【作者】 张勇晶；

【导师】 陈坤；

【作者基本信息】 浙江大学 ， 劳动卫生与环境卫生学， 2009， 博士

【摘要】 研究背景及目的结直肠癌是世界范围内最常见的消化道恶性肿瘤之一,北美、西欧、澳大利亚和新西兰等经济发达国家是结直肠癌的传统高发地区。虽然我国是结直肠癌的传统低发国家,但近年来随着人们的生活方式变化,我国结直肠癌的发病率也呈上升趋势,成为威胁我国人民健康和生活质量的重要危险因素结直肠癌的病因和发病机制尚未完全明了,大量的流行病学研究显示散发性结直肠癌的发生发展是一个多因素多步骤,受环境因素和遗传因素共同作用的复杂过程。许多环境因素如饮食习惯、吸烟和饮酒等生活方式、超重与肥胖、肠道疾病史等都与结直肠癌密切相关。近年来越来越多的证据显示TGF-β通路在恶性肿瘤发生发展过程中起关键作用,它广泛参与调控细胞的生长、分化、凋亡等多个生物学过程,可能成为影响结直肠癌易感性的潜在遗传因素。本研究以浙江省嘉善县作为研究现场,开展了以人群为基础的病例.对照研究,旨在综合宏观和微观两个方面的信息,全面分析影响结直肠癌发病风险的环境暴露因素和TGF-β通路基因多态位点,深入探讨基因与环境因素之间的潜在交互作用,为结直肠癌的病因学研究提供流行病学线索,并为结直肠癌的人群防治和干预措施的制定提供科学依据。材料和方法研究以浙江省嘉善县作为研究现场,采用以人群为基础的病例.对照研究设计。选择确诊日期在1990年5月至2007年5月之间确诊的原发性结直肠癌现患存活病例组成病例组。采用随机抽样的方法从健康人群中抽取无肿瘤患病史的嘉善县常住居民作为对照组。采取调查员现场入户的问卷调查方法,由经过统一培训并考核合格的调查员对研究对象进行面对面的访问。问卷调查结束后,在研究对象知情同意情况下收集每位调查对象外周静脉血共5mL,应用改良盐析法基本原理抽提基因组DNA。采用以PCR为基础的多种基因分型技术对TGF-β通路基因多态性进行检测。采用非条件Logistic回归模型计算以人口学特征等作为调整因素的调整OR值及其95%CI,估计各基因型与结直肠癌发病风险的关联强度。应用叉生分析的方法对两因素交互作用进行分析,应用分类回归树模型对高阶交互作用进行深入挖掘。结果人口学特征在病例组和对照组中的分布差异均没有统计学意义。肥胖、饮酒和肿瘤家族史与结直肠癌发病风险没有统计学关联。与不吸入肺的吸烟者相比,深吸入肺的吸烟者直肠癌患病危险度OR高达2.15(95%CI=1.23～3.76),而对结肠癌的患病风险则无影响。饮茶可以显著降低罹患结直肠癌的风险40%左右(OR=0.59,95%CI=0.42～0.82),特别是饮用绿茶有显著的降低结肠癌和直肠癌风险的作用,其OR值分别为0.56(95%CI=0.35～0.89)和0.60(95%CI=0.40～0.92)。TGF-β1 G-800A、codon25、codon263和TGFβR2 A-364G等4个SNP没有检测到变异基因型,在研究人群中均以野生纯合基因型存在。TGF-β1-509TC和TT基因型都可以显著降低结直肠癌的发病风险,调整后的OR值分别为0.69(95%CI=0.51～0.94)和0.50(95%CI=0.36～0.71)。C-509T和codon10(T+29C)之间存在较强的连锁不平衡关系(D’=0.724,r2=0.431),与.509T/+29T相比,-509C/+29C可以显著的增加机体罹患结直肠癌的风险,其OR值为1.38(95%CI=1.13～1.68)。LTBP-1L GA-CC只有在隐性遗传模式下表现为具有统计学意义的关联,其变异基因型可以显著的增加结直肠癌约53%的发病风险,并且对结肠癌和直肠癌的作用基本相同(结肠癌OR=1.48,95%CI=1.02～2.16,直肠癌OR=1.58,95%CI=1.11～2.25)。叉生分析和分类回归树模型显示基因-基因、基因-环境之间存在着复杂的相互作用。LTBP-1L GA-CC在与TGF-β1 C-509T、TGF-β1 codon10和TGFβR1int7G24A等3个SNP联合作用时,以同时携带低风险基因型的个体相比,同时携带高风险基因型的个体罹患结直肠癌的风险显著升高。饮茶与基因之间多存在联合作用,在所有研究因素中肠道疾病是最重要的影响因素。结论TGF-β1及其受体基因中的多态性位点各基因型分布特征与其他种族人群存在差异。该通路中,TGF-β1C-509T基因多态是影响结直肠癌易感性主要多态位点,它和LTBP-1L GA/CC基因多态位点可以显著改变结直肠癌的患病风险,他们可能单独或联合通路中其他位点对结直肠癌罹患风险产生影响。影响结直肠癌发病风险的基因之间、基因和环境之间存在着复杂的交互作用。从构建的分类回归树模型中可以发现肠息肉、慢性结直肠炎是影响结直肠癌发病最重要的高风险因素,饮茶和吸烟等生活习惯也可以对结直肠癌发病产生影响。环境因素和基因相互交织,在不同特征的人群中高风险因素可能产生不同的效应。应当以通路为基本单位,根据研究设计和数据结构等的不同采用CART和MDR等新型统计分析方法深入挖掘基因、环境和结直肠癌之间的关系。更多还原

【Abstract】 Backgrouds and ObjectivesColorectal cancer,with approximately 1.02 million new cancer cases and 529 000 deaths worldwide in 2002,is the second most prevalent cancer after breast cancer in the world.Colorectal cancer is especially common in the North America,Australia and Western Europe,while the incidence tends to be low in Africa and Asia.However, during the past decades,there have been remarkable changes in Asian countries in the incidence of colorectal cancer,the rates of which are increasing rather rapidly in countries where the risk was formerly low.The similar trend was observed in China as well.According to the Chinese National Cancer Database of 2003,colorectal cancer is one of the three cancers with most rapidly increasing incidence in the country between 1991 and 2003,and finally it ranks the third commonest malignant tumor.Most common human cancers,including colorectal cancer,have a multifactorial etiology involving complex interplay of genetic susceptibility and environmental exposures,and studying these factors together can improve the statistical power for detection of the underlying risk factors,give insight into their biologic effects and lead to public health strategies for prevention.It is widely accepted that environmental factors,such as diet,smoking,drinking and overweight,play key roles in the susceptibility to colorectal cancer development and progression.On the other hand, although numerous genes,in critical pathways of metabolism,DNA repair and apoptosis,implicated in low penetrance genetic predisposition to colorectal cancer have been identified,the polymorphisms in transforming growth factor-β(TGF-β) signaling pathway that contribute to the risk of colorectal cancer have not been fully demonstrated.The TGF-βsignaling pathway is involved in the control of several biological processes,including cell proliferation,differentiation,migration and apoptosis.Although there is accumulating evidence showing the importance of the TGF-β1 signaling pathway in carcinogenesis,no investigation has been carried out on the role of the polymorphisms in TGF-βpathway in relation to colorectal cancer in Chinese population.In this study,we hypothesized that the genetic polymorphisms in TGF-βsignaling pathway together with environmental factors were associated with colorectal cancer susceptibility.To verify this hypothesis,we conducted a population-based case-control study to evaluate the effects of TGF-β1 and its receptor gene polymorphisms on the risk of colorectal cancer in a Chinese population.Materials and MethodsThis population-based case-control study recruited eligible patients with histologically confirmed colorectal cancer reported by the cancer registry system as cases.Although there were no restrictions on patients’ age,gender or tumor stage,only those patients who were free of metastases or other cancers were included in our study. Simultaneously,population controls who did not have a history of cancer were selected randomly and recruited from all permanent residents listed in the cancer registry system during the same period.All the participants were ethnic Han Chinese and residents in Jiashan County. At the beginning of investigation,written informed consent was obtained from each participant,and then they were face-to-face interviewed by trained personnel using a structured questionnaire,including demographic characteristics,personal habits (cigarette smoking,alcohol drinking,etc) and health factors(family history of cancer at any site including all first- and second-degree relatives of both genders,medical and dietary history,etc).In addition,a 5 ml venous blood sample was draw from each subject with the permission and then the genomic DNA was extracted from peripheral blood samples using modified salting-out procedure.For determination of the genetic polymorphisms of TGF-βsignaling pathway,Polymerase Chain Reaction- Restriction Fragment Length Polymorphism(PCR-RFLP) assay was performed.Unconditional logistic regression analysis was performed to calculate the odds ratios(ORs) with 95%confidence intervals(95%CIs) for estimating the association between certain genotypes and cancers with adjustment for the possible confounders. Stratified analyse and classification and regression tree model were used to explore potential low-order and high-order gene-gene and gene-environment interactions.ResultsThe demographic characteristics did not differ significantly between cases and controls.In smokers,those who get the smog into lung have a significantly increasing risk of rectal cancer(OR=2.15,95%CI=1.23～3.76).Tea drinking could significantly decreasd the colorectal cancer risk about 40%(OR=0.59,95%CI=0.42～0.82), especially the green tea has the protective effects on both colon and rectal cancer (OR=0.56,95%CI=0.35～0.89 and OR=0.60,95%CI=0.40～0.92,respectively).No polymorphism of G-800A,codon25,codon263 of TGF-β1 gene TGFβR2 A-364G was found in the study population and all the subjects carried wild-genotype. As compared with -509CC genotype,the -509CT genotype and TT genotype were associated with significantly decreased risk for colorectal cancer(OR=0.69, 95%CI=0.51～0.94 and OR=0.50,95%CI=0.36～0.71,respectively).TGF-β1 C-509T and codon10 polymorphisms were in strong linkage disequilibrium(D’=0.724, r2=0.431).Compared with the -509T/+29T haplotype,the -509C/+29C was associated with a significantly increased risk of colorectal cancer(OR=1.38,95%CI 1.13～1.68). LTBP-1L GA-CC was significantly associated with the colorectal cancer susceptibility in the recessive model and the varited genotypes could significantly increase the risk of colon caner and rectal cancer(OR=1.48,95%CI=1.02～2.16 and OR=1.58, 95%CI=1.11～2.25,respectively).Complex gene-gene and gene-enviornmental interactions were found according to the results of stratified analyse and classification and regression tree model.LTBP-1L GA-CC had combined effects with TGF-β1 C-509T,TGF-β1 codon10 and TGFβR1 int7G24A,the high risk genotypes carriers had significant increased risk suffering colorectal cancer comparing with those who carried low risk genotypes.Several combined effects were also found between tea drinking and SNPs.ConclusionsThe frequency patterns of polymorphisms in TGF-βsignaling pathway vary greatly among different ethnic groups.In this pathway,TGF-β1 C-509T is the most important SNP affecting the susceptibility to colorectal cancer independently or together with LTBP-1L GA/CC and other SNPs.There are complex interactions of genetic susceptibility and environmental exposures,CART might be a useful tool for exploring the high-order interactions.更多还原