Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

N-Hydroxypyridine-2-thione (2-HPT), known to release hydroxyl radicals on irradiation with visible light, and two related compounds, viz. N-hydroxypyridine-4-thione (4-HPT) and N-hydroxyacridine-9-thione (HAT), were tested for their potency to induce DNA damage in L1210 mouse leukemia cells and in isolated DNA from bacteriophage PM2. DNA single-strand breaks and modifications sensitive to various repair endonucleases (Fpg protein, endonuclease III, exonuclease III, T4 endonuclease V) were quantified. Illumination of cell-free DNA in the presence of 2-HPT and 4-HPT gave rise to damage profiles characteristic for hydroxyl radicals, i.e. single-strand breaks and the various endonuclease-sensitive modifications were formed in the same ratios as after exposure to established hydroxyl radical sources. In contrast, HAT plus light gave rise to a completely different DNA damage profile, namely that characteristic for singlet oxygen. Experiments with various scavengers (t-butanol, catalase, superoxide dismutase) and in D2O as solvent confirmed that hydroxyl radicals are directly responsible for the DNA damage caused by photoexcited 2-HPT and 4-HPT, while the damage by HAT plus light is mediated by singlet oxygen and type I reactions. The type of DNA damage characteristic of hydroxyl radicals was also observed in L1210 mouse leukemia cells when treated with 2-HPT plus light or with H2O2 at 0 degrees C. t-Butanol (2%) inhibited the cellular DNA damage by approximately 50%. A dose of 2-HPT plus light that generated single-strand breaks at a frequency of 5 x 10(-7)/bp was associated with 50% cell survival. No DNA damage and cytotoxicity was observed after treatment with 2-HPT in the dark. We propose that 2-HTP and 4-HTP may serve as new agents to study the consequences of DNA damage induced by hydroxyl radicals in cells. In addition, the data provide direct evidence that hydroxyl radicals are ultimately responsible for the genotoxic effects caused by H2O2 in the dark.
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PMID:Photolysis of N-hydroxpyridinethiones: a new source of hydroxyl radicals for the direct damage of cell-free and cellular DNA. 864 78

The nucleoside analogue cordycepin (3'-deoxyadenosine), when protected against ADA deamination, is specifically cytotoxic for TdT-positive leukemia cells. Cordycepin-treated, ADA-inhibited, TdT-positive cells undergo the classic changes associated with drug-induced apoptosis: reduction in cell volume, chromatin clumping, membrane blebbing, and 180-bp multimer DNA laddering on agarose gels. In common with the apoptosis seen in normal TdT-positive thymocytes, following exposure to various agents, apoptosis induced by cordycepin in TdT-positive leukemia cells was associated with increased protein kinase A (PK-A) activity. Unlike thymocyte apoptosis however, no elevation in cAMP levels was seen preceding the rise in PK-A activity. Ex vivo we show that cordycepin monophosphate can activate PK-A as efficiently as cAMP. On this basis we speculate that cordycepin monophosphate in TdT-positive cells may be able to activate PK-A in place of cAMP, and that PK-A may phosphorylate TdT, augmenting its activity as an endonuclease. In cell-free experiments, the activity of recombinant TdT as an endonuclease digesting supercoiled plasmid DNA into linear fragments was dramatically increased following phosphorylation of TdT by PK-A. A role for TdT as an apoptotic endonuclease in TdT-positive leukemia cells following cordycepin exposure is now the subject of on-going work.
Leukemia 1996 Jun
PMID:Induction of apoptosis by cordycepin in ADA-inhibited TdT-positive leukemia cells. 866 37

Restriction endonuclease in situ digestion (REISD) with Sau3A of human metaphase chromosomes and interphase nuclei produces a conspicuous banding pattern involving pericentromeric regions of chromosomes 9 and 3. Constitutive heterochromatin of chromosome 9 is never digested by this enzyme while that of chromosome 3 is polymorphic, giving rise to three possible karyotypes: homozygous digested (3--), homozygous undigested (3++) or heterozygous individuals (3+-). Discrimination of this polymorphism between donor and recipient cells constitutes a rapid sex-independent method to monitor quantitatively the chimaerism achieved after bone marrow transplantation. An image processing and analysis (IPA)-assisted procedure which resolves residual fluorescent regions in metaphase chromosomes or interphase nuclei after REISD has been developed. IPA-REISD has interesting advantages over the basic REISD method by allowing a rapid, objective and precise discrimination of the polymorphism in large cell samples.
Leukemia 1996 Jul
PMID:Improving chimaerism quantification in bone marrow transplant recipients by image processing and analysis after restriction endonuclease in situ digestion (IPA-REISD). 868 7

To establish the most effective and reasonable mode of combining and administrering ara-C with other antileukemic agents in chemotherapy for acute leukemia, the action mechanisms of ara-C was investigated in terms of intracellular pharmacodynamics and the biochemical action mechanism of ara-C was investigated in leukemic cell. Rensonable methods of administering the agent was considered as follows. 1. A low level of ara-C in the incubation medium induced a higher concentration of ara-CTP in leukemic cells. Therefore, maintenance of even a low plasma ara-C level after ara-C therapy could enhance the antileukemic effect of the agent. 2. Ara-C activation was increased in the presence of 6MP by suppressing elevation of deaminase activity in the cell suspection medium. Therefore, administration of 6MP prior to ara-C therapy could enhance the antileukemic effect of the agent. 3. Ten micrograms/ml of ara-C, corresponding to intermediate dose ara-C therapy, induced rapid endonuclease activation, DNA ladder fragmentation and subsequent apoptosis in large numbers of leukemic cells, suggesting that intermediate dose ara-C therapy is effective in reducing residual leukemic cells after therapy. 4. Blood transfusion for patients with high grade anemia prior to bebenoyl ara-C therapy prolonged higher and longer plasma drug maintenance. 5. Flowcytometry of cell cycle progression of L1210 cells treated by ara-C and daunorubicin revealed that a combination of ara-C first and daunorubicin second was superior to the reverse sequential combination. These improvements in the mode of administering ara-C could provide better results following chemotherapy for leukemia.
Leukemia 1997 Apr
PMID:Intracellular pharmacodynamics of ara-C and flowcytometric analysis of cell cycle progression in leukemia chemotherapy. 920 53

The human leukemia cell line, HL60 is very sensitive to various apoptotic stimuli and p53-null. The death-related cysteine proteases of the caspases family play a central role in the execution phase of apoptosis, and we recently reported the importance of serine protease activation in camptothecin-induced apoptotic endonuclease activation in HL60 cells. In the present study, we investigated the role of caspases (ICE/CED-3-related cysteine proteases) and serine proteases in cell death induced by the topoisomerase I inhibitor, camptothecin, in HL60 cells and in a cell-free system. We found that CPP32 is activated during camptothecin-induced apoptosis, and that N-benzyloxycarbony-Val-Ala-Asp (O-methyl) -fluoromethyketone (Z-VAD-fmk), a cell permeable caspase inhibitor blocks all features of apoptosis: morphological changes, cleavage of caspase 3 (CPP32/Yama/Apopain) and poly(ADP-ribose) polymerase, lamin B degradation and DNA fragmentation. However, Z-VAD-fmk and two other ICE/CED-3 inhibitors, YVAD-CHO and DEVD-CHO, were inactive in a cell-free system reconstituted from nuclei of untreated HL60 cells and cytosol from camptothecin-treated cells, suggesting that caspases are not required for endonuclease activation or lamin B cleavage in the cell-free system. By contrast, the serine protease inhibitors, 3,4-dichloroisocoumarin (DCI) and L-1-chloro-3-(4-tosylamido)-4-phenyl-2-butanone tosyl-L-phenylalanine chloromethyl ketone (TPCK), abolished the apoptosis-associated biochemical changes induced by camptothecin both in whole cells and in a cell-free system. DCI also inhibited CPP32 cleavage. Taken together, these results suggest that in HL60 cells, both CPP32 and serine proteases are activated in camptothecin-induced apoptosis.
Leukemia 1997 Aug
PMID:Camptothecin-induced apoptosis in p53-null human leukemia HL60 cells and their isolated nuclei: effects of the protease inhibitors Z-VAD-fmk and dichloroisocoumarin suggest an involvement of both caspases and serine proteases. 926 76

The extent of the indirect DNA damage generated in mammalian cells by visible light because of the presence of endogenous photosensitizers was studied by means of repair endonucleases. In immortalized human keratinocytes (HaCaT cells) exposed to low doses of natural sunlight, the yield of oxidative DNA base modifications sensitive to the repair endonuclease formamidopyrimidine-DNA glycosylase (Fpg protein) generated by this indirect mechanism was 10% of that of pyrimidine dimers (generated by direct DNA excitation). A similar yield of Fpg-sensitive modifications, which include 8-hydroxyguanine, was observed in primary keratinocytes. The relative yield of oxidative base modifications decreased at higher light doses, probably as a result of photodecomposition of the endogenous chromophore involved. For the three cell lines tested, viz. HaCaT cells, L1210 mouse leukemia cells and AS52 Chinese hamster cells, the yield of oxidative base modifications generated by a low dose of visible light appeared to be correlated with the basal concentrations of porphyrins in the cells. Induction of cellular porphyrin synthesis by pretreatment with 5-aminolaevulinic acid increased the light-induced oxidative damage in L1210 cells several-fold. In both induced and uninduced cells, the damage was inhibited by more than 50% in the presence of ascorbic acid (100 microM), while alpha-tocopherol and the iron chelator alpha-phenanthroline had no effect and beta-carotene even increased the damage. Even high doses of visible light did not significantly increase the numbers of micronuclei in L1210 cells or of gpt mutations in AS52 cells. The negative outcome can be fully explained by the photobleaching of the endogenous photosensitizers, which prevents the generation of sufficiently high levels of oxidative DNA damage. Therefore, the mutagenic risk arising from the indirectly generated oxidative DNA modifications induced by sunlight may be underestimated when results obtained at high doses are extrapolated to low doses or low dose rates.
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PMID:Oxidative DNA damage induced by visible light in mammalian cells: extent, inhibition by antioxidants and genotoxic effects. 973 16

The stem cell leukaemia (SCL) gene is a member of the basic helix-loop-helix family of transcription factors and is essential for the development of all haematopoietic lineages. SCL is expressed in pluripotent haematopoietic stem cells and also following commitment to the erythroid, mast and megakaryocytic lineages. The mechanisms responsible for this pattern of expression are poorly understood, but are likely to illuminate the molecular basis for stem cell development and lineage commitment. Here we present the first description of the regulation of the SCL gene in mast cells. In this study we systematically analysed the chromatin structure of a 45 kb region of the murine SCL locus in mast cells. The pattern of DNase 1 and restriction endonuclease hypersensitive sites in mast cells was distinct from, but overlapped with, the pattern previously described in erythroid and primitive myeloid cells. Each potential regulatory element was tested using transient reporter assays to assess their functional significance in mast cells. These studies identified two potent enhancers, one of which was downstream of the SCL gene. Further characterisation of this 3' enhancer demonstrated that it required the presence of two distinct DNase 1 hypersensitive sites for full activity, and that it was capable of stimulating transcription from both promoter 1a and 1b. Since the 3' enhancer is active in both erythroid and mast cells, it will now be important to see whether it is independently activated in these lineages, or whether it is also active in haematopoietic stem cells.
Leukemia 1999 May
PMID:Chromatin structure and transcriptional regulation of the stem cell leukaemia (SCL) gene in mast cells. 1037 80


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