Novel regulation of the transcription factor ZHX2 by N-terminal methylation

N-terminal methylation (Nα-methylation) by the methyltransferase NRMT1 is an important post-translational modification that regulates protein-DNA interactions. Accordingly, its loss impairs functions that are reliant on such interactions, including DNA repair and transcriptional regulation. Global loss of Nα-methylation results in severe developmental and premature aging phenotypes, but given over 300 predicted substrates, it is hard to discern which physiological substrates contribute to each phenotype. One of the most striking phenotypes in NRMT1 knockout (Nrmt1-/-) mice is early liver degeneration. To identify the disrupted signaling pathways leading to this phenotype and the NRMT1 substrates involved, we performed RNA-sequencing analysis of control and Nrmt1-/- adult mouse livers. We found both a significant upregulation of transcripts in the cytochrome P450 (CYP) family and downregulation of transcripts in the major urinary protein (MUP) family. Interestingly, transcription of both families is inversely regulated by the transcription factor zinc fingers and homeoboxes 2 (ZHX2). ZHX2 contains a non-canonical NRMT1 consensus sequence, indicating its function could be directly regulated by Nα-methylation. We confirmed misregulation of CYP and MUP mRNA and protein levels in Nrmt1-/- livers and verified NRMT1 can methylate ZHX2 in vitro. In addition, we used mutants of ZHX2 that cannot be methylated to directly demonstrate Nα-methylation promotes ZHX2 transcription factor activity. Finally, we show Nrmt1-/- mice also exhibit early postnatal de-repression of ZHX2 targets involved in fetal liver development. Taken together, these data implicate continual ZHX2 misregulation as a driving force behind the liver phenotype seen in Nrmt1-/- mice.

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Mef2C is a lineage-restricted target of Scl/Tal1 and regulates megakaryopoiesis and B-cell homeostasis

Blood ◽

10.1182/blood-2008-07-167577 ◽

2009 ◽

Vol 113 (15) ◽

pp. 3461-3471 ◽

Cited By ~ 37

Author(s):

Christos Gekas ◽

Katrin E. Rhodes ◽

Laurraine M. Gereige ◽

Hildur Helgadottir ◽

Roberto Ferrari ◽

...

Keyword(s):

Transcription Factor ◽

B Cell ◽

Fetal Liver ◽

Premature Aging ◽

Functional Requirements ◽

Helix Loop Helix ◽

B Cell Homeostasis ◽

B Lymphoid ◽

Deficient Mice

Abstract The basic helix-loop-helix transcription factor stem cell leukemia gene (Scl) is a master regulator for hematopoiesis essential for hematopoietic specification and proper differentiation of the erythroid and megakaryocyte lineages. However, the critical downstream targets of Scl remain undefined. Here, we identified a novel Scl target gene, transcription factor myocyte enhancer factor 2 C (Mef2C) from Sclfl/fl fetal liver progenitor cell lines. Analysis of Mef2C−/− embryos showed that Mef2C, in contrast to Scl, is not essential for specification into primitive or definitive hematopoietic lineages. However, adult VavCre+Mef2Cfl/fl mice exhibited platelet defects similar to those observed in Scl-deficient mice. The platelet counts were reduced, whereas platelet size was increased and the platelet shape and granularity were altered. Furthermore, megakaryopoiesis was severely impaired in vitro. Chromatin immunoprecipitation microarray hybridization analysis revealed that Mef2C is directly regulated by Scl in megakaryocytic cells, but not in erythroid cells. In addition, an Scl-independent requirement for Mef2C in B-lymphoid homeostasis was observed in Mef2C-deficient mice, characterized as severe age-dependent reduction of specific B-cell progenitor populations reminiscent of premature aging. In summary, this work identifies Mef2C as an integral member of hematopoietic transcription factors with distinct upstream regulatory mechanisms and functional requirements in megakaryocyte and B-lymphoid lineages.

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Altered Development and Cytokine Responses of Myeloid Progenitors in the Absence of Transcription Factor, Interferon Consensus Sequence Binding Protein

Blood ◽

10.1182/blood.v94.11.3764 ◽

1999 ◽

Vol 94 (11) ◽

pp. 3764-3771 ◽

Cited By ~ 86

Author(s):

Marina Scheller ◽

John Foerster ◽

Clare M. Heyworth ◽

Jeffrey F. Waring ◽

Jürgen Löhler ◽

...

Keyword(s):

Bone Marrow ◽

Transcription Factor ◽

Progenitor Cells ◽

Fetal Liver ◽

Binding Protein ◽

Marrow Cell ◽

Consensus Sequence ◽

Myeloid Progenitor ◽

Myeloid Progenitor Cells

Abstract Mice deficient for the transcription factor, interferon consensus sequence binding protein (ICSBP), are immunodeficient and develop disease symptoms similar to human chronic myeloid leukemia (CML). To elucidate the hematopoietic disorder of ICSBP−/− mice, we investigated the growth, differentiation, and leukemogenic potential of ICSBP−/−myeloid progenitor cells in vitro, as well as by cell-transfers in vivo. We report that adult bone marrow, as well as fetal liver of ICSBP-deficient mice harbor increased numbers of progenitor cells, which are hyperresponsive to both granulocyte macrophage colony-stimulating factor (GM-CSF) and G-CSF in vitro. In contrast, their response to M-CSF is strongly reduced and, surprisingly, ICSBP−/− colonies formed in the presence of M-CSF are mostly of granulocytic morphology. This disproportional differentiation toward cells of the granulocytic lineage in vitro parallels the expansion of granulocytes in ICSBP−/− mice and correlates with a 4-fold reduction of M-CSF receptor expressing cells in bone marrow. Cell transfer studies showed an intrinsic leukemogenic potential and long-term reconstitution capability of ICSBP−/− progenitors. Further experiments demonstrated strongly reduced adhesion of colony-forming cells from ICSBP−/− bone marrow to fibronectin. In summary, ICSBP−/− myeloid progenitor cells share several abnormal features with CML progenitors, suggesting that the distal parts of signaling pathways of these two disorders are overlapping.

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Altered Development and Cytokine Responses of Myeloid Progenitors in the Absence of Transcription Factor, Interferon Consensus Sequence Binding Protein

Blood ◽

10.1182/blood.v94.11.3764.423k03_3764_3771 ◽

1999 ◽

Vol 94 (11) ◽

pp. 3764-3771 ◽

Cited By ~ 2

Author(s):

Marina Scheller ◽

John Foerster ◽

Clare M. Heyworth ◽

Jeffrey F. Waring ◽

Jürgen Löhler ◽

...

Keyword(s):

Bone Marrow ◽

Transcription Factor ◽

Progenitor Cells ◽

Fetal Liver ◽

Binding Protein ◽

Marrow Cell ◽

Consensus Sequence ◽

Myeloid Progenitor ◽

Myeloid Progenitor Cells

Mice deficient for the transcription factor, interferon consensus sequence binding protein (ICSBP), are immunodeficient and develop disease symptoms similar to human chronic myeloid leukemia (CML). To elucidate the hematopoietic disorder of ICSBP−/− mice, we investigated the growth, differentiation, and leukemogenic potential of ICSBP−/−myeloid progenitor cells in vitro, as well as by cell-transfers in vivo. We report that adult bone marrow, as well as fetal liver of ICSBP-deficient mice harbor increased numbers of progenitor cells, which are hyperresponsive to both granulocyte macrophage colony-stimulating factor (GM-CSF) and G-CSF in vitro. In contrast, their response to M-CSF is strongly reduced and, surprisingly, ICSBP−/− colonies formed in the presence of M-CSF are mostly of granulocytic morphology. This disproportional differentiation toward cells of the granulocytic lineage in vitro parallels the expansion of granulocytes in ICSBP−/− mice and correlates with a 4-fold reduction of M-CSF receptor expressing cells in bone marrow. Cell transfer studies showed an intrinsic leukemogenic potential and long-term reconstitution capability of ICSBP−/− progenitors. Further experiments demonstrated strongly reduced adhesion of colony-forming cells from ICSBP−/− bone marrow to fibronectin. In summary, ICSBP−/− myeloid progenitor cells share several abnormal features with CML progenitors, suggesting that the distal parts of signaling pathways of these two disorders are overlapping.

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Hypermethylation of APC2 Is a Predictive Epigenetic Biomarker for Chinese Colorectal Cancer

Disease Markers ◽

10.1155/2018/8619462 ◽

2018 ◽

Vol 2018 ◽

pp. 1-7 ◽

Cited By ~ 3

Author(s):

Yuan He ◽

Li-Yue Sun ◽

Jing Wang ◽

Rui Gong ◽

Qiong Shao ◽

...

Keyword(s):

Colorectal Cancer ◽

Cox Regression ◽

The Cancer Genome Atlas ◽

Sequencing Analysis ◽

Primary Tumors ◽

Protein Levels ◽

Normal Tissues ◽

Ffpe Tissues ◽

Epigenetic Biomarker

Objective. To investigate methylation of the adenomatosis polyposis coli homologue (APC2) promoter and its correlation with prognostic implications in Chinese colorectal cancer (CRC). Methods. The mRNA expression of APC2 in colorectal tissues was evaluated using the database of The Cancer Genome Atlas (TCGA). Methylation analysis of APC2 in tumor (n=66) and corresponding adjacent formalin-fixed and paraffin-embedded (FFPE) tissues (n=44) was performed by Sequenom EpiTYPER® and verified by cloning-based bisulfite sequencing analysis. Demethylation and retrieval of APC2 expression in cell lines HT29, HCT116, and SW480 were treated with 5-aza-2′-deoxycytidine (5-AZC). Results. Analysis of TCGA showed that APC2 mRNA was significantly downregulated in primary tumors when compared to normal tissues (p<0.05). APC2 methylation was upregulated (43.93% vs 7.31%, p<0.05) in tumors compared to adjacent FFPE tissues. In vitro experiments demonstrated that 5-AZC downregulated the methylation of APC2 and retrieved its expression of mRNA and protein levels (p<0.05). Multivariate Cox regression indicated that APC2_CPG_14 was an independent risk factor for overall survival (HR = 6.38, 95% CI: 1.59–25.64, p<0.05). Conclusion. This study indicates that APC2 is hypermethylated and may be a tumorigenesis biomarker for Chinese CRC patients.

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The SCL Transcription Factor Supports Erythroid Cell Survival and Differentiation Downstream of the Erythropoietin Receptor.

Blood ◽

10.1182/blood.v104.11.818.818 ◽

2004 ◽

Vol 104 (11) ◽

pp. 818-818

Author(s):

Rachid Lahlil ◽

Richard Martin ◽

Peter D. Aplan ◽

C. Glenn Begley ◽

Jacqueline E. Damen ◽

...

Keyword(s):

Transcription Factor ◽

Cell Survival ◽

Cell Fate ◽

Genetic Interaction ◽

Fetal Liver ◽

Erythropoietin Receptor ◽

Erythroid Cell ◽

Loss Of Function

Abstract Erythroid cell development critically depends on the SCL/Tal1 transcription factor and on erythropoietin signalling. In the present study, we have taken several approaches to show that the two genes operate within the same pathway to consolidate the erythroid lineage. Signaling through the erythropoietin receptor (EpoR) upregulates SCL protein levels in a clonal cell line (TF-1) in vitro, and in murine fetal liver cells in vivo, when Epor−/− cells were compared to those of wild type littermates at E12.5. In addition, we provide functional evidence for a linear pathway from EpoR to SCL that regulates erythropoiesis. Interfering with SCL induction or SCL function prevents the anti-apoptotic effect of Epo in TF-1 cells and conversely, ectopic SCL expression is sufficient to substitute for Epo to transiently maintain cell survival. In vivo, SCL gain of function complements the cellular defects in Epor−/− embryos to support cell survival and maturation during primitive and definitive erythropoiesis, as assessed by cellular and histological analyses of Epor−/− SCLtg embryos. Moreover, several erythroid specific genes that are decreased in Epor−/− embryos are rescued by the SCL transgene including glycophorinA, bH1 and bmaj globin, providing molecular confirmation of the functional and genetic interaction between Epor and SCL. Conversely, erythropoiesis becomes deficient in compound Epor+/−SCL+/− heterozygote mice, indicating that the genetic interaction between EpoR and SCL is synthetic. Finally, using EpoR mutants that harbour well defined signalling deficiencies, combined with gain and loss of function approaches for specific kinases, we identify MAPK as the major signal transduction pathway downstream of EpoR that upregulates SCL function, necessary for erythroid cell survival and differentiation. Taken together, our observations are consistent with the view that cytokines can influence cell fate by altering the dosage of lineage transcriptional regulators.

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Mef2C Is a Lineage-Restricted Target Gene of Scl/Tal1 and Regulates Megakaryopoiesis and B-Cell Homeostasis

Blood ◽

10.1182/blood.v112.11.278.278 ◽

2008 ◽

Vol 112 (11) ◽

pp. 278-278

Author(s):

Katrin E Rhodes ◽

Christos Gekas ◽

Laurraine Gereige ◽

Hildur Helgadottir ◽

Roberto Ferrari ◽

...

Keyword(s):

Transcription Factor ◽

B Cell ◽

Muscle Development ◽

Target Genes ◽

Fetal Liver ◽

Premature Aging ◽

Bhlh Transcription Factor ◽

Functional Requirements ◽

B Lymphoid ◽

Deficient Mice

Abstract The bHLH transcription factor stem cell leukemia/T-cell acute leukemia gene (Scl/Tal1) is a master regulator for hematopoiesis, essential for hematopoietic specification and proper differentiation of the erythroid and megakaryocyte lineages. However, the critical downstream targets of Scl remain undefined. To identify Scl target genes in hematopoietic cells, we performed gene expression analysis on HOX11-immortalized Sclfl/fl fetal liver cell lines. Analysis of the top 50 downregulated genes revealed several genes related to hematopoiesis including erythroid and megakaryocyte development, vasculogenesis, as well as genes/unknown ESTs that have not been previously linked to blood development. One of the top downregulated genes was transcription factor myocyte enhancer factor 2C (Mef2C). Mef2C−/− embryos die at E9.5, the same time as Scl−/− embryos, and exhibit severe defects in cardiac and muscle development. Analysis of Mef2C−/− embryos showed that, Mef2C, in contrast to Scl, is not required for specification into primitive or definitive hematopoietic lineages. To bypass the embryonic lethality, we utilized a conditionally targeted Mef2Cfl/fl strain and crossed it with a hematopoietic cell-specific VavCre strain that deactivates Mef2C shortly after the emergence of HSCs. Interestingly, adult VavCre+Mef2Cfl/fl mice exhibited severe platelet defects highly reminiscent to those observed in Scl deficient mice. The platelet counts were reduced, while platelet size was increased and the platelet shape and granularity was altered. Furthermore, megakaryopoiesis was severely impaired in vitro. ChIP-on-chip analysis revealed that Mef2C is directly regulated by Scl in megakaryocytic cells, but not in erythroid cells. In addition, an Scl independent requirement for Mef2C in B-lymphoid homeostasis was observed in Mef2C-deficient mice, characterized as severe age-dependent reductions of specific B-cell progenitor populations reminiscent of premature aging. In summary, this work identifies Mef2C as an integral member of hematopoietic transcription factors with distinct upstream regulatory mechanisms and functional requirements in megakaryocyte and B-lymphoid lineages.

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Involvement of Negative Cofactor NC2 in Active Repression by Zinc Finger-Homeodomain Transcription Factor AREB6

Molecular and Cellular Biology ◽

10.1128/mcb.18.1.10 ◽

1998 ◽

Vol 18 (1) ◽

pp. 10-18 ◽

Cited By ~ 43

Author(s):

Keiko Ikeda ◽

Jörn-Peter Halle ◽

Gertraud Stelzer ◽

Michael Meisterernst ◽

Kiyoshi Kawakami

Keyword(s):

Amino Acids ◽

Transcription Factor ◽

Rna Polymerase Ii ◽

Zinc Finger ◽

Transcriptional Repression ◽

Consensus Sequence ◽

Nuclear Extract ◽

Transcription System ◽

Repression Domain

ABSTRACT The transcription factor AREB6 contains a homeodomain flanked by two clusters of Krüppel type C2H2 zinc fingers. AREB6 binds to the E-box consensus sequence, CACCTGT, through either the N- or the C-terminal zinc finger cluster. To gain insights into the molecular mechanism by which AREB6 activates and represses gene expression, we analyzed the domain structure of AREB6 in the context of a heterologous DNA-binding domain by transient-transfection assays. The C-terminal region spanning amino acids 1011 to 1124 was identified as a conventional acidic activation domain. The region containing amino acids 754 to 901, which was identified as a repression domain, consists of 40% hydrophobic amino acids displaying no sequence similarities to other known repression domains. This region repressed transcription in vitro in a HeLa nuclear extract but not in reconstituted transcription systems consisting of transcription factor IID (TFIID), TFIIB, TFIIE, TFIIH/F, and RNA polymerase II. The addition of recombinant negative cofactor NC2 (NC2α/DRAP1 and NC2β/Dr1) to the reconstituted transcription system restored the activity of the AREB6 repression domain. We further demonstrated interactions between the AREB6 repression domain and NC2α in yeast two-hybrid assay. Our findings suggest a mechanism of transcriptional repression that is mediated by the general cofactor NC2.

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DNA Methylation Profile of Runx1 Regulatory Regions Is Correlated with Transition From Primitive to Definitive Hematopoietic Potential In Vitro and In Vivo

Blood ◽

10.1182/blood.v118.21.389.389 ◽

2011 ◽

Vol 118 (21) ◽

pp. 389-389

Author(s):

Beau Webber ◽

Michelina Iacovino ◽

Michael Kyba ◽

Bruce R. Blazar ◽

Jakub Tolar

Keyword(s):

Dna Methylation ◽

Stem Cells ◽

Transcription Factor ◽

Fetal Liver ◽

Methylation Status ◽

Differential Methylation ◽

Promoter Usage ◽

Highly Correlated

Abstract Abstract 389 Introduction: The Runt-related transcription factor Runx1 (AML1) is a central regulator of mammalian hematopoiesis and is required for the generation of hematopoietic stem cells (HSC) from hemogenic endothelium in the embryo. It has been shown that Runx1 is alternatively expressed from two promoters in a temporal fashion, and that their differential activities are influenced by a conserved intronic enhancer (+23) element. Intriguingly, promoter usage follows a pattern whereby the proximal (P2) initiates early in primitive hematopoiesis, while the distal (P1) becomes active later at the time of HSC emergence and is the predominant isoform expressed in fetal liver and adult HSC. While some transcription factor binding sites and cis-regulatory elements have been identified, an explanation for the alternative promoter usage remains elusive. We hypothesized that this regulation may be at the level of chromatin accessibility, and therefore investigated the DNA methylation status of Runx1 cis-elements. Methods/Results: We analyzed bisulfite-treated genomic DNA from E14.5 fibroblast (MEF), E8.5 yolk sac CD41+ (YS), E14.5 fetal liver Lin-Sca-1+CD48-CD150+ (FL), and adult marrow Lin-cKit+Sca-1+ (KLS); representing non-hematopoietic, primitive hematopoietic, and two stages of definitive HSC respectively. In addition, we also examined methylation in hematopoietic populations derived in vitro from murine embryonic stem cells (mESC). Initial exploratory analysis focused on classically defined CpG islands upstream of each promoter, however no significant differential methylation was observed within these regions. Subsequent analysis focused on CpGs near the transcription start site (TSS) and within the +23 enhancer. The P2 promoter was uninformative as it was unmethylated in all populations analyzed, whereas methylation within the +23 enhancer differentiated between hematopoietic and non-hematopoietic cell populations. At the P1 promoter, methylation status was remarkably correlated with primitive vs. definitive status. P1 was highly methylated in MEFs (77%), mESC embryoid body (EB) derived cKit+CD41+ (66%), and E8.5 YS CD41+ (58%); but significantly less methylated in vivo in FL HSC (8.1%) and adult KLS cells (18%). We are currently using this correlation of demethylation and definitive HSC potential to identify conditions that may drive definitive HSC generation from mESC-derived blood progenitors. Since overexpression of HoxB4 coupled with OP9 co-culture is the only confirmed method capable of producing definitive HSC from mESC, and HoxB4 has been shown to bind within the P1 promoter region of Runx1, we cultured HoxB4 or control EB-derived hematopoietic progenitors on OP9 stroma. We observed progressive demethylation in the HoxB4 arm: after 6 days of co-culture 47% vs. 71% in controls, and after 11 days 27% in the HoxB4 arm while the control population failed to proliferate past day 6. Isoform specific RT-PCR confirmed that HoxB4 overexpression resulted in Runx1 expression from the P1 promoter whereas the control vector did not. Within P1, we identify a single CpG that is most highly correlated with definitive HSC potential in vivo, and most significantly demethylated upon HoxB4 overexpression in vitro. Conclusions: These data indicate that differential methylation occurs at Runx1 regulatory regions during hematopoietic development in vitro and in vivo. The +23 enhancer is demethylated in cells with hematopoietic potential, whereas demethylation of the Runx1 P1 promoter is highly correlated with definitive HSPC populations and is promoted in vitro by HoxB4. These data are the first to identify a role for DNA methylation in the regulation of alternative promoter usage at the Runx1 locus, and may serve as a novel biomarker of HSC potential during embryonic development. Disclosures: No relevant conflicts of interest to declare.

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Inducible Gata1 Suppression As a Novel Strategy to Expand Physiologic Megakaryocyte Production from Embryonic Stem Cells

Blood ◽

10.1182/blood.v124.21.3846.3846 ◽

2014 ◽

Vol 124 (21) ◽

pp. 3846-3846

Author(s):

Ji-Yoon Noh ◽

Shilpa Gandre-Babbe ◽

Yuhuan Wang ◽

Vincent Hayes ◽

Yu Yao ◽

...

Keyword(s):

Transcription Factor ◽

Conflicts Of Interest ◽

Fetal Liver ◽

Es Cells ◽

Embryonic Stem ◽

Hematopoietic Progenitors ◽

Erythroid Progenitors ◽

Transfusion Therapy ◽

Ips Cell

Abstract Embryonic stem (ES) and induced pluripotent stem (iPS) cells represent potential sources of megakaryocytes and platelets for transfusion therapy. However, most current ES/iPS cell differentiation protocols are limited by low yields of hematopoietic progeny, including platelet-releasing megakaryocytes. Mutations in the mouse and human genes encoding transcription factor GATA1 cause accumulation of proliferating, developmentally arrested megakaryocytes. Previously, we reported that in vitro differentiation of Gata1-null murine ES cells generated self-renewing hematopoietic progenitors termed G1ME cells that differentiated into erythroblasts and megakaryocytes upon restoration of Gata1 cDNA by retroviral transfer. However, terminal maturation of Gata1-rescued megakaryocytes was aberrant with immature morphology and no proplatelet formation, presumably due to non-physiological expression of GATA1. We now engineered wild type (WT) murine ES cells that express doxycycline (dox)-regulated Gata1 short hairpin (sh) RNAs to develop a strategy for Gata1-blockade that upon its release, restores physiologic GATA1 expression during megakaryopoiesis. In vitro hematopoietic differentiation of control scramble shRNA-expressing ES cells with dox and thrombopoietin (TPO) produced megakaryocytes that underwent senescence after 7 days. Under similar differentiation conditions, Gata1 shRNA-expressing ES cells produced immature hematopoietic progenitors, termed G1ME2 cells, which replicated continuously for more than 40 days, resulting in ~1013-fold expansion (N=4 separate experiments). Upon dox withdrawal with multi-lineage cytokines present (EPO, TPO, SCF, GMCSF and IL3), endogenous GATA1 expression was restored to G1ME2 cells followed by differentiation into erythroblasts and megakaryocytes, but no myeloid cells. In clonal methylcellulose assays, dox-deprived G1ME2 cells produced a mixture of erythroid, megakaryocytic and erythro-megakaryocytic colonies. In liquid culture with TPO alone, dox-deprived G1ME2 cells formed mature megakaryocytes in 5-6 days, as determined by morphology, ultrastructure, acetylcholinesterase staining, upregulated megakaryocytic gene expression (Vwf, Pf4, Gp1ba, Selp, Ppbp), CD42b surface expression, increased DNA ploidy and proplatelet production. Compared to G1ME cells rescued with Gata1 cDNA retrovirus, dox-deprived G1ME2 cells exhibited more robust megakaryocytic maturation, similar to that of megakaryocytes produced from cultured fetal liver. Importantly, G1ME2 cell-derived megakaryocytes generated proplatelets in vitro and functional platelets in vivo (~40 platelets/megakaryocyte with a circulating half life of 5-6 hours). These platelets were actively incorporated into growing arteriolar thrombi at sites of laser injury and subsequently expressed the platelet activation marker p-selectin (N=3-4 separate experiments). Our findings indicate that precise timing and magnitude of a transcription factor is required for proper terminal hematopoiesis. We illustrate this principle using a novel, readily reproducible strategy to expand ES cell-derived megakaryocyte-erythroid progenitors and direct their differentiation into megakaryocytes and then into functional platelets in clinically relevant numbers. Disclosures No relevant conflicts of interest to declare.

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Fli1 Expression Level Affects Megakaryopoiesis and Thrombopoiesis: More Is Not Always a Bad Thing

Blood ◽

10.1182/blood.v128.22.3876.3876 ◽

2016 ◽

Vol 128 (22) ◽

pp. 3876-3876

Author(s):

Karen K Vo ◽

Danuta Jadwiga Jarocha ◽

Randolph B Lyde ◽

Spencer K. Sullivan ◽

Deborah French ◽

...

Keyword(s):

Transcription Factor ◽

Genome Editing ◽

Platelet Activation ◽

Transgene Expression ◽

Conflicts Of Interest ◽

Function Analysis ◽

Ipsc Line ◽

Protein Levels ◽

Platelet Disorder

Abstract Friend leukemia integration 1 (FLI1) is a critical transcription factor responsible for terminal megakaryocyte differentiation. This transcription factor is amongst the genes missing in the inherited disorder Jacobsen syndrome, resulting from a hemizygous deletion on chromosome 11q. The deletion causes dysmegakaryopoiesis and macrothrombocytopenia termed Paris Trousseau syndrome (PTSx). Also, FLI1 mutations in its DNA-binding domain region results in thrombocytopenia in affected patients. We examined induced pluripotent stem cell- (iPSC) derived megakaryocytes (iMegs) to determine if the platelet disorder observed in PTSx could be replicated and if varied levels of Fli1 expression affected megakaryopoiesis and thrombopoiesis. Beginning with a normal control (WT) iPSC line, genome editing was performed to generate three lines with: 1) one copy of FLI1 disrupted (FLI1+/-), 2) hemizygous transgene expression of Fli1 in the adeno-associated virus site 1 (AAVS1) safe harbor locus using a megakaryocyte-specific GP1balpha promoter (WT-overexpressing line, WT-OE), and 3) homozygous transgene expression in AAVS1 (WT-OE2). Additionally, we established an iPSC line from a PTSx patient and edited this line for a similar hemizygous transgene expression of FLI1 (PTSx-OE). Data described here are summarized in the tables below. We confirm our genome editing strategies by examining mRNA and protein levels of iMegs and found WT-OE and WT-OE2 iMegs have ~3X higher mRNA and ~7X higher protein levels than WT iMegs. FLI1+/- and PTSx iMegs both have lower mRNA and ~0.5X the protein levels of WT iMegs, while PTSx-OE iMegs had comparable levels of mRNA and protein as WT-OE iMegs. Megacult colony assays showed WT-OE and WT-OE2 yielded more CFU-Megs than WT HPCs (p²0.01, p²0.05, respectively). PTSx and FLI1+/- had much less CFU-Megs compared to PTSx-OE and WT (p²0.0001). After growth in liquid culture, WT-OE and -OE2 lines had an increase in iMeg numbers (p=0.29, p²0.01) while FLI1+/- and PTSx iMeg numbers were 43% and 10% that of the WT control (p²0.01, p²0.001). PTSx-OE iMeg numbers were comparable to WT. Surface marker CD41 and CD42b levels were increased compared to WT iMegs in the WT-OE and -OE2 iMegs (p=0.25, p²0.05) and less on FLI1+/- and PTSx iMegs (p²0.01, p²0.05). PTSx-OE iMegs were normal compared to WT, but p²0.05 vs. PTSx. Infused CD41+CD42b+ iMegs into NSG mice showed a trend toward same yield of platelets in the OE lines and lower yield in FLI1+/- and PTSx lines compared to WT. However, when calculations were made from HPCs rather than iMegs infused, the FLI1+/- and PTSx iMegs generated significantly less number of released platelets (p²0.05, p²0.01). The half-life of WT-OE and -OE2 released platelets were increased at 4 and 10 hours compared to WT, whereas FLI1+/- and PTSx released platelets have lower half-lives of 2 hours and 0.5 hours, respectively. These decreased platelet half-lives are due to the majority of platelets being defective and cleared at a higher rate. This was corrected to WT in the PTSx-OE-released platelets. Both in vitro iMegs and in vivo released platelets within the murine blood were assessed for function. Analysis of activation by thrombin was performed via FACS for PAC-1 binding and cell surface P-selectin levels, which are both indicators of platelet activation. Initial studies show no difference between WT and the WT-OE and WT-OE2 lines, but FLI1+/- platelet activation was slightly impaired. In summary, we show that studies of iMegs with decreased Fli1 levels replicate many of the clinical features previously described: less iMegs, lower CD41 and CD42b density with less platelets released while having shorter half-lives. On the other hand, increased Fli1 levels resulted in higher number of iMegs with more surface antigen density and released platelets with increased half-lives. Based on overexpression studies of other transcription factors during megakaryopoiesis, such as GATA1, the expectation would have been that the excess of Fli1 in the OE lines would have also resulted in defects in megakaryopoiesis and thrombopoiesis, but instead improvements were seen. The basis for this difference when overexpressing different transcriptional factors needs further analysis. That high Fli1 levels enhance iMeg yield with maintained numbers and function of released platelets may be of value for generating platelets for clinical use from in vitro grown Megs. Figure 1 Figure 1. Figure 2 Figure 2. Disclosures No relevant conflicts of interest to declare.

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