Central role for the XRCC1 BRCT I domain in mammalian DNA single-strand break repair

XRCC1 Polymorphisms p.Arg194Trp, p.Arg280His, and p.Arg399Gln, Polycyclic Aromatic Hydrocarbons, and Infertility: A Case-Control and In Silico Study

XRCC1 is involved in repair of single-strand breaks generated by mutagenic exposure. Polymorphisms within XRCC1 affect its ability to efficiently repair DNA damage. Polycyclic aromatic hydrocarbons or PAHs are genotoxic compounds which form bulky DNA adducts that are linked with infertility. Few reports suggest combined role of XRCC1 polymorphisms and PAHs in infertility. Present study investigates association of three XRCC1 polymorphisms (p.Arg194Trp, p.Arg280His, p.Arg399Gln) with male and female infertility in a North-West Indian population using case-control approach. Additionally, in silico approach has been used to predict whether XRCC1 polymorphisms effect interaction of XRCC1 with different PAHs. For case-control study, XRCC1 polymorphisms were screened in peripheral blood samples of age- and gender-matched 201 infertile cases (♂-100, ♀-101) and 201 fertile controls (♂-100, ♀-101) using PCR-RFLP method. For in silico study, AutoDock v4.2.6 was used for molecular docking of B[a]P, BPDE-I, ( ±)-anti-BPDE, DB[a,l]P, 1-N, 2-N, 1-OHP, 2-OHF with XRCC1 and assess effect of XRCC1 polymorphisms on their interaction. In case-control study, statistical analysis showed association of XRCC1 p.Arg280His GA genotype (p = 0.027), A allele (p = 0.019) with reduced risk of male infertility. XRCC1 p.Arg399Gln AA genotype (p = 0.021), A allele (p = 0.014) were associated with reduced risk for female primary infertility. XRCC1 p.Arg194Trp T allele was associated with increased risk for female infertility (p = 0.035). In silico analysis showed XRCC1-PAH interaction with non-significant effect of XRCC1 polymorphisms on predicted binding. Therefore, present study concludes that XRCC1 polymorphism-modified risk for male and female infertility in North-West Indians without significant effect on predicted XRCC1-PAH interactions. This is the first report on XRCC1 in female infertility.

Chromosomal single-strand break repair and neurological disease: Implications on transcription and emerging genomic tools

Cells are constantly exposed to various sources of DNA damage that pose a threat to their genomic integrity. One of the most common types of DNA breaks are single-strand breaks (SSBs). Mutations in the repair proteins that are important for repairing SSBs have been reported in several neurological disorders. While several tools have been utilised to investigate SSBs in cells, it was only through recent advances in genomics that we are now beginning to understand the architecture of the non-random distribution of SSBs and their impact on key cellular processes such as transcription and epigenetic remodelling. Here, we discuss our current understanding of the genome-wide distribution of SSBs, their link to neurological disorders and summarise recent technologies to investigate SSBs at the genomic level.

Base Excision DNA Repair in Plants: Arabidopsis and Beyond

Base excision DNA repair (BER) is a key pathway safeguarding the genome of all living organisms from damage caused by both intrinsic and environmental factors. Most present knowledge about BER comes from studies of human cells, E. coli, and yeast. Plants may be under an even heavier DNA damage threat from abiotic stress, reactive oxygen species leaking from the photosynthetic system, and reactive secondary metabolites. In general, BER in plant species is similar to that in humans and model organisms, but several important details are specific to plants. Here, we review the current state of knowledge about BER in plants, with special attention paid to its unique features, such as the existence of active epigenetic demethylation based on the BER machinery, the unexplained diversity of alkylation damage repair enzymes, and the differences in the processing of abasic sites that appear either spontaneously or are generated as BER intermediates. Understanding the biochemistry of plant DNA repair, especially in species other than the Arabidopsis model, is important for future efforts to develop new crop varieties.

Species variations in XRCC1 recruitment strategies for FHA domain-containing proteins

DNA repair scaffolds XRCC1 and XRCC4 utilize a phosphopeptide FHA domain binding motif (FBM) of the form Y-x-x-pS-pT-D-E that supports recruitment of three identified FHA domain-containing DNA repair proteins: polynucleotide kinase/phosphatase (PNKP), aprataxin (APTX), and a third protein, APLF, that functions as a scaffold in support of non-homologous end joining (NHEJ). Mammalian dimeric XRCC4 is able to interact with two of these proteins at any given time, while monomeric XRCC1 binds only one. However, sequence analysis indicates that amphibian and teleost XRCC1 generally contain two FHA binding motifs. X1-FBM1, is similar to the single mammalian XRCC1 FBM and probably functions similarly. X1-FBM2, is more similar to mammalian XRCC4 FBM; it is located closer to the XRCC1 BRCT1 domain and probably is less discriminating among its three likely binding partners. Availability of an additional PNKP or APTX recruitment motif may alleviate the bottleneck that results from using a single FBM motif for recruitment of multiple repair factors. Alternatively, recruitment of APLF by X1-FBM2 may function to rescue a misdirected or unsuccessful SSB repair response by redirecting the damaged DNA to the NHEJ pathway, - a need that results from the ambiguity of the PARP1 signal regarding the nature of the damage. Evaluation of XRCC4 FBMs in acanthomorphs, which account for a majority of the reported teleost sequences, reveals the presence of an additional XRCC4-like paralog, distinct from other previously described members of the XRCC4 superfamily. The FBM is typically absent in acanthomorph XRCC4, but present in the XRCC4-like paralog. Modeling suggests that XRCC4 and its paralog may form homodimers or XRCC4-XRCC4-like heterodimers.

Repair pathways for radiation DNA damage under normoxic and hypoxic conditions: Assessment with a panel of repair-deficient human TK6 cells

Various types of DNA lesions are produced when cells are exposed to ionizing radiation (IR). The type and yield of IR-induced DNA damage is influenced by the oxygen concentration. Thus, different DNA repair mechanisms may be involved in the response of normoxic and hypoxic cells to irradiation with IR. However, differences between the repair mechanisms of IR-induced DNA damage under normoxic versus hypoxic conditions have not been clarified. Elucidating the relative contribution of individual repair factors to cell survival would give insight into the repair mechanisms operating in irradiated normoxic and hypoxic cells. In the present study, we used a panel of repair-deficient human TK6 cell lines that covered seven repair pathways. Cells were irradiated with X-rays under normoxic and hypoxic conditions, and the sensitivities of each mutant relative to the wild-type (i.e. relative sensitivity) were determined for normoxic and hypoxic conditions. The sensitivity of cells varied depending on the type of repair defects. However, for each repair mutant, the relative sensitivity under normoxic conditions was comparable to that under hypoxic conditions. This result indicates that the relative contribution of individual repair pathways to cell survival is comparable in normoxic and hypoxic cells, although the spectrum of IR-induced DNA damage in hypoxic cells differs from that of normoxic cells.

Activated STAT3 Is a Novel Regulator of the XRCC1 Promoter and Selectively Increases XRCC1 Protein Levels in Triple Negative Breast Cancer

Base Excision Repair (BER) addresses base lesions and abasic sites induced by exogenous and endogenous stressors. X-ray cross complementing group 1 (XRCC1) functions as a scaffold protein in BER and single-strand break repair (SSBR), facilitating and coordinating repair through its interaction with a host of critical repair proteins. Alterations of XRCC1 protein and gene expression levels are observed in many cancers, including colorectal, ovarian, and breast cancer. While increases in the expression level of XRCC1 are reported, the transcription factors responsible for this up-regulation are not known. In this study, we identify the signal transducer and activator of transcription 3 (STAT3) as a novel regulator of XRCC1 through chromatin immunoprecipitation. Activation of STAT3 through phosphorylation at Y705 by cytokine (IL-6) signaling increases the expression of XRCC1 and the occupancy of STAT3 within the XRCC1 promoter. In triple negative breast cancer, the constitutive activation of STAT3 upregulates XRCC1 gene and protein expression levels. Increased expression of XRCC1 is associated with aggressiveness and resistance to DNA damaging chemotherapeutics. Thus, we propose that activated STAT3 regulates XRCC1 under stress and growth conditions, but constitutive activation in cancers results in dysregulation of XRCC1 and subsequently BER and SSBR.

An atypical BRCT-BRCT interaction with the XRCC1 scaffold protein compacts human DNA Ligase IIIα within a flexible DNA repair complex

The XRCC1–DNA ligase IIIα complex (XL) is critical for DNA single-strand break repair, a key target for PARP inhibitors in cancer cells deficient in homologous recombination. Here, we combined biophysical approaches to gain insights into the shape and conformational flexibility of the XL as well as XRCC1 and DNA ligase IIIα (LigIIIα) alone. Structurally-guided mutational analyses based on the crystal structure of the human BRCT–BRCT heterodimer identified the network of salt bridges that together with the N-terminal extension of the XRCC1 C-terminal BRCT domain constitute the XL molecular interface. Coupling size exclusion chromatography with small angle X-ray scattering and multiangle light scattering (SEC-SAXS–MALS), we determined that the XL is more compact than either XRCC1 or LigIIIα, both of which form transient homodimers and are highly disordered. The reduced disorder and flexibility allowed us to build models of XL particles visualized by negative stain electron microscopy that predict close spatial organization between the LigIIIα catalytic core and both BRCT domains of XRCC1. Together our results identify an atypical BRCT–BRCT interaction as the stable nucleating core of the XL that links the flexible nick sensing and catalytic domains of LigIIIα to other protein partners of the flexible XRCC1 scaffold.

The Impact of the Genetic Polymorphism in DNA Repair Pathways on Increased Risk of Glioblastoma Multiforme in the Arab Jordanian Population: A Case-Control Study

Introduction

Among the Jordanian population, brain tumors are the tenth most common type of cancers in both males and females, comprising 2.8% of all newly diagnosed neoplasms. Diffuse gliomas are the most prevalent and the most aggressive primary brain tumors in adults. The incidence of diffuse gliomas varies among different populations; this variation is partially linked to genetic polymorphisms. The purpose of the study is to examine the association between (BRCA1 rs799917G>A, rs1799966T>C, EXO1 rs1047840G>A, EME1 rs12450550T>C, ERCC2 rs13181T>G, rs1799793C>T, and XRCC1 rs1799782G>A) DNA repair gene polymorphisms and glioblastoma multiforme (GBM) susceptibility, and survival in the Jordanian Arab population.

Methods

Eighty-four patients diagnosed with glioblastoma multiforme at the King Abdullah University Hospital (KAUH) between 2013 and 2018 and 225 healthy cancer-free control subjects with similar geographic and ethnic backgrounds to the patients were included in the study. Genomic DNA was extracted from the formalin-fixed paraffin-embedded tissues of the subjects. The Sequenom MassARRAY^® sequencer system (iPLEX GOLD) was used. The analyses included assessments of population variability and survival.

Results

This study is the first to address the relationship between BRCA1 rs1799966 and rs799917 SNP, and the risk of GBM among the Arab Jordanian population. The findings of the study show that BRCA1 rs799917 is associated with decreased risk of GBM in the recessive model (AA vs G/G-A/G: OR, 0.46, 95% CI, 0.26-0.82, p=0.01) and the same SNP is associated with increased risk of GBM in the overdominant model (AG vs G/G-A/A: OR, 1.72, 95% CI, 1.02-2.89, p=0.04).

Urinary and Genetic Biomonitoring of Polycyclic Aromatic Hydrocarbons in Egyptian Coke Oven Workers: Associations between Exposure, Effect, and Carcinogenic Risk Assessment

Background:

Coke oven workers are exposed to polycyclic aromatic hydrocarbons (PAHs) with possible genotoxicity and carcinogenicity. Metabolizing enzymes genes and DNA repair genes are suspected to be correlated with the level of DNA damage. They may contribute to variable individual sensitivity to DNA damage induced by PAHs exposure at workplace.

Objective:

To investigate the relationship between biomarkers of PAHs: 1-hydroxypyrene (1-OHP), DNA adducts, and 8-hydroxy-2-deoxyguanosine (8-OHdG) in coke oven workers, and to assess the role of cytochrome P2E1 (CYP2E1) gene expression and DNA repairing gene (XRCC1) polymorphism in detecting workers at risk.

Methods:

85 exposed workers and 85 unexposed controls were enrolled into this study. Urinary 1-OHP, 8-OHdG, and BPDE-DNA adduct were measured. CYP2E1 gene expression and genotyping of XRCC1 399 Arg/Gln were evaluated by real-time PCR.

Results:

The median urinary 1-OHP levels (6.3 µmol/mol creatinine), urinary 8-OHdG (7.9 ng/mg creatinine), DNA adducts (6.7 ng/μg DNA) in the exposed group were significantly higher than those in the unexposed group. Carriers of the variant allele (Gln) of XRCC1 had the highest levels of 1-OHP, DNA adducts and 8-OHdG, and the lowest level of CYP2E1 gene expression. In exposed workers, significant positive correlations were found between 1-OHP level and each of the work duration, 8-OHdG, and DNA adducts levels. There was a significant negative correlation between 1-OHP level and CYP2E1 gene expression. Work duration and CYP2E1 gene expression were predictors of DNA adducts level; 1-OHP level and work duration were predictors of urinary 8-OHdG level.

Conclusion:

Workers with higher exposure to PAH were more prone to oxidative DNA damage and cancer development. DNA adducts level reflects the balance between their production by CYP2E1 and elimination by XRCC1 gene.

DNA Base Excision Repair in Plants: An Unfolding Story With Familiar and Novel Characters

Base excision repair (BER) is a critical genome defense pathway that deals with a broad range of non-voluminous DNA lesions induced by endogenous or exogenous genotoxic agents. BER is a complex process initiated by the excision of the damaged base, proceeds through a sequence of reactions that generate various DNA intermediates, and culminates with restoration of the original DNA structure. BER has been extensively studied in microbial and animal systems, but knowledge in plants has lagged behind until recently. Results obtained so far indicate that plants share many BER factors with other organisms, but also possess some unique features and combinations. Plant BER plays an important role in preserving genome integrity through removal of damaged bases. However, it performs additional important functions, such as the replacement of the naturally modified base 5-methylcytosine with cytosine in a plant-specific pathway for active DNA demethylation.

PML-like subnuclear bodies, containing XRCC1, juxtaposed to DNA replication-based single-strand breaks

DNA lesions induce recruitment and accumulation of various repair factors, resulting in formation of discrete nuclear foci. Using superresolution fluorescence microscopy as well as live cell and quantitative imaging, we demonstrate that X-ray repair cross-complementing protein 1 (XRCC1), a key factor in single-strand break and base excision repair, is recruited into nuclear bodies formed in response to replication-related single-strand breaks. Intriguingly, these bodies are assembled immediately in the vicinity of these breaks and never fully colocalize with replication foci. They are structurally organized, containing canonical promyelocytic leukemia (PML) nuclear body protein SP100 concentrated in a peripheral layer, and XRCC1 in the center. They also contain other factors, including PML, poly(ADP-ribose) polymerase 1 (PARP1), ligase IIIα, and origin recognition complex subunit 5. The breast cancer 1 and -2 C terminus domains of XRCC1 are essential for formation of these repair foci. These results reveal that XRCC1-contaning foci constitute newly recognized PML-like nuclear bodies that accrete and locally deliver essential factors for repair of single-strand DNA breaks in replication regions.-Kordon, M. M., Szczurek, A., Berniak, K., Szelest, O., Solarczyk, K., Tworzydło, M., Wachsmann-Hogiu, S., Vaahtokari, A., Cremer, C., Pederson, T., Dobrucki, J. W. PML-like subnuclear bodies, containing XRCC1, juxtaposed to DNA replication-based single-strand breaks.

Efficient Single-Strand Break Repair Requires Binding to Both Poly(ADP-Ribose) and DNA by the Central BRCT Domain of XRCC1

XRCC1 accelerates repair of DNA single-strand breaks by acting as a scaffold protein for the recruitment of Polβ, LigIIIα, and end-processing factors, such as PNKP and APTX. XRCC1 itself is recruited to DNA damage through interaction of its central BRCT domain with poly(ADP-ribose) chains generated by PARP1 or PARP2. XRCC1 is believed to interact directly with DNA at sites of damage, but the molecular basis for this interaction within XRCC1 remains unclear. We now show that the central BRCT domain simultaneously mediates interaction of XRCC1 with poly(ADP-ribose) and DNA, through separate and non-overlapping binding sites on opposite faces of the domain. Mutation of residues within the DNA binding site, which includes the site of a common disease-associated human polymorphism, affects DNA binding of this XRCC1 domain in vitro and impairs XRCC1 recruitment and retention at DNA damage and repair of single-strand breaks in vivo.

DNA Repair Gene (XPD, XRCC4, and XRCC1) Polymorphisms in Patients with Endometrial Hyperplasia: A Pilot Study

Background

In this study, we aimed to evaluate the association between endometrial hyperplasia and DNA repair gene (XPD, XRCC4, and XRCC1) polymorphisms.

Material/Methods

There were 114 cases enrolled in the study in 4 groups: simple endometrial hyperplasia (SH) (Group 1), complex endometrial hyperplasia without atypia (CH) (Group 2), complex atypical endometrial hyperplasia (CAH) (Group 3), and normal endometrium (NE) (Group 4). Of these cases, 37 cases had SH, 36 cases had CH, 16 cases had CAH, and 25 cases had NE. To evaluate an association between atypia and DNA repair genes, we consider a group that included both SH and CH, the endometrial hyperplasia without atypia cases (Group 5). Genomic DNA was isolated from paraffin-embedded endometrial tissue collected from the Pathology Department of Gaziantep University Medical School. Polymerase chain reaction (PCR) and/or restriction fragment length polymorphism (RFLP) method was used for evaluating of XPD (−751), XRCC4 (−1394 and a variable number of tandem repeats in intron 3), and XRCC1 (−399) genes.

Results

We observed a notable distinction in patients having endometrial hyperplasia without atypia (the SH+CH group) and the CAH group in terms of XPD (−751) gene polymorphisms. A notable contrast was observed in patients with endometrial hyperplasia without atypia (the SH+CH group) and the NE group in terms of XRCC4 (VNTR intron 3) polymorphisms (P=0.026, P=0.018, respectively).

Conclusions

It was evident the DNA repair gene XPD and XRCC4 polymorphisms had a role in the pathophysiology of endometrial hyperplasia.

Biophysical evaluation to categorize pathogenicity of cancer-predisposing mutations identified in the BARD1 BRCT domain

The BRCT domain of BARD1 (BARD1 BRCT) is involved in many cellular processes such as DNA damage repair (DDR) and cell-cycle checkpoint regulation. BARD1 BRCT performs tumor suppressor function by recruiting BRCA1 at DNA damage site via interactions with other DNA damage repair (DDR) proteins. Considering the importance of the BRCT domain in genomic integrity, we decided to evaluate reported mutations of BARD1 BRCT Cys645Arg, Val695Leu, and Ser761Asn for their pathogenicity. To explore the effect of the mutation on the structure and function, BARD1 BRCT wild-type proteins and the mutant proteins were studied using different biochemical, biophysical and in silico techniques. Comparative fluorescence, circular dichroism (CD) spectroscopy and limited proteolysis studies demonstrate the well-folded structural conformation of wild-type and mutant proteins. However, thermal and chemical denaturation studies revealed similarity in the folding pattern of BARD1 BRCT wild-type and Cys645Arg mutant proteins, whereas there was a significant loss in the thermodynamic stability of Val695Leu and Ser761Asn mutants. Molecular dynamics (MD) simulation studies on wild-type and mutant protein structures indicate the loss in structural integrity of mutants compared with the wild-type protein.

PARP1 and PARP2 stabilise replication forks at base excision repair intermediates through Fbh1-dependent Rad51 regulation

PARP1 regulates the repair of DNA single-strand breaks generated directly, or during base excision repair (BER). However, the role of PARP2 in these and other repair mechanisms is unknown. Here, we report a requirement for PARP2 in stabilising replication forks that encounter BER intermediates through Fbh1-dependent regulation of Rad51. Whereas PARP2 is dispensable for tolerance of cells to SSBs or homologous recombination dysfunction, it is redundant with PARP1 in BER. Therefore, combined disruption of PARP1 and PARP2 leads to defective BER, resulting in elevated levels of replication-associated DNA damage owing to an inability to stabilise Rad51 at damaged replication forks and prevent uncontrolled DNA resection. Together, our results demonstrate how PARP1 and PARP2 regulate two independent, but intrinsically linked aspects of DNA base damage tolerance by promoting BER directly, and by stabilising replication forks that encounter BER intermediates.

Polymorphisms in BER genes and risk of breast cancer: evidences from 69 studies with 33760 cases and 33252 controls

Recently, numerous studies have reported an association between single nucleotide polymorphisms in base-excision repair genes and the risk of developing breast cancer, however there is no consensus. The aim of this meta-analysis was to review and quantitatively assess the relationship between single nucleotide polymorphisms in base-excision repair genes and breast cancer risk. The results suggested that a mutation of T to G in rs1760944 may lead to a higher risk of developing breast cancer in the Mongoloid population, and G to A of rs25487 significantly reduced the risk of breast cancer in Mongoloid and Caucasoid populations. In contrast to the CC and CG genotypes, the GG genotype of rs1052133 located on theOGG1 gene appeared to be a protective factor against developing breast cancer in both Mongoloid and Caucasoid populations. There was no evidence to suggest that rs25489, rs1799782, rs1130409, rs1805414 and rs1136410 were associated with breast cancer risk. In conclusion, this study provides evidence to support the theory that DNA repair genes are associated with breast cancer risk, providing information to further understand breast cancer etiology. and The potential biological pathways linking DNA repair, ethnic background, environment and breast cancer require further investigation.

Occupational Pesticide Exposure, Impaired DNA Repair, and Diseases

Pesticides are a mixture of chemical substances used to kill pests. Apart from their toxicity to pests, thy affect nontarget organisms. They also generate free radicals producing reactive oxygen species (ROS) which can disturb cellular pathways by inhibiting various enzymes or receptors. Pesticides also induce oxidative DNA damage, DNA adducts, and single or double strand DNA breaks. Various mechanisms of DNA repair deal with such damages and help to maintain cell integrity. Alteration in DNA repair genes modulates the individual's susceptibility towards DNA repair and various diseases. Biological monitoring provides a useful tool for the estimation of genetic risk in populations exposed to pesticides. Large numbers of evidences show that occupational exposure to pesticides in agricultural workers has been associated with an increased incidence of various diseases such as cancer, Parkinson's disease, Alzheimer's disease, reproductive disorders, and birth defects. In this review, we have discussed occupational pesticide exposure, various mechanisms of DNA damage caused by pesticides, DNA repair mechanisms, biomonitoring tools, and various diseases caused by pesticide exposure.

Genetic Predisposition to Cervical Cancer and the Association With XRCC1 and TGFB1 Polymorphisms

Objective

Cervical carcinoma (CC), a multifactorial cancer, is assumed to have a host genetic predisposition component that modulates its susceptibility in various populations. We investigated the association between CC risk in Saudi women and 6 single-nucleotide polymorphisms (SNPs) in hypothesis-driven candidate genes.

Methods

A total of 545 females were included, comprising 232 CC patients and 313 age-/sex-matched control subjects. Six SNPs (CDKN1A C31A, ATM G1853A, HDM2 T309G, TGFB1 T10C, XRCC1 G399A, and XRCC3 C241T) were genotyped by direct sequencing.

Results

Of the 6 SNPs studied, TGFB1 T10C (odds ratio, 0.74; 95% confidence interval, 0.57–0.94) and XRCC1 G399A (odds ratio, 1.45; 95% confidence interval, 1.11–1.90) displayed different frequencies in cancer patients and control subjects and showed statistically significant association in univariate (P = 0.017, P = 0.005, respectively) analysis. The Cochran-Armitage trend test had confirmed the results (P = 0.027 and P = 0.006, respectively), indicating an ordering in the effect of the risk alleles in CC patients. The 2 SNPs, TGFB1 T10C and XRCC1 G399A, showed also degrees of deviation from Hardy-Weinberg equilibrium in cancer patients (P = 0.001 and P = 0.083, respectively) but not in the control subjects. Furthermore, correction for multiple testing using multivariate logistic regression to assess the joint effect of all SNPs has sustained significant statistical association (P = 0.025 and P = 0.009, respectively).

Conclusions

TGFB1 T10C and XRCC1 G399A SNPs were associated with CC risk in univariate and multivariate analysis and displayed allele-dosage effects and coselection in cancer patients. Patients harboring the majority allele TGFB1 T10 (Leu) or the variant allele XRCC1 399A (Gln) have approximately 1.5-fold increased risk to develop CC. Host SNPs genotyping may provide relevant biomarkers for CC risk assessment in personalized preventive medicine.

Association between polymorphisms in DNA repair gene XRCC1 and non-melanoma skin cancer risk: a meta-analysis

Objective

Non-melanoma skin cancer (NMSC) is the most common malignancy with annually rising incidence. The aim of this study was to estimate the association between three coding polymorphisms (Arg399Gln, Arg194Trp, and Arg280His) of the DNA repair gene X-ray repair cross-complementing group 1 (XRCC1) and NMSC susceptibility.

Methods

Online databases were searched to retrieve case–control studies published between January 2000 and November 2016. Pooled odds ratio (OR) and 95% confidence interval (CI) were employed to assess the strength of association. Overall, 10 relevant studies were finally included for analysis, including 3,143 NMSC patients and 3,540 controls. For each polymorphism of XRCC1 gene, there were 3,050 cases and 3,463 controls for Arg399Gln, 914 cases and 1,182 controls for Arg194Trp, and 279 cases and 413 controls for Arg280His.

Results

Our results showed that these three polymorphisms in the XRCC1 coding region were not associated with increased risk of NMSC in the total studied population. However, subgroup analysis by ethnicities demonstrated that Gln/Arg genotype of Arg399Gln polymorphism was associated with increased risk of NMSC under the heterogeneous model in Asian populations (Gln/Arg vs Arg/Arg: OR =1.39, 95% CI =1.04–1.87, P=0.03); subgroup analysis by tumor types showed that Trp/Trp genotype of Arg194Trp was positively associated with decreased cancer risk in squamous-cell skin cancer (SCC) type under the homogeneous model (Trp/Trp vs Arg/Arg: OR =0.38, 95% CI =0.16–0.92, P=0.03).

Conclusion

Our results suggested that Arg399Gln variant of XRCC1 gene might be a risk factor for NMSC in Asian populations, and Arg194Trp variant of XRCC1 gene might be a protective factor for patients with SCC. In addition, future case–control studies are still needed to further evaluate the effect of XRCC1 polymorphisms in NMSC risk.

Association Between Twelve Polymorphisms in Five X-ray Repair Cross-complementing Genes and the Risk of Urological Neoplasms: A Systematic Review and Meta-Analysis

Polymorphisms in X-ray repair cross-complementing (XRCC) genes have been implicated in altering the risk of various urological cancers. However, the results of reported studies are controversial. To ascertain whether polymorphisms in XRCC genes are associated with the risk of urological neoplasms, we conducted present updated meta-analysis and systematic review. Summary odds ratios (ORs) and corresponding 95% confidence intervals (CIs) were used to estimate the association. Finally, 54 publications comprising 129 case-control studies for twelve polymorphisms in five XRCC genes were enrolled. We identified that XRCC1-rs25489 polymorphism was associated with an increased risk of urological neoplasms in heterozygote and dominant models. Moreover, in the subgroup analysis by cancer type, we found that XRCC1-rs25489 polymorphism was associated with an increased risk of bladder cancer (BC) in heterozygote model. Although overall analyses suggested a null result for XRCC1-rs25487 polymorphism, in the stratified analysis by ethnicity, an increased risk of urological neoplasms for Asians in allelic and homozygote models was identified. While for other polymorphisms in XRCC genes, no significant association was uncovered. To sum up, our results indicated that XRCC1-rs25489 polymorphism is a risk factor for urological neoplasms, particularly for BC. Further studies with large sample size are needed to validate these findings.

Common genetic variations in cell cycle and DNA repair pathways associated with pediatric brain tumor susceptibility

Knowledge on the role of genetic polymorphisms in the etiology of pediatric brain tumors (PBTs) is limited. Therefore, we investigated the association between single nucleotide polymorphisms (SNPs), identified by candidate gene-association studies on adult brain tumors, and PBT risk.The study is based on the largest series of PBT cases to date. Saliva DNA from 245 cases and 489 controls, aged 7-19 years at diagnosis/reference date, was genotyped for 68 SNPs. Data were analyzed using unconditional logistic regression.The results showed EGFRrs730437 and EGFRrs11506105 may decrease susceptibility to PBTs, whereas ERCC1rs3212986 may increase risk of these tumors. Moreover, stratified analyses indicated CHAF1Ars243341, CHAF1Ars2992, and XRCC1rs25487 were associated with a decreased risk of astrocytoma subtype. Furthermore, an increased risk of non-astrocytoma subtype associated with EGFRrs9642393, EME1rs12450550, ATMrs170548, and GLTSCRrs1035938 as well as a decreased risk of this subtype associated with XRCC4rs7721416 and XRCC4rs2662242 were detected.This study indicates SNPs in EGFR, ERCC1, CHAF1A, XRCC1, EME1, ATM, GLTSCR1, and XRCC4 may be associated with the risk of PBTs. Therefore, cell cycle and DNA repair pathways variations associated with susceptibility to adult brain tumors also seem to be associated with PBT risk, suggesting pediatric and adult brain tumors might share similar etiological pathways.

Polymorphisms in DNA Repair Gene and Susceptibility to Glioma: A Systematic Review and Meta-Analysis Based on 33 Studies with 15 SNPs in 9 Genes

At present, many publications have evaluated the correlation between the DNA repair gene polymorphisms and glioma susceptibility. However, the results remain inconclusive. The aim of this research is to exhaustively assess the association of genetic polymorphisms in DNA repair genes with glioma risk in human. Meta-analysis method was conducted, and 33 studies with 15 SNPs in 9 genes were included (12553 glioma cases and 17178 controls). Correlation strength was evaluated by odds ratio with a 95 % confidence interval. Rs1799782 T allele and rs25487A allele might bring about higher risk of glioma in Asian population. Rs1805377 G allele was an increased risk genetic factor of glioma. Asian carried with rs3212986 A allele was more likely to have glioma. Rs1800067 G allele was a risk factor of developing glioma. Carriers with rs12917 CC genotype in MGMT gene had higher risk of glioma in Caucasian than other non-CC genotype carriers. Carriers with rs1136410 T allele in PARP1 gene could more likely to develop glioma in Caucasian. This meta-analysis suggests that glioma susceptibility is associated with rs1799782 and rs25487 of X-ray repair complementing defective repair in Chinese hamster cells 1 (XRCC1), rs1805377 of XRCC4, rs1800067 of excision repair cross-complementing rodent repair deficiency complementation group 4 (ERCC4) and rs3212986 of ERCC1 in Asian population, and rs12917 of O-6-methylguanine-DNA methyltransferase (MGMT) and rs1136410 of poly(ADP-ribose) polymerase 1 (PARP1) in Caucasian population.

Nuclear Localization of the DNA Repair Scaffold XRCC1: Uncovering the Functional Role of a Bipartite NLS

We have characterized the nuclear localization signal (NLS) of XRCC1 structurally using X-ray crystallography and functionally using fluorescence imaging. Crystallography and binding studies confirm the bipartite nature of the XRCC1 NLS interaction with Importin α (Impα) in which the major and minor binding motifs are separated by >20 residues, and resolve previous inconsistent determinations. Binding studies of peptides corresponding to the bipartite NLS, as well as its major and minor binding motifs, to both wild-type and mutated forms of Impα reveal pronounced cooperative binding behavior that is generated by the proximity effect of the tethered major and minor motifs of the NLS. The cooperativity stems from the increased local concentration of the second motif near its cognate binding site that is a consequence of the stepwise binding behavior of the bipartite NLS. We predict that the stepwise dissociation of the NLS from Impα facilitates unloading by providing a partially complexed intermediate that is available for competitive binding by Nup50 or the Importin β binding domain. This behavior provides a basis for meeting the intrinsically conflicting high affinity and high flux requirements of an efficient nuclear transport system.

The XRCC1 phosphate-binding pocket binds poly (ADP-ribose) and is required for XRCC1 function

Poly (ADP-ribose) is synthesized at DNA single-strand breaks and can promote the recruitment of the scaffold protein, XRCC1. However, the mechanism and importance of this process has been challenged. To address this issue, we have characterized the mechanism of poly (ADP-ribose) binding by XRCC1 and examined its importance for XRCC1 function. We show that the phosphate-binding pocket in the central BRCT1 domain of XRCC1 is required for selective binding to poly (ADP-ribose) at low levels of ADP-ribosylation, and promotes interaction with cellular PARP1. We also show that the phosphate-binding pocket is required for EGFP-XRCC1 accumulation at DNA damage induced by UVA laser, H2O2, and at sites of sub-nuclear PCNA foci, suggesting that poly (ADP-ribose) promotes XRCC1 recruitment both at single-strand breaks globally across the genome and at sites of DNA replication stress. Finally, we show that the phosphate-binding pocket is required following DNA damage for XRCC1-dependent acceleration of DNA single-strand break repair, DNA base excision repair, and cell survival. These data support the hypothesis that poly (ADP-ribose) synthesis promotes XRCC1 recruitment at DNA damage sites and is important for XRCC1 function.

The structural basis of XRCC1-mediated DNA repair

Scaffold proteins play a central role in DNA repair by recruiting and organizing sets of enzymes required to perform multi-step repair processes. X-ray cross complementing group 1 protein (XRCC1) forms enzyme complexes optimized for single-strand break repair, but participates in other repair pathways as well. Available structural data for XRCC1 interactions is summarized and evaluated in terms of its proposed roles in DNA repair. Mutational approaches related to the abrogation of specific XRCC1 interactions are also discussed. Although substantial progress has been made in elucidating the structural basis for XRCC1 function, the molecular mechanisms of XRCC1 recruitment related to several proposed roles of the XRCC1 DNA repair complex remain undetermined.

Monitoring regulation of DNA repair activities of cultured cells in-gel using the comet assay

Base excision repair (BER) is the predominant cellular mechanism by which human cells repair DNA base damage, sites of base loss, and DNA single strand breaks of various complexity, that are generated in their thousands in every human cell per day as a consequence of cellular metabolism and exogenous agents, including ionizing radiation. Over the last three decades the comet assay has been employed in scientific research to examine the cellular response to these types of DNA damage in cultured cells, therefore revealing the efficiency and capacity of BER. We have recently pioneered new research demonstrating an important role for post-translational modifications (particularly ubiquitylation) in the regulation of cellular levels of BER proteins, and that subtle changes (∼20-50%) in protein levels following siRNA knockdown of E3 ubiquitin ligases or deubiquitylation enzymes can manifest in significant changes in DNA repair capacity monitored using the comet assay. For example, we have shown that the E3 ubiquitin ligase Mule, the tumor suppressor protein ARF, and the deubiquitylation enzyme USP47 modulate DNA repair by controlling cellular levels of DNA polymerase β, and also that polynucleotide kinase phosphatase levels are controlled by ATM-dependant phosphorylation and Cul4A-DDB1-STRAP-dependent ubiquitylation. In these studies we employed a modification of the comet assay whereby cultured cells, following DNA damage treatment, are embedded in agarose and allowed to repair in-gel prior to lysis and electrophoresis. Whilst this method does have its limitations, it avoids the extensive cell culture-based processing associated with the traditional approach using attached cells and also allows for the examination of much more precise DNA repair kinetics. In this review we will describe, using this modified comet assay, our accumulating evidence that ubiquitylation-dependant regulation of BER proteins has important consequences for overall cellular DNA repair capacity.

Among 45 variants in 11 genes, HDM2 promoter polymorphisms emerge as new candidate biomarker associated with radiation toxicity

Due to individual variations in radiosensitivity, biomarkers are needed to tailor radiation treatment to cancer patients. Since single nucleotide polymorphisms (SNPs) are frequent in human, we hypothesized that SNPs in genes that mitigate the radiation response are associated with radiotoxicity, in particular late complications to radiotherapy and could be used as genetic biomarkers for radiation sensitivity. A total of 155 patients with nasopharyngeal cancer were included in the study. Normal tissue fibrosis was scored using RTOG/EORTC grading system. Eleven candidate genes (ATM, XRCC1, XRCC3, XRCC4, XRCC5, PRKDC, LIG4, TP53, HDM2, CDKN1A, TGFB1) were selected for their presumed influence on radiosensitivity. Forty-five SNPs (12 primary and 33 neighboring) were genotyped by direct sequencing of genomic DNA. Patients with severe fibrosis (cases, G3–4, n = 48) were compared to controls (G0–2, n = 107). Results showed statistically significant (P < 0.05) association with radiation complications for six SNPs (ATM G/A rs1801516, HDM2 promoter T/G rs2279744 and T/A rs1196333, XRCC1 G/A rs25487, XRCC5 T/C rs1051677 and TGFB1 C/T rs1800469). We conclude that these six SNPs are candidate genetic biomarkers for radiosensitivity in our patients that have cumulative effects as patients with severe fibrosis harbored significantly higher number of risk alleles than the controls (P < 0.001). Larger cohort, independent replication of these findings and genome-wide association studies are required to confirm these results in order for SNPs to be used as biomarkers to individualize radiotherapy on genetic basis.

Association between DNA repair gene polymorphisms and risk of glioma: a systematic review and meta-analysis

BACKGROUND

Association studies of germline DNA repair single nucleotide polymorphisms (SNPs) and glioma risk have yielded inconclusive results. We therefore performed a systematic review and meta-analysis of studies investigating this association.

METHODS

We identified 27 eligible studies investigating 105 SNPs in 42 DNA repair genes. Of these, 10 SNPs in 7 genes were analyzed in at least 4 studies and were therefore included in our meta-analysis. The meta-analysis was performed for homozygote comparison, heterozygote comparison, and dominant and recessive models by applying a fixed- or random-effects model. The funnel and forest plots were created using RevMan software.

RESULTS

We found that SNPs rs3212986 (odds ratio [OR] = 1.35 (1.08-1.68), P = .008), rs13181 (OR = 1.18 (1.06-1.31), P = .002), and rs25487 (OR = 1.12 (1.03-1.22), P = .007) in DNA repair genes ERCC1, ERCC2 (XPD), and XRCC1 may increase the risk of glioma, while polymorphisms rs1136410 (OR = 0.78 (0.68-0.89), P = .0004) and rs12917 (OR = 0.84 (0.73-0.96), P = .01) in PARP1(ADPRT) and MGMT are associated with decreased susceptibility to glioma. No evidence of significant associations between ERCC2 rs1799793, OGG1 rs1052133, XRCC1 rs25489, XRCC1 rs1799782, or XRCC3 rs861539 and risk of glioma was observed.

CONCLUSION

This study provides evidence that DNA repair genes ERCC1, ERCC2, and XRCC1 might be low-penetrance glioma-risk genes, while MGMT and PARP1 polymorphisms may confer protection against glioma.

Strategic Combination of DNA-Damaging Agent and PARP Inhibitor Results in Enhanced Cytotoxicity

PARP inhibitors (PARPi) are under clinical trial for combination cancer chemotherapy. In the presence of a PARPi, PARP-1 binds DNA strand breaks but cannot produce poly(ADP-ribose) polymers or undergo auto-poly(ADP-ribosyl)ation. DNA binding is persistent, hindering DNA repair. Methylated bases formed as a result of cellular exposure to DNA-methylating agents are repaired by DNA polymerase β (pol β)-dependent base excision repair (BER) producing a 5′-deoxyribose phosphate (5′-dRP) repair intermediate. PARP-1 binds and is activated by the 5′-dRP, and PARPi-mediated sensitization to methylating agents is considerable, especially in pol β-deficient cells. Cells deficient in the BER factor XRCC1 are less sensitized by PARPi than are wild-type cells. PARPi sensitization is reduced in cells expressing forms of XRCC1 deficient in interaction with either pol β or PARP-1. In contrast, agents producing oxidative DNA damage and 3′- rather than 5′-repair intermediates are modestly PARPi sensitized. We summarize PARPi experiments in mouse fibroblasts and confirm the importance of the 5′-dRP repair intermediate and functional pol β and XRCC1 proteins. Understanding the chemistry of repair is key to enhancing the clinical success of PARPi.

XRCC1 deficiency increased the DNA damage induced by γ-ray in HepG2 cell: Involvement of DSB repair and cell cycle arrest

γ-ray irradiation can induce DNA damages which include base damages, single-strand breaks and double-strand breaks in various type cells. The DNA repair protein XRCC1, as a part of the BER pathway, forms complexes with DNA polymerase beta, DNA ligase III and poly-ADP-ribose polymerase (PARP) in the repair of DNA single strand breaks and also affects the repair of double strand breaks. However, it is still not known well whether XRCC1 contributes to affect the irradiation sensitivity and DNA damage in HepG2 cell and the potential mechanism. Hence, the purpose of this study was to explore whether abrogation of XRCC1 gene expression by shRNA could reduce DNA repair and thus sensitize HepG2 cells to γ-ray. Cell viability was measured by Trypan blue staining and cloning efficiency assay. The DNA damage was detected by Comet assay. Apoptosis and cell cycle were detected by flow cytometry. The DNA-PKcs and gadd153 mRNA expression were determined by Real-time PCR. Our results showed that abrogation of XRCC 1 could sensitize HepG2 cells to γ-ray. This enhanced sensitivity could be attributed to the increased DNA damage and increased cell cycle arrest, which might be related with the increasing of DNA-PKcs and gadd153 mRNA expression. Therefore, our results suggested that the γ-ray irradiation sensitivity could be increased by targeting inhibition of XRCC1 in HepG2 cell.

Damage response of XRCC1 at sites of DNA single strand breaks is regulated by phosphorylation and ubiquitylation after degradation of poly(ADP-ribose)

Single-strand breaks (SSBs) are the most common type of oxidative DNA damage and they are related to aging and many genetic diseases. The scaffold protein for repair of SSBs, XRCC1, accumulates at sites of poly(ADP-ribose) (pAR) synthesized by PARP, but it is retained at sites of SSBs after pAR degradation. How XRCC1 responds to SSBs after pAR degradation and how this affects repair progression are not well understood. We found that XRCC1 dissociates from pAR and is translocated to sites of SSBs dependent on its BRCTII domain and the function of PARG. In addition, phosphorylation of XRCC1 is also required for the proper dissociation kinetics of XRCC1 because (1) phosphorylation sites mutated in XRCC1 (X1 pm) cause retention of XRCC1 at sites of SSB for a longer time compared to wild type XRCC1; and (2) phosphorylation of XRCC1 is required for efficient polyubiquitylation of XRCC1. Interestingly, a mutant of XRCC1, LL360/361DD, which abolishes pAR binding, shows significant upregulation of ubiquitylation, indicating that pARylation of XRCC1 prevents the poly-ubiquitylation. We also found that the dynamics of the repair proteins DNA polymerase beta, PNK, APTX, PCNA and ligase I are regulated by domains of XRCC1. In summary, the dynamic damage response of XRCC1 is regulated in a manner that depends on modifications of polyADP-ribosylation, phosphorylation and ubiquitylation in live cells.

Association between XRCC1 gene polymorphisms and risk of glioma development: a meta-analysis

OBJECTIVE

Previous studies of the association between X-ray cross-complementing group 1 (XRCC1) gene polymorphisms and the gliomas risk have yielded conflicting results, and thus a meta-analysis was performed to provide a more accurate estimation.

METHODS

A computerized literature search of 5 electronic databases was conducted to identify the relevant studies. Fixed or random effect models were selected based on the heterogeneity test. Publication bias was estimated using Begg's funnel plots and Egger's regression test.

RESULTS

A total of 11 studies (3,810 cases and 6,079 controls), 7 studies (2,928 cases and 5,048 controls), and 4 studies (1,461 cases and 2,593 controls) were finally included in the analyses of the association between XRCC1 Arg399Gln, Arg194Trp, and Arg280His polymorphisms and glioma risk, respectively. The pooled results showed that GlnGln carriage was associated with moderately increased risk of gliomas in Asians (GlnGln vs. ArgArg, OR=1.490, 95%CI 1.031-2.153; GlnGln/ArgGln vs. ArgArg, OR=1.321, 95%CI 1.037- 1.684), whereas a marginal association was revealed in Caucasians. For the Arg194Trp polymorphism, although a significant association was shown in the homozygous genotype comparisons (TrpTrp vs. ArgArg, OR = 2.209, 95%CI 1.398- 2.945), no significant link was found on subgroup analysis stratified by ethnicity. With regard to the Arg280His polymorphism, no significant association was found in each comparison. No particular study was found to significantly influence the pooled results, and no potential publication bias was detected.

CONCLUSIONS

This meta-analysis suggested that the XRCC1 Arg399Gln polymorphism is moderately associated with increased risk of gliomas in Asians, while Arg194Trp and Arg280His polymorphisms demonstrated no significant influence. Due to the limited studies and the potential confounders, further studies are needed to confirm these results.

XRCC1 Arg194Trp and Arg280His polymorphisms increase bladder cancer risk in Asian population: evidence from a meta-analysis

Background

A lot of studies have investigated the correlation between x-ray cross complementing group 1 (XRCC1) polymorphisms and bladder cancer risk, but the results in Asian population were still inconclusive. We conducted a meta-analysis to ascertain the association of XRCC1 Arg194Trp, Arg280His and Arg399Gln polymorphisms with bladder cancer risk in Asian population.

Methodology/Principal findings

The association strength was measured with odds ratios (ORs) and 95% confidence intervals (95% CIs). A total of 9 eligible studies, conducted in China, India and Japan, were identified. We observed a significant increased risk of bladder cancer in dominant model (OR = 1.199, 95% CI: 1.021,1.408, P_{heterogeneity} = 0.372), allele comparison (OR = 1.200, 95% CI: 1.057,1.362, P_{heterogeneity} = 0.107) of Arg194Trp, heterozygote comparison (OR = 1.869, 95% CI: 1.205,2.898, P_{heterogeneity} = 0.011) and dominant model (OR = 1.748, 95% CI: 1.054,2.900, P_{heterogeneity} = 0.01) of Arg280His. Pooled results estimated from adjusted ORs further validated these findings. No publication bias was detected. Subgroup analyses found that significant increased risk was only found among community-based studies not hospital-based studies. There was no evidence of publication bias.

Conclusion

This is the first meta-analysis conducted in Asian investigating the correlation between XRCC1 polymorphisms and susceptibility to bladder cancer. Our meta-analysis shows that XRCC1 Arg194Trp and Arg280His polymorphisms are associated with a significantly increased risk of bladder cancer in Asian population.

HPV prevalence and genetic predisposition to cervical cancer in Saudi Arabia

Background

Cervical cancer incidence is low in Saudi Arabian women, suggesting low prevalence to HPV infection due to environmental, cultural and genetic differences. Therefore, we investigated HPV prevalence and genotype distribution in cervical cancer as well as the association with 9 genetic single nucleotide polymorphisms (SNPs): CDKN1A (p21) C31A, TP53 C72G, ATM G1853A, HDM2 promoter T309G, HDM2 A110G, LIG4 A591G, XRCC1 G399A, XRCC3 C241T and TGFβ1 T10C, presumed to predispose to cancer.

Methods

One hundred cervical cancer patients (90 squamous cell carcinoma and 10 adenocarcinoma) and 100 age/sex-matched controls were enrolled. SNPs were genotyped by direct sequencing and HPV was detected and typed in tumors using the HPV Linear Array Test.

Results

Eighty-two cases (82%) were positive for HPV sequences. Seven HPV genotypes were present as single infections (16, 18, 31, 45, 56, 59, 73) and five double infections (16/18, 16/39, 16/70, 35/52, 45/59) were detected. Most common genotypes were HPV-16 (71%), 31 (7%), and 18, 45, 73 (4% each). Only XRCC1 SNP was significantly associated with cervical cancer (P=0.02, OD=1.69; 95% CI= 1.06–2.66). However, nested analysis revealed a preponderance of HPV-positivity in patients harboring the presumed risk allele TP53 G (P=0.06). Both XRCC1 and TP53 SNPs tended to deviate from Hardy-Weinberg equilibrium (HWE; P=0.03-0.07).

Conclusions

HPV prevalence (82%) in cervical cancer is at the lower range of the worldwide estimation (85 - 99%). While XRCC1 G399A was significantly associated with cervical cancer, TP53 G72C showed borderline association only in HPV-positive patients. Deviation from HWE in HPV-positive patients indicates co-selection, hence implicating the combination of HPV and SNPs in cancer predisposition. Thus, SNPs could be more relevant biomarkers of susceptibility to cervical cancer when associated with HPV infection.

XRCC1 polymorphisms increase bladder cancer risk in Asians: a meta-analysis

X-ray cross complementing group 1 (XRCC1) polymorphisms and bladder cancer risk has been investigated for years, but the result in Asian population is till inconclusive. Thus, we performed this meta-analysis to determine the association of XRCC1 Arg194Trp, Arg280His, and Arg399Gln polymorphisms with bladder cancer risk in the Asian population. PubMed, EMBASE, and China National Knowledge Infrastructure were searched up to January 2013 to identify eligible studies. The association strength was measured with odd ratios (ORs) and 95 % confidence intervals (95 % CIs). A total of nine eligible studies, including 1,931 bladder cancer patients and 2,192 controls, were identified. Significant increased risk of bladder cancer was observed for Arg194Trp polymorphism (allele comparison OR = 1.20, 95 % CI: 1.06-1.36, P heterogeneity = 0.11; dominant model OR = 1.20, 95 % CI: 1.02-1.41, P heterogeneity = 0.37) and Arg280His polymorphism (heterozygote comparison OR = 1.87, 95 % CI: 1.21-2.90, P heterogeneity = 0.01; dominant model OR = 1.75, 95 % CI: 1.05-2.90, P heterogeneity = 0.01); however, Arg399Gln was not associated with susceptibility to bladder cancer. No evidence of publication bias was detected. Our meta-analysis results suggest that XRCC1 Arg194Trp and Arg280His polymorphisms are associated with significantly increased risk of bladder cancer in Asians.

Polymorphisms in DNA repair genes and susceptibility to glioma in a chinese population

The excision repair cross-complementing rodent repair deficiency complementation group 1 (ERCC1), and X-ray repair cross-complementing group 1 (XRCC1) genes appear to protect mammalian cells from the harmful effects of ionizing radiation. We conducted a large case-control study to investigate the association of polymorphisms in ERCC1 C118T, ERCC1 C8092A, XRCC1 A194T, XRCC1 A194T, and XRCC3 C241T, with glioma risk in a Chinese population. Five single nucleotide polymorphisms (SNPs) were genotyped, using the MassARRAY IPLEX platform, in 443 glioma cases and 443 controls. Association analyses based on an χ² test and binary logistic regression were performed to determine the odds ratio (OR) and a 95% confidence interval (95% CI) for each SNP. For XRCC1 Arg194Trp, the variant genotype T/T was strongly associated with a lower risk of glioma cancer when compared with the wild type C/C (OR = 2.45, 95% CI = 1.43–4.45). Individuals carrying the XRCC1 399A allele had an increased risk of glioma (OR = 1.33, 95% CI = 1.02–1.64). The XRCC3 241T/T genotype was associated with a strong increased glioma risk (OR = 3.78, 95% CI = 1.86–9.06). Further analysis of the interactions of two susceptibility-associated SNPs, XRCC1 Arg194Trp and XRCC3 Thr241Met, showed that the combination of the XRCC1 194T and XRCC3 241T alleles brought a large increase in glioma risk (OR = 2.75, 95% CI = 1.54–4.04). XRCC1 Arg194Trp, XRCC1 Arg399Gln, and XRCC3 C241T, appear to be associated with susceptibility to glioma in a Chinese population.

The DNA repair protein XRCC1 functions in the plant DNA demethylation pathway by stimulating cytosine methylation (5-meC) excision, gap tailoring, and DNA ligation

DNA methylation patterns are the dynamic outcome of antagonist methylation and demethylation mechanisms, but the latter are still poorly understood. Active DNA demethylation in plants is mediated by a family of DNA glycosylases typified by Arabidopsis ROS1 (repressor of silencing 1). ROS1 and its homologs remove 5-methylcytosine and incise the sugar backbone at the abasic site, thus initiating a base excision repair pathway that finally inserts an unmethylated cytosine. The DNA 3'-phosphatase ZDP processes some of the incision products generated by ROS1, allowing subsequent DNA polymerization and ligation steps. In this work, we examined the possible role of plant XRCC1 (x-ray cross-complementing group protein 1) in DNA demethylation. We found that XRCC1 interacts in vitro with ROS1 and ZDP and stimulates the enzymatic activity of both proteins. Furthermore, extracts from xrcc1 mutant plants exhibit a reduced capacity to complete DNA demethylation initiated by ROS1. An anti-XRCC1 antibody inhibits removal of the blocking 3'-phosphate in the single-nucleotide gap generated during demethylation and reduces the capacity of Arabidopsis cell extracts to ligate a nicked DNA intermediate. Our results suggest that XRCC1 is a component of plant base excision repair and functions at several stages during active DNA demethylation in Arabidopsis.

X-ray repair cross complementing protein 1 in base excision repair

X-ray Repair Cross Complementing protein 1 (XRCC1) acts as a scaffolding protein in the converging base excision repair (BER) and single strand break repair (SSBR) pathways. XRCC1 also interacts with itself and rapidly accumulates at sites of DNA damage. XRCC1 can thus mediate the assembly of large multiprotein DNA repair complexes as well as facilitate the recruitment of DNA repair proteins to sites of DNA damage. Moreover, XRCC1 is present in constitutive DNA repair complexes, some of which associate with the replication machinery. Because of the critical role of XRCC1 in DNA repair, its common variants Arg194Trp, Arg280His and Arg399Gln have been extensively studied. However, the prevalence of these variants varies strongly in different populations, and their functional influence on DNA repair and disease remains elusive. Here we present the current knowledge about the role of XRCC1 and its variants in BER and human disease/cancer.

Tumor growth is suppressed in mice expressing a truncated XRCC1 protein

Tumor progression depends on the support of cells in the microenvironment, and is driven in part by the generation of reactive oxygen species (ROS). ROS can damage DNA, and the repair of damaged DNA is a well-known process involved in tumor initiation and promotion, but the role of DNA repair in tumor progression is not fully understood. In this regard the X-ray cross complementing 1 (XRCC1) protein is known to orchestrate the assembly of repair complexes at sites of DNA single strand breaks either directly or indirectly through repair of damaged bases, largely as the result of ROS-induced damage. XRCC1 polymorphisms have been shown to be associated with increased cancer. It was therefore of interest to investigate the effect of XRCC1 gene mutations on cancer progression. In an attempt to make XRCC1 point mutant mice, we generated a truncated protein (XRCC1tp) by the insertion of a neomycin cassette in intron12 of the XRCC1 gene. This unique finding allowed us to investigate cellular and tumor progression phenotypes in mice associated with expression and function of an altered XRCC1 protein on one allele. XRCC1tp cells showed increased toxicity to MMS, enhanced MMS-induced depletion of NADH suggesting increased PARP activity, and normal functional repair of MMS-induced DNA damage. Six months following treatment with the alkylating carcinogen azoxymethane (AOM) at 10 mg/kg once a week for 6 weeks, XRCC1tp mice had a decrease in average colon tumor volume of 14±3 mm(3) compared to 34±4 mm(3) in WT littermates (p ≤ 0.03, N= 20/genotype). XRCC1tp mice had a 72 per cent decrease in B16 melanoma tumor burden compared to wt littermates. Average tumor volume in transgenic PyMT metastatic breast cancer mice expressing XRCC1tp was 359 cubic mm in PyMT mice expressing XRCC1tp compared to 730 cubic mm in PyMT mice expressing XRCC1wt (p ≤ 0.001, N= 20/genotype). These data suggest that the presence of an XRCC1 truncated protein alters XRCC1 function independent of DNA repair, and is associated with anti-tumor activity.

The region of XRCC1 which harbours the three most common nonsynonymous polymorphic variants, is essential for the scaffolding function of XRCC1

XRCC1 functions as a non-enzymatic, scaffold protein in single strand break repair (SSBR) and base excision repair (BER). Here, we examine different regions of XRCC1 for their contribution to the scaffolding functions of the protein. We found that the central BRCT1 domain is essential for recruitment of XRCC1 to sites of DNA damage and DNA replication. Also, we found that ectopic expression of the region from residue 166-436 partially rescued the methyl methanesulfonate (MMS) hypersensitivity of XRCC1-deficient EM9 cells, suggesting a key role for this region in mediating DNA repair. The three most common amino acid variants of XRCC1, Arg194Trp, Arg280His and Arg399Gln, are located within the region comprising the NLS and BRCT1 domains, and these variants may be associated with increased incidence of specific types of cancer. While we could not detect differences in the intra-nuclear localization or the ability to support recruitment of POLβ or PNKP to micro-irradiated sites for these variants relative to the conservative protein, we did observe lower foci intensity after micro-irradiation and a reduced stability of the foci with the Arg280His and Arg399Gln variants, respectively. Furthermore, when challenged with MMS or hydrogen peroxide, we detected small but consistent differences in the repair profiles of cells expressing these two variants in comparison to the conservative protein.

Hodgkin lymphoma risk: role of genetic polymorphisms and gene-gene interactions in DNA repair pathways

DNA repair variants may play a potentially important role in an individual's susceptibility to developing cancer. Numerous studies have reported the association between genetic single nucleotide polymorphisms (SNPs) in DNA repair genes and different types of hematologic cancers. However, to date, the effects of such SNPs on modulating Hodgkin lymphoma (HL) risk have not yet been investigated. We hypothesized that gene-gene interaction between candidate genes in direct reversal, nucleotide excision repair (NER), base excision repair (BER) and double strand break (DSB) pathways may contribute to susceptibility to HL. To test this hypothesis, we conducted a study on 200 HL cases and 220 controls to assess associations between HL risk and 21 functional SNPs in DNA repair genes. We evaluated potential gene-gene interactions and the association of multiple polymorphisms in a chromosome region using a multi-analytic strategy combining logistic regression, multi-factor dimensionality reduction and classification and regression tree approaches. We observed that, in combination, allelic variants in the XPC Ala499Val, NBN Glu185Gln, XRCC3 Thr241Me, XRCC1 Arg194Trp, and XRCC1 399Gln polymorphisms modify the risk for developing HL. Moreover, the cumulative genetic risk score revealed a significant trend where the risk for developing HL increases as the number of adverse alleles in BER and DSB genes increase. These findings suggest that DNA repair variants in BER and DSB pathways may play an important role in the development of HL.

XRCC1 and base excision repair balance in response to nitric oxide

Inflammation associated reactive oxygen and nitrogen species (RONs), including peroxynitrite (ONOO(-)) and nitric oxide (NO), create base lesions that potentially play a role in the toxicity and large genomic rearrangements associated with many malignancies. Little is known about the role of base excision repair (BER) in removing these endogenous DNA lesions. Here, we explore the role of X-ray repair cross-complementing group 1 (XRCC1) in attenuating RONs-induced genotoxicity. XRCC1 is a scaffold protein critical for BER for which polymorphisms modulate the risk of cancer. We exploited CHO and human glioblastoma cell lines engineered to express varied levels of BER proteins to study XRCC1. Cytotoxicity and the levels of DNA repair intermediates (single-strand breaks; SSB) were evaluated following exposure of the cells to the ONOO(-) donor, SIN-1, and to gaseous NO. XRCC1 null cells were slightly more sensitive to SIN-1 than wild-type cells. We used small-scale bioreactors to expose cells to NO and found that XRCC1-deficient CHO cells were not sensitive. However, using a molecular beacon assay to test lesion removal in vitro, we found that XRCC1 facilitates AAG-initiated excision of two key NO-induced DNA lesions: 1,N(6)-ethenoadenine and hypoxanthine. Furthermore, overexpression of AAG rendered XRCC1-deficient cells sensitive to NO-induced DNA damage. These results show that AAG is a key glycosylase for BER of NO-induced DNA damage and that XRCC1's role in modulating sensitivity to RONs is dependent upon the cellular level of AAG. This demonstrates the importance of considering the expression of other components of the BER pathway when evaluating the impact of XRCC1 polymorphisms on cancer risk.