Pharmaceutical inhibition of glycogen synthetase kinase-3β reduces multiple myeloma-induced bone disease in a novel murine plasmacytoma xenograft model

Stat3 loss in mesenchymal progenitors causes Job syndrome-like skeletal defects by reducing Wnt/β-catenin signaling

Job syndrome is a rare genetic disorder caused by STAT3 mutations and primarily characterized by immune dysfunction along with comorbid skeleton developmental abnormalities including osteopenia, recurrent fracture of long bones, and scoliosis. So far, there is no definitive cure for the skeletal defects in Job syndrome, and treatments are limited to management of clinical symptoms only. Here, we have investigated the molecular mechanism whereby Stat3 regulates skeletal development and osteoblast differentiation. We showed that removing Stat3 function in the developing limb mesenchyme or osteoprogenitor cells in mice resulted in shortened and bow limbs with multiple fractures in long bones that resembled the skeleton symptoms in the Job Syndrome. However, Stat3 loss did not alter chondrocyte differentiation and hypertrophy in embryonic development, while osteoblast differentiation was severely reduced. Genome-wide transcriptome analyses as well as biochemical and histological studies showed that Stat3 loss resulted in down-regulation of Wnt/β-catenin signaling. Restoration of Wnt/β-catenin signaling by injecting BIO, a small molecule inhibitor of GSK3, or crossing with a Lrp5 gain of function (GOF) allele, rescued the bone reduction phenotypes due to Stat3 loss to a great extent. These studies uncover the essential functions of Stat3 in maintaining Wnt/β-catenin signaling in early mesenchymal or osteoprogenitor cells and provide evidence that bone defects in the Job Syndrome are likely caused by Wnt/β-catenin signaling reduction due to reduced STAT3 activities in bone development. Enhancing Wnt/β-catenin signaling could be a therapeutic approach to reduce bone symptoms of Job syndrome patients.

GSK-3α Inhibition in Drug-Resistant CML Cells Promotes Susceptibility to NK Cell-Mediated Lysis in an NKG2D- and NKp30-Dependent Manner

Simple Summary

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine protein kinase that has gained considerable interest as a therapeutic target for cancer due to its key involvement in growth arrest and apoptosis of tumor cells. Moreover, GSK-3, especially GSK-3β, limits the activation of NK cells, key innate effectors in cancer immunosurveillance, triggered by diverse activating receptors. However, the role of GSK-3 in the regulation of activating ligands on target cells that confer susceptibility to NK cells remains unclear and is the aim of this study. Here, we provide evidence that GSK-3α primarily restrains the expression of ligands for activating receptors such as NKG2D, NKp30 but not DNAM-1, thereby reducing target susceptibility to NK cells. Thus, our results suggest a distinct role of GSK-3 isoforms in target cells vs NK cells for regulating NK cell reactivity and GSK-3α inhibition as a relevant strategy to enhance target susceptibility to NK cells.

Abstract

Natural killer (NK) cells are innate cytotoxic lymphocytes that provide early protection against cancer. NK cell cytotoxicity against cancer cells is triggered by multiple activating receptors that recognize specific ligands expressed on target cells. We previously demonstrated that glycogen synthase kinase (GSK)-3β, but not GSK-3α, is a negative regulator of NK cell functions via diverse activating receptors, including NKG2D and NKp30. However, the role of GSK-3 isoforms in the regulation of specific ligands on target cells is poorly understood, which remains a challenge limiting GSK-3 targeting for NK cell-based therapy. Here, we demonstrate that GSK-3α rather than GSK-3β is the primary isoform restraining the expression of NKG2D ligands, particularly ULBP2/5/6, on tumor cells, thereby regulating their susceptibility to NK cells. GSK-3α also regulated the expression of the NKp30 ligand B7-H6, but not the DNAM-1 ligands PVR or nectin-2. This regulation occurred independently of BCR-ABL1 mutation that confers tyrosine kinase inhibitor (TKI) resistance. Mechanistically, an increase in PI3K/Akt signaling in concert with c-Myc was required for ligand upregulation in response to GSK-3α inhibition. Importantly, GSK-3α inhibition improved cancer surveillance by human NK cells in vivo. Collectively, our results highlight the distinct role of GSK-3 isoforms in the regulation of NK cell reactivity against target cells and suggest that GSK-3α modulation could be used to enhance tumor cell susceptibility to NK cells in an NKG2D- and NKp30-dependent manner.

Naringin increases osteoprotegerin expression in fibroblasts from periprosthetic membrane by the Wnt/β-catenin signaling pathway

Background

The osteoclast bone resorption is critical in aseptic loosening after joint replacement. The balance between activator of nuclear factor kappa B ligand (RANKL) and osteoprotegerin (OPG) is considered to play a central role in osteoclast maturation. Fibroblasts from the periprosthetic membrane express RANKL and promote osteoclast formation. Studies have demonstrated that naringin inhibited osteoclastogenesis and wear particle-induced osteolysis. In this study, the naringin-induced OPG/RANKL effects and its underlying mechanism were studied in fibroblasts from periprosthetic membrane.

Methods

Fibroblasts were isolated from the periprosthetic membrane during hip arthroplasty for revision due to aseptic loosening. Fibroblasts were cultured and treated with or without naringin and DKK-1 (the classical inhibitor of Wnt/β-catenin signaling pathway). OPG and RANKL mRNA and protein levels, gene expression of β-catenin, and cyclin D1, which participate in the Wnt signaling pathway, were examined by real-time polymerase chain reaction and enzyme-linked immunosorbent assay.

Results

The mRNA and protein levels of OPG were enhanced by naringin in a dose-dependent manner compared to that of the non-treated control. In contrast, naringin did not affect the expression of RANKL. Importantly, DKK-1 attenuated OPG expression in fibroblasts under naringin treatment. Moreover, naringin stimulated the gene expression of β-catenin and cyclin D1 in fibroblasts, and the effect could be inhibited by DKK-1.

Conclusion

The results indicated that naringin enhanced OPG expression through Wnt/β-catenin signaling pathway in fibroblasts from periprosthetic membrane, which may be useful to inhibit periprosthetic osteolysis during aseptic loosening after total joint arthroplasty.

Aberrant Wnt signaling in multiple myeloma: molecular mechanisms and targeting options

Aberrant activation of Wnt/β-catenin signaling plays a central role in the pathogenesis of a wide variety of malignancies and is typically caused by mutations in core Wnt pathway components driving constitutive, ligand-independent signaling. In multiple myelomas (MMs), however, these pathway intrinsic mutations are rare despite the fact that most tumors display aberrant Wnt pathway activity. Recent studies indicate that this activation is caused by genetic and epigenetic lesions of Wnt regulatory components, sensitizing MM cells to autocrine Wnt ligands and paracrine Wnts emanating from the bone marrow niche. These include deletion of the tumor suppressor CYLD, promotor methylation of the Wnt antagonists WIF1, DKK1, DKK3, and sFRP1, sFRP2, sFRP4, sFRP5, as well as overexpression of the co-transcriptional activator BCL9 and the R-spondin receptor LGR4. Furthermore, Wnt activity in MM is strongly promoted by interaction of both Wnts and R-spondins with syndecan-1 (CD138) on the MM cell-surface. Functionally, aberrant canonical Wnt signaling plays a dual role in the pathogenesis of MM: (I) it mediates proliferation, migration, and drug resistance of MM cells; (II) MM cells secrete Wnt antagonists that contribute to the development of osteolytic lesions by impairing osteoblast differentiation. As discussed in this review, these insights into the causes and consequences of aberrant Wnt signaling in MM will help to guide the development of targeting strategies. Importantly, since Wnt signaling in MM cells is largely ligand dependent, it can be targeted by drugs/antibodies that act upstream in the pathway, interfering with Wnt secretion, sequestering Wnts, or blocking Wnt (co)receptors.

Three-dimensional in vitro modeling of malignant bone disease recapitulates experimentally accessible mechanisms of osteoinhibition

Malignant bone disease (MBD) occurs when tumors establish in bone, causing catastrophic tissue damage as a result of accelerated bone destruction and inhibition of repair. The resultant so-called osteolytic lesions (OL) take the form of tumor-filled cavities in bone that cause pain, fractures, and associated morbidity. Furthermore, the OL microenvironment can support survival of tumor cells and resistance to chemotherapy. Therefore, a deeper understanding of OL formation and MBD progression is imperative for the development of future therapeutic strategies. Herein, we describe a novel in vitro platform to study bone-tumor interactions based on three-dimensional co-culture of osteogenically enhanced human mesenchymal stem cells (OEhMSCs) in a rotating wall vessel bioreactor (RWV) while attached to micro-carrier beads coated with extracellular matrix (ECM) composed of factors found in anabolic bone tissue. Osteoinhibition was recapitulated in this model by co-culturing the OEhMSCs with a bone-tumor cell line (MOSJ-Dkk1) that secretes the canonical Wnt (cWnt) inhibitor Dkk-1, a tumor-borne osteoinhibitory factor widely associated with several forms of MBD, or intact tumor fragments from Dkk-1 positive patient-derived xenografts (PDX). Using the model, we observed that depending on the conditions of growth, tumor cells can biochemically inhibit osteogenesis by disrupting cWnt activity in OEhMSCs, while simultaneously co-engrafting with OEhMSCs, displacing them from the niche, perturbing their activity, and promoting cell death. In the absence of detectable co-engraftment with OEhMSCs, Dkk-1 positive PDX fragments had the capacity to enhance OEhMSC proliferation while inhibiting their osteogenic differentiation. The model described has the capacity to provide new and quantifiable insights into the multiple pathological mechanisms of MBD that are not readily measured using monolayer culture or animal models.

Polymersome nanoparticles for delivery of Wnt-activating small molecules

Spatiotemporal control of drug delivery is important for a number of medical applications and may be achieved using polymersome nanoparticles (PMs). Wnt signalling is a molecular pathway activated in various physiological processes, including bone repair, that requires precise control of activation. Here, we hypothesise that PMs can be stably loaded with a small molecule Wnt agonist, 6-bromoindirubin-3'-oxime (BIO), and activate Wnt signalling promoting the osteogenic differentiation in human primary bone marrow stromal cells (BMSCs). We showed that BIO-PMs induced a 40% increase in Wnt signaling activation in reporter cell lines without cytotoxicity induced by free BIO. BMSCs incubated with BIO-PMs showed a significant up-regulation of the Wnt target gene AXIN2 (14 ± 4 fold increase, P < 0.001) and a prolonged activation of the osteogenic gene RUNX2. We conclude that BIO-PMs could represent an innovative approach for the controlled activation of Wnt signaling for promoting bone regeneration after fracture.

Kinase inhibitors as potential agents in the treatment of multiple myeloma

Recent years have witnessed a dramatic increase in the number of therapeutic options available for the treatment of multiple myeloma (MM) - from immunomodulating agents to proteasome inhibitors to histone deacetylase (HDAC) inhibitors and, most recently, monoclonal antibodies. Used in conjunction with autologous hematopoietic stem cell transplantation, these modalities have nearly doubled the disease's five-year survival rate over the last three decades to about 50%. In spite of these advances, MM still is considered incurable as resistance and relapse are common. While small molecule protein kinase inhibitors have made inroads in the therapy of a number of cancers, to date their application to MM has been less than successful. Focusing on MM, this review examines the roles played by a number of kinases in driving the malignant state and the rationale for target development in the design of a number of kinase inhibitors that have demonstrated anti-myeloma activity in both in vitro and in vivo xenograph models, as well as those that have entered clinical trials. Among the targets and their inhibitors examined are receptor and non-receptor tyrosine kinases, cell cycle control kinases, the PI3K/AKT/mTOR pathway kinases, protein kinase C, mitogen-activated protein kinase, glycogen synthase kinase, casein kinase, integrin-linked kinase, sphingosine kinase, and kinases involved in the unfolded protein response.

Wnt activation followed by Notch inhibition promotes mitotic hair cell regeneration in the postnatal mouse cochlea

Hair cell (HC) loss is the main cause of permanent hearing loss in mammals. Previous studies have reported that in neonatal mice cochleae, Wnt activation promotes supporting cell (SC) proliferation and Notch inhibition promotes the trans-differentiation of SCs into HCs. However, Wnt activation alone fails to regenerate significant amounts of new HCs, Notch inhibition alone regenerates the HCs at the cost of exhausting the SC population, which leads to the death of the newly regenerated HCs. Mitotic HC regeneration might preserve the SC number while regenerating the HCs, which could be a better approach for long-term HC regeneration. We present a two-step gene manipulation, Wnt activation followed by Notch inhibition, to accomplish mitotic regeneration of HCs while partially preserving the SC number. We show that Wnt activation followed by Notch inhibition strongly promotes the mitotic regeneration of new HCs in both normal and neomycin-damaged cochleae while partially preserving the SC number. Lineage tracing shows that the majority of the mitotically regenerated HCs are derived specifically from the Lgr5⁺ progenitors with or without HC damage. Our findings suggest that the co-regulation of Wnt and Notch signaling might provide a better approach to mitotically regenerate HCs from Lgr5⁺ progenitor cells.

Rapid Osteogenic Enhancement of Stem Cells in Human Bone Marrow Using a Glycogen-Synthease-Kinase-3-Beta Inhibitor Improves Osteogenic Efficacy In Vitro and In Vivo

Non‐union defects of bone are a major problem in orthopedics, especially for patients with a low healing capacity. Fixation devices and osteoconductive materials are used to provide a stable environment for osteogenesis and an osteogenic component such as autologous human bone marrow (hBM) is then used, but robust bone formation is contingent on the healing capacity of the patients. A safe and rapid procedure for improvement of the osteoanabolic properties of hBM is, therefore, sought after in the field of orthopedics, especially if it can be performed within the temporal limitations of the surgical procedure, with minimal manipulation, and at point‐of‐care. One way to achieve this goal is to stimulate canonical Wingless (cWnt) signaling in bone marrow‐resident human mesenchymal stem cells (hMSCs), the presumptive precursors of osteoblasts in bone marrow. Herein, we report that the effects of cWnt stimulation can be achieved by transient (1–2 hours) exposure of osteoprogenitors to the GSK3β‐inhibitor (2′Z,3′E)‐6‐bromoindirubin‐3′‐oxime (BIO) at a concentration of 800 nM. Very‐rapid‐exposure‐to‐BIO (VRE‐BIO) on either hMSCs or whole hBM resulted in the long‐term establishment of an osteogenic phenotype associated with accelerated alkaline phosphatase activity and enhanced transcription of the master regulator of osteogenesis, Runx2. When VRE‐BIO treated hBM was tested in a rat spinal fusion model, VRE‐BIO caused the formation of a denser, stiffer, fusion mass as compared with vehicle treated hBM. Collectively, these data indicate that the VRE‐BIO procedure may represent a rapid, safe, and point‐of‐care strategy for the osteogenic enhancement of autologous hBM for use in clinical orthopedic procedures. stemcellstranslationalmedicine2018;7:342–353

Titanium particle-induced osteogenic inhibition and bone destruction are mediated by the GSK-3β/β-catenin signal pathway

Wear debris-induced osteogenic inhibition and bone destruction are critical in the initiation of peri-prosthetic osteolysis. However, the molecular mechanism underlying this phenomenon is poorly understood. In this study, we analyzed the involvement of the GSK-3β/β-catenin signal pathway, which is important for bone formation in this pathological condition. We established a titanium (Ti) particle-stressed murine MC3T3-E1 cell culture system and calvariae osteolysis model to test the hypothesis that Ti particle-induced osteogenic inhibition and bone destruction are mediated by the GSK-3β/β-catenin signal pathway. Our findings showed that Ti particles reduced osteogenic differentiation induced by osteogenesis-related gene expression, alkaline phosphatase activity and matrix mineralization, as well as pSer9-GSK-3β expression and β-catenin signal activity. Downregulation of GSK-3β activity attenuated Ti particle-induced osteogenic inhibition, whereas the β-catenin inhibitor reversed this protective effect. Moreover, the GSK-3β/β-catenin signal pathway mediated the upregulation of RANKL and downregulation of OPG in Ti particle-stressed MC3T3-E1 cells. In addition, our in vivo results showed that Ti particles induced bone loss via regulating GSK-3β and β-catenin signals. Based on these results, we concluded that the GSK-3β/β-catenin signal pathway mediates the adverse effects of Ti particles on osteoblast differentiation and bone destruction, and can be used as a potential therapeutic target for the treatment of peri-prosthetic osteolysis.

NKG2D and DNAM-1 Ligands: Molecular Targets for NK Cell-Mediated Immunotherapeutic Intervention in Multiple Myeloma

A pivotal strategy to improve NK cell-mediated antitumor activity involves the upregulation of activating ligands on tumor cells. Enhancement of NK cell-mediated recognition of multiple myeloma cells was reported by us and others showing increased surface expression of NKG2D and DNAM-1 ligands on tumor cells following treatment with a number of chemotherapeutic agents, such as genotoxic drugs or inhibitors of proteasome, histone deacetylases, GSK3, and HSP-90. These compounds have the capability to affect tumor survival but also to activate specific transduction pathways associated with the upregulation of different NK cell activating ligands on the tumor cells. Here, we will summarize and discuss the molecular pathways whereby these drugs can regulate the expression of NK cell activating ligands in multiple myeloma cells.

MicroRNA-214 controls skin and hair follicle development by modulating the activity of the Wnt pathway

miRNA-214 regulates hair follicle development and cycling by targeting β-catenin and thereby modulating Wnt pathway transduction.

Skin development is governed by complex programs of gene activation and silencing, including microRNA-dependent modulation of gene expression. Here, we show that miR-214 regulates skin morphogenesis and hair follicle (HF) cycling by targeting β-catenin, a key component of the Wnt signaling pathway. miR-214 exhibits differential expression patterns in the skin epithelium, and its inducible overexpression in keratinocytes inhibited proliferation, which resulted in formation of fewer HFs with decreased hair bulb size and thinner hair production. The inhibitory effects of miR-214 on HF development and cycling were associated with altered activities of multiple signaling pathways, including decreased expression of key Wnt signaling mediators β-catenin and Lef-1, and were rescued by treatment with pharmacological Wnt activators. Finally, we identify β-catenin as one of the conserved miR-214 targets in keratinocytes. These data provide an important foundation for further analyses of miR-214 as a key regulator of Wnt pathway activity and stem cell functions during normal tissue homeostasis, regeneration, and aging.

Indirubin-3'-oxime, an activator of Wnt/β-catenin signaling, enhances osteogenic commitment of ST2 cells and restores bone loss in high-fat diet-induced obese male mice

Obesity is a growing issue of the modern world, and its negative impact on bones in obese male patients has been recently reported. The Wnt/β-catenin pathway has an established role in the regulation of body fat content and bone density. We investigated the effects of indirubin-3'-oxime (I3O), the GSK3β inhibitor that activates Wnt/β-catenin signaling, on trabecular bone in high-fat diet (HFD)-induced obese male mice. I3O reverses the downregulating effect of fatty acid (FA) on Wnt/β-catenin signaling and enhances the osteogenic commitment of the bone marrow-derived stromal cell line ST2. FA induces the adipogenic differentiation of bone marrow stromal cells in vitro. In a male mouse model of HFD-induced obesity, trabecular bone loss was observed in the femora, with a gross increase in abdominal fat; however, the HFD effects were rescued with the activation of Wnt/β-catenin signaling by I3O treatment. I3O administration also reversed the increase in the number of HFD-induced adipocytes in the femur bone marrow in trabecular bone. Overall, our results indicate that I3O could be a potential therapeutic agent for obese male patients through downregulation of abdominal fat and net increment in trabecular bone density.

Mouse Flk-1+Sca-1- mesenchymal stem cells: functional plasticity in vitro and immunoregulation in vivo

OBJECTIVES

Mesenchymal stem cells (MSCs) represent a powerful tool in regenerative medicine because of their differentiation and migration capacities. Moreover, the immunomodulatory ability of MSCs may be used to develop therapies for the treatment of autoimmune diseases.

METHODS

In this study, we isolated Flk-1Sca-1 MSCs from bone marrow (bMSCs). Next, we studied their biological characteristics and immunologic functions. We also investigated their effects on graft-versus-host disease (GVHD) associated with allogeneic bone marrow transplantation in mice.

RESULTS

Flk-1Sca-1 bMSCs were able to differentiate into fat and cartilage cells, indicating that the isolated cells had stem cell properties. They could also suppress alloantigen-induced T cell proliferation in vitro in a dose-dependent manner. Infusion of bMSCs into allogeneic bone marrow-transplanted mice alleviated the lethal GVHD that occurred in control recipient mice. There was significantly lower mortality among the recipients of the Flk-1Sca-1 bMSCs that also ameliorated the clinical symptoms and GVHD histopathology. Beneficial effects on GVHD by Flk-1Sca-1 bMSCs were also observed when MSCs were engineered to express anti-inflammatory cytokines IL-4 and IL-10 and decrease expression of proinflammatory cytokines IFN-γ, TNF-α, and IL-2.

CONCLUSION

Flk-1Sca-1 bMSCs have stem cell properties and can efficiently ameliorate the GVHD associated with allogeneic bone marrow transplantation in mice.

An unexpected role for a Wnt-inhibitor: Dickkopf-1 triggers a novel cancer survival mechanism through modulation of aldehyde-dehydrogenase-1 activity

It is widely accepted that canonical Wnt (cWnt) signaling is required for the differentiation of osteoprogenitors into osteoblasts. Furthermore, tumor-derived secretion of the cWnt-antagonist Dickkopf-1 (Dkk-1) is known to cause bone destruction, inhibition of repair and metastasis in many bone malignancies, but its role in osteosarcoma (OS) is still under debate. In this study, we examined the role of Dkk-1in OS by engineering its overexpression in the osteochondral sarcoma line MOS-J. Consistent with the known role of Dkk-1 in osteoblast differentiation, Dkk-1 inhibited osteogenesis by the MOSJ cells themselves and also in surrounding tissue when implanted in vivo. Surprisingly, Dkk-1 also had unexpected effects on MOSJ cells in that it increased proliferation and resistance to metabolic stress in vitro and caused the formation of larger and more destructive tumors than controls upon orthotopic implantation. These effects were attributed in part to upregulation of the stress response enzyme and cancer stem cell marker aldehyde-dehydrogenase-1 (ALDH1). Direct inhibition of ALDH1 reduced viability under stressful culture conditions, whereas pharmacological inhibition of cWnt or overexpression of ALDH1 had a protective effect. Furthermore, we observed that ALDH1 was transcriptionally activated in a c-Jun-dependent manner through a pathway consisting of RhoA, MAP-kinase-kinase-4 and Jun N-terminal Kinase (JNK), indicating that noncanonical planar cell polarity-like Wnt signaling was the mechanism responsible. Together, our results therefore demonstrate that Dkk-1 enhances resistance of OS cells to stress by tipping the balance of Wnt signaling in favor of the non-canonical Jun-mediated Wnt pathways. In turn, this results in transcriptional activation of ALDH1 through Jun-responsive promoter elements. This is the first report linking Dkk-1 to tumor stress resistance, further supporting the targeting of Dkk-1 not only to prevent and treat osteolytic bone lesions but also to reduce numbers of stress-resistant tumor cells.

Inhibition of glycogen synthase kinase-3β suppresses inflammatory responses in rheumatoid arthritis fibroblast-like synoviocytes and collagen-induced arthritis

OBJECTIVES

Glycogen synthase kinase (GSK)-3β, a serine/threonine protein kinase, has been implicated as a regulator of the inflammatory response. This study was performed to evaluate the effect of selective GSK-3β inhibitors in rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS) and collagen-induced arthritis (CIA).

METHOD

FLS from RA patients were treated with selective GSK-3β inhibitors, including lithium chloride, 6-bromoindirubin-3'-oxime (BIO), or 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8). The effects of GSK-3β inhibition on pro-inflammatory mediators were determined by real-time PCR and ELISA. The levels of NF-κB, phosphorylated JNK, c-jun, ATF-2 and p-38 proteins were evaluated by western blot analysis. The in vivo effects of GSK-3β inhibitors were examined in mice with CIA.

RESULTS

Treatment of RA FLS with GSK-3β inhibitors induced dose-dependent reductions in gene expression and the production of pro-inflammatory mediators. The levels of NF-κB, phosphorylated JNK, c-jun, ATF-2 and p-38 were decreased following treatment with GSK-3β inhibitors. GSK-3β inhibitors treatment attenuated clinical and histological severities of CIA in mice. Infiltration of T-cells, macrophages, and tartrate-resistant acid phosphatase positive cells was decreased in joint sections of CIA mice by GSK-3β inhibitors treatment. Serum levels of IL-1β, IL-6, TNF-α and IFN-γ in CIA mice were also significantly decreased in dose-dependent manners by treatment with GSK-3β inhibitors.

CONCLUSION

Treatment with GSK-3β inhibitors suppressed inflammatory responses in RA FLS and CIA mice. These findings suggest that the inhibition of GSK-3β can be used as an effective therapeutic agent for RA.

Dickkopf-1 is a key regulator of myeloma bone disease: opportunities and challenges for therapeutic intervention

Myeloma bone disease (MBD) is the most visible aspect of plasma cell myeloma (PCM), which is characterized by the displacement of hematopoiesis and the formation of osteolytic bone lesions. The secreted glycoprotein Dickkopf-1 (DKK1), an inhibitor of the Wnt signaling pathway, is broadly expressed in myeloma cells but highly restricted in normal tissues. DKK1 plays a critical role in several aspects of bone biology and actively participates in regulating MBD by inhibiting osteoblasts and by activating osteoclasts. Based on these findings, ongoing research has been targeting DKK1 to find novel therapeutic strategies for MBD, such as DKK1-neutralizing antibodies, proteasome inhibitors, and vaccines. All these strategies have produced encouraging clinical results and consequently, revealed the significance of DKK1 in MBD. This review discusses the recent advances in our understanding of the DKK1 pathway signaling and how DKK1 can be exploited in the therapeutic intervention of MBD.

Myeloma plasma cells alter the bone marrow microenvironment by stimulating the proliferation of mesenchymal stromal cells

Multiple myeloma is an incurable hematologic cancer characterized by the clonal proliferation of malignant plasma cells within the bone marrow. Numerous studies suggest that the myeloma plasma cells occupy and alter the stromal tissue of the bone marrow as a means of enhancing their survival and growth. However, the nature and magnitude of the changes to the stromal cell tissue remain to be determined. In this study, we used mesenchymal stromal cell and osteoblast-related cell surface marker expression (STRO-1 and alkaline phosphatase, respectively) and flow cytometry to enumerate mesenchymal stromal cell and osteoblast numbers in bone marrow recovered from myeloma patients at the time of diagnosis. Using this approach, we identified an increase in the number of STRO-1 positive colony forming mesenchymal stromal cells and a concomitant decrease in alkaline phophatase osteoblasts. Notably, this increase in mesenchymal stromal cell numbers correlated closely with plasma cell burden at the time of diagnosis. In addition, in comparison with the osteoblast population, the STRO-1+ mesenchymal stromal cell population was found to express higher levels of plasma cell- and osteoclast-activating factors, including RANKL and IL-6, providing a mechanism by which an increase in mesenchymal stromal cells may promote and aid the progression of myeloma. Importantly, these findings were faithfully replicated in the C57BL/KaLwRij murine model of myeloma, suggesting that this model may present a unique and clinically relevant system in which to identify and therapeutically modulate the bone microenvironment and, in turn, alter the progression of myeloma disease.

Multifaceted roles of GSK-3 and Wnt/β-catenin in hematopoiesis and leukemogenesis: opportunities for therapeutic intervention

Glycogen synthase kinase-3 (GSK-3) is well documented to participate in a complex array of critical cellular processes. It was initially identified in rat skeletal muscle as a serine/threonine kinase that phosphorylated and inactivated glycogen synthase. This versatile protein is involved in numerous signaling pathways that influence metabolism, embryogenesis, differentiation, migration, cell cycle progression and survival. Recently, GSK-3 has been implicated in leukemia stem cell pathophysiology and may be an appropriate target for its eradication. In this review, we will discuss the roles that GSK-3 plays in hematopoiesis and leukemogenesis as how this pivotal kinase can interact with multiple signaling pathways such as: Wnt/β-catenin, phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/Akt/mammalian target of rapamycin (mTOR), Ras/Raf/MEK/extracellular signal-regulated kinase (ERK), Notch and others. Moreover, we will discuss how targeting GSK-3 and these other pathways can improve leukemia therapy and may overcome therapeutic resistance. In summary, GSK-3 is a crucial regulatory kinase interacting with multiple pathways to control various physiological processes, as well as leukemia stem cells, leukemia progression and therapeutic resistance. GSK-3 and Wnt are clearly intriguing therapeutic targets.

Inhibition of glycogen synthase kinase-3 increases NKG2D ligand MICA expression and sensitivity to NK cell-mediated cytotoxicity in multiple myeloma cells: role of STAT3

Engagement of NKG2D and DNAX accessory molecule-1 (DNAM-1) receptors on lymphocytes plays an important role for anticancer response and represents an interesting therapeutic target for pharmacological modulation. In this study, we investigated the effect of inhibitors targeting the glycogen synthase kinase-3 (GSK3) on the expression of NKG2D and DNAM-1 ligands in multiple myeloma (MM) cells. GSK3 is a pleiotropic serine-threonine kinase point of convergence of numerous cell-signaling pathways, able to regulate the proliferation and survival of cancer cells, including MM. We found that inhibition of GSK3 upregulates both MICA protein surface and mRNA expression in MM cells, with little or no effects on the basal expression of the MICB and DNAM-1 ligand poliovirus receptor/CD155. Moreover, exposure to GSK3 inhibitors renders myeloma cells more efficient to activate NK cell degranulation and to enhance the ability of myeloma cells to trigger NK cell-mediated cytotoxicity. We could exclude that increased expression of β-catenin or activation of the heat shock factor-1 (transcription factors inhibited by active GSK3) is involved in the upregulation of MICA expression, by using RNA interference or viral transduction of constitutive active forms. On the contrary, inhibition of GSK3 correlated with a downregulation of STAT3 activation, a negative regulator of MICA transcription. Both Tyr(705) phosphorylation and binding of STAT3 on MICA promoter are reduced by GSK3 inhibitors; in addition, overexpression of a constitutively active form of STAT3 significantly inhibits MICA upregulation. Thus, we provide evidence that regulation of the NKG2D-ligand MICA expression may represent an additional immune-mediated mechanism supporting the antimyeloma activity of GSK3 inhibitors.

Novel players in multiple myeloma pathogenesis: role of protein kinases CK2 and GSK3

Multiple myeloma (MM) is an incurable plasma cell malignancy, which causes a significant morbidity due to organ damage and bone tissue destruction. In recent years, novel drugs have become available for MM therapy thanks to a more deepened knowledge of this disease's pathogenesis. The perspective of employing targeted therapies has considerably changed the expectations on the clinical outcome for patients affected by this malignancy and among the targetable molecules identified for MM therapy are several protein kinases, which have been proven to play relevant roles in supporting malignant plasma cell growth by regulating critical signaling cascades and by sustaining oncogenic mechanisms. Protein kinase CK2 (formerly known as casein kinase 2) and GSK3 (glycogen synthase kinase 3) are two multifaceted serine-threonine kinases whose task in the pathogenesis of malignant cell growth is increasingly emerging both in solid and blood tumors. In hematologic malignancies, CK2 and GSK3 have been shown to play an oncogenic function in chronic and acute leukemias as well as in MM. They have been demonstrated to act by impinging on pivotal signaling pathways that control malignant clone growth. We will herein briefly review the more recent advancements on the role of these two kinases in regulating the NF-κB, STAT3 and endoplasmic reticulum (ER) stress/unfolded protein response (UPR) signaling in MM and discuss the rationale of using small selective inhibitors as a therapeutic strategy to hamper the growth of malignant plasma cells or to improve the MM-associated bone disease.

Targeting Wnt pathways in disease

Wnt-mediated signal transduction pathways have long been recognized for their roles in regulating embryonic development, and have more recently been linked to cancer, neurologic diseases, inflammatory diseases, and disorders of endocrine function and bone metabolism in adults. Although therapies targeting Wnt signaling are attractive in theory, in practice it has been difficult to obtain specific therapeutics because many components of Wnt signaling pathways are also involved in other cellular processes, thereby reducing the specificity of candidate therapeutics. New technologies, and advances in understanding the mechanisms of Wnt signaling, have improved our understanding of the nuances of Wnt signaling and are leading to promising new strategies to target Wnt signaling pathways.

Tug of war in the haematopoietic stem cell niche: do myeloma plasma cells compete for the HSC niche?

In the adult mammal, normal haematopoiesis occurs predominantly in the bone marrow, where primitive haematopoietic stem cells (HSC) and their progeny reside in specialised microenvironments. The bone marrow microenvironment contains specific anatomical areas (termed niches) that are highly specialised for the development of certain blood cell types, for example HSCs. The HSC niche provides important cell–cell interactions and signalling molecules that regulate HSC self-renewal and differentiation processes. These same signals and interactions are also important in the progression of haematological malignancies, such as multiple myeloma (MM). This review provides an overview of the bone marrow microenvironment and its involvement in normal, physiological HSC maintenance and plasma cell growth throughout MM disease progression.

Wnt and Wnt inhibitors in bone metastasis

Bone metastasis is a clinically devastating development of progressive cancers including prostate carcinoma, breast carcinoma and multiple myeloma. Bone metastases are typically painful, lead to adverse skeletal-related events, such as fracture, and are highly resistant to therapy. A major contribution to the ability of cancers to successfully establish bone metastases is their ability to exploit mechanisms of normal bone remodeling. Wnts are a large family of morphogenic proteins that are critical for bone development and contribute to maintaining bone mass in the mature organism. Wnt function is balanced by the presence of a variety of endogenous inhibitors, such as the dickkopf family members, secreted frizzled related proteins and sclerostin. Together, these factors contribute to normal bone homeostasis, allowing for dynamic changes in bone to withstand alterations in physical forces and physiological needs. In this review, we describe the role that Wnts and their inhibitors have in normal bone biology and cancer-related bone pathology. An overview of Wnt signaling pathways is discussed and key bone microenvironment cellular players, as they pertain to Wnt biology, are examined. Finally, we describe clinical trials of several Wnt inhibitor antagonists for patients with tumor-related bone disease. As few options currently exist for the treatment of bone-metastatic disease, Wnt proteins and their inhibitors offer promise for the development of novel therapeutics.

Targeting bone in myeloma

Myeloma bone disease (BD) not only impairs quality of life, but is also associated with impaired survival. Studies of the biology underlying BD support the notion that the increased osteoclastogenesis and suppressed osteoblastogenesis is both a consequence and a necessity for tumour growth and clonal expansion. Survival and expansion of the myeloma clone are dependent on its interactions with bone elements; thus, targeting these interactions should have anti-myeloma activities. Indeed, both experimental and clinical findings indicate that bone-targeted therapies, not only improve BD, but also create an inhospitable environment for myeloma cell growth and survival, favouring improved clinical outcome. This chapter summarizes recent progress in our understandings of the biology of myeloma BD, highlighting the role of osteoclasts and osteoblasts in this process and how they can be targeted therapeutically. Unravelling the mechanisms underlying myeloma-bone interactions will facilitate the development of novel therapeutic agents to treat BD, which as a consequence are likely to improve the clinical outcome of myeloma patients.

Targeting bone as a therapy for myeloma

Myeloma bone disease (BD) not only impairs quality of life, but is also associated with impaired survival. Studies of the biology underlying BD support the notion that the increased osteoclastogenesis and suppressed osteoblastogenesis, is both a consequence and a necessity for tumour growth and clonal expansion. Survival and expansion of the myeloma clone is dependent on its interactions with bone elements, thus targeting these interactions should have antimyeloma activities. Indeed both experimental and clinical findings indicate that bone-targeted therapies not only improve BD, but also create an inhospitable environment for myeloma cell growth and survival, favouring improved clinical outcome. This review summarizes recent progress in our understandings of the biology of myeloma BD, highlighting the role of osteoclasts and osteoblasts in this process and how they can be targeted therapeutically. Unravelling the mechanisms underlying myeloma-bone interactions will facilitate the development of novel therapeutic agents to treat BD, which as a consequence are likely to improve the clinical outcome of myeloma patients.