Inhibition of NF-κB Binding to DNA by Chromium, Cadmium, Mercury, Zinc, and Arsenitein Vitro:Evidence of a Thiol Mechanism

NF-κB binding to DNA in the presence of thiol-reactive metals has been exploredin vitro.Gel mobility shift assays using total nuclear extracts isolated from tumor necrosis factor alpha-treated A549 cells demonstrated dose-dependent inhibition of NF-κB binding by chromium, cadmium, mercury, zinc, and arsenite. Maximum inhibition of binding occurred when these metals were preincubated with the nuclear proteins prior to addition of radiolabeled oligonucleotide. The potency of mercury, cadmium, and zinc for inhibiting binding closely correlated to the affinity of these metals for protein thiols. Further addition of dithiothreitol competitively blocked the effects of all of the metals, except chromium(III), on NF-κB binding. This study demonstrates mechanisms for metals to inhibit NF-κB–DNA binding through interactions with critical protein sulfhydryls.