Chemoproteomic Approach for Identifying Nuclear Arsenite-Binding Proteins

Trivalent arsenic, i.e., As(III), is the main form of arsenic species in the environment. Prolonged exposure to arsenicals through ingesting contaminated food and water has been implicated in the development of cancer and diabetes as well as cardiovascular and neurodegenerative diseases. A number of studies have been conducted to examine the mechanisms underlying the toxic effects of arsenite exposure, where As(III) was shown to displace Zn(II) and impair the functions of zinc-binding proteins. Considering that many zinc-binding proteins can bind to nucleic acids, we reason that systematic identification of arsenite-binding proteins in the nucleus may provide additional insights into the molecular targets of arsenite, thereby improving our understanding of the mechanisms of arsenic toxicity. Here, we conducted a quantitative proteomics experiment relying on affinity pull-down from nuclear protein lysate with a biotin-As(III) probe to identify nuclear arsenite-binding proteins. We uncovered a number of candidate As(III)-binding proteins that are involved in mRNA splicing, DNA repair, and replication. We also found that As(III) could bind to splicing factor 1 (SF1) and that this binding perturbs mRNA splicing in human cells. Together, our work provided insights into the mechanisms of As(III) toxicity by revealing new nuclear protein targets of As(III).