Distinct roles of secreted HtrA proteases from gram-negative pathogens in cleaving the junctional protein and tumor suppressor E-cadherin

HIV-associated penile anaerobes disrupt epithelial barrier integrity

Specific anaerobic taxa within the penile microbiome-the Bacteria Associated with Seroconversion, Inflammation and Immune Cells (BASIC) species-enhance HIV-1 susceptibility, in part by recruiting susceptible cells to the inner foreskin. However, their effect on epithelial barrier integrity has not been described. Using foreskin tissues and penile swabs from 116 males undergoing voluntary medical male circumcision, we assessed the relationship between BASIC species and foreskin epithelial thickness, junction protein expression, and cellular proliferation. The absolute abundance of BASIC species was associated with reduced tissue expression of the epithelial junction proteins claudin-1 and E-cadherin, and with elevated soluble E-cadherin in penile secretions, suggesting proteolytic cleavage. These effects were not seen in participants with a high abundance of control taxa without high levels of BASIC species. The BASIC species Prevotella bivia, but not Peptostreptococcus anaerobius or Dialister micraerophilus, was shown to directly degrade recombinant human E-cadherin and to increase the release of soluble E-cadherin from foreskin epithelial cells in vitro. In vivo BASIC species absolute abundance was also linked to a thicker nucleated epithelium and increased keratinocyte proliferation, with no change in stratum corneum thickness. Therefore, BASIC species may enhance penile HIV susceptibility by directly disrupting epithelial integrity, in addition to previously described target cell recruitment.

Role of E-cadherin in epithelial barrier dysfunction: implications for bacterial infection, inflammation, and disease pathogenesis

Epithelial barriers serve as critical defense lines against microbial infiltration and maintain tissue homeostasis. E-cadherin, an essential component of adherens junctions, has emerged as a pivotal molecule that secures epithelial homeostasis. Lately, its pleiotropic role beyond barrier function, including its involvement in immune responses, has become more evident. Herein, we delve into the intricate relationship between (dys)regulation of epithelial homeostasis and the versatile functionality of E-cadherin, describing complex mechanisms that underlie barrier integrity and disruption in disease pathogenesis such as bacterial infection and inflammation, among others. Clinical implications of E-cadherin perturbations in host pathophysiology are emphasized; downregulation, proteolytic phenomena, abnormal localization/signaling and aberrant immune reactions are linked with a broad spectrum of pathology beyond infectious diseases. Finally, potential therapeutic interventions that may harness E-cadherin to mitigate barrier-associated tissue damage are explored. Overall, this review highlights the crucial role of E-cadherin in systemic health, offering insights that could pave the way for strategies to reinforce/restore barrier integrity and treat related diseases.

Pathogenicity and virulence of Campylobacter jejuni: What do we really know?

Campylobacter jejuni is the leading cause of bacterial gastroenteritis and is a major public health concern worldwide. Despite its importance, our understanding of how C. jejuni causes diarrhoea and interacts with its hosts is limited due to the absence of appropriate infection models and established virulence factors found in other enteric pathogens. Additionally, despite its genetic diversity, non-pathogenic C. jejuni strains are unknown. Regardless of these limitations, significant progress has been made in understanding how C. jejuni uses a complex array of factors which aid the bacterium to survive and respond to host defences. This review provides an update on fitness and virulence determinants of this important pathogen and questions our knowledge on these determinants that are often based on inferred genomics knowledge and surrogate infection models.

Cleavage of cell junction proteins as a host invasion strategy in leptospirosis

Infection and invasion are the prerequisites for developing the disease symptoms in a host. While the probable mechanism of host invasion and pathogenesis is known in many pathogens, very little information is available on Leptospira invasion/pathogenesis. For causing systemic infection Leptospira must transmigrate across epithelial barriers, which is the most critical and challenging step. Extracellular and membrane-bound proteases play a crucial role in the invasion process. An extensive search for the proteins experimentally proven to be involved in the invasion process through cell junction cleavage in other pathogens has resulted in identifying 26 proteins. The similarity searches on the Leptospira genome for counterparts of these 26 pathogenesis-related proteins identified at least 12 probable coding sequences. The proteins were either extracellular or membrane-bound with a proteolytic domain to cleave the cell junction proteins. This review will emphasize our current understanding of the pathogenic aspects of host cell junction-pathogenic protein interactions involved in the invasion process. Further, potential candidate proteins with cell junction cleavage properties that may be exploited in the diagnostic/therapeutic aspects of leptospirosis will also be discussed. KEY POINTS: • The review focussed on the cell junction cleavage proteins in bacterial pathogenesis • Cell junction disruptors from Leptospira genome are identified using bioinformatics • The review provides insights into the therapeutic/diagnostic interventions possible.

The immunopathogenesis of Helicobacter pylori-induced gastric cancer: a narrative review

Helicobacter pylori infection is a well-established risk factor for the development of gastric cancer (GC). Understanding the immunopathogenesis underlying this association is crucial for developing effective preventive and therapeutic strategies. This narrative review comprehensively explores the immunopathogenesis of H. pylori-induced GC by delving into several key aspects, emphasizing the pivotal roles played by H. pylori virulence factors, including cytotoxin-associated gene A (cagA) and vacuolating cytotoxin A (vacA), blood group antigen-binding adhesin (babA), and sialic acid binding adhesin (sabA). Moreover, the review focuses on the role of toll-like receptors (TLRs) and cytokines in the complex interplay between chronic infection and gastric carcinogenesis. Finally, the study examines the association between H. pylori evasion of the innate and adaptive immune response and development of GC. A comprehensive understanding of the immunopathogenesis of H. pylori-induced GC is essential for designing targeted interventions to prevent and manage this disease. Further research is warranted to elucidate the intricate immune responses involved and identify potential therapeutic targets to improve patient outcomes.

The Balance between Protealysin and Its Substrate, the Outer Membrane Protein OmpX, Regulates Serratia proteamaculans Invasion

Serratia are opportunistic bacteria, causing infections in plants, insects, animals and humans under certain conditions. The development of bacterial infection in the human body involves several stages of host-pathogen interaction, including entry into non-phagocytic cells to evade host immune cells. The facultative pathogen Serratia proteamaculans is capable of penetrating eukaryotic cells. These bacteria synthesize an actin-specific metalloprotease named protealysin. After transformation with a plasmid carrying the protealysin gene, noninvasive E. coli penetrate eukaryotic cells. This suggests that protealysin may play a key role in S. proteamaculans invasion. This review addresses the mechanisms underlying protealysin's involvement in bacterial invasion, highlighting the main findings as follows. Protealysin can be delivered into the eukaryotic cell by the type VI secretion system and/or by bacterial outer membrane vesicles. By cleaving actin in the host cell, protealysin can mediate the reversible actin rearrangements required for bacterial invasion. However, inactivation of the protealysin gene leads to an increase, rather than decrease, in the intensity of S. proteamaculans invasion. This indicates the presence of virulence factors among bacterial protealysin substrates. Indeed, protealysin cleaves the virulence factors, including the bacterial surface protein OmpX. OmpX increases the expression of the EGFR and β1 integrin, which are involved in S. proteamaculans invasion. It has been shown that an increase in the invasion of genetically modified S. proteamaculans may be the result of the accumulation of full-length OmpX on the bacterial surface, which is not cleaved by protealysin. Thus, the intensity of the S. proteamaculans invasion is determined by the balance between the active protealysin and its substrate OmpX.

Host-Cell-Dependent Roles of E-Cadherin in Serratia Invasion

Bacteria use cell surface proteins to mediate host-pathogen interactions. Proteins responsible for cell adhesion, including E-cadherin, serve as receptors for entry into the host cell. We have previously shown that an increase in eukaryotic cell sensitivity to Serratia grimesii correlates with an increase in E-cadherin expression. On the other hand, Serratia proteamaculans invasion involves the EGFR, which can interact with E-cadherin on the surface of host cells. Therefore, we investigated the role of E-cadherin in Serratia invasion into M-HeLa and Caco-2 cells. Bacterial infection increased E-cadherin expression in both cell lines. Moreover, E-cadherin was detected in the Caco-2 cells in a full-length form and in the M-HeLa cells in only a truncated form in response to incubation with bacteria. Transfection with siRNA targeting E-cadherin inhibited S. proteamaculans invasion only into the Caco-2 cells. Thus, only full-length E-cadherin is involved in S. proteamaculans invasion. On the other hand, transfection with siRNA targeting E-cadherin inhibited S. grimesii invasion into both cell lines. Thus, not only may full-length E-cadherin but also truncated E-cadherin be involved in S. grimesii invasion. Truncated E-cadherin can be formed as a result of cleavage by bacterial proteases or the Ca2+-activated cellular protease ADAM10. The rate of Ca2+ accumulation in the host cells depends on the number of bacteria per cell upon infection. During incubation, Ca2+ accumulates only when more than 500 S. grimesii bacteria are infected per eukaryotic cell, and only under these conditions does the ADAM10 inhibitor reduce the sensitivity of the cells to bacteria. An EGFR inhibitor has the same quantitative effect on S. grimesii invasion. Apparently, as a result of infection with S. grimesii, Ca2+ accumulates in the host cells and may activate the ADAM10 sheddase, which can promote invasion by cleaving E-cadherin and, as a result, triggering EGFR signaling. Thus, the invasion of S. proteamaculans can only be promoted by full-length E-cadherin, and S. grimesii invasion can be promoted by both full-length and truncated E-cadherin.

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 β-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.

Oncogenic potential of Campylobacter infection in the gastrointestinal tract: narrative review

BACKGROUND

Campylobacter jejuni is the leading cause of zoonotic gastroenteritis. The other emerging group of Campylobacters spp. are part of human oral commensal, represented by C. concisus (CC), which has been recently linked to non-oral conditions. Although long-term gastrointestinal (GI) complications from these two groups of Campylobacters have been previously reviewed individually, overall impact of Campylobacter infection on GI carcinogenesis and their inflammatory precursor lesions has not been assessed collectively.

AIMS

To evaluate the available evidence concerning the association between Campylobacter infection/colonization and inflammatory bowel disease (IBD), reflux esophagitis/metaplasia colorectal cancer (CRC) and esophageal cancer (EC).

METHODS

We performed a comprehensive literature search of PubMed for relevant original publications and systematic reviews/meta-analyses of epidemiological and clinical studies. In addition, we gathered additional information concerning microbiological data, animal models and mechanistic data from in vitro studies.

RESULTS

Both retrospective and prospective studies on IBD showed relatively consistent increased risk associated with Campylobacter infection. Despite lack of supporting prospective studies, retrospective studies based on tissue/fecal microbiome revealed consistent enrichment of Campylobacter in CRC samples. Studies on EC precursor lesions (esophagitis and metaplasia) were generally supportive for the association with Campylobacter, while inconsistent observations on EC. Studies on both IBD and EC precursors suggested the predominant role of CC, but studies on CRC were not informative of species.

CONCLUSIONS

There is sufficient evidence calling for concerted effort in unveiling direct and indirect connection of this organism to colorectal and esophageal cancer in humans.

Identification and Characterization of an HtrA Sheddase Produced by Coxiella burnetii

Having previously shown that soluble E-cadherin (sE-cad) is found in sera of Q fever patients and that infection of BeWo cells by C. burnetii leads to modulation of the E-cad/β-cat pathway, our purpose was to identify which sheddase(s) might catalyze the cleavage of E-cad. Here, we searched for a direct mechanism of cleavage initiated by the bacterium itself, assuming the possible synthesis of a sheddase encoded in the genome of C. burnetii or an indirect mechanism based on the activation of a human sheddase. Using a straightforward bioinformatics approach to scan the complete genomes of four laboratory strains of C. burnetii, we demonstrate that C. burnetii encodes a 451 amino acid sheddase (CbHtrA) belonging to the HtrA family that is differently expressed according to the bacterial virulence. An artificial CbHtrA gene (CoxbHtrA) was expressed, and the CoxbHtrA recombinant protein was found to have sheddase activity. We also found evidence that the C. burnetii infection triggers an over-induction of the human HuHtrA gene expression. Finally, we demonstrate that cleavage of E-cad by CoxbHtrA on macrophages-THP-1 cells leads to an M2 polarization of the target cells and the induction of their secretion of IL-10, which "disarms" the target cells and improves C. burnetii replication. Taken together, these results demonstrate that the genome of C. burnetii encodes a functional HtrA sheddase and establishes a link between the HtrA sheddase-induced cleavage of E-cad, the M2 polarization of the target cells and their secretion of IL-10, and the intracellular replication of C. burnetii.

Bacterial extracellular vesicles and their interplay with the immune system

The mammalian intestinal tract harbors trillions of microorganisms confined within this space by mucosal barriers. Despite these barriers, bacterial components may still be found elsewhere in the body, even in healthy subjects. Bacteria can release small lipid-bound particles, also named bacterial extracellular vesicles (bEV). While bacteria themselves cannot normally penetrate the mucosal defense, bEVs may infiltrate the barrier and disseminate throughout the body. The extremely diverse cargo that bEVs can carry, depending on their parent species, strain, and growth conditions, grant them an equally broad potential to interact with host cells and influence immune functions. Herein, we review the current knowledge of processes underlying the uptake of bEVs by mammalian cells, and their effect on the immune system. Furthermore, we discuss how bEVs could be targeted and manipulated for diverse therapeutic purposes.

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.

HtrA is involved in stress response and adhesion in Glaesserella parasuis serovar 5 strain Nagasaki

Glaesserella parasuis is an important pathogen that causes fibrinous polyserositis, peritonitis and meningitis in pigs, leading to considerable economic losses to the swine industry worldwide. It is well established that the serine protease HtrA is closely associated with bacterial virulence, but the role of HtrA in G. parasuis pathogenesis remains largely unknown. To characterize the function of the htrA gene in G. parasuis, a ΔhtrA mutant was constructed. We found that the ΔhtrA mutant showed significant growth inhibition under heat shock and alkaline stress conditions, indicating HtrA is involved in stress tolerance and survival of G. parasuis. In addition, deletion of htrA gene resulted in decreased adherence to PIEC and PK-15 cells and increased phagocytic resistance to 3D4/2 macrophages, suggesting that htrA is essential for adherence of G. parasuis. Scanning electron microscopy revealed morphological surface changes of the ΔhtrA mutant, and transcription analysis confirmed that a number of adhesion-associated genes are downregulated, which corroborated the aforementioned phenomenon. Furthermore, G. parasuis HtrA induced a potent antibody response in piglets with Glässer's disease. These observations confirmed that the htrA gene is related to the survival and pathogenicity of G. parasuis.

Impact of enteric bacterial infections at and beyond the epithelial barrier

The mucosal lining of the gut has co-evolved with a diverse microbiota over millions of years, leading to the development of specialized mechanisms to actively limit the invasion of pathogens. However, some enteric microorganisms have adapted against these measures, developing ways to hijack or overcome epithelial micro-integrity mechanisms. This breach of the gut barrier not only enables the leakage of host factors out of circulation but can also initiate a cascade of detrimental systemic events as microbiota, pathogens and their affiliated secretions passively leak into extra-intestinal sites. Under normal circumstances, gut damage is rapidly repaired by intestinal stem cells. However, with substantial and deep perturbation to the gut lining and the systemic dissemination of gut contents, we now know that some enteric infections can cause the impairment of host regenerative processes. Although these local and systemic aspects of enteric disease are often studied in isolation, they heavily impact one another. In this Review, by examining the journey of enteric infections from initial establishment to systemic sequelae and how, or if, the host can successfully repair damage, we will tie together these complex interactions to provide a holistic overview of the impact of enteric infections at and beyond the epithelial barrier.

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.

Proteolytic Activity of DegP Is Required for the Burkholderia Symbiont To Persist in Its Host Bean Bug

Symbiosis requires the adaptation of symbiotic bacteria to the host environment. Symbiotic factors for bacterial adaptation have been studied in various experimental models, including the Burkholderia-bean bug symbiosis model. Previously identified symbiotic factors of Burkholderia symbionts of bean bugs provided insight into the host environment being stressful to the symbionts. Because DegP, which functions as both a protease and a chaperone, supports bacterial growth under various stressful conditions, we hypothesized that DegP might be a novel symbiotic factor of Burkholderia symbionts in the symbiotic association with bean bugs. The expression level of degP was highly elevated in symbiotic Burkholderia cells in comparison with cultured cells. When the degP-deficient strain competed for symbiotic association against the wild-type strain, the ΔdegP strain showed no symbiotic competitiveness. In vivo monoinfection with the ΔdegP strain revealed a lower symbiont titer in the symbiotic organ than that of the wild-type strain, indicating that the ΔdegP strain failed to persist in the host. In in vitro assays, the ΔdegP strain showed susceptibility to heat and high-salt stressors and a decreased level of biofilm formation. To further determine the role of the proteolytic activity of DegP in symbiosis, we generated missense mutant DegP^S248A exhibiting a defect in protease activity only. The ΔdegP strain complemented with degP^S248A showed in vitro characteristics similar to those of the ΔdegP strain and failed to persist in the symbiotic organ. Together, the results of our study demonstrated that the proteolytic activity of DegP, which is involved in the stress resistance and biofilm formation of the Burkholderia symbiont, plays an essential role in symbiotic persistence in the host bean bug. IMPORTANCE Bacterial DegP has dual functions as a protease and a chaperone and supports bacterial growth under stressful conditions. In symbioses involving bacteria, bacterial symbionts encounter various stressors and may need functional DegP for symbiotic association with the host. Using the Burkholderia-bean bug symbiosis model, which is a useful model for identifying bacterial symbiotic factors, we demonstrated that DegP is indeed a symbiotic factor of Burkholderia persistence in its host bean bug. In vitro experiments to understand the symbiotic mechanisms of degP revealed that degP confers resistance to heat and high-salt stresses. In addition, degP supports biofilm formation, which is a previously identified persistence factor of the Burkholderia symbiont. Furthermore, using a missense mutation in a protease catalytic site of degP, we specifically elucidated that the proteolytic activity of degP plays essential roles in stress resistance, biofilm formation, and, thus, symbiotic persistence in the host bean bug.

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.

Immune evasion and persistence in enteric bacterial pathogens

The major function of the mammalian immune system is to prevent and control infections caused by enteropathogens that collectively have altered human destiny. In fact, as the gastrointestinal tissues are the major interface of mammals with the environment, up to 70% of the human immune system is dedicated to patrolling them The defenses are multi-tiered and include the endogenous microflora that mediate colonization resistance as well as physical barriers intended to compartmentalize infections. The gastrointestinal tract and associated lymphoid tissue are also protected by sophisticated interleaved arrays of active innate and adaptive immune defenses. Remarkably, some bacterial enteropathogens have acquired an arsenal of virulence factors with which they neutralize all these formidable barriers to infection, causing disease ranging from mild self-limiting gastroenteritis to in some cases devastating human disease.

Pathogenomics of Helicobacter pylori

The human stomach bacterium Helicobacter pylori, the causative agent of gastritis, ulcers and adenocarcinoma, possesses very high genetic diversity. H. pylori has been associated with anatomically modern humans since their origins over 100,000 years ago and has co-evolved with its human host ever since. Predominantly intrafamilial and local transmission, along with genetic isolation, genetic drift, and selection have facilitated the development of distinct bacterial populations that are characteristic for large geographical areas. H. pylori utilizes a large arsenal of virulence and colonization factors to mediate the interaction with its host. Those include various adhesins, the vacuolating cytotoxin VacA, urease, serine protease HtrA, the cytotoxin-associated genes pathogenicity island (cagPAI)-encoded type-IV secretion system and its effector protein CagA, all of which contribute to disease development. While many pathogenicity-related factors are present in all strains, some belong to the auxiliary genome and are associated with specific phylogeographic populations. H. pylori is naturally competent for DNA uptake and recombination, and its genome evolution is driven by extraordinarily high recombination and mutation rates that are by far exceeding those in other bacteria. Comparative genome analyses revealed that adaptation of H. pylori to individual hosts is associated with strong selection for particular protein variants that facilitate immune evasion, especially in surface-exposed and in secreted virulence factors. Recent studies identified single-nucleotide polymorphisms (SNPs) in H. pylori that are associated with the development of severe gastric disease, including gastric cancer. Here, we review the current knowledge about the pathogenomics of H. pylori.

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-β-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.

Bacterial membrane vesicles in inflammatory bowel disease

Inflammatory bowel disease (IBD) is characterized by chronic intestinal inflammation with no cure. The intestine is fundamental in controlling human health. Disruption of the microbial ecosystem in the intestine is considered an important cause of IBD. The interaction between the host and microbiota significantly impacts the intestinal epithelial barrier and immune function. Bacterial membrane vesicles (MVs) are vital participants in bacteria-bacteria and host-microbiota communication. Currently, MVs have been found to exhibit many important regulating effects for intestinal microecology and have excellent application potential in clinical disease therapies. In the present review, we review the current knowledge on MVs, and specifically focus on gut bacterial MVs and their roles in the IBD. In addition, we summarized the potential utility of MVs as a novel therapeutic approach in IBD patients.

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.

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.

E-Cadherin Orthologues as Substrates for the Serine Protease High Temperature Requirement A (HtrA)

Helicobacter pylori (H. pylori) expresses the serine protease and chaperone High temperature requirement A (HtrA) that is involved in periplasmic unfolded protein stress response. Additionally, H. pylori-secreted HtrA directly cleaves the human cell adhesion molecule E-cadherin leading to a local disruption of intercellular adhesions during pathogenesis. HtrA-mediated E-cadherin cleavage has been observed in response to a broad range of pathogens, implying that it is a prevalent mechanism in humans. However, less is known whether E-cadherin orthologues serve as substrates for bacterial HtrA. Here, we compared HtrA-mediated cleavage of human E-cadherin with murine, canine, and simian E-cadherin in vitro and during bacterial infection. We found that HtrA targeted mouse and dog E-cadherin equally well, whereas macaque E-cadherin was less fragmented in vitro. We stably re-expressed orthologous E-cadherin (Cdh1) in a CRISPR/Cas9-mediated cdh1 knockout cell line to investigate E-cadherin shedding upon infection using H. pylori wildtype, an isogenic htrA deletion mutant, or complemented mutants as bacterial paradigms. In Western blot analyses and super-resolution microscopy, we demonstrated that H. pylori efficiently cleaved E-cadherin orthologues in an HtrA-dependent manner. These data extend previous knowledge to HtrA-mediated E-cadherin release in mammals, which may shed new light on bacterial infections in non-human organisms.

Biomarkers to Detect Early-Stage Colorectal Cancer

Colorectal cancer is a leading cause of mortality worldwide. The high incidence and the acceleration of incidence in younger people reinforces the need for better techniques of early detection. The use of noninvasive biomarkers has potential to more accurately inform how patients are prioritised for clinical investigation, which, in turn, may ultimately translate into improved survival for those subsequently found to have curable-stage CRC. This review surveys a wide range of CRC biomarkers that may (alone or in combination) identify symptomatic patients presenting in primary care who should be progressed for clinical investigation.

Delivery of Toxins and Effectors by Bacterial Membrane Vesicles

Pathogenic bacteria interact with cells of their host via many factors. The surface components, i.e., adhesins, lipoproteins, LPS and glycoconjugates, are particularly important in the initial stages of colonization. They enable adhesion and multiplication, as well as the formation of biofilms. In contrast, virulence factors such as invasins and toxins act quickly to damage host cells, causing tissue destruction and, consequently, organ dysfunction. These proteins must be exported from the bacterium and delivered to the host cell in order to function effectively. Bacteria have developed a number of one- and two-step secretion systems to transport their proteins to target cells. Recently, several authors have postulated the existence of another transport system (sometimes called "secretion system type zero"), which utilizes extracellular structures, namely membrane vesicles (MVs). This review examines the role of MVs as transporters of virulence factors and the interaction of toxin-containing vesicles and other protein effectors with different human cell types. We focus on the unique ability of vesicles to cross the blood-brain barrier and deliver protein effectors from intestinal or oral bacteria to the central nervous system.

Cleavage of E-cadherin by porcine respiratory bacterial pathogens facilitates airway epithelial barrier disruption and bacterial paracellular transmigration

Airway epithelial cells are the first line of defense against respiratory pathogens. Porcine bacterial pathogens, such as Bordetella bronchiseptica, Actinobacillus pleuropneumoniae, Glaesserella (Haemophilus) parasuis, and Pasteurella multocida, breach this barrier to lead to local or systematic infections. Here, we demonstrated that respiratory bacterial pathogen infection disrupted the airway epithelial intercellular junction protein, E-cadherin, thus contributing to impaired epithelial cell integrity. E-cadherin knocking-out in newborn pig tracheal cells via CRISPR/Cas9 editing technology confirmed that E-cadherin was sufficient to suppress the paracellular transmigration of these porcine respiratory bacterial pathogens, including G. parasuis, A. pleuropneumoniae, P. multocida, and B. bronchiseptica. The E-cadherin ectodomain cleavage by these pathogens was probably attributed to bacterial HtrA/DegQ protease, but not host HtrA1, MMP7 and ADAM10, and the prominent proteolytic activity was further confirmed by a serine-to-alanine substitution mutation in the active center of HtrA/DegQ protein. Moreover, deletion of the htrA gene in G. parasuis led to severe defects in E-cadherin ectodomain cleavage, cell adherence and paracellular transmigration in vitro, as well as bacterial breaking through the tracheal epithelial cells, systemic invasion and dissemination in vivo. This common pathogenic mechanism shared by other porcine respiratory bacterial pathogens explains how these bacterial pathogens destroy the airway epithelial cell barriers and proliferate in respiratory mucosal surface or other systemic tissues.

Emerging therapeutic targets for gastric cancer from a host-Helicobacter pylori interaction perspective

INTRODUCTION

Gastric cancer (GC) has the higher genetic, cytologic, and architectural heterogeneity compared to other gastrointestinal cancers. By inducing gastric inflammation, Helicobacter pylori (HP) may lead to GC through combining bacterial factors with host factors. In this regard, identification of the major therapeutic targets against the host-HP interactions plays a critical role in GC prevention, diagnosis, and treatment.

AREAS COVERED

This study offers new insights into the promising therapeutic targets against the angiogenesis, invasion, or metastasis of GC from a host-HP interaction perspective. To this end, MEDLINE, EMBASE, LILACS, AIM, and IndMed databases were searched for relevant articles since 1992.

EXPERT OPINION

Wnt signaling and COX pathway have a well-documented history in the genesis of GC by HP and might be considered as the most promising targets for early GC treatment. Destroying HP may decrease the risk of GC, but it cannot fully hinder the GC development induced by HP infection. Therefore, targeting HP-activated pathways, especially COX-2/Wnt/beta-catenin/VEGF, TLR2/TLR9/COX-2, COX2-PGE2, and NF-κB/COX-2, as well as EPHA2, MMPs, and miR-543/SIRT1 axis, can be an effective measure in the early treatment of GC. However, different clinical trials and large, multi-center cohorts are required to validate these potentially effective targets for GC therapy.

Targeted Protein Degradation: The New Frontier of Antimicrobial Discovery?

Targeted protein degradation aims to hijack endogenous protein quality control systems to achieve direct knockdown of protein targets. This exciting technology utilizes event-based pharmacology to produce therapeutic outcomes, a feature that distinguishes it from classical occupancy-based inhibitor agents. Early degrader candidates display resilience to mutations while possessing potent nanomolar activity and high target specificity. Paired with the rapid advancement of our knowledge in the factors driving targeted degradation, the expansion of this style of therapeutic agent to a range of disease indications is eagerly awaited. In particular, the area of antibiotic discovery is sorely lacking in novel approaches, with the Antimicrobial Resistance (AMR) crisis looming as the next potential global health calamity. Here, the current advances in targeted protein degradation are highlighted, and potential approaches for designing novel antimicrobial protein degraders are proposed, ranging from adaptations of current strategies to completely novel approaches to targeted protein degradation.

Gut Serpinome: Emerging Evidence in IBD

Inflammatory bowel diseases (IBD) are incurable disorders whose prevalence and global socioeconomic impact are increasing. While the role of host genetics and immunity is well documented, that of gut microbiota dysbiosis is increasingly being studied. However, the molecular basis of the dialogue between the gut microbiota and the host remains poorly understood. Increased activity of serine proteases is demonstrated in IBD patients and may contribute to the onset and the maintenance of the disease. The intestinal proteolytic balance is the result of an equilibrium between the proteases and their corresponding inhibitors. Interestingly, the serine protease inhibitors (serpins) encoded by the host are well reported; in contrast, those from the gut microbiota remain poorly studied. In this review, we provide a concise analysis of the roles of serine protease in IBD physiopathology and we focus on the serpins from the gut microbiota (gut serpinome) and their relevance as a promising therapeutic approach.

Diarrheal Mechanisms and the Role of Intestinal Barrier Dysfunction in Campylobacter Infections

Campylobacter enteritis is the most common cause of foodborne bacterial diarrhea in humans. Although various studies have been performed to clarify the pathomechanism in Campylobacter infection, the mechanism itself and bacterial virulence factors are yet not completely understood. The purpose of this chapter is to (i) give an overview on Campylobacter-induced diarrheal mechanisms, (ii) illustrate underlying barrier defects, (iii) explain the role of the mucosal immune response and (iv) weigh preventive and therapeutic approaches. Our present knowledge of pathogenetic and diarrheal mechanisms of Campylobacter jejuni is explained in the first part of this chapter. In the second part, the molecular basis for the Campylobacter-induced barrier dysfunction is compared with that of other species in the Campylobacter genus. The bacteria are capable of overcoming the intestinal epithelial barrier. The invasion into the intestinal mucosa is the initial step of the infection, followed by a second step, the epithelial barrier impairment. The extent of the impairment depends on various factors, including tight junction dysregulation and epithelial apoptosis. The disturbed intestinal epithelium leads to a loss of water and solutes, the leak flux type of diarrhea, and facilitates the uptake of harmful antigens, the leaky gut phenomenon. The barrier dysfunction is accompanied by increased pro-inflammatory cytokine secretion, which is partially responsible for the dysfunction. Moreover, cytokines also mediate ion channel dysregulation (e.g., epithelial sodium channel, ENaC), leading to another diarrheal mechanism, which is sodium malabsorption. Future perspectives of Campylobacter research are the clarification of molecular pathomechanisms and the characterization of therapeutic and preventive compounds to combat and prevent Campylobacter infections.

Cadherin-mediated host-pathogen interactions

Cell adhesion molecules mediate cell-to-cell and cell-to-matrix adhesions and play an immense role in a myriad of physiological processes during the growth and development of a multicellular organism. Cadherins belong to a major group of membrane-bound cell surface proteins that, in coordination with nectins, drive the formation and maintenance of adherens junctions for mediating cell to cell adhesion, cellular communication and signalling. Alongside adhesive function, the involvement of cadherins in mediating host-pathogen interactions has been extensively explored in recent years. In this review, we provide an in-depth understanding of microbial pathogens and their virulence factors that exploit cadherins for their strategical invasion into the host cell. Furthermore, macromolecular interactions involving cadherins and various microbial factors such as secretory toxins and adhesins lead to the disintegration of host cell junctions followed by the entry of the pathogen or triggering downstream signalling pathways responsible for successful invasion of the pathogenic microbes are discussed. Besides providing a comprehensive insight into some of the structural complexes involving cadherins and microbial factors to offer the mechanistic details of host-pathogen interactions, the current review also highlights novel constituents of various cell signalling events such as endocytosis machinery elicited upon microbial infections.

Helicobacter pylori Virulence Factors-Mechanisms of Bacterial Pathogenicity in the Gastric Microenvironment

Gastric cancer constitutes one of the most prevalent malignancies in both sexes; it is currently the fourth major cause of cancer-related deaths worldwide. The pathogenesis of gastric cancer is associated with the interaction between genetic and environmental factors, among which infection by Helicobacter pylori (H. pylori) is of major importance. The invasion, survival, colonization, and stimulation of further inflammation within the gastric mucosa are possible due to several evasive mechanisms induced by the virulence factors that are expressed by the bacterium. The knowledge concerning the mechanisms of H. pylori pathogenicity is crucial to ameliorate eradication strategies preventing the possible induction of carcinogenesis. This review highlights the current state of knowledge and the most recent findings regarding H. pylori virulence factors and their relationship with gastric premalignant lesions and further carcinogenesis.

Importance of two PDZ domains for the proteolytic and chaperone activities of Helicobacter pylori serine protease HtrA

The Helicobacter pylori HtrA protein (HtrA_Hp ) is an important virulence factor involved in the infection process by proteolysis of components of the tight (claudin-8 and occludin) and adherens junctions (E-cadherin) between epithelial cells. As a protease and chaperone, HtrA_Hp is involved in protein quality control, which is particularly important under stress conditions. HtrA_Hp contains a protease domain and two C-terminal PDZ domains (PDZ1 and PDZ2). In the HtrA protein family, the PDZ domains are proposed to play important roles, including regulation of proteolytic activity. We therefore mutated the PDZ1 and PDZ2 domains in HtrA_Hp and studied the maintenance of proteolytic activity, assembly and rearrangement of the corresponding oligomeric forms. Our in vitro experiments demonstrated that at least PDZ1 is important for efficient substrate cleavage_, while both PDZ domains are dispensable for the chaperone-like activity. However, in living H. pylori cells, only the mutant containing at least PDZ1, but not PDZ2, ensured bacterial growth under stressful conditions. Moreover, we can demonstrate that PDZ1 is crucial for HtrA_Hp oligomerization. Interestingly, all truncated proteolytically active HtrA_Hp variants were functional in the in vitro infection assay and caused damage to the E-cadherin-based adherens junctions. These findings provide valuable new insights into the function of HtrA_Hp in an important pathogen of humans.

Campylobacter jejuni Serine Protease HtrA Cleaves the Tight Junction Component Claudin-8

Campylobacter jejuni express the high temperature requirement protein A (HtrA), a secreted serine protease, which is implicated in virulence properties of the pathogen. Previous studies have shown that C. jejuni HtrA can cleave the epithelial transmembrane proteins occludin and E-cadherin in the tight and adherens junctions, respectively. In the present report, we studied the interaction of HtrA with another human tight junction protein, claudin-8. Confocal immunofluorescence experiments have shown that C. jejuni infection of the intestinal polarized epithelial cells in vitro leads to a relocation of claudin-8. Wild-type C. jejuni induced the downregulation of claudin-8 signals in the tight junctions and an accumulation of claudin-8 agglomerates in the cytoplasm, which were not seen during infection with isogenic ΔhtrA knockout deletion or protease-inactive S197A point mutants. Western blotting of protein samples from infected vs. uninfected cells revealed that an 18-kDa carboxy-terminal fragment is cleaved-off from the 26-kDa full-length claudin-8 protein, but not during infection with the isogenic ΔhtrA mutant. These results were confirmed by in vitro cleavage assays using the purified recombinant C. jejuni HtrA and human claudin-8 proteins. Recombinant HtrA cleaved purified claudin-8 in vitro giving rise to the same 18-kDa sized carboxy-terminal cleavage product. Mapping studies revealed that HtrA cleavage occurs in the first extracellular loop of claudin-8. Three-dimensional modeling of the claudin-8 structure identified an exposed HtrA cleavage site between the amino acids alanine 58 and asparagine 59, which is in well agreement with the mapping studies. Taken together, HtrA operates as a secreted virulence factor targeting multiple proteins both in the tight and adherens junctions. This strategy may help the bacteria to open the cell-to-cell junctions, and to transmigrate across the intestinal epithelium by a paracellular mechanism and establish an acute infection.

Functional analysis and cryo-electron microscopy of Campylobacterjejuni serine protease HtrA

Campylobacter jejuni is a predominant zoonotic pathogen causing gastroenteritis and other diseases in humans. An important bacterial virulence factor is the secreted serine protease HtrA (HtrA _Cj ), which targets tight and adherens junctional proteins in the gut epithelium. Here we have investigated the function and structure of HtrA _Cj using biochemical assays and cryo-electron microscopy. Mass spectrometry analysis identified differences and similarities in the cleavage site specificity for HtrA _Cj by comparison to the HtrA counterparts from Helicobacter pylori and Escherichia coli. We defined the architecture of HtrA _Cj at 5.8 Å resolution as a dodecamer, built of four trimers. The contacts between the trimers are quite loose, a fact that explains the flexibility and mobility of the dodecameric assembly. This flexibility has also been studied through molecular dynamics simulation, which revealed opening of the dodecamer to expose the proteolytically active site of the protease. Moreover, we examined the rearrangements at the level of oligomerization in the presence or absence of substrate using size exclusion chromatography, which revealed hexamers, dodecamers and larger oligomeric forms, as well as remarkable stability of higher oligomeric forms (> 12-mers) compared to previously tested homologs from other bacteria. Extremely dynamic decay of the higher oligomeric forms into lower forms was observed after full cleavage of the substrate by the proteolytically active variant of HtrA _Cj . Together, this is the first report on the in-depth functional and structural analysis of HtrA _Cj , which may allow the construction of therapeutically relevant HtrA _Cj inhibitors in the near future.

Peptidase PepP is a novel virulence factor of Campylobacter jejuni contributing to murine campylobacteriosis

Mechanisms of host-pathogen interactions resulting in immunopathological responses upon human Campylobacter jejuni infection are not completely understood, but the recent availability of murine infection models mimicking key features of campylobacteriosis helps solving this dilemma. During a screen for proteases expressed by C. jejuni, we identified a peptidase of the M24 family as a potential novel virulence factor, which was named PepP. The gene is strongly conserved in various Campylobacter species. A constructed deletion mutant ΔpepP of C. jejuni strain 81-176 grew as efficiently compared to isogenic wild-type (WT) or pepP complemented bacteria. To shed light on the potential role of this protease in mediating immunopathological responses in the mammalian host, we perorally challenged microbiota-depleted IL-10-/- mice with these strains. All strains stably colonized the murine gastrointestinal tract with comparably high loads. Remarkably, pepP deficiency was associated with less severe induced malaise, with less distinct apoptotic and innate immune cell responses, but also with more pronounced proliferative/regenerative epithelial cell responses in the large intestine at d6post-infection. Furthermore, pro-inflammatory mediators were lower in the colon, ileum, and mesenteric lymph nodes of mice that had been challenged with the ΔpepP mutant compared to the WT or pepP complemented strains. This also held true for extra-intestinal organs including liver, kidneys, and lungs, and, strikingly, to systemic compartments. Taken together, protease PepP is a novel virulence determinant involved in mediating campylobacteriosis. The finding that apoptosis in the colon is significantly diminished in mice infected with the pepP mutant highlights the epithelial layer as the first and main target of PepP in the intestine.

Activity-Based Probes for the High Temperature Requirement A Serine Proteases

The high temperature requirement A (HTRA) family of serine proteases mediates protein quality control. These proteins process misfolded proteins in several diseases including Alzheimer's disease (AD) and Parkinson's disease (PD). While their structures and activation mechanisms have been studied, the precise details of the regulation of their activity under physiological conditions have not been completely elucidated, partly due to the lack of suitable chemical probes. In the present study, we developed novel activity-based probes (ABPs) targeting the HTRAs and demonstrated their utility in the monitoring and quantification of changes in enzyme activity in live cells. Using our probes, we found the activity of HTRA1 to be highly elevated in an AD-like cell-based model. We also observed the active HTRA2 in live cells by using a mitochondrion-targeted probe. We believe that our probes can serve as a useful tool to study the role of human HTRAs in neurodegenerative diseases.

High‐contiguity genome assembly of the chemosynthetic gammaproteobacterial endosymbiont of the cold seep tubeworm Lamellibrachia barhami

Symbiotic relationships between vestimentiferan tubeworms and chemosynthetic Gammaproteobacteria build the foundations of many hydrothermal vent and hydrocarbon seep ecosystems in the deep sea. The association between the vent tubeworm Riftia pachyptila and its endosymbiont Candidatus Endoriftia persephone has become a model system for symbiosis research in deep‐sea vestimentiferans, while markedly fewer studies have investigated symbiotic relationships in other tubeworm species, especially at cold seeps. Here we sequenced the endosymbiont genome of the tubeworm Lamellibrachia barhami from a cold seep in the Gulf of California, using short‐ and long‐read sequencing technologies in combination with Hi‐C and Dovetail Chicago libraries. Our final assembly had a size of ~4.17 MB, a GC content of 54.54%, 137X coverage, 4153 coding sequences, and a checkm completeness score of 97.19%. A single scaffold contained 99.51% of the genome. Comparative genomic analyses indicated that the L. barhami symbiont shares a set of core genes and many metabolic pathways with other vestimentiferan symbionts, while containing 433 unique gene clusters that comprised a variety of transposases, defence‐related genes and a lineage‐specific CRISPR/Cas3 system. This assembly represents the most contiguous tubeworm symbiont genome resource to date and will be particularly valuable for future comparative genomic studies investigating structural genome evolution, physiological adaptations and host‐symbiont communication in chemosynthetic animal‐microbe symbioses.

Helicobacter pylori Oncogenicity: Mechanism, Prevention, and Risk Factors

Helicobacter pylori (H. pylori) is the most common cause of gastric ulcer; however, its association with gastric cancer has been proved through a variety of studies. Importantly, H. pylori infection affects around half of the world's population leading to a variety of gastric problems and is mostly present in asymptomatic form. Although about 20% of people infected with H. pylori develop preneoplastic gastric lesions in later stages of their life, around 2% of infected individuals develop gastric cancer. Nevertheless, the outcome of H. pylori infection is determined by complex interaction between the host genetics, its environment, and virulence factors of infecting strain. There are several biomarkers/traits of H. pylori that have been linked with the onset of cancer. Among these, presence of certain major virulence factors including cytotoxin-associated gene A (CagA), vacuolating cytotoxin (VacA), and outer inflammatory protein A (OipA) plays a significant role in triggering gastric cancer. These factors of H. pylori make it a potent carcinogen. Therefore, eradication of H. pylori infection has shown positive effects on decreasing the risk of gastric cancer, but this has become a challenge due to the development of antibiotic resistance in H. pylori against the antibiotics of choice. Thus, the unmet need is to develop new and effective treatments for H. pylori infection, considering the antimicrobial resistance in different regions of the world. This review discusses the properties of H. pylori associated with increased risk of gastric cancer, antibiotic resistance pattern, and the possible role of eradication of H. pylori in preventing gastric cancer.

A novel FRET peptide assay reveals efficient Helicobacter pylori HtrA inhibition through zinc and copper binding

Helicobacter pylori (H. pylori) secretes the chaperone and serine protease high temperature requirement A (HtrA) that cleaves gastric epithelial cell surface proteins to disrupt the epithelial integrity and barrier function. First inhibitory lead structures have demonstrated the essential role of HtrA in H. pylori physiology and pathogenesis. Comprehensive drug discovery techniques allowing high-throughput screening are now required to develop effective compounds. Here, we designed a novel fluorescence resonance energy transfer (FRET) peptide derived from a gel-based label-free proteomic approach (direct in-gel profiling of protease specificity) as a valuable substrate for H. pylori HtrA. Since serine proteases are often sensitive to metal ions, we investigated the influence of different divalent ions on the activity of HtrA. We identified Zn++ and Cu++ ions as inhibitors of H. pylori HtrA activity, as monitored by in vitro cleavage experiments using casein or E-cadherin as substrates and in the FRET peptide assay. Putative binding sites for Zn++ and Cu++ were then analyzed in thermal shift and microscale thermophoresis assays. The findings of this study will contribute to the development of novel metal ion-dependent protease inhibitors, which might help to fight bacterial infections.

Helicobacter pylori infection impairs chaperone-assisted maturation of Na-K-ATPase in gastric epithelium

Helicobacter pylori infection always induces gastritis, which may progress to ulcer disease or cancer. The mechanisms underlying mucosal injury by the bacteria are incompletely understood. Here, we identify a novel pathway for H. pylori-induced gastric injury, the impairment of maturation of the essential transport enzyme and cell adhesion molecule, Na-K-ATPase. Na-K-ATPase comprises α- and β-subunits that assemble in the endoplasmic reticulum (ER) before trafficking to the plasma membrane. Attachment of H. pylori to gastric epithelial cells increased Na-K-ATPase ubiquitylation, decreased its surface and total levels, and impaired ion balance. H. pylori did not alter degradation of plasmalemma-resident Na-K-ATPase subunits or their mRNA levels. Infection decreased association of α- and β-subunits with ER chaperone BiP and impaired assembly of α/β-heterodimers, as was revealed by quantitative mass spectrometry and immunoblotting of immunoprecipitated complexes. The total level of BiP was not altered, and the decrease in interaction with BiP was not observed for other BiP client proteins. The H. pylori-induced decrease in Na-K-ATPase was prevented by BiP overexpression, stopping protein synthesis, or inhibiting proteasomal, but not lysosomal, protein degradation. The results indicate that H. pylori impairs chaperone-assisted maturation of newly made Na-K-ATPase subunits in the ER independently of a generalized ER stress and induces their ubiquitylation and proteasomal degradation. The decrease in Na-K-ATPase levels is also seen in vivo in the stomachs of gerbils and chronically infected children. Further understanding of H. pylori-induced Na-K-ATPase degradation will provide insights for protection against advanced disease.NEW & NOTEWORTHY This work provides evidence that Helicobacter pylori decreases levels of Na-K-ATPase, a vital transport enzyme, in gastric epithelia, both in acutely infected cultured cells and in chronically infected patients and animals. The bacteria interfere with BiP-assisted folding of newly-made Na-K-ATPase subunits in the endoplasmic reticulum, accelerating their ubiquitylation and proteasomal degradation and decreasing efficiency of the assembly of native enzyme. Decreased Na-K-ATPase expression contributes to H. pylori-induced gastric injury.

Helicobacter pylori Virulence Factors Exploiting Gastric Colonization and its Pathogenicity

Helicobacter pylori colonizes the gastric epithelial cells of at least half of the world's population, and it is the strongest risk factor for developing gastric complications like chronic gastritis, ulcer diseases, and gastric cancer. To successfully colonize and establish a persistent infection, the bacteria must overcome harsh gastric conditions. H. pylori has a well-developed mechanism by which it can survive in a very acidic niche. Despite bacterial factors, gastric environmental factors and host genetic constituents together play a co-operative role for gastric pathogenicity. The virulence factors include bacterial colonization factors BabA, SabA, OipA, and HopQ, and the virulence factors necessary for gastric pathogenicity include the effector proteins like CagA, VacA, HtrA, and the outer membrane vesicles. Bacterial factors are considered more important. Here, we summarize the recent information to better understand several bacterial virulence factors and their role in the pathogenic mechanism.

The proteolytic activity of Listeria monocytogenes HtrA

Background

High temperature requirement A (HtrA) is a widely expressed chaperone and serine protease in bacteria. HtrA proteases assemble and hydrolyze misfolded proteins to enhance bacterial survival under stress conditions. Listeria monocytogenes (L. monocytogenes) is a foodborne pathogen that induces listeriosis in humans. In previous studies, it was shown that deletion of htrA in the genome of L. monocytogenes increased the susceptibility to cellular stress and attenuated virulence. However, expression and protease activity of listerial HtrA (LmHtrA) were never analyzed in detail.

Results

In this study, we cloned LmHtrA wildtype (LmHtrA^wt) and generated a proteolytic inactive LmHtrA^SA mutant. Recombinant LmHtrA^wt and LmHtrA^SA were purified and the proteolytic activity was analyzed in casein zymography and in vitro cleavage assays. LmHtrA activity could be efficiently blocked by a small molecule inhibitor targeting bacterial HtrA proteases. The expression of LmHtrA was enhanced in the stationary growth phase of L. monocytogenes and significantly contributed to bacterial survival at high temperatures.

Conclusions

Our data show that LmHtrA is a highly active caseinolytic protease and provide a deeper insight into the function and mechanism, which could lead to medical and biotechnological applications in the future.

The E-Cadherin Cleavage Associated to Pathogenic Bacteria Infections Can Favor Bacterial Invasion and Transmigration, Dysregulation of the Immune Response and Cancer Induction in Humans

Once bound to the epithelium, pathogenic bacteria have to cross epithelial barriers to invade their human host. In order to achieve this goal, they have to destroy the adherens junctions insured by cell adhesion molecules (CAM), such as E-cadherin (E-cad). The invasive bacteria use more or less sophisticated mechanisms aimed to deregulate CAM genes expression or to modulate the cell-surface expression of CAM proteins, which are otherwise rigorously regulated by a molecular crosstalk essential for homeostasis. Apart from the repression of CAM genes, a drastic decrease in adhesion molecules on human epithelial cells can be obtained by induction of eukaryotic endoproteases named sheddases or through synthesis of their own (prokaryotic) sheddases. Cleavage of CAM by sheddases results in the release of soluble forms of CAM. The overexpression of soluble CAM in body fluids can trigger inflammation and pro-carcinogenic programming leading to tumor induction and metastasis. In addition, the reduction of the surface expression of E-cad on epithelia could be accompanied by an alteration of the anti-bacterial and anti-tumoral immune responses. This immune response dysfunction is likely to occur through the deregulation of immune cells homing, which is controlled at the level of E-cad interaction by surface molecules α_E integrin (CD103) and lectin receptor KLRG1. In this review, we highlight the central role of CAM cell-surface expression during pathogenic microbial invasion, with a particular focus on bacterial-induced cleavage of E-cad. We revisit herein the rapidly growing body of evidence indicating that high levels of soluble E-cad (sE-cad) in patients’ sera could serve as biomarker of bacterial-induced diseases.

Establishment of serine protease htrA mutants in Helicobacter pylori is associated with secA mutations

Helicobacter pylori plays an essential role in the pathogenesis of gastritis, peptic ulcer disease, and gastric cancer. The serine protease HtrA, an important secreted virulence factor, disrupts the gastric epithelium, which enables H. pylori to transmigrate across the epithelium and inject the oncogenic CagA protein into host cells. The function of periplasmic HtrA for the H. pylori cell is unknown, mainly due to unavailability of the htrA mutants. In fact, htrA has been described as an essential gene in this bacterium. We have screened 100 worldwide H. pylori isolates and show that only in the N6 strain it was possible to delete htrA or mutate the htrA gene to produce proteolytically inactive HtrA. We have sequenced the wild-type and mutant chromosomes and we found that inactivation of htrA is associated with mutations in SecA – a component of the Sec translocon apparatus used to translocate proteins from the cytoplasm into the periplasm. The cooperation of SecA and HtrA has been already suggested in Streptococcus pneumonia, in which these two proteins co-localize. Hence, our results pinpointing a potential functional relationship between HtrA and the Sec translocon in H. pylori possibly indicate for the more general mechanism responsible to maintain bacterial periplasmic homeostasis.

Tailor-Made Detection of Individual Phosphorylated and Non-Phosphorylated EPIYA-Motifs of Helicobacter pylori Oncoprotein CagA

The gastric pathogen and carcinogen Helicobacter pylori(H. pylori) encodes a type IV secretion system for translocation of the effector protein CagA into host cells. Injected CagA becomes tyrosine-phosphorylated at the five amino acid residue Glutamate-Proline- Isoleucine-Tyrosine-Alanine (EPIYA)-sequence motifs. These phosphorylated EPIYA-sites represent recognition motifs for binding of multiple host factors, which then manipulate signaling pathways to trigger gastric disease. Thus, efficient detection of single phosphorylated EPIYA-motifs in CagA is required. Detection of phospho-CagA is primarily performed using commercial pan-phosphotyrosine antibodies. However, those antibodies were originally generated to recognize many phosphotyrosines in various mammalian proteins and are not optimized for use in bacteria. To address this important limitation, we synthesized 11-mer phospho- and non-phospho-peptides from EPIYA-motifs A, B, and C, and produced three phospho-specific and three non-phospho-specific rabbit polyclonal CagA antibodies. These antibodies specifically recognized the corresponding phosphorylated and non-phosphorylated EPIYA-motifs, while the EPIYA-C antibodies also recognized the related East-Asian EPIYA-D motif. Otherwise, no cross-reactivity of the antibodies among EPIYAs was observed. Western blotting demonstrated that each EPIYA-motif can be predominantly phosphorylated during H. pylori infection. This represents the first complete set of phospho-specific antibodies for an effector protein in bacteria, providing useful tools to gather information for the categorization of CagA phosphorylation, cancer signaling, and gastric disease progression.

Properties of the HtrA Protease From Bacterium Helicobacter pylori Whose Activity Is Indispensable for Growth Under Stress Conditions

The protease high temperature requirement A from the gastric pathogen Helicobacter pylori (HtrA_Hp) belongs to the well conserved family of serine proteases. HtrA_Hp is an important secreted virulence factor involved in the disruption of tight and adherens junctions during infection. Very little is known about the function of HtrA_Hp in the H. pylori cell physiology due to the lack of htrA knockout strains. Here, using a newly constructed ΔhtrA mutant strain, we found that bacteria deprived of HtrA_Hp showed increased sensitivity to certain types of stress, including elevated temperature, pH and osmotic shock, as well as treatment with puromycin. These data indicate that HtrA_Hp plays a protective role in the H. pylori cell, presumably associated with maintenance of important periplasmic and outer membrane proteins. Purified HtrA_Hp was shown to be very tolerant to a wide range of temperature and pH values. Remarkably, the protein exhibited a very high thermal stability with the melting point (T_m) values of above 85°C. Moreover, HtrA_Hp showed the capability to regain its active structure following treatment under denaturing conditions. Taken together, our work demonstrates that HtrA_Hp is well adapted to operate under harsh conditions as an exported virulence factor, but also inside the bacterial cell as an important component of the protein quality control system in the stressed cellular envelope.