Models for studying of the role of stem cell competition in field cancerization

描述（由申请人提供）：该提案概述了阐明肿瘤抑制基因在果蝇和小鼠上皮细胞干细胞龛竞争调节中的作用的策略。实现这一提案中的目标将是我们实现长期目标的一个重要里程碑，即开发和使用果蝇和小鼠实地癌变模型，以确定早期癌症诊断和治疗的目标。区域癌变是许多上皮癌的特征，其中肿瘤产生于克隆相关的、突变的但组织学上正常的细胞的癌前区域。由于癌前区域在肿瘤出现之前形成，并且通常在肿瘤切除后仍然存在，因此识别这些区域的诊断和靶向它们的治疗将具有巨大的临床益处。然而，尽管经过50多年的研究，癌前病变形成的机制和突变类型仍然不清楚。我们的中心假设是，现场癌变从获得肿瘤抑制基因突变的干细胞开始，并通过干细胞生态位占据的“超竞争”扩散到邻近的生态位。该模型得到了我们对果蝇卵巢上皮滤泡干细胞（FSC）维持的研究和已发表的小鼠上皮细胞肿瘤抑制表型研究的支持。我们发现FSC与邻近FSC产生的细胞竞争生态位占有，并且我们已经确定了导致过度竞争的三种肿瘤抑制因子的突变。小鼠和人类上皮细胞中的同源突变导致癌症易感性。因此，我们的假设提供了一个解释，为什么一个大的组织区域可能有一个单克隆起源，为什么这些大的组织补丁将特别容易患癌。然而，在我们能够实现我们的目标，产生现场癌变的实验模型，这将是必不可少的（1）确定与人类癌症相关的体细胞突变，导致超竞争的果蝇FSC生态位和（2）确定是否FSC超竞争突变引起小鼠肠上皮细胞的超竞争。为了实现第一个目标，我们将使用镶嵌分析来测试67个果蝇同源的人类肿瘤抑制FSC超竞争表型。为了实现第二个目标，我们将使用小鼠肠干细胞特异性cre与Bmpr1a和Dlg1的floxed等位基因组合，以在成年小鼠中产生条件性敲除，并测定肠上皮中的干细胞过度竞争。该项目具有重要意义，因为它将建立研究上皮干细胞竞争的新模型，并将成为开发实地癌变动物模型的关键第一步。这是一个创新的出发，从以前的研究中，它侧重于了解保守的现场癌变机制，将提供一个理论框架，合理选择候选分子或形态学生物标志物，以测试人体组织样本。 公共卫生相关性：拟议的研究与公共卫生有关，因为它将为实地癌变动物模型的开发铺平道路，这对于确定早期癌症诊断和治疗的临床相关目标非常有用。这将是对NIH改善健康的使命和NCI开发癌症诊断、预防和治疗方法的使命的重大贡献。拟议中的项目也将大大有助于美国国立卫生研究院的使命，以促进基本的创造性发现，通过提供一种新的策略，调查癌症生物学的长期存在的问题，如何癌前区域的形成。

DESCRIPTION (provided by applicant): This proposal outlines a strategy for elucidating the role of tumor suppressor genes in the regulation of stem cell niche competition in Drosophila and mouse epithelia. Accomplishing the aims in this proposal will be an important milestone toward our long-term goal of developing and using Drosophila and mouse models of field cancerization to identify targets for early-stage cancer diagnostics and therapeutics. Field cancerization is a feature of many epithelial cancers in which tumors arise from a precancerous field of clonally related, mutant but histologically normal cells. Since precancerous fields form before tumors arise and often remain after tumor resection, diagnostics that identify these fields and therapeutics that target them would have enormous clinical benefit. Yet, despite over 50 years of research, the mechanism of precancerous field formation and type(s) of mutations responsible remain unclear. Our central hypothesis is that field cancerization initiates from a stem cell that acquires a tumor suppressor mutation and spreads to neighboring niches through "hyper-competition" for stem cell niche occupancy. This model is supported by our studies of epithelial follicle stem cell (FSC) maintenance in the Drosophila ovary and published studies on tumor suppressor phenotypes in mouse epithelia. We found that FSCs compete for niche occupancy with cells produced from neighboring FSCs and we have identified mutations in three tumor suppressors that cause hyper-competition. The homologous mutations in mouse and human epithelia cause a predisposition to cancer. Thus, our hypothesis provides an explanation for how a large region of tissue could have a monoclonal origin and for why these large patches of tissue would be particularly cancer-prone. However, before we can achieve our goal of generating experimental models of field cancerization, it will be essential to (1) identify somatic mutations associated with human cancer that cause hyper-competition in the Drosophila FSC niche and (2) determine whether FSC hyper-competition mutations cause hyper-competition in the mouse intestinal epithelium. To achieve the first aim, we will use mosaic analysis to test 67 Drosophila homologs of human tumor suppressors for FSC hyper-competition phenotypes. To achieve the second aim, we will use a mouse intestinal stem cell specific cre in combination with floxed alleles of Bmpr1a and Dlg1 to generate conditional knockouts in adult mice and assay for stem cell hyper-competition in the intestinal epithelium. This project is significant because it will establish new models for the study of epithelial stem cell competition and will be a critical first step toward the development of animal models of field cancerization. It is an innovative departure from previous studies in that it focuses on understanding conserved mechanisms of field cancerization that will provide a theoretical framework for rational selection of candidate molecular or morphological biomarkers to test on human tissue samples. PUBLIC HEALTH RELEVANCE: The proposed research is relevant to public health because it will pave the way for the development of animal models of field cancerization, which would be extremely useful for identifying clinically relevant targets for early-stage cancer diagnostics and therapies. This would be a significant contribution to the NIH mission to improve health and the NCI mission to develop methods for the diagnosis, prevention and treatment of cancer. The proposed project will also contribute significantly to the NIH mission to foster fundamental creative discoveries by providing a novel strategy for investigating the long-standing question in cancer biology of how precancerous fields form.