Differences in induction of lysosomal protease activity by protease inhibitors in B16 melanoma cell lines.

1. The effects of potent protease inhibitors in vitro (leupeptin, pepstatin and E-64[N-[L-3-trans-carboxyoxirane-2-carbonyl)-L-leucyl]agmatine]) on intracellular cathepsin B (EC 3.4.22.1), hemoglobin (Hb)-hydrolase and acid phosphatase (EC 3.1.3.2) from cultured B16 melanoma variants (B16-F1, F10 and BL6) were studied. 2. E-64 induced all the cultured B16 melanoma variants to decrease the activity of intracellular cathepsin B but did not have this effect with Hb-hydrolase or acid phosphatase. Furthermore, E-64 decreased the activity of cathepsin B in both the lysosomal and cytosol fractions. 3. Leupeptin induced all the cultured B16 melanoma variants to increase the activities of intracellular cathepsin B and Hb-hydrolase but not that of acid phosphatase. An increase in the level of cathepsin B activity was most significant in B16-BL6 followed by F10 and then F1 variants. 4. Leupeptin induced all the cultured B16 melanoma variants to increase the cathepsin B activity in the lysosomal fraction. Our data differed from the results of Tanaka et al. (1981) in that leupeptin induced rat cultured hepatocytes to inhibit the activity of intracellular cathepsin B and increase the Hb-hydrolase activity, especially in the cytosol fraction.