Procollagen synthesis and extracellular matrix deposition in MG-63 osteosarcoma cells

Abstract

We compared the procollagen synthetic properties of MG‐63 osteosarcoma cells with those of cultured human skin fibroblasts. In both cells, the expressions of type I and III procollagens are largely dependent on the constant presence of ascorbate and coordinately decreased by the neutral polymer dextran T‐40. The amino‐terminal propeptides of pro‐α₁ and pro‐α₂ chains of type I procollagen are phosphorylated and those of the pro‐α₁ and pN‐α₁ chains of type III procollagen both phosphorylated and sulfated, there being no difference in net charge in the propeptides between these cell types. The major differences between MG‐63 and normal fibroblasts are the exceptionally high relative synthesis of type III procollagen by MG‐63 cells, up to about 40% of the total of types I and III (6% in cultured skin fibroblasts), and the inability of ascorbate‐supplemented MG‐63 cells to deposit collagens into an insoluble pericellular matrix. A longer dextran treatment shifts up to one‐fourth of the proline‐labeled extracellular macromolecules into the matrix fraction within 4 days (in control 4%). Despite processing of the procollagens to the respective collagens in the matrix, neither control matrices nor those induced by dextran induced increased production of alkaline phosphatase. In cultures up to 4 days postconfluence the proportion of type III collagen produced tended to increase over that in early confluent cultures. With respect to collagen production, the MG‐63 cell line is not a representative of the osteoblast lineage but rather resembles a proliferative wound fibroblast.