Fig. 3. Mitochondrial membrane potential is lost during apoptin treatment, and anti-apoptotic Bcl-2 family members block apoptin-induced death. (A) Mitochondrial membrane potential (m) determination in Jurkat control cells, caspase-8^(-/-) Jurkat cells and FADD-DN Jurkat cells either left untreated or treated with TAT-apoptin for the indicated time periods. m was determined by using a cationic carbocyanine dye, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1), which shows a decrease in the red fluorescence upon loss of membrane potential. (B) Apoptosis (hypodiploid nuclei) detection, measured by flow cytometry, in Jurkat cells and clones stably transfected with either Bcl-2 or Bcl-X_L treated with TAT-apoptin (1 µM) for the indicated time. (C) MCF7, MCF7-Bcl-2 and MCF7-caspase-3 breast cancer adenocarcinoma cells treated with TAT-Apoptin (1 µM) for the indicated period of time assessed for cell viability by the MTT assay. To exclude solvent- or TAT-peptide-related effects, some control cells (A-C) were treated with recombinant TAT-GFP (1 µM) instead of TAT-apoptin.