DNA Synthesis in Human Fibroblasts: Stimulation by Insulin and by Nonsuppressible Insulin-like Activity (NSILA-S)

Abstract

The effects of acid-soluble nonsuppressible insulin-like activity (NSILA-S) and insulin on DNA synthesis by cultured human fibroblasts have been compared. NSILA-S and insulin, like serum, stimulated [³H]thymidine incorporation into DNA after an 8- to 10-hour lag, reaching maximum levels after 16 to 20 hr. Insulin was effective only at high concentrations, 0.02 μg/ml or greater, whereas NSILA-S was active at concentrations that have been reported in human serum. Combined addition of maximally effective concentrations of insulin and NSILA-S failed to give additive stimulation, suggesting that the two polypeptides act by a common mechanism. In contrast, combined addition of insulin and serum, or NSILA-S and serum, gave additive responses.