Identification and characterization of the insulin-like growth factor I receptor in mature rabbit osteoclasts.
In this study, the insulin-like growth factor I (IGF-I) receptor was identified in rabbit osteoclasts at mRNA and protein levels by in situ hybridization and autoradiography, respectively. Using highly purified mature osteoclasts, the IGF-I receptor was characterized on the molecular level according to its size and its affinity and number per osteoclast by isolation of the receptor-ligand complex and by binding studies, respectively, and on the cellular level according to the response of mature osteoclasts to IGF-I stimulation. In situ hybridization and autoradiography experiments showed that osteoclasts express IGF-I receptor mRNA and IGF-I binding sites. Chemical cross-linking of 125I-IGF-I bound to the purified mature osteoclasts and subsequent sodium dodecyl sulfide-polyacrylamide gel electrophoresis revealed the specific binding of 125I-IGF-I in complexes with molecular masses of 130 and 230-RD consistent with binding to the IGF-I receptor. In competition experiments, 125I-IGF-I binding to mature osteoclasts was dose-dependently reduced by unlabeled IGF-I in the picomolar range, whereas 20 nM insulin did not reduce the binding of 125I-IGF-I binding. The calculated receptor number was 6000 per osteoclast, and the Kd was 0.10 nM. Searching for a role of the IGF-I receptor in mature osteoclasts, we found no significant influence of IGF-I on the levels of the proform of matrix metaloproteinase 9 and tartrate-resistant acid phosphatase. However, the induction of nuclear fragmentation in serum-depleted cultures of purified mature osteoclasts was dose-dependently inhibited by IGF-I in the picomolar range, but not by 1 nM insulin. These data show that functionally active IGF-I receptor is present in mature osteoclasts.
Hou
P
P
Department of Basic Research, Center for Clinical and Basic Research, Ballerup, Denmark.
Sato
T
T
Hofstetter
W
W
Foged
N T
NT
D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001667:Binding, Competitive; D002116:Calcitonin / Q000378:metabolism; D002469:Cell Separation / Q000379:methods; D002478:Cells, Cultured; D017364:Collagenases / Q000378:metabolism; D017403:In Situ Hybridization; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D007700:Kinetics; D020780:Matrix Metalloproteinase 9; D010010:Osteoclasts / Q000737:chemistry* / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D017526:Receptor, IGF Type 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
D011498:Protein Precursors; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D002116:Calcitonin; D017526:Receptor, IGF Type 1; D017364:Collagenases; D020780:Matrix Metalloproteinase 9