GATA and CACC elements commonly are codistributed within the regulatory domains of a variety of erythroid genes. Using Drosophila S2 cells, the actions of GATA1, Sp1, and erythroid Kruppel-like factor (EKLF) at these elements within model erythroid promoters have been assessed. For each promoter studied (erythroid pyruvate kinase, glycophorin B, and a murine betamaj globin-derived construct, GCT) Sp1 and EKLF each activated transcription despite differences in CACC element sequence, orientation, and positioning. However, GATA1 acted in apparent cooperativity with Sp1 at the pyruvate kinase promoter; with EKLF at the betamaj globin-derived GCT promoter; and with either Sp1 or EKLF at the glycophorin B promoter. Thus, GATA1 may functionally interact with each of these Krüppel-like factors depending on promoter context; and at the GCT promoter, transcriptional activation by GATA1 and EKLF was > or = 10-fold higher than levels attributable to additive effects. The possibility that interactions between these activators may be direct was supported by the specific binding of baculoviral-expressed EKLF to GATA1. This report underlines the likelihood that discrete roles exist for Sp1 and EKLF in erythroid gene activation, and supports a mechanism of direct cooperativity for EKLF and GATA1 as coregulators.
