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

描述(由申请人提供)：这项建议概述了一种策略，用于阐明肿瘤抑制基因在调节果蝇和小鼠上皮干细胞生态位竞争中的作用。实现这项提案中的目标将是我们实现长期目标的一个重要里程碑，我们的长期目标是开发和使用果蝇和小鼠的现场癌变模型来确定早期癌症诊断和治疗的靶点。野生性癌变是许多上皮性癌症的一个特征，在这些肿瘤中，肿瘤是由克隆相关的、突变的但组织学上正常的细胞组成的癌前野生区。由于癌前野是在肿瘤发生之前形成的，在肿瘤切除后往往会保留下来，因此识别这些野的诊断和针对这些野的治疗将具有巨大的临床益处。然而，尽管经过了50多年的研究，癌前病区形成的机制和相关突变的类型(S)仍然不清楚。我们的中心假设是，野生性癌变始于一种干细胞，该干细胞获得一种肿瘤抑制基因突变，并通过“超级竞争”来占据干细胞的位置，从而扩散到邻近的壁龛。这一模型得到了我们对果蝇卵巢上皮滤泡干细胞(FSC)维持的研究和对小鼠卵巢上皮细胞肿瘤抑制表型的研究的支持。我们发现，FSCs与邻近FSCs产生的细胞争夺利基位置，我们已经确定了三个肿瘤抑制基因的突变，这些突变导致了超竞争。小鼠和人类上皮细胞中的同源突变会导致癌症的易感性。因此，我们的假设提供了一种解释，解释了为什么一大片组织可能具有单克隆性起源，以及为什么这些大片组织特别容易患癌症。然而，在我们能够实现建立现场癌变实验模型的目标之前，(1)鉴定与人类癌症相关的导致果蝇FSC生态位过度竞争的体细胞突变，以及(2)确定FSC过度竞争突变是否导致小鼠肠道上皮的过度竞争，这是至关重要的。为了实现第一个目标，我们将使用镶嵌分析来测试67个人类肿瘤抑制基因的果蝇同源物的FSC高竞争表型。为了实现第二个目标，我们将使用小鼠肠道干细胞特异性cre与BMPR1A和Dlg1的Floated等位基因相结合，在成年小鼠中产生条件基因敲除，并检测干细胞在肠道上皮中的超竞争。这个项目意义重大，因为它将为研究上皮干细胞竞争建立新的模型，并将是发展野生型癌变动物模型的关键的第一步。这是与以往研究的创新之处，因为它侧重于了解野外癌变的保守机制，这将为合理选择候选分子或形态生物标记物在人体组织样本上进行测试提供理论框架。 公共卫生相关性：拟议的研究与公共卫生相关，因为它将为野外癌变动物模型的发展铺平道路，这将对确定早期癌症诊断和治疗的临床相关靶点非常有用。这将对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做出重大贡献。拟议的项目还将为NIH促进基本创造性发现的任务做出重大贡献，通过提供一种新的策略来研究癌症生物学中长期存在的癌前病区如何形成的问题。

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.