title: Regulation of RANKL-induced osteoclastogenesis by TGF-β through molecular interaction between Smad3 and Traf6.
abstract: Previous studies have shown that transforming growth factor β (TGF-β) promotes receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis. However, the underlying molecular mechanisms have not been elucidated. When TGF-β signals were blocked either by a specific inhibitor of TGF-β type 1 receptor kinase activity, SB431542, or by introducing a dominant-negative mutant of TGF-β type 2 receptor, RANKL-induced osteoclastogenesis was almost completely suppressed. Blockade of Smad signaling by overexpression of Smad7 or c-Ski markedly suppressed RANKL-induced osteoclastogenesis, and retroviral induction of an activated mutant of Smad2 or Smad3 reversed the inhibitory effect of SB431542. Immunoprecipitation analysis revealed that Smad2/3 directly associates with the TRAF6-TAB1-TAK1 molecular complex, which is generated in response to RANKL stimulation and plays an essential role in osteoclast differentiation. TRAF6-TAB1-TAK1 complex formation was not observed when TGF-β signaling was blocked. Analysis using deletion mutants revealed that the MH2 domain of Smad3 is necessary for TRAF6-TAB1-TAK1 complex formation, downstream signal transduction, and osteoclast formation. In addition, gene silencing of Smad3 in osteoclast precursors markedly suppressed RANKL-induced osteoclast differentiation. In summary, TGF-β is indispensable in RANKL-induced osteoclastogenesis, and the binding of Smad3 to the TRAF6-TAB1-TAK1 complex is crucial for RANKL-induced osteoclastogenic signaling.
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medicine, University of Tokyo, Tokyo, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Yasui
authors.forename: Yuho
authors.initials: Y
authors.lastname: Kadono
authors.forename: Masaki
authors.initials: M
authors.lastname: Nakamura
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Oshima
authors.forename: Takumi
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Hironari
authors.initials: H
authors.lastname: Masuda
authors.forename: Jun
authors.initials: J
authors.lastname: Hirose
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Omata
authors.forename: Hisataka
authors.initials: H
authors.lastname: Yasuda
authors.forename: Takeshi
authors.initials: T
authors.lastname: Imamura
authors.forename: Kozo
authors.initials: K
authors.lastname: Nakamura
authors.forename: Sakae
authors.initials: S
authors.lastname: Tanaka
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology; D002460:Cell Line; D020868:Gene Silencing / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D008297:Male; D051379:Mice; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism*; D010012:Osteogenesis / Q000187:drug effects*; D011485:Protein Binding / Q000187:drug effects; D017434:Protein Structure, Tertiary; D053245:RANK Ligand / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D051899:Smad2 Protein / Q000737:chemistry / Q000378:metabolism; D051900:Smad3 Protein / Q000737:chemistry / Q000378:metabolism*; D048029:TNF Receptor-Associated Factor 6 / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*
chemical_list: D053245:RANK Ligand; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D048029:TNF Receptor-Associated Factor 6; D016212:Transforming Growth Factor beta