Characterization of cis-Acting Sequences and trans-Acting Signals Regulating Early Growth Response 1 and c-fosPromoters Through the Granulocyte-Macrophage Colony-Stimulating Factor Receptor in BA/F3 Cells

Abstract

AbstractHuman granulocyte-macrophage colony-stimulating factor (hGM-CSF ) activates a set of genes such as c-fos, jun, myc, and early growth response gene 1 (egr-1). Studies on BA/F3 cells that express hGM-CSF receptor (hGMR) showed that two different signaling pathways controlled by distinct regions within the β subunit are involved in activation of c-fos/c-jun genes and in c-myc, respectively. However, the region(s) of the β subunit responsible for activation of the egr-1 gene and other regulatory genes has not been identified. We describe here how egr-1 promoter is activated by hGMR through two regions of the β subunit, with these regions being required for activation of the c-fos promoter. Coexpression of dominant negative (dn) Ras (N17ras) or dn JAK2 almost completely suppressed the activation of egr-1 and c-fos promoters. Deletion analysis of egr-1 promoter showed two cis-acting regions responsible for activation by hGM-CSF or mouse interleukin-3 (mIL-3), one between nucleotide positions (nt) −56 and −116, and the other between nt −235 and −480, which contains tandem repeats of the serum response element (SRE) sites. Similar experiments with the c-fos promoter showed that cis-acting regions containing the SRE/AP-1 sites is sufficient for activation by hGM-CSF. Based on these observations, we propose that signaling pathways activating egr-1 and c-fos promoters are controlled by SRE elements, either through the same or overlapping pathways that involve JAK2 and Ras.