Molecular Modeling of Pediatric Skeletal Muscle Tumors

摘要 横纹肌肉瘤(RMS)是一种表现不同程度的肿瘤的异质性集合 骨骼肌分化的特征。虽然占儿童恶性实体肿瘤的8%，但RMS是 14岁以下儿童最常见的软组织肉瘤。两种主要的组织学亚型 胚胎型(ERMS)和肺泡型(ARM)。高危患者的5年存活率为30%， 对于肿瘤表达PAX3-FKHR融合基因的儿童来说，预后非常差；当转移时，他们的 5年生存率为8%。这种标志性的基因变化只在手臂上发现，并被认为是肿瘤特有的 癌基因，但没有分子靶向治疗。为了解决RMS知识方面的差距，我们有 创造了一种治疗这种疾病的新模型，这种模型是基于人类骨骼肌原代细胞转化为 致癌的对应物，使用一组定义的基因变化。使用这个模型，我们发现人类 骨骼肌成肌细胞可以转化为产生肿瘤的细胞，当测试为 免疫缺陷小鼠的异种移植。已经确定了起源于骨骼肌的原代人类细胞 可以引起RMS，我们研究了在它们中表达PAX3-FKHR的反应，发现了两个 表型可能是其致癌行为的基础。首先，当PAX3-FKHR稳定表达为 早期基因改变，使其能够绕过衰老检查点，并作为启动致癌 因骨骼肌肿瘤的发展而受到打击。第二，当PAX3-FKHR稳定表达为晚期 基因改变，它将体内肿瘤形成的潜伏期从11周缩短到2周，可能是通过 激活RAS通路，因为在对照实验中，PAX3-FKHR可以在功能上取代 RAS癌基因。 在这个方案中，我们希望了解PAX3-FKHR如何使衰老成为可能 检查点，以及它如何加速先前转化的细胞中的肿瘤形成。为了实现这一目标，我们将 (1)研究PAX3-FKHR下游的候选蛋白质在克服 衰老检查点，使用功能增益和功能损失方法，以及(2)检查 加速肿瘤细胞在生长信号、凋亡和/或血管生成方面增强自给自足，以及 RAS通路在PAX3-FKHR增强的肿瘤发生中的作用。实现这些目标 AIMS将提供对这种儿童恶性肿瘤的起源的洞察，并提供新的治疗靶点 学习。此外，这一基因定义的模型将作为系统研究的模板。 其他人类肉瘤。

ABSTRACT Rhabdomyosarcoma (RMS) is a heterogeneous collection of cancers demonstrating varying degrees of skeletal muscle differentiation. Although accounting for ~8% of pediatric malignant solid tumors, RMS is the most common soft tissue sarcoma in children younger than 14 years. The two major histologic subtypes of RMS are embryonal (eRMS) and alveolar (aRMS). High risk patients have a 5-year survival of 30%, and outcome is very poor for children whose tumors express the PAX3-FKHR fusion gene; when metastatic, their 5-year survival is <8%. This signature genetic change is found only in aRMS and considered a tumor-specific oncogene, but has no molecularly targeted treatment. To address gaps in knowledge of RMS, we have created a new model for this disease based on the conversion of primary human skeletal muscle cells to their tumorigenic counterpart, using a defined set of genetic changes. Using this model, we found that human skeletal muscle myoblasts may be converted to cells that generate tumors mimicking RMS when tested as xenografts in immunodeficient mice. Having established that primary human cells of skeletal muscle origin can give rise to RMS, we studied the repercussions of expressing PAX3-FKHR in them, and discovered two phenotypes that may underlie its oncogenic behavior. First, when PAX3-FKHR was stably expressed as an early genetic change, it enabled bypass of the senescence checkpoint and served as an initiating oncogenic hit for the development of skeletal muscle tumors. Second, when PAX3-FKHR was stably expressed as a late genetic change, it shortened the latency of in vivo tumor formation from 11 to 2 weeks, possibly through activation of the Ras pathway, since in control experiments PAX3-FKHR could functionally substitute for the RAS oncogene. In this proposal, we wish to understand how PAX3-FKHR enables bypass of the senescence checkpoint, and how it accelerates tumorigenesis in previously transformed cells. To accomplish this, we will (1) examine candidate proteins that are downstream of PAX3-FKHR for their role in overcoming the senescence checkpoint, using both gain-of-function and loss-of-function approaches, and (2) examine the accelerated tumor cells for enhanced self-sufficiency in growth signaling, apoptosis, and/or angiogenesis, and the role of the Ras pathway in this PAX3-FKHR-augmented tumorigenesis. The accomplishment of these aims will provide insight into the genesis of this pediatric malignancy, and provide new therapeutic targets for study. In addition, this genetically defined model will serve as a template for the systematic investigation of other human sarcomas.