Microfluidic-Based Detection of AML-Specific Biomarkers Using the Example of Promyelocyte Leukemia.

A microfluidic assay for the detection of promyelocytic leukemia (PML)-retinoic acid receptor α (RARα) fusion protein was developed. This microfluidic-based system can be used for rapid personalized differential diagnosis of acute promyelocyte leukemia (APL) with the aim of early initiation of individualized therapy. The fusion protein PML-RARα occurs in 95% of acute promyelocytic leukemia cases and is considered as diagnostically relevant. The fusion protein is formed as a result of translocation t(15,17) and is detected in the laboratory by fluorescence in situ hybridization (FISH) or reverse transcriptase polymerase chain reaction (RT-PCR). Diagnostic methods require many laboratory steps with specialized staff. The developed microfluidic assay includes a sandwich enzyme-linked immunosorbent assay (ELISA) system for PML-RARα on surface of magnetic microparticles in a microfluidic chip. A rapid detection of PML-RARα in cell lysates is achieved in less than one hour. A biotinylated PML-antibody on the surface of magnetic streptavidin coated microparticles is used as capture antibody. The bound translocation product is detected by a RARα antibody conjugated with horseradish peroxidase and the substrate QuantaRed. The analysis is performed in microfluidic channels which involves automated liquid processing with stringent washing and short incubation times. The results of the developed assay show that cell lysates of PML-RARα-positive cells (NB-4) can be clearly distinguished from PML-RARα-negative cells (HL-60, MV4-11).

Inhibitor of cyclin-dependent kinase (CDK) interacting with cyclin A1 (INCA1) regulates proliferation and is repressed by oncogenic signaling.

The cell cycle is driven by the kinase activity of cyclin·cyclin-dependent kinase (CDK) complexes, which is negatively regulated by CDK inhibitor proteins. Recently, we identified INCA1 as an interaction partner and a substrate of cyclin A1 in complex with CDK2. On a functional level, we identified a novel cyclin-binding site in the INCA1 protein. INCA1 inhibited CDK2 activity and cell proliferation. The inhibitory effects depended on the cyclin-interacting domain. Mitogenic and oncogenic signals suppressed INCA1 expression, whereas it was induced by cell cycle arrest. We established a deletional mouse model that showed increased CDK2 activity in spleen with altered spleen architecture in Inca1(-/-) mice. Inca1(-/-) embryonic fibroblasts showed an increase in the fraction of S-phase cells. Furthermore, blasts from acute lymphoid leukemia and acute myeloid leukemia patients expressed significantly reduced INCA1 levels highlighting its relevance for growth control in vivo. Taken together, this study identifies a novel CDK inhibitor with reduced expression in acute myeloid and lymphoid leukemia. The molecular events that control the cell cycle occur in a sequential process to ensure a tight regulation, which is important for the survival of a cell and includes the detection and repair of genetic damage and the prevention of uncontrolled cell division.

Pim2 cooperates with PML-RARalpha to induce acute myeloid leukemia in a bone marrow transplantation model.

Although the potential role of Pim2 as a cooperative oncogene has been well described in lymphoma, its role in leukemia has remained largely unexplored. Here we show that high expression of Pim2 is observed in patients with acute promyelocytic leukemia (APL). To further characterize the cooperative role of Pim2 with promyelocytic leukemia/retinoic acid receptor alpha (PML/RARalpha), we used a well-established PML-RARalpha (PRalpha) mouse model. Pim2 coexpression in PRalpha-positive hematopoietic progenitor cells (HPCs) induces leukemia in recipient mice after a short latency. Pim2-PRalpha cells were able to repopulate mice in serial transplantations and to induce disease in all recipients. Neither Pim2 nor PRalpha alone was sufficient to induce leukemia upon transplantation in this model. The disease induced by Pim2 overexpression in PRalpha cells contained a slightly higher fraction of immature myeloid cells, compared with the previously described APL disease induced by PRalpha. However, it also clearly resembled an APL-like phenotype and showed signs of differentiation upon all-trans retinoic acid (ATRA) treatment in vitro. These results support the hypothesis that Pim2, which is also a known target of Flt3-ITD (another gene that cooperates with PML-RARalpha), cooperates with PRalpha to induce APL-like disease.

BCR-ABL enhances differentiation of long-term repopulating hematopoietic stem cells.

In a previously developed inducible transgenic mouse model of chronic myeloid leukemia, we now demonstrate that the disease is transplantable using BCR-ABL(+) Lin(-)Sca-1(+)c-kit(+) (LSK) cells. Interestingly, the phenotype is more severe when unfractionated bone marrow cells are transplanted, yet neither progenitor cells (Lin(-)Sca-1(-)c-kit(+)), nor mature granulocytes (CD11b(+)Gr-1(+)), nor potential stem cell niche cells (CD45(-)Ter119(-)) are able to transmit the disease or alter the phenotype. The phenotype is largely independent of BCR-ABL priming before transplantation. However, prolonged BCR-ABL expression abrogates the potential of LSK cells to induce full-blown disease in secondary recipients and increases the fraction of multipotent progenitor cells at the expense of long-term hematopoietic stem cells (LT-HSCs) in the bone marrow. BCR-ABL alters the expression of genes involved in proliferation, survival, and hematopoietic development, probably contributing to the reduced LT-HSC frequency within BCR-ABL(+) LSK cells. Reversion of BCR-ABL, or treatment with imatinib, eradicates mature cells, whereas leukemic stem cells persist, giving rise to relapsed chronic myeloid leukemia on reinduction of BCR-ABL, or imatinib withdrawal. Our results suggest that BCR-ABL induces differentiation of LT-HSCs and decreases their self-renewal capacity.

Profiling of histone H3 lysine 9 trimethylation levels predicts transcription factor activity and survival in acute myeloid leukemia.

Acute myeloid leukemia (AML) is commonly associated with alterations in transcription factors because of altered expression or gene mutations. These changes might induce leukemia-specific patterns of histone modifications. We used chromatin-immunoprecipitation on microarray to analyze histone 3 lysine 9 trimethylation (H3K9me3) patterns in primary AML (n = 108), acute lymphoid leukemia (n = 28), CD34(+) cells (n = 21) and white blood cells (n = 15) specimens. Hundreds of promoter regions in AML showed significant alterations in H3K9me3 levels. H3K9me3 deregulation in AML occurred preferentially as a decrease in H3K9me3 levels at core promoter regions. The altered genomic regions showed an overrepresentation of cis-binding sites for ETS and cyclic adenosine monophosphate response elements (CREs) for transcription factors of the CREB/CREM/ATF1 family. The decrease in H3K9me3 levels at CREs was associated with increased CRE-driven promoter activity in AML blasts in vivo. AML-specific H3K9me3 patterns were not associated with known cytogenetic abnormalities. But a signature derived from H3K9me3 patterns predicted event-free survival in AML patients. When the H3K9me3 signature was combined with established clinical prognostic markers, it outperformed prognosis prediction based on clinical parameters alone. These findings demonstrate widespread changes of H3K9me3 levels at gene promoters in AML. Signatures of histone modification patterns are associated with patient prognosis in AML.

E3 ligase-defective Cbl mutants lead to a generalized mastocytosis and myeloproliferative disease.

Somatic mutations of Kit have been found in leukemias and gastrointestinal stromal tumors. The proto-oncogene c-Cbl negatively regulates Kit and Flt3 by its E3 ligase activity and acts as a scaffold. We recently identified the first c-Cbl mutation in human disease in an acute myeloid leukemia patient, called Cbl-R420Q. Here we analyzed the role of Cbl mutants on Kit-mediated transformation. Coexpression of Cbl-R420Q or Cbl-70Z with Kit induced cytokine-independent proliferation, survival, and clonogenic growth. Primary murine bone marrow retrovirally transduced with c-Cbl mutants and transplanted into mice led to a generalized mastocytosis, a myeloproliferative disease, and myeloid leukemia. Overexpression of these Cbl mutants inhibited stem cell factor (SCF)-induced ubiquitination and internalization of Kit. Both Cbl mutants enhanced the basal activation of Akt and prolonged the ligand-dependent activation. Importantly, transformation was observed also with kinase-dead forms of Kit and Flt3 in the presence of Cbl-70Z, but not in the absence of Kit or Flt3, suggesting a mechanism dependent on receptor tyrosine kinases, but independent of their kinase activity. Instead, transformation depends on the Src family kinase Fyn, as c-Cbl coimmunoprecipitated with Fyn and inhibition abolished transformation. These findings may explain primary resistance to tyrosine kinase inhibitors targeted at receptor tyrosine kinases.

Activation of Wnt signalling in acute myeloid leukemia by induction of Frizzled-4.

Wnt signalling regulates proliferation, self renewal and cell fate. Aberrant Wnt signalling is thought to contribute to AML pathogenesis by enhancing self renewal. Herein, we provide evidence for increased expression of Frizzled-4, a receptor for Wnt ligands, in primary AML blasts compared to normal bone marrow on the protein level. In addition, Frizzled-4 is highly expressed in human CD34 positive cells as well as in lineage negative sorted mouse bone marrow cells. Functionally, Frizzled-4 expression modulates apoptosis and enhances Wnt3a induced beta-catenin stability in myeloid progenitor cells. Frizzled-4-dependent beta-catenin stabilization is dkk-1 sensitive, implicating a specific Wnt-ligand/Frizzled-receptor interaction. These findings indicate enhanced sensitivity of AML blasts for Wnt-ligands and suggest an additional mechanism of Wnt signalling activation in the pathogenesis of AML.

Activation of Wnt signaling in cKit-ITD mediated transformation and imatinib sensitivity in acute myeloid leukemia.

The Wnt-signaling pathway plays a critical role in directing cell fate during embryogenesis and also in the pathogenesis of cancer. In leukemia, it is well described that activating internal tandem duplications (ITD) mutations in receptor tyrosine kinases like cKit or Flt3 confer to the pathogenesis of cancer. Here, we analyzed whether Wnt-signaling plays a role in cKit-ITD mediated transformation. Stably transfected 32D cells with cKit-ITD cells had higher beta-Catenin protein levels compared to the cKit-WT. Analysis of beta-Catenin mRNA and protein levels revealed that beta-Catenin was regulated at post-transcriptional level in cKit-ITD as well as Flt3-ITD compared to the wildtype. Signaling analyses revealed higher-phosphorylation of GSK3beta by oncogenic cKit-ITD. Moreover, activation of Wnt signaling was confirmed by constitutive activation of c-myc luciferase by cKit-ITD cells. Importantly, using dominant negative TCF4, we show that activation of Wnt signaling plays an important role in cKit mediated transformation of myeloid cells. Application of specific receptor tyrosine kinase inhibitors for Flt3 or cKit result in a decrease of beta-Catenin that underwent with a decrease of GSK3beta phosphorylation, suggesting an indirect mechanism of beta-Catenin regulation by oncogenic receptor tyrosine kinases in both ITD mutations. Our study shows the importance of activation of Wnt signaling in leukemia and suggests as attractive target for future therapeutical approaches.

Lipocalin 24p3 is regulated by the Wnt pathway independent of regulation by iron.

Lipocalin 24p3 plays a direct role in iron transport and regulates the levels of important proteins of the iron metabolism. Iron-loaded 24p3 binds to its specific receptor (24p3R) on the cell surface. Upon binding to its receptor, 24p3 is internalized into the cell, where it releases its bound iron. Iron-free 24p3 can withdraw iron from inside the cell to the outside by a reverse mechanism. We analyzed the role of the murine 24p3 gene Lcn2 (alias 24p3) as a target of the Wnt pathway. In cells with activated Wnt pathway, the levels of 24p3 protein and RNA were decreased. The withdrawal of iron led to 24p3 downregulation, and iron addition to iron-deprived cells induced 24p3 expression. Despite its strong inhibitory effect on 24p3 expression, Wnt pathway activation had no effect on the intracellular iron level. In cells with nonactivated Wnt pathway, we found an as yet unidentified transcript of 24p3R. Our results indicate independent regulation of 24p3 expression by the Wnt pathway and by the intracellular iron level. Differential splicing of the 24p3R transcript, depending on the activation state of the Wnt pathway, may modify the function of 24p3.

Translocation products in acute myeloid leukemia activate the Wnt signaling pathway in hematopoietic cells.

The acute myeloid leukemia (AML)-associated translocation products AML1-ETO, PML-retinoic acid receptor alpha (RARalpha), and PLZF-RARalpha encode aberrant transcription factors. Several lines of evidence suggest similar pathogenetic mechanisms for these fusion proteins. We used high-density oligonucleotide arrays to identify shared target genes in inducibly transfected U937 cells expressing AML1-ETO, PML-RARalpha, or PLZF-RARalpha. All three fusion proteins significantly repressed the expression of 38 genes and induced the expression of 14 genes. Several of the regulated genes were associated with Wnt signaling. One of these, plakoglobin (gamma-catenin), was induced on the mRNA and protein level by all three fusion proteins. In addition, primary AML blasts carrying one of the fusion proteins significantly overexpressed plakoglobin. The plakoglobin promoter was cloned and shown to be induced by AML1-ETO, with promoter activation depending on the corepressor and histone deacetylase binding domains. The induction of plakoglobin by AML fusion proteins led to downstream signaling and transactivation of TCF- and LEF-dependent promoters, including the c-myc promoter, which was found to be bound by plakoglobin in vivo after AML1-ETO expression. beta-Catenin protein levels and TCF and LEF target genes such as c-myc and cyclin D1 were found to be induced by the fusion proteins. On the functional level, a dominant negative TCF inhibited colony growth of AML1-ETO-positive Kasumi cells, whereas plakoglobin transfection into myeloid 32D cells enhanced proliferation and clonal growth. Injection of plakoglobin-expressing 32D cells into syngeneic mice accelerated the development of leukemia. Transduction of plakoglobin into primitive murine hematopoietic progenitor cells preserved the immature phenotype during colony growth, suggesting enhanced self-renewal. These data provide evidence that activation of Wnt signaling is a common feature of several balanced translocations in AML.

Wnt signaling regulates transendothelial migration of monocytes.

The Wnt-signaling pathway plays a critical role in directing cell fate during embryogenesis. Several lines of evidence also suggest a role in inflammatory processes. Here, we analyzed whether Wnt signaling plays a role in leukocyte inflammatory responses. Monocytes from healthy donors expressed different Frizzled receptors, which are ligands for the Wnt molecules. Activation of the Wnt/beta-catenin pathway by LiCl or Wnt3a increased beta-catenin protein levels in monocytes but not in granulocytes. It is interesting that the activation of Wnt/beta-catenin signaling via Wnt3a in monocytes resulted in a decrease in migration through an endothelial layer (human dermal microvascular endothelial cell-1). Further experiments revealed that the decrease in transendothelial migration was associated with specific monocyte adherence to endothelial cells after Wnt exposure. The specificity was verified by a lack of Wnt3a-induced adhesion to fibronectin, laminin, or collagen compared with endothelial interaction. Analysis of the distribution of beta-catenin revealed a Wnt3a-induced increase of beta-catenin in the cytoplasm. Wnt3a exposure did not result in any activation of the classical Wnt-target gene c-myc or a Wnt-target gene involved in cell adhesion (Connexin43). Our study implicates for the first time a role of canonical Wnt signaling in inflammatory processes in monocytes.

Emerging Flt3 kinase inhibitors in the treatment of leukaemia.

Acute myeloid leukaemia (AML) is characterised by the infiltration of the bone marrow with highly proliferative leukaemic cells that stop to differentiate at different stages of myeloid development and carry survival advantages. Conventionally, AML is treated with aggressive cytotoxic therapy, in eligible patients followed by allogeneic bone marrow transplantation. However, despite this aggressive treatment, many patients relapse and eventually die from the disease. Activating mutations in the coding sequence of the receptor tyrosine kinase Flt3 are found in leukaemic blasts from approximately 30% of AML patients. The mutations have been described to severely alter the signalling properties of this receptor and to have transforming activity in cell-line models and in primary mouse bone marrow. The prognosis of patients harbouring the most common Flt3 mutations tends to be worse than that of comparable patients without the mutations. Thus, Flt3 seems a promising target for therapeutic intervention. Several small molecules that inhibit Flt3 kinase activity are being evaluated for the treatment of AML in clinical trials. This review article discusses the signal transduction and biological function of Flt3 and its mutations in normal and malignant haematopoiesis and recent progress in drug development aiming at the inhibition of Flt3 kinases.

S100 family members and trypsinogens are predictors of distant metastasis and survival in early-stage non-small cell lung cancer.

Distant metastasis is the predominant cause of death in early-stage non-small cell lung cancer (NSCLC). Currently, it is impossible to predict the occurrence of metastasis at early stages and thereby separate patients who could be cured by surgical resection alone from patients who would benefit from additional chemotherapy. In this study, we applied a comparative microarray approach to identify gene expression differences between early-stage NSCLC patients whose cancer ultimately did or did not metastasize during the course of their disease. Transcriptional profiling of 82 microarrays from two patient groups revealed differential expression of several gene families including known predictors of metastasis (e.g., matrix metalloproteinases). In addition, we found S100P, S100A2, trypsinogen C (TRY6), and trypsinogen IVb (PRSS3) to be overexpressed in tumors that metastasized during the course of the disease. In a third group of 42 patients, we confirmed the induction of S100 proteins and trypsinogens in metastasizing tumors and its significant correlation with survival by real-time quantitative reverse transcription-PCR. Overexpression of S100A2, S100P, or PRSS3 in NSCLC cell cultures led to increased transendothelial migration, corroborating the role of S100A2, S100P, and PRSS3 in the metastatic process. Taken together, we provide evidence that expression of S100 proteins and trypsinogens is associated with metastasis and predicts survival in early stages of NSCLC. For the first time, this implicates a role of S100 proteins and trypsinogens in the metastatic process of early-stage NSCLC.

The serine-threonine kinase MNK1 is post-translationally stabilized by PML-RARalpha and regulates differentiation of hematopoietic cells.

Microarray analyses were performed to identify target genes that are shared by the acute myeloid leukemia (AML) translocation products PML-RARalpha, PLZF-RARalpha and AML1-ETO in inducibly transfected U937 cell lines. The cytoplasmic serine and threonine kinase MNK1 was identified as one of the target genes. At the protein level, MNK1 was significantly induced by each of the three fusion proteins. Protein half-life analyses showed that PML-RARalpha enhanced MNK1 protein stability in U937 cells and ATRA exposure decreased MNK1 half-life in NB4 cells. EIF4E, the main MNK1 substrate, plays a role in the pathogenesis of a variety of cancers. Upon MNK1 overexpression, eIF4E phosphorylation increased as a sign of functional activation. Interestingly, MNK1 protein expression decreased during myeloid differentiation. Inhibition of MNK1 activity by a specific inhibitor (CGP57380) enhanced differentiation of HL60 and 32D cells, further suggesting a role for MNK1 in the myeloid differentiation. In addition, kinase dead mutants of MNK1 significantly impaired proliferation of 32D cells. Immunohistochemistry of primary AML bone marrow biopsies showed strong cytoplasmic MNK1 expression in 25 of 99 AML specimens (25%). MNK1 expression was associated with high levels of c-myc expression. Taken together, we identified MNK1 as a target gene of several leukemogenic fusion proteins in AML. MNK1 plays a role in myeloid differentiation. These data suggest a role for MNK1 in the AML fusion protein-associated differentiation block.

Novel target genes of the Wnt pathway and statistical insights into Wnt target promoter regulation.

The Wnt pathway controls biological processes via the regulation of target gene expression. The expression of direct Wnt target genes, e.g. cyclin D1 and MYC, is activated by the transcription factor TCF, which binds to specific sequence motifs in the promoter. Indirect target genes are regulated via transcription regulators, which are targets of the Wnt pathway. As an example, MYC regulates the MYC interacting zinc finger protein-1 (MIZ-1), which is able to inhibit the expression of the indirect target p21WAF1. We intended to identify new Wnt target genes and to get a deeper insight into the regulatory mechanisms of Wnt target gene expression. For this we analyzed the differential expression pattern of Wnt-1 activated cells by microarray analysis. We identified 43 sequences including eight expressed sequence tags (ESTs), which showed increased transcript levels, and 104 sequences including 19 ESTs with decreased RNA levels. Northern blot and real-time quantitative PCR analysis of the differential expression levels of 15 genes confirmed the differential expression trends of eight candidate genes. When the Wnt pathway was regulated at the lower level of glycogen synthase kinase-3 beta (GSK-3 beta) or adenomatous polyposis coli (APC), we detected discrepant expression trends. We compared the number of binding sites of transcription factors in the genomic regions of all candidate target genes with the number of sites in control genes. We found that the genomic regions of the down-regulated genes include an increased number of putative MIZ-1 binding sites. Our study introduces several new Wnt target genes and provides indications that the specific gene expression pattern depends on the type of the activation trigger or the level of interference with the Wnt pathway. Furthermore, our data indicate that a high proportion of Wnt target genes are regulated by indirect mechanisms.

Differences between the interaction of beta-catenin with non-phosphorylated and single-mimicked phosphorylated 20-amino acid residue repeats of the APC protein.

The tumour suppressor protein adenomatous polyposis coli (APC) regulates the level and the intracellular localisation of the proto-oncoprotein beta-catenin. There are indications that a region comprising seven homologous 20-amino acid residue repeats within the APC protein is responsible for the interaction with beta-catenin and that the phosphorylation of conserved serine residues within these repeats increases the affinity for beta-catenin. We used biophysical methods to analyse the beta-catenin binding of single repeats or repeat combinations as non-phosphorylated or phosphorylated recombinant proteins. The non-phosphorylated repeats showed similar affinities, no matter whether they were tested as single recombinant repeats or in combination with neighbouring repeats. This result makes a cooperative influence between the repetitive motifs unlikely. The phosphorylation of the APC protein was mimicked by specific serine/aspartate mutations, which align to serine residues in the cytoplasmic beta-catenin binding domain of E-cadherin. Remarkably, the mimicked phosphorylation of a serine, which is not involved in beta-catenin interaction in the E-cadherin/beta-catenin complex, led to a significant increase in the APC affinity for beta-catenin. These results indicate structural differences between the E-cadherin/beta-catenin and the APC/beta-catenin complexes and provide quantitative evidence for the importance of the APC phosphorylation for its interaction with beta-catenin.

Proteinase-Activated Receptor 1 (PAR1) regulates leukemic stem cell functions.

External signals that are mediated by specific receptors determine stem cell fate. The thrombin receptor PAR1 plays an important role in haemostasis, thrombosis and vascular biology, but also in tumor biology and angiogenesis. Its expression and function in hematopoietic stem cells is largely unknown. Here, we analyzed expression and function of PAR1 in primary hematopoietic cells and their leukemic counterparts. AML patients' blast cells expressed much lower levels of PAR1 mRNA and protein than CD34+ progenitor cells. Constitutive Par1-deficiency in adult mice did not affect engraftment or stem cell potential of hematopoietic cells. To model an AML with Par1-deficiency, we retrovirally introduced the oncogene MLL-AF9 in wild type and Par1-/- hematopoietic progenitor cells. Par1-deficiency did not alter initial leukemia development. However, the loss of Par1 enhanced leukemic stem cell function in vitro and in vivo. Re-expression of PAR1 in Par1-/- leukemic stem cells delayed leukemogenesis in vivo. These data indicate that Par1 contributes to leukemic stem cell maintenance.

DNA methyltransferase inhibition reverses epigenetically embedded phenotypes in lung cancer preferentially affecting polycomb target genes.

PURPOSE: Cancer cell phenotypes are partially determined by epigenetic specifications, such as DNA methylation. Metastasis development is a late event in cancerogenesis and might be associated with epigenetic alterations. EXPERIMENTAL DESIGN: An in vivo selection approach was used to generate highly aggressive non-small cell lung cancer (NSCLC) cell lines (A549 and HTB56) followed by genome-wide DNA methylation analysis. Furthermore, the therapeutic effects of the epigenetic agent azacytidine on DNA methylation patterns and the in vivo phenotypes were explored. RESULTS: Widespread changes of DNA methylation were observed during development of highly aggressive cell lines. Up to 2.5% of the CpG-rich region was differentially methylated as identified by reduced representation bisulfite sequencing compared with the less aggressive parental cell lines. DNA methyltransferase inhibition by azacytidine reversed the prometastatic phenotype; this was highly associated with the preferential loss of DNA methylation at sites that were hypermethylated during the in vivo selection. Of note, polycomb (PRC2) binding sites were particularly affected by DNA methylation changes after azacytidine exposure that persisted over time. CONCLUSIONS: We could show that metastatic capability of NSCLC is closely associated with DNA methylome alterations. Because inhibition of DNA methyltransferase reversed metastasis-prone phenotype, epigenetic modulation seems to be a potential therapeutic approach to prevent metastasis formation.

Increased HDAC1 deposition at hematopoietic promoters in AML and its association with patient survival.

Epigenetic changes play a crucial role in leukemogenesis. HDACs are frequently recruited to target gene promoters by balanced translocation derived oncogenic fusion proteins. As important epigenetic effector mechanisms, histone deacetylases (HDAC) have emerged as potential therapeutic targets. However, the patterns of HDAC1 localization and the role of HDACs in leukemia pathogenesis remain to be elucidated. Using ChIP-Chip analyses we analyzed HDAC1 deposition patterns at more than 10,000 gene promoters in a large cohort of leukemia patients and CD34+ controls. HDAC1 binding was significantly increased in AML blasts compared to CD34+ progenitor cells at 130 gene promoters whereas decreased binding was observed at 66 gene promoters. Distinct HDAC1 binding patterns occurred in AML subtypes with balanced translocations t(15;17), t(8;21) and inv(16). In addition, a more generalized signature was established, that revealed an AML specific pattern of HDAC1 distribution. Many of the HDAC1-binding altered promoters regulate genes involved in hematopoiesis, transcriptional regulation and signal transduction. HDAC1 binding patterns were associated with patients' event free survival. This is the first study to determine HDAC1 modification patterns in a large number of AML and ALL specimens. Our findings suggest that dyslocalization of HDAC1 is a common feature in AML. Importantly, HDAC1 modifications possess prognostic power for patient survival. Our findings suggest that altered HDAC1 localization is an explanation for the observed benefit of HDAC inhibitors in AML therapy.