Cys106 Oxidation of High Mobility Group Box 1 (HMGB1) Promotes Self-Oligomerization and Cytokine Release

Oxidative stress can induce covalent disulfide bonds to form between protein-protein thiol groups. HMGB1, a DNA chaperon and damage associated molecular pattern molecule, is integral to oxidative stress. As a redox-sensitive protein, HMGB1 contains three cysteines: Cys23, Cys45, and Cys106. In this study, we focused on the oxidative oligomerization and pro-inflammatory cytokine induction by Cys106. HMGB1 oligomerization is positively modulated by copper and hydrogen peroxide. Mutagenesis of the Cys106 residue within HMGB1 blocks the formation of such oligomers. Addition of copper and hydrogen peroxide in HEK293T cell enhanced the oxidative self-oligomerization of HMGB1, while inhibiting it for mutant HMGB1 C106A. Furthermore, we used a bimolecular fluorescence complementation assay to directly visualize the Cys106 oxidation-induced HMGB1 oligomerization in live cells under oxidative stress conditions. And we were able to reproduce the oligomerization effect of HMGB1 using FRET analysis. Interestingly, the oligomerized-HMGB1 binds to TLR4/MD2 complex with higher affinity than monomer HMGB1. Oligomerized HMGB1 transferred nuclear factor-κB signaling at significant levels using HEK293/TLR4 cells, and the cytokine production by oligomerized-HMGB1 is now under investigation. In conclusion, the oligomerized-HMGB1 most likely plays a regulatory role in the secretion of pro-inflammatory cytokines under physiological conditions.