[Mechanism of miR-221 contributes to gefitinib resistance in PC-9 cells].

Objective: To investigate the effect of microRNA-221 (miR-221) overexpression on gefitinib resistance in PC-9 cells and study its underlying mechanisms. Methods: PC-9 cells were transfected with LV-NC and LV-miR-221 to establish cell stabilizing strains (PC-9/NC and PC-9/miR-221), then they were used to detect the relative expression of miR-221 and apoptotic protease activating factor-1 (APAF-1) mRNA by real-time fluorescence quantitative PCR (qRT-PCR). The effects of gefitinib (0-4 μmol/L) on the growth and proliferation of cell stabilizing strains were detected by CCK-8 Assay. After gefitinib treatment, cell apoptosis was detected by Flow Cytometry Assays. The expression of epidermal growth factor receptor (EGFR), phosphorylated epidermal growth factor receptor (p-EGFR), APAF-1 and cleaved cysteinyl aspartate specific proteinase-3 (Cleaved-caspase-3) were detected by Western blot. Dual-Luciferase Reporter Assay was used to evaluate the relationship between APAF-1 and miR-221. Results: The relative expression of miR-221 in PC-9/NC cells was significantly lower than that in PC-9/miR-221 cells[(1.00±0.082) vs (40.24±0.017)]( P <0.01). The half maximal inhibitory concentration (IC(50)) in PC-9/NC cells was significantly lower than that in PC-9/miR-221 cells[(IC(50)=0.1 μmol/L) vs (IC(50)>4 μmol/L)]( P <0.05). Apoptosis rate of PC-9/NC cell was significantly higher than PC-9/miR-221[(33.42±4.28)% vs (10.27±1.12)%]( P <0.05); APAF-1 mRNA expression was significantly higher in PC-9/NC cells than PC-9/miR-221[(1.000+ 0.069) vs (0.701±0.072)]( P <0.05), and the expression of APAF-1 protein in PC-9/NC cells was significantly higher than that of PC-9/miR-221 cells. The dual luciferase reporter gene results showed that miR-221a inhibited luciferase activity significantly stronger than transfected miRNA negative control group after co-transfection of luciferase plasmids pmir-REPORT-APAF-1-wt and miR-221a mimics ( P <0.01). p-EGFR was down-regulated in both PC-9/NC and PC-9/miR-221 cells after treatment with gefitinib. APAF-1 and Cleaved-caspase-3 proteins were significantly down-regulated in PC-9/miR-221 cells compared with PC-9/NC cells, while APAF-1 and Cleaved-caspase-3 proteins were up-regulated in PC-9/NC cells treated with gefitinib compared with PC-9/miR-221 cells ( P <0.05). Conclusion: miR-221 induces resistance to gefitinib in PC-9 cells by downregulating APAF-1 expression.