Opa proteins of pathogenic neisseriae initiate Src kinase-dependent or lipid raft-mediated uptake via distinct human carcinoembryonic antigen-related cell adhesion molecule isoforms

Mechanisms of host manipulation by Neisseria gonorrhoeae

Neisseria gonorrhoeae (also known as gonococcus) has been causing gonorrhoea in humans since ancient Egyptian times. Today, global gonorrhoea infections are rising at an alarming rate, in concert with an increasing number of antimicrobial-resistant strains. The gonococcus has concurrently evolved several intricate mechanisms that promote pathogenesis by evading both host immunity and defeating common therapeutic interventions. Central to these adaptations is the ability of the gonococcus to manipulate various host microenvironments upon infection. For example, the gonococcus can survive within neutrophils through direct regulation of both the oxidative burst response and maturation of the phagosome; a concerning trait given the important role neutrophils have in defending against invading pathogens. Hence, a detailed understanding of how N. gonorrhoeae exploits the human host to establish and maintain infection is crucial for combating this pathogen. This review summarizes the mechanisms behind host manipulation, with a central focus on the exploitation of host epithelial cell signaling to promote colonization and invasion of the epithelial lining, the modulation of the host immune response to evade both innate and adaptive defenses, and the manipulation of host cell death pathways to both assist colonization and combat antimicrobial activities of innate immune cells. Collectively, these pathways act in concert to enable N. gonorrhoeae to colonize and invade a wide array of host tissues, both establishing and disseminating gonococcal infection.

Phagocytosis mediated by the human granulocyte receptor CEACAM3 is limited by the receptor-type protein tyrosine phosphatase PTPRJ

Carcinoembryonic Antigen-related Cell Adhesion Molecule 3 (CEACAM3) is a human granulocyte receptor mediating the efficient phagocytosis of a subset of human-restricted bacterial pathogens. Its function depends on phosphorylation of a tyrosine-based sequence motif, but the enzyme(s) responsible for reversing this modification are unclear. Here, we identify the receptor-type protein tyrosine phosphatase PTPRJ as a negative regulator of CEACAM3-mediated phagocytosis. We show depletion of PTPRJ results in a gain-of-function phenotype, while overexpression of a constitutively active PTPRJ phosphatase strongly reduces bacterial uptake via CEACAM3. We also determined that recombinant PTPRJ directly dephosphorylates the cytoplasmic tyrosine residues of purified full-length CEACAM3 and recognizes synthetic CEACAM3-derived phospho-peptides as substrates. Dephosphorylation of CEACAM3 by PTPRJ is also observed in intact cells, thereby limiting receptor-initiated cytoskeletal re-arrangements, lamellipodia formation, and bacterial uptake. Finally, we show that human phagocytes deficient for PTPRJ exhibit exaggerated lamellipodia formation and enhanced opsonin-independent phagocytosis of CEACAM3-binding bacteria. Taken together, our results highlight PTPRJ as a bona fide negative regulator of CEACAM3-initiated phagocyte functions, revealing a potential molecular target to limit CEACAM3-driven inflammatory responses.

The Host-Pathogen Interactions and Epicellular Lifestyle of Neisseria meningitidis

Neisseria meningitidis is a gram-negative diplococcus and a transient commensal of the human nasopharynx. It shares and competes for this niche with a number of other Neisseria species including N. lactamica, N. cinerea and N. mucosa. Unlike these other members of the genus, N. meningitidis may become invasive, crossing the epithelium of the nasopharynx and entering the bloodstream, where it rapidly proliferates causing a syndrome known as Invasive Meningococcal Disease (IMD). IMD progresses rapidly to cause septic shock and meningitis and is often fatal despite aggressive antibiotic therapy. While many of the ways in which meningococci survive in the host environment have been well studied, recent insights into the interactions between N. meningitidis and the epithelial, serum, and endothelial environments have expanded our understanding of how IMD develops. This review seeks to incorporate recent work into the established model of pathogenesis. In particular, we focus on the competition that N. meningitidis faces in the nasopharynx from other Neisseria species, and how the genetic diversity of the meningococcus contributes to the wide range of inflammatory and pathogenic potentials observed among different lineages.

Variable Expression of Opa Proteins by Neisseria gonorrhoeae Influences Bacterial Association and Phagocytic Killing by Human Neutrophils

Neisseria gonorrhoeae infection is characterized by local and abundant recruitment of neutrophils. Despite neutrophils' antimicrobial activities, viable N. gonorrhoeae is recovered from infected individuals, leading to the question of how N. gonorrhoeae survives neutrophil attack. One feature impacting N. gonorrhoeae-neutrophil interactions is the phase-variable opacity-associated (Opa) proteins. Most Opa proteins engage human carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) to facilitate bacterial binding and invasion. Neutrophils express two transmembrane CEACAMs, CEACAM1 and the granulocyte-specific CEACAM3. While N. gonorrhoeae isolated from infected individuals is frequently Opa⁺, expression of OpaD from strain FA1090, which interacts with CEACAMs 1 and 3, is associated with reduced N. gonorrhoeae survival after exposure to human neutrophils. In this study, we hypothesized that the receptor-binding capability of individual Opa proteins impacts bacterial survival in the presence of neutrophils. To test this hypothesis, we introduced opa genes that are constitutively expressed into a derivative of strain FA1090 with all 11 opa genes deleted. The engineered genes encode Opa proteins that bind CEACAM1 and -3, CEACAM1 but not CEACAM3, or neither CEACAM1 nor -3. N. gonorrhoeae expressing CEACAM3-binding Opa proteins survived significantly less well than bacteria expressing other Opa proteins when exposed to primary human neutrophils. The CEACAM3-binding N. gonorrhoeae had significantly greater association with and internalization by neutrophils. However, once internalized, bacteria were similarly killed inside neutrophils, regardless of Opa expression. Furthermore, Opa expression did not significantly impact neutrophil granule mobilization. Our findings indicate that the extent to which Opa proteins mediate nonopsonic binding is the predominant determinant of bacterial survival from neutrophils. IMPORTANCE Neisseria gonorrhoeae, the cause of gonorrhea, is an urgent-threat pathogen due to increasing numbers of infections and increased antibiotic resistance. Many surface components of N. gonorrhoeae are phase variable, including the Opa protein family of adhesins and invasins. While Opa protein expression is selected for in vivo, bacteria expressing some Opa proteins are readily killed by neutrophils, which are recruited to sites of infection. The reason for this discrepancy has remained unresolved. Our work shows that Opa-dependent differences in bacterial survival after exposure to primary human neutrophils correlates with Opa-dependent bacterial binding and phagocytosis. These findings underscore how the ability of N. gonorrhoeae to change Opa expression through phase variation contributes to bacterial resistance to neutrophil clearance.

Gonococcal invasion into epithelial cells depends on both cell polarity and ezrin

Neisseria gonorrhoeae (GC) establishes infection in women from the cervix, lined with heterogeneous epithelial cells from non-polarized stratified at the ectocervix to polarized columnar at the endocervix. We have previously shown that GC differentially colonize and transmigrate across the ecto and endocervical epithelia. However, whether and how GC invade into heterogeneous cervical epithelial cells is unknown. This study examined GC entry of epithelial cells with various properties, using human cervical tissue explant and non-polarized/polarized epithelial cell line models. While adhering to non-polarized and polarized epithelial cells at similar levels, GC invaded into non-polarized more efficiently than polarized epithelial cells. The enhanced GC invasion in non-polarized epithelial cells was associated with increased ezrin phosphorylation, F-actin and ezrin recruitment to GC adherent sites, and the elongation of GC-associated microvilli. Inhibition of ezrin phosphorylation inhibited F-actin and ezrin recruitment and microvilli elongation, leading to a reduction in GC invasion. The reduced GC invasion in polarized epithelial cells was associated with non-muscle myosin II-mediated F-actin disassembly and microvilli denudation at GC adherence sites. Surprisingly, intraepithelial GC were only detected inside epithelial cells shedding from the cervix by immunofluorescence microscopy, but not significantly in the ectocervical and the endocervical regions. We observed similar ezrin and F-actin recruitment in exfoliated cervical epithelial cells but not in those that remained in the ectocervical epithelium, as the luminal layer of ectocervical epithelial cells expressed ten-fold lower levels of ezrin than those beneath. However, GC inoculation induced F-actin reduction and myosin recruitment in the endocervix, similar to what was seen in polarized epithelial cells. Collectively, our results suggest that while GC invade non-polarized epithelial cells through ezrin-driven microvilli elongation, the apical polarization of ezrin and F-actin inhibits GC entry into polarized epithelial cells.

Neisseria gonorrhoeae (GC) causes gonorrhea in women by infecting the female reproductive tract. GC entry of epithelial cells has long been observed in patients’ biopsies and studied in various types of epithelial cells. However, how GC invade into the heterogeneous epithelia of the human cervix is unknown. This study reveals that both the expression level of ezrin, an actin-membrane linker protein, and the polarization of ezrin-actin networks in epithelial cells regulate GC invasion. GC interactions with non-polarized squamous epithelial cells expressing ezrin induce ezrin activation, ezrin-actin accumulation, and microvilli elongation at GC adherent sites, leading to invasion. Low ezrin expression levels in the luminal ectocervical epithelial cells are associated with low levels of intraepithelial GC. In contrast, apical polarization of ezrin-actin networks in columnar endocervical epithelial cells reduces GC invasion. GC interactions induce myosin activation, which causes disassembly of ezrin-actin networks and microvilli modification at GC adherent sites, extending GC-epithelial contact. Expression of opacity-associated proteins on GC promotes GC invasion by enhancing ezrin-actin accumulation in squamous epithelial cells and inhibiting ezrin-actin disassembly in columnar endocervical epithelial cells. Thus, reduced ezrin expression and ezrin-actin polarization are potential ways for cervical epithelial cells to curtail GC invasion.

Antibody ligation of CEACAM1, CEACAM3, and CEACAM6, differentially enhance the cytokine release of human neutrophils in responses to Candida albicans

Invasive candidiasis is a healthcare-associated fungal infection with a high mortality rate. Neutrophils, the first line of defense during fungal infections, express the immunoregulatory Candida albicans receptors CEACAM1, CEACAM3, and CEACAM6. We analyzed the effects of specific antibodies on C. albicans-induced neutrophil responses. CEACAM6 ligation by 1H7-4B and to some extent CEACAM1 ligation by B3-17, but not CEACAM3 ligation by 308/3-3, resulted in the immediate release of stored CXCL8 and altered transcriptional responses of the C. albicans-stimulated neutrophils. Integrated network analyses and dynamic simulations of signaling cascades predicted alterations in apoptosis and cytokine secretion. We verified that CEACAM6 ligation enhanced Candida-induced neutrophil apoptosis and increased long-term IL-1β/IL-6 release in responses to C. albicans. CEACAM3 ligation, but not CEACAM1 ligation, increased the long-term release of pro-inflammatory IL-1β/IL-6. Taken together, we demonstrated for the first time that ligation of CEACAM receptors differentially affects the regulation of C. albicans-induced immune functions in human neutrophils.

Invasion of the choroid plexus epithelium by Neisseria meningitidis is differently mediated by Arp2/3 signaling and possibly by dynamin dependent on the presence of the capsule

Neisseria meningitis (Nm) is a human-specific bacterial pathogen that can cause sepsis and meningitis. To cause meningitis Nm must enter the central nervous system (CNS) across one of the barriers between the blood and the brain. We have previously shown that a capsule-depleted Serogroup B strain of Nm displays enhanced invasion into human choroid plexus (CP) epithelial papilloma (HIBCPP) cells, which represent an in vitro model of the blood-cerebrospinal fluid barrier (BCSFB). Still, the processes involved during CNS invasion by Nm, especially the role of host cell actin cytoskeleton remodeling, are not investigated in detail. Here, we demonstrate that invasion into CP epithelial cells by encapsulated and capsule-depleted Nm is mediated by distinct host cell pathways. Whereas a Serogroup B wild-type strain enters HIBCPP cells by a possibly dynamin-independent, but actin related protein 2/3 (Arp2/3)-dependent mechanism, invasion by a capsule-depleted mutant is reduced by the dynamin inhibitor dynasore and Arp2/3-independent. Both wild-type and mutant bacteria require Src kinase activity for entry into HIBCPP cells. Our data show that Nm can employ different mechanisms for invasion into the CP epithelium dependent on the presence of a capsule.

Key sunitinib-related biomarkers for renal cell carcinoma

Background

Renal cell carcinoma (RCC) contributed to 403,262 new cases worldwide in 2018, which constitutes 2.2% of global cancer, nevertheless, sunitinib, one of the major targeted therapeutic agent for RCC, often developed invalid due to resistance. Emerging evidences suggested sunitinib can impact tumor environment which has been proven to be a vital factor for tumor progression.

Methods

In the present study, we used ssGSEA to extract the immune infiltrating abundance of clear cell RCC (ccRCC) and normal control samples from GSE65615, TCGA, and GTEx; key immune cells were determined by Student's t‐test and univariable Cox analysis. Co‐expression network combined with differentially expressed analysis was then applied to derive key immune‐related genes for ccRCC, followed by the identification of hub genes using differential expression analysis. Subsequently, explorations and validations of the biological function and the immune‐related and sunitinib‐related characteristics were conducted in KEGG, TISIDB, Oncomine, ICGC, and GEO databases.

Results

We refined immature dendritic cells and central memory CD4 T cells which showed associations with sunitinib and ccRCC. Following, five hub genes (CRYBB1, RIMBP3C, CEACAM4, HAMP, and LYL1) were identified for their strong relationships with sunitinib and immune infiltration in ccRCC. Further validations in external data refined CRYBB1, CEACAM4, and HAMP which play a vital role in sunitinib resistance, immune infiltrations in ccRCC, and the development and progression of ccRCC. In conclusion, our findings could shed light on the resistance of sunitinib in ccRCC and provide novel biomarkers or drug targets for ccRCC.

Neisseria gonorrhoeae Blocks Epithelial Exfoliation by Nitric-Oxide-Mediated Metabolic Cross Talk to Promote Colonization in Mice

Several pathogens suppress exfoliation, a key defense of epithelia against microbial colonization. Common among these pathogens, exemplified by Neisseria gonorrhoeae, is their ability to bind carcinoembryonic antigen-related cell adhesion molecules (CEACAMs). Gonococcal CEACAM engagement triggers the expression of CD105, which is necessary to block epithelial exfoliation, whereas homotypic CEACAM-CEACAM interactions or antibody-mediated CEACAM clustering does not lead to CD105 expression. Here, we show that CEACAM-associated bacteria release nitric oxide (NO) during anaerobic respiration, and membrane-permeable NO initiates a eukaryotic signaling pathway involving soluble guanylate cyclase (sGC), protein kinase G, and the transcription factor CREB to upregulate CD105 expression. A murine vaginal infection model with N. gonorrhoeae reveals this metabolic cross communication allows bacterial suppression of epithelial exfoliation to facilitate mucosal colonization. Disrupting NO-initiated responses in host cells re-establishes epithelial exfoliation and inhibits mouse genital tract colonization by N. gonorrhoeae, suggesting a host-directed approach to prevent bacterial infections.

Nanosphere Loaded with Curcumin Inhibits the Gastrointestinal Cell Death Signaling Pathway Induced by the Foodborne Pathogen Vibrio vulnificus

Curcumin, a hydrophobic polyphenol of turmeric, has a variety of biological functions as a herbal supplement, but its poor gastric absorption rate is one of the major factors limiting its oral bioavailability. In the present study, we have investigated the functional role of a nanosphere loaded with curcumin (CN) during host cell death elicited by the Gram-negative bacterium V. vulnificus in human gastrointestinal epithelial HT-29 cells and an ileal-ligated mouse model. The recombinant protein (r) VvhA produced by V. vulnificus significantly reduced the viability of HT-29 cells. The cytotoxic effect of rVvhA was restored upon a treatment with CN (100 ng/mL), which had shown 1000-fold higher anti-apoptotic efficacy than curcumin. CN inhibited the phosphorylation of c-Src and PKC mediated by intracellular ROS responsible for the distinctive activation of the MAPKs in rVvhA-treated HT-29 cells. Interestingly, CN significantly restored the expression of Bax, Bcl-2, and cleaved caspase-3 as regulated by the phosphorylation of NF-κB. In mouse models of V. vulnificus infection, treatment with CN had a blocking effect that elevated the levels of TUNEL-positive DNA fragmentation and apoptosis-related proteins. These results indicate that CN is a functional agent that manipulates the V. vulnificus VvhA signaling pathway responsible for gastrointestinal cell death.

CEACAM3-A Prim(at)e Invention for Opsonin-Independent Phagocytosis of Bacteria

Phagocytosis is one of the key innate defense mechanisms executed by specialized cells in multicellular animals. Recent evidence suggests that a particular phagocytic receptor expressed by human polymorphonuclear granulocytes, the carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3), is one of the fastest-evolving human proteins. In this focused review, we will try to resolve the conundrum why a conserved process such as phagocytosis is conducted by a rapidly changing receptor. Therefore, we will first summarize the biochemical and structural details of this immunoglobulin-related glycoprotein in the context of the human CEACAM family. The function of CEACAM3 for the efficient, opsonin-independent detection and phagocytosis of highly specialized, host-restricted bacteria will be further elaborated. Taking into account the decisive role of CEACAM3 in the interaction with pathogenic bacteria, we will discuss the evolutionary trajectory of the CEACAM3 gene within the primate lineage and highlight the consequences of CEACAM3 polymorphisms in human populations. From a synopsis of these studies, CEACAM3 emerges as an important component of human innate immunity and a prominent example of a dedicated receptor for professional phagocytosis.

Neisseria gonorrhoeae infects the heterogeneous epithelia of the human cervix using distinct mechanisms

Sexually transmitted infections are a critical public health issue. However, the mechanisms underlying sexually transmitted infections in women and the link between the infection mechanism and the wide range of clinical outcomes remain elusive due to a lack of research models mimicking human infection in vivo. We established a human cervical tissue explant model to mimic local Neisseria gonorrhoeae (GC) infections. We found that GC preferentially colonize the ectocervix by activating integrin-β1, which inhibits epithelial shedding. GC selectively penetrate into the squamocolumnar junction (TZ) and endocervical epithelia by inducing β-catenin phosphorylation, which leads to E-cadherin junction disassembly. Epithelial cells in various cervical regions differentially express carcinoembryonic antigen-related cell adhesion molecules (CEACAMs), the host receptor for GC opacity-associated proteins (Opa_CEA). Relatively high levels were detected on the luminal membrane of ecto/endocervical epithelial cells but very low levels intracellularly in TZ epithelial cells. CEACAM-Opa_CEA interaction increased ecto/endocervical colonization and reduced endocervical penetration by increasing integrin-β1 activation and inhibiting β-catenin phosphorylation respectively, through CEACAM downstream signaling. Thus, the intrinsic properties of cervical epithelial cells and phase-variation of bacterial surface molecules both play a role in controlling GC infection mechanisms and infectivity, preferential colonization or penetration, potentially leading to asymptomatic or symptomatic infection.

Gonorrhea, caused by Neisseria gonorrhoeae (GC), is a common sexually transmitted infection and has become a public health crisis due to a steady increase in antibiotic-resistant cases. How GC infect the female reproductive tract (FRT) and cause various clinical outcomes is still unknown. This study used human cervical explants to examine the mechanism by which GC infect the heterogeneous mucosa of the human cervix, the gate of the FRT. We show that GC preferentially colonize stratified epithelial cells in the vaginal-cervical region by enhancing epithelial cell adherence. GC selectively penetrate into tissues of the squamocolumnar junction and cervical-endometrial regions but not the vaginal-cervical region by loosening epithelial cell-cell junctions. The expression of opacity-associated proteins on GC regulates the infection patterns depending on the expression of the host receptors on various types of epithelia and receptor downstream signaling. These data suggest that both intrinsic properties of cervical epithelial cells and phase-variation of bacterial surface molecules play a role in determining GC infectivity. Our findings can explain how GC infection leads to asymptomatic or symptomatic infection.

Progress Toward a Gonococcal Vaccine: The Way Forward

The concept of immunizing against gonorrhea has received renewed interest because of the recent emergence of strains of Neisseria gonorrhoeae that are resistant to most currently available antibiotics, an occurrence that threatens to render gonorrhea untreatable. However, despite efforts over many decades, no vaccine has yet been successfully developed for human use, leading to pessimism over whether this goal was actually attainable. Several factors have contributed to this situation, including extensive variation of the expression and specificity of many of the gonococcal surface antigens, and the ability of N. gonorrhoeae to resist destruction by complement and other innate immune defense mechanisms. The natural host restriction of N. gonorrhoeae for humans, coupled with the absence of any definable state of immunity arising from an episode of gonorrhea, have also complicated efforts to study gonococcal pathogenesis and the host's immune responses. However, recent findings have elucidated how the gonococcus exploits and manipulates the host's immune system for its own benefit, utilizing human-specific receptors for attachment to and invasion of tissues, and subverting adaptive immune responses that might otherwise be capable of eliminating it. While no single experimental model is capable of providing all the answers, experiments utilizing human cells and tissues in vitro, various in vivo animal models, including genetically modified strains of mice, and both experimental and observational human clinical studies, have combined to yield important new insight into the immuno-pathogenesis of gonococcal infection. In turn, these have now led to novel approaches for the development of a gonococcal vaccine. Ongoing investigations utilizing all available tools are now poised to make the development of an effective human vaccine against gonorrhea an achievable goal within a foreseeable time-frame.

Molecular interactions between Neisseria meningitidis and its human host

Neisseria meningitidis is a Gram‐negative bacterium that asymptomatically colonises the nasopharynx of humans. For an unknown reason, N. meningitidis can cross the nasopharyngeal barrier and invade the bloodstream where it becomes one of the most harmful extracellular bacterial pathogen. This infectious cycle involves the colonisation of two different environments. (a) In the nasopharynx, N. meningitidis grow on the top of mucus‐producing epithelial cells surrounded by a complex microbiota. To survive and grow in this challenging environment, the meningococcus expresses specific virulence factors such as polymorphic toxins and MDAΦ. (b) Meningococci have the ability to survive in the extra cellular fluids including blood and cerebrospinal fluid. The interaction of N. meningitidis with human endothelial cells leads to the formation of typical microcolonies that extend overtime and promote vascular injury, disseminated intravascular coagulation, and acute inflammation. In this review, we will focus on the interplay between N. meningitidis and these two different niches at the cellular and molecular level and discuss the use of inhibitors of piliation as a potent therapeutic approach.

Adaptation to Host-Specific Bacterial Pathogens Drives Rapid Evolution of a Human Innate Immune Receptor

The selective pressure by infectious agents is a major driving force in the evolution of humans and other mammals. Members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family serve as receptors for bacterial pathogens of the genera Haemophilus, Helicobacter, Neisseria, and Moraxella, which engage CEACAMs via distinct surface adhesins. While microbial attachment to epithelial CEACAMs facilitates host colonization, recognition by CEACAM3, a phagocytic receptor expressed by granulocytes, eliminates CEACAM-binding bacteria. Sequence analysis of primate CEACAM3 orthologs reveals that this innate immune receptor is one of the most rapidly evolving human proteins. In particular, the pathogen-binding extracellular domain of CEACAM3 shows a high degree of non-synonymous versus synonymous nucleotide exchanges, indicating an exceptionally strong positive selection. Using CEACAM3 domains derived from different primates, we find that the amino acid alterations found in CEACAM3 translate into characteristic binding patterns for bacterial adhesins. One such amino acid residue is F62 in human and chimp CEACAM3, which is not present in other primates and which is critical for binding the OMP P1 adhesin of Haemophilus aegyptius. Incorporation of the F62-containing motif into gorilla CEACAM3 results in a gain-of-function phenotype with regard to phagocytosis of H. aegyptius. Moreover, CEACAM3 polymorphisms found in human subpopulations widen the spectrum of recognized bacterial adhesins, suggesting an ongoing multivariate selection acting on this innate immune receptor. The species-specific detection of diverse bacterial adhesins helps to explain the exceptionally fast evolution of CEACAM3 within the primate lineage and provides an example of Red Queen dynamics in the human genome.

Abnormal Golgi pH Homeostasis in Cancer Cells Impairs Apical Targeting of Carcinoembryonic Antigen by Inhibiting Its Glycosyl-Phosphatidylinositol Anchor-Mediated Association with Lipid Rafts

AIMS

Carcinoembryonic antigen (CEACAM5, CEA) is a known tumor marker for colorectal cancer that localizes in a polarized manner to the apical surface in normal colon epithelial cells whereas in cancer cells it is present at both the apical and basolateral surfaces of the cells. Since the Golgi apparatus sorts and transports most proteins to these cell surface domains, we set out here to investigate whether any of the factors commonly associated with tumorigenesis, including hypoxia, generation of reactive oxygen species (ROS), altered redox homeostasis, or an altered Golgi pH, are responsible for mistargeting of CEA to the basolateral surface in cancer cells.

RESULTS

Using polarized nontumorigenic Madin-Darby canine kidney (MDCK) cells and CaCo-2 colorectal cancer cells as targets, we show that apical delivery of CEA is not affected by hypoxia, ROS, nor changes in the Golgi redox state. Instead, we find that an elevated Golgi pH induces basolateral targeting of CEA and increases its TX-100 solubility, indicating impaired association of CEA with lipid rafts. Moreover, disruption of lipid rafts by methyl-β-cyclodextrin induced accumulation of the CEA protein at the basolateral surface in MDCK cells. Experiments with the glycosylphosphatidylinositol (GPI)-anchorless CEA mutant and CEA-specific GPI-anchored enhanced green fluorescent protein (EGFP-GPI) fusion protein revealed that the GPI-anchor was critical for the pH-dependent apical delivery of the CEA in MDCK cells. Innovation and Conclusion: The findings indicate that an abnormal Golgi pH homeostasis in cancer cells is an important factor that causes mistargeting of CEA to the basolateral surface of cancer cells via inhibiting its GPI-anchor-mediated association with lipid rafts.

Phasome analysis of pathogenic and commensal Neisseria species expands the known repertoire of phase variable genes, and highlights common adaptive strategies

Pathogenic Neisseria are responsible for significantly higher levels of morbidity and mortality than their commensal relatives despite having similar genetic contents. Neisseria possess a disparate arsenal of surface determinants that facilitate host colonisation and evasion of the immune response during persistent carriage. Adaptation to rapid changes in these hostile host environments is enabled by phase variation (PV) involving high frequency, stochastic switches in expression of surface determinants. In this study, we analysed 89 complete and 79 partial genomes, from the NCBI and Neisseria PubMLST databases, representative of multiple pathogenic and commensal species of Neisseria using PhasomeIt, a new program that identifies putatively phase-variable genes and homology groups by the presence of simple sequence repeats (SSR). We detected a repertoire of 884 putative PV loci with maxima of 54 and 47 per genome in gonococcal and meningococcal isolates, respectively. Most commensal species encoded a lower number of PV genes (between 5 and 30) except N. lactamica wherein the potential for PV (36–82 loci) was higher, implying that PV is an adaptive mechanism for persistence in this species. We also characterised the repeat types and numbers in both pathogenic and commensal species. Conservation of SSR-mediated PV was frequently observed in outer membrane proteins or modifiers of outer membrane determinants. Intermittent and weak selection for evolution of SSR-mediated PV was suggested by poor conservation of tracts with novel PV genes often occurring in only one isolate. Finally, we describe core phasomes—the conserved repertoires of phase-variable genes—for each species that identify overlapping but distinctive adaptive strategies for the pathogenic and commensal members of the Neisseria genus.

The Helicobacter pylori adhesin protein HopQ exploits the dimer interface of human CEACAMs to facilitate translocation of the oncoprotein CagA

Helicobacter pylori infects half of the world's population, and strains that encode the cag type IV secretion system for injection of the oncoprotein CagA into host gastric epithelial cells are associated with elevated levels of cancer. CagA translocation into host cells is dependent on interactions between the H. pylori adhesin protein HopQ and human CEACAMs. Here, we present high-resolution structures of several HopQ-CEACAM complexes and CEACAMs in their monomeric and dimeric forms establishing that HopQ uses a coupled folding and binding mechanism to engage the canonical CEACAM dimerization interface for CEACAM recognition. By combining mutagenesis with biophysical and functional analyses, we show that the modes of CEACAM recognition by HopQ and CEACAMs themselves are starkly different. Our data describe precise molecular mechanisms by which microbes exploit host CEACAMs for infection and enable future development of novel oncoprotein translocation inhibitors and H. pylori-specific antimicrobial agents.

The ironclad truth: how in vivo transcriptomics and in vitro mechanistic studies shape our understanding of Neisseria gonorrhoeae gene regulation during mucosal infection

Neisseria gonorrhoeae is one of the most prevalent sexually transmitted infections worldwide. This obligate human pathogen has been extensively studied in vitro, where bacterial factors that are known to contribute to gonococcal disease and their regulation are relatively well defined. However, these in vitro experimental conditions only loosely replicate the host specific environment encountered by the bacteria in vivo. We recently reported on the complete gonococcal transcriptome expressed during natural human mucosal infection using RNA-seq analysis. Gene transcripts expressed in vivo (in vivo expressed factors) included genes encoding antibiotic resistance determinants, and a large number of hypothetical genes. A comparison of the gonococcal transcriptome expressed in vivo with the corresponding strain grown in vitro identified sets of genes regulated by infection, including those regulated by iron and the transcriptional regulatory protein Fur. We highlight here the role of Fur and gonococcal-specific regulatory processes important for infection and pathogenicity. We have determined that the genes controlled by Fur follow the same expression pattern in vivo as described previously in vitro, confirming Fur's regulatory role during infection. Collectively, these studies provide new insights into how bacterial fitness and pathogenicity are modulated during human mucosal infection.

Neisseria gonorrhoeae infects the human endocervix by activating non-muscle myosin II-mediated epithelial exfoliation

Colonization and disruption of the epithelium is a major infection mechanism of mucosal pathogens. The epithelium counteracts infection by exfoliating damaged cells while maintaining the mucosal barrier function. The sexually transmitted bacterium Neisseria gonorrhoeae (GC) infects the female reproductive tract primarily from the endocervix, causing gonorrhea. However, the mechanism by which GC overcome the mucosal barrier remains elusive. Using a new human tissue model, we demonstrate that GC can penetrate into the human endocervix by inducing the exfoliation of columnar epithelial cells. We found that GC colonization causes endocervical epithelial cells to shed. The shedding results from the disassembly of the apical junctions that seal the epithelial barrier. Apical junction disruption and epithelial exfoliation increase GC penetration into the endocervical epithelium without reducing bacterial adherence to and invasion into epithelial cells. Both epithelial exfoliation and junction disruption require the activation and accumulation of non-muscle myosin II (NMII) at the apical surface and GC adherent sites. GC inoculation activates NMII by elevating the levels of the cytoplasmic Ca²⁺ and NMII regulatory light chain phosphorylation. Piliation of GC promotes, but the expression of a GC opacity-associated protein variant, OpaH that binds to the host surface proteins CEACAMs, inhibits GC-induced NMII activation and reorganization and Ca²⁺ flux. The inhibitory effects of OpaH lead to reductions in junction disruption, epithelial exfoliation, and GC penetration. Therefore, GC phase variation can modulate infection in the human endocervix by manipulating the activity of NMII and epithelial exfoliation.

Neisseria gonorrhoeae (GC) infects human genital epithelium causing gonorrhea, a common sexually transmitted infection. Gonorrhea is a critical public health issue due to increased prevalence of antibiotic-resistant strains. Because humans are the only host for GC, a lack of a human infection model has been a major obstacle to our understanding of GC infection. Here we use a human tissue explant model to examine the mechanism by which GC infect the human endocervix, the primary site for GC infection in women. We show that GC penetrate into the human endocervix by activating the actin motor myosin and epithelial shedding. Myosin activation causes the disruption of the endocervical epithelial barrier by inducing apical junction disassembly and epithelial cell shedding, allowing GC penetration into the human endocervical tissue. GC activate myosin by inducing Ca²⁺-dependent phosphorylation of myosin light chain. We further show that GC can enhance and reduce the penetration by expressing pili and the opacity-associated protein that promotes and inhibits myosin activation, respectively. Our study is the first demonstration of GC penetration into the human endocervix. Our results provide new insights into the mechanism by which GC manipulate signaling and cytoskeletal apparatus in epithelial cells to achieve penetrating and non-penetrating infection.

Vibrio vulnificus VvhA induces autophagy-related cell death through the lipid raft-dependent c-Src/NOX signaling pathway

VvhA, a virulent factor of Vibrio (V.) vulnificus, induces acute cell death in a destructive manner. Autophagy plays an important role in cell death, but the functional role of VvhA in autophagy-related cell death has not been elucidated yet. We found that rVvhA significantly increased LC3 puncta formation and autophagic flux in promoting the cell death of human intestinal epithelial Caco-2 cells. The cell death induced by rVvhA was independent of lysosomal permeabilizaton and caspase activation. rVvhA induced rapid phosphorylation of c-Src in the membrane lipid raft, which resulted in an increased interaction between lipid raft molecule caveolin-1 and NADPH oxidase (NOX) complex Rac1 for ROS production. NOX-mediated ROS signaling induced by rVvhA increased the phosphorylation of extracellular signal-regulated kinase (ERK) and eukaryotic translation initiation factor 2α (eIF2α) which are required for mRNA expression of Atg5 and Atg16L1 involved in autophagosome formation. In an in vivo model, VvhA increased autophagy activation and paracellular permeabilization in intestinal epithelium. Collectively, the results here show that VvhA plays a pivotal role in the pathogenesis and dissemination of V. vulnificus by autophagy upregulation, through the lipid raft-mediated c-Src/NOX signaling pathway and ERK/eIF2α activation.

Uropathogenic E. coli Exploit CEA to Promote Colonization of the Urogenital Tract Mucosa

Attachment to the host mucosa is a key step in bacterial pathogenesis. On the apical surface of epithelial cells, members of the human carcinoembryonic antigen (CEA) family are abundant glycoproteins involved in cell-cell adhesion and modulation of cell signaling. Interestingly, several gram-negative bacterial pathogens target these receptors by specialized adhesins. The prototype of a CEACAM-binding pathogen, Neisseria gonorrhoeae, utilizes colony opacity associated (Opa) proteins to engage CEA, as well as the CEA-related cell adhesion molecules CEACAM1 and CEACAM6 on human epithelial cells. By heterologous expression of neisserial Opa proteins in non-pathogenic E. coli we find that the Opa protein-CEA interaction is sufficient to alter gene expression, to increase integrin activity and to promote matrix adhesion of infected cervical carcinoma cells and immortalized vaginal epithelial cells in vitro. These CEA-triggered events translate in suppression of exfoliation and improved colonization of the urogenital tract by Opa protein-expressing E. coli in CEA-transgenic compared to wildtype mice. Interestingly, uropathogenic E. coli expressing an unrelated CEACAM-binding protein of the Afa/Dr adhesin family recapitulate the in vitro and in vivo phenotype. In contrast, an isogenic strain lacking the CEACAM-binding adhesin shows reduced colonization and does not suppress epithelial exfoliation. These results demonstrate that engagement of human CEACAMs by distinct bacterial adhesins is sufficient to blunt exfoliation and to promote host infection. Our findings provide novel insight into mucosal colonization by a common UPEC pathotype and help to explain why human CEACAMs are a preferred epithelial target structure for diverse gram-negative bacteria to establish a foothold on the human mucosa.

Mucous surfaces are a hallmark of the nasal cavity and the throat as well as the intestinal and urogenital tracts. These surfaces serve as primary entry portals for a large number of pathogenic bacteria. To get a foothold on the mucosa, bacteria not only need to tightly attach to this tissue, but also need to overcome an intrinsic defence mechanism called exfoliation. During the exfoliation process, the outermost cell layer, together with attached bacteria, is released from the tissue surface reducing the microbial burden. A comprehensive understanding of the molecular strategies, which bacteria utilize to undermine this host defence, is currently lacking. Our results suggest that different bacterial pathogens have found a surprisingly similar answer to this problem by targeting a common set of proteins on the tissue surface. Accordingly, these bacteria express unrelated proteins that engage the same host receptors called CEA-related cell adhesion molecules (CEACAMs). Binding of microbes to CEACAMs triggers, via intracellular signaling pathways, an increased stickiness of the infected cells. Thereby, the pathogens suppress the release of superficial host cells from the tissue and effectively block exfoliation. Detailed mechanistic insight into this process and the ability to manipulate exfoliation might help to prevent or treat bacterial infections.

Immunoreceptors on neutrophils

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Neutrophil activities must be tightly controlled to maintain immune homeostasis.

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Activating and inhibitory receptors balance the outcome of immune cell activation.

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Immunoreceptors contain Ig-like extracellular domains and signal via ITAMs or ITIMs.

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Syk or SHP/SHIP mediate downstream signaling after immunoreceptor activation.

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Targeting immunoreceptors provides opportunities for therapeutic interventions.

Neutrophils play a critical role in the host defense against infection, and they are able to perform a variety of effector mechanisms for this purpose. However, there are also a number of pathological conditions, including autoimmunity and cancer, in which the activities of neutrophils can be harmful to the host. Thus the activities of neutrophils need to be tightly controlled. As in the case of other immune cells, many of the neutrophil effector functions are regulated by a series of immunoreceptors on the plasma membrane. Here, we review what is currently known about the functions of the various individual immunoreceptors and their signaling in neutrophils. While these immunoreceptors allow for the recognition of a diverse range of extracellular ligands, such as cell surface structures (like proteins, glycans and lipids) and extracellular matrix components, they commonly signal via conserved ITAM or ITIM motifs and their associated downstream pathways that depend on the phosphorylation of tyrosine residues in proteins and/or inositol lipids. This allows for a balanced homeostatic regulation of neutrophil effector functions. Given the number of available immunoreceptors and their fundamental importance for neutrophil behavior, it is perhaps not surprising that pathogens have evolved means to evade immune responses through some of these pathways. Inversely, some of these receptors evolved to specifically recognize these pathogens. Finally, some interactions mediated by immunoreceptors in neutrophils have been identified as promising targets for therapeutic intervention.

Proteomics of Neisseria gonorrhoeae: the treasure hunt for countermeasures against an old disease

Neisseria gonorrhoeae is an exquisitely adapted, strictly human pathogen and the causative agent of the sexually transmitted infection gonorrhea. This ancient human disease remains a serious problem, occurring at high incidence globally and having a major impact on reproductive and neonatal health. N. gonorrhoeae is rapidly evolving into a superbug and no effective vaccine exists to prevent gonococcal infections. Untreated or inadequately treated gonorrhea can lead to severe sequelae, including pelvic inflammatory disease and infertility in women, epididymitis in men, and sight-threatening conjunctivitis in infants born to infected mothers. Therefore, there is an immediate need for accelerated research toward the identification of molecular targets for development of drugs with new mechanisms of action and preventive vaccine(s). Global proteomic approaches are ideally suited to guide these studies. Recent quantitative proteomics (SILAC, iTRAQ, and ICAT) have illuminated the pathways utilized by N. gonorrhoeae to adapt to different lifestyles and micro-ecological niches within the host, while comparative 2D SDS-PAGE analysis has been used to elucidate spectinomycin resistance mechanisms. Further, high-throughput examinations of cell envelopes and naturally released membrane vesicles have unveiled the ubiquitous and differentially expressed proteins between temporally and geographically diverse N. gonorrhoeae isolates. This review will focus on these different approaches, emphasizing the role of proteomics in the search for vaccine candidates. Although our knowledge of N. gonorrhoeae has been expanded, still far less is known about this bacterium than the closely related N. meningitidis, where genomics- and proteomics-driven studies have led to the successful development of vaccines.

Expression of Opacity Proteins Interferes with the Transmigration of Neisseria gonorrhoeae across Polarized Epithelial Cells

Neisseria gonorrhoeae (GC) establishes infection at the mucosal surface of the human genital tract, most of which is lined with polarized epithelial cells. GC can cause localized as well as disseminated infections, leading to various complications. GC constantly change their surface structures via phase and antigenic variation, which has been implicated as a means for GC to establish infection at various anatomic locations of male and female genital tracks. However, the exact contribution of each surface molecule to bacterial infectivity remains elusive due to their phase variation. Using a GC derivative that is genetically devoid of all opa genes (MS11∆Opa), this study shows that Opa expression interferes with GC transmigration across polarized human epithelial cells. MS11∆Opa transmigrates across polarized epithelial cells much faster and to a greater extent than MS11Opa+, while adhering at a similar level as MS11Opa+. When MS11Opa+, able to phase vary Opa expression, was inoculated, only those bacteria that turn off Opa expression transmigrate across the polarized epithelial monolayer. Similar to bacteria alone or co-cultured with non-polarized epithelial cells, MS11∆Opa fails to form large microcolonies at the apical surface of polarized epithelial cells. Apical inoculation of MS11Opa+, but not MS11∆Opa, induces the recruitment of the Opa host-cell receptor carcinoembryonic antigen–related cell adhesion molecules (CEACAMs) to the apical junction and the vicinity of bacterial adherent sites. Our results suggest that Opa expression limits gonococcal ability to invade into subepithelial tissues by forming tight interactions with neighboring bacteria and by inducing CEACAM redistribution to cell junctions.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

The granulocyte orphan receptor CEACAM4 is able to trigger phagocytosis of bacteria

Human granulocytes express several glycoproteins of the CEACAM family. One family member, CEACAM3, operates as a single-chain phagocytic receptor, initiating the detection, internalization, and destruction of a limited set of gram-negative bacteria. In contrast, the function of CEACAM4, a closely related protein, is completely unknown. This is mainly a result of a lack of a specific ligand for CEACAM4. By generating chimeric proteins containing the extracellular bacteria-binding domain of CEACAM3 and the transmembrane and cytoplasmic part of CEACAM4 (CEACAM3/4) we demonstrate that this chimeric receptor can trigger efficient phagocytosis of attached particles. Uptake of CEACAM3/4-bound bacteria requires the intact ITAM of CEACAM4, and this motif is phosphorylated by Src family PTKs upon receptor clustering. Furthermore, SH2 domains derived from Src PTKs, PI3K, and the adapter molecule Nck are recruited and associate directly with the phosphorylated CEACAM4 ITAM. Deletion of this sequence motif or inhibition of Src PTKs blocks CEACAM4-mediated uptake. Together, our results suggest that this orphan receptor of the CEACAM family has phagocytic function and prompt efforts to identify CEACAM4 ligands.

Signaling by epithelial members of the CEACAM family - mucosal docking sites for pathogenic bacteria

Carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) comprise a group of immunoglobulin-related vertebrate glycoproteins. Several family members, including CEACAM1, CEA, and CEACAM6, are found on epithelial tissues throughout the human body. As they modulate diverse cellular functions, their signaling capacity is in the focus of current research. In this review we will summarize the knowledge about common signaling processes initiated by epithelial CEACAMs and suggest a model of signal transduction by CEACAM family members lacking significant cytoplasmic domains. As pathogenic and non-pathogenic bacteria exploit these receptors during mucosal colonization, we try to highlight the connection between CEACAMs, microbes, and cellular responses. Special emphasis in this context is placed on the functional interplay between CEACAMs and integrins that influences matrix adhesion of epithelial cells. The cooperation between these two receptor families provides an intriguing example of the fine tuning of cellular responses and their manipulation by specialized microorganisms.

CEACAM6 promotes tumor migration, invasion, and metastasis in gastric cancer

Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) shows increased expression in a wide variety of human cancers, and its over-expression is associated with enhanced migration, invasion, and in vivo metastasis. Here, we reported that CEACAM6 was up-regulated in gastric cancer (GC) cell lines and tumor tissues. Over-expression of CEACAM6 in MKN-45 and SGC-7901 GC cells promoted migration and invasion in vitro and metastasis in athymic mice, whereas migration and invasion of MKN-28 and SNU-16 GC cells were suppressed by knockdown of CEACAM6. We also observed that steroid receptor coactivator (C-SRC) phosphorylation was increased when CEACAM6 was over-expressed in SGC-7901 cells. Taken together, these results suggested that CEACAM6 functions as an oncoprotein in GC and may be an important metastatic biomarker and therapeutic target.

Meningococcal resistance to antimicrobial peptides is mediated by bacterial adhesion and host cell RhoA and Cdc42 signalling

Antimicrobial peptides (AMPs) constitute an essential part of the innate immune defence. Pathogenic bacteria have evolved numerous strategies to withstand AMP-mediated killing. The influence of host epithelia on bacterial AMP resistance is, however, still largely unknown. We found that adhesion to pharyngeal epithelial cells protected Neisseria meningitidis, a leading cause of meningitis and sepsis, from the human cathelicidin LL-37, the cationic model amphipathic peptide (MAP) and the peptaibol alamethicin, but not from polymyxin B. Adhesion to primary airway epithelia resulted in a similar increase in LL-37 resistance. The inhibition of selective host cell signalling mediated by RhoA and Cdc42 was found to abolish the adhesion-induced LL-37 resistance by a mechanism unrelated to the actin cytoskeleton. Moreover, N. meningitidis triggered the formation of cholesterol-rich membrane microdomains in pharyngeal epithelial cells, and host cell cholesterol proved to be essential for adhesion-induced resistance. Our data highlight the importance of Rho GTPase-dependent host cell signalling for meningococcal AMP resistance. These results indicate that N. meningitidis selectively exploits the epithelial microenvironment in order to protect itself from LL-37.

Innate recognition by neutrophil granulocytes differs between Neisseria gonorrhoeae strains causing local or disseminating infections

Members of the carcinoembryonic antigen-related cell adhesion molecule (CEACAM) family serve as cellular receptors for Neisseria gonorrhoeae. More specifically, neisserial colony opacity (OpaCEA)) proteins bind to epithelial CEACAMs (CEACAM1, CEA, CEACAM6) to promote bacterial colonization of the mucosa. In contrast, recognition by CEACAM3, expressed by human granulocytes, results in uptake and destruction of Opa(CEA)-expressing bacteria. Therefore, CEACAM3-mediated uptake might limit the spread of gonococci. However, some strains can cause disseminating gonococcal infections (DGIs), and it is currently unknown how these strains escape detection by granulocyte CEACAM3. Therefore, the opa gene loci from N. gonorrhoeae strain VP1, which was derived from a patient with disseminated gonococcal disease, were cloned and constitutively expressed in Escherichia coli. Similar to Opa proteins of the nondisseminating strain MS11, the majority of Opa proteins from strain VP1 bound epithelial CEACAMs and promoted CEACAM-initiated responses by epithelial cells. In sharp contrast to the Opa proteins of strain MS11, the Opa proteins of strain VP1 failed to interact with the human granulocyte receptor CEACAM3. Accordingly, bacteria expressing VP1 Opa proteins were not taken up by primary human granulocytes and did not trigger a strong oxidative burst. Analysis of Opa variants from four additional clinical DGI isolates again demonstrated a lack of CEACAM3 binding. In summary, our results reveal that particular N. gonorrhoeae strains express an Opa protein repertoire allowing engagement of epithelial CEACAMs for successful mucosal colonization, while avoiding recognition and elimination via CEACAM3-mediated phagocytosis. A failure of CEACAM3-mediated innate immune detection might be linked to the ability of gonococci to cause disseminated infections.

Moraxella catarrhalis: from interactions with the host immune system to vaccine development

Moraxella catarrhalis is a human-restricted commensal that over the last two decades has developed into an emerging respiratory tract pathogen. The bacterial species is equipped with various adhesins to facilitate its colonization. Successful evasion of the human immune system is a prerequisite for Moraxella infection. This strategy involves induction of an excessive proinflammatory response, intervention of granulocyte recruitment to the infection site, activation of selected pattern recognition receptors and cellular adhesion molecules to counteract the host bacteriolytic attack, as well as, finally, reprogramming of antigen presenting cells. Host immunomodulator molecules are also exploited by Moraxella to aid in resistance against complement killing and host bactericidal molecules. Thus, breaking the basis of Moraxella immune evasion mechanisms is fundamental for future invention of effective therapy in controlling Moraxella infection.

Grb14 is a negative regulator of CEACAM3-mediated phagocytosis of pathogenic bacteria

Carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3) is a phagocytic receptor on human granulocytes, which mediates the opsonin-independent recognition and internalization of a restricted set of Gram-negative bacteria such as Neisseria gonorrhoeae. In an unbiased screen using a SH2 domain microarray we identified the SH2 domain of growth factor receptor-bound protein 14 (Grb14) as a novel binding partner of CEACAM3. Biochemical assays and microscopic studies demonstrated that the Grb14 SH2 domain promoted the rapid recruitment of this adaptor protein to the immunoreceptor-based activation motif (ITAM)-like sequence within the cytoplasmic domain of CEACAM3. Furthermore, FRET-FLIM analyses confirmed the direct association of Grb14 and CEACAM3 in intact cells at the sites of bacteria-host cell contact. Knockdown of endogenous Grb14 by RNA interference as well as Grb14 overexpression indicate an inhibitory role for this adapter protein in CEACAM3-mediated phagocytosis. Therefore, Grb14 is the first negative regulator of CEACAM3-initiated bacterial phagocytosis and might help to focus granulocyte responses to the subcellular sites of pathogen-host cell contact.

Extracellular IgC2 constant domains of CEACAMs mediate PI3K sensitivity during uptake of pathogens

Background

Several pathogenic bacteria utilize receptors of the CEACAM family to attach to human cells. Binding to different members of this receptor family can result in uptake of the bacteria. Uptake of Neisseria gonorrhoeae, a Gram-negative human pathogen, via CEACAMs found on epithelial cells, such as CEACAM1, CEA or CEACAM6, differs mechanistically from phagocytosis mediated by CEACAM3, a CEACAM family member expressed selectively by human granulocytes.

Principal Findings

We find that CEACAM1- as well as CEACAM3-mediated bacterial internalization are accompanied by a rapid increase in phosphatidylinositol-3,4,5 phosphate (PI(3,4,5)P) at the site of bacterial entry. However, pharmacological inhibition of phosphatidylinositol-3′ kinase (PI3K) selectively affects CEACAM1-mediated uptake of Neisseria gonorrhoeae. Accordingly, overexpression of the PI(3,4,5)P phosphatase SHIP diminishes and expression of a constitutive active PI3K increases CEACAM1-mediated internalization of gonococci, without influencing uptake by CEACAM3. Furthermore, bacterial uptake by GPI-linked members of the CEACAM family (CEA and CEACAM6) and CEACAM1-mediated internalization of N. meningitidis by endothelial cells require PI3K activity. Sensitivity of CEACAM1-mediated uptake toward PI3K inhibition is independent of receptor localization in cholesterol-rich membrane microdomains and does not require the cytoplasmic or the transmembrane domain of CEACAM1. However, PI3K inhibitor sensitivity requires the Ig_C2-like domains of CEACAM1, which are also present in CEA and CEACAM6, but which are absent from CEACAM3. Accordingly, overexpression of CEACAM1 Ig_C2 domains blocks CEACAM1-mediated internalization.

Conclusions

Our results provide novel mechanistic insight into CEACAM1-mediated endocytosis and suggest that epithelial CEACAMs associate in cis with other membrane receptor(s) via their extracellular domains to trigger bacterial uptake in a PI3K-dependent manner.

Neisseria gonorrhoeae selectively suppresses the development of Th1 and Th2 cells, and enhances Th17 cell responses, through TGF-β-dependent mechanisms

Infection with Neisseria gonorrhoeae does not induce specific immunity or immune memory. Our previous studies in a murine model of vaginal gonococcal infection showed that innate immunity governed by Th17 cells was a critical aspect of the immune response elicited by this pathogen. Herein we show that N. gonorrhoeae selectively inhibited Th1 and Th2 cells and enhanced Th17 cell development through the induction of TGF-β. Whereas Th17 responses depended on gonococcal lipooligosaccharide acting through TLR4, the inhibitory effect of N. gonorrhoeae on Th1/Th2 responses involved gonococcal Opa proteins. In vitro Th17 responses to N. gonorrhoeae could be diverted to Th1/Th2 by blockade of TGF-β, but not by blockade of IL-17. The results reveal that N. gonorrhoeae suppresses Th1/Th2-mediated adaptive immune response through mechanisms dependent on TGF-β, and that this effect can be manipulated to promote the development of adaptive immunity.

The adaptor molecule Nck localizes the WAVE complex to promote actin polymerization during CEACAM3-mediated phagocytosis of bacteria

BACKGROUND

CEACAM3 is a granulocyte receptor mediating the opsonin-independent recognition and phagocytosis of human-restricted CEACAM-binding bacteria. CEACAM3 function depends on an intracellular immunoreceptor tyrosine-based activation motif (ITAM)-like sequence that is tyrosine phosphorylated by Src family kinases upon receptor engagement. The phosphorylated ITAM-like sequence triggers GTP-loading of Rac by directly associating with the guanine nucleotide exchange factor (GEF) Vav. Rac stimulation in turn is critical for actin cytoskeleton rearrangements that generate lamellipodial protrusions and lead to bacterial uptake.

PRINCIPAL FINDINGS

In our present study we provide biochemical and microscopic evidence that the adaptor proteins Nck1 and Nck2, but not CrkL, Grb2 or SLP-76, bind to tyrosine phosphorylated CEACAM3. The association is phosphorylation-dependent and requires the Nck SH2 domain. Overexpression of the isolated Nck1 SH2 domain, RNAi-mediated knock-down of Nck1, or genetic deletion of Nck1 and Nck2 interfere with CEACAM3-mediated bacterial internalization and with the formation of lamellipodial protrusions. Nck is constitutively associated with WAVE2 and directs the actin nucleation promoting WAVE complex to tyrosine phosphorylated CEACAM3. In turn, dominant-negative WAVE2 as well as shRNA-mediated knock-down of WAVE2 or the WAVE-complex component Nap1 reduce internalization of bacteria.

CONCLUSIONS

Our results provide novel mechanistic insight into CEACAM3-initiated phagocytosis. We suggest that the CEACAM3 ITAM-like sequence is optimized to co-ordinate a minimal set of cellular factors needed to efficiently trigger actin-based lamellipodial protrusions and rapid pathogen engulfment.

New prognostic markers, determined using gene expression analyses, reveal two distinct subtypes of chronic myelomonocytic leukaemia patients

Chronic myelomonocytic leukaemia (CMML) is a heterogeneous haematopoietic disorder characterized by myeloproliferative or myelodysplastic features. At present, the pathogenesis of this malignancy is not completely understood. In this study, we sought to analyse gene expression profiles of CMML in order to characterize new molecular outcome predictors. A learning set of 32 untreated CMML patients at diagnosis was available for TaqMan low-density array gene expression analysis. From 93 selected genes related to cancer and cell cycle, we built a five-gene prognostic index after multiplicity correction. Using this index, we characterized two categories of patients with distinct overall survival (94% vs. 19% for good and poor overall survival, respectively; P = 0·007) and we successfully validated its strength on an independent cohort of 21 CMML patients with Affymetrix gene expression data. We found no specific patterns of association with traditional prognostic stratification parameters in the learning cohort. However, the poor survival group strongly correlated with high-risk treated patients and transformation to acute myeloid leukaemia. We report here a new multigene prognostic index for CMML, independent of the gene expression measurement method, which could be used as a powerful tool to predict clinical outcome and help physicians to evaluate criteria for treatments.

Intruders below the radar: molecular pathogenesis of Bartonella spp

Bartonella spp. are facultative intracellular pathogens that employ a unique stealth infection strategy comprising immune evasion and modulation, intimate interaction with nucleated cells, and intraerythrocytic persistence. Infections with Bartonella are ubiquitous among mammals, and many species can infect humans either as their natural host or incidentally as zoonotic pathogens. Upon inoculation into a naive host, the bartonellae first colonize a primary niche that is widely accepted to involve the manipulation of nucleated host cells, e.g., in the microvasculature. Consistently, in vitro research showed that Bartonella harbors an ample arsenal of virulence factors to modulate the response of such cells, gain entrance, and establish an intracellular niche. Subsequently, the bacteria are seeded into the bloodstream where they invade erythrocytes and give rise to a typically asymptomatic intraerythrocytic bacteremia. While this course of infection is characteristic for natural hosts, zoonotic infections or the infection of immunocompromised patients may alter the path of Bartonella and result in considerable morbidity. In this review we compile current knowledge on the molecular processes underlying both the infection strategy and pathogenesis of Bartonella and discuss their connection to the clinical presentation of human patients, which ranges from minor complaints to life-threatening disease.

Defining the roles of human carcinoembryonic antigen-related cellular adhesion molecules during neutrophil responses to Neisseria gonorrhoeae

Symptomatic infection of humans with Neisseria gonorrhoeae is characterized by a neutrophil-rich cervical or urethral exudate, suggesting that neutrophils are important both for the clearance of these bacteria and for the pathogenesis of gonorrhea. Neisseria interacts with neutrophils through ligation of human carcinoembryonic antigen related-cellular adhesion molecules (CEACAMs) by their surface-expressed Opa proteins, resulting in bacterial binding, engulfment, and neutrophil activation. Multiple CEACAMs are expressed by human neutrophils, and yet their coexpression has precluded understanding of the relative contribution of each CEACAM to functional responses of neutrophils during neisserial infection. In this work, we directly address the role of each CEACAM during infection by introducing individual human CEACAMs into a differentiated murine MPRO cell line-derived neutrophil model. Murine neutrophils cannot bind the human-restricted Neisseria; however, we show that introducing any of the Opa-binding CEACAMs of human neutrophils (CEACAM1, CEACAM3, and CEACAM6) allows binding and entry of Neisseria into murine neutrophils. While CEACAM1- and CEACAM6-expressing neutrophils bind more bacteria, neisserial uptake via these two receptors unexpectedly proceeds without appreciable neutrophil activation. In stark contrast, neisserial engulfment via CEACAM3 recapitulates the oxidative burst and intracellular granule release seen during human neutrophil infection. Finally, by coexpressing multiple CEACAMs in our model, we show that the expression of CEACAM1 and CEACAM6 potentiate, rather than hinder, CEACAM3-dependent responses of neutrophils, exposing a cooperative role for this family of proteins during neisserial infection of neutrophils. These observations illustrate a divergence in function of CEACAMs in neutrophils and implicate the human-restricted CEACAM3 in the neutrophil innate response to neisserial infection.

Establishment of a human CEACAM1 transgenic mouse model for the study of gonococcal infections

Neisseria gonorrhoeae is the causative microorganism for the sexually transmitted disease (STD) gonorrhea and humans are its only natural host. An animal model would be a useful tool for gonorrhea research, therefore we developed the hCEACAM1 transgenic mice, using an eukaryotic expression vector, pCDPCAM1-GI. This construct was microinjected into the zygotes of C57BL/6 mice and 22 F0 generation transgenic mice were obtained. Four (lines 50, 53, 54, and 59) of the F0 generation were found to carry the transgene by PCR and sequence analysis, respectively. Western blotting and Fluorescence-Activated Cell Sorting Analysis demonstrated that hCEACAM1 was expressed on the cell membrane of various tissues in the line 53 transgenic mouse. To initiate the disease in the animal model, the F2 or F3 transgenic mice were inoculated with N. gonorrhoeae intravaginally. Compared with normal mice, N. gonorrhoeae can successfully infect and cause inflammation in the transgenic mice. These data suggested the feasibility of using hCEACAM1 transgenic mice as an animal model for gonococcal infections.

The Pathobiology of Neisseria gonorrhoeae Lower Female Genital Tract Infection

Infection and disease associated with Neisseria gonorrhoeae, the gonococcus, continue to be a global health problem. Asymptomatic and subclinical gonococcal infections occur at a high frequency in females; thus, the true incidence of N. gonorrhoeae infections are presumed to be severely underestimated. Inherent to this asymptomatic/subclinical diseased state is the continued prevalence of this organism within the general population, as well as the medical, economic, and social burden equated with the observed chronic, disease sequelae. As infections of the lower female genital tract (i.e., the uterine cervix) commonly result in subclinical disease, it follows that the pathobiology of cervical gonorrhea would differ from that observed for other sites of infection. In this regard, the potential responses to infection that are generated by the female reproductive tract mucosa are unique in that they are governed, in part, by cyclic fluctuations in steroid hormone levels. The lower female genital tract has the further distinction of being able to functionally discriminate between resident commensal microbiota and transient pathogens. The expression of functionally active complement receptor 3 by the lower, but not the upper, female genital tract mucosa; together with data indicating that gonococcal adherence to and invasion of primary cervical epithelial cells and tissue are predominately aided by this surface-expressed host molecule; provide one explanation for asymptomatic/subclinical gonococcal cervicitis. However, co-evolution of the gonococcus with its sole human host has endowed this organism with variable survival strategies that not only aid these bacteria in successfully evasion of immune detection and function but also enhance cervical colonization and cellular invasion. To this end, we herein summarize current knowledge pertaining to the pathobiology of gonococcal infection of the human cervix.

Integrin-mediated uptake of fibronectin-binding bacteria

Invasion of mammalian cells via cell adhesion molecules of the integrin family is a common theme in bacterial pathogenesis. Whereas some microorganisms directly bind to integrins, other pathogens such as Staphylococcus aureus indirectly engage these receptors via fibronectin-binding proteins (FnBPs). In this review, we summarize the structure-function relationship of FnBPs and the current view of the role of these proteins during pathogenesis in vivo. A major focus will be on recent findings on the role of cholesterol- and sphingolipid-rich membrane microdomains for integrin-initiated uptake of fibronectin-binding bacteria and the surprising inhibitory function of caveolin-1 in this process. The detailed mechanistic understanding of host cell invasion by fibronectin-binding S. aureus can not only serve as a paradigm for other fibronectin-binding pathogenic bacteria, but might also reveal the physiological regulation of endocytosis of ligand-occupied integrins.

Role of Src kinases in mobilization of glycosylphosphatidylinositol-anchored decay-accelerating factor by Dr fimbria-positive adhering bacteria

Afa/Dr fimbriae constitute the major virulence factor of diffusely adhering Escherichia coli (Afa/Dr DAEC). After recognizing membrane-bound signaling receptors, they trigger cell responses. One of these receptors is the human decay-accelerating factor (hDAF). It has previously been reported that the binding of Afa/Dr fimbriae to hDAF quickly induces recruitment of hDAF around adhering bacteria. The aim of our study is to analyze the role of Src kinases in the Dr fimbria-induced recruitment of hDAF. Using biochemical methods and confocal microscopy followed by 3-dimensional (3D) analysis, we have shown that the activation and cell membrane targeting of Src kinases are necessary for the recruitment and organization of hDAF around adhering bacteria. We identified c-Src to be the specific kinase involved in this process. Using a set of Src-green fluorescent protein mutants, we showed that the catalytic activity and the Src homology 2 (SH2) and SH3 domains of the Src kinases are necessary for Dr fimbria-induced hDAF mobilization to occur. In addition, using mutated Dr fimbriae and a set of mutated hDAFs in which each of the complement control protein (CCP) domains had successively been deleted, we found that the aspartic acids at position 54 in the Dr fimbriae and in CCP domain 4 of hDAF played pivotal roles in the mobilization of the Src kinases and hDAF, respectively.

Neisseria meningitidis has two independent modes of recognizing its human receptor CEACAM1

BACKGROUND

Several human-restricted gram-negative bacteria exploit carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) for host colonization. For example, Neisseria meningitidis engages these human receptors via outer membrane proteins of the colony opacity-associated (Opa) protein family triggering internalization into non-phagocytic cells.

PRINCIPAL FINDINGS

We report that a non-opaque strain of N. meningitidis selectively interacts with CEACAM1, but not other CEACAM family members. Using functional assays of bacterial adhesion and internalisation, microscopic analysis, and a panel of CEACAM1 deletion mutants we demonstrate that the engagement of CEACAM1 by non-opaque meningococci occurs in a manner distinct from Opa protein-mediated association. In particular, the amino-terminal domain of CEACAM1 is necessary, but not sufficient for Opa protein-independent binding, which requires multiple extracellular domains of the human receptor in a cellular context. Knock-down of CEACAM1 interferes with binding to lung epithelial cells, whereas chemical or pharmacological disruption of host protein glycosylation does not abrogate CEACAM1 recognition by non-opaque meningococci. The previously characterized meningococcal invasins NadA or Opc do not operate in a CEACAM1-dependent manner.

CONCLUSIONS

The results demonstrate a mechanistically distinct, Opa protein-independent interaction between N. meningitidis and human CEACAM1. Our functional investigations suggest the presence of a second CEACAM1-binding invasin on the meningococcal surface that associates with the protein backbone and not the carbohydrate structures of CEACAM1. The redundancy in meningococcal CEACAM1-binding factors further highlights the important role of CEACAM recognition in the biology of this human-adapted pathogen.

Opa proteins and CEACAMs: pathways of immune engagement for pathogenic Neisseria

Neisseria meningitidis and Neisseria gonorrhoeae are globally important pathogens, which in part owe their success to their ability to successfully evade human immune responses over long periods. The phase-variable opacity-associated (Opa) adhesin proteins are a major surface component of these organisms, and are responsible for bacterial adherence and entry into host cells and interactions with the immune system. Most immune interactions are mediated via binding to members of the carcinoembryonic antigen cell adhesion molecule (CEACAM) family. These Opa variants are able to bind to different receptors of the CEACAM family on epithelial cells, neutrophils, and T and B lymphocytes, influencing the innate and adaptive immune responses. Increased epithelial cell adhesion creates the potential for prolonged infection, invasion and dissemination. Furthermore, Opa proteins may inhibit T-lymphocyte activation and proliferation, B-cell antibody production, and innate inflammatory responses by infected epithelia, in addition to conferring increased resistance to antibody-dependent, complement-mediated killing. While vaccines containing Opa proteins could induce adhesion-blocking and bactericidal antibodies, the consequence of CEACAM binding by a candidate Opa-containing vaccine requires further investigation. This review summarizes current knowledge of the immunological consequences of the interaction between meningococcal and gonococcal Opa proteins and human CEACAMs, considering the implications for pathogenesis and vaccine development.

Phosphatidylinositol 3'-kinase activity is critical for initiating the oxidative burst and bacterial destruction during CEACAM3-mediated phagocytosis

Carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3) is an immunoglobulin-related receptor expressed on human granulocytes. CEACAM3 functions as a single chain phagocytotic receptor recognizing gram-negative bacteria such as Neisseria gonorrhoeae, which possess CEACAM-binding adhesins on their surface. The cytoplasmic domain of CEACAM3 contains an immunoreceptor tyrosine-based activation motif (ITAM)-like sequence that is phosphorylated upon receptor engagement. Here we show that the SH2 domains of the regulatory subunit of phosphatidylinositol 3'-kinase (PI3K) bind to tyrosine residue 230 of CEACAM3 in a phosphorylation-dependent manner. PI3K is rapidly recruited and directly associates with CEACAM3 upon bacterial binding as shown by FRET analysis. Although PI3K activity is not required for efficient uptake of the bacteria by CEACAM3-transfected cells or primary human granulocytes, it is critical for the stimulated production of reactive oxygen species by infected phagocytes and the intracellular degradation of CEACAM-binding bacteria. Together, our results highlight the ability of CEACAM3 to coordinate signaling events that not only mediate bacterial uptake, but also trigger the killing of internalized pathogens.

Caveolin limits membrane microdomain mobility and integrin-mediated uptake of fibronectin-binding pathogens

Staphylococcus aureus, which is a leading cause of hospital-acquired infections, binds via fibronectin to integrin α5β1, a process that can promote host colonization in vivo. Integrin engagement induces actin cytoskeleton rearrangements that result in the uptake of S. aureus by non-professional phagocytic cells. Interestingly, we found that fibronectin-binding S. aureus trigger the redistribution of membrane microdomain components. In particular, ganglioside GM1 and GPI-linked proteins were recruited upon integrin β1 engagement, and disruption of membrane microdomains blocked bacterial internalization. Several membrane-microdomain-associated proteins, such as flotillin-1 and flotillin-2, as well as caveolin, were recruited to sites of bacterial attachment. Whereas dominant-negative versions of flotillin-2 did not affect bacterial attachment or internalization, cells deficient for caveolin-1 (Cav1(-/-)) showed increased uptake of S. aureus and other Fn-binding pathogens. Recruitment of membrane microdomains to cell-associated bacteria was unaltered in Cav1(-/-) cells. However, fluorescence recovery after photobleaching (FRAP) revealed an enhanced mobility of membrane-microdomain-associated proteins in the absence of caveolin-1. Enhanced membrane microdomain mobility and increased uptake of S. aureus was repressed by expression of wild-type caveolin-1, but not caveolin-1 G83S, which harbors a point mutation in the caveolin scaffolding domain. Similarly, chemical or physical stimulation of membrane fluidity led to increased uptake of S. aureus. These results highlight a crucial role for caveolin-1 in negative regulation of membrane microdomain mobility, thereby affecting endocytosis of bacteria-engaged integrins. This process might not only limit host cell invasion by integrin-binding bacterial pathogens, but might also be physiologically relevant for integrin-mediated cell adhesion.

Fluorescence resonance energy transfer (FRET)-based subcellular visualization of pathogen-induced host receptor signaling

Background

Bacteria-triggered signaling events in infected host cells are key elements in shaping the host response to pathogens. Within the eukaryotic cell, signaling complexes are spatially organized. However, the investigation of protein-protein interactions triggered by bacterial infection in the cellular context is technically challenging. Here, we provide a methodological approach to exploit fluorescence resonance energy transfer (FRET) to visualize pathogen-initiated signaling events in human cells.

Results

Live-cell microscopy revealed the transient recruitment of the Src family tyrosine kinase Hck upon bacterial engagement of the receptor carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3). In cells expressing a CEACAM3 variant lacking the cytoplasmic domain, the Src homology 2 (SH2) domain of Hck (Hck-SH2) was not recruited, even though bacteria still bound to the receptor. FRET measurements on the basis of whole cell lysates revealed intimate binding between Hck-SH2 (using enhanced yellow fluorescent protein (YPet)-Hck-SH2) and the tyrosine-phosphorylated enhanced cyan fluorescent protein-labeled cytoplasmic domain of wild-type CEACAM3 (CEACAM3 WT-CyPet) and a flow cytometry-based FRET approach verified this association in intact cells. Using confocal microscopy and acceptor photobleaching, FRET between Hck-SH2 and CEACAM3 was localized to the sites of bacteria-host cell contact.

Conclusion

These data demonstrate not only the intimate binding of the SH2 domain of Hck to the tyrosine-phosphorylated cytoplasmic domain of CEACAM3 in intact cells, but furthermore, FRET measurements allow the subcellular localization of this process during bacterial infection. FRET-based assays are valuable tools to resolve bacteria-induced protein-protein interactions in the context of the intact host cell.