Characterization of the human elk-1 promoter. Potential role of a downstream intronic sequence for elk-1 gene expression in monocytes.

To characterize the human elk-1 promoter, we mapped the transcriptional start site and isolated elk-1-specific genomic phage clones that contained extensive upstream and downstream sequences. A TATA-like motif was identified immediately upstream of the transcriptional start site. Functional analyses of DNA fragments containing the TATA element and the identification of a DNase I-hypersensitive chromatin site (HS 1) in close proximity to the TATA box suggest that the identified TATA motif is important for elk-1 transcription in vivo. Sequences upstream and downstream from the TATA box were found to contribute to elk-1 promoter activity. A second hypersensitive site (HS 2) was identified within the first intron in pre-monocytic cells, which express Elk-1 only when differentiating to monocytes. In a variety of other cell types, which display a constitutive Elk-1 expression, HS 2 did not exist, suggesting that inducibility of elk-1 expression is associated with the presence of HS 2. Egr-1 and the serum response factor were found to interact specifically with the intronic sequence at +265 and +448, respectively. Because Egr-1 mRNA and protein levels were observed to increase significantly before induction of elk-1 expression, we propose that Egr-1 is important for the regulation of elk-1 transcription in differentiating monocytes.