Fig. 6.

Inhibition of cathepsin V activity decreases cystatin F activation and increases NK-92 and TALL-104 cell cytotoxicity. (A) Representative western blot showing decreased expression of the active cystatin F form in U-937 cells (5 × 10⁵/mL) after treatment with the broad-spectrum peptidase inhibitor E-64d (10 and 20 μM) or the cathepsin V inhibitor compound 7 (10 and 20 μM), compared to DMSO (0.1 %) used as a control. Arrowheads indicate the dimeric (black) and monomeric (white) forms of cystatin F. Multiple bands are due to different N-glycosylation forms of cystatin F (left). Relative abundance of the cystatin F dimer/monomer ratio in U-937 cells, normalized to DMSO (0.1 %). Data are presented as means ± SD of at least two independent experiments. (B and C) The cytotoxicity of effector cells NK-92 (B) and TALL-104 (C) on target K-562 cells is decreased after treatment with E-64d (10 μM) but increased after treatment with the specific cathepsin V inhibitor compound 7 (10 μM). Left panels indicate % cytotoxicity determined at different E:T ratios. Right panels indicate lytic units calculated at 30 % cytotoxicity. Data are presented as means ± SD (n = 3). *P < 0.05, **P < 0.01 (one-way ANOVA).