MPP8-Mediated Epigenetic Network and Its Roles in Tumor Progression

描述（由申请人提供）：mpp8介导的表观遗传网络及其在肿瘤进展中的作用表观遗传学通常被定义为不改变DNA序列而发生的基因表达的可遗传变化。研究最广泛的两种表观遗传机制，组蛋白修饰和DNA甲基化是更广泛的表观遗传“密码”的一部分，它决定了基因组结构域的转录潜力。因此，表观遗传修饰对于控制基因表达模式和细胞身份至关重要，而这些过程的破坏可能导致基因功能改变和恶性细胞转化。作为两种主要的抑制性表观遗传修饰，组蛋白H3K9甲基化和DNA甲基化与肿瘤进展过程中基因抑制模式的建立和维持明显相关。与这一观点一致，我们最近的研究表明，一种新的甲基- h3h9结合蛋白MPP8在EMT（上皮-间质转化）中具有重要功能，EMT是赋予上皮肿瘤细胞迁移和侵袭能力的重要程序，与转移能力相关。MPP8在不同的人类原发性癌症组织中表达升高，而在转移性乳腺癌和肺癌细胞中敲低MPP8可重建上皮表型，并显著降低迁移和侵袭能力。在分子水平上，MPP8直接靶向E-cadherin启动子并抑制这一关键的EMT调节因子。MPP8还与H3K9 mtase G9a/GLP和新生DNMT3A相互作用，重要的是，招募DNMT3A来指导E-cadherin CpG岛上的DNA甲基化。MPP8蛋白相互作用的表征进一步揭示了G9a/GLP在K47位点甲基化DNMT3A以及它们自己的n端赖氨酸。所有甲基化标记在体内和体外都能被MPP8识别，这表明MPP8协调了一种新的表观遗传复合物，将H3K9甲基化和DNA甲基化结合在一起，实现肿瘤抑制基因的沉默。此外，我们证明MPP8和G9a与emt激活的主要转录因子ZEB1密切相关。这些结果共同提示了EMT和肿瘤进展过程中的一种新的抑制途径，其中ZEB1招募G9a-MPP8-DNMT3A复合物建立H3K9和DNA甲基化，从而实现各种上皮基因的转录沉默。为了进一步扩展这项研究，我们提出了进一步的实验来阐明这一途径的分子机制，并了解DNMT3A- K47甲基化的功能意义。我们还将评估MPP8在体外和体内EMT和肿瘤进展中的重要性。这些研究的完成不仅将对我们对肿瘤进展中的表观遗传调控的理解产生重大影响，而且还将促进癌症治疗中可能的表观遗传策略的发展。

DESCRIPTION (provided by applicant): MPP8-Mediated Epigenetic Network and Its Roles in Tumor Progression Epigenetics are commonly defined as heritable changes in gene expression that occur without changes in DNA sequence. Two of the most extensively studied epigenetic mechanisms, histone modifications and DNA methylation are part of broader epigenetic 'code' that dictates the transcriptional potential of genomic domains. Therefore, epigenetic modifications are essential to control gene expression patterns and cell identity while disruption of these processes can lead to altered gene function and malignant cellular transformation. As two major repressive epigenetic modifications, histone H3K9 methylation and DNA methylation have been clearly implicated in establishing and maintaining gene repression patterns during tumor progression. Consistent with this notion, our recent studies suggest that a novel methyl-H3H9 binding protein MPP8 has important functions in EMT (epithelial-to-mesenchymal transition), an essential program to endow epithelial tumor cells with migratory and invasive capabilities associated with metastatic competence. MPP8 displays an elevated expression in different human primary cancer tissues while knockdown of MPP8 in metastatic breast and lung cancer cells re-establishes epithelial phenotypes attended by a significantly reduces migration and invasion abilities. At the molecular level, MPP8 directly targets E-cadherin promoter and represses this key EMT regulator. MPP8 also interacts with H3K9 MTases G9a/GLP and de novo DNMT3A, and importantly, recruits DNMT3A to direct DNA methylation on E-cadherin CpG island. Characterization of MPP8 protein interactions further reveals that G9a/GLP methylate DNMT3A at K47 as well as their own N-terminal lysines. All the resultant methylation marks are recognized by MPP8 in vitro and in vivo, suggesting that MPP8 coordinates a novel epigenetic complex which couples H3K9 methylation and DNA methylation for tumor suppressor gene silencing. Furthermore, we demonstrate that MPP8 and G9a robustly associate with a major EMT-activating transcription factor ZEB1. These results together suggest a novel repression pathway during EMT and tumor progression, in which ZEB1 recruits G9a-MPP8-DNMT3A complex to establish H3K9 and DNA methylations for transcriptional silencing of various epithelial genes. To extend this study, we propose further experiments to elucidate molecular mechanisms of this pathway and to understand the functional significance of DNMT3A- K47 methylation. We will also assess the importance of MPP8 in EMT and tumor progression in vitro and in vivo. Completion of the proposed studies will not only significantly impact on our understanding of epigenetic regulations in tumor progression, but also facilitate the development of possible epigenetic strategies for the cancer treatment.