Fig. 2. Depletion of cortactin by RNA interference. (A) Lysates of A375MM cells 72 hours after mock or cortactin-specific siRNA transfection were subjected to SDS-PAGE, transferred to nitrocellulose and probed with anti-cortactin and anti-GAPDH as a loading control. (B) The relative amount of cortactin in mock-transfected and knockdown cells was measured. A 95% reduction in the amount of cortactin was observed. (C) Immunofluorescence labeling with anti-cortactin and phalloidin of cortactin siRNA-treated A375MM cells. Depletion of cortactin blocks the formation of invadopodia and hence, matrix degradation. (D) Transfection of cortactin^WT 48 hours after knockdown. Normal invadopodia form and degrade the extracellular matrix. Scale bars: 10 µm.