Colony stimulating factor-1-induced osteoclast spreading depends on substrate and requires the vitronectin receptor and the c-src proto-oncogene

The colony stimulating factor 1 (CSF-1) regulates osteoclastogenesis and bone resorption, Mutations in the CSF-1 gene cause an osteopetrosis characterized by the absence of osteoclasts. Mature osteoclasts respond to CSF-1 with inhibition of bone resorption and an increment of cell spreading, Herein we demonstrate that CSF-1-induced osteoclast spreading depends on the substrate the osteoclast interacts with and requires integrity of the vitronectin receptor and of the c-src proto-oncogene. Rabbit osteoclasts were allowed to attach to glass, serum, osteopontin, and bone substrates, and were treated with 10 ng/ml human recombinant CSF-1 for 4 h, In osteoclasts plated on glass, the cytokine induced 70+ACU- inhibition of bone resorption and 1.8-fold stimulation of cell spreading, without changes in podosome expression and microfilament array. In contrast, CSF-1 induced a 2.5-fold increase of osteoclasts showing filopodia, and a 9.5-fold increase of osteoclasts presenting lamellipodia, indicating that membrane motility was required for cell spreading. Osteoclasts plated on serum substrates showed a 50+ACU- reduction of spontaneous spreading, However, in this circumstance, CSF-1 still stimulated an increase of osteoclast area, In osteoclasts cultured on osteopontin substrate or on bone slices, an inhibition of CSF-1-induced osteoclast spreading was observed, To establish involvement of the vitronectin receptor and c-src proto-oncogene, cells were treated with the alpha(v) beta(3) integrin neutralizing antibody, LM609, or c-src antisense oligonucleotides, which reduced CSF-1-induced osteoclast spreading by 57+ACU- and 60+ACU-, respectively. The results demonstrate that CSF-1-induced osteoclast spreading requires both the vitronectin receptor and the c-src proto-oncogene and that this action is modulated by the adhesion substrata.