Evidence for cell-specific regulation of transcription of the rat alpha2A-adrenergic receptor gene.

We investigated the transcriptional activity of the -131 to -92 region of the rat alpha2A-adrenergic receptor gene. In HT29 cells, this region has a positive effect on transcription, whereas in RINm5F cells, this region has a negative effect on transcription. The -131 to -92 region has a GC box (GGGGCGG) surrounded by overlapping GGAGG repeats. To analyze nuclear factor binding to this region, we made a series of sequence substitutions in the GGAGG repeats, the GC box, or both regions. Gel mobility shift assays indicated that most of the nuclear factor 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 box did not eliminate the binding of Sp1 or related nuclear factors, suggesting that both the GGAGG repeats and the GC box could bind Sp1-related factors. Mutation of both these sites eliminated the binding of Sp1-related factors. In the absence of SP1 binding sites, this region had 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 expression and suggest that the -131/-92 region may be involved in regulating tissue-specific levels of alpha2A-adrenergic receptor gene expression.