岩藻糖基化之膜蛋白與癌症轉移之間關係

The relationship between fucosylated membrane proteins and cancer metastasis

白昕永(Hsin-Yung Pai)

指導教授 ： 陳水田

國立臺灣大學/生命科學院/生化科學研究所/碩士(2012年)

https://doi.org/10.6342/NTU.2012.01821

摘要

根據世界衛生組織統計，在人類眾多癌症中，十大死因排名第三名的疾病。在臨床檢體的分析中，惡性的肺癌細胞周邊組織及血清會表現較大量的第四型岩藻糖轉酶，其功能為將岩藻糖以α-1,3/4 的方式接上N-乙醯葡萄醣胺(N-acetylglucosamine)為核心的N端連結糖蛋白。岩藻糖基化是屬於轉錄後修飾中糖基化的一部分，由於岩藻糖基化的增加，導致細胞表面特定糖結構大量表現，會影響細胞內外的訊息傳遞、細胞貼附能力以及細胞與細胞間的辨識功能。在先前的研究中，利用已建立穩定表現第四型岩藻糖轉酶的肺腺癌細胞株(A549-FutIV)與轉入空質體的肺腺癌細胞株(A549-Mock)比較，發現當中有十九種N端連結的膜蛋白上，有較多或較少的鹽藻糖基化現象。在這十九種N端連結糖蛋白中，大部份蛋白的功能並未明確被研究出。
在本篇研究裡，我們想要去探討關於這些岩藻糖基化改變的膜蛋白與癌症的惡性轉移之間的關係，利用小干擾核醣核酸將特定基因的信使核醣核酸分解，達到蛋白質表現下降，來探討SLC3A2, CD166以及CD44對於癌症轉移的影響。由於CD166與CD44的表現量對於癌症惡性程度是有相關性，當CD166，CD44基因敲除後，對於癌症轉移能力有顯著性的減少，CD166本身與細胞外基質的結合能力透過實驗得知其具有貼附能力。SLC3A2本身為氨基酸轉運子重鏈，在纖維連接蛋白的聚集上扮演調控的角色，同時，在腎細胞癌中扮演著生物標記。由實驗結果得知，SLC3A2對於癌症的轉移能力並無顯著性的差異，但確實對於纖維連接蛋白擁有貼附能力。CD44基因敲除後，雖然會抑制惡性癌症的轉移，但並非因細胞外基質的貼附能力所致。結合侵犯實驗及貼附實驗發現，SLC3A2的貼附能力對於易轉移之癌細胞有抑制功效，CD166及CD44所造成的抑制癌症轉移效果並非經由貼附能力所致。

關鍵字

肺癌 ； 第四型岩藻糖轉酶癌症轉移 ； 膜蛋白 ； 轉錄後修飾 ； N端連結糖基化 ； 細胞侵犯實驗

並列摘要

Lung cancer is a disease and ranked as third among the ten leading causes of human deaths according to statistics reports of the world health organization. In clinical studies, lung cancer of a more malignant state may express more fucosyltransferase IV(Fut IV), which is an enzyme that transfers a fucose to a core N-acetylglucosamine sugar of N-linked glycoprotein via α-1,3/4 linkage. Fucosylation is a common glycosylation process in posttranscriptional modification that can affect signal transduction, cell adhesion and cell-cell recognition. In previous studies, the A549-FutIV cell line was established, which expresses relatively high amounts of Fut IV. A549-FutIV, consists of nineteen membrane proteins with more or less higher degree of fucosylation of their N-glycoproteins when compared with A549-Mock. The functions of most of these membrane proteins remain unknown.
In this study, we focus on the relationship between these membrane proteins and cancer metastasis in A549-FutIV. The protein (SLC3A2, CD166 or CD44) was knockdown by siRNA. CD166 and CD44 expressions correlated with the degree of cancer malignancy. After CD166 and CD44 knockdown, the cancer invasion ability had significantly decreased compared to the control and CD166 could also bind to the extracellular matrix(ECM). SLC3A2 was an amino acid transporter heavy chain that played an important roles as a mediator of fibronectin assembling and also as a biomarker in renal cell cancer. According to our experiments, SLC3A2 did not cause any significantly changed to cancer metastasis, but it could bind to fibronectin. Although CD44 knockdown could inhibit cancer invasion, it did not result from its adhesion ability. By combining invasion assay and adhesion assay results, we found that SLC3A2 knockdown could inhibit cancer invasion through its adhesion ability. However, the inhibition of cancer invasion after CD166 and CD44 knockdown did not occur via their adhesion abilities.

並列關鍵字

Lung cancer ； Fucosyltransferase IV ； Metastasis ； membrane protein ； PTM ； N-linked glycosylation ； invasion assay

參考文獻

Aruffo A, Stamenkovic I, Melnick M, Underhill CB, Seed B (1990) Cd44 Is the Principal Cell-Surface Receptor for Hyaluronate. Cell 61: 1303-1313

2. Beck-Sickinger AG, Mörl K (2006) Posttranslational modification of proteins : Expanding nature's inventory, Vol. 45: Roberts and Co.

3. Becker WM, Kleinsmith LJ, Hardin J (2004) The world of the cell, sixth edn.: Pearson.

4. Borsig L, Wong R, Hynes RO, Varki NM, Varki A (2002) Synergistic effects of L- and P-selectin in facilitating tumor metastasis can involve non-mucin ligands and implicate leukocytes as enhancers of metastasis. Proceedings of the National Academy of Sciences of the United States of America 99: 2193-2198

5. Broer A, Friedrich B, Wagner CA, Fillon S, Ganapathy V, Lang F, Broer S (2001) Association of 4F2hc with light chains LAT1, LAT2 or y(+)LAT2 requires different domains. Biochem J 355: 725-731