Boar spermatozoa successfully predict mitochondrial modes of toxicity: implications for drug toxicity testing and the 3R principles

Replacement of animal testing by in vitro methods (3-R principles) requires validation of suitable cell models, preferably obtained non-invasively, defying traditional use of explants. Ejaculated spermatozoa are highly dependent on mitochondrial production and consumption of ATP for their metabolism, including motility display, thus becoming a suitable model for capturing multiple modes of action of drugs and other chemicals acting via mitochondrial disturbance. In this study, a hypothesis was tested that the boar spermatozoon is a suitable cell type for toxicity assessment, providing a protocol for 3R-replacement of animals for research and drug-testing. Boar sperm kinetics was challenged with a wide variety of known frank mito-toxic chemicals with previously shown mitochondrial effects, using a semi-automated motility analyser allied with real-time fluorescent probing of mitochondrial potential (MitoTracker & JC-1). Output of this sperm assay (obtained after 30 min) was compared to cell viability (ATP-content, data obtained after 24-48 h) of a hepatome-cell line (HepG2). Results of compound effects significantly correlated (P<0.01) for all sperm variables and for most variables in (HepG2). Dose-dependent decreases of relative ATP content in HepG2 cells correlated to sperm speed (r=0.559) and proportions of motile (r=0.55) or progressively motile (r=0.53) spermatozoa. The significance of the study relies on the objectivity of computerized testing of sperm motility inhibition which is comparable albeit of faster output than somatic cell culture models. Sperm suspensions, easily and painlessly obtained from breeding boars, are confirmed as suitable biosensors for preclinical toxicology screening and ranking of lead compounds in the drug development processes.

[Analysis of extracellular matrix proteins produced by cultured cells]

Extracellular matrix (ECM) is a highly organized multimolecular structure essential for vital function of any organism. Although a lot of data on the extracellular matrix components has been accumulated, an isolation of the entire set of these proteins still remains to be a complex procedure since ECM contains fibrillar proteins and proteoglycans, which form multidomain net-like structures. In the presented study, we developed a method for isolation of ECM proteins from cell cultures. Human epidermoid carcinoma cells A431 and fibroblasts obtained from normal and scar human skin were used. We showed that EDTA solution removed cells from culture plates without destroying the cell membrane. Following treatment of remaining ECM proteins with acetic acid in order to dissociate collagen fibrils significantly improved fractioning of ECM proteins. Extraction of the remained proteins from culture plate surface was preformed using a buffer developed on the basis of Laemmli probe buffer. With this method, we isolated ECM proteins synthesized by culturing cells and suitable for a future analysis by SDS PAGE and two-dimentional electrophoresis as well as for identification of individual proteins by mass-spectrometry. This study may allow comparing protein contents of ECMs isolated from different sources, and elucidate influences of various proteins on the protein and the properties of extracellular matrix of investigated cells.

[The comparative analysis of subcellular fractionation methods for revealing of alpha-actinin 1 and alpha-actinin 4 in A431 cells]

Alpha-actinin 1 and alpha-actinin 4 belong to a family of actin-binding proteins with shared structural function and regulation of several processes in a cell. Based on previous data on different distribution of these proteins in the nucleus and cytoplasm, we have explored in detail the distribution of alpha-actinin 1 and alpha-actinin 4 in subcellular fractions in A431 cells spread on fibronectin. Several methods of subcellular fractionation were used. Complex approach allowed resuming that revealing of alpha-actinin isoforms in fractions depended on the composition of lysis buffer and preliminary low-temperature freezing of the cells. We have drawn a conclusion that alpha-actinin 4 can be found in all cytoplasmic and nuclear subfractions, while alpha-actinin 1 is characterized by cytoplasmic and membrane localization with specificity of its distribution tightly to the nuclear membrane.

[Analysis of nuclear protein complexes comprising alpha-actinin-4 by 2D-electrophoresis and mass-spectrometry]

Actin-binding protein alpha-actinin-4 is a member of spectrin super family. It is located in the cytoplasm and in the nucleus. However, nuclear functions of alpha-actinin-4 are still not clear. In this study, we analyzed composition of nuclear protein complexes associated with alpha-actinin-4 in A431 cells. Using 2D electrophoresis, we have determined that about 50 different proteins may be associated with nuclear alpha-actinin-4. Using mass-spectrometry, we analyzed major proteins of these complexes. beta-Actin, alpha- and beta-tubulins, ribonucleoprotein A2/B1, which regulates splicing and is associated with beta-actin, peroxiredoxin-1, which is involved in oxidative stress, and glycolytic enzyme D-3-phosphoglycerate dehydrogenase were identified by MALDI-TOF. Detection of these proteins in nuclear complexes with alpha-actinin-4 may suggest that alpha-actinin-4 is involved in transcription and splicing. Presence of beta-actin in the investigated complexes was confirmed by tandem mass-spectrometry (MALDI-TOF-TOF). Immunoprecipitation of nuclear proteins with antibodies against alpha-tubulin confirmed association of alpha-actinin-4 with alpha-tubulin in the protein complex. Nuclear alpha-actinin-4 constitutes of 105 KDa fullsize isoform and two truncated isoforms of 65 and 75 kDa, whereas only the truncated isoform have been found in nuclear complexes with alpha-tubulin. These data suggest that alpha-actinin-4 is associated with a number of different nuclear protein complexes which may carry out different functions in the cell nucleus.

Antibodies to oat prolamines (avenins) in children with coeliac disease

BACKGROUND

The use of oats in a gluten-free diet for children with coeliac disease is presently under investigation. In this study we measured the content of antibodies to oat prolamines (avenin) in sera from coeliac children and reference children.

METHODS

Crude avenin was prepared by extraction with ethanol and salt-solution and used as antigen in a three-step ELISA. Sera from 81 children, including 34 children with verified coeliac disease, were analysed for both IgA and IgG antibodies to avenin and gliadin. Sera were also incubated with gliadin before exposure to avenin, and vice versa, to assess a possible cross-reaction between the species. Keyhole limpet hemocyanin (KLH) was used as a negative control.

RESULTS

Children with coeliac disease on a normal diet had significantly higher levels of antibodies to avenin, both IgG and IgA, than reference children (P < 0.001) and the levels correlated positively with gliadin antibodies, especially of IgA-type (r = 0.798). Both anti-avenin and anti-gliadin antibodies were only absorbed by the corresponding protein.

CONCLUSIONS

Children with coeliac disease have antibodies to oat proteins at significantly higher levels than reference children. The absorption test did not indicate a cross-reactivity between the prolamines of wheat and oats. The method will be employed for repeated sampling of anti-avenin antibodies during a prospective interventional study with a gluten-free diet supplemented with oats.

Altered impedance during pigment aggregation in Xenopus laevis melanophores

Melanophores are dark-brown pigment cells located in the skin of amphibia, fish and many invertebrates. The skin colour of these organisms is regulated by the translocation of pigment organelles, and the pigment distribution can be altered by external stimuli. The ability to change colour in response to stimuli makes these cells of interest for biosensing applications. It was investigated whether pigment aggregation in Xenopus laevis melanophores can be detected by impedance measurements performed in transparent microvials. The results show that cell attachment, cell spreading and pigment aggregation all resulted in impedance changes, seen particularly at the highest frequency tested (10 kHz). The mechanisms behind the impedance changes were investigated by the addition of latrunculin or melatonin, both of which cause pigment aggregation. The latrunculin-induced aggregation was associated with cell area decrease and filamentous actin (F-actin) breakdown, processes that can influence the impedance. Lack of F-actin breakdown and an increase in cell area during melatonin-induced aggregation suggest that some other intracellular process also contributes to the impedance decrease seen for melatonin. It was shown that impedance measurements reflect not only cell attachment and cell spreading, but also intracellular events.

Parallel assessment of tyrosine phosphorylation and nuclear targeting of proteins

Phosphotyrosine signaling plays a vital role in cell regulation--from receptor activation, through stimulation of signal networks and nuclear targeting, to final cellular responses. Here, we propose a new approach to monitor the spatial and temporal aspects of tyrosine phosphorylation and dephosphorylation. The method can be used to determine whether protein tyrosine phosphorylations and dephosphorylations occur in the cytosol or the nucleus and to ascertain whether such modifications are associated with nuclear traffic. Promyelocytic leukemia (HL-60) cells are used as the experimental model. Biotinylated cytosolic proteins from donor cells are used to trace nuclear transport in permeabilized recipient cells. Thereafter, 2-D gel electrophoresis is applied to fractionate the cytosolic and nuclear proteins of the recipient cells, which are subsequently blotted onto polyvinylidene difluoride membranes. The membranes are developed with streptavidin and then reprobed with anti-phosphotyrosine antibodies. The major advantages of the protocol are that it is simple to perform, and reproducible results are obtained by overlaying the patterns of biotinylated and/or tyrosine-phosphorylated proteins. Moreover, several hundred cytosolic and nuclear proteins can be analyzed in parallel. Thus, by comparing the 2-D gel electrophoresis maps of biotinylated and tyrosine-phosphor lated proteins, it is possible to determine the involvement of trafficking of the latter proteins in cell signaling.

Leishmania donovani lipophosphoglycan causes periphagosomal actin accumulation: correlation with impaired translocation of PKCalpha and defective phagosome maturation

Lipophosphoglycan (LPG) is the major surface glycoconjugate of Leishmania donovani promastigotes. The repeating disaccharide-phosphate units of LPG are crucial for promastigote survival inside macrophages and establishment of infection. LPG has a number of effects on the host cell, including inhibition of PKC activity, inhibition of nitric oxide production and altered expression of cytokines. LPG also inhibits phagosomal maturation, a process requiring depolymerization of periphagosomal F-actin. In the present study, we have characterized the dynamics of F-actin during the phagocytosis of L. donovani promastigotes in J774 macrophages. We observed that F-actin accumulated progressively around phagosomes containing wild-type L. donovani promastigotes during the first hour of phagocytosis. Using LPG-defective mutants and yeast particles coated with purified LPG, we obtained evidence that this effect could be attributed to the repeating units of LPG. LPG also disturbed cortical actin turnover during phagocytosis. The LPG-dependent accumulation of periphagosomal F-actin correlated with an impaired recruitment of the lysosomal marker LAMP1 and PKCalpha to the phagosome. Accumulation of periphagosomal F-actin during phagocytosis of L. donovani promastigotes may contribute to the inhibition of phagosomal maturation by physically preventing vesicular trafficking to and from the phagosome.

Assessment of neutrophil N-formyl peptide receptors by using antibodies and fluorescent peptides

Enrichment of chemoattractant receptors on the neutrophil surface has been difficult to assess, primarily because of limitations in sensitivity of visualization. Using an ultrasensitive, cooled charge-coupled device camera, we investigated spatial-temporal relationships between N-formyl peptide receptor distribution and directional motility of human neutrophils. Live cells were labeled with fluorescent receptor ligands, i.e., fluoresceinated tert-butyl-oxycarbonyl-Phe-(D)-Leu-Phe-(D)-Leu-Phe-OH (Boc-FLFLF) and formyl-Nle-Leu-Phe-Nle-Tyr-Lys (fnLLFnLYK), while fixed cells were labeled with either fluorescent peptides or monoclonal antibodies. Double labeling of receptors and filamentous actin (F-actin) was done to investigate possible colocalization. N-Formyl peptide receptors on unstimulated cells were randomly distributed. However, on polarized neutrophils, the receptors accumulated toward regions involved in motility and distributed nonuniformly. In fixed neutrophils, antibody-labeled receptors colocalized with the F-actin-rich leading edge whereas peptide-labeled receptors lagged behind this region. We suggest that neutrophils use an asymmetric receptor distribution for directional sensing and sustained migration. A separation between receptors labeled with peptides and those labeled with antibodies reflects two functionally distinct receptor populations at the membrane of motile neutrophils.

Cytokines influence mRNA expression of cytochrome P450 3A4 and MDRI in intestinal cells

Inflammation and infection may have the potential to increase the bioavailability of drugs. This effect could be because of a reduced metabolism of xenobiotics in the liver and/or the intestines, or because of alterations in small intestinal permeability, mucosal flow, and expression of drug efflux transporters such as P-glycoprotein (Pgp). To assess the impact on intestinal epithelium of some proinflammatory cytokines and macrophages on permeability and mRNA expression of CYP3A4 and MDRI (multidrug resistance, coding for Pgp), we used the Caco-2 cell line as a model. Exposure to proinflammatory cytokines and macrophages decreased the mRNA expression of CYP3A4 and increased the expression of MDR1 mRNA in the Caco-2 cells. In parallel, the cell layer permeability, as measured by sodium fluorescein flux, increased for all cytokine and macrophage treatments, whereas the effect on transepithelial electrical resistance (TEER) varied. Our findings suggest that inflammation and infection trigger several different cellular responses that may affect drug bioavailability; that is hampered CYP3A4 expression, increased permeability of the epithelial cell layer, and enhanced Pgp-mediated counteractive transport.

NSP4 enterotoxin of rotavirus induces paracellular leakage in polarized epithelial cells

The nonstructural NSP4 protein of rotavirus has been described as the first viral enterotoxin. In this study we have examined the effect of NSP4 on polarized epithelial cells (MDCK-1) grown on permeable filters. Apical but not basolateral administration of NSP4 was found to cause a reduction in the transepithelial electrical resistance, redistribution of filamentous actin, and an increase in paracellular passage of fluorescein isothiocyanate-dextran. Significant effects on transepithelial electrical resistance were noted after a 20- to 30-h incubation with 1 nmol of NSP4. Most surprisingly, the epithelium recovered its original integrity and electrical resistance upon removal of NSP4. Preincubation of nonconfluent MDCK-1 cells with NSP4 prevented not only development of a permeability barrier but also lateral targeting of the tight-junction-associated Zonula Occludens-1 (ZO-1) protein. Taken together, these data indicate new and specific effects of NSP4 on tight-junction biogenesis and show a novel effect of NSP4 on polarized epithelia.

Tyrosine phosphorylation of cytoplasmic proteins in proliferating, differentiating, apoptotic HL-60 cells and blood neutrophils

Two-dimensional electrophoretic analysis was used to assess quantitative and qualitative changes in the expression and tyrosine phosphorylation of cytoplasmic proteins of proliferating, differentiating HL-60 cells and mature human blood neutrophils. The total tyrosine phosphorylation level of cytoplasmic proteins appeared approximately constant during the pre-commitment period, i.e., 6-24 h after induction of differentiation by 700 nM all-trans retinoic acid. At the time of granulocytic phenotype formation (48-120 h), the total level of tyrosine phosphorylation of cytoplasmic proteins increased significantly. Tyrosine phosphorylation of cytoplasmic proteins in matured blood neutrophils was significantly lower than that of cytoplasmic proteins of HL-60 cells differentiated for 96 h with retinoic acid. Immunoblotting with anti-Erk2 and anti-phosphotyrosine monoclonal IgG2bk antibodies showed that Erk2 was expressed and tyrosine-phosphorylated at different levels in HL-60 proliferating cells and in cells at all stages of differentiation. Our data showed that tyrosine phosphorylation of cytoplasmic proteins in differentiating HL-60 cells changes dramatically during the period of phenotype formation and is accompanied by increasing activity of Erk2. An increasing number of apoptotic cells appeared in the differentiating HL-60 cell population during the granulocyte maturation stage (48-120 h of differentiation). The appearance at this time of differentiation of a new set of tyrosine-phosphorylated cytoplasmic proteins (also distinctive for apoptotic HL-60 cells mediated by etoposide) together with an increasing number of apoptotic cells in the differentiating population strongly suggests that these proteins are associated with the apoptotic process.

Colocalization of leukotriene C synthase and microsomal glutathione S-transferase elucidated by indirect immunofluorescence analysis

We have previously shown that the two membrane bound enzymes leukotriene C synthase and microsomal glutathione S-transferase interact in vitro and in vivo. Rat basophilic leukemia cells and murine mastocytoma cells, two well-known sources of leukotriene C synthase, both expressed microsomal glutathione S-transferase as determined by Western blot analyses. Several human tissues were found to contain both leukotriene C synthase and microsomal glutathione S-transferase mRNA. These data suggest that the interaction may be physiologically important. To study this further, expression vectors encoding the two enzymes were cotransfected into mammalian cells and the subcellular localization of the enzymes was determined by indirect immunofluorescence using confocal laser scanning microscopy. The results showed that leukotriene C synthase and microsomal glutathione S-transferase were both localized on the nuclear envelope and adjacent parts of the endoplasmic reticulum. Image overlay demonstrated virtually identical localization. We also observed that coexpression substantially reduced the catalytic activity of each enzyme suggesting that a mechanism involving protein-protein interaction may contribute to the regulation of LTC4 production.

Apically exposed, tight junction-associated beta1-integrins allow binding and YopE-mediated perturbation of epithelial barriers by wild-type Yersinia bacteria

Using polarized epithelial cells, primarily MDCK-1, we assessed the mode of binding and effects on epithelial cell structure and permeability of Yersinia pseudotuberculosis yadA-deficient mutants. Initially, all bacteria except the invasin-deficient (inv) mutant adhered apically to the tight junction areas. These contact points of adjacent cells displayed beta1-integrins together with tight junction-associated ZO-1 and occludin proteins. Indeed, beta1-integrin expression was maximal in the tight junction area and then gradually decreased along the basolateral membranes. Wild-type bacteria also opened gradually the tight junction to paracellular permeation of different-sized markers, viz., 20-, 40-, and 70-kDa dextrans and 45-kDa ovalbumin, as well as to their own translocation between adjacent cells in intimate contact with beta1-integrins. The effects on the epithelial cells and their barrier properties could primarily be attributed to expression of the Yersinia outer membrane protein YopE, as the yopE mutant bound but caused no cytotoxicity. Moreover, the apical structure of filamentous actin (F-actin) was disturbed and tight junction-associated proteins (ZO-1 and occludin) were dispersed along the basolateral membranes. It is concluded that the Yersinia bacteria attach to beta1-integrins at tight junctions. Via this localized injection of YopE, they perturb the F-actin structure and distribution of proteins forming and regulating tight junctions. Thereby they promote paracellular translocation of bacteria and soluble compounds.

A new method to visualize the Helicobacter pylori-associated Lewis(b)-binding adhesin utilizing SDS-digested freeze-fracture replica labeling

Freeze-fracture replica labeling has become a versatile tool to visualize both membrane components and other cell structures using SDS-replica cleaning before specific immunogold labeling of proteins or lipids. We report here for the first time the adoption and optimization of the method to studies of bacterial envelopes, as applied to structural analysis of the distribution of the unique BabA-adhesin of the gastric pathogen Helicobacter pylori. BabA is important for bacterial adherence to the human epithelial cell lining of the stomach. The adhesin was found to be distributed all over the bacterial cell surfaces. Our results suggest that the SDS-replica labeling allows assessment of protein localization to distinct cell compartments and analysis of co-localization with neighboring membrane structures.

Both intra- and extracellular Ca2+ participate in the regulation of the lateral diffusion of the PDGF-beta2 receptor

When the receptors for platelet-derived growth factor (PDGF) are activated they aggregate, become tyrosine-phosphorylated and elicit a cascade of down-stream signals, including mobilization of Ca2+ from intra- and extracellular stores. Receptor mobility in the plane of the membrane is a prerequisite for receptor aggregation and further signalling. Using human foreskin fibroblasts (AG 1523) and fluorescence recovery after photobleaching (FRAP), we therefore assessed the lateral mobility characteristics of PDGF-beta2 receptors by their diffusion coefficient (D), and fraction of mobile receptors (R). This was done on cells stimulated with either normal human serum (NHS) or PDGF under different Ca2+-conditions. The results suggest that both intra- and extracellular free Ca2+ influence the mobility characteristics of the PDGF-beta2 receptor. Interestingly, the extracellular Ca2+ seems to impose general restrictions on the mobility of receptors, since R increased when extracellular Ca2+ was quenched with EGTA, whereas intracellular clamping of Ca2+ transients with MABTAM (BAPT/AM) primarily affected D. When both intra- and extracellular Ca2+ were quenced, D remained low and R high, further supporting the proposition that they achieve distinct effects. Inhibition of tyrosine phosphorylation with Erbstatin, partly inhibited the NHS effects and released PDGF-induced receptor immobilization. Ratio imaging with Fura-2 displayed that both NHS and PDGF induced changes in intracellular free [Ca2+]. In view of the present data it might have important effects on the state of the receptor in the membrane, for instance by regulating its lateral mobility, communication with other receptors and signalling functions in the membrane.

Nitric oxide induces dose-dependent CA(2+) transients and causes temporal morphological hyperpolarization in human neutrophils

We exposed adherent neutrophils to the nitric oxide (NO)-radical donors S-nitroso-N-acetylpenicillamine (SNAP), S-nitrosoglutathione (GSNO), and sodium nitroprusside (SNP) to study the role of NO in morphology and Ca(2+) signaling. Parallel to video imaging of cell morphology and migration in neutrophils, changes in intracellular free Ca(2+) ([Ca(2+)](i)) were assessed by ratio imaging of Fura-2. NO induced a rapid and persistent morphological hyperpolarization followed by migrational arrest that usually lasted throughout the 10-min experiments. Addition of 0.5-800 microM SNAP caused concentration-dependent elevation of [Ca(2+)](i) with an optimal effect at 50 microM. This was probably induced by NO itself, because no change in [Ca(2+)](i) was observed after treatment with NO donor byproducts, i.e. D-penicillamine, glutathione, or potassium cyanide. Increasing doses of SNAP (>/=200 microM) attenuated the Ca(2+) response to the soluble chemotactic stimulus formyl-methionyl-leucyl-phenylalanine (fMLP), and both NO- and fMLP-induced Ca(2+) transients were abolished at 800 microM SNAP or more. In kinetic studies of fluorescently labeled actin cytoskeleton, NO markedly reduced the F-actin content and profoundly increased cell area. Immunoblotting to investigate the formation of nitrotyrosine residues in cells exposed to NO donors did not imply nitrosylation, nor could we mimic the effects of NO with the cell permeant form of cGMP, i.e., 8-Br-cGMP. Hence these processes were probably not the principal NO targets. In summary, NO donors initially increased neutrophil morphological alterations, presumably due to an increase in [Ca(2+)](i), and thereafter inhibited such shape changes. Our observations demonstrate that the effects of NO donors are important for regulation of cellular signaling, i.e., Ca(2+) homeostasis, and also affect cell migration, e.g., through effects on F-actin turnover. Our results are discussed in relation to the complex mechanisms that govern basic cell shape changes, required for migration.

Distinct effects of Vibrio cholerae haemagglutinin/protease on the structure and localization of the tight junction-associated proteins occludin and ZO-1

Vibrio cholerae produces a little-studied cytotoxin, haemagglutinin/protease (HA/P), in addition to several better-characterized enterotoxins, i.e. cholera toxin (CT), zonula occludens toxin (ZOT) and accessory cholera enterotoxin (Ace). We have found recently that HA/P perturbs the barrier function of Mardin-Darby canine kidney epithelial cell line I (MDCK-I) by affecting the intercellular tight junctions (TJs) and the F-actin cytoskeleton. In the present study we have assessed more specifically how TJs are affected by HA/P by investigating the cellular localization and biochemical integrity of two well-characterized TJ-associated proteins, occludin and ZO-1. Western blot analysis showed that occludin bands of 66-85 kDa were digested by HA/P to two predominant bands of around 50 kDa and 35 kDa, and that this degradation was greatly attenuated when the specific bacterial metalloproteinase inhibitor Zincov was co-administered. Trypsin, on the other hand, did not degrade occludin when it was applied in the same way, suggesting that the degradation of occludin by HA/P is an early and specific event. The other TJ-associated protein ZO-1 was not degraded by HA/P in parallel experiments, suggesting the selectivity of HA/P-associated protein degradation. Moreover, immunofluorescence labelling and confocal microscopy showed that ZO-1, but not occludin, around cell-cell boundaries was rearranged by HA/P treatment. Since ZO-1 is located on the inside of the plasma membrane and is directly associated with occludin, the results indicate that breakdown of occludin may send signals to ZO-1 that affect its organization and the structure of the F-actin cytoskeleton. Our finding that the zinc-containing metalloprotease of V. cholerae specifically degraded occludin suggests that specific degradation of important host proteins by bacterial zinc-containing metalloproteases may be an important mechanism in microbial pathogenesis.

Localization of the insulin receptor in caveolae of adipocyte plasma membrane

The insulin receptor is a transmembrane protein of the plasma membrane, where it recognizes extracellular insulin and transmits signals into the cellular signaling network. We report that insulin receptors are localized and signal in caveolae microdomains of adipocyte plasma membrane. Immunogold electron microscopy and immunofluorescence microscopy show that insulin receptors are restricted to caveolae and are colocalized with caveolin over the plasma membrane. Insulin receptor was enriched in a caveolae-enriched fraction of plasma membrane. By extraction with beta-cyclodextrin or destruction with cholesterol oxidase, cholesterol reduction attenuated insulin receptor signaling to protein phosphorylation or glucose transport. Insulin signaling was regained by spontaneous recovery or by exogenous replenishment of cholesterol. beta-Cyclodextrin treatment caused a nearly complete annihilation of caveolae invaginations as examined by electron microscopy. This suggests that the receptor is dependent on the caveolae environment for signaling. Insulin stimulation of cells prior to isolation of caveolae or insulin stimulation of the isolated caveolae fraction increased tyrosine phosphorylation of the insulin receptor in caveolae, demonstrating that insulin receptors in caveolae are functional. Our results indicate that insulin receptors are localized to caveolae in the plasma membrane of adipocytes, are signaling in caveolae, and are dependent on caveolae for signaling.

Epithelial permeability to proteins in the noninflamed ileum of Crohn's disease?

BACKGROUND & AIMS

Crohn's disease (CD) is associated with a disturbed intestinal barrier. Permeability studies have focused on inert molecules, but little is known about transepithelial transport of macromolecules with antigenic potential in humans. The aim of this study was to quantify permeation and to characterize passage routes for macromolecules in ileal mucosa in CD.

METHODS

Noninflamed and inflamed ileal mucosa specimens from patients with CD (n = 12) and ileal specimens from patients with colon cancer (n = 7) were studied regarding transmucosal permeation of ovalbumin, dextran (mol wt, 40,000), and 51Cr-EDTA for 90 minutes in vitro in Ussing chambers. Transepithelial passage routes for fluorescent ovalbumin and dextran 40,000 were investigated by confocal microscopy.

RESULTS

Noninflamed ileum from CD patients showed increased permeation of ovalbumin compared with ileum from colon cancer patients (P < 0.05). Dextran permeation was equal in the three groups, whereas 51Cr-EDTA permeability was increased in inflamed ileum. Ovalbumin passed both transcellularly and paracellularly, but dextran followed a strictly paracellular route. Both markers were subsequently endocytosed by cells of the lamina propria.

CONCLUSIONS

Noninflamed ileal mucosa from patients with CD shows increased epithelial permeability to ovalbumin, probably by augmented transcytosis. This increase in antigen load to the lamina propria could be an initiating pathogenic event in CD.

Mechanical manipulation of polymorphonuclear leukocyte plasma membranes with optical tweezers causes influx of extracellular calcium through membrane channels

Optical tweezers are used mechanically to manipulate the plasma membrane of polymophonuclear leukocytes attached to the bottom of a glass manipulation chamber. The laser trapping beam is dragged across the membrane of cells in calcium-containing and calcium-depleted extracellular medium. This treatment causes a significant rise in the intracellular calcium concentration compared with controls, in cells in calcium-containing medium (239.8 +/- 49.0% against 75.4 +/- 16.4%, respectively), but not in cells in calcium-depleted medium (69.1 +/- 9.6% against 83.4 +/- 18.5%, respectively), indicating that the calcium rise is caused by an influx of calcium from the environment. The rise in calcium concentration is blocked (23.5 +/- 7.1% against 17.1 +/- 4.1%, respectively) by the addition of lansoprazole, indicating that the influx is not due to unspecific membrane damage caused by the mechanical manipulation of the cell. It can therefore be concluded that mechanical manipulation of the neutrophil membrane, in the piconewton force range exerted by the optical tweezer, does not damage the plasma membrane but stimulates a mechanically inducible, membrane channel-mediated influx of extracellular calcium.

Yersinia pseudotuberculosis-induced calcium signaling in neutrophils is blocked by the virulence effector YopH

Pathogenic species of the genus Yersinia evade the bactericidal functions of phagocytes. This evasion is mediated through their virulence effectors, Yops, which act within target cells. In this study we investigated the effect of Yersinia pseudotuberculosis on Ca2+ signaling in polymorphonuclear neutrophils. The intracellular free calcium concentration in single adherent human neutrophils was monitored during bacterial infection and, in parallel, the encounter between the bacteria and cells was observed. When a plasmid-cured strain was used for infection, adherence of a single bacterium to the cellular surface induced a beta1 integrin-dependent transient increase in the intracellular concentration of free calcium. This was, however, not seen with Yop-expressing wild-type bacteria, which adhered to the cell surface without generating any Ca2+ signal. Importantly, the overall Ca2+ homeostasis was not affected by the wild-type strain; the Ca2+ signal mediated by the G-protein-coupled formyl-methionyl-leucyl-phenylalanine receptor was still functioning. Hence, the blocking effect was restricted to certain receptors and their signaling pathways. The use of different Yop mutant strains revealed that the protein tyrosine phosphatase YopH was responsible for the inhibition. This virulence determinant has previously been implicated in very rapid Yersinia-mediated effects on target cells as the key effector in the blockage of phagocytic uptake. The present finding, that Y. pseudotuberculosis, via YopH, specifically inhibits a self-induced immediate-early Ca2+ signal in neutrophils, offers more-detailed information concerning the effectiveness of this virulence effector and implies an effect on Ca2+-dependent, downstream signals.

The role of glutamine, serum and energy factors in growth of enterocyte-like cell lines

BACKGROUND

Glutamine is routinely added to most cell cultures. Glutamine has been found to be the preferential nutrient to the rapidly replicating intestinal mucosa, but whether this is a metabolic effect or due to other properties of this amino acid is not determined. To study the importance of glutamine on the growth of two enterocyte-like cell lines, the effects of depriving the media or supplementing it with glutamine were assessed in media with different serum and energy supplements.

METHODS

CaCo-2 and HT-29 cells were grown in serum-free medium, with fetal bovine or synthetic serum, and with or without glucose or galactose. The glutamine content was varied between 0 and 4 mM. All growth assays were performed in triplicate by counting in a hemocytometer.

RESULTS

Both cell lines were dependent of serum factors for growth, but displayed distinct requirements on glutamine supplementation. Glutamine was an obligate supplement with dose-dependent correlation to growth (r = 0.87, p < 0.01) for CaCo-2 cells cultured in synthetic, but not in fetal bovine serum. In HT-29 cells, the correlation between glutamine and growth was significant (r = 0.68, p < 0.05) only in fetal bovine serum in the absence of galactose.

CONCLUSION

This study shows that glutamine has different growth stimulating effects on two enterocyte-like cell lines studied. This could reflect different modes of action of glutamine on proliferation and differentiation in an enterocyte cell population.

Children with celiac disease express inducible nitric oxide synthase in the small intestine during gluten challenge

BACKGROUND

Childhood celiac disease in Sweden is presently seen at an incidence of around 1/250 and is thus one of the commonest chronic diseases in children. It has recently been shown that children with untreated celiac disease have increased levels of nitrate/nitrite in the urine, most likely reflecting an increased production of nitric oxide in the inflamed mucosa. Nitric oxide is produced from L-arginine by an inducible or a constitutive nitric oxide synthase. The inducible nitric oxide synthase (iNOS) can be stimulated in various cells by, for instance, inflammatory mediators. The present study has been done to find a possible source of nitric oxide in the small intestine that could result in the increased levels of nitrate/nitrite in the urine in children with active celiac disease.

METHODS

Small-intestinal biopsy specimens from children with active celiac disease were labeled with rabbit-anti-human antibodies to iNOS and visualized with fluorescent pig anti-rabbit antibodies. The specimens were then analyzed with confocal microscopy to assess the labeling pattern.

RESULTS

In all of seven specimens from children with increased levels of nitrate/nitrite in the urine, we detected antibodies to iNOS, whereas in five of six control specimens--that is, from children with normal nitrate/nitrite levels--we could not detect any iNOS.

CONCLUSIONS

Children with active celiac disease have a gluten-induced nitric oxide production in the small intestine reflected by increased urine levels of nitrate/nitrite and iNOS expression in the intestine. We conclude that the increased production of nitric oxide could presumably, directly or indirectly, result in injury of the small-intestinal tissue.

Organization and mobility of CD11b/CD18 and targeting of superoxide on the surface of degranulated human neutrophils

A monoclonal IgM, specifically recognizing both CD11b and CD18 of human neutrophils, was used to examine the organization and mobility of CD11b/CD18 in the plasma membrane of human neutrophils degranulated by dihydrocytochalasin B (dhCB) treatment and fMet-Leu-Phe (fMLF) stimulation. Subcellular fractionation analysis of untreated or dhCB-treated control neutrophils indicated that 20% of CD11b/CD18 cosedimented with plasma membrane and the remainder with specific granules. In contrast, fMLF stimulation of dhCB-treated cells caused a major reorganization of CD11b/CD18, in which 60-70% of CD11b/CD18 sedimented in dense plasma membrane fractions that were also enriched in superoxide-generating NADPH oxidase activity. Similarly pretreated neutrophils were fixed, immunogold labeled, and examined by scanning electron microscopy. Immunogold particles were distributed uniformly over the symmetrically ruffled surface of unstimulated neutrophils. On dhCB-treated cells, immunogold was mostly uniformly distributed on a smooth membrane with a small percentage of particles lining up into linear arrays. After fMLF + dhCB stimulation, CD11b/CD18 gold label was more abundant on the cell surface and formed large aggregates on polarized membrane protrusions. However, when cells were adhered to an albumin-coated quartz surface and stimulated with fMLF in the presence of dhCB, immunogold was excluded on the articulated and rounded cell body but concentrated on the periphery of adherent lamellae. Fluorescence photobleaching recovery indicated that in unstimulated cells 38 +/- 3% of CD11b/CD18 was mobile (R) with a diffusion constant D of 3.1 +/- 0.3 x 10(-10) cm2/s. Treatment with dhCB raised R and D 24 and 74%, respectively. Stimulation using 1 microM fMLF with dhCB lowered D and R to near control levels. Since NADPH oxidase and CD11b/CD18 cosediment in high-density plasma membrane domains after fMLF + dhCB stimulation, we speculate that a stimulus-induced reorganization of CD11b/CD18 and NADPH oxidase to common membrane domains may occur in fMLF + dhCB-degranulated neutrophils.

Significantly increased levels of nitric oxide products in urine of children with celiac disease

BACKGROUND

Celiac disease is characterized by morphologic and functional aberrations of the small intestinal mucosa, i.e., crypt hyperplasia, villous atrophy, infiltration of intraepithelial lymphocytes, and alteration of permeability. Nitric oxide has been shown to affect mucosal permeability after ischemia-reperfusion, but little is known about the regulatory role of nitric oxide in celiac disease. The purpose of this study was to assess nitric oxide production in children with celiac disease and in control subjects.

METHODS

The sum of nitrite and nitrate in the urine was measured with a colorimetric method in 137 children with a median age of 3 years, 84 patients and 53 reference children, all of whom underwent a small intestinal biopsy to confirm or overrule suspicion of celiac disease.

RESULTS

Median urinary nitrite-nitrate concentration in celiac children was 3323 microM (4147 +/- 1102; mean +/- SEM) at first clinical examination and 2501 microM (2939 +/- 386) after gluten challenge, which was significantly higher than concentrations in reference children (1029 microM; 1174 +/- 116) and in children with celiac disease on a gluten-free diet (882 microM; 1369 +/- 360) (p < 0.0001).

CONCLUSIONS

A gluten-containing diet is associated with an increased nitrite-nitrate secretion in the urine in children with celiac disease, presumably as a result of nitric oxide synthase activation and nitric oxide production in the diseased small intestinal mucosa.

Endogenous nitric oxide in MDCK-I cells modulates the Vibrio cholerae haemagglutinin/protease (HA/P)-mediated cytotoxicity

Previously, we have shown that the Vibrio cholerae haemagglutinin/protease (HA/P) accounts for significant remaining toxicity of CVD110, an attenuated V. cholerae 01 El Tor live oral vaccine-strain. The present report demonstrates that endogenous nitric oxide (NO) production modulates HA/P-mediated cytotoxicity in Madin-Darby canine kidney cell strain I (MDCK-I) epithelial cells. The basal levels of endogenous NO suppressed the cytotoxicity of HA/P, whereas inhibition of NO production with nitro-L-arginine methyl-ester (L-NAME) made the MDCK-I cells susceptible even to low concentrations of the cytotoxin. The inhibition of NO production caused a reinforcement of the HA/P- mediated distortion of a tight junction-associated protein ZO-1 and increment of filamentous actin at the apical and the lateral membrane domains. The mechanism by which NO exerts its modulatory action is not likely to be from its direct interaction with the zinc-containing catalytic domain of HA/P, since two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetyl-D, L-penicillamine (SNAP), did not affect the proteolytic activity of HA/P. In conclusion, the endogenous NO in the MDCK-I cells has a modulating effect on the cytotoxicity of HA/P and thus protects the cells against the cytotoxin.

Role of annexins in endocytosis of antigens in immature human dendritic cells

We have evaluated the uptake of a soluble protein antigen, denitrophenylated human serum albumin (DNP-HSA), and two different intracellular bacteria; Chlamydia trachomatis serovar L2 and Mycobacterium tuberculosis strain H37Ra, by immature human dendritic cells. These were generated by culturing progenitor cells from blood in the presence of cytokines (granulocyte-macrophage colony-stimulating factor and interleukin-4). Dendritic cells play a crucial part in antigen presentation for the induction of T-cell-dependent immune responses in various tissues. Recently, macropinocytic and phagocytic activity has been shown for immature dendritic cells of mouse, rat and human origin. In the present study, macropinocytosis characterized the uptake of the soluble protein-antigen DNP-HSA, whereas the C. trachomatis were ingested via receptor-mediated endocytosis in coated pits, and opsonized M. tuberculosis via phagocytosis. To follow the intracellular routes of the antigens, their positions were compared with the localization of annexins, a family of Ca(2+)-and phospholipid-binding proteins, involved in membrane fusion, aggregation and transport of different vesicles. To elucidate further the intracellular pathway of the antigens, two other proteins, lysosome-associated membrane protein-1 (LAMP-1) and cathepsin D, were labelled. They are known to colocalize with major histocompatibility complex class II compartments in the immature dendritic cells. We observed a distinct translocation of annexin V to DNP-HSA containing endosomes, and annexin III to vesicles with C. trachomatis. Furthermore, annexin III, IV and V redistributed to phagosomes with M. tuberculosis. Both LAMP-1 and cathepsin D colocalized with DNP-HSA endosomes, and with phagosomes with M. tuberculosis. Thus, immature human dendritic cells have the capacity to phagocytose. Moreover, the handling of these antigens by dendritic cells may represent three distinct intracellular pathways, albeit some properties and compartments are shared.

YopK of Yersinia pseudotuberculosis controls translocation of Yop effectors across the eukaryotic cell membrane

Introduction of anti-host factors into eukaryotic cells by extracellular bacteria is a strategy evolved by several Gram-negative pathogens. In these pathogens, the transport of virulence proteins across the bacterial membranes is governed by closely related type III secretion systems. For pathogenic Yersinia, the protein transport across the eukaryotic cell membrane occurs by a polarized mechanism requiring two secreted proteins, YopB and YopD. YopB was recently shown to induce the formation of a pore in the eukaryotic cell membrane, and through this pore, translocation of Yop effectors is believed to occur (Håkansson et al., 1996b). We have previously shown that YopK of Yersinia pseudotuberculosis is required for the development of a systemic infection in mice. Here, we have analysed the role of YopK in the virulence process in more detail. A yopK-mutant strain was found to induce a more rapid YopE-mediated cytotoxic response in HeLa cells as well as in MDCK-1 cells compared to the wild-type strain. We found that this was the result of a cell-contact-dependent increase in translocation of YopE into HeLa cells. In contrast, overexpression of YopK resulted in impaired translocation. In addition, we found that YopK also influenced the YopB-dependent lytic effect on sheep erythrocytes as well as on HeLa cells. A yopK-mutant strain showed a higher lytic activity and the induced pore was larger compared to the corresponding wild-type strain, whereas a strain overexpressing YopK reduced the lytic activity and the apparent pore size was smaller. The secreted YopK protein was found not to be translocated but, similar to YopB, localized to cell-associated bacteria during infection of HeLa cells. Based on these results, we propose a model where YopK controls the translocation of Yop effectors into eukaryotic cells.

Oral immunoglobulin treatment in Crohn's disease

Two patients with severe Crohn's disease who failed to respond to traditional medical treatment were given immunoglobulin orally. We used the 6-h urinary recovery of mixture of polyethyleneglycols PEG 400 and 1000 (molecular weight range 282-1250 Da) to test the intestinal permeability. Both patients showed a similar permeability pattern with an increased leakage of large-sized PEGs before treatment and a lower urinary recovery of probes after treatment with immunoglobulin. This might indicate that the inflammatory process in Crohn's disease can be affected from the luminal side of the mucosa.

Aggregation of PDGF-beta receptors in human skin fibroblasts: characterization by image correlation spectroscopy (ICS)

Receptor aggregation is believed to be an important, early step when growth factors such as PDGF stimulate proliferation and differentiation of cell populations. To investigate receptor aggregation, we utilized a novel biophysical technique, image correlation spectroscopy, to study the distribution and aggregation state of PDGF-beta receptors on the surface of human dermal fibroblasts under various experimental conditions. It was found that the cell surface receptors were pre-clustered at 4 degrees C and receptor aggregation increased for samples measured at 37 degrees C. Treatment with PDGF-BB had no measurable effect on the receptor aggregation state. The results also indicate that additions of 10% serum or an inhibitor of tyrosine kinase activity, may disperse the receptors. The results of this study are consistent with organization of PDGF-beta receptors in pre-existing membrane domains.

The N-formyl methionyl peptide, formyl-methionyl-leucyl phenylalanine (fMLF) increases the lateral diffusion of complement receptor 1 (CR1/CD35) in human neutrophils; a causative role for oxidative metabolites?

The effects of the N-formyl methionyl peptide, formyl-methionyl-leucyl phenylalanine (fMLF) on the lateral mobility of the complement receptor type 1 (CR1/CD35) in glass-adherent human neutrophils were investigated, using fluorescence recovery after photobleaching (FRAP) and confocal microscopy (CSLM). It was found that addition of 0.1-1 microM fMLF increased the diffusion constant (D) of CR1/CD35 to 167-228% of controls. No effect was observed on the receptor distribution or the mobile fraction of receptors. The effect of fMLF on the lateral diffusion of CR1/CD35 could be totally inhibited by addition of pertussis toxon (PD, 250 ng/ml) or of the free radical scavenger enzymes superoxide dismutase (SOD, 2000 U/ml) and catalase (CAT, 200 U/ml), added together the results show that oxidative metabolites produced by neutrophils in response to fMLF can modulate CR1/CD35 diffusion, and indicate a regulatory role for oxygen radicals in phagocytosis.

Modulation of virulence factor expression by pathogen target cell contact

Upon contact with the eukaryotic cell, Yersinia pseudotuberculosis increased the rate of transcription of virulence genes (yop), as determined by in situ monitoring of light emission from individual bacteria expressing luciferase under the control of the yopE promoter. The microbe-host interaction triggered export of LcrQ, a negative regulator of Yop expression, via the Yop-type III secretion system. The intracellular concentration of LcrQ was thereby lowered, resulting in increased expression of Yops. These results suggest a key role for the type III secretion system of pathogenic bacteria to coordinate secretion with expression of virulence factors after physical contact with the target cell.

Modulation of the junctional integrity by low or high concentrations of cytochalasin B and dihydrocytochalasin B is associated with distinct changes in F-actin and ZO-1

In a study of Necturus gallbladder epithelium Benzel et al. (Benzel et al., 1980) found that low (0.2-1.2 microM) and higher concentrations (1.5 microM and more) of cytochalasin B (CB) caused an increase and decrease in the transepithelial electrical resistance (TER), respectively. Moreover, there were slight changes in the height and complexicity of tight junction (TJ) strands, as visualized by freeze-fracture and freeze-etching. To elucidate the mechanisms of these findings, we first demonstrated that the effect is also present in monolayers of Madin-Darby Canine Kidney strain 1 (MDCK-1) cells. Thus, a low concentration (0.1 ng/ml) cytochalasin B (CB) strengthened the permeability barrier, as evidenced quantitatively by increases in TER on transepithelial electrical measurements. Furthermore, indirect immunofluorescence and confocal microscopy demonstrated that this effect was paralleled with an accumulation of F-actin and the tight junction marker protein, ZO-1, at the level of TJ. Equimolar concentrations of dihydrocytochalasin B (dhCB), on the other hand, did not lead to a tightening of the epithelium. Confirming previous studies, there was a general decrease in epithelial resistance after treatment with high concentrations (1 microgram/ml) of CB and dhCB, which was accompanied by distinct changes in the F-actin network and distribution of ZO-1. We speculate that the divergent effects of CB and dhCB on the F-actin and ZO-1 organization might be due to specific effects on the transport of monosaccharides across the plasma membrane, or that CB and dhCB in distinct ways involve the turnover of phosphatidylinositols in the membrane, thereby modulating junctional permeability and F-actin structure.

Vibrio cholerae hemagglutinin/protease (HA/protease) causes morphological changes in cultured epithelial cells and perturbs their paracellular barrier function

In this report, we describe the cytotoxic activity of the cholera hemagglutinin/protease (HA/protease). A concentrated protein sample from the 37 degrees C overnight culture supernatant of CVD110, a delta ctxA, delta zot, delta Ace and hlyA::(ctxB mer) mutant of El Tor biotype Ogawa serotype strain E7946 caused morphological changes in cultured MDCK-I epithelial cells and altered their arrangement of filamentous actin (F-actin) and Zonula occludens-associated protein ZO-1. The drastic morphological changes can be inhibited by Zincov, a specific bacterial metalloprotease inhibitor. The cytotoxic fractions of the sample after FPLC gelfiltration fractionation showed two visible protein bands with molecular weights of approximately 34- and 32 kDa. Microsequencing of these two proteins revealed that they were the cholera HA/protease.

Liver cell uptake and degradation of soluble immunoglobulin G immune complexes in vivo and in vitro in rats

Immune complexes were formed between dinitrophenylated human serum albumin (DNP-HSA) and polyclonal rabbit immunoglobulin G (IgG) anti-DNP antibodies at antibody excess. The antigen was labelled with isotope (125I-tyramine-cellobiose) or fluorochrome, (6-[fluorescein-5-(and-6)-carboxamido] hexanoic-acid, succinimidyl ester). The radiolabelled antigen, native or antibody complexed, was given intravenously to rats. Radioactivity was measured in various organs at 1 hour following injection. The liver was the main site for removal of the antigen as well as of the immune complexes. Within the liver, immune complexes were mainly associated with nonparenchymal liver cells, the total recovery from Kupffer cells being about 10 times greater than from the liver endothelial cells. The uncomplexed radiolabelled antigen was readily degraded by both cells types. After IgG complexing, the degradation decreased, both in Kupffer cells and in liver endothelial cells. In vitro experiments with isolated liver cells, showed that IgG complexing increased antigen uptake to about the same extent in Kupffer cells and in liver endothelial cells. The degradation of both antigen and immune complexes was less efficient in vitro than in vivo. Immune complex uptake in vitro was shown also by confocal fluorescence microscopy in Kupffer cells and in liver endothelial cells. Also in vitro, only minor uptake was found in the hepatocytes. We conclude that both liver endothelial cells and Kupffer cells are involved in the hepatic handling of soluble IgG immune complexes, but we found no evidence for substantial uptake by hepatocytes.

Studies with wortmannin and cytochalasins suggest a pivotal role of phosphatidylinositols in the regulation of tight junction integrity

Wortmannin, a selective inhibitor of phosphatidylinositol 3-kinase (P13K), was found to give a dose and time-dependent, bimodal effect-initial increase, followed by decrease on the tight junction integrity of MDCK-1 monolayers, as assessed by electrical resistance measurement of the epithelia. Moreover, dihydrocytochalasin B inhibited the wortmannin-induced alteration, whereas cytochalasin B had a negligible influence on the wortmannin effect. Wortmannin was also found to cause changes in the cytoskeleton structure. These alterations were also seen when wortmannin was combined with cytochalasin B. However, in accordance with the electrical resistance measurements, dihydrocytochalasin B was able to abolish wortmannin-induced filamentous (F-) actin changes. These findings suggest that the P13K, phosphatidylinositols, and filamentous actin rearrangements, in combination, play an important role in the modulation of the junctional integrity.

YopH of Yersinia pseudotuberculosis interrupts early phosphotyrosine signalling associated with phagocytosis

The PTPase YopH of Yersinia is essential to the ability of these bacteria to block phagocytosis. Wild-type Yersinia pseudotuberculosis, but not the yopH mutant strain, resisted phagocytosis by J774 cells. Ingestion of a yopH mutant was dependent on tyrosine kinase activity. Transcomplementation with wild-type yopH restored the anti-phagocytic effect, whereas introduction of the gene encoding the catalytically inactive yopHC403A was without effect. The PTPase inhibitor orthovanadate impaired the anti-phagocytic effect of the wild-type strain, further demonstrating the importance of bacteria-derived PTPase activity for this event. The ability to resist phagocytosis indicates that the effect of the bacterium is immediately exerted when it becomes associated with the phagocyte. Within 30 s after the onset of infection, wild-type Y. pseudotuberculosis caused a YopH-dependent dephosphorylation of phosphotyrosine proteins in J774 cells. Furthermore, interaction of the cells with phagocytosable strains led to a rapid and transient increase in tyrosine phosphorylation of paxillin and some other proteins, an event dependent on the presence of the bacterial surface-located protein invasin. Co-infection with the phagocytosable strain and the wild-type strain abolished the induction of tyrosine phosphorylation. Taken together, the present findings demonstrate an immediate YopH-mediated dephosphorylation of macrophage phosphotyrosine proteins, suggesting that this PTPase acts by preventing early phagocytosis-linked signalling in the phagocyte.

In vitro effects of ethanol on polymorphonuclear leukocyte membrane receptor expression and mobility

The hampered inflammation and host defense seen in alcoholics may be due to impairment of functional responses of neutrophil polymorphonuclear leukocytes (PMN). We have shown that ethanol inhibits the oxidative metabolism of PMN induced by surface receptor dependent stimuli, such as N-formyl-methionyl-leucyl-phenylalanine (fMLP) and opsonized zymosan. Because the unresponsiveness might be due to reduced numbers of surface receptors, we assessed the expression of CR1, Fc-gamma, and fMLP receptors as well as membrane fluidity after treatment of PMN with ethanol in vitro. Ethanol impaired the induced expression of CR1 and fMLP receptors to 71% and 51% of control, respectively, but did not affect the resting level of CR1 nor Fc-gamma receptor expression. Furthermore, the mobility of cell membrane glycoconjugates was increased by ethanol. However, phagocytosis, a functional response dependent on membrane rheology, was unaffected. Because the results indicated an effect of ethanol on mobilization of receptors from intracellular stores, we assessed lactoferrin release, which was reduced to 59%. Thus, ethanol appeared to hamper the upregulation of PMN surface receptors or functional subsets of those stored in granules. Ethanol also increased the mobility of the cell membrane. These reactions were accompanied by reductions in the functional responses mediated by either class of receptors.

Mobilization of annexin V during the uptake of DNP-albumin by human dendritic cells

Dendritic cells play a crucial role in antigen presentation in various tissues. The endocytic capacity of these cells has been regarded as minimal, but recent work on dendritic cells from mouse spleen has disclosed that the fluid-phase traffic through late endosomes is as active in dendritic cells as in other antigen-presenting cell types. We show that cultured human dendritic cells express the annexins I, III, IV, V and VI, as detected by immunofluorescence staining. The annexins are cytosolic Ca(2+)-dependent proteins with the ability to promote vesicle aggregation and membrane fusion through their capacity to bind to membrane phospholipids. Annexin I and VI appeared to outline the cytoskeleton and the plasma membrane in cultured human dendritic cells. Studies using confocal laser scanning microscopy showed that during the endocytosis of fluorescent dinitrophenyl-conjugated albumin by dendritic cells, there was a redistribution of annexin V which was found to colocalize with vesicles containing dinitrophenyl-FITC-conjugated albumin.

Yersinia pseudotuberculosis inhibits Fc receptor-mediated phagocytosis in J774 cells

Nonopsonized as well as immunoglobulin-G (IgG)-opsonized Yersinia pseudotuberculosis resists phagocytic uptake by the macrophage-like cell line J774 by a mechanism involving the plasmid-encoded proteins Yops. The tyrosine phosphatase YopH was of great importance for the antiphagocytic effect of the bacteria. YopH-negative mutants did not induce antiphagocytosis; instead, they were readily ingested, almost to the same extent as that of the translocation mutants YopB and YopD and the plasmid-cured strain. The bacterial determinant invasin was demonstrated to mediate phagocytosis of nonopsonized bacteria by these cells. In addition to inhibiting uptake of itself, Y. pseudotuberculosis also interfered with the phagocytic uptake of other types of prey: J774 cells that had been exposed to virulent Y. pseudotuberculosis exhibited a reduced capacity to ingest IgG-opsonized yeast particles. This effect was impaired when the bacterium-phagocyte interaction occurred in the presence of gentamicin, indicating a requirement for in situ bacterial protein synthesis. The Yersinia-mediated antiphagocytic effect on J774 cells was reversible: after 18 h in the presence of gentamicin, the phagocytic capacity of Yersinia-exposed J774 cells was completely restored. Inhibition of the uptake of IgG-opsonized yeast particles was dependent on the Yops in a manner similar to that seen for blockage of Yersinia phagocytosis. This similarity suggests that the pathogen affected a general phagocytic mechanism. Despite a marked reduction in the capacity to ingest IgG-opsonized yeast particles, no effect was observed on the binding of the prey. Taken together, these results demonstrate that Yop-mediated antiphagocytosis by Y. pseudotuberculosis affects regulatory functions downstream of the phagocytic receptor and thereby extends to other types of phagocytosis.

Elevated levels of serum antibodies to the lectin wheat germ agglutinin in celiac children lend support to the gluten-lectin theory of celiac disease

Lectins recognize carbohydrate moities of glycoproteins and glycolipids, and can elicit several biological effects, including cell agglutination, cell activation and mitogenesis. According to the gluten-lectin theory, celiac lesions represent a response to a toxic lectin, putatively wheat germ agglutinin (WGA). In this study we compared the serum antibody levels IgA, IgG and IgM to WGA and to gliadin in children under investigation for celiac disease (CD), as compared to reference children. We found that the levels of IgA and IgG to WGA as well as gliadin were significantly higher in celiac children on a gluten-containing diet, compared to children on gluten-free diet and reference children. These findings lend support to the concept that WGA is a biologically significant component of gluten. Since WGA can mimic the effects of epidermal growth factor (EGF) at the cellular level, we hypothesize that the crypt hyperplasia seen in celiac children could be due to a mitogenic response induced by WGA.

Different subcellular localization of cytochrome b and the dormant NADPH-oxidase in neutrophils and macrophages: effect on the production of reactive oxygen species during phagocytosis

When neutrophils and macrophages phagocytose a prey, e.g., complement (C3b)-opsonized yeast particles, the oxygen radical generating NADPH-oxidase is activated. In neutrophils, most of the production of oxygen metabolites occurred in an intracellular compartment, possibly in the phagolysosome. In contrast, no intracellular production could be detected in human macrophages. In these cells, the subcellular localization of the superoxide-generating NADPH-oxidase and associated cytochrome b was assessed in intact cells with indirect immunofluorescence and confocal laser scanning microscopy, and with subcellular fractionation, using centrifugation on Percoll density gradients. A dual localization of the cytochrome b as well as the dormant NADPH-oxidase activity in neutrophils was in agreement with earlier immunocytochemical, biochemical, and subcellular fractionation studies. Furthermore, most of the activity was recovered from the specific granules, whereas only a small fraction was retained in the plasma membrane. In contrast, the cytochrome b/NADPH-oxidase activity in macrophages localized primarily in the plasma membrane fraction. We suggest that the macrophages are incapable of producing reactive oxygen species intraphagosomally, due to an absence of a granule-localized pool of the membrane components of the NADPH-oxidase.

Confocal laser scanning microscopy of small-intestinal mucosa in celiac disease

BACKGROUND

Light microscopy of jejunal biopsy specimens is routinely used to diagnose celiac disease. Confocal laser scanning microscopy offers research advantages, since thin optical sectioning can be performed without mechanical damage to the specimen. Fixed as well as non-fixed specimens can be studied.

METHODS

Confocal laser scanning microscopy was used to study the stanining of wheat germ agglutinin, which binds to glycoconjugates of the enterocyte, and rhodamine phalloidin, which binds to the F-actin of the cells.

RESULTS

In healthy mucosa the wheat germ agglutinin labeling showed a strong and punctate staining of microvilli, which outlined a convoluted surface. Phalloidin-labeled actin formed a three-dimensional cage at the cell membrane. In the crypt-hyperplastic mucosa, both staining patterns were irregular, and the cytoskeleton was disorganized.

CONCLUSIONS

Confocal laser scanning microscopy offers the possibility to study the distribution of surface and cytoskeleton markers in thick, structurally intact specimens.

Enteral glutamine increases growth and absorptive capacity of intestinal mucosa in the malnourished rat

BACKGROUND

Glutamine is an important nutrient for the small intestine. Beneficial effects of glutamine could be related to restoration of optimal intestinal barrier functions.

METHODS

Thirty-eight Sprague-Dawley rats were allocated to three main groups. Experimental groups (n = 22) were malnourished and laparotomized. Sham groups (n = 11) were laparotomized without prior malnutrition. These groups were refed with or without oral glutamine for 3 days. The control group (n = 5) was given chow. Permeability was assessed by the 6-h urinary recovery of orally given polyethylene glycols, PEG 400/1000. Mucosal proliferation was estimated by DNA content and 1-h incorporation of 3H-thymidine intravenously.

RESULTS

In the malnourished groups glutamine resulted in higher thymidine incorporation (p < 0.05) and better absorption of small PEG molecules (p < 0.05).

CONCLUSION

The effects of oral glutamine on permeability after malnourishment and laparotomy are proposed to be related to an increase in absorptive area.

Target cell contact triggers expression and polarized transfer of Yersinia YopE cytotoxin into mammalian cells

Pathogenic bacteria of the species Yersinia, including Yersinia pestis, block phagocytosis by macrophages. This process involves the YopE protein, which induces disruption of the host cell actin microfilament structure. Here, we show that the contact between the pathogen and the mammalian cell induces expression and then polarized transfer of YopE into the eukaryotic cell. While the bacteria remain at the surface of the target cell, the YopE cytotoxin is transferred through the host cell plasma membrane and YopE is only recovered within the cytosol of the target cell. The results suggest that the pathogen senses cell structures and focuses the transfer of YopE to occur solely at the interaction zone between the bacterium and the eukaryotic cell. The regulation of this process is shown to involve surface-located YopN sensor protein of the bacterium.