Combined Drug Targeting of p53-dependent and -independent Pathways Depletes Myelofibrosis Hematopoietic Stem/Progenitor Cells

AbstractCurrent therapy for myelofibrosis (MF) results in a limited prolongation of patient survival. In order to improve treatment outcomes, we developed a strategy to effectively deplete MF hematopoietic stem/progenitor cells (HSPCs). In the present study, an imipridone, ONC201, was combined with RG7112, an antagonist of MDM2, a p53 negative regulator, to activate downstream events of the p53 and TNF-related apoptosis-inducing ligand (TRAIL)/death receptor (DR) pathways. As compared to treatment with the individual drugs, the combination of ONC201 and RG7112 promoted greater degrees of apoptosis of MF CD34+ cells through activation of both p53-dependent and -independent pathways. Importantly, treatment with ONC201-RG7112 not only decreased the number of JAK2V617F+ and calreticulin mutated colonies assayed from MF CD34+ cells, but allowed for the persistence or appearance of JAK2 wild type colonies. Treatment with ONC201 combined with RG7112 could be a potentially effective strategy for treating MF patients.

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Slug Plays an Essential Role in the Radioprotection of Hematopoietic Progenitors In Vivo by Antagonizing p53-Mediated Apoptotic Pathways.

Blood ◽

10.1182/blood.v104.11.31.31 ◽

2004 ◽

Vol 104 (11) ◽

pp. 31-31

Author(s):

Wen-Shu Wu ◽

Dong Xu ◽

Stefan Heinrichs ◽

A. Thomas Look

Keyword(s):

Bone Marrow ◽

Progenitor Cells ◽

Leukemia Cells ◽

Dependent Manner ◽

Wild Type ◽

Γ Irradiation ◽

Aberrant Expression ◽

Hematopoietic Stem ◽

Myeloid Progenitors

Abstract An antiapoptotic role for Slug/Snail in mammals was suggested by studies in C. elegans, where CES-1/Scratch, a member of the Slug/Snail superfamily, was found to control the apoptotic death of NSM sister neurons by acting as a transcriptional repressor of EGL-1, a BH3-only proapoptotic protein. Identification of Slug as the target gene of the E2A-HLF oncoprotein in human pro-B leukemia cells led us to demonstrate its antiapoptotic function in IL-3-dependent murine pro-B cells. In contrast to its aberrant expression in pro-B leukemia cells, endogenous Slug is normally expressed in both LT-HSC and ST-HSC, as well as committed progenitors of the myeloid series, but not in pro-B and pro-T cells, implying its function in myelopoiesis. Using Slug−/− mice produced in our laboratory, we showed that these knockouts are much more radiosensitive than Slug+/− and wild-type mice, and that apoptotic cells increase significantly in the hematopoietic progenitor cells of Slug−/− mice as compared to wild-type mice following γ-irradiation, indicating a radioprotective function in vivo. We showed here that although the development of myeloid progenitors is not impaired under steady-state conditions, their repopulation is incomplete γ-irradiated in in Slug−/− mice. We demonstrate further the radiation-induced death of Slug−/− mice is exclusively a result of bone marrow failure with no apparent contribution from systemic injures to other tissues. By two-way bone marrow transplantation, we provide firm evidence that Slug protects mice from γ-irradiation-induced death in a cell-autonomous manner. Interestingly, regenerative capacity of hematopoietic stem cells (HSC) was retained in irradiated Slug−/− mice, which could be rescued by wild-type bone marrow cells after irradiation, indicating that Slug exerts its radioprotective function in myeloid progenitors rather than HSCs. Furthermore, we establish that Slug radioprotects mice by antagonizing downstream of the p53-mediated apoptotic signaling through inhibition of the p53-resposive proapoptotic gene Puma, leading in turn to inhibition of the mitochondria-dependent apoptotic pathway activated by γ-irradiation in myeloid progenitors. More interestingly, we observed that Slug is inducible by γ-irradiation in a p53-dependent manner. Together, our findings implicate a novel Slug-mediated feedback mechanism by which p53 control programmed cell death in myeloid progenitor cells in vivo in response to γ-irradiation.

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Murine Mast Cells Express Mpl, the Thrombopoietin Receptor, and Thrombopoietin Is a Potent Regulator of Mast Cell Differentiation.

Blood ◽

10.1182/blood.v108.11.1335.1335 ◽

2006 ◽

Vol 108 (11) ◽

pp. 1335-1335

Author(s):

Fabrizio Martelli ◽

Giovanni Amabile ◽

Barbara Ghinassi ◽

Rodolfo Lorenzini ◽

Alessandro M. Vannucchi ◽

...

Keyword(s):

Bone Marrow ◽

Mast Cell ◽

Cell Differentiation ◽

Mast Cells ◽

Progenitor Cells ◽

Peritoneal Cavity ◽

Surface Protein ◽

Wild Type ◽

Hematopoietic Stem ◽

Progenitor Cell Proliferation

Abstract Mast cells are hematopoietic cells localized in extramedullary sites where they engage themselves in the process of allergic response and in the immune reaction against parasites. Mast cells derive from multilineage c-KitlowCD34lowSca-1pos progenitor cells present in the marrow. These cells give rise to Linnegc-KitposSca-1neg T1/ST2pos mast cell restricted progenitor cells (MCP) whose futher maturation in the marrow remains limited under steady state conditions. MCP migrate through the blood in extramedullary sites were they mature into tissue-retricted c-KitposFceRIpos mast cells characterized by a specific mast cell protease (MMCP) profiling (dermal, mucosal and serosal mast cells in skin, gut and peritoneal cavity, respectively). The molecular mechanism that, in normal mice, restricts the mastocytopoietic potential of progenitor cells to the extramedullary sites, as well as the factors that guide the tissue-restricted differentiation of these cells, are unknown. Thrombopoietin (TPO)-Mpl interactions play an important role in the regulation of hematopoietic stem/progenitor cell proliferation and differentiation in the marrow. Here we report that mast cells, and their precursors, express Mpl (both as mRNA and cell surface protein) (see Table). Furthermore, targeted deletion of this gene (Mplnull mutation) decrease the number of MCP (by 1-log) and increases that of mast cells in dermis (by 3-fold), peritoneal cavity (by 3-fold), bone marrow (2-log) and spleen (2-log). Furthermore, because of their higher (by 2-log) MMCP-7 expression, serosal Mplnull mast cells resemble more wild-type dermal rather than serosal mast cells. On the other hand, either treatment of mice with TPO or addition of TPO to bone marrow-derived mast cell cultures induces mast cell apoptosis (by Tunel and Annexin staining) and severely hampers mast cell differentiation (by expression profiling). These data are consistent with a regulatory mechanism for murine mastocytopoiesis according to which TPO favours the transition from multilineage progenitors to CMP but blocks differentiation of MCP to mature mast cells. We propose TPO as the growth factor that restrict mast cell differentiation to extramedullaty sites and that control the switch between serosal vs dermal mast cell differentiation. Mpl expression mRNA 2-ΔCt Protein (AFU) Cy7-A Protein (AFU) Cy7-AMM2 AFU= arbitrary fluorescence intensity. p< 0.01 with respect to Cy7-A (irrilevant antibody) Wild type Marrow B cells (B220pos) b.d. 120±4 205±4 Wild type Marrow Megakaryocytes (CD61pos/CD41pos) 5.0±0.1 × 10-2 178±3 978±74* Wild type Marrow MCP (cKitpos/T1ST2pos) 1.3±0.01 × 10-2 139±16 1658±73* Wild-type Marrow Mast Cells (cKitpos/Fcε RIpos) 1.9±0.1 × 10-2 110±1 868±71* Serosal Mast Cells (cKitpos/FcεRIpos) 7.2±2.1 × 10-4 393±1 1374±25* Mplnull Marrow Megakaryocytes (CD61pos/CD41pos) b.d. 365±28 469±50 Mplnull Marrow Mast Cells (cKitpos/FcεRIpos) b.d 107±1 109±3

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Differential Expression of Mll-AF9 Up-Regulated Genes Correlates with Enhanced Self-Renewal of Hematopoietic Progenitors.

Blood ◽

10.1182/blood.v108.11.733.733 ◽

2006 ◽

Vol 108 (11) ◽

pp. 733-733 ◽

Cited By ~ 1

Author(s):

Ashish R. Kumar ◽

Wendy A. Hudson ◽

Weili Chen ◽

Rodney A. Staggs ◽

Anne-Francoise Lamblin ◽

...

Keyword(s):

Gene Expression ◽

Progenitor Cells ◽

Fusion Gene ◽

Expression Profiles ◽

Cell Types ◽

Third Generation ◽

Wild Type ◽

Self Renewal ◽

Hematopoietic Stem ◽

The Third

Abstract In order to understand the pathophysiology of leukemia, we need to study the effects of leukemic oncogenes on the rare hematopoietic stem and progenitor cells. We investigated the self-renewal capabilities of the various hematopoietic cell types derived from Mll-AF9 knock-in mice. We used the murine knock-in model since it offers the advantage of a single copy of the Mll-fusion gene under the control of the endogenous promoter present in every hematopoietic stem/progenitor cell. In methylcellulose cultures, we compared myeloid colony formation of Mll-AF9 cells to wild type progenitor populations over three generations of plating. In the first generation of plating, the Mll-AF9 common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) formed more colonies than the hematopoietic stem cells (HSCs) and common lymphoid progenitors (CLPs). However, at the third generation of plating, colony numbers formed by Mll-AF9 HSCs and CLPs were significantly greater than those formed by CMPs and GMPs. By the third generation only occasional colonies were found in the wild type groups. These results demonstrate that while Mll-AF9 led to an increase in self-renewal of all 4 cell types studied, these effects were more pronounced in HSCs and CLPs. To identify the downstream genes that mediate the growth deregulatory effects of Mll-AF9, we compared gene expression profiles of Mll-AF9 derived cells to their wild type counterparts. To assess gene expression levels, we extracted RNA from wild type and Mll-AF9 HSCs, CLPs, CMPs and GMPs. We then amplified and labeled the RNA for analysis by Affymetrix murine 430 2.0 genome arrays. In an unsupervised analysis, the various Mll-AF9 cells clustered with their corresponding wild type counterparts, indicating that the expression of most genes was not significantly altered by Mll-AF9. To identify the genes that are differentially expressed in the Mll-AF9 derived cells, we performed a two-way ANOVA (with the genotype and cell type as the two variables) allowing for a false discovery rate of 10%. In this analysis, we found that 76 genes were up-regulated in all Mll-AF9 progenitor cells compared to their wild-type counterparts. This list included known targets of Mll-fusion proteins Hoxa5, Hoxa7, Hoxa9 and Hoxa10. Also included were Evi1 and Mef2c, two genes that have been implicated in promoting enhanced self-renewal of murine hematopoietic cells. Importantly, in wild type mice, these 6 genes were expressed at higher levels in HSCs and CLPs compared to CMPs and GMPs (average 3–25 fold). While we observed an average 2–10 fold increase in expression of these genes in all Mll-AF9 cell types compared to their respective wild type controls, the expression level was 3–8 fold higher in Mll-AF9 HSCs and CLPs compared to CMPs and GMPs. Thus, the expression of genes known to be intrinsically related to self-renewal is further enhanced as a result of the Mll-AF9 fusion gene. In conclusion, while activation of the Mll-AF9 genetic program and the resulting enhanced self-renewal occurs in all 4 cell types studied, these effects are greatest in HSCs and CLPs. Thus, HSCs and CLPs are likely to be more efficient than CMPs and GMPs in producing cellular expansion and targets for cooperating mutations resulting in leukemia.

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Sequence-Specific Conversion of βA- to βS-Globin by Small Fragment Homologous Replacement In Hematopoietic Stem/Progenitor Cells.

Blood ◽

10.1182/blood.v116.21.3754.3754 ◽

2010 ◽

Vol 116 (21) ◽

pp. 3754-3754

Author(s):

Alireza Abdolmohammadi ◽

Rosalie Maurisse ◽

Babek Bedayat ◽

David DeSemir ◽

Damian Laber ◽

...

Keyword(s):

Progenitor Cells ◽

Sickle Cell ◽

Sickle Cell Anemia ◽

Dna Sequences ◽

Conflicts Of Interest ◽

Globin Gene ◽

Specific Gene ◽

Small Fragment ◽

Wild Type ◽

Hematopoietic Stem

Abstract Abstract 3754 Introduction: An ultimate goal of gene therapy is the development of effective strategies to correct mutant genomic sequences in pathologic cells. To that end, studies have been undertaken to evaluate the therapeutic potential of an oligo/polynucleotide-based sequence-specific gene modification strategy, small fragment homologous replacement (SFHR) in the correction of the mutation giving rise to sickle cell anemia. Small DNA fragments (SDFs) comprising the sickle cell anemia mutation (an A>T transversion in codon 6) and flanking DNA sequences in the human b-globin gene were introduced into Hematopoietic Stem/Progenitor Cells (HSPCs). The studies presented indicated modification at the level of DNA, RNA, and protein when cells were differentiated into erythrocytes. Methods: In this study, SFHR was used to convert A>T in codon 6 of the b-globin gene in CD34+/CD38-/Lin- HSPCs isolated from full term umbilical cord blood as a proof of principle. HSPCs were transfected with a defined number of a 559-bp SDF using the Amaxa electroporation (nucleofection) system. After growing the transfected cells in stem cell media containing EPO for different time intervals up to 32 days, RNA was extracted and DNase I-treated before further analysis. Erythrocytes were also analyzed using antibodies that differentiate between wild-type hemoglobin A (HBA) and sickle cell hemoglobin S (HBS). Results: RFLP analysis of a 430-bp PCR product generated from mRNA-derived cDNA with the DdeI enzyme indicated conversion of bA- to bS-globin. Sequencing of the 430-bp amplicon showed the A > T conversion. Analysis of the transfected wild-type HSPC-derived erythrocytes with HBA and HBS specific antibodies demonstrated the presence of a subpopulation of cells expressing HBS. These data are consistent with previous studies showing both conversion of bS- to bA-globin in SC1 cells and bA- to bS-globin in HSPCs after electroporation and microinjection of SDF, respectively. Conclusion: These studies represent a critical next step in developing SFHR as a therapy for sickle cell disease, in that they demonstrate long-term SFHR-mediated modification of b-globin following mass transfection by electroporation of HSPCs. Disclosures: No relevant conflicts of interest to declare.

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Sqstm1 Is Required to Retain Hematopoietic Stem Cell/ Progenitors As a Negative Regulator of Macrophage-Dependent Inflammatory Signaling in the Bone Marrow Osteoblastic Niche

Blood ◽

10.1182/blood.v124.21.350.350 ◽

2014 ◽

Vol 124 (21) ◽

pp. 350-350

Author(s):

Kyung-Hee Chang ◽

Amitava Sengupta ◽

Ramesh C Nayak ◽

Angeles Duran ◽

Sang Jun Lee ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Research Funding ◽

Negative Regulator ◽

Wild Type ◽

Hematopoietic Stem ◽

P Retention

Abstract In the bone marrow (BM), hematopoietic stem cells and progenitors (HSC/P) reside in specific anatomical niches. Among these niches, a functional osteoblast (Ob)-macrophage (MΦ) niche has been described where Ob and MΦ (so called "osteomacs") are in direct relationship. A connection between innate immunity surveillance and traffic of hematopoietic stem cells/progenitors (HSC/P) has been demonstrated but the regulatory signals that instruct immune regulation from MΦ and Ob on HSC/P circulation are unknown. The adaptor protein sequestosome 1 (Sqstm1), contains a Phox bemp1 (PB1) domain which regulates signal specificities through PB1-PB1 scaffolding and processes of autophagy. Using microenvironment and osteoblast-specific mice deficient in Sqstm1, we discovered that the deficiency of Sqstm1 results in macrophage contact-dependent activation of Ob IKK/NF-κB, in vitro and in vivo repression of Ccl4 (a CCR5 binding chemokine that has been shown to modulate microenvironment Cxcl12-mediated responses of HSC/P), HSC/P egress and deficient BM homing of wild-type HSC/P. Interestingly, while Ccl4 expression is practically undetectable in wild-type or Sqstm1-/- Ob, primary Ob co-cultured with wild-type BM-derived MΦ strongly upregulate Ccl4 expression, which returns to normal levels upon genetic deletion of Ob Sqstm1. We discovered that MΦ can activate an inflammatory pathway in wild-type Ob which include upregulation of activated focal adhesion kinase (p-FAK), IκB kinase (IKK), nuclear factor (NF)-κB and Ccl4 expression through direct cell-to-cell interaction. Sqstm1-/- Ob cocultured with MΦ strongly upregulated p-IKBα and NF-κB activity, downregulated Ccl4 expression and secretion and repressed osteogenesis. Forced expression of Sqstm1, but not of an oligomerization-deficient mutant, in Sqstm1-/- Ob restored normal levels of p-IKBα, NF-κB activity, Ccl4 expression and osteogenic differentiation, indicating that Sqstm1 dependent Ccl4 expression depends on localization to the autophagosome formation site. Finally, Ob Sqstm1 deficiency results in upregulation of Nbr1, a protein containing a PB1 interacting domain. Combined deficiency of Sqstm1 and Nbr1 rescues all in vivo and in vitro phenotypes of Sqstm1 deficiency related to osteogenesis and HSC/P egression in vivo. Together, this data indicated that Sqstm1 oligomerization and functional repression of its PB1 binding partner Nbr1 are required for Ob dependent Ccl4 production and HSC/P retention, resulting in a functional signaling network affecting at least three cell types. A functional ‘MΦ-Ob niche’ is required for HSC/P retention where Ob Sqstm1 is a negative regulator of MΦ dependent Ob NF-κB activation, Ob differentiation and BM HSC/P traffic to circulation. Disclosures Starczynowski: Celgene: Research Funding. Cancelas:Cerus Co: Research Funding; P2D Inc: Employment; Terumo BCT: Research Funding; Haemonetics Inc: Research Funding; MacoPharma LLC: Research Funding; Therapure Inc.: Consultancy, Research Funding; Biomedical Excellence for Safer Transfusion: Research Funding; New Health Sciences Inc: Consultancy.

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Gtpase Immunity-Associated Protein Family Member 4 Contributes to the Enhanced Expansion of HSPCs in RUNX1 Deficient Mice

Blood ◽

10.1182/blood.v124.21.4344.4344 ◽

2014 ◽

Vol 124 (21) ◽

pp. 4344-4344

Author(s):

Amanda Scholl ◽

Kentson Lam ◽

Alex Muselman ◽

Tingdong Tang ◽

Shinobu Matsuura ◽

...

Keyword(s):

Family Member ◽

Conflicts Of Interest ◽

Protein Family ◽

Dominant Negative ◽

Negative Regulator ◽

Wild Type ◽

Double Knockout ◽

Hematopoietic Stem ◽

Myeloid Progenitor

Abstract RUNX1 is the transcription factor described as the master regulator of hematopoiesis. Due to its central role during blood development, numerous RUNX1 mutations have been reported in hematologic abnormalities. Mice null for Runx1 die during embryogenesis, lacking definitive HSCs. Conditional Runx1Δ/Δ mice are viable, but exhibit a variety of blood abnormalities. The most salient defect in these Runx1Δ/Δ mice is expansion of the hematopoietic stem and progenitor cell (HSPC) population, measured as an increase in number of lineage negative, Sca1 positive, cKit positive (LSK) cells. A shortened form of RUNX1 (RUNX1SF) lacking the C-terminal and part of the N-terminal domain (41-214) acts as a dominant negative regulator of RUNX1 and hence also models RUNX1 loss-of-function. A differential gene expression analysis of HSPCs derived from Runx1Δ/Δ compared to wild type mice uncovered GTPase immunity-associated protein family member 4 (GIMAP4) as one of the genes most highly upregulated. Previous studies have focused almost exclusively on the role of GIMAP4 as a pro-apoptotic protein during T-cell development. This study illuminates a novel non-apoptotic role of GIMAP4 in a formerly unstudied HSPC context. Runx1Δ/Δ mice were crossed with Gimap4-/- mice to generate a double knockout (dKO) mouse line. These dKO mice exhibited attenuated HSPC proliferation in comparison to Runx1Δ/Δ mice, suggesting that GIMAP4 functions in this HSPC expansion phenotype. BMT experiments using lethally irradiated C57 mice and RUNX1SF transduced wild type versus Gimap4-/-bone marrow confirmed this result. GIMAP4 also worked independently and coordinately with RUNX1 to influence individual progenitor populations. Common lymphoid progenitors (CLP) were affected only by GIMAP4. Gimap4-/- mice exhibited an expansion of the CLP population, consistent with its pro-apoptotic role in lymphoid populations. Conversely, both RUNX1 and GIMAP4 coordinately exerted an effect on myeloid progenitor populations. Runx1Δ/Δ mice harbored expanded granulocyte-macrophage progenitor (GMP) and common myeloid progenitor (CMP) populations. This expansion was not observed when GIMAP4 was also ablated. This suggests a pro-proliferative role of GIMAP4 specifically in myeloid populations. These opposing roles of GIMAP4 in lymphoid versus myeloid cells suggest a more contextual, cell-specific role of this GTPase protein. Ultimately, this study provides insight into how RUNX1 and GIMAP4 may coordinate to maintain HSPC homeostasis. Disclosures No relevant conflicts of interest to declare.

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Sox4 Is Required for the Formation and Maintenance of Multipotent Progenitors

Blood ◽

10.1182/blood.v124.21.1577.1577 ◽

2014 ◽

Vol 124 (21) ◽

pp. 1577-1577 ◽

Cited By ~ 1

Author(s):

Hong Zhang ◽

Min Ye ◽

Robert S. Welner ◽

Daniel G. Tenen

Keyword(s):

Progenitor Cells ◽

Absolute Number ◽

Brdu Incorporation ◽

Binding Motif ◽

Wild Type ◽

Hematopoietic Stem ◽

Genetic Ablation ◽

Qpcr Analysis ◽

Multipotent Progenitors ◽

Deficient Mice

Abstract Introduction Hematopoiesis is maintained by a hierarchical system, whereas aberrant control of hematopoiesis is the underlying cause of many diseases. Within the hematopoietic hierarchy, hematopoietic stem cells (HSCs) give rise to multipotent progenitors that have lost their self-renewal capacity but remain multipotent to differentiate into mature blood cells. However, the precise molecular mechanisms that modulate this transition are not fully understood yet. Results We recently discovered that genetic ablation of SRY sex determining region Y-box 4 gene (Sox4) in the murine hematopoietic system resulted in dramatic loss of multipotent progenitor population (CD48+CD150-Lin-kit+Sca1+, or CD48+CD150-LSK) both relatively (to the total LSK population) and in absolute number. Interestingly, the absolute number of HSCs (CD48-CD150+Lin-kit+Sca1+, or SLAM+LSK) in these conditional Sox4-deficient mice was comparable to their wild-type counterparts. Transcriptional factor Sox4 belongs to the high-mobility group (HMG) domain superfamily which also includes other Sox proteins, TCF-1 (T-cell factor 1) and LEF-1 (lymphoid enhancer factor 1). Sox4 has been implicated in leukemogenesis and may potentially contribute to stem cell properties. Nevertheless, the precise roles of Sox4 in hematopoietic stem/progenitor cells and the underlying mechanisms have not been defined yet. Further analysis of stem/progenitor compartment defined by Flt3 and CD34 expression demonstrated a major loss in lymphoid-primed multipotent progenitors (LMPPs) (CD34+Flt3+LSK) with relatively normal formation of LT-HSCs (CD34-Flt3-LSK) and ST-HSCs (CD34+Flt3-LSK) upon the loss of Sox4, suggesting that Sox4 is essential for the development from HSCs to multipotent progenitors. Such observation is in line with the expression pattern of Sox4. Quantitative PCR (qPCR) analysis of wild-type mice revealed that expression of Sox4 increased from HSCs to multipotent progenitors which expressed Sox4 at the highest level among all the hematopoietic compartments. Studies of biological behaviors further indicateed that disruption of Sox4 had no effect on proliferative capacity of HSCs and multipotent progenitors, as evidenced by BrdU incorporation assay. However, Annexin V/propidium iodide staining revealed an increased frequency of apoptotic multipotent progenitors, but not that of HSCs upon the ablation of Sox4. In a transplantation setting, although Sox4-deficient LSKs homed appropriately to the bone marrow, they exhibited severely impaired ability to give rise to multipotent progenitors, but contributed normally to HSCs compared to the wild-type donors. Among a set of genes crucial to the biological properties of stem/progenitor cells, qPCR analysis revealed that upon the loss of Sox4, only the levels of Ikaros1 and Ikaros2, the two major Ikaros isoforms in stem/progenitor cells, were downregulated specifically in multipotent progenitors, but remained normal in HSCs. Intriguingly, in a reminiscent manner of Sox4-deficient mice, mice lacking both Ikaros 1 and Ikaros 2 proteins, also exhibited disrupted B cell development and selectively impaired LMPPs. Previous study identified an enhancer of Ikaros locus as the only cis-regulatory element that was capable of stimulating reporter expression in the LMPPs. Our sequence analysis revealed a highly conserved Sox4 binding motif within this enhancer, therefore potentially connecting Sox4 with the known regulatory networks that modulate the differentiation of HSCs. Currently, we are working on (1) confirming the direct transcriptional regulation of Ikaros by Sox4; (2) assessing whether Ikaros mediates the functions of Sox4 in the formation or maintenance of the multipotent progenitors population in vivo; and (3) delineating the downstream regulatory network of Sox4 in stem/progenitor cells. Conclusion In summary, out study reveals a novel role for Sox4 gene in early hematopoiesis and brings important insights into the regulatory mechanisms underlying the commitment of HSCs toward multipotent progenitors. Disclosures No relevant conflicts of interest to declare.

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C-CBL Is a Critical Negative Regulator of Megakaryopoesis

Blood ◽

10.1182/blood.v124.21.1581.1581 ◽

2014 ◽

Vol 124 (21) ◽

pp. 1581-1581

Author(s):

Sebastian J. Saur ◽

Melanie Märklin ◽

Alexandra Poljak ◽

Manuela Ganser ◽

David E. James ◽

...

Keyword(s):

Bone Marrow ◽

Conflicts Of Interest ◽

Negative Regulator ◽

Cytokine Signaling ◽

Wild Type ◽

Platelet Factor ◽

Physiological Level ◽

Hematopoietic Stem ◽

Primary Mouse

Abstract Megakaryopoiesis is controlled by a variety of hematopoietic growth factors in order to maintain a physiological level of circulating platelets. Thrombopoietin (TPO) is the main regulator of megakaryopoiesis modulating megakaryocyte differentiation, promoting endomitosis and proplatelet formation and as such supports the self-renewal and survival of hematopoietic stem cells. To allow proper proliferation and differentiation of different hematopoetic lineages, TPO signal transduction must be tightly regulated. Several mechanisms negatively modulating hematopoiesis and differentiation of the megakaryocytic lineage have previously been identified. Among those are suppressors cytokine signaling, protein phosphatases as well as a multitude of negative regulatory signaling pathways. However, one of the most effective mechanisms to permanently disable activated signaling proteins is by targeted degradation via lysosomes or proteasomes. In this study, we investigated the mechanisms that regulate TPO-mediated MPL degradation in primary mouse cells. Previous studies have identified CBL as an E3 ligase responsible for the ubiquitination of MPL in cell lines. In order to determine the potential role of c-CBL in murine thrombopoiesis, we used Cre/loxP technology to specifically delete c-CBL in the megakaryocytic lineage. Mice expressing two floxed c-CBL alleles were crossed to mice expressing Cre recombinase under the control of the platelet factor 4 (PF4) promoter. This yielded progeny with the desired genotype of c-CBLfl/fl PF4-Cre (CBL ko) after two generations of breeding. The desired cohort exhibited a quantitative absence of c-CBL in megakaryocytes and platelets as assessed by western blotting compared with wild type C57/BL6 mice. The expression of CBL in other hematopoietic cells such as B cells, T cells, neutrophils, monocytes and dendritic cells remained unaffected in this conditional ko strain. The experimental cohort showed significantly higher numbers of megakaryocytes in the bone marrow and of platelets in the peripheral blood as compared to wild type mice (1.2 mio vs. 1.8 mio cells/µl, p<0.0001). In addition, the platelets from the mutant mouse strain were of significantly smaller size (43 vs. 38 fL, p=0.0022). To evaluate the role of c-CBL in mature megakaryocytes, total bone marrow was collected from 12 wk old CBL ko mice and grown in TPO-containing culture medium for 72 h. Megakaryocytes derived from the bone marrow of wild type mice served as controls. Mature megakaryocytes were eventually isolated on a BSA-density gradient. Subsequent Western Blot analysis revealed a significant reduction of MPL ubiquitination in the CBL ko mice as compared to wild type mice, thereby identifying c-CBL as a critical negative regulator of megakaryopoesis. Taken together, we have successfully ablated c-CBL specifically from the megakaryocyte lineage and could demonstrate that this has profound effects on platelet counts and platelet size. In addition, we were able to show that c-CBL ablation leads to reduced ubiquitination of MPL and a consecutively longer half life of this protein culminating in substantially increased megakaryopoiesis in the c-CBL ko cohort. In summary, these data enhance our understanding of the regulation of TPO signaling and the physiological role of CBL in the megakaryocytic lineage. Disclosures No relevant conflicts of interest to declare.

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Combinatorial effect of miR-486-5p & miR-22-3p mimics thrombopoietin's impact on hematopoietic stem & progenitor cells

10.1101/2020.02.09.941104 ◽

2020 ◽

Author(s):

Chen-Yuan Kao ◽

Jinlin Jiang ◽

ELEFTHERIOS TERRY PAPOUTSAKIS

Keyword(s):

Progenitor Cells ◽

Single Molecule ◽

Kinase Inhibitors ◽

Negative Regulator ◽

Hematopoietic Stem ◽

Megakaryocytic Differentiation ◽

Peripheral Blood Cd34 ◽

Mtor Phosphorylation ◽

Direct Target ◽

Differentiation And Proliferation

Megakaryocytes shed and release submicron size microparticles (MkMPs), the most abundant microparticle in circulation. We have previously reported that MkMPs target peripheral-blood CD34+ hematopoietic stem/progenitor cells (HSPCs) to induce megakaryocytic differentiation and proliferation, and that small RNAs delivered to HSPCs via MkMPs play an important role in the development of this phenotype. Here, using single-molecule real-time (SMRT) RNA sequencing (RNAseq), we identify the top seven most abundant microRNAs (miRs) in MkMPs as potential candidates in mediating the effect of MkMPs on HSPCs. Using miR mimics, we demonstrate that among the seven most abundant miRs, two, miR-486-5p and miR-22-3p, are able to drive the Mk differentiation of HSPCs in the absence of thrombopoietin (TPO). The effect of these two miRs is comparable to the TPO- or MkMP-induced megakaryocytic differentiation of HSPCs, thus suggesting that these two miRs are responsible for this MkMP-induced phenotype. To probe the signaling through which MkMPs might enable this phenotype, we used kinase inhibitors of potential signaling pathways engaged in megakaryocytic differentiation. Our data suggest that MkMP-induced Mk differentiation of HSPCs is enabled through JNK and PI3K/Akt/mTOR signaling. Our data show that MkMPs activate Akt and mTOR phosphorylation. Furthermore, MkMPs downregulate PTEN expression, a direct target of miR-486-5p and a negative regulator of PI3K/Akt signaling, via JNK signaling. Taken together, our data provide a mechanistic understanding of the biological effect of MkMPs in inducing megakaryocytic differentiation of HSPCs, which, as was previously suggested, is a phenotype of potential physiological significance in stress megakaryopoiesis.

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Inflammatory Niche Signalling Drives Genotoxic Stress in Hematopoietic Stem Cells and Predicts Leukemic Evolution in Human Leukemia Predisposition Syndromes

Blood ◽

10.1182/blood.v128.22.428.428 ◽

2016 ◽

Vol 128 (22) ◽

pp. 428-428

Author(s):

Si Chen ◽

Noemi A. Zambetti ◽

Zhen Ping ◽

Keane Kenswil ◽

Maria Mylona ◽

...

Keyword(s):

Cell Cycle ◽

Dna Damage ◽

Progenitor Cells ◽

Transcriptional Activation ◽

Genotoxic Stress ◽

Wild Type ◽

Hematopoietic Stem ◽

Skeletal Defects ◽

Bona Fide

Abstract Primary alterations of the mesenchymal niche can induce myelodysplasia and acute myeloid leukemia in mouse models, introducing a concept of niche-driven leukemogenesis (Raaijmakers et al, Nature 2010). The molecular mechanisms and human relevance of this concept, however, have remained elusive. We addressed these key questions by modelling Shwachman-Diamond-Syndrome (SDS), a human monogenic congenital disorder caused by loss-of function mutation in the SBDS gene and characterized by skeletal defects, bone marrow failure and a striking propensity for leukemic evolution. Targeted Sbds deletion from mesenchymal progenitor cells (MPCs) in mice (OsxCre/+Sbdsf/f; OCSf/f) resulted in bone abnormalities faithfully recapitulating human disease, including short stature and early-onset osteoporosis. Skeletal defects were associated with genotoxic stress in hematopoietic stem and progenitor cells (HSPCs) as demonstrated by mitochondrial membrane hyperpolarization, oxidative stress, DNA damage and cell cycle checkpoint activation (transcriptional modulation of DNA damage response/repair pathways and G0-G1 cell cycle arrest). DNA damage could be partially rescued by in vivo administration of the ROS scavenger N-acetylcysteine supporting the notion of niche induced DNA damage in HSPCs induced by mitochondria-derived superoxide radicals. Mechanistically, Sbds deficiency caused activation of the p53 tumor suppressorpathway in MPCs (upregulation of P53 and transcriptional activation of downstream targets (GSEA). Genetic deletion of Trp53 from MPCs (Osxcre/+Sbdsf/fTrp53f/f mice) rescued the skeletal phenotype and genotoxic stress in HSPCs. Comparison of the transcriptome of MPCs from OCSf/f mice to their highly FACS-purified mesenchymal (CD45-CD235-7AAD-CD31-CD271+CD105+) human equivalents from SDS patients (RNAseq; n=5) demonstrated a striking overlap in disrupted gene programs (GSEA), including ribosome biogenesis and significant overexpression of the proinflammatory molecules such as S100A8 and S100A9, bona fide p53 downstream targets. Activation of p53 and inflammatory molecules was an MPC-autonomous consequence of Sbds depletion as demonstrated by ex vivo knockdown of the gene in OP9 cells. S100A8/A9 overexpression and secretion from MPCs from OCSf/f mice was confirmed by FCM and serum ELISA. Exposure of HSPCs to recombinant murine S100A8/9 resulted in increased DNA damage and apoptosis associated with transcriptional activation of TLR4 downstream signaling, a bona fide S100A8A9 receptor. In vivo TLR4 blockade by neutralizing antibodies resulted in reduced γH2AX foci in HSPCs from OCSf/f mice, in support of the existence of a Tpr53-S100A8/A9-TLR4 axis driving genotoxic stress. Formal demonstration that niche-derived S100A8/9 is sufficient to drive genotoxic stress in HSPCs was provided by transplantation of wild-type hematopoietic cells into recipient S100A8/A9 transgenic mice (Cheng et al., 2008) resulting in accumulation of mitochondrial superoxide radicals and DNA-damage in wild-type HSPCs. Finally, to further define the clinical relevance of this inflammatory MPC-HSPC axis to human disease, we performed massive parallel RNA-sequencing of FACS purified mesenchymal cells from homogeneously treated low-risk MDS patients (n=45). Overexpression of S100A8 and S100A9 in MPCs(confirmed by IHC) was found in a considerable subset of patients (17/45; 38%). S100A8/9+ mesenchymal cells displayed transcriptional activation of p53 and TLR programs, in line with findings in the mouse model. Strikingly, patients in the niche-S100A8/9+ group displayed a higher frequency of leukemia evolution (29.4% vs. 14.2%) with significantly shorter evolution time (average 3.4 (1-7.5) vs 18.5 (7-40); p=.03) and progression-free survival (median 11.5 vs. 53 months, p=.03), independent of established prognostic factors and risk classification systems. Collectively, the data define niche-HSPC inflammatory signaling through the p53-S100A8/A9-TLR axis as an actionable determinant of genotoxic stress and disease outcome in human preleukemia, opening the way to niche-instructed, therapeutic targeting to attenuate leukemic evolution. Disclosures No relevant conflicts of interest to declare.

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