PHOSPHORYLATION OF SURFACE E-SELECTIN AND THE EFFECT OF SOLUBLE LIGAND (SIALYL LEWIS(X)) 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 (sLe(x)) ligands in the medium. Surface E-selectin is phosphorylated on one or more serine residues, but this modification is not obviously related to internalization.