Mechanism of heterochromatin assembly and oncogenic histone mutations

项目摘要 组蛋白的共价修饰，如乙酰化、甲基化、磷酸化和泛素化， 染色质结构和功能的重要调节因子。对这些修改的监管缺陷 在许多发育障碍和疾病中的因果作用。然而，针对 将组蛋白修饰酶定位于特定基因组位置并调节其酶活性 明白我们的长期目标是了解不同的组蛋白修饰活动如何协调， 利用异染色质装配和致癌组蛋白启动和维持不同表观遗传状态 突变作为实验模型。 异染色质优先在重复的DNA元件上组装，并且它对于调节 基因表达和基因组完整性的维持。异染色质的形成是至关重要的 依赖于H3赖氨酸9（H3 K9）的甲基化，并且通常认为精确靶向H3赖氨酸9（H3 K9）是不可能的。 组蛋白H3 K9甲基转移酶将异染色质限制在特定的基因组区域。然而，我们最近 研究表明，在裂殖酵母中，H3 K9甲基转移酶Clr 4的靶向不是非常精确， 细胞严重依赖于负调控因子，如Mst 2组蛋白乙酰转移酶和Epe 1组蛋白 去甲基酶，以去除不适当位置的异染色质。因此，我们将分析 Mst 2和Epe 1在异染色质形成中的功能，并检查它们的活性如何响应 来调节异染色质动力学。 最近的高通量测序分析发现，体细胞组蛋白赖氨酸对 甲硫氨酸（K-to-M）突变在多种癌症。这些突变阻断了野生型组蛋白的甲基化。 然而，这些突变功能的分子细节知之甚少， 争议我们已经建立了裂殖酵母模型，其中H3 K9 M或H3 K36 M的引入 转基因消除了野生型组蛋白上相应赖氨酸的甲基化，类似于 哺乳动物系统中的这些突变。我们将研究这些突变如何调节细胞功能， 确定可以靶向选择性杀死含有K至M突变的细胞的途径。 这些研究的最终目标是全面了解组蛋白甲基化是如何调节的， 它们的突变和失调如何导致人类疾病。

Project Summary Covalent modifications of histones, such as acetylation, methylation, phosphorylation, and ubiquitylation, are essential regulators of chromatin structure and function. Defects in the regulation of these modifications have causal roles in numerous developmental disorders and diseases. However, the mechanisms that target histone-modifying enzymes to specific genomic locations and regulate their enzymatic activities are not well understood. Our long-term goal is to understand how diverse histone modification activities are coordinated to initiate and maintain different epigenetic states using heterochromatin assembly and oncogenic histone mutations as experimental models. Heterochromatin preferentially assembles at repetitive DNA elements and it is essential for the regulation of gene expression and the maintenance of genome integrity. Formation of heterochromatin is critically dependent on the methylation of H3 lysine 9 (H3K9), and it is generally assumed that precise targeting of histone H3K9 methyltransferases confines heterochromatin to specific genomic regions. However, our recent studies demonstrate that in fission yeast the targeting of H3K9 methyltransferases Clr4 is not very precise, and cells rely critically on negatively regulators, such as the Mst2 histone acetyltransferase and the Epe1 histone demethylase, to remove heterochromatin at inappropriate locations. We will therefore analyze the molecular functions of Mst2 and Epe1 in heterochromatin formation, and examine how their activities change in response to environmental signals to regulate heterochromatin dynamics. Recent high throughput sequencing analyses discovered high incidences of somatic histone lysine-to- methionine (K-to-M) mutations in multiple cancers. These mutations block the methylation of wild type histones. However, the molecular details by which these mutations function are poorly understood and are highly controversial. We have established fission yeast models in which the introduction of H3K9M or H3K36M transgenes abolished the methylation of corresponding lysines on wild type histones, similar to the effects of these mutations in mammalian systems. We will examine how these mutations regulate cellular functions and identify pathways that can be targeted to selectively kill cells containing K-to-M mutations. The ultimate goal of these studies is a complete understanding of how histone methylations are regulated and how their mutations and dysregulation contribute to human diseases.