AGGREGATION OF THE HIGH-AFFINITY IGE RECEPTOR RESULTS IN THE TYROSINEPHOSPHORYLATION OF THE SURFACE-ADHESION PROTEIN PECAM-1 (CD31)

One of the earliest events after aggregation of the high affinity rece ptor for IgE (Fc epsilon RI) on mast cells is the activation of protei n tyrosine kinases resulting in tyrosine phosphorylation of numerous p roteins, Using a monoclonal antibody raised against the rat basophilic leukemia RBL-2H3 cells, we identified that platelet/endothelial cell adhesion molecule 1 (PECAM-1 or CD31) was tyrosine phosphorylated in t hese cells, Aggregation of PECAM-1 did not induce a detectable increas e in its tyrosine phosphorylation, nor did it result in degranulation, However, the minimal tyrosine phosphorylation of PECAM-1 in nonstimul ated cells was dramatically increased after Fc epsilon RI aggregation, This receptor-induced tyrosine phosphorylation of PECAM-1 was an earl y event, independent of Ca2+ influx or of the activation of protein ki nase C and of cell adhesion, PECAM-1 is an adhesion molecule that is r equired for the transmigration of leukocytes across the endothelium in to sites of inflammation, Therefore tyrosine phosphorylation of PECAM- 1 may modulate its interaction with other molecules, thereby regulatin g the migration of basophils into inflammatory sites.