Contribution of miR-218-dependent EGFR-signaling to the radiation response of breast cancer cells

Wischmann F, Patzel M, Kumar A, Braun T, Kemper B, Ernst I, Eich H, Gotte M, Greve B

Abstract

Introduction: The response of cells to irradiation is associated with complex modifications in the expression profile of cell cycle-, repair- and cell death-related genes and requires complex regulation by cytokines. Micro-RNAs are small regulatory RNAs which postranscriptionally intervene with gene expression (1). We here investigated the contribution of miR-218 to cytokine signalling during the radiation response of human MCF-7 and MDA-MB-231 breast cancer cells in vitro. Methods: After transient transfection of precursor miRNA, target gene expression was measured by qPCR, apoptotic cell death by Annexin V-assay and cell survival by colony formation ability. Metastatic potential was determined using matrigel invasion chambers and digital holographic microscopy. Protein expression was analysed by Western blotting. Results: Clonogenic survival decreased significantly while apoptosis increased. Cell motility was lower by increasing miR-218 expression and proliferation was decreased. Overexpression of miR-218 leads to survivin and EGFR downregulation at the gene and protein level while PODXL is upregulated. As a consequence, EGF-induced MAPK signalling via the EGFR was reduced. Constitutive miR-218 expression in untreated cells correlated inversely with EGFR expression but was significantly reduced after irradiation. Conclusion: As irradiation induces the translocation of EGFR to the nucleus (2) and might inactivate the RISC complex on its way (3), we conclude that regulation of EGFR-mediates cytokine signalling via miR-218 is a novel key element in regulating the cellular stress response.