Transient expression of PU.1 commits multipotent progenitors to a myeloid fate whereas continued expression favors macrophage over granulocyte differentiation

Objective. The Ets-family transcription factor PU.1 is expressed specifically in the hematopoietic system, in which it is absolutely required for the generation of B lymphocytes and macrophages. In contrast. overexpression of PU.1 blocks terminal differentiation of the erythroid lineage, in which it can act as an oncogene. In this study we used a multipotential progenitor cell line to examine the effects of PU.1 overexpression on myeloerythroid commitment within a single model system. Materials and Methods. PU.1 cDNA was introduced transiently and stably into the multipotent, nonleukemic hemopoietic cell line FDCPmix. Transiently transfected cells were isolated by fluorescence-activated cell sorting within 18 hours of transfection. Stable transfectants were selected by antibiotic resistance over a number of weeks. The effects of short- and long-term overexpression of PU.1 on self-renewal, proliferation, and differentiation were investigated. Results. A transient pulse of expression in multipotent progenitor cells eliminated the options of self-renewal and erythroid differentiation, resulting in commitment to the myeloid lineage. However, this transient pulse of expression did not affect the subsequent lineage choice of bi-potent granulocyte/macrophage progenitors. In contrast, continuous expression of PU.1 resulted in a strong bias toward macrophage rather than granulocyte differentiation. Conclusion. These results demonstrate promyeloid effects of PU.1 at two distinct stages of hematopoiesis. (C) 2003 International Society for Experimental Hematology. Published by Elsevier Science Inc.