A rat hepatoma cell line was shown to synthesize heparan sulfate and chondroitin sulfate proteoglycans . Unlike cultured hepatocytes, the hepatoma cells did not deposit these proteoglycans into an extracellular matrix, and most of the newly synthesized heparan sulfate proteoglycans were secreted into the culture medium . Heparan sulfate proteoglycans were also found associated with the cell surface . These proteoglycans could be solubilized by mild trypsin or detergent treatment of the cells but could not be displaced from the cells by incubation with heparin . The detergent-solubilized heparan sulfate proteoglycan had a hydrophobic segment that enabled it to bind to octyl-Sepharose . This segment could conceivably anchor the molecule in the lipid interior of the plasma membrane . The size of the hepatoma heparan sulfate proteoglycans was similar to that of proteoglycans isolated from rat liver microsomes or from primary cultures of rat hepatocytes . Ion-exchange chromatography on DEAE-Sephacel indicated that the hepatoma heparan sulfate proteoglycans had a lower average charge density than the rat liver heparan sulfate proteoglycans . The lower charge density of the hepatoma heparan sulfate can be largely attributed to a reduced number of Nsulfated glucosamine units in the polysaccharide chain compared with that of rat liver heparan sulfate. Hepatoma heparan sulfate proteoglycans purified from the culture medium had a considerably lower affinity for fibronectin-Sepharose compared with that of rat liver heparan sulfate proteoglycans . Furthermore, the hepatoma proteoglycan did not bind to the neoplastic cells, whereas heparan sulfate from normal rat liver bound to the hepatoma cells in a timedependent reaction . The possible consequences of the reduced sulfation of the heparan sulfate proteoglycan produced by the hepatoma cells are discussed in terms of the postulated roles of heparan sulfate in the regulation of cell growth and extracellular matrix formation .Heparan sulfate proteoglycans are present in a large variety ofvertebrate tissues and appear to be preferentially located at the surface of cells, either directly associated with the cell membrane (1) or in close contact with cells, as in basement membranes (2) and in the pericellular matrix ofcultured cells (3,4).Previous studies in our laboratory have indicated that heparan sulfate proteoglycans are associated with the plasma membrane of rat liver cells by two independent mechanisms (5). The proteoglycan may be bound via its polysaccharide portion to cell surface receptors, or the core protein may be inserted into the lipid interior of the membrane (6). The mechanisms responsible for the anchorage of heparan sulfate in the basement membrane or in extracellular matrices are not clear. Immunofluorescent studies have shown a codistribution between heparan sulfate proteoglycans and fibronectin in the extracellular matrix (7, 8) and a direct binding of heparan sulfate chains to fibronectin has been demonstrated (7, 9).Transformed cells usually do not...

The binding of the basement-membrane glycoprotein laminin to glycosaminoglycans (aggregating and non-aggregating subsets of heparan sulphates and dermatan sulphates, as well as heparin, chondroitin sulphates and hyaluronic acid) was studied by affinity chromatography. Partially periodate-oxidized chains of glycosaminoglycans were coupled to adipic acid dihydrazide-substituted agarose. Co-polymeric glycosaminoglycans reveal high affinity for laminin, whereas hyaluronic acid does not. Competitive-release experiments indicate that glycosaminoglycans share a common binding site on the laminin molecule.

Balb/c 3T3 cultures grown in the absence of serum release both plasminogen activator and plasminogen activator inhibitor in the culture medium. Cellular transformation with SV-40 virus increased the level of the activator, whereas dexamethasone increased the level of the inhibitor. Heparin added to the medium potentiated the glucocorticoid-induced inhibitory activity, strongly decreasing or completely abolishing the activity of plasminogen activator. Heparin sulfate showed similar effects to heparin, although at higher concentrations. It is suggested that heparin-like compounds are involved in the regulation of plasminogen activator, acting as inhibitory cofactors.