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)

A carcinogen-transformed rat hepatoma cell line (Reuber H-35) was utilized as a model system for investigation of the biochemical factors which may limit the effectiveness of chemotherapy in intrinsically resistant tumors such as hepatocellular carcinoma. Northern blotting demonstrated expression of mRNA coding for the P-170 membrane-glycoprotein associated with the multi-drug resistance phenotype, while Western blotting identified the P-170 glycoprotein in the hepatoma cell membrane. Consistent with these observations, tumor cell sensitivity to the vinca alkaloids, vincristine and vinblastine, to the anthracycline antibiotics, Adriamycin and daunorubicin, and to the demethylepipodophyllotoxin derivative, VM-26, was enhanced by continuous incubation in the presence of the calcium channel antagonist, verapamil. Verapamil produced a minimal change in cell sensitivity to the demethylepipodophyllotoxin derivative, VP-16, and to the aminoacridine, m-AMSA. Relatively high detoxification potential via the glutathione metabolic pathway was also observed in the hepatoma cell. The capacity of topoisomerase II in nuclear extracts from the hepatoma cell to mediate cleavable complex formation stimulated by VM-26, VP-16 and m-AMSA appeared to be at least comparable to, if not greater than that from drug-sensitive HL-60 cells, suggesting that drug resistance may not occur at the level of this enzyme. Consistent with findings in a number of tumor cell lines resistant to antineoplastic drugs, the antiproliferative activity of the topoisomerase II inhibitors VM-26, VP-16 and m-AMSA appeared to be dissociable from the induction of DNA strand breaks, suggesting that such lesions in DNA may fail to fully account for the antiproliferative activity of these agents in the hepatoma cell.
...
PMID:Components of intrinsic drug resistance in the rat hepatoma. 131 Aug 53

The cutting sites specificity of topoisomerase II from porcine spleen were determined by a modified Sanger's DNA sequencing method. The topoisomerase II prefers to cut DNA at the 3' side of A and leave 5' protruding end with two staggering bases. Through the free energy analysis for DNA duplex, we also found that the topoisomerase II seemed cut DNA preferably at energetically unstable regions. So it is concluded that the specific DNA cutting by porcine spleen topoisomerase II has two structural recognition factors: one is to localize around the energetically unstable region and another is to act at the 3' side of A base.
...
PMID:The recognition of DNA cleavage sites by porcine spleen topoisomerase II. 131 Oct 75

During purification of the type I DNA topoisomerase from calf thymus mitochondria, two polypeptides, p78 and p63, cofractionate with the enzymatic activity (Lazarus et al., (1987) Biochemistry 26, 6195-6203). The two polypeptides are released from a mitochondrial inner membrane preparation by nonionic detergent lysis and both adsorb strongly to a single-stranded DNA agarose column. We have attempted to characterize the relationship between these two polypeptides and have found the following: (i) the mitochondrial topoisomerase is active in free (monomer) and associated (heterodimer) form; (ii) the catalytic activity resides solely in p78, as adjudged by both the covalent linkage of the enzyme to substrate DNA and the ability of the enzyme to relax supercoils; (iii) at low ionic strength the enzyme is active in monomer form with p78 alone being sufficient for activity; (iv) in high salt, the high molecular weight species is a 140-kDa heterodimer composed of one p78 and one p63; and (v) the two polypeptides are not structurally related as digestion with V8 protease results in distinct proteolytic fragment patterns. These results suggest that p63 may have an important role in the metabolism of the mitochondrial topoisomerase.
...
PMID:DNA topoisomerase I from calf thymus mitochondria is associated with a DNA binding, inner membrane protein. 131 Nov 59

We have identified two classes of in vivo topoisomerase II cleavage sites in the Drosophila histone gene repeat. One class co-localizes with DNase I-hypersensitive regions and another novel class maps to a subset of consecutive nucleosome linker sites in the scaffold-associated region (SAR) of the histone gene loop. Prominent topoisomerase II cleavage is also observed in one of the linker regions of the two nucleosomes spanning satellite III, a centromeric SAR-like DNA sequence with a repeat length of 359 bp. At the sequence level, in vivo topoisomerase II cleavage is highly site specific. Comparison of 10 nucleosome linker sites defines an in vivo cleavage sequence whose major characteristic is a prominent GC-rich core. These GC-rich cleavage sites are flanked by extensive arrays of oligo(dA).oligo(dT) tracts characteristic of SAR sequences. Treatment of cells with distamycin selectively enhances cleavage at nucleosome linker sites of the SAR and satellite regions, suggesting that AT-rich sequences flanking cleavage sites may be involved in determining topoisomerase II activity in the cell. These observations provide evidence for the association of topoisomerase II with SARS in vivo.
...
PMID:In vivo topoisomerase II cleavage of the Drosophila histone and satellite III repeats: DNA sequence and structural characteristics. 131 Dec 55

A group of chrysophanol and emodin derivatives with DNA-intercalating capability and with or without alkylating potential have been synthesized and shown to have antitumor activity in vitro. The topoisomerase II (Topo II)-mediated DNA cleavage activities induced by representative compounds 3-(2-chloroethylamino) methyl-1,8-dihydroxy-9,10-anthraquinone (SK-31690), 3-bis [(2-chloroethyl)amino]methyl-1,8-dihydroxy-9,10-anthraquinone (SK-31662), and 3-(2-hydroxyethylamino)methy-1,8-dihydroxy-9,10-anthraquinon e (SK-31694), and their cytotoxicities, have been investigated. All three compounds inhibited the kinetoplast DNA decatenation catalyzed by DNA Topo II. These compounds inhibited leukemia cell growth and stimulated, in a dose-dependent manner from 0.5 to 60 microM, the formation of Topo II-DNA cleavable complexes, when 3'-32P-labeled DNA was used. The mapping of Topo II-mediated DNA cleavage sites using HindIII-digested 3'-32P-labeled DNA showed that, at 10 microM, these compounds induced protein-linked DNA breaks that correlated with cytotoxicity, with respect to their maximal efficacy or the reciprocal concentration for the half-maximal effect. The reversibility study showed that the amounts of protein-linked DNA cleavage induced by 4'-(9-acridinylamino)methanesulfon-m-anisidide and VP-16 as well as SK-31694, which lacks alkylating potential, were markedly decreased during 30-sec exposure to 65 degrees or 0.5 M NaCl. In contrast, protein-linked DNA cleavages induced by SK-31662, which has two alkylating functionalities, and by SK-31690, which has one alkylating functionality in its structure, cannot be reversed during the 15-min exposure to 65 degrees or 0.5 M NaCl. These data suggest that Topo II is a major cellular target for cytotoxicity of these compounds. Furthermore, DNA intercalators with alkylating potential interact with Topo II-DNA cleavable complexes in an irreversible manner, with enhanced toxicity.
...
PMID:Topoisomerase II-mediated DNA cleavage activity and irreversibility of cleavable complex formation induced by DNA intercalator with alkylating capability. 131 6

The ATP-independent type I topoisomerase from the crustacean Artemia franciscana was purified to near-homogeneity. Its activity was measured by an assay that uses the formation of an enzyme-cleaved DNA complex in the presence of the specific inhibitor camptothecin. The purification procedure is reported. Purified topoisomerase is a single-subunit enzyme with a molecular mass of 63 kDa. Immunoblot performed on the different steps of purification shows that the purified 63 kDa peptide is a proteolytic fragment of a protein with a molecular mass of 110 kDa. Similarly to the other purified eukaryotic topoisomerases, the crustacean enzyme does not require a bivalent cation for activity, but is stimulated in the presence of 10 mM-MgCl2; moreover, it can relax both negative and positive superhelical turns. The enzyme activity is strongly inhibited by the antitumour drug camptothecin. The enzyme inhibition is related to the stabilization of the cleavable complex between topoisomerase I and DNA.
...
PMID:Purification and characterization of a proteolytic active fragment of DNA topoisomerase I from the brine shrimp Artemia franciscana (Crustacea Anostraca). 131 54

A hybrid molecule, which combines an anilinoacridine chromophore related to the antitumour drug amsacrine (m-AMSA) and a bispyrrole moiety analogous to the antiviral agent netropsin, has been examined for its ability to bind chromatin and to modulate the activity of topoisomerase II. The results show that the presence of histones does not alter the bimodal DNA binding process. Intercalation of the acridine and groove binding of the netropsin part of the drug are both observed with chromatin preparations. Moreover, the hybrid has a clear topoisomerase II-DNA cleavable complex-inducing activity close to that of m-AMSA. The role of the two parts of the hybrid ligand is discussed in relation to ternary complex formation. Two cell lines (L1210 leukemia and MCF7 mammary carcinoma) were compared in their sensitivity to the tested ligand. The drug, which appears to be an efficient growth inhibitor of leukemic cells in vitro, reveals moderate activity against P388 leukemia in vivo. The biological activity of the hybrid may derive from a mechanism that involves DNA binding and topoisomerase II inhibition. This study demonstrates that agents which intercalate and bind to the minor groove of DNA simultaneously represent a new class of drugs interfering with topoisomerase II and provide opportunities for the development of new antitumour agents.
...
PMID:Biological activity and molecular interaction of a netropsin-acridine hybrid ligand with chromatin and topoisomerase II. 131 80

A type II DNA topoisomerase, topoIImt, was shown previously to be associated with the kinetoplast DNA of the trypanosomatid Crithidia fasciculata. The gene encoding this kinetoplast-associated topoisomerase has been cloned by immunological screening of a Crithidia genomic expression library with monoclonal antibodies raised against the purified enzyme. The gene CfaTOP2 is a single copy gene and is expressed as a 4.8-kb polyadenylated transcript. The nucleotide sequence of CfaTOP2 has been determined and encodes a predicted polypeptide of 1239 amino acids with a molecular mass of 138,445. The identification of the cloned gene is supported by immunoblot analysis of the beta-galactosidase-CfaTOP2 fusion protein expressed in Escherichia coli and by analysis of tryptic peptide sequences derived from purified topoIImt. CfaTOP2 shares significant homology with nuclear type II DNA topoisomerases of other eukaryotes suggesting that in Crithidia both nuclear and mitochondrial forms of topoisomerase II are encoded by the same gene.
...
PMID:Molecular cloning and expression of the gene encoding the kinetoplast-associated type II DNA topoisomerase of Crithidia fasciculata. 131 98

We have compared topoisomerase I and II cleavage sites on the actin 5C and 57A genes and the hsp70 genes in Drosophila Kc cells using the inhibitors camptothecin (topoisomerase I specific) and VM-26 (topoisomerase II specific) to assess the role of these enzymes in transcriptional regulation. Topoisomerase I cleavage sites were localized to the transcribed regions of the actin 5C and hsp70 genes and were present only when these genes were active. The actin 57A gene, shown previously to be inactive in Kc cells, had no detectable topoisomerase I cleavage sites. In contrast to topoisomerase I, topoisomerase II cleavage sites could be detected on transcriptionally active and inactive actin and hsp70 DNA sequences. Topoisomerase II cleavage sites on the inactive hsp70 gene were primarily localized to the very 5' end of the transcribed region of the gene. However, upon heat-induced activation of hsp70 transcription, topoisomerase II cleavage rapidly shifted from the 5' to the 3' end of the gene. Then, during the shutdown of hsp70 expression, there was a gradual reappearance of topoisomerase II cleavage at the 5' end of the gene that temporally correlated with the repression of hsp70 transcription. There was a similar preferential association of topoisomerase II with the 5' ends of transcriptionally repressed actin 5C and 57A genes. These results demonstrate that there are marked differences in how topoisomerases I and II interact with transcriptionally active and inactive regions of chromatin. In addition, we have identified an unusual type of topoisomerase II binding site that is preferentially associated with the 5' ends of inactive hsp70 and actin genes, suggesting that this enzyme may facilitate changes in chromatin structure that are associated with repression of gene transcription.
...
PMID:Analysis of topoisomerase I and II cleavage sites on the Drosophila actin and Hsp70 heat shock genes. 131 49

Patterns of drug sensitivities in relation to topoisomerase II gene expression and activity were studied in eight human lung cancer cell lines not selected in vitro for drug resistance. The cytotoxicities of doxorubicin, etoposide, teniposide, cisplatin, camptothecin, and 5-fluorouracil were measured and, remarkably, these unselected cell lines were shown to have a common pattern of multidrug sensitivity, i.e., a multidrug sensitivity phenotype. In fact, drug sensitivities were significantly correlated with each other in the studied cell lines, the correlation being best for the topoisomerase II-targeted agents and cisplatin, less strong with camptothecin, and weak with 5-fluorouracil. Almost 1-log range difference of topoisomerase II gene expression was found in these cell lines, and this was not explained by the cell-doubling time or cell cycle distribution. The level of topoisomerase II gene expression was positively and highly correlated with the cell sensitivity to epipodophyllotoxins, doxorubicin, and cisplatin in seven cell lines. Although weaker, an association was also observed between topoisomerase II gene expression and camptothecin cytotoxicity, while no association was observed with 5-fluorouracil. However, a non-small cell lung cancer cell line with neuroendocrine properties had very low levels of expression of the topoisomerase II gene, despite being highly sensitive to all drugs tested. The levels of topoisomerase I gene expression were not found to be correlated with the cytotoxicity of any drug tested. A specific enzymatic activity assay and a teniposide-stimulated DNA cleavage assay showed that the extent of active topoisomerase II present in nuclear extracts paralleled the level of topoisomerase II gene expression. Furthermore, in addition to the normal transcript, an abnormally sized topoisomerase II message and a rearrangement of the topoisomerase II gene were detected in a poorly sensitive small cell lung cancer cell line. Therefore, low levels of topoisomerase II gene expression, and possibly mutations, may predict a reduced sensitivity of unselected human lung cancer cell lines to several drugs, including agents with a cellular target other than topoisomerase II. It is hypothesized that topoisomerase II might be involved in a common pathway of cell death induced by drugs in tumor cell lines which present a multidrug sensitivity phenotype.
...
PMID:Multidrug sensitivity phenotype of human lung cancer cells associated with topoisomerase II expression. 131 95


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

---