Convergence of α_vβ₃Integrin–And Macrophage Colony Stimulating Factor–Mediated Signals on Phospholipase Cγ in Prefusion Osteoclasts

The macrophage colony stimulating factor (M-CSF) and α_vβ₃ integrins play critical roles in osteoclast function. This study examines M-CSF– and adhesion-induced signaling in prefusion osteoclasts (pOCs) derived from Src-deficient and wild-type mice. Src-deficient cells attach to but do not spread on vitronectin (Vn)-coated surfaces and, contrary to wild-type cells, their adhesion does not lead to tyrosine phosphorylation of molecules activated by adhesion, including PYK2, p130^Cas, paxillin, and PLC-γ. However, in response to M-CSF, Src^−/− pOCs spread and migrate on Vn in an α_vβ₃-dependent manner. Involvement of PLC-γ activation is suggested by using a PLC inhibitor, U73122, which blocks both adhesion- and M-CSF–mediated cell spreading. Furthermore, in Src^−/− pOCs M-CSF, together with filamentous actin, causes recruitment of β₃ integrin and PLC-γ to adhesion contacts and induces stable association of β₃ integrin with PLC-γ, phosphatidylinositol 3-kinase, and PYK2. Moreover, direct interaction of PYK2 and PLC-γ can be induced by either adhesion or M-CSF, suggesting that this interaction may enable the formation of integrin-associated complexes. Furthermore, this study suggests that in pOCs PLC-γ is a common downstream mediator for adhesion and growth factor signals. M-CSF–initiated signaling modulates the α_vβ₃ integrin-mediated cytoskeletal reorganization in prefusion osteoclasts in the absence of c-Src, possibly via PLC-γ.