TET2-mediated transcriptional and epigenetic control of normal and malignant hematopoiesis

TET2是成人髓系恶性肿瘤和正常骨髓中最常见的突变基因之一 70岁以上的个人。TET2基因缺失导致造血细胞数量增加 干细胞/祖细胞(HSPC)和随后的小鼠髓系恶性肿瘤的发展。 因此，TET2突变构成了HSPC早期干预的合适靶点 克隆性扩张。为了从治疗上利用TET2突变，更好地理解TET2突变 TET2缺失导致HSPC癌前病变和髓系恶性病变的机制 发展是必不可少的。作为甲基胞嘧啶双加氧酶家族的一员，TET2将5mC 到5hmC，可以相对稳定，也可以进一步氧化到5fC和5caC。我们 已经报道了TET2在其抑瘤功能中对催化活性的要求 HSPC。最近，我们发现了一种新的血液系统恶性肿瘤的发病机制。 TET2结合的基因组位置的突变负担，并与直觉相反，获得了5hmC TET2--失利。此外，我们还发现了TET2在RNA羟甲基化(Hm5C)和 小鼠靶向转录通过其伴侣和RNA结合蛋白(RBP)PSPC1失稳 胚胎干细胞。重要的是，我们发现PSPC1和它的异二聚体伙伴NONO是 两者均在HSPC中大量表达。我们的研究提出了关于TET2的两个关键问题 正常和恶性造血的生物学：1)获得的5hmC如何对 髓系恶性肿瘤的发病机制？2)TET2的催化活性与其功能相关 HSPC中的RNA hm5C水平？我们推测TET2可能通过以下途径发挥酶功能 5hmC-to-5fC/5caC优先氧化导致DNA去甲基化和转录 肿瘤抑制基因的激活和通过RNA hm5C修饰及其结果 致癌核糖核酸的不稳定。我们将研究DNA-5hmC和RNA-hm5C的失调是如何 TET2突变的介导性表观遗传控制可通过三种途径导致恶性血液病 明确的目标。目的1)确定TET2介导的5hmC-5fC/5caC对DNA的优先氧化 用OUR方法研究HSPC去甲基化及其在髓系恶性肿瘤发病机制中的作用 新建立了5hmC停滞和催化失活的敲入突变TET2小鼠模型。目标2) 确定TET2-RUNX1伙伴关系对TET2基因组定位的功能意义 目的基因在HSPC中的表达。RUNX1，一个TET2结合伙伴，据报道富含 TET2突变型AML的5hmC增高区，而不是低5hmC区。我们将研究RUNX1 TET2基因在HSPC中的调控作用及RUNX1在HSPC中的作用 TET2在5hmC-to-5fC/5caC在正常和 恶性血液病。目的3)研究RBP介导的TET2对RNA hm5C的募集 HSPC致癌RNA的修饰和失稳及其在血液学中的失调 恶毒。我们还将研究TET2突变如何损害其在HSPC中的PSPC1关联 导致恶性血液病。

TET2 is one of the most commonly mutated genes in adult myeloid malignancies and in normal individuals over 70 years of age. Tet2-loss leads to increased expansion of hematopoietic stem/progenitor cells (HSPCs) and subsequent development of myeloid malignancies in mice. Thus, TET2 mutations constitute a suitable target for intervention at the early stages of HSPC clonal expansion. To exploit TET2 mutations therapeutically, a better understanding of the mechanisms by which Tet2-loss leads to premalignant HSPC dysregulation and myeloid malignancy development is essential. As a member of the methylcytosine dioxygenase family, TET2 converts 5mC to 5hmC, which can be relatively stable or be further oxidized to 5fC and 5caC. We have reported the requirement of catalytic activity of TET2 in its tumor-suppressive functions in HSPCs. Recently, we identified a novel mechanism of hematological malignancy via the increased mutational burden at genomic sites where TET2 binds and, counterintuitively, with gained 5hmC upon TET2-loss. In addition, we discovered a novel role of TET2 in RNA hydroxymethylation (hm5C) and target transcripts destabilization via its partner and RNA-binding protein (RBP) PSPC1 in mouse embryonic stem cells. Importantly, we found that PSPC1 and its heterodimer partner NONO are both abundantly expressed in HSPCs. Our studies raise two critical questions on TET2 biology in normal and malignant hematopoiesis: 1) How does gained 5hmC contribute to the pathogenesis of myeloid malignancy? 2) Is catalytic activity of TET2 relevant and functional at the RNA hm5C level in HSPCs? We hypothesize that TET2 may exert enzymatic functions through preferential 5hmC- to-5fC/5caC oxidation leading to DNA demethylation and transcriptional activation of tumor suppressor genes and through RNA hm5C modification and consequent destabilization of oncogenic RNAs. We will study how dysregulation of DNA-5hmC and RNA-hm5C mediated epigenetic control upon TET2 mutations can lead to malignant hematopoiesis by three specific aims. Aim 1) Define preferential TET2-mediated 5hmC-5fC/5caC oxidation for DNA demethylation in HSPCs and its dysregulation for the pathogenesis of myeloid malignancy using our newly created 5hmC stalling and catalytically inactive knock-in mutant Tet2 mouse models. Aim 2) Determine the functional significance of the TET2-RUNX1 partnership for TET2 genomic localization and target gene expression in HSPCs. RUNX1, a TET2 binding partner, is reported to be enriched in regions of increased 5hmC, but not in hypo-5hmC regions in TET2 mutant AML. We will study RUNX1 functions in regulating TET2 genomic occupancy in HSPCs and examine the potential role of RUNX1 in imparting unique TET2 functions in preferential 5hmC-to-5fC/5caC oxidation during normal and malignant hematopoiesis. Aim 3) Investigate RBP- mediated TET2 recruitment for RNA hm5C modification and destabilization of oncogenic RNAs in HSPCs and its dysregulation in hematological malignancy. We will also investigate how mutation of TET2 may impair its PSPC1 association in HSPCs leading to malignant hematopoiesis.