Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:6.5.1.2 (DNA ligase)
 2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ferric nitrilotriacetate (Fe(3+)-NTA) catalyzes hydrogen peroxide-derived production of hydroxyl radicals, which are known to cause DNA damage. In the present work, Fe(3+)-NTA plus hydrogen peroxide-induced single-strand DNA breaks and repair of the DNA damage were studied in vitro by monitoring DNA damage- and DNA repair-dependent conformational changes of pUC18 plasmid DNA. Single-strand DNA breaks were induced in the pUC18 DNA by Fe(3+)-NTA plus hydrogen peroxide in a dose-dependent fashion. Induction of the DNA damage was inhibited by deferoxamine mesylate (an iron chelator) and by hydroxyl radical scavengers such as dimethyl sulfoxide (DMSO), D-mannitol and ethanol indicating that the DNA damage was caused by hydroxyl radicals which were generated by reaction of Fe(3+)-NTA with hydrogen peroxide. The oxygen radical-induced single-strand DNA breaks were repaired partly (more than 50%) by incubating the damaged DNA at 37 degrees C for 3 h with a partially purified preparation of APEX nuclease (a multifunctional DNA repair enzyme), DNA polymerase beta, four deoxyribonucleoside triphosphates, T4 DNA ligase and ATP. Analyses of the partially purified preparation of APEX nuclease revealed that a 45-kDa protein as well as APEX nuclease in the preparation were involved in the repair of the single-strand DNA breaks. APEX nuclease was suggested to initiate the repair by removing 3' termini blocked by the nucleotide fragments and also by incising the 5' side of AP sites. The 45-kDa protein was suggested to be required for removal of the 5' tags such as 5'-terminal deoxyribose phosphate residues produced by the action of APEX nuclease on AP sites.
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PMID:Oxygen radical-induced single-strand DNA breaks and repair of the damage in a cell-free system. 756 64

APEX nuclease is a mammalian DNA repair enzyme having apurinic/apyrimidinic endonuclease, 3'-5'-exonuclease, DNA 3' repair diesterase and DNA 3'-phosphatase activities. This report describes the organization of the gene (APEX gene) for human APEX nuclease. Human APEX gene was cloned using human APEX cDNA and a human leukocyte genomic library in bacteriophage vector EMBL-3. We proved that human APEX gene consists of 5 exons spanning 2.64 kilobases and suggested that the gene exists as a single copy in the haploid genome. The boundaries between exon and intron follow the GT/AG rule. The major transcription initiation site was assigned by primer extension analysis to C at 515 nucleotides upstream from the ATG initiation codon. The translation initiation and termination sites locate in the exon II and V, respectively. The 5' flanking region (0.89 kilobase) sequenced lacks typical TATA and CAAT boxes, but contains TATA- and CAAT-like sequences and putative cis-acting regulatory elements such as binding sites for Sp1, AP2 and ATF. A part of the 5' flanking region belongs to a CpG island, which extends to the intron II. The CpG island is thought to be a transcription regulatory region of APEX gene, a housekeeping gene. The promoter activity of the 5' upstream region was analyzed by introducing the region in HeLa cells in an expression construct containing luciferase gene as a reporter gene, and the region from position 130 bp upstream to position 205 bp downstream of the major transcription initiation site was shown to be enough for high promoter activity. Northern hybridization experiments suggested that the gene is expressed ubiquitously in human cells. The locus of APEX gene was mapped to human chromosome 14q11.2-q12 using the in situ hybridization technique.
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PMID:Structure, promoter analysis and chromosomal assignment of the human APEX gene. 808 53

Purification and characterization of a DNA repair enzyme having 5' apurinic/apyrimidinic (AP) endonuclease activity are reported. The enzyme extracted from mouse ascites sarcoma (SR-C3H/He) cells with 0.2 M potassium phosphate buffer (pH 7.5) was purified by successive chromatographies on phosphocellulose, DEAE-cellulose, phosphocellulose (a second time) and single-stranded DNA cellulose, and by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The purified enzyme has an apparent molecular mass of 30 kDa as determined by SDS-PAGE. It was shown to have nicking activity on acid-depurinated DNA but not on intact DNA, and to have priming activities for DNA polymerase on acid-depurinated DNA and bleomycin-treated DNA. The results indicate that it is a multifunctional DNA repair enzyme having 5' AP endonuclease and DNA 3' repair diesterase activities. The enzyme activity is dependent upon the presence of a divalent cation such as Mg2+. Its amino-terminal amino acid and internal amino acid sequences are determined.
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PMID:Purification and characterization of an AP endonuclease/DNA 3' repair diesterase from mouse ascites sarcoma cells. 854 4

Human DNA polymerase and DNA ligase utilization for the repair of a major class of ionizing radiation-induced DNA lesion [DNA single-strand breaks containing 3'-phosphoglycolate (3'-PG)] was examined using a novel, chemically defined vector substrate containing a single, site-specific 3'-PG single-strand break lesion. In addition, the major human AP endonuclease, HAP1 (also known as APE1, APEX, Ref-1), was tested to determine if it was involved in initiating repair of 3'-PG-containing single-strand break lesions. DNA polymerase beta was found to be the primary polymerase responsible for nucleotide incorporation at the lesion site following excision of the 3'-PG blocking group. However, DNA polymerase delta/straightepsilon was also capable of nucleotide incorporation at the lesion site following 3'-PG excision. In addition, repair reactions catalyzed by DNA polymerase beta were found to be most effective in the presence of DNA ligase III, while those catalyzed by DNA polymerase delta/straightepsilon appeared to be more effective in the presence of DNA ligase I. Also, it was demonstrated that the repair initiating 3'-PG excision reaction was not dependent upon HAP1 activity, as judged by inhibition of HAP1 with neutralizing HAP1-specific polyclonal antibody.
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PMID:Determination of human DNA polymerase utilization for the repair of a model ionizing radiation-induced DNA strand break lesion in a defined vector substrate. 1032 34

Nuclear uracil-DNA glycosylase UNG2 has an established role in repair of U/A pairs resulting from misincorporation of dUMP during replication. In antigen-stimulated B-lymphocytes UNG2 removes uracil from U/G mispairs as part of somatic hypermutation and class switch recombination processes. Using antibodies specific for the N-terminal non-catalytic domain of UNG2, we isolated UNG2-associated repair complexes (UNG2-ARC) that carry out short-patch and long-patch base excision repair (BER). These complexes contain proteins required for both types of BER, including UNG2, APE1, POLbeta, POLdelta, XRCC1, PCNA and DNA ligase, the latter detected as activity. Short-patch repair was the predominant mechanism both in extracts and UNG2-ARC from proliferating and less BER-proficient growth-arrested cells. Repair of U/G mispairs and U/A pairs was completely inhibited by neutralizing UNG-antibodies, but whereas added recombinant SMUG1 could partially restore repair of U/G mispairs, it was unable to restore repair of U/A pairs in UNG2-ARC. Neutralizing antibodies to APE1 and POLbeta, and depletion of XRCC1 strongly reduced short-patch BER, and a fraction of long-patch repair was POLbeta dependent. In conclusion, UNG2 is present in preassembled complexes proficient in BER. Furthermore, UNG2 is the major enzyme initiating BER of deaminated cytosine (U/G), and possibly the sole enzyme initiating BER of misincorporated uracil (U/A).
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PMID:Repair of U/G and U/A in DNA by UNG2-associated repair complexes takes place predominantly by short-patch repair both in proliferating and growth-arrested cells. 1547 84

Mice deficient in CuZn superoxide dismutase (CuZnSOD) showed no overt abnormalities during development and early adulthood, but had a reduced lifespan and increased incidence of neoplastic changes in the liver. Greater than 70% of Sod1-/- mice developed liver nodules that were either nodular hyperplasia or hepatocellular carcinoma (HCC). Cross-sectional studies with livers collected from Sod1-/- and age-matched +/+ controls revealed extensive oxidative damage in the cytoplasm and, to a lesser extent, in the nucleus and mitochondria from as early as 3 months of age. A marked reduction in cytosolic aconitase, increased levels of 8-oxo dG and F2-isoprostanes, and a moderate reduction in glutathione peroxidase activities and porin levels were observed in all age groups of Sod1-/- mice examined. There were also age-related reductions in Mn superoxide dismutase activities and carbonic anhydrase III. Parallel to the biochemical changes, there were progressive increases in the DNA repair enzyme APEX1, the cell cycle control proteins cyclin D1 and D3, and the hepatocyte growth factor receptor Met. Increased cell proliferation in the presence of persistent oxidative damage to macromolecules likely contributes to hepatocarcinogenesis later in life.
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PMID:CuZnSOD deficiency leads to persistent and widespread oxidative damage and hepatocarcinogenesis later in life. 1553 19

The base excision repair pathway is critical for the removal of oxidized and methylated bases from the DNA. Much of this DNA damage arises endogenously, as a result of oxygen metabolism. Several proteins including DNA glycosylases, the APE1 endonuclease, DNA polymerase beta and DNA ligase, act in a highly regulated and coordinated manner during base excision repair to excise the base adducts from the DNA and restore the normal DNA sequence. Both germline and tumor-associated variants of genes encoding these proteins have been identified in humans. In many cases, the protein variant has been shown to have properties that could contribute to the development of cancer, suggesting that base excision repair acts as a tumor suppressor mechanism in humans. Limited epidemiological studies are consistent with this view. Our review of the literature indicates that additional laboratory and epidemiological studies of the role of base excision repair in cancer etiology is warranted.
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PMID:Is base excision repair a tumor suppressor mechanism? 1641 80

DNA glycosylases/AP lyases initiate repair of oxidized bases in the genomes of all organisms by excising these lesions and then cleaving the DNA strand at the resulting abasic (AP) sites and generate 3' phospho alpha,beta-unsaturated aldehyde (3' PUA) or 3' phosphate (3' P) terminus. In Escherichia coli, the AP-endonucleases (APEs) hydrolyze both 3' blocking groups (3' PUA and 3' P) to generate the 3'-OH termini needed for repair synthesis. In mammalian cells, the previously characterized DNA glycosylases, NTH1 and OGG1, produce 3' PUA, which is removed by the only AP-endonuclease, APE1. However, APE1 is barely active in removing 3' phosphate generated by the recently discovered mammalian DNA glycosylases NEIL1 and NEIL2. We showed earlier that the 3' phosphate generated by NEIL1 is efficiently removed by polynucleotide kinase (PNK) and not APE1. Here we show that the NEIL2-initiated repair of 5-hydroxyuracil (5-OHU) similarly requires PNK. We have also observed stable interaction between NEIL2 and other BER proteins DNA polymerase beta (Pol beta), DNA ligase IIIalpha (Lig IIIalpha) and XRCC1. In spite of their limited sequence homology, NEIL1 and NEIL2 interact with the same domains of Pol beta and Lig IIIalpha. Surprisingly, while the catalytically dispensable C-terminal region of NEIL1 is the common interacting domain, the essential N-terminal segment of NEIL2 is involved in analogous interaction. The BER proteins including NEIL2, PNK, Pol beta, Lig IIIalpha and XRCC1 (but not APE1) could be isolated as a complex from human cells, competent for repair of 5-OHU in plasmid DNA.
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PMID:NEIL2-initiated, APE-independent repair of oxidized bases in DNA: Evidence for a repair complex in human cells. 1698 18

Tumor suppressor function for Annexin A7 (ANXA7; 10q21) is based on cancer-prone phenotype in Anxa7(+/-) mouse and ANXA7 prognostic role in human cancers. Because ANXA7-caused liposome aggregation can be promoted by arachidonic acid (AA), we hypothesized that the phospholipid-binding tumor suppressor ANXA7 is associated with AA cascade. In a comparative study of ANXA7 versus canonical tumor suppressor p53 effects on AA lipoxygenation pathway in the p53-mutant and androgen-insensitive DU145 prostate cancer cells, both tumor suppressors altered gene expression of major 5-lipoxygenase (LOX) and 15-LOXs, including response to T helper 2 (Th2)-cytokine [interleukin-4 (IL-4)] and endogenous steroids (mimicked by dexamethasone). Wild-type and mutant ANXA7 distinctly affected expression of the dexamethasone-induced 15-LOX-2 (a prostate-specific endogenous tumor suppressor) as well as the IL-4-induced 15-LOX-1. On the other hand, wild-type p53 restored 5-LOX expression in DU145 to levels comparable to benign prostate epithelial cells. Using mass spectrometry of DNA affinity-enriched nuclear proteins, we detected different proteins that were bound to adjacent p53 and estrogen response elements in the 5-LOX promoter in DU145 cells introduced with ANXA7 versus p53. Sex hormone regulator 17-beta hydroxysteroid dehydrogenase 4 was identified under p53 introduction, which induced the 5-LOX expression. Meantime, nuclear proteins bound to the same 5-LOX promoter site under introduction of ANXA7 (that was associated with the repressed 5-LOX) were identified as zinc finger proteins ZNF433 and Aiolos, pyrin domain-containing NALP10, and the p53-regulating DNA repair enzyme APEX1. Thus, ANXA7 and p53 can distinctly regulate LOX transcription that is potentially relevant to the AA-mediated cell growth control in tumor suppression.
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PMID:Distinct effects of annexin A7 and p53 on arachidonate lipoxygenation in prostate cancer cells involve 5-lipoxygenase transcription. 1701 18

Arsenite is a human carcinogen causing skin, bladder, and lung tumors, but the cellular mechanisms underlying these effects remain unclear. We investigated expression of the essential base excision DNA repair enzyme apurinic endonuclease 1 (Ape1) in response to sodium arsenite. In mouse 10T(1/2) fibroblasts, Ape1 induction in response to arsenite occurred about equally at the mRNA, protein, and enzyme activity levels. Analysis of the APE1 promoter region revealed an AP-1/CREB binding site essential for arsenite-induced transcriptional activation in both mouse and human cells. Electrophoretic mobility shift assays indicated that an ATF4/c-Jun heterodimer was the responsible transcription factor. RNA interference targeting c-Jun or ATF4 eliminated arsenite-induced APE1 transcription. Suppression of Ape1 or ATF4 sensitized both mouse fibroblasts (10T(1/2)) and human lymphoblastoid cells (TK6) to arsenite cytotoxicity. Expression of Ape1 from a transgene did not efficiently restore arsenite resistance in ATF4-depleted cells but did offset initial accumulation of abasic DNA damage following arsenite treatment. Mutagenesis by arsenite (at the TK and HPRT loci in TK6 cells) was observed only for ATF4-depleted cells, which was strongly offset by Ape1 expression from a transgene. Therefore, the ATF4-mediated up-regulation of Ape1 and other genes plays a key role against arsenite-mediated toxicity and mutagenesis.
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PMID:ATF4-dependent oxidative induction of the DNA repair enzyme Ape1 counteracts arsenite cytotoxicity and suppresses arsenite-mediated mutagenesis. 1793 2


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