1.
Linear ubiquitin chain assembly complex contributes to NLRP3-mediated pyroptotic cell death.
Abstract:
Activation of the NLRP3 inflammasome by infectious or sterile insults culminates in pyroptosis, a lytic and highly inflammatory form of programmed cell death. A safeguarded two-step process tightly regulates pyroptosis: priming, which drives NF-κB signaling, followed by execution, ultimately leading to plasma membrane rupture. Linear (Met1-linked) ubiquitination, catalyzed by the E3 ligase complex LUBAC, was previously shown to participate in pyroptosis, but the underlying mechanisms are not fully understood. In this study, we show that Met1-linked ubiquitin chains can assemble during both priming and execution phases, independently of the inflammasome sensor NLRP3. Genetic deletion of the LUBAC enzymes or pharmacological inhibition impairs pyroptosis. Conversely, cell death is enhanced without the deubiquitinase OTULIN, which selectively removes linear ubiquitination. Finally, using an optogenetic model to bypass priming, we demonstrate that Met-1-linked ubiquitination is required for the execution phase of pyroptosis. These findings offer insights into the regulation of pyroptotic cell death by linear ubiquitination.
2.
Optogenetically controlled inflammasome activation demonstrates two phases of cell swelling during pyroptosis.
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Nadjar, J
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Monnier, S
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Bastien, E
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Huber, AL
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Oddou, C
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Bardoulet, L
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Leloup, HB
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Ichim, G
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Vanbelle, C
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Py, BF
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Destaing, O
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Petrilli, V
Abstract:
Inflammasomes are multiprotein platforms that control caspase-1 activation, which process the inactive precursor forms of the inflammatory cytokines IL-1β and IL-18, leading to an inflammatory type of programmed cell death called pyroptosis. Studying inflammasome-driven processes, such as pyroptosis-induced cell swelling, under controlled conditions remains challenging because the signals that activate pyroptosis also stimulate other signaling pathways. We designed an optogenetic approach using a photo-oligomerizable inflammasome core adapter protein, apoptosis-associated speck-like containing a caspase recruitment domain (ASC), to temporally and quantitatively manipulate inflammasome activation. We demonstrated that inducing the light-sensitive oligomerization of ASC was sufficient to recapitulate the classical features of inflammasomes within minutes. This system showed that there were two phases of cell swelling during pyroptosis. This approach offers avenues for biophysical investigations into the intricate nature of cellular volume control and plasma membrane rupture during cell death.
