Growth on type I collagen promotes expression of the osteoblastic phenotype in human osteosarcoma MG‐63 cells

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Abstract
Using MG‐63 cells as a model system capable of partial osteoblastic differentiation, we have examined the effect of growth on extracellular matrix. MG‐63 cell matrix and purified type I collagen induced a morphological change characterized by long cytoplasmic processes reminiscent of those seen in osteocytes. Concurrent biochemical changes involving bone marker proteins included increased specific activity of cell‐associated alkaline phosphatase and increased secretion of osteonectin (up to 2.5‐fold for each protein); all changes occurred without alterations in the growth kinetics of the MG‐63 cells. The increase in alkaline phosphatase activity was maximal on days 6–8 following seeding; increased osteonectin secretion was most prominent immediately following seeding; all changes decreased as cells reached confluence. Growing cells on type I collagen resulted in an increased induction of alkaline phosphatase activity by 1,25 (OH)2D3 (with little change in the 1,25 (OH)2D3 induction of osteonectin and osteocalcin secretion), and increased TGF‐β induction of alkaline phosphatase activity as well (both TGF‐β1 and TGF‐β2). Both the 1,25 (OH)2D3 and TGF‐β effects appeared to be synergistic with growth on type I collagen. These studies support the hypothesis that bone extracellular matrix may play an important role in osteoblastic differentiation and phenotypic expression.

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