FRMD3-Hippo信号通路异常驱动早期大肠癌发生：关键化学预防靶点和化合物的发现

Colorectal cancer is a good model system for the study of pre-cancerous lesions, which allows early detection of abnormality through endoscopy and is also the first selection of cancers for chemical prevention. It was well recognized that cancer driver genes are the favorable targets for cancer chemoprevention. Recently, we performed a whole genome sequencing analysis using tissue samples from early colonic lesions of different stages and identifed a family of potential colon cancer driver genes based on sequencing data and also on the comparison to the big colon cancer databases of TCGA. Among them, membrane associated protein FRMD3 is a candidate driver gene, supported by horboring mutations and deletions in colon cancer patients as well as evidence from the FRMD3 gene knockout mice. We found that FRMD3 controls Hippo signaling pathway through protein interactions with MST1 and LATS1, two key kinases in the Hippo pathway. FRMD3 is also suggested to downregulate Wnt signaling pathway through inhibition of beta-catenin. Therefore, FRMD3 regulates Hippo and Wnt signaling pathways, two important pathways that are involved in the promotion of colon cancer. We have established FRMD3 knockout mice in the pilot studies and we will continue to establish the FRMD3 gene conditional knockout mice to precisely investigate the role of FRMD3 in the development of early colonic lesions and the promotion of colon cancer. We will also uncover the molecular mechanisms underlying FRMD3 regulation on Hippo and Wnt signaling pathways. We will validate FRMD3 as a regulator of the two pathways and will also examine the possibility for MST1 and LATS1 as targets to inhibit Hippo signaling activation that drives colon cancer development. We plan to screen for compound libraries for identifying compounds that upregulate the level of FRMD3 in living cells and compounds that are able to activate MST1 or LATS1 kinase activity. These compounds are candidate drug leads for the chemoprevention of colon cancer. Taken together, we anticipate to unravel novel mechanism(s) accounting for early colon cancer development and also pinpoint targets for chemical intervention of colon cancer as well as new lead compounds as candidates for future drug development.

大肠癌是研究癌前病变发生过程，早期镜下筛查、建立化学预防的首选癌种。肿瘤驱动基因是早期化学干预的良好靶点。我们近期对早期不同阶段大肠病变组织进行了全基因组测序，经大数据分析发现了一组新的大肠癌潜在驱动基因。其中，膜结合蛋白FRMD3在大肠癌中有基因突变和缺失，结合FRMD3基因敲除小鼠提示FRMD3是个抑癌基因。我们发现FRMD3通过与MST1及LATS1的分子互作调控Hippo通路的激活，通过下调beta-catenin抑制Wnt通路，从而调控两个与大肠癌发生密切相关的通路。我们将在FRMD3基因条件敲除小鼠中阐明FRMD3在大肠癌发生早期阶段的作用及其调节Hippo和Wnt通路的分子机制、并以FRMD3和关键激酶MST1及LATS1作为抑制大肠癌发生的靶点，筛选能上调FRMD3或激活MST1及LATS1的化合物。预期将揭示大肠癌早期病变产生的新机制、发现新的化学干预靶点及先导化合物。

大多数恶性肿瘤的发生是缓慢的、分阶段的。早期发现、早期治疗对大多数肿瘤是有效的，故肿瘤治疗要关口前移。肿瘤驱动基因使正常上皮细胞转化为癌细胞，原癌基因的激活或抑癌基因的失活都可能驱使肿瘤的发生。我们前期研究发现敲除FRMD3基因引发Hippo通路异常，并促进小鼠早期大肠腺瘤发生，提示FRMD3是个潜在的大肠癌抑癌基因。随后揭示出FRMD3与Hippo信号通路核心激酶MST1及LATS1相互作用，控制Hippo信号通路的激活。据此我们提出早期大肠癌发生的一个新科学假设：抑癌基因FRMD3出现缺失或功能异常使之成为肿瘤驱动基因。我们研究了FRMD3对Hippo信号通路的调控异常导致大肠上皮的早期病变（增生和炎症）和早期大肠癌的发生；研究了FRMD3及MST1和LATS1作为防控大肠癌的新化学干预靶点的可能性，并进行了LATS1激动剂化合物的筛选。研究的主要结果包括发现并证实了FRMD3是个大肠癌抑癌基因; 提出FRMD3是Hippo信号通路激活不可或缺的调节分子的概念;提出Hippo信号通路核心激酶可能是在FRMD3分子上完成系列活化的科学假设; 确立了大肠癌的新化学预防靶点LATS1; 筛选出LATS1激动剂和抑制剂的前体化合物。关键的数据是FRMD3是一个调控Hippo信号通路核心激酶LATS1激活的重要抑癌基因。本研究发现FRMD3是一个大肠癌的新抑制基因加深了对大肠癌发生机制的认识，FRMD3激活LATS1并且是Hippo信号通路激活不可或缺的调控分子的发现进一步丰富了对Hippo信号通路调节复杂性的认识，而LATS1激动剂和抑制剂前体化合物的发现对Hippo信号通路的化学干预和肿瘤的早期预防提供了新的候选靶点和前体化合物。总之，本研究实践了所有研究内容的探索，实现了所预期的所有研究目标，达到了预期的目的。