Fluid flow and osmotic stress induce tyrosine phosphorylation of an endothelial cell 128 kDa surface glycoprotein

To investigate the flow sensing and the early signaling events in vascular endothelial cells (ECs), we surveyed changes in phosphotyrosine levels of glycoproteins using immunoblot analyses. Cultured bovine arterial ECs were exposed to steady laminar flow by using a coneplate type flow apparatus and glycoprotein fractions were partially purified by lectin affinity column chromatography. A 128 kDa protein band in the Ricinus-communis-agglutinin-bound fraction showed a rapid and consistent augmentation of tyrosine phosphorylation by flow. Cell surface domain-restricted biotinylation revealed that the 128 kDa glycoprotein has extracellular domain(s). Tyrosine phosphorylation of the 128 kDa protein was also observed in ECs subjected to hyper- or hypo-osmotic shock but not in ECs stimulated by Ca2+ mobilizing agents.