抑癌基因Nkx2.8抑制神经胶质瘤干细胞自我更新的生物学功能及分子机制

It has been reported that cancer stem cells, a small subset of cancer cells with high self-renewal properties, play key roles in tumorigenesis, metastasis, drug resistance and tumor recurrence. The mechanisms of cancer stem cells self-renewal, however, still remain largely unclear. Previously, we have demonstrated that protein Nkx2.8 suppresses cancer cell proliferation [Carcinogenesis.2012]. Importantly, our recent preliminary data showed that overexpression of Nkx2.8 significantly downregulated the expression levels of multiple reprogram factors in glioma stem cell, including Sox2, OCT-4, KLF4 and c-myc. Furthermore, we found that ectopically expressing Nkx2.8 dramatically reduced glioma stem cell sphere-formation. Meanwhile, Nkx2.8-transduced cells could inhibit glioma stem cell tumorigenesis in the nude mice brain as compared with control cells. Thus, these results indicate that Nkx2.8 could suppresse the glioma stem cells self-renewal. Moreover, we also found that Nkx2.8 could downregulate the expression of Bmi-1, and overexpresson of Nkx2.8 supressed the Wnt/β-catenin signaling pathway. Therefore we present the hypothesis: Nkx2.8 could bind to the promoter of Bmi-1 to downregulate the expression of Bmi-1 or supresse the Wnt/β-catenin signaling pathway，which could suppresse the glioma stem cells self-renewal. In the current study, using in vivo and in vitro systems, and combined with clinical samples, we aim to further investigate the molecular mechanisms and biological effect of Nkx2.8 on self-renewal of glioma stem cells, which would provide novel insight for treatment of gliomas.

目前已知肿瘤干细胞是肿瘤发生、转移、耐药与复发的主要原因；然而肿瘤干细胞自我更新的调控机制仍不清楚。前期研究中我们报道抑癌基因Nkx2.8抑制肿瘤的增殖(Carcinogenesis.2012)；近期预实验结果显示Nkx2.8在胶质瘤中低表达，并且高表达Nkx2.8可显著抑制胶质瘤干细胞内重编程因子表达，抑制干细胞的球囊形成；高表达Nkx2.8还可显著抑制细胞在裸鼠脑部形成高度恶性肿瘤。结果表明Nkx2.8具有调控神经胶质瘤干细胞自我更新的功能；同时，我们发现Nkx2.8抑制Bmi-1表达，且高表达Nkx2.8抑制Wnt/β-catenin信号通路，进而提出假说：Nkx2.8通过结合到Bmi-1启动子从而抑制肿瘤干细胞自我更新。本项目将在前期研究基础上，采用体内体外系统，并结合临床样品，深入探讨Nkx2.8调控肿瘤干细胞自我更新的分子机制及生物学功能，为高度恶性胶质瘤的治疗提供新的策略。

近年来的研究发现，肿瘤干细胞与恶性肿瘤发生、转移、耐药及复发等肿瘤发生发展的生物学功能密切相关，对肿瘤干细胞进行深入的研究具有重要临床研究意义和应用前景。抑癌基因Nkx2.8在膀胱癌，胰腺癌，非小细胞肺癌等多种肿瘤中低表达，但Nkx2.8在神经胶质瘤中的表达，生物学功能及分子机制仍不清楚，Nkx2.8是否具有调控肿瘤干细胞肿瘤形成的生物学功能仍未有研究报道。本项目的最新研究进展发现Nkx2.8在神经胶质瘤细胞系及临床标本中低表达，构建Nkx2.8稳定高表达的胶质瘤干细胞样肿瘤细胞模型后发现Nkx2.8可在不同水平调控神经胶质瘤干细胞的肿瘤形成等生物学功能，进一步研究其分子机制时发现另一调控神经胶质瘤干细胞的关键促癌基因Setd7，由此深入挖掘二者的相互作用机制以及二者共同调控的下游基因和通路的作用机制：高表达Nkx2.8可通过结合于Setd7的转录启动区并抑制Setd7的转录表达，Setd7在胶质瘤细胞以及胶质瘤干细胞中主要表达于胞浆中（这与已有文献报道Setd7定位在其他肿瘤细胞胞核中不一致），Setd7很可能通过甲基化LEF1或者甲基化胞浆中的PEA-15使得Erk1/2的磷酸化激活受限，进一步调控Wnt/β-catenin下游基因表达。这对揭示肿瘤发生发展的分子作用模式、完善对肿瘤干细胞分子调控网络体系的认识，具有重要的学术意义；并在此基础上，对寻找肿瘤特异性诊断和预后判断标志物，以及治疗高度恶性胶质瘤提供新的分子靶点，具有潜在的临床意义。