NLRC3 protein inhibits inflammation by disrupting NALP3 inflammasome assembly via competition with the adaptor protein ASC for pro-caspase-1 binding

Abstract

Inflammasomes are multiprotein complexes that sense pathogen-associated and danger-associated molecular patterns and induce inflammation in cells. The NALP3 inflammasome is tightly regulated by recently discovered control mechanisms, but other modulators still remain to be characterized. NLR family CARD-containing 3 (NLRC3) protein, a caspase recruitment domain (CARD)-containing member of the nucleotide oligomerization domain-like receptor (NLR) family, was found to down-regulate the NF-κB pathway and stimulator of interferon genes (STING)-dependent cytokine secretion. However, the effect of NLRC3 on the NALP3 inflammasome or other inflammasomes is still unknown. We hypothesized that NLRC3 might inhibit NALP3 inflammasome complex assembly. Toward this end, we tested whether NLRC3 overexpression or knockdown influences NALP3 activity in human monocyte and HEK293FT cells when the complex is ectopically reconstituted. We found that NLRC3 indeed decreases NALP3-induced IL-1β maturation and secretion, pro-caspase-1 cleavage, and speck formation by apoptosis-associated speck-like protein containing a CARD (ASC) protein in response to NALP3 activators. We also show that endogenous NLRC3 interacts with both ASC and pro-caspase-1 but not with NALP3, disrupts ASC speck formation through its CARD, and impairs the ASC and pro-caspase-1 interaction. Moreover, the NLRC3 CARD alone could dampen IL-1β secretion and ASC speck formation induced by NALP3 mutants associated with autoinflammatory diseases. In conclusion, we show here that, besides its role in the inhibition of the NF-κB pathway, NLRC3 interferes with the assembly and activity of the NALP3 inflammasome complex by competing with ASC for pro-caspase-1 binding.

Inflammasome activation and regulation: toward a better understanding of complex mechanisms

“…A stress granule protein DDX3X, which is involved in both NLRP3 inflammasome and stress granules assembly, regulates NLRP3 inflammasome, thereby constituting a critical checkpoint in stressed cells 163 . Other molecules inhibiting NLRP3-ASC interaction include the orphan nuclear receptor small heterodimer partner 164 , heat shock protein 70 165 , and NLR family CARD-containing 3 (NLRC3) protein 166 .…”

The Role of NLRP3 Inflammasome in the Pathogenesis of Traumatic Brain Injury

“…Different regulators may positively modulate NLRP3 inflammasome such as DDX3X, GBP5 and cathepsin, thus inducing NLRP3 oligomerization and promoting ASC assembly [ 89 , 90 , 91 ]. On the other hand, HSP70, PRDX1, NLRC3, SHP and POPs may negatively modulate NLRP3 assembly, acting on NLRP3 itself or inhibiting the formation of NLRP3/ASC complex or the interaction between ASC and procaspase-1 [ 92 , 93 , 94 , 95 , 96 ]. Post-translational modification may also promote NLRP3 assembly and interaction, in fact, the dephosphorylation of pyrin domain mediated by PP2A significantly inhibited NLRP3 inflammasome activation thus blocking ASC assembly that requires pyrin domain (PYD)–PYD interactions [ 97 ].…”

The Evolving Role of TRAFs in Mediating Inflammatory Responses

“…This interaction then allows IKKα to phosphorylate TRAF4, which results in its dissociation from NOD2 and inhibition of NOD2 signaling (61). NLRC3 has been shown to attenuate NLRP3 inflammasome by with ASC for pro-caspase-1 binding (62).…”