Molecular mechanism of action of major Helicobacter pylori virulence factors

Association of Helicobacter pylori babA2 gene and gastric cancer risk: a meta-analysis

Background

The association of Helicobacter pylori (H. pylori) babA2 gene with gastric cancer (GC) was reported by several studies, but results were inconsistent. This meta-analysis was performed to investigate the relationship between H. pylori babA2 gene and GC risk.

Methods

Case-control studies involving the association between H. pylori babA2 gene and GC risk were systematically identified from PubMed databases. A meta-analysis was used to pool studies and to estimate odds ratios (ORs) with 95% confidence intervals (CIs) of H. pylori babA2 gene associated with GC risk.

Results

Twenty studies were identified with a total of 1289 GC cases and 1081 controls. H. pylori babA2 gene was associated with an increased risk of GC by 2.05 fold (95% CI, 1.30–3.24, P = 0.002). In subgroup analysis, we found that H. pylori babA2 gene was significantly associated with GC risk in Asian population (OR = 2.63, 95% CI: 1.36–5.09 P = 0.004) but not in South American population (OR = 1.35, 95% CI: 0.69–2.64, P = 0.379).

Conclusions

This meta-analysis indicates that H. pylori babA2 gene may be associated with increased risk of GC, especially in Asian population.

How does Helicobacter pylori cause gastric cancer through connexins: An opinion review

Helicobacter pylori (H. pylori) is a Gram-negative bacterium with a number of virulence factors, such as cytotoxin-associated gene A, vacuolating cytotoxin A, its pathogenicity island, and lipopolysaccharide, which cause gastrointestinal diseases. Connexins function in gap junctional homeostasis, and their downregulation is closely related to gastric carcinogenesis. Investigations into H. pylori infection and the fine-tuning of connexins in cells or tissues have been reported in previous studies. Therefore, in this review, the potential mechanisms of H. pylori-induced gastric cancer through connexins are summarized in detail.

Syk: a new target for attenuation of Helicobacter pylori-induced gastric mucosal inflammatory responses

The magnitude of gastric mucosal inflammatory response to H. pylori relies primarily on the extent of its key endotoxin, LPS, engagement of Toll-like receptor-4 (TLR4) and the initiation of signal transduction events converging on mitogen-activated protein kinase (MAPK) and IκB complex (IKK) cascades. These cascades, in turn, exert their control over the assembly of transcription factors, NFκB and AP1, implicated in the induction of the expression of iNOS and COX-2 proinflammatory genes. The LPS-induced TLR4 activation and the ensuing phosphorylation of its intracellular tyrosine domain by Src-family kinases not only leads to recruitment to the cytoplasmic domain of TLR4 of adaptor molecules directly involved in propagation of the signaling cascades converging on MAPK and IKK, but also provides a propitious docking site for a non-receptor tyrosine kinase, spleen tyrosine kinase (Syk), the activation of which apparently leads to upregulation in the expression of proinflammatory genes. Here, we review the pathways engaged by H. pylori in the recruitment and interaction of Syk with TLR4 in gastric mucosa, and discuss the cascades involved in Syk-mediated amplification in proinflammatory signaling. We focus, moreover, on the potential role of drugs targeting Syk and TLR4 in the treatment of H. pylori-related gastric disease.

Role of LPS-elicited signaling in triggering gastric mucosal inflammatory responses to H. pylori: modulatory effect of ghrelin

Infection with Helicobacter pylori is a primary culprit in the etiology of gastric disease, and its cell-wall lipopolysaccharide (LPS) is recognized as a potent endotoxin responsible for triggering a pattern of the mucosal inflammatory responses. The engagement by the LPS of gastric mucosal Toll-like receptor 4 (TLR4) leads to initiation of signal transduction events characterized by the activation of mitogen-activated protein kinase (MAPK) cascade, induction of phosphoinositide-specific phospholipase C (PLC)/protein kinase C (PKC)/phosphatidylinositol 3-kinase (PI3K) pathway, and up-regulation in Src/Akt. These signaling events in turn exert their influence over H. pylori-elicited excessive generation of NO and PGE2 caused by the disturbances in nitric oxide synthase and cyclooxygenase isozyme systems, increase in epidermal growth factor receptor transactivation, and the induction in matrix metalloproteinase-9 (MMP-9) release. Interestingly, the extent of gastric mucosal inflammatory response to H. pylori is influenced by a peptide hormone, ghrelin, the action of which relays on the growth hormone secretagogue receptor type 1a (GHS-R1a)-mediated mobilization of G-protein dependent transduction pathways. Yet, the signals triggered by TLR-4 activation as well as those arising through GHS-R1a stimulation converge at MAPK and PLC/PKC/PI3K pathways that form a key integration node for proinflammatory signals generated by H. pylori LPS as well as for those involved in modulation of inflammation by ghrelin. Hence, therapeutic targeting these signals' convergence and integration node could provide a novel and attractive opportunities for developing more effective treatments of H. pylori-related gastric disease.

Molecular and Proteomic Analysis of Levofloxacin and Metronidazole Resistant Helicobacter pylori

Antibiotic resistance in bacteria incurs fitness cost, but compensatory mechanisms may ameliorate the cost and sustain the resistance even under antibiotics-free conditions. The aim of this study was to determine compensatory mechanisms of antibiotic resistance in H. pylori. Five strains of levofloxacin-sensitive H. pylori were induced in vitro to develop resistance. In addition, four pairs of metronidazole-sensitive and -resistant H. pylori strains were isolated from patients carrying dual H. pylori populations that consist of both sensitive and resistant phenotypes. Growth rate, virulence and biofilm-forming ability of the sensitive and resistant strains were compared to determine effects of compensatory response. Proteome profiles of paired sensitive and resistant strains were analyzed by liquid chromatography/mass spectrophotometry (LC/MS). Although there were no significant differences in growth rate between sensitive and resistant pairs, bacterial virulence (in terms of abilities to induce apoptosis and form biofilm) differs from pair to pair. These findings demonstrate the complex and strain-specific phenotypic changes in compensation for antibiotics resistance. Compensation for in vitro induced levofloxacin resistance involving mutations of gyrA and gyrB was functionally random. Furthermore, higher protein translation and non-functional protein degradation capabilities in naturally-occuring dual population metronidazole sensitive-resistant strains may be a possible alternative mechanism underlying resistance to metronidazole without mutations in rdxA and frxA. This may explain the lack of mutations in target genes in ~10% of metronidazole resistant strains.

Molecular characterization and polyclonal antibody generation against core component CagX protein of Helicobacter pylori type IV secretion system

Gram-negative bacteria Helicobacter pylori cause gastric ulcer, duodenal cancer, and found in almost half of the world's residents. The protein responsible for this disease is secreted through type IV secretion system (TFSS) of H. pylori. TFSS is encoded by 40-kb region of chromosomal DNA known as cag-pathogenicity island (PAI). TFSS comprises of three major components: cytoplasmic/inner membrane ATPase, transmembrane core-complex and outer membranous pilli, and associated subunits. Core complex consists of CagX, CagT, CagM, and Cag3(δ) proteins as per existing knowledge. In this study, we have characterized one of the important component of core-complex forming sub-unit protein, i.e., CagX. Complete ORF of CagX except signal peptide coding region was cloned and expressed in pET28a vector. Purification of CagX protein was performed, and polyclonal anti-sera against full-length recombinant CagX were raised in rabbit model. We obtained a very specific and high titer, CagX anti-sera that were utilized to characterize endogenous CagX. Surface localization of CagX was also seen by immunofluorescence microscopy. In short for the first time a full-length CagX was characterized, and we showed that CagX is the part of high molecular weight core complex, which is important for assembly and function of H. pylori TFSS.

Intracellular locations of replication proteins and the origin of replication during chromosome duplication in the slowly growing human pathogen Helicobacter pylori

We followed the position of the replication complex in the pathogenic bacterium Helicobacter pylori using antibodies raised against the single-stranded DNA binding protein (HpSSB) and the replicative helicase (HpDnaB). The position of the replication origin, oriC, was also localized in growing cells by fluorescence in situ hybridization (FISH) with fluorescence-labeled DNA sequences adjacent to the origin. The replisome assembled at oriC near one of the cell poles, and the two forks moved together toward the cell center as replication progressed in the growing cell. Termination and resolution of the forks occurred near midcell, on one side of the septal membrane. The duplicated copies of oriC did not separate until late in elongation, when the daughter chromosomes segregated into bilobed nucleoids, suggesting sister chromatid cohesion at or near the oriC region. Components of the replication machinery, viz., HpDnaB and HpDnaG (DNA primase), were found associated with the cell membrane. A model for the assembly and location of the H. pylori replication machinery during chromosomal duplication is presented.

Comparative proteomics analysis of sarcosine insoluble outer membrane proteins from clarithromycin resistant and sensitive strains of Helicobacter pylori

Helicobacter pylori causes disease manifestations in humans including chronic gastric and peptic ulcers, gastric cancer, and lymphoid tissue lymphoma. Increasing rates of H. pylori clarithromycin resistance has led to higher rates of disease development. Because antibiotic resistance involves modifications of outer membrane proteins (OMP) in other Gram-negative bacteria, this study focuses on identification of H. pylori OMP's using comparative proteomic analyses of clarithromycin-susceptible and -resistant H. pylori strains. Comparative proteomics analyses of isolated sarcosine-insoluble OMP fractions from clarithromycin-susceptible and -resistant H. pylori strains were performed by 1) one dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis protein separation and 2) in-gel digestion of the isolated proteins and mass spectrometry analysis by Matrix Assisted Laser Desorption Ionization-tandem mass spectrometry. Iron-regulated membrane protein, UreaseB, EF-Tu, and putative OMP were down-regulated; HopT (BabB) transmembrane protein, HofC, and OMP31 were up-regulated in clarithromycin-resistant H. pylori. Western blotting and real time PCR, respectively, validated UreaseB subunit and EF-Tu changes at the protein level, and mRNA expression of HofC and HopT. This limited proteomic study provides evidence that alteration of the outer membrane proteins' profile may be a novel mechanism involved in clarithromycin resistance in H. pylori.

Two type IV secretion systems with different functions in Burkholderia cenocepacia K56-2

Bacterial type IV secretion systems (T4SS) perform two fundamental functions related to pathogenesis: the delivery of effector molecules to eukaryotic target cells, and genetic exchange. Two T4SSs have been identified in Burkholderia cenocepacia K56-2, a representative of the ET12 lineage of the B. cepacia complex (Bcc). The plant tissue watersoaking (Ptw) T4SS encoded on a resident 92 kb plasmid is a chimera composed of VirB/D4 and F-specific subunits, and is responsible for the translocation of effector(s) that have been linked to the Ptw phenotype. The bc-VirB/D4 system located on chromosome II displays homology to the VirB/D4 T4SS of Agrobacterium tumefaciens. In contrast to the Ptw T4SS, the bc-VirB/D4 T4SS was found to be dispensable for Ptw effector(s) secretion, but was found to be involved in plasmid mobilization. The fertility inhibitor Osa did not affect the secretion of Ptw effector(s) via the Ptw system, but did disrupt the mobilization of a RSF1010 derivative plasmid.

Helicobacter pylori proteins response to nitric oxide stress

Helicobacter pylori is a highly pathogenic microorganism with various strategies to evade human immune responses. Nitric oxide (NO) and reactive nitrogen species (RNS) generated via nitric oxide synthase pathway are important effectors during the innate immune response. However, the mechanisms of H. pylori to survive the nitrosative stress are not clear. Here the proteomic approach has been used to define the adaptive response of H. pylori to nitrosative stress. Proteomic analysis showed that 38 protein spots were regulated by NO donor, sodium nitroprusside (SNP). These proteins were involved in protein processing, anti-oxidation, general stress response, and virulence, as well as some unknown functions. Particularly, some of them were participated in iron metabolism, potentially under the control of ferric uptake regulator (Fur). Real time PCR revealed that fur was induced under nitrosative stress, consistent with our deduction. One stress-related protein up-regulated under nitrosative conditions was thioredoxin reductase (TrxR). Inactivation of fur or trxR can lead to increased susceptivity to nitrosative stress respectively. These studies described the adaptive response of H. pylori to nitric oxide stress, and analyzed the relevant role of Fur regulon and TrxR in nitrosative stress management.

Helicobacter pylori: phenotypes, genotypes and virulence genes

Helicobacter pylori is a Gram-negative, microaerophilic bacterium that colonizes the gastric mucus overlying the epithelium of the stomach in more than 50% of the world's population. This gastric colonization induces chronic gastric inflammation in all infected individuals, but only induces clinical diseases in 10-20% of infected individuals. These include peptic ulcers, acute and atrophic gastritis, intestinal metaplasia, gastric adenocarcinoma and gastric B-cell lymphoma. Various bacterial virulence factors are associated with the development of such gastric diseases, and the characterization of these markers could aid medical prognosis, which could be extremely important in predicting clinical outcomes. The purpose of this review is to summarize the role of the phenotypes, virulence-related genes and genotypes of H. pylori in the establishment of gastric colonization and the development of associated diseases.

Association between chronic atrophic gastritis and serum antibodies to 15 Helicobacter pylori proteins measured by multiplex serology

Infection with Helicobacter pylori is a major risk factor for chronic atrophic gastritis (CAG), a precursor lesion of intestinal gastric cancer. The pathogenicity of the bacterium is thought to play an important role in determining the extent and severity of clinical outcome. We aimed to assess the associations between CAG and the serostatus of antibodies to 15 H. pylori proteins. The analyses were based on 534 cases with serologically defined CAG and 1,068 age-matched and sex-matched controls participating in a population-based study conducted in Saarland, Germany among 9,953 men and women ages 50 to 74 years. A newly developed H. pylori multiplex serology method was used to detect antibodies specific to 15 H. pylori antigens. Significant associations were observed between seropositivity for all 15 specific antibodies and the presence of CAG. Exclusion of severe cases, who might have lost the infection in the course of CAG progression, substantially increased the observed associations. In H. pylori-seropositive subjects, cytotoxin-associated gene A (CagA), vacuolating toxin (VacA), helicobacter cysteine-rich protein C (HcpC), and the chaperonin GroEL were identified as independent virulence factors for CAG with adjusted odds ratios (95% confidence interval) of 3.52 (2.01-6.10), 3.19 (1.44-7.05), 4.03 (1.53-10.65), and 2.65 (1.06-6.62), respectively; the simultaneous presence of all four independent virulence factors was associated with an 18-fold risk of CAG. In conclusion, HcpC and GroEL were identified as new independent virulence factors, and in combination with the established virulence factors, CagA and VacA, were strongly associated with CAG.

Helicobacter pylori single-stranded DNA binding protein--functional characterization and modulation of H. pylori DnaB helicase activity

Helicobacter pylori, an important bacterial pathogen, causes gastric ulcer and gastric adenocarcinoma in humans. The fundamentals of basic biology such as DNA replication are poorly understood in this pathogen. In the present study, we report the cloning and functional characterization of the single-stranded DNA (ssDNA) binding protein from H. pylori. The N-terminal DNA binding domain shows significant homology with E. coli single-stranded DNA binding protein (SSB), whereas the C-terminal domain shows less homology. The overall DNA-binding activity and tetramerization properties, however, remain unaffected. In in vitro experiments with purified proteins, H. pylori (Hp) SSB bound specifically to ssDNA and modulated the enzymatic ATPase and helicase activity of HpDnaB helicase. HpSSB and HpDnaB proteins were co-localized in sharp, distinct foci in exponentially growing H. pylori cells, whereas both were spread over large areas in its dormant coccoid form, suggesting the absence of active replication forks in the latter. These results confirm the multiple roles of SSB during DNA replication and provide evidence for altered replicative metabolism in the spiral and coccoid forms that may be central to the bacterial physiology and pathogenesis.

Phytoceuticals: mighty but ignored weapons against Helicobacter pylori infection

Helicobacter pylori (H. pylori) infection causes peptic ulcer disease, mucosa-associated lymphoid tissue (MALT) lymphomas and gastric adenocarcinomas, for which the pathogenesis of chronic gastric inflammation prevails and provides the pathogenic basis. Since the role of H. pylori infection is promoting carcinogenesis rather than acting as a direct carcinogen, as several publications show, eradication alone cannot be the right answer for preventing H. pylori-associated gastric cancer. Therefore, a non-antimicrobial approach has been suggested to attain microbe-associated cancer prevention through controlling H. pylori-related chronic inflammatory processes and mediators responsible for carcinogenesis. Phytoceutical is a term for plant products that are active on biological systems. Phytoceuticals such as Korean red ginseng, green tea, red wine, flavonoids, broccoli sprouts, garlic, probiotics and flavonoids are known to inhibit H. pylori colonization, decrease gastric inflammation by inhibiting cytokine and chemokine release, and repress precancerous changes by inhibiting nuclear factor-kappa B DNA binding, inducing profuse levels of apoptosis and inhibiting mutagenesis. Even though further unsolved issues are awaited before phytoceuticals are accepted as a standard treatment for H. pylori infection, phytoceuticals can be a mighty weapon for either suppressing or modulating the disease-associated footprints of H. pylori infection.

Relevance of MUC1 mucin variable number of tandem repeats polymorphism in H pylori adhesion to gastric epithelial cells

AIM: To evaluate the influence of MUC1 mucin variable number of tandem repeats (VNTR) variability on H pylori adhesion to gastric cells.

METHODS: Enzyme linked immunosorbent assay (ELISA)-based adhesion assays were performed to measure the adhesion of different H pylori strains (HP26695 and HPTx30a) to gastric carcinoma cell lines (GP202 and MKN45) and GP202 clones expressing recombinant MUC1 with different VNTR lengths.

RESULTS: Evaluation of adhesion results shows that H pylori pathogenic strain HP26695 has a significantly higher (P < 0.05) adhesion to all the cell lines and clones tested, when compared to the non-pathogenic strain HPTx30a. Bacteria showed a significantly higher (P < 0.05) adhesion to the GP202 cell line, when compared to the MKN45 cell line. Furthermore, both strains showed a significantly higher (P < 0.05) adhesion to GP202 clones with larger MUC1 VNTR domains.

CONCLUSION: This work shows that MUC1 mucin variability conditions H pylori binding to gastric cells. The extent of bacterial adhesion depends on the size of the MUC1 VNTR domain. The adhesion is further dependent on bacterial pathogenicity and the gastric cell line. MUC1 mucin variability may contribute to determine H pylori colonization of the gastric mucosa.

CagA-producing Helicobacter pylori and increased risk of gastric cancer: a nested case-control study in Korea

In a nested-case control study of 100 cases of gastric cancer and 400 matched controls in relation to virulence factors of Helicobacter pylori in a Korean cohort, CagA seropositivity was significantly associated with a higher risk of gastric cancer among H. pylori-infected subjects (OR=3.57, 95% CI 1.05–12.14).

Growth-induced changes in the proteome ofHelicobacter pylori

Helicobacter pylori is a major human pathogen that is responsible for a number of gastrointestinal infections. We have used 2-DE to characterise protein synthesis in bacteria grown either on solid agar-based media or in each of two broth culture media (Brucella and brain heart infusion (BHI) broth). Significant differences were observed in the proteomes of bacteria grown either on agar-based or in broth media. Major changes in protein abundance were identified using principal component analysis (PCA), which delineated the profiles derived for the three key growth conditions (i.e. agar plates, Brucella and BHI broth). Proteins detected across the gel series were identified by peptide mass mapping and Edman sequencing. A number of proteins associated with protein synthesis in general as well as specific amino acid synthesis were depressed in broth-grown bacteria compared to plate-grown bacteria. A similar reduction was also observed in the abundance of proteins involved in detoxification. Two of the most abundant spots, identified as UreB and GroEL, in plate-grown bacteria showed a >140-fold drop in abundance in bacteria grown in Brucella broth compared to bacteria grown on agar plates. Two protein spots induced in bacteria grown in broth culture were both identified as glyceraldehyde 3-phosphate dehydrogenase based on their N-terminal amino acid sequences derived by Edman degradation. The underlying causes of the changes in the proteins abundance were not clear, but it was likely that a significant proportion of the changes were due to the alkaline pH of the broth culture media.

Involvement of a plasmid-encoded type IV secretion system in the plant tissue watersoaking phenotype of Burkholderia cenocepacia

Burkholderia cenocepacia strain K56-2, a representative of the Burkholderia cepacia complex, is part of the epidemic and clinically problematic ET12 lineage. The strain produced plant tissue watersoaking (ptw) on onion tissue, which is a plant disease-associated trait. Using plasposon mutagenesis, mutants in the ptw phenotype were generated. The translated sequence of a disrupted gene (ptwD4) from a ptw-negative mutant showed homology to VirD4-like proteins. Analysis of the region proximal to the transfer gene homolog identified a gene cluster located on the 92-kb resident plasmid that showed homology to type IV secretion systems. The role of ptwD4, ptwC, ptwB4, and ptwB10 in the expression of ptw activity was determined by conducting site-directed mutagenesis. The ptw phenotype was not expressed by K56-2 derivatives with a disruption in ptwD4, ptwB4, or ptwB10 but was observed in a derivative with a disruption in ptwC. Complementation of ptw-negative K56-2 derivatives in trans resulted in complete restoration of the ptw phenotype. In addition, analysis of culture supernatants revealed that the putative ptw effector(s) was a secreted, heat-stable protein(s) that caused plasmolysis of plant protoplasts. A second chromosomally encoded type IV secretion system with complete homology to the VirB-VirD system was identified in K56-2. Site-directed mutagenesis of key secretory genes in the VirB-VirD system did not affect expression of the ptw phenotype. Our findings indicate that in strain K56-2, the plasmid-encoded Ptw type IV secretion system is responsible for the secretion of a plant cytotoxic protein(s).