Early Activation of Sphingosine Kinase in Mast Cells and Recruitment to FcεRI Are Mediated by Its Interaction with Lyn Kinase

Abstract

ABSTRACT Sphingosine kinase has been recognized as an essential signaling molecule that mediates the intracellular conversion of sphingosine to sphingosine-1-phosphate. In mast cells, induction of sphingosine kinase and generation of sphingosine-1-phosphate have been linked to the initial rise in Ca 2+ , released from internal stores, and to degranulation. These events either precede or are concomitant with the activation of phospholipase C-γ and the generation of inositol trisphosphate. Here we show that sphingosine kinase type 1 (SPHK1) interacts directly with the tyrosine kinase Lyn and that this interaction leads to the recruitment of this lipid kinase to the high-affinity receptor for immunoglobulin E (FcεRI). The interaction of SPHK1 with Lyn caused enhanced lipid and tyrosine kinase activity. After FcεRI triggering, enhanced sphingosine kinase activity was associated with FcεRI in sphingolipid-enriched rafts of mast cells. Bone marrow-derived mast cells from Lyn −/ − mice, compared to syngeneic wild-type cells, were defective in the initial induction of SPHK1 activity, and the defect was overcome by retroviral Lyn expression. These findings position the activation of SPHK1 as an FcεRI proximal event.