The regulation of type-I collagen synthesis by insulin-like growth factor-I in human osteoblast-like SaOS-2 cells.

The effect of insulin-like growth factor-I on collagen synthesis was studied using cultured human osteoblast-like SaOS-2 cells by measuring the incorporation of tritiated L-proline into immunoprecipitable type-I collagen. Tritiated L-proline incorporation into collagen was significantly stimulated by insulin-like growth factor-I in a time- and concentration-dependent manner. Unlabelled L-proline and alpha-(methylamino) isobutyric acid inhibited either the influx into cells, or the incorporation into collagen, of tritiated L-proline. The increase in incorporation of tritiated L-proline was significantly reduced by cycloheximide and actinomycin D. L-Proline incorporation into collagen was also stimulated by insulin-like growth factor-II, insulin-like growth factor-I analogues and insulin. The insulin-like growth factor-I-stimulated L-proline incorporation was inhibited by one of its binding proteins, insulin-like growth factor binding protein-4, in a concentration-dependent manner.