The role of HMGB1's critical cysteines are explored in human monocytes (CAM1P.151)

High Mobility Group Box 1 protein, HMGB1 is a prototypical DAMPs. While HMGB1 is present in the nucleus of every cell under homeostatic conditions, cellular stress leads to its release into the extracellular milieu, where it activates a variety of pattern recognition receptors. HMGB1 has multiple functions. Under certain conditions HMGB1 acts as a cytokine, causing the release of pro-inflammatory cytokines including TNFα. In addition, HMGB1 may act as a chemokine. We now know that HMGB1 contains three critical redox-sensitive cysteines (C23, C45, C106). Modifying the redox state of these cysteines determines the action of HMGB1. Here we created 3 HMGB1 mutants replacing the cysteines with serines and systematically evaluated their role in human monocytes based on cytokine expression. Human monocytes are classically used to evaluate HMGB1’s ability to produce TNFα thus creating a comparison to other published work on HGMB1. While it is known that a disulfide bond between C23 and C45 is necessary for the cytokine like effect of HMGB1 our data show that the presence of all three cysteines is necessary for this action. Also, mutation of C23 or C106 to serine led to suppression of basal TNF release, changes in autophagy induction and signaling events. This suggests that terminal oxidation of either of these cysteines acts to suppress inflammation. Understanding the role of these cysteines hopefully will allow us to create better therapeutics targeting diseases driven by HMGB1.