Abstract
Nuclear factor κB (NF-κB) is an inducible transcription factor that positively regulates the expression of proimmune and proinflammatory genes, while glucocorticoids are potent suppressors of immune and inflammatory responses. NF-κB and the glucocorticoid receptor (GR) physically interact, resulting in repression of NF-κB transactivation. In transient cotransfection experiments, we demonstrate a dose-dependent, mutual antagonism between NF-κB and GR. Functional dissection of the NF-κB p50 and p65 subunits and deletion mutants of GR indicate that the GR antagonism is specific to the p65 subunit of NF-κB heterodimer, whereas multiple domains of GR are essential to repress p65-mediated transactivation. Despite its repression of GR transactivation, p65 failed to block the transrepressive GR homologous down-regulation function. We also demonstrate that negative interactions between p65 and GR are not selective for GR, but also occur between NF-κB and androgen, progesterone B, and estrogen receptors. However, although each of these members of the steroid hormone receptor family is repressed by NF-κB, only GR effectively inhibits p65 transactivation. Further, in cotransfections using a chimeric estrogen-GR, the presence of the GR DNA-binding domain is insufficient to confer mutual antagonism to the p65-estrogen receptor interaction. Selectivity of p65 repression for each steroid receptor is demonstrated by IκB rescue from NF-κB-mediated inhibition. Together these data suggest that NF-κB p65 physically interacts with multiple steroid hormone receptors, and this interaction is sufficient to transrepress each steroid receptor. Further, the NF-κB status of a cell has the potential to significantly alter multiple steroid signaling pathways within that cell.
Distinct RNA motifs are important for coactivation of steroid hormone receptors by steroid receptor RNA activator (SRA)
