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

Mouse teratocarcinoma cells (OTT6050) deficient for thymidine kinase were fused with rat hepatoma cells ( Fu5AH ) deficient for hypoxanthine phosphoribosyltransferase using inactivated Sendai virus. The hybrid cells were selected and cultured in the presence of HAT medium. A clonally established hybrid cell line ( As3 ), which in addition to its mouse genome contains several rat chromosomes, expresses rat specific enzyme variants and produces large primarily undifferentiated tumors, with some hepatoma characteristics in athymic nude mice. To reveal the in vivo developmental potential of these cells and to determine whether, under different experimental conditions, they are capable of participating in tissue differentiation, the As3 cells were injected into mouse blastocysts from the C57BL/6 strain. The experimental blastocysts were then transferred into the uteri of pseudopregnant foster mothers to allow further development. From a total of 212 blastocysts transplanted, 61 fetuses developed and were analysed for As3 contributions between the 10th and 18th day of gestation. Four fetuses at day 18 showed hybrid cell participation in their livers and a few organs of only endo-mesodermal origin, as judged from the presence of rat-specific enzyme variants. The enzymes were organ-specifically expressed (e.g., lactate dehydrogenase) or appeared newly during in situ differentiation while being absent in the original hybrid cells (e.g., glycerol-3-phosphate dehydrogenase). During short in vitro culture of the chimaeric organs, it was possible to select for the hybrid cells which reverted to an enzyme pattern simiar to but not identical with the As3 cell line and different to that observed in situ.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Tissue preference and differentiation of malignant rat x mouse hybrid cells in chimaeric mouse fetuses. 718 53

P388 mouse leukemia lines, one sensitive (P388/S) and the other resistance (P388/R) to vincristine (VCR), cultured in vitro, were hybridized with polyethylene glycol (PEG). A thymidine kinase-deficient mutant (TK-) was isolated from the sensitive line, and a hypoxanthine-guanine phosphoribosyltransferase-deficient mutant (HPRT-) from the resistant line. The hybrid line grows slower than the mutants. The modal chromosome numbers are: TK- = 38, HPRT- = 40, hybrid = 69 (72). The TK- cells contain a large metacentric marker which is missing from the HPRT- cells. Hybrid cells are as resistant to VCR as the P388/R and HPRT- cells.
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PMID:Drug resistance studies on intraspecific hybridomas. 725 34

Mutant T-lymphocytes at the HLA-A locus were isolated using a recently developed flow-cytometric assay either immediately after drawing blood (in vivo mutants) or after X-irradiation in vitro. Mutants were subsequently propagated clonally for cytogenetic and molecular analyses. Among the 38 in vivo mutants, none contained an abnormal chromosome 6 on which the HLA-A locus resides (6p21.3). In contrast, mutants recovered after in vitro irradiation frequently carried abnormalities in the short arm of chromosome 6: 11/19 and 5/5 independent mutants for the 1-Gy and 2-Gy groups, respectively. Characteristically, the majority of the aberrations were deletions, commonly involving chromosome 6p21-p23. Because chromosomal deletions involving the selected gene are rare among radiation-induced mutants at the hypoxanthine phosphoribosyltransferase (chromosome X) and thymidine kinase (chromosome 17) loci, the HLA-A locus can be considered as highly prone to chromosomal deletions after radiation exposure. It is generally believed that ionizing radiation randomly breaks DNA, and the higher frequency of chromosomal deletions at the HLA-A locus is unlikely to be due to preferential induction but more likely to the better survivability of the deletion-bearing mutants. Consequently, the results suggest that the human genome is quite heterogeneous with regard to the survivability of cells bearing a chromosomal deletion including different loci.
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PMID:Frequent involvement of visible chromosomal deletion in X-ray-induced mutants at the HLA-A locus in human T-lymphocytes. 751 34

Rapamycin (RAP) disrupts signaling events implicated in cytokine-dependent proliferation of lymphocytes and other cells. This action is known to involve the formation of molecular complexes between the drug and intracellular binding proteins, termed FKBPs. However, the biochemical target(s) for the effector RAP-FKBP complexes remain uncharacterized. As an approach to explore the mechanism of action of RAP, we have isolated three independent sets of somatic mutants of the YAC-1 murine T cell line with markedly reduced sensitivity to the drug's inhibitory effects on proliferation and on IL-1-induced IFN-gamma production. These mutants were still fully sensitive to FK-506, an immunosuppressant structurally related to RAP whose mode of action also involves an interaction with FKBPs. Furthermore, the 12-kDa FKBP, FKBP12, was detectable in immunoblots from cytosolic extracts and eluates from RAP-affinity matrix in the mutants as in wild-type cells, suggesting that the resistance to RAP in the mutants is not due to a lack of FKBP12 expression. Cell fusion experiments were conducted to further define the nature of the alterations imparting RAP resistance in these mutants. Clones deficient in either thymidine kinase or hypoxanthine-guanine phosphoribosyltransferase, suitable as fusion partners for aminopterin-based selection of hybrids were generated from the wild-type or mutant lines. In most instances, the hybrids derived from the fusion between RAP-sensitive clones and RAP-resistant clones exhibited a RAP-resistant phenotype. Similar results were obtained with hybrids between RAP-resistant YAC-1 clones and the RAP-sensitive EL-4 cell line. Therefore, the mutations that confer resistance to RAP in the present system are dominant. Altogether, our observations are consistent with a model where pharmacologically relevant targets for the RAP-FKBP complex, rather than FKBP, might be altered in the mutants such that the inactivation of these targets by the effector complex is prevented.
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PMID:Dominant mutations confer resistance to the immunosuppressant, rapamycin, in variants of a T cell lymphoma. 753 11

The potent mouse skin tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) was examined for its mutagenic and recombinagenic activity at the heterozygous thymidine kinase (tk +/-) locus and the hemizygous hypoxanthine phosphoribosyltransferase (hprt +/0) locus in the TK6 human lymphoblastoid cell line. TPA at concentrations of 0.01-1.0 micrograms/ml induced a low frequency of tk mutants showing the slow growth phenotype in a dose-dependent manner, but few normal growth tk mutants or hprt mutants. Concentrations of 1.0-10 micrograms/ml TPA induced all three types of mutants. The molecular structure of tk mutants arising spontaneously or induced by 1.0 and 10 micrograms/ml TPA was investigated by Southern hybridization with a human tk cDNA probe: 86% of all mutants arising after incubation with 10 micrograms/ml TPA lost the entire active tk allele, resulting in loss of heterozygosity (LOH), while 71% of spontaneously arising mutants showed LOH. Densitometric analysis indicated that the majority of LOH mutants induced by TPA were homozygous at the tk locus (retained two copies of the mutant allele), consistent with the occurrence of interchromosomal homologous recombination. These results support the hypothesis that tumor promoters such as TPA may increase the rate of chromosomal mitotic recombination and hence facilitate the segregation of recessive mutations. TPA may thus induce a type of genetic instability during the process of tumor promotion that involves enhanced recombinagenic activity.
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PMID:Recombinagenic activity of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate in human lymphoblastoid cells. 763 95

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), a heterocyclic aromatic amine that is formed in abundance in cooked meats, has been found to be mutagenic in human lymphoblastoid TK6 cells at the thymidine kinase and hypoxanthine-guanine phosphoribosyl transferase (hgprt) loci. The mutations induced at the hgprt locus have been analysed. Of the mutations that have been identified, 60% were found in the coding sequence of the gene. Forty percent were in the introns which resulted in aberrant splicing and consequently, leading to exon losses in the mature hprt mRNA. Mutations resulting in a loss of exonIII appeared most frequently followed by losses of exonVI, exonVIII and partial loss of exonIX. All identified mutations occurred at GC base pairs, consistent with the adducts of PhIP that have been found previously and suggesting that the N-(deoxyguanosin-8-yl)-2-amino-1-methyl-6-phenylimidazo[4,5- b]pyridine, (dG-C8-PhIP) adduct may be the premutagenic lesion. Most of the mutations are GC-->TA transversions except for a cluster of single base pair deletions in a run of guanines. There appears to be strand bias in the induction of mutations with 85% of the mutations on the non-transcribed strand. Although the number of mutations analysed is limited (54 mutants), there are several sites (positions 166 and 207 of the coding sequence, and the splice acceptor site of exonIII) which are overrepresented. There is a preference for a 5' purine but not a strong bias for 3' A as has been found for other mutagens that form a premutagenic lesion at G. Triplet analysis shows that the triplets, 5'GGA3' and 5'AGG3', where the middle base is mutated are preferred.
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PMID:Analysis of mutations induced by 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human lymphoblastoid cells. 772 48

Chromosomal aberrations in human gliomas are principally numerical. In tumours of low malignancy, karyotypes are frequently normal, but occasionally an excess of chromosome 7 and a loss of sex chromosome are observed. In highly malignant tumours, the most frequent aberrations are gain of chromosome 7, loss of chromosome 10 and less frequently losses or deletions of chromosomes 9, 22, 6, 13 and 14 or gains of chromosomes 19 and 20. To understand the meaning of these chromosome imbalances, the relationships between chromosome abnormalities and metabolic disturbances were studied. The losses or deletions observed affected principally chromosomes carrying genes encoding enzymes involved in purine metabolism. The activities of ten enzymes were measured: adenosine kinase, adenine phosphoribosyltransferase, adenylate kinase, methylthioadenosine phosphorylase, hypoxanthine phosphoribosyltransferase, adenylosuccinate lyase, inosine monophosphate dehydrogenase, adenosine deaminase, nucleoside phosphorylase and adenosine monophosphate deaminase. In parallel, two enzymes involved in pyrimidine metabolism, thymidine kinase and thymidylate synthase (TS), were studied. The activities of all these enzymes were measured on samples from 30 human primary glial tumours with low or high malignancy, six xenografted tumours at different passages, four portions of normal brain tissue and four non-glial brain neoplasms. As suggested by cytogenetic data, the enzymatic results showed a relatively low activity of purine metabolism in glial tumours when compared with normal brain and non-glial brain neoplasms. Considering the two enzymes involved in pyrimidine metabolism, only TS had higher activity in glial tumours of high malignancy than in normal brain. In comparison with normal brain, the balance between salvage and de novo pathways changes in gliomas, and even more in grafted tumours, in favour of de novo synthesis. The relation between chromosomes and metabolic imbalances does not correspond to a simple gene dosage effect in these tumours. These data suggest that the decrease of adenosine metabolism occurs before chromosomal aberrations appear, since it is observed in tumours of low malignancy when most karyotypes are still normal, and that the de novo pathway increases with tumour progression.
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PMID:Purine and pyrimidine metabolism in human gliomas: relation to chromosomal aberrations. 805 68

5-(Hydroxymethyl)furfural (HMF), one of the major intermediate products in the Maillard reaction, is present in a wide variety of foods. This aldehyde is formed as a decomposition product of glucose and fructose in foodstuffs subject to cooking or heat sterilization. It has been found to possess mutagenic and DNA strand-breaking activity. However, the mechanisms by which HMF exerts its genotoxicity remain unclear. The present study was undertaken to determine if HMF could be metabolically activated via esterification of the allylic hydroxyl group. In support of this concept, the chemically synthesized sulfuric acid ester,5-[(sulfooxy)-methyl]furfural (SMF), exhibited direct mutagenicity at both thymidine kinase and hypoxanthine-guanine phosphoribosyltransferase loci in human lymphoblasts. This reactive ester also induced 8-azaguanine-resistant mutants in Salmonella typhimurium TM677 in a dose-dependent manner. The intrinsic mutagenicity of SMF was enhanced by addition of extra chloride ion to the assay medium. The model allylic derivative, 5-(chloromethyl)furfural, was also mutagenic and cytotoxic in bacteria, but much more active than the sulfuric acid ester in this regard. In contrast to (sulfooxy)methyl and chloromethyl derivatives of HMF,2-[(sulfooxy)-methyl]- and 2-(chloromethyl)furans which lack the aldehyde functionality did not exhibit significant mutagenicity. Rodent hepatic cytosols contained sulfotransferase activity responsible for the formation of the reactive allylic sulfuric acid ester metabolite from HMF.
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PMID:Activation of the Maillard reaction product 5-(hydroxymethyl)furfural to strong mutagens via allylic sulfonation and chlorination. 807 62

Guidelines have been proposed to assess the potential of chemicals to affect human health. Written into these guidelines is the requirement that information be submitted on mutagenic activity. Although regulatory agencies accept mutagenicity data from both the hprt and tk loci in mammalian cells, many studies suggest that the L5178Y mouse lymphoma assay at the thymidine kinase locus is likely to detect a greater spectrum of mutagenic lesions. Thus, there is increasing emphasis being placed on this assay in many proposed and published guidelines. The L5178Y mouse lymphoma suspension protocol produces both small and large colonies which are the products of mutants growing at different rates. There is a reduction in the proportion of slowly growing mutants with respect to the total population of cells when expression is carried out in suspension. This potentially leads to quantitatively inaccurate assessments of the mutagenic activity of chemicals. Therefore an in situ procedure was developed that more accurately assesses the mutagenic activity of chemicals by maximizing the detection of small colonies. Many guidelines recommend tests that assess the clastogenic activity of chemicals. Some regulatory agencies accept data from the mouse lymphoma mutation assay to detect clastogens if the protocol is optimized for the detection of small colonies or if colony sizing data are submitted. The conventional suspension assay protocol is not sufficiently validated for this purpose. The in situ protocol has greater potential to meet these requirements.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:The use of L5178Y mouse lymphoma cells to assess the mutagenic, clastogenic and aneugenic properties of chemicals. 854 53

In order to define further the effects of differences in recombinational proficiency on cell survival and mutation by ionizing radiation, we exposed the syngenic cell lines TK6 and WTK1 to continuous low dose-rate gamma-irradiation. We previously demonstrated that acute X-ray exposure results in lower survival and lower mutation induction at both the thymidine kinase (tk) and the hypoxanthine-guanine phosphoribosyltransferase (hprt) loci in TK6 cells compared with WTK1 cells. These differences were attributed in part to reduced levels of recombination in the TK6 line relative to WTK1. Using a low dose rate 137Cs irradiator, we exposed asynchronous growing populations of these cells to gamma-rays at 14.3, 6.7 and 2.7 cGy/h. Both cell lines exhibited a dose-rate effect on survival. Compared with acute doses, the low dose-rates also protected against mutation induction at the hrpt locus in WTK1, but protection was inversely related to dose-rate. There was also a slight inverse dose-rate effect in TK6, with mutation induction at the lowest dose-rate exceeding that at acute exposures.
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PMID:Inverse dose-rate effect for mutation induction by gamma-rays in human lymphoblasts. 864 43


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