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

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

doi:10.3389/fonc.2019.00298

Abstract

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.

Highlights

Osteosarcoma (OS) is the most common primary bone tumor in children and adolescents
We found that the miR-214 expression in U2OS cells was significantly higher than that in others, with a low level of Pleckstrin homology-like domain family A member 2 (PHLDA2) protein, while MG63 cells with the lowest miR-214 expression showed an 87% increase of PHLDA2 protein than U2OS cells (Figures 1E,F)
The overexpression of miR-214 was confirmed after transfecting miR-214 mimics into MG63 cells (Figure 1G), and miR-214 mimics showed a significant decrease of PHLDA2 mRNA and protein levels compared to a scrambled control transfection (Figures 1H,I)

Summary

Introduction

Osteosarcoma (OS) is the most common primary bone tumor in children and adolescents. Neoadjuvant chemotherapy, followed by surgical resection and additional adjuvant chemotherapy, is the typical treatment approach for resectable high-grade osteosarcoma. Resistance to radiotherapy as a major obstacle occurs in 80% of osteosarcoma patients [2]. Pleckstrin homology-like domain family A member 2 (PHLDA2, known as TSSC3) was the first apoptosisrelated gene, paternally imprinted in placenta and most fetal tissues [3]. It is a PH domain-containing protein with phosphoinositide-binding capacity, located in the tumor suppressor region p15.5 of human chromosome 11 [4]. The PHLDA2 expression has been considered as an independent prognostic factor with longer survival in osteosarcoma patients, and the inhibition of PHLDA2 has functioned to promote malignant phenotypes of osteosarcoma cells, including proliferation, self-renewal, and therapeutic resistance [8, 9]. The precise mechanism by which PHLDA2 is suppressed remains poorly understood in osteosarcoma

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Conclusion