Gfi‐1B Promoter Remains Associated with Active Chromatin Marks Throughout Erythroid Differentiation of Human Primary Progenitor Cells

Growth Factor Independent‐1B (Gfi‐1B) is a transcriptional repressor that plays critical roles in the control of erythropoiesis and megakaryopoiesis. Gfi‐1B expression was described to be repressed by an autoregulatory feedback control loop. Here, we show that Gfi‐1 transcription is positively regulated early after induction of erythroid differentiation and remains highly active to late erythroblasts. Using chromatin immunoprecipitation assays in CD34 + cells from human cord blood, we found that Gfi‐1 and GATA‐2 in immature progenitors and then Gfi‐1B and GATA‐1 in erythroblasts are bound to the Gfi‐1B promoter as well as to the promoter of c‐myc , a known Gfi‐1B target gene. Surprisingly, this Gfi‐1/GATA‐2–Gfi‐1B/GATA‐1 switch observed at erythroblast stages is associated to an increase in the Gfi‐1B transcription whereas it triggers repression of c‐myc transcription. Accordingly, analysis of chromatin modification patterns shows that HDAC, CoREST, and LSD1 are recruited to the c‐myc promoter leading to appearance of repressive chromatin marks. In contrast, the Gfi‐1B promoter remains associated with a transcriptionally active chromatin configuration as highlighted by an increase in histone H3 acetylation and concomitant release of the LSD1 and CoREST corepressors. The repressive function of Gfi‐1B therefore depends on the nature of the proteins recruited to the target gene promoters and on chromatin modifications. We conclude that Gfi‐1B behaves as a lineage‐affiliated gene with an open chromatin configuration in multipotent progenitors and sustained activation as cells progress throughout erythroid differentiation. STEM CELLS 2009;27:2153–2162