MODULATION OF GLUCOCORTICOID-INDUCIBLE GENE-EXPRESSION BY METAL-IONS

We examined the effects of various metal ions on the DNA-binding activ ity of the glucocorticoid receptor. Electrophoretic mobility shift ass ays demonstrated that the sequence-specific DNA binding activity of th e receptor was decreased by metal ions in a dose-dependent fashion. Th e most potent inhibitor was Au(I). Cu(II), Cd(II), and Zn(II) were, in that order, less potent as inhibitors, whereas Fe(III), AI(III), and Mg(II) had no apparent effect, The inhibitory actions of metal ions we re efficiently counteracted by the sulfhydryl reducing reagents 2-merc aptoethanol and N-acetyl-L-cysteine, indicating that metal ions interf ere with the DNA binding activity of the glucocorticoid receptor throu gh modification of sulfhydryl groups in the receptor molecule. Modific ation of sulfhydryls by metals seems to involve neither disulfide bond formation nor permanent destruction of the GR protein and is reversib le, 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 demonstrate that metal ions are capable of mod ulating glucocorticoid receptor mediated intracellular signalling path ways.