Cell adhesion molecule which is required for leukocyte transendothelial migration (TEM) under most inflammatory conditions (By similarity). Tyr-679 plays a critical role in TEM and is required for efficient trafficking of PECAM1 to and from the lateral border recycling compartment (LBRC) and is also essential for the LBRC membrane to be targeted around migrating leukocytes (By similarity). Trans-homophilic interaction may play a role in endothelial cell-cell adhesion via cell junctions (By similarity). Heterophilic interaction with CD177 plays a role in transendothelial migration of neutrophils (By similarity). Homophilic ligation of PECAM1 prevents macrophage-mediated phagocytosis of neighboring viable leukocytes by transmitting a detachment signal (By similarity). Promotes macrophage-mediated phagocytosis of apoptotic leukocytes by tethering them to the phagocytic cells; PECAM1-mediated detachment signal appears to be disabled in apoptotic leukocytes (By similarity). Modulates bradykinin receptor BDKRB2 activation (By similarity). Regulates bradykinin- and hyperosmotic shock-induced ERK1/2 activation in endothelial cells (By similarity). Induces susceptibility to atherosclerosis (PubMed:19048083). Trans-homodimer (via Ig-like C2-type 1 and Ig-like C2-type 2 domains); trans-homodimerization is required for cell-cell interaction. Forms a complex with BDKRB2 and GNAQ. Interacts with BDKRB2 and GNAQ. Interacts with PTPN11; Tyr-702 is critical for PTPN11 recruitment. Interacts with FER. Interacts with CD177; the interaction is Ca(2+)-dependent; the interaction is direct. Localizes to the lateral border recycling compartment (LBRC) and recycles from the LBRC to the junction in resting endothelial cells. Cell surface expression on neutrophils is down-regulated upon fMLP or CXCL8/IL8-mediated stimulation. Isoform 1 and isoform 3 are expressed in lung and platelets. The Ig-like C2-type domains 2 and 3 contribute to formation of the complex with BDKRB2 and in regulation of its activity. Phosphorylated on Ser and Tyr residues by src kinases after cellular activation (PubMed:16731527). Upon activation, phosphorylated on Ser-718 which probably initiates the dissociation of the membrane-interaction segment (residues 698-718) from the cell membrane allowing the sequential phosphorylation of Tyr-702 and Tyr-679 (By similarity). Constitutively phosphorylated on Ser-723 in resting platelets (By similarity). Phosphorylated on tyrosine residues by FER and FES in response to FCER1 activation (PubMed:16731527). In endothelial cells Fyn mediates mechanical-force (stretch or pull) induced tyrosine phosphorylation (By similarity). Palmitoylation by ZDHHC21 is necessary for cell surface expression in endothelial cells and enrichment in membrane rafts. Mice show reduced atherosclerotic lesions. There is down-regulation of ICAM-1 in endothelial cells at the lesion periphery, and reduced disruption of Cx43 junctional staining at arterial branch points and in the descending aorta. PECAM-1