Figure 7.

Mitochondrial membrane stabilization by Bcl-2 or vMIA prevent CPX-induced cell death. (A) HeLa cells stably transfected with vector only (Neo), or cDNAs coding for human Bcl-2 or cytomegalovirus-derived vMIA were treated with NFX* or CPX, and the frequency of DiOC₆(3)^low or PI^high cells was assessed. Note that Bcl-2– and vMIA-expressing cells are more susceptible to cell death induction by NFX*, yet relatively resistant to CPX. (B) Mitochondrial, not ER-localized, Bcl-2 prevents CPX-induced cell death. Rat1 cells stably transfected with vector only (Neo), WT Bcl-2, mitochondrion-targeted Bcl-2 (Bcl-2 acta), and ER-targeted Bcl-2 (Bcl-2 cathepsin B5), were subjected to the indicated treatment, and the loss of mitochondrial and plasma membrane integrity was assessed with DiOC₆(3) and PI, respectively. (C) Failure of Bcl-2 or vMIA to confer lysosomal stabilization. HeLa cells expressing Neo, Bcl-2, or vMIA were treated with NFX* or CPX, fixed, and immunostained for cathepsin B. Note that all cells exhibit a diffuse cathepsin B staining, although Bcl-2 and vMIA do inhibit CPX-induced MMP (A) and cell death (B) as an internal control of their efficacy.