Cytokine Stimulation by MRGPRX2 Occurs with Lower Potency than by FcεRI Aggregation but with Similar Dependence on the Extracellular Signal–Regulated Kinase 1/2 Module in Human Skin Mast Cells

Skin mast cells (MCs) contribute to chronic dermatoses that partially rely on MC-derived cytokines. The discovery of MRGPRX2 explains MC-dependent symptoms independently of FcεRI activation. In this study, we investigated whether MRGPRX2 can elicit cytokines, determined its relative potency versus that of FcεRI, and addressed the underlying mechanisms. MRGPRX2 activation by compound 48/80 or substance P on skin MCs induced TNF-α, IL-8, IL-13, CCL1, and CCL2 protein and mRNA; yet, induction was typically reduced compared with FcεRI crosslinking. Generally, cytokine secretion required de novo synthesis with maximum accumulation at ∼8 hours. Addressing key kinases revealed robust, rapid (1 minute), and lasting (30 minutes) phosphorylation of extracellular signal‒regulated kinase 1/2 after MRGPRX2 ligation, whereas phosphorylated p38 and phosphorylated protein kinase B signals were weaker, and phosphorylated c-Jun N-terminal kinase was hardly detectable. The kinase spectrum after FcεRI aggregation was comparable, but responses were considerably delayed. The MAPK/extracellular signal‒regulated kinase kinase/extracellular signal‒regulated kinase pathway was essential for all cytokines examined, and four inhibitors of this module led to complete suppression. A variable and weaker contribution was found for phosphatidylinositol 3-kinase than for c-Jun N-terminal kinase than for p38. Strikingly, cytokine profiles and signaling prerequisites were similar for MRGPRX2 and FcεRI and were likely mainly dictated by the MC subset. Collectively, in skin MCs, the physiological producers of MRGPRX2, agonist binding elicits cytokines, yet less efficiently than in FcεRI aggregation. MRGPRX2-associated inflammation may thus be less tissue destructive than responses to allergic challenges.