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PubMedDate not supplied

[Bacterial enterotoxin receptors].

Bacterial enterotoxin receptors. Enteric bacterial toxins display a great diversity in their structure, molecular weight and mechanism of action. The interaction of enterotoxins with the intestinal mucosa either leads to a direct effect on the cell membrane or an effect on signal transduction within eukaryotic cells. However, before a toxin can affect a cell, it must after its secretion by a microorganism, recognise and bind to a specific surface molecule, its receptor. Membrane receptors of bacterial enterotoxins have been identified as protein, glycoprotein or glycolipid in nature. The chemical nature of the molecules acting as receptors is crucial and during evolution they have been carefully selected. Some toxins, after their interaction with a receptor molecule, will transduce a signal across the cell membrane while remaining at the cell surface. Other toxins, after this initial binding step with a receptor, will be internalised. Others can form pores leading to leakage of cellular components and cell lysis. Receptors that have been identified often comprise a saccharidic chain that is directly involved in the recognition and binding of the toxin. Today, models explaining toxin-receptor interactions are more complex, including multistep events. This review summarises the knowledge of the interactions between bacterial toxins and membrane receptors present on intestinal mucosa.

Animals↗
PubMed1996

The significance of Ser1029 of the heat-stable enterotoxin receptor (STaR): relation of STa-mediated guanylyl cyclase activation and signaling by phorbol myristate acetate.

To characterize Ser1029 in STaR at a consensus sequence of phosphorylation site by PKC, two mutants of mS1029A with replacement of Ser1029 to Ala1029 and C delta 1029 lacking 22 amino acids including Ser1029 were prepared. Preincubation of the wild type-STaR (wt-STaR) transfectant with 1 microM PMA caused additional STa-mediated guanylyl cyclase (GC) activation compared to control, whereas the mS1029A- and C delta 1029-transfected cells did not show a similar enhanced GC activation by PMA. After metabolic labeling with [32P]phosphate, transfected cells with wt-STaR and mutants were incubated with 1 microM PMA. Subsequent 32P-radiolabeled proteins were immunoprecipitated using anti-STaR antibody, and analyzed by autoradiography after separation on SDS-PAGE. The immunoprecipitated wt-STaR but not mS1029A and C delta 1029 had a significant radioactivity. These results suggest that the effect of PMA on wt-STaR transfectants may be caused by phosphorylation of Ser1029. The C delta 1012 mutant, with further truncation (Gln1012-Phe1050) of the carboxy terminus, did not show STa-mediated GC activation. Based on these data, these 17 amino acids (Gln1012-Ala1028), essential for signaling of GC activation by STa, have an abundance of basic amino acids which might be functionally influenced by phosphorylation of Ser1029.

Amino Acid Sequence↗
PubMed1991

Isolation and expression of a guanylate cyclase-coupled heat stable enterotoxin receptor cDNA from a human colonic cell line.

Heat stable enterotoxins (STs) are low molecular-weight peptides secreted by enterotoxigenic bacteria. One type of these enterotoxins (STa) induces intestinal secretion leading to acute diarrhea by binding to a membrane form of guanylate cyclase. We have isolated a cDNA from a human colonic cell line, T84, encoding for a guanylate cyclase-coupled enterotoxin receptor (STaR). The predicted amino acid sequence of the human STa receptor is 81% identical with the previously cloned enterotoxin receptor (GC-C) from rat intestine. COS-7 cells transiently transfected with the cloned cDNA expressed specific concentration-dependent response to STa as measured by cyclic GMP accumulation and is about 20 times more sensitive to the stimulation by STa than has been shown for GC-C.

Amino Acid Sequence↗
PubMed1991

Human major histocompatibility complex class II-negative colon carcinoma cells present staphylococcal superantigens to cytotoxic T lymphocytes: evidence for a novel enterotoxin receptor.

The staphylococcal enterotoxins (SE) bind to major histocompatibility complex (MHC) class II molecules on target cells and activate T cells expressing particular T cell receptor V beta sequences. In this report we demonstrate that SE bind to the MHC class II- SW620, Colo320DM and WiDr human colon carcinoma cell lines and direct cytotoxic T lymphocytes (CTL) to mediate strong target cell killing. Flow cytometry analysis, immunoprecipitation and Northern blotting experiments failed to demonstrate any surface expression of HLA-DR, HLA-DP and HLA-DQ isotypes on the SW620 colon carcinoma cell line, whereas abundant expression of these isotypes was seen on Raji cells, SEB and SEC1 were efficiently presented at picomolar concentration by the MHC class II- colon carcinoma cells and MHC class II+ Raji cells, whereas SEA and SED were preferentially presented on the MHC class II+ Raji cells. An anti-HLA-DR monoclonal antibody inhibited SEB-induced CTL targeting to Raji, but did not influence the killing of SW620 cells. Our data suggests the existence of functionally active SE-binding structures on human colon carcinoma cells which are distinct from the conventional MHC class II molecules. The possibility that these putative new SE receptors play a role in the enterotoxin action of SE must be considered.

Antigens, Bacterial↗
PubMed1989

Escherichia coli enterotoxin receptors: localization in opossum kidney, intestine, and testis.

The distribution of receptors for Escherichia coli enterotoxin were examined in opossum kidney, intestine, and testis. E. coli enterotoxin stimulated guanosine 3',5'-cyclic monophosphate (cGMP) production in renal cortex, testis, and small intestinal mucosa but had only a small effect in the colon. Atrial natriuretic factor enhanced the cGMP content of renal cortex and small intestine but had no effect on testis or colon. The enterotoxin receptors were observed to be localized in proximal tubules, to epithelial cells of crypts and villi of small intestine, to crypts of colon, and in seminiferous tubules. Both convoluted and straight portions of proximal tubules exhibited specific binding sites for 125I-labeled enterotoxin. Glomeruli and distal tubules did not have receptors. Binding of 125I-enterotoxin to brush-border membranes of kidney cortex or intestinal mucosa and to testis membranes was markedly temperature dependent. The binding affinities of these receptors for E. coli enterotoxin were similar (i.e., IC50 approximately equal to 0.4-0.5 nM). Daily administration of 20 micrograms of enterotoxin intramuscularly to opossums increased urine cGMP excretion with no apparent changes in urine volume, Na+, or K+ excretion. Thus receptors for heat-stable enterotoxins are localized to proximal tubules of kidney and to enterocytes and seminiferous tubules of intestine and testis, respectively. Apical membranes may be the site of enterotoxin receptors in these epithelia.

Animals↗
PubMed1993

Ligand-based histochemical localization and capture of cells expressing heat-stable enterotoxin receptors.

The heat stable enterotoxins (ST) of enterotoxigenic Escherichia coli (ETEC) cause diarrhoea by binding specific intestinal receptors. Precise histochemical localization of ST receptors could provide more information about the pathophysiology of secretory diarrhoea and the role of ST receptors in normal biology. To accomplish this, we quantitatively coupled biotin to the N-terminus of ST1b using biotin-X-X-N-hydroxysuccinimide ester. The derivatized toxin (BST) has an apparent Kd of 11.7 +/- 10 nM for rat brush border receptors. We used BST in an affinity panning cell-capture system, to validate its ability to discriminate between receptor-positive and receptor-negative cells. Cell lines expressing ST receptors (human colon carcinoma T84, and COS cells transfected with guanylyl cyclase-C (GC-C) ST receptor cDNA) were captured to streptavidin and anti-biotin-coated plates with high efficiency and specificity. This system provides a novel approach to screening cells for the presence of unique ST-binding proteins. BST was then used with streptavidin-gold to demonstrate the cellular topography of ST receptors at the light microscopic level. Villus enterocytes were intensely stained, but only a faint signal was observed in upper crypts of rat small intestine. Thus, a gradient of increasing receptor density was seen as upper crypt cells matured into villus enterocytes. Higher magnification revealed that ST receptors are concentrated at the apical aspect of villus enterocytes. Recently, guanylin, a putative endogenous ligand for ST receptors, has been localized to Paneth cells, at the base of intestinal crypts. Thus, ST receptors are concentrated in villus enterocytes, while guanylin appears to be produced at the base of the crypts.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed2001

Colonocyte basolateral membranes contain Escherichia coli heat-stable enterotoxin receptors.

Heat-stable enterotoxin (ST(a)) elaborated by E. coli is a major cause of diarrhea. The transmembrane protein guanylyl cyclase C (GC-C) is the acknowledged receptor for ST(a) and for the mammalian peptides guanylin and uroguanylin. Binding to GC-C results in generation of cGMP, activation of type II cGMP-dependent protein kinase, phosphorylation of CFTR and increased chloride and bicarbonate secretion. We had previously shown that ST(a) receptors (GC-C) are found on the brush border membranes of small intestinal enterocytes and of colonocytes. However, since it has subsequently been shown that the endogenous ligands for these receptors, guanylin and uroguanylin, circulate in blood, we proposed the existence of ST(a) binding sites on the basolateral membranes (BLM) of colonocytes. Specific binding of 125I-ST(a) to rat colonocyte BLM was seen. The kinetics of binding to the BLM were similar to binding to BBM. The nature of the BLM receptor is unknown. This suggests that circulating guanylin and uroguanylin, analogues of ST(a), may also function via the basolateral surface.

Animals↗
PubMed1998

Brain capillary endothelial cells express MBEC1, a protein that is related to the Clostridium perfringens enterotoxin receptors.

Brain capillary endothelial cells compose the blood-brain barrier, which has a crucial role in maintaining the normal extracellular environment of the central nervous system. We have developed a method to isolate endothelial cells from mouse brain and maintain them in a relatively pure primary culture. Using a subtractive hybridization technique, a novel cDNA, termed MBEC1 (mouse brain endothelial cell 1), has been isolated from the cultured mouse brain capillary endothelial cells. MBEC1 is a 1435-bp cDNA predicted to encode a protein of 218 amino acids. The predicted protein is similar to those of the newly characterized Clostridium perfringens enterotoxin receptors and is the mouse homolog of a recently described human cDNA clone, which is hemizygously deleted in individuals with velo-cardio-facial syndrome and DiGeorge syndrome. MBEC1 was expressed in our cultured MBEC, in freshly isolated MBEC, in a variety of mouse organs, and in mouse embryos as early as embryonic Day 7. In situ hybridization and immunocytochemical analyses revealed the presence of the MBEC1 mRNA and its protein product in brain capillary endothelial cells, as well as in a subset of other endothelial and epithelial cells. Moreover, developmental regulation of expression of MBEC1 was present in respiratory epithelium. Our research thus provides a new molecule for further study of the function of normal and abnormal blood-brain barrier as well as of other specialized endothelia and epithelia.

Amino Acid Sequence↗
PubMed1990

Guanylyl cyclase is a heat-stable enterotoxin receptor.

Plasma membrane forms of guanylyl cyclase have been shown to function as natriuretic peptide receptors. We describe a new clone (GC-C) encoding a guanylyl cyclase receptor for heat-stable enterotoxin. GC-C encodes a protein containing an extracellular amino acid sequence divergent from that of previously cloned guanylyl cyclases; however, the protein retains the intracellular protein kinase-like and cyclase catalytic domains. Expression of GC-C in COS-7 cells results in high guanylyl cyclase activity. In addition, heat-stable enterotoxin from E. coli, but not natriuretic peptides, causes marked elevations of cyclic GMP and is specifically bound by cells transfected with GC-C. The enterotoxin fails to elevate cyclic GMP in nontransfected cells or in cells transfected with the natriuretic peptide/guanylyl cyclase receptors. These results show that a heat-stable enterotoxin receptor responsible for acute diarrhea is a plasma membrane form of guanylyl cyclase.

1-Methyl-3-isobutylxanthine↗
PubMed1992

A gradient in expression of the Escherichia coli heat-stable enterotoxin receptor exists along the villus-to-crypt axis of rat small intestine.

Binding of Escherichia coli heat-stable enterotoxin to its receptor is critical to the initiation of toxin-induced secretion and diarrheal disease; it is also likely, however, that this receptor binds an endogenous ligand. In order to characterize the expression of the heat-stable enterotoxin receptor in the small intestine, we isolated epithelial cells from villus tip to crypt in rat jejunum and ileum. Binding of radiolabeled toxin was maximal in the villus preparations and gradually decreased along the villus-to-crypt axis, paralleling the decline of sucrase activity. Northern blots of total RNA identified a single heat stable enterotoxin receptor transcript (3.8 kb), predominantly in the villus cell fractions. In situ hybridization demonstrated clear signal in the villus cells with no apparent signal in the crypt cells, lamina propria or muscularis. Expression of this receptor was greatest after enterocytes leave the proliferative cycle and enter villi. This pattern of gene and protein expression may reflect a role of this receptor in binding endogenous ligands which in turn may regulate intestinal ion flux along the villus-to-crypt axis.

Animals↗
PubMed1996

Identification of ligand recognition sites in heat-stable enterotoxin receptor, membrane-associated guanylyl cyclase C by site-directed mutational analysis.

Guanylyl cyclase C (STaR), a receptor protein for heat-stable enterotoxin (STa) elaborated by Escherichia coli, is associated with and spans the plasma membrane of mammalian intestinal cells. The extracellular domain functions in the binding of STa and the association of each domain to an oligomeric form. Two amino acid residues, Arg-136 and Asp-347, were identified as the residues binding to STa in the extracellular domain of pig STaR by site-directed mutagenesis and analysis of expression on 293T cells. Replacement of these residues by other amino acid residues resulted in the loss of binding of pig STaR to STa, and as a result, STa-induced guanylyl cyclase activity was eliminated. Furthermore, mutation in a region (from Asp-347 to Val-401) which is close to the transmembrane domain caused a significant reduction in both STa-binding activity and guanylyl cyclase catalytic activity. These results suggest that the region adjacent to the transmembrane domain plays an important role in facilitating a favorable conformation of STaR for STa binding.

Animals↗
PubMed1996

Expression of the extracellular domain of the human heat-stable enterotoxin receptor in Escherichia coli and generation of neutralizing antibodies.

The entire extracellular domain of the human heat-stable enterotoxin (ST) receptor as well as a truncated N-terminal domain were cloned as glutathione S-transferase fusion proteins and expressed in Escherichia coli. The recombinant fusion proteins were purified from both the cytosol and the inclusion body fractions by selective detergent extraction followed by glutathione-agarose affinity chromatography. The purified protein, corresponding to the entire extracellular domain, bound the stable toxin peptide with an affinity comparable to that of the native receptor characterized from the human colonic T84 cell line. No binding was observed with the N-terminal truncated fragment of the receptor under similar conditions. Polyclonal antibodies were raised to the entire extracellular domain fusion protein as well as the truncated extracellular domain fusion protein, and the antibodies were purified by affinity chromatography. Addition of the purified antibodies to T84 cells inhibited ST binding and abolished ST-mediated cGMP production, indicating that critical epitopes involved in ligand interaction are present in the N-terminal fragment of the receptor. Purified antibodies recognized a single protein of Mr 160,000 Da on Western blotting with T84 membranes, corresponding to a size of the native glycosylated receptor in T84 cells. These studies are the first report of the expression, purification, and characterization of any member of the guanylyl cyclase family of receptors in E. coli and show that binding of the toxin to the extracellular domain of the receptor is possible in the absence of any posttranslational modifications such as glycosylation. The recombinant fusion proteins as well as the antibodies that we have generated could serve as useful tools in the identification of critical residues of the extracellular domain involved in ligand interaction.

Antibodies↗
PubMed1987

Anti-idiotypic antibodies as staphylococcal enterotoxin receptor probes on monkey mast cells.

The immediate-type skin reaction in unsensitized monkeys upon challenge with staphylococcal enterotoxin B (SEB) was studied to define the role of mast cell receptors in the action of the toxin. For this purpose anti-idiotypic antibodies (anti-Id) were raised in BALB/c mice against monoclonal anti-SEB antibodies and purified by idiotype affinity chromatography. Anti-Id completely abolished skin reactions upon challenge with SEB without having biological functions itself. The data are compatible with the view that receptors for staphylococcal enterotoxin actually exist on the mast cell membrane of primates and anti-Id may be of potential value to influence the course of staphylococcal enterotoxin-mediated effects.

Animals↗
PubMed2001

Escherichia coli heat stable enterotoxin receptors & guanylyl cyclase activity in the intestinal brush border membrane of hamsters & guinea pigs.

BACKGROUND & OBJECTIVES: Although Escherichia coli heat stable enterotoxin (STa) causes diarrhoea in laboratory animals, no studies were done to find out the species specific variation of distribution of the STa receptors in laboratory animals. The present investigation evaluates the density of STa receptors and the guanylyl cyclase (GC) activity in the small intestinal epithelial cells of hamsters and guinea pigs. METHODS: Brush border membrane (BBM) was prepared from the small intestines of hamsters and guinea pigs. Receptor binding assay, GC assay and autoradiography were performed to determine the density of STa receptors, the GC activity and molecular weights of the STa binding proteins respectively. RESULTS: The receptor densities, per mg BBM protein at equilibrium, were found to be 4.1 x 10(9) and 1.5 x 10(12) in hamsters and guinea pigs respectively. The GC activity was found to be lower in STa treated hamster BBM compared to that of guinea pig. Scatchard analysis of the stoichiometric data showed a linear plot, and STa bound with association constants of 0.31 x 10(12) M-1 and 1.04 x 10(12) M-1 in hamsters and guinea pigs respectively. Autoradiographic analysis of the SDS-PAGE, revealed that 125I-STa bound apparently to a 45 kDa membrane protein in hamster and a 115 kDa membrane protein in guinea pig. INTERPRETATION & CONCLUSIONS: It appears that a lower density of STa receptor exists in hamsters compared to that in guinea pigs. STa binds with a single population of STa receptors in each species with different ligand binding affinities. Also, the molecular weights of the STa binding proteins differ in these species. Moreover, the GC activity was found to be lower in hamsters than in guinea pigs.

Animals↗
PubMed1992

Novel sites for expression of an Escherichia coli heat-stable enterotoxin receptor in the developing rat.

Escherichia coli heat-stable enterotoxin (STa) mediates diarrheal disease by binding to and activating an intestinal transmembrane receptor, guanylate cyclase C (GC-C). To test the hypotheses that there was 1) increased perinatal expression of GC-C in rat intestine and 2) GC-C expression and STa binding in extraintestinal tissues of immature rat, we prepared whole cell membranes and total RNA from jejunum, ileum, colon, liver, kidney, heart, lung, brain, testis, and placenta of rats ranging in age from 12 days gestation to adult. Northern analysis demonstrated the presence of a unique 3.8-kb mRNA transcript at all ages in the jejunum, ileum, colon, and, to a lesser degree, in the testis. GC-C was also detected by Northern analysis in liver (from gestational age 18 days through 14 days postnatal) and in placenta. Steady-state mRNA encoding GC-C was not detected by Northern analysis in the other organs examined. GC-C-specific mRNA expression was greatest in the perinatal period in the jejunum, ileum, and liver. Specific binding of 125I-labeled STa was found in each of the tissue membranes in which GC-C mRNA was present; binding was not present in those tissues that had no detectable GC-C mRNA. The existence of GC-C in extraintestinal organs in the rat, and the development changes in GC-C expression support our hypothesis that GC-C, apart from its role as an STa receptor in mediating diarrheal disease, also serves as a receptor for an endogenous ligand.

Animals↗
PubMed1989

Regulation of particulate guanylate cyclase by Escherichia coli heat-stable enterotoxin: receptor binding and enzyme kinetics.

1. Escherichia coli heat-stable enterotoxin (ST) induces a secretory diarrhea by binding to receptors on brush borders of intestinal villus cells, activating particulate guanylate cyclase and increasing intracellular concentrations of guanosine 3',5'-cyclic monophosphate (cyclic GMP). 2. However, little is known concerning coupling of receptor-ligand interaction to enzyme activation. 3. This study compares the kinetics of toxin-receptor binding and enzyme activation to better understand this transmembrane signal cascade. 4. Toxin receptor binding was linear and saturable with 50% of maximum displacement of [125I]ST by unlabeled toxin observed at 1.1 x 10(-7) M. ST increased the maximum velocity (Vmax) of guanylate cyclase with magnesium or manganese as the cation substrate without altering the affinity of the enzyme for its substrate or its positive cooperativity. 5. The concentration of toxin yielding half-maximum stimulation of guanylate cyclase was 1.2 x 10(-6) M, 10-fold higher than the affinity of the ligand for its receptor. 6. These data are consistent with the suggestion that ST-receptor interaction is coupled to activation of particulate guanylate cyclase. 7. However, the discrepancy between the affinity of ST for its receptor and its efficacy in activating the enzyme suggests that this coupling is complex. 8. Possible mechanisms underlying this coupling are discussed.

Animals↗
PubMed2001

Expression of Clostridium perfringens enterotoxin receptors claudin-3 and claudin-4 in prostate cancer epithelium.

The mRNA for Rvp.1 (rat ventral prostate) increases in abundance before gland involution after androgen deprivation. Rvp.1 is homologous to CPE-R, the high-affinity intestinal epithelial receptor for Clostridium perfringens enterotoxin (CPE), and is sufficient to mediate CPE binding and trigger subsequent toxin-mediated cytolysis. Rvp.1 (claudin-3) and CPE-R (claudin-4) are members of a larger family of transmembrane tissue-specific claudin proteins that are essential components of intercellular tight junction structures regulating paracellular ion flux. However, claudin-3 and claudin-4 are the only family members capable of mediating CPE binding and cytolysis. The present study was designed to study the expression of claudin-3 and claudin-4 in human prostate tissue as potential targets for CPE toxin-mediated therapy for prostate cancer. On human multiple-tissue Northern blot analysis, mRNAs for both claudin-3 and claudin-4 were expressed at high levels in prostate tissue. In normal prostate tissue, expression of claudin-3 was localized exclusively within acinar epithelial cells by in situ mRNA hybridization. Compared with expression within prostate epithelial cells in surrounding normal glandular tissue, expression of claudin-3 mRNA remained high in the epithelium of prostate adenocarcinoma (10 of 10) and prostatic intraepithelial neoplasia (five of five). Prostate adenocarcinoma cells metastatic to bone were obtained from a patient with disease progression during antiandrogen therapy. These metastatic cells were prostate-specific antigen-positive by immunohistochemical staining and also expressed functional CPE receptors as measured by sensitivity to CPE-induced cell lysis. The persistent high level of claudin-3 expression in prostate adenocarcinoma and functional cytotoxicity of CPE in metastatic androgen-independent prostate adenocarcinoma suggests a new potential therapeutic strategy for prostate cancer.

Adenocarcinoma↗