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:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To investigate the role of topoisomerases in the production of sister chromatid exchanges, the effects of inhibitors of type I and II topoisomerases on baseline and mutagen-induced sister chromatid exchanges were compared. V79 cells were treated with VM-26 and m-AMSA, known inhibitors of type II topoisomerase, or with camptothecin, the only known inhibitor of type I topoisomerase. We observed that inhibitors of both type I and II topoisomerases induced high levels of sister chromatid exchanges at 10(-6) M, and that the dose-response curves of these drugs were very similar. A clear heterogeneity in the distribution patterns of exchanges induced by inhibitors of topoisomerases was observed. We believe that this heterogeneity in response to these compounds is due to variation in sensitivity within the cell cycle. We also studied interactions of these agents with mitomycin-C and with PUVA (8-methoxypsoralen + UVA), both cross-linking agents and potent sister chromatid exchange inducers, and with x-rays, an agent that induces high levels of DNA strand breaks. No significant change in exchange levels was observed in interactions between topoisomerase inhibition and the levels induced by the agents studied. We conclude that double-strand break prevalence, known to be increased through inhibition of type II topoisomerase, is not the primary mechanism for induction of sister chromatid exchanges. We further conclude that acute inhibition of type I and type II topoisomerases does not influence substantially the induction of exchanges by other agents.
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PMID:Induction of sister chromatid exchanges by inhibitors of topoisomerases. 285 99

Recently, the antitumor agent 4'-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA) was shown to revert a frameshift mutant of T4 (rFC11), and its mutagenicity was shown to be mediated by T4 DNA topoisomerase II [Ripley et al.: J Mol Biol 200: 665-680, 1988]. Here we report dose-response data on the mutagenicity and toxicity of m-AMSA in T4 rFC11. We find that m-AMSA is among the most potent frameshift mutagens observed in T4, inducing a 10-fold increase in mutant frequency in the absence of toxicity and a 500-fold increase in mutant frequency at 31% survival. In addition to m-AMSA, the topoisomerase-active agents ellipticine, oxolinic acid, and nalidixic acid also reverted rFC11; however, they required concentrations 10-100 times greater than those required by m-AMSA in order to be mutagenic, and they did not produce mutant frequencies as high as those produced by m-AMSA. Unlike m-AMSA, all three agents were mutagenic only at toxic doses. The other agents evaluated--actinomycin D, adriamycin, 9-aminoellipticine, 9-methoxyellipticine, teniposide (VM-26), and novobiocin--were toxic but not mutagenic to T4 rFC11. Thus, m-AMSA appears to be distinctly different from the other topoisomerase-active agents in exhibiting such potent mutagenic activity in T4 rFC11. Because E. coli DNA gyrase may substitute for T4 topoisomerase II, we examined the ability of two inhibitors of E. coli DNA gyrase, novobiocin and nalidixic acid, to inhibit m-AMSA's mutagenicity. Both agents substantially reduced the mutagenicity of m-AMSA in T4 rFC11, further suggesting that topoisomerase mediates the mutagenicity of m-AMSA.
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PMID:Mutagenicity of topoisomerase-active agents in bacteriophage T4. 290 38

The antitumor agent 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) inhibits topoisomerase II activity through the formation of a complex of DNA and covalently bound enzyme which, upon protein denaturation, yields DNA breaks (single strand breaks). In the present study, this complex served as a standard for analysis of radiation-induced DNA-protein cross-links (DPC). Following the treatment of exponentially growing mouse L929 cells with 0-100 ng/ml of m-AMSA for 1 h, a linear dose-dependent increase was found in the amount of DNA retained on nitrocellulose filters during subsequent analysis. This result indicates that the assay can detect DPC that have a single protein bound to each DNA fragment. The results of fractionation of nuclear DNA show that m-AMSA induces 20- to 45-fold more DPC in nuclear matrix-associated DNA than in the majority distal loop DNA, supporting the notion that topoisomerase II is located at the nuclear matrix. The frequency of single strand breaks induced by m-AMSA, which should be equal to the frequency of DPC, was determined by alkaline elution. Results of the alkaline elution assay could be correlated with the percentage of DNA retained on nitrocellulose filters; i.e., 1% DNA retention corresponded to 2560 DPC per log-phase L929 cell, which has been determined to have a DNA content of 22.25 pg. Using this standard curve, DPC induced by gamma-irradiation in air were estimated to be formed at a frequency of 133 DPC/cell/Gy, a frequency approximately 3% that of gamma-ray-induced single strand breaks. The radiation dose response for DPC production was unaffected by the high levels of DPC present in cells previously treated with m-AMSA. In addition, DPC induced by m-AMSA were rapidly reversed after the removal of the drug, in contrast to a slower removal of DPC induced by gamma-radiation. These observations suggest that although m-AMSA and gamma-radiation both preferentially induce DPC with matrix-attached DNA, they produce independent types of DPC.
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PMID:Comparison of DNA-protein cross-links induced by 4'-(9-acridinylamino)-methanesulfon-m-anisidide and by gamma-radiation. 291 61

Treatment of mouse leukemia L1210 cells with the polyamine biosynthesis inhibitor alpha-difluoromethylornithine (DFMO) increased the magnitude of the DNA scission produced by the DNA intercalator 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). This enhanced DNA scission was protein concealed and protein associated, as was the m-AMSA-induced scission in cells unexposed to DFMO. The effect of DFMO required more than 6 hr to develop and was greater at 48 hr than at 24 hr of exposure to DFMO. Exogenously added putrescine partially reversed the effects of DFMO, while exerting no effect on m-AMSA-induced DNA scission in cells unexposed to DFMO. The cellular uptake of [14C]-m-AMSA was the same in DFMO-treated or untreated cells. The DNA scission and DNA-protein cross-linking produced by m-AMSA appear to represent the stabilization of an intermediate in the normal cycle of topoisomerase II function (Nelson, E.M., Tewey, K.M., and Liu, L.F., Proc. Natl. Acad. Sci. USA, 81: 1361-1365, 1984). Since polyamine depletion appears to affect the magnitude of this effect in cells, and since polyamines can alter topoisomerase II function in vitro, polyamines may be involved in topoisomerase function in vivo either directly or through secondary effects, such as alterations of the conformation of chromatin, the intracellular site at which topoisomerase acts.
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PMID:Effect of difluoromethylornithine, an inhibitor of polyamine biosynthesis, on the topoisomerase II-mediated DNA scission produced by 4'-(9-acridinylamino)methanesulfon-m-anisidide in L1210 murine leukemia cells. 298 83

The antitumor drug, m-AMSA (4'-(9-acridinylamino)-methanesulfon-m-anisidide), is known to interfere with the breakage-reunion reaction of mammalian DNA topoisomerase II by blocking the enzyme-DNA complex in its putative cleavable state. Treatment of SV40 virus infected monkey cells with m-AMSA resulted in both single- and double-stranded breaks on SV40 viral chromatin. These strand breaks are unusual because they are covalently associated with protein. Immunoprecipitation results suggest that the covalently linked protein is DNA topoisomerase II. These results are consistent with the proposal that the drug action in vivo involves the stabilization of a cleavable complex between topoisomerase II and DNA in chromatin. Mapping of these double-stranded breaks on SV40 viral DNA revealed multiple topoisomerase II cleavage sites. A major topoisomerase II cleavage site was preferentially induced during late infection and was mapped in the DNAase I hypersensitive region of SV40 chromatin.
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PMID:In vivo mapping of DNA topoisomerase II-specific cleavage sites on SV40 chromatin. 298 41

Intercalator-induced DNA double-strand breaks (DSB) presumably represent topoisomerase II DNA cleavage sites in mammalian cells. Isolated L1210 cell nuclei were used to determine the saturability of this reaction at high drug concentrations. 4'-(9-Acridinylamino)methanesulfon-m-anisidide (m-AMSA) and 5-iminodaunorubicin (5-ID) both produced DSB in a concentration-dependent manner, and the production of these breaks leveled off above 10 microM. Addition of m-AMSA to 5-ID-treated nuclei did not raise the plateau level. Thus, both drugs seemed to interact similarly on identical targets. The ellipticine derivative 2-methyl-9-hydroxyellipticinium (2-Me-9-OH-E+) had two effects on the production of DSB. Below 10 microM, 2-Me-9-OH-E+ produced DSB as did ellipticine, m-AMSA, or 5-ID. Above 10 microM, 2-Me-9-OH-E+ did not induce DSB and inhibited the DSB induced by m-AMSA, 5-ID, or ellipticine. 2-Me-9-OH-E+ and m-AMSA competed with each other to produce either double-strand break formation (m-AMSA-induced reaction) or double-strand break inhibition (2-Me-9-OH-E+-induced reaction at concentrations greater than 10 microM). Because these results were reproduced in experiments using DNA topoisomerase II isolated from L1210 nuclei, it is likely that the intercalator-induced protein-associated DNA breaks detected by alkaline elution in nuclei represent DNA topoisomerase II-DNA complexes.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Effects of DNA intercalating agents on topoisomerase II induced DNA strand cleavage in isolated mammalian cell nuclei. 300 39

DNA topoisomerase II is believed to be the enzyme that produces the protein-associated DNA strand breaks observed in mammalian cell nuclei treated with various intercalating agents. Two intercalators--4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA, amsacrine) and 2-methyl-9-hydroxyellipticinium (2-Me-9-OH-E+)--differ in their effects on protein-associated double-strand breaks in isolated nuclei. m-AMSA stimulates their production at all concentrations, whereas 2-Me-9-OH-E+ stimulates at low concentrations and inhibits at high concentrations. We have reproduced these differential effects in experiments carried out in vitro with purified L1210 DNA topoisomerase II, and we have found that concentrations of 2-Me-9-OH-E+ above 5 microM prevent the trapping of DNA-topoisomerase II cleavable complexes irrespective of the presence of m-AMSA. It also stimulated topoisomerase II mediated DNA strand passage, again with or without inhibitory amounts of m-AMSA (this result suggests that extensive intercalation by 2-Me-9-OH-E+ destabilized the cleavable complexes). From these data, it is concluded that intercalator-induced protein-associated DNA strand breaks observed in intact eukaryotic cells and isolated nuclei are generated by DNA topoisomerase II and that intercalators can affect mammalian DNA topoisomerase II in more than one way. They can trap cleavable complexes and inhibit DNA topoisomerase II mediated DNA relaxation (m-AMSA and low concentrations of 2-Me-9-OH-E+) or destabilize cleavable complexes and stimulate DNA relaxation (high concentrations of 2-Me-9-OH-E+).
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PMID:Effects of the DNA intercalators 4'-(9-acridinylamino)methanesulfon-m-anisidide and 2-methyl-9-hydroxyellipticinium on topoisomerase II mediated DNA strand cleavage and strand passage. 300 40

Protein-associated DNA cleavage is produced in mammalian cells treated with active antileukemic DNA intercalating agents such as 4'(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). We have examined the ability of m-AMSA to produce DNA cleavage in 3 human myeloid leukemic cell lines with different sensitivities to the cytotoxic actions of m-AMSA to see if the magnitude of DNA cleavage correlated with the degree of m-AMSA sensitivity. DNA alkaline elution was used to quantify DNA cleavage. The amount of m-AMSA-induced DNA cleavage in the two lines sensitive to m-AMSA was 1-2 orders of magnitude greater than that in an m-AMSA-resistant leukemic line. The m-AMSA resistant line had been developed by prolonged exposure of one of the sensitive lines to m-AMSA. This finding was not secondary to a decreased uptake of m-AMSA in the resistant cell line. m-AMSA treatment of the nuclei isolated from the three lines produced DNA cleavage frequencies comparable to the cleavage frequencies produced by m-AMSA treatment of the whole cells from which the nuclei were isolated. The DNA cleaving ability stimulated by m-AMSA is thought to be mediated by drug-induced effects on topoisomerase II, a nuclear enzyme that mediates alterations in DNA conformation. Alterations in the manner in which this enzyme interacts with antineoplastic agents may explain the emergence of resistant cells following initially successful chemotherapy.
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PMID:The production of topoisomerase II-mediated DNA cleavage in human leukemia cells predicts their susceptibility to 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA). 300 58

Antitumor drugs from many chemical classes have been shown to induce protein-linked DNA breaks in cultured mammalian cells and in vitro in the presence of purified mammalian DNA topoisomerase II. The possibility that mammalian DNA topoisomerase II is an intracellular target which mediates drug-induced DNA breaks is supported by the following studies using 4'-(9-acridinylamino)methane-sulfon-m-anisidide (m-AMSA): (a) a single m-AMSA-dependent DNA cleavage activity copurified with calf thymus DNA topoisomerase II activity at all chromatographic steps of the enzyme purification; (b) m-AMSA-induced DNA cleavage by this purified activity resulted in the covalent attachment of protein to the 5'-ends of the DNA via a tyrosyl phosphate bond. This covalently linked protein has the same reduced molecular weight as purified calf thymus DNA topoisomerase II. The possibility that topoisomerase II-mediated DNA breaks may be responsible for cytotoxicity has also been investigated using a number of m-AMSA-related acridines. The level of topoisomerase II-mediated DNA breaks in vitro strongly correlates with the level of protein-linked DNA breaks in cultured cells and drug-induced cytotoxicity. These results suggest that mammalian DNA topoisomerase II may be a cytotoxic target of antitumor acridines.
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PMID:DNA damage by antitumor acridines mediated by mammalian DNA topoisomerase II. 300 16

DNA topoisomerase II from Drosophila was phosphorylated effectively by protein kinase C. With a Km of about 100 nM, the reaction was rapid, occurring at 4 degrees C as well as at 30 degrees C and requiring as little as 0.6 ng of the protein kinase per 170 ng of topoisomerase. About 0.85 mol of phosphate could be incorporated per mol of topoisomerase II, with phosphoserine as the only phospho amino acid produced. The reaction was dependent on Ca2+ and phosphatidylserine and was stimulated by phorbol esters. Calmodulin-dependent protein kinase II, but not cyclic AMP-dependent protein kinase, was also able to phosphorylate the topoisomerase. Phosphorylation of topoisomerase II by protein kinase C resulted in appreciable activation of the topoisomerase, suggesting that it may represent a possible target for the regulation of nuclear events by protein kinase C. This possibility is supported by the finding that the phorbol ester-induced differentiation of HL-60 cells was blocked by the topoisomerase II inhibitors novobiocin and 4'-(9-acridinylamino)methanesulfon-m-anisidide(m-AMSA), but not by the inactive analog o-AMSA.
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PMID:Protein kinase C phosphorylates topoisomerase II: topoisomerase activation and its possible role in phorbol ester-induced differentiation of HL-60 cells. 300 58


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