An unexpected signaling output for the tumor suppressor APC

总结 该建议确定了腺瘤性结肠息肉病（APC）的新功能，APC是一种肿瘤抑制因子， Wnt信号的负调节因子。APC的纯合丢失导致人类息肉病和结肠癌 并且早期胚胎中的缺失导致模式生物中的多种发育表型， 果蝇、斑马鱼和老鼠。Apc突变导致β-连环蛋白的积累，其激活Wnt靶点 基因如c-myc和细胞周期蛋白D1。然而，核β-catenin是不能检测到的早期腺瘤， 具有生殖系APC突变（家族性腺瘤性息肉病（FAP））的患者，也不在发育中的肠道中 的apc突变斑马鱼，这表明额外的效应器需要下游的APC。我们发现 APC直接增强糖原合成酶激酶-3（GSK-3）的活性，提供了意想不到的结果。 APC依赖性抑制多个下游靶点的机制，包括营养传感器 mTOR（雷帕霉素的机制靶点）和β-连环蛋白。APC突变降低GSK-3活性，从而 在不同的体内环境中激活mTORC 1，包括来自FAP患者的腺瘤、肠腺瘤 在小鼠和APC突变的斑马鱼胚胎中。我们的总体假设是APC直接激活GSK-3 并且该信号基序调节多种途径，包括β-连环蛋白和mTOR信号。 该模型揭示了APC的一个关键的新功能，提供了一种mTOR激活的机制， APC突变，并表明APC和其他信号通路之间的联系，是独立的 Wnt/β-连环蛋白。在本提案的目标1中，我们将绘制APC的GSK-3激活结构域。在目标2中，我们将 探讨APC在体内对mTOR的调控机制，包括FAP患者。目标3探索 APC突变在3天内在斑马鱼中引起显著的肿瘤表型 需要激活mTOR我们将在斑马鱼中使用分子和遗传方法来表征 这些肿瘤作为一个高度可及的，在体内模型，以探讨APC信号和肿瘤发生。

Summary This proposal identifies a new function for Adenomatous polyposis coli (APC), a tumor suppressor and negative regulator of Wnt signaling. Homozygous loss of APC causes polyposis and colon cancer in humans and deletion in early embryos causes multiple developmental phenotypes in model organisms such as Drosophila, zebrafish, and mouse. Apc mutations cause accumulation of ß-catenin, which activates Wnt target genes such as c-myc and cyclin D1. However, nuclear ß-catenin is not detectable in early adenomas of patients with germline APC mutations (familial adenomatous polyposis (FAP)) nor in the developing intestines of apc mutant zebrafish, suggesting that additional effectors are required downstream of APC. We find that APC directly enhances the activity of glycogen synthase kinase-3 (GSK-3), providing an unexpected mechanism for APC-dependent suppression of multiple downstream targets, including the nutrient sensor mTOR (mechanistic Target of Rapamycin) and ß-catenin. APC mutations reduce GSK-3 activity, thereby activating mTORC1 in diverse in vivo settings including adenomas from patients with FAP, intestinal adenomas in mice, and apc mutant zebrafish embryos. Our overall hypothesis is that APC directly activates GSK-3 and that this signaling motif regulates multiple pathways, including ß-catenin and mTOR signaling. This model reveals a critical, new function for APC, provides a mechanism for mTOR activation caused by APC mutations, and suggests a link between APC and other signaling pathways that are independent of Wnt/ß-catenin. In aim 1 of this proposal, we will map the GSK-3 activation domain of APC. In aim 2, we will explore the mechanism of mTOR regulation by APC in vivo, including FAP patients. Aim 3 explores the surprising observation that apc mutation causes a dramatic neoplastic phenotype in zebrafish within 3 days that requires mTOR activation. We will use molecular and genetic approaches in zebrafish to characterize these tumors as a highly accessible, in vivo model to explore APC signaling and tumorigenesis.