Molecular Targeting of MLL and Associated Factors

描述(由申请人提供)：混合谱系白血病(MLL)基因编码一种组蛋白甲基转移酶，该酶在人类白血病中经常因染色体易位而突变，临床结果较差。在这项竞争性更新申请中提出的研究解决了这样的假设，即MLL癌蛋白的致白血病作用严重依赖于最近发现的与MLL或其融合伙伴相关的蛋白质，并且这些相关因子的活性或相互作用构成了分子治疗的潜在靶点。这一假说是基于当前获奖期间的重大发现，这些发现极大地促进了我们对MLL白血病分子机制的理解。我们已经证明，薄荷素，一种肿瘤抑制蛋白和MLL相关因子，在MLL介导的白血病发生中矛盾地需要。Menin作为MLL癌蛋白的转录辅助因子，我们证明了它的唯一作用是促进与一种新发现的MLL相关蛋白LEDGF/p75的相互作用。后者是一种染色质相关蛋白，具有共激活活性，但分子功能未知，以前与白血病和HIV的发病机制有关。第一个特定目标的研究将在临床前和细胞系转化模型系统中使用生化和遗传学方法表征MLL介导的白血病发生所需的LEDGF/p75的分子功能。这些研究将确定LEDGF/p75假定的甲基赖氨酸识别基序的潜在配体，并建立拮抗它们之间相互作用作为分子治疗策略的可行性。第二个目标的研究将利用遗传和生化技术来确定白血病中通过染色体易位而激活LEDGF/p75自身致癌基因的分子机制，并确定其在通过MLL和/或Myc转录途径介导的白血病发生中的特定作用。第三个特定目的的研究是基于我们发现的一个多蛋白复合体(AEP)，它包含几个MLL融合伙伴和P-TEFb转录延伸因子。这种新的复合体是由MLL癌蛋白的一部分与MLL白血病细胞中的关键靶基因相连的，然而它在白血病发生中所需的分子作用尚未完全确定。我们的研究将进一步表征AEP复合体，它的关键酶活性，它对MLL转录调控的一般意义，以及它在MLL介导的白血病发生中的作用。在MLL白血病中，靶向AEP成分的活性或相互作用与致病作用的治疗价值将使用临床前转化模型进行询问。 公共卫生相关性：该应用程序建议调查导致造血细胞癌的关键分子过程。高度精确的遗传和生化模型系统将被用来研究正常干细胞及其癌变对应物和后代中与癌症相关的途径。更好地了解正常干细胞和癌症干细胞之间的异同，将有助于努力选择性地针对后者，同时避免前者，以实现更有效的治疗。

DESCRIPTION (provided by applicant):The Mixed Lineage Leukemia (MLL) gene codes for a histone methyltransferase that is frequently mutated by chromosomal translocations in human leukemias associated with a poor clinical outcome. The studies proposed in this competitive renewal application address the hypothesis that the leukemogenic actions of MLL oncoproteins are critically dependent on proteins recently discovered to associate with MLL or its fusion partners, and that the activities or interactions of these associated factors constitute potential targets for molecular therapies. This hypothesis is based on major discoveries during the current award period that have substantially advanced our understanding of the molecular mechanisms of MLL leukemias. We have shown that menin, a tumor suppressor protein and MLL- associated factor, is paradoxically required for MLL-mediated leukemogenesis. Menin functions as a transcriptional co-factor for MLL oncoproteins, and in this capacity we demonstrated that its only role is to promote interactions with a newly discovered MLL- associated protein known as LEDGF/p75. The latter is a chromatin-associated protein with co-activator activity but unknown molecular function, previously implicated in leukemia and HIV pathogenesis. Studies in the first specific aim will characterize the molecular functions of LEDGF/p75 required for MLL-mediated leukemogenesis using biochemical and genetic approaches in pre-clinical and cell line transformation model systems. These studies will identify a potential ligand for the putative methyl-lysine recognition motif of LEDGF/p75 and also establish the feasibility of antagonizing their interactions as a molecular therapeutic strategy. Studies in the second aim will employ genetic and biochemical techniques to determine the molecular mechanisms that underlie oncogenic activation of LEDGF/p75 itself by chromosomal translocations in leukemias, and establish its specific roles in leukemogenesis mediated through the MLL and/or Myc transcriptional pathways. Studies in the third specific aim are based on our discovery of a multi-protein complex (AEP) that contains several MLL fusion partners and the P-TEFb transcription elongation factor. This novel complex is tethered by a subset of MLL oncoproteins to critical target genes in MLL leukemia cells, however its molecular contributions required for leukemogenesis have not been fully defined. Our studies will further characterize the AEP complex, its critical enzymatic activities, its implications for MLL transcriptional regulation in general, and its role in MLL-mediated leukemogenesis. The therapeutic value of targeting the activities or interactions of AEP components with pathogenic roles in MLL leukemia will be interrogated using preclinical transformation models. PUBLIC HEALTH RELEVANCE: This application proposes to investigate the critical molecular processes that cause cancers of blood-forming cells. Highly refined genetic and biochemical model systems will be employed to study cancer-associated pathways in normal stem cells as well as their cancerous counterparts and progeny. A greater understanding of the similarities and differences among normal and cancer stem cells will facilitate efforts to selectively target the latter while sparing the former to achieve more efficacious therapies.