C/EBP, c-Myb, and PU.1 Cooperate To Regulate the Neutrophil Elastase Promoter

Abstract

The murine neutrophil elastase (NE) gene is expressed specifically in immature myeloid cells. A 91-bp NE promoter region contains three cis elements which are conserved evolutionarily and are essential for activation of the promoter in differentiating 32D cl3 myeloid cells. These elements bound c-Myb (at –49), C/EBPα (at –57), and PU.1 (at –82). In NIH 3T3 cells, the NE promoter was activated by c-Myb, C/EBPα, and PU.1, via their respective binding sites. Cooperative activation was seen by any combination of c-Myb, C/EBPα, and PU.1, including all three together, again via their DNA-binding sites. In CV-1 cells, but not in NIH 3T3 cells, cooperation between Myb and C/EBPα depended on the integrity of the PU.1-binding site. In addition to C/EBPα, C/EBPδ strongly activated the NE promoter, alone or with c-Myb, but C/EBPβ was less active. Either of C/EBPα’s two transactivation domains cooperatively activated the promoter with c-Myb, in both NIH 3T3 and 32D cl3 cells. Synergistic binding to DNA in a gel shift assay between C/EBPα, c-Myb, and PU.1 could not be demonstrated. Also, separation of the C/EBP- and c-Myb-binding sites by 5 or 10 bp did not prevent cooperativity. These results suggest that a coactivator protein mediates cooperative activation of the NE promoter by a C/EBP and c-Myb. These factors, together with PU.1, direct restricted expression of the NE promoter to immature myeloid cells.