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. Receptor 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 start site is identical in each of these tissues. A 1,391-bp fragment of the G-CSF receptor promoter is both active in myeloid cell lines and tissue specific. We have also found two regions that are important for G-CSF receptor promoter activity. One region, located at bp -49, contains a GCAAT site that specifically binds the C/EBP alpha transcription factor in myeloid nuclear extracts. Mutation of this site prevents C/EBP alpha binding and reduces promoter activity by 60%. The other functionally important region of the G-CSF receptor promoter is in the 5' untranslated region, at bp +36 and +43, where there are two sites for the ets family member PU.1. Mutation of these sites prevents PU.1 binding and reduces promoter activity by 75%. These results reinforce the importance of both PU.1 and C/EBP alpha in the expression of myeloid-specific genes and neutrophil development.