The role of TCF7L2 in colorectal tumorigenesis - oncogene or tumorsuppressor?

TCF7L2在结直肠肿瘤发生中的作用——癌基因还是抑癌基因？

基本信息

批准号：
315268620
负责人：
Professor Dr. Andreas Hecht
金额：
--
依托单位：
Institut für Molekulare Medizin und Zellforschung
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2019-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/315268620?language=en
关键词：
role TCF7L2 colorectal tumorigenesis oncogene

项目摘要

The transcription factor TCF7L2 (alias: TCF4) is a binding partner of beta-catenin and key nuclear effector of Wnt/beta-catenin signaling. TCF7L2 is essential for intestinal development and in adult tissue homeostasis. Paradoxically, up to 30% of human colorectal tumors carry mutations in the TCF7L2 gene. This makes TCF7L2 one of the most frequently mutated genes in colorectal cancer. Three different TCF7L2 mutational patterns are apparent: selective inactivation of a subset of TCF7L2 splice variants, 50% reduction of TCF7L2 expression by inactivation of one gene copy, and biallelic deletion. All three patterns lead to partial or complete loss of TCF7L2 function which is at odds with the absolute requirements for TCF7L2 in the healthy intestine and its role as driver of oncogene expression. Hence, the overall goal of the proposed studies is to clarify this apparent contradiction and to shed light on the pro- and anti-tumorigenic functions of TCF7L2 in colorectal cancer. Specifically we will test three hypotheses that could explain the occurrence of TCF7L2 mutational patterns and their impact on colorectal carcinogenesis. First, mutations that reduce the overall expression of TCF7L2 and particular TCF7L2 isoforms could provide a growth advantage to tumor cells by blocking the pro-differentiation function of Wnt/beta-catenin signaling while retaining its mitogenic activity. Second, the functional substitution of TCF7L2 by other TCF/LEF proteins which are pathologically upregulated in colorectal cancer cells, could allow the partial or complete inactivation of TCF7L2. Third, metastatic colorectal tumors might be able to tolerate complete TCF7L2 deletion because they might have acquired independence of beta-catenin/TCF7L2 driven transcription due to activation of Hedgehog/GLI signaling or overexpression of the intestinal stem cell transcription factor ASCL2. To test our hypotheses, we will use CRISPR/Cas9-mediated genome editing of colorectal cancer cells and intestinal organoid cultures from genetically modified mouse models to reconstruct the mutational patterns of TCF7L2 observed in human tumors. We will investigate how alterations of the TCF7L2 genotype affect tumor-relevant phenotypic traits, whether the TCF7L2 gene is essential in colorectal cancer cells, and whether upregulation of TCF/LEF family members, ASCL2 or Hedgehog/GLI activity can compensate for loss of TCF7L2. Bioinformatic analyses of publicly available transcriptome and genome data sets will be used as an independent strategy to interrogate relationships between TCF7L2 mutations, the expression of TCF/LEF family members, ASCL2, signature genes specifying Hedgehog/GLI activity, and as yet unknown features. Overall, the proposed studies will lead to novel insights into the biology of TCF7L2 and the molecular pathology of colorectal cancer. Thereby, they will provide the necessary basis for a rational evaluation of the beta-catenin::TCF7L2 complex as a suitable therapeutic target.

转录因子TCF7L2（Alias：TCF4）是β-catenin和Wnt/beta-catenin信号传导的关键核效应子的结合伴侣。 TCF7L2对于肠发展和成人组织稳态至关重要。矛盾的是，多达30％的人结直肠肿瘤在TCF7L2基因中携带突变。这使TCF7L2成为结直肠癌中最常见的突变基因之一。三种不同的TCF7L2突变模式很明显：选择性失活TCF7L2剪接变体，通过灭活一个基因拷贝而降低了TCF7L2表达的50％，而双重缺失。所有三种模式都会导致TCF7L2功能的部分或完全丧失，这与健康肠道中TCF7L2的绝对要求及其作为癌基因表达的驱动力的绝对要求。因此，拟议的研究的总体目标是阐明这一明显的矛盾，并阐明结直肠癌中TCF7L2的促和抗肿瘤功能。具体而言，我们将检验三个假设，可以解释TCF7L2突变模式的发生及其对结直肠癌发生的影响。首先，减少TCF7L2和特定TCF7L2同工型的总体表达的突变可以通过阻止Wnt/beta-catenin信号的促分化功能，同时保留其有丝分裂活性，从而为肿瘤细胞提供生长优势。其次，在大肠癌细胞中在病理上上调的其他TCF/LEF蛋白将TCF7L2的功能取代可以使TCF7L2的部分或完全失活。第三，转移性结直肠肿瘤可能能够忍受完整的TCF7L2缺失，因为由于刺猬/GLI信号的激活或肠道干细胞转录因子的过度表达，它们可能已经获得了β-catenin/tcf7L2驱动转录的独立性。为了检验我们的假设，我们将使用CRISPR/CAS9介导的结肠直肠癌细胞和肠道器官培养物的基因组编辑，从转基因小鼠模型中重建人类肿瘤中观察到的TCF7L2的突变模式。我们将研究TCF7L2基因型的改变如何影响与肿瘤相关的表型特征，TCF7L2基因在结直肠癌细胞中是否必不可少，以及TCF/LEF家族成员，ASCL2还是HEDGEHOG/GLI活性的上调是否可以补偿TCF7L2的损失。对公共可用转录组和基因组数据集的生物信息学分析将被用作独立策略，以询问TCF7L2突变之间的关系，TCF/LEF家族成员的表达，ASCL2，签名基因，指定刺猬/Gli活动的签名基因，以及尚不清楚的特征。总体而言，拟议的研究将导致对TCF7L2生物学和大肠癌的分子病理学的新见解。因此，他们将为合理评估β-catenin :: TCF7L2复合物作为合适的治疗靶标提供必要的基础。