A Blueprint for Oncogenic Epigenetic Reprogramming

描述（由申请人提供） 摘要：虽然癌症是一种遗传疾病，但癌细胞状态与多种表观遗传改变相关，包括异常DNA甲基化和组蛋白修饰模式。癌症生物学中的一个重大挑战是阐明肿瘤发生和发展过程中表观遗传改变的精确顺序及其对转化表型的贡献。为了应对这一挑战，人们需要一个从正常到恶性状态在时间上可追踪的细胞转化模型。癌细胞系不一定是好的模型，因为它们已经积累了数百到数千个遗传和表观遗传改变。在这里，我建议研究正常人类细胞的致癌转化病毒癌蛋白作为一个模型，以确定精确的表观遗传重编程事件发生沿着路径的肿瘤转化。腺病毒小e1 a或乳头状瘤病毒E7等病毒癌蛋白在描述调节细胞增殖的中心分子（例如视网膜母细胞瘤（RB）和p53肿瘤抑制因子）方面非常有用。我们最近的工作阐明了一种病毒癌蛋白e1 a的定义的全局表观遗传重编程，它迫使正常细胞逃避静止期癌症的标志。重要的是，e1 a直接实现了数千个宿主细胞基因的精确和协调的调节机制，通过以时间依赖性方式在整个基因组中相互作用和重排特定的表观遗传修饰剂，导致细胞转化。这提供了一个强大的模型，是服从时间序列测量表型定义的终点，使人们能够描绘的表观遗传改变，有助于致癌转化的连续顺序。通过了解e1 a如何协调细胞转化的表观遗传改变的特定序列，我们应该大大了解正常生物学和人类疾病，特别是癌症中基本表观遗传过程的功能和机制。 公共卫生相关性：癌细胞依赖于各种分子途径的多种改变来克服针对不受控制的细胞复制的正常防御机制。然而，这些变化如何及时合作将正常细胞转化为癌细胞还不是很清楚。某些病毒编码的蛋白质，如腺病毒e1 a，可以迫使正常细胞克服其防御机制并进行复制（癌症的标志），从而产生更多的病毒后代。由于病毒使用细胞自身的机制，它们已经非常揭示了癌症发生必须改变的过程。我们发现e1 a蛋白在感染后的不同时间表现出与不同宿主基因组结合的高度协调的程序。通过这种时间有序的结合模式，e1 a蛋白重新排列一组特定的基因调控酶，以促进细胞生长和复制，并抑制通常会阻止细胞分裂的抗病毒反应和分子途径。这类似于重新安排主人家的家具，以服务客人的险恶目的。该提案旨在使用e1 a介导的细胞转化来生成癌症发展必须以精确方式发生的连续事件顺序的蓝图。这项工作可以为导致癌症发展的初始分子事件提供基本见解，使我们能够设计更好的治疗方法和/或开发可能有助于个性化治疗的诊断和预后测定。

DESCRIPTION (Provided by the applicant) Abstract: While cancer is a genetic disease, the cancerous cellular state is associated with multiple epigenetic alterations including aberrant DNA methylation and histone modification patterns. A significant challenge in cancer biology is to elucidate the precise order of epigenetic alterations during tumor initiation and progression and their contributions to the transformed phenotype. To meet this challenge, one requires a model of cellular transformation that is temporally traceable from a normal to a malignant state. Cancer cell lines are not necessarily good models as they have already accumulated hundreds to thousands of genetic and epigenetic alterations. Here I propose to study the oncogenic transformation of normal human cells by viral oncoproteins as a model to determine the precise epigenetic reprogramming events occurring along the path of neoplastic transformation. Viral oncoproteins such as the Adenovirus small e1a or Papilloma virus E7 have been extraordinarily useful in delineating the central molecular players that regulate cell proliferation such as the retinoblastoma (RB) and p53 tumor suppressors. Our work has recently elucidated a defined global epigenetic reprogramming by one viral oncoprotein, e1a, that forces normal cells to escape quiescence-a hallmark of cancer. Importantly, e1a directly implements a precise and coordinated mechanism of regulation of thousands of host cell genes leading to cellular transformation by interacting and rearranging specific epigenetic modifiers across the whole genome in a time-dependent manner. This provides a powerful model that is amenable to time-series measurements with phenotypically defined endpoints, enabling one to delineate the successive order of epigenetic alterations that contribute to oncogenic transformation. By understanding how e1a orchestrates a specific sequence of epigenetic alterations for cellular transformation, we should learn greatly about the functions and mechanisms of fundamental epigenetic processes in normal biology and human disease, especially cancer. Public Health Relevance: Cancer cells depend on multiple alterations in various molecular pathways to overcome normal defense mechanisms against uncontrolled cell replication. However, how these changes cooperate in time to transform a normal cell to a cancerous one is not very well understood. Certain viruses encode proteins, such as the Adenovirus e1a, that can force a normal cell to overcome its defense mechanism and to replicate-a hallmark of cancer-so that more viral progenies are produced. Because viruses use the cell's own machinery, they have been extraordinarily revealing about processes that must be altered for cancer to arise. We have discovered that the e1a protein displays a highly coordinated program of binding to different sets of host genes at different times after infection. Through such temporally-ordered pattern of binding, the e1a protein rearranges a specific set of gene regulatory enzymes so as to promote cell growth and replication and to repress antiviral responses and molecular pathways that would normally stop the cell from dividing. This is akin to rearranging the furniture in the host's house to serve the guest's sinister purposes. This proposal aims to use e1a-mediated cellular transformation to generate a blueprint for the successive order of events that must occur in a precise manner for cancer to develop. This work may provide fundamental insights into the initial molecular events that lead to cancer development, enabling us to design better therapeutics and/or develop diagnostic and prognostic assays that may aid in personalization of therapy.