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

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Query: EC:5.99.1.3 (topoisomerase)
9,911 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An experimental model of advanced human neuroblastoma, IGR-N-91, which is able to disseminate in the nude mouse, has been described. The present study was designed to ascertain which cell population from the IGR-N-91 primary tumour actually disseminates throughout the animals. In s.c. IGR-N-91 tumour xenografts, 3 areas, called pearly, vascularized and haemorrhagic, depending on the presence of blood vessels and haemorrhagic suffusions, were consistently observed and independently resected. Molecular analysis of tumour materials revealed a significant increase in MYCN and max gene transcript levels in the haemorrhagic area, as compared with the pearly and vascularized areas. Given the growth kinetics observed both in vitro and in vivo, and the DNA flow-cytometry profiles of tumour cells obtained from the haemorrhagic area, this transcriptional increase did not appear to be associated with enhanced proliferation. In this area of the tumours, multidrug-resistance-related genes, i.e., MDRI, MRP, GST-pi and topoisomerase II alpha were activated concomitantly with MYCN and max genes. The same observations were made, except for the topoisomerase-II alpha gene, when sub-lines derived from metastases were compared with that derived from the primary tumour. These data demonstrate that over-expression of several genes determining the multi-drug-resistance phenotype precedes the metastatic spread of IGR-N-91 NB tumour cells in the nude mouse. Data also suggest that the cell sub-population exhibiting this pleiotropic over-expression within the primary tumour undergoes selection during metastatic dissemination.
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PMID:Pleiotropic over-expression of multidrug-resistance-related genes is correlated to MYCN and max mRNA accumulation during tumour progression in the IGR-N-91 human neuroblastoma model. 903 51

Drug-resistance in cell lines and in malignant human tumours is associated with dysregulation of several genes including mdr1, MRP1, GST-pi, bcl-2, DNA topoisomerase II alpha and beta, and thymidine kinase I. mRNA expression was evaluated by quantitative RT-PCR coupled with HPLC in three human tumour cell lines and drug-resistant (DR)-sublines. DR sublines from RPMI-8226 and KB cells specifically overexpressed the mdr1 gene without major changes observed in other putative DR-associated genes. In contrast, the DR-H69 cells exhibited a 34-fold overexpression of the MRP gene accompanied by significant down-regulation of both DNA topoisomerase II alpha and bcl-2 mRNA gene expression, by factors of 43 and 13 respectively. These results demonstrate the concomitant down regulation of topoisomerase II alpha and bcl-2 genes in response to DR. Furthermore, differential patterns of gene dysregulations appear to vary depending upon both the drug used to select resistance and cellular origin.
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PMID:Assessment of drug-induced dysregulations among seven resistance-associated genes in human tumour cell lines. 904 17

Topoisomerases are nuclear enzymes that remove torsional stress in DNA. Their function is important for replication, transcription, chromosome condensation, and chromosome segregation during mitosis and meiosis. The goal of this work is to analyze both expression and function of topoisomerases during the meiotic stages of mammalian spermatogenesis. The patterns of expression of topoisomerase I and topoisomerase II alpha genes were followed on Northern blots of RNA from testes of mice of different ages and from specific germ cell populations. The transcript of the topoisomerase I gene was highest in somatic cells of the testis and in the mitotically proliferating spermatogonia and meiotic prophase spermatocytes, with the level of transcript decreasing dramatically in postmeiotic spermatids. In contrast, the levels of topoisomerase II alpha transcript were negligible in germ-cell free testes and highest in late meiotic prophase cells and round spermatids. Enzyme activity for both topoisomerase I and topoisomerase II was detected in both pachytene spermatocytes and in round spermatids; topoisomerase II exhibited a higher level of activity in meiotic spermatocytes than in round spermatids. In cultured cells, camptothecin, an inhibitor of topoisomerase I, caused some abnormalities of paired meiotic homologs, but did not inhibit the transition to metaphase. In contrast, teniposide and ICRF-193, inhibitors of topoisomerase II, dramatically inhibited the formation of metaphase chromosomes in cells induced to progress from prophase to metaphase. However, the disassembly of the synaptonemal complex was not inhibited, indicating that this process could be uncoupled from condensation of chromatin to form chromosomes. These studies constitute evidence for a functional requirement for topoisomerase II activity in the transition from meiotic prophase to meiotic metaphase I in mammalian spermatocytes.
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PMID:Analysis of expression and function of topoisomerase I and II during meiosis in male mice. 909 96

Several chemotherapeutic agents act via inhibition of topoisomerase (topo) II activity. Topo II levels appear to correlate with drug sensitivity in vivo. The DNA immediately 5' to the topo II alpha coding region contains five potentially regulatory inverted CCAAT boxes (ICB). Electrophoretic mobility shift assays (EMSA) using oligomers containing the wild type forms of these ICBs show specific DNA-protein binding. Mutations in these ICBs result in loss of protein binding. EMSA competition studies indicate that the four most 3' ICBs (1-4) bind to the same protein(s), while the most 5' ICB (5) binds to a different protein(s). EMSA supershift assays with antibodies to two known CCAAT binding proteins, CBF and CEB/P, indicate that ICBs 1-4 are binding to CBF, but ICB 5 is not bound by either of these proteins.
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PMID:Evaluation of a potential regulatory role for inverted CCAAT boxes in the human topoisomerase II alpha promoter. 912 21

AMCA (methyl N-[4-(9-acridinylamino)-2-methoxyphenyl]carbamate hydrochloride), an amsacrine analogue containing a methylcarbamate rather than a methylsulphonamide side chain, contrasts with amsacrine, doxorubicin and etoposide in its relatively high cytotoxicity against non-cycling tumour cells. AMCA bound DNA more tightly than amsacrine, but the DNA base selectivity of binding, as measured by ethidium displacement from poly[dA-dT].[dA-dT] and poly[dG-dC].[dG-dC], was unchanged. AMCA-induced topoisomerase cleavage sites on pBR322, C-MYC and SV40 DNA were investigated using agarose or sequencing gels. DNA fragments were end-labelled, incubated with purified topoisomerase II from different mammalian sources and analysed after treatment with sodium dodecylsulphate/proteinase K. AMCA stimulated the cleavage activity of topoisomerase II, but the DNA sequence selectivity of cleavage was different from that of amsacrine and other topoisomerase inhibitors. It was similar to that of the methoxy derivative of AMCA, indicating that the changed specificity resulted from the carbamate group rather than from the methoxy group. The pattern of DNA cleavage induced by AMCA was similar for topoisomerase II alpha and II beta.
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PMID:A carbamate analogue of amsacrine with activity against non-cycling cells stimulates topoisomerase II cleavage at DNA sites distinct from those of amsacrine. 913 99

DNA topoisomerase II alpha is a nuclear enzyme essential for DNA metabolism and cell cycle progression. Previous studies have shown that human tumor cell lines can express more than one topoisomerase II alpha isoform through alternative splicing. A 160-kDa isoform of topoisomerase II alpha has been described in several cell lines selected for resistance to inhibitors of DNA topoisomerase, but its physiological function has not been defined. In the present study, we have identified two major (160 and 140 kDa) and two minor (150 and 145 kDa) isoforms of topoisomerase II alpha in drug-sensitive human leukemic CEM cells, all of which have lost C-terminal regions that produce epitopes recognized by specific antibodies. Reverse transcription-polymerase chain reaction and molecular cloning identified four alternatively spliced transcripts of topoisomerase II alpha from CEM cells. Furthermore, nucleotide sequencing indicated that the 160-kDa isoform is encoded by two transcripts derived from alternative splicing at a different C-terminal site and that the other two transcripts likely code for the 150-kDa isoform. Although the full-length topoisomerase II alpha resided in the cell nucleus, all altered isoforms, except the 160 kDa that was located in both cytoplasmic and nuclear extracts in about equal amount, were shown to be present predominantly in the cytosol. In contrast to the observations of other groups, we have not found an association of the topoisomerase II alpha isoforms with drug resistance. Rather, our results suggest that expression of topoisomerase II alpha isoforms is cell type specific or might be associated with the neoplastic phenotype of the cells. Thus, although T-lineage tumor cell lines examined (CEM, Jurkat, and H9) displayed altered topoisomerase II alpha isoforms, normal T cells expressed only a full-length copy of the gene. Together, these results suggest that expression of altered topoisomerase II alpha isoforms is not limited to drug resistance, but might be a feature of neoplastic cells.
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PMID:Heterogeneous expression of DNA topoisomerase II alpha isoforms in tumor cell lines. 926 90

Variants of the human ovarian carcinoma cell line, OAW42, exhibiting low-level intrinsic resistance (OAW42-SR) and drug-induced higher-level resistance (OAW42-A1 & OAW42-A), were studied along with a sensitive clonal population (OAW42-S) which was isolated from OAW42-SR. Expression of the MDR-associated protein P-170, the more recently discovered LRP (lung resistance-related protein) and MRP (multidrug resistance-associated protein), topoisomerase II alpha and beta, GST pi and the cytoskeletal proteins, cytokeratin 8 and vimentin, were studied (using immunocytochemistry and Western blotting techniques) in conjunction with drug (doxorubicin) accumulation and subcellular distribution. Expression of mRNA for P-170, MRP, topoisomerase 11 alpha and beta and GST pi was studied using RT-PCR (reverse transcriptase polymerase chain reaction). Results indicate differential co-expression of four MDR-associated parameters (P-170, MRP, LRP and reduced topoisomerase II alpha and beta) in the OAW42-SR and OAW42-A1 variants, whereas resistance in the OAW42-A variant appeared to be mainly P-170 mediated. Comparable amounts of MRP and greater amounts of LRP were detected in the OAW42-S cells compared to the OAW42-SR variant (which showed increased resistance compared to the OAW42-S cells), but all cell lines expressed similar low-level amounts of MRP mRNA (by RT-PCR). GST pi levels did not differ markedly between variants. Increased levels of the cytoskeletal proteins were observed with increasing levels of resistance. The relative resistance of the variants, OAW42-SR and OAW42-A1, compared with OAW42-S was seen to change during increased serial passaging of the cells. There was greater drug accumulation by the sensitive OAW42-S cell line compared with that of the resistant variants, particularly the most highly resistant OAW42-A cells. Both verapamil and cyclosporin A effectively restored the accumulation defects seen in the resistant variants, cyclosporin A being the more effective of the two. Sub-cellular location of drug was predominantly in the nucleus with maximum levels seen in the sensitive OAW42-S variant and minimum levels in the most resistant OAW42-A clone.
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PMID:Co-expression of MDR-associated markers, including P-170, MRP and LRP and cytoskeletal proteins, in three resistant variants of the human ovarian carcinoma cell line, OAW42. 927 50

Acquisition of resistance to anticancer agents is a serious problem for cancer chemotherapy. The present study analyzed the relationship between expression of the alpha isoform of deoxyribonucleic acid (DNA) topoisomerase II (topo II alpha) and chemosensitivity to topo II inhibitors by modulating the level of topo II alpha expression. A phosphorothioate analogue of an 18-nucleotide oligomer which is complementary to the translation initiation site of the human topo II alpha messenger ribonucleic acid sequence was used to suppress the expression of topo II alpha in a human glioma cell line (U373MG). The topo II alpha activity of the treated cells was reduced to 1/3 of untreated cells in a decatenation assay using kinetoplast DNA. Antisense oligoDNA-treated cells showed mild resistance to the topo II inhibitors, etoposide and adriamycin, of about 2.0 fold and 1.5 fold, respectively, compared to control cells. Only partial reduction in the activity of topo II alpha in the glioma cell line can cause a measurable resistance to topo II inhibitors, implying that the degree of topo II expression is correlated with chemosensitivity to topo II inhibitors.
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PMID:Induction of resistance to etoposide and adriamycin in a human glioma cell line treated with antisense oligodeoxynucleotide complementary to the messenger ribonucleic acid of deoxyribonucleic acid topoisomerase II alpha. 933 May 28

In the Chinese hamster lung cell line DC-3F/9-OH-E, made resistant to 9-OH-ellipticine and cross-resistant to other topoisomerase II inhibitors, the amount of topoisomerase II alpha is 4-5-fold lower than in the parental DC-3F cells. A mutation in position 1710 of topoisomerase II beta cDNA, generating a stop codon, completely abolishes the expression of this isoform in DC-3F/9-OH-E cells. To analyze the contribution of the loss of topoisomerase II beta to the resistance phenotype, DC-3F/9-OH-E cells were cotransfected with two plasmids, one conferring the resistance to G418, the other carrying the topoisomerase II beta cDNA. Among 200 G418-resistant clones, one was found to contain a topoisomerase II beta activity similar to that in the parental cells. These cells constitute an in vivo mammalian model to study the pharmacological role of topoisomerase II beta. In the transfected cells, different levels of cleavable complex formation and resistance reversion were observed with each topoisomerase II inhibitor examined. This work demonstrates that topoisomerase II beta is a pharmacological target for 9-OH-ellipticine, etoposide, or 4'-(9-acridinylamino)methanesulfon-m-anisidide and plays a role in the cytotoxicity of these agents. Furthermore, topoisomerase II beta is the preferential target for 4'-(9-acridinylamino)methanesulfon-m-anisidide. The loss of topoisomerase II beta activity in the DC-3F/9-OH-E cells is then in part responsible for their resistance to topoisomerase II inhibitors.
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PMID:Role of topoisomerase II beta in the resistance of 9-OH-ellipticine-resistant Chinese hamster fibroblasts to topoisomerase II inhibitors. 933 Oct 91

Identifying transcriptional regulators of DNA topoisomerase II alpha (topo II alpha) is essential to decipher the mechanisms underlying leukemia cell resistance to topo II-directed antitumor drugs. We have previously reported that the proto-oncogene transcription factor c-Myb transactivates the topo II alpha promoter in several hematopoietic cell lines. Currently, we investigate whether NF-M, a C/EBP beta family member, cooperates with c-Myb in activating topo II alpha transcription. Although NF-M is the most efficacious trans-activator of topo II alpha that we have examined (approximately 38-fold over basal), NF-M does not appear to be involved in the endogenous transcriptional regulation of topo II alpha. Interestingly, we report that the sodium butyrate-dependent induction of the topo II alpha promoter observed previously appears to be mediated by c-Myb, independent of NF-M.
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PMID:NF-M trans-activates the human DNA topoisomerase II alpha promoter independently of c-Myb in HL-60 cells. 944 36


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