Mitochondrial oxidative phosphorylation (OXPHOS) generates ATP, but OXPHOS also supports biosynthesis during proliferation. In contrast, the role of OXPHOS during quiescence, beyond ATP production, is not well understood. Using mouse models of inducible OXPHOS deficiency in all cell types or specifically in the vascular endothelium that negligibly relies on OXPHOS-derived ATP, we show that selectively during quiescence OXPHOS provides oxidative stress resistance by supporting macroautophagy/autophagy. Mechanistically, OXPHOS constitutively generates low levels of endogenous ROS that induce autophagy via attenuation of ATG4B activity, which provides protection from ROS insult. Physiologically, the OXPHOS-autophagy system (i) protects healthy tissue from toxicity of ROS-based anticancer therapy, and (ii) provides ROS resistance in the endothelium, ameliorating systemic LPS-induced inflammation as well as inflammatory bowel disease. Hence, cells acquired mitochondria during evolution to profit from oxidative metabolism, but also built in an autophagy-based ROS-induced protective mechanism to guard against oxidative stress associated with OXPHOS function during quiescence.Abbreviations: AMPK: AMP-activated protein kinase; AOX: alternative oxidase; Baf A: bafilomycin A1; CI, respiratory complexes I; DCF-DA: 2',7'-dichlordihydrofluorescein diacetate; DHE: dihydroethidium; DSS: dextran sodium sulfate; ΔΨmi: mitochondrial inner membrane potential; EdU: 5-ethynyl-2'-deoxyuridine; ETC: electron transport chain; FA: formaldehyde; HUVEC; human umbilical cord endothelial cells; IBD: inflammatory bowel disease; LC3B: microtubule associated protein 1 light chain 3 beta; LPS: lipopolysaccharide; MEFs: mouse embryonic fibroblasts; MTORC1: mechanistic target of rapamycin kinase complex 1; mtDNA: mitochondrial DNA; NAC: N-acetyl cysteine; OXPHOS: oxidative phosphorylation; PCs: proliferating cells; PE: phosphatidylethanolamine; PEITC: phenethyl isothiocyanate; QCs: quiescent cells; ROS: reactive oxygen species; PLA2: phospholipase A2, WB: western blot.

• Keywords
• ATG4B, biosynthesis, cell death, electron transport chain, endothelial cells, mitochondria, oxidative phosphorylation, oxidative stress, reactive oxygen species,
• MeSH
• Adenosine Triphosphate metabolism   MeSH
• Autophagy * MeSH
• Cysteine metabolism   MeSH
• Dextrans metabolism   MeSH
• Respiration MeSH
• Endothelial Cells metabolism   MeSH
• Fibroblasts metabolism   MeSH
• Formaldehyde metabolism   MeSH
• Phosphatidylethanolamines metabolism   MeSH
• Inflammatory Bowel Diseases * metabolism   MeSH
• Isothiocyanates MeSH
• Humans MeSH
• Lipopolysaccharides metabolism   MeSH
• DNA, Mitochondrial metabolism   MeSH
• Mitochondria metabolism   MeSH
• Mechanistic Target of Rapamycin Complex 1 metabolism   MeSH
• Mice MeSH
• AMP-Activated Protein Kinases metabolism   MeSH
• Microtubule-Associated Proteins metabolism   MeSH
• Reactive Oxygen Species metabolism   MeSH
• Sirolimus MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Adenosine Triphosphate MeSH
• Cysteine MeSH
• Dextrans MeSH
• Formaldehyde MeSH
• Phosphatidylethanolamines MeSH
• Isothiocyanates MeSH
• Lipopolysaccharides MeSH
• DNA, Mitochondrial MeSH
• Mechanistic Target of Rapamycin Complex 1 MeSH
• phenethyl isothiocyanate MeSH Browser
• AMP-Activated Protein Kinases MeSH
• Microtubule-Associated Proteins MeSH
• Reactive Oxygen Species MeSH
• Sirolimus MeSH

p53-mutated tumors often exhibit increased resistance to standard chemotherapy and enhanced metastatic potential. Here we demonstrate that inhibition of dihydroorotate dehydrogenase (DHODH), a key enzyme of the de novo pyrimidine synthesis pathway, effectively decreases proliferation of cancer cells via induction of replication and ribosomal stress in a p53- and checkpoint kinase 1 (Chk1)-dependent manner. Mechanistically, a block in replication and ribosomal biogenesis result in p53 activation paralleled by accumulation of replication forks that activate the ataxia telangiectasia and Rad3-related kinase/Chk1 pathway, both of which lead to cell cycle arrest. Since in the absence of functional p53 the cell cycle arrest fully depends on Chk1, combined DHODH/Chk1 inhibition in p53-dysfunctional cancer cells induces aberrant cell cycle re-entry and erroneous mitosis, resulting in massive cell death. Combined DHODH/Chk1 inhibition effectively suppresses p53-mutated tumors and their metastasis, and therefore presents a promising therapeutic strategy for p53-mutated cancers.

• MeSH
• Checkpoint Kinase 1 antagonists & inhibitors   genetics   metabolism   MeSH
• Dihydroorotate Dehydrogenase MeSH
• Phenylurea Compounds pharmacology   MeSH
• Genes, erbB-2 MeSH
• HCT116 Cells MeSH
• Protein Kinase Inhibitors pharmacology   MeSH
• Cell Cycle Checkpoints * drug effects   MeSH
• Leflunomide pharmacology   MeSH
• Humans MeSH
• MCF-7 Cells MeSH
• Mice, Inbred BALB C MeSH
• Mice, Inbred NOD MeSH
• Mice, SCID MeSH
• Mice, Transgenic MeSH
• Tumor Suppressor Protein p53 deficiency   genetics   MeSH
• Breast Neoplasms drug therapy   genetics   metabolism   pathology   MeSH
• Oxidoreductases Acting on CH-CH Group Donors antagonists & inhibitors   genetics   metabolism   MeSH
• Cell Proliferation * drug effects   MeSH
• Antineoplastic Combined Chemotherapy Protocols pharmacology   MeSH
• Pyrazines pharmacology   MeSH
• Pyrimidines biosynthesis   MeSH
• Gene Expression Regulation, Neoplastic MeSH
• Ribosomes genetics   metabolism   MeSH
• Signal Transduction MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Checkpoint Kinase 1 MeSH
• CHEK1 protein, human MeSH Browser
• Chek1 protein, mouse MeSH Browser
• Dihydroorotate Dehydrogenase MeSH
• Phenylurea Compounds MeSH
• Protein Kinase Inhibitors MeSH
• Leflunomide MeSH
• LY2603618 MeSH Browser
• Tumor Suppressor Protein p53 MeSH
• Oxidoreductases Acting on CH-CH Group Donors MeSH
• Pyrazines MeSH
• Pyrimidines MeSH
• TP53 protein, human MeSH Browser
• Trp53 protein, mouse MeSH Browser

Cancer cells without mitochondrial DNA (mtDNA) do not form tumors unless they reconstitute oxidative phosphorylation (OXPHOS) by mitochondria acquired from host stroma. To understand why functional respiration is crucial for tumorigenesis, we used time-resolved analysis of tumor formation by mtDNA-depleted cells and genetic manipulations of OXPHOS. We show that pyrimidine biosynthesis dependent on respiration-linked dihydroorotate dehydrogenase (DHODH) is required to overcome cell-cycle arrest, while mitochondrial ATP generation is dispensable for tumorigenesis. Latent DHODH in mtDNA-deficient cells is fully activated with restoration of complex III/IV activity and coenzyme Q redox-cycling after mitochondrial transfer, or by introduction of an alternative oxidase. Further, deletion of DHODH interferes with tumor formation in cells with fully functional OXPHOS, while disruption of mitochondrial ATP synthase has little effect. Our results show that DHODH-driven pyrimidine biosynthesis is an essential pathway linking respiration to tumorigenesis, pointing to inhibitors of DHODH as potential anti-cancer agents.

• Keywords
• OXPHOS, cancer, coenzyme Q, dihydroorotate dehydrogenase, mitochondria, pyrimidine biosynthesis, respiration,
• MeSH
• Cell Respiration MeSH
• Dihydroorotate Dehydrogenase MeSH
• Humans MeSH
• DNA, Mitochondrial metabolism   MeSH
• Mitochondria metabolism   MeSH
• Mice, Inbred BALB C MeSH
• Mice, Inbred C57BL MeSH
• Mice MeSH
• Cell Line, Tumor MeSH
• Neoplasms metabolism   MeSH
• Oxidative Phosphorylation MeSH
• Oxidoreductases Acting on CH-CH Group Donors physiology   MeSH
• Pyrimidines metabolism   MeSH
• Ubiquinone metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Intramural MeSH
• Names of Substances
• Dihydroorotate Dehydrogenase MeSH
• DNA, Mitochondrial MeSH
• Oxidoreductases Acting on CH-CH Group Donors MeSH
• pyrimidine MeSH Browser
• Pyrimidines MeSH
• Ubiquinone MeSH

Cellular senescence is a form of cell cycle arrest that limits the proliferative potential of cells, including tumour cells. However, inability of immune cells to subsequently eliminate senescent cells from the organism may lead to tissue damage, inflammation, enhanced carcinogenesis and development of age-related diseases. We found that the anticancer agent mitochondria-targeted tamoxifen (MitoTam), unlike conventional anticancer agents, kills cancer cells without inducing senescence in vitro and in vivo. Surprisingly, it also selectively eliminates both malignant and non-cancerous senescent cells. In naturally aged mice treated with MitoTam for 4 weeks, we observed a significant decrease of senescence markers in all tested organs compared to non-treated animals. Mechanistically, we found that the susceptibility of senescent cells to MitoTam is linked to a very low expression level of adenine nucleotide translocase-2 (ANT2), inherent to the senescent phenotype. Restoration of ANT2 in senescent cells resulted in resistance to MitoTam, while its downregulation in non-senescent cells promoted their MitoTam-triggered elimination. Our study documents a novel, translationally intriguing role for an anticancer agent targeting mitochondria, that may result in a new strategy for the treatment of age-related diseases and senescence-associated pathologies.

• MeSH
• Apoptosis drug effects   genetics   MeSH
• Gene Knockdown Techniques MeSH
• Antineoplastic Agents, Hormonal pharmacology   MeSH
• Humans MeSH
• MCF-7 Cells MeSH
• Mitochondria drug effects   metabolism   MeSH
• Mice, Inbred NOD MeSH
• Mice, SCID MeSH
• Mice, Transgenic MeSH
• Mice MeSH
• Cell Proliferation drug effects   MeSH
• Cellular Senescence drug effects   MeSH
• Tamoxifen pharmacology   MeSH
• Transfection MeSH
• Adenine Nucleotide Translocator 2 genetics   metabolism   MeSH
• Cell Survival drug effects   genetics   MeSH
• Xenograft Model Antitumor Assays MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Antineoplastic Agents, Hormonal MeSH
• Tamoxifen MeSH
• Adenine Nucleotide Translocator 2 MeSH

Cell growth and survival depend on a delicate balance between energy production and synthesis of metabolites. Here, we provide evidence that an alternative mitochondrial complex II (CII) assembly, designated as CIIlow, serves as a checkpoint for metabolite biosynthesis under bioenergetic stress, with cells suppressing their energy utilization by modulating DNA synthesis and cell cycle progression. Depletion of CIIlow leads to an imbalance in energy utilization and metabolite synthesis, as evidenced by recovery of the de novo pyrimidine pathway and unlocking cell cycle arrest from the S-phase. In vitro experiments are further corroborated by analysis of paraganglioma tissues from patients with sporadic, SDHA and SDHB mutations. These findings suggest that CIIlow is a core complex inside mitochondria that provides homeostatic control of cellular metabolism depending on the availability of energy.

• MeSH
• Biosynthetic Pathways physiology   MeSH
• Energy Metabolism physiology   MeSH
• Stress, Physiological * MeSH
• Gene Knockout Techniques MeSH
• HEK293 Cells MeSH
• S Phase Cell Cycle Checkpoints physiology   MeSH
• Humans MeSH
• RNA, Small Interfering metabolism   MeSH
• Mitochondria metabolism   MeSH
• Mutation MeSH
• Mice, Inbred BALB C MeSH
• Mice, Nude MeSH
• Mice MeSH
• Cell Line, Tumor MeSH
• Paraganglioma genetics   pathology   MeSH
• Electron Transport Complex II genetics   metabolism   MeSH
• Succinate Dehydrogenase genetics   metabolism   MeSH
• Xenograft Model Antitumor Assays MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• RNA, Small Interfering MeSH
• Electron Transport Complex II MeSH
• respiratory complex II MeSH Browser
• SDHA protein, human MeSH Browser
• SDHB protein, human MeSH Browser
• Succinate Dehydrogenase MeSH