H 2 Se Induces Reductive Stress in HepG2 Cells and Activates Cell Autophagy by Regulating the Redox of HMGB1 Protein under Hypoxia.

Rationale: Selenium has been shown to have chemotherapeutic effects against cancer. However, the anti-cancer mechanism of selenium is not fully understood, and the role of hydrogen selenide (H ₂ Se), which is a common metabolite of dietary selenium compounds, has not been elucidated due to the lack of detection methods. In this study, we revealed a new anti-cancer mechanism of selenite with the help of a H ₂ Se fluorescent probe. Methods: HepG2 cells were cultured under a simulated tumor hypoxic microenvironment. The H ₂ Se and H ₂ O ₂ levels were detected by fluorescent probes in living cells and in mice. Autophagic and apoptotic proteins were detected by Western blotting. The redox of HMGB1 protein were analyzed by non-reducing sodium dodecyl sulfate polyacrylamide gel electrophoresis. Results: After pharmacological doses of Na ₂ SeO ₃ treatment of HepG2 cells under hypoxic conditions, high levels of H ₂ Se were produced before cell death. The H ₂ Se accumulation resulted in reductive stress instead of oxidative stress, which was induced by Na ₂ SeO ₃ treatment under normoxic conditions. Furthermore, H ₂ Se targeted the HMGB1 protein and induced cell autophagy. H ₂ Se could interrupt the disulfide bond in HMGB1 and promote its secretion. The reduced HMGB1 outside the cells stimulated cell autophagy by inhibiting the Akt/mTOR axis. Here, autophagy played a dual role, i.e., mild autophagy inhibited apoptosis, while excessive autophagy led to autophagy-associated cell death. Conclusions: These results show that H ₂ Se plays a key role during HepG2 cell death induced by selenite. Our findings reveal a new anti-cancer mechanism of selenite and provide a new research area for selenium studies.
Competing Interests: Competing Interests: The authors have declared that no competing interest exists.