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)

Treatment of diploid human fibroblasts with stereoisomeric benzo[alpha]pyrene anti and syn diol epoxides has been shown to induce anchorage-independent clones of cells with a dose dependence and frequency [(0.5-12) X 10(-4)] not significantly different from mutations at the hypoxanthine-guanine phosphoribosyltransferase locus [(1-8) X 10(-4)] in these cells. The majority of the anchorage-independent clones that were picked retained their mutagen-induced, anchorage-independent phenotype through at least 20 generations of expansion in monolayer culture. No variant cells showing extended life-span were detected among survivors in any of the mutagen treatment groups (less than 1.6 X 10(-7) frequency). Extensive analysis of a pool of 15 cellular protooncogenes (Ha-ras, Ki-ras, N-ras, mos, fos, fes, myc, abl, sis, myb, erbA, erbB, src, raf, N-myc), using Southern and northern blot analysis, was done to determine whether mutagen-induced rearrangement, amplification or overexpression of any of these genes was responsible for the mutagen-induced, anchorage-independent phenotype. We found no evidence that the genomic arrangement or expression level of any of these genes had been altered, thus indicating that an alternative form of mutation, or an alternative gene not included in this screening was responsible for the mutagen-induced, anchorage-independent phenotype.
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PMID:Benzo[a]pyrene-diol-epoxide-induced anchorage-independence in diploid human fibroblasts. Analysis of cellular protooncogenes. 249 1

The polymerase chain reaction technique is widely employed to amplify short segments of genomic DNA to determine if a specific change has occurred. However, some investigators need to sequence the entire coding region of mammalian genes, e.g., cellular ras genes or the gene encoding hypoxanthine (guanine) phosphoribosyl transferase (HPRT), to determine what specific changes have occurred. To do so, they isolate RNA from large populations of cells, amplify cDNA from the gene of interest, subclone the product, and sequence two or more isolates to determine the common mutation. We have developed a method to simplify this procedure by copying mRNA of the hprt gene directly from the lysate of a clone of mutant diploid human fibroblasts (e.g., 100 cells). We amplified the first and second strand of the cDNA of the gene of interest 10(10)- to 10(11)-fold, obtained 5 to 10 micrograms of DNA in less than 10 h, and sequenced the coding region directly without the need for RNA extraction or DNA template purification. By our method cDNA can be amplified directly from the lysate of just one human cell, but to avoid detecting random changes introduced by the polymerase, we lysed approx. 200 cells from a clone, each containing the identical mutation, amplified the cDNA, and determined the consensus sequence by direct nucleotide sequencing.
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PMID:Amplification and direct nucleotide sequencing of cDNA from the lysate of low numbers of diploid human cells. 268 90

In cancer cells, particularly in leukaemic cells, guanylate biosynthesis is up-regulated as shown by the increased activities of IMP dehydrogenase, the rate-limiting enzyme of de novo GTP biosynthesis, and of the salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HGPRT). In enzyme pattern-targeted chemotherapy, tiazofurin inhibits IMP dehydrogenase activity in cancer cells and allopurinol-induced high serum hypoxanthine levels inhibit HGPRT activity. A triad of responses was observed in the blast cells of patients treated with tiazofurin infusions: chemotherapy, induced differentiation, and down-regulation of c-Ki-ras and c-myc oncogenes. Tiazofurin was synergistic in cytotoxicity and in causing differentiation with ribavirin, retinoic acid, and gemcitabine [corrected]. Induced differentiation plays an important role in the overall impact of antipurine agents.
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PMID:Role of differentiation induction in action of purine antimetabolites. 803 45

Chinese hamster cell clones of independent origin, which were resistant to purine base analogs and induced by the activated c-Ha-ras1 oncogene, were isolated. It was shown that the isolated clones stably retained resistance after cultivation on a medium without an analog, confirming mutational nature of the resistance. Most of the clones are able to grow on the HAT medium, retaining partial activity of the hypoxanthine phosphoribosyltransferase enzyme (HPRT); i.e., they are leaky mutants. Analysis by blot-hybridization did not reveal the presence of human ras-sequences in any of the mutants studied. Evidently, the mutagenic action of the oncogene is not insertional, and resistance is not linked to the stably integrated oncogene. The mutagenic effect of c-Ha-ras1 is likely to be of the "hit-and-run" type.
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PMID:[Characteristics of mutants induced by the c-Ha-ras1 oncogene and the nature of the oncogene's mutagenic action]. 860 5

DNA adducts have been investigated extensively during the past decade. This research has been advanced, in part, by the development of ultrasensitive analytical methods, such as 32P-postlabeling and mass spectrometry, that enable detection of DNA adducts at concentrations as low as one adduct per 10(9) to 10(10) normal nucleotides. Studies of mutations in activated oncogenes such as ras, inactivated tumor suppressor genes such as p53, and surrogate genes such as hprt provide linkage between DNA adducts and carcinogenesis. The measurement of DNA adducts, or molecular dosimetry, has important applications for cancer risk assessment. Cancer risk assessment currently involves estimating the probable effects of carcinogens in humans based on results of animal bioassays. Estimates of risk are then derived from mathematical models that fit data of tumor incidence at the high animal exposures and extrapolate to probable human exposures that may be orders of magnitude lower. Molecular dosimetry could extend the observable range of mechanistic data several orders of magnitude lower than can be achieved in carcinogenesis bioassays. This measurement also compensates automatically for individual and species differences in toxicokinetic factors, as well as any nonlinearities that affect the quantitative relationships between exposure and molecular dose. As a result, molecular dosimetry can provide a basis for conducting high- to low-dose, route-to-route, and interspecies extrapolations. The incorporation of such data into risk assessment promises to reduce uncertainties and produce more accurate estimates of risk compared to current methods.
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PMID:DNA adducts: biological markers of exposure and potential applications to risk assessment. 889 94

Inosine 5 -monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme for the synthesis of GTP and dGTP. Two isoforms of IMPDH have been identified. IMPDH Type I is ubiquitous and predominantly present in normal cells, whereas IMPDH Type II is predominant in malignant cells. IMPDH plays an important role in the expression of cellular genes, such as p53, c-myc and Ki-ras. IMPDH activity is transformation and progression linked in cancer cells. IMPDH inhibitors, tiazofurin, selenazofurin, and benzamide riboside share similar mechanism of action and are metabolized to their respective NAD analogues to exert antitumor activity. Tiazofurin exhibits clinical responses in patients with acute myeloid leukemia and chronic myeloid leukemia in blast crisis. These responses relate to the level of the NAD analogue formed in the leukemic cells. Resistance to tiazofurin and related IMPDH inhibitors relate mainly to a decrease in NMN adenylyltransferase activity. IMPDH inhbitors induce apoptosis. IMPDH inhitors are valuable probes for examining biochemical functions of GTP as they selectively reduce guanylate concentration. Incomplete depletion of cellular GTP level seems to down-regulate G-protein function, thereby inhibit cell growth or induce apoptosis. Inosine 5'-monophosphate dehydrogenase (IMPDH, EC 1.1.1.205) catalyzes the dehydrogenation of IMP to XMP utilizing NAD as the proton acceptor. Studies have demonstrated that IMPDH is a rate-limiting step in the de novo synthesis of guanylates, including GTP and dGTP. The importance of IMPDH is central because dGTP is required for the DNA synthesis and GTP plays a major role not only for the cellular activity but also for cellular regulation. Two isoforms of IMPDH have been demonstrated. IMPDH Type I is ubiquitous and predominately present in normal cells, whereas the IMPDH Type II enzyme is predominant in malignant cells. Although guanylates could be salvaged from guanine by the enzyme hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), the level of circulating guanine is low in dividing cells and this route is probably insufficient to satisfy the needs of guanylates in the cells.
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PMID:Consequences of IMP dehydrogenase inhibition, and its relationship to cancer and apoptosis. 1039 Jun 1

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