MTT assay

Following specific treatments, cell viability was detected by MTT assay. The day before cell transfection, HUVECs were seeded into a 96-well plate (5×103 cells per well) and incubated at 37°C. Following transfection with or without inhibitor control, miR-221 inhibitor, mimic control, miR-221 mimic, miR-221 mimic + control-plasmid, or miR-221 mimic + PTEN-plasmid for 48-h, 20 µl MTT reagent was added to each well. Then the cells were incubated at 37°C for a further 4 h following which 150 µl dimethyl sulfoxide (DMSO) was applied in each well to dissolve the purple formazan crystals. Finally, the absorbance was detected at 490 nm wavelength using the FLUOstar^® Omega Microplate Reader (BMG Labtech GmbH).