Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.1.21 (thymidine kinase)
7,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Wild-type cells and thymidine kinase-deficient clones from two mouse lymphoma cell lines, P388 and L5178Y, were compared for sensitivity to killing by the mutagens, ultraviolet irradiation (UV), ethyl methane sulfonate (EMS), and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Two out of three thymidine kinase-deficient P388 clones showed significantly enhanced sensitivity to killing by all three mutagens. This increased sensitivity to killing was also reflected in increased mutagenesis by the three mutagens. In the L5178Y cell line, wild-type cells showed little difference to two thymidine kinase-deficient clones in terms of mutagen sensitivity. This indicates that thymidine kinase may be significant for DNA repair processes in P388 but not in L5178Y cells. Unscheduled DNA synthesis (UDS) experiments were carried out on P388 and L5178Y wild-type cells and wild-type Friend leukemia cells (which are mutagen-sensitive when deficient in thymidine kinase). The UDS experiments showed the L5178Y cells were low in excision repair abilities relative to the P388 cells and the Friend cell clone. This indicates that the increased mutagen sensitivity in thymidine kinase-deficient P388 and clone 707 Friend cells may be due to thymidine kinase playing an indirect role in DNA excision repair, a process which is of little significance in the L5178Y cell line.
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PMID:Evidence for indirect involvement of thymidine kinase in excision repair processes in mouse cell lines. 385 20

Three classes of TFTr variants of L5178Y/TK+/- -3.7.2C mouse lymphoma cells can be identified--large colony (lambda), small colony (sigma), and tiny colony (tau). The sigma and lambda mutants are detectable in the routine mutagenesis assay using soft agar cloning. The tau mutants are extremely slow growing and are quantitated only in suspension cloning in microwells. Variants of all three classes have been analyzed in the process of evaluating the usefulness of the thymidine kinase locus in L5178Y/TK+/- mouse lymphoma cells for detecting induced mutational damage. 150 of 152 variants from mutagen treated cultures and 163 of 168 spontaneous mutants were TFTr when rechallenged approximately 1 week after isolation (3 weeks after induction). All of the 41 mutants assayed for enzyme activity were TK-deficient. The sigma and tau phenotypes were found to correlate with slow cellular growth rates (doubling time greater than 12 h), rather than from effects of the TFT selection or mutagen toxicity. Cytogenetic analysis of sigma mutants approximately 3 weeks after induction shows an association between the sigma phenotype and readily observable (at the 230-300 band level) chromosomal abnormalities (primarily translocations involving that chromosome 11 carrying the functional TK gene) in 30 of 51 induced mutants studied. Using an early clonal analysis of mutants (approximately 2 weeks after induction) 28 of 30 sigma mutants showed chromosome 11 rearrangements. All lambda mutants studied (17 of 17 evaluated 3 weeks after induction and 8 of 8 evaluated 2 weeks after induction) showed normal karyotypes (at the 230-300 band resolution level), including the chromosome 11s. These observations support the hypothesis that sigma (and likely tau) mutants represent chromosomal mutations and lambda mutants represent less extensive mutations affecting the TK locus. The inclusion of sigma mutants in the total induced mutant frequency, as well as distinguishing them as a separate subpopulation of TK-deficient mutants, is, therefore, essential in obtaining maximum utility of the information provided by the L5178Y/TK+/- mouse lymphoma assay.
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PMID:Analysis of trifluorothymidine-resistant (TFTr) mutants of L5178Y/TK+/- mouse lymphoma cells. 392 57

Mutagenic potency at the thymidine kinase (TK) locus in mouse lymphoma L5178Y cells (expressed as induced trifluorothymidine (TFT)-resistant mutants/total dose) was assessed for 4 agents (ethyl methanesulphonate (EMS), benzidine, 1,8-dinitropyrene (1,8-DNP) and ICRF 159) using short (3-4 h) and long (21-24 h) exposure times. The mutagenic potency of EMS was found to be essentially independent of concentration and exposure time when tested over a cytotoxic range consistent with routine testing procedures. Similar results were obtained with benzidine but for both 1,8-DNP and ICRF 159 mutagenic potency was found to be highly dependent on the concentration and exposure time. 1,8-DNP failed to induce any significant increases in mutant frequency when tested at concentrations up to 5 micrograms/ml using short exposure times, whereas the compound was active at concentrations as low as 0.1 microgram/ml when the exposure period was extended to 21 h. Under the latter conditions, however, the molar potency of 1,8-DNP was found to be inversely related to concentration over a range extending from 0.1 to 5 micrograms/ml. ICRF 159 induced increases in the frequency of TFT-resistant mutants using short or long exposure times. When a short exposure time was used, however, the mutagenic potency of the antitumour agent decreased with increasing concentration between 1 and 500 micrograms/ml. Although possible explanations can be offered to account for these observations the results illustrate potential problems which may arise in this system when comparing mutagenic potency values for a range of compounds with a view to assessing relative risk.
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PMID:The mutagenic potency of 4 agents at the thymidine kinase locus in mouse lymphoma L5178Y cells in vitro: effects of exposure time. 402 42

The cytogenetic characterization of the L5178Y TK+/-3.7.2C mouse lymphoma cell line was carried out, utilizing G-banded metaphase chromosomes, to provide a karyotypic basis for the precise delineation of induced rearrangements in TK-/- mutants. Band-pattern measurements were used to construct ideograms which represent the position, number, size and staining intensity of the chromosome bands. The TK+/-3.7.2C cell line has been shown to provide quantitation of forward mutations induced at the autosomal thymidine kinase (TK) locus in this cell line. Chromosome analysis of the TK+/-3.7.2C cell line and derived TK-/- mutants has become important in demonstrating that the TK+/-----TK-/- assay may detect and distinguish between chromosomal events and smaller, perhaps point-mutation, events in mutant colonies.
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PMID:Cytogenetic characterization of the L5178Y TK+/-3.7.2C mouse lymphoma cell line. 404 79

Deoxyadenosine toxicity toward lymphocytes may produce immune dysfunction in patients with adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4) deficiency. The relationship between endogenous deoxynucleoside synthesis in adenosine deaminase-deficient cells and sensitivity to adenosine and deoxyadenosine toxicity is unclear. The human histiocytic lymphoma cell line (DHL-9) naturally lacks adenosine deaminase, and has minimal levels of thymidine kinase. Dividing DHL-9 cells excrete deoxyadenosine and thymidine into the extracellular space. The present experiments have analyzed nucleoside synthesis and excretion in a mutagenized clone of DHL-9 cells, selected for increased resistance to deoxyadenosine toxicity. The deoxyadenosine-resistant cells excreted both deoxyadenosine and thymidine at a 6-7-fold higher rate than wild-type lymphoma cells. The deoxyadenosine overproduction was accompanied by a reduced ability to form dATP from exogenous deoxyadenosine, and a 2.5-fold increase in ribonucleotide reductase activity. The pace of adenosine excretion, the growth rate, and the levels of multiple other enzymes involved in deoxyadenosine and adenosine metabolism were equivalent in the two cell types. These results suggest that the excretion of deoxyadenosine and thymidine, but not adenosine, is exquisitely sensitive to alterations in the rate of endogenous deoxynucleotide synthesis. Apparently, small changes in deoxynucleotide synthesis can significantly influence cellular sensitivity to deoxyadenosine toxicity.
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PMID:Deoxynucleoside overproduction in deoxyadenosine-resistant, adenosine deaminase-deficient human histiocytic lymphoma cells. 637 66

The levels of the purine catabolic enzymes, adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP), together with the pyrimidine activities, thymidine phosphorylase (TP) and thymidine kinase isozymes (TK) have been determined for cells obtained from solid lymphoid tissue of 38 patients with non-Hodgkin's lymphoma (NHL) and 14 individuals exhibiting benign reactive lymphoid hyperplasia. Within each NHL histological group subtyped according to the Rappaport classification, and in the reactive hyperplasia group, there was considerable variation in these activities. However, higher levels of TK and TP activities occurred in cells of the histologically unfavourable prognostic NHL groups compared with those of favourable histology or reactive hyperplasia. There was an inverse relationship between survival and elevated TK isozyme 1 and TP levels, which was independent of histological classification and clinical staging. These results indicate that, in addition to morphology, estimations of TK and TP of involved lymphoma cells in NHL is of clinical relevance.
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PMID:Pyrimidine and purine activities in non-Hodgkin's lymphoma. Correlation with histological status and survival. 642 90

Mutants of mouse T-lymphoma S49 cells lacking thymidine kinase activity or deficient in nucleoside transport were selected by growth in the presence of 5'-fluorodeoxyuridine and their sensitivity to interferon tested. All five thymidine kinase and both transport deficient mutants were sensitive to the antiproliferative effects of interferon. The replication of encephalomyocarditis virus was also inhibited by interferon, and the intracellular levels of (2'-5')oligo-adenylate synthetase were elevated in all mutants tested. These results suggest that an intact nucleoside transport system or thymidine kinase activity are not essential for the expression of interferon sensitivity in these cells.
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PMID:The effect of interferon on cells deficient in nucleoside transport or lacking thymidine kinase activity. 669 50

Trifluorothymidine (TFT), a thymidine analog, was analyzed for its ability to select for thymidine kinase-deficient (TK-/-) mutants. In comparison with BUdR, the traditional selective agent for TK-/- cells, it was determined that TFT at 1/50th the dose (1 microgram/ml vs. 50 microgram/ml) is a more effective and versatile selective agent for TK-/- mutants arising from the TK+/- -3.7.2C heterozygote of L5178Y mouse lymphoma cells. Since TFT acts more rapidly than BUdR, it can be utilized in procedures (such as the analysis of the phenotypic lag) requiring the fast arrest of cell division. Reconstruction analyses of effective TK-/- mutant recovery indicate that TFT can be used to recover mutants from significantly higher densities of TK+/- cells than can BUdR. In addition, TK-/- mutants can attain larger colony size in TFT than in BudR where severe stunting of growth occurs at high TK-/- cell densities. 190 of 194 isolated TFT-resistant large and small colony mutants (both spontaneous and induced).
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PMID:The utilization of trifluorothymidine (TFT) to select for thymidine kinase-deficient (TK-/-) mutants from L5178Y/TK+/- mouse lymphoma cells. 679 99

A detailed cytogenetic investigation was carried out on P388 mouse lymphoma cells. The cells have a mean chromosome number of 36.86 with a mode and median of 37 chromosomes. G-banding analysis of 12 spreads revealed a total of 15 marker chromosomes with chromosome 11, the determinant of thymidine kinase, being present only in single copy per cell. It is therefore concluded that the P388 cell line is hemizygous at the thymidine kinase locus. Thymidine kinase activities were assayed in P388 cells and two other malignant cell lines, clone 707 Friend mouse leukaemia cells and L5178Y mouse lymphoma cells. No clear relationship was observed between enzyme activity and gene dosage.
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PMID:Cytogenetic evidence for hemizygosity at the thymidine kinase locus in P388 mouse lymphoma cells. 685 81

The predominant test system uses a near-diploid L5178Y mouse lymphoma cell line and is based on the quantitation of forward mutations occurring at the heterozygous thymidine kinase (TK) locus (TK+/- leads to TK-/-). (Other markers, such as ouabain- or methothrexate-resistance and alanine independence, in other L5178Y mouse lymphoma cells were also examined, but our criteria for the acceptability of data or the paucity of data considerably reduced the value of these mutagenesis test systems to this study.) The biochemical basis for the L5178Y/TK+/- assay depends on the ability of TK-competent cells to phosphorylate 5-bromo-2'-deoxyuridine or trifluorothymidine. The phosphorylated product or its metabolites kill these cells, thus, medium containing 5-bromo-2'-deoxyuridine or trifluorothymidine is capable of selecting for cells that are lacking the TK enzyme (TK-/-). TK-/- cells eventually give rise to a bimodal distribution of colony sizes. The relative proportion of small and large colonies appears to be characteristic of the mutagen, its dose, and the length of the expression period. A total of 108 references were reviewed and 48 chemical agents were evaluated. Of these, in vivo carcinogenicity data existed for 44 and covered a wide variety of chemical classes (43 compounds) and a complex mixture. In this system, 39 agents were positive, 1 was negative, and 4 yielded inconclusive results. The 44 test substances evaluated were insufficient to single out agents or agent classes for which the assay was particularly well suited; however, with the exception of thymidine analogs, the system seems to be versatile. The correlation of the TK locus assay results with the carcinogenicity data revealed that 2 agents were definite false positives (sodium azide and methotrexate) and 1 agent was a definite false negative (1,1-dimethylhydrazine). Further evaluation suggested that 4-acetylaminofluorene and diphenylnitrosamine were questionable false positives, while benzo[e]pyrene was a questionable false negative. (The term questionable was used to imply uncertainties concerning the mutagenicity and/or carcinogenicity data). Thus, the assay is of value in the battery approach to mutagenicity/carcinogenicity screening.
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PMID:Specific gene mutations in L5178Y cells in culture. 685 86


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