Signaling specificity of Brk-dependent cell migration. HaCaT (a), MDA-MB-231 (b) and T47D (c) cells were transiently transfected with non-targeting (control) siRNA or Brk siRNA and either vehicle (water) or 50 ng/ml HGF was used as the chemoattractant for each Boyden chamber migration assay. As described in the Materials and Methods, migration assays were performed for 6 hr. A concentration of 20 ng/ml EGF was used as a positive control chemoattractant for migration. Error bars indicate the mean (plus standard deviation) of triplicate measures of cell migration. Single asterisks (*) denote significance (P < 0.05) determined by an unpaired Student's t-test between vehicle and HGF treated cells expressing control siRNA. Double asterisks (**) denote significance between control and Brk siRNA with either HGF or EGF used as chemoattractants. Results were confirmed in three independent experiments.