Transcriptional control of the human glucocorticoid receptor: identification and analysis of alternative promoter regions.
Glucocorticoid receptor levels are thought to be controlled by multiple alternative first exons. Seven of these exons are located in an upstream CpG island. In this study, we investigated the promoter activity of the intronic regions between these exons, and their susceptibility to CpG methylation and sequence variability. The seven promoters were cloned into luciferase reporter genes, and their activity measured in ten cell lines. CpG islands of 221 donors were genotyped and the effects of these SNPs were investigated in a reporter gene assay. We showed that each of the first exons was independently controlled by a unique promoter located directly upstream. Promoter activities were cell type-specific, and varied considerably between cell types. Irrespective of the cell type, in vitro methylation effectively silenced all reporter constructs. Eleven SNPs were observed within the CpG island of 221 donors, and a new promoter-specific haplotype was revealed. Four of the minor alleles reduced the reporter gene activity, with cell type specific effects. This complexity within the CpG island helps to explain the variable, tissue-specific transcriptional control of the GR, and provides insight into the mechanisms underlying tissue specific deregulation of GR levels.