Diversity Supplement for Meredith Eckstein: The Role of Chromatin Structural and Epigenetic Changes in Arsenic-Induced Gene Expression

Abstract Exposure to inorganic arsenic, a ubiquitous environmental toxic metalloid, leads to carcinogenesis. However, the mechanism is unknown. Several studies have shown that inorganic arsenic exposure alters specific gene expression patterns, possibly through alterations in chromatin structure. While most studies on understanding the mechanism of chromatin-mediated gene regulation have focused on histone post-translational modifications, the role of histone variants remains largely unknown. To understand the global dynamics of chromatin structure and function in arsenic-mediated carcinogenesis, analysis of the histone variants incorporated into the nucleosome and their covalent modifications is required. Here we report the first global mass spectrometric analysis of histone H2B variants as cells undergo arsenic-mediated epithelial to mesenchymal transition. We used electron capture dissociation-based top-down tandem mass spectrometry analysis validated with quantitative reverse transcription real-time polymerase chain reaction to identify changes in the expression levels of H2B variants in inorganic arsenic-mediated epithelial-mesenchymal transition. Recent studies have highlighted the role of iAs on the expression of histones. Implicated as a possible mechanism is the depletion of the stem-loop binding protein by iAs, leading to depletion of canonical histones 1. We hypothesize that these histone variants because of the stable polyadenylated tails are not subject to degradation and thus are expressed more to counterbalance the loss of the canonical histones. In fact expressing of canonical histone proteins with polyadenylated tails, recapitulated the iAs-transformation state 1. These studies and ours suggest that the dynamic control and incorporation of histones is important and plays a role in arsenic-induced transformation. The analysis of these histone variants provides a first step toward an understanding of the functional significance of the diversity of histone structures, especially in inorganic arsenic-mediated gene expression and carcinogenesis.