TYROSINE PHOSPHORYLATION OF P130(CAS) IS INVOLVED IN ACTIN ORGANIZATION IN OSTEOCLASTS

Integrin-mediated interaction with the extracellular matrix plays a cr itical role in the function of osteoclasts, the bone-resorbing cells. This study examines the role of p130(Cas) (Crk-associated substrate (C as)) in actin organization in osteoclasts. Multinucleated osteoclast-l ike cells (OCLs) were obtained in a co-culture of murine bone marrow c ells and primary osteoblasts. After plating on culture dishes, OCLs fo rmed a ringlike structure consisting of F-actin dots at cell periphery (actin ring). The percentage of OCLs with actin rings and its diamete r increased with time and cell spreading. Tyrosine phosphorylation of a protein (p130) increased with actin ring formation. Treatment with c ytochalasin D disrupted actin rings and reduced tyrosine phosphorylati on of p130. Using specific antibodies, p130 was identified as Gas. Ey immunocytochemistry, Cas was localized to the peripheral regions of OC Ls and its distribution overlapped that of F-actin. In OCLs derived fr om Src(-/-) mice, in which osteoclast activity is severely compromised , tyrosine phosphorylation of Cas was markedly reduced. Moreover, Cas was diffusely distributed in the cytoplasm and actin ring formation is not observed. These findings suggest that Src-dependent tyrosine phos phorylation of Cas is involved in the adhesion-induced actin organizat ion associated with osteoclast activation.