探討⼤腸癌細胞中調控 CD44v6 表現之機制

Abstract

癌症的復發及轉移，被認為是造成大腸癌病患低生存率的原因。近年來許多研究發現，癌幹細胞具有自我更新、抗藥的能力，且在化學治療的過程中，能夠生存下來並轉移。癌幹細胞的辨識多半是藉由其表面的幹細胞標記。其中，CD44v6 就是一個極具代表性的大腸癌幹細胞標記，並且被證明會促進大腸癌的轉移。另外，臨床數據也指出，低表現量的 CD44v6 提升了大腸癌病患的生存率。然而，大腸癌幹細胞為什麼傾向將 CD44 的 mRNA 剪接成 CD44v6 這個形式仍然未知。在本篇論文中，發現兩個與剪接反應有關的因子在大腸癌腫瘤組織中有很高的表現量，且能夠促進 CD44v6 轉錄層次的表現量。另外，本研究也證明，兩因子間有交互作用，且影響兩因子入核的現象。然而，在之後進行 minigene reporter assay，卻發現 兩因子似乎無法藉由調控選擇性剪接反應的機制，使外顯子v6被保留下來。因此本論文推測其可能藉由別的機制，例如：調控轉錄，達到調節 CD44v6 表現量的目的。綜上所述，此篇研究說明了關鍵二因子調控了 CD44v6 的表現量，以及細胞轉移的能力，在大腸癌幹細胞中扮演了很重要的角色。

In colorectal cancer (CRC), relapse and metastasis are the main reasons that decrease patients’ probability of survival. In recent years, many studies revealed that the existence of cancer stem cell (CSC) resulted in difficulty in completely curing cancer. The CSC which is defined by its capacity for self-renewal and drug resistance is believed to survive after cancer therapies and then starts metastasis. In tumor tissue, CSCs are commonly identified by their cell surface markers. According to previous studies, CD44v6 was regarded as a crucial cell-surface marker of CSC that confers the ability to promote colorectal cancer metastasis. Besides, lower CD44v6 expression increases CRC patients’ survival rate in clinical studies. However, the alternative splicing mechanism of CD44v6 in CSC is still unknown. In this thesis, I reported that Factor A and Factor B highly expressed in primary colon cancer tissues comparing to their adjacent normal colon tissues and were positively correlated with CD44v6 expression. Moreover, I clarified that there was an interaction between Factor A and Factor B by co-immunoprecipitation. Besides, nucleus-translocated Factor B resulted in poor prognosis in cancer progression. I also found Factor A had ability to enhance the nucleic subcellular localization of Factor B. However, while utilizing minigene reporter assay, I recognized that Factor A and Factor B seemed not regulate CD44v6 expression by changing alternative splicing site choice. Therefore, I supposed that Factor A and Factor B might regulate the expression of CD44v6 via other mechanism such as transcriptional regulation. Overall, these finding revealed that Factor A and Factor B played an important role in regulating CD44v6 expression and cell migration ability which were both considered to be major features of colon CSC.