Antagonistic effects of PU.1 on Gfi-1B-induced erythroid colony formation inhuman cord blood cells

Gfi-1B is a hematopoietic transcription factor essential for growth and differentiation of the erythroid/megakaryocytic lineages, and PU.1 is a master regulator for myeloid development. Herein, we demonstrate that PU.1 interacted with Gfi-1B in vivo by immunoprecipitation assay. GST pull-down assays showed that the binding sites were located in the Ets domain of PU.1 and the zinc finger domain of Gfi-1B. Luciferase reporter assays revealed that PU.1 and Gfi-1B antagonized each other's transcriptional activity in a dose-dependent manner. The transduction of Gfi-1B alone in human cord blood progenitor cells strongly enhanced erythroid colony formation. However, the transduction of PU.1 along with Gfi-1B in the progenitors significantly inhibited erythroid colony formation. Co-expression of Gfi-1B with a mutant PU.1, which bound to Gfi-1B but not to GATA1, another erythroid master regulator, also inhibited Gfi-1B-induced erythroid colony formation. Our results suggest that the function of Gfi-1B in the growth and differentiation of erythroid cells is antagonized by the expression of PU.1.