Role of G-protein Coupled Receptor Kinases GRK2 and GRK3 in C3a Receptor Signaling in Human Mast Cells (133.12)

Abstract

Abstract Studies with animal models have shown that complement components C3a and C5a play an important role in the effector phase of allergic asthma. We have previously shown that C3a activates human CD34+-derived mast cells to induce degranulation. To determine the role of GRKs on C3a receptor (C3aR) signaling in human mast cells, we used shRNA to knockdown GRK2 and GRK3 a human mast cell line, HMC-1 and CD34+-derived cultures of primary mast cells. We found that GRK2 and GKR3 knockdown inhibited C3aR desensitization as measured by enhanced C3a-induced Ca2+ mobilization in HMC-1 cells and greater degranulation in CD34+ mast cells but had no effect on receptor internalization. In addition, GRK3-knockdown in HMC-1 cells showed increased expression of cell surface C3aR and this was correlated with enhanced extracellular-signal-regulated kinase (ERK) activation and a four-fold increase in C3a-induced chemotaxis. Surprisingly, there was no enhancement of these responses in GRK2 knockdown mast cells. These findings suggest that while GRK2 and GRK3 are required for C3aR sensitization, presumably by promoting receptor phosphorylation, they play distinct roles in modulating downstream signaling such as ERK phosphorylation and chemotaxis.