Secretion of proteases in vitro by the LM38 sublines. (a) Quantification of secreted urokinase-type plasminogen activator (uPA) activity by radial caseinolysis. The LM38-HP cells and LM38-D2 clone secreted significantly less uPA than LM38-LP cells. (b) Upper panel: zymogram of media conditioned by LM38-LP, LM38-HP, and LM38-D2 cells showing a main 48 kDa uPA band, confirming the differential activity observed in the radial assay. Lower panel: gelatin co-polymerized zymogram showing that only the highly metastatic LM38-LP cells were able to secrete matrix metalloproteinase (MMP)-2 to the culture medium. *P < 0.05 compared with LM38-LP.