ABSTRACT
The transcription factor Ikaros regulates the development of hematopoietic cells. Ikaros-deficient animals fail to develop B cells and display a T-cell malignancy, which is correlated with altered Notch signaling. Recently, loss of Ikaros was associated with progression of myeloproliferative neoplasms to acute myeloid leukemia and increasing evidence shows that Ikaros is also critical for the regulation of myeloid development. Previous studies showed that Ikaros-deficient mice have increased megakaryopoiesis, but the molecular mechanism of this phenomenon remains unknown. Here, we show that Ikaros overexpression decreases NOTCH-induced megakaryocytic specification, and represses expression of several megakaryocytic genes including GATA-1 to block differentiation and terminal maturation. We also demonstrate that Ikaros expression is differentially regulated by GATA-2 and GATA-1 during megakaryocytic differentiation and reveal that the combined loss of Ikzf1 and Gata1 leads to synthetic lethality in vivo associated with prominent defects in erythroid cells and an expansion of megakaryocyte progenitors. Taken together, our observations demonstrate an important functional interplay between Ikaros, GATA factors, and the NOTCH signaling pathway in specification and homeostasis of the megakaryocyte lineage.
Subject(s)
GATA1 Transcription Factor/metabolism , Ikaros Transcription Factor/physiology , Receptors, Notch/metabolism , Thrombopoiesis/genetics , Animals , Cell Differentiation/genetics , Cell Differentiation/immunology , Cell Proliferation , Cells, Cultured , Down-Regulation/genetics , Embryo, Mammalian , Gene Expression Regulation, Developmental , Ikaros Transcription Factor/genetics , Ikaros Transcription Factor/metabolism , Megakaryocytes/metabolism , Megakaryocytes/physiology , Mice , Mice, Knockout , Models, Biological , Protein Binding/genetics , Protein Binding/physiology , Signal Transduction/genetics , Signal Transduction/physiologyABSTRACT
The NOTCH signaling pathway is implicated in a broad range of developmental processes, including cell fate decisions. However, the molecular basis for its role at the different steps of stem cell lineage commitment is unclear. We recently identified the NOTCH signaling pathway as a positive regulator of megakaryocyte lineage specification during hematopoiesis, but the developmental pathways that allow hematopoietic stem cell differentiation into the erythro-megakaryocytic lineages remain controversial. Here, we investigated the role of downstream mediators of NOTCH during megakaryopoiesis and report crosstalk between the NOTCH and PI3K/AKT pathways. We demonstrate the inhibitory role of phosphatase with tensin homolog and Forkhead Box class O factors on megakaryopoiesis in vivo. Finally, our data annotate developmental mechanisms in the hematopoietic system that enable a decision to be made either at the hematopoietic stem cell or the committed progenitor level to commit to the megakaryocyte lineage, supporting the existence of 2 distinct developmental pathways.
Subject(s)
Cell Differentiation , Cell Lineage/physiology , Megakaryocytes/physiology , Oncogene Protein v-akt/metabolism , Receptors, Notch/metabolism , Animals , Cell Differentiation/genetics , Cell Differentiation/physiology , Cell Lineage/genetics , Cells, Cultured , Forkhead Transcription Factors/genetics , Forkhead Transcription Factors/metabolism , Forkhead Transcription Factors/physiology , Megakaryocytes/metabolism , Mice , Mice, Inbred C57BL , Mice, Transgenic , Oncogene Protein v-akt/genetics , Oncogene Protein v-akt/physiology , PTEN Phosphohydrolase/genetics , PTEN Phosphohydrolase/metabolism , PTEN Phosphohydrolase/physiology , Receptor Cross-Talk/physiology , Receptors, Notch/genetics , Receptors, Notch/physiology , Signal Transduction/genetics , Signal Transduction/physiology , Thrombopoiesis/geneticsABSTRACT
Acute megakaryoblastic leukemia (AMKL) is a heterogeneous disease generally associated with poor prognosis. Gene expression profiles indicate the existence of distinct molecular subgroups, and several genetic alterations have been characterized in the past years, including the t(1;22)(p13;q13) and the trisomy 21 associated with GATA1 mutations. However, the majority of patients do not present with known mutations, and the limited access to primary patient leukemic cells impedes the efficient development of novel therapeutic strategies. In this study, using a xenotransplantation approach, we have modeled human pediatric AMKL in immunodeficient mice. Analysis of high-throughput RNA sequencing identified recurrent fusion genes defining new molecular subgroups. One subgroup of patients presented with MLL or NUP98 fusion genes leading to up-regulation of the HOX A cluster genes. A novel CBFA2T3-GLIS2 fusion gene resulting from a cryptic inversion of chromosome 16 was identified in another subgroup of 31% of non-Down syndrome AMKL and strongly associated with a gene expression signature of Hedgehog pathway activation. These molecular data provide useful markers for the diagnosis and follow up of patients. Finally, we show that AMKL xenograft models constitute a relevant in vivo preclinical screening platform to validate the efficacy of novel therapies such as Aurora A kinase inhibitors.