CITED2 Cooperates with Low PU.1 and DNMT3A to Maintain Self-Renewal in Hematopoietic Stem Cells

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 309-309
Author(s):  
Hein Schepers ◽  
Patrick Korthuis ◽  
Marjan Geugien ◽  
Jennifer Jaques ◽  
Tihomira I. Todorova ◽  
...  
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Stem Cells ◽  
Conflicts Of Interest ◽  
Ectopic Expression ◽  
Gene Expression Pattern ◽  
Dependent Manner ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Specific Subset

Abstract CITED2 has a conserved role in the maintenance of normal hematopoiesis. We have recently shown that ~70% of acute myeloid leukemia (AML) patients display enhanced CITED2 expression levels. Interfering with CITED2 expression is detrimental for leukemia maintenance in vitro and in vivo, demonstrating that CITED2 is critically important for the survival of leukemic stem cells (LSCs). Ectopic expression of CITED2 in normal CD34+ stem and progenitor cells (HSPCs) led to significantly better human engraftment in transplanted NSG mice, consistent with the maintenance of very primitive lin- CD34+ CD38- CD90+ CD45RA- HSCs within the bone marrow 28 weeks after transplantation. Although the CITED2-engrafted mice displayed enlarged spleens, blood development appeared normal, as measured through myeloid, B and T cell staining. This indicates that CITED2 as a single hit is not sufficient to transform human CD34+ cells. CITED2 expression frequently coincides with low expression of the myeloid transcription factor PU.1, suggesting that combined effects, rather than single events are important during AML development. To investigate this, we combined lentiviral downregulation of PU.1 with overexpression of CITED2 (PU.1Low-CITED2High) and studied hematopoietic development. CITED2 increased the percentage of immature CD34+ CD38- cells 5-fold, which was not further increased by the additional downregulation of PU.1. However, functional analysis through limiting dilution LTC-iC assays indicated that combining PU.1 down-, with CITED2 upregulation led to a synergistic 8.5-fold increase in LTC-iC frequency, whereas only changing PU.1 or CITED2 induced a respective 1.4 to 3-fold change in HSC frequency. To more stringently assess self-renewal, we cultured transduced cells for 4 weeks on MS5 cells under myeloid differentiating conditions (G-CSF, IL3 and TPO) and subsequently performed CFC assays. Whereas after 4 weeks all groups displayed similar colony numbers, secondary and tertiary replatings demonstrated that self-renewal could only be maintained for more than 10 weeks when CITED2 upregulation was combined with PU.1 downregulation. This replating capacity of PU.1Low-CITED2High cells was limited to CD34+ CD38- HSCs, as replating of CD34+ CD38+ progenitor-derived colonies did not yield new CFCs. In order to investigate the underlying mechanisms, we performed transcriptome analysis on human HSCPs after knockdown of PU.1, overexpression of CITED2 or the combination of both. PU.1Low-CITED2High cells displayed a gene expression pattern different from the PU.1Low or CITED2High only cells, suggesting that the two events have synergistic effects. Some genes, like HLX and SF3B1 have been shown to cause or are mutated in AML, demonstrating that the synergistic changes are related to AML. When comparing the differentially regulated genes in the PU.1Low -CITED2High cells to the gene expression in the Hemaexplorer database, a similar pattern was observed, when compared between AML and normal cells. In order to investigate the effects of the PU.1low CITED2high combination on AML development, we resorted to a PU.1-dependent mouse model of AML development. CITED2 expression in BM cells from PU.1KD/KD mice (in which deletion of an Upstream Regulatory Element leads to an 80% downregulation of PU.1), led to a steady increase of GFP+ cells over time as compared to control cells and demonstrated a dramatic expansion of Gr-1+ Mac-1+ cells, a hallmark of AML in these mice. This suggests that CITED2 contributes to a faster progression towards AML upon lowering of PU.1. To identify if our model corresponds to AMLs with a specific subset of mutations, we clustered publically available AML data (TCGA), based on the gene expression changes in the PU.1Low -CITED2High cells. The majority of AMLs clustered together in 2 groups, in which FLT3, p53 and DNMT3A mutations were most prevalent. FLT3 mutations, through its activation of STAT5, are consistent with high CITED2 expression, whereas p53 mutations are consistent with our data indicating that CITED2 loss regulates HSCs in a p53-dependent manner. The presence of DNMT3A mutations suggests that DNA methylation changes collaborate with high CITED2 and low PU.1 during leukemogenesis. This is currently under investigation. In summary, our data imply that CITED2, low PU.1 and potentially changes in DNA methylation all contribute to maintenance of self-renewal and leukemogenesis. Disclosures No relevant conflicts of interest to declare.

scholarly journals DNMT3A Regulates Hematopoietic Stem Cell Function Via DNA Methylation-Independent Functions

Blood ◽  
2021 ◽  
Vol 138 (Supplement 1) ◽  
pp. 24-24
Author(s):  
Won Kyun Koh ◽  
Hamza Celik ◽  
Jacob Tao ◽  
Jake Fairchild ◽  
Ostap Kukhar ◽  
...  
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Dna Methyltransferase ◽  
Molecular Mechanisms ◽  
Conflicts Of Interest ◽  
Ectopic Expression ◽  
Wild Type ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Independent Functions

Abstract The balance between self-renewal and differentiation of hematopoietic stem cells (HSCs) is strictly regulated to sustain blood production throughout adult life. De novo DNA methyltransferase 3-alpha (DNMT3A) is one of the major epigenetic regulators that is essential for efficient HSC differentiation. DNMT3A mutations are prevalent in myeloid diseases that include acute myeloid leukemia (AML; ~22%) and myelodysplastic syndrome (MDS; ~10%) where they act as initiating events However, the precise molecular mechanisms of how DNMT3A regulates normal hematopoiesis and its mutations prime HSCs for leukemic formation are unclear. Although DNMT3A is described as a DNA methyltransferase enzyme, the lack of consistent correlation between changes in DNA methylation and differential gene expression in Dnmt3a-null HSCs in mouse models, and AML patients with DNMT3A mutations undermine the conventional understanding of DNMT3A's canonical role in hematopoietic cells. Hence, we hypothesized that DNMT3A may have novel functions outside of DNA methylation that regulate HSC fate decisions. To answer this question, we first ectopically expressed GFP-labeled Dnmt3a constructs (wild-type Dnmt3a, Dnmt3aE752A; complete DNA methylation dead, and Dnmt3aR832A; reduced DNA methylation target recognition) and empty vector (negative control) in Dnmt3a-null (Vav-Cre: Dnmt3afl/fl = Dnmt3a-/- in hematopoiesis) bone marrow (BM) cells. The result showed that similar to restoring wild-type Dnmt3a, ectopic expression of Dnmt3aE752A as well as Dnmt3aR832A showed a rescue effect of decreased engraftment of transduced cells in the peripheral blood as well as reduced HSC numbers in the BM. Analysis of DNA methylation by whole-genome bisulfite sequencing (WGBS) in transduced cells showed this phenotypic and functional rescue of the Dnmt3a-/- phenotype occurred in the absence of restored DNA methylation patterns. To study the importance of Dnmt3a-mediated DNA methyltransferase activity in a more physiological system, we generated knock-in mice that have one copy of either wild-type Dnmt3a, Dnmt3aE752A, or Dnmt3aR832A (CAGG-Cre-ER T2 = ER T2-Cre: Dnmt3afl/+, Dnmt3afl/E752A, and Dnmt3afl/R832A) to be compared to the Dnmt3a-null group (ER T2-Cre: Dnmt3afl/-). These mice contain one allele with loxP-flanked Dnmt3a that is deleted by tamoxifen-inducible Cre-mediated recombination and one allele of either wild-type Dnmt3a, Dnmt3aE752A, Dnmt3aR832A, or germline knockout Dnmt3anull. 5-weeks post-tamoxifen (~93% floxed allele recombination), competitive transplantation of 250 phenotypically defined test HSCs against with 2.5x10 5 congenic competitor BM cells was performed. Dnmt3a fl/R832A recipients had higher engraftment (35.6 % +/- 6.1) than Dnmt3afl/+ (28.5% +/- 7.2) and Dnmt3afl/- (10.7% +/- 2.79), while Dnmt3afl/E752A had slightly higherengraftment (12.5% +/- 3) than Dnmt3afl/-. Analysis of the BM 18 weeks post-transplant showed that Dnmt3afl/E752A and Dnmt3afl/R832A HSCs phenocopied the HSC self-renewal potential phenotype of heterozygous Dnmt3a fl/+HSCs (Fig. 1). The absolute count of donor-derived HSCs per mouse after the transplant were: ER T2-Cre control (675.7 +/- 299.3), Dnmt3afl/+ (1870 +/- 961.4), Dnmt3afl/- (3546 +/- 1019), Dnmt3afl/E752A (1130 +/- 362.7), and Dnmt3afl/R832A (1184 +/- 344.5) (mean +/- S.E.M.). While the described clonal expansion of Dnmt3a-null HSCs was observed, HSCs with one copy of full-length Dnmt3a but devoid of its methyltransferase capacity mimicked the heterozygous state rather than the homozygous loss-of-function. This is the first evidence to suggest that DNMT3A potentially regulates HSCs by non-canonical (DNA methylation independent) mechanisms. DNA methylation analysis by WGBS is ongoing to determine if Dnmt3afl/E752A and Dnmt3afl/R832A HSCs show a methylome comparable to Dnmt3a-null HSCs whilst having the functional potential of Dnmt3a-heterozygous HSCs, which will be complemented with other molecular analyses including gene expression. Our study opens new avenues for investigations into the molecular mechanisms of DNMT3A function in HSC biology, which could ultimately benefit clinical practice by identifying new therapeutic approaches for the patients with DNMT3A mutations. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.

KLF4 Regulates Self-Renewal of Leukemic Stem Cells in Chronic Myeloid Leukemia By Repressing Gbl Expression and Altering mTORC2 Activity

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 1789-1789
Author(s):  
Chun Shik Park ◽  
Ye Shen ◽  
Takeshi Yamada ◽  
Koramit Suppipat ◽  
Monica Puppi ◽  
...  
Keyword(s):  
Gene Expression ◽  
Stem Cells ◽  
Chronic Myeloid Leukemia ◽  
Progenitor Cells ◽  
Myeloid Leukemia ◽  
Conflicts Of Interest ◽  
Chronic Phase ◽  
Leukemic Stem Cells ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Tyrosine kinase inhibitors (TKIs) are the standard treatment for eradicating BCR-ABL-positive progenitor cells in chronic myeloid leukemia (CML); however, disease often relapses upon drug discontinuation because TKIs do not effectively eliminate leukemic stem cells (LSC). The development of novel strategies aimed at eradicating LSC without harming normal hematopoietic stem cells (HSC) is essential for the cure of CML patients. The generation of LSC-directed therapy relies on the identification of novel molecular pathways that selectively regulate LSC function independent of BCR-ABL. The Krüppel-like factor 4(KLF4) is a transcription factor that can either activate or repress gene transcription acting as an oncogene or a tumor suppressor depending on the cellular context. Analysis of a published dataset from chronic phase CML patients revealed elevated levels of KLF4 in LSC compared to progenitor cells indicating that KLF4 is likely implicated in LSC regulation. To study the role of KLF4 in LSC function, we used a CML mouse model combining somatic deletion of the Klf4 gene and retroviral transduction and transplantation of HSC. In contrast to mice receiving BCR-ABL-transduced Klf4fl/fl HSC that developed and succumbed to CML, mice transplanted with BCR-ABL-transduced Klf4Δ/Δ (Klf4fl/fl Vav-iCre+) HSC showed a progressive loss of leukemia despite an initial expansion of myeloid leukemic cells, which led to increased overall survival. This inability to sustain CML in the absence of KLF4 was caused by attrition of LSC in bone marrow and the spleen. Furthermore, deletion of KLF4 impaired the ability of LSC to recapitulate leukemia in secondary recipients suggesting a loss of self-renewal capacity. In contrast to LSC, KLF4 deletion led to increased self-renewal of normal HSC assessed by serial competitive transplantation. To identify KLF4 target genes involved in LSC self-renewal, we performed a global gene expression analysis using Klf4Δ/Δ LSC purified by cell sorting from leukemic mice. Analysis of gene expression in Klf4Δ/Δ LSC revealed significant upregulation of GβL, a component of mTOR complexes. Finally, we identified that KLF4 binds to GβL promoter by Chip-Seq analysis and that silencing resulted in inhibition of mTORC2 but not mTORC1 activity in 32D-BCR-ABL-positive CML cells. Our findings suggest that KLF4 transcriptionally represses GβL expression in LSC and that mTORC2 inhibition has the potential to completely eradicate LSC and induce treatment-free remission. Disclosures No relevant conflicts of interest to declare.

scholarly journals Epigenetic Signature of Leukemia Stem Cells Defines Subgroups Associated with Clinical Outcome and Cell of Origin in AML

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 2147-2147
Author(s):  
Namyoung Jung ◽  
Bo Dai ◽  
Andrew J. Gentles ◽  
Peter Murakami ◽  
Ravindra Majeti ◽  
...  
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Stem Cells ◽  
Conflicts Of Interest ◽  
Cell Model ◽  
Leukemia Stem Cells ◽  
Functional Difference ◽  
Cell Of Origin ◽  
Hematopoietic Stem ◽  
Blast Cells

Abstract Acute myeloid leukemia (AML) is a hematologic malignancy initiated by leukemia-initiating or leukemia stem cells (LSC) which can differentiate into clonally related leukemic blast cells. This leukemia stem cell model proposes that functional properties of LSC and their blast progeny must be derived by epigenetic differences. Here, we examined genome wide DNA methylation of LSC-enriched populations and blast cells from 15 AML patients, along with 6 well-defined hematopoietic stem and progenitor cell (HSPC) populations from 5 normal controls using Illumina Infinium Human Methylation 450 BeadChip array. Strikingly, LSC-enriched populations exhibited global hypomethylation compared to non-engrafting blast cells, demonstrating that epigenetic change could drive the functional difference of LSC and their blast progeny. We defined an LSC epigenetic signature by integrating DNA methylation and gene expression analysis. The signature independently predicted overall survival of patients in both DNA methylation and gene expression data sets. Finally, we identified that LSC-enriched populations formed two major clusters when compared to normal HSPC: a granulocyte-macrophage progenitor (GMP)-like and a lymphoid-primed multipotential progenitor (L-MPP)-like subgroup that may reflect the cell of origin for these cases. These subgroups showed strong association with cytogenetic abnormalities and molecular mutations associated with the cell of origin. These results provide the first evidence for epigenetic variation between LSC and their blast progeny that are prognostic, and for epigenetically defined cell of origin of AML LSC. Disclosures No relevant conflicts of interest to declare.

scholarly journals Maintenance of Hematopoietic Stem Cells Through Regulation of Wnt and mTOR Pathways.

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 2309-2309
Author(s):  
Jian Huang ◽  
Peter S. Klein
Keyword(s):  
Stem Cells ◽  
Hematopoietic Stem Cells ◽  
Signaling Pathways ◽  
Glycogen Synthase ◽  
Dependent Manner ◽  
Mtor Inhibition ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract Abstract 2309 Hematopoietic stem cells (HSCs) maintain the ability to self-renew and to differentiate into all lineages of the blood. The signaling pathways regulating hematopoietic stem cell (HSCs) self-renewal and differentiation are not well understood. We are very interested in understanding the roles of glycogen synthase kinase-3 (Gsk3) and the signaling pathways regulated by Gsk3 in HSCs. In our previous study (Journal of Clinical Investigation, December 2009) using loss of function approaches (inhibitors, RNAi, and knockout) in mice, we found that Gsk3 plays a pivotal role in controlling the decision between self-renewal and differentiation of HSCs. Disruption of Gsk3 in bone marrow transiently expands HSCs in a b-catenin dependent manner, consistent with a role for Wnt signaling. However, in long-term repopulation assays, disruption of Gsk3 progressively depletes HSCs through activation of mTOR. This long-term HSC depletion is prevented by mTOR inhibition and exacerbated by b-catenin knockout. Thus GSK3 regulates both Wnt and mTOR signaling in HSCs, with opposing effects on HSC self-renewal such that inhibition of Gsk3 in the presence of rapamycin expands the HSC pool in vivo. In the current study, we found that suppression of the mammalian target of rapamycin (mTOR) pathway, an established nutrient sensor, combined with activation of canonical Wnt/ß-catenin signaling, allows the ex vivo maintenance of human and mouse long-term HSCs under cytokine-free conditions. We also show that combining two clinically approved medications that activate Wnt/ß-catenin signaling and inhibit mTOR increases the number of long-term HSCs in vivo. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Maximal STAT5-Induced Proliferation and Self-Renewal at Intermediate STAT5 Activity Levels

2008 ◽  
Vol 28 (21) ◽  
pp. 6668-6680 ◽  
Author(s):  
Albertus T. J. Wierenga ◽  
Edo Vellenga ◽  
Jan Jacob Schuringa
Keyword(s):  
Gene Expression ◽  
Cell Fate ◽  
Target Genes ◽  
Expression Patterns ◽  
Activity Levels ◽  
Dependent Manner ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Cell Fate Decisions

ABSTRACT The level of transcription factor activity critically regulates cell fate decisions, such as hematopoietic stem cell (HSC) self-renewal and differentiation. We introduced STAT5A transcriptional activity into human HSCs/progenitor cells in a dose-dependent manner by overexpression of a tamoxifen-inducible STAT5A(1*6)-estrogen receptor fusion protein. Induction of STAT5A activity in CD34+ cells resulted in impaired myelopoiesis and induction of erythropoiesis, which was most pronounced at the highest STAT5A transactivation levels. In contrast, intermediate STAT5A activity levels resulted in the most pronounced proliferative advantage of CD34+ cells. This coincided with increased cobblestone area-forming cell and long-term-culture-initiating cell frequencies, which were predominantly elevated at intermediate STAT5A activity levels but not at high STAT5A levels. Self-renewal of progenitors was addressed by serial replating of CFU, and only progenitors containing intermediate STAT5A activity levels contained self-renewal capacity. By extensive gene expression profiling we could identify gene expression patterns of STAT5 target genes that predominantly associated with a self-renewal and long-term expansion phenotype versus those that identified a predominant differentiation phenotype.

scholarly journals microRNA-29a induces aberrant self-renewal capacity in hematopoietic progenitors, biased myeloid development, and acute myeloid leukemia

2010 ◽  
Vol 207 (3) ◽  
pp. 475-489 ◽  
Author(s):  
Yoon-Chi Han ◽  
Christopher Y. Park ◽  
Govind Bhagat ◽  
Jinping Zhang ◽  
Yulei Wang ◽  
...  
Keyword(s):  
Stem Cells ◽  
Acute Myeloid Leukemia ◽  
Myeloid Leukemia ◽  
Ectopic Expression ◽  
Hematopoietic Progenitors ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Myeloid Development ◽  
Acute Myeloid ◽  
Myeloid Progenitors

The function of microRNAs (miRNAs) in hematopoietic stem cells (HSCs), committed progenitors, and leukemia stem cells (LSCs) is poorly understood. We show that miR-29a is highly expressed in HSC and down-regulated in hematopoietic progenitors. Ectopic expression of miR-29a in mouse HSC/progenitors results in acquisition of self-renewal capacity by myeloid progenitors, biased myeloid differentiation, and the development of a myeloproliferative disorder that progresses to acute myeloid leukemia (AML). miR-29a promotes progenitor proliferation by expediting G1 to S/G2 cell cycle transitions. miR-29a is overexpressed in human AML and, like human LSC, miR-29a-expressing myeloid progenitors serially transplant AML. Our data indicate that miR-29a regulates early hematopoiesis and suggest that miR-29a initiates AML by converting myeloid progenitors into self-renewing LSC.

Oncogenic Nras Increases Hematopoietic Stem Cell Proliferation and Self-Renewal Through a Bimodal Effect

Blood ◽  
2012 ◽  
Vol 120 (21) ◽  
pp. 119-119
Author(s):  
Qing Li ◽  
Natacha Bohin ◽  
Tiffany Wen ◽  
Kevin M. Shannon ◽  
Sean J. Morrison
Keyword(s):  
Stem Cells ◽  
Conflicts Of Interest ◽  
Myeloproliferative Neoplasm ◽  
Mek Inhibitor ◽  
Ras Signaling ◽  
Self Renewal ◽  
Hematopoietic Stem ◽  
Activating Mutations ◽  
Cycle Regulation

Abstract Abstract 119 Accumulating evidence suggests that most leukemias are initiated by rare leukemic stem cells (LSC) that are transformed from the normal hematopoietic stem cells and progenitors (HSC/P) by genetic lesions that lead to activation of oncogenes and inactivation of tumor suppressor genes. However, the signaling mechanisms by which these genes transform HSC/P into LSC are poorly understood. Activating mutations of NRAS and KRAS are highly prevalent in acute myeloid leukemia (AML), some myeloproliferative neoplasm (MPN) and myelodysplastic syndromes (MDS). In addition other leukemia associated genetic lesions, such as the BCR-ABL fusion, PTPN11 mutations, FLT3 internal tandem duplications, and NF1 inactivation all deregulate Ras signaling. We previously developed a mouse strain that conditionally expresses an oncogenic NrasG12D allele from the endogenous locus. This consistently resulted in an indolent MPD with delayed onset and prolonged survival in Mx1-cre, NrasG12D/+ mice (referred to as NrasG12D). Oncogenic NrasG12D, however, cooperated with the MOL4070LTR retrovirus to induce AMLs that share molecular and morphologic features with human M4/M5 AML. Here we report that NrasG12D directly affects HSC/P functions. While normal HSCs must remain quiescent to maintain the long term self-renewal capacity and mutations that drive HSC into cycle often lead to HSC depletion, NrasG12D increased HSC proliferation but at the same time increased the self-renewal and competitiveness of HSCs. Serial transplantations revealed that NrasG12D HSCs were able to give higher level of reconstitution than wild-type (WT) HSCs and gave rise to long term multi-lineage reconstitution in lethally irradiated mice after up to four rounds of transplantation while WT HSCs failed to reconstitute beyond two rounds. These effects were not associated with the development of leukemia suggesting oncogenic Nras dys-regulates HSC at a pre-leukemic stage and therefore plays an important role in leukemia initiation. Using histone-2B-GFP (H2B-GFP) label-retaining assays, we further detected a “bimodal” effect of NrasG12D on HSCs: NrasG12D induced a subpopulation of rapid “cycling” HSCs that lost GFP labeling and reconstitution activity faster than WT HSC but another HSC subpopulation that remained more “quiescent” than WT HSCs and retained higher reconstitution when transplanted to irradiated mice. The canonical Ras effector, ERK, was not activated in NrasG12D HSC/Ps and inhibition of ERK with a MEK inhibitor, PD325901, did not have any effect on the Nras induced increase of HSC proliferation. Stat5, on the other hand, was significantly activated in NrasG12D HSC/Ps and heterozygous knockout of Stat5ab abolished the increased proliferation in NrasG12D HSCs, suggesting that Stat5 signaling mediates at least part of the Nras induced increase in HSC proliferation. Nras is thus the first signaling pathway that simultaneously increases HSC proliferation, self-renewal and competitiveness without inducing frank leukemogenesis. This is likely through a “bimodal” effect of Nras signaling on HSC cell cycle regulation. Our studies also identified Stat5 as a novel therapeutic target to inhibit early events in Ras mediated leukemic transformation. Disclosures: No relevant conflicts of interest to declare.

Epigenetic Effects of IDH1/IDH2 Mutations

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. SCI-33-SCI-33 ◽  
Author(s):  
Ari M. Melnick ◽  
Ross L Levine ◽  
Maria E Figueroa ◽  
Craig B. Thompson ◽  
Omar Abdel-Wahab
Keyword(s):  
Gene Expression ◽  
Dna Methylation ◽  
Stem Cells ◽  
Hematopoietic Stem Cells ◽  
Malignant Transformation ◽  
Covalent Modification ◽  
Specific Gene ◽  
Gene Promoters ◽  
Loss Of Function ◽  
Hematopoietic Stem

Abstract Abstract SCI-33 Epigenetic deregulation of gene expression through aberrant DNA methylation or histone modification plays an important role in the malignant transformation of hematopoietic cells. In particular, acute myeloid leukemias (AMLs) can be classified according to epigenetic signatures affecting DNA methylation or histone modifications affecting specific gene sets. Heterozygous somatic mutations in the loci encoding isocitrate dehydrogenase 1 and 2 (IDH1/2) occur in ∼20% of AMLs and are accompanied by global DNA hypermethylation and hypermethylation and silencing of a number of specific gene promoters. IDH1/2 mutations are almost completely mutually exclusive with somatic loss-of-function mutations in TET2, which hydroxylates methylcytosine (mCpG). DNA hydroxymethylation can function as an intermediate step in mCpG demethylation. TET2 mutant de novo AMLs also display global and promoter specific hypermethylation partially overlapping with IDH1/2 mutant cases. Mutations in the IDH1/2 loci result in a neomorphic enzyme that generates the aberrant oncometabolite 2-hydroxyglutarate (2HG) using α-ketoglutarate (αKG) as a substrate. 2HG can disrupt the activity of enzymes that use αKG as a cofactor, including TET2 and the jumonji family of histone demethylases. Expression of mutant IDH isoforms inhibits TET2 hydroxymethylation and jumonji histone demethylase functions. IDH and TET2 mutant AMLs accordingly exhibit reduced levels of hydroxymethylcytosine and a trend towards increased histone methylation. Mutant IDH or TET2 loss of function causes differentiation blockade and expansion of hematopoietic stem cells and TET2 knockout results in a myeloproliferative phenotype in mice. Hydroxymethylcytosine is in abundance in hematopoietic stem cells and displays specific distribution patterns, yet the function of this covalent modification is not fully understood. Recent data link TET2 with the function of cytosine deaminases as a pathway towards DNA demethylation, which has implications as well for B cell lymphomas and CML lymphoid blast crisis, which are linked with the actions of activation induced cytosine deaminase. Altogether, the available data implicate mutations in IDH1/2 and TET2 in promoting malignant transformation in several tissues, by disrupting epigenomics programming and altering gene expression patterning. Disclosures: Thompson: Agios Pharmaceuticals: Consultancy.

Efficiency of Leukemic Stem Cell Separation From Patients with Acute Myeloid Leukemia

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 4997-4997
Author(s):  
Lu Zhang ◽  
Susanne Hofmann ◽  
Lars Bullinger ◽  
Marlies Goetz ◽  
Markus Wiesneth ◽  
...  
Keyword(s):  
Gene Expression ◽  
Stem Cells ◽  
Cell Sorting ◽  
Peripheral Blood ◽  
Recovery Rate ◽  
Mononuclear Cells ◽  
Separation Efficiency ◽  
Conflicts Of Interest ◽  
Cell Number ◽  
Hematopoietic Stem

Abstract Abstract 4997 Leukemic stem cells (LSC) are the source for leukemic disease self-renewal and account for disease relapse after treatment. Therefore LSCs probably represent a critical target for therapeutic options. Xenograft models confirmed repeatedly that LSCs from AML patients reside mainly in CD34+CD38- compartment of leukemic blasts which makes the pure and efficient separation of this population mandatory to identify new therapeutic drugs to target LSC in different AML subtypes. We separated this subpopulation out of primary AML peripheral blood mononuclear cells (PBMC) samples with fluorescence-activated cell sorting (FACS) and magnetic-activated cell sorting (MACS) and compared the efficiency of both methods. In order to profile gene expression of LSCs and hematopoietic stem cells (HSC) MicroArrays were performed using GeneChip Human Genome U133 Plus 2.0 from Affymetrix. The CD34+CD38- subpopulation was separated from PBMCs of 12 AML patients and 5 healthy volunteers using FACS. Concerning the 12 primary AML samples, the ratio of CD34+CD38- cells ranges between 0.79% and 86.2% using 1–5×107 PBMC for separation. After sorting, the purity of those AML samples increased to 88.4–98.4% while 2×104-3.6×106 cells were obtained. MACS was used to separate 2 representative samples, in which the CD34+CD38- subpopulation was rather small (sample1: 0.78%) or large (sample2: 86.1%). Those sorted subpopulations were compared to the samples sorted via FACS. In order to evaluate separation efficiency in a standardized manner, we defined the recovery rate: (CD34+CD38- cell number obtained /total CD34+CD38- cell number) × 100%. The total CD34+CD38- cell number was calculated through a pre-sorting FACS analysis. For sample 1, MACS resulted in a recovery rate of 4.2–6.4% with a purity of 86.6–90.3%, which is inferior to the recovery rate of 17% and the purity of 92.1% using FACS. For Sample 2, MACS resulted in a recovery rate of 0.4% with a purity of 98.8%, compared to the recovery rate of 11.6% with a purity of 98.1% by FACS. Comparing both methods it is obvious that the purity doesn't differ a lot, but the yield is much higher using FACS. This could represent a powerful tool, when managing rare samples. Finally, by comparing purity and yield, we showed that FACS is the adequate separation method. At the moment MicroArrays are being performed in order to investigate the gene expression profile for 12–15 AML patients and 5 HVs. Taken together, we showed a widely efficient method to routinely separate LSCs from patients with different subtypes of AML. Microarrays, that have been performed, represent a method that allows the comparison of the characteristics of LSCs in different AML subtypes and also of LSCs from bone-marrow with LSCs from peripheral blood and with HVs. These array data analyses are ongoing and will be presented. Disclosures: No relevant conflicts of interest to declare.

MiR-29a Maintains Hematopoietic Stem Cell Self-Renewal and Is Required For Myeloid Leukemogenesis

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 1190-1190
Author(s):  
Wenhuo Hu ◽  
James Dooley ◽  
Stephen S. Chung ◽  
Safak Yalcin ◽  
Yu Sup Shin ◽  
...  
Keyword(s):  
Stem Cell ◽  
Colony Formation ◽  
Target Genes ◽  
Conflicts Of Interest ◽  
Ectopic Expression ◽  
Null Mouse ◽  
Cell Cycle Regulators ◽  
Self Renewal ◽  
Hematopoietic Stem

Abstract microRNAs (miRNAs) are important regulators of both embryonic and adult tissue stem cell self-renewal. We previously showed that ectopic expression of miR-29a, a miRNA highly expressed in HSCs as well as in human acute myeloid leukemia (AML) stem cells, in immature mouse hematopoietic cells is sufficient to induce a myeloproliferative disorder that progresses to AML. During the early phase of this disease, miR-29a induces aberrant self-renewal of committed myeloid progenitors, strongly suggesting a role for miR-29a in regulating HSC self-renewal. In order to determine the role of miR-29a in HSC function, we have evaluated our recently described miR-29a/b1 null mouse. Homozygous deletion of miR-29a/b1 resulted in reduced bone marrow cellularity and reduced colony forming capacity of hematopoietic stem and progenitor cells (HSPCs). The phenotype was mediated specifically by miR-29a since miR-29b expression was not significantly altered in HSCs and reconstitution of miR-29a/b1 null HSPCs with miR-29a, but not miR-29b, rescued in vitro colony formation defects. Self-renewal defects were observed in miR-29a deficient HSCs in both competitive and non-competitive transplantation assays, and these deficits were associated with increased HSC cell cycling and apoptosis. Gene expression studies of miR-29a deficient HSCs demonstrated widespread gene dysregulation including a number of up-regulated miR-29a target genes including DNA methylation enzymes (Dnmt3a, -3b) and cell cycle regulators (e.g. Cdk6, Tcl1, Hbp1, Pten). Knockdown of one of these targets, Dnmt3a, in miR-29a deficient HSCs resulted in partial restoration of colony formation, providing functional validation that Dnmt3a mediates part of miR-29a null HSPCs functional defects. miR-29a loss also abrogated leukemogenesis in the MLL-AF9 retroviral AML model. Together, our results demonstrate that miR-29a positively regulates HSC self-renewal and is required for myeloid leukemogenesis. Disclosures: No relevant conflicts of interest to declare.

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