Thrombopoietin Induces HOXA9 Nuclear Transport in Immature Hematopoietic Cells: Potential Mechanism by Which the Hormone Favorably Affects Hematopoietic Stem Cells

ABSTRACT Members of the homeobox family of transcription factors are major regulators of hematopoiesis. Overexpression of either HOXB4 or HOXA9 in primitive marrow cells enhances the expansion of hematopoietic stem cells (HSCs). However, little is known of how expression or function of these proteins is regulated during hematopoiesis under physiological conditions. In our previous studies we demonstrated that thrombopoietin (TPO) enhances levels of HOXB4 mRNA in primitive hematopoietic cells (K. Kirito, N. Fox, and K. Kaushansky, Blood 102:3172-3178, 2003). To extend our studies, we investigated the effects of TPO on HOXA9 in this same cell population. Although overall levels of the transcription factor were not affected, we found that TPO induced the nuclear import of HOXA9 both in UT-7/TPO cells and in primitive Sca-1+/c-kit+/Gr-1− hematopoietic cells in a mitogen-activated protein kinase-dependent fashion. TPO also controlled MEIS1 expression at mRNA levels, at least in part due to phosphatidylinositol 3-kinase activation. Collectively, TPO modulates the function of HOXA9 by leading to its nuclear translocation, likely mediated by effects on its partner protein MEIS1, and potentially due to two newly identified nuclear localization signals. Our data suggest that TPO controls HSC development through the regulation of multiple members of the Hox family of transcription factors through multiple mechanisms.

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Blood and Cancer: Cancer Stem Cells as Origin of Hematopoietic Cells in Solid Tumor Microenvironments

Cells ◽

10.3390/cells9051293 ◽

2020 ◽

Vol 9 (5) ◽

pp. 1293 ◽

Cited By ~ 1

Author(s):

Ghmkin Hassan ◽

Masaharu Seno

Keyword(s):

Stem Cells ◽

Tumor Microenvironment ◽

Cancer Stem Cells ◽

Hematopoietic Stem Cells ◽

Cancer Cells ◽

Solid Tumor ◽

Immune Cells ◽

Hematopoietic Cells ◽

Hematopoietic Stem ◽

Tumor Microenvironments

The concepts of hematopoiesis and the generation of blood and immune cells from hematopoietic stem cells are some steady concepts in the field of hematology. However, the knowledge of hematopoietic cells arising from solid tumor cancer stem cells is novel. In the solid tumor microenvironment, hematopoietic cells play pivotal roles in tumor growth and progression. Recent studies have reported that solid tumor cancer cells or cancer stem cells could differentiate into hematopoietic cells. Here, we discuss efforts and research that focused on the presence of hematopoietic cells in tumor microenvironments. We also discuss hematopoiesis from solid tumor cancer stem cells and clarify the notion of differentiation of solid tumor cancer stem cells into non-cancer hematopoietic stem cells.

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Negative Regulation of the Differentiation of Flk2− CD34− LSK Hematopoietic Stem Cells by EKLF/KLF1

International Journal of Molecular Sciences ◽

10.3390/ijms21228448 ◽

2020 ◽

Vol 21 (22) ◽

pp. 8448

Author(s):

Chun-Hao Hung ◽

Keh-Yang Wang ◽

Yae-Huei Liou ◽

Jing-Ping Wang ◽

Anna Yu-Szu Huang ◽

...

Keyword(s):

Stem Cells ◽

Hematopoietic Stem Cells ◽

Gene Knockout ◽

Hematopoietic Cells ◽

Hematopoietic Stem ◽

Stem And Progenitor Cells ◽

Interesting Correlation ◽

Regulatory Effects ◽

High Level

Erythroid Krüppel-like factor (EKLF/KLF1) was identified initially as a critical erythroid-specific transcription factor and was later found to be also expressed in other types of hematopoietic cells, including megakaryocytes and several progenitors. In this study, we have examined the regulatory effects of EKLF on hematopoiesis by comparative analysis of E14.5 fetal livers from wild-type and Eklf gene knockout (KO) mouse embryos. Depletion of EKLF expression greatly changes the populations of different types of hematopoietic cells, including, unexpectedly, the long-term hematopoietic stem cells Flk2− CD34− Lin− Sca1+ c-Kit+ (LSK)-HSC. In an interesting correlation, Eklf is expressed at a relatively high level in multipotent progenitor (MPP). Furthermore, EKLF appears to repress the expression of the colony-stimulating factor 2 receptor β subunit (CSF2RB). As a result, Flk2− CD34− LSK-HSC gains increased differentiation capability upon depletion of EKLF, as demonstrated by the methylcellulose colony formation assay and by serial transplantation experiments in vivo. Together, these data demonstrate the regulation of hematopoiesis in vertebrates by EKLF through its negative regulatory effects on the differentiation of the hematopoietic stem and progenitor cells, including Flk2− CD34− LSK-HSCs.

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Exhaustion of Donor Hematopoietic Stem Cells in Lethally-Irradiated Hosts Can Be Sbstantially Mitigated by Targeting p18INK4C.

Blood ◽

10.1182/blood.v104.11.1200.1200 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1200-1200

Author(s):

Hui Yu ◽

Youzhong Yuan ◽

Xianmin Song ◽

Feng Xu ◽

Hongmei Shen ◽

...

Keyword(s):

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Kinase Inhibitor ◽

Hematopoietic Cells ◽

Hematopoietic Stem ◽

Total Period ◽

Over Expression

Abstract Hematopoietic stem cells (HSCs) are significantly restricted in their ability to regenerate themselves in the irradiated hosts and this exhausting effect appears to be accelerated in the absence of the cyclin-dependent kinase inhibitor (CKI), p21. Our recent study demonstrated that unlike p21 absence, deletion of the distinct CKI, p18 results in a strikingly positive effect on long-term engraftment owing to increased self-renewing divisions in vivo (Yuan et al, 2004). To test the extent to which enhanced self-renewal in the absence of p18 can persist over a prolonged period of time, we first performed the classical serial bone marrow transfer (sBMT). The activities of hematopoietic cells from p18−/− cell transplanted mice were significantly higher than those from p18+/+ cell transplanted mice during the serial transplantation. To our expectation, there was no detectable donor p18+/+ HSC progeny in the majority (4/6) of recipients after three rounds of sBMT. However, we observed significant engraftment levels (66.7% on average) of p18-null progeny in all recipients (7/7) within a total period of 22 months. In addition, in follow-up with our previous study involving the use of competitive bone marrow transplantation (cBMT), we found that p18−/− HSCs during the 3rd cycle of cBMT in an extended long-term period of 30 months were still comparable to the freshly isolated p18+/+ cells from 8 week-old young mice. Based on these two independent assays and the widely-held assumption of 1-10/105 HSC frequency in normal unmanipulated marrow, we estimated that p18−/− HSCs had more than 50–500 times more regenerative potential than p18+/+ HSCs, at the cellular age that is equal to a mouse life span. Interestingly, p18 absence was able to significantly loosen the accelerated exhaustion of hematopoietic repopulation caused by p21 deficiency as examined in the p18/p21 double mutant cells with the cBMT model. This data directly indicates the opposite effect of these two molecules on HSC durability. To define whether p18 absence may override the regulatory mechanisms that maintain the HSC pool size within the normal range, we performed the transplantation with 80 highly purified HSCs (CD34-KLS) and then determined how many competitive reconstitution units (CRUs) were regenerated in the primary recipients by conducting secondary transplantation with limiting dilution analysis. While 14 times more CRUs were regenerated in the primary recipients transplanted with p18−/−HSCs than those transplanted with p18+/+ HSCs, the level was not beyond that found in normal non-transplanted mice. Therefore, the expansion of HSCs in the absence of p18 is still subject to some inhibitory regulation, perhaps exerted by the HSC niches in vivo. Such a result was similar to the effect of over-expression of the transcription factor, HoxB4 in hematopoietic cells. However, to our surprise, the p18 mRNA level was not significantly altered by over-expression of HoxB4 in Lin-Sca-1+ cells as assessed by real time PCR (n=4), thereby suggesting a HoxB4-independent transcriptional regulation on p18 in HSCs. Taken together, our current results shed light on strategies aimed at sustaining the durability of therapeutically transplanted HSCs for a lifetime treatment. It also offers a rationale for the feasibility study intended to temporarily target p18 during the early engraftment for therapeutic purposes.

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NF-kB Family Proteins Participate in Multiple Steps of Hematopoiesis through Elimination of Reactive Oxygen Species (ROS).

Blood ◽

10.1182/blood.v104.11.1694.1694 ◽

2004 ◽

Vol 104 (11) ◽

pp. 1694-1694

Author(s):

Soichi Nakata ◽

Itaru Matsumura ◽

Hirokazu Tanaka ◽

Yusuke Satoh ◽

Takumi Era ◽

...

Keyword(s):

Stem Cells ◽

Hematopoietic Stem Cells ◽

Progenitor Cells ◽

Es Cells ◽

Hematopoietic Cells ◽

Hematopoietic Stem ◽

Growth And Survival ◽

Ros Accumulation ◽

Dependent Growth ◽

Induced Apoptosis

Abstract NF-kB family proteins have been reported to induce the expression of over 150 target genes, thereby crucially regulating immune responses, stress responses, and inflammation. These proteins also play important roles in cell growth and survival in various cell types. However, the precise roles of NF-kB in hematopoiesis and their mechanisms remain undetermined. To examine the roles for NF-kB family proteins in the growth and survival of hematopoietic cells, we expressed dominant negative NF-kB (IkBSR) in a murine IL-3-dependent cell line Ba/F3 using a Lac-inducible system, in which IkBSR was inducibly expressed by the IPTG treatment; this clone was designated Ba/F3/IkBSR. Furthermore, we introduced EPO receptor (R), TPOR, and G-CSFR/gp130 consisting of the extracelluar domain of G-CSFR and cytoplasmic domain of gp130 into this clone. At first, we confirmed that these clones could survive and proliferate under the cultures with IL-3, EPO, TPO, G-CSF, respectively. Although IPTG-induced IkBSR slightly suppressed IL-3- and EPO-dependent growth at low concentrations, it did not affect TPO- or gp130L-dependent growth, suggesting that NF-kB might not be so important for cytokine-dependent growth of hematopoietic cells. In contrast, IkBSR prominently enhanced factor-deprived apoptosis, which was accompanied by the ROS accumulation. To access the roles of ROS in IkBSR-enhanced apoptosis, we overexpressed ROS scavenger enzymes MnSOD and thioredoxin X (TRX) in Ba/F3/IkBSR, respectively. As a result, MnSOD and TRX significantly canceled IkB-SR-enhanced apoptosis, suggesting that ROS would be responsible for this apoptosis. We next analyzed the effects of IkBSR on the growth and survival of normal hematopoietic cells. When IkBSR was introduced into murine Lin−Sca-1+ hematopoietic stem/progenitor cells with the retrovirus system, it induced apoptosis even in the presence of appropriate cytokines. This apoptosis was also accompanied by the ROS accumulation due to the downregulated expression of anti-oxidants such as glutathione, MnSOD, glutathione peroxidase, and TRX. In addition, the expression of antiapoptotic BCl-2 family members, Bcl-XL, Bcl-2, and A1 was found to be repressed by IkBSR. However, since antioxidants such as MCI (3-methyl-1-phenyl-2-pyrazolin-5-one), N-acetylecysteine and TRX cancelled this apoptosis, ROS were supposed to be more important for IkBSR-induced apoptosis in normal hematopoietic stem/progenitor cells. To further analyze the roles for NF-kB proteins in the development of hematopoietic cells, we expressed IkBSR in an inducible fashion at various stages of hematopoiesis using the OP9 system, in which hematopoietic cells are induced to develop from ES cells. When IkBSR was expressed at the stage of hemangioblasts, IkBSR induced apoptosis and inhibited the development of hematopoietic stem cells, which was also cancelled by MCI. Furthermore, when IkBSR was expressed after the development of hematopoietic stem cells, it also inhibited terminal differentiation towards granulocytes, erythrocytes, and megakaryocytes through ROS-mediated apoptosis; IkBSR inhibited granulopoiesis before the development of myeloblasts, erythropoiesis after the development of proerythroblasts, and megakaryopoiesis during polyploidization of megakaryocytes. These results indicate that NF-kB family proteins play essential roles to prevent apoptosis at multiple steps of hematopoiesis by eliminating ROS.

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Transforming Activity of AML1-ETO Oncoprotein Is Independent of CBFβ and ETO but Requires Homo-Oligomeric Interaction.

Blood ◽

10.1182/blood.v112.11.3348.3348 ◽

2008 ◽

Vol 112 (11) ◽

pp. 3348-3348

Author(s):

Bernd B Zeisig ◽

Colin Kwok ◽

Jihui Qiu ◽

Shuo Dong ◽

Chi Wai Eric So

Keyword(s):

Stem Cells ◽

Transcription Factors ◽

Structure Function ◽

Hematopoietic Cells ◽

Primary Cells ◽

Hematopoietic Stem ◽

Endogenous Expression ◽

Function Data ◽

Essential Components ◽

Transforming Activity

Abstract AML1/RUNX1 and CBFb encode two critical transcription factors essential for the generation of hematopoietic stem cells (HSC). In acute myeloid leukemia, where leukemic stem cells (LSCs) have been functionally identified, AML1 and CBFb also represent the most commonly mutated targets. While animal models indicate that AML1 fusions per se are not sufficient to induce full-blown leukemia, they enhance self-renewal and expand targeted HSC and early progenitors, a property also reported for other oncogenic transcription factors involved in acute leukemia. Although attempts had been made to identify the critical domains required for AML-ETO (AE) mediated transformation, conflicting results were presented from most of these studies using exploited wellestablished cell lines, which suffer from the pitfall of carrying irrelevant genetic aberrants that may not reflect the normal biology of the disease. The only available structure/ function data on primary cells was limited to NHR2 of the ETO portion of the fusion, but it does not distinguish the functional contribution between homo-oligomerization and hetero-oligomerization. The lack of comprehensive structure/function data has not only significantly impeded the progress of understanding the biology of the disease, but also hinders the development of specific therapeutics. To this end, we performed extensive functional analysis to identify the key components essential for AE-mediated transformation of primary hematopoietic cells. In spite of the critical role of CBFb for wild type AML1 functions and its direct involvement in chromosomal translocation, we demonstrate that multiple AE single point mutants defective in CBFb interaction were still capable of transforming primary hematopoietic cells. Consistently, shRNA mediated knockdown of the endogenous expression of CBFb in primary cells did not compromise the transforming activity of AE, strongly suggesting a dispensable function of CBFb in AE mediated transformation. On the other hand, we demonstrate that NHR2 as the only domain in the ETO portion of the fusion is essential for transformation, but its heterooligomeric function including interaction with transcriptional repressor ETO family proteins is dispensable for the transforming activity. In contrast, synthetic FKBP homooligomerization modules could functionally replace NHR2, indicating that AE mediated transformation is critically dependent on homo-oligomeric property of the resultant fusion. Moreover, the transformation can also be abolished by a small molecule inhibitor that specifically dissociates homo-oligomerization. Together, these results not only identify the essential components and refine potential avenues for therapeutic targeting of AE oncogenic complexes, but also strongly endorse a common homo-oligomerization dependent mechanism shared by the most prevalent leukemia associated transcription factors.

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Heterogenous Nuclear Ribonucleoprotein L (hnRNPL) Is Required for the Functional Integrity of Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v114.22.1486.1486 ◽

2009 ◽

Vol 114 (22) ◽

pp. 1486-1486

Author(s):

Marie-Claude Gaudreau ◽

Ehssan Sharif Askari ◽

Florian Heyd ◽

Tarik Moroy

Keyword(s):

Stem Cells ◽

Alternative Splicing ◽

Hematopoietic Stem Cells ◽

Hematopoietic Cells ◽

Regulation Of Transcription ◽

Hematopoietic Differentiation ◽

Short Term ◽

Hematopoietic Stem ◽

Functional Integrity ◽

Nuclear Ribonucleoprotein

Abstract Abstract 1486 Poster Board I-509 Hematopoietic differentiation has to be tightly regulated since uncontrolled or exaggerated development of blood cells may lead to the development of leukemia or autoimmune diseases. Many mechanisms exist to control hematopoiesis on a molecular level, including the regulation of transcription, which has been intensely studied. However, new evidence suggests the process of alternative splicing to be an important regulator of the maturation and activation of blood- and immune effector cells. One of the factors that has been identified as a potential regulator of the immune response and controls alternative splicing is “heterogenous nuclear ribonucleoprotein L” (hnRNP L). This factor affects among others the alternative splicing of the CD45 gene, which encodes the major tyrosine phosphatase expressed on all hematopoietic cells. To investigate the biological role of hnRNP L as a regulator of alternative splicing in hematopoiesis, we have generated conditional hnRNP L knockout (KO) mice carrying floxed alleles that can be deleted by co expression of Cre recombinase. Both the inducible MxCre transgene or Vav-Cre transgene, which is active in all hematopoietic cells were introduced into hnRNP Lfl/fl mice. We found that the conditional deletion of hnRNP L by the Vav Cre transgene led to early mortality before birth (at stage E17.5) and flow cytometric analysis of fetal liver of hnRNP Lfl/fl, Vav-Cre mice or bone marrow from pIpC induced hnRNP Lfl/fl Mx-Cre mice showed a deficit in erythrocyte maturation. In addition, fetal thymi from hnRNP Lfl/fl X Vav-Cre mice were severely reduced in cellularity and showed disturbed T cell maturation. Moreover, the deletion of hnRNP L results in reduced numbers of Lin−Sca1+ckit+ (LSK) cells, common lymphoid progenitors (CLPs), common myeloid progenitors (CMPs), granulocyte-monocyte progenitors (GMPs) and megakaryocyte-erythrocyte progenitors (MEPs). Strikingly, while most of the progenitors and the short-term hematopoietic stem cells (HSCs) were affected by the deletion of hnRNP L, the population of long term HSCs was not reduced. We found a high percentage of Annexin V positive cells in the LSK population suggesting that the loss of progenitors and short term HSCs in hnRNP L deficient mice is due to an accelerated cell death. To test whether stem cells lacking hnRNP L were still functional, we sorted Lin−Sca1+ckit+ (LSK) cells and cultured them on either methylcellulose or the feeder cell lines OP9 and OP9-DL1. The co-culture with OP9 or OP9-DL1 cells demonstrated that hnRNP L−/− LSK cells had lost their potential to differentiate into B and T lymphocytes. Similarly, hnRNP L deficient LSK cells were unable to give rise to lymphoid, myeloid or erythroid colonies on methylcellulose. This suggests that hnRNP L is required to maintain not only the numbers of hematopoietic stem cells, but also their ability for multilineage differentiation. We conclude that the regulation of alternative splicing is an essential component of the regulatory network required to maintain hematopoietic differentiation and the functional integrity of hematopoietic stem cells. Disclosures: No relevant conflicts of interest to declare.

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Geminin Regulates Hematopoietic Stem Cell Proliferation and Differentiation.

Blood ◽

10.1182/blood.v114.22.1478.1478 ◽

2009 ◽

Vol 114 (22) ◽

pp. 1478-1478

Author(s):

Kathryn M. Shinnick ◽

Kelly A. Barry ◽

Elizabeth A. Eklund ◽

Thomas J. McGarry

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Transcription Factors ◽

Cell Division ◽

Dna Replication ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Regulatory Protein ◽

Hematopoietic Stem ◽

Proliferation And Differentiation

Abstract Abstract 1478 Poster Board I-501 Hematopoietic stem cells supply the circulation with mature blood cells throughout life. Progenitor cell division and differentiation must be carefully balanced in order to supply the proper numbers and proportions of mature cells. The mechanisms that control the choice between continued cell division and terminal differentiation are incompletely understood. The unstable regulatory protein Geminin is thought to maintain cells in an undifferentiated state while they proliferate. Geminin is a bi-functional protein. It limits the extent of DNA replication to one round per cell cycle by binding and inhibiting the essential replication factor Cdt1. Loss of Geminin leads to replication abnormalities that activate the DNA replication checkpoint and the Fanconi Anemia (FA) pathway. Geminin also influences patterns of cell differentiation by interacting with Homeobox (Hox) transcription factors and chromatin remodeling proteins. To examine how Geminin affects the proliferation and differentiation of hematopoietic stem cells, we created a mouse strain in which Geminin is deleted from the proliferating cells of the bone marrow. Geminin deletion has profound effects on all three hematopoietic lineages. The production of mature erythrocytes and leukocytes is drastically reduced and the animals become anemic and neutropenic. In contrast, the population of megakaryocytes is dramatically expanded and the animals develop thrombocytosis. Interestingly, the number of c-Kit+ Sca1+ Lin- (KSL) stem cells is maintained, at least in the short term. Myeloid colony forming cells are also preserved, but the colonies that grow are smaller. We conclude that Geminin deletion causes a maturation arrest in some lineages and directs cells down some differentiation pathways at the expense of others. We are now testing how Geminin loss affects cell cycle checkpoint pathways, whether Geminin regulates hematopoietic transcription factors, and whether Geminin deficient cells give rise to leukemias or lymphomas. Disclosures: No relevant conflicts of interest to declare.

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Poly I:C Stimulates Sca-1 Expression in Murine Bone Marrow and Increases the Number of Phenotypic Hematopoietic Stem Cells.

Blood ◽

10.1182/blood.v114.22.2504.2504 ◽

2009 ◽

Vol 114 (22) ◽

pp. 2504-2504

Author(s):

Russell Garrett ◽

Gerd Bungartz ◽

Alevtina Domashenko ◽

Stephen G. Emerson

Keyword(s):

Cell Cycle ◽

Stem Cells ◽

Bone Marrow ◽

Hematopoietic Stem Cells ◽

Conflicts Of Interest ◽

Hematopoietic Cells ◽

Poly I:C ◽

Hematopoietic Stem ◽

Marrow Cells ◽

Myeloid Progenitors

Abstract Abstract 2504 Poster Board II-481 Polyinosinic:polycytidlyic acid (poly I:C) is a synthetic double-stranded RNA used to mimic viral infections in order to study immune responses and to activate gene deletion in lox-p systems employing a Cre gene responsive to an Mx-1 promoter. Recent observations made by us and others have suggested hematopoietic stem cells, responding to either poly I:C administration or interferon directly, enter cell cycle. Twenty-two hours following a single 100mg intraperitoneal injection of poly I:C into 10-12 week old male C57Bl/6 mice, the mice were injected with a single pulse of BrdU. Two hours later, bone marrow was harvested from legs and stained for Lineage, Sca-1, ckit, CD48, IL7R, and BrdU. In two independent experiments, each with n = 4, 41 and 33% of Lin- Sca-1+ cKit+ (LSK) IL-7R- CD48- cells from poly I:C-treated mice had incorporated BrdU, compared to 7 and 10% in cells from PBS-treated mice. These data support recently published reports. Total bone marrow cellularity was reduced to 45 and 57% in the two experiments, indicating either a rapid death and/or mobilization of marrow cells. Despite this dramatic loss of hematopoietic cells from the bone marrow of poly I:C treated mice, the number of IL-7R- CD48- LSK cells increased 145 and 308% in the two independent experiments. Importantly, the level of Sca-1 expression increased dramatically in the bone marrow of poly I:C-treated mice. Both the percent of Sca-1+ cells and the expression level of Sca-1 on a per cell basis increased after twenty-four hours of poly I:C, with some cells acquiring levels of Sca-1 that are missing from control bone marrow. These data were duplicated in vitro. When total marrow cells were cultured overnight in media containing either PBS or 25mg/mL poly I:C, percent of Sca-1+ cells increased from 23.6 to 43.7%. Within the Sca-1+ fraction of poly I:C-treated cultures, 16.7% had acquired very high levels of Sca-1, compared to only 1.75% in control cultures. Quantitative RT-PCR was employed to measure a greater than 2-fold increase in the amount of Sca-1 mRNA in poly I:C-treated cultures. Whereas the numbers of LSK cells increased in vivo, CD150+/− CD48- IL-7R- Lin- Sca-1- cKit+ myeloid progenitors almost completely disappeared following poly I:C treatment, dropping to 18.59% of control marrow, a reduction that is disproportionately large compared to the overall loss of hematopoietic cells in the marrow. These cells are normally proliferative, with 77.1 and 70.53% accumulating BrdU during the 2-hour pulse in PBS and poly I:C-treated mice, respectively. Interestingly, when Sca-1 is excluded from the analysis, the percent of Lin- IL7R- CD48- cKit+ cells incorporating BrdU decreases following poly I:C treatment, in keeping with interferon's published role as a cell cycle repressor. One possible interpretation of these data is that the increased proliferation of LSK cells noted by us and others is actually the result of Sca-1 acquisition by normally proliferating Sca-1- myeloid progenitors. This new hypothesis is currently being investigated. Disclosures: No relevant conflicts of interest to declare.

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FIP200 is required for the cell-autonomous maintenance of fetal hematopoietic stem cells

Blood ◽

10.1182/blood-2010-06-288589 ◽

2010 ◽

Vol 116 (23) ◽

pp. 4806-4814 ◽

Cited By ~ 140

Author(s):

Fei Liu ◽

Jae Y. Lee ◽

Huijun Wei ◽

Osamu Tanabe ◽

James D. Engel ◽

...

Keyword(s):

Stem Cells ◽

Hematopoietic Stem Cells ◽

Hematopoietic Cells ◽

Cellular Functions ◽

Interacting Protein ◽

Hematopoietic Stem ◽

Conditional Deletion ◽

Perinatal Lethality ◽

Fetal Hematopoiesis ◽

And Function

Abstract Little is known about whether autophagic mechanisms are active in hematopoietic stem cells (HSCs) or how they are regulated. FIP200 (200-kDa FAK-family interacting protein) plays important roles in mammalian autophagy and other cellular functions, but its role in hematopoietic cells has not been examined. Here we show that conditional deletion of FIP200 in hematopoietic cells leads to perinatal lethality and severe anemia. FIP200 was cell-autonomously required for the maintenance and function of fetal HSCs. FIP200-deficient HSC were unable to reconstitute lethally irradiated recipients. FIP200 ablation did not result in increased HSC apoptosis, but it did increase the rate of HSC proliferation. Consistent with an essential role for FIP200 in autophagy, FIP200-null fetal HSCs exhibited both increased mitochondrial mass and reactive oxygen species. These data identify FIP200 as a key intrinsic regulator of fetal HSCs and implicate a potential role for autophagy in the maintenance of fetal hematopoiesis and HSCs.

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Predominant expression of a receptor tyrosine kinase, TIE, in hematopoietic stem cells and B cells

Blood ◽

10.1182/blood.v87.1.93.93 ◽

1996 ◽

Vol 87 (1) ◽

pp. 93-101 ◽

Cited By ~ 44

Author(s):

M Hashiyama ◽

A Iwama ◽

K Ohshiro ◽

K Kurozumi ◽

K Yasunaga ◽

...

Keyword(s):

Stem Cells ◽

B Cells ◽

Tyrosine Kinase ◽

Hematopoietic Stem Cells ◽

Receptor Tyrosine Kinase ◽

Hematopoietic Cells ◽

Erythroid Differentiation ◽

Northern Blotting ◽

Hematopoietic Stem ◽

Epidermal Growth

Abstract A receptor tyrosine kinase (RTK), TIE (tyrosine kinase that contains immunoglobulin-like loops and epidermal growth factor [EGF] homology domains), is expressed in vascular endothelial and hematopoietic cells. We generated monoclonal antibodies (MoAbs) against the extracellular domain of TIE and a polyclonal antibody against the TIE carboxyterminus and used them to analyze expression of TIE in hematopoietic cells. Western blotting detected two forms of TIE protein with a molecular mass of 135 and 130 kD in hematopoietic and endothelial cells. Northern blotting analysis revealed that TIE was expressed preferentially in undifferentiated cell lines, especially when megakaryocytic, but not erythroid differentiation was induced. Reverse transcriptase-polymerase chain reaction (RT-PCR) showed that TIE was predominantly expressed in the human hematopoietic progenitor fraction, CD34+ cells. Fluorescence- activated cell sorting (FACS) showed that 42% of CD34+ and 17% of KIT- positive (KIT+) cells were TIE-positive (TIE+). The majority (81%) of the primitive hematopoietic stem cells, CD34+CD38- cells, were TIE+. Assays of progenitor cells and long-term culture-initiating cells (LTC- IC) showed that the TIE+ fraction contained more primitive cells than the TIE- fraction. Some TIE+ cells were in the CD34- fraction, which were CD19+ and CD20+ (B cells). These findings indicate that TIE has a unique spectrum of expression in primitive hematopoietic stem cells and B cells. Although its ligand has not been identified, TIE and its ligand may establish a novel regulatory pathway not only in early hematopoiesis, but also in the differentiation and/or proliferation of B cells.

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