title: Helicobacter pylori vacuolating cytotoxin enters cells, localizes to the mitochondria, and induces mitochondrial membrane permeability changes correlated to toxin channel activity.
abstract: The Helicobacter pylori vacuolating cytotoxin (VacA) intoxicates mammalian cells resulting in reduction of mitochondrial transmembrane potential (Delta Psi m reduction) and cytochrome c release, two events consistent with the modulation of mitochondrial membrane permeability. We now demonstrate that the entry of VacA into cells and the capacity of VacA to form anion-selective channels are both essential for Delta Psi m reduction and cytochrome c release. Subsequent to cell entry, a substantial fraction of VacA localizes to the mitochondria. Neither Delta Psi m reduction nor cytochrome c release within VacA-intoxicated cells requires cellular caspase activity. Moreover, VacA cellular activity is not sensitive to cyclosporin A, suggesting that VacA does not induce the mitochondrial permeability transition as a mechanism for Delta Psi m reduction and cytochrome c release. Time-course and dose-response studies indicate that Delta Psi m reduction occurs substantially before and at lower concentrations of VacA than cytochrome c release. Collectively, these results support a model that VacA enters mammalian cells, localizes to the mitochondria, and modulates mitochondrial membrane permeability by a mechanism dependent on toxin channel activity ultimately resulting in cytochrome c release. This model represents a novel mechanism for regulation of a mitochondrial-dependent apoptosis pathway by a bacterial toxin.
authors.affiliation: Department of Biology and Biochemistry, University of Houston, 369 Science and Research Building II, Houston, TX 77204-5001, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Willhite
authors.forename: Steven R
authors.initials: SR
authors.lastname: Blanke
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects*; D045304:Cytochromes c / Q000378:metabolism; D006367:HeLa Cells; D016480:Helicobacter pylori / Q000472:pathogenicity*; D006801:Humans; D007473:Ion Channels / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects*; D008928:Mitochondria / Q000378:metabolism* / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D007473:Ion Channels; C074689:VacA protein, Helicobacter pylori; D045304:Cytochromes c