Acetylation-dependent regulation of Skp2 function.

Aberrant Skp2 signaling has been implicated as a driving event in tumorigenesis. Although the underlying molecular mechanisms remain elusive, cytoplasmic Skp2 correlates with more aggressive forms of breast and prostate cancers. Here, we report that Skp2 is acetylated by p300 at K68 and K71, which is a process that can be antagonized by the SIRT3 deacetylase. Inactivation of SIRT3 leads to elevated Skp2 acetylation, which leads to increased Skp2 stability through impairment of the Cdh1-mediated proteolysis pathway. As a result, Skp2 oncogenic function is increased, whereby cells expressing an acetylation-mimetic mutant display enhanced cellular proliferation and tumorigenesis in vivo. Moreover, acetylation of Skp2 in the nuclear localization signal (NLS) promotes its cytoplasmic retention, and cytoplasmic Skp2 enhances cellular migration through ubiquitination and destruction of E-cadherin. Thus, our study identifies an acetylation-dependent regulatory mechanism governing Skp2 oncogenic function and provides insight into how cytoplasmic Skp2 controls cellular migration.

NOTCH2 Hajdu-Cheney Mutations Escape SCFFBW7-Dependent Proteolysis to Promote Osteoporosis.

Hajdu-Cheney syndrome (HCS), a rare autosomal disorder caused by heterozygous mutations in NOTCH2, is clinically characterized by acro-osteolysis, severe osteoporosis, short stature, neurological symptoms, cardiovascular defects, and polycystic kidneys. Recent studies identified that aberrant NOTCH2 signaling and consequent osteoclast hyperactivity are closely associated with the bone-related disorder pathogenesis, but the exact molecular mechanisms remain unclear. Here, we demonstrate that sustained osteoclast activity is largely due to accumulation of NOTCH2 carrying a truncated C terminus that escapes FBW7-mediated ubiquitination and degradation. Mice with osteoclast-specific Fbw7 ablation revealed osteoporotic phenotypes reminiscent of HCS, due to elevated Notch2 signaling. Importantly, administration of Notch inhibitors in Fbw7 conditional knockout mice alleviated progressive bone resorption. These findings highlight the molecular basis of HCS pathogenesis and provide clinical insights into potential targeted therapeutic strategies for skeletal disorders associated with the aberrant FBW7/NOTCH2 pathway as observed in patients with HCS.

Cdh1 regulates osteoblast function through an APC/C-independent modulation of Smurf1.

The APC/Cdh1 E3 ubiquitin ligase plays an essential role in both mitotic exit and G1/S transition by targeting key cell-cycle regulators for destruction. There is mounting evidence indicating that Cdh1 has other functions in addition to cell-cycle regulation. However, it remains unclear whether these additional functions depend on its E3 ligase activity. Here, we report that Cdh1, but not Cdc20, promotes the E3 ligase activity of Smurf1. This is mediated by disruption of an autoinhibitory Smurf1 homodimer and is independent of APC/Cdh1 E3 ligase activity. As a result, depletion of Cdh1 leads to reduced Smurf1 activity and subsequent activation of multiple downstream targets, including the MEKK2 signaling pathway, inducing osteoblast differentiation. Our studies uncover a cell-cycle-independent function of Cdh1, establishing Cdh1 as an upstream component that governs Smurf1 activity. They further suggest that modulation of Cdh1 is a potential therapeutic option for treatment of osteoporosis.

mTOR drives its own activation via SCF(ßTrCP)-dependent degradation of the mTOR inhibitor DEPTOR.

The activities of both mTORC1 and mTORC2 are negatively regulated by their endogenous inhibitor, DEPTOR. As such, the abundance of DEPTOR is a critical determinant in the activity status of the mTOR network. DEPTOR stability is governed by the 26S-proteasome through a largely unknown mechanism. Here we describe an mTOR-dependent phosphorylation-driven pathway for DEPTOR destruction via SCF(ßTrCP). DEPTOR phosphorylation by mTOR in response to growth signals, and in collaboration with casein kinase I (CKI), generates a phosphodegron that binds ßTrCP. Failure to degrade DEPTOR through either degron mutation or ßTrCP depletion leads to reduced mTOR activity, reduced S6 kinase activity, and activation of autophagy to reduce cell growth. This work expands the current understanding of mTOR regulation by revealing a positive feedback loop involving mTOR and CKI-dependent turnover of its inhibitor, DEPTOR, suggesting that misregulation of the DEPTOR destruction pathway might contribute to aberrant activation of mTOR in disease.

[NF-κB signaling pathways and the future perspectives of bone disease therapy using selective inhibitors of NF-κB].

The transcriptional factor nuclear factor κB(NF-κB)regulates the expression of a wide variety of genes that are involved in immune and inflammatory responses, proliferation, and tumorigenesis. NF-κB consists of five members, such as p65(RelA), RelB, c-Rel, p50/p105(NF-κB1), and p52/p100(NF-κB2). There are two distinct NF-κB activation pathways, termed the classical and alternative NF-κB signaling pathways. Since mice lacking both p50 and p52 subunits developed typical osteopetrosis, due to total lack of osteoclasts, NF-κB is also important osteoclast differentiation. A selective NF-κB inhibitor blocked receptor activator of NF-κB ligand(RANKL)-induced osteoclastogenesis both in vitro and in vivo. Recent findings have shown that inactivation of NF-κB enhances osteoblast differentiation in vitro and bone formation in vivo. NF-κB is constitutively activated in many cancers including oral squamous cell carcinoma(OSCC), and is involved in the invasive characteristics of OSCC. A selective NF-κB inhibitor also prevented jaw bone destruction by OSCC by reduced osteoclast numbers in animal model. Thus the inhibition of NF-κB might useful for the treatment of bone diseases, such as arthritis, osteoporosis, periodontitis, and bone invasion by OSCC by inhibiting bone resorption and by stimulating bone formation.

RelB-induced expression of Cot, an MAP3K family member, rescues RANKL-induced osteoclastogenesis in alymphoplasia mice by promoting NF-κB2 processing by IKKα.

The alternative nuclear factor-κB (NF-κB) pathway, mainly the RelB-p52 heterodimer, plays important roles in bone metabolism through an unknown mechanism. We have previously reported that alymphoplasia (aly/aly) mice, which lack active NF-κB-inducing kinase (NIK), show mild osteopetrosis due to the inhibition of osteoclastogenesis. p100 retains RelB in the cytoplasm and inhibits RANKL-induced osteoclastogenesis in aly/aly cells. Furthermore, the overexpression of RelB in aly/aly cells rescues RANKL-induced osteoclastogenesis by inducing p100 processing. In contrast, the overexpression of p65 in aly/aly cells has no effect. However, the overexpression of RelB fails to rescue RANKL-induced osteoclastogenesis in the presence of p100ΔGRR, which cannot be processed to p52, suggesting that p100 processing is a key step in RelB-rescued, RANKL-induced osteoclastogenesis in aly/aly cells. In this study, Cot (cancer Osaka thyroid), an MAP3K, was up-regulated by RelB overexpression. Analysis of the Cot promoter demonstrated that p65 and RelB bound to the distal NF-κB-binding site and that RelB but not p65 bound to the proximal NF-κB-binding site in the Cot promoter. The knocking down of Cot expression significantly reduced the RANKL-induced osteoclastogenesis induced by RelB overexpression. The phosphorylation of IKKα at threonine 23 and its kinase activity were indispensable for the processing of p100 and osteoclastogenesis by RelB-induced Cot. Finally, constitutively activated Akt enhanced osteoclastogenesis by RelB-induced Cot, and a dominant-negative form of Akt significantly inhibited it. Taken together, these results indicate that the overexpression of RelB restores RANKL-induced osteoclastogenesis by activation of Akt/Cot/IKKα-induced p100 processing.

Skp2: a novel potential therapeutic target for prostate cancer.

Prostate cancer is the most frequently diagnosed tumor in men and the second most common cause of cancer-related death for males in the United States. It has been shown that multiple signaling pathways are involved in the pathogenesis of prostate cancer, such as androgen receptor (AR), Akt, Wnt, Hedgehog (Hh) and Notch. Recently, burgeoning amounts of evidence have implicated that the F-box protein Skp2 (S-phase kinase associated protein 2), a well-characterized oncoprotein, also plays a critical role in the development and progression of prostate cancer. Therefore, this review discusses the recent literature regarding the function and regulation of Skp2 in the pathogenesis of prostate cancer. Furthermore, we highlight that Skp2 may represent an attractive therapeutic target, thus warrants further development of agents to target Skp2, which could have significant therapeutic impact on prostate cancer.

Emerging roles of the FBW7 tumour suppressor in stem cell differentiation.

FBW7 is a ubiquitin E3 ligase substrate adaptor that targets many important oncoproteins-such as Notch, c-Myc, cyclin E and c-Jun-for ubiquitin-dependent proteolysis. By doing so, it plays crucial roles in many cellular processes, including cell cycle progression, cell growth, cellular metabolism, differentiation and apoptosis. Loss of FBW7 has been observed in many types of human cancer, and its role as a tumour suppressor was confirmed by genetic ablation of FBW7 in mice, which leads to the induction of tumorigenesis. How FBW7 exerts its tumour suppression function, and whether loss of FBW7 leads to de-differentiation or acquisition of stemness-a process frequently seen in human carcinomas-remains unclear. Emerging evidence shows that FBW7 controls stem cell self-renewal, differentiation, survival and multipotency in various stem cells, including those of the haematopoietic and nervous systems, liver and intestine. Here, we focus on the function of FBW7 in stem cell differentiation, and its potential relevance to human disease and therapeutics.

The two faces of FBW7 in cancer drug resistance.

Chemotherapy is an important therapeutic approach for cancer treatment. However, drug resistance is an obstacle that often impairs the successful use of chemotherapies. Therefore, overcoming drug resistance would lead to better therapeutic outcomes for cancer patients. Recently, studies by our own and other groups have demonstrated that there is an intimate correlation between the loss of the F-box and WD repeat domain-containing 7 (FBW7) tumor suppressor and the incurring drug resistance. While loss of FBW7 sensitizes cancer cells to certain drugs, FBW7-/- cells are more resistant to other types of chemotherapies. FBW7 exerts its tumor suppressor function by promoting the degradation of various oncoproteins that regulate many cellular processes, including cell cycle progression, cellular metabolism, differentiation, and apoptosis. Since loss of the FBW7 tumor suppressor is linked to drug resistance, FBW7 may represent a novel therapeutic target to increase drug sensitivity of cancer cells to conventional chemotherapeutics. This paper thus focuses on the new functional aspects of FBW7 in drug resistance.

The inhibition of RANKL/RANK signaling by osteoprotegerin suppresses bone invasion by oral squamous cell carcinoma cells.

Oral squamous cell carcinomas (OSCCs) are malignant tumors that frequently invade the maxilla and mandibular bone. However, the molecular mechanisms underlying bone invasion by OSCC are unclear. Recent studies showed that receptor activator of nuclear factor κB (RANK) was expressed not only in osteoclast precursors but also in tumor cells. Therefore, we examined whether RANK ligand (RANKL)/RANK signaling regulates bone invasion by OSCC cells in vivo and in vitro. We first injected human OSCC B88 cells into the masseter region of nude mice. Mice were treated for 3 weeks with osteoprotegerin (OPG), the decoy receptor for RANKL. Treatment with OPG decreased bone invasion by B88 cells, reduced the number of osteoclasts and increased B88 cell apoptosis. However, OPG did not affect apoptosis and proliferation in B88 cells in vitro, suggesting that the effects of OPG on apoptosis in B88 cells are restricted in a bone environment. RANK was expressed in the B88 cells and in OSCC cells from patients. RANKL induced NF-κB activation and extracellular signal-regulated kinase phosphorylation in B88 cells and enhanced B88 cell migration in a modified chemotaxis chamber equipped with a gelatin-coated filter. OPG inhibited RANKL-induced NF-κB activation, extracellular signal-regulated kinase phosphorylation and cell migration. Our data clearly indicate that RANKL/RANK inhibition suppresses bone invasion by inhibiting osteoclastogenesis and cancer cell migration and by inducing apoptosis of cancer cells via indirect anticancer action in vivo.

Lactacystin, a proteasome inhibitor, enhances BMP-induced osteoblastic differentiation by increasing active Smads.

Proteasome inhibitors enhance bone formation and osteoblastic differentiation in vivo and in vitro. In the present study, we examined whether the molecular mechanisms of lactacystin, one of many proteasome inhibitors, stimulated the osteoblastic differentiation of C2C12 cells that is induced by bone morphogenetic proteins (BMPs). Pretreatment with lactacystin enhanced the alkaline phosphatase (ALP) activity induced by BMP2, BMP4 or BMP7, but lactacystin did not induce ALP in the absence of BMPs. In addition, lactacystin-stimulated BMP2 induced mRNA expression of ALP, type I collagen, osteonectin, osteocalcin, Id1, Osterix, and Runx2. Lactacystin maintained BMP2-induced phosphorylation of Smad1/5/8 and increased the length of time that these Smads were bound to target DNA. Moreover, lactacystin prevented BMP receptor-induced Smad degradation. This enhancement of BMP2-induced ALP activity and Smad phosphorylation by lactacystin was also observed in primary osteoblasts. These findings suggest that pretreatment with lactacystin accelerates BMP-induced osteoblastic differentiation by increasing the levels of phosphorylated Smads, which are maintained because BMP receptor-induced degradation is inhibited. We propose that optimized stimulation by proteasome inhibitors in a clinical setting may facilitate autogenous or BMP-induced bone formation in areas of defective bone.

Selective inhibition of NF-kappa B blocks osteoclastogenesis and prevents inflammatory bone destruction in vivo.

Bone destruction is a pathological hallmark of several chronic inflammatory diseases, including rheumatoid arthritis and periodontitis. Inflammation-induced bone loss of this sort results from elevated numbers of bone-resorbing osteoclasts. Gene targeting studies have shown that the transcription factor nuclear factor-kappa B (NF-kappa B) has a crucial role in osteoclast differentiation, and blocking NF-kappa B is a potential strategy for preventing inflammatory bone resorption. We tested this approach using a cell-permeable peptide inhibitor of the I kappa B-kinase complex, a crucial component of signal transduction pathways to NF-kappa B. The peptide inhibited RANKL-stimulated NF-kappa B activation and osteoclastogenesis both in vitro and in vivo. In addition, this peptide significantly reduced the severity of collagen-induced arthritis in mice by reducing levels of tumor necrosis factor-alpha and interleukin-1 beta, abrogating joint swelling and reducing destruction of bone and cartilage. Therefore, selective inhibition of NF-kappa B activation offers an effective therapeutic approach for inhibiting chronic inflammatory diseases involving bone resorption.

Tumor necrosis factor alpha represses bone morphogenetic protein (BMP) signaling by interfering with the DNA binding of Smads through the activation of NF-kappaB.

Bone morphogenetic proteins (BMPs) induce not only bone formation in vivo but also osteoblast differentiation of mesenchymal cells in vitro. Tumor necrosis factor alpha (TNFalpha) inhibits both osteoblast differentiation and bone formation induced by BMPs. However, the molecular mechanisms of these inhibitions remain unknown. In this study, we found that TNFalpha inhibited the alkaline phosphatase activity and markedly reduced BMP2- and Smad-induced reporter activity in MC3T3-E1 cells. TNFalpha had no effect on the phosphorylation of Smad1, Smad5, and Smad8 or on the nuclear translocation of the Smad1-Smad4 complex. In p65-deficient mouse embryonic fibroblasts, overexpression of p65, a subunit of NF-kappaB, inhibited BMP2- and Smad-induced reporter activity in a dose-dependent manner. Furthermore, this p65-mediated inhibition of BMP2- and Smad-responsive promoter activity was restored after inhibition of NF-kappaB by the overexpression of the dominant negative IkappaBalpha. Although TNFalpha failed to affect receptor-dependent formation of the Smad1-Smad4 complex, p65 associated with the complex. Chromatin immunoprecipitation and electrophoresis mobility shift assays revealed that TNFalpha suppressed the DNA binding of Smad proteins to the target gene. Importantly, the specific NF-kappaB inhibitor, BAY11-7082, abolished these phenomena. These results suggest that TNFalpha inhibits BMP signaling by interfering with the DNA binding of Smads through the activation of NF-kappaB.

Low-level laser irradiation enhances BMP-induced osteoblast differentiation by stimulating the BMP/Smad signaling pathway.

Low-level laser irradiation (LLLI) has been shown to induce bone formation and osteoblast differentiation both in vivo and in vitro. However, the molecular mechanism by which LLLI stimulates osteoblast differentiation is still unclear. The aim of the present study was to examine whether Ga-Al-As laser irradiation could enhance BMP2-induced alkaline phosphatase (ALP) activity in C2C12 cells. Laser irradiation at 0.5 W for 20 min enhanced BMP2-induced ALP activity. Laser treatment alone did not affect ALP activity. To exclude the effect of pH or temperature changes during irradiation, we shortened the exposure time to 2 min, with various levels of laser power. At 2.5 W, irradiation stimulated BMP2-induced ALP activity but not cell proliferation, whereas 1 or 5 W laser power did not induce any significant effects. Irradiation stimulated BMP2-induced phosphorylation of Smad1/5/8 and BMP2 expression, but had no effect on the expression of inhibitory Smads 6 and 7, BMP4, or insulin-like growth factor 1. Laser irradiation enhanced Smad-induced Id1 reporter activity as well as expression of bone morphogenetic protein (BMP)-induced transcription factors such as Id1, Osterix, and Runx2. Laser irradiation also stimulated BMP-induced expressions of type I collagen, osteonectin, and osteocalcin mRNA, markers of osteoblasts. This enhancement of BMP2-induced ALP activity and Smad phosphorylation by laser irradiation was also observed in primary osteoblasts. These results suggest that LLLI accelerates the differentiation of BMP-induced osteoblasts by stimulating the BMP/Smad signaling pathway.

Characteristics of ClC7 Cl- channels and their inhibition in mutant (G215R) associated with autosomal dominant osteopetrosis type II in native osteoclasts and hClcn7 gene-expressing cells.

ClC7 Cl(-) channels (Clcn7) are crucial for osteoclastic bone resorption and have heterozygous mutation in autosomal osteopetrosis type II (ADO II) patients. Although extracellular acidification is known to induce ClC7 Cl(-) currents in Clcn7-transfected oocytes, other characteristics of this acid-induced Cl(-) current, as well as the effects of mutant Clcn7 in ADO II, remain to be determined. The present study showed that extracellular acidification evoked outward Cl(-) currents in mouse osteoclasts. Expression of wild-type human Clcn7 in HEK293 cells also induced a significant increase in acid-activated Cl(-) currents. These acid-activated Cl(-) currents were independent of intracellular acidification and [Ca(2+)]( i ) increase. HEK293 cells with the Clcn7 mutation associated with ADO II at G215R did not display these Cl(-) currents. These results suggest that osteoclastic ClC7 Cl(-) channels are activated under extracellar acidification and suppressed in Clcn7 mutant associated with ADO II during bone resorption.

Nutrient-induced FNIP degradation by SCFß-TRCP regulates FLCN complex localization and promotes renal cancer progression.

Folliculin-interacting protein 1 and 2 (FNIP1 and FNIP2) play critical roles in preventing renal malignancy through their association with the tumor suppressor FLCN. Mutations in FLCN are associated with Birt-Hogg-Dubé (BHD) syndrome, a rare disorder with increased risk of renal cancer. Recent studies indicated that FNIP1/FNIP2 double knockout mice display enlarged polycystic kidneys and renal carcinoma, which phenocopies FLCN knockout mice, suggesting that these two proteins function together to suppress renal cancer. However, the molecular mechanism functionally linking FNIP1/FNIP2 and FLCN remains largely elusive. Here, we demonstrated that FNIP2 protein is unstable and subjected to proteasome-dependent degradation via ß-TRCP and Casein Kinase 1 (CK1)-directed ubiquitination in a nutrition-dependent manner. Degradation of FNIP2 leads to lysosomal dissociation of FLCN and subsequent lysosomal association of mTOR, which in turn promotes the proliferation of renal cancer cells. These results indicate that SCFß-TRCP negatively regulates the FLCN complex by promoting FNIP degradation and provide molecular insight into the pathogenesis of BHD-associated renal cancer.

The SCFß-TRCP E3 ubiquitin ligase complex targets Lipin1 for ubiquitination and degradation to promote hepatic lipogenesis.

The SCFß-TRCP E3 ubiquitin ligase complex plays pivotal roles in normal cellular physiology and in pathophysiological conditions. Identification of ß-transducin repeat-containing protein (ß-TRCP) substrates is therefore critical to understand SCFß-TRCP biology and function. We used a ß-TRCP-phosphodegron motif-specific antibody in a ß-TRCP substrate screen coupled with tandem mass spectrometry and identified multiple ß-TRCP substrates. One of these substrates was Lipin1, an enzyme and suppressor of the family of sterol regulatory element-binding protein (SREBP) transcription factors, which activate genes encoding lipogenic factors. We showed that SCFß-TRCP specifically interacted with and promoted the polyubiquitination of Lipin1 in a manner that required phosphorylation of Lipin1 by mechanistic target of rapamycin 1 (mTORC1) and casein kinase I (CKI). ß-TRCP depletion in HepG2 hepatocellular carcinoma cells resulted in increased Lipin1 protein abundance, suppression of SREBP-dependent gene expression, and attenuation of triglyceride synthesis. Moreover, ß-TRCP1 knockout mice showed increased Lipin1 protein abundance and were protected from hepatic steatosis induced by a high-fat diet. Together, these data reveal a critical physiological function of ß-TRCP in regulating hepatic lipid metabolic homeostasis in part through modulating Lipin1 stability.

IL-1-induced receptor activator of NF-kappa B ligand in human periodontal ligament cells involves ERK-dependent PGE2 production.

Periodontitis, an inflammatory disorder of the supporting tissue of teeth, is one of the most common infectious diseases in humans. Periodontal pathogens promote inflammatory cytokines such as interleukin-1 (IL-1) and prostaglandin E2 (PGE2), resulting in alveolar bone destruction. In the present study, we examined the cellular and molecular mechanisms of IL-1-induced osteoclastogenesis using a coculture system of human periodontal ligament (PDL) cells and mouse spleen cells. IL-1alpha induced tartrate-resistant acid phosphatase positive (TRAP+) cell formation in a dose-dependent manner. IL-1alpha up-regulated receptor activator of NF-kappaB ligand (RANKL) and down-regulated osteoprotegerin (OPG) mRNA expression in PDL cells. The addition of cell-permeable PKI, an inhibitor of the cAMP/PKA signaling pathway, to the cocultures 8 h after the IL-1alpha stimulation inhibited IL-1alpha-induced TRAP+ cell formation. IL-1alpha-induced TRAP+ cell formation was completely blocked by either NS398, a selective inhibitor of cyclooxygenase (COX)-2, or PD98059, a specific inhibitor of extracellular signal-regulated kinase (ERK). Pretreatment with NS398 and PD98059 also inhibited both the up-regulation of RANKL and the down-regulation of OPG expression by IL-1alpha in PDL cells. IL-1alpha activated ERK phosphorylation and PD98059 greatly inhibited both COX-2 mRNA expression and PGE(2) production induced by IL-1alpha in PDL cells. In contrast, NEMO binding domain (NBD) peptide, a specific inhibitor of NF-kappaB signaling, did not affect COX2, RANKL, or OPG mRNA expression induced by IL-1alpha. These results suggest that IL-1alpha stimulates osteoclast formation by increasing the expression level of RANKL versus OPG via ERK-dependent PGE2 production in PDL cells.

Occlusal guidance of two Kabuki make-up syndrome patients: case reports.

Kabuki make-up syndrome (KMS) has been reported since 1981 by Niikawa et al. Complications of KMS were moderate mental retardation, skeletal and dermatoglyphic abnormalities. A 7 year-old boy, who had severe permanent tooth deficiency, anterior open bite, tongue thrust and mild mental retardation, was referred to our clinic. Oral characters of another patient were an anterior open bite, transposition of maxillary central and lateral incisor. Orthodontic treatment in two patients is reported and suggested future treatment plans in these patients is given.

SCFß-TRCP regulates osteoclastogenesis via promoting CYLD ubiquitination.

CYLD negatively regulates the NF-κB signaling pathway and osteoclast differentiation largely through antagonizing TNF receptor-associated factor (TRAF)-mediated K63-linkage polyubiquitination in osteoclast precursor cells. CYLD activity is controlled by IκB kinase (IKK), but the molecular mechanism(s) governing CYLD protein stability remains largely undefined. Here, we report that SCFß-TRCP regulates the ubiquitination and degradation of CYLD, a process dependent on prior phosphorylation of CYLD at Ser432/Ser436 by IKK. Furthermore, depletion of ß-TRCP induced CYLD accumulation and TRAF6 deubiquitination in osteoclast precursor cells, leading to suppression of RANKL-induced osteoclast differentiation. Therefore, these data pinpoint the IKK/ß-TRCP/CYLD signaling pathway as an important modulator of osteoclastogenesis.