Abstract
Agonist-induced phosphorylation of G protein-coupled receptors (GPCRs) by GPCRkinases (GRKs) promotes their desensitization and internalization. Here, we sought to determine the role of GRK2 on Fc∈RI signaling and mediator release in mast cells. The strategies utilized included lentiviral shRNA-mediated GRK2 knockdown, GRK2 gene deletion (GRK2(flox/flox)/cre recombinase) and overexpression of GRK2 and its regulator of G protein signaling homology (RH) domain (GRK2-RH). We found that silencing GRK2 expression caused ~50% decrease in antigen-induced Ca(2+) mobilization and degranulation but resulted in ablation of cytokine (IL-6 and IL-13) generation. The effect of GRK2 on cytokine generation does not require its catalytic activity but is mediated via the phosphorylation of p38 and Akt. Overexpression of GRK2 or its RH domain (GRK2-RH) enhanced antigen-induced mast cell degranulation and cytokine generation without affecting the expression levels of any of the Fc∈RI subunits (α, β, and γ). GRK2 or GRK2-RH had no effect on antigen-induced phosphorylation of Fc∈RIγ or Src but enhanced tyrosine phosphorylation of Syk. These data demonstrate that GRK2 modulates Fc∈RI signaling in mast cells via at least two mechanisms.One involves GRK2-RH and modulates tyrosine phosphorylation of Syk, and the other is mediated via the phosphorylation of p38 and Akt.
Highlights
Aggregation of high affinity IgE receptors (Fc⑀RI) on mast cells by antigen triggers allergic diseases
We demonstrate that GRK2 modulates Fc⑀RI signaling in mast cells via at least two mechanisms; one involves its RH domain and modulates tyrosine phosphorylation of Spleen tyrosine kinase (Syk), and the other is mediated via the phosphorylation of p38 and Akt
We used the same cells to determine the role of GRK2 on antigen-induced degranulation in human mast cells
Summary
Aggregation of high affinity IgE receptors (Fc⑀RI) on mast cells by antigen triggers allergic diseases. The strategies utilized included lentiviral shRNA-mediated GRK2 knockdown, GRK2 gene deletion (GRK2flox/flox/cre recombinase) and overexpression of GRK2 and its regulator of G protein signaling homology (RH) domain (GRK2-RH). It has recently been shown that antigen-induced mast cell activation leads to the generation of C3a, which stimulates its cognate GPCR in mast cells to enhance IgE-mediated inflammation [6, 7] These findings suggest that C3aR expressed on mast cells contributes to allergic responses in vivo. Because GRK2Ϫ/Ϫ mice are embryonic lethal, the strategies we utilized included lentiviral shRNA-mediated GRK2 knockdown, GRK2 gene deletion (GRK2flox/flox/cre recombinase) and overexpression of GRK2 and its RH domain (GRK2-RH) Using these combined approaches we demonstrate the novel finding that GRK2 acts as an important regulator of Fc⑀RI signaling in mast cells. We demonstrate that GRK2 modulates Fc⑀RI signaling in mast cells via at least two mechanisms; one involves its RH domain and modulates tyrosine phosphorylation of Syk, and the other is mediated via the phosphorylation of p38 and Akt
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