Effect of pro-u-PA on actin cytoskeleton organization and on morphology of RSMC. Subconfluent (50% to 70%) cells were incubated in the absence (A) or in the presence of 1 nmol/L pro-u-PA for 30 (B) or 120 minutes (C). Actin filaments were visualized using FITC-coupled phalloidin as described.