GATA1s induces hyperproliferation of eosinophil precursors in Down syndrome transient leukemia

Transient leukemia (TL) is evident in 5–10% of all neonates with Down syndrome (DS) and associated with N-terminal truncating GATA1-mutations (GATA1s). Here we report that TL cell clones generate abundant eosinophils in a substantial fraction of patients. Sorted eosinophils from patients with TL and eosinophilia carried the same GATA1s-mutation as sorted TL-blasts, consistent with their clonal origin. TL-blasts exhibited a genetic program characteristic of eosinophils and differentiated along the eosinophil lineage in vitro. Similarly, ectopic expression of Gata1s, but not Gata1, in wild-type CD34+-hematopoietic stem and progenitor cells induced hyperproliferation of eosinophil promyelocytes in vitro. While GATA1s retained the function of GATA1 to induce eosinophil genes by occupying their promoter regions, GATA1s was impaired in its ability to repress oncogenic MYC and the pro-proliferative E2F transcription network. ChIP-seq indicated reduced GATA1s occupancy at the MYC promoter. Knockdown of MYC, or the obligate E2F-cooperation partner DP1, rescued the GATA1s-induced hyperproliferative phenotype. In agreement, terminal eosinophil maturation was blocked in Gata1Δe2 knockin mice, exclusively expressing Gata1s, leading to accumulation of eosinophil precursors in blood and bone marrow. These data suggest a direct relationship between the N-terminal truncating mutations of GATA1 and clonal eosinophilia in DS patients

Nuclear PLC beta(1) acts as a negative regulator of p45/NF-E2 expression levels in Friend erythroleukemia cells

It is well established that phospholipase C (PLC) ??1 plays a role in the nuclear compartment and is involved in the signalling pathway that controls the switching of the erythroleukemia cells programming from an undifferentiated to a differentiated state. Constitutive overexpression of nuclear PLC??1 has been previously shown to inhibit Friend cells differentiation. For further characterization, we investigated the localization of PLC??1a and PLC??1b in Friend cells by fusing their cDNA to enhanced green fluorescent protein (GFP). To investigate the potential target of nuclear PLC??1 in Friend differentiation, we studied the expression of p45/NF-E2 transcription factor, which is an enhancer binding protein for expression of the ??-globin gene and the expression of GATA proteins that are important for the survival and differentiation of erythroid cells. Our data suggest that the overexpression of PLC??1 (both 1a and 1b) only in the nuclear compartment significantly reduces the expression of p45/NF-E2. The effect observed is attributable to the specific action of nuclear PLC??1 signalling given that GATA-1 and GATA-3 are not affected at all. Here we show the existence of a unique target, i.e. the transcription factor p45/NF-E2, whose expression is specifically inhibited by the nuclear signalling evoked by PLC??1 forms.close333

Perturbed hematopoiesis in the Tc1 mouse model of Down syndrome

Trisomy of human chromosome 21 (Hsa21) results in Down syndrome (DS), a disorder that affects many aspects of physiology, including hematopoiesis. DS children have greatly increased rates of acute lymphoblastic leukemia and acute megakaryoblastic leukemia (AMKL); DS newborns present with transient myeloproliferative disorder (TMD), a preleukemic form of AMKL. TMD and DS-AMKL almost always carry an acquired mutation in GATA1 resulting in exclusive synthesis of a truncated protein (GATA1s), suggesting that both trisomy 21 and GATA1 mutations are required for leukemogenesis. To gain further understanding of how Hsa21 contributes to hematopoietic abnormalities, we examined the Tc1 mouse model of DS, which carries an almost complete freely segregating copy of Hsa21, and is the most complete model of DS available. We show that although Tc1 mice do not develop leukemia, they have macrocytic anemia and increased extramedullary hematopoiesis. Introduction of GATA1s into Tc1 mice resulted in a synergistic increase in megakaryopoiesis, but did not result in leukemia or a TMD-like phenotype, demonstrating that GATA1s and trisomy of approximately 80% of Hsa21 perturb megakaryopoiesis but are insufficient to induce leukemia

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iv Foreword Since the turn of the century, scientists have become increasingly interested in the effects of tobacco on health. Only within the past few decades, however, has a broad experimental and clinical approach to the subject been manifest; within this period the most extensive and definitive studies have been undertaken since 1950. Few medical questions have stirred such public interest or created more scientific debate than the tobacco-health controversy. The interrelationships of smoking and health undoubtedly are complex. The subject does not lend itself to easy answers. Nevertheless, it has been increasingly apparent that answers must be found. As the principal Federal agency concerned broadly with the health of the American people, the Public Health Service has been conscious of its deep responsibility for seeking these answers. As steps in that direction it has seemed necessary to determine, as precisely as possible, the direction o