Sp1/Egr1 motif: a new candidate in the regulation of rat tyrosine hydroxylase gene transcription by immobilization stress.

The rat tyrosine hydroxylase (TH) promoter contains a GC box (Sp1 motif) whose function is currently unclear. In this study, we examined the effect of immobilization (IMO) stress on binding of adrenomedullary transcription factors to that site. DNase I footprinting analysis reveals the binding of proteins to the Sp1 motif. Extracts from the adrenal medulla of IMO-treated rats generate a footprint on the Sp1 motif that is smaller than that generated by control extracts. Electrophoretic mobility shift assays using an oligonucleotide containing the Sp1 region show that two Sp1 protein-containing complexes (I and III) form with control extracts. In contrast, extracts from the adrenal medulla of IMO-treated rats form a novel complex (II) that contains the Egr1 protein. This is the first report to reveal changes in the binding pattern on the TH Sp1 motif in response to stress and to identify an overlapping Egr1 site.