α hematopoietic stem/progenitor cells involves downmodulation of C/EBP STAT5-induced self-renewal and impaired myelopoiesis of human

Abstract Previously, we demonstrated that enforced activation of STAT5A in human cord blood (CB)-derived stem/progenitor cells results in enhanced self-renewal and impaired myelopoiesis. The present study identifies C/EBPα as a critical component that is downregulated by STAT5. Microarray and RT-PCR analysis on STAT5A(1*6)-transduced CD34 + cells identified C/EBPα as the most prominently downregulated gene. To determine the cell-biological relevance of these observations, a 4-OHT-inducible C/EBPα-ER protein was co-expressed with the STAT5A(1*6) mutant in CB CD34 + cells using a retroviral approach. Re-expression of C/EBPα in STAT5A(1*6) cells resulted in a marked restoration of myelopoiesis. The proliferative advantage imposed on CD34 + cells by STAT5A(1*6) depended on the downmodulation of C/EBPα as reintroduction of C/EBPα induced a quick cell cycle arrest and the onset of myeloid differentiation. LTC-IC frequencies were elevated from 0.8±0.6% to 7.8±1.9% by STAT5A(1*6) as compared to controls, but these elevated LTC-IC frequencies were strongly reduced upon re-introduction of C/EBPα in STAT5A(1*6) cells and no 2nd CAFCs could be generated from double transduced cells. Enumeration of progenitors revealed that the number of CFCs was reduced over 20-fold when C/EBPα was co-expressed in STAT5A(1*6) cells. Our data indicate that downmodulation of C/EBPα is a prerequisite for STAT5-induced effects on self-renewal and myelopoiesis. From bloodjournal.hematologylibrary.org by guest on June 10, 2013. For personal use only.