MicroRNA-506-3p initiates mesenchymal-to-epithelial transition and suppresses autophagy in osteosarcoma cells by directly targeting SPHK1.

Osteosarcoma (OS) is the most common malignant bone tumor. In cancer cells, autophagy is related to epithelial-to-mesenchymal transition (EMT). Although microRNA (miR)-506-3p has been demonstrated to act as a tumor suppressor in OS, its role in regulating the EMT process and autophagy remains unknown. The results showed that miR-506-3p directly inhibited the expression of sphingosine kinase 1 (SPHK1) in 143B and SaOS-2 cells. The invasive capability of OS cells was reduced following miR-506-3p mimics transfection, and restored when SPHK1 was overexpressed simultaneously. Further, miR-506-3p mimics initiated mesenchymal-to-epithelial transition (MET) - E-cadherin expression was upregulated, whilst vimentin and fibronectin were downregulated. The basal autophagy flux (LC3II/I) was suppressed by miR-506-3p mimics. The alterations induced by miR-506-3p mimics were partly reversed by SPHK1 overexpression or treatment of rapamycin. Meanwhile, treatment of SPHK1-transfected cells with 3-methyladenine inhibited EMT. The data suggest that miR-506-3p initiates MET and suppresses autophagy in OS cells by targeting SPHK1.