Arsenicals, the Integrated Stress Response, and Epstein-Barr Virus Lytic Gene Expression

Following our observation that clofoctol led to Epstein-Barr virus (EBV) lytic gene expression upon activation of the integrated stress response (ISR), we decided to investigate the impact of As₂O₃ on viral lytic gene expression. As₂O₃ has also been reported to activate the ISR pathway by its activation of the heme-regulated inhibitor (HRI). Our investigations show that As₂O₃ treatment leads to eIF2α phosphorylation, upregulation of ATF4 and TRB3 expression, and an increase of EBV Zta gene expression in lymphoid tumor cell lines as well as in naturally infected epithelial cancer cell lines. However, late lytic gene expression and virion production were blocked after arsenic treatment. In comparison, a small molecule HRI activator also led to increased Zta expression but did not block late lytic gene expression, suggesting that As₂O₃ effects on EBV gene expression are also mediated through other pathways.