β1 integrin/focal adhesion kinase-mediated signaling induces intercellular adhesion molecule 1 and receptor activator of nuclear factor κB ligand on Osteoblasts and osteoclast maturation

We have assessed characteristics of primary human osteoblasts, shedding light on signaling mediated by beta(1) integrin. beta(1) integrins are major receptors for these matrix glycoproteins. 1) Integrins beta(1), alpha(2), alpha(3), alpha(4), alpha(5), alpha(6), and alpha(v) were highly expressed on primary osteoblasts. 2) Engagement of beta(1) integrins on osteoblasts by cross-linking with specific antibody or ligand matrices, such as fibronectin or collagen, augmented expression of intercellular adhesion molecule 1 (ICAM-1) and receptor activator of nuclear factor kappaB ligand (RANKL) on the surface. 3) Up-regulation of ICAM-1 and RANKL on osteoblasts by beta(1) stimulation was completely abrogated by pretreatment with herbimycin A and genistein, tyrosine kinase inhibitors, or transfection of dominant negative truncations of focal adhesion kinase (FAK). 4) Engagement of beta(1) integrins on osteoblasts induced tartrate-resistant acid phosphatase-positive multinuclear cell formation in the coculture system of osteoblasts and peripheral monocytes. 5) Up-regulation of tartrate-resistant acid phosphatase-positive multinuclear cell formation by beta(1) stimulation was completely abrogated by transfection of dominant negative truncations of FAK. Our results indicate that beta(1) integrin-dependent adhesion of osteoblasts to bone matrices induces ICAM-1 and RANKL expression and osteoclast formation via tyrosine kinase, especially FAK. We here propose that beta(1) integrin/FAK-mediated signaling on osteoblasts could be involved in ICAM-1- and RANKL-dependent osteoclast maturation.