Cortactin-dependent control of Par1b-regulated epithelial cell polarity in Helicobacter infection.

Cell polarity is crucial for gastric mucosal barrier integrity and mainly regulated by polarity-regulating kinase partitioning-defective 1b (Par1b). During infection, the carcinogen Helicobacter pylori hijacks Par1b via the bacterial oncoprotein CagA leading to loss of cell polarity, but the precise molecular mechanism is not fully clear. Here we discovered a novel function of the actin-binding protein cortactin in regulating Par1b, which forms a complex with cortactin and the tight junction protein zona occludens-1 (ZO-1). We found that serine phosphorylation at S405/418 and the SH3 domain of cortactin are important for its interaction with both Par1b and ZO-1. Cortactin knockout cells displayed disturbed Par1b cellular localization and exhibited morphological abnormalities that largely compromised transepithelial electrical resistance, epithelial cell polarity, and apical microvilli. H. pylori infection promoted cortactin/Par1b/ZO-1 abnormal interactions in the tight junctions in a CagA-dependent manner. Infection of human gastric organoid-derived mucosoids supported these observations. We therefore hypothesize that CagA disrupts gastric epithelial cell polarity by hijacking cortactin, and thus Par1b and ZO-1, suggesting a new signaling pathway for the development of gastric cancer by Helicobacter.

Cancer-associated SNPs in bacteria: lessons from Helicobacter pylori.

Several single-nucleotide polymorphisms (SNPs) in human chromosomes are known to predispose to cancer. However, cancer-associated SNPs in bacterial pathogens were unknown until discovered in the stomach pathogen Helicobacter pylori. Those include an alanine-threonine polymorphism in the EPIYA-B phosphorylation motif of the injected effector protein CagA that affects cancer risk by modifying inflammatory responses and loss of host cell polarity. A serine-to-leucine change in serine protease HtrA is associated with boosted proteolytic cleavage of epithelial junction proteins and introduction of DNA double-strand breaks (DSBs) in host chromosomes, which co-operatively elicit malignant alterations. In addition, H. pylori genome-wide association studies (GWAS) identified several other SNPs potentially associated with increased gastric cancer (GC) risk. Here we discuss the clinical importance, evolutionary origin, and functional advantage of the H. pylori SNPs. These exciting new data highlight cancer-associated SNPs in bacteria, which should be explored in more detail in future studies.

Campylobacter jejuni Surface-Bound Protease HtrA, but Not the Secreted Protease nor Protease in Shed Membrane Vesicles, Disrupts Epithelial Cell-to-Cell Junctions.

Fundamental functions of the intestinal epithelium include the digestion of food, absorption of nutrients, and its ability to act as the first barrier against intruding microbes. Campylobacter jejuni is a major zoonotic pathogen accounting for a substantial portion of bacterial foodborne illnesses. The germ colonizes the intestines of birds and is mainly transmitted to humans through the consumption of contaminated poultry meat. In the human gastrointestinal tract, the bacterium triggers campylobacteriosis that can progress to serious secondary disorders, including reactive arthritis, inflammatory bowel disease and Guillain-Barré syndrome. We recently discovered that C. jejuni serine protease HtrA disrupts intestinal epithelial barrier functions via cleavage of the tight and adherens junction components occludin, claudin-8 and E-cadherin. However, it is unknown whether epithelial damage is mediated by the secreted soluble enzyme, by HtrA contained in shed outer-membrane vesicles (OMVs) or by another mechanism that has yet to be identified. In the present study, we investigated whether soluble recombinant HtrA and/or purified OMVs induce junctional damage to polarized intestinal epithelial cells compared to live C. jejuni bacteria. By using electron and confocal immunofluorescence microscopy, we show that HtrA-expressing C. jejuni bacteria trigger efficient junctional cell damage, but not soluble purified HtrA or HtrA-containing OMVs, not even at high concentrations far exceeding physiological levels. Instead, we found that only bacteria with active protein biosynthesis effectively cleave junctional proteins, which is followed by paracellular transmigration of C. jejuni through the epithelial cell layer. These findings shed new light on the pathogenic activities of HtrA and virulence strategies of C. jejuni.

A single-nucleotide polymorphism in Helicobacter pylori promotes gastric cancer development.

Single-nucleotide polymorphisms (SNPs) in various human genes are key factors in carcinogenesis. However, whether SNPs in bacterial pathogens are similarly crucial in cancer development is unknown. Here, we analyzed 1,043 genomes of the stomach pathogen Helicobacter pylori and pinpointed a SNP in the serine protease HtrA (position serine/leucine 171) that significantly correlates with gastric cancer. Our functional studies reveal that the 171S-to-171L mutation triggers HtrA trimer formation and enhances proteolytic activity and cleavage of epithelial junction proteins occludin and tumor-suppressor E-cadherin. 171L-type HtrA, but not 171S-HtrA-possessing H. pylori, inflicts severe epithelial damage, enhances injection of oncoprotein CagA into epithelial cells, increases NF-κB-mediated inflammation and cell proliferation through nuclear accumulation of ß-catenin, and promotes host DNA double-strand breaks, collectively triggering malignant changes. These findings highlight the 171S/L HtrA mutation as a unique bacterial cancer-associated SNP and as a potential biomarker for risk predictions in H. pylori infections.

Detection of Fusobacterium nucleatum in Patients with Colitis-Associated Colorectal Cancer.

Fusobacterium nucleatum is supposed to play a critical role in the development of colorectal cancer. The species has also been associated with ulcerative colitis (UC) that can progress into colorectal cancer, however, the involvement of bacteria in this process remains unclear. We analysed 177 colon biopsies obtained from patients during screening, including 20 healthy controls, 56 UC cases and 69 cases at different stages of progression to colitis-associated cancer (CAC); 32 samples of sporadic colorectal carcinoma (sCRC) were also included. The presence of F. nucleatum was detected by quantitative real-time PCR (qPCR). Our data show an association between the presence of the bacteria and the progression of carcinogenesis in UC patients. In 39.5% of CAC samples F. nucleatum was detected, compared to only 1.8% in UC cases. The bacteria were detected in 6.3% of samples with initial neoplastic transformation, so-called low-grade dysplasia (LGD), whereas high-grade dysplasia (HGD) resulted in 33.3% of samples positive for F. nucleatum. The fraction of F. nucleatum-positive samples from sCRC cases was 56.3%, which was not significantly different to the CAC group. We conclude that F. nucleatum is associated with the occurrence and progression of colon carcinogenesis, rather than with UC itself.

Trimer stability of Helicobacter pylori HtrA is regulated by a natural mutation in the protease domain.

The human pathogen Helicobacter pylori is a major risk factor for gastric disease development. Serine protease HtrA is an important bacterial virulence factor that cleaves the cell junction proteins occludin, claudin-8 and E-cadherin, which causes gastric tissue damage. Using casein zymography, we discovered that HtrA trimer stability varies in clinical H. pylori strains. Subsequent sequence analyses revealed that HtrA trimer stability correlated with the presence of leucine or serine residue at position 171. The importance of these amino acids in determining trimer stability was confirmed by leucine-to-serine swapping experiments using isogenic H. pylori mutant strains as well as recombinant HtrA proteins. In addition, this sequence position displays a high sequence variability among various bacterial species, but generally exhibits a preference for hydrophilic amino acids. This natural L/S171 polymorphism in H. pylori may affect the protease activity of HtrA during infection, which could be of clinical importance and may determine gastric disease development.

Masking of typical TLR4 and TLR5 ligands modulates inflammation and resolution by Helicobacter pylori.

Helicobacter pylori is a paradigm of chronic bacterial infection and is associated with peptic ulceration and malignancies. H. pylori uses specific masking mechanisms to avoid canonical ligands from activating Toll-like receptors (TLRs), such as lipopolysaccharide (LPS) modification and specific flagellin sequences that are not detected by TLR4 and TLR5, respectively. Thus, it was believed for a long time that H. pylori evades TLR recognition as a crucial strategy for immune escape and bacterial persistence. However, recent data indicate that multiple TLRs are activated by H. pylori and play a role in the pathology. Remarkably, H. pylori LPS, modified through changes in acylation and phosphorylation, is mainly sensed by other TLRs (TLR2 and TLR10) and induces both pro- and anti-inflammatory responses. In addition, two structural components of the cag pathogenicity island-encoded type IV secretion system (T4SS), CagL and CagY, were shown to contain TLR5-activating domains. These domains stimulate TLR5 and enhance immunity, while LPS-driven TLR10 signaling predominantly activates anti-inflammatory reactions. Here, we discuss the specific roles of these TLRs and masking mechanisms during infection. Masking of typical TLR ligands combined with evolutionary shifting to other TLRs is unique for H. pylori and has not yet been described for any other species in the bacterial kingdom. Finally, we highlight the unmasked T4SS-driven activation of TLR9 by H. pylori, which mainly triggers anti-inflammatory responses.

Molecular Targets in Campylobacter Infections.

Human campylobacteriosis results from foodborne infections with Campylobacter bacteria such as Campylobacter jejuni and Campylobacter coli, and represents a leading cause of bacterial gastroenteritis worldwide. After consumption of contaminated poultry meat, constituting the major source of pathogenic transfer to humans, infected patients develop abdominal pain and diarrhea. Post-infectious disorders following acute enteritis may occur and affect the nervous system, the joints or the intestines. Immunocompromising comorbidities in infected patients favor bacteremia, leading to vascular inflammation and septicemia. Prevention of human infection is achieved by hygiene measures focusing on the reduction of pathogenic food contamination. Molecular targets for the treatment and prevention of campylobacteriosis include bacterial pathogenicity and virulence factors involved in motility, adhesion, invasion, oxygen detoxification, acid resistance and biofilm formation. This repertoire of intervention measures has recently been completed by drugs dampening the pro-inflammatory immune responses induced by the Campylobacter endotoxin lipo-oligosaccharide. Novel pharmaceutical strategies will combine anti-pathogenic and anti-inflammatory effects to reduce the risk of both anti-microbial resistance and post-infectious sequelae of acute enteritis. Novel strategies and actual trends in the combat of Campylobacter infections are presented in this review, alongside molecular targets applied for prevention and treatment strategies.

Evolution and Role of Proteases in Campylobacter jejuni Lifestyle and Pathogenesis.

Infection with the main human food-borne pathogen Campylobacter jejuni causes campylobacteriosis that accounts for a substantial percentage of gastrointestinal infections. The disease usually manifests as diarrhea that lasts for up to two weeks. C. jejuni possesses an array of peptidases and proteases that are critical for its lifestyle and pathogenesis. These include serine proteases Cj1365c, Cj0511 and HtrA; AAA+ group proteases ClpP, Lon and FtsH; and zinc-dependent protease PqqE, proline aminopeptidase PepP, oligopeptidase PepF and peptidase C26. Here, we review the numerous critical roles of these peptide bond-dissolving enzymes in cellular processes of C. jejuni that include protein quality control; protein transport across the inner and outer membranes into the periplasm, cell surface or extracellular space; acquisition of amino acids and biofilm formation and dispersal. In addition, we highlight their role as virulence factors that inflict intestinal tissue damage by promoting cell invasion and mediating cleavage of crucial host cell factors such as epithelial cell junction proteins. Furthermore, we reconstruct the evolution of these proteases in 34 species of the Campylobacter genus. Finally, we discuss to what extent C. jejuni proteases have initiated the search for inhibitor compounds as prospective novel anti-bacterial therapies.

Helicobacter pylori-Induced Host Cell DNA Damage and Genetics of Gastric Cancer Development.

Gastric cancer is a very serious and deadly disease worldwide with about one million new cases every year. Most gastric cancer subtypes are associated with genetic and epigenetic aberrations caused by chromosome instability, microsatellite instability or Epstein-Barr virus infection. Another risk factor is an infection with Helicobacter pylori, which also triggers severe alterations in the host genome. This pathogen expresses an extraordinary repertoire of virulence determinants that take over control of important host cell signaling functions. In fact, H. pylori is a paradigm of persistent infection, chronic inflammation and cellular destruction. In particular, H. pylori profoundly induces chromosomal DNA damage by introducing double-strand breaks (DSBs) followed by genomic instability. DSBs appear in response to oxidative stress and pro-inflammatory transcription during the S-phase of the epithelial cell cycle, which mainly depends on the presence of the bacterial cag pathogenicity island (cagPAI)-encoded type IV secretion system (T4SS). This scenario is closely connected with the T4SS-mediated injection of ADP-glycero-ß-D-manno-heptose (ADP-heptose) and oncoprotein CagA. While ADP-heptose links transcription factor NF-κB-induced innate immune signaling with RNA-loop-mediated DNA replication stress and introduction of DSBs, intracellular CagA targets the tumor suppressor BRCA1. The latter scenario promotes BRCAness, a disease characterized by the deficiency of effective DSB repair. In addition, genetic studies of patients demonstrated the presence of gastric cancer-associated single nucleotide polymorphisms (SNPs) in immune-regulatory and other genes as well as specific pathogenic germline variants in several crucial genes involved in homologous recombination and DNA repair, all of which are connected to H. pylori infection. Here we review the molecular mechanisms leading to chromosomal DNA damage and specific genetic aberrations in the presence or absence of H. pylori infection, and discuss their importance in gastric carcinogenesis.

Gastric Epithelial Barrier Disruption, Inflammation and Oncogenic Signal Transduction by Helicobacter pylori.

Helicobacter pylori exemplifies one of the most favourable bacterial pathogens worldwide. The bacterium colonizes the gastric mucosa in about half of the human population and constitutes a major risk factor for triggering gastric diseases such as stomach cancer. H. pylori infection represents a prime example of chronic inflammation and cancer-inducing bacterial pathogens. The microbe utilizes a remarkable set of virulence factors and strategies to control cellular checkpoints of inflammation and oncogenic signal transduction. This chapter emphasizes on the pathogenicity determinants of H. pylori such as the cytotoxin-associated genes pathogenicity island (cagPAI)-encoded type-IV secretion system (T4SS), effector protein CagA, lipopolysaccharide (LPS) metabolite ADP-glycero-ß-D-manno-heptose (ADP-heptose), cytotoxin VacA, serine protease HtrA, and urease, and how they manipulate various key host cell signaling networks in the gastric epithelium. In particular, we highlight the H. pylori-induced disruption of cell-to-cell junctions, pro-inflammatory activities, as well as proliferative, pro-apoptotic and anti-apoptotic responses. Here we review these hijacked signal transduction events and their impact on gastric disease development.

Cortactin: A universal host cytoskeletal target of Gram-negative and Gram-positive bacterial pathogens.

Pathogenic bacteria possess a great potential of causing infectious diseases and represent a serious threat to human and animal health. Understanding the molecular basis of infection development can provide new valuable strategies for disease prevention and better control. In host-pathogen interactions, actin-cytoskeletal dynamics play a crucial role in the successful adherence, invasion, and intracellular motility of many intruding microbial pathogens. Cortactin, a major cellular factor that promotes actin polymerization and other functions, appears as a central regulator of host-pathogen interactions and different human diseases including cancer development. Various important microbes have been reported to hijack cortactin signaling during infection. The primary regulation of cortactin appears to proceed via serine and/or tyrosine phosphorylation events by upstream kinases, acetylation, and interaction with various other host proteins, including the Arp2/3 complex, filamentous actin, the actin nucleation promoting factor N-WASP, focal adhesion kinase FAK, the large GTPase dynamin-2, the guanine nucleotide exchange factor Vav2, and the actin-stabilizing protein CD2AP. Given that many signaling factors can affect cortactin activities, several microbes target certain unique pathways, while also sharing some common features. Here we review our current knowledge of the hallmarks of cortactin as a major target for eminent Gram-negative and Gram-positive bacterial pathogens in humans.

Campylobacter jejuni Serine Protease HtrA Induces Paracellular Transmigration of Microbiota across Polarized Intestinal Epithelial Cells.

Campylobacter jejuni represents an eminent zoonotic germ responsible for foodborne infections causing campylobacteriosis. In addition, infections with C. jejuni constitute a risk factor for the occurrence of inflammatory bowel disease (IBD). In the latter case, patients show inflammatory reactions not only against C. jejuni, but also against the non-infectious microbiota. However, the involved mechanisms and molecular basis are still largely unclear. We recently reported that C. jejuni breaches the intestinal epithelial barrier by secretion of serine protease HtrA (high temperature requirement A), which cleaves several major tight and adherens junction proteins. In the present study, we aimed to study if HtrA-expressing C. jejuni may also trigger the transepithelial migration of non-pathogenic gastrointestinal microbiota. Using confocal immunofluorescence and scanning electron microscopy, we demonstrate that C. jejuni wild-type (wt) as well as the isogenic ∆htrA mutant bind to the surface of polarized intestinal Caco-2 epithelial cells, but do not invade them at the apical side. Instead, C. jejuni wt, but not ∆htrA mutant, disrupt the cellular junctions and transmigrate using the paracellular route between neighboring cells. Using transwell filter systems, we then co-incubated the cells with C. jejuni and non-invasive microbiota strains, either Escherichia coli or Lactococcus lactis. Interestingly, C. jejuni wt, but not ∆htrA mutant, induced the efficient transmigration of these microbiota bacteria into the basal compartment. Thus, infection of the intestinal epithelium with C. jejuni causes local opening of cellular junctions and paracellular translocation in an HtrA-dependent manner, which paves the way for transmigration of microbiota that is otherwise non-invasive. Taken together, these findings may have impacts on various Campylobacter-associated diseases such as IBD, which are discussed here.

Unique TLR9 Activation by Helicobacter pylori Depends on the cag T4SS, But Not on VirD2 Relaxases or VirD4 Coupling Proteins.

The genomes of the gastric bacterial pathogen Helicobacter pylori harbor multiple type-IV secretion systems (T4SSs). Here we analyzed components of three T4SSs, the cytotoxin-associated genes (cag) T4SS, TFS3 and TFS4. The cag T4SS delivers the effector protein CagA and the LPS-metabolite ADP-heptose into gastric epithelial cells, which plays a pivotal role in chronic infection and development of gastric disease. In addition, the cag T4SS was reported to facilitate conjugative transport of chromosomal bacterial DNA into the host cell cytoplasm, where injected DNA activates intracellular toll-like receptor 9 (TLR9) and triggers anti-inflammatory signaling. Canonical DNA-delivering T4SSs in a variety of bacteria are composed of 11 VirB proteins (VirB1-11) which assemble and engage VirD2 relaxase and VirD4 coupling proteins that mediate DNA processing and guiding of the covalently bound DNA through the T4SS channel. Nevertheless, the role of the latter components in H. pylori is unclear. Here, we utilized isogenic knockout mutants of various virB (virB9 and virB10, corresponding to cagX and cagY), virD2 (rlx1 and rlx2), virD4 (cag5, traG1/2) and xerD recombinase genes in H. pylori laboratory strain P12 and studied their role in TLR9 activation by reporter assays. While inactivation of the structural cag T4SS genes cagX and cagY abolished TLR9 activation, the deletion of rlx1, rlx2, cag5, traG or xerD genes had no effect. The latter mutants activated TLR9 similar to wild-type bacteria, suggesting the presence of a unique non-canonical T4SS-dependent mechanism of TLR9 stimulation by H. pylori that is not mediated by VirD2, VirD4 and XerD proteins. These findings were confirmed by the analysis of TLR9 activation by H. pylori strains of worldwide origin that possess different sets of T4SS genes. The exact mechanism of TLR9 activation should be explored in future studies.

Rapid Detection of Quinolone Resistance Mutations in gyrA of Helicobacter pylori by Real-Time PCR.

The treatment of infections by the gastric pathogen Helicobacter pylori (H. pylori) has become more difficult due to increased rates of resistances against various antibiotics. Typically, atriple therapy, employing a combination of at least two antibiotics and a proton pump inhibitor, is used to cure H. pylori infections. In case of first-line therapy failure, quinolones are commonly applied in a second-line therapy. To prevent second-line treatment failures, we developed an improved method to detect the most common quinolone-resistance mutations located in the quinolone-resistance-determining region (QRDR) of the bacterial gyrA gene. Biopsy material from the gastric mucosa of infected patients was used to identify quinolone-resistant strains before the onset of drug administration. Two different wild-type and six mutant QRDR sequences were included. Melting curve analyses were performed with corresponding gyrA plasmid DNAs using a real-time polymerase chain reaction (RT-PCR) assay. By applying a combination of only two different fluorescent probes, this assay allows wild-type sequences to be unambiguously distinguished from all known mutant QRDR sequences of H. pylori. Next, the Tm values of patient DNAs were established, and the genotypes were confirmed by sequencing. Thus, quinolone-resistant H. pylori strains can be easily and quickly diagnosed before treatment, which will help to avoid the administration of ineffective drug regimes.

Importance of cortactin for efficient epithelial NF-ĸB activation by Helicobacter pylori, Salmonella enterica and Pseudomonas aeruginosa, but not Campylobacter spp.

Transcription factors of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-ĸB) family control important signaling pathways in the regulation of the host innate immune system. Various bacterial pathogens in the human gastrointestinal tract induce NF-ĸB activity and provoke pro-inflammatory signaling events in infected epithelial cells. NF-ĸB activation requires the phosphorylation-dependent proteolysis of inhibitor of ĸB (IĸB) molecules including the NF-ĸB precursors through ubiquitin-mediated proteolysis. The canonical NF-ĸB pathway merges on IĸB kinases (IKKs), which are required for signal transduction. Using CRISPR-Cas9 technology, secreted embryonic alkaline phosphatase (SEAP) reporter assays and cytokine enzyme-linked immunosorbent assay (ELISA), we demonstrate that the actin-binding protein cortactin is involved in NF-ĸB activation and subsequent interleukin-8 (IL-8) production upon infection by Helicobacter pylori, Salmonella enterica and Pseudomonas aeruginosa. Our data indicate that cortactin is needed to efficiently activate the c-Sarcoma (Src) kinase, which can positively stimulate NF-ĸB during infection. In contrast, cortactin is not involved in activation of NF-ĸB and IL-8 expression upon infection with Campylobacter species C. jejuni, C. coli or C. consisus, suggesting that Campylobacter species pluralis (spp.) induce a different signaling pathway upstream of cortactin to trigger the innate immune response.

Early and late genome-wide gastric epithelial transcriptome response during infection with the human carcinogen Helicobacterpylori.

Infection of the stomach by Helicobacter pylori is a major risk factor for the development of gastric cancer. Colonization of the gastric epithelium leads to the activation of multiple disease-related signaling pathways. Serine protease HtrA represents an important secreted virulence factor that mediates cleavage of cellular junctions. However, its potential role in nuclear responses is unknown. Here, we performed a genome-wide RNA-seq analysis of polarized gastric epithelial cells infected by wild-type (wt) and ΔhtrA mutant bacteria. Fluorescence microscopy showed that H. pylori wt, but not ΔhtrA bacteria, preferably localized at cellular junctions. Our results pinpointed early (2 h) and late (6 h) transcriptional responses, with most differentially expressed genes at 6 h post infection. The transcriptomes revealed HtrA-dependent targeting of genes associated with inflammation and apoptosis (e.g. IL8, ZFP36, TNF). Accordingly, infection with the ΔhtrA mutant induced increased apoptosis rates in host cells, which was associated with reduced H. pylori CagA expression. In contrast, transcription of various carcinogenesis-associated genes (e.g. DKK1, DOCK8) was affected by H. pylori independent of HtrA. These findings suggest that H. pylori disturbs previously unknown molecular pathways in an HtrA-dependent and HtrA-independent manner, and provide valuable new insights of this significant pathogen in humans and thus potential targets for better controlling the risk of malignant transformation.

Campylobacteriose ­ eine zoonotische Infektionskrankheit.

Campylobacter jejuni represents an important zoonotic pathogen that is causing foodborne enteric infections. In the human gut, C. jejuni bacteria induce intestinal campylobacteriosis which can develop into systemic post-infectious sequelae such as Guillain-Barré syndrome or rheumatoid arthritis. Here, we review the pathobiology and molecular mechanisms of C. jejuni infections as well as promising strategies to combat campylobacteriosis within the "One World - One Health" approach.

Helicobacter pylori CagA Induces Cortactin Y-470 Phosphorylation-Dependent Gastric Epithelial Cell Scattering via Abl, Vav2 and Rac1 Activation.

The pathogen Helicobacter pylori is the first reported bacterial type-1 carcinogen playing a role in the development of human malignancies, including gastric adenocarcinoma. Cancer cell motility is an important process in this scenario, however, the molecular mechanisms are still not fully understood. Here, we demonstrate that H. pylori subverts the actin-binding protein cortactin through its type-IV secretion system and injected oncoprotein CagA, e.g., by inducing tyrosine phosphorylation of cortactin at Y-470, which triggers gastric epithelial cell scattering and motility. During infection of AGS cells, cortactin was discovered to undergo tyrosine dephosphorylation at residues Y-421 and Y-486, which is mediated through inactivation of Src kinase. However, H. pylori also profoundly activates tyrosine kinase Abl, which simultaneously phosphorylates cortactin at Y-470. Phosphorylated cortactin interacts with the SH2-domain of Vav2, a guanine nucleotide exchange factor for the Rho-family of GTPases. The cortactin/Vav2 complex then stimulates a previously unrecognized activation cascade including the small GTPase Rac1, to effect actin rearrangements and cell scattering. We hypothesize that injected CagA targets cortactin to locally open the gastric epithelium in order to get access to certain nutrients. This may disturb the cellular barrier functions, likely contributing to the induction of cell motility, which is important in gastric cancer development.

Vitamin D Reverses Disruption of Gut Epithelial Barrier Function Caused by Campylobacter jejuni.

Infections by the zoonotic foodborne bacterium Campylobacter jejuni (C. jejuni) are among the most frequent causes of bacterial gastroenteritis worldwide. The aim was to evaluate the relationship between epithelial barrier disruption, mucosal immune activation, and vitamin D (VD) treatment during C. jejuni infection, using intestinal epithelial cells and mouse models focused on the interaction of C. jejuni with the VD signaling pathway and VD treatment to improve C. jejuni-induced barrier dysfunction. Our RNA-Seq data from campylobacteriosis patients demonstrate inhibition of VD receptor (VDR) downstream targets, consistent with suppression of immune function. Barrier-preserving effects of VD addition were identified in C. jejuni-infected epithelial cells and IL-10-/- mice. Furthermore, interference of C. jejuni with the VDR pathway was shown via VDR/retinoid X receptor (RXR) interaction. Paracellular leakiness of infected epithelia correlated with tight junction (TJ) protein redistribution off the TJ domain and apoptosis induction. Supplementation with VD reversed barrier impairment and prevented inhibition of the VDR pathway, as shown by restoration of transepithelial electrical resistance and fluorescein (332 Da) permeability. We conclude that VD treatment restores gut epithelial barrier functionality and decreases bacterial transmigration and might, therefore, be a promising compound for C. jejuni treatment in humans and animals.