(PQD4) Epigenetic loss of heterozygosity as a driver of the cancer field effect

描述(由申请人提供)：表观遗传杂合性丢失(ELoH)是正常人类和小鼠发育中的一个常见过程，超过了众所周知的X染色体失活的例子。最近的研究表明，ELoH比以前认识的要普遍得多：在人类和小鼠中，超过10%的常染色体基因受到单等位基因沉默的影响，其方式类似于X-失活。作为ELoH的结果，即使是同一个体中相同类型的细胞，其命运也可能截然不同。当肿瘤抑制基因受到影响时，具有“好”等位基因的表观遗传沉默的细胞会产生肿瘤，而具有相反等位基因选择的细胞则保持正常。事实上，ELoH影响许多与癌症相关的常染色体基因。受影响基因的单等位基因沉默在有丝分裂中是稳定的，并导致组织中形成马赛克，每个斑块中的细胞共享一个 特定的全基因组ELoH模式。我们假设，一些ELH模式通过导致关键基因的功能性LOH而使细胞易于发生肿瘤启动。在这种情况下，癌症野效应将通过分享克隆细胞斑块内侵袭性的ELoH模式来解释，而邻近斑块中的细胞将具有肿瘤抗药性，因为它们携带无害的模式。该项目结合了两个领先实验室在乳腺癌建模和全基因组ELoH分析方面的独特专业知识。我们将结合我们对ELH表观基因组学的开创性方法和在小鼠乳腺肿瘤发展模型中的专业知识，系统地探索和表征表观遗传LOH在癌症领域效应中的作用。利用RNA和染色质的深度测序，我们将绘制多灶性乳腺肿瘤的全基因组ELoH模式，并将它们与纯化的正常导管上皮细胞中的模式进行比较。如果成功，这项拟议的工作将建立一个新的概念框架，用于理解在正常发育和分化过程中形成的克隆谱系背景下的癌症视野效应。我们还将创建一个强大的实验平台，用于系统研究广泛存在的表观遗传杂合性缺失现象。我们相信，这将对我们理解癌症视野效应背后的表观遗传机制产生重大影响。由于表观遗传过程原则上是可逆的，我们的发现应该会建议使用表观遗传修饰物治疗和预防癌症的新策略。

DESCRIPTION (provided by applicant): Epigenetic loss of heterozygosity (eLOH) is a common process in normal human and mouse development, above and beyond the well-known example of X chromosome inactivation. Recent work has shown that eLOH is much more common than previously appreciated: over 10% of autosomal genes in human and mouse are subject to monoallelic silencing in a way that resembles X-inactivation. As a result of eLOH, even cells of the same type in the same individual can have dramatically different fates. When a tumor suppressing gene is affected, cells with the epigenetic silencing of the "good" allele give rise to tumors, while the cells with the opposite allelic choice remain normal. In fact, eLOH affects many cancer-related autosomal genes. Monoallelic silencing of the affected genes is mitotically stable and leads to formation of a mosaic in tissue, with cells in each patch sharing a particular genome-wide eLOH pattern. We hypothesize that some eLOH patterns predispose cells to tumor initiation by causing functional LOH in critical genes. The cancer field effect woul be explained in this case by sharing the offensive eLOH pattern within clonal cell patches, while cells in neighboring patches would be tumor resistant because they carried harmless patterns. This project combines the unique expertise of two leading laboratories in breast cancer modeling and in genome-wide eLOH analysis. We will systematically explore and characterize the role of epigenetic LOH in the cancer field effect by combining our pioneering approaches to epigenomics of eLOH and expertise in mouse models of mammary tumor development. Using deep sequencing of RNA and chromatin, we will map genome- wide eLOH patterns in multifocal mammary tumors and compare them to such patterns in purified normal duct epithelial cells. If successful, the proposed work will establish a new conceptual framework for understanding the cancer field effect in the context of clonal lineages formed during normal development and differentiation. We will also have created a robust experimental platform for systematic study of the widespread phenomenon of epigenetic LOH. We believe this will have a major impact on our understanding of the epigenetic mechanisms underlying the cancer field effect. Since epigenetic processes are in principle reversible, our findings should suggest new strategies in cancer treatment and prevention using epigenetic modifiers.