Antioxidant defense in quiescent cells determines selectivity of electron transport chain inhibition-induced cell death

Abstract

Mitochondrial electron transport chain (ETC) targeting shows a great promise in cancer therapy. It is particularly effective in tumors with high ETC activity where ETC-derived reactive oxygen species (ROS) are efficiently induced. Why modern ETC-targeted compounds are tolerated on the organismal level remains unclear. As most somatic cells are in non-proliferative state, the features associated with the ETC in quiescence could account for some of the specificity observed. Here we report that quiescent cells, despite increased utilization of the ETC and enhanced supercomplex assembly, are less susceptible to cell death induced by ETC disruption when glucose is not limiting. Mechanistically, this is mediated by the increased detoxification of ETC-derived ROS by mitochondrial antioxidant defense, principally by the superoxide dismutase 2 - thioredoxin axis. In contrast, under conditions of glucose limitation, cell death is induced preferentially in quiescent cells and is correlated with intracellular ATP depletion but not with ROS. This is related to the inability of quiescent cells to compensate for the lost mitochondrial ATP production by the upregulation of glucose uptake. Hence, elevated ROS, not the loss of mitochondrially-generated ATP, are responsible for cell death induction by ETC disruption in ample nutrients condition, e.g. in well perfused healthy tissues, where antioxidant defense imparts specificity. However, in conditions of limited glucose, e.g. in poorly perfused tumors, ETC disruption causes rapid depletion of cellular ATP, optimizing impact towards tumor-associated dormant cells. In summary, we propose that antioxidant defense in quiescent cells is aided by local glucose limitations to ensure selectivity of ETC inhibition-induced cell death.

Reactivation of Dihydroorotate Dehydrogenase-Driven Pyrimidine Biosynthesis Restores Tumor Growth of Respiration-Deficient Cancer Cells

“…Native Blue Gel Electrophoresis (NBGE) NBGE was accomplished basically as published (Wittig et al, 2006). In brief, mitochondria were isolated using a Balch-style homogenizer as detailed elsewhere (Schmitt et al, 2013;Blecha et al, 2017). Digitonin-solubilised mitochondria were separated on NativePAGE Novex Bis-Tris 3%-12% gradient gels.…”

Replication and ribosomal stress induced by targeting pyrimidine synthesis and cellular checkpoints suppress p53-deficient tumors

“…The gel-purified PCR product was cleaved by fast-digest EcoRI and BamHI enzymes (Thermo Fisher) and ligated into the pCDH-CMV-MCS-EF1-Puro lentiviral vector (System Biosciences) digested in the same way. Lentiviral particles were produced as described 55 and used to transduce 4T1 DHODH KO cells, followed by puromycin selection. Expression of the DHODH protein was verified by western blotting.…”

Glucose‐induced oxidative stress and accelerated aging in endothelial cells are mediated by the depletion of mitochondrial SIRTs

“…In diabetes, increases in oxidative stress disrupt EC homeostasis (Kimura et al, 2017). In response to high glucose levels, proton gradients in the mitochondrial electron transport chain (ETC) are elevated, which initiate oxidative stress and the overproduction of superoxides (Blecha et al, 2017). Oxidative stress changes cellular transcriptional machinery leading to increased production of vasoactive factors (endothelin-1 [ET-1] and vascular endothelial growth factor [VEGF]), growth factors, and cytokines that ultimately cause alterations of organ hemodynamics, increased production of extracellular matrix (ECM) proteins (i.e., fibronectin; FN) (Abd El-Kader & Saiem Al-Dahr, 2016;Iwona, 2016;Ohshiro et al, 2006;Xu, Chiu, Feng, Chen, & Chakrabarti, 2008), structural alterations (i.e., endothelial-to-mesenchymal transition), and neovascularization.…”