DPP9 sequesters the C terminus of NLRP1 to repress inflammasome activation

Abstract

NLRP1 is a cytosolic inflammasome sensor that mediates activation of caspase-1, which in turn induces cytokine maturation and pyroptotic cell death 1-6 . Gain-of-function NLPR1 mutations cause skin inflammatory diseases including carcinoma, keratosis, and papillomatosis 7-14 . NLRP1 contains a unique function-to-find domain (FIIND) that autoproteolyzes into noncovalently associated subdomains [15][16][17][18] . Proteasomal degradation of the autoinhibitory N-terminal fragment (NT) activates NLRP1 by releasing the inflammatory C-terminal fragment (CT) 19,20 . Cytosolic dipeptidyl peptidases 8 and 9 (DPP8/9) interact with NLRP1, and small-molecule DPP8/9 inhibitors activate NLRP1 by poorly characterized mechanisms 11,19,21 . Here, we report cryo-EM structures of the human NLRP1-DPP9 complex, alone and in complex with the DPP8/9 inhibitor Val-boroPro (VbP). Surprisingly, the NLRP1-DPP9 complex is a ternary complex comprised of DPP9, one intact FIIND of a non-degraded full-length NLRP1 (NLRP1-FL) and one NLRP1-CT freed by NT degradation. The N-terminus of the NLRP1-CT unfolds and inserts into the DPP9 active site but is not cleaved by DPP9, and this binding is disrupted by VbP. Structure-based mutagenesis reveals that the binding of NLRP1-CT to DPP9 requires NLRP1-FL and vice versa, and inflammasome activation by ectopic NLRP1-CT expression is rescued by co-expressing autoproteolysis-deficient NLRP1-FL. Collectively, these data indicate that DPP9 functions as a "bomb-diffuser" to prevent NLRP1-CTs from inducing inflammation during homeostatic protein turnover..

Inflammation-related pyroptosis, a novel programmed cell death pathway, and its crosstalk with immune therapy in cancer treatment

“…Hollingsworth et al indicated that cytosolic dipeptidyl peptidase 9 (DDP9) interacts with full-length NLRP1 and NLRP1 CT to form a ternary complex, which sequesters NLRP1 CT and inhibits inflammation. Conversely, the inhibitory effect is rescued by Val-boroPro (VbP), an inhibitor of DPP8/DPP9 132 .…”

Oxidized thioredoxin-1 restrains the NLRP1 inflammasome

“…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 ).…”

Identification of Dipeptidyl Peptidase (DPP) Family Genes in Clinical Breast Cancer Patients via an Integrated Bioinformatics Approach

“…Knockdown of DPP7 increased apoptosis by upregulating Bax–Bcl2 signaling in the HepG2 liver cancer cell line [ 19 ]. NLR family pyrin domain-containing 1 (NLRP1) can interact with DPP8 and DPP9, which can serve as a checkpoint for activating the NLRP1 inflammasome [ 20 ]. A DPP8 and DPP9 inhibitor can promote apoptosis by activating poly(ADP ribose) polymerase (PARP) and caspase-3 in multiple myelomas [ 21 ].…”