Identification of target genes involved in the antiproliferative effect of glucocorticoids reveals a role for nuclear factor-κB repression

Glucocorticoid hormones (GCs) exert an antiproliferative effect on most cells. However, the molecular mechanism is still largely unclear. We investigated the antiproliferative mechanism by GCs in human embryonic kidney 293 cells with stably introduced glucocorticoid receptor ( GR) mutants that discriminate between cross-talk with nuclear factor-kappaB (NF-kappaB) and activator protein-1 signaling, transactivation and transrepression, and antiproliferative vs. non-antiproliferative responses. Using the GR mutants, we here demonstrate a correlation between repression of NF-kappaB signaling and antiproliferative response. Gene expression profiling of endogenous genes in cells containing mutant GRs identified a limited number of genes that correlated with the antiproliferative response. This included a GC-mediated up-regulation of the NF-kappaB-inhibitory protein IkappaBalpha, in line with repression of NF-kappaBsignaling being important in the GC-mediated antiproliferative response. Interestingly, the GC-stimulated expression of IkappaBalpha was a direct effect despite the inability of the GR mutant to transactivate through a GC-responsive element. Selective expression of IkappaBalpha in human embryonic kidney 293 cells resulted in a decreased percentage of cells in the S/G2/M phase and impaired cell proliferation. These results demonstrate that GC-mediated inhibition of NF-kappaB is an important mechanism in the antiproliferative response to GCs.