Abstract
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 NFkappaB 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 beta3 and beta1, indicating that OA co-localizes with integrin beta3 and/or beta1 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.