ATP binding by NLRP7 is required for inflammasome activation in response to bacterial lipopeptides

Abstract

Nucleotide-binding oligimerization domain (NOD)-like receptors (NLRs) are pattern recognition receptors (PRRs) involved in innate immune responses. NLRs encode a central nucleotide-binding domain (NBD) consisting of the NAIP, CIITA, HET-E and TP1 (NACHT) domain and the NACHT associated domain (NAD), which facilitates receptor oligomerization and downstream inflammasome signaling. The NBD contains highly conserved regions, known as Walker motifs, that are required for nucleotide binding and hydrolysis. The NLR containing a PYRIN domain (PYD) 7 (NLRP7) has been recently shown to assemble an ASC and caspase-1-containing high molecular weight inflammasome complex in response to microbial acylated lipopeptides and Staphylococcus aureus infection. However, the molecular mechanism responsible for NLRP7 inflammasome activation is still elusive. Here we demonstrate that the NBD of NLRP7 is an ATP binding domain and has ATPase activity. We further show that an intact nucleotide-binding Walker A motif is required for NBD-mediated nucleotide binding and hydrolysis, oligomerization, and NLRP7 inflammasome formation and activity. Accordingly, THP-1 cells expressing a mutated Walker A motif display defective NLRP7 inflammasome activation, interleukin (IL)-1β release and pyroptosis in response to acylated lipopeptides and S. aureus infection. Taken together, our results provide novel insights into the mechanism of NLRP7 inflammasome assembly.

Exome sequencing and genotyping identify a rare variant inNLRP7gene associated with ulcerative colitis

“…For example, it is required for bacterial acylated lipoprotein-mediated Caspase-1 activation and maturation of IL-1β and IL-18, but has also been shown to inhibit NLRP3 and Caspase-1-mediated IL-1β release. This contradiction may reflect a role for NLRP7 in preventing inflammasome formation and IL-1β release in quiescent cells while activating the inflammasome in response to bacterial infection 25 . In either case, this would be consistent with the association of NLRP7 mutations with immune-mediated disorders such as IBD.…”

Inflammasomes in Myeloid Cells: Warriors Within

“…Activation of NLRP7 promoted ASC-dependent caspase-1 activation, IL-1β and IL-18 maturation and restriction of intracellular bacterial replication, but not caspase-1-independent secretion of the pro-inflammatory cytokines IL-6 and tumor necrosis factor-α. Radian et al utilized the THP-1 monocytic cell line expressing a mutated Walker A motif to show defective NLRP7 inflammasome activation, thus suggesting that the NBD of NLRP7 is responsible for ATP binding and ATPase activity(138). This mutant cell line also showed defective IL-1β release and pyroptosis in response to acylated lipopeptides and S. aureus infection.…”

Dynamic interactions between dermal macrophages and Staphylococcus aureus

“…Upon stimulation with S. aureus, a high molecular weight complex of NLRP7, the adaptor protein apoptosis-associated speck-like protein containing C-terminal caspase-recruitment domain, and caspase-1, the so-called inflammasome, assembles, leading to processing of IL-1b and IL-18. Acylated lipopeptides from S. aureus have been identified in vitro as stimuli for NLRP7, which furthermore depends on ATP binding and hydrolysis for proper oligomerization and assembly [55,56]. In addition, pore-forming toxins, such as a-hemolysin, which are expressed in dependence of the accessory gene regulator system, induce NLRP3-dependent caspase-1 activation, finally resulting in pyroptosis and the secretion of IL-1b and IL-18 [38].…”