Search results for "dimer"
showing 10 items of 558 documents
Selective targeting of avidin/mannose 6-phosphate receptor chimeras to early or late endosomes
2000
Summary In this study we have used the Semliki forest virus expression system to transiently express chimeric proteins that contain transmembrane and cytoplasmic domains of the cation-independent mannose 6-phosphate receptor (CI-MPR) fused to chicken avidin. Immunofluorescence and electron microscopy studies showed that the chimeric protein with the entire cytoplasmic domain of CI-MPR was transported to late endosomes, where it accumulated. We made use of the biotin-binding capacity of lumenal avidin, and found that, in agreement with this distribution, the chimeric protein could be labelled with biotinylated HRP endocytosed for a long, but not a brief, period of time. However, truncation o…
DNA oxidation products determined with repair endonucleases in mammalian cells: Types, basal levels and influence of cell proliferation
1999
Purified repair endonucleases such as Fpg protein, endonuclease III and IV allow a very sensitive quantification of various types of oxidative DNA modifications in mammalian cells. By means of these assays, the numbers of base modifications sensitive to Fpg protein, which include 8-hydroxyguanine (8-oxoG), were determined to be less than 0.3 per 10(6) bp in several types of untreated cultured mammalian cells and human lymphocytes and less than 10 per 10(6) bp in mitochondrial DNA from rat and porcine liver. Oxidative 5,6-dihydropyrimidine derivatives sensitive to endonuclease III and sites of base loss sensitive to endonuclease IV or exonuclease III were much less frequent than Fpg-sensitiv…
Poly(ADP-ribosyl)ation accelerates DNA repair in a pathway dependent on Cockayne syndrome B protein
2003
Activation of poly(ADP-ribose)polymerases 1 and 2 (PARP-1 and PARP-2) is one of the earliest responses of mammalian cells to DNA damage by numerous genotoxic agents. We have analysed the influence of PARP inhibition, either achieved by over-expression of the DNA binding domain of PARP-1 or by treatment with 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-isoquinolinone, on the repair of single-strand breaks (SSB), pyrimidine dimers and oxidative base modifications sensitive to Fpg protein (mostly 8-hydroxyguanine) in mammalian cells at very low, non-cytotoxic levels of DNA damage. The data show that the repair rates of all three types of DNA damage are significantly lower in PARP-inhibited c…
Molecular and functional analysis of the (6-4) photolyase from the hexactinellid Aphrocallistes vastus.
2003
The hexactinellid sponges (phylum Porifera) represent the phylogenetically oldest metazoans that evolved 570-750 million years ago. At this period exposure to ultraviolet (UV) light exceeded that of today and it may be assumed that this old taxon has developed a specific protection system against UV-caused DNA damage. A cDNA was isolated from the hexactinellid Aphrocallistes vastus which comprises high sequence similarity to genes encoding the protostomian and deuterostomian (6-4) photolyases. Subsequently functional studies were performed. It could be shown that the sponge gene, after transfection into mutated Escherichia coli, causes resistance of the bacteria against UV light. Recombinan…
Oxidative stress impairs the repair of oxidative DNA base modifications in human skin fibroblasts and melanoma cells.
2008
Irradiation of mammalian cells with solar light is associated with the generation of reactive oxygen species (ROS) and oxidative stress, which is mediated in part by endogenous photosensitizers absorbing in the visible range of the solar spectrum. Accordingly, oxidative DNA base modifications such as 7,8-dihydro-8-oxoguanine (8-oxoG) are the predominant types of DNA damage in cells irradiated at wavelengths >400 nm. We have analysed the repair of oxidative purine modifications in human skin fibroblasts and melanoma cells using an alkaline elution technique, both under normal conditions and after depletion of glutathione. Similar repair rates were observed in fibroblasts and melanoma cells f…
Influences of histone deacetylase inhibitors and resveratrol on DNA repair and chromatin compaction
2013
Accessibility of DNA is a prerequisite for both DNA damage and repair. Therefore, the chromatin structure is expected to have major impact on both processes, with opposite consequences for the stability of the genome. To analyse the influence of chromatin compaction on the generation and repair of various types of DNA modifications, we modulated the global chromatin structure of AS52 Chinese hamster ovary cells and HeLa cells by treatment with either histone deacetylase inhibitors or resveratrol and measured the repair kinetics of (i) pyrimidine dimers induced by ultraviolet B, (ii) oxidised purines generated by photosensitisation and (iii) single-strand breaks induced by H2O2, using an alk…
c-Fos is required for excision repair of UV-light induced DNA lesions by triggering the re-synthesis of XPF
2006
Cells deficient in c-Fos are hypersensitive to ultraviolet (UV-C) light. Here we demonstrate that mouse embryonic fibroblasts lacking c-Fos (fos-/-) are defective in the repair of UV-C induced DNA lesions. They show a decreased rate of sealing of repair-mediated DNA strand breaks and are unable to remove cyclobutane pyrimidine dimers from DNA. A search for genes responsible for the DNA repair defect revealed that upon UV-C treatment the level of xpf and xpg mRNA declined but, in contrast to the wild type (wt), did not recover in fos-/- cells. The observed decline in xpf and xpg mRNA is due to impaired re-synthesis, as shown by experiments using actinomycin D. Block of xpf transcription resu…
How DNA lesions are turned into powerful killing structures: Insights from UV-induced apoptosis
2008
Mammalian cells treated with ultraviolet (UV) light provide one of the best-known experimental systems for depicting the biological consequences of DNA damage. UV irradiation induces the formation of DNA photoproducts, mainly cyclobutane pyrimidine dimers (CPDs) and (6-4) pyrimidine-pyrimidone photoproducts [(6-4)PPs], that drastically impairs DNA metabolism, culminating in the induction of cell death by apoptosis. While CPDs are the most important apoptosis-inducing lesions in DNA repair proficient cells, recent data indicates that (6-4)PPs also signals for apoptosis in DNA repair deficient cells. The toxic effects of these unrepaired DNA lesions are commonly associated with transcription …
Modulation of Base Excision Repair Alters Cellular Sensitivity to UVA1 but not to UVB¶
2007
Abstract Oxidative DNA damage has been implicated in some of the biological properties of UVA but so far not in the acute photosensitivity or cellular sensitivity. In contrast to pyrimidine dimers, oxidative DNA damage is predominantly processed by base excision repair (BER). In order to further clarify the role of oxidative DNA damage and its repair in the acute cellular response to UV light, we studied UVA1 and UVB sensitivities in three different cell model systems with modified BER. 8-Oxoguanine-DNA-glycosylase 1–/– (OGG1–/–) mouse embryonal fibroblasts and human fibroblasts in which BER was inhibited by incubation with methoxyamine were hypersensitive to UVA1, in particular to low dose…
Experimental and theoretical studies on thymine photodimerization mediated by oxidatively generated DNA lesions and epigenetic intermediates.
2020
[EN] Interaction of nucleic acids with light is a scientific question of paramount relevance not only in the understanding of life functioning and evolution, but also in the insurgence of diseases such as malignant skin cancer and in the development of biomarkers and novel light-assisted therapeutic tools. This work shows that the UVA portion of sunlight, not absorbed by canonical DNA nucleobases, can be absorbed by 5-formyluracil (ForU) and 5-formylcytosine (ForC), two ubiquitous oxidatively generated lesions and epigenetic intermediates present in living beings in natural conditions. We measure the strong propensity of these molecules to populate triplet excited states able to transfer th…