Calcium sensing receptor activates the NLRP3 inflammasome via a chaperone-assisted degradative pathway involving Hsp70 and LC3-II

Calcium sensing receptor (CaSR) activates the NLRP3 inflammasome with consequences on homeostatic responses. However, little is known about how this process is orchestrated. Since proteolysis of critical regulators of NLRP3 inflammasome contribute to its activation, we aimed to understand how CaSR stimulates proteolytic pathways to activate the NLRP3 inflammasome. We found that proteasome and lysosome-dependent mechanisms are activated by CaSR to promote the degradation of important regulators of NLRP inflammasome. The pathway involves G alpha q/PLC/PKC and G beta gamma/P13K signaling cascades and IRAK1 ubiquitination. In addition, CaSR stimulates Hsp70 expression activating a chaperone-assisted protein degradation that dictates the fate of ASC, NLRP3 (NOD-like receptor family protein 3), IRAK1 and TRAF6 proteins, turning on the NLRP3 inflammasome. In response to CaSR signaling, these proteins are degraded through the combination of CUPS (chaperone-assisted ubiquitin proteasome pathway) and CAEMI (chaperone-assisted endosomal microautophagy) systems being integrated by autophagosomes (chaperone-assisted macroautophagy, CAMA), as indicated by LC3-II, a classical marker for autophagy, that is induced in the process. Furthermore, CaSR triggers the proteolytic cleavage of pro-IL-1 beta (IL-1 beta, 31 kDa) into mature 1L-1 beta (IL-1 beta, 17 kDa), via the proteasome. Taken together, our results indicate that CaSR promotes NLRP3 inflammasome activation and proteolytic maturation of 1L-1 beta by inducing CUPS and CAEMI, chaperone-assisted degradation pathways. Overall, these results support the inclusion of CaSR as an activator of homeostasis-altering molecular processes. (C) 2018 Elsevier Inc. All rights reserved.