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干细胞生态位竞争调控中的作用的策略。完成本提案的目标将是我们开发和使用果蝇和小鼠野癌模型来确定早期癌症诊断和治疗靶点的长期目标的重要里程碑。野区癌化是许多上皮性癌症的一个特征，其中肿瘤起源于克隆相关的癌前野区，突变但组织学上正常的细胞。由于癌前野在肿瘤出现之前就形成了，并且通常在肿瘤切除后仍然存在，因此识别这些野的诊断和针对它们的治疗方法将具有巨大的临床效益。然而，尽管有超过50年的研究，癌前野形成的机制和突变类型仍然不清楚。我们的中心假设是，野区癌变始于获得肿瘤抑制突变的干细胞，并通过干细胞生态位占有的“超竞争”扩散到邻近的生态位。我们对果蝇卵巢上皮卵泡干细胞（epithelial follicle stem cell， FSC）维持的研究以及已发表的小鼠上皮肿瘤抑制表型的研究支持了这一模型。我们发现FSCs与邻近FSCs产生的细胞竞争生态位占用，我们已经确定了三种肿瘤抑制因子的突变，这些突变导致了过度竞争。小鼠和人类上皮细胞的同源突变导致易患癌症。因此，我们的假设解释了为什么大面积的组织可能具有单克隆起源，以及为什么这些大面积的组织特别容易发生癌症。然而，在我们能够实现产生野区癌变实验模型的目标之前，有必要(1)确定与人类癌症相关的体细胞突变，这些突变在果蝇FSC生态位中引起超竞争；(2)确定FSC超竞争突变是否在小鼠肠上皮中引起超竞争。为了实现第一个目标，我们将使用马赛克分析来测试67种人类肿瘤抑制因子的果蝇同源物对FSC超竞争表型的影响。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的固定等位基因结合，在成年小鼠中产生条件敲除，并测定肠上皮中干细胞的超竞争。该项目意义重大，因为它将为上皮干细胞竞争的研究建立新的模型，并将是开发野区癌变动物模型的关键的第一步。与以往的研究相比，这是一个创新之处，因为它专注于理解野肿瘤的保守机制，这将为合理选择候选分子或形态生物标志物以在人体组织样本上进行测试提供理论框架。

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.