Gene Summary

Gene:XRCC6; X-ray repair cross complementing 6
Aliases: ML8, KU70, TLAA, CTC75, CTCBF, G22P1
Summary:The p70/p80 autoantigen is a nuclear complex consisting of two subunits with molecular masses of approximately 70 and 80 kDa. The complex functions as a single-stranded DNA-dependent ATP-dependent helicase. The complex may be involved in the repair of nonhomologous DNA ends such as that required for double-strand break repair, transposition, and V(D)J recombination. High levels of autoantibodies to p70 and p80 have been found in some patients with systemic lupus erythematosus. [provided by RefSeq, Jul 2008]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:X-ray repair cross-complementing protein 6
Source:NCBIAccessed: 13 March, 2017


What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 13 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 13 March, 2017 using data from PubMed, MeSH and CancerIndex

Latest Publications: XRCC6 (cancer-related)

Sanie-Jahromi F, Saadat I, Saadat M
Effects of extremely low frequency electromagnetic field and cisplatin on mRNA levels of some DNA repair genes.
Life Sci. 2016; 166:41-45 [PubMed] Related Publications
AIMS: It has been shown that exposure to extremely-low frequency (˂300Hz) oscillating electromagnetic field (EMF) can affect gene expression. The effects of different exposure patterns of 50-Hz EMF and co-treatment of EMF plus cisplatin (CDDP) on mRNA levels of seven genes involved in DNA repair pathways (GADD45A, XRCC1, XRCC4, Ku70, Ku80, DNA-PKcs and LIG4) were evaluated.
MAIN METHODS: Two 50-Hz EMF intensities (0.25 and 0.50mT), three exposure patterns (5min field-on/5min field-off, 15min field-on/15min field-off, 30min field-on continuously) and two cell lines (MCF-7 and SH-SY5Y) were used. The mRNA levels were measured using quantitative real-time PCR.
KEY FINDINGS: The examined genes had tendency to be down-regulated in MCF-7 cells treated with EMF. In the pattern of 15min field-on/15min field-off of the 0.50mT EMF, no increase in mRNA levels were observed, but the mRNA levels of GADD45A, XRCC1, XRCC4, Ku80, Ku70, and LIG4 were down-regulated. A significant elevation in IC50 of CDDP was observed when MCF-7 and SH-SY5Y cells were co-treated with CDDP+EMF in comparison with the cells treated with CDDP alone. GADD45A mRNA levels in MCF-7 and SH-SY5Y cells co-treated with CDDP+EMF were increased and at the same time the mRNA levels of XRCC4, Ku80, Ku70 and DNA-PKcs were down-regulated.
SIGNIFICANCE: Present study provides evidence that co-treatment of CDDP+EMF can enhance down-regulation of the genes involved in non-homologous end-joining pathway. It might be suggested that co-treatment of CDDP+EMF could be more promising for sensitizing cancer cells to DNA double strand breaks.

Hada M, Subramanian C, Andrews PC, Kwok RP
Cytosolic Ku70 regulates Bax-mediated cell death.
Tumour Biol. 2016; 37(10):13903-13914 [PubMed] Free Access to Full Article Related Publications
The first known function of Ku70 is as a DNA repair factor in the nucleus. Using neuronal neuroblastoma cells as a model, we have established that cytosolic Ku70 binds to the pro-apoptotic protein Bax in the cytosol and blocks Bax's cell death activity. Ku70-Bax binding is regulated by Ku70 acetylation in that when Ku70 is acetylated Bax dissociates from Ku70, triggering cell death. We propose that Ku70 may act as a survival factor in these cells such that Ku70 depletion triggers Bax-dependent cell death. Here, we addressed two fundamental questions about this model: (1) Does all Bax, which is a cytosolic protein, bind to all cytosolic Ku70? and (2) Is Ku70 a survival factor in cells types other than neuronal neuroblastoma cells? We show here that, in neuronal neuroblastoma cells, only a small fraction of Ku70 binds to a small fraction of Bax; most Bax is monomeric. Interestingly, there is no free or monomeric Ku70 in the cytosol; most cytosolic Ku70 is in complex with other factors forming several high molecular weight complexes. A fraction of cytosolic Ku70 also binds to cytosolic Ku80, Ku70's binding partner in the nucleus. Ku70 may not be a survival factor in some cell types (Ku70-depletion less sensitive) because Ku70 depletion does not affect survival of these cells. These results indicate that, in addition to Ku70 acetylation, other factors may be involved in regulating Ku70-Bax binding in the Ku70-depletion less sensitive cells because Ku70 acetylation in these cells is not sufficient to dissociate Bax from Ku70 or to activate Bax.

Dimberg J, Skarstedt M, Slind Olsen R, et al.
Gene polymorphism in DNA repair genes XRCC1 and XRCC6 and association with colorectal cancer in Swedish patients.
APMIS. 2016; 124(9):736-40 [PubMed] Related Publications
The DNA repair genes XRCC1 and XRCC6 have been proposed to participate in the pathological process of cancer by modulating the DNA repair capacity. This study evaluated the susceptibility of the single-nucleotide polymorphisms (SNPs) XRCC1 (rs25487, G > A) and XRCC6 (rs2267437, C > G) to colorectal cancer (CRC) and their association with clinical parameters in Swedish patients with CRC. Using the TaqMan system, these SNPs were screened in 452 patients and 464 controls. No significant difference in genotype distribution was found between the patients and controls, or any significant association with cancer-specific or disease-free survival in patients. However, we showed that the carriers of allele A in XRCC1 (rs25487, G > A) were connected with a higher risk of disseminated CRC (Odds Ratio = 1.64; 95% Confidence Interval = 1.12-2.41, p = 0.012).

Guo YX, Lin ZM, Wang MJ, et al.
Jungermannenone A and B induce ROS- and cell cycle-dependent apoptosis in prostate cancer cells in vitro.
Acta Pharmacol Sin. 2016; 37(6):814-24 [PubMed] Free Access to Full Article Related Publications
AIM: Jungermannenone A and B (JA, JB) are new ent-kaurane diterpenoids isolated from Chinese liverwort Jungermannia fauriana, which show anti-proliferation activities in cancer cells. In this study we investigated the mechanisms underlying the anticancer action of JA and JB in PC3 human prostate cancer cells in vitro.
METHODS: A panel of 9 human cancer cell lines was tested. Cell proliferation was assessed with a real-time cell analyzer and MTT assay. Cell apoptosis, cell cycle distribution and ROS levels were measured using cytometry. Mitochondrial damage was examined by transmission electron microscopy. DNA damage was detected with comet assay. Apoptotic, DNA damage- and cell cycle-related proteins were analyzed using Western blotting. The expression of DNA repair genes was measured with qRT-PCR.
RESULTS: Both JA and JB exerted potent anti-proliferative action against the 9 cancer cell lines, and PC3 cells were more sensitive with IC50 values of 1.34±0.09 and 4.93±0.20 μmol/L, respectively. JA (1.5 μmol/L) and JB (5 μmol/L) induced PC3 cell apoptosis, which was attenuated by the caspase inhibitor Z-VAD. Furthermore, both JA and JB caused mitochondrial damage and ROS accumulation in PC3 cells, whereas vitamin C blocked the ROS accumulation and attenuated the cytotoxicity of JA and JB. Moreover, both JA and JB induced DNA damage, accompanied by downregulated DNA repair proteins Ku70/Ku80 and RDA51. JA induced marked cell cycle arrest at the G0/G1 phase, which was related to c-Myc suppression, whereas JB enforced the cell cycle blockade in the G2/M phase, which associated with activation of the JNK signaling.
CONCLUSION: Both JA and JB induce prostate cancer apoptosis via ROS accumulation and induction of cell cycle arrest.

Soret C, Martin E, Duluc I, et al.
Distinct mechanisms for opposite functions of homeoproteins Cdx2 and HoxB7 in double-strand break DNA repair in colon cancer cells.
Cancer Lett. 2016; 374(2):208-15 [PubMed] Related Publications
Homeobox genes, involved in embryonic development and tissues homeostasis in adults, are often deregulated in cancer, but their relevance in pathology is far from being fully elucidated. In colon cancers, we report that the homeoproteins HoxB7 and Cdx2 exhibit different heterogeneous patterns, Cdx2 being localized in moderately altered neoplasic glands in contrast to HoxB7 which predominates in poorly-differentiated areas; they are coexpressed in few cancer cells. In human colon cancer cells, both homeoproteins interact with the DNA repair factor KU70/80, but functional studies reveal opposite effects: HoxB7 stimulates DNA repair and cell survival upon etoposide treatment, whereas Cdx2 inhibits both processes. The stimulatory effect of HoxB7 on DNA repair requires the transactivation domain linked to the homeodomain involved in the interaction with KU70/80, whereas the transactivation domain of Cdx2 is dispensable for its inhibitory function, which instead needs the homeodomain to interact with KU70/80 and the C-terminal domain. Thus, HoxB7 and Cdx2 respectively use transcription-dependent and -independent mechanisms to stimulate and inhibit DNA repair. In addition, in cells co-expressing both homeoproteins, Cdx2 lessens DNA repair activity through a novel mechanism of inhibition of the transcriptional function of HoxB7, whereby Cdx2 forms a molecular complex with HoxB7 and prevents it to recognize its target in the chromatin. These results point out the complex interplay between the DSB DNA repair activity and the homeoproteins HoxB7 and Cdx2 in colon cancer cells, making the balance between these factors a determinant and a potential indicator of the efficacy of genotoxic drugs.

Ghaleb AM, Elkarim EA, Bialkowska AB, Yang VW
KLF4 Suppresses Tumor Formation in Genetic and Pharmacological Mouse Models of Colonic Tumorigenesis.
Mol Cancer Res. 2016; 14(4):385-96 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
UNLABELLED: The zinc finger transcription factor Krüppel-like factor 4 (KLF4) is frequently downregulated in colorectal cancer. Previous studies showed that KLF4 is a tumor suppressor in the intestinal tract and plays an important role in DNA damage-repair mechanisms. Here, the in vivo effects of Klf4 deletion were examined from the mouse intestinal epithelium (Klf4(ΔIS)) in a genetic or pharmacological setting of colonic tumorigenesis:Apc(Min/⁺) mutation or carcinogen treatment with azoxymethane (AOM), respectively.Klf4 (ΔIS)/Apc (Min/⁺) mice developed significantly more colonic adenomas with 100% penetrance as compared with Apc(Min/⁺) mice with intact Klf4 (Klf4(fl/fl)/Apc (Min/⁺)). The colonic epithelium of Klf4 (ΔIS)/Apc (Min/⁺)mice showed increased mTOR pathway activity, together with dysregulated epigenetic mechanism as indicated by altered expression of HDAC1 and p300. Colonic adenomas from both genotypes stained positive for γH2AX, indicating DNA double-strand breaks. InKlf4 (ΔIS)/Apc (Min/+) mice, this was associated with reduced nonhomologous end joining (NHEJ) repair and homologous recombination repair (HRR) mechanisms as indicated by reduced Ku70 and Rad51 staining, respectively. In a separate model, following treatment with AOM, Klf4 (ΔIS) mice developed significantly more colonic tumors than Klf4 (fl/fl) mice, with more Klf4 (ΔIS) mice harboring K-Rasmutations than Klf4 (fl/fl)mice. Compared with AOM-treated Klf4 (fl/fl)mice, adenomas of treated Klf4 (ΔIS) mice had suppressed NHEJ and HRR mechanisms, as indicated by reduced Ku70 and Rad51 staining. This study highlights the important role of KLF4 in suppressing the development of colonic neoplasia under different tumor-promoting conditions.
IMPLICATIONS: The study demonstrates that KLF4 plays a significant role in the pathogenesis of colorectal neoplasia.

Zhang T, Zhang X, Shi W, et al.
The DNA damage repair protein Ku70 regulates tumor cell and hepatic carcinogenesis by interacting with FOXO4.
Pathol Res Pract. 2016; 212(3):153-61 [PubMed] Related Publications
The capability for DNA double-strand breaks (DSBs) repair is crucial for chromatin dramatic changes and DNA damage in normal and tumor cells. We have investigated the clinicopathological significance of DNA repair gene Ku70 expression in hepatocellular carcinoma. We demonstrated that Ku70 expression was significantly increased in HCC, and the high expression levels were significantly correlated with gender, maximal tumor size, HBsAg status, tumor nodule number, distant metastasis and Ki-67 expression by clinicopathological analysis. The Kaplan-Meier survival curves revealed that increasing Ku70 expression was associated with poor prognosis in HCC patients. Ku70 expression was an independent prognostic marker of overall HCC patient survival in a multivariate analysis. In addition, through serum starvation and refeeding, we found that Ku70 was lowly expressed in serum-starved Huh7 and HepG2 HCC cells, and was progressively increased after serum-additioning. Furthermore, knockdown of Ku70 inhibited cell proliferation accompanying an increase in p27(kip1) levels through interacting with FOXO4. These findings provide a rational framework for the progression of HCC and could be a potential molecular therapy by targeting the Ku70-FOXO4 interaction.

Li M, Li JJ, Gu QH, et al.
EGCG induces lung cancer A549 cell apoptosis by regulating Ku70 acetylation.
Oncol Rep. 2016; 35(4):2339-47 [PubMed] Related Publications
Lung cancer is the leading cause of cancer-related death worldwide. (-)-Epigallocatechin-3-gallate (EGCG) is a potential chemopreventive and therapeutic agent for lung cancer. Induction of apoptosis was examined using Annexin V/PI double staining flow cytometry. Western blot analysis detected the protein expression of cleaved caspase-3, Bax and Bcl-xL. Co-immunoprecipitation was used to detect the interaction of Ku70-Bax and the acetylation status of Ku70. Treatment of A549 cells with EGCG-induced apoptosis via increased expression of cleaved caspase-3 and Bax, but decreased expression of Bcl-xL. EGCG upregulated the K70 acetylation status of A549 cells and downregulated the interaction of Bax-Ku70 in a concentration- and time-dependent manner. The apoptosis-promoting effect of EGCG on A549 cells was obviously weakened, along with strengthening of the Bax-Ku70 interaction, after pCDNA3.1(+)-Ku70 plasmid and pCDNA3.1(+)-Ku70539/542R plasmid transfection. Our results established a role of EGCG in inducing cell apoptosis by suppressing Bax activity. Regulating Ku70 acetylation by EGCG, that block the interaction between Ku70 and Bax, will result in lung cancer cell apoptosis.

Chang HY, Chang TC, Huang WY, et al.
RON Nuclear Translocation under Hypoxia Potentiates Chemoresistance to DNA Double-Strand Break-Inducing Anticancer Drugs.
Mol Cancer Ther. 2016; 15(2):276-86 [PubMed] Related Publications
Tumor hypoxia is associated with radioresistance, chemoresistance, and metastasis, which eventually lead to cancer progression and a poor patient prognosis. RON [also known as macrophage-stimulating protein receptor (MST1R)] belongs to the c-MET [also known as hepatocyte growth factor receptor (HGFR)] receptor tyrosine kinase (RTK) superfamily. To identify the interaction partners of RON nuclear translocation in response to hypoxia, the nuclear extract of TSGH8301 bladder cancer cells was immunoprecipitated for tandem mass profiling analysis. Nuclear RON interacted with adenosine triphosphate (ATP)-dependent DNA helicase 2 (Ku70) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) to activate nonhomologous end joining (NHEJ) DNA repair. The interaction was time dependent, extending 3 to 24 hours posthypoxia or until the components had been exposed to the chemotherapeutic drugs doxorubicin and epirubicin. Stable knockdown experiments in vitro suggest the importance of RON for the chemoresistance of cancer cells under hypoxia. In addition, the tyrosine kinase domain of nuclear RON is crucial for interaction with Ku70 under hypoxia. J82 cells transfected with RON showed a survival advantage in the presence of epirubicin and hypoxia. This suggests that nuclear RON activates NHEJ repair by interacting with Ku70/DNA-PKcs and inhibiting RON activity to increase cancer cell chemosensitivity. Mol Cancer Ther; 15(2); 276-86. ©2016 AACR.

Henríquez-Hernández LA, Valenciano A, Foro-Arnalot P, et al.
Association between single-nucleotide polymorphisms in DNA double-strand break repair genes and prostate cancer aggressiveness in the Spanish population.
Prostate Cancer Prostatic Dis. 2016; 19(1):28-34 [PubMed] Related Publications
BACKGROUND: Novel predictors of prognosis and treatment response for prostate cancer (PCa) are required to better individualize treatment. Single-nucleotide polymorphisms (SNPs) in four genes directly (XRCC5 (X-ray repair complementing defective repair in Chinese hamster cells 5) and XRCC6 (X-ray repair complementing defective repair in Chinese hamster cells 6)) or indirectly (PARP1 and major vault protein (MVP)) involved in non-homologous end joining were examined in 494 Spanish PCa patients.
METHODS: A total of 22 SNPs were genotyped in a Biotrove OpenArray NT Cycler. Clinical tumor stage, diagnostic PSA serum levels and Gleason score at diagnosis were obtained for all participants. Genotypic and allelic frequencies were determined using the web-based environment SNPator.
RESULTS: (XRCC6) rs2267437 appeared as a risk factor for developing more aggressive PCa tumors. Those patients carrying the GG genotype were at higher risk of developing bigger tumors (odds ratio (OR)=2.04, 95% confidence interval (CI) 1.26-3.29, P=0.004), present higher diagnostic PSA levels (OR=2.12, 95% CI 1.19-3.78, P=0.011), higher Gleason score (OR=1.65, 95% CI 1.01-2.68, P=0.044) and D'Amico higher risk tumors (OR=2.38, 95% CI 1.24-4.58, P=0.009) than those patients carrying the CC/CG genotypes. Those patients carrying the (MVP) rs3815824 TT genotype were at higher risk of presenting higher diagnostic PSA levels (OR=4.74, 95% CI 1.40-16.07, P=0.013) than those patients carrying the CC genotype. When both SNPs were analyzed in combination, those patients carrying the risk genotypes were at higher risk of developing D'Amico higher risk tumors (OR=3.33, 95% CI 1.56-7.17, P=0.002).
CONCLUSIONS: We believe that for the first time, genetic variants at XRCC6 and MVP genes are associated with risk of more aggressive disease, and would be taken into account when assessing the malignancy of PCa.

Tarish FL, Schultz N, Tanoglidi A, et al.
Castration radiosensitizes prostate cancer tissue by impairing DNA double-strand break repair.
Sci Transl Med. 2015; 7(312):312re11 [PubMed] Related Publications
Chemical castration improves responses to radiotherapy in prostate cancer, but the mechanism is unknown. We hypothesized that this radiosensitization is caused by castration-mediated down-regulation of nonhomologous end joining (NHEJ) repair of DNA double-strand breaks (DSBs). To test this, we enrolled 48 patients with localized prostate cancer in two arms of the study: either radiotherapy first or radiotherapy after neoadjuvant castration treatment. We biopsied patients at diagnosis and before and after castration and radiotherapy treatments to monitor androgen receptor, NHEJ, and DSB repair in verified cancer tissue. We show that patients receiving neoadjuvant castration treatment before radiotherapy had reduced amounts of the NHEJ protein Ku70, impaired radiotherapy-induced NHEJ activity, and higher amounts of unrepaired DSBs, measured by γ-H2AX foci in cancer tissues. This study demonstrates that chemical castration impairs NHEJ activity in prostate cancer tissue, explaining the improved response of patients with prostate cancer to radiotherapy after chemical castration.

Zhou C, Tang H, Yu J, et al.
Blood-based DNA methylation of DNA repair genes in the non-homologous end-joining (NEHJ) pathway in patient with glioma.
Int J Clin Exp Pathol. 2015; 8(8):9463-7 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
UNLABELLED: To investigate the blood-based DNA methylation of repair genes including LIG4, XRCC4, XRCC5, XRCC6 and XRCC7 that involved in non-homologous end-joining (NEHJ) DNA repair pathway in patients with glioma. Blood samples were obtained from 114 glioma patients, 96 normal controls, and 81 glioma patients after radiotherapy and chemotherapy. Blood-based DNA methylation of the five NHEJ repair genes was assayed by methylation-specific polymerase chain reaction (MSP). The DNA methylation level of XRCC5 and XRCC7 in glioma group are significantly higher than those of normal group (P<0.001). Moreover, radiotherapy treatment significantly increased methylation level of XRCC5 and XRCC7 compared to glioma group. No significant difference for the methylation of the other three genes, LIG4, XRCC4 and XRCC6 were detected among three groups.
IN CONCLUSION: our findings indicate that DNA methylation modification plays an important role to regulate the gene expression of XRCC5 and XRCC7, from the results that the gene methylation level of the glioma group is higher than that of the normal group. Increased methylation of XRCC5 and XRCC7 in blood samples of glioma patients and patients with radiotherapy and chemotherapy suggests that blood-based methylation level of XRCC5 and XRCC7 could be a potential indicator for evaluating of the effect of radiotherapy and chemotherapy for glioma patient.

Alsubhi N, Middleton F, Abdel-Fatah TM, et al.
Chk1 phosphorylated at serine345 is a predictor of early local recurrence and radio-resistance in breast cancer.
Mol Oncol. 2016; 10(2):213-23 [PubMed] Related Publications
Radiation-induced DNA damage activates the DNA damage response (DDR). DDR up-regulation may predict radio-resistance and increase the risk of early local recurrence despite radiotherapy in early stage breast cancers. In 1755 early stage breast cancers, DDR signalling [ATM, ATR, total Ckh1, Chk1 phosphorylated at serine(345) (pChk1), Chk2, p53], base excision repair [PARP1, POLβ, XRCC1, FEN1, SMUG1], non-homologous end joining (Ku70/Ku80, DNA-PKcs) and homologous recombination [RAD51, BRCA1, γH2AX, BLM, WRN, RECQL5, PTEN] protein expression was correlated to time to early local recurrence. Pre-clinically, radio-sensitization by inhibition of Chk1 activation by ATR inhibitor (VE-821) and inhibition of Chk1 (V158411) were investigated in MDA-MB-231 (p53 mutant) and MCF-7 (p53 wild-type) breast cancer cells. In the whole cohort, 208/1755 patients (11.9%) developed local recurrence of which 126 (61%) developed local recurrence within 5 years of initiation of primary therapy. Of the 20 markers tested, only pChk1 and p53 significantly associated with early local recurrence (p value = 0.015 and 0.010, respectively). When analysed together, high cytoplasmic pChk1-nuclear pChk1 (p = 0.039), high cytoplasmic pChk1-p53 (p = 0.004) and high nuclear pChk1-p53 (p = 0.029) co-expression remain significantly linked to early local recurrence. In multivariate analysis, cytoplasmic pChk1 level independently predicted early local recurrence (p = 0.025). In patients who received adjuvant local radiotherapy (n = 949), p53 (p = 0.014) and high cytoplasmic pChk1-p53 (p = 0.017) remain associated with early local recurrence. Pre-clinically, radio-sensitisation by VE-821 or V158411 was observed in both MCF-7 and MDA-MB-231 cells and was more pronounced in MCF-7 cells. We conclude that pChk1 is a predictive biomarker of radiotherapy resistance and early local recurrence.

Hu S, Fu S, Xu X, et al.
The mechanism of radiosensitization by YM155, a novel small molecule inhibitor of survivin expression, is associated with DNA damage repair.
Cell Physiol Biochem. 2015; 37(3):1219-30 [PubMed] Related Publications
BACKGROUND/AIMS: Survivin, a member of the inhibitor of apoptosis protein family, is an attractive target for cancer therapy. We investigated the effects of YM155, a small molecule inhibitor of survivin expression, on the radiosensitivity of human non-small cell lung cancer (NSCLC) cell lines and elucidated a relationship between the cellular localization of survivin and DNA double-strand break repair.
METHODS: The cellular distribution of survivin was determined by Western blotting of subcellular fractions and by immunofluorescent staining in A549 NSCLC cells. Radiation-induced DNA damage was evaluated based on histone H2AX phosphorylation and foci formation. The relationship between the cellular localization of survivin and DNA double-strand break repair was analyzed by Western blotting and co-immunoprecipitations.
RESULTS: YM155 down-regulated survivin expression in NSCLC cells in a concentration- and time-dependent manner. An in vitro clonogenic survival assay revealed that YM155 increased the sensitivity of NSCLC cells to radiation. After irradiation, we observed a rapid accumulation of survivin in the nucleus. An immunofluorescent analysis of histone x03B3;-H2AX demonstrated that the inhibition of survivin expression by YM155 resulted in impaired DNA double-strand break repair. Co-immunoprecipitation assays using nuclear extracts revealed an interaction between survivin, Ku70, x03B3;-H2AX, and DNA-PKcs. Furthermore, S2056 autophosphorylation of DNA-PKcs was reduced in survivin-depleted cells.
CONCLUSIONS: These results suggested that YM155 sensitized NSCLC cells to radiation, at least in part by inhibiting DNA repair and enhancing apoptosis via the down-regulation of survivin expression. YM155 pretreatment inhibited DNA-PKcs autophosphorylation at S2056. Nuclear survivin was involved in DNA double-strand break repair via interactions with members of the DNA double-strand break repair machinery.

Chen J, Wu L, Wang Y, et al.
Effect of transporter and DNA repair gene polymorphisms to lung cancer chemotherapy toxicity.
Tumour Biol. 2016; 37(2):2275-84 [PubMed] Related Publications
Lung cancer is the first leading cause of cancer deaths. Chemotherapy toxicity is one of factors that limited the efficacy of platinum-based chemotherapy in lung cancer patients. Transporters and DNA repair genes play critical roles in occurrence of platinum-based chemotherapy toxicity. To investigate the relationships between transporter and DNA repair gene polymorphisms and platinum-based chemotherapy toxicity in lung cancer patients, we selected 60 polymorphisms in 14 transporters and DNA repair genes. The polymorphisms were genotyped in 317 lung cancer patients by Sequenom MassARRAY. Logistic regression was performed to estimate the association of toxicity outcome with the polymorphisms by PLINK. Our results showed that polymorphisms of SLC2A1 (rs3738514, rs4658, rs841844) were significantly related to overall toxicity. XRCC5 (rs1051685, rs6941) and AQP2 (10875989, rs3759125) polymorphisms were associated with hematologic toxicity. AQP2 polymorphisms (rs461872, rs7305534) were correlated with gastrointestinal toxicity. In conclusion, genotypes of these genes may be used to predict the platinum-based chemotherapy toxicity in lung cancer patients.

Bouley J, Saad L, Grall R, et al.
A new phosphorylated form of Ku70 identified in resistant leukemic cells confers fast but unfaithful DNA repair in cancer cell lines.
Oncotarget. 2015; 6(29):27980-8000 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Ku70-dependent canonical nonhomologous end-joining (c-NHEJ) DNA repair system is fundamental to the genome maintenance and B-cell lineage. c-NHEJ is upregulated and error-prone in incurable forms of chronic lymphocytic leukemia which also displays telomere dysfunction, multiple chromosomal aberrations and the resistance to DNA damage-induced apoptosis. We identify in these cells a novel DNA damage inducible form of phospho-Ku70. In vitro in different cancer cell lines, Ku70 phosphorylation occurs in a heterodimer Ku70/Ku80 complex within minutes of genotoxic stress, necessitating its interaction with DNA damage-induced kinase pS2056-DNA-PKcs and/or pS1981-ATM. The mutagenic effects of phospho-Ku70 are documented by a defective S/G2 checkpoint, accelerated disappearance of γ-H2AX foci and kinetics of DNA repair resulting in an increased level of genotoxic stress-induced chromosomal aberrations. Together, these data unveil an involvement of phospho-Ku70 in fast but inaccurate DNA repair; a new paradigm linked to both the deregulation of c-NHEJ and the resistance of malignant cells.

Dickreuter E, Eke I, Krause M, et al.
Targeting of β1 integrins impairs DNA repair for radiosensitization of head and neck cancer cells.
Oncogene. 2016; 35(11):1353-62 [PubMed] Related Publications
β1 Integrin-mediated cell-extracellular matrix interactions allow cancer cell survival and confer therapy resistance. It was shown that inhibition of β1 integrins sensitizes cells to radiotherapy. Here, we examined the impact of β1 integrin targeting on the repair of radiation-induced DNA double-strand breaks (DSBs). β1 Integrin inhibition was accomplished using the monoclonal antibody AIIB2 and experiments were performed in three-dimensional cell cultures and tumor xenografts of human head and neck squamous cell carcinoma (HNSCC) cell lines. AIIB2, X-ray irradiation, small interfering RNA-mediated knockdown and Olaparib treatment were performed and residual DSB number, protein and gene expression, non-homologous end joining (NHEJ) activity as well as clonogenic survival were determined. β1 Integrin targeting impaired repair of radiogenic DSB (γH2AX/53BP1, pDNA-PKcs T2609 foci) in vitro and in vivo and reduced the protein expression of Ku70, Rad50 and Nbs1. Further, we identified Ku70, Ku80 and DNA-PKcs but not poly(ADP-ribose) polymerase (PARP)-1 to reside in the β1 integrin pathway. Intriguingly, combined inhibition of β1 integrin and PARP using Olaparib was significantly more effective than either treatment alone in non-irradiated and irradiated HNSCC cells. Here, we support β1 integrins as potential cancer targets and highlight a regulatory role for β1 integrins in the repair of radiogenic DNA damage via classical NHEJ. Further, the data suggest combined targeting of β1 integrin and PARP as promising approach for radiosensitization of HNSCC.

Someya M, Yamamoto H, Nojima M, et al.
Relation between Ku80 and microRNA-99a expression and late rectal bleeding after radiotherapy for prostate cancer.
Radiother Oncol. 2015; 115(2):235-9 [PubMed] Related Publications
BACKGROUND AND PURPOSE: Late rectal bleeding is one of the severe adverse events after radiotherapy for prostate cancer. New biomarkers are needed to allow a personalized treatment.
MATERIALS AND METHODS: Four patients each with grade 0-1 or grade 2-3 rectal bleeding were randomly selected for miRNA array to examine miRNA expression in peripheral blood lymphocytes (PBLs). Based on results of miRNA array, 1 of 348 miRNAs was selected for microRNA assays. Then, expression of DNA-dependent protein kinase mRNA and miR-99a was analyzed in the PBLs of 97 patients. PBLs were exposed to 4Gy of X-ray ex-vivo.
RESULTS: In the discovery cohort, grade 2-3 rectal bleeding was significantly higher in the Ku80 <1.09 expression group compared with ⩾1.09 group (P=0.011). In radiation-induced expression of miR-99a, grade 2-3 rectal bleeding was significantly higher in the miR-99a IR(+)/IR(-) >0.93 group compared with ⩽0.93 group (P=0.013). Most patients with grade 2-3 rectal bleeding were in the group with low Ku80 and high miR-99a expression. In the validation cohort, similar results were obtained.
CONCLUSION: A combination of low Ku80 expression and highly-induced miR-99a expression could be a promising marker for predicting rectal bleeding after radiotherapy.

Qi D, Hu Y, Li J, et al.
Hyperthermia Induces Apoptosis of 786-O Cells through Suppressing Ku80 Expression.
PLoS One. 2015; 10(4):e0122977 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Hyperthermia as an anticancer method has been paid increasing attention in recent years. Several studies have shown that hyperthermia can kill tumor cells by inducing apoptosis. However, the underlying molecular mechanisms of hyperthermia-induced apoptosis are largely unknown. To investigate the effects and molecular mechanism of hyperthermia on the apoptosis in renal carcinoma 786-O cells, we firstly examined apoptosis and Ku expression in 786-O cell line treated with heat exposure (42°C for 0-4 h). The results showed that hyperthermia induced apoptosis of 786-O cells, and suppressed significantly Ku80 expression, but not Ku70 expression. Next, we knock-down Ku80 in 786-O cells, generating stable cell line 786-O-shKu80, and detected apoptosis, cell survival and cell cycle distribution. Our data showed higher apoptotic rate and lower surviving fraction in the stable cell line 786-O-shKu80 compared with those in control cells, exposed to the same heat stress (42°C for 0-4 h). Moreover, the results also showed suppression of Ku80 led to G2/M phase arrest in the stable cell line 786-O-shKu80 following heat treatment. Together, these findings indicate that Ku80 may play an important role in hyperthermia-induced apoptosis and heat-sensitivity of renal carcinoma cells through influencing the cell cycle distribution.

Xiao Y, Wang J, Qin Y, et al.
Ku80 cooperates with CBP to promote COX-2 expression and tumor growth.
Oncotarget. 2015; 6(10):8046-61 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Cyclooxygenase-2 (COX-2) plays an important role in lung cancer development and progression. Using streptavidin-agarose pulldown and proteomics assay, we identified and validated Ku80, a dimer of Ku participating in the repair of broken DNA double strands, as a new binding protein of the COX-2 gene promoter. Overexpression of Ku80 up-regulated COX-2 promoter activation and COX-2 expression in lung cancer cells. Silencing of Ku80 by siRNA down-regulated COX-2 expression and inhibited tumor cell growth in vitro and in a xenograft mouse model. Ku80 knockdown suppressed phosphorylation of ERK, resulting in an inactivation of the MAPK pathway. Moreover, CBP, a transcription co-activator, interacted with and acetylated Ku80 to co-regulate the activation of COX-2 promoter. Overexpression of CBP increased Ku80 acetylation, thereby promoting COX-2 expression and cell growth. Suppression of CBP by a CBP-specific inhibitor or siRNA inhibited COX-2 expression as well as tumor cell growth. Tissue microarray immunohistochemical analysis of lung adenocarcinomas revealed a strong positive correlation between levels of Ku80 and COX-2 and clinicopathologic variables. Overexpression of Ku80 was associated with poor prognosis in patients with lung cancers. We conclude that Ku80 promotes COX-2 expression and tumor growth and is a potential therapeutic target in lung cancer.

Wang S, Wang Z, Liu X, et al.
Prognostic significance of Ku80 in pT2N0M0 esophageal squamous cell carcinoma after Ivor-Lewis esophagectomy.
Tumour Biol. 2015; 36(8):6181-9 [PubMed] Related Publications
Recent studies have shown that Ku80, a DNA repair protein, was involved in progression of malignant tumors. This study aimed to clarify the clinicopathological significance and prognostic value of Ku80 in pT2N0M0 esophageal squamous cell carcinoma (ESCC). We enrolled 217 patients with pT2N0M0 midthoracic ESCC who had undergone Ivor-Lewis esophagectomy. The expression profile of Ku80 was examined by immunohistochemistry. The results were correlated with the clinicopathological variables, overall survival (OS) and disease-free survival (DFS), in pT2N0M0 ESCC patients. The expression of Ku80 were higher in ESCC tissues than the corresponding health esophageal mucosa (P < 0.001). Clinically, the Ku80 expression levels were significantly related to tumor size (P = 0.018), differentiation degree (P = 0.010), and tumor-node-metastasis (TNM) stage (P = 0.001). Subsequent multivariate analysis demonstrated that tumor size, differentiation degree, TNM stage, and Ku80 expression were independent prognostic factors for the OS and the DFS of pT2N0M0 ESCC patients. Our data indicated that Ku80 expression level associates with key clinicopathological features and is an independent predictor of the OS and the DFS in pT2N0M0 ESCC patients.

Li K, Yin X, Yang H, et al.
Association of the genetic polymorphisms in XRCC6 and XRCC5 with the risk of ESCC in a high-incidence region of North China.
Tumori. 2015 Jan-Feb; 101(1):24-9 [PubMed] Related Publications
BACKGROUND: The XRCC6 and XRCC5 genes are part of the nonhomologous end-joining (NHEJ) pathway, which is the main mechanism repairing DNA double-strand breaks (DSBs) in human cells. Genetic variations of XRCC6 and XRCC5 might contribute to esophageal squamous cell carcinoma (ESCC) susceptibility.
METHODS: ESCC patients (n = 189) and cancer-free controls (n = 189) were recruited in an ESCC high-risk area of north China. Then the rs2267437 (XRCC6), rs3835 (XRCC5) and rs16855458 (XRCC5) polymorphisms were genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis.
RESULTS: A significant difference in genotype distribution and allele frequency of rs2267437 (XRCC6) was observed between the cases and controls. The CG carriers were at higher risk of ESCC (p = 0.001, odds ratio [OR] = 2.040, 95% confidence interval [95% CI], 1.323-3.147). G allele carriers were also associated with an increased ESCC risk (p = 0.003, OR = 1.868, 95% CI, 1.230-2.836). In the 2 polymorphisms of XRCC5, no significant difference was found between both groups in the distribution of either genotype or allelic frequency. But in the haplotypes established by the single nucleotide polymorphisms (SNPs) of XRCC5, the haplotype AT and CC separately increased by 4.28- and 2.31-fold the risk ratio of ESCC (p = 0.01, OR = 4.28, 95% CI, 1.40-13.05; p = 0.03, OR = 2.31, 95% CI, 1.11-4.80, respectively). In addition, gene-smoking or gene-drinking interactions, and their effect on the risk of ESCC were observed, but no significant gene-environment interaction was demonstrated.
CONCLUSIONS: In conclusion, both the CG carriers/G allele carriers of rs2267437 (XRCC6) and the haplotype AT/CC established by the SNPs of XRCC5 are associated with ESCC susceptibility.

Meng J, Zhang F, Zhang XT, et al.
Ku70 is essential for histone deacetylase inhibitor trichostatin A-induced apoptosis.
Mol Med Rep. 2015; 12(1):581-6 [PubMed] Related Publications
It was previously reported that the histone deacetylase inhibitor (HDACI) trichostatin A (TSA) induced B cell lymphoma 2 (Bcl-2)-associated X protein (Bax)-dependent apoptosis in colorectal cancer (CRC) cells. In addition, Ku70 has been identified as a regulator of apoptosis, the mechanism of which proceeds via interacting with Bax. The aim of the present study was to investigate the role of Ku70 in TSA-induced apoptosis in the CRC cell lines HCT116 and HT29. The results showed that TSA induced the acetylation of Ku70, which was found to be associated with increased apoptosis. In addition, TSA treatment promoted the release of Bax from its complex with Ku70. Bax was then detected to have translocated from the cytoplasm into the mitochondria, while cytochrome c was detected to have translocated from the mitochondria into the cytoplasm. Furthermore, knockdown of Ku70 using small interfering RNA decreased TSA-induced apoptosis as well as downregulated the expression of Bax. These effects were rescued through pre-treatment of cells with the proteasome inhibitor MG132. In conclusion, the results of the present study suggested that Ku70 acetylation mediated TSA-induced apoptosis in CRC cells. In addition, Ku70 was found to be indispensable in TSA-induced apoptosis due to its role in protecting Bax from proteosomal degradation.

Aleskandarany M, Caracappa D, Nolan CC, et al.
DNA damage response markers are differentially expressed in BRCA-mutated breast cancers.
Breast Cancer Res Treat. 2015; 150(1):81-90 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Cells have stringent DNA repair pathways that are specific for each different set of DNA lesions which is accomplished through the integration of complex array of proteins. However, BRCA-mutated breast cancer (BC) has defective DNA repair mechanisms. This study aims to investigate differential expression of a large panel of DNA repair markers to characterise DNA repair mechanisms in BRCA-associated tumours compared to sporadic tumours in an attempt to characterise these tumours in routine practice. Immunohistochemistry and tissue microarray technology were applied to a cohort of clinically annotated series of sporadic (n = 1849), BRCA1-mutated (n = 48), and BRCA2-mutated (n = 27) BC. The following DNA damage response (DDR) markers are used; BRCA1, BRCA2, RAD51, Ku70/Ku80, BARD, PARP1 (cleaved), PARP1 (non-cleaved), and P53 in addition to basal cytokeratins, ER, PR, and HER2. A significant proportion of BRCA1 tumours were positive for PARP1 (non-cleaved), and negative for BARD1 and RAD51 compared with sporadic BC. BRCA2 tumours were significantly positive for PARP1 (non-cleaved) compared with sporadic tumours. RAD51 was significantly higher in BRCA1 compared with BRCA2 tumours (p = 0.005). When BRCA1/2 BCs were compared to triple-negative (TN) sporadic tumours of the studied DDR proteins, BARD1 (p < 0.001), PARP1 (non-cleaved) (p < 0.001), and P53 (p = 0.002) remained significantly different in BRCA1/2 tumours compared with TN BC. DNA repair markers showed differential expression in BRCA-mutated tumours, with a substantial degree of disruption of DNA repair pathways in sporadic BC especially TN BC. DNA double-strand break (DSB) repair is assisted by PARP1 expression in BRCA-mutated tumours, whereas the loss of DSB repair via RAD51 is predominant in BRCA1 rather than BRCA2 BC.

Al-Kaabi MM, Alshareeda AT, Jerjees DA, et al.
Checkpoint kinase1 (CHK1) is an important biomarker in breast cancer having a role in chemotherapy response.
Br J Cancer. 2015; 112(5):901-11 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
BACKGROUND: Checkpoint kinase1 (CHK1), which is a key component of DNA-damage-activated checkpoint signalling response, may have a role in breast cancer (BC) pathogenesis and influence response to chemotherapy. This study investigated the clinicopathological significance of phosphorylated CHK1 (pCHK1) protein in BC.
METHOD: pCHK1 protein expression was assessed using immunohistochemistry in a large, well-characterized annotated series of early-stage primary operable invasive BC prepared as tissue microarray (n=1200).
RESULT: pCHK1 showed nuclear and/or cytoplasmic expression. Tumours with nuclear expression showed positive associations with favourable prognostic features such as lower grade, lower mitotic activity, expression of hormone receptor and lack of expression of KI67 and PI3K (P<0.001). On the other hand, cytoplasmic expression was associated with features of poor prognosis such as higher grade, triple-negative phenotype and expression of KI67, p53, AKT and PI3K. pCHK1 expression showed an association with DNA damage response (ATM, RAD51, BRCA1, KU70/KU80, DNA-PKCα and BARD1) and sumoylation (UBC9 and PIASγ) biomarkers. Subcellular localisation of pCHK1 was associated with the expression of the nuclear transport protein KPNA2. Positive nuclear expression predicted better survival outcome in patients who did not receive chemotherapy in the whole series and in ER-positive tumours. In ER-negative and triple-negative subgroups, nuclear pCHK1 predicted shorter survival in patients who received cyclophosphamide, methotrexate and 5-florouracil chemotherapy.
CONCLUSIONS: Our data suggest that pCHK1 may have prognostic and predictive significance in BC. Subcellular localisation of pCHK1 protein is related to its function.

Lombardi AJ, Hoskins EE, Foglesong GD, et al.
Acquisition of Relative Interstrand Crosslinker Resistance and PARP Inhibitor Sensitivity in Fanconi Anemia Head and Neck Cancers.
Clin Cancer Res. 2015; 21(8):1962-72 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
PURPOSE: Fanconi anemia is an inherited disorder associated with a constitutional defect in the Fanconi anemia DNA repair machinery that is essential for resolution of DNA interstrand crosslinks. Individuals with Fanconi anemia are predisposed to formation of head and neck squamous cell carcinomas (HNSCC) at a young age. Prognosis is poor, partly due to patient intolerance of chemotherapy and radiation requiring dose reduction, which may lead to early recurrence of disease.
EXPERIMENTAL DESIGN: Using HNSCC cell lines derived from the tumors of patients with Fanconi anemia, and murine HNSCC cell lines derived from the tumors of wild-type and Fancc(-/-) mice, we sought to define Fanconi anemia-dependent chemosensitivity and DNA repair characteristics. We utilized DNA repair reporter assays to explore the preference of Fanconi anemia HNSCC cells for non-homologous end joining (NHEJ).
RESULTS: Surprisingly, interstrand crosslinker (ICL) sensitivity was not necessarily Fanconi anemia-dependent in human or murine cell systems. Our results suggest that the increased Ku-dependent NHEJ that is expected in Fanconi anemia cells did not mediate relative ICL resistance. ICL exposure resulted in increased DNA damage sensing and repair by PARP in Fanconi anemia-deficient cells. Moreover, human and murine Fanconi anemia HNSCC cells were sensitive to PARP inhibition, and sensitivity of human cells was attenuated by Fanconi anemia gene complementation.
CONCLUSIONS: The observed reliance upon PARP-mediated mechanisms reveals a means by which Fanconi anemia HNSCCs can acquire relative resistance to the ICL-based chemotherapy that is a foundation of HNSCC treatment, as well as a potential target for overcoming chemoresistance in the chemosensitive individual.

Zhang ZY, Fu SL, Xu SQ, et al.
By downregulating Ku80, hsa-miR-526b suppresses non-small cell lung cancer.
Oncotarget. 2015; 6(3):1462-77 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Ku80 is involved in DNA double-strand breaks (DSBs) repair. Ku80 is overexpressed in lung cancer tissues, yet, molecular mechanisms have not been examined. We identified that miRNA, hsa-miR-526b, is bound to the 3'-UTR of Ku80 mRNA, thus decreasing Ku80 expression in NSCLC cells. Hsa-miR-526b was downregulated in NSCLC tissues compared with corresponding non-tumorous tissues, and its expression was inversely correlated with Ku80 upregulation. Overexpression of Ku80 and downregulation of hsa-miR-526b were associated with poor clinical outcomes of NSCLC patients. Hsa-miR-526b suppressed NSCLC cell proliferation, clonogenicity, and induced cell cycle arrest and apoptosis. Hsa-miR-526b inhibited xenografts and orthotopic lung tumor growth. Further, Ku80 knockdown in NSCLC cells suppressed tumor properties in vitro and in vivo similar to hsa-miR-526b overexpression. In agreement, Ku80 restoration partially reversed cell cycle arrest and apoptosis induced by hsa-miR-526b in NSCLC cells in vitro and in vivo. In addition, hsa-miR-526b overexpression or Ku80 knockdown increased p53 and p21CIP1/WAF1 expression. These findings reveal that hsa-miR-526b is a potential target in cancer therapy.

Green AR, Caracappa D, Benhasouna AA, et al.
Biological and clinical significance of PARP1 protein expression in breast cancer.
Breast Cancer Res Treat. 2015; 149(2):353-62 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Poly(ADP-ribose) polymerase-1 (PARP1) is a key facilitator of DNA repair. PARP inhibitors have gained recent attention as promising therapeutic agents for the treatment of solid tumours including breast cancer (BC). However, the biological and clinical significance of PARP1 expression in BC and its role in DNA-damage response (DDR) remain to be defined. We investigated the expression of PARP1 expression, cleaved (PARP1c) and non-cleaved (PAR1nc) forms, in a large and well-characterised cohort of clinically annotated stage I-III operable BCs (n = 1,269) and 43 BRCA1-mutated BCs using immunohistochemistry. PARP1 expression was correlated to clinicopathological variables, outcome and expression of other key DNA repair proteins (BRCA1, RAD51, Ku70/80, PIASγ and CHK1). Expression of PARP1 was exclusively nuclear. 49 and 85 % of sporadic BC showed expression PARP1nc and PARP1c, respectively. In BRCA1-mutated tumours, PARP1nc/PARP1c was highly expressed (95 and 79 %, respectively). PARP1nc expression was positively associated with premenopausal younger age patients, larger size and higher tumour grade. PARP1 was positively associated with DDR-proteins; RAD51, BRCA1, CHK1 and PIASγ (p < 0.001). Negative association was found between PARP1nc and Ki67. PARP1c was associated with ER (p < 0.001). Different associations between PARP1 and DDR-proteins were observed when stratified based on ER/BRCA1 status. PARP1 was not an independent predictor of outcome in sporadic or BRCA1-mutated BC. Our results demonstrate a potential biological role for PARP1c and PARP1nc in DNA repair in BC based on the significant association with other key DNA damage repair proteins. These associations were not restricted to ER-negative or triple-negative subgroup.

Saadat M, Pashaei S, Amerizade F
Susceptibility to gastric cancer and polymorphisms of insertion/deletion at the intron 3 of the XRCC4 and VNTR at the promoter region of the XRCC5.
Pathol Oncol Res. 2015; 21(3):689-93 [PubMed] Related Publications
The genes encoding X-ray repair cross-complementing group 4 (XRCC4; OMIM: 194363) and 5 (XRCC5; OMIM: 194364) are involved in repair of DNA double-strand breaks. To investigating the associations between polymorphisms of Insertion/Deletion (I/D, rs28360071) in the intron 3 of the XRCC4 and VNTR in the promoter region of the XRCC5 and risk of gastric cancer, the present study was carried out. We included 159 (56 females, 103 males) with gastric cancer and 242 (75 females, 167 males) healthy blood donors frequency matched for age and gender. Using PCR-based methods, the genotypes of the study polymorphisms were determined. The alleles of VNTR XRCC5 polymorphism divided into two groups: L (0 and 1 repeats) and H (2 and 3 repeats) alleles. For the I/D XRCC4 polymorphism, after stratification of the subjects according to their family history (FH) of cancer, either the ID (OR = 3.19, 95%CI: 1.35-7.50, P = 0.008) or the DD genotypes (OR = 4.62, 95%CI: 1.63-13.0, P = 0.004) among positive FH persons, increased the risk of gastric cancer compared with the reference group (persons who have negative FH and II genotype). For the VNTR XRCC5 polymorphism, the LH + HH genotypes among positive FH persons, increased the risk of gastric cancer compared with the reference group (persons who have negative FH and LL genotype) (OR = 2.88, 95%CI: 1.34-6.18, P = 0.006). Sensitivity analysis showed that the above mentioned associations were not occurred due to the maldistribution of the genotypes among missing data. The present study suggests that both polymorphisms of the XRCC4 and XRCC5 might be risk factors for gastric cancer development especially among persons with positive FH.

Li H, Chen X, Yu Y, et al.
Metformin inhibits the growth of nasopharyngeal carcinoma cells and sensitizes the cells to radiation via inhibition of the DNA damage repair pathway.
Oncol Rep. 2014; 32(6):2596-604 [PubMed] Related Publications
Nasopharyngeal carcinoma (NPC) is a leading cause of cancer-related mortality. Radiotherapy is one of the primary modalities for NPC treatment. However, in patients in the late stages of the disease, the local control rate and overall survival rate remain low. Therefore, it is urgent to identify new targets that can improve the outcome of radiotherapy in this neoplasm. In the present study, we investigated the effects of metformin on the radiosensitivity of NPC cells and explored the potential mechanisms. The radiosensitizing effects of metformin on NPC cells were measured by colony formation assay. Cell apoptosis was assessed by Hoechst 33342 staining analysis. DNA damage was detected by monitoring γ-H2AX foci with immunofluorescence. The changes in apotosis-related and DNA damage repair-related proteins were detected by western blotting. Our study demonstrated that metformin significantly reduced the cell viability, enhanced radiosensitivity and potentiated radiation-induced caspase-9/-3 cleavage in the NPC cells. In addition, metformin plus radiation significantly upregulated the expression of p-ATM, p-ATR, γ-H2AX and downregulated the expression of ATM, ATR, p95/NBS1, Rad50, DNA-PK, Ku70 and Ku80. Therefore, our results suggest that metformin possesses a strong radiosensitizing potential in NPC cells. This radiosensitizing effect was associated with inhibition of DNA double-strand break repair processes through HR repair and the NHEJ repair signaling pathway, thereby enhancing radiation-induced cell apoptosis. These findings imply that metformin is a potent radiation-sensitizing agent and may be a promising candidate for clinical evaluation as part of a combined regimen for the treatment of nasopharyngeal carcinoma.

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