Formation of stress granules and non-canonical survival responses in arsenite-exposed cells

The concentration-dependent decrease in viable cells is a well-documented phenomenon in cytotoxicity assays for most toxic substances. We report that arsenite (As 3+ ), a widely recognized oxidative toxicant, exhibited lower cytotoxic effects at 300 µM compared to 100 µM As 3+ in CHO-K1 and Jurkat cells. Formation of stress granules (SGs), which appear in the cytoplasm shortly after exposure to hypertonicity, heat shock, and high concentrations of As 3+ is considered as a pro-survival cellular event. We hypothesized that unusual cytotoxicity profile of As 3+ could be attributed to SG formation. In both CHO-K1 and Jurkat cells stably expressing GFP-tagged G3BP1, SGs were more rapidly and distinctly induced by 300 µM As 3+ than 100 µM As 3+ . Other toxic metals and a metalloid such as Cd 2+ , Cu 2+ , Ag + , and Se 4+ did not clearly induce SG formation and instead reduced the viability in a concentration-dependent manner. Exposure to As 3+ led to phosphorylation of eIF2α, a key regulator of polysome stability and a hallmark of SG formation. Depletion of intracellular glutathione (GSH) increased the susceptibility of cells to As 3+ , highlighting its role in cellular defense mechanisms. Exposure to As 3+ activated small ubiquitin-like modifier (SUMO) which is implicated in phase separation. However, neither depletion of GSH nor overexpression of SUMO contributed As 3+ -induced SG formation. Consistently, THP-1 and HL60 cells exposed to As 3+ also exhibited non-canonical cytotoxic features, albeit at higher concentrations (1 mM). These findings underscore the need for further mechanistic investigations into As 3+ -induced SG formation, given that As 3+ is a promising anti-cancer agent, and resistance of tumor cells to As 3+ is a critical issue.