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Mechanisms of trans-repression by Myc in Drosophila

果蝇中 Myc 的反式抑制机制

基本信息

批准号：
7909730
负责人：
Julie M. Goodliffe
金额：
$ 7万
依托单位：
UNIVERSITY OF NORTH CAROLINA CHARLOTTE
依托单位国家：
美国
项目类别：
财政年份：
2008
资助国家：
美国
起止时间：
2008-07-01 至 2012-06-30
项目状态：
已结题

项目摘要

DESCRIPTION (provided by applicant): The long-term objective of this project is to understand how the process of differentiation prevents over-proliferation during embryogenesis. More specifically, the transcription factor and onco-protein Myc is required for proliferation during embryogenesis, and yet an over-abundance of Myc protein induces tumors; how do embryonic cells achieve the correct balance of Myc function? Myc is a transcriptional regulator with the ability to activate and repress transcription of different targets. Transcriptional activation by Myc requires its binding to DNA, and though repression by Myc is not necessarily mediated by its binding to DNA, a Myc mutant that is unable to bind DNA is unable to repress. One of the first identified targets of Myc repression was the c-myc gene itself, and all human tumor-derived cell lines tested are defective for this auto-repression of myc. In an effort to understand the mechanism of myc auto-repression, along with Eric Wieschaus and Michael Cole at Princeton University, I developed a novel genetic screen using Drosophila melanogaster. We found that mutations in Polycomb, a chromatin binding repressor required for maintenance of cell fates, eliminate auto-repression of the Drosophila myc gene, and also the majority of repression mediated by ectopic Myc in the embryo. Mutations in Polycomb also led to increased expression of many of Myc's targets of activation, suggesting a link between Polycomb, repression by Myc and transactivation by Myc. Though biologically important, the link between Polycomb and Myc is not known to be direct or indirect. In fact, in the Drosophila embryo, Myc induces the expression of gene products functionally related to Polycomb: Su(z)2, Esc and Pho (homologs of mammalian bmi-1, eed and YY1, respectively). In this proposal, I hypothesize that Myc activation of Polycomb Group gene products Su(z)2, Esc and Pho causes Myc's downstream repression of targets, and that the relative abundance of these repressors throughout embryogenesis affects Myc trans-repression of targets. To test this hypothesis, my specific aims are: (1) to determine whether Myc binds directly to Su(z)2, pho and/or esc genes, causing their activation; (2) to determine whether Su(z)2 and/or Esc are required for repression by Myc; and (3) to determine what proteins associate with Myc throughout embryogenesis. Genetic alterations that lead to increased Myc expression cause uncontrolled proliferation and tumorigenesis. In an embryo, however, Myc levels are high and proliferation is controlled. The research described in this proposal will provide insight into the mechanisms operating in embryonic cells that maintain normal proliferation and prevent tumorigenesis. The genetic and molecular biological tools available in Drosophila will rapidly provide a depth of understanding that is difficult, if not impossible, to obtain using mammalian systems. PUBLIC HEALTH RELEVANCE: Organisms require cellular proliferation for normal processes such as growth during development and blood production. A protein called Myc is required for normal proliferation, although Myc causes cancer when over-abundant. This proposal investigates mechanisms of Myc activity in a tissue with naturally high levels of Myc.

描述（由申请人提供）：本项目的长期目标是了解分化过程如何防止胚胎发生过程中的过度增殖。更具体地说，转录因子和癌蛋白Myc是胚胎发生过程中增殖所必需的，然而Myc蛋白的过度丰富会诱导肿瘤;胚胎细胞如何实现Myc功能的正确平衡？Myc是一种转录调节因子，具有激活和抑制不同靶点转录的能力。Myc的转录激活需要其与DNA结合，尽管Myc的抑制不一定通过其与DNA的结合介导，但不能结合DNA的Myc突变体不能抑制。Myc抑制的第一个鉴定的靶点之一是c-myc基因本身，并且所有测试的人肿瘤衍生细胞系对于myc的这种自动抑制都是有缺陷的。为了理解myc基因自动抑制的机制，我与普林斯顿大学的埃里克·维斯肖斯（Eric Wieschaus）和迈克尔·科尔（Michael Cole）一起，沿着开发了一种新的基因筛选方法，使用的是黑腹果蝇。我们发现Polycomb（一种维持细胞命运所需的染色质结合阻遏物）的突变消除了果蝇myc基因的自动阻遏，也消除了胚胎中异位Myc介导的大多数阻遏。Polycomb中的突变也导致许多Myc激活靶点的表达增加，表明Polycomb、Myc的抑制和Myc的反式激活之间存在联系。虽然在生物学上很重要，但Polycomb和Myc之间的联系并不直接或间接。事实上，在果蝇胚胎中，Myc诱导功能上与Polycomb相关的基因产物的表达：Su（z）2、ESC和Pho（分别是哺乳动物bmi-1、eed和YY 1的同源物）。在这个建议中，我假设Myc激活Polycomb组基因产物Su（z）2，ESC和Pho导致Myc的下游抑制的目标，并且这些抑制物在整个胚胎发生中的相对丰度影响Myc反式抑制的目标。为了验证这一假设，我的具体目标是：（1）确定Myc是否直接与Su（z）2、pho和/或esc基因结合，导致它们的激活;（2）确定Su（z）2和/或Esc是否是Myc抑制所必需的;（3）确定在整个胚胎发生过程中与Myc相关的蛋白质。导致Myc表达增加的遗传改变引起不受控制的增殖和肿瘤发生。然而，在胚胎中，Myc水平很高，增殖受到控制。本提案中描述的研究将深入了解胚胎细胞维持正常增殖和预防肿瘤发生的机制。在果蝇中可用的遗传和分子生物学工具将迅速提供一个深度的理解，这是很难的，如果不是不可能的，获得使用哺乳动物系统。公共卫生相关性：生物体需要细胞增殖来进行正常过程，例如发育和血液生产期间的生长。一种叫做Myc的蛋白质是正常增殖所必需的，尽管Myc在过量时会导致癌症。该提案研究了Myc活性在具有天然高水平Myc的组织中的机制。