TRAF Family Member-associated NF-κB Activator (TANK) Is a Negative Regulator of Osteoclastogenesis and Bone Formation

Kenta Maruyama,Tatsukata Kawagoe,Takeshi Kondo,Shizuo Akira,Osamu Takeuchi

doi:10.1074/jbc.m112.347799

Abstract

The differentiation of bone-resorbing osteoclasts is induced by RANKL signaling, and leads to the activation of NF-κB via TRAF6 activation. TRAF family member-associated NF-κB activator (TANK) acts as a negative regulator of Toll-like receptors (TLRs) and B-cell receptor (BCR) signaling by inhibiting TRAF6 activation. Tank(-/-) mice spontaneously develop autoimmune glomerular nephritis in an IL-6-dependent manner. Despite its importance in the TCRs and BCR-activated TRAF6 inhibition, the involvement of TANK in RANKL signaling is poorly understood. Here, we report that TANK is a negative regulator of osteoclast differentiation. The expression levels of TANK mRNA and protein were up-regulated during RANKL-induced osteoclastogenesis, and overexpression of TANK in vitro led to a decrease in osteoclast formation. The in vitro osteoclastogenesis of Tank(-/-) cells was significantly increased, accompanied by increased ubiquitination of TRAF6 and enhanced canonical NF-κB activation in response to RANKL stimulation. Tank(-/-) mice showed severe trabecular bone loss, but increased cortical bone mineral density, because of enhanced bone erosion and formation. TANK mRNA expression was induced during osteoblast differentiation and Tank(-/-) osteoblasts exhibited enhaced NF-κB activation, IL-11 expression, and bone nodule formation than wild-type control cells. Finally, wild-type mice transplanted with bone marrow cells from Tank(-/-) mice showed trabecular bone loss analogous to that in Tank(-/-) mice. These findings demonstrate that TANK is critical for osteoclastogenesis by regulating NF-κB, and is also important for proper bone remodeling.

Highlights

Osteoclasts and osteoblasts are major players in bone metabolism
TANK Expression Is Induced by RANKL Stimulation—First, we examined the expression pattern of TANK during the course of RANKL-induced osteoclastogenesis
We treated the M-CSF-derived macrophages (MDMs) with increasing concentrations of RANKL, and TRAPpositive multinucleated cells were identified as mature osteoclasts after 3 days

Summary

Background

Osteoclasts and osteoblasts are major players in bone metabolism. Results: TRAF family member-associated NF-␬B activator (TANK) is induced during osteoclastogenesis and osteoblastogenesis. The differentiation of bone-resorbing osteoclasts is induced by RANKL signaling, and leads to the activation of NF-␬B via TRAF6 activation. TRAF family member-associated NF-␬B activator (TANK) acts as a negative regulator of Toll-like receptors (TLRs) and B-cell receptor (BCR) signaling by inhibiting TRAF6 activation. Role of TANK in Osteoclastogenesis macrophage cell fusion is abrogated in DC-STAMP-deficient mice [6, 7] Mice lacking both NF-␬B1 and NF-␬B2 develop typical osteopetrosis through defective development of osteoclasts [8], thereby confirming the importance of NF-␬B signaling in controlling bone homeostasis. Macrophages and B cells from TANK-deficient (TankϪ/Ϫ) mice exhibit more enhanced NF-␬B and AP-1 activation in response to stimulation of TLRs and B-cell receptor (BCR) [19]. Despite the importance of TRAF6 in the RANKL signaling, the involvement of TANK in RANKL-induced osteoclast differentiation and bone homeostasis is poorly understood. These findings provide unexpected insights into the roles of TANK in bone remodeling

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION