B型肝炎病毒調控雄性激素受體表現量之機制研究

Abstract

B肝病毒(Hepatitis B Virus, HBV)慢性感染引起之肝細胞癌 (Hepatocellular carcinoma, HCC)，是台灣重要的癌症死因。自慢性感染階段開始，B肝病毒造成的相關疾病皆好發於男性，根據本實驗室過往之研究，好發於男性可能是由於男性病患特有之雄性激素路徑的影響。受雄性激素活化的肝臟雄性激素受體(Androgen receptor, AR)能透過B肝病毒的Enhancer I區域上Androgen-responsive element序列，加強病毒轉錄與複製；而B肝病毒也能藉由非結構蛋白質HBx增強AR的轉錄活性。此病毒與雄性激素路徑間的互相影響，是造成男性病患較高之病毒量以及較高之肝癌風險之主因。然而由於生理狀態下男性肝臟AR表現量極低，本論文因此提出一假說，即B肝病毒不只能增強AR的活性，更能調控AR表現量，來建立於肝細胞中HBx與AR之間的正回饋作用。 為了探討此假說之可能性，我們使用B肝病毒基因轉殖鼠動物模式，比較之下發現轉殖鼠之肝臟中AR表現量在禁食情況下確實有增加的現象。進一步利用此小鼠動物模式探討其分子機制，將小鼠進行去勢以抑制雄性激素合成，更發現調控機制可能與雄性激素活性有關。雄性激素抑制AR之表現量，而B肝病毒基因之轉殖會造成與去勢類似之作用。本論文實驗結果同時指出B肝病毒有可能藉由增加胰島素路徑之活性造成對AR表現之影響。有鑑於利用磷酸酶對胰島素受體進行去磷酸化，為細胞調控胰島素路徑的機制之一，本論文因而探究B肝病毒是否藉由特定磷酸酶影響胰島素路徑之可能性，初步結果顯示胰島素路徑之增加與PTP1B磷酸酶之磷酸化相關，此初步結果仍需進一步實驗以探究其對維持AR較高之表現量之重要性。本論文的發現將有助於釐清B肝病毒在調控AR轉錄活性之前，究竟是如何增加AR表現量，以建立後續更有效率的病毒複製之分子機制。

There exists a gender difference in the incidence of hepatitis B virus (HBV)-related HCC, starting from the chronic hepatitis stage, which leads to a higher risk to HCC in men than in women. Our previous studies demonstrated that this male predominance could be attributed to the androgen pathway. The androgen activated androgen receptor (AR) can promote HBV transcription via binding to the androgen-responsive elements (AREs) located in the HBV enhancer I region. The HBV X protein (HBx) can in turn enhance the transcriptional activity of AR. The interaction between HBx and AR leads to the higher HBV titer and a higher risk to HCC in men. Regarding to the very low AR protein level in normal male liver, this study was proposed to test if HBV infection could also increase the level of hepatic AR to further enhance this HBx-AR loop in male liver. We proposed to test this hypothesis in the HBV-transgenic (HBV-Tg) mouse model. We found that the AR protein was significantly higher in HBV-Tg than in control wild type male mice under fasting, similar as that caused by castration. Meanwhile, an increase of insulin pathway activity was identified both in HBV-Tg mice and in castrated wild type male mice under fasting. Our preliminary results further showed an association of increased IR phosphorylation with the phosphorylation of protein tyrosine phosphatase 1B (PTP1B). The critical role of this phosphorylation in regulating the elevation of hepatic AR is worthy to be further investigated. We expect the results can help clarify if HBV infection can stimulate the activity of androgen pathway through increasing both the expression level and the transcription activity of AR.