Characterization of proteoglycans synthesized by rat chondrosarcoma chondrocytes treated with multiplication-stimulating activity and insulin.

The structures of proteoglycans synthesized and secreted by Swarm rat chondrosarcoma chondrocytes cultured in the presence of insulin, multiplication-stimulating activity (MSA), and fetal calf serum were investigated. Proteoglycans produced in all cultures were found as link protein stabilized aggregates. Monomeric proteoglycans from cultures treated with MSA or insulin were slightly larger in hydrodynamic size than those synthesized by chondrocytes maintained in unsupplemented medium. This increase reflected a 25 to 30% increase in the length of the covalently bound chondroitin sulfate side chains. No free glycosaminoglycans were detected in any cultures, although the presence of a lower molecular weight proteoglycan at a significant concentration was observed in the medium fraction of serum-maintained cultures. MSA and insulin treatments did not result in the synthesis of a proteoglycan containing other types of glycosaminoglycans nor did they alter the degree or position of sulfation of the chondroitin sulfate glycosaminoglycans. The small changes in proteoglycan structure do not account for the larger differences in the levels of incorporation of radioactivity indicating that the primary effect of MSA and insulin on proteoglycan synthesis in this in vitro system is an increased rate of synthesis and secretion of proteoglycan.