Wnt Signaling in Colon Cancer

描述（由申请人提供）：Wnt信号传导是与肠道致癌相关的最常见途径之一。介导Wnt信号的转录因子是类淋巴细胞增强因子/T细胞因子（LEF/TCF）家族的成员。该四成员家族是复杂的，因为存在全长激活形式、截短的显性负性形式和修饰Wnt靶基因识别的可变剪接同种型。TCF-1和TCF-4是在肠的上皮隐窝隔室中表达的两个家族成员。正常情况下，TCF-1表达为显性阴性同种型，并且它抵消表达为Wnt介导的活性同种型的TCF-4的作用。这种模式在癌症中发生变化，因为TCF-1表达切换到全长Wnt介导形式。我们在TCF-1和TCF-4亚型中发现了第二个DNA结合结构域，称为C-夹。我们已经表明，C-钳是重要的调节结肠癌细胞的细胞增殖。我们还鉴定了在结肠癌细胞中触发TCF-1输出的Wnt。TCF-1的输出在细胞核中留下TCF-4的C-钳形式以介导异常的Wnt信号传导。为这个项目提出了三个目标。首先，将定义指导TCF-1核输出的细胞外Wnt和细胞内组分（Aim 1）。其次，将在结肠癌细胞和结肠癌启动3D培养物中定义导出的生物学影响（Aim 2）。第三，TCF-1和TCF-4的C-夹形式的DNA结合特异性和靶基因选择将通过全基因组结合测定（ChIP-Seq）、高通量蛋白结合微阵列和体外生化分析（Aim 3）来定义。总体目标是确定结肠癌发生中TCF表达变化背后的机制，并确定细胞外Wnt和TCF的DNA结合特异性如何影响稳定的？连环蛋白。 公共卫生相关性：在结肠癌中，Wnt信号是肿瘤发生和进展的过度活跃和强烈信号。Wnt信号是由TCF转录因子介导的，我们已经发现它们的活性和表达在结肠癌与正常结肠组织中是不同的。本项目研究TCF定位和基因靶向的基本机制，并询问这些属性的差异如何影响癌细胞表型。

DESCRIPTION (provided by applicant): Wnt signaling is one of the most common pathways linked to carcinogenesis in the intestine. The transcription factors that mediate Wnt signals are members of the Lymphoid Enhancer Factor/T Cell Factor (LEF/TCF) family. This four-member family is complex in that there are full-length activating forms, truncated dominant negative forms, and alternatively spliced isoforms that modify Wnt target gene recognition. TCF-1 and TCF-4 are the two family members expressed in the epithelial crypt compartment of the intestine. Normally, TCF-1 is expressed as a dominant negative isoform and it counteracts the action of TCF-4 which is expressed as a Wnt-mediating, active isoform. This pattern changes in cancer because TCF-1 expression switches to a full-length, Wnt mediating form. We have discovered a second DNA binding domain in TCF-1 and TCF-4 isoforms called the C-clamp. We have shown that the C-clamp is important for regulating cell proliferation of colon cancer cells. We have also identified Wnts that trigger TCF-1 export in colon cancer cells. Export of TCF-1 leaves the C-clamp form of TCF-4 in the nucleus to mediate aberrant Wnt signaling. Three aims are proposed for this project. First, the extracellular Wnts and intracellular components that direct TCF-1 nuclear export will be defined (Aim1). Second, the biological impact of export will be defined in colon cancer cells and colon cancer initiating 3D cultures (Aim2). Third, the DNA binding specificities and target gene selection of C-clamp forms of TCF-1 and TCF-4 will be defined through genome-wide binding assays (ChIP-Seq), high-throughput protein binding microarrays, and in vitro biochemical analysis (Aim3). The overall goal is to define the mechanisms behind changes in TCF expression in colon carcinogenesis, and to define how extracellular Wnts and DNA binding specificities of TCFs influence aberrant signaling in colon cancer cells with stabilized ?-catenin. PUBLIC HEALTH RELEVANCE: In colon cancer, Wnt signaling is an overactive and strong signal for tumor initiation and progression. Wnt signaling is mediated by the TCF transcription factors and we have discovered their activities and expression to be different in colon cancer versus normal colon tissue. This project investigates basic mechanisms of TCF localization and gene targeting and asks how differences in these attributes contribute to the cancer cell phenotype.