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Suppression of ribosomal function triggers innate immune signaling through activation of the NLRP3 inflammasome.

Vyleta ML, Wong J, Magun BE - PLoS ONE (2012)

Bottom Line: Processing and release of IL-1ß was reduced or absent from cells deficient in NLRP3, ASC, or caspase-1, demonstrating the role of the NLRP3 inflammasome.For agents that inhibit translation through decreased cellular potassium, the application of high extracellular potassium restores protein translation and suppresses activation of the NLRP inflammasome.For agents that inhibit translation through mechanisms that do not involve loss of potassium, high extracellular potassium suppresses IL-1ß processing through a mechanism that remains undefined.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Oregon Health and Science University, Portland, Oregon, United States of America.

ABSTRACT
Some inflammatory stimuli trigger activation of the NLRP3 inflammasome by inducing efflux of cellular potassium. Loss of cellular potassium is known to potently suppress protein synthesis, leading us to test whether the inhibition of protein synthesis itself serves as an activating signal for the NLRP3 inflammasome. Murine bone marrow-derived macrophages, either primed by LPS or unprimed, were exposed to a panel of inhibitors of ribosomal function: ricin, cycloheximide, puromycin, pactamycin, and anisomycin. Macrophages were also exposed to nigericin, ATP, monosodium urate (MSU), and poly I:C. Synthesis of pro-IL-ß and release of IL-1ß from cells in response to these agents was detected by immunoblotting and ELISA. Release of intracellular potassium was measured by mass spectrometry. Inhibition of translation by each of the tested translation inhibitors led to processing of IL-1ß, which was released from cells. Processing and release of IL-1ß was reduced or absent from cells deficient in NLRP3, ASC, or caspase-1, demonstrating the role of the NLRP3 inflammasome. Despite the inability of these inhibitors to trigger efflux of intracellular potassium, the addition of high extracellular potassium suppressed activation of the NLRP3 inflammasome. MSU and double-stranded RNA, which are known to activate the NLRP3 inflammasome, also substantially inhibited protein translation, supporting a close association between inhibition of translation and inflammasome activation. These data demonstrate that translational inhibition itself constitutes a heretofore-unrecognized mechanism underlying IL-1ß dependent inflammatory signaling and that other physical, chemical, or pathogen-associated agents that impair translation may lead to IL-1ß-dependent inflammation through activation of the NLRP3 inflammasome. For agents that inhibit translation through decreased cellular potassium, the application of high extracellular potassium restores protein translation and suppresses activation of the NLRP inflammasome. For agents that inhibit translation through mechanisms that do not involve loss of potassium, high extracellular potassium suppresses IL-1ß processing through a mechanism that remains undefined.

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Graphic depiction of proposed mechanisms by which different stimuli activate the NLRP3 inflammasome.Inhibition of protein synthesis leads to activation of the NLRP3 inflammasome by preventing the synthesis of short-lived inhibitory protein(s) that are degraded by proteasomes. Inhibition of protein synthesis is mediated by a variety of physiological cell stressors acting through phosphorylation of eIF-2alpha, leading to a transient decrease in protein synthesis. Toxins such as ricin, Shiga toxins, and sarcin inhibit protein synthesis by interfering with the structure of the sarcin/ricin loop of 28S rRNA. Antibiotics act through various ribosome-associated mechanisms to inhibit translational initiation and/or elongation. Potassium ionophores (and receptors such as P2X7) inhibit translation by mediating loss of cellular potassium. Monosodium urate inhibits translation by inducing cell swelling, which leads to dilution of intracellular potassium.
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pone-0036044-g007: Graphic depiction of proposed mechanisms by which different stimuli activate the NLRP3 inflammasome.Inhibition of protein synthesis leads to activation of the NLRP3 inflammasome by preventing the synthesis of short-lived inhibitory protein(s) that are degraded by proteasomes. Inhibition of protein synthesis is mediated by a variety of physiological cell stressors acting through phosphorylation of eIF-2alpha, leading to a transient decrease in protein synthesis. Toxins such as ricin, Shiga toxins, and sarcin inhibit protein synthesis by interfering with the structure of the sarcin/ricin loop of 28S rRNA. Antibiotics act through various ribosome-associated mechanisms to inhibit translational initiation and/or elongation. Potassium ionophores (and receptors such as P2X7) inhibit translation by mediating loss of cellular potassium. Monosodium urate inhibits translation by inducing cell swelling, which leads to dilution of intracellular potassium.

Mentions: The current study demonstrates that suppression of ribosomal function by molecules acting by disparate mechanisms is sufficient to activate the NLRP3 inflammasome. These data suggest that inhibition of translation may constitute a common stimulus by which seemingly dissimilar activators promote the processing and release of IL-1ß. A decreased rate of translation may constitute a regulatory node that integrates signals from toxins, pathogens, and metabolic disturbances, thereby enhancing systemic inflammation by promoting the processing and release of IL-1ß. The suppression of IL-1ß release by proteasome inhibitors suggests that labile protein(s) may be responsible for blocking the activation of the NLRP3 inflammasome under non-stressed conditions. A decrease in translation rate may lead to reduction in cellular levels of these protein(s), thereby leading to formation of active NLRP3 inflammasomes. Further studies that focus on identification of labile inhibitors of inflammasome function are clearly necessary to test the validity of this hypothesis. A graphic depiction of the proposed mechanisms underlying NLRP3 activation by different stimuli is shown in Figure 7.


Suppression of ribosomal function triggers innate immune signaling through activation of the NLRP3 inflammasome.

Vyleta ML, Wong J, Magun BE - PLoS ONE (2012)

Graphic depiction of proposed mechanisms by which different stimuli activate the NLRP3 inflammasome.Inhibition of protein synthesis leads to activation of the NLRP3 inflammasome by preventing the synthesis of short-lived inhibitory protein(s) that are degraded by proteasomes. Inhibition of protein synthesis is mediated by a variety of physiological cell stressors acting through phosphorylation of eIF-2alpha, leading to a transient decrease in protein synthesis. Toxins such as ricin, Shiga toxins, and sarcin inhibit protein synthesis by interfering with the structure of the sarcin/ricin loop of 28S rRNA. Antibiotics act through various ribosome-associated mechanisms to inhibit translational initiation and/or elongation. Potassium ionophores (and receptors such as P2X7) inhibit translation by mediating loss of cellular potassium. Monosodium urate inhibits translation by inducing cell swelling, which leads to dilution of intracellular potassium.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3351443&req=5

pone-0036044-g007: Graphic depiction of proposed mechanisms by which different stimuli activate the NLRP3 inflammasome.Inhibition of protein synthesis leads to activation of the NLRP3 inflammasome by preventing the synthesis of short-lived inhibitory protein(s) that are degraded by proteasomes. Inhibition of protein synthesis is mediated by a variety of physiological cell stressors acting through phosphorylation of eIF-2alpha, leading to a transient decrease in protein synthesis. Toxins such as ricin, Shiga toxins, and sarcin inhibit protein synthesis by interfering with the structure of the sarcin/ricin loop of 28S rRNA. Antibiotics act through various ribosome-associated mechanisms to inhibit translational initiation and/or elongation. Potassium ionophores (and receptors such as P2X7) inhibit translation by mediating loss of cellular potassium. Monosodium urate inhibits translation by inducing cell swelling, which leads to dilution of intracellular potassium.
Mentions: The current study demonstrates that suppression of ribosomal function by molecules acting by disparate mechanisms is sufficient to activate the NLRP3 inflammasome. These data suggest that inhibition of translation may constitute a common stimulus by which seemingly dissimilar activators promote the processing and release of IL-1ß. A decreased rate of translation may constitute a regulatory node that integrates signals from toxins, pathogens, and metabolic disturbances, thereby enhancing systemic inflammation by promoting the processing and release of IL-1ß. The suppression of IL-1ß release by proteasome inhibitors suggests that labile protein(s) may be responsible for blocking the activation of the NLRP3 inflammasome under non-stressed conditions. A decrease in translation rate may lead to reduction in cellular levels of these protein(s), thereby leading to formation of active NLRP3 inflammasomes. Further studies that focus on identification of labile inhibitors of inflammasome function are clearly necessary to test the validity of this hypothesis. A graphic depiction of the proposed mechanisms underlying NLRP3 activation by different stimuli is shown in Figure 7.

Bottom Line: Processing and release of IL-1ß was reduced or absent from cells deficient in NLRP3, ASC, or caspase-1, demonstrating the role of the NLRP3 inflammasome.For agents that inhibit translation through decreased cellular potassium, the application of high extracellular potassium restores protein translation and suppresses activation of the NLRP inflammasome.For agents that inhibit translation through mechanisms that do not involve loss of potassium, high extracellular potassium suppresses IL-1ß processing through a mechanism that remains undefined.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell and Developmental Biology, Oregon Health and Science University, Portland, Oregon, United States of America.

ABSTRACT
Some inflammatory stimuli trigger activation of the NLRP3 inflammasome by inducing efflux of cellular potassium. Loss of cellular potassium is known to potently suppress protein synthesis, leading us to test whether the inhibition of protein synthesis itself serves as an activating signal for the NLRP3 inflammasome. Murine bone marrow-derived macrophages, either primed by LPS or unprimed, were exposed to a panel of inhibitors of ribosomal function: ricin, cycloheximide, puromycin, pactamycin, and anisomycin. Macrophages were also exposed to nigericin, ATP, monosodium urate (MSU), and poly I:C. Synthesis of pro-IL-ß and release of IL-1ß from cells in response to these agents was detected by immunoblotting and ELISA. Release of intracellular potassium was measured by mass spectrometry. Inhibition of translation by each of the tested translation inhibitors led to processing of IL-1ß, which was released from cells. Processing and release of IL-1ß was reduced or absent from cells deficient in NLRP3, ASC, or caspase-1, demonstrating the role of the NLRP3 inflammasome. Despite the inability of these inhibitors to trigger efflux of intracellular potassium, the addition of high extracellular potassium suppressed activation of the NLRP3 inflammasome. MSU and double-stranded RNA, which are known to activate the NLRP3 inflammasome, also substantially inhibited protein translation, supporting a close association between inhibition of translation and inflammasome activation. These data demonstrate that translational inhibition itself constitutes a heretofore-unrecognized mechanism underlying IL-1ß dependent inflammatory signaling and that other physical, chemical, or pathogen-associated agents that impair translation may lead to IL-1ß-dependent inflammation through activation of the NLRP3 inflammasome. For agents that inhibit translation through decreased cellular potassium, the application of high extracellular potassium restores protein translation and suppresses activation of the NLRP inflammasome. For agents that inhibit translation through mechanisms that do not involve loss of potassium, high extracellular potassium suppresses IL-1ß processing through a mechanism that remains undefined.

Show MeSH
Related in: MedlinePlus