A large-scale quantitative proteomic approach to identifying sulfur mustard-induced protein phosphorylation cascades.

Sulfur mustard [SM, bis-(2-chloroethyl) sulfide] is a potent alkylating agent and chemical weapon. While there are no effective treatments for SM-induced injury, current research focuses on understanding the molecular changes upon SM exposure. Indeed, efforts that seek a more comprehensive analysis of proteins and post-translational modifications are critical for understanding SM-induced toxicity on a more global scale. Furthermore, these studies can uncover proteins previously uncharacterized in SM-exposed cells, which in turn leads to potential targets for therapeutic intervention. Here, we apply a quantitative proteomic approach termed stable isotope-labeling with amino acids in cell culture combined with immobilized metal affinity chromatography to study the large-scale protein phosphorylation changes resulting from SM exposure in a human keratinocyte cell culture model. This resulted in the characterization of over 2300 nonredundant phosphorylation sites, many of which exhibit altered levels in response to SM. Our results point toward several proteins previously implicated in SM-induced toxicity as well as many additional proteins previously uncharacterized. Further de novo analysis of these phosphoproteins using interaction mapping software revealed both known and novel pathways that may serve as future therapeutic targets of SM exposure.