PU.1 (SPI-1) AND C EBP-ALPHA REGULATE THE GRANULOCYTE-COLONY-STIMULATING FACTOR-RECEPTOR PROMOTER IN MYELOID CELLS/

Cytokines, important for lineage commitment and differentiation during hematopoiesis, exert their influence by binding specific receptors. R eceptor expression is tightly regulated and examining the factors that govern their expression will allow better understanding of the events that determine lineage commitment, The granulocyte colony-stimulating factor (G-CSF) receptor is expressed exclusively in myeloid cells and the placenta. We show here that the G-CSF receptor transcription star t site is identical in each of these tissues. A 1,391-bp fragment of t he G-CSF receptor promoter is both active in myeloid cell lines and ti ssue specific. We have also found two regions that are important for G -CSF receptor promoter activity. One region, located at bp -49, contai ns a GCAAT site that specifically binds the C/EBP alpha transcription factor in myeloid nuclear extracts. Mutation of this site prevents C/E BP alpha binding and reduces promoter activity by 60%, The other funct ionally important region of the G-CSF receptor promoter is in the 5' u ntranslated region, at bp +36 and +43, where there are two sites for t he ets family member PU.1. Mutation of these sites prevents PU.1 bindi ng and reduces promoter activity by 75%. These results reinforce the i mportance of both PU.1 and C/EBP alpha in the expression of myeloid-sp ecific genes and neutrophil development, (C) 1996 by The American Soci ety of Hematology.