Molecular Pathogenic Mechanism of Rhabdomyosarcoma

PAX 3-FKHR融合蛋白存在于大多数与侵袭性增加和预后不良相关的肺泡型横纹肌肉瘤中。为了更好地了解PAX 3-FKHR的分子发病机制，我们在腺泡横纹肌肉瘤中首次进行了PAX 3-FKHR结合位点和相关靶基因的无偏倚全基因组鉴定。数据显示PAX 3-FKHR在MYF 5和MYOD增强子处与PAX 3结合相同的位点。全基因组分析显示PAX 3-FKHR位点（a）大多位于转录起始位点的远端，（B）保守，（c）富含PAX 3基序，（d）与PAX 3-FKHR阳性横纹肌肉瘤细胞和肿瘤中过表达的基因密切相关。在我们的数据集中几乎没有PAX 3-FKHR在启动子序列处结合的证据。全基因组分析进一步说明了PAX 3和E-box基序在这些结合位点之间的强烈关联，表明许多靶基因存在共同的共调控。我们还提供了第一个直接证据表明FGFR 4和IGF 1 R是PAX 3-FKHR的靶点。PAX 3-FKHR结合位点的图谱为理解PAX 3-FKHR的致病作用以及其分子靶标提供了框架，以允许系统地评价针对这种侵袭性横纹肌肉瘤的药剂（Cao et al.，2010年）。 我们目前的一些研究旨在通过分析PAX 3和PAX 3-FKHR的表观基因组修饰来了解其表达的转录调控。 此外，PAX 3-FKHR上调HDAC基因，我们已经证明这是横纹肌肉瘤细胞生存所必需的。 我们正在探索使用这些信息进行HDAC抑制剂对肿瘤的临床前评价的可能性，并鉴定预测对这类药物反应的生物标志物。

The PAX3-FKHR fusion protein is present in a majority of alveolar rhabdomyosarcomas associated with increased aggressiveness and poor prognosis. To better understand the molecular pathogenesis of PAX3-FKHR, we carried out the first, unbiased genome-wide identification of PAX3-FKHR binding sites and associated target genes in alveolar rhabdomyosarcoma. The data shows that PAX3-FKHR binds to the same sites as PAX3 at both MYF5 and MYOD enhancers. The genome-wide analysis reveals that the PAX3-FKHR sites are (a) mostly distal to transcription start sites, (b) conserved, (c) enriched for PAX3 motifs, and (d) strongly associated with genes overexpressed in PAX3-FKHRpositive rhabdomyosarcoma cells and tumors. There is little evidence in our data set for PAX3-FKHR binding at the promoter sequences. The genome-wide analysis further illustrates a strong association between PAX3 and E-box motifs in these binding sites, suggestive of a common coregulation for many target genes. We also provide the first direct evidence that FGFR4 and IGF1R are the targets for PAX3-FKHR. The map of PAX3-FKHR binding sites provides a framework for understanding the pathogenic roles of PAX3-FKHR, as well as its molecular targets to allow a systematic evaluation of agents against this aggressive rhabdomyosarcoma (Cao et al., 2010). Some of our current studies are aim to understand the transcription regulation of PAX3 and PAX3-FKHR expression via the analysis of their epigenomic modification. Also, PAX3-FKHR up-regulates a HDAC gene which we have showed to be essential for the survival of rhabdomyosarcoma cells. We are exploring the possibility of using this information for the preclinical evaluation of HDAC inhibitors against the tumor and the identification of biomarkers predictive of response to this class of agents.