SiRNA-transfected cells were re-seeded on the top compartment of trans-well Boyden chambers (8 μm, Corning, USA) in serum-free media, and then allowed to migrate to the lower compartment contained complete media with 10% FBS (fetal bovine serum) in a humidified, 5% CO2 atmosphere incubator at 37 °C for 36 h. Cells that did not migrate into the lower compartment were wiped away with a cotton swab. The inserts were fixed with fixative solution (acetic acid: methanol = 1:3) for 15 min and stained with 0.1% crystal violet for 10 min. After washing with PBS extensively, migrated cells were photographed and quantified using Image J. Three images of each well were taken and representative images were shown.