Receptors for insulin-like growth factors-I and -II in osteoblast-enriched cultures from fetal rat bone.
Insulin-like growth factors-I and -II (IGF-I and IGF-II) are produced by bone cells and stored in bone matrix, and stimulate bone cell DNA synthesis and type I collagen production. Earlier studies in cells from an assortment of tissues indicate that IGF-I binds to membrane receptors of various relative molecular mass (Mr), whereas IGF-II binds predominantly to the mannose-6-phosphate transferase. In the present studies we have examined the IGF receptor profile in osteoblast-enriched cultures prepared from fetal rat parietal bone. Scatchard binding kinetics with either 125I-IGF-I or 125I-IGF-II were curvilinear, indicating high and low affinity receptor classes for each ligand. Chemical cross-linking and polyacrylamide gel analysis revealed that 125I-IGF-I bound at Mr 130,000, 240,000, and 260,000, whereas 125I-IGF-II bound predominantly at Mr 240,000. Unlabeled IGF-I displaced 125I-IGF-I with high affinity at Mr 260,000 and 130,000 and with lower affinity at Mr 240,000. Unlabeled IGF-II preferentially displaced either radioactive ligand at Mr 240,000, but at high concentrations displaced 125I-IGF-I at all binding sites. Furthermore, mannose-6-phosphate enhanced binding by both 125I-IGF-I and 125I-IGF-II at Mr 240,000, and antibody to the rat IGF-II receptor prevented binding only at this location. The relative affinities of IGF-I and IGF-II for the primary IGF-I receptor correlate with their anabolic activities in bone cultures and suggest that the IGF-I receptor mediates the growth-promoting effects of both agents in bone.
Centrella
M
M
Research Laboratory, Saint Francis Hospital and Medical Center, Hartford, Connecticut 06105.
McCarthy
T L
TL
Canalis
E
E
D000818:Animals; D001667:Binding, Competitive; D001842:Bone and Bones / Q000166:cytology / Q000196:embryology / Q000378:metabolism*; D002478:Cells, Cultured; D005333:Fetus / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007335:Insulin-Like Growth Factor II / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017451:Receptors, Somatomedin; D013002:Somatomedins / Q000378:metabolism*
D011956:Receptors, Cell Surface; D017451:Receptors, Somatomedin; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II