Molecular Mechanisms for the Assembly and Regulation of the MLL1 Core Complex

描述(申请人提供)：混合血统白血病蛋白-1(MLL1)催化组蛋白H3赖氨酸4(H3K4)甲基化，这是一个表观遗传标记，在造血和发育过程中调节HOX基因是必不可少的。破坏MLL1基因的易位存在于一组独特的急性白血病中，通常预示着预后不良。其他MLL1重排和扩增可增加MLL1‘S的酶活性，并具有致癌作用。MLL1含有一个进化保守的~130个氨基酸集结构域，催化H3K4甲基化。最近的研究表明，MLL1的酶活性受WDR5、RbBP5和ASH2L等蛋白质的保守复合体调控。这些蛋白质形成一个独立的复合体，与MLL1结合，调节其对H3K4底物单甲基化、双甲基化或三甲基化的能力，这一现象被称为“产品特异性”。由于不同水平的H3K4甲基化与不同的转录结果相关，了解MLL1产物特异性调节的分子机制是非常必要的。尽管MLL1具有重要的生物学作用及其在人类白血病中的作用，但目前关于MLL1核心复合体的酶活性的蛋白质结构特征的信息很少。这项研究的长期目标是充分表征MLL1核心复合体调节H3K4甲基化的机制。本建议采用结构-功能方法研究MLL1核心复合体的酶活性的分子机制。我们获得了新的初步结果，表明MLL1 SET结构域的内在产物专一性是一个慢的单甲基转移酶，但当与WDR5，RbBP5和Ash2L形成复合体时，它变成了一个快速的二甲基转移酶。在这里，我们建议确定导致MLL1核心复合体H3K4二甲基化活性的机制。此外，我们将确定解释其组装的蛋白质结构特征。为了解决这些目标，我们结合分子、生化和生物物理方法来研究MLL1核心复合体对H3K4甲基化的调节。这些信息将增加我们对关键酶复合体的理解，以及它是如何在控制真核生物转录激活的途径中调节的。这项研究很重要，因为它可能导致更好的诊断和合理设计抑制MLL1‘S酶活性的抗癌药物。 与公共卫生相关：真核生物中调控基因转录的机制还不是很清楚。我们将使用生物物理分析混合血统白血病蛋白-1(MLL1)核心复合体，以了解其在转录调控中的作用。我们希望这些知识将导致抗癌药物的开发，用于治疗某些人类白血病。

DESCRIPTION (provided by applicant): The Mixed Lineage Leukemia protein-1 (MLL1) catalyzes histone H3 lysine 4 (H3K4) methylation, which is an epigenetic mark essential for the regulation of HOX genes in hematopoiesis and development. Translocations that disrupt the MLL1 gene are present in a unique group of acute leukemias, often predicting a poor prognosis. Other MLL1 rearrangements and amplifications increase MLL1's enzymatic activity and are oncogenic. MLL1 contains an evolutionarily conserved ~130 amino acid SET domain that catalyzes H3K4 methylation. Recent studies indicate that the enzymatic activity of MLL1 is regulated by a conserved complex of proteins including WDR5, RbBP5, and ASH2L. These proteins form an independent complex that binds to MLL1 and regulates its ability to mono-, di-, or trimethylate H3K4 substrates, a phenomenon known as 'Product Specificity'. Since different levels of methylation of H3K4 are associated with different transcriptional outcomes, it is imperative to understand the molecular mechanisms by which the product specificity of MLL1 is regulated. Despite the important biological role of MLL1 and its involvement in human leukemia, there is currently little information about the protein-structural features that are responsible for the enzymatic activity of the MLL1 core complex. The long-term goal of this research is to fully characterize the mechanisms for the regulation of H3K4 methylation by the MLL1 core complex. This proposal takes a structure-function approach to investigate the molecular mechanisms for the enzymatic activity of the MLL1 core complex. We have obtained novel preliminary results indicating that the intrinsic product specificity of the MLL1 SET domain is that of a slow monomethyltransferase, but becomes a fast dimethyltransferase when in complex with WDR5, RbBP5, and Ash2L. Here we propose to determine the mechanisms responsible for H3K4 dimethylation activity of the MLL1 core complex. In addition, we will determine the protein-structural features that account for its assembly. To address these aims, we combine molecular, biochemical, and biophysical approaches to investigate the regulation of H3K4 methylation by the MLL1 core complex. This information will increase our understanding of a key enzyme complex and how it is regulated in the pathways that control transcriptional activation in eukaryotes. This investigation is important because it may lead to better diagnostics and the rational design of anti-cancer drugs that inhibit MLL1's enzymatic activity. PUBLIC HEALTH RELEVANCE: The mechanisms that regulate gene transcription in eukaryotes are not well understood. We will employ a biophysical analysis of the Mixed Lineage Leukemia protein-1 (MLL1) core complex to gain insight into its role in transcriptional regulation. We expect this knowledge will lead to the development of anti-cancer agents for the treatment of certain human leukemias.