(a) Survivin protein expression in JR8 parental cells and melanoma cell clones transfected with the active ribozymes RZ1 (RZ1/C clone) and RZ7 (RZ7/H clone) or with the mutant ribozyme mutRZ1 (mutRZ1/B clone). Western blots were probed with a polyclonal antibody for survivin. Proliferating cell nuclear antigen (PCNA) was used as a control for loading. (b and c) Induction of apoptosis in melanoma cell clones exposed to 10 μg/ml cisplatin for 1 hour. Seventy-two hours after treatment, cells were collected and the occurrence of apoptosis was determined. (b) The percentage of cells with an apoptotic morphology with respect to the overall population was assessed by fluorescence microscopy after cell staining with propidium iodide. White bars, control (no drug) cells; gray bars, cisplatin-treated cells. Data represent mean values ± SD of three experiments. (c) The caspase-3 catalytic activity was determined by hydrolysis of the fluorogenic substrate N-Acetyl-Asp-Glu-Val-Asp-aldehyde (Ac-DEVD-AMC) in the presence or absence of the caspase-3 inhibitor Ac-DEVD-CHO. White bars, control (no drug) cells; gray bars, cisplatin-treated cells; black bars, cisplatin-treated cells + CHO. Data represent mean values ± SD of three experiments.