Osteoactivin is a novel osteoclastic protein and plays a key role in osteoclast differentiation and activity

This study presents gene expression, protein expression, and in situ immunohistochemical evidence that osteoclasts express high levels of osteoactivin (OA), which had previously been reported to be an osteoblast-specific protein in bone. OA expression in osteoclasts was up-regulated upon receptor activator of NF kappa B ligand-induced differentiation. Suppression of functional activity of OA with neutralizing antibody reduced cell size, number of nuclei, fusion, and bone resorption activity of osteoclasts. OA was co-immunoprecipitated with integrin beta(3) and beta(1), indicating that OA co-localizes with integrin beta(3) and/or beta(1) in a hetero-polymeric complex in osteoclasts. These findings indicate that OA is a novel osteoclastic protein and plays a role in osteoclast differentiation and/or activity. (C) 2008 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.