Guanylin GUCY2C axis in Colorectal Cancer Initiation

项目摘要/摘要 APC(~85%)或β-连环蛋白(~5%)突变可引发90%的散发性结直肠癌。这些突变 产生β-连环蛋白积累和核转位，激活驱动转录程序的Tcf 潜在的肿瘤发生机制。GUCY2C是肠道激素鸟苷素的受体，表达于 结肠直肠。在健康状态下，鸟苷-GUCY2C信号调节组织的动态平衡过程 隐窝表面轴，部分通过一种未知的机制，阻止β-连环蛋白的积累。的 意义：鸟苷素是结直肠癌中最常见的缺失的mRNA转录本。荷尔蒙丢失，这 沉默GUCY2C，发生在转化的最早阶段，通过一种未知的保守机制 在老鼠和人类身上。初步研究表明，鸟苷素丢失是由突变体apc-β-catenin-Tcf介导的 发信号。此外，转基因鸟苷素表达消除了致癌物诱导的小鼠肿瘤形成 老鼠。基于这些观察结果，我们认为突变的apc-β-catenin-Tcf信号在转录水平上 沉默鸟苷素是肿瘤发生中的必需步骤，因为鸟苷素-GUC2C信号通路阻断了β-连锁素 转化所需的积累。相关的化学预防假说表明鸟苷素 替换应消除由APC-β-连环蛋白信号驱动的肿瘤发生。在这里，病理生理学 目的研究突变体Apc-β-catenin-Tcf介导鸟苷丢失的转录机制。这些 研究将在突变型Apc-β-连环蛋白-Tcf信号、鸟苷 抑制，和GUCY2C沉默，这是肿瘤发生所必需的。机械目标测试 假设鸟苷素丢失是因为GUCy2C阻止了肿瘤发生所需的β-连环蛋白积聚。 这些研究将证明鸟苷-GUC2C轴通过阻断来限制β-连环蛋白的积累 蛋白质翻译(合成)和诱导蛋白酶体降解。预防目标测试 结直肠癌反映鸟苷素表达抑制和GUCY2C信号转导的假说 可以通过激素替代来克服。这些研究将证明转基因鸟苷的能力 表达修复致癌的β-连环蛋白信号，重建内源性GUC2C激素表达， 并防止小鼠双等位基因APC失活后的肿瘤形成。总而言之，这些研究将揭示 涉及鸟苷素缺失和GUCY2C的结直肠癌启动中先前未预料到的必要步骤 沉默。他们将改变结直肠癌的病理生理学范式，从一种不可逆转的疾病 基因突变是一种可逆性激素缺乏。从机制上讲，他们将识别一个独特的 致癌级联顶端的脆弱性，其中β-连环蛋白依赖事件需要 肿瘤的发生可以通过GUCY2C信号来克服。此外，它们还将确立原则证明 结直肠癌可以通过激素替代来预防。即时翻译的潜力是 口服GUCY2C配体利纳氯肽被批准用于治疗慢性便秘。

PROJECT SUMMARY/ABSTRACT Mutations in APC (~85%) or β-catenin (~5%) initiate >90% of sporadic colorectal cancers. These mutations produce β-catenin accumulation and nuclear translocation, activating Tcf which drives transcriptional programs underlying tumorigenesis. GUCY2C is the intestinal receptor for the hormone guanylin expressed in colorectum. In the healthy state, guanylin-GUCY2C signaling regulates homeostatic processes that organize the crypt-surface axis, in part through an unknown mechanism which blocks β-catenin accumulation. Of significance, guanylin is the most commonly lost mRNA transcript in colorectal cancer. Hormone loss, which silences GUCY2C, occurs at the earliest stages of transformation through an unknown mechanism conserved in mice and humans. Preliminary studies reveal that guanylin loss is mediated by mutant APC-β-catenin-Tcf signaling. Moreover, transgenic guanylin expression eliminated carcinogen-induced tumor formation in mice. Based on these observations, we propose that mutant APC-β-catenin-Tcf signaling transcriptionally silences guanylin as an obligatory step in tumorigenesis because guanylin-GUCY2C signaling blocks β-catenin accumulation required for transformation. The correlative chemoprevention hypothesis suggests that guanylin replacement should eliminate tumorigenesis driven by APC-β-catenin signaling. Here, the Pathophysiologic Aim will identify the transcriptional mechanisms mediating guanylin loss by mutant APC-β-catenin-Tcf. These studies will establish a novel molecular link between mutant APC-β-catenin-Tcf signaling, guanylin suppression, and GUCY2C silencing which is obligatory for tumorigenesis. The Mechanistic Aim tests the hypothesis that guanylin is lost because GUCY2C blocks β-catenin accumulation required for tumorigenesis. These studies will demonstrate that the guanylin-GUCY2C axis restricts β-catenin accumulation by blocking protein translation (synthesis) and inducing proteosomal degradation. The Prevention Aim tests the hypothesis that colorectal cancer reflects suppression of guanylin expression and GUCY2C signaling which can be overcome by hormone replacement. These studies will demonstrate the ability of transgenic guanylin expression to repair oncogenic β-catenin signaling, reconstitute endogenous GUCY2C hormone expression, and prevent tumorigenesis following biallelic APC inactivation in mice. Together, these studies will reveal a previously unanticipated required step in colorectal cancer initiation involving guanylin loss and GUCY2C silencing. They will shift the pathophysiological paradigm for colorectal cancer from a disease of irreversible gene mutations to one of reversible hormone insufficiency. Mechanistically, they will identify a unique vulnerability at the apex of the oncogenic cascade in which β-catenin-dependent events required for tumorigenesis can be overcome by GUCY2C signaling. Moreover, they will establish the proof of principle that colorectal cancer can be prevented by hormone replacement. The potential for immediate translation is underscored by the approval of the oral GUCY2C ligand linaclotide to treat chronic constipation.