X-ray Cross-complementing Group Research Articles

Significant association of XRCC4 single nucleotide polymorphisms with prostate cancer susceptibility in Taiwanese males

The DNA repair gene X-ray cross-complementing group 4 (XRCC4), a member of the non-homologous end-joining (NHEJ) repair system, plays a major role in the repair of the double-strand breaks of the DNA sequence. This gene is critical to the maintenance of overall genome stability, and is also thought to play a key role in human carcinogenesis. In this case-control study, several novel polymorphic variants of XRCC4, including C-1622T (rs7727691), G-1394T (rs6869366), C-571T (rs2075686) and intron3 DIP (rs28360071), were investigated, and the correlation of these variants to prostate cancer susceptibility in a Taiwanese population was observed. A total of 134 prostate cancer patients were recruited along with 134 age-matched healthy controls, and the association of their selected genotypes with susceptibility to prostate cancer was determined. The G-1394T variant of XRCC4 proved, after analysis of the frequencies of each variant in the prostate cancer and control groups, to be a significant single nucleotide polymorphism (SNP) in prostate carcinogenesis. Our data clearly indicate that the heterogeneous G of G-1394T increases the risk of suceptibility to prostate cancer (P=0.0106), while no difference in distribution of XRCC4 C-1622T (rs7727691), C-571T (rs2075686) or intron3 DIP (rs28360071) between the prostate cancer and control groups was found. In conclusion, our findings suggest that the G allele of XRCC4 G-1394T may be responsible for prostate carcinogenesis, and could be useful in the early detection and prevention of the disease.

The Polymorphism of XRCC3 Codon 241 and AFB1-Related Hepatocellular Carcinoma in Guangxi Population, China

The relationship between aflatoxin B1 (AFB1) exposure and hepatocellular carcinoma (HCC) has been previously demonstrated and supported with strong epidemiological evidence. However, the role of genetic polymorphism of X-ray cross-complementing group 3 (XRCC3) codon 241 (namely: Thr241Met), which may be involved in the repair of DNA double-strand breaks caused by carcinogens such as AFB1, been less well elaborated. We conducted a case-control study including 491 cases and 862 controls to evaluate the associations between this polymorphism and HCC risk for Guangxi population by means of polymerase chain reaction-restriction fragment length polymorphism analysis. We found that individuals with the XRCC3 genotypes with codon 241 Met (namely XRCC3-TM or XRCC3-MM) had an increased risk of HCC than those with the homozygote of XRCC3 codon 241 Thr alleles (namely XRCC3-TT, adjusted odds ratios 2.22 and 7.19; 95% confidence intervals 1.72-2.88 and 4.52-11.42, respectively). The risk of HCC, moreover, did appear to differ more significantly among individuals featuring high-level AFB1-DNA adducts, whose adjusted odds ratios (95% confidence intervals) were 11.59 (5.73-23.47) and 37.54 (16.32-86.32), respectively. These findings support the hypothesis that the XRCC3 Thr241Met polymorphism may be associated with the risk of AFB1-related HCC among the Guangxi population.

XRCC1 and XRCC3 variants and risk of glioma and meningioma

Several single nucleotide polymorphisms (SNPs) affecting DNA repair capacity and modifying cancer susceptibility have been described. We evaluated the association of SNPs Arg194Trp, Arg280His, and Arg399Gln in the X-ray cross-complementing group 1 (XRCC1) and Thr241Met in the X-ray cross-complementing group 3 (XRCC3) DNA repair genes with the risk of brain tumors. The Caucasian study population consisted of 701 glioma (including 320 glioblastoma) cases, 524 meningioma cases, and 1,560 controls in a prospective population-based case-control study conducted in Denmark, Finland, Sweden, and the UK. The studied SNPs were not significantly associated with the risk of brain tumors. The highest odds ratios (ORs) for the associations were observed between the homozygous variant genotype XRCC1 Gln399Gln and the risk of glioma (OR = 1.32; 95% confidence interval, CI, 0.97-1.81), glioblastoma (OR = 1.48; 95% CI, 0.98-2.24), and meningioma (OR = 1.34; 95% CI, 0.96-1.86). However, in pair-wise comparisons a few SNP combinations were associated with the risk of brain tumors: Among others, carriers of both homozygous variant genotypes, i.e., XRCC1 Gln399Gln and XRCC3 Met241Met, were associated with a three-fold increased risk of glioma (OR = 3.18; 95% CI, 1.26-8.04) and meningioma (OR = 2.99; 95% CI, 1.16-7.72). In conclusion, no significant association with brain tumors was found for any of the polymorphisms, when examined one by one. Our results indicated possible associations between combinations of XRCC1 and XRCC3 SNPs and the risk of brain tumors.

DNA Repair Polymorphisms XRCC1 and MGMT and Risk of Adult Gliomas

X-ray cross complementing group 1 (XRCC1) and O6-methylguanine-DNA methyltransferase (MGMT) are pivotal repair genes focused on repairing lesions due to ionizing radiation, alkylating agents, and oxidative DNA damage, risk factors previously linked to gliomas. Using the population based San Francisco Adult Glioma study, we evaluated associations between XRCC1 Arg399Gln, MGMT Leu84Phe, and MGMT Ile143Val polymorphisms with glioma risk among white cases (n = 441 to 453) and controls (n = 487 to 526). We found no evidence of an association between XRCC1 genotypes and glioma. We observed a weak positive association for the MGMT Leu84Phe polymorphism (Leu or Phe/Phe versus Leu/Leu: adjusted OR = 1.26; CI 0.90–1.75) and the MGMT Ile143Val polymorphism (Ile or Val/Val versus Ile/Ile: adjusted OR = 1.20; CI 0.85–1.71).

DNA-repair and carcinogen-metabolising enzymes genetic polymorphisms as an independent risk factor for hepatocellular carcinoma in Caucasian liver-transplanted patients

We studied polymorphisms of three genes, UDP-glucuronosyltransferase1A7 ( UGT1A7), Glutathione-S-transferaseM1 ( GSTM1) and X-Ray Cross Complementing group 1 ( XRCC1), involved in detoxification of xenobiotics or DNA-repair in a population of 133 liver-transplanted patients, including 56 patients with hepatocellular carcinoma (HCC) and 77 without HCC, and in 89 healthy controls originating from the south of France. Multiple logistic regression analysis showed that, among liver-transplanted patients, interactions between XRCC1-G/G or -G/A and GSTM1-nul polymorphisms were independently associated with hepatocellular carcinoma ( p interaction = 0.027) concurrently with increasing age ( p < 0.001), male sex ( p = 0.037) and chronic hepatitis B or C virus infection ( p = 0.018 and p = 0.001 respectively). On the contrary, no relationship was observed between UGT1A7 polymorphisms considered alone or in interaction with GSTM1 or XRCC1 polymorphisms and HCC. This suggests that concomitant impaired metabolism of carcinogenic compounds and impaired DNA-repair function play an important role in liver carcinogenesis in high-risk cirrhotic patients originating from the south of France.

Polymorphisms of DNA repair genes XPD and XRCC1 and risk of cataract development

The association between oxidative or ultraviolet (UV) light induced DNA damage in the lens epithelium and the development of lens opacities, and the existence of DNA repair in lens epithelial cells have been reported. Polymorphisms of DNA repair enzymes may affect repair efficiency. In this study, we aimed to determine the frequency of polymorphisms in two DNA repair enzyme genes, xeroderma pigmentosum complementation group D (XPD) codon 751 and X-ray cross-complementing group 1 (XRCC1) codon 399, in a sample of Turkish patients with maturity onset cataract. By using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP), we analysed XRCC1-Arg399Gln and XPD-Lys751Gln polymorphisms in 195 patients with cataract (75 patients with cortical, 53 with nuclear, 37 with posterior subcapsular, and 30 with mixed type) and in 194 otherwise healthy control group of similar age. There was a significant difference between frequencies for XPD-751 Gln/Gln genotype in cataract patients (12%) and healthy controls (20%) ( P = 0.008, OR = 0.40, 95% CI = 0.20–0.81). After stratification by the cataract subtypes, XPD-751 Gln/Gln genotype was found to be significantly different in patients with cortical (4%) type cataract in respect to control subjects (20%) ( P = 0.038, OR = 0.16, 95% CI = 0.04–0.64). In addition, the allele frequency of the C (Gln)-allele of XPD-Lys751Gln was found to be significantly different in mixed type cataract group ( P = 0.008, OR = 0.48, 95% CI: 0.26–0.90). No statistically significant difference was found for the genotypic and allelic distributions of the polymorphisms in XRCC1 gene between the groups. These findings suggest that polymorphism in XPD codon 751 may be associated with the development of maturity onset cataract.

XRCC1 codon 399 and ERCC2 codon 751 polymorphism, smoking, and drinking and risk of esophageal squamous cell carcinoma in a North Indian population

XRCC1 (X-ray cross-complementing group 1) codon 399 and ERCC2 (excision repair cross-complementing group 2) codon 751 polymorphisms were studied in esophageal squamous cell carcinoma (ESQCC) in a North Indian population. Peripheral blood samples of 120 cases and 160 age-and-gender matching controls were collected from North India and the two polymorphisms were studied by means of polymerase chain reaction–restriction fragment length polymorphism techniques. The data were analyzed with a logistic regression model. The XRCC1 codon 399 Gln/Gln genotype was significantly associated with reduced risk of ESQCC (OR = 0.31, 95% CI = 0.12–0.78, P = 0.01). In smokers, the XRCC1 Arg/Gln genotype was marginally and statistically nonsignificantly (OR = 1.5) associated with increased risk of this cancer. In drinkers, the XRCC1 Gln/Gln genotype was significantly protective (OR = 0.06, 95% CI = 0.007–0.605, P = 0.03), whereas ERCC2 ( Lys/Gln– Gln/Gln) was marginally associated with increased risk (OR = 2.1, 95% CI = 0.46–9.44). Upon analysis of gene–gene interaction, a relationship was observed, although statistically nonsignificant, between combined genotypes of XRCC1 ( Arg/Gln– Gln/Gln)– ERCC2 Gln/Gln (OR = 0.33, 95% CI = 0.09–1.16) and XRCC1 ( Gln/Gln)– ERCC2 ( Lys/Gln) (OR = 0.36, 95% CI = 0.11–1.17) and reduced risk of ESQCC in the North Indian population. These observations suggest that the Gln/Gln genotype of XRCC1 might play an important role in DNA repair in ESQCC.

Chk2 Mediates Stabilization of the FoxM1 Transcription Factor To Stimulate Expression of DNA Repair Genes

The forkhead box M1 (FoxM1) transcription factor regulates expression of cell cycle genes essential for DNA replication and mitosis during organ repair and cancer progression. Here, we demonstrate that FoxM1-deficient (-/-) mouse embryonic fibroblasts and osteosarcoma U2OS cells depleted in FoxM1 levels by small interfering RNA transfection display increased DNA breaks, as evidenced by immunofluorescence focus staining for phosphospecific histone H2AX. FoxM1-deficient cells also exhibit stimulation of p53 transcriptional activity, as evidenced by increased expression of the p21(cip1) gene. FoxM1-deficient cells display reduced expression of the base excision repair factor X-ray cross-complementing group 1 (XRCC1) and breast cancer-associated gene 2 (BRCA2), the latter of which is involved in homologous recombination repair of DNA double-strand breaks. Furthermore, FoxM1 protein is phosphorylated by checkpoint kinase 2 (Chk2) in response to DNA damage. This phosphorylation of FoxM1 on serine residue 361 caused increased stability of the FoxM1 protein with corresponding increased transcription of XRCC1 and BRCA2 genes, both of which are required for repair of DNA damage. These results identify a novel role for FoxM1 in the transcriptional response during DNA damage/checkpoint signaling and show a novel mechanism by which Chk2 protein regulates expression of DNA repair enzymes.

Mammary carcinogenesis in transgenic mice expressing a dominant-negative mutant of DNA polymerase β in their mammary glands

DNA polymerase beta (polbeta) is a major contributor to mammalian DNA damage repair through its gap-filling DNA synthesis and 5'-deoxyribose phosphate lyase activities. In this way, polbeta plays pivotal roles in the repair of oxidative DNA damage, replication, embryonic survival, neuronal development, meiosis, apoptosis and telomere function. A 36 kDa truncated polbetaDelta protein is expressed in human colorectal, breast, lung and renal carcinomas, but not in normal matched tissues. Interestingly, a binary protein-protein complex of polbetaDelta and X-ray cross-complementing group 1 acts as dominant-negative mutant. In this study, the potential tumorigenic activity of polbetaDelta was examined in nude and transgenic mouse models. Mouse embryonic fibroblasts (MEFs) expressing polbetaDelta in the absence of endogenous polbeta exhibited increased susceptibility to N-methyl-N-nitrosourea (MNU)-induced morphological transformation as compared with cells expressing wild-type (WT) polbeta. This was accompanied by reduced gap-filling DNA synthesis activity. Anchorage-independent transformed cells derived from polbetaDelta-expressing MEFs induced 100% tumor occurrence in nude mice. To support these data, we established transgenic mice expressing polbetaDelta specifically in the mammary glands from a whey acidic protein promoter-driven transgene. This is the first report of transgenic mice with tissue-specific expression of polbetaDelta. MNU-induced tumor formation was analyzed in transgenic mice expressing polbetaDelta together with endogenous WT polbeta in their mammary glands and in normal control mice expressing only WT polbeta. The latent period of tumor appearance was markedly shorter and tumor incidence was significantly higher in transgenic animals than in control animals treated under the same conditions. These results indicate that cells expressing the mutant polbetaDelta display an enhanced sensitivity to MNU that probably underlies an increased susceptibility to tumorigenesis.

Rapid analysis of XRCC1 polymorphisms using real-time polymerase chain reaction

DNA repair plays a critical role in protecting the genome from carcinogens or ionizing radiation. Three coding polymorphisms at codons 194, 280, and 399 in X-ray cross-complementing group 1 (XRCC1) DNA repair gene have been identified that may affect DNA repair and alter cancer susceptibility. In order to study their role in molecular-epidemiology studies we developed a single-step procedure for genotyping these polymorphisms using real-time polymerase chain reaction (rt-PCR) and subsequent melting curve analysis. Genotypes of 622 unrelated Caucasians without prior history of cancer were determined by real-time PCR and compared to genotypes obtained by restriction fragment length polymorphism PCR. In the population studied, the allele frequency of the XRCC1 26304 site (C-->T) of codon 194 in exon 6 was 0.065, the allele frequency of the XRCC1 27466 site (G-->A) of codon 280 in exon 9 was 0.048 and of the XRCC1 28152 site (G-->A) of codon 399 in exon 10 was 0.35. There was no disagreement between the two methods. These findings confirm the real-time fluorescence PCR method as a rapid and reliable assay for the analysis of large numbers of samples.

SUMO Modification of Human XRCC4 Regulates Its Localization and Function in DNA Double-Strand Break Repair

The nonhomologous end-joining (NHEJ) pathway is responsible for rejoining the majority of double-strand breaks in mammalian cells, including the programmed breaks introduced by V(D)J recombination. The regulation of the enzymatic activities associated with this recombination pathway is still largely unknown. Here we report that human XRCC4 (for X-ray cross-complementation group 4), a protein essential for NHEJ, is subject to posttranslational protein modification. The modifier peptide, SUMO, can be added to XRCC4 both in vitro and in vivo. The site of modification is mapped to lysine 210 by using specific mutagenesis. A protein mutated such that it cannot be SUMOylated remains localized in the cytoplasm rather than accumulating in the nucleus. Cells expressing only the mutated protein are radiation sensitive and fail to complete V(D)J recombination. Genetic fusion of the SUMO sequence to the C terminus of the mutant restores nuclear localization and radiation resistance. The modification may serve a regulatory role. Our finding fits with an emerging literature associating SUMO modification with the control of the repair and recombination associated with DNA breaks.

A prospective study of XRCC1(X-ray cross-complementing group 1) polymorphisms and breast cancer risk

IntroductionThe gene XRCC1 (X-ray repair cross-complementing group 1) encodes a protein involved in DNA base excision repair. Two non-synonymous polymorphisms in XRCC1 (Arg194Trp and Arg399Gln) have been shown to alter DNA repair capacity in some studies in vitro. However, results of previous association studies of these two XRCC1 variants and breast cancer have been inconsistent. We examined the association between polymorphisms in XRCC1 and breast cancer in the American Cancer Society Cancer Prevention Study II (CPS-II) Nutrition Cohort, a large prospective study of cancer incidence in the USA.MethodsAmong the 21,965 women who were cancer-free in 1992 and gave blood between 1998 and 2001, 502 postmenopausal breast cancer cases were diagnosed between 1992 and 2001; 502 controls were matched to cases on age, race/ethnicity, and date of blood collection. Genotyping on DNA extracted from buffy coat was performed with Taqman. Conditional logistic regression was used to examine the association between each polymorphism and breast cancer risk controlling for breast cancer risk factors. We also examined whether factors associated with DNA damage, such as smoking and antioxidant intake, modified the association between XRCC1 polymorphisms and breast cancer.ResultsWe observed a significant inverse association between Trp194 carriers (Trp/Trp and Trp/Arg) compared with Trp194 non-carriers in relation to breast cancer (Arg/Arg) (odds ratio (OR) 0.62, 95% confidence interval (CI) 0.40 to 0.95). The inverse association between breast cancer and Trp194 carriers compared with non-carriers was slightly stronger among smokers (OR 0.47, 95% CI 0.24 to 0.94) than never smokers (OR 0.78, 95% CI 0.43 to 1.40). An increased risk associated with the Arg399Gln polymorphism (Gln/Gln versus Arg/Arg) was observed only among women who reported ever smoking cigarettes (OR 2.76, 95% CI 1.36 to 5.63), and not in women who were lifelong non-smokers (OR 0.64, 95% CI 0.33 to 1.26). No other factor examined modified the association between XRCC1 polymorphisms and breast cancer risk.ConclusionOur results support the hypothesis that genetic variation in XRCC1, particularly in Arg194Trp, may influence postmenopausal breast cancer risk. In our study, genetic variation in XRCC1 Arg399Gln was associated with breast cancer risk only among women with a history of smoking cigarettes.

Polymorphisms in DNA Repair Genes, Medical Exposure to Ionizing Radiation, and Breast Cancer Risk

An epidemiologic study was conducted to determine whether polymorphisms in DNA repair genes modify the association between breast cancer risk and exposure to ionizing radiation. Self-reported exposure to ionizing radiation from medical sources was evaluated as part of a population-based, case-control study of breast cancer in African-American (894 cases and 788 controls) and White (1,417 cases and 1,234 controls) women. Genotyping was conducted for polymorphisms in four genes involved in repair of radiation-induced DNA damage, the double-strand break repair pathway: X-ray cross-complementing group 3 (XRCC3) codon 241 Thr/Met, Nijmegen breakage syndrome 1 (NBS1) codon 185 Glu/Gln, X-ray cross-complementing group 2 (XRCC2) codon 188 Arg/His, and breast cancer susceptibility gene 2 (BRCH2) codon 372 Asn/His. Allele and genotype frequencies were not significantly different in cases compared with controls for all four genetic polymorphisms, and odds ratios for breast cancer were close to the null. Combining women with two, three, and four variant genotypes, a positive association was observed between breast cancer and number of lifetime mammograms (P(trend) < 0.0001). No association was observed among women with zero or one variant genotype (P = 0.86). Odds ratios for radiation treatments to the chest and number of lifetime chest X-rays were slightly elevated but not statistically significant among women with two to four variant genotypes. The study has several limitations, including inability to distinguish between diagnostic and screening mammograms or reliably classify prediagnostic mammograms and chest X-rays in cases. Prospective studies are needed to address whether common polymorphisms in DNA repair genes modify the effects of low-dose radiation exposure from medical sources.

Polymorphisms in the DNA repair gene XRCC1 and survival of non-small cell lung cancer

9585 Background: X-ray cross-complementing group 1 (XRCC1) protein is known to be mainly involved in BER(base excision repair) of DNA repair process. We investigated the association of three polymorphisms (codon 194, 280, and 399) of XRCC1 with lung cancer, whether these polymorphisms have an effect on survival of lung cancer patients received radiotherapy. Methods: 229 lung cancer patients with NSCLC in stage I-IV were recruited at Asan Medical Center and followed up at least every 3 months from the time of study entry. Genotyping was performed by single base primer exclusion assay using SNapShot Kit with blood samples from all patients. Kaplan-Meier survival curve was used for polymorphism effect on progression-free and overall survival. Hazard ratio by Cox-proportional hazard regression was calculated after adjustment for age, gender, histology, stage, and alcohol consumption. These variables were selected through the univariate analysis performed previously. The haplotype of XRCC1 polymorphisms was estimated by PHASE version 2.1. Results: The subjects were consisted of 191(83.4%) males and 38(16.6%) females. The median age was 62 (range 26 - 88) and 60% of patients were included in stage I-IIIa. More than 85% of patients had squamous cell carcinoma and adenocarcinoma. The mean survival time was 20.2 months and 22.5 months in progression-free and overall survival, respectively. XRCC1 codon 194, histology, and stage were shown to be a significant predictor in progression-free survival and alcohol consumption seemed to have protective effect significantly (p=0.028). The six haplotypes among XRCC1 polymorphisms (194, 280, and 399) were estimated by PHASE v.2.1. The patients with the haplotype pairs other than homozygous TGG haplotype pairs seemed to survive longer significantly compared with those with them (p=0.04). Conclusions: In the present study, we suggest that polymorphisms of XRCC1 have an effect on survival of lung cancer patients treated with radiotherapy and the effect appears more strongly considering haplotype pairs. No significant financial relationships to disclose.

Comparison of methods for pharmacogenomics: SNaPshot, SNPstream UHT, Nanogen, and RFLP

The inter-individual variation of response to cancer chemotherapy and radiation therapy has a substantial genetic component and is a subject of pharmacogenetic studies. Our goal is to develop assays to analyze selected single nucleotide polymorphisms (SNPs) in genes with proven relevance for pharmacogenetics. Today's research in the field needs technological platforms for which the demands both in terms of quality and throughput are high. Pharmacogenomics utilizes various genotyping techniques as well as gene-expression studies in studying the effect of different pharmaceuticals as well as the pathways that influence them. Here we provide an overview of the platforms currently in use, and discuss their efficiency, precision and technological stability. The amount of hands-on time needed and the cost-effectiveness are discussed. We also compared the success rate of several methods. SNaPshot is a homogeneous-phase-based primer extension method and SNPstream UHT is a solid-phase-based primer extension method. The Nanogen chip employs binding of a biotinylated probe to a chip coated with hydrogel enriched with streptavidin. This universal design presents the possibility to perform both genotyping as well as gene-expression experiments, even on the same chip. Results were compared with the classical enzymatic restriction enzyme fragment polymorphism (RFLP) assay. The initial set included eight SNPs in the X-ray cross-complementing group 1 protein, XRCC1; APEX nuclease (multifunctional DNA repair enzyme) 1, APEX1; multidrug resistance gene, MDR1; gluthation-S-transferase P1, GSTP1; and tumor protein p53, TP53. Functional SNPs in these genes have been shown to influence the therapeutic effect of a series of anti-cancer drugs such as 5-fluorouracyl, doxorubicin, etoposide, thioguanine and irinotekan. Three series of 36 breast cancer patients treated with 5-fluorouracyl and mitomycin, of 92 breast cancer patients treated with doxorubicin and of 109 control individuals have been genotyped. This resulted in 1527 genotypes. Of these, 391 had been analysed by SNaPshot, 900 by SNPstream UHT, 454 by Nanogen and 966 by RFLP. The success rate was 91% for SNaPshot, 97% for SNPstream UHT, 96% for Nanogen, and 99% for RFLP. When comparing the methods pairwise, the lowest variation was observed between SNPstream UHT and Nanogen (0.4%). SNPstream UHT and Nanogen had similar rates of discrepancy when compared with RFLP: 3.2% and 2.6%, respectively. Close re-analysis of those samples revealed false calls due to incomplete cutting during the RFLP. The highest observed dis-concordance observed was between SNaPshot and SNPstream UHT (8.9%). Careful evaluation of genotyping quality is needed both for large epidemiological studies and smaller clinical trials, and especially in prospective pharmacogenetic studies of separate individuals in clinical settings.

The Association of XRCC1 Haplotypes and Chromosomal Damage Levels in Peripheral Blood Lymphocyte among Coke-Oven Workers

Theoretically, a haplotype has a higher level of heterozygosity than individual single nucleotide polymorphism (SNP) and the association study based on the haplotype may have an increased power for detecting disease associations compared with SNP-based analysis. In this study, we investigated the effects of four haplotype-tagging SNPs (htSNP) and the inferred haplotype pairs of the X-ray cross-complementing group 1 (XRCC1) gene on chromosome damage detected by the cytokinesis-block micronucleus assay. The study included 141 coke-oven workers with exposure to a high level of polycyclic aromatic hydrocarbons and 66 nonexposed controls. The frequencies of total MN and MNed cells were borderline associated with the Arg(194)Trp polymorphism (P = 0.053 and P = 0.050, respectively) but not associated with the Arg(280)His, Arg(399)Gln and Gln(632)Gln polymorphisms among coke-oven workers. Five haplotypes, including CGGG, TGGG, CAGG, CGAG, and CGGA, were inferred based on the four htSNPs of XRCC1 gene. The haplotype CGGG was associated with the decreased frequencies of total MN and MNed cells, and the haplotypes TGGG and CGAG were associated with the increased frequencies of total MN and MNed cells with adjustment for covariates among coke-oven workers. This study showed that the haplotypes derived from htSNPs in the XRCC1 gene were more likely than single SNPs to correlate with the polycyclic aromatic hydrocarbon-induced chromosome damage among coke-oven workers.

The SOD2 Val/Val genotype enhances the risk of nonsmall cell lung carcinoma by p53 and XRCC1 polymorphisms

Exogenous reactive oxygen species (ROS) induces DNA damage. Manganese superoxide dismutase (SOD2) catalyzes the dismutation of superoxide radicals, a major type of ROS, into hydrogen peroxide. p53 is a tumor suppressor gene, and X-ray cross-complementing group 1 (XRCC1) is involved in the base-excision repair of ROS-induced DNA damage. The authors investigated whether the SOD2 Ala16Val polymorphism modifies the associations between p53 Arg72Pro and XRCC1 Arg399Gln polymorphisms and the risk of nonsmall cell lung carcinoma (NSCLC) in a case-control study of 935 Caucasian patients with NSCLC and 1233 healthy control participants. The results were analyzed using logistic regression models that were adjusted for possible confounding variables. There was no association between p53 or XRCC1 polymorphism and NSCLC risk for individuals with SOD2 Ala/Ala or Ala/Val genotype. For individuals with the SOD2 Val/Val genotype, greater risks were found in association with p53 (variant Pro allele vs. Arg/Arg), XRCC1 (variant Gln allele vs. Arg/Arg), and the combination of the two polymorphisms ("double variant" vs. "double wild type"), with the adjusted odds ratios (ORs) of 1.84 (95% confidence interval [95% CI], 1.20-2.82), 1.39 (95% CI, 0.98-2.21), and 2.54 (95% CI, 1.38-4.68), respectively. Furthermore, the greater risk for the double variant of p53 and XRCC1 in the SOD2 Val/Val genotype group was specific only for patients with adenocarcinoma and not for patients with squamous cell carcinoma, with adjusted ORs of 3.31 (95% CI, 1.68-6.51) and 0.69 (95% CI, 0.24-2.02), respectively. The SOD2 Val/Val genotype may increase the risk of NSCLC carried by XRCC1 and p53 polymorphisms, particularly for adenocarcinoma.

Phosphorylation and Regulation of DNA Ligase IV Stability by DNA-dependent Protein Kinase

DNA ligase IV (Lig4), x-ray cross-complementation group 4 (XRCC4), and DNA-dependent protein kinase (DNA-PK) are essential mammalian nonhomologous end joining proteins used for V(D)J recombination and DNA repair. Previously a Lig4 peptide was reported to be an in vitro substrate for DNA-PK, but the phosphorylation state of Lig4 protein in vivo is not known. In this study, we report that a full-length Lig4 construct was expressed as a phosphoprotein in the cell. Also the full-length Lig4 protein, in complex with XRCC4, was an in vitro substrate for DNA-PK. Using tandem mass spectrometry, we identified a DNA-PK phosphorylation site at Thr-650 in human Lig4 and a potential second phosphorylation site at Ser-668 or Ser-672. Phosphorylation of Lig4 per se was not required for Lig4 DNA end joining activity. Substitution of these amino acids with alanine, individually or in combination, led to changes in Lig4 protein stability of mouse Lig4. The phosphomimetic mutation S650D returned Lig4 stability to that of the wild-type protein. Furthermore DNA-PK was found to negatively regulate Lig4 protein stability. Our results suggest that Lig4 stability is regulated by multiple factors, including interaction with XRCC4, phosphorylation status, and possibly Lig4 conformation.

DNA repair polymorphism XRCC1 and risk of recurrence of head and neck cancer

Statement of the Problem: Morbidity and mortality from squamous cell carcinoma of the head and neck (SCCHN) remain a significant public health problem. Almost 50% of the 40,400 newly diagnosed cases this year in the United States will end in either death or disease recurrence. Identification of patients at the time of diagnosis likely to undergo disease recurrence could help in decreasing morbidity and mortality. Genetic variability in repairing DNA damage may be an important prognostic indicator since DNA repair plays an important role in maintaining genomic stability. Materials and Methods: A prospective university cohort of 190 men and women with newly diagnosed SCCHN were enrolled for study and genotyped for two polymorphisms of a gene involved in DNA repair: X-ray cross complementing group 1 (XRCC1). Two polymorphisms have been identified at XRCC1: at codon 194, an arginine to tryptophan change in exon 6, and at codon 399, an arginine to glutamine change in exon 10. DNA was collected from either buccal swabs or serum lymphocytes. Polymorphisms of XRCC1 codon 194 and 399 genotypes were examined utilizing multiplex polymerase chain reaction and restriction fragment length polymorphism methodologies. Clinical information was collected on vital status, TNM stage, lymph node involvement, grade, and treatment. Disease recurrence was classified by the treating surgeon. Method of Data Analysis: Cox proportional hazards models were estimated utilizing SAS software. Results: Follow up time for the cohort ranged from 37 days to 64 months with an estimated overall median survival time of 42 months. Of the 190 patients enrolled in the study, three were lost to follow up. During the follow up period, 44 patients (23%) were diagnosed with disease recurrence. Of all variables examined, age, marital status, stage, distant metastasis, tumor size, therapy, and the XRCC1 399 GLN allele were predictive of disease recurrence. After multivariate modeling, individuals with the 399 GLN allele were 2.4 times less likely to have disease recurrence after adjustment for age and treatment. Conclusion: DNA repair is an important process in the management of cellular genomic instability. Our data suggest that the 399 GLN allele of the DNA repair gene XRCC1 is a strong predictor of disease recurrence. Further studies are needed to elucidate the 399 GLN repair pathways. References Olshan A, Watson M, Weissler M, et al: XRCC1 polymorphisms and head and neck cancer. Cancer Lett 178:181, 2002 Cheng L, Sturgis E, Eicher S, et al: Expression of nucleotide excision repair genes and the risk for squamous cell carcinoma of the head and neck. Cancer 94:393, 2002 Yu Z, Chen J, Ford B, et al: Human DNA repair systems: An overview. Environ Mol Mutagenesis 33:3, 1999 Funding Source: NIH grant CA61188; NIEHS grant P30ES10126; Oral and Maxillofacial Surgery Foundation.

Gene-environment interactions between the smoking habit and polymorphisms in the DNA repair genes, APE1 Asp148Glu and XRCC1 Arg399Gln, in Japanese lung cancer risk.

APE1 (apurinic/apyrimidinic endonuclease 1) and XRCC1 (X-ray cross-complementing group 1) are DNA repair proteins that play important roles in the base excision repair (BER) pathway. Polymorphisms in their encoding genes are associated with altered DNA repair capacity and thus may impact on cancer risk. In the present case-control study with 178 Japanese incident lung cancer cases and 449 age- and sex-matched controls, we investigated the gene-environment interaction among APE1 Asp148Glu, XRCC1 Arg399Gln and smoking habit in lung cancer risk. The results were analyzed by using conditional logistic regression models, adjusted for age, sex and smoking status. The adjusted odds ratio for the current smokers with APE1 148Asp/Asp, Asp/Glu and Glu/Glu genotype as compared with the never smokers with the Asp/Asp genotype were 3.01 (95% CI 1.39-6.51, P = 0.005), 2.73 (95% CI 1.29-5.77, P = 0.008) and 7.33 (95% CI 2.93-18.3, P < 0.001), respectively. The gene-environment interaction between current smoking and APE1 148Glu/Glu genotype was statistically significant (OR 3.59, 95% CI 1.28-10.1, P = 0.015). When APE1 Asp148Glu and XRCC1 Arg399Gln polymorphisms were evaluated together, the adjusted odds ratios for the current smokers with 0-1, 2 and 3-4 of APE1 148Glu or XRCC1 399Gln alleles as compared with never smokers with the 0 of these alleles were 2.96 (95% CI 1.57-5.58, P = 0.001), 3.86 (95% CI 1.85-8.05, P < 0.001) and 6.01 (95% CI 2.25-16.1, P < 0.001), respectively. The gene-environment interaction between current smoking and three or more APE1 148Glu or XRCC1 399Gln alleles was statistically significant (OR 2.44, 95% CI 1.00-9.22, P = 0.049). The OR for the gene-environment interaction of Glu/Glu genotype of APE1 codon 148 with heavy smoking was 1.04 (95% CI 0.38-2.90, P = 0.936) and that with light smoking was 2.67 (95% CI 1.00-7.68, P = 0.049). These results suggest that APE1 Asp148Glu and XRCC1 Arg399Gln polymorphisms might modify the risk of lung cancer attributable to cigarette smoking exposure.