Polymorphisms in the DNA repair gene XRCC1 and age-related disease

Simultaneous Short- and Long-Patch Base Excision Repair (BER) Assay in Live Mammalian Cells

The base excision repair (BER) pathway repairs small, non-bulky DNA lesions, including oxidized, alkylated, and deaminated bases, and is responsible for the removal of at least 20,000 DNA lesions per cell per day. BER is initiated by DNA damage-specific DNA glycosylases that excise the damaged base and generates an abasic (AP) site or single-strand breaks, which are subsequently repaired in mammalian cells either by single-nucleotide (SN) or multiple-nucleotide incorporation via the SN-BER or long-patch BER (LP-BER) pathway, respectively. This chapter describes a plaque-based host cell reactivation (PL-HCR) assay system for measuring BER mechanisms in live mammalian cells using a plasmid-based assay. After transfection of a phagemid (M13mp18) containing a single modified base (representative BER DNA substrates) within a restriction site into human cells, restriction digestions detect the presence or absence (complete repair) of the adduct by the transformation of the digestion products into E. coli and counting the transformants as plaques. To monitor the patch size, different plasmids are constructed containing C:A mismatches within different restriction sites (inhibiting digestion) at various distances on both sides (5' or 3') of the modified base-containing restriction sites. Using this assay, the percentage of repair events that occur via 5' and 3' patch formation can be quantified.

Association of Polymorphisms in the DNA Repair Genes XRCC1 and XRCC3 with Systemic Lupus Erythematosus

Background:

Evidence suggests that DNA damage is implicated in the development of Systemic Lupus Erythematosus (SLE).

Objective:

Investigate the possible association of polymorphisms in the DNA repair genes XRCC1 and XRCC3 with SLE and its clinical and laboratory features.

Methods:

This is a case-control study comparing the polymorphisms in the DNA repair genes XRCC1 and XRCC3 in SLE patients and control individuals. Genotyping for DNA repair genes was performed by polymerase chain reaction-restriction fragment length polymorphism in 76 patients and 82 healthy control individuals.

Results:

Our data indicated that the genotype frequencies in patients with the XRCC1 Arg399Gln and XRCC3 Thr241Met polymorphisms were similar to those observed in the control group (p > 0.05). However, the frequencies of the 399Gln allele (p = 0.023, OR = 0.58, 95% CI = 0.36–0.93) and 241Met allele (p = 0.0039, OR = 0.59, 95% CI = 0.36–0.98) were significantly lower in the patients than those in the control subjects.

Conclusion:

We demonstrated that 399Gln and 241Met alleles may play a protective role in SLE susceptibility.

Polymorphism of the XRCC1 Gene Is Associated with Susceptibility and Short-Term Recovery of Ischemic Stroke

Background: Base excision repair (BER) is the primary DNA repair system with the ability to fix base lesions caused by oxidative damage. Genetic variants influencing the BER pathway may affect the susceptibility and the outcomes of ischemic stroke. Here, we examined how single nucleotide polymorphisms (SNPs) associated with BER impact susceptibility and short-term recovery of ischemic stroke. Methods: We selected 320 ischemic stroke patients and 303 controls. Then we genotyped SNPs of NEIL1 rs4462560, NEIL3 rs12645561 and XRCC1 rs25487 in both groups. Results: Polymorphism in XRCC1 rs25487 was significantly associated with reduced ischemic stroke (IS) risk (dominant model: OR = 0.53, 95% CI = 0.36-0.79, p = 0.002), a milder initial stroke (dominant model: OR = 0.57, 95% CI = 0.33-0.98, p = 0.043), and also a better short-term recovery (dominant model: OR = 0.57, 95% CI = 0.35-0.92, p = 0.022). No association was observed in the other two SNPs. Conclusions: Our study suggests that the genetic variant of XRCC1 rs25487 may contribute to the etiology of ischemic stroke.

Interaction with OGG1 is required for efficient recruitment of XRCC1 to base excision repair and maintenance of genetic stability after exposure to oxidative stress

XRCC1 is an essential protein required for the maintenance of genomic stability through its implication in DNA repair. The main function of XRCC1 is associated with its role in the single-strand break (SSB) and base excision repair (BER) pathways that share several enzymatic steps. We show here that the polymorphic XRCC1 variant R194W presents a defect in its interaction with the DNA glycosylase OGG1 after oxidative stress. While proficient for single-strand break repair (SSBR), this variant does not colocalize with OGG1, reflecting a defect in its involvement in BER. Consistent with a role of XRCC1 in the coordination of the BER pathway, induction of oxidative base damage in XRCC1-deficient cells complemented with the R194W variant results in increased genetic instability as revealed by the accumulation of micronuclei. These data identify a specific molecular role for the XRCC1-OGG1 interaction in BER and provide a model for the effects of the R194W variant identified in molecular cancer epidemiology studies.

Genes and SNPs associated with non-hereditary and hereditary colorectal cancer

BACKGROUND

Colorectal cancer is the third most common cancer in both men and women in the world and the second leading cause of cancer-related deaths. The incidence of colorectal cancer has increased in Iran in the past three decades and is now considered as a serious problem for our society. This cancer has two types hereditary and non-hereditary, 80% of cases being the latter. Considering that the relationship between SNPs with diseases is a concern, many researchers believed that they offer valuable markers for identifying genes responsible for susceptibility to common diseases. In some cases, they are direct causes of human disease. One SNP can increase risk of cancer, but when considering the rate of overlap and frequency of DNA repair pathways, it might be expected that SNP alone cannot affect the final result of cancer, although several SNPs together can exert a significant influence. Therefore identification of these SNPs is very important. The most important loci which include mutations are: MLH1, MSH2, PMS2, APC, MUTYH, SMAD7, STK11, XRCC3, DNMT1, MTHFR, Exo1, XRCC1 and VDR. Presence of SNPs in these genes decreases or increases risk of colorectal cancer.

MATERIALS AND METHODS

In this article we reviewed the Genes and SNPs associated with non-hereditary and hereditary of colorectal cancer that recently were reported from candidate gene y, meta-analysis and GWAS studies.

RESULTS

As with other cancers, colorectal cancer is associated with SNPs in gene loci. Generally, by exploring SNPs, it is feasible to predict the risk of developing colorectal cancer and thus establishing proper preventive measures.

CONCLUSIONS

SNPs of genes associated with colorectal cancer can be used as a marker SNP panel as a potential tool for improving cancer diagnosis and treatment planning.

XRCC-1 Gene Polymorphism (Arg399Gln) and Susceptibility to Development of Lung Cancer in Cohort of North Indian Population: A Pilot Study

BACKGROUND

Smoking has been considered to be the major cause of lung cancer. However, only a fraction of cigarette smokers develop this disease. This suggests the importance of genetic constitution in predicting the individual's susceptibility towards lung cancer. This genetic susceptibility may result from inherited polymorphisms in genes controlling carcinogen metabolism and repair of damaged deoxyribonucleic acid (DNA). These repair systems are fundamental to the maintenance of genomic integrity. X-ray repair cross complimenting group I (XRCC1), a major DNA repair gene in the base excision repair (BER) pathway. It is involved in repair by interacting with components of DNA at the site of damage. Inconsistent results have been reported regarding the associations between the Arg399Gln polymorphism of XRCC1. This study demonstrates the importance of recognition of this relationship of lung carcinoma and genetic constitution of the person which will help guide clinicians on the optimal screening of this disease.

AIM

To assess the role of XRCC1 gene polymorphism (Arg399Gln) directly on the variation in susceptibility to development of lung cancer in North Indian subjects.

MATERIALS AND METHODS

One hundred males with diagnosed cases of lung cancer were recruited from Delhi State Cancer Institute (DSCI). Hundred healthy volunteers were taken as controls. DNA isolation was done and Polymerase chain reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) procedure undertaken to amplify the region containing Arg/Gln substitution at codon 399 (in exon 10).

RESULTS

XRCC1 gene polymorphism is associated with increased risk of lung cancer when the Arg/Arg genotype was used as the reference group. The Arg/Gln and Gln/Gln was associated with statistically increased risk for cancer.

CONCLUSION

Arg399Gln polymorphism in XRCC1 gene polymorphism is associated with lung cancer in North Indian subjects and screening for this polymorphism will help in targeting predisposed individuals and its prevention.

XRCC1 Arg399Gln and Arg194Trp polymorphisms and risk of systemic lupus erythematosus in an Iranian population: a pilot study

Background. Evidences are suggesting that DNA damage is implicated in development of systemic lupus erythematosus (SLE). Therefore we focused on two common XRCC1 polymorphisms (Arg399Gln and Arg194Trp) in SLE susceptibility in South East of Iran. Methods. Peripheral blood DNA was extracted from 163 SLE patients and 180 healthy controls. PCR-restriction fragment length polymorphism method was used for genotyping of XRCC1 Arg399Gln and Arg194Trp polymorphisms. Results. The frequency of Arg/Gln genotype of the XRCC1 Arg399Gln polymorphism was significantly lower in SLE patients than controls. Moreover, lower frequency of Arg/Gln genotype was found in SLE patients with malar rash compared to patients without this manifestation. No association was observed between XRCC1 Arg194Trp polymorphism and increased risk of SLE in studied population. Haplotype analysis revealed no correlation between four haplotypes of XRCC1 Arg399Gln and Arg194Trp polymorphisms and SLE risk. Conclusion. These findings suggest that XRCC1 399 Arg/Gln heterozygous genotype plays a protective role in SLE susceptibility.

XRCC1 Arg399Gln genetic polymorphism and the risk of hepatocellular carcinoma: a meta-analysis

The X-ray repair cross-complementing group 1 (XRCC1) gene, one of over 20 genes that participate in the base excision repair pathway, is thought to account for differences in susceptibility to hepatocellular carcinoma. To assess the relationship between the XRCC1 Arg399Gln polymorphism and the risk of hepatocellular carcinoma (HCC), we performed a meta-analysis. All the relevant studies were extracted from PubMed, Embase, the Chinese biomedicine databases, the Chinese national knowledge infrastructure, and the Wanfang databases (prior to August 2012). The meta-analysis was performed using all eligible studies, which covered a total of 2,554 cases and 3,320 controls, to examine the association between XRCC1 Arg399Gln polymorphism and the risk of HCC. Our analysis suggested that the variant genotypes of the XRCC1 Arg399Gln gene were associated with a significantly increased risk of HCC in a co-dominant model (Arg/Gln vs. Arg/Arg, odd ratios [OR] 1.39, 95 % confidence interval [CI] 1.08-1.79; Gln/Gln vs. Arg/Arg, OR 1.26, 95 % CI 1.04-1.52) and a dominant model (Arg/Gln + Gln/Gln vs. Arg/Arg OR 1.36, 95 % CI 1.07-1.72), whereas no association was observed in the recessive model (Gln/Gln vs. Arg/Gln + Arg/Arg, OR 1.05, 95 % CI 0.91-1.21). The results of the subgroup analysis by ethnicity indicated that the XRCC1 Arg399Gln polymorphism was associated with increased risk of HCC in Asian populations using the co-dominant model (Arg/Gln vs. Arg/Arg, OR 1.41, 95 % CI 1.06-1.87) and the dominant model (Gln/Gln vs. Arg/Gln + Arg/Arg, OR 1.35, 95 % CI 1.03-1.76). Our analysis provides evidence that the XRCC1 Arg399Gln polymorphism may be associated with a higher risk of HCC, especially among Asian populations.

Association between genetic variants of DNA repair genes and coronary artery disease

Polymorphisms in DNA repair genes may be associated with differences in the repair efficiency of DNA damage and may influence an individual's risk of atherosclerosis. Genetic research on coronary artery disease (CAD) has traditionally focused on investigation aimed at identifying disease-susceptibility genes. The aim of this study was to investigate the relationship between AP-endonuclease-1 (Asp148Glu), XRCC1 (Arg399Gln), XRCC3 (Thr241Met), XPD (Lys751Gln), XPG (Asp1104His), and hOGG1 (Ser326Cys), gene polymorphisms and the risk of developing CAD in a Turkish population. The study population consisted of 197 patients with acute coronary syndrome (ACS) with chronic CAD and 135 healthy subjects' age and sex matched. Gene polymorphisms were determined by the polymerase chain reaction-restriction fragment length polymorphism method. We demonstrated for the first time, a positive association of XRCC3 and hOGG1 DNA repair gene variants with CAD risk. XRCC3 Thr/Thr genotype and Thr allele frequencies were significantly increased in ACS and chronic CAD patients compared with the control group (p<0.05). It was also observed that there is a protective role of XRCC3 Met alleles against both ACS and chronic CAD (p<0.05). hOGG1 Cys alleles were found significantly higher in ACS patients than in the control group and carriers of the Cys allele had a 1.7-fold increased risk for ACS. In addition, we confirmed the association of XRCC3 Thr241Met and hOGG1 Ser326Cys gene variants with CAD by haplotype analysis. We found that CAD risk is associated with XRCC3 Thr: hOGG1 Cys haplotype, whereas XRCC3 Met: hOGG1 Ser haplotype was found to be protective against the disease. The preliminary results suggested that XRCC3 and hOGG1 genetic variants may be risk factors by affecting the enzyme's function that may lead to development of CAD.

Genetic polymorphisms of XRCC1, alcohol consumption, and the risk of colorectal cancer in Japan

Background

X-ray cross-complementing group 1 (XRCC1) polymorphisms affect DNA repair capacity and may therefore be of importance in colorectal carcinogenesis. Alcohol consumption, an important risk factor for colorectal cancer, may induce carcinogenesis through DNA damage caused by the toxic effects of alcohol or its metabolites. Therefore, we examined the associations of XRCC1 Arg399Gln, Arg280His, and Arg194Trp polymorphisms with colorectal cancer and the impact of the association between alcohol consumption and colorectal cancer risk.

Methods

This case-control study in Fukuoka, Japan including 685 cases and 778 controls. The cases were incident patients with histologically confirmed colorectal adenocarcinoma. The controls were randomly selected community subjects.

Results

The XRCC1 399Gln/Gln genotype was significantly associated with colorectal cancer risk (adjusted odds ratio [OR] 1.57, 95% CI 1.01–2.42; relative to 399Arg/Arg genotype). The association was strongest in individuals with high alcohol consumption. The Arg280His polymorphism modified the association between alcohol consumption and colorectal cancer risk (interaction P = 0.049). The OR of colorectal cancer in individuals with the 280His allele was 0.45 (95% CI 0.26–0.78) as compared with the 280Arg/Arg genotype limited to the 399Gln allele (interaction P = 0.001). The adjusted ORs for 399Gln/Gln-280Arg/Arg-194Arg/Arg and 399Arg/Gln-280Arg/Arg-194Arg/Trp were 1.71 (95% CI 1.02–2.87) and 1.57 (95% CI 1.05–2.33), respectively, with 399Arg/Arg-280Arg/Arg-194Arg/Arg as reference (interaction P = 0.418).

Conclusions

The findings are additional evidence that individuals with the XRCC1 399Gln/Gln genotype have an increased risk of colorectal cancer, and that XRCC1 polymorphisms have an important role in colorectal cancer risk associated with alcohol consumption or gene-gene interaction.

Databases and bioinformatics tools for the study of DNA repair

DNA is continuously exposed to many different damaging agents such as environmental chemicals, UV light, ionizing radiation, and reactive cellular metabolites. DNA lesions can result in different phenotypical consequences ranging from a number of diseases, including cancer, to cellular malfunction, cell death, or aging. To counteract the deleterious effects of DNA damage, cells have developed various repair systems, including biochemical pathways responsible for the removal of single-strand lesions such as base excision repair (BER) and nucleotide excision repair (NER) or specialized polymerases temporarily taking over lesion-arrested DNA polymerases during the S phase in translesion synthesis (TLS). There are also other mechanisms of DNA repair such as homologous recombination repair (HRR), nonhomologous end-joining repair (NHEJ), or DNA damage response system (DDR). This paper reviews bioinformatics resources specialized in disseminating information about DNA repair pathways, proteins involved in repair mechanisms, damaging agents, and DNA lesions.

ERCC1 and XRCC1 as biomarkers for lung and head and neck cancer

Advanced stage non-small cell lung cancer and head and neck squamous cell carcinoma are both treated with DNA damaging agents including platinum-based compounds and radiation therapy. However, at least one quarter of all tumors are resistant or refractory to these genotoxic agents. Yet the agents are extremely toxic, leading to undesirable side effects with potentially no benefit. Alternative therapies exist, but currently there are no tools to predict whether the first-line genotoxic agents will work in any given patient. To maximize therapeutic success and limit unnecessary toxicity, emerging clinical trials aim to inform personalized treatments tailored to the biology of individual tumors. Worldwide, significant resources have been invested in identifying biomarkers for guiding the treatment of lung and head and neck cancer. DNA repair proteins of the nucleotide excision repair pathway (ERCC1) and of the base excision repair pathway (XRCC1), which are instrumental in clearing DNA damage caused by platinum drugs and radiation, have been extensively studied as potential biomarkers of clinical outcomes in lung and head and neck cancers. The results are complex and contradictory. Here we summarize the current status of single nucleotide polymorphisms, mRNA, and protein expression of ERCC1 and XRCC1 in relation to cancer risk and patient outcomes.

Detection of p16 promoter methylation in premature rats with chronic lung disease induced by hyperoxia

BACKGROUND

The aim of the present study was to investigate p16 promoter methylation in premature rats with chronic lung disease (CLD) induced by hyperoxia.

METHODS

Eighty Wistar rats were randomized into the hyperoxia group (fraction of inspired oxygen [FiO(2)] = 900 mL/L) or the control group (FiO(2) = 210 mL/L), 40 for each group. Semi-nested methylation-specific polymerase chain reaction (sn-MSP) was applied to detect p16 promoter hypermethylation in lung tissues. Additionally, p16 mRNA and protein expression was detected on reverse transcription-polymerase chain reaction (RT-PCR), western blot and the strept actividin-biotin complex method.

RESULTS

Extended exposure to hyperoxia led to increased methylation, and the methylation level reached a peak in the period of maximum pulmonary fibrosis in the hyperoxia group, while the methylation did not occur in the control group. The methylation rates on semi-nested PCR (sn-PCR) and nested-MSP were, respectively, 52.5% and 42.5% in the hyperoxia group. There was no statistically significant difference between the two methods. The p16 mRNA and protein expression was significantly higher in those with p16 promoter hypermethylation than those without.

CONCLUSION

Exposure to hyperoxia may induce p16 promoter hypermethylation in lung tissues in premature rats, and methylation risk increases as exposure extends. p16 promoter methylation induced by hyperoxia may be one of the mechanisms for low p16 mRNA and protein expression.

A functional -77T>C polymorphism in XRCC1 is associated with risk of breast cancer

X-ray repair cross-complementing 1 (XRCC1) plays a critical role in base excision repair and genetic variations of XRCC1 may be associated with cancer susceptibility. We tested this hypothesis by examining the contribution of polymorphism in the regulatory region of XRCC1 -77T>C to risk of breast cancer in 995 patients and 1,004 controls. We found this polymorphism was associated with an increased risk of breast cancer, with an OR of 1.25 (95% CI, 1.00-1.56) for the -77TC genotype and 2.55 (95% CI, 1.11-5.86) for the -77CC genotype compared with the -77TT genotype. Haplotype analysis combining the -77T>C with three well-studied non-synonymous polymorphisms (Arg194Trp, Arg280His, and Arg399Gln) showed that only the -77C-containing haplotype was associated with the risk. Moreover, the C allele had more than 3-fold decreased luciferase expression compared with the T allele in breast cancer cell line MCF-7 (P < 0.001). A meta-analysis of seven publications with a total 2,888 cancer cases and 3,177 controls demonstrated that -77C was significantly associated with cancer risk, with an OR of 1.34 (95% CI, 1.18-1.51) for the TC genotype and 1.53 (95% CI, 1.14-2.07) for the CC genotype compared with the TT genotype. In conclusion, these findings indicated that XRCC1 -77T>C polymorphism may be a genetic determinant for developing breast cancer.

Polymorphisms in DNA repair genes XRCC1, XRCC3 and XPD, and colorectal cancer risk: a case-control study in an Indian population

PURPOSE

Genetic polymorphisms in DNA repair genes may influence variations in individual DNA repair capacity, which could be associated with the development of cancer. We detected the distributions of three single-nucleotide polymorphisms (XRCC1 Arg399Gln, XRCC3 Thr241Met and XPD Lys751Gln) in DNA repair genes, and assessed the associations of these genetic polymorphisms with colon and rectal cancer susceptibility as well as evaluated the interactions of gene-gene and gene-environment in a case-control study of an Indian population.

METHODS

This case-control study was conducted with 302 cases (including 59 colon and 243 rectal cancer patients) and 291 cancer-free healthy controls. Genotypes were determined by PCR-RLFP assays. The effects [odds ratios (ORs) and 95% confidence intervals (95% CIs)] of genetic polymorphisms on colorectal cancer were estimated using unconditional logistic regression.

RESULTS

The XRCC1 399Gln allele was found to be associated with a significantly increased rectal cancer risk among men (OR = 1.65, 95% CI 1.04-2.64). Whereas the XRCC3 241Met allele showed a protective tendency against rectal cancer (OR = 0.68, 95% CI 0.46-1.02) for both men and women. Furthermore, a combination of the XRCC1 399Gln allele with XRCC3 Thr/Thr genotype and the XPD 751Gln allele demonstrated the highest rectal cancer risk (OR = 3.52, 95% CI 1.43-9.44).

CONCLUSIONS

The combined effects of putative risk alleles/genotypes for different DNA repair pathways may strengthen the susceptibility to rectal cancer.

A meta-analysis on XRCC1 and XRCC3 polymorphisms and colorectal cancer risk

PURPOSE

Studies on polymorphism of X-ray repair cross-complementing group 1 (XRCC1), group 3 (XRCC3), and colorectal cancer risk are inconclusive. The purpose of this study is to evaluate the role of XRCC1 R399Q, R194W, and XRCC3 T241M genotypes in colorectal cancer susceptibility.

METHODS

We performed a meta-analysis on all available studies that provided 3,514/4,686 cases/controls for R399Q, 2,767/3,907 cases/controls for R194W and 3,183/3,926 cases/controls for T241M.

RESULTS

Overall, no apparent effects of 194 W allele compared to 194R on colorectal cancer risk were found in all subjects and subgroups (Asians and Caucasians). Insignificant effects were also found under other genetic contrasts (homologous contrast, dominant model, and recessive model). The same pattern of results was produced in T241M polymorphism. The 399Q allele compared to 399R showed no significant association with colorectal cancer risk in all subjects and subgroups. However, protective effects of 399QQ genotype were observed under recessive model (QQ/QR + RR) [P = 0.02, OR = 0.84, 95% CI (0.72, 0.97)] and homozygote contrast (QQ/RR) [P = 0.01, OR = 0.81; 95% CI (0.69, 0.95)] in all subjects.

CONCLUSION

Results suggested that 399Q allele might act as a recessive allele in its association with colorectal cancer.

DNA repair gene polymorphism is associated with the genetic basis of atherosclerotic coronary artery disease

BACKGROUND

Atherosclerotic coronary artery disease (CAD) is a multifactorial process that appears to be caused by the interaction of environmental risk factors with multiple predisposing genes. It is nowadays accepted that increased levels of DNA damage induced by xenobiotics play an important role in the early phases of atherogenesis. Therefore, in this study, we focus on determining whether genetic variations in xenobiotic-metabolizing [glutathione-S-transferase theta 1 (GSTT1), glutathione-S-transferase mu 1 (GSTM1), cytochrome P450 IIEI (CYP2E1)] and DNA repair [X-ray cross-complementing group 1 (XRCC1)] genes might be associated with increased risk for CAD.

METHODS

A case-control study was conducted with 400 individuals who underwent subjected to coronary angiography. A total of 299 were patients diagnosed with effective coronary atherosclerosis (case group; >20% obstructive lesion), and 101 (control group) were individuals diagnosed as negative for CAD (<20% obstructive lesions). The polymorphism identifications for GSTM1 and GSTT1, and for CYP2E1 and XRCC1 genes were performed by polymerase chain reaction (PCR) amplification and by PCR-RFLP, respectively.

RESULTS AND CONCLUSIONS

The XRCC1 homozygous wild-type genotype Arg/Arg for codon 399 was statistically less pronounced in the case subjects (21.4%) than in controls (38.5%); individuals with the variant XRCC1 genotype had a 2.3-fold increased risk for coronary atherosclerosis than individuals with the wild-type genotype (OR=2.3, 95% CI=1.13-4.69). Conversely, no association between GSTM1, GSTT1, and CYP2E1gene polymorphisms and coronary atherosclerosis was detected. The results provide evidence of the role of DNA damage and repair in cardiovascular disease.

XRCC1 Arg399Gln, Arg194Trp and Arg280His polymorphisms in breast cancer risk: a meta-analysis

X-ray repair cross-complementing group 1 (XRCC1) plays an important role in base excision and single-strand break repair, as a scaffold protein that brings together proteins of the DNA repair complex, and appears to be a candidate for cancer risk. However, studies on the association between polymorphisms in this protein and cancer have yielded conflicting results. We performed a meta-analysis to investigate the association between the breast cancer and the XRCC1 polymorphisms Arg194Trp (9411 cases and 9783 controls), Arg399Gln (22 481 cases and 23 905 controls) and Arg280His (6062 cases and 5864 controls) in different inheritance models. Our analysis suggested that Arg399Gln was associated with a trend of increased breast cancer risk when using both dominant [odds ratio (OR) = 1.06, 95% confidence interval (CI): 1.00-1.13] and recessive models (OR = 1.12, 95% CI: 1.02-1.23) to analyse the data. In ethnic subgroups and using recessive model analysis: Arg399Gln increased breast cancer risk in Asians (OR = 1.26, 95% CI: 0.96-1.64) and Africans (OR = 1.80, 95% CI: 0.97-3.32), and also while only slightly increasing the breast cancer risk in Caucasians (OR = 1.08, 95% CI: 0.95-1.22). However, Arg194Trp (recessive model, OR = 0.95, 95% CI: 0.75-1.20) and Arg280His (recessive model, OR = 1.28, 95% CI: 0.64-2.55) did not appear to be risk factors for breast cancer. Larger scale primary studies are required to further evaluate the interaction of XRCC1 polymorphisms and breast cancer risk in specific populations.

DNA repair gene XPD and XRCC1 polymorphisms and the risk of childhood acute lymphoblastic leukemia

Polymorphisms have been identified in several DNA repair genes. These polymorphisms may effect DNA repair capacity and modulate cancer susceptibility. In this study, we aimed to determine the four polymorphisms in two DNA repair genes, xeroderma pigmentosum complementation group D (XPD) and X-ray repair cross-complementing group 1 (XRCC1), in a sample of Turkish patients with childhood acute lymphoblastic leukemia (ALL), and evaluate their association with childhood ALL development. We used polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP), to analyze XPD Asp312Asn, XPD Lys751Gln, XRCC1 Arg194Trp, and XRCC1 Arg399Gln polymorphisms in 70 patients with childhood ALL and in 75 disease-free controls, who were of a similar age. No significant differences were observed among the study groups with regard to the XPD codon 312, XPD codon 751, XRCC1 codon 194, and XRCC1 codon 399 polymorphisms. However, the combined XRCC1 Arg194Trp/Trp194Trp variant genotypes were associated with increased risk for ALL in females (OR=5.47; 95% CI=1.49-20.10; p=0.008). This finding indicates that females carrying XRCC1 194Trp allele are at increased risk of developing childhood ALL. These results suggest that the risk of childhood ALL may be associated with DNA repair mechanisms, and understanding these mechanisms will help identify individuals at increased risk of developing childhood ALL, and also should be lead to improved treatment of ALL.

Biomarkers of Psychological Stress in Health Disparities Research

Psychological stress can contribute to health disparities in populations that are confronted with the recurring stress of everyday life. A number of biomarkers have been shown to be affected by psychological stress. These biomarkers include allostatic load, which is a summary measure of the cumulative biological burden of the repeated attempts to adapt to daily stress. Allostatic load includes effects on the hypothalamic-pituitary axis, the sympathetic nervous system and the cardiovascular system. These in turn affect the immune system via bidirectional signaling pathways. Evidence is also building that psychological stress, perhaps via heightened inflammatory states, can increase oxidative stress levels and DNA damage. The inter-relationships of ethnicity, genotype, gene expression and ability to adequately mitigate stress response are just starting to be appreciated. The need to conduct these studies in disadvantaged populations is clear and requires methods to address potential logistical barriers. Biomarkers can help characterize and quantify the biological impact of psychological stress on the etiology of health disparities.

Genetic polymorphism in the DNA repair gene XRCC1 and susceptibility to schizophrenia

The X-ray repair cross-complementation group 1 (XRCC1) protein plays an important role in base excision repair. A high level of XRCC1 mRNA and/or protein has been found in rat and baboon brains. An exon 10 variant at codon 399 of XRCC1 leads to an Arg to Gln amino acid change. The 399Gln allele is associated with an increased risk of several types of cancers, increased DNA adducts and chromosomal changes; therefore, it appears that the 399Gln allele may alter the role of the XRCC1 protein in DNA repair. The present case-control study was performed on 303 (223 males, 80 females) in-patients with chronic schizophrenia and 303 healthy blood donors matched to the patients by age (+/-5 years) and gender. The XRCC1 genotypes were determined using a PCR-based method. Heterozygosity (OR=1.48, 95% CI: 1.05-2.09) and homozygosity (OR=2.00, 95% CI: 1.17-3.42) for the Gln399 allele increased the risk of schizophrenia. There was a significant linear trend in risk associated with zero, one, and two 399Gln alleles. The present finding indicates that XRCC1 is a candidate gene for susceptibility to schizophrenia.

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.

Analysis of the XRCC1 gene as a modifier of the cerebral response in ischemic stroke

Background

Although there have been studies of the genetic risk factors in the development of stroke, there have been few investigations of role of genes in the cerebral response to ischemia. The brain responds to ischemia in a series of reactions that ultimately influence the volume of a stroke that, in general, correlates with disability. We hypothesize that polymorphisms in genes encoding proteins involved in these reactions could act as modifiers of this response and impact stroke volume. One of the pathways participating in the cerebral ischemic response involves reactive oxygen species which can cause oxidative damage to nucleic acids. DNA repair mechanisms are in place to protect against such damage and imply a role for DNA repair genes in the response of the brain to ischemia and are potential candidate genes for further investigation.

Methods

We studied two common polymorphisms in the DNA repair gene, XRCC1, C26304T and G28152A, in 134 well characterized patients with non lacunar ischemic strokes. We also performed a case control association study with 113 control patients to assess whether these variants represent risk factors in the development of ischemic stroke.

Results

Independent of etiology, the "T" allele of the C26304T polymorphism is significantly associated with larger stroke volumes (T-test analysis, p < 0.044; multivariate regression analysis, β = 0.23, p < 0.008). In the case control association study, we found that neither of these polymorphisms represented a risk factor for the development of stroke.

Conclusion

Our study suggests a major gene effect of the "T" allele of the C26304T polymorphism modulating the cerebral response to ischemia in non lacunar ischemic stroke.

DNA repair polymorphisms might contribute differentially on familial and sporadic breast cancer susceptibility: a study on a Portuguese population

The purpose of this study was to evaluate the role of polymorphisms in DNA repair genes as genetic indicators of susceptibility to familial and sporadic breast cancer. We analysed DNA samples from 285 breast cancer patients and 442 control subjects, for XRCC1 Arg399Gln, XPD Lys751Gln, RAD51 G135C and XRCC3 Thr241Met polymorphisms using PCR-RFLP. We observed that women carriers of XRCC1 399Gln genotypes and without family history of breast cancer have a protective effect concerning this disease (OR = 0.54 95% CI 0.35-0.84; p = 0.006). Furthermore, we found that carriers of XRCC3 241Met genotypes without FH have an increased susceptibility of breast cancer (OR = 2.21 95% CI 1.42-3.44; p < 0.001). Additionally, we verified an increased risk of breast cancer in women with FH and carrying RAD51 135C genotypes (OR = 2.17 95% CI 1.19-3.98; p = 0.012). Our results suggest XRCC1 Arg399Gln and XRCC3 Thr241Met DNA repair polymorphisms as important biomarkers to sporadic breast cancer susceptibility, as well as, RAD51 G135C polymorphism as a real risk modifier in familial breast cancer cases.

Variation in DNA repair genes ERCC2, XRCC1, and XRCC3 and risk of follicular lymphoma

The reasons for the positive association between skin cancer and non-Hodgkin's lymphoma are not known but may be due to common susceptibility involving suboptimal DNA repair. Therefore, we investigated selected polymorphisms and haplotypes in three DNA repair genes, previously associated with skin cancer and DNA repair capacity, in risk of follicular lymphoma, including possible gene interaction with cigarette smoking and sun exposure. We genotyped 19 single nucleotide polymorphisms (SNP) in the ERCC2, XRCC1, and XRCC3 genes in 430 follicular lymphoma patients and 605 controls within a population-based case-control study in Denmark and Sweden. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated using unconditional logistic regression and haplotype associations were assessed with a global score test. We observed no associations between variation in the ERCC2 and XRCC1 genes and follicular lymphoma risk. In XRCC3, increased risk of follicular lymphoma was suggested for rare homozygotes of three SNPs [Rs3212024: OR, 1.8 (95% CI, 1.1-2.8); Rs3212038: OR, 1.5 (95% CI, 1.0-2.4); Rs3212090: OR, 1.5 (95% CI, 1.0-2.5)]. These results were strengthened in current cigarette smokers. However, evidence of differences in XRCC3 haplotype distributions between follicular lymphoma cases and controls was weak, both overall and in current smokers. We conclude that polymorphic variation in the XRCC3 gene, but not in ERCC2 or XRCC1, may be of importance for susceptibility to follicular lymphoma, perhaps primarily in current smokers. The link between skin cancer and follicular lymphoma is unlikely to be mediated through common variation in the studied DNA repair gene polymorphisms.

Polymorphisms of XRCC1 gene, alcohol consumption and colorectal cancer

To evaluate contribution of polymorphisms of the XRCC1 gene to the risk of colorectal cancer, we conducted a case-control study of 209 colorectal cancer cases and 209 age- and gender-matched controls in the Korean population. We tested the hypothesis by constructing allele combinations with known SNP. Allelic variants of the XRCC1 gene at codons 194, 280 and 399 were analyzed in lymphocyte DNA by PCR-RFLP. We observed an increased risk of colorectal cancer associated with the 399Gln allele. The odds ratio (OR) was 1.61 (95% confidence interval [CI] 1.09-2.39) for the 399Gln allele. When combined allele-specific OR were calculated after estimating frequencies, 3 common allele combinations were found to be associated with an increased risk of colorectal cancer. The OR for the 194Trp-280Arg-399Arg was 1.48 (95% CI = 1.06-2.07) using 194Arg-280Arg-399Arg as the reference. The OR for the 194Arg-280His-399Arg and the 194Arg-280Arg-399Gln were 1.78 (95% CI = 1.09-2.89) and 1.78 (95% CI = 1.23-2.59), respectively. Analysis after controlling for smoking, exercise and dietary habits indicated that alcohol consumption (> or =80 g/week) is a significant risk factor of colorectal cancer (OR = 2.60, 95% CI = 1.46-4.62). An increased risk for colorectal cancer was identified in alcohol drinkers with the risky allele combinations. Our results suggest that polymorphisms in the XRCC1 genes may contribute to colorectal cancer susceptibility, and some evidence was obtained of a genetic modification for the relationship between alcohol intake and colorectal cancer.

Approaches to determine clinical significance of genetic variants

The clinical significance of genetic variants (single nucleotide polymorphisms, SNPs) has implications for risk assessment and also for predicting the outcome of a disease process, especially in response to intervention. Approaches to determine the clinical significance of genetic polymorphisms are now beginning to be developed. The technology tools and procedures currently available have significant potential in identifying and validating polymorphisms associated with environmentally sensitive phenotypes. Numerous concepts can now provide the methodology to selectively identify SNPs with the potential for impacting gene function. These include computational algorithms, biochemical assays, yeast mutagenicity assays, and epidemiological studies, either as a stand-alone screen, or in various combinations depending on the gene of interest. Proof of principle will ultimately depend on large-scale epidemiological and clinical studies, but will require intensive resources. Therefore, the use of the mouse as a preclinical biological model is paramount in helping screen valid SNPs or combinations of SNPs for human studies. But more importantly, mouse modeling will help answer the question of what role gene variants play in sensitivity or resistance to a wide variety of environmental insults ranging from toxic chemicals and carcinogens to more mundane and routine exposure items, such as dietary factors, air quality, over the counter and prescription medications, and ultraviolet light. Our focus on SNPs that result in an amino acid change is a matter of expediency because these variants are more amenable to the prescreening approaches currently available that are expected to help identify SNPs that affect protein function. The mouse models generated to evaluate the environmental relevance of selected SNPs will be extremely valuable biological tools to validate gene variant and environment interaction in a variety of settings. Informative mouse models will also provide the basis of pursuing relevant SNPs in epidemiological and clinical investigations.

Polymorphisms in XRCC1 Modify the Association between Polycyclic Aromatic Hydrocarbon-DNA Adducts, Cigarette Smoking, Dietary Antioxidants, and Breast Cancer Risk

The variability in DNA repair capacity of the general population may depend in part upon common variants in DNA repair genes. X-ray repair cross complementing group 1 (XRCC1) is an important DNA base excision repair gene and exhibits polymorphic variation. Using the Long Island Breast Cancer Study Project, a population-based case-control study, we evaluated the hypothesis that two common single nucleotide polymorphisms of XRCC1 (codon 194 Arg-->Trp and 399 Arg-->Gln) influence breast cancer susceptibility and interact with polycyclic aromatic hydrocarbon (PAH)-DNA adducts, cigarette smoking, and intake of fruits and vegetables and antioxidants. The available sample for genotyping included 1,067 cases and 1,110 controls. Genotyping was done by a high-throughput single-nucleotide extension assay with fluorescence polarization detection of the incorporated nucleotide. We observed no significant increases in risk among all subjects who were carriers of XRCC1 194Trp or 399Gln alleles. Among never smokers, we observed an increased risk of breast cancer in 399Gln carriers [odds ratio (OR), 1.3; 95% confidence interval (CI), 1.0-1.7). Further analysis indicated a suggestive weak additive interaction between the 399Gln allele and detectable PAH-DNA adducts (OR for exposure with mutant genotype, 1.9; 95% CI, 1.2-3.1). The estimated age-adjusted interaction contrast ratio (ICR) and 95% CI (ICR, 0.38; 95% CI, -0.32 to 1.10) indicated that the departure from additivity was not statistically significant, but that there was some suggestion of a relative excess risk due to the interaction. In subjects with at least one copy of XRCC1 194Trp allele, there was a moderate interaction with high intake of fruits and vegetables (>/=35 half-cup servings per week of any fruits, fruit juices, and vegetables, OR, 0.58; 95% CI, 0.38-0.89; ICR, -0.49; 95% CI, -0.03 to -0.95), and dietary plus supplement antioxidant intake with 33% to 42% decreases in breast cancer risk compared with those with the Arg194Arg genotype and low-intake individuals. These results do not show that the two genetic polymorphisms of XRCC1 independently influence breast cancer risk. However, there is evidence for interactions between the two XRCC1 single nucleotide polymorphisms and PAH-DNA adducts or fruit and vegetable and antioxidant intake on breast cancer risk. Further understanding of the biological function of XRCC1 variants and their interactions with PAH-DNA adducts, antioxidants, and other genes in the pathway are needed.

Translocation of XRCC1 and DNA ligase IIIalpha from centrosomes to chromosomes in response to DNA damage in mitotic human cells

DNA single-strand breaks (SSBs) are the most frequent lesions caused by oxidative DNA damage. They disrupt DNA replication, give rise to double-strand breaks and lead to cell death and genomic instability. It has been shown that the XRCC1 protein plays a key role in SSBs repair. We have recently shown in living human cells that XRCC1 accumulates at SSBs in a fully poly(ADP-ribose) (PAR) synthesis-dependent manner and that the accumulation of XRCC1 at SSBs is essential for further repair processes. Here, we show that XRCC1 and its partner protein, DNA ligase IIIα, localize at the centrosomes and their vicinity in metaphase cells and disappear during anaphase. Although the function of these proteins in centrosomes during metaphase is unknown, this centrosomal localization is PAR-dependent, because neither of the proteins is observed in the centrosomes in the presence of PAR polymerase inhibitors. On treatment of metaphase cells with H₂O₂, XRCC1 and DNA ligase IIIα translocate immediately from the centrosomes to mitotic chromosomes. These results show for the first time that the repair of SSBs is present in the early mitotic chromosomes and that there is a dynamic response of XRCC1 and DNA ligase IIIα to SSBs, in which these proteins are recruited from the centrosomes, where metaphase-dependent activation of PAR polymerase occurs, to mitotic chromosomes, by SSBs-dependent activation of PAR polymerase.

Role of XRCC1 in the coordination and stimulation of oxidative DNA damage repair initiated by the DNA glycosylase hOGG1

XRCC1 participates in DNA single strand break and base excision repair (BER) to preserve genetic stability in mammalian cells. XRCC1 participation in these pathways is mediated by its interactions with several of the acting enzymes. Here, we report that XRCC1 interacts physically and functionally with hOGG1, the human DNA glycosylase that initiates the repair by BER of the mutagenic oxidized base 8-oxoguanine. This interaction leads to a 2- to 3-fold stimulation of the DNA glycosylase activity of hOGG1. XRCC1 stimulates the formation of the hOGG1 Schiff-base DNA intermediate without interfering with the endonuclease activity of APE1, the second enzyme in the pathway. On the contrary, the stimulation in the appearance of the incision product seems to reflect the addition of the effects of XRCC1 on the two first enzymes of the pathway. The data presented support a model by which XRCC1 will pass on the DNA intermediate from hOGG1 to the endonuclease APE1. This results in an acceleration of the overall repair process of oxidized purines to yield an APE1-cleaved abasic site, which can be used as a substrate by DNA polymerase beta. More importantly, the results unveil a highly coordinated mechanism by which XRCC1, through its multiple protein-protein interactions, extends its orchestrating role from the base excision step to the resealing of the repaired DNA strand.