(PQ1) GUCY2C hormone loss translates APC-Beta-catenin mutations into epithelial transformation

 描述（由申请人提供）：结直肠癌是第四大常见癌症，也是第二大癌症死亡原因。在>90%的散发病例中，结直肠癌起始于APC（~85%）或其下游降解靶点β-连环蛋白（~5%）的突变。这些突变导致β-连环蛋白的积累，其易位到细胞核并调节转录，从而驱动上皮功能障碍和恶变前区域（腺瘤）的形成。虽然APC和β-连环蛋白突变在转化中的作用已经确立，但知识的差距反映了对将这些突变与癌前病变形成联系起来的病理生理事件、介导这些事件的机制及其作为癌症化学预防基础的可逆性的不完全理解。在这种情况下，鸟苷素是一种旁分泌 由结肠直肠上皮细胞产生的肽激素。鸟苷素与GUCY 2C结合，GUCY 2C是一种通过调节增殖、染色体稳定性和代谢编程（部分通过防止β-连环蛋白积累）来维持上皮稳态的受体。最近，我们发现鸟苷素缺失沉默GUCY 2C发生在所有结直肠肿瘤中。此外，鸟苷素在所有腺瘤和腺瘤形成前的癌前上皮中丢失。出乎意料的是，鸟苷素在小鼠中的转基因表达（不能丢失）消除了由致癌物氧化偶氮甲烷（AOM）诱导的转化，该致癌物可产生β-连环蛋白突变。基于这些观察结果，我们提出测试新的假设，即存在相互反馈回路，其中突变APC-β-连环蛋白的核信号传导诱导转化所需的鸟苷素损失，因为鸟苷素-GUCY 2C阻断肿瘤发生所需的β-连环蛋白积累。在此，病理生理学目的将检验鸟苷素缺失沉默GUCY 2C是形成突变APC-β-连环蛋白产生的癌前区域所必需的假设。这些研究将证明，消除鸟苷素在肠细胞概括的病理生理学的转变（鸟苷素损失介导的疾病）。机制目的将检验突变APC-β-连环蛋白抑制鸟苷素转录的假设，因为鸟苷素-GUCY 2C阻断转化所需的β-连环蛋白积累（该分子机制介导鸟苷素损失）。这些研究将使结直肠癌的模式从不可逆APC-β-连环蛋白突变的遗传性疾病转变为可逆鸟苷素不足的疾病。化学预防目的将检验转基因鸟苷素替代阻断β-连环蛋白积累、上皮功能障碍和APC-β-连环蛋白突变诱导的转化（阻断鸟苷素损失可预防疾病）的假设。这些研究将建立鸟苷素替代消除肠道转化的化学预防范式。反过来，这些新的机制见解将为结直肠癌预防提供新的机会，包括口服GUCY 2C配体补充剂。口服GUCY 2C配体利那洛肽（linaclotide）获批用于治疗慢性便秘强调了立即翻译的潜力。

 DESCRIPTION (provided by applicant): Colorectal cancer is the 4th most common cancer and 2nd leading cause of cancer death. In >90% of sporadic cases, colorectal cancer initiates as mutations in APC (~85%) or its downstream degradation target, β-catenin (~5%). These mutations result in accumulation of β-catenin which translocates to the nucleus and regulates transcription driving epithelial dysfunction and formation of the premalignant field (adenomas). While a role for APC and β-catenin mutations in transformation is established, gaps in knowledge reflect an incomplete understanding of the pathophysiological events linking these mutations to formation of the premalignant field, the mechanisms mediating those events, and their reversibility as a basis for cancer chemoprevention. In that context, guanylin is a paracrine peptide hormone produced by epithelial cells in the colo-rectum. Guanylin binds to GUCY2C, a receptor which maintains epithelial homeostasis by regulating proliferation, chromosomal stability, and metabolic programming, in part, by preventing β-catenin accumulation. Recently, we revealed that guanylin loss silencing GUCY2C occurs in all colorectal tumors. Further, guanylin is lost in all adenomas, and in premalignant epithelia that precede adenoma formation. Unexpectedly, transgenic expression of guanylin (cannot be lost) in mice eliminated transformation induced by the carcinogen azoxymethane (AOM) which produces β-catenin mutations. Based on these observations, we propose testing the novel hypothesis that that there is a reciprocal feedback loop in which nuclear signaling by mutant APC-β-catenin induces guanylin loss required for transformation because guanylin-GUCY2C blocks β-catenin accumulation necessary for tumorigenesis. Here, the Pathophysiological Aim will test the hypothesis that guanylin loss silencing GUCY2C is required to form the premalignant field produced by mutant APC-β-catenin. These studies will demonstrate that eliminating guanylin in intestinal cells recapitulates the pathophysiology of transformation (guanylin loss mediates the disease). The Mechanistic Aim will test the hypothesis that mutant APC-β-catenin suppresses guanylin transcription because guanylin-GUCY2C blocks β-catenin accumulation required for transformation (this molecular mechanism mediates guanylin loss). These studies will shift the paradigm in colorectal cancer from a genetic disease of irreversible APC-β-catenin mutations to a disease of reversible guanylin insufficiency. The Chemoprevention Aim will test the hypothesis that transgenic guanylin replacement blocks β-catenin accumulation, epithelial dysfunction, and transformation induced by APC-β-catenin mutations (blocking guanylin loss prevents the disease). These studies will establish the chemoprevention paradigm that guanylin replacement eliminates intestinal transformation. In turn, these novel mechanistic insights will provide new opportunities for colorectal cancer prevention, including oral GUCY2C ligand supplementation. The potential for immediate translation is underscored by the approval of the oral GUCY2C ligand, linaclotide, to treat chronic constipation.