微小RNA(miRNAs)過去已被證實可以透過結合至訊息RNA(mRNAs) 的3’非轉譯區(3’UTR)抑制表觀遺傳調控者的表現，除此之外，miRNAs也被觀察出可以藉由結合DNA透過表觀遺傳調控抑制基因的表現，不過其中詳細的機制以及微小RNA的角色仍有需多依舊沒被探討。在本篇研究，CCAAT/enhancer-binding protein delta (CEBPD) 已知會被臨床上已使用的抗癌藥物Bortezomib所誘導，Bortezomib 是在臨床上常用於白血病的治療去促使癌細胞凋亡。有趣的是，透過發現CEBPD所調控的微小RNA 我們找到了一些miRNAs (miR-744/3154/3162) 可以結合至CEBPD 5’非編碼區的CpG 聚集區域。而過去在實驗室的研究當中我們發現YY1/PcG 還有DNMT蛋白對於CEBPD的抑制扮演著要的角色，更進一步，我們發現Ago2 (屬於微小RNA的結合蛋白) 可以和YY1有交互作用而一起結合至CEBPD的促進區域。重要的是微小RNA以及Ago2/YY1/PcG 聚合一起導致CEBPD以及位於同樣位置的基因（PRKEC, MCM4 還有UBE2V2）的表現抑制在Bortezomib的治療下。總結以上，我們發現微小RNA對於Ago2/YY1/PcG 複合物所導致的基因抑制扮演著重要的角色，而也發現這些複合物的結合提高了甲基化的程度在Bortezomib治療之下的白血病細胞。本篇研究不只探討出微小RNA與Ago2/YY1以及PcG 複合體的形成，也提供了微小RNA所導致的表觀遺傳調控在Bortezomib治療白血病引發細胞週期停滯以及細胞凋亡。

Several microRNAs (miRNAs) was identified to repress the expression of epigenetic regulators via binding to their 3’Untranslated Region (3’-UTR) of mRNAs. Though miRNA directly targeting onto genomic DNA and repressing gene expression through an epigenetic regulation that was observed, the details and consequent effect in response to the miRNA-mediated epigenetic regulation remain largely uninvestigated. In this study, transcription factor CCAAT/enhancer binding protein delta (CEBPD) was responsive to bortezomib, a clinical and highly selective drug for leukemia treatment, and contributed to bortezomib-induced cell death. Interestingly, following the identification of CEBPD-induced miRNAs, we found that several miRNAs (miRNA-744, miR-3154 and miR-3162) could target to CpG island of the 5’-flanking region of CEBPD gene. We previously demonstrated that Yin Yang 1 (YY1)/PcG group proteins/DNMTs complex is important for CEBPD gene inactivation; we further found that Ago2 (a miRNA binding protein) could interact with YY1 and bound to CEBPD promoter. The miRNA/Ago2/YY1/PcG group proteins/DNMTs complex linked the inactivation of CEBPD and its 5’-flanking genes, including PRKDC, MCM4 and UBE2V2, upon bortezomib treatment. Finally, we revealed that the binding of miRNAs is necessary for YY1/PcG group proteins/DNMTs complex-mediated epigenetic gene silencing and associated with bortezomib-induced methylation level. The study not only successfully link the interaction of miRNA/Ago2/YY1/PcG group proteins/DNMTs complex and also provide new insight for miRNA-mediated epigenetic regulation in Bortezomib-induced leukemia cell arrest and death.

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