Digital signaling network drives the assembly of the AIM2-ASC inflammasome

Abstract

The AIM2-ASC inflammasome is a filamentous signaling platform essential for mounting host defense against cytoplasmic dsDNA arising not only from invading pathogens but also from damaged organelles. Currently, the design principles of its underlying signaling network remain poorly understood at the molecular level. We show here that longer dsDNA is more effective in inducing AIM2 assembly, its self-propagation, and downstream ASC polymerization. This observation is related to the increased probability of forming the base of AIM2 filaments, and indicates that the assembly discerns small dsDNA as noise at each signaling step. Filaments assembled by receptor AIM2, downstream ASC, and their joint complex all persist regardless of dsDNA, consequently generating sustained signal amplification and hysteresis. Furthermore, multiple positive feedback loops reinforce the assembly, as AIM2 and ASC filaments accelerate the assembly of nascent AIM2 with or without dsDNA. Together with a quantitative model of the assembly, our results indicate that an ultrasensitive digital circuit drives the assembly of the AIM2-ASC inflammasome.

Cryo-EM structure of the NLRC4CARD filament provides insights into how symmetric and asymmetric supramolecular structures drive inflammasome assembly

“…perpendicular filament base to the helical axis) (16,28). Previously, we found that dsDNA long enough to accommodate at least 20 AIM2 molecules maximizes the probability of assembling the hexameric filament base ideal for the recognition of ASC (17). Here, our structure shows that even though NLRC4 assembles into an (un)decamer, the signal transduction to caspase-1 occurs via a tetrameric interface between two CARD filaments.…”

“…Assembly mechanism of the NLRC4 CARD filament molecules per duplex, regulates the probability of assembling the hexameric base of the AIM2 PYD filament (17). A key phenotype of this assembly mechanism is that both self-assembly and signaling activity of AIM2 nonlinearly increase with the length of dsDNA up to where it would provide the maximal probability for assembling the hexameric base (Ͼ200 bp, ϳ20 AIM2 molecules per duplex) (17,28,30). Unlike the AIM2 PYD ⅐ASC PYD complex, the recognition between the NLRC4 CARD ⅐casp1 CARD complex occurs via a tetrameric interface (Fig.…”

“…To induce polymerization, 3 M TEVp was added to each sample and incubated for 1.5 h at room temperature (24 Ϯ 2°C). nsEM imaging experiments were performed using glow-discharged carbon-coated copper grids and 0.75% uranyl formate staining solution as described previously (17,28).…”

“…That is, incoming signals induce oligomerization of upstream receptors, resulting in filament assembly of their PYDs (16). Upstream PYD filaments then nucleate the polymerization of ASC PYD (PYD of ASC), dramatically accelerating the assembly of the downstream filament (16,17)). The ASC PYD filament in turn promotes the filament assembly of its CARD (ASC CARD ) (16,18), which then nucleates the filament assembly of the CARD of caspase-1 (casp1 CARD ).…”

Excessive ENaC-mediated sodium influx drives NLRP3 inflammasome-dependent autoinflammation in cystic fibrosis

“…1 D). The presence of ASC specks in the serum reflects the presence of NLRP3 inflammasome-mediated inflammation and pyroptosis (Baroja-Mazo, Martin-Sanchez et al, 2014, Fernandes-Alnemri & Alnemri, 2008, Franklin et al, 2014, but ASC filament formation can also serve as an amplification mechanism for a range of different inflammasomes, such as NLRC4 (Dick, Sborgi et al, 2016) and AIM-2 (Matyszewski, Morrone et al, 2018).…”