TAT fusion proteins containing tyrosine 42-deleted IkappaBalpha arrest osteoclastogenesis

Cell-penetrating peptide-mediated delivery of therapeutic peptides/proteins to manage the diseases involving oxidative stress, inflammatory response and apoptosis

OBJECTIVES

Peptides and proteins represent great potential for modulating various cellular processes including oxidative stress, inflammatory response, apoptosis and consequently the treatment of related diseases. However, their therapeutic effects are limited by their inability to cross cellular barriers. Cell-penetrating peptides (CPPs), which can transport cargoes into the cell, could resolve this issue, as would be discussed in this review.

KEY FINDINGS

CPPs have been successfully exploited in vitro and in vivo for peptide/protein delivery to treat a wide range of diseases involving oxidative stress, inflammatory processes and apoptosis. Their in vivo applications are still limited due to some fundamental issues of CPPs, including nonspecificity, proteolytic instability, potential toxicity and immunogenicity.

SUMMARY

Totally, CPPs could potentially help to manage the diseases involving oxidative stress, inflammatory response and apoptosis by delivering peptides/proteins that could selectively reach proper intracellular targets. More studies to overcome related CPP limitations and confirm the efficacy and safety of this strategy are needed before their clinical usage.

Decoy peptide targeted to Toll-IL-1R domain inhibits LPS and TLR4-active metabolite morphine-3 glucuronide sensitization of sensory neurons

Accumulating evidence indicates that Toll-like receptor (TLR) signaling adapter protein interactions with Toll/Interleukin-1 Receptor (TIR) domains present in sensory neurons may modulate neuropathic pain states. Following ligand interaction with TLRs, TIR serves to both initiate intracellular signaling and facilitate recruitment of signaling adapter proteins to the intracytoplasmic domain. Although TLR TIR is central to a number of TLR signaling cascades, its role in sensory neurons is poorly understood. In this study we investigated the degree to which TLR TIR decoy peptide modified to include a TAT sequence (Trans-Activator of Transcription gene in HIV; TAT-4BB) affected LPS-induced intracellular calcium flux and excitation in sensory neurons, and behavioral changes due to TLR4 active metabolite, morphine-3-glucuronide (M3G) exposure in vivo. TAT-4BB inhibited LPS-induced calcium changes in a majority of sensory neurons and decreased LPS-dependent neuronal excitability in small diameter neurons. Acute systemic administration of the TAT-4BB reversed M3G-induced tactile allodynia in a dose-dependent manner but did not affect motor activity, anxiety or responses to noxious thermal stimulus. These data suggest that targeting TLR TIR domains may provide novel pharmacological targets to reduce or reverse TLR4-dependent pain behavior in the rodent.

Calebin A downregulates osteoclastogenesis through suppression of RANKL signalling

Osteoporosis is a bone disease that is exacerbated by aging and age-associated chronic diseases such as cancer. Cancer-induced bone loss is usually treated with bisphosphonates or denosumab, an antibody against receptor activator of nuclear factor (NF)-κB ligand (RANKL). Because these drugs are expensive and have numerous side effects and high rates of toxicity, safer, more effective, and more affordable therapies for osteoporosis are still needed. We identified a compound, calebin A (CA), derived from turmeric (Curcuma longa) that affects osteoclastogenesis through modulation of the RANKL signalling pathway. The CA's effect on NF-κB activation was examined by electrophoretic mobility shift assay. Using mouse macrophages in vitro model, we found that CA suppressed RANKL-induced osteoclast differentiation of macrophages into osteoclasts, and downregulate RANKL-induced osteoclastogenesis-related marker gene expression, including NFATc-1, TRAP, CTR, and cathepsin K. CA also suppressed the osteoclastogenesis induced by multiple myeloma and breast cancer cells. This effect of CA was correlated with suppression of the phosphorylation and degradation of inhibitor of κB and, thus, inhibition of NF-κB activation. Furthermore, we found that an NF-κB-specific inhibitory peptide blocked RANKL-induced osteoclastogenesis, demonstrating that the NF-κB signalling pathway is mandatory for RANKL-induced osteoclastogenesis. Our results conclusively indicate that CA downmodulates the osteoclastogenesis induced by RANKL and by tumour cells through suppression of NF-κB pathway.

Disulfiram attenuates osteoclast differentiation in vitro: a potential antiresorptive agent

Disulfiram (DSF), a cysteine modifying compound, has long been clinically employed for the treatment of alcohol addiction. Mechanistically, DSF acts as a modulator of MAPK and NF-κB pathways signaling pathways. While these pathways are crucial for osteoclast (OC) differentiation, the potential influence of DSF on OC formation and function has not been directly assessed. Here, we explore the pharmacological effects of DSF on OC differentiation, activity and the modulation of osteoclastogenic signaling cascades. We first analyzed cytotoxicity of DSF on bone marrow monocytes isolated from C57BL/6J mice. Upon the establishment of optimal dosage, we conducted osteoclastogenesis and bone resorption assays in the presence or absence of DSF treatment. Luciferase assays in RAW264.7 cells were used to examine the effects of DSF on major transcription factors activation. Western blot, reverse transcription polymerase chain reaction, intracellular acidification and proton influx assays were employed to further dissect the underlying mechanism. DSF treatment dose-dependently inhibited both mouse and human osteoclastogenesis, especially at early stages of differentiation. This inhibition correlated with a decrease in the expression of key osteoclastic marker genes including CtsK, TRAP, DC-STAMP and Atp6v0d2 as well as a reduction in bone resorption in vitro. Suppression of OC differentiation was found to be due, at least in part, to the blockade of several key receptor activators of nuclear factor kappa-B ligand (RANKL)-signaling pathways including ERK, NF-κB and NFATc1. On the other hand, DSF failed to suppress intracellular acidification and proton influx in mouse and human osteoclasts using acridine orange quenching and microsome-based proton transport assays. Our findings indicate that DSF attenuates OC differentiation via the collective suppression of several key RANKL-mediated signaling cascades, thus making it an attractive agent for the treatment of OC-mediated disorders.

Water extract of Magnolia officinalis cortex inhibits osteoclastogenesis and bone resorption by downregulation of nuclear factor of activated T cells cytoplasmic 1

Background

Magnolia officinalis cortex has been traditionally used to treat stomach and intestine diseases in traditional Korean medicine. In this study, we investigated the effect of water extract of M. officinalis cortex (WEMC) on osteoclast differentiation and function.

Methods

Phytochemical characterization of WEMC was performed by high-performance liquid chromatography analysis. Osteoclast differentiation of bone marrow-derived macrophages was determined by tartrate-resistant acid phosphatase activity assay. Receptor activator of nuclear factor-κB ligand (RANKL) signaling factors and transcription factors regulating osteoclast differentiation were analyzed by Western blot and real-time polymerase chain reaction. Bone resorption function of mature osteoclasts was examined by using culture plate coated with inorganic crystalline calcium phosphate. Furthermore, the in vivo effect of WEMC on osteoporosis was examined using RANKL-induced bone loss model, characterized by micro-computed tomography and bone metabolism marker analysis.

Results

WEMC inhibited RANKL-induced osteoclast differentiation and the bone resorbing activity of mature osteoclasts. WEMC contains gallic acid and honokiol as active constituents contributing to the inhibitory effect of WEMC on osteoclast differentiation. Further, WEMC suppressed RANKL-induced activation of p38 and nuclear factor-κB pathways and expression of osteoclastogenic transcription factors such as c-Fos for AP-1 and nuclear factor of activated T cells cytoplasmic 1. Ectopic overexpression of a constitutive active form of nuclear factor of activated T cells cytoplasmic 1 rescued the antiosteoclastogenic effect of WEMC. Consistent with the in vitro results, WEMC suppressed RANKL-induced trabecular bone loss in mice.

Conclusion

WEMC might have a therapeutic potential to treat pathological bone diseases due to increased osteoclast differentiation and function.

Regulation of NF-κB signaling in osteoclasts and myeloid progenitors

The transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is crucial for immune responses and skeletal development. Work in recent years has shown that various members of the NF-κB family are viable targets to regulate activity and survival of bone cells and hence bone metabolism. In this regard, deletion of upstream kinases or distal NF-κB subunits resulted with bone deformities. Thus, it has become increasingly apparent that detailed investigation of NF-κB in bone cells may provide opportunities to design new therapeutic modalities. In this chapter we present modified methodology describing efficient approaches to regulate the NF-κB pathway in vitro and in vivo to assess its function in bone cells and tissues.

Ubiquitin-like domain of IKKβ regulates osteoclastogenesis and osteolysis

The transcription factor NF-κB family is central for osteoclastogenesis and inflammatory osteolysis. Activation of NF-κB dimers is regulated by a kinase complex predominantly containing IKKα (IKK1), IKKβ (IKK2), and a regulatory subunit, IKKγ/NEMO. IKKα and IKKβ catalyze the cytoplasmic liberation and nuclear translocation of various NF-κB subunits. The requirement of IKKα and IKKβ for normal bone homeostasis has been established. Congruently, mice devoid of IKKα or IKKβ exhibit in vitro and in vivo defects in osteoclastogenesis, and IKKβ-null mice are refractory to inflammatory arthritis and osteolysis. To better understand the molecular mechanism underlying IKKβ function in bone homeostasis and bone pathologies, we conducted structure-function analysis to determine IKKβ functional domains in osteoclasts. IKKβ encompasses several domains, of which the ubiquitination-like domain (ULD) has been shown essential for IKKβ activation. In this study, we examined the role of ULD in IKKβ-mediated NF-κB activation in osteoclast precursors and its contribution to osteoclastogenesis and osteolysis. We generated and virally introduced IKKβ in which the ULD domain has been deleted (IKKβ∆ULD) into osteoclast progenitors. The results show that deletion of ULD diminishes IKKβ activity and that IKKβ∆ULD strongly inhibits osteoclastogenesis. In addition, unlike wild type (WT)-IKKβ, IKKβ∆ULD fail to restore RANKL-induced osteoclastogenesis by IKKβ-null precursors. Finally, we provide evidence that IKKβ∆ULD blocks inflammatory osteolysis in a model of murine calvarial osteolysis. Thus, we identified the ULD as crucial for IKKβ activity and osteoclastogenesis and found that ULD-deficient IKKβ is a potent inhibitor of osteoclastogenesis and osteolysis.

Okadaic acid activates the PKR pathway and induces apoptosis through PKR stimulation in MG63 osteoblast-like cells

Double-stranded RNA-dependent protein kinase (PKR) is one of the players in the cellular antiviral responses and is involved in transcriptional stimulation through activation of NF-κB. Treatment of the human osteosarcoma cell line MG63 with the protein phosphatase inhibitor okadaic acid stimulated the expression and phosphorylation of IκBα, as judged from the results of real-time PCR and western blot analysis. We investigated the functional relationship between PKR and signal transduction of NF-κB by establishing PKR-K/R cells that produced a catalytically inactive mutant of PKR. Phosphorylation of eIF-2α, a substrate of PKR, was not stimulated by okadaic acid in the PKR-K/R cells, whereas okadaic acid induced phosphorylation of eIF-2α in MG63 cells. Phosphorylation of NF-κB in MG63 cells was stimulated by okadaic acid; however, okadaic acid did not induce phosphorylation of NF-κB in the PKR-K/R cells. Finally, okadaic acid-induced apoptosis was inhibited in the PKR-K/R cells. Our results suggest that okadaic acid-induced phosphorylation of IκBα was mediated by PKR kinase activity, thus, indicating the involvement of this kinase in the control mechanism governing the activation of NF-κB and induction of apoptosis.

Selaginella tamariscina water extract inhibits receptor activator for the nuclear factor-κB ligand-induced osteoclast differentiation by blocking mitogen-activated protein kinase and NF-κB signaling

Background:

Selaginella tamariscina has been traditionally used in Korea for treating hematochezia, hematuria, and prolapse of the anus. The aim of this study was to evaluate the inhibitory effect of Selaginella tamariscina water extract (ST-WE) on osteoclast differentiation, and to determine the underlying molecular mechanism.

Materials and Methods:

RAW264.7 cells were used as a model to examine receptor activator for the nuclear factor-κB ligand (RANKL)-induced osteoclast differentiation. Expression of osteoclastic genes and transcription factors was evaluated by real-time quantitative polymerase chain reaction (QPCR). Activation of the mitogen-activated protein kinases, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, and NF-κB were determined by Western blot analysis.

Results:

ST-WE significantly inhibited RANKL-induced tartrate-resistant acid phosphatase (TRAP) activity and formation of multinucleated osteoclasts in RAW264.7 cells. ST-WE also significantly inhibited the RANKL-induced mRNA expression of TRAP, cathepsin K, and the d2 isoform of vacuolar ATPase V(0) domain (ATPv0d2) gene. In addition, ST-WE inhibited the RANKL-induced phosphorylation of ERK, JNK, and p38, phosphorylation of I-κB_α and NF-κB p65, and the expression of transcription factors c-fos, Fra-2, and nuclear factor of activated T cells 1. Furthermore, ST inhibited the bone resorptive activity of osteoclasts.

Conclusion:

ST-WE might have beneficial effects on bonedisease by inhibiting osteoclastogenesis and osteoclastic activity.

Thiocolchicoside suppresses osteoclastogenesis induced by RANKL and cancer cells through inhibition of inflammatory pathways: a new use for an old drug

BACKGROUND AND PURPOSE

Most patients with cancer die not because of the tumour in the primary site, but because it has spread to other sites. Common tumours, such as breast, multiple myeloma, and prostate tumours, frequently metastasize to the bone. To search for an inhibitor of cancer-induced bone loss, we investigated the effect of thiocolchicoside, a semi-synthetic colchicoside derived from the plant Gloriosa superba and clinically used as a muscle relaxant, on osteoclastogenesis induced by receptor activator of NF-κB ligand (RANKL) and tumour cells.

EXPERIMENTAL APPROACH

We used RAW 264.7 (murine macrophage) cells, a well-established system for osteoclastogenesis, and evaluated the effect of thiocolchicoside on RANKL-induced NF-κB signalling and osteoclastogenesis as well as on osteoclastogenesis induced by tumour cells.

KEY RESULTS

Thiocolchicoside suppressed osteoclastogenesis induced by RANKL, and by breast cancer and multiple myeloma cells. Inhibition of the NF-κB pathway was responsible for this effect since the colchicoside inhibited RANKL-induced NF-κB activation, activation of IκB kinase (IKK) and suppressed inhibitor of NF-κBα (IκBα) phosphorylation and degradation, an inhibitor of NF-κB. Furthermore, an inhibitor of the IκBα kinase γ or NF-κB essential modulator, the regulatory component of the IKK complex, demonstrated that the NF-κB signalling pathway is mandatory for osteoclastogenesis induced by RANKL.

CONCLUSIONS AND IMPLICATIONS

Together, these data suggest that thiocolchicoside significantly suppressed osteoclastogenesis induced by RANKL and tumour cells via the NF-κB signalling pathway. Thus, thiocolchicoside, a drug that has been used for almost half a century to treat muscle pain, may also be considered as a new treatment for bone loss.

Evidence that the kinase-truncated c-Src regulates NF-κB signaling by targeting NEMO

The tyrosine kinase c-Src and transcription factor NF-κB are considered crucial components required for normal osteoclastogenesis. Genetic ablation of either pathway leads to detrimental osteopetrotic phenotypes in mice. Similarly, obstruction of either pathway halts osteoclastogenesis and lessens various forms of bone loss. It has been shown previously that mice expressing a kinase domain-truncated c-Src, termed Src251, develop severe osteopetrosis owing to increased osteoclast apoptosis. It was further suggested that this phenomenon is associated with reduced Akt kinase activity. However, the precise mechanism underlying the osteoclast inhibitory effect of Src251 remains obscure. C-Src associates with TRAF6-p62 interacting with receptor activator of NF-κB (RANK) distal region and the complex facilitate activation of RANK down stream signal transduction cascades including NF-κB. Given this proximity between c-Src and NF-κB signaling in osteoclasts, we surmised that inhibition of osteoclastogenesis by Src251 may be achieved through inhibition of NF-κB signaling. We have demonstrated recently that NEMO, the regulatory subunit of the IKK complex, is crucial for osteoclastogenesis and interacts with c-Src in osteoclast progenitors. Transfection studies, in which we employed various forms of c-Src and NEMO, revealed that the dominant negative form of c-Src, namely Src251, mediates degradation of NEMO thus halting NF-κB signaling. Furthermore, degradation of NEMO requires its intact zinc finger domain which is located at the ubiquitination domain. This process also requires appropriate cellular localization of Src251, since deletion of its myristoylation domain ablates its degradation capacity. Buttressing these findings, the expression of NEMO and NF-κB signaling were significantly reduced in monocytes collected from Src251 transgenic mice.

Embelin suppresses osteoclastogenesis induced by receptor activator of NF-κB ligand and tumor cells in vitro through inhibition of the NF-κB cell signaling pathway

Most patients with cancer die not because of the tumor in the primary site, but because it has spread to other sites. Common tumors, such as breast, multiple myeloma, and prostate tumors, frequently metastasize to the bone. It is now well recognized that osteoclasts are responsible for the osteolysis observed in bone metastases of the tumor. Receptor activator of NF-κB ligand (RANKL), a member of the tumor necrosis factor superfamily and an activator of the NF-κB signaling pathway, has emerged as a major mediator of bone loss, commonly associated with cancer and other chronic inflammatory diseases. Embelin (2,5-dihydroxy-3-undecyl-1,4-benzoquinone), derived from the Ayurvedic medicinal plant Embelia ribes, has been shown to bind and inhibit X-linked inhibitor of apoptosis protein and inhibit inflammatory pathways. We investigated whether embelin could inhibit osteoclastogenesis-associated bone loss induced by RANKL and by tumor cells in vitro. We found that embelin suppressed the RANKL-induced differentiation of monocytes into osteoclasts. This benzoquinone also suppressed the osteoclastogenesis induced by multiple myeloma and by breast cancer cells. This effect of embelin correlated with the suppression of NF-κB activation and inhibition of IκBα phosphorylation and IκBα degradation. Inhibition of IκBα phosphorylation was due to the inhibition of IκBα kinase (IKK) activation. Furthermore, by using an inhibitor of the IKKγ or NF-κB essential modulator (NEMO), the regulatory component of the IKK complex, we showed that the NF-κB signaling pathway is mandatory for RAW 264.7 cell differentiation into osteoclasts. Thus, embelin, an inhibitor of RANKL-induced NF-κB activation has great potential as a therapeutic agent for osteoporosis and cancer-linked bone loss.

Tyrosine phosphorylation is required for IkappaB kinase-beta (IKKbeta) activation and function in osteoclastogenesis

The transcription factor NF-kappaB is crucial for numerous cellular functions such as survival, differentiation, immunity, and inflammation. A key function of this family of transcription factors is regulation of osteoclast differentiation and function, which in turn controls skeletal homeostasis. The IkappaB kinase (IKK) complex, which contains IKKalpha, IKKbeta, and IKKgamma, is required for activation of NF-kappaB, and deletion of either IKKalpha or IKKbeta resulted with defective osteoclast differentiation and survival. We have recently investigated the details of the mechanisms governing the role of IKKbeta in osteoclastogenesis and found that constitutively active IKKbeta in which serine residues 177/181 were mutated into negatively charged glutamic acids instigates spontaneous bona fide receptor activator of NF-kappaB ligand (RANKL)-independent osteoclastogenesis. To better understand and define the functional role of IKKbeta domains capable of regulating the osteoclastogenic activity of IKK, we investigated key motifs in the activation T loop of IKKbeta, which are potentially capable of modulating its osteoclastogenic activity. We discovered that dual serine (traditional serine residues 177/181) and tyrosine (188/199) phosphorylation events are crucial for IKKbeta activation. Mutation of the latter tyrosine residues blunted the NF-kappaB activity of wild type and constitutively active IKKbeta, and tyrosine 188/199-deficient IKKbeta inhibited osteoclastogenesis. Thus, tyrosines 188/199 are a novel target for regulating IKKbeta activity, at least in osteoclasts.

Inhibiting NF-κB activation by small molecules as a therapeutic strategy

Because nuclear factor-κB (NF-κB) is a ubiquitously expressed proinflammatory transcription factor that regulates the expression of over 500 genes involved in cellular transformation, survival, proliferation, invasion, angiogenesis, metastasis, and inflammation, the NF-κB signaling pathway has become a potential target for pharmacological intervention. A wide variety of agents can activate NF-κB through canonical and noncanonical pathways. Canonical pathway involves various steps including the phosphorylation, ubiquitination, and degradation of the inhibitor of NF-κB (IκBα), which leads to the nuclear translocation of the p50-p65 subunits of NF-κB followed by p65 phosphorylation, acetylation and methylation, DNA binding, and gene transcription. Thus, agents that can inhibit protein kinases, protein phosphatases, proteasomes, ubiquitination, acetylation, methylation, and DNA binding steps have been identified as NF-κB inhibitors. Because of the critical role of NF-κB in cancer and various chronic diseases, numerous inhibitors of NF-κB have been identified. In this review, however, we describe only small molecules that suppress NF-κB activation, and the mechanism by which they block this pathway.

Impediment of NEMO oligomerization inhibits osteoclastogenesis and osteolysis

The transcription factor NF-kappaB is essential for osteoclastogenesis and is considered an immune-modulator of rheumatoid arthritis and inflammatory osteolysis. Activation of NF-kappaB subunits is regulated by the upstream IkappaB kinase (IKK) complex which contains IKKalpha, IKKbeta, and IKKgamma; the latter also known as NF-kappaB essential modulator (NEMO). The role of IKKalpha and IKKbeta in the skeletal development and inflammatory osteolysis has been described, whereas little is known regarding the role of NEMO in this setting. Typically, signals induced by RANK ligand (RANKL) or TNF prompt oligomerization of NEMO monomers through the coiled-coil-2 (CC2) and leucine zipper (LZ) motifs. This step facilitates binding to IKKs and further relaying signal transduction. Given the central role of NF-kappaB in osteoclastogenesis, we asked whether NEMO is essential for osteoclastogenesis and whether interruption of NEMO oligomerization impedes osteoclast differentiation in vitro and in vivo. Using cell-permeable short peptides overlapping the CC2 and LZ motifs we show that these peptides specifically bind to NEMO monomers, prevent trimer formation, and render NEMO monomers susceptible for ubiquitin-mediated degradation. Further, CC2 and LZ peptides attenuate RANKL- and TNF-induced NF-kappaB signaling in bone marrow-derived osteoclast precursors (OCPs). More importantly, these peptides potently inhibit osteoclastogenesis, in vitro, and arrest RANKL-induced osteolysis, in mice. To further ascertain its role in osteoclastogenesis, we were able to block osteoclastogenesis using NEMO siRNA knockdown approach. Collectively, our data establish that obstruction of NEMO oligomerization destabilizes NEMO monomers, inhibits NF-kappaB activation, impedes osteoclastogenesis and arrests inflammatory osteolysis. Thus, NEMO presents itself as a promising target for anti-osteolytic intervention.

Potential pharmacological control of the NF-κB pathway

Nuclear factor (NF)-kappaB governs the expression of numerous genes that are important for various cellular responses. Its activation is induced by a wide variety of stimuli including stress, cigarette smoke, viral and bacterial products, cytokines, free radicals, carcinogens and tumor promoters to name a few. Deregulation of the NF-kappaB pathway has been observed in and attributed to the development of a variety of human ailments including cancers, autoimmune disorders, pulmonary, cardiovascular, neurodegenerative and skin diseases. Efforts to develop modulators of NF-kappaB have yielded several candidates, some of which are currently in Phase I/II of clinical trials. In addition, it is now becoming apparent that several of the approved drugs being currently used also work, in part, owing to their ability to influence the NF-kappaB pathway. In this article, we focus on the druggable components of the NF-kappaB signaling system and on the recent development of novel therapeutics that target NF-kappaB in various diseases.

Synergistic inhibition of T-cell activation by a cell-permeable ZAP-70 mutant and ctCTLA-4

T-cell activation requires TcR-mediated and co-stimulatory signals. ZAP-70 participates in the initial step of TcR signal transduction, while a co-receptor, CTLA-4, inhibits T-cell activation. In previous studies, the overexpression of a ZAP-70 mutant (ZAP-70-Y319F) inhibited the TcR-induced activation of NFAT and IL-2 production, while Hph-1-ctCTLA-4 prevented allergic inflammation. To develop an effective immunosuppressive protein drug that blocks both TcR-mediated and co-stimulatory signaling pathways, a fusion protein of ZAP-70-Y319F and the Hph-1 protein transduction domain was generated. Hph-1-ZAP-70-Y319F inhibited the phosphorylation of ZAP-70-Tyr319, LAT-Tyr191, and p44/42 MAPK induced by TcR stimulation, NFAT- and AP-1-mediated gene transcription, and the induction of CD69 expression and IL-2 secretion. Hph-1-ZAP-70-Y319F and Hph-1-ctCTLA-4 synergistically inhibited signaling events during T-cell activation. This is the first report to demonstrate the synergistic inhibition of signals transmitted via TcR and its co-stimulatory receptor by cell-permeable forms of intracellular signal mediators.

RelA/p65 promotes osteoclast differentiation by blocking a RANKL-induced apoptotic JNK pathway in mice

Osteoclasts (OCs) function to reabsorb bone and are responsible for the bone loss associated with inflammatory arthritis and osteoporosis. OC numbers are elevated in most disorders of accelerated bone destruction, reflecting altered rates of precursor differentiation and apoptosis. Both of these processes are regulated by the JNK family of MAP kinases. In this study, we have demonstrated that the NF-kappaB subunit RelA/p65 inhibits JNK-mediated apoptosis during a critical period of commitment to the OC phenotype in response to the cytokine RANKL. This RelA/p65-mediated arrest of cell death led to enhanced OC differentiation. Hence, Rela-/- OC precursors displayed prolonged JNK activation in response to RANKL, and this was accompanied by an increase in cell death that prevented efficient differentiation. Although complete blockade of JNK activity inhibits osteoclastogenesis, both short-term blockade in RelA-deficient cultures and suppression of the downstream mediator, Bid rescued apoptosis and differentiation. These antiapoptotic effects were RelA specific, as overexpression of RelA, but not RelB, blocked apoptosis and rescued differentiation in Rela-/- precursors. Thus, RelA blocks a RANKL-induced, apoptotic JNK-Bid pathway, thereby promoting OC differentiation. Consistent with this, mice lacking RelA/p65 in the hematopoietic compartment were shown to have a deficient osteoclastogenic response to RANKL and were protected from arthritis-induced osteolysis.

NF-kappaB inhibitor dehydroxymethylepoxyquinomicin suppresses osteoclastogenesis and expression of NFATc1 in mouse arthritis without affecting expression of RANKL, osteoprotegerin or macrophage colony-stimulating factor

Inhibition of NF-κB is known to be effective in reducing both inflammation and bone destruction in animal models of arthritis. Our previous study demonstrated that a small cell-permeable NF-κB inhibitor, dehydroxymethylepoxyquinomicin (DHMEQ), suppresses expression of proinflammatory cytokines and ameliorates mouse arthritis. It remained unclear, however, whether DHMEQ directly affects osteoclast precursor cells to suppress their differentiation to mature osteoclasts in vivo. The effect of DHMEQ on human osteoclastogenesis also remained elusive. In the present study, we therefore examined the effect of DHMEQ on osteoclastogenesis using a mouse collagen-induced arthritis model, and using culture systems of fibroblast-like synovial cells obtained from patients with rheumatoid arthritis, and of osteoclast precursor cells from peripheral blood of healthy volunteers. DHMEQ significantly suppressed formation of osteoclasts in arthritic joints, and also suppressed expression of NFATc1 along the inner surfaces of bone lacunae and the eroded bone surface, while serum levels of soluble receptor activator of NF-κB ligand (RANKL), osteoprotegerin and macrophage colony-stimulating factor were not affected by the treatment. DHMEQ also did not suppress spontaneous expression of RANKL nor of macrophage colony-stimulating factor in culture of fibroblast-like synovial cells obtained from patients with rheumatoid arthritis. These results suggest that DHMEQ suppresses osteoclastogenesis in vivo, through downregulation of NFATc1 expression, without significantly affecting expression of upstream molecules of the RANKL/receptor activator of NF-κB/osteoprotegerin cascade, at least in our experimental condition. Furthermore, in the presence of RANKL and macrophage colony-stimulating factor, differentiation and activation of human osteoclasts were also suppressed by DHMEQ, suggesting the possibility of future application of NF-κB inhibitors to rheumatoid arthritis therapy.

Nuclear factor-kappaB activation: from bench to bedside

Nuclear factor-kappaB (NF-kappaB) is a proinflammatory transcription factor that has emerged as an important player in the development and progression of malignant cancers. NF-kappaB targets genes that promote tumor cell proliferation, survival, metastasis, inflammation, invasion, and angiogenesis. Constitutive or aberrant activation of NF-kappa is frequently encountered in many human tumors and is associated with a resistant phenotype and poor prognosis. The mechanism of such persistent NF-kappaB activation is not clear but may involve defects in signaling pathways, mutations, or chromosomal rearrangements. Suppression of constitutive NF-kappaB activation inhibits the oncogenic potential of transformed cells and thus makes NF-kappaB an interesting new therapeutic target in cancer.

A transmembrane osteoclastic protein-tyrosine phosphatase regulates osteoclast activity in part by promoting osteoclast survival through c-Src-dependent activation of NFκB and JNK2

This study evaluated the effects of overexpression of wild-type (WT) or phosphatase-deficient (PD) mutant of an osteoclastic protein-tyrosine phosphatase (PTP-oc) in RAW/C4 cells. Osteoclast-like cells derived from WT-PTP-oc overexpressing clones increased, while those derived from PD-PTP-oc expressing clones decreased, their resorption activity. WT-PTP-oc clones had lower apoptosis, lower caspase 3/7 activity, reduced c-Src tyr-527 phosphorylation (PY527) and IkappaBalpha cellular levels, and increased NFkappaB activation and JNK phosphorylation. Overexpression of PD-PTP-oc or PTP-oc siRNA treatment increased apoptosis, caspase 3/7 activity, PY527 and IkappaBalpha levels, and decreased NFkappaB and JNK2 activation. Inhibition of the c-Src kinase blocked the PTP-oc-mediated NFkappaB and JNK2 activation. Blocking the NFkappaB activation had no effect on the JNK2 activation. Inhibiting the NFkappaB and/or JNK2 pathway prevented the PTP-oc-mediated reduction in apoptosis. In conclusion, PTP-oc activates osteoclast activity in part by promoting osteoclast survival through the PTP-oc-mediated c-Src-dependent activation of NFkappaB and JNK2.

Osteoclasts: what do they do and how do they do it?

As Americans live longer, degenerative skeletal diseases, such as osteoporosis, become increasingly prevalent. Regardless of cause, osteoporosis reflects a relative enhancement of osteoclast activity. Thus, this unique bone resorptive cell is a prominent therapeutic target. A number of key observations provide insights into the mechanisms by which precursors commit to the osteoclast phenotype and how the mature cell degrades bone. The osteoclast is a member of the monocyte/macrophage family that differentiates under the aegis of two critical cytokines, namely RANK ligand and M-CSF. Tumor necrosis factor (TNF)-alpha also promotes osteoclastogenesis, particularly in states of inflammatory osteolysis such as that attending rheumatoid arthritis. Once differentiated, the osteoclast forms an intimate relationship with the bone surface via the alphavbeta3 integrin, which transmits matrix-derived, cytoskeleton-organizing, signals. These integrin-transmitted signals include activation of the associated proteins, c-src, syk, Vav3, and Rho GTPases. The organized cytoskeleton generates an isolated microenvironment between the cell's plasma membrane and the bone surface in which matrix mineral is mobilized by the acidic milieu and organic matrix is degraded by the lysosomal protease, cathepsin K. This review focuses on these and other molecules that mediate osteoclast differentiation or function and thus serve as candidate anti-osteoporosis therapeutic targets.

Characterization of a novel cell penetrating peptide derived from Bag-1 protein

A highly cationic peptide (BagP), located within the normally expressed human protein Bag-1, was tested for its capacity to act as a cell penetrating peptide. BagP was found to translocate and transport high molecular weight cargos in several cell types, in varying degrees with a preference for adherent cells. The penetration phenomenon was not found to be subject to saturation for the highest amount of peptide tested (100 microM), whereas the time needed for maximum translocation to be achieved, was cell type-dependent. Finally, BagP internalization depends on its charge, cellular metabolism and cell-surface heparan sulfate proteoglycans.

Inhibition of IKK activation, through sequestering NEMO, blocks PMMA-induced osteoclastogenesis and calvarial inflammatory osteolysis

Osteoclasts, the primary bone-resorbing cells, play a crucial role in periprosthetic bone loss in response to implant-derived wear debris. Differentiation and activation of osteoclasts at the implant-bone interface are fueled by elevated levels of locally secreted inflammatory cytokines that heighten the osteolytic response. Among these cytokines are members of the TNF superfamily, including TNF and RANKL, which primarily act through activation of the transcription factor NF-kappaB. Activation of NF-kappaB is required for osteoclast formation, and its inhibition hampers osteoclastogenesis and bone loss. Activation of NF-kappaB is permitted following its dissociation from the inhibitory protein IkappaBalpha, an event subsequent to phosphorylation of the latter protein by the upstream IkappaBalpha kinase (IKK) complex. Our recent findings show that attenuating IKK complex assembly, by using a short peptide termed NEMO-binding domain (NBD) peptide, that blocks binding of IKK2 and IKK1 to IKKgamma/NEMO, inhibits NF-kappaB activation, and arrests RANKL-induced osteoclastogenesis. In this study, we examined if NBD is capable of blocking inflammatory osteolysis by PMMA particles. Our findings indicate that NBD peptide inhibits PMMA-induced IKK2 and NF-kappaB activation. More importantly, this peptide potently arrests PMMA-stimulated osteoclastogenesis and alleviates PMMA-induced inflammatory and osteolytic responses in mice. Thus, NBD peptide is considered as a promising modality to regulate inflammatory osteolysis.

Medium-sized peptides as built in carriers for biologically active compounds

A growing number of oligopeptides of natural and/or synthetic origin have been described and considered as targeting structures for delivery bioactive compounds into various cell types. This review will outline the discovery of peptide sequences and the corresponding mid-sized oligopeptides with membrane translocating properties and also summarize de novo designed structures possessing similar features. Conjugates and chimera constructs derived from these sequences with covalently attached bioactive peptide, epitope, oligonucleotide, PNA, drug, reporter molecule will be reviewed. A brief note will refer to the present understanding on the uptake mechanism at the end of each section.

NFATc1 regulation of the human beta3 integrin promoter in osteoclast differentiation

The transcription factor NFATc1 plays an essential role in transducing signals from RANKL in osteoclast differentiation. To date, however, the specific transcriptional targets of NFATc1 are unknown. Expression of the beta3 integrin is required for normal osteoclast function. We therefore examined the role of NFATc1 in human beta3 integrin expression in osteoclast differentiation. Analysis of the mouse and human beta3 gene promoters revealed considerable sequence homology across a 1.3 kb region upstream of the transcription start site (TSS), with conserved NFAT binding elements present. The region -1242 to +29 (relative to the TSS) was cloned as a luciferase reporter construct (pB3-1.3) and a deletion construct removing to -997 (pB3-1) made. The deletion of 245 bp 5' removed three conserved NFAT sites including a consensus NFAT:AP-1 site. The pB3-1.3 reporter construct was induced by treatment with RANKL in the range 2.5-40 ng/ml and dose-dependently induced by co-transfection with human NFATc1 in RAW264.7 cells. The pB3-1 deletion construct was minimally induced with RANKL treatment and unresponsive to co-transfected NFATc1. Direct NFAT binding to two of the consensus NFAT sites within this 245 bp 5' region was demonstrated by EMSA and supershift with anti-NFAT antibodies. Mutation of two of the conserved NFAT sites in the -1242 to -997 fragment was required to prevent binding. The double NFAT mutant, in the context of the full-length promoter was unresponsive to RANKL treatment or co-transfected NFATc1. We generated cell-permeable TAT-dominant-negative (dn)NFATc1 fusion proteins to assess the effect of blockade of NFAT signaling. Transduction with dnNFAT inhibited RANKL induction of the human beta3 integrin promoter. Involvement of the NFATc1-calcineurin pathway in regulating the human beta3 integrin promoter was further confirmed using the calcineurin pathway inhibitory peptide 11R-VIVIT. Together these results establish the beta3 gene as a direct target of NFATc1 in RANKL-dependent osteoclast formation.

Okadaic acid induces tyrosine phosphorylation of IkappaBalpha that mediated by PKR pathway in human osteoblastic MG63 cells

Treatment of human osteosarcoma cell line MG 63 cells with okadaic acid stimulated phosphorylation of IkappaBalpha, as judged from the results of Western blot analysis and a lambda protein phosphatase dephosphorylation assay. The stimulated phosphorylation of IkappaBalpha was both time- and dose-dependent. The phosphorylation sites of IkappaBalpha were taken to be tyrosine residues because the anti-phospho-tyrosine antibody bound to the samples immunoprecipitated with the anti-IkappaBalpha antibody. In the cells treated with 100 nM okadaic acid consequential translocation of NF-kappaB p65 from the cytosol to the nucleus occurred. Double-stranded RNA-dependent protein kinase (PKR) is a player in the cellular antiviral response and is involved in transcriptional stimulation through activation of NF-kappaB. We investigated the functional relationship between PKR and IkappaBalpha phosphorylation by constructing MG 63 PKR K/R cells that produced a catalytically inactive mutant PKR. NF-kappaB p65 was detected in the nucleus of these cells, even in the unstimulated cells. Although IkappaBalpha was degraded phosphorylation of eIF-2 alpha, a substrate of PKR, did not occur in the mutant cells treated with okadaic acid. Our results suggest that okadaic acid-induced tyrosine phosphorylation of IkappaBalpha was mediated by PKR kinase activity, thus indicating the involvement of this kinase in the control mechanism governing the activation of NF-kappaB.

D-TAT transporter as an ocular peptide delivery system

BACKGROUND

Future treatment for genetic diseases may involve the replacement of malfunctioning genes through virus-mediated gene therapy. However, this approach is plagued with many problems, both ethical and scientific. Therefore, alternative treatments based on new molecules may represent a safer option. Molecular treatment of many eye diseases will need to bring active molecules into the photoreceptors. Recently, the trans-activator protein (TAT) human immunodeficiency virus type 1 (HIV-1) transcriptional factor has proven to be effective in transporting molecules across cellular membranes. The half-life of these molecules does not exceed 48 hours. The potential use of the retro-inverso form of the TAT (D-TAT) peptide, the protein transducing domain of the HIV-1 transcriptional factor, as a molecular transporter was investigated.

METHODS

FITC-labelled D-TAT (D-TAT FITC) was applied to the 661W murine photoreceptor cell line in culture. The labelled peptide was also injected into the vitreous body or the subretinal space of adult mice. Cells and cryosections of eyes were analysed under fluorescence microscopy at various time points after peptide treatment. Coimmunostaining with various antibodies was performed in order to characterize the transduces cells.

RESULTS

D-TAT was effective in transducing photoreceptor cells in culture. Transduction of D-TAT FITC was also effective when injected into the vitreous or subretinal space and was observed for a longer period of time than L-TAT FITC.

CONCLUSIONS

The retro-inverso form of the TAT sequence is effective in transducing cells from various compartments of the eye. After 14 days, the D-TAT FITC was clearly visible in the retina whereas L-TAT FITC had almost disappeared. The D-TAT peptide represents an interesting molecular transporter that, when coupled to a specific effector, may have potential therapeutic future, especially when a long-lasting action is needed.

Osteoclasts; culprits in inflammatory osteolysis

Periarticular osteolysis, a crippling complication of rheumatoid arthritis, is the product of enhanced osteoclast recruitment and activation. The osteoclast, which is a member of the monocyte/macrophage family, is the exclusive bone resorptive cell, and its differentiation and activation are under the aegis of a variety of cytokines. Receptor activator of NF-kappaB ligand (RANKL) and macrophage colony-stimulating factor are the essential osteoclastogenic cytokines and are increased in inflammatory joint disease. Tumor necrosis factor-alpha, which perpetrates arthritic bone loss, exerts its osteoclastogenic effect in the context of RANKL with which it synergizes. Achieving an understanding of the mechanisms by which the three cytokines affect the osteoclast has resulted in a number of active and candidate therapeutic targets.

Inhibition of inflammatory bone erosion by constitutively active STAT-6 through blockade of JNK and NF-kappaB activation

OBJECTIVE

NF-kappaB and JNK signaling pathways play key roles in the pathogenesis of inflammatory arthritis. Both factors are also activated in response to osteoclastogenic factors, such as RANKL and tumor necrosis factor alpha. Inflammatory arthritis and bone erosion subside in the presence of antiinflammatory cytokines such as interleukin-4 (IL-4). We have previously shown that IL-4 inhibits osteoclastogenesis in vitro through inhibition of NF-kappaB and JNK activation in a STAT-6-dependent manner. This study was undertaken to investigate the potential of constitutively active STAT-6 to arrest the activation of NF-kappaB and JNK and to subsequently ameliorate the bone erosion associated with inflammatory arthritis in mice.

METHODS

Inflammatory arthritis was induced in wild-type and STAT-6-null mice by intraperitoneal injection of arthritis-eliciting serum derived from K/BxN mice. Bone erosion was assessed in the joints by histologic and immunostaining techniques. Cell-permeable Tat-STAT-6 fusion proteins were administered intraperitoneally. Cells were isolated from bone marrow and from joints for the JNK assay, the DNA-binding assays (electrophoretic mobility shift assays), and for in vitro osteoclastogenesis.

RESULTS

Activation of NF-kappaB and JNK in vivo was increased in extracts of cells retrieved from the joints of arthritic mice. Cell-permeable, constitutively active STAT-6 (i.e., STAT-6-VT) was effective in blocking NF-kappaB and JNK activation in RANKL-treated osteoclast progenitors. More importantly, STAT-6-VT protein significantly inhibited the in vivo activation of NF-kappaB and JNK, attenuated osteoclast recruitment in the inflamed joints, and decreased bone destruction.

CONCLUSION

Our findings indicate that the administration of STAT-6-VT presents a novel approach to the alleviation of bone erosion in inflammatory arthritis.

Inhibition of RANKL-induced osteoclastogenesis by (-)-DHMEQ, a novel NF-kappaB inhibitor, through downregulation of NFATc1

(-)-DHMEQ, a newly designed NF-kappaB inhibitor, inhibited RANKL-induced osteoclast differentiation in mouse BMMs through downregulation of the induction of NFATc1, an essential transcription factor of osteoclastogenesis.

INTRODUCTION

Bone destruction is often observed in advanced case of rheumatoid arthritis and neoplastic diseases, including multiple myeloma. Effective and nontoxic chemotherapeutic agents are expected for the suppression of these bone destructions. RANKL induces activation of NF-kappaB and osteoclastogenesis in bone marrow-derived monocyte/macrophage precursor cells (BMMs). Targeted disruption or pharmacological suppression of NF-kappaB result in impaired osteoclastogenesis, but how NF-kappaB is involved in the regulation of osteoclastogenesis is not known.

MATERIALS AND METHODS

The effect of (-)-dehydroxymethylepoxyquinomicin [(-)-DHMEQ] on osteoclast differentiation was studied using a culture system of mouse BMMs stimulated with RANKL and macrophage colony-stimulating factor. The mechanism of the inhibition was studied by biochemical analysis such as immunoblotting and retroviral transfer experiments.

RESULTS

(-)-DHMEQ strongly inhibited RANKL-induced NF-kappaB activation in BMMs and inhibited RANKL-induced formation of TRACP(+) multinucleated cells. Interestingly, (-)-DHMEQ specifically inhibited the RANKL-induced expression of NFATc1 but not the expressions of TRAF6 or c-fos. Inhibition of osteoclast differentiation by (-)-DHMEQ was rescued by overexpression of NFATc1, suggesting that the inhibition is not caused by a toxic effect. Moreover, pit formation assays showed that (-)-DHMEQ also inhibited the bone-resorbing activity of mature osteoclasts.

CONCLUSION

The inhibition of NF-kappaB suppresses osteoclastogenesis by downregulation of NFATc1, suggesting that NFATc1 expression is regulated by NF-kappaB in RANKL-induced osteoclastogenesis. Our results also indicate the possibility of (-)-DHMEQ becoming a new therapeutic strategy against bone erosion.

Delivery of bioactive molecules into the cell: the Trojan horse approach

In recent years, vast amounts of data on the mechanisms of neural de- and regeneration have accumulated. However, only in disproportionally few cases has this led to efficient therapies for human patients. Part of the problem is to deliver cell death-averting genes or gene products across the blood-brain barrier (BBB) and cellular membranes. The discovery of Antennapedia (Antp)-mediated transduction of heterologous proteins into cells in 1992 and other "Trojan horse peptides" raised hopes that often-frustrating attempts to deliver proteins would now be history. The demonstration that proteins fused to the Tat protein transduction domain (PTD) are capable of crossing the BBB may revolutionize molecular research and neurobiological therapy. However, it was only recently that PTD-mediated delivery of proteins with therapeutic potential has been achieved in models of neural degeneration in nerve trauma and ischemia. Several groups have published the first positive results using protein transduction domains for the delivery of therapeutic proteins in relevant animal models of human neurological disorders. Here, we give an extensive review of peptide-mediated protein transduction from its early beginnings to new advances, discuss their application, with particular focus on a critical evaluation of the limitations of the method, as well as alternative approaches. Besides applications in neurobiology, a large number of reports using PTD in other systems are included as well. Because each protein requires an individual purification scheme that yields sufficient quantities of soluble, transducible material, the neurobiologist will benefit from the experiences of other researchers in the growing field of protein transduction.

Inhibition of NF-κB by a cell permeable form of IκBα induces apoptosis in eosinophils

An 11 amino acid HIV-TAT peptide can deliver target proteins into a variety of cells in a receptor-independent manner. To generate a highly specific inhibitor of the transcription factor NF-kappa B, we have fused the TAT-peptide to a version of I kappa B alpha that is resistant to signal-induced degradation. TAT-I kappa B alpha(S32A, S36A) inhibited NF-kappa B-dependent transcription in HeLa and A549 cells by retaining NF-kappa B p65 in the cytoplasm. Introduction of TAT-I kappa B alpha(S32A, S36A) into human eosinophils inhibited the nuclear translocation of NF-kappa B and induced apoptosis. Thus, continuous NF-kappa B-dependent transcription is important for eosinophil survival. While eosinophils are normally refractive to standard methods of gene delivery, the ability of TAT fusion proteins to be taken up by these cells should enable a detailed molecular analysis of survival pathways in these cells.

An osteoclastic protein-tyrosine phosphatase may play a role in differentiation and activity of human monocytic U-937 cell-derived, osteoclast-like cells

This study investigated if an osteoclastic protein-tyrosine phosphatase (PTP), PTP-oc, plays a role in the functional activity and differentiation of osteoclastic cells by determining the effects of overexpression of wild-type (WT)- or phosphatase-deficient (PD)-PTP-oc on bone resorption activity and differentiation of human promyelomonocytic U-937 cells, which could be induced to differentiate into "osteoclast-like" cells by phorbol ester/1,25(OH)(2)D(3) treatment. U-937 cells overexpressing WT- or PD-PTP-oc were produced with a transposon-based vector. The size and depth of resorption pits created by WT-PTP-oc-overexpressing osteoclast-like cells were greater, while those by PD-PTP-oc-overexpressing osteoclast-like cells were less, than those created by control osteoclast-like cells. Overexpression of WT-PTP-oc also enhanced, while overexpression of PD-PTP-oc suppressed, their differentiation into osteoclast-like cells. Overexpression of WT-PTP-oc increased apoptosis and proliferation of U-937 cells, and overexpression of PD-PTP-oc reduced cell proliferation. Cells overexpressing WT-PTP-oc has also led to greater c-Src and NF-kappabeta activation, whereas cells overexpressing PD-PTP-oc resulted in less c-Src and NF-kappabeta activation. c-Src activation and NF-kappabeta activation each correlated with resorption activity and differentiation into osteoclast-like cells. In summary, these results show that 1) PTP-oc regulates both the activity and the differentiation of osteoclast-like cells derived from U-937 cells; 2) PTP-oc enzymatic activity is important to these processes; 3) high PTP-oc enzymatic activity caused an increase in U-937 cell apoptosis and proliferation, leading to no significant changes in the number of viable cells; and 4) some of the PTP-oc actions are mediated in part by the c-Src and/or NF-kappabeta pathways.

The IkappaB kinase (IKK) inhibitor, NEMO-binding domain peptide, blocks osteoclastogenesis and bone erosion in inflammatory arthritis

Activation of NF-kappaB leads to expression of ample genes that regulate inflammatory and osteoclastogenic responses. The process is facilitated by induction of IkappaB kinase (IKK) complex that phosphorylates IkappaB and leads to its dissociation from the NF-kappaB complex, thus permitting activation of NF-kappaB. The IKK complex contains primarily IKKalpha, IKKbeta, and the regulatory kinase IKKgamma, also known as NEMO. NEMO regulates the IKK complex activity through its binding to carboxyl-terminal region of IKKalpha and IKKbeta, termed NEMO-binding domain (NBD). In this regard, a cell-permeable NBD peptide has been shown to block association of NEMO with the IKK complex and inhibit activation of NF-kappaB. Given the pivotal role of cytokine-induced NF-kappaB in osteoclastogenesis and inflammatory bone loss, we deduced that cell-permeable TAT-NBD peptide may hinder osteoclastogenesis and bone erosion in inflammatory arthritis. Using NBD peptides, we show that wild type, but not mutant, NBD blocks IKK activation and reduces cytokine-induced promoter and DNA binding activities of NF-kappaB and inhibits cytokine-induced osteoclast formation by osteoclast precursors. Consistent with the key role of NF-kappaB in osteoinflammatory responses in vivo, wild type TAT-NBD administered into mice prior to induction of inflammatory arthritis efficiently block in vivo osteoclastogenesis, inhibits focal bone erosion, and ameliorates inflammatory responses in the joints of arthritic mice. The mutant NBD peptide fails to exert these functions. These results provide strong evidence that IKKs are potent regulators of cytokine-induced osteoclastogenesis and inflammatory arthritis. More importantly, blockade of NEMO assembly with the IKK complex is a viable strategy to avert inflammatory osteolysis.

Biological applications of protein transduction technology

The impermeable nature of the cell membrane to peptides, proteins, DNA and oligonucleotides limits the therapeutic potential of these biological agents. However, the recent discovery of short cationic peptides that cross the plasma membrane efficiently is opening up new possibilities for the intracellular delivery of such agents. These peptides are commonly referred to as protein transduction domains (PTDs) and are successfully used to transport heterologous proteins, peptides and other types of cargo into cells. Several recent reports have used the membrane transducing technology in vivo to deliver biologically active cargo into various tissues. This review discusses the structure of the most commonly used PTDs and how their ability to transduce membranes is used to regulate biological functions. It also considers future directions and the potential of this technology to move from the laboratory into the clinic.

IkappaBalpha and IkappaBbeta possess injury context-specific functions that uniquely influence hepatic NF-kappaB induction and inflammation

IkappaB proteins play an important role in regulating NF-kappaB induction following a diverse range of environmental injuries. Studies evaluating IkappaBbeta knock-in mice (AKBI), in which the IkappaBalpha gene is replaced by the IkappaBbeta cDNA, have uncovered divergent properties of IkappaBalpha and IkappaBbeta that influence their ability to activate hepatic NF-kappaB and subsequent downstream proinflammatory processes in a stimulus-specific manner. While AKBI mice demonstrated identical levels of hepatic NF-kappaB activation in response to endotoxin, a significantly reduced level of hepatic NF-kappaB activation was observed in AKBI mice after liver ischemia/reperfusion (I/R) injury. This reduced level of NF-kappaB activation in AKBI mice after liver I/R also correlated with decreased induction of serum TNF-alpha, reduced hepatic inflammation, and increased survival. In contrast, no differences in any of these indicators were observed between AKBI mice and WT littermates after a lethal injection of LPS. Molecular studies suggest that the specificity of IkappaBalpha, but not IkappaBbeta, to properly regulate NF-kappaB induction during the acute phase of I/R injury is due to injury context-specific activation of c-Src and subsequent tyrosine phosphorylation of IkappaBalpha on Tyr42. These results demonstrate that IkappaBalpha and IkappaBbeta play unique injury context-specific roles in activating NF-kappaB-mediated proinflammatory responses and suggest that strategies aimed at inhibiting IkappaBalpha gene expression may be of potential therapeutic benefit in hepatic I/R injury.

Antitumour effects of PLC-gamma1-(SH2)2-TAT fusion proteins on EGFR/c-erbB-2-positive breast cancer cells

Due to its pivotal role in the growth factor-mediated tumour cell migration, the adaptor protein phospholipase C-gamma1 (PLC-gamma1) is an appropriate target to block ultimately the spreading of EGFR/c-erbB-2-positive tumour cells, thereby minimising metastasis formation. Here, we present an approach to block PLC-gamma1 activity by using protein-based PLC-gamma1 inhibitors consisting of PLC-gamma1 SH2 domains, which were fused to the TAT-transduction domain to ensure a high protein transduction efficiency. Two proteins were generated containing one PLC-gamma1-SH2-domain (PS1-TAT) or two PLC-gamma1-SH2 domains (PS2-TAT). PS2-TAT treatment of the EGFR/c-erbB-2-positive cell line MDA-HER2 resulted in a reduction of the EGF-mediated PLC-gamma1 tyrosine phosphorylation of about 30%, concomitant with a complete abrogation of the EGF-driven calcium influx. In addition to this, long-term PS2-TAT treatment both reduces the EGF-mediated migration of about 75% combined with a markedly decreased time locomotion of single MDA-HER2 cells as well as decreases the proliferation of MDA-HER2 cells by about 50%. Due to its antitumoral capacity on EGFR/c-erbB-2-positive breast cancer cells, we conclude from our results that the protein-based PLC-gamma1 inhibitor PS2-TAT may be a means for novel adjuvant antitumour strategies to minimise metastasis formation because of the blockade of cell migration and proliferation.

Direct inhibition of NF-kappa B blocks bone erosion associated with inflammatory arthritis

Inflammatory arthritis is associated with devastating joint tissue destruction and periarticular bone erosion. Although secreted products of infiltrating immune cells perpetuate the inflammatory response, the osteolytic component of this disease is a direct result of localized recruitment and activation of osteoclasts. Given that NF-kappaB plays a central role in both processes, the function of this transcription factor was examined. Using a mouse model of autoreactive Ig transfer that engenders inflammatory arthritis, we show numerous osteoclasts in the articular joint tissue associated with progressive periarticular osteolytic lesions. Moreover, cells retrieved from these joints exhibit heightened NF-kappaB activity. Importantly, direct administration of dominant negative*I-kappaB or tyrosine 42-mutated I-kappaB (Y42F*I-kappaB) proteins into mice before induction of the disease attenuates in vivo activation of the transcription factor. More importantly, these I-kappaB mutant forms significantly inhibit in vivo production of TNF and receptor activator of NF-kappaB ligand, and block joint swelling, osteoclast recruitment, and osteolysis. Thus, NF-kappaB appears to be the centerpiece of inflammatory-osteolytic arthritis and direct inhibition of this transcription factor by unique and novel I-kappaB mutant proteins blocks manifestation of the disease.

NF-kB signaling blockade abolishes implant particle-induced osteoclastogenesis

In this study we investigated the effect of NF-kB signaling blockade on polymethylmethacrylate (PMMA) particle-induced osteoclastogenesis in vitro. We first established effective blockade of NF-kB activity as tested by electrophoretic mobility shift assays (EMSA). Particle-induced NF-kB activation in murine osteoclast precursor cells (CSF-1-dependent bone marrow macrophages) was markedly reduced by co-treatment of the cells with the NF-kB inhibitors N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) and Calpain Inhibitor I (CPI). This inhibition of NF-kB activity was associated with blockade of p50 NF-kB subunit nuclear translocation. We then established a direct NF-kB inhibition approach by utilizing a TAT-bound, mutant IkB (TAT:IkB(46-317)), and demonstrated an inhibitory effect evidenced by decreased NF-kB DNA binding activity. Having established that these strategies (TPCK, CPI, TAT: IkB(46-317)) effectively block NF-kB activation, we next investigated the effect of these agents on particle-stimulated osteoclast formation. PMMA particle stimulation of mature osteoclast formation from RANKL-primed osteoclast precursor cells was blocked by all three inhibitors. To further test the efficacy of NF-kB blockade, experiments were performed with the TAT:IkB(46-317) mutant peptide in whole bone marrow cultures that contain supporting stromal cells. Again, this inhibitor efficiently blocked particle-induced osteoclastogenesis. Thus, we have shown that pharmaceutical and molecular blockade of NF-kB activation inhibits PMMA particle-directed osteoclastogenesis in vitro.