: PARP cleavage and the effect of zVAD-fmk on the viability of MCF-7 breast cancer cells. Cells were treated for 24 h with 1 μg/ml of PE, PRL, G129R, or G129R-PE40-KDEL in the absence or presence of a broad spectrum caspase inhibitor, zVAD-fmk (A, B). The cell lysate was separated by SDS-PAGE, and immunblotted with anti-PARP antibody. The caspase mediated cleavage of PARP is indicated by the presence of a 24 kDa PARP fragment as shown by the arrow (A). The role of activated caspases in cell killing caused by PE or G129R-PE40-KDEL was examined by measuring the reduction of MTS by living cells in the absence or presence of zVAD-fmk (B). Data presented is representative of the mean + SD from assays performed in quadruplicate on two separate occasions.