Hedgehog信号诱导神经前体细胞恶性转化中miRNA的作用及其机制

The activation of Hedgehog (Hh) signaling is pivotally involved in the malignant transformation of cells from various tissues, the underlying mechanism of which remains largely elusive. Using the mouse medulloblastoma model induced by transgenic expression of the Hh receptor Smo, we have established in neural progenitors that miR-224 is transcriptionally activated by the classical Hh pathway transcriptional factor, Gli2, whereas the tumor suppressor, miR-34a, was significantly downregulated due to HDAC1-mediated histone H3K27 deacetylation. Based on the studies concerning candidate miRNA target genes, we propose that Hh signaling upregulates miR-224 to repress its candidate target gene, the ubiqutin ligase REN, which consequently abrogates REN-mediated degradation of HDAC1. Increased cellular HDAC1 leads to epigenetic silencing of tumor suppressors including miR-34a, which in turn enhances the expression of candidate miR-34a targets, e.g. the Smo activator GRK2, thus forming a positive feedback circuit to maintain Hh signaling and promote the proliferation and transformation of neural progenitors. The present study aims to verify the aforementioned regulatory circuit of Hh signaling, to identify other genes regulated by the Hh/miR-224/REN/HDAC1 pathway, and to validate the critical involvement of this pathway in the transformation of neural progenitor cells, which will provide novel insights into the roles of Hh signaling and related miRNAs in the progression of the nervous system malignancies.

Hedgehog（Hh）信号的活化与细胞恶性转化密切相关，但其下游机制有待阐明。我们前期以Hh受体Smo转基因小鼠髓母细胞瘤为模型，发现神经前体细胞中Hh途径转录因子Gli2能够转录激活miR-224，而抑癌基因miR-34a则由于HDAC1介导的组蛋白H3K27去乙酰化而显著下调。结合miRNA靶基因研究结果，我们提出Hh信号通过上调miR-224抑制泛素连接酶REN，阻断后者对HDAC1的降解，以组蛋白去乙酰化机制沉默miR-34a，解除了其对包括Smo激活因子GRK2在内的靶基因的抑制作用，从而构成了Hh信号调控的正反馈环路，促进细胞恶性转化。本项目旨在验证上述Hh信号调控环路的存在，进而鉴定Hh/miR-224/REN/HDAC1通路调控的其他靶基因，揭示它们在神经前体细胞恶性转化中的关键作用，为系统认识Hh信号及相关miRNA在神经系统肿瘤演进中的作用提供依据。

髓母细胞瘤（MB）是起源于小脑颗粒神经元前体细胞（CGNPs）的最常见的儿童颅内肿瘤，Hedgehog信号的异常或过度活化见于约30%的MB病例，构成了Sonic Hedgehog （Shh）型MB，且预后较差，分子机制有待深入研究。在本项目中，我们借助Hedgehog受体Smo组成性活化的MB小鼠模型进行研究，发现长链非编码RNA（lncRNA）Nkx2-2as的表达失调促进MB的发生，Shh信号通过转录因子FoxD1抑制Nkx2-2as的表达。Nkx2-2as发挥竞争性内源RNA（ceRNA）的作用，通过结合miR-103/-107和miR-548m，解除了后者对其靶基因BTG2和LATS1/2的抑制作用，BTG2作为细胞周期的抑制分子、LATS1/2作为Hippo通路的负调控因子均抑制了MB的发生和发展。上述分子在Shh型髓母细胞瘤临床标本中的表达呈现明显的相关性，而过表达Nkx2-2as抑制了体内MB的生长和恶性进展。项目按照计划完成了既定的研究任务，主要研究结果2018年发表在本领域权威杂志Cancer Research，相关研究还另外发表SCI论文4篇，其中影响因子大于5的2篇。这些研究发现揭示了非编码RNA在Hedgehog信号通路和MB发生中的重要作用，并为寻找MB临床治疗新的候选靶点提供了重要线索。