利用iPS细胞建立家族性结直肠癌体外模型并研究其发病机制

Familial adenomatous polyposis (FAP) is a severe hereditary disease mainly caused by APC gene mutation. The canceration rate of FAP to colorectal cancer (CRC) is very high. Nowadays, there is lack of effective research model and treatment. Therefore, modeling this disease in vitro which provides opportunities for personalized research, treatment and drug selection is very significant. The strategy becomes feasible by the discovery and application of induced pluripotent stem (iPS) cells. We have collected FAP familial patients which have representative APC mutation site. The blood monocytes of these candidates have been successfully reprogrammed to iPS cells. In this study, we focus on how to induce the committed differentiation of FAP patients derived-iPS cells into colonic epithelial cells, followed by evaluate the tumor characteristics of the colonic epithelial cells to determine whether these cells can be used as FAP related CRC model. Using this model we will explore the mechanism of YY1 in promoting CRC. Previous study showed that YY1 was highly expressed in CRC, but the mechanism was not clear yet. Our preliminary data showed that YY1 interacted with BAF complex to active transcription. YY1 was enriched at the promoter regions of APC, β-catenin and TCF-4, all of which belong to Wnt signaling pathway. Moreover, YY1 bound at super-enhancer to regulate gene expression. These results will help us to clarify the mechanism of YY1 in promoting CRC via the new established CRC model.

家族性腺瘤性息肉病(FAP)是一种由APC基因突变导致的遗传性疾病，结直肠癌(CRC)变率很高，目前缺少有效的研究手段和治疗方法。因此，建立一种能够模拟患者发育过程的CRC模型，达到个性化机制研究和药物筛选的目的极具意义。iPS细胞的应用使得这种建模策略成为可能。我们已收集到有代表性APC突变位点的FAP家族样本，并成功将受试者血液单核细胞重编程为iPS细胞。我们将研究如何把iPS细胞定向分化为结肠上皮细胞，并对该细胞是否具有肿瘤细胞特性进行评估，判断其是否可用作FAP相关性CRC的细胞模型。应用该模型我们将探索YY1的致癌机制。YY1在CRC中高表达，但其机制尚不明确。预实验发现YY1与BAF复合物互作激活转录，且YY1富集于Wnt通路因子APC、β-catenin和TCF-4的启动子区，YY1还作用于超级增强子调控基因表达，这些发现将有助于我们在新模型中揭示YY1促进CRC的分子机制。

染色体三维结构的改变与细胞命运息息相关，然而染色体三维结构的异常变化如何调控结直肠癌的发生发展，目前还不十分明确。本项目旨在通过对比正常结肠上皮细胞和结直肠癌细胞染色体三维结构的差异，探索结直肠癌发生发展的新机制，并揭示致癌基因YY1调控基因表达的新机制。研究发现，染色体三维结构在正常和癌变的结肠细胞中有着重要差异，这些差异主要包括染色体间隔区域（Compartment）的转变和拓扑相关结构域（TAD）结构的改变，而后者对于超级增强子及其靶基因的调控更为重要。TAD结构的变化通过改变超级增强子在TAD中的分布，从而激活靶致癌基因来促进结直肠癌的发生发展。我们通过超级增强子的分布以及三维结构的改变鉴定出了受超级增强子调控的新型致癌基因，并通过功能学实验验证了这些基因对于结直肠癌的促进作用，说明了该方法预测新型致癌基因的可靠性。我们还揭示了YY1蛋白和BAF复合物互作通过超级增强子调控基因表达的新机制。本研究在结直肠癌细胞中通过三维基因组和超级增强子的变化特点，鉴定出了新型致癌基因，为临床研究和抗癌药物开发提供了新的分子靶标。该鉴定新型致病基因的方法可推广到其他疾病当中。