Receptor Activator of NF-κB Ligand (RANKL) Activates TAK1 Mitogen-Activated Protein Kinase Kinase Kinase through a Signaling Complex Containing RANK, TAB2, and TRAF6

Abstract

The receptor activator of NF-B (RANK) and its ligand RANKL are key molecules for differentiation and activation of osteoclasts. RANKL stimulates transcription factors AP-1 through mitogen-activated protein kinase (MAPK) activation, and NF-B through IB kinase (IKK) activation. Tumor necrosis factor receptorassociated factor 6 (TRAF6) is essential for activation of these kinases. In the interleukin-1 signaling pathway, TAK1 MAPK kinase kinase (MAPKKK) mediates MAPK and IKK activation via interaction with TRAF6, and TAB2 acts as an adapter linking TAK1 and TRAF6. Here, we demonstrate that TAK1 and TAB2 participate in the RANK signaling pathway. Dominant negative forms of TAK1 and TAB2 inhibit NF-B activation induced by overexpression of RANK. In 293 cells stably transfected with full-length RANK, RANKL stimulation facilitates the formation of a complex containing RANK, TRAF6, TAB2, and TAK1, leading to the activation of TAK1. Furthermore, in murine monocyte RAW 264.7 cells, dominant negative forms of TAK1 and TAB2 inhibit NF-B activation induced by RANKL and endogenous TAK1 is activated in response to RANKL stimulation. These results suggest that the formation of the TRAF6-TAB2-TAK1 complex is involved in the RANK signaling pathway and may regulate the development and function of osteoclasts.Skeletal remodeling is a dynamic and continual process that involves the coupled events of bone formation by osteoblasts and bone resorption by osteoclasts. Osteoclasts are professional bone-resorbing polykaryons derived from hematopoietic cells of the monocyte-macrophage lineage (27, 34). The receptor activator of NF-B (RANK) is a member of the tumor necrosis factor (TNF) receptor family and is involved in osteoclastogenesis and lymph node development (1, 10). The ligand for RANK, RANKL (also called osteoclast differentiation factor [46], TNF-related activation induced cytokine [44], and osteoprotegerin ligand [21]), is a TNF receptor family ligand that regulates the functions of dendritic cells and osteoclasts. RANKL is expressed on osteoblasts and bone marrow stromal cells, while its receptor RANK is expressed on osteoclast progenitors or mature osteoclasts. RANKL interacts with RANK via direct cell-cell contact, thereby promoting the differentiation, survival, and bone-resorbing capability of osteoclasts (reviewed in references 13 and 35). RANK interacts with members of the family of TNF receptor-associated factors (TRAFs) that mediate activation of NF-B and c-Jun NH 2 -terminal kinase (JNK) (8,11,17,43). Furthermore, the RANK cytoplasmic tail associates with c-Src kinase, which is responsible for the activation of Akt/PKB, a factor that has an antiapoptotic effect on osteoclasts (42). However, the proximal molecular components of RANK signal transduction and their interactions are not well understood.The TRAF family consists of six distinct proteins, each containing a ring and zinc finger motif in their N terminus and C-terminal TRAF domains that are responsible for self-association and protein interaction. The TRAF protei...

Adenosine A1 receptor regulates osteoclast formation by altering TRAF6/TAK1 signaling

“…A 1 R blockade disrupts RANKL-induced formation of TRAF6-TAK1 complex in primary BMMs TAK1, a MAPK kinase kinase can form complexes with RANK and TRAF6, and was up-regulated in RANKLinduced osteoclastogenesis ( [23][24][25]. RANKL-induced osteoclast differentiation requires TAK1 for NF-κB activation [25].…”

“…Another signaling protein, transformation growth factor-β (TGF-β) activated kinase-1 (TAK1) has been implicated in RANKL-induced osteoclastogenesis [23][24][25]. Upon RANK receptor engagement, the cytoplasmic domain of RANK interacts with an adaptor protein, tumor necrosis factor-receptorassociated factor 6 (TRAF6), and endogenous TAK1 is recruited to the TRAF6 complex.…”

Osteoclast differentiation requires TAK1 and MKK6 for NFATc1 induction and NF-κB transactivation by RANKL

“…26 TAK1 has been suggested to contribute to NF-kB activation by TNFa and RANKL. 15,27 Therefore, we investigated whether the TAK1-MKK6-p38 pathway is relevant to NF-kB activation by RANKL. We first examined the effect of TAK1-DN on IkB phosphorylation and degradation, steps required for release and nuclear translocation of NF-kB, by RANKL.…”

“…A study showed that transforming growth factor-beta-activated kinase 1 (TAK1), a MAPKKK, can form complexes with RANK, TRAF6, and TAB2 in RANK-overexpressing 293 cells. 15 The activity of TAK1 was stimulated by RANKL in the RANK-expressing 293 and RAW264.7 cells. 15 However, the effect of TAK1 activation on RANKL-induced Oc differentiation has not been demonstrated.…”

“…15 The activity of TAK1 was stimulated by RANKL in the RANK-expressing 293 and RAW264.7 cells. 15 However, the effect of TAK1 activation on RANKL-induced Oc differentiation has not been demonstrated.…”