Purification and some properties of Shiga-like toxin from Escherichia coli O157:H7 that is immunologically identical to Shiga toxin

Enhanced production of Shiga toxin 1 in enterohaemorrhagic Escherichia coli by oxygen

Enterohaemorrhagic Escherichia coli (EHEC) produces Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2). Although stx1 and stx2 were found within the late operons of the Stx-encoding phages (Stx-phages), stx1 could mainly be transcribed from the stx1 promoter (P _Stx1), which represents the functional operator-binding site (Fur box) for the transcriptional regulator Fur (ferric uptake regulator), upstream of stx1. In this study, we found that the production of Stx1 by EHEC was affected by oxygen concentration. Increased Stx1 production in the presence of oxygen is dependent on Fur, which is an Fe²⁺-responsive transcription factor. The intracellular Fe²⁺ pool was lower under microaerobic conditions than under anaerobic conditions, suggesting that lower Fe²⁺ availability drove the formation of less Fe²⁺-Fur, less DNA binding to the P _Stx1 region, and an increase in Stx1 production.

Detection and Characterization of Enteropathogenic and Shiga Toxin-Producing Escherichia coli Strains in Rattus spp. from Buenos Aires

Enteropathogenic Escherichia coli (EPEC) and Shiga toxin-producing E. coli (STEC) are pathovars of E. coli that impact human health by causing childhood diseases. In this work, 118 synanthropic rodents of the genus Rattus from Buenos Aires, Argentina were evaluated as EPEC and STEC carriers. Rectal swab samples from captured animals were evaluated by conventional PCR to detect the presence of the eae, stx1, stx2, and rfbO157 genes. Twenty-one isolates were obtained (17 EPEC isolates from seven animals and four STEC isolates from the same animal). All EPEC isolates tested negative for the presence of the bfpA gene. One EPEC isolate carried the iha gene, and five EPEC isolates carried the toxB gene. STEC isolates exhibited two different virulence profiles: stx1a/stx2a/stx2c/stx2d/saa/ehxA/subA (3/4) and stx1a/stx2a/saa/ehxA/subA (1/4). EPEC isolate serotypes included O109:H46 (7), O71:H40 (4), O71:NM (2), O138:H40 (1), O108:H21 (1), O88:H25 (1), and O76:NM (1), and STEC isolates belonged to the O108:H11 (4) serotype. Antimicrobial susceptibility testing was carried out, and resistance to tetracycline was observed in one EPEC strain. Our results demonstrate that Rattus spp. may act as carriers of EPEC and STEC strains and may be involved in the epidemiology of diarrheal disease in infancy.

Nitric oxide-enhanced Shiga toxin production was regulated by Fur and RecA in enterohemorrhagic Escherichia coli O157

Enterohemorrhagic Escherichia coli (EHEC) produces Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2). Nitric oxide (NO), which acts as an antimicrobial defense molecule, was found to enhance the production of Stx1 and Stx2 in EHEC under anaerobic conditions. Although EHEC O157 has two types of anaerobic NO reductase genes, an intact norV and a deleted norV, in the deleted norV‐type EHEC, a high concentration of NO (12–29 μmol/L, maximum steady‐state concentration) is required for enhanced Stx1 production and a low concentration of NO (~12 μmol/L, maximum steady‐state concentration) is sufficient for enhanced Stx2 production under anaerobic conditions. These results suggested that different concentration thresholds of NO elicit a discrete set of Stx1 and Stx2 production pathways. Moreover, the enhancement of Shiga toxin production in the intact norV‐type EHEC required treatment with a higher concentration of NO than was required for enhancement of Shiga toxin production in the deleted norV‐type EHEC, suggesting that the specific NorV type plays an important role in the level of enhancement of Shiga toxin production in response to NO. Finally, Fur derepression and RecA activation in EHEC were shown to participate in the NO‐enhanced Stx1 and Stx2 production, respectively.

Characterization of a Shiga-Toxin 1-Resistant Stock of Vero Cells

Shiga toxins (Stxs, also referred to as verotoxins) were first described as a novel cytotoxic activity against Vero cells. In this study, we report the characterization of an Stx1-resistant (R-) stock of Vero cells. (1) When the susceptibility of R-Vero cells to Stx1 cytotoxicity was compared to that of Stx1-sensitive (S-) Vero cells by methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, cell viability after 48-hr exposure to 10 pg/ml of Stx1 was greater than 80% and less than 15%, respectively. (2) Although both a binding assay of fluorescence-labeled Stx1 and lipid analysis indicated considerable expression of Gb3Cer, a functional receptor for Stxs, in both Vero cells, anti-Gb3Cer monoclonal antibodies capable of binding to S-Vero cells failed to effectively label R-Vero cells, suggesting a conformational difference in the Gb3Cer expressed on R-Vero cells. (3) The lipid analysis also showed that the R-Vero cells contained significant amounts of Gb4Cer. In addition, introduction of exogenous Gb4Cer into S-Vero cells slightly inhibited Stx1 cytotoxicity, suggesting some correlation between glycosphingolipid composition and Stx1 resistance. (4) Both butyrate treatment and serum depression eliminated the Stx1 resistance of R-Vero cells. (5) The results of the analysis by confocal microscopy suggest a difference in intracellular transport of Stx1 between R-Vero and S-Vero cells. Further study of R-Vero cells may provide a model of Stx1 resistance via distinct intracellular transport of Stx1.

Synthesis and assessment of globotriose-chitosan conjugate, a novel inhibitor of shiga toxins produced by Escherichia coli

Shiga toxin (Stx)-producing Escherichia coli (STEC) causes diarrhea and colitis in humans that can develop into a life-threatening hemolytic uremic syndrome (HUS). Developing efficient means of controlling STEC diseases, for which no drugs or vaccines are currently available, remains a high priority. We report here the construction and development of chitosan conjugates bearing the Stx ligand trisaccharide globotriose to demonstrate their potential as STEC disease treatment agents. The synthesis was accomplished by grafting a globotriose derivative containing an aldehyde-functionalized aglycone to chitosan amino groups. The obtained globotriose-chitosan conjugate bound with high affinity to Stx and efficiently neutralized its toxicity on Vero cells. Moreover, Stx levels in the gut of infected mice receiving oral doses of the conjugate were greatly diminished, enabling the mice to resist a fatal STEC challenge. The conjugate appears to function as a Stx adsorbent in the gut, preventing toxin entry into the bloodstream and consequent development of HUS. As such, the conjugate could act as a novel agent against STEC disease.

The interactions of human neutrophils with shiga toxins and related plant toxins: danger or safety?

Shiga toxins and ricin are well characterized similar toxins belonging to quite different biological kingdoms. Plant and bacteria have evolved the ability to produce these powerful toxins in parallel, while humans have evolved a defense system that recognizes molecular patterns common to foreign molecules through specific receptors expressed on the surface of the main actors of innate immunity, namely monocytes and neutrophils. The interactions between these toxins and neutrophils have been widely described and have stimulated intense debate. This paper is aimed at reviewing the topic, focusing particularly on implications for the pathogenesis and diagnosis of hemolytic uremic syndrome.

Microbead-based immunoassay for simultaneous detection of Shiga toxins and isolation of Escherichia coli O157 in foods

Shiga toxin-producing Escherichia coli (STEC) is a significant foodborne pathogen with great economic consequences. There has been an increased food safety concern with this organism since outbreaks of human illnesses caused by this pathogen were first reported in 1982. Therefore, developing a reliable, sensitive, and rapid assay capable of detecting E. coli O157 and the main toxins produced by STEC (i.e., Shiga toxins 1 [Stx(1)] and 2 [Stx(2)]) will directly benefit regulatory agencies by minimizing analysis time. Here, we use Luminex technology to detect multiple analytes in a single 50-ml sample. Using commercially available monoclonal antibodies coupled to carboxylated magnetic microbeads, we developed an immunoassay capable of simultaneously serotyping E. coli O157 and detecting Stx(1) and/or Stx(2). The specificity and sensitivity of this immunoassay was tested against a collection of 34 E. coli isolates belonging to various O serogroups phenotypically different for Stx. The results were compared with microplate sandwich enzyme-linked immunosorbent assay (ELISA), and no cross-reactivity was observed for any of the monoclonal antibodies used. An increased sensitivity up to 1,000 times was observed in the microbead-based immunoassay when compared with the microplate sandwich ELISA. The results indicate that Luminex technology has the potential to simultaneously detect multiple targets without loss of specificity and/or sensitivity. A blind experiment was conducted with 48 samples of ground beef, lettuce, and milk spiked with ≤2 CFU/g E. coli. All the samples were correctly identified, with no false positives or false negatives. This microbead-based immunoassay could be extended to simultaneously detect additional foodborne pathogens and their toxic markers.

Construction of a novel bioluminescent reporter system for investigating Shiga toxin expression of enterohemorrhagic Escherichia coli

A novel chromosome-plasmid hybrid bioluminescent reporter system (C-P reporter system) utilizing Photorhabdus luminescens luxCDABE genes has been constructed to monitor the expression of Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2) in enterohemorrhagic Escherichia coli (EHEC) in real time. The luxCDABE genes of P. luminescens have been cloned and divided into a luxCDAB cassette and a luxE gene. A promoter-less luxE gene introduced downstream from stx1 and from stx2 on EHEC chromosomes in single copies, and other luxCDAB genes were expressed on a multicopy number expression plasmid into the same cells. These Stx1- and Stx2-bioluminescent reporter strains expressed bioluminescence into bacteria cells when the expression of the promoter-less luxE gene was expressed in response to the promoter activity of stx1 and stx2, respectively. The expression levels of bioluminescence were identical to the production levels of Stx1 and Stx2 in the Stx1- and Stx2-bioluminescent reporter strains, and these strains produced both Stxs at the same respective levels as those of the parent EHEC strains. Using these reporter strains, we examined the profiles of Stx1 and Stx2 expression in EHEC. We found that production of both Stx1 and Stx2 in EHEC was enhanced upon contact with intestinal epithelial cells and within macrophages. However, the expression profiles between Stx1 and Stx2 in EHEC were different from each other under these conditions. Thus, these results suggested that this C-P reporter system is useful for determining the gene expression profile of bacteria.

Vibrio parahaemolyticus, enterotoxigenic Escherichia coli, enterohemorrhagic Escherichia coli and Vibrio cholerae

This review highlighted the following: (i) pathogenic mechanism of the thermostable direct hemolysin produced by Vibrio parahaemolyticus, especially on its cardiotoxicity, (ii) heat-labile and heat-stable enterotoxins produced by enterotoxigenic Escherichia coli, especially structure-activity relationship of heat-stable enterotoxin, (iii) RNA N-glycosidase activity of Vero toxins (VT1 and VT2) produced by enterohemorrhagic Escherichia coli O157:H7, (iv) discovery of Vibrio cholerae O139, (v) isolation of new variant of Vibrio cholerae O1 El Tor that carries classical ctxB, and production of high concentration of cholera toxin by these strains, and (vi) conversion of viable but nonculturable (VBNC) Vibrio cholerae to culturable state by co-culture with eukaryotic cells.

Escherichia coli Subtilase Cytotoxin

Subtilase cytotoxin (SubAB) is the prototype of a new AB(5) toxin family produced by a subset of Shiga toxigenic Escherichia coli (STEC) strains. Its A subunit is a subtilase-like serine protease and cytotoxicity for eukaryotic cells is due to a highly specific, single-site cleavage of BiP/GRP78, an essential Hsp70 family chaperone located in the endoplasmic reticulum (ER). This cleavage triggers a severe and unresolved ER stress response, ultimately triggering apoptosis. The B subunit has specificity for glycans terminating in the sialic acid N-glycolylneuraminic acid. Although its actual role in human disease pathogenesis is yet to be established, SubAB is lethal for mice and induces pathological features overlapping those seen in the haemolytic uraemic syndrome, a life-threatening complication of STEC infection. The toxin is also proving to be a useful tool for probing the role of BiP and ER stress in a variety of cellular functions.

Mammalian cell-based sensor system

Use of living cells or cellular components in biosensors is receiving increased attention and opens a whole new area of functional diagnostics. The term "mammalian cell-based biosensor" is designated to biosensors utilizing mammalian cells as the biorecognition element. Cell-based assays, such as high-throughput screening (HTS) or cytotoxicity testing, have already emerged as dependable and promising approaches to measure the functionality or toxicity of a compound (in case of HTS); or to probe the presence of pathogenic or toxigenic entities in clinical, environmental, or food samples. External stimuli or changes in cellular microenvironment sometimes perturb the "normal" physiological activities of mammalian cells, thus allowing CBBs to screen, monitor, and measure the analyte-induced changes. The advantage of CBBs is that they can report the presence or absence of active components, such as live pathogens or active toxins. In some cases, mammalian cells or plasma membranes are used as electrical capacitors and cell-cell and cell-substrate contact is measured via conductivity or electrical impedance. In addition, cytopathogenicity or cytotoxicity induced by pathogens or toxins resulting in apoptosis or necrosis could be measured via optical devices using fluorescence or luminescence. This chapter focuses mainly on the type and applications of different mammalian cell-based sensor systems.

An orally applicable Shiga toxin neutralizer functions in the intestine to inhibit the intracellular transport of the toxin

Shiga toxin 2 (Stx2) is a major virulence factor in infections with Stx-producing Escherichia coli (STEC), which causes gastrointestinal diseases and sometimes fatal systemic complications. Recently, we developed an oral Stx2 inhibitor known as Ac-PPP-tet that exhibits remarkable therapeutic potency in an STEC infection model. However, the precise mechanism underlying the in vivo therapeutic effects of Ac-PPP-tet is unknown. Here, we found that Ac-PPP-tet completely inhibited fluid accumulation in the rabbit ileum caused by the direct injection of Stx2. Interestingly, Ac-PPP-tet accumulated in the ileal epithelial cells only through its formation of a complex with Stx2. The formation of Ac-PPP-tet-Stx2 complexes in cultured epithelial cells blocked the intracellular transport of Stx2 from the Golgi apparatus to the endoplasmic reticulum, a process that is essential for Stx2 cytotoxicity. Thus, Ac-PPP-tet is the first Stx neutralizer that functions in the intestine by altering the intracellular transport of Stx2 in epithelial cells.

Shiga toxin as a bacterial defense against a eukaryotic predator, Tetrahymena thermophila

Bacterially derived exotoxins kill eukaryotic cells by inactivating factors and/or pathways that are universally conserved among eukaryotic organisms. The genes that encode these exotoxins are commonly found in bacterial viruses (bacteriophages). In the context of mammals, these toxins cause diseases ranging from cholera to diphtheria to enterohemorrhagic diarrhea. Phage-carried exotoxin genes are widespread in the environment and are found with unexpectedly high frequency in regions lacking the presumed mammalian "targets," suggesting that mammals are not the primary targets of these exotoxins. We suggest that such exotoxins may have evolved for the purpose of bacterial antipredator defense. We show here that Tetrahymena thermophila, a bacterivorous predator, is killed when cocultured with bacteria bearing a Shiga toxin (Stx)-encoding temperate bacteriophage. In cocultures with Tetrahymena, the Stx-encoding bacteria display a growth advantage over those that do not produce Stx. Tetrahymena is also killed by purified Stx. Disruption of the gene encoding the StxB subunit or addition of an excess of the nontoxic StxB subunit substantially reduced Stx holotoxin toxicity, suggesting that this subunit mediates intake and/or trafficking of Stx by Tetrahymena. Bacterially mediated Tetrahymena killing was blocked by mutations that prevented the bacterial SOS response (recA mutations) or by enzymes that breakdown H(2)O(2) (catalase), suggesting that the production of H(2)O(2) by Tetrahymena signals its presence to the bacteria, leading to bacteriophage induction and production of Stx.

Shiga toxin 2 is specifically released from bacterial cells by two different mechanisms

Shiga toxin 1 (Stx1) is located in the periplasmic fraction, while Stx2 is found in the extracellular fraction, suggesting that enterohemorrhagic Escherichia coli (EHEC) contains a specific Stx2 release system. Both stx(1) and stx(2) are found within the late operons of Stx-encoding phages. Stx2 production is greatly induced by mitomycin C, suggesting that stx(2) can transcribe from the late phage promoter of the Stx2-encoding phage. However, the Stx1 promoter adjacent to stx(1) is a dominant regulatory element in Stx1 production. With the deletion of phage lysis genes of the Stx2-encoding phage, Stx2 remains in the bacterial cells. Further, we demonstrate that the Stx2-encoding phage, but not the Stx1-encoding phage, is spontaneously induced at extremely low rates. These results indicate that spontaneously specific Stx2-encoding phage induction is involved in specific Stx2 release from bacterial cells. Furthermore, to examine whether another system for specific Stx2 release is present in EHEC, we analyze the stx-replaced mutants. As expected, Stx2 derived from the Stx1 promoter is located in both the extracellular and cell-associated fractions, while mutant Stx2 (B subunit, S31N) derived from the Stx1 promoter is found only in the cell-associated fraction. These results indicate that EHEC has another Stx2 release system that strictly recognizes the serine 31 residue of the B subunit. Overall, we present evidence that specific Stx2 release from bacterial cells is involved in both the Stx2-encoding phage induction system and another Stx2 release system.

Receptor affinity, stability and binding mode of Shiga toxins are determinants of toxicity

The closely related Shiga toxins, Shiga toxin 1 (Stx1) and Shiga toxin 2 (Stx2), can bind to Gb3 receptors. However, Stx2-producing enterohemorrhagic Escherichia coli (EHEC) strains are more commonly associated with serious human disease (viz., hemolytic-uremic syndrome) than Stx1-producing strains. To clarify the relationship between properties and toxicity of these toxins, we constructed and analyzed a hybrid holotoxin composed of Stx2A and Stx1B, designated as Stx2A1B, and a B subunit chimeric holotoxin composed of Stx2A and Stx2B (III V), designated as Stx2A2B (III V). The affinity of Stx2A1B to Gb3 was lower than that of Stx1, higher than that of Stx2 and identical to that of Stx2A2B (III V). On the other hand, the 50% lethal dose (LD(50)) for mice of Stx2A1B was lower than that of Stx1, but higher than that of Stx2. These results suggested that pathogenicity in mice was inversely related to the receptor affinity of the holotoxins. However, LD(50) of Stx2A1B was not identical to that of Stx2A2B (III V). Gel filtration analysis indicated that Stx2A2B (III V) was relatively less stable than Stx2A1B. Moreover, cross-linking experiments demonstrated that the modes of cell surface binding of Stx2A2B (III V) and Stx2A1B were different. These results indicated that the receptor affinity, stability and binding mode of Shiga toxins might be important determinants for toxicity in mice.

The serine 31 residue of the B subunit of Shiga toxin 2 is essential for secretion in enterohemorrhagic Escherichia coli

Shiga toxins produced by enterohemorrhagic Escherichia coli (EHEC) include Shiga toxin 1 (Stx1) as well as Shiga toxin 2 (Stx2). Stx1 is cell associated, whereas Stx2 is localized to the culture supernatant. We have analyzed the secretion of Stx2 by generating histidine-tagged StxB (StxB-H). Although neither StxB1-H nor StxB2-H was secreted in StxB-H-overexpressed EHEC, StxB2-H-overexpressed EHEC showed inhibited Stx2 secretion. On the other hand, StxB1-H-overexpressed EHEC showed no alteration of Stx2 secretion. B-subunit chimeras of Stx1 and Stx2 were used to identify the specific residue of StxB2 that the Stx2 secretory system recognizes. Alteration of the serine 31 residue to an asparagine residue (S31N) in StxB2-H enabled the recovery of Stx2 secretion. On the other hand, alteration of the asparagine 32 residue to a serine residue (N32S) in StxB1-H caused the partial secretion of a point-mutated histidine-tagged B subunit in EHEC. Based on the evidence, it appeared possible that this residue might contain secretion-related information for Stx2 secretion. To investigate this hypothesis, we constructed an isogenic mutant EHEC (Stx1B subunit, N32S) strain and an isogenic mutant EHEC (Stx2B subunit, S31N) strain. Although the mutant Stx2 was cell associated in isogenic mutant EHEC, mutant Stx1 was not extracellular. However, when we used plasmids for the expression of the mutant holotoxins, the overexpressed mutant Stx1 was found in the supernatant fraction, and the overexpressed mutant Stx2 was found in the cell-associated fraction in mutant holotoxin gene-transformed EHEC. These results indicate that the serine 31 residue of the B subunit of Stx2 contains secretion-related information.

Neutralizing activity of bovine colostral antibody against verotoxin derived from enterohemorrhagic Escherichia coli O157:H7 in mice

The neutralization efficacy of bovine colostral antibody against verotoxin (VT) 1 and 2 was investigated. Cows were immunized with VT1 or VT2 fourteen times at 7-day intervals. A colostral antibody exhibiting high titers was obtained from immunized cows. Survival rates were evaluated in mice administered VT1 or VT2, and those infected with Escherichia coli (E. coli) O157:H7 producing VT1 or VT2. Survival rates after VT1 administration were 100% in the single-administration group, 90% in the repeat-administration group, and 78.6% in the control group. Survival rates after VT2 were 75.0% in the single-administration group, and 100% in the repeat-administration group. All mice in the control group died. Colostral antibody and fosfomycin (FOM) in the colostral antibody group and FOM and skim milk in the control group were administered three times per day for 5 days to mice infected with E. coli O157:H7 producing VT1 or VT2. Survival rates after inoculation with E. coli O157:H7 producing VT1 were 80.0% in the colostral antibody group, and 63.6% in the control group. Survival rates after inoculation with E. coli O157:H7 producing VT2 were 83.3% in the colostral antibody group, and 20.0% in the control group. The survival rate in mice without treatment following inoculation with E. coli O157:H7 producing VT2 was 88.2%. The survival rates in mice infected with E. coli O157:H7 strains producing VT1 or VT2 improved after administration of this colostral antibody, which exhibited neutralization efficacy against VT.

Inhibitory effect of tyrphostin 47 on Shiga toxin-induced cell death

The inhibitory effects of tyrosine kinase inhibitors including tyrphostins 25, 47 and 51 on Shiga toxin 1-induced cell death and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation were examined in Vero cells. Tyrphostin 47 significantly inhibited Shiga toxin 1-induced cell death and p38 MAPK phosphorylation. In contrast, tyrphostins 25 and 51 had no significant effect on the Shiga toxin 1-induced responses. These data indicate that Shiga toxin 1-induced cell injury occurs through a pathway sensitive to tyrphostin 47, and the target molecule for tyrphostin 47 opens up new opportunities for pharmacological intervention against Shiga toxin-producing Escherichia coli infectious diseases.

Shiga toxin 1 causes direct renal injury in rats

Infection with Shiga toxin (Stx)-producing Escherichia coli has been implicated to cause hemolytic uremic syndrome, which is characterized by histological abnormalities such as microvascular thrombi and tubular cell damage in the kidney. Although Stx is known to be the major virulence factor of the pathogen, it is still unclear whether Stx directly impairs renal cells in vivo to cause such histological changes and deterioration of renal function. To assess the consequence of the direct action of Stx on renal cells, left kidneys of rats were perfused with Stx1 from the renal artery through the renal vein and then revascularized. Kidneys of control animals were perfused with the vehicle alone. On day 1, apoptosis and induction of tumor necrosis factor alpha gene expression were noticed to occur in the medulla of the Stx1-perfused kidneys. On day 3, extensive tubular injuries were observed by light microscopy: aggregated platelets and monocytic infiltrates in both glomeruli and the medullary interstitium were detected by immunostaining. Tubular changes were more extensive on day 9, with areas of infarction seen in the cortex and medulla. These changes were not found to occur in the sham-operated kidneys. No obvious glomerular changes were detected by light microscopy at any time point. When nonperfused right kidneys were removed after the Stx1 perfusion of the left kidneys, the serum creatinine and blood urea nitrogen levels were increased from day 2, and acute renal failure followed on day 3. These results indicate that Stx1 caused glomerular platelet aggregation, tubular damage, and acute deterioration of renal function by acting directly on renal cells.

Prevalence of Shiga toxin-producing Escherichia coli in beef cattle

A large number of Shiga toxin-producing Escherichia coli (STEC) strains have caused major outbreaks and sporadic cases of human illnesses, including mild diarrhea, bloody diarrhea, hemorrhagic colitis, and the life-threatening hemolytic uremic syndrome. These illnesses have been traced to both O157 and non-O157 STEC. In a large number of STEC-associated outbreaks, the infections were attributed to consumption of ground beef or other beef products contaminated with cattle feces. Thus, beef cattle are considered reservoirs of STEC and can pose significant health risks to humans. The global nature of the human food supply suggests that safety concerns with beef will continue and the challenges facing the beef industry will increase at the production and processing levels. To be prepared to address these concerns and challenges, it is critical to assess the role of beef cattle in human STEC infections. In this review, published reports on STEC in beef cattle were evaluated to achieve the following specific objectives: (i) assess the prevalence of STEC in beef cattle, and (ii) determine the potential health risks of STEC strains from beef cattle. The latter objective is critically important because many beef STEC isolates are highly virulent. Global testing of beef cattle feces revealed wide ranges of prevalence rates for O157 STEC (i.e., 0.2 to 27.8%) and non-O157 STEC (i.e., 2.1 to 70.1%). Of the 261 STEC serotypes found in beef cattle, 44 cause hemolytic uremic syndrome and 37 cause other illnesses.

A new family of potent AB(5) cytotoxins produced by Shiga toxigenic Escherichia coli

The Shiga toxigenic Escherichia coli (STEC) O113:H21 strain 98NK2, which was responsible for an outbreak of hemolytic uremic syndrome, secretes a highly potent and lethal subtilase cytotoxin that is unrelated to any bacterial toxin described to date. It is the prototype of a new family of AB(5) toxins, comprising a single 35-kilodalton (kD) A subunit and a pentamer of 13-kD B subunits. The A subunit is a subtilase-like serine protease distantly related to the BA_2875 gene product of Bacillus anthracis. The B subunit is related to a putative exported protein from Yersinia pestis, and binds to a mimic of the ganglioside GM2. Subtilase cytotoxin is encoded by two closely linked, cotranscribed genes (subA and subB), which, in strain 98NK2, are located on a large, conjugative virulence plasmid. Homologues of the genes are present in 32 out of 68 other STEC strains tested. Intraperitoneal injection of purified subtilase cytotoxin was fatal for mice and resulted in extensive microvascular thrombosis, as well as necrosis in the brain, kidneys, and liver. Oral challenge of mice with E. coli K-12-expressing cloned subA and subB resulted in dramatic weight loss. These findings suggest that the toxin may contribute to the pathogenesis of human disease.

Characterisation of Shiga toxin-producingEscherichia coli(STEC) isolated from seafood and beef

Shiga toxin-producing Escherichia coli (STEC) strains isolated in Mangalore, India, were characterised by bead-enzyme-linked immunosorbent assay (bead-ELISA), Vero cell cytotoxicity assay, PCR and colony hybridisation for the detection of stx1 and stx2 genes. Four strains from seafood, six from beef and one from a clinical case of bloody diarrhoea were positive for Shiga toxins Stx1 and Stx2 and also for stx1and stx2 genes. The seafood isolates produced either Stx2 alone or both Stx1 and Stx2, while the beef isolates produced Stx1 alone. The stx1 gene of all the beef STEC was found to be of recently reported stx1c type. All STEC strains and one non-STEC strain isolated from clam harboured EHEC-hlyA. Interestingly, though all STEC strains were negative for eae gene, two STEC strains isolated from seafood and one from a patient with bloody diarrhoea possessed STEC autoagglutinating adhesion (saa) gene, recently identified as a gene encoding a novel autoagglutinating adhesion.

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.

Genetic and immunological analysis of a novel variant of Shiga toxin 1 from bovine Escherichia coli strains and development of bead-ELISA to detect the variant toxin

A novel variant of Shiga toxin 1 (Stx1) was identified from bovine Escherichia coli strains. The stx1 variant genes designated as stx1v51 and stx1v52 were cloned and sequenced. The two variant genes differed each other by 2 bp, but the deduced amino acid sequences of the two Stx1 variant toxins were the same and had 94% and 92% homology to that of prototype A and B subunits of Stx1, respectively. The variant toxin designated as Stx1v52 was purified to homogeneity. Although inhibition of protein synthesis in vitro by purified Stx1v52 was almost equal to that of purified Stx1, Vero cell cytotoxicity and mouse lethality of Stx1v52 were several folds lower than those of prototype Stx1. In Ouchterlony double gel diffusion test, the precipitin line between Stx1v52 and Stx1 formed a spur against anti-Stx1 serum but was fused against anti-Stx1v52 serum. Stx1v52 and Stx1v52-specific-bead-ELISA was developed, and both Stx1 and Stx1v52 could be detected with high sensitivity using Stx1v52 conjugate. However, Stx1v52 but not Stx1 could be detected with Stx1v52-specific bead-ELISA.

Nitrobenzylthioinosine (NBT), a nucleoside transport inhibitor, protects against Shiga toxin cytotoxicity in human microvascular endothelial cells

Infections with Shiga toxin (Stx)-producing Escherichia coli (STEC) cause microvascular endothelial cell damage, resulting in hemorrhagic colitis and hemolytic uremic syndrome. The prevention of endothelial cell damage is therefore a crucial step in overcoming this disorder. Here, we report that nitrobenzylthioinosine (NBT), a nucleoside transport inhibitor, has a protective effect against the cytotoxicity of Stxs in human microvascular endothelial cells (HMVECs). The relative viability of cells treated with 1.5-15 pM of Stx1 was reduced to 10-20% of that without Stx1. However, the viability of cells treated with NBT (10-100 microM) remained higher than 80%, even in the presence of Stx1. NBT also protected against Stx1 cytotoxicity in sodium butyrate-treated hypersensitive HMVECs. The protective effect of NBT against Stx cytotoxicity may be due to the depletion of ATP in the cells, thereby inhibiting the entry of Stx1.

An association of 27- and 40-kDa molecules with glycolipids that bind A-B bacterial enterotoxins to cultured cells

It is well recognized that the Shiga-like toxins (Stxs) preferentially bind to Gb3 glycolipids and the cholera toxin (CT) and heat-labile enterotoxin (LTp) bind to GM1 gangliosides. After binding to the cell surface, A-B bacterial enterotoxins have to be internalized by endocytosis. The transport of the toxin-glycolipid complex has been documented in several manners but the actual mechanisms are yet to be clarified. We applied a heterobifunctional cross-linker, sulfosuccinimidyl-2-(p-azidosalicylamido)-1,3'-dithiopropionate (SASD), to detect the membrane proteins involved in the binding and the transport of A-B bacterial enterotoxins in cultured cells. Both Stx1 and Stx2 bound to the detergent-insoluble microdomain (DIM) of Vero cells and Caco-2 cells, which were susceptible to the toxin, but neither was bound to insusceptible CHO-K1 cells. Both CT and LTp bound to the DIM of Vero cells, Caco-2 cells, and CHO-K1 cells. In a cross-linking experiment, Stx1 cross-linked only with a 27-kDa molecule, while Stx2, which was more potently toxic than Stx1, cross-linked with 27- and 40-kDa molecules of Vero cells as well as of Caco-2 cells; moreover, no molecules were cross-linked with the insusceptible CHO-K1 cells. LTp was cross-linked only to the 27-kDa molecule of these three cell types but the CT, which was more toxic than LTp, was also cross-linked with 27- and 40-kDa molecules of Vero cells, Caco-2 cells, and CHO-K1 cells. The 27- and the 40-kDa molecules might play a role in the endocytosis and retrograde transport of A-B bacterial enterotoxins.

Effects of azithromycin on shiga toxin production by Escherichia coli and subsequent host inflammatory response

Shiga toxin (Stx)-producing Escherichia coli (STEC) colonizes the human intestinal mucosa, produces Stx from phage, and causes the development of hemolytic-uremic syndrome via Stx-induced inflammatory cytokine production. Azithromycin exhibited strong in vitro activity against STEC without inducing Stx-converting phage, in marked contrast to norfloxacin. Azithromycin decreased the tumor necrosis factor alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 production from Stx-treated human peripheral mononuclear cells or monocytes to a greater extent than did clarithromycin. In Stx-injected mice, azithromycin significantly suppressed Stx-induced TNF-alpha, IL-1beta, and IL-6 levels in serum and improved the outcome as assessed by survival rate. In the STEC oral infection experiment using immature mice immediately after weaning (weaned immature-mouse model), all mice died within 7 days postinfection. Azithromycin administration gave the mice 100% protection from killing, while ciprofloxacin administration gave them 67% protection. The data suggest that azithromycin (at least at higher concentrations) has a strong effect on Stx production by STEC and on the Stx-induced inflammatory host response and prevents death in mice. Azithromycin may have a beneficial effect on STEC-associated disease.

Shiga toxin 2 induces macrophage-granulocyte colonies from human bone marrow and cord blood stem cells

Addition of Shiga toxin 2 to human bone marrow or cord blood cell culture induced macrophage-granulocyte colonies. Although Shiga toxin 2 alone induced colonies mainly composed of macrophages, it induced colonies mainly consisting of granulocytes when combined with physiological doses of interleukin-1beta, granulocyte colony-stimulating factor, or stem cell factor with interleukin-3.

Effect of Shiga toxins on granulocyte function

We already showed that injection of Shiga toxin (Stx) 2 into mice caused severe granulocytosis in the peripheral blood. In this study we further clarified changes of granulocyte function by Stx 2. The activity of medullasin, a neutral serine protease in granulocytes that injures endothelial cells in vessels, significantly increased when Stx 2 was injected into mice intraperitoneally. Since granulocyte count in the peripheral blood of mice was markedly increased after intraperitoneal injection of Stx 2, medullasin activity in the peripheral blood was remarkably elevated. In contrast to Stx 2, injection of Stx 1 into mice caused no elevation of medullasin activity in granulocytes nor increase in granulocyte count in the peripheral blood. Cathepsin G levels in granulocytes increased only slightly after Stx 2 injection. Granulocytes obtained from mice injected with Stx 2 showed reduced superoxide-producing activity compared with those from controls. Addition of Stx 2 or Stx 1 to human mature granulocytes in vitro decreased their superoxide-producing activity when stimulated with agonists. Therefore, these toxins produced from Escherichia coli augment toxic effect of the bacteria by reducing bactericidal activity of granulocytes. Tissue injury in organisms infected with Shiga toxin-producing E. coli is mainly derived from elevated neutral proteases, such as medullasin, in granulocytes rather than direct toxic effect of superoxide from granulocytes. Hemolytic uremic syndrome caused by Shiga toxin-producing E. coli infection is due, at least in part, to the elevation of medullasin levels produced by granulocytes.

Development of humanized monoclonal antibody TMA-15 which neutralizes Shiga toxin 2

A murine monoclonal antibody (MAb), VTm1.1, specifically recognizing and neutralizing Shiga toxin 2 (Stx2), was obtained. To prevent a humoral response against murine antibody when used clinically, a humanized antibody was constructed by combining the complementarity-determining regions of VTm1.1 with human framework and constant regions. In addition, several amino acids in the framework were changed to improve the binding affinity of the antibody and further reduce its potential immunogenicity. The humanized antibody, TMA-15, recognized the B-subunit of Stx2 and had affinity for Stx2 of 3.3 x 10(-9) M, within two-fold of that of the original murine antibody. TMA-15 neutralized the cytotoxicity of Stx2 and several different Stx2 variants in vitro, and it completely protected mice from death in a Stx2-challenged mice model. These results suggest that TMA-15 will have clinical potency in Stx-producing Escherichia coli infections, including E. coli O157 infections.

Urinary concentrating defect in rats given Shiga toxin: elevation in urinary AQP2 level associated with polyuria

Shiga toxin (Stx) plays a central role in the etiology of hemolytic uremic syndrome (HUS) associated with Stx-producing Escherichia coli infection. The deposition of Stx2 in the renal collecting duct epithelial cells of rats administered Stx2 intravenously has been demonstrated by immunohistochemistry, and these rats were shown to develop substantial morphological changes in the kidney tubules, associated with polyuria. Severe polyuria was observed as an early event with no other obvious sequelae after Stx administration, in parallel with elevated urinary level of aquaporin 2 (AQP2) water channel protein that was determined by a sandwich EIA assay. Immunoblotting revealed that Stx treatment markedly induced an elevation in urinary AQP2 level and reduction in AQP2 protein in the renal plasma membranes. Elevated urinary AQP2 level was a more sensitive marker to assess Stx-induced renal tubular damage than urinary beta2-microglobulin or N-acetyl-beta-D-glucosaminidase in rats. Stx2 caused more severe renal tubular impairment than Stx1. Change in urinary AQP2 level by Stx1 and Stx2 at non-lethal doses of 40 ng/kg and 10 ng/kg, respectively, was reversed at 7 days in association with recovery of urinary concentrating ability, suggesting that there is a causative link.

A therapeutic agent with oriented carbohydrates for treatment of infections by Shiga toxin-producing Escherichia coli O157:H7

Infection with Shiga toxin (Stx)-producing Escherichia coli O157:H7, which causes diarrhea and hemorrhagic colitis in humans, often results in fatal systemic complications, such as neurological damage and hemolytic-uremic syndrome. Because Stx circulating in the blood is a major causative factor of these complications, the development of a Stx neutralizer that functions in the circulation holds promise as a viable therapy. Here we developed a series of carbosilane dendrimers, in which trisaccharides of globotriaosyl ceramide, a receptor for Stx, were variously oriented at their termini (referred to as SUPER TWIG), and identified a SUPER TWIG with six trisaccharides as a Stx neutralizer functioning in the circulation. This SUPER TWIG specifically bound to Stx with high affinity (K(d) = 1.1 x 10(-6) M) and inhibited the incorporation of the toxin into target cells. Intravenous administration of the SUPER TWIG along with Stx to mice substantially reduced the fatal brain damage and completely suppressed the lethal effect of Stx. Moreover, the SUPER TWIG protected mice from challenge with a fatal dose of E. coli O157:H7, even when administered after the establishment of the infection. The SUPER TWIG neutralized Stx in vivo by a mechanism in which the accumulation and immediate degradation of Stx by phagocytic macrophages present in the reticuloendothelial system were induced. Taken together, our findings indicate that this SUPER TWIG is therapeutic agent against infections by Stx-producing E. coli.

A rapid bioluminescent enzyme immunoassay (BLEIA) for the detection of Shiga toxin types 1 and 2

In recent years, Escherichia coli O157: H7 has emerged as a global public health concern. Among the more important virulence characteristics of this strain is its ability to produce one or more Shiga toxins (Stx). Traditional culture-based methods for assay of enteric toxins in foods and clinical samples are relatively slow and results can be ambiguous. In this work, we established a toxin-detection system based on bioluminescent enzyme immunoassay (BLEIA) using a simple and inexpensive device. The system could detect both Shiga toxin types 1 and 2 individually within 150 min with a detection limit for each toxin at 5 pg/ml. In our study of previously characterized Shigatoxigenic and all non-Shigatoxigenic E. coli and other bacterial species, we found all Shigatoxigenic strains to be positive and non-Shigatoxigenic E. coli and other bacterial species to be negative. This assay was also used to detect Stxs in milk and supernatant fluids from minced chicken and beef. For clinical stool samples we noted a tendency for the system to give unexpectedly high background level. Our results suggest the feasibility of using BLEIA methodology for the simple, rapid and sensitive detection of toxins from culture supernatant, various foods and clinical samples.

Serum amyloid P component is the Shiga toxin 2-neutralizing factor in human blood

It has been suggested that some factor present in human plasma binds to Shiga toxin 2 (Stx2) and neutralizes it in vitro (Bitzan, M., Klemt, M., Steffens, R., and Muller-Wiefel, D. E. (1993) Infection 21, 140-145). This factor does not exist in other species (Caprioli, A., Luzzi, I., Seganti, L., Marchetti, M., Karmali, M., Clarke, I., and Boyd, B. (1994) Recent Adv. VTEC Infect. 353-356). Because analysis of this factor is important to understanding the pathology induced by Shiga toxin-producing Escherichia coli, we purified this factor from human plasma and identified it. Purification was carried out by serially subjecting human plasma to Con A-Sepharose, DEAE-Sepharose, hydroxyapatite, and gel-filtration high performance liquid chromatography (HPLC), using Stx2-neutralizing activity as the indicator. The gel-filtration HPLC fraction yielded a single band on SDS-polyacrylamide gel electrophoresis. Twenty N-terminal amino acid residues of this fraction were analyzed and found to correspond perfectly to human serum amyloid P component (HuSAP). Because commercially available HuSAP also showed Stx2 binding and neutralizing activity, we identified this factor as HuSAP.

Single-step method for purification of Shiga toxin-1 B subunit using receptor-mediated affinity chromatography by globotriaosylceramide-conjugated octyl sepharose CL-4B

A new single-step purification method for Shiga toxin (Stx) was developed using receptor-mediated affinity chromatography, in which Gb3Cer (globotriaosylceramide) was conjugated to octyl Sepharose CL-4B as a carrier. This method achieves high yield and high purity in a small column on which Gb3Cer has been immobilized at high density. Using this affinity column, the Stx1 B subunit was purified with homogeneity by a one-step procedure from a crude extract of recombinant Stx1 B subunit-producing Escherichia coli. The purified Stx1 B subunit conserved a natural pentamer structure confirmed by gel filtration and sedimentation equilibrium analysis. Furthermore, the purified Stx1 B subunit was able to bind specifically to Gb3Cer expressed on Burkitt's lymphoma cells. This versatile purification method can be used to isolate various types of natural as well as recombinant Stx, facilitating fundamental studies of human diseases caused by this toxin.

Genetically modified Shiga toxin 2e (Stx2e) producing Escherichia coli is a vaccine candidate for porcine edema disease

Porcine edema disease (ED) is an enterotoxaemia in pigs after weaning, caused by Shiga toxin 2e (Stx2e) producing Escherichia coli. Recently in Japan, outbreaks of ED are re-emerging in pig production. In this study we constructed a mutant that retained immunogenicity but lost Vero cell cytotoxicity, which produced genetically modified toxin (Stx2e*) by replacing glutamate with glutamine at position 167 and arginine with leucine at position 170 of the A subunit. The stx(2e)* gene was replaced with the stx(2e)gene of the wild type virulent strain by homologous recombination. As the parent wild strain was pathogenic to pigs but the mutant was not, the mutant named as YT106 was given to the pigs to examine its protective immunity against ED. All 20 pigs vaccinated with YT106 survived, but only eight of the 20 non-vaccinated pigs survived after the challenge with a wild strain. Also, the eight pigs that survived had decreased rates of gain relative to those of the controls. Blood IgG and intestinal IgA titres increased 3.3 and 1.6 times more than the control, respectively, showing that YT106 might be a good candidate of a live attenuated vaccine strain to protect against ED.

Activation of the caspase cascade during Stx1-induced apoptosis in Burkitt's lymphoma cells

Shiga toxin 1 (Stx1) produced by Escherichia coli has been reported to induce apoptosis in many different cell types, including Burkitt's lymphoma (BL) cells. Since it has been established that the caspases play essential roles as the effector molecules in the apoptotic process in most cases, we examined the kinetics of caspase activation during the process of Stx1-mediated apoptosis of BL cells. Using Ramos BL cells that are highly sensitive to Stx1-mediated cytotoxicity, we observed that multiple caspases, including caspase-3, -7, and -8 were promptly activated following Stx1 treatment, as indicated by both the procaspase cleavages and enhancement of cleavage of the tetrapeptide substrates of the caspases. In addition, the inhibition assay revealed that caspase-8 is located upstream of both caspase-3 and -7, suggesting that Stx1-mediated apoptosis utilizes a similar caspase cascade to that involved in Fas-mediated apoptosis. Neither anti-Fas mAb nor TNF-alpha, however, affected the Stx1-mediated apoptosis of Ramos cells. Although the precise mechanism of Stx1-mediated activation of caspase-8 is still unclear, we have demonstrated that crosslinkage of CD77, a functional receptor for Stx1, with specific antibody is sufficient to induce activation of caspase-8. Our findings should provide new insight into the understanding of the molecular basis of Stx1-mediated cell injury.

Enhanced low shear stress induced platelet aggregation by Shiga-like toxin 1 purified from Escherichia coli O157

The effect of Shiga-like toxin 1 (Stx1) produced by Escherichia coli O157 on platelets was studied with an argon laser light-assisted shear-induced platelet aggregometer and with binding assays. Stx1 markedly enhanced the platelet aggregation under low shear stress but did not affect it under high shear stress. Minimal concentration of Stx1 required for the enhancement was 0.25 ng/ml, and almost maximal enhancement was observed at a final concentration of > or =2.5 ng/ml. This enhanced platelet aggregation disappeared after leukocyte depletion from normal platelet-rich plasma with a specific filter. In contrast, a standard platelet aggregometer was unable to detect this enhanced platelet aggregation in either the presence or the absence of ADP. 125I-labeled purified Stx1 did not specifically bind to normal washed platelets depleted of leukocytes, and thin-layer chromatographic analysis of glycolipids extracted from normal platelet lysates also confirmed that leukocyte-depleted normal platelets lack Stx1-specific receptor globotriaosylceramide (Gb3). Supernatant from the monocyte suspension stimulated with Stx1 exhibited the enhanced low shear stress induced platelet aggregation, but that from the polymorphonuclear cell suspension did not. Several cytokines produced from monocytes reproduced this event in vitro. Further, plasmas from six out of seven patients with hemolytic uremic syndrome (HUS) had activity similar to the purified Stx1. This activity was almost totally impaired after treatment of HUS plasmas with Gb3 in accord with reduction of plasma Stx1 levels. Taken together, these results indicate that platelets lack Gb3, and Stx1 appears to modulate platelet aggregation in an indirect fashion, presumably by the release of cytokines or chemical compounds from the target tissues.

Protective effect of Lactobacillus casei strain Shirota on Shiga toxin-producing Escherichia coli O157:H7 infection in infant rabbits

We examined colonization patterns of Shiga toxin-producing Escherichia coli (STEC), concentrations of Shiga toxins (Stxs) and specific immunoglobulin A (lgA) against Stxs and STEC bacterial cell surface antigen in various portions of the gastrointestinal tract in an infant rabbit infection model. After inoculation of 3-day-old infant rabbits with STEC strain 89020087 at low doses (approximately 10(3) CFU/body), numbers of colonizing STEC bacteria and concentrations of Stxs in the intestine increased dramatically and the animals developed diarrhea within a couple of days after infection. Daily administration of Lactobacillus casei from the day of birth dramatically decreased the severity of diarrhea and lowered STEC colonization levels in the gastrointestinal tract 100-fold day 7 after infection. Both Stx1 and Stx2 concentrations in the intestines and histological damage to the intestinal mucus induced by STEC infection were decreased by the administration of L. casei. Examination of the concentrations of volatile fatty acids and pH of the intestinal contents revealed that the protective effect of L. casei administration against STEC infection was not due to fermented products such as lactic acid in the gastrointestinal tract. Administration of L. casei increased levels of lgAs against Stx1, Stx2, and formalin-killed STEC cells in the colon approximately two-, four-, and threefold, respectively, compared with those of the untreated controls by day 7 after infection. These results suggest that administration of L. casei strain Shirota enhances the local immune responses to STEC cells and Stxs and leads to elimination of STEC and thus decreases Stx concentrations in the intestines.

Caspase-3 activation and apoptosis induction coupled with the retrograde transport of shiga toxin: inhibition by brefeldin A

Caspase proteolytic activities, such as caspase-3, -2 and -6, of THP-1 human monocytic cells were markedly increased in a time- and dose-dependent manner by treatment with purified Shiga toxin 1 (Stx1) or Stx2. Caspase-3 activation was strictly correlated with internucleosomal DNA fragmentation and chromatin condensation of the cells. In addition, the specific caspase-3 inhibitor, Ac-DEVD-CHO, decreased the percentage of apoptotic cells. The purified B-subunit of Stx1 did not induce apoptosis in THP-1 cells. Caspase-3 activation, DNA fragmentation and chromatin condensation caused by Stx were completely blocked by pretreatment of cells with brefeldin A, an inhibitor of Golgi functions. The findings suggest that Stx1 as well as Stx2 activate caspase-3, which plays a critical role in apoptosis, and that the apoptotic signals rise after Stx is transported to the Golgi apparatus.

Shiga toxin activates p38 MAP kinase through cellular Ca(2+) increase in Vero cells

We examined whether the mitogen-activated protein kinase (MAPK) pathway is involved in Shiga toxin (Stx)-induced Vero cell injury. Consonant with cell injury, Stx caused a transient extracellular signal-regulated kinase1/2 (ERK1/2) and a sustained p38 MAPK phosphorylation. p38 MAPK inhibitors (SB 203580 and PD 169316), but not an ERK1/2 kinase inhibitor (PD 98059), partially inhibited the Stx-induced cell death. BAPTA-AM, a Ca(2+) chelator, reduced both cell injury and p38 MAPK phosphorylation. Antioxidants reduced Stx1-induced p38 MAPK phosphorylation. These data indicate that Stx activates p38 MAPK through an increase in intracellular Ca(2+) and reactive oxygen species, and this signaling is involved in Stx-induced cell death.

Globotriaosyl ceramide (CD77/Gb3) in the glycolipid-enriched membrane domain participates in B-cell receptor-mediated apoptosis by regulating lyn kinase activity in human B cells

The role of CD77 expressed on a fraction of germinal center B cells, also known as glycosphyngolipid Gb3, and as a functional receptor for Shiga toxins (Stx) in B-cell receptor (BCR)-mediated apoptosis was investigated. Using Stx1-sensitive Burkitt's lymphoma Ramos cells as an in vitro model of CD77(+) germinal center B cells, intracellular signaling events mediated by either Stx1 or anti-CD77 antibody were examined immunobiochemically and immunocytologically. We observed prompt activation of Lyn and Syk kinases leading to increased binding of these proteins to surface IgM (sIgM) in Ramos cells after Stx1 treatment. We also observed microscopic colocalization of CD77 and sIgM after stimulation with Stx1. Along with the synergism between the cross-linking of CD77 and that of sIgM in their effect on apoptosis induction, it was highly probable that CD77 cross-linking induces activation of the BCR signaling cascade. Analysis using sucrose density gradient centrifugation suggested that Stx1 binding to CD77 induced recruitment and activation of Lyn in the glycolipid-enriched membrane (GEM) fractions. Once activated, however, Lyn seemed to acquire an increased detergent solubility and moved outside of the GEM fractions. This study describes the participation of the GEM domain in BCR-signaling cascade and suggests a possible role of CD77 as a regulator of BCR-induced apoptosis in human B cells.

Binding of avian ovomucoid to shiga-like toxin type 1 and its utilization for receptor analog affinity chromatography

Development of a simple and efficient purification procedure for Shiga-like toxin I (Stx1) was attempted. Since it has been suggested that pigeon egg white ovomucoid carries a P1 antigenic determinant, we examined its ability to bind Stx1. The ovomucoid glycoprotein fraction (GPro) was prepared from pigeon egg white by acetone precipitation, and a portion of the GPro was treated with pronase to obtain the glycopeptide fraction (GPep). When both GPro and GPep were coupled to CNBr-activated Sepharose 4B and subjected to affinity chromatography, Stx1 specifically bound to both columns. The Stx1 eluted with a buffer containing 4.5 M MgCl2 was shown to be highly purified to homogeneity by polyacrylamide gel electrophoresis under denatured condition; only two protein bands with molecular weights of 32,000 and 8000, which correspond to the A and the B subunits of Stx1, respectively, were recognized. The purified toxin showed cytotoxicity on Vero cells with a specific activity of approximately 6 x 10(8) CD50/mg protein; almost 100% of the activity was recovered from Escherichia coli cell lysate. We propose that the utilization of avian ovmucoid for the affinity chromatography provides a potentially simple, convenient, and widely available method to purify Shiga-like toxins.