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Immunol."],"abstract":"<jats:p>Mast cells (MCs) are tissue resident immune cells that play important roles in the pathogenesis of allergic disorders. These responses are mediated <jats:italic>via<\/jats:italic> the cross-linking of cell surface high affinity IgE receptor (Fc\u03f5RI) by antigen resulting in calcium (Ca<jats:sup>2+<\/jats:sup>) mobilization, followed by degranulation and release of proinflammatory mediators. In addition to Fc\u03f5RI, cutaneous MCs express Mas-related G protein-coupled receptor X2 (MRGPRX2; mouse ortholog MrgprB2). Activation of MRGPRX2\/B2 by the neuropeptide substance P (SP) is implicated in neurogenic inflammation, chronic urticaria, mastocytosis and atopic dermatitis. Although Ca<jats:sup>2+<\/jats:sup> entry is required for MRGPRX2\/B2-mediated MC responses, the possibility that calcium release-activated calcium (CRAC\/Orai) channels participate in these responses has not been tested. Lentiviral shRNA-mediated silencing of Orai1, Orai2 or Orai3 in a human MC line (LAD2 cells) resulted in partial inhibition of SP-induced Ca<jats:sup>2+<\/jats:sup> mobilization, degranulation and cytokine\/chemokine generation (TNF-\u03b1, IL-8, and CCL-3). Synta66, which blocks homo and hetero-dimerization of Orai channels, caused a more robust inhibition of SP-induced responses than knockdown of individual Orai channels. Synta66 also blocked SP-induced extracellular signal-regulated kinase 1\/2 (ERK1\/2) and Akt phosphorylation and abrogated cytokine\/chemokine production. It also inhibited SP-induced Ca<jats:sup>2+<\/jats:sup> mobilization and degranulation in primary human skin MCs and mouse peritoneal MCs. Furthermore, Synta66 attenuated both SP-induced cutaneous vascular permeability and leukocyte recruitment in mouse peritoneum. These findings demonstrate that Orai channels contribute to MRGPRX2\/B2-mediated MC activation and suggest that their inhibition could provide a novel approach for the modulation of SP-induced MC\/MRGPRX2-mediated disorders.<\/jats:p>","DOI":"10.3389\/fimmu.2021.803335","type":"journal-article","created":{"date-parts":[[2022,1,20]],"date-time":"2022-01-20T05:47:44Z","timestamp":1642657664000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":20,"title":["Inhibition of Orai Channel Function Regulates Mas-Related G Protein-Coupled Receptor-Mediated Responses in Mast 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