title: The calcium-sensing receptor regulates the NLRP3 inflammasome through Ca2+ and cAMP.
abstract: Mutations in the gene encoding NLRP3 cause a spectrum of autoinflammatory diseases known as cryopyrin-associated periodic syndromes (CAPS). NLRP3 is a key component of one of several distinct cytoplasmic multiprotein complexes (inflammasomes) that mediate the maturation of the proinflammatory cytokine interleukin-1β (IL-1β) by activating caspase-1. Although several models for inflammasome activation, such as K(+) efflux, generation of reactive oxygen species and lysosomal destabilization, have been proposed, the precise molecular mechanism of NLRP3 inflammasome activation, as well as the mechanism by which CAPS-associated mutations activate NLRP3, remain to be elucidated. Here we show that the murine calcium-sensing receptor (CASR) activates the NLRP3 inflammasome, mediated by increased intracellular Ca(2+) and decreased cellular cyclic AMP (cAMP). Ca(2+) or other CASR agonists activate the NLRP3 inflammasome in the absence of exogenous ATP, whereas knockdown of CASR reduces inflammasome activation in response to known NLRP3 activators. CASR activates the NLRP3 inflammasome through phospholipase C, which catalyses inositol-1,4,5-trisphosphate production and thereby induces release of Ca(2+) from endoplasmic reticulum stores. The increased cytoplasmic Ca(2+) promotes the assembly of inflammasome components, and intracellular Ca(2+) is required for spontaneous inflammasome activity in cells from patients with CAPS. CASR stimulation also results in reduced intracellular cAMP, which independently activates the NLRP3 inflammasome. cAMP binds to NLRP3 directly to inhibit inflammasome assembly, and downregulation of cAMP relieves this inhibition. The binding affinity of cAMP for CAPS-associated mutant NLRP3 is substantially lower than for wild-type NLRP3, and the uncontrolled mature IL-1β production from CAPS patients' peripheral blood mononuclear cells is attenuated by increasing cAMP. Taken together, these findings indicate that Ca(2+) and cAMP are two key molecular regulators of the NLRP3 inflammasome that have critical roles in the molecular pathogenesis of CAPS.
authors.affiliation: Inflammatory Disease Section, Medical Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Geun-Shik
authors.initials: GS
authors.lastname: Lee
authors.forename: Naeha
authors.initials: N
authors.lastname: Subramanian
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Kim
authors.forename: Ivona
authors.initials: I
authors.lastname: Aksentijevich
authors.forename: Raphaela
authors.initials: R
authors.lastname: Goldbach-Mansky
authors.forename: David B
authors.initials: DB
authors.lastname: Sacks
authors.forename: Ronald N
authors.initials: RN
authors.lastname: Germain
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Kastner
authors.forename: Jae Jin
authors.initials: JJ
authors.lastname: Chae
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D056587:Cryopyrin-Associated Periodic Syndromes / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D058847:Inflammasomes / Q000378:metabolism*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053583:Interleukin-1beta / Q000096:biosynthesis / Q000378:metabolism; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D051379:Mice; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; D011485:Protein Binding; D044169:Receptors, Calcium-Sensing / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D010738:Type C Phospholipases / Q000378:metabolism
chemical_list: C577923:CASR protein, mouse; D002352:Carrier Proteins; D058847:Inflammasomes; D053583:Interleukin-1beta; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; D044169:Receptors, Calcium-Sensing; D043562:Receptors, G-Protein-Coupled; D015544:Inositol 1,4,5-Trisphosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D010738:Type C Phospholipases; D002118:Calcium