Rapid dephosphorylation of the GTPase dynamin after FcepsilonRI aggregation in a rat mast cell line

As part of our studies aimed at exploring the potential role(s) of protein phosphatases in mast cell signaling, we analyzed the phosphorylation status of tyrosine-containing proteins in a rat mast (RBL) cell line that expresses both native rat high affinity IgE receptors (FcepsilonRI) and functional human FcepsilonRIalpha. After FcepsilonRI aggregation, there was a rapid increase in the tyrosine phosphorylation of a number of proteins, including those of m.w. 72 and 110 kDa. Concurrent with these events, however, there was a rapid dephosphorylation of a 100-kDa protein that was constitutively phosphorylated in the unstimulated cells. Using a specific mAb, this 100-kDa protein was identified as the GTPase dynamin. Dynamin was shown to associate with the SH3 domain of the src-related tyrosine kinase p56lyn in RBL 2H3 cells both in vitro and in vivo. FcepsilonRI aggregation causes rapid internalization 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.