FoxM1-ATX/LPAR-Hippo正反馈环路促进胰腺癌发生发展的作用机理

The ATX/LPAR signaling axis and the Hippo signaling pathway play tivotal roles during the occurrence and development of this cancer. Previous study showed that pancreatic cancer had high expression of FoxM1,whereas upregulation of FoxM1 expression may promote expression of ATX and LPAR, and facilitate generation of LPA. LPA was proved as one of the most important regulator of Hippo signaling pathway, and YAP, the effector of the Hippo pathway could increase FoxM1 expression. Thereout, we proposed hypothesis: FoxM1 increased the generation of LPA through transcriptional regulation of ATX/LPAR axis, and promoted YAP nuclear translocation and improved the transcription activity, which could upregulation of FoxM1 expression, which formed finally a FoxM1-ATX/LPAR-Hippo positive feedback loop. Our study will investigate the role of FoxM1 on the generation of LPA and the expression of ATX and LPAR in pancreatic cancer cell lines. By construction of deletion mutant in ATX and LPAR promoter region， we will verify the contribution of FoxM1 on these two promoters transcription. Further, the ChIP and EMSA will be adopted to investigate whether the regulation role of FoxM1 is based on the direct binding with ATX and LPAR promoters. Finally, we will inspect the activity of Hippo signaling pathway and the expression level of FoxM1 after treating with LPA.

研究证实ATX/LPAR信号轴及Hippo 信号通路在胰腺癌发生发展中起重要作用。课题组前期研究发现FoxM1在胰腺癌高表达，上调FoxM1可促进ATX、LPAR的表达及LPA的产生。而LPA是Hippo信号通路最重要的上游调控因子之一，Hippo效应分子YAP又可促进FoxM1表达。由此提出假说：FoxM1通过转录调节ATX/LPAR信号轴，促进LPA产生，进而抑制Hippo信号通路，促进YAP入核和转录活性，上调FoxM1表达，形成FoxM1-ATX/LPAR-Hippo正反馈环路。本研究拟构建ATX和LPAR启动子区各种缺失突变体，采用Chip、EMSA等探讨FoxM1是否直接结合ATX和LPAR启动子区发挥转录调控作用，以LPA处理胰腺癌细胞系后观察Hippo信号通路的活化状态以及FoxM1表达水平的变化，阐明该正反馈环路促进胰腺癌的作用机理，以期为胰腺癌的预防及诊治提供新思路。

在多种类型的人恶性肿瘤中，autotaxin（ATX）和Forkhead Box M1（FOXM1）均被公认为癌基因。但是，人们对ATX在胰腺导管腺癌（PDAC）中的表达和生物学功能及其与FOXM1的相关性了解甚少。本研究旨在研究它们在胰腺癌发展中的相关性和生物学效应。通过双荧光素酶报告基因和染色质免疫沉淀试验，我们发现ATX是FOXM1的下游转录靶基因，进一步的细胞功能实验表明FOXM1对PDAC细胞增殖和迁移能力的积极影响是由ATX介导的。此外，分子生物学实验表明，ATX通过抑制Hippo信号通路而增强了FOXM1的表达，这表明ATX和FOXM1形成了一个正反馈回路，以促进胰腺癌的发展。使用免疫组织化学（IHC）方法，发现胰腺癌肿瘤组织中ATX和FOXM1的表达与相邻正常组织相比被上调，并且升高的ATX和FOXM1的表达彼此正相关。总之，本课题研究确定了ATX和FOXM1之间的正反馈回路，该回路可促进胰腺癌细胞增殖和迁移。同时也表明抑制ATX和FOXM1可能胰腺癌的有前途的治疗策略。