Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:5.99.1.2 (topoisomerase)
 9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The antitumor drug teniposide (VM-26) is a potent inducer of DNA breaks (Long et al., Cancer Res., (1985) 45, 3106), but it is only weakly mutagenic at the hprt locus in CHO cells (Singh and Gupta, Cancer Res., (1983) 43, 577). In the present study, the mutagenic and clastogenic activities of teniposide were evaluated in L5178Y/TK +/- -3.7.2C mouse lymphoma cells. Although teniposide is a weak mutagen at the hprt locus, it is a potent mutagen at the tk locus, with as little as 0.5 ng/ml producing 220 TK mutants/10(6) survivors at 96% survival (background = 100/10(6) survivors). This same dose of teniposide induced 38 aberrations per 100 metaphases (background = 7/100 cells). At 7 ng/ml, teniposide induced approximately 2700 TK mutants/10(6) survivors at approximately 10% survival. At the highest dose sampled for aberration analysis (5 ng/ml), teniposide induced 44 aberrations/100 cells. Most of the aberrations were chromosomal rather than chromatid events. As expected for a compound acting primarily by a clastogenic mechanism, most of the TK mutants were small colonies. Thus, teniposide is a potent clastogen, and it is a potent mutagen at the tk locus but not at the hprt locus. These results support the hypothesis that the location of the target gene affects the ability of the assay to detect both intragenic events and events causing functional multilocus effects. Thus, a heterozygous locus (like tk) but not a functionally hemizygous locus (like hprt) may permit the detection of mutagens that act primarily by a clastogenic mechanism. Because teniposide induces topoisomerase II-associated DNA breaks, and because there is evidence that teniposide may not interact directly with DNA, we discuss the possibility that the potent clastogenic/mutagenic activity of teniposide may be mediated by topoisomerase II.
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PMID:Mutagenicity and clastogenicity of teniposide (VM-26) in L5178Y/TK +/- -3.7.2C mouse lymphoma cells. 382 67

Amsacrine, [4'-(9-acridinylamino)-methanesulfon-m-auisidide], belongs to the class of cancer chemotherapeutic agents that target DNA topoisomerase II. We show that, over its cytotoxic range, amsacrine is a potent mutagen of the S1 phenotype in the AL (human x hamster) hybrid cell line. By contrast, amsacrine induction of the HPRT- phenotype in AL cells is at least two decades less frequent and is not concentration dependent. Such differential mutation frequencies are hypothesized to reflect the concomitant loss of essential genes neighboring the hprt locus. It may be that some amsacrine cytotoxicity is due to the inactivation of essential genes by large deletions. The AL mutation system is well suited for the detection and mapping of mutations which are large deletions because its MIC1 locus, which controls the expression of the selectable cell surface antigen S1, is on a single human chromosome. This human chromosome 11 is in addition to the genome of the Chinese hamster ovary cell and is basically nonessential. Since there are no sister human chromosomes in AL cells, deletions which extend beyond the MIC1 locus may be conveniently and unambiguously mapped. We have detected the presence or absence of 9 different chromosome 11 markers in 48 S1- mutants cloned from amsacrine-treated cultures. We find that almost all (92%) of the mutants have deletions of at least 1.5-2 megabase pairs in length. The distribution of marker loss frequencies flanking the MIC1 locus does not appear symmetric with respect to distance from that locus. We speculate that amsacrine-induced deletions are mediated by a series of subunit exchanges between overlapping topoisomerase II dimers at the bases of replicons or larger chromosomal structures such as replicon clusters or chromosome minibands.
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PMID:Megabase pair deletions in mutant mammalian cells following exposure to amsacrine, an inhibitor of DNA topoisomerase II. 831 66

DNA sequences of the deletion breakpoints of 24 human T-lymphocyte hprt gene mutations are reported. These independent deletions ranged in size from 18 to 15655 base pairs. Seven of the 21 in vivo mutations arose in normal adults, three in normal children, eight in radioimmunotherapy patients and three in platinum chemotherapy patients. One in vitro mutation was isolated after 93cGy radon exposure and two after 300cGy gamma radiation. The breakpoints were found to be non-random and a cluster of small deletions in exon 6 is reported. Ten of the mutations had 2-5bp direct repeats at the breakpoints. There was no excess of "deletion-associated" motifs over that expected by chance. Some breakpoints do occur at consensus topoisomerase II cleavage sites and the centromeric end of a Donehower sequence occurs exactly at a telomeric breakpoint. Three mutants had breakpoints at hairpins expected by the model of Glickman and Ripley.
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PMID:Breakpoints and junctional regions of intragenic deletions in the HPRT gene in human T-Cells. 861 28

Etoposide, a topoisomerase II inhibitor, is a chemotherapeutic agent that is used in the treatment of a wide variety of neoplasms, including small cell lung cancer, germ cell cancer, testicular cancer, acute leukemia, and lymphoma. Although it has proven valuable, etoposide is also a known mutagen and has been implicated as a causative agent of treatment-related secondary acute nonlymphocytic leukemia. We have investigated the induction of mutation following etoposide treatment in vivo using the hypoxanthine phosphoribosyltransferase (hprt) T-cell cloning assay in small cell lung cancer patients receiving single-drug etoposide chemotherapy. This report presents results on the monitoring of 12 patients (mean age, 74.8 +/- 6.0 years; range, 66-83 years) before, during, and after chemotherapy. The treatment regimen included up to six cycles of oral etoposide given in twice-daily 50-mg tablets for 10-14 days, separated by 2 weeks of rest. Peripheral blood samples were collected on the first day of each cycle prior to treatment. Patients received one to six etoposide cycles and were followed for 0.7-5.3 months after the start of chemotherapy (total etoposide dose, 1.4-8.4 g). Results from the pooled data show no significant increase in the hprt mutant frequency (pretreatment, 46 x 10(-6) +/- 38 x 10(-6), versus posttreatment, 55 x 10(-6) +/- 46 x 10(-6)), although considerable interpatient variability was observed. Of a total of 424 selected mutants, 228 were analyzed by sequencing hprt cDNA. Spectra of 56 pretreatment and 147 posttreatment mutations revealed significant enhancement of AT-->TA transversions and a concomitant decrease in the number of GC-->TA transversions in posttreatment spectra, when they were compared with pretreatment or control spectra. No evidence for the induction of gross deletions or rearrangements was found in the spectra of mutants that were recovered from patients after etoposide treatment. The lack of enhanced mutant frequency after treatment suggests that the etoposide chemotherapy was not particularly effective in inducing mutation, as measured by the hprt assay. It is proposed that mutated cells are eliminated through apoptosis due to accumulated DNA damage.
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PMID:Mutation frequency and spectrum in lymphocytes of small cell lung cancer patients receiving etoposide chemotherapy. 933 Nov 3

The expression of seven enzymes involved in the biosynthesis of DNA was measured in HL-60 promyelocytic leukemia cells treated with dimethylsulfoxide (DMSO) or all-trans retinoic acid (RA) to gain information on their role in the termination of proliferation in cells undergoing granulocytic differentiation. The steady-state levels of the mRNAs for topoisomerase I, topoisomerase II. DNA polymerase-alpha, thymidylate synthase, thymidine kinase and hypoxanthine-guanine phosphoribosyltransferase progressively declined from day 3 to day 7 of exposure to the polar solvent or the retinoid suggesting that the expression of these enzymes is coordinately regulated. In contrast, a pronounced difference between the two inducers of differentiation occurred in the expression of the mRNA of the M2 subunit of ribonucleotide reductase, with DMSO causing virtually complete inhibition of the expression of the M2 subunit of the enzyme from day 5 through day 7, with no change in the steady-state levels of the mRNA being produced by retinoic acid. Measurement of the enzymatic activities of two of these catalysts, thymidylate synthase and thymidine kinase, in cells exposed to the two inducers of maturation corroborated the findings at the level of the mRNAs, with corresponding decreases in the activity of these enzymes. The findings collectively demonstrate that the down-regulation of the expression of a relatively wide variety of enzymes involved in DNA replication occurs as late events in the granulocytic differentiation of HL-60 cells, ensuring that cellular replication cannot occur in terminally differentiated cells.
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PMID:Regulation of the expression of enzymes involved in the replication of DNA in chemically-induced granulocytic differentiation of HL-60 leukemia cells. 968 95

We have mapped the positions in a approximately 1.4-Mb region of genomic DNA around the human hprt gene which are accessible in vivo to cleavage by topoisomerase II associated with the nuclear matrix. These positions, which are interpreted as the boundaries of DNA loop domains, were mapped in K562 cells by examining the truncation of rare-cutter restriction fragments separated by pulsed field gel electrophoresis after topoisomerase II-mediated cleavage, using seven linked markers mapped in this region as probes for indirect end-labeling. Eleven cleavage positions were detected and were interpreted as defining ten loop domains of lengths between 70 and 210 kb (average approximately 135 kb); the hprt gene resides in a 150-kb loop domain. Loop domain boundaries coincided with three of the fifteen deletion breakpoints mapped in a 600-kb sector of this region in human lymphocytes, within the limits of resolution of pulsed field gel electrophoresis; this correlation was not statistically significant.
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PMID:DNA loop domains in a 1.4-Mb region around the human hprt gene mapped by cleavage mediated by nuclear matrix-associated topoisomerase II. 989 10

A study was made of the influence of inhibitors of poly(ADP-ribose)polymerase, topoisomerase I and topoisomerase II on the frequency of gene targeting of hprt gene as well as on the frequency of random integration of targeting vector pRV9.1 into genome of mouse F9 teratocarcinoma cells. We found that the treatment of cells with the inhibitor of poly(ADP-ribose)polymerase 3-aminobenzamide after electroporation resulted in 3-4-times increase of homologous integration of exogenic vector into chromosomal DNA, and did not affect the frequency of random insertion of transfected DNA. The treatment of cells after electroporation with inhibitors of topoisomerases VP-16, ICRF-193 enhanced random integration of transfected DNA but exerted no effect on the frequency of gene targeting in this experimental system.
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PMID:[Effect of inhibitors of topoisomerases and poly(ADP-ribosylation) on homologous and non-homologous integration of exogenous DNA in genes of mammalian somatic cells]. 1064 51

The RAD51 protein has been shown to participate in homologous recombination by promoting ATP-dependent homologous pairing and strand transfer reactions. In the present study, we have investigated the possible involvement of RAD51 in non-homologous recombination. We demonstrate that overexpression of CgRAD51 enhances the frequency of spontaneous non-homologous recombination in the hprt gene of Chinese hamster cells. However, the rate of non-homologous recombination induced by the topoisomerase inhibitors campothecin and etoposide was not altered by overexpression of RAD51. These results indicate that the RAD51 protein may perform a function in connection with spontaneous non-homologous recombination that is not essential to or not rate-limiting for non-homologous recombination induced by camptothecin or etoposide. We discuss the possibility that the role played by RAD51 in non-homologous recombination observed here may not be linked to non-homologous end-joining.
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PMID:RAD51 supports spontaneous non-homologous recombination in mammalian cells, but not the corresponding process induced by topoisomerase inhibitors. 1116 Aug 87