Chromatin Modification by Histone Ubiquitination and Methylations

描述（由申请人提供）：我们的长期目标是了解基因表达失调如何导致肿瘤发生，并学习如何修复转录缺陷。我们一直在研究酿酒酵母染色质修饰和转录延伸控制的机制。组蛋白的无数修饰对于基因表达的适当调节是重要的。在这些组蛋白修饰中，重要的是H3在其第4和第79赖氨酸（H3K4和H3K79）上的甲基化，它们与转录活性基因相关。这些残基的甲基化需要组蛋白H2B被Rad6/Bre1蛋白复合体单泛素化，这是一种从酵母到人类保守的组蛋白串扰途径。我们确定了一个与Set1 （COMPASS）相关的蛋白质复合物，作为酵母H3K4甲基转移酶。Set1是人类混合谱系白血病蛋白的同源物，由MLL基因编码，MLL基因在多种侵袭性急性白血病中重排。我们现在知道，人类MLL蛋白也存在于能够催化H3K4甲基化的compass样复合体中。我们已经开发了酵母蛋白质组的强大筛选，以确定适当的H3K4甲基化所需的机制。我们建议在此基础上进一步定义参与组蛋白H3K4和K79甲基化的安装和去除的分子机制，分别由COMPASS和Dot1催化。我们还建议利用我们的生化，酶学和遗传学专业知识来开发H3K4和K79甲基化酶和去甲基化酶的抑制剂。这类抑制剂可作为先导化合物用于开发治疗白血病的靶向治疗剂。

DESCRIPTION (provided by applicant): Our long-term goal is to understand how misregulation of gene expression leads to oncogenesis, and to learn how to repair transcriptional defects. We have been studying the mechanisms of chromatin modifications and control of transcriptional elongation in the yeast S. cerevisiae. Myriad modifications of histones are important for proper regulation of gene expression. Important among these histone modifications are methylation of H3 on its 4th and 79th lysines (H3K4 and H3K79), which are associated with transcriptionally active genes. Methylation of these residues requires histone H2B to be monoubiquitinated by the Rad6/Bre1 protein complex, a histone cross-talk pathway that is conserved from yeasts to humans. We identified a complex of proteins associated with Set1 (COMPASS) as the yeast H3K4 methyltransferase. Set1 is the homologue of the human mixed lineage leukemia protein, encoded by the MLL gene that is rearranged in a variety of aggressive acute leukemias. We now know that human MLL protein is also found in a COMPASS-like complex capable of catalyzing the methylation of H3K4. We have developed a robust screen of the yeast proteome to identify the machinery required for proper H3K4 methylation. We propose to build on this foundation to define further the molecular machinery involved in the installation and removal of histone H3K4 and K79 methylations, catalyzed by COMPASS and Dot1, respectively. We also propose to leverage our biochemical, enzymological, and genetical expertise to develop inhibitors of H3K4 and K79 methylases and demethylases. Such inhibitors may be useful as lead compounds for the development of targeted therapeutic agents for the treatment of leukemia. Our specific aims are: Aim 1: Define how monoubiquitination of histone H2B regulates histone methylation by COMPASS and Dot1. Aim 2: Define the machinery involved in H3K4 and K79 demethylation. Aim 3: Identify small molecule inhibitors of H3K4 methylating and demethylating enzymes. Continuation of our yeast studies promises not only to lead to a better understanding of the diverse functional and physiological significance of H3K4 and K79 methylations, but also to forge a link between the basic biology of histone methylation and the treatment of leukemia caused by chromosomal translocations involving the MLL gene.