The ASC speck and NLRP3 inflammasome function are spatially and temporally distinct

A Nagar, T Rahman, JA Harton - Frontiers in Immunology, 2021 - frontiersin.org
A Nagar, T Rahman, JA Harton
Frontiers in Immunology, 2021frontiersin.org
Although considered the ternary inflammasome structure, whether the singular, perinuclear
NLRP3: ASC speck is synonymous with the NLRP3 inflammasome is unclear. Herein, we
report that the NLRP3: ASC speck is not required for nigericin-induced inflammasome
activation but facilitates and maximizes IL-1β processing. Furthermore, the NLRP3 agonists
H2O2 and MSU elicited IL-1β maturation without inducing specks. Notably, caspase-1
activity is spatially distinct from the speck, occurring at multiple cytoplasmic sites …
Although considered the ternary inflammasome structure, whether the singular, perinuclear NLRP3:ASC speck is synonymous with the NLRP3 inflammasome is unclear. Herein, we report that the NLRP3:ASC speck is not required for nigericin-induced inflammasome activation but facilitates and maximizes IL-1β processing. Furthermore, the NLRP3 agonists H2O2 and MSU elicited IL-1β maturation without inducing specks. Notably, caspase-1 activity is spatially distinct from the speck, occurring at multiple cytoplasmic sites. Additionally, caspase-1 activity negatively regulates speck frequency and speck size, while speck numbers and IL-1β processing are negatively correlated, cyclical and can be uncoupled by NLRP3 mutations or inhibiting microtubule polymerization. Finally, when specks are present, caspase-1 is likely activated after leaving the speck structure. Thus, the speck is not the NLRP3 inflammasome itself, but is instead a dynamic structure which may amplify the NLRP3 response to weak stimuli by facilitating the formation and release of small NLRP3:ASC complexes which in turn activate caspase-1.
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