Recombination-Based In Vivo Expression Technology Identifies Helicobacter pylori Genes Important for Host Colonization (original) (raw)
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The human gastric pathogen Helicobacter pylori occurs in two basic variants, either exhibiting a functional cagPAI-encoded type-4-secretion-system (T4SS) or not. Only a few cagPAI positive strains have been successfully adapted for long-term infection of mice, including the pre-mouse Sydney strain 1 (PMSS1). Here we confirm that PMSS1 induces gastric inflammation and neutrophil infiltration in mice, progressing to intestinal metaplasia. Complete genome analysis of PMSS1 revealed 1,423 coding sequences, encompassing the cagPAI gene cluster and, unusually, location of the cytotoxin-associated gene A (cagA) approximately 15 kb downstream of the island. PMSS1 harbours three genetically exchangeable loci that are occupied by hopQ coding sequences. HopQ represents a critical co-factor required for translocation of CagA translocation into the host cell and activation of NF-κB by via the T4SS. Long-term colonization of mice led to an impairment of cagPAI functionality. One of the bacterial ...
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The complete genome of the gram-negative bacterial pathogen Helicobacter pylori, an important etiological agent of gastroduodenal disease in humans, has recently been published. This sequence revealed that the putative products of roughly one-third of the open reading frames (ORFs) have no significant homology to any known proteins. To be able to analyze the functions of all ORFs, we constructed an
Infection and Immunity, 2012
The best-studied Helicobacter pylori virulence factor associated with development of peptic ulcer disease or gastric cancer (GC) rather than asymptomatic nonatrophic gastritis (NAG) is the cag pathogenicity island (cagPAI), which encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into host epithelial cells. Here we used real-time reverse transcription-PCR (RT-PCR) to measure the in vivo expression of genes on the cagPAI and of other virulence genes in patients with NAG, duodenal ulcer (DU), or GC. In vivo expression of H. pylori virulence genes was greater overall in gastric biopsy specimens of patients with GC than in those of patients with NAG or DU. However, since in vitro expression of cagA was not greater in H. pylori strains from patients with GC than in those from patients with NAG or DU, increased expression in GC in vivo is likely a result of environmental conditions in the gastric mucosa, though it may in turn cause more severe pathology. Increased expression of virulence genes in GC may represent a stress response to elevated pH or other environmental conditions in the stomach of patients with GC, which may be less hospitable to H. pylori colonization than the acidic environment in patients with NAG or DU.
Proceedings of The National Academy of Sciences, 1996
cagA, a gene that codes for an immunodominant antigen, is present only in Helicobacter pylori strains that are associated with severe forms of gastroduodenal disease (type I strains). We found that the genetic locus that contains cagA (cag) is part of a 40-kb DNA insertion that likely was acquired horizontally and integrated into the chromosomal glutamate racemase gene. This pathogenicity island is f lanked by direct repeats of 31 bp. In some strains, cag is split into a right segment (cagI) and a left segment (cagII) by a novel insertion sequence (IS605). In a minority of H. pylori strains, cagI and cagII are separated by an intervening chromosomal sequence. Nucleotide sequencing of the 23,508 base pairs that form the cagI region and the extreme 3 end of the cagII region reveals the presence of 19 ORFs that code for proteins predicted to be mostly membrane associated with one gene (cagE), which is similar to the toxin-secretion gene of Bordetella pertussis, ptlC, and the transport systems required for plasmid transfer, including the virB4 gene of Agrobacterium tumefaciens. Transposon inactivation of several of the cagI genes abolishes induction of IL-8 expression in gastric epithelial cell lines. Thus, we believe the cag region may encode a novel H. pylori secretion system for the export of virulence determinants.
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Although Helicobacter pylori infects 50% of the total human population, only a small fraction of the infected people suffer from severe diseases like peptic ulcers and gastric adenocarcinoma. H. pylori strains, host genotypes and environmental factors play important role in deciding the extent and severity of the gastroduodenal diseases. The bacteria has developed a unique set of virulence factors to survive in the extreme ecological niche of human stomach. Together these virulence factors make H. pylori one of the most successful human pathogenic bacteria colonizing more than half of the human population. Understanding the mechanism of action of the major H. pylori virulence factors will shed light into the molecular basis of its pathogenicity.
The interaction of host genetic factors and Helicobacter pylori infection
Inflammopharmacology, 2007
Helicobacter pylori plays an important role in the development of atrophic gastritis that represents the most recognized pathway in multistep gastric carcinogenesis. Recent studies suggest that a combination of host genetic factors, bacterial virulence factors, and environmental and lifestyle factors determine the severity of gastric damage and the eventual clinical outcome of Helicobacter pylori infection. As to bacterial virulence factors, a high proportion of Japanese strains are cagA + vacAs1. The CagA protein is injected from attached Helicobacter pylori into gastric epithelial cells and the CagA-SHP-2 interactions elicit cellular changes that increase the risk of carcinogenesis. Host cytokine gene polymorphisms and a frequent single nucleotide polymorphism in the PTPN11 gene that encodes SHP-2 may associate with gastric atrophy among Helicobacter pylori-infected subjects. Prevention of gastric cancer requires the development of better screening strategies for determining eradication candidates and further improvement of treatments of Helicobacter pylori infection.
Defining Helicobacter pylori as a Pathogen: Strain Heterogeneity and Virulence
The American Journal of Medicine, 1996
Helicobacter pylori, the etiologic agent of gastritis and peptic ulceration, may infect the gastric mucosa of over half of the world's population. Despite the high infection rate, symptomatic disease beyond gastritis (characterized by gastric or duodenal ulcer) is noted in a small, but nevertheless significant, fraction of this population. What defines an H. pylori strain as a pathogen that can cause the more serious clinical manifestations? In addition to the more well recognized virulence determinants, such as urease, flagella. and vacuolating cytotoxin, evidence is emerging that the more virulent strains possess well defined segments of DNA. These "pathogenicity islands" include cytotoxin-associated gene A and encode proteins involved In signal transduction events that may facUitate Intimate attachment to host cells, cytoskeletal rearrangement via actin polymerization, and host cell protein phosphorylation.