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)

The regulation of DNA topology by topoisomerase II from Drosophila melanogaster has been studied extensively by biochemical methods but little is known about its roles in vivo. We have performed experiments on the inhibition of topoisomerase II in living Drosophila blastoderm embryos. We show that the enzymatic activity can be specifically disrupted by microinjection of antitopoisomerase II antibodies as well as the epipodophyllotoxin VM26, a known inhibitor of topoisomerase II in vitro. By labeling the chromatin of live embryos with tetramethylrhodamine-coupled histones, the effects of inhibition on nuclear morphology and behaviour was followed in vivo using confocal laser scanning microscopy. Both the antibodies and the drug prevented or hindered the segregation of chromatin daughter sets at the anaphase stage of mitosis. In addition, high concentrations of inhibitor interfered with the condensation of chromatin and its proper arrangement into the metaphase plate. The observed effects yielded non-functional nuclei, which were drawn into the inner yolk mass of the embryo. Concurrently, undamaged nuclei surrounding the affected region underwent compensatory division, leading to the restoration of the nuclear population, and thereby demonstrating the regulative capacity of Drosophila blastoderm embryos.
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PMID:Consequences of topoisomerase II inhibition in early embryogenesis of Drosophila revealed by in vivo confocal laser scanning microscopy. 839 Oct 15

Cytotoxic drugs currently remain as the basis for the chemotherapy of metastatic cancer. Why they fail to kill sufficient tumour cells in the major human solid cancers, such as the carcinomas, is suggested in this review to be due to the inherent inability of these cells to engage apoptosis after drug-induced damage. As a paradigm for drug resistant cancers, the resistance of bladder carcinoma cell lines to DNA damaging drugs is described here in terms of their response to the topoisomerase II poison etoposide. 60%-70% of bladder carcinomas have mutant p53; this can prevent the detection of and response to DNA damage. In vitro studies with a bladder carcinoma cell line containing a wild type p53 showed that it underwent a G1 checkpoint after etoposide, potentially allowing DNA damage repair, as well as apoptosis. In lines with mutant or non-functional p53 there is no checkpoint and no apoptosis. All lines showed constitutive expression of bcl-2 and bcl-XL (the suppressors of apoptosis) with low and non-inducible levels of bax (a promoter of apoptosis). Taken together, this menu of gene expression is more favourable to survival than apoptosis after the imposition of drug-induced DNA damage and may contribute to their inherent drug resistance.
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PMID:Apoptosis and cancer chemotherapy. 895 Apr 79

UCN-01 is undergoing Phase I evaluation and is a candidate for combination strategies in the clinic. UCN-01 has been shown to have a variety of effects on cellular targets and the cell cycle. It has also been reported to sensitize cells to several clinical drugs in vitro, possibly in a manner related to p53 status. Thus, combinations of UCN-01 with a series of clinical agents in variety of cell lines have been investigated in vitro. Certain cell lines demonstrated synergistic interactions with combinations of UCN-01 (20-150 nM) and thiotepa, mitomycin C, cisplatin, melphalan, topotecan, gemcitabine, fludarabine or 5-fluorouracil. In contrast, UCN-01 combinations with the antimitotic agents, paclitaxel and vincristine, or topoisomerase II inhibitors, adriamycin and etoposide, did not result in synergy, only in additive toxicity. Cells with non-functional p53 were significantly more susceptible to the supra-additive effects of certain DNA-damaging agents and UCN-01 combinations, than cells expressing functional p53 activity. In contrast, there was no significant relationship between p53 status and susceptibility to synergy between antimetabolites and UCN-01. The mechanism behind the observed synergy appeared unrelated to effects on protein kinase C or abrogation of the cell cycle in G2. Moreover, increased apoptosis did not fully explain the supradditive response. These data indicate that UCN-01 sensitizes a variety of cell lines to certain DNA-damaging agents (frequently covalent DNA-binding drugs) and antimetabolites in vitro, but the mechanism underlying this interaction remains undefined.
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PMID:UCN-01 enhances the in vitro toxicity of clinical agents in human tumor cell lines. 1085 90

A substantial literature exists characterizing transgene locus structure from plants transformed via Agrobacterium and direct DNA delivery. However, there is little comprehensive sequence analysis of transgene loci available, especially from plants transformed by direct delivery methods. The goal of this study was to completely sequence transgene loci from two oat lines transformed via microprojectile bombardment that were shown to have simple transgene loci by Southern analysis. In line 3830, transformed with a single plasmid, one major and one of two minor loci were completely sequenced. Both loci exhibited rearranged delivered DNA and flanking genomic sequences. The minor locus contained only 296 bp of two non-contiguous fragments of the delivered DNA flanked by genomic (filler) DNA that did not originate from the integration target site. Predicted recognition sites for topoisomerase II and a MAR region were observed in the transgene integration target site for this non-functional minor locus. Line 11929, co-transformed with two different plasmids, had a single relatively simple transgene locus composed of truncated and rearranged sequences from both delivered DNAs. The transgene loci in both lines exhibited multiple transgene and genomic DNA rearrangements and regions of scrambling characteristic of complex transgene loci. The similar characteristics of recombined fragments and junctions in both transgenic oat lines implicate similar mechanisms of transgene integration and rearrangement regardless of the number of co-transformed plasmids and the level of transgene locus complexity.
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PMID:Complete sequence analysis of transgene loci from plants transformed via microprojectile bombardment. 1285 47

Giant adenomas comprise a clinical/therapeutic subset of pituitary adenomas that pose a surgical challenge. The study population consisted of 28 patients who had giant pituitary adenomas, which are defined as tumors with a diameter greater than 5cm. Clinically, five tumors (18%) were endocrinologically functional and 23 (82%) were not. During surgery, one tumor was radically excised, four were subtotally excised, 12 were partially excised, and 11 were biopsied. All of the tumors showed typical histological features of pituitary adenoma. Of the 23 clinically non-functional adenomas, 18 were gonadotrophic tumors, four were null cell adenomas and one was a silent corticotroph adenoma. The MIB-1 labeling indices ranged from 0.1% to 2.0%. The mean topoisomerase labeling index was 0.75%. Microvessel density ranged from 0.42% to 5.55%, and there was moderately intense immunostaining for vascular endothelial growth factor. The present study found giant adenomas to be invasive but slow growing, histologically benign and often gonadotrophic in subtype.
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PMID:Clinicopathologic correlates of giant pituitary adenomas. 1928 7

Our previous studies have shown that murine fibroblast cells, in which PARP-1 gene was inactivated by gene disruption, are extremely sensitive to triazoloacridone compound C-1305, an inhibitor of DNA topoisomerase II with unusual properties. Here, we show that pharmacological inhibition of PARP-1 activity by its inhibitor compound NU1025, sensitizes human cervical carcinoma HeLa cells to compound C-1305 compared to treatment with drug alone. Cytotoxic effect of drug/NU1025 of other topoisomerase II inhibitors varied depending on the dose of PARP-1 inhibitor. Increased cytotoxicity of topoisomerase II inhibitor/NU1025 combinations was attributable to the re-activation of the p53 pathway in drug-treated HeLa cells. This lead to a more stringent cell cycle checkpoint control during G2 and M and enhanced cell death by mitotic catastrophe induced by drug/NU1025 combinations. Interestingly, treatment of HeLa cells with NU1025 alone also increased p53 expression. This effect is, at least in part, related to the inhibition of proteasome activity by drug treatments. Together, our results show that concomitant inhibition of topoisomerase II and PARP-1 leads to the synergistic cytotoxic effect toward tumor cells that may be important for combination therapies with NU1025 and topoisomerase II inhibitors. We also confirmed our earlier work and show the important role of PARP-1 activity in the maintenance of the G2 arrest induced by DNA damaging drugs. Finally, based on our studies we propose that NU1025 and possibly other inhibitors of PARP-1 may be used as non-genotoxic agents to activate p53 in tumor cells with non-functional p53 pathways.
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PMID:Increased cytotoxicity of an unusual DNA topoisomerase II inhibitor compound C-1305 toward HeLa cells with downregulated PARP-1 activity results from re-activation of the p53 pathway and modulation of mitotic checkpoints. 2006 69

During chromosome duplication the parental DNA molecule becomes overwound, or positively supercoiled, in the region ahead of the advancing replication fork. To allow fork progression, this superhelical tension has to be removed by topoisomerases, which operate by introducing transient DNA breaks. Positive supercoiling can also be diminished if the advancing fork rotates along the DNA helix, but then sister chromatid intertwinings form in its wake. Despite these insights it remains largely unknown how replication-induced superhelical stress is dealt with on linear, eukaryotic chromosomes. Here we show that this stress increases with the length of Saccharomyces cerevisiae chromosomes. This highlights the possibility that superhelical tension is handled on a chromosome scale and not only within topologically closed chromosomal domains as the current view predicts. We found that inhibition of type I topoisomerases leads to a late replication delay of longer, but not shorter, chromosomes. This phenotype is also displayed by cells expressing mutated versions of the cohesin- and condensin-related Smc5/6 complex. The frequency of chromosomal association sites of the Smc5/6 complex increases in response to chromosome lengthening, chromosome circularization, or inactivation of topoisomerase 2, all having the potential to increase the number of sister chromatid intertwinings. Furthermore, non-functional Smc6 reduces the accumulation of intertwined sister plasmids after one round of replication in the absence of topoisomerase 2 function. Our results demonstrate that the length of a chromosome influences the need of superhelical tension release in Saccharomyces cerevisiae, and allow us to propose a model where the Smc5/6 complex facilitates fork rotation by sequestering nascent chromatid intertwinings that form behind the replication machinery.
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PMID:Chromosome length influences replication-induced topological stress. 2158 91