Gene Summary

Gene:LIG4; DNA ligase 4
Aliases: LIG4S
Summary:The protein encoded by this gene is a DNA ligase that joins single-strand breaks in a double-stranded polydeoxynucleotide in an ATP-dependent reaction. This protein is essential for V(D)J recombination and DNA double-strand break (DSB) repair through nonhomologous end joining (NHEJ). This protein forms a complex with the X-ray repair cross complementing protein 4 (XRCC4), and further interacts with the DNA-dependent protein kinase (DNA-PK). Both XRCC4 and DNA-PK are known to be required for NHEJ. The crystal structure of the complex formed by this protein and XRCC4 has been resolved. Defects in this gene are the cause of LIG4 syndrome. Alternatively spliced transcript variants encoding the same protein have been observed. [provided by RefSeq, Jul 2008]
Databases:OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:DNA ligase 4
Source:NCBIAccessed: 31 August, 2019


What does this gene/protein do?
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Cancer Overview

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Publications Per Year (1994-2019)
Graph generated 31 August 2019 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 31 August, 2019 using data from PubMed, MeSH and CancerIndex

Latest Publications: LIG4 (cancer-related)

Balmus G, Pilger D, Coates J, et al.
ATM orchestrates the DNA-damage response to counter toxic non-homologous end-joining at broken replication forks.
Nat Commun. 2019; 10(1):87 [PubMed] Free Access to Full Article Related Publications
Mutations in the ATM tumor suppressor gene confer hypersensitivity to DNA-damaging chemotherapeutic agents. To explore genetic resistance mechanisms, we performed genome-wide CRISPR-Cas9 screens in cells treated with the DNA topoisomerase I inhibitor topotecan. Thus, we here establish that inactivating terminal components of the non-homologous end-joining (NHEJ) machinery or of the BRCA1-A complex specifically confer topotecan resistance to ATM-deficient cells. We show that hypersensitivity of ATM-mutant cells to topotecan or the poly-(ADP-ribose) polymerase (PARP) inhibitor olaparib reflects delayed engagement of homologous recombination at DNA-replication-fork associated single-ended double-strand breaks (DSBs), allowing some to be subject to toxic NHEJ. Preventing DSB ligation by NHEJ, or enhancing homologous recombination by BRCA1-A complex disruption, suppresses this toxicity, highlighting a crucial role for ATM in preventing toxic LIG4-mediated chromosome fusions. Notably, suppressor mutations in ATM-mutant backgrounds are different to those in BRCA1-mutant scenarios, suggesting new opportunities for patient stratification and additional therapeutic vulnerabilities for clinical exploitation.

Yang G, Qiu J, Wang D, et al.
Traditional Chinese Medicine Curcumin Sensitizes Human Colon Cancer to Radiation by Altering the Expression of DNA Repair-related Genes.
Anticancer Res. 2018; 38(1):131-136 [PubMed] Related Publications
BACKGROUND/AIM: The aim of the present study was to investigate the radio-sensitizing efficacy of curcumin, a traditional Chinese medicine (TCM) on colon cancer cells in vitro and in vivo.
MATERIALS AND METHODS: Human colon cancer HT-29 cells were treated with curcumin (2.5 μM), irradiation (10 Gy) and the combination of irradiation and curcumin. Cell proliferation was assessed using the MTT assay. Apoptotic cells were detected by Annexin V-PE/7-AAD analysis. PCR was performed to determine differential-expression profiling of 95 DNA-repair genes in irradiated cells and cells treated with both irradiation and curcumin. Differentially-expressed genes were confirmed by Western blotting. In vivo radio-sensitizing efficacy of curcumin was assessed in a xenograft mouse model of HT-29 colon cancer. Curcumin was administrated daily by intraperitoneal injection at 20 mg/kg/dose. Mice received irradiation (10 Gy) twice weekly. Apoptosis of the cancer cells following treatment was determined by TUNEL staining.
RESULTS: Irradiation induced proliferation inhibition and apoptosis of HT-29 cells in vitro. Concurrent curcumin treatment sensitized the HT-29 tumor to irradiation (p<0.01). DNA repair-related genes CCNH and XRCC5 were upregulated and LIG4 and PNKP downregulated by the combination of curcumin and irradiation compared with irradiation alone (p<0.05). Combined treatment of curcumin and irradiation resulted in a significantly greater tumor-growth inhibition and apoptosis compared to irradiation treatment alone (p<0.01).
CONCLUSION: Curcumin sensitizes human colon cancer in vitro and in vivo to radiation. Downregulation of LIG4 and PNKP and upregulation of XRCC5 and CCNH DNA-repair-related genes were involved in the radio-sensitizing efficacy of curcumin in colon cancer.

Wang X, Sun CL, Hageman L, et al.
Clinical and Genetic Risk Prediction of Subsequent CNS Tumors in Survivors of Childhood Cancer: A Report From the COG ALTE03N1 Study.
J Clin Oncol. 2017; 35(32):3688-3696 [PubMed] Free Access to Full Article Related Publications
Purpose Survivors of childhood cancer treated with cranial radiation therapy are at risk for subsequent CNS tumors. However, significant interindividual variability in risk suggests a role for genetic susceptibility and provides an opportunity to identify survivors of childhood cancer at increased risk for these tumors. Methods We curated candidate genetic variants from previously published studies in adult-onset primary CNS tumors and replicated these in survivors of childhood cancer with and without subsequent CNS tumors (82 participants and 228 matched controls). We developed prediction models to identify survivors at high or low risk for subsequent CNS tumors and validated these models in an independent matched case-control sample (25 participants and 54 controls). Results We demonstrated an association between six previously published single nucleotide polymorphisms (rs15869 [ BRCA2], rs1805389 [ LIG4], rs8079544 [ TP53], rs25489 [ XRCC1], rs1673041 [ POLD1], and rs11615 [ ERCC1]) and subsequent CNS tumors in survivors of childhood cancer. Including genetic variants in a Final Model containing age at primary cancer, sex, and cranial radiation therapy dose yielded an area under the curve of 0.81 (95% CI, 0.76 to 0.86), which was superior ( P = .002) to the Clinical Model (area under the curve, 0.73; 95% CI, 0.66 to 0.80). The prediction model was successfully validated. The sensitivity and specificity of predicting survivors of childhood cancer at highest or lowest risk of subsequent CNS tumors was 87.5% and 83.5%, respectively. Conclusion It is possible to identify survivors of childhood cancer at high or low risk for subsequent CNS tumors on the basis of genetic and clinical information. This information can be used to inform surveillance for early detection of subsequent CNS tumors.

Sanie-Jahromi F, Saadat M
Different profiles of the mRNA levels of DNA repair genes in MCF-7 and SH-SY5Y cells after treatment with combination of cisplatin, 50-Hz electromagnetic field and bleomycin.
Biomed Pharmacother. 2017; 94:564-568 [PubMed] Related Publications
Neurotoxicity is known to be a major dose-limiting adverse effect of cisplatin (CDDP), alone or in combination with other chemicals. DNA repair capacity serve as a neuroprotective factor against CDDP. The purpose of this study was to evaluate the effect of 50-Hz electromagnetic field (EMF) in combination with CDDP and bleomycin (Bleo) on expression of some of DNA repair genes (GADD45A, XRCC1, XRCC4, Ku70, Ku80, DNA-PKcs and LIG4) in MCF-7 (breast cancer) and SH-SY5Y (neuroblastoma) cell lines. MCF-7 and SH-SY5Y cells were pre-treated with CDDP in the presence or absence of EMF and then exposed to different concentration of Bleo. EMF (0.50mT intensity) was used in the intermittenet pattern of "15min field on/15min field off" with 30min total exposure. Cell viability assay was done and then the transcript levels of the examined genes were measured using quantitative real-time PCR in "CDDP+Bleo" and "CDDP+EMF+Bleo" treatments. Our results indicated that MCF-7 cells treated with "CDDP+EMF+Bleo" showed more susceptibility compared with "CDDP+Bleo" treated ones, while SH-SY5Y susceptibility was not changed between the two treatments. The represented data indicated that MCF-7 and SH-SY5Y cells showed non-random disagreement in DNA repair gene expression in 11 conditions (out of 14 conditions) with each other (χ

De Gregoriis G, Ramos JA, Fernandes PV, et al.
DNA repair genes PAXIP1 and TP53BP1 expression is associated with breast cancer prognosis.
Cancer Biol Ther. 2017; 18(6):439-449 [PubMed] Free Access to Full Article Related Publications
Despite remarkable advances in diagnosis, prognosis and treatment, advanced or recurrent breast tumors have limited therapeutic approaches. Many treatment strategies try to explore the limitations of DNA damage response (DDR) in tumor cells to selectively eliminate them. BRCT (BRCA1 C-terminal) domains are present in a superfamily of proteins involved in cell cycle checkpoints and the DDR. Tandem BRCT domains (tBRCT) represent a distinct class of these domains. We investigated the expression profile of 7 tBRCT genes (BARD1, BRCA1, LIG4, ECT2, MDC1, PAXIP1/PTIP and TP53BP1) in breast cancer specimens and observed a high correlation between PAXIP1 and TP53BP1 gene expression in tumor samples. Tumors with worse prognosis (tumor grade 3 and triple negative) showed reduced expression of tBRCT genes, notably, PAXIP1 and TP53BP1. Survival analyses data indicated that tumor status of both genes may impact prognosis. PAXIP1 and 53BP1 protein levels followed gene expression results, i.e., are intrinsically correlated, and also reduced in more advanced tumors. Evaluation of both genes in triple negative breast tumor samples which were characterized for their BRCA1 status showed that PAXIP1 is overexpressed in BRCA1 mutant tumors. Taken together our findings indicate that PAXIP1 status correlates with breast cancer staging, in a manner similar to what has been characterized for TP53BP1.

Martinez AR, Kaul Z, Parvin JD, Groden J
Differential requirements for DNA repair proteins in immortalized cell lines using alternative lengthening of telomere mechanisms.
Genes Chromosomes Cancer. 2017; 56(8):617-631 [PubMed] Related Publications
Cancer cells require telomere maintenance to enable uncontrolled growth. Most often telomerase is activated, although a subset of human cancers are telomerase-negative and depend on recombination-based mechanisms known as ALT (Alternative Lengthening of Telomeres). ALT depends on proteins that are essential for homologous recombination, including BLM and the MRN complex, to extend telomeres. This study surveyed the requirement for requisite homologous recombination proteins, yet to be studied in human ALT cell lines, by protein depletion using RNA interference. Effects on ALT were evaluated by measuring C-circle abundance, a marker of ALT. Surprisingly, several proteins essential for homologous recombination, BARD1, BRCA2, and WRN, were dispensable for C-circle production, while PALB2 had varying effects on C-circles among ALT cell lines. Depletion of homologous recombination proteins BRCA1 and BLM, which have been previously studied in ALT, decreased C-circles in all ALT cell lines. Depletion of the non-homologous end joining proteins 53BP1 and LIG4 had no effect on C-circles in any ALT cell line. Proteins such as chromatin modifiers that recruit double-strand break proteins, RNF8 and RNF168, and other proteins loosely grouped into excision DNA repair processes, XPA, MSH2, and MPG, reduced C-circles in some ALT cell lines. MSH2 depletion also reduced recombination at telomeres as measured by intertelomeric exchanges. Collectively, the requirement for DNA repair proteins varied between the ALT cell lines compared. In sum, our study suggests that ALT proceeds by multiple mechanisms that differ between cell lines and that some of these depend on DNA repair proteins not associated with homologous recombination pathways.

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 IC
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.

Czyż M, Toma M, Gajos-Michniewicz A, et al.
PARP1 inhibitor olaparib (Lynparza) exerts synthetic lethal effect against ligase 4-deficient melanomas.
Oncotarget. 2016; 7(46):75551-75560 [PubMed] Free Access to Full Article Related Publications
Cancer including melanoma may be ''addicted" to double strand break (DSB) repair and targeting this process could sensitize them to the lethal effect of DNA damage. PARP1 exerts an important impact on DSB repair as it binds to both single- and double- strand breaks. PARP1 inhibitors might be highly effective drugs triggering synthetic lethality in patients whose tumors have germline or somatic defects in DNA repair genes. We hypothesized that PARP1-dependent synthetic lethality could be induced in melanoma cells displaying downregulation of DSB repair genes. We observed that PARP1 inhibitor olaparib sensitized melanomas with reduced expression of DNA ligase 4 (LIG4) to an alkylatimg agent dacarbazine (DTIC) treatment in vitro, while normal melanocytes remained intact. PARP1 inhibition caused accumulation of DSBs, which was associated with apoptosis in LIG4 deficient melanoma cells. Our hypothesis that olaparib is synthetic lethal with LIG4 deficiency in melanoma cells was supported by selective anti-tumor effects of olaparib used either alone or in combination with dacarbazine (DTIC) in LIG4 deficient, but not LIG4 proficient cells. In addition, olaparib combined with DTIC inhibited the growth of LIG4 deficient human melanoma xenografts. This work for the first time demonstrates the effectiveness of a combination of PARP1 inhibitor olaparib and alkylating agent DTIC for treating LIG4 deficient melanomas. In addition, analysis of the TCGA and transcriptome microarray databases revealed numerous individual melanoma samples potentially displaying specific defects in DSB repair pathways, which may predispose them to synthetic lethality triggered by PARP1 inhibitor combined with a cytotoxic drug.

Jiao K, Qin J, Zhao Y, Zhang H
Genetic effects of XRCC4 and ligase IV genes on human glioma.
Neuroreport. 2016; 27(14):1024-30 [PubMed] Related Publications
Ligase IV and XRCC4 genes, important molecules in the nonhomologous end-joining pathway for repairing DNA double-strand breaks, may play crucial roles in carcinogenesis. To detect their effects on the risk of human glioma, their gene expression differences between 110 human glioma tissues and 50 healthy brain tissues were determined using quantitative real-time PCR. Furthermore, two tagging single nucleotide polymorphisms (SNPs) in ligase IV and four SNPs in XRCC4 genes were genotyped in 317 glioma patients and 352 healthy controls. The association of glioma and ligase IV/XRCC4 was evaluated using methods for SNP, haplotype, and gene-gene interaction analysis. Compared with those in normal brain tissues, the relative gene expression levels of ligase IV and XRCC4 were significantly downregulated in glioma tissue (P=0.0017 and 0.0006, respectively). Single SNP analysis indicated that only rs10131 in ligase IV remained significantly associated with glioma (P=0.0036) after 10 000 permutation tests. Haplotype analysis showed that the haplotype profiles of ligase IV and XRCC4 were significantly different between glioma patients and healthy controls (P=0.004 and 3.13E-6, respectively). Finally, the gene-gene interaction analysis suggested that the three-locus model (rs1805388, rs10131, and rs2075685) was the best model for ligase IV and XRCC4 to have interaction effects on the risk of glioma. In conclusion, both ligase IV and XRCC4 may act in concert to modulate the development of glioma.

Ribeiro HL, Soares Maia AR, Costa MB, et al.
Influence of functional polymorphisms in DNA repair genes of myelodysplastic syndrome.
Leuk Res. 2016; 48:62-72 [PubMed] Related Publications
Myelodysplastic syndromes (MDS) are a heterogeneous group of hematopoietic stem cell (HSC) malignances characterized by peripheral cytopenias and predisposition to acute myeloid leukemia transformation. Several studies show that the MDS pathogenesis is a complex and heterogeneous process that involves multiple steps through a sequence of genetic lesions in the DNA which lead to functional changes in the cell and the emergence and subsequent evolution of pre-malignant clone. Double strand breaks (DSB) lesions are the most severe type of DNA damage in HSCs, which, if not properly repaired, might contribute to the development of chromosomal abnormalities, which in turn may lead to leukemia development. We assessed the mRNA expression levels of ATM, BRCA1, BRCA2, RAD51, XRCC5, XRCC6 and LIG4 genes in bone marrow samples of 47 MDS patients in order to evaluate the association with functional polymorphisms rs228593, rs4793191, rs9567623, rs1801320, rs3835, rs2267437 and rs1805388, respectively, and try to detect clinical associations. We found that the rs228593, rs2267437 and rs1805388 functional polymorphisms probably alter the level of expression of the ATM, XRCC6 and LIG4 genes, respectively, being important in the maintenance of genomic instability in MDS.

Jun S, Jung YS, Suh HN, et al.
LIG4 mediates Wnt signalling-induced radioresistance.
Nat Commun. 2016; 7:10994 [PubMed] Free Access to Full Article Related Publications
Despite the implication of Wnt signalling in radioresistance, the underlying mechanisms are unknown. Here we find that high Wnt signalling is associated with radioresistance in colorectal cancer (CRC) cells and intestinal stem cells (ISCs). We find that LIG4, a DNA ligase in DNA double-strand break repair, is a direct target of β-catenin. Wnt signalling enhances non-homologous end-joining repair in CRC, which is mediated by LIG4 transactivated by β-catenin. During radiation-induced intestinal regeneration, LIG4 mainly expressed in the crypts is conditionally upregulated in ISCs, accompanied by Wnt/β-catenin signalling activation. Importantly, among the DNA repair genes, LIG4 is highly upregulated in human CRC cells, in correlation with β-catenin hyperactivation. Furthermore, blocking LIG4 sensitizes CRC cells to radiation. Our results reveal the molecular mechanism of Wnt signalling-induced radioresistance in CRC and ISCs, and further unveils the unexpected convergence between Wnt signalling and DNA repair pathways in tumorigenesis and tissue regeneration.

Liddiard K, Ruis B, Takasugi T, et al.
Sister chromatid telomere fusions, but not NHEJ-mediated inter-chromosomal telomere fusions, occur independently of DNA ligases 3 and 4.
Genome Res. 2016; 26(5):588-600 [PubMed] Free Access to Full Article Related Publications
Telomeres shorten with each cell division and can ultimately become substrates for nonhomologous end-joining repair, leading to large-scale genomic rearrangements of the kind frequently observed in human cancers. We have characterized more than 1400 telomere fusion events at the single-molecule level, using a combination of high-throughput sequence analysis together with experimentally induced telomeric double-stranded DNA breaks. We show that a single chromosomal dysfunctional telomere can fuse with diverse nontelomeric genomic loci, even in the presence of an otherwise stable genome, and that fusion predominates in coding regions. Fusion frequency was markedly increased in the absence of TP53 checkpoint control and significantly modulated by the cellular capacity for classical, versus alternative, nonhomologous end joining (NHEJ). We observed a striking reduction in inter-chromosomal fusion events in cells lacking DNA ligase 4, in contrast to a remarkably consistent profile of intra-chromosomal fusion in the context of multiple genetic knockouts, including DNA ligase 3 and 4 double-knockouts. We reveal distinct mutational signatures associated with classical NHEJ-mediated inter-chromosomal, as opposed to alternative NHEJ-mediated intra-chromosomal, telomere fusions and evidence for an unanticipated sufficiency of DNA ligase 1 for these intra-chromosomal events. Our findings have implications for mechanisms driving cancer genome evolution.

Sharapova SO, Chang EY, Guryanova IE, et al.
Next generation sequencing revealed DNA ligase IV deficiency in a "developmentally normal" patient with massive brain Epstein-Barr virus-positive diffuse large B-cell lymphoma.
Clin Immunol. 2016; 163:108-10 [PubMed] Related Publications
INTRODUCTION: Here we present an unusual case of DNA ligase IV deficiency syndrome without dysmorphic facial findings and microcephaly complicated with Epstein-Barr virus-associated large B-cell lymphoma with the right lung involvement and a massive brain tumor lesion in a two-year-old female.
METHODS: PID panel was used for sequencing 55 genes. Most genes have >98% exon coverage including splicing sites. LIG4 gene has 100% exon and splicing site coverage. This was used in Ion Torrent PGM system, the library kit was made by Agilent with Haloplex technology. The sequence analysis software was Alamut, direct sequencing of LIG4 gene was performed after NGS results.
RESULT: We identified three heterozygous mutations in LIG4 gene c.2736+3delC and c.8 C>T (p.A3V) inherited from mother and c.26C>T (p.T9I) - from father after PID panel sequencing and some additional polymorphisms in ATM, NOD2 and NLRP3 genes.
CONCLUSION: This case broadens the clinical spectrum of DNA ligase IV deficiency.

Ma H, Takahashi A, Yoshida Y, et al.
Combining carbon ion irradiation and non-homologous end-joining repair inhibitor NU7026 efficiently kills cancer cells.
Radiat Oncol. 2015; 10:225 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Our previous data demonstrated that targeting non-homologous end-joining repair (NHEJR) yields a higher radiosensitivity than targeting homologous recombination repair (HRR) to heavy ions using DNA repair gene knockouts (KO) in mouse embryonic fibroblast (MEF). In this study, we determined if combining the use of an NHEJR inhibitor with carbon (C) ion irradiation was more efficient in killing human cancer cells compared with only targeting a HRR inhibitor.
METHODS: The TP53-null human non-small cell lung cancer cell line H1299 was used for testing the radiosensitizing effect of NHEJR-related DNA-dependent protein kinase (DNA-PK) inhibitor NU7026, HRR-related Rad51 inhibitor B02, or both to C ion irradiation using colony forming assays. The mechanism underlying the inhibitor radiosensitization was determined by flow cytometry after H2AX phosphorylation staining. HRR-related Rad54-KO, NHEJR-related Lig4-KO, and wild-type TP53-KO MEF were also included to confirm the suppressing effect specificity of these inhibitors.
RESULTS: NU7026 showed significant sensitizing effect to C ion irradiation in a concentration-dependent manner. In contrast, B02 showed a slight sensitizing effect to C ion irradiation. The addition of NU7026 significantly increased H2AX phosphorylation after C ion and x-ray irradiations in H1299 cells, but not B02. NU7026 had no effect on radiosensitivity to Lig4-KO MEF and B02 had no effect on radiosensitivity to Rad54-KO MEF in both irradiations.
CONCLUSION: These results suggest that inhibitors targeting the NHEJR pathway could significantly enhance radiosensitivity of human cancer cells to C ion irradiation, rather than targeting the HRR pathway.

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] Free Access to Full Article 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.

Gan W, Liu P, Wei W
Akt promotes tumorigenesis in part through modulating genomic instability via phosphorylating XLF.
Nucleus. 2015; 6(4):261-5 [PubMed] Free Access to Full Article Related Publications
To maintain genome stability, mammalian cells have developed a delicate, yet efficient, system to sense and repair damaged DNA, including two evolutionarily conserved DNA damage repair (DDR) pathways: homologous recombination (HR) and non-homologous-end-joining (NHEJ). Deregulation in these repair pathways may lead to genomic instability and subsequent human diseases, including cancer. On the other hand, hyper-activation of the oncogenic Akt signaling pathway has been observed in almost all solid tumors. Emerging evidence has begun to reveal a possible role of active Akt in regulating DDR, possibly through suppression of HR. However, whether and how Akt regulates NHEJ remains largely undefined. To this end, we recently reported that Akt impairs NHEJ by phosphorylating XLF at T181, to trigger its dissociation from the functional DNA ligase IV (LIG4)/XRCC4 complex. Here, we provide an additional perspective discussing how Akt is activated upon DNA damage to regulate DNA repair pathways as well as the cellular apoptotic responses.

Wagner W, Ciszewski WM, Kania KD
L- and D-lactate enhance DNA repair and modulate the resistance of cervical carcinoma cells to anticancer drugs via histone deacetylase inhibition and hydroxycarboxylic acid receptor 1 activation.
Cell Commun Signal. 2015; 13:36 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The consideration of lactate as an active metabolite is a newly emerging and attractive concept. Recently, lactate has been reported to regulate gene transcription via the inhibition of histone deacetylases (HDACs) and survival of cancer cells via hydroxycarboxylic acid receptor 1 (HCAR1). This study examined the role of L- and D-lactate in the DNA damage response in cervical cancer cells.
METHODS: Three cervical cancer cell lines were examined: HeLa, Ca Ski and C33A. The inhibitory activity of lactate on HDACs was analysed using Western blot and biochemical methods. The lactate-mediated stimulation of DNA repair and cellular resistance to neocarzinostatin, doxorubicin and cisplatin were studied using γ-H2AX, comet and clonogenic assays. HCAR1 and DNA repair gene expression was quantified by real-time PCR. DNA-PKcs activity and HCAR1 protein expression were evaluated via immunocytochemistry and Western blot, respectively. HCAR1 activation was investigated by measuring intracellular cAMP accumulation and Erk phosphorylation. HCAR1 expression was silenced using shRNA.
RESULTS: L- and D-lactate inhibited HDACs, induced histone H3 and H4 hyperacetylation, and decreased chromatin compactness in HeLa cells. Treating cells with lactate increased LIG4, NBS1, and APTX expression by nearly 2-fold and enhanced DNA-PKcs activity. Based on γ-H2AX and comet assays, incubation of cells in lactate-containing medium increased the DNA repair rate. Furthermore, clonogenic assays demonstrated that lactate mediates cellular resistance to clinically used chemotherapeutics. Western blot and immunocytochemistry showed that all studied cell lines express HCAR1 on the cellular surface. Inhibiting HCAR1 function via pertussis toxin pretreatment partially abolished the effects of lactate on DNA repair. Down-regulating HCAR1 decreased the efficiency of DNA repair, abolished the cellular response to L-lactate and decreased the effect of D-lactate. Moreover, HCAR1 shRNA-expressing cells produced significantly lower mRNA levels of monocarboxylate transporter 4. Finally, the enhancement of DNA repair and cell survival by lactate was suppressed by pharmacologically inhibiting monocarboxylate transporters using the inhibitor α-cyano-4-hydroxycinnamic acid (α-CHCA).
CONCLUSIONS: Our data indicate that L- and D-lactate present in the uterine cervix may participate in the modulation of cellular DNA damage repair processes and in the resistance of cervical carcinoma cells to anticancer therapy.

Su Y, Qi S, Dou C, et al.
Association of LIG4 and XRCC4 gene polymorphisms with the risk of human glioma in a Chinese population.
Int J Clin Exp Pathol. 2015; 8(2):2057-62 [PubMed] Free Access to Full Article Related Publications
We conducted a case-control study to assess the LIG4 and XRCC4 genes polymorphisms and development of glioma. A case-control study including 162 glioma cases and 324 controls was conducted in a Chinese population. Genotypes of rs10131 and rs1805388 in LIG4 and rs2075685 and rs1805377 in XRCC4 were conducted by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) assay. Conditional logistic regression analysis showed that subjects carrying AA genotype of LIG4 rs10131 was associated with increased risk of glioma when compared with GG genotype, and the OR (95% CI) was 3.26 (1.50-7.23). We found that GA+AA of LIG4 rs10131 was associated with increased risk of glioma in those without family history of cancer, and the OR (95% CI) was 1.78 (1.12-2.83). However, no association was found between variants of LIG4 rs1805388, XRCC4 rs2075685 and XRCC4 rs1805377 and development of glioma. In conclusion, our results suggest that LIG4 rs10131 polymorphism in the DNA repair pathways plays an important role in the risk of glioma in a Chinese population.

Xu F, Han JC, Zhang YJ, et al.
Associations of LIG4 and HSPB1 genetic polymorphisms with risk of radiation-induced lung injury in lung cancer patients treated with radiotherapy.
Biomed Res Int. 2015; 2015:860373 [PubMed] Free Access to Full Article Related Publications
OBJECTIVE: This study aims to explore the correlations of genetic polymorphisms in LIG4 and HSPB1 genes with the radiation-induced lung injury (RILI), especially radiation pneumonitis (RP), in lung cancer patients.
METHODS: A total of 160 lung cancer patients, who were diagnosed with inoperable lung cancer and received radiotherapy, were included in the present study from September 2009 to December 2011. TaqMan Real-Time PCR (RT-PCR) was used to verify the SNPs of LIG4 and HSPB1 genes. Chi-square criterion was used to compare the differences in demographic characteristics, exposure to risk factors, and SNPs genotypes. Crude odds ratios (ORs) with 95% confidence intervals (95% CI) were calculated by logistic regression analysis. All statistical analyses were conducted in SPSS 18.0.
RESULTS: A total of 32 (20.0%) lung cancer patients had RP after receiving radiotherapy. Of the 32 cases, 4 cases were of grade 2, 24 cases were of grade 3, and 4 cases were of grade 4. However, our results indicated that the general condition and treatment of all patients had no significant difference with RP risk (P > 0.05). Meanwhile, our results revealed that there was no significant association between the frequencies of LIG4 rs1805388 and HSPB1 rs2868371 genotype distribution and the risk of RP (P > 0.05).
CONCLUSION: In conclusion, we demonstrated that the genetic polymorphisms in LIG4 rs1805388 and HSPB1 rs2868371 were not obviously correlated with the risk of RP and RILI of lung cancer.

Kim DH, Oh SY, Kim SY, et al.
DNA ligase4 as a prognostic marker in nasopharyngeal cancer patients treated with radiotherapy.
Asian Pac J Cancer Prev. 2014; 15(24):10985-9 [PubMed] Related Publications
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 (±) were 43.1% and 56.9% respectively. The 5-year OS rate of patients with LIG4 (±) were 90% and 67.9%, respectively (p=0.035). The 5-year TTP rate of patients with LIG4 (±) 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.

Newman EA, Lu F, Bashllari D, et al.
Alternative NHEJ Pathway Components Are Therapeutic Targets in High-Risk Neuroblastoma.
Mol Cancer Res. 2015; 13(3):470-82 [PubMed] Related Publications
UNLABELLED: In neuroblastoma, MYCN genomic amplification and segmental chromosomal alterations including 1p or 11q loss of heterozygocity and/or 17q gain are associated with progression and poor clinical outcome. Segmental alterations are the strongest predictor of relapse and result from unbalanced translocations attributable to erroneous repair of chromosomal breaks. Although sequence analysis of affected genomic regions suggests that these errors arise by nonhomologous end-joining (NHEJ) of DNA double-strand breaks (DSB), abnormalities in NHEJ have not been implicated in neuroblastoma pathogenesis. On this basis, the hypothesis that an error-prone mechanism of NHEJ is critical for neuroblastoma cell survival was tested. Plasmid-based DSB repair assays demonstrated efficient NHEJ activity in human neuroblastoma cells with repair products that were error-prone relative to nontransformed cells. Neuroblastoma cells derived from tumorigenic neuroblastic phenotypes had differential DNA repair protein expression patterns compared with nontumorigenic cells. Tumorigenic neuroblastoma cells were deficient in DNA ligase IV (Lig4) and Artemis (DCLRE1C), mediators of canonical NHEJ. Conversely, enzymes required for an error-prone alternative NHEJ pathway (alt-NHEJ), DNA Ligase IIIα (Lig3), DNA Ligase I (Lig1), and PARP1 protein were upregulated. Inhibition of Lig3 and Lig1 led to DSB accumulation and cell death, linking alt-NHEJ to cell survival in neuroblastoma. Neuroblastoma cells demonstrated sensitivity to PARP1 inhibition (PARPi) that paralleled PARP1 expression. In a dataset of human neuroblastoma patient tumors, overexpression of genes encoding alt-NHEJ proteins associated with poor survival.
IMPLICATIONS: These findings provide an insight into DNA repair fidelity in neuroblastoma and identify components of the alt-NHEJ pathway as promising therapeutic targets.

Henríquez-Hernández LA, Valenciano A, Foro-Arnalot P, et al.
Single nucleotide polymorphisms in DNA repair genes as risk factors associated to prostate cancer progression.
BMC Med Genet. 2014; 15:143 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Besides serum levels of PSA, there is a lack of prostate cancer specific biomarkers. It is need to develop new biological markers associated with the tumor behavior which would be valuable to better individualize treatment. The aim of this study was to elucidate the relationship between single nucleotide polymorphisms (SNPs) in genes involved in DNA repair and prostate cancer progression.
METHODS: A total of 494 prostate cancer patients from a Spanish multicenter study were genotyped for 10 SNPs in XRCC1, ERCC2, ERCC1, LIG4, ATM and TP53 genes. The SNP genotyping was made 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: SNPs rs11615 (ERCC1) and rs17503908 (ATM) appeared as risk factors for prostate cancer aggressiveness. Patients wild homozygous for these SNPs (AA and TT, respectively) were at higher risk for developing cT2b - cT4 (OR = 2.21 (confidence interval (CI) 95% 1.47 - 3.31), p < 0.001) and Gleason scores ≥ 7 (OR = 2.22 (CI 95% 1.38 - 3.57), p < 0.001), respectively. Moreover, those patients wild homozygous for both SNPs had the greatest risk of presenting D'Amico high-risk tumors (OR = 2.57 (CI 95% 1.28 - 5.16)).
CONCLUSIONS: Genetic variants at DNA repair genes are associated with prostate cancer progression, and would be taken into account when assessing the malignancy of prostate cancer.

Xie S, Shan XF, Shang K, et al.
Relevance of LIG4 gene polymorphisms with cancer susceptibility: evidence from a meta-analysis.
Sci Rep. 2014; 4:6630 [PubMed] Free Access to Full Article Related Publications
Polymorphisms of LIG4 gene may influence DNA repair ability, thus altering the genetic stability and resulting in carcinogenesis. A growing number of studies have investigated the relevance of LIG4 T9I (rs1805388) and D501D (rs1805386) polymorphisms with cancer risk, however, the results are conflicting. To obtain a comprehensive conclusion, we searched relevant literatures from PubMed, Web of Science, Ovid and Embase databases on May 15, 2014 and performed a meta-analysis. In this meta-analysis, a total of 17 articles were included. Of them, there were 15 studies with 5873 cases and 5771 controls for rs1805388 and 6 studies with 4161 cases and 4881 controls for rs1805386. Overall, our results suggested that there was no obvious relevance of LIG4 T9I polymorphism with cancer susceptibility. However, in subgroup analysis, we found the LIG4 T9I was associated with a slightly decreased cancer risk among Caucasians. As to the rs1805386, the genetic variant had no significant association with cancer risk. In conclusion, despite several limitations, this meta-analysis suggested that LIG4 T9I genetic variant is associated with a decreased risk of cancer among Caucasians, however, the rs1805386 gene polymorphism is not a risk factor of cancer.

Zhang MY, Keel SB, Walsh T, et al.
Genomic analysis of bone marrow failure and myelodysplastic syndromes reveals phenotypic and diagnostic complexity.
Haematologica. 2015; 100(1):42-8 [PubMed] Free Access to Full Article Related Publications
Accurate and timely diagnosis of inherited bone marrow failure and inherited myelodysplastic syndromes is essential to guide clinical management. Distinguishing inherited from acquired bone marrow failure/myelodysplastic syndrome poses a significant clinical challenge. At present, diagnostic genetic testing for inherited bone marrow failure/myelodysplastic syndrome is performed gene-by-gene, guided by clinical and laboratory evaluation. We hypothesized that standard clinically-directed genetic testing misses patients with cryptic or atypical presentations of inherited bone marrow failure/myelodysplastic syndrome. In order to screen simultaneously for mutations of all classes in bone marrow failure/myelodysplastic syndrome genes, we developed and validated a panel of 85 genes for targeted capture and multiplexed massively parallel sequencing. In patients with clinical diagnoses of Fanconi anemia, genomic analysis resolved subtype assignment, including those of patients with inconclusive complementation test results. Eight out of 71 patients with idiopathic bone marrow failure or myelodysplastic syndrome were found to harbor damaging germline mutations in GATA2, RUNX1, DKC1, or LIG4. All 8 of these patients lacked classical clinical stigmata or laboratory findings of these syndromes and only 4 had a family history suggestive of inherited disease. These results reflect the extensive genetic heterogeneity and phenotypic complexity of bone marrow failure/myelodysplastic syndrome phenotypes. This study supports the integration of broad unbiased genetic screening into the diagnostic workup of children and young adults with bone marrow failure and myelodysplastic syndromes.

Ciszewski WM, Wagner W, Kania KD, Dastych J
Interleukin-4 enhances PARP-dependent DNA repair activity in vitro.
J Interferon Cytokine Res. 2014; 34(9):734-40 [PubMed] Free Access to Full Article Related Publications
Eukaryotic cells possess several DNA repair mechanisms, including homologous recombination and the non-homologous end-joining (NHEJ) system. There are two known NHEJ systems. The major mechanism depends on the catalytic unit of DNA-dependent protein kinase (DNA-PKcs) and DNA ligase IV, and an alternative mechanism (B-NHEJ) depends on poly(ADP-ribose) polymerase (PARP). These systems are upregulated by genotoxic agents. Interleukin 4 (IL-4) is an immunoregulatory cytokine that is secreted by immune cells upon contact with certain genotoxic compounds and is known to regulate several genes encoding components of DNA repair systems in human monocytes. We have investigated the possible effects of IL-4 on the DNA repair process within murine and human cells exposed to selected genotoxic compounds. In a series of experiments, including the comet assay, cell surface annexin V staining, analysis of histone H2AX phosphorylation, and a DNA end-joining assay, we observed that IL-4 decreased DNA damage in murine fibroblasts and human glioblastoma cells exposed to genotoxic agents and increased DNA ligation activity in the nuclei of these cells in a process that depended on PARP. These observations suggest that IL-4 is capable of upregulating the alternative NHEJ DNA repair mechanism in murine and human cells.

Jiang YH, Xu XL, Ruan HH, et al.
The impact of functional LIG4 polymorphism on platinum-based chemotherapy response and survival in non-small cell lung cancer.
Med Oncol. 2014; 31(5):959 [PubMed] Related Publications
DNA repair capacity is correlated with the sensitivity of cancer cells toward platinum-based chemotherapy. The aim of this study was to investigate whether single-nucleotide polymorphisms (SNPs) in DNA repair genes NBS1, LIG4, and RAD51 were correlated with tumor response in advanced non-small cell lung cancer (NSCLC) patients in a Chinese population who received platinum-based chemotherapy. The treatment outcomes of 146 advanced NSCLC patients who were treated with platinum-based chemotherapy were evaluated. The polymorphic status of three SNPs was determined by genotyping via the polymerase chain reaction-restriction fragment length polymorphism method. Forty-five patients in the group with the CC genotype (45/90) showed a good response to treatment, while only 18 patients in the CT+TT group (18/55) showed a good response, indicating a substantial differences in the chemotherapy response rate based on the LIG4 Thr9Ile polymorphism (P = 0.042). Patients with the GG genotype for the NSB1 Glu185Gln polymorphism were more sensitive to platinum-based chemotherapy compared with patients with either the CG or CC genotype (P = 0.001). Kaplan-Meier analysis of all patients showed a significant association between the LIG4 Thr9Ile CC polymorphism and superior progression-free survival and overall survival (log-rank P = 0.045 and 0.031, respectively). However, there were no significant differences in survival based on the LIG4 Thr9Ile or the RAD51 135G>C polymorphisms. Polymorphisms in the NSB1 and LIG4 genes may be a predictive marker for treatment response and for advanced NSCLC patients in stage IIIB + IV. The CC genotype of the LIG4 Thr9Ile polymorphism may also serve as an independent prognosis factor.

Usmani N, Leong N, Martell K, et al.
Single-nucleotide polymorphisms studied for associations with urinary toxicity from (125)I prostate brachytherapy implants.
Brachytherapy. 2014 May-Jun; 13(3):285-91 [PubMed] Related Publications
PURPOSE: To identify clinical, dosimetric, and genetic factors that are associated with late urinary toxicity after a (125)I prostate brachytherapy implant.
METHODS AND MATERIALS: Genomic DNA from 296 men treated with (125)I prostate brachytherapy monotherapy was extracted from saliva samples for this study. A retrospective database was compiled including clinical, dosimetric, and toxicity data for this cohort of patients. Fourteen candidate single-nucleotide polymorphism (SNPs) from 13 genes (TP53, ERCC2, GSTP1, NOS, TGFβ1, MSH6, RAD51, ATM, LIG4, XRCC1, XRCC3, GSTA1, and SOD2) were tested in this cohort for correlations with toxicity.
RESULTS: This study identified 217 men with at least 2 years of followup. Of these, 39 patients developed Grade ≥2 late urinary complications with a transurethral resection of prostate, urethral stricture, gross hematuria, or a sustained increase in their International Prostate Symptom Score. The only clinical or dosimetric factor that was associated with late urinary toxicity was age (p = 0.02). None of the 14 SNPs tested in this study were associated with late urinary toxicity in the univariate analysis.
CONCLUSIONS: This study identified age as the only variable being associated with late urinary toxicity. However, the small sample size and the candidate gene approach used in this study mean that further investigations are essential. Genome-wide association studies are emerging as the preferred approach for future radiogenomic studies to overcome the limitations from a candidate gene approach.

Nishida Y, Mizutani N, Inoue M, et al.
Phosphorylated Sp1 is the regulator of DNA-PKcs and DNA ligase IV transcription of daunorubicin-resistant leukemia cell lines.
Biochim Biophys Acta. 2014; 1839(4):265-74 [PubMed] Related Publications
Multidrug resistance (MDR) is a serious problem faced in the treatment of malignant tumors. In this study, we characterized the expression of non-homologous DNA end joining (NHEJ) components, a major DNA double strand break (DSB) repair mechanism in mammals, in K562 cell and its daunorubicin (DNR)-resistant subclone (K562/DNR). K562/DNR overexpressed major enzymes of NHEJ, DNA-PKcs and DNA ligase IV, and K562/DNR repaired DSB more rapidly than K562 after DNA damage by neocarzinostatin (MDR1-independent radiation-mimetic). Overexpressed DNA-PKcs and DNA ligase IV were also observed in DNR-resistant HL60 (HL60/DNR) cells as compared with parental HL60 cells. Expression level of DNA-PKcs mRNA paralleled its protein level, and the promoter activity of DNA-PKcs of K562/DNR was higher than that of K562, and the 5'-region between -49bp and the first exon was important for its activity. Because this region is GC-rich, we tried to suppress Sp1 family transcription factor using mithramycin A (MMA), a specific Sp1 family inhibitor, and siRNAs for Sp1 and Sp3. Both MMA and siRNAs suppressed DNA-PKcs expression. Higher serine-phosphorylated Sp1 but not total Sp1 of both K562/DNR and HL60/DNR was observed compared with their parental K562 and HL60 cells. DNA ligase IV expression of K562/DNR was also suppressed significantly with Sp1 family protein inhibition. EMSA and ChIP assay confirmed higher binding of Sp1 and Sp3 with DNA-PKcs 5'-promoter region of DNA-PKcs of K562/DNR than that of K562. Thus, the Sp1 family transcription factor affects important NHEJ component expressions in anti-cancer drug-resistant malignant cells, leading to the more aggressive MDR phenotype.

Kuhmann C, Li C, Kloor M, et al.
Altered regulation of DNA ligase IV activity by aberrant promoter DNA methylation and gene amplification in colorectal cancer.
Hum Mol Genet. 2014; 23(8):2043-54 [PubMed] Related Publications
Colorectal cancer (CRC) presents as a very heterogeneous disease which cannot sufficiently be characterized with the currently known genetic and epigenetic markers. To identify new markers for CRC we scrutinized the methylation status of 231 DNA repair-related genes by methyl-CpG immunoprecipitation followed by global methylation profiling on a CpG island microarray, as altered expression of these genes could drive genomic and chromosomal instability observed in these tumors. We show for the first time hypermethylation of MMP9, DNMT3A and LIG4 in CRC which was confirmed in two CRC patient groups with different ethnicity. DNA ligase IV (LIG4) showed strong differential promoter methylation (up to 60%) which coincided with downregulation of mRNA in 51% of cases. This functional association of LIG4 methylation and gene expression was supported by LIG4 re-expression in 5-aza-2'-deoxycytidine-treated colon cancer cell lines, and reduced ligase IV amounts and end-joining activity in extracts of tumors with hypermethylation. Methylation of LIG4 was not associated with other genetic and epigenetic markers of CRC in our study. As LIG4 is located on chromosome 13 which is frequently amplified in CRC, two loci were tested for gene amplification in a subset of 47 cases. Comparison of amplification, methylation and expression data revealed that, in 30% of samples, the LIG4 gene was amplified and methylated, but expression was not changed. In conclusion, hypermethylation of the LIG4 promoter is a new mechanism to control ligase IV expression. It may represent a new epigenetic marker for CRC independent of known markers.

Henríquez-Hernández LA, Valenciano A, Foro-Arnalot P, et al.
Polymorphisms in DNA-repair genes in a cohort of prostate cancer patients from different areas in Spain: heterogeneity between populations as a confounding factor in association studies.
PLoS One. 2013; 8(7):e69735 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: Differences in the distribution of genotypes between individuals of the same ethnicity are an important confounder factor commonly undervalued in typical association studies conducted in radiogenomics.
OBJECTIVE: To evaluate the genotypic distribution of SNPs in a wide set of Spanish prostate cancer patients for determine the homogeneity of the population and to disclose potential bias.
DESIGN SETTING AND PARTICIPANTS: A total of 601 prostate cancer patients from Andalusia, Basque Country, Canary and Catalonia were genotyped for 10 SNPs located in 6 different genes associated to DNA repair: XRCC1 (rs25487, rs25489, rs1799782), ERCC2 (rs13181), ERCC1 (rs11615), LIG4 (rs1805388, rs1805386), ATM (rs17503908, rs1800057) and P53 (rs1042522). The SNP genotyping was made in a Biotrove OpenArray® NT Cycler.
OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Comparisons of genotypic and allelic frequencies among populations, as well as haplotype analyses were determined using the web-based environment SNPator. Principal component analysis was made using the SnpMatrix and XSnpMatrix classes and methods implemented as an R package. Non-supervised hierarchical cluster of SNP was made using MultiExperiment Viewer.
RESULTS AND LIMITATIONS: We observed that genotype distribution of 4 out 10 SNPs was statistically different among the studied populations, showing the greatest differences between Andalusia and Catalonia. These observations were confirmed in cluster analysis, principal component analysis and in the differential distribution of haplotypes among the populations. Because tumor characteristics have not been taken into account, it is possible that some polymorphisms may influence tumor characteristics in the same way that it may pose a risk factor for other disease characteristics.
CONCLUSION: Differences in distribution of genotypes within different populations of the same ethnicity could be an important confounding factor responsible for the lack of validation of SNPs associated with radiation-induced toxicity, especially when extensive meta-analysis with subjects from different countries are carried out.

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