CDH1基因启动子区-73SNP影响DNA甲基化的机制

The genetic variations in transcription regulation region can affect gene transcription through epigenetic pathways such as histone modification and DNA methylation. But it is not well understood how these epigenetic modifications developed based on the gene structure variations. The person with CDH1 genetic inactivation is prone to familial gastric cancer. The abnormal methylation of CDH1 gene can lead to transcriptional inactivation, which plays an important role in tumor cell epithelial-mesenchymal transition (EMT). Our recent results showed that the gastric cancer patients carrying -73CC genotype in CDH1 promoter have a longer survival and lower rate of lymph node metastasis than patients with -73AC and -73AA. Furthermore, the methylation of CDH1 gene CpG island is significantly lower in -73C alleles than in -73A alleles in gastric cancer tissues and tumor cell lines. In this project, we want to verify the correlation of -73SNP and metastasis and survival of gastric cancer in a new cohort, and then detect the mechanism of CDH1 allelic specific methylation controlled by the effect of -73SNP on binding of transcription repressors. Furthermore, we will analyze the roles of DNMTs, hydromethylation and chromatin conformation on the allelic specific methylation. At last, whether this CDH1 methylation variation is necessary for the effects of this SNP on migration and invasion of tumor cells is also studied. This project has an ethnic value and demonstrating role on elucidating the mechanism of how genetic variations affect epigenetic modification.

基因转录调控区的结构变异可通过组蛋白修饰和DNA甲基化等表观遗传方式影响基因转录，但这种表观遗传修饰形成的具体过程尚不清楚。CDH1遗传性失活者易患家族性胃癌；其启动子异常甲基化可导致转录失活，后者是肿瘤细胞上皮间质转换过程中的关键环节。我们近期发现CDH1启动子区-73CC基因型胃癌患者存活期为AC和AA基因型者的2倍，并且不易发生淋巴结和远处转移。进一步研究发现不论在胃癌组织还是肿瘤细胞系中，-73C等位基因的甲基化频率明显低于-73A。本项目将在对-73A/C基因型与胃癌转移和患者生存期关系进行验证的基础上，根据已有线索深入分析该SNP通过影响转录抑制因子结合控制CDH1甲基化状态的具体过程，探索 DNMTs、羟甲基化、染色质构象等在这种差异甲基化形成中的作用，确定这种DNA甲基化差异是否为该SNP影响胃癌转移所必需。对揭示遗传学变异影响表观遗传修饰的机制有理论价值和示范意义。

CDH1遗传性失活者易患家族性胃癌；其启动子异常甲基化可导致转录失活，后者是肿瘤细胞上皮间质转换过程中的关键环节。然而基因组水平的变异是否影响甲基化形成并不清楚。本项目首先在中国和韩国两个国家的胃癌队列中均验证了初期的发现，证实CDH1基因启动子区-73SNP是胃癌的独立预后因素，-73CC基因型患者预后较好。并进一步在胃癌组织中分析发现，-73CC基因型组织中CDH1表达水平较高，而-73AA基因型组织中CDH1甲基化和羟甲基化率均显著高于-73CC基因型组织。通过对多个组织的克隆测序，深入分析了-73SNP与甲基化和羟甲基化位点分布的关系。最后，本课题证实转录抑制因子Snail可能通过影响不同基因型CDH1启动子与DNA甲基转移酶DNMT3a的结合和局部染色质构象的变化，进而影响甲基化的形成。不同甲基化状态细胞中CDH1启动子区染色质空间构象也存在差异。