Upregulation of miR-214 Induced Radioresistance of Osteosarcoma by Targeting PHLDA2 via PI3K/Akt Signaling.

Osteosarcoma is an aggressive bone tumor with high resistance to radiotherapy. Pleckstrin homology-like domain family A member 2 (PHLDA2) displays low expression in human osteosarcoma as a proapoptosis factor. miRNAs have been shown to be important in modulating translation and therapeutic responsiveness in solid tumors. Herein, we used luciferase assay to show that miR-214 downregulates the PHLDA2 expression by targeting its 3'-untranslated region (UTR). A high level of miR-214 was identified in tumor tissues from 30 osteosarcoma patients via qPCR analysis, associated positively with lung metastasis. Ectopic expression miR-214 enhanced radioresistance in osteosarcoma cells, with decreased IR-induced apoptosis. Moreover, the depletion of miR-214 enhanced radiosensitivity in both osteosarcoma cells and mouse xenograft models. Importantly, we showed that miR-214 regulated the activation of phosphatidylinositol-3-kinase/Akt signaling pathway by inhibiting PHLDA2. Finally, the introduction of PHLDA2 cDNA lacking the 3'-UTR or treatment with Akt inhibitor LY294002 partially abrogated miR-214-induced radioresistance. In summary, our results reveal that the upregulation of miR-214 as a frequent event in osteosarcoma contributes to radioresistance by regulating the PHLDA2/Akt pathway. The miR-214/PHLDA2/Akt axis provides a new avenue toward understanding the mechanism of radiosensitivity and may be a potential target for osteosarcoma intervention.