(PQ4) Mutations in the histone chaperone DAXX drive pancreatic neuroendocrine tumors not ductal adenocarcinomas

项目摘要 虽然最近的肿瘤测序工作提供了一份发生在许多不同类型的 对于肿瘤类型，现在的挑战是了解哪些突变直接导致肿瘤发生。它有 同样清楚的是，组织和细胞环境对突变导致 癌症，因此有必要在稳健和相关的模型系统中研究这些影响。尽管产生了 同样的器官，两种最常见的胰腺癌是不同的，发病率和 自然历史，以及独特的突变模式。胰腺导管腺癌(PDAC)有 KRAS癌基因的近穿透性功能获得突变和TP53的功能丧失突变 肿瘤抑制基因。因为这些是人类癌症中最常见的突变之一，健壮的小鼠 已经为这种疾病建立了模型。另一方面，胰腺神经内分泌肿瘤(PanNETs)， 表观遗传调控基因MEN1、DAXX和ATRX经常发生功能缺失突变。这些都是 第一个被发现有DAXX和ATRX突变的肿瘤，因此我们对这些 突变对癌症的贡献是有限的。Daxx和ATRX相互作用并作为组蛋白的伴侣发挥作用 变异体H3.3，特异性地将H3.3装载到DNA的异染色区，包括端粒和 着丝粒。这一提议旨在更好地理解生理后果和分子水平 DAXX缺失下游促进肿瘤发生的机制和解决挑衅性 为什么内分泌胰腺的肿瘤发生与外分泌的肿瘤发生显著不同的问题 胰腺。利用我们最近在小鼠身上开发的条件Daxx等位基因，我们将使用全基因组芯片- Daxx和H3.3的测序实验确定Daxx作为表观遗传调控因子的具体作用 在胰腺里。我们还将利用这个新的等位基因来建立相关的Daxx突变的小鼠肿瘤模型 PanNETs。我们将确定Daxx Lost是单独发生，还是与MEN1 Lost(共同发生在 人类肿瘤的亚群)，可以促进肿瘤的发生。此外，我们将进行CRISPR/CAS9筛查以 在活体内识别新的协同损伤和机制。由于PanNET是罕见的，拥有强大和忠诚的 模型对于了解疾病的发病机制和发现新的 脆弱性和治疗目标。结合起来，这项工作旨在揭示潜在的细胞类型特异性 影响胰腺肿瘤发生的差异，以促进我们对分子的理解 Daxx丢失在PANETs中的作用机制和开发新的模型和试剂 未来的研究。

Project Summary While recent tumor sequencing efforts have provided a catalog of mutations that occur across many different tumor types, the challenge now is to understand which mutations directly contribute to tumorigenesis. It has also become clear that tissue and cellular context contribute a great deal to the ability of a mutation to cause cancer, making it essential to study these effects in robust and relevant model systems. Despite arising from the same organ, the two most frequent cancers of the pancreas are distinct, with different incidences and natural histories, as well as unique mutation patterns. Pancreatic ductal adenocarcinomas (PDACs) have nearly penetrant gain-of-function mutation in the KRAS oncogene, and loss-of-function mutations in the TP53 tumor suppressor gene. As these are amongst the most frequent mutations in human cancers, robust mouse models have been built for this disease. Pancreatic neuroendocrine tumors (PanNETs), on the other hand, have frequent loss of function mutations in the epigenetic regulators MEN1, DAXX and ATRX. These were the first tumors identified to have mutations in DAXX and ATRX, and as such our understanding of how these mutations contribute to cancer is limited. DAXX and ATRX interact and function as a chaperone for the histone variant H3.3, specifically loading H3.3 into heterochromatic regions of DNA, including telomeres and centromeres. This proposal aims to better understand the physiological consequences and molecular mechanism downstream of DAXX loss that contribute to tumorigenesis and to address the provocative question of why tumorigenesis in the endocrine pancreas is dramatically different than in the exocrine pancreas. Using our recently developed conditional Daxx allele in the mouse, we will use genome-wide ChIP- sequencing experiments for both Daxx and H3.3 to define the specific role of Daxx as an epigenetic regulator in the pancreas. We will also use this new allele to build a relevant mouse tumor model of Daxx mutant PanNETs. We will determine if Daxx loss alone, or in cooperation with Men1 loss (lesions that co-occur in a subset of human tumors), can promote tumorigenesis. Additionally, we will conduct a CRISPR/Cas9 screen to identify novel cooperating lesions and mechanisms in vivo. As PanNETs are rare, having a robust and faithful model become even more valuable for understanding the pathogenesis of the disease and to identify novel vulnerabilities and therapeutic targets. Combined, this work aims to uncover the potential cell-type specific differences that impact tumorigenesis in the pancreas to advance our understanding of the molecular mechanisms through which Daxx loss contributes to PanNETs and to develop novel models and reagents for future studies.