Ref: SHP-2 Tyrosine Phosphatase as an Intracellular Target of Helicobacter pylori CagA Protein.

Higashi et al., 2002. SHP-2 tyrosine phosphatase as an intracellular target of Helicobacter pylori CagA protein. Science. 295(5555), 683-686. PMID-11743164; Full Text: Science,  Science (Download PDF)

This research article investigates how the Helicobacter pylori CagA protein manipulates host epithelial cells by targeting the SHP-2 tyrosine phosphatase. This study provides important insights into the molecular mechanisms by which H. pylori infection may contribute to cellular transformation and gastric disease development.

Key Findings:

• CagA becomes tyrosine-phosphorylated inside host cells following its translocation by the bacterial type IV secretion system. 
  • Experimental approach: Infection of gastric epithelial cells (AGS cells) with H. pylori followed by immunoprecipitation and Western blotting using anti-phosphotyrosine antibodies to detect phosphorylated CagA.
• Phosphorylated CagA specifically binds to the SH2 domains of SHP-2, a host protein tyrosine phosphatase involved in cell signaling. 
  • Experimental approach: Co-immunoprecipitation assays were performed showing that SHP-2 was pulled down with phosphorylated CagA; binding specificity to SH2 domains was confirmed using domain-deletion mutants and in vitro binding assays.
• CagA binding leads to constitutive activation of SHP-2 phosphatase activity. 
  • Experimental approach: Measurement of SHP-2 enzymatic activity after co-expression with CagA, using phosphatase activity assays compared to controls.
• Activated SHP-2 leads to morphological changes in epithelial cells, including cell elongation and scattering (“hummingbird phenotype”). 
  • Experimental approach:
    
• The cellular effects mimic those seen with oncogenic activation of SHP-2, implicating CagA in H. pylori-associated pathogenesis and possibly gastric carcinogenesis. 
  • Experimental approach: Comparative analysis between CagA-induced morphology and known effects of oncogenic SHP-2 mutants (previous literature cited); parallels drawn based on phenotypic resemblance.
• Mutational analysis showed that CagA mutants defective in SHP-2 binding fail to induce these cellular changes, highlighting the critical role of CagA-SHP-2 interaction.
  • Experimental approach: Generation of CagA mutants (mutated at key tyrosine phosphorylation sites), followed by infection assays and microscopy, showing loss of the “hummingbird phenotype” when SHP-2 binding was disrupted.