miR-1225-5p Functions as a Tumor Suppressor in Osteosarcoma by Targeting Sox9

microRNA plays an important role in the development of tumors, including osteosarcoma. However, the role of miR-1225-5p in osteosarcoma is currently unclear. First, we found that miR-1225-5p was downregulated in osteosarcoma cells relative to its levels in normal bone tissue by analyzing GSE28423 data in the GEO database. Using GSE39040, we found that low miR-1225-5p expression is associated with poor prognosis in patients with osteosarcoma, and we also found low miR-1225-5p expression in patients with recurrent osteosarcoma. We later demonstrated that osteosarcoma cell lines transfected with miR-1225-5p mimic had decreased ability to proliferate, migrate, and invade relative to control cells. To elucidate the mechanism by which miR-1225-5p inhibits the development of osteosarcoma, we identified Sox9 as a target gene of miR-1225-5p using the TargetScan website. We confirmed that Sox9 is the target gene of miR-1225-5p using the luciferase reporter assay. We then found that Sox9 is highly expressed in osteosarcoma by analyzing the GSE16088 and GSE42352 datasets and that high expression of Sox9 is associated with poor prognosis in patients with osteosarcoma using the R2 database. Further analysis using the TARGET database uncovered that high Sox9 expression is associated with a high recurrence rate in patients with osteosarcoma. Transfection of Sox9 siRNA inhibited the proliferation, migration, and invasiveness of osteosarcoma cells. We transfected miR-1225-5p together with Sox9 siRNA into osteosarcoma cells, observing strong inhibition of proliferation, migration, and invasiveness. Finally, exogenous expression of Sox9 partially reversed the anticancer effects of miR-1225-5p in osteosarcoma cells. Taken together, our findings suggest that miR-1225-5p functions as a tumor suppressor in osteosarcoma by targeting Sox9, thereby revealing new therapeutic targets for osteosarcoma.