The Research Of SNPs On Igκ Gene Associated With Epithelial Cancer Susceptibility And The Heterogeneity Of Ig Expressed In Cancer Cells

Immunoglobulin(Ig) is the one of most important molecules mediating humoral immune response.By classic immunology theory, although all of the body cell contains germline gDNA that encodes Ig chains,only those in B lymphocytes are transcripted and expressed. Recently,accumulating evidences showed that cancer cells of epithelium origins could also carry out unique B cell processings such as V(D)J rearrangement and class switching,which led to Ig molecule transcription and expression.From a human nasopharyngeal carcinoma cell line,we have cloned an aberrant Igκgene(Tx).Aberrant Igκgene gene was shown to have transforming activity,including clone formation in soft agar and tumorigenesis in mude mice.Previous study identified 4 SNP loci on Igκgene,and their relationship with nasopharyngeal carcinoma(NPC) was analyzed.Results suggested that SNP3 and SNP5 were associated with NPC susceptibility. SNP3-CG genotype was distributed at a higher frequency in NPC patients than that in healthy individuals.Thus SNP loci on Igκgene gene is possibly a risk factor for NPC carcinogenesis.Based on that Ig expressed in cancer cells of various tissue origion and was we have confirmed its associated with NPC susceptibility,the first part of this project is focused on the relationship of SNPs on Igκgene with the susceptibility of lung,breast,esophagus,gastric,colon,and cervics cancers.Using bioinformatic methods,we predicted the changes of the 3-dimensional structures of Ig molecule caused by the different genotypes of SNP3,which located in the C region of Igκgene.Results implied that SNP3 could lead an amino acid change located on the surface of the Ig molecule,which had no direct impact on specific antigen-antibody binding,but might still have certain effects on its function,yet to be defined.Distribution for genotypes of SNPs on Igκgene was determined and analysed in all the clinical samples,which revealed significant differences between gastric,breast cancer cases and corresponding controls,implied that SNPs on Igκgene was associated with susceptibility of these two cancers.In gastric cancer cases and controls,the OR values for risk genotype SNP3-G and SNP5-G were 1.64 and 1.67 respectively, suggesting that the carriers might have 1.64 and 1.67 folds risks for developing gastric cancer compared with noncarriers.In breast cancer, the OR values were 1.94 and 1.57,suggesting that the risks for developing breast cancer was 1.94 and 1.56 folds higher in carriers than in noncarriers.By sequencing,a new SNP locus nt3324 was identified.Its genotype was G/A,completely linked with SNP6-5,the linkage genotype is G-A-T&A-G-C.It is known that SNPs have a micro-effect and cumulative effect.The risks for diseases associated with SNPs may correlate with other risk factors.In the second part of the research,stratified analyses for SNPs on Igκgene were carried out.The results revealed that in gastric cancer,the risks associated with SNP3-G and SNP5-C mainly presented in the cases with negative helicobacter pylori(HP) infection,OR value were 2.61(1.22-5.57) and 2.57(1.20-5.49) respectively,which suggested that risk genotypes of SNP3,5 played a role in gastric cancer carcinogenesis only in population without HP infection.Risk genotypes of SNP3 and SNP5 were associated with gastric cancer susceptibility in population aged below 49,with OR value being 3.06(1.23-7.60),2.83(1.24-6.43) respectively;SNP3-G also related to gastric cancer susceptibility in population aged between 58 and 65,with OR value being 2.89(1.28-6.53). The results implied that the risk genotypes of SNP3 and SNP5 may play a role in gastric cancer carcinogenesis in a population of a particular age group.In breast cancer cases and controls,the risk genotypes SNP3-G and SNP5-C were related to susceptibility in a population aged above 56,with OR value being 2.53(1.31-4.88) and 2.28(1.19-4.35),while,increased risk associated with SNP3G and SNP5 was observed in cases with negative estrogen receptor(ER) and progestogen receptor(PR) expression.The OR values for SNP3-G and SNP5-C in ER(-) cases were 2.71(1.52-4.85) and 2.41(1.32-4.41),in PR(-) cases were 2.42(1.42-4.41) and 2.00(1.16-3.44).The studies above revealed that SNP loci on Igκgene were risk factors for gastric cancer and breast cancer,associated with the diseases' susceptibility,and correlated with other risk factors such as HP infection, age and ER/PR expression.The investigation provided new insights into the phenomenon of cancers expressing the Ig molecule.The third part of this research focused on the heterogeneity of Ig expression in different cancer cells including NPC,cervical cancer,breast cancer,gastric cancer and colon cancer.Normal Igκis a 26KD molecule combined with heavy chains to form an integral Ig tetramer.It was found that there were 2 types of Igκlight chain monomers expressed in cancer cells with molecular weight being 26KD and 55KD respectively.The 55KD chain was the major one and could not combine with heavy chains. It has been reported that truncated Ig is a class of Ig molecules with abnormal molecular weight and varied structures,exsiting under pathological conditions.We speculated that the 55KD Igκbelongs to the class of truncated Ig.Normalαheavy chain is a 55KD molecule,combined with light chains to form an integral IgA.In cancer cells,αheavy chain also had two types of Igαmonomers,molecular weight being 40KD and 60KD respectively.The 40KD chain has an Fc domain recognizable by protein A,and the 60KD chain lacks an Fc domain,they are both truncated.The epithelial cancer cells were also capable of expressing mIg in cell membrane and secreting sIg into cell culture medium.The expression and secretion level were varied in cell lines of different tissue origins.Theαheavy chain secreted by Hela cell line was moderately higher than that of other cells.Using NPC cell lines as a model,the regulation of cancer cell's mIg and sIg by an exogenous oncoprotein latent membrane protein 1(LMP 1) encoded by EB virus was also explored.It was found that LMP1 could up-regulate the level of sIgκsecreted by NPC cancer cells.Our research established a new connection between virus oncogenic factors and the regulation mechanism of Ig expressed in cancer cells.This finding provided clues for exploring the biological significance of Ig expression in cancer cells.Tumor is a kind of immune deficiency disease;various clusters of related immuno-proteins are involved in carcinogenesis and tumor development.Our research focused on the SNP loci on Igκgene associated with cancer susceptibility;established the correlationship between risk genotypes of SNP loci on Igκgene and other environmental/host risk factors;and clarified heterogeneity of Ig expressed in cancer cells and its regulation mechanism.Our research have shed light on the significance of deficiency immuno-molecule in carcinogenesis.