Abstract
Aggregation of the high affinity receptor for IgE (FcεRI) on mast cells results in the rapid phosphorylation of tyrosines on the β and γ chains of the receptor by the Src family kinase Lyn, which initiates the signaling cascades leading to secretion of inflammatory mediators. The detergent-resistant membranes (DRMs) have been implicated in FcεRI signaling because aggregated receptors emigrate to DRMs that are enriched in certain signaling components. We evaluated the role of DRMs in FcεRI signaling by disruption of DRMs using a cholesterol-binding agent, methyl-β-cyclodextrin (MBCD). While treatment of rat basophilic leukemia cells with MBCD inhibits degranulation and Ca2+ mobilization upon aggregation of FcεRI, MBCD hardly affects the aggregation-induced tyrosine phosphorylation of FcεRI as well as other signaling molecules such as phospholipase C-γ1 (PLC-γ1). MBCD delocalizes phosphatidylinositol 4, 5-bisphosphate from DRMs, which may prevent MBCD-treated cells from producing inositol 1, 4, 5-trisphosphate by means of activated PLC-γ1. These data suggest an indispensable role for DRMs in the Ca2+ response rather than tyrosine phosphorylation, and support a model of receptor phosphorylation in which aggregated FcεRI is tyrosine phosphorylated outside DRMs by constitutively associated Src family kinase Lyn via a transphosphorylation mechanism.
