Deciphering the role of heterochromatin in telomere function and maintenance mechanisms

破译异染色质在端粒功能和维持机制中的作用

• 批准号: 10452688
• 负责人: Nausica C. Arnoult
• 金额: $ 38.5万
• 依托单位: UNIVERSITY OF COLORADO
• 依托单位国家: 美国
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2026-05-31
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/10452688
• 关键词: Aging; Biology; Buffers; Cancerous; Cell Aging; Cell Cycle Arrest; Cells; Chromatin; Chromosomes; Code; Complex; Consensus; DNA; DNA Damage; Data; Defect; Development; Enzymes; Genetic Recombination; Genetic Transcription; Genome Stability; Heterochromatin; Histones; Maintenance; Methods; Mitotic; Nucleoproteins; Nucleosomes; Pathway interactions; Play; Property; Proteins; Regulation; Repression; Role; Signal Transduction; Structure; Telomerase; Telomere Maintenance; Telomeric Repeat Binding Protein 1; base; chromosome replication; histone methylation; histone modification; neglect; non-histone protein; novel strategies; prevent; repaired; senescence; telomere; tumor

PROJECT SUMMARY Telomeres are nucleoprotein structures that protect the ends of linear chromosomes and thereby maintain genome stability. Telomeres solve both the end-protection and the end-replication problems: 1) They inhibit DNA damage at chromosome ends, which would otherwise resemble broken DNA, 2) Since chromosome ends shorten during replication, telomeres act as buffer sequences to prevent loss of coding regions, 3) Once telomeres become too short, they can no longer inhibit DNA damage, leading to permanent cell cycle arrest (senescence). This “mitotic clock” is a critical tumor-suppressive barrier that forces aging cells to stop dividing. To become cancerous, cells must acquire unlimited division potential by activating a telomere maintenance mechanism, either reactivation of telomerase, the enzyme that elongates telomeres during development, or through the alternative lengthening of telomeres (ALT) mechanism, which is based on recombination. Telomeres consist of 5-15kb of (TTAGGG)n repeats organized into tightly packed nucleosomes and bound by the shelterin, a complex of six non-histone proteins. Telomeres are considered as heterochromatin and are enriched in the repressive H3K9me3 “histone mark”. Intense focus has been placed on trying to decipher the exact chromatin status of telomeres, but the much more important question has been neglected and remains unanswered: What is the role and function of heterochromatin at telomeres? While the roles of shelterin proteins have been extensively studied, the function of heterochromatin at telomeres remains largely unexplored. Using a novel approach to locally and specifically modulate histone methylation at telomeres, we will thoroughly dissect the function of H3K9me3 in telomere protection and maintenance. By fusing histone modifying enzymes to the shelterin protein TRF1, we can locally enrich or deplete H3K9me3 at telomeres. Our preliminary data revealed that loss of H3K9me3 leads to severe replication defects and de-repression of telomere transcription. These data suggest that heterochromatin could play unanticipated roles in the regulation of replicative aging and the onset of senescence. Moreover, while the general consensus is that ALT is associated with less condensed chromatin at telomeres, we found that H3K9me3 is a driver of ALT activity. Using this unique approach to manipulate H3K9 trimethylation at telomeres, we will methodically determine the function of this heterochromatin mark on the protective properties of telomeres (end- protection, end-replication, entry into senescence) as well as on the ALT mechanism of telomere maintenance.

项目总结 端粒是保护线性染色体末端的核蛋白结构，因此 保持基因组稳定。端粒解决了末端保护和末端复制问题：1) 它们抑制染色体末端的DNA损伤，否则就像断裂的DNA，2)因为 染色体末端在复制过程中缩短，端粒作为缓冲序列防止编码丢失 区域，3)一旦端粒变得太短，它们就不能再抑制DNA损伤，导致 永久性细胞周期停滞(衰老)。这种“有丝分裂钟”是一种关键的肿瘤抑制屏障， 迫使老化的细胞停止分裂。要变成癌细胞，细胞必须获得无限的分裂潜力 通过激活端粒维持机制，端粒酶的重新激活 在发育过程中延长端粒，或通过交替延长端粒(ALT) 机制，这是基于重组。 端粒由5-15kb的(TTAGGG)n重复序列组成，排列成紧密排列的核小体 由六种非组蛋白蛋白组成的复合体，与保护素结合。端粒被认为是 异染色质，并在抑制性H3K9me3“组蛋白标记”中富含。强烈的关注一直是 致力于破译端粒染色质的确切状态，但更重要的是 问题一直被忽视，仍然没有得到回答：什么是角色和功能 端粒上的异染色质？虽然避难所蛋白的作用已经被广泛研究，但 异染色质在端粒中的功能在很大程度上仍未被研究。 使用一种新的方法来局部和特异地调节组蛋白端粒的甲基化，我们 将深入剖析H3K9me3在端粒保护和维持中的作用。通过 将组蛋白修饰酶与Shelterin蛋白TRF1融合，我们可以局部富含或枯竭 端粒H3K9me3。 我们的初步数据显示，H3K9me3的丢失会导致严重的复制缺陷和抑制 端粒转录。这些数据表明，异染色质可能在 复制衰老的调节和衰老的开始。此外，虽然普遍的共识是 ALT与端粒染色质浓缩程度较低相关，我们发现H3K9me3是一个驱动因素 丙氨酸氨基转移酶活性。 使用这种独特的方法来操纵端粒上的H3K9三甲基化，我们将有条不紊地 确定这种异染色质标记对端粒保护特性的作用(完 保护、末端复制、进入衰老)以及端粒的ALT机制 维修。