The Mechanism of Telomere Recombination in Yeast

描述（由申请人提供）：生物学的中心问题之一是端粒如何参与遗传稳定性的问题。端粒延长（RTE）是一种细胞在缺乏端粒酶活性的情况下延长其端粒的机制。人ALT（端粒的替代性延长）肿瘤依赖于RTE来延长端粒并在端粒酶不存在时继续细胞分裂，就像大多数人体细胞中的情况一样。参与端粒维持和稳态的组分之一是Mre 11，一种多功能蛋白，其主要作用是识别和修复双链断裂。拟议研究的长期目标是确定细胞进行重组端粒延长（RTE）的机制，并将这些知识应用于治疗由ALT细胞引起的人类癌症，如骨肉瘤。该项目的具体目标是更清楚地描述特定重组的特点， 在酵母中负责端粒延长的机制。这些实验使用新的功能获得等位基因mre 11-A470 T，它能够在端粒酶阴性细胞中诱导端粒重组的不寻常变化。这种变化是负责在端粒酶阴性，mre 11-A470 T细胞中观察到的衰老旁路。核心假设是酵母中的RTE是通过断裂诱导复制（BIR）途径完成的，并且mre 11-A470 T等位基因诱导异常端粒BIR事件。BIR途径的这种改变可能通过BIR酶机制的活性、调节或特异性的普遍或特异性增强而发生。所提出的实验背后的基本原理是，mre 11-A470 T的研究提供了一个极好的和独特的机会来探测端粒重组的Mre 11的调节。这项工作的意义在于，它将使我们更好地了解重组端粒延伸的调控、要求和特征以及Mre 11在这一过程中的作用。这些信息对于我们理解和治疗人类ALT细胞的癌症进展至关重要。 公共卫生相关性：在人类体细胞中，端粒酶，负责从头端粒添加的酶，以有限的量表达，导致端粒逐渐缩短和复制性衰老。端粒的延长通过端粒酶独立的重组机制发生在大约10-15%的人类癌症中。了解这一过程的机制对于对抗癌性人类ALT（端粒替代延长）细胞至关重要。拟议的研究与公共卫生有关，因为它将增加我们对重组端粒延长机制的理解，特别是关于Mre 11在调控断裂诱导复制和端粒延长中的作用。这些信息将适用于进一步了解人ALT细胞的存活机制。该项目与NIH的使命相关，因为它旨在增加我们关于通过MRN复合物调节端粒延长及其与细胞衰老和存活的联系的基本知识。

DESCRIPTION (provided by applicant): One of the central issues in biology is the question of how telomeres are involved in genetic stability. Recombinational telomere elongation (RTE) is a mechanism by which cells elongate their telomeres in the absence of telomerase activity. Human ALT (alternative lengthening of telomeres) tumors depend upon RTE to lengthen telomeres and continue cellular division when telomerase is absent, as is the case in most human somatic cells. One of the components involved in telomere maintenance and homeostasis is Mre11, a multifunctional protein whose primary role is the recognition and repair of double-strand breaks. The long-term goal of the proposed research is to determine the mechanism by which cells undergo recombinational telomere elongation (RTE) and to apply this knowledge to the treatment of human cancers, such as osteosarcomas, caused by ALT cells. The specific objective of this project is to more clearly characterize the specific recombinational mechanism responsible for telomere elongation in yeast. These experiments use the novel gain-of-function allele, mre11- A470T, which is capable of inducing an unusual variation of telomeric recombination in telomerase-negative cells. This variation is responsible for an observed bypass of senescence in telomerase-negative, mre11-A470T cells. The central hypothesis is that RTE in yeast is accomplished via the break-induced replication (BIR) pathway and that the mre11-A470T allele induces aberrant telomeric BIR events. This alteration of the BIR pathway may occur by a generalized or specific enhancement of the activity, regulation, or specificity of BIR enzymatic machinery. The rationale behind the proposed experiments is that study of mre11-A470T provides an excellent and unique opportunity to probe the regulation of telomere recombination by Mre11. The significance of this work is that it will provide us with a greater understanding of the regulation, requirements, and characteristics of recombinational telomere elongation and the role of Mre11 in this process. This information will be essential to our understanding and treatment of the cancer progression of human ALT cells. PUBLIC HEALTH RELEVANCE: In human somatic cells, telomerase, the enzyme responsible for de novo telomere addition, is expressed in limited amounts, resulting in the gradual shortening of telomeres and replicative senescence. The lengthening of telomeres through telomerase-independent, recombinational mechanisms occur in approximately 10-15% of human cancers. Understanding the mechanism of this process is essential in the fight against cancerous human ALT (alternative lengthening of telomeres) cells. The proposed research is relevant to public health in that it will increase our understanding of the mechanisms of recombinational telomere elongation, particularly with regard to the role of Mre11 in the regulation of break-induced replication and telomere elongation. This information will be applicable to the further understanding of the mechanisms of survival of human ALT cells. This project is relevant to the mission of the NIH in that it seeks to increase our fundamental knowledge regarding the regulation of telomere elongation through the MRN complex and its connection to cellular senescence and survival.