MicroRNA-200c (miR-200c) recently was found to have tumor-suppressive properties by inhibiting the epithelial-mesenchymal transition (EMT) in several cancers. miR-200c also interacts with various cellular signaling molecules and regulates many important signaling pathways. In this study, we investigated the radiosensitizing effect of miR-200c and its mechanism in a panel of human cancer cell lines. Malignant glioma (U251, T98G), breast cancer (MDA-MB-468), and lung carcinoma (A549) cells were transfected with control pre-microRNA, pre-miR-200c, or anti-miR-200c. Then, RT-PCR, clonogenic assays, immunoblotting, and immunocytochemisty were performed. To predict the potential targets of miR-200c, microRNA databases were used for bioinformatics analysis. Ectopic overexpression of miR-200c downregulated p-EGFR and p-AKT and increased the radiosensitivity of U251, T98G, A549, and MDA-MB-468 cells. In contrast, miR-200c inhibition upregulated p-EGFR and p-AKT, and decreased radiation-induced cell killing. miR-200c led to persistent γH2AX focus formation and downregulated pDNA-PKc expression. Autophagy and apoptosis were major modes of cell death. Bioinformatics analysis predicted that miR-200c may be associated with EGFR, AKT2, MAPK1, VEGFA, and HIF1AN. We also confirmed that miR-200c downregulated the expression of VEGF, HIF-1α, and MMP2 in U251 and A549 cells. In these cells, overexpressing miR-200c inhibited invasion, migration, and vascular tube formation. These phenotypic changes were associated with E-cadherin and EphA2 downregulation and N-cadherin upregulation. miR-200c showed no observable cytotoxic effect on normal human fibroblasts and astrocytes. Taken together, our data suggest that miR-200c is an attractive target for improving the efficacy of radiotherapy via a unique modulation of the complex regulatory network controlling cancer pro-survival signaling and EMT.
Keywords: EGFR-associated signaling network; human cancer cells; microRNA-200c; radiosensitization.