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At least 775 records · Page 43Linked to original sources
PubMed1996

DNA damage induction by 125I-estrogen.

DNA damage induced by the radioactive decay of 125I-estrogen (125I-VME2) in an estrogen receptor expressing CHO cell line, CHO-ER, was measured. 125I-VME2 targeted 125I atoms proximal to DNA estrogen response elements (EREs). 125I decays were accumulated at -135 degrees C, and thereafter assayed by alkaline and neutral filter elution techniques to measure DNA single strand break (ssb) and double strand break (dsb) induction respectively. Increasing DNA damage (both ssbs and dsbs) was detected after exposure of cells to increasing concentrations of 125I-VME2. DNA ssb and dsb dose-response curves for 125I-VME2 were multiphasic. The rates of DNA damage induction by the decay of 125I-VME2 was determined by comparing slopes of all data or by comparing initial slopes. DNA ssb induction per 125I-VME2 decay was approximately 2 times greater compared with DNA dsb induction. 125I-VME2 decay induced approximately 4-8 times more DNA dsbs than 125IUdR decay.

Animals↗
PubMed1996

Double-strand breaks in DNA induced by the K-shell ionization of calcium atoms.

A calcium (Ca)-DNA complex in a buffered aqueous solution was irradiated with monochromatic x-rays at around the K-shell absorption edge of the Ca atom. The energies were 4.030 and 4.071 keV, which correspond to slightly below and above the K-shell absorption edge of Ca (4.047 keV). The number of double-strand breaks (DSB) and single-strand breaks (SSB) per one molecule of Col E1 DNA was calculated using Povirk's equation after the electrophoretic separation of three forms of plasmid DNA (forms I, II and III, which are supercoiled closed circular, open circular and linear, respectively). In a solution with Ca ions, the DSB yield in DNA irradiated with 4.071 keV x-rays is 1.27 times higher than that with 4.030 keV x-rays. In contrast, in the absence of Ca ions, the DSB yield is the same at both the x-ray energies. The SSB yields are also independent of the x-ray energy in the presence and absence of Ca ions. A reference experiment regarding irradiation with 60Co gamma-rays shows that the ratio of the DSB yield to the SSB yield upon irradiation with 4.071 keV x-rays is higher (factor of 3.2) than that with 60Co gamma-rays.

Calcium↗
PubMed1990

10,11-Methylenedioxycamptothecin, a topoisomerase I inhibitor of increased potency: DNA damage and correlation to cytotoxicity in human colon carcinoma (HT-29) cells.

We had previously shown that 10,11-methylenedioxy-20-(RS)-camptothecin (MDO-CPT) is a more potent inhibitor of purified DNA topoisomerase I than 20-(S)-camptothecin (CPT). The current studies compared the cytotoxicity and DNA damage induced by MDO-CPT and CPT in the human colon carcinoma cell line, HT-29. MDO-CPT was 7- to 10-fold more potent than CPT both for cytotoxicity (ID50 = 25 vs. 180 nM) and production of DNA single-strand breaks (SSB). Kinetics of SSB formation and reversal were similar for MDO-CPT and CPT. DNA-protein crosslinks (DPC) were also produced by both drugs with a SSB/DPC ratio of 1/1. Moreover, no SSB were detected under non-deproteinizing conditions, indicating that both CPT and MDO-CPT produced protein-linked DNA single-strand breaks. A good correlation between cytotoxic potency and protein-linked DNA single-strand break production was observed for CPT and MDO-CPT, implying a causal relationship between drug-induced cytotoxicity and topoisomerase I inhibition. The sensitivity of human colon HT-29 cancer cells to camptothecins may be a selective phenomenon since these cells normally express natural resistance to current chemotherapeutic drugs, including topoisomerase II inhibitors.

Camptothecin↗
PubMed1990

Comparative pharmacokinetics of DNA lesion formation and removal following treatment of L1210 cells with nitrogen mustards.

The kinetics of formation and removal of DNA interstrand crosslinks (ISC), DNA-protein crosslinks (DPC), and single strand breaks (SSB) by several nitrogen mustards were compared in order to determine the degree to which lesion selectivity may vary. The kinetic measurements using DNA alkaline elution methodology were obtained in mouse L1210 cells treated with mechlorethamine (HN2), phenylalanine mustard (L-PAM), uracil mustard (UM), 6-methyl-UM, and quinacrine mustard (QM). The ISC or DPC challenge delivered to cells was gauged on the basis of the kinetics as either total ISC or DPC produced, or as the area under the lesions versus time curve (AUC). By either measure (excepting QM), ISC correlated well with loss of colony survival, whereas DPC did not. The ISC/DPC ratio may therefore be a useful index of lesion selectivity. This ratio was significantly greater for 6-methyl-UM than for HN2. The ratio was also greater for L-PAM than for HN2 but only when gauged by AUC; this was attributable to an unusually slow rate for ISC removal in the case of L-PAM. The preferential reaction of UM at some 5'-GC-3' sites in purified DNA had suggested that UM might produce ISC with increased efficacy. UM, however, was somewhat less efficacious in ISC production than was 6-methyl-UM, which lacked selectivity for alkylation at 5'-GC-3'. QM was the only compound that produced detectable SSB, and the SSB were so numerous that ISC could not be quantitated.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Detection of DNA damage in peripheral lymphocytes by 7 compounds using comet assay.

AIM: To detect the DNA single strand breaks (SSB) in peripheral lymphocytes of mice, rats, and human induced by hydrogen peroxide (H2O2), ethyl methane sulphonate (EMS), dimethylnitrosamine (DMNA), mitomycin C (MMC), benzo (a) pyrene (BaP), cyclophosphamide (CP), and 2-aminofluorene (2-AF). METHODS: Alkaline single cell microgel electrophoresis assay in vitro (comet assay). RESULTS: All were positive with 2 exceptions: EMS (0.97 mmol.L-1) in mice and MMC (30 mumol.L-1) in mice and human. The lowest concentrations detectable were H2O2 (1 mumol.L-1), EMS (0.48 mmol.L-1), BaP (5.0 mumol.L-1), CP (2.0 mmol.L-1), MMC (10 mumol.L-1), DMNA (27.3 mmol.L-1), and 2-AF (62.5 mumol.L-1). CP, BaP, and 2-AF were positive only in the presence of metabolic activation system. CONCLUSION: H2O2, DMNA, BaP, CP, and 2-AF induce SSB in peripheral lymphocytes of mice, rats, and human detected by comet assay, whereas MMC induces SSB only in rats, and EMS in rats and human lymphocytes.

Animals↗
PubMed2002

[Neonatal cutaneous lupus. Necessary interdisciplinary collaboration].

INTRODUCTION: Neonatal lupus erythematosus is a rare syndrome (affecting 5% of the children born of mothers with lupus), characterized essentially by cutaneous lesions and/or congenital auricular-ventricular heart block. It is due to the transplacental passage of maternal antibodies (anti-SSA or anti-SSB, or occasionally anti-U1RNP antibodies) into the fetal circulation. OBSERVATION: We report a case of neonatal lupus erythematosus, having appeared 4 weeks after birth. The 26 years old mother exhibited systemic lupus erythematosus concomitant to Gougerot-Sjögren's syndrome, with positive antinuclear factors (1/2560), native anti-DNA, anti-SSA and anti-SSB antibodies and anticardiolipin antibodies. During pregnancy, the mother had been treated with aspirin at the dose of 100 mg/day, followed by subcutaneous enoxaparin 0.4 ml/day, and combined with prednisone 10 mg/d and hydroxychloroquine 400 mg/day. Early and regular cardiac monitoring of the foetus was performed. The clinical examination and the electrocardiogram at birth were normal. Four weeks later, the infant presented with erythematous cutaneous lesions with atrophic center. No systemic treatment was initiated and the lesions partially regressed. CONCLUSION: Cutaneous lesions can also appear after the 4th week of life. It is important that the pediatricians clinically monitor all the children born to mothers exhibiting anti-SSA or anti-SSB antibodies, at least during the first 7 months of life.

Adult↗
PubMed2004

Squaraine dyes for photodynamic therapy: mechanism of cytotoxicity and DNA damage induced by halogenated squaraine dyes plus light (>600 nm).

Halogenated squaraine dyes 1 and 2 possess favorable photophysical and in vitro photobiological properties that make these new class of molecules interesting for photodynamic therapeutic applications. For a better understanding of the mechanism of their photobiological activity, we have analyzed the DNA damage and the cytotoxicity induced by these photosensitizers in mammalian cells and cell-free systems in the presence and absence of various additives and scavengers. Both photoactivated squaraines were found to be similar efficient in inducing single-strand breaks (SSB) in cell-free DNA when compared with the cellular DNA. Superoxide dismutase and catalase did not show any influence. However, the presence of tert-butanol and glutathione inhibited the formation of the DNA SSB, indicating an indirect (possibly squaraine radical mediated) mechanism under cell-free conditions. Replacing H2O in the buffer by D2O resulted in a five- to six-fold increase in the number of the SSB in cell-free DNA and a significant enhancement of the photocytotoxicity in mouse lymphoma cells. The results demonstrate that singlet oxygen is the major reactive species under cell-free and cellular conditions and confirm that squaraine-based sensitizers 1 and 2 can have potential applications in photodynamic therapy.

Animals↗
PubMedDate not supplied

[Stimulation of replicative DNA synthesis by eukaryotic proteins bound to single-stranded DNA].

The paper deals with the effect of the single-strand (ss) DNA-binding proteins (SSB-proteins) from the Ehrlich ascites tumor (EAT) cells and from the eggs of silkworm, as well as the mouse serum blood proteins, having preferential affinity to ss DNA, on the DNA replicative synthesis in the EAT cells permeable for the macromolecules, and, for the silkworm proteins and on the DNA replicative synthesis in the nuclei from the eggs of silkworm proteins and on the DNA replicative synthesis in the nuclei from the eggs of silkworm permeable for macromolecules. SSB-proteins of EAT to considerable extent stimulated the DNA synthesis. At the same time, the other proteins (from the silkworm and from the serum) activated the DNA synthesis in the permeable cells to the less extent. It was found that SSB-proteins from the silkworm had a 1.5-13 fold stimulating effect on the DNA replicative synthesis in the homologous system (in the permeable nuclei). If the permeability for the macromolecules of the cells and nuclei treatment with Triton X-100 may be different, it is supposed that the activation of the DNA synthesis by the exogenous proteins depends on the homologous system of the DNA replicative complex. It is possible that the effect of the serum proteins on the DNA synthesis is connected with the masking of the ss regions of DNA which inhibited DNA-polymerase alpha. Perhaps the mechanisms of the activation of the DNA replicative synthesis by the proteins in vitro with the purified DNA polymerase alpha and in vivo are of different nature and are conditioned by homology of the deoxyribonucleoproteins.

Animals↗
PubMed1992

Enhancement of recA protein-promoted DNA strand exchange activity by volume-occupying agents.

To investigate the in vivo effects of macromolecular crowding we examined the effect of inert macromolecules such as polyvinyl alcohol and polyethylene glycol on the in vitro activity of recA protein. The addition of either of these volume-occupying agents enables recA protein to promote homologous pairing and exchange of DNA strands at an otherwise nonpermissive magnesium ion concentration. In the presence of these macromolecules, both the rate of recA protein association with single-stranded DNA (ssDNA) and the steady-state affinity of recA protein for ssDNA are increased. Consequently, the ability of recA protein to compete with ssDNA-binding protein (SSB protein) is enhanced, and the inhibitory effects of SSB protein on the formation of recA protein-ssDNA presynaptic complexes are eliminated. Because the ability of recA protein to bind to ssDNA-containing secondary structures is also enhanced in volume-occupied solution, joint molecule formation is not greatly reduced when SSB protein is omitted from the reaction. Thus, increased recA protein interactions with ssDNA contribute to enhanced presynaptic complex formation. In addition, polyvinyl alcohol and polyethylene glycol must also affect another property of recA protein, i.e. self-association, which is required for synapsis and DNA strand exchange. Our examination of DNA strand exchange in the presence of volume-occupying agents helps to reconcile the requirement for elevated magnesium ion concentrations in recA protein-promoted recombination reactions in vitro, with a presumably low magnesium ion concentration in vivo.

Adenosine Triphosphatases↗
PubMed1991

Isolation of a DNA helicase from HeLa cells requiring the multisubunit human single-stranded DNA-binding protein for activity.

A DNA helicase, dependent on the multisubunit human single-stranded DNA binding protein (HSSB), was isolated from HeLa cells. At low levels of helicase, only the multisubunit SSBs, HSSB and yeast SSB, stimulated DNA helicase activity. At high levels of the helicase Escherichia coli SSB partially substituted for HSSB whereas other SSBs such as T4 gene 32 and adenovirus DNA binding protein did not stimulate the enzyme activity. Maximal activation of helicase activity occurred in the presence of one molecule of HSSB for every 20 nucleotides of single-stranded DNA. The addition of E. coli SSB significantly lowered the amount of HSSB required for strand displacement, suggesting that the HSSB plays at least two roles in the activation of the helicase. One is to bind single-stranded DNA, thereby preventing sequestration of the helicase, the other involves the interaction of the HSSB with the helicase. Monoclonal antibodies that interact with the 70- and 34-kDa subunits of HSSB inhibited its stimulation of the helicase activity. The DNA helicase acted catalytically in displacing duplex DNA and translocated in the 3' to 5' direction. The helicase displaced fragments from both ends of a DNA substrate that contained duplex region at both termini, but the 3' to 5' fragment was displaced 20 times faster than the 5' to 3' fragment. Since this helicase also displaced fully duplex DNA, the release of the 5' to 3' fragment may have occurred by entry of the helicase through the duplex end in a 3' to 5' direction.

Adenosine Triphosphatases↗
PubMed1992

A mutation in the consensus ATP-binding sequence of the RecD subunit reduces the processivity of the RecBCD enzyme from Escherichia coli.

We have constructed a mutant form of the RecBCD enzyme from Escherichia coli with a lysine to glutamine change in the consensus ATP-binding sequence in the RecD subunit (Korangy, F., and Julin, D.A. (1992a, 1992b) J. Biol. Chem., 1727-1732; 1733-1740). We compare here the kinetics of double-stranded DNA-dependent ATP hydrolysis by the mutant (RecBCD-K177Q) and wild-type enzymes. We included heparin to trap enzyme not bound to DNA, or the single-stranded DNA-binding (SSB) protein from Escherichia coli to prevent the enzyme from binding to single-stranded DNA products and partially single-stranded reaction intermediates. The ATP hydrolysis kinetics in either case show a rapid burst phase followed by a slower second phase. The wild-type enzyme hydrolyzes an amount of ATP about equal to the DNA nucleotide concentration in the rapid phase. The amount of ATP hydrolyzed by the RecBCD-K177Q enzyme in the burst is about 8-10-fold lower than the wild-type, in the presence of either heparin or SSB. The burst magnitude of the wild-type enzyme with heparin is proportional to the size of the DNA from about 1,420 to 22,400 base pairs whereas that of the mutant is independent of the DNA size. The wild-type enzyme completely degrades a 6,250-base pair DNA substrate with no partially degraded molecules visible on agarose gels. RecBCD-K177Q enzyme reaction mixtures in the presence of SSB protein contain a heterogeneous mixture of partially degraded molecules of 2,000-5,000 base pairs. These results indicate that the RecBCD-K177Q enzyme is less processive than the wild-type enzyme.

Adenosine Triphosphate↗
PubMed1991

Detection of single-strand breaks in DNA induced by mitoxantrone in experimental tumors after in vivo treatment.

The fluorometric assay of DNA alkaline unwinding [15] was applied to murine tumor DNA after in vivo treatment. Mitoxantrone (MX) whose cytostatic effect has been extensively investigated was tested as DNA damaging compound. The single-strand breaks of DNA (SSB) in ascitic tumors (EAT. P388) and in solid tumors (B16a, B16) were detected after intraperitoneal administrations of 1 and 10 mg/kg MX in the course of 1 to 96 hours. The maximal number of SSB was measured after 1 to 6 hours and DNA damage outlasted 24 to 96 hours in dependence on the dose of MX and on the type of tumor. A dependence of DNA damage induced by MX on the route of tumor implantation was found. Ascitic tumor P388 and EAT were more than 5 times more sensitive to the effects of MX than solid melanomas. The SSB correlated well with the intracellular concentration of MX in the EAT cells.

Animals↗
PubMed1990

The preference for a 3' homologous end is intrinsic to RecA-promoted strand exchange.

The recA protein (RecA) promotes DNA pairing and strand exchange optimally in the presence of single-stranded binding protein (SSB). Under these conditions, 3' homologous ends are essential for stable joint molecule formation between linear single-stranded DNA (ssDNA) and supercoiled DNA (i.e. 3' ends are 50-60 times more reactive than 5' ends). Linear ssDNAs with homology at the 5' end do not participate in pairing. In the absence of SSB, the strand exchange reaction is less efficient; however, linear ssDNAs with 3' end homology are still 5- to 10-fold more reactive than those with 5' end homology. The preference for a 3' homologous end in the absence of SSB suggests that this is an intrinsic property of RecA-promoted strand exchange. The preferential reactivity of 3' homologous ends is likely to be a consequence of the polarity of polymerization of RecA on ssDNA. Specifically, since RecA polymerizes in the 5'----3' direction, 3' ends are more likely to be coated with RecA and, hence, will be more reactive than 5' ends.

DNA, Circular↗
PubMed1989

[Isolated symplasts and stromal syncytial buds of the normal human placenta at 6 to 14 weeks of pregnancy].

Formation of isolated symplasts (IS) ("deported trophoblast", according to English nomenclature) and stromal syncytial buds (SSB) has been studied in 10 normal patients at pregnancy of 6-14 weeks by means of the indirect immunoperoxidase method. Monoclonal antibodies against beta-subunit of the human chorionic gonadotropin (beta-HCG), serial paraffin slices, stained with hematoxylin-eosin, semithin slices, stained with toluidin blue-pyronine and scanning electron microscopy have been used. A great amount of syncytiotrophoblastic processes and IS, analogous by their structure to syncytiotrophoblast are revealed. Presence of beta-HCG in the syncytiotrophoblast and its absence in the cytotrophoblast are proved. Concentration of beta-HCG in the IS is higher than in the syncytiotrophoblast of the villi. Maximal concentration of beta-HCG in the SSB is described for the first time. The functional role of the IS and SSB is discussed in the system mother-placenta-fetus.

Cell Fusion↗
PubMedDate not supplied

Anti-CD3 and anti-CD2-induced T-cell activation in primary Sjögren's syndrome.

Because T-cell dysfunctions have been reported in patients with primary Sjögren's syndrome (SS), peripheral blood mononuclear cell (PBMC) proliferation obtained with anti-CD3 and anti-CD2 monoclonal antibodies was evaluated in these patients. Anti-CD3-induced mitogenesis, which varied widely among the patients, was lower in subjects with evidence of anti-SSA and anti-SSB antibodies than in controls. Moreover, the anti-CD2-induced response was depressed in about half the patients and the nonresponders were mainly those with anti-SSA and anti-SSB antibodies. Phorbol myristate acetate, a protein kinase C activator, used alone or added to anti-CD3, induced greater proliferation in patients than in control PBMC. In contrast, exogenous recombinant interleukin 2 (rIL-2) did not significantly enhance the anti-CD2-induced response of patients' PBMC, as it did in normal PBMC. Peripheral blood and parotid T cells from a patient with well-defined primary SS and parotid enlargement also responded poorly to anti-CD2 stimulation. Exogenous rIL-2 restored T-cell proliferation only in the salivary gland cultures of this patient. The present findings suggest that there is a T-cell activation defect in subjects with primary SS, particularly in those with circulating anti-SSA and anti-SSB antibodies. In addition, the difference in the response to IL-2 of peripheral blood and parotid-infiltrating T cells would seem to indicate that T-cell subsets are differently distributed in the blood and inflammation site.

Adult↗
PubMedDate not supplied

Neonatal lupus erythematosus: report of one case.

A female newborn of SLE mother developed transient typical discoid-like lupus skin lesions over her face soon after birth and had severe relapse with generalized spreading following an episode of upper respiratory tract infection at 50 days of age. Blood picture showed anemia, transient thrombocytopenia and high ESR. Cardiac echo disclosed small ASD with minimal TR. Both EKG and 24 hrs EKG monitor presented normal findings. Serological studies at the early relapse stage of this disease showed increased serum ANA, IgA and IgM level with normal IgG and decrease of C3 and C4. Both Ro(SSA) and La(SSB) antibody systems were positive in mother but only positive for La(SSB) antibody system in this baby. The alpha-anticardiolipin antibody was negative. We suggest that the Ro(SSA) and/or La(SSB) antibody systems may play a role in the pathogenesis of neonatal lupus erythematosus.

Adult↗
PubMed1988

The effect of the T7 and Escherichia coli DNA-binding proteins at the replication fork of bacteriophage T7.

In this paper we compare the effect of single-stranded DNA-binding proteins of bacteriophage T7 (gene 2.5 protein) and of Escherichia coli (SSB) at the T7 replication fork. The T7 gene 4 protein acts processively as helicase to promote leading strand synthesis and distributively as primase to initiate lagging strand synthesis by T7 DNA polymerase. On a nicked double-stranded template, the formation of a replication fork requires partial strand displacement so that gene 4 protein may bind to the displaced strand and unwind the helix catalytically. Both the T7 gene 2.5 protein and E. coli SSB act stoichiometrically to promote this initial strand displacement step. Once initiated, processive leading strand synthesis is not greatly stimulated by the single-stranded DNA-binding proteins. However, the T7 gene 2.5 protein, but not E. coli SSB, increases the frequency of initiation of lagging strand synthesis by greater than 10-fold. The results suggest a specific interaction of the T7 gene 2.5 protein with the T7 replication apparatus.

DNA Helicases↗
PubMed1988

Antibodies to Epstein-Barr virus and cytomegalovirus in primary Sjogren's syndrome.

Sera from 28 patients with Primary Sjögren's Syndrome (SS) and 20 healthy subjects were tested for the presence of antibodies to Epstein-Barr Virus (EBV) and Cytomegalovirus (CMV). No difference was noted in the mean titre of anti-CMV antibodies in patients and in controls. For what concerns EBV, the mean titre of anti-EBNA antibodies was significantly higher in SS patients than in normals (p less than 0.001); moreover, within the SS population, titres were higher in SSB-positive than in SSB-negative patients (p less than 0.05). These results, together with the fact that anti-SSB antibodies (characteristic of Sjögren's Syndrome) recognize also two EBV-encoded RNAs, strengthen the hypothesis that EBV is involved in the pathogenesis of SS.

Adult↗