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（ICCs）。大多数GIST含有激活KIT突变，这被认为是GIST发病机制的主要致癌驱动因素。伊马替尼是晚期gist的有效治疗方法。然而，耐药性不可避免地会发展，因此更好地了解GIST的发病机制和确定GIST管理的新治疗靶点是必要的。我们的初步研究表明，ETV1是一个ETS家族转录因子，与包括前列腺癌在内的其他恶性肿瘤的发病机制有关，是一个转录程序的主要调节剂，该转录程序是属于ICC-GIST谱系的细胞的特征，并且是其维持和生存所必需的。我们进一步表明，ETV1主要通过在基因组水平上结合其顺式调控区域/增强子来调控gist特征基因。此外，我们的研究表明，具有激活突变的KIT通过稳定ETV1蛋白水平，至少在一定程度上与ETV1在肿瘤发生中密切合作。我们的研究结果表明，ETV1可能定义了GIST中KIT驱动的肿瘤发生的最佳细胞环境，并提供了一个基本原理，解释了为什么具有生殖系激活KIT突变的患者和小鼠只在icc谱系中发生肿瘤，而不发生已知受KIT发育调节的其他细胞系，包括黑素细胞、生殖细胞和造血细胞。这些观察结果导致了以下具体目标：进一步表征胃肠道间质瘤细胞背景下ETV1转录调控的基因组和表观基因组方面，剖析KIT信号与ETV1转录程序的功能相互作用，并更严格地研究ETV1在胃肠道间质瘤发生和维持中的作用。目的是更好地了解GIST的发病机制，并确定新一代GIST靶向治疗的新策略。我建议对ETV1的增强子和启动子进行全基因组定位和组蛋白修饰，并结合ETV1转录组学研究，全面了解ETV1转录程序的基因组和表观基因组调控，从而奠定GIST肿瘤发生的细胞背景。其次，我建议定义参与调节ETV1蛋白稳定性的下游KIT途径；我还建议直接评估ETV1转录程序是否是激活KIT信号下游介导GIST肿瘤发生的关键途径，在伊马替尼拯救实验中使用抗降解的ETV1突变体。第三，我建议使用预先存在的GIST和ETV1敲除小鼠模型来检查ETV1对体内GIST启动和/或维持的要求。这些研究将全面了解由ETV1转录程序介导的GIST发病机制，并对其他依赖ETS转录因子的恶性肿瘤具有广泛的意义。同样重要的是，它将为伊马替尼耐药GIST和其他可能依赖etv1的恶性肿瘤提供一种新的治疗策略。该项目将在洛克菲勒大学的C. David Allis博士和MSKCC的Charles L. Sawyers博士的联合指导下进行，后者是世界知名的表观遗传学和转录调控专家，他最初开发了用于慢性骨髓性白血病治疗的伊马替尼，在细胞信号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，我将熟练掌握多个领域，运用多种技术解决ETV1在GIST发病机制中的作用。在这段时间结束后，我的目标是成为一名独立的医师-科学家，结合实验室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.