中文摘要
內皮唾酸蛋白(endosialin)，又稱為CD248或是第一型腫瘤內皮標誌蛋白，是一個穿膜醣蛋白。它由六個結構區域組成，包括一個C型類凝集功能區，一個sushi功能區，一個由三個類內皮生長因子重複區塊組成的功能區，一個類黏蛋白功能區，一個穿膜區以及膜內片段。研究顯示內皮唾酸蛋白會高量表現在大部分腫瘤的基質區域以及血管周圍。除此之外，藉由腹腔腸部原位癌移植的動物實驗模式，內皮唾酸蛋白的基因剔除小鼠較野生型小鼠有較嚴重的腫瘤生成以及轉移，而且這些長在內皮唾酸蛋白基因剔除小鼠的腫瘤都有較多的未成熟小血管及較少的成熟大血管，顯示內皮唾酸蛋白似乎藉由透過血管新生作用以調控腫瘤生成過程。然而，在腫瘤血管新生時內皮唾酸蛋白的來源以及功能仍是未知。腫瘤相關的纖維母細胞 (Cancer-associated fibroblasts, CAFs) 是腫瘤基質區域的主要細胞族群。我們分離了口腔癌病人的腫瘤相關的纖維母細胞以及其周圍正常組織的齒齦纖維母細胞，發現腫瘤相關的纖維母細胞有較高量的內皮唾酸蛋白的表現，顯示它可能是一個腫瘤相關的纖維母細胞的標誌蛋白。除此之外，我們也在腫瘤相關的纖維母細胞的細胞培養液中發現了內皮唾酸蛋白片段的存在，此細胞培養液可以顯著的促進人類臍帶靜脈內皮細胞的生長以及其管狀結構的形成，而加入專一性針對內皮唾酸蛋白的抗體則可以阻斷這樣的現象。另外，我們使用酵母菌蛋白表現系統純化出了內皮唾酸蛋白的類內皮生長因子重複區塊的蛋白，此重組蛋白亦可以顯著的促進人類臍帶靜脈內皮細胞的生長以及其管狀結構形成。而此蛋白在動物實驗中也具有促進血管新生的功能。綜合以上結果，我們發現內皮唾酸蛋白的片段會被腫瘤相關的纖維母細胞所釋放出來，而且其類內皮生長因子重複區塊具有血管新生因子的功能。

Endosialin (also known as CD248 or tumor endothelial marker 1) is a transmembrane glycoprotein. It is composed of six domains, including a lectin-like domain, a sushi domain, a three epidermal growth factor (EGF)-like repeats, a mucin-like domain, a transmembrane domain, and a cytoplasmic tail. Previous studies showed that endosialin was highly expressed in fibroblasts-rich stroma and vasculature of carcinomas. Furthermore, reduced tumor growth and metastasis were observed in endosialin knockout mice but not in wild type mice in an abdominal orthotopic xenograft model. Meanwhile, the tumors from endosialin knockout mice contained more small and immature vessels but less large and mature vessels, suggesting that endosialin may play a role in tumor progression by promoting angiogenesis. However, the source and function of endosialin in angiogenesis remain unknown. Cancer-associated fibroblasts (CAFs) are the major cell population in tumor stroma. We collected CAFs and human gingival fibroblasts (HGFs) from oral cancer patients. We found that the expression level of endosialin in CAFs was higher than HGFs, indicating that endosialin may be a marker of CAFs. Meanwhile, endosialin fragments were also identified in conditioned medium of CAFs. CAFs-conditioned medium could promote human umbilical vein endothelial cells (HUVECs) proliferation and tube formation in vitro whereas addition of endosialin specific antibody could effectively attenuate these effects. In addition, recombinant EGF-like repeats of endosialin (ESD3) protein functioned as an angiogenic factor in vitro and in vivo. ESD3 could activate angiogenesis-associated signaling pathways such as extracellular signal-regulated kinase and Akt in HUVECs. It also promoted cell proliferation and tube formation of HUVECs and induced angiogenesis in a murine Matrigel plug assay. Based on these observations, soluble endosialin fragments may be released from CAFs and the EGF domain of endosialin may be an angiogenic factor in CAFs-mediated angiogenesis.

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