Altering the chromostasis and genome stability by modulating histone methylation

摘要 染色质稳定的概念或染色质动态平衡是指抑制染色质的环境 细胞可塑性和基因组的不稳定性。基因表达的调控依赖于组蛋白翻译后 修饰(PTM)、DNA甲基化、组蛋白变体和效应蛋白不仅影响结构 和染色质的功能，但也影响必要的过程，如DNA修复能力，以及细胞 扩散。组蛋白密码假说预测PTM控制之间的串扰直接特定的和 独特的DNA模板化程序，如转录、复制和DNA修复。尽管组蛋白PTMS可以 尽管它们的职能作用是相互排斥的，但它们仍然可以对彼此产生强大的影响。一目了然 例如，H3K36me3-H3K27me3轴。虽然H3K36me3与活性转录有关， H3K27me3是由多梳抑制复合体2(PRC2)产生的，维持基因抑制。 H3K36me3和H3K27me3对DNA双链断裂(DSB)修复途径也有拮抗作用 选择，并因此控制基因组的稳定状态。此外，这些PTM之间的串扰是 很明显，H3K36me3的缺失对细胞H3K27me3水平有很大影响，反之亦然。 然而，这两个PTM如何在功能上相互作用来控制基因转录和基因组稳定性仍然是个未知数 不清楚。使用组蛋白H3中自然发生的突变作为模型系统，我们将解决组蛋白的作用 染色质稳定中的甲基化。值得注意的是，组蛋白H3上的赖氨酸36突变为蛋氨酸(H3K36M)，AS 在头颈部疾病中发现，导致全球H3K36me2/3水平下降。H3K36M的作用及其应用 与H3K27me3和其他PTM的串扰及其对表观基因组和基因组维持的影响 稳定，人们对此知之甚少。在这里，我们旨在了解H3K27me3和H3K27me3之间的平衡是如何 H3K36me2/3控制人类细胞的基因转录和基因组稳定性。为此，我们将决定如何 H3K36M影响表观遗传格局，以及重新连接潜在的表观遗传机制是否可以 被利用来维持基因组的完整性。我们新的初步数据揭示了H3K36M和H3K36M之间的新联系， 人类细胞中的多梳复合体PRC1和PRC2、DNA甲基化和基因组不稳定性。此外， 我们发现了一个由H3K36M隔离的新的表观遗传复合体。最后，我们的研究表明，H3K27me3水平 通过同源重组(HR)确定DNA修复的熟练程度和对复制的敏感性- 从属DSB。在本提案中，我们将阐明H3K36M介导的基因调控机制(AIM 1)以及H3K36M和H3K27me3在DNA修复和基因组稳定性中的作用(Aim 2)和体内(Aim 3)。综上所述，我们的研究将及时揭示关键的表观遗传过程 基因，以避免可能导致细胞转化和发育的染色质稳定中断 精神错乱。我们的工作将揭示调节染色质活动的基本分子线索，这些分子线索可能是 易受治疗靶向影响。

Abstract The concept “chromostasis” or chromatin homeostasis refers to a chromatin environment that suppresses cellular plasticity and genome instability. Regulation of gene expression depends on histone post-translational modifications (PTM), DNA methylation, histone variants, and effector proteins that not only influence the structure and function of chromatin, but also affect essential processes such as DNA repair capacity, and cellular proliferation. The histone code hypothesis predicts that crosstalk between PTMs controls direct specific and distinct DNA-templated programs such as transcription, replication and DNA repair. Although histone PTMs can be mutually exclusive in their functional role, they still can have a strong influence into each other. A clear example of this is the H3K36me3-H3K27me3 axis. While H3K36me3 is associated with active transcription, H3K27me3, which is produced by the Polycomb repressive complex 2 (PRC2), maintains gene repression. H3K36me3 and H3K27me3 also have an antagonistic role on DNA double strand break (DSB) repair pathway choice and consequently controls genome stability status. Furthermore, the crosstalk between these PTMs is evident since depletion of H3K36me3 greatly influences the cellular H3K27me3 levels, and viceversa. Nevertheless, how these two PTMs functionally interact to control gene transcription and genome stability is still unclear. Using naturally occurring mutations in histone H3 as a model system, we will address the role of histone methylation in chromostasis. Notably, mutations in the lysine 36 on histone H3 to a methionine (H3K36M), as found in head and neck disorders, lead to a global reduction of H3K36me2/3 levels. The role of H3K36M and its crosstalk with H3K27me3 and other PTMs, as well as its influence in the epigenome and maintenance of genome stability, is poorly understood. Here we aim to understand how the balance between H3K27me3 and H3K36me2/3 controls gene transcription and genome stability in human cells. To this end, we will determine how H3K36M impacts the epigenetic landscape and whether rewiring the underlying epigenetic mechanisms can be exploited to maintain genome integrity. Our new preliminary data reveals a novel connection between H3K36M, the Polycomb complexes PRC1 and PRC2, DNA methylation, and genome instability in human cells. Moreover, we found a novel epigenetic complex sequestered by H3K36M. Finally, our studies show that H3K27me3 levels determine the proficiency of DNA repair via homologous recombination (HR) and sensitivity to replication- dependent DSBs. In this proposal, we will elucidate the H3K36M-mediated mechanisms of gene regulation (aim 1), and the role of H3K36M and H3K27me3 in DNA repair and genome stability in vitro (aim 2) and in vivo (aim 3). Taken together, our studies will reveal critical epigenetic processes needed at a timely manner at the right genes, to avoid disruptions in “chromostasis” that could cause cellular transformation and developmental disorders. Our work will uncover fundamental molecular cues that regulate activities on chromatin that may be amenable to therapeutic targeting.