A novel and critical role for tyrosine 663 in platelet endothelial cell adhesion molecule-1 trafficking and transendothelial migration.

PECAM-1/CD31 is required for leukocyte transendothelial migration (TEM) under most inflammatory conditions. A critical pool of PECAM-1 resides in the lateral border recycling compartment (LBRC). During TEM, membrane from the LBRC is redirected to surround the leukocyte, and this targeted recycling per se is required for TEM. The cytoplasmic domain of PECAM-1 contains two tyrosine residues that have been implicated in PECAM-1 signaling in other cells but never examined in the context of TEM. We found that expression of PECAM-1 imparts on cells the ability to support TEM and that tyrosine 663 (but not tyrosine 686) is required. Furthermore, tyrosine 663 is required for PECAM-1 to efficiently enter and exit the LBRC. Most important, mutation of tyrosine 663 abolishes the ability of the endothelial cells to support targeted recycling of the LBRC. These data define a novel role for tyrosine 663 and suggest that it is part of a recognition motif for trafficking to and/or from the LBRC.