Investigating a Wnt-telomere feedback loop in the colorectal adenoma-carcinoma sequence

摘要： 结直肠腺癌(CRC)是全球癌症死亡的主要原因。结直肠癌的致瘤作用 通过结肠上皮从良性腺瘤到侵袭性腺瘤的逐步转化模型进行 癌症。这种遗传过程通常始于APC功能丧失突变，这种突变是过度激活的 Wnt信号通路，并需要p53的最终突变来促进肿瘤的进展和侵袭。多数人 结直肠癌的特点还表现为染色体不稳定(CIN)，它早期发生，并通过 肿瘤进展，并使突变，从而推动癌症的发生。尽管实现了转型 在CIN中，CIN的发生机制尚不完全清楚。强有力的候选人贡献者 早期结直肠癌中的CIN是端粒功能障碍，发生在染色体末端变短和 解帽并激活导致染色体最终融合的DNA损伤反应(DDR)。端粒 在腺瘤和癌组织中观察到侵蚀和融合，并被证明是相关的。 对于CIN，与端粒可能作为致癌驱动因素的可能性一致。考虑到这些 观察，对调节端粒封顶的机制及其后果有了更深入的了解 在结直肠癌进展过程中端粒脱帽是必要的。我们的实验室此前发现了一种新的反馈 端粒封顶和Wnt信号之间的环路有助于维持小鼠肠道内环境平衡 和人类。通过这个环，端粒封顶的丢失导致Wnt途径活性的广泛抑制 在肠腺上皮和下层基质中。我们确定，在小鼠中，这一调控涉及P53- 介导表达miR-34a，一种针对Wnt途径组件的P53激活的microRNA。此外， Wnt途径的激活通过上调Shelterin蛋白TRF2来加强端粒的封顶。 因此，肠道中的端粒封顶和Wnt信号是相互支持的，并且这种反馈的失调 对于端粒功能异常的细胞，CRC中的循环可能是允许的。在此提出的研究旨在 了解可能损害WNT-端粒反馈的致癌CRC突变如何影响端粒 结直肠癌进展过程中的状态，以及端粒被干扰封顶促进肿瘤的程度 成长。我的中心假设是Wnt信号和端粒封顶之间的调控回路是 在结直肠癌中被破坏，功能失调的端粒促进而不是抑制肿瘤的发生。在《目标1》中，我将 使用人类结肠器官模型来确定APC和P53突变是如何破坏Wnt-端粒反馈的。 在目标2中，我将描述这些突变与Wnt信号/TRF2表达之间的关系 在APC和P53缺失的背景下检测人类结直肠癌样本并确定是否导致端粒功能障碍 促进小鼠异种移植瘤中有机物质的生长。综上所述，这些研究将提供前所未有的 洞察端粒功能障碍是早期结直肠癌发生的驱动因素，并揭示有关端粒功能障碍的新信息 发展中的结肠肿瘤的突变景观。

ABSTRACT: Colorectal adenocarcinoma (CRC) is a leading cause of cancer deaths globally. CRC tumorigenesis proceeds through a model of stepwise transformation of the colonic epithelium from benign adenoma to invasive carcinoma. This genetic process generally initiates from loss-of-function mutations in APC, which hyperactivate the Wnt signaling pathway, and requires eventual mutations in p53 for tumor progression and invasion. A majority of CRC cases is also characterized by chromosomal instability (CIN), which arises early and increases through tumor progression and which enables mutations that drive carcinogenesis. Despite enablement of transformation by CIN, the mechanisms by which CIN arises are not completely understood. A strong candidate contributor to CIN in early CRC is telomere dysfunction, which occurs when chromosome ends become shortened and uncapped and activate a DNA damage response (DDR) that leads to chromosome end-fusions. Telomere erosion and fusions have been observed in adenoma and carcinoma biopsies and have been shown to correlate with CIN, consistent with the possibility that telomeres may function as a driver of carcinogenesis. Given these observations, a deeper understanding of the mechanisms that regulate telomere capping and the consequences of telomere uncapping during CRC progression is needed. Our laboratory previously uncovered a novel feedback loop between telomere capping and Wnt signaling that contributes to homeostatic intestinal maintenance in mice and humans. Through this loop, loss of telomere capping leads to a broad suppression of Wnt pathway activity in intestinal crypt epithelia and underlying stroma. We determined that in mice this regulation involves p53- mediated expression miR-34a, a p53-activated microRNA which targets Wnt pathway components. Moreover, activation of the Wnt pathway reinforces telomere capping through upregulation of the shelterin protein TRF2. Thus, telomere capping and Wnt signaling in the gut are mutually supportive, and dysregulation of this feedback loop in CRC may be permissive for cells harboring dysfunctional telomeres. The study proposed herein aims to understand how oncogenic CRC mutations that might compromise Wnt-telomere feedback impact telomere status during CRC progression, as well as the extent to which perturbed telomere capping promotes tumor growth. My central hypothesis is that the regulatory loop between Wnt signaling and telomere capping is disrupted in CRC such that dysfunctional telomeres enhance, rather than inhibit, tumorigenesis. In Aim 1, I will use a human colonic organoid model to determine how APC and p53 mutations disrupt Wnt-telomere feedback. In Aim 2, I will characterize the relationship between these mutations and Wnt signaling/TRF2 expression in human CRC samples and determine whether induced telomere dysfunction in the setting of APC and p53 loss enhances organoid growth in murine xenografts. Taken together, these studies will provide unprecedented insight into telomere dysfunction as a driver of early CRC tumorigenesis and reveal new information about the mutational landscape of developing colon tumors.