ISOLATION AND CHARACTERIZATION OF THE PROMOTER OF THE HUMAN GABA(A) RECEPTOR ALPHA-1-SUBUNIT GENE

The GABA(A) receptor, as assessed by ligand binding and chloride flux measurement in vivo and in vitro, is down-regulated in response to chronic benzodiazepine exposure. The mRNA levels of the alpha1 and gamma2 subunits of the receptor are also reduced. We have isolated the promoter of the gene encoding the alpha1 subunit of the GABA(A) receptor to elucidate the regulatory mechanism of its expression. A DNA segment 650 bp long has been isolated that includes 151 bp of untranslated 5' end of the cDNA sequence and 500 bp of potential promoter-enhancer region. The transcriptional activity of this DNA segment linked to the firefly luciferase gene showed a strong orientation specificity. The promoter activity was localized to a 60-bp segment by deletion mapping. Mobility shift binding assay results suggest that this segment may interact with one or more factors in HeLa cell nuclear extracts to form a transcriptional complex. Primary cultures of embryonic chick cortical cells transfected with the promoter-luciferase construct were treated chronically with lorazepam. Transcriptional activity of this promoter construct was strongly repressed by chronic administration of lorazepam.