title: STAT5-induced self-renewal and impaired myelopoiesis of human hematopoietic stem/progenitor cells involves down-modulation of C/EBPalpha.
abstract: Previously, we demonstrated that enforced activation of signal transducer and activator of transcription 5 (STAT5A) in human cord blood (CB)-derived stem/progenitor cells results in enhanced self-renewal and impaired myelopoiesis. The present study identifies C/EBPalpha as a critical component that is down-regulated by STAT5. Microarray and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis on STAT5A(1*6)-transduced CD34(+) cells identified C/EBPalpha as the most prominently down-regulated gene. To determine the cell-biological relevance of these observations, a 4-OHT-inducible C/EBPalpha-ER protein was co-expressed with the STAT5A(1*6) mutant in CB CD34(+) cells using a retroviral approach. Re-expression of C/EBPalpha 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 down-modulation of C/EBPalpha, as reintroduction of C/EBPalpha induced a quick cell-cycle arrest and the onset of myeloid differentiation. Long-term culture-initiating cell (LTC-IC) frequencies were elevated from 0.8% +/- 0.6% to 7.8% +/- 1.9% by STAT5A(1*6) as compared with controls, but these elevated LTC-IC frequencies were strongly reduced upon re-introduction of C/EBPalpha in STAT5A(1*6) cells, and no second cobble-stone area-forming cells (CAFCs) could be generated from double-transduced cells. Enumeration of progenitors revealed that the number of colony-forming cells (CFCs) was reduced more than 20-fold when C/EBPalpha was co-expressed in STAT5A(1*6) cells. Our data indicate that down-modulation of C/EBPalpha is a prerequisite for STAT5-induced effects on self-renewal and myelopoiesis.
authors.affiliation: Department of Hematology, University Medical Center Groningen, Hanzeplein 1, 9700 RB Groningen, The Netherlands.
authors.forename: Albertus T J
authors.initials: AT
authors.lastname: Wierenga
authors.forename: Hein
authors.initials: H
authors.lastname: Schepers
authors.forename: Malcolm A S
authors.initials: MA
authors.lastname: Moore
authors.forename: Edo
authors.initials: E
authors.lastname: Vellenga
authors.forename: Jan Jacob
authors.initials: JJ
authors.lastname: Schuringa
mesh_terms: D022762:CCAAT-Enhancer-Binding Proteins / Q000235:genetics*; D002453:Cell Cycle / Q000235:genetics; D049109:Cell Proliferation; D002478:Cells, Cultured; D015536:Down-Regulation / Q000235:genetics*; D005312:Fetal Blood; D020869:Gene Expression Profiling; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D006801:Humans; D038042:Myelopoiesis; D050799:STAT5 Transcription Factor / Q000235:genetics / Q000502:physiology*; D014161:Transduction, Genetic; D025521:Tumor Suppressor Proteins
chemical_list: D022762:CCAAT-Enhancer-Binding Proteins; D050799:STAT5 Transcription Factor; C494092:STAT5A protein, human; D025521:Tumor Suppressor Proteins