Apical secretion of chondroitin sulphate in polarized Madin-Darby canine kidney (MDCK) cells.

Sugar moieties have been shown to contain sufficient and necessary information to target examples of secreted and transmembrane glycoproteins to the apical surface of epithelial MDCK cells. We have investigated if the sugar chains of proteoglycans, the glycosaminoglycans, also contain structural determinants for apical transport. Here we show that although 75% of the proteoglycan secretion from MDCK cell monolayers is into the basolateral medium, 75% of the proteoglycans of the chondroitin sulphate type are secreted apically. The sorting information in the chondroitin sulphate proteoglycans is localized to the sugar chains, since protein-free chondroitin sulphate chains, initiated on hexyl beta-D-thioxyloside, were also predominantly secreted to the apical medium.