Cloning and characterization of the 5′ upstream region of the human primary response gene EGR-3

Egr-3 is an immediate-early primary response gene encoding a zinc finger transcription factor. We cloned the human Egr-3 genomic locus including greater than 1100 bp of the 5′ flanking region and analyzed this region for putative cis-acting elements. The GC-rich promoter forms part of a representative CpG island that extends into the genomic locus. The Egr-3 promoter contains a region of TATA homology located 25bp upstream from a major transcriptional start site. One serum response element and two variant Egr consensus sequences were identified. Features that distinguished Egr-3 from other human Egr gene promoters included the presence of at least five E-box motifs and a retinoblastoma response element. In addition, an overlapping tandem repeat of 16 GC-rich nonamers was identified in the flanking region that may represent a novel regulatory region for this primary response gene. Reporter constructs coupled with Egr-3 flanking sequences in sense and antisense orientation were tested in transient transfection assays. The functional activity of the Egr-3 regulatory region was position-specific. Deletional analysis in serum stimulated embryonic lung fibroblasts identified that the major elements responsible for growth-induced Egr-3 expression are located within the first 378 bp upstream of the major transcription start site. Analysis of the human Egr-3 genomic locus revealed a complex regulatory organization with significant differences from other Egr genes. These findings may provide insights into the expression of Egr-3 in normal and neoplastic tissues.