BMP4 regulation of human megakaryocytic differentiation is involved in thrombopoietin signaling

BMP signaling in cancer stemness and differentiation

The BMP (Bone morphogenetic protein) signaling pathway plays a central role in metazoan biology, intricately shaping embryonic development, maintaining tissue homeostasis, and influencing disease progression. In the context of cancer, BMP signaling exhibits context-dependent dynamics, spanning from tumor suppression to promotion. Cancer stem cells (CSCs), a modest subset of neoplastic cells with stem-like attributes, exert substantial influence by steering tumor growth, orchestrating therapy resistance, and contributing to relapse. A comprehensive grasp of the intricate interplay between CSCs and their microenvironment is pivotal for effective therapeutic strategies. Among the web of signaling pathways orchestrating cellular dynamics within CSCs, BMP signaling emerges as a vital conductor, overseeing CSC self-renewal, differentiation dynamics, and the intricate symphony within the tumor microenvironment. Moreover, BMP signaling's influence in cancer extends beyond CSCs, intricately regulating cellular migration, invasion, and metastasis. This multifaceted role underscores the imperative of comprehending BMP signaling's contributions to cancer, serving as the foundation for crafting precise therapies to navigate multifaceted challenges posed not only by CSCs but also by various dimensions of cancer progression. This article succinctly encapsulates the diverse roles of the BMP signaling pathway across different cancers, spanning glioblastoma multiforme (GBM), diffuse intrinsic pontine glioma (DIPG), colorectal cancer, acute myeloid leukemia (AML), lung cancer, prostate cancer, and osteosarcoma. It underscores the necessity of unraveling underlying mechanisms and molecular interactions. By delving into the intricate tapestry of BMP signaling's engagement in cancers, researchers pave the way for meticulously tailored therapies, adroitly leveraging its dualistic aspects-whether as a suppressor or promoter-to effectively counter the relentless march of tumor progression.

Perivascular niche cells sense thrombocytopenia and activate hematopoietic stem cells in an IL-1 dependent manner

Hematopoietic stem cells (HSCs) residing in specialized niches in the bone marrow are responsible for the balanced output of multiple short-lived blood cell lineages in steady-state and in response to different challenges. However, feedback mechanisms by which HSCs, through their niches, sense acute losses of specific blood cell lineages remain to be established. While all HSCs replenish platelets, previous studies have shown that a large fraction of HSCs are molecularly primed for the megakaryocyte-platelet lineage and are rapidly recruited into proliferation upon platelet depletion. Platelets normally turnover in an activation-dependent manner, herein mimicked by antibodies inducing platelet activation and depletion. Antibody-mediated platelet activation upregulates expression of Interleukin-1 (IL-1) in platelets, and in bone marrow extracellular fluid in vivo. Genetic experiments demonstrate that rather than IL-1 directly activating HSCs, activation of bone marrow Lepr+ perivascular niche cells expressing IL-1 receptor is critical for the optimal activation of quiescent HSCs upon platelet activation and depletion. These findings identify a feedback mechanism by which activation-induced depletion of a mature blood cell lineage leads to a niche-dependent activation of HSCs to reinstate its homeostasis.

The Hematopoietic TALE-Code Shows Normal Activity of IRX1 in Myeloid Progenitors and Reveals Ectopic Expression of IRX3 and IRX5 in Acute Myeloid Leukemia

Homeobox genes encode transcription factors that control basic developmental decisions. Knowledge of their hematopoietic activities casts light on normal and malignant immune cell development. Recently, we constructed the so-called lymphoid TALE-code that codifies expression patterns of all active TALE class homeobox genes in early hematopoiesis and lymphopoiesis. Here, we present the corresponding myeloid TALE-code to extend this gene signature, covering the entire hematopoietic system. The collective data showed expression patterns for eleven TALE homeobox genes and highlighted the exclusive expression of IRX1 in megakaryocyte-erythroid progenitors (MEPs), implicating this TALE class member in a specific myeloid differentiation process. Analysis of public profiling data from acute myeloid leukemia (AML) patients revealed aberrant activity of IRX1 in addition to IRX3 and IRX5, indicating an oncogenic role for these TALE homeobox genes when deregulated. Screening of RNA-seq data from 100 leukemia/lymphoma cell lines showed overexpression of IRX1, IRX3, and IRX5 in megakaryoblastic and myelomonocytic AML cell lines, chosen as suitable models for studying the regulation and function of these homeo-oncogenes. Genomic copy number analysis of IRX-positive cell lines demonstrated chromosomal amplification of the neighboring IRX3 and IRX5 genes at position 16q12 in MEGAL, underlying their overexpression in this cell line model. Comparative gene expression analysis of these cell lines revealed candidate upstream factors and target genes, namely the co-expression of GATA1 and GATA2 together with IRX1, and of BMP2 and HOXA10 with IRX3/IRX5. Subsequent knockdown and stimulation experiments in AML cell lines confirmed their activating impact in the corresponding IRX gene expression. Furthermore, we demonstrated that IRX1 activated KLF1 and TAL1, while IRX3 inhibited GATA1, GATA2, and FST. Accordingly, we propose that these regulatory relationships may represent major physiological and oncogenic activities of IRX factors in normal and malignant myeloid differentiation, respectively. Finally, the established myeloid TALE-code is a useful tool for evaluating TALE homeobox gene activities in AML.

Altered BMP2/4 Signaling in Stem Cells and Their Niche: Different Cancers but Similar Mechanisms, the Example of Myeloid Leukemia and Breast Cancer

Understanding mechanisms of cancer development is mandatory for disease prevention and management. In healthy tissue, the microenvironment or niche governs stem cell fate by regulating the availability of soluble molecules, cell-cell contacts, cell-matrix interactions, and physical constraints. Gaining insight into the biology of the stem cell microenvironment is of utmost importance, since it plays a role at all stages of tumorigenesis, from (stem) cell transformation to tumor escape. In this context, BMPs (Bone Morphogenetic Proteins), are key mediators of stem cell regulation in both embryonic and adult organs such as hematopoietic, neural and epithelial tissues. BMPs directly regulate the niche and stem cells residing within. Among them, BMP2 and BMP4 emerged as master regulators of normal and tumorigenic processes. Recently, a number of studies unraveled important mechanisms that sustain cell transformation related to dysregulations of the BMP pathway in stem cells and their niche (including exposure to pollutants such as bisphenols). Furthermore, a direct link between BMP2/BMP4 binding to BMP type 1 receptors and the emergence and expansion of cancer stem cells was unveiled. In addition, a chronic exposure of normal stem cells to abnormal BMP signals contributes to the emergence of cancer stem cells, or to disease progression independently of the initial transforming event. In this review, we will illustrate how the regulation of stem cells and their microenvironment becomes dysfunctional in cancer via the hijacking of BMP signaling with main examples in myeloid leukemia and breast cancers.

Proanthocyanidin A1 promotes the production of platelets to ameliorate chemotherapy-induced thrombocytopenia through activating JAK2/STAT3 pathway

BACKGROUND

Chemotherapy-induced thrombocytopenia (CIT) is a severe adverse drug reaction, and the main reason for CIT is the destruction of megakaryocytes (MKs, precursor cells of platelet) in bone marrow by chemotherapy. Peanut skin, the seed coat of Arachis hypogaea L., is a traditional Chinese medicine commonly used to treat thrombocytopenia. However, its active compounds and the mechanisms remain unclear.

PURPOSE

This study aims to clarify the active compounds of peanut skin to exhibit thrombogenic effects against CIT and their underlying mechanisms in vitro and in vivo.

STUDY DESIGN

The bioassay-guided isolation based on the proliferation of MKs was used to explore the possible platelet-enhancing ingredients in peanut skin. HSCCC technique coupled with preparative HPLC was used to separate the active compounds. Dami cells and carboplatin-treated mice model were used to evaluate the thrombogenic effects of PS-1. Network pharmacology, molecular docking, dynamics simulation studies, kinase activity, surface plasmon resonance (SPR), cellular thermal shift assay (CETSA), isothermal dose-response fingerprint (ITDRF_CETSA) and western blot analysis were performed to investigate the mechanisms of PS-1.

RESULTS

Proanthocyanidin A1 (PS-1) and its stereoisomers (PS-2-4) were demonstrated to promote the proliferation of MKs (Dami cells), especially PS-1 (EC₅₀ = 8.58 μM). Further studies demonstrated that PS-1 could induce the differentiation of Dami cells in dose/time-dependent manner. Biological target analysis showed that PS-1 directly bound to JAK2 (KD = 2.06 μM) to exert potent activating effect (EC₅₀ = 0.66 μM). Oral administration of PS-1 (25 or 50 mg/kg) significantly improved CIT, but this effect was confirmed to be inhibited by JAK2 inhibitor AG490, indicating that PS-1 exerted its efficacy through JAK2 in vivo.

CONCLUSION

Proanthocyanins (PS-1-4) derived from peanut skin were first clarified as platelet-enhancing ingredients to improve CIT. The underlying mechanism of PS-1 was proved to promote the proliferation and differentiation of MKs via JAK2/STAT3 pathway both in vitro and in vivo.

A minimal standardized human bone marrow microphysiological system to assess resident cell behavior during normal and pathological processes

Bone marrow is a complex and dynamic microenvironment that provides essential cues to resident cells. We developed a standardized three-dimensional (3D) model to decipher mechanisms that control human cells during hematological and non-hematological processes. Our simple 3D-model is constituted of a biphasic calcium phosphate-based scaffold and human cell lines to ensure a high reproducibility. We obtained a minimal well-organized bone marrow-like structure in which various cell types and secreted extracellular matrix can be observed and characterized by in situ imaging or following viable cell retrieval. The complexity of the system can be increased and customized, with each cellular component being independently modulated according to the issue investigated. Introduction of pathological elements in this 3D-system accurately reproduced changes observed in patient bone marrow. Hence, we have developed a handy and flexible standardized microphysiological system that mimics human bone marrow, allowing histological analysis and functional assays on collected cells.

BMP signaling is required for postnatal murine hematopoietic stem cell self-renewal

Life-long production of blood from hematopoietic stem cells (HSC) is a process of strict modulation. Intrinsic and extrinsic signals govern fate options like self-renewal – a cardinal feature of HSC. Bone morphogenetic proteins (BMP) have an established role in embryonic hematopoiesis, but less is known about its functions in adulthood. Previously, SMAD-mediated BMP signaling has been proven dispensable for HSC. However, the BMP type-II receptor (BMPR-II) is highly expressed in HSC, leaving the possibility that BMP function via alternative pathways. Here, we establish that BMP signaling is required for selfrenewal of adult HSC. Through conditional knockout we show that BMPR-II deficient HSC have impaired self-renewal and regenerative capacity. BMPR-II deficient cells have reduced p38 activation, implying that non-SMAD pathways operate downstream of BMP in HSC. Indeed, a majority of primitive hematopoietic cells do not engage in SMADmediated responses downstream of BMP in vivo. Furthermore, deficiency of BMPR-II results in increased expression of TJP1, a known regulator of self-renewal in other stem cells, and knockdown of TJP1 in primitive hematopoietic cells partly rescues the BMPR-II null phenotype. This suggests TJP1 may be a universal stem cell regulator. In conclusion, BMP signaling, in part mediated through TJP1, is required endogenously by adult HSC to maintain self-renewal capacity and proper resilience of the hematopoietic system during regeneration.

The quiescent fraction of chronic myeloid leukemic stem cells depends on BMPR1B, Stat3 and BMP4-niche signals to persist in patients in remission

Chronic myeloid leukemia arises from the transformation of hematopoietic stem cells by the BCR-ABL oncogene. Though transformed cells are predominantly BCR-ABL-dependent and sensitive to tyrosine kinase inhibitor treatment, some BMPR1B⁺ leukemic stem cells are treatment-insensitive and rely, among others, on the bone morphogenetic protein (BMP) pathway for their survival via a BMP4 autocrine loop. Here, we further studied the involvement of BMP signaling in favoring residual leukemic stem cell persistence in the BM of patients having achieved remission under treatment. We demonstrate by single-cell RNASequencing analysis that a sub-fraction of surviving BMPR1B⁺ leukemic stem cells are co-enriched in BMP signaling, quiescence and stem cell signatures, without modulation of the canonical BMP target genes, but enrichment in actors of the Jak2/Stat3 signaling pathway. Indeed, based on a new model of persisting CD34⁺CD38^– leukemic stem cells, we show that BMPR1B⁺ cells display co-activated Smad1/5/8 and Stat3 pathways. Interestingly, we reveal that only the BMPR1B⁺ cells adhering to stromal cells display a quiescent status. Surprisingly, this quiescence is induced by treatment, while non-adherent BMPR1B⁺ cells treated with tyrosine kinase inhibitors continued to proliferate. The subsequent targeting of BMPR1B and Jak2 pathways decreased quiescent leukemic stem cells by promoting their cell cycle re-entry and differentiation. Moreover, while Jak2-inhibitors alone increased BMP4 production by mesenchymal cells, the addition of the newly described BMPR1B inhibitor (E6201) impaired BMP4-mediated production by stromal cells. Altogether, our data demonstrate that targeting both BMPR1B and Jak2/Stat3 efficiently impacts persisting and dormant leukemic stem cells hidden in their BM microenvironment.

Targeting BMP signaling in the bone marrow microenvironment of myeloid leukemia

The bone morphogenetic protein (BMP) pathway regulates the fate and proliferation of normal hematopoietic stem cells (HSC) as well as interactions with their niche. While BMP2 and BMP4 promote HSC differentiation, only BMP4 maintains HSC pool and favors interactions with their niche. In myeloid leukemia, we have identified intrinsic and extrinsic dysregulations of the BMP pathway in Chronic Myeloid Leukemia (CML) and Acute Myeloid leukemia (AML) responsible for leukemic stem cells (LSC) survival. In AML, BMP pathway alterations sustain and promote resistant immature-like leukemic cells by activating a new signaling cascade. Binding of BMP4 to BMPR1A leads to ΔNp73 expression, which in turn induces NANOG, altogether associated with a poor patient's prognosis. Despite efficient targeted therapies, like Tyrosine Kinase Inhibitors (TKI) in CML, many patients retain LSCs. Our laboratory demonstrated that the BMP pathway sustains a permanent pool of LSCs expressing high levels of BMPR1B receptor, that evolve upon treatment to progressively implement a BMP4 autocrine loop, leading to TKI-resistant cells. Single cell RNA-Seq analysis of TKI-persisting LSCs showed a co-enrichment of BMP with Jak2-signaling, quiescence and stem cell (SC) signatures. Using a new model of persisting LSCs, we recently demonstrated that BMPR1B+ cells display co-activated Smad1/5/8 and Stat3 pathways and could be targeted by blocking BMPR1B/Jak2 signal. Lastly, a specific BMPR1B inhibitor impaired BMP4-mediated LSC protection against TKIs. Altogether, data based on various studies including ours, indicate that BMP targeting could eliminate leukemic cells within a protective bone marrow microenvironment to efficiently impact residual resistance or persistence of LSCs in myeloid leukemia.

Bone marrow niche crosses paths with BMPs: a road to protection and persistence in CML

Chronic myeloid leukaemia (CML) is a paradigm of precision medicine, being one of the first cancers to be treated with targeted therapy. This has revolutionised CML therapy and patient outcome, with high survival rates. However, this now means an ever-increasing number of patients are living with the disease on life-long tyrosine kinase inhibitor (TKI) therapy, with most patients anticipated to have near normal life expectancy. Unfortunately, in a significant number of patients, TKIs are not curative. This low-level disease persistence suggests that despite a molecularly targeted therapeutic approach, there are BCR-ABL1-independent mechanisms exploited to sustain the survival of a small cell population of leukaemic stem cells (LSCs). In CML, LSCs display many features akin to haemopoietic stem cells, namely quiescence, self-renewal and the ability to produce mature progeny, this all occurs through intrinsic and extrinsic signals within the specialised microenvironment of the bone marrow (BM) niche. One important avenue of investigation in CML is how the disease highjacks the BM, thereby remodelling this microenvironment to create a niche, which enables LSC persistence and resistance to TKI treatment. In this review, we explore how changes in growth factor levels, in particular, the bone morphogenetic proteins (BMPs) and pro-inflammatory cytokines, impact on cell behaviour, extracellular matrix deposition and bone remodelling in CML. We also discuss the challenges in targeting LSCs and the potential of dual targeting using combination therapies against BMP receptors and BCR-ABL1.

A new signaling cascade linking BMP4, BMPR1A, ΔNp73 and NANOG impacts on stem-like human cell properties and patient outcome

In a significant number of cases cancer therapy is followed by a resurgence of more aggressive tumors derived from immature cells. One example is acute myeloid leukemia (AML), where an accumulation of immature cells is responsible for relapse following treatment. We previously demonstrated in chronic myeloid leukemia that the bone morphogenetic proteins (BMP) pathway is involved in stem cell fate and contributes to transformation, expansion, and persistence of leukemic stem cells. Here, we have identified intrinsic and extrinsic dysregulations of the BMP pathway in AML patients at diagnosis. BMP2 and BMP4 protein concentrations are elevated within patients’ bone marrow with a BMP4-dominant availability. This overproduction likely depends on the bone marrow microenvironment, since MNCs do not overexpress BMP4 transcripts. Intrinsically, the receptor BMPR1A transcript is increased in leukemic samples with more cells presenting this receptor at the membrane. This high expression of BMPR1A is further increased upon BMP4 exposure, specifically in AML cells. Downstream analysis demonstrated that BMP4 controls the expression of the survival factor ΔNp73 through its binding to BMPR1A. At the functional level, this results in the direct induction of NANOG expression and an increase of stem-like features in leukemic cells, as shown by ALDH and functional assays. In addition, we identified for the first time a strong correlation between ΔNp73, BMPR1A and NANOG expression with patient outcome. These results highlight a new signaling cascade initiated by tumor environment alterations leading to stem-cell features and poor patients’ outcome.

A network map of thrombopoietin signaling

Thrombopoietin (THPO), also known as megakaryocyte growth and development factor (MGDF), is a cytokine involved in the production of platelets. THPO is a glycoprotein produced by liver and kidney. It regulates the production of platelets by stimulating the differentiation and maturation of megakaryocyte progenitors. It acts as a ligand for MPL receptor, a member of the hematopoietic cytokine receptor superfamily and is essential for megakaryocyte maturation. THPO binding induces homodimerization of the receptor which results in activation of JAKSTAT and MAPK signaling cascades that subsequently control cellular proliferation, differentiation and other signaling events. Despite the importance of THPO signaling in various diseases and biological processes, a detailed signaling network of THPO is not available in any publicly available database. Therefore, in this study, we present a resource of signaling events induced by THPO that was manually curated from published literature on THPO. Our manual curation of thrombopoietin pathway resulted in identification of 48 molecular associations, 66 catalytic reactions, 100 gene regulation events, 19 protein translocation events and 43 activation/inhibition reactions that occur upon activation of thrombopoietin receptor by THPO. THPO signaling pathway is made available on NetPath, a freely available human signaling pathway resource developed previously by our group. We believe this resource will provide a platform for scientific community to accelerate further research in this area on potential therapeutic interventions.

The BMP pathway: A unique tool to decode the origin and progression of leukemia

The microenvironment (niche) governs the fate of stem cells (SCs) by balancing self-renewal and differentiation. Increasing evidence indicates that the tumor niche plays an active role in cancer, but its important properties for tumor initiation progression and resistance remain to be identified. Clinical data show that leukemic stem cell (LSC) survival is responsible for disease persistence and drug resistance, probably due to their sustained interactions with the tumor niche. Bone morphogenetic protein (BMP) signaling is a key pathway controlling stem cells and their niche. BMP2 and BMP4 are important in both the normal and the cancer context. Several studies have revealed profound alterations of the BMP signaling in cancer SCs, with major deregulations of the BMP receptors and their downstream signaling elements. This was illustrated in the hematopoietic system by pioneer studies in chronic myelogenous leukemia that may now be expanded to acute myeloid leukemia and lymphoid leukemia, as reviewed here. At diagnosis, cells from the leukemic microenvironment are the major providers of soluble BMPs. Conversely, LSCs display altered receptors and downstream BMP signaling elements accompanied by altered functional responses to BMPs. These studies reveal the role of BMPs in tumor initiation, in addition to their known effects in later stages of transformation and progression. They also reveal the importance of BMPs in fueling cell transformation and expansion by overamplifying a natural SC response. This mechanism may explain the survival of LSCs independently of the initial oncogenic event and therefore may be involved in resistance processes.

Comparison of newly developed anti-bone morphogenetic protein 4 llama-derived antibodies with commercially available BMP4 inhibitors

Due to improved understanding of the role of bone morphogenetic protein 4 (BMP4) in an increasing number of diseases, the development of selective inhibitors of BMP4 is an attractive therapeutic option. The currently available BMP4 inhibitors are not suitable as therapeutics because of their low specificity and low effectiveness. Here, we compared newly generated anti-BMP4 llama-derived antibodies (VHHs) with 3 different types of commercially available BMP4 inhibitors, natural antagonists, small molecule BMPR inhibitors and conventional anti-BMP4 monoclonal antibodies. We found that the anti-BMP4 VHHs were as effective as the natural antagonist or small molecule inhibitors, but had higher specificity. We also showed that commercial anti-BMP4 antibodies were inferior in terms of both specificity and effectiveness. These findings might result from the fact that the VHHs C4C4 and C8C8 target a small region within the BMPR1 epitope of BMP4, whereas the commercial antibodies target other areas of the BMP4 molecule. Our results show that the newly developed anti-BMP4 VHHs are promising antibodies with better specificity and effectivity for inhibition of BMP4, making them an attractive tool for research and for therapeutic applications.

Immature CML cells implement a BMP autocrine loop to escape TKI treatment

The BCR-ABL specific tyrosine kinase inhibitors (TKI) changed the outcome of chronic myeloid leukemia (CML), turning a life-threatening disease into a chronic illness. However, TKI are not yet curative, because most patients retain leukemic stem cells (LSC) and their progenitors in bone marrow and relapse following treatment cessation. At diagnosis, deregulation of the bone morphogenetic protein (BMP) pathway is involved in LSC and progenitor expansion. Here, we report that BMP pathway alterations persist in TKI-resistant patients. In comparison with patients in complete cytogenetic remission, TKI-resistant LSC and progenitors display high levels of BMPR1b expression and alterations of its cellular localization. In vitro treatment of immature chronic phase CML cells with TKI alone, or in combination with interferon-α, results in the preferential survival of BMPR1b⁺ cells. We demonstrated persistent and increasing BMP4 production by patients' mesenchymal cells with resistance. Patient follow-up revealed an increase of BMPR1b expression and in BMP4 expression in LSC from TKI-resistant patients in comparison with diagnosis, while remaining unchanged in sensitive patients. Both leukemic and nonleukemic cells exhibit higher BMP4 levels in the bone marrow of TKI-resistant patients. Exposure to BMP2/BMP4 does not alter BCR-ABL transcript expression but is accompanied by the overexpression of TWIST-1, a transcription factor highly expressed in resistant LSC. By modulating BMP4 or BMPR1b expression, we show that these elements are involved in TKI resistance. In summary, we reveal that persistence of BMP alterations and existence of an autocrine loop promote CML-primitive cells' TKI resistance.

Emerging roles of the bone morphogenetic protein pathway in cancer: potential therapeutic target for kinase inhibition

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor-β (TGF-β) family signalling pathway. Similar to TGF-β, the complex roles of BMPs in development and disease are demonstrated by their dichotomous roles in various cancers and cancer stages. Although early studies implicated BMP signalling in tumour suppressive phenotypes, the results of more recent experiments recognize BMPs as potent tumour promoters. Many of these complexities are becoming illuminated by understanding the role of BMPs in their contextual role in unique cell types of cancer and the impact of their surrounding tumour microenvironment. Here we review the emerging roles of BMP signalling in cancer, with a focus on the molecular underpinnings of BMP signalling in individual cancers as a valid therapeutic target for cancer prevention and treatment.

Megakaryocytic Smad4 Regulates Platelet Function through Syk and ROCK2 Expression

Smad4, a key transcription factor in the transforming growth factor-β signaling pathway, is involved in a variety of cell physiologic and pathologic processes. Here, we characterized megakaryocyte/platelet-specific Smad4 deficiency in mice to elucidate its effect on platelet function. We found that megakaryocyte/platelet-specific loss of Smad4 caused mild thrombocytopenia and significantly extended first occlusion time and tail bleeding time in mice. Smad4-deficient platelets showed reduced agonist-induced platelet aggregation. Further studies showed that a severe defect was seen in integrin α_IIbβ₃-mediated bidirectional (inside-out and outside-in) signaling in Smad4-deficient platelets, as evidenced by reduced fibrinogen binding and α-granule secretion, suppressed platelet spreading and clot retraction. Microarray analysis showed that the expression levels of multiple genes were altered in Smad4-deficient platelets. Among these genes, spleen tyrosine kinase (Syk) and Rho-associated coiled-coil containing protein kinase 2 (ROCK2) were downregulated several times as confirmed by quantitative reverse-transcription polymerase chain reaction and immunoblotting. Further research showed that Smad4 directly regulates ROCK2 transcription but indirectly regulates Syk. Megakaryocyte/platelet-specific Smad4 deficiency caused decreased expression levels of Syk and ROCK2 in platelets. These results suggest potential links among Smad4 deficiency, attenuated Syk, and ROCK2 expression and defective platelet activation.

Long-term exposure to bisphenol A or benzo(a)pyrene alters the fate of human mammary epithelial stem cells in response to BMP2 and BMP4, by pre-activating BMP signaling

Bone morphogenetic protein 2 (BMP2) and BMP4 are key regulators of the fate and differentiation of human mammary epithelial stem cells (SCs), as well as of their niches, and are involved in breast cancer development. We established that MCF10A immature mammary epithelial cells reliably reproduce the BMP response that we previously identified in human primary epithelial SCs. In this model, we observed that BMP2 promotes luminal progenitor commitment and expansion, whereas BMP4 prevents lineage differentiation. Environmental pollutants are known to promote cancer development, possibly by providing cells with stem-like features and by modifying their niches. Bisphenols, in particular, were shown to increase the risk of developing breast cancer. Here, we demonstrate that chronic exposure to low doses of bisphenol A (BPA) or benzo(a)pyrene (B(a)P) alone has little effect on SCs properties of MCF10A cells. Conversely, we show that this exposure affects the response of immature epithelial cells to BMP2 and BMP4. Furthermore, the modifications triggered in MCF10A cells on exposure to pollutants appeared to be predominantly mediated by altering the expression and localization of type-1 receptors and by pre-activating BMP signaling, through the phosphorylation of small mothers against decapentaplegic 1/5/8 (SMAD1/5/8). By analyzing stem and progenitor properties, we reveal that BPA prevents the maintenance of SC features prompted by BMP4, whereas promoting cell differentiation towards a myoepithelial phenotype. Inversely, B(a)P prevents BMP2-mediated luminal progenitor commitment and expansion, leading to the retention of stem-like properties. Overall, our data indicate that BPA and B(a)P distinctly alter the fate and differentiation potential of mammary epithelial SCs by modulating BMP signaling.

BMP2, a key to uncover luminal breast cancer origin linked to pollutant effects on epithelial stem cells niche

Chronic exposure of epithelial cells to high levels of bone morphogenetic protein 2 (BMP2) has recently been demonstrated to initiate stem cell transformation toward a luminal tumor-like phenotype through a BMP2–BMPR1B-dependent mechanism. Carcinogen-driven deregulation of the stem cell niche could therefore represent a driving force to promote transformation and dictate the ultimate breast tumor subtype.

Disequilibrium of BMP2 levels in the breast stem cell niche launches epithelial transformation by overamplifying BMPR1B cell response

Understanding the mechanisms of cancer initiation will help to prevent and manage the disease. At present, the role of the breast microenvironment in transformation remains unknown. As BMP2 and BMP4 are important regulators of stem cells and their niches in many tissues, we investigated their function in early phases of breast cancer. BMP2 production by tumor microenvironment appeared to be specifically upregulated in luminal tumors. Chronic exposure of immature human mammary epithelial cells to high BMP2 levels initiated transformation toward a luminal tumor-like phenotype, mediated by the receptor BMPR1B. Under physiological conditions, BMP2 controlled the maintenance and differentiation of early luminal progenitors, while BMP4 acted on stem cells/myoepithelial progenitors. Our data also suggest that microenvironment-induced overexpression of BMP2 may result from carcinogenic exposure. We reveal a role for BMP2 and the breast microenvironment in the initiation of stem cell transformation, thus providing insight into the etiology of luminal breast cancer.

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High BMP2 levels are provided by endothelial and stroma cells in luminal tumors

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Chronic exposure to high BMP2 levels initiate mammary epithelial transformation

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Luminal tumors likely arise from an amplified BMP2/BMPR1B-mediated normal response

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Radiation and bisphenols perturbed BMP2 production by the mammary niche stroma

miR-99a/100~125b tricistrons regulate hematopoietic stem and progenitor cell homeostasis by shifting the balance between TGFβ and Wnt signaling

miR-99a/100, let-7, and miR-125b paralogs are encoded in two tricistrons and are highly expressed in hematopoietic stem cells (HSCs). Emmrich et al. demonstrate that miR-99a/100∼125b tricistrons are transcribed as a polycistronic message and functionally converge at the combinatorial block of the TGFβ pathway. Down-regulating tumor suppressor genes APC/APC2 stabilized active β-catenin and enhanced Wnt signaling. These tricistronic miRNAs promoted sustained expansion of murine and human HSCs by switching the balance between Wnt and TGFβ signaling.

Although regulation of stem cell homeostasis by microRNAs (miRNAs) is well studied, it is unclear how individual miRNAs genomically encoded within an organized polycistron can interact to induce an integrated phenotype. miR-99a/100, let-7, and miR-125b paralogs are encoded in two tricistrons on human chromosomes 11 and 21. They are highly expressed in hematopoietic stem cells (HSCs) and acute megakaryoblastic leukemia (AMKL), an aggressive form of leukemia with poor prognosis. Here, we show that miR-99a/100∼125b tricistrons are transcribed as a polycistronic message transactivated by the homeobox transcription factor HOXA10. Integrative analysis of global gene expression profiling, miRNA target prediction, and pathway architecture revealed that miR-99a/100, let-7, and miR-125b functionally converge at the combinatorial block of the transforming growth factor β (TGFβ) pathway by targeting four receptor subunits and two SMAD signaling transducers. In addition, down-regulation of tumor suppressor genes adenomatous polyposis coli (APC)/APC2 stabilizes active β-catenin and enhances Wnt signaling. By switching the balance between Wnt and TGFβ signaling, the concerted action of these tricistronic miRNAs promoted sustained expansion of murine and human HSCs in vitro or in vivo while favoring megakaryocytic differentiation. Hence, our study explains the high phylogenetic conservation of the miR-99a/100∼125b tricistrons controlling stem cell homeostasis, the deregulation of which contributes to the development of AMKL.

Primitive CML cell expansion relies on abnormal levels of BMPs provided by the niche and on BMPRIb overexpression

Leukemic stem cells in chronic phase chronic myelogenous leukemia (CP-CML) are responsible for disease persistence and eventual drug resistance, most likely because they survive, expand, and are sustained through interactions with their microenvironment. Bone morphogenetic proteins 2 (BMP2) and 4 (BMP4) regulate the fate and proliferation of normal hematopoietic stem cells, as well as interactions with their niche. We show here that the intrinsic expression of members of the BMP response pathway are deregulated in CML cells with differences exhibited in mature (CD34(-)) and immature (CD34(+)) compartments. These changes are accompanied by altered functional responses of primitive leukemic cells to BMP2 and BMP4 and strong increases in soluble BMP2 and BMP4 in the CML bone marrow. Using primary cells and a cell line mimicking CP-CML, we found that myeloid progenitor expansion is driven by the exposure of immature cells overexpressing BMP receptor Ib to BMP2 and BMP4. In summary, we demonstrate that deregulation of intracellular BMP signaling in primary CP-CML samples corrupts and amplifies their response to exogenous BMP2 and BMP4, which are abnormally abundant within the tumor microenvironment. These results provide new insights with regard to leukemic stem cell biology and suggest possibilities for the development of novel therapeutic tools specifically targeting the CML niche.

Thrombocytopenia induced by the histone deacetylase inhibitor abexinostat involves p53-dependent and -independent mechanisms

Abexinostat is a pan histone deacetylase inhibitor (HDACi) that demonstrates efficacy in malignancy treatment. Like other HDACi, this drug induces a profound thrombocytopenia whose mechanism is only partially understood. We have analyzed its effect at doses reached in patient plasma on in vitro megakaryopoiesis derived from human CD34⁺ cells. When added at day 0 in culture, abexinostat inhibited CFU-MK growth, megakaryocyte (MK) proliferation and differentiation. These effects required only a short incubation period. Decreased proliferation was due to induction of apoptosis and was not related to a defect in TPO/MPL/JAK2/STAT signaling. When added later (day 8), the compound induced a dose-dependent decrease (up to 10-fold) in proplatelet (PPT) formation. Gene profiling from MK revealed a silencing in the expression of DNA repair genes with a marked RAD51 decrease at protein level. DNA double-strand breaks were increased as attested by elevated γH2AX phosphorylation level. Moreover, ATM was phosphorylated leading to p53 stabilization and increased BAX and p21 expression. The use of a p53 shRNA rescued apoptosis, and only partially the defect in PPT formation. These results suggest that HDACi induces a thrombocytopenia by a p53-dependent mechanism along MK differentiation and a p53-dependent and -independent mechanism for PPT formation.

DNA damage in mammalian neural stem cells leads to astrocytic differentiation mediated by BMP2 signaling through JAK-STAT

The consequences of DNA damage generation in mammalian somatic stem cells, including neural stem cells (NSCs), are poorly understood despite their potential relevance for tissue homeostasis. Here, we show that, following ionizing radiation-induced DNA damage, NSCs enter irreversible proliferative arrest with features of cellular senescence. This is characterized by increased cytokine secretion, loss of stem cell markers, and astrocytic differentiation. We demonstrate that BMP2 is necessary to induce expression of the astrocyte marker GFAP in irradiated NSCs via a noncanonical signaling pathway engaging JAK-STAT. This is promoted by ATM and antagonized by p53. Using a SOX2-Cre reporter mouse model for cell-lineage tracing, we demonstrate irradiation-induced NSC differentiation in vivo. Furthermore, glioblastoma assays reveal that irradiation therapy affects the tumorigenic potential of cancer stem cells by ablating self-renewal and inducing astroglial differentiation.

RAD001-mediated STAT3 upregulation and megakaryocytic differentiation

RAD001 is currently used as an immunosuppressant and anticancer drug. Megakaryocyte (MK) differentiation includes development from pluripotent stem cells to proliferation and differentiation toward MK formation and platelet maturation. Our preliminary assay showed that RAD001 might stimulate MK differentiation; however, the exact regulatory mechanisms needed to be elucidated. By the ex vivo assay, RAD001 induced MK differentiation in human haematopoietic stem cells, with both the stimulation of CFU-GM colony formation and CD61 surface marker expression. Then, BALB/c mice were orally administrated with or without agrylin and/or RAD001 for 15 days. The platelet count and bone marrow CFU-MK colony formation were eliminated by agrylin, but unchanged in RAD001 and RAD001 plus agrylin mice. An ex vivo assay of bone marrow-derived stem cells demonstrated that RAD001 increased the number of CFU-MK colonies. The MK count in bone section indicated the decreased effect by agrylin and then recovered by RAD001. The level of plasma thrombopoietin was also enhanced in RAD001-treated mice. The effect of RAD001 on human leukaemic K562 and HEL cells showed the growth inhibition and MK differentiation activities; including morphological observation, CD41 and CD61 expression, and platelet factor 4 secretion. In RAD001-treated HEL cells, p-STAT3 expression, STAT3 translocation, and STAT3-DNA binding activity were up-regulated. Furthermore, STAT3 siRNA decreased the p-STAT3 and CD61 expression, as well as the CD61 fluorescence intensity, indicating that STAT3 may be critical in RAD001-mediated MK differentiation. Conclusion, the present study demonstrated that RAD001 might have the capacity to induce MK differentiation through the up-regulation of STAT3 signalling.

BMP meets AML: induction of BMP signaling by a novel fusion gene promotes pediatric acute leukemia

In this issue of Cancer Cell, Gruber et al. report that a significant proportion of children with acute megakaryoblastic leukemia acquire a translocation that confers enhanced BMP signaling and promotes self-renewal of hematopoietic progenitors. This study presents novel therapeutic targets that may lead to improved therapies for this aggressive leukemia.

An Inv(16)(p13.3q24.3)-encoded CBFA2T3-GLIS2 fusion protein defines an aggressive subtype of pediatric acute megakaryoblastic leukemia

To define the mutation spectrum in non-Down syndrome acute megakaryoblastic leukemia (non-DS-AMKL), we performed transcriptome sequencing on diagnostic blasts from 14 pediatric patients and validated our findings in a recurrency/validation cohort consisting of 34 pediatric and 28 adult AMKL samples. Our analysis identified a cryptic chromosome 16 inversion (inv(16)(p13.3q24.3)) in 27% of pediatric cases, which encodes a CBFA2T3-GLIS2 fusion protein. Expression of CBFA2T3-GLIS2 in Drosophila and murine hematopoietic cells induced bone morphogenic protein (BMP) signaling and resulted in a marked increase in the self-renewal capacity of hematopoietic progenitors. These data suggest that expression of CBFA2T3-GLIS2 directly contributes to leukemogenesis.

Characterization of novel genomic alterations and therapeutic approaches using acute megakaryoblastic leukemia xenograft models

Acute megakaryoblastic leukemia (AMKL) is a heterogeneous disease generally associated with poor prognosis. Gene expression profiles indicate the existence of distinct molecular subgroups, and several genetic alterations have been characterized in the past years, including the t(1;22)(p13;q13) and the trisomy 21 associated with GATA1 mutations. However, the majority of patients do not present with known mutations, and the limited access to primary patient leukemic cells impedes the efficient development of novel therapeutic strategies. In this study, using a xenotransplantation approach, we have modeled human pediatric AMKL in immunodeficient mice. Analysis of high-throughput RNA sequencing identified recurrent fusion genes defining new molecular subgroups. One subgroup of patients presented with MLL or NUP98 fusion genes leading to up-regulation of the HOX A cluster genes. A novel CBFA2T3-GLIS2 fusion gene resulting from a cryptic inversion of chromosome 16 was identified in another subgroup of 31% of non-Down syndrome AMKL and strongly associated with a gene expression signature of Hedgehog pathway activation. These molecular data provide useful markers for the diagnosis and follow up of patients. Finally, we show that AMKL xenograft models constitute a relevant in vivo preclinical screening platform to validate the efficacy of novel therapies such as Aurora A kinase inhibitors.

BDNF, produced by a TPO-stimulated megakaryocytic cell line, regulates autocrine proliferation

While human platelets release endogenous brain-derived neurotrophic factor (BDNF) upon activation, a previous report on MEG-01, a megakaryocytic cell line, found no trace of BDNF production, and the pathophysiological function of platelet BDNF has remained elusive. In the present study, we demonstrate that MEG-01 produces BDNF in the presence of TPO and that this serves to potentiate cell proliferation. Our in vitro findings suggest that BDNF regulates MEG-01 proliferation in an autocrine manner, and we suggest that BDNF may be a physiological autocrine regulator of megakaryocyte progenitors.

[BMP and cancer: the Yin and Yang of stem cells]

In a normal context, bone morphogenetic proteins (BMPs), members of the TGFβ superfamily, are key players in adult stem cell biology. They are involved in the control of the overall functional and phenotypic properties of the stem cell population (self-renewal, proliferation, differentiation, apoptosis, quiescence, etc.). They can act directly on the stem cell or through its microenvironment, contributing to the tight balance of this system. In the tumorigenic context, alterations of the BMP signalling are involved in the deregulation of the interaction between stem cells and their microenvironment and, as such, participate to the different steps of the transformation process.

Lineage regulators direct BMP and Wnt pathways to cell-specific programs during differentiation and regeneration

BMP and Wnt signaling pathways control essential cellular responses through activation of the transcription factors SMAD (BMP) and TCF (Wnt). Here, we show that regeneration of hematopoietic lineages following acute injury depends on the activation of each of these signaling pathways to induce expression of key blood genes. Both SMAD1 and TCF7L2 co-occupy sites with master regulators adjacent to hematopoietic genes. In addition, both SMAD1 and TCF7L2 follow the binding of the predominant lineage regulator during differentiation from multipotent hematopoietic progenitor cells to erythroid cells. Furthermore, induction of the myeloid lineage regulator C/EBPα in erythroid cells shifts binding of SMAD1 to sites newly occupied by C/EBPα, whereas expression of the erythroid regulator GATA1 directs SMAD1 loss on nonerythroid targets. We conclude that the regenerative response mediated by BMP and Wnt signaling pathways is coupled with the lineage master regulators to control the gene programs defining cellular identity.

Sensitivity and gene expression profile of fresh human acute myeloid leukemia cells exposed ex vivo to AS602868

PURPOSE

The need for new treatment options for acute myeloid leukemia (AML) is increasing. AS602868 is a novel investigational drug with reported activity on AML cells.

METHODS

We studied gene expression profiles in AML blasts exposed to AS602868 in order to better understand its mechanism of action. We analyzed the in vitro cytotoxicity of AS602868 alone or in combination with daunorubicin, etoposide or cytarabine. To document AS602868-induced IKK2 inhibition in fresh AML cells, a flow cytometry analysis of IκB was performed. Finally, the effect of AS602868 on gene expression in fresh AML cells was analyzed.

RESULTS

The results show that AML cells are globally as sensitive to AS602868 as they are to cytarabine, with large interindividual variations. Combinations with conventional antileukemic agents showed enhanced cytotoxic activity in subsets of patients. IKK2 appeared to be effectively inhibited by 100 μM AS602868 in fresh leukemic cells. Gene expression profiling and gene ontology analyses identified several groups of genes induced/inhibited by exposure to AS602868 and/or exhibiting a correlation with sensitivity to this agent in vitro. Of note, the expression of several genes related to immune function was found to be significantly altered after exposure to AS602868.

CONCLUSION

These data suggest that AS602868 is cytotoxic against fresh human AML blasts and provide insights regarding the mechanisms of cytotoxicity.

Inducible Fli-1 gene deletion in adult mice modifies several myeloid lineage commitment decisions and accelerates proliferation arrest and terminal erythrocytic differentiation

This study investigated the role of the ETS transcription factor Fli-1 in adult myelopoiesis using new transgenic mice allowing inducible Fli-1 gene deletion. Fli-1 deletion in adult induced mild thrombocytopenia associated with a drastic decrease in large mature megakaryocytes number. Bone marrow bipotent megakaryocytic-erythrocytic progenitors (MEPs) increased by 50% without increase in erythrocytic and megakaryocytic common myeloid progenitor progeny, suggesting increased production from upstream stem cells. These MEPs were almost unable to generate pure colonies containing large mature megakaryocytes, but generated the same total number of colonies mainly identifiable as erythroid colonies containing a reduced number of more differentiated cells. Cytological and fluorescence-activated cell sorting analyses of MEP progeny in semisolid and liquid cultures confirmed the drastic decrease in large mature megakaryocytes but revealed a surprisingly modest (50%) reduction of CD41-positive cells indicating the persistence of a megakaryocytic commitment potential. Symmetrical increase and decrease of monocytic and granulocytic progenitors were also observed in the progeny of purified granulocytic-monocytic progenitors and common myeloid progenitors. In summary, this study indicates that Fli-1 controls several lineages commitment decisions at the stem cell, MEP, and granulocytic-monocytic progenitor levels, stimulates the proliferation of committed erythrocytic progenitors at the expense of their differentiation, and is a major regulator of late stages of megakaryocytic differentiation.

CpG-oligodeoxynucleotide inhibits Smad-dependent bone morphogenetic protein signaling: effects on myeloma cell apoptosis and in vitro osteoblastogenesis

The TLR9 agonist CpG-oligodeoxynucleotide (CpG-ODN) with a phosphorothioate backbone (PTO-CpG-ODN) is evaluated in clinical trials as a vaccine adjuvant or as treatment of cancers. Bone morphogenetic proteins (BMPs) regulate growth and differentiation of several cell types, and also induce apoptosis of cancer cells. Cross-talk between BMP- and TLR-signaling has been reported, and we aimed to investigate whether CpG-ODN influenced BMP-induced osteoblast differentiation or BMP-induced apoptosis of malignant plasma cells. We found that PTO-CpG-ODN inhibited BMP-2-induced osteoblast differentiation from human mesenchymal stem cells. Further, PTO-CpG-ODN counteracted BMP-2- and BMP-6-induced apoptosis of the human myeloma cell lines IH-1 and INA-6, respectively. In contrast, PTO-CpG-ODN did not antagonize the antiproliferative effect of BMP-2 on hMSCs or IH-1 cells. Inhibition of Smad-signaling and p38 MAPK-signaling indicated that apoptosis of IH-1 cells is dependent on Smad-signaling downstream of BMP, whereas the antiproliferative effect of BMP-2 on IH-1 cells also involves p38 MAPK-signaling. Together, the data suggested a specific inhibition by PTO-CpG-ODN on BMP-Smad-signaling. Supporting this we found that PTO-CpG-ODN inhibited BMP-induced phosphorylation of receptor-Smads in human mesenchymal stem cells and myeloma cell lines. This effect appeared to be independent of TLR9 because GpC-ODN and other ODNs with the ability to form multimeric structures inhibited Smad-signaling as efficiently as PTO-CpG-ODNs, and because knockdown of TLR9 by small interfering RNA in INA-6 cells did not blunt the effect of PTO-CpG-ODN. In conclusion, our results demonstrate that PTO-CpG-ODN inhibits BMP-signaling, and thus might provoke unwanted TLR9-independent side effects in patients.

Highly efficient osteogenic differentiation of human mesenchymal stem cells by eradication of STAT3 signaling

Human bone marrow-derived mesenchymal stem cells (hMSCs) are promising candidates for cellular therapy owing to their multipotency to differentiate into several cell lineages. Elucidating the signaling events involved in the response of hMSCs to diverse stimulants affecting their differentiation may considerably promote their clinical use. In this study, we attempted to illuminate the molecular signaling networks involved in bone morphogenetic protein (BMP)-stimulated hMSC osteogenic differentiation. We demonstrate that eradication of signal transducers and activators of transcription (STAT) signaling considerably enhances BMP-induced osteogenic differentiation of hMSCs. BMP 2 and 4 are shown for the first time to activate the Janus-activated kinase (JAK)-STAT pathway in hMSC. Specifically, we reveal that JAK2 mediates STAT3 tyrosine phosphorylation in response to the two BMPs, whereas BMP2- and BMP4-induced STAT3 serine phosphorylation involves two divergent cascades, namely the mTOR and ERK1/2 cascades, respectively. Furthermore, elimination of the STAT3 signaling pathway by the inhibitors, AG490 or STAT3 siRNA, results in the acceleration and augmentation of BMPs-induced osteogenic differentiation, thus proposing a role for JAK-STAT signaling as a negative regulator of this process in MSCs. We believe that the findings presented in this study may be the basis for the development of a useful strategy to better control stem cell fate through intervention in molecular signaling networks. Hopefully, such a strategy will include the development of more efficient and controllable protocols for hMSC differentiation and facilitate their use in regenerative medicine.

BMP4 regulates the hematopoietic stem cell niche

Bone morphogenetic protein 4 (BMP4) is required for mesoderm commitment to the hematopoietic lineage during early embryogenesis. However, deletion of BMP4 is early embryonically lethal and its functional role in definitive hematopoiesis is unknown. Consequently, we used a BMP4 hypomorph to investigate the role of BMP4 in regulating hematopoietic stem cell (HSC) function and maintaining steady-state hematopoiesis in the adult. Reporter gene expression shows that Bmp4 is expressed in cells associated with the hematopoietic microenvironment including osteoblasts, endothelial cells, and megakaryocytes. Although resting hematopoiesis is normal in a BMP4-deficient background, the number of c-Kit+, Sca-1+, Lineage- cells is significantly reduced. Serial transplantation studies reveal that BMP4-deficient recipients have a microenvironmental defect that reduces the repopulating activity of wild-type HSCs. This defect is even more pronounced in a parabiosis model that demonstrates a profound reduction in wild-type hematopoietic cells within the bone marrow of BMP4-deficient recipients. Furthermore, wild-type HSCs that successfully engraft into the BMP4-deficient bone marrow show a marked decrease in functional stem cell activity when tested in a competitive repopulation assay. Taken together, these findings indicate BMP4 is a critical component of the hematopoietic microenvironment that regulates both HSC number and function.

Regulation of megakaryocyte maturation and platelet formation

Each day in every human, approximately 1 x 10(11) platelets are produced by the cytoplasmic fragmentation of megakaryocytes (MK), their marrow precursor cells. Platelets are the predominating factor in the process of hemostasis and thrombosis. Recent studies have shown that platelets also play a hitherto unsuspected role in several other processes such as inflammation, innate immunity, neoangiogenesis and tumor metastasis. The late phases of MK differentiation identified by polyploidization, maturation and organized fragmentation of the cytoplasm leading to the release of platelets in the blood stream represent a unique model of differentiation. The molecular and cellular mechanisms regulating platelet biogenesis are better understood and may explain several platelet disorders. This review focuses on MK polyploidization, and platelet formation, and discusses their alteration in some platelet disorders.