title: Fyn positively regulates the activation of DAP12 and FcRγ-mediated costimulatory signals by RANKL during osteoclastogenesis.
abstract: Osteoclasts (OCs) are the only bone-resorbing cells and are critically involved in various bone-associated diseases, including osteoporosis and rheumatoid arthritis. Differentiation of OCs from bone marrow macrophage cells (BMMs) is regulated by RANK and the adaptor protein (DAP12/FcRγ)-mediated costimulatory signals. However, it is unknown how RANKL/RANK signal stimulates phosphorylation of DAP12/FcRγ to initiate the costimulatory signals. As reported here, we found that OC differentiation and acquisition of bone resorption capacity were suppressed in RANKL-stimulated Fyn(-/-) or Fyn-siRNA-transfected BMMs, but could be restored by overexpression of Fyn kinase in Fyn(-/-) BMMs. However, the RANKL-stimulated proliferation of BMMs was unaffected by the absence of Fyn. In addition, RANKL-stimulated Fyn(-/-) BMMs no longer exhibited the optimal induction of typical OC markers such as NFATc1, c-Fos, c-Src, TRAF6, and cathepsin K or costimulatory signals such as the activating phosphorylations of Syk, PLCγ2, and Gab2. These were restored by overexpression of Fyn in Fyn(-/-) BMMs. Immunoprecipitation studies also indicated that the adaptor proteins DAP12/FcRγ and Syk interacted with RANK during RANKL stimulation in BMMs in a Fyn-dependent manner. Phosphorylation of the DAP12/FcRγ and the recruitment of Syk by DAP12/FcRγ were suppressed in Fyn(-/-) BMMs. This is the first demonstration that Fyn relays the initial RANK/RANKL signal to the ITAM-containing adaptors DAP12/FcRγ for OC differentiation.
authors.affiliation: Department of Immunology, College of Medicine, Konkuk University, Chungju 380-701, Republic of Korea.
authors.forename: H S
authors.initials: HS
authors.lastname: Kim
authors.forename: D K
authors.initials: DK
authors.lastname: Kim
authors.forename: A R
authors.initials: AR
authors.lastname: Kim
authors.forename: S H
authors.initials: SH
authors.lastname: Mun
authors.forename: S K
authors.initials: SK
authors.lastname: Lee
authors.forename: J H
authors.initials: JH
authors.lastname: Kim
authors.forename: Y M
authors.initials: YM
authors.lastname: Kim
authors.forename: W S
authors.initials: WS
authors.lastname: Choi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D017353:Gene Deletion; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D010010:Osteoclasts / Q000166:cytology* / Q000378:metabolism; D051076:Proto-Oncogene Proteins c-fyn / Q000235:genetics / Q000378:metabolism*; D053245:RANK Ligand / Q000378:metabolism*; D017452:Receptors, IgG / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D053245:RANK Ligand; D017452:Receptors, IgG; C484963:Tyrobp protein, mouse; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn