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)

Constitutional loss or inactivation of one copy of a tumor-suppressor gene, as exemplified by hereditary retinoblastoma, increases the propensity for malignancies by reducing the number of events necessary for the complete loss of the negative regulatory function. We developed a selectable mutation assay employing a human lymphoblastoid cell line (LCL) derived from a heterozygous carrier of 2,8-dihydroxyadenine urolithiasis, adenine phosphoribosyltransferase (APRT) deficiency, for dissecting the second step in loss-of-function mutations and for determining the potential of physical and chemical agents for producing such mutations. The mode of mutational events arising in the wild-type allele of the functionally heterozygous APRT gene resembled that reported for tumor-suppressor genes in malignancies in that mitotic non-disjunctions or recombinations as well as deletions prevailed. Ultraviolet light (UV) was much less efficient in inducing these types of mutations than ionizing radiation. A group of autosomal recessive cancer-prone diseases, including xeroderma pigmentosum (XP), has been characterized as being more susceptible to genomic insults, owing to some defects in DNA processing, such as replication, repair, or recombination. This increased genomic instability may accelerate the gain-of-function mutation at a proto-oncogene and/or the loss-of-function mutation at a tumor-suppressor gene. XP complementation group A (XP-A) LCLs were extremely sensitive to UV-mutagenesis at the hypoxanthine phosphoribosyltransferase (HPRT) locus even at equicytotoxic doses. Some unique mechanism may operate in UV-mutagenesis in XP-A. We have succeeded for the first time in rendering XP-A cells tumorigenic in athymic mice by applying multiple exposures to UV and subsequent treatment with TPA.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Molecular bases for hereditary cancer-prone diseases. 129 55

The reaction product of N-methyl-N-nitrosourea (MNU) with DNA, O6-methylguanine (O6-MeG), is responsible for the mutagenic and carcinogenic effects of this carcinogen. These involve activation of the H-ras proto-oncogene in rat mammary tumors by MNU, with a high frequency of GC to AT transitions in codon 12 of this gene. The present study aimed to investigate the types and position specificities of mutations induced by MNU in another gene, the hprt gene of V79 Chinese hamster cells. Furthermore, since processes involved in the expression of genetic damage, e.g. the state of the DNA precursor pool, have been suggested to be important factors in carcinogenesis, the mutagenic specificity of MNU was also studied in the presence of an imbalanced nucleotide pool. Isolation of independent hprt mutant clones from three groups treated in different manners was performed. Two different doses of MNU and a low dose of MNU in combination with hydroxyurea (HU) were employed. Comparison of the results with the two doses of MNU did not indicate any shift in mutation specificity. The majority of the mutations induced by MNU were base substitutions, mostly transitions of GC to AT showing high affinity for the middle base in 5'-purine-G-N-3' sequences (15/18) in the nontranscribing strand, suggesting a difference in repair capacity for the two strands. The relatively high frequency of the base substitutions resulting in splicing defects is explained by the presence of a consensus sequence (5'-purine-g-N-3') in the splice sites of the hprt gene. The results from the HU/MNU group showed a few more GC to TA transversions, though not statistically significant, which may be caused by a shift from miscoding to non-coding recognition of the O6-MeG lesion. The same reactive decomposition products formed from MNU are also formed from a variety of other carcinogenic compounds, e.g. N-methyl-N'-nitro-N-nitrosoguanidine, dimethylnitrosamine, nitrosocimetidine and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, suggesting that our findings concerning the mutagenic specificity of MNU in mammalian cells are valid also for these other compounds as well.
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PMID:Site specificity of N-methyl-N-nitrosourea-induced transition mutations in the hprt gene. 193 71

Removal of UVB-induced cyclobutane pyrimidine dimers (CPD) from each of the two strands of the transcriptionally active p53 tumor suppressor gene and the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene was determined in the epidermis of the hairless mouse using the CPD-specific enzyme T4 endonuclease V. Mice were exposed to a single dose of UVB (2 kJ/m2) and kept in darkness for up to 24 h. About 80% of the CPD were removed from the transcribed strand of the p53 and HPRT genes within 24 h. Most rapid removal was observed during the first 4 h. In contrast, very little removal of CPD from the nontranscribed strand of the p53 and the HPRT genes was observed in 24 h. The same low level of repair was observed in the inactive c-mos proto-oncogene. The efficient repair of the transcribed strand compared to the nontranscribed strand of transcriptionally active genes in the epidermis of the hairless mouse resembles the repair of CPD in cultured rodent cells. Moreover, the selective removal of CPD from the transcribed strand of the p53 gene correlates well with the known strand bias of u.v.-induced mutations at dipyrimidine sites in the p53 gene of u.v.-induced mouse skin tumors.
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PMID:Strand-specific removal of cyclobutane pyrimidine dimers from the p53 gene in the epidermis of UVB-irradiated hairless mice. 797 Jul 1

Chinese hamster V79 cells were exposed to a high or low concentration of the highly carcinogenic (R,S,S,R) or the less active (S,R,R,S) bay- or fjord-region diol epoxides of benzo[a]pyrene, benzo[c]phenanthrene or dibenz[c,h]acridine. Independent 8-azaguanine-resistant clones were isolated, and base substitutions at the hypoxanthine (guanine) phosphoribosyltransferase (hprt) locus were determined. For the three (R,S,S,R) diol epoxides studied, the proportion of mutations at AT base pairs increased as the concentration of diol epoxide decreased. Concentration-dependent differences in the mutational profile were not observed, however, for the three (S,R,R,S) diol epoxides. In studies, with V-H1 cells (a DNA repair deficient variant of V79 cells), a concentration-dependent difference in the profile of mutations for the (R,S,S,R) diol epoxide of benzo[a]pyrene was not observed. These results suggest that concentration-dependent differences in the mutational profile are dependent on an intact DNA repair system. In additional studies, we initiated mouse skin with a high or low dose of benzo[a]pyrene and promoted the mice for 26 weeks with 12-O-tetradecanoylphorbol-13-acetate. Papillomas were examined for mutations in the c-Ha-ras proto-oncogene. Dose-dependent differences in the profile of c-Ha-ras mutations in the tumors were observed. In summary, (i) dose-dependent differences in mutational profiles at the hprt locus were observed in Chinese hamster V79 cells treated with several highly mutagenic and carcinogenic (R,S,S,R) bay- or fjord-region diol epoxides but not with their less active (S,R,R,S) diol epoxide enantiomers, (ii) a dose-dependent difference in the mutational profile was not observed for the (R,S,S,R) diol epoxide of benzo[a]pyrene in a DNA-repair defective V79 cell line, and (iii) a dose-dependent difference in the mutational profile in the c-Ha-ras proto-oncogene was observed in tumors from mice treated with a high or low dose of benzo[a]pyrene.
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PMID:Dose-dependent differences in the profile of mutations induced by carcinogenic (R,S,S,R) bay- and fjord-region diol epoxides of polycyclic aromatic hydrocarbons. 1176 16