Insulin-like growth factor-binding protein-1 inhibits binding of IGF-I on fetal skin fibroblasts but stimulates their DNA synthesis

Insulin-like growth factor-binding protein-1 (IGFBP-1) was purified from human midtrimester amniotic fluid using monoclonal anti-IGFBP-1 affinity column. Two peaks were obtained in anion exchange chromatography. Both had the same molecular mass of 30 kDa. In monolayer cultures of fetal skin fibroblasts both forms of IGFBP-1 inhibited binding of [ 125I]IGF-I onto the cells, but amplified the IGF-I-stimulated [ 3H]thymidine incorporation into the same cells. Radiolabeled IGFBP-1 did not bind to the cells. No detectable IGFBP-1 was released into conditioned medium from the cells, and they contained no specific IGFBP-1 mRNA. Recently we found that the same IGFBP-1 preparation inhibits IGF-I-stimulated [ 3H]thymidine incorporation into human hyperstimulated granulosa cells (1). These results show that, depending on target cells, the same protein is capable of either stimulating or inhibiting DNA synthesis.