Deregulation of Ras Signaling in MLL-Induced Leukemia

描述(由申请人提供)：这项为期5年的计划的目标是为申请人提供一个综合的研究、培训和指导计划，以确保她成功地发展为一名独立的内科科学家。我们建议研究混合谱系白血病(MLL)癌蛋白的一个子集的转化机制和建立模型系统，这些蛋白可能具有双重作用，同时激活RAS信号和MLL转录途径。组蛋白甲基转移酶MLL是胚胎造血所必需的转录调节因子，在婴儿和继发性白血病中经常与多种配对蛋白融合。MLL融合蛋白的转化能力被认为是由融合伙伴赋予的异常转录效应属性引起的，但确切的机制尚不清楚。我们已经确定MLL融合伙伴AF6的RAS关联1结构域对于激活MLL的致癌特性至关重要，将MLL诱导的白血病发生与RAS联系起来。最近发现，由于与MLL的融合，细胞质中的EEN及其相互作用伙伴EEN结合蛋白(EBP)被绑架到细胞核。因此，EBP不再对RAS途径发挥抑制作用。同样，RASGAP与MLL的融合会导致RASGAP在细胞核内的隔离，并干扰其抑制RAS的能力。我们推测MLL-AF6、MLL-EEN和MLL-RASGAP的转化部分是通过激活RAS介导的，抑制RAS通路是治疗这些MLL融合蛋白诱导的白血病的合适途径。为了验证这一假设，我们提出了以下具体目标。1.研究AF6、RASGAP和EEN融合激活MLL致癌潜能的分子机制。2.评估各自MLL融合蛋白对RAS途径的潜在调节作用，并研究抑制RAS途径对其体外转化能力的影响。3a)用转导MLL融合蛋白的人脐血细胞建立MLL-AF6、MLL-EEN和MLL-RASGAP诱导的小鼠白血病异种移植模型。3b)评价RAS途径抑制剂对MLL-AF6、MLL-EEN和MLL-RASGAP诱导的白血病异种移植模型的疗效。这些研究将有助于更好地理解MLL融合蛋白亚群介导的白血病发生的分子机制，并可能促进新型靶向治疗的开发和测试。

DESCRIPTION (provided by applicant): The objective of this 5-year proposal is to provide the applicant with an integrated research training and mentoring program that will ensure her successful development as an independent physician scientist. We propose to investigate the mechanisms and develop model systems of transformation by a subset of mixed lineage leukemia (MLL) oncoproteins that may share dual roles to simultaneously activate Ras signaling and MLL transcriptional pathways. The histone methyltransferase MLL is a transcriptional regulator essential for embryonal hematopoiesis, and is frequently fused to various partner proteins in infant and secondary leukemia. The transforming ability of MLL fusion proteins is thought to be caused by aberrant transcriptional effector properties conferred by the fusion partner, but the exact mechanisms are poorly understood. We have identified the Ras association 1 domain of the MLL fusion partner AF6 as critical for activation of the oncogenic properties of MLL linking MLL-induced leukemogenesis to Ras. Also, it was recently found that due to fusion with MLL, cytoplasmic EEN and its interaction partner EEN binding protein (EBP) are abducted to the nucleus. As a result EBP no longer exerts its inhibitory function on the Ras pathway. Similarly, fusion of RASGAP to MLL results in sequestration of RASGAP in the nucleus and interferes with its ability to inhibit Ras. We hypothesize that transformation by MLL-AF6, MLL-EEN and MLL-RASGAP is in part mediated by activation of Ras and that inhibition of the Ras pathway is a suitable treatment approach for leukemias induced by these MLL-fusion proteins. To test this hypothesis, we propose the following specific aims. 1. Investigate the molecular mechanisms by which fusion with AF6, RASGAP and EEN activate the oncogenic potential of MLL. 2. Assess potential deregulation of the Ras pathway by the respective MLL fusion protein and investigate the effect of Ras pathway inhibition on their transforming ability in vitro. 3a) Establish a murine xenograft of MLL-AF6, MLL-EEN and MLL-RASGAP-induced leukemia using human cord blood cells transduced with the respective MLL fusion protein. 3b) Assess the efficacy of Ras-pathway inhibitors in the xenograft model for treatment of leukemia induced by MLL-AF6, MLL-EEN and MLL-RASGAP. These studies will lead to a better understanding of the molecular mechanisms of leukemogenesis mediated by a subset of MLL fusion proteins and may facilitate the development and testing of novel targeted therapies.