Abstract: Objective To explore the role of miR-671-5p in regulating the migration and invasion of osteosarcoma and the underlying mechanisms. Methods The differentially expressed microRNAs (miRNAs) in osteosarcoma were screened in the NCBI online database, and the target proteins of these miRNAs were predicted and their functions were analyzed. Osteosarcoma cells were transfected with a plasmid overexpressing miR-671-5p, and the transfection efficiency was assessed using quantitative real-time PCR (qRT-PCR). The changes in the migration and invasion of the transfected cells were examined with Transwell assay, and the expressions of proteins related with epithelial-mesenchymal transition (EMT) were detected using Western blotting. Dual-luciferase reporter assay was performed to determine whether the 3'UTR of SMAD3 contained a targeted binding site of miR-671-5p. Results MiR-671-5p was significantly down-regulated in both osteosarcoma tissues and osteosarcoma cells (P<0.05). The osteosarcoma cells overexpressing miR-671-5p showed significantly reduced migration and invasion abilities (P<0.05) with obviously lowered expressions of EMT-related proteins (P<0.05). SMAD3 was highly expressed in osteosarcoma cells (P<0.05), and dual-luciferase reporter assay confirmed the presence of a targeted binding site between miR-671-5p and the 3'UTR of SMAD3 (P<0.05). In osteosarcoma cells transfected with a SMAD3-overexpressing plasmid (P<0.05), the high expression of SMAD3 significantly inhibited by miR-671-5p overexpression (P<0.05). Transwell assay demonstrated that SMAD3 overexpression significantly promoted the migration and invasion of osteosarcoma cells (P<0.05), and while miR-671-5p overexpression obviously reversed this effect (P<0.05). Conclusion MiR-671-5p can inhibit the invasion and migration of osteosarcoma cells by negatively regulating SMAD3.

Key words: miR-671-5p, SMAD3, migration, invasion, epithelial-mesenchymal transition, osteosarcoma