FIG. 9.

Effects of caspase inhibitors on caspase-3 activity induced by Stx1. HeLa cells were preincubated for 1 h with specific inhibitors (20 μM) of caspase-3, -6, or -8 followed by a second incubation without or with Stx1 (10 ng/ml) for 3 h. Caspase-3 enzymatic activity was then measured with a specific fluorescent substrate in a microtiter plate format as described in Materials and Methods. Inhibitors were capase-3 inhibitor (Z-DEVD-fmk), caspase-6 inhibitor (Z-VEID-fmk), and capase-8 inhibitor (Z-IETD-fmk). Comparisons were made between no-pretreatment and caspase-inhibitor-pretreatment groups with Stx1 (*, P < 0.05, t test).