Genetic Susceptibility Of Head And Neck Cancer In Chinese Han Populations

Head and neck cancer (HNC), comprising the oral and maxillofacial region,pharynx, laryngeal and other parts of the upper aerodigestive tract, is the sixth mostcommon malignancy, which seriously threatened human’s health and life. However,the exact molecular mechanisms to develop head and neck caner are still unclear. It iswell accepted that interaction of environmental factors and genetic factors maycontribute to the etiology of head and neck cancer. Genetic biology studys indicatedthat the differences on genetic background resulted in different susceptibility of headand neck cancer. Therefore, it is important to find the head and neck cancersusceptibility genes in a high-risk population and to prevent the occurrence of headand neck cancer.With the completion of Human Genome Project (HGP), it is now known thatgenetic variations play an important role in gene structure and function, which couldchange the biological functions of genes and affect individual susceptibility to diseaseand drug reactivity. Single nucleotide polymorphisms (SNPs) are the most commontypes of genetic variations. In the study of molecular epidemiology and genetics,SNPs have been widely used for gene mapping of molecular markers, by comparingthe normal and patients of SNPs to locate and identify specific disease-related genes.SNPs in genes can impact the gene structure and function, leading to increase risk ofcancer. Many studies have suggested that the genes in DNA repair, apoptosis, andfolate metabolism were associated with head and neck cancer risk. Most functionalSNPs singly or jointly contribute to the risk of head and neck cancer, and possiblyhave gene-gene and gene-environment interactions. Recently, evidence shows thatsmall, non-coding RNA molecules, called microRNAs (miRNAs), function as tumorsuppressors or oncogenes. Mutation, mis-expression or altered mature miRNAprocessing are implicated in carcinogenesis and tumor progression. And agenome-wide association studies(GWAS) in European populations had identified the upper aerodigestive tract cancer susceptibility loci. However, there are no studiesconducted in Chinese populations to replicate these findings.With the development of high-throughput genotyping technology and thedeepening of cognition on the human genome and genetics, associationstudies of cancer susceptibility have focused three important strategies: candidategene, candidate biological pathway and GWAS. In the present study, we will applythese strategies, combining with medthods of epidemiology and molecular biology tohave the following aims:(1) To explore the relationship between the hereditaryvariants in key DNA repair genes and risk of head and neck cancer in Chinese Hanpopulation.(2) To evaluate the correlation between the functional geneticpolymorphisms on miRNA biosynthesis pathway and head and neck cancersusceptibility of Chinese Han people.(3) To verify whether the susceptibility locifound by the upper aerodigestive tract cancer GWAS in Caucasians are related tohead and neck cancer in China. The research will provide theoretical basis to furtherreveal the biological mechanisms of head and neck carcinogenesis, and search headand neck cancer susceptibility biomarkers for high-risk population screening,individualized prevention, intervention and treatment.Part I: Association Study on Functional GeneticPolymorphisms of Key DNA Damage Repair Pathway andHead and Neck Cancer SusceptibilityHuman have a variety of DNA damage repair mechanisms, including baseexcision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR),and so on. Among these DNA repair pathways, BER repairs DNA damage resultingfrom reactive oxygen, alkylating agents and DNA single-strand breaks arise fromdeaminase, spontaneous hydrolysis, while NER is the major repair mechanism for theDNA damage caused by tobacco smoking. Studies have shown that mutation existedin key genes on this pathway change the risk of cancer. XRCC1, APE1, ADPRT andXPD, XPG play an important role in their pathways respectively. We hypothesized that functional SNPs on these pathways could affect the risk of head and neck cancerindividually or jointly.To test the hypothesis above, we genotyped5functional SNPs—APEX1(Asp148Glu, rs1130409), XRCC1(Arg399Gln, rs25487), ADPRT （Val762Ala,rs1136410）, XPD (Lys751Gln, rs13181), and XPG (His1104Asp, rs17655) withTaqMan technology in a case-control study of397head and neck cancer cases and900cancer-free controls matched by sex and age in a Chinese Han population.Data analyses showed that there were no significant associations between these5SNPs and head and neck cancer risk in the dominant model (rs13181: OR=0.97，95%CI=0.69-1.35; rs17655: OR=0.99,95%CI=0.72-1.24; rs1130409: OR=0.86,95%CI=0.67-1.11; rs25487: OR=0.93,95%CI=0.73-1.19; rs1136410: OR=0.96,95%CI=0.75-1.24). We further conducted the stratification analyses, but the differencewas also nonsignificant in every stratum.In conclusion, this study provided evidence that5SNPs in key DNA repairgenes were not associated with head and neck cancer risk in China. The findings needto be validated by larger studies.Part II: Study on the Functional Polymorphisms ofMiRNA Biosynthesis Pathway Related Genes and Head andNeck Cancer SusceptibilityMiRNAs are small (21–24nucleotides) non–coding RNAs which can bind to the3’ untranslate region of its target gene in an incomplete complementary way, playinga negative regulation in the transcriptional level and stability of the gene. Researchsindicated that abnormal expression of miRNAs might be regulated by the miRNAbiosynthesis pathway related genes. We hypothesized that snps in the3’ UTR regionof some important genes of the miRNA biosynthesis pathway might affect thestability of this pathway, resulting in the genetic susceptibility of head and neckcancer.To validate the hypothesis，we performed a case-control study concerning about the association of three functional SNPs(rs1057035in DICER, rs3803012in RAN andrs10773771in HIWI) and the genetic susceptibility of head and neck cancer. Based onthe association study results, we investigated the functional meaning of SNPs inDICER using molecular biology methods.We found all3SNPs were not significantly associated with risk of head and neckcancer (rs1057035: OR=0.77,95%CI=0.57-1.03; rs3803012: OR=1.18,95%CI=0.81-1.72; rs10773771: OR=0.92,95%CI=0.72-1.19). Further stratificationanalysis indicated that rs1057035TC/CC genotype could significantly reduce oralcancer risk compared with wild genotype (OR=0.65,95%CI=0.46-0.92). Functionalstudy found that rs1057035T>C change might affect the combination ofhsa-miR-574-3p and DICER3’ UTR region by constructing luciferase report gene(P<0.05).In conclusion, our results indicated that rs1057035T>C change could affect thecombinationin of hsa-miR-574-3p and the3’ UTR region of DICER, which mightaffect the expression level of DICER, resulting in the genetic susceptibility of oralcancer.Part III: Replication Study on the GeneticSusceptibility of Head and Neck Cancer Based on GWASRecently, McKay. et al conducted a genome-wide association study concerningupper aerodigestive tract tumors among Caucasians. They found that rs1229984,rs971074, rs1789924at4q23, rs1494961at4q21and rs476736at12q24contributedto the risk of upper aerodigestive tract cancer. And some resrarchs also found thatrs671at the12q24region contributed to head and neck cancer risk based on Asianpopulation. We hypothesized the SNPs identified in these region were also importantin the development of head and neck cancer in Chinese Han population.In order to verify the above hypothesis,6SNPs （rs1494961、 rs1229984、rs1789924、rs971074、rs671and rs4767364）were selected according to GWAS andprevious findings among Asian populations. We then genotyped these variants using the TaqMan allelic discrimination assay in a case-control study.We observed that the rs1229984combined variant AG/GG genotypes increasedthe risk of head and neck cancer by1.37fold compared with the AA genotype(OR=1.37,95%CI=1.08-1.74) and rs671AA genotypes were associated with areduced head and neck cancer risk compared with the GG/GA genotype (OR=0.36,95%CI=0.20-0.66). Combining both variants, we found individuals carrying3-4riskalleles have1.96fold HNC risks than those carrying0-1risk alleles (OR=1.96,95%CI=1.08-3.58).The results of this study showed that rs1229984at4q23and rs671at q24wereassociated with head and neck cancer risk in Chinese Han population.