Up-Regulation of MiRNA-125a-5p Inhibits Cell Proliferation and Increases EGFR-TKI Induced Apoptosis in Lung Cancer Cells

BACKGROUND: Despite the dramatic efficacy of erlotinib, an EGFR tyrosine kinase inhibitor (TKI), most of non-small cell lung cancer (NSCLC) patients ultimately acquire resistance to this agent. Different studies indicated that miRNA-125a-5p is down-regulated in human lung cancer cells and may function as a tumor suppressor by targeting EGFR. However, the biological function of miRNA-125a-5p in NSCLC resistance to EGFR-TKIs is not fully understood. In this study the effect of miRNA-125a-5p on cell proliferation, apoptosis and sensitivity of the A549 lung cancer cells to erlotinib was investigated. METHODS: After miRNA-125a-5p transfection, the expression levels of EGFR mRNA were measured by QRT-PCR. Trypan blue assays were performed to evaluate the proliferation of the A549 lung cancer cells. The cytotoxic effects of miRNA-125a-5p and erlotinib, alone and in combination, were determined using MTT assay. Combination index study was performed using the method of Chou-Talalay. Apoptosis was assessed using an ELISA cell death assay kit. RESULTS: MiRNA-125a-5p clearly reduced the expression of EGFR mRNA in a time dependent manner, causing marked cell proliferation inhibition and spontaneous apoptosis (p<0.05, relative to control). Pretreatment with miRNA-125a-5p synergistically increased the cytotoxic effect of erlotinib and decreased its IC(50). Furthermore, miRNA-125a-5p significantly enhanced the apoptotic effect of erlotinib. Negative control miRNA had no significant effect on biological parameter of the tumor cells. CONCLUSIONS: Our data suggest that suppression of EGFR by miRNA-125a-5p can effectively trigger apoptosis and overcome EGFR-TKs resistance of lung cancer cells. Therefore, miRNA-125a-5p may be a potential therapeutic adjuvant in patients with lung cancer.