Holotoxin A 1 induces apoptosis through extrinsic pathway activation in human leukemic cells. ( A ) Analysis of the mechanism underlying apoptosis. Western blot of K562 cell proteins after treating cells with 0.06 μM holotoxin A 1 shows changes in protein levels over time. β-actin served as a loading control. This blot is representative of three separate experiments. Densitometry values above the bands indicate the fractional changes in protein levels, compared to initial levels at time 0; ( B ) Functional involvement of caspases in holotoxin A 1 -induced apoptosis in K562 cells. Cells were pretreated for 1 h with the pan-caspase inhibitor Z-VAD-FMK (25 μM), the caspase-8 inhibitor Z-IETD-FMK (20 μM), the caspase-9 inhibitor Z-LEHD-FMK (20 μM), or the caspase-3 inhibitor Z-DEVD-FMK (50 μM), followed by treatment with 0.06 μM holotoxin A 1 for 6 h. (Upper panel) Representative flow cytometry results indicate the extent of apoptosis (Lower panel) The mean ± SD of three independent experiments. ** p
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