Morphological and biochemical study of cytoskeletal changes in cultured cells after extracellular application of Clostridium novyi alpha-toxin

Clostridium novyi’s Alpha-Toxin Changes Proteome and Phosphoproteome of HEp-2 Cells

C. novyi type A produces the alpha-toxin (TcnA) that belongs to the large clostridial glucosylating toxins (LCGTs) and is able to modify small GTPases by N-acetylglucosamination on conserved threonine residues. In contrast, other LCGTs including Clostridioides difficile toxin A and toxin B (TcdA; TcdB) modify small GTPases by mono-o-glucosylation. Both modifications inactivate the GTPases and cause strong effects on GTPase-dependent signal transduction pathways and the consequent reorganization of the actin cytoskeleton leading to cell rounding and finally cell death. However, the effect of TcnA on target cells is largely unexplored. Therefore, we performed a comprehensive screening approach of TcnA treated HEp-2 cells and analyzed their proteome and their phosphoproteome using LC-MS-based methods. With this data-dependent acquisition (DDA) approach, 5086 proteins and 9427 phosphosites could be identified and quantified. Of these, 35 proteins were found to be significantly altered after toxin treatment, and 1832 phosphosites were responsive to TcnA treatment. By analyzing the TcnA-induced proteomic effects of HEp-2 cells, 23 common signaling pathways were identified to be altered, including Actin Cytoskeleton Signaling, Epithelial Adherens Junction Signaling, and Signaling by Rho Family GTPases. All these pathways are also regulated after application of TcdA or TcdB of C. difficile. After TcnA treatment the regulation on phosphorylation level was much stronger compared to the proteome level, in terms of both strength of regulation and the number of regulated phosphosites. Interestingly, various signaling pathways such as Signaling by Rho Family GTPases or Integrin Signaling were activated on proteome level while being inhibited on phosphorylation level or vice versa as observed for the Role of BRCA1 in DNA Damage Response. ZIP kinase, as well as Calmodulin-dependent protein kinases IV & II, were observed as activated while Aurora-A kinase and CDK kinases tended to be inhibited in cells treated with TcnA based on their substrate regulation pattern.

Pathobiology and diagnosis of clostridial hepatitis in animals

Clostridia can cause hepatic damage in domestic livestock, and wild and laboratory animals. Clostridium novyi type B causes infectious necrotic hepatitis (INH) in sheep and less frequently in other species. Spores of C. novyi type B can be present in soil; after ingestion, they reach the liver via portal circulation where they persist in phagocytic cells. Following liver damage, frequently caused by migrating parasites, local anaerobic conditions allow germination of the clostridial spores and production of toxins. C. novyi type B alpha toxin causes necrotizing hepatitis and extensive edema, congestion, and hemorrhage in multiple organs. Clostridium haemolyticum causes bacillary hemoglobinuria (BH) in cattle, sheep, and rarely, horses. Beta toxin is the main virulence factor of C. haemolyticum, causing hepatic necrosis and hemolysis. Clostridium piliforme, the causal agent of Tyzzer disease (TD), is the only gram-negative and obligate intracellular pathogenic clostridia. TD occurs in multiple species, but it is more frequent in foals, lagomorphs, and laboratory animals. The mode of transmission is fecal-oral, with ingestion of spores from a fecal-contaminated environment. In affected animals, C. piliforme proliferates in the intestinal mucosa, resulting in necrosis, and then disseminates to the liver and other organs. Virulence factors for this microorganism have not been identified, to date. Given the peracute or acute nature of clostridial hepatitis in animals, treatment is rarely effective. However, INH and BH can be prevented, and should be controlled by vaccination and control of liver flukes. To date, no vaccine is available to prevent TD.

Vaccine Production to Protect Animals Against Pathogenic Clostridia

Clostridium is a broad genus of anaerobic, spore-forming, rod-shaped, Gram-positive bacteria that can be found in different environments all around the world. The genus includes human and animal pathogens that produce potent exotoxins that cause rapid and potentially fatal diseases responsible for countless human casualties and billion-dollar annual loss to the agricultural sector. Diseases include botulism, tetanus, enterotoxemia, gas gangrene, necrotic enteritis, pseudomembranous colitis, blackleg, and black disease, which are caused by pathogenic Clostridium. Due to their ability to sporulate, they cannot be eradicated from the environment. As such, immunization with toxoid or bacterin-toxoid vaccines is the only protective method against infection. Toxins recovered from Clostridium cultures are inactivated to form toxoids, which are then formulated into multivalent vaccines. This review discusses the toxins, diseases, and toxoid production processes of the most common pathogenic Clostridium species, including Clostridiumbotulinum, Clostridiumtetani, Clostridiumperfringens, Clostridiumchauvoei, Clostridiumsepticum, Clostridiumnovyi and Clostridiumhemolyticum.

Ostreocin-D impact on globular actin of intact cells

Ostreocin-D, discovered in the past decade, is a marine toxin produced by dinoflagellates. It shares structure with palytoxin, a toxic compound responsible for the seafood intoxication named clupeotoxism. At the cellular level, the action sites and pharmacological effects for ostreocin-D are still almost unknown. Previously, we demonstrated that these toxins change the filamentous actin cytoskeleton, which is essential for multiple cellular functions. However, nothing has yet been reported about what happens with the unpolymerized actin pool. Here (i) the effects induced by ostreocin-D on unpolymerized actin, (ii) the Ca2+ role in such a process, and (iii) the cytotoxic activity of ostreocin-D on the human neuroblastoma BE(2)-M17 cell line are shown for the first time. Fluorescently labeled DNase I was used for staining of monomeric actin prior to detection with both laser-scanning cytometry and confocal microscopy techniques. Cellular viability was tested through a microplate metabolic activity assay. Ostreocin-D elicited a rearrangement of monomeric actin toward the nuclear region. This event was not accompanied by changes in its content. In addition, the presence or absence of external Ca2+ did not change these results. This toxin was also found to cause a decrease in the viability of neuroblastoma cells, which was inhibited by the specific blocker of Na+/K+-ATPase, ouabain. All these responses were comparable to those obtained with palytoxin under identical conditions. The data suggest that ostreocin-D modulates the unassembled actin pool, activating signal transduction pathways not related to Ca2+ influx in the same way as palytoxin.

Clostridial Rho-inhibiting protein toxins

Rho proteins are master regulators of a large array of cellular functions, including control of cell morphology, cell migration and polarity, transcriptional activation, and cell cycle progression. They are the eukaryotic targets of various bacterial protein toxins and effectors, which activate or inactivate the GTPases. Here Rho-inactivating toxins and effectors are reviewed, including the families of large clostridial cytotoxins and C3-like transferases, which inactivate Rho GTPases by glucosylation and ADP-ribosylation, respectively.

Large clostridial cytotoxins

The large clostridial cytotoxins are a family of structurally and functionally related exotoxins from Clostridium difficile (toxins A and B), C. sordellii (lethal and hemorrhagic toxin) and C. novyi (alpha-toxin). The exotoxins are major pathogenicity factors which in addition to their in vivo effects are cytotoxic to cultured cell lines causing reorganization of the cytoskeleton accompanied by morphological changes. The exotoxins are single-chain protein toxins, which are constructed of three domains: receptor-binding, translocation and catalytic domain. These domains reflect the self-mediated cell entry via receptor-mediated endocytosis, translocation into the cytoplasm, and execution of their cytotoxic activity by an inherent enzyme activity. Enzymatically, the toxins catalyze the transfer of a glucosyl moiety from UDP-glucose to the intracellular target proteins which are the Rho and Ras GTPases. The covalent attachment of the glucose moiety to a conserved threonine within the effector region of the GTPases renders the Rho-GTPases functionally inactive. Whereas the molecular mode of cytotoxic effects is fully understood, the mechanisms leading to inflammatory processes in the context of disease (e.g., antibiotic-associated pseudomembranous colitis caused by Clostridium difficile) are less clear.

Detection of Clostridium novyi type B alpha toxin by cell culture systems

Ten permanent cell lines were examined for their reaction to the Clostridium novyi alpha toxin. The action of the toxin was determined after 3 days by microscopic examination and the MTT assay. The alpha toxin exhibited the strongest effect on ESH-L cells rather than other cell lines. Vero and SFT-R cells reacted in a comparable way, but less sensitively. We were able to show that the cytopathic effect on the three types of cells was neutralised by the international standard for gas gangrene antitoxin (C. novyi) but in no case by heterologous antisera. Our results have shown that the three cell lines were specific indicators for the detection of the cytopathic effect of alpha toxin. The cytopathic effect can be measured reproducibly by the cell culture assay used. These results are suitable as the starting point for the development of the neutralisation test using cell cultures.

Aquaporin-2 expression in primary cultured rat inner medullary collecting duct cells

Cultured renal epithelial cells rapidly downregulate expression of the vasopressin-regulated water channel aquaporin-2 (AQP-2). Our aim was to define conditions that favor maintenance of AQP-2 expression in vitro without genetic manipulation. We show here that primary cultures of rat inner medullary collecting duct (IMCD) cells retain AQP-2 expression for at least 6 days when grown with dibutyryl cAMP (DBcAMP) supplementation. We also found that coating the culture dishes with type IV collagen, rather than rat-tail collagen, retards AQP-2 downregulation. Immunofluorescence and biochemical studies indicate a shuttling of AQP-2-bearing vesicles after stimulation with vasopressin or forskolin. Rab3 proteins, known to be involved in regulated exocytosis, were detected only in cells grown in the presence of DBcAMP. Using the adenylyl cyclase assay, we confirmed the functional integrity of the vasopressin V2 receptor in a broken cell preparation. Our data show that cAMP supplementation is sufficient for the maintenance of AQP-2 expression in primary cultured cells. The model system established here allows the study of the regulation of genes encoding the antidiuretic machinery at the cellular level.

The protective effect of Clostridium novyi type B alpha-toxoid against challenge with spores in guinea pigs

Clostridium novyi (C. novyi) Type B alpha-toxin was purified from culture supernatant by column chromatography, and was inactivated by formalin. A purified alpha-toxoid vaccine was prepared by mixing it with an aluminum phosphate gel adjuvant. Guinea pigs immunized twice with 4 micrograms or more of alpha-toxin survived against challenge with C. novyi Type B spores. Anti-alpha-toxin (antitoxin) titer was measured by toxin neutralization test using Vero cells. All of the guinea pigs having antitoxin titers of 10 units (U) or more at challenge were survived. In another experiment, guinea pigs were immunized with crude alpha-toxoid vaccines prepared by inactivated culture supernatant or by adding broken bacterial cells to the former. In this experiment, 10 U of antitoxin titer was the border of survival or death after challenge. Guinea pigs with antitoxin titers of less than 5 U, 5 U and 10 U died at 2, 3 to 4 and 4 days, respectively, after challenge. These results suggest that C. novyi alpha-toxin was the main protective antigen against challenge exposure to spores in guinea pigs.

Clostridium novyi alpha-toxin-catalyzed incorporation of GlcNAc into Rho subfamily proteins

The lethal and edema-inducing alpha-toxin from Clostridium novyi causes rounding up of cultured cell lines by redistribution of the actin cytoskeleton. alpha-Toxin belongs to the family of large clostridial cytotoxins that encompasses Clostridium difficile toxin A and B and the lethal toxin from Clostridium sordellii. Toxin A and toxin B have been recently identified as monoglucosyltransferases to modify the low molecular mass GTPases of the Rho subfamily (Just, I., Selzer, J., Wilm, M., Von Eichel-Streiber, C., Mann, M., and Aktories, K. (1995) Nature 375, 500-503 and Just, I., Wilm, M., Selzer, J., Rex, G., Von Eichel-Streiber, C., Mann, M., and Aktories, K. (1995) J. Biol. Chem. 270, 13932-13936). We report here the identification of the alpha-toxin-catalyzed modification of Rho. Using electrospray mass spectrometry, the mass of the modification was determined as 203 Da, consistent with a N-acetyl-hexosamine moiety. UDP-N-acetyl-glucosamine selectively served as cosubstrate for alpha-toxin-catalyzed modification into the Rho subfamily proteins Rho, Rac, Cdc42, and RhoG. The acceptor amino acid of N-acetyl-glucosaminylation was identified by mutagenesis as Thr-37 in Rho (equivalent to Thr-35 in Rac/Cdc42), which is located in the effector domain of the GTPases. C. novyi alpha-toxin seems to mediate its cytotoxic effects on cells by mimicking endogenous post-translational modification of cellular proteins.

Sequencing and analysis of the gene encoding the alpha-toxin of Clostridium novyi proves its homology to toxins A and B of Clostridium difficile

A library of total Clostridium novyi DNA was established and screened for the alpha-toxin gene (tcn alpha) by hybridization with oligonucleotides derived from a partial N-terminal sequence and by using specific antisera. Overlapping subgenic tcn alpha fragments were isolated and subsequently the total sequence of tcn alpha was determined. The 6534 nucleotide open reading frame encodes a polypeptide of M(r) 250,166 and pI 5.9. The N-terminal alpha-toxin (Tcn alpha) sequence MLITREQLMKIASIP determined by Edman degradation confirmed the identity of the reading frame and the assignment of the translation start point. The toxin is not modified posttranslationally at its N-terminus nor does it consist of different subunits. Overall the amino acid sequence shows 48% homology between the Tcn alpha and both toxins A (TcdA) and B (TcdB) of Clostridium difficile. The C-terminal 382 residues of Tcn alpha constitute a repetitive domain similar to those reported for TcdA and TcdB of C. difficile. The individual repeat motifs of these three toxins consist of oligopeptides some 19-52 amino acids in length, arranged in four to five different groups. Genetic, biochemical and pharmacological data thus confirm that the three toxins belong to one subgroup, designated large clostridial cytotoxins (LCT). Further definition of their structure and detailed molecular action should allow the LCTs to be used tools for the analysis of microfilament assembly and function.

Clostridium sordellii cytotoxin induces phosphorylation of an 80,000 mol. wt protein in McCoy cultured cells

The cytotoxins from Clostridium difficile (toxin B) and Clostridium sordellii (toxin L) induce rounding of cultured cells. The cellular effects induced by these two cytotoxins are clearly distinct, suggesting that both toxins use a similar, but not identical mechanism for cell intoxication. We have employed the technique of two-dimensional PAGE for the separation of 32P-labelled cell lysates of McCoy cultured cells to investigate changes in the phosphorylation status of cellular proteins after treatment with toxin B and with toxin L. The two-dimensional electrophoresis patterns suggest the implication of an 80,000 mol. wt cellular protein (named pp80c) in the cytopathic action of the cytotoxin from C. sordellii. This protein shows immunoreactivity with non-muscle caldesmon. Toxin B, however, does not affect the phosphorylation of pp80c, but alters the phosphorylation of another cellular protein, pp77, indicating another mechanism for cell intoxication. In addition, our experiments suggest that the mechanism of action of okadaic acid, a phosphatase inhibitor which causes cell rounding similar to that induced by C. sordellii, and these two cytotoxins are different.

Purification and characterization of alpha-toxin produced by Clostridium novyi type A

Our study describes the production, purification, and properties of alpha-toxin from Clostridium novyi type A 19402. The bacterium produced maximal amounts of alpha-toxin when grown at 37 degrees C for 72 h in dialysis flask cultures containing brain heart infusion supplemented with 0.75% Tween 80 and 2% glycerol. The alpha-toxin was purified by precipitation with polyethylene glycol 6000, followed by chromatography on Q-Sepharose, phenyl-agarose, and Mono-Q. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the toxin exhibited a single band with an M(r) of 200,000. The toxin also exhibited a single immunoprecipitin arc by crossed immunoelectrophoresis with antiserum against crude toxin. It was stable when stored at 4 degrees C and also following exposure to buffers with pHs in the range of 4 to 7. The toxin had a minimum lethal dose in mice of 5 to 10 ng, caused rounding of a variety of cells in tissue culture, and was negative in the rabbit ileal loop assay. The cytotoxic activity was inhibited by agents that affect receptor-mediated processes, and the toxin was less active on a CHO mutant cell line that is defective in endosomal acidification. The analysis of the amino acid composition revealed an unusually high proline content. The N-terminal sequence is Met-Leu-Ile-Thr-Arg-Glu-Gln-Leu-Met-Lys.

Morphological changes of cultured endothelial cells after microinjection of toxins that act on the cytoskeleton

Clostridium novyi alpha-toxin and C. difficile toxins A and B (all 200 to 300 kDa) and C. botulinum C2-I toxin (50 kDa) caused a delayed and persistent retraction and rounding of microinjected cells. Microinjected phalloidin acted fast and reversibly. Unlike C2-I toxin, phalloidin passed through the intercellular junctions. Specific antitoxin applied to the medium did not prevent the action of microinjected C. novyi or C. difficile toxin B. Microinjected antitoxin protected against the toxins applied with the medium or injected into the same cells.