| Summary: | 碩士 === 國立臺灣大學 === 生理學研究所 === 104 === Hypoxia is a crucial factor that can lead to solid tumor aggressiveness by driving multiple signaling pathways. Long non-coding RNAs (lncRNAs) respond to several extrinsic stimuli, causing changes in cancer function by participating in multiple steps of gene expression. However, it is unclear whether lncRNAs respond to oxygen concentrations in breast cancer. Therefore, the aims of this study are to identify oxygen responsive lncRNAs, and to delineate their regulatory mechanisms in breast cancer MCF-7 cells. The expression profiling of lncRNAs in MCF-7 cells growing under normoxic, hypoxic, and re-oxygenated conditions was examined using next-generation sequencing technology. The criteria for selecting oxygen-responsive lncRNAs consisted of greater than 3-fold change, significant differences (P < 0.001), and opposite expression profiling between normoxia and hypoxia, as well as between hypoxia and re-oxygenation. Four hundred and seventy-two lncRNAs that met these rules were identified. Examining the top five differentially expressed lncRNAs in hypoxia, we selected NDRG1-OT1 for further study. Among the five isoforms of NDRG1-OT1, NDRG1-OT1_v4 was chosen for further investigation because it was the most responsive isoform to oxygen changes. We overexpressed NDRG1-OT1_v4 under normoxia and performed microarray analysis to identify 108 NDRG1-OT1_v4 regulated genes and their functions. Among these genes, we focused on the effect of NDRG1-OT1_v4 on NDRG1, and found that both NDRG1 mRNA and NDRG1 protein were inhibited by NDRG1-OT1_v4. Finally, we used co-immunoprecipitation and discovered that NDRG1-OT1_v4 destabilized NDRG1 by promoting ubiquitin-mediated proteolysis. Our findings revealed a new form of epigenetic regulation of NDRG1 by NDRG1-OT1_v4 in breast cancer.
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