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 effectiveness of purines and purine analogues as inducers of erythroid differentiation in cultured murine erythroleukemia cells has been investigated. These cell lines have previously been shown to differentiate in vitro in response to dimethylsulfoxide (DMSO) and a number of other polar solvents. Two purine analogues, 6-thioguanine and 6-mercaptopurine, as well as the naturally occuring purine, purine, hypoxanthine, are shown to be extremely potent inducers. 6-Thioguanine is effective at a concentration of 0.06 mM, 750 fold lower than the DMSO concentration required for equivalent induction. 6-Mercaptopurine and hypoxanthine are effective inducers at a concentration of approximately 2 mM. Accumulation of globin mRNA was monitored during induction with purine inducers and shown to be similar in amount to globin mRNA levels reached in DMSO-induced cultures. Induction of differentiation by all three compounds follows a similar time course to induction with DMSO. All three compounds are potent inducers of HGPRT (hypoxanthine-guanine phosphoribosyltransferase)-negative cell lines; hence incorporation of purines into DNA is not required for induction of differentiation. Comparison of these compounds with other purines and purine analogues suggests a high degree of specificity in their interaction with a cellular target.
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PMID:Induction of erythroid differentiation in vitro by purines and purine analogues. 97 85

6-Thioguanine (6-TG)-induced differentiation of hypoxanthine phosphoribosyltransferase (IMP: pyrophosphate phosphoribosyltransferase, EC 2.4.2.8)-deficient HL-60 cells is characterized by 2 days of growth, after which morphological differentiation proceeds. Addition of the tRNA wobble base queuine, in the presence of 6-TG, maintains the proliferative capability of the cells. The ability of 6-TG to induce differentiation correlates with c-myc mRNA down-regulation, but queuine has no effect on this parameter. Treatment with 6-TG for 2-3 days commits HL-60 cells to granulocytic differentiation, and, once committed, these cells do not respond to the monocytic inducer phorbol 12-myristate 13-acetate. Nonetheless, when cells are treated with queuine and 6-TG, they maintain the promyelocytic morphology and are capable of being induced down the monocytic pathway by phorbol 12-myristate 13-acetate as indicated by stabilization of c-fms mRNA and cell adherence. In the absence of queuine, phorbol 12-myristate 13-acetate is incapable of inducing monocytic markers in the 6-TG-treated cells. The data presented indicate that 6-TG-induced differentiation of HL-60 cells is a tRNA-facilitated event and that the tRNA wobble base queuine is capable of maintaining both the proliferative and pluripotent potential of the cells.
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PMID:Queuine, a tRNA anticodon wobble base, maintains the proliferative and pluripotent potential of HL-60 cells in the presence of the differentiating agent 6-thioguanine. 198 36

Thioguanine-resistant primary clones were grown from single cell suspensions obtained from dog and human kidneys by enzymatic digestion. In medium containing a relatively high concentration (10 micrograms/ml) of thioguanine, thioguanine-resistant primary clones arose from each source at frequencies ranging from 10(-4) to 10(-5). A reduction in total hypoxanthine uptake was found in the thioguanine-resistant primary clones which had developed in thioguanine medium, consistent with a reduction in hypoxanthine phosphoribosyltransferase activity. When these thioguanine-resistant primary clones were subsequently grown in the absence of thioguanine and assayed for the thioguanine-resistant phenotype and hypoxanthine phosphoribosyltransferase activity, it was found that most were now thioguanine-sensitive and yielded cell-free extracts with substantial amounts of hypoxanthine phosphoribosyltransferase activity. In contrast, thioguanine-resistant human clones grown continuously in the presence of thioguanine yielded cell-free extracts with little or no detectable hypoxanthine phosphoribosyltransferase activity. Southern blot analysis demonstrated no structural alterations in the hypoxanthine phosphoribosyltransferase gene in thioguanine-resistant primary human kidney clones. These results suggest that a novel mechanism(s) for thioguanine resistance and the control of hypoxanthine phosphoribosyltransferase expression may occur in dog and human kidney cells.
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PMID:A novel class of unstable 6-thioguanine-resistant cells from dog and human kidneys. 323 32

Treatment of hypoxanthine-guanine phosphoribosyltransferase (HGPRT)-deficient human promyelocytic leukemia (HL-60) cells with 6-thioguanine results in growth inhibition and cell differentiation. 6-Thioguanine is a substrate for the tRNA modification enzyme tRNA-guanine ribosyltransferase, which normally catalyzes the exchange of queuine for guanine in position 1 of the anticodon of tRNAs for asparagine, aspartic acid, histidine, and tyrosine. During the early stages of HGPRT-deficient HL-60 cell differentiation induced by 6-thioguanine, there was a transient decrease in the queuine content of tRNA, and changes in the isoacceptor profiles of tRNA(His) indicate that 6-thioguanine was incorporated into the tRNA in place of queuine. Reversing this structural change in the tRNA anticodon by addition of excess exogenous queuine reversed the 6-thioguanine-induced growth inhibition and differentiation. Similar results were obtained when 8-azaguanine (another inhibitor of queuine modification of tRNA that can be incorporated into the anticodon) replaced 6-thioguanine as the inducing agent. The data suggest a primary role for the change in queuine modification of tRNA in mediating the differentiation of HGPRT-deficient HL-60 cells induced by guanine analogs.
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PMID:Guanine analog-induced differentiation of human promyelocytic leukemia cells and changes in queuine modification of tRNA. 347 81

The enzyme xanthine-guanine phosphoribosyltransferase from Escherichia coli cells harboring the plasmid pSV2gpt has been purified 30-fold to near homogeneity by single-step GMP-agarose affinity chromatography. It has a Km value of 2.5, 42 and 182 microM for the substrates guanine, xanthine and hypoxanthine, respectively, with guanine being the most preferred substrate. The enzyme exhibits a Km value of 38.5 microM for PRib-PP with guanine as second substrate and of 100 microM when xanthine is used as the second substrate. It is markedly inhibited by 6-thioguanine, GMP and to a lesser extent by some other purine analogues. Thioguanine has been found to be the most potent inhibitor. The subunit molecular weight of xanthine-guanine phosphoribosyltransferase was determined to be 19 000. The in situ activity assay on a nondenaturing polyacrylamide gel electrophoresis gel has indicated that a second E. coli phosphoribosyltransferase preferentially uses hypoxanthine as opposed to guanine as a substrate, and it does not use xanthine.
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PMID:Purification and characterization of Escherichia coli xanthine-guanine phosphoribosyltransferase produced by plasmid pSV2gpt. 388 14

Most drugs available for cancer chemotherapy exert their effects through cytodestruction. Although significant advances have been attained with these cytotoxic agents in several malignant diseases, response is often accompanied by significant morbidity and many common malignant tumours respond poorly to existing cytotoxic therapy. Development of chemotherapeutic agents with non-cytodestructive actions appears desirable. Considerable evidence exists which indicates that (a) the malignant state is not irreversible and represents a disease of altered maturation, and (b) some experimental tumour systems can be induced by chemical agents to differentiate to mature end-stage cells with no proliferative potential. Thus, it is conceivable that therapeutic agents can be developed which convert cancer cells to benign forms. To study the phenomenon of blocked maturation, squamous carcinoma SqCC/Y1 cells were employed in culture. Using this system it was possible to demonstrate that physiological levels of retinoic acid and epidermal growth factor were capable of preventing the differentiation of these malignant keratinocytes into a mature tissue-like structure. The terminal differentiation caused by certain antineoplastic agents was investigated in HL-60 promyelocytic leukaemia cells to provide information on the mechanism by which chemotherapeutic agents induce cells to by-pass a maturation block. The anthracyclines aclacinomycin A and marcellomycin were potent inhibitors of N-glycosidically linked glycoprotein biosynthesis and transferrin receptor activity, and active inducers of maturation; temporal studies suggested that the biochemical effects were associated with the differentiation process. 6-Thioguanine produced cytotoxicity in parental cells by forming analog nucleotide. In hypoxanthine-guanine phosphoribosyltransferase negative HL-60 cells the 6-thiopurine initiated maturation; this action was due to the free base (and possibly the deoxyribonucleoside), a finding which separated termination of proliferation due to cytotoxicity from that caused by maturation.
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PMID:The 1985 Walter Hubert lecture. Malignant cell differentiation as a potential therapeutic approach. 389 54

Hypoxanthine phosphoribosyltransferase-deficient (HPRT-) F9-derived teratocarcinoma stem cells carrying an SV40 genome (12-16TG cells) were fused with Mus caroli (M. car.) spleen cells, and a stem cell hybrid containing reduced numbers of M. car. chromosomes was isolated (BC6 stem cell). The BC6 cells containing an active X chromosome from each parental cell were induced to differentiate in retinoic acid, and differentiated clones were isolated. Most differentiated clones retained both parental X chromosomes in active form. One differentiated clone, BC6-13, grew equally well in hypoxanthine/aminopterin/thymidine (HAT) selective medium (which requires an active M. car. HPRT (E.C.2.4.2.8) locus) or in 6-thioguanine (6TG, which would require either loss or inactivation of the M. car. HPRT locus). Using cDNA probes for HPRT and phosphoglycerate kinase (PGK) (E.C.2.7.2.3) loci and biochemical assays for HPRT and PGK enzymes, it was shown that BC6-13 cells, whether grown in nonselective medium, HAT medium, or 6TG-containing medium, retain the HPRT and PGK genes of both parental cells, but the M. car. forms of HPRT and PGK were inactivated in cells treated with 6TG. 6-Thioguanine seems to act as an inducer, one effect of which is X chromosome inactivation, which seems to be complete and irreversible as early as 24 h after addition of 6TG to BC6-13 cells.
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PMID:Activity of X-linked genes in stem and differentiated Mus musculus X Mus caroli hybrid cells. 654 51

Thioguanine-resistant T lymphoblast populations were selectively amplified using T cell growth factor in the cultures of peripheral blood T cells from four Lesch-Nyhan heterozygotes. Although Lesch-Nyhan T lymphoblasts were all thioguanine-resistant, none of the cultures from 13 control subjects yielded the growth of such defective cell populations. These data provide direct evidence for the existence of a small percentage (5%-40%) of hypoxanthine-guanine phosphoribosyltransferase (HGPRT) deficient T cells in the heterozygotes, but not in normal individuals. Conversely, culture of the T lymphoblasts with azaserine plus hypoxanthine permitted the growth of the other part of the cell population that was enzyme positive. The low percentages of HGPRT-negative cells among T cells in heterozygotes suggest that the presence of this enzyme is beneficial for differentiation of lymphocytes of T cell linkage. Considering the ease and the reliability, culture of the peripheral T cells with thioguanine and T cell growth factor is very likely of practical use for detecting Lesch-Nyhan syndrome carriers among predisposed females.
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PMID:A new method for the detection of Lesch-Nyhan heterozygotes by peripheral blood T cell culture using T cell growth factor. 660 83

Schmid et al. (Cancer Treat. Rep., 60: 23-27, 1976) reported rapid emergence of resistance of L1210 leukemia cells in mice to two schedules of six antimetabolites and much slower development of resistance to a third schedule. Such rapid development of resistance to six drugs presents a striking puzzle, and one whose solution gives some insights into the basis for general emergence of drug resistance. Our approach was to examine the consequences of applying these drugs singly or in pairs and, from the results, to infer interactions in six-drug combinations. 6-Thioguanine (TG) and 6-mercaptopurine are the key drugs since, as shown by Schmid et al., resistance of leukemic cells appeared to six-drug combinations at the same time as did resistance to the purine analogs; sensitivity to the other drugs remained. We demonstrated that cells which emerged were resistant to both of the purine analogs, owing to a deficiency of the activating enzyme hypoxanthine-guanine phosphoribosyltransferase. TG resistance arose in the presence of TG because of an overgrowth of TG-resistance mutants that were present as one cell in 10(4) in the original L1210 population. L1210 cultures were prepared free of TG-resistant mutants. With these cells, TG administered shortly after inoculation was very effective in delaying their death. The cells that finally grew out were still TG sensitive. Simultaneous treatment with all the drugs greatly delayed appearance of TG resistance in vivo and in vitro. Methotrexate alone was responsible for this result, owing to its ability preferentially to kill TG-resistant cells. The other three drugs were not effective in delaying TG resistance. Methotrexate was effective only if it was added daily; one large injection was ineffective. Therefore, TG and methotrexate added daily for 6 days (simultaneous schedule) was the most effective drug regimen tested.
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PMID:Basis of observed resistance of L1210 leukemia in mice: methotrexate, 6-thioguanine, 6-methylmercaptopurine riboside, 6-mercaptopurine, 5-fluorouracil, and 1-beta-D-arabinofuranosylcytosine administered in different combinations. 719 6

Thioguanine resistant CHO cells (HPRT-) were stably cotransfected with pSV2-gpt and pi H3-CD2 vectors using the calcium phosphate coprecipitation technique. The effects of single low doses of ionizing radiation were studied in a CD2+ CHO clone. The CD2+ phenotype responsible for binding sheep erythrocytes and rosette formation, was not affected by X-rays doses in the range 2-6 cGy. However, after 10 cGy of X-irradiation, 50% of the cells lost the CD2+ phenotype. These results suggest that this CD2+ clone might be a very sensitive indicator of very low X-ray doses. The implications of the phenotypic changes, observed after very low doses of irradiation, are discussed.
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PMID:Effects of low-doses of X-rays on the expression of human cell surface CD2 antigen in CD2+ CHO cells. 790 2


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