COLONY-STIMULATING FACTOR-1-INDUCED OSTEOCLAST SPREADING DEPENDS ON SUBSTRATE AND REQUIRES THE VITRONECTIN RECEPTOR AND THE C-SRC PROTOONCOGENE

The colony stimulating factor 1 (CSF-1) regulates osteoclastogenesis a nd bone resorption, Mutations in the CSF-1 gene cause an osteopetrosis characterized by the absence of osteoclasts. Mature osteoclasts respo nd to CSF-1 with inhibition of bone resorption and an increment of cel l spreading, Herein we demonstrate that CSF-1-induced osteoclast sprea ding depends on the substrate the osteoclast interacts with and requir es integrity of the vitronectin receptor and of the c-src proto-oncoge ne. Rabbit osteoclasts were allowed to attach to glass, serum, osteopo ntin, and bone substrates, and were treated with 10 ng/ml human recomb inant CSF-1 for 4 h, In osteoclasts plated on glass, the cytokine indu ced 70% inhibition of bone resorption and 1.8-fold stimulation of cell spreading, without changes in podosome expression and microfilament a rray. In contrast, CSF-1 induced a 2.5-fold increase of osteoclasts sh owing filopodia, and a 9.5-fold increase of osteoclasts presenting lam ellipodia, indicating that membrane motility was required for cell spr eading. Osteoclasts plated on serum substrates showed a 50% reduction of spontaneous spreading, However, in this circumstance, CSF-1 still s timulated an increase of osteoclast area, In osteoclasts cultured on o steopontin substrate or on bone slices, an inhibition of CSF-1-induced osteoclast spreading was observed, To establish involvement of the vi tronectin receptor and c-src proto-oncogene, cells were treated with t he alpha(v) beta(3) integrin neutralizing antibody, LM609, or c-src an tisense oligonucleotides, which reduced CSF-1-induced osteoclast sprea ding by 57% and 60%, respectively. The results demonstrate that CSF-1- induced osteoclast spreading requires both the vitronectin receptor an d the c-src proto-oncogene and that this action is modulated by the ad hesion substrata.