Extracellular catalase activity protects cysteine cathepsins from inactivation by hydrogen peroxide

The resistance of secreted cysteine cathepsins to peroxide inactivation was evaluated using as model THP-1 cells. Differentiated cells released mostly cathepsin B, but also cathepsins H, K, and L, with a maximum of endopeptidase activity at day 6. Addition of non- cytotoxic concentrations of H2O2 did not affect mRNA expression levels and activity of cathepsins, while the catalase activity remained also unchanged, consistently with RT- PCR analysis. Conversely inhibition of extracellular catalase led to a striking inactivation of secreted cysteine cathepsins by H2O2. This report suggests that catalase may participate in the protection of extracellular cysteine proteases against peroxidation. (c) 2008 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.