组蛋白H3K9甲基化结合蛋白MPP8参与的蛋白-蛋白相互作用在肿瘤细胞上皮-间充质转化中的功能和机制研究

肿瘤转移是肿瘤致死的主要原因。上皮-间充质转化（EMT）被认为是肿瘤转移的重要机制之一，其需要上皮基因的失活。我们发现新的组蛋白H3K9甲基化结合蛋白MPP8对维持EMT表型有重要意义，它可结合E-钙粘蛋白启动子并招募DNA甲基化酶3A和组蛋白去乙酰化酶SIRT1致基因失活。为揭示MPP8基因靶向的机制，我们检测了MPP8和EMT相关转录因子的相互作用，发现其可结合ZEB1。我们以往也发现MPP8的K439受到乙酰化修饰并促进其泛素化-降解。为揭示K439乙酰化促进MPP8泛素化的机制，我们初步鉴定了与MPP8相互作用的E3泛素连接酶。我们希望深入研究MPP8参与的这些蛋白-蛋白相互作用及其生物学意义，以揭示：1)MPP8-ZEB1相互作用对MPP8基因特异性靶向以及ZEB1的生物学功能的贡献；2)K439乙酰化促进MPP8泛素化-降解的机制以及MPP8的E3泛素连接酶在EMT中的功能。

Metastasis is the leading cause to cancer-related mortality. Epithelial-Mesenchymal transition (EMT) is one of the mechanisms by which tumor cells gains high motile and metastatic capacity. At the molecular level, EMT requires silencing of epithelial genes. We identified MPP8, a novel H3K9me binding protein, is necessary for the maintenance of EMT phenotype. MPP8 can localize to the E-Cadherin gene promoter and further recruits DNA methyltransferase 3A as well as histone deacetylase SIRT1 to cause gene repression. In this study, to uncover the mechanism by which MPP8 targets to specific genes, we examined interaction between MPP8 and EMT-related transcription factors. We found MPP8 interacts with ZEB1. In previous study, we also found MPP8 Lysine-439 is subject to acetylation which leads to increased degradation of MPP8 protein through the ubiquitin-proteasome pathway. To uncover the mechanism by which K439 acetylation promotes MPP8 ubiquitination, we investigated the interaction between MPP8 and ubiquitin E3 ligases. We will further investigate the biological significance of abovementioned new protein-protein interaction involving MPP8. We hope to uncover 1) the contribution of MPP8-ZEB1 interaction to the gene-specific targeting of MPP8 and function of ZEB1; 2) the mechanism of K439Ac promoting ubiquitination-mediated degradation of MPP8 and the role of MPP8’s E3 ligase in EMT.