Different galactosaminoglycan composition of small proteoglycans from osteosarcoma cells

The expression of the core proteins and the co-polymeric structure of the glycosaminoglycan chains of three different small proteoglycans (biglycan, decorin, proteoglycan-100) have been examined in the human osteosarcoma cell line MG-63. The three proteoglycans, which are carrying either one or two chondroitin/dermatan sulphate chains, were synthesized in a similar molar ratio, as determined by [35S]methionine as well as by [35S]sulphate incorporation. After sulphate ester formation, they were secreted into the culture medium with similar kinetics. Immune staining with monospecific antibodies revealed that at least biglycan and proteoglycan-100 were present in all individual cells. However, in contrast to these similarities, the glycosaminoglycan moiety of proteoglycan-100 was composed exclusively of chondroitin 4- and 6-sulphate repeating units, whereas biglycan and decorin contained hybrid polymers of chondroitin and dermatan sulphate with approximately 90% 4-sulphated disaccharide repeating units. Treatment with transforming growth factor-beta resulted in a marked down-regulation of proteoglycan-100 synthesis without significant alteration of its glycosaminoglycan structure. Up-regulation of biglycan and moderate down-regulation of decorin were accompanied by a small decrease in the conversion of chondroitin to dermatan sulphate disaccharide units in both cases. The specific stimulation of the biosynthesis of proteoglycan-100 by tumour necrosis factor-alpha was without consequence for its glycosaminoglycan composition. Treatment with tumour necrosis factor-alpha had no influence on the synthesis and glycosaminoglycan structure of biglycan and decorin. These findings support the proposal of the importance of the core protein for the determination of the extent of glycosaminoglycan modification.