EVIDENCE THAT HUMAN BONE-CELLS IN CULTURE CONTAIN BINDING-SITES FOR OSTEOGENIC PROTEIN-1

Recent studies have shown that osteogenic protein (OF)-1 or bone morphogenetic protein (BMP)-7 increases proliferation and differentiation of human bone cells (HBCs) in culture and modulates production of IGF system components. In order to study the mechanism by which OP-1 causes these effects, we sought to test the hypothesis that the effects of OP-1 are mediated at least in part by specific receptors (for OP-1) in HBCs. Binding studies with serum-free cultures of normal HBCs and human osteosarcoma cells showed a maximum binding of 15 - 25% for [I-125]OP-1; the binding was time- and temperature-dependent in different experiments. Scatchard analysis of [(125)]OP-1 binding to TE85 human osteosarcoma cells showed at least two binding sites, about 30,000 and 60,000 per cell with apparent K-d of 2.5 x 10(-10)M and 1 x 10(-9)M, respectively. [(125)]OP-1 binding to TE85 cells was displaced by unlabeled OP-1 (16-1000 ng/ml) with a 50% displacement at 250 ng/ml. BMP-2 effectively displaced [(125)]OP-1 binding to HBCs while TGF-beta 1 did not. Affinity cross-linking studies showed that [(125)]OP-1 interacted specifically with three binding sites with apparent M(r) of 34, 65 and > 205kDa. The findings of this study demonstrate that the effects of OP-1 on HBCs may be mediated in part via BMP-specific receptors. (C) 1994 Academic Press, Inc.