長鏈非編碼核糖核酸NDRG1-OT1_v4不同片段在缺氧的乳癌細胞中對NDRG1轉錄調控有不同的影響

Abstract

缺氧的環境對侵襲性腫瘤而言是一個重要的因子並伴隨著不同的訊號傳遞途徑。近年來，各國研究學者們紛紛發現長鏈非編碼核酸(long non-conding RNA, lncRNA)能夠調節基因表現進而促進或抑制侵襲性腫瘤的進程。本實驗團隊藉由高通量次世代定序技術(next generation sequencing, NGS)找到了在缺氧下表現量顯著差異的lncRNA NDRG1-OT1_v4。藉由基因微陣列技術我們找到被NDRG1-OT1_V4抑制的下游基因之一N-myc downregulated gene 1 (NDRG1)。同時我們發現在大量表現NDRG1-OT1_V4會顯著地抑制NDRG1的核糖核酸及蛋白質表現量。在先前的研究中我們發現NDRG1蛋白質表現量會被顯著地抑制是藉由促進NDRG1參與泛素化調控路徑，但是我們仍舊不明白核糖核酸階層的抑制機制。 本篇我們發現NDRG1-OT1_V4在缺氧的細胞中是藉由抑制NDRG1促進子活性造成NDRG1表現量被抑制。接著我們發現NDRG1-OT1_V4第150–263核苷酸的位置主要是藉由增加促進子與hnRNPA1連結能力進而抑制NDRG1促進子及核糖核酸表現量。另一方面，在NDRG-OT1_v4第264–392核苷酸的位置能藉由與缺氧促進因子(hypoxia induced factor-1 alpha)結合而促進NDRG1促進子活性並增加NDRG1表現量。最終，我們首度發現長鏈非編碼核糖核酸中的不同片段對於同一個基因有著南轅北轍的調節方式。

Hypoxia is a crucial factor in aggressiveness of solid tumor by driving multiple signaling pathways. Recent researchers indicated that long non-coding RNA (lncRNA) could promote or inhibit tumor aggressiveness by regulating gene expression. Previous studies in our laboratory found the expression of lncRNA NDRG1-OT1_v4 significantly increased under hypoxia by next-generation sequencing (NGS). Moreover, it was discovered that the NDRG1-OT1_v4 inhibited NDRG1 at both mRNA and protein levels of NDRG1. At the protein level, NDRG1-OT1_v4 improved NDRG1 degradation via ubiquitin-mediated proteolysis pathway. However, the repressive mechanism of NDRG1 at RNA level was still unknown. In this studies, we found that NDRG1-OT1_v4 decreased the NDRG1 promoter activities when we overexpressed NDRG1-OT1_v4 under hypoxia. The fragment (150-263 nt) of NDRG1-OT1_v4 repressed NDRG1 promoter activity significantly by increasing the binding affinity of hnRNPA1. On the other hand, another fragment (264-392 nt) of NDRG1-OT1_v4 improved NDRG1 promoter activity by recruiting HIF-1 alpha. In conclusion, we found a novel mechanism that different fragments of same lncRNA could cause opposite effects on the identical target gene.