Novel antigens of Helicobacter pylori correspond to ulcer-related antibody pattern of sera from infected patients

SurA-like and Skp-like Proteins as Important Virulence Determinants of the Gram Negative Bacterial Pathogens

In the Gram-negative bacteria, many important virulence factors reach their destination via two-step export systems, and they must traverse the periplasmic space before reaching the outer membrane. Since these proteins must be maintained in a structure competent for transport into or across the membrane, they frequently require the assistance of chaperones. Based on the results obtained for the model bacterium Escherichia coli and related species, it is assumed that in the biogenesis of the outer membrane proteins and the periplasmic transit of secretory proteins, the SurA peptidyl-prolyl isomerase/chaperone plays a leading role, while the Skp chaperone is rather of secondary importance. However, detailed studies carried out on several other Gram-negative pathogens indicate that the importance of individual chaperones in the folding and transport processes depends on the properties of client proteins and is species-specific. Taking into account the importance of SurA functions in bacterial virulence and severity of phenotypes due to surA mutations, this folding factor is considered as a putative therapeutic target to combat microbial infections. In this review, we present recent findings regarding SurA and Skp proteins: their mechanisms of action, involvement in processes related to virulence, and perspectives to use them as therapeutic targets.

Helicobacter pylori flagellin: TLR5 evasion and fusion-based conversion into a TLR5 agonist

Helicobacter pylori is a flagellated bacterium of the Epsilonproteobacteria class that causes peptic ulcers. Flagellin is a primary structural protein that assembles into the flagellar filament. Flagellins from bacteria that belong to the Gammaproteobacteria and Firmicutes groups are detected by Toll-like receptor 5 (TLR5) in the host, triggering the innate immune response, and thus have been studied for the development of vaccines against diverse infections through fusion with protein antigens. However, H. pylori flagellin (hFlg) does not stimulate TLR5, allowing H. pylori to evade TLR5-mediated immune surveillance. The unresponsiveness of TLR5 to hFlg, along with the tendency of the hFlg protein to precipitate, limits the utility of hFlg for H. pylori vaccine development. Here, we report a soluble hFlg derivative protein that activates TLR5. We performed expression and purification screens with full-length and fragment hFlg proteins and identified the hypervariable domains as the soluble part of hFlg. The hypervariable domains of hFlg were engineered into a TLR5 agonist through fusion with the TLR5-activating Bacillus subtilis flagellin. Furthermore, based on comparative sequence and mutation analyses, we reveal that hFlg evolved to evade TLR5 detection by modifying residues that correspond to a TLR5-activation hot spot.

Genome-wide mRNA-miRNA profiling uncovers a role of the microRNA miR-29b-1-5p/PHLPP1 signalling pathway in Helicobacter pylori-driven matrix metalloproteinase production in gastric epithelial cells

Aberrant expression of microRNAs (miRNAs) is associated with tumour progression, extracellular matrix remodelling, and cell proliferation. miRNAs modulate host gene expression during infection by pathogens such as Helicobacter pylori, which is associated with varying degrees of gastric pathology. In order to gain insight into the regulation of gene expression by miRNAs during H. pylori infection of gastric epithelial cells and its likely downstream consequences, we analysed the transcriptomes and miRnomes of AGS cells infected with H. pylori. In silico analysis of miRNA-mRNA interactions suggested that miR-29b-1-5p was a likely regulator of pathways associated with gastric epithelial cell pathology. We validated PH domain leucine rich phosphatase 1 (PHLPP1), a negative regulator of the Akt signalling pathway, as a target of miR-29b-1-5p. In an in vivo mouse model, we observed that infection with H. pylori was associated with upregulation of miR-29b-1-5p and downregulation of PHLPP1. Transfection with either a mimic or an inhibitor of miR-29b-1-5p confirmed that downregulation of PHLPP1 upregulates Akt-dependent NF-κB signalling leading to activation of matrix metalloproteinases 2 and 9, players in the degradation of extracellular matrix during H. pylori infection. The secreted antigen HP0175 was associated with upregulation of miR-29b-1-5p, regulation of metalloproteinase activity, and migration of AGS cells. Our study suggests that targeting the miR-29b-1-5p/PHLPP1 signalling axis could be a potential host-directed approach for regulating the outcome of H. pylori infection.

Helicobacter pylori Peptidyl Prolyl Isomerase Expression Is Associated with the Severity of Gastritis

PURPOSE

Helicobacter pylori secretory peptidyl prolyl isomerase, HP0175, is progressively identified as a pro-inflammatory and pro-carcinogenic protein, which serves to link H. pylori infection to its more severe clinical outcomes. Here, we have analyzed host HP0175-specific antibody responses in relation to the severity of gastritis.

METHODS

The HP0175 gene fragment was PCR-amplified, cloned, expressed and purified by Ni-NTA affinity chromatography. Serum antigen-specific antibody responses of non-ulcer dyspeptic patients (N = 176) against recombinant HP0175 were detected by western blotting. The infection status of these subjects was determined by rapid urease test, culture, histology, and serology. The grade of inflammation and stage of atrophy were scored blindly according to the OLGA staging system.

RESULTS

The recombinant HP0175 (rHP0175) was expressed as a ~35 kDa protein and its identity was confirmed by western blotting using anti-6X His tag antibody and pooled H. pylori-positive sera. Serum IgG antibodies against rHP0175 segregated our patients into two similar-sized groups of sero-positives (90/176, 51.1 %) and sero-negatives (86/176, 48.9 %). The former presented with higher grades of gastric inflammation (OR = 4.4, 95 % CI = 1.9-9.9, P = 0.001) and stages of gastric atrophy (OR = 18.3, 95 %CI = 1.4-246.6, P = 0.028).

CONCLUSION

Our findings lend further support to the pro-inflammatory nature of H. pylori peptidyl prolyl isomerase (HP0175) and recommends this antigen as a non-invasive serum biomarker of the severity of H. pylori-associated gastritis.

Helicobacter pylori cell binding factor 2: Insights into domain motion

Helicobacter pylori cell binding factor 2 (HpCBF2) is an antigenic virulence factor belonging to the SurA-like peptidyl-prolyl cis-trans isomerase family with implications for pathogenicity in the human gastrointestinal tract. HpCBF2 possesses PPIase activity and could act as a periplasmic chaperone to regulate outer membrane protein assembly. Here, we measured the isomerization and chaperone activity of HpCBF2, and determined the crystal structure of HpCBF2 in complex with an inhibitor, indole-2-carboxylic acid (I2CA), at 2.4Å resolution. HpCBF2-I2CA forms a homodimer encasing a large central hydrophobic cavity with a basket-like structure, and each monomer contains a PPIase and a chaperone domain. In the HpCBF2-I2CA dimer, the two PPIase domains separate by a distance of 22.8Å, while the two chaperone domains arrange in a domain-swap manner. The PPIase domains bound with I2CA ligand face towards the chaperone domains and are shielded by surrounding hydrophobic residues. With the aid of SAXS experiments, we also revealed domain motion between the apo- and I2CA-bound states of HpCBF2. The domain motion in HpCBF2 might be necessary for the isomerization activity of PPIase and the accommodation of the unfolded and partially folded peptides to refold by chaperone domain.

Differential distribution of the PPIase gene in Helicobacter pylori strains isolated from patients with different gastric diseases

AIM: To explore the distribution of the peptidyl-prolyl cis-trans isomerase (PPIase) gene in Helicobacter pylori (H. pylori) strains isolated from patients with different gastric diseases.

METHODS: Biopsy specimens were taken from the gastric mucosa of patients with superficial gastritis (GS), atrophic gastritis (GA) or gastric cancer (GC) and used to isolate a total of 64 H. pylori strains. The distribution of the PPIase gene in these strains was analyzed by PCR.

RESULTS: The GA group had the highest distribution frequency (94.4%) of the PPIase gene, which was significantly higher than those in the GS (57.7%) and GC (65.0%) groups (P = 0.014, 0.045). Although the frequency of the PPIase gene was higher in the GC group than in the GS group, there was no statistical difference between them (P > 0.05).

CONCLUSION: H. pylori strains isolated from patients with AG carried a higher frequency of the PPIase gene.

Bacterial virulence in the moonlight: multitasking bacterial moonlighting proteins are virulence determinants in infectious disease

Men may not be able to multitask, but it is emerging that proteins can. This capacity of proteins to exhibit more than one function is termed protein moonlighting, and, surprisingly, many highly conserved proteins involved in metabolic regulation or the cell stress response have a range of additional biological actions which are involved in bacterial virulence. This review highlights the multiple roles exhibited by a range of bacterial proteins, such as glycolytic and other metabolic enzymes and molecular chaperones, and the role that such moonlighting activity plays in the virulence characteristics of a number of important human pathogens, including Staphylococcus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Helicobacter pylori, and Mycobacterium tuberculosis.

Race, African ancestry, and Helicobacter pylori infection in a low-income United States population

BACKGROUND

Gastric cancer incidence in African Americans is twice that of whites, and differing prevalence of Helicobacter pylori strain-specific isolates may help explain the disparity.

METHODS

Serum levels of antibodies to each of 15 H. pylori proteins were assessed using multiplex serology for a sample of 689 African American and white participants from the Southern Community Cohort Study. African and European admixture was estimated using a panel of 276 ancestry genetic markers, with "low," "medium," and "high" categories of African ancestry defined as <85%, 85% to 95%, and ≥95%.

RESULTS

The majority (79%) of our study population were sero-positive for H. pylori. African American race was associated with a two- to sixfold increased odds for sero-positivity to eight H. pylori proteins, including the cancer-associated virulence constituents CagA [odds ratio (OR), 6.4; 95% CI, 4.5-9.1], and VacA (OR, 2.3; 95% CI, 1.5-3.5). Compared to whites, African Americans of low, medium, and high African ancestry had 1.6-, 4.1-, and 5.2-fold increased odds of sero-positivity to H. pylori, primarily related to CagA sero-positive strains, for which increasing African ancestry led to 2.5-, 9.6-, and 13.1-fold increased odds. Among African Americans alone, compared to those of low African ancestry, African Americans of medium and high African ancestry had 2.5- and 3.4-fold increased odds of sero-positivity to H. pylori, and 3.5- and 4.9-fold increased odds of CagA sero-positive H. pylori strains.

CONCLUSIONS

Host genetic variation and/or lifestyle factors associated with African ancestry contribute to the likelihood of infection with H. pylori, particularly its virulent strains, in this low-income U.S. southern population.

IMPACT

Our findings that low-income African Americans of high African ancestry have a particularly high prevalence of antibodies against H. pylori provides a framework for further research into better detection and prevention of gastric cancer in this population.

Helicobacter pylori infection and gastric cancer risk: evaluation of 15 H. pylori proteins determined by novel multiplex serology

Infection with Helicobacter pylori is a major cause of gastric cancer (GC). The association likely has been underestimated in the past due to disease-related clearance of the infection. On the other hand, only a minority of the infected individuals develop GC, and better risk stratification is therefore highly desirable. We aimed to assess the association of GC with antibodies to 15 individual H. pylori proteins, determined by novel multiplex serology, to identify potentially relevant risk markers. This analysis was based on 123 GC cases aged 50 to 74 years and 492 age-matched and sex-matched controls from Saarland, Germany. Eight of the antibodies were significantly associated with noncardia GC and seven of them were significantly related to GC at any site. More pronounced associations were observed for noncardia GC; adjusted odds ratios (95% confidence intervals) ranged from 1.60 (1.01-2.54) for HyuA to 5.63 (3.20-9.91) for cytotoxin-associated antigen A (CagA). A dose-response relationship was found between the number of seropositivities and GC (P < 0.001). The seropositivities of CagA and GroEL were found to be independent predictors of GC, which were strongly related to GC risk in a dose-response manner (P < 0.001). In conclusion, GroEL was identified as a new independent risk marker that may contribute to enhanced quantification of H. pylori-related GC risk.

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.

Proteomic Helicobacter pylori biomarkers discriminating between duodenal ulcer and gastric cancer

Protein patterns of 129 Helicobacter pylori strains isolated from Korean and Colombian patients suffering from duodenal ulcer or gastric cancer were analyzed by the high-throughput methodology SELDI-TOF-MS. Eighteen statistically significant candidate biomarkers discriminating between the two clinical outcomes were selected by using the Mann-Whitney test. Three biomarker proteins were purified and identified as a neutrophil-activating protein NapA (HU HPAG1_0821), a RNA-binding protein (HPAG1_0813), and a DNA-binding histone-like protein HU, respectively (jhp0228). These novel biomarkers can be used for development of diagnostic assays predicting the evolution to gastric cancer in H. pylori-infected patients.

Duodenal ulcer-related antigens from Helicobacter pylori: immunoproteome and protein microarray approaches

Helicobacter pylori is an important risk factor of duodenal ulcer (DU). Although many virulence factors of H. pylori have been identified, few have been reported to show an association with the pathogenesis of DU. The aims of this study were to identify H. pylori antigens showing a high seropositivity in DU and to develop a platform for rapid and easy diagnosis for DU. Because DU and gastric cancer (GC) are considered clinical divergent gastroduodenal diseases, we compared two-dimensional immunoblots of an acid-glycine extract of an H. pylori strain from a patient with DU probed with serum samples from 10 patients with DU and 10 with GC to identify DU-related antigens. Of the 11 proteins that were strongly recognized by serum IgG from DU patients, translation elongation factor EF-G (FusA), catalase (KatA), and urease alpha subunit (UreA) were identified as DU-related antigens, showing a higher seropositivity in DU samples (n = 124) than in GC samples (n = 95) (FusA, 70.2 versus 45.3%; KatA, 50.8 versus 41.1%; UreA, 44.4 versus 27.4%). In addition, we found that the use of multiple antigens improved the discrimination between patients with DU and those with GC as the odds ratios increased from 1.82 (95% confidence interval (CI), 0.79-4.21; p = 0.1607) for seropositivity for FusA, KatA, or UreA alone to 4.95 (95% CI, 2.05-12.0; p = 0.0004) for two of the three antigens and to 5.71 (95% CI, 1.86-17.6; p = 0.0024) for all three antigens. Moreover a protein array containing the three DU-related antigens was developed to test the idea of using multiple biomarkers in diagnosis. We conclude that FusA, KatA, and UreA are DU-related antigens of H. pylori, and the combination of these on a protein array provided a rapid and convenient method for detecting serum antibody patterns of DU patients.

TLR4-dependent NF-kappaB activation and mitogen- and stress-activated protein kinase 1-triggered phosphorylation events are central to Helicobacter pylori peptidyl prolyl cis-, trans-isomerase (HP0175)-mediated induction of IL-6 release from macrophages

Helicobacter pylori infection is associated with the local production of chemokines and cytokines, of which IL-6 is overexpressed at the margin of gastric ulcer in H. pylori-positive gastritis. Cells of the monocytic lineage are the major sources of IL-6, and mononuclear cell infiltration in the lamina propria is characteristic of H. pylori-induced chronic infection. Our study shows for the first time that a secreted peptidyl prolyl cis-, trans-isomerase, HP0175 elicits IL-6 gene expression and IL-6 release from macrophages. An isogenic strain inactivated in the HP0175 gene (knockout) was attenuated in its IL-6-inducing ability, which was restored after complementation with the HP0175 gene. The specificity of the HP0175-induced effect was confirmed by the fact that rHP0175 purified from HEK293 cells could also induce IL-6 release, ruling out the possibility that the observed effect was due to bacterial contaminants. HP0175 was capable of interacting directly with the extracellular domain of TLR4. HP0175-induced IL-6 gene expression was critically dependent on TLR4-dependent NF-kappaB and MAPK activation. TLR4/PI3K-dependent ERK1/2 and p38 MAPK signaling converged upon activation of mitogen- and stress-activated protein kinase 1 (MSK1). The central role of MSK1 was borne out by the fact that silencing of MSK1 expression abrogated HP0175-mediated NF-kappaB-dependent IL-6 gene transcription. MSK1 regulated the recruitment of p65 and phopho-Ser(10)-histone H3 to the IL-6 promoter. HP0175 therefore regulated IL-6 gene transcription through chromatin modification at the IL-6 promoter.

The secreted peptidyl prolyl cis,trans-isomerase HP0175 of Helicobacter pylori induces apoptosis of gastric epithelial cells in a TLR4- and apoptosis signal-regulating kinase 1-dependent manner

Apoptosis contributes to the pathology of gastric epithelial cell damage that characterizes Helicobacter pylori infection. The secreted peptidyl prolyl cis, trans-isomerase of H. pylori, HP0175 executed apoptosis of the gastric epithelial cell line AGS in a dose- and time-dependent manner. The effect of HP0175 was confirmed by generating an isogenic mutant of H. pylori disrupted in the HP0175 gene. The apoptosis-inducing ability of this mutant was impaired compared with that of the wild type. The effect of HP0175 was mediated through TLR4. Preincubation of the gastric epithelial cell line AGS with anti-TLR4 mAb inhibited apoptosis induced by HP0175. Downstream of TLR4, apoptosis signal-regulating kinase 1 activated MAPK p38, leading to the caspase 8-dependent cleavage of Bid, its translocation to the mitochondria, mitochondrial pore formation, cytochrome c release, and activation of caspases 9 and 3. We show for the first time that a secreted bacterial Ag with peptidyl prolyl cis,trans-isomerase activity signals through TLR4, and that this Ag executes gastric epithelial cell apoptosis through a signaling pathway in which TLR4 and apoptosis signal-regulating kinase 1 are central players.

Two-year follow-up of Helicobacter pylori infection in C57BL/6 and Balb/cA mice

Helicobacter pylori infection is associated with chronic gastritis, peptic ulcer disease, gastric adenocarcinoma and MALT lymphoma. We previously found high-grade lymphoma after 13 months' H. pylori infection in C57BL/6 mice. In this study we followed H. pylori infection by three different isolates in C57BL/6 and Balb/cA mice for 23 months. Six-week-old C57BL/6 and Balb/cA mice were infected with H. pylori strains 119p (CagA+, VacA+), SS1 (CagA+, VacA+) and G50 (CagA-, VacA-). Mice were followed at 2 weeks, 10 weeks and 23 months post-inoculation (p.i.) by culture, histopathology and serology. Strain G50 was only reisolated from mice 2 weeks p.i. There was no difference in colonization between strain 119p and SS1 at 10 weeks p.i., whereas SS1 gave 100% colonization versus 119p gave 50% 23 months p.i. Interestingly, the inflammation score was higher in mice infected with strain 119p than with SS1 10-week p.i., and there were lymphoepithelial lesions in mice infected with strain 119p and G50 but not with SS1 at 23 months post-infection. Eight mice infected with strains 119p and G50 developed gastric lymphoma (grade 5 and 4). One C57BL/6 mouse infected with strain 119p developed hepatocellular carcinoma after 23 months. Immunoblot showed specific bands of 26-33 kDa against H. pylori in infected mice, and two mice infected with strain SSI reacted with antibodies to the 120 kDa CagA toxin.

CONCLUSION

A reproducible animal model for H. pylori-induced lymphoma and possibly hepatocellular carcinoma is described. Strain diversity may lead to different outcomes of H. pylori infection.

Proteins released by Helicobacter pylori in vitro

Secretion of proteins by Helicobacter pylori may contribute to gastric inflammation and epithelial damage. An in vitro analysis was designed to identify proteins released by mechanisms other than nonspecific lysis. The radioactivity of proteins in the supernatant was compared with that of the intact organism by two-dimensional gel phosphorimaging following a 4-h pulse-chase. The ratio of the amount of UreB, a known cytoplasmic protein, in the supernatant to that in the pellet was found to be 0.25, and this was taken as an index of lysis during the experiments (n = 6). Ratios greater than that of UreB were used to distinguish proteins that were selectively released into the medium. Thus, proteins enriched more than 10-fold in the supernatant compared to UreB were identified by mass spectrometry. Sixteen such proteins were present in the supernatant: VacA; a conserved secreted protein (HP1286); putative peptidyl cis-trans isomerase (HP0175); six proteins encoded by HP0305, HP0231, HP0973, HP0721, HP0129, and HP0902; thioredoxin (HP1458); single-stranded-DNA-binding 12RNP2 precursor (HP0827); histone-like DNA-binding protein HU (HP0835); ribosomal protein L11 (HP1202); a putative outer membrane protein (HP1564); and outer membrane proteins Omp21 (HP0913) and Omp20 (HP0912). All except HP0902, thioredoxin, HP0827, HP0835, and HP1202 had a signal peptide. When nalidixic acid, a DNA synthesis inhibitor, was added to inhibit cell division but not protein synthesis, to decrease possible contamination due to outer membrane shedding, two outer membrane proteins (Omp21 and Omp20) disappeared from the supernatant, and the amount of VacA also decreased. Thus, 13 proteins were still enriched greater than 10-fold in the medium after nalidixic acid treatment, suggesting these were released specifically, possibly by secretion. These proteins may be implicated in H. pylori-induced effects on the gastric epithelium.