Molecular Modeling of Pediatric Skeletal Muscle Tumors

摘要 横纹肌肉瘤（RMS）是一种异质性的癌症集合， 骨骼肌的分化。虽然RMS占儿童恶性实体瘤的8%，但它是一种恶性肿瘤。 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 RMS分为胚胎型（eRMS）和腺泡型（aRMS）。高风险患者的5年生存率为30%， 对于肿瘤表达PAX 3-FKHR融合基因的儿童，结果非常差;当转移时， 5-年生存率<8%。这种标志性的遗传变化仅在aRMS中发现，并被认为是肿瘤特异性的。 癌基因，但没有分子靶向治疗。为了弥补RMS知识方面的差距，我们 他为这种疾病创造了一种新的模型，该模型基于原代人类骨骼肌细胞向其 致瘤对应物，使用一组定义的遗传变化。使用这个模型，我们发现人类 当测试为 免疫缺陷小鼠中的异种移植物。已经确定骨骼肌来源的原代人类细胞 可以引起RMS，我们研究了在其中表达PAX 3-FKHR的影响，并发现了两个 可能是其致癌行为的基础。首先，当PAX 3-FKHR稳定表达为一种 早期的遗传变化，它使绕过衰老检查点，并作为一个启动致癌 骨骼肌肿瘤的发展。第二，当PAX 3-FKHR稳定表达为晚期细胞时， 基因改变，它缩短了体内肿瘤形成的潜伏期，从11周到2周，可能是通过 Ras途径的激活，因为在对照实验中，PAX 3-FKHR可以在功能上替代Ras途径。 RAS癌基因。 在该提案中，我们希望了解PAX 3-FKHR如何能够绕过衰老， 检查点，以及它如何加速先前转化细胞的肿瘤发生。为了实现这一目标，我们将 (1)检查PAX 3-FKHR下游的候选蛋白质在克服 衰老检查点，使用功能获得和功能丧失方法，和（2）检查 加速肿瘤细胞的生长，以增强生长信号传导、凋亡和/或血管生成的自给自足，和 Ras通路在PAX 3-FKHR增强的肿瘤发生中的作用。完成这些 aims将为这种儿科恶性肿瘤的发生提供深入的了解，并为治疗提供新的治疗靶点。 study.此外，这种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.