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 analysed the contribution of several parameters, e.g. drug accumulation, MDR1 P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP) and topoisomerase (topo) II, to drug resistance in a large set of drug-resistant variants of the human non-small-cell lung cancer cell line SW-1573 derived by selection with low concentrations of doxorubicin or vincristine. Selection with either drug nearly always resulted in MDR clones. The resistance of these clones could be explained by reduced drug accumulation and was associated with a decrease rather than an increase in the low MDR1 mRNA level. To test whether a decrease in MDR1 mRNA indirectly affected resistance in these cells, we introduced a MDR1-specific hammerhead ribozyme into wild-type SW-1573 cells. Although this led to a substantial reduction in MDR1 mRNA, it did not result in resistance. In all resistant clones we found an altered form of the multidrug resistance-associated protein (MRP), migrating slightly slower during SDS-polyacrylamide gel electrophoresis than MRP in parental cells. This altered MRP was also present in non-P-gp MDR somatic cell hybrids of the SW-1573 cells, demonstrating a clear linkage with the MDR phenotype. Treatment of crude cellular membrane fractions with N-glycanase, endoglycosidase H or neuraminidase showed that the altered migration of MRP on SDS-PAGE is due to a post-translational modification. There was no detectable difference in sialic acid content. In most but not all doxorubicin-selected clones, this MDR phenotype was accompanied by a reduction in topo II alpha mRNA level. No reduction was found in the clones selected with vincristine. We conclude from these results that selection of the SW-1573 cell line for low levels of doxorubicin or vincristine resistance, predominantly results in MDR with reduced drug accumulation associated with the presence of an altered MRP protein. This mechanism can be accompanied by other resistance mechanisms, such as reduced topo II alpha mRNA in case of doxorubicin selection.
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PMID:Altered MRP is associated with multidrug resistance and reduced drug accumulation in human SW-1573 cells. 764 Feb 9

Saccharomyces cerevisiae top2 mutants deficient in topoisomerase II activity are defective in chromosome segregation during both mitotic and meiotic cell divisions. To identify proteins that act in concert with topoisomerase II during chromosome segregation in S.cerevisiae, we have used a two-hybrid cloning approach. We report the isolation of the PAT1 gene (for protein associated with topoisomerase II), which encodes a novel 90 kDa proline- and glutamine-rich protein that interacts with a highly conserved, leucine-rich region of topoisomerase II in vivo. Strains lacking Pat1p exhibit a slow growth rate and a phenotype reminiscent of conditional top2 mutants grown at the semi-permissive temperature; most notably, a reduced fidelity of chromosome segregation during both mitosis and meiosis. These findings indicate that the PAT1 gene is necessary for accurate chromosome transmission during cell division in eukaryotic cells and suggest that the interaction of Pat1p and topoisomerase II is an important component of this function.
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PMID:Pat1: a topoisomerase II-associated protein required for faithful chromosome transmission in Saccharomyces cerevisiae. 897 67

Topoisomerases catalyse changes in the topological state of DNA and are required for many aspects of DNA metabolism. While the functions of topoisomerases I and II in eukaryotes are well established, the role of topoisomerase III remains poorly defined. We have identified a gene in the fission yeast Schizosaccharomyces pombe, designated top3 (+), which shows significant sequence similarity to genes encoding topoisomerase III enzymes in other eukaryotic species. In common with murine TOP3 alpha, but in contrast to Saccharomyces cerevisiae TOP3, the S.pombe top3 (+)gene is essential for long-term cell viability. Fission yeast haploid spores containing a disrupted top3 (+)gene germinate successfully, but then undergo only a limited number of cell divisions. Analysis of these top3 mutants revealed evidence of aberrant mitotic chromosome segregation, including the 'cut' phenotype, where septation is completed prior to nuclear division. Consistent with the existence of an intimate association (originally identified in S.cerevisiae ) between topoisomerase III and DNA helicases of the RecQ family, deletion of the rqh1 (+)gene encoding the only known RecQ helicase in S.pombe suppresses lethality in top3 mutants. This conservation of genetic interaction between two widely diverged yeasts suggests that the RecQ family helicases encoded by the Bloom's and Werner's syndrome genes are likely to act in concert with topoisomerase III isozymes in human cells. Our data are consistent with a model in which the association of a RecQ helicase and topoisomerase III is important for facilitating decatenation of late stage replicons to permit faithful chromosome segregation during anaphase.
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PMID:Topoisomerase III is essential for accurate nuclear division in Schizosaccharomyces pombe. 1049 70

Topoisomerase II is a ubiquitous enzyme that removes knots and tangles from the genetic material by generating transient double-strand DNA breaks. While the enzyme cannot perform its essential cellular functions without cleaving DNA, this scission activity is inherently dangerous to chromosomal integrity. In fact, etoposide and other clinically important anticancer drugs kill cells by increasing levels of topoisomerase II-mediated DNA breaks. Cells rely heavily on recombination to repair double-strand DNA breaks, but the specific pathways used to repair topoisomerase II-generated DNA damage have not been defined. Therefore, Saccharomyces cerevisiae was used as a model system to delineate the recombination pathways that repair DNA breaks generated by topoisomerase II. Yeast cells that expressed wild-type or a drug-hypersensitive mutant topoisomerase II or overexpressed the wild-type enzyme were examined. Based on cytotoxicity and recombination induced by etoposide in different repair-deficient genetic backgrounds, double-strand DNA breaks generated by topoisomerase II appear to be repaired primarily by the single-strand invasion pathway of homologous recombination. Non-homologous end joining also was triggered by etoposide treatment, but this pathway was considerably less active than single-strand invasion and did not contribute significantly to cell survival in S.cerevisiae.
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PMID:Yeast recombination pathways triggered by topoisomerase II-mediated DNA breaks. 1288 96