miR-199a-3p negatively regulates the progression of osteosarcoma through targeting AXL.

Dysregulation of micro-RNAs has been shown to contribute to multiple tumorigenic processes, as well as to correlate with tumor progression and prognosis. miR-199a has been shown to be dysregulated in many different tumor types; however, the association between miR-199a and the clinicopathological features of osteosarcoma is unknown, and the target gene for miR-199a and the regulatory mechanism are also unknown. In this study, we demonstrated that miR-199a-3p is expressed at low levels in osteosarcoma cells, which may inhibit the migration and invasion of these tumor cells. The downregulation of miR-199a-3p expression is significantly correlated with the recurrence and lung metastasis of patients with osteosarcoma. Using multivariate Cox regression analysis, low level of expression of miR-199a-3p was shown to be an independent predictor for worse prognosis in osteosarcoma. Furthermore, we showed that miR-199a-3p mimics can decrease the expression of the mRNA and protein of the receptor tyrosine kinase AXL, and miR-199a-3p targets directly the 3'-UTR of AXL mRNA, suggesting that miR-199a-3p may downregulate the expression of the AXL gene to inhibit the progression of osteosarcoma. In patients' osteosarcoma samples, we also showed a statistically significant inverse relation between the levels of miR-199a-3p and AXL, which is consistent with the results in osteosarcoma cell lines. Interestingly, miR-199a-3p mimics reduced the level of phosphorylation of AKT. Together with the previous data, we conclude that miR-199a-3p negatively contributes to the progression of osteosarcoma by downregulating the expression of AXL mRNA and protein. By this mechanism, a regulatory pathway comprised of miR-199a-3p and AXL may exist in osteosarcoma cells, which may as a result regulate the progression of osteosarcoma through the AKT pathway.