Polymorphisms of DNA repair gene XRCC1 in squamous cell carcinoma of the head and neck

Polymorphisms of the XRCC1 DNA repair gene in head and neck cancer

Inherited polymorphisms in the genes controlling the cell cycle or functioning in the DNA repair mechanisms may impair their function and contribute to genetic susceptibility. Abnormalities in the DNA repair have been reported in head and neck cancer. The XRCC1 gene functions in singlestrand break and base excision repair processes. In this study, two polymorphisms of the XRCC1 gene, Arg194Trp and Arg399Gln were investigated in 95 patients with head and neck carcinoma. The polymorphic regions were amplified by PCR followed by digestion with methylation-specific restriction enzymes, and analyzed electrophoretically. Genotype and allele frequencies were calculated, and association with cancer risk or clinical parameters was investigated. No association was observed between the genotypes and head and neck cancer for either polymorphism. Distribution of the alleles did not significantly differ between the patients and the control group. A significant association was only found for the Trp194 allele among the smoking individuals. Our data indicate that the Arg194Trp and Arg399Gln polymorphisms do not confer a significant risk for head and neck carcinogenesis.

Commentary: DNA base excision repair defects in human pathologies

DNA base excision repair (BER) is the main pathway for repair of endogenous damage in human cells. It was expected that a number of degenerative diseases could derive from BER defects. On the contrary, the link between BER defects and human pathology is elusive and the literature is full of conflicting results. The fact that most studies have investigated DNA variations but not their functional consequences has probably contributed to this confusing picture. From a functional point of view, it is likely that gross BER defects are simply not compatible with life and only limited reductions can be observed. Notwithstanding those limits, the pathological consequences of partial BER defects might be widespread and significant at the population level. This starts to emerge in particular for colorectal and lung cancer.

DNA repair gene XRCC1 polymorphisms in childhood acute lymphoblastic leukemia

Defective DNA repair has been reported to be a risk factor for various malignancies. Genetic polymorphisms of DNA repair genes are thought to result in different phenotypic features compared to the wild type. Genetic polymorphisms in XRCC1 gene could, through alteration of protein structure, lead to defective functioning of DNA Polbeta, PARP and LIG3 enzymes resulting in defective DNA repair and increased risk of childhood acute lymphoblastic leukemia (ALL). The role of DNA repair gene XRCC1 in susceptibility to childhood ALL has, however, not been widely studied and no data exists from Indian children. In this pilot study, through the use of PCR and RFLP, further confirmed by DNA sequencing, we have shown an increased risk of ALL among children with XRCC1 codons 194 and 399 variant genotypes. Among the three variants, only the association between codon 399 variant and risk of ALL appeared to be significant. The risk of ALL was higher in males with codons 194 and 399 polymorphisms than in females. However, no relation was found between the presence of these variant genotypes and treatment outcome.

Polymorphisms of the XRCC1, XRCC3, & XPD genes, and colorectal cancer risk: a case-control study in Taiwan

BACKGROUND

Recent studies relating to the association between DNA repair-gene polymorphisms and colorectal cancer risk would, to the best of our knowledge, appear to be very limited. This study was designed to examine the polymorphisms associated with three DNA repair genes, namely: XRCC1 Arg399Gln, XRCC3 Thr241Met and XPD Lys751Gln, and investigate their role as susceptibility markers for colorectal cancer.

METHODS

We conducted a case-control study including 727 cases of cancer and 736 hospital-based age- and sex-matched healthy controls to examine the role of genetic polymorphisms of three DNA-repair genes (XRCC1, XRCC3 and XPD) in the context of colorectal cancer risk for the Taiwanese population. Genomic DNA isolated from 10 ml whole blood was used to genotype XRCC1 Arg399Gln, XRCC3 Thr241Met and XPD Lys751Gln by means of polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis.

RESULTS

The risk for colorectal cancer did not appear to differ significantly amongst individuals featuring the XRCC1 399Arg/Arg genotype (OR = 1.18; 95% CI, 0.96-1.45), the XRCC3 241Thr/Thr genotype (OR = 1.25; 95% CI, 0.88-1.79) or the XPD 751Gln allele (OR = 1.20; 95% CI, 0.90-1.61), although individuals featuring a greater number of risk genotypes (genotype with OR greater than 1) did experience a higher risk for colorectal cancer when compared to those who didn't feature any risk genotypes (Trend test P = 0.03). Compared with those individuals who didn't express any putative risk genotypes, individuals featuring all of the putative risk genotypes did experience a significantly greater cancer risk (OR = 2.43, 95% CI = 1.21-4.90), particularly for individuals suffering tumors located in the rectum (OR = 3.18, 95% CI = 1.29-7.82) and diagnosed prior to the age of 60 years (OR = 4.90, 95% CI = 1.72-14.0).

CONCLUSIONS

Our results suggest that DNA-repair pathways may simultaneously modulate the risk of colorectal cancer for the Taiwanese population, and, particularly for rectal cancer and younger patients.

Use of biomarkers to characterize functions of polymorphic DNA repair genotypes

Inheritance of variant DNA repair genes is believed to influence individual susceptibility to the development of environmental cancer. However, the validity of the belief is dependent upon understanding the functions of the variant genes. Consequently, a variety of studies have been conducted to investigate the functions of variant DNA repair genes, e.g. using biomarkers. These studies on several representative polymorphic DNA repair genes are reviewed in this report. From a general overview, it appears that the biomarker investigations did not provide consistent observations. However, from a more careful evaluation, it is clear that the inconsistencies are probably caused by the use of populations and biomarkers that are not appropriate for investigating the repair activities of the genes. For example, the use of cigarette smokers and patients may not generate precise information for this type of investigations because these conditions can modify the functions of the investigated genes. Thus, the use of healthy non-smokers would be more appropriate. Other problems with these studies includes the small sample size used and the fact that some of the biomarkers used, such as sister chromatid exchanges, are not appropriate because the mechanisms for formation of the biomarkers and their biological significance are unknown. Nevertheless, the following conclusions can be derived from the review of the various biomarker studies that have been published. XRCC1 194Trp, OGG1 326Cys and APE1 148Glu probably have limited alterations in repair activities compared to the wild-type genotypes. XRCC1 399Gln and XRCC3 241Met are deficient in the repair of X-ray-, but not UV-light-induced chromosome aberrations, therefore the variant genes are defective in base excision repair. XPD 312Asn and XPD 751Gln are deficient in the repair of UV-light- but not X-ray-induced chromosome aberrations, therefore they are defective in nucleotide excision repair.

DNA repair gene XRCC1 polymorphisms, smoking, and esophageal cancer risk

To investigate the effect of X-ray repair cross complementing 1 (XRCC1) genetic polymorphisms on esophageal cancer risk, we determined XRCC1 polymorphisms at codon 194 (Arg --> Trp) and codon 399 (Arg --> Gln) in 135 patients with esophageal squamous cell carcinoma (ESCC) and 152 normal controls from hospitals. Although polymorphism at codon 194 was not associated with risk for ESCC, we found that the frequency of XRCC1 399 Gln/Gln genotype in ESCC patients (14.1%) was significantly higher than that in normal controls (3.3%), and that XRCC1 399 Gln/Gln genotype was associated with an increased risk of ESCC (odds ratio (OR) = 5.15, 95% confidence interval (CI): 2.42-0.93). In addition, we found that the risk for smoker increased 4.2-fold than non-smokers in the 399 Gln/Gln genotype (OR = 4.20, 95% CI: 2.37-7.44). These results suggest that XRCC1 399 Gln/Gln genotype may contribute to the risk of ESCC and modify risk associated with smoking.

Genetic polymorphisms of DNA repair and xenobiotic-metabolizing enzymes: effects on levels of sister chromatid exchanges and chromosomal aberrations

Elevated levels of chromosomal aberrations (CAs) in peripheral blood lymphocytes, widely used as a cytogenetic biomarker of genotoxic effects, have been linked to cancer predisposition. However, tobacco smoking, occupational carcinogen exposure, or time since CA analysis do not appear to explain the cancer predictivity of CAs. Alternatively, the observed CA-cancer association could reflect unidentified exposures or individual susceptibility. We assessed the effects of genetic polymorphisms of DNA repair proteins and xenobiotic-metabolizing enzymes (XMEs) on the levels of CAs and sister chromatid exchanges (SCEs) in peripheral lymphocytes of 145 (CAs) and 60 (SCEs) healthy Caucasians. Genotypes of DNA repair genes X-ray repair cross-complementation group 1 (XRCC1 codons 194, 280, 399) and 3 (XRCC3 codon 241 [corrected]), and XME genes glutathione-S-transferase (GST) M1 and T1 and N-acetyl transferase 2 (NAT2) were determined using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP)-based methods. After Poisson regression adjustment for age, sex, smoking, country, and genotypes, a higher frequency of chromosome-type breaks was observed for NAT2 slow acetylators (in nonsmokers) and GSTT1 null subjects (in smokers). Individuals carrying variant alleles for XRCC1 codons 280 and 194 showed a decreased level of chromosome-type breaks. The effect of GSTM1 null and XRCC1 codon 399 genotypes on the frequency of CAs was modified by smoking. In linear regression models adjusting for age, sex, smoking, and genotypes, none of the polymorphisms significantly affected SCE frequency, although GSTT1 null subjects had a slightly elevated SCE level. Our results are in line with earlier findings on the influence of NAT2, GSTT1, and GSTM1 polymorphisms on the level of lymphocyte chromosome damage and suggest that also XRCC1 polymorphism affects CA frequencies, thus apparently influencing DNA repair phenotype. It remains to be examined whether these or other genetic polymorphisms could explain the observed cancer risk predictivity of high CA frequency.

Association of DNA repair gene XRCC1 polymorphisms with head and neck cancer in Korean population

Squamous cell carcinoma of the head and neck (SCCHN), which is relatively prevalent in Korea, is believed to be induced by environmental carcinogens and host genetic factors. Accumulating evidence has shown that genetic differences in DNA repair capacity resulting from genetic polymorphism influence the risk of environmental carcinogenesis. We therefore examined the associations of genetic polymorphisms in the DNA repair genes XRCC1 with the risk of SCCHN in a Korean population (hospital-based, case-control study; 147 cases and 168 controls). Three known polymorphisms in the XRCC1 gene were genotyped: R194W(C>T) in exon 6, R280H(G>A) in exon 9 and R399G(G>A) in exon 10. Although no significant associations were apparent with R280H(G>A) and R399G(G>A), a highly significant association (p = 0.0005) of R194W(C>T) with the increased risk (OR = 2.61; 95% CI 1.53-4.46) of SCCHN was detected among patients and normal controls under dominant model. The frequency of minor allele-containing genotypes (TT and CT) was much higher in SCCHN patients (51.8%) compared to that in normal controls (30.3%) (p = 0. 0005). When considering a relatively small number of cases (n = 147) and controls (n = 168) in our study, larger studies are needed to validate the genetic effects of XRCC1 polymorphisms in Asian populations. In conclusion, the result from our study provides additional evidence of an association of the XRCC1 polymorphism (Arg194Trp) with SCCHN as markers of genetic susceptibility in the Korean population.

Polymorphisms of DNA Repair Genes and Risk of Glioma

DNA repair genes play a major role in maintaining genomic stability through different repair pathways that are mediated by cell cycle control genes such as p53. We found previously that glioma patients were susceptible to gamma-ray-induced chromosomal breaks, which may be influenced by genetic variation in genes involved in DNA strand breaks, such as XRCC1 in single-strand break repair, XRCC3 and RAD51 in homologous recombination repair, and XRCC7 in nonhomologous end joining double-strand break repair. Therefore, we tested the hypothesis that genetic polymorphisms in XRCC1, XRCC3, RAD51, XRCC7, and p53 were associated with risk of glioma in 309 patients with newly diagnosed glioma and 342 cancer-free control participants frequency matched on age (+/- 5 years), sex, and self-reported ethnicity. We did not find any statistically significant differences in the distributions of XRCC1 Arg399Gln, XRCC3 Thr241Met, RAD51 G135C, and P53 Arg72Pro polymorphisms between the cases and the controls. However, the XRCC7 G6721T variant T allele and TT genotype were more common in the cases (0.668 and 43.4%, respectively) than in the controls (0.613 and 38.9%, respectively), and the differences were statistically significant (P = 0.045 and 0.040, respectively). The adjusted odds ratios were 1.78 (95% confidence interval, 1.08-2.94) and 1.86 (95% confidence interval, 1.12-3.09) for the GT heterozygotes and TT homozygotes, respectively. The combined T variant genotype (GT+TT) was associated with a 1.82-fold increased risk of glioma (95% confidence interval, 1.13-2.93). These results suggest that the T allele may be a risk allele, and this XRCC7 polymorphism may be a marker for the susceptibility to glioma. Larger studies are needed to confirm our findings and unravel the underlying mechanisms.

Rescue of Xrcc1 knockout mouse embryo lethality by transgene-complementation

Xrcc1 knockout embryos show increased DNA breakage and apoptosis in tissues of the embryo proper prior to death at embryonic day E6.5. An additional deficiency in Trp53 allows Xrcc1(-/-) embryos to enlarge slightly and initiate gastrulation although ultimately death is delayed by less than 24h. Death presumably results from DNA damage that reaches toxic levels in the post-implantation mouse embryo. To investigate the level of XRCC1 protein needed for successful mouse development, we derived Xrcc1 transgene-complemented Xrcc1(-/-) mice that express Xrcc1 within the normal range or at a greatly reduced level (<10% normal). The greatly reduced XRCC1 protein level destabilized the XRCC1 partner protein DNA ligase III (LIG3) but still allowed for successful mouse development and healthy, fertile adults. Fibroblasts from these animals exhibited almost normal alkylation sensitivity measured by differential cytotoxicity. Thus, a large reduction of both XRCC1 and DNA ligase III has no observable effect on mouse embryogenesis and post-natal development, and no significant effect on cellular sensitivity to DNA alkylation. The presence of XRCC1, even at reduced levels of expression, is therefore capable of supporting mouse development and DNA repair.

The role of genomic instability in the pathogenesis of squamous cell carcinoma of the head and neck

Measurements of genomic instability, or identification of genes responsible for instability, may potentially be used as molecular markers to predict disease course and response to therapy. Other possible applications include use of genomic instability measurements, or genes, as tools to screen for primary or recurrent disease. Methodologies for detection of genetic mutations in saliva, blood, and sputum have already been described[61,62]. Brennan et al [63] have described a molecular technique for analyzing histopathologically negative margins and lymph nodes for the presence of p53 gene mutation. This study showed that a positive molecular margin significantly predicted disease recurrence. The recognition that HNSCC is a genetically heterogeneous disease represents a major step toward developing an understanding of its underlying genetic basis. To develop an insight into this genetically heterogeneous disease, investigators must not only focus their efforts on specific head and neck disease sites. Laser-capture microdissection represents a powerful tool for isolating very specific cell populations from tumors [64]. Leethanakul et al[65] performed laser-capture microdissection on oral cavity SCC to construct stage-specific cDNA libraries. Sequencing of 96 clones from each of the six libraries constructed suggested the existence of 132 novel genes, which may play a role in the pathogenesis of HNSCC. The current literature suggests that many individuals diagnosed withHNSCC are genetically predisposed to developing malignancy because of some inherent deficiency of their capacity to maintain their genome in the presence of environmental stressors. Head and neck cancers are highly heterogeneous tumors and exhibit a wide variety of forms of genomic instability. Thus, genomic instability may be viewed as a fundamental force driving head and neck tumorigenesis and evolution. Future study of the specific genetic mechanisms that underlie genomic instability in the HNSCCpatient population is needed. It is only through study of this fundamental force that drives the development of these tumors that clinicians may gain the insight required to develop new diagnostic and therapeutic modalities to benefit the HNSCC patient population as a whole.

Sensing DNA damage by PARP-like fingers

PARP-like zinc fingers are protein modules, initially described as nick-sensors of poly(ADP-ribosyl)-polymerases (PARPs), which are found at the N-terminus of different DNA repair enzymes. I chose to study the role of PARP-like fingers in AtZDP, a 3' DNA phosphoesterase, which is the only known enzyme provided with three such finger domains. Here I show that PARP-like fingers can maintain AtZDP onto damaged DNA sites without interfering with its DNA end repair functions. Damage recognition by AtZDP fingers, in fact, relies on the presence of flexible joints within double-strand DNA and does not entail DNA ends. A single AtZDP finger is already capable of specific recognition. Two fingers strengthen the binding and extend the contacts on the bound DNA. A third finger further enhances the specific binding to damaged DNA sites. Unexpectedly, gaps but not nicks are bound by AtZDP fingers, suggesting that nicks on a naked DNA template do not provide enough flexibility for the recognition. Altogether these results indicate that AtZDP PARP-like fingers, might have a role in positioning the enzyme at sites of enhanced helical flexibility, where single-strand DNA breaks are present or are prone to occur.

High frequency of HPV16-associated head and neck squamous cell carcinoma in the Puerto Rican population

BACKGROUND

Recent evidence has accumulated suggesting that human papillomavirus (HPV) plays a role in the development of head and neck squamous cell carcinoma (HNSCC). HPV16 is the most common of the HPV subtypes associated with oral and laryngeal malignancies. This study estimated the prevalence of HPV16 DNA in Puerto Rican patients with HNSCC.

METHODS

DNA was extracted from frozen tissue of 118 HNSCCs. Genomic DNA was screened for the presence of HPV16 DNA with E6-specific and E7-specific primers.

RESULTS

HPV16 was detected in tumor tissue of 52 patients (44%) with HNSCC. The oropharynx had a slightly higher incidence of HPV16 DNA. Fifteen of 66 patients with HPV16-negative HNSCC later had recurrences. Positivity for HPV16 was independent of the tumor grade, tumor stage, nodal status, and tobacco or alcohol use. The 3-year survival rate was higher in HPV16-positive patients than in HPV16-negative patients (36% vs 21%).

CONCLUSIONS

Our findings suggest that HPV16 may play a role in the etiology of a subgroup of HNSCC in Puerto Ricans. Overall survival times of the HPV16-positive patients were not significantly different from those of HPV16-negative patients. Increasing our understanding of the role of HPV16 in the etiology of HNSCC might facilitate the development of new treatment modalities for this subgroup of HNSCC.

Lack of association between DNA base excision repair gene XRCC1 Gln399Arg polymorphism and risk of malignant lymphoma in Japan

Growing evidence suggests that the polymorphism of DNA base excision repair gene XRCC1 Arg399Gln is associated with altered DNA repair proficiency and subsequent cancer susceptibility; however, no evidence is available for malignant lymphoma. We therefore conducted a case-control study (372 cases, 500 controls) to evaluate links with malignant lymphoma risk in Japan. The risk was evaluated in terms of odds ratio (OR) and 95% confidence interval (CI) adjusted for age and sex in an unconditional logistic regression model. There was no statistical risk change with the Arg/Gln (adjusted OR 0.89; 0.65-1.23, P = 0.492) or the Gln/Gln (0.57; 0.27-1.17, P = 0.127) compared with the Arg/Arg of the XRCC1 Arg399Gln polymorphism. The results were unchanged in analyses according to histological subtype (diffuse large lymphoma, follicular lymphoma, low-grade lymphoma of mucosa-associated lymphoid tissue, and others). These data suggest that XRCC1 Gln399Arg polymorphism plays a limited role in lymphomagenesis. Further study on the interaction between the polymorphism and environmental exposure is required.

Polymorphisms XRCC1-R399Q and XRCC3-T241M and the Risk of Breast Cancer at the Ontario Site of the Breast Cancer Family Registry

This study investigates the role of two nonsynonymous single nucleotide polymorphisms in DNA repair genes, X-ray repair cross-complementing group 1 (XRCC1)-R399Q and X-ray repair cross-complementing group 3 (XRCC3)-T241M, in breast cancer. Incident cases of invasive breast cancer in Caucasian women [n = 402, mean age = 45.7 (SD = 6.2) years] and female Caucasian controls [n = 402, mean age = 45.2 (6.5) years] frequency matched on 5-year age intervals were identified from the Ontario Familial Breast Cancer Registry. No evidence for a main effect of the XRCC1-R399Q genotype on breast cancer risk was observed. Estimates of risk for a family history (FH) of breast cancer compared with no FH differed by XRCC1-R399Q genotype (P value for interaction = 0.001). Homozygote XRCC1-399 R/R individuals and FH+ were at a 2.92-fold [95% confidence interval (95% CI) = 1.47–5.79] increased risk of disease compared with FH− individuals; the estimate of risk increased for R/Q heterozygotes with FH+ [odds ratio (OR) = 3.85, 95% CI = 1.94–7.65] but not for Q/Q homozygotes with FH+ (OR = 0.54, 95% CI = 0.20–1.47) compared with homozygous R/R and FH− individuals. A marginal positive association for XRCC3-241 M/M compared with T/T genotype was found (OR = 1.44, 95% CI = 0.94–2.19), but the heterozygous T/M was not associated with an increase in risk (OR = 0.96, 95% CI = 0.71–1.32). There was also some evidence for a combined effect of body mass index and XRCC3-T241M on estimates of risk. Our results suggest that these polymorphisms may influence breast cancer risk by modifying the effect of risk factors such as FH. There is a need for further study into the role of these polymorphisms as effect modifiers.

Impact of Types of Lymphocyte Chromosomal Aberrations on Human Cancer Risk

The frequency of cells with structural chromosomal aberrations (CAs) in peripheral blood lymphocytes is the first genotoxicity biomarker that has shown an association with cancer risk. CAs are usually divided into chromosome-type (CSAs) and chromatid-type aberrations (CTAs), with different mechanisms of formation. From a mechanistic point of view, it is of interest to clarify whether the cancer predictivity of CAs is different with respect to CSAs and CTAs. We report here cancer risk for cytogenetically tested, healthy subjects with respect to frequency of CAs, CSAs, and CTAs in peripheral blood lymphocytes, using Nordic (1981 subjects with CA data, 1871 subjects with CSA/CTA data) and Italian (1573 subjects with CA data, 877 subjects with CTA/CSA data) cohorts, with a median follow-up of 17 years. High levels of CAs at test were clearly associated with increased total cancer incidence in the Nordic cohorts and increased total cancer mortality in the Italian cohort. In the Nordic cohorts, significantly elevated cancer risks were observed for subjects with both high CSAs and high CTAs at test, and these variables showed equally strong cancer predictivity. The results of the Italian cohort did not indicate any clear-cut difference in cancer predictivity between the CSA and CTA biomarkers. There was no significant effect modification by age at test, gender, country, or time since test. The results suggest that both DNA double-strand breaks and other initial DNA lesions responsible for CSAs and CTAs are associated with cancer risk.

Molecular epidemiology of pancreatic cancer

Pancreatic cancer is the fourth leading cause of cancer-related death in the United States. Currently there is no early diagnostic test and no effective treatment options for this deadly disease. Prevention of pancreatic cancer is difficult because little is known about its etiology. The main modifiable risk factors for pancreatic cancer include cigarette smoking and dietary factors. Information from molecular epidemiological study of pancreatic cancer is very limited. DNA adducts derived from exposure to polycyclic aromatic hydrocarbon, aromatic amines, and heterocyclic amines have been detected in human pancreatic tissues. DNA damages derived from oxidative stress and lipid peroxidation are also present in the pancreas. No study has demonstrated a main effect of carcinogen-metabolizing genes and DNA repair genes on the risk of pancreatic cancer thus far. However, significant effects of these genes have been observed among individuals with known carcinogen exposure, such as smoking. A number of environmental and lifestyle factors, such as smoking, alcohol, coffee consumption, and exposure to organochlorine or hydrocarbon solvent, have been associated with the frequency and spectrum of K-ras mutation in pancreatic tumors. Dietary folate intake and serum levels of folate have been associated with the risk of pancreatic cancer among male smokers. These findings demonstrate the potential of the molecular epidemiology approach in understanding the etiology of pancreatic cancer. Further efforts should be made to understand the interactive relationship between genetic and environmental factors in the etiology of pancreatic cancer, which will in turn be important in identifying the high-risk population for the primary prevention of this deadly disease.

Effect of XPD/ERCC2 polymorphisms on chromosome aberration frequencies in smokers and on sensitivity to the mutagenic tobacco-specific nitrosamine NNK

Polymorphisms in DNA-repair genes could contribute to the interindividual differences in cancer susceptibility in smokers. By reducing DNA-repair capacity, these polymorphisms may influence the net level of smoking-induced genetic damage significantly, a critical step in the cascade of events leading to cancer. In this biomonitoring study, we examined the relationship between polymorphisms in the DNA-repair gene XPD/ERCC2 and genetic damage. We tested the hypothesis that coding polymorphisms in XPD/ERCC2 limit DNA-repair efficiency in humans leading to increased frequencies of chromosome aberration (CA) in their lymphocytes. We also used the mutagen-sensitivity assay, with the tobacco-specific nitrosamine NNK as a model mutagen, to determine whether lymphocytes from individuals with the variant XPD alleles are more sensitive to this tobacco-specific carcinogen. We calculated odds ratios (ORs) as estimates of relative risk of increased frequencies of CA associated with two XPD polymorphisms (Asp312Asn in exon 10 and Lys751Gln in exon 23). We observed a 2.57-fold (95% confidence limit [CL] = 0.88-7.50; P = 0.10) increase in risk of elevated in vivo frequencies of CA associated with the variant 312Asn allele in the total population. The relative risk was more pronounced in smokers (OR = 4.67; 95% CL = 1.04-20.90; P = 0.04) and in all subjects >48 years old (OR = 7.33; 95% CL = 1.53-35.10; P = 0.01). Similarly, elevations in NNK-induced aberrations were significantly associated with the 312Asn allele (OR = 3.69; 95% CL = 1.29-10.56; P = 0.02). The risk was higher in smokers (OR = 4.62; 95% CL = 1.14-18.70; P = 0.04) and in subjects >48 years old (OR = 5.76; 95% CL = 1.30-25.41; P = 0.03). No significant effect was observed with the 715Gln variant allele in relation to either in vivo or NNK-induced CA. These data suggest that the Asp312Asn polymorphism may alter the phenotype of the XPD protein, resulting in reduced DNA-repair capacity.

DNA Repair Gene XRCC1 and XPD Polymorphisms and Risk of Prostate Cancer

The X-ray repair cross-complementing group 1 (XRCC1) and xeroderma pigmentosum group D (XPD) genes are involved in base excision repair and nucleotide excision repair of DNA repair pathways, respectively. A growing body of evidence suggests that XRCC1 and XPD are important in environmentally induced cancers, and polymorphisms in both genes have been identified. To determine whether the XRCC1 (codon Arg399Gln) and XPD (codon Asp312Asn and codon Lys751Gln) polymorphisms are associated with prostate cancer susceptibility, we genotyped these polymorphisms in a primarily Caucasian sample of 506 sibships (n = 1,117) ascertained through a brother with prostate cancer. Sibships were analyzed with a Cox proportional hazards model with age at prostate cancer diagnosis as the outcome. Of the three polymorphisms investigated, only the XPD codon 312 Asn/Asn genotype had an odds ratio (OR) significantly different from one (OR, 1.61; 95% CI, 1.03-2.53). Analyses stratified by the clinical characteristics of affected brothers in the sibship did not reveal any significant heterogeneity in risk. In exploring two-way gene interactions, we found a markedly elevated risk for the combination of the XPD codon 312 Asn/Asn and XRCC1 codon 399 Gln/Gln genotypes (OR, 4.81; 95% CI, 1.66-13.97). In summary, our results suggest that the XPD codon 312 Asn allele may exert a modest positive effect on prostate cancer risk when two copies of the allele are present, and this effect is enhanced by the XRCC codon 399 Gln allele in its recessive state.

CYP1A1 and XRCC1 gene polymorphisms in SCC of the larynx

The present study was undertaken to examine CYP1A1 and XRCC1 polymorphisms as potential genetic susceptibility markers for laryngeal squamous cell carcinoma (SCC). Eighty-eight patients with laryngeal SCC and 178 randomly selected healthy blood donors from the same Caucasian population (Porto, Northern Portugal) were analysed for CYP1A1 (MspI and NcoI) and XRCC1 (Arg194Trp and Arg399Gln) polymorphisms, using PCR-RFLP techniques. CYP1A1 MspI MH (mutant homozygous) and CYP1A1 NcoI HT (heterozygous) genotypes were more frequent in patients than in controls, with those carrying a CYP1A1 NcoI HT genotype having a 2.3-fold higher risk for tumour development. On the other hand, polymorphisms in XRCC1 codon 399 and codon 194 do not seem to play a role in the aetiology of smoking-related laryngeal SCC, once its distribution was similar in both analysed groups. All the significant associations observed were exclusively due to differences between controls and larynx glottic cancer patient subgroup. Furthermore, lower lifetime tobacco consumption was observed in laryngeal SCC patients carrying the MspI and NcoI polymorphisms, than in those who did not show the polymorphic variants. This investigation seems to support the importance of CYP1A1 gene polymorphism as a potential genetic marker of laryngeal cancer development, specially concerning smokers who have inherited the at-risk genotypes CYP1A1 MspI MH or CYP1A1 NcoI HT, who do appear to be more susceptible to the development of SCC of the glottic larynx.

From genotype to phenotype: correlating XRCC1 polymorphisms with mutagen sensitivity

This study correlated the extent of induced in vitro chromosomal damage, assessed by the mutagen sensitivity assay, with genotypes of the X-ray repair cross complementing group 1 (XRCC1) gene, which encodes for a base excision repair protein. There are two common polymorphisms that cause amino acid substitutions in XRCC1, one at codon 194 in exon 6 and another at codon 399 in exon 10. We genotyped these two polymorphisms in 524 healthy subjects and performed mutagen sensitivity assays using both bleomycin and benzo[a]pyrene-diol-epoxide (BPDE) as challenge mutagens. Our results showed that individuals with the wildtype exon 6 Arg/Arg exhibited significantly higher values of chromosomal breaks per cell (b/c) than those with one or two variant Trp alleles (P=0.005 for bleomycin and P=0.05 for BPDE). For the exon 10 polymorphism, subjects who were Gln/Gln homozygotes had higher b/c than did those with other genotypes, with evidence of a gene dosage effect. When we combined the two polymorphic sites and used the exon 6 Arg/Trp and Trp/Trp and exon 10 Arg/Arg genotypes as the reference category, these differences were enhanced for bleomycin sensitivity (P for trend = 0.032), but not for BPDE sensitivity (P for trend = 0.821). These data are biologically plausible since codon 399 is located within the BRCA1 C-terminus functional domain and codon 194 is in the linker region of the XRCC1 N-terminal functional domain. To our knowledge, this is the largest study conducted evaluating the functional relevance of these polymorphisms.

Lack of involvement of nucleotide excision repair gene polymorphisms in colorectal cancer

DNA repair has an essential role in protecting the genome from damage by endogenous and environmental agents. Polymorphisms in DNA repair genes and differences in repair capacity between individuals have been widely documented. For colorectal cancer, the loss of mismatch repair gene activity is a key genetic determinant. Nucleotide excision repair (NER), recombination repair (RR) and base excision repair (BER) pathways have critical roles in protection against other cancers, and we wished to investigate their role in colorectal cancer. We have compared the frequency of polymorphisms in the NER genes, XPD, XPF, XPG, ERCC1; in the BER gene, XRCC1; and in the RR gene, XRCC3; in colorectal cancer patients and in a control group. No significant associations were found for any of the NER gene polymorphisms or for the XRCC1 polymorphism. The C allele (position 18067) of the XRCC3 gene was weakly but significantly associated with colorectal cancer (odds ratio 1.52, 95% confidence interval 1.04-2.22, P=0.03). For all patients who were heterozygous for any of the repair genes studied, tumour tissue was investigated for loss of heterozygosity (LOH). Only one example of LOH was found for all the genes examined. From the association and LOH data, we conclude that these genes do not have an important role in protection against colorectal carcinogenesis.

Genetic instability in bladder cancer assessed by the comet assay

BACKGROUND

Latent genetic instability has been associated with an increased risk for several cancers. We used the comet assay (single-cell gel electrophoresis) to assess whether genetic instability, as reflected by susceptibility to DNA damage, was associated with the risk of bladder cancer in a case-control study.

METHODS

We used the comet assay to measure baseline and benzo[a]pyrene diol epoxide (BPDE)- and gamma-radiation-induced DNA damage in individual peripheral blood lymphocytes from 114 incident case patients with bladder cancer and 145 matched healthy control subjects. All subjects provided personal information, including smoking history. DNA damage was visualized with the comet assay and quantified by the Olive tail moment parameter, a relative measure. Multivariable analysis was used to assess relative risks for bladder cancer associated with DNA damage. All statistical tests were two-sided.

RESULTS

Baseline levels of DNA damage were statistically significantly higher in case patients (tail moment = 1.40) than in control subjects (tail moment = 1.21) (difference = 0.19, 95% confidence interval [CI] = 0.04 to 0.32; P =.015), as were gamma-radiation-induced (tail moment = 4.76 versus 4.22; difference = 0.54, 95% CI = 0.11 to 0.96; P =.013) and BPDE-induced (tail moment = 4.06 versus 3.45; difference = 0.61, 95% CI = 0.23 to 0.99; P =.002) DNA damage. When data were dichotomized at the median value for DNA damage in control subjects and adjusted for age, sex, ethnicity, and smoking status, an increased estimated relative risk of bladder cancer was statistically significantly associated with DNA damage at baseline (odds ratio [OR] = 1.84, 95% CI = 1.07 to 3.15) and after gamma-radiation (OR = 1.81, 95% CI = 1.04 to 3.14) but not after BPDE treatment (OR = 1.69, 95% CI = 0.98 to 2.93).

CONCLUSION

Latent genetic instability as measured by the comet assay is associated with an increased estimated relative risk of bladder cancer.

Polymorphisms in the DNA repair genes XPD, XRCC1, XRCC3, and APE/ref-1, and the risk of lung cancer among male smokers in Finland

Associations between lung cancer risk and common polymorphisms in the DNA repair genes xeroderma pigmentosum complementation group D (XPD), X-ray repair cross-complementing group 1 (XRCC1), XRCC3 and apurinic/apyrimidinic endonuclease/redox factor 1 were examined within a randomized clinical trial designed to determine whether alpha-tocopherol, beta-carotene, or both would reduce cancer incidence among male smokers in Finland. We found no direct association between lung cancer risk and any of the DNA repair genotypes studied, however, the association between XPD codon 751 genotype and lung cancer was modified by alpha-tocopherol supplementation, and the association between XRCC1 codon 399 genotype and lung cancer was modified by the amount of smoking. Our results suggest that common alterations in single DNA repair genes are not major determinants of lung cancer susceptibility among smokers.

Promoter hypermethylation and inactivation of hMLH1, a DNA mismatch repair gene, in head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is a multistage process during which adverse genetic alterations accumulate resulting in loss of cell cycle control, selective cell overgrowth, and ultimately formation of malignancy. Among various genetic alterations in HNSCC is increased microsatellite instability (MSI). hMLH1 is one of the major mismatch DNA repair genes, the inactivation of which caused increased MSI in a variety of human cancers including HNSCC. While somatic mutation is a major mechanism of the hMLH1 gene inactivation in hereditary form of human cancer, promoter hypermethylation appears to be primarily involved in the inactivation of the hMLH1 gene in sporadic form of human cancers. In the current study, we analyzed 78 cases of HNSCC for hMLH1 protein expression and promoter hypermethylation by IHC and methylation-specific PCR (MSP). Twenty-four of 78 cases (31%) of HNSCC contained markedly reduced levels of the hMLH1 protein. Based on the IHC results, 8 cases without and 8 with hMLH1 protein expression (total of 16) were further analyzed by MSP. Seven of 8 cases (88%) that were negative for the hMLH1 protein displayed promoter hypermethylation, whereas 7 of 7 cases (100%) strongly positive for the protein were free of promoter methylation. This study confirms our previous conclusion that promoter hypermethylation represents a major mechanism of the hMLH1 gene inactivation in HNSCC.

Polymorphisms of XRCC1 and XRCC3 genes and susceptibility to breast cancer

Mammalian cells are constantly exposed to a wide variety of genotoxic agents from both endogenous and exogenous sources. Genetic variability in DNA repair may contribute to human cancer risk. We used a case-control study design (162 cases and 302 controls) to test the association between three amino acid substitution variants of DNA repair genes (XRCC1 Arg194Trp, XRCC1 Arg399Gln, and XRCC3 Thr241Met) and breast cancer susceptibility. We found a weak association between the XRCC1 194Trp allele and breast cancer risk (adjusted odds ratio (OR)=1.98; 95% confidence interval (CI)=0.85-4.63). We also found a potential gene-gene interaction between the XRCC1 194Trp allele and XRCC3 241Met allele and breast cancer risk (adjusted OR=8.74; 95% CI=1.13-67.53). Although larger studies are needed to validate the study results, our data suggest that amino acid substitution variants of XRCC1 and XRCC3 genes may contribute to breast cancer susceptibility.

Influence of common XPD and XRCC1 variant alleles on p53 mutations in lung tumors

The DNA repair proteins XPD and XRCC1 are involved in the nucleotide and base excision repair of DNA lesions induced by many tobacco and environmental carcinogens. Common variant alleles at the XPD (312Asn, 751Gln) and XRCC1 (399Gln) loci have been identified and associated with increased risk for lung cancer. We therefore investigated a possible effect of these variant alleles on the frequency and spectrum of p53 mutations in the tumors of 97 Swedish lung cancer patients (56 never-smokers and 41 age-, gender-, and hospital-matched ever-smokers). The p53 gene was mutated in 4 never-smokers (7%) and 11 ever-smokers (27%). Smoking-related transversion-type mutations predominated over transitions among smokers (8:3), but not among never-smokers (1:3). None of the variant alleles altered the overall frequency of p53 mutation. Transversions, however, were marginally increased among patients with at least one XPD variant allele compared with patients who were wild-type homozygotes (73% vs. 25% for the Asp312Asn polymorphism, P = 0.095; 78% vs. 33% for Lys751Gln, P = 0.085). Five of six women or six of seven smokers who carried at least one XPD 751Gln allele had p53 transversion. The XRCC1 variant allele did not show any effect on the p53 mutation. We conclude that the XPD variant alleles may be associated with an increased frequency of smoking-related p53 mutations in lung tumors, presumably due to reduced DNA repair proficiency.

Coding variants in human double-strand break DNA repair genes

DNA repair is essential for the maintenance of genomic integrity. Consequently, altered repair capacity may impact individual health in such areas as aging and susceptibility to certain diseases. Defects in some DNA repair genes, for example, have been shown to increase cancer risk, accelerate aging and impair neurological functions. Now that over 115 genes directly involved in human DNA repair have been characterized at the DNA sequence level, the identification of single nucleotide polymorphisms (SNPs) in DNA repair genes is becoming a reality. This information will likely lead to the identification of alleles, or combinations of alleles that affect disease predisposition. This communication summarizes SNPs identified to date in the coding region of 24 human double-strand break repair (DSBR) genes. SNP data for four of these genes were obtained by screening at least 100 individuals in our laboratory. For each SNP, the codon number, amino acid substitution, allele frequency and population information is supplied.

The genotype distribution of the XRCC1 gene indicates a role for base excision repair in the development of therapy-related acute myeloblastic leukemia

Polymorphisms in several DNA repair genes have been described. These polymorphisms may affect DNA repair capacity and modulate cancer susceptibility by means of gene-environment interactions. We investigated DNA repair capacity and its association with acute myeloblastic leukemia (AML). We studied polymorphisms in 3 DNA repair genes: XRCC1, XRCC3, and XPD. We also assessed the incidence of a functional polymorphism in the NQO1 gene, which is involved in protection of cells from oxidative damage. We genotyped the polymorphisms by using polymerase chain reaction-restriction fragment-length polymorphism analysis in 134 patients with de novo AML, 34 with therapy-related AML (t-AML), and 178 controls. The distributions of the XRCC3 Thr241Met and NQO1 Pro187Ser genotypes were not significantly different in patients and controls. However, the distribution of the XRCC1 Arg399Gln genotypes was significantly different when comparing the t-AML and control groups (chi(2), P =.03). The presence of at least one XRCC1 399Gln allele indicated a protective effect for the allele in controls compared with patients with t-AML (odds ratio 0.44; 95% confidence interval, 0.20-0.93). We found no interactions between the XRCC1 or XRCC3 and NQO1 genotypes. We also found no differences in the distribution of the XPD Lys751Gln or XRCC1 Arg194Trp genotypes. Our data provide evidence of a protective effect against AML in individuals with at least one copy of the variant XRCC1 399Gln allele compared with those homozygous for the common allele.

DNA adduct burden and tobacco carcinogenesis

DNA adducts associated with tobacco smoking could provide a marker of biologically effective dose of tobacco carcinogens and improve individual cancer risk prediction. A significant number of clinical and epidemiologic studies have reported associations of increased DNA adduct levels with the occurrence of the prevalent tobacco related cancers including cancer of the lung, head and neck, and bladder. The inducibility of DNA adducts following in vitro treatments using blood lymphocytes also appears to be a risk factor in the development of lung and head and neck cancer. Corroborative evidence pointing to the importance of DNA adducts in tobacco carcinogenesis include numerous studies showing associations of tobacco smoke exposure with the induction of DNA adducts in humans in vivo. Further effort is necessary, however, to more fully characterize the dose-response relationship between smoking and DNA adducts in exposed target and surrogate tissues. The relationship between gene polymorphisms thought to modify tobacco-related cancer risk and DNA adduct levels is complex. Results of some DNA adduct studies (both in vitro and in vivo) appear inconsistent with the epidemiologic findings. This is evident for polymorphisms involving both carcinogen metabolism (e.g. GSTP1) and DNA repair (e.g. XRCC1). Molecular studies of human tumors suggest associations of p53 mutation with DNA adducts and have revealed correlations of DNA adduct levels with somatic alterations (e.g. 3p21 LOH) that are thought to occur at the very earliest stages of tobacco carcinogenesis. More research is needed to assess the relationship between endogenous sources of DNA adducts and tobacco smoke exposure and the relative oncogenic effects of chemically stable versus unstable DNA adducts. Many potentially fruitful new avenues of cancer research are emerging that integrate DNA adduct analyses with assessments of smoking, genetics, diet and ambient air quality. These investigations aim to understand the multifactorial nature of interindividual variability in response to tobacco carcinogens. As these trends continue a variety of innovative study designs and approaches will become important in human populations.

P53 codon 72 polymorphism and risk of squamous cell carcinoma of the head and neck: a case-control study

p53 plays an important role in cell-cycle control, as it facilitates DNA repair activities in response to DNA damage. An aberrant cell cycle impairs DNA repair and increases the probability of mutations that lead to carcinogenesis. The p53 codon 72 Arg/Pro polymorphism has been suggested to be associated with susceptibility to tobacco-related cancers, but this association remains controversial. In this hospital-based case-control study of 304 patients newly diagnosed with squamous cell carcinoma of the head and neck (SCCHN) and 333 cancer-free controls, we evaluated the association between this p53 polymorphism and the risk of SCCHN. All subjects were non-Hispanic whites, and the controls were frequency-matched to the cases by age (+/-5 years), sex and smoking status. Our results suggested that there was no difference in the distributions of p53 codon 72 genotypes between cases and controls (odds ratio (OR)=1.04, 95% confidence interval (CI) 0.75-1.44 for Pro/Pro vs. Arg/Arg and OR=1.01, 95% CI 0.54-1.91 for Arg/Pro vs. Arg/Arg). However, there was evidence that the Pro allele was associated with an early age of onset of SCCHN. The median ages of onset of SCCHN were 59, 56 and 53 years for Arg/Arg, Arg/Pro and Pro/Pro cases, respectively (P=0.151 among three genotypes; P=0.057 for Pro/Pro and Arg/Pro combined vs. Arg/Arg). The median ages at onset of oral cancers were 62, 57 and 51 years for Arg/Arg, Arg/Pro and Pro/Pro, respectively (P=0.091 among three genotypes; P=0.046 for Pro/Pro vs. Arg/Arg; P=0.066 for Pro/Pro and Arg/Pro combined vs. Arg/Arg). While the results suggest that the P53 codon 72 polymorphism may contribute to oral cancer susceptibility, larger studies are needed to confirm these findings.

Interference of papillomavirus E6 protein with single-strand break repair by interaction with XRCC1

XRCC1 protein is required for the repair of DNA single-strand breaks and genetic stability, and is essential for viability in mammals. XRCC1 functions as a scaffold protein by interacting and modulating polypeptide components of the single-strand break repair machinery, including AP endonuclease-1, DNA ligase IIIalpha, poly (ADP-ribose) polymerase, DNA polymerase beta and human polynucleotide kinase. We show here that the E6 protein of human papillomavirus type 1, 8 and 16 directly binds XRCC1. When tested in CHO derived XRCC1 'knock out' EM9 cells, co-expression of human papillomavirus 16 E6 with human XRCC1 reduced the ability of the latter protein to correct the methyl methane sulfate sensitivity of XRCC1 mutant CHO cell line EM9. These data identify a novel link between small DNA tumour viruses and DNA repair pathways, and suggest a novel explanation for the development of genomic instability in tissue cells persistently infected with papillomaviruses.

Effects on sister chromatid exchange frequency of polymorphisms in DNA repair gene XRCC1 in smokers

The association between metabolic polymorphisms and cigarette smoking-induced cancers has been documented. However, the role of DNA repair polymorphism in carcinogenesis is less clear. To investigate if the polymorphisms of metabolic traits and DNA repair modulate smoking-related DNA damage, we used sister chromatid exchange (SCE) as a marker of genetic damage to explore the relationship of microsomal epoxide hydrolase (mEH), glutathione S-transferase M1 (GSTM1), and X-ray cross-complementing group 1 (XRCC1) and cigarette smoking-induced SCE. Sixty-one workers without significant exposure to mutagens were recruited. Questionnaires were completed to obtain detailed occupational, smoking, and medical histories. SCE frequency in peripheral lymphocytes was determined using a standard cytogenetic assay and GSTM1, mEH (exons 3 and 4), XRCC1 (codon 399) genotypes were determined using polymerase chain reaction-restriction fragment length polymorphism (PCR/RFLP). Smokers had higher SCE frequency than non-smokers (8.4 versus 7.1, P<0.05). Among workers who had smoked equal to or greater than 10 cigarettes each day, those with XRCC1 Arg/Gln+Gln/Gln had higher SCE frequency than those with XRCC1 Arg/Arg after adjusting for potential confounders (9.0 versus 7.9, P<0.05). The interaction of XRCC1 and cigarettes smoked per day on SCE frequency was also observed (P=0.02). There was no significant interaction between cigarettes smoked per day with GSTM1 and mEH on SCE frequency. Our results support previous epidemiological studies that XRCC1 may play a role in cigarette smoking-induced lung cancer.

Polymorphisms of DNA repair genes XRCC1 and XPD and their associations with risk of esophageal squamous cell carcinoma in a Chinese population

Esophageal squamous cell carcinoma (ESCC), which is prevalent in China, is believed to be induced by environmental carcinogens. Accumulating evidence has shown that individual variation in DNA repair capacity resulting from genetic polymorphism influences risk of environmental carcinogenesis. We therefore investigated the associations between genetic polymorphisms in the DNA repair genes XRCC1 (Arg194Trp and Arg399Gln) and XPD (Asp312Asn and Lys751Gln) and risk of ESCC in an at-risk Chinese population. Genotypes were determined by a PCR-based approach in 433 patients with ESCC and 524 frequency-matched normal controls. We found that individuals with Trp/Trp genotype at XRCC1 Arg194Trp site had a 2-fold increased risk of this disease compared to Arg/Arg genotype (adjusted OR = 1.98; 95% CI 1.26-3.12). Furthermore, when compared to Arg/Arg and Arg/Trp genotype combined, homozygote for Trp/Trp genotype significantly increased the risk of developing ESCC, with the adjusted OR being 2.07 (95% CI 1.34-3.20). However, the XRCC1 Arg399Gln polymorphism was not significantly associated with risk of ESCC, with the adjusted OR being 0.87 (95% CI 0.55-1.37). Neither Asp312Asn nor Lys751Gln polymorphisms in the XPD gene influenced risk of ESCC in our study. These findings suggest that DNA repair gene XRCC1 but not XPD might play a role in esophageal carcinogenesis and might represent a genetic determinant in the development of the cancer.

DNA repair gene XRCC1 and XPD polymorphisms and risk of lung cancer in a Chinese population

X-ray repair cross-complementing group 1 (XRCC1) and xeroderma pigmentosum group D (XPD) are mainly involved in base excision repair (BER) and nucleotide excision repair (NER) of DNA repair pathways, respectively. Polymorphisms of DNA repair gene XRCC1 and XPD has recently been identified, and there is a growing body of evidence that these polymorphisms may have some phenotypic significance. To investigate the role of XRCC1 polymorphisms (codon 194 and codon 399) and XPD polymorphism (codon 751) in lung cancer, a population-based case-control study of 109 lung cancer patients and 109 healthy control subjects (individually matched on age and gender) in a Chinese population was conducted. XRCC1 and XPD genotypes were identified using PCR-restriction fragments length polymorphism technique. Conditional logistic regression analysis revealed that XRCC1 codon 194Trp/Trp genotype was associated with a borderline increased risk of lung cancer [adjusted odd ratio (OR) = 3.06; confidence interval (CI) 0.94-9.92]. The XPD 751 Lys allele (combined Lys/Lys and Lys/Gln genotypes) was associated with a significantly increased risk of lung cancer (OR = 3.19; CI 1.01-10.07). The risk of lung cancer increased more than additive interaction (adjusted OR = 8.77; CI 1.47-52.31) for the individuals with both putative high-risk genotypes of XRCC1 194 Trp/Trp and XPD 751 Lys allele. Our results suggested that the genotypes of XRCC1 194Trp/Trp and XPD 751 Lys allele might be the risk genotypes for lung cancer in Chinese population.

Does variability in normal tissue reactions after radiotherapy have a genetic basis – where and how to look for it?

Cancer patients exhibit large patient-to-patient variability in normal tissue reactions after radiotherapy. Several observations support the hypothesis that clinical normal tissue radiosensitivity is influenced by genetic factors. However, very little is known about the genetic variation possibly underlying inter-individual differences in normal tissue reactions when unselected cancer patients undergo radiotherapy. It seems reasonable to assume that clinical radiosensitivity of normal tissues should be regarded as a so-called complex trait depending on the combined effect of several different genetic alterations. Single nucleotide polymorphisms (SNPs) make up 90% of naturally occurring sequence variation in the human genome and SNPs in genes related to the biological response to ionising radiation may affect clinical radiosensitivity. Rare genetic variants could also possibly play an important role. Thus, the 'allelic architecture' underlying differences in normal tissue reactions may be rather complicated. Recent advances in high throughput genotyping and bio-informatics provide unprecedented opportunities to unravel the genetic basis of clinical normal tissue radiosensitivity. However, to achieve maximum benefit from these advances, carefully designed clinical studies with an accrual of hundreds or thousands of patients are probably needed.

XPD/ERCC2 EXON 8 Polymorphisms: rarity and lack of significance in risk of squamous cell carcinoma of the head and neck

BACKGROUND

Inherited polymorphisms of DNA repair genes may contribute to genetic susceptibility to squamous cell carcinoma of the head and neck (SCCHN). The objective was to assess whether two polymorphisms in the nucleotide excision repair gene XPD (ERCC2) are markers of SCCHN risk.

METHODS

We performed a hospital-based case-control study of 180 SCCHN patients and 400 cancer-free controls frequency matched on age, sex, smoking, and alcohol use. All subjects were non-Hispanic whites. XPD alleles 23047 and 23051 were assessed by digestion with the restriction enzymes XhoII and SphI after PCR amplification.

RESULTS

The XPD 23047 G and XPD 23051 T alleles were extremely rare among both the cases and controls (allele frequencies<1.0%), and not statistically different between groups (P>0.6).

CONCLUSIONS

The 23047 and 23051 variants of the DNA repair gene XPD are extremely rare and do not contribute significantly to the risk of SCCHN in the non-Hispanic white population.

Polymorphisms in the DNA repair gene XRCC1 and susceptibility to alcoholic liver cirrhosis in older Southeastern Brazilians

The population of Southeastern Brazil has a very high mortality rate from liver cirrhosis, a disease that is considered an irreversible pre-malignant condition. This is largely due to the high prevalence of alcohol abuse in the region. Chronic alcohol consumption is associated with the production of free radical intermediates that can cause several DNA lesions. Reduced repair of these DNA lesions would, therefore, constitute a significant risk factor for liver cirrhosis and subsequent cancer. Recently, a number of polymorphisms in several DNA repair genes have been discovered, and it is possible that these polymorphisms may affect DNA repair capacity and thus modulate susceptibility to the disease. In this study, we tested the hypothesis that polymorphisms in the DNA repair gene XRCC1 are associated with increased risk of liver cirrhosis in Southeastern Brazilians. We conducted a pilot case-control study of 97 liver cirrhosis cases and 96 controls (matched for age, sex, and ethnicity) to investigate the role of two allelic variants coding for amino acid changes in the XRCC1 gene (the Arg194Trp and the Arg399Gln polymorphisms). Overall, we observed a 1.8-fold increase in the relative risk of liver cirrhosis associated with the 399Gln allele (either the heterozygous Arg/Gln or the homozygous Gln/Gln genotypes). The adjusted odds ratio (OR) was 1.82 (95% confidence limit (CL) 1.10-3.30). The relative risk appears to be highest among the Mestiso ethnic group (OR 2.60, 95% CL 0.92-7.34). There was a significant association between the 399Gln polymorphism and the risk of liver cirrhosis in older individuals over the age of 45 years (OR 2.70 (95% CL 1.14-6.48) compared to an OR of 1.24 (95% CL 0.55-2.78) for those under 45 years of age. No association was observed between the XRCC1 194Trp polymorphism and risk of liver cirrhosis. These preliminary results suggest that the XRCC1 399Gln polymorphism may be a significant risk modifier for alcoholic liver cirrhosis and justifies additional studies in that direction.

A variant of the DNA repair gene XRCC3 and risk of squamous cell carcinoma of the head and neck: a case-control analysis

Individuals differ in their ability to repair DNA damage induced by carcinogens. Studies have shown that polymorphisms in DNA repair genes contribute to individual variation in DNA repair capacity and cancer risk. In a hospital-based case-control study, we tested the hypothesis that a C to T variant (Thr241Met) of DNA repair gene X-ray repair cross-complementing group 3 (XRCC3) is associated with risk of developing squamous cell carcinoma of the head and neck (SCCHN). We genotyped for this variant in 367 non-Hispanic white patients newly diagnosed with SCCHN and 354 frequency-matched cancer-free controls. Compared with the XRCC3 18067CC and 18607CT genotypes, the variant XRCC3 18067TT genotype was associated with a non-statistically significantly increased risk of SCCHN (adjusted odds ratio [ORadj], 1.36; 95% confidence interval [CI], 0.89-2.08), but this risk was significantly increased among female subjects (ORadj 2.23, 95% CI, 1.00-4.98) and current smokers (ORadj, 2.26; 95% CI, 1.02-4.99). These findings suggest that the variant XRCC3 18067TT genotype may not play a major role in the etiology of SCCHN but may contribute to a subset of SCCHN. Larger studies are needed to verify these findings.

Genetic polymorphisms of DNA repair and xenobiotic-metabolizing enzymes: role in mutagen sensitivity

Mutagen sensitivity, measuring the extent of chromosome damage induced by an in vitro treatment of peripheral lymphocytes with bleomycin, has been associated with an increased risk of various human cancers. Sensitivity to bleomycin appears to have high heritability and is usually considered to reflect individual capacity to repair DNA lesions. Another potential contributor to variation in bleomycin sensitivity could be inherited differences in the metabolism of bleomycin. We assessed whether genetic polymorphisms of DNA repair and xenobiotic-metabolizing enzymes (XMEs) could explain bleomycin sensitivity. Frequencies of bleomycin-induced chromatid breaks per cell (b/c) were determined for 80 healthy Caucasians. Genotypes of DNA repair genes XRCC (X-ray repair cross-complementing) 1 and 3 and XME genes bleomycin hydrolase (BLHX), glutathione S-transferase M1 (GSTM1) and T1 (GSTT1) and N-acetyltransferase 2 (NAT2) were analyzed from leukocyte DNA using methods based on polymerase chain reaction. The mean number of chromatid b/c was increased in individuals with XRCC1 codon 280 variant allele (P = 0.002; two-sided Mann-Whitney test). Smokers carrying BLHX codon 1450 variant allele showed a decrease in the mean number of chromatid b/c (P = 0.036). In multiple linear regression models including adjustment for age, sex, smoking and genotype, the adjusted relative risks (and 95% confidence intervals) were 1.18 (0.98-1.41) and 0.84 (0.69-1.00) for carriers of XRCC1 codon 280 and BLHX codon 1450 variant alleles, respectively. XRCC1 codon 280 polymorphism had a significant effect (P = 0.012) in predetermining whether the individual was classified as non-sensitive, sensitive or hypersensitive to bleomycin. Although based on relatively few individuals, our results suggest that bleomycin sensitivity is partially explained by genetic polymorphisms affecting DNA repair (XRCC1) and in vitro metabolism of bleomycin (BLHX).

Polymorphisms of the DNA repair gene XRCC1 and the frequency of somatic mutations at the glycophorin A locus in newborns

Two DNA polymorphisms in the XRCC1 gene, a microsatellite repeat region in the 3' un-translated region (3'UTR) of the gene and a G-->A substitution resulting in an Arg to Gln amino acid change in codon 399, were examined in 189 newborns who had previously been studied for glycophorin A (GPA) N0 and NN variant frequencies (Vfs) in cord blood erythrocytes. The GPA analysis had revealed that 14 of the 189 had extreme NN Vfs ranging from 40 x 10(-6) to 1787 x 10(-6). Mean Vfs for the remaining 175 were N0=(4.8+/-2.80)x10(-6) and NN=(2.62+/-2.01)x10(-6). Seven alleles of a polymorphic tandem [AC](n) region of the XRCC1 gene were identified. No association between [AC](n) genotype and either N0 or NN Vfs was found amongst the group of 175 nor was the distribution of genotypes unusual for the group of 14 with extreme NN Vfs. Analysis of the 399Gln polymorphism revealed that for the group of 175, 36.0% were Arg/Arg, 49.7% Arg/Gln and 14.3% Gln/Gln and genotype had no influence on N0 and NN Vfs. However, the distribution of genotypes was significantly different in the group of 14 with extreme NN Vfs, 14.3% being Arg/Arg, 42.8% Arg/Gln and 42.8% Gln/Gln. The 14 newborns with extreme NN Vfs may represent a sub-group with an unidentified genotoxic exposure and/or predisposition to gene-duplication mutations or alternatively the high values could have arisen by increased clonal expansion of haemopoietic precursor cells carrying NN mutations. Our results suggest that carriers of the Gln/Gln genotype are over represented in this group but the role that the genotype has in the derivation of high NN Vfs remains to be resolved.

Genetic susceptibility--molecular epidemiology of head and neck cancer

In parts of the developing world (South Central Asia in particular), squamous cell carcinoma of the head and neck (SCCHN) is one of the most common malignancies encountered. Although tobacco and alcohol are clearly defined as etiologic factors in these malignancies, clinical observations have suggested that inherited genetic factors put some individuals at increased risk for SCCHN. Emerging data (both phenotypic and genotypic) support this concept of genetic susceptibility to SCCHN and point to differences in DNA repair ability, carcinogen metabolism, and cell cycle control as the systems important to the risk of tobacco-induced malignancies. The ability to identify such high-risk individuals will have major influences on the practice of cancer prevention in the future.

XRCC1 polymorphisms and head and neck cancer

Inter-individual differences in DNA repair capacity have been demonstrated using a variety of phenotypic assays, including reduced repair among patients with squamous cell carcinoma of the head and neck (SCCHN). The XRCC1 DNA repair gene may facilitate DNA strand break and base excision repair. A recent case-control study of SCCHN reported associations with two polymorphisms of the XRCC1 including the exon 6, 194Arg/Arg genotype and the exon 10, 399 Gln/Gln genotype. We conducted an analysis of these two XRCC1 polymorphisms using data from a case-control study of SCCHN. Among white subjects, we found a weak elevation in risk associated with the Arg194Trp polymorphism [odds ratio (OR)=1.3; 95% confidence interval (CI)=0.6-2.9] and a decreased risk for the Arg399Gln polymorphism (OR=0.6; CI=0.4-1.1). We found a markedly decreased odds ratio for the Gln/Gln genotype among whites (OR=0.1; CI=0.04-0.6) and blacks (OR=0.01; CI=0.0004-0.3). We also found a suggestion of an interaction between the Arg194Trp and Arg399Gln polymorphisms and tobacco use. Additional epidemiologic and functional studies are needed to resolve the importance of these XRCC1 polymorphisms in SCCHN.

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

The DNA single-strand break repair (SSBR) protein XRCC1 is required for genetic stability and for embryonic viability. XRCC1 possesses two BRCA1 carboxyl-terminal (BRCT) protein interaction domains, denoted BRCT I and II. BRCT II is required for SSBR during G(1) but is dispensable for this process during S/G(2) and consequently for cell survival following DNA alkylation. Little is known about BRCT I, but this domain has attracted considerable interest because it is the site of a genetic polymorphism that epidemiological studies have associated with altered cancer risk. We report that the BRCT I domain comprises the evolutionarily conserved core of XRCC1 and that this domain is required for efficient SSBR during both G(1) and S/G(2) cell cycle phases and for cell survival following treatment with methyl methanesulfonate. However, the naturally occurring human polymorphism in BRCT I supported XRCC1-dependent SSBR and cell survival after DNA alkylation equally well. We conclude that while the BRCT I domain is critical for XRCC1 to maintain genetic integrity and cell survival, the polymorphism does not impact significantly on this function and therefore is unlikely to impact significantly on susceptibility to cancer.

Modulation of repair of ultraviolet damage in the host-cell reactivation assay by polymorphic XPC and XPD/ERCC2 genotypes

DNA repair capacity (DRC) plays an important role in genetic susceptibility to cancer. Polymorphisms of a number of DNA repair genes involved in several distinct pathways have been identified. However, their effects on repair function have not been well characterized. We demonstrated previously that DRC for removal of benzo[a]pyrene diol epoxide-induced DNA damage measured by a host-cell reactivation assay was modulated by two XPD/ERCC2 polymorphisms in lung cancer. In this report, we investigated the association between the repair phenotype of ultraviolet (UV)-induced damage and genotypes of three DNA repair genes, XPC and XPD [involved in nucleotide excision repair (NER)] and XRCC1 [involved in base excision repair (BER)]. We measured DRC for removal of UV photoproducts by the host-cell reactivation assay in cryopreserved lymphocytes from 102 healthy non-Hispanic white subjects. We also typed these subjects for five polymorphisms in these three DNA repair genes (at intron 9 of XPC; exons 6, 10 and 23 of XPD and exon 10 of XRCC1). Compared with wild-type homozygotes, subjects homozygous for polymorphisms of the two NER genes consistently had suboptimal DRC. The DRC was consistently lower in subjects homozygous for XPC, XPD or both than in subjects with other genotypes, although the difference was not statistically significant for XPD variants. In contrast, the polymorphic allele of the BER gene, XRCC1, had no consistent effect on DRC. We concluded that these NER polymorphisms may modulate DRC and may be useful biomarkers for identifying individuals at risk of developing cancer.

Expression of nucleotide excision repair genes and the risk for squamous cell carcinoma of the head and neck

BACKGROUND

Phenotypic differences in the ability to repair genetic damage induced by tobacco carcinogens may reflect genetic differences in susceptibility to squamous cell carcinoma of the head and neck (SCCHN). The objective of this study was to assess the variation in baseline expression of five nucleotide excision repair genes between individuals with SCCHN and cancer free controls.

METHODS

The authors conducted a hospital-based case-control study of 57 SCCHN patients and 105 cancer free controls. Using peripheral blood lymphocytes, a multiplex reverse transcriptase-polymerase chain reaction assay was used to quantitate in vitro the mRNA levels of five genes (ERCC1, XPB/ERCC3, XPG/ERCC5, CSB/ERCC6, and XPC) involved in the nucleotide excision repair pathway.

RESULTS

The levels of ERCC1, XPB/ERCC3, XPG/ERCC5, and CSB/ERCC6 transcripts were lower in cases than in controls (P =0.0001, 0.096, 0.001, and 0.0001, respectively). In multivariate logistic regression analysis (adjusting for age, gender, race, smoking status, and alcohol use), low expression of ERCC1, XPB/ERCC3, XPG/ERCC5, and CSB/ERCC6 was associated with a statistically significant increased risk for SCCHN (adjusted odds ratios [95% confidence intervals] 6.42 [2.63-15.69], 2.86 [1.39-5.90], 3.69 [1.73-7.90], and 2.46 [1.19-5.09], respectively).

CONCLUSIONS

Reduced expression of ERCC1, XPB/ERCC3, XPG/ERCC5, and CSB/ERCC6 is associated with a more than two-fold increased risk of SCCHN.

Genetic regulation of ionizing radiation sensitivity and breast cancer risk

Genetic variability in DNA repair may contribute to hypersensitivity to ionizing radiation (IR) and susceptibility to breast cancer. We used samples collected from a clinic-based breast cancer case-control study to test the working hypothesis that amino acid substitution variants of DNA repair genes may contribute to prolonged cell-cycle delay following IR and breast cancer risk. Fluorescence-activated cell sorter (FACS) analysis was used to measure cell-cycle delay. PCR-restriction fragment length polymorphism (RFLP) assays were used to determine four genotypes of three DNA repair genes: XRCC1, 194 Arg/Trp and 399 Arg/Gln; XRCC3, 241 Thr/Met; and APE1, 148 Asp/Glu. The data showed that breast cancer patients had a significantly higher delay index than that of controls (P < 0.001); the means +/- SD for cases and controls were 36.0 +/- 13.1 (n = 118) and 31.4 +/- 11.5 (n = 225), respectively. There was a significant dose-response relationship between delay index, categorized into quartiles, and an increasing risk of breast cancer (crude odds ratios: 1.00, 1.00, 1.27, and 2.46, respectively; P(trend) = 0.002). In controls, prolonged cell-cycle delay was significantly associated with the number of variant alleles in APE1 Asp148Glu and XRCC1 Arg399Gln genotypes (P(trend) = 0.001). Although larger studies are needed to validate the results, our data suggest that an inherited hypersensitivity to IR may contribute to human breast carcinogenesis.

Gene mutation as a target for early detection in cancer diagnosis

The increasing number of genetic aberrations implicated in the development of human cancer has prompted a search to detect them at the earliest possible stage of their formation. Of the many such genetic changes identified thus far, relatively few meet the standard for markers in early diagnosis and prognosis, namely that the genetic modifications occur during the early onset phase of cancer development. Parallel to the increasing number of such genes is the growing availability of technologies using more powerful and cost-efficient methods that enable mass screening for genetic alterations. The purpose of this review is to summarize the currently available genes that can serve as markers for early detection of cancers and methods that allow their detection.

Genetic polymorphism of XRCC1 and lung cancer risk among African-Americans and Caucasians

Reduced DNA repair capacity may influence susceptibility to lung cancer. XRCC1 plays an important role in base excision repair and in rejoining DNA strand breaks. In the XRCC1 gene, two common polymorphisms induce amino acid changes in codon 194 and codon 399 and correlate with levels of genotoxic damage. We examined the relation between these two polymorphisms and susceptibility to lung cancer among 334 incident cases and 704 population controls of African-American and Caucasian ethnicity in Los Angeles County, California. African-American and Caucasian subjects smoking 20+ cigarettes/day and carrying at least one copy of the codon 194 variant allele were at somewhat decreased risk of lung cancer (African-Americans OR=0.2, 95% CI 0.1-0.9; Caucasians OR=0.5, 95% CI 0.2-1.1). Similarly, for the codon 399 polymorphism, there was some evidence of a decreased risk for the homozygous variant genotype among heavier smokers (African-Americans OR=0.3, 95% CI 0.0-2.9; Caucasians OR=0.4, 95% CI 0.2-1.0). These results suggest that genetic variation in XRCC1 might contribute to lung cancer and may interact with the amount smoked.