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)

Interleukin-8 (IL-8) is a chemokine for neutrophils and an angiogenic factor. Human tumors that express IL-8 may exhibit intense neutrophil infiltration and increased vascularization. Mutatect cells are a murine fibrosarcoma that can be grown as subcutaneous tumors in syngeneic C57BL/6 mice. Since neutrophils are a source of cytotoxic and genotoxic species, we constructed Mutatect cell lines that constitutively express human IL-8 to explore the involvement of neutrophils in tumor biology and genetic instability. An IL-8/neo expression plasmid was stably transfected into Mutatect MC17-51 cells and clone MIL-4 was isolated. Tumors initiated with 5x10(5) MIL-4 cells grew very slowly compared with tumors from pure MC17-51 cells or from 0.5 to 4x10(5) MIL-4 cells mixed with 5x10(5) MC17-51 cells. Over 95% of cells recovered from slow-growing pure MIL-4 tumors lost the transgene as measured by loss of (i) resistance to G418, (ii) expression of IL-8 protein and (iii) IL-8-specific DNA sequences. When tumors from mixed cell types were examined, loss of the transgene did not occur; rather, IL-8 producing cells appeared to have some growth advantage. The neutrophil content of tumors (as measured by myeloperoxidase) was directly proportional to the level of IL-8 expressed at the time tumors were excised. As reported earlier, the frequency of mutations at the hypoxanthine phosphoribosyltransferase locus was also directly proportional to neutrophil content. To explain some of these biological findings, we postulate that early in development of pure MIL-4 tumors, genotoxic/cytotoxic neutrophils are attracted by IL-8, which in turn leads to loss of the transgene and to localized cytotoxicity of IL-8 producing cells. In mixed tumors, where the initial IL-8 concentration may be lower, tumors might become established more readily because fewer neutrophils may be attracted. This relatively simple experimental paradigm has revealed some of the complex biological changes that can occur as a result of IL-8 in tumors.
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PMID:Constitutive expression of interleukin-8 by Mutatect cells markedly affects their tumor biology. 1118 44

Neutrophils represent a potential source of genotoxic reactive oxygen and nitrogen species in the tumor microenvironment. Using Mutatect cell lines, which can form subcutaneous tumors in syngeneic C57BL/6 mice, we have previously established that the number of spontaneously infiltrating neutrophils correlates with the number of mutations at the hypoxanthine phosphoribosyltransferase (Hprt) locus. We now describe the properties of four lines that express different levels of the neutrophil chemokine, interleukin-8 (IL-8), from a tetracycline (TET)-responsive promoter. In a series involving 45 animals, IL-8-expressing lines produced tumors with a higher neutrophil content than the control line. Analysis of the 45 tumors revealed that the neutrophil level again strongly correlated with hprt mutant frequency (MF) (P<.0001, r=0.88). Administration of TET was effective in lowering the neutrophil content of low IL-8-expressing tumors, but not high IL-8-expressing tumors. Although the IL-8 transgene was stable in all lines in vitro, high IL-8-expressing lines completely lost the transgene in vivo whereas low IL-8-expressing lines showed no evidence of transgene instability. These results provide further evidence, based on the study of an endogenous gene (hprt) and an IL-8 transgene, that neutrophils may contribute to genetic instability in tumors.
Neoplasia
PMID:Expression of interleukin-8 promotes neutrophil infiltration and genetic instability in mutatect tumors. 1122 49

In a previous study, we found that treating transgenic Big Blue rats with the hepatocarcinogen N-hydroxy-2-acetylaminofluorene (N-OH-AAF) produced the same major DNA adduct in the target liver and the nontarget spleen lymphocytes and bone marrow cells, induced lacI mutants in the liver, and induced much lower frequencies of lacI and hprt mutants in spleen lymphocytes. In the present study, sequence analysis was conducted on lacI DNA and hprt cDNA from the mutants, to determine the mutational specificity of N-OH-AAF in the rat. All the mutation spectra from N-OH-AAF-treated rats differed significantly from corresponding mutation profiles from untreated animals (P = 0.02 to P < 0.0001). Although there were similarities among the mutational patterns derived from N-OH-AAF-treated rats (e.g., G:C --> T:A transversion was the most common mutation in all mutation sets), there were significant differences in the patterns of basepair substitution and frameshift mutation between the liver and spleen lymphocyte lacI mutants (P = 0.02) and between the spleen lymphocyte lacI and hprt mutants (P = 0.04). Also, multiplex PCR analysis of genomic DNA from the hprt mutants indicated that 12% of mutants from treated rats had major deletions in the hprt gene; no corresponding incidence of large deletions was evident among lacI mutations. All the mutation profiles reflect the general mutational specificity of the major DNA adduct formed by N-OH-AAF. The differences between N-OH-AAF mutation in the endogenous gene and transgene can be partially explained by the structures of the two genes. The tissue-specificity of the mutation spectra may contribute to targeting tumor formation to the liver. Environ. Mol. Mutagen. 37:203-214, 2001. Published 2001 Wiley-Liss, Inc.
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PMID:Gene- and tissue-specificity of mutation in Big Blue rats treated with the hepatocarcinogen N-hydroxy-2-acetylaminofluorene. 1131 38

Genetic or epigenetic inactivation of one of the DNA mismatch repair (MMR) genes in tumor precursor cells causes a profound mutator phenotype, known as the microsatellite mutator phenotype (MMP). This mutator phenotype induces mutations not only in cancer genes that drive tumorigenesis but also in other DNA repair genes. The functional significance of these successive DNA repair gene mutations, however, has not been substantiated. Here we show that the concomitant inactivation of two DNA MMR genes (hMLH1 and hMSH6) increases the mutator phenotype. We isolated cell clones of the SW48 MMP-positive cell line with either active or inactive hMSH6. All of these clones lacked expression of hMLH1 because of promoter hypermethylation. Compared with inactivation of hMLH1 alone, the additional inactivation of hMSH6 produced a higher mutation rate and a different spectrum of mutations in the endogenous hprt gene. These results confirm our model that the mutator phenotype can increase during tumorigenesis by the consecutive inactivation of different members of the DNA MMR system. Thus, a stronger mutator phenotype accelerates the accumulation of mutations in target cancer genes, which, in turn, speeds up tumor progression. The results of this study also have significant impact on our understanding of the mechanism of DNA MMR.
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PMID:Functional significance of concomitant inactivation of hMLH1 and hMSH6 in tumor cells of the microsatellite mutator phenotype. 1174 74

An important limitation of standard transgenic assays is that multiple copies of the transgene are inserted randomly into the mouse genome, resulting in line-to-line variation in expression. One way to control for these variables is to target a single copy of the transgene to a defined locus of the mouse genome by homologous recombination. In the present study, we have used such an approach to target the promoters of 2 different genes, namely von Willebrand factor (VWF) and Flt-1, to the hypoxanthine phosphoribosyltransferase (Hprt) gene locus. Consistent with previous findings in standard transgenic animals, we report that the VWF promoter contains information for expression in a subset of endothelial cells in the heart, skeletal muscle, and brain. In contrast, the Flt-1 promoter directs expression in all vascular beds except for the liver. The Flt-1 transgene was active in the endothelium of tumor xenografts, whereas the VWF promoter was not. Under in vitro conditions, conditioned medium from tumor cells resulted in a significant up-regulation of Flt-1 mRNA and promoter activity, but no change in VWF levels. Taken together, these results suggest that (1) Hprt locus targeting is a valuable tool for studying vascular bed-specific gene regulation, (2) the VWF and Flt-1 promoters are regulated by distinct transcriptional mechanisms in the intact endothelium, and (3) tumor angiogenesis results in the differential activation of endothelial cell-specific promoters.
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PMID:Differential regulation of the von Willebrand factor and Flt-1 promoters in the endothelium of hypoxanthine phosphoribosyltransferase-targeted mice. 1239 68

6-Mercaptopurine (6MP) and 6-thioguanine (6TG) are analogs of the natural purines: hypoxanthine and guanine. Both mercaptopurine and thioguanine are substrates for hypoxanthine-guanine phosphoribosyltransferase and are converted into the ribonucleotides 6-thioguanosine monophosphate (6-thioGMP) and 6-thioinosine monophosphate (T-IMP) respectively. The accumulation of these monophosphates inhibits several vital metabolic reactions. Today, these thiopurine bases remain valuable agents for the induction and maintenance of remissions in patients with myelocytic and acute lymphocytic leukemia. Despite their proved clinical importance, 6MP and 6TG have certain therapeutic disadvantages, which have continued to stimulate the search for purine derivatives enhancing therapeutic efficacy. Considerable efforts have been made to prepare other novel mercaptopurine and thioguanine analogs and their nucleosides to improve the antitumor efficacy. The effectiveness of these thiopurines against certain tumor cell lines suggested that some of these mercaptopurine analogs and their nucleosides would be worthy of consideration in order to determine whether they exert a more selective effect against neoplastic cells than against normal cells or they might be useful in patients whose disease has become resistant to 6MP or 6TG. This review will focus on mercaptopurine analogs and their nucleosides as antimetabolite agents.
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PMID:Thioguanine, mercaptopurine: their analogs and nucleosides as antimetabolites. 1452 46

A multiplex PCR procedure for analysis of genomic DNA mutations in the mouse hypoxanthine-guanine phosphoribosyltransferase (Hprt) gene was developed and then used with other established methods for the coincident identification of large- and small-scale genetic alterations in the Hprt gene of mutant T-cell isolates propagated from sham- and 1,3-butadiene (BD)-exposed mice and rats. The spectra data for RT-PCR/cDNA analysis and multiplex PCR of genomic DNA from Hprt mutants were combined, and statistical analyses of the mutant fractions for the classes of mutations identified in control versus exposed animals were conducted. Under the assumption that the mutant fractions are distributed as Poisson variates, BD exposure of mice significantly increased the frequencies of (1) nearly all types of base substitutions; (2) single-base deletions and insertions; and (3) all subcategories of deletions. Significantly elevated fractions of G:C-->C:G and A:T-->T:A transversions in the Hprt gene of BD-exposed mice were consistent with the occurrence of these substitutions as the predominant ras gene mutations in multiple tumor types increased in incidence in carcinogenicity studies of BD in mice. BD exposure of rats produced significant increases in (1) base substitutions only at A:T base pairs; (2) single-base insertions; (3) complex mutations; and (4) deletions (mainly 5' partial and complete gene deletions). Future coincident analyses of large- and small-scale mutations in rodents exposed to specific BD metabolites should help identify species differences in the sources of deletion mutations and other types of mutations induced by BD exposures in mice versus rats.
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PMID:Characterization of Hprt mutations in cDNA and genomic DNA of T-cell mutants from control and 1,3-butadiene-exposed male B6C3F1 mice and F344 rats. 1499 48

Vitamin E in foodstuffs is a mixture of tocopherols. In mouse Mutatect tumors, a model designed to detect DNA mutations, the hypoxanthine phosphoribosyltransferase (Hprt) gene mutation frequency is associated with the number of tumor-infiltrating neutrophils and both are markedly decreased in mice fed high levels of alpha-tocopherol. Dietary alpha-tocopherol is also associated with a decrease in neutrophil-associated loss of an interleukin 8 (IL-8)-expressing transgene in this tumor model. We examined Hprt gene mutation frequency (expressed as the number of 6-thioguanine-resistant colonies per 10(5) clonable tumor cells), IL-8 transgene loss, and myeloperoxidase activity (an indirect measure of neutrophil number) in tumors from Mutatect mice fed diets supplemented with various concentrations of D-alpha-tocopherol acetate and/or D-gamma-tocopherol acetate or neither tocopherol for 4 weeks. Hprt gene mutation frequency and myeloperoxidase activity were statistically significantly lower in tumor cells from mice fed alpha-tocopherol at 50 or 100 mg/kg body weight per day than in tumor cells from mice fed 0 mg/kg body weight per day alpha-tocopherol (P<.001 for each comparison). IL-8 transgene loss occurred in 28 of 28 tumors (100%; 95% confidence interval [CI] = 86% to 100%) from mice fed alpha-tocopherol at 50 mg or less/kg body weight per day and seven of 18 tumors (39%; 95% CI = 24% to 54%) from mice fed 100 mg/kg body weight per day (P<.001, Fisher's exact test, referent groups [pooled] 0, 25, and 50 mg/kg). gamma-Tocopherol had no detectable effect on any of the three endpoints. Thus, dietary alpha-tocopherol decreases two forms of genetic instability in a dose-dependent manner in this experimental tumor model.
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PMID:Dose-dependent effects of dietary alpha- and gamma-tocopherols on genetic instability in mouse Mutatect tumors. 1515 Mar 8

Titanium dioxide is frequently used in the production of paints, paper, plastics, welding rod-coating material, and cosmetics, because of its low toxicity. However, recent studies have shown that nano-sized or ultrafine TiO(2) (UF-TiO(2)) (<100 nm in diameter) can generate pulmonary fibrosis and lung tumor in rats. Cytotoxicity induced by UF-TiO(2) in rat lung alveolar macrophages was also observed. This generates great concern about the possible adverse effects of UF-TiO(2) for humans. The cytotoxicity and genotoxicity of UF-TiO(2) were investigated using the methyl tetrazolium cytotoxicity (MTT) assay, the population growth assay, the apoptosis assay by flow cytometry, the cytokinesis block micronucleus (CBMN) assay, the comet assay, and the hypoxanthine-guanine phosphoribosyltransferase (HPRT) gene mutation assay. WIL2-NS cells were incubated for 6, 24 and 48 h with 0, 26, 65 and 130 microg/ml UF-TiO(2). Significant decreases in viability were seen in the MTT assay at higher doses; for example, 61, 7 and 2% relative viability at 130 microg/ml for 6, 24 and 48-h exposure (P<0.01). A dose-dependent relationship was observed, while a time-dependent relationship was seen only at the highest dose (130 microg/ml) after exposure for 24 and 48 h. Treatment with 130 microg/ml UF-TiO(2) induced approximately 2.5-fold increases in the frequency of micronucleated binucleated cells (P<0.01). In addition, a significant reduction in the cytokinesis block proliferation index was observed by the CBMN assay (P<0.05). In the comet assay, treatment with 65 microg/ml UF-TiO(2) induced approximately 5-fold increases in olive tail moment (P<0.05). In the HPRT mutation assay, treatment with 130 microg/ml UF-TiO(2) induced approximately 2.5-fold increases in the mutation frequency (P<0.05). The results of this study indicate that UF-TiO(2) can cause genotoxicity and cytotoxicity in cultured human cells.
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PMID:Cyto- and genotoxicity of ultrafine TiO2 particles in cultured human lymphoblastoid cells. 1770 89

Enhanced linear growth, hyperplasia, and tumorigenesis are well-known characteristics of "viable yellow" agouti A(vy)/- mice (Wolff GL, Roberts DW, Mountjoy KG. Physiol Genomics 1:151-163, 1999); however, the functional basis for this aspect of the phenotype is unknown. In the present study, we ascertained whether agouti signaling protein (ASIP) levels in A(vy)/a or a/a livers are associated with hepatocyte proliferation as a possible factor in promotion of hepatocellular tumor formation. Proliferating cell nuclear antigen (PCNA) assays and quantitative real-time reverse transcriptase polymerase chain reaction assays were performed on liver samples from mottled yellow A(vy)/a, pseudoagouti A(vy)/a, and black a/a VY mice to determine mitotic indices and expression levels of A(vy )and a in relation to the expression level of the housekeeping gene hprt. We found that ASIP levels were approximately 100-fold higher in yellow than in pseudoagouti or black mice and that the proportion of PCNA-positive hepatocytes was greater (P < 0.001) in yellow than in pseudoagouti or black mice.
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PMID:Agouti signaling protein stimulates cell division in "viable yellow" (A(vy)/a) mouse liver. 1795 45


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