探討 forkhead box protein O3A 於大腸癌幹細胞中所扮演之角色

Abstract

癌幹細胞往往是造成癌症轉移及復發的主因之一。如同正常的幹細胞，癌幹細胞所具有的自我更新、細胞休眠以及抵抗外來壓力的能力也讓研究推測它與正常幹細胞使用許多共同的因子。不過，因為純化及研究癌幹細胞的困難，加上目前較少針對癌幹細胞進行的全面研究，使得那些重要的因子尚未明瞭。在本研究中，我探討在正常幹細胞中扮演重要角色的轉錄因子 forkhead box protein O3A (FOXO3A) 是否也對於大腸癌幹細胞也有著同樣地位。藉由分析細胞休眠的族群顯示：FOXO3A knock-down 的大腸癌細胞株中細胞休眠的族群較低。此外，由較低的球體 (sphere) 生成數目也可得知，FOXO3A 表現降低會影響癌細胞自我更新的能力。因為 FOXO3A 可以促進自我更新及細胞休眠，所以確定了 FOXO3A 對於大腸癌幹細胞的維持扮演著不可或缺的角色。實驗結果也顯示 FOXO3A 在大腸癌細胞中始終保持著活化的狀態，並且不受到 AKT/PI3K 以及 TGF/SMAD 調控路徑影響，顯示 FOXO3A 的活性可能不取決於表現量。因此，我推測 FOXO3A 能藉由開啟與先前研究不同甚至是全新的基因來維持癌幹細胞型細胞自的能力。

Cancer stem cell (CSC) is one of the main reasons leading to the recurrence and the metastasis of several cancers. While having abilities as self-renew, quiescence and stress resistance as a normal stem cell, CSC is believed to share many key factors with a normal stem cell. However, due to the less of comprehensive researches and the difficulty in isolation and investigation of CSC, the factors which are essential to the CSC are not yet clear. In this thesis, I tested whether the transcription factor forkhead box protein O3A (FOXO3A), which is known as a necessary factor for normal stem cells, plays an important role in colon CSCs. Through analysis of quiescence population, the knock-down of FOXO3A in colon cancer cell lines decrease the quiescent population of cancer cells. Through sphere forming assay, I also show that the decrease of FOXO3A in cancer cells eliminates the self-renew ability since sphere numbers become significant lower than control. I confirmed that FOXO3A is critical for the maintenance of colon CSCs by promoting self-renew and quiescence. I also show that FOXO3A is constantly activated in colon cancer and independent to AKT/PI3K and TGF/SMAD pathways. Therefore FOXO3A may function in a dose-independent manner. Furthermore, these results indicate that FOXO3A may activate different or even novel gene sets during self-renew in colon CSCs.