Changes in proteoglycan composition of F9 teratocarcinoma cells upon differentiation

Teratocarcinoma cells (F9) were induced to differentiate by retinoic acid and then labelled with [3H]-glucosamine and [35S]-sulphate. Proteoglycans were then isolated from the plasma membranes and the culture medium by mild, dissociative, non-shear-dependent techniques. The undifferentiated cells were devoid of hyaluronic acid and contained negligible quantities of heparan sulphate, dermatan sulphate and chondroitin sulphate. Upon differentiation, the cells synthesized large amounts of hyaluronic acid and there was a threefold increase in the amount of membrane-bound sulphated proteoglycans. The differentiated cells also synthesized a proteoglycan (PGM-2) which was shed completely into the medium. It consisted of a large protein core with covalently linked sugar chains which were sulphated and had an approximate molecular weight of 12000. These sugar chains consisted of glucosamine and galactose in a molar ratio of 1:1 and contained a small quantity of mannose. Upon differentiation of the cells the amount of this molecule increased by threefold. This molecule was distinct from other proteoglycans since it was resistant to degradation by heparanase, chondroitinases, hyaluronidase and neuraminidase, but could be degraded by keratanase. Structurally it was very similar to keratan sulphate, consisting of alternating residues of (-Gal-GlcNAc-) in chains of approximately 20 such disaccharide units.