胆汁酸核受体FXR在肝癌中的作用和分子机制研究

Elucidating the mechanisms of liver tumorigenesis could lead to life-saving therapy for a large number of patients with liver cancer. Our publication has shown that bile acid nuclear receptor Farnesoid X receptor (FXR) negatively regulates hepatic inflammatory response through antagonizing NF-κB signaling pathway, which indicates that FXR is a key negative regulator in chronic inflammation. We and Gonzalez's group found that FXR knockout mice after 15 months of age spontaneously develope liver tumors. Most recently, our preliminary data show that FXR activation is able to suppress proliferation of human liver cancer HepG2 cells. Furthermore, our preliminary data show that FXR activation significantly inhibits c-Jun N-terminal kinase (JNK) activity in vitro and in vivo. These results indicate that FXR plays a critical role in liver tumour development as a negative regulator of carcinogenesis. Sustained JNK activity is often found in liver tumor, and inhibition of JNK leads to antitumor activity in liver cancer. Therefore, to better understand the molecular mechanisms by which FXR suppresses liver cancer, we will focus on the potential relationship between FXR and JNK signaling pathway in this proposal. In Specific Aim 1 of this proposal, we will determine whether FXR antagonizes JNK signaling pathway in liver carcinogenesis by activating superoxide dismutase 3 (SOD3) transcription and then suppressing the production of reactivate oxygen species (ROS). In Specific Aim 2, we propose to identify the levels of endogenous FXR ligands such as bile acids, oxysterols and others, at different stages of liver cancer. In this specific aim, we will reveal the molecular mechanisms by which FXR expression is decreased during liver tumour development. These results from this proposal will help us determine whether FXR is a potential therapeutic candidate for prevention and treatment of liver cancer, which may also have potential implications for treatment of many other types of cancer.

阐明肝癌的分子机制有助于新药开发，挽救肝癌患者的生命。我们已发表的工作表明，胆汁酸核受体FXR是关键的炎症抑制子，它能够通过拮抗NF-κB信号通路抑制炎症。我们和其他研究组发现15个月以上的FXR基因敲除小鼠可发生自发性肝癌。在预实验中，我们发现FXR激活可以抑制HepG2肝癌细胞的增殖和JNK信号通路。这些结果表明FXR在肝癌中起重要作用，可能是肝癌的抑制子。在本课题中我们将考察FXR抑制JNK信号通路和抑制肝癌细胞增殖的作用和分子机制。此外，在本课题中我们还将鉴定肝脏肿瘤病变过程中FXR调控失衡的内在分子机制：具体是鉴定内源性FXR配体各成份在个体病变过程中的变化情况，以及FXR在正常肝细胞中高表达和肝癌细胞中低表达的转化分子机制。该项目内容均属首次阐述，集中揭示FXR在肝癌中的作用和机制，所得结果有助于鉴定FXR是否是潜在的治疗肝癌的药物靶向，并对其它器官癌症的治疗具有潜在指导意义。

阐明肝癌发生的分子机制有助于新药开发，挽救肝癌患者的生命。在本课题中我们考察了胆汁酸核受体FXR是否通过拮抗JNK信号通路抑制肝癌的发生。我们已发表的工作表明，15个月以上的FXR基因敲除小鼠可自发形成肝癌，FXR基因敲除小鼠肝脏中的JNK1水平明显升高，敲除JNK1基因能够抑制DEN（Diethylnitrosamine）诱导的FXR基因敲除小鼠肝癌的发生。我们还发现在人或小鼠肝原代细胞中特异性配体激活FXR能够抑制DCA（Deoxycholic acid）或H2O2诱导的JNK磷酸化。FXR通过直接靶向激活SOD3基因的表达抑制ROS的产生和JNK信号通路，进而抑制了肝癌细胞的增殖和肝癌的发生。此外，FXR和其内源配体调控机制的失衡是诱发肝癌的重要因素，通过检测肝癌发生前后FXR内源配体（重点是胆汁酸成分）的变化图谱，初步揭示出内源配体调控失衡与肝癌发生的关系。我们还筛选出引起FXR低表达的癌性微小RNA分子miR-382-5p，鉴定出miR-382-5p在肝癌组织中高表达并与FXR表达水平相反，过表达miR-382-5p能够通过靶向抑制FXR的表达及其功能的发挥促进肝癌细胞的增殖，揭示了肝癌发生过程中FXR调控失衡的机制。在本课题中我们揭示了FXR通过靶向JNK通路抑制肝癌发生的分子机制，以及肝癌病变过程中癌性微小RNA分子抑制FXR表达的内在分子机制，初步明确肝癌发生前后胆汁酸成分变化与肝癌发生之间的关系。该项目所得结果有助于鉴定FXR及其调控因子是否是潜在的治疗肝癌的药物靶向，对其它器官癌症的治疗也具有潜在指导意义。