implication of the structure of the Helicobacter pylori cag pathogenicity island in induction of interleukin-8 secretion

Systematic mutagenesis of the Helicobacter pylori cag pathogenicity island: essential genes for CagA translocation in host cells and induction of interleukin-8

Helicobacter pylori (Hp) carries a type IV secretion system encoded by the cag pathogenicity island (cag-PAI), which is used to: (i) translocate the bacterial effector protein CagA into different types of eukaryotic cells; and (ii) induce the synthesis and secretion of chemokines, such as interleukin-8 (IL-8). The cag-PAI in Hp 26695 consists of 27 putative genes, six of which were identified as homologues to the basic type IV secretion system represented by the Agrobacterium tumefaciens virB operon. To define the role and contribution of each of the 27 genes, we applied a precise deletion/insertion mutagenesis procedure to knock out each individual gene without causing polar effects on the expression of downstream genes. Seventeen out of 27 genes were found to be absolutely essential for translocation of CagA into host cells and 14 out of 27 for the ability of Hp fully to induce transcription of IL-8. The products of hp0524 (virD4 homologue), hp0526 and hp0540 are absolutely essential for the translocation of CagA, but not for the induction of IL-8. In contrast, the products of hp0520, hp0521, hp0534, hp0535, hp0536 and hp0543 are not necessary for either translocation of CagA or for IL-8 induction. Our data argue against a translocated IL-8-inducing effector protein encoded by the cag-PAI. We isolated a variant of Hp 26695, which spontaneously switched off its capacity for IL-8 induction and translocation of CagA, but retained the complete cag-PAI. We identified a point mutation in gene hp0532, causing a premature translational stop in the corresponding polypeptide chain, providing a putative explanation for the defect in the type IV secretion system of the spontaneous mutant.

Impact of Helicobacter pylori virulence on the outcome of gastroduodenal diseases: lessons from the microbiologist

Two main pathogenic factors have been described in Helicobacter pylori strains: the cag pathogenicity island (cag PAI) and the vacuolating cytotoxin VacA. The cag PAI is comprised of approximately 40 open reading frames probably originating from another species. It encodes a type IV secretion system, i.e., an apparatus derived from pili which may contribute to the transfer of bacterial molecules to epithelial cells. One of the most well known is the CagA protein which is involved in cell actin rearrangement. Another important property is the induction of interleukin 8, a proinflammatory mediator, which is the consequence of other cag PAI genes. VacA has also been the subject of numerous studies. In vitro, it leads to vacuoles in epithelial cells from the late endosome compartment. However, its main impact could be to induce apoptosis by acting on mitochondria, as was shown in a recent study. The presence of cag PAI as well as VacA has been associated with a higher pathogenic potential of H. pylori strains. Indeed, both are often found simultaneously, but it may well be that the combination of the two, with specific adherence properties, increases even more the pathogenicity of the strains.