PAK4多靶点调控Wnt信号通路在胃癌发生过程中的作用及机制

It has been reported that PAK4 is overexpressed in human gastric cancer tissues and regulates apoptosis, migration and invasion of gastric cancer cells by phosphorylating downstream substrates. However, it has not been reported whether PAK4 can affect the occurrence of gastric cancer in vivo. Numerous studies have shown that the abnormal activation of the canonical Wnt signaling pathway is closely related to the occurrence of gastric cancer. Our group found that PAK4 could phosphorylate β-catenin, a key effector of Wnt pathway, and promote its entry into the nucleus. However, it was confirmed that the mechanism of PAK4 regulation of Wnt pathway is not limited to this. Therefore, we constructed the gastric mucosal epithelial-specific transgenic mice expressing PAK4 and Wnt1 as well as the PAK4/Wnt1 double transgenic mice, respectively. We observed the spontaneous gastric cancer phenotype in PAK4/Wnt1 double transgenic mice. Meanwhile, the new PAK4 interacting proteins including GSK3β and RACK1 were screened by protein spectrum. The purpose of this project is to further expand the samples to confirm the stomach phenotypes of the three kinds of transgenic mice and to compare their differences. To explore the specific molecular mechanism by which PAK4 can promote the carcinogenesis of gastric cancer through the multi-target regulation of Wnt pathway by GSK3β, RACK1 and β-catenin. We hope it will be helpful to provide a theoretical basis for individualized targeted therapy of gastric cancer.

已有研究表明PAK4在人胃癌组织中呈过表达，并可通过磷酸化下游底物调控胃癌细胞的凋亡及迁移侵袭能力。但PAK4在生物活体内能否影响胃癌发生至今尚无报道。大量研究表明经典Wnt信号通路的异常激活与胃癌的发生密切相关。本课题组前期发现PAK4能够磷酸化Wnt通路关键效应蛋白β-catenin并促进其入核，同时证实了PAK4调控Wnt通路的机制并非仅限于此。于是我们分别构建了胃粘膜上皮特异性表达PAK4、Wnt1、PAK4/Wnt1转基因小鼠，并初步观察到PAK4/Wnt1双转基因小鼠的自发胃癌表型。同时利用免疫沉淀结合蛋白质谱筛选出Wnt通路中PAK4新的互作蛋白GSK3β和RACK1。本课题旨在进一步扩大样本明确三种转基因鼠的胃部表型并比较其差异，探索PAK4通过GSK3β、RACK1、β-catenin多靶点调控Wnt通路促进胃癌发生的分子机制，以期为胃癌的个体化靶向治疗提供新的理论依据。

胃癌是常见的消化道恶性肿瘤，治疗选择有限。经典Wnt信号通路的遗传改变和异常激活与胃癌发生密切相关。我们前期研究发现PAK4在人胃癌组织中过表达，且通过磷酸化β-catenin与Wnt通路交互。但PAK4与Wnt/β-catenin通路的协同作用是否在生物活体内诱发胃癌尚不清楚。本课题研究发现胃粘膜特异性表达PAK4/Wnt1的双转基因小鼠自发发展为胃腺癌。机制探索中发现PAK4可以直接互作并磷酸化GSK3β，揭示了PAK4激活Wnt/β-catenin通路的新机制，丰富了PAK4多靶点调控Wnt通路的信息。相反，激活的Wnt/β-catenin通路又增强了PAK4的转录活性，从而形成正反馈环。二者相互作用促癌效应不断放大，最终导致胃癌发生。此外，PAK4抑制剂表现出抗肿瘤作用，并通过靶向经典Wnt通路使胃癌对5-FU治疗更加敏感。通过上述研究，阐明PAK4与Wnt/β-catenin通路相互作用诱发胃癌的作用及具体分子机制，为寻找胃癌治疗靶点提供新的理论依据。