Calcium mobilization via sphingosine kinase in signalling by the FcεRI antigen receptor

Calcium mobilization through antigen receptors, including high-affinity IgE receptors (FcεRI), is thought to be mediated by inositol-1,4,5-trisphosphate production (InsP₃). Here we show that antigen clustering of FcεRI on the rat mast-cell line (RBL-2H3) activates a sphingosine kinase (SK) and produces sphingosine-1-phosphate (S1P), an alternative second messenger for intracellular calcium mobilization. The sphingosine analogue, D-L-threo-dihydrosphingosine (DHS), inhibits the SK enzyme competitively with a dissociation constant, K(i) of 5 to 18 μM. This inhibition substantially suppresses the FcεRI-mediated calcium signal, but leaves intact the syk tyrosine kinase activation and the small InsP₃ production. The entire InsP₃ dependent pathway activated by a transfected G-protein coupled receptor, used here as a positive control, also remained intact. Thus FcεRI principally utilizes a SK pathway to mobilize calcium.