Naturally Occurring Missense MRGPRX2 Variants Display Loss of Function Phenotype for Mast Cell Degranulation in Response to Substance P, Hemokinin-1, Human β-Defensin-3, and Icatibant

Abstract

<p class="first" id="P1">Human mast cells (MCs) express a novel G protein-coupled receptor (GPCR), known as Mas-related G protein coupled receptor X2 (MRGPRX2). Activation of this receptor by a diverse group of cationic ligands such as neuropeptides (NPs), host defense peptides (HDPs) and FDA-approved drugs contributes to chronic inflammatory diseases and pseudo-allergic drug reactions. For most GPCRs, the extracellular domains and their associated transmembrane domains display the greatest structural diversity and are responsible for binding different ligands. The goal of the present study was to determine if naturally occurring missense variants within MRGPRX2’s extracellular/transmembrane domains contribute to gain or loss of function phenotype for MC degranulation in response to NPs (substance P; SP and hemokinin-1, HK-1), an HDP (human β-defensin-3, hBD3) and an FDA-approved cationic drug (bradykinin B2 receptor antagonist, icatibant). We have identified eight missense variants within MRGPRX2’s extracellular/transmembrane domains from publically available exome-sequencing databases. We investigated the ability of MRGPRX2 ligands to induce degranulation in RBL-2H3 (RBL) cells individually expressing these naturally occurring MRGPRX2 missense variants. Using stable and transient transfections, we found that all variants express in RBL cells. However, four natural MRGPRX2 variants, G165E (rs141744602), D184H (rs372988289), W243R (rs150365137) and H259Y (rs140862085) failed to respond to any of the ligands tested. Thus, diverse MRGPRX2 ligands utilize common sites on the receptor to induce MC degranulation. These findings have important clinical implications for MRGPRX2 and MC-mediated pseudo-allergy and chronic inflammatory diseases. </p>