Structural and biochemical mechanisms of NLRP1 inhibition by DPP9

Abstract

Nucleotide-binding domain, leucine-rich repeat receptors (NLRs) mediate innate immunity by forming inflammasomes. Activation of the NLR protein NLRP1 requires autocleavage within its function-to-find domain (FIIND)1–7. In resting cells, the dipeptidyl peptidases DPP8 and DPP9 interact with the FIIND of NLRP1 and suppress spontaneous NLRP1 activation8,9; however, the mechanisms through which this occurs remain unknown. Here we present structural and biochemical evidence that full-length rat NLRP1 (rNLRP1) and rat DPP9 (rDPP9) form a 2:1 complex that contains an autoinhibited rNLRP1 molecule and an active UPA–CARD fragment of rNLRP1. The ZU5 domain is required not only for autoinhibition of rNLRP1 but also for assembly of the 2:1 complex. Formation of the complex prevents UPA-mediated higher-order oligomerization of UPA–CARD fragments and strengthens ZU5-mediated NLRP1 autoinhibition. Structure-guided biochemical and functional assays show that both NLRP1 binding and enzymatic activity are required for DPP9 to suppress NLRP1 in human cells. Together, our data reveal the mechanism of DPP9-mediated inhibition of NLRP1 and shed light on the activation of the NLRP1 inflammasome.

Oxidized thioredoxin-1 restrains the NLRP1 inflammasome

“…However, the entire NACHT-LRR region bound more strongly to TRX1 than the isolated NACHT, indicating that these two domains together mediate this protein-protein interaction. DPP9 associates with the NLRP1 FIIND ( 6, 7, 14 ), and, as expected, only the full-length NLRP1 protein and isolated FIIND bound to DPP9. Thus, TRX1 and DPP9 bind to distinct regions of NLRP1.…”

“…The proteasome-mediated degradation of the NT fragments releases the CT fragments from autoinhibition ( 4, 5) . Initially, each freed CT fragment is restrained in a ternary complex with one copy of the full-length (FL) sensor protein (NLRP1 or CARD8) and one copy of either dipeptidyl peptidase 8 or 9 (DPP8/9) ( 6, 7 ). However, if enough CT fragments are released or if the ternary complex is disrupted by DPP8/9-binding ligands, the CT fragments assemble into caspase-1-activating structures called inflammasomes and trigger pyroptosis.…”

“…dsRNA directly interacts with the NACHT-LRR region, triggering ATP hydrolysis, and presumably NT degradation and CT release, via unknown mechanisms. DPP8/9 inhibitors, including Val-boroPro (VbP), both accelerate the proteasome-mediated degradation of the NT fragment through a poorly characterized pathway and destabilize the NLRP1 FL -NLRP1 CT -DPP8/9 repressive ternary complex ( 6, 7, 14, 16, 17 ). Of these three triggers, only DPP8/9 inhibitors also activate the rat and mouse NLRP1 inflammasomes ( 15 ) and the human CARD8 inflammasome (rodents do not express CARD8) ( 13, 18 ).…”

“…repressive ternary complex (6,7,14,16,17). Of these three triggers, only DPP8/9 inhibitors also activate the rat and mouse NLRP1 inflammasomes (15) and the human CARD8 inflammasome (which was not certified by peer review) is the author/funder.…”

Dipeptidyl Peptidase Inhibition Enhances CD8 T Cell Recruitment and Activates Intrahepatic Inflammasome in a Murine Model of Hepatocellular Carcinoma

“…DPP4 inhibition blocks the cleavage of CXCL10 by DPP4, thereby increasing the chemotaxis of immune cells towards tumour tissue via the cognate receptor of CXCL10, CXCR3 [ 14 , 16 ]. DPP9 sequesters the C-terminus of NLRP1 and thereby acts as an endogenous inhibitor of NLRP1 [ 17 , 18 ]. DPP9 inhibition activates the NLRP1 inflammasome, leading to caspase-1 activation, secretion of cleaved interleukin-1β (IL-1β) and interleukin-18 (IL-18), and pyroptotic cell death [ 19 , 20 ].…”