A role for RUNX1 in hematopoiesis and myeloid leukemia

Acquired TET2 mutation in one patient with familial platelet disorder with predisposition to AML led to the development of pre-leukaemic clone resulting in T2-ALL and AML-M0

Familial platelet disorder with predisposition to acute myeloid leukaemia (FPD/AML) is characterized by germline RUNX1 mutations, thrombocytopaenia, platelet dysfunction and a risk of developing acute myeloid and in rare cases lymphoid T leukaemia. Here, we focus on a case of a man with a familial history of RUNX1^R174Q mutation who developed at the age of 42 years a T2‐ALL and, 2 years after remission, an AML‐M0. Both AML‐M0 and T2‐ALL blast populations demonstrated a loss of 1p36.32‐23 and 17q11.2 regions as well as other small deletions, clonal rearrangements of both TCRγ and TCRδ and a presence of 18 variants at a frequency of more than 40%. Additional variants were identified only in T2‐ALL or in AML‐M0 evoking the existence of a common original clone, which gave rise to subclonal populations. Next generation sequencing (NGS) performed on peripheral blood‐derived CD34⁺ cells 5 years prior to T2‐ALL development revealed only the missense TET2^P1962T mutation at a frequency of 1%, which increases to more than 40% in fully transformed leukaemic T2‐ALL and AML‐M0 clones. This result suggests that TET2^P1962T mutation in association with germline RUNX1^R174Q mutation leads to amplification of a haematopoietic clone susceptible to acquire other transforming alterations.

Novel function of FAXDC2 in megakaryopoiesis

FAXDC2 (fatty acid hydroxylase domain containing 2) is a member of the fatty acid hydroxylase superfamily. Given the important role of fatty acids in megakaryocytes, we have studied the role of this gene in the development of this lineage. Here we show that the expression of FAXDC2 is constantly elevated during megakaryocyte maturation. In contrast, FAXDC2 is significantly downregulated in acute myeloid leukemia and acute megakaryoblastic leukemia. Moreover, FAXDC2 overexpression promotes the differentiation of megakaryocytic cell lines and primary cells, whereas its knockdown disrupts their maturation. Mechanism study shows that FAXDC2 overexpression enhances extracellular signal-regulated kinase (ERK) signaling and increases RUNX1 (Runt-related transcription factor 1) expression. FAXDC2 also restores megakaryocytic differentiation in cells exposed to an ERK inhibitor or those expressing a dominant negative form of RUNX1. Finally, FAXDC2 overexpression leads to an increase in sphingolipid GM3 synthase, suggesting a potential role of FAXDC2 in lipid metabolism that increases ERK signaling and facilitates megakaryocyte differentiation. Together, these results show that FAXDC2 plays a novel role in development of megakaryocytes and its dysregulation may contribute to abnormal hematopoietic cell development in leukemia.

Systems Pharmacogenomics Finds RUNX1 Is an Aspirin-Responsive Transcription Factor Linked to Cardiovascular Disease and Colon Cancer

Aspirin prevents cardiovascular disease and colon cancer; however aspirin's inhibition of platelet COX-1 only partially explains its diverse effects. We previously identified an aspirin response signature (ARS) in blood consisting of 62 co-expressed transcripts that correlated with aspirin's effects on platelets and myocardial infarction (MI). Here we report that 60% of ARS transcripts are regulated by RUNX1 - a hematopoietic transcription factor - and 48% of ARS gene promoters contain a RUNX1 binding site. Megakaryocytic cells exposed to aspirin and its metabolite (salicylic acid, a weak COX-1 inhibitor) showed up regulation in the RUNX1 P1 isoform and MYL9, which is transcriptionally regulated by RUNX1. In human subjects, RUNX1 P1 expression in blood and RUNX1-regulated platelet proteins, including MYL9, were aspirin-responsive and associated with platelet function. In cardiovascular disease patients RUNX1 P1 expression was associated with death or MI. RUNX1 acts as a tumor suppressor gene in gastrointestinal malignancies. We show that RUNX1 P1 expression is associated with colon cancer free survival suggesting a role for RUNX1 in aspirin's protective effect in colon cancer. Our studies reveal an effect of aspirin on RUNX1 and gene expression that may additionally explain aspirin's effects in cardiovascular disease and cancer.

MYC-dependent recruitment of RUNX1 and GATA2 on the SET oncogene promoter enhances PP2A inactivation in acute myeloid leukemia

The SET (I2PP2A) oncoprotein is a potent inhibitor of protein phosphatase 2A (PP2A) that regulates many cell processes and important signaling pathways. Despite the importance of SET overexpression and its prognostic impact in both hematologic and solid tumors, little is known about the mechanisms involved in its transcriptional regulation. In this report, we define the minimal promoter region of the SET gene, and identify a novel multi-protein transcription complex, composed of MYC, SP1, RUNX1 and GATA2, which activates SET expression in AML. The role of MYC is crucial, since it increases the expression of the other three transcription factors of the complex, and supports their recruitment to the promoter of SET. These data shed light on a new regulatory mechanism in cancer, in addition to the already known PP2A-MYC and SET-PP2A. Besides, we show that there is a significant positive correlation between the expression of SET and MYC, RUNX1, and GATA2 in AML patients, which further endorses our results. Altogether, this study opens new directions for understanding the mechanisms that lead to SET overexpression, and demonstrates that MYC, SP1, RUNX1 and GATA2 are key transcriptional regulators of SET expression in AML.

MiR144/451 Expression Is Repressed by RUNX1 During Megakaryopoiesis and Disturbed by RUNX1/ETO

A network of lineage-specific transcription factors and microRNAs tightly regulates differentiation of hematopoietic stem cells along the distinct lineages. Deregulation of this regulatory network contributes to impaired lineage fidelity and leukemogenesis. We found that the hematopoietic master regulator RUNX1 controls the expression of certain microRNAs, of importance during erythroid/megakaryocytic differentiation. In particular, we show that the erythorid miR144/451 cluster is epigenetically repressed by RUNX1 during megakaryopoiesis. Furthermore, the leukemogenic RUNX1/ETO fusion protein transcriptionally represses the miR144/451 pre-microRNA. Thus RUNX1/ETO contributes to increased expression of miR451 target genes and interferes with normal gene expression during differentiation. Furthermore, we observed that inhibition of RUNX1/ETO in Kasumi1 cells and in RUNX1/ETO positive primary acute myeloid leukemia patient samples leads to up-regulation of miR144/451. RUNX1 thus emerges as a key regulator of a microRNA network, driving differentiation at the megakaryocytic/erythroid branching point. The network is disturbed by the leukemogenic RUNX1/ETO fusion product.

Evolution of myeloid leukemia in children with Down syndrome

Children with Down syndrome (DS) have a markedly increased risk of leukemia. They are at particular risk of acute megakaryoblastic leukemia, known as myeloid leukemia associated with DS (ML-DS), the development of which is closely linked to a preceding temporary form of neonatal leukemia called transient abnormal myelopoiesis (TAM). Findings from recent clinical and laboratory studies suggest that constitutional trisomy 21 and GATA1 mutation(s) cause TAM, and that additional genetic alteration(s) including those in epigenetic regulators and signaling molecules are involved in the progression from TAM to ML-DS. Thus, this disease progression represents an important model of multi-step leukemogenesis. The present review focuses on the evolutionary process of TAM to ML-DS, and advances in the understanding of perturbed hematopoiesis in DS with respect to GATA1 mutation and recent findings, including cooperating genetic events, are discussed.

Transcriptional Auto-Regulation of RUNX1 P1 Promoter

RUNX1 a member of the family of runt related transcription factors (RUNX), is essential for hematopoiesis. The expression of RUNX1 gene is controlled by two promoters; the distal P1 promoter and the proximal P2 promoter. Several isoforms of RUNX1 mRNA are generated through the use of both promoters and alternative splicing. These isoforms not only differs in their temporal expression pattern but also exhibit differences in tissue specificity. The RUNX1 isoforms derived from P2 are expressed in a variety of tissues, but expression of P1-derived isoform is restricted to cells of hematopoietic lineage. However, the control of hematopoietic-cell specific expression is poorly understood. Here we report regulation of P1-derived RUNX1 mRNA by RUNX1 protein. In silico analysis of P1 promoter revealed presence of two evolutionary conserved RUNX motifs, 0.6kb upstream of the transcription start site, and three RUNX motifs within 170bp of the 5'UTR. Transcriptional contribution of these RUNX motifs was studied in myeloid and T-cells. RUNX1 genomic fragment containing all sites show very low basal activity in both cell types. Mutation or deletion of RUNX motifs in the UTR enhances basal activity of the RUNX1 promoter. Chromatin immunoprecipitation revealed that RUNX1 protein is recruited to these sites. Overexpression of RUNX1 in non-hematopoietic cells results in a dose dependent activation of the RUNX1 P1 promoter. We also demonstrate that RUNX1 protein regulates transcription of endogenous RUNX1 mRNA in T-cell. Finally we show that SCL transcription factor is recruited to regions containing RUNX motifs in the promoter and the UTR and regulates activity of the RUNX1 P1 promoter in vitro. Thus, multiple lines of evidence show that RUNX1 protein regulates its own gene transcription.

MicroRNA-378-mediated suppression of Runx1 alleviates the aggressive phenotype of triple-negative MDA-MB-231 human breast cancer cells

The Runx1 transcription factor, known for its essential role in normal hematopoiesis, was reported in limited studies to be mutated or associated with human breast tumor tissues. Runx1 increases concomitantly with disease progression in the MMTV-PyMT transgenic mouse model of breast cancer. Compelling questions relate to mechanisms that regulate Runx1 expression in breast cancer. Here, we tested the hypothesis that dysregulation of Runx1-targeting microRNAs (miRNAs) allows for pathologic increase of Runx1 during breast cancer progression. Microarray profiling of the MMTV-PyMT model revealed significant downregulation of numerous miRNAs predicted to target Runx1. One of these, miR-378, was inversely correlated with Runx1 expression during breast cancer progression in mice and in human breast cancer cell lines MCF7 and triple-negative MDA-MB-231 that represent early- and late-stage diseases, respectively. MiR-378 is nearly absent in MDA-MB-231 cells. Luciferase reporter assays revealed that miR-378 binds the Runx1 3' untranslated region (3'UTR) and inhibits Runx1 expression. Functionally, we demonstrated that ectopic expression of miR-378 in MDA-MB-231 cells inhibited Runx1 and suppressed migration and invasion, while inhibition of miR-378 in MCF7 cells increased Runx1 levels and cell migration. Depletion of Runx1 in late-stage breast cancer cells resulted in increased expression of both the miR-378 host gene PPARGC1B and pre-miR-378, suggesting a feedback loop. Taken together, our study identifies a novel and clinically relevant mechanism for regulation of Runx1 in breast cancer that is mediated by a PPARGC1B-miR-378-Runx1 regulatory pathway. Our results highlight the translational potential of miRNA replacement therapy for inhibiting Runx1 in breast cancer.

The Transcription Factor ARID3a Is Important for In Vitro Differentiation of Human Hematopoietic Progenitors

We recently reported that the transcription factor ARID3a is expressed in a subset of human hematopoietic progenitor stem cells in both healthy individuals and in patients with systemic lupus erythematosus. Numbers of ARID3a(+) lupus hematopoietic stem progenitor cells were associated with increased production of autoreactive Abs when those cells were introduced into humanized mouse models. Although ARID3a/Bright knockout mice died in utero, they exhibited decreased numbers of hematopoietic stem cells and erythrocytes, indicating that ARID3a is functionally important for hematopoiesis in mice. To explore the requirement for ARID3a for normal human hematopoiesis, hematopoietic stem cell progenitors from human cord blood were subjected to both inhibition and overexpression of ARID3a in vitro. Inhibition of ARID3a resulted in decreased B lineage cell production accompanied by increases in cells with myeloid lineage markers. Overexpression of ARID3a inhibited both myeloid and erythroid differentiation. Additionally, inhibition of ARID3a in hematopoietic stem cells resulted in altered expression of transcription factors associated with hematopoietic lineage decisions. These results suggest that appropriate regulation of ARID3a is critical for normal development of both myeloid and B lineage pathways.

Internal tandem duplication of FLT3 deregulates proliferation and differentiation and confers resistance to the FLT3 inhibitor AC220 by Up-regulating RUNX1 expression in hematopoietic cells

Internal tandem duplication in the FLT3 gene (FLT3/ITD), which is found in patients with acute myeloid leukemia (AML), causes resistance to FLT3 inhibitors. We found that RUNX1, a transcription factor that regulates normal hematopoiesis, is up-regulated in patients with FLT3/ITD(+) AML. While RUNX1 can function as a tumor suppressor, recent data have shown that RUNX1 is required for AML cell survival. In the present study, we investigated the functional role of RUNX1 in FLT3/ITD signaling. FLT3/ITD induced growth factor-independent proliferation and impaired G-CSF mediated myeloid differentiation in 32D hematopoietic cells, coincident with up-regulation of RUNX1 expression. Silencing of RUNX1 expression significantly decreased proliferation and secondary colony formation, and partially abrogated the impaired myeloid differentiation of FLT3/ITD(+) 32D cells. Although the number of FLT3/ITD(+) 32D cells declined after incubation with the FLT3/ITD inhibitor AC220, the cells became refractory to AC220, concomitant with up-regulation of RUNX1. Silencing of RUNX1 abrogated the emergence and proliferation of AC220-resistant FLT3/ITD(+) 32D cells in the presence of AC220. Our data indicate that FLT3/ITD deregulates cell proliferation and differentiation and confers resistance to AC220 by up-regulating RUNX1 expression. These findings suggest an oncogenic role for RUNX1 in FLT3/ITD(+) cells and that inhibition of RUNX1 function represents a potential therapeutic strategy in patients with refractory FLT3/ITD(+) AML.

Transcriptome Profiling of Pediatric Core Binding Factor AML

The t(8;21) and Inv(16) translocations disrupt the normal function of core binding factors alpha (CBFA) and beta (CBFB), respectively. These translocations represent two of the most common genomic abnormalities in acute myeloid leukemia (AML) patients, occurring in approximately 25% pediatric and 15% of adult with this malignancy. Both translocations are associated with favorable clinical outcomes after intensive chemotherapy, and given the perceived mechanistic similarities, patients with these translocations are frequently referred to as having CBF-AML. It remains uncertain as to whether, collectively, these translocations are mechanistically the same or impact different pathways in subtle ways that have both biological and clinical significance. Therefore, we used transcriptome sequencing (RNA-seq) to investigate the similarities and differences in genes and pathways between these subtypes of pediatric AMLs. Diagnostic RNA from patients with t(8;21) (N = 17), Inv(16) (N = 14), and normal karyotype (NK, N = 33) were subjected to RNA-seq. Analyses compared the transcriptomes across these three cytogenetic subtypes, using the NK cohort as the control. A total of 1291 genes in t(8;21) and 474 genes in Inv(16) were differentially expressed relative to the NK controls, with 198 genes differentially expressed in both subtypes. The majority of these genes (175/198; binomial test p-value < 10⁻³⁰) are consistent in expression changes among the two subtypes suggesting the expression profiles are more similar between the CBF cohorts than in the NK cohort. Our analysis also revealed alternative splicing events (ASEs) differentially expressed across subtypes, with 337 t(8;21)-specific and 407 Inv(16)-specific ASEs detected, the majority of which were acetylated proteins (p = 1.5x10^-51 and p = 1.8x10^-54 for the two subsets). In addition to known fusions, we identified and verified 16 de novo fusions in 43 patients, including three fusions involving NUP98 in six patients. Clustering of differentially expressed genes indicated that the homeobox (HOX) gene family, including two transcription factors (MEIS1 and NKX2-3) were down-regulated in CBF compared to NK samples. This finding supports existing data that the dysregulation of HOX genes play a central role in biology CBF-AML hematopoiesis. These data provide comprehensive transcriptome profiling of CBF-AML and delineate genes and pathways that are differentially expressed, providing insights into the shared biology as well as differences in the two CBF subsets.

Runx1 is associated with breast cancer progression in MMTV-PyMT transgenic mice and its depletion in vitro inhibits migration and invasion

Runx1 is a transcription factor essential for definitive hematopoiesis, and genetic abnormalities in Runx1 cause leukemia. Runx1 is functionally promiscuous and acts as either an oncogene or tumor suppressor gene in certain epithelial cancers. Recent evidence suggests that Runx1 is an important factor in breast cancer, however, its role remains ambiguous. Here, we addressed whether Runx1 has a specific pathological role during breast cancer progression and show that Runx1 has an oncogenic function. We observed elevated Runx1 expression in a subset of human breast cancers. Furthermore, throughout the course of disease progression in a classical mouse model of breast cancer (i.e., the MMTV-PyMT transgenic model), Runx1 expression increases in the primary site (mammary gland) and is further upregulated in tumors and distal lung metastatic lesions. Ex vivo studies using tumor epithelial cells derived from these mice express significantly higher levels of Runx1 than normal mammary epithelial cells. The tumor cells exhibit increased rates of migration and invasion, indicative of an aggressive cancer phenotype. Inhibition of Runx1 expression using RNA interference significantly abrogates these cancer-relevant phenotypic characteristics. Importantly, our data establish that Runx1 contributes to murine mammary tumor development and malignancy and potentially represents a key disease-promoting and prognostic factor in human breast cancer progression and metastasis.

Runx3-regulated expression of two Ntrk3 transcript variants in dorsal root ganglion neurons

Somatosensation is divided into proprioception and cutaneous sensation. Dorsal root ganglion (DRG) neurons project their fibers toward peripheral targets including muscles and skin, and centrally to the spinal cord. Proprioceptive DRG neurons transmit information from muscle spindles and Golgi tendon organs to the spinal cord. We previously showed that Runt-related transcription factor 3 (Runx3) is expressed in these neurons and their projections to the ventral spinal cord and muscle spindles are lost in Runx3-deficient (Runx3(-/-) ) mouse embryos. Although Runx3 is likely to contribute to the fate decision and projection of proprioceptive DRG neurons, the precise roles for Runx3 in these phenomena are unknown. To identify genes regulated by Runx3 in embryonic DRGs, we performed microarray analyses using cDNAs isolated from wild-type and Runx3(-/-) DRGs of embryonic day (E) 12.5 and selected two transcript variants of the tyrosine kinase receptor C (TrkC) gene. These variants, Ntrk3 variant 1 (Ntrk3-v1) and variant 2 (Ntrk3-v2), encode full-length and truncated receptors of neurotrophin-3, respectively. Using double in situ hybridization, we found that most of Ntrk3-v1 mRNA expression in E14.5 DRGs depended on Runx3 but that more than half of Ntrk3-v2 mRNA one were expressed in a Runx3-independent manner. Furthermore, our data revealed that the rate of Ntrk3-v1 and Ntrk3-v2 colocalization in DRGs changed from E14.5 to E18.5. Together, our data suggest that Runx3 may play a crucial role in the development of DRGs by regulating the expression of Ntrk3 variants and that DRG neurons expressing Ntrk3-v1 but not Ntrk3-v2 may differentiate into proprioceptive ones.

Contribution of the Runx1 transcription factor to axonal pathfinding and muscle innervation by hypoglossal motoneurons

The runt-related transcription factor Runx1 contributes to cell type specification and axonal targeting projections of the nociceptive dorsal root ganglion neurons. Runx1 is also expressed in the central nervous system, but little is known of its functions in brain development. At mouse embryonic day (E) 17.5, Runx1-positive neurons were detected in the ventrocaudal subdivision of the hypoglossal nucleus. Runx1-positive neurons lacked calcitonin gene-related peptide (CGRP) expression, whereas Runx1-negative neurons expressed CGRP. Expression of CGRP was not changed in Runx1-deficient mice at E17.5, suggesting that Runx1 alone does not suppress CGRP expression. Hypoglossal axon projections to the intrinsic vertical (V) and transverse (T) tongue muscles were sparser in Runx1-deficient mice at E17.5 compared to age-matched wild-type littermates. Concomitantly, vesicular acetylcholine transporter-positive axon terminals and acetylcholine receptor clusters were less dense in the V and T tongue muscles of Runx1-deficient mice. These abnormalities in axonal projection were not caused by a reduction in the total number hypoglossal neurons, failed synaptogenesis, or tongue muscles deficits. Our results implicate Runx1 in the targeting of ventrocaudal hypoglossal axons to specific tongue muscles. However, Runx1 deficiency did not alter neuronal survival or the expression of multiple motoneuron markers as in other neuronal populations. Thus, Runx1 appears to have distinct developmental functions in different brain regions.

Aberrant nuclear factor-kappa B activity in acute myeloid leukemia: from molecular pathogenesis to therapeutic target

The overall survival of patients with acute myeloid leukemia (AML) has not been improved significantly over the last decade. Molecularly targeted agents hold promise to change the therapeutic landscape in AML. The nuclear factor kappa B (NF-κB) controls a plethora of biological process through switching on and off its long list of target genes. In AML, constitutive NF-κB has been detected in 40% of cases and its aberrant activity enable leukemia cells to evade apoptosis and stimulate proliferation. These facts suggest that NF-κB signaling pathway plays a fundamental role in the development of AML and it represents an attractive target for the intervention of AML. This review summarizes our current knowledge of NF-κB signaling transduction including canonical and non-canonical NF-κB pathways. Then we specifically highlight what factors contribute to the aberrant activation of NF-κB activity in AML, followed by an overview of 8 important clinical trials of the first FDA approved proteasome inhibitor, Bortezomib (Velcade), which is a NF-κB inhibitor too, in combination with other therapeutic agents in patients with AML. Finally, this review discusses the future directions of NF-κB inhibitor in treatment of AML, especially in targeting leukemia stem cells (LSCs).

Novel function of PITH domain-containing 1 as an activator of internal ribosomal entry site to enhance RUNX1 expression and promote megakaryocyte differentiation

INTRODUCTION

Altered gene expression coincides with leukemia development and may affect distinct features of leukemic cells. PITHD1 was significantly downregulated in leukemia and upregulated upon PMA induction in K562 cells undergoing megakaryocyte differentiation. We aimed to study the function of PITHD1 in megakaryocyte differentiation.

MATERIALS AND METHODS

K562 cells and fetal liver cells were used for either overexpression or downregulation of PITHD1 by retroviral or lentiviral transduction. FACS was used to detect the expression of CD41 and CD42 to measure megakaryocyte differentiation in these cells. Western blot and quantitative RT-PCR were used to measure gene expression. Dual luciferase assay was used to detect promoter or internal ribosomal entry site (IRES) activity.

RESULTS

Ectopic expression of PITHD1 promoted megakaryocyte differentiation and increased RUNX1 expression while PITHD1 knockdown showed an opposite phenotype. Furthermore, PITHD1 efficiently induced endogenous RUNX1 expression and restored megakaryocyte differentiation suppressed by a dominant negative form of RUNX1. PITHD1 regulated RUNX1 expression at least through two distinct mechanisms: increasing transcription activity of proximal promoter and enhancing translation activity of an IRES element in exon 3. Finally, we confirmed the function of PITHD1 in regulating RUNX1 expression and megakaryopoiesis in mouse fetal liver cells.

CONCLUSION AND SIGNIFICANCE

PITHD1 was a novel activator of IRES and enhanced RUNX1 expression that subsequently promoted megakaryocyte differentiation. Our findings shed light on understanding the mechanisms underlying megakaryopoiesis or leukemogenesis.

miR-17 deregulates a core RUNX1-miRNA mechanism of CBF acute myeloid leukemia

Background

Core Binding Factor acute myeloid leukemia (CBF-AML) with t(8;21) RUNX1-MTG8 or inv(16) CBFB-MYH11 fusion proteins often show upregulation of wild type or mutated KIT receptor. However, also non-CBF-AML frequently displays upregulated KIT expression. In the first part of this study we show that KIT expression can be also upregulated by miR-17, a regulator of RUNX1, the gene encoding a CBF subunit. Interestingly, both CBF leukemia fusion proteins and miR-17, which targets RUNX1-3′UTR, negatively affect a common core RUNX1-miRNA mechanism that forces myeloid cells into an undifferentiated, KIT-induced, proliferating state. In the second part of this study we took advantage of the conservation of the core RUNX1-miRNA mechanism in mouse and human, to mechanistically demonstrate in a mouse myeloid cell model that increased KIT-induced proliferation is per se a mechanism sufficient to delay myeloid differentiation.

Methods

Human (U937) or mouse (32D) myeloid clonal lines were used, respectively, to test: 1) the effect of RUNX1-MTG8 and CBFB-MYH11 fusion proteins, or upregulation of miR-17, on KIT-induced proliferation and myeloid differentiation, and 2) the effect of upregulation of KIT-induced proliferation per se on myeloid cell differentiation.

Results

In the first part of this study we found that stable miR-17 upregulation affects, like the CBF-AML fusion proteins (RUNX1-MTG8 or CBFB-MYH11), a core RUNX1-miRNA mechanism leading to KIT-induced proliferation of differentiation-arrested U937 myeloid cells. In the second part of the study we harnessed the conservation of this core mechanism in human and mouse to demonstrate that the extent of KIT upregulation in 32D mouse myeloid cells with wild type RUNX1 can per se delay G-CSF-induced differentiation. The integrated information gathered from the two myeloid cell models shows that RUNX1 regulates myeloid differentiation not only by direct transcriptional regulation of coding and non-coding myeloid differentiation functions (e.g. miR-223), but also by modulating KIT-induced proliferation via non-coding miRNAs (e.g. miR-221).

Conclusions

The novelty of this study is dual. On the one hand, miRNAs (e.g. miR-17) can mimic the effects of CBF-AML fusion proteins by affecting a core RUNX1-miRNA mechanism of KIT-induced proliferation of undifferentiated myeloid cells. On the other hand, the extent of KIT-induced proliferation itself can modulate myeloid differentiation of cells with wild type RUNX1 function.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-014-0283-z) contains supplementary material, which is available to authorized users.

Sp1/Sp3 transcription factors regulate hallmarks of megakaryocyte maturation and platelet formation and function

Sp1 and Sp3 belong to the specificity proteins (Sp)/Krüppel-like transcription factor family. They are closely related, ubiquitously expressed, and recognize G-rich DNA motifs. They are thought to regulate generic processes such as cell-cycle and growth control, metabolic pathways, and apoptosis. Ablation of Sp1 or Sp3 in mice is lethal, and combined haploinsufficiency results in hematopoietic defects during the fetal stages. Here, we show that in adult mice, conditional pan-hematopoietic (Mx1-Cre) ablation of either Sp1 or Sp3 has minimal impact on hematopoiesis, whereas the simultaneous loss of Sp1 and Sp3 results in severe macrothrombocytopenia. This occurs in a cell-autonomous manner as shown by megakaryocyte-specific (Pf4-Cre) double-knockout mice. We employed flow cytometry, cell culture, and electron microscopy and show that although megakaryocyte numbers are normal in bone marrow and spleen, they display a less compact demarcation membrane system and a striking inability to form proplatelets. Through megakaryocyte transcriptomics and platelet proteomics, we identified several cytoskeleton-related proteins and downstream effector kinases, including Mylk, that were downregulated upon Sp1/Sp3 depletion, providing an explanation for the observed defects in megakaryopoiesis. Supporting this notion, selective Mylk inhibition by ML7 affected proplatelet formation and stabilization and resulted in defective ITAM receptor-mediated platelet aggregation.

Recurrent CDC25C mutations drive malignant transformation in FPD/AML

Familial platelet disorder (FPD) with predisposition to acute myelogenous leukaemia (AML) is characterized by platelet defects with a propensity for the development of haematological malignancies. Its molecular pathogenesis is poorly understood, except for the role of germline RUNX1 mutations. Here we show that CDC25C mutations are frequently found in FPD/AML patients (53%). Mutated CDC25C disrupts the G2/M checkpoint and promotes cell cycle progression even in the presence of DNA damage, suggesting a critical role for CDC25C in malignant transformation in FPD/AML. The predicted hierarchical architecture shows that CDC25C mutations define a founding pre-leukaemic clone, followed by stepwise acquisition of subclonal mutations that contribute to leukaemia progression. In three of seven individuals with CDC25C mutations, GATA2 is the target of subsequent mutation. Thus, CDC25C is a novel gene target identified in haematological malignancies. CDC25C is also useful as a clinical biomarker that predicts progression of FPD/AML in the early stage.

Expressional changes of genes and miRNA in common megakaryocyte-erythroid progenitors from lower-risk myelodysplastic syndrome

Myelodysplastic syndrome (MDS) is a stem cell tumor characterized by dysplastic features and ineffective hematopoiesis in the early phase and leukemic progression in the late phase. Speculating that differences in the expression of genes and microRNA (miRNA) in control and MDS-derived erythroid progenitors may cause ineffective erythropoiesis, we sorted common megakaryocyte-erythroid progenitors (MEPs) in bone marrow cells from three lower-risk MDS patients, and compared expression levels of genes and miRNA with those from controls. In apoptosis-related pathways, the expression of some pro-apoptotic genes, such as cell death-inducing DFFA-like effector A, caspase 5, and Fas ligand, was elevated in MDS-derived MEPs, while those of anti-apoptotic CD40 and tumor necrosis factor were lower. In hematopoiesis-regulating pathways, RUNX1 and ETV6 genes showed reduced expression. Expression profiling revealed that three and 35 miRNAs were significantly up- and down-regulated in MDS-derived MEPs. MIR9 exhibited robust expression in MEPs and CD71+GlyA+ erythroid cells derived from one of the three patients. Interestingly, overexpression of MIR9 inhibited the accumulation of hemoglobin in UT-7/GM cells. Some of these alterations in gene and miRNA expression may contribute to the pathogenesis of ineffective hematopoiesis in lower-risk MDS and provide molecular markers for sub-classification and making a prognosis.

Hematopoietic myeloid cell differentiation diminishes nucleotide excision repair

Myeloid cell differentiation is the process by which stem cells develop into mature monocytes or granulocytes. This process is achieved by the sequential activation of variety of genes. Disruption of this process can result in immunodeficiency, bone marrow failure syndrome, or leukemia. Acute promyelocytic leukemia (APL) is characterized by the t(15;17) translocation and can be treated by a combination of all-trans retinoic acid (ATRA) and anthracycline. This treatment can induce leukemic cell differentiation, leading to extremely high remission rates. XAB2, a molecule involved in nucleotide excision repair (NER), is downregulated during granulocyte differentiation and shows reduced expression in NB4 APL-derived cells in vitro. Differentiation of APL by ATRA treatment reduced XAB2 expression levels in vivo. These observations suggest that cellular differentiation is associated with reduced NER activity and provides new insights into combined differentiation induction. NB4 cells were more susceptible than the immature myeloid leukemic cell lines, Kasumi-3 and Kasumi-1, to the DNA interstrand crosslinking agent cisplatin.

-7/7q- syndrome in myeloid-lineage hematopoietic malignancies: attempts to understand this complex disease entity

The recurrence of chromosomal abnormalities in a specific subtype of cancer strongly suggests that dysregulated gene expression in the corresponding region has a critical role in disease pathogenesis. -7/7q-, defined as the entire loss of chromosome 7 and partial deletion of its long arm, is among the most frequently observed chromosomal aberrations in myeloid-lineage hematopoietic malignancies such as myelodysplastic syndrome and acute myeloid leukemia, particularly in patients treated with cytotoxic agents and/or irradiation. Tremendous efforts have been made to clarify the molecular mechanisms underlying the disease development, and several possible candidate genes have been cloned. However, the study is still underway, and the entire nature of this syndrome is not completely understood. In this review, we focus on the attempts to identify commonly deleted regions in patients with -7/7q-; isolate the candidate genes responsible for disease development, cooperative genes and the factors affecting disease prognosis; and determine effective and potent therapeutic approaches. We also refer to the possibility that the accumulation of multiple gene haploinsufficiency, rather than the loss of a single tumor suppressor gene, may contribute to the development of diseases with large chromosomal deletions such as -7/7q-.

Aldehyde dehydrogenases in acute myeloid leukemia

Acute myeloid leukemia (AML) affects approximately 15,000 persons per year in the United States and is the sixth leading cause of cancer-related deaths. The treatment of AML has advanced little in the past thirty years, in part because of the biologic heterogeneity of the disease and the difficulty in targeting AML cells while sparing normal hematopoietic cells. Advances in preventing and treating AML are likely to occur once the cellular and molecular differences between leukemia and normal hematopoietic cells are better understood. Aldehyde dehydrogenase (ALDH) activity is highly expressed in hematopoietic stem cells (HSCs), while, in contrast, a subset of AMLs are lacking this activity. This difference may be relevant to the development of AML and may also provide a better avenue for treating this disease. In this review, we summarize what is known about the ALDHs in normal HSCs and AML and propose strategies for capitalizing on these differences in the treatment of acute leukemia, and possibly other cancers as well.

Analysis of the minimal specificity of caspase-2 and identification of Ac-VDTTD-AFC as a caspase-2-selective peptide substrate

Caspase-2 is an evolutionarily conserved but enigmatic protease whose biological role remains poorly understood. To date, research into the functions of caspase-2 has been hampered by an absence of reagents that can distinguish its activity from that of the downstream apoptotic caspase, caspase-3. Identification of protein substrates of caspase-2 that are efficiently cleaved within cells may also provide clues to the role of this protease. We used a yeast-based transcriptional reporter system to define the minimal substrate specificity of caspase-2. The resulting profile enabled the identification of candidate novel caspase-2 substrates. Caspase-2 cleaved one of these proteins, the cancer-associated transcription factor Runx1, although with relatively low efficiency. A fluorogenic peptide was derived from the sequence most efficiently cleaved in the context of the transcriptional reporter. This peptide, Ac-VDTTD-AFC, was efficiently cleaved by purified caspase-2 and auto-activating caspase-2 in mammalian cells, and exhibited better selectivity for caspase-2 relative to caspase-3 than reagents that are currently available. We suggest that this reagent, used in parallel with the traditional caspase-3 substrate Ac-DEVD-AFC, will enable researchers to monitor caspase-2 activity in cell lysates and may assist in the determination of stimuli that activate caspase-2 in vivo.

Deletion of the RUNX1 binding site in the erythroid cell-specific regulatory element of the ABO gene in two individuals with the Am phenotype

BACKGROUND AND OBJECTIVES

An erythroid cell-specific regulatory element, referred to as the +5·8-kb site, had been identified in the first intron of the human ABO blood group gene. Subsequent studies revealed that either a 5·8-kb deletion including the +5·8-kb site or disruption of a GATA factor binding motif at the site was present in all Bm and ABm individuals examined. We investigated the molecular mechanism of the Am phenotype, which is analogous to the Bm phenotype.

MATERIALS AND METHODS

Genomic DNAs were prepared from peripheral blood of two Am individuals, and the nucleotide sequences were investigated using PCR and direct sequencing. Electrophoretic mobility shift assay (EMSA) and promoter assay with K562 cells were carried out.

RESULTS

A novel 23-bp nucleotide deletion was found at the +5·8-kb site in both individuals. EMSAs demonstrated binding of the transcription factor RUNX1 to the nucleotides within the deletion. Promoter assays showed that the deletion reduced the transcriptional activity of the +5·8-kb site.

CONCLUSION

Deletion of the 23-bp nucleotides including the RUNX1 binding site decreases transcription of the A allele, resulting in the reduction in A antigen expression in the Am phenotype.