TMEM16A激活Rac1促进胃癌细胞EMT及侵袭转移的分子机制

TMEM16A is newly identified as calcium activated chloride channel, and has been reported to be overexpressed by various solid malignant cancers and promote proliferation and invasion, yet little is known about its role in gastric cancer(GC). Although our previous study found that TMEM16A expression was significantly upregulated in GC and promoted invasion and migration by TGF-β signaling, which might correlate with EMT, molecular mechanism of GC metastasis is elusive. It is recently reported that TMEM16A interacts with Ezrin-Radixin-Moesin (ERM), TGF-β and ERM are demonstrated to activate Rac1,which is proved to promote EMT in various solid tumors. Our preliminary experiment found that knockdown TMEM16A reduced GTP-Rac1, and previous study found inhibition of TGF-β could not completely revert the influence of TMEM16A on invasion and migration of GC cells. It is suggested that TMEM16A might promote GC EMT ,migration and invasion by both of TGF-β and ERM signaling which eventually activate Rac1. We will validate the new mechanism in GC cell lines, animal tumor model, and clinical specimens, which favors the diagnosis and treatment of GC.

我们前期发现钙激活氯通道TMEM16A通过促进胃癌细胞分泌TGF-β参与其侵袭转移，具体机制尚不清楚，可能与调控EMT有关；但抑制TGF-β不能完全逆转TMEM16A促进胃癌细胞迁移侵袭的作用，提示TMEM16A可能通过除TGF-β外的信号调控侵袭转移。新近研究报道TMEM16A可与膜-细胞骨架连接蛋白（ERM）结合，ERM及TGF-β均可激活Rac1，Rac1调控肿瘤细胞EMT及侵袭转移已被证实。我们预实验发现下调TMEM16A可明显抑制Rac1激活。因此，我们提出假设：TMEM16A可能通过TGF-β信号及与ERM结合两种分子机制协同激活Rac1，促进胃癌细胞EMT而介导侵袭转移。本课题拟采用胃癌细胞、临床标本和裸鼠种植瘤模型为研究对象，运用免疫共沉淀、免疫共定位、基因过表达、shRNA干扰等技术，阐明TMEM16A促进胃癌细胞EMT及侵袭转移的分子机制，为胃癌的靶向治疗提供理论依据。

局部侵犯及转移是胃癌患者治疗失败和死亡的重要原因，在分子水平上找到可预测胃癌转移和预后的标志物，有助于预警高危个体，并为针对该分子的靶向治疗提供理论依据。我们前期发现TMEM16A 蛋白在胃癌中高表达并促进胃癌侵袭转移。但是，TMEM16A蛋白在胃癌中高表达与其基因扩增并不一致，因此，我们推测TMEM16A在胃癌中的高表达可能存在其他机制。通过文献复习及数据库分析我们发现MicroRNA-381(miR-381)可以调节TMEM16A的表达，并在临床组织标本、细胞及动物水平证明了miR-381 在胃癌中表达降低，通过靶向负调控TMEM16A 表达从而抑制胃癌侵袭转，其结果发表在2017年Journal of Experimental & Clinical Cancer Research。这些研究提示TMEM16A 蛋白可能为胃癌的诊断提供潜在靶点，并可能为胃癌的治疗提供有效的辅助手段。此外，在本课题的支持下，我们发现TBL1XR1在胃癌中高表达，并促进胃癌细胞转移（研究结果已经发表在2016年Disease Markers），我们预实验发现沉默TMEM16A后TBL1XR1表达降低，且TBL1XR1可与VEGF-C启动子结合促进其表达，VEGF-C促进癌细胞淋巴转移。我们前期研究发现TMEM16A与胃癌细胞淋巴转移相关，而TBL1XR1与TMEM16A的关系我们课题组在进一步研究及探讨。