SOX9通过调控肝细胞去分化影响肝癌发生的机制

Sox9 is a transcription factor that plays a critical role in organ development and cell differentiation. The dysregulation of SOX9 has been reported in many cancers. Recent studies show that hepatocytes can dedifferentiate into SOX9-positive bipotential liver progenitor cells during chorionic liver injury, but the molecular mechanisms by which Sox9 regulates the dedifferentiation of hepatocyte and its role in hepatocarcinogenesis remain unclear. Hepatocyte nuclear factor 4α (HNF4α) is a transcription factor that plays a key role in hepatocyte differentiation and the maintenance of hepatic function. Our previous studies have revealed that upregulation of HNF4α blocks hepatocellular carcinoma (HCC) occurrence and exerted significant therapeutic effect on xenograft of HCC cells. Our recent experiments demonstrated that HNF4α regulates the expression of SOX9. Moreover, the lineage tracing experiment showed that the diethylnitrosamine (DEN)-induced HCC originates from SOX9-positive bipotential liver progenitor cells in mice. These data indicate that the differentiation status of hepatocytes affects hepatocarcinogenesis. In this study, we will clarify the relationship between hepatocyte dedifferentiation and hepatocarcinogenesis by using the SOX9-Flp/Ai65D transgenic mouse, a reporter mouse for hepatocyte dedifferentiation, in various primary HCC models. Moreover, hepatocyte-specific knockout or overexpression of SOX9 will be performed in mice to elucidate the effect of SOX9 on hepatocarcinogenesis and its related signaling pathways. Finally, the molecular mechanisms of HNF4α regulating SOX9 expression and its effect on prevention of HCC occurrence will be further illustrated. This study will shed new light on the molecular mechanism of hepatocarcinogenesis and provide novel targets for the prevention and treatment of HCC.

SOX9是调控器官发育和细胞分化的重要转录因子，在多种肿瘤中表达异常。近年研究表明肝细胞在慢性损伤过程中可去分化为SOX9阳性的兼性肝干细胞，但SOX9影响肝细胞去分化的机制及其在肝癌发生中的作用尚不明确。我们既往的研究发现上调维持肝细胞分化和功能的肝细胞核因子HNF4α可预防肝癌的发生，并有效治疗多种肝癌种植瘤；近期研究发现 DEN诱导的小鼠原发性肝癌源自SOX9阳性的兼性肝干细胞，HNF4α可调控SOX9的表达，提示维持肝细胞的分化状态影响肝癌的发生。本课题拟在多种原发性肝癌小鼠模型中利用可示踪肝细胞属性转换过程的SOX9-Flp/Ai65D小鼠追踪肝癌发生的过程，明确肝细胞属性转换过程是否参与肝癌的形成；在小鼠模型中特异性敲除或过表达肝细胞SOX9表达，确定SOX9对肝癌发生的影响及相关分子通路；并揭示HNF4α通过调控SOX9抑制肝癌发生的机制，以期为肝癌防治提供新的靶点。

SOX9是调控器官发育和细胞分化的重要转录因子，在多种肿瘤中表达异常。近年研究表明在慢性肝损伤过程中产生大量表达SOX9的肝细胞，这些细胞参与了慢性损伤的肝脏再生；同时SOX9在肝癌中表达升高，促进肝癌的恶性表型。本课题在此基础上系统的分析了SOX9在不同肝脏病理过程中的作用，揭示SOX9对肝癌发生发展过程中的影响及机制，并探讨了SOX9在急性肝再生和肝囊肿发生过程中的作用。我们首先利用SOX9阳性肝细胞示踪小鼠和肝细胞特异性SOX9基因敲除小鼠，明确SOX9在肝癌发生过程中的作用，发现肝细胞表达SOX9不是发生肝癌的必要条件。在小鼠原发性肝癌模型中，正常肝细胞SOX9的表达可减少原发性肝癌的发生，而在肝癌中SOX9的表达则促进了肝癌的进展，表明SOX9在肝癌的发生和发展阶段存在不同在作用。我们进一步分析了SOX9促进肝癌进展的机制，发现SOX9通过与YAP的直接结合介导YAP蛋白的核转位，进而促进YAP的活性，首次明确了YAP核转位的分子机制。我们还发现在急性肝再生过程中，肝细胞的SOX9表达也显著升高， SOX9表达是急性肝再生过程中肝细胞的增殖的重要调控分子， 而HNF4α可通过其下游microRNA调控SOX9表达,在肝再生早期HNF4α表达下降，SOX9表达升高，肝细胞增殖增加；而在肝再生晚期，HNF4α表达升高抑制SOX9表达，从而促进肝细胞的成熟。另一方面，我们还发现胆管细胞SOX9的表达与肝囊肿的发生相关，肝囊肿致病基因SEC63是SOX9的下游基因，缺失SOX9表达的胆管细胞的增殖显著增加，进而导致肝囊肿的发生，从而提出了肝囊肿发病的新机制。综上，我们一系列的研究对SOX9在急慢性肝病及肝癌中的作用进行了系统研究，进一步阐明的急慢性肝病及肝癌的发生发展机制，为肝病及肝癌治疗提供了新的靶点和思路。