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:6.5.1.2 (DNA ligase)
2,749 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Base excision-repair, which is required for correction of spontaneous hydrolytic and oxidative damage to DNA as well as lesions inflicted by alkylating agents, is a relatively well understood repair pathway. Mammalian factors involved in this pathway are reviewed, with emphasis on current uncertainties. Most DNA replication and repair enzymes in mammalian cell nuclei, e.g. DNA polymerases alpha, beta, delta, and epsilon, have direct counterparts in yeast. In contrast, the abundant enzymes in mammalian cell nuclei that bind and are activated specifically by DNA strand interruptions, poly(ADP-ribose) polymerase and DNA-dependent protein kinase, have not been detected in yeast; nor has p53, which is elevated in response to DNA strand breaks. We have found a family of four distinct DNA ligases in human cell nuclei, whereas only a single DNA ligase has been detected in yeast. It would appear that the cellular responses to DNA strand breaks may differ markedly between higher and lower eukaryotes.
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PMID:Recognition and processing of damaged DNA. 865 50

Interleukin 1 beta-converting enzyme (ICE)-like proteases (caspases) play an important role in programmed cell death (apoptosis), and elucidating the consequences of their proteolytic activity is central to our understanding of the molecular mechanisms of cell death. Diverse structural and regulatory proteins and enzymes, including protein kinase C delta, the retinoblastoma protein (a protein involved in cell survival), the DNA repair enzyme DNA-dependent protein kinase and the nuclear lamins, undergo specific and limited endoproteolytic cleavage by various caspases during apoptosis. Since individual caspases can cleave multiple substrates, the consequences of cleavage of only a single substrate are still poorly understood. Nevertheless, proteolytic activation of protein kinase C delta may be an important early step in the cell death pathway, and cleavage of the retinoblastoma protein could suppress its cell survival function, whereas proteolytic inactivation of DNA repair enzymes might compromise the ability of the cell to reverse DNA fragmentation. On the other hand, cleavages of nuclear and cytoplasmic structural proteins (e.g. the lamins and Gas2) appear to be required for or contribute to the dramatic rearrangements in cellular architecture that are necessary for the completion of the cell death process. An emerging theme is that parallel and sequential proteolytic activation and inactivation of key protein substrates occurs during the multiple steps of apoptosis.
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PMID:Death substrates come alive. 920 67

Genetic approaches have provided evidence that DNA end-joining problems serve an essential role in neuronal survival during development of mammalian embryos. In the present study, we tested whether the DNA repair enzyme, DNA dependent protein kinase, plays an important role in the survival of cerebral cortical neurons in mice. DNA-PK is comprised of a DNA-binding subunit called Ku and a catalytic subunit called DNA-PKcs. In mice with the scid mutation, DNA-PKcs is truncated near the kinase domain, which causes loss of kinase activity. We compared the spatial and temporal aspects of neuronal cell death in scid versus isogenic wild-type embryos and found a significant increase in dying cells in scid mice, as assessed by nuclear changes, DNA fragmentation and caspase-3 activity. Additional biochemical and immunocytochemical studies indicated that of several DNA repair enzymes investigated, only PARP was increased in scid mice, possibly in response to elevated DNA strand breaks.
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PMID:Elevated DNA double strand breaks and apoptosis in the CNS of scid mutant mice. 1131 7

DNA-dependent protein kinase (DNA-PK) is a DNA repair enzyme composed of a DNA-binding component called Ku70/80 and a catalytic subunit called DNA-PKcs. Many investigators have utilized DNA-PKcs-deficient cells and cell lines derived from severe combined immunodeficiency (scid) mice to study DNA repair and apoptosis. However, little is known about the CNS of these mice. This study was carried out using primary neuronal cultures derived from the cerebral hemispheres of new-born wild-type and scid mice to investigate the effects of loss of DNA-PK function on neuronal maturation and survival. Purified neuronal cultures developed comparably in terms of neurite formation and expression of neuronal markers, but scid cultures showed a significant increase in the percentage of dying cells. Furthermore, when apoptosis was induced by staurosporine, scid neurons died more rapidly and in higher numbers. Apoptotic scid neurons exhibited nuclear condensation, DNA fragmentation and caspase-3 activation, but treatment with the general caspase inhibitor, N-benzyloxycarbonyl-Val-Ala-Asp-(O-methyl) fluoromethyl ketone did not prevent staurosporine-induced apoptosis. We conclude that a DNA-PK deficiency in cultured scid neurons may cause an accumulation of DNA damage and increased susceptibility to caspase-independent forms of programmed cell death.
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PMID:Role of DNA-dependent protein kinase in neuronal survival. 1143 81

6-aryl-2-morpholin-4-yl-4H-pyran-4-ones and 6-aryl-2-morpholin-4-yl-4H-thiopyran-4-ones were synthesised and evaluated as potential inhibitors of the DNA repair enzyme DNA-dependent protein kinase (DNA-PK). Several compounds in each series exhibited superior activity to the chromenone LY294002, and were of comparable potency to the benzochromenone NU7026 (IC(50)=0.23 microM). Importantly, members of both structural classes were found to be selective inhibitors of DNA-PK over related phosphatidylinositol 3-kinase-related kinase (PIKK) family members. A multiple-parallel synthesis approach, employing Suzuki cross-coupling methodology, was utilised to prepare libraries of thiopyran-4-ones with a range of aromatic groups at the 3'- and 4'-positions on the thiopyran-4-one 6-aryl ring. Screening of the libraries resulted in the identification of 6-aryl-2-morpholin-4-yl-4H-thiopyran-4-ones bearing naphthyl or benzo[b]thienyl substituents at the 4'-position, as potent DNA-PK inhibitors with IC(50) values in the 0.2-0.4 microM range.
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PMID:2,6-disubstituted pyran-4-one and thiopyran-4-one inhibitors of DNA-Dependent protein kinase (DNA-PK). 1294 39

Recent studies have shown that recombinant adeno-associated virus (rAAV) can persist in episomal form; however, factors affecting rAAV persistence are poorly understood. DNA-dependent PK (DNA-PK) is a DNA repair enzyme, which we previously found played an important role in determining the molecular fate of the rAAV genome in mouse skeletal muscle. In the present study, we tested the effect of DNA-PK on AAV serotype 2 integration in vitro and in vivo in mouse liver. In an in vitro integration system, addition of DNA-PK decreased AAV integration, whereas antibody against DNA-PKcs increased integration. In vivo, matched doses of a recombinant AAV serotype 2 vector were injected into the portal vein of either C57BL/6 (DNA-PKcs(+/+)) or severe combined immunodeficient (DNA-PKcs(-/-)) mice. After partial hepatectomy to stimulate hepatocyte proliferation, retention of vector genomes and of transgene expression was substantially higher in severe combined immunodeficient mice, indicating that in the absence of DNA-PKcs, a greater proportion of genomes integrated into the cellular genome. In summary, we have provided evidence that DNA-PK inhibits AAV integration both in vitro and in vivo.
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PMID:DNA-dependent PK inhibits adeno-associated virus DNA integration. 1476 68

Pre-treatment with bryostatin 1 (bryo) has been shown to potentiate the efficacy of (2-chloro-2-deoxyadenosine, cladribine, 2-CdA) in B-cell chronic lymphocytic leukemia (B-CLL) by increasing the ratio of deoxycytidine kinase (dCK) to 5'-nucleotidase (5'-NT) activity. The bryo-induced increase in dCK/5'-NT activity alone has not been a conclusive indication of final clinical outcome. Therefore, we used an ex vivo assay to investigate factors which may affect the bryo-induced enhancement of 2-CdA efficacy in B-CLL patient-derived samples. Bryo-induced increase in dCK/5'-NT was inversely associated with Rai stage CLL (r=-0.86). Increased dCK/5'-NT activity was not correlated with increased efficacy (cell death) or percentage of cellular [8-3H]-2-CdA converted to [8-3H]-2-CdATP ex vivo. Bryo pre-treatment increased the cellular uptake of [8-3H]-2-CdA and incorporation of [8-3H]-2-CdA metabolites into the DNA fraction. Cell death from 2-CdA was inversely correlated with bryo-induced activity of the DNA repair enzyme, DNA-PKcs, (r=-0.77). Thus, the ability of B-CLL to repair damaged DNA may be a more important predictor of the response to bryo/2-CdA and eventual clinical outcome than dCK/5'-NT activity. Additional CLL patients under bryo-2-CdA therapy are needed to verify these important observations.
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PMID:Factors affecting bryostatin 1-enhanced 2-CdA cytotoxicity in resistant B-cell chronic lymphocytic leukemia. 1520 25

Non-homologous end joining (NHEJ) is one of the primary pathways for the repair of ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) in mammalian cells. Proteins required for NHEJ include the catalytic subunit of the DNA-dependent protein kinase (DNA-PKcs), Ku, XRCC4 and DNA ligase IV. Current models predict that DNA-PKcs, Ku, XRCC4 and DNA ligase IV assemble at DSBs and that the protein kinase activity of DNA-PKcs is essential for NHEJ-mediated repair of DSBs in vivo. We previously identified a cluster of autophosphorylation sites between amino acids 2609 and 2647 of DNA-PKcs. Cells expressing DNA-PKcs in which these autophosphorylation sites have been mutated to alanine are highly radiosensitive and defective in their ability to repair DSBs in the context of extrachromosomal assays. Here, we show that cells expressing DNA-PKcs with mutated autophosphorylation sites are also defective in the repair of IR-induced DSBs in the context of chromatin. Purified DNA-PKcs proteins containing serine/threonine to alanine or aspartate mutations at this cluster of autophosphorylation sites were indistinguishable from wild-type (wt) protein with respect to protein kinase activity. However, mutant DNA-PKcs proteins were defective relative to wt DNA-PKcs with respect to their ability to support T4 DNA ligase-mediated intermolecular ligation of DNA ends. We propose that autophosphorylation of DNA-PKcs at this cluster of sites is important for remodeling of DNA-PK complexes at DNA ends prior to DNA end joining.
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PMID:Autophosphorylation-dependent remodeling of the DNA-dependent protein kinase catalytic subunit regulates ligation of DNA ends. 1531 5

A solution-phase multiple-parallel synthesis approach was employed for the preparation of 6-, 7- and 8-aryl-substituted chromenone libraries, which were screened as inhibitors of the DNA repair enzyme DNA-dependent protein kinase (DNA-PK). These studies resulted in the identification of 8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one (NU7441) as a highly potent and selective DNA-PK inhibitor (IC50=14 nM), exhibiting ATP-competitive inhibition kinetics.
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PMID:Identification of a highly potent and selective DNA-dependent protein kinase (DNA-PK) inhibitor (NU7441) by screening of chromenone libraries. 1554 35

A diverse range of chromen-2-one, chromen-4-one and pyrimidoisoquinolin-4-one derivatives was synthesized and evaluated for inhibitory activity against the DNA repair enzyme DNA-dependent protein kinase (DNA-PK), with a view to elucidating structure-activity relationships for potency and kinase selectivity. DNA-PK inhibitory activity varied widely over the series of compounds evaluated (IC(50) values ranged from 0.19 to >10 microM), with excellent activity being observed for the 7,8-benzochromen-4-one and pyrimido[2,1-a]isoquinolin-4-one templates. By contrast, inhibitors based on the benzochromen-2-one (coumarin) or 2-aryl-7,8-benzochromen-4-one (flavone) scaffolds were less potent. Crucially, these studies revealed a very constrained structure-activity relationship at the 2-position of the benzopyranone and pyrimido[2,1-a]isoquinolin-4-one pharmacophore, with only a 2-morpholino or 2-(2'-methylmorpholino) group being tolerated at this position. More detailed biological studies conducted with the most potent inhibitor NU7163 (48; IC(50) = 0.19 microM) demonstrated ATP-competitive DNA-PK inhibition, with a K(i) value of 24 nM, and 48 exhibited selectivity for DNA-PK compared with the related enzymes ATM, ATR, mTOR, and PI 3-K (p110alpha). Compound 48 sensitized the HeLa human tumor cell line to the cytotoxic effects of ionizing radiation in vitro, a dose modification factor of 2.3 at 10% survival being observed with an inhibitor concentration of 5 microM. This study identified these structural classes as novel DNA-PK inhibitors and delineated initial structure-activity relationships against DNA-PK.
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PMID:Selective benzopyranone and pyrimido[2,1-a]isoquinolin-4-one inhibitors of DNA-dependent protein kinase: synthesis, structure-activity studies, and radiosensitization of a human tumor cell line in vitro. 1565 70


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