Distinct Roles of p130Cas and c-Cbl in Adhesion-Induced or Macrophage Colony-Stimulating Factor-Mediated Signaling Pathways in Prefusion Osteoclasts

Abstract

Both p130Cas and c-Cbl have been reported to play critical roles in osteoclast function as downstream targets of c-Src kinase. The purpose of this study was to examine adhesion-and macrophage colony-stimulating factor (M-CSF)-induced tyrosine phosphorylation of these two molecules in prefusion osteoclasts (pOCs) derived from either Src+/? or Src-/- mice and to directly compare the roles of p130Cas and c-Cbl in osteoclast function. Cell attachment of normal pOCs to vitronectin induces tyrosine phosphorylation of p130Cas and, to a much lesser extent, of c-Cbl. Treatment with M-CSF results in further tyrosine phosphorylation of both p130Cas and c-Cbl, suggesting cooperation between α vβ3 integrin and the M-CSF receptor, c-Fms, in osteoclasts. However, M-CSF induces tyrosine phosphorylation of c-Cbl, but not p130Cas in pOCs in suspension, confirming the role of c-Cbl as a downstream effector of c-Fms. This observation also suggests that M-CSF-mediated p130Cas phosphorylation requires ligand engagement of αvβ3 integrin. In Src-deficient pOCs plated on vitronectin, although M-CSF highly induces Cbl phosphorylation, it does not affect p130Cas phosphorylation. These results suggest that in osteoclasts 1) tyrosine phosphorylation of p130Cas depends on αvβ3 integrin-mediated cell adhesion, even in the presence of M-CSF; 2) on the other hand, c-Cbl phosphorylation is predominantly activated by M-CSF and is independent of cell adhesion; 3) lastly, although c-Src is essential for both adhesion- and M-CSF-mediated phosphorylation of p130Cas, it is clearly not required for c-Cbl phosphorylation in M-CSF-treated pOCs. Taken together, p130Cas and c-Cbl play distinct roles in the signal transduction pathways that mediate cytoskeletal organization in osteoclasts.