A Novel Epigenetic Circuit in Acute Leukemia

描述（由申请人提供）：癌症是由直接影响关键癌基因和肿瘤抑制因子功能的遗传或表观遗传改变驱动的。这些关键蛋白共同构成了癌症发展的基本机制。虽然已经做出了重大努力来阐述典型的癌基因/肿瘤抑制电路，但理解癌症表观遗传基础的新时代正在开始。癌细胞中这些新的表观遗传变化如何整合癌基因/肿瘤抑制功能尚不清楚。本申请的中心概念是核受体结合SET结构域（NSD）家族和含SET结构域2（SET D2）代表控制组蛋白-H3赖氨酸-36甲基化（H3 K36 me）的新的癌基因/肿瘤抑制电路。NSD 1、NSD 2和/或NSD 3是指定H3 K36的单甲基化和二甲基化的组蛋白甲基转移酶（H3 K36 me 1、H3 K36 me 2）。SETD 2是一种组蛋白甲基转移酶，对H3 K36（H3 K36 me 3）的三甲基化具有特异性; H3 K36是与活性染色质相关的甲基化标记。因此，在正常细胞中，这些蛋白质以逐步方式起作用以修饰H3 K36以提供染色质活化标记，所述染色质活化标记用作转录机制和其它H3 K36 me 3结合蛋白的对接位点以维持染色质结构。在癌细胞中，编码NSD和SETD 2的基因经常发生突变。在急性淋巴细胞白血病（ALL）中发现了对H3 K36 me 2具有功能获得（GOF）效应的NSD突变。我们最近在ALL和AML中发现了复发性SETD 2突变。我们发现SETD 2突变与H3 K36 me 3标记的显著减少和H3 K36 me 2标记的积累相关。因此，我们得出结论，SETD 2遗传变异导致SETD 2功能丧失（LOF），H3 K36 me 3减少和H3 K36 me 2积累。基于这些新颖、独特和令人兴奋的初步结果，我们假设，尽管急性白血病相关突变导致NSD和SETD 2的相互生化效应，但这些变化的最终产物是相同的; H3 K36 me 3减少和H3 K36 me 2积累（低H3 K36 me 3/H3 K36 me 2比率）。因此，在本申请中，我们将建模并靶向在白血病中鉴定的新型NSD 2 GOF突变。我们还将建模和靶向在我们的白血病筛查中发现的新型SETD 2 LOF突变。我们将研究它们对细胞生长和白血病发展、H3 K36 me 3/H3 K36 me 2比率和H3 K27状态的功能。这项拟议的研究应该定义NSD和SETD 2在白血病背景下的功能关系，确认新的SETD 2-H3 K36 me 3肿瘤抑制通路，并确定对这些表观遗传改变进行治疗干预的新的互补机会。

DESCRIPTION (provided by applicant): Cancer is driven by genetic or epigenetic alterations that directly affect the function of critical oncogenes and tumor suppressors. Together, these pivotal proteins underlie fundamental mechanisms of cancer development. While there have been significant efforts towards elaborating canonical oncogene/tumor suppressor circuits, a new era of understanding the epigenetic basis of cancer is beginning. How these new epigenetic changes in cancer cells integrate oncogene/tumor suppressor functions is not known. The central concept of this application is that the Nuclear receptor binding SET domain (NSD) family and SET-domain- containing 2 (SETD2) represent a new oncogene/tumor suppressor circuit controlling histone-H3 lysine-36 methylation (H3K36me). NSD1, NSD2, and/or NSD3 are histone methyltransferases that specify mono- and di-methylation of H3K36 (H3K36me1, H3K36me2). SETD2 is a histone methyltransferase that is specific for tri-methylation of H3K36 (H3K36me3); a methylation mark associated with active chromatin. Thus, in normal cells these proteins function in a stepwise manner to modify H3K36 to provide chromatin activation marks which serve as docking sites for transcriptional machinery and other H3K36me3 binding proteins to maintain chromatin structure. In cancer cells, the genes encoding both NSDs and SETD2 are frequently mutated. NSD mutations with gain of function (GOF) effects on H3K36me2 are found in acute lymphoblastic leukemia (ALL). We recently identified recurrent SETD2 mutations in both ALL and AML. We found that SETD2 mutations were associated with a dramatic reduction in the H3K36me3 mark and accumulation of H3K36me2 mark. Thus, we conclude that SETD2 genetic alterations lead to SETD2 loss of function (LOF), reduction of H3K36me3, and accumulation of H3K36me2. Based upon these novel, unique and exciting preliminary results, we hypothesize that although acute-leukemia-relevant mutations cause reciprocal biochemical effects in NSDs and SETD2, the end product of these changes is the same; a reduction in H3K36me3 and an accumulation of H3K36me2 (low H3K36me3/H3K36me2 ratio). Thus, in this application we will model and target novel NSD2 GOF mutations identified in leukemia. We will also model and target novel SETD2 LOF mutations identified in our leukemia screen. We will study their function on cell growth and leukemia development, on H3K36me3/H3K36me2 ratios and on H3K27 status. This proposed research should define functional relationships between NSDs and SETD2 in the context of leukemia, confirm the novel SETD2-H3K36me3 tumor suppressor pathway and identify novel complementary opportunities for therapeutic intervention on these epigenetic alterations.