To be helped or not helped, that is the question

Diphtheria toxin (DT)* is the paradigm of the powerful A-B toxins. These bacterial poisons bind to cells, are endocytosed, and inject their catalytic domain into the cytosol causing the irreversible modification of a key component of the the host cellular machinery. The mechanism by which the hydrophilic enzymatic fragment of DT crosses the endosomal membrane and is released into the cytosol remains controversial. In this issue, Ratts et al. (2003) demonstrate that delivery of the DT catalytic domain from the lumen of purified early endosomes to the external medium requires the addition of a cytosolic translocation factor complex composed in part of Hsp90 and thioredoxin reductase

Escherichia coli Cytotoxic Necrotizing Factor 1 (CNF1), a Toxin That Activates the Rho GTPase

Cytotoxic necrotizing factor 1 (CNF1), a 110-kDa protein toxin from pathogenic Escherichia coli induces actin reorganization into stress fibers and retraction fibers in human epithelial cultured cells allowing them to spread. CNF1 is acting in the cytosol since microinjection of the toxin into HEp-2 cells mimics the effects of the externally applied CNF1. Incubation in vitro of CNF1 with recombinant small GTPases induces a modification of Rho (but not of Rac, Cdc42, Ras, or Rab6) as demonstrated by a discrete increase in the apparent molecular weight of the molecule. Preincubation of cells with CNF1 impairs the cytotoxic effects of Clostridium difficile toxin B, which inactivates Rho but not those of Clostridium sordellii LT toxin, which inhibits Ras and Rac. As shown for Rho-GTP, CNF1 activates, in a time- and dose-dependent manner, a cytoskeleton-associated phosphatidylinositol 4-phosphate 5-kinase. However, neither the phosphatidylinositol 4,5-bisphosphate (PIP2) nor the phosphatidylinositol 3,4-bisphosphate (PI 3,4-P2) or 3,4,5-trisphosphate (PIP3) cellular content were found increased in CNF1 treated HEp-2 cells. Cellular effects of CNF1 were not blocked by LY294002, a stable inhibitor of the phosphoinositide 3-kinase. Incubation of HEp-2 cells with CNF1 induces relocalization of myosin 2 in stress fibers but not in retraction fibers. Altogether, our data indicate that CNF1 is a toxin that selectively activates the Rho GTP-binding protein, thus inducing contractility and cell spreading

Helicobacter pylori Counteracts the Apoptotic Action of Its VacA Toxin by Injecting the CagA Protein into Gastric Epithelial Cells

Infection with Helicobacter pylori is responsible for gastritis and gastroduodenal ulcers but is also a high risk factor for the development of gastric adenocarcinoma and lymphoma. The most pathogenic H. pylori strains (i.e., the so-called type I strains) associate the CagA virulence protein with an active VacA cytotoxin but the rationale for this association is unknown. CagA, directly injected by the bacterium into colonized epithelium via a type IV secretion system, leads to cellular morphological, anti-apoptotic and proinflammatory effects responsible in the long-term (years or decades) for ulcer and cancer. VacA, via pinocytosis and intracellular trafficking, induces epithelial cell apoptosis and vacuolation. Using human gastric epithelial cells in culture transfected with cDNA encoding for either the wild-type 38 kDa C-terminal signaling domain of CagA or its non-tyrosine-phosphorylatable mutant form, we found that, depending on tyrosine-phosphorylation by host kinases, CagA inhibited VacA-induced apoptosis by two complementary mechanisms. Tyrosine-phosphorylated CagA prevented pinocytosed VacA to reach its target intracellular compartments. Unphosphorylated CagA triggered an anti-apoptotic activity blocking VacA-induced apoptosis at the mitochondrial level without affecting the intracellular trafficking of the toxin. Assaying the level of apoptosis of gastric epithelial cells infected with wild-type CagA+/VacA+ H. pylori or isogenic mutants lacking of either CagA or VacA, we confirmed the results obtained in cells transfected with the CagA C-ter constructions showing that CagA antagonizes VacA-induced apoptosis. VacA toxin plays a role during H. pylori stomach colonization. However, once bacteria have colonized the gastric niche, the apoptotic action of VacA might be detrimental for the survival of H. pylori adherent to the mucosa. CagA association with VacA is thus a novel, highly ingenious microbial strategy to locally protect its ecological niche against a bacterial virulence factor, with however detrimental consequences for the human host

Intérêt du dosage urinaire de l'interleukine 8 dans le diagnostic des infections du tractus urinaire (thèse)

NICE-BU Médecine Odontologie (060882102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Sepsis sévère et choc septique (influence de l'haplogroupe mitochondrial H sur la genèse du stress oxydant)

NICE-BU Médecine Odontologie (060882102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Endocytose et trafic intracellulaire de la toxine CNF1 activatrice des Rho-GTPases

Le facteur cytotoxique nécrosant 1 (CNF1) d'Escherichia coli est une toxine de type AB qui active les GTPases de la famille Rho. CNF1 a une structure tripartite, regroupant trois domaines fonctionnels, chacun étant responsable d'une étape du processus d'intoxication. Le domaine amino-terminal de la toxine est responsable de sa fixation avec une haute affinité à une protéine intégrale de membrane de 85 kDa relativement abondante (50 000 récepteurs par cellule HEp-2). Le complexe toxine-récepteur est internalisé d'une façon similaire à la toxine du ricin qui emprunte plusieurs voies d'endocytose différentes (voie dépendante de la clathrine et voies indépendantes). Le complexe toxine-récepteur suit la voie de dégradation et traverse successivement le compartiment endosomal précoce puis tardif. Comme DT, CNF1 transloque son activité catalytique sous l'effet du pH acide de l'endosome. Cependant, alors que DT transloque son activité catalytique dans la membrane de l'endosome précoce, CNF1 doit rejoindre le compartiment endosomal tardif pour transloquer son activité catalytique. Une fois dans le cytoplasme, le domaine catalytique active les protéines Rho impliquées notamment dans la régulation du cytosquelette d'actine, induisant la formation de fibres de tension (voie dépendante de Rho), de lamellipodes (voie dépendante de Rac) et de filopodes (voie dépendante de Cdc42).NICE-BU Sciences (060882101) / SudocSudocFranceF