Glycolipid binding of purified and recombinant Escherichia coli produced verotoxin in vitro

Cisplatin-induced expression of Gb3 enables verotoxin-1 treatment of cisplatin resistance in malignant pleural mesothelioma cells

Background:

A major problem with cisplatin treatment is the development of acquired-drug resistance of the tumour cells. Verotoxin-1 (VT-1) exerts its cytotoxicity by targeting the membrane glycolipid globotriasosylceramide (Gb3), a molecule associated with drug resistance. Cisplatin- and VT-1-induced apoptosis involves mitogen-activated protein kinase (MAPK) activation, and deactivation of MAPKs is associated with cisplatin resistance. This study aimed to investigate whether a sub-toxic concentration of VT-1 could enhance cisplatin-induced apoptosis and overcome acquired-cisplatin resistance in cultured cancer cell lines.

Method:

P31 and H1299 cells with corresponding cisplatin-resistant sub-lines (P31res/H1299res) were incubated with VT-1 and/or cisplatin followed by determination of Gb3 expression, cell viability, apoptosis, and signalling pathways.

Results:

Cells from the resistant sub-lines had elevated Gb3 expression compared with the parental cell lines, and cisplatin further increased Gb3 expression, whereas VT-1 reduced the percentage of Gb3-expressing cells. Combination of cisplatin and sub-toxic concentrations of VT-1 led to a super-additive increase of cytotoxicity and TUNEL staining, especially in the cisplatin-resistant sub-lines. Blockade of Gb3 synthesis by a Gb3 synthesis inhibitor not only led to eradicated TUNEL staining of P31 cells, but also sensitised P31res cells to the induction of apoptosis by cisplatin alone. Cisplatin- and VT-1-induced apoptosis involved the MAPK pathways with increased C-Jun N-terminal kinase and MAPK kinase-3 and -6 phosphorylation.

Conclusions:

We show the presence of Gb3 in acquired-cisplatin resistance in P31res and H1299res cells. Cisplatin up-regulated Gb3 expression in all cells and thus sensitised the cells to VT-1-induced cytotoxicity. A strong super-additive effect of combined cisplatin and a sub-toxic concentration of VT-1 in cisplatin-resistant malignant pleural mesothelioma cells were observed, indicating a new potential clinical-treatment approach.

N-Glycosylation profiling of turtle egg yolk: expression of galabiose structure

To understand the roles of species-specific carbohydrates, systematic studies of interspecific glycan analyses are imperative. An extensive series of glycomics studies on approximately 180 kinds of bird eggs have demonstrated that 60-70% of the birds, which are closely related in phylogeny, express the alpha-Galp-(1-->4)-Galp structure on their egg glycoproteins. This prompted us to investigate the glycosylation profiles of eggs from an evolutionarily related organism, a sea turtle (reptilian). We performed N-glycosylation profiling of turtle egg yolk by using HPLC mapping in conjunction with mass spectrometric methods and thereby demonstrated that the alpha-Galp-(1-->4)-Galp groups are displayed on approximately 38% of total N-glycans. Our findings suggest that the ability to express the galabiose structure was acquired at an early stage of diversification in amniotes.

Enterohemorrhagic Escherichia coli suppresses inflammatory response to cytokines and its own toxin

Infection with the enteric pathogen enterohemorrhagic Escherichia coli (EHEC) causes a variety of symptoms ranging from nonbloody diarrhea to more severe sequelae including hemorrhagic colitis, altered sensorium and seizures, and even life-threatening complications, such as hemolytic uremic syndrome and thrombotic thrombocytopenic purpura. The more severe consequences of EHEC infection are attributable to the production of Shiga toxin (Stx) and its subsequent effects on the vasculature, which expresses high levels of the Stx receptor, Gb3. Interestingly, the intestinal epithelium does not express Gb3. Despite the lack of Gb3 receptor expression, intestinal epithelial cells translocate Stx. The effect of Stx on intestinal epithelial cells is controversial with some studies demonstrating induction of inflammation and others not. This may be difficult to resolve because EHEC expresses both proinflammatory molecules, such as flagellin, and factor(s) that dampen the inflammatory response of epithelial cells. The goal of our study was to define the effect of Stx on the inflammatory response of intestinal epithelial cells and to determine whether infection by EHEC modulates this response. Here we show that Stx is a potent inducer of the inflammatory response in intestinal epithelial cells and confirm that EHEC attenuates the induction of IL-8 by host-derived proinflammatory cytokines. More importantly, however, we show that infection with EHEC attenuates the inflammatory response by intestinal epithelial cells to its own toxin. We speculate that the ability of EHEC to dampen epithelial cell inflammatory responses to Stx and cytokines facilitates intestinal colonization.

A novel, promoter-based, target-specific assay identifies 2-deoxy-D-glucose as an inhibitor of globotriaosylceramide biosynthesis

Abnormal biosynthesis of globotriaosylceramide (Gb3) is known to be associated with Gb3-related diseases, such as Fabry disease. The Gb3 synthase gene (Gb3S) codes for alpha1,4-galactosyltransferase, which is a key enzyme involved in Gb3 biosynthesis in vivo. Transcriptional repression of Gb3S is a way to control Gb3 biosynthesis and may be a suitable target for the treatment of Gb3-related diseases. To find a transcriptional inhibitor for Gb3S, we developed a convenient cell-based chemical screening assay system by constructing a fusion gene construct of the human Gb3S promoter and a secreted luciferase as reporter. Using this assay, we identified 2-deoxy-D-glucose as a potent inhibitor for the Gb3S promoter. In cultured cells, 2-deoxy-D-glucose markedly reduced endogenous Gb3S mRNA levels, resulting in a reduction in cellular Gb3 content and a corresponding accumulation of the precursor lactosylceramide. Moreover, cytokine-induced expression of Gb3 on the cell surface of endothelial cells, which is closely related to the onset of hemolytic uremic syndrome in O157-infected patients, was also suppressed by 2-deoxy-D-glucose treatment. These results indicate that 2-deoxy-D-glucose can control Gb3 biosynthesis through the inhibition of Gb3S transcription. Furthermore, we demonstrated the general utility of our novel screening assay for the identification of new inhibitors of glycosphingolipid biosynthesis.

Assembly and stability of the shiga toxins investigated by electrospray ionization mass spectrometry

A systematic investigation into the assembly and stability of native and modified subunits of the Shiga toxins (Stx) in vitro is described. Analysis of the assembly of native and modified B subunits of Stx1 and Stx2 in solution, carried out using electrospray ionization mass spectrometry (ES-MS), suggests that the lower thermodynamic stability of the B subunit homopentamer of Stx2, compared to that of Stx1, is due to the presence of a repulsive interaction involving Asp70 of the Stx2 B subunit. In Stx1 B, the corresponding (spatially) residue is Arg. Using temperature-controlled ES-MS, it is shown that the Stx1 and Stx2 holotoxins exhibit differences in their resistance to temperature- and acid-induced dissociation. However, both Stx1 and Stx2 are fully assembled at pH >3.5 and 37 degrees C. This finding has several important biological implications. First, it argues against the likelihood that the difference in Stx1 and Stx2 toxicity arises from differential dissociation of the toxins during the intracellular trafficking steps of the cellular intoxication process. Second, it implies that the activation of the A subunits of Stx1 and Stx2 by enzymatic cleavage must occur while the A subunit is assembled with the B subunit homopentamer. It is, therefore, proposed that the differential toxicities of Stx1 and Stx2 reflect the relative efficiencies of intracellular activation of the A subunits.

[Glycosphingolipids Gb3 and iGb3. In vivo roles in hemolytic-uremic syndrome and iNKT cell function]

The glycosphingolipids globotrihexosylceramide (Gb3, CD77) and isoglobotrihexosylceramide (iGb3) are isomers differing only in one glycosidic bond and have been implicated in several processes of the innate and adaptive immune system.

AIMS

1) To verify the function of Gb3 in the pathogenesis of hemolytic-uremic syndrome as the cellular receptor responsible for cytotoxicity caused by verotoxin (VT) elaborated by Shigella and certain strains of E.coli. 2) To investigate in vivo the previously implicated function of iGb3 as the endogenous lipid ligand responsible for positive selection of invariant natural killer T-cells (iNKT), which have an essential regulatory function in infection, tumor rejection and tolerance.

METHODS

Generation of mice deficient in Gb3 and iGb3 synthesizing enzymes and VT injection into Gb3-deficient mice. Analysis of iNKT cell development and function by flow cytometry and by administration of the exogenous agonist alpha-galactosylceramide in iGb3-deficient mice.

RESULTS

For 1) Gb3-deficient mice were insensitive to otherwise lethal doses of VT, and 2) iGb3-deficient mice showed normal numbers of iNKT cells. Furthermore the function of iNKT cells evolving in iGb3-deficient mice was unaffected.

CONCLUSIONS

1) Gb3 is the cellular receptor mediating verotoxin cytotoxicity in haemolytic-uremic syndrome. 2) In contrast to previous indirect implications, iGb3 cannot be regarded as an endogenous ligand responsible for the positive selection of iNKT cells.

Host and pathogen determinants of verocytotoxin-producing Escherichia coli-associated hemolytic uremic syndrome

Verocytotoxin (VT)-producing Escherichia coli (VTEC) infection is associated with a spectrum of clinical manifestations that includes diarrhea, hemorrhagic colitis, and the hemolytic uremic syndrome (HUS). The occurrence of HUS in a minority of individuals in outbreaks of VTEC infection is a function of several pathogen and host factors. Pathogen factors include the inoculum size and serotype of the infecting strain, horizontally acquired genetic elements known as pathogenicity islands, and probably the VT type. Host factors that increase the risk of developing HUS include age, pre-existing immunity, gastric acidity, the use of antibiotics and anti-motility agents, and, probably, stress and genetic factors that modulate host response to infection, such as innate immunity and toxin receptor type, expression, and distribution. A better understanding of the pathogen and host determinants of HUS can aid in the development of more effective public health strategies to reduce the risk of developing HUS.

Structural analysis of N-glycans from gull egg white glycoproteins and egg yolk IgG

We previously showed that the expression of (Gal alpha 1-4Gal)-bearing glycoproteins among birds is related to their phylogeny. However, precise structures of (Gal alpha 1-4Gal)-containing N-glycans were only known for pigeon egg white glycoproteins and IgG. To compare structural features of (Gal alpha 1-4Gal)-containing N-glycans from other species, we analyzed N-glycans of gull egg white (GEW)-glycoproteins, ovomucoid, and ovotransferrin, and gull egg yolk IgG by HPLC, mass spectrometry (MS), and MS/MS analyses. GEW-glycoproteins included neutral, monosialyl, and disialyl N-glycans, and some of them contained Gal alpha 1-4Gal sequences. Bi-, tri-, and tetra-antennary oligosaccharides that lacked bisecting GlcNAc were the major core structures, and incomplete alpha-galactosylation and sialylation as well as the presence of diLacNAc on the branches generated microheterogeneity of the N-glycan structures. Moreover, unlike pigeon egg white glycoproteins, the major sialylation in GEW-glycoproteins is alpha2,3-, but not alpha2,6-linked sialic acids (NeuAc). In addition to the complex-type oligosaccharide, hybrid-type oligosaccharides that lack bisecting GlcNAc were also abundant in GEW-glycoproteins. Gull egg yolk IgG also contained Gal alpha 1-4Gal beta 1-4GlcNAc beta 1- sequences, but unlike pigeon IgG, no Gal alpha 1-4Gal beta 1-4Gal beta 1-4GlcNAc beta 1- sequence was detected. Bi- and tri-antennary complex-type oligosaccharides with bisecting GlcNAc and with core fucosylation as well as high-mannose-type oligosaccharides were the major structures in gull IgG. Our data indicated that some N-glycans from both GEW-glycoproteins and gull IgG contain the Gal alpha 1-4Gal beta 1-4GlcNAc beta 1- sequence, but the ratio of alpha-Gal-capped residues to non-alpha-Gal-capped residues in the nonreducing termini of N-glycans is much lower than that in those of pigeon glycoproteins.

Characterization of monoclonal immunoglobulin a and g against shiga toxin binding subunits produced by intranasal immunization

Immunoglobulin A (IgA) is considered to play a major role in protection of the mucosal surface. However, its immunological and biological properties have not been extensively studied because the production of IgA class monoclonal antibodies (mAbs) is difficult. We compared the properties of IgA and IgG mAbs against Shiga toxin B subunits (Stx1B). These mAbs were secreted from hybridomas that had been produced from mice after intranasal immunization with recombinant Stx1B and cholera toxin. The dose response curves for the binding of the IgA (clone G2G7) and IgG (clone D11C6) mAbs to immobilized Stx1B were similar, as revealed on ELISA. The majority of the IgA mAb formed dimers while the IgG mAb was monomeric, as judged by immunoblot analysis. The IgG mAb completely inhibited the binding of Stx1B to Burkitt's lymphoma cell line Ramos, while the inhibition by the IgA mAb was only partial. The IgG mAb was able to neutralize the cytotoxicity of Stx1 holotoxin towards Vero cells, whereas the IgA mAb was not. The binding affinity of each binding site was compared by means of surface plasmon resonance analysis involving a capture method, with which the binding of soluble Stx1B to immobilized mAb was detected. The association rate was similar but the dissociation rate was twofold faster in the case of the IgA mAb, resulting in twofold higher affinity of the IgG mAb. These results suggest that one can obtain high affinity IgA mAb but toxin neutralization is another challenge as to therapeutic antibodies of the IgA class.

Identification and characterization of the human Gb3/CD77 synthase gene promoter

Hemolytic uremic syndrome (HUS) is triggered by verotoxin (VT) produced by the Escherichia coli O157 strain. Several studies have demonstrated that VT induces endothelial cell (EC) death via the VT receptor globotriaosylceramide (Gb3/CD77) leading to this symptom. Inflammatory mediators which are produced as a result of E. coli O157 infection, increase the expression level of Gb3 in EC. Therefore increased expression of Gb3 is considered as a progression step for HUS. The increased expression of Gb3 is due to the transcriptional upregulation of Gb3/CD77 synthase gene (Gb3S, also known as alpha1,4-galactosyltransferase gene), the mechanism of which still remains unknown. To understand the transcriptional machinery and to elucidate the onset mechanism of HUS, we cloned and characterized the human Gb3S promoter. A modified 5'-RACE was used to determine the transcriptional initiation site, which revealed the presence of a TATA-less GC-rich sequence in the proximal region. Promoter activity measured using a luciferase assay demonstrated that the GC-rich sequence is necessary for the basal transcriptional activity, and two silencer elements located 5'-upstream of this GC-rich region regulated the transcriptional level. Furthermore, we found that the GC-rich sequence contained three potential Sp1 binding sites and that all three Sp1 binding elements acted as positive regulators. Since Sp1 is an inducer of several genes in the presence of the inflammatory cytokines in EC, our results suggest that the transcriptional regulation of the Gb3S gene by Sp1 might affect the VT sensitivity of EC and HUS progression.

Mouse model of hemolytic-uremic syndrome caused by endotoxin-free Shiga toxin 2 (Stx2) and protection from lethal outcome by anti-Stx2 antibody

Hemolytic-uremic syndrome (HUS) results from infection by Shiga toxin (Stx)-producing Escherichia coli and is the most common cause of acute renal failure in children. We have developed a mouse model of HUS by administering endotoxin-free Stx2 in multiple doses over 7 to 8 days. At sacrifice, moribund animals demonstrated signs of HUS: increased blood urea nitrogen and serum creatinine levels, proteinuria, deposition of fibrin(ogen), glomerular endothelial damage, hemolysis, leukocytopenia, and neutrophilia. Increased expression of proinflammatory chemokines and cytokines in the sera of Stx2-treated mice indicated a systemic inflammatory response. Currently, specific therapeutics for HUS are lacking, and therapy for patients is primarily supportive. Mice that received 11E10, a monoclonal anti-Stx2 antibody, 4 days after starting injections of Stx2 recovered fully, displaying normal renal function and normal levels of neutrophils and lymphocytes. In addition, these mice showed decreased fibrin(ogen) deposition and expression of proinflammatory mediators compared to those of Stx2-treated mice in the absence of antibody. These results indicate that, when performed during progression of HUS, passive immunization of mice with anti-Stx2 antibody prevented the lethal effects of Stx2.

Shiga toxin 2 causes apoptosis in human brain microvascular endothelial cells via C/EBP homologous protein

Shiga toxin 1 (Stx1) and Stx2 produced by Escherichia coli O157 are known to be cytotoxic to Vero and HeLa cells by inhibiting protein synthesis and by inducing apoptosis. In the present study, we have demonstrated that 10 ng/ml Stx2 induced DNA fragmentation in human brain microvascular endothelial cells (HBMEC), with cleavage activation of caspase-3, -6, -8, and -9. A microarray approach used to search for apoptotic potential signals in response to Stx2 revealed that Stx2 treatment induced a marked upregulation of C/EBP homologous protein (CHOP)/growth arrest and DNA damage-inducible protein 153 (GADD153). Increased CHOP expression was dependent on enzymatically active Stx1. Knockdown of CHOP mRNA reduced the activation of caspase-3 and prevented apoptotic cell death. These results suggest that Stx2-induced apoptosis is mediated by CHOP in HBMEC and involves activation of both the intrinsic and extrinsic pathways of apoptosis.

Tumor-specific Hsp70 plasma membrane localization is enabled by the glycosphingolipid Gb3

BACKGROUND

Human tumors differ from normal tissues in their capacity to present Hsp70, the major stress-inducible member of the HSP70 family, on their plasma membrane. Membrane Hsp70 has been found to serve as a prognostic indicator of overall patient survival in leukemia, lower rectal and non small cell lung carcinomas. Why tumors, but not normal cells, present Hsp70 on their cell surface and the impact of membrane Hsp70 on cancer progression remains to be elucidated.

METHODOLOGY/PRINCIPAL FINDINGS

Although Hsp70 has been reported to be associated with cholesterol rich microdomains (CRMs), the partner in the plasma membrane with which Hsp70 interacts has yet to be identified. Herein, global lipid profiling demonstrates that Hsp70 membrane-positive tumors differ from their membrane-negative counterparts by containing significantly higher amounts of globotriaoslyceramide (Gb3), but not of other lipids such as lactosylceramide (LacCer), dodecasaccharideceramide (DoCer), galactosylceramide (GalCer), ceramide (Cer), or the ganglioside GM1. Apart from germinal center B cells, normal tissues are Gb3 membrane-negative. Co-localization of Hsp70 and Gb3 was selectively determined in Gb3 membrane-positive tumor cells, and these cells were also shown to bind soluble Hsp70-FITC protein from outside in a concentration-dependent manner. Given that the latter interaction can be blocked by a Gb3-specific antibody, and that the depletion of globotriaosides from tumors reduces the amount of membrane-bound Hsp70, we propose that Gb3 is a binding partner for Hsp70. The in vitro finding that Hsp70 predominantly binds to artificial liposomes containing Gb3 (PC/SM/Chol/Gb3, 17/45/33/5) confirms that Gb3 is an interaction partner for Hsp70.

CONCLUSIONS/SIGNIFICANCE

These data indicate that the presence of Gb3 enables anchorage of Hsp70 in the plasma membrane of tumors and thus they might explain tumor-specific membrane localization of Hsp70.

Subtilase cytotoxin, produced by Shiga-toxigenic Escherichia coli, transiently inhibits protein synthesis of Vero cells via degradation of BiP and induces cell cycle arrest at G1 by downregulation of cyclin D1

Subtilase cytotoxin (SubAB) is a AB(5) type toxin produced by Shiga-toxigenic Escherichia coli, which exhibits cytotoxicity to Vero cells. SubAB B subunit binds to toxin receptors on the cell surface, whereas the A subunit is a subtilase-like serine protease that specifically cleaves chaperone BiP/Grp78. As noted previously, SubAB caused inhibition of protein synthesis. We now show that the inhibition of protein synthesis was transient and occurred as a result of ER stress induced by cleavage of BiP; it was closely associated with phosphorylation of double-stranded RNA-activated protein kinase-like ER kinase (PERK) and eukaryotic initiation factor-2alpha (eIF2alpha). The phosphorylation of PERK and eIF2alpha was maximal at 30-60 min and then returned to the control level. Protein synthesis after treatment of cells with SubAB was suppressed for 2 h and recovered, followed by induction of stress-inducible C/EBP-homologous protein (CHOP). BiP degradation continued, however, even after protein synthesis recovered. SubAB-treated cells showed cell cycle arrest in G1 phase, which may result from cyclin D1 downregulation caused by both SubAB-induced translational inhibition and continuous prolonged proteasomal degradation.

Alternative methods of globotrioside production using Vero cells: a microcarrier system procedure

Background

Glycolipids are one component of cell membranes, and are found most prevalently at the surface of the plasma membrane. Animal cells take in amphipathic glycosides, which are later glycosylated after assimilation in biosynthetic pathways. Gycosylated glycosides are released outside of cells to the surrounding culture medium. This represents an accessible method of obtaining complex glycosides.

Results

Vero cells are sensitive to Shiga toxins and are known to express the glycosides globotriaosyl ceramide (Gb3) and globotetraosyl ceramide (Gb4) on the surface of the plasma membrane. By administering amphipathic lactosides to Vero cells, the above mentioned glycolipids could be produced by the action of cellular enzymes. In our study, the optimum conditions (seeded cell number, incubated time period, 12-azidododecyl lactoside concentration and medium volume) for the production of Gb3 analogue were investigated. The 87.9 μg/100 mm dish (11.7 % yield) Gb3 analogue was produced under appropriate conditions. The large-scale culture of Vero cells using a microcarrier culture method with repetitions produced about 30 mg of the Gb3 analogue.

Conclusion

The mass production of glycosides in Vero cells was carried out on a microcarrier with repeated administration of 12-azidododecyl lactoside. The results indicated that the use of both a microcarrier culture and repetition were highly effective in the production of Gb3, Gb4 and sialyl lactoside (GM3) type-oligosaccharides.

Monovalent Gb3-/Gb2-derivatives conjugated with a phosphatidyl residue: a novel class of Shiga toxin-neutralizing agent

Shiga toxin (Stx) exerts toxic activity by binding to glycosphingolipids, mainly globotriaosyl (Gb(3)) ceramide, on the surface of target cells. The inhibition of toxin-receptor binding is a promising therapeutic approach to prevent Stx-mediated diseases. In this study, we synthesized monovalent Stx-ligands of phosphatidylethanolamine dipalmitoyl-Gb(3) (Gb(3)-PEDP) and galabiosyl (Gb(2))-PEDP and we examined their neutralizing activity against Stx-1 and Stx-2 in vitro. Both Gb(3)-PEDP and Gb(2)-PEDP strongly neutralized the cytotoxicity of Stx-1 and Stx-2. It is likely that the mechanism of neutralization involved formation of liposomes and consequently clustering of sugar units. We propose monovalent Gb(3)-/Gb(2)-derivatives conjugated with phosphatidyl residue as a novel class of Stx-neutralizing agent.

Neutralizing activity of polyvalent Gb3, Gb2 and galacto-trehalose models against Shiga toxins

Shiga toxin (Stx) is one of the most critical factors in the development of hemolytic uremic syndrome and other systemic complications following enterohemorrhagic Escherichia coli (EHEC) infection. Substances neutralizing Stx by interfering with toxin-receptor binding have been explored as therapeutic candidates for EHEC infection. In this study, we examined globotriaosyl (Gb3), galabiosyl (Gb2) and galacto-trehalose, each of which was synthetically conjugated with a polyacrylamide backbone, for Stxneutralizing activity. Galacto-trehalose was designed as a Gb2 mimicking, unnatural Stx-ligand that was expected to show tolerance to enzymatic degradation in vivo. Galacto-trehalose copolymer showed neutralizing activity against Stx-1 but not Stx-2 in a HeLa cell cytotoxicity assay. It was thought that galactotrehalose copolymer could be a lead compound for the treatment of Stx-mediated diseases, although it requires modification to show neutralizing activity to Stx-2. The Gb3 copolymer with high sugar unit density showed stronger neutralizing activity against Stx-2 than those with lower density. However, the density-dependency of the neutralizing activity was less obvious against Stx-1. Intravenous administration of the Gb3 copolymer prevented death in mice lethally infected with Stx-1- and Stx-2-producing E. coli O157:H7. Thus, we demonstrated that the artificial Gb3 copolymer could neutralize Stx-1 and the more clinically relevant Stx-2 in vitro and effectively inhibit Stx toxicity in vivo.

Effect of sterol carrier protein-2 expression on sphingolipid distribution in plasma membrane lipid rafts/caveolae

Although sphingolipids are highly important signaling molecules enriched in lipid rafts/caveolae, relatively little is known regarding factors such as sphingolipid binding proteins that may regulate the distribution of sphingolipids to lipid rafts/caveolae of living cells. Since early work demonstrated that sterol carrier protein-2 (SCP-2) enhanced glycosphingolipid transfer from membranes in vitro, the effect of SCP-2 expression on sphingolipid distribution to lipid rafts/caveolae in living cells was examined. Using a non-detergent affinity chromatography method to isolate lipid rafts/caveolae and non-rafts from purified L-cell plasma membranes, it was shown that lipid rafts/caveolae were highly enriched in multiple sphingolipid species including ceramides, acidic glycosphingolipids (ganglioside GM1); neutral glycosphingolipids (monohexosides, dihexosides, globosides), and sphingomyelin as compared to non-raft domains. SCP-2 overexpression further enriched the content of total sphingolipids and select sphingolipid species in the lipid rafts/caveolae domains. Analysis of fluorescence binding and displacement data revealed that purified human recombinant SCP-2 exhibited high binding affinity (nanomolar range) for all sphingolipid classes tested. The binding affinity decreased in the following order: ceramides > acidic glycosphingolipid (ganglioside GM1) > neutral glycosphingolipid (monohexosides, hexosides, globosides) > sphingomyelin. Enrichment of individual sphingolipid classes to lipid rafts/caveolae versus non-rafts in SCP-2 expressing plasma membranes followed closely with those classes most strongly bound to SCP-2 (ceramides, GM1 > the neutral glycosphingolipids (monohexosides, dihexosides, and globosides) > sphingomyelin). Taken together these data suggested that SCP-2 acts to selectively regulate sphingolipid distribution to lipid rafts/caveolae in living cells.

Molecular, biochemical and structural characterization of osmotin-like protein from black nightshade (Solanum nigrum)

A full-length 910bp cDNA encoding osmotin-like protein with an open reading frame of 744bp encoding a protein of 247 amino acids with a calculated molecular mass of 26.8kDa was cloned from Solanum nigrum (SniOLP). Phylogenetic analysis revealed the evolutionary conservation of this protein among diverse taxa. The genomic DNA gel blot showed that SniOLP belongs to a small multigene family and it showed organ-specific expression. Time-course studies revealed that the expression of SniOLP was upregulated by treatment with various signaling molecules, osmotic and oxidative stress inducers. Recombinant protein purified from overexpressed Escherichia coli cells showed hyphal growth inhibition in Rhizoctonia batiticola and Sclerotinia sclerotiorum but without any endo-beta-1,3-glucanase activity. Model built by homology modeling showed that the protein consists of an acidic cleft region that is capable of interacting with the carbohydrate components of the fungal cell walls. Analysis of the structure and functional relationship was carried out by docking of the beta-(1,3)-glucan onto the acidic cleft region on the surface of the protein (SniOLP).

Evaluation of enrichment-free PCR-based detection on the rfbE gene of Escherichia coli O157--application to municipal wastewater

Escherichia coli O157 strains have emerged as important human enteric pathogens. Strains that express the O-antigen 157 are commonly associated with severe clinical manifestations, including bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. E. coli O157 strains may be transmitted in a variety of ways, including food, water and person-to-person or animal-to-person contact. Fecal contamination is one source of environmental contamination and is responsible for the presence of these pathogens in the environment. We used a specific and sensitive PCR assay based on the rfbE gene to detect low levels of these pathogens in wastewater. The set of primers used was designed to amplify an intragenic segment of the rfbE gene. The amplification assay detected 200 CFU of E. coli O157 in pure water. The prevalence of E. coli O157 in the effluents of 44 wastewater treatment plants was determined (7%).

Shiga toxin binding in normal and inflamed human intestinal mucosa

Shiga toxins are associated with haemolytic uraemic syndrome but human intestinal epithelium does not express the Gb3 receptor. We describe Gb3 expression and Shiga toxin binding in histologically normal intestine and demonstrate that the pattern is unaltered in inflammatory disease states. Gb3 expression and Shiga toxin binding were identified in Paneth cells in both normal and inflamed mucosae.

Trafficking of Shiga toxin/Shiga-like toxin-1 in human glomerular microvascular endothelial cells and human mesangial cells

This study has determined the intracellular transport route of Shiga-like toxin (Stx) and the highly related Shiga toxin in human glomerular microvascular endothelial cells (GMVECs) and mesangial cells. In addition, the effect of tumor necrosis factor-alpha (TNF-alpha), which contributes to the pathogenesis of hemolytic-uremic syndrome, was evaluated more profound. Establishing the transport route will provide better understanding of the cytotoxic effect of Stx on renal cells. For our studies, we used receptor-binding B-subunit (StxB), which is identical between Shiga toxin and Stx-1. The transport route of StxB was studied by immunofluorescence microscopy and biochemical assays that allow quantitative analysis of retrograde transport from plasma membrane to Golgi apparatus and endoplasmic reticulum (ER). In both cell types, StxB was detergent-resistant membrane associated and followed the retrograde route. TNF-alpha upregulated Gb3 expression in mesangial cells and GMVECs, without affecting the efficiency of StxB transport to the ER. In conclusion, our study shows that in human GMVECs and mesangial cells, StxB follows the retrograde route to the Golgi apparatus and the ER. TNF-alpha treatment increases the amount of cell-associated StxB, but not retrograde transport as such, making it likely that the strong TNF-alpha-induced sensitization of mesangial cells and GMVECs for the toxic action of Stx is not due to a direct effect on the intracellular trafficking of the toxin.

Comparative analysis of the abilities of Shiga toxins 1 and 2 to bind to and influence neutrophil apoptosis

Hemolytic-uremic syndrome (HUS), the life-threatening complication following infection by the intestinal pathogen Escherichia coli O157:H7, is due to the ability of the pathogen to produce toxins in the Shiga toxin (Stx) family. Activated neutrophils are observed in HUS patients, yet it is unclear whether Stx exerts a direct effect on neutrophils or whether the toxin acts indirectly. The effect of Stx1 and Stx2 on human neutrophils was examined. Neither Stx1 nor Stx2 altered the rate of neutrophil apoptosis. Minimal binding of either toxin to neutrophils was observed, and the toxin was easily eluted from the cells. Stx1 and Stx2 were found to circulate in the plasma of mice following intravenous injection, and both toxins were cleared rapidly from the blood. Together these results suggest that neither Stx1 nor Stx2 interacts directly with neutrophils.

Two distinct cytotoxic activities of subtilase cytotoxin produced by shiga-toxigenic Escherichia coli

Subtilase cytotoxin (SubAB) is a recently identified AB5 subunit toxin produced by Shiga-toxigenic Escherichia coli. The A subunit is thought to be a subtilase-like, serine protease, whereas the B subunit binds to the toxin receptor on the cell surface. We cloned the genes from a clinical isolate; the toxin was produced as His-tagged proteins. SubAB induced vacuolation at concentrations greater than 1 microg/ml after 8 h, in addition to the reported cytotoxicity induced at a ng/ml level after 48 h. Vacuolation was induced with the B, but not the A, subunit and was dependent on V-type ATPase. The cytotoxicity of SubAB at low concentrations was associated with the inhibition of protein synthesis; the 50% inhibitory dose was approximately 1 ng/ml. The A subunit, containing serine 272, which is thought to be a part of the catalytic triad of a subtilase-like serine protease, plus the B subunit was necessary for this activity, both in vivo and in vitro. SubAB did not cleave azocasein, bovine serum albumin, ovalbumin, or synthetic peptides. These data suggest that SubAB is a unique AB toxin: first, the B subunit alone can induce vacuolation; second, the A subunit containing serine 272 plus the B subunit inhibited protein synthesis, both in vivo and in vitro; and third, the A subunit proteolytic activity may have a strict range of substrate specificity.

About lipids and toxins

Many mono or multicellular organisms secrete soluble proteins, referred to as protein toxins, which alter the behavior of foreign, or target cells, possibly leading to their death. These toxins affect either the cell membrane by forming pores or modifying lipids, or some intracellular target. To reach this target, they must cross one of the cellular membranes, generally that of an intracellular organelle. As described in this minireview, lipids play crucial roles in the intoxication process of most if not all toxins, by allowing/promoting binding, endocytosis, trafficking and/or translocation into the cytoplasm.

Histidine-tagged shiga toxin B subunit binding assay: simple and specific determination of gb3 content in mammalian cells

A two-step binding assay for globotriaosylceramide (Gb3) content was developed by histidine-tagging strategy, which is a well-established method for the purification of recombinant proteins. The complete binding of the recombinant His-tagged Shiga toxin 1B subunit (1B-His) (1 microg/ml) to the standard Gb3 adsorbed on a multi-well H type plate was observed within 30 min at 37 degrees C; and its binding could be visualized by the following applications of HisProbe-HRP (8 microg/ml) and tetramethylbenzidine (TMB) peroxidase substrate. The 1B-His binding assay was linear over the range of 1 to 100 ng of Gb3 per well. The binding of 1B-His was specific to Gb3 separated from HeLa cells, and no major cross-reactivity of other glycolipids in Folch's lower fractions extracted from HeLa cells was detected. The glycolipids in Folch's lower fractions from HeLa cells, human fibroblasts and mouse heart were suitable for this assay, but the further purification was needed for glycolipids from human plasma, thus sample preparation is critical factor for the reliable determination of Gb3 content. The 1B-His binding to Gb3 was inhibited by the addition of galactose, but not mannose. This 1B-His binding assay will be useful not only for the determination of Gb3 content, but also for screening for the compounds which inhibit the toxin-binding to Gb3. The strategy of our present method may be applicable for other binding assay, such as Cholera toxin B-subunit for ganglioside GM1.

Targeted Disruption of Gb3/CD77 Synthase Gene Resulted in the Complete Deletion of Globo-series Glycosphingolipids and Loss of Sensitivity to Verotoxins

To examine whether globotriaosylceramide (Gb3/CD77) is a receptor for verotoxins (VTs) in vivo, sensitivity of Gb3/CD77 synthase null mutant mice to VT-2 and VT-1 was analyzed. Although wild-type mice died after administration of 0.02 microg of VT-2 or 1.0 microg of VT-1, the mutant mice showed no reaction to doses as much as 100 times that administered to wild types. Expression analysis of Gb3/CD77 in mouse tissues with antibody revealed that low, but definite, levels of Gb3/CD77 were expressed in the microvascular endothelial cells of the brain cortex and pia mater and in renal tubular capillaries. Corresponding to the Gb3/CD77 expression, tissue damage with edema, congestion, and cytopathic changes was observed, indicating that Gb3/CD77 (and its derivatives) exclusively function as a receptor for VTs in vivo. The lethal kinetics were similar regardless of lipopolysaccharide elimination in VT preparation, suggesting that basal Gb3/CD77 levels are sufficient for lethal effects of VTs.

Escherichia coliverotoxin 1 mediates apoptosis in human HCT116 colon cancer cells by inducing overexpression of the GADD family of genes and S phase arrest

The Escherichia coli verotoxin 1 (VT1) inhibits protein synthesis, cell proliferation, and damages endothelial cell in the hemolytic uremic syndrome. VT1 can specifically bind and act on endothelial cells as well as on many tumor cells because these cells express its high affinity receptor, globotriaosylceramide. This indicates that VT1 may have both antiangiogenic and antineoplastic activities. We investigated this potential of VT1 by incubating several colon cancer cell lines with VT1 for different time periods and found that HCT116 cells were especially sensitive to VT1. A combination of morphological studies, flow cytometry, DNA laddering and annexin V staining confirmed that VT1 irreversibly arrests these cells in S phase within 24 h and prolonged incubation triggers DNA fragmentation. Concomitant to the activation of the S phase checkpoint, increased levels of mRNA and proteins of growth arrest and DNA damage-inducible gene family that include GADD34, GADD45alpha, and GADD45beta was observed. Interestingly, no significant changes in expression of key cell cycle related proteins such as cdk2, cdk4, p21, p27, and p53 was found during the S phase arrest and apoptosis. We therefore suggest that GADD proteins might play an important role in VT1 induced S phase arrest and programmed cell death in HCT116 cells.

Tracing the history of Galalpha1-4Gal on glycoproteins in modern birds

Galalpha1-4Gal is typically found in mammalian glycolipids in small quantities, and recognized by some pathogens, such as uropathogenic Escherichia coli. In contrast, glycoproteins containing Galalpha1-4Gal were rarely found in vertebrates except in a few species of birds and amphibians until recently. However, we had previously reported that pigeon (Columba livia) egg white and serum glycoproteins are rich in N-glycans with Galalpha1-4Gal at non-reducing termini. Our investigation with egg white glycoproteins from 181 avian species also revealed that the distribution of (Galalpha1-4Gal)-containing glycoproteins was not rare among avians, and is correlated with the phylogeny of birds. The differentiated expression was most likely emerged at earlier stage of diversification of modern birds, but some birds might have lost the facility for the expression relatively recently.

Oral immunization with a shiga toxin B subunit::rotavirus NSP490 fusion protein protects mice against gastroenteritis

A fusion protein containing the shiga toxin-1 B subunit (STB) linked to a 90 amino acid peptide (aa residues 86--175) from simian rotavirus (SA--11) nonstructural protein NSP4 was synthesized in Escherichia coli. Mice orally inoculated with 60 microg of STB::NSP4(90) fusion protein per dose generated higher humoral and intestinal antibody titers than mice inoculated with 30 microg of NSP4 alone. Serum anti-NSP4 IgG2a isotype titers were substantially greater than IgG1 titers, suggesting a dominant Th1 immune response. ELISA measurement of cytokines secreted from splenocytes isolated from immunized mice confirmed the STB::NSP4(90) fusion protein stimulation of a strong Th1 cell mediated immune response. Diarrhea in SA-11 rotavirus challenged neonates suckling from STB::NSP4 immunized dams was significantly reduced in severity and duration in comparison with virus challenged neonates from unimmunized mice. Together, our experiments demonstrate for the first time that the shiga toxin B subunit provides ligand mediated delivery of virus antigens to the gut-associated lymphoid tissues for enhanced stimulation of humoral and cellular responses against rotavirus gastroenteritis.

[Catfish (Silurus asotus) lectin enhances the cytotoxic effects of doxorubicin]

Rhamnose-binding lectins are widely found in fish eggs. However, their biologic effects on cultured cells are still unknown. Since catfish (Silurus asotus) egg lectin (SAL) bound to globotriaosylceramide (Gb3) expressed on the surface of cells, we analyzed the relationship between Gb3 expression and SAL binding in tumor cell lines using Raji, Daudi, ACHN, P388, and K562 cells. Gb3 was highly expressed on Raji cells but not on K562 cells. SAL bound abundantly to Raji cells but not to K562 cells, and SAL binding depended on the amount of Gb3 on the cell surface. SAL caused a reduction in cell size and increased annexin-V binding to and propidium iodide (PI) incorporation into Raji cells. Although this effect on Raji cells might represent damage at the late apoptosis or necrosis stage, SAL-treated Raji cells remained alive. Thus SAL enhanced PI incorporation into Raji cells without induction of cell death. We examined whether the effects of chemotherapeutic agent(s) are influenced by SAL. SAL increased the incorporation of doxorubicin (Dox) into Raji cells and consequently enhanced the cytotoxic effects of Dox. These results indicate that SAL may induce cell permeability without cytotoxity.

Differential Activities of Plant Polyphenols on the Binding and Internalization of Cholera Toxin in Vero Cells

Plant polyphenols, RG-tannin, and applephenon had been reported to inhibit cholera toxin (CT) ADP-ribosyltransferase activity and CT-induced fluid accumulation in mouse ileal loops. A high molecular weight fraction of hop bract extract (HBT) also inhibited CT ADP-ribosyltransferase activity. We report here the effect of those polyphenols on the binding and entry of CT into Vero cells. Binding of CT to Vero cells or to ganglioside GM1, a CT receptor, was inhibited in a concentration-dependent manner by HBT and applephenon but not RG-tannin. These observations were confirmed by fluorescence microscopy using Cy3-labeled CT. Following toxin binding to cells, applephenon, HBT, and RG-tannin suppressed its internalization. HBT or applephenon precipitated CT, CTA, and CTB from solution, creating aggregates larger than 250 kDa. In contrast, RG-tannin precipitated CT poorly; it formed complexes with CT, CTA, or CTB, which were demonstrated with sucrose density gradient centrifugation and molecular weight exclusion filters. In agreement, CTA blocked the inhibition of CT internalization by RG-tannin. These data suggest that some plant polyphenols, similar to applephenon and HBT, bind CT, forming large aggregates in solution or, perhaps, on the cell surface and thereby suppress CT binding and internalization. In contrast, RG-tannin binding to CT did not interfere with its binding to Vero cells or GM1, but it did inhibit internalization.

A role for the protease-sensitive loop region of Shiga-like toxin 1 in the retrotranslocation of its A1 domain from the endoplasmic reticulum lumen

Shiga-like toxin I (Slt-I) is a ribosome-inactivating protein that undergoes retrograde transport to the endoplasmic reticulum to exert its cytotoxic effect on eukaryotic cells. Its catalytically active A(1) domain subsequently migrates from the endoplasmic reticulum (ER) lumen to the cytoplasm. To study this final retrotranslocation event, a suicide assay was developed based on the cytoplasmic expression and ER-targeting of the cytotoxic Slt-I A(1) fragment in Saccharomyces cerevisiae. Expression of the Slt-I A(1) domain (residues 1-251) with and without an ER-targeting sequence was lethal to the host and demonstrated that this domain can efficiently migrate from the ER compartment to the cytosol. Deletion analyses revealed that residues 1-239 represent the minimal A(1) segment displaying full enzymatic activity. This fragment, however, accumulates in the ER lumen when directed to this compartment. The addition of residues 240-251 restores the translocation property of the A(1) chain in yeast. However, single mutations within this region do not significantly alter this function in the context of the 251-residue long A(1) domain or affect the toxicity of the resulting Slt-I variants toward Vero cells in the context of the holotoxin. Since this mechanism of retrotranslocation is common to other protein toxins lacking a peptide motif similar in sequence to residues 240-251, the present results suggest that the ER export mechanism may involve the recognition of a more universal structural element, such as a misfolded or altered peptide domain localized at the C terminus of the A(1) chain (residues 240-251) rather than a unique ER export signal sequence.

Comparative evaluation of apoptosis induced by Shiga toxin 1 and/or lipopolysaccharides in human monocytic and macrophage-like cells

The enteric pathogens Shigella dysenteriae serotype 1 and Shiga toxin-producing Escherichia coli share the property of expressing the structurally and functionally related cytotoxins that comprise the Shiga toxin (Stx) family. Stx-producing bacteria are causative agents of bloody diarrheal diseases that may progress to life threatening complications involving the destruction of blood vessels in the kidneys and the central nervous system (CNS). The precise mechanisms of toxin transport across the gut epithelial barrier, and the role of innate immunity in the development of systemic complications, remain to be fully characterized. Earlier studies suggested that Stxs and lipopolysaccharides (LPS) induce the expression of proinflammatory cytokines from differentiated (macrophage-like) THP-1 cells. These cytokines may exacerbate vascular damage by up-regulating the expression of toxin receptors on endothelial cells. Purified Stxs have also been shown to induce apoptosis of epithelial and endothelial cells in vitro, but a comparative evaluation of Stx-induced apoptosis of monocytes and macrophages has not been reported. We used FACS, TUNEL, and DNA laddering analyses to show that Shiga toxin-1 (Stx1) and LPS induce apoptosis in undifferentiated and differentiated THP-1 cells, although the kinetics and extent of apoptosis induction differ between monocytic and macrophage-like cells. Stx1-induced apoptosis is A-subunit-dependent. Stx1 and LPS trigger DNA fragmentation and caspase-3 activation, as evidenced by the cleavage of poly(ADP-ribose) polymerase (PARP). Induction of apoptosis in response to Stx1 and/or LPS treatment occurs without the widespread transcriptional activation of apoptosis-related genes. Finally, we present a model of the role of macrophages and monocytes in the pathogenesis of disease caused by Stxs.

Chemokine expression in the monocytic cell line THP-1 in response to purified shiga toxin 1 and/or lipopolysaccharides

Infections with Shiga toxin (Stx)-producing bacteria are associated with bloody diarrhea and postdiarrheal sequelae, including hemolytic uremic syndrome and central nervous system (CNS) abnormalities. Stx-induced intestinal, renal, and CNS vascular lesions may involve a localized production of proinflammatory cytokines in target organs, as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) up-regulate Stx receptor globotriaosylceramide (Gb(3)) expression on vascular endothelial cells. However, leukocyte recruitment to injured sites may also exacerbate vascular damage. A cytokine macroarray analysis of transcripts derived from macrophage-like THP-1 cells treated with Stx1, lipopolysaccharides (LPS), or both demonstrated a consistent up-regulation of TNF-alpha, IL-1beta, and four genes encoding the chemokines interleukin-8 (IL-8), macrophage inflammatory protein-1alpha (MIP-1alpha), MIP-1beta, and growth-related oncogene beta (GRO-beta). Real-time PCR analysis verified the macroarray results. Northern blot analyses after the addition of the transcriptional inhibitor actinomycin D revealed increased IL-8 mRNA stability in THP-1 cells treated with Stx1 or Stx1 plus LPS. Finally, enzyme-linked immunosorbent assay data for Stx1- plus LPS-treated cells demonstrated a poor correlation between IL-8, MIP-1alpha, MIP-1beta, and GRO-beta mRNA levels and protein production, indicating a posttranscriptional regulatory effect. Our data suggest that in response to Stx1 and LPS, macrophages may be a source of chemokines that promote tissue damage through leukocyte recruitment and activation.

Inhibition ofStreptococcussuisAdhesion by Dendritic Galabiose Compounds at Low Nanomolar Concentration

A series of mono-, di-, and tetravalent galabiose (Galalpha1-4Gal) compounds were synthesized in good yields by coupling of a general carboxylic acid-bearing sugar building block to dendritic scaffolds based on the 3,5-di-(2-aminoethoxy)benzoic acid branching unit. Furthermore, a poly(amidoamine)- (PAMAM-) based dendritic galabioside was synthesized containing eight galabiose units. All galabiosides were tested in a hemagglutination assay and a surface plasmon resonance (SPR) competition assay in order to establish their potency in the binding to the bacterial Gram-positive pathogen Streptococcus suis. A monovalent galabioside containing a short spacer was used as a reference compound in all the assays. Variations in the scaffold as well as in the spacer arms were introduced to determine their influence on the inhibition. The best inhibitor of hemagglutination was an octavalent galabioside with a minimal inhibitory concentration (MIC) of 0.3 nM, to the best of our knowledge the first example of inhibition of bacterial binding by a soluble carbohydrate at a subnanomolar concentration.

Marasmius oreades lectin induces renal thrombotic microangiopathic lesions

The present studies demonstrate that infusion of a type B specific lectin derived from the mushroom Marasmius oreades (MOA) into mice binds selectively to the glomerular endothelial cells via surface carbohydrate moieties resulting in cell injury and death associated with platelet-fibrin thrombi. This selective MOA binding to the endothelial cells can be abrogated by a sugar specific for the carbohydrate sequence. Hemolytic-Uremic Syndrome (HUS) and the closely associated Thrombotic Thrombocytopenic Purpura (TTP) are diseases associated with widespread microvascular injury in various organs. Clinically, these diseases are associated with microangiopathic hemolytic anemia and thrombocytopenia. The kidney glomerulus is a primary target of this microvascular injury. There are many underlying etiologies including bacterial toxins. Experimentally, such toxins injure endothelial cells in vitro but in vivo studies have failed to reproduce the characteristic renal pathology. We suggest that MOA-induced glomerular microangiopathic injury could be used to study the pathophysiology of endothelial cell injury as related to glomerular microangiopathic injury.

Peptides binding to a Gb3 mimic selected from a phage library

Peptides binding to a Gb3 mimic were selected from 12-mer peptide library. The self-assembled monolayer (SAM) of a Gb3 mimic was formed on the gold surface, and biopanning was carried out with the phage display peptide library. After three rounds of biopanning, four individual sequences were obtained from 10 phage clones, and the selected peptides having the specific 7-mer sequence (FHENWPS) showed affinities to the Gb3 mimic as strong as to RCA120. Molecular dynamics calculations suggested that the peptides bound to the Gb3 mimic by hydrophobic interaction and hydrogen bonding formation, and the cooperative interactions played an important role in the recognition. The Stx-1 binding was inhibited by the peptides.

Pore worms: using Caenorhabditis elegans to study how bacterial toxins interact with their target host

The interaction of pathogenic bacteria with a target host is regulated both by bacterial virulence factors and by host components that either protect the host or that promote pathogenesis. The soil nematode Caenorhabditis elegans is a host for a number of bacterial pathogens, as briefly reviewed here. Bacillus thuringiensis (Bt) is a pathogenic bacteria that C. elegans is likely to encounter naturally in the soil. The pore-forming Crystal (Cry) toxins made by Bt are recognized as the dominant virulence factor in this host-pathogen interaction. Forward genetic screens for C. elegans mutants resistant to the Cry toxin, Cry5B, have identified a host carbohydrate structure that promotes pathogenesis. Data suggest this structure is likely to be a Cry5B receptor expressed in the host intestine. This finding is discussed in light of other carbohydrate receptors for bacterial toxins. To investigate host-toxin interactions on a global level, the response of C. elegans to the pore-forming Cry5B is also being investigated by gene transcription profiling (microarrays). These data are beginning to reveal a diverse intracellular response to toxin exposure. To put these investigations in perspective, host responses to other pore-forming toxins are discussed. Investigations with Cry5B in C. elegans show a promising beginning in helping to elucidate host-toxin and host-pathogen interactions.

Verotoxin induces rapid elimination of human renal tumor xenografts in SCID mice

PURPOSE

Verotoxins (VTs) are subunit toxins produced by enteropathogenic Escherichia coli. The VT receptor glycolipid Gb3, which mediates the cytotoxicity of VTs, has been reported to be elevated on the surface of several tumor cell lines. In this study the effect of VT1 as an antineoplastic agent was assessed using various human urological cancer cell lines.

MATERIALS AND METHODS

The expression of Gb3 on human cancer cell lines originating from renal cell carcinoma (ACHN, A-704, CAKI-1 and CAKI- 2), prostate cancer (LNCaP and PC3) and testicular tumor (2102Ep) were examined by FACScan (Becton Dickinson, Sunnyvale, California). These cell lines were cultured with various concentrations of VT1 and subjected to microculture tetrazolium dye assay for determination of cell viability. Furthermore, ACHN cells were inoculated into the backs of SCID mice and intratumor injection of VT1 was performed. Pathological samples were examined by hematoxylin and eosin staining as well as by TUNEL assay.

RESULTS

The growth of ACHN, CAKI-1, A-704, 2102Ep and LNCaP but not CAKI-2 and PC3 was significantly inhibited by co-incubation with VT1, as determined by microculture tetrazolium dye assays, consistent with FACScan results for Gb3 expression. When mice bearing ACHN tumors were injected with VT1, rapid reduction in the size of subcutaneous tumors was observed with complete regression within 5 to 7 days. Pathological examination by the TUNEL method indicated that the cytotoxicity of VT1 was mediated by apoptosis.

CONCLUSIONS

These results suggest that VTs could be candidates for antineoplastic agents against Gb3 expressing tumors for clinical use.

Fascination with bacteria-triggered cell death: the significance of Fas-mediated apoptosis during bacterial infection in vivo

Increasing evidence indicates that bacterial pathogens have developed mechanisms to modulate the apoptotic signaling cascade of host cells and thereby cause disease. The Fas death receptor pathway is one of the most extensively investigated apoptotic signaling pathways. In this review we discuss the role of Fas signaling during the interplay between bacterial pathogens and the host in vivo.

Pentamerization of single-domain antibodies from phage libraries: a novel strategy for the rapid generation of high-avidity antibody reagents

We describe a novel type of molecule in which single-domain antibodies (sdAbs) isolated from a nai;ve llama single domain antibody library are linked to an oligomerization domain to generate high-avidity, antigen-binding reagents. An sdAb is fused to the B-subunit of Escherichia coli verotoxin, or shiga-like toxin, which self-assembles to form a homopentamer and results in simultaneous sdAb pentamerization and introduction of avidity. Molecular modeling indicated that this fusion protein (PDB: 1OJF), termed pentabody, has structural flexibility for binding to surface-presented antigen. In the instance of an sdAb specific for a peptide antigen, pentamerization resulted in a dramatic increase in functional affinity for immobilized antigen. The pentabody was expressed in high yield in E.coli in a non-aggregated state, and exhibited excellent thermostability and protease resistance. This technology provides a relatively rapid means of generating novel antigen-binding molecules that bind strongly to immobilized antigen. It is expected that pentavalent sdAbs will have general applicability in proteomics, immunochemical staining, cancer diagnosis and other applications in which antigens are presented multivalently.