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（别名：TCF4）是 β-连环蛋白的结合伴侣，也是 Wnt/β-连环蛋白信号传导的关键核效应子。 TCF7L2 对于肠道发育和成人组织稳态至关重要。矛盾的是，高达 30% 的人类结直肠肿瘤携带 TCF7L2 基因突变。这使得 TCF7L2 成为结直肠癌中最常见的突变基因之一。三种不同的 TCF7L2 突变模式是明显的：TCF7L2 剪接变体子集的选择性失活、通过一个基因拷贝失活使 TCF7L2 表达减少 50%，以及双等位基因删除。所有三种模式都会导致 TCF7L2 功能部分或完全丧失，这与健康肠道中 TCF7L2 的绝对需求及其作为癌基因表达驱动因素的作用不一致。因此，拟议研究的总体目标是澄清这一明显的矛盾，并阐明 TCF7L2 在结直肠癌中的促肿瘤和抗肿瘤功能。具体来说，我们将测试三个假设，这些假设可以解释 TCF7L2 突变模式的发生及其对结直肠癌发生的影响。首先，降低 TCF7L2 和特定 TCF7L2 亚型总体表达的突变可以通过阻断 Wnt/β-连环蛋白信号传导的促分化功能，同时保留其促有丝分裂活性，从而为肿瘤细胞提供生长优势。其次，TCF7L2 被其他在结直肠癌细胞中病理上调的 TCF/LEF 蛋白替代，可能会导致 TCF7L2 部分或完全失活。第三，转移性结直肠肿瘤可能能够耐受TCF7L2的完全缺失，因为它们可能由于Hedgehog/GLI信号的激活或肠道干细胞转录因子ASCL2的过度表达而获得了β-连环蛋白/TCF7L2驱动的转录的独立性。为了检验我们的假设，我们将使用 CRISPR/Cas9 介导的结直肠癌细胞和来自转基因小鼠模型的肠类器官培养物的基因组编辑来重建在人类肿瘤中观察到的 TCF7L2 突变模式。我们将研究 TCF7L2 基因型的改变如何影响肿瘤相关的表型特征，TCF7L2 基因在结直肠癌细胞中是否是必需的，以及 TCF/LEF 家族成员、ASCL2 或 Hedgehog/GLI 活性的上调是否可以补偿 TCF7L2 的损失。对公开转录组和基因组数据集的生物信息分析将用作独立策略，以询问 TCF7L2 突变、TCF/LEF 家族成员的表达、ASCL2、指定 Hedgehog/GLI 活性的特征基因以及迄今未知的特征之间的关系。总体而言，拟议的研究将为 TCF7L2 的生物学和结直肠癌的分子病理学带来新的见解。因此，它们将为合理评估 β-catenin::TCF7L2 复合物作为合适的治疗靶点提供必要的基础。