Assessment of apoptosis of 32D cells and BCR/ABL-transformed 32D cells permanently or inducibly expressing ICSBP. Apoptosis was determined by examining the uptake of annexin V-FITC and PI. Percentage of cells appearing as annexin- and PI-negative (annexin^-/PI^-) were counted as viable, whereas dead cells were defined as either annexin⁺/PI^- (apoptotic), or annexin⁺/PI⁺ (necrotic). In the case of 32D/BA-ICSBP on/off cells, only PI⁺ cells could be counted as dead and PI^- as vital, because these cells contained green fluorescent protein (GFP), which excluded the possibility of evaluation of annexin V-FITC staining. (A) Percentage of dead cells under nonlimiting culture conditions is indicated in the right upper quadrants. (B) Percentage of viable cells of ICSBP⁺ and ICSBP-stable cell lines cells after 18 hours of starvation without IL-3 (BA^- cells) versus 36 hours of serum withdrawal (BA⁺ cells) or exposure to indicated chemotherapeutic drugs (24 hours versus 48 hours for BA^- versus BA⁺ cells, respectively). (C) Percentage of viable cells of ICSBP-inducible cell lines (ICSBP off versus on) after 18 hours of starvation without IL-3 (BA^- cells) versus 36 hours of serum withdrawal (BA⁺ cells) or exposure to indicated chemotherapeutic drugs (24 hours versus 48 hours for BA^- versus BA⁺ cells, respectively). Bars represent mean values ± SEM of at least 3 independent experiments. Statistically significant differences in the apoptosis rates of cell line pairs were marked with brackets.