EVIDENCE FOR CELL-SPECIFIC REGULATION OF TRANSCRIPTION OF THE RAT ALPHA(2A)-ADRENERGIC RECEPTOR GENE

We investigated the transcriptional activity of the -131 to -92 region of the rat alpha(2A)-adrenergic receptor gene. In HT29 cells, this re gion has a positive effect on transcription, whereas in RINm5F cells, this region has a negative effect on transcription. The -131 to -92 re gion has a GC box (GGGGCGG) surrounded by overlapping GGAGG repeats. T o analyze nuclear factor binding to this region, we made a series of s equence substitutions in the GGAGG repeats, the GC box, or botti regio ns. Gel mobility shift assays indicated that most of the nuclear facto r complexes formed between the wild-type -131/-92 sequence and either HT29 or RINm5F extracts were specific for Sp1 or related proteins that recognize a GC box. Mutation of either the GGAGG repeats or the GC bo x did not eliminate the binding of Spl or related nuclear factors, sug gesting that both the GGAGG repeats and the GC box could bind Sp1-rela ted factors. Mutation of both these sites eliminated the binding of Sp 1-related factors. In the absence of Sp1 binding sites, this region ha d a negative effect on transcription in HT29 and a positive effect on transcription in RINm5F cells. These data support the notion that Sp1 and/or a related factor may control both positive and negative gene ex pression and suggest that the -131/-92 region may be involved in regul ating tissue-specific levels of alpha(2A)-adrenergic receptor gene exp ression.