Identification and Characterization of the Insulin-like Growth Factor I Receptor in Mature Rabbit Osteoclasts

Publisher Website
Google Scholar
Abstract
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 of125I-IGF-I bound to the purified mature osteoclasts and subsequent sodium dodecyl sulfide-polyacrylamide gel electrophoresis revealed the specific binding of125I-IGF-I in complexes with molecular masses of 130 and 230 kD 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 of125I-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.

This publication has 34 references indexed in Scilit: