TY - JOUR T1 - PMX-53 as a dual CD88 antagonist and an agonist for Mas-related gene 2 (MrgX2) in Human mast cells JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.111.071472 SP - mol.111.071472 AU - Hariharan Subramanian AU - Sakeen W Kashem AU - Sarah J Collington AU - Hongchang Qu AU - John D Lambris AU - Hydar Ali Y1 - 2011/03/11 UR - http://molpharm.aspetjournals.org/content/early/2011/03/11/mol.111.071472.abstract N2 - Human mast cells express the G protein coupled receptor (GPCR) for C5a (CD88). Previous studies indicated that C5a could cause mast cell degranulation, at least in part, via a mechanism similar to that proposed for basic neuropeptides such as substance P, possibly involving Mas-related gene 2 (MrgX2). We therefore sought to more clearly define the receptor specificity for C5a-induced mast cell degranulation. We found that a human mast cell line, LAD2 and CD34+ cell-derived primary mast cells express functional MrgX1 and MrgX2 but an immature human mast cell line HMC-1 does not. A potent CD88 antagonist, PMX-53 (10 nM) inhibited C5a-induced Ca2+ mobilization in HMC-1 cells but at higher concentrations (≈30 nM) it caused degranulation in LAD2 mast cells, CD34+ cell-derived mast cells and RBL-2H3 cells stably expressing MrgX2. PMX-53 did not, however, activate RBL-2H3 cells expressing MrgX1. Although C5a induced degranulation in LAD2 and CD34+ cell-derived mast cells, it did not activate RBL-2H3 cells expressing MrgX1 or MrgX2. Replacement of Trp with Ala and Arg with dArg abolished PMX-53's ability to inhibit C5a-induced Ca2+ mobilization in HMC-1 cells and to cause degranulation in RBL-2H3 cells expressing MrgX2. These findings demonstrate that C5a does not utilize MrgX1 or MrgX2 for mast cell degranulation. Moreover, it reveals the novel finding that PMX-53 functions as a potent CD88 antagonist and a low affinity ligand for MrgX2. Furthermore, Trp and Arg residues are required for PMX53's ability to act both as a CD88 antagonist and MrgX2 agonist. ER -