The Association Between The Genetic Variant In EME1 Gene And Risk Of Lung Cancer In The Southern Chinese Population

Backgrounds:Lung cancer is a common malignant tumor of human being. In recent decades,the death rate of lung cancer has been increasing very quickly either in developed or in developing countries. In China, lung Cancer had been the first cause of death, and its etiology and pathogenesis had been the hot topics for many years.Epidemiological studies have established many risk factors that influence the development of this disease including reactive oxygen species, radiation, UV light, and various carcinogens. DSBs are the most lethal types of DNA lesions, unrepaired DSBs can easily lead to chromosomal aberrations, increased genetic instability and ultimately to cancer development. Two main pathways remove DSBs, homologous recombination (HR) and non-homologous end-joining (NHEJ) repairs. DNA repair capacity may confer to the genetic susceptibility to lung cancer. DNA repair gene polymorphisms, particularly single nucleotide polymorphisms (SNP) and gene-environment interaction maybe underlying molecular mechanisms of the lung cancer.DSBs form under a normal metabolization process or during environmental factors cause pathologic state, tobacco smoke and endogenous forms DSBs too. Unrepaired DSBs can easily lead to chromosomal aberrations, increased genetic instability and ultimately to cancer development. EME1 could play a role in DSBs repair. EME1 cleaves nicked Holliday junctions, aberrant replication fork structures, D-loops, and 3'-flap structure. The human EME1 gene is associated with leukemia, and other forms of cancer. However, there is no similar study in China.To investigate the risk factors of human lung cancers in Guangzhou and to provide the scientific basis for controlling and preventing lung cancer, we tested the hypothesis in current hospital-based case-control study with 1056 lung cancer cases and 1056 age-sex frequency-matched controls in Southern Chinese population, compare their difference in EME1 variant's distribution, and further we had adopted a multivariate logistic model to investigate other risk factors and their relationship with the risk of lung cancer. Additionally, these factors were used in the later stratification analysis and gene-environment interaction analysis.Methods:According to the bronchoscope and pathologic diagnoses, 1056 newly diagnosed primary lung cancer cases and equal number of control, matched for age and sex, were recruited and interviewed in Guangzhou during 2007 to 2009. The questionnaire consists of 91 items about lung cancer etiological factors was applied. Single-factor and multivariate conditional logistic regression were performed to calculate the ORs and their 95% C.I. Based on the integrity information of investigation, each subject was asked to donate 5 mL of blood after giving informed consent. DNA was extracted and separated as work solution and stock solution. Biophtometer 6131 was used to detect the concentration and purity of DNA. Based on the Genebank dbSNP database (http://www.ncbi.nlm.nih.gov), according to the principle that the minor allele frequency >5%, we identified possible functional SNPs in the EME1 gene: Ile350Thr (rs12450550). Taqman method was carried out to analyze the genotype and a few samples were chosen to sequence with the help of Invitrogen Company. The study was approved by the institutional review boards of Guangzhou Medical University.Statistic analysisChi-square (χ2) tests were used to assess differences in the distribution of age, sex, menstrual history, BMI, and family history of lung cancer between cases and controls. The Hardy-Weinberg equilibrium (HWE) was tested by a goodness-of-fit chi-square test compare the expected genotype frequencies with observed genotype frequencies in cancer-free controls. Unconditional logistic was used to calculate crude and adjusted odd ratios (OR) and their 95% confidence intervals (95% CI) with and without adjustment for age, sex, menstrual history, BMI, and family history of lung cancer. Logistic modeling was also used for the trend test. In the stratification analysis, we assessed the main effect of EME1 polymorphisms in subgroup and the interaction among the EME1 polymorphisms and selected variables on cancer risk. A multiplicative interaction was suggested when OR 11 > OR 10×OR 01, in which OR 11 = the OR when both factors were present, OR 01 = the OR when only factor 1 was present, OR 10 = the OR when only factor 2 was present. The tests were analyzed using the SAS software (version9.1; SAS Institute, Cary, NC, USA). All statistical tests were 2-sided and p<0.05 was considered statistically significant.Results:This study included 1056 lung cancer patients and 1056 cancer-free controls. Of the 1056 cases, there were 384 (36.4%) cases of adenocarcinomas, 369 (34.9%) squamous cell carcinomas, 43 (4.1%) large cell carcinomas, 128 (12.1%) small cell lung cancers, and 132 (12.5%) mixed-cell or undifferentiated carcinomas. According to the IASLC staging classifications, there were 154 (14.5%) cases of stage I, 94 (8.9%) stage II, 333 (31.5%) stage III, and 475 (45.0%) stage IV. The difference in distributions of age, sex, and sub-ethic between the cases and cancer-free controls were not statistically significant (P>0.05).The observed genotype frequency of Ile350Thr among the control subjects was in agreement with the Hardy–Weinberg equilibrium (P= 0.4459). Compared with the Ile/Ile genotype, Ile/Thr heterozygotes had a 1.41-fold increased risk of lung cancer (adjusted OR=1.41; 95%CI=1.03-1.92;P= 0.042), and the Thr/Thr homozygote had a significant critical risk of lung cancer (adjusted OR=3.85; 95%CI=0.94-11.26;P= 0.062). There was a significant trend for an allele dose effect on risk of lung cancer (Ptrend = 0.0193). The combined Ile/Thr and Thr/Thr variant also had a increased risk of lung cancer (adjusted OR=1.43; 95%CI=1.06-1.93; P= 0.0190). The increased risk of lung cancer associated with Thr variant genotypes (Ile/Thr and Thr/Thr) can be observed in subgroups age (older than 60 years)(adjusted OR=1.63; 95%CI=1.09-2.44; P=0.018), sex (male or female), smoking status (ever)(adjusted OR=1.72; 95%CI=1.19-2.50; P=0.004), drinking status (never)(adjusted OR=1.65; 95%CI=1.21-2.26; P=0.002), BMI <18kg/m2 (adjusted OR=7.87; 95%CI=1.00-61.80; P=0.049) and 18kg/m2<BMI<25 kg/m2 (adjusted OR=1.41; 95%CI=1.02-1.94; P=0.036) , and family history of cancer (no)(adjusted OR=1.52; 95%CI=1.13-2.03; P=0.005)(P <0.05 for all subgroups).We also performed an interaction analysis of the associations between EME1 variant genotypes and the risk of lung cancer in subgroups by age, sex, smoking and alcohol drinking, BMI (all the p>0.05).Conclusions:The EME1 Ile/Thr and Thr/Thr variants can significantly increase the risk of lung cancer in southern Chinese population, especially in people age>60, ever smoker and BMI(<18 kg/m~2 and18-25 kg/m~2) subgroups.