MicroRNA-27a Promotes Proliferation, Migration and Invasion by Targeting MAP2K4 in Human Osteosarcoma Cells

Background: Osteosarcoma is a high-grade malignant bone neoplasm. Although the introduction of chemotherapy has reduced its mortality, more than 50% of patients develop chemoresistance and have an extremely poor prognosis due to pulmonary metastasis. Several molecular pathways contributing to osteosarcoma development and progression have recently been discovered. Various studies have addressed the genes involved in the metastasis of osteosarcoma. However, the highly complex molecular mechanisms of metastasis are still poorly understood. Recently, the decisive role of microRNAs in the regulation of molecular pathways has been uncovered. miRNAs may function as either oncogenes or tumor suppressors, depending on their target genes. miR-27a, a member of an evolutionarily conserved miRNA family, is abnormally increased in several types of cancers. It has been shown to be upregulated in osteosarcoma and plays a pro-metastatic role in osteosarcoma cell lines. However, the effects of miR-27a on osteosarcoma have not been clearly elucidated. The present study thus addressed the miR-27a sensitive mechanisms in osteosarcoma. Methods: In this study, three biological programs were used to predict whether MAP2K4 was a target of miR-27a. A specific miR-27a inhibitor was used to inhibit the endogenous activity of miR-27a in the human osteosarcoma cell line MG63. Cell proliferation, colony formation, migration and invasion assays were performed to assess the effects of miR-27a on the proliferation, metastasis and invasion of MG63 cells. The expression levels of several proteins evolved in the JNK/p38 signaling pathway were detected using western blot analysis. Results: The luciferase activity of the wild-type pGL3-MAP2K4 3'UTR vector was significantly inhibited after the miR-27a precursor or the control precursor was transfected into the MG63 cells. However, the luciferase activity was not inhibited after transfection of the mutant pGL3-MAP2K4 3'UTR vector. The inhibition of miR-27a increased the luciferase activity of the wild-type pGL3-MAP2K4 3'UTR vector after MG63 cells were transfected with the miR-27a inhibitor or the control inhibitor. Thus, MAP2K4 is a potential target of miR-27a and can be directly regulated by miR-27a. Inhibition of miR-27a significantly suppressed cell proliferation after 72 hours compared to the negative control group. Inhibition of miR-27a significantly suppressed colony formation of the MG63 cells by 39 6%. Transwell migration and invasion assays demonstrated that the number of migratory and invasive cells transfected with the miR-27a inhibitor was reduced by 63.5% and 69.1%, respectively. After transfection of the miR-27a inhibitor into the MG63 cells, the level of phospho-JNK1 and phospho-p38 increased by 25% and 29%, respectively, along with the up-regulation of MAP2K4 protein. Conclusion: This is the first study showing that miR-27a can function as an oncogene by targeting MAP2K4 in the osteosarcoma MG63 cell line. Inhibition of miR-27a increases MAP2K4 expression, which in turn inhibits cell proliferation and migration through the JNK/p38 signaling pathway in MG63 cells. These findings may help us understand the molecular mechanism of miR-27a in the tumorigenesis of osteosarcoma and may provide new diagnostic and therapeutic options for the treatment of this neoplasia.