组蛋白去甲基化酶JMJD1B对MLL相关白血病成因的机制研究

Histone methylation is one of the major epigenetic regulation mechanisms which plays critical roles in various patho-physiological processes, including MLL-related leukemia. The interplays among histone methyltransferases, demethylases and their effectors, which can recognize histone methylated sites, contribute to the establishment and maintenance of different histone methylation statuses and the regulation of their downstream gene expression. Histone methylation mainly occurs on lysines and arginines. Till now, a plethora of demethylases which mediate the removal of methyl groups from different lysine residues on histones have been identified. However, demethylases which specifically demethylate arginines remain to be discovered. Our preliminary studies suggested that JMJD1B could demethylate histone H4 at arginine 3 (H4R3). In this proposal, we aim to investigate the effect of methylated H4R3(H4R3me2a, H4R3me2s) on gene expression, with a focus on those genes involved in leukemia, and to explore the contribution of JMJD1B in these processes. We will study the effects of JMJD1B knockdown on other histone epigenetic modifications to explore the crosstalks between different histone epigenetic modifications. We also aim to identify JMJD1B-interacting proteins and study its regulatory biochemical mechanisms. We also plan to generate JMJD1B knockout mice to investigate its physiological in vivo functions and its contributions to MLL-related leukemia.

组蛋白的甲基化修饰是表观遗传的重要调控机制之一，这一过程需要组蛋白甲基转移酶、去甲基化酶及下游效应蛋白的共同参与和协调调控。组蛋白甲基化修饰异常与许多疾病如MLL基因重排导致的白血病的发生密切相关。目前针对组蛋白去甲基化酶的研究主要是作用于赖氨酸的去甲基化酶，特异性作用于精氨酸的组蛋白去甲基化酶尚无明确报道。前期工作中，我们初步鉴定出JMJD1B具有针对组蛋白精氨酸H4R3位点的去甲基化酶活性。本申请中，我们拟通过质谱等相关手段验证这一全新的结果，检测不同甲基化修饰状态的H4R3对白血病相关基因转录和表达水平的影响，观察JMJD1B基因沉默对这一相互作用模式的效应及对组蛋白其它表观遗传修饰状态的影响。我们将鉴定JMJD1B互作蛋白，深入研究JMJD1B功能发挥的调控机制，并通过构建JMJD1B特异性敲除小鼠模型研究JMJD1B的生理功能及JMJD1B缺失所引发的MLL相关白血病的分子机制。

组蛋白的甲基化修饰是表观遗传的重要调控机制之一，这一过程需要组蛋白甲基转移酶、去甲基化酶及下游效应蛋白的共同参与和协调调控。组蛋白甲基化修饰状态与诸多生命过程密切相关，如DNA损伤应答、基因转录、细胞周期、信号转导及细胞分化等。目前针对组蛋白去甲基化酶的研究主要是集中在作用于赖氨酸的去甲基化酶，特异性作用于精氨酸的组蛋白去甲基化酶尚无明确报道。本项目中，我们发现并证明JMJC去甲基化酶家族成员JMJD1B具有针对组蛋白精氨酸H4R3位点对称性双甲基化修饰（H4R3me2s）和单甲基化修饰（H4R3me1）的去甲基化酶活性。JMJD1B在造血干细胞HSPC中高表达，并与HSPC中遗传标记H3K9me2及H4R3me2s的去甲基化状态具有直接相关性。JMJD1B通过对H4R3me2s及 H3K9me2遗传标记的去甲基化作用调控对HSPC的生存，增殖及分化有重要影响的基因表达。造血干细胞HSPC中去甲基化酶JMJD1B同甲基转移酶PRMT5协同作用调控H4R3me2s遗传标记的动态平衡及造血相关基因的表达。造血干细胞中敲除JMJD1B导致造血功能缺陷。此外，我们也有实验结果表明JMJD1B通过调控H4R3me2s的去甲基化水平参与DNA损伤修复过程及小鼠眼部神经发育。我们希望通过后续的实验继续探讨JMJD1B影响下游基因表达调控的具体途径及参与造血干细胞发育、DNA损伤修复过程及小鼠眼部神经发育的具体机理。