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Toxins 2010, 2(6), 1500-1514; doi:10.3390/toxins2061500
Article

Ricin Toxin Activates the NALP3 Inflammasome

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Received: 20 April 2010 / Revised: 30 April 2010 / Accepted: 4 May 2010 / Published: 17 June 2010
(This article belongs to the Special Issue Novel Properties of Well-Characterized Toxins)
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Abstract

Ricin exhibits well characterized ribotoxic actions that lead to the inhibition of protein synthesis and the phosphorylation of stress activated protein kinases (SAPKs). Proinflammatory effects of ricin are thought to be caused by upregulation of genes encoding proinflammatory transcripts as a result of the activation of c-Jun N-terminal kinase (JNK) and p38 MAPK. We reported previously that macrophages and interleukin-1β (IL-1β) signaling are required for murine host immune responses to ricin delivered to the lungs. Here we report that ricin-mediated IL-1β release from bone-marrow derived macrophages is dependent on the NALP3 inflammasome, a scaffolding complex that mediates pro-IL-1β cleavage to active IL-1β by caspase-1. Release of IL-1β from macrophages was suppressed by the reactive oxygen species (ROS) scavenger N-acetyl cysteine (NAC) and high extracellular K+, which are two agents known to inhibit NALP3/cryopyrin/CIAS1 inflammasome formation. By employing inhibitors of p38 MAPK and JNK, we demonstrated that ricin-mediated release of IL-1β was enhanced, rather than suppressed, by inhibition of SAPK phosphorylation. In contrast, proteasomal inhibitors bortezomib and MG-132 completely suppressed ricin-induced IL-1β release from macrophages. These data suggest that ricin-mediated translational inhibition itself, by fostering the disappearance of labile protein(s) that normally suppress inflammasome formation, may constitute the mechanism underlying IL-1-dependent inflammatory signaling by ricin.
Keywords: ricin; NALP3; inflammasome; IL-1 ricin; NALP3; inflammasome; IL-1
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Lindauer, M.; Wong, J.; Magun, B. Ricin Toxin Activates the NALP3 Inflammasome. Toxins 2010, 2, 1500-1514.

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