The molecular mechanisms of leukmogenesis by GATA1

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We performed this study to understand the molecular mechanisms of leukemogenesis by GATA1, and found the following results.1. To clarify the functional differences between GATA1 and GATA1 mutant, we constructed the retroviral expression vector for GATA1/estrogen receptor (ER) fusion protein and transduced a Stem cell factor (SCF)-dependent Down syndrome-associated acute megakaryoblastic leukemia (DS-AMKL) cell line. Conditional activation of both GATA1/ER and GATA1s/ER with Tamoxifen resulted in the growth inhibition and down-regulation of KIT expression.2. We demonstrate the abundant expression of KIT in all transient myeloproliferative disorder (TMD) patients examined. SCF stimulated the proliferation of the blast cells and treatment with the tyrosine kinase inhibitor imatinib suppressed the proliferation effectively in vitro. To investigate the signal cascade downstream from the SCF/KIT pathway, we analyzed a DS-AMKL cell line. SCF activated the RAS/MAPK and PI3K/AKT pathways in this cell line, followed by downregulation of the pro-apoptotic factor BIM and upregulation of the anti-apoptotic factor MCL1. These results suggest the essential role of SCF/KIT signaling in the proliferation of DS-related leukemia.3. The RUNX1 gene is localized to chromosome 21, within the critical region for DS. In this study, we show that GATA1 binds to RUNX1 through its zinc-finger domains, and that the C-finger is indispensable for synergy with RUNX1. All of the patient-specific GATA1 mutants interacted efficiently with RUNX1 and retained their ability to act synergistically with RUNX1 on the megakaryocytic GP1bα promoter, whereas the levels of transcriptional activities were diverse among the mutants. Thus our data indicate that physical interaction and synergy between GATA1 and RUNX1 are retained in DS-AMKL, although it is still possible that increased RUNX1 activity plays a role in the development of leukemia in DS.