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Dynamic changes in the osteoclast cytoskeleton in response to growth factors and cell attachment are controlled by beta3 integrin.

Faccio R, Novack DV, Zallone A, Ross FP, Teitelbaum SL - J. Cell Biol. (2003)

Bottom Line: 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 beta integrin cytoplasmic tail, we examined the effect of these growth factors on OC precursors.Instead, its activation is dependent upon intracellular calcium, and on the beta2 integrin.Thus, the beta3 cytoplasmic domain is responsible for activation of specific intracellular signals leading to cytoskeletal reorganization critical for OC function.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Washington University School of Medicine, 216 South Kingshighway, St. Louis, MO 63110, USA.

ABSTRACT
The beta3 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 beta integrin cytoplasmic tail, we examined the effect of these growth factors on OC precursors. To this end, we retrovirally expressed various beta3 integrins with cytoplasmic tail mutations in beta3-deficient OC precursors. We find that S752 in the beta3 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 beta3 subunit. Activation of the upstream mediators c-Src and c-Cbl is also dependent on beta3. Interestingly, although the FAK-related kinase Pyk2 interacts with c-Src and c-Cbl, its activation is not disrupted in the absence of functional beta3. Instead, its activation is dependent upon intracellular calcium, and on the beta2 integrin. Thus, the beta3 cytoplasmic domain is responsible for activation of specific intracellular signals leading to cytoskeletal reorganization critical for OC function.

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Model of OC αvβ3 integrin activation and signal transduction. (A) αvβ3 in its basal conformation (//) exists within the actin ring. Resorption is stimulated by growth factors and requires activated αvβ3 (Λ), which localizes in newly formed membrane extensions. (B) Binding of a growth factor (GF) to its receptor changes the conformation of the external domain of αvβ3 from the basal to the activated state. The GF receptor tyrosine kinase (RTK) and αvβ3 collaboratively induce cytoskeletal rearrangements via activation of Rho family proteins from their GDP-bound to GTP-bound forms. Pyk2 is phosphorylated (*) by αMβ2 binding an unknown ligand (?) or increased intracellular calcium. Upon ligand (RGD) occupancy of αvβ3, phosphorylated (*) Pyk2 forms a complex at the β3 cytoplasmic domain with phosphorylated c-Src and c-Cbl. Whereas Pyk2 is constitutively associated with paxillin, formation of the Pyk2–c-Src–c-Cbl adhesive complex, and thus efficient bone resorption, requires αvβ3.
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fig10: Model of OC αvβ3 integrin activation and signal transduction. (A) αvβ3 in its basal conformation (//) exists within the actin ring. Resorption is stimulated by growth factors and requires activated αvβ3 (Λ), which localizes in newly formed membrane extensions. (B) Binding of a growth factor (GF) to its receptor changes the conformation of the external domain of αvβ3 from the basal to the activated state. The GF receptor tyrosine kinase (RTK) and αvβ3 collaboratively induce cytoskeletal rearrangements via activation of Rho family proteins from their GDP-bound to GTP-bound forms. Pyk2 is phosphorylated (*) by αMβ2 binding an unknown ligand (?) or increased intracellular calcium. Upon ligand (RGD) occupancy of αvβ3, phosphorylated (*) Pyk2 forms a complex at the β3 cytoplasmic domain with phosphorylated c-Src and c-Cbl. Whereas Pyk2 is constitutively associated with paxillin, formation of the Pyk2–c-Src–c-Cbl adhesive complex, and thus efficient bone resorption, requires αvβ3.

Mentions: We propose, therefore, that in OCs, cytokines stimulate the formation of new membrane extensions that contain activated αvβ3 (Fig. 10 A). These cytoskeletal rearrangements are under the control of Rho family GTPases and require functional αvβ3 (Fig. 10 B). Upon αvβ3 occupancy, phosphorylated Pyk2, an event independent of the integrin, forms a complex at the β3 cytoplasmic domain with phosphorylated c-Src and c-Cbl (Fig. 10 B). In the absence of functional αvβ3, Pyk2 may be activated by other means, such as αMβ2 or increased calcium. These alternative means of activating Pyk2 permit its association with paxillin, but the Pyk2–c-Src–c-Cbl adhesive complex fails to form, resulting in poorly resorptive OCs.


Dynamic changes in the osteoclast cytoskeleton in response to growth factors and cell attachment are controlled by beta3 integrin.

Faccio R, Novack DV, Zallone A, Ross FP, Teitelbaum SL - J. Cell Biol. (2003)

Model of OC αvβ3 integrin activation and signal transduction. (A) αvβ3 in its basal conformation (//) exists within the actin ring. Resorption is stimulated by growth factors and requires activated αvβ3 (Λ), which localizes in newly formed membrane extensions. (B) Binding of a growth factor (GF) to its receptor changes the conformation of the external domain of αvβ3 from the basal to the activated state. The GF receptor tyrosine kinase (RTK) and αvβ3 collaboratively induce cytoskeletal rearrangements via activation of Rho family proteins from their GDP-bound to GTP-bound forms. Pyk2 is phosphorylated (*) by αMβ2 binding an unknown ligand (?) or increased intracellular calcium. Upon ligand (RGD) occupancy of αvβ3, phosphorylated (*) Pyk2 forms a complex at the β3 cytoplasmic domain with phosphorylated c-Src and c-Cbl. Whereas Pyk2 is constitutively associated with paxillin, formation of the Pyk2–c-Src–c-Cbl adhesive complex, and thus efficient bone resorption, requires αvβ3.
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Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2172699&req=5

fig10: Model of OC αvβ3 integrin activation and signal transduction. (A) αvβ3 in its basal conformation (//) exists within the actin ring. Resorption is stimulated by growth factors and requires activated αvβ3 (Λ), which localizes in newly formed membrane extensions. (B) Binding of a growth factor (GF) to its receptor changes the conformation of the external domain of αvβ3 from the basal to the activated state. The GF receptor tyrosine kinase (RTK) and αvβ3 collaboratively induce cytoskeletal rearrangements via activation of Rho family proteins from their GDP-bound to GTP-bound forms. Pyk2 is phosphorylated (*) by αMβ2 binding an unknown ligand (?) or increased intracellular calcium. Upon ligand (RGD) occupancy of αvβ3, phosphorylated (*) Pyk2 forms a complex at the β3 cytoplasmic domain with phosphorylated c-Src and c-Cbl. Whereas Pyk2 is constitutively associated with paxillin, formation of the Pyk2–c-Src–c-Cbl adhesive complex, and thus efficient bone resorption, requires αvβ3.
Mentions: We propose, therefore, that in OCs, cytokines stimulate the formation of new membrane extensions that contain activated αvβ3 (Fig. 10 A). These cytoskeletal rearrangements are under the control of Rho family GTPases and require functional αvβ3 (Fig. 10 B). Upon αvβ3 occupancy, phosphorylated Pyk2, an event independent of the integrin, forms a complex at the β3 cytoplasmic domain with phosphorylated c-Src and c-Cbl (Fig. 10 B). In the absence of functional αvβ3, Pyk2 may be activated by other means, such as αMβ2 or increased calcium. These alternative means of activating Pyk2 permit its association with paxillin, but the Pyk2–c-Src–c-Cbl adhesive complex fails to form, resulting in poorly resorptive OCs.

Bottom Line: 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 beta integrin cytoplasmic tail, we examined the effect of these growth factors on OC precursors.Instead, its activation is dependent upon intracellular calcium, and on the beta2 integrin.Thus, the beta3 cytoplasmic domain is responsible for activation of specific intracellular signals leading to cytoskeletal reorganization critical for OC function.

View Article: PubMed Central - PubMed

Affiliation: Department of Pathology, Washington University School of Medicine, 216 South Kingshighway, St. Louis, MO 63110, USA.

ABSTRACT
The beta3 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 beta integrin cytoplasmic tail, we examined the effect of these growth factors on OC precursors. To this end, we retrovirally expressed various beta3 integrins with cytoplasmic tail mutations in beta3-deficient OC precursors. We find that S752 in the beta3 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 beta3 subunit. Activation of the upstream mediators c-Src and c-Cbl is also dependent on beta3. Interestingly, although the FAK-related kinase Pyk2 interacts with c-Src and c-Cbl, its activation is not disrupted in the absence of functional beta3. Instead, its activation is dependent upon intracellular calcium, and on the beta2 integrin. Thus, the beta3 cytoplasmic domain is responsible for activation of specific intracellular signals leading to cytoskeletal reorganization critical for OC function.

Show MeSH
Related in: MedlinePlus