抑癌基因PDCD4调控miR-370靶向Bmi-1抑制肺癌干细胞富集的研究

The main reason for the recurrence and metastasis of lung cancer patients may be the persistence of lung cancer stem cells (CSCs). Our previous studies were shown as follows: 1) PDCD4 participated in the pathogenesis of lung cancer through suppressing lung cancer stem cells enrichment. 2) MiR-370 was shown to be significantly upregulated in lung cancer cells with stably PDCD4 overexpressed by means of miRNAs array and qPCR which were used to examine the diffenentially expressed miRNAs. 3) MiR-370 inhibited lung cancer stem cells enrichment. Accordingly, we speculated that miR-370 was invovled in the regualtion of PDCD4-mediated inhibition of lung cancer stem cells enrichment. In order to validate this hypothesis, further studies will be performed as follows: 1) Identifying PI3K/Akt/ C-Myc pathway mediated by PDCD4 controls the expression of miR-370. 2) Validating transcription factor C-Myc controls the expression of miR-370 through directly regulating its promoter. 3) Confirming miR-370 directly targeting Bmi-1, which participated in PDCD4-mediated pathway of suppressing lung cancer stem cells enrichment. If the project is successfully implemented, we will clarify the molecular mechanism of lung cancer stem cells, and it may provide a new experimental theoretical basis for metastasis and treatment resistance of lung caner.

肺癌患者治疗后出现复发和转移的主要原因可能是肺癌干细胞的持续存在。前期研究发现：1）PDCD4能够抑制肺癌干细胞的富集从而参与了肺癌发病过程。2）miRNA芯片和荧光定量PCR检测发现，肺癌细胞过表达PDCD4后能显著上调miR-370表达。3）miR-370也能够抑制肺癌干细胞的富集。在此基础上，我们推测PDCD4可能通过调控miR-370从而抑制肺癌干细胞的富集。为验证假说，进一步工作将从如下方面开展：1）明确PDCD4通过PI3K/Akt/C-Myc调节miR-370的表达；2）验证转录因子C-Myc直接调节miR-370启动子影响其表达；3）验证miR-370直接靶向干细胞相关癌基因Bmi-1参与PDCD4介导的抑制肺癌干细胞表面标记的信号通路。如果该项目能顺利实施，将为肺癌干细胞调控的分子机制提供新的理论依据。

基于前人研究结果PDCD4表达水平与肺癌的进展及预后密切相关的基础上，我们发现PDCD4能够抑制肺癌干细胞的富集。随后利用miRNAs表达谱芯片和实时荧光定量PCR分析发现，肺癌细胞中过表达或抑制PDCD4后能显著上调或下调miR-370的表达水平，这表明PDCD4在肺癌细胞H1975中正向调miR-370的表达。同时我们也发现miR-370能够抑制肺癌干细胞的富集。机制方面，PDCD4能够调控PI3K/Akt/C-Myc信号通路，而转录因子C-Myc直接调节miR-370启动子影响其表达，因此PDCD4能够通过PI3K/Akt/C-Myc调节miR-370表达。但miR-370不能直接靶向Bmi-1，因此我们怀疑miR-370可能通过靶向其它与干细胞相关标记密切的基因从而抑制肺癌干细胞的富集，进而参与PDCD4介导的抑制肺癌干细胞富集的信号通路。这一部分后续研究正在进行中。PDCD4与miR-370在肺癌中的表达水平及相关性的研究方面，目前正在进一步扩大标本的收集。我们在研究PDCD4的功能时发现，PDCD4在鼻咽癌的发生发展中起重要的作用。结果显示miR-374a抑制鼻咽癌细胞生长、侵袭转移及顺铂耐药。机制研究表明miR-374a直接靶向CCND1抑制pPI3K/pAKT/c-JUN形成一个负反馈环路，并且抑制其下游细胞周期进展和EMT信号。有趣的是我们发现，miR-374a直接靶向CCND1被PDCD4通过抑制pPI3K/pAKT/c-JUN信号通路所调控。临床组织标本中，miR-374a分别与PDCD4和CCND1成正相关和负相关。因此，抑癌基因PDCD4能够通过调控miR-374a-CCND1-pPI3K/AKT-c-JUN环路抑制鼻咽癌细胞生长、侵袭转移，并促进其对顺铂化疗敏感，这部分论文已经发表在Oncogene 上。