TRANSCRIPTIONAL CONTROL OF THE RAT SEROTONIN-2 RECEPTOR GENE

Previous reports have indicated that, in vivo, the serotonin-2 (5-HT2) receptor is responsive to exogenously administered glucocorticoids. T he ability of the glucocorticoid receptor (GR) to influence transcript ion of the rat 5-HT2 receptor gene was tested in two different experim ental paradigms. In both sets of experiments transcription of the 5-HT 2 gene was monitored with a promoter-reporter plasmid in which the pro moter for the 5-HT2 gene was driving the expression of the firefly luc iferase gene. In the first, the 5-HT2 promoter-reporter plasmid was tr ansfected directly into RS1 cells followed by dexamethasone treatment. In the second set of experiments, the cDNA encoding the GR carried on a separate expression vector was cotransfected into CCL-39 or Neuro-2 a cells along with the 5-HT2 promoter-reporter plasmid. These cells we re then exposed to dexamethasone. In the RS-1 and CCL-39 transfection experiments, the dexamethasone treatment caused an inhibition of trans cription of the 5-HT2 promoter, whereas in the Neuro-2a cells, the dex amethasone treatment stimulated transcription from the 5-HT2 promoter. These responses were dependent on the presence of the GR. The effect of the activated GR would seem to be indirect as sequence analysis of the 4.2 kb preceding the site of transcription initiation revealed onl y an 11/15 nt match to a putative glucocorticoid response element (GRE ), and deletion of this sequence did not alter the response to dexamet hasone. Sequence analysis revealed a variety of potential response ele ments for other known transcription factors, including four potential AP-1 response elements. To examine the functionality of these response elements, the components of the AP-1 complex, c-Fos and c-Jun were te sted separately and in combination as AP-1 for their ability to influe nce transcription of the 5-HT2 promoter-reporter plasmid. Cell-selecti ve enhancement or suppression by c-Fos and c-Jun of 5-HT2 transcriptio n was observed in these experiments.