Sphingosine 1‐phosphate induces platelet/endothelial cell adhesion molecule‐1 phosphorylation in human endothelial cells through cSrc and Fyn

Abstract

Sphingosine 1‐phosphate (S1P) is a multifunctional lysophospholipid. Through binding with a specific family of G protein‐coupled receptors, S1P activates various cellular functions in endothelial cells. Platelet/endothelial cell adhesion molecule‐1 (PECAM‐1) is a 130‐kDa transmembrane protein expressed predominantly on the surface of platelets and endothelial cells. Upon activation, the cytoplasmic tyrosine residues could be phosphorylated and regulate several cellular functions, including endothelial integrin activation and diapedesis. In this study, we first demonstrated that S1P induced PECAM‐1 tyrosine phosphorylation in human umbilical cord vein cells (HUVEC) by immunoprecipitation and western blot. The induction was blocked by pertussis toxin and PP2, the inhibitor for Gi and Src family kinases (SFK). In addition, S1P‐induced SFK activation at endothelial cell borders was also observed by western blot and confocal microscopy. Two members of SFK, cSrc and Fyn, were dominantly expressed in HUVEC and targeted with specific siRNA. The induction effect of S1P on PECAM‐1 tyrosine phosphorylation was significantly suppressed in HUVEC cotrasfected with both siRNA. These results would help to elucidate the regulatory mechanism of S1P in PECAM‐1 functions in human endothelial cells.