UTX, MLL AND PATHOGENIC DEREGULATION OF HISTONE METHYLATION IN MULTIPLE MYELOMA

描述（由申请人提供）：基因组测序的进展表明，染色质调控因子的复发性突变是恶性肿瘤的共同特征，包括多发性骨髓瘤（MM）。在这些病变中，组蛋白甲基转移酶（hmt）和组蛋白去甲基化酶的突变是突出的。这些突变可能导致染色质的全基因组功能障碍，强烈影响基因调控，并可能影响其他染色质依赖的过程。与基因沉默相关的组蛋白3赖氨酸27三甲基化（H3K27me3）和与基因激活相关的H3K4甲基化之间的平衡对正常基因表达至关重要。PRC2复合体（Polycomb suppression complex 2）的核心包含h3k27特异性HMT EZH2。EZH2或伴侣蛋白如ASXL1的功能突变缺失导致H3K27me3的全局缺失，而淋巴瘤中EZH2功能突变的增加则增加了H3K27me3。在儿童脑肿瘤中发现H3K27->M突变，阻止组蛋白修饰20并阻断EZH2的作用21，从而强调了该残基的重要性。此外，我们发现MMSET（一种h3k36特异性的HMT）在MM中的过表达会导致H3K27me3的全基因组减少。基因激活需要去除H3K27标记，并在基因启动子和增强子上放置H3K4me修饰。这是由包含H3K27特异性组蛋白去甲基化酶UTX （X染色体上的泛素转录四肽重复）、MLL（混合谱系白血病）hmt家族成员（包括MLL2和MLL3）、组蛋白乙酰转移酶p300和CREBBP以及SWI/SNF染色质重塑机制成员的多蛋白复合物完成的。这些复合物的几乎所有成员都可以在淋巴恶性肿瘤中发生突变。具体来说，UTX（官方基因名称KDM6A）在多达30%的MM中发生突变或缺失。此外，MLL2，特别是MLL3在MM中显示失活突变。我们假设UTX和MLL3突变在MM发病机制中具有类似的功能，导致H3K27me/H3K4me异常失衡和关键靶基因抑制。因此，一种降低H3K27甲基化的EZH2抑制剂正处于临床前和早期临床开发阶段，可能能够重新平衡染色质修饰，并提供一种新的治疗方法。为了验证这些想法，我们提出以下具体目标：1)确定UTX和MLL3在MM和淋巴样细胞染色质结构、细胞生长和稳态控制中的重要性；2)确定MM中UTX和MLL3缺失影响的遗传靶点和途径；3)确定UTX在B细胞成熟和MM发展中的重要性

DESCRIPTION (provided by applicant): Advances in genome sequencing revealed that recurrent mutations in chromatin regulators are a common feature in malignancy, including multiple myeloma (MM). Among these lesions, mutations in histone methyltransferases (HMTs) and histone demethylases are prominent. These mutations may yield global, genome-wide dysfunction of chromatin, strongly affecting gene regulation and possibly influencing other chromatin-dependent processes. The balance between histone 3 lysine 27 trimethylation (H3K27me3), associated with gene silencing and H3K4 methylation, linked to gene activation, is critical for normal gene expression. The PRC2 complex (Polycomb Repressive Complex 2) contains at its core a H3K27-specifc HMT, EZH2. Loss of function mutations of EZH2 or partner proteins such as ASXL1 lead to global loss of H3K27me3, while gain of function mutations of EZH2 in lymphoma increases H3K27me3. The importance of this residue was underscored by discovery of H3K27->M mutation in pediatric brain tumors, precluding histone modification 20 and blocking EZH2 action 21. Furthermore, we found that overexpression of MMSET, an H3K36-specific HMT, in MM causes a genome-wide decrease in H3K27me3. Gene activation requires the removal of the H3K27 mark and placement of the H3K4me modification at gene promoters and enhancers. This is accomplished by a multi-protein complex containing the H3K27- specific histone demethylase UTX, (Ubiquitously transcribed Tetratricopeptide repeat, X chromosome), members of the MLL (Mixed Lineage Leukemia) family of HMTs (including MLL2 and MLL3), histone acetyltransferases p300 and CREBBP, and members of the SWI/SNF chromatin remodeling machinery. Almost all members of these complexes can be mutated in lymphoid malignancies. Specifically, UTX (Official gene name KDM6A) is mutated or deleted in up to 30% of MM. Moreover, MLL2 and especially MLL3 display inactivating mutations in MM. We hypothesize that UTX and MLL3 mutations have a similar function in MM pathogenesis to cause an aberrant imbalance of H3K27me/H3K4me and suppression of critical target genes. Accordingly, an EZH2 inhibitor that decreases H3K27 methylation is in preclinical and early clinical development may be able to rebalance chromatin modifications and offer a new therapeutic approach. To test these ideas we propose the following specific Aims: 1) Determine the Importance of UTX and MLL3 in the Control of Chromatin Structure, Cell Growth and Homeostasis of MM and Lymphoid Cells 2) Determine the Genetic Targets and Pathways Affected by Loss of UTX and MLL3 in MM 3) Determine the Importance of UTX in B Cell Maturation and in the Development of MM