Positive and negative regulation of granulocyte-macrophage colony- stimulating factor promoter activity by AML1-related transcription factor, PEBP2

The granulocyte-macrophage colony-stimulating factor (GM-CSF) gene promoter contains a consensus sequence for the polyomavirus enhancer binding- protein 2 (PEBP2) transcription factor, which consists of α and β subunits. There are at least two genes, αA and αB, encoding the α subunit. αB is the mouse homologue of human AML1 gene detected at the breakpoints of t(8;21) and t(3;21) myeloid leukemias. We examined αA1 (an αA-gene product) and αB1 and αB2 (two αB-encoded isomers) for their effects on the GM-CSF promoter. PEBP2αA1, αB1, and αB2 proteins bound the PEBP2 site within the mouse GM-CSF promoter. PEBP2αA1 and αB1 enhanced the expression of the GM- CSF promoter-driven reporter plasmid in unstimulated and 12-O- tetradecanoylphorbol 13-acetate/phytohemagglutinin-stimulated human Jurkat T cells. In contrast, the promoter activity was suppressed by αB2. Coexpression of αB1 and αB2 showed that the promoter activity could be determined by the αB1/αB2 ratio. Jurkat cell extract contained PEBP2 site- binding protein(s) that cross-reacted with antimouse αA1 antibodies. Northern blot analysis indicated the expression of human PEBP2αA, αB (AML1), and β genes in Jurkat cells. Although further studies are required to determine the precise role of PEBP2 in the GM-CSF promoter activity, the present findings suggested the importance of the relative ratio of different PEBP2 isoforms in regulating the levels of the promoter activity.