【作者】 张晔；

【导师】 袁媛；

【作者基本信息】 中国医科大学 ， 肿瘤学， 2006， 硕士

【摘要】 前言 胃癌是全世界最常见的恶性肿瘤之一。在我国其年患病率为300.87/10万,死亡率29.31/10万,属胃癌高发国家。尤其在我国北方胃癌高发地区死亡率男性为49.55/10万,女性为22.23/10万。目前在研究胃癌发病机制过程中,人们逐渐意识到不同个体易感性不同在其发生、发展中的重要作用。人群中存在易感个体是由于一些与肿瘤相关的基因存在多态性。各种易感因素破坏了基因组的稳定性后,携带易感基因型的人当暴露于相似诱因条件下,更易于患肿瘤。 谷胱甘肽-S-转硫酶(GST)属Ⅱ相代谢酶,是由两个同源二聚体亚基组成的一组同功酶家族,主要包括4个家族:A、M、T、P(旧命名分别为α、μ、θ、π)。其中GSTM1和GSTT1的人群多态性以及与肿瘤易感性关系的研究开展较早,GSTPI的人群多态性近年来引起医学界注意。hGSTP1是hGSTS家族中酸性同功酶P1的编码基因,1989年Board等分离了人类GSTP1基因的cDNA克隆,将其定位于染色体的11q13,并首次报道了GSTP1基因的外显子5(Ile105→Val)和外显子6(Alal14→Val)存在多态性。GSTP1基因编码产物GSTP1酶含有210个氨基酸,有研究表明位于第105位点的氨基酸序列对于蛋白质的的生物学功能十分重要,该位点氨基酸的替代改变了氨基酸的体积和疏水性,从而影响了酶的热稳定性。据报道GSTP1酶-Val105的热稳定性比GSTP1酶-Ile105的低2-3倍。而第114位氨基酸位于酶与疏水底物结合位点之外,GSTP1酶-Val114的酶活力较GSTP1酶-Alal14并无明显下降。 胃癌一直是我国重点防治的恶性肿瘤之一。我国胃癌高发于东南沿海和西北、华北、东北等部分人口众多的农村地区。流行病学调查资料表明,辽宁省庄河市每年新发现胃癌和因胃癌死亡的病例均在400例左右,占当更多还原

【Abstract】 PrefaceIn the world, gastric cancer is still one of the most frequent types of cancer. Gastric cancer is a leading cause of malignancy - related death in China, especially in high incidence areas. The estimate for 2004 points, in China, to the second place in incidence and mortality with about 300. 87/100,000 and 29. 31/ 100,000. Specially, in the Northeast China, mortality of male was 49. 55/100, 000 and that of female was 22. 23/100,000. So far, through the investigations about pathogenesis of gastric cancer, increasing evidence suggests that interaction between various inherited cancer susceptibility genes, also known as risk — modifier genes, particularly genes whose allelic polymorphism are responsible from impaired ability to metabolize environmental carcinogens and/or repair DNA damage from oxidative stress, coule affect an individual‘s risk of developing cancer.Since the first description that the polymorphisms of the RAS gene can be used to value the risk of oncogenesis by Krontiris in 1985, more studies have begun to demonstrate associations between the polymorphisms and gastric cancer susceptibility that included the metabolic enzymes genes, oncogenes, anti - on-cogenes and immuno - modifier genes. It has been suggested that genetic susceptibility genes, specially metabolising enzymes genes, may confer a risk for the development of gastric cancer. Cytochrome P450, as phase I metabolic enzymes , can be induced by ethanol and catalyses the oxidation of many substrates , including several potential carcinogens and drugs that are transformed totheir ultimate reactiveforms. Glutathione S - transferases ( GSTS) consist of a su-perfamily of dimeric phase II metabolic enzymes that are separated into the four classes: GSTA( alpha) .GSTM(mu),GSTT(theta) and GSTP( pi). The polymorphisms in GSTM1 and GSTT1 were investigated in cancers for a long time, however, only recently some studies were conducted to investigate the association of various cancers with GSTPl variants. In 1989, Board reported the isolation of full - length cDNAs of GSTPl gene. The GSTPl gene has been mapped to a relatively small region of chromosome Ilql3. Polymorphisms of GSTPl have been reported for example, isoleucine(He) 105 valine(Val) in exon5, alanine (Ala) 114 valine( Val) in exon 6. GSTPl is subject to polymorphic variations;the single — nudeotide substitution A/G results in an amino acide change at co-don 105 (He—?Val) that is associated with lower substrate - specific catalytic activity and lower thermal stability for the encoded protein ( GSTir). A 2^3 fold reduction in thermal stability has been shown in association with the GSTPl 105Val variant compared with the GSTPl 105Ile variant. But the polymorphic site at nucleotide 114 ( exon 6) was detected and found to no modify the enzyme’s activity and affinity for electrophilic substrates. That is to say, the two GSTPl proteins differ in specific activity, affinity for electrophilic substrates and heat stability. The GSTPl — valine variant has lower activity toward 1 - chloro — 2,4- dinitrobenzene but greater activity toward bromosulfophthalein and ethacrynic acid. In addition, the GSTPl -isoleucine, which has higher activity for most substrates than GSTPl -Valine, is less thermostable.To date, the nucleotide sequences of the complete human GSTPl cDNA and the structures of GSTPl gene reported from different laboretories have been identical, leading to the notion that the different GSTPl isoenzymes have distinctly specific metabolic activities to carcinogens. Some studies observed a different relation between the GSTPl polymorphism and an increased resk for oral, breast, colorectal, prostate and lung cancers. For example, the GSTPl 105Val allele was found to increase in patients with breast Cancer whereas the GSTPl 105He allele to increase with esophageal cancer. Regarding gastric cancer, only a few studies were conducted to investigate its association with GSTPl variants. Accordingly we described a case - control study to determine if this GSTPl poly-morphism influences suseceptibility to gastric cancer using a polymerase chain reaction(PCR) to detect variant forms of GSTPl, as well as the interaction between the polymorphism and environmental factor(anti -H. pylori immunoglobu-lin G(IgG) status) involved in gastric carcinogenensis.Study ObjectiveTo analysis the distribution of polymorphism of GSTPl in population in the northeast China and the relationship between the polymorphic BsmAI site in ex-tron 5 of glutathione - S - transferase PI ( GSTPl ) with susceptibility to gastric cancer and evaluate the combined effect between genetic polymorphic of GSTPl and H. pylori infection on gastric cancer.Study MethodsPolymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were performed to analyze the genotype GSTPl polymorphisms in exon 5 (IlelO5Val). Blood samples were taken from 1,612 subjects in the Northeast China, including high and low risk areas of gastric cancer. Subjects underwent H. pylori/IgG examination by serology.Study ResultsAmong subjects in the Northeast China, 22% were the GSTPl 105A/G variant allele frequencies, which is siginificantly different from western people. The difference in GSTPl allele gene distribution between the area of high incidence of gastric cancer(23% ) and low incidence (20% ) has statistical significance. Further analysis combinedthe sex effect of the polymorphisms, the proportion of GSTPl variant allele gene was significantly higher in the men than in the women(24% vs 20% ) , specially in Zhuanghe region, a high risk area of gastric cancer in the north of China (X2 =5.100, P <0.05);The frequency of GSTPl Val/Val genotypes was statistically higher in thegastric cancer group compared with the non - gastric cancer population. The a-nalysis showed a statistically significant 1. 587 - fold increase in gastric cancer risk associated with GSTPl V105 allele gene;Moreover, there was a statistically significant interaction (odd ratio, 17. 571;95% confidence interval, 6.207-49. 742) between GSTPl Val/Val genotype and Hp/IgG difference positive status;Study ConclusionOur results indicate that the distribution of GSTPl polymorphism has statistical significance with sexual and geOgraphic difference. The individuals with GSTPl V105 allele gene show an increased risk in suffering from gastric cancer. Association of the GSTPl ( Val/Val) genotype with Hp/IgG positive factor could significantly increase gastric cancer risk assessment.更多还原