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)

The relationship between gene expression and the patterns of histone methylation in Drosophila cells has been investigated using inhibitors of transcription acting at various levels. Inhibition of ribosomal RNA synthesis and processing by 5-fluorouridine or of general RNA synthesis by camptothecin, an inhibitor of topoisomerase I, does not affect the methylation pattern of core histones. This suggests that the arrest of transcription per se is not involved in the changes in histone methylation such as those encountered in heat-shocked cells. However, ethidium bromide and novobiocin, which are known to disrupt nucleosome structure, and VM-26 (teniposide), a specific inhibitor of topoisomerase II, induce changes in histone methylation patterns which, though less severe, are similar to those observed under cellular stress. These results suggest that chromatin conformation is probably an important factor in the accessibility of histones to methyltransferases.
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PMID:Transcriptional inhibitors affecting topoisomerase II induce changes in histone methylation patterns similar to those induced by heat shock. 254 90

A well defined extrachromosomal DNA element, referred to as an episome (Ostrowski, M., Richard-Foy, H., Wolford, R., Berard, D., and Hager, G. (1983) Mol. Cell. Biol. 3, 2045-2057), was employed as a target for the topoisomerase II inhibitors amsacrine and teniposide. Both drugs have distinct mechanisms of action in cleaving the episome, as defined by topological forms conversion assays. The concentration ranges required to measure episomal cleavage are similar. The onset of damage induced by amsacrine begins within 1 min and is maintained at that level for at least 1 h. Teniposide induces damage that peaks between 30 and 60 min. The amsacrine-induced damage is only partially reversible, whereas teniposide-induced damage is almost completely reversible. Sites of specific cleavage are quite dissimilar. Multiple cleavage sites are formed in the episomal regulatory regions after amsacrine treatment, whereas a single cleavage in the regulatory region and one outside this region are found after teniposide treatment. Transcriptional activation using dexamethasone does not change the amount or site preference of episomal cleavage induced by either agent. Damage to the episome was quantitatively compared with damage produced in genomic DNA between 500 and 24,000 rad equivalents. The study showed that amsacrine has a significant (33-38-fold) preference for episomal DNA over genomic DNA.
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PMID:A study of drug-induced topoisomerase II-mediated DNA lesions on episomal chromatin. 255 Apr 34

Incubation of cultured rat aortic smooth muscle cells (A-10, ATCC CRL 1476) with [8-arginine]vasopressin (AVP) or thrombin increased the amount of DNA strand breakage induced by camptothecin, an inhibitor of topoisomerase I (DNA topoisomerase; EC 5.99.1.2) and transiently stimulated the extractable activity of this enzyme. Both topoisomerase-related responses were prevented by treatment of the cells with AVP or thrombin plus the appropriate receptor antagonist. The increase in strand breakage mediated by AVP and thrombin depended on the concentration of hormone. Neither AVP nor thrombin had any effect on strand breaks obtained with the epipodophyllotoxin VM-26, an inhibitor of topoisomerase II [DNA topoisomerase (ATP-hydrolysing); EC 5.99.1.3]. Pretreatment of the cells with pertussis toxin partially inhibited thrombin-mediated increases in camptothecin-induced strand breakage whereas AVP-mediated increases were unaffected. These results are consistent with the notion that AVP and thrombin induce a transient increase in intracellular topoisomerase I activity via interactions with their respective cell surface receptors and that the effects of the activation of these receptors are mediated by different G-proteins.
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PMID:Stimulation of intracellular topoisomerase I activity by vasopressin and thrombin. Differential regulation by pertussis toxin. 255 99

The p170 and p180 forms of topoisomerase II have been compared. The concentration dependence of ATP for catalytic activity of the two forms of the enzyme was identical, and each was equally sensitive to novobiocin. Orthovanadate was found to be a potent inhibitor of catalytic activity of both p170 and p180, with an IC50 value of about 2 microM for each. Under standard reaction conditions, relaxation of supercoiled pBR322 by p180 was highly processive, while p170 performed the same reaction in a distributive manner. The optimal concentration of KCl for catalytic activity of p180 was 20-30 mM higher than that for p170. Comparison of their thermal stability showed that p180 was inactivated at twice the rate of p170. Teniposide and merbarone selectively inhibited catalytic activity of p170, requiring concentrations 3-fold and 8-fold lower, respectively, than those required for equivalent inhibition of p180. Similar selectivity for p170 was seen for teniposide-stimulated DNA cleavage or its inhibition by merbarone. Analysis of sites of DNA cleavage indicated a subset of sites that were either preferred or unique for each of the enzymes. A synthetic oligonucleotide representative of p170 sites selectively inhibited the p170 enzyme. Immunoblotting of p170 and p180 from U937 cells at different stages of proliferation showed that p170 levels declined as the cells reached the plateau phase of growth, while p180 levels were low during rapid proliferation and increased as the growth rate slowed. The data indicate that the p170 and p180 forms of topoisomerase II can be distinguished biochemically, pharmacologically, and by differential cellular regulation.
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PMID:Biochemical and pharmacological properties of p170 and p180 forms of topoisomerase II. 255 97

Specific inhibitors of eukaryotic DNA topoisomerases I and II (camptothecin and VM-26, respectively) were used to examine the involvement of topoisomerases in DNA replication and chromatin assembly in vivo. When used singly, either camptothecin or VM-26 inhibited DNA synthesis in HeLa cells by more than 80%; when used simultaneously, the inhibitors effectively stopped replication, demonstrating that at least one class of topoisomerase must be active for fork propagation in vivo. To study nucleosome assembly during topoisomerase inhibition, three experimental strategies were employed: (1) pulse-chase experiments; (2) analyses of chromatin synthesized during residual replication in the presence of either camptothecin or VM-26; and (3) the assembly of previously replicated, unassembled DNA, generated in the presence of protein synthesis inhibitors. Using sensitivity to micrococcal nuclease and the maturation of non-nucleosomal replication intermediates as criteria, neither camptothecin nor VM-26, alone or in concert, inhibited nucleosome assembly under any experimental protocol tested. These data provide evidence that, although topoisomerase activity is essential for DNA replication, neither continuous fork propagation nor topoisomerase activity is required for chromatin assembly on new DNA.
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PMID:Inhibitors of topoisomerases I and II arrest DNA replication, but do not prevent nucleosome assembly in vivo. 255 22

K6-1 and 50B-3 cell lines, resistant to VP-16, a DNA topoisomerase II inhibitor, were established from two different types of cells respectively: human T-cell derived acute lymphoblastic leukemia cell line RPMI8402 and mouse mammary tumor cell line FM3A. IC50 values of K6-1 and 50B-3 cells to VP-16, evaluated by the colony forming ability on methyl cellulose medium, were 11- and 84-fold higher than their sensitive parental cell lines, respectively. Membrane permeability of the drug was not responsible for the resistance in K6-1 and 50B-3 cells. Quantitative analysis of drug-induced DNA cleavage (so called cleavable complex formation) was performed using 32P end-labeled pBR322 restriction fragments. The formation of the topoisomerase II-DNA cleavable complex stimulated by VP-16 in 50B-3 cells was approximately 1/5 compared with that of FM3A wild-type cells. Dot blot analysis of RNA extracted from these cell lines showed that the levels of mRNA for DNA topoisomerase II in 50B-3 cells were markedly decreased and that catalytic activity was reduced to 1/2-1/3 compared with that of parent cells. There was a slight reduction of DNA topoisomerase II mRNA in K6-1 cells. However, DNA topoisomerase II activities were similar in wild-type and K6-1 cells. In addition, 50B-3 cells showed cross resistance to VM-26, m-AMSA and adriamycin, whereas K6-1 cells exhibited increased resistance only to VM-26. These resistant cell lines did not show collateral sensitivity to CPT-11, a DNA topoisomerase I inhibitor. Southern blot analysis of genomic DNA did not show any change in the restriction pattern of the DNA topoisomerase II gene between the parental and their resistant lines. These findings suggest that the reduced levels in DNA topoisomerase II contribute to the drug resistance of 50B-3 cells.
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PMID:DNA topoisomerase: the mechanism of resistance to DNA topoisomerase II inhibitor VP-16. 256 62

We showed previously that nuclear extracts from teniposide (VM-26)-resistant sublines of the human leukemic cell line, CCRF-CEM, exhibited decreased DNA topoisomerase II activity and ability to form drug-stabilized covalent protein-DNA complexes (Danks et al., Biochemistry 27:8861-8869; 1988). In the present study, we found that nuclear extracts of these sublines (approximately 50- and approximately 140-fold resistant to VM-26) required 2 and 8 times more adenosine 5'-triphosphate (ATP), respectively, to achieve half-maximal stimulation of unknotting activity compared to extracts from the sensitive cells. When novobiocin, a competitive inhibitor of ATP binding to topoisomerase II, was included in the reaction, this ATP requirement increased 2.5- to 4-fold with the CEM cell extracts and 3.5- to 12-fold with the resistant cell extracts. ATP produced a dose-dependent increase in VM-26-stabilized topoisomerase II-DNA covalent complexes with nuclear extracts from all three cell lines. Extracts from resistant cells, however, formed 40-80% fewer complexes than those from sensitive cells. A similar decrease was seen with 4'-[(9-acridinyl)amino]methanesulphon-m-anisidide, to which the cells are cross-resistant. With nuclear extracts from sensitive cells, the tetralithium salt of 5'-adenylylimidodiphosphate (AMP-PNP), a nonhydrolyzable analog of ATP, was as effective as ATP in promoting the formation of drug-stabilized enzyme-DNA complexes. With extracts from the resistant cell nuclei, however, AMP-PNP was about half as effective as ATP in promoting complex formation. Our results demonstrate that the effect of ATP on strand passing activity of and drug-stabilized complex formation by topoisomerase II is decreased in the nuclear extracts from the drug-resistant cells and suggest a possible basis for this form of drug resistance.
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PMID:Increased ATP requirement for activity of and complex formation by DNA topoisomerase II from human leukemic CCRF-CEM cells selected for resistance to teniposide. 256 33

The effect of the ATP pool on the cytotoxic action of teniposide (VM-26) has been studied in mouse leukemia cells (L1210). L1210 cells in tissue culture were treated with VM-26 (10 microM) in the presence of DNP, an uncoupler of oxidative phosphorylation. The simultaneous treatment of DNP (1 mM) increased cell survival 100-200 fold. Pre- or post-treatment with DNP had little effect on cell survival. Other uncouplers and inhibitors of ATP synthesis had effects similar to DNP. The interference of DNP with the cytotoxic action of VM-26 was also seen with another topoisomerase II-targetting drug, m-AMSA, but not with the topoisomerase I-targetting drug camptothecin. Studies using either purified topoisomerase II or cultured mammalian cells had shown that DNP had little effect on the amount of cleavable complexes induced by VM-26. We propose that an ATP requiring process(es) which occurs subsequent to the formation of the cleavable complexes is involved in the cytotoxic action of topoisomerase II-targetting drugs.
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PMID:Involvement of intracellular ATP in cytotoxicity of topoisomerase II-targetting antitumor drugs. 281 29

The events following a mild heat exposure to cells that appear to be closely linked are: enhanced synthesis of hsp's and thermotolerance. In some cases, thermotolerance is also associated with drug resistance. We have recently examined the role that DNA topoisomerase II may play in the induction of these phenomena. VM-26 was found to both initiate hsp synthesis and to cause thermotolerance. Furthermore, the permanent heat resistant or transient thermotolerant cells were more resistant to VM-26 than controls. These results suggest that topoisomerase II, or more likely topoisomerase II-DNA complexes, are affected by heat or by VM-26 in a phenomenologically overlapping manner. Elevated levels of hsp's apparently protect cells against the cytotoxic action of both heat and VM-26.
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PMID:Heat shock proteins: role in thermotolerance, drug resistance, and relationship to DNA topoisomerases. 281 40

We characterized a DNA repair system in frog oocytes by comicroinjection of UV-irradiated pBR322 DNA and radiolabeled nucleotides. Repair synthesis was monitored by incorporation of label into recovered pBR322 DNA and by a novel method in which the removal of UV photoproducts was determined from the shift of DNA topoisomers that occurs during gel electrophoresis upon repair of these lesions. We investigated the effects of several drugs in the oocyte system and found that although novobiocin, an inhibitor of topoisomerase II, was an effective inhibitor of repair, VM-26, another inhibitor of topoisomerase II, was not. In addition, the topoisomerase I inhibitor camptothecin had no effect on repair in this system. Finally, circular DNA (either supercoiled or nicked circular) was repaired at least 50 times more rapidly than linear DNA.
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PMID:Repair of UV-induced lesions in Xenopus laevis oocytes. 283 Apr 88


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