Abstract
miR‑214 has been reported to be downregulated in several cancer types, such as bladder cancer. However, its involvement in apoptosis and chemoresistance has not been investigated. The present study aimed to clarify the biological function of miR‑214 and potential mechanisms in chemoresistance of bladder cancer cells. Reverse transcription‑quantitative polymerase chain reaction demonstrated that miR‑214 was downregulated in bladder cancer tissues compared with the level in normal tissues. miR‑214 was downregulated in bladder cancer cell lines compared with the level in the normal cell line SV‑HUC‑1. miR‑214 mimics were transfected into T24 and J82 cell lines to restore its expression. The results indicated that miR‑214 mimic inhibited proliferation and invasion in these cell lines. In addition, miR‑214 mimic reduced cisplatin resistance in T24 and J82 cells, indicated by the inhibition of cell viability and upregulation of cell apoptosis. Western blotting demonstrated that miR‑214 mimic was able to upregulate cleaved caspase‑3 and cleaved poly (ADP‑ribose) polymerase (PARP), while downregulate caspase‑3 and PARP expression, and AKT phosphorylation. Using prediction software, it was revealed that the netrin‑1 oncoprotein is on the target list of miR‑214. miR‑214 also downregulated netrin‑1 protein and mRNA expression levels in the T24 and J82 cell lines. Luciferase reporter assays demonstrated that netrin‑1 acted as a direct target of miR‑214. A negative correlation between netrin‑1 and miR‑214 expression in bladder cancer tissues was also observed. In addition, cisplatin treatment could induce netrin‑1 protein expression in bladder cancer cells and miR‑214 mimic partly blocked this phenomenon. Netrin‑1 plasmid transfection inhibited cisplatin‑induced apoptosis, upregulated AKT phosphorylation, and downregulated caspase‑3 and PARP cleavage. Netrin‑1 was restored in cells transfected with miR‑214 mimic using plasmid transfection. Netrin‑1 transfection restored AKT phosphorylation and blocked caspase/PARP cleavage in the T24 and J82 cell lines. In conclusion, the present study demonstrated that miR‑214 is downregulated in bladder cancer tissues and cell lines. miR‑214 reduces chemoresistance by targeting netrin‑1 in bladder cancer cell lines.