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Tyrosine phosphorylation of the Helicobacter pylori CagA antigen after cag-driven host cell translocation
M Stein1, R Rappuoli, A Covacci
1Immunobiological Research Institute of Siena, Chiron SpA, Via Fiorentina 1, 53100 Siena, Italy.
Insights
The bacterial protein CagA, not a host protein, is injected into epithelial cells by Helicobacter pylori. This virulence factor disrupts cell signaling and alters cell structure, contributing to peptic ulcer disease.
Area of Science:
- Microbiology
- Cell Biology
- Molecular Biology
Background:
- Helicobacter pylori infection is linked to severe gastric tissue damage and inflammation.
- The cag pathogenicity island encodes a type IV secretion system crucial for H. pylori virulence.
- Previous studies indicated host cell protein phosphorylation upon H. pylori co-cultivation.
Purpose of the Study:
- To identify the 145-kDa protein phosphorylated in epithelial cells during H. pylori co-cultivation.
- To elucidate the role of the bacterial protein CagA in host cell signaling.
Main Methods:
- Co-cultivation of epithelial cells with H. pylori strains.
- Analysis of protein phosphorylation using tyrosine-specific antibodies.
- Identification of the phosphorylated protein via immunological and biochemical methods.
Main Results:
- The 145-kDa phosphorylated protein was identified as the bacterial antigen CagA, not a host-derived protein.
- CagA is delivered into host epithelial cells by the H. pylori cag type IV secretion system.
- Delivered CagA is phosphorylated by a host cell kinase and integrates into host cell signaling pathways, affecting the cytoskeleton.
Conclusions:
- CagA is a key virulence factor delivered by H. pylori's type IV secretion system.
- CagA directly manipulates host cell signaling and cytoskeletal dynamics.
- This interaction contributes to the pathogenesis of H. pylori-associated diseases like peptic ulcer disease.
Abstract:
Helicobacter pylori strains associated with severe tissue damage and inflammation possess a unique genetic locus, cag, containing 31 genes originating from a distant event of horizontal transfer and retained as a pathogenicity island. The cag system is an Helicobacter-specific type IV secretion engine involved in cellular responses like induction of pedestals, secretion of IL-8, and phosphorylation of proteic targets. It has previously been reported that cocultivation of epithelial cells with Helicobacter pylori triggers signal transduction and tyrosine phosphorylation of a 145-kDa putative host cell protein. Herein, we demonstrate that this protein is not derived from the host but rather is the bacterial immunodominant antigen CagA, a virulence factor commonly expressed in peptic ulcer disease and thought to be an orphan of a specific biological function. Thus, CagA is delivered into the epithelial cells by the cag type IV secretion system where it is phosphorylated on tyrosine residues by an as yet unidentified host cell kinase and wired to eukaryotic signal transduction pathways and cytoskeletal plasticity.