Detergent-resistant membrane domains are required for mast cell activation but dispensable for tyrosine phosphorylation upon aggregation of the high affinity receptor for IgE

Aggregation of the high affinity receptor for IgE (Fc epsilon RI) on mast cells results in the rapid phosphorylation of tyrosines on the beta and gamma 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 Fc epsilon RI signaling because aggregated receptors emigrate to DRMs that are enriched in certain signaling components. We evaluated the role of DRMs in Fc epsilon RI signaling by disruption of DRMs using a cholesterol-binding agent, methyl-beta -cyclodextrin (MBCD), While treatment of rat basophilic leukemia cells with MBCD inhibits degranulation and Ca2+ mobilization upon aggregation of Fc epsilon RI, MBCD hardly affects the aggregation-induced tyrosine phosphorylation of Fc epsilon RI as well as other signaling molecules such as phospholipase C-gammal (PLC-gammal), 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-gammal, 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 Fc epsilon RI is tyrosine phosphorylated outside DRMs by constitutively associated Src family kinase Lyn via a transphosphorylation mechanism.