Identification, tissue expression, and glucocorticoid responsiveness of alternative first exons of the human glucocorticoid receptor.

Transcripts for the human glucocorticoid receptor (NR3C1) are known to contain alternative first exons 1A1, 1A2, and 1A3 from the distal promoter or 1D, 1E, 1B, 1F, 1C, or 1H from the proximal promoter. Here, we report two additional alternative first exons identified by Rapid amplification of cDNA ends (RACE)-PCR. The first, exon 1I, starts approximately 700 bp downstream of the splice donor site of the longest form of exon 1A, 1A3, considerably extending the known distal promoter region with a region containing conserved transcription factor-binding sites as well as a potential glucocorticoid response element (GRE) that differs from the consensus GRE in only two positions. The second, exon 1J, is part of the proximal promoter region and resides between exons 1D and 1E. Since this has been determined by quantitative real-time reverse transcriptase (RT)-PCR, exon 1I is used foremost in cells of the T-lymphocyte lineage. In the T-ALL cell line CEM-C7H2, which is sensitive to glucocorticoid-induced apoptosis, transcripts containing alternative first exons from the distal as well as the proximal promoter regions were markedly autoinduced by glucocorticoid treatment, with more pronounced relative induction in the distal promoter. Neither transcript was autoinduced in the related, resistant cell lines CEM-C1, and CEM-C7R5. In contrast, the glucocorticoid-sensitive PreB697 cell line strongly autoinduced transcripts from the proximal promoter, but not transcripts from the distal promoter, to relevant levels. Therefore, the autoinductive feedback loop implicated in glucocorticoid-induced apoptosis cannot universally rely on the distal promoter of the glucocorticoid receptor.