FBW7介导的Brg1泛素化降解在胃癌转移中的作用和机制研究

The abnormality of SWI/SNF chromatin remodeling complex is closely related to the initiation and progression of tumors including gastric cancer. Brg1/SMARCA4 serves as the ATPase catalytic subunit for the multi-component SWI/SNF chromatin remodeling complex, which plays a pivotal role in governing chromatin structure and gene transcription. However, upstream regulatory signaling pathway(s) controlling Brg1 protein stability and its contribution to carcinogenesis remains largely elusive. Our data showed that Brg1 is a novel ubiquitin substrate of FBW7. Moreover, an inverse correlation between FBW7 and Brg1 expression was found in human gastric cancer clinical samples. Elevation in Brg1 protein abundance positively correlated with tumor progression and tumor metastasis and predicted poor survival in gastric cancer patients. These data revealed the important roles of FBW7-Brg1 signalling axis in gastric cancer progression and metastasis. However, the underlying biochemical mechanism and epigenetic reprogramming still remain obscure and should be explored. In the planning project, we aim to explore the biochemical mechanism of Brg1 ubiquitination and degradation mediated by FBW7, and to elucidate the underlying mechanism by which the deregulated FBW7-Brg1 signalling contributes to gastric cancer EMT (Epithelial-Mesenchymal Transition) and metastasis. Our study provides the rationale to develop new targets for the gastric cancer therapy.

SWI/SNF染色质重塑复合物异常与肿瘤包括胃癌发生发展有密切关系，Brg1作为SWI/SNF染色质重塑复合物的ATP酶核心亚基，在染色质重构和基因调控上发挥重要作用，但对于Brg1蛋白稳定性调节及在肿瘤中的作用尚不清楚。本项目前期工作发现Brg1是泛素连接酶FBW7新的泛素化底物，受FBW7泛素化降解调控；在胃癌样本中，Brg1和FBW7的蛋白表达呈现负相关，Brg1表达与胃癌的进展、转移有密切关联，Brg1高表达的患者预后差，提示FBW7-Brg1泛素化调节途径在胃癌发展和转移发挥重要作用，但其内在的生化机制和表观遗传调控有待进一步揭示。本项目将揭示Brg1受FBW7介导的泛素化降解的生化机制；并阐明FBW7-Brg1信号异常对胃癌上皮-间充质转化（EMT）等相关基因的表观遗传调控改变及对胃癌转移性状的影响，为胃癌的靶向治疗提供新的潜在靶点。

SWI/SNF染色质重塑复合物异常与肿瘤包括胃癌发生发展有密切关系，Brg1作为SWI/SNF染色质重塑复合物的ATP酶核心亚基，在染色质重构和基因调控上发挥重要作用，但对于Brg1蛋白稳定性调节及在肿瘤中的作用尚不清楚。本项目研究发现Brg1被鉴定为泛素连接酶FBW7新的泛素化底物，我们发现磷酸激酶CK1δ可以磷酸化修饰Brg1的丝氨酸31/35位点进而促进Brg1与FBW7结合，导致泛素介导的Brg1蛋白降解。在胃癌中，FBW7作为重要抑癌基因，在胃癌样本中表现为高频缺失、突变或低表达。我们发现Brg1和FBW7在胃癌中的蛋白表达呈现负相关，并且Brg1表达与胃癌的进展、转移有密切关联，Brg1高表达的患者预后差。进一步机制研究发现FBW7的缺失或突变，导致Brg1蛋白累积，通过促进胃癌上皮-间充质转化（EMT）调节因子Snail的转录，抑制E-cadherin等的表达，进而促进胃癌EMT的发生和肿瘤进展，而通过敲低Brg1或使用Brg1小分子抑制剂可以显著抑制胃癌细胞的体外迁移和体内的转移能力。这些研究说明FBW7-Brg1泛素化调节途径在胃癌发展和转移中发挥重要作用，为靶向Brg1治疗FBW7功能缺失型胃癌提供重要理论基础。