EFFECTS OF INSULIN-LIKE GROWTH-FACTOR (IGF) BINDING-PROTEINS (BPS)-3 AND BPS-6 ON DNA-SYNTHESIS OF RAT OSTEOBLASTS - FURTHER EVIDENCE FOR AROLE OF AUTO- PARACRINE IGF-I BUT NOT IGF-II IN STIMULATING OSTEOBLAST GROWTH/

IGFBP-3 and IGFBP-6 were used to study whether both IGF I and IGF II p lay a role in auto-/paracrine stimulation of rat osteoblast growth. Bo th IGFBPs decreased basal DNA synthesis in neonatal rat calvaria cells but with different potencies. Consistent with their IGF binding affin ities, IGFBP-3 blocked both IGF I- and IGFII-stimulated DNA synthesis, whereas IGFBP-6 preferentially blocked IGFII-stimulated DNA synthesis . These inhibitory effects of the two IGFBPs can be fully explained by the sequestration of IGFs. Because IGFBP-6 preferentially binds IGF I I and is much less potent than IGFBP-3 in decreasing basal DNA synthes is in calvaria cells, IGF I but not IGF II appears to be an important auto-/paracrine stimulator of DNA synthesis. (C) 1995 Academic Press, Inc.