Fig. 1. Exogenous expression of WT or MT caspase-8 in HeLa-CASP8 KO cells.

A HeLa parental cells and HeLa-CASP8 KO cells were subjected to immunoblotting for caspase-8 or GAPDH (left panel). In the right panel, parental HeLa cells and HeLa-CASP8 KO cells were treated for 48 h with the indicated concentrations of TRAIL, followed by the performance of MTT assays. Data were plotted as percent of cell growth relative to no TRAIL treatment. Columns represent the means from five wells; error bars represent the SEM. One-way ANOVA was performed for the comparison of differences between multiple groups. The experiment was performed three times, with similar results. B HeLa-CASP8 KO cells engineered for DOX-inducible expression of FLAG-tagged, WT caspase-8, MT caspase-8 proteins, or the control protein LacZ, were treated for 24 h in the absence or presence of DOX (1 μg/mL), followed by immunoblotting with anti-FLAG. Immunoblotting for GAPDH was used as a loading control. To allow comparison of expression levels between gels, an equivalent amount of the D303G mutant was loaded on each gel. T272del indicates the T272_T273del mutant, an in-frame mutant lacking three nucleotides. The experiments were performed three times with similar results.