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)

We have investigated the in vivo DNA supercoiling sensitivity of the Escherichia coli tRNA(1tyr) gene (tyrT) promoter in its normal chromosomal location. Here, the native tyrT promoter is found to be exquisitely sensitive to mutations and to drugs which alter the level of DNA supercoiling. We show that the response of the tyrT promoter to supercoiling is qualitatively similar to that of a known supercoiling-sensitive tRNA gene promoter, hisR. Specifically, treatments which increase in vivo DNA supercoiling levels enhance transcription of these tRNA genes. Particularly striking is the strong enhancement of expression from both promoters by a transposon insertion mutation in the topA gene encoding DNA toposisomerase I. This phenotypic effect can be complemented by providing active topoisomerase I in trans from a recombinant plasmid. Interestingly, it can also be complemented by overexpression of the genes encoding the subunits of DNA topoisomerase IV. We believe that this is the first demonstration that DNA topoisomerase IV can influence gene expression and it suggests that DNA topoisomerase I is partially redundant, at least in E. coli.
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PMID:Escherichia coli tyrT gene transcription is sensitive to DNA supercoiling in its native chromosomal context: effect of DNA topoisomerase IV overexpression on tyrT promoter function. 783 May 53

The cytotoxic plant alkaloid camptothecin promotes DNA topoisomerase I-linked nicks in DNA by stabilizing a covalently bound enzyme-DNA complex. In the yeast Saccharomyces cerevisiae, substitution of Arg and Ala for the amino acid residues immediately N-terminal to the active site tyrosine in the yeast and human DNA topoisomerase I mutants, top1 vac, results in camptothecin resistance. To examine the mechanism of drug resistance, we assessed the sensitivity of these enzymes to several classes of DNA topoisomerase poisons. Yeast cells expressing the camptothecin-resistant top1 vac mutants were resistant to all of the camptothecin derivatives cytotoxic to wild-type TOP1-expressing cells. This correlated with a significant reduction in drug-induced DNA cleavage in vitro. However, the yeast and human mutant enzymes differed in their responses to the minor groove binding ligand netropsin and to saintopin, a DNA intercalator that targets both DNA topoisomerase I and II. The yeast mutant enzyme demonstrated enhanced sensitivity to the action of saintopin but was resistant to the inhibitory effects of netropsin. In contrast, the human Top1 vac enzyme was resistant to saintopin and indistinguishable from the wild-type enzyme in its response to the netropsin. These results are discussed in terms of enzyme function and the different modes of action of these DNA topoisomerase poisons.
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PMID:A camptothecin-resistant DNA topoisomerase I mutant exhibits altered sensitivities to other DNA topoisomerase poisons. 789 Jul 48

DNA topoisomerase I isolated from the lower eukaryote Neurospora crassa mitochondria was characterized. Molar mass of the enzyme in the native state is 120 kDa and 60-65 kDa when denatured. The pH optimum of the enzyme is 7.8 and the KCl optimum concentration is 40 mmol/L. This topoisomerase is independent of ATP and Mg2+. N-Ethylmaleimide, 4-chloromercuribenzoate, SDS, guanidinium chloride, polyethylene glycol, heparin and ethidium bromide inhibit its activity, while novobiocin, nalidixic acid, Triton X-100 and chloroquine do not. Polyamines and histone H1 stimulate the topoisomerase activity. We classify this DNA topoisomerase as type I and eukaryotic. Conversion of the topoisomerase to a nonspecific endonuclease at increased temperature is proposed.
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PMID:Characterization of mitochondrial DNA topoisomerase I from Neurospora crassa. 795 26

Homologous recombination is a fundamental biological process. Biochemical understanding of this process is most advanced for Escherichia coli. At least 25 gene products are involved in promoting genetic exchange. At present, this includes the RecA, RecBCD (exonuclease V), RecE (exonuclease VIII), RecF, RecG, RecJ, RecN, RecOR, RecQ, RecT, RuvAB, RuvC, SbcCD, and SSB proteins, as well as DNA polymerase I, DNA gyrase, DNA topoisomerase I, DNA ligase, and DNA helicases. The activities displayed by these enzymes include homologous DNA pairing and strand exchange, helicase, branch migration, Holliday junction binding and cleavage, nuclease, ATPase, topoisomerase, DNA binding, ATP binding, polymerase, and ligase, and, collectively, they define biochemical events that are essential for efficient recombination. In addition to these needed proteins, a cis-acting recombination hot spot known as Chi (chi: 5'-GCTGGTGG-3') plays a crucial regulatory function. The biochemical steps that comprise homologous recombination can be formally divided into four parts: (i) processing of DNA molecules into suitable recombination substrates, (ii) homologous pairing of the DNA partners and the exchange of DNA strands, (iii) extension of the nascent DNA heteroduplex; and (iv) resolution of the resulting crossover structure. This review focuses on the biochemical mechanisms underlying these steps, with particular emphases on the activities of the proteins involved and on the integration of these activities into likely biochemical pathways for recombination.
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PMID:Biochemistry of homologous recombination in Escherichia coli. 796 21

Altered DNA topoisomerase I and II have been shown in many cell lines resistant to topoisomerase inhibitors, showing that topoisomerases are main molecular targets of these inhibitors. In this paper, recent studies on the mechanism of resistance to DNA topoisomerase I and II inhibitors are reviewed.
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PMID:[Recent progress in the study of the mechanism of resistance to DNA topoisomerase inhibitors]. 800 33

The apoptosis-associated DNA strand breaks were detected in situ, in individual leukemic cells in peripheral blood and bone marrow of over 110 patients with different types of leukemia (ALL, AML, CML in blastic crisis, APL), prior to and during routine chemotherapy. The DNA strand breaks were labeled with digoxigenin- or biotin-conjugated dUTP in the reaction catalyzed by exogenous terminal deoxynucleotidyl transferase, and the cells, counterstained for DNA, were analyzed by bivariate flow cytometry. The proportion of cells with DNA strand breaks prior to therapy, most likely reflecting spontaneous apoptosis, varied from 0.1 to 16%, but in the large majority of cases was below 3%. Administration of drugs of different classes, which included DNA topoisomerase I (Topotecan) and II (mitoxantrone, VP-16) inhibitors, antimetabolite (ara-C) or microtubule poison (Taxol), all triggered the appearance of cells with extensive DNA breakage, typical of apoptosis, to up to 80%. The peak of the response, measured as maximal percent of cells with DNA strand breaks, which varied between individual patients by as much as factor 10, was generally seen between 8 to 24 h after the initial administration of DNA topoisomerase inhibitors, and somewhat later (48-72 h) during the response to Taxol or ara-C. Thus, the data show that the response to treatment with a variety of drugs, in terms of induction of apoptosis, can be conveniently measured by the present method. The prognostic value of the apoptotic index, before, as well as during treatment, is being estimated for each type of leukemia, in the ongoing prospective studies.
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PMID:Apoptotic cell death during treatment of leukemias. 807 83

Over the past decade, DNA topoisomerase I and II appeared to be the targets of some antitumor agents: CPT-11 and Topotecan derived from Camptothecin which interact with topoisomerase I; Actinomycin D, Adriamycin and Daunorubicin, Elliptinium Acetate, Mitoxantrone, Etoposide and Teniposide, Amsacrine which interact with topoisomerase II. The multiple functions of these enzymes are important as they play a role during replication, transcription, recombination, repair and chromatine organisation. Particularly, they relax torsional constraints which appear when intertwined DNA strands are separated while replication fork or RNA polymerases are moving. To some extent, topoisomerase I and II are structurally and functionally different. Moreover, topoisomerase I is not indispensable for a living cell whereas topoisomerase II is. Drug-topoisomerase interaction which probably leads to antitumoral effect of the compounds studied in this review is not a trivial inhibition of the enzyme but rather a poisoning due to stabilization of cleavable complexes between the enzyme and DNA. These stabilized complexes are likely to induce apoptosis-like programmed cell death, which is characterised by DNA fragmentation. However, it appears that it is the collision of the replication fork with the drug-stabilized cleavable complex that is responsible for the cytotoxicity of the drug: poisoning of topoisomerases by antitumor agents leads to a new concept of "dynamic toxicity". Although they interact with a common target, topoisomerase II poisons have differential effects on macromolecules syntheses, cell cycle and chromosome fragmentation; a few compounds may produce free radicals. Because of these differential effects in addition to quantitative and qualitative variations of stabilized cleavable complexes, in particular DNA sequences on which topoisomerase II is stabilized, these antitumor agents do not resemble each other. Cellular resistance to topoisomerases poisons results of two principal types of alteration: target and/or drug transport modification. Decreased ability to form the cleavable complex in resistant cells may be the consequence of both decreased amount of topoisomerase or altered enzyme. On the other hand, overexpression of membrane P-glycoprotein, which pumps drugs out of the cell by an energy dependent process provokes a decreased accumulation of these drugs. Cross resistances to other drugs are mainly under control of these two different mechanisms of resistance. A complete knowledge of their individual effects and mechanisms of resistance would allow a better clinical use of topoisomerases poisons, especially when administered in combination chemotherapy.
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PMID:[Poisons of DNA topoisomerases I and II]. 808 Oct 34

Titration of Escherichia coli DNA topoisomerase I with PMPS and 65Zn(II) binding showed independent release and binding of the three Zn(II) in each enzyme molecule. Removal of Zn(II) from topoisomerase I or top85 (truncated topoisomerase I with the Zn(II) binding domain at the carboxyl terminal) affected their sensitivity to Glu-C and Asp-N endoproteases but there was no significant effect on their rate of proteolysis by trypsin or Lys-C endoprotease. This suggested that Zn(II) removal did not result in complete unfolding of topoisomerase enzyme structure but only affected folding of small local regions. Digestion with carboxypeptidase Y further demonstrated that the folding of the zinc binding region itself was altered upon Zn(II) removal.
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PMID:Binding of Zn(II) to Escherichia coli DNA topoisomerase I. 808 Dec 8

In order to clarify the mechanism of drug resistance in human myeloma cells, we investigated the expressions of DNA topoisomerase I and topoisomerase II gene and the genes possibly related to drug resistance; multi-drug resistant gene 1 (MDR-1), glutathione S-transferase class pi gene (GST-pi), by Northern blotting. Myeloma cells in eight of 15 cases prior to chemotherapy expressed topoisomerase I mRNA considerably, while the expression of topoisomerase II mRNA was detected weakly in only one of 16 myeloma patients. There was not any correlation between expression of topoisomerase I mRNA and clinical drug resistance. Significant expression of MDR-1 mRNA and P-glycoprotein was not detected in 25 cases of multiple myeloma prior to chemotherapy and even after several courses of VAD (vincristine, adriamycin and dexamethasone) therapy by Northern blotting and immunostaining using monoclonal anti-P-glycoprotein antibody (MRK-16), respectively. On the other hand, 16 of 21 myeloma cases showed significant expression of GST-pi protein and GST-pi mRNA with the various strengths, but there was no apparent correlation between GST-pi mRNA expression and clinical response. Therefore these data suggest that expression of the genes we tested may not determine the level of drug resistance in multiple myeloma, but lower or no significant expression of topoisomerase II mRNA in most myeloma cells indicates the possibility that topoisomerase II inhibitors such as VP-16 and topoisomerase II-mediated cytotoxic drugs such as adriamycin, are not so effective for the treatment of multiple myeloma.
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PMID:Expressions of DNA topoisomerase I and II gene and the genes possibly related to drug resistance in human myeloma cells. 809 26

The three-dimensional structure of the 67K amino-terminal fragment of Escherichia coli DNA topoisomerase I has been determined to 2.2 A resolution. The polypeptide folds in an unusual way to give four distinct domains enclosing a hole large enough to accommodate a double-stranded DNA. The active-site tyrosyl residue, which is involved in the transient breakage of a DNA strand and the formation of a covalent enzyme-DNA intermediate, is present at the interface of two domains. The structure suggests a plausible mechanism by which E. coli DNA topoisomerase I and other members of the same DNA topoisomerase subfamily could catalyse the passage of one DNA strand through a transient break in another strand.
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PMID:Three-dimensional structure of the 67K N-terminal fragment of E. coli DNA topoisomerase I. 811 10


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