MYB silencing in CD34+ progenitor cells

The c-Myb transcription factor is highly expressed in immature hematopoietic cells and down-regulated during differentiation. To define the role of c-Myb in human hematopoietic lineage commitment, we studied the effects of its silencing during the commitment of human CD34+ Hematopoietic stem/progenitor cells. In CD34+ cells c-Myb silencing determined a cell cycle arrest in G0/G1 phase which strongly decreased the clonogenic efficiency, togheter with a reduction of erythroid colonies coupled with an increase of the macrophage and megakaryocyte ones. Moreover, morphological and flow cytometry data supported the preferential macrophage and megakaryocyte differentiation of c-Myb-silenced CD34+ cells. Taken together our data indicate that c-Myb is essential for the commitment along the erythroid and granulocyte lineages but not for the macrophage and megakaryocyte differentiation. Gene expression profiling of c-Myb-silenced CD34+ cells identified some potential c-Myb targets which can account for these effects, to study by Chromatin Immunoprecipitation and Luciferase Reporter Assay. To maximize siRNA transfection efficiency, we utilized the NucleofectorTM technology (Amaxa). CD34+ cells were transfected with a mixture of 3 siRNAs targeting c-Myb mRNA and with a non-targeting siRNA as a negative control. The expression level of c-Myb protein on control cells (MOCK and negative control treated cells) and MYBsiRNA treated cells was assessed by Western Blot at 24 and 48h post-nucleofection.