New mutant mouse models clarify the role of NAIPs, phosphorylation, NLRP3, and tumors in NLRC4 inflammasome activation

Abstract

The NAIP/NLRC4 inflammasome is a cytosolic sensor of bacteria that activates Caspase-1 and initiates potent downstream immune responses. Structural, biochemical, and genetic data all demonstrate that the NAIP proteins act as receptors for specific bacterial ligands, while NLRC4 is a downstream adaptor protein that multimerizes with NAIPs to form a macromolecular structure called an inflammasome. However, several aspects of NLRC4 biology remain unresolved. For example, in addition to its clear function in responding to bacteria, NLRC4 has also been proposed to initiate anti-tumor responses, though the underlying mechanism is unknown. NLRC4 has also been shown to be phosphorylated on serine 533, and this modification was suggested to be important for NLRC4 function. In the absence of S533 phosphorylation, it was further proposed that another inflammasome component, NLRP3, can induce NLRC4 activation. We generated a new Nlrc4deficient mouse line as well as mice encoding phosphomimetic S533D and nonphosphorylatable S533A NLRC4 proteins. Using these genetic models in vivo and in vitro, we fail to observe a role for phosphorylation in NLRC4 inflammasome function.Furthermore, we find no role for NLRP3 in NLRC4 function, or for NLRC4 in a model of melanoma. These results simplify and clarify our understanding of the mechanism of NAIP/NLRC4 activation and its biological functions.

Toward targeting inflammasomes: insights into their regulation and activation

“…109,110 In contrast, a recent study suggests that phosphorylation of Ser533 plays no role in the activation of NLRC4. 111 Indirect activation of NLRP1 and Pyrin In contrast to the AIM2 and NAIP-NLRC4 inflammasomes, the conformational changes that induce NLRP1 and Pyrin activation do not occur as the result of direct ligand binding. The NLRP1 inflammasome is regulated through a unique process of functional degradation, while the Pyrin inflammasome senses the inactivation of other host proteins (Fig.…”

NAIP–NLRC4-deficient mice are susceptible to shigellosis

“…B6.∆Naip mice were generated as described previously (Rauch et al, 2016). B6.Nlrc4 -/- (Tenthorey et al, 2020) and iNlrc4 (Rauch et al, 2017) mice were previously described. iNlrc4 mice were crossed to the Nlrc4 -/line and then further crossed to Vil1-cre (Jax strain 004586) transgenic lines on a Nlrc4 -/background.…”