Regulatory mechanisms and function of hypoxia-induced long noncoding RNA NDRG1-OT1 in breast cancer cells

Hypoxia is a classic feature of the tumor microenvironment that has profound effects on cancer progression and is tightly associated with poor prognosis. Long noncoding RNAs (lncRNAs), a component of the noncoding genome, have been increasingly investigated due to their diverse roles in tumorigenesis. Previously, a hypoxia-induced lncRNA, NDRG1-OT1, was identified in MCF-7 breast cancer cells using next-generation sequencing. However, the regulatory mechanisms of NDRG1-OT1 remain elusive. Therefore, the purpose of this study was to investigate the regulatory mechanisms and functional roles of NDRG1-OT1 in breast cancer cells. Expression profiling of NDRG1-OT1 revealed that it was upregulated under hypoxia in different breast cancer cells. Overexpression and knockdown of HIF-1α up- and downregulated NDRG1-OT1, respectively. Luciferase reporter assays and chromatin immunoprecipitation assays validated that HIF-1α transcriptionally activated NDRG1-OT1 by binding to its promoter (−1773 to −1769 and −647 to −643 bp). Next, to investigate whether NDRG1-OT1 could function as a miRNA sponge, results of in silico analysis, expression profiling of predicted miRNAs, and RNA immunoprecipitation assays indicated that NDRG1-OT1 could act as a miRNA sponge of miR-875-3p. In vitro and in vivo functional assays showed that NDRG1-OT1 could promote tumor growth and migration. Lastly, a small peptide (66 a.a.) translated from NDRG1-OT1 was identified. In summary, our findings revealed novel regulatory mechanisms of NDRG1-OT1 by HIF-1α and upon miR-875-3p. Also, NDRG1-OT1 promoted the malignancy of breast cancer cells and encoded a small peptide.