Polymorphisms in DNA repair genes in the molecular pathogenesis of esophageal (Barrett) adenocarcinoma
Alan G. Casson 1, 2, *,
Zuoyu Zheng 2,
Susan C. Evans 2,
Paul J. Veugelers 3,
Geoffrey A. Porter 1 and
Duane L. Guernsey 1, 2
1 Department of Surgery and 2 Department of Pathology, Division of Molecular Pathology and Molecular Genetics, Dalhousie University, Halifax, Nova Scotia, Canada and 3 Department of Public Health Sciences, University of Alberta, Edmonton, Alberta, Canada
* To whom correspondence should be addressed Email: alan.casson{at}dal.ca
 |
Abstract
|
---|
To test the hypothesis that aberrations of DNA repair contribute to susceptibility for the progression of gastroesophageal reflux disease (GERD) into Barrett esophagus (BE) and esophageal adenocarcinoma (EADC), we studied the frequency of polymorphisms of selected DNA repair genes in patients with GERD (n = 126), BE (n = 125) and EADC (n = 56) enrolled in a 2-year prospective casecontrol study. Controls comprised 95 strictly asymptomatic healthy individuals. Using genomic DNA extracted from blood samples, we identified wild-type and polymorphic variants of XPD (Arg156Arg and Lys751Gln), XRCC1 (Arg194Trp and Arg399Gln) and XRCC3 (Thr241Met), and the poly (AT) insertion/deletion of XPC (PAT). Allelic frequencies were compared between cases and controls using logistic regression to calculate age, gender, smoking and alcohol-adjusted odds ratios (OR) and 95% confidence intervals (CI). Patients with EADC demonstrated a significantly higher frequency of the XPC PAT homozygous variant genotype compared with asymptomatic controls (OR = 3.82; 95% CI = 1.0513.93). Significantly reduced frequencies were seen for the XPD Lys751Gln homozygous variant genotype in patients with EADC (OR = 0.24; 95% CI = 0.070.88), and for the XRCC1 Arg399Gln homozygous variant genotype in patients with BE (OR = 0.38; 95% CI = 0.120.64) and GERD (OR = 0.29; 95% CI = 0.120.66). We conclude that the malignant phenotype probably results from a summation of polymorphic nucleotide excision repair genes showing opposing effects (an increased risk of XPC versus a protective effect of XPD). The protective effect of the homozygous variant of XRCC1 Arg399Gln for GERD and BE suggests that base excision repair alterations may occur early in progression to EADC, likely in response to GERD-induced endogenous oxidative or inflammatory DNA damage. As GERD and BE are highly prevalent in the general population, this protective effect may well explain why only a fraction of individuals with GERD and BE progress into invasive EADC.
Abbreviations: BE, Barrett esophagus; BER, base excision repair; CI, confidence interval; EADC, esophageal adenocarcinoma; GERD, gastroesophageal reflux disease; MMR, mismatch repair; MSI, microsatellite instability; NER, nucleotide excision repair; OR, odds ratio; PCR, polymerase chain reaction; PAT, poly(AT); XPG genes, xeroderma pigmentosum group genes; XRCC genes, X-ray repair cross-complementing genes.
 |
Introduction
|
---|
Over the past three decades, there has been a marked change in the epidemiology of esophageal malignancy in North America and Europe, with an increasing incidence of primary esophageal adenocarcinoma (EADC) (1,2). Though the reasons for this are largely unknown, several lifestyle risk factors including tobacco and alcohol exposure, obesity and dietary factors have been proposed (36). EADC is thought to arise from Barrett esophagus (BE), an acquired condition in which the normal esophageal squamous epithelium is replaced by a metaplastic columnar cell-lined epithelium (7). Progression of BE into invasive EADC is reflected histologically by the metaplasiadysplasiacarcinoma sequence (8). As gastroesophageal reflux disease (GERD) is a risk factor for BE, there is a plausible link between GERD, BE and EADC (9). The identification of molecular markers associated with Barrett metaplasiadysplasiaadenocarcinoma progression may provide further insight into the molecular pathogenesis of this disease (1012). However, as GERD and BE are highly prevalent in the general population (9), and only a fraction of individuals progress into invasive EADC, it is likely that both molecular and lifestyle risk factors may modulate individual susceptibility to malignant progression.
Decreased efficiency of DNA repair is viewed as a crucial event in carcinogenesis, as such defects accelerate genetic instability and the rate of genetic change (13,14). Numerous links have been identified between oncogenesis and acquired or inherited alterations in genes regulating DNA repair processes, highlighting a key role for DNA protection. Genetic differences in the ability to repair DNA damage may contribute to cancer risk in the general population, and recent studies have evaluated the role of common polymorphisms of selected DNA repair genes and the susceptibility or risk of human malignancy (15). For example, the xeroderma pigmentosum group C (XPC) gene is integral to nucleotide excision repair (NER), and a common poly (AT) insertion/deletion polymorphism within the intron 9 of XPC (16) has been associated with increased risk for squamous cell carcinoma of the head and neck (17). Similar associations have been reported for polymorphisms in codons 156 (Arg156Arg, C22541A) and 751 (Lys751Gln, A35931C) of the xeroderma pigmentosum group D (XPD) gene (18), which is essential for transcription during NER (19). The X-ray repair cross-complementing 1 (XRCC1) gene encodes a protein that complexes with DNA ligase to repair DNA gaps resulting from base excision repair (BER) (20). Three polymorphisms (Arg194Trp, C26304T; Arg280His, G27466A and Arg399Gln, G28152T, in codons 194, 280 and 399 respectively) of XRCC1 have been associated with susceptibility to lung (2123), bladder (24), gastric (25) and esophageal squamous cell carcinomas (26,27). Similarly, a polymorphism (Thr241Met, C18067T) in codon 241 of the X-ray repair cross-complementing 3 (XRCC3) gene, which encodes a protein involved in DNA double-strand break/recombination repair, has been associated with the development of malignant melanoma (28). To date, most of the studies have analyzed individual NER or BER genes only, and no study has evaluated the role of DNA repair gene polymorphisms in human EADC or its precursor lesions (BE, GERD).
We recently studied DNA mismatch repair (MMR) and microsatellite instability (MSI) in human EADC; low-level MSI suggests an inherent baseline genomic instability and potentially increased susceptibility to mutations during the molecular pathogenesis of EADC (29). To test the hypothesis that aberrations of DNA repair are associated with risk of EADC progression, we studied the frequency of common polymorphisms of selected DNA repair genes (Table I) in patients with GERD, BE and EADC. Although dozens of genes are potentially involved in DNA repair (1315), we selected XPC PAT, XPD Arg156Arg and XPD Lys751Gln variants as representatives of the NER pathway that is involved in repairing the genetic damage induced by tobacco carcinogens, an important exogenous risk factor in the molecular pathogenesis of EADC (3). The other principal DNA repair pathway, BER, is responsible for the repair of DNA damage resulting from oxidative endogenous processes, possibly mediated by reactive oxygen species resulting from chronic GERD, a well recognized risk factor associated with both BE and EADC (4). We therefore studied XRCC1 Arg194Trp and Arg399Gln, and XRCC3 Thr241Met variants as representatives of the BER pathway in human EADC.
 |
Materials and methods
|
---|
Study subjects
The study population comprised a total of 402 individuals who were enrolled (between February 2001 and February 2003) in a prospective casecontrol study to evaluate lifestyle risk factors and molecular alterations in patients with GERD (n = 126), BE (n = 125) and EADC (n = 56). Because GERD is common in the general population, we selected strictly asymptomatic frequency matched controls (n = 95) to alleviate the comparison with GERD cases. The study was hospital-based at the QEII Health Science Centre, Halifax NS, the largest tertiary referral centre in Atlantic Canada. All participants gave informed, written consent. Approval for this study was granted by the Capital Health Research Ethics Board (QE-2000-277), and all blood and tissue samples were collected in accordance with the 1998 Canadian Tri-Council Policy Statement on Ethical Conduct for Research Involving Humans.
Cases and controls were identified over the 2 year period by collaborating physicians (see Appendix). For each participant, a 102-point structured questionnaire was administered by a trained research nurse. This included sociodemographic information, family and medical history, measured height and weight, and lifestyle risk factors such as tobacco and alcohol consumption, dietary intake and physical activity. All cases and controls were asked to provide a 10 ml blood sample for DNA analysis. All cases underwent diagnostic esophagogastroscopy with biopsy to confirm the diagnosis of tumor (EADC), columnar epithelium (BE) or inflamed esophageal mucosa (GERD-induced esophagitis).
Strict clinicopathologic criteria were used to define adenocarcinomas of primary esophageal origin (Siewert classification, Type I), as previously reported (29). These included: (i) the presence of an associated Barrett epithelium, (ii) >75% of the tumor mass involving the tubular esophagus, (iii) direct invasion of periesophageal tissues, (iv) minimal gastric involvement and (v) clinical symptoms of esophageal obstruction (dysphagia). The diagnosis of BE was established by the histological finding of intestinal metaplasia, which was confirmed independently by two consultant gastrointestinal histopathologists. Associated dysplasia (if present) was classified as indefinite, low-grade or high-grade. Patients were diagnosed with GERD on the basis of dominant symptoms of heartburn and/or regurgitation, previous response to acid suppression therapy and with or without the evidence of esophagitis. Asymptomatic individuals (controls) were recruited concurrently from two ambulatory general surgery outpatient clinics. Patients who attended consultation regarding unrelated benign conditions, including inguinal hernia and miscellaneous non-malignant lumps and bumps, were screened for GERD-related symptoms, a history of hiatus hernia, dyspepsia, antacid use, previous malignancy and upper gastrointestinal surgery, and if negative, were asked to participate as controls.
DNA extraction and genotype analysis
Blood samples were collected from 126 patients with GERD, 125 patients with BE, 56 patients with EADC and 95 controls. Genomic DNA was extracted from each blood sample according to standard protocols. Polymerase chain reaction (PCR) was used to amplify regions of intron 9 of XPC (17), exons 6 and 23 of XPD (18), exons 6 and 10 of XRCC1 (20) and exon 7 of XRCC3 (30), containing polymorphisms of interest. Each PCR (10 µl vol) generally comprised 100 ng genomic DNA, 0.3 pM of each primer (Table II), 0.1 mM of dNTP mix, 0.5 U Taq DNA polymerase (Invitrogen, Burlington, ON), 2.0 mM MgCl2 and 1.0x PCR buffer. Thermal cycling conditions were: an initial denaturation at 92°C for 2 min; 35 cycles of denaturation at 92°C for 30 s, 30 s of annealing (60°C for XRCC3, 61°C for XPD, 66°C for XPC, 68°C for XRCC1) and 1 min of elongation at 72°C; followed by a final extension at 72°C for 5 min.
For XPC, PCR products were evaluated in a 2% agarose gel, incorporating a DNA sequence ladder to identify 344 bp (PAT+) and 266 bp (PAT) fragments. All other PCR products (10 µl of each in a 20 µl vol) were digested overnight at 37°C (65°C for XPD, exon 6) with the following restriction enzymes: XPD exon 6, 0.4 µl TfiI; XPD exon 23, 2.0 µl PstI; XRCC1 exons 6 and 10, 0.5 µl MspI; XRCC3 exon 7, 1.0 µl Hsp92II, followed by electrophoresis in a 2% agarose gel (16% acrylamide gel for XRCC3), to identify wild-type and polymorphic variants. Genotypes were defined by their characteristic banding patterns as follows: for XPD exon 6, the wild-type allele had a single restriction site resulting in two bands (587 and 57 bp), whereas the Arg156Arg variant produced three bands (474, 113 and 57 bp); for XPD exon 10, the wild-type allele had a single restriction site resulting in two bands (243 and 110 bp), whereas the Lys751Gln variant produced three bands (117, 110 and 63 bp) (18). For XRCC1 exon 6, an invariant MspI restriction site resulted (174 bp) in all samples; the wild-type genotype produced two additional bands (21 and 292 bp), the heterozygous Arg194Trp variant produced three additional bands (21, 292 and 313 bp) and the homozygous Arg194Trp variant produced an additional 313 bp band (20). For XRCC1 exon 10, the wild-type allele had a single restriction site resulting in two bands (221 and 374 bp), whereas the Arg399Gln variant produced only one (undigested) band (615 bp) (20). For XRCC3 exon 7, digestion with Hsp92II results in the wild-type allele in a single 136 bp fragment, whereas for theThr241Met, two fragments (39 and 97 bp) are seen (28). All assays were performed in duplicate, with 100% concordance.
Statistical analysis
The fit of genotypic frequencies among controls to HardyWeinberg proportions was tested with a
2 goodness of fit test. The frequency of genotypes among cases of GERD, BE and EADC were compared with asymptomatic controls, while adjusting for differences in age, gender, smoking and use of alcohol by using logistic regression. Statistical significance was set at P < 0.05. All analyses were conducted using S-Plus (Seattle, WA).
 |
Results
|
---|
Selected demographic variables for GERD, BE, EADC and controls are summarized in Table III. As expected, significant differences were seen between groups with respect to age and gender. The distribution and frequency of XPC, XPD, XRCC1 and XRCC3 genotypes (wild-type, heterozygous and homozygous polymorphic variants) for cases (GERD, BE and EADC) and asymptomatic controls are shown in Table IV. For controls, the frequency of selected polymorphic variants was: XPC PAT, 0.35; XPD Arg156Arg, 0.40; XPD Lys751Gln, 0.42; XRCC1 Arg194Trp, 0.04; XRCC1 Arg399Gln, 0.50; XRCC3 Thr241Met, 0.39. Genotype frequencies were consistent with previously reported studies, and were in agreement with the HardyWeinberg equilibrium model: XPC PAT, P = 0.97; XPD Arg156Arg, P = 0.84; XPD Lys751Gln, P = 1.00; XRCC1 Arg194Trp, P = 0.93; XRCC1 Arg399Gln, P = 1.00; XRCC3 Thr241Met, P = 0.95.
View this table:
[in this window]
[in a new window]
|
Table IV. Frequency of XPC, XPD, XRCC1 and XRCC3 genotypes and risk for GERD, BE and EADC relative to asymptomatic controls
|
|
Compared with asymptomatic controls, a large and statistically significant increased frequency for the XPC PAT+/+ homozygous variant genotype was seen in patients with EADC (OR = 3.82; 95% CI = 1.0513.93), after adjusting for age, gender, smoking status and alcohol use (Table III). However, a significant protective effect was observed for the XPD Lys751Gln homozygous variant (C/C) genotype in patients with EADC (OR = 0.24; 95% CI = 0.070.88). A significant protective effect was also seen for the XRCC1 Arg399Gln homozygous variant (A/A) genotype in patients with GERD (OR = 0.29; 95% CI = 0.120.66) and BE (OR = 0.38; 95% CI = 0.120.64).
 |
Discussion
|
---|
Maintenance of the genomic integrity by DNA repair genes is an essential component of normal cellular growth and differentiation (13,14). There is increasing evidence that reduced DNA repair capacity, resulting from genetic polymorphisms of various DNA repair genes, is associated with increased risk and susceptibility to various human solid tumors (1530). To test the hypothesis that aberrations of DNA repair are associated with risk of progression from GERD, to BE and to EADC, we studied a panel of six polymorphic variants of DNA repair genes, representative of NER and BER mechanisms. A protective effect of the homozygous Arg399Gln variant of XRCC1 for GERD and BE was found, suggesting that BER repair alterations occur early in progression, whereas the malignant phenotype (EADC) probably results from a summation of polymorphic NER genes showing opposing effects (increased risk of XPC versus a protective effect of XPD) and mutation burden.
The BER pathway is an important mechanism to repair single base damage and single-strand DNA breaks resulting from endogenous oxidative or inflammatory DNA damaging processes. In our model, such processes most likely arise as a consequence of chronic GERD, a well recognized risk factor for both BE and EADC (4,79). The XRCC1 protein is an integral component of BER, and interacts with multiple enzymes involved in each stage of DNA strand break repair, including PARP-1, AP endonuclease-1, polynucleotide kinase, DNA polymerase-ß and DNA ligase III (reviewed in 31). XRCC1 protein appears to be essential to the normal growth and development, as XRCC1 knockout is lethal in the mouse model (32). Although the functional relevance of most XRCC1 polymorphic variants is unknown, at least three (Arg194Trp, Arg280His, and Arg399Gln) have been associated with susceptibility to lung (2123), bladder (24), gastric (25) and esophageal squamous cell carcinomas (26,27). However, there is some controversy regarding XRCC1 polymorphisms, where, depending on the type of cancer and the population studied, a protective effect may be found. For example, with respect to risk for lung cancer, conflicting results have been found for the XRCC1 Arg399Gln polymorphism (2123,33). Similarly, a protective effect of the homozygous variant was recently reported for bladder cancer risk (24).
To date, only two studies have evaluated XRCC1 and the susceptibility for esophageal squamous cell carcinoma, neither finding a significant risk for the Arg399Gln polymorphism (26,27), and no studies have evaluated primary EADC or its precursor lesions (BE, GERD). In the present study, we found a statistically significant protective effect of the homozygous Arg399Gln variant of XRCC1 for GERD (OR = 0.29; 95% CI = 0.120.66) and BE (OR = 0.38; 95% CI = 0.120.64), suggesting that BER repair alterations occur early, likely in response to GERD-induced endogenous oxidative or inflammatory DNA damage, and may modulate individual susceptibility for progression to EADC. As GERD and BE are highly prevalent in the general population, the observed protective effect of the XRCC1 Arg399Gln polymorphism may well explain why only a fraction of individuals with GERD and BE actually progress to invasive EADC (9).
Biologically, the observed protective effect of the Arg399Gln XRCC1 variant may be explained as follows. First, reduced efficacy of the XRCC1 protein (a consequence of the polymorphic variant) may result in the impaired ability of esophageal epithelia to repair DNA damage resulting from chronic GERD, and such cells may be more likely to undergo apoptosis, avoiding clonal expansion of cells with mutations arising from impaired BER. Second, there is little evidence to support the notion that the polymorphic variant results in improved XRCC1 protein function. Finally, XRCC1 may be in linkage disequilibrium with other DNA repair genes (e.g. Lig-1, ERCC1, ERCC2, and PKN) on the chromosome 19. Of these associated genes, we found a significant protective effect for the Lys751Gln homozygous variant of XPD in patients with EADC (OR = 0.24; 95% CI = 0.070.88), and although a similar trend was seen for patients with GERD and BE, this was not statistically significant (Table IV).
The NER pathway generally removes bulky adducts caused by exogenous carcinogens, especially from cigarette smoke, a well defined risk factor for EADC (3). The XPD protein possesses both single-strand DNA-dependent ATPase and 5'-3' DNA helicase activities, and is essential for transcription and NER (19). To date, only a limited number of studies have evaluated the XPD Lys751Gln homozygous variant in other human solid tumors, with conflicting results (34). While this polymorphism was reported to be associated with increased risk for squamous cell carcinoma of the head and neck (18), conflicting results were found for lung cancer (22,30,3538), and only a borderline protective effect was reported for basal cell carcinoma (39). Although the functional significance of XPD polymorphic variants is still unclear, the A to C base substitution at codon 751 leads to a complete change in the electronic configuration of the resulting amino acid, and reduced DNA repair efficiency (40). Furthermore, the common XPD Lys751Lys allele has been shown to result in suboptimal repair of X-ray-induced DNA damage in vitro (19). These findings are in keeping with the observed protective effects associated with the XPD Lys751Gln polymorphism observed in the present study for GERD, BE and in particular for EADC.
We found no significant association between the XPD Arg156Arg variant and risk for GERD, BE and EADC. This is not surprising as this polymorphism does not result in an amino acid substitution, although a previous study suggested that this variant may exert a biological effect by altering RNA stability (39). In contrast, a large and statistically significant increased frequency for the recently reported poly (AT) insertion/deletion polymorphism within intron 9 of XPC was seen in patients with EADC (OR = 3.82; 95% CI = 1.0513.93). A similar association was reported for patients with squamous cell carcinoma of the head and neck (17), another tobacco-associated malignancy. This polymorphic variant, which likely has a role in initiating NER (16), has been reported to modulate DNA repair capacity, and was recently proposed as a potentially useful biomarker to identify individuals at increased risk for developing cancer (41,42).
The strength of this study is its prospective design in a relatively stable population. With just under one million inhabitants, the population of Nova Scotia has experienced little migration or ethnic diversity. In addition to studying a relatively uncommon cancer (EADC), we also evaluated patients with premalignant lesions (GERD, BE) associated with malignant progression. Furthermore, strict clinicopathologic criteria were used to define patients with GERD, BE and primary EADCs, thereby excluding adenocarcinomas of the gastric cardia. However, potential limitations of this study relate to patient numbers. Despite the striking changes reported for the epidemiology of esophageal cancer in North America (1), EADC is still a relatively uncommon tumor in this province. As all cancers must legally be reported, data from the Nova Scotia Cancer Registry revealed that 69 adenocarcinomas of the esophagus were registered for the corresponding 2-year interval of this study. Therefore, the 56 EADCs included in this hospital-based study represent 81% of all EADCs seen in the province, and given the rarity of this malignancy, would appear to be representative of the general population of Nova Scotia. A further potential limitation is the use of hospital-based controls. However, every effort was made to identify strictly asymptomatic individuals (with respect to GERD), and there is no theoretical basis to suggest that alterations of DNA repair genes would be involved in the etiology of their benign (non-malignant) conditions. Finally, allelic frequencies in all controls were similar to larger, previously reported population-based studies (1630).
It is likely that multiple molecular genetic changes contribute to the progression of GERD and BE to EADC (1012). From these studies, we conclude that the contribution of DNA repair gene polymorphisms to the molecular pathogenesis of EADC is complex, and that the malignant phenotype probably results from the summation of polymorphic NER genes showing opposing effects (increased risk for XPC versus a protective effect for XPD) and mutation burden, likely in key cell-cycle related genes such as p53 (38,43,44). We have recently demonstrated that for EADC, the predominant p53 mutations are G:C to A:T transitions at CpG dinucleotides, suggesting that these mutations primarily arise through endogenous mechanisms, involving the spontaneous deamination of the 5' methylated cytosine into thymine that frequently occurs at CpG dinucleotides (45). In this regard, the recently reported biological interactions between XPD variants and p53 mutations in lung cancer, especially lung adenocarcinoma, are of particular interest (38,43,44). Although the characterization of p53 mutations, by DNA sequencing, detected in cases from this study is ongoing, multivariate analysis incorporating XPD Lys751Gln variants and p53 protein overexpression, detected immunohistochemically in tissue sections from cases (data not shown), indicates that p53 immunopositivity may be a significant independent risk factor for progression of GERD to BE (OR = 8.47; 95% CI = 3.5420.27) and to EADC (OR = 13.91; 95% CI = 4.246.04). The protective effect of the homozygous Arg399Gln variant of XRCC1 for GERD and BE suggests that BER alterations may occur early in progression to EADC, likely in response to GERD-induced endogenous oxidative or inflammatory DNA damage. As GERD and BE are highly prevalent in the general population, this protective effect may well explain why only a fraction of individuals with GERD and BE progress into invasive EADC. Further validation and investigation of these preliminary findings in larger population-based trials will now be necessary.
 |
APPENDIX 1: COLLABORATORS IN THE NOVA SCOTIA BARRETT ESOPHAGUS STUDY
|
---|
Principal Investigator: Alan G. Casson FRCSC
Study Co-ordinator: Susan Winch RN
Collaborating Gastroenterologists (case accrual): Nina Abraham MD, Bernard Badley MD, Dana Farina MD, Mani Kareemi MD, Des Leddin MD, Jonathan Love MD, Don Macintosh MD, Sunil Patel MD, Kervork Peltekian MD, Ron Tanton MD, Geoff Turnbull MD, Sander van Zanten MD, Noel Williams MD
Collaborating Internists (case accrual): Benedict Cookey MD, Brian O'Brian MD
Collaborating General Surgeons (control accrual): John Curry MD, Bob Stone MD
Collaborating Thoracic Surgeons (case accrual): Drew Bethune MD, Harry Henteleff MD
Pathologists: Laurette Geldenhuys MD, Dickran Malatjalian MD, Heidi Sapp MD
Molecular Pathology Laboratory: Susan Evans BSc, Kim Gallant BSc, Duane Guernsey PhD, Christie Riddell MD, Nadine Vaninetti BSc, Zuoyu Zheng MD
Data Management: John Fris, Sarah Maaten MSc
Statistical Analysis: Angela Fitzgerald MSc, Judy Guernsey PhD, Geoff Porter MD, Paul Veugelers PhD
Administrative Assistance: Joanne Dibblee, Dianne Russell, Lesli Smith
 |
Acknowledgments
|
---|
We thank Drs Dickran Malatjalian and Heidi Sapp for expert independent histopathological review of esophageal tissue sections, Ron Dewar for provincial cancer registry data, and the nursing staff of the Endoscopy Unit at the QE II Health Sciences Centre for their enthusiastic support. We also thank Dr Keith Caldicott (University of Sussex, UK) for critical review of these data and the paper. This study was supported in part by the National Cancer Institute of Canada with funds from the Canadian Cancer Society; the Dalhousie University Department of Surgery, the Dalhousie Cancer Research Program, and the Nova Scotia Health Research Foundation. A.G.C. is supported by a Senior Clinical Research Scholarship from the Dalhousie University Faculty of Medicine. Conflict of Interest Statement: None declared.
 |
References
|
---|
- Blot,W.J. and McLaughlin,J.K. (1999) The changing epidemiology of esophageal cancer. Semin. Oncol., 26, 28.[Medline]
- Botterweck,A.A.M. Schouten,L.J. Volovics,A. Dorant,E. and van den Brandt,P.A. (2000) Trends in incidence of adenocarcinoma of the oesophagus and gastric cardia in ten European countries. Int. J. Epidemiol., 29, 645654.[Abstract/Free Full Text]
- Gammon,M.D. Schoenberg,J.B., Ahsan,H. et al. (1997) Tobacco, alcohol and socioeconomic status and adenocarcinomas of the esophagus and gastric cardia. J. Natl. Cancer Inst., 89, 12771284.[Abstract/Free Full Text]
- Lagergren,J., Bergstrom,R., Lindgren,A. and Nyren,O. (1999) Symptomatic gastroesophageal reflux as a risk factor for esophageal adenocarcinoma. N. Engl. J. Med., 340, 825831.[Abstract/Free Full Text]
- Mayne,S.T. Risch,H.A. Dubrow,R. et al. (2001) Nutrient intake and risk of subtypes of esophageal and gastric cancer. Cancer Epidemiol. Biomark. Prev., 10, 10551062.[Abstract/Free Full Text]
- Vaughan,T.L., Kristal,A.R., Blount,P.L., Levine,D.S., Galipeau,P.C., Prevo,L.J., Sanchez,C.A., Rabinovitch,P.S. and Reid,B.J. (2002) Nonsteroidal anti-inflammatory drug use, body mass index and anthropometry in relation to genetic and flow cytometric abnormalities in Barrett's esophagus. Cancer Epidemiol. Biomark. Prev., 11, 745752.[Abstract/Free Full Text]
- Specher,S.J. (2002) Clinical practice. Barrett's esophagus. N. Engl. J. Med., 346, 836842.[Free Full Text]
- Jankowski,J.A., Wright,N.A., Meltzer,S.J., Triadafilopoulos,G., Geboes,K., Casson,A.G., Kerr,D. and Young,L.S. (1999) Molecular evolution of the metaplasiadysplasiaadenocarcinoma sequence in the esophagus. Am. J. Pathol., 154, 965973.[Abstract/Free Full Text]
- Shaheen,N. and Ransohoff,D.F. (2002) Gastroesophageal reflux, Barrett's esophagus and esophageal cancer. JAMA, 287, 19721981.[Abstract/Free Full Text]
- Casson,A.G. (2002) Role of molecular biology in the follow-up of patients who have Barrett's esophagus. Chest Surg. Clin. N. Am., 12, 93111.[CrossRef][Medline]
- Reid,B.J., Blount,P.L. and Rabinovitch,P.S. (2003) Biomarkers in Barrett's esophagus. Gastrointest. Clin. N. Am., 13, 369397.[CrossRef]
- McManus,D.T., Olaru,A. and Meltzer,S.J. (2004) Biomarkers of esophageal adenocarcinoma and Barrett's esophagus. Cancer Res., 64, 15611569.[Abstract/Free Full Text]
- Hoeijmakers,J.H.J. (2001) Genome maintenance mechanisms for preventing cancer. Nature, 411, 366374.[CrossRef][ISI][Medline]
- Wood,R.D., Mitchell,M., Sgouros,J. and Lindahl,T. (2001) Human DNA repair genes. Science, 291, 12841289.[Abstract/Free Full Text]
- Zhi,Y., Spitz,M.R., Amos,C.I., Lin,J., Schabath,M.B. and Wu,X. (2004) An evolutionary perspective on single-nucleotide polymorphism screening in molecular cancer epidemiology. Cancer Res., 64, 22512257.[Abstract/Free Full Text]
- Khan,S.G., Metter,E.J., Tarone,R.E., Bohr,V.A., Grossman,L., Hedayati,M., Bale,S.J., Emmert,S. and Kraemer,K.H. (2000) A new xeroderma pigmentosum group C poly (AT) insertion/deletion polymorphism. Carcinogenesis, 21, 18211825.[Abstract/Free Full Text]
- Shen,H., Sturgis,E.M., Khan,S.G., Qiao,Y., Shahlavi,T., Eicher,S.A., Xu,Y., Wang,X., Strom,S.S., Spitz,M.R., Kraemer,K.H. and Wei,Q. (2001) An intronic poly (AT) polymorphism of the DNA repair gene XPC and risk of squamous cell carcinoma of the head and neck: a case-control study. Cancer Res., 61, 33213325.[Abstract/Free Full Text]
- Sturgis,E.M., Zheng,R., Li,L., Castillo,E.J., Eicher,S.A., Chen,M., Strom,S.S., Spitz,M.R. and Wei,Q. (2000) XPD/ERCC2 polymorphisms and risk of head and neck cancer: a case-control analysis. Carcinogenesis, 21, 22192223.[Abstract/Free Full Text]
- Lunn,R.M., Helzlsouer,K.J., Parshad,R., Umbach,D.M., Harris,E.L., Sanford,K.K. and Bell,D.A. (2000) XPD polymorphisms: effects on DNA repair proficiency. Carcinogenesis, 21, 551555.[Abstract/Free Full Text]
- Lunn,R.M., Langlois,R.G., Hsieh,L.L., Thompson,C.L. and Bell,D.A. (1999) XRCC1 polymorphisms: effects on aflatoxin B1-DNA adducts and glycophorin A variant frequency. Cancer Res., 59, 25572561.[Abstract/Free Full Text]
- Ratnasinghe,D., Yao,S-X., Tangrea,J.A., Qiao,Y.-L., Andersen,M.R., Barrett,M.J., Giffen,C.A., Erozan,Y., Tockman,M.S. and Taylor,P.R. (2001) Polymorphisms of the DNA repair gene XRCC1 and lung cancer risk. Cancer Epidemiol. Biomark. Prev., 10, 119123.[Abstract/Free Full Text]
- Butkiewicz,D., Rusin,M., Enewold,L., Shields,P.G., Chorazy,M. and Harris,C.C. (2001) Genetic polymorphisms in DNA repair genes and risk of lung cancer. Carcinogenesis, 22, 593597.[Abstract/Free Full Text]
- Zhang,X., Miao,X., Liang,G., Hao,B., Wang,Y., Tan,W., Li,Y., Guo,Y., He,F., Wei,Q. and Lin,D. (2005) Polymorphisms in DNA base excision repair genes ADPRT and XRCC1 and risk of lung cancer. Cancer Res., 65, 722726.[Abstract/Free Full Text]
- Stern,M.C., Umbach,D.M., van Gils,C.H., Lunn,R.M. and Taylor,J.A. (2001) DNA repair gene XRCC1 polymorphisms, smoking, and bladder cancer risk. Cancer Epidemiol. Biomark. Prev., 10, 125131.[Abstract/Free Full Text]
- Shen,H., Xu,Y., Qian,Y., Yu,R., Qin,Y., Zhou,L., Wang,X., Spitz,M.R. and Wei,Q. (2000) Polymorphisms of the DNA repair gene XRCC1 and risk of gastric cancer in a Chinese population. Int. J. Cancer, 88, 601606.[CrossRef][ISI][Medline]
- Lee,J.-M., Lee,Y.-C., Yang,S.-Y., Yang,P.-W., Luh,S.-P., Lee,C.-J., Chen,C.-J. and Wu,M.-T. (2001) Genetic polymorphisms of XRCC1 and risk of the esophageal cancer. Int. J. Cancer (Pred. Oncol.), 95, 240246.[CrossRef][ISI][Medline]
- Hao,B., Wang,H., Zhou,K., Li,Y., Chen,X., Zhou,G., Zhu,Y., Miao,X., Tan,W., Wei,Q., Lin,D. and He,F. (2004) Identification of genetic variants in base excision repair pathway and their associations with risk of esophageal squamous cell carcinoma. Cancer Res., 64, 43784384.[Abstract/Free Full Text]
- Winsey,S.L., Haldar,N.A., Marsh,H.P., Bunce,M., Marshall,S.E., Harris,A.L., Wojnarowska,F. and Welsh,K.I. (2000) A variant within the DNA repair gene XRCC3 is associated with the development of melanoma skin cancer. Cancer Res., 60, 56125616.[Abstract/Free Full Text]
- Evans,S.C., Gillis,A., Geldenhuys,L., Vaninetti,N.M., Malatjalian,D.A., Porter,G.A., Guernsey,D.L. and Casson,A.G. (2004) Microsatellite instability in esophageal adenocarcinoma. Cancer Lett., 212, 241251.[CrossRef][ISI][Medline]
- David-Beabes,G.L., Lunn,R.M. and London,S.J. (2001) No association between XPD (Lys751)Gln) polymorphism or the XRCC3 (Thr241Met) polymorphism and lung cancer risk. Cancer Epidemiol. Biomark. Prev., 10, 911912.[Free Full Text]
- Caldecott,K.W. (2003) XRCC1 and DNA strand break repair. DNA Repair, 2, 955969.[CrossRef][ISI][Medline]
- Tebbs,R.S., Flannery,M.L., Meneses,J.J., Hartmann,A., Tucker,J.D., Thompson,L.H., Cleaver,J.E. and Pedersen,R.A. (1999) Requirement for the XRCC1 DNA base excision repair gene during early mouse development. Dev. Biol., 208, 513529.[CrossRef][ISI][Medline]
- Taylor,R.M., Thistlewaite,A. and Caldecott,K.W. (2002) Central role for the XRCC1 BRCT I dimain in mammalian DNA single-strand break repair. Mol. Cell. Biol., 22, 25562563.[Abstract/Free Full Text]
- Goode,E.L., Ulrich,C.M. and Potter,J.D. (2002). Polymorphisms in DNA repair genes and associations with cancer risk. Cancer Epidemiol. Biomark. Prev., 11, 15131530.[Abstract/Free Full Text]
- Zhou,W., Liu,G., Miller,D.P., Thurston,S.W., Xu,L.L., Wain,J.C., Lynch,T.J., Su,L. and Christiani,D.C. (2002) Geneenvironment interaction for the ERCC2 polymorphisms and cumulative cigarette smoking exposure in lung cancer. Cancer Res., 62, 13771381.[Abstract/Free Full Text]
- Matullo,G., Palli,D., Peluso,M., Guarrera,S., Carturan,S., Celentano,E., Munnia,A., Tumino,R., Polidoro,S., Piazza,A. and Vineis,P. (2001) XRCC1, XRCC3, XPD gene polymorphisms, smoking and (32)P-DNA adducts in a sample of healthy subjects. Carcinogenesis, 22, 14371445.[Abstract/Free Full Text]
- Spitz,M.R., Wu,X., Wang,Y., WangL.E., Shete,S., Amos,C.I., Guo,Z., Lei,L., Mohrenweiser,H. and Wei,Q. (2001) Modulation of nucleotide excision repair capacity by XPD polymorphisms in lung cancer patients. Cancer Res., 61, 13541347.[Abstract/Free Full Text]
- Mechanic,L.E., Marrogi,A.J., Welsh,J.A., Bowman,E.D., Khan,M.A., Enewold,L., Zheng,Y.-L., Chanock,S., Shields,P.G. and Harris,C.C. (2005) Polymorphisms in XPD and TP53 and mutation in human lung cancer. Carcinogenesis, 26, 597604.[Abstract/Free Full Text]
- Dybdahl,M., Vogel,U., Frentz,G., Wallin,H. and Nexo,B.A. (1999) Polymorphisms in the DNA repair gene XPD: correlations with risk and age of onset of basal cell carcinoma. Cancer Epidemiol. Biomark. Prev., 8, 7781.[Abstract/Free Full Text]
- Benhamou,S. and Sarasin,A. (2002) ERCC2/XPD gene polymorphisms and cancer risk. Mutagenesis, 17, 463469.[Abstract/Free Full Text]
- Qiao,Y., Spitz,M.R., Shen,H., Guo,Z., Shete,S., Hedayati,M., Grossman,L., Mohrenweiser,H. and Wei,Q. (2002) Modulation of repair of ultraviolet damage in the host-cell reactivation assay by polymorphic XPC and XPD/ERCC2 genotypes. Carcinogenesis, 23, 295299.[Abstract/Free Full Text]
- Qiao,Y., Spitz,M.R., Guo,Z., Hedayati,M., Grossman,L., Kraemer,K.H. and Wei,Q. (2002) Rapid assessment of repair of ultraviolet DNA damage with a modified host-cell reactivation assay using a luciferase reporter gene and correlation with polymorphisms of DNA repair genes in normal human lymphocytes. Mutat. Res., 509, 165174.[ISI][Medline]
- Gao,W.M., Romkes,M., Day,R.D., Siegfried,J.M., Luketich,J.D., Mady,H.H., Melhem,M.F. and Keohavong,P. (2003) Association of the DNA repair gene XPD Asp312Asn polymorphism with p53 gene mutations in tobacco-related non-small cell lung cancer. Carcinogenesis, 24, 16711676.[Abstract/Free Full Text]
- Hou,S.M., Ryk,C., Kannio,A., Angrelini,S., Falt,S., Nyberg,F. and Husgafvel-Pursiainen,K. (2003) Influence of common XPD and XRCC1 variant alleles on p53 mutations in lung tumors. Environ. Mol. Mutagen., 41, 3742.[CrossRef][ISI][Medline]
- Casson,A.G., Evans,S.C., Gillis,A., Porter,G.A., Veugelers,P., Darnton,S.J., Guernsey,D.L. and Hainaut,P. (2003) Clinical implications of p53 tumor suppressor gene mutation and protein expression in esophageal adenocarcinomas: results of a ten-year prospective study. J. Thorac. Cardiovasc. Surg., 125, 11211131.[Abstract/Free Full Text]
Received March 14, 2005;
revised April 21, 2005;
accepted April 26, 2005.