Myeloid leukemia factor 1 stabilizes tumor suppressor C/EBPα to prevent Trib1-driven acute myeloid leukemia

Abstract C/EBPα is a key transcription factor regulating myeloid differentiation and leukemogenesis. The Trib1-COP1 complex is an E3 ubiquitin ligase that targets C/EBPα for degradation, and its overexpression specifically induces acute myeloid leukemia (AML). Here we show that myeloid leukemia factor 1 (MLF1) stabilizes C/EBPα protein levels by inhibiting the ligase activity of the Trib1-COP1 complex. MLF1 directly interacts with COP1 in the nucleus and interferes with the formation of the Trib1-COP1 complex, thereby blocking its ability to polyubiquitinate C/EBPα for degradation. MLF1 overexpression suppressed the Trib1-induced growth advantage in a murine bone marrow (BM) culture and Trib1-induced AML development in BM-transplanted mouse models. MLF1 was expressed in hematopoietic stem cells and myeloid progenitors (common myeloid progenitors and granulocyte-macrophage progenitors) in normal hematopoiesis, which is consistent with the distribution of C/EBPα. An MLF1 deficiency conferred a more immature phenotype on Trib1-induced AML development. A higher expression ratio of Trib1 to MLF1 was a key determinant for AML development in mouse models, which was also confirmed in human patient samples with acute leukemia. These results indicate that MLF1 is a positive regulator that is critical for C/EBPα stability in the early phases of hematopoiesis and leukemogenesis.

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Hematopoietic Stem Cells Are Intrinsically Protected Against MLL-ENL Mediated Transformation

Blood ◽

10.1182/blood.v124.21.839.839 ◽

2014 ◽

Vol 124 (21) ◽

pp. 839-839

Author(s):

Amol Sanjay Ugale ◽

Gudmundur Logi Norddahl ◽

Martin Wahlestedt ◽

Petter Säwén ◽

Pekka Jaako ◽

...

Keyword(s):

Stem Cells ◽

Acute Myeloid Leukemia ◽

Hematopoietic Stem Cells ◽

Mouse Models ◽

Myeloid Leukemia ◽

Mixed Lineage Leukemia ◽

Hematopoietic Stem ◽

Normal Differentiation ◽

Acute Myeloid ◽

Myeloid Progenitors

Abstract Studies on the developmental pathways of hematopoietic stem cells (HSCs) have led to roadmaps of differentiation and resulted in key information concerning lineage relationships and restriction points in the blood system. This knowledge is also central to understand the etiology of acute myeloid leukemia (AML), where recent work has proposed that the heterogeneity and aggressiveness of AML can associate with the developmental stage of transformation. Balanced chromosomal translocations that result in fusion proteins with aberrant transcriptional regulatory activities are frequent initiating events in acute myeloid leukemia, and a prototype family of such chimeric transcription factors is represented by fusions involving the mixed lineage leukemia-1 (MLL1) gene. Previous work using mouse models have suggested that at some stage of normal differentiation there is a loss of competence to induce AML. However discrepancies exists between these mouse models concerning the target cells of MLL fusion genes. While it is clear that cells can lose competence for leukemic transformation as part of their normal differentiation, the question remains whether the most primitive HSCs are always imbued with leukemogenic competency as part of their normal biology. To address this, we developed a Doxycycline inducible transgenic mouse model of the human chimeric transcription factor Mixed Lineage Leukemia-Eleven Nineteen Leukemia (MLL-ENL). Prospective isolations of candidate leukemia-initiating cells followed by adoptive transfers allowed us to detail leukemia-initiation and competence throughout the hematopoietic hierarchy. We show that AML can origin from multiple HPC subsets with intrinsic granulocytic/monocytic potential. Closely related myeloid progenitors displayed distinct leukemic- and functional capacity in response to physiological levels of MLL-ENL, highlighting the importance of a careful prospective isolation of progenitor populations. AML could also develop efficiently from common lymphoid progenitors, supporting a latent myeloid potential of these cells. By contrast, early commitment to the megakaryocytic/erythroid lineages was incompatible with leukemic development. By contrast, disease failed to arise from the most primitive progenitor subsets, including HSCs. Investigations of the immediate transcriptional responses to MLL-ENL showed evidence for a block in differentiation in both myeloid progenitors and HSCs, while MLL-ENL restricted cell cycle progression uniquely in HSCs. Our study highlights how an oncogene can exert unique functions depending on the developmental position of its cellular targets and demonstrate the existence of a mechanism, operational at the level of immature HSCs/progenitors, which act to prevent leukemic development. Figure 1 Graphical abstract Figure 1. Graphical abstract Disclosures No relevant conflicts of interest to declare.

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Alternative polyadenylation dysregulation contributes to the differentiation block of acute myeloid leukemia

Blood ◽

10.1182/blood.2020005693 ◽

2021 ◽

Author(s):

Amanda G Davis ◽

Daniel T. Johnson ◽

Dinghai Zheng ◽

Ruijia Wang ◽

Nathan D. Jayne ◽

...

Keyword(s):

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Alternative Polyadenylation ◽

Hematopoietic Stem ◽

Global Trends ◽

Protein Levels ◽

Mtorc1 Signaling ◽

Differentiation Block ◽

Acute Myeloid

Post-transcriptional regulation has emerged as a driver for leukemia development and an avenue for therapeutic targeting. Among post-transcriptional processes, alternative polyadenylation (APA) is globally dysregulated across cancer types. However, limited studies have focused on the prevalence and role of APA in myeloid leukemia. Furthermore, it is poorly understood how altered poly(A) site (PAS) usage of individual genes contributes to malignancy or whether targeting global APA patterns might alter oncogenic potential. In this study, we examined global APA dysregulation in acute myeloid leukemia (AML) patients by performing 3' Region Extraction And Deep Sequencing (3'READS) on a subset of AML patient samples along with healthy hematopoietic stem and progenitor cells (HSPCs) and by analyzing publicly available data from a broad AML patient cohort. We show that patient cells exhibit global 3' untranslated region (UTR) shortening and coding sequence (CDS) lengthening due to differences in PAS usage. Among APA regulators, expression of FIP1L1, one of the core cleavage and polyadenylation factors, correlated with the degree of APA dysregulation in our 3'READS dataset. Targeting global APA by FIP1L1 knockdown reversed the global trends seen in patients. Importantly, FIP1L1 knockdown induced differentiation of t(8;21) cells by promoting 3'UTR lengthening and downregulation of the fusion oncoprotein AML1-ETO. In non-t(8;21) cells, FIP1L1 knockdown also promoted differentiation by attenuating mTORC1 signaling and reducing MYC protein levels. Our study provides mechanistic insights into the role of APA in AML pathogenesis and indicates that targeting global APA patterns can overcome the differentiation block of AML patients.

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

Journal of Experimental Medicine ◽

10.1084/jem.20090831 ◽

2010 ◽

Vol 207 (3) ◽

pp. 475-489 ◽

Cited By ~ 211

Author(s):

Yoon-Chi Han ◽

Christopher Y. Park ◽

Govind Bhagat ◽

Jinping Zhang ◽

Yulei Wang ◽

...

Keyword(s):

Stem Cells ◽

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Ectopic Expression ◽

Hematopoietic Progenitors ◽

Self Renewal ◽

Hematopoietic Stem ◽

Myeloid Development ◽

Acute Myeloid ◽

Myeloid Progenitors

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

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MicroRNA-155 Promotes Myeloid Proliferation and Is Overexpressed in Acute Myeloid Leukemia.

Blood ◽

10.1182/blood.v110.11.715.715 ◽

2007 ◽

Vol 110 (11) ◽

pp. 715-715

Author(s):

Dinesh S. Rao ◽

Ryan M. O’Connell ◽

Aadel A. Chaudhuri ◽

Mark Boldin ◽

Konstantin Taganov ◽

...

Keyword(s):

Bone Marrow ◽

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Regulatory Networks ◽

Quantitative Polymerase Chain Reaction ◽

Retroviral Infection ◽

Hematopoietic Stem ◽

Murine Bone Marrow ◽

Myeloid Development ◽

Acute Myeloid

Abstract Recent discoveries have implicated microRNAs, which are small 22–24 nucleotide long RNA molecules, as important regulators of many cellular processes, including differentiation and development. The microRNA-155 (miR-155) is known to be overexpressed in subsets of B-cell neoplasms and is thought to be important in the activation and function of B-lymphocytes. Here, we show that miR-155 is signficantly overexpressed in human acute myeloid leukemia and that its overexpression is most consistently seen in acute myelomonocytic leukemia. These findings led us to investigate the effects of overexpression of miR-155 in hematopoietic cells. By utilizing retroviral infection and transfer of murine bone marrow, we introduced miR-155 overexpressing hematopoietic stem cells into lethally irradiated recipient mice. Following reconstitution of hematopoietic organs, the mice demonstrated a profound myeloproliferative condition in the bone marrow characterized by replacement of the marrow by proliferating and dysplastic myelomonocytic cells. In addition, extramedullary hematopoiesis was observed in the spleen and examination of the peripheral blood revealed anemia and thrombocytopenia. To begin to explore the mechanisms whereby miR-155 overexpression results in this myeloproliferative phenotype, we utilized computational methods to identify targets predicted to be regulated by miR-155. This revealed several genes that have previously been implicated in myeloid development and neoplasia, which were confirmed to be targets of miR-155 by reverse-transcription/quantitative polymerase chain reaction (RT/QPCR) and by downregulation of luciferase protein upon fusion of the luc gene with the respective 3′ untranslated regions. These studies show a hitherto uncharacterized role of miR-155 in myeloid development and proliferation. Importantly, these findings lay the groundwork for understanding the complex regulatory networks underlying myeloid development in the context of microRNAs, and may point to new therapeutic opportunities in the treatment of myeloid malignancies.

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HOXB6 overexpression in murine bone marrow immortalizes a myelomonocytic precursor in vitro and causes hematopoietic stem cell expansion and acute myeloid leukemia in vivo

Blood ◽

10.1182/blood-2004-04-1583 ◽

2005 ◽

Vol 105 (4) ◽

pp. 1456-1466 ◽

Cited By ~ 82

Author(s):

Neal A. Fischbach ◽

Sofia Rozenfeld ◽

Weifang Shen ◽

Stephen Fong ◽

Daniel Chrobak ◽

...

Keyword(s):

Bone Marrow ◽

Acute Myeloid Leukemia ◽

Myeloid Leukemia ◽

Hox Genes ◽

Cooperative Interaction ◽

Hematopoietic Stem ◽

Murine Bone Marrow ◽

Acute Myeloid

AbstractThe HOX family of homeobox genes plays an important role in normal and malignant hematopoiesis. Dysregulated HOX gene expression profoundly effects the proliferation and differentiation of hematopoietic stem cells (HSCs) and committed progenitors, and aberrant activation of HOX genes is a common event in human myeloid leukemia. HOXB6 is frequently overexpressed in human acute myeloid leukemia (AML). To gain further insight into the role of HOXB6 in hematopoiesis, we overexpressed HOXB6 in murine bone marrow using retrovirus-mediated gene transfer. We also explored structure-function relationships using mutant HOXB6 proteins unable to bind to DNA or a key HOX-binding partner, pre–B-cell leukemia transcription factor-1 (PBX1). Additionally, we investigated the potential cooperative interaction with myeloid ecotropic viral integration site 1 homolog (MEIS1). In vivo, HOXB6 expanded HSCs and myeloid precursors while inhibiting erythropoiesis and lymphopoiesis. Overexpression of HOXB6 resulted in AML with a median latency of 223 days. Coexpression of MEIS1 dramatically shortened the onset of AML. Cytogenetic analysis of a subset of HOXB6-induced AMLs revealed recurrent deletions of chromosome bands 2D-E4, a region frequently deleted in HOXA9-induced AMLs. In vitro, HOXB6 immortalized a factor-dependent myelomonocytic precursor capable of granulocytic and monocytic differentiation. These biologic effects of HOXB6 were largely dependent on DNA binding but independent of direct interaction with PBX1.

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