Inhibition of the type IV secretion system from antibiotic-resistant Helicobacter pylori clinical isolates supports the potential of Cagα as an anti-virulence target

Helicobacter pylori resistance to antibiotics is a growing problem and it increasingly leads to treatment failure. While the bacterium is present worldwide, the severity of clinical outcomes is highly dependent on the geographical origin and genetic characteristics of the strains. One of the major virulence factors identified in H. pylori is the cag pathogenicity island (cagPAI), which encodes a type IV secretion system (T4SS) used to translocate effectors into human cells. Here, we investigated the genetic variability of the cagPAI among 13 antibiotic-resistant H. pylori strains that were isolated from patient biopsies in Québec. Seven of the clinical strains carried the cagPAI, but only four could be readily cultivated under laboratory conditions. We observed variability of the sequences of CagA and CagL proteins that are encoded by the cagPAI. All clinical isolates induce interleukin-8 secretion and morphological changes upon co-incubation with gastric cancer cells and two of them produce extracellular T4SS pili. Finally, we demonstrate that molecule 1G2, a small molecule inhibitor of the Cagα protein from the model strain H. pylori 26695, reduces interleukin-8 secretion in one of the clinical isolates. Co-incubation with 1G2 also inhibits the assembly of T4SS pili, suggesting a mechanism for its action on T4SS function.

Hp0521 inhibited the virulence of H. pylori 26,695 strain via regulating CagA expression

Hp0521 is the number of cag pathogenicity island (cagPAI) family in Helicobacter pylori (H. pylori, Hp), which encoded Cag2 protein. The aim of this study was to investigate the role of hp0521 on the H. pylori 26,695 strain. We constructed the recombinant prokaryotic expression plasmid pET-32a-hp0521 and pET-32a-hpc0521. Then, we co-cultured the H. pylori wild strain 26,695 and Δhp0521 strain with GES-1 cells to detect CagA protein transport and IL-8 secretion. We found that Δhp0521 mutation increased the expression of cagA, rpoB and promoted the transportation of CagA protein in GES-1 cells. In addition, we also observed that Δhp0521 mutation had no effect on other cagPAI protein stability and the expression of IL-8. Our findings suggested that hp0521 may down-regulated the expression of cagA, rpoB and inhibited the transportation of CagA protein in GES-1 cells and had no effect on growth.

Helicobacter pylori cagE, cagG, and cagM can be a prognostic marker for intestinal and diffuse gastric cancer

It is known that Helicobacter pylori is the main cause of peptic ulceration and gastric cancer. However, there is a lack of information on whether H. pylori strains may differ in gastric cancer histological subtypes. This study aimed to investigate different H. pylori strains considering six cag Pathogenicity Island - cagPAI genes (cagA, cagE, cagG, cagM, cagT, and virb11), and vacuolating cytotoxin - vacA alleles, and their relation to gastric cancer histologic subtypes. For this purpose, tumor samples from 285 patients with gastric carcinoma were used. H. pylori infection and genotypes were determined by polymerase chain reaction (PCR). H. pylori was detected in 93.9% of gastric tumors. For comparative analyzes between histopathological subtypes considering H. pylori cagPAI genes the strains were grouped according to the vacA s1/s2 alleles. In the vacAs1 group, the strains cagA(-)cagE(+), cagA(+)cagE(+)cagG(+), cagA(+)cagM(+), or only cagE(+) strains were more frequent in the intestinal subtype (P = .009; P = .024; P = .046, respectively). In contrast, cagM(+)cagG(+)cagA(-) and cagE(-) were associated with diffuse tumors (P = .036), highlighting the presence of cagE in the development of intestinal tumors, and the presence of cagG and absence of cagE in diffuse tumors. Furthermore, WEKA software and Decision Tree (CART) analyses confirmed these findings, in which cagE presence was associated with intestinal tumors, and cagE absence and cagG(+) with diffuse tumors. In conclusion our results showed that vacAs1 (cagG + cagM) strains, mainly cagG positive with cagE absence, were relevant in the studied population for the diffuse outcome, while the presence of cagE was relevant for the intestinal outcome. These findings suggest the relevance of these H. pylori genes as potential markers for gastric cancer histological outcomes.

Presence of cagPAI genes and characterization of vacA s, i and m regions in Helicobacter pylori isolated from Alaskans and their association with clinical pathologies

Introduction. Gastric cancer is a health disparity in the Alaska Native people. The incidence of Helicobacter pylori infection, a risk factor for non-cardia gastric adenocarcinoma, is also high. Gastric cancer is partially associated with the virulence of the infecting strain.Aim. To genotype the vacA s, m and i and cag pathogenicity island (cagPAI) genes in H. pylori from Alaskans and investigate associations with gastropathy.Methodology. We enrolled patients with gastritis, peptic ulcer disease (PUD) and intestinal metaplasia (IM) in 1998-2005 and patients with gastric cancer in 2011-2013. Gastric biopsies were collected and cultured and PCR was performed to detect the presence of the right and left ends of the cagPAI, the cagA, cagE, cagT and virD4 genes and to genotype the vacA s, m and i regions.Results. We recruited 263 people; 22 (8 %) had no/mild gastritis, 121 (46 %) had moderate gastritis, 40 (15%) had severe gastritis, 38 (14 %) had PUD, 30 (11 %) had IM and 12 (5 %) had gastric cancer. H. pylori isolates from 150 (57%) people had an intact cagPAI; those were associated with a more severe gastropathy (P≤0.02 for all comparisons). H. pylori isolates from 77 % of people had either the vacA s1/i1/m1 (40 %; 94/234) or s2/i2/m2 (37 %; 86/234) genotype. vacA s1/i1/m1 was associated with a more severe gastropathy (P≤0.03 for all comparisons).Conclusions. In this population with high rates of gastric cancer, we found that just over half of the H. pylori contained an intact cagPAI and 40 % had the vacA s1/i1/m1 genotype. Infection with these strains was associated with a more severe gastropathy.

Cortactin: A Major Cellular Target of the Gastric Carcinogen Helicobacter pylori

Cortactin is an actin binding protein and actin nucleation promoting factor regulating cytoskeletal rearrangements in nearly all eukaryotic cell types. From this perspective, cortactin poses an attractive target for pathogens to manipulate a given host cell to their own benefit. One of the pathogens following this strategy is Helicobacter pylori, which can cause a variety of gastric diseases and has been shown to be the major risk factor for the onset of gastric cancer. During infection of gastric epithelial cells, H. pylori hijacks the cellular kinase signaling pathways, leading to the disruption of key cell functions. Specifically, by overruling the phosphorylation status of cortactin, H. pylori alternates the activity of molecular interaction partners of this important protein, thereby manipulating the performance of actin-cytoskeletal rearrangements and cell movement. In addition, H. pylori utilizes a unique mechanism to activate focal adhesion kinase, which subsequently prevents host epithelial cells from extensive lifting from the extracellular matrix in order to achieve chronic infection in the human stomach.

Genetic diversity and virulence characteristics of Helicobacter pylori isolates in different human ethnic groups

Helicobacter pylori is the most predominant bacterium in almost 50% of the world's population and colonization causes a persistent inflammatory response leading to chronic gastritis. It shows high genetic diversity and individuals generally harbour a distinct bacterial population. With the advancement of whole-genome sequencing technology, new H. pylori subpopulations have been identified that show admixture between various H. pylori strains. Genotypic variation of H. pylori may be related to the presence of virulence factors among strains and is associated with different outcomes of infection in different individuals. This review summarizes the genetic diversity in H. pylori strain populations and its virulence characteristics responsible for variable outcomes in different ethnic groups.

Helicobacter pylori Virulence Factors Exploiting Gastric Colonization and its Pathogenicity

Helicobacter pylori colonizes the gastric epithelial cells of at least half of the world's population, and it is the strongest risk factor for developing gastric complications like chronic gastritis, ulcer diseases, and gastric cancer. To successfully colonize and establish a persistent infection, the bacteria must overcome harsh gastric conditions. H. pylori has a well-developed mechanism by which it can survive in a very acidic niche. Despite bacterial factors, gastric environmental factors and host genetic constituents together play a co-operative role for gastric pathogenicity. The virulence factors include bacterial colonization factors BabA, SabA, OipA, and HopQ, and the virulence factors necessary for gastric pathogenicity include the effector proteins like CagA, VacA, HtrA, and the outer membrane vesicles. Bacterial factors are considered more important. Here, we summarize the recent information to better understand several bacterial virulence factors and their role in the pathogenic mechanism.

Tailor-Made Detection of Individual Phosphorylated and Non-Phosphorylated EPIYA-Motifs of Helicobacter pylori Oncoprotein CagA

The gastric pathogen and carcinogen Helicobacter pylori(H. pylori) encodes a type IV secretion system for translocation of the effector protein CagA into host cells. Injected CagA becomes tyrosine-phosphorylated at the five amino acid residue Glutamate-Proline- Isoleucine-Tyrosine-Alanine (EPIYA)-sequence motifs. These phosphorylated EPIYA-sites represent recognition motifs for binding of multiple host factors, which then manipulate signaling pathways to trigger gastric disease. Thus, efficient detection of single phosphorylated EPIYA-motifs in CagA is required. Detection of phospho-CagA is primarily performed using commercial pan-phosphotyrosine antibodies. However, those antibodies were originally generated to recognize many phosphotyrosines in various mammalian proteins and are not optimized for use in bacteria. To address this important limitation, we synthesized 11-mer phospho- and non-phospho-peptides from EPIYA-motifs A, B, and C, and produced three phospho-specific and three non-phospho-specific rabbit polyclonal CagA antibodies. These antibodies specifically recognized the corresponding phosphorylated and non-phosphorylated EPIYA-motifs, while the EPIYA-C antibodies also recognized the related East-Asian EPIYA-D motif. Otherwise, no cross-reactivity of the antibodies among EPIYAs was observed. Western blotting demonstrated that each EPIYA-motif can be predominantly phosphorylated during H. pylori infection. This represents the first complete set of phospho-specific antibodies for an effector protein in bacteria, providing useful tools to gather information for the categorization of CagA phosphorylation, cancer signaling, and gastric disease progression.

Impact of Helicobacter pylori Virulence Factors on the Host Immune Response and Gastric Pathology

Helicobacter pylori chronically infects nearly half the world's population, yet most of those infected remain asymptomatic throughout their lifetime. The outcome of infection-peptic ulcer disease or gastric cancer versus asymptomatic colonization-is a product of host genetics, environmental influences, and differences in bacterial virulence factors. Here, we review the current understanding of the cag pathogenicity island (cagPAI), the vacuolating cytotoxin (VacA), and a large family of outer membrane proteins (OMPs), which are among the best understood H. pylori virulence determinants that contribute to disease. Each of these virulence factors is characterized by allelic and phenotypic diversity that is apparent within and across individuals, as well as over time, and modulates inflammation. From the bacterial perspective, inflammation is probably a necessary evil because it promotes nutrient acquisition, but at the cost of reduction in bacterial load and therefore decreases the chance of transmission to a new host. The general picture that emerges is one of a chronic bacterial infection that is dependent on both inducing and carefully regulating the host inflammatory response. A better understanding of these regulatory mechanisms may have implications for the control of chronic inflammatory diseases that are increasingly common causes of human morbidity and mortality.

Role of NOD1 and ALPK1/TIFA Signalling in Innate Immunity Against Helicobacter pylori Infection

The human pathogen Helicobacter pylori interacts intimately with gastric epithelial cells to induce inflammatory responses that are a hallmark of the infection. This inflammation is a critical precursor to the development of peptic ulcer disease and gastric cancer. A major driver of this inflammation is a type IV secretion system (T4SS) encoded by the cag pathogenicity island (cagPAI), present in a subpopulation of more virulent H. pylori strains. The cagPAI T4SS specifically activates signalling pathways in gastric epithelial cells that converge on the transcription factor, nuclear factor-κB (NF-κB), which in turn upregulates key immune and inflammatory genes, resulting in various host responses. It is now clear that H. pylori possesses several mechanisms to activate NF-κB in gastric epithelial cells and, moreover, that multiple signalling pathways are involved in these responses. Two of the dominant signalling pathways implicated in NF-κB-dependent responses in epithelial cells are nucleotide-binding oligomerisation domain 1 (NOD1) and a newly described pathway involving alpha-kinase 1 (ALPK1) and tumour necrosis factor (TNF) receptor-associated factor (TRAF)-interacting protein with forkhead-associated domain (TIFA). Although the relative roles of these two pathways in regulating NF-κB-dependent responses still need to be clearly defined, it is likely that they work cooperatively and non-redundantly. This chapter will give an overview of the various mechanisms and pathways involved in H. pylori induction of NF-κB-dependent responses in gastric epithelial cells, including a 'state-of-the-art' review on the respective roles of NOD1 and ALPK1/TIFA pathways in these responses.

H. pylori-associated pathologic findings among Alaska native patients

Helicobacter pylori infection is common among Alaska native (AN) people, however scant gastric histopathologic data is available for this population. This study aimed to characterise gastric histopathology and H. pylori infection among AN people. We enrolled AN adults undergoing upper endoscopy. Gastric biopsy samples were evaluated for pathologic changes, the presence of H. pylori, and the presence of cag pathogenicity island-positive bacteria. Of 432 persons; two persons were diagnosed with gastric adenocarcinoma, two with MALT lymphoma, 40 (10%) with ulcers, and 51 (12%) with intestinal metaplasia. Fifty-five per cent of H. pylori-positive persons had cag pathogenicity island positive bacteria. The gastric antrum had the highest prevalence of acute and chronic moderate-severe gastritis. H. pylori-positive persons were 16 and four times more likely to have moderate-severe acute gastritis and chronic gastritis (p < 0.01), respectively. An intact cag pathogenicity island positive was correlated with moderate-severe acute antral gastritis (53% vs. 31%, p = 0.0003). H. pylori-positive persons were more likely to have moderate-severe acute and chronic gastritis compared to H. pylori-negative persons. Gastritis and intestinal metaplasia were most frequently found in the gastric antrum. Intact cag pathogenicity island positive was correlated with acute antral gastritis and intestinal metaplasia.

Biochemical characterization of the Helicobacter pylori Cag Type 4 Secretion System protein CagN and its interaction partner CagM

Highly virulent Helicobacter pylori strains contain the cag pathogenicity island (cagPAI). It codes for about 30 proteins forming a type IV secretion system (T4SS) which translocates the pro-inflammatory protein CagA into epithelial host cells. While CagA and various other Cag proteins have been extensively studied, several cagPAI proteins are poorly characterized or of unknown function. CagN (HP0538) is of unknown function but highly conserved in the cagPAI suggesting an important role. cagM (HP0537) is the first gene of the cagMN operon and its product is part of the CagT4SS core complex. Both proteins do not have detectable homologs in other type IV secretion systems. We have characterized the biochemical and structural properties of CagN and CagM and their interaction. We demonstrate by circular dichroism, Multi-Angle Light Scattering (MALS) and small angle X-ray scattering (SAXS) that CagN is a folded, predominantly monomeric protein with an elongated shape in solution. CagM is folded and forms predominantly dimers that are also elongated in solution. We found by various in vivo and in vitro methods that CagN and CagM directly interact with each other. CagM self-interacts stably with a low nanomolar K_D and can form stable multimers. Finally, in vivo experiments show that deletion of CagM reduces the amounts of CagN and other outer CagPAI proteins in H. pylori cells.

Status of Helicobacter pylori cag pathogenicity island (cagPAI) integrity and significance of its individual genes

One of the most important virulence factors of H. pylori is the intact cagPAI. The aim of the present study is to investigate cagPAI intactness among Bulgarian H. pylori isolates, its associations with clinical outcomes and vacA alleles, and to evaluate the significance of individual cagPAI genes.

MATERIAL AND METHODS

Totally, 156 isolates from 156 patients with endoscopic findings for duodenal or gastric ulcer (33 subjects), non-ulcer disease (121) and other diseases, such as Crohn's disease and hepatitis (2) were tested. Polymerase chain reaction (PCR) was used to detect 14 essential cagPAI genes, including cagA, as well as vacA s, i and m alleles.

RESULTS

CagA positive were 81.4% of all H. pylori isolates. Intact cagPAI was found in 64.1% of the all isolates, 16.7% and 19.2% showed complete and partial cagPAI absence, respectively. The prevalence of all cagPAI genes and intact cagPAI was significantly higher in isolates from ulcer patients compared with those from non-ulcer patients (p = 0.001). The most frequently missing genes among the isolates with partially deleted cagPAIs were cagE or/and cagY (28 of 30 isolates). Overall prevalence of vacA s1a allele was 80.1% and that of vacA i1 was 64.1%. The vacA s1a, m1 and i1 alleles were more prevalent in H. pylori isolates from ulcer patients (p = 0.03, p = 0.009, and p = 0.0003, respectively) and were associated with isolates with intact cagPAI.

CONCLUSIONS

In Bulgaria the prevalence of intact cagPAI was high. cagE or/and cagY absence was the most important predictor of cagPAI status.

Comparative analysis of selected cagPAI genes and different vacA genotypes in Iranian and Turkish H. pylori-positive patients suffering from gastric adenocarcinoma and active chronic gastritis

BACKGROUND/AIM

Helicobacter pylori is a pathogen that colonizes a majority of the world's population. Genetic diversity within the virulence genes of bacteria such as cagPAI and vacA may have a modified effect on the pathogenic potential of the bacteria. This study aimed to investigate which genes can be suggested as potentially related virulence factors for H. pylori-associated active chronic gastritis and stomach adenocarcinoma in the northwest of Iran and south of Turkey.

MATERIALS AND METHODS

Formalin-fixed, paraffin-embedded stomach biopsy tissue samples were obtained from Iranian and Turkish patients from selected geographical regions. The prevalence of selected cagPAI genes and vacA genotypes were studied in H. pylori-positive samples by using polymerase chain reaction and specific primers.

RESULTS

Out of 320 patients, H. pylori was detected in 28.43% of patients. We found that the vacAs1, vacAm2, and cagA genes with mean prevalences of 82.41%, 71.42%, and 69.23%, respectively, were dominant in Iranian and Turkish patients.

CONCLUSION

In the south of Turkey and northwest of Iran the studied genes were homogeneous and there were no significant differences in bacterial genetics. The results of this study indicate that cagA and vacAs1 are dominant genes in people with gastric disorders in our selected geographical regions.

Association of heterogenicity of Helicobacter pylori cag pathogenicity island with peptic ulcer diseases and gastric cancer

OBJECTIVE

To investigate the frequency and integrity of certain cag pathogenicity island genes (cagPAI) in Helicobacter pylori strains and their association with peptic ulcer disease (PUD) and gastric cancer.

MATERIAL AND METHODS

We enrolled 240 adult patients [120 with functional dyspepsia (FD), 50 with PUD and 70 with gastric cancer] undergoing upper gastrointestinal endoscopy. H. pylori infection was diagnosed when either culture or any two of the three tests (rapid urease test, histopathology and specific ureA PCR) were positive. DNA extracted from H. pylori isolates and positive gastric tissues were tested by PCR for the presence of different genes of cagPAI using specific primers.

RESULTS

A total of 122 (51%) patients were H. pylori positive. Frequencies of cagPAI genes cagA, cagE, cagT and cagM in H. pylori strains from different groups of patients were as follows: functional dyspepsia 73, 83, 76 and 60%, PUD 70, 94, 91, 70% and gastric cancer 75, 95, 90 and 70%, respectively. Risk associated for the presence of PUD and gastric cancer with cagPAI genes cagE, cagT and cagM was 5.0-, 4.6- and 4.1- and 3.0-, 2.8- and 2.5-folds, respectively. Prevalence of intact cagPAI was significantly higher in PUD and gastric cancer compared to functional dyspepsia (PUD vs. functional dyspepsia, 71% vs. 38%, P = 0.01; gastric cancer vs. functional dyspepsia, 75% vs. 38%, P < 0.01). Intact cagPAI was associated with increased risk for the presence of PUD (odds ratio 5.2, 95% CI 2.4-11.3) and for the presence of gastric cancer (odds ratio 4.5, 95% CI 2.3-7.1).

CONCLUSIONS

cagPAI integrity and its different genes are linked to different forms of gastric disease and so may have a role in pathogenesis, diagnosis and management.

Crystal structure of the type IV secretion system component CagX from Helicobacter pylori

The structure of the C-terminal domain of CagX is presented and structural comparisons with TraO, its homologue from another bacterial T4S system, reveal distinct and conserved features.

Helicobacter pylori, a Gram-negative bacterial pathogen prevalent in the human population, is the causative agent of severe gastric diseases. An H. pylori type IV secretion (T4S) system encoded by the cytotoxin-associated gene pathogenicity island (cagPAI) is responsible for communication with host cells. As a component of the cagPAI T4S system core complex, CagX plays an important role in virulence-protein translocation into the host cells. In this work, the crystal structure of the C-terminal domain of CagX (CagXct), which is a homologue of the VirB9 protein from the VirB/D4 T4S system, is presented. CagXct is only the second three-dimensional structure to be elucidated of a VirB9-like protein. Another homologue, TraO, which is encoded on the Escherichia coli conjugative plasmid pKM101, shares only 19% sequence identity with CagXct; however, there is a remarkable similarity in tertiary structure between these two β-sandwich protein domains. Most of the residues that are conserved between CagXct and TraO are located within the protein core and appear to be responsible for the preservation of this domain fold. The studies presented here will contribute to our understanding of different bacterial T4S systems.

Helicobacter pylori with East Asian-type cagPAI genes is more virulent than strains with Western-type in some cagPAI genes

The severity of Helicobacter pylori-related disease is correlated with the presence and integrity of a cag pathogenicity island (cagPAI). cagPAI genotype may have a modifying effect on the pathogenic potential of the infecting strain. After analyzing the sequences of cagPAI genes, some strains with the East Asian-type cagPAI genes were selected for further analysis to examine the association between the diversity of the cagPAI genes and the virulence of H. pylori. The results showed that gastric mucosal inflammatory cell infiltration was significantly higher in patients with East Asian-type cagPAI genes H. pylori strain compared with mosaicism cagPAI genes H. pylori strain (p < 0.05). H. pylori strains with the East Asian-type cagPAI genes were closely associated with IL-8 secretion in vitro and in vivo compared with H. pylori strains with the mosaicism cagPAI genes (p < 0.01). H. pylori strains with East Asian-type cagPAI genes are able to strongly translocate CagA to host cells. These results suggest that H. pylori strains with East Asian-type cagPAI genes are more virulent than the strains of cagPAI gene/genes that are Western type.

Systematic analysis of phosphotyrosine antibodies recognizing single phosphorylated EPIYA-motifs in CagA of East Asian-type Helicobacter pylori strains

BACKGROUND

Highly virulent strains of the gastric pathogen Helicobacter pylori encode a type IV secretion system (T4SS) that delivers the effector protein CagA into gastric epithelial cells. Translocated CagA undergoes tyrosine phosphorylation by members of the oncogenic c-Src and c-Abl host kinases at EPIYA-sequence motifs A, B and D in East Asian-type strains. These phosphorylated EPIYA-motifs serve as recognition sites for various SH2-domains containing human proteins, mediating interactions of CagA with host signaling factors to manipulate signal transduction pathways. Recognition of phospho-CagA is mainly based on the use of commercial pan-phosphotyrosine antibodies that were originally designed to detect phosphotyrosines in mammalian proteins. Specific anti-phospho-EPIYA antibodies for each of the three sites in CagA are not forthcoming.

RESULTS

This study was designed to systematically analyze the detection preferences of each phosphorylated East Asian CagA EPIYA-motif by pan-phosphotyrosine antibodies and to determine a minimal recognition sequence. We synthesized phospho- and non-phosphopeptides derived from each predominant EPIYA-site, and determined the recognition patterns by seven different pan-phosphotyrosine antibodies using Western blotting, and also investigated representative East Asian H. pylori isolates during infection. The results indicate that a total of only 9-11 amino acids containing the phosphorylated East Asian EPIYA-types are required and sufficient to detect the phosphopeptides with high specificity. However, the sequence recognition by the different antibodies was found to bear high variability. From the seven antibodies used, only four recognized all three phosphorylated EPIYA-motifs A, B and D similarly well. Two of the phosphotyrosine antibodies preferentially bound primarily to the phosphorylated motif A and D, while the seventh antibody failed to react with any of the phosphorylated EPIYA-motifs. Control experiments confirmed that none of the antibodies reacted with non-phospho-CagA peptides and in accordance were able to recognize phosphotyrosine proteins in human cells.

CONCLUSIONS

The results of this study disclose the various binding preferences of commercial anti-phosphotyrosine antibodies for phospho-EPIYA-motifs, and are valuable in the application for further characterization of CagA phosphorylation events during infection with H. pylori and risk prediction for gastric disease development.

Composition, structure and function of the Helicobacter pylori cag pathogenicity island encoded type IV secretion system

Many Gram-negative pathogens harbor type IV secretion systems (T4SS) that translocate bacterial virulence factors into host cells to hijack cellular processes. The pathology of the gastric pathogen Helicobacter pylori strongly depends on a T4SS encoded by the cag pathogenicity island. This T4SS forms a needle-like pilus, and its assembly is accomplished by multiple protein-protein interactions and various pilus-associated factors that bind to integrins followed by delivery of the CagA oncoprotein into gastric epithelial cells. Recent studies revealed the crystal structures of six T4SS proteins and pilus formation is modulated by iron and zinc availability. All these T4SS interactions are crucial for deregulating host signaling events and disease progression. New developments in T4SS functions and their importance for pathogenesis are discussed.

CagA-mediated pathogenesis of Helicobacter pylori

Helicobacter pylori has been described as the main etiologic agent of gastric cancer, causing a considerable rate of mortality and morbidity in human population across the world. Although the infection mainly begins asymptomatically, but simply develops to peptic ulcer, chronic gastritis, lymphoma of the gastric mucosa and eventually adenocarcinoma. The major pathological feature of H. pylori infection is due to the activity of the cytotoxin-associated gene A (CagA), a 125-140 kDa protein encoded by the cag pathogenicity island (cagPAI). CagA is also known as the first bacterial onco-protein, ranking the H. pylori-mediated adenocarcinoma as the second most deadly cancer type worldwide. Upon cytoplasmic translocation CagA undergoes interacting with numerous proteins in phosphorylation dependent and independent manners within the gastric epithelial cells. The profound effect of CagA on multiple intracellular pathways causes major consequences such as perturbation of intracellular actin trafficking, stimulation of inflammatory responses and disruption of cellular tight junctions. Such activities of CagA further participate in development of the hummingbird phenotype and gastric cancer. This review is sought to provide a structural and functional analysis of the CagA protein with focus on demonstrating the molecular basis of the mechanism of CagA intracellular translocation and its interaction with intracellular targets.

Macrophages recognize the Helicobacter pylori type IV secretion system in the absence of toll-like receptor signalling

Helicobacter pylori strains carrying the cag pathogenicity island (cagPAI) provoke an increased inflammatory response, conferring an increased risk of ulcer formation and carcinogenesis. How the immune system recognizes the presence of cagPAI positive strains is yet unclear. By comparing the transcriptional response of wild type and MyD88/Trif(-/-) bone marrow macrophages to infection with H. pylori, we found that the majority of regulated genes were dependent on toll-like receptor (TLR) signalling. To determine the role of TLR-independent responses, we analysed the transcriptome of MyD88/Trif(-/-) bone marrow macrophages at different time points after infection with cagPAI positive versus negative strains. We identified a group of genes that exhibited different kinetic behaviour depending on whether cagPAI was present. Analysis of their gene expression kinetics demonstrated that this responsiveness to cagPAI was observed only in MyD88/Trif(-/-) macrophages. This group of cagPAI-sensing genes was enriched for AU-rich element containing early response genes involved in immune regulation, including interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α). Recognition of cagPAI positive strains was found to be mediated by the type IV secretion system (cagT4SS), rather than its effector protein CagA. We hypothesize that anergic macrophages of the gastric mucosa initiate an innate immune response following detection of the T4SS of H. pylori.