Biosynthesis of cell surface sulfated glycoproteins by cultured vascular endothelial cells

Cultured vascular endothelial cells incorporate 35SO4 into a class of oligosaccharides which are N-glycosidically linked to cell-surface or extracellular proteins. This type of sulfated oligosaccharide was not synthesized by smooth muscle cell cultures and may represent sulfation of vascular tissue glycoproteins which are unique to endothelial cells. These endothelial cell 35S-labeled oligosaccharides are not released from the polypeptides under alkaline conditions that cleave O-glycosidically linked chains. The incorporation of both [3H]hexosamine and 35SO4 into these oligosaccharides is inhibited by tunicamycin, an antibiotic which inhibits protein N-glycosylation. 35S-Labeled oligosaccharides, isolated as glycopeptides, were resistant to a variety of chemical and enzymatic treatments which degraded vascular cell sulfated glycosaminoglycans but appear to contain terminal sialic acid residues. Endothelial cell sulfated oligosaccharide chains could also be distinguished from sulfated glycosaminoglycans by the apparent size and charge. Endothelial cells released or secreted 35S-labeled glycoproteins into the culture medium. These soluble 35S-labeled glycoproteins were partially purified by DEAE-cellulose chromatography and separated from the 35S-labeled proteoglycans, which are also released into the medium. The major 35S-labeled glycoproteins released from the cells had apparent molecular weights of 24 000--66 000. The cell-associated 35S-labeled glycoproteins, released with ethylenediaminetetraacetate or extracted with 0.5% octyl glucoside, were partially purified on DEAE-cellulose and had apparent molecular weights of 45 000--250 000.