DU145, PC3 scramble shRNA or SUB1 stable knockdown cells were seeded in 6-well plates in growth medium containing 10% fetal bovine serum and puromycin (10 μg/ml) for DU145 and PC3, and then allowed to grow to confluent monolayer. For DU145 and PC3, the cells were serum starved for 12 h and replenished with 10% fetal bovine serum-RPMI medium. The wound-induced migration was triggered by scraping the cells with a 200 ul pipette tip, washed with Dulbecco's phosphate-buffered saline and replenished with respective medium. The wound was imaged immediately (0 h) and at 24 h with an inverted phase-contrast microscope under × 4 objective.