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

---

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

It has been reported that human promyelocytic leukemic HL-60 cells which undergo differentiation fail to respond by apoptosis when treated with antitumor drugs, predominantly DNA topoisomerase inhibitors. Because S phase cells are selectively sensitive to these drugs, and during differentiation there is a reduction in the proportion of cells in S phase, the reported decrease in the number of apoptotic cells could simply be a reflection of the paucity of sensitive cells in these cultures. Using cytometric methods which allow apoptosis to be related to cell cycle position, we have compared the apoptotic response of HL-60 cells growing exponentially and induced to myeloid differentiation by dimethyl sulfoxide (DMSO). The cells were treated with: (i) the DNA topoisomerase I inhibitor camptothecin (CAM), which selectively triggers apoptosis or S phase cells; (ii) the nucleoside antimetabolite 5-azacytidine (AZC) and hyperthermia, both of which preferentially affects G1 cells; and (iii) gamma radiation, which causes apoptosis predominantly of G2 + M cells. The cells exposed to 1.4% DMSO for 24 or 48 h were significantly more resistant to response by apoptosis, regardless of the nature of the agent and regardless of their position in the cell cycle. Thus, induction of differentiation lowers the cell's ability to respond to a variety of damaging agents by apoptosis and this effect is not correlated with cell cycle position. In addition, the difference in response was unrelated to expression of the apoptosis-modulating protein bcl-2, which appeared unchanged following 48 h exposure to DMSO. On the other hand, when the cells were pretreated with low concentrations of CAM or AZC, washed free of drug, and then treated with DMSO, the proportion of cells undergoing apoptosis was markedly increased, relative to drug-treated cells returned to DMSO-free medium. The present data may indicate that while the drug-induced damage screening mechanisms, which are linked to triggering apoptosis, may be more proficient in proliferating cells, the effectors of apoptosis are more expressed in cells undergoing differentiation. The data also suggest that the efficiency of chemotherapeutic agents or radiation may be reduced if a differentiating agent is used in combination therapy and is administered first. An enhancement of apoptosis, however, may be expected if the differentiating drug is administered in the reverse sequence.
...
PMID:Altered susceptibility of differentiating HL-60 cells to apoptosis induced by antitumor drugs. 750 35

DNA topoisomerases are enzymes governing the multitude of conformational changes DNA undergoes during the cell cycle. Several compounds are likely to interfere with specific steps of the catalytic cycle of these enzymes. Camptothecin arrests the activity of DNA topoisomerase I by provoking the formation of a single-stranded DNA break with the enzyme molecule covalently attached to the DNA. Exposure to m-AMSA arrests DNA topoisomerase II by the formation of a ternary complex involving the drug, the enzyme, and DNA carrying a double-stranded break. Netropsin, distamycin A, and berenil inhibit DNA topoisomerase-mediated relaxation of supercoiled DNA by an as-yet unknown mechanism. Here, we analyze the cell cycle kinetic effects of exposure to camptothecin, m-AMSA, netropsin, distamycin A, and berenil by using continuous bromodeoxyuridine labeling followed by bivariate Hoechst 33258/ethidium bromide flow cytometry. Camptothecin elicits an accumulation of cells in all compartments of the cell cycle, while exposure to m-AMSA leads mainly to retention of cells in the G0/G1 compartment and to accumulation in the G2 phase. Neither camptothecin nor m-AMSA shows a synergism with bromodeoxyuridine incorporation into the DNA. These results point toward distinct functions of the two DNA topoisomerases in the process of cell cycle traverse. The compounds binding to the minor groove of DNA interfere with all phases of the cell cycle, but with a relative emphasis on the G2 phase. Neither camptothecin nor m-AMSA exhibits a synergistic effect in combination with berenil. Hence, at the level of perturbed cell cycle kinetics a distinction can be made between compounds provoking an abortive inhibition of the catalytic cycle of DNA topoisomerases (e.g., camptothecin, m-AMSA) and those interfering with the activity of the enzyme by a distinct mechanism.
...
PMID:Distinct patterns of cell cycle disturbance elicited by compounds interfering with DNA topoisomerase I and II activity. 753 96

The interaction of DNA topoisomerase I (topo I) with a set of single- and double-stranded oligonucleotides containing 5-27 mononucleotides was investigated. All single- and double-stranded oligonucleotides were found to inhibit competitively the supercoiled DNA relaxation reaction catalyzed by topo I. The enzyme affinity for specific sequence pentanucleotides of the scissile (GACTT, Ki = 2 microM) and non-cleaved chain (AAGTC, Ki = 110 microM) is about 2-4 orders of magnitude higher than that for non-specific oligonucleotides. This specific sequence affinity increases in several cases; lengthening of single-stranded oligonucleotides, formation of stable duplexes between complementary oligonucleotides and preincubation of the enzyme with ligands before addition of supercoiled DNA. We assume that oligonucleotides having a high affinity to the enzyme can offer a unique opportunity for rational design of topoisomerase-targeting drugs.
...
PMID:High affinity interaction of mammalian DNA topoisomerase I with short single- and double-stranded oligonucleotides. 761 96

Camptothecins are DNA topoisomerase I-directed anti-tumour drugs with a novel mechanism of action. Topotecan (TPT), a hydrophilic derivative of camptothecin, is currently undergoing phase II clinical trials in small-cell lung cancer (SCLC). Human SCLC OC-NYH cells were made more than 6-fold resistant to topotecan by stepwise drug exposure and resistance was stable for 70 passages without drug. NYH/TPT cells had half the topoisomerase I level and activity of wild-type cells. However, no difference in camptothecin or topotecan inhibition of topoisomerase I-mediated DNA relaxation was found, indicating that the enzyme itself was unchanged in the resistant cell. In NYH/TPT cells, topoisomerase II alpha and beta levels were increased approximately 2-fold. Accordingly, the topoisomerase II-directed drug etoposide (VP-16) induced an increased number of DNA single-strand breaks in NYH/TPT cells. However, sensitivity to different topoisomerase II-targeting agents in NYH/TPT cells varied from increased to decreased, indicating a role for as yet unidentified factors acting on the pathway to cell death after topoisomerase II-induced DNA damage has occurred. Of 20 anti-cancer agents tested, only hydroxyurea showed marked collateral hypersensitivity in NYH/TPT cells.
...
PMID:Characterisation of a human small-cell lung cancer cell line resistant to the DNA topoisomerase I-directed drug topotecan. 764 Feb 25

The antineoplastic quinobenoxazines A-62176 and A-74932 were shown to be potent inhibitors of mammalian DNA topoisomerase II in vivo. This was demonstrated by their selective inhibition of the SV40 DNA replication stages that require topoisomerase II. Neither drug stabilized a covalent complex of the enzyme with SV40 DNA, which suggests that they are not poisons of DNA topoisomerase II. A-77601, an analog having little antitumor activity, barely inhibited DNA topoisomerase II in vivo, even at high concentrations. These findings were supported by in vitro studies which showed that A-62176 and A-74932, but not A-77601, strongly inhibited the catalytic activity of mammalian DNA topoisomerase II. A-62176 did not cause topoisomerase II-mediated DNA strand breaks in vitro under conditions in which adriamycin produced extensive DNA breakage. The antineoplastic and topoisomerase inhibitory activities of the quinobenoxazines correlate with their ability to unwind DNA. A-62176 antagonized the poisoning of topoisomerase II by VM-26 in vivo and in vitro, but had no effect on DNA breakage induced by camptothecin, a DNA topoisomerase I poison. A-62176 and A-74932 thus inhibit DNA topoisomerase II reactions at a step prior to the formation of the "cleavable complex" intermediate. These findings indicate that stabilization of the DNA topoisomerase II-DNA cleavable complex is not necessary for the antitumor activity of this class of quinolones and that the catalytic inhibition of DNA topoisomerase II may contribute significantly to the anticancer activity of other DNA topoisomerase II inhibitors.
...
PMID:Quinobenoxazines: a class of novel antitumor quinolones and potent mammalian DNA topoisomerase II catalytic inhibitors. 772 84

CPT-11-resistant human gastric and colonic xenograft lines were established by direct intratumoral injection of CPT-11 into subcutaneous SC-1-NU and CC-2-NU tumors in nude mice once a week for 10 months. The resistance of these xenograft lines to CPT-11 was confirmed by growth inhibition rate, to be 36.3% and 45.4%, respectively, compared to each parent cell line. DNA topoisomerase I activity of the nuclear extracts of SC-1-NU/CPT-11 and CC-2-NU/CPT-11, as assayed by relaxation of supercoiled DNA Col-E1, was significantly less than those of the parent lines. The cellular levels of topoisomerase I in those resistant lines measured by Western blot analysis were 0.57- and 0.79-fold lower than those of the parental lines, respectively. However, the activity of DNA topoisomerase II of those resistant cell lines assayed by decatenation of kinetoplast DNA was higher than that of the parental lines and the cellular levels of topoisomerase II in the resistant lines measured by Western blot analysis were 10.8- and 8.1-fold higher than those of the parent lines. Intracellular accumulation of CPT-11 in CPT-11-resistant tumors was not changed as compared to that of the parental lines, but hydrolysis of CPT-11 to more active SN-38 was reduced in the resistant tumors.
...
PMID:Establishment and characterization of human gastric and colonic xenograft lines resistant to CPT-11 (a new derivative of camptothecin). 777 52

Introducing the Escherichia coli topA20::Tn10 allele to Shigella flexneri results in osmotic sensitivity, a reduced growth rate, an increase in reporter plasmid supercoiling (all common to the E. coli mutants), an inability to grow on MacConkey agar and a loss of virulence gene expression. E. coli mutants harbouring this topA allele often compensate for the loss of DNA topoisomerase I by amplifying the genes coding for topoisomerase IV. Unlike the E. coli topA mutants, derivatives of S. flexneri harbouring this topA allele did not appear to acquire any compensatory mutations. We investigated the possibility that this was due in part to an inability of the S. flexneri topoisomerase IV genes to compensate for loss of DNA topoisomerase I when overexpressed. The S. flexneri genes encoding the alpha- and beta subunits of topoisomerase IV were detected and cloned in separate multicopy plasmids. These plasmids complemented well-characterized Salmonella typhimurium temperature-sensitive topoisomerase IV mutations, showing that the S. flexneri and S. typhimurium proteins are capable of combining to form active complexes. When the S. flexneri topoisomerase IV genes were cloned in the same multicopy plasmid and introduced into a S. flexneri topA mutant, the plasmid restored osmotic tolerance, improved the growth rate, allowed growth on MacConkey indicator plates and resulted in a relaxation of reporter plasmid supercoiling. The same plasmid also partially restored S. flexneri virulence gene transcription. These data show that overexpression of the S. flexneri topoisomerase IV genes can compensate for the loss of topoisomerase I in terms of general viability of the cell, DNA supercoiling, and (partially) virulence gene expression. The fact that S. flexneri does not exploit topoisomerase IV gene amplification as E. coli does points to a significant difference in the abilities of these species to adapt to the loss of topoisomerase I.
...
PMID:Overexpression of the Shigella flexneri genes coding for DNA topoisomerase IV compensates for loss of DNA topoisomerase I: effect on virulence gene expression. 778 21

DNA topoisomerase was isolated from pea leaf chloroplasts. The relaxation activity of this topoisomerase was Mg2+ dependent and sensitive to ethidium bromide and novobiocin, a gyrase inhibitor. Chloroplast topoisomerase (Topo I) was ATP independent, as shown by the characteristic gel distribution of topoisomers. Topoisomerase, compared with the known eucaryotic topoisomerase I, was not stimulated by polyamines as are spermidine, spermine, and cadaverine. Ethidium bromide, DAPI, heparin, nalidixic acid, and m-AMSA (but not camptothecin) were able to inhibit the relaxation activity of chloroplast topo I. Nalidixic acid, novobiocin, m-AMSA, camptothecin, and amiloride were tested for their effects on the topoisomerase-catalyzed "cleavage complex" between DNA and chloroplast DNA topoisomerase I.
...
PMID:The influence of antibiotics and antitumor agents on the relaxation activity of Pisum sativum leaf chloroplast topoisomerase I. 779 78

The pH dependences of the internal equilibrium (Kcl) and rate constants for site-specific DNA strand cleavage (kcl) and resealing (kr) catalyzed by Vaccinia DNA topoisomerase I have been investigated using single-turnover conditions in the pH range 4.6-9.8 at 20 degrees C. The pH dependence of the rate constant for strand cleavage (kcl) shows a bell-shaped profile with apparent pKa values of 6.3 +/- 0.2 and 8.4 +/- 0.2, suggesting base catalysis of the attack of the active site Tyr-274 on the phosphodiester phosphorus, and acid catalysis of the expulsion of the 5'-deoxyribose oxygen. A low pKa (i.e., 6.3) for Tyr-274 in the free enzyme is ruled out by NMR titration from pH 5.1 to 8.8 monitoring the C-zeta chemical shift of [zeta-13C]-tyrosine-enriched topoisomerase. The dependence of the internal equilibrium constant (Kcl) on pH reveals very similar pKa values as kcl (5.8 +/- 0.2 and 8.6 +/- 0.2). However, kr is found to be independent of pH. The differing response of kcl and kr to pH rules out a simple two-state internal cleavage equilibrium and suggests that a conformational change occurs following formation of the covalent complex which retains the correct protonation state for strand religation. A conformation step is further indicated by a 4.6-fold "thio effect" on kcl upon substitution of the nonbridging oxygen atom of the attacked phosphoryl group by sulfur [Stivers, J. T., Shuman, S., & Mildvan, A. S. (1994) Biochemistry 33, 327], and the absence of such an effect on kr, (krphos/krthio = 0.9 +/- 0.2), indicating the rates of cleavage and religation to be limited by covalent chemistry and a conformational step, respectively. The rate constant of this conformational change in the direction of religation agrees with the average rate constant for supercoil release from plasmid substrates, suggesting this conformational change to be a part of the topoisomerization step. Although the general acid and general base catalysts have not yet been identified, the quantitative roles of these and other residues in catalysis are discussed.
...
PMID:Vaccinia DNA topoisomerase I: kinetic evidence for general acid-base catalysis and a conformational step. 780 9

Two synthetic DNA molecules that can be knotted have been employed as substrates for E. coli DNA topoisomerases I and III. Both molecules contain 104 nucleotides, including sequences that can form two single-turn helical domains, connected by single-stranded oligo(dT) linkers in an X-Y-X'-Y' pairing motif. One of the knots can be ligated to form cyclic molecules with the topologies of a circle, a trefoil knot with negative nodes, or a figure-8 knot. Cyclic molecules constructed from the other molecule can form a circle, a figure-8 knot, and trefoil knots with either positive or negative nodes. The topologically negative nodes in these knots are derived from right-handed B-DNA, and the positive nodes are derived from left-handed Z-DNA. The topoisomerases can catalyze the interconversion of the different topological forms of these molecules, as a function of solution conditions and the extent to which they favor B-DNA or Z-DNA. The enzymes appear to catalyze a single strand-passage event at a time. The topoisomerases can catalyze strand passage events involving both positive and negative nodes as substrates. Gel retention experiments show that both knots can bind up to four molecules of E. coli DNA topoisomerase I. The thermal denaturation of the domains of a trefoil knot closely related to these knots suggests that the two helical domains are uncoupled, so the single-stranded linkers in the knots are not taut. Chemical ligation experiments yield a distribution of products similar to those of enzymatic ligation, showing that the ATP cofactor in DNA knot ligation does not appear to skew the products markedly. Knots that are stressed by being placed in unfavorable solution conditions have been shown to be a highly sensitive system for detecting topoisomerase activity.
...
PMID:Topological transformations of synthetic DNA knots. 781 63


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---