Identification of endogenous glucocorticoid repressed genes differentially regulated by a glucocorticoid receptor mutant able to separate between nuclear factor-kappaB and activator protein-1 repression.

Glucocorticoids are commonly used in the clinic, but long-term treatment is often associated with severe side effects. One way to reduce unwanted effects is to restrict glucocorticoid receptor (GR) signaling through defined pathways. In this study, we examine endogenous target genes regulated by a GR mutant that in contrast to the wild-type GR is unable to repress stimulated nuclear factor-kappaB (NF-kappaB) activity, whereas repression of activator protein-1 (AP-1) activity is maintained. This GR mutant (GRR488Q) harbors a point mutation in the second zinc finger of the DNA binding domain. Its ability to distinguish between NF-kappaB and AP-1 repression is defined using reporter genes regulated by both simple and natural promoters. The inability of GRR488Q to repress NF-kappaB was not related to its inability to activate target genes through a glucocorticoid response element. Furthermore, the discriminating property was observed in three different cell lines, suggesting that this is not a cell-specific effect. These results show that different receptor surfaces or mechanisms are involved in repression of NF-kappaB and AP-1, respectively. It is interesting that the GRR488Q still interacted physically with NF-kappaB. Gene expression profiling of human embryonic kidney 293 cells, which express the wild-type GR and the GRR488Q mutant allowed identification of endogenous genes preferentially repressed by GR interference with NF-kappaB activity. The genes differentially regulated by GRR488Q mutant versus the wild-type GR after 2 h of treatment seem mainly to be involved in control of transcription and cell growth. At 8 h, no such distinction could be seen.