Proteolytic activities of mouse sarcoma 180 cells that are inhibited by Bowman‐Birk and Kunitz protease inhibitors

In this study, using zymogram analysis two proteolytic activities were identified in the mouse sarcoma 180 (S-180) cells that were activated by trypsin treatment and inhibited by both BBI and ACTI. These enzymes, with molecular weights of 46 kDa (dominant band) and 62 kDa (minor band), were mainly localized in the cytosol, and had optimal activity at pH 7 and 8 respectively. Their inhibition by DFP, BBI and ACTI but not EDTA and TPCK indicated they were trypsin-like serine proteases and may be the intracellular target-enzymes of protease inhibitors. The level of the precursor of the 62 kDa protease was significantly increased in the S-180 solid and soft tumors, whereas the level of the 46 kDa precursor was almost undetectable, implying that a physiological role may be played by these serine proteases during tumor invasion.