Dynamic changes in the osteoclast cytoskeleton in response to growth factors and cell attachment are controlled by β3 integrin

Abstract

The β3 integrin cytoplasmic domain, and specifically S752, is critical for integrin localization and osteoclast (OC) function. Because growth factors such as macrophage colony–stimulating factor and hepatocyte growth factor affect integrin activation and function via inside-out signaling, a process requiring the β integrin cytoplasmic tail, we examined the effect of these growth factors on OC precursors. To this end, we retrovirally expressed various β3 integrins with cytoplasmic tail mutations in β3-deficient OC precursors. We find that S752 in the β3 cytoplasmic tail is required for growth factor–induced integrin activation, cytoskeletal reorganization, and membrane protrusion, thereby affecting OC adhesion, migration, and bone resorption. The small GTPases Rho and Rac mediate cytoskeletal reorganization, and activation of each is defective in OC precursors lacking a functional β3 subunit. Activation of the upstream mediators c-Src and c-Cbl is also dependent on β3. Interestingly, although the FAK-related kinase Pyk2 interacts with c-Src and c-Cbl, its activation is not disrupted in the absence of functional β3. Instead, its activation is dependent upon intracellular calcium, and on the β2 integrin. Thus, the β3 cytoplasmic domain is responsible for activation of specific intracellular signals leading to cytoskeletal reorganization critical for OC function.

Rho GTPases in osteoclasts: Orchestrators of podosome arrangement

“…In  3 -/-osteoclasts, RhoA and Rac activation is impaired and osteoclast migration in response to M-CSF or HGF is defective. Reexpression of full length  3 integrin restores both migration and Rho GTPases activation, whereas a mutant  3 integrin lacking the C-terminal domain or bearing a Ser752 to Pro mutation does not (Faccio et al, 2003). It shows that RhoA and Rac are activated downstream of  3 integrin and that this is essential for osteoclast migration and function.…”

“…Indeed, macrophage stimulating factor (M-CSF) or hepatocyte growth factor (HGH) induces cytoskeletal remodeling of osteoclast by activating both RhoA and Rac proteins. As a consequence, osteoclast migration is increased (Faccio et al, 2003). In  3 -/-osteoclasts, RhoA and Rac activation is impaired and osteoclast migration in response to M-CSF or HGF is defective.…”

Differentiation of normal and cancer cells induced by sulfhydryl reduction: biochemical and molecular mechanisms

“…[16][17][18] In particular, tyrosine phosphorylation of E-cadherin and b-catenin induces their disassembly from adhesion junctions. We therefore investigated whether the observed increase in cell-cell and cell-substratum adhesions was dependent on an inhibition of c-Src kinase after NAC treatment.…”

Modulation of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) receptors in a human osteoclast model in vitro

“…Typically, integrins mediate matrix contact through focal adhesions, containing signaling and cytoskeletal molecules, and lead to the formation of stress fibers. The osteoclast, however, organizes its fibrillar actin into sealing zones rather than forming stress fibers, and forms podosomes, instead of focal adhesions (Faccio et al, 2003).…”

“…Now it is known that c-Src regulates osteoclasts both through its role as a kinase and as an adaptor molecule (Miyazaki et al, 2004) Also notable is that the osteoclast cytoskeleton is influenced by the interaction between ovft and M-CSF/c-Fms pathways. Through c-Fms, M-CSF activates the integrin by targeting its cytoplasmic domain, altering the conformation of the extracellular, ligandbinding region (Faccio et al, 2003). This can emulate to a degree the activation of the ovft integrin.…”