Regulation and function of HOX genes in Ewing sarcoma pathogenesis

项目摘要 正常发育程序的劫持是肿瘤发生和表观遗传的共同机制 发育转录程序的失调是大多数（如果不是全部）儿科疾病发生的核心。 癌的尤因肉瘤，侵袭性骨和软组织肿瘤，主要发生在青春期， 仍然与高死亡率相关，因此需要新的治疗方法。尤因 肉瘤的特征在于存在特异性驱动融合癌基因， EWS/FLI 1，它们可能的细胞来源是间充质干/祖细胞（MSC）。EWS/FLI 1启动 通过诱导广泛的转录调节的破坏，作为改变的结果， 将染色质重塑物募集到靶基因增强子和启动子。我们已经报道过， HOXD基因，特别是HOXD 13，在尤文肉瘤中异常过表达， HOXD基因有助于维持肿瘤发生表型。我们的初步研究表明， EWS/FLI 1可以以细胞环境依赖的方式诱导HOXD 13的表达，并且这种激活是细胞内的一个重要因素。 由发育增强子的异常激活介导，所述发育增强子在其他情况下仅在非常离散的 时空发展窗口此外，染色质免疫沉淀（ChIP）研究 证明在EWS/FLI 1+细胞中，HOXD 13启动子优先富集MLL-1。 依赖性活化组蛋白修饰H3 K4 me 3，并与MLL和menin蛋白结合。值得注意的是， 尤文肉瘤细胞暴露于MLL的新型小分子抑制剂：menin相互作用，目前 在MLL融合阳性白血病的临床前开发中，导致致瘤性的显著丧失， 伴随后HOXD基因表达缺失。因此，这些研究表明，像ML融合一样， 阳性白血病，尤文肉瘤的致癌表型的维持主要依赖于 MLL：发育HOX基因的menin依赖性激活。在本提案中，我们将检验假设 HOXD 13在尤文肉瘤中起着一种专性协同癌基因的作用， 持续的表达呈现出以前未被认识到的肿瘤特异性脆弱性， 治疗性剥削In Aim 1将使用创新的Bru-seq技术和功能验证研究， 定义促进致瘤性的HOXD 13的下游转录靶点。在目标2中，我们将使用 靶向ChIP测定和染色质构象研究，以确定EWS/FLI 1如何导致表观遗传 HOXD 13的激活。在目标3中，我们将测试MI-503的治疗潜力，MI-503是一种小分子抑制剂， MLL：menin蛋白：蛋白相互作用，体内肿瘤模型。这些研究将共同阐明 HOXD 13对尤文肉瘤发病机制的贡献，并测试一类新的表观遗传 尤文肉瘤靶向治疗的修饰剂。

PROJECT SUMMARY Hijacking of normal developmental programs is a common mechanism of tumorigenesis and epigenetic deregulation of developmental transcription programs is central to the genesis of most, if not all, pediatric cancers. Ewing sarcomas, aggressive bone and soft tissue tumors that predominately arise in adolescence, continue to be associated with high rates of mortality and novel approaches to therapy are needed. Ewing sarcomas are characterized by the presence of pathognomonic driver fusion oncogenes, most commonly EWS/FLI1, and their likely cellular origin is mesenchymal stem/progenitor cells (MSC). EWS/FLI1 initiates tumorigenesis by inducing widespread disruption of transcriptional regulation as a consequence of altered recruitment of chromatin remodelers to target gene enhancers and promoters. We have reported that posterior HOXD genes, in particular HOXD13, are aberrantly over-expressed by Ewing sarcoma and that posterior HOXD genes contribute to maintenance of the tumorigenic phenotype. Our preliminary studies suggest that EWS/FLI1 can induce expression of HOXD13, in a cell context dependent fashion, and that this activation is mediated by aberrant activation of developmental enhancers that are otherwise active in only very discrete spatiotemporal developmental windows. In addition, chromatin immunoprecipitation (ChIP) studies have demonstrated that in EWS/FLI1+ cells the HOXD13 promoter is preferentially enriched with the MLL- dependent activating histone modification H3K4me3 and bound by both MLL and menin proteins. Significantly, exposure of Ewing sarcoma cells to novel small molecule inhibitors of MLL:menin interaction, that are currently in preclinical development for MLL-fusion positive leukemias, leads to a dramatic loss tumorigenicity and concomitant loss posterior HOXD gene expression. Thus, these studies demonstrate that that, like MLL-fusion positive leukemias, maintenance of the oncogenic phenotype of Ewing sarcoma is critically dependent on MLL:menin-dependent activation of developmental HOX genes. In this proposal, we will test the hypothesis that HOXD13 functions an obligate cooperative oncogene in Ewing sarcoma and that dependency on its continued expression presents a previously unrecognized tumor-specific vulnerability that can be therapeutically exploited. In Aim 1 will use innovative Bru-seq technologies and functional validation studies to define the downstream transcriptional targets of HOXD13 that promote tumorigenicity. In Aim 2 we will use targeted ChIP assays and chromatin conformation studies to determine how EWS/FLI1 leads to epigenetic activation of HOXD13. In Aim 3 we will test the therapeutic potential of MI-503, a small molecule inhibitor of MLL:menin protein:protein interaction, in in vivo tumor models. These studies will together elucidate the contribution of HOXD13 to Ewing sarcoma pathogenesis and test the potential of a new class of epigenetic modifying agents for Ewing sarcoma-targeted therapies.