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N-terminal degradation activates the NLRP1B inflammasome

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Science  05 Apr 2019:
Vol. 364, Issue 6435, pp. 82-85
DOI: 10.1126/science.aau1208

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Degradation triggers the alarm

Inflammasomes are multiprotein complexes that orchestrate proinflammatory cytokine secretion and cell death. Proteases such as anthrax lethal factor can activate an inflammasome known as NLRP1B, but the mechanism for this activation has been unclear. Chui et al. used genome-wide knockout screens to show that proteolysis of NLRP1B by lethal factor induces proteasomal degradation of the amino-terminal domains of NLRP1B and eventual cell death. Sandstrom et al. found that degradation of the amino-terminal domains of NLRP1B resulted in the release of a carboxyl-terminal fragment that activates caspase-1. This process, called “functional degradation,” allows the immune system to detect pathogen-associated activities, much as it recognizes pathogen-associated antigens.

Science, this issue p. 82, p. eaau1330

Abstract

Intracellular pathogens and danger signals trigger the formation of inflammasomes, which activate inflammatory caspases and induce pyroptosis. The anthrax lethal factor metalloprotease and small-molecule DPP8/9 inhibitors both activate the NLRP1B inflammasome, but the molecular mechanism of NLRP1B activation is unknown. In this study, we used genome-wide CRISPR-Cas9 knockout screens to identify genes required for NLRP1B-mediated pyroptosis. We discovered that lethal factor induces cell death via the N-end rule proteasomal degradation pathway. Lethal factor directly cleaves NLRP1B, inducing the N-end rule–mediated degradation of the NLRP1B N terminus and freeing the NLRP1B C terminus to activate caspase-1. DPP8/9 inhibitors also induce proteasomal degradation of the NLRP1B N terminus but not via the N-end rule pathway. Thus, N-terminal degradation is the common activation mechanism of this innate immune sensor.

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