mTORC2/AKT1信号通路在C-MYC诱导肝细胞癌发生中的作用及分子机制

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors and leading cause of cancer death worldwide. Yet, molecular mechanisms underlying hepatic carcinogenesis are still poorly understood. The C-MYC proto-oncogene is considered to be a critical driver oncogene in HCC pathogenesis and represent one of the HCC subtypes of molecular classification. Experimental evidence indicates that activation of the mammalian target of rapamycin target 1 (mTORC1) axis is required for C-MYC-driven hepatocarcinogenesis, whereas C-MYC-driven hepatocarcinogenesis is independent of AKT2, the major AKT isoform in the liver. Unfortunately, phase III clinical trials of Everolimus, a Rapamycin derivative, have failed in the treatment of advanced liver cancer. Thus, it is particularly important to study the interaction between oncogenes and mTOR in the development of liver cancer. In our recent studies, we demonstrate that mammalian target of rapamycin complex 2 (mTORC2) play a critical role during liver tumor development by human HCC samples and in vivo study. However, whether mTORC2 pathway is required for C-MYC driven liver tumor development in mice remains unknown..To investigate whether the mTORC2 pathway is involved in the carcinogenesis of C-MYC, we investigated the functional contribution of mTORC2 in C-MYC-induced HCC. Using Rictor conditional knockout mice, we found that C- MYC did not result in any HCC formation in mice up to 20 weeks post treatment by deletion of Rictor in mice. Based on these preliminary data, we hypothesize that mTORC2 is required for C-MYC induced liver tumor formation in mice. In this project, we will systematically characterize the functional role of mTORC2 and AKT1 during C-MYC-driven hepatocarcinogenesis based on mice models via hydrodynamic tail vein injection and liver tumor cell lines. The study will provide novel mechanistic insight into the requirement of mTORC2 and AKT1 pathway in C-MYC driven hepatic carcinogenesis. It will also provide strong evidence for the development of molecular targeted therapy for HCC prevention and treatment.

肝细胞癌(HCC)是最常见恶性肿瘤之一，原癌基因C-MYC是HCC发生的一个关键驱动基因。实验证据表明，哺乳类雷帕霉素靶点复合物1(mTORC1)通路的激活是C-MYC诱导HCC形成的必要条件。我们通过肝癌样本、小鼠体内实验证实哺乳类雷帕霉素靶点复合物2(mTORC2)在肝癌发生中发挥关键作用。为研究mTORC2通路是否与C-MYC的致癌作用有关，在预实验中我们通过条件性基因敲除小鼠mTORC2关键分子Rictor，观察发现可完全阻止C-MYC诱导的HCC形成。因此，我们提出假设：C-MYC首先激活mTORC2通路，进而诱导mTORC1的活化导致肝癌的发生。本项目拟结合动物模型和细胞实验，通过高压尾静脉注射法建立肝癌小鼠模型，以Rictor及其下游分子AKT1为主要研究对象，阐释mTORC2信号通路在C-MYC诱导HCC形成中的作用及机制。本研究将为探索分子靶向治疗肝癌新方法提供理论依据。

肝细胞癌（HCC）是最常见的恶性肿瘤之一，转录因子C-MYC是HCC发病机制中的关键驱动基因，但肝脏中C-MYC致癌的机制仍有待阐明。雷帕霉素复合物2（mTORC2）主要底物AGC激酶，尤其是AKT蛋白与癌症有关。在肝脏中，AKT1和AKT2广泛表达，AKT2是活化的PI3K下游的主要亚型，而AKT1在肝癌发生中的确切功能尚不清楚。基于前期结果，本研究拟探讨mTORC2在介导C-MYC诱导肝癌形成中的分子机制。本研究在条件性基因敲除小鼠中，用高压尾静脉注射法建立肝癌模型，检测mTORC2通路相关分子的表达情况；在相关肝癌细胞系中，沉默Rictor或AkT1后，检测mTORC2通路相关分子表达的变化，并检测细胞的增殖和凋亡情况；小鼠肝癌模型中，新一代mTOR抑制剂MLN0128处理小鼠，以雷帕霉素及未处理组为对照，观察对C-MYC诱导小鼠肝癌形成的影响。用免疫组织化学方法在人肝癌标本中检测c-My、Rictor、AKT1、AKT2等相关蛋白的表达。结果发现，mTORC2在C-MYC诱导的小鼠肝癌中被激活，导致AKT1而非AKT2的磷酸化/激活。体内实验显示敲除Rictor阻止C-MYC诱导的肝癌形成。我们发现AKT1的缺失，而非AKT2的缺失，完全阻止了小鼠C-MYC诱导 HCC的形成。在C-MYC诱导的肝癌细胞株中，沉默Rictor或AkT1可抑制p-FoxO1的表达，并在体外强烈抑制癌细胞的生长。在人肝癌标本中，C-MYC的激活与p- AKT1的表达密切相关。Rictor和AKT1的高表达与肝癌患者的生存率低有关，而AKT2的表达与肝癌的生存率无关。在C-MYC诱导小鼠肝癌模型中，mTORC1抑制剂雷帕霉素在预防C-MYC诱导肝癌进展方面的作用有限，而MLN0128可通过诱导凋亡和坏死有效地促进肿瘤的消退。本研究证实了mTORC2/AKT1在C-MYC诱导肝癌发生中的关键作用。AKT亚型，AKT1和AKT2，在肝癌的发展和进展中具有不同的作用。同时靶向mTORC1和mTORC2可能是有效治疗显示C-MYC相关肝癌所必需的。