The rat galanin-gene promoter: Response to members of the nuclear hormone receptor family, phorbol ester and forskolin

We have cloned a rat genomic DNA fragment of approximate to 12.5 kb. Nine kb of the cloned fragment lie in the 5'-flanking region of the gene and contain the promoter elements, while the remaining 3.5 kb contain the first four complete exons, the first three introns, and part of the fourth intron of the rat galanin gene. We have partially analysed some of the elements within the proximal sequence of this promoter which may influence the transcriptional regulation of the rat galanin gene. The rat galanin-gene promoter contains many regions which share homology with both the human and the bovine galanin genes and certain cis-elements appear to be conserved among the three species. In an attempt to test whether some of these elements are functional in the rat gene, transient transfection studies were carried out in selected cell lines. Estrogen, thyroid hormone and retinoic acid all showed a minimal degree of promoter stimulation when the rat galanin-gene promoter was co-transfected with the appropriate hormone receptors in Neuro 2A cells, while co-transfection of the nuclear orphan receptor ELP1 was able to stimulate transcription of a galanin promoter-driven reporter gene construct (-374 bp) by 35-fold. The galanin promoter mediated a 3-4-fold induction in response to forskolin or TPA. Deletion of a 5-bp element at -50 bp from the start of transcription was able to greatly reduce the forskolin response but not the TPA response. These results point to several elements that may be targets of transcription factors linked to extracellular stimuli. (C) 1997 Elsevier Science B.V.