Menin招募Daxx/ATRX调控胰腺神经内分泌肿瘤的表观遗传学机制

MEN1, Daxx and ATRX are frequently mutated in pancreatic neuroendocrine tumors and expression of menin, Daxx and ATRX is always decreased in pancreatic neuroendocrine tumors. We found that, ectopic expressed menin interacted with both Daxx and ATRX; Menin and Daxx significantly inhibited proliferation of insulinoma cells, respectively. However, whether menin and Daxx form a functional complex and play a role in suppressing pancreatic neuroendocrine tumors was not well defined. Thus, in this proposal, how menin interacts with Daxx or ATRX, directly or indirectly and the precise binding sites between menin and Daxx will be investigated. Second, the impact of menin-Daxx/ATRX complex on suppressing pancreatic neuroendocrine tumors will be examined. Third, the epigenetic mechanisms underlying the interplay between menin-Daxx/ATRX complex and SUV39H1, which catalyzes suppressive H3K9me3 modification, in controlling gene transcription will be elucidated. These studies will likely unravel novel mechanisms in control of pancreatic neuroendocrine tumors by menin-Daxx/ATRX complex through epigenetic regulation of gene transcription. The proposed studies may pave the way to target the menin-Daxx/ATRX inhibited signaling pathway for treating pancreatic neuroendocrine tumors.

MEN1、Daxx及ATRX基因在胰腺神经内分泌肿瘤中具有非常高的突变率，在胰腺神经内分泌肿瘤中常有menin、Daxx及ATRX蛋白表达量的降低。我们发现，menin与Daxx/ATRX蛋白在体内相互结合；Menin与Daxx分别过表达明显抑制胰岛瘤细胞增殖，但menin与Daxx/ATRX是否形成复合物并在胰腺神经内分泌肿瘤中协同发挥生物学功能尚不清楚。本项目拟明确menin与Daxx/ATRX之间的相互关系；证实menin与Daxx/ATRX在胰腺神经内分泌肿瘤中的关键生物学功能；阐明menin-Daxx/ATRX通过调控SUV39H1介导的H3K9me3等组蛋白甲基化修饰调控靶基因转录的表观遗传学机制。这将有助于深入揭示menin-Daxx/ATRX新复合物参与的表观遗传学调控，为以menin-Daxx/ATRX抑制的通路为靶点的胰腺神经内分泌肿瘤诊断和治疗提供新的思路。

胰腺神经内分泌肿瘤主要包括胰岛瘤、胃泌素瘤及胰高血糖素瘤等。胰腺神经内分泌肿瘤不仅恶性度高，患者十年存活率仅40%，并且其发病过程中常伴随有多种综合症的产生，如多发性内分泌肿瘤1型综合症（Multiple Endocrine Neoplasia type 1，MEN1）等。近20年中，胰腺神经内分泌肿瘤的发病率逐年增长，但至今仍缺乏对其发生相关关键分子及信号网络的深入认识。MEN1、Daxx及ATRX基因在胰腺神经内分泌肿瘤中具有非常高的突变率，在胰腺神经内分泌肿瘤中常有menin、Daxx及ATRX蛋白表达量的降低，提示menin与Daxx/ATRX可能共同参与胰腺神经内分泌肿瘤发生发展过程，但menin与Daxx/ATRX如何调控胰腺神经内分泌肿瘤及其精确的分子机制尚不清楚。. 本项目研究发现menin与Daxx蛋白在体内及体外相互直接结合，而menin通过Daxx与ATRX间接结合。Menin与Daxx/ATRX形成功能性复合物，通过调控金属蛋白酶Mme（membrane metallo-endopeptidase）的表达，进而抑制胰腺神经内分泌肿瘤细胞的增殖。进一步研究显示，menin与Daxx/ATRX复合物结合在Mme基因启动子上，在表观遗传学水平通过上调SUV39H1组蛋白甲基转移酶介导的组蛋白3号第9位的赖氨酸三甲基化（H3K9me3）进而抑制Mme的表达。Menin突变体T429K不能与Daxx/ATRX结合，进而丧失抑制Mme表达及胰腺神经内分泌肿瘤细胞增殖的能力。本研究成果有助于深入揭示menin-Daxx/ATRX新复合物参与的表观遗传学调控，为以menin-Daxx/ATRX抑制的通路为靶点的胰腺神经内分泌肿瘤诊断和治疗提供新的思路。