RACK1与Nanog相互作用参与肝细胞癌干细胞自我更新的分子机制研究

The cancer stem cell model, a milestone in cancer biology, provides clues to cure liver cancer. Hepatocellular carcinoma (HCC) is the most common type of liver cancer. Recently, it has been revealed that Nanog, a transcription factor essential for the pluripotency and self-renewal of ES cells, plays a central role in the maintenance of the stemness of HCC stem cells. However, the molecular mechanisms underlying Nanog overexpression in HCC stem cells and the molecular mechanisms by which Nanog contributes to the stemness of these cells remain elusive. We have disclosed that RACK1, an important member of WD40 family, exhibits elevated expression in HCC cells and augments in vitro HCC cell proliferation and resistance to TRAIL- or Fas-mediated apoptosis as well as in vivo tumor growth. More importantly, RACK1 promotes the stemness of HCC stem cells, directly binds to Nanog, and augments the stability of Nanog (Hepatology 2013 and unpublished data). This project aims to elucidate the roles of RACK1 in modulating the post-translational modification as well as the transcriptional activity of Nanog and the underlying mechanisms, to analyze whether RACK1 promotes the stemness of HCC stem cells mainly through Nanog, to explore whether Nanog also contributes to the stemness of these cells partially through RACK1. The corresponding findings might reveal an important mechanism underlying the generation and self-renewal of HCC stem cells and provide novel strategies and potential drugs for the treatment of liver cancer.

肿瘤干细胞学说是人类认识肿瘤的里程碑式进展，为治愈肝癌提供了契机。肝细胞癌(HCC)是最常见的肝癌，最近，维持胚胎干细胞多能性和自我更新的转录因子Nanog在HCC干细胞中的核心作用已得到揭示，但Nanog在这群细胞中高水平表达和维持"干性"特征的机制还很不清楚。我们发现WD40家族重要成员RACK1在HCC细胞中高表达、促进HCC细胞恶性生长。更重要的是，RACK1是"干性"维持的关键分子，与Nanog直接结合并增强Nanog蛋白的稳定性 (Hepatology 2013和待发表数据)。本项目将分析RACK1对Nanog翻译后修饰和活性的影响与机制，揭示对Nanog的调控作用是否为RACK1参与"干性"维持的关键机制，探讨Nanog是否也通过RACK1促进"干性"，我们的结果可望为肿瘤干细胞调控机制的研究取得理论上的突破，并为发展新型干预治疗措施提供线索。

肝细胞癌(HCC)是全球第三大癌症死亡原因，具有高度异质性和高复发率的特点。酪氨酸激酶抑制剂索拉菲尼是最常用的治疗肝癌的药物，但在患者中经常发生固有的或继发的耐药性，因此影响临床治疗效果。肿瘤干细胞（CSCs）具有较强的自我更新能力和耐药性，是肿瘤复发和耐药的重要原因。因此靶向CSCs是根除包括HCC在内的恶性肿瘤的新策略，但CSCs维持自我更新和耐药的作用机制还不明确。.接头蛋白RACK1是Trp-Asp (WD)重复蛋白家族的一员，RACK1表达与HCC临床分期及不良预后密切相关。在这项研究中，研究人员发现RACK1可以促进人肝细胞癌CSCs的自我更新和耐药，并维持小鼠胚胎干细胞（ESC）的干性，RACK1在人肝癌细胞和小鼠ESCs中均能增强Nanog的表达，且临床HCC组织中RACK1蛋白水平与Nanog蛋白水平呈正相关，提示RACK1和Nanog在CSCs中的重要作用。进一步的研究揭示了RACK1在CSCs中稳定Nanog表达的作用机制，RACK1可以直接与Nanog结合，阻止其募集E3泛素连接酶FBXW8和泛素依赖性降解，从而稳定Nanog表达，促进人肝细胞癌CSCs的自我更新和耐药。.除HCC外，在多种癌症中都观察到RACK1蛋白水平的升高，RACK1对Nanog表达的调节可能是多种干细胞维持的通用分子机制。该研究发现RACK1在人HCC中增强CSCs自我更新和耐药能力的重要作用，并揭示了RACK1稳定Nanog表达的调控机制，为通过靶向CSCs治疗癌症提供了一个新的思路。