bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2020‒01‒12
thirty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. FASEB J. 2020 Jan;34(1): 303-315
    Kľučková K, Thakker A, Vettore L, Escribano-Gonzalez C, Hindshaw RL, Tearle JLE, Goncalves J, Kaul B, Lavery GG, Favier J, Tennant DA.
      Mutations in succinate dehydrogenase (SDH) lead to the development of tumors in a restricted subset of cell types, including chromaffin cells and paraganglia. The molecular basis for this specificity is currently unknown. We show that loss of SDH activity in a chromaffin cell model does not perturb complex I function, retaining the ability to oxidize NADH within the electron transport chain. This activity supports continued oxidation of substrates within the tricarboxylic acid (TCA) cycle. However, due to the block in the TCA cycle at SDH, the high glutamine oxidation activity is only maintained through an efflux of succinate. We also show that although the mitochondria of SDH-deficient cells are less active per se, their higher mass per cell results in an overall respiratory rate that is comparable with wild-type cells. Finally, we observed that when their mitochondria are uncoupled, SDH-deficient cells are unable to preserve their viability, suggesting that the mitochondrial metabolic network is unable to compensate when exposed to additional stress. We therefore show that in contrast to models of SDH deficiency based on epithelial cells, a chromaffin cell model retains aspects of metabolic "health," which could form the basis of cell specificity of this rare tumor type.
    Keywords:  electron transport chain; metabolism; mitochondria; pheochromocytoma; succinate dehydrogenase
    DOI:  https://doi.org/10.1096/fj.201901456R
  2. Nat Commun. 2020 Jan 07. 11(1): 36
    Nie H, Ju H, Fan J, Shi X, Cheng Y, Cang X, Zheng Z, Duan X, Yi W.
      Many cancer cells display enhanced glycolysis and suppressed mitochondrial metabolism. This phenomenon, known as the Warburg effect, is critical for tumor development. However, how cancer cells coordinate glucose metabolism through glycolysis and the mitochondrial tricarboxylic acid (TCA) cycle is largely unknown. We demonstrate here that phosphoglycerate kinase 1 (PGK1), the first ATP-producing enzyme in glycolysis, is reversibly and dynamically modified with O-linked N-acetylglucosamine (O-GlcNAc) at threonine 255 (T255). O-GlcNAcylation activates PGK1 activity to enhance lactate production, and simultaneously induces PGK1 translocation into mitochondria. Inside mitochondria, PGK1 acts as a kinase to inhibit pyruvate dehydrogenase (PDH) complex to reduce oxidative phosphorylation. Blocking T255 O-GlcNAcylation of PGK1 decreases colon cancer cell proliferation, suppresses glycolysis, enhances the TCA cycle, and inhibits tumor growth in xenograft models. Furthermore, PGK1 O-GlcNAcylation levels are elevated in human colon cancers. This study highlights O-GlcNAcylation as an important signal for coordinating glycolysis and the TCA cycle to promote tumorigenesis.
    DOI:  https://doi.org/10.1038/s41467-019-13601-8
  3. Front Oncol. 2019 ;9 1373
    de la Cruz López KG, Toledo Guzmán ME, Sánchez EO, García Carrancá A.
      Continuous proliferation of tumor cells requires constant adaptations of energy metabolism to rapidly fuel cell growth and division. This energetic adaptation often comprises deregulated glucose uptake and lactate production in the presence of oxygen, a process known as the "Warburg effect." For many years it was thought that the Warburg effect was a result of mitochondrial damage, however, unlike this proposal tumor cell mitochondria maintain their functionality, and is essential for integrating a variety of signals and adapting the metabolic activity of the tumor cell. The mammalian/mechanistic target of rapamycin complex 1 (mTORC1) is a master regulator of numerous cellular processes implicated in proliferation, metabolism, and cell growth. mTORC1 controls cellular metabolism mainly by regulating the translation and transcription of metabolic genes, such as peroxisome proliferator activated receptor γ coactivator-1 α (PGC-1α), sterol regulatory element-binding protein 1/2 (SREBP1/2), and hypoxia inducible factor-1 α (HIF-1α). Interestingly it has been shown that mTORC1 regulates mitochondrial metabolism, thus representing an important regulator in mitochondrial function. Here we present an overview on the role of mTORC1 in the regulation of mitochondrial functions in cancer, considering new evidences showing that mTORC1 regulates the translation of nucleus-encoded mitochondrial mRNAs that result in an increased ATP mitochondrial production. Moreover, we discuss the relationship between mTORC1 and glutaminolysis, as well as mitochondrial metabolites. In addition, mitochondrial fission processes regulated by mTORC1 and its impact on cancer are discussed. Finally, we also review the therapeutic efficacy of mTORC1 inhibitors in cancer treatments, considering its use in combination with other drugs, with particular focus on cellular metabolism inhibitors, that could help improve their anti neoplastic effect and eliminate cancer cells in patients.
    Keywords:  cancer; mTORC1; mitochondria; mitochondrial functions; therapy
    DOI:  https://doi.org/10.3389/fonc.2019.01373
  4. Antioxid Redox Signal. 2020 Jan 05.
    Esparza-Moltó PB, Cuezva JM.
      SIGNIFICANCE: Cancer is a major disease imposing high personal and economic burdens draining large part of National Health Care and Research budgets worldwide. In the last decade, research in cancer has underscored the reprogramming of metabolism to an enhanced aerobic glycolysis as a major trait of the cancer phenotype with great potential for targeted therapy. Recent advances: Mitochondria are essential organelles in metabolic reprogramming by controlling the production of biological energy through oxidative phosphorylation (OXPHOS) and the supply of metabolic precursors that sustain proliferation. In addition, mitochondria are critical hubs that integrate different signaling pathways that control cellular metabolism and cell fate. The mitochondrial ATP synthase plays a fundamental role in OXPHOS and cellular signaling.CRITICAL ISSUES: This review overviews mitochondrial metabolism and OXPHOS and the major changes reported in the expression and function of mitochondrial proteins of OXPHOS in oncogenesis and in cellular differentiation. We summarize the prominent role that RNA-binding proteins exert in the sorting and localized translation of nuclear-encoded mRNAs that help to define the mitochondrial cell-type specific phenotype. Moreover, we emphasize the mechanisms that contribute to restrain the activity and expression of the mitochondrial ATP synthase in carcinomas, and illustrate that the dysregulation of proteins that control energy metabolism correlates with patients' survival.
    FUTURE DIRECTIONS: Future research should elucidate the mechanisms and RNA-binding proteins that promote the specific alterations of the mitochondrial phenotype in carcinomas arising in different tissues with the final aim of developing new therapeutic strategies to treat cancer.
    DOI:  https://doi.org/10.1089/ars.2019.7988
  5. FASEB J. 2019 Dec 13.
    Kim YY, Um JH, Yoon JH, Lee DY, Lee YJ, Kim DH, Park JI, Yun J.
      Cellular senescence acts as an important barrier to tumorigenesis by eliminating precancerous cells. Previous studies have shown an essential role of the tumor suppressor p53 in cellular senescence, but how p53 induces cellular senescence is not fully understood. We found that p53 promoted the formation of highly interconnected and elongated mitochondria prior to the onset of cellular senescence. The inhibition of mitochondrial elongation upon p53 expression suppressed cellular senescence, suggesting that mitochondrial elongation is required for the induction of p53-dependent senescence. p53-induced mitochondrial elongation resulted in mitochondrial dysfunction and subsequent increases in intracellular reactive oxygen species (ROS) levels, an important mediator of cellular senescence. Mechanistically, the inhibitory phosphorylation of Drp1 Ser637 increased upon p53 expression, suppressing the translocation of Drp1 into mitochondria. The transcriptional function of p53 was crucial for controlling the inhibitory phosphorylation of Drp1, whereas p21 was nonessential. Protein kinase A (PKA) activity was responsible for p53-mediated Drp1 Ser637 phosphorylation and mitochondrial dysfunction. Taken together, these results suggest that p53 regulates mitochondrial dynamics through the PKA-Drp1 pathway to induce cellular senescence.
    Keywords:  Drp1; PKA; cellular senescence; mitochondria dynamics; p53; senescence
    DOI:  https://doi.org/10.1096/fj.201901747RR
  6. Commun Biol. 2019 Jan 03. 2(1): 3
    Araki K, Kawauchi K, Sugimoto W, Tsuda D, Oda H, Yoshida R, Ohtani K.
      Mitochondrial damage is caused by changes in the micro-environmental conditions during tumor progression. Cancer cells require mechanisms for mitochondrial quality control during this process; however, how mitochondrial integrity is maintained is unclear. Here we show that E2F3d, a previously unidentified E2F3 isoform, mediates hypoxia-induced mitophagy in cancer cells. Aberrant activity and expression of the E2F3 transcription factor is frequently observed in many cancer cells. Loss of retinoblastoma (Rb) protein family function increases the expression of E2F3d and E2F3a. E2F3d localizes to the outer mitochondrial membrane and its cytosolic domain contains an LC3-interacting region motif. Overexpression of E2F3d induces mitochondrial fragmentation and mitophagy, suggesting that E2F3d plays an important role in mitophagy. Furthermore, depletion of E2F3s attenuates hypoxia-induced mitophagy and increases intracellular levels of reactive oxygen species, which is reversed by the reintroduction of E2F3d. This study presents another key player that regulates mitochondrial quality control in cancer cells.
    DOI:  https://doi.org/10.1038/s42003-018-0246-9
  7. Arch Biochem Biophys. 2020 Jan 06. pii: S0003-9861(19)30972-5. [Epub ahead of print] 108258
    Algieri C, Trombetti F, Pagliarani A, Ventrella V, Nesci S.
      Phenylglyoxal (PGO), known to cause post-translational modifications of Arg residues, was used to highlight the role of arginine residues of the F1FO-ATPase, which may be crucial to yield the mitochondrial permeability transition pore (mPTP). In swine heart mitochondria PGO inhibits ATP hydrolysis by the F1FO-ATPase either sustained by the natural cofactor Mg2+ or by Ca2+ by a similar uncompetitive inhibition mechanism, namely the tertiary complex (ESI) only forms when the ATP substrate is already bound to the enzyme, and with similar strength, as shown by the similar K'i values (0.82 ± 0.07 mM in presence of Mg2+ and 0.64 ± 0.05 mM in the presence of Ca2+). Multiple inhibitor analysis indicates that features of the F1 catalytic sites and/or the FO proton binding sites are apparently unaffected by PGO. However, PGO and F1 or FO inhibitors can bind the enzyme combine simultaneously. However they mutually hinder to bind the Mg2+-activated F1FO-ATPase, whereas they do not mutually exclude to bind the Ca2+-activated F1FO-ATPase. The putative formation of PGO-arginine adducts, and the consequent spatial rearrangement in the enzyme structure, inhibits the F1FO-ATPase activity but, as shown by the calcium retention capacity evaluation in intact mitochondria, apparently favours the mPTP formation.
    Keywords:  Divalent cations; F(1)F(O)-ATPase; Inhibition kinetics; Mitochondria; Permeability transition pore; Phenylglyoxal
    DOI:  https://doi.org/10.1016/j.abb.2020.108258
  8. Nat Metab. 2019 Feb;1(2): 189-200
    Chouchani ET, Kajimura S.
      Adipose tissue possesses the remarkable capacity to control its size and function in response to a variety of internal and external cues, such as nutritional status and temperature. The regulatory circuits of fuel storage and oxidation in white adipocytes and thermogenic adipocytes (brown and beige adipocytes) play a central role in systemic energy homeostasis, whereas dysregulation of the pathways is closely associated with metabolic disorders and adipose tissue malfunction, including obesity, insulin resistance, chronic inflammation, mitochondrial dysfunction, and fibrosis. Recent studies have uncovered new regulatory elements that control the above parameters and provide new mechanistic opportunities to reprogram fat cell fate and function. In this Review, we provide an overview of the current understanding of adipocyte metabolism in physiology and disease and also discuss possible strategies to alter fuel utilization in fat cells to improve metabolic health.
    DOI:  https://doi.org/10.1038/s42255-018-0021-8
  9. Commun Biol. 2019 Jul 11. 2(1): 258
    MacDonald JA, Bothun AM, Annis SN, Sheehan H, Ray S, Gao Y, Ivanov AR, Khrapko K, Tilly JL, Woods DC.
      Mitochondria are well-characterized regarding their function in both energy production and regulation of cell death; however, the heterogeneity that exists within mitochondrial populations is poorly understood. Typically analyzed as pooled samples comprised of millions of individual mitochondria, there is little information regarding potentially different functionality across subpopulations of mitochondria. Herein we present a new methodology to analyze mitochondria as individual components of a complex and heterogeneous network, using a nanoscale and multi-parametric flow cytometry-based platform. We validate the platform using multiple downstream assays, including electron microscopy, ATP generation, quantitative mass-spectrometry proteomic profiling, and mtDNA analysis at the level of single organelles. These strategies allow robust analysis and isolation of mitochondrial subpopulations to more broadly elucidate the underlying complexities of mitochondria as these organelles function collectively within a cell.
    DOI:  https://doi.org/10.1038/s42003-019-0513-4
  10. Front Immunol. 2019 ;10 2915
    Slattery K, Gardiner CM.
      NK cells are innate lymphocytes which play an essential role in protection against cancer and viral infection. Their functions are dictated by many factors including the receptors they express, cytokines they respond to and changes in the external environment. These cell processes are regulated within NK cells at many levels including genetic, epigenetic and expression (RNA and protein) levels. The last decade has revealed cellular metabolism as another level of immune regulation. Specific immune cells adopt metabolic configurations that support their functions, and this is a dynamic process with cells undergoing metabolic reprogramming during the course of an immune response. Upon activation with pro-inflammatory cytokines, NK cells upregulate both glycolysis and oxphos metabolic pathways and this supports their anti-cancer functions. Perturbation of these pathways inhibits NK cell effector functions. Anti-inflammatory cytokines such as TGFβ can inhibit metabolic changes and reduce functional outputs. Although a lot remains to be learned, our knowledge of potential molecular mechanisms involved is growing quickly. This review will discuss our current knowledge on the role of TGFβ in regulating NK cell metabolism and will draw on a wider knowledge base regarding TGFβ regulation of cellular metabolic pathways, in order to highlight potential ways in which TGFβ might be targeted to contribute to the exciting progress that is being made in terms of adoptive NK cell therapies for cancer.
    Keywords:  NK cells; TGFβ; immunotherapy; metabolism; mitochondria
    DOI:  https://doi.org/10.3389/fimmu.2019.02915
  11. Nat Commun. 2020 Jan 07. 11(1): 52
    Affronti HC, Rowsam AM, Pellerite AJ, Rosario SR, Long MD, Jacobi JJ, Bianchi-Smiraglia A, Boerlin CS, Gillard BM, Karasik E, Foster BA, Moser M, Wilton JH, Attwood K, Nikiforov MA, Azabdaftari G, Pili R, Phillips JG, Casero RA, Smiraglia DJ.
      Prostatic luminal epithelial cells secrete high levels of acetylated polyamines into the prostatic lumen, sensitizing them to perturbations of connected metabolic pathways. Enhanced flux is driven by spermidine/spermine N1-acetyltransferase (SSAT) activity, which acetylates polyamines leading to their secretion and drives biosynthetic demand. The methionine salvage pathway recycles one-carbon units lost to polyamine biosynthesis to the methionine cycle to overcome stress. Prostate cancer (CaP) relies on methylthioadenosine phosphorylase (MTAP), the rate-limiting enzyme, to relieve strain. Here, we show that inhibition of MTAP alongside SSAT upregulation is synergistic in androgen sensitive and castration recurrent CaP models in vitro and in vivo. The combination treatment increases apoptosis in radical prostatectomy ex vivo explant samples. This unique high metabolic flux through polyamine biosynthesis and connected one carbon metabolism in CaP creates a metabolic dependency. Enhancing this flux while simultaneously targeting this dependency in prostate cancer results in an effective therapeutic approach potentially translatable to the clinic.
    DOI:  https://doi.org/10.1038/s41467-019-13950-4
  12. Cancer Metab. 2020 ;8 1
    Nelson BS, Lin L, Kremer DM, Sousa CM, Cotta-Ramusino C, Myers A, Ramos J, Gao T, Kovalenko I, Wilder-Romans K, Dresser J, Davis M, Lee HJ, Nwosu ZC, Campit S, Mashadova O, Nicolay BN, Tolstyka ZP, Halbrook CJ, Chandrasekaran S, Asara JM, Crawford HC, Cantley LC, Kimmelman AC, Wahl DR, Lyssiotis CA.
      Background: Metabolic programs in cancer cells are influenced by genotype and the tissue of origin. We have previously shown that central carbon metabolism is rewired in pancreatic ductal adenocarcinoma (PDA) to support proliferation through a glutamate oxaloacetate transaminase 1 (GOT1)-dependent pathway.Methods: We utilized a doxycycline-inducible shRNA-mediated strategy to knockdown GOT1 in PDA and colorectal cancer (CRC) cell lines and tumor models of similar genotype. These cells were analyzed for the ability to form colonies and tumors to test if tissue type impacted GOT1 dependence. Additionally, the ability of GOT1 to impact the response to chemo- and radiotherapy was assessed. Mechanistically, the associated specimens were examined using a combination of steady-state and stable isotope tracing metabolomics strategies and computational modeling. Statistics were calculated using GraphPad Prism 7. One-way ANOVA was performed for experiments comparing multiple groups with one changing variable. Student's t test (unpaired, two-tailed) was performed when comparing two groups to each other. Metabolomics data comparing three PDA and three CRC cell lines were analyzed by performing Student's t test (unpaired, two-tailed) between all PDA metabolites and CRC metabolites.
    Results: While PDA exhibits profound growth inhibition upon GOT1 knockdown, we found CRC to be insensitive. In PDA, but not CRC, GOT1 inhibition disrupted glycolysis, nucleotide metabolism, and redox homeostasis. These insights were leveraged in PDA, where we demonstrate that radiotherapy potently enhanced the effect of GOT1 inhibition on tumor growth.
    Conclusions: Taken together, these results illustrate the role of tissue type in dictating metabolic dependencies and provide new insights for targeting metabolism to treat PDA.
    Keywords:  CRC; Colorectal cancer; Fluxomics; Metabolomics; NADPH; PDA; Pancreatic cancer; Redox; Stable isotope tracing
    DOI:  https://doi.org/10.1186/s40170-019-0202-2
  13. Front Immunol. 2019 ;10 2716
    Shi H, Chi H.
      Regulatory T (Treg) cells are crucial for peripheral immune tolerance and prevention of autoimmunity and tissue damage. Treg cells are inherently defined by the expression of the transcription factor Foxp3, which enforces lineage development and immune suppressive function of these cells. Under various conditions as observed in autoimmunity, cancer and non-lymphoid tissues, a proportion of Treg cells respond to specific environmental signals and display altered stability, plasticity and tissue-specific heterogeneity, which further shape their context-dependent suppressive functions. Recent studies have revealed that metabolic programs play pivotal roles in controlling these processes in Treg cells, thereby considerably expanding our understanding of Treg cell biology. Here we summarize these recent advances that highlight how cell-extrinsic factors, such as nutrients, vitamins and metabolites, and cell-intrinsic metabolic programs, orchestrate Treg cell stability, plasticity, and tissue-specific heterogeneity. Understanding metabolic regulation of Treg cells should provide new insight into immune homeostasis and disease, with important therapeutic implications for autoimmunity, cancer, and other immune-mediated disorders.
    Keywords:  Foxp3; Treg cell; metabolism; plasticity; stability; tissue-specific heterogeneity
    DOI:  https://doi.org/10.3389/fimmu.2019.02716
  14. Commun Biol. 2019 Nov 14. 2(1): 414
    Sinkala M, Mulder N, Patrick Martin D.
      Malignant cells reconfigure their metabolism to support oncogenic processes such as accelerated growth and proliferation. The mechanisms by which this occurs likely involve alterations to genes that encode metabolic enzymes. Here, using genomics data for 10,528 tumours of 32 different cancer types, we characterise the alterations of genes involved in various metabolic pathways. We find that mutations and copy number variations of metabolic genes are pervasive across all human cancers. Based on the frequencies of metabolic gene alterations, we further find that there are two distinct cancer supertypes that tend to be associated with different clinical outcomes. By utilising the known dose-response profiles of 825 cancer cell lines, we infer that cancers belonging to these supertypes are likely to respond differently to various anticancer drugs. Collectively our analyses define the foundational metabolic features of different cancer supertypes and subtypes upon which discriminatory strategies for treating particular tumours could be constructed.
    DOI:  https://doi.org/10.1038/s42003-019-0666-1
  15. Nat Commun. 2020 Jan 10. 11(1): 220
    Wang G, Xu J, Zhao J, Yin W, Liu D, Chen W, Hou SX.
      Cancer stem cells (CSCs) may be responsible for treatment resistance, tumor metastasis, and disease recurrence. Here we demonstrate that the Arf1-mediated lipid metabolism sustains cells enriched with CSCs and its ablation induces anti-tumor immune responses in mice. Notably, Arf1 ablation in cancer cells induces mitochondrial defects, endoplasmic-reticulum stress, and the release of damage-associated molecular patterns (DAMPs), which recruit and activate dendritic cells (DCs) at tumor sites. The activated immune system finally elicits antitumor immune surveillance by stimulating T-cell infiltration and activation. Furthermore, TCGA data analysis shows an inverse correlation between Arf1 expression and T-cell infiltration and activation along with patient survival in various human cancers. Our results reveal that Arf1-pathway knockdown not only kills CSCs but also elicits a tumor-specific immune response that converts dying CSCs into a therapeutic vaccine, leading to durable benefits.
    DOI:  https://doi.org/10.1038/s41467-019-14046-9
  16. Cancers (Basel). 2019 Dec 30. pii: E90. [Epub ahead of print]12(1):
    Lyssiotis CA, Nagrath D.
      Metabolic programs are rewired in tumors to support growth, progression, and immune evasion. A wealth of work in the past decade has delineated how these metabolic rearrangements are facilitated by signaling pathways downstream of oncogene activation and tumor suppressor loss. More recently, this field has expanded to include metabolic interactions among the diverse cell types that exist within a tumor and how this impacts the immune system. In this special issue, 17 review articles discuss these phenomena, and, alongside four original research manuscripts, the vulnerabilities associated with deregulated metabolic programming are highlighted and examined.
    Keywords:  amino acids; cancer associated fibroblasts; cancer metabolism; carbohydrates; iron; lipids; nucleotides; reactive oxygen species; redox; tumor microenvironment
    DOI:  https://doi.org/10.3390/cancers12010090
  17. J Biol Chem. 2020 Jan 08. pii: jbc.RA119.010565. [Epub ahead of print]
    Olson AK, Bouchard B, Zhu WZ, Chatham JC, Des Rosiers C.
      The hexosamine biosynthesis pathway (HBP) branches from glycolysis and forms uridine diphosphate-β-N-acetylglucosamine (UDP-GlcNAc), the moiety for O-linked β-N-acetylglucosamine (O-GlcNAc) posttranslational modifications.  An inability to directly measure HBP flux has hindered our understanding of the factors regulating protein O-GlcNAcylation.  Our goals in this study were to (i) validate a LC-MS method that assesses HBP flux as UDP-GlcNAc (13C)-molar percent enrichment (MPE) and concentration; and (ii) determine whether glucose availability or workload regulate cardiac HBP flux.  For (i), we perfused isolated murine working hearts with [U-13C6]glucosamine (1, 10, 50 or 100 µM), which bypasses the rate limiting HBP enzyme.  We observed a concentration-dependent increase in UDP-GlcNAc levels and MPE, with the latter reaching a plateau of 56.3±2.9%.  For (ii), we perfused isolated working hearts with [U-13C6]glucose (5.5 or 25 mM).  Glycolytic efflux doubled with 25 mM [U-13C6]glucose; however, the calculated HBP flux was similar among the glucose concentrations at approximately 2.5 nmole/g heart protein/min, representing ~0.003-0.006% of glycolysis.  Reducing cardiac workload in beating and non-beating Langendorff perfusions had no effect on the calculated HBP flux at approximately 2.3 and 2.5 nmole/g heart protein/min, respectively.  To the best of our knowledge, this is the first direct measurement of glucose flux through the HBP in any organ.  We anticipate that these methods will enable foundational analyses of the regulation of HBP flux and protein O-GlcNAcylation.  Our results suggest that in the healthy ex vivo perfused heart, HBP flux does not respond to acute changes in glucose availability or cardiac workload.
    Keywords:  O-linked N-acetylglucosamine (O-GlcNAc); UDP-GlcNAc; carbohydrate metabolism; cardiac metabolism; glucosamine; glucose; glucose metabolism; hexosamine biosynthesis pathway; metabolic flux; post-translational modification (PTM); protein glycosylation
    DOI:  https://doi.org/10.1074/jbc.RA119.010565
  18. Mitochondrion. 2020 Jan 07. pii: S1567-7249(19)30208-9. [Epub ahead of print]
    Besse A, Brezavar D, Hanson J, Larson A, Bonnen PE.
      LONP1 is an ATP-dependent protease and chaperone that plays multiple vital roles in mitochondria. LONP1 is essential for mitochondrial homeostasis due to its role in maintenance of the mitochondrial genome and its central role in regulating mitochondrial processes such as oxidative phosphorylation, mitophagy, and heme biosynthesis. Bi-allelic LONP1 mutations have been reported to cause a constellation of clinical presentations. We report a patient heterozygous for a de novo mutation in LONP1: c.901C>T,p.R301W presenting as a neonate with seizures, encephalopathy, pachygyria and microcephaly. Assays of respiratory chain activity in muscle showed complex II-III function at 8% of control. Functional studies in patient fibroblasts showed a signature of dysfunction that included significant decreases in known proteolytic targets of LONP1 (TFAM, PINK1, phospho-PDH E1α) as well as loss of mitochondrial ribosome subunits MRPL44 and MRPL11 with concomitant decreased activity and level of protein subunits of oxidative phosphorylation complexes I and IV. These results indicate excessive LONP1 proteolytic activity and a loss of LONP1 chaperone activity. Further, we demonstrate that the LONP1 N-terminal domain is involved in hexamer stability of LONP1 and that the ability to make conformational changes is necessary for LONP1 to regulate proper functioning of both its proteolytic and chaperone activities.
    Keywords:  LONP1; chaperone; encephalopathy; mitochondria; oxidative phosphorylation; protease; seizures
    DOI:  https://doi.org/10.1016/j.mito.2020.01.004
  19. Commun Biol. 2019 Aug 14. 2(1): 313
    Kim BG, Sung JS, Jang Y, Cha YJ, Kang S, Han HH, Lee JH, Cho NH.
      Tumor growth increases compressive stress within a tissue, which is associated with solid tumor progression. However, very little is known about how compressive stress contributes to tumor progression. Here, we show that compressive stress induces glycolysis in human breast cancer associated fibroblast (CAF) cells and thereby contributes to the expression of epithelial to mesenchymal (EMT)- and angiogenesis-related genes in breast cancer cells. Lactate production was increased in compressed CAF cells, in a manner dependent on the expression of metabolic genes ENO2, HK2, and PFKFB3. Conditioned medium from compressed CAFs promoted the proliferation of breast cancer cells and the expression of EMT and/or angiogenesis-related genes. In patient tissues with high compressive stress, the expression of compression-induced metabolic genes was significantly and positively correlated with EMT and/or angiogenesis-related gene expression and metastasis size. These findings illustrate a mechanotransduction pathway involving stromal glycolysis that may be relevant also for other solid tumours.
    DOI:  https://doi.org/10.1038/s42003-019-0553-9
  20. Front Cell Dev Biol. 2019 ;7 355
    Denisenko TV, Gorbunova AS, Zhivotovsky B.
      Mitochondria in addition to be a main cellular power station, are involved in the regulation of many physiological processes, such as generation of reactive oxygen species, metabolite production and the maintenance of the intracellular Ca2+ homeostasis. Almost 100 years ago Otto Warburg presented evidence for the role of mitochondria in the development of cancer. During the past 20 years mitochondrial involvement in programmed cell death regulation has been clarified. Moreover, it has been shown that mitochondria may act as a switchboard between various cell death modalities. Recently, accumulated data have pointed to the role of mitochondria in the metastatic dissemination of cancer cells. Here we summarize the modern knowledge concerning the contribution of mitochondria to the invasion and dissemination of tumor cells and the possible mechanisms behind that and attempts to target metastatic cancers involving mitochondria.
    Keywords:  cell death; invasion; metastasis; migration; mitochondria
    DOI:  https://doi.org/10.3389/fcell.2019.00355
  21. Oncogene. 2020 Jan 07.
    Liu Y, Mao C, Wang M, Liu N, Ouyang L, Liu S, Tang H, Cao Y, Liu S, Wang X, Xiao D, Chen C, Shi Y, Yan Q, Tao Y.
      Dysregulated metabolism contributes to cancer initiation and progression, but the key drivers of these pathways are just being discovered. Here, we report a critical role for proline catabolism in non-small cell lung cancer (NSCLC). Proline dehydrogenase (PRODH) is activated to reduce proline levels by the chromatin remodeling factor lymphoid-specific helicase (LSH), an epigenetic driver of NSCLC. PRODH promotes NSCLC tumorigenesis by inducing epithelial to mesenchymal transition (EMT) and IKKα-dependent inflammatory genes, including CXCL1, LCN2, and IL17C. Consistently, proline addition promotes the expression of these inflammatory genes, as well as EMT, tumor cell proliferation, and migration in vitro and tumor growth in vivo, while the depletion or inhibition of PRODH blocks these phenotypes. In summary, we reveal an essential metabolic pathway amenable to targeting in NSCLC.
    DOI:  https://doi.org/10.1038/s41388-019-1151-5
  22. Trends Biochem Sci. 2019 Dec 31. pii: S0968-0004(19)30265-8. [Epub ahead of print]
    Liberti MV, Locasale JW.
      Lactate is an end product of glucose metabolism, which serves metabolic and nonmetabolic functions. A new study by Zhang et al. establishes a novel function for lactate whereby it is utilized in a new histone modification, histone lysine lactylation, to regulate gene expression in macrophages.
    Keywords:  Warburg effect; histone lactylation; lactate; macrophage polarization
    DOI:  https://doi.org/10.1016/j.tibs.2019.12.004
  23. Nature. 2020 Jan 08.
    Xue JY, Zhao Y, Aronowitz J, Mai TT, Vides A, Qeriqi B, Kim D, Li C, de Stanchina E, Mazutis L, Risso D, Lito P.
      KRAS GTPases are activated in one-third of cancers, and KRAS(G12C) is one of the most common activating alterations in lung adenocarcinoma1,2. KRAS(G12C) inhibitors3,4 are in phase-I clinical trials and early data show partial responses in nearly half of patients with lung cancer. How cancer cells bypass inhibition to prevent maximal response to therapy is not understood. Because KRAS(G12C) cycles between an active and inactive conformation4-6, and the inhibitors bind only to the latter, we tested whether isogenic cell populations respond in a non-uniform manner by studying the effect of treatment at a single-cell resolution. Here we report that, shortly after treatment, some cancer cells are sequestered in a quiescent state with low KRAS activity, whereas others bypass this effect to resume proliferation. This rapid divergent response occurs because some quiescent cells produce new KRAS(G12C) in response to suppressed mitogen-activated protein kinase output. New KRAS(G12C) is maintained in its active, drug-insensitive state by epidermal growth factor receptor and aurora kinase signalling. Cells without these adaptive changes-or cells in which these changes are pharmacologically inhibited-remain sensitive to drug treatment, because new KRAS(G12C) is either not available or exists in its inactive, drug-sensitive state. The direct targeting of KRAS oncoproteins has been a longstanding objective in precision oncology. Our study uncovers a flexible non-uniform fitness mechanism that enables groups of cells within a population to rapidly bypass the effect of treatment. This adaptive process must be overcome if we are to achieve complete and durable responses in the clinic.
    DOI:  https://doi.org/10.1038/s41586-019-1884-x
  24. Aging Clin Exp Res. 2020 Jan 10.
    Lefkimmiatis K, Grisan F, Iannucci LF, Surdo NC, Pozzan T, Di Benedetto G.
      Mitochondria constantly contribute to the cell homeostasis and this, during the lifespan of a cell, takes its toll. Indeed, the functional decline of mitochondria appears correlated to the aging of the cell. The initial idea was that excessive production of reactive oxygen species (ROS) by functionally compromised mitochondria was the causal link between the decline of the organelle functions and cellular aging. However, in recent years accumulating evidence suggests that the contribution of mitochondria to cellular aging goes beyond ROS production. In this short review, we discuss how intracellular signalling, specifically the cAMP-signalling cascade, is involved in the regulation of mitochondrial functions and potentially in the processes that link mitochondrial status to cellular aging.
    Keywords:  Aging; Mitochondria; Signalling; cAMP
    DOI:  https://doi.org/10.1007/s40520-019-01451-9
  25. EMBO J. 2020 Jan 08. e102817
    Protasoni M, Pérez-Pérez R, Lobo-Jarne T, Harbour ME, Ding S, Peñas A, Diaz F, Moraes CT, Fearnley IM, Zeviani M, Ugalde C, Fernández-Vizarra E.
      Mitochondrial respiratory chain (MRC) enzymes associate in supercomplexes (SCs) that are structurally interdependent. This may explain why defects in a single component often produce combined enzyme deficiencies in patients. A case in point is the alleged destabilization of complex I in the absence of complex III. To clarify the structural and functional relationships between complexes, we have used comprehensive proteomic, functional, and biogenetical approaches to analyze a MT-CYB-deficient human cell line. We show that the absence of complex III blocks complex I biogenesis by preventing the incorporation of the NADH module rather than decreasing its stability. In addition, complex IV subunits appeared sequestered within complex III subassemblies, leading to defective complex IV assembly as well. Therefore, we propose that complex III is central for MRC maturation and SC formation. Our results challenge the notion that SC biogenesis requires the pre-formation of fully assembled individual complexes. In contrast, they support a cooperative-assembly model in which the main role of complex III in SCs is to provide a structural and functional platform for the completion of overall MRC biogenesis.
    Keywords:  complex I; complex III; cytochrome b mutation; mitochondrial respiratory chain assembly; supercomplexes
    DOI:  https://doi.org/10.15252/embj.2019102817
  26. Nat Commun. 2020 Jan 10. 11(1): 174
    D'Hulst G, Soro-Arnaiz I, Masschelein E, Veys K, Fitzgerald G, Smeuninx B, Kim S, Deldicque L, Blaauw B, Carmeliet P, Breen L, Koivunen P, Zhao SM, De Bock K.
      mTORC1 is an important regulator of muscle mass but how it is modulated by oxygen and nutrients is not completely understood. We show that loss of the prolyl hydroxylase domain isoform 1 oxygen sensor in mice (PHD1KO) reduces muscle mass. PHD1KO muscles show impaired mTORC1 activation in response to leucine whereas mTORC1 activation by growth factors or eccentric contractions was preserved. The ability of PHD1 to promote mTORC1 activity is independent of its hydroxylation activity but is caused by decreased protein content of the leucyl tRNA synthetase (LRS) leucine sensor. Mechanistically, PHD1 interacts with and stabilizes LRS. This interaction is promoted during oxygen and amino acid depletion and protects LRS from degradation. Finally, elderly subjects have lower PHD1 levels and LRS activity in muscle from aged versus young human subjects. In conclusion, PHD1 ensures an optimal mTORC1 response to leucine after episodes of metabolic scarcity.
    DOI:  https://doi.org/10.1038/s41467-019-13889-6
  27. J Biol Chem. 2019 Dec 30. pii: jbc.RA119.011471. [Epub ahead of print]
    Joly JH, Delfarah A, Phung PS, Parrish S, Graham NA.
      Metabolic reprogramming in cancer cells can increase their dependence on metabolic substrates such as glucose. As such, the vulnerability of cancer cells to glucose deprivation creates an attractive opportunity for therapeutic intervention. Because it is not possible to starve tumors of glucose in vivo, here we sought to identify the mechanisms in glucose deprivation-induced cancer cell death and then designed inhibitor combinations to mimic glucose deprivation-induced cell death. Using metabolomic profiling, we found that cells undergoing glucose deprivation-induced cell death exhibited dramatic accumulation of intracellular L-cysteine and its oxidized dimer, L-cystine, and depletion of the antioxidant glutathione. Building on this observation, we show that glucose deprivation-induced cell death is driven not by lack of glucose, but rather by L-cystine import. Following glucose deprivation, the import of L-cystine and its subsequent reduction to L-cysteine depleted both NADPH and glutathione pools, thereby allowing toxic accumulation of reactive oxygen species. Consistent with this model, we found that the glutamate/cystine antiporter xCT is required for increased sensitivity to glucose deprivation. We searched for glycolytic enzymes whose expression is essential for survival of cancer cells with high xCT expression and identified glucose transporter type 1 (GLUT1). Testing a drug combination that co-targeted GLUT1 and glutathione synthesis, we found that this combination induces synthetic lethal cell death in high xCT-expressing cell lines susceptible to glucose deprivation. These results indicate that co-targeting GLUT1 and glutathione synthesis may offer a potential therapeutic approach for targeting tumors dependent on glucose for survival.
    Keywords:  L-cystine; NADPH; SLC7A11; Warburg effect; cancer biology; glucose metabolism; metabolomics; redox regulation
    DOI:  https://doi.org/10.1074/jbc.RA119.011471
  28. Sci Adv. 2019 Dec;5(12): eaay2118
    Rudler DL, Hughes LA, Perks KL, Richman TR, Kuznetsova I, Ermer JA, Abudulai LN, Shearwood AJ, Viola HM, Hool LC, Siira SJ, Rackham O, Filipovska A.
      Mammalian mitochondrial ribosomes are unique molecular machines that translate 11 leaderless mRNAs; however, it is not clear how mitoribosomes initiate translation, since mitochondrial mRNAs lack untranslated regions. Mitochondrial translation initiation shares similarities with prokaryotes, such as the formation of a ternary complex of fMet-tRNAMet, mRNA and the 28S subunit, but differs in the requirements for initiation factors. Mitochondria have two initiation factors: MTIF2, which closes the decoding center and stabilizes the binding of the fMet-tRNAMet to the leaderless mRNAs, and MTIF3, whose role is not clear. We show that MTIF3 is essential for survival and that heart- and skeletal muscle-specific loss of MTIF3 causes cardiomyopathy. We identify increased but uncoordinated mitochondrial protein synthesis in mice lacking MTIF3, resulting in loss of specific respiratory complexes. Ribosome profiling shows that MTIF3 is required for recognition and regulation of translation initiation of mitochondrial mRNAs and for coordinated assembly of OXPHOS complexes in vivo.
    DOI:  https://doi.org/10.1126/sciadv.aay2118
  29. Cell Death Differ. 2020 Jan 06.
    Liu W, Duan X, Xu L, Shang W, Zhao J, Wang L, Li JC, Chen CH, Liu JP, Tong C.
      The mitochondrion is a highly dynamic organelle that is critical for energy production and numerous metabolic processes. Drosophila Chchd2, a homolog of the human disease-related genes CHCHD2 and CHCHD10, encodes a mitochondrial protein. In this study, we found that loss of Chchd2 in flies resulted in progressive degeneration of photoreceptor cells and reduced muscle integrity. In the flight muscles of adult Chchd2 mutants, some mitochondria exhibited curling cristae and a reduced number of cristae compared to those of controls. Overexpression of Chchd2 carrying human disease-related point mutations failed to fully rescue the mitochondrial defects in Chchd2 mutants. In fat body cells, loss of Chchd2 resulted in fragmented mitochondria that could be partially rescued by Marf overexpression and enhanced by Opa1 RNAi. The expression level of Opa1 was reduced in Chchd2 mutants and increased when Chchd2 was overexpressed. The chaperone-like protein P32 co-immunoprecipitated with Chchd2 and YME1L, a protease known to processes human OPA1. Moreover, the interaction between P32 and YME1L enhanced YME1L activity and promoted Opa1 degradation. Finally, Chchd2 stabilized Opa1 by competing with P32 for YME1L binding. We propose a model whereby Chchd2 regulates mitochondrial morphology and tissue homeostasis by fine-tuning the levels of OPA1.
    DOI:  https://doi.org/10.1038/s41418-019-0482-7
  30. Autophagy. 2020 Jan 10.
    Dai E, Han L, Liu J, Xie Y, Kroemer G, Klionsky DJ, Zeh HJ, Kang R, Wang J, Tang D.
      KRAS is the most frequently mutated oncogene in human neoplasia. Despite a large investment to understand the effects of KRAS mutation in cancer cells, the direct effects of the oncogenetic KRAS activation on immune cells remain elusive. Here, we report that extracellular KRASG12D is essential for pancreatic tumor-associated macrophage polarization. Oxidative stress induces KRASG12D protein release from cancer cells succumbing to autophagy-dependent ferroptosis. Extracellular KRASG12D packaged into exosomes then is taken up by macrophages through an AGER-dependent mechanism. KRASG12D causes macrophages to switch to an M2-like pro-tumor phenotype via STAT3-dependent fatty acid oxidation. Consequently, the disruption of KRASG12D release and uptake can abolish the macrophage-mediated stimulation of pancreatic adenocarcinomas in mouse models. Importantly, the level of KRASG12D expression in macrophages correlates with poor survival in pancreatic cancer patients. These findings not only identify extracellular KRASG12D as a key mediator of cancer cell-macrophage communication, but also provide a novel KRAS-targeted anticancer strategy.
    Keywords:  AGER; DAMP; KRAS; autophagy; exosomes; ferroptosis; macrophage; pancreatic cancer
    DOI:  https://doi.org/10.1080/15548627.2020.1714209
  31. Nat Commun. 2020 Jan 10. 11(1): 180
    Charpentier JC, Chen D, Lapinski PE, Turner J, Grigorova I, Swanson JA, King PD.
      Macropinocytosis is an evolutionarily-conserved, large-scale, fluid-phase form of endocytosis that has been ascribed different functions including antigen presentation in macrophages and dendritic cells, regulation of receptor density in neurons, and regulation of tumor growth under nutrient-limiting conditions. However, whether macropinocytosis regulates the expansion of non-transformed mammalian cells is unknown. Here we show that primary mouse and human T cells engage in macropinocytosis that increases in magnitude upon T cell activation to support T cell growth even under amino acid (AA) replete conditions. Mechanistically, macropinocytosis in T cells provides access of extracellular AA to an endolysosomal compartment to sustain activation of the mechanistic target of rapamycin complex 1 (mTORC1) that promotes T cell growth. Our results thus implicate a function of macropinocytosis in mammalian cell growth beyond Ras-transformed tumor cells via sustained mTORC1 activation.
    DOI:  https://doi.org/10.1038/s41467-019-13997-3
  32. Nat Protoc. 2020 Jan 10.
    Ferreira F, Luxardi G, Reid B, Ma L, Raghunathan V, Zhao M.
      Reactive molecular oxygen (O2) plays important roles in bioenergetics and metabolism and is implicated in biochemical pathways underlying angiogenesis, fertilization, wound healing and regeneration. Here we describe how to use the scanning micro-optrode technique (SMOT) to measure extracellular fluxes of dissolved O2. The self-referencing O2-specific micro-optrode (also termed micro-optode and optical fiber microsensor) is a tapered optical fiber with an O2-sensitive fluorophore coated onto the tip. The O2 concentration is quantified by fluorescence quenching of the fluorophore emission upon excitation with blue-green light. The micro-optrode presents high spatial and temporal resolutions with improved signal-to-noise ratio (in the picomole range). In this protocol, we provide step-by-step instructions for micro-optrode calibration, validation, example applications and data analysis. We describe how to use the technique for cells (Xenopus oocyte), tissues (Xenopus epithelium and rat cornea), organs (Xenopus gills and mouse skin) and appendages (Xenopus tail), and provide recommendations on how to adapt the approach to different model systems. The basic, user-friendly system presented here can be readily installed to reliably and accurately measure physiological O2 fluxes in a wide spectrum of biological models and physiological responses. The full protocol can be performed in ~4 h.
    DOI:  https://doi.org/10.1038/s41596-019-0231-x
  33. Nature. 2020 Jan 08.
    Su J, Morgani SM, David CJ, Wang Q, Er EE, Huang YH, Basnet H, Zou Y, Shu W, Soni RK, Hendrickson RC, Hadjantonakis AK, Massagué J.
      Epithelial-to-mesenchymal transitions (EMTs) are phenotypic plasticity processes that confer migratory and invasive properties to epithelial cells during development, wound-healing, fibrosis and cancer1-4. EMTs are driven by SNAIL, ZEB and TWIST transcription factors5,6 together with microRNAs that balance this regulatory network7,8. Transforming growth factor β (TGF-β) is a potent inducer of developmental and fibrogenic EMTs4,9,10. Aberrant TGF-β signalling and EMT are implicated in the pathogenesis of renal fibrosis, alcoholic liver disease, non-alcoholic steatohepatitis, pulmonary fibrosis and cancer4,11. TGF-β depends on RAS and mitogen-activated protein kinase (MAPK) pathway inputs for the induction of EMTs12-19. Here we show how these signals coordinately trigger EMTs and integrate them with broader pathophysiological processes. We identify RAS-responsive element binding protein 1 (RREB1), a RAS transcriptional effector20,21, as a key partner of TGF-β-activated SMAD transcription factors in EMT. MAPK-activated RREB1 recruits TGF-β-activated SMAD factors to SNAIL. Context-dependent chromatin accessibility dictates the ability of RREB1 and SMAD to activate additional genes that determine the nature of the resulting EMT. In carcinoma cells, TGF-β-SMAD and RREB1 directly drive expression of SNAIL and fibrogenic factors stimulating myofibroblasts, promoting intratumoral fibrosis and supporting tumour growth. In mouse epiblast progenitors, Nodal-SMAD and RREB1 combine to induce expression of SNAIL and mesendoderm-differentiation genes that drive gastrulation. Thus, RREB1 provides a molecular link between RAS and TGF-β pathways for coordinated induction of developmental and fibrogenic EMTs. These insights increase our understanding of the regulation of epithelial plasticity and its pathophysiological consequences in development, fibrosis and cancer.
    DOI:  https://doi.org/10.1038/s41586-019-1897-5
  34. Mol Metab. 2020 Jan;pii: S2212-8778(19)30934-2. [Epub ahead of print]31 36-44
    Wang Y, Kwon H, Su X, Wondisford FE.
      OBJECTIVE: Fasting results in major metabolic changes including a switch from glycogenolysis to gluconeogenesis to maintain glucose homeostasis. However, the relationship between the length of fasting and the relative contribution of gluconeogenic substrates remains unclear. We investigated the relative contribution of glycogen, lactate, and glycerol in glucose production of male C57BL/6 J-albino mice after 6, 12, and 18 h of fasting.METHODS: We used non-perturbative infusions of 13C3 lactate, 13C3 glycerol, and 13C6 glucose combined with liquid chromatography mass spectrometry and metabolic flux analysis to study the contribution of substrates in gluconeogenesis (GNG).
    RESULTS: During infusion studies, both lactate and glycerol significantly label about 60% and 30-50% glucose carbon, respectively, but glucose labels much more lactate (∼90%) than glycerol carbon (∼10%). Our analyses indicate that lactate, but not glycerol is largely recycled during all fasting periods such that lactate is the largest direct contributor to GNG via the Cori cycle but a minor source of new glucose carbon (overall contribution). In contrast, glycerol is not only a significant direct contributor to GNG but also the largest overall contributor to GNG regardless of fasting length. Prolonged fasting decreases both the whole body turnover rate of glucose and lactate but increases that of glycerol, indicating that the usage of glycerol in GNG become more significant with longer fasting.
    CONCLUSION: Collectively, these findings suggest that glycerol is the dominant overall contributor of net glucose carbon in GNG during both short and prolonged fasting.
    Keywords:  Fasting; Gluconeogenesis; Glycerol; Metabolic flux analysis; Substrate contribution
    DOI:  https://doi.org/10.1016/j.molmet.2019.11.005