Interaction of a glucocorticoid-responsive element with regulatory sequences in the promoter region of the mouse tyrosine hydroxylase gene

The purpose of the work reported here was to determine whether the tyrosine hydroxylase glucocorticoid-responsive element (TH-GRE) interacts with the cyclic AMP pathway and the CRE in regulating mouse TH promoter activity, and whether an additional, previously identified downstream GRE-like element also participates in the function of the TH-GRE and CRE. To determine the role of the cAMP pathway on TH-GRE function, we compared the effects of forskolin and dexamethasone on TH mRNA, TH gene transcription and TH promoter activity in a mutant PC12 cell line (A126-1B2) deficient in cAMP-dependent protein kinase A (PKA) with their effects in the wild-type parental strain. Forskolin treatment increased TH mRNA content, transcriptional activity and the activity of a chimeric gene with 3.6 kb of the TH promoter in wild-type cells, but not in PKA-deficient cells. In contrast, dexamethasone treatment stimulated equivalent increases in TH mRNA, TH gene transcription and TH promoter activity in each cell type. Mutation of the CRE in chimeric constructs containing 3.6 kb of the 5′ flanking sequence of the mouse TH gene or coexpression of a dominant-negative mutant of CREB prevented the stimulation of TH promoter activity by forskolin. However, neither the mutation of the CRE nor inhibition of CREB influenced basal or dexamethasone -stimulated promoter activity. Site-directed mutagenesis of the TH-GRE eliminated the response of the promoter to dexamethasone, However, the mutagenesis of a more proximal 15-bp region with a GRE-like sequence had no demonstrable effect on the ability of dexamethasone to stimulate TH promoter activity. Neither mutagenesis of the TH-GRE or the downstream GRE-like sequence had an effect on the ability of forskolin to activate this chimeric gene. Taken together, these results provide evidence that a single GRE is sufficient for maximal induction of transcriptional activity by glucocorticoids and that the CRE is not required for either partial or full activity of this upstream GRE sequence.