• Journal of Preventive Medicine and Public Health
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• v.29 no.3 s.54
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• pp.597-607
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• 1996

Genotoxic agents can induce various DNA lesions. DNA-Protein Crosslinks(DPCs) were known as the important DNA lesions which could impair gene expression because DPCs had a high probability of resisting repair and persisting through cell cycle. This repair resistance of DPCs could have biological significance but had not been evaluated clearly yet. Most of the studies that have evaluated the repair of DPCs only compared the extent of DPCs repair with other DNA lesions. We injected $K_2CrO_4$, a genotoxic agent, into Sprague-Dawley rats intraperitoneally(5mg/kg) and isolated blood lymphocytes 12 hours later. These lymphocytes were cultured in the mitogen added growth media and mitogen free media separately. The degree of the repair of DPCs was monitored for 4 days by the K-SDS assay. 4 days later, the amount of DPCs decreased by 4.6% in the mitogen added media high increased by 10.9% in the mitogen free media. These results showed that DPCs induced by $K_2CrO_4$ were not repaired easily and the DPCs were biologically significant DNA lesions. We thought the decrease of DPCs in the mitogen added media was not due to the repair of DPCs, but from the increase of normal cell proliferation. Therefore, it is very important to consider the proliferation of normal cells when estimating the repair of DPCs.

• Asian Pacific Journal of Cancer Prevention
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• v.16 no.8
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• pp.3457-3461
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• 2015

Background: Previous studies have suggested that Morinda citrifolia (Noni) has potential to reduce cancer risk. Objective: The purpose of this study was to investigate the effect of Noni, cisplatin, and their combination on DNA repair genes in the SiHa cervical cancer cell line. Materials and Methods: SiHa cells were cultured and treated with 10% Noni, $10{\mu}g/dl$ cisplatin or their combination for 24 hours. Post culturing, the cells were pelleted, RNA extracted, and processed for investigating DNA repair genes by real time PCR. Results: The expression of nucleotide excision repair genes ERCC1, ERCC2, and ERCC4 and base excision repair gene XRCC1 was increased 4 fold, 8.9 fold, 4 fold, and 5.5 fold, respectively, on treatment with Noni as compared to untreated controls (p<0.05). In contrast, expression was found to be decreased 22 fold, 13 fold, 16 fold, and 23 fold on treatment with cisplatin (p<0.05). However, the combination of Noni and cisplatin led to an increase of 2 fold, 1.6 fold, 3 fold, 1.2 fold, respectively (p<0.05). Conclusions: Noni enhanced the expression of DNA repair genes by itself and in combination with cisplatin. However, high expression of DNA repair genes at mRNA level only signifies efficient DNA transcription of the above mentioned genes; further investigations are needed to evaluate the DNA repair protein expression.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.17
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• pp.7043-7048
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• 2014

Inhibition of heat shock protein 90 (Hsp90) leads to inappropriate processing of proteins involved in DNA damage repair pathways after DNA damage and may enhance tumor cell radio- and chemotherapy sensitivity. To investigate the potentiation of antitumor efficacy of lidamycin (LDM), an enediyne agent by the Hsp90 inhibitorgeldanamycin (GDM), and possible mechanisms, we have determined effects on ovarian cancer SKOV-3, hepatoma Bel-7402 and HepG2 cells by MTT assay, apoptosis assay, and cell cycle analysis. DNA damage was investigated with H2AX C-terminal phosphorylation (${\gamma}H2AX$) assays. We found that GDM synergistically sensitized SKOV-3 and Bel-7402 cells to the enediyne LDM, and this was accompanied by increased apoptosis. GDM pretreatment resulted in a greater LDM-induced DNA damage and reduced DNA repair as compared with LDM alone. However, in HepG2 cells GDM did not show significant sensitizing effects both in MTT assay and in DNA damage repair. Abrogation of LDM-induced $G_2/M$ arrest by GDM was found in SKOV-3 but not in HepG2 cells. Furthermore, the expression of ATM, related to DNA damage repair responses, was also decreased by GDM in SKOV-3 and Bel-7402 cells but not in HepG2 cells. These results demonstrate that Hsp90 inhibitors may potentiate the antitumor efficacy of LDM, possibly by reducing the repair of LDM-induced DNA damage.

• Animal cells and systems
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• v.7 no.2
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• pp.159-164
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• 2003

The RAD3 gene of Saccharomyces cerevisiae is required for excision repair and is essential for cell viability. The RAD3 encoded protein possesses a single stranded DNA-dependent ATPase and DNA and DNA-RNA helicase activities. To examine the extent of conservation of structure and function of a S. pombe RAD3 during eukaryotic evolution, the RAD3 homolog gene was isolated by screening of genomic DNA library. The isolated gene was designated as HRD3 (homolog of RAD3 gene). Southern blot analysis confirmed that S. pombe chromosome contains the same DNA as HRD3 gene and this gene exists as a single copy in S. pombe. The transcript of 2.8 kb was detected by Northern blot analysis, The level of transcripts increased by ultraviolet (UV) irradiation, indicating that HRD3 is one of the UV-inducible genes in S. pombe. Furthermore, the predicted partial sequence of HRD3 protein has 60％ identity to S. cerevisiae RAD3 gene. This homology was particularly striking in the regions identified as being conserved in a group of DNA helicases. Gene deletion experiments indicate that the HRD3 gene is essential for viability and DNA repair function. These observations suggest evolutionary conservation of other protein components with which HRD3 might interact in mediating its DNA repair and viability functions.

• Journal of Photoscience
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• v.9 no.2
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• pp.479-481
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• 2002

UV-induced DNA damage causes cell killing and mutations leading to carcinogenesis. In normal human cells, UV damage such as cyclobutane pyrimidine dimers (CPDs) and primidine-prymidone (6-4) photoproducts are mainly repaired by nucleotide excision repair mechanism. The molecular processes have been well characterized recently. To know the influence of mitochondrial genome on the nucleotide excision repair mechanism against CPDs, we comparatively examined the production of CPDs by UVC irradiation and their repair kinetics in human cells completely lacking mitochondrial DNA (mtDNA) and the parental HeLa S cells. Whole DNA extracted from the cells exposed to UVC was treated with T4-endonuclease V to break the phosphodiester bond adjacent to CPDs. The DNA was electrophoresed in a denaturing agarose gel, which was visualized by ethidium bromide staining. The relative amount of CPDs was determined by image analysis using NIH Image software. MtDNA- less (rho-O) cells were apparently more sensitive to UVC than HeLa S cells, while the level of induction of CPDs in rho-O and HeLa cells was comparable. The repair of CPDs was less efficient in rho-O cells compared with HeLa cells. The residual amount of CPDs after 24-h repair was larger in rho-O cells than in HeLa cells where more than 90 % of CPDs were repaired by then. The non-repaired CPDs would lead to apoptosis in rho-O cells. These results suggest that mitochondrial genome may contribute to some ATP-dependent steps in nucletide excision repair by supplying sufficient ATP which is generated through a respiratory chain in mitochondria.

• Asian Pacific Journal of Cancer Prevention
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• v.13 no.12
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• pp.6469-6474
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• 2012

Background: DNA repair is one of the crucial defense mechanism against mutagenic exposure. Inherited SNPs of DNA repair genes may contribute to variation in DNA repair capacity and susceptibility to cancer. Due to the presence of these variants, inter-individual and ethnic differences in DNA repair capacity have been established in various populations. India harbors enormous genetic and cultural diversity. Materials and Methods: In the present study we aimed to determine the genotypes and allele frequencies of XRCC1 Arg399Gln (rs25487), XRCC3 Thr241Met (rs861539), XPD Lys751Gln (rs13181), and OGG1 Ser326Cys (rs1052133) gene polymorphisms in 186 healthy individuals residing in the Hyderabad region of India and to compare them with HapMap and other populations. Results and Conclusions: The genotype and allele frequency distribution at the four DNA repair gene loci among Hyderabad population of India revealed a characteristic pattern. Comparison of these gene polymorphisms with other populations revealed a distinctiveness of Hyderabad population from the Deccan region of India. To the best of our knowledge, this is the first report of such DNA repair gene polymorphisms in the Deccan Indian population.

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.1
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• pp.9-14
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• 2003

Recent studies indicated that cancer cells become resistant to ionizing radiation (IR) and chemotherapy drugs by enhanced DNA repair of the lesions. Therefore, it is expected to increase the killing of cancer cells and reduce drug resistance by inhibiting DNA repair pathways that tumor cells rely on to escape chemotherapy. There are a number of key human DNA repair pathways which depend on multimeric polypeptide activities. For example, Ku heterodimer regulatory DNA binding subunits (Ku70/Ku80) on binding to double strand DNA breaks (DSBs) are able to interact with 470-kDa DNA-dependent protein kinase catalytic subunit (DNA-PKcs), and are essential for DNA-dependent protein kinase (DNA-PK) activity. It has been known that DNA-PK is an important factor for DNA repair and also is a sensor-transmitting damage signal to downstream targets, leading to cell cycles arrest. Our ultimate goal is to develop a treatment of breast tumors by targeting proteins involved in damage-signaling pathway and/or DNA repair. This would greatly facilitate tumor cell cytotoxic activity and programmed cell death through DNA damaging drug treatment. Therefore, we designed a domain of Ku80 mutants that binds to Ku70 but not DNA end binding activity and used the peptide in co-therapy strategy to see whether the targeted inhibition of DNA-PK activity sensitized breast cancer cells to irradiation or chemotherapy drug. We observed that the synthesized peptide (HNI-38) prevented DNA-PKcs from binding to Ku70/Ku80, thus resulting in inactivation of DNA-PK activity. Consequently, the peptide treated cells exhibited poor to no DNA repair, and became highly sensitive to IR or chemotherapy drugs, and the growth of breast cancer cells was inhibited. Additionally, the results obtained in the present study also support the physiological role of resistance of cancer cells to IR or chemotherapy.

• Toxicological Research
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• v.34 no.4
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• pp.297-302
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• 2018

Cells are constantly exposed to endogenous and exogenous chemical and physical agents that damage their genome by forming DNA lesions. These lesions interfere with the normal functions of DNA such as transcription and replication, and need to be either repaired or tolerated. DNA lesions are accurately removed via various repair pathways. In contrast, tolerance mechanisms do not remove lesions but only allow replication to proceed despite the presence of unrepaired lesions. Cells possess two major tolerance strategies, namely translesion synthesis (TLS), which is an error-prone strategy and an accurate strategy based on homologous recombination (homology-dependent gap repair [HDGR]). Thus, the mutation frequency reflects the relative extent to which the two tolerance pathways operate in vivo. In the present paper, we review the present understanding of the mechanisms of TLS and HDGR and propose a novel and comprehensive view of the way both strategies interact and are regulated in vivo.

• The Korean Journal of Zoology
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• v.20 no.2
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• pp.93-99
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• 1977

Dose response forDNA repair synthesis induced by various concentrations of MMC (0.05 $\\sim$ 0.5 $\\mu$g/ml) in HeLa $S_3$ cells was not dose-dependent and the amounts of it were relatively lower, representing $7\\sim9%$ of total DNA synthesizing cells in $0.1\\sim0.5 \\mug/ml$ concentrations. Time dependence study showed that MMC-induced DNA repair synthesis occurred as long as for 24 hours with similar incidences in all time courses. Pretreatment with BUdR was found to have a sensitization effect on MMC-induced DNA repair synthesis, but that with IUdR was not. Combined treatment with BUdR of IUdR and MMC suppressed remarkably the semiconservative DNA synthesis especially at later time course. These results seem to suggest that damages induced in DNA by MMC might be repaired by both fast and slow excision processes.

• Environmental Mutagens and Carcinogens
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• v.8 no.1
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• pp.1-12
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• 1988

The effects of aphidicolin (APC), an inhibitor of DNA polymerase alpha, or 2', 3'-dideoxythymidine 5'-triphosphate (ddTTP), an inhibitor of DNA polymerase beta, on the repair of DNA damage induced by ethyl methanesulfonate (EMS) or bleomycin (BLM) were investigated in Chinese hamster ovary (CHO)-K1 cells. Three assays were employed in this study: unscheduled DNA synthesis, alkaline elution and alkaline sucrose gradient sedimentation. It was shown that APC or ddTTP inhibited DNA induced by EMS, and thus, the post-treatment with APC or ddTTP following EMS treatment was resulted in the more amount of unscheduled DNA synthesis, and the more accumulation of DNA single-stand breaks than the cells post-incubated without APC or ddTTP. While, in the BLM induced DNA repair, only ddTTP inhibited DNA repair induced by BLM. And thus, the groups post-incubated with or without APC after BLM treatment had the same value in the amount of unscheduled DNA synthesis and of DNA single-strand breaks, while post-treatment with ddTTP was resulted in the increased amount of unscheduled DNA synthesis and the increased DNA sin -strand breaks than the group without ddTTP. These results suggested that both of DNA polymerase $\alpha$ and $\beta$ participated in the repair of DNA damage induced by EMS, but in BLM-induced DNA repair, polymerase $\beta$ participated.ipated.