Vacuolation induced by VacA toxin of Helicobacter pylori requires the intracellular accumulation of membrane permeant bases, Cl⁻ and water

Glycosylphosphatidylinositol-anchored Proteins and Actin Cytoskeleton Modulate Chloride Transport by Channels Formed by the Helicobacter pylori Vacuolating Cytotoxin VacA in HeLa Cells

“…This latter hypothesis was strengthened by the observation that expression into HeLa cells of a dominant negative mutant of VacA was able to antagonize the cell vacuolation induced by the wild-type toxin also expressed within the cytosol (39,40). That removing GPI-Ps from the cell surface strongly reduced both the influx and efflux of chloride ions of the toxin pore and greatly affected the formation of large vacuoles in cells indicates that the VacA channel is formed at the level of the cell surface and responsible for the vacuolation as postulated (11,12,35).…”

“…The mechanism by which VacA causes large Rab7-positive vacuoles may involve the transport of chloride ions by toxin channels (2,11,12,35). This is likely because (i) the anion channel blocker NPPB inhibits VacA-induced vacuolation (11,12, this study); (ii) it is well established that VacA-induced vacuolation requires the V-ATPase activity (2), and it has been recently documented that the rate-limiting step in late endosome acidification by the V-ATPase is the endosomal influx of chloride ions by specific channels that could be inhibited by NPPB (36,37); and (iii) VacA mutant proteins, with an impaired capacity to form active channels, are unable (or poorly able) to vacuolate cells (38,39).…”

“…It is not clear, however, where the toxin channel is formed in the cell. On one hand it is hypothesized that the VacA channel might be formed at the level of the cell plasma membrane and then endocytosed into late endosome to provoke vacuolation (11,12,35). On the other hand, the demonstration that vacuolation could be observed in cells transfected with VacA DNA and expressing the toxin (13,14) has pushed forward the idea that VacA, upon its translocation into the cytosol, could form channels into endomembranes such as those of late endosomes (2,13,14).…”

Random Mutagenesis of Helicobacter pylori vacA To Identify Amino Acids Essential for Vacuolating Cytotoxic Activity

“…VacA channels are formed in the plasma membrane of cells and also may be present in the membranes of endocytic vesicles (47,49). One model proposes that entry of Cl Ϫ into vesicle compartments through the VacA channel is accompanied by increased pumping of protons by the vacuolar ATPase, influx of weak bases (such as ammonium ions), and accumulation of H 2 O, thereby driving endosome swelling (1,37,49). It has been suggested that VacA mimics the electrophysiological behavior of host chloride channels (11).…”

Characteristics of weak base-induced vacuoles formed around individual acidic organelles

“…Vacuolar H + --ATPase inhibitor bafilomycin A1 and Cl --free medium blocked vacuole formation and subsequent cell death. These components have been demonstrated to be necessary for the vacuole formation induced by weak bases [6] and bacterial toxins, Helicobacter pylori toxin VacA [18,19,22] and Vibrio cholerae toxin [4]. The vacuolization induced by these toxins probably needs weak bases [4,21].…”