scholarly journals Reduced DNA repair during differentiation of a myogenic cell line.

1976 ◽  
Vol 70 (3) ◽  
pp. 685-691 ◽  
Author(s):  
A C Chan ◽  
I G Walker
Keyword(s):  
Strand Break ◽  
Post Treatment ◽  
Single Strand ◽  
Repair Synthesis ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Single Strand Breaks ◽  
Before And After ◽  
Dna Strands ◽  
A Minor

Repair synthesis induced by 4-nitroquinoline-1-oxide (4NQO) in L6 myoblasts before and after cellular fusion was measured by [3H] thymidine incorporation into unreplicated DNA. The level of repair synthesis was reuced after the cells had fused into myotubes. The terminal addition of radioactive nucleotides into DNA strands occurred only to a minor extent, and the dilution of [3H] thymidine by intracellular nucleotide pools was shown not to be responsible for the observed difference in repair synthesis, Both the initial rate and the overall incorporation of [3H] thymidine were found to be 50% lower in the myotubes. 4NQO treatment of myoblasts and myotubes induced modifications in the DNA which were observed as single-strand breaks during alkaline sucrose sedimentation. After the myoblasts were allowed a post-treatment incubation, most of the single-strand breaks were not longer apparent. In contrast, a post-treatment incubation of myotubes did not change the extent of single-strand breakage seen. Both myoblasts and myotubes were equally effective in repairing single-strand breaks induced by X radiation. It would appear that when myoblasts fuse, a repair enzyme activity is lost, probably an endonuclease that recognizes one of the 4 NQO modifications of DNA. The result observed is a partial loss of repair synthetic ability and a complete loss of ability to remove the modification that appears as a single-strand break in alkali.

scholarly journals Single-Strand Break End Resection in Genome Integrity: Mechanism and Regulation by APE2

2018 ◽  
Vol 19 (8) ◽  
pp. 2389 ◽  
Author(s):  
Md. Hossain ◽  
Yunfeng Lin ◽  
Shan Yan
Keyword(s):  
Dna Damage ◽  
Genome Instability ◽  
Strand Break ◽  
Single Strand ◽  
Genome Integrity ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Single Strand Breaks ◽  
Damage Response ◽  
End Resection

DNA single-strand breaks (SSBs) occur more than 10,000 times per mammalian cell each day, representing the most common type of DNA damage. Unrepaired SSBs compromise DNA replication and transcription programs, leading to genome instability. Unrepaired SSBs are associated with diseases such as cancer and neurodegenerative disorders. Although canonical SSB repair pathway is activated to repair most SSBs, it remains unclear whether and how unrepaired SSBs are sensed and signaled. In this review, we propose a new concept of SSB end resection for genome integrity. We propose a four-step mechanism of SSB end resection: SSB end sensing and processing, as well as initiation, continuation, and termination of SSB end resection. We also compare different mechanisms of SSB end resection and DSB end resection in DNA repair and DNA damage response (DDR) pathways. We further discuss how SSB end resection contributes to SSB signaling and repair. We focus on the mechanism and regulation by APE2 in SSB end resection in genome integrity. Finally, we identify areas of future study that may help us gain further mechanistic insight into the process of SSB end resection. Overall, this review provides the first comprehensive perspective on SSB end resection in genome integrity.

scholarly journals Manipulating chromosome structure and metaphase status with ultraviolet light and repair synthesis inhibitors

1985 ◽  
Vol 73 (1) ◽  
pp. 159-186
Author(s):  
A.M. Mullinger ◽  
R.T. Johnson
Keyword(s):  
Simian Virus 40 ◽  
Human Cells ◽  
Single Strand ◽  
Dna Breaks ◽  
Intact Cells ◽  
Repair Synthesis ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Single Strand Breaks ◽  
Chromosome Decondensation

DNA repair occurs in metaphase-arrested cells in response to ultraviolet irradiation. In the presence of the repair synthesis inhibitors hydroxyurea and 1-beta-D-arabinofuranosylcytosine the chromosomes of such cells, as seen in Carnoy-fixed preparations, are decondensed. The extent of decondensation is related to both the u.v. dose and the duration of incubation in the presence of inhibitors. For any particular cell type there is a reasonable correlation between the amount of decondensation and the number of single-strand DNA breaks generated by the repair process under the same inhibitory conditions, though the chromosome changes continue after the number of single-strand breaks has reached a plateau. The dose response of chromosome decondensation varies between different cell types but is in general correlated with differences in levels of single-strand breaks accumulated under comparable inhibitory conditions. Decondensation can be detected after 0.5 Jm-2 in repair-competent human cells. In human cells defective in excision repair there is much less chromosome decondensation in response to the same u.v. dose and time of repair inhibition. However, a simian virus 40-transformed muntjac cell displays pronounced chromosome decondensation but has limited incision ability. Both chromosome decondensation and single-strand break accumulation in the presence of inhibitors are reversed when DNA precursors are provided, but reversal after higher u.v. doses and longer periods of incubation leads to recondensed chromosomes that are fragmented. Elution of the DNA from such cells through polycarbonate filters under non-denaturing conditions reveals that double-strand DNA breaks are generated during the period of incubation with inhibitors. Although the chromosomes of repair-inhibited metaphase cells are decondensed in fixed preparations, their morphology appears normal in intact cells. The cells also retain a capacity to induce prematurely condensed chromosomes (PCC) when fused with interphase cells: compared with control mitotic cells, the speed of induction is sometimes reduced but the final amount of PCC produced is similar.

scholarly journals Poly(ADP-Ribose) Polymerase 1 Accelerates Single-Strand Break Repair in Concert with Poly(ADP-Ribose) Glycohydrolase

2007 ◽  
Vol 27 (15) ◽  
pp. 5597-5605 ◽  
Author(s):  
Anna E. O. Fisher ◽  
Helfrid Hochegger ◽  
Shunichi Takeda ◽  
Keith W. Caldecott
Keyword(s):  
A549 Cells ◽  
Strand Break ◽  
Single Strand ◽  
Single Strand Break ◽  
Single Strand Breaks ◽  
Single Strand Break Repair ◽  
Break Repair ◽  
A Minor ◽  
Parp 1 ◽  
Human A549

ABSTRACT Single-strand breaks are the commonest lesions arising in cells, and defects in their repair are implicated in neurodegenerative disease. One of the earliest events during single-strand break repair (SSBR) is the rapid synthesis of poly(ADP-ribose) (PAR) by poly(ADP-ribose) polymerase (PARP), followed by its rapid degradation by poly(ADP-ribose) glycohydrolase (PARG). While the synthesis of poly(ADP-ribose) is important for rapid rates of chromosomal SSBR, the relative importance of poly(ADP-ribose) polymerase 1 (PARP-1) and PARP-2 and of the subsequent degradation of PAR by PARG is unclear. Here we have quantified SSBR rates in human A549 cells depleted of PARP-1, PARP-2, and PARG, both separately and in combination. We report that whereas PARP-1 is critical for rapid global rates of SSBR in human A549 cells, depletion of PARP-2 has only a minor impact, even in the presence of depleted levels of PARP-1. Moreover, we identify PARG as a novel and critical component of SSBR that accelerates this process in concert with PARP-1.

scholarly journals Neuronal Enhancers are Hotspots For DNA Single-Strand Break Repair

2020 ◽  
Author(s):  
Wei Wu ◽  
Sarah E. Hill ◽  
William J. Nathan ◽  
Jacob Paiano ◽  
Kenta Shinoda ◽  
...  
Keyword(s):  
Dna Repair ◽  
Genome Stability ◽  
Cell Types ◽  
Strand Break ◽  
Single Strand ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Single Strand Breaks ◽  
Single Strand Break Repair ◽  
The Central Nervous System

Genome stability is essential for all cell types. However, defects in DNA repair frequently lead to neurodevelopmental and neurodegenerative diseases, underscoring the particular importance of DNA repair in long-lived post-mitotic neurons. The neuronal genome is subjected to a constant barrage of endogenous DNA damage due to high levels of oxidative metabolism in the central nervous system. Surprisingly, we know little about the identity of the lesion(s) that accumulate in neurons and whether they accrue throughout the genome or at specific loci. Here, we show that neurons, but not other post-mitotic cells, accumulate unexpectedly high numbers of DNA single-strand breaks (SSBs) at specific sites within the genome. These recurrent SSBs are found within enhancers, and trigger DNA repair through recruitment and activation of poly(ADP-ribose) polymerase-1 (PARP1) and XRCC1, the central SSB repair scaffold protein. Notably, deficiencies in PARP1, XRCC1, or DNA polymerase β elevate the localized incorporation of nucleotides, suggesting that the ongoing DNA synthesis at neuronal enhancers involves both short-patch and long-patch SSB repair processes. These data reveal unexpected levels of localized and continuous DNA single-strand breakage in neurons, suggesting an explanation for the neurodegenerative phenotypes that occur in patients with defective SSB repair.

Protein–protein interactions during mammalian DNA single-strand break repair

2003 ◽  
Vol 31 (1) ◽  
pp. 247-251 ◽  
Author(s):  
K.W. Caldecott
Keyword(s):  
Protein Interactions ◽  
Mammalian Cells ◽  
Strand Break ◽  
Double Strand Breaks ◽  
Single Strand ◽  
Protein Protein Interactions ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Single Strand Breaks ◽  
Single Strand Break Repair

The genetic stability of living cells is continually threatened by endogenous reactive oxygen species and other genotoxic molecules. Of particular threat are the thousands of single-strand breaks that arise in each cell every day. If left unrepaired, such breaks can give rise to potentially clastogenic or lethal chromosomal double-strand breaks. This article summarizes our current understanding of how mammalian cells detect and repair single strand breaks, and provides insights into novel polypeptide components of this process.

scholarly journals Effects of variation in glutathione peroxidase activity on DNA damage and cell survival in human cells exposed to hydrogen peroxide and t-butyl hydroperoxide

1990 ◽  
Vol 271 (1) ◽  
pp. 17-23 ◽  
Author(s):  
B E Sandström ◽  
S L Marklund
Keyword(s):  
Glutathione Peroxidase ◽  
Cell Survival ◽  
Peroxidase Activity ◽  
Strand Break ◽  
Single Strand ◽  
Glutathione Peroxidase Activity ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Butyl Hydroperoxide ◽  
Single Strand Breaks

The selenium-dependent glutathione peroxidase activities of two human cell lines, the colon carcinoma HT29 and the mesothelioma P31, cultured in medium containing 2% serum, increased from 195 to 541 and from 94 to 361 units/mg of protein respectively after supplementation with 100 nM-selenite. The catalase activity remained unchanged by this treatment. The effects of the obtained variation in glutathione peroxidase activities were investigated by exposing cells to H2O2 and t-butyl hydroperoxide. Selenite supplementation resulted in a decrease in H2O2-induced DNA single-strand breaks in both HT29 and P31 cells. A small, but significant, decrease in the number of DNA single-strand breaks for low doses (10-50 microM) of t-butyl hydroperoxide was found only in P31 cells and not in HT29 cells. We could detect neither induction of double-strand breaks (detection limit approx. 1000 breaks per cell) nor DNA-protein cross-links after exposing the cells to the two peroxides. In spite of the apparent protective effect of increased glutathione peroxidase activity on DNA single-strand break formation, there were no differences between selenite-supplemented and non-supplemented cells in cell survival after exposure to peroxide.

scholarly journals Pathological mutations in PNKP trigger defects in DNA single-strand break repair but not DNA double-strand break repair

2020 ◽  
Vol 48 (12) ◽  
pp. 6672-6684 ◽  
Author(s):  
Ilona Kalasova ◽  
Richard Hailstone ◽  
Janin Bublitz ◽  
Jovel Bogantes ◽  
Winfried Hofmann ◽  
...  
Keyword(s):  
Strand Break ◽  
Single Strand ◽  
Dna Double Strand Breaks ◽  
Fha Domain ◽  
Single Strand Break ◽  
Strand Breaks ◽  
Charcot Marie Tooth Disease ◽  
Single Strand Break Repair ◽  
Primary Determinant ◽  
Break Repair

Abstract Hereditary mutations in polynucleotide kinase-phosphatase (PNKP) result in a spectrum of neurological pathologies ranging from neurodevelopmental dysfunction in microcephaly with early onset seizures (MCSZ) to neurodegeneration in ataxia oculomotor apraxia-4 (AOA4) and Charcot-Marie-Tooth disease (CMT2B2). Consistent with this, PNKP is implicated in the repair of both DNA single-strand breaks (SSBs) and DNA double-strand breaks (DSBs); lesions that can trigger neurodegeneration and neurodevelopmental dysfunction, respectively. Surprisingly, however, we did not detect a significant defect in DSB repair (DSBR) in primary fibroblasts from PNKP patients spanning the spectrum of PNKP-mutated pathologies. In contrast, the rate of SSB repair (SSBR) is markedly reduced. Moreover, we show that the restoration of SSBR in patient fibroblasts collectively requires both the DNA kinase and DNA phosphatase activities of PNKP, and the fork-head associated (FHA) domain that interacts with the SSBR protein, XRCC1. Notably, however, the two enzymatic activities of PNKP appear to affect different aspects of disease pathology, with reduced DNA phosphatase activity correlating with neurodevelopmental dysfunction and reduced DNA kinase activity correlating with neurodegeneration. In summary, these data implicate reduced rates of SSBR, not DSBR, as the source of both neurodevelopmental and neurodegenerative pathology in PNKP-mutated disease, and the extent and nature of this reduction as the primary determinant of disease severity.

scholarly journals Loss of DNA repair capacity during successive subcultures of primary rat fibroblasts.

1977 ◽  
Vol 74 (2) ◽  
pp. 365-370 ◽  
Author(s):  
A C Chan ◽  
I G Walker
Keyword(s):  
Dna Repair ◽  
Excision Repair ◽  
Strand Break ◽  
Single Strand ◽  
Velocity Sedimentation ◽  
Early Passage ◽  
Repair Capacity ◽  
Repair Synthesis ◽  
Single Strand Break ◽  
Passage Cells

Cultures of fibroblasts from newborn rats and successive subcultures of these cells were treated with 4-nitroquinoline-1-oxide to induce DNA repair. DNA from the cultures was examined by velocity sedimentation in alkaline sucrose gradients immediately after drug treatment and after a post-treatment incubation period of 3 h. Early passage cells were able to repair the damage that appeared as single strand breaks, however, by the seventh subculture this activity was not apparent. Measurements of repair synthesis showed a partial loss of this capacity with successive subculture. The results fit a model in which 4NQO causes two kinds of DNA modification, one of which is alkali labile and appears as a single-strand break. Both modifications are subject to excision repair, but each is recognized initially by a specific endonuclease. In the late passage cells, the endonuclease specific for the alkali labile modification is absent.

scholarly journals Repair of adjacent single-strand breaks is often accompanied by the formation of tandem sequence duplications in plant genomes

2016 ◽  
Vol 113 (26) ◽  
pp. 7266-7271 ◽  
Author(s):  
Simon Schiml ◽  
Friedrich Fauser ◽  
Holger Puchta
Keyword(s):  
Excision Repair ◽  
Strand Break ◽  
Single Strand ◽  
Direct Repeats ◽  
Genomic Context ◽  
Replication Slippage ◽  
Strand Breaks ◽  
Plant Genomes ◽  
Major Mechanism ◽  
Single Strand Breaks

Duplication of existing sequences is a major mechanism of genome evolution. It has been previously shown that duplications can occur by replication slippage, unequal sister chromatid exchange, homologous recombination, and aberrant double-strand break-induced synthesis-dependent strand annealing reactions. In a recent study, the abundant presence of short direct repeats was documented by comparative bioinformatics analysis of different rice genomes, and the hypothesis was put forward that such duplications might arise due to the concerted repair of adjacent single-strand breaks (SSBs). Applying the CRISPR/Cas9 technology, we were able to test this hypothesis experimentally in the model plant Arabidopsis thaliana. Using a Cas9 nickase to induce adjacent genomic SSBs in different regions of the genome (genic, intergenic, and heterochromatic) and at different distances (∼20, 50, and 100 bps), we analyzed the repair outcomes by deep sequencing. In addition to deletions, we regularly detected the formation of direct repeats close to the break sites, independent of the genomic context. The formation of these duplications as well as deletions may be associated with the presence of microhomologies. Most interestingly, we found that even the induction of two SSBs on the same DNA strand can cause genome alterations, albeit at a much lower level. Because such a scenario reflects a natural step during nucleotide excision repair, and given that the germline is set aside only late during development in plants, the repair of adjacent SSBs indeed seems to have an important influence on the shaping of plant genomes during evolution.

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