(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已经提供了一个发生在许多不同肿瘤中的突变目录， 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 也变得清楚，组织和细胞环境有助于很大的能力，突变，造成 癌症，因此在稳健且相关的模型系统中研究这些影响至关重要。尽管产生于 同一个器官，两种最常见的胰腺癌是不同的，发病率不同， 自然历史以及独特的突变模式。胰腺导管腺癌（PDAC）具有 KRAS癌基因中几乎渗透性的功能获得突变和TP 53中的功能丧失突变 肿瘤抑制基因由于这些是人类癌症中最常见的突变之一， 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（PanNET）， 在表观遗传调节因子MEN 1、DAXX和ATRX中经常发生功能缺失突变。以上这些都是 第一个被鉴定出在DAXX和ATRX中有突变的肿瘤，因此我们对这些突变如何发生的理解， 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蛋白发挥作用 变体H3.3，特异性地将H3.3装载到DNA的异染色质区域，包括端粒， 着丝粒这项建议旨在更好地了解生理后果和分子 DAXX损失的下游机制，有助于肿瘤发生，并解决挑衅 为什么内分泌胰腺的肿瘤发生与外分泌胰腺的肿瘤发生显著不同 胰腺使用我们最近在小鼠中开发的条件性Daxx等位基因，我们将使用全基因组ChIP- Daxx和H3.3的测序实验，以确定Daxx作为表观遗传调节因子的特定作用 在胰腺中。我们还将利用这个新的等位基因建立相关的Daxx突变小鼠肿瘤模型 泛网络。我们将确定Daxx丢失是否单独或与Men 1丢失（在一种疾病中同时发生的病变）合作， 人肿瘤的子集），可以促进肿瘤发生。此外，我们将进行CRISPR/Cas9筛查， 在体内识别新的协同病变和机制。由于PanNET非常罕见，具有强大而忠实的 模型对于理解疾病的发病机制和鉴定新的 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，以促进我们对胰腺癌分子机制的理解。 Daxx损失有助于PanNET的机制，并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.