title: Mitochondrial electron-transport-chain inhibitors of complexes I and II induce autophagic cell death mediated by reactive oxygen species.
abstract: Autophagy is a self-digestion process important for cell survival during starvation. It has also been described as a form of programmed cell death. Mitochondria are important regulators of autophagy-induced cell death and damaged mitochondria are often degraded by autophagosomes. Inhibition of the mitochondrial electron transport chain (mETC) induces cell death through generating reactive oxygen species (ROS). The role of mETC inhibitors in autophagy-induced cell death is unknown. Herein, we determined that inhibitors of complex I (rotenone) and complex II (TTFA) induce cell death and autophagy in the transformed cell line HEK 293, and in cancer cell lines U87 and HeLa. Blocking the expression of autophagic genes (beclin 1 and ATG5) by siRNAs or using the autophagy inhibitor 3-methyladenine (3-MA) decreased cell death that was induced by rotenone or TTFA. Rotenone and TTFA induce ROS production, and the ROS scavenger tiron decreased autophagy and cell death induced by rotenone and TTFA. Overexpression of manganese-superoxide dismutase (SOD2) in HeLa cells decreased autophagy and cell death induced by rotenone and TTFA. Furthermore, blocking SOD2 expression by siRNA in HeLa cells increased ROS generation, autophagy and cell death induced by rotenone and TTFA. Rotenone- and TTFA-induced ROS generation was not affected by 3-MA, or by beclin 1 and ATG5 siRNAs. By contrast, treatment of non-transformed primary mouse astrocytes with rotenone or TTFA failed to significantly increase levels of ROS or autophagy. These results indicate that targeting mETC complex I and II selectively induces autophagic cell death through a ROS-mediated mechanism.
authors.affiliation: Manitoba Institute of Cell Biology, 675 McDermot Avenue, Winnipeg, Manitoba R3E 0V9, Canada.
authors.forename: Yongqiang
authors.initials: Y
authors.lastname: Chen
authors.forename: Eileen
authors.initials: E
authors.lastname: McMillan-Ward
authors.forename: Jiming
authors.initials: J
authors.lastname: Kong
authors.forename: Sara J
authors.initials: SJ
authors.lastname: Israels
authors.forename: Spencer B
authors.initials: SB
authors.lastname: Gibson
mesh_terms: D001343:Autophagy / Q000187:drug effects / Q000502:physiology*; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D042967:Electron Transport Complex I / Q000037:antagonists & inhibitors* / Q000648:ultrastructure; D042963:Electron Transport Complex II / Q000037:antagonists & inhibitors* / Q000648:ultrastructure; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005910:Glioma / Q000473:pathology; D006367:HeLa Cells; D006801:Humans; D007668:Kidney / Q000166:cytology; D008928:Mitochondria / Q000201:enzymology* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012402:Rotenone / Q000494:pharmacology; D013804:Thenoyltrifluoroacetone / Q000494:pharmacology; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D017382:Reactive Oxygen Species; D012402:Rotenone; D013804:Thenoyltrifluoroacetone; D042963:Electron Transport Complex II; D042967:Electron Transport Complex I