EFFECTS OF INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEIN COMPLEXES ON HUMAN FIBROBLAST GROWTH

Insulin-like growth factor binding protein (IGF-BP) complexes containi ng either IGF-I or IGF-II were purified from human plasma and coincuba ted with human foreskin fibroblasts. Incorporation of [H-3]thymidine i nto fibroblasts was measured to determine the mitogenic effects of the IGF-BP complexes in comparison with purified recombinant IGF-I or IGF -II. The IGF-I-BP complex was shown to have no stimulatory activity wh en added to cultures at a comparable Non Suppressible Insulin-Like Act ivity (NSILA) dose level to that of purified recombinant IGF-I which p roduced maximal stimulation. In contrast, the IGF-II-BP complex produc ed a similar stimulatory activity to that of purified recombinant IGF- II when added at comparable NSILA doses. NSILA-p, a contaminating fact or in the purified preparations of IGF-BP complexes, was shown to have no effect on fibroblast growth. This study suggests that plasma IGF b inding proteins may have a differential effect on the stimulatory acti vities of IGFs I and II on human fibroblasts.