CagA: a role at last

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Abstract
Previously, H pylori has been shown to induce changes in gastric epithelial cells during attachment.5 The microvilli disappear at the site of attachment, the cytoskeleton is rearranged beneath the bacterium, and a cup shaped pedestal forms beneath the bacterium. At the same time, intracellular signalling changes can be detected inside the epithelial cell with phosphorylation of proteins on tyrosine residues—a classic cellular signalling pathway. The major phosphorylated protein has now been shown not to be a host cell protein, but H pylori CagA.1-4 The four groups involved have shown this conclusively using a variety of methods: the phosphorylated protein varies in size according to the size of CagA in theH pylori strain and is not induced by CagA negative mutants; it is 35S labelled if the bacterium is so labelled before allowing it to interact with cultured epithelial cells; it reacts with anti-CagA and antiphosphotyrosine antibodies; and if antiphosphotyrosine antibodies are used for purification, direct sequencing shows the protein to be CagA. Furthermore, indirect immunofluorescence and confocal microscopy elegantly show colocalisation of CagA and phosphotyrosine next to the attachment site of the bacterium.1

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