SIRT1在调控肝癌干细胞自我更新中的作用及分子机制

It has been demonstrated that cancer stem cells (CSCs) participate tumor initiation, metastasis, relapse after tumor resection and drug resistance. Targeting CSCs is becoming a great promise for treatment of cancer. Therefore, it is important to understand molecular mechanisms related to self-renewal of CSCs. Our previous studies have demonstrated that histone deacetylase SIRT1 plays a critical role in self-renewal of liver CSCs mediated by IGF signal transduction. However, its mechanisms are not elucidated yet. In this study, we explore mechanisms related to regulation of SIRT1 activity by IGF signal transduction and self-renewal of liver CSCs by SIRT1 at molecular and cellular levels. Using our previous established liver CSCs model, we firstly will investigate how IGF signal transduction modulates SIRT1 activity by transcriptional level and cellular localization. Then, we will investigate biological functions of SIRT1 on acetylation of key proteins, such as HIF-2α and β-catenin and the functions of de-acetylated HIF-2α and β-catenin on self-renewal of liver CSCs. Furthermore, we will investigate transcription of pluripotency transcription factor Nanog by de-acetylated HIF-2α and β-catenin. Finally, we will investigate clinic-pahtological significance of expression of SIRT1 and its related genes in human liver cancer and explore gene therapeutic strategy by targeting these molecules for therapy of liver cancer. The results from this study will strongly support new mechanisms in self-renewal of liver CSCs and provide new targets for prognosis and therapy of liver cancer.

阐明肝癌干细胞自我更新调控的分子机制，对靶向肝癌干细胞治疗肝癌具有重要意义。我们前期研究结果表明，肝癌微环境相关的IGF信号通路可通过组蛋白去乙酰化酶SIRT1关键蛋白调控肝癌干细胞自我更新，然而其分子作用机制尚不明确。据此，本项目拟以SIRT1为重点和突破口，以Nanog为标记的肝癌干细胞以及动物体内移植瘤为主要研究模型，结合人肝癌组织样本，围绕“IGF信号通路及其下游关键分子SIRT1在肝癌干细胞自我更新中作用”这一关键科学问题，从分子、细胞、组织和整体多个层次，研究IGF信号通路如何调节SIRT1的活性，SIRT1如何通过相关分子的去乙酰化修饰，调控Nanog的表达，参与肝癌干细胞自我更新，并探讨多分子靶标对肝癌临床预后及治疗意义。该项研究的顺利实施将有助于加深基于微环境支撑下的肝癌干细胞自我更新机制的认识，也将为制定更加有效的肝癌治疗策略，提供新的研究思路。

肝癌中的肿瘤干细胞是肝癌复发及预后差的根源，但其调控的内在和外在分子机制还有待进一步研究。本项目在前期建立的肝癌干细胞分选模型之上，研究发现SIRT1在肝癌干细胞和肝癌组织中异常高表达。在肝癌干细胞中，干扰SIRT1或采用SIRT1酶活性抑制剂可显著抑制肝癌干细胞的自我更新、肿瘤形成、迁徙转移、对称分裂及肝癌耐药特性；而在非肝癌干细胞中过表达SIRT1可显著促进自我更新、肿瘤形成及干性指标的表达；同时进一步发现IL-17E/NF-kB/STAT3轴及MiR-120促进肝癌干细胞和非肝癌干细胞的相互作用关系，促进增殖抑制凋亡及Sorafenib肝癌耐药。通过内在的分子调控机制发现SIRT1可转录激活下游效应因子-SOX2及Fra-1促进“干性”特征的维持，促进耐药及侵袭转移的能力；SIRT1可去乙酰化修饰其蛋白复合物去甲基化酶-LSD1蛋白低乙酰化水平，促进肝癌干细胞自我更新及肿瘤的形成。进一步发现肿瘤成纤维细胞可活化Notch3信号通路转录激活SIRT1的表达，而IGF-1及MEK1信号通路可维持SIRT1蛋白稳态，抑制其蛋白泛素化降解，协同促进肝癌的发生发展。本项目的研究成果为寻找特异性靶向肝癌干细胞治疗肝癌提供了坚实的理论基础和数据支撑，具有重要的临床价值。