title: The Helicobacter pylori VacA toxin is a urea permease that promotes urea diffusion across epithelia.
abstract: Urease and the cytotoxin VacA are two major virulence factors of the human pathogen Helicobacter pylori, which is responsible for severe gastroduodenal diseases. Diffusion of urea, the substrate of urease, into the stomach is critically required for the survival of infecting H. pylori. We now show that VacA increases the transepithelial flux of urea across model epithelia by inducing an unsaturable permeation pathway. This transcellular pathway is selective, as it conducts thiourea, but not glycerol and mannitol, demonstrating that it is not due to a loosening of intercellular junctions. Experiments performed with different cell lines, grown in a nonpolarized state, confirm that VacA permeabilizes the cell plasma membrane to urea. Inhibition studies indicate that transmembrane pores formed by VacA act as passive urea transporters. Thus, their inhibition by the anion channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid significantly decreases toxin-induced urea fluxes in both polarized and nonpolarized cells. Moreover, phloretin, a well-known inhibitor of eukaryotic urea transporters, blocks VacA-mediated urea and ion transport and the toxin's main biologic effects. These data show that VacA behaves as a low-pH activated, passive urea transporter potentially capable of permeabilizing the gastric epithelium to urea. This opens the novel possibility that in vivo VacA may favor H. pylori infectivity by optimizing urease activity.
authors.affiliation: Centro Consiglio Nazionale delle Ricerche Biomembrane, Department of Biomedical Sciences, University of Padova, Padova, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Tombola
authors.forename: L
authors.initials: L
authors.lastname: Morbiato
authors.forename: G
authors.initials: G
authors.lastname: Del Giudice
authors.forename: R
authors.initials: R
authors.lastname: Rappuoli
authors.forename: M
authors.initials: M
authors.lastname: Zoratti
authors.forename: E
authors.initials: E
authors.lastname: Papini
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000633:toxicity*; D001427:Bacterial Toxins / Q000633:toxicity*; D001693:Biological Transport, Active; D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000378:metabolism; D002463:Cell Membrane Permeability / Q000187:drug effects; D002478:Cells, Cultured; D004285:Dogs; D004848:Epithelium / Q000187:drug effects / Q000378:metabolism; D005753:Gastric Mucosa / Q000378:metabolism; D016480:Helicobacter pylori / Q000201:enzymology* / Q000472:pathogenicity*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D010693:Phloretin / Q000494:pharmacology; D013270:Stomach / Q000187:drug effects; D014508:Urea / Q000378:metabolism*; D014510:Urease / Q000633:toxicity; D014774:Virulence; D000096982:Urea Transporters
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D010693:Phloretin; D014508:Urea; D014510:Urease; D000096982:Urea Transporters; C074689:VacA protein, Helicobacter pylori