The Smad5 Gene Is Involved in the Intracellular Signaling Pathways That Mediate the Inhibitory Effects of Transforming Growth Factor-β on Human Hematopoiesis

New approaches to tackle cytopenic myelofibrosis

Myelofibrosis (MF) is a clonal hematopoietic stem cell neoplasm characterized by constitutional symptoms, splenomegaly, and risks of marrow failure or leukemic transformation and is universally driven by Jak/STAT pathway activation. Despite sharing this pathogenic feature, MF disease behavior can vary widely. MF can generally be categorized into 2 distinct subgroups based on clinical phenotype: proliferative MF and cytopenic (myelodepletive) MF. Compared to proliferative phenotypes, cytopenic MF is characterized by lower blood counts (specifically anemia and thrombocytopenia), more frequent additional somatic mutations outside the Jak/STAT pathway, and a worse prognosis. Cytopenic MF presents unique therapeutic challenges. The first approved Jak inhibitors, ruxolitinib and fedratinib, can both improve constitutional symptoms and splenomegaly but carry on-target risks of worsening anemia and thrombocytopenia, limiting their use in patients with cytopenic MF. Supportive care measures that aim to improve anemia or thrombocytopenia are often ineffective. Fortunately, new treatment strategies for cytopenic MF are on the horizon. Pacritinib, selective Jak2 inhibitor, was approved in 2022 to treat patients with symptomatic MF and a platelet count lower than 50 × 109/L. Several other Jak inhibitors are in development to extend therapeutic benefits to those with either anemia or thrombocytopenia. While many other novel non-Jak inhibitor therapies are in development for MF, most carry a risk of hematologic toxicities and often exclude patients with baseline thrombocytopenia. As a result, significant unmet needs remain for cytopenic MF. Here, we discuss clinical implications of the cytopenic MF phenotype and present existing and future strategies to tackle this challenging disease.

Management of Myeloproliferative Neoplasms in the Molecular Era: From Research to Practice

The 1960 discovery of the Philadelphia chromosome in chronic myeloid leukemia (CML) marked the beginning of the modern genomic era of oncology. In the following years, the molecular underpinnings of CML were unraveled, culminating in the development of the first molecularly targeted therapy: imatinib. Imatinib revolutionized CML management, inducing deep molecular responses for most patients and aligning survival curves with those of age-matched control participants. Five additional tyrosine kinase inhibitors are now approved for CML: dasatinib, nilotinib, bosutinib, ponatinib, and asciminib (approved October 2021). The 2005 discovery of JAK2 mutations in myelofibrosis (MF) sparked enthusiasm that molecularly targeted therapies could have a similar impact in that disease. Three JAK inhibitors are now available for MF: ruxolitinib, fedratinib, and pacritinib (approved February 2022). JAK inhibitors are helpful for improving symptoms and splenomegaly but still only scratch the surface of MF pathophysiology. Clinical research testing novel agents, next-generation JAK inhibitors, and combinations of JAK inhibitors plus novel agents is moving at a tremendous pace in the hope that outcomes for patients with MF may mirror those with CML one day. This review provides an update on the status of clinical care and research for MF and addresses ongoing issues related to CML management.

Resident Self-Tissue of Proinflammatory Cytokines Rather than Their Systemic Levels Correlates with Development of Myelofibrosis in Gata1low Mice

Serum levels of inflammatory cytokines are currently investigated as prognosis markers in myelofibrosis, the most severe Philadelphia-negative myeloproliferative neoplasm. We tested this hypothesis in the Gata1low model of myelofibrosis. Gata1low mice, and age-matched wild-type littermates, were analyzed before and after disease onset. We assessed cytokine serum levels by Luminex-bead-assay and ELISA, frequency and cytokine content of stromal cells by flow cytometry, and immunohistochemistry and bone marrow (BM) localization of GFP-tagged hematopoietic stem cells (HSC) by confocal microscopy. Differences in serum levels of 32 inflammatory-cytokines between prefibrotic and fibrotic Gata1low mice and their wild-type littermates were modest. However, BM from fibrotic Gata1low mice contained higher levels of lipocalin-2, CXCL1, and TGF-β1 than wild-type BM. Although frequencies of endothelial cells, mesenchymal cells, osteoblasts, and megakaryocytes were higher than normal in Gata1low BM, the cells which expressed these cytokines the most were malignant megakaryocytes. This increased bioavailability of proinflammatory cytokines was associated with altered HSC localization: Gata1low HSC were localized in the femur diaphysis in areas surrounded by microvessels, neo-bones, and megakaryocytes, while wild-type HSC were localized in the femur epiphysis around adipocytes. In conclusion, bioavailability of inflammatory cytokines in BM, rather than blood levels, possibly by reshaping the HSC niche, correlates with myelofibrosis in Gata1low mice.

Cell Signaling Pathway Reporters in Adult Hematopoietic Stem Cells

Hematopoietic stem cells (HSCs) develop at several anatomical locations and are thought to undergo different niche regulatory cues originating from highly conserved cell signaling pathways, such as Wnt, Notch, TGF-β family, and Hedgehog signaling. Most insight into these pathways has been obtained by reporter models and loss- or gain of function experiments, yet results differ in many cases according to the approach. In this review, we discuss existing murine reporter models regarding these pathways, considering the genetic constructs and reporter proteins in the context of HSC studies; yet these models are relevant for all other stem cell systems. Lastly, we describe a multi-reporter model to properly study and understand the cross-pathway interaction and how reporter models are highly valuable tools to understand complex signaling dynamics in stem cells.

Colon cancer therapy by focusing on colon cancer stem cells and their tumor microenvironment

Despite many advances and optimization in colon cancer treatment, tumor recurrence and metastases make the development of new therapies necessary. Colon cancer stem cells (CCSCs) are considered as the main triggering factor of cancer progression, recurrence, and metastasis. CCSCs as a result of accumulated genetic and epigenetic alterations and also complex interconnection with the tumor microenvironment (TME) can evolve and convert to full malignant cells. Mounting evidence suggests that in cancer therapy both CCSCs and non-CCSCs in TME have to be regarded to break through the limitation of current therapies. In this regard, stem cell capabilities of some non-CCSCs may arise inside the TME condition. Therefore, a deep knowledge of regulatory mechanisms, heterogeneity, specific markers, and signaling pathways of CCSCs and their interconnection with TME components is needed to improve the treatment of colorectal cancer and the patient's life quality. In this review, we address current different targeted therapeutic options that target cell surface markers and signaling pathways of CCSCs and other components of TME. Current challenges and future perspectives of colon cancer personalized therapy are also provided here. Taken together, based on the deep understanding of biology of CCSCs and using three-dimensional culture technologies, it can be possible to reach successful colon cancer eradication and improvise combination targeted therapies against CCSCs and TME.

Novel strategies for the treatment of myelofibrosis driven by recent advances in understanding the role of the microenvironment in its etiology

Myelofibrosis is the advanced stage of the Philadelphia chromosome-negative myeloproliferative neoplasms (MPNs), characterized by systemic inflammation, hematopoietic failure in the bone marrow, and development of extramedullary hematopoiesis, mainly in the spleen. The only potentially curative therapy for this disease is hematopoietic stem cell transplantation, an option that may be offered only to those patients with a compatible donor and with an age and functional status that may face its toxicity. By contrast, with the Philadelphia-positive MPNs that can be dramatically modified by inhibitors of the novel BCR-ABL fusion-protein generated by its genetic lesion, the identification of the molecular lesions that lead to the development of myelofibrosis has not yet translated into a treatment that can modify the natural history of the disease. Therefore, the cure of myelofibrosis remains an unmet clinical need. However, the excitement raised by the discovery of the genetic lesions has inspired additional studies aimed at elucidating the mechanisms driving these neoplasms towards their final stage. These studies have generated the feeling that the cure of myelofibrosis will require targeting both the malignant stem cell clone and its supportive microenvironment. We will summarize here some of the biochemical alterations recently identified in MPNs and the novel therapeutic approaches currently under investigation inspired by these discoveries.

MicroRNA-130b is involved in bovine granulosa and cumulus cells function, oocyte maturation and blastocyst formation

Background

Oocyte maturation and preimplantation embryo development are controlled by array of genes that are post-transcriptionally regulated by microRNAs. With respect to this, previously, we identified altered expression of microRNA-130b (miR-130b) during oocyte maturation. Here, we aimed to investigate the role of miR-130b in bovine granulosa and cumulus cell function, oocyte maturation and preimplantation embryo development using gain- and loss-of- function approach.

Methods

For this study, the granulosa cells, cumulus cells and the oocytes were collected from ovaries obtained from slaughterhouse. The genes targeted by miR-130b were identified using dual-luciferase reporter assay. The role of miR-130b in granulosa and cumulus cell function was investigated by increasing and inhibiting its expression in in vitro cultured cells using miR-130b precursor and inhibitor, respectively while the role of miR-130b on oocyte development, immature oocytes were microinjected with miR-130b precursor and inhibitor and the polar body extrusion, the proportion of oocytes reaching to metaphase II stage and the mitochondrial were determined in each oocyte group 22 h after microinjection. Moreover, to investigate the role of miR-130b during preimplantation embryo development, zygote stage embryos were microinjected with miR-130b precursor or inhibitor and the cleavage rate, morula and blastocyst formation was analyzed in embryos derived from each zygote group after in vitro culture.

Results

The luciferase assay showed that SMAD5 and MSK1 genes were identified as the direct targets of miR-130b. Overexpression of miR-130b increased the granulosa and cumulus cell proliferation, while inhibition showed the opposite phenotype. Apart from these, modulation of miR-130b altered the lactate production and cholesterol biosynthesis in cumulus cells. Furthermore, inhibition of miR-130b expression during oocyte in vitro maturation reduced the first polar body extrusion, the proportion of oocytes reaching to metaphase II stage and the mitochondrial activity, while inhibition of miR-130b during preimplantation embryo development significantly reduced morula and blastocyst formation.

Conclusion

This study demonstrated that in vitro functional modulation of miR-130b affected granulosa and cumulus cell proliferation and survival, oocyte maturation, morula and blastocyst formation suggesting that miR-130b is involved in bovine oocyte maturation and preimplantation embryo development.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-017-0336-1) contains supplementary material, which is available to authorized users.

Preclinical rationale for TGF-β inhibition as a therapeutic target for the treatment of myelofibrosis

To assess the role of abnormal transforming growth factor-beta (TGF-β) signaling in the pathogenesis of primary myelofibrosis (PMF), the effects of the TGF-β receptor-1 kinase inhibitor SB431542 on ex vivo expansion of hematopoietic cells in cultures from patients with JAK2V617+-polycythemia vera (PV) or PMF (JAK2V617F+, CALRpQ365f+, or unknown) and from normal sources (adult blood, AB, or cord blood, CB) were compared. In cultures of normal sources, SB431542 significantly increased by 2.5-fold the number of progenitor cells generated by days 1-2 (CD34+) and 6 (colony-forming cells) (CB) and that of precursor cells, mostly immature erythroblasts, by days 14-17 (AB and CB). In cultures of JAK2V617F+-PV, SB431542 increased by twofold the numbers of progenitor cells by day 10 and had no effect on that of precursors cells by days 12-17 (∼fourfold increase in all cases). In contrast, SB431542 had no effect on the number of either progenitor or precursor cells in cultures of JAK2V617F+ and CALR pQ365fs+ PMF. These ontogenetic- and disease-specific effects were associated with variegation in the ability of SB431542 to induce CD34+ cells from AB (increased), CB (decreased), or PV and PMF (unaffected) into cycle and erythroblasts in proliferation (increased for AB and PV and unaffected for CB and PMF). Differences in expansion of erythroblasts from AB, CB, and PV were associated with differences in activation of TGF-β signaling (SHCY317, SMAD2S245/250/255, and SMAD1S/S/SMAD5S/S/SMAD8S/S) detectable in these cells by phosphoproteomic profiling. In conclusion, treatment with TGF-β receptor-1 kinase inhibitors may reactivate normal hematopoiesis in PMF patients, providing a proliferative advantage over the unresponsive malignant clone.

TGF-β signalling in tumour associated macrophages

Tumour associated macrophages (TAM) represent an important component of tumour stroma. They develop under the influence of tumour microenvironment where transforming growth factor (TGF)β is frequently present. Activities of TAM regulated by TGFβ stimulate proliferation of tumour cells and lead to tumour immune escape. Despite high importance of TGFβ-induction of TAM activities till now our understanding of the mechanism of this induction is limited. We have previously developed a model of type 2 macrophages (M2) resembling certain properties of TAM. We established that in M2 TGFβRII is regulated on the level of subcellular sorting by glucocorticoids. Further studies revealed that in M2 with high levels of TGFβRII on the surface TGFβ activates not only its canonical Smad2/3-mediated signaling, but also Smad1/5-mediated signaling, what is rather typical for bone morphogenetic protein (BMP) stimulation. Complexity of macrophage populations, however, allows assumption that TGFβ signalling may function in different ways depending on the functional state of the cell. To understand the peculiarities of TGFβ signalling in human TAMs experimental systems using primary cells have to be developed and used together with the modern mathematical modelling approaches.

Experimental and investigational therapies for chemotherapy-induced anemia

INTRODUCTION

In cancer patients, anemia is frequently observed, particularly as a consequence to chemotherapy (chemotherapy-induced anemia, CIA). CIA is treated with Red Blood Cell transfusions and erythropoiesis-stimulating agents (ESAs). However, the use of ESAs in anemic cancer patients is associated with reduced survival time and time to progression. Consequently, new therapeutic options are needed.

AREAS COVERED

In this article, the authors discuss new erythroid-enhancing agents (EEAs) that act differently to erythropoietin. Specifically, the article summarizes the early clinical development of activin antagonists (Sotatercep [ACE-011] and ACE-536) and hepcidin antagonists [NOX-H94]).

EXPERT OPINION

Both Activin RIIA trap agents and hepcidin inhibitors are promising new EEAs, but their safety profile, and their impact on treating CIA, needs to be carefully assessed in controlled clinical trials over longer periods of time. It is also important to carefully evaluate CIA patients to properly assess the physiopathological mechanisms responsible for the development of their anemic condition and provide patients with the most appropriate treatment plan.

The ESA scenario gets complex: from biosimilar epoetins to activin traps

Recombinant human erythropoietin (rhEpo, epoetin) has proved beneficial in preventing transfusion-dependent anaemia in patients with chronic kidney disease. Apart from copied epoetins distributed in less regulated markets, 'biosimilar' epoetins have gained currency in many regions, where they compete with the originals and with rhEpo analogues with prolonged survival in circulation ('biobetter'). Recombinant erythropoiesis stimulating agents are potent and well tolerated. However, their production is costly, and they must be administered by the parenteral route. Hence, other anti-anaemia treatments are being evaluated. Clinical trials are being performed with stabilizers of the hypoxia-inducible transcription factors (HIFs), which increase endogenous Epo production. HIF stabilizers are chemical drugs and they are active on oral administration. However, there is fear that they may promote tumour growth. Epo mimetic peptides have also raised expectations. Yet the prototype peginesatide was recalled after just 1 year of its widespread use in the USA because of serious side-effects including cases of death. Most recently, clinical trials have been initiated with sotatercept, a recombinant soluble activin receptor type 2A IgG-Fc fusion protein. Sotatercept binds distinct members of the transforming growth factor-β family, thereby preventing the inhibitory action of these factors in erythropoiesis. Taken together, rhEpo and its long-acting recombinant analogues will likely remain mainstay of anti-anaemia therapies in the near future.

Complex and context dependent regulation of hematopoiesis by TGF-beta superfamily signaling

The transforming growth factor (TGF)-beta superfamily of growth factors, including the TGF-betas, activins, and bone morphogenetic proteins (BMPs), provide cells with a broad spectrum of regulatory signals through the intracellular Smad pathway. Since loss-of-function studies of a majority of the TGF-beta superfamily members result in embryonic lethality, much of our current knowledge of the TGF-beta superfamily's role in hematopoiesis is generated from studies performed in vitro, or in very early stages of embryonic development. TGF-beta is well documented as a potent inhibitor of hematopoietic stem cell (HSC) proliferation in vitro, while its role in vivo is largely unknown. BMP signaling is crucial for the initiation of hematopoiesis in the developing embryo, although its role in adult hematopoiesis remains elusive. More recently we and others have used conditional knockout models to unravel the role of several components of TGF-beta family signaling in adult hematopoiesis. Here we review the currently known functions for the major factors of this signaling family in embryonic and adult hematopoietic regulation and discuss the context dependency and complexity that permeate this regulation.

Transforming Growth Factor-βSignaling in Normal and Malignant Hematopoiesis

Transforming growth factor-beta (TGF-beta) is an important physiologic regulator of cell growth and differentiation. TGF-beta has been shown to inhibit the proliferation of quiescent hematopoietic stem cells and stimulate the differentiation of late progenitors to erythroid and myeloid cells. Insensitivity to TGF-beta is implicated in the pathogenesis of many myeloid and lymphoid neoplasms. Loss of extracellular TGF receptors and disruption of intracellular TGF-beta signaling by oncogenes is seen in a variety of malignant and premalignant states. TGF-beta can also affect tumor growth and survival by influencing the secretion of other growth factors and manipulation of the tumor microenvironment. Recent development of small molecule inhibitors of TGF-beta receptors and other signaling intermediaries may allow us to modulate TGF signaling for future therapeutic interventions in cancer.

Inactivation of Smad5 in endothelial cells and smooth muscle cells demonstrates that Smad5 is required for cardiac homeostasis

Smads are intracellular signaling proteins that transduce signals elicited by members of the transforming growth factor (TGF)-beta superfamily. Smad5 and Smad1 are highly homologous, and they mediate primarily bone morphogenetic protein (Bmp) signals. We used the Cre-loxP system and Sm22-Cre and Tie-1-Cre mice to study the function of Smad5 in the developing blood vessel wall. Analysis of embryos demonstrated that deletion of Smad5 in endothelial or smooth muscle cells resulted in a normal organization of embryonic and extra-embryonic vasculature. Angiogenic assays performed in adult mice revealed that mutant mice display a comparable angiogenic and vascular remodeling response to control mice. In Sm22-Cre; Smad5(fl/-) mice, Smad5 is also deleted in cardiomyocytes. Echocardiographic analysis on those 9-month-old female mice demonstrated larger left ventricle internal diameters and decreased fractional shortening compared with control littermates without signs of cardiac hypertrophy. The decreased cardiac contractility was associated with a decreased performance in a treadmill experiment. In isolated cardiomyocytes, fractional shortening was significantly reduced compared with control cells. These data demonstrate that restricted deletion of Smad5 in the blood vessel wall results in viable mice. However, loss of Smad5 in cardiomyocytes leads to a mild heart defect.

Signal transduction pathways that contribute to myeloid differentiation

The production of mature, differentiated myeloid cells is regulated by the action of hematopoietic cytokines on progenitor cells in the bone marrow. Cytokines drive the process of myeloid differentiation by binding to specific cell-surface receptors in a stage- and lineage-specific manner. Following the binding of a cytokine to its cognate receptor, intracellular signal-transduction pathways become activated that facilitate the myeloid differentiation process. These intracellular signaling pathways may promote myelopoiesis by stimulating expansion of a progenitor pool, supporting cellular survival during the differentiation process, or by directly driving the phenotypic changes associated with differentiation. Ultimately, pathways that drive the differentiation process converge on myeloid transcription factors, including PU.1 and the C/EBP family, that are critical for differentiation to proceed. While much is known about the cytokines, cytokine receptors and transcription factors that regulate myeloid differentiation, less is known about the precise roles that specific signaling mediators play in promoting myeloid differentiation. Recently, however, the application of novel pharmacologic inhibitors, siRNA strategies, and transgenic and knockout models has begun to shed light on the involvement and function of signaling pathways in normal myeloid differentiation. This review will discuss the roles that key signaling pathways and mediators play in myeloid differentiation.

Smad5 is dispensable for adult murine hematopoiesis

Smad5 is known to transduce intracellular signals from bone morphogenetic proteins (BMPs), which belong to the transforming growth factor-β (TGF-β) superfamily and are involved in the regulation of hematopoiesis. Recent findings suggest that BMP4 stimulates proliferation of human primitive hematopoietic progenitors in vitro, while early progenitors from mice deficient in Smad5 display increased self-renewal capacity in murine embryonic hematopoiesis. Here, we evaluate the role of Smad5 in the regulation of hematopoietic stem cell (HSC) fate decisions in adult mice by using an inducible MxCre-mediated conditional knockout model. Surprisingly, analysis of induced animals revealed unperturbed cell numbers and lineage distribution in peripheral blood (PB), bone marrow (BM), and the spleen. Furthermore, phenotypic characterization of the stem cell compartment revealed normal numbers of primitive lin–Sca-1+c-Kit+ (LSK) cells in Smad5–/– BM. When transplanted in a competitive fashion into lethally irradiated primary and secondary recipients, Smad5-deficient BM cells competed normally with wild-type (wt) cells, were able to provide long-term reconstitution for the hosts, and displayed normal lineage distribution. Taken together, Smad5-deficient HSCs from adult mice show unaltered differentiation, proliferation, and repopulating capacity. Therefore, in contrast to its role in embryonic hematopoiesis, Smad5 is dispensable for hematopoiesis in the adult mouse.

Genetic polymorphisms in patients with myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a family of clonal disorders characterized by dyshematopoiesis and susceptibility to acute myelogenous leukemia. Tumor necrosis factor-a (TNF-alpha) and transforming growth factor-beta (TGF-beta) are cytokines that play key roles in the pathogenesis of MDS. There have been several reports on the presence of genetic polymorphisms in the DNA sequence encoding the leader sequence of the TGF-beta protein, and in the -308 promoter region of TNF-alpha. The association between TNF-alpha and TGF-beta1 gene polymorphism and the susceptibility to MDS and the progression of the disease was investigated. As compared with healthy control subjects (n = 74), patients with MDS (n = 55) showed no significant deviations in genotype or allele frequencies of TNF-alpha. Similarly, there were no differences in the distribution of TNF-alpha genotypes between the MDS patients with only anemia (mild group) and those with bi- or pancytopenia (severe group). On the other hand the TT homozygosity at codon 10 in exon 1 of TGF-beta1 gene was associated with a severe degree of cytopenia [95% CI OR = 4.889, p = 0.0071]. These findings suggest that the investigated genetic polymorphisms do not predispose to the development of MDS, but that TGF-beta1 gene polymorphism may affect the disease progression.

Gene Expression Analysis of Human Epidermal Keratinocytes after N-Acetyl L-Cysteine Treatment Demonstrates Cell Cycle Arrest and Increased Differentiation

OBJECTIVES

Several cancer prevention programmes have previously been executed using treatment of antioxidant compounds. The antioxidant N-acetyl L-cysteine (NAC), a membrane-permeable aminothiol, is a sulfhydryl reductant reducing oxidised glutathione, as well as being a precursor of intracellular cysteine and glutathione. A previous report based on the cellular response to NAC treatment showed that NAC induced a 10-fold more rapid differentiation in normal primary keratinocytes as well as a reversion of a colon carcinoma cell line from neoplastic proliferation to apical-basolateral differentiation. In order to investigate molecular events underlying the changes in proliferation and differentiation induced by NAC treatment, we performed global gene expression analysis of normal human epidermal keratinocytes in a time series.

METHODS

Treated samples were compared to untreated samples through a reference design using a spotted cDNA array comprising approximately 30,000 features. B statistics was used to identify differentially expressed genes, and RT-PCR of a selected set of genes was performed to verify differential expression.

RESULTS

The number of differentially expressed genes increased over time, starting with 0 at 30 min, 73 at 3 h and increasing to 952 genes at 48 h. Results of the expression analysis showed arrest of the cell cycle and an upregulation of cytoskeletal reorganisation, implicating increased differentiation. A comparison to gene ontology groups indicated downregulation of a large number of genes involved in cell proliferation and regulation of the cell cycle.

CONCLUSIONS

A significant fraction of the differentially expressed genes could be classified according to their role in the differentiation process, demonstrating that NAC regulates the conversion from proliferation to differentiation at a transcriptional level.

Clinical Importance of Transforming Growth Factor-β but Not of Tumor Necrosis Factor-α Gene Polymorphisms in Patients with the Myelodysplastic Syndrome Belonging to the Refractory Anemia Subtype

OBJECTIVES

Tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta (TGF-beta) are cytokines that play key roles in the myelodysplastic syndrome (MDS). There have been several reports on the presence of genetic polymorphisms in the DNA sequence encoding the leader sequence of the TGF-beta1 protein, located in codon 10 in exon 1 and in the -308 promoter region of TNF-alpha. The objective of this study was to investigate the association between TNF-alpha and TGF-beta1 gene polymorphisms and the susceptibility to MDS and the progression of the disease among patients with MDS belonging to the refractory anemia (RA) subtype.

METHODS

The diagnosis of MDS (n = 50) was based on the FAB criteria. The TNF-alpha genotypes were analyzed by PCR-RFLP and the TGF-beta genotypes were analyzed using an amplification refractory mutation system.

RESULTS AND CONCLUSIONS

Compared with healthy control subjects, patients with RA showed no significant deviations in genotype or allele frequencies of TNF-alpha. The TT homozygosity at codon 10 of TGF-beta1 was significantly higher among patients with bi- or pancytopenia (severe group) than in the patients with anemia only (mild group; odds ratio = 6.99, p = 0.003). These findings suggest that the TGF-beta1 gene polymorphism in codon 10 and the -308 TNF-alpha gene polymorphism do not predispose to the development of RA, but the TGF-beta1 gene polymorphism may affect disease progression.

Smad5: signaling roles in hematopoiesis and osteogenesis

Smad5 belongs to the receptor-activated Smad that function as intracellular signal transducers for transforming growth factor-beta superfamily. Smad5 protein is composed of N-terminal domain responsible for DNA-binding, C-terminal domain primarily required for protein-protein interaction, and the linker region containing motif essential for ubiquitinized degradation. Recent investigation reveals Smad5 as a negative regulator of embryonic hematopoiesis in a haploinsufficiency fashion, helping to elucidate the cytogenetic mechanism, by which Smad5 acts as leukemia suppressor. To date, osteogenesis governed by Smad5-mediated signals is delicately orchestrated by its comprehensive interactions with global osteogenesis regulator Runx2, transcriptional repressor Rob and Smad-interacting protein 1. Further delineation of its roles in hematopoiesis and osteogenesis will undoubtedly provide valuable insights into leukemia therapy and tissue engineering.

Molecular Mechanisms Behind the Dose-Dependent Differential Activation of MAPK Pathways Induced by Transforming Growth Factor-β1 in Hematopoietic Cells

Transforming growth factor-beta (TGF-beta) controls a wide range of cellular responses, including cell proliferation, lineage determination, differentiation, and apoptosis, and figures prominently in animal development. It is considered as a pleiotropic factor because it can exert a positive or negative effect on various cellular processes depending on developmental stage of the target cell, its microenvironment, and also its biochemical make up. It has been shown to have a strong inhibitory effect on hematopoietic stem cell proliferation and differentiation. We have earlier shown that TGF-beta1 exerts a bidirectional effect on hematopoietic cell proliferation as a function of its concentration. Although it acted as an inhibitor at high concentrations, at low concentrations it stimulated the stem/progenitor cells. We also provided evidence that the differential activation of mitogen-activated protein kinase pathways was responsible for the observed bidirectional effect. In the present study, we examined the molecular mechanism behind this phenomenon. We observed that the high inhibitory concentrations of TGF-beta1 induced a strong phosphorylation of SMAD 3 and also activated stress kinase-related transcription factors, namely c-Jun and ATF-2. On the other hand, low stimulatory concentrations acted in a SMAD 3-independent pathway and activated STAT proteins. Our results clearly show that differential activation of signal transduction pathways by TGF-beta1 as a function of its concentration underlies its bidirectional effect on hematopoietic cells.

Different steroids co-regulate long-term expansion versus terminal differentiation in primary human erythroid progenitors

Outgrowth, long-term self-renewal, and terminal maturation of human erythroid progenitors derived from umbilical cord blood in serum-free medium can be modulated by steroid hormones. Homogeneous erythroid cultures, as characterized by flow cytometry and dependence on a specific mixture of physiologic proliferation factors, were obtained within 8 days from a starting population of mature and immature mononuclear cells. Due to previous results in mouse and chicken erythroblasts, the proliferation-promoting effect of glucocorticoids was not unexpected. Surprisingly, however, androgen had a positive effect on the sustained expansion of human female but not male erythroid progenitors. Under optimal conditions, sustained proliferation of erythroid progenitors resulted in a more than 10(9)-fold expansion within 60 days. Terminal erythroid maturation was significantly improved by adding human serum and thyroid hormone (3,5,3'-triiodothyronine [T3]) to the differentiation medium. This resulted in highly synchronous differentiation of the cells toward enucleated erythrocytes within 6 days, accompanied by massive size decrease and hemoglobin accumulation to levels comparable to those in peripheral blood erythrocytes. Thus, obviously, different ligand-activated nuclear hormone receptors massively influence the decision between self-renewal and terminal maturation in the human erythroid compartment.

Differential activation of MAPK signaling pathways by TGF-beta1 forms the molecular mechanism behind its dose-dependent bidirectional effects on hematopoiesis

We have earlier reported that transforming growth factor-beta1 (TGF-beta1), a well-known inhibitor of hematopoiesis, stimulated colony formation from adult human bone marrow mononuclear cells (BM MNC) when used at low concentrations. We examined the possible molecular mechanism behind this bidirectional effect using CD34+ cells isolated from human BM for clonal assays and the KG1a cell line as a model system for analysis of proteins for signaling pathways by immunoblotting. We found that TGF-beta1 at low doses (picogram levels) stimulated the colony formation from CD34+ cells, indicating that these progenitors form the direct target of stimulatory action of TGF-beta1. CD34+ cells were found to be more sensitive to the TGF-beta1 concentration than the total MNC. We used the KG1a cell line as a model system for identification of mitogen-activated protein kinase (MAPK) and AKT signaling pathways involved in the process. Low doses strongly induced p44/42 MAPK phosphorylation, whereas high doses induced p38 activation. Use of specific p44/42 MAPK inhibitor PD 98059 in the colony assay abrogated the stimulatory effect of low TGF-beta1. On the other hand, use of p38 MAPK inhibitor SB 203580 along with low TGF-beta1 concentrations had a synergistic effect on stimulation of colony formation. Treatment of BM MNC with Anisomycin, which activates stress kinases, resulted in a dose-dependent inhibition of colony formation. This inhibition could not be rescued by stimulatory doses of TGF-beta1. Phosphorylation of AKT was found to occur in a dose-dependent way but declined slightly at the highest concentration used (10 ng/ml). Inhibition of the AKT pathway by LY 294002 strongly suppressed colony formation. These data indicate clearly that sustained activation of p44/42 MAPK perhaps forms the stimulatory signal induced by low TGF-beta1, whereas activation of p38 forms the inhibitory pathway.

Generation of a floxed allele of Smad5 for cre-mediated conditional knockout in the mouse

Smad5 is a member of the Smad family of intracellular mediators of BMP signals and in endothelial cells of TGF-beta signals. We and others previously showed that loss of Smad5 in the mouse results in embryonic lethality (between E9.5-E11.5) due to multiple embryonic and extraembryonic defects. To circumvent the early embryonic lethality and to allow tissue- and time-specific Smad5 inactivation, we created a conditional Smad5 allele in the mouse. Floxed Smad5 (Smad5(flE2,Neo/flE2,Neo)) mice were generated in which both exon2 and the Neo-cassette were flanked by loxP sites. Here we demonstrate that embryos with ubiquitous Cre-mediated deletion of Smad5 (Smad5(flDeltaE2/flDeltaE2)) phenocopy the conventional Smad5 knockout mice. Smad5(flE2/flE2) mice are now available and will be a valuable tool to analyze the role of Smad5 beyond its crucial early embryonic function throughout development and postnatal life.

Up-regulated Smad5 mediates apoptosis of gastric epithelial cells induced by Helicobacter pylori infection

The gastric pathogen Helicobacter pylori activates epithelial cell signaling pathways, and its infection induces changes in the expression of several genes in infected human gastric tissues. Recent studies have indicated that the ability of H. pylori to regulate epithelial cell responses depends on the presence of an intact cag pathogenicity island (cagPAI). We investigated altered mRNA expression of gastric epithelial cells after infection with H. pylori, both cagPAI-positive and cagPAI-negative strains, by cDNA microarray, reverse transcription PCR, and Northern blot analysis. Our results indicated that cagPAI-positive H. pylori strains (ATCC 43504 and clinical isolated strains) significantly activated Smad5 mRNA expression of human gastric epithelial cells (AGS, KATOIII, MKN28, and MKN45). We further examined whether the up-regulated Smad5 was related to apoptosis of gastric epithelial cells induced by H. pylori. Smad5 RNA interference completely inhibited H. pylori-induced apoptosis. These results suggest that Smad5 is up-regulated in gastric epithelial cells through the presence of cagPAI of H. pylori and that Smad5 mediates apoptosis of gastric epithelial cells induced by H. pylori infection.

Levels of phospho-Smad2/3 are sensors of the interplay between effects of TGF-beta and retinoic acid on monocytic and granulocytic differentiation of HL-60 cells

We have investigated the role of Smad family proteins, known to be important cytoplasmic mediators of signals from the transforming growth factor-beta (TGF-beta) receptor serine/threonine kinases, in TGF-beta-dependent differentiation of hematopoietic cells, using as a model the human promyelocytic leukemia cell line, HL-60. TGF-beta-dependent differentiation of these cells to monocytes, but not retinoic acid-dependent differentiation to granulocytes, was accompanied by rapid phosphorylation and nuclear translocation of Smad2 and Smad3. Vitamin D(3) also induced phosphorylation of Smad2/3 and monocytic differentiation; however the effects were indirect, dependent on its ability to induce expression of TGF-beta1. Simultaneous treatment of these cells with TGF-beta1 and all-trans-retinoic acid (ATRA), which leads to almost equal numbers of granulocytes and monocytes, significantly reduced the level of phospho-Smad2/3 and its nuclear accumulation, compared with that in cells treated with TGF-beta1 alone. TGF-beta1 and ATRA activate P42/44 mitogen-activated protein (MAP) kinase with nearly identical kinetics, ruling out its involvement in these effects on Smad phosphorylation. Addition of the inhibitor-of-protein serine/threonine phosphatases, okadaic acid, blocks the ATRA-mediated reduction in TGF-beta-induced phospho-Smad2 and shifts the differentiation toward monocytic end points. In HL-60R mutant cells, which harbor a defective retinoic acid receptor-alpha (RAR-alpha), ATRA is unable to reduce levels of TGF-beta-induced phospho-Smad2/3, coincident with its inability to differentiate these cells along granulocytic pathways. Together, these data suggest a new level of cross-talk between ATRA and TGF-beta, whereby a putative RAR-alpha-dependent phosphatase activity limits the levels of phospho-Smad2/3 induced by TGF-beta, ultimately reducing the levels of nuclear Smad complexes mediating the TGF-beta-dependent differentiation of the cells to monocytic end points.

Molecular profiling of anemia in acute renal allograft rejection using DNA microarrays

Compromised renal function after renal allograft transplantation often results in anemia in the recipient. Molecular mechanisms leading to anemia during acute rejection are not fully understood; inadequate erythropoietin production and iron deficiency have been reported to be the main contributors. To increase our understanding of the molecular events underlying anemia in acute rejection, we analyzed the gene expression profiles of peripheral blood lymphocytes (PBL) from four pediatric renal allograft recipients with acute rejection and concurrent anemia, using DNA microarrays containing 9000 human cDNA clones (representing 7469 unique genes). In these anemic rejecting patients, an 'erythropoiesis cluster' of 11 down-regulated genes was identified, involved in hemoglobin transcription and synthesis, iron and folate binding and transport. Additionally, some alloimmune response genes were simultaneously down-regulated. An independent data set of 36 PBL samples, some with acute rejection and some with concurrence of acute rejection and anemia, were analyzed to support a possible association between acute rejection and anemia. In conclusion, analysis using DNA microarrays has identified a cluster of genes related to hemoglobin synthesis and/or erythropoeisis that was altered in kidneys with renal allograft rejection compared with normal kidneys. The possible relationship between alterations in the expression of this cluster, reduced renal function, the alloimmune process itself, and other influences on the renal transplant awaits further analysis.

Disruption of Smad5 gene leads to enhanced proliferation of high-proliferative potential precursors during embryonic hematopoiesis

SMAD proteins are downstream signal transducers of the transforming growth factor beta (TGF-beta) superfamily, which serve as pleiotropic regulators in embryonic and adult hematopoiesis. SMAD5, initially considered to mediate bone morphogenetic proteins (BMPs) signals, can also transduce the inhibitory signal of TGF-beta1 on proliferation of hematopoietic progenitors derived from human bone marrow. To define its specific role in regulation of primitive multipotential progenitors during early embryonic hematopoiesis, we examined Smad5(-/-) yolk sacs at E9.0 to 9.5 and detected an elevated number of high-proliferative potential colony-forming cells (HPP-CFCs) with enhanced replating potential. To exclude the possible influence of microenvironmental deficit on embryonic hematopoiesis in vivo, we performed in vitro embryonic stem (ES) cell differentiation assay and investigated the HPP-CFCs in particular. Smad5(-/-) embryoid bodies (EBs) contained an elevated number of blast colony-forming cells (BL-CFCs), the in vitro equivalent of hemangioblast, in contrast to reduced proliferation of primitive erythroid precursors (Ery/Ps) within the mutant EBs. More importantly, profoundly increased frequency of HPP-CFCs, featured with a gene-dosage effect, was detected within day 6 Smad5(-/-) EBs compared with the wild type. In addition, Smad5(-/-) HPP-CFCs displayed enhanced self-renewal capacity and decreased sensitivity to TGF-beta1 inhibition, suggesting a critical role of Smad5 in TGF-beta1 regulation of embryonic HPP-CFCs. Consistently, reverse transcription-polymerase chain reaction analysis detected alterations of the transcription factors including GATA-2 and AML1 as well as cytokine receptors in Smad5(-/-) HPP-CFC colonies. Together, these data define an important function of SMAD5 in negative regulation of high-proliferative potential precursors during embryonic hematopoiesis.

Activation of the p38 mitogen-activated protein kinase mediates the suppressive effects of type I interferons and transforming growth factor-beta on normal hematopoiesis

Type I interferons (IFNs) are potent regulators of normal hematopoiesis in vitro and in vivo, but the mechanisms by which they suppress hematopoietic progenitor cell growth and differentiation are not known. In the present study we provide evidence that IFN alpha and IFN beta induce phosphorylation of the p38 mitogen-activated protein (Map) kinase in CD34+-derived primitive human hematopoietic progenitors. Such type I IFN-inducible phosphorylation of p38 results in activation of the catalytic domain of the kinase and sequential activation of the MAPK-activated protein kinase-2 (MapKapK-2 kinase), indicating the existence of a signaling cascade, activated downstream of p38 in hematopoietic progenitors. Our data indicate that activation of this signaling cascade by the type I IFN receptor is essential for the generation of the suppressive effects of type I IFNs on normal hematopoiesis. This is shown by studies demonstrating that pharmacological inhibitors of p38 reverse the growth inhibitory effects of IFN alpha and IFN beta on myeloid (colony-forming granulocytic-macrophage) and erythroid (burst-forming unit-erythroid) progenitor colony formation. In a similar manner, transforming growth factor beta, which also exhibits inhibitory effects on normal hematopoiesis, activates p38 and MapKapK-2 in human hematopoietic progenitors, whereas pharmacological inhibitors of p38 reverse its suppressive activities on both myeloid and erythroid colony formation. In further studies, we demonstrate that the primary mechanism by which the p38 Map kinase pathway mediates hematopoietic suppression is regulation of cell cycle progression and is unrelated to induction of apoptosis. Altogether, these findings establish that the p38 Map kinase pathway is a common effector for type I IFN and transforming growth factor beta signaling in human hematopoietic progenitors and plays a critical role in the induction of the suppressive effects of these cytokines on normal hematopoiesis.

Inhibition of Smad5 in human hematopoietic progenitors blocks erythroid differentiation induced by BMP4

Patients with secondary myelodysplasias and acute myeloid leukemias (MDS/AML) frequently exhibit interstitial deletions of the chromosome-5q resulting in hemizygous loss of the transcription transactivator Smad5. Smad5 is a member of the signal transducer family conveying the pleiotropic TGF-gb/BMP cytokine signals with roles in development, cell growth control, and tumor progression. Here we present a study of the Smad5 expression and its functional role in leukemia cell lines as well as in primary CD34+ progenitors of MDS/AML patients and healthy individuals. Consistent Smad5 gene expression in these cell types and the gradual increase in its mRNA and protein levels in a model of induced erythroid differentiation of murine erythroleukemia (MEL) cells suggest a role of the gene in hematopoiesis. We show that bone morphogenetic protein 4 (BMP4) directs Smad5 activation in human hematopoietic cells, as monitored at the levels of protein phosphorylation, nuclear translocation, and specific transcription response. In vitro induction of normal human CD34+ cells by BMP4 results in significantly increased proliferation of erythroid progenitors (BFU-E) and formation of glycophorin-A+ cells, whereas perturbation of Smad5 expression by antisense oligonucleotides causes significantly decreased rates of BMP4-induced erythroid differentiation. We have not detected any effects of Smad5 inhibition on BMP4-stimulated progenitors of the granulocyteNmacrophage lineage. We propose that the BMP4/Smad5 signal transduction pathway activates hematopoietic differentiation programs that may be impaired in anemia manifestations in MDS and AML patients with Smad5 haploinsufficiency.

Transient disruption of autocrine TGF-beta signaling leads to enhanced survival and proliferation potential in single primitive human hemopoietic progenitor cells

Hemopoietic stem cells (HSCs) are maintained at relative quiescence by the balance between the positive and negative regulatory factors that stimulate or inhibit their proliferation. Blocking the action of negative regulatory factors may provide a new approach for inducing HSCs into proliferation. A variety of studies have suggested that TGF-beta negatively regulates cell cycle progression of HSCs. In this study, a dominant negatively acting mutant of TGF-beta type II receptor (TbetaRIIDN) was transiently expressed in HSCs by using adenoviral vector-mediated gene delivery, such that the effects of disrupting the autocrine TGF-beta signaling in HSCs can be directly examined at a single cell level. Adenoviral vectors allowing the expression of TbetaRIIDN and green fluorescence protein in the same CD34(+)CD38(-)Lin(-) cells were constructed. Overexpression of TbetaRIIDN specifically disrupted TGF-beta-mediated signaling. Autocrine TGF-beta signaling in CD34(+)CD38(-)Lin(-) cells was studied in single cell assays under serum-free conditions. Transient blockage of autocrine TGF-beta signaling in CD34(+)CD38(-)Lin(-) cells enhanced their survival. Furthermore, the overall proliferation potential and proliferation kinetics in these cells were significantly enhanced compared with the CD34(+)CD38(-)Lin(-) cells expressing green fluorescence protein alone. Therefore, we have successfully blocked the autocrine TGF-beta-negative regulatory loop of primitive hemopoietic progenitor cells.

Bone morphogenetic proteins act synergistically with haematopoietic cytokines in the differentiation of haematopoietic progenitors

We examined the effects of bone morphogenetic protein-2 (BMP-2), -3, -4, -5, -6, and -7 on the proliferation and differentiation of bone marrow CD34+ haematopoietic progenitors in semi-solid medium. The BMPs had no effect on haematopoietic colony development when added to medium containing erythropoietin (Epo) or Interleukin-3 plus Epo. Synergistic effects with the haematopoietic cytokines stem cell factor (SCF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) were observed. In conjunction with GM-CSF and Epo, BMP-4 increased the number of both erythroid and granulocyte/monocyte colonies formed in semi-solid medium (P<0.01). No other BMP stimulated erythroid colony development under these conditions, while BMP-3, BMP-7 (P<0.01), BMP-5, and BMP-6 (P<0.05) stimulated granulocyte/monocyte colony formation. BMP-7 acted synergistically with stem cell factor to increase granulocyte/monocyte colony formation but not erythroid colony formation. The other BMPs did not affect either erythroid or granulocyte/monocyte colony development under these conditions. These results suggest that individual BMPs form part of the complement of cytokines regulating the development of haematopoietic progenitors, and in particular, point to a role for BMP-4 in the control of definitive, as well as embryonic erythropoiesis.

Mutation and methylation analysis of the transforming growth factor beta receptor II gene in polycythaemia vera

Polycythaemia vera (PV) is a myeloproliferative disorder (MPD) thought to result from transformation of a haemopoietic stem cell. Transforming growth factor beta1 (TGF-beta1) is a negative regulator of haemopoietic stem cells, an effect mediated by direct binding to TGF-beta receptor II (TGF-beta RII). Reduced levels of TGF-beta RII mRNA or protein have been reported in several MPDs including PV, suggesting a role for TGF-beta RII in PV. No mutational analysis of the TGF-beta RII gene has yet been performed in PV. To investigate whether genetic or epigenetic alteration of the TGF-beta RII gene contributes to the pathogenesis of PV, we performed mutation and methylation analysis in 15 PV patients. The promoter, all seven exons and all intron/exon junctions were studied using single-strand conformation polymorphism (SSCP) and heteroduplex analysis (HA). In total, three single nucleotide polymorphisms (SNPs) were identified. These were located in the promoter, intron 2 and exon 5. No acquired mutations were detected in any patient sample. We also present a novel method, termed methylation-specific strand extension (MSSE), for the detection of methylated CpG dinucleotides. The combination of bisulphite modification and MSSE permits rapid analysis of the methylation status of CpG dinucleotides in multiple samples. We analysed the methylation status of the promoter and of a CpG island within exon 1 in 15 PV patients. No aberrant methylation was detected in either of these regions. These data demonstrate that neither mutation nor abnormal methylation of the TGF-beta RII gene is associated with the pathogenesis of PV. Furthermore, MSSE is a rapid and robust approach for assessing the methylation status of a given genomic region.

Intracellular BMP signaling regulation in vertebrates: pathway or network?

Bone morphogenetic proteins (BMPs), members of the TGF-beta superfamily of secreted signaling molecules, have important functions in many biological contexts. They bind to specific serine/threonine kinase receptors, which transduce the signal to the nucleus through Smad proteins. The question of how BMPs can have such diverse effects while using the same canonical Smad pathway has recently come closer to an answer at the molecular level. Nuclear cofactors have been identified that cooperate with the Smads in regulating specific target genes depending on the cellular context. In addition, the pivotal role BMP signaling plays is underscored by the identification of factors that regulate members of this pathway at the cell surface, in the cytoplasm, and in the nucleus. Many of these factors are BMP-inducible and inhibit the BMP pathway, thus establishing negative feedback loops. Members of the BMP-Smad pathway can also physically interact with components of other signaling pathways to establish crosstalk. Finally, there is accumulating evidence that an alternative pathway involving MAP kinases can transduce BMP signals. The evidence and implications of these findings are discussed with an emphasis on early embryonic development of Xenopus and vertebrates.

Transforming growth factor-beta signal transduction in epithelial cells

Transforming growth factor (TGF)-beta is a natural and potent growth inhibitor of a variety of cell types, including epithelial, endothelial, and hematopoietic cells. The ability of TGF-beta to potently inhibit the growth of many solid tumors of epithelial origin, including breast and colon carcinomas, is of particular interest. However, many solid tumor cells become refractory to the growth inhibitory effects of TGF-beta due to defects in TGF-beta signaling pathways. In addition, TGF-beta may stimulate the invasiveness of tumor cells via the paracrine effects of TGF-beta. Accordingly, in order to develop more effective anticancer therapeutics, it is necessary to determine the TGF-beta signal transduction pathways underlying the growth inhibitory effects and other cellular effects of TGF-beta in normal epithelial cells. Thus far, two primary signaling cascades downstream of the TGF-beta receptors have been elucidated, the Sma and mothers against decapentaplegic homologues and the Ras/mitogen-activated protein kinase pathways. The major objective of this review is to summarize TGF-beta signaling in epithelial cells, focusing on recent advances involving the Sma and mothers against decapentaplegic homologues and Ras/mitogen-activated protein kinase pathways. This review is particularly timely in that it provides a comprehensive summary of both signal transduction mechanisms and the cell cycle effects of TGF-beta.

Transforming growth factor beta signalling in vitro and in vivo: activin ligand-receptor interaction, Smad5 in vasculogenesis, and repression of target genes by the deltaEF1/ZEB-related SIP1 in the vertebrate embryo

The identification and characterization of components of the transforming growth factor beta (TGFbeta) signalling pathway are proceeding at a very fast pace. To illustrate a number of our activities in this field, we first summarize our work aiming at the selection from a large collection of single residue substitution mutants of two activin A polypeptides in which D27 and K102, respectively, have been modified. This work has highlighted the importance of K102 and its positive charge for binding to activin type II receptors. Activin K102E, which did not bind to high-affinity receptor complexes, may be a valuable beta chain, when incorporated in recombinant inhibin to unambiguously detect novel inhibin binding sites at the cell surface. We then illustrate how Smad5 knockout mice and an overexpression approach with a truncated TGFbeta type II receptor in the mouse embryo can contribute to the identification of a novel TGFbeta-->TbetaRII/ALK1-->Smad5 pathway in endothelial cells in the embryo proper and the yolk sac vasculature. We conclude with a summary of our results with a Smad-interacting transcriptional repressor but focus on its biological significance in the vertebrate embryo.

TGF beta-induced SMAD2 phosphorylation predicts inhibition of thymidine incorporation in CD34+ cells from healthy donors, but not from patients with AML after MDS

Cells from patients with MDS-derived AML display heterogeneous proliferative responses to transforming growth factor beta (TGF beta). We analyzed growth inhibition and SMAD2 phosphorylation by TGF beta in CD34+ cells from nine patients, as compared to normal controls. While TGF beta consistently inhibited thymidine incorporation of normal cells (41% of control, P < 0.05), cells from patients with AML were growth-inhibited in only four of seven cases (40%), whereas TGF beta stimulated thymidine incorporation in the three other samples (166%). Remarkably, TPO reverted the stimulatory effect of TGF beta to profound growth inhibition. Upon exposure to TGF beta, SMAD2 protein was phosphorylated in normal CD34+ cells (n = 3), CD34+ leukemic blasts from all examined patients with AML (n = 4), and in the myeloid leukemic cell lines M-07e and HEL. TGF beta inhibited TPO-mediated thymidine incorporation, cell proliferation and survival in all samples analyzed. In M-07e cells and CD34+ cells from healthy donors, this inhibition was enhanced by an antagonist of JAK2 (AG490), but not a MEK-1 antagonist (PD098059). Conversely, in CD34+ cells from a patient with AML, both AG490 and PD098059 significantly enhanced TGF beta-mediated suppression of TPO-induced thymidine incorporation. Thus, in MDS-derived AML, altered responses to TGF beta may be due to defects downstream of SMAD2 and may involve MAPK activation.

Methylation profiling in acute myeloid leukemia

Aberrant methylation of multiple CpG islands has been described in acute myeloid leukemia (AML), but it is not known whether these are independent events or whether they reflect specific methylation defects in a subset of cases. To study this issue, the methylation status of 14 promoter-associated CpG islands was analyzed in 36 cases of AML previously characterized for estrogen-receptor methylation (ERM). Cases with methylation density of 10% or greater were considered positive. Seventeen cases (47%) were ERM(+) while 19 cases were ERM(-). Hypermethylation of any of the following, p15, p16, CACNA1G, MINT1, MINT2, MDR1, THBS1, and PTC1 (2 promoters), was relatively infrequent (6% to 31% of patients). For each of these CpG islands, the methylation density was positively correlated with ERM density (rank order correlation coefficients, 0.32-0.59; 2-tailed P < or = .058 for each gene). Hypermethylation of MYOD1, PITX2, GPR37, and SDC4 was frequently found in AML (47% to 64% of patients). For each of these genes as well, methylation density was positively correlated with ERM density (correlation coefficients 0.43 to 0.69, P < or = .0087 for each gene). MLH1 was unmethylated in all cases. Hypermethylation of p15, MDR1, and SDC4 correlated with reduced levels of expression. There was an inverse correlation between age and the number of genes methylated (P = .0030). It was concluded that CpG-island methylation in AML results from methylation defects in subsets of cases. These results have potential implications for the classification and prognosis of AML and for the identification of patients who may benefit from treatment with methylation inhibitors.

Transforming growth factor-β1 interferes with thrombopoietin-induced signal transduction in megakaryoblastic and erythroleukemic cells

OBJECTIVE

Thrombopoietin (TPO) and transforming growth factor-beta(1) (TGF-beta(1)) have been shown to exert opposite effects on proliferation and megakaryocytic differentiation of hematopoietic cells. To determine whether TGF-beta(1) interferes directly with TPO-induced signal transduction in hematopoietic cells, we compared the regulatory effects in the TPO-responsive cell lines Mo-7e and HEL.

MATERIALS AND METHODS

The cells were stimulated by 100 ng/mL TPO and/or 100 ng/mL TGF-beta1 and analyzed for proliferation (3H thymidine incorporation), viability (trypan blue exclusion), and protein expression and phosphorylation (Western blot).

RESULTS

TPO enhanced the proliferation of Mo-7e cells as determined by 3H-thymidine incorporation, whereas TGF-beta1 suppressed baseline cell growth and antagonized the proliferative effect of TPO. TPO-induced proliferation also was reduced by a specific inhibitor of the mitogen-activated protein kinase (MAPK) pathway (PD098059), which inhibits activation of the MAPK extracellular signal-regulated kinases (ERK) ERK1 and ERK2, and AG490, an inhibitor of Janus kinase-2, which completely blocked TPO-induced proliferation. As demonstrated by Western blotting, TGF-beta1 reduced the TPO-stimulated ERK1/ERK2 and STAT5 phosphorylation in Mo-7e and HEL cells. This effect was completely reversed by preincubation with a tyrosine phosphatase inhibitor (Na3VO4), which suggests that TGF-beta1 activated a phosphatase. Although STAT3 also was activated by TPO, STAT3 activation remained unaltered by TGF-beta1.

CONCLUSION

Taken together, these data suggest that TGF-beta1 modulates TPO-mediated effects on megakaryocytic proliferation by interfering with TPO-induced signal transduction, particularly by reducing the activities of MAPK ERK1/ERK2 and STAT5.

TGF-beta signaling by Smad proteins

Members of the transforming growth factor-beta (TGF-beta) family bind to type II and type I serine/threonine kinase receptors, which initiate intracellular signals through activation of Smad proteins. Receptor-regulated Smads (R-Smads) are anchored to the cell membrane by interaction with membrane-bound proteins, including Smad anchor for receptor activation (SARA). Upon ligand stimulation, R-Smads are phosphorylated by the receptors and form oligomeric complexes with common-partner Smads (Co-Smads). The oligomeric Smad complexes then translocate into the nucleus, where they regulate the transcription of target genes by direct binding to DNA, interaction with various DNA-binding proteins, and recruitment of transcriptional coactivators or corepressors. A third class of Smads, inhibitory Smads (I-Smads), inhibits the signals from the serine/threonine kinase receptors. Since the expression of I-Smads is induced by the TGF-beta superfamily proteins, Smads constitute an autoinhibitory signaling pathway. The functions of Smads are regulated by other signaling pathways, such as the MAP kinase pathway. Moreover, Smads interact with and modulate the functions of various transcription factors which are downstream targets of other signaling pathways. Loss of function of certain Smads is involved in tumorigenesis, e.g., pancreatic and colorectal cancers. Analyses by gene targeting revealed pivotal roles of Smads in early embryogenesis, angiogenesis, and immune functions in vivo.

Human mortalin (HSPA9): a candidate for the myeloid leukemia tumor suppressor gene on 5q31

Human mortalin (HSPA9) was originally identified by its close homology to murine mortalins, which play important roles in cellular senescence. The two murine genes, mot-1 and mot-2, differ in only two amino acid residues, but have opposite functions in cellular immortalization. HSPA9 was recently localized to chromosome 5, band q31, a region that is frequently deleted in myeloid leukemias and myelodysplasia (MDS), making it a candidate tumor suppressor gene, which is consistent with the biological function of its murine homologue. To evaluate mortalin in this capacity, its expression in normal and leukemic cell lines was investigated, and its genomic structure was determined in order to facilitate mutation detection. RT-PCR and Northern blot analysis revealed a broad distribution in normal tissues and in leukemia cell lines, producing a single 2.8 kb transcript. Genomic characterization showed that the gene spans 18 kb, and consisted of 17 exons with boundaries that were almost identical to its murine counterpart. Using intron-based primers to flank each exon, sequence of the complete protein-coding regions was obtained for three AML cell lines, including two lines with chromosome 5 loss (KG-1 and HL-60) and one without (AML-193) compared to normal DNA. No mutations were identified although one conservative nucleotide sequence variant was observed in exon 16. We have shown that mortalin is highly conserved in genomic structure as well as sequence, and the designed primers will be suitable for future studies to detect mutations in clinical samples.

Transforming growth factor-β: pleiotropic role in the regulation of hematopoiesis

Hematopoiesis is a remarkable cell-renewal process that leads to the continuous generation of large numbers of multiple mature cell types, starting from a relatively small stem cell compartment. A highly complex but efficient regulatory network is necessary to tightly control this production and to maintain the hematopoietic tissue in homeostasis. During the last 3 decades, constantly growing numbers of molecules involved in this regulation have been identified. They include soluble cytokines and growth factors, cell–cell interaction molecules, and extracellular matrix components, which provide a multifunctional scaffolding specific for each tissue. The cloning of numerous growth factors and their mass production have led to their possible use for both fundamental research and clinical application.

Differential expression of a novel C-terminally truncated splice form of SMAD5 in hematopoietic stem cells and leukemia

SMADs are evolutionarily conserved transducers of the differentiation and growth arrest signals from the transforming growth factor/BMP (TGF/BMP) family of ligands. Upon receptor activation, the ligand-restricted SMADs1–35 are phosphorylated in the C-terminal MH2 domain and recruit the common subunit SMAD4/DPC-4 gene to the nucleus to mediate target gene expression. Frequent inactivating mutations of SMAD4, or less common somatic mutations ofSMAD2 seen in solid tumors, suggest that these genes have a suppressor function. However, there have been no identified mutations of SMAD5, although the gene localizes to the critical region of loss in chromosome 5q31.1 (chromosome 5, long arm, region 3, band 1, subband 1) in myelodysplasia (MDS) and acute myelogenous leukemia (AML). A ubiquitously expressed novel isoform,SMAD5β, encodes a 351 amino acid protein with a truncated MH2 domain and a unique C-terminal tail of 18 amino acids, which may be the functional equivalent of inactivating mutations. The levels of SMAD5β transcripts are higher in the undifferentiated CD34+ hematopoietic stem cells than in the terminally differentiated peripheral blood leukocytes, thereby implicating the β form in stem cell homeostasis. Yeast 2-hybrid interaction assays reveal the lack of physical interactions between SMAD5β and SMAD5 or SMAD4. The expression ofSMAD5β may represent a novel mechanism to protect pluripotent stem cells and malignant cells from the growth inhibitory and differentiation signals of BMPs.

Differential expression of a novel C-terminally truncated splice form of SMAD5 in hematopoietic stem cells and leukemia

SMADs are evolutionarily conserved transducers of the differentiation and growth arrest signals from the transforming growth factor/BMP (TGF/BMP) family of ligands. Upon receptor activation, the ligand-restricted SMADs1–35 are phosphorylated in the C-terminal MH2 domain and recruit the common subunit SMAD4/DPC-4 gene to the nucleus to mediate target gene expression. Frequent inactivating mutations of SMAD4, or less common somatic mutations ofSMAD2 seen in solid tumors, suggest that these genes have a suppressor function. However, there have been no identified mutations of SMAD5, although the gene localizes to the critical region of loss in chromosome 5q31.1 (chromosome 5, long arm, region 3, band 1, subband 1) in myelodysplasia (MDS) and acute myelogenous leukemia (AML). A ubiquitously expressed novel isoform,SMAD5β, encodes a 351 amino acid protein with a truncated MH2 domain and a unique C-terminal tail of 18 amino acids, which may be the functional equivalent of inactivating mutations. The levels of SMAD5β transcripts are higher in the undifferentiated CD34+ hematopoietic stem cells than in the terminally differentiated peripheral blood leukocytes, thereby implicating the β form in stem cell homeostasis. Yeast 2-hybrid interaction assays reveal the lack of physical interactions between SMAD5β and SMAD5 or SMAD4. The expression ofSMAD5β may represent a novel mechanism to protect pluripotent stem cells and malignant cells from the growth inhibitory and differentiation signals of BMPs.

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.

Smad7 selectively interferes with different pathways of activin signaling and inhibits erythroid leukemia cell differentiation

Smad family proteins are essential for transforming growth factor β (TGF-β) signal mediation downstream of a heteromeric complex of the type I and type II receptor serine/threonine kinases. A distant family member, Smad7, is expressed in most mammalian tissues and cells and prevents TGF-β signaling. In this study, we examined the physiologic role of Smad7 in mediating the effects of activin, a member of the TGF-β superfamily of peptides that functions in a number of processes, including blood-cell development. We report here that Smad7 expression is specifically absent in particular hematopoietic cells that respond to activin by differentiating into the erythroid lineage and that ectopic production of Smad7 causes mouse erythroid leukemia (F5-5) cells to become resistant to activin induction of erythroid differentiation. When coexpressed with type I activin receptor ActR-I or ActR-IB in concert with type II receptor ActR-II, Smad7 efficiently reduced an early transcriptional response mediated by ActR-I but had only a minimal effect on the response mediated by ActR-IB. In the presence of Smad7, overexpression of an activated form of ActR-IB, but not of an activated form of ActR-I, induced F5-5 cells to differentiate. These results suggest that Smad7 selectively interferes with the ActR-I pathway in activin signal transduction. The findings also indicate the existence of a novel activity of Smad7 that inhibits erythroid differentiation by blocking intracellular signaling of activin.