A new function for the C-terminal zinc finger of the glucocorticoid receptor. Repression of RelA transactivation

Glucocorticoids inhibit NF-κB signaling by interfering with the NF-κB transcription factor RelA. Previous studies have identified the DNA-binding domain (DBD) in the glucocorticoid receptor (GR) as the major region responsible for this repressive activity. Using GR mutants with chimeric DBDs the repressive function was found to be located in the C-terminal zinc finger. As predicted from these results the mineralocorticoid receptor that contains a C-terminal zinc finger identical to that of the GR was also able to repress RelA-dependent transcription. Mutation of a conserved arginine or a lysine in the second zinc finger of the GR DBD (Arg-488 or Lys-490 in the rat GR) abolished the ability of GR to inhibit RelA activity. In contrast, C- terminal zinc finger GR mutants with mutations in the dimerization box or mutations necessary for full transcriptional GR activity were still able to repress RelA-dependent transcription. In addition, we found that the steroid analog ZK98299 known to induce GR transrepression of AP-1 had no inhibitory effect on RelA activity. In summary, these results demonstrate that the inhibition of NF-κB by glucocorticoids involves two critical amino acids in the C-terminal zinc finger of the GR. Furthermore, the results from the use of mineralocorticoid receptor and anti-glucocorticoids suggest that the mechanisms for GR-mediated repression of NF-κB and AP-1 are different.