Oxidative DNA damage and apoptosis induced by benzene metabolites

Benzene is a widely recognized human carcinogen. The mechanism of DNA damage induced by major benzene metabolites 1,4-benzoquinone (1,4-BQ) and hydroquinone (1,4-HQ) was investigated in relation to apoptosis and carcinogenesis. Pulsed-field gel electrophoresis showed that cellular DNA strand breakage was induced by benzene metabolites. Internucleosomal DNA fragmentation and morphological changes of apoptotic cells were observed at higher concentrations of benzene metabolites. Flow cytometry showed an increase of peroxides in cultured cells treated with benzene metabolites. 1,4-BQ induced these changes at a much lower concentration than 1,4-HQ. Damage to DNA fragments obtained from the c-Ha-ras-1 proto-oncogene was investigated by a DNA sequencing technique. 1,4-BQ + NADH and 1,4-HQ induced piperidine-labile sites frequently at thymine residues in the presence of Cu(II). Catalase and bathocuproine inhibited DNA damage, suggesting that H2O2 reacts with Cu(I) to produce active species causing DNA damage. Electron spin resonance studies showed that semiquinone radical was produced by NADH-mediated reduction of 1,4-BQ and autoxidation of 1,4-HQ, suggesting that benzene metabolites produce O2- and H2O2 via the formation of semiquinone radical. These results suggest that these benzene metabolites cause DNA damage through H2O2 generation in cells, preceding internucleosomal DNA fragmentation leading to apoptosis. The fates of the cells to apoptosis or mutation might be dependent on the intensity of DNA damage and the ability to repair DNA.     

Curing Saccharomyces cerevisiae of the 2 micron plasmid by targeted DNA damage

Powerful mutagenic screens of yeast Saccharomyces cerevisiae have recently been developed which require strains that lack the endogenous 2 micron plasmid (Burns et al., 1994). Here, we describe a simple and reliable method for curing yeast of the highly stable genetic element. The approach employs heterologous expression of a 'step-arrest' mutant of the Flp recombinase. The mutant, Flp H305L (Parsons et al., 1988), forms long-lived covalent protein-DNA complexes exclusively at 2 micron-borne recombinase target sites. In vivo, the complexes serve as sites of targeted DNA damage. Using Southern hybridization and a colony color assay for plasmid loss, we show that expression of the mutant enzyme results in the effective elimination of the 2 micron from cells.     

Sequence-specific changes in the metal site of ferric bleomycin induced by the binding of DNA

The binding of the iron complex of the antineoplastic glycopeptide bleomycin A2 (Fe-BLM) to calf thymus DNA and the self-complementary oligonucleotides d(CGCGCG) and d(ATATAT) has been studied using optical, EPR, and resonance Raman spectroscopies. An increase in the intensity of the bands at 365 and 384 nm is observed in the optical spectrum of Fe(III)-BLM when the drug binds to either oligonucleotide. However, in the presence of phosphate, this increase is observed only with d(CGCGCG) and not with d(ATATAT). In addition, the gmax feature in the EPR spectrum of low spin Fe(III)-BLM is narrowed in a way suggesting a reduction of possible conformers that the drug can achieve when it is bound to d(CGCGCG) or to calf thymus DNA but not when bound to d(ATATAT). When Fe(III)-BLM is bound to d(CGCGCG), changes in the resonance Raman spectrum of the metal drug complex suggest conformational changes in three of the ligands to iron: the beta-hydroxyhistidyl amide, the pyrimidine, and the axial hydroxide. In addition, the Fe-OH band undergoes narrowing, again consistent, with the reduction of conformers of the drug. No such resonance Raman changes are observed upon binding to d(ATATAT). The changes in the pyrimidine modes upon binding d(CGCGCG) to the drug are consistent with a recently proposed model (Wu, W., Vanderwall, D. E., Turner, C. J., Kozarich, J. W., and Stubbe, J. (1996) J. Am. Chem. Soc. 118, 1281-1294) of DNA recognition by activated bleomycin, HOO-Fe(III)-BLM, in which the pyrimidine moiety of the drug is important for the preferential cleavage of 5'-GpPy-3' sequences.     

DNA damage induced by fotemustine in cultured HL60 cells

AIM: To detect DNA damage caused by fotemustine (Fot). METHODS: DNA damage in HL60 cells was evaluated by modified alkaline elution technique. DNA interstrand crosslink (ISC) and DNA-protein crosslink (DPC) were determined. Carmustine (Car) was used as control. Drug treatment time was 1 h. RESULTS: After treatment with Fot 300 mumol.L-1, ISC and DPC index were 5.4 and 6.1 at 6 h, 2.7 and 1.2 at 12 h, respectively. ISC reached the maximum at about 6 h. For Fot 100 mumol.L-1, ISC and DPC index at ISC peak time were 2.1 +/- 0.9 and 3.55 +/- 0.23, 5.0 +/- 0.5 and 7.7 +/- 1.1 for Car 100 mumol.L-1, respectively. Single strand break (SSB) was induced by Fot. CONCLUSION: Fot caused HL60 cell DNA ISC, DPC, and SSB. ISC was formed more quickly by Fot than that by Car.     

Direct evidence for bimodal DNA damage induced by tirapazamine

The ability of tirapazamine (1, 3-amino-1,2,4-benzotriazine 1, 4-dioxide, SR4233) to fix DNA radical lesions is demonstrated by studying the reaction between the antitumor drug and an oligonucleotide radical that is independently produced at a defined site within a biopolymer. Using beta-mercaptoethanol as a competitor, it was determined that tirapazamine traps a C1'-nucleotide radical with a rate constant of approximately 2 x 10(8) M-1 s-1. Product and isotopic labeling studies suggest that tirapazamine reacts with the radical via covalent adduct formation, resulting primarily from reaction at the N-oxide oxygen. Intermediate covalent adducts could not be observed, but are postulated to decompose to the alkaline labile 2'-deoxyribonolactone lesion. These experiments affirm recent proposals suggesting that tirapazamine can serve as a surrogate for O2 in converting DNA radicals into toxic strand damage events.     

Modelling DNA damage induced by different energy photons and tritium beta-particles

PURPOSE: To model the production of single- and double-strand breaks (ssb and dsb) in DNA by ionizing radiations. To compare the predicted effectiveness of different energy photon radiations and tritium beta-particles. MATERIALS AND METHODS: Modelling is carried out by Monte Carlo and includes consideration of direct energy depositions in DNA molecules, the production of species, their diffusion and interactions with each other and DNA. Computer-generated electron tracks in liquid water are used to model energy deposition and to derive the initial positions of chemical species. Atomistic representation of the DNA in B form with a first hydration shell is used. Photon radiations in the energy range 70keV-1MeV and tritium beta-particles are considered. RESULTS: A tentative increase for dsb yield has been predicted for 70 keV photons and tritium compared with 137Cs. This increase is more pronounced for complex dsb. Double-strand breaks are much more prone compared with ssb to combine with additional strand breaks and base damage, which contributes to break complexity. At least half of DNA breaks are hydroxyl radical mediated. CONCLUSIONS: The developed model makes predictions compatible with features of available experimental data. Break complexity has to be addressed in biophysical modelling when the relative effectiveness of radiations in DNA damage is studied. Obtained data strongly argue against the dominance of direct radiation action in DNA damage in the cellular environment predicted by some theoretical studies.     

Neighboring base damage induced by permanganate oxidation of 8-oxoguanine in DNA

We found that single-stranded DNA oligomers containing a 7, 8-dihydro-8-oxoguanine (8-oxo-G) residue have high reactivity toward KMnO4; the oxidation of 8-oxo-G induces damage to the neighboring nucleotide residues. This paper describes the novel reaction in detail, including experiments that demonstrate the mechanism involved in the induction of DNA damage. The results using DNAs of various base compositions indicated that damaged G, T and C (but not A) sites caused strand scissions after hot piperidine treatment and that the damage around the 8-oxo-G occurred at G sites in both single and double strands with high frequency. The latter substrates were less sensitive to damage. Further, kinetic studies of the KMnO4reaction of single-stranded oligomers suggested that thereactivity of the DNA bases at the site 5'-adjacent to the 8-oxo-G was in the order G >A >T, C. This preference correlates with the electron donating abilities of the bases. In addition, we found that the DNA damage at the G site, which was connected with the 8-oxo-G by a long abasic chain, was inhibited in the above order by the addition of dG, dA or dC. On the other hand, the damage reactions proceeded even after the addition of scavengers for active oxygen species. This study suggests the involvement of a redox process in the unique DNA damage initiated by the oxidation of the 8-oxo-G.     

Protection against tuberculosis by a plasmid DNA vaccine

BACKGROUND: Incidence of smooth muscle tumors is increased in patients with human immunodeficiency virus infection and organ transplant recipients. Smooth muscle tumors in immunocompromised patients often occur in unusual locations and exhibit evidence of latent infection by clonal, presumably tumorigenic, Epstein-Barr virus (EBV). OBJECTIVE: To investigate the presence of EBV latent infection in smooth muscle tumors in patients with acquired immunodeficiency syndrome and in immunocompetent patients. DESIGN: Twenty-two extrauterine, extraintestinal smooth muscle and myofibroblastic tumors were reviewed pathologically, and clinical charts were screened. Tumors were malignant (15 patients), benign (6 patients), and borderline (1 patient). Tissue specimens were investigated for latent EBV infection by latent membrane protein immunocytochemistry and EBV-encoded RNA in situ hybridization. SETTING: University Hospital of the University of Nancy, France. PATIENTS: Patients were 18 adults and four children. Two adults had acquired immunodeficiency syndrome. Both had low-grade leiomyosarcomas located in adrenal gland. Moreover, in patient 1, leiomyosarcoma was multifocal in pericardium and lymph node; in lymph node, muscle tumor was adjacent to nodal and skin Kaposi's lesions. RESULTS: In both patients with acquired immunodeficiency syndrome and leiomyosarcoma, latent infection by EBV could be demonstrated in tumor cells, contrasting with absence of detectable EBV infection in adjacent non-neoplastic tissues and nearby Kaposi's lesions. Latent infection by EBV could not be demonstrated in smooth muscle and myofibroblastic tumors in immunocompetent patients. CONCLUSIONS: Latent EBV infection is associated with smooth muscle cell tumors in immunocompromised patients, but not in immunocompetent patients.     

Mutations induced by gamma-irradiation of M13 bacteriophages containing single-stranded DNA

Astringent compounds were applied to oral epithelium of the clawed toad, Xenopus laevis, and rapidly rising and highly sensitive responses could be recorded from the whole glossopharyngeal nerve, but not at all from the trigeminal nerve. The response to 10 mM tannic acid decreased progressively with repetitive application. These responses to tannic acid, however, recovered completely by treating with chemicals capable of forming strong hydrogen and hydrophobic bonds. These chemical bondings are generally recognized as a model for polyphenol (tannin)-protein interactions based on physico-chemical measurements in vitro. The high affinities of these chemicals for tannic acid may be effective in releasing both bonds in the interaction of tannic acid with the receptor molecules. Our results provide in vivo evidence for this model.     

Nuclear localization of Cdc25 is regulated by DNA damage and a 14-3-3 protein

DNA damage activates a cell-cycle checkpoint that prevents mitosis while DNA repair is under way. The protein Chk1 enforces this checkpoint by phosphorylating the mitotic inducer Cdc25. Phosphorylation of Cdc25 by Chk1 creates a binding site in Cdc25 for 14-3-3 proteins, but it is not known how 14-3-3 proteins regulate Cdc25. Rad24 is a 14-3-3 protein that is important in the DNA-damage checkpoint in fission yeast. Here we show that Rad24 controls the intracellular distribution of Cdc25. Elimination of Rad24 causes nuclear accumulation of Cdc25. Activation of the DNA-damage checkpoint causes the net nuclear export of Cdc25 by a process that requires Chk1, Rad24 and nuclear-export machinery. Mutation of a putative nuclear-export signal in Rad24 impairs the nuclear exclusion of Rad24, the damage-induced nuclear export of Cdc25 and the damage checkpoint. Thus, Rad24 appears to function as an attachable nuclear-export signal that enhances the nuclear export of Cdc25 in response to DNA damage.     

DNA damage induced by m-phenylenediamine and its derivative in the presence of copper ion

We have previously reported that long-term priming of human polymorphonuclear neutrophilic granulocytes (PMN) with interferon-gamma (IFN-gamma) increased the fMLP-stimulated calcium influx. We now show that also after short-term incubation with IFN-gamma, PMN calcium metabolism is modulated. Single adherent cells in three different calcium-containing buffers (high, normal, and low [Ca2+]) were stimulated with the bacterial peptide fMLP or the Ca-ATPase inhibitor thapsigargin (Tg) after about 5 min preincubation with IFN-gamma. The results of this protocol indicated that IFN-gamma increases both calcium influx and calcium sequestration. Store dependent Ca2+ influx, directly measured on readdition of calcium to Tg-treated cells incubated in EGTA buffer, was significantly enhanced in IFN-gamma-treated cells. This effect of IFN-gamma was enhanced by the tyrosine kinase inhibitor herbimycin A. Strikingly, in low extracellular calcium concentrations, IFN-gamma induced calcium transients in 20%-60% of the cells. The proportion of PMN responding with Ca2+ transients increased with decreasing extracellular calcium concentration. Average lagtime from addition of IFN-gamma to a response that could be measured was 7.3 sec, and average increase in [Ca2+] above the basal level was 790 nM. These IFN-gamma-induced transients could not be depressed by herbimycin A. Thus, IFN-gamma can increase capacitative calcium influx, induce calcium transients, and possibly affect calcium sequestration in human PMN.     

Tests for DNA and chromosomal damage induced by nuclear magnetic resonance imaging

Chinese hamster ovary (CHO) cells in culture were exposed in a nuclear magnetic resonance (NMR) imaging apparatus to a strong magnetic field, pulsed field gradients, and radio frequency emissions. No chromosomal aberrations were induced even after an exposure of approximately 14 hours. No sister chromatid exchanges were induced by four-hour exposures to either low (average 7.2 mW) or high (average 61.2 mW) radio frequency power. When HeLa cells were exposed for 16 hours to an average radio frequency power of 61.2 mW, no inhibition of DNA synthesis was detectable. These data indicate that the conditions used for NMR imaging do not cause genetic damage which is detectable by any of these methods.     

KARP-1 is induced by DNA damage in a p53- and ataxia telangiectasia mutated-dependent fashion

The KARP-1 (Ku86 Autoantigen Related Protein-1) gene, which is expressed from the human Ku86 autoantigen locus, appears to play a role in mammalian DNA double-strand break repair as a regulator of the DNA-dependent protein kinase complex. Here we demonstrate that KARP-1 gene expression is significantly up-regulated following exposure of cells to DNA damage. KARP-1 mRNA induction was completely dependent on the ataxia telangiectasia and p53 gene products, consistent with the presence of a p53 binding site within the second intron of the KARP-1 locus. These observations link ataxia telangiectasia, p53, and KARP-1 in a common pathway.     

T4 DNA ligase reduces chromosome damage and enhances cell survival in CHO cells treated with bleomycin

OBJECTIVE: Recent clinical studies suggest that the reflex increase in sympathetic nervous activity accompanying a reduction in blood pressure may contribute to the untoward effects of dihydropyridine calcium antagonists. The aim of this study was to examine whether plasma noradrenaline levels and renin activity are increased with the reduction of blood pressure during the initial phase of administration of the long-acting dihydropyridine calcium antagonist amlodipine. METHODS: The effects of amlodipine on ambulatory blood pressure and on diurnal variations in plasma noradrenaline and renin activity were examined 1, 4, and 7 days after the start of amlodipine administration in eight inpatients with essential hypertension. RESULTS: The 24-h mean systolic and diastolic blood pressure on day 7 was significantly lower than it was 1 day before the start of treatment. There was no change in the mean heart rate. The mean trough to peak ratios of systolic and diastolic blood pressure of seven patients were 61% and 71%, respectively. Diurnal patterns of plasma noradrenaline levels and renin activity 1, 4, and 7 days after the start of amlodipine administration were unchanged. CONCLUSION: The antihypertensive effects of amlodipine were of slow onset and long duration and were not accompanied by an increase in sympathetic activity or activation of the renin-angiotensin system.     

Probable pulmonary damage caused by bleomycin. Communication of 4 cases

Four patients with advanced germinal cell testicular tumors were treated with cisplatinum, vinblastine and bleomycin. Histopathologic studies revealed pulmonary damage and various degrees of respiratory insufficiency developed in all patients, one of whom died. There was no instance of opportunistic infections in any patient. The pathophysiology relating pulmonary damage to the action of bleomycin is discussed.     

Determination of DNA damage in F344 rats induced by geometric isomers of tamoxifen and analogues

The transformation of Trypanosoma cruzi epimastigotes to mammal-infective metacyclic trypomastigotes (metacyclogenesis) can be performed in vitro under chemically defined conditions (TAU 3AAG medium). During this process, changes in the nature of cell surface sugar composition and sugar distribution was evaluated using FITC and gold-labeled lectins and observed by flow cytometry and transmission electron microscopy. The pattern of labeling with the lectins from Triticum vulgaris (WGA), Arachis hypogaea (PNA), Limax flavus (LFA), Canavalia ensiformis (Con-A), and Ricinus communis (RCA-I) significantly changed during the metacyclogenic process. The results obtained are discussed in relation to the role played by T. cruzi cell surface carbohydrate residues on the process of parasite-host cell interaction.     

Oxidative DNA damage induced by Cu(II)-oligopeptide complexes and hydrogen peroxide

At physiological pH values, Cu(II)-tetraglycine and Cu(II) complexes with peptides containing a histidyl residue at the N-terminal caused DNA strand breakage in the presence of H2O2, whereas Cu(II) complexes with peptides containing histidyl residue in the second or third position did not. Because of the correlation between the generation of hydroxyl radical and DNA strand scission, a mechanism for the reaction is proposed.     

In vivo damage and recA-dependent repair of plasmid and chromosomal DNA in the radiation-resistant bacterium Deinococcus radiodurans

Deinococcus radiodurans R1 and other members of this genus share extraordinary resistance to the lethal and mutagenic effects of ionizing radiation. We have recently identified a RecA homolog in strain R1 and have shown that mutation of the corresponding gene causes marked radiosensitivity. We show here that following high-level exposure to gamma irradiation (1.75 megarads, the dose required to yield 37% of CFU for plateau-phase wild-type R1), the wild-type strain repairs > 150 double-strand breaks per chromosome, whereas a recA-defective mutant (rec30) repairs very few or none. A heterologous Escherichia coli-D. radiodurans shuttle plasmid (pMD68) was constructed and found to be retained in surviving D. radiodurans R1 and rec30 following any radiation exposure up to the highest dose tested, 3 megarads. Plasmid repair was monitored in vivo following irradiation with 1.75 megarads in both R1/pMD68 and rec30/pMD68. Immediately after irradiation, plasmids from both strains contained numerous breaks and failed to transform E. coli. While irradiation with 1.75 megarads was lethal to rec30 cultures, a small amount of supercoiled plasmid was regenerated, but it lacked the ability to transform E. coli. In contrast, wild-type cultures showed a cell division arrest of about 10 h, followed by exponential growth. Supercoiled plasmid was regenerated at normal levels, and it readily transformed E. coli. These studies show that D. radiodurans retains a heterologous plasmid following irradiation and repairs it with the same high efficiency as its chromosomal DNA, while the repair defect in rec30 prevents repair of the plasmid. Taken together, the results of this study suggest that plasmid DNA damaged in vivo in D. radiodurans is repaired by recA-dependent mechanisms similar to those employed in the repair of chromosomal DNA.     

Nuclear localization of cyclin B1 controls mitotic entry after DNA damage

While the Vpr protein of HIV-1 has been implicated in import of the viral preintegration complex across the nuclear pore complex (NPC) of nondividing cellular hosts, the mechanism by which Vpr enters the nucleus remains unknown. We now demonstrate that Vpr contains two discrete nuclear targeting signals that use two different import pathways, both of which are distinct from the classical nuclear localization signal (NLS)- and the M9-dependent pathways. Vpr import does not appear to require Ran-mediated GTP hydrolysis and persists under conditions of low energy. Competition experiments further suggest that Vpr directly engages the NPC at two discrete sites. These sites appear to form distal components of a common import pathway used by NLS- and M9-containing proteins. Together, our data suggest that Vpr bypasses many of the soluble receptors involved in import of cellular cargoes. Rather, this viral protein appears to directly access the NPC, a property that may help to ensure the capacity of HIV to replicate in nondividing cellular hosts.