Functional involvement of caspases in 15d-PGJ₂-induced apoptosis. (A) HS-Sultan cells were treated with 10 μM 15d-PGJ₂, 0.25 μM proteasome inhibitor MG-132, 10 μM dexamethasone (DexaM), or control diluent for 8 or 24 hours. Whole-cell lysates at 8 hours after treatment were immunoblotted with the indicated antibodies (left panel). Apoptosis was evaluated at 24 hours by annexin V-PI staining using flow cytometry (right panel). (B) HS-Sultan cells were pretreated with 20 μM of the pancaspase inhibitor ZVAD-FMK (ZVAD), the caspase-8 inhibitor IETD-FMK (IEDT), the caspase-9 inhibitor LEHD-FMK (LEHD), or with a combination of IETD-FMK and LEHD-FMK (I + L), one hour before exposure to 15d-PGJ₂ (10 μM). Cell survival, evaluated at 24 hours after 15d-PGJ₂ treatment, is expressed as the percentage of annexin V^--PI^- cells measured by FACS analysis. The results are representative of 3 independent experiments.