Endosome–mitochondria juxtaposition during apoptosis induced by H. pylori VacA

Abstract

The vacuolating cytotoxin (VacA) is an important virulence factor of Helicobacter pylori with pleiotropic effects on mammalian cells, including the ability to trigger mitochondria-dependent apoptosis. However, the mechanism by which VacA exerts its apoptotic function is unclear. Using a genetic approach, in this study we show that killing by VacA requires the proapoptotic Bcl-2 family members BAX and BAK at the mitochondrial level, but not adequate endoplasmic reticulum Ca 2 þ levels, similarly controlled by BAX and BAK. A combination of subcellular fractionation and imaging shows that wild-type VacA, but not mutants in its channel-forming region, induces the accumulation of BAX on endosomes and endosome-mitochondria juxtaposition that precedes the retrieval of active BAX on mitochondria. It is noteworthy that in Bax-and Bak-deficient cells, VacA is unable to cause endosome-mitochondria juxtaposition and is not retrieved in mitochondria. Thus, VacA causes BAX/BAK-dependent juxtaposition of endosomes and mitochondria early in the process of cell death, revealing a new function for these proapoptotic proteins in the regulation of relative position of organelles.

Mis-Trafficking of Endosomal Urokinase Proteins Triggers Drug-Induced Glioma Nonapoptotic Cell Death

“…Confocal microscopy and quantitative image analysis confirmed that UCD38B initiates a 3.5-fold increase in early and late endosomes colocalizing with mitochondrial regions and that 35% of endosomes appear to be relocated following drug treatment. Similar trafficking between endosomes and mitochondria has been reported following cell death caused by the vacuolating cytotoxin A toxin produced by Helicobacter pylori (Calore et al, 2010), tumor necrosis factor a (Garcia- Ruiz et al, 2002), and Fas (Ouasti et al, 2007).…”

Helicobacter pylori vacuolating cytotoxin A (VacA) engages the mitochondrial fission machinery to induce host cell death

“…S7A), it is unlikely that VacA membrane channels formed on the surface of mammalian cells (54) are required for toxin-mediated activation of Drp1-dependent mitochondrial fission. Alternatively, VacA might act directly at mitochondria, as several previous studies reported that a portion of VacA taken up from the cell surface localizes to this organelle (16,29,55). Preliminary studies to address a possible relationship between the location of intracellular VacA and the perturbation of mitochondrial dynamics revealed that VacA localization to mitochondria (Fig.…”

Helicobacter pylori VacA Induces Programmed Necrosis in Gastric Epithelial Cells

“…Previous studies have reported that VacA is capable of causing death of AGS gastric epithelial cells and several other cell lines (5,7,16,39,44). On the basis of the observations that VacA-induced cell death is preceded by the activation of Bax and Bak (75), that VacA can localize to mitochondria (7,21,27,30,70), and that incubation of cells with VacA results in reduction of the mitochondrial transmembrane potential and release of cytochrome c (30,39,70), VacA-induced cell death of these cell lines was classified as an apoptotic process (5,16,44,54,71).…”

“…On the basis of the observations that VacA-induced cell death is preceded by the activation of Bax and Bak (75), that VacA can localize to mitochondria (7,21,27,30,70), and that incubation of cells with VacA results in reduction of the mitochondrial transmembrane potential and release of cytochrome c (30,39,70), VacA-induced cell death of these cell lines was classified as an apoptotic process (5,16,44,54,71). However, these phenomena can occur in cells undergoing either apoptotic or nonapoptotic cell death (33,40,41).…”

“…Multiple receptors for VacA have been identified, including sphingomyelin, receptor protein-tyrosine phosphatase alpha ␣ (RPTP␣), and RPTP␤ on the surface of gastric epithelial cells and ␤2 integrin on the surface of T cells (28,35,53,62,73,74). Upon internalization by cells, VacA localizes to endosomal compartments (31) as well as to mitochondria (3,7,21,27,30,70).…”