β3 integrin is required for Rac activation in uPAR-expressing cells. (A) Tumor cells were transfected with siRNAs and Rac activation was quantitated. Closed bars, BE; open bars, MDA-MB-231; shaded bars, SNB19 (mean + SEM; n ≥ 4). *, P < 0.05; **, P < 0.01; unpaired Student's t test. (B) BE (closed bars) and MDA-MB-231 cells (open bars) were transfected with siRNAs and assayed for collagen-I invasion (mean + SEM; n ≥ 4). *, P < 0.05; **, P < 0.01; unpaired Student's t test. (C) BE cells were seeded for invasion assays in serum-free DME or DME + 5% serum and either control IgG or antivitronectin antibody (mean + SEM; n ≥ 4). **, P < 0.01; unpaired Student's t test. (D) HEK 293T cells were transfected with siRNAs, and after 48 h, transfected with uPAR or empty vector. Rac activity was measured 24 h later. (E) Quantitation of Rac-activation assays in HEK 293T cells (mean + SEM; n ≥ 5). *, P < 0.05; unpaired Student's t test versus nontargeting. Immunoblots showing knockdown are in Fig. S2 (C and D).
