DIFFERENTIAL HORMONE-DEPENDENT TRANSCRIPTIONAL ACTIVATION AND REPRESSION BY NATURALLY-OCCURRING HUMAN GLUCOCORTICOID RECEPTOR VARIANTS

The molecular mechanisms underlying primary glucocorticoid resistance or hypersensitivity are not well understood. Using transfected COS-1 c ells as a model system, we studied gene regulation by naturally occurr ing mutants of the glucocorticoid receptor (GR) with single-point muta tions in the regions encoding the ligand-binding domain or the N-termi nal domain reflecting different phenotypic expression. We analyzed the capacity of these GR variants to regulate transcription from differen t promoters, either by binding directly to positive or negative glucoc orticoid-response elements on the DNA or by interfering with protein-p rotein interactions. Decreased dexamethasone (DEX) binding to GR varia nts carrying mutations in the ligand-binding domain correlated well wi th decreased capacity to activate transcription from the mouse mammary tumor virus (MMTV) promoter. One variant, D641V, which suboptimally a ctivated MMTV promoter-mediated transcription, repressed a PRL promote r element containing a negative glucocorticoid-response element with w ild type activity. DEX-induced repression of transcription from elemen ts of the intercellular adhesion molecule-1 promoter via nuclear facto r-KB by the D641V variant was even more efficient compared with the wi ld type GR. We observed a general DEX-responsive AP-1-mediated transcr iptional repression of the collagenase-1 promoter, even when receptor variants did not activate transcription from the MMTV promoter. Our fi ndings indicate that different point mutations in the GR can affect se parate pathways of gene regulation in a differential fashion, which ca n explain the various phenotypes observed.