Relocations of u-PAR, VNR, β1, and c-Src proteins to membranes at the leading edge of migrating RSMC in response to pro-u-PA. Subconfluent (50% to 70%) cultures were incubated in the absence (A, B, C, and D) or in the presence of 1 nmol/L pro-u-PA for 30 minutes (E, F, G, and H). The cells were then fixed and stained with antibodies against u-PAR (A and E), VNR (B and F), β1 (C and G), or c-Src (D and H).