Helicobacter pylori picB, a homologue of the Bordetella pertussis toxin secretion protein, is required for induction of IL‐8 in gastric epithelial cells

Abstract

Approximately 60% of Helicobacter pylori strains are cagA+ and this genotype is more frequently associated with duodenal ulcer disease. Although most wild-type cagA+ strains are both cytotoxigenic and induce enhanced Interleukin-8 (IL-8) secretion in gastric epithelial cells, isogenic cagA- mutants retain full activity in these assays; thus, cagA appears to be a marker of enhanced virulence. Delineation of the nucleotide sequence of a 4 kb region upstream of cagA allowed the identification of 966 bp (picA) and 2655 bp (picB) open reading frames encoding 36 kDa and 101 kDa polypeptides, respectively. picA and picB constitute an operon in opposite orientation to cagA. The deduced picB product showed significant homology (26% identity and 50% similarity) with the Bordetella pertussis toxin secretion protein (PtlC). Of 55 H. pylori clinical isolates, the picA and picB segment was conserved exclusively in cagA+ strains and present in all isolates from patients with duodenal ulceration, versus 59% of isolates from patients with gastritis alone (P = 0.01). Using gene-replacement techniques, we constructed picA and picB mutant H. pylori strains and demonstrated that the picB gene product is involved in the induction of IL-8 expression in gastric epithelial cells. Further, Northern blot hybridization and RT-PCR data showed that picA and picB are co-transcribed and an insertional mutation in picA ablates picB expression. These studies indicate a role of picA and picB in the induction of an inflammatory response in gastric epithelial cells either directly or by enabling secretion of an unidentified product, and suggest a mechanism for the overrepresentation of strains possessing these genes in patients with peptic ulceration.

Analyses of the cag pathogenicity island of Helicobacter pylori

“…It is clear that there are four ORFs in cagII with protein level homologies to some of the A. tumefaciens vir genes that are needed for T DNA transfer to target plant cells, and corresponding transfer genes from conjugative bacterial plasmids. Three of these four genes are homolouges of the ptl genes of B. pertussis that are needed to deliver pertussis toxin to mammalian cells [vir B11/ ptl H (ORF11), vir B10/ptlG (ORF13ؒ14) and vir B9/ptl F (ORF15)], whereas a homologue of the fourth [virD4 (ORF10)] has not been found in B. pertussis; a homologue of a fifth such vir/ptl gene also was found in the right (cagI) half of this PAI (picB, Tummuru et al, 1995; or cagE, Censini et al, 1996). The H. pylori genes for these five vir/ptl homolouges are scattered in the cag PAI, not tightly clustered as in A. tumefaciens or B. pertussis.…”

Helicobacter pylori adherence to gastric epithelial cells: a role for non-adhesin virulence genes

“…The cagA gene is a marker for a large 40-kb locus containing .40 genes, termed the cag pathogenicity island (cag PAI), and the majority of these genes encode membrane-associated proteins with features similar to other bacterial secretion systems, particularly the type IV system epitomised by Bordetella pertussis toxin secretion [27][28][29]. A cagE mutant induced only mild inflammation in Mongolian gerbils, whereas the wild-type strain and vacA mutants induced more severe gastritis [30]. Mutation of cagE abolishes the ability of H. pylori to induce the cytokine interleukin-8 (IL-8), a neutrophil chemotactic factor, in Kato-3 cells [27,29,31,32].…”

Helicobacter pylori: recent advances in the study of its pathogenicity and prevention

“…Recent studies using isogenic mutants strains lacking the cagA gene have shown that IL-8 induction may not be directly due to CagA protein but to the products of cag PAI genes. 95,105,106,107 cag PAI is a 40 kilobase segment of DNA containing over 31 genes inserted into the chromosomal glutamate racemase gene. The presence in cag PAI of the short repeated sequences similar to that found in the insertion sequence 605 (IS605), and its different proportion of G+C in comparison with the chromosomal DNA, suggests that this has been acquired by horizontal transfer.…”

“…82 In this way, the bacterial protein CagA is the virulence determinant that is actively translocated across the membrane of the gastric epithelial cells. 95,107 The gastric epithelium represents the first line of active defense against H. pylori infection. However, this tissue not only serves as barrier to exclude pathogens but also secrets a number of inflammatory mediators that initiate the host immune response to pathogen invasion.…”

“…99,114,115 However, mutant strains with disruption of many other genes in the cag PAI suppress their ability to stimulate IL-8 production. 95,106,107,116,117 Censini and colleagues demonstrated that mutants in cagE, cagG, cagH, cagI, cagL, and cagM genes lost their ability to induce IL-8 and blocked the tyrosine phosphorylation of CagA protein, while cagN mutants were not affected. 95,116 Knockout of cagE gene affected the activation of the immediate early response transcription factor nuclear factor κB (NF-κB) in a gastric epithelial cell line.…”