Loss of caspase-8/10 expression does not impede paclitaxel-induced apoptosis in human tumor cell lines. (A-C) Apoptosis in SHEP and SH-SY5Y cells. (A) Caspase-8 and caspase-10 are not expressed in SH-SY5Y neuroblastoma cells, as demonstrated by immunoblot analysis using antibodies against caspase-10, caspase-8, and β-actin. (B) Paclitaxel induces caspase-3 activation regardless of caspase-8 and caspase-10 expression. Lysates of SHEP and SH-SY5Y cells were subjected to immunoblot analysis using caspase-3 and β-actin antibodies. The positions of the uncleaved proteins are indicated by closed arrowheads; cleaved fragments of caspase-3 are indicated by open arrowheads. (C) SHEP (left panel) and SH-SY5Y cells (right panel) were treated with increasing concentrations of paclitaxel for 48 hours in the presence or absence of 10 μM pancaspase inhibitor QVD-oPh. Apoptosis was assessed by FACS analysis of hypodiploid nuclei and is given as means (± SD). (D) Reconstitution of caspase-10 does not enhance the sensitivity of MCF-7 cells to paclitaxel. Left panel shows status of caspase expression in the different MCF-7 cells. Lysates of parental cells (WT) and cell clones stably expressing caspase-3, caspase-10, or both were immunoblotted for the indicated proteins. Middle panel shows that reconstitution of caspase-10 or caspase-3 does not sensitize cells to paclitaxel-mediated toxicity. Parental cells and the caspase-3– and/or caspase-10–reconstituted clones were treated for 48 hours with 0.1 μM paclitaxel. The percentage of cell death was assessed by crystal violet staining and compared with the untreated controls. Right panel shows parental and the reconstituted derivatives, stably expressing caspase-3, caspase-10, or both, treated with 0.1 μM paclitaxel for 72 hours. Apoptotic, hypodiploid cells were measured by flow cytometry. The percentage of apoptotic cells is given as mean (± SD).