Altered Synthesis of Cartilage-Specific Proteoglycans by Mutant Human Cartilage Oligomeric Matrix Protein

BACKGROUND: The mechanism by which mutant cartilage oligomeric matrix protein (COMP) induces a pseudoachondroplasia phenotype remains unknown, and the reason why a mutation of a minor protein of the growth plate cartilage causes total disruption of endochondral bone formation has not yet been determined. The current study was performed to investigate the effects of mutated COMP on the synthesis of the cartilage-specific major matrix proteins of Swarm rat chondrosarcoma chondrocytes. METHODS: The Swarm rat chondrosarcoma chondrocytes transfected with a chimeric construct, which consisted of a mutant gene of human COMP and an amino acid FLAG tag sequence, were cultured in agarose gel. Formation of extracellular proteoglycan and type-II collagen by the cells was evaluated by immunohistochemical staining and measuring the (35)S-sulfate incorporation. RESULTS: No difference was observed for the detection of type-II collagen among the cell lines expressing mutant COMP and the control cell lines. Histochemical staining of sulfated proteoglycans with safranin-O showed that lesser amounts of proteoglycans were incorporated into the extracellular matrix of the chondrocytes transfected with the mutant gene. (35)S-sulfate incorporation into the cell/matrix fractions demonstrated markedly lower radiolabel incorporation, as compared to that of the control cells. CONCLUSIONS: Mutation of COMP has an important impact on the processing of proteoglycans, rather than type-II collagen, in the three-dimensional culture of Swarm rat chondrosarcoma chondrocytes.

Effects of Mutant Cartilage Oligomeric Matrix Protein on the Synthesis of Extracellular Matrix in the Swarm Rat Chondrosarcoma Cell Line / 대한정형외과연구학회지

PURPOSE: To investigate the effects of mutated cartilage oligomeric matrix protein (COMP) on the synthesis of cartilage-specific major matrix proteins of Swarm rat chondrosarcoma chondrocytes. MATERIALS AND METHODS: The Swarm rat chondrosarcoma chondrocytes transfected with chimeric construct consisting of a mutant gene of human COMP and an amino acid FLAG tag sequence were cultured in agarose gel. Formation of extracellular proteoglycan and type-II collagen of the cells were evaluated by immunohistochemical staining and measuring 35S-sulfate incorporation. RESULTS: No difference was observed in type-II collagen detection among the cell line expressing mutant COMP and control cell lines. Histochemical staining of sulfated proteoglycans with safranin-O showed lower amounts of proteoglycans were incorporated into the extracellular matrix of chondrocytes transfected with mutant gene. 35S-sulfate incorporation into the cell/matrix fractions demonstrates marked lower radiolabel incorporation compared to control cells. CONCLUSION: Mutation of COMP impacts the processing of proteoglycans rather than type-II collagen in three-dimensional culture of Swarm rat chondrosarcoma chondrocytes.