Beta adrenergic receptors are critical to cardiovascular function during development and in adulthood. While agonists and hormones regulate receptor density in adults at the transcriptional level, neither do in developing animals. Moreover, up until now there have been no data on specific regulatory mechanisms or functional analysis of the 5' flanking sequence of theβ1-adrenergic receptor (β1AR) gene at any age. We inserted random deletion fragments of the ovine β1AR 5' flanking sequence into a luciferase reporter vector, pGL2B. Transient expression of mutant constructs in C6 glioma cells, SK-N-MC neuroblastoma cells and W1 cells, a human embryonic myocardial cell line, indicated that sequences between - 1530 and-953 may contain a repressor element. Dexamethasone increased transcription activity 4-5 fold in the same construct in C6 cells and W1 cells. T3 alone had no effect and co-treatment with T3 did not augment the effects of dexamethasone. However, there was a significant 3-5 fold increase in transcription in response to T3 when the full-length promoter was co-transfected with a rat thyroid receptor-α1 expression vector. Thyroid responsiveness was localized to sequences -1890 to -1687. Conclusion: Specific sequences with the 5' flanking region confer repression of basal transcription, as well glucocorticoid and thyroid hormone mediated increase in transcription. Speculation: The sequences which we have identified may explain the novel mechanism(s) for transcription regulation within the same region during development. (Supported by grant HD29713).
