- 學位論文
探討第八型岩藻醣轉移酶在人類非小細胞肺癌中過度表現之功能與調控機制
The Functional Role and Regulatory Mechanism of FUT8 Overexpression in Human Non-Small Cell Lung Cancer
摘要
第八型岩藻醣轉移酶(fucosyltransferase 8, FUT8)是哺乳類動物中唯一一種可將岩藻醣以α1,6的鍵結方式連接到醣蛋白上的醣化酵素。在過去的研究中，FUT8過度表現的現象曾在多種癌症中被發現，其中包括肝癌、卵巢癌、甲狀腺癌以及大腸直腸癌，且其表現量與這些腫瘤的惡性程度具有正相關性。而在我們先前的研究中，為了解岩藻醣轉移酶與肺癌細胞轉移的相關性，也曾利用即時定量聚合酶連鎖反應(quantitative real time PCR, Q-PCR)比較兩株源自同細胞、但具有不同轉移能力的肺癌細胞株CL1-0與CL1-5之中各種岩藻醣轉移酶的表現量，結果發現與CL1-0相比，FUT8在具有高轉移能力的肺癌細胞株CL1-5中亦有大量表現的現象。然而，雖然已知FUT8的表現量在臨床上與腫瘤的惡性程度有正相關性，但對於FUT8在腫瘤發展的過程中所扮演的角色，至今仍然十分地不清楚。在本研究中，我們首先利用臨床檢體證實FUT8在人類非小細胞肺癌中具有過度表現的現象，且表現量越高的病人，其腫瘤轉移與復發的機率越高，存活率也顯著降低。接著藉由核酸干擾技術(shRNA)，我們發現在降低FUT8的表現量後，不論是在試管中(in vitro)或是小鼠體內(in vivo)，肺癌細胞的生長、轉移都被顯著地抑制。而我們也透過醣蛋白質體學與核酸微陣列分析技術，分別找到受FUT8所修飾的醣蛋白，以及受其活性所影響的下游基因。結果顯示，FUT8可廣泛地修飾細胞表面的表面抗原(surface antigens)、受體(receptors)以及黏附分子(adhesion molecules)，並藉此影響許多與腫瘤發展相關的基因的表現。此外，在這個研究裡我們也找到FUT8在腫瘤發展的過程中過度表現的調控機制：在腫瘤轉移中扮演關鍵角色的一個名為上皮-間葉細胞轉換(epithelial-mesenchymal transition, EMT)的過程中，FUT8的基因表現會受到β-catenin/lymphoid enhancer-binding factor-1 (LEF-1)所活化。而從一個初步的實驗結果我們也發現，FUT8的表現可能與p53的突變與否有關，值得進一步的研究。總結來說，本研究不但提出了一個新的模型來解釋FUT8與肺癌發展之間的因果關係，也提供了一個可能的方向供預後判斷、甚至是治療非小細胞肺癌。
並列摘要
In the past decade, overexpression of fucosyltransferase 8 (FUT8), the only enzyme catalyzing α1,6-fucosylation in mammals, has been shown to correlate with malignancy of several human cancers including liver, ovarian, thyroid, and colorectal cancers. We previous also found that FUT8 is dramatically upregulated in a highly aggressive lung cancer cell line CL1-5 comparing to its non-aggressive parental cell line CL1-0. However, little is known about the pathological role of FUT8 in the progression of tumor. Here, we identify FUT8 as a prognostic factor and a functional regulator of nonsmall cell lung cancer (NSCLC). Overexpression of FUT8 in NSCLC is associated with tumor metastasis, disease recurrence and poor patient survival. Experimental knocking down FUT8 in aggressive lung cancer cell lines significantly suppresses their invasion, migration and growth abilities in vivo and in vitro. In addition, we categorize glycoproteins and genes regulated by FUT8 activity using glycoproteomic and microarray approaches. Results from the comprehensive omics analysis indicate that FUT8 globally modifies surface antigens, receptors, and adhesion molecules as well as controls dozens of genes associated with malignancy, suggesting that FUT8 promotes lung cancer progression through multiple mechanisms. Furthermore, in the current study, we unraveled the regulatory mechanism of FUT8 expression in cancer progression. During epithelial-mesenchymal transition (EMT), one of the critical steps in cancer metastasis, the expression of FUT8 is transactivated by β-catenin/lymphoid enhancer-binding factor-1 (LEF-1). Besides, a preliminary study suggests that p53 may also regulate FUT8 expression via cross-talk with β-catenin signaling pathway. Taken together, our results not only provide a novel model to link FUT8 expression with tumor progression, but also point out a promising direction for the prognosis and therapy of NSCLC.
參考文獻
延伸閱讀
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