Convergence of αvβ3 integrin- and macrophage colony stimulating factor-mediated signals on phospholipase Cγ in prefusion osteoclasts

The macrophage colony stimulating factor (M-CSF) and (alpha (v)beta (3) 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-gamma. However, in response to M-CSF Src(-/-) pOCs spread and migrate on Vn in an alpha (v)beta (3)-dependent manner. Involvement of PLC-gamma 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 beta (3) integrin and PLC-gamma to adhesion contacts and induces stable association of beta (3) integrin with PLC-gamma, phosphatidylinositol 3-kinase, and PYK2. Moreover, direct interaction of PYK2 and PLC-gamma 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-gamma is a common downstream mediator for adhesion and growth factor signals. M-CSF-initiated signaling modulates the alpha (v)beta (3) integrin-mediated cytoskeletal reorganization in prefusion osteoclasts in the absence of c-Src, possibly via PLC-gamma.