Mechanisms of aggressive Rhabdomyosarcoma.

摘要 横纹肌肉瘤(RMS)是美国最常见的儿童软组织肉瘤 显示发育早期停止的骨骼肌的特征。咄咄逼人的MYOD1L122R 突变的纺锤体/硬化性RMS亚型占儿科诊断的10%，并具有极差的 预后，即使通过手术、放疗和化疗等多种方式进行治疗。L122R 突变被预测为调节肌源性分化1(MYOD1)的DNA结合特异性 转录因子，并调节未知的转录基因程序，以提高攻击性和 治疗耐药。到目前为止，对MYOD1L122R如何影响MYOD1L122R发病的详细分子理解 RMS，其进展和驱动治疗耐药尚不清楚。没有细胞或分子机制的研究 MYOD1L122R在RMS中的作用已有报道，但尚无易于处理的转基因动物模型 目前也不清楚MYOD1L122R是否是人类肿瘤持续生长所必需的，或者它是否是一种 疾病侵袭性、治疗抵抗或癌症干细胞(CSCs)的修饰物。长期目标和 我们的研究目的是确定MYOD1L122R突变的RMS的新的分子机制和药物靶点 调节攻击性、治疗抵抗力和CSCs。我们的中心假设是MYOD1L122R是一颗近地天体- 一种形态转录因子，调节肿瘤维持所需的途径和产生 治疗耐药的CSCs。我们方法的理由和可行性在于我们小组最近发现了 MYOD1L122R突变体RMS中分子上不同的CSCs，强有力的数据表明CSCs的路径和数量 在同基因敲入和多西环素诱导的MYOD1L122R RMS人类细胞模型中增加，以及 MYOD1L122R诱导的RMS斑马鱼模型的建立 正在繁殖的细胞。AIM 1将评估MYOD1L122R在促进肿瘤发生、生长、CSCs和 治疗抵抗。Aim 1a将创新MYOD1L122R突变的RMS斑马鱼模型，测试 假设MYOD1L122R本身不是致癌的，但只有在与MYOD1L122R复合时才会导致攻击性增强 其他致癌因素包括激活RAS和PIK3CA的突变。我们还假设 MYOD1L122R的部分作用是通过增加肿瘤增殖细胞的总比例来发挥作用。目标1b将延长这些 人类RMS的发现，验证了MYOD1L122R是肿瘤持续维持所必需的假设 并调节细胞状态，包括产生耐药的CSCs。AIM 2将揭开MYOD1L122R RMS中受调控的转录靶点、途径和机制，验证MYOD1L122R的假设 改变DNA结合位点的特异性并转录调节一组新的基因以促进 RMS攻击性、治疗抵抗和癌症干细胞命运。这部作品将会有一个积极的翻译 通过定义杀死MYOD1L122R突变RMS的新途径产生的影响，包括那些针对治疗耐药的途径 CSCs，并确定可能在RMS亚型之间共享的潜在治疗靶点。

ABSTRACT Rhabdomyosarcoma (RMS) is the most common pediatric soft tissue sarcoma in the United States and displays features of skeletal muscle arrested at early stages of development. The aggressive MYOD1L122R mutated spindle/sclerosing RMS subtype accounts for 10% of pediatric diagnoses and have an extremely poor prognosis, even despite multi-modal treatment with surgery, radiation, and chemotherapy. The L122R mutation is predicted to modulate the DNA binding specificity of the Myogenic Differentiation 1 (MYOD1) transcription factor and regulates as of yet unknown transcriptional gene programs to elevate aggression and treatment resistance. To date, a detailed molecular understanding of how MYOD1L122R affects the genesis of RMS, its progression and drives therapy resistance is unknown. No cellular or molecular mechanistic studies of MYOD1L122R in RMS have been reported, no tractable genetically-engineered animal models have been developed, nor is it known if MYOD1L122R is required for continued human tumor growth or if it is rather a modifier of disease aggression, therapy resistance, or cancer stem cells (CSCs). The long-term goal and objective of our studies is to identify new molecular mechanisms and drug targets in MYOD1L122R mutant RMS that regulate aggression, therapy resistance, and CSCs. Our central hypothesis is that MYOD1L122R is a neo- morphic transcription factor that regulates pathways required for tumor maintenance and the production of therapy-resistant CSCs. The rationale and feasibility of our approach lies in our group’s recent discovery of molecularly distinct CSCs in MYOD1L122R mutant RMS, robust data showing that CSCs pathways and numbers are increased in isogenic knock-in and doxycycline-inducible MYOD1L122R RMS human cell models, and development of a new zebrafish model of MYOD1L122R-induced RMS that has elevated numbers of tumor- propagating cells. Aim 1 will assess roles for MYOD1L122R in enhancing tumor onset, growth, CSCs, and therapy resistance. Aim 1a will innovate new MYOD1L122R mutant RMS zebrafish models, testing the hypothesis that MYOD1L122R is itself not oncogenic, but drives elevated aggression only when complexed with other oncogenic drivers including activating mutations in RAS and PIK3CA. We also hypothesize that MYOD1L122R acts in part by increasing the overall fraction of tumor-propagating cells. Aim 1b will extend these findings to human RMS, testing the hypothesis that MYOD1L122R is required for continued tumor maintenance and regulates cell states including the production of therapy-resistance CSCs. Aim 2 will uncover MYOD1L122R regulated transcriptional targets, pathways, and mechanisms in RMS, testing the hypothesis that MYOD1L122R alters the DNA binding site specificity and transcriptionally regulates a novel set of genes to promote elevated RMS aggression, therapy resistance, and cancer stem cell fate. This work will have a positive translational impact by defining new pathways to kill MYOD1L122R mutant RMS, including those that target therapy-resistant CSCs, and identifying potential therapeutic targets that are likely shared across RMS subtypes.