探討Wnt/β-catenin訊息傳遞路徑與雄性激素路徑於男性肝癌形成過程中之交互作用

Abstract

Wnt/β-catenin訊息傳遞路徑在50~70%肝細胞癌(HCC) 中有不正常活化的現象，顯示其可能參與肝癌形成過程。先前研究利用基因轉殖小鼠，在肝臟特定性表現活化型的β-catenin，以檢測其對肝癌形成之影響，結果造成肝臟變大，但並未產生腫瘤；然而加上H-ras致癌基因或是施以二乙基亞硝胺(DEN)致癌化合物，則可明顯增加此小鼠產生HCC的機率。由以上研究推論，Wnt/β-catenin路徑之活化可能必須協同另一個致癌因子以促成肝癌的產生。本研究之目的即設定為找出在肝臟中協同Wnt/β-catenin路徑促成肝癌發生的因子。基於肝細胞腺瘤(HCA) 之研究，指出男性性別為具有活化型突變β-catenin之HCA轉變為HCC之重要危險因子。本研究因此提出如下假說，即雄性激素路徑可能為協同Wnt/β-catenin路徑促使肝癌發生的另一個因子，並利用本實驗室先前建立之肝臟特定性β-catenin剔除(BKO) 小鼠肝癌動物模型進行測試。 此動物模型之特點為小鼠在年紀約10個月開始，肝臟中會出現具β-catenin表現之肝臟前趨細胞之增生，逐漸取代原有之肝細胞，並在大約16-18個月時自發性產生源自前趨細胞之肝腫瘤。我們首先發現BKO小鼠肝臟前趨細胞中的雄性激素受體AR蛋白會受到活化態Wnt/β-catenin路徑調控而增加。為探討AR在前趨細胞中扮演的角色，針對年紀大於12個月的雄性BKO小鼠進行去勢手術及追蹤，發現去勢後的小鼠之肝臟相較於同年紀控制組之BKO小鼠有縮小的現象。進一步發現去勢後BKO小鼠肝臟中的前趨細胞量減少，而僅存的前趨細胞中Wnt/β-catenin路徑處於低活化的狀態，且失去增生能力。此結果因此顯示活化之AR路徑對於肝臟前趨細胞的存活及增生可能扮演調控的角色。此結論及其詳細機制有待後續進一步確認及深入研究。

Wnt/β-catenin pathway is abnormally activated in 50%~70% of hepatocellular carcinoma (HCC), suggesting its involvement in the carcinogenic process. However, the hepatic specific transgenic mice expressing constitutively active β-catenin only caused hepatomegaly but not the liver tumors. But the tumor incidence could be increased by adding some other carcinogenic events, for example transgenic with mutant H-ras or treated with DEN (diethylnitrosamine). It indicates that the Wnt/β-catenin pathway might need to collaborate with some other oncogenic factor(s) to trigger the hepatocarcinogenesis, which remained to be identified. According to the clues from hepatocellular adenoma (HCA), in which a male gender specific factor was considered as the key for the transformation of HCA with activated-β-catenin mutations into HCC. Therefore, we hypothesized that the androgen pathway could be the candidate factor in collaborating with β-catenin pathway in hepatocarcinogenesis. This possibility will be tested in conditional β-catenin knockout mouse model (BKO, Alb-Cre;Ctnnb1flx/flx). The BKO mouse model is a unique animal model with HCC derived from hepatic progenitor cells (HPCs). The HPCs start to proliferate at 8~10 months old (m.o.), which gradually replace the β-catenin(-) mature hepatocytes, and the spontaneous liver tumors derived from HPCs occur at 16~18 m.o.. In male BKO mice, we first noted that the AR protein was elevated in HPCs containing active Wnt/β-catenin pathway. To further address the function of AR pathway, we conducted castration in male BKO mice (>12 m.o.). Interestingly, the liver mass was decreased in BKO mice after castration, compared to those without castration. The immunofluorescence staining revealed that HPCs were decreased in the livers of castrated BKO mice. Meanwhile, the Wnt/β-catenin pathway activity and also the proliferation activity was diminished in the survived HPC clusters. The results thus suggested the function of active AR pathway in regulating the proliferation and survival of HPCs in BKO male mice, which form the basis for further validation and mechanistic studies.