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:5.99.1.2 (topoisomerase)
9,166 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Accumulation of gadd153 mRNA is strongly stimulated in mammalian cells by treatments which arrest growth or damage DNA (A. J. Fornace, Jr. et al., Mol. Cell. Biol., 9: 4196-4203, 1989). In previous studies, we demonstrated that the increased expression of gadd153 following treatment with several DNA-damaging agents was mediated transcriptionally (J. D. Luethy et al., J. Biol. Chem., 265: 16521-16526, 1990). To better define the specificity of this response, we have established a sensitive reporter system in which we have stably integrated a chimeric gene containing the gadd153 promoter linked to the coding region of the chloramphenicol acetyltransferase (CAT) gene into the genome of HeLa cells. Transcriptional activation from the gadd153 promoter was monitored by determining levels of CAT activity in cellular lysates prepared from gadd153CAT/HeLa cells treated with a variety of agents. The gadd153 promoter was strongly activated by a broad spectrum of genotoxic agents including UV-mimetic agents, DNA-cross-linking and alkylating agents, DNA intercalators, and topoisomerase inhibitors. Of the DNA-damaging agents tested, only X-irradiation and bleomycin treatments failed to induce gadd153 promoter activity. Agents which inhibit replication and cell division and agents which otherwise result in cytotoxicity or growth arrest also had little influence on gadd153 promoter activity. Expression of the gadd153CAT chimeric gene in xeroderma pigmentosum Group A cells, which are deficient in nucleotide excision DNA repair of pyrimidine dimers, was maximally induced at UV doses at least 6-fold lower than those required for similar induction in repair-proficient HeLa cells. However, the methyl methanesulfonate-induced gadd153 promoter activities were similar in both cell lines. Novobiocin pretreatment inhibited both UV- and methyl methanesulfonate-induced gadd153CAT expression. Collectively, these data indicate that: (a) the gadd153 promoter is activated rapidly and specifically by DNA damage; (b) the altered DNA structure is the inducing signal for the activation of the signal transduction pathway responsible for enhanced gadd153 expression; and (c) regulation of gadd153 by growth arrest is distinct from that of DNA damage. Thus, the gadd153CAT/HeLa cells are a useful model for examining the molecular mechanisms associated with the response to DNA damage and provide a reporter system for the screening of potential genotoxic agents.
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PMID:Activation of the gadd153 promoter by genotoxic agents: a rapid and specific response to DNA damage. 172 86

The aim of our work was to investigate whether DNA topoisomerase II participates in the repair-specific incision of UV-irradiated genomic DNA. Therefore, the influence upon DNA incision of the topoisomerase II inhibitors (nalidixic and oxolinic acid, novobiocin and coumermycin A1) as well as the intercalating agent quinacrine has been measured in normal human fibroblasts using the alkaline elution technique. In addition, inhibition by novobiocin has been determined in fibroblast strains from 11 normal donors and from 16 xeroderma pigmentosum (XP) patients belonging to the complementation groups A, C, D, E, and XP variant. Nalidixic and oxolonic acid did not inhibit endonucleolytic cleavage, whereas novobiocin was a potent inhibitor of DNA incision. It was observed that in normal and in all XP strains 50% inhibition by novobiocin occurred on average in the dose range 315-590 microM. Since inhibition by novobiocin was not paralleled by that with the other topoisomerase II inhibitors nalidixic and oxolinic acid, it must be concluded that reduction of enzyme-catalysed breaks was not due to the participation of topoisomerase II in the incision step, but to the displacement of ATP at the binding site of the DNA-incising enzyme. This enzyme absolutely requires ATP as a cofactor for endonucleolytic cleavage. Quinacrine, however, inhibited DNA incision in normal fibroblasts at a mean Ki of 318 microM. Inhibition by this intercalating agent seems to be caused by structural perturbations in DNA, which render it a poor substrate for endonucleolytic cleavage.
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PMID:The effects of inhibitors of topoisomerase II and quinacrine on ultraviolet-light-induced DNA incision in normal and xeroderma pigmentosum fibroblasts. 184

Abnormal expression of the nuclear-associated enzyme DNA topoisomerase II (topoisomerase II) has been implicated in the in vitro phenotype of radiation hypersensitive ataxia-telangiectasia (A-T) cells and in modifying sensitivity of eukaryotic cells to topoisomerase II-inhibitor drugs [e.g., the DNA intercalator amsacrine (mAMSA)]. To study such relationships, various SV40- and Epstein-Barr Virus-transformed human cell lines derived from normal, A-T, or UV-sensitive xeroderma pigmentosum donors have been assayed for their sensitivity to mAMSA together with direct and indirect measurements of topoisomerase II expression. We report on the identification of an SV40-transformed A-T fibroblast cell line with abnormally high levels of topoisomerase II in nuclear protein extracts as determined by immunoblotting, measurement of kinetoplast DNA decatenation activity, and mAMSA-dependent DNA-protein cross-linking activity in a filter binding assay. Using a flow cytometric assay for the analysis of reactivity of nuclei with a polyclonal antitopoisomerase II antibody, overproduction was found to occur in all phases of the cell cycle. High levels of topoisomerase II were associated with hypersensitivity (5-10-fold) to mAMSA-induced cell cycle delay, cell kill, and DNA strand breakage (assayed under protein-denaturing conditions). Xeroderma pigmentosum (group A) cells demonstrated normal responses to mAMSA. The results provide evidence that cellular potential for the generation of topoisomerase II-dependent DNA damage is a major factor in governing the sensitivity to mAMSA. Furthermore, underexpression of topoisomerase II does not appear to be a primary factor in describing the in vitro A-T phenotype. The findings also relate to how changes in chromatin structure and function may either reflect or dictate the expression of topoisomerase II in human cells.
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PMID:Cellular consequences of overproduction of DNA topoisomerase II in an ataxia-telangiectasia cell line. 253 42

The efficiency of stable transformation of human cells by integrative (non-replicating) plasmids carrying a selectable gene has been shown to be markedly enhanced by the introduction into the plasmid DNA of bulky damage, such as cyclobutane pyrimidine dimers or psoralen photoadducts. Enhanced transformation (ET) occurs in all human cells tested, including DNA repair-deficient cells from the hereditary syndrome xeroderma pigmentosum, but significantly less, if at all, in rodent cells. ET has been observed with a variety of integrative plasmid constructs, suggesting the generality of the phenomenon; as expected, ET is due to an increase in the number of cells carrying integrated plasmid sequences. In contrast to integrative plasmids, stable transformation by episomal (autonomously replicating) plasmids derived from the Epstein-Barr virus is only depressed by the introduction of photoproducts; furthermore, pronounced inactivation of transformation mediated by episomal plasmids becomes apparent in xeroderma pigmentosum cells. Altogether, these results suggest that DNA damage increases the probability of stable insertion of heterologous non-replicating DNA into human chromosomes. Moreover, the differential sensitivity to DNA damage of human cell transformation mediated by integrative versus episomal plasmids suggests caution in using such assay to measure host cell reactivation capacity; processing of DNA damage in mammalian cells might differ significantly between intra- versus extra-chromosomal DNA. Since ET may be induced by damage outside the selectable gene carried on integrative plasmids, we propose a model that involves local disruption of chromatin structure by helix-distorting DNA lesions flanking actively transcribed sequences; alternatively, reorganization of such altered DNA structure might be favored by the presence of topoisomerase-like activities in the proximity of active genes. Because ET can also be induced by DNA damage to the recipient cells, it is speculated that similar mechanism(s) might be involved in the generation of other types of non-homologous DNA recombination in damaged human chromosomes, including oncogenic cell transformation mediated by integrative DNA viruses.
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PMID:Effect of DNA damage on stable transformation of mammalian cells with integrative and episomal plasmids. 292 24

The frequency of sister chromatid exchanges (SCEs), both spontaneous and induced by UV-light, X-rays, mitomycin C and ethylmetansulphonate (EMS), has been investigated in cultured human peripheral blood lymphocytes. Besides, frequency of spontaneous and induced SCEs was studied under the action of the inhibitors of topoisomerase II, polymerase poly(ADP-ribose), and DNA repair, i. e. novobiocin, 3-metoxybenzamide, and caffeine, respectively. It is shown that the base-line SCEs in lymphocytes of the patient with xeroderma pigmentosum II (XP2LE) is dramatically higher compared to that in normal and pigmented xerodermoid cells (XP3LE). The above inhibitors of DNA synthesis and repair enhance the rate of spontaneous SCEs in normal, XP2LE and XP3LE cells. UV-, X-ray and chemical mutagens induced an increased frequency of SCEs in these cells. Simultaneous treatment with mutagenes and inhibitors of DNA synthesis and DNA repair enhanced the rate of SCEs in lymphocytes of healthy donors and in the XP3LE patient. The frequency of the XP2LE cells. Novobiocin, 3-MBA and caffeine significantly decreased the frequency of SCEs in mitomycin C- and EMS-treated XP2LE lymphocyte, which nevertheless was much higher than that in normal cells treated with the same agents.
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PMID:[Spontaneous and induced sister chromatid exchanges in the blood lymphocytes of healthy persons and of xeroderma pigmentosum patients exposed to the inhibitors of DNA repair and replication caffeine, 3-methoxybenzamide and novobiocin]. 308 51

The frequency of sister-chromatid exchanges (SCE) was studied in peripheral blood lymphocytes from a xeroderma pigmentosum (form II, XPII) patient. The cells were irradiated with UV or X-rays. In some experiments novobiocin (NB), inhibitor of topoisomerase II, or caffeine (CA), inhibitor of DNA repair were added to the cultures. The level of spontaneous SCE in the patient's lymphocytes was found to be significantly increased in comparison to that in the cells from normal donors. The inhibitors and UV-light caused a rise in the frequency of SCE in the cells taken from normal donors and except for NB, in the lymphocytes from the patient XPII. X-Rays did not increase SCE frequency in normal lymphocytes and lowered it in the patient's cells. SCE frequency rose when inhibitors of DNA replication and repair were used in combination with mutagens.
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PMID:Sister-chromatid exchanges in a special form of xeroderma pigmentosum (form II). 362 39

The tumor suppressor protein p53 serves as a critical regulator of a G1 cell cycle checkpoint and of apoptosis following exposure of cells to DNA-damaging agents. The mechanism by which DNA-damaging agents elevate p53 protein levels to trigger G1/S arrest or cell death remains to be elucidated. In fact, whether damage to the DNA template itself participates in transducing the signal leading to p53 induction has not yet been demonstrated. We exposed human cell lines containing wild-type p53 alleles to several different DNA-damaging agents and found that agents which rapidly induce DNA strand breaks, such as ionizing radiation, bleomycin, and DNA topoisomerase-targeted drugs, rapidly triggered p53 protein elevations. In addition, we determined that camptothecin-stimulated trapping of topoisomerase I-DNA complexes was not sufficient to elevate p53 protein levels; rather, replication-associated DNA strand breaks were required. Furthermore, treatment of cells with the antimetabolite N(phosphonoacetyl)-L-aspartate (PALA) did not cause rapid p53 protein increases but resulted in delayed increases in p53 protein levels temporally correlated with the appearance of DNA strand breaks. Finally, we concluded that DNA strand breaks were sufficient for initiating p53-dependent signal transduction after finding that introduction of nucleases into cells by electroporation stimulated rapid p53 protein elevations. While DNA strand breaks appeared to be capable of triggering p53 induction, DNA lesions other than strand breaks did not. Exposure of normal cells and excision repair-deficient xeroderma pigmentosum cells to low doses of UV light, under conditions in which thymine dimers appear but DNA replication-associated strand breaks were prevented, resulted in p53 induction attributable to DNA strand breaks associated with excision repair. Our data indicate that DNA strand breaks are sufficient and probably necessary for p53 induction in cells with wild-type p53 alleles exposed to DNA-damaging agents.
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PMID:DNA strand breaks: the DNA template alterations that trigger p53-dependent DNA damage response pathways. 811 14

An antibody-based method was used to examine genomic DNA cleavage by endogenous topoisomerases in living cells. The method quantifies cleavable (covalent) complex formation in vivo after exposure to topoisomerase poisons, as reported previously (D. Subramanian et al., Cancer Res., 55: 2097-2103, 1995). Unexpectedly, exposing cells to UVB irradiation stimulated endogenous topoisomerase I-DNA covalent complex formation by as much as 8-fold, even in the absence of drugs that stabilize the cleavable complex. Covalent complexes are not a result of nonspecific UV protein-DNA cross-linking; rather, they result from the enzymatic activity of topoisomerase I on genomic DNA. Because the action of topoisomerase II on genomic DNA was not affected by UVB exposure, the observation appears to be specific for type I. Topoisomerase I is rapidly mobilized onto the genome (within 12 min after UVB exposure); however, topoisomerase I polypeptide levels did not show a corresponding increase, suggesting that preexisting enzyme is being recruited to sites of DNA damage. Complexes persist up to 5 h post-UV exposure (concurrent with the period of active DNA repair), and their formation is independent of S phase. These findings can be partially explained by the fact that in vitro topoisomerase I activity on UV-damaged DNA tends to favor formation of cleavage complexes; thus, a higher yield of covalent complexes are detected at or near cyclopyrimidine dimer lesions. Because repair-deficient cells are additionally compromised in their ability to recruit topoisomerase I, a direct role for the enzyme in DNA excision repair process in vivo is proposed that may be related to the activity of the xeroderma pigmentosum complementation group D helicase. Finally, these results collectively demonstrate that topoisomerase I is a repair-proficient topoisomerase in vivo.
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PMID:Ultraviolet-induced DNA damage stimulates topoisomerase I-DNA complex formation in vivo: possible relationship with DNA repair. 950 Apr 59

The metabolic fate of covalently linked DNA-protein complexes (cross-links) is not clearly understood. Our aim was to investigate the processing of protein-DNA cross-links by cellular enzymes. As an example of a DNA-protein cross-link, we have constructed frozen topoisomerase-DNA conjugates and investigated their processing by human cell-free extracts. A suicide DNA substrate was constructed that upon reaction with vaccinia type I topoisomerase yielded a highly stable covalent DNA-protein cross-link. When this conjugate was treated with human nuclear or whole cell extracts, two sites of DNA breakpoints were detected: one set of double-stranded breaks occurred close to the 3' side of the topoisomerase (topo) conjugation site, and there was another set of nicks about 30 nucleotides 3' to the topo site. The double-stranded breaks were not made by extracts from xeroderma pigmentosum group A mutant cells, suggesting that the xeroderma pigmentosum group A damage recognition protein may be required for the occurrence of DNA breakage. In addition to these DNA breakage reactions, there was an activity that resulted in the delinking of the frozen topoisomerase (or proteolytic fragments thereof) from the DNA substrate, which was followed by a ligation step that restored the continuity of the broken DNA strand at the erstwhile topo attachment site. We suggest that frozen topoisomerase-DNA conjugates (and perhaps other types of covalent DNA-protein complexes) are processed by multiple pathways that may involve the cleavage of the DNA in the covalent protein-DNA complex and/or enzymatic delinking followed by ligation of the broken DNA ends. These processes may represent the "repair" of DNA-protein cross-links.
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PMID:Mechanisms for the processing of a frozen topoisomerase-DNA conjugate by human cell-free extracts. 954 38

DNA topoisomerase IIalpha was monitored with the monoclonal antibody Ki-S1 in human fibroblasts after irradiation of cells with gamma rays from a 137Cs source or treatment with the DNA topoisomerase II inhibitor doxorubicin. DNA topoisomerase IIalpha was localized immunohistochemically as bright fluorescent dots in the karyoplasm. The fibroblasts investigated originated from normal human donors and a xeroderma pigmentosum (XP) patient (XP12BE). All cell lines examined showed a time- and dose-dependent increase in DNA topoisomerase IIalpha abundance after irradiation or treatment with doxorubicin. No principal difference in response was seen between normal and XP fibroblasts towards either treatment alone. After irradiation with 9 Gy, the effect was detectable after as little as 30 min and lasted for at least 6 h. After doxorubicin treatment, topoisomerase II overexpression occurred within less than 2 h. It passed through a maximum and began to decrease after approximately 6 h. In principle, the increase in DNA topoisomerase IIalpha may result from (i) architectural changes of interphase chromatin leading to enhanced accessibility of preformed enzyme to the antibody, (ii) enhanced gene expression, or (iii) enhanced stabilization of mRNA or protein molecules. The increase in enzyme levels may be part of the well-known DNA damage responses that operate in cell-protective or DNA-reparative pathways. Thus, the action of DNA topoisomerase II would serve to catalyze preparatory steps in DNA repair. We also found overexpression of the Bax protein and p16 predominantly in treated XP cells, suggesting that the DNA-damaging protocols elicited signals for apoptosis and cell-cycle arrest. From the simultaneous increase in DNA topoisomerase IIalpha and Bax, one may conclude that DNA topoisomerase IIalpha also plays role in apoptosis.
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PMID:Doxorubicin and gamma rays increase the level of DNA topoisomerase IIalpha in nuclei of normal and xeroderma pigmentosum fibroblasts. 971 98


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