NSD2 E1099K癌频发突变获得三甲基化酶活的分子和致癌机制的研究

The proposed research plan is within the scope of the guideline direction #2. The dynamic regulation of histone methylation is an important epigenetics mechanism, plays crucial roles in normal development, and when compromised often leads to various diseases. NSD2 is a di-methyltransferase of histone H3 lysine 36 site, and is subject to frequent gain-of-function mutations in hematopoietic malignances through chromosomal T(4;14) translocation and E1099K point mutation. Although both mutations lead to gain-of-function of NSD2 and drastically elevated H3K36me2 of the cancer epigenomes, there are differences between the two mutations. For instances, E1099K does not lead to NSD2 overexpression and also occurs in solid tumors, such as lung, intestine, bibiary tract and kidney cancers, unlike T(4;14). However, what are the exact differences in promoting tumorigenesis between the two mutations remain unclear. Here, our in vitro and in cell studies revealed that NSD2 E1099K unexpectedly gains tri-methyltransferase activity towards histone H3K36 site, thus represents a new type of gain-of-neofunction mutation. We propose to systematically investigate the underlining tumorigenic mechanism of this mutation in terms of its abnormal H3K36me3 activity in compromising the epigenome and transcriptome through crosstalking to other modifications and chromatin pathways. Our preliminary data also indicate that the abnormal H3K36me3 mediated by NSD2 E1099K displayed very different distribution pattern compared to the normal H3K36me3 mediated by SETD2. The findings from this study will acquire previously inaccessible knowledge of H3K36me3 malfunction when mis-deposited to intergenic regions or untranscribed regions, and connect such epigenetic abnormalities to tumorigenesis. Our findings will also provide critical mechanistic insights of the pathogenesis of E1099K tumors and the therapeutic approach of personalized medicine against this malignant mutation.

本研究符合指南方向二支持方向。组蛋白甲基化修饰的动态调控是一类十分重要的表观遗传机制，在发育和疾病中发挥重要的功能。NSD2是组蛋白H3K36位点的二甲基化酶，在血液类癌症中可通过染色质T(4;14)易位或频发点突变E1099K提高活性，并介导全基因组H3K36me2水平显著上升，从而致瘤。不同的是，E1099K突变还发生在肺癌、肠癌、胆管癌和肾癌等实体瘤中，且并不伴随NSD2过表达，提示其致癌机制可能与T(4;14)不完全一致，但是具体差异仍不清晰。本研究组发现NSD2 E1099K突变体在体外和细胞内均具备H3K36三甲基化酶活，提示该突变是一类获得性新功能突变。在本项目中，将系统而深入研究这类特殊基因突变导致的下游表观遗传编程紊乱以及致癌机制。由于E1099K引发的全局H3K36me3调控紊乱十分罕见，本研究成果具有明确的学术创新性，并将为这类恶性肿瘤的精准治疗提供重要的参考信息。

在培育项目支持下，本研究组围绕生物大分子动态修饰的调控和功能开展了一系列研究，已发表4篇学术论文。在染色质调控方面，主要研究对象是组蛋白甲基化的病理生理功能，发现了组蛋白甲基化酶NSD2、去甲基化酶KDM5A对于血液肿瘤的促癌作用，阐明了PRC1核心组分RING1A在心脏发育中的重要功能。在蛋白翻译调控方面，发现了核糖体18S rRNA的m6A甲基化酶METTL5，证明了其对于乳腺癌细胞生长的促进作用，且利用线虫模型发现其缺失可导致抗压能力提高和寿命延长。染色质和核糖体是参与基因表达两大关键步骤—转录和翻译—的生物大分子，本研究揭示了甲基化修饰对于两大步骤的重要调控机制，明确了数类生物大分子甲基化修饰紊乱的致病机理，并提出了潜在疾病治疗靶标。