AUTHOR=Li Yi , Song Xinmao , Liu Zegang , Li Qiutian , Huang Meijin , Su Bin , Mao Yuchi , Wang Yuanyuan , Mo Wenqian , Chen Hong 

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

JOURNAL=Frontiers in Oncology

VOLUME=Volume 9 - 2019

YEAR=2019

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2019.00298

DOI=10.3389/fonc.2019.00298

ISSN=2234-943X

ABSTRACT=Osteosarcoma is an aggressive bone tumor with high resistance to radiotherapy. However, the cellular mechanisms responsible for radio resistance in these tumors are not well understood. Previous research showed that miR-214 played a role in sensitivity of osteosarcoma cells to cisplatin and Pleckstrin homology-like domain family A member 2 (PHLDA2) is a proapoptic factor with reduced expression in many tumors including human ostersarcoma. In this study we wanted to study the molecular mechanism of miR-214 hypothesized that miR-214 induced radioresistance of osteosarcoma by targeting PHLDA2. We used luciferase assays in HEK293T cells transfected with miR-214 mimic and a scrambled control to show miR-214 downregulates PHLDA2 protein by targeting its 3’-untranslated region (UTR). QPCR analysis of miR-214 expression in tissues and adjacent non-tumor tissues derived from 30 osteosarcoma patients showed a significant increase in miR-214 levels and also associated positively with lung metastasis. Ectopic expression miR-214 enhanced radioresistance in osteosarcoma cells, with decreased IR-induced apoptosis. Depletion of miR-214 enhanced sensitivity of IR in both osteosarcoma cells and mouse xenograft models. Importantly, we show that miR-214 regulated activation of phosphatidylinositol-3-kinase/Akt signaling pathway targeting PHLDA2. Finally, introduction of PHLDA2 cDNA lacking the 3’-UTR or treatment with Akt inhibitor LY294002 partially abrogated miR-214-induced radioresistance. We demonstrated that miR-214 overexpression as a common event in osteosarcoma contributed to radioresistance by regulating the PHLDA2/Akt pathway, which may be a potential target to sensitize radiotherapy in osteosarcoma. In summary, our results reveal that upregulation of miR-214 is a frequent event and negatively associated with PHLDA2 expression in ostoesarcoma. Furthermore, miR-214 depletion enhanced apoptosis and radiosensitivity by inhibiting Akt pathway via PHLDA2. 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.