Y-box binding protein 1 於肝癌幹細胞之功能解析

Abstract

肝癌是世界上致死率前三名的癌症，而其高復發率、高轉移率及抗藥性是現今治療上的主要難題。而近年來快速發展的癌幹細胞理論，提供了一個新的癌症治療觀點。癌幹細胞是腫瘤中存在的類幹細胞群落，具有生長、分化及自我更新的能力。這些癌幹細胞能夠獨立生長分化為腫瘤細胞進而形成腫瘤，為癌症的起始細胞。同時其對傳統癌症藥物具有較高的耐受性，能在化療過程中維持其細胞群落，而在化療結束後繼續分化生長，造成腫瘤復發；除此之外，近年來的研究亦顯示這些癌幹細胞的種種特性如高遷移性、免疫特異性和代謝特殊性，都遠不同於我們原本對癌細胞的認識，成為癌症治療上的缺口，因此發展針對癌幹細胞的治療方法將是未來癌症治療的方向。而多功能蛋白質 YB-1 已被發現在許多癌症中，具有促進幹細胞標記表現、提高癌細胞的移動性和提升抗藥基因表現等癌幹細胞常見的特性；此外在肝臟的發育及再生的過程中， YB-1 亦被發現是重要的調控者，顯示其在幹細胞性質調控上的重要性。 為了進一步研究 YB-1 是否為肝癌幹細胞中的重要調控者，我利用 Sphere Forming 的方式培養肝癌幹細胞，發現在 Sphere 形成過程中， YB-1 和其他多能基因的表現是提升的；進一步利用 RNA 干擾的方式降低 YB-1 表現後，亦發現形成 Sphere 及細胞自我更新的能力明顯下降，而 YB-1 抑制細胞株中癌幹細胞的比例也有所下降；而在肝癌細胞在形成 Sphere 後 YB-1 的核轉移，暗示了其在肝癌幹細胞種基因調控的功能。此外在抑制 YB-1表現後肝癌細胞株的幹細胞標記、細胞移動力還有抗藥基因的表現皆下降；而細胞凋亡的基因反而上升。這些結果可能由 YB-1 影響 Wnt/β-catenin 路徑和表觀遺傳調控因子有關。從以上結果可知 YB-1 在肝癌幹細胞中具有關鍵的角色。

Hepatocellular Carcinoma (HCC) is the third cause of cancer mortality in the world. The important issues for the treatment of HCC are the high recurrence rate, easy metastasis and drug resistance. Recently, the concept of cancer stem cells (CSCs) provides a new consideration in the cancer therapy including HCC. Cancer stem cells are a subpopulation of cells in the tumor, which have the capability of self-renewal and differentiation and drug resistance in chemotherapy. Previous studies showed that many properties of CSCs, such as high cell mobility, evading immune destruction and reprogramming of energy metabolism, are very different from the original understanding of cancer. As a result, development of the therapy targeting CSCs is one of the novel therapeutic strategies for the cancer in the future. YB-1 is a protein with multiple functions, which has been found associated with many kinds of cancers. YB-1 can increase the expression of stemness marker genes, enhance cell mobility and up-regulate MDR gene expression. Besides, YB-1 is known as a significant regulator during liver development and regeneration. To investigate the regulatory function of YB-1 in CSCs of HCC, I used sphere forming method to enrich CSCs. In the sphere cells, the expression of YB-1 and some pluripotent genes was up-regulated. In addition, the sphere forming ability of YB-1-shRNA knockdown HuH7 HCC cell line was decreased. YB-1 would translocalize to the nucleus of sphere forming cells or side-population cells, and the cancer stem cell population sorted from HCC cell line. These results indicated YB-1 might be involved in the transcriptional regulation in the cancer stem cell-like cells in HCC. Additionally, knock down of YB-1 also down-regulated the stemness, drug resistance and epithelial-mesenchymal transition (EMT) genes expression by qPCR analysis. The detail mechanism would be regulated by Wnt/β-catenin pathway and epigenetic regulation. From these results, YB-1 may play a key role in HCC cancer stem cells.