谷氨酸胺连接酶结合N-Cadherin蛋白抑制胃癌上皮间质转化的作用和机制研究

Epithelial-mesenchymal transition (EMT) initiates the invasion and metastasis in gastric cancer, which is the main death reason of patients with gastric cancer. Our preliminary work has shown that the protein levels of glutamate-ammonia ligase (GLUL) is significantly lower in gastric cancer cell lines and tissues compared with normal gastric cell lines and adjacent tissues, and correlated with prognosis. Knockdown of GLUL induces EMT and promotes the growth, migration and invasion of gastric cancer cells, and these are reversed by restoration of GLUL expression. Moreover, GLUL can bind with N-Cadherin, interupt the interaction of N-Cadherin and β-Catenin, promote β-Catenin degradation, and suppress EMT. However, the function and mechanism of GLUL binding with N-Cadherin to inhibit EMT in gastric cancer is still unclear. This project will use a series of methods and technologies as well as clinical data to address these issues at the molecular, cellular and animal levels. It will be a rich complement to understand the biological characteristics and functions of GLUL and N-Cadherin, provide the important clue to know the mechanism of EMT, and also contribute to the development of new targets and strategies of therapy as well as diagnosis in gastric cancer.

上皮间质转化（EMT)）是胃癌发生侵袭转移导致患者死亡的重要原因。申请人前期研究发现谷氨酸胺连接酶（GLUL）在胃癌组织中表达明显低于癌旁组织，并与患者预后密切相关。在胃癌细胞中敲低GLUL引起EMT变化使细胞增殖、迁移和侵袭能力显著增强，而恢复GLUL表达可逆转这些变化。随后发现GLUL可能通过与N-Cadherin蛋白相互结合，抑制N-Cadherin与β-Catenin蛋白的结合，引起β-Catenin蛋白降解，抑制EMT，但其确切的作用和机制还不清楚。本项目将采用一系列实验方法和技术，结合胃癌患者临床病理和预后随访数据，在分子、细胞和动物水平上深入系统地研究GLUL结合N-Cadherin蛋白抑制胃癌EMT的作用和机制，这将为揭示GLUL和N-Cadherin的生物学特性及功能提供重要的补充，也将为阐明胃癌EMT的机制提供重要的理论依据，有助于探索并开发新的胃癌治疗靶点和诊疗策略。

谷氨酸胺连接酶（GLUL）是参与氮代谢过程中的一个关键酶类，可以把体内游离的谷氨酸与铵离子在 ATP 的催化下合成谷氨酰胺，进而为细胞代谢提供重要的碳源、氮源与能量。GLUL已被证实在多种肿瘤发生发展中起到关键性作用，然而其在胃癌中的表达和上皮间质转化（EMT）中的作用仍不清楚。在本研究中，我们发现GLUL在胃癌组织中低表达，并与患者的N分期和TNM分期密切相关，且GLUL低表达患者的生存期明显低于GLUL高表达的患者。功能研究发现GLUL可以在体内外抑制胃癌细胞生长、迁移、侵袭与转移，而这些均不依赖于其酶活性。进一步机制研究发现GLUL蛋白和β-Catenin蛋白可以竞争性与N-Cadherin蛋白结合，从而抑制N-Cadherin蛋白泛素化降解增加其稳定性，促进β-Catenin泛素化降解降低其稳定性。此外，N-Cadherin在胃癌组织中低表达，而β-Catenin在胃癌组织中高表达，GLUL表达在胃癌组织中与N-Cadherin表达相关并且可作为预后因素。我们的结果发现了GLUL不依赖于其酶活性的一个新功能，为阐明胃癌EMT的机制提供重要的理论依据。