DNA-protein cross-linking by 1,2,3,4-diepoxybutane

1,2,3,4-Diepoxybutane (DEB) is a strongly genotoxic diepoxide hypothesized to be the ultimate carcinogenic metabolite of the common industrial chemical and environmental carcinogen 1,3-butadiene. DEB is a bis-electrophile capable of cross-linking cellular biomolecules to form DNA-DNA and DNA-protein cross-links (DPCs), which are thought to play a central role in its biological activity. Previous studies with recombinant proteins have shown that the biological outcomes of DEB-induced DPCs are strongly influenced by protein identities. The present work combines affinity capture methodology with mass spectrometry-based proteomics and immunological detection to identify the proteins that form DPCs in nuclear extracts from human cervical carcinoma (HeLa) cells. We identified 39 human proteins that form covalent DPCs in the presence of DEB. DNA-protein cross-linking efficiency following treatment with 25 mM DEB was 2-12%, depending on protein identity. High-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (HPLC-ESI⁺-MS/MS) analysis of the total proteolytic digests of cross-linked proteins revealed the presence of 1-(S-cysteinyl)-4-(guan-7-yl)-2,3-butanediol conjugates, suggesting that DEB forms DPCs between cysteine thiols within proteins and the N-7 guanine positions within DNA.