吲哚胺2,3-雙加氧酶活化多環芳香烴感受器路徑和β-連環蛋白訊息傳遞路徑促進肝細胞癌惡化

Understanding the role of Indoleamine 2,3-dioxygenase-induced Aryl hydrocarbon receptor and β-catenin pathway in Hepatocellular Carcinoma Cells

吳沛樺(Pei-Hua Wu)

指導教授 ： 周綠蘋

國立臺灣大學/醫學院/生物化學暨分子生物學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903174

摘要

肝細胞癌(Hepatocellular carcinoma)為原發性肝癌中最常見的一型，也是全球致死率第二名的癌症。肝炎病毒感染所引起的慢性肝臟發炎是造成HCC最主要的危險因子，當促發炎因子：丙型干擾素(Interferon-γ, IFN-γ)刺激肝癌細胞後，細胞內酵素：吲哚胺2,3-雙加氧酶(Indoleamine 2,3-dioxygenase, IDO)的表現量會大量上升並參與在抑制免疫反應的過程，進而改變腫瘤微環境。近年來，IDO對於非免疫細胞的調控開始受到關注，然而IDO對於HCC細胞自身的影響目前還有待探討。
在本篇研究中我們發現利用IFN-γ刺激Huh7 shCtrl細胞後，IDO的表現量與活性都會大量上升，我們也觀察到IDO的活性與癌細胞的增生和轉移能力呈正相關，在給予細胞犬尿胺酸(kynurenine, KYN)後，可以回復Huh7 shIDO cells增生和轉移的能力，因此暗示著IDO和其代謝產物會促進肝癌細胞的惡化。KYN為多環芳香烴感受器 (aryl hydrocarbon receptor, AhR)的內源性配體，在過去研究中AhR的活化被報導會參與在多種癌症中，我們發現在細胞受到IFN-γ刺激後，KYN表現量的提升會活化並促進AhR進入細胞核，活化的AhR會提升snail的轉錄，進而抑制E-cadherin的表現量，當E-cadherin的表現量下降時會釋放β-連環蛋白(β-catenin)，因此β-catenin可以進入細胞核中調控與增生相關分子的轉錄。此外，在細胞核中AhR和β-catenin會有物理上的連接並共同調控snail轉錄的提升，進而促進細胞轉移的能力。我們也推測活化的AhR會釋放Src來抑制PTEN的蛋白表現量，使Akt訊息傳遞路徑不斷活化，因此β-catenin將不再受destruction complex抑制，得以進入細胞核。根據本篇論文的實驗結果，我們觀察到IDO促進肝癌細胞發展的機制，其中AhR和β-catenin訊息傳遞路徑的活化扮演重要角色。

關鍵字

肝細胞癌 ； 丙型干擾素 ； 吲哚胺2,3-雙加氧酶 ； 犬尿胺酸 ； 多環芳香烴感受器 ； β-連環蛋白 ； Src ； PTEN ； Akt

並列摘要

Hepatocellular carcinoma (HCC), the major type of primary liver cancer, is the second most common cause of cancer-related death worldwide. Chronic liver inflammation caused by hepatitis virus infection is the main risk factor of HCC. Once pro-inflammatory factor IFN-γ stimulates liver cancer cell, Indoleamine 2,3- dioxygenase (IDO) will be activated to mediate tumor immune escape, which is crucial in the promotion of HCC. Recently, IDO has been the focus of much attention because of its non-immunological role. However, the role of IDO in liver cancer remains to be elucidated.
In our studies, we showed that IFN-γ induced IDO expression and activity in Huh7 cells, and there was a positive correlation between IDO activity and cell proliferation and metastatic abilities. Moreover, the proliferation and metastatic capability could be rescued after kynurenine (KYN) treatment in Huh7 shIDO cells. These results implicated that IDO and its metabolite were involved in HCC progression. KYN was an endogenous ligand of aryl hydrocarbon receptor (AhR), which had been reported to play a role in tumorigenesis. We found that KYN enhanced signaling activation and nuclear translocation of AhR. Activated AhR promoted transcription of snail and reduced E-cadherin expression. Downregulation of E-cadherin led to release of β-catenin, then β-catenin was able to translocate to the nucleus and promoted the expression of proliferation-related molecules. In the nucleus, AhR and β-catenin had physical interaction and corporately promoted transcription of snail, which was responsible for the increased cell migratory and invasive abilities. We also speculated AhR released Src to downregulate PTEN expression and promote Akt signaling, which abolished the destruction complex from β-catenin, and finally led to activation of β-catenin. In conclusion, these results showed the tumor-promoting function of IDO in HCC, and it was mediated by activating both AhR and β-catenin signaling pathway.

並列關鍵字

HCC ； IFN-γ ； IDO ； kynurenine ； AhR ； β-catenin ； Src ； PTEN ； Akt

參考文獻

1.El-Serag, H.B. and K.L. Rudolph, Hepatocellular carcinoma: epidemiology and molecular carcinogenesis. Gastroenterology, 2007. 132(7): p. 2557-76.

2.McGlynn, K.A., J.L. Petrick, and W.T. London, Global epidemiology of hepatocellular carcinoma: an emphasis on demographic and regional variability. Clin Liver Dis, 2015. 19(2): p. 223-38.

3.Wang, C.-K. and R.-A. Branch, Management consensus guideline for hepatocellular carcinoma: 2016 updated by the Taiwan Liver Cancer Association and the Gastroenterological Society of Taiwan. J Formos Med Assoc, 2018. 117(5): p. 381-403.

4.Ferlay, J., et al., Cancer incidence and mortality worldwide: sources, methods and major patterns in GLOBOCAN 2012. Int J Cancer, 2015. 136(5): p. E359-86.

5.Farazi, P.A. and R.A. DePinho, Hepatocellular carcinoma pathogenesis: from genes to environment. Nat Rev Cancer, 2006. 6(9): p. 674-87.