Induction of cytokines by toxins that have an identical RNA N-glycosidase activity: Shiga toxin, ricin, and modeccin
ABSTRACT Shiga toxin (Stx) has an A1-B5 subunit structure, and the A subunit is an RNA N-glycosidase that inhibits cellular protein synthesis. We previously reported that in Caco-2 cells Stx induced cytokines and that the RNA N-glycosidase activity was essential for the cytokine induction. It is known that the binding of the Stx-B subunit to its receptor glycolipid, Gb3, mediates an A subunit-independent signal in some types of cells, but the involvement of this signal in the cytokine induction is unclear. In this study, we investigated whether RNA N-glycosidase itself induces cytokines. IL-8 production was enhanced by Stx, ricin, and modeccin, three toxins that inhibit protein synthesis through an identical RNA N-glycosidase activity, but not by two other types of protein synthesis inhibitors, diphtheria toxin and cycloheximide. The RNA N-glycosidase-type toxins showed a similar induction pattern of cytokine mRNAs. Brefeldin A, a Golgi apparatus inhibitor, completely suppressed the cytokine induction by the toxins. Analysis by using inhibitors of toxin binding and also Stx-B subunit showed that the cytokine-inducing activity was independent of Gb3-mediated signaling. These results indicate that RNA N-glycosidase itself induces the cytokine production and that intracellular transport of toxins through the Golgi apparatus is essential for the activity.
- SourceAvailable from: Qing-Yu Zhang
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- "In vitro, application of ricin to the apical surfaces of polarized intestinal epithelial cell monolayers results in an arrest of protein synthesis within 3–4 hrs3031. One consequence of protein synthesis arrest is activation of the so-called ribotoxic stress response (RSR), which triggers cellular stress-activated protein kinase pathways (SAPKs) in intestinal epithelial cells, resulting in gross changes in gene expression and the secretion of an array of pro-inflammatory cytokines and chemokines3233343536. Ricin, which is known to traffic retrograde to the endoplasmic reticulum (ER) may also affect physiology of the ER and thereby indirectly perturb microsomal enzymes, including CYPs37. "
ABSTRACT: Cytochrome P450 (P450) enzymes are a superfamily of heme-containing enzymes involved in the metabolism of various endogenous compounds, including retinoids, glucocorticoids, and eicosanoids, that are postulated to participate in the maintenance and/or development of inflammatory and immune reactions in the intestinal mucosa. To investigate the role of P450 enzymes in intestinal inflammation and immunity, we took advantage of IE-Cpr-null mice, which are deficient in intestinal epithelium of NADPH-cytochrome P450 reductase (CPR), the obligate redox partner of all microsomal P450 enzymes. We report that IE-Cpr-null mice, following an acute toxin challenge, had higher levels of pro-inflammatory chemokines and increased tissue damage compared to wild-type mice. IE-Cpr-null mice had normal Peyer's patch numbers and elicited normal secretory IgA (SIgA) responses. However, SIgA baseline levels in IE-Cpr-null mice were consistently elevated over WT littermates. While neither retinoic acid nor glucocorticoid levels in serum and intestinal homogenates were altered in IE-Cpr-null mice, basal levels of arachidonic acid metabolites (11,12-DiHETE and 14,15-DiHETE) with known anti-inflammatory property were significantly lower compared to WT controls. Overall, these findings reveal immunological and metabolic changes resulting from a genetic deficiency in CPR expression in the intestine, and support a role for microsomal P450 enzymes in mucosal homeostasis and immunity.Scientific Reports 07/2014; 4:5551. DOI:10.1038/srep05551 · 5.58 Impact Factor
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- "In contrast, Yamasaki et al. showed that there is not a direct link between cytokine inducing activity and Gb3 mediated signaling in human colon Caco- 2 cells at the mRNA level by mutant Stx which lacked N-glycosidase activity (29). "
ABSTRACT: Shiga toxins (Stxs) are bacterial virulence factors produced by Shigella dysenteriae serotype 1 and Escherichia coli strains. Stxs are critical factors for the development of diseases such as severe bloody diarrhea and hemolytic uremic syndrome. Additionally, Stxs trigger the secretion of pro- inflammatory cytokines and chemokines, particularly in monocytes or macrophages. The inflammatory cytokines result in the modulation of the immune system, local inflammations and enhancement of cytotoxicity. In this study, stimulation of the pro- inflammatory cytokines IL-1α, IL-1β, IL-6, IL-8, and TNF-α was assessed by recombinant Stx (rStx) and its subunits (rStxA and rStxB). Cytokines expression at mRNA level was investigated by Reverse Transcription-Polymerase Chain Reaction (RT-PCR) method in HeLa cells and THP1 monocyte/ macrophage cell lines. After incubation with rStx and its recombinant subunits, the expression of IL-1α, IL- 6 and IL- 8 mRNAs was strongly induced in HeLa cells. In HeLa cells, low expression of IL-1α mRNA was shown by rStxB induction. Furthermore, the expression of IL-1α and IL-1β mRNAs in undifferentiated THP1 cells was only induced by rStx. In differentiated THP1 cells, rStx and its recombinant subunits elicited the expression of IL-1α, IL-1β, IL-8 and IL- 6 mRNAs. On the other hand, expression of TNF-α mRNA was only induced by rStx. Based on the data, the profile of cytokine induction in response to the rStx, and its subunits differs depending on the cell types.02/2014; 3(2):108-17.
01/2014; , ISBN: 978-1-60805-879-2
- "It also appears that there was no advantage, and perhaps a disadvantage, for multiple vaccinations over extended times, the best titres being after 3 vaccinations over 7 weeks, then declining afterwards. Possible explanations for this decrease in anti-toxoid antibody titres could be the occurrence of immune-tolerance to the antigen , or a shift from antibody to other immune responses such as the production of mannose binding lectins acting against the toxoid's mannose glycosylation   or expression of cellmediated cytokines . Regardless of this decrease in anti-toxoid antibody, it should be noted that the titres were still excellent, in high amounts and capable of rescuing mice after several lethal doses of ricin, as will be seen in the next section. "