A GROWTH-REGULATED PROTEASE ACTIVITY THAT IS INHIBITED BY THE ANTICARCINOGENIC BOWMAN-BIRK PROTEASE INHIBITOR

The Bowman-Birk protease inhibitor (BBI) has been shown to be an effec tive suppressor of carcinogenesis in vivo and in vitro. To elucidate t he mechanism(s) by which BBI suppresses carcinogenesis, we believe it will be necessary to identify and characterize the target enzymes that specifically interact with the BBI. We have shown previously that sev eral cellular proteins in C3H/10T1/2 mouse embryo fibroblast cells spe cifically bind to a BBI affinity resin. In the current report, we demo nstrate that one of these proteins has proteolytic activity as judged by its ability to degrade gelatin. The enzyme has a mass of 45 kDa and subcellular fractionation experiments demonstrate that this enzyme is located in the cytosol. Furthermore, the proteolytic activity was inh ibited by diisopropyl-fluorophosphate but was not affected by EDTA, in dicating that this enzyme is a serine protease. Higher levels of prote ase activity were found in logarithmic-phase C3H/10T1/2 cells compared with nondividing (confluent) cells, suggesting that this protease act ivity is growth regulated. Similar levels of this activity were presen t in nontransformed and in radiation-transformed C3H/10T1/2 cells. Tre atment of nontransformed C3H/10T1/2 cells with phorbol 12-myristate 13 -acetate increased the specific activity of this protease 5- to 10-fol d. Our results suggest that this protease is a target enzyme of the BB I in these cells.