Gonococcal opacity protein promotes bacterial entry-associated rearrangements of the epithelial cell actin cytoskeleton

Tissue Models for Neisseria gonorrhoeae Research—From 2D to 3D

Neisseria gonorrhoeae is a human-specific pathogen that causes gonorrhea, the second most common sexually transmitted infection worldwide. Disease progression, drug discovery, and basic host-pathogen interactions are studied using different approaches, which rely on models ranging from 2D cell culture to complex 3D tissues and animals. In this review, we discuss the models used in N. gonorrhoeae research. We address both in vivo (animal) and in vitro cell culture models, discussing the pros and cons of each and outlining the recent advancements in the field of three-dimensional tissue models. From simple 2D monoculture to complex advanced 3D tissue models, we provide an overview of the relevant methodology and its application. Finally, we discuss future directions in the exciting field of 3D tissue models and how they can be applied for studying the interaction of N. gonorrhoeae with host cells under conditions closely resembling those found at the native sites of infection.

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.

The Transmembrane Mucin MUC1 Facilitates β1-Integrin-Mediated Bacterial Invasion

At the intestinal host-microbe interface, the transmembrane mucin MUC1 can function as a physical barrier as well as a receptor for bacteria. MUC1 also influences epithelial cell morphology and receptor function. Various bacterial pathogens can exploit integrins to infect eukaryotic cells. It is yet unclear whether MUC1 influences the interaction of bacteria with integrins. We used Escherichia coli expressing the invasin (inv) protein of Yersinia pseudotuberculosis (E. coli inv) to assess the effects of MUC1 on β1 integrin (ITGB1)-mediated bacterial invasion. Our results show that expression of full-length MUC1 does not yield a physical barrier but slightly enhances E. coli inv uptake. Enzymatic removal of the MUC1 extracellular domain (ED) using a secreted protease of C1 esterase inhibitor (StcE) of pathogenic Escherichia coli had no additional effect on E. coli inv invasion. In contrast, expression of a truncated MUC1 that lacks the cytoplasmic tail (CT) reduced bacterial entry substantially. Substitution of tyrosine residues in the MUC1 CT also reduced bacterial uptake, while deletion of the C-terminal half of the cytoplasmic tail only had a minor effect, pointing to a regulatory role of tyrosine phosphorylation and the N-terminal region of the MUC1 CT in integrin-mediated uptake process. Unexpectedly, StcE removal of the ED in MUC1-ΔCT cells reversed the block in bacterial invasion. Together, these findings indicate that MUC1 can facilitate β1-integrin-mediated bacterial invasion by a concerted action of the large glycosylated extracellular domain and the membrane-juxtaposed cytoplasmic tail region.IMPORTANCE Bacteria can exploit membrane receptor integrins for cellular invasion, either by direct binding of bacterial adhesins or utilizing extracellular matrix components. MUC1 is a large transmembrane glycoprotein expressed by most epithelial cells that can have direct defensive or receptor functions at the host-microbe interface and is involved in facilitating integrin clustering. We investigated the role of epithelial MUC1 on β1 integrin-mediated bacterial invasion. We discovered that MUC1 does not act as a barrier but facilitates bacterial entry through β1 integrins. This process involves a concerted action of the MUC1 O-glycosylated extracellular domain and cytoplasmic tail. Our findings add a new dimension to the complexity of bacterial invasion mechanisms and provide novel insights into the distinct functions of MUC1 domains at the host-microbe interface.

Neisseria gonorrhoeae evades autophagic killing by downregulating CD46-cyt1 and remodeling lysosomes

The Gram-negative human pathogen N. gonorrhoeae (Ngo) quickly attaches to epithelial cells, and large numbers of the bacteria remain on the cell surface for prolonged periods. Ngo invades cells but few viable intracellular bacteria are recovered until later stages of infection, leading to the assumption that Ngo is a weak invader. On the cell surface, Ngo quickly recruits CD46-cyt1 to the epithelial cell cortex directly beneath the bacteria and causes its cleavage by metalloproteinases and Presenilin/γSecretease; how these interactions affect the Ngo lifecycle is unknown. Here, we show Ngo induces an autophagic response in the epithelial cell through CD46-cyt1/GOPC, and this response kills early invaders. Throughout infection, the pathogen slowly downregulates CD46-cyt1 and remodeling of lysosomes, another key autophagy component, and these activities ultimately promote intracellular survival. We present a model on the dynamics of Ngo infection and describe how this dual interference with the autophagic pathway allows late invaders to survive within the cell.

The T6SSs of Pseudomonas aeruginosa Strain PAO1 and Their Effectors: Beyond Bacterial-Cell Targeting

Pseudomonas aeruginosa is an opportunistic pathogen responsible for many diseases such as chronic lung colonization in cystic fibrosis patients and acute infections in hospitals. The capacity of P. aeruginosa to be pathogenic toward several hosts is notably due to different secretion systems. Amongst them, P. aeruginosa encodes three Type Six Secretion Systems (T6SS), named H1- to H3-T6SS, that act against either prokaryotes and/or eukaryotic cells. They are independent from each other and inject diverse toxins that interact with different components in the host cell. Here we summarize the roles of these T6SSs in the PAO1 strain, as well as the toxins injected and their targets. While H1-T6SS is only involved in antiprokaryotic activity through at least seven different toxins, H2-T6SS and H3-T6SS are also able to target prokaryotic as well as eukaryotic cells. Moreover, recent studies proposed that H2- and H3-T6SS have a role in epithelial cells invasion by injecting at least three different toxins. The diversity of T6SS effectors is astounding and other effectors still remain to be discovered. In this review, we present a table with other putative P. aeruginosa strain PAO1 T6SS-dependent effectors. Altogether, the T6SSs of P. aeruginosa are important systems that help fight other bacteria for their ecological niche, and are important in the pathogenicity process.

PEGylated Carbon Nanocapsule: A Universal Reactor and Carrier for In Vivo Delivery of Hydrophobic and Hydrophilic Nanoparticles

We have developed PEGylated mesoporous carbon nanocapsule as a universal nanoreactor and carrier for the delivery of highly crystalline hydrophobic/hydrophilic nanoparticles (NPs) which shows superior biocompatibility, dispersion in body fluids, good biodistribution and NPs independent cellular uptake mechanism. The hydrophobic/hydrophilic NPs without surface modification were synthesized in situ inside the cavities of mesoporous carbon capsules (200-850 nm). Stable and inert nature of carbon capsules in a wide range of reaction conditions like high temperature and harsh solvents, make it suitable for being used as nano/microreactors for the syntheses of a variety of NPs for bioimaging applications, such as NaYF4:Eu(3+)(5%), LaVO4:Eu(3+)(10%), GdVO4:Eu(3+)(10%), Y2O3:Eu(3+)(5%), GdF3:Tb(3+)(10%), Mo, Pt, Pd, Au, and Ag. Multiple types of NPs (Y2O3:Eu(3+)(5%) (hydrophobic) and GdF3:Tb(3+)(10%) (hydrophilic)) were coloaded inside the carbon capsules to create a multimodal agent for magneto-fluorescence imaging. Our in vivo study clearly suggests that carbon capsules have biodistribution in many organs including liver, heart, spleen, lungs, blood pool, and muscles.

Internalization of Pseudomonas aeruginosa Strain PAO1 into Epithelial Cells Is Promoted by Interaction of a T6SS Effector with the Microtubule Network

Invasion of nonphagocytic cells through rearrangement of the actin cytoskeleton is a common immune evasion mechanism used by most intracellular bacteria. However, some pathogens modulate host microtubules as well by a still poorly understood mechanism. In this study, we aim at deciphering the mechanisms by which the opportunistic bacterial pathogen Pseudomonas aeruginosa invades nonphagocytic cells, although it is considered mainly an extracellular bacterium. Using confocal microscopy and immunofluorescence, we show that the evolved VgrG2b effector of P. aeruginosa strain PAO1 is delivered into epithelial cells by a type VI secretion system, called H2-T6SS, involving the VgrG2a component. An in vivo interactome of VgrG2b in host cells allows the identification of microtubule components, including the γ-tubulin ring complex (γTuRC), a multiprotein complex catalyzing microtubule nucleation, as the major host target of VgrG2b. This interaction promotes a microtubule-dependent internalization of the bacterium since colchicine and nocodazole, two microtubule-destabilizing drugs, prevent VgrG2b-mediated P. aeruginosa entry even if the invasion still requires actin. We further validate our findings by demonstrating that the type VI injection step can be bypassed by ectopic production of VgrG2b inside target cells prior to infection. Moreover, such uncoupling between VgrG2b injection and bacterial internalization also reveals that they constitute two independent steps. With VgrG2b, we provide the first example of a bacterial protein interacting with the γTuRC. Our study offers key insight into the mechanism of self-promoting invasion of P. aeruginosa into human cells via a directed and specific effector-host protein interaction.

Innate immunity and specifically professional phagocytic cells are key determinants in the ability of the host to control P. aeruginosa infection. However, among various virulence strategies, including attack, this opportunistic bacterial pathogen is able to avoid host clearance by triggering its own internalization in nonphagocytic cells. We previously showed that a protein secretion/injection machinery, called the H2 type VI secretion system (H2-T6SS), promotes P. aeruginosa uptake by epithelial cells. Here we investigate which H2-T6SS effector enables P. aeruginosa to enter nonphagocytic cells. We show that VgrG2b is delivered by the H2-T6SS machinery into epithelial cells, where it interacts with microtubules and, more particularly, with the γ-tubulin ring complex (γTuRC) known as the microtubule-nucleating center. This interaction precedes a microtubule- and actin-dependent internalization of P. aeruginosa. We thus discovered an unprecedented target for a bacterial virulence factor since VgrG2b constitutes, to our knowledge, the first example of a bacterial protein interacting with the γTuRC.

Flavone-resistant Leishmania donovani overexpresses LdMRP2 transporter in the parasite and activates host MRP2 on macrophages to circumvent the flavone-mediated cell death

In parasites, ATP-binding cassette (ABC) transporters represent an important family of proteins related to drug resistance and other biological activities. Resistance of leishmanial parasites to therapeutic drugs continues to escalate in developing countries, and in many instances, it is due to overexpressed ABC efflux pumps. Progressively adapted baicalein (BLN)-resistant parasites (pB(25)R) show overexpression of a novel ABC transporter, which was classified as ABCC2 or Leishmania donovani multidrug resistance protein 2 (LdMRP2). The protein is primarily localized in the flagellar pocket region and in internal vesicles. Overexpressed LdABCC2 confers substantial BLN resistance to the parasites by rapid drug efflux. The BLN-resistant promastigotes when transformed into amastigotes in macrophage cells cannot be cured by treatment of macrophages with BLN. Amastigote resistance is concomitant with the overexpression of macrophage MRP2 transporter. Reporter analysis and site-directed mutagenesis assays demonstrated that antioxidant response element 1 is activated upon infection. The expression of this phase II detoxifying gene is regulated by NFE2-related factor 2 (Nrf2)-mediated antioxidant response element activation. In view of the fact that the signaling pathway of phosphoinositol 3-kinase controls microfilament rearrangement and translocation of actin-associated proteins, the current study correlates with the intricate pathway of phosphoinositol 3-kinase-mediated nuclear translocation of Nrf2, which activates MRP2 expression in macrophages upon infection by the parasites. In contrast, phalloidin, an agent that prevents depolymerization of actin filaments, inhibits Nrf2 translocation and Mrp2 gene activation by pB(25)R infection. Taken together, these results provide insight into the mechanisms by which resistant clinical isolates of L. donovani induce intracellular events relevant to drug resistance.

Epithelial Cells Secrete Interleukin-8 in Response to Adhesion and Invasion of Diffusely AdheringEscherichia coliLacking Afa/Dr Genes

Escherichia coli that sparsely adhere to human epithelial cells are known as diffusely adherent E. coli (DAEC), and the role of the Afa/Dr family of adhesins is now understood. Strains that do not possess Afa/Dr, however, comprise another group of DAEC, of which the pathogenicity remains unknown. The ability to induce interleukin-8 (IL-8) secretion from intestinal epithelial cells might be a feature of enterovirulent bacteria. We previously found that some Afa/Dr DAEC strains induce IL-8 by stimulating epithelial cells with flagella. The present study examines whether non-Afa/Dr DAEC can induce IL-8 in epithelial cells (HEp-2, INT407, and T84). Among 21 strains, 11 (52%; 11/21) induced as much IL-8 as high inducer strains of Afa/Dr DAEC. Adhesion did not significantly differ between high and low inducers; therefore diffuse adhesion alone is probably insufficient to induce IL-8. It was shown that IL-8 induction and the number of intracellular bacteria directly correlated. Wortmannin, an inhibitor of the phosphatidylinositol-3-phosphate kinase, reduced both intracellular bacteria and IL-8 secretion. Motile strains were significantly more prevalent among high (10/11) than low (4/10) inducers. However, 4 low invasive strains hardly induced IL-8 despite their motility. In conclusion, some non-Afa/Dr DAEC invoke the induction of high levels of inflammatory cytokines. Unlike Afa/Dr DAEC, however, non-Afa/Dr strains may require invasion to cause strong induction. These non-Afa/Dr high inducers can be enteropathogenic for the cytokine-inducing properties.

Basolateral invasion and trafficking of Campylobacter jejuni in polarized epithelial cells

Campylobacter jejuni is a major cause of bacterial diarrheal disease. Most enteropathogenic bacteria including C. jejuni can invade cultured eukaryotic cells via an actin- and/or microtubule-dependent and an energy-consuming uptake process. Recently, we identified a novel highly efficient C. jejuni invasion pathway that involves bacterial migration into the subcellular space of non-polarized epithelial cells (termed subvasion) followed by invasion from the cell basis. Here we report cellular requirements of this entry mechanism and the subsequent intracellular trafficking route of C. jejuni in polarized islands of Caco-2 intestinal epithelial cells. Advanced microscopy on infected cells revealed that C. jejuni invades the polarized intestinal cells via the subcellular invasion pathway. Remarkably, invasion was not blocked by the inhibitors of microtubule dynamics colchicine or paclitaxel, and was even enhanced after disruption of host cell actin filaments by cytochalasin D. Invasion also continued after dinitrophenol-induced cellular depletion of ATP, whereas this compound effectively inhibited the uptake of invasive Escherichia coli. Confocal microscopy demonstrated that intracellular C. jejuni resided in membrane-bound CD63-positive cellular compartments for up to 24 h. Establishment of a novel luciferase reporter-based bacterial viability assay, developed to overcome the limitations of the classical bacterial recovery assay, demonstrated that a subset of C. jejuni survived intracellularly for up to 48 h. Taken together, our results indicate that C. jejuni is able to actively invade polarized intestinal epithelial cells via a novel actin- and microtubule-independent mechanism and remains metabolically active in the intracellular niche for up to 48 hours.

Bacterial infections and ceramide

Ceramide is released from sphingomyelin primarily by the activity of acid, neutral, or alkaline sphingomyelinases or is synthesized de novo. Several bacteria, viruses, and even parasites infect mammalian cells by exploiting the acid sphingomyelinase or the neutral sphingomyelinase-ceramide system, or both. Sphingomyelinases and ceramide have been shown to be crucially involved in the internalization of pathogens, the induction of apoptosis in infected cells, the intracellular activation of signaling pathways, and the release of cytokines. The diverse functions of ceramide in infections suggest that the sphingomyelinase-ceramide system is a key player in the host response to many pathogens.

Targeted delivery of antibiotics to intracellular chlamydial infections using PLGA nanoparticles

Chlamydia trachomatis and Chlamydia pneumoniae are intracellular bacterial pathogens that have been shown to cause, or are strongly associated with, diverse chronic diseases. Persistent infections by both organisms are refractory to antibiotic therapy. The lack of therapeutic efficacy results from the attenuated metabolic rate of persistently infecting chlamydiae in combination with the modest intracellular drug concentrations achievable by normal delivery of antibiotics to the inclusions within which chlamydiae reside in the host cell cytoplasm. In this research, we evaluated whether nanoparticles formulated using the biodegradable poly(d-L-lactide-co-glycolide) (PLGA) polymer can enhance the delivery of antibiotics to the chlamydial inclusion complexes. We initially studied the trafficking of PLGA nanoparticles in Chlamydia-infected cells. We then evaluated nanoparticles for the delivery of antibiotics to the inclusions. Intracellular trafficking studies show that PLGA nanoparticles efficiently concentrate in inclusions in both acutely and persistently infected cells. Further, encapsulation of rifampin and azithromycin antibiotics in PLGA nanoparticles enhanced the effectiveness of the antibiotics in reducing microbial burden. Combination of rifampin and azithromycin was more effective than the individual drugs. Overall, our studies show that PLGA nanoparticles can be effective carriers for targeted delivery of antibiotics to intracellular chlamydial infections.

Neisseria gonorrhoeae-induced transactivation of EGFR enhances gonococcal invasion

Neisseria gonorrhoeae, the causative agent of the sexually transmitted infection gonorrhoea, adheres to and invades into genital epithelial cells. Here, we investigate host components that are used by the bacteria for their entry into epithelial cells. We found that gonococcal microcolony formation on the surface of HEC-1-B cells disrupted the polarized, basolateral distribution of both epidermal growth factor receptor (EGFR) and ErbB2, a related family member, and induced their accumulation under the microcolonies at the apical membrane. Gonococcal infection increased EGFR and ErbB2 phosphorylation. The EGFR kinase inhibitor, AG1478, reduced gonococcal invasion by 80%, but had no effect on adherence or the recruitment of EGFR and ErbB2 to the microcolonies. Gonococcal inoculation upregulated the mRNA levels of several ligands of EGFR. Prevention of EGFR ligand shedding by blocking matrix metalloproteinase activation reduced gonococcal invasion without altering their adherence, while the addition of the EGFR ligand, HB-EGF, was able to restore invasion to 66% of control levels. These data indicate that N. gonorrhoeae modulates the activity and cellular distribution of host EGFR, facilitating their invasion. EGFR activation does not appear to be due to direct gonococcal binding to EGFR, but instead by its transactivation by gonococcal induced increases in EGFR ligands.

Cell-surface accumulation of flock house virus-derived peptide leads to efficient internalization via macropinocytosis

Arginine-rich cell-penetrating peptides (CPPs), including human immunodeficiency virus type 1 (HIV-1) Tat (48-60) and oligoarginines, have been applied as carriers for delivery of cargo molecules, because of their capacity to internalize into cells and penetrate biological membranes. Despite the fact that they have been extensively studied, the factors required for the efficient internalization of CPPs are still unclear. In this report, we evaluated the internalization efficiencies of seven CPPs derived from DNA/RNA-binding peptides, and discovered that a peptide derived from the flock house virus (FHV) coat protein was internalized most efficiently into Chinese hamster ovary (CHO-K1), HeLa, and Jurkat cells. Comparison of the factors facilitating the internalization with those of the Tat peptide revealed that the FHV peptide induces macropinocytosis much more efficiently than the Tat peptide, which leads to its high cellular uptake efficiency. Additionally, the strong adsorption of the FHV peptide on cell membranes via glycosaminoglycans (GAGs) was shown to be a key factor for induction of macropinocytosis, and these steps were successfully monitored by live imaging of the peptide internalization into cells in relation to the actin organization. The remarkable methods of FHV peptide internalization thus highlighted the critical factors for internalizations of the arginine-rich CPPs.

Role of bacterial OmpA and host cytoskeleton in the invasion of human intestinal epithelial cells by Enterobacter sakazakii

Enterobacter sakazakii is an emerging pathogen in neonates and infants. Interactions of E. sakazakii with intestinal epithelium could be vital in the pathogenesis of enteric infections and in its systemic dissemination. The present study investigated the interaction of E. sakazakii with human intestinal epithelial (INT407) cells and the role of bacterial outer membrane protein A (OmpA) and host cytoskeleton in these interactions. E. sakazakii invaded INT407 cells with moderate efficiency. An ompA mutant of E. sakazakii was significantly attenuated in its invasiveness, and complementation restored the invasive phenotype significantly. Drugs acting on host cell microfilaments (MF) and microtubules (MT) significantly inhibited bacterial invasion. Localization of both microfilaments (MF) and microtubules (MT) was observed in INT407 cells following E. sakazakii infection. The results suggest that E. sakazakii invasion of INT407 cells involves participation of both MF and MT and bacterial OmpA plays a critical role in invasion.

Cytoskeleton and motor proteins are required for the transcytosis of Neisseria gonorrhoeae through polarized epithelial cells

Neisseria gonorrhoeae interact with polarized T84 epithelial cells by engaging carcinoembryonic antigen-related cellular adhesion molecule (CEACAM) receptors. Adherent bacteria that are taken up by the cells are able to traverse the epithelial layer from the apical to the basal side. Herein, we demonstrate that the actin cytoskeleton of the cells is not required for the initial adherence of the bacteria, however, it is essential for invasion into and traversal through T84 cells. Furthermore, microtubule inhibitors blocked the traversal, but not the adherence and invasion of the bacteria. Inhibition of the motor activity of myosins reduced invasion and traversal, but not bacterial adherence. Immunofluorescence confocal laser scanning microscopy revealed the colocalization of the microtubule-based kinesin and dynein motors, and the actin-based motor myosin with adherent and intracellular gonococci. Transcytosis was reduced by blocking kinesin and myosin with specific antibodies. This underlines the importance of these motor proteins for the transcytosis of epithelial monolayers by N. gonorrhoeae.

Inhibition of macropinocytosis blocks antigen presentation of type II collagen in vitro and in vivo in HLA-DR1 transgenic mice

Professional antigen-presenting cells, such as dendritic cells, macrophages and B cells have been implicated in the pathogenesis of rheumatoid arthritis, constituting a possible target for antigen-specific immunotherapy. We addressed the possibility of blocking antigen presentation of the type II collagen (CII)-derived immunodominant arthritogenic epitope CII_259–273 to specific CD4 T cells by inhibition of antigen uptake in HLA-DR1-transgenic mice in vitro and in vivo. Electron microscopy, confocal microscopy, subcellular fractionation and antigen presentation assays were used to establish the mechanisms of uptake, intracellular localization and antigen presentation of CII by dendritic cells and macrophages. We show that CII accumulated in membrane fractions of intermediate density corresponding to late endosomes. Treatment of dendritic cells and macrophages with cytochalasin D or amiloride prevented the intracellular appearance of CII and blocked antigen presentation of CII_259–273 to HLA-DR1-restricted T cell hybridomas. The data suggest that CII was taken up by dendritic cells and macrophages predominantly via macropinocytosis. Administration of amiloride in vivo prevented activation of CII-specific polyclonal T cells in the draining popliteal lymph nodes. This study suggests that selective targeting of CII internalization in professional antigen-presenting cells prevents activation of autoimmune T cells, constituting a novel therapeutic strategy for the immunotherapy of rheumatoid arthritis.

The role of clathrin-dependent endocytosis in bacterial internalization

Internalization of bacteria into mammalian host cells has been studied extensively in the past two decades. These studies have highlighted the amazingly diverse strategies used by bacterial pathogens to induce their entry in non-phagocytic cells. The roles of actin and of the whole cytoskeletal machinery have been investigated in great detail for several invasive organisms, such as Salmonella, Shigella, Yersinia and Listeria. Recent results using Listeria highlight a role for the endocytosis machinery in bacterial entry, suggesting that clathrin-dependent endocytic mechanisms are also involved in internalization of large particles. This contrasts with the generally accepted dogma but agrees with previous studies of bacterial and viral infections and also of phagocytosis.

Low-phosphate-dependent invasion resembles a general way for Neisseria gonorrhoeae to enter host cells

Obligate human-pathogenic Neisseria gonorrhoeae expresses numerous variant surface proteins mediating adherence to and invasion of target cells. The invariant major outer membrane porin PorB of serotype A (P.IA) gonococci triggers invasion into Chang cells only if the medium is devoid of phosphate. Since gonococci expressing PorB(IA) are frequently isolated from patients with severe disseminating infections, the interaction initiated by the porin may be of major relevance for the development of this serious disease. Here, we investigated the low-phosphate-dependent invasion and compared it to the well-known pathways of entry initiated by Opa proteins. P.IA-triggered invasion requires clathrin-coated pit formation and the action of actin and Rho GTPases. However, in contrast to Opa-initiated invasion via heparan sulfate proteoglycans, microtubules, acidic sphingomyelinase, phosphatidylinositol 3-kinase, and myosin light chain kinase are not involved in this entry pathway. Nor are Src kinases required, as they are in invasion, e.g., via the CEACAM3 receptor. Invasion by PorB(IA) occurs in a wide spectrum of cell types, such as primary human epithelial and endothelial cells and in cancer cells of human and animal origin. Low-phosphate-dependent invasion is thus a pathway of gonococcal entry distinct from Opa-mediated invasion.

Leishmania lipophosphoglycan activates the transcription factor activating protein 1 in J774A.1 macrophages through the extracellular signal-related kinase (ERK) and p38 mitogen-activated protein kinase

Leishmania donovani is an obligatory intracellular pathogen that resides and multiplies in the phagolysosomes of macrophages. The outcome of this infection depends on the balance between the host ability to activate macrophage killing and the parasite ability to suppress or evade this host immune response. Lipophosphoglycan (LPG) glycoconjugate, the surface molecule of the protozoan parasite is a virulence determinant and a major parasite molecule involved in this process. In this study, we examined the ability of Leishmania and its surface molecule, lipophosphoglycan to activate activating protein 1 (AP-1) through the mitogen-activated protein kinase (MAPK) cascade. We report here that the Leishmania surface molecule, lipophosphoglycan stimulates the simultaneous activation of all three classes of MAP kinases, extracellular signal-related kinases (ERKs), the c-jun amino-terminal kinase (JNK) and the p38 MAP kinase with differential kinetics in J774A.1 macrophage cell line. Furthermore, both L. donovani and its surface molecule lipophosphoglycan resulted in a dose- and time-dependent induction of AP-1 DNA-binding activity. We have also shown a dose-dependent increase of AP-1 binding activity in both low and high virulent strains of parasite. The use of inhibitors selective for ERK (PD98059) and p38 (SB203580) pathway showed that pre-incubation of cells with either SB203580 or PD98059 affected the binding activity of AP-1 suggesting that both p38 and ERK MAP kinase activation appear to be necessary for AP-1 activation by LPG. Lipophosphoglycan induced IL-12 production and generation of nitric oxide in murine macrophages. These results demonstrate that L. donovani LPG activates pro-inflammatory, endotoxin-like response pathway in J774A.1 macrophages and the interaction may play a pivotal role in the elimination of the parasite.

The anti-inflammatory compound curcumin inhibits Neisseria gonorrhoeae-induced NF-κB signaling, release of pro-inflammatory cytokines/chemokines and attenuates adhesion in late infection

Neisseria gonorrhoeae(Ngo) is a Gram-negative pathogenic bacterium responsible for an array of diseases ranging from urethritis to disseminated gonococcal infections. Early events in the establishment of infection involve interactions betweenNgoand the mucosal epithelium, which induce a local inflammatory response. Here we analyzed the molecular mechanism involved in theNgo-induced induction of the proinflammatory cytokines tumor necrosis factor α (TNFα), interleukin-6 (IL-6), and IL-8. We identified the immediate early response transcription factor nuclear factor κB (NF-κB) as a key molecule for the induction of cytokine release.Ngo-induced activation of direct upstream signaling molecules was demonstrated for IκB kinase α and β (IKKα and IKKβ) by phosphorylation of IκBα as a substrate and IKK autophosphorylation. Using dominant negative cDNAs encoding kinase-dead IKKα, IKKβ, and NF-κB-inducing kinase (NIK),Ngo-induced NF-κB activity was significantly inhibited. Curcumin, the yellow pigment derived fromCurcuma longa, inhibited IKKα, IKKβ and NIK, indicating its strong potential to block NF-κB-mediated cytokine release and the innate immune response. In addition to the inhibition ofNgo-induced signaling, curcumin treatment of cells completely abolished the adherence of bacteria to cells in late infection, underlining the high potential of curcumin as an anti-microbial compound without cytotoxic side effects.

Leishmania donovani activates nuclear transcription factor-kappaB in macrophages through reactive oxygen intermediates

Interaction of Leishmania donovani with macrophages antagonizes host defense mechanisms by interfering with a cascade of cell signaling processes in the macrophages. An early intracellular signaling event that follows receptor engagement is the activation of transcription factor NF-kappaB. It has been reported earlier that NF-kappaB-dependent signaling pathway regulates proinflammatory cytokine release. We therefore investigated the effect of L. donovani infectivity on this nuclear transcription factor in macrophage cell line J774A.1. Both L. donovani and its surface molecule lipophosphoglycan (LPG) resulted in a dose- and time-dependent activation of NF-kappaB-DNA binding activity in an electrophoretic mobility shift assay. We also report the involvement of IkappaB-alpha and IkappaB-beta in the persistent activation of NF-kappaB by L. donovani. We demonstrate that the NF-kappaB activation was independent of viability of the parasite. Electrophoretic mobility supershift assay indicated that the NF-kappaB complex consists of p65 and c-rel subunits. The interaction of parasite with the macrophages and not the cellular uptake was important for NF-kappaB activation. Both p38 and ERK mitogen activated protein kinase (MAP) activation appears to be necessary for NF-kappaB activation by LPG. Preincubation of cells with antioxidants resulted in inhibition of L. donovani induced NF-kappaB activation, thereby suggesting a potential role of reactive oxygen species in L. donovani induced intracellular signaling. The present data indicate that antioxidants could play an important role in working out various therapeutic modalities to control leishmaniasis.

The molecular mechanisms used by Neisseria gonorrhoeae to initiate infection differ between men and women

The molecular mechanisms used by the gonococcus to initiate infection exhibit gender specificity. The clinical presentations of disease are also strikingly different upon comparison of gonococcal urethritis to gonococcal cervicitis. An intimate association occurs between the gonococcus and the urethral epithelium and is mediated by the asialoglycoprotein receptor. Gonococcal interaction with the urethral epithelia cell triggers cytokine release, which promotes neutrophil influx and an inflammatory response. Similarly, gonococcal infection of the upper female genital tract also results in inflammation. Gonococci invade the nonciliated epithelia, and the ciliated cells are subjected to the cytotoxic effects of tumor necrosis factor alpha induced by gonococcal peptidoglycan and lipooligosaccharide. In contrast, gonococcal infection of the lower female genital tract is typically asymptomatic. This is in part the result of the ability of the gonococcus to subvert the alternative pathway of complement present in the lower female genital tract. Gonococcal engagement of complement receptor 3 on the cervical epithelia results in membrane ruffling and does not promote inflammation. A model of gonococcal pathogenesis is presented in the context of the male and female human urogenital tracts.

Leishmania donovani induces interferon regulatory factor in murine macrophages: a host defense response

Macrophages play a key role in directing the host immune response to infection. Interaction of Leishmania donovani with macrophages results in the antagonization of host defense mechanisms by interfering with a cascade of cell signaling processes in the macrophages. Macrophages secrete interferon (IFN), as well as other cytokines, following lipopolysaccharide (LPS) stimulation. The interferon regulatory factors (IRFs) comprise a family of DNA-binding proteins that have been implicated in the transcriptional regulation of IFN and certain IFN-inducible genes. IRF-1 is a transcription factor, which regulates induction of several macrophage effectors and is known to bind to IRF-E site in the inducible nitric oxide synthase (iNOS) promoter. We for the first time report that L. donovani and its surface molecule lipophosphoglycan (LPG) result in a dose- and time-dependent activation of IRF-DNA-binding activity in macrophages. The components of this novel LPG-stimulated IRF-like complex are unclear. The interaction of parasite with the macrophages and not the cellular uptake was important for IRF activation. The use of inhibitors selective for ERK (PD98059) and p38 (SB203580) mitogen-activated protein (MAP) kinase pathway showed that preincubation of cells with either SB203580 or PD98059 did not affect the binding activity of IRF-E, suggesting that both p38 and ERK MAP kinase activation are not necessary for IRF-E activation. It is likely that induction of IRF in response to infection by L. donovani represents a host defense mechanism.

Role of microfilaments and microtubules in the invasion of INT-407 cells by Campylobacter jejuni

The internalization mechanisms triggered by Campylobacter jejuni were studied by invasion assays conducted with different inhibitors that act on the cytoskeleton structure of eukaryotic cells. The depolymerization of microfilaments by cytochalasin-D and that of microtubules by colchicines and nocodazole inhibited the uptake of C. jejuni into INT-407 cells in a dose-dependent manner. The inhibitory effect of microfilament depolymerization on C. jejuni internalization was more pronounced than that of microtubule depolymerization. By immunofluorescence microscopic observations, it was demonstrated that both microfilaments and microtubules were localized in INT-407 cells after C. jejuni infection. These data suggest that the internalization mechanism triggered by C. jejuni is associated with the combined effect of microfilaments and microtubules of host cells.

Exploiting host microtubule dynamics: a new aspect of bacterial invasion

During infection, many pathogenic bacteria modulate the actin cytoskeleton of eukaryotic host cells to facilitate various infectious processes such as the attachment to or invasion of epithelial cells. Additionally, some pathogenic bacteria are capable of modulating the dynamics of host microtubule (MTs). Although the molecular basis for this is still poorly understood, a recent study of the Shigella VirA effector protein, which is delivered via a type III secretion system, suggests that MT destabilization plays an important role in Shigella infection.

The route of bacterial uptake by macrophages influences the repertoire of epitopes presented to CD4 T cells

We studied MHC class II (MHC-II)-restricted antigen processing of viable Streptococcus pyogenes by murine macrophages for presentation of two CD4 T cell epitopes of the surface M5 protein. We show that presentation of both epitopes was prevented if actin polymerization was inhibited by cytochalasin D, but not if clathrin-dependent receptor-mediated endocytosis was prevented, suggesting uptake of streptococci by phagocytosis or macropinocytosis was required for presentation of the surface M protein. However, treatment of macrophages with amiloride, which selectively blocks membrane ruffling and subsequent macropinocytosis, inhibited the response to one epitope (M5(308-319)), but had no effect on presentation of the other (M5(17-31)). The effect of the inhibitors on uptake of streptococci was analyzed by electron microscopy. Cytochalasin D completely blocked uptake of streptococci, while dimethyl-amiloride only inhibited uptake into spacious compartments. Neither of the inhibitors altered the cell-surface expression of MHC-II and costimulatory molecules analyzed by flow cytometry. The data suggest that distinct epitopes of a protein associated with viable bacteria may be presented optimally following different uptake mechanisms in the same antigen-presenting cells.

Uptake of Aspergillus fumigatus Conidia by phagocytic and nonphagocytic cells in vitro: quantitation using strains expressing green fluorescent protein

Several pathogenic fungal organisms enter eukaryotic cells and manipulate the host cell environment to favor their own growth and survival. Aspergillus fumigatus is a saprophytic fungus that causes invasive lung disease in the immunocompromised host. To determine whether A. fumigatus could enter eukaryotic cells, we studied the uptake of two different GFP-expressing A. fumigatus strains into A549 lung epithelial cells, human umbilical vein endothelial (HUVE) cells, and J774 murine macrophages in vitro. A549 cells internalized 30% of the bound conidia whereas HUVE and J774 cells internalized 50 and 90%, respectively. Conidia within A549 cells remained viable for 6 h; however, 60 to 80% of conidia within J774 cells were killed after only 4 h. Live and heat-killed conidia were internalized to the same extent by A549 cells. After 6 h, almost none of the conidia inside A549 cells had germinated, whereas extracellular conidia had developed germ tubes. Internalization of conidia by A549 cells was a temperature-dependent process and required rearrangement of the underlying host cell cytoskeleton; uptake was inhibited by 75% with 0.5 microM cytochalasin D and by 65% with 5 microM colchicine. Fluorescent labeling of infected A549 cells with rhodamine phalloidin provided visible evidence of cytoskeletal alteration as many of the intracellular conidia were contained in actin-coated phagosomes. These data provide evidence that significant numbers of A. fumigatus conidia can be internalized by nonprofessional phagocytes in vitro and these cells may serve as reservoirs for immune cell evasion and dissemination throughout the host.

Distinct mechanisms of internalization of Neisseria gonorrhoeae by members of the CEACAM receptor family involving Rac1- and Cdc42-dependent and -independent pathways

Opa adhesins of pathogenic Neisseria species target four members of the human carcinoembryonic antigen-related cellular adhesion molecule (CEACAM) family. CEACAM receptors mediate opsonization-independent phagocytosis of Neisseria gonorrhoeae by human granulocytes and each receptor individually can mediate gonococcal invasion of epithelial cells. We show here that gonococcal internalization occurs by distinct mechanisms depending on the CEACAM receptor expressed. For the invasion of epithelial cell lines via CEACAM1 and CEACAM6, a pathogen-directed reorganization of the actin cytoskeleton is not required. In marked contrast, ligation of CEACAM3 triggers a dramatic but localized reorganization of the host cell surface leading to highly efficient engulfment of bacteria in a process regulated by the small GTPases Rac1 and Cdc42, but not Rho. Two tyrosine residues of a cytoplasmic immune receptor tyrosine-based activating motif of CEACAM3 are essential for the induction of phagocytic actin structures and subsequent gonococcal internalization. The granulocyte-specific CEACAM3 receptor has properties of a single chain phagocytic receptor and may thus contribute to innate immunity by the elimination of Neisseria and other CEACAM-binding pathogens that colonize human mucosal surfaces.

Receptor-mediated endocytosis of Neisseria gonorrhoeae into primary human urethral epithelial cells: the role of the asialoglycoprotein receptor

Urethral epithelial cells are invaded by Neisseria gonorrhoeae during gonococcal infection in men. To understand further the mechanisms of gonococcal entry into host cells, we used the primary human urethral epithelial cells (PHUECs) tissue culture system recently developed by our laboratory. These studies showed that human asialoglycoprotein receptor (ASGP-R) and the terminal lactosamine of lacto-N-neotetraose-expressing gonococcal lipooligosaccharide (LOS) play an important role in invasion of PHUECs. Microscopy studies showed that ASGP-R traffics to the cell surface after gonococcal challenge. Co-localization of ASGP-R with gonococci was observed. As ASGP-R-mediated endocytosis is clathrin dependent, clathrin localization in PHUECs was examined after infection. Infected PHUECs showed increased clathrin recruitment and co-localization of clathrin and gonococci. Preincubating PHUECs in 0.3 M sucrose or monodansylcadaverine (MDC), which both inhibit clathrin-coated pit formation, resulted in decreased invasion. N. gonorrhoeae strain 1291 produces a single LOS glycoform that terminates with Gal(beta1-4)GlcNac(beta1-3)Gal(beta1-4)Glc (lacto-N-neotetraose). Invasion assays showed that strain 1291 invades significantly more than four isogenic mutants expressing truncated LOS. Sialylation of strain 1291 LOS inhibited invasion significantly. Preincubation of PHUECs in asialofetuin (ASF), an ASGP-R ligand, significantly reduced invasion. A dose-response reduction in invasion was observed in PHUECs preincubated with increasing concentrations of NaOH-deacylated 1291 LOS. These studies indicated that an interaction between lacto-N-neotetraose-terminal LOS and ASGP-R allows gonococcal entry into PHUECs.

Signal transduction pathways induced by virulence factors of Neisseria gonorrhoeae

The obligate human pathogen Neisseria gonorrhoeae infects a variety of human tissues. In recent years, several host cell receptors for the major bacterial adhesins have been identified. While the knowledge of the molecular mechanism of colonisation has helped to understand special aspects of the infection, like the explicit tropism of gonococci for human tissues, the long-term consequences of engaging these receptors are still unknown. A variety of signalling pathways initiated by the activated receptors and by bacterial proteins transferred to the infected cell have been defined which include lipid second messenger, protein kinases, proteases and GTPases. These pathways control important steps of the infection, such as tight adhesion and invasion, the induction of cytokine release, and apoptosis. The detailed knowledge of bacteria-induced signalling pathways could allow the design of new therapeutic approaches which might be advantageous over the classical antibiotics therapy.

Interactions of pathogenic neisseriae with epithelial cell membranes

The closely related bacterial pathogens Neisseria gonorrhoeae (gonococci, GC) and N. meningitidis (meningococci, MC) initiate infection at human mucosal epithelia. Colonization begins at apical epithelial surfaces with a multistep adhesion cascade, followed by invasion of the host cell, intracellular persistence, transcytosis, and exit. These activities are modulated by the interaction of a panoply of virulence factors with their cognate host cell receptors, and signals are sent from pathogen to host and host to pathogen at multiple stages of the adhesion cascade. Recent advances place us on the verge of understanding the colonization process at a molecular level of detail. In this review we describe the Neisseria virulence factors in the context of epithelial cell biology, placing special emphasis on the signaling functions of type IV pili, pilus-based twitching motility, and the Opa and Opc outermembrane adhesin/invasin proteins. We also summarize what is known about bacterial intracellular trafficking and growth. With the accelerated integration of tools from cell biology, biochemistry, biophysics, and genomics, experimentation in the next few years should bring unprecedented insights into the interactions of Neisseriae with their host.

Effect of alpha-oligosaccharide phenotype of Neisseria gonorrhoeae strain MS11 on invasion of Chang conjunctival, HEC-1-B endometrial, and ME-180 cervical cells

The genes encoding the glycosyltransferases responsible for the addition of the five sugars in the alpha-oligosaccharide (alpha-OS) moiety of lipooligosaccharide (LOS) have been identified. Disruption of these glycosyltransferase genes singly or in combination results in corresponding truncations in LOS. In the present work we show that sequential deletion of the terminal four sugar residues of gonococcal alpha-OS had no discernible effect on the invasion of human conjunctival, endometrial, and cervical cell lines. However, deletion of the proximal glucose, which resulted in the complete deletion of alpha-OS, significantly impaired invasion of the gonococci into all three cell lines. The effect of deleting alpha-OS on invasion was independent of and additive to the known invasion-promoting factor OpaA. These data suggest that the proximal glucose residue of the alpha-OS chain of LOS is required for efficient invasion of gonococci into host mucosa.

Uptake pathways of clinical and healthy animal isolates of Campylobacter jejuni into INT-407 cells

Campylobacter jejuni isolates obtained from human and animal sources showed different invasion levels into human embryonic intestinal (INT-407) cells. There was no significant relation between the degree of invasion and cytotoxins production. The depolymerization of both microfilaments by cytochalasin-D and microtubules by colchicine, demecolcine and nocodazole or stabilization of microtubules by paclitaxel reduced the invasiveness of C. jejuni, although microfilament depolymerization showed greater inhibition than microtubule depolymerization. Interference with receptor-mediated endocytosis by G-strophanthin and monodansylcadaverine and inhibition of endosome acidification by monensin reduced the number of viable intracellular C. jejuni cells. Furthermore inhibition of only host protein kinases by staurosporine, but not phosphoinositide 3-kinase by wortmannin or protein kinase-C by calphostin-C, significantly reduced invasion of epithelial cells by C. jejuni. These data suggest that the internalization mechanism triggered by C. jejuni is strikingly different from the microfilament-dependent invasion mechanism exhibited by many of the well-studied enteric bacteria such as enteroinvasive strains of Escherichia coli, Salmonella typhimurium, Shigella flexneri, Yersinia enterocolitica and Yersinia pseudotuberculosis.

Role of ribosomal protein L12 in gonococcal invasion of Hec1B cells

Previous studies led to the development of a model of contact-induced enhanced gonococcal invasion of human reproductive cells that utilizes the lutropin receptor (LHr) as both the induction signal for conversion to this enhanced-gonococcal-invasion phenotype (Inv(+) GC) and as the specific Inv(+) GC uptake mechanism. This model proposes that gonococci express a surface feature that mimics human chorionic gonadotropin (hCG), the cognate ligand for LHr, and that this structure is responsible for the specific and productive interaction of GC with LHr. In this report, we identify a 13-kDa gonococcal protein with immunological similarities to hCG. The antiserum reactivity is specific since interaction with the 13-kDa gonococcal protein can be blocked by the addition of highly purified hCG. This gonococcal "hCG-like" protein, purified from two-dimensional gels and by immunoprecipitation, was determined by N-terminal sequencing to be the ribosomal protein L12. We present evidence that gonococcal L12 is membrane associated and surface exposed in gonococci, as shown by immunoblot analysis of soluble and insoluble gonococcal protein and antibody adsorption studies with fixed GC. Using highly purified recombinant gonococcal L12, we show that preincubation of Inv(-) GC with micromolar amounts of rL12 leads to a subsequent five- to eightfold increase in invasion of the human endometrial cell line, Hec1B. In addition, nanomolar concentrations of exogenous L12 inhibits gonococcal invasion to approximately 70% of the level in controls. Thus, we propose a novel cellular location for the gonococcal ribosomal protein L12 and concomitant function in LHr-mediated gonococcal invasion of human reproductive cells.

Neisseria gonorrhoeae elicits membrane ruffling and cytoskeletal rearrangements upon infection of primary human endocervical and ectocervical cells

Neisseria gonorrhoeae is a strict human pathogen that is, primarily, transmitted by close sexual contact with an infected individual. Gonococcal infection of the male urogenital tract has been well studied in experimental human models and in urethral cell culture systems. Recent studies, using tissue culture cell systems, have suggested a role for the cervical epithelium in gonococcal infection of females; however, the nature of gonococcal infection of the normal uterine cervix remains controversial. To address this enigma, we have developed two primary human cervical epithelial cell systems from surgical biopsies. Gonococcal infection studies and electron microscopy show that N. gonorrhoeae is capable of infecting and invading both the endo- and the ectocervix. Invasion was found to occur primarily in an actin-dependent manner, but it does not appear to require de novo protein synthesis by either the bacterium or the host cervical cell. Membrane ruffles appear to be induced in response to gonococci. Consistent with membrane ruffling, gonococci were found residing within macropinosomes, and a concentrated accumulation of actin-associated proteins was observed to occur in response to gonococcal infection. Electron microscopy of clinically derived cervical biopsies show that lamellipodia formation and cytoskeletal changes, suggestive of membrane ruffles, also occur in the cervical epithelium of women with naturally acquired gonococcal cervicitis. These studies demonstrate the ability of N. gonorrhoeae to infect and invade both the endo- and the ectocervix of the normal uterine cervix. Gonococcal induced ruffling is a novel finding and may be unique to the cervical epithelium.

Cytoskeletal rearrangements induced by Helicobacter pylori strains in epithelial cell culture: possible role of the cytotoxin

The relationship between Helicobacter pylori adherence, cytotoxin production, and modification of the cytoskeletal structure was investigated by studying the effects of 12 H. pylori strains cocultured with Hep-2 epithelial cells. Bacterial strains were isolated from patients with peptic ulcer disease or nonulcer dyspepsia. Presence of the cag pathogenicity island and vacA subtypes of the strains were determined as was the production of vacuolating cytotoxin. We found that cytoskeletal rearrangements, as observed by confocal microscopy after double staining of the bacteria and the cell actin with Texas red and fluorescein-conjugated phalloidin, respectively, occurred essentially when the strains were cytotoxin producers and that the supernatants alone could also lead to these modifications.

Early events and implication of F-actin and annexin I associated structures in the phagocytic uptake of Brucella suis by the J-774A.1 murine cell line and human monocytes

Brucella spp. are facultative, intracellular pathogenic bacteria that cause brucellosis, a zoonosis affecting mammalian species. Brucella entry into myelomonocytic cell lines is highly enhanced by opsonization. Few studies have been undertaken to unravel the first interactions between these bacteria and their host cells. This paper deals with early events following contact of Brucella suis with the J-774A.1 phagocytic cell line and differentiated monocytes. Phagocytic uptake of bacteria was documented under a fluorescence microscope using GFP-expressing B. suis. Unlike entry in the J-774A. 1 cell line, non-opsonized Brucella entered differentiated human monocytes as efficiently as opsonized bacteria. However, following 1 h infections, a mean of only three bacteria were phagocytized and the whole monocyte population was only infected after a 4 h infection. Contact of non-opsonized Brucella with phagocytes did not induce marked structural changes at the cell surface, as revealed by scanning electron microscopy. Contact of Brucella (opsonized or not) elicited transient local recruitment of F-actin, revealed by phalloidin labelling, and of annexin I-associated structures, revealed by immunofluorescence staining. Finally, bacteria appeared to be rapidly internalized in monocytes once they had adhered to the cell surface. A low percentage of infected cells and few adhered and/or internalized bacteria following short-term infections could have resulted either from the fact that there were few sites of entry or the weak bacterial initial interactions with the host-cell membrane or the bacterial receptor.

Neisseria gonorrhoeae MS11mkC opacity protein expression in vitro and during human volunteer infectivity studies

BACKGROUND AND OBJECTIVES

Neisseria gonorrhoeae MS11mkC harbors 11 independently expressed opacity (Opa) protein genes with distinct in vitro expression frequencies. In experimental infections in which human male volunteers were inoculated with transparent (Opa), piliated (P+) strains, the authors associate onset of symptoms with recovery of opaque (Opa+) gonococci.

GOALS

In vitro and recovered (Opa) protein expression rates were compared to determine if the human host influences Opa expression.

STUDY DESIGN

Opa expression was determined using Western immunoblot analysis; Opa sizes were determined using a scanning densitometer.

RESULTS

Seven of 10 Opa proteins were identified in gonococci recovered from all of the volunteers at frequencies consistent with in vitro results (Opa C, 29.5 kDa; Opa K, 30 kDa; Opa G, 31 kDa; Opa I, 32 kDa; Opa J, 33 kDa; Opa D, 34 kDa; and Opa H, 37 kDa) (P > or = 0.01, Fisher exact test). Opa B (30.5 kDa) was identified at lower than expected frequencies, whereas Opa E (31.2) and F (31.5) were identified at higher' than expected frequencies. When recovered gonococci were reanalyzed for in vitro expression frequencies, they were consistent with preinfection frequencies.

CONCLUSIONS

The host may influence the prevalence of some Opa proteins.

Role of lipooligosaccharide in Opa-independent invasion of Neisseria gonorrhoeae into human epithelial cells

Lipooligosaccharide (LOS) has been implicated in the adhesion and invasion of host epithelial cells. We examined the adhesive and invasive abilities of isogenic gonococcal opacity-associated outer membrane protein-negative, pilus-positive (Opa-Pil+) Neisseria gonorrhoeae strains expressing genetically defined LOS. Strain F62 (Opa-Pil+), expressing the lacto-N-neotetraose and the galNac-lacto-N-neotetraose LOS, and its isogenic derivative that expressed only the lacto-N-neotetraose LOS (F62 Delta lgtD), adhered to, and invaded, to the same extent the human cervical epidermoid carcinoma cell line, ME180. While the adhesive abilities of Opa-Pil+ isogenic strains that express LOS molecules lacking the lacto-N-neotetraose structure were similar to that seen for F62, their invasive abilities were much lower than the strains expressing lacto-N-neotetraose. Fluorescence microscopy studies showed that the adherence of F62, but not the strains lacking lacto-N-neotetraose, induced the rearrangement of actin filaments under the adherent sites. Electron microscopy studies demonstrated that F62, but not the strains lacking lacto-N-neotetraose, formed extensive and intimate associations with epithelial cell membranes. Thus, in the absence of detectable Opa protein, the lacto-N-neotetraose LOS promotes gonococcal invasion into ME180 cells. The data also suggest that LOS is involved in the mobilization of actin filaments in host cells, and in the formation of a direct interaction between the bacterial outer membrane and the plasma membrane of ME180 cells.

Macropinocytosis as a mechanism of entry into primary human urethral epithelial cells by Neisseria gonorrhoeae

Gonococcal entry into primary human urethral epithelial cells (HUEC) can occur by macropinocytosis. Scanning and transmission electron microscopy revealed lamellipodia surrounding gonococci, and confocal laser scanning microscopy analysis showed organisms colocalized with M(r) 70,000 fluorescein isothiocyanate-labeled dextran within the cells. Phosphoinositide 3-kinase inhibitors and an actin polymerization inhibitor prevented macropinocytic entry of gonococci into HUEC.

Effects of the immunoglobulin A1 protease on Neisseria gonorrhoeae trafficking across polarized T84 epithelial monolayers

We previously demonstrated that the Neisseria IgA1 protease cleaves LAMP1 (lysosome-associated membrane protein 1), a major integral membrane glycoprotein of lysosomes, thereby accelerating its degradation rate in infected A431 human epidermoid carcinoma cells and resulting in the alteration of lysosomes in these cells. In this study, we determined whether the IgA1 protease also affects the trafficking of Neisseria gonorrhoeae across polarized T84 epithelial monolayers. We report that N. gonorrhoeae infection of T84 monolayers, grown on a solid substrate or polarized on semiporous membranes, also results in IgA1 protease-mediated reduction of LAMP1. We demonstrate that iga mutants in two genetic backgrounds exited polarized T84 monolayers in fewer numbers than the corresponding wild-type strains. Finally, we present evidence that these mutants have a statistically significant and reproducible defect in their ability to traverse T84 monolayers. These results add to our previous data by showing that the IgA1 protease alters lysosomal content in polarized as well as unpolarized cells and by demonstrating a role for the protease in the traversal of epithelial barriers by N. gonorrhoeae.

Syndecan-1 and syndecan-4 can mediate the invasion of OpaHSPG-expressing Neisseria gonorrhoeae into epithelial cells

Neisseria gonorrhoeae (Ngo) expressing the outer membrane protein OpaHSPG can adhere to and invade epithelial cells via binding to heparan sulphate proteoglycan (HSPG) receptors. In this study, we have investigated the role of syndecan-1 and syndecan-4, two members of the HSPG family, in the uptake of Ngo by epithelial cells. When overexpressed in HeLa cells, both syndecans co-localize with adherent Ngo on the host cell surface. This overexpression of syndecan-1 and syndecan-4 leads to a three- and sevenfold increase in Ngo invasion respectively. In contrast, transfection with the syndecan-1 and syndecan-4 mutant constructs lacking the intracellular domain results in an abrogation of the invasion process, characteristic of a dominant-negative mode of action. A concomitant loss of the capacity to mediate Ngo uptake was also observed with syndecan-4 mutant constructs carrying lesions in the dimerization motif necessary for the binding of protein kinase C (PKC) and phosphatidylinositol 4,5-bisphosphate (PIP2), and mutants that are deficient in a C-terminal EFYA amino acid motif responsible for binding to syntenin or CASK. We conclude that syndecan-1 and syndecan-4 can both mediate Ngo uptake into epithelial cells, and that their intracellular domains play a crucial role in this process, perhaps by mediating signal transduction or anchorage to the cytoskeleton.

Outer membrane protein A-promoted actin condensation of brain microvascular endothelial cells is required for Escherichia coli invasion

Escherichia coli is the most common gram-negative bacterium that causes meningitis during the neonatal period. We have previously shown that the entry of circulating E. coli organisms into the central nervous system is due to their ability to invade the blood-brain barrier, which is composed of a layer of brain microvascular endothelial cells (BMEC). In this report, we show by transmission electron microscopy that E. coli transmigrates through BMEC in an enclosed vacuole without intracellular multiplication. The microfilament-disrupting agents cytochalasin D and latrunculin A completely blocked E. coli invasion of BMEC. Cells treated with the microtubule inhibitors nocodazole, colchicine, vincristin, and vinblastine and the microtubule-stabilizing agent taxol also exhibited 50 to 60% inhibition of E. coli invasion. Confocal laser scanning fluorescence microscopy showed F-actin condensation associated with the invasive E. coli but no alterations in microtubule distribution. These results suggest that E. coli uses a microfilament-dependent phagocytosis-like endocytic mechanism for invasion of BMEC. Previously we showed that OmpA expression significantly enhances the E. coli invasion of BMEC. We therefore examined whether OmpA expression is related to the recruitment of F-actin. OmpA(+) E. coli induced the accumulation of actin in BMEC to a level similar to that induced by the parental strain, whereas OmpA(-) E. coli did not. Despite the presence of OmpA, a noninvasive E. coli isolate, however, did not show F-actin condensation. OmpA(+)-E. coli-associated condensation of F-actin was blocked by synthetic peptides corresponding to the N-terminal extracellular domains of OmpA as well as BMEC receptor analogues for OmpA, chitooligomers (GlcNAcbeta1-4GlcNAc oligomers). These findings suggest that OmpA interaction is critical for the expression or modulation of other bacterial proteins that will subsequently cause actin accumulation for the uptake of bacteria.

Invasive ability of an Escherichia coli strain isolated from the ileal mucosa of a patient with Crohn's disease

Crohn's disease (CD) is an inflammatory bowel disease in which Escherichia coli strains have been suspected of being involved. We demonstrated previously that ileal lesions of CD are colonized by E. coli strains able to adhere to intestinal Caco-2 cells but devoid of the virulence genes so far described in the pathogenic E. coli strains involved in gastrointestinal infections. In the present study we compared the invasive ability of one of these strains isolated from an ileal biopsy of a patient with CD, strain LF82, with that of reference enteroinvasive (EIEC), enteropathogenic (EPEC), enterotoxigenic (ETEC), enteraggregative (EAggEC), enterohemorrhagic (EHEC), and diffusely adhering (DAEC) E. coli strains. Gentamicin protection assays showed that E. coli LF82 was able to efficiently invade HEp-2 cells. Its invasive level was not significantly different from that of EIEC and EPEC strains (P > 0.5) but significantly higher than that of ETEC (P < 0.03), EHEC (P < 0. 005), EAggEC (P < 0.004) and DAEC (P < 0.02) strains. Strain LF82 also demonstrated efficient ability to invade intestinal epithelial cultured Caco-2, Intestine-407, and HCT-8 cells. Electron microscopy examination of infected HEp-2 cells revealed the presence of numerous intracellular bacteria located in vacuoles or free in the host cell cytoplasm. In addition, the interaction of strain LF82 with epithelial cells was associated with the elongation of microvillar extensions that extruded from the host cell membranes and engulfed the bacteria. This internalization mechanism strongly resembles Salmonella- or Shigella-induced macropinocytosis. The use of cytochalasin D and colchicine showed that the uptake of strain LF82 by HEp-2 cells was mediated by both an actin microfilament-dependent mechanism and microtubule involvement. In addition, strain LF82 survived for at least 24 h in HEp-2 and Intestine-407 cells and efficiently replicated intracellularly in HEp-2 cells. PCR and hybridization experiments did not reveal the presence of any of the genetic determinants encoding EIEC, EPEC, or ETEC proteins involved in bacterial invasion. Thus, these findings show that LF82, which colonized the ileal mucosa of a patient with CD, is a true invasive E. coli strain and suggest the existence of a new potentially pathogenic group of E. coli, which we propose be designated adherent-invasive E. coli.

Citrobacter freundii invades and replicates in human brain microvascular endothelial cells

Neonatal bacterial meningitis remains a disease with unacceptable rates of morbidity and mortality despite the availability of effective antimicrobial therapy. Citrobacter spp. cause neonatal meningitis but are unique in their frequent association with brain abscess formation. The pathogenesis of Citrobacter spp. causing meningitis and brain abscess is not well characterized; however, as with other meningitis-causing bacteria (e.g., Escherichia coli K1 and group B streptococci), penetration of the blood-brain barrier must occur. In an effort to understand the pathogenesis of Citrobacter spp. causing meningitis, we have used the in vitro blood-brain barrier model of human brain microvascular endothelial cells (HBMEC) to study the interaction between C. freundii and HBMEC. In this study, we show that C. freundii is capable of invading and trancytosing HBMEC in vitro. Invasion of HBMEC by C. freundii was determined to be dependent on microfilaments, microtubules, endosome acidification, and de novo protein synthesis. Immunofluorescence microscopy studies revealed that microtubules aggregated after HBMEC came in contact with C. freundii; furthermore, the microtubule aggregation was time dependent and seen with C. freundii but not with noninvasive E. coli HB101 and meningitic E. coli K1. Also in contrast to other meningitis-causing bacteria, C. freundii is able to replicate within HBMEC. This is the first demonstration of a meningitis-causing bacterium capable of intracellular replication within BMEC. The important determinants of the pathogenesis of C. freundii causing meningitis and brain abscess may relate to invasion of and intracellular replication in HBMEC.