LncRNA Taurine-Upregulated Gene 1 Promotes Cell Proliferation by Inhibiting MicroRNA-9 in MCF-7 Cells

PURPOSE This study was designed to investigate the role of taurine-upregulated gene 1 (TUG1) in MCF-7 breast cancer cells and the molecular mechanism involved in the regulation of microRNA-9 (miR-9). METHODS The expression of TUG1 in breast cancer tissues and cells was evaluated using quantitative reverse transcription polymerase chain reaction. Cell viability was examined using a 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay; cell cycle progression and apoptosis were analyzed using flow cytometry. A dual luciferase reporter assay was used to detect the relationship between TUG1 and miR-9. The expression of methylenetetrahydrofolate dehydrogenase 2 (MTHFD2) was measured by western blot. RESULTS Higher expression of TUG1 was observed in breast cancer tissues and cell lines than in the corresponding controls. TUG1 knockdown reduced proliferation, suppressed cell cycle progression, and promoted apoptosis of MCF-7 cells. The dual luciferase reporter assay showed that TUG1 could negatively regulate the expression of miR-9. MiR-9 inhibition abrogated the effect of TUG1 knockdown on the proliferation, cell cycle progression, and apoptosis of MCF-7 cells. TUG1 positively regulated the expression of MTHFD2 in breast cancer cells. CONCLUSION TUG1 knockdown was significantly associated with decreased cell proliferation and it promoted apoptosis of breast cancer cells through the regulation of miR-9.