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)

Chinese hamster V79 cells grown in suspension culture as spheroids are more resistant than monolayers to killing and mutation by ionizing radiation. A change in DNA conformation appears to accompany this increase in radiation resistance. We were therefore interested in whether the activity of topoisomerase II, a nuclear enzyme involved in DNA conformational changes and possibly in DNA repair, might differ in monolayers and small spheroids. One-day-old spheroid cells were more resistant than monolayer cells to the toxic effects of etoposide, a topoisomerase II inhibitor. Fewer strand breaks were induced by etoposide in spheroid DNA than monolayer DNA, as measured by the DNA precipitation and alkali unwinding assays, although identical amounts of damage were produced in monolayers and spheroids by the topoisomerase I inhibitor camptothecin, and the cell cycle specific agent, 5-fluorouracil. There was no evidence of a subpopulation of spheroid cells which were more resistant to etoposide, and no change in the rate of incorporation or DNA chain elongation in spheroids compared to monolayers. Topoisomerase II activity in 1-day-old spheroids, measured by decatenation of trypanosome kinetoplast DNA, was reduced to 68% of the monolayer value; in 3-4-day-old spheroids the level was 32.5%. These results indicate that topoisomerase II activity and sensitivity to a topoisomerase II inhibitor are reduced in 1-day-old spheroid cells. We suggest that the decrease in the activity of this enzyme may be linked to the change in DNA conformation in spheroids and the decrease in their radiation sensitivity.
Int J Radiat Biol 1991 Sep
PMID:Etoposide sensitivity and topoisomerase II activity in Chinese hamster V79 monolayers and small spheroids. 167 86

Acridine and its derivatives are planar polycyclic aromatic molecules which bind tightly but reversibly to DNA by intercalation, but do not usually covalently interact with it. Acridines have a broad spectrum of biological activities, and a number of derivatives are widely used as antibacterial, antiprotozoal and anticancer drugs. Simple acridines show activity as frameshift mutagens, especially in bacteriophage and bacterial assays, by virtue of their intercalative DNA-binding ability. Acridines bearing additional fused aromatic rings (benzacridines) show little activity as frameshift mutagens, but interact covalently with DNA following metabolic activation (forming predominantly base-pair substitution mutations). Compounds where the acridine acts as a carrier to target alkylating agents to DNA (e.g. the ICR compounds) cause predominantly frameshift as well as base-pair substitution mutations in both bacterial and mammalian cells. Nitroacridines may act as simple acridines or (following nitro group reduction) as alkylating agents, depending upon the position of the nitro group. Acridine-based topoisomerase II inhibitors, although frameshift mutagens in bacteria and bacteriophage systems, are primarily chromosomal mutagens in mammalian cells. These mutagenic activities are important, since the compounds have considerable potential as clinical antitumour drugs. Although evidence suggests that simple acridines are not animal or human carcinogens, a number of the derived compounds are highly active in this capacity.
Mutat Res 1991 Sep
PMID:The genetic toxicology of acridines. 188 2

The genome of herpes simplex virus type 1 contains a large number of recognition sites for eucaryotic DNA type II topoisomerase. Topoisomerase II sites were identified by means of the consensus sequence described previously (J.R. Spitzner and M.T. Muller, Nucleic Acids Res. 16:5553-5556, 1988) and then confirmed by sequencing DNA cleavages introduced by purified topoisomerase II. In vivo, host topoisomerase II also introduced double-stranded DNA breaks in the viral genome at sites predicted by the consensus sequence. Host topoisomerase II acted on all immediate-early genes as well as on genes from other temporal classes; however, cleavages were not detected until 4 to 5 h postinfection and were most intense at 10 h postinfection. Topoisomerase II cleavages were not detected when viral DNA replication was prevented with phosphonoacetic acid. These data indicate that, although progeny viral genomes are acted upon by host topoisomerase II, this enzyme either does not act on parental viral genomes before DNA replication or acts on them with such low efficiency that cleavages are beyond our limit of detection. The findings suggest that host topoisomerase II is involved in aspects of viral replication at late times in the infectious cycle.
J Virol 1990 Sep
PMID:Topoisomerase II cleavage of herpes simplex virus type 1 DNA in vivo is replication dependent. 216 4

The carboxyl-terminal one-third of human topoisomerase II polypeptide expressed in Escherichia coli was used as antigen to generate polyclonal antibodies in rabbits. With the use of antiserum, DNA topoisomerase II levels of phytohemagglutinin-stimulated human lymphocytes were measured by immunoblotting. Our results showed that the increase in intracellular topoisomerase II level paralleled the entry of cells into proliferation. We also found that the increase in the topoisomerase II level resulted from an increase in the amount of topoisomerase II mRNA. The time course study indicated that the appearance of topoisomerase II mRNA was first observed at 36 h after phytohemagglutinin stimulation. The maximal level of topoisomerase II mRNA was seen at 45 h after stimulation. The same RNA blot was rehybridized with a thymidine kinase probe. The maximal level of thymidine kinase mRNA was observed at 39 h after phytohemagglutinin stimulation. In a comparison of the time course of topoisomerase II gene expression with that of [3H]thymidine incorporation and thymidine kinase gene expression, it was found that the expression of the topoisomerase II gene was later than the onset of DNA replication. Thus, this study suggests that topoisomerase I, which is constantly expressed throughout the cell cycle, might participate in the initiation of DNA replication, while topoisomerase II is involved in solving the DNA topological problems accompanying DNA strand separation during DNA replication.
Cancer Res 1990 Sep 01
PMID:Induction of topoisomerase II gene expression in human lymphocytes upon phytohemagglutinin stimulation. 216 62

The Chinese hamster ovary cell line xrs-1 is hypersensitive to gamma-radiation. This sensitivity has been attributed to an inability of this cell line to efficiently repair gamma-ray induced double-strand breaks (DSBs). We have recently reported that xrs-1 is also sensitive to topoisomerase II inhibitors that stabilize the cleavable complex. In this study, we have investigated the basis of this sensitivity by monitoring cleavable complex formation and loss in xrs-1 and its parent CHO-KI following treatment with the topoisomerase II inhibitors etoposide and 4'-(9-acridinylamino)methanesulfon-m-anisidide. Our studies indicate that xrs and CHO-K1 cells accumulate drug-induced cleavable complexes at equal rates and to an equal extent. However, studies on the loss of cleavable complexes after drug removal suggest that protein-free DSBs arise in cells treated with topoisomerase II inhibitors. Furthermore, a larger number of these DSBs persist in repair-deficient xrs cells than in repair-proficient Chinese hamster ovary-KI cells. The persistence of DSBs appears to account for the cytotoxic effects of topoisomerase II inhibitors that stabilize the cleavable complex. These results suggest that the xrs repair pathway is required for efficient removal of potentially cytotoxic DSBs that arise in cells treated with topoisomerase II inhibitors.
Cancer Res 1990 Sep 15
PMID:DNA double-strand break repair pathways and cellular tolerance to inhibitors of topoisomerase II. 216 80

The cytotoxic actions of several classes of antitumor DNA intercalators are thought to result from some disturbance to DNA metabolism following trapping of the nuclear enzyme DNA topoisomerase II as a covalent complex on DNA. Here we have studied topoisomerase II trapping and DNA synthesis patterns in relation to the acute cytotoxic actions of 4'-(9-acridinylamino)methanesulfon-m-anisidide (mAMSA) or mitoxantrone on SV40 transformed human fibroblasts. These two DNA intercalators differed significantly in their cytotoxic potential, mitoxantrone being 24-fold more toxic than mAMSA when assayed by the inhibition of clonogenicity. Although both drugs induced G2 delay at cytotoxic concentrations, mAMSA-treated cells recovered normal cell cycle phase distributions within 24 h of removal of drug, while mitoxantrone-treated cells continued to accumulate in G2 up to 48 h following drug treatment with evidence of complete inhibition of entry into mitosis. Compared with mAMSA, mitoxantrone showed a similar capacity to induce cleavable complexes in cellular DNA, and only a 2-fold greater ability to inhibit DNA synthesis. Within a 4-h posttreatment period, mAMSA-treated cells recovered normal rates of DNA synthesis, whereas a continued depression of DNA synthesis was observed in mitoxantrone-treated cells. The recovery patterns of DNA synthesis correlated with the rapid disappearance of mAMSA-induced complexes (less than 27% lesions remaining 2 h after drug removal) and the persistence of mitoxantrone-induced complexes during a 4-h posttreatment period. This difference in complex longevity was observed in other human transformed fibroblast cell lines irrespective of differences in the absolute levels of complexes induced by either agent. We suggest that the results provide evidence that DNA intercalators may differ in the forms of complexes induced and that the comparatively high cytotoxicity of mitoxantrone relates to the ability of the drug to trap topoisomerase II complexes in a form which effects a long-term inhibition of DNA replication and G2 traverse.
Cancer Res 1990 Sep 15
PMID:Long-term inhibition of DNA synthesis and the persistence of trapped topoisomerase II complexes in determining the toxicity of the antitumor DNA intercalators mAMSA and mitoxantrone. 216 81

We have isolated stable teniposide (VM26)-resistant cell lines from human cancer KB cells by stepwise exposure to increasing doses of the drug. At each step, we have purified VM26-resistant cell lines. KB/VM-a, KB/VM-b, KB/VM-1, KB/VM-2, KB/VM-3, and KB/VM-4 showed 3-, 6-, 12-, 16-, 74-, and 95-fold higher resistance to VM26 than did KB. We have further characterized KB/VM-2 and KB/VM-4 which showed about 15- and 100-fold higher resistance to VM26 or etoposide (VP16) than did KB. Both VM26-resistant cell lines showed 4- to 11-fold higher relative resistance to daunomycin and Adriamycin than did KB. Steady-state levels of the cellular accumulation of radioactive VP16 in KB/VM-2 and KB/VM-4 cells were about 40% of that of KB cells, whereas similar levels of radioactive daunomycin accumulation were observed in KB/VM-2 and KB/VM-4 cells as KB cells. Topoisomerase II activity of nuclear extracts of both KB/VM-2 and KB/VM-4 assayed by decatenation of kinetoplast DNA was consistently two-thirds or less the activity of KB cells. A similar reduction was seen in both immunoblot assays with specific anti-topoisomerase II antibody and Northern blot analysis with specific human DNA topoisomerase II complementary DNA. DNA topoisomerase I activity, however, was similar between the mutants and their parent. Furthermore, cell growth of KB/VM-2 and KB/VM-4 was more thermolabile than that of KB, while KB/VM-b already showed temperature-sensitive growth. KB/VM-1 did show reduced accumulation of VP16 as in KB/VM-2 or KB/VM-4, but it had a normal level of topoisomerase II content as in KB cells. These data suggest that the reduced expression of DNA topoisomerase II, possibly combined with decreased permeability to the drugs, can account for the acquired VM26 resistance of KB/VM-2 and KB/VM-4 cells and also that the temperature-sensitive phenotype might not be obligatorily coupled with the reduced expression of topoisomerase II or the decreased permeability.
Cancer Res 1990 Sep 15
PMID:Reduction of drug accumulation and DNA topoisomerase II activity in acquired teniposide-resistant human cancer KB cell lines. 216 82

Streptonigrin, a nonintercalative antitumor antibiotic, induced mammalian topoisomerase II dependent DNA cleavage in vitro. The cleavage activity of streptonigrin was comparable to that of demethylepipodophyllotoxin ethylidene-beta-D-glucoside at a low concentration (less than or equal to 10 microM) but one-third lower at a higher concentration (greater than 250 microM). Exposure of a reaction mixture containing streptonigrin, DNA, and topoisomerase II to an elevated temperature (65 degrees C) resulted in substantial reduction in DNA cleavage, suggesting that the mechanism of the topoisomerase II dependent DNA cleavage induced by streptonigrin was through the formation of a cleavage complex previously reported for topoisomerase II poisons such as 4'-(9-acridinylamino) methanesulfon-m-anisidide and epipodophyllotoxins.
Cancer Res 1990 Sep 15
PMID:Induction of mammalian DNA topoisomerase II dependent DNA cleavage by antitumor antibiotic streptonigrin. 216 83

A human bladder carcinoma cell line was irradiated at high and low dose rates and exposed to camptothecin and VP16, inhibitors of topoisomerase I and topoisomerase II respectively. Although camptothecin substantially modified the cytotoxic effects of high dose rate irradiation, abolished low dose rate sparing and inhibited the repair of sublethal and potentially lethal damage, VP16 had no effect on the survival curves even at highly cytotoxic doses. Thus, it is argued that there is a role for topoisomerase I but not topoisomerase II in the repair of DNA damage induced by ionising radiation.
Br J Cancer 1990 Sep
PMID:The inhibition of cellular recovery in human tumour cells by inhibitors of topoisomerase. 216 51

The interaction between calf thymus topoisomerase II and DNA has been characterized using a transcription assay. A highly preferred recognition sequence for topoisomerase II was inserted in either direction downstream from a promoter specific for a bacteriophage RNA polymerase. The presence of topoisomerase II-DNA complexes on the template provoked blockage of transcription, yielding RNA transcripts terminated 5' to the topoisomerase II binding site. A footprint of topoisomerase II, derived from transcription towards the complex from either side, revealed that eukaryotic topoisomerase II binds a region of 28 base-pairs with a highly protected central core of 22 base-pairs. The binding region was located symmetrically around the topoisomerase II-mediated cleavage site. In agreement with this result, optimal topoisomerase II-mediated cleavage was observed with a DNA substrate consisting of a 28-mer oligonucleotide homologous to the protected region. Stepwise removal of base-pairs from the ends of the 28-mer gradually reduced the level of enzyme-mediated cleavage.
J Mol Biol 1990 Sep 20
PMID:Characterization of the interaction between topoisomerase II and DNA by transcriptional footprinting. 217 Jun 62


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