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)

DNA topoisomerase (topo) II mediates DNA strand passage in an ATP-dependent reaction. Human cell lines express at least two genetically distinct forms of the enzyme, topo II alpha (p170) and II beta (p180). Previously, we isolated a novel HeLa cDNA clone (CAA5) that partially encodes a protein homologous to topo II alpha (Austin, C.A. and Fisher, L.M. (1990) FEBS Lett. 266, 115-117). In this paper we show that CAA5 encodes a C-terminal segment of human topo II beta. We report here for the first time cDNA clones spanning the entire coding sequence. Overlapping clones specifying the 3' end of the cDNA have been isolated, mapped and sequenced. The missing 5' coding sequence was obtained by an inverse PCR protocol and from a specifically primed cDNA library. Human topo II beta is a 1621 amino acid protein which is closely homologous to topo II alpha in the N-terminal three quarters of its sequence. In contrast, the C-terminal segments of the alpha and beta sequences show considerable divergence suggesting these regions may mediate different cellular functions of the two isoforms. Southern blot analysis of yeast and Drosophila DNA using human alpha and beta specific probes detected a single topo II homologue in these lower eukaryotes. Comparison of the protein sequence for human topo II beta with other type II topoisomerases revealed several conserved motifs and has allowed identification of the likely ATPase- and DNA breakage-reunion domains.
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PMID:Novel HeLa topoisomerase II is the II beta isoform: complete coding sequence and homology with other type II topoisomerases. 838 37

Using reverse transcription polymerase chain reaction, we determined mRNA expression of topoisomerase (topo) II alpha and beta in adriamycin- and etoposide-resistant small cell lung cancer sublines, SBC-3/ADM 100 and SBC-3/ETP. The expression of topo II alpha mRNA decreased substantially in SBC-3/ADM 100 and SBC-3/ETP as compared with the parent cell line, SBC-3; 0.71-fold in the former and 0.38-fold in the latter. Similarly, that of topo II beta mRNA decreased to an extent of 0.68-fold in SBC-3/ADM 100 and 0.28-fold in SBC-3/ETP as compared with the parent cell line. SBC-3/ADM 100 and SBC-3/ETP were highly resistant to topo II inhibitors such as daunorubicin, epirubicin, pirarubicin, mitoxantrone, and teniposide. However, SBC-3/ADM 100 showed a less resistance to aclarubicin, and SBC-3/ETP was as sensitive to the drug as was in the parent cell line. The resistance to topo II inhibitors excluding for aclarubicin might be partially explained by the decreased expression of topo II alpha and beta mRNA.
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PMID:[Cytotoxic effect of topoisomerase II inhibitors against adriamycin- and etoposide-resistant small cell lung cancer sublines]. 838 62

We have developed a method to quantify topoisomerase (topo) II activities in partially purified nuclear extracts from human leukemia cells. By virtue of their different pH optima in the reaction buffer, two different topo II activities were found with activity optima at pH 7.9 and at pH 8.9 under high stringency conditions. The activities could be identified as topo II beta activity (pH 7.9) and topo II alpha activity (pH 8.9) by their different sensitivities to topo II alpha inhibitors, dephosphorylation experiments and immunoprecipitation with polyclonal antibodies. Seventy-two bone marrow or blood samples from patients with acute myeloid leukemias have been examined and their in vitro sensitivities to anthracyclines and epipodophyllotoxines correlated to the activities of topo II alpha and topo II beta. Although the topo II alpha activity could be directly inhibited by incubation of the cells with the mentioned drugs, no correlation between the topo II alpha activity and the sensitivity of the cells could be found. In contrast, the topo II beta activity which was not substantially inhibited by the drugs inversely correlated with the sensitivity of the cells. These findings were statistically significant for idarubicin (P=0.017) and daunorubicin (P=0.006). Vice versa, resistant cells (IC90 > median) had a higher topo II beta activity. Clinical relevance might be indicated by the finding that cells from patients that relapsed after initial treatment with anthracyclin-containing regiments had a significantly higher topo II alpha/beta activity ratio (P=0.0276). Obviously, the sensitivity of AML cells is substantially influenced by the activity of the resistant topo II (topo II beta) which gives evidence that the remaining topo II activity after treatment helps the cell to survive the DNA repair phase.
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PMID:Topoisomerase II activities in AML blasts and their correlation with cellular sensitivity to anthracyclines and epipodophyllotoxines. 865

We have developed a method to quantify topoisomerase (topo) II activities in partially purified nuclear extracts from human leukemia cells. By virtue of their different pH optima in the reaction buffer, two different topo II activities were found with activity optima at pH 7.9 and at pH 8.9 under high stringency conditions. The activities could be identified as topo II beta activity (pH 7.9) and topo II alpha activity (pH 8.9) by their different sensitivities to topo II alpha inhibitors, dephosphorylation experiments and immunoprecipitation with polyclonal antibodies. Seventy-two bone marrow or blood samples from patients with acute myeloid leukemias have been examined and their in vitro sensitivities to anthracyclines and epipodophyllotoxines correlated to the activities of topo II alpha and topo II beta. Although the topo II alpha activity could be directly inhibited by incubation of the cells with the mentioned drugs, no correlation between the topo II alpha activity and the sensitivity of the cells could be found. In contrast, the topo II beta activity which was not substantially inhibited by the drugs inversely correlated with the sensitivity of the cells. These findings were statistically significant for idarubicin (P= 0.017) and daunorubicin (P = 0.006). Vice versa, resistant cells (IC50 > median) had a higher topo II beta activity. Clinical relevance might be indicated by the finding that cells from patients that relapsed after initial treatment with anthracyclin-containing regiments had a significantly higher topo II alpha/beta activity ratio (P=0.0276). Obviously, the sensitivity of AML cells is substantially influenced by the activity of the resistant topo II (topo II beta) which gives evidence that the remaining topo II activity after treatment helps the cell to survive the DNA repair phase.
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PMID:Topoisomerase II activities in AML and their correlation with cellular sensitivity to anthracyclines and epipodophyllotoxines. 868 99

V511 and V513 cell lines, derived from Chinese hamster V79 cells following alkylating agent mutagenesis and subsequent selection with VP-16, showed resistance to cytotoxicity and DNA strand breaks induced by topoisomerase (topo) II inhibitors and were resistant to VP-16-induced sister chromatid exchanges. They showed no amplification of the multidrug-resistant p-glycoprotein. In a kinetoplast-DNA decatenation assay, V511 and V513 showed 51% and 49% topo II activity relative to parental V79 cells, respectively. By western-blot analysis all three logarithmically growing cell lines showed similar levels of topo II beta (M(r) 180,000), which increased as cells progressed to quiescence. In contrast, immunoreactive levels of topo II alpha (M(r) 170,000) were 6.8% in V511 and 62.4% in V513 relative to V79. V511 showed drastically decreased topo II alpha in both log growth and quiescence. In a second approach, immunoreactive topo II was analyzed in different phases of the cell cycle in logarithmically growing cells fractionated by fluorescence-activated cell sorting. All cell lines demonstrated relatively stable topo II beta throughout the cell cycle. Topo II alpha showed little cell cycle variation in V79 or V513. However, in V511, it was only detectable at low levels in G2/M phase. When cell growth parameters were measured, V511 and V513 showed a 17% increase in cell doubling time relative to V79. These studies indicate that cells with a drastic reduction in topo II alpha (V511) or mutant topo II alpha (V513) but with normal levels of topo II beta show only minor perturbations of cell growth.
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PMID:Drastic reduction of topoisomerase II alpha associated with major acquired resistance to topoisomerase II active agents but minor perturbations of cell growth. 874 4

Recently, we reported that alterations in topoisomerase II (topo II) activity appear to contribute to mitomycin C (MMC) resistance in HT-29R13 human colon cancer cells under aerobic conditions. In this study, the expression of topo II alpha and topo II beta in parent HT-29 and MMC resistant variant HT-29R13 cells was investigated under aerobic, acute hypoxic (after 4 hr in 95% N2, 5% CO2 < 0.01% O2), and chronic intermittent hypoxic (after 4 hr hypoxia/day x 7 days) conditions. Acute hypoxia induced topo II alpha mRNA and protein, effects that were more pronounced in HT-29 cells. Chronic intermittent hypoxia caused a decrease in topo alpha mRNA and protein, changes that were again more pronounced in HT-29 cells. The observed changes in topo II alpha protein were associated with parallel changes in topo II activity under all conditions tested. Topo II beta mRNA was expressed at a very low level in both cell lines under aerobic and hypoxic conditions. Compared with cells under aerobic conditions, HT-29 cells were more sensitive to MMC under acute hypoxia but more resistant under chronic intermittent hypoxia. In contrast, the senstivity of HT-29R13 cells was unchanged under acute hypoxia, but the cells were more resistant under chronic intermittent hypoxia. Under all conditions tested, the degree of cytotoxicity corresponded to the frequency of MMC-induced DNA cross-links and topo II alpha protein levels and activity. Our results demonstrated that MMC cytotoxicity in hypoxic cells is highly dependent upon the type of hypoxia and the cell type. Hypoxia has significant effects on topo II alpha expression in HT-29 and HT-29R13 cells which correlate with MMC cytotoxicity.
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PMID:Effect of acute and chronic intermittent hypoxia on DNA topoisomerase II alpha expression and mitomycin C-induced DNA damage and cytotoxicity in human colon cancer cells. 875 40

Acquired resistance to chemotherapy is the major obstacle to cure of small cell lung cancer (SCLC). Some of the most active drugs in the treatment of this tumor exert their cytotoxicity by interacting with the nuclear enzyme topoisomerase II (topo II), which in mammalian cells occurs in two isoforms, alpha and beta. We examined the relationship between levels of topo II alpha and beta and drug response in a panel of 25 unselected SCLC cell lines. Chemosensitivity to several topo II-interactive drugs, as well as other chemotherapeutic agents, was quantitated previously using a modified MTT assay. Topo II levels were determined by immunoblot analysis of whole cell lysates, with topo II alpha and beta isoform-specific antibodies, and results were expressed relative to levels found in NCI-H209 cells which had the highest topo II alpha in this series of cell lines. Levels of topo II alpha and beta mRNA were determined by Northern blotting. Pearson correlation analysis was used to determine the significance of the relationship between topo II alpha and beta levels and response to the various chemotherapeutic drugs, as well as the treatment history of the patients from whom the cell lines were derived. These analyses revealed an inverse correlation between topo II alpha levels and resistance to all of the tested drugs, including several drugs which are not known to interact with topo II. This correlation was statistically significant for doxorubicin, cisplatin, epirubicin, melphalan, nitrogen mustard, and vinblastine. With one exception (cisplatin), there were no significant correlations between topo II beta levels and drug response. There was no significant correlation between topo II alpha and beta levels and treatment history. Taken together, our results are consistent with the hypothesis that levels of topo II alpha are important determinants of drug response in SCLC.
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PMID:Topoisomerase II levels and drug response in small cell lung cancer. 2153 58

Using molecular dynamics simulations, we show here that growing plectonemes resulting from transcription-induced supercoiling have the ability to actively push cohesin rings along chromatin fibres. The pushing direction is such that within each topologically associating domain (TAD) cohesin rings forming handcuffs move from the source of supercoiling, constituted by RNA polymerase with associated DNA topoisomerase TOP1, towards borders of TADs, where supercoiling is released by topoisomerase TOPIIB. Cohesin handcuffs are pushed by continuous flux of supercoiling that is generated by transcription and is then progressively released by action of TOPIIB located at TADs borders. Our model explains what can be the driving force of chromatin loop extrusion and how it can be ensured that loops grow quickly and in a good direction. In addition, the supercoiling-driven loop extrusion mechanism is consistent with earlier explanations proposing why TADs flanked by convergent CTCF binding sites form more stable chromatin loops than TADs flanked by divergent CTCF binding sites. We discuss the role of supercoiling in stimulating enhancer promoter contacts and propose that transcription of eRNA sends the first wave of supercoiling that can activate mRNA transcription in a given TAD.
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PMID:Transcription-induced supercoiling as the driving force of chromatin loop extrusion during formation of TADs in interphase chromosomes. 2914 Apr 66


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