肿瘤细胞中凋亡诱导因子表达下调导致EMT的机制

Apoptosis-inducing factor (AIF), a flavin adenine dinucleotide-containing, NADH-dependent oxidoreductase residing in the mitochondrial intermembrane space whose specific enzymatic activity remains unknown, is originally identified to play a key role in execution of caspase-independent cell death. Upon an apoptotic insult, it undergoes proteolysis and translocates to the nucleus, where it triggers chromatin condensation and large-scale DNA degradation in a caspase-independent manner. Recent works show that AIF is also a protein critical for cell survival and the complexity and multilevel regulation of AIF-mediated signal transduction is revealed. It is also believed that AIF plays an important role in the maintenance of mitochondrial morphology and energy metabolism, and the redox activity of AIF is essential for optimal oxidative phosphorylation. Our preliminary work showed that AIF has a much lower expression in colorectal cancer with low differentiation, and hypoxia, one of hallmarks of cancers, significantly decreases AIF expression via hypoxia-inducible factor-1 (HIF-1). These interesting findings pushed us to investigate the potential role of decreased AIF expression in the pathogenesis of cancers. More interestingly, silence of AIF expression by its specific RNA significantly induces epithelial-mesenchymal transition (EMT) in colorectal cancer cell lines, as assessed by morphology, markers for epithelial and mesenchymal cells, and others. Based on these original findings, in this project, we will focus on the works as followed: .(1) how HIF-1 reduces AIF expression, .(2) It is common or specific to colorectal cancer that low expression of AIF induces EMT; .(3) how AIF, as a mitochondrial protein, regulates EMT process; .(4) whether lower expression of AIF contributes to HIF-1 mediated EMT. .Then, we also want to confirm our results in animal and cancer tissues from patients. Collectively, all these works would shed new sight for understanding the novel function of AIF and its specific enzymatic activity, especially, they will provide novel findings for mechanisms of EMT induction.

凋亡诱导因子（apoptosis-inducing factor，AIF）不仅参与了细胞凋亡，而且参与细胞代谢、活性氧（ROS）生成等事件，但是其在肿瘤发病学中的作用却鲜有研究。最近，课题申请人发现低分化的结直肠癌组织低表达AIF，而低氧以低氧诱导因子-1alpha?（HIF-1a）依赖的方式明显下调AIF的表达。尤其是，敲除AIF后，结直肠癌细胞发生上皮-间充质细胞转化（epithelial-mesenchymal transition，EMT）。本课题将以这些重要发现为基础，深入探寻HIF-1抑制AIF表达，尤其是AIF表达减少诱导EMT发生的分子机制及其在低氧诱导EMT效应中的重要性，并通过小鼠模型和临床样本研究挖掘这些效应在肿瘤尤其是结直肠癌中的作用。这些研究工作不仅可能为研究EMT的分子机制提出新的观点和揭示AIF的新功能，并可望为针对EMT这一过程的药物靶点的发现提供新的线索。

凋亡诱导因子（apoptosis-inducing factor，AIF）不仅参与了细胞凋亡，而且参与细胞代谢、活性氧（ROS）生成等事件，但是其在肿瘤发病学中的作用却鲜有研究。本项目拟从不同层面明确低氧下调AIF表达和AIF表达下调诱导EMT的分子机制，进而揭示AIF与肿瘤转移的相关性。通过项目的实施，我们报道低氧通过低氧诱导因子1（HIF-1）抑制AIF及其分子机制，发现AIF下调诱导结直肠癌细胞发生上皮-间充质细胞转化（epithelial-mesenchymal transition，EMT）， 并初步揭示其分子机制，即AIF与肿瘤抑制蛋白PTEN直接相互作用，保护PTEN蛋白不被氧化，从而维持其脂质磷酸酶活性。相应地，细胞内AIF下调引起PTEN氧化失活，引起下游AKT/GSK-3Beta磷酸化水平增加而失活，从而引起其底物Beta-catenin入核，活化WNT信号通路。与此同时，我们也利用小鼠模型明确AIF下调在肿瘤转移中的作用。此外，我们也掘核内PTEN相互作用组，发现PTEN能够与剪接体结合并调控pre-mRNA剪接。这些研究工作已发表并标注该项目资助的代表性SCI论文8篇，培养7名博士研究生。相关发现不仅可能为研究EMT的分子机制提出新的观点和揭示AIF的新功能，并可望为针对EMT这一过程的药物靶点的发现提供新的线索，可望产生新的学术生长点。