• Radiation Oncology Journal
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• v.13 no.2
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• pp.113-120
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• 1995

Purpose : To investigate the effect of alkaloid fraction from Korean ginseng on radiation-induced DNA double strand breaks (dsb) formation and repair in murine lymphocytes Materials and Methods : We used the neutral filter elution technique to assay $^{60}Co\;{\gamma}$ ray-induced DNA double strand breaks formation and repair in C57BL/6 mouse spleen lymphocytes for evaluating the dose-response relationship in the presence of alkaloid fraction as a radioprotective agent. The lymphocytes were stimulated with Phytohemagglutinin (PHA, 2 u g/ml) to label $^3[H]-thymidine.$ Isotope-labelled lymphocytes in suspension were exposed to 100 Gy at $0^{\cdot}C$ in the alkaloid fraction-treated group and elution procedure was performed at PH 9.6. The extents of formation of radiation-induced DNA double strand breaks and repair were compared respectively via strand scission factor (SSF) and relative strand scission factor (RSSF). Results: Alkaloid fraction reduced the formation of double strand breaks with dose modification factor of 2 15, compared to control group Rejoining of DNA dsb appeared to take place via two components. The first fast component was completed within 20.4 minutes, but the second slow component was not completed until 220.2 minutes after irradiation. About $30\%$ of dsb formed by irradiation was ultimately unrejoined despite the administration of alkaloid fraction. The administration of alkaloid fraction had a great effect on the second slow component of repair; the half-time of fast component repair was not changed, but that of slow component was 621.8 minutes. Conclusion: Neutral filter elution assay Proved to be a very effective method to quantitate the extents of DNA dsb formation and its repair. By using this technique, we were able to evaluate the efficiency of alkaloid fraction from Korean ginseng as a valuable radioprotector. Alkaloid fraction can be used prophylactically to prevent or ameliorate the severe radiation damages in workers and neighbors around the atomic power plants. For more refined study, however, more advanced purification of alkaloid fraction wil be needed in the near future.

• Molecules and Cells
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• v.39 no.3
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• pp.204-210
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• 2016

DNA damage responses are important for the maintenance of genome stability and the survival of organisms. Such responses are activated in the presence of DNA damage and lead to cell cycle arrest, apoptosis, and DNA repair. In Caenorhabditis elegans, double-strand breaks induced by DNA damaging agents have been detected indirectly by antibodies against DSB recognizing proteins. In this study we used a comet assay to detect DNA strand breaks and to measure the elimination of DNA strand breaks in mitotic germline nuclei of C. elegans. We found that C. elegans brc-1 mutants were more sensitive to ionizing radiation and camptothecin than the N2 wild-type strain and repaired DNA strand breaks less efficiently than N2. This study is the first demonstration of direct measurement of DNA strand breaks in mitotic germline nuclei of C. elegans. This newly developed assay can be applied to detect DNA strand breaks in different C. elegans mutants that are sensitive to DNA damaging agents.

• Asian Pacific Journal of Cancer Prevention
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• v.14 no.12
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• pp.7091-7094
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• 2013

DNA repair capacity is crucial in maintaining cellular functions and homeostasis. However, it can be altered based on DNA sequence variations in DNA repair genes and this may lead to the development of many diseases including malignancies. Identification of genetic polymorphisms responsible for reduced DNA repair capacity is necessary for better prevention. Homologous recombination (HR), a major double strand break repair pathway, plays a critical role in maintaining the genome stability. The present study was performed to determine the frequency of the HR gene XRCC3 Exon 7 (C18067T, rs861539) polymorphisms in Saudi Arabian population in comparison with epidemiological studies by "MEDLINE" search to equate with global populations. The variant allelic (T) frequency of XRCC3 (C>T) was found to be 39%. Our results suggest that frequency of XRCC3 (C>T) DNA repair gene exhibits distinctive patterns compared with the Saudi Arabian population and this might be attributed to ethnic variation. The present findings may help in high-risk screening of humans exposed to environmental carcinogens and cancer predisposition in different ethnic groups.

• BMB Reports
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• v.55 no.11
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• pp.541-546
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• 2022

The repair of DNA double-strand breaks (DSBs) by homologous recombination (HR) is crucial for maintaining genomic integrity and is involved in numerous fundamental biological processes. Post-translational modifications by proteins play an important role in regulating DNA repair. Here, we report that the methyltransferase SET7 regulates HR-mediated DSB repair by methylating TIP60, a histone acetyltransferase and tumor suppressor involved in gene expression and protein stability. We show that SET7 targets TIP60 for methylation at K137, which facilitates DSB repair by promoting HR and determines cell viability against DNA damage. Interestingly, TIP60 demethylation is catalyzed by LSD1, which affects HR efficiency. Taken together, our findings reveal the importance of TIP60 methylation status by SET7 and LSD1 in the DSB repair pathway.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.35 no.1
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• pp.1-6
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• 2009

DNA double-strand breaks (DSBs) occur commonly in the all living and in cycling cells. They constitute one of the most severe form of DNA damage, because they affect both strand of DNA. DSBs result in cell death or a genetic alterations including deletion, loss of heterozygosity, translocation, and chromosome loss. DSBs arise from endogenous sources like metabolic products and reactive oxygen, and also exogenous factors like ionizing radiation. Defective DNA DSBs can lead to toxicity and large scale sequence rearrangement that can cause cancer and promote premature aging. There are two major pathways for their repair: homologous recombination(HR) and non-homologous end-joining(NHEJ). The HR pathway is a known "error-free" repair mechanism, in which a homologous sister chromatid serves as a template. NHEJ, on the other hand, is a "error-prone" pathway, in which the two termini of the broken DNA molecule are used to form compatible ends that are directly ligated. This review aims to provide a fundamental understanding of how HR and NHEJ pathways operate, cause genome instability, and what kind of genes during the pathways are associated with head and neck cancer.

• The Korean Journal of Physiology and Pharmacology
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• v.13 no.5
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• pp.343-348
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• 2009

53BP1 is an important genome stability regulator, which protects cells against double-strand breaks. Following DNA damage, 53BP1 is rapidly recruited to sites of DNA breakage, along with other DNA damage response proteins, including ${\gamma}$-H2AX, MDC1, and BRCA1. The recruitment of 53BP1 requires a tandem Tudor fold which associates with methylated histones H3 and H4. It has already been determined that the majority of DNA damage response proteins are phosphorylated by ATM and/or ATR after DNA damage, and then recruited to the break sites. 53BP1 is also phosphorylated at several sites, like other proteins after DNA damage, but this phosphorylation is not critically relevant to recruitment or repair processes. In this study, we evaluated the functions of phosphor-53BP1 and the role of the BRCT domain of 53BP1 in DNA repair. From our data, we were able to detect differences in the phosphorylation patterns in Ser25 and Ser1778 of 53BP1 after neocarzinostatin-induced DNA damage. Furthermore, the foci formation patterns in both phosphorylation sites of 53BP1 also evidenced sizeable differences following DNA damage. From our results, we concluded that each phosphoryaltion site of 53BP1 performs different roles, and Ser1778 is more important than Ser25 in the process of DNA repair.

• Molecules and Cells
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• v.42 no.7
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• pp.546-556
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• 2019

Protein phosphatase 4 (PP4) is a crucial protein complex that plays an important role in DNA damage response (DDR), including DNA repair, cell cycle arrest and apoptosis. Despite the significance of PP4, the mechanism by which PP4 is regulated remains to be elucidated. Here, we identified a novel PP4 inhibitor, protein phosphatase 4 inhibitory protein (PP4IP) and elucidated its cellular functions. PP4IP-knockout cells were generated using the CRISPR/Cas9 system, and the phosphorylation status of PP4 substrates (H2AX, KAP1, and RPA2) was analyzed. Then we investigated that how PP4IP affects the cellular functions of PP4 by immunoprecipitation, immunofluorescence, and DNA double-strand break (DSB) repair assays. PP4IP interacts with PP4 complex, which is affected by DNA damage and cell cycle progression and decreases the dephosphorylational activity of PP4. Both overexpression and depletion of PP4IP impairs DSB repairs and sensitizes cells to genotoxic stress, suggesting timely inhibition of PP4 to be indispensable for cells in responding to DNA damage. Our results identify a novel inhibitor of PP4 that inhibits PP4-mediated cellular functions and establish the physiological importance of this regulation. In addition, PP4IP might be developed as potential therapeutic reagents for targeting tumors particularly with high level of PP4C expression.

• Molecules and Cells
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• v.46 no.4
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• pp.200-205
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• 2023

DNA-dependent protein kinase catalytic subunit (DNA-PKcs), a member of the phosphatidylinositol 3-kinase-related kinase family is a well-known player in repairing DNA double-strand break through non-homologous end joining pathway. This mechanism has allowed us to understand its critical role in T and B cell development through V(D)J recombination and class switch recombination, respectively. We have also learned that the defects in these mechanisms lead to the severely combined immunodeficiency (SCID). Here we highlight some of the latest evidence where DNA-PKcs has been shown to localize not only in the nucleus but also in the cytoplasm, phosphorylating various proteins involved in cellular metabolism and cytokine production. While it is an exciting time to unveil novel functions of DNA-PKcs, one should carefully choose experimental models to study DNA-PKcs as the experimental evidence has been shown to differ between cells of defective DNA-PKcs and those of DNA-PKcs knockout. Moreover, while there are several DNA-PK inhibitors currently being evaluated in the clinical trials in an attempt to increase the efficacy of radiotherapy or chemotherapy, multiple functions and subcellular localization of DNA-PKcs in various types of cells may further complicate the effects at the cellular and organismal level.

• Journal of Microbiology and Biotechnology
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• v.30 no.3
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• pp.469-475
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• 2020

During meiosis I, programmed DNA double-strand breaks (DSBs) occur to promote chromosome pairing and recombination between homologs. In Saccharomyces cerevisiae, Mec1 and Tel1, the orthologs of human ATR and ATM, respectively, regulate events upstream of the cell cycle checkpoint to initiate DNA repair. Tel1^ATM and Mec1^ATR are required for phosphorylating various meiotic proteins during recombination. This study aimed to investigate the role of Tel1^ATM and Mec1^ATR in meiotic prophase via physical analysis of recombination. Tel1^ATM cooperated with Mec1^ATR to mediate DSB-to-single end invasion transition, but negatively regulated DSB formation. Furthermore, Mec1^ATR was required for the formation of interhomolog joint molecules from early prophase, thus establishing a recombination partner choice. Moreover, Mec1^ATR specifically promoted crossover-fated DSB repair. Together, these results suggest that Tel1^ATM and Mec1^ATR function redundantly or independently in all post-DSB stages.

• Molecules and Cells
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• v.41 no.2
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• pp.127-133
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• 2018

Chromatin remodeling factors are involved in many cellular processes such as transcription, replication, and DNA damage response by regulating chromatin structure. As one of chromatin remodeling factors, remodeling and spacing factor 1 (RSF1) is recruited at double strand break (DSB) sites and regulates ataxia telangiectasia mutated (ATM) -dependent checkpoint pathway upon DNA damage for the efficient repair. RSF1 is overexpressed in a variety of cancers, but regulation of RSF1 levels remains largely unknown. Here, we showed that protein levels of RSF1 chromatin remodeler are temporally upregulated in response to different DNA damage agents without changing the RSF1 mRNA level. In the absence of SNF2h, a binding partner of RSF1, the RSF1 protein level was significantly diminished. Intriguingly, the level of RSF1-3SA mutant lacking ATM-mediated phosphorylation sites significantly increased, and upregulation of RSF1 levels under DNA damage was not observed in cells overexpressing ATM kinase. Furthermore, failure in the regulation of RSF1 level caused a significant reduction in DNA repair, whereas reconstitution of RSF1, but not of RSF1-3SA mutants, restored DSB repair. Our findings reveal that temporal regulation of RSF1 levels at its post-translational modification by SNF2h and ATM is essential for efficient DNA repair.