Taurine modulates host cell responses to Helicobacter pylori VacA toxin.

Colonization of the human stomach with Helicobacter pylori strains producing active forms of the secreted toxin VacA is associated with an increased risk of peptic ulcer disease and gastric cancer, compared with colonization with strains producing hypoactive forms of VacA. Previous studies have shown that active s1m1 forms of VacA cause cell vacuolation and mitochondrial dysfunction. In this study, we sought to define the cellular metabolic consequences of VacA intoxication. Untargeted metabolomic analyses revealed that several hundred metabolites were significantly altered in VacA-treated gastroduodenal cells (AGS and AZ-521) compared with control cells. Pathway analysis suggested that VacA caused alterations in taurine and hypotaurine metabolism. Treatment of cells with the purified active s1m1 form of VacA, but not hypoactive s2m1 or Δ6-27 VacA-mutant proteins (defective in membrane channel formation), caused reductions in intracellular taurine and hypotaurine concentrations. Supplementation of the tissue culture medium with taurine or hypotaurine protected AZ-521 cells against VacA-induced cell death. Untargeted global metabolomics of VacA-treated AZ-521 cells or AGS cells in the presence or absence of extracellular taurine showed that taurine was the main intracellular metabolite significantly altered by extracellular taurine supplementation. These results indicate that VacA causes alterations in cellular taurine metabolism and that repletion of taurine is sufficient to attenuate VacA-induced cell death. We discuss these results in the context of previous literature showing the important role of taurine in cell physiology and the pathophysiology or treatment of multiple pathologic conditions, including gastric ulcers, cardiovascular disease, malignancy, inflammatory diseases, and other aging-related disorders.

Identification of an Essential LolD-Like Protein in Helicobacter pylori.

The localization of lipoprotein (Lol) system is used by Gram-negative bacteria to export lipoproteins to the outer membrane. Lol proteins and models of how Lol transfers lipoproteins from the inner to the outer membrane have been extensively characterized in the model organism Escherichia coli, but in numerous bacterial species, lipoprotein synthesis and export pathways deviate from the E. coli paradigm. For example, in the human gastric bacterium Helicobacter pylori, a homolog of the E. coli outer membrane component LolB is not found, E. coli LolC and LolE correspond to a single inner membrane component (LolF), and a homolog of the E. coli cytoplasmic ATPase LolD has not been identified. In the present study, we sought to identify a LolD-like protein in H. pylori. We used affinity-purification mass spectrometry to identify interaction partners of the H. pylori ATP-binding cassette (ABC) family permease LolF and identified the ABC family ATP-binding protein HP0179 as its interaction partner. We engineered H. pylori to conditionally express HP0179 and showed that HP0179 and its conserved ATP binding and ATP hydrolysis motifs are essential for H. pylori growth. We then performed affinity purification-mass spectrometry using HP0179 as the bait and identified LolF as its interaction partner. These results indicate that H. pylori HP0179 is a LolD-like protein and provide a more complete understanding of lipoprotein localization processes in H. pylori, a bacterium in which the Lol system deviates from the E. coli paradigm. IMPORTANCE Lipoproteins are critical in Gram-negative-bacteria for cell surface assembly of LPS, insertion of outer membrane proteins, and sensing envelope stress. Lipoproteins also contribute to bacterial pathogenesis. For many of these functions, lipoproteins must localize to the Gram-negative outer membrane. Transporting lipoproteins to the outer membrane involves the Lol sorting pathway. Detailed analyses of the Lol pathway have been performed in the model organism Escherichia coli, but many bacteria utilize altered components or are missing essential components of the E. coli Lol pathway. Identifying a LolD-like protein in Helicobacter pylori is important to better understand the Lol pathway in diverse bacterial classes. This becomes particularly relevant as lipoprotein localization is targeted for antimicrobial development.

Role of the CagY antenna projection in Helicobacter pylori Cag type IV secretion system activity.

Helicobacter pylori strains containing the cag pathogenicity island (PAI) are associated with the development of gastric adenocarcinoma and peptic ulcer disease. The cag PAI encodes a secreted effector protein (CagA) and a type IV secretion system (Cag T4SS). Cag T4SS activity is required for the delivery of CagA and non-protein substrates into host cells. The Cag T4SS outer membrane core complex (OMCC) contains a channel-like domain formed by helix-loop-helix elements (antenna projections, AP) from 14 copies of the CagY protein (a VirB10 ortholog). Similar VirB10 antenna regions are present in T4SS OMCCs from multiple bacterial species and are predicted to span the outer membrane. In this study, we investigated the role of the CagY antenna region in Cag T4SS OMCC assembly and Cag T4SS function. An H. pylori mutant strain with deletion of the entire CagY AP (∆AP) retained the capacity to produce CagY and assemble an OMCC, but it lacked T4SS activity (CagA translocation and IL-8 induction in AGS gastric epithelial cells). In contrast, a mutant strain with Gly-Ser substitutions in the unstructured CagY AP loop retained Cag T4SS activity. Mutants containing CagY AP loops with shortened lengths were defective in CagA translocation and exhibited reduced IL-8-inducing activity compared to control strains. These data indicate that the CagY AP region is required for Cag T4SS activity and that Cag T4SS activity can be modulated by altering the length of the CagY AP unstructured loop.

Essential role of Helicobacter pylori apolipoprotein N-acyltransferase (Lnt) in stomach colonization.

Bacterial lipoproteins are post-translationally modified with acyl chains, anchoring these proteins to bacterial membranes. In Gram-negative bacteria, three enzymes complete the modifications. Lgt (which adds two acyl chains) and LspA (which removes the signal peptide) are essential. Lnt (which adds a third acyl chain) is not essential in certain bacteria including Francisella tularensis, Neisseria gonorrhoeae, and Acinetobacter baumannii. Deleting lnt results in mild to severe physiologic changes. We previously showed lnt is not essential for Helicobacter pylori growth in vitro. Here, the physiologic consequences of deleting lnt in H. pylori and the role of Lnt in the host response to H. pylori were examined using in vitro and in vivo models. Comparing wild-type, Δlnt, and complemented mutant H. pylori, no changes in growth rates or sensitivity to acid or antibiotics were observed. Since deleting lnt changes the number of acyl chains on lipoproteins and the number of acyl chains on lipoproteins impacts the innate immune response through Toll-like receptor 2 (TLR2) signaling, primary human gastric epithelial cells were treated with a purified lipoprotein from wild-type or lnt mutant H. pylori. Differential gene expression analysis indicated that lipoprotein from the lnt mutant induced a more robust TLR2 response. In a complementary approach, we infected wild-type and Tlr2-/- mice and found that both the wild-type and complemented mutant strains successfully colonized the animals. However, the lnt mutant strain was unable to colonize either mouse strain. These results show that lnt is essential for H. pylori colonization and identifies lipoprotein synthesis as a target for therapeutic intervention.

A Positively Selected fur-R88H Mutation Enhances Helicobacter pylori Fitness in a High-Salt Environment and Alters Fur-Dependent Regulation of Gene Expression.

Both Helicobacter pylori infection and a high-salt diet are risk factors for gastric cancer. We previously showed that a mutation in fur (encoding the ferric uptake regulator variant Fur-R88H) was positively selected in H. pylori strains isolated from experimentally infected Mongolian gerbils receiving a high-salt diet. In the present study, we report that continuous H. pylori growth in high-salt conditions in vitro also leads to positive selection of the fur-R88H mutation. Competition experiments with strains containing wild-type fur or fur-R88H, each labeled with unique nucleotide barcodes, showed that the fur-R88H mutation enhances H. pylori fitness under high-salt conditions but reduces H. pylori fitness under routine culture conditions. The fitness advantage of the fur-R88H mutant under high-salt conditions was abrogated by the addition of supplemental iron. To test the hypothesis that the fur-R88H mutation alters the regulatory properties of Fur, we compared the transcriptional profiles of strains containing wild-type fur or fur-R88H. Increased transcript levels of fecA2, which encodes a predicted TonB-dependent outer membrane transporter, were detected in the fur-R88H variant compared to those in the strain containing wild-type fur under both high-salt and routine conditions. Competition experiments showed that fecA2 contributes to H. pylori fitness under both high-salt and routine conditions. These results provide new insights into mechanisms by which the fur-R88H mutation confers a selective advantage to H. pylori in high-salt environments.

Positive Selection of Mutations in the Helicobacter pylori katA 5' Untranslated Region in a Mongolian Gerbil Model of Gastric Disease.

To evaluate potential effects of gastric inflammation on Helicobacter pylori diversification and evolution within the stomach, we experimentally infected Mongolian gerbils with an H. pylori strain in which Cag type IV secretion system (T4SS) activity is controlled by a TetR/tetO system. Gerbils infected with H. pylori under conditions in which Cag T4SS activity was derepressed had significantly higher levels of gastric inflammation than gerbils infected under conditions with repressed Cag T4SS activity. Mutations in the 5' untranslated region (UTR) of katA (encoding catalase) were detected in strains cultured from 8 of the 17 gerbils infected with Cag T4SS-active H. pylori and none of the strains from 17 gerbils infected with Cag T4SS-inactive H. pylori. Catalase enzymatic activity, steady-state katA transcript levels, and katA transcript stability were increased in strains with these single nucleotide polymorphisms (SNPs) compared to strains in which these SNPs were absent. Moreover, strains harboring these SNPs exhibited increased resistance to bactericidal effects of hydrogen peroxide, compared to control strains. Experimental introduction of the SNPs into the wild-type katA 5' UTR resulted in increased katA transcript stability, increased katA steady-state levels, and increased catalase enzymatic activity. Based on site-directed mutagenesis and modeling of RNA structure, increased katA transcript levels were correlated with higher predicted thermal stability of the katA 5' UTR secondary structure. These data suggest that high levels of gastric inflammation positively select for H. pylori strains producing increased levels of catalase, which may confer survival advantages to the bacteria in an inflammatory gastric environment.

Functional Properties of Oligomeric and Monomeric Forms of Helicobacter pylori VacA Toxin.

Helicobacter pylori VacA is a secreted toxin that assembles into water-soluble oligomeric structures and forms anion-selective membrane channels. Acidification of purified VacA enhances its activity in cell culture assays. Sites of protomer-protomer contact within VacA oligomers have been identified by cryoelectron microscopy, and in the current study, we validated several of these interactions by chemical cross-linking and mass spectrometry. We then mutated amino acids at these contact sites and analyzed the effects of the alterations on VacA oligomerization and activity. VacA proteins with amino acid charge reversals at interprotomer contact sites retained the capacity to assemble into water-soluble oligomers and retained cell-vacuolating activity. Introduction of paired cysteine substitutions at these sites resulted in formation of disulfide bonds between adjacent protomers. Negative-stain electron microscopy and single-particle two-dimensional class analysis revealed that wild-type VacA oligomers disassemble when exposed to acidic pH, whereas the mutant proteins with paired cysteine substitutions retain an oligomeric state at acidic pH. Acid-activated wild-type VacA caused vacuolation of cultured cells, whereas acid-activated mutant proteins with paired cysteine substitutions lacked cell-vacuolating activity. Treatment of these mutant proteins with both low pH and a reducing agent resulted in VacA binding to cells, VacA internalization, and cell vacuolation. Internalization of a nonoligomerizing mutant form of VacA by host cells was detected without a requirement for acid activation. Collectively, these results enhance our understanding of the molecular interactions required for VacA oligomerization and support a model in which toxin activity depends on interactions of monomeric VacA with host cells.

Enhanced Fitness of a Helicobacter pylori babA Mutant in a Murine Model.

Helicobacter pylori genomes encode over 60 predicted outer membrane proteins (OMPs). Several OMPs in the Hop family act as adhesins, but the functions of most Hop proteins are unknown. To identify hop mutant strains exhibiting differential fitness in vivo compared to in vitro, we used a genetic barcoding method that allowed us to track changes in the proportional abundance of H. pylori strains within a mixed population. We generated a library of hop mutant strains, each containing a unique nucleotide barcode, as well as a library of control strains, each containing a nucleotide barcode in an intergenic region predicted to be a neutral locus unrelated to bacterial fitness. We orogastrically inoculated each of the libraries into mice and analyzed compositional changes in the populations over time in vivo compared to changes detected in the populations during library passage in vitro. The control library proliferated as a relatively stable community in vitro, but there was a reduction in the population diversity of this library in vivo and marked variation in the dominant strains recovered from individual animals, consistent with the existence of a nonselective bottleneck in vivo. We did not identify any OMP mutants exhibiting fitness defects exclusively in vivo without corresponding fitness defects in vitro. Conversely, a babA mutant exhibited a strong fitness advantage in vivo but not in vitro. These findings, when taken together with results of other studies, suggest that production of BabA may have differential effects on H. pylori fitness depending on the environmental conditions.

Delineation of the pH-Responsive Regulon Controlled by the Helicobacter pylori ArsRS Two-Component System.

Helicobacter pylori encounters a wide range of pH within the human stomach. In a comparison of H. pylori cultured in vitro under neutral or acidic conditions, about 15% of genes are differentially expressed, and corresponding changes are detectable for many of the encoded proteins. The ArsRS two-component system (TCS), comprised of the sensor kinase ArsS and its cognate response regulator ArsR, has an important role in mediating pH-responsive changes in H. pylori gene expression. In this study, we sought to delineate the pH-responsive ArsRS regulon and further define the role of ArsR in pH-responsive gene expression. We compared H. pylori strains containing an intact ArsRS system with an arsS null mutant or strains containing site-specific mutations of a conserved aspartate residue (D52) in ArsR, which is phosphorylated in response to signals relayed by the cognate sensor kinase ArsS. We identified 178 genes that were pH-responsive in strains containing an intact ArsRS system but not in ΔarsS or arsR mutants. These constituents of the pH-responsive ArsRS regulon include genes involved in acid acclimatization (ureAB, amidases), oxidative stress responses (katA, sodB), transcriptional regulation related to iron or nickel homeostasis (fur, nikR), and genes encoding outer membrane proteins (including sabA, alpA, alpB, hopD [labA], and horA). When comparing H. pylori strains containing an intact ArsRS TCS with arsRS mutants, each cultured at neutral pH, relatively few genes are differentially expressed. Collectively, these data suggest that ArsRS-mediated gene regulation has an important role in H. pylori adaptation to changing pH conditions.

Functional Properties of Helicobacter pylori VacA Toxin m1 and m2 Variants.

Helicobacter pylori colonizes the gastric mucosa and secretes a pore-forming toxin (VacA). Two main types of VacA, m1 and m2, can be distinguished by phylogenetic analysis. Type m1 forms of VacA have been extensively studied, but there has been relatively little study of m2 forms. In this study, we generated H. pylori strains producing chimeric proteins in which VacA m1 segments of a parental strain were replaced by corresponding m2 sequences. In comparison to the parental m1 VacA protein, a chimeric protein (designated m2/m1) containing m2 sequences in the N-terminal portion of the m region was less potent in causing vacuolation of HeLa cells, AGS gastric cells, and AZ-521 duodenal cells and had reduced capacity to cause membrane depolarization or death of AZ-521 cells. Consistent with the observed differences in activity, the chimeric m2/m1 VacA protein bound to cells at reduced levels compared to the binding levels of the parental m1 protein. The presence of two strain-specific insertions or deletions within or adjacent to the m region did not influence toxin activity. Experiments with human gastric organoids grown as monolayers indicated that m1 and m2/m1 forms of VacA had similar cell-vacuolating activities. Interestingly, both forms of VacA bound preferentially to the basolateral surface of organoid monolayers and caused increased cell vacuolation when interacting with the basolateral surface compared to the apical surface. These data provide insights into functional correlates of sequence variation in the VacA midregion (m region).

Bacterial Energetic Requirements for Helicobacter pylori Cag Type IV Secretion System-Dependent Alterations in Gastric Epithelial Cells.

Helicobacter pylori colonizes the stomach in about half of the world's population. H. pylori strains containing the cag pathogenicity island (cag PAI) are associated with a higher risk of gastric adenocarcinoma or peptic ulcer disease than cag PAI-negative strains. The cag PAI encodes a type IV secretion system (T4SS) that mediates delivery of the CagA effector protein as well as nonprotein bacterial constituents into gastric epithelial cells. H. pylori-induced nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation and interleukin-8 (IL-8) secretion are attributed to T4SS-dependent delivery of lipopolysaccharide metabolites and peptidoglycan into host cells, and Toll-like receptor 9 (TLR9) activation is attributed to delivery of bacterial DNA. In this study, we analyzed the bacterial energetic requirements associated with these cellular alterations. Mutant strains lacking Cagα, Cagß, or CagE (putative ATPases corresponding to VirB11, VirD4, and VirB4 in prototypical T4SSs) were capable of T4SS core complex assembly but defective in CagA translocation into host cells. Thus, the three Cag ATPases are not functionally redundant. Cagα and CagE were required for H. pylori-induced NF-κB activation, IL-8 secretion, and TLR9 activation, but Cagß was dispensable for these responses. We identified putative ATP-binding motifs (Walker-A and Walker-B) in each of the ATPases and generated mutant strains in which these motifs were altered. Each of the Walker box mutant strains exhibited properties identical to those of the corresponding deletion mutant strains. These data suggest that Cag T4SS-dependent delivery of nonprotein bacterial constituents into host cells occurs through mechanisms different from those used for recruitment and delivery of CagA into host cells.

Role of a Stem-Loop Structure in Helicobacter pylori cagA Transcript Stability.

Helicobacter pylori CagA is a secreted effector protein that contributes to gastric carcinogenesis. Previous studies showed that there is variation among H. pylori strains in the steady-state levels of CagA and that a strain-specific motif downstream of the cagA transcriptional start site (the +59 motif) is associated with both high levels of CagA and premalignant gastric histology. The cagA 5' untranslated region contains a predicted stem-loop-forming structure adjacent to the +59 motif. In the current study, we investigated the effect of the +59 motif and the adjacent stem-loop on cagA transcript levels and cagA mRNA stability. Using site-directed mutagenesis, we found that mutations predicted to disrupt the stem-loop structure resulted in decreased steady-state levels of both the cagA transcript and the CagA protein. Additionally, these mutations resulted in a decreased cagA mRNA half-life. Mutagenesis of the +59 motif without altering the stem-loop structure resulted in reduced steady-state cagA transcript and CagA protein levels but did not affect cagA transcript stability. cagA transcript stability was not affected by increased sodium chloride concentrations, an environmental factor known to augment cagA transcript levels and CagA protein levels. These results indicate that both a predicted stem-loop structure and a strain-specific +59 motif in the cagA 5' untranslated region influence the levels of cagA expression.

The Myelin and Lymphocyte Protein MAL Is Required for Binding and Activity of Clostridium perfringens ε-Toxin.

Clostridium perfringens ε-toxin (ETX) is a potent pore-forming toxin responsible for a central nervous system (CNS) disease in ruminant animals with characteristics of blood-brain barrier (BBB) dysfunction and white matter injury. ETX has been proposed as a potential causative agent for Multiple Sclerosis (MS), a human disease that begins with BBB breakdown and injury to myelin forming cells of the CNS. The receptor for ETX is unknown. Here we show that both binding of ETX to mammalian cells and cytotoxicity requires the tetraspan proteolipid Myelin and Lymphocyte protein (MAL). While native Chinese Hamster Ovary (CHO) cells are resistant to ETX, exogenous expression of MAL in CHO cells confers both ETX binding and susceptibility to ETX-mediated cell death. Cells expressing rat MAL are ~100 times more sensitive to ETX than cells expressing similar levels of human MAL. Insertion of the FLAG sequence into the second extracellular loop of MAL abolishes ETX binding and cytotoxicity. ETX is known to bind specifically and with high affinity to intestinal epithelium, renal tubules, brain endothelial cells and myelin. We identify specific binding of ETX to these structures and additionally show binding to retinal microvasculature and the squamous epithelial cells of the sclera in wild-type mice. In contrast, there is a complete absence of ETX binding to tissues from MAL knockout (MAL-/-) mice. Furthermore, MAL-/- mice exhibit complete resistance to ETX at doses in excess of 1000 times the symptomatic dose for wild-type mice. We conclude that MAL is required for both ETX binding and cytotoxicity.

A Nonoligomerizing Mutant Form of Helicobacter pylori VacA Allows Structural Analysis of the p33 Domain.

Helicobacter pylori secretes a pore-forming VacA toxin that has structural features and activities substantially different from those of other known bacterial toxins. VacA can assemble into multiple types of water-soluble flower-shaped oligomeric structures, and most VacA activities are dependent on its capacity to oligomerize. The 88-kDa secreted VacA protein can undergo limited proteolysis to yield two domains, designated p33 and p55. The p33 domain is required for membrane channel formation and intracellular toxic activities, and the p55 domain has an important role in mediating VacA binding to cells. Previous studies showed that the p55 domain has a predominantly ß-helical structure, but no structural data are available for the p33 domain. We report here the purification and analysis of a nonoligomerizing mutant form of VacA secreted by H. pylori The nonoligomerizing 88-kDa mutant protein retains the capacity to enter host cells but lacks detectable toxic activity. Analysis of crystals formed by the monomeric protein reveals that the ß-helical structure of the p55 domain extends into the C-terminal portion of p33. Fitting the p88 structural model into an electron microscopy map of hexamers formed by wild-type VacA (predicted to be structurally similar to VacA membrane channels) reveals that p55 and the ß-helical segment of p33 localize to peripheral arms but do not occupy the central region of the hexamers. We propose that the amino-terminal portion of p33 is unstructured when VacA is in a monomeric form and that it undergoes a conformational change during oligomer assembly.

Role of connexin 43 in Helicobacter pylori VacA-induced cell death.

Helicobacter pylori colonizes the human stomach and confers an increased risk for the development of peptic ulceration, noncardia gastric adenocarcinoma, and gastric lymphoma. A secreted H. pylori toxin, VacA, can cause multiple alterations in gastric epithelial cells, including cell death. In this study, we sought to identify host cell factors that are required for VacA-induced cell death. To do this, we analyzed gene trap and short hairpin RNA (shRNA) libraries in AZ-521 human gastric epithelial cells and selected for VacA-resistant clones. Among the VacA-resistant clones, we identified multiple gene trap library clones and an shRNA library clone with disrupted expression of connexin 43 (Cx43) (also known as gap junction protein alpha 1 [GJA1]). Further experiments with Cx43-specific shRNAs confirmed that a reduction in Cx43 expression results in resistance to VacA-induced cell death. Immunofluorescence microscopy experiments indicated that VacA did not colocalize with Cx43. We detected production of the Cx43 protein in AZ-521 cells but not in AGS, HeLa, or RK-13 cells, and correspondingly, AZ-521 cells were the most susceptible to VacA-induced cell death. When Cx43 was expressed in HeLa cells, the cells became more susceptible to VacA. These results indicate that Cx43 is a host cell constituent that contributes to VacA-induced cell death and that variation among cell types in susceptibility to VacA-induced cell death is attributable at least in part to cell type-specific differences in Cx43 production.

Fatty acids of Helicobacter pylori lipoproteins CagT and Lpp20.

Bacterial lipoproteins are post-translationally modified by the addition of acyl chains that anchor the protein to bacterial membranes. This modification includes two ester-linked and one amide-linked acyl chain on lipoproteins from Gram-negative bacteria. Helicobacter pylori lipoproteins have important functions in pathogenesis (including delivering the CagA oncoprotein to mammalian cells) and are recognized by host innate and adaptive immune systems. The number and variety of acyl chains on lipoproteins impact the innate immune response through Toll-like receptor 2. The acyl chains added to lipoproteins are derived from membrane phospholipids. H. pylori membrane phospholipids have previously been shown to consist primarily of C14:0 and C19:0 cyclopropane-containing acyl chains. However, the acyl composition of H. pylori lipoproteins has not been determined. In this study, we characterized the acyl composition of two representative H. pylori lipoproteins, Lpp20 and CagT. Fatty acid methyl esters were prepared from both purified lipoproteins and analyzed by gas chromatography-mass spectrometry. For comparison, we also analyzed H. pylori phospholipids. Consistent with previous studies, we observed that the H. pylori phospholipids contain primarily C14:0 and C19:0 cyclopropane-containing fatty acids. In contrast, both the ester-linked and amide-linked fatty acids found in H. pylori lipoproteins were observed to be almost exclusively C16:0 and C18:0. A discrepancy between the acyl composition of membrane phospholipids and lipoproteins as reported here for H. pylori has been previously reported in other bacteria including Borrelia and Brucella. We discuss possible mechanisms.IMPORTANCEColonization of the stomach by Helicobacter pylori is an important risk factor in the development of gastric cancer, the third leading cause of cancer-related death worldwide. H. pylori persists in the stomach despite an immune response against the bacteria. Recognition of lipoproteins by TLR2 contributes to the innate immune response to H. pylori. However, the role of H. pylori lipoproteins in bacterial persistence is poorly understood. As the host response to lipoproteins depends on the acyl chain content, defining the acyl composition of H. pylori lipoproteins is an important step in characterizing how lipoproteins contribute to persistence.

Remodeling of the gastric environment in Helicobacter pylori-induced atrophic gastritis.

Helicobacter pylori colonization of the human stomach is a strong risk factor for gastric cancer. To investigate H. pylori-induced gastric molecular alterations, we used a Mongolian gerbil model of gastric carcinogenesis. Histologic evaluation revealed varying levels of atrophic gastritis (a premalignant condition characterized by parietal and chief cell loss) in H. pylori-infected animals, and transcriptional profiling revealed a loss of markers for these cell types. We then assessed the spatial distribution and relative abundance of proteins in the gastric tissues using imaging mass spectrometry and liquid chromatography with tandem mass spectrometry. We detected striking differences in the protein content of corpus and antrum tissues. Four hundred ninety-two proteins were preferentially localized to the corpus in uninfected animals. The abundance of 91 of these proteins was reduced in H. pylori-infected corpus tissues exhibiting atrophic gastritis compared with infected corpus tissues exhibiting non-atrophic gastritis or uninfected corpus tissues; these included numerous proteins with metabolic functions. Fifty proteins localized to the corpus in uninfected animals were diffusely delocalized throughout the stomach in infected tissues with atrophic gastritis; these included numerous proteins with roles in protein processing. The corresponding alterations were not detected in animals infected with a H. pylori ∆cagT mutant (lacking Cag type IV secretion system activity). These results indicate that H. pylori can cause loss of proteins normally localized to the gastric corpus as well as diffuse delocalization of corpus-specific proteins, resulting in marked changes in the normal gastric molecular partitioning into distinct corpus and antrum regions.IMPORTANCEA normal stomach is organized into distinct regions known as the corpus and antrum, which have different functions, cell types, and gland architectures. Previous studies have primarily used histologic methods to differentiate these regions and detect H. pylori-induced alterations leading to stomach cancer. In this study, we investigated H. pylori-induced gastric molecular alterations in a Mongolian gerbil model of carcinogenesis. We report the detection of numerous proteins that are preferentially localized to the gastric corpus but not the antrum in a normal stomach. We show that stomachs with H. pylori-induced atrophic gastritis (a precancerous condition characterized by the loss of specialized cell types) exhibit marked changes in the abundance and localization of proteins normally localized to the gastric corpus. These results provide new insights into H. pylori-induced gastric molecular alterations that are associated with the development of stomach cancer.

Helicobacter pylori exploits a unique repertoire of type IV secretion system components for pilus assembly at the bacteria-host cell interface.

Colonization of the human stomach by Helicobacter pylori is an important risk factor for development of gastric cancer. The H. pylori cag pathogenicity island (cag PAI) encodes components of a type IV secretion system (T4SS) that translocates the bacterial oncoprotein CagA into gastric epithelial cells, and CagL is a specialized component of the cag T4SS that binds the host receptor α5ß1 integrin. Here, we utilized a mass spectrometry-based approach to reveal co-purification of CagL, CagI (another integrin-binding protein), and CagH (a protein with weak sequence similarity to CagL). These three proteins are encoded by contiguous genes in the cag PAI, and are detectable on the bacterial surface. All three proteins are required for CagA translocation into host cells and H. pylori-induced IL-8 secretion by gastric epithelial cells; however, these proteins are not homologous to components of T4SSs in other bacterial species. Scanning electron microscopy analysis reveals that these proteins are involved in the formation of pili at the interface between H. pylori and gastric epithelial cells. ΔcagI and ΔcagL mutant strains fail to form pili, whereas a ΔcagH mutant strain exhibits a hyperpiliated phenotype and produces pili that are elongated and thickened compared to those of the wild-type strain. This suggests that pilus dimensions are regulated by CagH. A conserved C-terminal hexapeptide motif is present in CagH, CagI, and CagL. Deletion of these motifs results in abrogation of CagA translocation and IL-8 induction, and the C-terminal motifs of CagI and CagL are required for formation of pili. In summary, these results indicate that CagH, CagI, and CagL are components of a T4SS subassembly involved in pilus biogenesis, and highlight the important role played by unique constituents of the H. pylori cag T4SS.

Identification of amino acids important for binding of Clostridium perfringens epsilon toxin to host cells and to HAVCR1.

Clostridium perfringens epsilon toxin belongs to the aerolysin-like family of pore-forming toxins and is one of the most potent bacterial toxins known. The epsilon toxin causes fatal enterotoxemia in sheep, goats, and possibly humans. Evidence indicates that the toxin binds to protein receptors including hepatitis A virus cellular receptor 1 (HAVCR1), but the region of the toxin responsible for cell binding has not been identified. In the present study, we identify amino acids within the epsilon toxin important for this cell interaction. Site-specific mutagenesis was used to investigate the role of a surface-accessible cluster of aromatic amino acids, and purified mutant proteins were tested in a series of cell-culture assays to assess cytotoxic activity and cell binding. When added to cells, four mutant proteins (Etx-Y29E, Etx-Y30E, Etx-Y36E and Etx-Y196E) were severely impaired in their ability to not only kill host cells, but also in their ability to permeabilize the plasma membrane. Circular dichroism spectroscopy and thermal stability studies revealed that the wild-type and mutant proteins were similarly folded. Additional experiments revealed that these mutant proteins were defective in binding to host cells and to HAVCR1. These data indicate that an amino acid motif including Y29, Y30, Y36, and Y196 is important for the ability of epsilon toxin to interact with cells and HAVCR1.

The intermediate region of Helicobacter pylori VacA is a determinant of toxin potency in a Jurkat T cell assay.

Colonization of the human stomach with Helicobacter pylori is a risk factor for peptic ulceration, noncardia gastric adenocarcinoma, and gastric lymphoma. The secreted VacA toxin is an important H. pylori virulence factor that causes multiple alterations in gastric epithelial cells and T cells. Several families of vacA alleles have been described, and H. pylori strains containing certain vacA types (s1, i1, and m1) are associated with an increased risk of gastric disease, compared to strains containing other vacA types (s2, i2, and m2). Thus far, there has been relatively little study of the role of the VacA intermediate region (i-region) in toxin activity. In this study, we compared the ability of i1 and i2 forms of VacA to cause functional alterations in Jurkat cells. To do this, we manipulated the chromosomal vacA gene in two H. pylori strains to introduce alterations in the region encoding the VacA i-region. We did not detect any differences in the capacity of i1 and i2 forms of VacA to cause vacuolation of RK13 cells. In comparison to i1 forms of VacA, i2 forms of VacA had a diminished capacity to inhibit the activation of nuclear factor of activated T cells (NFAT) and suppress interleukin-2 (IL-2) production. Correspondingly, i2 forms of VacA bound to Jurkat cells less avidly than did i1 forms of VacA. These results indicate that the VacA i-region is an important determinant of VacA effects on human T cell function.