• Asian Pacific Journal of Cancer Prevention
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• v.13 no.7
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• pp.3417-3422
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• 2012

Objective: Non-homologous end joining (NHEJ) is one of the pathways of repair of DNA double-strand breaks. A number of genes involved in NHEJ have been implicated as breast cancer susceptibility genes such as LIG4. However, some studies have generated conflicting results. The aim of this Human Genome Epidemiology (HuGE) review and meta-analysis was to investigate association between LIG4 gene polymorphisms in the NHEJ pathway and breast cancer risk. Methods: Studies focusing on the relationship between LIG4 gene polymorphisms and susceptibility to breast cancer were selected from the Pubmed, Cochrane library, Embase, Web of Science, Springerlink, CNKI and CBM databases. Data were extracted by two independent reviewers and the meta-analysis was performed with Review Manager Version 5.1.6 and STATA Version 12.0 software, calculating odds ratios (ORs) with 95% confidence intervals (95%CIs). Results: According to the inclusion criteria, we final included seven studies with a total of 10,321 breast cancer cases and 10,160 healthy controls in the meta-analysis. The results showed no association between LIG4 gene polymorphisms (rs1805386 T>C, rs1805389 C>T, rs1805388 C>T and rs2232641 A>G) and breast cancer risk, suggesting that the mutant situation of these SNPs neither increased nor decreased the risk for breast cancer. In the subgroup analysis by Hardy-Weinberg equilibrium (HWE) and ethnicity, we also found no associations between the variants of LIG4 gene and breast cancer risk among HWE, non-HWE, Caucasians, Asians and Africans. Conclusion: This meta-analysis suggests that there is a lack of any association between LIG4 gene polymorphisms and the risk of breast cancer.

• Toxicological Research
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• v.29 no.1
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• pp.35-42
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• 2013

Quantum dots (QDs) have received considerable attention due to their potential role in photosensitization during photodynamic therapy. Although QDS are attractive nanomaterials due to their novel and unique physicochemical properties, concerns about their toxicity remain. We suggest a combination strategy, CdSe/ZnS QDs together with curcumin, a natural yellow pigment from turmeric, to reduce QD-induced cytotoxicity. The aim of this study was to explore a potentially effective cancer treatment: co-exposure of HL-60 cells and human normal lymphocytes to CdSe/ZnS QDs and curcumin. Cell viability, apoptosis, reactive oxygen species (ROS) generation, and DNA damage induced by QDs and/or curcumin with or without ultraviolet A (UVA) irradiation were evaluated in both HL-60 cells and normal lymphocytes. In HL-60 cells, cell death, apoptosis, ROS generation, and single/double DNA strand breaks induced by QDs were enhanced by treatment with curcumin and UVA irradiation. The protective effects of curcumin on cell viability, apoptosis, and ROS generation were observed in normal lymphocytes, but not leukemia cells. These results demonstrated that treatment with QD combined with curcumin increased cell death in HL-60 cells, which was mediated by ROS generation. However, curcumin acted as an antioxidant in cultured human normal lymphocytes.

• Journal of Embryo Transfer
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• v.25 no.2
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• pp.111-116
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• 2010

Sperm chromatin integrity is essential for successful fertilization and development of an embryo. Reported here is a quantification of DNA fragments which is intimately associated with reproductive potential to provide one of criteria for sperm chromatin integrity. Three sperm populations were considered: CONTROL (no treatment), UV irradiation (48mW/$cm^2$, 1h) and $H_2O_2$ (oxidative stress induced by hydrogen peroxide, 10 mM, 50 mM and 100 mM). DNA fragments in boar sperm were evaluated by using ligation-mediated quantitative real-time polymerase chain reaction (LM-qPCR) assay, which relies on real-time qPCR to provide a measure of blunt 5' phosphorylated double strand breaks in genomic DNA. The results in agarose gel electrophoresis showed no significant DNA fragmentation and no dose-dependent response to $H_2O_2$. However, the remarkable difference in shape and position was observed in melting curve of LM-qPCR. This result supported that the melting curve analysis of LM-qPCR presented here, could be more sensitive and accurate than previous DNA fragmentation assay method.

• Molecules and Cells
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• v.26 no.1
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• pp.5-11
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• 2008

Stalled DNA replication forks activate specific DNA repair mechanism called post-replication repair (PRR) pathways that simply bypass DNA damage. The bypassing of DNA damage by PRR prevents prolonged stalling of DNA replication that could result in double strand breaks (DSBs). Proliferating cell nuclear antigen (PCNA) functions to initiate and choose different bypassing pathways of PRR. In yeast, DNA replication forks stalled by DNA damage induces monoubiquitination of PCNA at K164, which is catalyzed by Rad6/Rad18 complex. PCNA monoubiquitination triggers the replacement of replicative polymerase with special translesion synthesis (TLS) polymerases that are able to replicate past DNA lesions. The PCNA interaction motif and/or the ubiquitin binding motif in most TLS polymerases seem to be important for the regulation of TLS. The TLS pathway is usually error-prone because TLS polymerases have low fidelity and no proofreading activity. PCNA can also be further polyubiquitinated by Ubc13/ Mms2/Rad5 complex, which adds an ubiquitin chain onto monoubiquitinated K164 of PCNA. PCNA polyubiquitination directs a different PRR pathway known as error-free damage avoidance, which uses the newly synthesized sister chromatid as a template to bypass DNA damage presumably through template switching mechanism. Mammalian homologues of all of the yeast PRR proteins have been identified, thus PRR is well conserved throughout evolution. Mutations of some PRR genes are associated with a higher risk for cancers in mice and human patients, strongly supporting the importance of PRR as a tumor suppressor pathway.

• The Journal of the Korean bone and joint tumor society
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• v.3 no.2
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• pp.69-79
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• 1997

Objective : The objective of this study was to compare expression of various proto-oncogenes and rates of apoptosis in osteosarcoma patients. Modulation of apoptosis may influence resistance to chemotherapy and therefore affect the outcome of cancer treatment. Osteosarcoma is one of the most fatal malignancies in young adolescents and investigation of the role of apoptotic cell death is warranted in relation to chemotherapy and tumor outcome. Design : The terminal deoxynucleotidyl transferase to exposed 3'-hydroxyl termini of DNA (TUNEL method) staining method has been applied for the in situ detection of DNA double strand breaks. Patients : Thirty-three osteosarcomas in various stages of differentiation from twenty-nine patients were investigated immunohistochemically for p53, Bcl-2 and TUNEL method for apoptosis. Results and conclusion; We have found that higher level of wild type p53 were correlated with enhanced expression of apoptosis. Increased apoptosis rates were found in cases of negative Bcl-2 expression. In the present study, we have concluded that a significant proportion of osteosarcoma, a tumor in which resistance to chemotherapy often occurs, express high levels of p53 and low levels of Bcl-2. Our data provide further evidence for cross-talk between Bcl-2 and p53 and suggests that these genes are important determinants of drug-induced apoptosis.

• BMB Reports
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• v.52 no.3
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• pp.208-213
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• 2019

Chemoresistance is the primary obstacle in the treatment of locally advanced and metastatic nasopharyngeal carcinoma (NPC). Recent evidence suggests that the transcription factor forkhead box M1 (FoxM1) is involved in chemoresistance. Our group previously confirmed that FoxM1 is overexpressed in NPC. In this study, we investigated the role of FoxM1 in cisplatin resistance of the cell lines 5-8F and HONE-1 and explored its possible mechanism. Our results showed that FoxM1 and NBS1 were both overexpressed in NPC tissues based on data from the GSE cohort (GSE12452). Then, we measured FoxM1 levels in NPC cells and found FoxM1 was overexpressed in NPC cell lines and could be stimulated by cisplatin. MTT and clonogenic assays, flow cytometry, ${\gamma}H2AX$ immunofluorescence, qRT-PCR, and western blotting revealed that downregulation of FoxM1 sensitized NPC cells to cisplatin and reduced the repair of cisplatin-induced DNA double-strand breaks via inhibition of the MRN (MRE11-RAD50-NBS1)-ATM axis, which might be related to the ability of FoxM1 to regulate NBS1. Subsequently, we demonstrated that enhanced sensitivity of FoxM1 knockdown cells could be reduced by overexpression of NBS1. Taken together, our data demonstrate that downregulation of FoxM1 could improve the sensitivity of NPC cells to cisplatin through inhibition of MRN-ATM-mediated DNA repair, which could be related to FoxM1-dependent regulation of NBS1.

• BMB Reports
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• v.54 no.2
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• pp.98-105
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• 2021

The clustered regularly interspaced short palindromic repeats (CRISPR) system is a family of DNA sequences originally discovered as a type of acquired immunity in prokaryotes such as bacteria and archaea. In many CRISPR systems, the functional ribonucleoproteins (RNPs) are composed of CRISPR protein and guide RNAs. They selectively bind and cleave specific target DNAs or RNAs, based on sequences complementary to the guide RNA. The specific targeted cleavage of the nucleic acids by CRISPR has been broadly utilized in genome editing methods. In the process of genome editing of eukaryotic cells, CRISPR-mediated DNA double-strand breaks (DSB) at specific genomic loci activate the endogenous DNA repair systems and induce mutations at the target sites with high efficiencies. Two of the major endogenous DNA repair machineries are non-homologous end joining (NHEJ) and homology-directed repair (HDR). In case of DSB, the two repair pathways operate in competition, resulting in several possible outcomes including deletions, insertions, and substitutions. Due to the inherent stochasticity of DSB-based genome editing methods, it was difficult to achieve defined single-base changes without unanticipated random mutation patterns. In order to overcome the heterogeneity in DSB-mediated genome editing, novel methods have been developed to incorporate precise single-base level changes without inducing DSB. The approaches utilized catalytically compromised CRISPR in conjunction with base-modifying enzymes and DNA polymerases, to accomplish highly efficient and precise genome editing of single and multiple bases. In this review, we introduce some of the advances in single-base level CRISPR genome editing methods and their applications.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.8
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• pp.3637-3643
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• 2012

Objective: Non-homologous end joining (NHEJ) is a pathway for repairing DNA double-strand breaks. Recent publications indicated that XRCC5, XRCC6 and XRCC7 genes may participate in the pathogenesis of breast cancer. The aim of this Human Genome Epidemiology (HuGE) review and meta-analysis was to investigate associations between XRCC5, XRCC6 and XRCC7 genetic polymorphisms in the NHEJ pathway and breast cancer risk. Methods: Studies focusing on the relationship between genetic polymorphisms in XRCC5, XRCC6 and XRCC7 genes and susceptibility to breast cancer were selected from the Pubmed, Cochrane library, Embase, Web of Science, Springerlink, CNKI and CBM databases. Data were extracted by two independent reviewers. The meta-analysis was performed with Review Manager Version 5.1.6 and STATA Version 12.0 software. The odds ratio (OR) with 95% confidence interval (95%CI) was calculated based on the extracted data. Results: According to the inclusion criteria, we final included seven studies with a total of 2,864 breast cancer cases and 3,060 healthy controls. Meta-analysis results showed that rs3835 (G>A) and rs828907 (G>T) in XRCC5 gene, and rs132793 (G>A) in XRCC6 gene might increase the risk of breast cancer, while rs132788 G>T and rs6002421 (A>G) might be protective factors. However, there was no relationship between XRCC7 genetic polymorphisms and the risk of breast cancer. Conclusion: This meta-analysis suggests that the rs3835 G>A and rs828907 G>T in XRCC5 gene, rs6002421 (A>G), rs132788 (G>T) and rs132793 (G>A) in XRCC6 gene might be risk factors for breast cancer, while the rs132788 (G>T) and rs6002421 (A>G) in XRCC6 gene might be protective.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.8
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• pp.3301-3306
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• 2015

Nucleolin (C23) is an important anti-apoptotic protein that is ubiquitously expressed in exponentially growing eukaryotic cells. In order to understand the impact of C23 in radiation therapy, we attempted to investigate the relationship of C23 expression with the radiosensitivity of human non-small cell lung cancer (NSCLC) cells. We investigated the role of C23 in activating the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs), which is a critical protein for DNA double-strand breaks (DSBs) repair. As a result, we found that the expression of C23 was negatively correlated with the radiosensitivity of NSCLC cell lines. In vitro clonogenic survival assays revealed that C23 knockdown increased the radiosensitivity of a human lung adenocarcinoma cell line, potentially through the promotion of radiation-induced apoptosis and adjusting the cell cycle to a more radiosensitive stage. Immunofluorescence data revealed an increasing quantity of ${gamma}$-H2AX foci and decreasing radiation-induced DNA damage repair following knockdown of C23. To further clarify the mechanism of C23 in DNA DSBs repair, we detected the expression of DNA-PKcs and C23 proteins in NSCLC cell lines. C23 might participate in DNA DSBs repair for the reason that the expression of DNA-PKcs decreased at 30, 60, 120 and 360 minutes after irradiation in C23 knockdown cells. Especially, the activity of DNA-PKcs phosphorylation sites at the S2056 and T2609 was significantly suppressed. Therefore we concluded that C23 knockdown can inhibit DNA-PKcs phosphorylation activity at the S2056 and T2609 sites, thus reducing the radiation damage repair and increasing the radiosensitivity of NSCLC cells. Taken together, the inhibition of C23 expression was shown to increase the radiosensitivity of NSCLC cells, as implied by the relevance to the notably decreased DNA-PKcs phosphorylation activity at the S2056 and T2609 clusters. Further research on targeted C23 treatment may promote effectiveness of radiotherapy and provide new targets for NSCLC patients.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.24
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• pp.10985-10989
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• 2015

Background: The capability for DNA double-strand breaks (DSBs) repair is crucial for inherent radiosensitivity of tumor and normal cells. We have investigated the clinicopathologic significance of DNA repair gene expression in nasopharyngeal (NP) carcinoma. Materials and Methods: A total of 65 NP cancer patients who received radiotherapy were included. The immunopositivity to Ku 70, DNA-PKcs, MRN, RAD50, XRCC4, and LIG4 were examined in all tumor tissues. Results: The patients comprised 42 males and 23 females, with a median age of 56 years (range, 18-84). The expression levels of RAD50 (0,+1,+2,+3) were 27.7%, 32.3%, 21.5%, and 18.5%. LIG4 (${\pm}$) were 43.1% and 56.9% respectively. The 5-year OS rate of patients with LIG4 (${\pm}$) were 90% and 67.9%, respectively (p=0.035). The 5-year TTP rate of patients with LIG4 (${\pm}$) were 75.9%, 55.5%, respectively (P=0.039). Conclusions: Our results suggest the possibility of predicting the radiosensitivity of NP cancer by performing immunohistochemical analysis of LIG4.