CUL4B调控MST1/2-Hippo-YAP信号通路促进胃癌侵袭转移的机制研究

Tumor invasion and metastasis are the important causes leading to death in patients with gastric cancer. Our previous studies have demonstrated that the Hippo-YAP signalling pathway played an important role in the metastasis of gastric cancer. Our recent preliminary data showed CUL4B expression was markedly upregulated in both gastric cancer tissues and cell lines, and patients with high expression level of CUL4B had a poor prognosis. We also found CUL4B downregulation inhibited gastric cancer cell migration and invasion. Moreover, CUL4B and YAP protein expressions were positively correlated in gastric cancer tissues. In addition, knockdown of CUL4B upregulated MST1/2 mRNA expression, and downregulated the expression levels of downstream target genes of the Hippo signalling pathway. However, the underlying molecular mechanism remains unclear. In the present study, we will confirm the biological function of CUL4B in promoting gastric cancer cell invasion and metastasis in both in vivo and in vitro models. ChIP and Co-IP will be performed to explore how CUL4B regulates the Hippo signaling pathway. Finally, the clinical value of CUL4B expression in gastric cancer will be clarified in clinical samples. Our study will illuminate the molecular mechanism of how CUL4B promotes gastric cancer cell invasion and metastasis through regulating the Hippo signalling pathway, and provide new insights into the diagnosis and treatment of gastric cancer.

侵袭转移是导致胃癌患者死亡的重要原因。我们前期研究发现:（1）Hippo-YAP信号通路在胃癌侵袭转移过程中发挥重要作用（已发表）；（2）CUL4B在胃癌组织和细胞中表达明显升高，是预后不良的分子指标，干扰CUL4B的表达显著抑制胃癌细胞的迁移和侵袭；（3）CUL4B和YAP在胃癌组织中表达呈正相关，干扰CUL4B表达能上调MST1/2 mRNA的表达，抑制Hippo通路下游癌基因的表达，但具体的分子机制尚待阐明。在本项目中，我们拟用细胞实验、裸鼠模型等方法，明确CUL4B促进胃癌细胞侵袭转移的生物学功能；利用染色质免疫共沉淀等技术探讨CUL4B调控Hippo通路的分子机制；并通过临床标本验证进一步揭示CUL4B在胃癌中的临床意义。本项目将阐明CUL4B通过调控Hippo信号通路促进胃癌侵袭转移的分子机制，并为胃癌的诊治提供新的靶点和思路。

侵袭转移是导致胃癌患者死亡的重要原因，彻底阐明胃癌发生侵袭转移的机制对提高患者的预后生存具有重要意义。我们前期结果发现:（1）CUL4B在胃癌组织和细胞中表达明显升高，是预后不良的分子指标；（2）CUL4B能调控Hippo通路下游癌基因的表达促进胃癌细胞侵袭转移。基于此研究基础，本项目组进一步探讨了CUL4B在胃癌发生发展中的作用及机制。本项目研究发现：CUL4B在胃癌组织中的表达明显升高（90/161，56%），且其高表达与患者的临床分期、浸润深度、淋巴结转移及预后差密切相关。干扰CUL4B能通过抑制Wnt/β-catenin信号通路减弱胃癌细胞的增殖、克隆形成、迁移及侵袭能力。荧光素酶报告基因实验等证实CUL4B是miR-381/miR-489的下游靶基因，CUL4B与miR-381/miR-489在胃癌组织和细胞中的表达呈负相关关系。此外，过表达 CUL4B能部分逆转miR-381和miR-489对胃癌细胞增殖和侵袭能力的抑制作用，提示miR-381/miR-489在胃癌组织中的低表达是导致CUL4B在胃癌中异常激活的重要原因，CUL4B是介导miR-381/miR-489功能的重要靶基因。本项目进一步的研究发现CUL4B在结肠癌中的表达显著升高，且其高表达与肿瘤大小、浸润深度、淋巴结转移、肿瘤（TNM）分期及预后差显著相关。CUL4B可能通过与MDM2结合，促进p53蛋白被泛素化降解进而增强肿瘤细胞增殖和侵袭转移的能力。既往研究显示Wnt/β-catenin和p53信号通路均与Hippo信号通路之间存在“crosstalk”，鉴此，我们认为CUL4B是通过调控Wnt及p53信号通路，间接调控Hippo信号通路的活性，形成复杂的分子调控网络促进肿瘤侵袭转移。综上，我们的研究结果揭示了一种新的导致胃癌发生侵袭转移的分子调控机理，对胃癌的诊治及预后评估有着重要的意义。