Genomic Health & Safety: Does Elg1 maintain genome stability by resetting chromatin factors used in DNA replication and repair?

保存正确和准确的信息在生活的几乎所有方面都是至关重要的。使生命得以存在的信息编码在DNA中，DNA与细胞内的蛋白质折叠形成染色体。不能维持染色体会导致重要信息的丢失或重写，这可能导致癌症和其他疾病。被称为Elg1的蛋白质是一种细胞因子，在维持染色体方面非常重要。这种蛋白质的缺陷会导致人类和小鼠的肿瘤，但我们不知道为什么。这项工作的目的是了解Elg1蛋白如何维持染色体稳定性，以便我们可以利用这些发现来开发新的癌症疗法。每当一个细胞分裂产生两个新细胞时，染色体中的遗传信息必须精确复制。这个复制过程称为DNA复制。在大多数情况下，细胞实现精确的DNA复制，没有任何错误。细胞中的数百种蛋白质有助于这种精确的DNA复制。如果这种“染色体稳定性”蛋白不能发挥其应有的功能，细胞就不能精确地复制遗传信息，导致重要信息的丢失或重写，最终导致癌症、遗传疾病和衰老。一种名为Elg1的蛋白质是这些染色体稳定蛋白质之一。最近，我发现Elg1的分子功能是在DNA复制过程中从DNA中移除称为PCNA的滑动夹。PCNA呈环状，包围DNA。PCNA稳定复制DNA的机制，此外，PCNA环就像一个工具带，招募许多其他对染色体维护和精确DNA复制很重要的合作蛋白。在DNA复制过程中，PCNA工具带反复加载在DNA上，并在DNA复制任务的每个部分完成后通过Elg 1反复从DNA上移除。在缺乏Elg1的细胞中，PCNA工具带及其工具（即其协作蛋白）积累在染色体上，因为即使在完成每个新的DNA片段后，PCNA工具带也不会被去除。PCNA工具带的这种异常积累就像一个建筑工人身上有十个工具带，每个工具带都有几个不必要的工具。携带十条工具带和大量不必要的工具的工人可能无法灵活地移动他们的身体，对突发事件做出有效反应，或有效地使用工具，因此更容易出错。在染色体稳定性方面，即使是偶然的错误也可能导致灾难。我的假设是，PCNA工具带及其相关工具在DNA上的异常积累导致染色体复制过程中遗传信息的丢失或重写，最终导致癌症。我的目标是了解为什么PCNA去除Elg1是重要的染色体维护，以及是否涉及其合作蛋白。首先，通过操作PCNA工具带，我将测试是否不必要的积累的PCNA工具带直接干扰染色体的维护。接下来，我将测试特定的不必要工具的积累（即不必要的协作蛋白质保留）是否有助于染色体不稳定性。这些实验将使用面包酵母系统进行，该系统允许使用复杂的分子遗传学方法来仔细解剖染色体稳定性机制。在第三部分中，我热衷于扩展这项研究，以测试Elg 1在人类细胞中的作用，因为Elg 1的缺失直接涉及哺乳动物肿瘤。由于该项目研究与癌症相关的基因的作用机制，因此这项工作具有长期的癌症治疗潜力。

The preservation of correct and accurate information is critical in almost all aspects of life. The information that enables life is encoded in DNA, which is folded up with proteins inside cells to form chromosomes. The failure to maintain chromosomes leads to the loss of or rewriting of important information, which can cause cancer and other diseases. The protein called Elg1 is a cellular factor that is very important in maintaining chromosomes. Defects in this one protein cause tumors in humans and mice, but we do not know why. The aim of this work is to understand how the Elg1 protein maintains chromosome stability so that we may exploit these findings to develop new cancer therapies.Whenever a cell divides to produce two new cells, the genetic information in the chromosomes must be duplicated precisely. This duplication process is called DNA replication. In most cases, cells achieve precise DNA replication without any mistakes. Hundreds of proteins in cells contribute to such precise DNA replication. If such 'chromosome stability' proteins cannot carry out their proper functions, cell cannot duplicate genetic information precisely, resulting in loss of or rewriting of important information, and leading eventually to cancer, genetic disorders, and ageing. A protein called Elg1 is one of these chromosome stability proteins. Recently I discovered that the molecular function of Elg1 is removal of a sliding clamp called PCNA from DNA during DNA replication. PCNA is ring-shaped and encircles DNA. PCNA stabilises the machinery that copies DNA, and additionally the PCNA ring acts like a tool-belt, recruiting many other collaborating proteins that are important for chromosome maintenance and precise DNA replication. During DNA replication, the PCNA tool-belt is repeatedly loaded on DNA, and repeatedly removed from DNA by Elg1 after each section of the DNA replication task is complete. In cells lacking Elg1, the PCNA tool-belt and its tools (i.e. its collaborating proteins) accumulate on chromosomes since the PCNA tool-belt is not removed even after completion of each new DNA section. This abnormal accumulation of the PCNA tool-belt resembles a construction worker with ten tool-belts around his body, each containing several unnecessary tools. Workers carrying ten tool-belts and lots of unnecessary tools may be not able to move their bodies flexibly, respond effectively to unexpected events, or use tools efficiently-and so will be more liable to make mistakes. In chromosome stablity, even occasional mistakes may cause catastrophe. My hypothesis is that the aberrant accumulation on DNA of the PCNA tool-belt and its associated tools causes loss of or rewriting of genetic information during chromosome duplication, ultimately resulting in cancer. I aim to understand why PCNA removal by Elg1 is important for chromosome maintenance, and whether its collaborating proteins are involved. First, by manipulating the PCNA tool-belt, I will test whether unwanted accumulation of the PCNA tool-belt interferes directly with chromosome maintenance. Next I will test whether the accumulation of particular unnecessary tools (i.e. unwanted retention of the collaborating proteins) contributes to chromosome instability. These experiments will be carried out using the baker's yeast system, which allows sophisticated molecular genetic approaches to be used for careful dissection of the chromosome stability machinery. In the third part, I am keen to extend this investigation to test the role of Elg1 in human cells, since loss of Elg1 is directly implicated in mammalian tumors. Since this project studies the mechanism of action of gene that is associated with cancer, this work holds long-term potential for cancer therapy.