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Abstract: A distinctive metabolic trait of tumors is their enforced aerobic glycolysis. This phenotype was first reported by Otto Warburg, who suggested that the increased glucose consumption of cancer cells under aerobic conditions might result from an impaired bioenergetic activity of their mitochondria. A central player in defining the bioenergetic activity of the cell is the mitochondrial H+-ATP synthase. The expression of its catalytic subunit β-F1-ATPase is tightly regulated at post-transcriptional levels during mammalian development and in the cell cycle. Moreover, the down-regulation of β-F1-ATPase is a hallmark of most human carcinomas. In this review we summarize our present understanding of the molecular mechanisms that participate in promoting the “abnormal” aerobic glycolysis of prevalent human carcinomas. The role of the ATPase Inhibitor Factor 1 (IF1) and of Ras-GAP SH3 binding protein 1 (G3BP1), controlling the activity of the H+-ATP synthase and the translation of β-F1-ATPase mRNA respectively in cancer cells is emphasized. Furthermore, we underline the role of mitochondrial dysfunction as a pivotal player of tumorigenesis. This article is part of a Special Issue entitled: Bioenergetics of Cancer. [Copyright &y& Elsevier]

Increasing evidences show that the ATPase Inhibitory Factor 1 (IF1), the physiological inhibitor of the ATP synthase, is overexpressed in a large number of carcinomas contributing to metabolic reprogramming and cancer progression. Herein, we show that in contrast to the findings in other carcinomas, the overexpression of IF1 in a cohort of colorectal carcinomas (CRC) predicts less chances of disease recurrence, IF1 being an independent predictor of survival. Bioinformatic and gene expression analyses of the transcriptome of colon cancer cells with differential expression of IF1 indicate that cells overexpressing IF1 display a less aggressive behavior than IF1 silenced (shIF1) cells. Proteomic and functional in vitro migration and invasion assays confirmed the higher tumorigenic potential of shIF1 cells. Moreover, shIF1 cells have increased in vivo metastatic potential. The higher metastatic potential of shIF1 cells relies on increased cFLIP-mediated resistance to undergo anoikis after cell detachment. Furthermore, tumor spheroids of shIF1 cells have an increased ability to escape from immune surveillance by NK cells. Altogether, the results reveal that the overexpression of IF1 acts as a tumor suppressor in CRC with an important anti-metastatic role, thus supporting IF1 as a potential therapeutic target in CRC. [ABSTRACT FROM AUTHOR]

Owing to an oversight, the authors omitted to note that Dr Taub is a co-founder of and equity holder in Cardero Therapeutics. [ABSTRACT FROM AUTHOR]

The post-transcriptional regulation of nuclear mRNAs that encode core components of mitochondria has relevant implications in cell physiology. The mRNA that encodes the catalytic subunit of the mitochondrial H+-ATP synthase subunit β (ATP5B, β-F1-ATPase) is localized in a large ribonucleoprotein (RNP) complex (β-F1-RNP), which is subjected to stringent translational control during development and the cell cycle, and in carcinogenesis. Because downregulation of β-F1-ATPase is a conserved feature of most prevalent human carcinomas, we have investigated the molecular composition of the human β-F1-RNP. By means of an improved affinity-chromatography procedure and protein sequencing we have identified nine RNA-binding proteins (RNABPs) of the β-F1-RNP. Immunoprecipitation assays of Ras-GAP SH3 binding protein 1 (G3BP1) and fluorescent in-situ hybridization of mRNA indicate a direct interaction of the endogenous G3BP1 with mRNA of β-F1-ATPase (β-F1 mRNA). RNA-bridged trimolecular fluorescence complementation (TriFC) assays confirm the interaction of G3BP1 with the 3′-UTR of β-F1 mRNA in cytoplasmic RNA-granules. Confocal and high-resolution immunoelectron-microscopy experiments suggest that the β-F1-RNP is sorted to the periphery of mitochondria. Molecular and functional studies indicate that the interaction of G3BP1 with β-F1 mRNA inhibits its translation at the initiation level, supporting a role for G3BP1 in the glycolytic switch that occurs in cancer. [ABSTRACT FROM AUTHOR]

It is controversial whether mitochondrial dysfunction in skeletal muscle is the cause or consequence of metabolic disorders. Herein, we demonstrate that in vivo inhibition of mitochondrial ATP synthase in muscle alters whole‐body lipid homeostasis. Mice with restrained mitochondrial ATP synthase activity presented intrafiber lipid droplets, dysregulation of acyl‐glycerides, and higher visceral adipose tissue deposits, poising these animals to insulin resistance. This mitochondrial energy crisis increases lactate production, prevents fatty acid β‐oxidation, and forces the catabolism of branched‐chain amino acids (BCAA) to provide acetyl‐CoA for de novo lipid synthesis. In turn, muscle accumulation of acetyl‐CoA leads to acetylation‐dependent inhibition of mitochondrial respiratory complex II enhancing oxidative phosphorylation dysfunction which results in augmented ROS production. By screening 702 FDA‐approved drugs, we identified edaravone as a potent mitochondrial antioxidant and enhancer. Edaravone administration restored ROS and lipid homeostasis in skeletal muscle and reinstated insulin sensitivity. Our results suggest that muscular mitochondrial perturbations are causative of metabolic disorders and that edaravone is a potential treatment for these diseases. Synopsis: Lipid homeostasis in skeletal muscle is dependent on mitochondrial activity. Inhibition of ATP synthase in the muscle alters whole‐body lipid metabolism and induces insulin resistance in mice, two phenotypes that can be reverted by edavarone treatment. Inhibition of oxidative phosphorylation (OXPHOS) in skeletal muscle promotes branched‐chain amino acids (BCAA) catabolism and de novo lipogenesis.Accumulation of Acetyl‐CoA feeds back onto OXPHOS dysfunction by inhibiting mitochondrial respiratory complex II and increasing ROS levels.Mice with low OXPHOS show increased lipid deposits and insulin resistance.Edaravone rescues mitochondrial activity, and lipid and glucose homeostasis in mice with low OXPHOS. [ABSTRACT FROM AUTHOR]

Background: Binding of the programmed death-1 (PD-1) receptor to its ligands (PD-L1/2) transduces inhibitory signals that promote exhaustion of activated T cells. Blockade of the PD-1 pathway is widely used for cancer treatment, yet the inhibitory signals transduced by PD-1 in T cells remain elusive. Methods: Expression profiles of human CD8+ T cells in resting, activated (CD3 + CD28) and PD-1-stimulated cells (CD3 + CD28 + PD-L1-Fc) conditions were evaluated by RNA-seq. Bioinformatic analyses were used to identify signaling pathways differentially regulated in PD-1-stimulated cells. Metabolic analyses were performed with SeaHorse technology, and mitochondrial ultrastructure was determined by transmission electron microscopy. PD-1- regulated mitochondrial genes were silenced using short-hairpin RNA in primary cells. Blue native gel electrophoresis was used to determine respiratory supercomplex assembly. Results: PD-1 engagement in human CD8+ T cells triggers a specific, progressive genetic program different from that found in resting cells. Gene ontology identified metabolic processes, including glycolysis and oxidative phosphorylation (OXPHOS), as the main pathways targeted by PD-1. We observed severe functional and structural alterations in the mitochondria of PD-1-stimulated cells, including a reduction in the number and length of mitochondrial cristae. These cristae alterations were associated with reduced expression of CHCHD3 and CHCHD10, two proteins that form part of the mitochondrial contact site and cristae organizing system (MICOS). Although PD-1-stimulated cells showed severe cristae alterations, assembly of respiratory supercomplexes was unexpectedly greater in these cells than in activated T cells. CHCHD3 silencing in primary CD8+ T cells recapitulated some effects induced by PD-1 stimulation, including reduced mitochondrial polarization and interferon-γ production following T cell activation with anti-CD3 and -CD28 activating antibodies. Conclusions: Our results suggest that mitochondria are the main targets of PD-1 inhibitory activity. PD-1 reprograms CD8+ T cell metabolism for efficient use of fatty acid oxidation; this mitochondrial phenotype might explain the long-lived phenotype of PD-1-engaged T cells. [ABSTRACT FROM AUTHOR]

Abstract A major challenge in mitochondrial diseases (MDs) is the identification of biomarkers that could inform of the mechanisms involved in the phenotypic expression of genetic defects. Herein, we have investigated the protein signature of metabolism and of the antioxidant response in muscle biopsies of clinically and genetically diagnosed patients with Progressive External Ophthalmoplegia due to single large-scale (PEO-sD) or multiple (PEO-mD) deletions of mtDNA and Mitochondrial Encephalopathy Lactic Acidosis and Stroke-like episode (MELAS) syndrome, and healthy donors. A high-throughput immunoassay technique that quantitates the expression of relevant proteins of glycolysis, glycogenolysis, pentose phosphate pathway, oxidative phosphorylation, pyruvate and fatty acid oxidation, tricarboxylic acid cycle and the antioxidant response in two large independent and retrospectively collected cohorts of PEO-sD, PEO-mD and MELAS patients revealed that despite the heterogeneity of the genetic alterations, the three MDs showed the same metabolic signatures in both cohorts of patients, which were highly divergent from those of healthy individuals. Linear Discriminant Analysis and Support Vector Machine classifier provided a minimum of four biomarkers to discriminate healthy from pathological samples. Regardless of the induction of a large number of enzymes involved in ameliorating oxidative stress, the down-regulation of mitochondrial superoxide dismutase (SOD2) and catalase expression favored the accumulation of oxidative damage in patients' proteins. Down-regulation of SOD2 and catalase expression in MD patients is not due to relevant changes in the availability of their mRNAs, suggesting that oxidative stress regulates the expression of the two enzymes post-transcriptionally. We suggest that SOD2 and catalase could provide specific targets to improve the detoxification of reactive oxygen species that affects muscle proteins in these patients. Graphical abstract Summary of the alterations found in protein expression of metabolic and antioxidant enzymes in muscle biopsies of two independent cohorts of PEO and MELAS patients using reverse phase protein arrays. Genetic alterations are identified by red stars on nDNA and mtDNA. Red and green colors respectively denote decreased and enhanced expression of the indicated enzymes. Oxidative damage is depicted in a black background. fx1 Highlights • Quantification of metabolic proteins in muscle of MDs patients by RPPA. • Biopsies of PEO and MELAS patients portray the same proteome of metabolism. • Four protein biomarkers discriminate healthy from pathological samples. • Down-regulation of SOD2 and catalase are hallmarks of PEO and MELAS samples. • Oxidative damage occurs despite the induction of enzymes of the antioxidant response. [ABSTRACT FROM AUTHOR]