Association Of DNA Repair Genes XPC And XPG Polymorphisms With Genetic Susceptibility To Hepatocellular Carcinoma

Background and objectHepatocellular carcinoma (HCC) is one of the most malignant tumors worldwide and ranks third in tumor death cause spectrum. Multiple genes and environmental risk factors are involved in HCC carcinogenesis. The most important environmental risk factor for HCC is chronic HBV infection in China. However, only a small fraction of HBV infection individuals develop HCC, suggesting that individual susceptibility may play an important role in the etiology of HCC.DNA repair system, consisting of at least four distinct pathways, is essential to maintain genomic integrity and stability. DNA damages, which are induced by various carcinogenic factors, if left unrepaired or repaired incorrectly, may result in genetic instability, and subsequently lead to cancer development. Nucleotide excision repair (NER) is one of the most important pathways in DNA repair system, which mainly repairs bulky DNA lesions. Countless studies indicated that decreased DNA repair capacity may increase cancer susceptibility. The single nucleotide polymorphisms of DNA repair genes may change the activities of repair enzymes, and thus lead to individual differences of DNA repair capacity. Xeroderma pigmentosum group C (XPC) and xeroderma pigmentosum group G (XPG), which are the core DNA repair genes, play important roles of the early detection of bulky DNA damage and the incision 3' to the lesion in the NER pathway, respectively. It has been shown that the single nucleotide polymorphisms in XPC and XPG genes may be associated with the change of DNA repair capacity, and thus contributed to cancer development. Some evidences shown that the polymorphism of XPC Ala499Val may increase the risks of lung cancer, bladder cancer, and head and neck squamous cell carcinoma, while the polymorphism of XPC Lys939Gln may increase the risks of lung cancer, and bladder cancer. Similarly, it has been indicated that the XPG His1104Asp polymorphism was associated with increased lung cancer risk. In the current study, we hypothesized that the single nucleotide polymorphisms of XPC Ala499Val and Lys939Gln and XPG His1104Asp may modify the risk of HCC. The findings from our study will provide evidence for evaluating the roles of genetic and environmental risk factors in the etiololgy of HCC and helping to identify individuals at high-risk for HCC.Materials and methodsStudy population This hospital-based case-control study population included 500 patients with newly diagnosed HCC between June 2007 and December 2008, identified by the First Affiliated Hospital of Guangxi Medical University and the First Affiliated Hospital of Guangxi Traditional Chinese Medicine University (Nanning, China). Those patients with history of other cancers and hereditary diseases were excluded. All patients had not received chemotherapy and radiotherapy. The response rate of the eligible cases was approximately 95%. The 507 cancer-free controls we included in the same period were randomly selected from the genetically unrelated patients in the Spinal Orthopedic Department and Traumatic Department at the same hospitals, and were frequency matched to the cases by age (±5 years), sex, nationality and region. All controls had no history of cancers and hereditary diseases. The response rate of the eligible controls was approximately 96%. Having signed a written informed consent during the interview, all subjects enrolled in the study were interviewed to gather demographic data and history of alcohol and tobacco use. HBV infection and HCV antibody in all subjects were detected by Enzyme-linked immunoadsorbent assay (ELISA). The research protocol was approved by the Guangxi Medical University. Each subject donated 4 ml of peripheral blood, of which 1 ml used for genomic DNA extraction with a Phenol-Chloroform method.Genotyping Genotypes of XPC Ala499Val (rs2228000) and Lys939Gln (rs2228001) and XPG His1104Asp (rs17655) were detected using Applied Biosystems TaqMan genotyping platform according to the manufacture's recommendations. Briefly, the reactions were prepared by using TaqMan Universal PCR Master Mix (no AmpErase UNG),40×SNP Genotyping Assay Mix, Dnase-free water, and 1-10 ng/μl genomic DNA in a final volume of 25μl per reaction. Real-time PCR was run using the following conditions:95℃for 10 min, and 40 cycles of amplification (92℃for 15 s and 60℃for 1 min). The PCR amplification was run and the plate was read using a TaqMan 7500 HT sequence detection system (Applied Biosystems). The analyzed fluorescence results were then auto-called into genotypes using the built-in SDS software (version 1.3.1) of the system. Statistical analysis All data were analyzed with SSPS software (version 13.0) and SHEsis software (online version). The differences in the distributions of categorical variables, including demographic characteristics, HBV and HCV infection, alcohol use and tobacco smoking, family history of cancer, and genotypes of XPC Ala499Val and Lys939Gln and XPG His1104Asp between the cases and controls were evaluated using t test and Chi-square test, respectively. Departure from Hardy-Weinberg genetic equilibrium (HWE) for all three SNPs was tested in controls using Chi-square test. Crude and adjusted (for age, sex, HBV infection, drinking and smoking status, and family history of cancer) odds ratio (OR) and 95% confidence interval (CI) were obtained from unconditional univariate and multivariable logistic regression model to evaluate associations between all three SNPs and HCC risk. The associations of all three polymorphisms with the risk of HCC were further stratified by the factors of age, sex, HBV infection, drinking and smoking status. All statistical tests were two-sided with a is 0.05.ResultsCharacteristics of the study population There were no statistically differences in the distributions of age, sex, nationality, and occupation between cases and controls (P>0.05), respectively.Distibutions of environmental risk factors The cases were more likely than the controls to be HBV infection individuals, drinkers,>40 g/d of alcohol consumption, smokers,≥20 pack-years of smoking, and those with family history of cancer between two groups(P<0.05), with increased HCC risks of 25.14-fold,5.86-fold,2.82-fold,4.63-fold,2.26-fold, and 17.43-fold, respectively, suggesting these factors may be the independent risk factors of HCC.Distributions of genotypes and risk estimates of XPC Ala499Val and Lys939Gln and XPG His1104Asp between the cases and controls The genotype frequency distributions of XPC Ala499Val and Lys939Gln and XPG His 1104Asp were in accordance with the HWE among the controls (P for Ala499Val=0.787; P for Lys939Gln=0.507; P for His1104Asp=0.175, respectively).The genotype and allele frequencies of all three polymorphisms were not statistically different between cases and controls (P> 0.05), respectively. No significant association was observed between the CT genotype and the TT genotype of XPC Ala499Val compared with the CC genotype (adjusted OR,1.34,95%CI,0.85-2.12; adjusted OR,1.30,95%CI,0.68-2.51, respectively), the AC genotype and the CC genotype of Lys939Gln compared with the AA genotype (adjusted OR,1.20,95%CI,0.78-1.85; adjusted OR,1.81, 95%CI,0.88-3.73, respectively) or the CG genotype and the GG genotype of XPG His1104Asp compared with the CC genotype (adjusted OR,0.85,95%CI, 0.56-1.27; adjusted OR,1.12,95%CI,0.67-1.87, respectively) and the risk of HCC by genotype alone, adjusted with the factors of age, sex, nationality, HBV infection, drinking, smoking, and family history of cancer.Stratified analysis We further performed stratified analysis by the factors of age, sex, HBV infection, drinking and smoking status. Except the sex factor, no significant association was shown. We found that the female subjects carrying at least one minor C allele of XPC Lys939Gln had a 2.17-fold risk of HCC compared to those carrying AA genotype (95%CI,1.01-4.64). ConclusionOur results suggest that the single polymorphism, i.e. XPC Ala499Val, XPC Lys939Gln, or XPG His1104Asp may not be associated with susceptibility to HCC. However, the minor C allele of XPC Lys939Gln may modify the risk of HCC in women. Larger sample size studies are warranted to further confirm our findings.