Search

Transcriptional mechanisms responsible for low DAPK2 levels in particular AML subtypes. DAPK2 is a proapoptotic protein that is mostly expressed in the hematopoietic tissue. A detailed DAPK2 expression analysis in two large AML patient cohorts revealed particularly low DAPK2 mRNA levels in APL. DAPK2 levels were restored in APL patients undergoing ATRA therapy. PML‐RARA is the predominant lesion in APL causing transcriptional repression of genes important for neutrophil differentiation. We found binding of PML‐RARA and PU.1, a myeloid master regulator, to RARA and PU.1 binding sites in the DAPK2 promoter. Ectopic expression of PML‐RARA in non‐APL, as well as knocking down PU.1 in APL cells, resulted in a significant reduction of DAPK2 expression. Restoring DAPK2 expression in PU.1 knockdown APL cells partially rescued neutrophil differentiation, thereby identifying DAPK2 as a relevant PU.1 downstream effector. Moreover, low DAPK2 expression is also associated with C/EBPα‐mutated AML patients, and we found C/EBPα‐dependent regulation of DAPK2 during APL differentiation. In conclusion, we identified first inhibitory mechanisms responsible for the low DAPK2 expression in particular AML subtypes, and the regulation of DAPK2 by two myeloid transcription factors underlines its importance in neutrophil development.

The transcription factor, CCAAT enhancer binding protein alpha (C/EBPα), is crucial for granulopoiesis and is deregulated by various mechanisms in acute myeloid leukemia (AML). Mutations in the CEBPA gene are reported in 10% of human patients with AML. Even though the C/EBPα mutants are known to display distinct biologic function during leukemogenesis, the molecular basis for this subtype of AML remains elusive. We have recently showed the significance of deregulation of C/EBPα-regulated microRNA (miR) in AML. In this study, we report that miR-34a is a novel target of C/EBPα in granulopoiesis. During granulopoiesis, miR-34a targets E2F3 and blocks myeloid cell proliferation. Analysis of AML samples with CEBPA mutations revealed a lower expression of miR-34a and elevated levels of E2F3 as well as E2F1, a transcriptional target of E2F3. Manipulation of miR-34a reprograms granulocytic differentiation of AML blast cells with CEBPA mutations. These results define miR-34a as a novel therapeutic target in AML with CEBPA mutations.

Transcription factor CCAAT enhancer binding protein α (C/EBPα) is essential for granulopoiesis and its function is deregulated in leukemia. Inhibition of E2F1, the master regulator of cell-cycle progression, by C/EBPα is pivotal for granulopoiesis. Recent studies show microRNA-223 (miR-223), a transcriptional target of C/EBPα, as a critical player during granulopoiesis. In this report, we demonstrate that during granulopoiesis microRNA-223 targets E2F1. E2F1 protein was up-regulated in miR-223 null mice. We show that miR-223 blocks cell-cycle progression in myeloid cells. miR-223 is down-regulated in different subtypes of acute myeloid leukemia (AML). We further show that E2F1 binds to the miR-223 promoter in AML blast cells and inhibits miR-223 transcription, suggesting that E2F1 is a transcriptional repressor of the miR-223 gene in AML. Our study supports a molecular network involving miR-223, C/EBPα, and E2F1 as major components of the granulocyte differentiation program, which is deregulated in AML.

The translocation t(15;17) generates the chimeric PML-RARα transcription factor that is the initiating event of acute promyelocytic leukemia. A global view of PML-RARα transcriptional functions was obtained by genome-wide binding and chromatin modification analyses combined with genome-wide expression data. Chromatin immunoprecipitation (ChIP)–chip experiments identified 372 direct genomic PML-RARα targets. A subset of these was confirmed in primary acute promyelocytic leukemia. Direct PML-RARα targets include regulators of global transcriptional programs as well as critical regulatory genes for basic cellular functions such as cell-cycle control and apoptosis. PML-RARα binding universally led to HDAC1 recruitment, loss of histone H3 acetylation, increased tri-methylation of histone H3 lysine 9, and unexpectedly increased trimethylation of histone H3 lysine 4. The binding of PML-RARα to target promoters and the resulting histone modifications resulted in mRNA repression of functionally relevant genes. Taken together, our results reveal that the transcription factor PML-RARα regulates key cancer-related genes and pathways by inducing a repressed chromatin formation on its direct genomic target genes.

The clinical progression of chronic myeloid leukemia (CML) from chronic phase to blast crisis is characterized by the increasing failure of myeloid precursors to differentiate into mature granulocytes. This study was undertaken to investigate the influence of Bcr-Abl and of the small molecule Abl tyrosine–kinase inhibitor imatinib mesylate on granulocyte colony-stimulating factor (G-CSF)–induced neutrophilic differentiation. We show that differentiation of 32Dcl3 cells into mature granulocytes is accompanied by the increased expression of the antigens macrophage adhesion molecule–1 (Mac-1) and Gr-1, of the G-CSF receptor (G-CSFR), of myeloid transcription factors (CCAAT/enhancer-binding protein–α [C/EBPα], C/EBPε, and PU.1), and of the cyclin-dependent kinase inhibitor p27Kip1. In 32Dcl3 cells transfected with thebcr-abl gene (32DBcr-Abl), G-CSF did not trigger either granulocytic differentiation or the up-regulation of C/EBPα, C/EBPε, and the G-CSFR. This could be correlated to a defect in c-Myc down-regulation. In contrast, the up-regulation of PU.1 and p27Kip1 by G-CSF was not affected by Bcr-Abl. Importantly, incubation of 32DBcr-Ablwtcells with the kinase inhibitor imatinib mesylate prior to G-CSF stimulation completely neutralized the effects of Bcr-Abl on granulocytic differentiation and on C/EBPα and C/EBPε expression. Taken together, the results suggest that the Bcr-Abl kinase induces a reversible block of the granulocytic differentiation program in myeloid cells by disturbing regulation of hematopoietic transcription factors such as C/EBPα and C/EBPε.

The transcription factor PU.1 is required for normal blood cell development. PU.1 regulates the expression of a number of crucial myeloid genes, such as the macrophage colony-stimulating factor (M-CSF) receptor, the granulocyte colony-stimulating factor (G-CSF) receptor, and the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor. Myeloid cells derived from PU.1−/−mice are blocked at the earliest stage of myeloid differentiation, similar to the blast cells that are the hallmark of human acute myeloid leukemia (AML). These facts led us to hypothesize that molecular abnormalities involving the PU.1 gene could contribute to the development of AML. We identified 10 mutant alleles of the PU.1 gene in 9 of 126 AML patients. The PU.1 mutations comprised 5 deletions affecting the DNA-binding domain, and 5 point mutations in 1) the DNA-binding domain (2 patients), 2) the PEST domain (2 patients), and 3) the transactivation domain (one patient). DNA binding to and transactivation of the M-CSF receptor promoter, a direct PU.1 target gene, were deficient in the 7 PU.1 mutants that affected the DNA-binding domain. In addition, these mutations decreased the ability of PU.1 to synergize with PU.1-interacting proteins such as AML1 or c-Jun in the activation of PU.1 target genes. This is the first report of mutations in the PU.1 gene in human neoplasia and suggests that disruption of PU.1 function contributes to the block in differentiation found in AML patients.

Several transcription factors have been implicated as playing a role in myelopoiesis. PU.1, an ets-family transcription factor, is required for the development of myeloid and lymphoid lineages, whereas the transcription factor CCAAT–enhancer binding protein family member C/EBPα is essential for granulocyte development. We present here the first evidence that C/EBPα blocks the function of PU.1. PU.1 and C/EBPα interact physically and colocalize in myeloid cells. As a consequence of this interaction, C/EBPα can inhibit the function of PU.1 to activate a minimal promoter containing only PU.1 DNA-binding sites. We further demonstrate that the leucine zipper in the DNA-binding domain of C/EBPα interacts with the β3/β4 region in the DNA-binding domain of PU.1 and as a result displaces the PU.1 coactivator c-Jun. Finally, C/EBPα blocks PU.1-induced dendritic cell development from CD34+ human cord blood cells. The functional blocking of PU.1 by C/EBPα could be the mechanism by which C/EBPα inhibits cell fates specified by PU.1 and directs cell development to the granulocyte lineage.

Invasive fungal infections have increasingly become a matter of concern with regard to patients receiving intensive myelosuppressive therapy for hematologic malignancies. Such infections, especially prolonged neutropenia systemic fungal infections, may contribute substantially to infectious complications and early death. Measures for early detection and effective prophylactic strategies using active and nontoxic antifungal agents are therefore urgently needed. The current randomized study was initiated to assess the efficacy of oral fluconazole as systemic antifungal prophylaxis for high risk patients with recurrent acute myeloid leukemia undergoing intensive salvage therapy. Of 68 fully evaluable patients, 36 were randomized to fluconazole in addition to standard prophylaxis with oral co-trimoxazol, colistin sulphate, and amphotericin B suspension, and 32 were randomized to standard prophylaxis only. No major differences between the two groups were observed in the number of episodes of fever of unknown origin (61% vs. 50%) or clinically defined infections (56% vs. 50%). Microbiologically defined infections were more frequent in the fluconazole group (50% vs. 31%), mainly due to a higher incidence of bacteremias (42% vs. 22%). There were two cases of proven invasive fungal infections in each group. Systemic amphotericin B was administered more frequently to patients receiving fluconazole prophylaxis (56% vs. 28%). Fluconazole prophylaxis had no impact on the rate of early death or overall survival. For patients with high risk recurrent acute myeloid leukemia undergoing intensive salvage therapy, antifungal prophylaxis with fluconazole was not superior to standard prophylaxis only. Cancer 1998;83:291-301. © 1998 American Cancer Society.

In the original article, the affiliations were presented incorrectly. David Petroff is in fact the only author at affiliation 2. All other authors listed as being at affiliation 2 (Tina Weiße, Sebastian Beer, Franziska Gnatzy, Joachim Mössner, Michael Tröltzsch, Johannes Wiegand and Volker Keim) are in fact just at affiliation 1. These have now been corrected in the original article.

Since publication of this article, the authors identified an error in the acknowledgments section. The original sentence in acknowledgments reads as follows:

Franke: Novartis: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy; Jazz: Honoraria. Niederwieser:Miltenyi: Speakers Bureau; Novartis: Research Funding.

Acute myeloid leukemia (AML) is a very heterogeneous disease of the hematopoietic system which is characterized by a fast progress with poor survival options. Despite intensive research standard treatment strategies rely since decades on the same chemotherapeutics, and the overall survival options still remain poor.

Introduction:MicroRNA miR-1301is embedded in intron 1 in the DNMT3Agene, which encodes the DNA (cytosine-5)-methyltransferase 3A, is frequently mutated in older acute myeloid leukemia (AML) patients (pts) & has been associated with clonal hematopoiesis. In glioma cells miR-1301suppresses tumor cell invasion by regulating the activity & function of the p53 pathway & inhibits cell proliferation by targeting NRAS. The role of miR-1301in AML remains to be elucidated.

Introduction: Relapse of the disease remains a major burden after stem cell transplantation (HCT) following myeloablative conditioning and even more after reduced intensity and non-myeloablative conditioning. Efforts to reduce relapse incidence involve early immunosuppression withdrawal and prophylactic buffy coat infusion in high risk patients. In this phase II study we analyzed the role of disease-specific chimerism driven immunosuppression.

Introduction:Prognosis remains poor for most acute myeloid leukemia (AML) patients (pts). Enhanced risk-stratification, novel & individualized therapies to improve outcomes are needed. The RAS-pathway (NRAS, KRAS & HRAS& among others the regulator SHP-2 encoded by PTPN11) controls cell proliferation, cell differentiation & apoptosis & mutations in this pathway are common in many human malignancies, including AML. Previous studies of the prognostic impact of RASmutations (mut) in AML demonstrated variable & context specific results. The prognostic impact in pts receiving allogeneic stem cell transplantation (HSCT) remains to be elucidated.

In recent years expression levels of several genes & microRNAs (miR) were identified as strong prognostic markers, capable to refine AML risk stratification. So far technical difficulties, including the limitations of established methods for comparable, absolute quantification & the lack of defined cut points prevented translation of these findings into clinical practice. Innovative digital droplet PCR (ddPCR) is a novel technique with high sensitivity, specificity that allows absolute quantification - without the need for standard curves - & promises better inter-laboratory comparability.

Expression levels of miR-29family members (i.e. miR-29a, miR-29b, &miR-29c) are deregulated in various neoplastic diseases, including acute myeloid leukemia (AML), known to affect DNA-methylation profiles by targeting epigenetic modifiers, & have been shown to be important for normal hematopoietic stem cell function. Mir-29is organized in two distinctively regulated bi-cistronic clusters: the miR-29a/b-1cluster & the miR-29b-2/ccluster.

Introduction:The transcription factor ZBTB7A regulates early differentiation of hematopoietic progenitors & has been associated with oncogenic as well as oncosuppressive functions. While it was shown that ectopic overexpression of Zbtb7ain immature lymphocytes leads to the development of an aggressive T-cell lymphoblastic leukemia, high ZBTB7Aexpression in cytogenetically normal acute myeloid leukemia (CN-AML) is associated with improved outcomes. Furthermore, recently a leukemogenic cooperation between RUNX1/RUNX1T1&ZBTB7Amutations in t(8;21)-associated AML was suggested.

Allogeneic hematopoietic cell transplantation (HSCT) is a powerful consolidation option for acute myeloid leukemia (AML) patients (pts) in hematologic complete remission (CR). Disease recurrence after HSCT remains a major clinical problem & early identification of AML pts at risk of relapse is crucial to improve outcomes. High expression of the AML associated gene BAALC(Brain and acute leukemia, cytoplasmic) at diagnosis adversely impacts on outcomes in AML pts. Little is known about its prognostic capacity during disease course & as a marker of residual disease. Here we adopted digital droplet polymerase chain reaction (ddPCR) for absolute quantification of BAALCcopy numbers in peripheral blood (PB) prior to HSCT in AML pts in hematologic CR.

Introduction:Minimal residual disease (MRD) monitoring after achievement of hematologic complete remission (CR) in patients (pts) with acute myeloid leukemia (AML) aids in identifying pts at risk of relapse. Evaluating MRD markers for clinical practice is crucial for improving outcomes in AML.

Introduction:

Introduction:Outcomes of most acute myeloid leukemia (AML) patients (pts) remain poor. Enhanced risk-stratification and individualized treatment approaches are urgently needed. The Hedgehog (Hh) signaling pathway is important in embryonic development & stem cell biology & converges into activation of the transcription factor GLI1. In mice, loss of Gli1 increased the number of quiescent long-term hematopoietic stem cells with enhanced engraftment capacities & impaired myeloid development. Nevertheless, the biological role & prognostic impact of GLI1expression in human AML remains to be fully elucidated.

Background:Most acute myeloid leukemia (AML) patients (pts) stilldo not achieve long-term survival. Better risk stratification and novel therapeutic avenues are needed to improve pts outcomes. The expression of microRNAs has been demonstrated to be altered in AML & miR-based therapies are entering clinical trials. MiR-320a, maps to chromosome 8p21.3 & is known to play a role in several tumors; e.g. higher miR-320aexpression suppresses the progression of colorectal cancer. In AML miR-320ahas been shown to inhibit cell proliferation, likely by targeting the transferrin receptor 1.

Introduction:Despite progress in understanding acute myeloid leukemia (AML) biology, most patients (pts) still have a poor prognosis. MicroRNAs (miR) have emerged as important players in AML biology. High expression of miR-181ahas been associated with improved outcomes in AML pts. Mature miR-181aoriginates from two precursor molecules pri-miR-181a-1& pri-miR-181a-2which have been associated with distinct biological features & are derived from chromosome 1q32.1 & 9q33.3, respectively. Allogeneic stem cell transplantation (HCT) offers a potential curative treatment option for AML pts. With the introduction of reduced intensity conditioning (RIC) regimens, this procedure also became available for older or comorbid individuals. Here, we measured pri-miR-181a-1& pri-miR-181a-2and analyzed their impact on survival in RIC-HCT treated AML pts.

Allogeneic hematopoietic cell transplantation (HCT) represents a post-remission therapy offering potential cure for acute myeloid leukemia (AML) patients (pts). Reduced-Intensity Conditioning (RIC) is increasingly used in AML pts undergoing HCT ineligible for conventional conditioning.

Transcription factor CCAAT enhancer binding protein α (C/EBPα) is crucial for the differentiation of granulocytes. Experimental data from animal models as well as patient samples suggest that loss of function or expression of C/EBPα provides a platform on which acute myeloid leukemia (AML) develops. C/EBPα is mutated in around 9% of acute myeloid leukemia. The mutations reported in C/EBPα are frame shift mutations at N-terminal domain and point mutations at basic region Leucine zipper. The mutant form of C/EBPα ie C/EBPα-p30 exhibits dominant negative function over the wild type protein. Peptidyl-prolyl cis/transisomerase, Pin1 binds to and isomerizes the peptidyl-prolyl bond in specific phosphorylated Ser/Thr-Pro motifs. A growing number of studies show that Pin1 is overexpressed in many cancers and has significant role in tumorigenesis. In the present study we investigated the role of Pin1 in acute myeloid leukemia with C/EBPα mutation. Here we report C/EBPα-p30 could induce Pin1 transcription as assessed by quantitative Real-Time RT-PCR analysis. Affymetrix mRNA expression analysis show that Pin1 is upregulated in patients with acute myeloid leukemia. Silencing of Pin1 could overcome the dominant negative action of the C/EBPα-p30 over the C/EBPα-p42 transactivation capacity as analyzed by promoter assay. By silencing Pin1 with inhibitor against Pin1 (PiB), we could show myeloid differentiation in Kasumi-6 cells by FACS analysis with granulocytic specific markers. Western blot analysis shows that Pin1 inhibition by PiB could upregulate wild type C/EBPα protein level. Luciferase promoter assay for the Pin1 promoter shows that C/EBPα-p30 induces Pin1 promoter activity in association with E2F1. Mean while, wild type C/EBPα interferes with transactivation of the Pin1 promoter and downregulates Pin1 mRNA expression. We investigated the mechanism underlying the dominant negative action of C/EBPα-p30 over the wild type protein. We have previously shown that c-Jun expression is high in AML patients with C/EBPα mutation and c-Jun could block C/EBPα function by protein-protein interaction. Quantitative Real-Time RT-PCR analysis shows that overexpression of Pin1 induces c-Jun mRNA expression, while inhibition of Pin1 by the inhibitor PiB downregulates c-Jun mRNA expression. We show that c-Jun blocks the DNA binding and transactivation of wild type C/EBPα protein as assessed by gel shift assay and promoter assay respectively. In conclusion, inhibition of Pin1 leads to granulocytic differentiation of human myeloid cells. Our findings suggest inhibition of Pin1 as a novel strategy in treating AML patients with C/EBPα mutation.