Gold compound auranofin inhibits IκB kinase (IKK) by modifying Cys-179 of IKKβ subunit

Abstract

Antirheumatic gold compounds have been shown to inhibit NF-κB activation by blocking IκB kinase (IKK) activity. To examine the possible inhibitory mechanism of gold compounds, we expressed wild type and mutant forms of IKKα and β subunits in COS-7 cells and determined the effect of gold on the activity of these enzymes both in vivo and in vitro. Substitution of Cys-179 of IKKβ with alanine (C179A) rendered the enzyme to become resistant to inhibition by a gold compound auranofin, however, similar protective effect was not observed with an equivalent level of IKKα (C178A) mutant expressed in the cells. Auranofin inhibited constitutively active IKKα and β and variants; IKKα (S176E, S180E) or IKKβ (S177E, S181E), suggesting that gold directly cause inhibition of activated enzyme. The different inhibitory effect of auranofin on IKKα (C178A) and IKKβ (C179A) mutants indicates that gold could inhibit the two subunits of IKK in a different mode, and the inhibition of NFκB and IKK activation induced by inflammatory signals in gold-treated cells appears through its interaction with Cys-179 of IKKβ.