SIRT1促進大腸癌幹細胞之幹細胞特性研究

Abstract

近年來，許多研究發現癌幹細胞具有自我更新、抗藥性與轉移能力等特性，而癌幹細胞的存在也往往造成大腸癌病患具有較差的預後。表觀遺傳修飾對於維持癌幹細胞特性而言，扮演著相當重要的角色，根據先前的研究，去乙醯酶SIRT1可促進癌細胞增生能力與抗壓能力，它在表觀遺傳上可以針對組蛋白3的賴氨酸9 (histone 3 lysine 9, H3K9) 進行去乙醯化，進而造成染色質形成較緊密的結構並抑制轉錄活性，然而，SIRT1是否能夠透過調控表觀遺傳影響癌幹細胞特性仍然未知。在本研究中，證實SIRT1下游相關路徑能夠促進大腸癌癌幹細胞特性。首先，SIRT1會結合到微小核醣核酸miR-niChe啟動子，藉由去除組蛋白乙醯化降低其轉錄，其次，透過生物資訊工具的預測，發現miR-niChe能夠直接結合大腸癌幹細胞標記基因的mRNA，此結合作用能夠抑制癌幹細胞標記基因轉譯形成蛋白質，進一步地，在大腸癌細胞HT29以及DLD-1中過量表現miR-niChe後，癌幹細胞特性皆有顯著下降，並能利用過量表現癌幹細胞標記基因減緩該影響，證實miR-niChe是透過降低癌幹細胞標記基因表現達到抑制癌幹細胞特性的功能，除此之外，小鼠異體移植實驗中，過量表現miR-niChe的腫瘤大小明顯被抑制。綜上所述，我證明了這個預測的miRNA具有降低癌幹細胞特性的能力，並證實在大腸癌幹細胞中，可以透過表觀遺傳修飾抑制抑癌miRNA表現，進而開啟下游路徑促進癌幹細胞特性。

The cancer stem cell (CSC) properties such as self-renewal, drug resistance, and metastasis have been indicated to be responsible for poor prognosis of patients with colon cancers. In CSC, epigenetic modification plays a crucial role in maintaining CSC properties. According to previous studies, epigenetic regulator SIRT1 as a regulatory hub positively influences cancer related pathways such as proliferation and stress-resistance. It mediates deacetylation of histone H3 lysine 9 (H3K9), which results in repressive chromatin structure and low transcriptional activity. However, the precise mechanisms between CSC properties and abnormal histone modification by SIRT1 are still unknown. In this study, I report that SIRT1 signaling pathway is highly associated with CSC properties. The novel miRNA miR-niChe is predicted by bioinformatics databases with a potential of targeting Colon CSC Marker Gene. Inhibition of SIRT1 by RNA interference leading to elevated H3K9 acetylation in the promoter region of miR-niChe. This epigenetic reprogram results in elevation of miR-niChe expression, which further represses Colon CSC Marker Gene translation through targeting the 3’UTR of Colon CSC Marker Gene mRNA. Meanwhile, the repression of CSC properties caused by miR-niChe can be rescued by overexpression of Colon CSC Marker Gene. In subcutaneous xenograft model, tumors with miR-niChe overexpression reduced the tumor size. Therefore, the potential of the predicted miRNA for inhibiting CSC properties is demonstrated. Overall, these findings reveal how epigenetic regulator modulates gene expression and further CSC properties through repression of tumor-suppressing miRNAs in colon CSCs.