UNIPROT:P00492 - FACTA Search

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 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.
...
PMID:Relationship between adduct formation, rates of excision repair and the cytotoxic and mutagenic effects of structurally-related polycyclic aromatic carcinogens. 920 50

Bisphenol-A (BP-A) is a major component of epoxy, polycarbonate and other resins. For an assessment of in vitro carcinogenicity and related activity of BP-A, the abilities of this compound to induce cellular transformation and genetic effects were examined simultaneously using the Syrian hamster embryo (SHE) cell model. Cellular growth was reduced by continuous treatment with BP-A at doses > or = 100 microM. However, colony-forming efficiencies were not decreased significantly following treatment with up to 200 microM BP-A for 48 hr. Morphological transformation of SHE cells was induced by treatment of cells with BP-A at 50 to 200 microM for 48 hr. BP-A exhibited transforming activity at doses > or = 50 microM but was less active than the benzo[alpha]pyrene used as a positive control. Over the dose range that resulted in cellular transformation, treatment of SHE cells with BP-A failed to induce gene mutations at the Na+/K+ ATPase locus or the hprt locus. No statistically significant numbers of chromosomal aberrations were detected in SHE cells treated with BP-A. However, treatment of cells with BP-A induced numerical chromosomal changes in the near diploid range at doses that induced cellular transformation. 32P-Postlabeling analysis revealed that exposure of cells to BP-A also elicited DNA adduct formation in a dose-dependent fashion. Our results indicate that BP-A has cell-transforming and genotoxic activities in cultured mammalian cells and potential carcinogenic activity.
...
PMID:Bisphenol-A induces cellular transformation, aneuploidy and DNA adduct formation in cultured Syrian hamster embryo cells. 946 21

1-, 3-, and 6-nitrobenzo[a]pyrene (nitro-BaP) are environmental contaminants that can be metabolized to genotoxic derivatives by either nitroreduction or ring-oxidation. In this study, we examined the types of mutations produced by the primary nitroreduced metabolites, 1-, 3-, and 6-nitroso-BaP (NO-BaP) in the hprt gene of Chinese hamster ovary cells. RNA from 6-thioguanine-resistant mutants was reverse-transcribed to cDNA and the hprt coding sequence was amplified and sequenced. The mutational patterns produced by the three compounds exhibited extensive similarities: 1) base pair substitutions accounted for 67% (28/42) of 1-NO-BaP, 51% (26/51) of 3-NO-BaP, and 50% (11/22) of 6-NO-BaP mutations; 19-36% of the mutations were exon deletions and 14-18% were frameshifts; 2) most (64-84%) of the simple base pair substitutions occurred at G:C, mainly G:C-->T:A and G:C-->C:G transversions; 3) 98% (46/47) of the simple base pair substitutions at G:C had the mutated dG on the non-transcribed strand and 81% (38/47) were located with the mutated dG flanked 3' by at least one purine; and 4) most simple base pair substitutions (48/62, 77%) occurred in exons 2, 3, and 8 of the hprt gene. Although there were no significant differences among the mutation profiles of the NO-BaPs, a significant difference did exist between the mutation pattern produced by 3-NO-BaP and the mutation pattern previously determined for the ring-oxidized product of 3-nitro-BaP metabolism, trans-7,8-dihydroxy-anti-9,10-epoxy-7,8,9, 10-tetrahydro-3-nitrobenzo[a]pyrene. This observation indicates that differences in the structures of closely related adducts can be important enough to have an effect on mutation profiles.
...
PMID:Molecular characterization of hprt mutations from Chinese hamster ovary cells treated with 1-, 3-, and 6-nitrosobenzo[a]pyrene. 946 17

We have compared the response of the native hprt gene and the lacI, cII, and cI transgenes in Big Blue B6C3F1 mice following treatment with either N-nitroso-N-methylurea (MNU) or benzo[a]pyrene (BaP). Three weeks after mutagen treatment splenic T cells were isolated from the animals, and samples were either cultured to measure mutation at the native hprt locus or used to extract genomic DNA for transgene mutation analysis. Phage rescued from extracted DNA were plated in the presence of 5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside (X-gal) to score lacI mutations, or plated on a hflAB lawn to score cII and cI mutants. With MNU hprt mutant frequency increased in a dose-related, sublinear manner up to 78-fold above background at the highest dose tested (20 mg/kg). In comparison, the lacI transgene yielded only a 3.1-fold increase at this dose, and the cII and cI transgenes did not show any increase. With 150 mg/kg BaP a 5.8- and 8.7-fold increase in mutant frequency was observed at hprt and lacI, respectively, while only a 1.3-fold increase was observed at cII. DNA sequencing revealed an increase in GC-->TA transversions among the cII mutants, suggesting that the increase was related to BaP exposure. No significant increase in cI mutant frequency was observed. Therefore, the order of mutation assay sensitivity was hprt>lacI>cII/cI with MNU, and hprt approximately lacI> cII/cI with BaP. While the hflAB selection system offers significant advantages with respect to cost and effort when compared to the lacI assay, additional evaluation of its sensitivity is warranted.
...
PMID:A comparative study of in vivo mutation assays: analysis of hprt, lacI, cII/cI and as mutational targets for N-nitroso-N-methylurea and benzo[a]pyrene in Big Blue mice. 974 34

Dihydrodiol epoxides (DEs) are important carcinogenic metabolites of polycyclic aromatic hydrocarbons (PAHs). The metabolic formation of four stereoisomeric DEs (a pair of optically active diastereomers termed as syn- and anti-form) is possible. Glutathione tranferases (GSTs) have been demonstrated to catalyze the detoxification of DEs. Purified GSTs display remarkable differences in catalytic efficiencies towards bay- and fjord-region DEs along with a high degree of regio- and stereoselectivity. Here we determined to which extent heterologously expressed human GSTP1-1, a major GST isoform in lung, affects the mutagenicity of stereoisomeric bay-region DEs of benzo[a]pyrene in Chinese hamster V79 cells. To evaluate the influence of sterical crowding in the substrate on the activity of GSTP-1, the study was extended to the strongly mutagenic fjord-region (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene. GSTP1-1,reduced preferentially the mutagenicity (studied at the hprt locus) of (+)-anti and (+)-syn-DEs of benzo[a]pyrene (by 66 and 67%) as compared with the corresponding (-)-anti- and (-)-syn-enantiomers (by 15 and 13%). These results are in line with previous studies on the enantioselectivity of purified GSTP1-1 towards the DE isomers of benzo[a]pyrene and benzo[c]phenanthrene showing that enantiomers with (R)-configuration at the benzylic oxiranyl carbon are better substrates than those with (S)-configuration. Interestingly, the (-)-anti-DEs of benzo[c]phenanthrene and dibenzo[a,l]pyrene were efficiently detoxified by GSTP-1-1 in the constructed cell line (reduction of mutagenicity by 66 and 64%). This study demonstrates that differences in the caalytic activity seen for purified GST towards individual mutagens do not necessarily reflect the detoxification of DEs by the same enzyme in a living cell and provides further evidence that specific human GSTs play a role in the detoxification of DEs of PAHs.
...
PMID:Detoxification of optically active bay- and fjord-region polycyclic aromatic hydrocarbon dihydrodiol epoxides by human glutathione transferase P1-1 expressed in Chinese hamster V79 cells. 985 12

Earlier studies have shown that the profile of mutations induced by (+)-7R,8S-dihydroxy-9S,10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (+)-BPDE at the hypoxanthine (guanine) phosphoribosyltransferase (hprt) gene of Chinese hamster V79 cells was dependent on the concentration of (+)-BPDE. In the present study, we examined the effect of the concentration of (+)-BPDE on its mutational profile at the hprt gene in repair-deficient V-H1 cells (a derivative of V79 cells) to explore the role of DNA repair in the dose-dependent mutational profile of (+)-BPDE. Independent hprt mutant clones were isolated after exposing V-H1 cells to dimethylsulfoxide (DMSO) or to low (4-6 nM; 95% cell survival) or high (40-48 nM; 31% cell survival) concentrations of (+)-BPDE in DMSO. The mutation frequencies for the DMSO control and for the low and high concentration groups were 0.1, 2.1 and 32.9 mutant colonies/10(5) survivors, respectively. The profile of mutations at the hprt gene was characterized for 148 (+)-BPDE-induced mutant clones and the results from the present study were compared with those obtained earlier with V79 cells. The data indicated that: (i) V-H1 cells were approximately 9-fold more sensitive to the cytotoxic effects of (+)-BPDE than V79 cells; (ii) the mutation frequency in V-H1 cells was similar to that observed in V79 cells following exposure to similar concentrations of (+)-BPDE; (iii) (+)-BPDE-induced mutations at guanine on the transcribed strand of the hprt gene were common in V-H1 cells but were extraordinarily rare in V79 cells; (iv) (+)-BPDE-induced mutations at adenine on the transcribed strand of the hprt gene were common in both V-H1 and V79 cells; (v) although exposure of V79 cells to different doses of (+)-BPDE resulted in a dose-dependent mutational profile at the hprt gene, this was not observed in V-H1 cells. Our observations indicate a defect in the transcription-coupled repair of (+)-BPDE-DNA adducts in V-H1 cells and that the repair activity deficient in V-H1 cells is essential for the dose-dependent mutational profile observed with (+)-BPDE in V79 cells.
...
PMID:Characterization of the mutational profile of (+)-7R,8S-dihydroxy-9S, 10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene at the hypoxanthine (guanine) phosphoribosyltransferase gene in repair-deficient Chinese hamster V-H1 cells. 1059 Feb 20

Molecular analysis of mutations at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in peripheral blood T-lymphocytes can provide information on mechanisms of somatic in vivo mutation in populations exposed to exogenous carcinogens and in individuals with inherent susceptibility to cancer and other diseases. To study possible mutational changes associated with smoking as a risk factor for lung cancer, we analyzed HPRT mutations in T-cells of newly diagnosed, nonsmoking and smoking lung cancer patients before treatment. Reverse transcriptase polymerase chain reaction (RT-PCR) and DNA sequencing methods were used to identify 146 independent mutations, 73 each from 32 nonsmoking and 31 smoking cases. In 35 T-cell mutants, the HPRT cDNA showed loss of an entire exon, indicating a splicing mutation. Among the remaining 111 fully characterized mutations in the coding region, single base pair (bp) substitutions predominated with 79% (48/61) in nonsmokers and 90% (45/50) in smokers. Frameshift and small deletion (1-24 bp) mutations were found in 18 mutants. The distribution of base pair substitutions was nonrandom, with significant clustering at previously identified hotspot positions 143, 197 and 617 in the HPRT coding sequence (P< or =0.008). One additional hotspot, GC-->TA at position 606, was observed only in smokers (P=0.006). The frequency of GC>TA transversions was higher in smokers (13%) than in nonsmokers (6%). Conversely, smokers had a lower frequency of GC>AT transitions (24%) than nonsmokers (35%). This smoking-associated shift of the HPRT mutational spectrum, although not statistically significant, is consistent with the in vitro mutagenicity of benzo(a)pyrene (BaP), a prominent carcinogen of tobacco smoke, and with known differences in the TP53 mutational spectrum in lung tumors of smokers and nonsmokers. Among nonsmokers, the HPRT mutational spectra in healthy population controls and lung cancer patients were similar, but there was a marginally significant difference (P=0.07) in the distribution of base pair substitutions between smoking controls and patients. These results suggest that (i) general mechanisms of somatic mutagenesis in individuals with possible predisposition to cancer (e.g. nonsmoking lung cancer patients) are not different from those in normal healthy individuals, and (ii) the HPRT gene in T-cells is a useful reporter locus for smoking-associated somatic in vivo mutations occurring early in lung cancer development.
...
PMID:Mutational spectra at the hypoxanthine-guanine phosphoribosyltransferase (HPRT) locus in T-lymphocytes of nonsmoking and smoking lung cancer patients. 1086 57

Although chemicals usually induce very similar frequencies of mutations in transgenes and endogenous genes in vivo when given acutely, chronic exposure to N-ethyl-N-nitrosourea (ENU) produced a more complex pattern in which the endogenous locus was spared many mutations. Here, we demonstrate that the effect is neither ENU-specific nor locus-specific, and thus, may be important in the extrapolations of risk assessment and in understanding mutational mechanisms. During chronic mutagen exposure, mutations at the transgene accumulate linearly with time, i.e. in direct proportion to the dose received. In contrast, mutations at the endogenous gene are much less frequent than those of the transgene early in the exposure period and the accumulation is not linear with time, but rather accelerates as the exposure continues. Previous comparisons involved the endogenous Dlb-1 locus and the lacI transgene from the Big BlueMouse in the small intestine. These experiments involved the Dlb-1 locus and the lacZ transgene from the MutaMouse in the small intestine and the hprt locus and the lacZ transgene in splenocytes. Comparisons were made in both tissues after acute and chronic exposures to ENU, the original mutagen, and in the small intestine after exposures to benzo(a)pyrene. All comparisons showed that during chronic exposures mutations at the transgene accumulate linearly with the increasing duration of exposure, whereas induced mutations of the endogenous gene initially accumulate at a slower rate. Thus, the difference in mutational response observed during low chronic treatment is not unique to a particular transgene, endogenous gene, tissue, or mutagen used, but may be a general phenomenon of such genes.
...
PMID:Differential mutation of transgenic and endogenous loci in vivo. 1103 54

Cockayne syndrome (CS) patients are deficient in the transcription coupled repair (TCR) subpathway of nucleotide excision repair (NER) but in contrast to xeroderma pigmentosum patients, who have a defect in the global genome repair subpathway of NER, CS patients do not have an elevated cancer incidence. To determine to what extent a TCR deficiency affects carcinogen-induced mutagenesis and carcinogenesis, CS group B correcting gene (CSB)-deficient mice were treated with the genotoxic carcinogen benzo(a)pyrene (B[a]P) at an oral dose of 13 mg/kg body weight, three times a week. At different time points, mutant frequencies at the inactive lacZ gene (in spleen, liver, and lung) as well as at the active hypoxanthine phosphoribosyltransferase (Hprt) gene (in spleen) were determined to compare mutagenesis at inactive versus active genes. B[a]P treatment gave rise to increased mutant frequencies at lacZ in all of the organs tested without a significant difference between CSB-/- and wild-type mice, whereas B[a]P-induced Hprt mutant frequencies in splenic T-lymphocytes were significantly more enhanced in CSB-/- mice than in control mice. The sequence data obtained from Hprt mutants indicate that B[a]P adducts at guanine residues were preferentially removed from the transcribed strand of the Hprt gene in control mice but not in CSB-/- mice. On oral treatment with B[a]P, the tumor incidence increased in both wild-type and CSB-deficient animals. However, no differences in tumor rate were observed between TCR-deficient CSB-/- mice and wild-type mice, which is in line with the normal cancer susceptibility of CS patients. The mutagenic response at lacZ, in contrast to Hprt, correlated well with the cancer incidence in CSB-/- mice after B[a]P treatment, which suggests that mutations in the bulk of the DNA (inactive genes) are a better predictive marker for carcinogen-induced tumorigenesis than mutations in genes that are actively transcribed. Thus, the global genome repair pathway of NER appears to play an important role in the prevention of cancer.
...
PMID:The relationship between benzo[a]pyrene-induced mutagenesis and carcinogenesis in repair-deficient Cockayne syndrome group B mice. 1105 60

LC-MS and LC-MS/MS analyses were used to investigate the chemoselectivity of the carcinogenic diol epoxide metabolite, (-)-(1R,2S,3S,4R)-1,2-epoxy-3,4-dihydroxy-1,2,3, 4-tetrahydrobenzo[c]phenanthrene [(-)-(R,S,S,R)-BcPh DE-2], on reaction in vitro with an oligonucleotide dodecamer derived from the HPRT gene. The sequence of this dodecamer, 5'-T(1)A(2)G(3)T(4)C(5)A(6)A(7)G(8)G(9)G(10)C(11)A(12)-3', contains a base (corresponding to A(7)) which is a hot spot for mutagenesis in the hprt gene induced by the carcinogenic (R,S,S,R)-enantiomer of benzo[a]pyrene 7,8-diol 9,10-epoxide, and an adjacent base (corresponding to A(6)) which gave no mutations with this diol epoxide. Modified oligonucleotides were generated by reaction of (-)-BcPh DE-2 with both the single-stranded and duplex forms of the dodecamer. Multiple purine targets in both strands led to the formation of complex reaction mixtures of regioisomeric BcPh DE-modified oligonucleotides, which were partially separated by reverse phase HPLC on a polystyrene-divinylbenzene column. On-line LC-MS data allowed facile distinction between adducts on the two strands of the duplex, and MS/MS analysis permitted unambiguous assignment of the major sites of modification in the regioisomeric, adducted strands. In the duplex, these sites were at A(6), A(7), and G(8). Interestingly, the "hot spot" A(7)w as about 3 times more reactive with the BcPh DE than the "cold spot" A(6). Adduct formation from the single-stranded dodecamer was less selective, and resulted in more extensive alkylation of G residues.
...
PMID:HPLC-MS/MS identification of positionally isomeric benzo[c]phenanthrene diol epoxide adducts in duplex DNA. 1112 77

<< Previous 1 2 3 4 5 6 Next >>