Phosphorylation of surface E‐selectin and the effect of soluble ligand (Sialyl Lewisx) on the half‐life of E‐selectin

E‐selectin (ELAM‐1) is an adhesion molecule for leukocytes that is transiently expressed on endothelial cells. Following cell surface expression of E‐selectin on human umbilical vein endothelial cells (HUVEC) stimulated with tumor necrosis factor, the induced E‐selectin molecules are rapidly degraded. The kinetics of turnover of surface disposed E‐selectin were investigated. The rapid disappearance of surface E‐selectin is temperature dependent and sensitive to the lysosomotropic agent chloroquine. The half‐life of E‐selectin is not affected by inclusion of soluble sialyl Lewis x (sLex) ligands in the medium. Surface E‐selectin is phosphorylated on one or more serine residues, but this modification is not obviously related to internalization.