Store-operated Ca2⁺ release-activated Ca2⁺ channels regulate PAR2-activated Ca2⁺ signaling and cytokine production in airway epithelial cells

The G-protein-coupled protease-activated receptor 2 (PAR2) plays an important role in the pathogenesis of various inflammatory and auto-immune disorders. In airway epithelial cells (AECs), stimulation of PAR2 by allergens and proteases triggers the release of a host of inflammatory mediators to regulate bronchomotor tone and immune cell recruitment. Activation of PAR2 turns on several cell signaling pathways of which the mobilization of cytosolic Ca2⁺ is likely a critical but poorly understood event. In this study, we show that Ca2⁺ release-activated Ca2⁺ (CRAC) channels encoded by stromal interaction molecule 1 and Orai1 are a major route of Ca2⁺ entry in primary human AECs and drive the Ca2⁺ elevations seen in response to PAR2 activation. Activation of CRAC channels induces the production of several key inflammatory mediators from AECs including thymic stromal lymphopoietin, IL-6, and PGE₂, in part through stimulation of gene expression via nuclear factor of activated T cells (NFAT). Furthermore, PAR2 stimulation induces the production of many key inflammatory mediators including PGE₂, IL-6, IL-8, and GM-CSF in a CRAC channel-dependent manner. These findings indicate that CRAC channels are the primary mechanism for Ca2⁺ influx in AECs and a vital checkpoint for the induction of PAR2-induced proinflammatory cytokines.