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)

The model that transcription-coupled excision repair reflects the interference of DNA damage with the transcription process predicts that the rate of such excision repair will be related to the degree to which a particular type of lesion blocks transcription. We tested this by measuring the rate of excision repair of guanine adducts formed in the HPRT gene of diploid human fibroblasts and in the overall genome by two structurally related polycyclic carcinogens, 1-nitrosopyrene (1-NOP) and N-acetoxy-2-acetylaminofluorene (N-AcO-AAF) and comparing the results with those we found previously using benzo[a]pyrene diol epoxide (BPDE). We also measured the degree of interference with in vitro transcription by these adducts. Our results showed that, although BPDE adducts are four times more effective than 1-NOP adducts in blocking transcription, the preferential and strand-specific repair of 1-NOP adducts was twice as fast as that of BPDE adducts. Excision repair of N-AcO-AAF adducts was significantly slower than that of BPDE adducts and was not strand-specific. The efficiency of blocking of transcription by deacetylated N-AcO-AAF adducts was similar to 1-NOP adducts. Therefore, the extent to which a particular lesion blocks transcription in vitro does not predict its rate of preferential or transcription-coupled excision repair.
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PMID:Lack of correlation between degree of interference with transcription and rate of strand specific repair in the HPRT gene of diploid human fibroblasts. 759 80

The detection of an increase in the frequency of mutants in the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene of circulating T-cells has been proposed as a method to evaluate the biological effects of human exposure to environmental mutagens. We exposed adult human T-cells in vitro to 1-nitrosopyrene (1-NOP), a partially reduced metabolite of 1-nitropyrene, a ubiquitous environmental carcinogen. In populations of T-cells from two unrelated donors, a dose of 1-NOP that reduced survival to 40% of the untreated cells increased the HPRT mutant frequency 6 to 7 times over the background frequency of 5 x 10(-6). The coding region of 35 independent mutants was amplified by polymerase chain reaction and sequenced. Single base substitutions were found in 63% of the mutants (22 of 35). These were distributed randomly throughout the gene. Most of the substitutions (82%) involved G-C base pairs, mainly G.C-->A.T transitions and G.C-->T.A transversions. Fifteen mutants were lacking one or more exons; 9 of the 15 were lacking exons 2 and 3. Examination showed that at least four of the latter had resulted from V(D)J recombinase acting illegitimately to recombine sites located in introns 1 and 3 of the HPRT gene. T-cells from a second unrelated donor were exposed to 1-NOP and 38 additional independent mutants were analyzed. The results indicated that such mutations occurred at a frequency of 2.4 x 10(-6) compared to a background frequency of less than 0.3 x 10(-6). This recombinase, which plays an important role in leukemogenesis, is normally present in developing, but not mature, B- and T-cells such as those used here as target cells for 1-NOP. The present study is the first report showing that exposure to an environmental carcinogen can cause mutations induced by the action of this enzyme.
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PMID:Kinds and locations of mutations induced in the hypoxanthine-guanine phosphoribosyltransferase gene of human T-lymphocytes by 1-nitrosopyrene, including those caused by V(D)J recombinase. 803 53

Studies showing that different types of DNA adducts are repaired in human cells at different rates suggest that DNA adduct conformation is the major determinant of the rate of nucleotide excision repair. However, recent studies of repair of cyclobutane pyrimidine dimers or benzo[a]pyrene diol epoxide (BPDE)-induced adducts at the nucleotide level in DNA of normal human fibroblasts indicate that the rate of repair of the same adduct at different nucleotide positions can vary up to 10-fold, suggesting an important role for local DNA conformation. To see if site-specific DNA repair is a common phenomenon for bulky DNA adducts, we determined the rate of repair of 1-nitrosopyrene (1-NOP)-induced adducts in exon 3 of the hypoxanthine phosphoribosyltransferase gene at the nucleotide level using ligation-mediated PCR. To distinguish between the contributions of adduct conformation and local DNA conformation to the rate of repair, we compared the results obtained with 1-NOP with those we obtained previously using BPDE. The principal DNA adduct formed by either agent involves guanine. We found that rates of repair of 1-NOP-induced adducts also varied significantly at the nucleotide level, but the pattern of site-specific repair differed from that of BPDE-induced adducts at the same guanine positions in the same region of DNA. The average rate of excision repair of 1-NOP adducts in exon 3 was two to three times faster than that of BPDE adducts, but at particular nucleotides the rate was slower or faster than that of BPDE adducts or, in some cases, equal to that of BPDE adducts. These results indicate that the contribution of the local DNA conformation to the rate of repair at a particular nucleotide position depends upon the specific DNA adduct involved. However, the data also indicate that the conformation of the DNA adduct is not the only factor contributing to the rate of repair at different nucleotide positions. Instead, the rate of repair at a particular nucleotide position depends on the interaction between the specific adduct conformation and the local DNA conformation at that nucleotide.
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PMID:Site-specific excision repair of 1-nitrosopyrene-induced DNA adducts at the nucleotide level in the HPRT gene of human fibroblasts: effect of adduct conformation on the pattern of site-specific repair. 866 88

The cytotoxic and mutagenic effect of 1-nitrosopyrene (1-NOP) and N-acetoxy-2-acetylaminofluorene (N-AcO-AAF) were compared with that of (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) as a function of the initial frequency of adducts formed in the DNA of repair-proficient diploid human fibroblasts and the fraction remaining at the time the cells replicate their DNA. The principal adducts of all three agents involve guanine. The initial level of BPDE-, 1-NOP-, or N-AcO-AAF-induced adducts per 10(6) nucleotides required to lower the survival of these cells to 37% of the control was 8, 25, and 50, respectively. The frequency of mutants per 10(6) clonable cells induced at those levels of initial adduct formation was 160, 80, and 40, respectively. We determined the rate of excision repair of these adducts from the overall genome, from the individual strands of the hypoxanthine phosphoribosyltransferase (HPRT) gene, and in the case of 1-NOP and BPDE, at the level of individual nucleotides in the nontranscribed strand of exon 3 of that gene, a region where mutations induced by those agents are particularly frequent. 1-NOP-induced adducts were excised from the overall genome and from the individual strands of HPRT at a rate 2-3 times faster than BPDE-induced adducts. The average rate of repair of 1-NOP-induced adducts in exon 3 was also 2-3 times faster than the average rate of repair of BPDE-induced adducts. However, at particular nucleotides 1-NOP-induced adducts were repaired much faster, or slower, or in some cases at a rate equal to that of BPDE-induced adducts. Excision repair of N-AcO-AAF-induced adducts (i.e., deacetylated aminofluorene residues) was significantly slower than that of BPDE- or 1-NOP-induced adducts, and was not strand-specific. In an in vitro assay, BPDE adducts were four times more effective in blocking transcription than were 1-NOP or N-AcO-AAF-induced adducts. We conclude that the cytotoxic and mutagenic effect of these carcinogens reflect a complex interplay of adduct conformation, ability of adducts to block replication and transcription, and variation in the rate of excision repair, even at the nucleotide level.
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PMID:Relationship between adduct formation, rates of excision repair and the cytotoxic and mutagenic effects of structurally-related polycyclic aromatic carcinogens. 920 50