Characterization and function of the receptor for IGF-I in human preosteoclastic cells.
Using a coculture system, we have recently demonstrated that insulin-like growth factor I (IGF-I) is a mediator of preosteoclastic cell migration toward bone-derived endothelial cells. To better characterize the mechanisms of IGF-I action on preosteoclastic cells we evaluated the expression of type I IGFs receptor in the human leukemic cell line, FLG 29.1, which differentiates toward the osteoclastic phenotype following phorbol ester (TPA) treatment. Scatchard analysis of 125I-labeled IGF-I to FLG 29.1 cells revealed the presence of a single high affinity binding site in both untreated and TPA-treated cells with a similar Kd value (0.3 +/- 0.2 nmol/L and 0.4 +/- 0.1 nmol/L, respectively). In untreated cells, IGF-I binding capacity (1.43 +/- 0.41 fmol/10(6) cells) was significantly (p < 0.05) lower than in TPA-treated cells (2.62 +/- 0.87 fmol/10(6) cells). Competition analyses and crosslinking studies revealed the presence of type I IGF receptor both in untreated and TPA-treated cells. Northern analysis demonstrated that mRNA for IGF-I receptor was expressed by both untreated and TPA-treated FLG 29.1 cells. In addition, FLG 29.1 cells released in the conditioned medium IGFBP-2 and IGFBP-4, whose expression was increased by TPA treatment as demonstrated by ligand and immunoblot analyses. The previous observations of chemotactic action of IGF-I on FLG 29.1 cells was confirmed by ultrastructural observations. Indeed, these cells revealed a marked migratory activity in response to nanomolar concentrations of IGF-I. In addition, the IGF-I receptor alpha IR-3 antiserum inhibited the IGF-I-induced FLG 29.1 cell's migratory activity. These findings clearly show that type IIGF receptor is expressed by osteoclast precursors and that IGF-I induces migration of these through the binding to type I IGF receptors. Binding proteins expressed by osteoclast precursors may play an autocrine role in modulating the IGF-I bioeffects.
Fiorelli
G
G
Department of Clinical Physiopathology, University of Florence, School of Medicine, Italy.
Formigli
L
L
Zecchi Orlandini
S
S
Gori
F
F
Falchetti
A
A
Morelli
A
A
Tanini
A
A
Benvenuti
S
S
Brandi
M L
ML
D000328:Adult; D001667:Binding, Competitive; D015152:Blotting, Northern; D002454:Cell Differentiation / Q000187:drug effects; D002633:Chemotaxis / Q000187:drug effects / Q000235:genetics; D002999:Clone Cells; D005260:Female; D000091344:Filaggrin Proteins; D006801:Humans; D018969:Insulin-Like Growth Factor Binding Proteins / Q000096:biosynthesis / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism* / Q000494:pharmacology; D007457:Iodine Radioisotopes; D007553:Isotope Labeling; D008854:Microscopy, Electron; D010010:Osteoclasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D010641:Phenotype; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000633:toxicity; D014407:Tumor Cells, Cultured
C000717249:FLG protein, human; D000091344:Filaggrin Proteins; D018969:Insulin-Like Growth Factor Binding Proteins; D007457:Iodine Radioisotopes; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D017526:Receptor, IGF Type 1; D013755:Tetradecanoylphorbol Acetate