Epigenetic dysregulation of GATA1 is involved in myelodysplastic syndromes dyserythropoiesis

Role of epigenetic in cancer biology, in hematologic malignancies and in anticancer therapy

Major epigenetic changes are associated with carcinogenesis, including aberrant DNA methylations and post-translational modifications of histone. Indeed evidence accumulated in recent years indicates that inactivating DNA hypermethylation preferentially targets the subset of polycomb group (PcG) genes that are regulators of developmental processes. Conversely, activating DNA hypomethylation targets oncogenic signaling pathway genes, but outcomes of both events lead in the overexpression of oncogenic signaling pathways that contribute to the stem-like state of cancer cells. On the basis of recent evidence from population-basedclinical and experimental studies, we hypothesize that factors associated with risk for developing a hematologic malignancy (HM), such as metabolic syndrome and chronic inflammation, may trigger epigenetic mechanisms to increase the transcriptional expression of oncogenes and activate oncogenic signaling pathways. Signaling pathways associated with such risk factors include but are not limited to pro-inflammatory nuclear factor κB (NF-κB) and mitogenic, growth, and survival Janus kinase (JAK) intracellular non-receptor tyrosine kinase-triggered pathways. The latter includes signaling pathways such as transducer and activator of transcription (STAT), Ras GTPases/mitogen-activated protein kinases (MAPKs)/extracellular signal-related kinases (ERKs), phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR), and β-catenin pathways. Recent findings on epigenetic mechanisms at work in the biology of cancer and in HMs and their importance in the etiology and pathogenesis of these diseases are herein summarized and discussed. Furthermore, the role of epigenetic processes in the determination of biological identity, the consequences for interindividual variability in disease clinical profile, and the potential of epigenetic drugs in HMs are also considered.

Iron chelation improves ineffective erythropoiesis and iron overload in myelodysplastic syndrome mice

Myelodysplastic syndrome (MDS) is a heterogeneous group of bone marrow stem cell disorders characterized by ineffective hematopoiesis and cytopenias, most commonly anemia. Red cell transfusion therapy for anemia in MDS results in iron overload, correlating with reduced overall survival. Whether the treatment of iron overload benefits MDS patients remains controversial. We evaluate underlying iron-related pathophysiology and the effect of iron chelation using deferiprone on erythropoiesis in NUP98-HOXD13 transgenic mice, a highly penetrant well-established MDS mouse model. Our results characterize an iron overload phenotype with aberrant erythropoiesis in these mice which was reversed by deferiprone-treatment. Serum erythropoietin levels decreased while erythroblast erythropoietin receptor expression increased in deferiprone-treated MDS mice. We demonstrate, for the first time, normalized expression of the iron chaperones Pcbp1 and Ncoa4 and increased ferritin stores in late-stage erythroblasts from deferiprone-treated MDS mice, evidence of aberrant iron trafficking in MDS erythroblasts. Importantly, erythroblast ferritin is increased in response to deferiprone, correlating with decreased erythroblast ROS. Finally, we confirmed increased expression of genes involved in iron uptake, sensing, and trafficking in stem and progenitor cells from MDS patients. Taken together, our findings provide evidence that erythroblast-specific iron metabolism is a novel potential therapeutic target to reverse ineffective erythropoiesis in MDS.

Epigenetic and Transcriptional Control of Erythropoiesis

Erythropoiesis is a process of enormous magnitude, with the average person generating two to three million red cells every second. Erythroid progenitors start as large cells with large nuclei, and over the course of three to four cell divisions they undergo a dramatic decrease in cell size accompanied by profound nuclear condensation, which culminates in enucleation. As maturing erythroblasts are undergoing these dramatic phenotypic changes, they accumulate hemoglobin and express high levels of other erythroid-specific genes, while silencing much of the non-erythroid transcriptome. These phenotypic and gene expression changes are associated with distinct changes in the chromatin landscape, and require close coordination between transcription factors and epigenetic regulators, as well as precise regulation of RNA polymerase II activity. Disruption of these processes are associated with inherited anemias and myelodysplastic syndromes. Here, we review the epigenetic mechanisms that govern terminal erythroid maturation, and their role in human disease.

Transcription Factors, R-Loops and Deubiquitinating Enzymes: Emerging Targets in Myelodysplastic Syndromes and Acute Myeloid Leukemia

Simple Summary

The advent of DNA massive sequencing technologies has allowed for the first time an extensive look into the heterogeneous spectrum of genes and mutations underpinning myelodysplastic syndromes (MDSs) and acute myeloid leukemia (AML). In this review, we wish to explore the most recent advances and the rationale for the potential therapeutic interest of three main actors in myelo-leukemic transformation: transcription factors that govern myeloid differentiation; RNA splicing factors, which ensure proper mRNA maturation and whose mutations increase R-loops formation; and deubiquitinating enzymes, which contribute to genome stability in hematopoietic stem cells (HSCs).

Abstract

Myeloid neoplasms encompass a very heterogeneous family of diseases characterized by the failure of the molecular mechanisms that ensure a balanced equilibrium between hematopoietic stem cells (HSCs) self-renewal and the proper production of differentiated cells. The origin of the driver mutations leading to preleukemia can be traced back to HSC/progenitor cells. Many properties typical to normal HSCs are exploited by leukemic stem cells (LSCs) to their advantage, leading to the emergence of a clonal population that can eventually progress to leukemia with variable latency and evolution. In fact, different subclones might in turn develop from the original malignant clone through accumulation of additional mutations, increasing their competitive fitness. This process ultimately leads to a complex cancer architecture where a mosaic of cellular clones—each carrying a unique set of mutations—coexists. The repertoire of genes whose mutations contribute to the progression toward leukemogenesis is broad. It encompasses genes involved in different cellular processes, including transcriptional regulation, epigenetics (DNA and histones modifications), DNA damage signaling and repair, chromosome segregation and replication (cohesin complex), RNA splicing, and signal transduction. Among these many players, transcription factors, RNA splicing proteins, and deubiquitinating enzymes are emerging as potential targets for therapeutic intervention.

Epigenetic modifiers in normal and aberrent erythropoeisis

Erythroid differentiation program is comprised of lineage commitment, erythroid progenitor proliferation, and termination differentiation. Each stage of the differentiation program is heavily influenced by epigenetic modifiers that alter the epigenome in a dynamic fashion influenced by cytokines/humeral factors and are amicable to target by drugs. The epigenetic modifiers can be classified as DNA modifiers (DNMT, TET), mRNA modifiers (RNA methylases and demethylases) and histone protein modifiers (methyltransferases, acetyltransferases, demethylases, and deacetylases). Here we describe mechanisms by which these epigenetic modifiers influence and guide erythroid-lineage differentiation during normal and malignant erythropoiesis and also benign diseases that arise from their altered structure or function.

Smad2/3-pathway ligand trap luspatercept enhances erythroid differentiation in murine β-thalassaemia by increasing GATA-1 availability

In β‐thalassaemia, anaemia results from ineffective erythropoiesis characterized by inhibition of late‐stage erythroid differentiation. We earlier used luspatercept and RAP‐536 protein traps for certain Smad2/3‐pathway ligands to implicate Smad2/3‐pathway overactivation in dysregulated erythroid differentiation associated with murine β‐thalassaemia and myelodysplasia. Importantly, luspatercept alleviates anaemia and has been shown to reduce transfusion burden in patients with β‐thalassaemia or myelodysplasia. Here, we investigated the molecular mechanisms underlying luspatercept action and pSmad2/3‐mediated inhibition of erythroid differentiation. In murine erythroleukemic (MEL) cells in vitro, ligand‐mediated overactivation of the Smad2/3 pathway reduced nuclear levels of GATA‐1 (GATA‐binding factor‐1) and its transcriptional activator TIF1γ (transcription intermediary factor 1γ), increased levels of reactive oxygen species, reduced cell viability and haemoglobin levels, and inhibited erythroid differentiation. Co‐treatment with luspatercept in MEL cells partially or completely restored each of these. In β‐thalassaemic mice, RAP‐536 up‐regulated Gata1 and its target gene signature in erythroid precursors determined by transcriptional profiling and gene set enrichment analysis, restored nuclear levels of GATA‐1 in erythroid precursors, and nuclear distribution of TIF1γ in erythroblasts. Bone marrow cells from β‐thalassaemic mice treated with luspatercept also exhibited restored nuclear availability of GATA‐1 ex vivo. Our results implicate GATA‐1, and likely TIF1γ, as key mediators of luspatercept/RAP‐536 action in alleviating ineffective erythropoiesis.

GATA factor transcriptional activity: Insights from genome-wide binding profiles

The members of the GATA family of transcription factors have homologous zinc fingers and bind to similar sequence motifs. Recent advances in genome-wide technologies and the integration of bioinformatics data have led to a better understanding of how GATA factors regulate gene expression; GATA-factor-induced transcriptional and epigenetic changes have now been analyzed at unprecedented levels of detail. Here, we review the results of genome-wide studies of GATA factor occupancy in human and murine cell lines and primary cells (as determined by chromatin immunoprecipitation sequencing), and then discuss the molecular mechanisms underlying the mediation of transcriptional and epigenetic regulation by GATA factors.

Deubiquitylase USP7 regulates human terminal erythroid differentiation by stabilizing GATA1

Ubiquitination is an enzymatic post-translational modification that affects protein fate. The ubiquitin-proteasome system (UPS) was first discovered in reticulocytes where it plays important roles in reticulocyte maturation. Recent studies have revealed that ubiquitination is a dynamic and reversible process and that deubiquitylases are capable of removing ubiquitin from their protein substrates. Given the fact that the UPS is highly active in reticulocytes, it is speculated that deubiquitylases may play important roles in erythropoiesis. Yet, the role of deubiquitylases in erythropoiesis remains largely unexplored. In the present study, we found that the expression of deubiquitylase USP7 is significantly increased during human terminal erythroid differentiation. We further showed that interfering with USP7 function, either by short hairpin RNA-mediated knockdown or USP7-specific inhibitors, impaired human terminal erythroid differentiation due to decreased GATA1 level and that restoration of GATA1 levels rescued the differentiation defect. Mechanistically, USP7 deficiency led to a decreased GATA1 protein level that could be reversed by proteasome inhibitors. Furthermore, USP7 interacts directly with GATA1 and catalyzes the removal of K48-linked poly ubiquitylation chains conjugated onto GATA1, thereby stabilizing GATA1 protein. Collectively, our findings have identified an important role of a deubiquitylase in human terminal erythroid differentiation by stabilizing GATA1, the master regulator of erythropoiesis.

Overexpression of Short Variant Form of New Kelch Family Protein Leads to Erythroid and Megakaryocyte Dysplasia by Targeting Megakaryocyte-Erythroid Progenitors

Nd1-S is the nuclear-localizing short variant form of Nd1 (Ivns1abp) encoding a Kelch family transcription factor. While the function of Nd1 has been investigated in the context of metastasis and doxorubicin-induced cardiotoxicity, little is known about its role in hematopoiesis. In this study, we investigated the function of Nd1-S in hematopoiesis by transplanting the Nd1-S-overexpressing murine hematopoietic stem and progenitor cells (HSPCs) into recipient mice (Nd1-S mice). Enforced expression of Nd1-S led to erythroid and megakaryocyte dysplasia, demonstrated by dramatically decreased red blood cells and platelets, and megakaryocytes in the peripheral blood and bone marrow of the Nd1-S mice. Moreover, phenotypic megakaryocyte-erythroid progenitors (MEPs) accumulated in these Nd1-S mice with aberrant morphology and defective colony-forming capability. Furthermore, these phenotypic MEPs showed impaired pathways regulating erythroid differentiation and megakaryocyte development. Therefore, our study provides de novo evidence that overexpression of Nd1-S in HSPCs leads to erythroid and megakaryocyte dysplasia in vivo by targeting MEPs.

Protein-based therapeutic for anemia caused by dyserythropoiesis

INTRODUCTION

Major advances have been recently made in understanding the molecular determinants of dyserythropoiesis, particularly due to recent works in β-thalassemia. The purpose of this review is devoted to underline the role of some proteins recently evidenced in the field, that may be new alternative therapeutic targets in the near future to alleviate different types of anemia. Areas covered: This review covers the contemporary aspects of some proteins involved in various types of dyserythropoiesis, including the transcriptional factor GATA-1 and its protective chaperone HSP70, but also cytokines of the transforming growth factor beta (TFG-β) family, TGF-β1 and GDF-11, and hormones as erythroferrone. It will be not exhaustive, but based on major recent published works from the literature in the past three years. Expert commentary: Sotatercept and lustatercept, two activin receptor II ligand traps that block GDF-11, are candidate drugs providing therapeutic hope in different types of ineffective erythropoiesis, including myelodysplastic syndromes (MDS) and β-thalassemia. Furthermore, a new concept emerges to consider erythroid lineage in the bone marrow as an endocrine gland.

Somatic mutations and epigenetic abnormalities in myelodysplastic syndromes

During many years, very limited data had been available on specific gene mutations in MDS in particular due to the fact that balanced chromosomal translocations (which have allowed to discover many "leukemia" genes) are very rare in MDS, while chromosomal deletions are generally very large, making it difficult to identify genes of interest. Recently, the advent of next generation sequencing (NGS) techniques has helped identify somatic gene mutations in 75-80% of MDS, that cluster mainly in four functional groups, i.e. cytokine signaling (RAS genes), DNA methylation, (TET2, IDH1/2, DNMT3a genes) histone modifications (ASXL1 and EZH2 genes), and spliceosome (SF3B1 and SRSF2 genes) along with mutations of RUNX1 and TP 53 genes. Most of those mutations, except SF3B1 and TET2 mutations, are associated with an overall poorer prognosis, while some gene mutations (mainly TET2 mutation), may be associated to better response to hypomethylating agents. The frequent mutations of epigenetic modulators in MDS appear to largely contribute to the importance of epigenetic deregulation (in particular gene hypermethylation and histone deacetylation) in MDS progression, and may account at least partially for the efficacy of hypomethylating agents in the treatment of MDS.

TET2 plays an essential role in erythropoiesis by regulating lineage-specific genes via DNA oxidative demethylation in a zebrafish model

Although epigenetic modulation is critical for a variety of cellular activities, its role in erythropoiesis remains poorly understood. Ten-eleven translocation (TET) molecules participate in methylcytosine (5mC) hydroxylation, which results in DNA demethylation in several biological processes. In this research, the role of TETs in erythropoiesis was investigated by using the zebrafish model, where three TET homologs were identified. These homologs share conserved structural domains with their mammalian counterparts. Zebrafish TETs mediate the conversion of 5mC to hydroxymethylcytosine (5hmC) in zebrafish embryos, and the deletion of TET2 inhibits erythropoiesis by suppressing the expression of the scl, gata-1, and cmyb genes. TET2-upregulated lineage-specific genes and erythropoiesis are closely associated with the occurrence of 5hmC and demethylation in the intermediate CpG promoters (ICPs) of scl, gata-1, cmyb, which frequently occur at specific regions or CpG sites of these ICPs. Moreover, TET2 regulates the formation and differentiation of erythroid progenitors, and deletion of TET2 leads to erythrocyte dysplasia and anemia. Here, we preliminarily proved that TET2 plays an essential role in erythrocyte development by regulating lineage-specific genes via DNA oxidative demethylation. This report is anticipated to broaden current information on hematopoiesis and pathogenesis of hematopoiesis-related diseases.

Importance of epigenetic changes in cancer etiology, pathogenesis, clinical profiling, and treatment: what can be learned from hematologic malignancies?

Epigenetic alterations represent a key cancer hallmark, even in hematologic malignancies (HMs) or blood cancers, whose clinical features display a high inter-individual variability. Evidence accumulated in recent years indicates that inactivating DNA hypermethylation preferentially targets the subset of polycomb group (PcG) genes that are regulators of developmental processes. Conversely, activating DNA hypomethylation targets oncogenic signaling pathway genes, but outcomes of both events lead in the overexpression of oncogenic signaling pathways that contribute to the stem-like state of cancer cells. On the basis of recent evidence from population-based, clinical and experimental studies, we hypothesize that factors associated with risk for developing a HM, such as metabolic syndrome and chronic inflammation, trigger epigenetic mechanisms to increase the transcriptional expression of oncogenes and activate oncogenic signaling pathways. Among others, signaling pathways associated with such risk factors include pro-inflammatory nuclear factor κB (NF-κB), and mitogenic, growth, and survival Janus kinase (JAK) intracellular non-receptor tyrosine kinase-triggered pathways, which include signaling pathways such as transducer and activator of transcription (STAT), Ras GTPases/mitogen-activated protein kinases (MAPKs)/extracellular signal-related kinases (ERKs), phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR), and β-catenin pathways. Recent findings on epigenetic mechanisms at work in HMs and their importance in the etiology and pathogenesis of these diseases are herein summarized and discussed. Furthermore, the role of epigenetic processes in the determination of biological identity, the consequences for interindividual variability in disease clinical profile, and the potential of epigenetic drugs in HMs are also considered.

Epigenetic alterations and microRNAs: new players in the pathogenesis of myelodysplastic syndromes

The term epigenetics refers to the heritable changes in gene expression that do not represent changes in DNA sequence. DNA methylation and histone modification are the best studied epigenetic mechanisms. However, microRNAs, which affect gene expression at the posttranscriptional level, should be considered as members of the epigenetic machinery too. Myelodysplastic syndromes (MDS) are clone disorders of the hematopoietic stem cell with increased risk of leukemic transformation. Over the years, increased number of studies indicates the role of epigenetic mechanisms, including microRNAs, in MDS pathogenesis and prognosis. Indeed, epigenetic therapy with demethylating agents has already been applied to MDS. In this review we summarize current knowledge on the role of epigenetic alterations in MDS pathogenesis and treatment.

Acute myeloid leukemia (AML) with erythroid predominance exhibits clinical and molecular characteristics that differ from other types of AML

The clinical importance of erythroid predominance in bone marrow of patients with acute myeloid leukemia (AML) is controversial. These cases represent a heterogeneous group of diseases that historically have been classified into different categories. We studied 313 AML patients and specifically compared the clinical, cytogenetic, and molecular features of cases of AML with erythroid predominance, arbitrarily defined as ≥50% erythroid precursors, to AML cases without erythroid predominance. We also assessed 51 patients with a high-grade myelodysplastic syndrome (MDS), refractory anemia with excess blasts (RAEB). All neoplasms were classified according to the World Health Organization classification. With the exception of therapy-related AML/MDS, the presence of erythroid predominance in variously classified categories of AML was associated with a survival advantage. In addition, AML with erythroid predominance had a lower frequency of cytogenetic abnormalities as well as a lower frequency of mutations involving NPM1, NRAS and FLT3 as compared with AML without erythroid predominance. We conclude that the clinical, cytogenetic, and molecular features of AML with erythroid predominance in the non-therapy-related setting are much closer to those of a high-grade myelodysplastic syndrome than they are to other types of AML.

Effect of etafenone on total and regional myocardial blood flow

The distribution of blood flow to the subendocardial, medium and subepicardial layers of the left ventricular free wall was studied in anaesthetized dogs under normoxic (A), hypoxic (B) conditions and under pharmacologically induced (etafenone) coronary vasodilation (C). Regional myocardial blood flow was determined by means of the particle distribution method. In normoxia a transmural gradient of flow was observed, with the subendocardial layers receiving a significantly higher flow rate compared with the subepicardial layers. In hypoxia induced vasodilation this transmural gradient of flow was persistent. In contrast a marked redistribution of regional flow was observed under pharmacologically induced vasodilation. The transmural gradient decreased. In contrast to some findings these experiments demonstrate that a considerable vasodilatory capacity exists in all layers of the myocardium and can be utilized by drugs. The differences observed for the intramural distribution pattern of flow under hypoxia and drug induced vasodilation support the hypothesis that this pattern reflects corresponding gradients of regional myocardial metabolism.