Abstract
The X-ray repair cross-complementing group 3 (XRCC3), one of the DNA repair genes, was suggested to play an imperative role in the development of carcinogenesis. The objective of this study was to evaluate the role of the XRCC3 T241M polymorphism in bladder cancer susceptibility in a Chinese population. We genotyped 150 bladder cancer cases and 150 healthy controls who had been frequency matched to cases by age and sex. Genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism analysis. A significant association was found between smoker and bladder cancer [odds ratio (OR)=1.97, 95% confidence interval (CI)=1.24-3.13, p=0.004]. The XRCC3 241MM genotype was more frequent in the bladder cancer group than in the healthy controls group (OR=3.22, 95% CI=1.14-9.11, p=0.03). There were no significant associations between any genotypes and the stage, grade, and histological type of bladder cancer. Our study suggested an increased risk role of XRCC3 241MM genotype in bladder cancer susceptibility in a Chinese population.
Introduction
B
The X-ray repair cross-complementing group 3 (XRCC3) belongs to a family of genes responsible for repairing DNA double-strand breaks caused by normal metabolic processes and/or exposure to ionizing radiation (Sun et al., 2010). A recent meta-analysis of XRCC3 and bladder cancer, including 22 studies, including 3445 cases and 4599 controls, indicated that XRCC3 Thr241Met polymorphism might be weakly associated with the risk of bladder cancer (Sun et al., 2010). Another meta-analysis, which included 5298 cases and 6614 controls, suggested an increased risk role of XRCC3 241MM genotype in bladder cancer among all subjects, and that the effect of T241M polymorphism on bladder susceptibility should be studied with a larger, stratified population (Li et al., 2011).
The objective of this study was to evaluate the role of the XRCC3 T241M polymorphism in bladder cancer susceptibility in a Chinese population.
Materials and Methods
Study population
We genotyped 150 bladder cancer cases and 150 healthy controls who had been frequency matched to cases by age and sex in the Second Xiangya Hospital of Central South University from June 2009 to June 2011. Case patients and control subjects were interviewed by trained nurse interviewers using a structured questionnaire that detailed their smoking, occupational, and other exposure histories. All bladder cancer cases were newly diagnosed, previously untreated (with chemotherapy or radiotherapy or intravesical instillation therapies), and their diagnoses were histologically confirmed. Bladder tumors were staged using the TNM classification (1997) of the Union Internationale Contre le Cancer and graded using the World Health Organization system. The healthy control subjects had no previous diagnosis of any cancer type or any other chronic disease (chronic obstructive lung disease, diabetes mellitus, blood diseases, autoimmune disorders, etc.). Smoking status was defined as never and ever. The protocol was approved by the Ethics Committee of the University. After giving written informed consent, subjects provided blood samples collected under protocols approved by the institutional review boards of each participating institution, and these were stored at −80°C until they were extracted.
Genotype analyses
DNA was extracted from peripheral blood lymphocytes by standard phenol-chloroform extraction methods. Genomic DNA samples were stored at −20°C until use. The XRCC3 T241M genotype was determined by polymerase chain reaction (PCR)-restriction fragment length polymorphism assay. The following primers were used: 5′-TTGGGGCCTCTTTGAGA-3′ and 5′-AACGGCTGAGGGTCTTCT-3′. PCR reactions were carried out in a Perkin-Elmer 9700 thermocycler with an initial denaturation step of 8 min at 94°C, followed by 30 cycles at 94°C for 30 sec, annealing at 60°C for 30 sec, and extension at 72°C for 1 min. PCR products were digested with NlaIII restriction enzyme (New England Biolabs, Beverly, MA).
Statistical analysis
Distributions of demographic characteristics and smoking history were compared between cases and controls, and differences were tested by χ2 tests (2-sided). The same was done for distributions of XRCC3 T241M genotypes. Logistic regression models and fit models were used to estimate the odds ratios (OR) and 95% confidence interval (CI) for the effects of HRAS1 genotypes on bladder cancer risk using SAS software (SAS Institute, Inc., Cary, NC). Statistical significance was set at p<0.05.
Results
Subject characteristics
Table 1 shows distribution of selected characteristics of bladder cancer cases and controls. No statistically significant differences were found between cases and controls for the frequency-matched variables of sex (p=0.81) and age (p=0.78) at interview (Table 1). The mean ages were 58.8 years for cases and 59.1 years for controls. A significant association was found between smokers and bladder cancer (OR=1.97, 95% CI=1.24-3.13, p=0.004). The genotypic frequencies among controls were consistent with those expected from the Hardy-Weinberg law (p=0.68).
The XRCC3 241MM genotype was more frequent in the bladder cancer group than in the healthy controls group (OR=3.22, 95% CI=1.14-9.11, p=0.03) (Table 2). There were no significant associations between any genotypes and the stage, grade, and histological type of bladder cancer (Table 3).
Discussion
In this study, we investigated whether the XRCC3 T241M polymorphism affected bladder cancer risk in 150 bladder cancer cases and 150 healthy controls in a Chinese population. Our study suggested an increased risk role of XRCC3 241MM genotype in bladder cancer susceptibility in a Chinese population.
The main risk factor for bladder cancer is cigarette smoking, which can increase risk up to four times (Zeegers et al., 2000). Carcinogens such as aminobiphenyls found in tobacco have been implicated in bladder cancer etiology in smokers (Probst-Hensch et al., 2000). Although many people are exposed to this risk factor, bladder cancer develops in only a fraction of these individuals, which suggests variations in individual susceptibility to bladder carcinogenesis (Manolio et al., 2008; Rahim et al., 2008). The genetic polymorphisms in a number of metabolic enzymes have been found as the modulators of bladder cancer risk. A significant association was found between smokers and bladder cancer in this study.
Several studies have investigated the associations between XRCC3 Thr241Met polymorphism and the susceptibility to bladder cancer, but results have been inconclusive (Sanyal et al., 2004; Andrew et al., 2008; Fontana et al., 2008; Gangwar et al., 2009). Stern et al. (2002) found some evidence for a gene-gene interaction between the XRCC1 codon 194 and XRCC3 codon 241 polymorphisms and some support for a possible gene-gene-smoking three-way interaction. The XRCC3 codon 241 polymorphism had an overall protective effect against bladder cancer that was most apparent among heavy smokers (Shen et al., 2003). It was found that there was a statistical significance in XRCC3 T carriers between patient and control groups and so, there was a 4.87-fold protective role by the XRCC3 T allele against bladder cancer (Narter et al., 2009). In the study by Sanyal et al. (2004), no significant differences for genotype distributions and allele frequencies between the bladder cancer cases and the controls were observed. Another study found that none of the XRCC3 polymorphisms were associated with urothelial bladder cancer susceptibility (Mittal et al., 2011). A recent meta-analysis of XRCC3 and bladder cancer, including 22 studies, including 3445 cases and 4599 controls, indicated that XRCC3 Thr241Met polymorphism might be weakly associated with the risk of bladder cancer (Sun et al., 2010). Another meta-analysis, which included 5298 cases and 6614 controls, suggested an increased risk role of XRCC3 241MM genotype in bladder cancer among all subjects, and that the effect of T241M polymorphism on bladder susceptibility should be studied with a larger, stratified population (Li et al., 2011).
The mechanism of the association between XRCC3 Thr241Met polymorphism and bladder cancer is still relatively ambiguous. The XRCC3 is involved in homologous recombination repair and chromosomal double-strand breaks repair processes, and it is necessary to maintain genomic integrity. It was demonstrated that cell lines defective in XRCC3 had a 25-fold decrease in homology-directed repair of DNA double-strand breaks (Pierce et al., 1999; Sun et al., 2010). The study by Matullo et al. suggested that bladder cancer risk could be genetically modulated by XRCC3, which might repair DNA cross-link lesions produced by aromatic amines and other environmental chemicals (Matullo et al., 2001a; Matullo et al., 2005). The XRCC3 241Met variant was significantly associated with higher DNA adduct levels (Matullo et al., 2001b).
In conclusion, our study suggested an increased risk role of XRCC3 241MM genotype in bladder cancer susceptibility in a Chinese population. However, the immunogenic background, environmental factors, smoking history, and other factors should be considered appropriate. This study warrants further studies of a large population for the purpose of investigating the significance of XRCC3 241MM polymorphism as a marker for tumor susceptibility and the disease progression of bladder cancer.
Footnotes
Disclosure Statement
No competing financial interests exist.