Elucidating the roles of ETV1 in the pathogenesis of GIST

描述（由申请人提供）：胃肠道间质瘤（GIST）是最常见的人类肉瘤类型，起源于Cajal间质细胞（ICC）。大多数GIST携带激活KIT突变，这被认为是GIST发病机制中的主要致癌驱动。伊马替尼是治疗晚期胃肠道间质瘤的有效药物。然而，耐药性总是发展，这是当务之急，以更好地了解GIST的发病机制，并确定新的治疗目标，在GIST的管理。我们的初步研究表明，ETV 1，一个ETS家族的转录因子，涉及其他恶性肿瘤，包括前列腺癌的发病机制，是一个转录程序的主要调节器，其特征属于ICC-GIST谱系的细胞，并需要他们的维护和生存。我们进一步表明，ETV 1主要通过在基因组水平上与其顺式调节区/增强子结合来调节GIST签名基因。此外，我们的研究表明，具有激活突变的KIT至少部分地通过稳定ETV 1蛋白水平而与ETV 1在肿瘤发生中强烈合作。我们的研究结果表明，ETV 1可能定义了GIST中KIT驱动的肿瘤发生的最佳细胞环境，并为为什么具有生殖系激活KIT突变的患者和小鼠仅在ICC谱系中发生瘤形成，而不是已知由KIT发育调节的其他细胞谱系（包括黑素细胞、生殖细胞和造血细胞）的瘤形成提供了理论基础。这些观察结果导致了以下具体目的，以进一步表征ETV 1转录调控的基因组和表观基因组方面，其是GIST中细胞背景的基础，以剖析KIT信号传导与ETV 1转录程序的功能相互作用，并更严格地研究ETV 1在GIST起始和维持中的作用，目的是更好地了解GIST的发病机制，并确定新一代靶向治疗GIST管理的新策略。我建议进行ETV 1顺式组和增强子和启动子的组蛋白修饰特征的全基因组映射，并与ETV 1转录组研究相结合，以全面了解ETV 1转录程序的基因组和表观基因组调控，这些转录程序是GIST肿瘤发生的细胞背景。其次，我建议定义下游的KIT途径参与调控ETV 1蛋白的稳定性，我还建议直接评估是否ETV 1转录程序是关键的途径，介导下游激活KIT信号传导GIST肿瘤的发生，使用耐降解的ETV 1突变体伊马替尼拯救实验。第三，我建议使用预先存在的GIST和Etv 1基因敲除小鼠模型来检查ETV 1在体内启动和/或维持GIST的要求。这些研究将提供一个全面的了解GIST的发病机制介导的ETV 1的转录程序，并可能对其他ETS转录因子依赖性恶性肿瘤有广泛的影响。同样重要的是，它将为伊马替尼耐药GIST和可能的其他ETV 1依赖性恶性肿瘤提供一种新型治疗策略。该项目将在C博士的联合指导下进行。洛克菲勒大学的大卫阿利斯是表观遗传学和转录调控方面的世界知名专家，查尔斯L。MSKCC的Sawyers最初开发了伊马替尼用于慢性粒细胞白血病治疗，在细胞信号传导、小鼠建模和转化研究方面具有丰富的专业知识。在培训期间，我将使用不同的技术来解决ETV 1在GIST发病机制中的作用，从而在许多领域获得熟练程度。在这段时间结束时，我的目标是成为一个独立的医生，科学家结合基于实验室的研究和肉瘤患者的临床护理。

DESCRIPTION (provided by applicant): Gastrointestinal stromal tumor (GIST) is the most common type of human sarcomas, arising from the interstitial cells of Cajal (ICCs). The majority of GISTs harbor activating KIT mutations, which is thought to be the main oncogenic drive in GIST pathogenesis. Imatinib is an effective therapy in advanced GISTs. However, resistance invariably develops, and it is imperative to better understand the pathogenesis of GIST and to identify novel therapeutic targets in GIST management. Our preliminary studies show that ETV1, an ETS family transcription factor implicated in the pathogenesis of other malignancies including prostate cancer, is a master regulator of a transcriptional program that characterizes cells belonging to the ICC-GIST lineage and is required for their maintenance and survival. We further show that ETV1 regulates the GIST-signature genes primarily via binding to their cis-regulatory regions/enhancers at the genomic level. Additionally, our studies show that KIT with activating mutations strongly cooperates with ETV1 in tumorigenesis at least in part by stabilizing ETV1 protein levels. Our findings suggest that ETV1 may define the optimal cellular context for KIT- driven oncogenesis in GIST, and provide a rationale for why patients and mice with germ-line activating-KIT mutations exclusively develop neoplasia in the ICC-lineage, but not of other cell lineages that are known to be developmentally regulated by KIT, including melanocytes, germ cells, and hematopoietic cells. These observations led to the following specific aims to further characterize the genomic and epigenomic aspects of ETV1 transcriptional regulation that underlies the cellular context in GIST, to dissect the functional interplay of KIT signaling with ETV1 transcriptional program, and to more rigorously investigate the role of ETV1 in GIST initiation and maintenance, with the goal to better understand GIST pathogenesis and to identify novel strategies for next-generation of targeted therapy in GIST management. I propose to perform genome-wide mapping of ETV1 cistrome and histone modifications characteristic of enhancers and promoters, and integrate with ETV1 transcriptome studies to gain a comprehensive understanding of the genomic and epigenomic regulation of the ETV1 transcriptional program that underlie the cellular context in GIST oncogenesis. Second, I propose to define the downstream KIT pathway involved in regulation of ETV1 protein stability; I also propose to directly assess whether ETV1 transcriptional program is the critical pathway that mediates GIST oncogenesis downstream of activated KIT signaling, using degradation-resistant ETV1 mutants in imatinib rescuing experiments. Third, I propose to use pre-existing GIST and Etv1-knockout mouse models to examine the requirement of ETV1 for initiation and/or maintenance of GIST in vivo. These studies will provide a comprehensive understanding of the pathogenesis of GIST mediated by the ETV1 transcriptional program and can have broad implications on other ETS transcription factor dependent malignancies. As importantly, it will provide a novel therapeutic strategy in imatinib-resistant GIST and likely other ETV1-dependent malignancies. This project will be performed under the joint mentorship of Dr. C. David Allis at the Rockefeller University, a world renowned expert in epigenetics and regulation of transcription, and Dr. Charles L. Sawyers at MSKCC who initially developed imatinib for chronic myelogenous leukemia treatment with tremendous expertise in cell signaling mouse modeling and translational research. During the training period, I will gain proficiency in many areas using diverse techniques to tackle the role of ETV1 in GIST pathogenesis. At the end of the period, my goal is become an independent physician-scientist combining bench based research and clinical care of sarcoma patients.