Study On The Relationship Between The Polymorphism Of DNA Repair Gene XRCC1 And The Susceptibility To Lung Cancer

In recent years, lung cancer has become the leading cause of cancer deaths in China. The incidence and mortality of lung cancer in urban populations have reached the number one among malignant tumors. It is a cumulative course of polygenes mutants of developing lung cancer. Studies have reported smoking, air pollution and occupational exposure are three risk factors. However, lung cancer has familial clustering and obvious individual susceptibility.The single-nucleotide polymorphisms of DNA repair genes have unconservative amino acid replacements, of which the mutants can change the function of protein, repair capability and the risk of cancer. The DNA repair capability of individual is close to the polymorphic genotypes. The defect of DNA repair capability is connected with the function deletion of DNA repair protein resulting from gene mutations, mostly with the different repair capability from genetic polymorphisms.XRCCl plays an important role in repairing DNA single-strand breaks and base damages resulting from a series of intrinsic and extrinsic oxygens, including tobacco. XRCCl can be on single-strand breaks repairs with DNA LigⅢ, and base excision repair with DNA polβ. XRCCl is a 'scaffold' protein by binding to DNA polymeraseB, DNA Iigase Ⅲ, polynucleotide kinase(PNK), AP endonuclease and poly(ADP-ribose)polymerase l(PRAPl). Nowadays three single-nucleotide polymorphisms have been found, which are C26304T(Argl94Trp), G27466A(Arg280His) and G28152A (Arg399Gln) in coding regions. The variations can change the XRCCl activity. As amino acids have activity usually at protein-protein interaction of multiproteins and enzyme activated points of some residues. The polymorphisms of XRCCl may lead to the function defects of protein. The susceptibility to environmental carcinogens of individual will change with the single-nucleotide polymorphisms of some chain genes. The interaction between polymorphisms and environmental factors can increase the risk of cancer.A case-control study was conducted to test the allele frequencies and genotype frequencies of XRCCl C26304T and G28152A by PCR-RFLP, from which risk genotypes can be found. It can be helpful to analyze possible mechanism of lung cancer and their roles to discuss the association between the risk genotypes and lung cancer and the interaction between genotypes and smoking with lung cancer, which can be used in studying the etiology of lung cancer and cancer prevention. The relations between genotypes and histological type will provide an evidence for individual gene diagnosis.Materials and methods:1.Collecting samples: 149 tissue samples were collected from cases with lung cancer including 118 males and 31 females from Henan Han people, whose ages ranged from 32 to 80. No Radiation therapy and Chemical therapy before operation, removing other malignant tumors. Meanwhile 157 peripheral whole blood samples of healthy people were collected as controls, including 120 males and 37 females from Henan Han people, whose ages ranged from 35 to 80. No familial genetic diseases. 2.Analysing the genotypes: To amplify target fragments by PCR and to analyze theC26304 T and G28152A genotypes by PVUII and Msp I using RFLP. 3.Processing the data: To use chi-square test, Hardy-Weinberg Equilibrium test andunconditional logistic regression test of SPSS 10.0 ( ^=0.05) . Results: 1. The results of XRCCl C26304T (Argl94Trp) genotypesThe genotypes frequencies were fit for Hardy-Weinberg Equilibrium in controls (P>0.05). The allele frequencies of 26304C and 26304T were 71.9%, 28.0% incontrols respectively, and 68.1%, 31.9% in cases. There was no difference of allele frequencies and genotype frequency in two groups(P>0.05). C26304T mutant genotype was connected with lung cancer moderately and the adjusted OR was 2.62(95%C/1.11-6.15). The increasing risk of lung cancer was mainly in adenocarcinoma and the adjusted OR was 3.20(95%C71.05~9.76).The risk of lung cancer increased more than respective effect for the smoking individuals with mutant genotype. For the smokers with non-mutant genotype, the adjusted OR was 4.34(95%C/2.31~8.17). For non-smokers with mutant genotype, the adjusted OR was 3.84(95%C/1.27~11.60). For the individuals with smoking and mutant genotype, the adjusted OR was 8.36(95%C/2.36~29.59), but they had no interaction(P>0.05). For the smokers(the accumulative total smoking^580 cigarette ? year)and with mutant genotype, the adjusted OR was 8.89(95%C/4.28~18.45), and 6.84(95%C/1.87-24.96) respectively, which was associated with a significantly increased risk of lung cancer.2.The results of XRCC1 G28152A (Arg399Gln) genotypesThe genotypes frequencies were fit for Hardy-Weinberg Equilibrium in controls (P>0.05). The allele frequencies of 28152G and 28152A were 71.3%, 28.7% in controls respectively, and 66.4%, 33.6% in cases. There was no difference of allele frequencies and genotype frequency in two groups(P>0.05). G28152A mutant genotype was connected with lung cancer moderately and the adjusted OR was 2.68(95 %C/1.16-6.18). The increasing risk of lung cancer was mainly in adenocarcinoma and the adjusted OR was 5.32(95%C/1.90~14.90).The risk of lung cancer increased more than respective effect for the smoking individuals with mutant genotype. For the smokers with non-mutant genotype, the adjusted OR was 3.08(95%C71.67~5.67). For non-smokers with mutant genotype, the adjusted OR was 1.45(95%C/0.53~3.93). For the individuals with smoking and mutant genotype, the adjusted OR was 35.79(95%C/4.44~288.71) and they had interaction(P<0.05). For the smokers(the accumulative total smoking^580cigarette* year), the adjusted OR was 5.32(95%C/2.66~10.63), which was associated with a significantly increased risk of lung cancer.3.The influence of XRCC1 C26304T (Argl94Trp) and G28152A (Arg399Gln ) combined genotypes on susceptibility to lung cancerThere was no individual with combined mutant genotypes in controls, of which the frequency was low in common. From the analysis of interaction, the ￡ was 0.38 and the P value was 0.540, which indicated no interaction between XRCCl C26304T and G28152A. From the tendency of OR, there was possible interaction between two mutant genotypes.4.The interaction between gene polymorphisms and smoking on susceptibility to lung cancerFrom the analysis of unconditional Logistic regression that the two XRCCl C26304T and G28152A mutant genotypes entered the interaction model, the total /2 was 0.31 and the P value was 0.580. There was no possible interaction between two mutant genotypes and smoking.Conclusion:1. The allele frequencies of XRCCl maybe reflect the possible variation of common Han people in China.2. The mutant genotype of XRCCl C26304T was associated with a moderately increased risk of lung cancer. The increased risk was mainly in adenocarcinoma group. No interaction between mutant genotypes and smoking.3. The mutant genotype of XRCCl G28152A was associated with a moderately increased risk of lung cancer. The increased risk was mainly in adenocarcinoma group. There was interaction between mutant genotypes and smoking.4. The two combined mutant genotypes of XRCCl C26304T and G28152A was associated with a moderately increased risk of lung cancer. There were no possible interaction between the two mutant genotypes and between the two mutant genotypes and smoking.