Mediators Of Arrested Differentiation In Pediatric Rhabdomyosarcoma

项目总结/摘要 横纹肌肉瘤是儿童最常见的软组织肉瘤。尽管有严格的临床试验 高风险RMS儿童的生存率在过去的三十年里没有改变。那些活下来的孩子 经常由于积极的治疗而遭受终身的毁容。RMS细分为两个 主要类别，融合阳性（FP-RMS）和融合阴性（FN-RMS），基于是否存在 PAX 3-FOXO 1或PAX 7-FOXO 1基因融合体。RMS类似于发育中的骨骼肌， 推测其来源于基因受损的骨骼肌祖细胞。尽管表达了 骨骼肌主调节蛋白MYOD 1和肌生成素，RMS肿瘤和细胞不能终末 这表明RMS是肌肉发育的停滞状态。分子基础 RMS中的分化停滞和驱动分化的治疗方法是未知的。长期目标是 阐明确定RMS发育停滞的基础的机制，并设计新颖的，有针对性的 RMS的药物治疗最近的一项研究发现，PTEN启动子高甲基化， 在90%以上的FN-RMS肿瘤中表达。在RMS基因工程小鼠模型（GEMM）中， 肿瘤潜伏期缩短，肿瘤转移率增加， 类似于儿童的胚胎RMS。PTEN缺失并没有增加mTOR信号传导，而是局限于 核和增加PAX 7表达和异位DBX 1表达。DBX 1是一种神经元特异性 在另一个实施方案中，所述转录抑制因子是跨人FN-RMS和FP-RMS两者异位表达的转录抑制因子。强制DBX 1 表达阻断培养的成肌细胞中的肌原性分化。中心假设是PTEN-PAX 7- DBX 1轴在RMS的发育停滞中提供了一个关键节点，DBX 1作为转录因子发挥作用， 阻遏物阻断RMS的分化。本提案的目的是利用我们强大的RMS鼠标 模型结合体外测定来确定PTEN和DBX 1在RMS中的作用。为了实现这一目标， 我们提出以下具体目的：1）确定PTEN缺失在RMS中的作用。2)确定机制 DBX 1调节的RMS。3)确定DBX 1在阻断RMS肌源性分化中的作用。拟议 研究利用一种简单、快速的RMS GEMM来剖析有助于体内RMS生物学的基因， 深入了解维持RMS分化停滞状态的机制。我们会用得失- 在体内和体外的功能方法来剖析AKT 1，mTORC 1，PAX 7和DBX 1的作用， 调节PTEN缺失表型。胚胎性肿瘤的分化治疗已被证明是有效的 用13-顺式维甲酸治疗神经母细胞瘤和全反式维甲酸治疗急性早幼粒细胞性白血病 白血病RMS的分子和发育解剖将揭示新的弱点，以开发新的 促进RMS终末分化的治疗方法。这些研究将产生广泛的影响，因为DBX 1是高度 在儿科脑肿瘤中表达，并且PTEN扰动涉及许多癌症。

Project Summary/Abstract Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in childhood. Despite rigorous clinical trials the survival for children with high-risk RMS has not changed for three decades. The children that do survive often suffer from life-long disfigurements as a result of the aggressive treatment. RMS is subdivided into two major classes, fusion-positive (FP-RMS) and fusion-negative (FN-RMS), based on the presence or absence of the PAX3-FOXO1 or PAX7-FOXO1 gene fusions. RMS resembles developing skeletal muscle and has been speculated to originate from genetically compromised skeletal muscle progenitors. Despite the expression of skeletal muscle master regulator proteins MYOD1 and MYOGENIN, RMS tumors and cells fail to terminally differentiate, suggesting that RMS is an arrested state of muscle development. The molecular underpinnings of the differentiation arrest in RMS and therapeutics to drive differentiation are unknown. The long-term goal is to elucidate the mechanisms that determine the basis for developmental arrest in RMS and design novel, directed drug therapies for RMS. A study recently identified PTEN promoter hypermethylation with decrease PTEN expression in over 90% of FN-RMS tumors. In a RMS genetically engineered mouse model (GEMM), PTEN loss decreased tumor latency, increased tumor penetrance, and much less differentiated tumors more closely resembling the embryonal RMS in children. PTEN loss did not increase mTOR signaling but was localized in the nucleus and increased PAX7 expression and ectopic DBX1 expression. DBX1 is a neuronal specific transcriptional repressor that is ectopically expressed across both human FN-RMS and FP-RMS. Forced DBX1 expression blocks myogenic differentiation in cultured myoblasts. The central hypothesis is that the PTEN-PAX7- DBX1 axis provides a key node in the developmental arrest in RMS and that DBX1 functions as a transcriptional repressor blocking differentiation in RMS. The objective of this proposal is to leverage our robust RMS mouse models coupled with in vitro assays to define the role of PTEN and DBX1 in RMS. To accomplish this objective, we propose the following Specific Aims: 1) Define the role of PTEN loss in RMS. 2) Determine the mechanism of DBX1 regulation in RMS. 3) Identify role of DBX1 in blocking myogenic differentiation in RMS. The proposed studies leverage a simple, rapid RMS GEMM to dissect genes that contribute to RMS biology in vivo and provide insight into the mechanism maintaining an arrested state of differentiation in RMS. We will use gain- and loss- of-function approaches both in vivo and in vitro to dissect the roles of AKT1, mTORC1, PAX7 and DBX1 in modulation of the PTEN loss phenotype. Differentiation therapy of embryonal tumors has proven an efficacious venue for therapy with 13-cis-retinoic acid for neuroblastoma and all-trans-retinoic acid for acute promyelocytic leukemia. Molecular and developmental dissection of RMS will reveal new vulnerabilities to develop new therapeutics to drive terminal differentiation of RMS. These studies will have broad impact as DBX1 is highly expressed in pediatric brain tumors and PTEN perturbations are involved in many cancers.