role of this derivative in the enhancement of diol epoxide mutagenicity by sulfite is strongly suggested by these data.
Carcinogenesis 1996 May
PMID:Enhancement of benzo[a]pyrene diol epoxide mutagenicity by sulfite in a mammalian test system. 864 Sep 14

The kinds of mutations induced by 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) in the protein coding region of the hprt gene of Chinese hamster ovary (CHO) cells were determined by direct sequencing of polymerase chain reaction (PCR)-amplified cDNA. Primary mutations were found in 15 of 19 of the mutants: 11 were G:C-->T:A transversions, two were A:T-->T:A transversions and two were deletions of single G:C base pairs (-1 frameshifts). The remaining four mutants had large alterations in the cDNA that were explained by mRNA splicing errors. A group of control mutants had more diverse hprt cDNA alterations than MX-induced mutants. Transversions yielding an A:T base pair were the predominant type of MX-induced mutations, in agreement with previous findings in bacteria. This specificity may be explained by the 'A rule', that DNA polymerases preferentially insert adenine nucleotides opposite non-instructional lesions.
Carcinogenesis 1996 May
PMID:Kinds of mutations induced by 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) in the hprt gene of Chinese hamster ovary cells. 864 Sep 33

Radon exposure has been linked to lung carcinogenesis in both human and animal studies. Studies of smoking and nonsmoking uranium miners indicate that radon alone is a risk factor for lung cancer at the levels encountered by these miners, although the possibility exists that other substances in the mine environment affect the radon-induced response. The relevance of data from mines to the lower-exposure home environment is often questioned; still, a recent study of miners exposed to relatively low radon concentrations demonstrated a statistically significant increase for lung and laryngeal cancer deaths. In two major series of experiments with rats, the primary carcinogenic effect found was respiratory tract tumors, and evidence for an inverse exposure-rate effect was also noted. Although this inverse dose-rate effect also has been described in underground miner studies, it may not similarly apply to radon in the home environment. This observation is due to the fact that, below a certain exposure, cells are hit once or not at all, and one would not expect any dose-rate effect, either normal or inverse. Because some chromosome aberrations persist in cycling cells as stable events, cytogenetic studies with radon are being performed to help complete the understanding of the events leading to radon-induced neoplasia. Radon has been found to induce 13 times as much cytogenetic damage (as measured by the occurrence of micronuclei) than a similar dose of 60Co. A wide variety of mutation systems have demonstrated alpha-particle mutagenesis; recent investigations have focused on the molecular basis of alpha-induced mutagenesis. Gene mutations are induced by radon in a linear and dose-dependent fashion, and with a high biological effect relative to low-LET irradiation. Studies of the hprt locus show that approximately half of the alpha-induced mutations arise by complete deletion of the gene; the remaining mutations are split between partial deletions, rearrangements, and events not detectable by Southern blot or PCR exon analysis. Although other mutation systems do not show the same spectra as observed in the hprt gene (suggesting that the gene environment affects response), DNA deletions or multilocus lesions of various size appear to be predominant after radon exposure. As data emerge regarding radon-induced changes at the chromosomal and molecular level, the mechanisms involved in radon carcinogenesis are being clarified. This information should increase the understanding of risk at the low exposure levels typically found in the home.
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PMID:Genetic, cytogenetic, and carcinogenic effects of radon: a review. 869 77

We hypothesize that chronic exposure to environmental toxicants can induce genetic damage causing DNA repair deficiencies and leading to the postulated mutator phenotype of carcinogenesis. To test our hypothesis, a host cell reactivation (HCR) assay was used in which pCMVcat plasmids were damaged with UV light (175, 350 J/m2 UV light), inactivating the chloramphenicol acetyltransferase reporter gene, and then transfected into lymphocytes. Transfected lymphocytes were therefore challenged to repair the damaged plasmids, reactivating the reporter gene. Xeroderma pigmentosum (XP) and Gaucher cell lines were used as positive and negative controls for the HCR assay. The Gaucher cell line repaired normally but XP cell lines demonstrated lower repair activity. Additionally, the repair activity of the XP heterozygous cell line showed intermediate repair compared to the homozygous XP and Gaucher cells. We used HCR to measure the effects of benzene exposure on 12 exposed and 8 nonexposed workers from a local benzene plant. Plasmids 175 J/m2 and 350 J/m2 were repaired with a mean frequency of 66% and 58%, respectively, in control workers compared to 71% and 62% in exposed workers. Conversely, more of the exposed workers were grouped into the reduced repair category than controls. These differences in repair capacity between exposed and control workers were, however, not statistically significant. The lack of significant differences between the exposed and control groups may be due to extremely low exposure to benzene (< 0.3 ppm), small population size, or a lack of benzene genotoxicity at these concentrations. These results are consistent with a parallel hprt gene mutation assay.
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PMID:Measurement of DNA repair deficiency in workers exposed to benzene. 878 77

Understanding the significance of somatic mutations requires knowledge of the mutations that occur in vivo in healthy people. The molecular characterization of mutations in the hypoxanthine phosphoribosyltransferase (hprt) gene in 217 independent T-lymphocyte mutants from 172 donors, including smoking and non-smoking males and females, reveals a broad spectrum of in vivo somatic mutation occurring in a population of healthy people. Identification of the DNA alteration in individual mutant clones was accomplished using either one or a combination of multiplex polymerase chain reaction analysis of genomic DNA, sequencing of cDNA, and genomic DNA sequencing. The total spectrum consists of 59% (128/217) base substitutions: 126 simple and two tandem CC>TT base substitutions; 39% (85/217) deletion/insertion type mutations: 30 frameshifts, 26 small (3-200 basepairs) and 27 large deletions, and two duplications; and the remaining 2% (4/217) complex mutations involving the deletion of one to 11 basepairs which are replaced by 1 to 10 basepairs. No significant difference was detected between the base substitution spectra for the smokers and the non-smokers. Analysis of the number of mutations occurring at any one base position led to the identification of three hotspots for mutations at basepairs 197, 508 and 617, in the hprt gene coding region. Spontaneous deamination of CpG may be implicated in the creation of basepair 508 as a hotspot since all mutations detected are C>T transitions resulting in the nonsense mutation, TAG. At basepairs 197 and 617 both G>T transversions and G>A transitions were found indicating that at least two mechanisms were involved in creating mutations at these positions. Comparison of the mutation spectra from two populations can provide insight into the origin of the mutations. This study provides an excellent base for comparison of mutation spectra in other human populations.
Carcinogenesis 1996 Sep
PMID:Spectrum of somatic mutation at the hypoxanthine phosphoribosyltransferase (hprt) gene of healthy people. 882 8

The suitability of splenic T-lymphocytes as a substitute tissue for detection of genotoxic effects induced in vivo by chemical agents that are organ-specifically activated was tested in rats exposed to single doses at the potent lung-carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), acetoxymethylmethylnitrosamine (AMMN) or N-methyl-N-nitrosourea (MNU). NNK, AMMN and MNU methylate DNA most likely via the formation of a methanediazohydroxide ion that decomposes to a methyl diazonium ion. For all three agents, an increase in the levels of 06-methylguanine and 7-methylguanine in DNA of rat liver and lung was detected by reverse phase HPLC and electrochemical detection. Treatment with NNK did not result in the formation of O6-methylguanine and 7-methylguanine in DNA of bone marrow and spleen, corresponding with the absence of metabolic activation pathways for this compound in these tissues. For AMMN formation of both 06-methylguanine and 7-methylguanine was detectable in DNA of the spleen, whereas in DNA of bone marrow only very low frequencies of 7-methylguanine were found at a toxic dose. MNU induced O6-methylguanine and 7-methylguanine in both spleen and bone marrow. Using splenic T-lymphocytes from the rat no increase above control levels of the hprt mutant frequencies was found for NNK and AMMN for all exposure levels tested, 32 days after chemical exposure. For MNU a dose-dependent increase in hprt mutant frequency was found at exposure levels of 0.097 mmol/kg up to 0.582 mmol/kg. DNA sequence analysis was performed on PCR products of hprt cDNA from 39 MNU-induced 6-thioguanine-resistant T-lymphocyte clones. Single base pair substitutions were found in 25 of these mutants (64%), GC-->AT transitions being the predominant type of mutation (19 of 25; 76%). These mutations are probably caused by mispairing of 06-methylguanine with thymine during DNA replication. The results indicate that formation of mutagenic lesions in the spleen is not correlated with an enhanced frequency of 6-thioguanine-resistant splenic T-lymphocyte clones from rats, 32 days after exposure in vivo to DNA damaging agents. This suggests that mutation-fixation in T-lymphocytes does not occur in the spleen but at other sites in the body such as bone marrow, after which these mutated cells migrate to the spleen.
Carcinogenesis 1996 Oct
PMID:Induction of hprt gene mutations in splenic T-lymphocytes from the rat exposed in vivo to DNA methylating agents is correlated with formation of O6-methylguanine in bone marrow and not in the spleen. 889 87

DNA adducts have been investigated extensively during the past decade. This research has been advanced, in part, by the development of ultrasensitive analytical methods, such as 32P-postlabeling and mass spectrometry, that enable detection of DNA adducts at concentrations as low as one adduct per 10(9) to 10(10) normal nucleotides. Studies of mutations in activated oncogenes such as ras, inactivated tumor suppressor genes such as p53, and surrogate genes such as hprt provide linkage between DNA adducts and carcinogenesis. The measurement of DNA adducts, or molecular dosimetry, has important applications for cancer risk assessment. Cancer risk assessment currently involves estimating the probable effects of carcinogens in humans based on results of animal bioassays. Estimates of risk are then derived from mathematical models that fit data of tumor incidence at the high animal exposures and extrapolate to probable human exposures that may be orders of magnitude lower. Molecular dosimetry could extend the observable range of mechanistic data several orders of magnitude lower than can be achieved in carcinogenesis bioassays. This measurement also compensates automatically for individual and species differences in toxicokinetic factors, as well as any nonlinearities that affect the quantitative relationships between exposure and molecular dose. As a result, molecular dosimetry can provide a basis for conducting high- to low-dose, route-to-route, and interspecies extrapolations. The incorporation of such data into risk assessment promises to reduce uncertainties and produce more accurate estimates of risk compared to current methods.
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PMID:DNA adducts: biological markers of exposure and potential applications to risk assessment. 889 94

The molecular nature of mutations induced by Cd was investigated in this study to elucidate the role of Cd in the initiation of carcinogenesis. Exposing Chinese hamster ovary (CHO)-K1 cells to cadmium acetate markedly decreased the colony-forming ability of cells and induced mutation frequency in the hypoxanthine (guanine) phosphoribosyltransferase (hprt) gene. The mutation frequency induced by Cd at LD30-LD20 doses was approximately 20 times that of untreated cells. D-Mannitol, a scavenger of reactive oxygen species (ROS), significantly protects cells against Cd cytotoxicity and mutagenicity. Furthermore, non-cytotoxic doses of 3-amino-1,2,4-triazole, a catalase inhibitor, potentiates Cd cytotoxicity and mutagenicity. The cellular Cd uptake ability was not altered by the combined treatment with either D-mannitol or 3-amino-1,2,4-triazole. The GSH level and the activities of GSH peroxidase, GSSG reductase, and catalase in cells treated with Cd (4 microM, 4 h) decreased to 78%, 47%, 40%, and 22% of the untreated cells, respectively. Those enzymatic activities recovered to normal levels 8 h after removing Cd. Polymerase chain reaction and DNA sequencing analysis of 54 independent Cd mutants revealed Cd-induced base substitutions, splice mutations, and large genomic deletions. All six types of base substitutions were observed; however, base transversions (22/27; 81%) occurred more frequently than transitions (5/27; 19%). The frequencies of mutations occurring at T.A or G.C base pairs were roughly equal. Results in this study strongly suggest that Cd mutagenicity in CHO-K1 cells is ROS-dependent. Moreover, the unique mutational spectrum induced by Cd implies that specific DNA adducts generated through the interaction of Cd-DNA and ROS may play a role in the mutational specificity.
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PMID:Reactive oxygen species may participate in the mutagenicity and mutational spectrum of cadmium in Chinese hamster ovary-K1 cells. 895 Dec 41

Aminothiols such as WR-2721 and its active free thiol WR-1065 have previously been shown to reduce mutations resulting from ionizing radiation in exponentially growing cells. In this study, non-dividing human G0 T-lymphocytes were exposed to the aminothiol radioprotective agent, WR-1065, 30 min before or 3 h after external beam gamma-irradiation and subsequently assessed for survival and mutation induction at the hprt locus. Cytotoxicity due to gamma-irradiation was reduced only when the WR-1065 was present during irradiation. The frequency of hprt mutations, however, was reduced regardless of time of administration, although the reduction was statistically significant only when WR-1065 was added 30 min before irradiation (P < 0.01). This is the first study to demonstrate the protective effects of WR-1065 against radiation-induced mutation in a reporter gene using a human non-cycling cell. Hprt mutations arising in vivo in these cells may be useful for monitoring the radioprotective effect of aminothiols in human populations.
Carcinogenesis 1996 Dec
PMID:Hprt mutations in human T-lymphocytes reflect radioprotective effects of the aminothiol, WR-1065. 900 2


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