Studies of the t(2;13) of alveolar rhabdomyosarcoma

描述(申请人提供)：肺泡型横纹肌肉瘤(ARMS)是一种以2；13或1；13染色体易位为特征的横纹肌肉系侵袭性儿童癌症。这些事件将PAX3或PAX7与FKHR并列，产生编码PAX3-FKHR或PAX7-FKHR融合产物的融合基因。野生型基因编码转录因子，融合产物将PAX3或PAX7 DNA结合域与FKHR激活域结合，产生有效的转录激活因子。虽然一些初步研究表明，这些融合蛋白可以诱导致癌效应，但最近的研究揭示了遗传和表型的复杂性，需要改进这些融合产物在手臂肿瘤发生中的作用的模型。对这些融合基因的基因转移研究证明了这些复杂性，这些基因在某些条件下表现出致癌行为，在其他条件下表现出生长抑制行为。此外，在PAX3/PAX7-FKHR DNA结合域中存在频繁的选择性剪接事件，产生功能不同的亚型的混合物。最后，手臂细胞中存在二次遗传变化，包括基因放大和小突变，这些变化可能与易位事件相互作用。为了解释这些发现，提出了一个假设，即这些融合蛋白的生长效应最初依赖于转录活性的水平，在低活性时以致癌作用为主，在高活性时以生长抑制为主。这些生长效应和额外的表型活动之间的最终平衡被认为受到其他因素的调节，包括功能上不同的异构体和次级遗传变化的混合。目前的提案将集中在PAX3-FKHR融合蛋白上，并将通过使用显示这一范围的生长效应的可诱导细胞培养系统来探索这些假说，以分析与致癌效应和生长抑制相关的功能需求和基因表达事件。细胞培养和体外系统将被用来评估两种PAX3-FKHR亚型之间的DNA结合活性、表型效应和下游表达事件的差异。最后，这些研究将调查放大的癌基因和其他遗传事件在改变融合蛋白的功能和下游效应中的作用。这些联合研究将允许全面评估PAX3-FKHR转录功能、靶基因表达、表型效应和协作事件之间的关系，从而更好地确定这些融合基因在手臂肿瘤发生中的作用。

DESCRIPTION (provided by applicant): Alveolar rhabdomyosarcoma (ARMS) is an aggressive pediatric cancer of the striated muscle lineage that is characterized by 2;13 or 1;13 chromosomal translocations. These events juxtapose PAX3 or PAX7 with FKHR to create fusion genes encoding PAX3-FKHR or PAX7-FKHR fusion products. The wild-type genes encode transcription factors, and the fusion products combine the PAX3 or PAX7 DNA binding domain and FKHR activation domain to create potent transcriptional activators. Though some initial studies indicated that these fusion proteins induce oncogenic effects, more recent studies have revealed genetic and phenotypic complexities that require refinement of the model for the role of these fusion products in ARMS tumorigenesis. These complexities are evidenced by gene transfer studies of these fusion genes that show oncogenic behavior in some conditions and growth suppressive behavior in other conditions. In addition, there are frequent alternative splicing events in the PAX3/PAX7-FKHR DNA binding domain that generate a mixture of functionally distinct isoforms. Finally, there are secondary genetic changes in ARMS cells, including gene amplification and small mutations, which may interact with the translocation events. To explain these findings, the hypothesis is proposed that the growth effects of these fusion proteins are initially dependent on the level of transcriptional activity, with oncogenic effects predominating at lower activity and growth suppression predominating at higher activity. The final balance between these growth effects as well as additional phenotypic activities is postulated to be modulated by other factors, including the mixture of functionally distinct isoforms and secondary genetic changes. The current proposal will focus on the PAX3-FKHR fusion protein and will explore these hypotheses by using inducible cell culture systems that display this range of growth effects to analyze the functional requirements and gene expression events associated with oncogenic effects and growth suppression. Cell culture and in vitro systems will be used to assess differences in DNA binding activity, phenotypic effects, and downstream expression events between the two PAX3-FKHR isoforms. Finally, these studies will investigate the role of amplified oncogenes and other genetic events in modifying the function and downstream effects of the fusion protein. These combined studies will permit a comprehensive evaluation of the relationship between PAX3-FKHR transcriptional function, target gene expression, phenotypic effects, and collaborating events, and will thereby better define the role of these fusion genes in ARMS tumorigenesis.