The N-terminal 34 kDa fragment of Helicobacter pylori vacuolating cytotoxin targets mitochondria and induces cytochrome c release

The pathogenic bacterium Helicobacter pylori produces the cytotoxin VacA, w hich is implicated in the genesis of gastric epithelial lesions. By transfe cting HEp-2 cells with DNAs encoding either the N-terminal (p34) or the C-t erminal (p58) fragment of VacA, p34 was found localized specifically to mit ochondria, whereas p58 was cytosolic. Incubated in vitro with purified mito chondria, VacA and p34 but not p58 translocated into the mitochondria, Micr oinjection of DNAs encoding VacA-GFP and p34-GFP, but not GFP-VacA or GFP-p 34, induced cell death by apoptosis. Transient transfection of HeLa cells w ith p34-GFP or VacA-GFP induced the release of cytochrome c from mitochondr ia and activated the executioner caspase 3, as determined by the cleavage o f poly(ADP-ribose) polymerase (PARP). PARP cleavage was antagonized specifi cally by co-transfection of DNA encoding Bcl-2, known to block mitochondria -dependent apoptotic signals. The relevance of these observations to the in viva mechanism of VacA action was supported by the fact that purified acti vated VacA applied externally to cells induced cytochrome c release into th e cytosol.