Tyrosine phosphorylation of the<i>Helicobacter pylori</i>CagA antigen after<i>cag</i>-driven host cell translocation

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  • Markus Stein
    Immunobiological Research Institute of Siena, Chiron SpA, Via Fiorentina 1, 53100 Siena, Italy
  • Rino Rappuoli
    Immunobiological Research Institute of Siena, Chiron SpA, Via Fiorentina 1, 53100 Siena, Italy
  • Antonello Covacci
    Immunobiological Research Institute of Siena, Chiron SpA, Via Fiorentina 1, 53100 Siena, Italy

Abstract

<jats:p><jats:italic>Helicobacter pylori</jats:italic>strains associated with severe tissue damage and inflammation possess a unique genetic locus,<jats:italic>cag</jats:italic>, containing 31 genes originating from a distant event of horizontal transfer and retained as a pathogenicity island. The<jats:italic>cag</jats:italic>system is an<jats:italic>Helicobacter</jats:italic>-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<jats:italic>Helicobacter pylori</jats:italic>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<jats:italic>cag</jats:italic>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.</jats:p>

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