RAPID DEPHOSPHORYLATION OF THE GTPASE DYNAMIN AFTER FC-EPSILON-RI AGGREGATION IN A RAT MAST-CELL LINE

As part of our studies aimed at exploring the potential role(s) of pro tein phosphatases in mast cell signaling, we analyzed the phosphorylat ion status of tyrosine-containing proteins in a rat mast (RBL) cell li ne that expresses both native rat high affinity IgE receptors (Fc epsi lon RI) and functional human Fc epsilon RI alpha. After Fc epsilon RI aggregation, there was a rapid increase in the tyrosine phosphorylatio n of a number of proteins, including those of m.w. 72 and 110 kDa. Con current with these events, however, there was a rapid dephosphorylatio n of a 100-kDa protein that was constitutively phosphorylated in the u nstimulated cells. Using a specific mAb, this 100-kDa protein was iden tified as the GTPase dynamin, Dynamin was shown to associate with the SH3 domain of the src-related tyrosine kinase p56(lyn) in RBL 2H3 cell s both in vitro and in vivo, Fc epsilon RI aggregation causes rapid in ternalization of the aggregated receptors via clathrin-coated pits and dynamin is known to play a role in clathrin-mediated endocytosis, so the dephosphorylation of dynamin may provide the signal for targeting the aggregated receptors to the endocytic pathway.