Function of the PR domain of the MDSI-EVI1 in MLL fusion protein leukemogenesis

描述（由申请人提供）：混合系白血病（MLL）涉及超过70%的儿童AML和10%的成人AML。用化疗方案治疗报告了约25- 45%的婴儿存活率，其中移植前的高复发率是死亡率的主要原因。对于更有效的治疗，显然存在未满足的需求。来自临床患者样本以及来自小鼠模型的研究的最新证据表明，存在一个MLL融合蛋白（MFP）亚组，包括MLL-AF 9和MLL-ENL，其可以激活Mecom基因座，导致极差的预后。使用ME敲除小鼠模型，我们已经证明，在MFP诱导的小鼠白血病中，Mecom敲除导致48小时内活力完全丧失。此外，来自缺乏一种特定Mecom同种型（称为MDS 1-EVI 1或ME）的小鼠的骨髓对MFP引起的白血病转化具有完全抗性，但对其他致白血病癌蛋白没有抗性。重要的是，ME缺失不会导致正常细胞或生物体的死亡。与MFP的其他治疗干预途径相比，Mecom激活与MFP AML的极差预后相关的事实表明，我们靶向Mecom的策略具有显著的临床相关性。ME蛋白与其他Mecom同种型的不同之处在于它具有与组蛋白甲基转移酶（HMT）相关的PR结构域（或MEPRD），其在染色质修饰和基因表达调控中起关键作用。我们有证据表明MEPRD对MFP AML至关重要。在本申请中，我们提出测试ME蛋白，特别是MEPRD在MFP AML中起重要作用的假设。通过这些拟议的实验，我们希望探讨这些假设：ME构成的下游靶基因的MFP是必不可少的生存，PR域是至关重要的; ME功能在细胞核中作为一个holocomplex的一部分，并影响基因表达的变化的关键活性氧和细胞凋亡调节通过修改染色质。这些实验产生的结果将有助于为未来的小分子治疗开发奠定坚实的基础。

DESCRIPTION (provided by applicant): Mixed lineage leukemia (MLL) is involved over 70% of pediatric and 10% of adult AML. Treatment with chemotherapy regimens report infant survival rates of about 25-45%, with high relapse rates pre- transplantation being a major contributor of mortality. There is obviously unmet need for more effective therapy. Recent evidence from clinical patient samples as well as studies from mouse model suggest there exist a subgroup of MLL-fusion proteins (MFP), including MLL-AF9 and MLL-ENL, that can activate the Mecom locus, leading to extremely poor prognosis. Using ME knockout mouse model, we have demonstrated that in MFP-induced murine leukemias, knockout of Mecom results in complete loss of viability within 48 hrs. In addition, bone marrow from mice lacking one particular Mecom isoform (termed MDS1-EVI1, or ME) is completely resistant to leukemic transformation by MFPs but not other leukemogenic oncoproteins. Importantly, ME deletion does not result in lethality of normal cells or the organism. Compared to other avenues for therapeutic intervention for MFP, the fact that Mecom activation is linked to extreme poor prognosis in MFP AML, suggest our strategy to target Mecom has significant clinical relevance. The ME protein is distinct from other Mecom isoforms in that it has a PR domain (or MEPRD), related to histone methyltransferases (HMT), which play a critical role in chromatin modification and regulation of gene expression. We have evidence that MEPRD is critical for MFP AMLs. In this application, we propose testing the hypothesis that the ME protein, particularly the MEPRD plays an essential role in MFP AMLs. Through these proposed experiments, we wish to explore these hypotheses that: ME constitutes a downstream target gene of MFPs that is essential for survival, with the PR domain being of critical importance; that ME functions in the nucleus as part of a holocomplex and effecting changes in gene expression of key ROS and apoptosis regulators by modifying chromatin. The results generated from these experiments will help to set up a solid foundation for future small molecule therapeutic development.