Large cartilage proteoglycan (PG-LA) influences the biosynthesis of macromolecules by isolated chondrocytes

Bovine articular and tracheal chondrocytes were cultured at high density in multilayers. Intact or fragmented large aggregating proteoglycans (PG-LA) from cartilage were added to the cultures and the biosynthetic response studied by the incorporation of [3H]-leucine and [35S]-sulfate for proteins and proteoglycans respectively. Incorporated radiolabel and patterns of synthesized macromolecules were compared with control cultures without additives and cultures containing either of the synthetic polymers dextran or dextran sulfate. All proteoglycans and derivatives containing globular protein structures had a stimulatory effect on the biosynthesis of both proteins and proteoglycans as did the highly polyanionic polymer dextran sulfate. Distribution of the radiolabeled material between the cell- and medium pools were however different in the various cultures. A radiolabeled protein, migrating as a triplet band at a position of approximately 140 kDa after reduction, was detected by SDS-PAGE and fluorography. The protein was present in all cell extracts and in the media of cultures stimulated with proteoglycans and proteoglycan fragments, except chondroitin sulfate side chains. The protein was shown to be collagenous in nature by collagenase digestion and identified as procollagen II by immunoprecipitation.