Altering the chromostasis and genome stability by modulating histone methylation

摘要 “染色质稳态”或染色质稳态的概念是指一种染色质环境， 细胞可塑性和基因组不稳定性。基因表达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，但也影响基本过程，如DNA修复能力，和细胞 增殖组蛋白编码假说预测PTM之间的串扰控制直接特异性和 不同的DNA模板程序，如转录，复制和DNA修复。虽然组蛋白PTM可以 尽管它们在功能上相互排斥，但它们仍然可以相互产生强大的影响。一个明确 例如H3 K36 me 3-H3 K27 me 3轴。虽然H3 K36 me 3与活性转录相关， H3 K27 me 3由Polycomb阻遏复合物2（PRC 2）产生，维持基因阻遏。 H3 K36 me 3和H3 K27 me 3对DNA双链断裂（DSB）修复途径也具有拮抗作用 选择并因此控制基因组稳定性状态。此外，这些PTM之间的串扰是 这是明显的，因为H3 K36 me 3的消耗极大地影响细胞H3 K27 me 3水平，反之亦然。 然而，这两个PTM如何在功能上相互作用以控制基因转录和基因组稳定性仍然是未知的。 不清楚使用组蛋白H3中自然发生的突变作为模型系统，我们将讨论组蛋白H3在细胞中的作用。 甲基化在染色体停滞中的作用。值得注意的是，组蛋白H3上的赖氨酸36突变为甲硫氨酸（H3 K36 M），如 在头部和颈部疾病中发现，导致H3 K36 me 2/3水平的全球降低。H3 K36 M的作用及其 与H3 K27 me 3和其他PTM的串扰，以及其在表观基因组和基因组维持中的影响 对稳定性的认识很少。在这里，我们的目标是了解H3 K27 me 3和 H3 K36 me 2/3控制人类细胞中的基因转录和基因组稳定性。为此，我们将确定如何 H3 K36 M影响表观遗传景观，以及是否可以重新连接潜在的表观遗传机制。 用来维持基因组的完整性我们新的初步数据揭示了H3 K36 M之间的新联系， 多梳复合物PRC 1和PRC 2，DNA甲基化和人类细胞中的基因组不稳定性。此外，委员会认为， 我们发现了一种新的被H3 K36 M隔离的表观遗传复合体。最后，我们的研究表明，H3 K27 me 3水平 确定通过同源重组（HR）进行DNA修复的能力和对复制的敏感性- 从属DSB。在这个建议中，我们将阐明H3 K36 M介导的基因调控机制（目的 1），以及H3 K36 M和H3 K27 me 3在体外（aim 2）和体内（aim 2）DNA修复和基因组稳定性中的作用 3）。总之，我们的研究将揭示关键的表观遗传过程需要及时在正确的 基因，以避免破坏“染色体稳定”，可能导致细胞转化和发育 紊乱我们的工作将揭示调节染色质活动的基本分子线索， 适合于治疗靶向。

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.