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The functional interplay of Helicobacter pylori factors with gastric epithelial cells induces a multi-step process in pathogenesis

Abstract

Infections with the human pathogen Helicobacter pylori (H. pylori) can lead to severe gastric diseases ranging from chronic gastritis and ulceration to neoplastic changes in the stomach. Development and progress of H. pylori-associated disorders are determined by multifarious bacterial factors. Many of them interact directly with host cells or require specific receptors, while others enter the host cytoplasm to derail cellular functions. Several adhesins (e.g. BabA, SabA, AlpA/B, or OipA) establish close contact with the gastric epithelium as an important first step in persistent colonization. Soluble H. pylori factors (e.g. urease, VacA, or HtrA) have been suggested to alter cell survival and intercellular adhesions. Via a type IV secretion system (T4SS), H. pylori also translocates the effector cytotoxin-associated gene A (CagA) and peptidoglycan directly into the host cytoplasm, where cancer- and inflammation-associated signal transduction pathways can be deregulated. Through these manifold possibilities of interaction with host cells, H. pylori interferes with the complex signal transduction networks in its host and mediates a multi-step pathogenesis.

Review

The interaction between pathogens and tissue- or organ-specific target cells in their host determines the establishment and development of infectious diseases. Therefore, pathogens must expose adapted, but specialized factors to overcome the host defense mechanisms at the tissue surface. In the digestive tract, the gastric mucosa is covered by a thick mucus layer protecting the epithelium from protein-lysing enzymes, gastric acid and finally chyme, which can also contain unwanted bacteria and pathogens. Forming this first effective barrier, epithelial cells show an apico-basolateral organization, which is primarily maintained by tight junctions, adherence junctions and a strictly regulated actin cytoskeleton [1, 2]. Functional tight junctions are crucial for the maintenance of epithelial polarity and cell-to-cell adhesion, and form a paracellular barrier that precludes the free passage of molecules. Tight junctions are composed of several types of transmembrane proteins (e.g. occludin, claudins, junctional adhesion molecules [JAMs]) that bind to cytoplasmic peripheral proteins (e.g. zonula occludens [ZO] protein-1, -2 and −3, cingulin or multi-PDZ protein-1 [MUPP1]) and link the transmembrane proteins to the actin cytoskeleton. Adherence junctions mediate intercellular adhesions between neighboring cells, control the actin cytoskeleton and, therefore, exhibit anti-tumor properties. They consist of the transmembrane protein E-cadherin that bridges adjacent epithelial cells with the intracellular actin cytoskeleton. This involves a signaling complex composed of β-catenin, p120-catenin, α-catenin and epithelial protein lost in neoplasm (EPLIN), which is recruited to the intracellular domain of E-cadherin. These dynamic intercellular junctions are crucial for the integrity of the gastric epithelium and protect against intruding pathogens [1, 2].

Helicobacter pylori (H. pylori) is a bacterial class-I carcinogen [3] that specifically colonizes the gastric epithelium of humans as a unique niche, where it can induce inflammatory disorders (e.g. ulceration, chronic gastritis, etc.) and malignant neoplastic diseases (mucosa-associated lymphoid tissue [MALT] lymphoma and gastric cancer) [4, 5]. To resist the hostile environment in the stomach, H. pylori has developed highly sophisticated mechanisms to establish life-long infections in the stomach if not therapeutically eradicated. This is why it is considered as one of the most successful bacterial pathogens. H. pylori induces gastritis in all infected patients, but only a minority of approximately 10-15% suffers from clinical symptoms. The reason for the different responses to H. pylori is not clearly understood, but many reports point to individual genetic susceptibilities of the host to H. pylori-associated disorders. Accordingly, genetic polymorphisms associated with an elevated risk for gastric cancer have been identified in genes encoding interleukins (e.g. IL-1β), tumor necrosis factor (TNF), cyclooxygenase-2 (COX2), and other host factors [6, 7]. Aside from host factors, H. pylori isolates harbor different patterns of genetic elements encoding for bacterial factors that are crucially involved in persistent colonization and pathogenesis. Some of these have already been defined as virulence factors [8], while others might serve as important niche and colonization determinants [9] or are still under investigation for their pathological relevance.

In the last three decades, remarkable progress has been made in the understanding of pathogenicity-related factors of H. pylori and their functional interaction with gastric epithelial cell components. These virulence-related factors are either secreted, membrane-associated, or translocated into the cytosol of host cells, where they can directly interfere with host cell functions (Figure 1). As a consequence of their different locations during the infection process, H. pylori is able to exploit a plurality of mechanisms to manipulate host cellular processes and to deregulate signaling cascades. The influence of H. pylori on these signaling pathways results in adherence, induction of proinflammatory responses through cytokine/chemokine release, apoptosis, proliferation, and a pronounced motogenic response as characterized in vitro. Taken together, these eventually result in persistent colonization, severe inflammation, disruption of the epithelial barrier function, and possibly gastric cancer (Figure 1). These effects originate from selective pathogen–host interactions, which have been summarized in this review to give a comprehensive overview of the large number of specialized bacterial factors and how H. pylori utilizes them to manipulate the gastric epithelium. Many of these factors act cooperatively, eventually leading to a complex scenario of pathogenesis-related signaling events.

Figure 1
figure 1

Cellular responses to H. pylori upon colonization of a polarized epithelium. H. pylori expresses membrane-bound factors, secretes factors and exploits a type IV secretion system (T4SS) to inject effectors. These contribute to adhesion or induce signal transduction pathways leading to the induction of proinflammatory cytokine release, apoptosis, cell motility or proliferation. This network of diverse signaling pathways and cellular responses are involved in the establishment of persistent infection, inflammation and disruption of the epithelial polarity and integrity contributing to the development of gastritis, ulceration and gastric malignancies.

Membrane-associated factors: adhesins and beyond

Despite gastric peristalsis and transportation of chyme, H. pylori establishes a strong interaction with epithelial cells. In fact, adhesion of H. pylori is considered to be the first important step in pathogenesis in the stomach. The large group of outer membrane proteins (OMPs) contains some adhesins (e.g. blood-group-antigen-binding adhesin [BabA], sialic acid binding adhesin [SabA], adherence-associated lipoprotein A and B [AlpA/B], and outer inflammatory protein A [OipA]) that mediate binding of H. pylori to the host cell membrane, and other factors (e.g. lipopolysaccharide [LPS] and flagellin) that are able to trigger inflammatory responses in host tissues (Figure 2a).

Figure 2
figure 2

Model of H. pylori factors interacting with host cells. (a) At the apical side of the polarized epithelium H. pylori establishes the first adherence. SabA, BabA, AlpA/B, OipA, HopZ, HorB, etc. are considered as important adhesins that bind to host cell receptors (e.g. Leb, sLex, laminin) and might contribute to NF-кB or MAPK signaling. (b) H. pylori secretes VacA, which forms pores in the host membranes and localizes to mitochondria where it can interfere with apoptosis-related processes. Furthermore, VacA might influence the cellular barrier function by affecting tight junctions; an effect which has also been proposed for soluble urease. Together with H. pylori-secreted HtrA, which directly cleaves the adherence junction molecule E-cadherin, H. pylori efficiently disrupts the epithelial barrier. The T4SS injects the bacterial factor CagA. At the apical side of polarized cells, CagA might translocate via phosphatidylserine and cholesterol. In the cytosol of H. pylori-infected cells, CagA exhibits inhibitory effects on VacA-mediated apoptosis and the integrity of tight and adherence junctions. HtrA-triggered E-cadherin cleavage might be enhanced through H. pylori-induced MMPs and could increase the destabilization of the adherence complex composed of intracellular β-catenin and p120-catenin. Disruption of the E-cadherin complex might contribute to tumor-associated target gene expression in the nucleus and/or to the regulation of the actin cytoskeleton during cell morphological changes and motility. (c) Integrins are expressed at the basolateral side of a polarized epithelium and could be contacted by the T4SS adhesin CagL upon disruption of the intercellular adhesions. CagA translocates across α5β1-integrins and becomes rapidly tyrosine phosphorylated. Phosphorylated CagA then deregulates signal transduction pathways, leading to alterations in gene expression, and strongly interferes with the cytoskeletal rearrangement, which is important for the motogenic response to H. pylori. Peptidoglycan is considered to be another effector that binds Nod1, thereby activating the NF-кB signaling pathways.

Although bacterial adherence is crucially important for H. pylori pathogenesis, data showing direct effects of the above adherence factors on signaling pathways are scarce. This indicates that canonical adhesins may not directly activate signaling, but rather mediate a tight interaction between H. pylori and the host target cell, probably paving the way for additional bacterial factors to interact with their cognate receptors. In addition to OMPs and adhesins, flagellin and LPS have been widely investigated to address their role in H. pylori pathogenesis. In general, flagellin and LPS are important factors in many other bacterial infections, but it is unclear to what extent both factors contribute to H. pylori-induced signaling events. In contrast to the flagellin of other bacterial pathogens, H. pylori flagellin has only a very low capacity to stimulate toll-like receptor 5 (TLR5)-dependent interleukin-8 (IL-8) release [10]. This has been confirmed by the finding that purified H. pylori flagellin is a poor ligand for TLR5 [11]. Little information is available on the effects of H. pylori LPS on epithelial cells, indicating a yet undefined role in the H. pylori-infected epithelium as well. However, it has been suggested that H. pylori LPS might be a TLR2 agonist in gastric MKN45 cells, contributing to the activation of nuclear factor kappa B (NF-кB) and chemokine expression independently of the canonical LPS receptor TLR4 [12]. However, several factors have been well established as H. pylori adhesins that have the potential to alter signal transduction pathways, either by binding directly to cell surface receptors or acting indirectly, bringing other bacterial factors in a position to interact with cell surface structures which normally lack the capacity for signal transduction.

Blood-group-antigen-binding adhesin (BabA)

H. pylori adhesion has been correlated with the presence of fucosylated blood group antigens [13] and the OMP BabA was subsequently identified as the first adhesin of H. pylori that binds to the fucosylated blood group 0 antigens Lewis B (Leb) and the related H1 on the epithelium [14]. However, the binding specificity of BabA to blood group 0 antigens is restricted to certain H. pylori strains, termed “specialist” strains, while BabA from “generalist” strains equally binds fucosylated blood group A antigens [15]. Recently, Globo H hexaglycosylceramide was suggested as an additional BabA binding partner that might play a role in the infection of non-secretor individuals [16]. Interestingly, specialist strains were found predominantly in South American countries, where the blood group 0 phenotype predominates in the local population. This adaptability in the binding specificity of BabA could be attributed to the loss of selective pressure on blood group A and B binding, rather than active selection of specialist strains, for binding affinities in specialist strains do not excel those of generalist strains [15]. The analysis of the genetic basis of BabA revealed two BabA loci (BabA1 and BabA2, of which BabA1 is not expressed [17]) and a closely related paralogous BabB locus [14]. It has been suggested that BabA expression is regulated via phase variation and recombination events with the BabB locus, as several studies have shown loss- and gain-of-function mutations in vitro and in vivo[14, 1820]. Additionally, the genetic configuration of the bab genes has been shown to correlate with preferential localization in the stomach and the BabA/B setting correlates with the highest risk for gastric cancer [21].

BabA-mediated adhesion of H. pylori to gastric epithelial cells might enhance CagA translocation and the induction of inflammation [22]. Furthermore, triple-positive clinical H. pylori isolates (BabA+, VacAs1+, CagA+) show greater colonization densities, elevated levels of gastric inflammation and a higher incidence of intestinal metaplasia in H. pylori-infected patients as compared to VacAs1+, CagA+ double-positive variants [23]. Epidemiologically, triple-positive strains are correlated with the highest incidence of ulceration and gastric cancer [24].

Sialic acid-binding adhesin (SabA)

Independently of the adherence to fucosylated blood group antigens via BabA, H. pylori binds to sialic acid-modified glycosphingolipids, in particular sialyl-Lewis x/a (sLeX and sLea), via the bacterial adhesin SabA [25]. Interestingly, sLeX is absent in the healthy non-inflamed gastric mucosa, and therefore SabA-mediated adhesion becomes a relevant factor in bacterial persistence after successful colonization and establishment of inflammatory processes in the stomach [25]. Accordingly, Marcos and colleagues [26] were able to show that H. pylori-induced inflammation leads to elevated expression of the glycosyltransferase β3GnT5, which acts as an important factor in the biosynthesis of the sLeX antigen. The induction of β3GnT5 was dependent on tumor necrosis factor alpha (TNF-α), but not IL-8, and cells expressing ectopic β3GnT5 gave higher adhesion rates for SabA-positive H. pylori strains [26]. Like the situation with OipA and BabA, expression of SabA is subject to phase variation and gene conversion with its paralog SabB [27]. Additionally, acid-responsive signaling in H. pylori limits SabA transcription, which indicates that H. pylori adhesion is a dynamic and regulated process [28, 29].

Adherence-associated lipoprotein A and B (AlpA/B)

The OMPs AlpA and AlpB were initially described as proteins that facilitate binding of H. pylori to Kato-3 cells and the apical surface of gastric tissue sections [30, 31]. AlpA and AlpB share a high degree of homology and are co-transcribed from the same operon. Moreover, both proteins are necessary for H. pylori-mediated adhesion to gastric biopsies [31]. In contrast to other adhesins, AlpA and AlpB are not subjected to phase variation and virtually all clinical isolates express both Alp proteins [32, 33]. Importantly, deletion mutants lacking AlpA/B showed severe colonization defects in mouse and guinea pig animal models [33, 34]. In sharp contrast, a recent study in Mongolian gerbils suggests that AlpA/B-deficient strains lead to exuberant gastric inflammation, as compared to the isogenic gerbil-adapted wildtype strain [35]. The reason for these conflicting results in different experimental settings remains unclear.

Interestingly, Lu et al. described significant differences in the activation of signaling pathways (mitogen-activated protein kinases [MAPKs], c-Fos, and c-Jun-, cAMP response element-binding protein [CREB]-, activator protein-1 [AP-1]-, and NF-κB-related signaling) induced by H. pylori AlpA/B deletion mutants [33]. These data imply that AlpA/B-mediated adherence facilitates a stronger activation of certain signal transduction pathways. However, injection and phosphorylation of CagA, as well as IL-8 induction, were not significantly affected by AlpA/B deletion [36]. H. pylori has been shown to bind components of the extracellular matrix (ECM), especially collagen IV and laminin [37], which have been proposed as candidate host factors acting as receptors. In this context, AlpA/B has been implicated in the adhesion to laminin [35]. As one of the major components of the ECM, laminin binds to integrin; hence, it would be interesting to investigate whether AlpA/B can indirectly modulate integrin signaling through binding to laminin.

Outer inflammatory protein A (OipA)

OipA also belongs to the OMP group, and has been suggested to amplify IL-8 secretion via interferon-stimulated responsive element (ISRE) acting in parallel to the cag PAI-dependent mechanisms [38, 39]. This is in contrast to other re-complementation studies indicating that OipA primarily functions in H. pylori adhesion to host cells, while the IL-8 level remains unaffected [36, 40]. The reason for these opposing observations is not clear.

Yamaoka and co-workers have reported that the expression of functional OipA in H. pylori is phase-variable, and can be switched “on” or “off” by a slipped strand mispairing mechanism during chromosomal replication [39, 41, 42]. The OipA expression status is often associated with the presence of cag PAI, VacAs1, and VacAm1 allelic variants in western-type clinical isolates [40, 43, 44]. Therefore, it is difficult to provide relevant correlations between OipA status and clinical manifestation, for the OipA status does not seem to be completely independent of other disease-relevant genetic factors of the bacterium.

However, like other adhesins, OipA appears to be an important factor in the Mongolian gerbil infection model, since OipA-deficient strains failed to establish an infection and did not induce chronic inflammation and gastric metaplasia [45, 46]. To date, no specific receptor or surface molecule for OipA binding has been described.

Nevertheless, based on infections with an oipA deletion mutant, OipA has been suggested to induce phosphorylation of focal adhesion kinase (FAK), leading to downstream activation of the MAPKs extracellular signal-regulated kinases 1 and 2 (Erk1/2) and the formation of actin stress fibers [47]. Collectively, these data indicate a host cell receptor with the capability of transmitting signal transduction in response to OipA; hence, it would be interesting to investigate whether recombinant OipA can bind to a host cell receptor and induce FAK signaling. As implied by a genomic knock-out mutant, OipA-mediated FAK activation might be a consequence of altered epidermal growth factor receptor (EGFR) signaling [47, 48]. However, activation of EGFR has been convincingly shown to require a functional T4SS [49] and recombinant CagL alone is able to activate EGFR [50]. Additionally, an oipA-knock-out mutant of H. pylori was not able to trigger the EGFR signaling cascade involving phosphatidylinositide 3-kinases (PI3K) → phosphoinositide-dependent kinase-1 (PDK1) → Akt, which has been suggested to contribute to the regulation of FoxO forkhead transcription factor activity [51] and finally to the induction of IL-8 secretion [48]. In a recent study, it was proposed that EGFR/FAK/Akt signaling leads to phosphorylation of the focal adhesion protein paxillin, which then causes cytoskeletal reorganization and, subsequently, cell elongation [52].

In summary, OipA is an interesting H. pylori adhesion factor since it possibly interferes directly with signal transduction pathways that are predominantly activated by T4SS/CagA factors. This might indicate that OipA contributes to T4SS-dependent cellular responses, either through the direct activation of a yet unidentified receptor or indirectly through mediating tight adhesion between H. pylori and the host cell, leading to stronger T4SS/CagA-mediated signaling. In this context, it would be interesting to investigate whether the available oipA mutants still express fully functional T4SS pili.

Other putative adhesins

In addition to the well described group of adhesion molecules, several other factors have been implicated in H. pylori adhesion to the gastric mucosa. The phase-variable protein HopZ has been suggested to play a role in bacterial adhesion [53] and recent studies have been able to demonstrate a role in the early phase of colonization. Re-isolates from a healthy volunteer challenged with HopZ ‘off’ H. pylori showed a strong in vivo selection for the HopZ ‘on’ status [54]. Another report by Snelling and co-workers proposed an adhesion-related function for HorB [55]. As an additional OMP, HopQ might also have an influence on bacterial adhesion. In a subset of tested H. pylori strains, hopQ deletion increased H. pylori adherence to AGS cells and led to a hyperadherent phenotype and subsequently to increased CagA phosphorylation, while IL-8 induction was not affected [56]. Accordingly, HopQ significantly decreased CagA injection in co-infection experiments in gastric epithelial cells [57]. The question of whether HopQ interferes with the function of other adhesins in certain H. pylori strains is still to be answered. Hence, recent findings showing that a HopQ knock-out mutant in another H. pylori isolate did not affect bacterial adhesion are not necessarily contradictory. The expression of HopQ contributed to cag PAI-dependent signaling and CagA injection, as these could be restored through hopQ re-expression [58]. These data suggest that H. pylori adhesins might act in two ways, either in a cooperating or in a masking manner.

H. pylori-secreted urease, VacA and HtrA: priming factors in pathogenesis?

Secreted factors exhibit a high potential since they can act at the very beginning of microbial infections without requiring direct contact or adhesion to the host cells. In secretome analyses of H. pylori, a wide range of secreted or extracellular factors has been identified [5961]. Although most extracellular proteins from H. pylori remain largely uncharacterized, our knowledge of γ-glutamyl transpeptidase (GGT), H. pylori neutrophil-activating protein (HP-NAP), urease, vacuolating cytotoxin A (VacA), and high temperature requirement A (HtrA) is steadily increasing. For example, GGT has been identified in the soluble fraction of H. pylori[59], and has been shown to enhance colonization of mice [62]. Interestingly, recombinant GGT can induce apoptosis and cell cycle arrest in AGS cells [63, 64], but the molecular mechanism has not yet been elucidated. HP-NAP is a chemotactic factor of H. pylori that mainly attracts and activates neutrophils [65]; however, it does not play a prominent role during interactions with epithelial cells. Moreover, various direct effects of urease, VacA, and HtrA on gastric epithelial cells have been described, including induction of apoptosis and weakened integrity of intercellular adhesions (Figure 2b).

Urease

The urease complex has often been described as a surface-presented virulence factor of H. pylori. The primary function of the urease machinery is buffering the acidic pH by converting urea to CO2 and ammonia, which is required for neutralizing the gastric acid around the bacteria. It has long been assumed that urease is secreted or surface-localized and contributes significantly to H. pyloris ability to colonize and persist in the stomach, since it is actually considered to be an acid-sensitive bacterium [66]. The importance of urease for successful colonization has been highlighted in several studies [6668]; however, an individual report indicates that urease-negative H. pylori strains are still able to colonize Mongolian gerbils [69].

The various sequenced genomes of H. pylori contain a urease gene cluster, which consists of seven conserved genes (UreA–B and E–I). UreA and UreB represent the structural subunits of a Ni2+-dependent hexameric enzyme complex. UreE, UreF, UreG and UreH are accessory proteins involved in nickel incorporation and enzyme assembly. Together with arginase, UreI is responsible for a sustained supply of urea under acidic environmental conditions [70]. In contrast to the hypothesis of surface-localized urease, another current model assumes that the main urease activity resides in the bacterial cytoplasm [71].

Apart from its role in the successful colonization of H. pylori, urease might also indirectly interfere with host cell functions. Urease-dependent ammonia production contributes to the loss of tight junction integrity in the epithelium, as demonstrated by decreased trans-epithelial electric resistance (TEER) and enhanced occludin processing and internalization in in vitro cultures [72]. Apparently, disruption of the tight junction integrity was independent of VacA and CagA in these studies, which is in sharp contrast to previous reports [73, 74]. The effect of urease on tight junctions has been confirmed by another report showing that ureB deletion abrogates H. pyloris ability to disturb tight junctions as a CagA- or VacA-independent process. By regulating the myosin regulatory light chain kinase (MLCK) and Rho kinase, UreB expression seems to be required for phosphorylation of MLC [75]. Even if the detailed mechanism through which H. pylori urease activates this signaling pathway remains unclear, these data can explain how urease contributes to the inflammatory responses that accompany the disruption of the epithelial barrier.

Vacuolating cytotoxin A (VacA)

First evidence for a secreted vacuole-inducing toxin was found in experiments using filtrated H. pylori broth culture in 1988 [76]. This toxin was later identified as VacA [77, 78]. The cellular responses to VacA range from vacuolization and apoptosis to the inhibition of T cell functions [79, 80]. Due to these diverse cellular responses, VacA is considered to be a multifunctional toxin. However, in recent years it has become increasingly clear that most effects are due to the anion-channel function of VacA in multiple subcellular compartments and different cell types. Within the gene sequence, diversity of the signal sequence (allele types s1 or s2), intermediate region (allele types i1 or i2) and mid-region (allele types m1 or m2) has been observed [81, 82]. As a consequence of its mosaic gene structure, the VacA protein is very heterogeneous and exists in different variants with differing activities.

VacA is expressed as a 140 kDa protoxin with an N-terminal signal region, a central toxin-forming region of 88 kDa (p88), and a C-terminal autotransporter domain, which is required for secretion of the toxin [83]. Upon secretion, VacA is further processed into two subunits, termed VacAp33 and VacAp55 according to their respective molecular weight, which form membrane-spanning hexamers [84, 85]. It has been proposed that the VacAp55 domain is primarily responsible for target cell binding [86], while vacuolization requires a minimal sequence composed of the entire VacAp33 and the first ~100 amino acids of VacAp55[87, 88].

The precise mechanism of VacA entry into target cells is still divisive, reflected by the fact that several putative receptors have been described. Presented on epithelial cells, EGFR might serve as a potential candidate to bind VacA prior to its internalization [89, 90]. Further, receptor protein tyrosine phosphatases RPTPα [91] and RPTPβ [92] have been described as VacA receptors that promote VacA-dependent vacuolization. VacA binding to sphingomyelin in lipid rafts has also been shown to be an important event in VacA-mediated vacuolization [93]. In contrast to the induction of large vacuoles, VacA also promotes the formation of autophagosomes in gastric epithelial cells, which requires its channel-forming activity [94]. The low-density lipoprotein receptor-related protein-1 (LRP1) has been proposed to act as a receptor that interacts with VacA to promote autophagy and apoptosis [95]. Further putative host cell receptors for H. pylori VacA have been suggested; however, it remains uncertain whether they function as genuine receptors. Since it is not clear whether identified VacA receptors function independently of each other, the identification of such a diverse range of receptors implies a complex network of interactions and could explain the pleiotropic functions assigned to H. pylori VacA. In line with this assumption, purified and acid-activated VacA affected the transepithelial electrical resistance (TEER) of polarized epithelial cells [74], which is considered to be a strong indicator for the integrity of a polarized epithelial barrier. However, it is not known if this cellular phenotype requires a VacA receptor, although these reports indicate that VacA can exert very early effects during the multi-step infection by opening tight junctions and, consequentially, disrupting the epithelial barrier function.

It is well established that VacA is internalized and forms pores in membranes. This leads to an immense swelling, which consequently results in a vacuole-like phenotype of those organelles which harbor markers for both early and late endosomes [80]. In transfection experiments, the major consequence of VacA intoxication in gastric epithelial cells is clearly the induction of apoptosis in a mitochondria-dependent fashion [80]. A special hydrophobic N-terminal signal in VacAp33 subunit was identified in biochemical experiments that targets VacA to the inner mitochondrial membrane, where it also forms anion channels [96, 97]. However, the precise route of VacA trafficking from endosomes to the inner membrane of mitochondria is still unknown. A recent study has suggested an important role for the pro-apoptotic multi-domain proteins BAX and BAK (both members of the Bcl-2 family) in membrane trafficking after vacuolization [98]. In this study, it was shown that translocation of H. pylori VacA to mitochondria and the induction of apoptosis strongly depends on the channel function of VacA. This leads to recruitment of BAX and, in turn, close contact of the vacuoles and mitochondria, and consequently, to co-purification of otherwise compartment-restricted marker proteins [98]. From genomic VacA-deletion and re-complementation analyses, Jain and colleagues concluded that the induction of apoptosis is preceded by a dynamin-related protein 1 (Drp1)-dependent mitochondrial fission and BAX recruiting and activation [99]. In conclusion, VacA intoxication can severely interfere with membrane trafficking and consequently disintegrate mitochondrial stability, which finally leads to cytochrome C release and apoptosis [80]. In previous studies, the anion-channel function of VacA was suggested to disrupt the inner membrane potential of isolated mitochondria [100], yet in the light of these recent studies, it is questionable whether VacA-induced loss of membrane potential is key in the apoptosis-inducing process of cytochrome C release.

High temperature requirement A (HtrA)

In Escherichia coli, HtrA is a well-studied periplasmic chaperone and serine protease, and it has often been described as a bacterial factor contributing to the pathogenesis of a wide range of bacteria by increasing the viability of microbes under stress conditions [101]. Secretion of H. pylori HtrA was detected more than 10 years ago in comprehensive secretome analyses [60, 61]. In fact, H. pylori HtrA is highly stable under extreme acidic stress conditions, suggesting that it could contribute to the establishment of persistent infection in vivo[102]. Like HtrA proteases from other Gram-negative bacteria, H. pylori HtrA contains an N-terminal signal peptide, a serine protease domain with a highly conserved catalytic triad, and two PDZ (postsynaptic density protein [PSD95], Drosophila disc large tumor suppressor [Dlg1], and zonula occludens-1 protein [ZO-1]) domains. Although its extracellular localization has been determined, it was unknown for long time whether HtrA exhibits a functional role in H. pylori infections. The investigation of H. pylori HtrA function is limited by the fact that all attempts to create a deletion or a protease-inactive htra mutant in the genome of H. pylori have hitherto failed [103, 104].

Recently, a completely novel aspect of HtrA function has been discovered. It has been demonstrated that H. pylori HtrA is secreted into the extracellular space as an active serine protease [105] where it cleaves off the extracellular domain of the cell adhesion molecule and tumor suppressor E-cadherin [104]. Whether HtrA-mediated E-cadherin cleavage has an influence on the integrity and tumor-suppressive function of the intracellular E-cadherin signaling complex composed of β-catenin and p120 catenin is not yet known. Together with H. pylori-activated matrix-metalloproteases (MMPs) of the host cell [104, 106], several modes of shedding and modifying cell surface molecules are now known. Mechanistically, E-cadherin ectodomain shedding leads to a local disruption of adherence junctions of polarized gastric epithelial cells which allows bacterial entry into the intercellular space [104]. This is supported by the observation that intercellular H. pylori could actually be detected in biopsies of gastric cancer patients [107].

The ability of purified HtrA to cleave E-cadherin in vitro and on gastric epithelial cells has also been demonstrated for other pathogens of the gastro-intestinal tract, such as enteropathogenic E. coli (EPEC) [108], Shigella flexneri[108] and Campylobacter pylori[108, 109], but not for the urogenital pathogen Neisseria gonorrhoeae[108]. This indicates that HtrA-mediated E-cadherin cleavage is not unique to H. pylori, but might represent a more general mechanism to promote bacterial pathogenesis via bona fide virulence factors that requires transmigration across a polarized epithelium. The finding that HtrA cleaves E-cadherin supports the hypothesis that bacterial HtrA does not only indirectly influence microbial pathogenicity through improvement of bacterial fitness under stress conditions, but also exhibits direct effects on infected host cells.

The cag PAI type IV secretion system and effectors

Another group of H. pylori factors is translocated into the host cell cytoplasm via a type four secretion system (T4SS). As effectors, cytotoxin-associated gene A (CagA) and peptidoglycan have been described to alter and/or trigger host cell signaling. While CagA may primarily function in the regulation of cell morphology and polarity [110, 111], peptidoglycan has been described as a possible factor inducing nucleotide-binding oligomerization domain protein 1 (Nod1)-mediated NF-κB signaling (Figure 2c) [112, 113]. However, there are other models for the role of Nod1 in H. pylori infection [114].

The T4SS is encoded by the cag pathogenicity island (cag PAI), which carries—depending on the clinical isolate—about 30 genes encoding for proteins that are necessary for pilus formation and T4SS function. The known structural and functional aspects of the T4SS have been summarized in several excellent reviews [115117]. The current model of the T4SS involves structural core components forming a needle-shaped protrusion, which facilitates interaction with host-cell surface receptors and is indispensable for effector translocation into the host cell [115117]. A comprehensive knockout study of all individual cag PAI genes by Fischer et al. defined an essential cag PAI-encoded protein repertoire that is required for CagA translocation, and in addition, an overlapping, but different panel of proteins that is required for IL-8 induction [118]. To date, the detailed mechanism of CagA transmembrane transport remains unclear; nevertheless, several host cell interactions with T4SS pilus proteins have been characterized, as discussed below.

Interaction of the T4SS pilus with the cell membrane

In several in vitro studies, the interaction with β1-integrin has proven to be essential for CagA translocation [119, 120]. The first and best characterized T4SS-dependent host cell interaction occurs between CagL and the α5β1-integrin on gastric epithelial cells [120]. CagL is localized on the surface of T4SS pili and serves as an adhesin crucial for CagA translocation, phosphorylation and IL-8 induction [118, 120]. CagL harbors the classical integrin-activating Arg-Gly-Asp (RGD) motif, which is also found in natural integrin ligands like fibronectin or vitronectin [120, 121]. It has been suggested that CagL binding to β1-integrin leads to the activation of β1-integrin and, subsequently, to activation of several host kinases, including FAK, Src, EGFR and HER3 (heregulin receptor 3)/ErbB3 in an RGD-dependent manner [50, 120]. However, regulation of these signal transduction cascades might be more complex, since it has recently been proposed that a CagL/β5-integrin/ILK (integrin-linked kinase) stimulates EGFR → Raf → MAPK pathways independently of the RGD motif. In the same study, a weak interaction of CagL with the integrin β3-subunit was also observed, although no biological function has so far been described [122].

CagL binding to β1-integrin is necessary for the translocation of CagA [120]. In line with this, several other structural components of the T4SS pilus have been shown to bind to the β1-integrin subunit in Yeast-Two-Hybrid studies. These include CagI, CagY, and the translocated CagA itself, which are all thought to localize preferentially to the pilus surface and tip [119, 123].

Considering the in vivo localization of the α5β1-integrin at the basal side of the epithelium, which is not accessible prior to the disruption of the epithelial integrity, the idea of an omnipresent CagA injection was highly appealing. Murata-Kamiya and co-workers observed that CagA binding to phosphatidylserine is a prerequisite for CagA translocation across the apical membrane [124]. In addition, cholesterol also appears to be a crucial membrane component for CagA transport. Several studies indicate that H. pylori targets cholesterol-rich lipid rafts [125], and cholesterol depletion impairs CagA translocation [126]. Of note, lipid rafts also harbor the αVβ5 integrin complex [127]. However, no study has yet investigated the interplay of these putative entry mechanisms. Hence, it is conceivable that the above-mentioned molecules act in a cooperative fashion.

Another idea is that CagA is mainly translocated across the basolateral membrane of polarized cells, which is supported by the detection of tyrosine-phosphorylated CagA (CagApY) in basolaterally expressed β1-integrin-based focal adhesions [120]. These represent hotspots of tyrosine phosphorylation events in cultured cells, which are important for CagApY-dependent processes. In this context, the finding that the soluble H. pylori factors urease, VacA and finally HtrA can open tight junctions and adherence junctions supports this hypothesis, because H. pylori thereby directly disintegrates the polarized epithelium allowing direct contact between CagL and β1-integrin at the basolateral membrane of epithelial cells (Figure 2c).

Role of intracellular CagA in eukaryotic signaling

CagA is one of the most abundant H. pylori proteins and has been found to be translocated into several gastric and non-gastric cell lines upon infection (listed in: [110]). Once inside the cell, CagA becomes rapidly tyrosine phosphorylated in its C-terminally located Glu-Pro-Ile-Tyr-Ala (EPIYA) motifs by host cell kinases [128131]. CagL-β1-integrin interaction is required for CagA translocation; hence, tyrosine-phosphorylated CagApY is mainly localized in focal adhesions of cultured gastric epithelial cells along with CagA-phosphorylating kinases [120, 130]. CagApY exhibits pronounced effects on the cell morphology of gastric epithelial cells [132, 133], which putatively contribute to the disruption of the epithelial barrier in vivo. Depending on their surrounding sequence, the EPIYA motifs can be classified as EPIYA-A, EPIYA-B, EPIYA-C and EPIYA-D motifs. In western H. pylori strains, EPIYA-A, EPIYA-B, and varying numbers of EPIYA-C motifs have been found, whereas the combination of EPIYA-A and EPIYA-B with EPIYA-D motifs has been predominantly identified in East-Asian H. pylori isolates [134]. All types of EPIYA motifs can be phosphorylated, but not more than two simultaneously. Phosphorylation of EPIYA-C or EPIYA-D clearly primes phosphorylation of EPIYA-A or EPIYA-B, indicating a strict regulation of EPIYA motif phosphorylation, similar to what we know of tyrosine phosphorylation of mammalian factors [135]. Among the Src family kinases (SFKs), c-Src, Fyn, Lyn and Yes have been shown to phosphorylate CagA [128, 129]. Recently, it was found that SFKs target the EPIYA-C/D motif, but not EPIYA-A or EPIYA-B [135].

SFKs and FAK become rapidly inactivated via a negative feed-back loop, which comprises binding of CagApY to SHP-2 and/or Csk (C-terminal Src kinase) [136138]. The inactivation of SFKs then leads to the tyrosine dephosphorylation of ezrin, vinculin and cortactin, which are all important structural proteins in the regulation of the actin cytoskeleton [136, 139, 140]. Cortactin is also a substrate for Src, ERK, and PAK1, leading to a controlled phosphorylation pattern allowing regulated binding to FAK [141]. Although SFKs are inactive upon H. pylori infection, phosphorylation of CagA is maintained by c-Abl, which is obviously necessary for the functional activity of CagA in the cell morphological changes of cultured gastric epithelial cells [130, 131]. In contrast to SFKs, c-Abl can target EPIYA-A, EPIYA-B and EPIYA-C motifs [135].

The way in which translocated CagA and/or CagApY interfere with host cell functions has not been fully investigated. The idea that bacterial CagA might function as a eukaryotic signaling adaptor upon translocation has arisen from observations of a transgenic Drosophila model. In the absence of the Drosophila Grb2-associated binder (Gab) homolog Daughter of Sevenless (DOS), CagA restored photoreceptor development, supporting the hypothesis that CagA can mimic the function of Gab [142]. To date, more than 25 proteins have been identified as possible interaction partners of CagA (Table 1), although it remains unclear which of them bind directly or indirectly (listed in [143]). CagA binds to a subset of proteins (Par proteins, c-Met, E-cadherin, p120 catenin, ZO-1, etc.) that are well known regulators of cellular polarity and adhesion independently of its tyrosine phosphorylation [143]. Accordingly, CagA might directly target intercellular adhesions by disrupting tight [73] and adherence junctions [144].

Table 1 Overview of H. pylori factors that interfere with host cell functions

On the other hand, CagApY interacts with many SH2 domain-containing signaling molecules (c-Abl, Src, Crk proteins, Grb proteins, Shp proteins, etc.), which are important for the regulation of proliferation, cell scattering and morphology. Remarkably, a selectivity of the EPIYA-A, EPIYA-B and EPIYA-C/D motifs in binding of downstream targets has been detected [145]. The in vivo importance of CagA phosphorylation is highlighted in transgenic mice studies demonstrating that CagA has oncogenic potential and can lead to the development of gastrointestinal and hematological malignancies. The occurrence of these phenotypes was dependent upon intact EPIYA motifs, as phosphorylation-resistant mutants failed to develop disease in the same experimental settings [146]. Hence, it is tempting to speculate whether it might be possible to employ selective SH2-containing peptides as selective inhibitors of distinct signal transduction pathways. In summary, CagApY and the regulated activities of SFKs and c-Abl control a network of downstream signal transduction pathways leading to morphological changes and motility of cultured gastric epithelial cells [111, 147].

Interestingly, CagA and VacA functions antagonize each other in some experiments. VacA-induced apoptosis could be counteracted by both a phosphorylation-dependent and a phosphorylation-independent mechanism of injected CagA [148]. On the other hand, CagA-dependent cell elongation was decreased by VacA through inactivation of EGFR and HER2/Neu [149]. These studies underline the complex network of cellular effects which are induced by distinct bacterial factors.

Peptidoglycan

In addition to their important functions in forming H. pyloris cell shape and promoting colonization [150], peptidoglycans have also been described as H. pylori factors translocating into the cytoplasm of infected host cells where they bind to Nod1 in a T4SS-dependent manner [113]. Since it is well established that NF-κB activity is strictly T4SS-dependent, but CagA-independent [151], the finding of a T4SS-dependent intracellular peptidoglycan might add a piece to the puzzle of NF-κB regulation and could help to explain one possible upstream signal transduction pathway induced by H. pylori[112]. Nod1 might also influence the activity of AP-1 and MAPKs [152]. However, whether peptidoglycan prefers a T4SS-mediated translocation or transport across the membrane via outer membrane vesicles (OMVs) prior to NF-κB activation needs to be investigated in future studies [153].

Conclusions

H. pylori expresses a large number of bacterial factors allowing interaction and interference with its host in multiple ways. This is reflected by the diversity of molecules that are either presented on the bacterial surface, shed/secreted or internalized into host cells. However, less is known about the local and/or time-phased interplay of these factors, which might act simultaneously or at different times in different cellular localities. Furthermore, factors have been studied that obviously have an impact on this multi-step pathogenesis, while their cellular function is not yet understood. Duodenal ulcer promoting gene A (DupA), for instance, represents a very interesting factor, since expression of DupA is considered as a marker for developing duodenal ulcer and a reduced risk for gastric atrophy and cancer [154]. It induces proinflammatory cytokine secretion by mononuclear cells [155], but the molecular mechanism is completely unclear. This is just one example indicating the strong interest in unraveling the molecular and cellular mechanisms through which pathogens modulate host cell functions, since they represent attractive targets for novel compounds in the selective fight against pathogens.

References

  1. Wessler S, Backert S: Molecular mechanisms of epithelial-barrier disruption by Helicobacter pylori. Trends Microbiol. 2008, 16: 397-405.

    CAS  PubMed  Google Scholar 

  2. Wroblewski LE, Peek RM: Targeted disruption of the epithelial-barrier by Helicobacter pylori. Cell Commun Signal. 2011, 9: 29-

    PubMed Central  PubMed  Google Scholar 

  3. Schistosomes, liver flukes and Helicobacter pylori: IARC working group on the evaluation of carcinogenic risks to humans. Lyon, 7–14 June 1994. IARC Monogr Eval Carcinog Risks Hum. 1994, 61: 1-241.

    Google Scholar 

  4. Blaser MJ, Atherton JC: Helicobacter pylori persistence: biology and disease. J Clin Invest. 2004, 113: 321-333.

    CAS  PubMed Central  PubMed  Google Scholar 

  5. Peek RM, Crabtree JE: Helicobacter infection and gastric neoplasia. J Pathol. 2006, 208: 233-248.

    CAS  PubMed  Google Scholar 

  6. Machado JC, Figueiredo C, Canedo P, Pharoah P, Carvalho R, Nabais S, Castro Alves C, Campos ML, Van Doorn LJ, Caldas C, et al: A proinflammatory genetic profile increases the risk for chronic atrophic gastritis and gastric carcinoma. Gastroenterology. 2003, 125: 364-371.

    CAS  PubMed  Google Scholar 

  7. El-Omar EM, Carrington M, Chow WH, McColl KE, Bream JH, Young HA, Herrera J, Lissowska J, Yuan CC, Rothman N, et al: Interleukin-1 polymorphisms associated with increased risk of gastric cancer. Nature. 2000, 404: 398-402.

    CAS  PubMed  Google Scholar 

  8. Lu H, Yamaoka Y, Graham DY: Helicobacter pylori virulence factors: facts and fantasies. Curr Opin Gastroenterol. 2005, 21: 653-659.

    PubMed  Google Scholar 

  9. Hill C: Virulence or niche factors: what’s in a name?. J Bacteriol. 2012, 194: 5725-5727.

    CAS  PubMed Central  PubMed  Google Scholar 

  10. Lee SK, Stack A, Katzowitsch E, Aizawa SI, Suerbaum S, Josenhans C: Helicobacter pylori flagellins have very low intrinsic activity to stimulate human gastric epithelial cells via TLR5. Microbes Infect. 2003, 5: 1345-1356.

    CAS  PubMed  Google Scholar 

  11. Andersen-Nissen E, Smith KD, Strobe KL, Barrett SL, Cookson BT, Logan SM, Aderem A: Evasion of toll-like receptor 5 by flagellated bacteria. Proc Natl Acad Sci USA. 2005, 102: 9247-9252.

    CAS  PubMed Central  PubMed  Google Scholar 

  12. Smith MF, Mitchell A, Li G, Ding S, Fitzmaurice AM, Ryan K, Crowe S, Goldberg JB: Toll-like receptor (TLR) 2 and TLR5, but not TLR4, are required for Helicobacter pylori-induced NF-kappa B activation and chemokine expression by epithelial cells. J Biol Chem. 2003, 278: 32552-32560.

    CAS  PubMed  Google Scholar 

  13. Boren T, Falk P, Roth KA, Larson G, Normark S: Attachment of Helicobacter pylori to human gastric epithelium mediated by blood group antigens. Science. 1993, 262: 1892-1895.

    CAS  PubMed  Google Scholar 

  14. Ilver D, Arnqvist A, Ogren J, Frick IM, Kersulyte D, Incecik ET, Berg DE, Covacci A, Engstrand L, Boren T: Helicobacter pylori adhesin binding fucosylated histo-blood group antigens revealed by retagging. Science. 1998, 279: 373-377.

    CAS  PubMed  Google Scholar 

  15. Aspholm-Hurtig M, Dailide G, Lahmann M, Kalia A, Ilver D, Roche N, Vikstrom S, Sjostrom R, Linden S, Backstrom A, et al: Functional adaptation of BabA, the H. pylori ABO blood group antigen binding adhesin. Science. 2004, 305: 519-522.

    CAS  PubMed  Google Scholar 

  16. Benktander J, Ångström J, Breimer ME, Teneberg S: Redefinition of the carbohydrate binding specificity of helicobacter pylori BabA adhesin. J Biol Chem. 2012, 287: 31712-31724.

    CAS  PubMed Central  PubMed  Google Scholar 

  17. Yamaoka Y: Roles of helicobacter pylori BabA in gastroduodenal pathogenesis. World J Gastroenterol. 2008, 14: 4265-4272.

    CAS  PubMed Central  PubMed  Google Scholar 

  18. Backstrom A: Metastability of Helicobacter pylori bab adhesin genes and dynamics in Lewis b antigen binding. Proc Natl Acad Sci USA. 2004, 101: 16923-16928.

    PubMed Central  PubMed  Google Scholar 

  19. Solnick JV: Modification of Helicobacter pylori outer membrane protein expression during experimental infection of rhesus macaques. Proc Natl Acad Sci USA. 2004, 101: 2106-2111.

    CAS  PubMed Central  PubMed  Google Scholar 

  20. Styer CM, Hansen LM, Cooke CL, Gundersen AM, Choi SS, Berg DE, Benghezal M, Marshall BJ, Peek RM, Boren T, Solnick JV: Expression of the BabA adhesin during experimental infection with Helicobacter pylori. Infect Immun. 2010, 78: 1593-1600.

    CAS  PubMed Central  PubMed  Google Scholar 

  21. Sheu SM, Sheu BS, Chiang WC, Kao CY, Wu HM, Yang HB, Wu JJ: H. pylori clinical isolates have diverse babAB genotype distributions over different topographic sites of stomach with correlation to clinical disease outcomes. BMC Microbiol. 2012, 12: 89-

    CAS  PubMed Central  PubMed  Google Scholar 

  22. Ishijima N, Suzuki M, Ashida H, Ichikawa Y, Kanegae Y, Saito I, Borén T, Haas R, Sasakawa C, Mimuro H: BabA-mediated adherence is a potentiator of the helicobacter pylori type IV secretion system activity. J Biol Chem. 2011, 286: 25256-25264.

    CAS  PubMed Central  PubMed  Google Scholar 

  23. Rad R, Gerhard M, Lang R, Schoniger M, Rosch T, Schepp W, Becker I, Wagner H, Prinz C: The Helicobacter pylori blood group antigen-binding adhesin facilitates bacterial colonization and augments a nonspecific immune response. J Immunol. 2002, 168: 3033-3041.

    CAS  PubMed  Google Scholar 

  24. Gerhard M, Lehn N, Neumayer N, Boren T, Rad R, Schepp W, Miehlke S, Classen M, Prinz C: Clinical relevance of the Helicobacter pylori gene for blood-group antigen-binding adhesin. Proc Natl Acad Sci USA. 1999, 96: 12778-12783.

    CAS  PubMed Central  PubMed  Google Scholar 

  25. Mahdavi J, Sondén B, Hurtig M, Olfat FO, Forsberg L, Roche N, Ångström J, Larsson T, Teneberg S, Karlsson K-A, et al: Helicobacter pylori SabA adhesin in persistent infection and chronic inflammation. Science. 2002, 297: 573-578.

    CAS  PubMed Central  PubMed  Google Scholar 

  26. Marcos NT, Magalhaes A, Ferreira B, Oliveira MJ, Carvalho AS, Mendes N, Gilmartin T, Head SR, Figueiredo C, David L, et al: Helicobacter pylori induces beta3GnT5 in human gastric cell lines, modulating expression of the SabA ligand sialyl-Lewis x. J Clin Invest. 2008, 118: 2325-2336.

    CAS  PubMed Central  PubMed  Google Scholar 

  27. Talarico S, Whitefield SE, Fero J, Haas R, Salama NR: Regulation of Helicobacter pylori adherence by gene conversion. Mol Microbiol. 2012, 84: 1050-1061.

    CAS  PubMed Central  PubMed  Google Scholar 

  28. Goodwin AC, Weinberger DM, Ford CB, Nelson JC, Snider JD, Hall JD, Paules CI, Peek RM, Forsyth MH: Expression of the Helicobacter pylori adhesin SabA is controlled via phase variation and the ArsRS signal transduction system. Microbiology. 2008, 154: 2231-2240.

    CAS  PubMed Central  PubMed  Google Scholar 

  29. Sheu B-S, Odenbreit S, Hung K-H, Liu C-P, Sheu S-M, Yang H-B, Wu J-J: Interaction between host gastric sialyl-lewis X and H. Pylori SabA enhances H. Pylori density in patients lacking gastric Lewis B antigen. Am J Gastroenterol. 2006, 101: 36-44.

    CAS  PubMed  Google Scholar 

  30. Odenbreit S, Till M, Hofreuter D, Faller G, Haas R: Genetic and functional characterization of the alpAB gene locus essential for the adhesion of Helicobacter pylori to human gastric tissue. Mol Microbiol. 1999, 31: 1537-1548.

    CAS  PubMed  Google Scholar 

  31. Odenbreit S, Faller G, Haas R: Role of the AlpAB proteins and lipopolysaccharide in adhesion of Helicobacter pylori to human gastric tissue. Int J Med Microbiol. 2002, 292: 247-256.

    CAS  PubMed  Google Scholar 

  32. Odenbreit S, Swoboda K, Barwig I, Ruhl S, Borén T, Koletzko S, Haas R: Outer membrane protein expression profile in Helicobacter pylori clinical isolates. Infect Immun. 2009, 77: 3782-3790.

    CAS  PubMed Central  PubMed  Google Scholar 

  33. Lu H, Wu JY, Beswick EJ, Ohno T, Odenbreit S, Haas R, Reyes VE, Kita M, Graham DY, Yamaoka Y: Functional and intracellular signaling differences associated with the helicobacter pylori AlpAB adhesin from western and east Asian strains. J Biol Chem. 2007, 282: 6242-6254.

    CAS  PubMed Central  PubMed  Google Scholar 

  34. de Jonge R, Durrani Z, Rijpkema SG, Kuipers EJ, van Vliet AHM, Kusters JG: Role of the Helicobacter pylori outer-membrane proteins AlpA and AlpB in colonization of the guinea pig stomach. J Med Microbiol. 2004, 53: 375-379.

    CAS  PubMed  Google Scholar 

  35. Senkovich OA, Yin J, Ekshyyan V, Conant C, Traylor J, Adegboyega P, McGee DJ, Rhoads RE, Slepenkov S, Testerman TL: Helicobacter pylori AlpA and AlpB bind host laminin and influence gastric inflammation in gerbils. Infect Immun. 2011, 79: 3106-3116.

    CAS  PubMed Central  PubMed  Google Scholar 

  36. Odenbreit S, Kavermann H, Puls J, Haas R: CagA tyrosine phosphorylation and interleukin-8 induction by Helicobacter pylori are independent from alpAB, HopZ and bab group outer membrane proteins. Int J Med Microbiol. 2002, 292: 257-266.

    CAS  PubMed  Google Scholar 

  37. Trust TJ, Doig P, Emody L, Kienle Z, Wadstrom T, O’Toole P: High-affinity binding of the basement membrane proteins collagen type IV and laminin to the gastric pathogen Helicobacter pylori. Infect Immun. 1991, 59: 4398-4404.

    CAS  PubMed Central  PubMed  Google Scholar 

  38. Yamaoka Y, Kudo T, Lu H, Casola A, Brasier AR, Graham DY: Role of interferon-stimulated responsive element-like element in interleukin-8 promoter in Helicobacter pylori infection. Gastroenterology. 2004, 126: 1030-1043.

    CAS  PubMed  Google Scholar 

  39. Yamaoka Y, Kwon DH, Graham DY: A M(r) 34,000 proinflammatory outer membrane protein (oipA) of Helicobacter pylori. Proc Natl Acad Sci USA. 2000, 97: 7533-7538.

    CAS  PubMed Central  PubMed  Google Scholar 

  40. Dossumbekova A, Prinz C, Mages J, Lang R, Kusters JG, Van Vliet AHM, Reindl W, Backert S, Saur D, Schmid RM, Rad R: Helicobacter pylori HopH (OipA) and bacterial pathogenicity: genetic and functional Genomic analysis of hopH gene polymorphisms. J Infect Dis. 2006, 194: 1346-1355.

    CAS  PubMed  Google Scholar 

  41. Saunders NJ, Peden JF, Hood DW, Moxon ER: Simple sequence repeats in the Helicobacter pylori genome. Mol Microbiol. 1998, 27: 1091-1098.

    CAS  PubMed  Google Scholar 

  42. de Vries N, Duinsbergen D, Kuipers EJ, Pot RG, Wiesenekker P, Penn CW, van Vliet AH, Vandenbroucke-Grauls CM, Kusters JG: Transcriptional phase variation of a type III restriction-modification system in Helicobacter pylori. J Bacteriol. 2002, 184: 6615-6623.

    CAS  PubMed Central  PubMed  Google Scholar 

  43. Markovska R, Boyanova L, Yordanov D, Gergova G, Mitov I: Helicobacter pylori oipA genetic diversity and its associations with both disease and cagA, vacA s, m, and i alleles among Bulgarian patients. Diagn Microbiol Infect Dis. 2011, 71: 335-340.

    CAS  PubMed  Google Scholar 

  44. Ando T, Peek RM, Pride D, Levine SM, Takata T, Lee YC, Kusugami K, van der Ende A, Kuipers EJ, Kusters JG, Blaser MJ: Polymorphisms of Helicobacter pylori HP0638 reflect geographic origin and correlate with cagA status. J Clin Microbiol. 2002, 40: 239-246.

    CAS  PubMed Central  PubMed  Google Scholar 

  45. Sugimoto M, Ohno T, Graham DY, Yamaoka Y: Helicobacter pylori outer membrane proteins on gastric mucosal interleukin 6 and 11 expression in Mongolian gerbils. J Gastroenterol Hepatol. 2011, 26: 1677-1684.

    CAS  PubMed Central  PubMed  Google Scholar 

  46. Akanuma M, Maeda S, Ogura K, Mitsuno Y, Hirata Y, Ikenoue T, Otsuka M, Watanabe T, Yamaji Y, Yoshida H, et al: The evaluation of putative virulence factors of helicobacter pylori for gastroduodenal disease b Use of a short-term Mongolian gerbil infection model. J Infect Dis. 2002, 185: 341-347.

    CAS  PubMed  Google Scholar 

  47. Tabassam FH, Graham DY, Yamaoka Y: OipA plays a role in Helicobacter pylori-induced focal adhesion kinase activation and cytoskeletal re-organization. Cell Microbiol. 2008, 10: 1008-1020.

    CAS  PubMed Central  PubMed  Google Scholar 

  48. Tabassam FH, Graham DY, Yamaoka Y: Helicobacter pylori activate epidermal growth factor receptor- and phosphatidylinositol 3-OH kinase-dependent Akt and glycogen synthase kinase 3beta phosphorylation. Cell Microbiol. 2009, 11: 70-82.

    CAS  PubMed Central  PubMed  Google Scholar 

  49. Saha A, Backert S, Hammond CE, Gooz M, Smolka AJ: Helicobacter pylori CagL activates ADAM17 to induce repression of the gastric H, K-ATPase alpha subunit. Gastroenterology. 2010, 139: 239-248.

    CAS  PubMed Central  PubMed  Google Scholar 

  50. Tegtmeyer N, Hartig R, Delahay RM, Rohde M, Brandt S, Conradi J, Takahashi S, Smolka AJ, Sewald N, Backert S: A small fibronectin-mimicking protein from bacteria induces cell spreading and focal adhesion formation. J Biol Chem. 2010, 285: 23515-23526.

    CAS  PubMed Central  PubMed  Google Scholar 

  51. Tabassam FH, Graham DY, Yamaoka Y: Helicobacter pylori-associated regulation of forkhead transcription factors FoxO1/3a in human gastric cells. Helicobacter. 2012, 17: 193-202.

    CAS  PubMed Central  PubMed  Google Scholar 

  52. Tabassam FH, Graham DY, Yamaoka Y: Paxillin is a novel cellular target for converging Helicobacter pylori-induced cellular signaling. Am J Physiol Gastrointest Liver Physiol. 2011, 301: G601-G611.

    CAS  PubMed Central  PubMed  Google Scholar 

  53. Peck B, Ortkamp M, Diehl KD, Hundt E, Knapp B: Conservation, localization and expression of HopZ, a protein involved in adhesion of Helicobacter pylori. Nucleic Acids Res. 1999, 27: 3325-3333.

    CAS  PubMed Central  PubMed  Google Scholar 

  54. Kennemann L, Didelot X, Aebischer T, Kuhn S, Drescher B, Droege M, Reinhardt R, Correa P, Meyer TF, Josenhans C, et al: Helicobacter pylori genome evolution during human infection. Proc Natl Acad Sci USA. 2011, 108: 5033-5038.

    CAS  PubMed Central  PubMed  Google Scholar 

  55. Snelling WJ, Moran AP, Ryan KA, Scully P, McGourty K, Cooney JC, Annuk H, O’Toole PW: HorB (HP0127) is a gastric epithelial cell adhesin. Helicobacter. 2007, 12: 200-209.

    CAS  PubMed  Google Scholar 

  56. Loh JT, Torres VJ, Algood HM, McClain MS, Cover TL: Helicobacter pylori HopQ outer membrane protein attenuates bacterial adherence to gastric epithelial cells. FEMS Microbiol Lett. 2008, 289: 53-58.

    CAS  PubMed Central  PubMed  Google Scholar 

  57. Jimenez-Soto LF, Clausen S, Sprenger A, Ertl C, Haas R: Dynamics of the Cag-Type IV Secretion System of Helicobacter pylori as studied by bacterial co-infections. Cell Microbiol. 2013, Jul 11. doi: 10.1111/cmi.12166. [Epub ahead of print]

    Google Scholar 

  58. Belogolova E, Bauer B, Pompaiah M, Asakura H, Brinkman V, Ertl C, Bartfeld S, Nechitaylo TY, Haas R, Machuy N, et al: Helicobacter pylori outer membrane protein HopQ identified as a novel T4SS-associated virulence factor. Cell Microbiol. 2013, Jun 20. doi: 10.1111/cmi.12158. [Epub ahead of print]

    Google Scholar 

  59. Backert S, Kwok T, Schmid M, Selbach M, Moese S, Peek RM, Konig W, Meyer TF, Jungblut PR: Subproteomes of soluble and structure-bound Helicobacter pylori proteins analyzed by two-dimensional gel electrophoresis and mass spectrometry. Proteomics. 2005, 5: 1331-1345.

    CAS  PubMed  Google Scholar 

  60. Bumann D, Aksu S, Wendland M, Janek K, Zimny-Arndt U, Sabarth N, Meyer TF, Jungblut PR: Proteome analysis of secreted proteins of the gastric pathogen Helicobacter pylori. Infect Immun. 2002, 70: 3396-3403.

    CAS  PubMed Central  PubMed  Google Scholar 

  61. Smith TG, Lim JM, Weinberg MV, Wells L, Hoover TR: Direct analysis of the extracellular proteome from two strains of Helicobacter pylori. Proteomics. 2007, 7: 2240-2245.

    CAS  PubMed  Google Scholar 

  62. McGovern KJ, Blanchard TG, Gutierrez JA, Czinn SJ, Krakowka S, Youngman P: gamma-Glutamyltransferase is a Helicobacter pylori virulence factor but is not essential for colonization. Infect Immun. 2001, 69: 4168-4173.

    CAS  PubMed Central  PubMed  Google Scholar 

  63. Kim KM, Lee SG, Park MG, Song JY, Kang HL, Lee WK, Cho MJ, Rhee KH, Youn HS, Baik SC: Gamma-glutamyltranspeptidase of Helicobacter pylori induces mitochondria-mediated apoptosis in AGS cells. Biochem Biophys Res Commun. 2007, 355: 562-567.

    CAS  PubMed  Google Scholar 

  64. Kim KM, Lee SG, Kim JM, Kim DS, Song JY, Kang HL, Lee WK, Cho MJ, Rhee KH, Youn HS, Baik SC: Helicobacter pylori gamma-glutamyltranspeptidase induces cell cycle arrest at the G1-S phase transition. J Microbiol. 2010, 48: 372-377.

    CAS  PubMed  Google Scholar 

  65. D’Elios MM, Amedei A, Cappon A, Del Prete G, de Bernard M: The neutrophil-activating protein of Helicobacter pylori (HP-NAP) as an immune modulating agent. FEMS Immunol Med Microbiol. 2007, 50: 157-164.

    PubMed  Google Scholar 

  66. Eaton KA, Brooks CL, Morgan DR, Krakowka S: Essential role of urease in pathogenesis of gastritis induced by Helicobacter pylori in gnotobiotic piglets. Infect Immun. 1991, 59: 2470-2475.

    CAS  PubMed Central  PubMed  Google Scholar 

  67. Kavermann H, Burns BP, Angermuller K, Odenbreit S, Fischer W, Melchers K, Haas R: Identification and characterization of Helicobacter pylori genes essential for gastric colonization. J Exp Med. 2003, 197: 813-822.

    CAS  PubMed Central  PubMed  Google Scholar 

  68. Tsuda M, Karita M, Mizote T, Morshed MG, Okita K, Nakazawa T: Essential role of Helicobacter pylori urease in gastric colonization: definite proof using a urease-negative mutant constructed by gene replacement. Eur J Gastroenterol Hepatol. 1994, 6 (Suppl 1): S49-52.

    PubMed  Google Scholar 

  69. Mine T, Muraoka H, Saika T, Kobayashi I: Characteristics of a clinical isolate of urease-negative helicobacter pylori and its ability to induce gastric ulcers in Mongolian gerbils. Helicobacter. 2005, 10: 125-131.

    CAS  PubMed  Google Scholar 

  70. Zanotti G, Cendron L: Functional and structural aspects of Helicobacter pylori acidic stress response factors. IUBMB Life. 2010, 62: 715-723.

    CAS  PubMed  Google Scholar 

  71. Scott DR, Marcus EA, Weeks DL, Lee A, Melchers K, Sachs G: Expression of the Helicobacter pylori ureI gene is required for acidic pH activation of cytoplasmic urease. Infect Immun. 2000, 68: 470-477.

    CAS  PubMed Central  PubMed  Google Scholar 

  72. Lytton SD, Fischer W, Nagel W, Haas R, Beck FX: Production of ammonium by Helicobacter pylori mediates occludin processing and disruption of tight junctions in Caco-2 cells. Microbiology. 2005, 151: 3267-3276.

    CAS  PubMed  Google Scholar 

  73. Amieva MR, Vogelmann R, Covacci A, Tompkins LS, Nelson WJ, Falkow S: Disruption of the epithelial apical-junctional complex by Helicobacter pylori CagA. Science. 2003, 300: 1430-1434.

    CAS  PubMed Central  PubMed  Google Scholar 

  74. Papini E, Satin B, Norais N, de Bernard M, Telford JL, Rappuoli R, Montecucco C: Selective increase of the permeability of polarized epithelial cell monolayers by Helicobacter pylori vacuolating toxin. J Clin Invest. 1998, 102: 813-820.

    CAS  PubMed Central  PubMed  Google Scholar 

  75. Wroblewski LE, Shen L, Ogden S, Romero-Gallo J, Lapierre LA, Israel DA, Turner JR, Peek RM: Helicobacter pylori dysregulation of gastric epithelial tight junctions by urease-mediated myosin II activation. Gastroenterology. 2009, 136: 236-246.

    CAS  PubMed Central  PubMed  Google Scholar 

  76. Leunk RD, Johnson PT, David BC, Kraft WG, Morgan DR: Cytotoxic activity in broth-culture filtrates of Campylobacter pylori. J Med Microbiol. 1988, 26: 93-99.

    CAS  PubMed  Google Scholar 

  77. Cover TL, Blaser MJ: Purification and characterization of the vacuolating toxin from Helicobacter pylori. J Biol Chem. 1992, 267: 10570-10575.

    CAS  PubMed  Google Scholar 

  78. Catrenich CE, Chestnut MH: Character and origin of vacuoles induced in mammalian cells by the cytotoxin of Helicobacter pylori. J Med Microbiol. 1992, 37: 389-395.

    CAS  PubMed  Google Scholar 

  79. Cover TL, Blanke SR: Helicobacter pylori VacA, a paradigm for toxin multifunctionality. Nat Rev Microbiol. 2005, 3: 320-332.

    CAS  PubMed  Google Scholar 

  80. Rassow J: Helicobacter pylori vacuolating toxin A and apoptosis. Cell Commun Signal. 2011, 9: 26-

    CAS  PubMed Central  PubMed  Google Scholar 

  81. Atherton JC, Cao P, Peek RM, Tummuru MK, Blaser MJ, Cover TL: Mosaicism in vacuolating cytotoxin alleles of Helicobacter pylori. Association of specific vacA types with cytotoxin production and peptic ulceration. J Biol Chem. 1995, 270: 17771-17777.

    CAS  PubMed  Google Scholar 

  82. Rhead JL, Letley DP, Mohammadi M, Hussein N, Mohagheghi MA, Eshagh Hosseini M, Atherton JC: A new Helicobacter pylori vacuolating cytotoxin determinant, the intermediate region, is associated with gastric cancer. Gastroenterology. 2007, 133: 926-936.

    CAS  PubMed  Google Scholar 

  83. Sewald X, Fischer W, Haas R: Sticky socks: Helicobacter pylori VacA takes shape. Trends Microbiol. 2008, 16: 89-92.

    CAS  PubMed  Google Scholar 

  84. Czajkowsky DM, Iwamoto H, Cover TL, Shao Z: The vacuolating toxin from Helicobacter pylori forms hexameric pores in lipid bilayers at low pH. Proc Natl Acad Sci USA. 1999, 96: 2001-2006.

    CAS  PubMed Central  PubMed  Google Scholar 

  85. Iwamoto H, Czajkowsky DM, Cover TL, Szabo G, Shao Z: VacA from Helicobacter pylori: a hexameric chloride channel. FEBS Lett. 1999, 450: 101-104.

    CAS  PubMed  Google Scholar 

  86. Garner JA, Cover TL: Binding and internalization of the Helicobacter pylori vacuolating cytotoxin by epithelial cells. Infect Immun. 1996, 64: 4197-4203.

    CAS  PubMed Central  PubMed  Google Scholar 

  87. de Bernard M, Burroni D, Papini E, Rappuoli R, Telford J, Montecucco C: Identification of the Helicobacter pylori VacA toxin domain active in the cell cytosol. Infect Immun. 1998, 66: 6014-6016.

    CAS  PubMed Central  PubMed  Google Scholar 

  88. Ye D, Willhite DC, Blanke SR: Identification of the minimal intracellular vacuolating domain of the Helicobacter pylori vacuolating toxin. J Biol Chem. 1999, 274: 9277-9282.

    CAS  PubMed  Google Scholar 

  89. Pai R, Wyle FA, Cover TL, Itani RM, Domek MJ, Tarnawski AS: Helicobacter pylori culture supernatant interferes with epidermal growth factor-activated signal transduction in human gastric KATO III cells. Am J Pathol. 1998, 152: 1617-1624.

    CAS  PubMed Central  PubMed  Google Scholar 

  90. Seto K, Hayashi-Kuwabara Y, Yoneta T, Suda H, Tamaki H: Vacuolation induced by cytotoxin from Helicobacter pylori is mediated by the EGF receptor in HeLa cells. FEBS Lett. 1998, 431: 347-350.

    CAS  PubMed  Google Scholar 

  91. Yahiro K, Wada A, Nakayama M, Kimura T, Ogushi K, Niidome T, Aoyagi H, Yoshino K, Yonezawa K, Moss J, Hirayama T: Protein-tyrosine phosphatase alpha, RPTP alpha, is a Helicobacter pylori VacA receptor. J Biol Chem. 2003, 278: 19183-19189.

    CAS  PubMed  Google Scholar 

  92. Yahiro K, Niidome T, Kimura M, Hatakeyama T, Aoyagi H, Kurazono H, Imagawa K, Wada A, Moss J, Hirayama T: Activation of Helicobacter pylori VacA toxin by alkaline or acid conditions increases its binding to a 250-kDa receptor protein-tyrosine phosphatase beta. J Biol Chem. 1999, 274: 36693-36699.

    CAS  PubMed  Google Scholar 

  93. Gupta VR, Patel HK, Kostolansky SS, Ballivian RA, Eichberg J, Blanke SR: Sphingomyelin functions as a novel receptor for Helicobacter pylori VacA. PLoS Pathog. 2008, 4: e1000073-

    PubMed Central  PubMed  Google Scholar 

  94. Terebiznik MR, Raju D, Vazquez CL, Torbricki K, Kulkarni R, Blanke SR, Yoshimori T, Colombo MI, Jones NL: Effect of Helicobacter pylori’s vacuolating cytotoxin on the autophagy pathway in gastric epithelial cells. Autophagy. 2009, 5: 370-379.

    CAS  PubMed  Google Scholar 

  95. Yahiro K, Satoh M, Nakano M, Hisatsune J, Isomoto H, Sap J, Suzuki H, Nomura F, Noda M, Moss J, Hirayama T: Low-density lipoprotein receptor-related protein-1 (LRP1) mediates autophagy and apoptosis caused by Helicobacter pylori VacA. J Biol Chem. 2012, 287: 31104-31115.

    CAS  PubMed Central  PubMed  Google Scholar 

  96. Domanska G, Motz C, Meinecke M, Harsman A, Papatheodorou P, Reljic B, Dian-Lothrop EA, Galmiche A, Kepp O, Becker L, et al: Helicobacter pylori VacA toxin/subunit p34: targeting of an anion channel to the inner mitochondrial membrane. PLoS Pathog. 2010, 6: e1000878-

    PubMed Central  PubMed  Google Scholar 

  97. Galmiche A, Rassow J, Doye A, Cagnol S, Chambard JC, Contamin S, de Thillot V, Just I, Ricci V, Solcia E, et al: The N-terminal 34 kDa fragment of Helicobacter pylori vacuolating cytotoxin targets mitochondria and induces cytochrome c release. EMBO J. 2000, 19: 6361-6370.

    CAS  PubMed Central  PubMed  Google Scholar 

  98. Calore F, Genisset C, Casellato A, Rossato M, Codolo G, Esposti MD, Scorrano L, de Bernard M: Endosome-mitochondria juxtaposition during apoptosis induced by H. pylori VacA. Cell Death Differ. 2010, 17: 1707-1716.

    CAS  PubMed Central  PubMed  Google Scholar 

  99. Jain P, Luo ZQ, Blanke SR: Helicobacter pylori vacuolating cytotoxin A (VacA) engages the mitochondrial fission machinery to induce host cell death. Proc Natl Acad Sci USA. 2011, 108: 16032-16037.

    CAS  PubMed Central  PubMed  Google Scholar 

  100. Yamasaki E: Helicobacter pylori Vacuolating Cytotoxin Induces Activation of the Proapoptotic Proteins Bax and Bak, Leading to Cytochrome c Release and Cell Death, Independent of Vacuolation. J Biol Chem. 2006, 281: 11250-11259.

    CAS  PubMed  Google Scholar 

  101. Ingmer H, Brondsted L: Proteases in bacterial pathogenesis. Res Microbiol. 2009, 160: 704-710.

    CAS  PubMed  Google Scholar 

  102. Hoy B, Brandstetter H, Wessler S: The stability and activity of recombinant Helicobacter pylori HtrA under stress conditions. J Basic Microbiol. 2013, 53: 402-409.

    CAS  PubMed  Google Scholar 

  103. Salama NR, Shepherd B, Falkow S: Global transposon mutagenesis and essential gene analysis of Helicobacter pylori. J Bacteriol. 2004, 186: 7926-7935.

    CAS  PubMed Central  PubMed  Google Scholar 

  104. Hoy B, Lower M, Weydig C, Carra G, Tegtmeyer N, Geppert T, Schroder P, Sewald N, Backert S, Schneider G, Wessler S: Helicobacter pylori HtrA is a new secreted virulence factor that cleaves E-cadherin to disrupt intercellular adhesion. EMBO Rep. 2010, 11: 798-804.

    CAS  PubMed Central  PubMed  Google Scholar 

  105. Löwer M, Weydig C, Metzler D, Reuter A, Starzinski-Powitz A, Wessler S, Schneider G: Prediction of extracellular proteases of the human pathogen Helicobacter pylori reveals proteolytic activity of the Hp1018/19 protein HtrA. PLoS One. 2008, 3: e3510-

    PubMed Central  PubMed  Google Scholar 

  106. Schirrmeister W, Gnad T, Wex T, Higashiyama S, Wolke C, Naumann M, Lendeckel U: Ectodomain shedding of E-cadherin and c-Met is induced by Helicobacter pylori infection. Exp Cell Res. 2009, 315: 3500-3508.

    CAS  PubMed  Google Scholar 

  107. Necchi V, Candusso ME, Tava F, Luinetti O, Ventura U, Fiocca R, Ricci V, Solcia E: Intracellular, intercellular, and stromal invasion of gastric mucosa, preneoplastic lesions, and cancer by Helicobacter pylori. Gastroenterology. 2007, 132: 1009-1023.

    CAS  PubMed  Google Scholar 

  108. Hoy B, Geppert T, Boehm M, Reisen F, Plattner P, Gadermaier G, Sewald N, Ferreira F, Briza P, Schneider G, et al: Distinct roles of secreted HtrA proteases from gram-negative pathogens in cleaving the junctional protein and tumor suppressor E-cadherin. J Biol Chem. 2012, 287: 10115-10120.

    CAS  PubMed Central  PubMed  Google Scholar 

  109. Boehm M, Hoy B, Rohde M, Tegtmeyer N, Baek KT, Oyarzabal OA, Brondsted L, Wessler S, Backert S: Rapid paracellular transmigration of Campylobacter jejuni across polarized epithelial cells without affecting TER: role of proteolytic-active HtrA cleaving E-cadherin but not fibronectin. Gut Pathog. 2012, 4: 3-

    CAS  PubMed Central  PubMed  Google Scholar 

  110. Backert S, Clyne M, Tegtmeyer N: Molecular mechanisms of gastric epithelial cell adhesion and injection of CagA by Helicobacter pylori. Cell Commun Signal. 2011, 9: 28-

    CAS  PubMed Central  PubMed  Google Scholar 

  111. Wessler S, Gimona M, Rieder G: Regulation of the actin cytoskeleton in Helicobacter pylori-induced migration and invasive growth of gastric epithelial cells. Cell Commun Signal. 2011, 9: 27-

    CAS  PubMed Central  PubMed  Google Scholar 

  112. Backert S, Naumann M: What a disorder: proinflammatory signaling pathways induced by Helicobacter pylori. Trends Microbiol. 2010, 18: 479-486.

    CAS  PubMed  Google Scholar 

  113. Viala J, Chaput C, Boneca IG, Cardona A, Girardin SE, Moran AP, Athman R, Memet S, Huerre MR, Coyle AJ, et al: Nod1 responds to peptidoglycan delivered by the Helicobacter pylori cag pathogenicity island. Nat Immunol. 2004, 5: 1166-1174.

    CAS  PubMed  Google Scholar 

  114. Watanabe T, Asano N, Fichtner-Feigl S, Gorelick PL, Tsuji Y, Matsumoto Y, Chiba T, Fuss IJ, Kitani A, Strober W: NOD1 contributes to mouse host defense against Helicobacter pylori via induction of type I IFN and activation of the ISGF3 signaling pathway. J Clin Invest. 2010, 120: 1645-1662.

    CAS  PubMed Central  PubMed  Google Scholar 

  115. Terradot L, Waksman G: Architecture of the Helicobacter pylori Cag-type IV secretion system. FEBS J. 2011, 278: 1213-1222.

    CAS  PubMed  Google Scholar 

  116. Fischer W: Assembly and molecular mode of action of the Helicobacter pylori Cag type IV secretion apparatus. FEBS J. 2011, 278: 1203-1212.

    CAS  PubMed  Google Scholar 

  117. Backert S, Fronzes R, Waksman G: VirB2 and VirB5 proteins: specialized adhesins in bacterial type-IV secretion systems?. Trends Microbiol. 2008, 16: 409-413.

    CAS  PubMed  Google Scholar 

  118. Fischer W, Puls J, Buhrdorf R, Gebert B, Odenbreit S, Haas R: Systematic mutagenesis of the Helicobacter pylori cag pathogenicity island: essential genes for CagA translocation in host cells and induction of interleukin-8. Mol Microbiol. 2001, 42: 1337-1348.

    CAS  PubMed  Google Scholar 

  119. Jiménez-Soto LF, Kutter S, Sewald X, Ertl C, Weiss E, Kapp U, Rohde M, Pirch T, Jung K, Retta SF, et al: Helicobacter pylori Type IV Secretion Apparatus Exploits β1 Integrin in a Novel RGD-Independent Manner. PLoS Pathog. 2009, 5: e1000684-

    PubMed Central  PubMed  Google Scholar 

  120. Kwok T, Zabler D, Urman S, Rohde M, Hartig R, Wessler S, Misselwitz R, Berger J, Sewald N, Konig W, Backert S: Helicobacter exploits integrin for type IV secretion and kinase activation. Nature. 2007, 449: 862-866.

    CAS  PubMed  Google Scholar 

  121. Ruoslahti E: RGD and other recognition sequences for integrins. Ann Rev Cell Dev Biol. 1996, 12: 697-715.

    CAS  Google Scholar 

  122. Wiedemann T, Hofbaur S, Tegtmeyer N, Huber S, Sewald N, Wessler S, Backert S, Rieder G: Helicobacter pylori CagL dependent induction of gastrin expression via a novel αvβ5-integrin–integrin linked kinase signalling complex. Gut. 2012, 61: 986-996.

    CAS  PubMed  Google Scholar 

  123. Pham KT, Weiss E, Fischer W, Jimenez Soto LF, Breithaupt U, Haas R: CagI is an essential component of the Helicobacter pylori Cag type IV secretion system and forms a complex with CagL. PLoS One. 2012, 7: e35341-

    CAS  PubMed Central  PubMed  Google Scholar 

  124. Murata-Kamiya N, Kikuchi K, Hayashi T, Higashi H, Hatakeyama M: Helicobacter pylori exploits host membrane phosphatidylserine for delivery, localization, and pathophysiological action of the CagA Oncoprotein. Cell Host Microbe. 2010, 7: 399-411.

    CAS  PubMed  Google Scholar 

  125. Wunder C, Churin Y, Winau F, Warnecke D, Vieth M, Lindner B, Zahringer U, Mollenkopf HJ, Heinz E, Meyer TF: Cholesterol glucosylation promotes immune evasion by Helicobacter pylori. Nat Med. 2006, 12: 1030-1038.

    CAS  PubMed  Google Scholar 

  126. Lai CH, Chang YC, Du SY, Wang HJ, Kuo CH, Fang SH, Fu HW, Lin HH, Chiang AS, Wang WC: Cholesterol depletion reduces Helicobacter pylori CagA translocation and CagA-induced responses in AGS cells. Infect Immun. 2008, 76: 3293-3303.

    CAS  PubMed Central  PubMed  Google Scholar 

  127. Hutton ML, Kaparakis-Liaskos M, Turner L, Cardona A, Kwok T, Ferrero RL: Helicobacter pylori exploits cholesterol-rich microdomains for induction of NF-kappaB-dependent responses and peptidoglycan delivery in epithelial cells. Infect Immun. 2010, 78: 4523-4531.

    CAS  PubMed Central  PubMed  Google Scholar 

  128. Selbach M, Moese S, Hauck CR, Meyer TF, Backert S: Src is the kinase of the Helicobacter pylori CagA protein in vitro and in vivo. J Biol Chem. 2002, 277: 6775-6778.

    CAS  PubMed  Google Scholar 

  129. Stein M, Bagnoli F, Halenbeck R, Rappuoli R, Fantl WJ, Covacci A: c-Src/Lyn kinases activate Helicobacter pylori CagA through tyrosine phosphorylation of the EPIYA motifs. Mol Microbiol. 2002, 43: 971-980.

    CAS  PubMed  Google Scholar 

  130. Poppe M, Feller SM, Romer G, Wessler S: Phosphorylation of Helicobacter pylori CagA by c-Abl leads to cell motility. Oncogene. 2007, 26: 3462-3472.

    CAS  PubMed  Google Scholar 

  131. Tammer I, Brandt S, Hartig R, Konig W, Backert S: Activation of Abl by Helicobacter pylori: a novel kinase for CagA and crucial mediator of host cell scattering. Gastroenterology. 2007, 132: 1309-1319.

    CAS  PubMed  Google Scholar 

  132. Segal ED, Cha J, Lo J, Falkow S, Tompkins LS: Altered states: involvement of phosphorylated CagA in the induction of host cellular growth changes by Helicobacter pylori. Proc Natl Acad Sci USA. 1999, 96: 14559-14564.

    CAS  PubMed Central  PubMed  Google Scholar 

  133. Backert S, Moese S, Selbach M, Brinkmann V, Meyer TF: Phosphorylation of tyrosine 972 of the Helicobacter pylori CagA protein is essential for induction of a scattering phenotype in gastric epithelial cells. Mol Microbiol. 2001, 42: 631-644.

    CAS  PubMed  Google Scholar 

  134. Hatakeyama M: Linking epithelial polarity and carcinogenesis by multitasking Helicobacter pylori virulence factor CagA. Oncogene. 2008, 27: 7047-7054.

    CAS  PubMed  Google Scholar 

  135. Mueller D, Tegtmeyer N, Brandt S, Yamaoka Y, De Poire E, Sgouras D, Wessler S, Torres J, Smolka A, Backert S: c-Src and c-Abl kinases control hierarchic phosphorylation and function of the CagA effector protein in Western and East Asian Helicobacter pylori strains. J Clin Invest. 2012, 122: 1553-1566.

    CAS  PubMed Central  PubMed  Google Scholar 

  136. Selbach M, Moese S, Hurwitz R, Hauck CR, Meyer TF, Backert S: The Helicobacter pylori CagA protein induces cortactin dephosphorylation and actin rearrangement by c-Src inactivation. EMBO J. 2003, 22: 515-528.

    CAS  PubMed Central  PubMed  Google Scholar 

  137. Tsutsumi R, Higashi H, Higuchi M, Okada M, Hatakeyama M: Attenuation of Helicobacter pylori CagA x SHP-2 signaling by interaction between CagA and C-terminal Src kinase. J Biol Chem. 2003, 278: 3664-3670.

    CAS  PubMed  Google Scholar 

  138. Tsutsumi R, Takahashi A, Azuma T, Higashi H, Hatakeyama M: Focal adhesion kinase is a substrate and downstream effector of SHP-2 complexed with Helicobacter pylori CagA. Mol Cell Biol. 2006, 26: 261-276.

    CAS  PubMed Central  PubMed  Google Scholar 

  139. Moese S, Selbach M, Brinkmann V, Karlas A, Haimovich B, Backert S, Meyer TF: The Helicobacter pylori CagA protein disrupts matrix adhesion of gastric epithelial cells by dephosphorylation of vinculin. Cell Microbiol. 2007, 9: 1148-1161.

    CAS  PubMed  Google Scholar 

  140. Selbach M, Moese S, Backert S, Jungblut PR, Meyer TF: The Helicobacter pylori CagA protein induces tyrosine dephosphorylation of ezrin. Proteomics. 2004, 4: 2961-2968.

    CAS  PubMed  Google Scholar 

  141. Tegtmeyer N, Wittelsberger R, Hartig R, Wessler S, Martinez-Quiles N, Backert S: Serine phosphorylation of cortactin controls focal adhesion kinase activity and cell scattering induced by Helicobacter pylori. Cell Host Microbe. 2011, 9: 520-531.

    CAS  PubMed  Google Scholar 

  142. Botham CM, Wandler AM, Guillemin K: A transgenic Drosophila model demonstrates that the Helicobacter pylori CagA protein functions as a eukaryotic Gab adaptor. PLoS Pathog. 2008, 4: e1000064-

    PubMed Central  PubMed  Google Scholar 

  143. Backert S, Tegtmeyer N, Selbach M: The versatility of Helicobacter pylori CagA effector protein functions: the master key hypothesis. Helicobacter. 2010, 15: 163-176.

    CAS  PubMed  Google Scholar 

  144. Murata-Kamiya N, Kurashima Y, Teishikata Y, Yamahashi Y, Saito Y, Higashi H, Aburatani H, Akiyama T, Peek RM, Azuma T, Hatakeyama M: Helicobacter pylori CagA interacts with E-cadherin and deregulates the beta-catenin signal that promotes intestinal transdifferentiation in gastric epithelial cells. Oncogene. 2007, 26: 4617-4626.

    CAS  PubMed  Google Scholar 

  145. Selbach M, Paul FE, Brandt S, Guye P, Daumke O, Backert S, Dehio C, Mann M: Host cell interactome of tyrosine-phosphorylated bacterial proteins. Cell Host Microbe. 2009, 5: 397-403.

    CAS  PubMed  Google Scholar 

  146. Ohnishi N, Yuasa H, Tanaka S, Sawa H, Miura M, Matsui A, Higashi H, Musashi M, Iwabuchi K, Suzuki M, et al: Transgenic expression of Helicobacter pylori CagA induces gastrointestinal and hematopoietic neoplasms in mouse. Proc Natl Acad Sci. 2008, 105: 1003-1008.

    CAS  PubMed Central  PubMed  Google Scholar 

  147. Schneider S, Weydig C, Wessler S: Targeting focal adhesions: Helicobacter pylori-host communication in cell migration. Cell Commun Signal. 2008, 6: 2-

    PubMed Central  PubMed  Google Scholar 

  148. Oldani A, Cormont M, Hofman V, Chiozzi V, Oregioni O, Canonici A, Sciullo A, Sommi P, Fabbri A, Ricci V, Boquet P: Helicobacter pylori counteracts the apoptotic action of its VacA toxin by injecting the CagA protein into gastric epithelial cells. PLoS Pathog. 2009, 5: e1000603-

    PubMed Central  PubMed  Google Scholar 

  149. Tegtmeyer N, Zabler D, Schmidt D, Hartig R, Brandt S, Backert S: Importance of EGF receptor, HER2/Neu and Erk1/2 kinase signalling for host cell elongation and scattering induced by the Helicobacter pylori CagA protein: antagonistic effects of the vacuolating cytotoxin VacA. Cell Microbiol. 2009, 11: 488-505.

    CAS  PubMed  Google Scholar 

  150. Sycuro LK, Pincus Z, Gutierrez KD, Biboy J, Stern CA, Vollmer W, Salama NR: Peptidoglycan crosslinking relaxation promotes Helicobacter pylori’s helical shape and stomach colonization. Cell. 2010, 141: 822-833.

    CAS  PubMed Central  PubMed  Google Scholar 

  151. Schweitzer K, Sokolova O, Bozko PM, Naumann M: Helicobacter pylori induces NF-kappaB independent of CagA. EMBO Rep. 2010, 11: 10-11.

    CAS  PubMed Central  PubMed  Google Scholar 

  152. Allison CC, Kufer TA, Kremmer E, Kaparakis M, Ferrero RL: Helicobacter pylori induces MAPK phosphorylation and AP-1 activation via a NOD1-dependent mechanism. J Immunol. 2009, 183: 8099-8109.

    CAS  PubMed  Google Scholar 

  153. Kaparakis M, Turnbull L, Carneiro L, Firth S, Coleman HA, Parkington HC, Le Bourhis L, Karrar A, Viala J, Mak J, et al: Bacterial membrane vesicles deliver peptidoglycan to NOD1 in epithelial cells. Cell Microbiol. 2010, 12: 372-385.

    CAS  PubMed  Google Scholar 

  154. Lu H, Hsu PI, Graham DY, Yamaoka Y: Duodenal ulcer promoting gene of Helicobacter pylori. Gastroenterology. 2005, 128: 833-848.

    CAS  PubMed Central  PubMed  Google Scholar 

  155. Hussein NR, Argent RH, Marx CK, Patel SR, Robinson K, Atherton JC: Helicobacter pylori dupA is polymorphic, and its active form induces proinflammatory cytokine secretion by mononuclear cells. J Infect Dis. 2010, 202: 261-269.

    CAS  PubMed  Google Scholar 

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Acknowledgement

We apologize to all colleagues whose important works could not be cited here owing to space restrictions. We thank Catherine Haynes for critical reading of the manuscript. The work was supported by a grant from the Austrian Science Fund (FWF): P_24315 to SW.

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Posselt, G., Backert, S. & Wessler, S. The functional interplay of Helicobacter pylori factors with gastric epithelial cells induces a multi-step process in pathogenesis. Cell Commun Signal 11, 77 (2013). https://doi.org/10.1186/1478-811X-11-77

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