Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.4.2.7 (adenine phosphoribosyltransferase)
 692 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

As a first step in the development of a multiple-marker, mammalian cell mutagenesis assay system, we have isolated a Chinese hamster ovary (CHO) cell line that is heterozygous for both the adenine phosphoribosyltransferase (aprt) and thymidine kinase (tk) loci. Presumptive aprt+/- heterozygotes with intermediate levels of APRT activity were selected from unmutagenized CHO cell populations on the basis of resistance to low concentrations of the adenine analog, 8-azaadenine. a functional aprt+/ heterozygote with approximately 50% wild-type APRT activity was subsequently used to derive sublines that were also heterozygous for the tk locus. Biochemical and genetic characterization of one such subline, CHO-AT3-2, indicated that it was indeed heterozygous at both the aprt and tk loci. CHO-AT3-2 cells permitted single-step selection of mutants resistant for 8-azaadenine or 5-fluorodeoxyuridine, allowing quantitation and direct comparison of mutation induction at the autosomal aprt or tk loci, as well as in the gene involved in ouabain resistance or at the X-linked, hypoxanthine--guanine phosphoribosyltransferase (hgprt) locus. Significant dose-dependent increases in mutation frequency were observed for all 4 genetic markers after treatment of CHO-AT3-2 cells with ethyl methanesulfonate.
Mutat Res 1980 Sep
PMID:Mutagenicity testing in mammalian cells. I. Derivation of a Chinese hamster ovary cell line heterozygous for the adenine phosphoribosyltransferase and thymidine kinase loci. 644 63

Chinese hamster ovary (CHO) cell lines heterozygous at both the adenine phosphoribosyltransferase (aprt) and thymidine kinase (tk) loci were used for single-step selection of spontaneous and induced mutants resistant to 8-azaadenine (AAr), 6-thioguanine (TGr), ouabain (OUAR), or 5-fluorodeoxyuridine (FUdRr). Mutation data are reported for direct mutagens (EMS, ethyl methanesulfonate; MNNG, N-methyl-N'-nitro-N-nitrosoguanidine; NQO, 4-nitroquinoline 1-oxide) and promutagens (DMN, dimethylnitrosamine; BP, benzo[a]-pyrene) activated by rat-liver homogenates. Optimal plating densities were established for AAr, TGr, OUAR and FUdRr. The induced mutant frequencies as a function of relative cell survival after treatment with EMS, DMN or BP were 2--4 d for AAr, 6--8 d for TGr, 3 d for OUAR, and 1--3 d for FUdRr. The induced mutant frequencies as a function of relative cell survival after treatment with EMS, DMN or BP showed locus-specific differences in sensitivity. Of 61 clonal isolates resistant to AA and assayed for APRT activity, 87% had less than or equal to 5% wild-type activity; of 30 TGr clones assayed, 83% had less than or equal to 5% wild-type HGPRT activity. Of 42 FUdRr clones assayed, 98% had less than or equal to 1% wild-type TK activity. 50 clones selected in medium containing FUdR displayed cross-resistance to 5-bromodeoxyuridine (BUdR) and trifluorothymidine (TFT) and all were sensitive to HAT (hypoxanthine--amethopterin--thymidine) medium. The tk locus showed the largest mutational response as a function of cell survival after mutagen treatment. The rapid expression kinetics for FUdRr and the possibility that the locus detects a broader spectrum of genetic lesions than the other drug-resistance markers are discussed in terms of a sensitive screening assay for detecting potential mutagens.
Mutat Res 1980 Sep
PMID:Mutagenicity testing in mammalian cells. II. Validation of multiple drug-resistance markers having practical application for screening potential mutagens. 644 64

We present evidence for a two-step model for expression of the recessive phenotype at the diploid adenine phosphoribosyl transferase (aprt) locus in Chinese hamster ovary cells. This model proposes a high-frequency event leading to allelic inactivation and a low-frequency event leading to a structural alteration of the APRT protein. Either event can occur first, resulting in two types of heterozygous cells. The proposed model is based on analysis of Chinese hamster ovary presumptive aprt heterozygotes and APRT- mutants, derived by two different laboratories. The major class of heterozygotes (class 1) had approximately 50% parental APRT activity, 50% immunologically precipitable APRT protein, and only wild-type enzyme as based on two-dimensional gel electrophoresis and thermal inactivation studies. We propose that one allele at the aprt locus has been inactivated in these heterozygotes. APRT- mutants derived from any single class 1 heterozygote arose at a low frequency and contained either no immunologically detectable APRT protein or an APRT enzyme which was, in most cases, demonstrably altered. The second class of heterozygotes, consisting of two independent isolates, gave rise to APRT- cells at a high frequency (10(-3) to 10(-5). These heterozygous cell lines had 50% of parental APRT activity and only wild-type spot, or wild-type and an electrophoretic variant spot, on two-dimensional gels. These aprt heterozygotes appear to have arisen by mutation at one allele. APRT- mutants derived from either heterozygote of this class had all lost the wild-type activity, consistent with the proposed model.
Mol Cell Biol 1982 Sep
PMID:Model involving gene inactivation in the generation of autosomal recessive mutants in mammalian cells in culture. 689 Oct 22

The potent tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) was tested for its ability (a) to induce sister chromatid exchange, (b) to increase the rate of transition at the adenine phosphoribosyltransferase (apt) locus from the presumptive heterozygous state ((+/- to the homozygous state (-/ - or -), and (c) to enhance the frequency of mutations expressed after ultraviolet radiation mutagenesis. We have found no significant effect of TPA in any of these experiments. Sister chromatid exchange frequencies in both V79 and Chinese hamster ovary cells remained unchanged by TPA treatment under various conditions, a result inconsistent with the hypothesis that an important effect of TPA might be to increase the rate of chromosomal mitotic recombination (and hence segregation of recessive mutations) in a manner akin to increased chromatid recombination. We have also been unable to obtain evidence for mitotic recombination affecting the aprt locus in Chinese hamster ovary cells for which the rate of change to a high level of resistance to azaadenine was measured. The rate of 8.6 X 10(-7) mutation (and/or segregations) per cell generation assessed by fluctuation analysis was not increased by the continuous presence of TPA, 4 microgram/ml, in the medium. In the third set of experiments, mutant frequencies in Chinese hamster ovary cells after ultraviolet mutagenesis were measured for the markers ouabain resistance, thioguanine resistance, and azaadenine resistance, under conditions with and without pretreatment with TPA before mutant selection. No convincing enhancement in mutation expression was observed. In summary, these results argue that promotion by TPA does not proceed by a mechanism involving genetic recombination or the altered expression of newly mutated alleles.
Cancer Res 1980 Sep
PMID:Failure of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate to enhance sister chromatid exchange, mitotic segregation, or expression of mutations in Chinese hamster cells. 693 1

Transformation, or DNA-mediated gene transfer, permits the introduction of new genetic information into a cell and frequently results in a change in phenotype. The transforming DNA is ultimately integrated into a recipient cell chromosome. No unique chromosomal locations are apparent, different lines contain the transforming DNA on different chromosomes. Expression of transformed genes frequently results in the synthesis of new polypeptide products which restore appropriate mutant cells to the wild-type phenotype. Thus transformation provides an in vivo assay for the functional role of DNA sequence organization about specific genes. Transforming genes coding for selectable functions, such as adenine phosphoribosyltransferase or thymidine kinase, have now been isolated by utilizing transformation in concert with molecular cloning. Finally, transformation may provide a general approach to the analysis of complex heritable phenotypes by permitting the distinction between phenotypic changes without concomitant changes in DNA and functional genetic rearrangements.
Science 1980 Sep 19
PMID:Altering genotype and phenotype by DNA-mediated gene transfer. 741 20

The growth inhibitory mechanisms of mizoribine, an immunosuppressive imidazole nucleoside used clinically to inhibit rejection reactions after renal transplantation and in the treatment of systemic lupus erythematosus and rheumatoid arthritis, were studied in human and murine cells. We found that (a) human cells were 20- to 60-fold more resistant than murine cells to both mizoribine and its aglycone, (b) adenine phosphoribosyltransferase (APRT)-deficient human cells were resistant to aglycone but not to mizoribine, (c) hypoxanthine phosphoribosyltransferase (HPRT)-deficient human cells were at least 100-fold more sensitive to both mizoribine and aglycone, and (d) the decrease in intracellular GTP broadly paralleled the cytotoxicity in each case. Therefore, data obtained from studies using non-human tissues should be interpreted carefully before clinical application. Results indicate that the growth inhibitory effect of the aglycone but not of mizoribine is mediated by APRT, and depletion of guanine nucleotides is responsible for the effects of both drugs. Our data also suggest that the drugs may reduce mutant HPRT-deficient somatic cells in vivo, and may cause enhanced adverse reactions in HPRT-deficient individuals. The drug may have altered effects in patients receiving other purine or pyrimidine analogs.
Biochem Pharmacol 1995 Sep 28
PMID:Differential cytotoxic effects of mizoribine and its aglycone on human and murine cells and on normal and enzyme-deficient human cells. 757 67

Stable, oxygen-resistant cell lines (O2R) were isolated from P19 and P19H22 (APRT hemizygote) mouse embryonic carcinoma cells by serial exposures of increasing durations to 95% O2. Neurally differentiated progeny were also oxygen-resistant. P19O2R exhibited reduced oxygen-mediated micronucleation and a 10- to 20-fold reduction of the forward mutation rate at the HPRT locus in 20% O2. P19H22O2R cells showed reduced frequencies of colonies resistant to 2,6-diaminopurine. The modal karyotype of P19O2R was identical to that of a nonmodal karyotype present in the parental line [39,X,-Y, add(14)]. There was no evidence of enhanced resistance to ionizing radiation. We conclude that this general approach, when applied to pluripotent embryonic stem cells, has the potential to lead to the synthesis of antimutator strains of mice.
Somat Cell Mol Genet 1994 Sep
PMID:Oxygen-resistant multipotent embryonic carcinoma cell lines exhibit antimutator phenotypes. 782 58

Clone B is a CHO cell line that shows a moderate mutator phenotype as a consequence of a defect in mismatch recognition. To identify the classes of mutation that accumulate spontaneously in a functional gene, we isolated and sequenced 54 clone B spontaneous mutants at the adenine phosphoribosyltransferase gene. This spectrum was compared to 42 mutants collected in the parental cells. Rates of AT-->TA transversions and frameshifts were strikingly increased in clone B (almost eight- and sixfold, respectively). Minor increases were also observed for GC-->TA transversions and GC-->AT transition rates. Frameshifts occurred in repeated sequences, and a large proportion were losses of 2 bases occurring in dinucleotide runs of a type similar to microsatellite sequences. AT-->TA transversions clustered in regions of secondary structure and their formation might be explained by slippage-mediated mechanisms. These data indicate that an important function of mismatch recognition is in repair of extrahelical bases generated by misalignment during DNA replication.
Somat Cell Mol Genet 1994 Sep
PMID:Spontaneous mutations at aprt locus in a mammalian cell line defective in mismatch recognition. 782 63

Animal somatic cell DNA is characterized by a bimodal pattern of methylation: tissue-specific genes are methylated in most cell types whereas housekeeping genes have 5' CpG islands which are constitutively unmethylated. Because methyl moieties derived from the gametes are erased in the morula and early blastula, this profile must be re-established in every generation; this is apparently accomplished by a wave of non-CpG island de novo methylation that occurs at implantation. Using transfection into embryonic stem cells and transgenic mice as a model system, we now show that Sp1 elements play a key role in protecting a CpG island in the adenine phosphoribosyltransferase (APRT) gene from de novo methylation. This recognition mechanism represents a critical step in embryogenesis, as it is responsible for setting up the correct genome methylation pattern which, in turn, is involved in regulating basal gene expression in the organism.
Nature 1994 Sep 29
PMID:Sp1 elements protect a CpG island from de novo methylation. 809 Feb 26

We have analyzed spontaneous mutations in the adenine phosphoribosyltransferase gene of Chinese hamster clone B cells that exhibit a mutator phenotype because of defective mismatch binding. The mutator phenotype conferred increases in a limited number of mutational classes. The rates of transitions and most transversions were not significantly increased. The rates of A to T transversions and -2 frameshifts were strikingly elevated. These mutations were in repeated elements and 5 of 9 of the frameshifts were dinucleotide deletions in DNA sequences resembling microsatellites. The mismatch binding protein that is defective in the mutator line is a G-T mismatch recognition factor. Band-shift analysis indicated that the preferred substrate for the mismatch recognition protein is duplex DNA containing an extrahelical mono- or dinucleotide within repeated sequences. In agreement with a role in preventing minus frameshifts, a defective binding protein conferred an instability in clone B microsatellite DNA. A mismatch binding defect was also detected in Lo Vo, a human colorectal carcinoma cell line. Extracts of clone B or a second mismatch binding-deficient line, Raji-F12, did not complement Lo Vo extracts, indicating that these lines share a common defect. Our data provide a mechanistic explanation for the relation between defective mismatch recognition and the microsatellite instability of human colon cancer.
Proc Natl Acad Sci U S A 1994 Sep 13
PMID:A mismatch recognition defect in colon carcinoma confers DNA microsatellite instability and a mutator phenotype. 809 Jul 42


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