Bone morphogenetic proteins induce apoptosis in multiple myeloma cells by Smad-dependent repression of MYC

In Silico, In Vitro, and In Vivo Investigations on Adapalene as Repurposed Third Generation Retinoid against Multiple Myeloma and Leukemia

The majority of hematopoietic cancers in adults are incurable and exhibit unpredictable remitting-relapsing patterns in response to various therapies. The proto-oncogene c-MYC has been associated with tumorigenesis, especially in hematological neoplasms. Therefore, targeting c-MYC is crucial to find effective, novel treatments for blood malignancies. To date, there are no clinically approved c-MYC inhibitors. In this study, we virtually screened 1578 Food and Drug Administration (FDA)-approved drugs from the ZINC15 database against c-MYC. The top 117 compounds from PyRx-based screening with the best binding affinities to c-MYC were subjected to molecular docking studies with AutoDock 4.2.6. Retinoids consist of synthetic and natural vitamin A derivatives. All-trans-retinoic acid (ATRA) were highly effective in hematological malignancies. In this study, adapalene, a third-generation retinoid usually used to treat acne vulgaris, was selected as a potent c-MYC inhibitor as it robustly bound to c-MYC with a lowest binding energy (LBE) of -7.27 kcal/mol, a predicted inhibition constant (pKi) of 4.69 µM, and a dissociation constant (Kd value) of 3.05 µM. Thus, we examined its impact on multiple myeloma (MM) cells in vitro and evaluated its efficiency in vivo using a xenograft tumor zebrafish model. We demonstrated that adapalene exerted substantial cytotoxicity against a panel of nine MM and two leukemic cell lines, with AMO1 cells being the most susceptible one (IC50 = 1.76 ± 0.39 µM) and, hence, the focus of this work. Adapalene (0.5 × IC50, 1 × IC50, 2 × IC50) decreased c-MYC expression and transcriptional activity in AMO1 cells in a dose-dependent manner. An examination of the cell cycle revealed that adapalene halted the cells in the G2/M phase and increased the portion of cells in the sub-G0/G1 phase after 48 and 72 h, indicating that cells failed to initiate mitosis, and consequently, cell death was triggered. Adapalene also increased the number of p-H3(Ser10) positive AMO1 cells, which is a further proof of its ability to prevent mitotic exit. Confocal imaging demonstrated that adapalene destroyed the tubulin network of U2OS cells stably transfected with a cDNA coding for α-tubulin-GFP, refraining the migration of malignant cells. Furthermore, adapalene induced DNA damage in AMO1 cells. It also induced apoptosis and autophagy, as demonstrated by flow cytometry and western blotting. Finally, adapalene impeded tumor growth in a xenograft tumor zebrafish model. In summary, the discovery of the vitamin A derivative adapalene as a c-MYC inhibitor reveals its potential as an avant-garde treatment for MM.

High concentrations of soluble endoglin can inhibit BMP9 signaling in non-endothelial cells

Endoglin (ENG) is a single-pass transmembrane protein highly expressed on vascular endothelial cells, although low expression levels can be detected in many other cell types. Its extracellular domain can be found in circulation known as soluble endoglin (sENG). Levels of sENG are elevated in many pathological conditions, in particular preeclampsia. We have shown that while loss of cell surface ENG decreases BMP9 signaling in endothelial cells, knocking down ENG in blood cancer cells enhances BMP9 signaling. Despite sENG binding to BMP9 with high affinity and blocking the type II receptor binding site on BMP9, sENG did not inhibit BMP9 signaling in vascular endothelial cells, but the dimeric form of sENG inhibited BMP9 signaling in blood cancer cells. Here we report that in non-endothelial cells such as human multiple myeloma cell lines and the mouse myoblast cell line C2C12, both monomeric and dimeric forms of sENG inhibit BMP9 signaling when present at high concentrations. Such inhibition can be alleviated by the overexpression of ENG and ACVRL1 (encoding ALK1) in the non-endothelial cells. Our findings suggest that the effects of sENG on BMP9 signaling is cell-type specific. This is an important consideration when developing therapies targeting the ENG and ALK1 pathway.

FKBP12 is a major regulator of ALK2 activity in multiple myeloma cells

BACKGROUND

The immunophilin FKBP12 binds to TGF-β family type I receptors, including the BMP type I receptor ALK2. FKBP12 keeps the type I receptor in an inactive state and controls signaling activity. Removal of FKBP12 with drugs such as the FKBP-ligand FK506 enhances BMP activity in various cell types. In multiple myeloma cells, activation of SMAD1/5/8 leads to apoptosis. We hypothesized that removing FKBP12 from ALK2 in myeloma cells would potentiate BMP-induced ALK2-SMAD1/5/8 activity and in consequence cell death.

METHODS

Multiple myeloma cell lines were treated with FK506, or other FKBP-binding compounds, combined with different BMPs before analyzing SMAD1/5/8 activity and cell viability. SMAD1/5/8 activity was also investigated using a reporter cell line, INA-6 BRE-luc. To characterize the functional signaling receptor complex, we genetically manipulated receptor expression by siRNA, shRNA and CRISPR/Cas9 technology.

RESULTS

FK506 potentiated BMP-induced SMAD1/5/8 activation and apoptosis in multiple myeloma cell lines. By using FKBP-binding compounds with different affinity profiles, and siRNA targeting FKBP12, we show that the FK506 effect is mediated by binding to FKBP12. Ligands that typically signal via ALK3 in myeloma cells, BMP2, BMP4, and BMP10, did not induce apoptosis in cells lacking ALK3. Notably, BMP10 competed with BMP6 and BMP9 and antagonized their activity via ALK2. However, upon addition of FK506, we saw a surprising shift in specificity, as the ALK3 ligands gained the ability to signal via ALK2 and induce apoptosis. This indicates that the receptor complex can switch from an inactive non-signaling complex (NSC) to an active one by adding FK506. This gain of activity was also seen in other cell types, indicating that the observed effects have broader relevance. BMP2, BMP4 and BMP10 depended on BMPR2 as type II receptor to signal, which contrasts with BMP6 and BMP9, that activate ALK2 more potently when BMPR2 is knocked down.

CONCLUSIONS

In summary, our data suggest that FKBP12 is a major regulator of ALK2 activity in multiple myeloma cells, partly by switching an NSC into an active signaling complex. FKBP12 targeting compounds devoid of immunosuppressing activity could have potential in novel treatment strategies aiming at reducing multiple myeloma tumor load. Video Abstract.

Renal Impairment Detectors: IGFBP-7 and NGAL as Tubular Injury Markers in Multiple Myeloma Patients

Background and Objectives: Urine insulin-like growth factor-binding protein 7 (IGFBP-7), tissue inhibitor of matrix metalloproteinase 2 (TIMP-2), and neutrophil gelatinase-associated lipocalin (NGAL) monomer are novel tubular kidney injury biomarkers. In multiple myeloma (MM), immunoglobulin free light chains (FLCs) play an integral role in renal impairment. This study aimed to investigate the correlation between new biomarkers and acclaimed parameters of renal failure, MM stage, and prognosis. Materials and Methods: The examined parameters included: urinary and serum cystatin-C, IGFBP-7, and TIMP-2, and urinary NGAL monomer in 124 enrolled patients. Results: Urinary and serum IGFBP-7 and urinary NGAL were higher among patients with an estimated glomerular filtration rate (eGFR) < 60 mL/min/1.73 m2, and positively correlated with urine light chains. Serum and urine IGFBP-7 and urine NGAL were greater among patients with a higher disease stage. In the whole study group, urinary concentrations of the studied markers were positively correlated with each other. In multiple linear regression, urinary IGFBP-7 and NGAL were associated with lower eGFR, independently of other urinary markers. Conclusions: Urinary IGFBP-7 and NGAL monomer may be useful markers of tubular renal damage in patients with MM. Biomarker-based diagnostics may contribute to earlier treatment that may improve renal outcomes and life expectancy in MM.

Rebuilding the hematopoietic stem cell niche: Recent developments and future prospects

Hematopoietic stem cells (HSCs) have proven their clinical relevance in stem cell transplantation to cure patients with hematological disorders. Key to their regenerative potential is their natural microenvironment - their niche - in the bone marrow (BM). Developments in the field of biomaterials enable the recreation of such environments with increasing preciseness in the laboratory. Such artificial niches help to gain a fundamental understanding of the biophysical and biochemical processes underlying the interaction of HSCs with the materials in their environment and the disturbance of this interplay during diseases affecting the BM. Artificial niches also have the potential to multiply HSCs in vitro, to enable the targeted differentiation of HSCs into mature blood cells or to serve as drug-testing platforms. In this review, we will introduce the importance of artificial niches followed by the biology and biophysics of the natural archetype. We will outline how 2D biomaterials can be used to dissect the complexity of the natural niche into individual parameters for fundamental research and how 3D systems evolved from them. We will present commonly used biomaterials for HSC research and their applications. Finally, we will highlight two areas in the field of HSC research, which just started to unlock the possibilities provided by novel biomaterials, in vitro blood production and studying the pathophysiology of the niche in vitro. With these contents, the review aims to give a broad overview of the different biomaterials applied for HSC research and to discuss their potentials, challenges and future directions in the field. STATEMENT OF SIGNIFICANCE: Hematopoietic stem cells (HSCs) are multipotent cells responsible for maintaining the turnover of all blood cells. They are routinely applied to treat patients with hematological diseases. This high clinical relevance explains the necessity of multiplication or differentiation of HSCs in the laboratory, which is hampered by the missing natural microenvironment - the so called niche. Biomaterials offer the possibility to mimic the niche and thus overcome this hurdle. The review introduces the HSC niche in the bone marrow and discusses the utility of biomaterials in creating artificial niches. It outlines how 2D systems evolved into sophisticated 3D platforms, which opened the gateway to applications such as, expansion of clinically relevant HSCs, in vitro blood production, studying niche pathologies and drug testing.

Morphogens and growth factor signalling in the myeloma bone-lining niche

Multiple myeloma is a malignancy caused by the clonal expansion of abnormal plasma cells. Myeloma cells have proven to be incredibly successful at manipulating their microenvironment to promote growth and to evade modern therapies. They have evolved to utilise the integral signalling pathways of the bone and bone marrow to drive disease progression. The bone marrow is often described in the context of a single structure that fills the bone cavity and supports normal haematopoiesis. However, within that structure exists two anatomically different niches, the perivascular niche and the endosteal niche. These contain different cell types functioning to support normal immune and blood cell production as well as healthy bone. These cells secrete numerous signalling molecules that can influence myeloma cell biology and behaviour. The endosteal niche is home to specific bone cell lineages and plays a pivotal role in myeloma cell establishment and survival. This review will concentrate on some of the signalling pathways that are hijacked by myeloma cells to shape a favourable environment, and the different influences myeloma cells are exposed to depending on their spatial location within the bone marrow.

Receptor binding competition: A paradigm for regulating TGF-β family action

The transforming growth factor (TGF)-β family is a group of structurally related, multifunctional growth factors, or ligands that are crucially involved in the development, regulation, and maintenance of animal tissues. In humans, the family counts over 33 members. These secreted ligands typically form multimeric complexes with two type I and two type II receptors to activate one of two distinct signal transduction branches. A striking feature of the family is its promiscuity, i.e., many ligands bind the same receptors and compete with each other for binding to these receptors. Although several explanations for this feature have been considered, its functional significance has remained puzzling. However, several recent reports have promoted the idea that ligand-receptor binding promiscuity and competition are critical features of the TGF-β family that provide an essential regulating function. Namely, they allow a cell to read and process multi-ligand inputs. This capability may be necessary for producing subtle, distinctive, or adaptive responses and, possibly, for facilitating developmental plasticity. Here, we review the molecular basis for ligand competition, with emphasis on molecular structures and binding affinities. We give an overview of methods that were used to establish experimentally ligand competition. Finally, we discuss how the concept of ligand competition may be fundamentally tied to human physiology, disease, and therapy.

Targeted Disruption of Bone Marrow Stromal Cell-Derived Gremlin1 Limits Multiple Myeloma Disease Progression In Vivo

In most instances, multiple myeloma (MM) plasma cells (PCs) are reliant on factors made by cells of the bone marrow (BM) stroma for their survival and growth. To date, the nature and cellular composition of the BM tumor microenvironment and the critical factors which drive tumor progression remain imprecisely defined. Our studies show that Gremlin1 (Grem1), a highly conserved protein, which is abundantly secreted by a subset of BM mesenchymal stromal cells, plays a critical role in MM disease development. Analysis of human and mouse BM stromal samples by quantitative PCR showed that GREM1/Grem1 expression was significantly higher in the MM tumor-bearing cohorts compared to healthy controls (p < 0.05, Mann–Whitney test). Additionally, BM-stromal cells cultured with 5TGM1 MM PC line expressed significantly higher levels of Grem1, compared to stromal cells alone (p < 0.01, t-test), suggesting that MM PCs promote increased Grem1 expression in stromal cells. Furthermore, the proliferation of 5TGM1 MM PCs was found to be significantly increased when co-cultured with Grem1-overexpressing stromal cells (p < 0.01, t-test). To examine the role of Grem1 in MM disease in vivo, we utilized the 5TGM1/KaLwRij mouse model of MM. Our studies showed that, compared to immunoglobulin G (IgG) control antibody-treated mice, mice treated with an anti-Grem1 neutralizing antibody had a decrease in MM tumor burden of up to 81.2% (p < 0.05, two-way ANOVA). The studies presented here demonstrate, for the first time, a novel positive feedback loop between MM PCs and BM stroma, and that inhibiting this vicious cycle with a neutralizing antibody can dramatically reduce tumor burden in a preclinical mouse model of MM.

Activins as Dual Specificity TGF-β Family Molecules: SMAD-Activation via Activin- and BMP-Type 1 Receptors

Activins belong to the transforming growth factor (TGF)-β family of multifunctional cytokines and signal via the activin receptors ALK4 or ALK7 to activate the SMAD2/3 pathway. In some cases, activins also signal via the bone morphogenetic protein (BMP) receptor ALK2, causing activation of the SMAD1/5/8 pathway. In this study, we aimed to dissect how activin A and activin B homodimers, and activin AB and AC heterodimers activate the two main SMAD branches. We compared the activin-induced signaling dynamics of ALK4/7-SMAD2/3 and ALK2-SMAD1/5 in a multiple myeloma cell line. Signaling via the ALK2-SMAD1/5 pathway exhibited greater differences between ligands than signaling via ALK4/ALK7-SMAD2/3. Interestingly, activin B and activin AB very potently activated SMAD1/5, resembling the activation commonly seen with BMPs. As SMAD1/5 was also activated by activins in other cell types, we propose that dual specificity is a general mechanism for activin ligands. In addition, we found that the antagonist follistatin inhibited signaling by all the tested activins, whereas the antagonist cerberus specifically inhibited activin B. Taken together, we propose that activins may be considered dual specificity TGF-β family members, critically affecting how activins may be considered and targeted clinically.

A Signaling Crosstalk between BMP9 and HGF/c-Met Regulates Mouse Adult Liver Progenitor Cell Survival

During chronic liver disease, hepatic progenitor cells (HPC, oval cells in rodents) become activated, proliferate, and differentiate into cholangiocytes and/or hepatocytes contributing to the final outcome of the regenerative process in a context-dependent fashion. Here, we analyze the crosstalk between the hepatocyte growth factor (HGF)/c-Met signaling axis, key for liver regeneration, and bone morphogenetic protein (BMP)9, a BMP family ligand that has emerged as a critical regulator of liver pathology. Our results show that HGF/c-Met signaling blocks BMP9-mediated apoptotic cell death, while it potentiates small mothers against decapentaplegic (SMAD)1 signaling triggered by BMP9 in oval cells. Interestingly, HGF-induced overactivation of SMAD1, -5, -8 requires the upregulation of TGF-β type receptor activin receptor-like kinase (ALK)1, and both ALK1 and SMAD1 are required for the counteracting effect of HGF on BMP9 apoptotic activity. On the other hand, we also prove that BMP9 triggers the activation of p38MAPK in oval cells, which drives BMP9-apoptotic cell death. Therefore, our data support a model in which BMP9 and HGF/c-Met signaling axes establish a signaling crosstalk via ALK1 that modulates the balance between the two pathways with opposing activities, SMAD1 (pro-survival) and p38 mitogen-activated protein kinases (p38MAPK; pro-apoptotic), which determines oval cell fate. These data help delineate the complex signaling network established during chronic liver injury and its impact on the oval cell regenerative response.

Bone Morphogenetic Protein 4 Gene Therapy in Mice Inhibits Myeloma Tumor Growth, But Has a Negative Impact on Bone

Multiple myeloma is characterized by accumulation of malignant plasma cells in the bone marrow. Most patients suffer from an osteolytic bone disease, caused by increased bone degradation and reduced bone formation. Bone morphogenetic protein 4 (BMP4) is important for both pre‐ and postnatal bone formation and induces growth arrest and apoptosis of myeloma cells. BMP4‐treatment of myeloma patients could have the potential to reduce tumor growth and restore bone formation. We therefore explored BMP4 gene therapy in a human‐mouse model of multiple myeloma where humanized bone scaffolds were implanted subcutaneously in RAG2^−/− γC^−/−mice. Mice were treated with adeno‐associated virus serotype 8 BMP4 vectors (AAV8‐BMP4) to express BMP4 in the liver. When mature BMP4 was detectable in the circulation, myeloma cells were injected into the scaffolds and tumor growth was examined by weekly imaging. Strikingly, the tumor burden was reduced in AAV8‐BMP4 mice compared with the AAV8‐CTRL mice, suggesting that increased circulating BMP4 reduced tumor growth. BMP4‐treatment also prevented bone loss in the scaffolds, most likely due to reduced tumor load. To delineate the effects of BMP4 overexpression on bone per se, without direct influence from cancer cells, we examined the unaffected, non‐myeloma femurs by μCT. Surprisingly, the AAV8‐BMP4 mice had significantly reduced trabecular bone volume, trabecular numbers, as well as significantly increased trabecular separation compared with the AAV8‐CTRL mice. There was no difference in cortical bone parameters between the two groups. Taken together, BMP4 gene therapy inhibited myeloma tumor growth, but also reduced the amount of trabecular bone in mice. Our data suggest that care should be taken when considering using BMP4 as a therapeutic agent. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Transcriptomic profiling of the myeloma bone-lining niche reveals BMP signalling inhibition to improve bone disease

Multiple myeloma is an incurable, bone marrow-dwelling malignancy that disrupts bone homeostasis causing skeletal damage and pain. Mechanisms underlying myeloma-induced bone destruction are poorly understood and current therapies do not restore lost bone mass. Using transcriptomic profiling of isolated bone lining cell subtypes from a murine myeloma model, we find that bone morphogenetic protein (BMP) signalling is upregulated in stromal progenitor cells. BMP signalling has not previously been reported to be dysregulated in myeloma bone disease. Inhibition of BMP signalling in vivo using either a small molecule BMP receptor antagonist or a solubilized BMPR1a-FC receptor ligand trap prevents trabecular and cortical bone volume loss caused by myeloma, without increasing tumour burden. BMP inhibition directly reduces osteoclastogenesis, increases osteoblasts and bone formation, and suppresses bone marrow sclerostin levels. In summary we describe a novel role for the BMP pathway in myeloma-induced bone disease that can be therapeutically targeted.

BMPR2 inhibits activin and BMP signaling via wild-type ALK2

TGF-β/BMP superfamily ligands require heteromeric complexes of type 1 and 2 receptors for ligand-dependent downstream signaling. Activin A, a TGF-β superfamily member, inhibits growth of multiple myeloma cells, but the mechanism for this is unknown. We therefore aimed to clarify how activins affect myeloma cell survival. Activin A activates the transcription factors SMAD2/3 through the ALK4 type 1 receptor, but may also activate SMAD1/5/8 through mutated variants of the type 1 receptor ALK2 (also known as ACVR1). We demonstrate that activin A and B activate SMAD1/5/8 in myeloma cells through endogenous wild-type ALK2. Knockdown of the type 2 receptor BMPR2 strongly potentiated activin A- and activin B-induced activation of SMAD1/5/8 and subsequent cell death. Furthermore, activity of BMP6, BMP7 or BMP9, which may also signal via ALK2, was potentiated by knockdown of BMPR2. Similar results were seen in HepG2 liver carcinoma cells. We propose that BMPR2 inhibits ALK2-mediated signaling by preventing ALK2 from oligomerizing with the type 2 receptors ACVR2A and ACVR2B, which are necessary for activation of ALK2 by activins and several BMPs. In conclusion, BMPR2 could be explored as a possible target for therapy in patients with multiple myeloma.This article has an associated First Person interview with the first author of the paper.

C‑Myc inhibitor 10058‑F4 increases the efficacy of dexamethasone on acute lymphoblastic leukaemia cells

The long‑term survival rate in paediatric acute lymphoblastic leukaemia (ALL) exceeds 80%; however, the outcome of adult ALL remains to be poor. Glucocorticoids (GCs) are the preferred drugs in the traditional treatment of ALL patients. In the anti‑leukaemia molecular mechanisms of GCs, c‑Myc inhibition serves a critical role. In the present study, a c‑Myc inhibitor that increased the sensitivity to GCs in NALM6 cells of the B‑cell‑ALL cell line and CEM cells of the T‑cell‑ALL cell line was investigated. The data demonstrated that 10058‑F4, a c‑Myc inhibitor, increased the growth inhibition, G0/G1 phase arrest and apoptosis of the NALM6 and CEM cells as induced by dexamethasone (DXM), a type of GC. Additionally, 10058‑F4 reinforced the decreased expressions of c‑Myc, cyclin‑dependent kinase (CDK)‑4 and CDK6 in the NALM6 and CEM cells treated with DXM. These findings indicated that DXM in combination with the c‑Myc inhibitor 10058‑F4 may be a novel, potent therapeutic strategy for the treatment of ALL.

Cytoplasmic calcium increase via fusion with inactivated Sendai virus induces apoptosis in human multiple myeloma cells by downregulation of c-Myc oncogene

Because the emergence of drug resistance is a major limitation of current treatments for multiple myeloma (MM), it is necessary to continuously develop novel anticancer strategies. Here, using an inactivated Sendai virus (Hemagglutinating Virus of Japan; HVJ) envelope (HVJ-E), we discovered that increase of cytoplasmic Ca2+ by virus-cell fusion significantly induced apoptosis against human MM cells but not peripheral blood mononuclear cells from healthy donors. Interaction of F protein of HVJ-E with MM cells increased intracellular Ca2+ level of MMs by the induction of Ca2+ efflux from endoplasmic reticulum but not influx from extracellular region. The elevation of the Ca2+ cytoplasmic level induced SMAD1/5/8 phosphorylation and translocation into the nucleus, and SMAD1/5/8 and SMAD4 complex suppressed c-Myc transcription. Meanwhile, HVJ-E decreases S62 phosphorylation of c-Myc and promotes c-Myc protein degradation. Thus, HVJ-E-induced cell death of MM resulted from suppression of c-Myc by both destabilization of c-Myc protein and downregulation of c-Myc transcription. This study indicates that HVJ-E will be a promising tool for MM therapy.

Hypoxia promotes IL-32 expression in myeloma cells, and high expression is associated with poor survival and bone loss

Multiple myeloma (MM) is a hematologic cancer characterized by expansion of malignant plasma cells in the bone marrow. Most patients develop an osteolytic bone disease, largely caused by increased osteoclastogenesis. The myeloma bone marrow is hypoxic, and hypoxia may contribute to MM disease progression, including bone loss. Here we identified interleukin-32 (IL-32) as a novel inflammatory cytokine expressed by a subset of primary MM cells and MM cell lines. We found that high IL-32 gene expression in plasma cells correlated with inferior survival in MM and that IL-32 gene expression was higher in patients with bone disease compared with those without. IL-32 was secreted from MM cells in extracellular vesicles (EVs), and those EVs, as well as recombinant human IL-32, promoted osteoclast differentiation both in vitro and in vivo. The osteoclast-promoting activity of the EVs was IL-32 dependent. Hypoxia increased plasma-cell IL-32 messenger RNA and protein levels in a hypoxia-inducible factor 1α-dependent manner, and high expression of IL-32 was associated with a hypoxic signature in patient samples, suggesting that hypoxia may promote expression of IL-32 in MM cells. Taken together, our results indicate that targeting IL-32 might be beneficial in the treatment of MM bone disease in a subset of patients.

The anti-myeloma activity of bone morphogenetic protein 2 predominantly relies on the induction of growth arrest and is apoptosis-independent

Multiple myeloma (MM), a malignancy of the bone marrow, is characterized by a pathological increase in antibody-producing plasma cells and an increase in immunoglobulins (plasmacytosis). In recent years, bone morphogenetic proteins (BMPs) have been reported to be activators of apoptotic cell death in neoplastic B cells in MM. Here, we use bone morphogenetic protein 2 (BMP2) to show that the "apoptotic" effect of BMPs on human neoplastic B cells is dominated by anti-proliferative activities and cell cycle arrest and is apoptosis-independent. The anti-proliferative effect of BMP2 was analysed in the human cell lines KMS12-BM and L363 using WST-1 and a Coulter counter and was confirmed using CytoTox assays with established inhibitors of programmed cell death (zVAD-fmk and necrostatin-1). Furthermore, apoptotic activity was compared in both cell lines employing western blot analysis for caspase 3 and 8 in cells treated with BMP2 and FasL. Additionally, expression profiles of marker genes of different cell death pathways were analysed in both cell lines after stimulation with BMP2 for 48h using an RT-PCR-based array. In our experiments we observed that there was rather no reduction in absolute cell number, but cells stopped proliferating following treatment with BMP2 instead. The time frame (48–72 h) after BMP2 treatment at which a reduction in cell number is detectable is too long to indicate a directly BMP2-triggered apoptosis. Moreover, in comparison to robust apoptosis induced by the approved apoptotic factor FasL, BMP2 only marginally induced cell death. Consistently, neither the known inhibitor of apoptotic cell death zVAD-fmk nor the necroptosis inhibitor necrostatin-1 was able to rescue myeloma cell growth in the presence of BMP2.

BMP-7 induces apoptosis in human germinal center B cells and is influenced by TGF-β receptor type I ALK5

Selection and maturation of B cells into plasma cells producing high-affinity antibodies occur in germinal centers (GC). GCs form transiently in secondary lymphoid organs upon antigen challenge, and the GC reaction is a highly regulated process. TGF-β is a potent negative regulator, but the influence of other family members including bone morphogenetic proteins (BMPs) is less known. Studies of human peripheral blood B lymphocytes showed that BMP-6 suppressed plasmablast differentiation, whereas BMP-7 induced apoptosis. Here, we show that human naïve and GC B cells had a strikingly different receptor expression pattern. GC B cells expressed high levels of BMP type I receptor but low levels of type II receptors, whereas naïve B cells had the opposite pattern. Furthermore, GC B cells had elevated levels of downstream signaling components SMAD1 and SMAD5, but reduced levels of the inhibitory SMAD7. Functional assays of GC B cells revealed that BMP-7 suppressed the viability-promoting effect of CD40L and IL-21, but had no effect on CD40L- and IL-21-induced differentiation into plasmablasts. BMP-7-induced apoptosis was counteracted by a selective TGF-β type I receptor (ALK4/5/7) inhibitor, but not by a selective BMP receptor type I inhibitor. Furthermore, overexpression of truncated ALK5 in a B-cell line counteracted BMP-7-induced apoptosis, whereas overexpression of truncated ALK4 had no effect. BMP-7 mRNA and protein was readily detected in tonsillar B cells, indicating a physiological relevance of the study. Altogether, we identified BMP-7 as a negative regulator of GC B-cell survival. The effect was counteracted by truncated ALK5, suggesting greater complexity in regulating BMP-7 signaling than previously believed.

Utilizing BMP-2 muteins for treatment of multiple myeloma

Multiple myeloma (MM) represents a haematological cancer characterized by the pathological hyper proliferation of antibody-producing B-lymphocytes. Patients typically suffer from kidney malfunction and skeletal disorders. In the context of MM, the transforming growth factor β (TGFβ) member Activin A was recently identified as a promoter of both accompanying symptoms. Because studies have shown that bone morphogenetic protein (BMP)-2-mediated activities are counteracted by Activin A, we analysed whether BMP2, which also binds to the Activin A receptors ActRII and ActRIIB but activates the alternative SMAD-1/5/8 pathway, can be used to antagonize Activin A activities, such as in the context of MM. Therefore three BMP2 derivatives were generated with modified binding activities for the type II (ActRIIB) and/or type I receptor (BMPRIA) showing either increased or decreased BMP2 activity. In the context of MM these BMP2 muteins show two functionalities since they act as a) an anti-proliferative/apoptotic agent against neoplastic B-cells, b) as a bone-formation promoting growth factor. The molecular basis of both activities was shown in two different cellular models to clearly rely on the properties of the investigated BMP2 muteins to compete for the binding of Activin A to the Activin type II receptors. The experimental outcome suggests new therapeutic strategies using BMP2 variants in the treatment of MM-related pathologies.

MYC amplifications in myeloma cell lines: correlation with MYC-inhibitor efficacy

In multiple myeloma, elevated MYC expression is related to disease initiation and progression. We found that in myeloma cell lines, MYC gene amplifications were common and correlated with MYC mRNA and protein. In primary cell samples MYC mRNA levels were also relatively high; however gene copy number alterations were uncommon. Elevated levels of MYC in primary myeloma cells have been reported to arise from complex genetic aberrations and are more common than previously thought. Thus, elevated MYC expression is achieved differently in myeloma cell lines and primary cells. Sensitivity of myeloma cell lines to the MYC inhibitor 10058-F4 correlated with MYC expression, supporting that the activity of 10058-F4 was through specific inhibition of MYC.

Clinical features, tumor biology, and prognosis associated with MYC rearrangement and Myc overexpression in diffuse large B-cell lymphoma patients treated with rituximab-CHOP

MYC dysregulation, including MYC gene rearrangement and Myc protein overexpression, is of increasing clinical importance in diffuse large B-cell lymphoma (DLBCL). However, the roles of MYC and the relative importance of rearrangement vs overexpression remain to be refined. Gaining knowledge about the tumor biology associated with MYC dysregulation is important to understand the roles of MYC and MYC-associated biology in lymphomagenesis. In this study, we determined MYC rearrangement status (n=344) and Myc expression (n=535) in a well-characterized DLBCL cohort, individually assessed the clinical and pathobiological features of patients with MYC rearrangement and Myc protein overexpression, and analyzed the prognosis and gene expression profiling signatures associated with these MYC abnormalities in germinal center B-cell-like and activated B-cell-like DLBCL. Our results showed that the prognostic importance of MYC rearrangement vs Myc overexpression is significantly different in germinal center B-cell-like vs activated B-cell-like DLBCL. In germinal center B-cell-like DLBCL, MYC-rearranged germinal center B-cell-like DLBCL patients with Myc overexpression significantly contributed to the clinical, biological, and prognostic characteristics of the overall Myc-overexpressing germinal center B-cell-like DLBCL group. In contrast, in activated B-cell-like DLBCL, the occurrence, clinical and biological features, and prognosis of Myc overexpression were independent of MYC rearrangement. High Myc levels and Myc-independent mechanisms, either tumor cell intrinsic or related to tumor microenvironment, conferred significantly worse survival to MYC-rearranged germinal center B-cell-like DLBCL patients, even among Myc(high)Bcl-2(high) DLBCL patients. This study provides new insight into the tumor biology and prognostic effects associated with MYC dysregulation and suggest that detection of both MYC translocations and evaluation of Myc and Bcl-2 expression is necessary to predict the prognosis of DLBCL patients.

Activin A inhibits BMP-signaling by binding ACVR2A and ACVR2B

Background

Activins are members of the TGF-β family of ligands that have multiple biological functions in embryonic stem cells as well as in differentiated tissue. Serum levels of activin A were found to be elevated in pathological conditions such as cachexia, osteoporosis and cancer. Signaling by activin A through canonical ALK4-ACVR2 receptor complexes activates the transcription factors SMAD2 and SMAD3. Activin A has a strong affinity to type 2 receptors, a feature that they share with some of the bone morphogenetic proteins (BMPs). Activin A is also elevated in myeloma patients with advanced disease and is involved in myeloma bone disease.

Results

In this study we investigated effects of activin A binding to receptors that are shared with BMPs using myeloma cell lines with well-characterized BMP-receptor expression and responses. Activin A antagonized BMP-6 and BMP-9, but not BMP-2 and BMP-4. Activin A was able to counteract BMPs that signal through the type 2 receptors ACVR2A and ACVR2B in combination with ALK2, but not BMPs that signal through BMPR2 in combination with ALK3 and ALK6.

Conclusions

We propose that one important way that activin A regulates cell behavior is by antagonizing BMP-ACVR2A/ACVR2B/ALK2 signaling.

Electronic supplementary material

The online version of this article (doi:10.1186/s12964-015-0104-z) contains supplementary material, which is available to authorized users.

Insulin like growth factor binding protein 7 (IGFBP7) expression is linked to poor prognosis but may protect from bone disease in multiple myeloma

Background

Insulin like growth factor binding protein 7 (IGFBP7) is a secreted protein binding insulin like growth factor 1 (IGF-1), insulin, vascular endothelial growth factor A (VEGFA), and activin A. It antagonizes bone morphogenetic proteins and is involved in the tumour propagation of solid as well as haematological malignancies. Its role in multiple myeloma (MM) is not defined so far. We therefore aim here to investigate its prognostic and pathophysiological role in MM.

Methods

The clinical significance of IGFBP7 gene expression was investigated by gene expression profiling in two independent cohorts (n = 948) of newly-diagnosed MM patients. Methylation of the IGFBP7 promoter was analysed by pyrosequencing and treatment of MM cell lines with 5-aza-2-deoxycytidine. The impact of IGFBP7 on MM cells was studied by CCK-8 assay, BrdU assay and flow cytometry, respectively. IGFBP7 expression in bone marrow stromal cells (BMSCs) was studied by quantitative RT-PCR. For osteoblast development, immortalized and primary human BMSCs were cultured in osteogenic differentiation medium for 7–14 days in the presence of recombinant human IGFBP7 and/or activin A.

Results

Median IGFBP7 expression is significantly lower in CD138-purified plasma cells from individuals with MGUS and MM, compared to normal bone marrow plasma cells. IGFBP7 gene expression in MM cells is regulated by methylation, shown by pyrosequencing and exposure to demethylating agents (5-aza-2-deoxycytidine). High expression of IGFBP7 in MM cells is associated with adverse survival in two independent cohorts of 247 and 701 newly-diagnosed MM patients treated with high-dose therapy and autologous stem cell transplantation. IGFBP7 is associated with prognostically adverse chromosomal aberrations (t(4;14) and gain of 1q21), MMSET expression, and higher myeloma cell proliferation. In vitro, IGFBP7 overcomes activin A induced osteoblast suppression and promotes osteogenesis. MM cells downregulate IGFBP7 in stromal cells, possibly contributing to the osteoblast suppression found in MM. Conversely, higher IGFBP7 expression is associated with a lower probability of myeloma bone disease.

Conclusions

Our data indicate that IGFBP7 expression is a marker for a specific methylation pattern in myeloma, linked to translocation t(4;14) associated MMSET expression, showing clinical features of adverse prognosis with absence of myeloma bone disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s13045-014-0105-1) contains supplementary material, which is available to authorized users.

Intercellular network structure and regulatory motifs in the human hematopoietic system

The hematopoietic system is a distributed tissue that consists of functionally distinct cell types continuously produced through hematopoietic stem cell (HSC) differentiation. Combining genomic and phenotypic data with high-content experiments, we have built a directional cell-cell communication network between 12 cell types isolated from human umbilical cord blood. Network structure analysis revealed that ligand production is cell type dependent, whereas ligand binding is promiscuous. Consequently, additional control strategies such as cell frequency modulation and compartmentalization were needed to achieve specificity in HSC fate regulation. Incorporating the in vitro effects (quiescence, self-renewal, proliferation, or differentiation) of 27 HSC binding ligands into the topology of the cell-cell communication network allowed coding of cell type-dependent feedback regulation of HSC fate. Pathway enrichment analysis identified intracellular regulatory motifs enriched in these cell type- and ligand-coupled responses. This study uncovers cellular mechanisms of hematopoietic cell feedback in HSC fate regulation, provides insight into the design principles of the human hematopoietic system, and serves as a foundation for the analysis of intercellular regulation in multicellular systems.

10058-F4, a c-Myc inhibitor, markedly increases valproic acid-induced cell death in Jurkat and CCRF-CEM T-lymphoblastic leukemia cells

Adult T-cell acute lymphoblastic leukemia (T-ALL) has a poor prognosis. Although it has been found that activation of Notch1 signaling occurs in >50% T-ALL patients, γ-secretase inhibitors that target Notch1 signaling are of limited efficacy. However, c-Myc is an important direct target of Notch1 and, thus, c-Myc is another potential therapeutic target for T-ALL. Valproic acid (VPA), a histone deacetylase inhibitor, has been reported to treat various hematological malignancies. In the present study, we showed that c-Myc expression, at a transcriptional level, was dose-dependently downregulated in VPA-induced growth inhibition in T-ALL cell lines, Jurkat and CCRF-CEM cells. 10058-F4, a small molecule c-Myc inhibitor, could increase the downregulation of c-Myc and markedly increase the growth inhibition and cell death induced by VPA in Jurkat and CCRF-CEM cells, which was accompanied by obvious cleavage of capase-3. Z-VAD-FMK, a caspase inhibitor, partially prevented the anti-leukemic effect. The results of the present study suggest that c-Myc inhibitors increase cell death induced by VPA in a caspase-dependent and -independent manner, and their combination could be a potent therapeutic strategy for adult T-ALL patients.

The role of bone morphogenetic proteins in myeloma cell survival

Multiple myeloma is characterized by slowly growing clones of malignant plasma cells in the bone marrow. The malignant state is frequently accompanied by osteolytic bone disease due to a disturbed balance between osteoblasts and osteoclasts. Bone morphogenetic proteins (BMPs) are present in the bone marrow and are important for several aspects of myeloma pathogenesis including growth and survival of tumor cells, bone homeostasis, and anemia. Among cancer cells, myeloma cells are particularly sensitive to growth inhibition and apoptosis induced by BMPs and therefore represent good models to study BMP receptor usage and signaling. Our review highlights and discusses the current knowledge on BMP signaling in myeloma.

Multiple myeloma exacerbation following utilization of bone morphogenetic protein-2 in lateral lumbar interbody fusion: a case report and review of the literature

BACKGROUND CONTEXT

Recent studies generated antithetic results regarding the safety of bone morphogenetic protein-2 (BMP-2) use in spine surgery, and the effect of this biologic adjunct on myeloma cells remains to be fully elucidated.

PURPOSE

The purpose of this study was to present a case of multiple myeloma (MM) exacerbation after BMP-2 implantation in the setting of lateral lumbar interbody fusion (LLIF).

STUDY DESIGN

Case report and literature review.

METHODS

The medical records, laboratory findings, and radiographic imaging studies of an 86-year-old female patient with exacerbation of previously undiagnosed MM were reviewed.

RESULTS

The patient presented with a 10-year history of debilitating lower back pain and bilateral lower extremity claudication. Radiographic studies depicted lumbar scoliosis and lateral spondylolisthesis. Preoperative serum immunofixation electrophoresis showed a serum immunoglobulin A kappa paraprotein-peak; however, the patient had never been diagnosed with MM or reported any unexplained fever, night sweats, or weight loss indicative of MM. The patient underwent LLIF from L1-L5 supplemented by BMP-2. On postoperative day 1, the patient was evaluated by the hematology department for paraproteinemia. Serum electrophoresis showed decreased albumin, hypogammaglobulinemia, and suspicious broadening of the complement component in the beta region. Postoperative imaging studies (19 weeks) depicted progression of a previously visible intraosseous lesion, and anterior cortical breakthrough (L5), in addition to a soft tissue mass at the T10 level. Histological examination of iliac crest and T10 vertebral biopsies showed fatty marrow infiltration by plasma cells and plasma cell dyscrasia, proving the diagnosis of MM. The patient died 10 months after surgery due to complications related to a methicillin-resistant Staphylococcus aureus infection.

CONCLUSIONS

Based on the present case, perhaps one should consider that in patients with abnormal electrophoresis results, even in the absence of a prior diagnosis of MM as well as in the absence of symptoms indicative of MM, BMPs should be administered only after preoperative exclusion of neoplastic disease.

Bone morphogenetic protein-9 suppresses growth of myeloma cells by signaling through ALK2 but is inhibited by endoglin

Multiple myeloma is a malignancy of plasma cells predominantly located in the bone marrow. A number of bone morphogenetic proteins (BMPs) induce apoptosis in myeloma cells in vitro, and with this study we add BMP-9 to the list. BMP-9 has been found in human serum at concentrations that inhibit cancer cell growth in vitro. We here show that the level of BMP-9 in serum was elevated in myeloma patients (median 176 pg/ml, range 8–809) compared with healthy controls (median 110 pg/ml, range 8–359). BMP-9 was also present in the bone marrow and was able to induce apoptosis in 4 out of 11 primary myeloma cell samples by signaling through ALK2. BMP-9-induced apoptosis in myeloma cells was associated with c-MYC downregulation. The effects of BMP-9 were counteracted by membrane-bound (CD105) or soluble endoglin present in the bone marrow microenvironment, suggesting a mechanism for how myeloma cells can evade the tumor suppressing activity of BMP-9 in multiple myeloma.

PRIMA-1Met/APR-246 displays high antitumor activity in multiple myeloma by induction of p73 and Noxa

Targeting p53 by the small-molecule PRIMA-1(Met)/APR-246 has shown promising preclinical activity in various cancer types. However, the mechanism of PRIMA-1(Met)-induced apoptosis is not completely understood and its effect on multiple myeloma cells is unknown. In this study, we evaluated antitumor effect of PRIMA-1(Met) alone or its combination with current antimyeloma agents in multiple myeloma cell lines, patient samples, and a mouse xenograft model. Results of our study showed that PRIMA-1(Met) decreased the viability of multiple myeloma cells irrespective of p53 status, with limited cytotoxicity toward normal hematopoietic cells. Treatment of multiple myeloma cells with PRIMA-1(Met) resulted in induction of apoptosis, inhibition of colony formation, and migration. PRIMA-1(Met) restored wild-type conformation of mutant p53 and induced activation of p73 upregulating Noxa and downregulating Mcl-1 without significant modulation of p53 level. siRNA-mediated silencing of p53 showed a little effect on apoptotic response of PRIMA-1(Met), whereas knockdown of p73 led to substantial attenuation of apoptotic activity in multiple myeloma cells, indicating that PRIMA-1(Met)-induced apoptosis is, at least in part, p73-dependent. Importantly, PRIMA-1(Met) delayed tumor growth and prolonged survival of mice bearing multiple myeloma tumor. Furthermore, combined treatment of PRIMA-1(Met) with dexamethasone or doxorubicin displayed synergistic effects in both multiple myeloma cell lines and primary multiple myeloma samples. Consistent with our in vitro observations, cotreatment with PRIMA-1(Met) and dexamethasone resulted in enhanced antitumor activity in vivo. Our study for the first time shows antimyeloma activity of PRIMA-1(Met) and provides the rationale for its clinical evaluation in patients with multiple myeloma, including the high-risk group with p53 mutation/deletion.

Lymphoma and myeloma cells are highly sensitive to growth arrest and apoptosis induced by artesunate

OBJECTIVES

The use of new drugs has improved the treatment of multiple myeloma and diffuse large B-cell lymphoma (DLBCL). Nevertheless, over time many patients relapse and develop resistance to treatment, and efforts are needed to overcome drug resistance. The widely used malaria drug artesunate has been reported to have antitumor activity, and we aimed to test the effects of artesunate on a panel of myeloma and lymphoma cells.

METHODS

Myeloma and DLBCL cell lines were treated with artesunate in vitro. The effects of artesunate treatment were evaluated using ATP content measurements for proliferation and annexin V/propidium iodide labeling for apoptosis. Western blotting was used to look for artesunate-induced protein changes. In addition, we measured artesunate effects on patient myeloma cells in the presence of bone marrow stromal cells.

RESULTS

Artesunate treatment efficiently inhibited cell growth and induced apoptosis in cell lines. Apoptosis was induced concomitantly with downregulation of MYC and anti-apoptotic Bcl-2 family proteins, as well as with cleavage of caspase-3. The IC50 values of artesunate in cell lines varied between 0.3 and 16.6 μm. Furthermore, some primary myeloma cells were also sensitive to artesunate at doses around 10 μm. Concentrations of this order are pharmacologically relevant as they can be obtained in plasma after intravenous administration of artesunate for malaria treatment.

CONCLUSION

Our findings indicate that artesunate is a potential drug for treatment of multiple myeloma and DLBCL at doses of the same order as currently in use for treatment of malaria without serious adverse effects.

Canonical TGF-β pathway activity is a predictor of SHH-driven medulloblastoma survival and delineates putative precursors in cerebellar development

Medulloblastoma (MB) is the most common malignant brain tumor of childhood. Very little is known about aggressive forms of this disease, such as metastatic or recurrent MBs. In order to identify pathways involved in aggressive MB pathophysiology, we performed unbiased, whole genome microarrays on MB tumors at both the human and murine levels. Primary human MBs were compared, transcriptomically, to their patient-matched recurrent or metastatic tumors. Expression profiling was also performed on murine tumors from two spontaneously developing MB mouse models (Ptch+/- and Smo/Smo) that present with differing clinical severities. At both the human and murine levels we identified transforming growth factor-beta (TGF-β) as a potential contributor to MB progression/metastasis. Smad3, a major downstream component of the TGF-β pathway, was also evaluated using immunohistochemistry in malignant human tissues and was shown to correlate with MB metastasis and survival. Similarly, Smad3 expression during development identified a subset of cerebellar neuronal precursors as putative cells of origin for the Smad3-positive MBs. To our knowledge, this is the first study that links TGF-β to MB pathogenesis. Our research suggests that canonical activation of this pathway leads to better prognosis for patients.

Role of Smad proteins in resistance to BMP-induced growth inhibition in B-cell lymphoma

Bone morphogenetic protein (BMP) expression and signaling are altered in a variety of cancers, but the functional impact of these alterations is uncertain. In this study we investigated the impact of expression of multiple BMPs and their signaling pathway components in human B-cell lymphoma. BMP messages, in particular BMP7, were detected in normal and malignant B cells. Addition of exogenous BMPs inhibited DNA synthesis in most lymphoma cell lines examined, but some cell lines were resistant. Tumor specimens from three out of five lymphoma patients were also resistant to BMPs, as determined by no activation of the BMP effectors Smad1/5/8. We have previously shown that BMP-7 potently induced apoptosis in normal B cells, which was in contrast to no or little inhibitory effect of this BMP in the lymphoma cells tested. BMP-resistance mechanisms were investigated by comparing sensitive and resistant cell lines. While BMP receptors are downregulated in many cancers, we documented similar receptor levels in resistant and sensitive lymphoma cells. We found a positive correlation between activation of Smad1/5/8 and inhibition of DNA synthesis. Gene expression analysis of two independent data sets showed that the levels of inhibitory Smads varied across different B-cell lymphoma. Furthermore, stable overexpression of Smad7 in two different BMP-sensitive cell lines with low endogenous levels of SMAD7, rendered them completely resistant to BMPs. This work highlights the role of Smads in determining the sensitivity to BMPs and shows that upregulation of Smad7 in cancer cells is sufficient to escape the negative effects of BMPs.

Bone morphogenetic protein 4-a fascinating regulator of cancer cell behavior

Bone morphogenetic proteins (BMPs) are extracellular signaling molecules that belong to the transforming growth factor β (TGFβ) superfamily and are well-known for their indispensable roles in vertebrate development. In recent years, important new information has been generated on the contribution of BMP family members, such as BMP4, in cancer pathogenesis. First of all, BMP4 gene variants have been shown to predispose to colorectal cancer. In sporadic cancer, BMP4 expression levels are commonly altered in many tumor types and have been linked to patient prognosis in hepatocellular and ovarian cancer. In terms of BMP4 function in cancer cells, the majority of studies demonstrate that BMP4 suppresses cell growth both in vitro and in vivo, and at the same time is able to induce migration, invasion, and epithelial-mesenchymal transition. These latter phenotypes are typically associated with cancer metastasis and progression, and thus BMP4 seems to elicit effects that are both detrimental and beneficial for the cancer cells. The functional effects of BMP4 are not restricted to the control of cell proliferation and mobility, since it also contributes to the regulation of differentiation, apoptosis, and angiogenesis. The latter is especially intriguing since the formation of new blood vessels is a prerequisite for sustained tumor growth and cancer progression. Mainly due to its growth suppressive abilities, BMP4 has been suggested as a possible therapeutic target in cancer cells. However, the other functional characteristics of BMP4, especially the promotion of cell mobility, make such strategies less appealing. Improved knowledge of the downstream mediators of BMP4 effects in cancer cells may allow dissection of the different BMP4-induced phenotypes and thereby generation of specific targeted therapies.

Identification of pluripotent and adult stem cell genes unrelated to cell cycle and associated with poor prognosis in multiple myeloma

Gene expression-based scores used to predict risk in cancer frequently include genes coding for DNA replication, repair or recombination. Using two independent cohorts of 206 and 345 previously-untreated patients with Multiple Myeloma (MM), we identified 50 cell cycle-unrelated genes overexpressed in multiple myeloma cells (MMCs) compared to normal human proliferating plasmablasts and non-proliferating bone marrow plasma cells and which have prognostic value for overall survival. Thirty-seven of these 50 myeloma genes (74%) were enriched in genes overexpressed in one of 3 normal human stem cell populations--pluripotent (18), hematopoietic (10) or mesenchymal stem cells (9)--and only three genes were enriched in one of 5 populations of differentiated cells (memory B lymphocytes, T lymphocytes, polymorphonuclear cells, monocytes, osteoclasts). These 37 genes shared by MMCs and adult or pluripotent stem cells were used to build a stem cell score ((SC)score), which proved to be strongly prognostic in the 2 independent cohorts of patients compared to other gene expression-based risk scores or usual clinical scores using multivariate Cox analysis. This finding highlights cell cycle-unrelated prognostic genes shared by myeloma cells and normal stem cells, whose products might be important for normal and malignant stem cell biology.