肝癌居高不下的发病率和死亡率归结于癌细胞的增殖、侵袭和转移等恶性特征，也即细胞失极性的外在表现。Par3是Par极性复合物（Par3-Par6-aPKC）的中心分子，在不同组织或同一组织不同病理类型肿瘤中，Par3可发挥抑癌或促癌不同效应。与Par3调节细胞紧密连接（TJ）的功能有关。既往研究对Par3在肝癌中表达高/低，促癌/抑癌，结论矛盾。我们前期工作发现，Par3抑制肝癌发生发展。敲除小鼠肝脏Par3表达，未见TJ明显破坏，而发现1）肝细胞窦状隙面异常2）线粒体异常，提示Par3可能通过不依赖TJ的途径，而是通过调节肝细胞窦状隙面及线粒体功能参与肝癌发生发展。本项目拟结合使用转基因小鼠、活细胞实时成像等实验手段，深入研究Par3通过肝细胞窦状隙面和线粒体功能调控肝癌进程，及肝癌中Par3下调的分子机制。以期揭示肝癌发生发展新的分子机制，并因此提供新的诊治思路和靶标。

Cell polarity is essential in many biological processes and is also required for development as well as maintenance of tissue integrity. Loss of polarity is considered both a hallmark and precondition for human cancer. Hepatocellular carcinoma (HCC) is the primary cancer of the liver’s parenchyma and is the most common form of hepatic cancer. Aberrant expression of polarity proteins is closely associated with HCC development.. Three evolutionarily conserved protein complexes, Par, Scribble and Crumbs, are the key factors responsible for establishment of the apico-basal polarity. Among these complexes, Par has the widest range of functions. Par3 is the central component of the Par complex which consists of Par3, Par6 and an atypical protein kinase C. Par3 is also suggested as a tumor suppressor or pro-tumorigenic protein in different types of cancer. Conditional Par3 knockout in mouse skin delays the formation of Ras-induced papillomas due to reduced cell proliferation and increased apoptosis, suggesting a tumor-promoting role of Par3. However, the same condition predisposes skin to develop another type of cancer termed keratoacanthoma, con¬sistent with a tumor-suppressing function for Par3. Collectively, current data support an important role for Par3 in tumor progression and metastasis, although the specific mechanisms are context dependent.. The current studies from different groups found contradictory role of Par3 in HCC. For instance, Fang et al. reported that atypical PKC-binding domain deleted isoforms of asip, the human homolog of Par3, were downregulated in HCC. Whereas, Liou group found that the expression of Par-3 was increased in HCC and metastatic HCC specimens. Par-3 overexpression was significantly associated with extrahepatic metastasis and worse overall survival in HCC. The detailed molecular mechanisms of Par3 in HCC are still not clear. It was well known that Par polarity complex regulates cancer cell invasion and metastasis by controlling tight junction (TJ) assembly. In our preliminary experiments, we found that Par3 is downregulated in HCC and metastatic HCC specimens. Downregulation of Par3 induced cell proliferation, invasion and metastasis in vivo. However, we found that loss of APC didn’t show apparent TJ disruption, but led to dysfunctions of sinusoidal domains, such as increased local vacuoles and number of sinusoids, number of mitochondria, and severe swelling in mitochondria through electron microscopic and HE staining. These data suggested that Par3 might inhibited HCC development in a TJ independent pathway.. In this proposal, we plan to investigate the molecular connections and downstream signal pathways of Par3 and HCC development including Par3 regulated sinusoidal domain polarity, mitochondrial defects, and to further uncover the molecular mechanisms involved in decreased expression of Par3 in HCC. We will employ a multidiscipline approaches encompassing mouse genetics, time-lapse imaging, biochemistry and molecular biology and will use rodent as a model to pursue our aims above. The proposed studies in this application will not only allow us to advance the knowledge of molecular mechanisms in HCC, but may also produce new leads to diagnose and treat HCC.