Investigations of menin function in Ewing sarcoma

项目概要 小儿癌症可被视为发育障碍，其中致癌驱动因素劫持正常 促进肿瘤发生的发育计划。支架蛋白 menin 对于正常的生命活动至关重要 在人类癌症中，可以作为肿瘤抑制基因或癌基因发挥作用，具体取决于 上下文。 menin 的多种功能与其在基因转录调节中的作用有关 与 MLL 组蛋白甲基转移酶以及其他上下文依赖性结合伙伴的相互作用。在 MLL 重排白血病 (MLLr)，蛋白质：menin 和 MLL 融合蛋白驱动之间的蛋白质相互作用 致癌转录程序的表观遗传激活。 MLLr 白血病对这些的严重依赖 相互作用代表了一种独特的治疗脆弱性和 menin:MLL 的小分子抑制剂 正在开发用于白血病定向治疗的相互作用。尤因肉瘤是间叶质肿瘤 推测的干细胞 (MSC) 起源，由 EWS/ETS 融合驱动，最常见的是 EWS/FLI1。 EWS/FLI1 通过劫持正常的 MSC 分化来启动肉瘤形成。重要的是，menin 在 早期间充质发育，有助于谱系定型和成骨细胞 差异化。我们已经证明，尤文肉瘤相对于 MSC 过度表达 menin，并且这种缺失 menin 的缺失导致致瘤性丧失。然而，menin 发挥其致癌作用的机制 对这些肿瘤细胞的影响仍不清楚。我们的初步数据确定了丝氨酸合成途径 （SSP）作为尤文肉瘤中 menin 的关键下游靶点。我们已经确认 SSP 是超 在尤文肉瘤中以 menin 依赖性方式激活，并且抑制 PHGDH（速率限制） SSP 中的酶，导致尤文肉瘤活力严重丧失，揭示了尤文肉瘤的关键依赖性 路径上的肉瘤。我们的数据还表明 EWS/FLI1 本身有助于激活 PHGDH 和 SSP，并且 EWS/FLI1 诱导靶标子集的转录依赖于 menin。这些数据 共同支持这样的假设：menin 在尤文肉瘤中充当致癌中心。在这个 提案中，我们将研究 menin 功能的机制并测试创新假设： EWS/FLI1 通过劫持 menin 依赖性转录调节促进肿瘤发生。在目标 1 中，我们将 确定 menin 激活 SSP 的机制，并将阐明 EWS/FLI1 在此过程中的作用 过程。在目标 2 中，我们将定义有助于肿瘤维持的 SSP 关键代谢物，以便 以确定为什么尤文肉瘤细胞如此依赖于该途径。目标 3 将定义全基因组范围 MSC 和尤文肉瘤中 menin 的转录靶标以及 EWS/FLI1 如何影响它们。的 拟议的研究将增进尤文肉瘤生物学基础的基础知识和 发现 EWS/FLI1 如何劫持正常的男性生理学以促进肿瘤发生。这些见解的目标是 将为开发针对尤文肉瘤的新型、毒性较小、针对menin的疗法提供机会。

PROJECT SUMMARY Pediatric cancers can be considered developmental disorders in which oncogenic drivers hijack normal developmental programs to promote tumorigenesis. The scaffolding protein menin is essential for normal development and, in human cancer, can function as a tumor suppressor or an oncogene, depending on context. The diverse functions of menin are linked to its role in regulation of gene transcription via its interaction with MLL histone methyltransferases, as well as with other context-dependent binding partners. In MLL-rearranged leukemia (MLLr), protein:protein interactions between menin and MLL-fusion proteins drive epigenetic activation of oncogenic transcription programs. A critical dependence of MLLr leukemia on these interactions represents a unique therapeutic vulnerability and small molecule inhibitors of the menin:MLL interaction are being developed for leukemia-directed therapy. Ewing sarcomas are mesenchymal tumors of presumed stem cell (MSC) origin that are driven by EWS/ETS fusions, most commonly EWS/FLI1. EWS/FLI1 initiates sarcomagenesis by hijacking normal MSC differentiation. Importantly, menin plays an essential role in early mesenchymal development, where it contributes to both lineage commitment and osteoblastic differentiation. We have shown that menin is over-expressed by Ewing sarcoma relative to MSC and that loss of menin results in loss of tumorigenicity. However, the mechanisms by which menin exerts its oncogenic effects in these tumor cells remain unknown. Our preliminary data identified the serine synthesis pathway (SSP) as a key downstream target of menin in Ewing sarcoma. We have confirmed that the SSP is hyper- activated in Ewing sarcoma in a menin-dependent manner, and that inhibition of PHGDH, the rate limiting enzyme in the SSP, results in profound loss of Ewing sarcoma viability, revealing a key dependence of Ewing sarcoma on the pathway. Our data also suggest that EWS/FLI1 itself contributes to activation of PHGDH and the SSP, and that transcription of a subset of EWS/FLI1-induced targets is dependent on menin. These data collectively support the hypothesis that menin functions as an oncogenic hub in Ewing sarcoma. In this proposal, we will investigate the mechanisms of menin function and test the innovative hypothesis that EWS/FLI1 promotes tumorigenesis by hijacking menin-dependent transcriptional regulation. In Aim 1 we will determine the mechanism by which menin activates the SSP and will elucidate the role of EWS/FLI1 in this process. In Aim 2 we will define the key metabolites of the SSP that contribute to tumor maintenance in order to determine why Ewing sarcoma cells are so dependent on this pathway. In Aim 3 will define genome-wide transcriptional targets of menin in MSC and Ewing sarcoma and how they are impacted by EWS/FLI1. The proposed studies will advance fundamental knowledge of the biologic underpinnings of Ewing sarcoma and discover how EWS/FLI1 hijacks normal menin physiology to promote oncogenesis. It is goal that these insights will provide opportunities to develop novel, and less toxic, menin-directed therapies for Ewing sarcoma.