Role of ADP-ribosylation in Wnt Pathway Activation

Wnt信号转导通路指导胚胎发育的重要步骤。不适当 Wnt信号的激活触发了几种癌症的发展，包括绝大多数结直肠癌。 癌的因此，了解Wnt通路激活的基本机制将有助于 设计治疗大量疾病的创新战略。我们研究的一个主要目标是 为了阐明两种不同的多蛋白复合物的调节-称为“β-连环蛋白破坏 复合物”和“信号体”-这是基本的控制Wnt信号在“关闭”和“打开” 国，分别。Axin是一种浓度限制性支架蛋白，在细胞的组装中起重要作用。 两个复合体。Axin的这些不同作用是如何协调的仍然是一个谜。Axin的监管机构， 包括ADP-核糖聚合酶端锚聚合酶（Tnks）， 目标的在目前的模型中，Tnks的唯一作用是靶向Axin以进行蛋白酶体降解，从而使Axin与蛋白酶体结合。 在未刺激状态下控制稳态Axin水平。然而，我们意外地发现，ADP- Tnks对Axin的核糖基化作用也促进Axin在Wnt信号转导通路激活中的关键作用， 刺激.我们的研究结果迫使对Wnt信号转导中Tnks功能的流行模型进行重大修订， 可能是小分子Tnks抑制剂有效性的基础，这些抑制剂是最有前途的抗肿瘤药物之一。 Wnt通路药物正在开发中。因此，与流行的模型相比，我们假设Tnks 在控制破坏复合体（未受刺激状态）和 信号体（Wnt刺激后）。我们建议通过分析这些差异来检验这一假设。 基础和Wnt刺激条件下Axin ADP核糖基化状态。我们将确定Axin ADP- 核糖基化调节β-连环蛋白破坏复合物和信号体的组成和活性。我们 将解决ADP-核糖基化对未刺激和Wnt刺激的Axin活性的生理作用。 活体内的状态这些研究是由两名科学家之间正在进行的合作推动的，他们有一个共同的目标， 对Wnt信号传导感兴趣：Yashi Ahmed，一位经验丰富的果蝇遗传学家和细胞生物学家，和Ethan Lee， 他是在非洲爪蟾中使用体内方法和体外途径重建的专家。我们将联合收割机 在脊椎动物和无脊椎动物模型中采用创新的遗传学、细胞生物学和生物化学方法， 提供对Wnt信号调节的深入了解。该研究对我国的 为Wnt驱动的疾病开发新的治疗策略。

The Wnt signal transduction pathway directs essential steps in embryonic development. Inappropriate activation of Wnt signaling triggers the development of several cancers, including the vast majority of colorectal cancers. Thus, understanding the basic mechanisms that underlie Wnt pathway activation will facilitate the design of innovative strategies for the treatment of a large number of diseases. A major goal of our research is to elucidate the regulation of two distinct multiprotein complexes - termed the “beta-catenin destruction complex” and the “signalosome”- that are fundamental for the control of Wnt signaling in the “off” and “on” states, respectively. Axin, a concentration-limiting scaffold protein, plays important roles in the assembly of both complexes. How these distinct roles of Axin are coordinated remains a mystery. Regulators of Axin, including the ADP-ribose polymerase Tankyrase (Tnks) have recently emerged as promising therapeutic targets. In the current model, the sole role of Tnks is to target Axin for proteasomal degradation, and thereby to control steady state Axin levels in the unstimulated state. However, we have found, unexpectedly, that ADP- ribosylation of Axin by Tnks also promotes Axin's critical role in activation of the pathway following Wnt stimulation. Our findings force major revision of the prevailing model for Tnks function in Wnt signaling and may underlie the effectiveness of small molecule Tnks inhibitors, which are among the most promising anti- Wnt pathway agents under development. Thus, in contrast with the prevailing model, we hypothesize that Tnks plays key roles in controlling Axin activity both in the destruction complex (in the unstimulated state) and in the signalosome (following Wnt stimulation). We propose to test this hypothesis by analyzing differences in the state of Axin ADP-ribosylation under basal and Wnt-stimulated conditions. We will determine how Axin ADP- ribosylation regulates the composition and activity of the β-catenin destruction complex and signalosome. We will address the physiological roles of ADP-ribosylation on Axin activity in the unstimulated and Wnt-stimulated states in vivo. These studies are driven by an ongoing collaboration between two scientists who have a shared interest in Wnt signaling: Yashi Ahmed, an experienced Drosophila geneticist and cell biologist, and Ethan Lee, an expert in using in vivo approaches in Xenopus and in vitro pathway reconstitution. We will combine our innovative genetic, cell biological, and biochemical approaches in vertebrate and invertebrate models to provide insight into the regulation of Wnt signaling. The proposed research has significance for the development of new therapeutic strategies for Wnt-driven diseases.