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 Ca²(+) 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.
Subject(s)
Apoptosis/physiology , Bacterial Proteins/metabolism , Endosomes/metabolism , Helicobacter pylori/pathogenicity , Mitochondria/metabolism , bcl-2 Homologous Antagonist-Killer Protein/metabolism , bcl-2-Associated X Protein/metabolism , Animals , Apoptosis/drug effects , Apoptosis Regulatory Proteins/metabolism , Bacterial Proteins/genetics , Calcium/metabolism , Cells, Cultured , Cytochromes c/metabolism , Endoplasmic Reticulum/metabolism , Fluorescent Antibody Technique , Genes, bcl-2 , Helicobacter pylori/metabolism , Mice , Microscopy, Electron , Virulence Factors/metabolismABSTRACT
A case is described of retrobulbar optic neuritis in a 33-year-old female with acute type B hepatitis. The ocular distress, principally affecting the left eye, followed the normalisation of liver function tests and subsided after steroid therapy. At the onset of ocular symptomatology, complement activation, involving both classic and alternative pathways, and high levels of circulating immune complexes were present. HBsAg was positive. No relapse was observed during follow-up for 3 years. An association between HBV-infection, optic neuritis and an immune complexes-mediated neurotoxic activity are hypothetized.
