Novel G Protein-Coupled Responses in Leukocytes Elicited by a Chemotactic Bacteriophage Displaying a Cell Type-Selective Binding Peptide

Recently, we identified a neutrophil-binding phage displaying a novel peptide motif, GPNLTGRW. It was determined that this peptide, when displayed on bacteriophage (FGP phage), elicits a transient increase in cytosolic calcium. Here, we show that FGP phage stimulate neutrophil chemotaxis and induce a pertussis toxin-sensitive rise in cytosolic calcium in monocytes as well as in neutrophils. In contrast to the calcium response elicited by classical chemoattractants fMLP and IL-8, the FGP phage-elicited response in neutrophils is dependent on extracellular calcium and is mediated by receptor-activated, divalent cation channels. Consistent with G protein-coupled receptor signaling, FGP phage effect homologous and reciprocal heterologous desensitization with fMLP- and IL-8-stimulated calcium responses. Like non-G protein-coupled responses, the FGP-elicited calcium transient is abolished with phosphoinositide-3-kinase inactivation. Nonetheless, specific binding of GTP to neutrophil membranes follows stimulation with FGP phage, further supporting involvement of G proteins. However, FGP phage neither bind to nor elicit a calcium response from transfectant cells harboring known candidate G protein-coupled receptors. These data together suggest that the elicited responses are mediated by a novel G protein-coupled receptor or represent novel responses of a known receptor.