miR-126/ADAM9/DNMT1正反馈环路介导的EMT促进胃癌的恶性表型和“干性”转化

上皮间质转化（EMT）在胃癌等肿瘤恶性进展乃至“干性”转化中发挥关键作用。课题组前期研究发现下调miR-126可促进胃癌的生长和转移，但机制不明确。去整合素金属蛋白酶9(ADAM9)可降解E-cadherin而诱导EMT。我们预实验证实miR-126可靶向调控ADAM9。已知ADAM9可抑制DNA甲基转移酶1（DNMT1）的降解，DNMT1可甲基化miR-126的宿主基因Egfl7的启动子而抑制miR-126的表达。故推测胃癌中存在miR-126/ADAM9/DNMT1正反馈环路持续下调miR-126、上调ADAM9的表达以促进胃癌的EMT乃至“干性”转化。本课题拟从分析环路分子在胃癌表达的相关性入手，体外实验对环路各分子实施干预，明确其上下游调控关系及诱导EMT和干性表型的作用机制，然后经裸鼠实验进一步验证。可望为胃癌的靶向治疗、抑制/逆转EMT和“干性”转化提供新的理论依据和实验支持。

Metastasis is the main cause of high mortality of gastric cancer. There is still a lack of effective therapeutic method to prevent metastasis of gastric cancer till now. It was well documented that epithelial-mesenchymal transition (EMT) played a key role in tumor malignant progression and “stemness” transformation by which gastric cancer could obtain the ability of migration and invasion to form metastases. Our previous work showed that down-regulation of miR-126 could promote the growth and metastasis of gastric cancer, but the mechanism is not clear. It is reported that A disintegrin and metalloproteinase 9 (ADAM9) could induce EMT through its degradation effect on E-cadherin (E-cad). We found that ADAM9 was a negative regulative target of miR-126 by using biological information analysis, luciferase reporter assay and gastric cancer cell in vitro study. ADAM9 has been confirmed to inhibit the degradation of DNA methyltransferase 1 (DNMT1) through EGFR/Akt signaling pathway. DNMT1 can inhibit the expression of mature miR-126 through its host gene Egfl7 promoter methylation. We deduce there may be an miR-126/ADAM9/DNMT1 positive feedback loop to continuously downregulate miR-126 expression and upregulate ADAM9 expression which eventually result in the induction of EMT and “stemness” transformation in gastric cancer. To clarify this deduction, we plan to analysis the expression status and their relationship of each molecule of miR-126/ADAM9/DNMT1 loop in gastric cancer specimens. The regulatory relationships and the effects on induction of EMT and “stemness” in gastric cancer of miR-126/ADAM9/DNMT1 loop will also be determined in in vitro experiments and the effects will be further verified by nude mice experiments. The experimental results of the current project will give clues to the treatment for gastric cancer by targeting reversion of EMT and “stemness” of gastric cancer.