| Background and Object:Gastric cancer is one of the most frequently occurred cancers worldwide, with an estimated nearly0.99millions of new cases, just next to lung cancer, breast cancer and colorectal cancer, and an estimated nearly0.73millions of deathes, just next to lung cancer. The development of gastric cancer involves mutifactors and multiple stages. In addition to environment factors, DNA repair genes play a crucial role in maintaining the stability and integrity of genomic DNA. For example, inherited functional single nucleotide polymorphisms (SNPs) in DNA repair genes may alter DNA repair capacity. When damaged DNA was not repaired timely, accumulated DNA lesions may lead to cell proliferation and differentiation disorder and then contribute to cancer risk. Though China has a much higher incidence and death rate of gastric cancer than other parts of the world, few investigation of nucleotide excision repair (NER) core genes have been investigated for their involvement in the etiology, with a small number of cases and controls in the literature. This study was designed to explore potential role of functional SNPs of the NER core genes in gastric cancer susceptibility and to provide further evidence for gastric cancer diagnosis and preventation from a much larger study.Methods:Sixteen potential functional SNPs of NER core genes were genotyped for1125gastric cancer cases and1196cancer-free controls by TaqMan assays. We also analyed the genotype-based mRNA expression measured in the EBV-transformed B lymphoblastoid cell lines from270subjects used in HapMap with four different ethnicities. We further investigated the function of rs873601G>A located in the3’ UTR region of XPG, where miR-1227may bind to, by dual-luciferase report system. Differences in the frequencies of alleles and genotypes as well as demographic (e.g., age and sex) and other covariates (e.g., smoking and drinking status) between cases and controls were evaluated by the χ2test. Univariate and multivariate logistic regression models were applied to calculate crude and adjusted odds ratios (ORs) and95%confidence intervals (CIs), respectively. Student’s t test was used to compare the differences in the mRNA expression levels and the activity of luciferase between two strata. We performed heterogeneity tests to test for any difference in risk estimates among strata and false-positive report probabilities (FPRP) analysis to assess significant findings. We also performed multifactor dimensionality reduction (MDR) analyses to assess their associations with gastric cancer risk.Results:The rsults are summarized as follws:1. Genotype distributions were significantly different for ERCC1rs2298881(P=0.037) and rs11615(P=0.0496) between the cases and controls. When the rs2298881AA genotype was used as the reference, the C variant genotypes were associated with an increased risk of gastric cancer (adjusted OR=1.37,95%CI=1.08-1.74for AC, adjusted OR=1.26,95%CI=0.98-1.63for CC and adjusted OR=1.33;95%CI=1.05-1.67for AC/CC after adjustment for age, sex, smoking and drinking status); when the rsll615GG genotype was used as the reference, the A variant genotypes were associated with an increased risk of gastric cancer (adjusted OR=1.25,95%CI=1.05-1.48for AG, adjusted OR=1.13,95%CI=0.78-1.63for AA and adjusted OR=1.23;95%CI=1.05-1.46for AG/AA). Patients with2-3ERCC1risk genotypes had significant increased risk (adjusted OR=1.56,95%CI=1.27-1.93), compared with those with0-1ERCC1risk genotypes.In the stratification analysis, we found that the rs2298881variant AC/CC genotypes were associated with an increased risk that was more evident in females, current-smokers, never drinkers, NGCA and clinical stages I+II. Quite similar results were found for rs11615variant AG/AA genotypes, especially in the younger age group, females, current-smokers, ever drinkers, NGCA and clinical stages Ⅰ+Ⅱ. We also found that the patients carrying2-3risk genotypes had a more evident risk in older age group, females, current-smokers, ever drinkers, NGCA and clinical stages I+II.Compared to the most common "CCG" haplotype deduced from the genotype date from three selected SNPs, the "ACG" haplotype was associated with a decrease risk (adjusted OR=0.72,95%CI=0.61-0.86), which was consistent with the prior finding that the A allele had a protective role.The FPRP values at different prior probability levels for the observed significant findings suggested that for a prior probability of0.01and0.2as an FPRP threshold, the FPRP values were0.007for an association of the ERCC12-3risk genotypes, with an increased risk of gastric cancer in all individuals. We also found a significant association with gastric cancer risk for never drinkers, NGCA and clinical stages I+II among those patients with2-3risk genotypes. Hovever, the "ACG" haplotype had a significant decrease risk than the most common "CCG" haplotype was also noteworthy.Compared with the mRNA expression levels of the rs2298881AA genotype, the rs2298881CC and AC/AA genotypes were correlated with statistically higher levels (P=0.006and P=0.006, respectively) with an obvious trend (P=0.003) for CHB. The mRNA expression levels for the270individuals were similar to the CHB, and the rs2298881CC and AC/AA genotypes were correlated with statistically higher levels (P=0.001and P=0.004, respectively) also with an obvious trend (P<0.0001). As to the mRNA expression levels for rs11615, we did not find any significant correlation.2. The genotype distributions were significantly different for XPC rs1870134(P=0.009) between the cases and controls. When the rs1870134GG genotype was used as the reference, the C variant genotypes were associated with a decreased risk of gastric cancer (adjusted OR=0.80,95%CI=0.68-0.95for CG, adjusted OR=0.70,95%CI=0.50-0.97for CC and adjusted OR=0.79;95%CI=0.67-0.93for CG/CC after adjustment for age, sex, smoking and drinking status). Patients with2XPC risk genotypes had significant decreased risk (adjusted OR=0.79,95%CI=0.67-0.93), compared with those with0-1ERCC1risk genotypes.In the stratification analysis, we found that the rs2228001variant TG/TT genotypes were associated with a decreased risk that was more evident for drinkers and NGCA. We also found that the rs1870134variant CG/CC genotypes were associated with a decreased risk for the younger age group, males, never smokers, never drinkers, NGCA and clinical stages III+IV, and similar results were found for the patients carrying2risk genotypes as the rs1870134G/C polymorphism.Compared to the most common "TG" haplotype, which was deduced from the observed genotypes of two selected SNPs, the "GG" haplotype was associated with an increase risk (adjusted OR=1.15,95%CI=1.00-1.33).The FPRP values at different prior probability levels for significant findings suggested that for a prior probability of0.01and0.2as an FPRP threshold. We found a noteworthy association with gastric cancer risk for younger age group, NGCA and clinical stages III+IV among those patients with CG/CC genotypes, compared with the GG genotype and for the patients with2risk genotypes, compared with the0-1genotypes.Compared with the mRNA expression levels of the rs1870134GG genotype, the rs1870134CC had statistically lower levels (P=0.026) for CHB. The mRNA expression levels for the270individuals were similar to that of CHB, and the rs1870134CG, CC and CG/CC genotypes had statistically lower expression levels (P=0.0002, P=0.010and P<0.0001,respectively)3. No associations with risk of gastric cancer were found for the four selected SNPs of the XPD gene.4. No associations with risk of gastric cancer were found for the two selected SNPs of the XPF gene. Compared to the most common "CA" haplotype, which was deduced from the observed genotype data of two selected SNPs, the "GA" haplotype was associated with an increase risk (adjusted OR=1.19,95%CI=1.01-1.40).5. The genotype distributions for XPG rs873601G>A were significantly different (P=0.032for a recessive model) between the cases and controls. When the rs873601GG genotype was used as the reference, the A variant genotypes were associated with an increased risk of gastric cancer (adjusted OR=1.08,95%CI=0.89-1.32for AG, adjusted OR=1.30,95%CI=1.03-1.64for AA and adjusted OR=1.23;95%CI=1.01-1.49for recessive model after adjustment for age, sex, smoking and drinking status).Patients with3-4XPG risk genotypes had significant increased risk (adjusted OR=1.25,95%CI=1.04-1.51), compared with those with0-2XPG risk genotypes.In the stratification analysis, compared with the rs873601GG/AG genotypes, the rs873601AA genotype was associated with an increased risk that was more evident in older age group, males, smokers, NGCA and clinical stages Ⅰ+Ⅱ.The FPRP values at different prior probability levels for the observed significant findings suggested that for a prior probability of0.1and0.2as an FPRP threshold, the FPRP values were0.159for an association of the rs873601AA risk genotype, compared with rs873601GG genotype, with an increased risk of gastric cancer in all individuals. We found a noteworthy significant association with gastric cancer for older age group under a recessive model and patients with3-4risk genotypes. We also found a significant association with gastric cancer risk for males, NGCA and clinical stages Ⅰ+Ⅱ among those patients with3-4risk genotypes.Compared with the mRNA expression levels of the rs873601GG genotype, the rs873601AA genotype had statistically lower level (P=0.011) for CHB. The mRNA expression levels for the270individuals were similar to that of CHB, and the rs873601AA and AG/AA genotypes had statistically lower levels (P=0.002and P=0.029, respectively) with an obvious trend (P=0.001) under a dominant model, compared with the GG genotype. For mRNA expression levels of the XPG gene in141adjacent normal gastric tissues, the rs873601AA genotype had non-significantly lower expression levels than the GG genotype (P=0.096).We found a significantly decreased level of the relative luciferase activity in the psiCHECK2:rs873601GG group, compared with the psiCHECK2:rs873601AA group (P=4.85×10-6for HeLa, P=0.002for A549, P=0.007for N45and P=3.98×10-4for7901, respectively) when transfected with has-miR-1227.Compared to the "AGCG" haplotype deduced from the genotype data from four SNPs that were found to be associated with gastric cancer, the "AGCA" haplotype was associated with an increase risk (adjusted OR.=1.40,95%CI=1.02-1.93), and similar results were found for the "AGGG" haplotype (adjusted OR=1.38,95%CI=1.10-1.72),"CGGA" haplotype (adjusted OR=1.38,95%CI=1.10-1.72) and "CAGA" haplotype (adjusted OR=1.53,95%CI=1.22-1.92).Finally, we also found that smoking status was the best model for one-factor, with the highest CVC (100/100) and the lowest prediction error (45.2%); smoking status, rs1870134and age were the best model for three-factors, with the highest CVC (100/100) and the lowest prediction error (42.9%) among all the four selected SNPs and referred stratified factors by using the MDR analysis. Interestingly, the model with8-factors had a maximum CVC (100/100) and a minimum prediction error (39.0%), which presents a model with better prediction than one factor.Conclusions:The ERCC1rs229888C>A and rs11615G>A, XPC rs1870134G>C and XPG rs873601G>A variant genotypes may contribute to risk of gastric cancer. Larger, well-designed, prospective studies with different ethnic populations are warranted to validate our findings. |
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