Correlation Of XPC Genetic Polymorphisms To The Risk Of Prostate Cancer And Bladder Cancer In A Chinese Han Population

BackgroundEpidemiological studies suggest that smoking is associated with an increased incidenceof several types of cancer. Cigarette smoking is strongly associated with the risk of bladdercarcinoma. Cigarette smoking accounts for approximately65%of bladder cancer risk in menand20%–30%in women. Recent studies have also determined that there is an associationbetween smoking and prostate cancer incidence. As there are thousands of carcinogens incigarettes, it is not reasonable to try to find out each molecular mechanism that correspond toeach carcinogen in smoking. But it has been previously demonstrated that these carcinogenscause DNA damage through the introduction of bulky adducts, crosslinks, and single ordouble-stranded breaks. The association between DNA damage and increased cancer risk hasbeen confirmed by numerous basic and epidemiological studies.DNA damage repair is the primary defense mechanism against mutagenic exposure.There are four major DNA-repair pathways in human cells: nucleotide excision repair (NER),base excision repair (BER), mismatch repair (MMR), and double-strand break (DSB) repair.The BER pathway removes DNA damage caused by ionizing radiation, reactive oxidativespecies and methylating agents. NER plays a critical role in repairing various forms of DNAdamage: bulky adducts generated from genotoxic compounds, ultraviolet-induced photolesions and intrastrand cross-links. NER is initiated by recognition of these DNA lesions byXPC/RAD23B complex. The helicase activity of TFIIH serves to open up the DNA whereasrecruitment and activation of XPF/ERCC1and XPG endonucleases that incise the damagedDNA. Then the gap will be filled with DNA synthesis and ligation. MMR is a highlyconserved repair pathway that functions in improving replication fidelity by correctingreplication-associated base–base and insertion/deletion mispairs. Double-strand breaks mayresult in cell death or a wide variety of genetic alterations, including large-or small-scaledeletions, loss of heterozygosity, translocations and chromosome loss. Double-strand breaks are repaired by at least two major repair pathways, homologous recombination andnon-homologous end joining. There are currently over100known DNA repair genes, andmost are known to display genetic variation in humans. Due to the presence ofsingle-nucleotide polymorphisms (SNPs) in repair gene DNA, the functional properties ofrepair enzymes are changed or the level of transcription or translation is altered, all of which,in turn, reduce the capacity for DNA repair and induce genetic instability and carcinogenesis.The nucleotide excision repair (NER) pathway primarily removes the bulky DNAadducts most commonly generated by exposure to the polycyclic aromatic hydrocarbons intobacco smoke. Xeroderma pigmentosum, complementation group C (XPC) is a componentof the nucleotide excision repair (NER) pathway. It plays an important role in the early stepsof global genome NER, particularly as a damage sensor in open complex formation, and inthe repair of complex protein formations. Mutations in this gene result in Xerodermapigmentosum, a rare autosomal recessive disorder characterized by increased sensitivity tosunlight and the development of skin cancer at an early age. Previous studies havedemonstrated that XPC defective mice are highly prone to skin cancer following exposure toUV radiation and also are susceptible to common cancers, such as lung, esophageal, andbladder cancer when exposed to chemical carcinogens. These findings indicate that XPC mayplay a role in prevention of human carcinogenesis. The two most common non-synonymoussingle nucleotide polymorphisms (SNPs), Lys939Gln (rs2228001) in exon15and Ala499Val(rs2228000) in exon8, and a poly (AT) insertion/deletion polymorphism in intron9, havebeen associated with an increased risk of many human malignancies.It has long been observed that individuals with seemingly equal exposure to cigarettesmoking exhibit a great difference in the risk for developing bladder cancer. Men ofPolynesian ancestry, including native Hawaiians, exhibit a high rate of smoking but lowincidence of bladder cancer. These findings suggest that there is potentially wide variability inan individual's response to cigarette smoking which could potentially be linked to geneticfactors and interactions with cigarette smoking.However, recent molecular epidemiological studies in various populations have found aninconsistent correlation of XPC genetic polymorphisms to the risk of prostate cancer andbladder cancer.To date, the mechanism of the occurrence and the progression of prostate cancer and bladder cancer remain poorly understood, but it has been elucidated that both genetic andenvironmental factors are involved in the etiology. Little is known about the interactionsbetween XPC polymorphisms and smoking exposure on prostate cancer and bladder cancerrisk.Objectives1．To test the hypothesis that two SNPs of the XPC gene are associated with the risk ofdeveloping prostate cancer in a Chinese Han population.2．Examined bladder cancer risk in relation to three polymorphisms of the XPC gene andcigarette smoking as measured by smoking status and total exposure (pack-years).3．Assessed whether the interaction between the XPC gene polymorphisms and smokingcontributed to increased prostate cancer and bladder cancer susceptibility.Methods1． Blood samples from each subject were collected in tubes containingethylenediaminetetra-acetic acid (EDTA) and stored at4°C until performance of genomicDNA extraction.2．The XPC Ala499Val polymorphism was detected using primer-introduced restrictionanalysis (PIRA)-PCR. The sense primer introduced a mismatched C to replace A at-2bp fromthe polymorphic site (Genbank number AF261898) to create a SacII restriction site. The SacIIrestriction enzyme was used to distinguish the Ala499Val polymorphism (C>T).3．Genotyped the XPC-PAT by using PCR-based method.4．Genotyping of Lys939Gln of XPC was performed using the polymerase chain reactionrestriction fragment length polymorphism (PCR-RFLP) technique. The restriction enzymePvuⅡwas used to differentiate the Lys allele from the Gln allele.5．To confirm the genotype ascribed by based PCR methods,ten percent of the sampleswere randomly selected and run in duplicate.6．Statistical Package for the Social Sciences (SPSS) software (version13.0, SPSS Inc.,Chicago, Illinois) and the MATLAB program were used for data analysis. We used theHardy-Weinberg equilibrium (HWE) to test genotype and allele frequency by agoodness-of-fit χ2test, with one degree of freedom (df) to compare observed and expectedgenotype frequencies among cases and controls. Multivariate Logistic regression analysis adjusting for age and smoking status was used to estimate the association between eachgenotype and the risk of prostate cancer and bladder cancer by computing the adjusted oddsratio and95%confidence interval. The interactions between the XPC gene polymorphism andsmoking for prostate cancer and bladder cancer risk were analyzed by the Likelihood RatioChi-Square Tests and logistic regression model.Results1．A greater percentage of prostate cancer patients were smokers (48.0%) compared tothe controls (38.0%)(p=0.038), and the Odds Ratio [OR] for smoking-associated prostatecancer was1.51(95%CI:1.02-2.22). The bladder cancer cases represented a significantlyhigher percentage of ever smokers (52.7%) compared to controls (35.1%)(p<0.001), and agreater percentage of cases were heavy smokers (31.0%) compared to controls (17.1%)(p<0.001).2．In the3possible genetic models (additive, dominant, and recessive), we did not findan association between elevated prostate cancer risk and XPC Lys939Gln polymorphisms.However, we found that the estimated OR for XPC PAT＋/－was1.43(p=0.013),1.54(p=0.030), and1.84(P=0.051) for the additive, dominant, and recessive genetic models,respectively.3．The three common genetic models (additive, dominant, and recessive) did notdemonstrate an association between elevated bladder cancer risk and XPC Ala499Val andLys939Gln polymorphisms. However, we found that the estimated OR (95%CI) for XPCPAT＋/－was1.24(1.05-1.46)(p=0.013),1.30(1.03-1.65)(p=0.026), and1.37(0.98-1.92)(P=0.068) for the additive, dominant, and recessive genetic models, respectively.4．No significant association was determined between the XPC Lys939Gln genotype andthe risk of prostate cancer. However, individuals carrying the PAT+/+of XPC intron9demonstrated a significant two-fold increase in risk (OR:2.11;95%CI:1.12–3.99; p=0.033)associated with prostate cancer after adjustment for age and smoking status. The combiningsubjects with either PAT+/+or PAT＋/－genotype exhibited a1.54-fold increased riskassociated with prostate cancer (OR:1.54;95%CI:1.04–2.26; p=0.029).5．The XPC Ala499Val and Lys939Gln were not associated with the risk of bladdercancer. However, PAT+/+of XPC was significantly associated with bladder cancer (OR:1.52;95%CI:1.06–2.18; p=0.022) after adjustments for age, sex, and smoking (pack-years). The combined genotype PAT+/+and PAT＋/－exhibited a significant1.33-fold increase in riskfor bladder cancer (OR:1.33;95%CI:1.05–1.68; p=0.017).6．The XPC polymorphisms exhibited no statistically significant association with theclinical parameters in prostate cancer and bladder cancer patients.7．We did not find the interaction between smoking and XPC Lys939Gln to bestatistically significant association with prostate cancer risk (χ2=9.50,υ=5, P=0.091).However, there was evidence of an interaction between the XPC-PAT polymorphism andsmoking in risk for prostate cancer (χ2=11.32,υ=5, P=0.045). Smokers with PAT+/-orPAT+/+had a higher risk for prostate cancer(OR:1.98;95%CI:1.083.64; p=0.026and OR:3.56;95%CI:1.458.76; p=0.004,respectively) compared to never smokers carrying the PAT-/-.8．Ever smokers exhibited a higher risk of bladder cancer compared to never smokers(OR:2.48;95%CI:1.91-3.21). Among the ever smokers, risk estimates of bladder cancerwere significantly higher for both heavy smokers (OR:3.09;95%CI:2.24-4.25) and lightsmokers (OR:1.91;95%CI:1.37-2.68) compared to never smokers. In never smokers, noassociation was found between the three polymorphisms of the XPC gene and increasedbladder cancer risk. However, we found a significant dose-response correlation between theinteraction of the three XPC gene polymorphisms and total smoking exposure and risk ofbladder cancer. Subjects with the PAT+/+genotype who were exposed to light or heavysmoking demonstrated a higher risk for bladder cancer (OR:3.00;95%CI:1.31-6.88,p=0.009; OR:6.78;95%CI:3.00-15.54, p<0.001, respectively). Subjects homozygous forthe XPC939Gln/Gln genotype exposed to light or heavy smoking demonstrated a higherrisk for bladder cancer (OR:2.13,95%CI:0.97-4.70; OR:5.79,95%CI:2.53-13.28,respectively).Conclusions1．The environmental exposure of smoking may be a risk of prostate cancer in a ChineseHan population.2．The XPC PAT＋/－most likely acts in an additive or dominant genetic manner toincrease risk associated with prostate cancer.3．Smokers with XPC-PAT+/-or PAT+/+were at significantly elevated risk of prostatecancer. This study also revealed the direct association of environmental contribution (smoking) with a higher genetic risk for prostate cancer.4．The XPC-PAT polymorphism may contribute to susceptibility to bladder cancer in theChinese Han population.5．The gene-environment (total smoking exposure) interactions were associated with anelevated risk of bladder cancer.