Megakaryocytic and erythroid lineages derive from a common bipotential progenitor and share many transcription factors, most prominently factors of the GATA zinc-finger family. Little is known about transcription factors unique to the megakaryocytic lineage that might program divergence from the erythroid pathway. To identify such factors, we used the K562 system in which megakaryocyte lineage commitment is dependent on sustained extracellular regulatory kinase (ERK) activation and is inhibited by stromal cell contact. During megakaryocytic induction in this system, the myeloid transcription factor RUNX1 underwent upregulation, dependent on ERK signaling and inhibitable by stromal cell contact.Immunostaining of healthy human bone marrow confirmed a strong expression of RUNX1 and its cofactor, core-binding factor ␤ (CBF␤), in megakaryocytes and a minimal expression in erythroblasts. In primary human hematopoietic progenitor cultures, RUNX1 and CBF␤ up-regulation preceded megakaryocytic differentiation, and down-regulation of these factors preceded erythroid differentiation. Functional studies showed cooperation among RUNX1, CBF␤, and GATA-1 in the activation of a megakaryocytic promoter. By contrast, the RUNX1-ETO leukemic fusion protein potently repressed GATA-1-mediated transactivation. These functional interactions correlated with physical interactions observed between GATA-1 and IntroductionDespite divergent phenotypes, megakaryocytic and erythroid lineages originate from a common bipotent progenitor, known variously as the blast-forming unit erythroid/megakaryocyte (BFU-E/MK) or the megakaryocyte erythroid progenitor (MEP). [1][2][3] As further evidence of a developmental link, human erythroblasts at relatively late stages of development retain the potential for megakaryocytic transdifferentiation. 4 The molecular basis for this developmental relationship appears to reside in the extensive sharing of lineage-restricted transcription factors. Many transcription factors initially identified as critical in erythroid development have been found through gene knock-out experiments to be important in megakaryocytic development. [5][6][7] GATA-1 is the prototypic erythro-megakaryocytic transcription factor, cooperating with its cofactor FOG-1 to serve essential roles in erythroid and megakaryocytic differentiation. 8 Enforced GATA-1 expression in myeloid cell lines promotes erythroid, megakaryocytic, or combined differentiation, depending on the cell type. [9][10][11] Knock-out of either the GATA-1 or the FOG-1 gene results in midgestation embryonic lethality because of severe anemia associated with abnormal or absent megakaryopoiesis. 7,12 Lineageselective knock-down in mice of GATA-1 expression in megakaryocytes causes increased megakaryocyte proliferation coupled with impaired maturation. 6,13 Knock-in mice with compound GATA-1 and GATA-2 mutations, causing the loss of FOG-1 binding, display a complete absence of megakaryopoiesis, a phenocopy of FOG-1 null mice. 8 Human hereditary mutations in the amino terminal...

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Summary How inflammation causes cancer is unclear. IL-15 is a pro-inflammatory cytokine elevated in human large granular lymphocyte (LGL) leukemia. Mice overexpressing IL-15 develop LGL leukemia. Here we show that prolonged in vitro exposure of wild type (WT) LGL to IL-15 results in Myc-mediated up regulation of aurora kinases, centrosome aberrancies, and aneuploidy. Simultaneously, IL-15 represses miR-29b via induction of Myc/NF-κBp65/Hdac-1, resulting in Dnmt3b overexpression and DNA hypermethylation. All this is validated in human LGL leukemia. Strikingly, adoptive transfer of WT LGL cultured with IL-15 led to malignant transformation in vivo. Drug targeting which reverses miR-29b repression, cures otherwise fatal LGL leukemia. We show how excessive IL-15 initiates cancer and demonstrate effective drug targeting for potential therapy of human LGL leukemia.