转录因子GABP在肠道细胞稳态维持和直肠癌发生中的作用研究

The Hippo pathway plays a crucial role in controlling organ size by inhibiting cell proliferation and promoting cells death. Inhibition of the oncogenic transcriptional coactivator YAP by phosphorylation is a major function of the Hippo pathway. Loss of any component of the kinase core results in a YAP-dependent increase in proliferation, resistance to apoptosis and massive organ overgrowth. Yap gene is a candidate oncogene in humans, inasmuch as YAP mRNA levels, protein levels and/or nuclear localization are elevated in many human cancers. A very high prevalence (about 95%) of YAP overexpression was found in human colonic cancer specimens. These findings indicate that regulation of YAP protein abundance is a very important aspect of YAP's function as an oncogene. However, the regulation of Yap gene expression remains poorly defined. Recently, we found that the Ets family member GABP binds the YAP promoter and activates YAP transcription in vitro, and we hypothesize that GABP is the critical transcription factor for Yap gene expression in vivo. In this study, we will study how GABP regulates Yap gene expression in intestinal system, and the role of GABP in intestinal homeostasis and tumorigenesis. This work will expand our understanding of the mechanism of intestinal tumorigenesis and development, and thus shed a new light on therapeutic strategies for the treatment of human colonic tumor.

Hippo（Mst1/2）信号通路是参与调控器官大小的关键通路。它的中心职责是通过磷酸化转录活化因子YAP，抑制其转录激活功能，阻止细胞增殖和器官的过度生长，同时抑制癌症的产生。然而，除了YAP磷酸化水平的变化外，YAP的基因表达水平在很多人类肿瘤样品中显著增高，例如：和正常的癌旁组织相比，有95%的结肠直肠癌临床样品的YAP蛋白升高。因此YAP是和结肠直肠癌致病性紧密相关的重要致癌基因，但目前对YAP基因表达调控机制的研究却非常有限。最近，我们研究发现Ets转录因子家族成员，GABP，可以和YAP启动子上的16个Ets结合位点相作用，激活YAP启动子的荧光素酶报告基因。一些预实验进一步确认了GABP就是调控YAP基因表达的重要转录因子。在本基金项目中，我们将研究GABP调控YAP基因表达的机制，以及GABP在肠道细胞损伤修复，细胞分化，及直肠癌发生和发展中的生物学功能。

良好地完成了本项目所计划的研究内容，并取得了如下成果。. 首先，明确了GABP在肠道中结合于Yap的启动子调控其转录，并证明回补Yap可以挽救GABP敲低诱导的人类结肠癌中原发性结直肠癌分离得到的细胞系SW480细胞凋亡；同时敲低GABP可以降低SW480的克隆形成，而Yap的回补可回复该表型。. 其次，在机制上我们证明GABP对Yap的转录调控受到氧化应激的调节，且Yap可以抑制由氧化应激诱导的SW480细胞凋亡。. 最后，我们利用课题组筛选出Yap上游激酶Mst1/2的抑制剂XMU-BP-1，探索对DSS诱导肠炎的影响。结果显示该抑制剂可以缓解DSS诱导的肠炎，免疫组化显示其处理促进Yap的入何和细胞增殖。SW620细胞系是结肠癌转移至淋巴结后得到的，其恶性程度高，我们发现SW620比SW480细胞中GABPα和Yap水平更高，且EMT标记物Vimentin和Slug也升高，这提示我们GABP和Yap及人类结肠癌具有正相关性。. 通过本项目的资助与研究，我们已经在《Cancer Cell》、《Science Translational Medicine》、《Nature Immunology》(2015和2017)和《Nature Communications》等杂志上发表6篇SCI论文，总影响因子达到95.5分，同时培养了博士研究生两名和硕士研究生两名，使其获得了良好的专业素养。