Post-Translational Control of TET Function in Lymphoma

泰特DNA羟化酶是α-酮戊二酸（αKG）依赖性酶，催化5 mC的氧化 5-羟甲基胞嘧啶（5 hmC），从而促进DNA去甲基化。5 hmC标记单碱基定位 分辨率表明，泰特酶的主要作用是维持基因增强子的低甲基化， 活跃增强子是转录因子结合以调节基因表达程序的基因组区域。 被转录因子密集占据的增强子的过度活跃簇被称为超转录因子。 增强子，通常在癌症中发现。与启动子一样，增强子/超级增强子受其调控。 DNA甲基化状态，一个在癌症中经常出错的过程。因此，考虑到活性增强剂和超级- 增强子在本质上是致癌的，并且泰特酶使它们保持低甲基化和活性，我们 假设增加的泰特活性本身可能是致癌的。线粒体作为信号细胞器的功能， 产生促进表观遗传变化的底物，包括例如DNA的乙酰化和甲基化 和组蛋白。最近，我们和其他人描述了线粒体和线粒体之间微妙的相互作用。 表观遗传学，其中发现中间代谢产物αKG和2-羟基戊二酸的水平 调节泰特酶的活性，从而控制DNA甲基化。这些发现让我们假设 中间代谢在DNA甲基化的控制中起着重要的作用。我们特别 假设线粒体酶D-2-和L-2-羟戊二酸脱氢酶（D2 HGDH和 L2 HGDH），其催化2-HG到αKG的互变，是与α KG之间的串扰不可或缺的。 线粒体代谢、泰特功能和超级增强子去甲基化/活化。为了扩展这个最初的 概念，我们试图鉴定调节D2 HGDH和L2 HGDH表达的上游信号， 从而影响泰特功能和增强子甲基化/活性。使用报告基因和ChIP测定， 在诱导型细胞系和小鼠模型中，我们最近报道MYC转录激活D2 HGDH， L2 HGDH，并以D2 HGDH/L2 HGDH/α KG依赖性方式诱导泰特功能，导致DNA 在体外和体内的去甲基化。值得注意的是，我们发现MYC/D2-L2 HGDH/αKG轴也 促进TET 1、TET 2和TET 3的核积累，与增强的O-GlcNAc化相关， 由另一种线粒体酶O-GlcNAc转移酶（OGT）执行的翻译后修饰。 此外，我们初步表明，在弥漫性大B细胞淋巴瘤（DLBCL）中，MYC水平与 增强子甲基化和靶基因表达。总之，这些数据揭示了一种新的线粒体 信号传导轴，包括近端的MYC、中心的D2/L2 HGDH和OGT以及远端的泰特 活性和亚细胞位置。在本提案中，我们将在体外和体内使用人B细胞淋巴瘤模型， 为了检验中间代谢（部分由于MYC活性）诱导泰特的总体假设， 功能，保持致癌增强子/超级增强子低甲基化和活性并促进癌症。我们 具体目的是：1）确定由蛋白质介导的增加的O-GlcNAc酰化的机制基础。 MYC-D2/L2 HGDH-αKG轴及其在促进泰特核定位和增强子激活中的作用AIM 2） 定义泰特活化对MYC驱动的淋巴瘤发生的贡献AIM 3）表征MYC- B细胞淋巴瘤中5 hmC标记和超级增强子激活的驱动图。拟议的研究具有重要意义 因为它将定义并从机制上阐明MYC在癌症中的新作用，即，致癌激活 增强子/超级增强子。在MYC下游，D2 HGDH-L2 HGDH的贡献（通过αKG生成） 和O-GlucNAc化将赋予泰特功能的翻译后控制，这挑战了目前的 这些酶的功能仅仅是肿瘤抑制剂。

TET DNA hydroxylases are alpha-ketoglutarate (αKG)-dependent enzymes that catalyze the oxidation of 5mC to 5-hydroxymethylcytosine (5hmC), thus promoting DNA demethylation. Mapping of 5hmC marks at single base resolution demonstrated that the main role of TET enzymes is to maintain gene enhancers hypomethylated and active. Enhancers are genomic areas to which transcription factors bind to modulate gene expression programs. Hyperactive clusters of enhancers that are densely occupied by transcriptional factors are termed super- enhancers and are typically found in cancer. Like promoters, enhancers/super-enhancers are regulated by their DNA methylation status, a process that often goes awry in cancer. Thus, given that active enhancers and super- enhancers are oncogenic in nature, and that TET enzymes maintain them hypomethylated and active, we postulate that increased TET activity may itself be oncogenic. Mitochondria function as signaling organelles by generating substrates that fuel epigenetic changes, including for example acetylation and methylation of DNA and histones, respectively. Recently, we and others described a subtler interplay between mitochondria and epigenetics, wherein the levels of the intermediate metabolites αKG and 2-hydroxyglutarate were found to modulate the activity of TET enzymes, thus controlling DNA methylation. These findings led us to hypothesize that intermediary metabolism plays as an important role in the control of DNA methylation. Specifically, we posited that the mitochondrial enzymes D-2- and L-2-hydroxyglutarate dehydrogenase (D2HGDH and L2HGDH), which catalyze the interconversion of 2-HG to αKG, are integral to the cross talk between mitochondrial metabolism, TET function and super-enhancer demethylation/activation. To expand on this initial concept, we sought to identify upstream signals that regulate D2HGDH and L2HGDH expression and, consequently, influence TET function and enhancer methylation/activity. Using reporter and ChIP assays, inducible cell lines and mouse models, we recently reported that MYC transcriptionally activates D2HGDH and L2HGDH and, in a D2HGDH/L2HGDH/αKG-dependent manner, induces TET function leading to DNA demethylation in vitro and in vivo. Remarkably, we discovered that the MYC/D2-L2HGDH/αKG axis also promotes the nuclear accumulation of TET1, TET2 and TET3, in association with enhanced O-GlcNAcylation, a post-translational modification executed by another mitochondrial enzyme, O-GlcNAc transferase (OGT). Further, we preliminarily showed that in in diffuse large B cell lymphoma (DLBCL), MYC levels associated with enhancer methylation and target gene expression. Together, these data uncovered a novel mitochondrial signaling axis which includes MYC at the proximal point, D2/L2HGDH and OGT at the center, and, distally, TET activity and subcellular location. In this proposal, we will use human B cell lymphoma models in vitro and in vivo, to test the overarching hypothesis that intermediary metabolism, in part due to MYC activity, induces TET function, maintains oncogenic enhancers/super-enhancers hypomethylated and active and promote cancer. Our specific aims are: AIM 1) Determine the mechanistic basis for the increased O-GlcNAcylation mediated by the MYC-D2/L2HGDH-αKG axis and its role in promoting TET nuclear localization and enhancer activation. AIM 2) Define the contribution of the TET activation to MYC-driven lymphomagenesis AIM 3) Characterize the MYC- driven map of 5hmC marks and super-enhancer activation in B cell lymphoma. The proposed study is significant because it will define, and mechanistically elucidate, a novel role for MYC in cancer, i.e., activation of oncogenic enhancers/super-enhancers. Downstream to MYC, the contribution of D2HGDH-L2HGDH (via αKG generation) and O-GlucNAcylation will impart a post-translational control of TET function, which challenges the current dogma that these enzymes function exclusively as tumor suppressors.