Modulation of glucocorticoid-inducible gene expression by metal ions

We examined the effects of various metal ions on the DNA-binding activity of the glucocorticoid receptor. Electrophoretic mobility shift assays demonstrated that the sequence-specific DNA binding activity of the receptor was decreased by metal ions in a dose-dependent fashion. The most potent inhibitor was Au(I). Cu(II), Cd(II), and Zn(II) were, in that order, less potent as inhibitors, whereas Fe(III), Al(III), and Mg(II) had no apparent effect. The inhibitory actions of metal ions were efficiently counteracted by the sulfhydryl reducing reagents 2-mercaptoethanol and N-acetyl-L-cysteine, indicating that metal ions interfere with the DNA binding activity of the glucocorticoid receptor through modification of sulfhydryl groups in the receptor molecule. Modification of sulfhydryls by metals seems to involve neither disulfide bond formation nor permanent destruction of the GR protein and is reversible. We also show that metal ions inhibit glucocorticoid-inducible gene transcription in vivo, presumably by interfering with the interaction between the glucocorticoid receptor and cognate DNA target sequences. In summary, these data demonstrates that metal ions are capable of modulating glucocorticoid receptor mediated intracellular signalling pathways.