Autolytic Proteolysis within the Function to Find Domain (FIIND) Is Required for NLRP1 Inflammasome Activity

Background: NLRP1 mediates the release of the inflammatory cytokine IL-1β and is linked to several human inflammatory diseases. Results: Autolytic proteolysis occurs within the C terminus of NLRP1 and is modulated by polymorphisms and alternative mRNA splicing. Conclusion: Autolytic cleavage is a key regulator of the NLRP1 inflammasome and downstream IL-1β production. Significance: Understanding the mechanisms underlying NLRP1 activation is required to develop effective therapeutics. Nucleotide-binding domain leucine-rich repeat proteins (NLRs) play a key role in immunity and disease through their ability to modulate inflammation in response to pathogen-derived and endogenous danger signals. Here, we identify the requirements for activation of NLRP1, an NLR protein associated with a number of human pathologies, including vitiligo, rheumatoid arthritis, and Crohn disease. We demonstrate that NLRP1 activity is dependent upon ASC, which associates with the C-terminal CARD domain of NLRP1. In addition, we show that NLRP1 activity is dependent upon autolytic cleavage at Ser1213 within the FIIND. Importantly, this post translational event is dependent upon the highly conserved distal residue His1186. A disease-associated single nucleotide polymorphism near His1186 and a naturally occurring mRNA splice variant lacking exon 14 differentially affect this autolytic processing and subsequent NLRP1 activity. These results describe key molecular pathways that regulate NLRP1 activity and offer insight on how small sequence variations in NLR genes may influence human disease pathogenesis.