When there is not enough telomerase: telomerase insufficiency and genome integrity

当端粒酶不足时：端粒酶不足和基因组完整性

• 批准号: MR/R02068X/1
• 负责人: Svetlana Makovets
• 金额: $ 273.47万
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2018
• 资助国家: 英国
• 起止时间: 2018 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=MR%2FR02068X%2F1
• 关键词: When; there; enough; telomerase; insufficiency

Telomeres are the natural ends of linear chromosomes present in many organisms, from unicellular fungi and algae to humans. Telomeres do not encode any genes but are important for accurate chromosome maintenance by protecting chromosomes against degradation and fusion to other chromosomes. They consist of short DNA repeats (TTAGGG in humans) which allow cells to differentiate them from broken DNA ends. Cell replicate their chromosomes every time before they divide and telomeres require a special enzyme, telomerase, for their replication. If there is no or very little telomerase telomeres shorten with each cell division and once they have become critically short they resemble broken DNA ends and can no longer protect chromosomes. Consequently, chromosomes undergo DNA loss, fusions to other chromosomes and further genome-destabilizing events, which may abolish cells' ability to function and lead to cancer in humans. Most human cells express very little telomerase and due to the resultant telomerase insufficiency telomeres in our cells become shorter with age. This telomere shortening has been linked to impaired tissue homeostasis, wound healing and immune response in elderly. Furthermore, mutations in human telomerase genes result in accelerated telomere shortening, bone marrow failure, nail dystrophy, abnormal skin pigmentation and increased risk of cancer. Therefore, studying how telomerase is regulated and how cells deal with critically short telomeres is important for our understanding of certain human genetic disorders, cancer development and human ageing. This research proposal is focused on two major questions:1.How do cells deal with telomerase insufficiency? Telomerase insufficiency is not wide-spread in nature but importantly it is one of the key signatures of ageing human cells as well as pre-cancer cells on their way to malignancy. For the first time, we have reported a system for studying telomerase insufficiency in a simple model system of budding yeast and used it to show that cells with telomerase insufficiency can boost telomerase by altering their chromosome set (karyotype) so that it slows the rate of cell growth. We aim to investigate how the rate of cell growth affects telomerase and its ability to extend telomeres, and to identify and characterise other mechanisms of overcoming telomerase insufficiency. We will also study if short telomeres might trigger karyotype changes as we have preliminary evidence that recombination, which is known to be increased at short telomeres, is involved in altering karyotype.2.How are telomeres and telomerase regulated during DNA damage response? Critically short telomeres, often arising as a result of telomerase insufficiency, resemble DNA breaks and induce DNA damage response - a set of cell reactions directed at activation of DNA repair and pausing cell division until the repair is complete. In our prior experiments we discovered a pathway that regulates yeast telomerase in response to DNA damage. Intriguingly, the regulation had opposite effects on telomerase at broken chromosome ends and at telomeres: telomerase was inhibited at DNA breaks (to prevent erroneous break repair by telomerase) but stimulated at telomeres as a result of break repair by a specific mechanism called break induced replication. We are proposing to dissect this regulation at the molecular level to elucidate the interplay between telomerase, DNA repair and DNA damage response in order to understand regulatory pathways providing accurate DNA repair and telomere maintenance in cells with telomerase insufficiency and/or DNA damage.Because all the key proteins and pathways under study are highly conserved from yeast to humans our findings will be relevant to human cells. This research has important implications for approaching human health problems associated with genome instability, such as normal human ageing, multiple genetic disorders, and especially for understanding cancer cause and therapy.

端粒是存在于许多生物体中的线性染色体的天然末端，从单细胞真菌和藻类到人类。端粒不编码任何基因，但通过保护染色体免于降解和与其他染色体融合而对准确的染色体维持很重要。它们由短的DNA重复序列（人类中的TTAGGG）组成，使细胞能够将它们与断裂的DNA末端区分开来。细胞每次分裂前都会复制染色体，端粒的复制需要一种特殊的酶--端粒酶。如果没有或很少有端粒酶，端粒会随着每次细胞分裂而缩短，一旦它们变得非常短，它们就像断裂的DNA末端，不再能保护染色体。因此，染色体经历DNA丢失，与其他染色体融合以及进一步的基因组不稳定事件，这可能会破坏细胞的功能并导致人类癌症。大多数人类细胞表达很少的端粒酶，由于端粒酶不足，我们细胞中的端粒随着年龄的增长而变短。这种端粒缩短与老年人的组织稳态、伤口愈合和免疫反应受损有关。此外，人类端粒酶基因的突变导致端粒缩短加速、骨髓衰竭、指甲营养不良、皮肤色素异常和癌症风险增加。因此，研究端粒酶是如何调节的，以及细胞如何处理短端粒，对于我们理解某些人类遗传疾病，癌症发展和人类衰老非常重要。本研究主要围绕两个问题展开：1.细胞如何应对端粒酶缺乏？端粒酶功能不全在自然界中并不广泛，但重要的是，它是衰老人类细胞以及癌前细胞走向恶性肿瘤的关键标志之一。我们首次报道了一种在芽殖酵母的简单模型系统中研究端粒酶不足的系统，并用它来表明端粒酶不足的细胞可以通过改变它们的染色体组（核型）来提高端粒酶，从而减缓细胞生长的速率。我们的目的是研究细胞生长速度如何影响端粒酶及其延伸端粒的能力，并确定和验证克服端粒酶不足的其他机制。我们还将研究短端粒是否可能引发核型变化，因为我们有初步证据表明，重组，这是已知的增加在短端粒，涉及改变核型。2.端粒和端粒酶是如何调节DNA损伤反应过程中？端粒非常短，通常是由于端粒酶不足而产生的，类似于DNA断裂并诱导DNA损伤反应-一系列细胞反应，旨在激活DNA修复并暂停细胞分裂，直到修复完成。在我们之前的实验中，我们发现了一种调节酵母端粒酶以响应DNA损伤的途径。有趣的是，这种调节对断裂染色体末端和端粒处的端粒酶有相反的影响：端粒酶在DNA断裂处受到抑制（以防止端粒酶错误的断裂修复），但由于断裂修复的结果，端粒酶在端粒处受到刺激，这是一种称为断裂诱导复制的特殊机制。我们建议在分子水平上剖析这种调控，阐明端粒酶，DNA修复和DNA损伤反应之间的相互作用，以了解在端粒酶不足和/或DNA损伤的细胞中提供准确的DNA修复和端粒维护的调控途径。因为所有正在研究的关键蛋白和途径从酵母到人类都是高度保守的，我们的发现将与人类细胞相关。这项研究对于解决与基因组不稳定性相关的人类健康问题，如正常的人类衰老，多种遗传疾病，特别是了解癌症的原因和治疗具有重要意义。