Interferon pretreatment enhances the sensitivity of Vero cells to Clostridium perfringens type A enterotoxin

Overexpression of Claudin Proteins in Esophageal Adenocarcinoma and Its Precursor Lesions

Claudins are components of tight junctions important in intercellular barriers and cell polarity. The authors identified upregulation of Claudins 3, 4, and 7 in gastric adenocarcinoma using Affymetrix U-133 oligonucleotide microarrays and immunohistochemistry (IHC). While normal gastric mucosa lacked Claudin 3, 4, and 7 expression, intestinal metaplasia and dysplasia showed these proteins. The authors hypothesized that Claudins would be similarly overexpressed in Barrett's esophagus (BE)/adenocarcinoma. Claudins 3, 4, and 7 gene expression was analyzed by Affymetrix U-133 microarrays in three esophageal adenocarcinomas, one case of BE, and three normal esophagi. IHC validation was performed using tissue microarrays constructed from esophageal resection specimens containing squamous (44 cases), gastric (40 cases), and non-dysplastic BE (16 cases), low-grade and high-grade dysplasia (16 and 26 cases), adenocarcinoma (58 cases), and nodal metastases (27 cases). IHC staining was scored semiquantitatively (0+ to 4+). By microarray analysis, Claudin 3 showed a marked increase in mRNA expression compared with normal esophagus (approximately 100-fold). Claudins 4 and 7 were modestly increased (2.2- and 1.3-fold). By IHC, Claudin 3 expression was 1+ in most (>95%) normal squamous or gastric tissues and 2+ to 4+ in more than 80% of high-grade dysplasia, adenocarcinoma, and metastases specimens. Claudin 4 protein expression was 2+ or less in most squamous and gastric mucosa (>90%) but 3+ or 4+ in BE, low- and high-grade dysplasia, adenocarcinoma, and metastases specimens (>90%). Claudin 7 expression was minimal in squamous and gastric mucosa but strong (3+ to 4+) in BE and low-grade dysplasia. In high-grade dysplasia, adenocarcinoma, and metastases, Claudin 7 was less intense, with 60% to 70% staining 3+ or 4+ and 30% to 40% staining weakly (1+ or 2+). The findings suggest that alterations in Claudin proteins are an early event in tumorigenesis and may provide targets for diagnosis and directed therapy for esophageal adenocarcinoma and its precursors.

Mechanisms of host defense following severe acute respiratory syndrome-coronavirus (SARS-CoV) pulmonary infection of mice

We describe a model of severe acute respiratory syndrome-coronavirus (SARS-CoV) infection in C57BL/6 mice. A clinical isolate of the virus introduced intranasally replicated transiently to high levels in the lungs of these mice, with a peak on day 3 and clearance by day 9 postinfection. Viral RNA localized to bronchial and bronchiolar epithelium. Expression of mRNA for angiotensin converting enzyme 2, the SARS-CoV receptor, was detected in the lung following infection. The virus induced production in the lung of the proinflammatory chemokines CCL2, CCL3, CCL5, CXCL9, and CXCL10 with differential kinetics. The receptors for these chemokines were also detected. Most impressively, mRNA for CXCR3, the receptor for CXCL9 and CXCL10, was massively up-regulated in the lungs of SARS-CoV-infected mice. Surprisingly Th1 (and Th2) cytokines were not detectable, and there was little local accumulation of leukocytes and no obvious clinical signs of pulmonary dysfunction. Moreover, beige, CD1-/-, and RAG1-/- mice cleared the virus normally. Infection spread to the brain as it was cleared from the lung, again without leukocyte accumulation. Infected mice had a relative failure to thrive, gaining weight significantly more slowly than uninfected mice. These data indicate that C57BL/6 mice support transient nonfatal systemic infection with SARS-CoV in the lung, which is able to disseminate to brain. In this species, proinflammatory chemokines may coordinate a rapid and highly effective innate antiviral response in the lung, but NK cells and adaptive cellular immunity are not required for viral clearance.

Clostridium perfringens enterotoxin utilizes two structurally related membrane proteins as functional receptors in vivo

Human and mouse cDNAs showing homology to the Clostridium perfringens enterotoxin (CPE) receptor gene (CPE-R) from Vero cells (DDBJ/EMBL/GenBankTM accession no. D88492) (Katahira, J., Inoue, N., Horiguchi, Y., Matsuda, M., and Sugimoto, N. (1997) J. Cell Biol. 136, 1239-1247) were cloned. They were classified into two groups, the Vero cell CPE receptor homologues and rat androgen withdrawal apoptosis protein (RVP1; accession no. M74067) homologues, based on the similarities of primary amino acid sequences. L929 cells that were originally insensitive to CPE became sensitive to CPE on their transfection with cDNAs encoding either the CPE receptor or RVP1 homologues, indicating that these gene products are not only structurally similar but also functionally active as receptors for CPE. By binding assay, the human RVP1 homologue showed differences in affinity and capacity of binding from those of the human CPE receptor. Northern blot analysis showed that mouse homologues of the CPE receptor and RVP1 are expressed abundantly in mouse small intestine. The expression of CPE-R mRNA in the small intestine was restricted to cryptic enterocytes, indicating that the CPE receptor is expressed in intestinal epithelial cells. These results are consistent with reports that CPE binds to the small intestinal cells via two different kinds of receptors. High levels of expression of CPE-R and/or RVP1 mRNA were also detected in other organs, including the lungs, liver, and kidneys, but only low levels were expressed in heart and skeletal muscles. These results indicate that CPE uses structurally related cellular proteins as functional receptors in vivo and that organs that have not so far been recognized as CPE-sensitive have the potential to be targets of CPE.

Clostridium perfringens type A enterotoxin (CPE): more than just explosive diarrhea

The bacterial pathogen Clostridium perfringens is the most prolific toxin-producing species within the clostridial group. The toxins are responsible for a wide variety of human and veterinary diseases, many of which are lethal. C. perfringens type A strains are also associated with one of the most common forms of food-borne illness (FBI). The toxicosis results from the production and gastrointestinal absorption of a protein-enterotoxin known as CPE. The regulation, expression, and mechanism of action of CPE has been of considerable interest as the protein is unique. CPE expression is sporulation associated, although the mechanism of cpe-gene regulation is not fully elucidated. Cloning studies suggest the involvement of global regulators, but these have not been identified. Although very few type A strains are naturally enterotoxigenic, the cpe gene appears highly conserved. In FBI strains, cpe is chromosomally encoded; whereas in veterinary strains, cpe may be plasmid-encoded. Variation in cpe location suggests the involvement of transposable genetic element(s). CPE-like proteins are produced by some C. perfringens types C and D; and silent remnants of the cpe gene can be found in C. perfringens type E strains associated with the iota toxin gene. CPE has received attention for its biomedical importance. The toxin has been implicated in sudden infant death syndrome (SIDS) because of its superantigenic nature. CPE can destroy a wide variety of cell types both in vitro and in vivo, suggesting that it could have potential in the construction of immunotoxins to neoplastic cells. It is obvious that CPE is an interesting protein that deserves continued attention.

Can superantigens trigger sudden infant death?

A majority of sudden infant death syndrome (SIDS) victims have respiratory or gastrointestinal infections prior to death. This has led to an investigation of the role of pathogenic bacteria and the potentially lethal toxins they produce as triggers for sudden infant death. A small group of bacteria have been consistently identified in SIDS victims as compared to controls, and remarkably, three of these produce superantigenic toxins. Superantigens exert a powerful effect on the immune system, stimulating T-cells, which subsequently induces the formation of large amounts of cytokines. Generation of an overwhelming inflammatory response may lead to death by shock, or other, as yet unrecognized effects of the toxin on the respiratory or cardiac systems. A SIDS/superantigen model is proposed which may explain many of the pathological characteristics of SIDS and establish quantifiable markers for SIDS.

Sudden infant death syndrome (SIDS): are common bacterial toxins responsible, and do they have a vaccine potential?

Despite extensive research, no unifying concept has satisfactorily explained the cause of the sudden infant death syndrome (SIDS). The details are briefly outlined of some of the evidence supporting the hypothesis that common bacterial toxins are important in the aetiology of SIDS. These bacterial toxins act as triggers to initiate a biochemical cascade resulting in death. Data from four research groups, each working independently, indicated that the bacteria Clostridium perfringens, Escherichia coli, Staphylococcus aureus, Streptococcus spp. and Enterococcus spp. were present in higher numbers in infants who had suffered SIDS than in control infants. Certainly more detailed studies need to be performed on the role of bacterial infections in infants. There are many implications arising from this work, particularly the use of vaccination as a means of reducing infections, and consequently the number of SIDS deaths.

Clostridium perfringens enterotoxin acts by producing small molecule permeability alterations in plasma membranes

Clostridium perfringens enterotoxin (CPE) appears to utilize a unique mechanism of action to directly affect the plasma membrane permeability of mammalian cells. CPE action involves a multi-step action which culminates in cytotoxicity. Initially CPE binds to a protein receptor on mammalian plasma membranes. The membrane-bound CPE then becomes progressively more resistant to release by proteases (a phenomenon consistent with the insertion of CPE into membranes). This 'inserted' CPE then participates in the formation of a large complex in plasma membranes which contains one CPE: one 70 kDa membrane protein: one 50 kDa membrane protein. Upon formation of large complex, plasma membranes become freely permeable to small molecules such as ions and amino acids. This CPE-induced disruption of the cellular colloid-osmotic equilibrium then causes secondary cellular effects and cell death.

Evidence that alterations in small molecule permeability are involved in the Clostridium perfringens type A enterotoxin-induced inhibition of macromolecular synthesis in Vero cells

The mechanism by which Clostridium perfringens enterotoxin (CPE) simultaneously inhibits RNA, DNA, and protein synthesis is unknown. In the current study the possible involvement of small molecule permeability alterations in CPE-induced inhibition of macromolecular synthesis was examined. Vero cells CPE-treated in minimal essential medium (MEM) completely ceased net precursor incorporation into RNA and protein within 15 minutes of CPE treatment. However, RNA and protein synthesis continued for at least 30 minutes in Vero cells CPE-treated in buffer (ICIB) approximating intracellular concentrations of most ions. Addition of intracellular concentrations of amino acids to ICIB (ICIB-AA) caused a further small but detectable increase in protein synthesis in CPE-treated cells. ICIB did not affect CPE-specific binding levels or rates. Similar small molecule permeability changes (i.e., 86Rb-release) were observed in cells CPE-treated in either ICIB or in Hanks' balanced salt solution. Collectively these findings suggest that CPE-treatment of cells in ICIB-AA ameliorates CPE-induced changes in intracellular concentrations of ions and amino acids and permits the continuation of RNA and protein synthesis. These results are consistent with and support the hypothesis that permeability alterations for small molecules are involved in the CPE-induced inhibition of precursor incorporation into macromolecules in Vero cells.

Preliminary evidence that Clostridium perfringens type A enterotoxin is present in a 160,000-Mr complex in mammalian membranes

Clostridium perfringens type A 125I-enterotoxin (125I-CPE) was bound to rabbit intestinal brush border membranes (BBMs) or Vero cells and then solubilized with 3-[(3-cholamidopropyl)dimethyl-ammonio]-1-propanesulfonate (CHAPS). Solubilized radioactivity was analyzed by gel filtration chromatography on a Sepharose 4B column or by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) without sample boiling and autoradiography. Specifically bound 125I-CPE extracted from either BBMs or Vero cells was primarily associated with a complex of approximately 160,000 Mr. The CPE complex was partially purified by gel filtration or SDS-PAGE without sample boiling. SDS-PAGE analysis with sample boiling of the partially purified 125I-CPE complex from Vero cells or BBMs suggested that CPE complex contains both a 50,000-Mr protein and a 70,000-Mr protein in approximately equimolar amounts. This result is supported by affinity chromatography with CPE immobilized on Sepharose 4B, which showed the specific interaction of similar size proteins with CPE. The simplest explanation for these results is that CPE (Mr 35,000) interacts with 50,000-Mr and 70,000-Mr eucaryotic proteins to form a membrane-dependent complex of approximately 160,000 Mr. These results suggest that the receptor or target site(s) or both for CPE are similar in both BBMs and Vero cells. The significance of these findings in terms of CPE binding, insertion, and biologic action is discussed.

Clostridium perfringens enterotoxin

Current knowledge of CPE action is briefly summarized in Figure 1. After specific binding to a protein receptor(s), the entire CPE molecule rapidly inserts into membranes forming a complex of 150,000 Mr. Almost simultaneously with insertion, there is a sudden change in ion fluxes. The molecular events behind the induction of ion flux changes remain undefined, but might involve either direct formation of membrane pores by CPE or activation of pre-existing membrane pores. As intracellular ion levels change, cellular metabolism is affected and processes such as macromolecular syntheses are inhibited. One of the ion flux effects resulting from CPE treatment involves increased Ca2+ influx; as more Ca2+ enters the cell, morphologic damage and permeability alterations for larger molecules occur. It remains to be determined if both morphologic damage and larger permeability alterations are necessarily linked but, for example, it could be envisioned that CPE-induced Ca2+ influx causes a cytoskeletal collapse leading to altered membrane permeability. The cytoskeleton has been shown to be sensitive to intracellular Ca2+ levels and is important in normal membrane structure/function relationships. As the cumulative effects of CPE inhibit cellular metabolism, cell death occurs. The precise irreversible CPE lethal action still must be identified. As CPE-treated intestinal epithelial cells die in vivo, histopathologic damage appears. This damage results in loss of normal intestinal function causing secretion of fluids and electrolytes. This effect is clinically manifested as diarrhea. The strongly cytotoxic action of CPE clearly distinguished the action enterotoxin from STa or CT.(ABSTRACT TRUNCATED AT 250 WORDS)