上皮細胞黏附因子在間質幹細胞調控活化與訊息傳遞 的分子機制

Abstract

人類間質幹細胞可以分化成多種細胞類型，包括：軟骨細胞、成骨細胞、肌細胞及脂肪細胞。上皮細胞黏附因子（EpCAM），屬於第一型穿膜醣蛋白，在所有的腺狀細胞癌以及鱗狀上皮細胞癌中都有很高的表現量。並且是種很常見的癌症幹細胞標定物，也會促使惡性腫瘤的生長。近年來也發現EpCAM 於未分化的細胞中有高度表現，且在已經分化的胚胎幹細胞中表達較低，EpCAM 的蛋白和轉錄水平在，人類胚胎幹細胞一開始分化就會迅速減弱表現，後來研究發現EpCAM 可作為幹細胞的重要表面標記物。我們先前的研究發現EpCAM、EpICD 能直接接上幾個基因promoter，其中包括c-Myc，Oct4，Nanog，Sox2，Klf4，以幫助維持胚胎幹細胞的多能性。因此，我們推測EpCAM 可能在重編程的iPSCs 多能性，且有重要功能。在我們的研究中，也發現EpCAM 會表現在臍帶血間質幹細胞表並且EpEX 能促進臍帶血間質幹細胞和骨髓間質幹細胞的增生基因的表現。此外，我們還發現EpEX 可以促進細胞增生是透過增加STAT3 磷酸化和提高細胞週期調節因子的表現，並且是透過EGF 的接受器來影響到增生基因Lin28 的表現和STAT3 的磷酸化。因此，EpEX 不僅提高幹細胞自我修復、增生能力，也能夠在幹細胞重編程和多能性維持也起到重要作用。根據我們的研究，我們將提供EpCAM 的深入調控機制，有助於開發更高效的重編程方法以及策略，讓幹細胞維持iPS 的細胞形態以及細胞多能性的維護。

Mesenchymal stem cells, or MSCs, are multipotent stromal cells that can differentiate into a variety of cell types, including chondrocytes (cartilage cells), osteoblasts (bone cells), myocytes (muscle cells), and adipocytes (fat cells) (1). The epithelial cell adhesion molecule (EpCAM) is a type I transmembrane glycoprotein overexpressed in various carcinomas, such as adenocarcinomas and squamous cell carcinomas. Recently, EpCAM has been found as a well-known cancer stem cell marker and contributes to tumor growth. We have shown that EpCAM is highly expressed by undifferentiated rather than differentiated hESCs. In addition, EpCAM directly binds to the promoter of several reprogramming genes, including c-Myc, Oct4, Nanog, Sox2, and Klf4, to help maintain the pluripotency of hESCs, suggesting that in addition to being a potent stem cell marker, EpCAM also plays a crucial role in hESCs reprogramming and pluripotency maintenance. In the present study, we found that EpCAM is expressed in cord blood MSCs, and EpEX is also found to up-regulate the proliferation gene expressions in both cord blood MSCs and bone marrow MSCs. We also found that EpEX increases STAT3 phosphorylation, Lin28 protein level through EGF receptor and that phospho-STAT3 can interact with Lin28 to promote cell proliferation and cell cycle progression. Additionally, EpEX induces the expression of cell cycle regulators. We found that EpEX can serve as a cytokine and plays crucial roles in MSCs reprogramming a pluritpotency maintenance. Based on our study, we provided the molecular mechanism of EpCAM, in the regulation of stemness of MSCs. This results suggest that the stemness of MSCs and iPSCs can be further enhanced through EpCAM signaling.