GRK2 differentially regulates FcεRI and MRGPRB2-mediated responses in mast cells

In addition to high-affinity IgE receptor (FceRI), a subtype of mouse mast cells (MCs) expresses a G protein-coupled receptor known as Mas-related G protein-coupled receptor (GPCR)-B2 (MRGPRB2; human ortholog MRGPRX2). GPCR kinase 2 (GRK2) is a Serine/Threonine kinase that phosphorylates GPCRs to promote their desensitization and internalization. We previously showed that silencing GRK2 expression in mouse bone marrow-derived MCs (BMMCs) blocks IgE-mediated degranulation. Compound 48/80 (C48/80), substance P (SP) and LL-37 cause degranulation in human and mouse MCs via MRGPRX2 and MRGPRB2, respectively. We also reported that C48/80 and SP cause desensitization and internalization of MRGPRX2, but LL-37 does not. Here, we generated mice with MC-specific deletion of Grk2 (Cpa3Cre(+)/Grk2(fl/fl) ) to determine its role on IgE-mediated responses and to assess whether it differentially regulates degranulation in response to LL-37, C48/80 and SP. Absence of GRK2 substantially inhibited IgE-mediated tyrosine phosphorylation of STAT5, calcium mobilization, and degranulation in mouse primary lung-derived MCs (PLMCs). By contrast, peritoneal MCs (PMCs) from Cpa3Cre(+)/Grk2(fl/fl) mice demonstrated significant enhancement of degranulation in response to C48/80 and SP, but not LL-37. Deletion of Grk2 in MCs attenuated IgE-mediated passive cutaneous anaphylaxis (PCA) and itch but not passive systemic anaphylaxis (PSA). Surprisingly, PSA was significantly reduced in Mrgprb2(-/-) mice. These findings suggest that GRK2 contributes to PCA and itch but not PSA. By contrast, GRK2 desensitizes MRGPRX2/B2-mediated responses to C48/80 and SP but not LL-37. However, IgE-mediated PSA likely involves the activation of MRGPRB2 by LL-37 or a similar agonist, whose function is resistant to modulation by GRK2.

Automated summary

This article investigates the role of GRK2 in mouse mast cells. It is found that GRK2 inhibits the responses mediated by MRGPRX2/B2 for C48/80 and SP, but not for LL-37. It is also discovered that GRK2 plays a role in IgE-mediated PCA and itch, but not in PSA.