bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒11‒24
forty-three papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Cancer Res. 2019 Nov 19. pii: canres.0650.2019. [Epub ahead of print]
    Kaymak I, Maier CR, Schmitz W, Campbell AD, Dankworth B, Ade CP, Walz S, Paauwe M, Kalogirou C, Marouf H, Rosenfeldt MT, Gay DM, McGregor GH, Sansom OJ, Schulze A.
      Oncogene activation and loss of tumor suppressor function changes the metabolic activity of cancer cells to drive unrestricted proliferation. Moreover, cancer cells adapt their metabolism to sustain growth and survival when access to oxygen and nutrients is restricted, such as in poorly vascularized tumor areas. We show here that p53-deficient colon cancer cells exposed to tumor-like metabolic stress in spheroid culture activated the mevalonate pathway to promote the synthesis of ubiquinone. This was essential to maintain mitochondrial electron transport for respiration and pyrimidine synthesis in metabolically compromised environments. Induction of mevalonate pathway enzyme expression in the absence of p53 was mediated by accumulation and stabilization of mature SREBP2. Mevalonate pathway inhibition by statins blocked pyrimidine nucleotide biosynthesis and induced oxidative stress and apoptosis in p53-deficient cancer cells in spheroid culture. Moreover, ubiquinone produced by the mevalonate pathway was essential for the growth of p53-deficient tumor organoids. In contrast, inhibition of intestinal hyperproliferation by statins in an Apc/KrasG12D mutant mouse model was independent of de novo pyrimidine synthesis. Our results highlight the importance of the mevalonate pathway for maintaining mitochondrial electron transfer and biosynthetic activity in cancer cells exposed to metabolic stress. They also demonstrate that the metabolic output of this pathway depends on both genetic and environmental context.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-19-0650
  2. J Biol Chem. 2019 Nov 20. pii: jbc.RA119.010903. [Epub ahead of print]
    Liberti MV, Allen AE, Ramesh V, Dai Z, Singleton KR, Guo Z, Liu JO, Wood KC, Locasale JW.
      Aerobic glycolysis or the Warburg effect (WE) is characterized by increased glucose uptake and incomplete oxidation to lactate. Although the WE is ubiquitous, its biological role remains controversial and whether glucose metabolism is functionally different during fully oxidative glycolysis or during the WE is unknown. To investigate this question, here we evolved resistance to koningic acid (KA), a natural product that specifically inhibits glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a rate-controlling glycolytic enzyme during the WE. We found that KA-resistant cells lose the WE but continue to conduct glycolysis and surprisingly remain dependent on glucose as a carbon source and also on central carbon metabolism. Consequently, this altered state of glycolysis led to differential metabolic activity and requirements, including emergent activities in and dependencies on fatty acid metabolism. These findings reveal that aerobic glycolysis is a process functionally distinct from conventional glucose metabolism and leads to distinct metabolic requirements and biological functions.
    Keywords:  Warburg effect; cancer; glucose metabolism; glyceraldehyde-3-phosphate dehydrogenase GAPDH; glycolysis; mass spectrometry (MS); metabolic regulation; metabolic reprogramming; metabolomics; oxidative metabolism
    DOI:  https://doi.org/10.1074/jbc.RA119.010903
  3. Oxid Med Cell Longev. 2019 ;2019 1681254
    Granatiero V, Pacifici M, Raffaello A, De Stefani D, Rizzuto R.
      Neurodegenerative diseases are a large and heterogeneous group of disorders characterized by selective and progressive death of specific neuronal subtypes. In most of the cases, the pathophysiology is still poorly understood, although a number of hypotheses have been proposed. Among these, dysregulation of Ca2+ homeostasis and mitochondrial dysfunction represent two broadly recognized early events associated with neurodegeneration. However, a direct link between these two hypotheses can be drawn. Mitochondria actively participate to global Ca2+ signaling, and increases of [Ca2+] inside organelle matrix are known to sustain energy production to modulate apoptosis and remodel cytosolic Ca2+ waves. Most importantly, while mitochondrial Ca2+ overload has been proposed as the no-return signal, triggering apoptotic or necrotic neuronal death, until now direct evidences supporting this hypothesis, especially in vivo, are limited. Here, we took advantage of the identification of the mitochondrial Ca2+ uniporter (MCU) and tested whether mitochondrial Ca2+ signaling controls neuronal cell fate. We overexpressed MCU both in vitro, in mouse primary cortical neurons, and in vivo, through stereotaxic injection of MCU-coding adenoviral particles in the brain cortex. We first measured mitochondrial Ca2+ uptake using quantitative genetically encoded Ca2+ probes, and we observed that the overexpression of MCU causes a dramatic increase of mitochondrial Ca2+ uptake both at resting and after membrane depolarization. MCU-mediated mitochondrial Ca2+ overload causes alteration of organelle morphology and dysregulation of global Ca2+ homeostasis. Most importantly, MCU overexpression in vivo is sufficient to trigger gliosis and neuronal loss. Overall, we demonstrated that mitochondrial Ca2+ overload is per se sufficient to cause neuronal cell death both in vitro and in vivo, thus highlighting a potential key step in neurodegeneration.
    DOI:  https://doi.org/10.1155/2019/1681254
  4. Nat Commun. 2019 Nov 21. 10(1): 5284
    Fang EF, Hou Y, Lautrup S, Jensen MB, Yang B, SenGupta T, Caponio D, Khezri R, Demarest TG, Aman Y, Figueroa D, Morevati M, Lee HJ, Kato H, Kassahun H, Lee JH, Filippelli D, Okur MN, Mangerich A, Croteau DL, Maezawa Y, Lyssiotis CA, Tao J, Yokote K, Rusten TE, Mattson MP, Jasper H, Nilsen H, Bohr VA.
      Metabolic dysfunction is a primary feature of Werner syndrome (WS), a human premature aging disease caused by mutations in the gene encoding the Werner (WRN) DNA helicase. WS patients exhibit severe metabolic phenotypes, but the underlying mechanisms are not understood, and whether the metabolic deficit can be targeted for therapeutic intervention has not been determined. Here we report impaired mitophagy and depletion of NAD+, a fundamental ubiquitous molecule, in WS patient samples and WS invertebrate models. WRN regulates transcription of a key NAD+ biosynthetic enzyme nicotinamide nucleotide adenylyltransferase 1 (NMNAT1). NAD+ repletion restores NAD+ metabolic profiles and improves mitochondrial quality through DCT-1 and ULK-1-dependent mitophagy. At the organismal level, NAD+ repletion remarkably extends lifespan and delays accelerated aging, including stem cell dysfunction, in Caenorhabditis elegans and Drosophila melanogaster models of WS. Our findings suggest that accelerated aging in WS is mediated by impaired mitochondrial function and mitophagy, and that bolstering cellular NAD+ levels counteracts WS phenotypes.
    DOI:  https://doi.org/10.1038/s41467-019-13172-8
  5. Redox Biol. 2019 Nov 05. pii: S2213-2317(19)30884-5. [Epub ahead of print]28 101374
    Byrne FL, Olzomer EM, Marriott GR, Quek LE, Katen A, Su J, Nelson ME, Hart-Smith G, Larance M, Sebesfi VF, Cuff J, Martyn GE, Childress E, Alexopoulos SJ, Poon IK, Faux MC, Burgess AW, Reid G, McCarroll JA, Santos WL, Quinlan KG, Turner N, Fazakerley DJ, Kumar N, Hoehn KL.
      A hallmark of cancer cells is their ability to reprogram nutrient metabolism. Thus, disruption to this phenotype is a potential avenue for anti-cancer therapy. Herein we used a phenotypic chemical library screening approach to identify molecules that disrupted nutrient metabolism (by increasing cellular oxygen consumption rate) and were toxic to cancer cells. From this screen we discovered a 1,4-Naphthoquinone (referred to as BH10) that is toxic to a broad range of cancer cell types. BH10 has improved cancer-selective toxicity compared to doxorubicin, 17-AAG, vitamin K3, and other known anti-cancer quinones. BH10 increases glucose oxidation via both mitochondrial and pentose phosphate pathways, decreases glycolysis, lowers GSH:GSSG and NAPDH/NAPD+ ratios exclusively in cancer cells, and induces necrosis. BH10 targets mitochondrial redox defence as evidenced by increased mitochondrial peroxiredoxin 3 oxidation and decreased mitochondrial aconitase activity, without changes in markers of cytosolic or nuclear damage. Over-expression of mitochondria-targeted catalase protects cells from BH10-mediated toxicity, while the thioredoxin reductase inhibitor auranofin synergistically enhances BH10-induced peroxiredoxin 3 oxidation and cytotoxicity. Overall, BH10 represents a 1,4-Naphthoquinone with an improved cancer-selective cytotoxicity profile via its mitochondrial specificity.
    Keywords:  Cancer metabolism; Mitochondria; Peroxiredoxin; Quinone
    DOI:  https://doi.org/10.1016/j.redox.2019.101374
  6. Kidney Int. 2019 Sep 03. pii: S0085-2538(19)30846-4. [Epub ahead of print]
    Jang HS, Noh MR, Jung EM, Kim WY, Guda C, Foster KW, Oupicky D, Ferrer FA, Padanilam BJ.
      Regardless of the etiology, acute kidney injury involves aspects of mitochondrial dysfunction and ATP depletion. Fatty acid oxidation is the preferred energy source of the kidney and is inhibited during acute kidney injury. A pivotal role for the mitochondrial matrix protein, cyclophilin D in regulating overall cell metabolism is being unraveled. We hypothesize that mitochondrial interaction of proximal tubule cyclophilin D and the transcription factor PPARα modulate fatty acid beta-oxidation in cisplatin-induced acute kidney injury. Cisplatin injury resulted in histological and functional damage in the kidney with downregulation of fatty acid oxidation genes and increase of intrarenal lipid accumulation. However, proximal tubule-specific deletion of cyclophilin D protected the kidneys from the aforementioned effects. Mitochondrial translocation of PPARα, its binding to cyclophilin D, and sequestration led to inhibition of its nuclear translocation and transcription of PPARα-regulated fatty acid oxidation genes during cisplatin-induced acute kidney injury. Genetic or pharmacological inhibition of cyclophilin D preserved nuclear expression and transcriptional activity of PPARα and prevented the impairment of fatty acid oxidation and intracellular lipid accumulation. Docking analysis identified potential binding sites between PPARα and cyclophilin D. Thus, our results indicate that proximal tubule cyclophilin D elicits impaired mitochondrial fatty acid oxidation via mitochondrial interaction between cyclophilin D and PPARα. Hence, targeting their interaction may be a potential therapeutic strategy to prevent energy depletion, lipotoxicity and cell death in cisplatin-induced acute kidney injury.
    Keywords:  ATP depletion; acute kidney injury; chemotherapy; cisplatin nephrotoxicity; mitochondria; proximal tubule
    DOI:  https://doi.org/10.1016/j.kint.2019.08.019
  7. Nat Struct Mol Biol. 2019 Nov 18.
    Tucker K, Park E.
      Nearly all mitochondrial proteins are encoded by the nuclear genome and imported into mitochondria after synthesis on cytosolic ribosomes. These precursor proteins are translocated into mitochondria by the TOM complex, a protein-conducting channel in the mitochondrial outer membrane. We have determined high-resolution cryo-EM structures of the core TOM complex from Saccharomyces cerevisiae in dimeric and tetrameric forms. Dimeric TOM consists of two copies each of five proteins arranged in two-fold symmetry: pore-forming β-barrel protein Tom40 and four auxiliary α-helical transmembrane proteins. The pore of each Tom40 has an overall negatively charged inner surface attributed to multiple functionally important acidic patches. The tetrameric complex is essentially a dimer of dimeric TOM, which may be capable of forming higher-order oligomers. Our study reveals the detailed molecular organization of the TOM complex and provides new insights about the mechanism of protein translocation into mitochondria.
    DOI:  https://doi.org/10.1038/s41594-019-0339-2
  8. Cell Death Differ. 2018 Jan;25(1): 169-179
    Wu D, Prives C.
      In response to varying stress signals, the p53 tumor suppressor is able to promote repair, survival, or elimination of damaged cells - processes that have great relevance to organismal aging. Although the link between p53 and cancer is well established, the contribution of p53 to the aging process is less clear. Delineating how p53 regulates distinct aging hallmarks such as cellular senescence, genomic instability, mitochondrial dysfunction, and altered metabolic pathways will be critical. Mouse models have further revealed the centrality and complexity of the p53 network in aging processes. While naturally aged mice have linked longevity with declining p53 function, some accelerated aging mice present with chronic p53 activation, whose phenotypes can be rescued upon p53 deficiency. Further, direct modulation of the p53-MDM2 axis has correlated elevated p53 activity with either early aging or with delayed-onset aging. We speculate that p53-mediated aging phenotypes in these mice must have (1) stably active p53 due to MDM2 dysregulation or chronic stress or (2) shifted p53 outcomes. Pinpointing which p53 stressors, modifications, and outcomes drive aging processes will provide further insights into our understanding of the human aging process and could have implications for both cancer and aging therapeutics.
    DOI:  https://doi.org/10.1038/cdd.2017.187
  9. Biochem Biophys Res Commun. 2019 Nov 14. pii: S0006-291X(19)32181-3. [Epub ahead of print]
    Cho JH, Lee YM, Bae SH, Chou JY.
      Hepatocellular adenoma/carcinoma (HCA/HCC) is a long-term complication of the metabolic disorder glycogen storage disease type Ia (GSD-Ia) deficient in glucose-6-phosphatase-α (G6PC or G6Pase-α). We have shown previously that hepatic G6Pase-α deficiency leads to autophagy impairment, mitochondrial dysfunction, enhanced glycolysis, and augmented hexose monophosphate shunt, all of which can contribute to hepatocarcinogenesis. However, the mechanism underlying HCA/HCC development in GSD-Ia remains unclear. We now show that G6Pase-α deficiency-mediated hepatic autophagy impairment leads to sustained accumulation of an autophagy-specific substrate p62 which can activate tumor-promoting pathways including nuclear factor erythroid 2-related factor 2 (Nrf2) and mammalian target of rapamycin complex 1 (mTORC1). Consistently, the HCA/HCC lesions developed in the G6Pase-α-deficient livers display marked accumulation of p62 aggregates and phosphorylated p62 along with activation of Nrf2 and mTORC1 signaling. Furthermore, the HCA/HCC lesions exhibit activation of additional oncogenic pathways, β-catenin and Yes-associated protein (YAP) which is implicated in autophagy impairment. Intriguingly, hepatic levels of glucose-6-phosphate and glycogen which are accumulated in the G6Pase-α-deficient livers were significantly lower in HCC than those in HCA. Conversely, compared to HCA, the HCC lesion display increased expression of many oncogenes and the M2 isoform of pyruvate kinase (PKM2), a glycolytic enzyme critical for aerobic glycolysis and tumorigenesis. Collectively, our data show that hepatic G6Pase-α-deficiency leads to persistent autophagy impairment and activation of multiple tumor-promoting pathways that contribute to HCA/HCC development in GSD-Ia.
    Keywords:  Autophagy impairment; Liver cancer; Metabolism; p62 accumulation
    DOI:  https://doi.org/10.1016/j.bbrc.2019.11.061
  10. Nat Cell Biol. 2019 Nov 18.
    Pathria G, Lee JS, Hasnis E, Tandoc K, Scott DA, Verma S, Feng Y, Larue L, Sahu AD, Topisirovic I, Ruppin E, Ronai ZA.
      While amino acid restriction remains an attractive strategy for cancer therapy, metabolic adaptations limit its effectiveness. Here we demonstrate a role of translational reprogramming in the survival of asparagine-restricted cancer cells. Asparagine limitation in melanoma and pancreatic cancer cells activates receptor tyrosine kinase-MAPK signalling as part of a feedforward mechanism involving mammalian target of rapamycin complex 1 (mTORC1)-dependent increase in MAPK-interacting kinase 1 (MNK1) and eukaryotic translation initiation factor 4E (eIF4E), resulting in enhanced translation of activating transcription factor 4 (ATF4) mRNA. MAPK inhibition attenuates translational induction of ATF4 and the expression of its target asparagine synthetase (ASNS), sensitizing melanoma and pancreatic tumours to asparagine restriction, reflected in inhibition of their growth. Correspondingly, low ASNS expression is among the top predictors of response to inhibitors of MAPK signalling in patients with melanoma and is associated with favourable prognosis when combined with low MAPK signalling activity. These studies reveal an axis of adaptation to asparagine deprivation and present a rationale for clinical evaluation of MAPK inhibitors in combination with asparagine restriction approaches.
    DOI:  https://doi.org/10.1038/s41556-019-0415-1
  11. JCI Insight. 2019 Nov 21. pii: 132975. [Epub ahead of print]
    Martí I Líndez AA, Dunand-Sauthier I, Conti M, Gobet F, Núñez N, Hannich JT, Riezman H, Roger G, Piersigilli A, Hahn K, Lemeille S, Becher B, De Smedt T, Hugues S, Reith W.
      As sufficient extracellular arginine is crucial for T cell function, depletion of extracellular arginine by elevated Arginase 1 (Arg1) activity has emerged as a hallmark immunosuppressive mechanism. However, the potential cell-autonomous roles of arginases in T cells have remained unexplored. Here we show that the arginase isoform expressed by T cells, the mitochondrial Arginase 2 (Arg2), is a cell-intrinsic regulator of CD8+ T cell activity. Both germ-line Arg2 deletion and adoptive transfer of Arg2-/- CD8+ T cells significantly reduced tumor growth in preclinical cancer models by enhancing CD8+ T cell activation, effector function and persistence. Transcriptomic, proteomic and high-dimensional flow cytometry characterization revealed a CD8+ T cell-intrinsic role of Arg2 in modulating T cell activation, anti-tumor cytoxicity and memory formation, independently of extracellular arginine availability. Furthermore, specific deletion of Arg2 in CD8+ T cells strongly synergized with PD-1 blockade for the control of tumor growth and animal survival. These observations coupled with the finding that pharmacologic arginase inhibition accelerates activation of ex vivo human T cells unveil Arg2 as a new therapeutic target for T cell-based cancer therapies.
    Keywords:  Amino acid metabolism; Cancer immunotherapy; Immunology; Mitochondria; Oncology
    DOI:  https://doi.org/10.1172/jci.insight.132975
  12. Immunity. 2019 Nov 19. pii: S1074-7613(19)30374-7. [Epub ahead of print]51(5): 856-870.e5
    Ma EH, Verway MJ, Johnson RM, Roy DG, Steadman M, Hayes S, Williams KS, Sheldon RD, Samborska B, Kosinski PA, Kim H, Griss T, Faubert B, Condotta SA, Krawczyk CM, DeBerardinis RJ, Stewart KM, Richer MJ, Chubukov V, Roddy TP, Jones RG.
      Naive CD8+ T cells differentiating into effector T cells increase glucose uptake and shift from quiescent to anabolic metabolism. Although much is known about the metabolism of cultured T cells, how T cells use nutrients during immune responses in vivo is less well defined. Here, we combined bioenergetic profiling and 13C-glucose infusion techniques to investigate the metabolism of CD8+ T cells responding to Listeria infection. In contrast to in vitro-activated T cells, which display hallmarks of Warburg metabolism, physiologically activated CD8+ T cells displayed greater rates of oxidative metabolism, higher bioenergetic capacity, differential use of pyruvate, and prominent flow of 13C-glucose carbon to anabolic pathways, including nucleotide and serine biosynthesis. Glucose-dependent serine biosynthesis mediated by the enzyme Phgdh was essential for CD8+ T cell expansion in vivo. Our data highlight fundamental differences in glucose use by pathogen-specific T cells in vivo, illustrating the impact of environment on T cell metabolic phenotypes.
    DOI:  https://doi.org/10.1016/j.immuni.2019.09.003
  13. Mol Cell. 2019 Nov 05. pii: S1097-2765(19)30793-2. [Epub ahead of print]
    Zhu Y, Gu L, Lin X, Liu C, Lu B, Cui K, Zhou F, Zhao Q, Prochownik EV, Fan C, Li Y.
      PGAM5 is a mitochondrial serine/threonine phosphatase that regulates multiple metabolic pathways and contributes to tumorigenesis in a poorly understood manner. We show here that PGAM5 inhibition attenuates lipid metabolism and colorectal tumorigenesis in mice. PGAM5-mediated dephosphorylation of malic enzyme 1 (ME1) at S336 allows increased ACAT1-mediated K337 acetylation, leading to ME1 dimerization and activation, both of which are reversed by NEK1 kinase-mediated S336 phosphorylation. SIRT6 deacetylase antagonizes ACAT1 function in a manner that involves mutually exclusive ME1 S336 phosphorylation and K337 acetylation. ME1 also promotes nicotinamide adenine dinucleotide phosphate (NADPH) production, lipogenesis, and colorectal cancers in which ME1 transcripts are upregulated and ME1 protein is hypophosphorylated at S336 and hyperacetylated at K337. PGAM5 and ME1 upregulation occur via direct transcriptional activation mediated by β-catenin/TCF1. Thus, the balance between PGAM5-mediated dephosphorylation of ME1 S336 and ACAT1-mediated acetylation of K337 strongly influences NADPH generation, lipid metabolism, and the susceptibility to colorectal tumorigenesis.
    DOI:  https://doi.org/10.1016/j.molcel.2019.10.015
  14. Nat Commun. 2019 Nov 21. 10(1): 5277
    Lin Y, Li LL, Nie W, Liu X, Adler A, Xiao C, Lu F, Wang L, Han H, Wang X, Gan WB, Cheng H.
      Mitochondrial calcium ([Ca2+]mito) dynamics plays vital roles in regulating fundamental cellular and organellar functions including bioenergetics. However, neuronal [Ca2+]mito dynamics in vivo and its regulation by brain activity are largely unknown. By performing two-photon Ca2+ imaging in the primary motor (M1) and visual cortexes (V1) of awake behaving mice, we find that discrete [Ca2+]mito transients occur synchronously over somatic and dendritic mitochondrial network, and couple with cytosolic calcium ([Ca2+]cyto) transients in a probabilistic, rather than deterministic manner. The amplitude, duration, and frequency of [Ca2+]cyto transients constitute important determinants of the coupling, and the coupling fidelity is greatly increased during treadmill running (in M1 neurons) and visual stimulation (in V1 neurons). Moreover, Ca2+/calmodulin kinase II is mechanistically involved in modulating the dynamic coupling process. Thus, activity-dependent dynamic [Ca2+]mito-to-[Ca2+]cyto coupling affords an important mechanism whereby [Ca2+]mito decodes brain activity for the regulation of mitochondrial bioenergetics to meet fluctuating neuronal energy demands as well as for neuronal information processing.
    DOI:  https://doi.org/10.1038/s41467-019-13142-0
  15. Diabetes. 2019 Nov 18. pii: db190379. [Epub ahead of print]
    Taddeo EP, Alsabeeh N, Baghdasarian S, Wikstrom JD, Ritou E, Sereda S, Erion K, Li J, Stiles L, Abdulla M, Swanson Z, Wilhelm J, Bellin MD, Kibbey RG, Liesa M, Shirihai O.
      Fasting hyperinsulinemia precedes the development of type 2 diabetes. However, it is unclear whether fasting insulin hypersecretion is a primary driver of insulin resistance or a consequence of the progressive increase in fasting glycemia induced by insulin resistance in the pre-diabetic state. Herein, we have discovered a mechanism specifically regulating non-glucose stimulated insulin secretion (NGSIS) in pancreatic islets that is activated by non-esterified free fatty acids, the major fuel utilized by beta cells during fasting. We show that the mitochondrial permeability transition pore regulator Cyclophilin D (CypD) promotes NGSIS, but not glucose-stimulated insulin secretion (GSIS), by increasing mitochondrial proton leak. Islets from pre-diabetic obese mice show significantly higher CypD-dependent proton leak and NGSIS compared to lean mice. Proton leak-mediated NGSIS is conserved in human islets and is stimulated by exposure to non-esterified free fatty acids at concentrations observed in obese subjects. Mechanistically, proton leak activates islet NGSIS independently of mitochondrial ATP synthesis but ultimately requires closure of the KATP channel. In summary, we have described a novel non-esterified free fatty acid-stimulated pathway selectively driving pancreatic islet NGSIS, which may be therapeutically exploited as an alternative way to halt fasting hyperinsulinemia and the progression of type 2 diabetes.
    DOI:  https://doi.org/10.2337/db19-0379
  16. Mol Cell. 2019 Oct 30. pii: S1097-2765(19)30792-0. [Epub ahead of print]
    Vivas-García Y, Falletta P, Liebing J, Louphrasitthiphol P, Feng Y, Chauhan J, Scott DA, Glodde N, Chocarro-Calvo A, Bonham S, Osterman AL, Fischer R, Ronai Z, García-Jiménez C, Hölzel M, Goding CR.
      Phenotypic and metabolic heterogeneity within tumors is a major barrier to effective cancer therapy. How metabolism is implicated in specific phenotypes and whether lineage-restricted mechanisms control key metabolic vulnerabilities remain poorly understood. In melanoma, downregulation of the lineage addiction oncogene microphthalmia-associated transcription factor (MITF) is a hallmark of the proliferative-to-invasive phenotype switch, although how MITF promotes proliferation and suppresses invasion is poorly defined. Here, we show that MITF is a lineage-restricted activator of the key lipogenic enzyme stearoyl-CoA desaturase (SCD) and that SCD is required for MITFHigh melanoma cell proliferation. By contrast MITFLow cells are insensitive to SCD inhibition. Significantly, the MITF-SCD axis suppresses metastasis, inflammatory signaling, and an ATF4-mediated feedback loop that maintains de-differentiation. Our results reveal that MITF is a lineage-specific regulator of metabolic reprogramming, whereby fatty acid composition is a driver of melanoma phenotype switching, and highlight that cell phenotype dictates the response to drugs targeting lipid metabolism.
    Keywords:  ATF4; MITF; fatty acid saturation; melanoma; metastatic dissemination; phenotype switching; stearoyl CoA desaturase
    DOI:  https://doi.org/10.1016/j.molcel.2019.10.014
  17. Nature. 2019 Nov 20.
    Galmozzi A, Kok BP, Kim AS, Montenegro-Burke JR, Lee JY, Spreafico R, Mosure S, Albert V, Cintron-Colon R, Godio C, Webb WR, Conti B, Solt LA, Kojetin D, Parker CG, Peluso JJ, Pru JK, Siuzdak G, Cravatt BF, Saez E.
      Haem is an essential prosthetic group of numerous proteins and a central signalling molecule in many physiologic processes1,2. The chemical reactivity of haem means that a network of intracellular chaperone proteins is required to avert the cytotoxic effects of free haem, but the constituents of such trafficking pathways are unknown3,4. Haem synthesis is completed in mitochondria, with ferrochelatase adding iron to protoporphyrin IX. How this vital but highly reactive metabolite is delivered from mitochondria to haemoproteins throughout the cell remains poorly defined3,4. Here we show that progesterone receptor membrane component 2 (PGRMC2) is required for delivery of labile, or signalling haem, to the nucleus. Deletion of PGMRC2 in brown fat, which has a high demand for haem, reduced labile haem in the nucleus and increased stability of the haem-responsive transcriptional repressors Rev-Erbα and BACH1. Ensuing alterations in gene expression caused severe mitochondrial defects that rendered adipose-specific PGRMC2-null mice unable to activate adaptive thermogenesis and prone to greater metabolic deterioration when fed a high-fat diet. By contrast, obese-diabetic mice treated with a small-molecule PGRMC2 activator showed substantial improvement of diabetic features. These studies uncover a role for PGRMC2 in intracellular haem transport, reveal the influence of adipose tissue haem dynamics on physiology and suggest that modulation of PGRMC2 may revert obesity-linked defects in adipocytes.
    DOI:  https://doi.org/10.1038/s41586-019-1774-2
  18. Mol Cell. 2019 Nov 06. pii: S1097-2765(19)30794-4. [Epub ahead of print]
    Odle RI, Walker SA, Oxley D, Kidger AM, Balmanno K, Gilley R, Okkenhaug H, Florey O, Ktistakis NT, Cook SJ.
      Since nuclear envelope breakdown occurs during mitosis in metazoan cells, it has been proposed that macroautophagy must be inhibited to maintain genome integrity. However, repression of macroautophagy during mitosis remains controversial and mechanistic detail limited to the suggestion that CDK1 phosphorylates VPS34. Here, we show that initiation of macroautophagy, measured by the translocation of the ULK complex to autophagic puncta, is repressed during mitosis, even when mTORC1 is inhibited. Indeed, mTORC1 is inactive during mitosis, reflecting its failure to localize to lysosomes due to CDK1-dependent RAPTOR phosphorylation. While mTORC1 normally represses autophagy via phosphorylation of ULK1, ATG13, ATG14, and TFEB, we show that the mitotic phosphorylation of these autophagy regulators, including at known repressive sites, is dependent on CDK1 but independent of mTOR. Thus, CDK1 substitutes for inhibited mTORC1 as the master regulator of macroautophagy during mitosis, uncoupling autophagy regulation from nutrient status to ensure repression of macroautophagy during mitosis.
    Keywords:  ATG13; ATG14; CDK1; RAPTOR; TFEB; ULK1; autophagy; mTOR; mitosis
    DOI:  https://doi.org/10.1016/j.molcel.2019.10.016
  19. Biochem Biophys Res Commun. 2019 Nov 19. pii: S0006-291X(19)32147-3. [Epub ahead of print]
    Bo T, Yamamori T, Yamamoto K, Fujimoto M, Yasui H, Inanami O.
      Mitochondrial dynamics are crucial for cellular survival in response to various stresses. Previously, we reported that Drp1 promoted mitochondrial fission after x-irradiation and its inhibition resulted in reduced cellular radiosensitivity and mitotic catastrophe. However, the mechanisms of radiation-induced mitotic catastrophe related to mitochondrial fission remain unclear. In this study, we investigated the involvement of cellular ATP production, ROS generation, and Ca2+ levels in mitotic catastrophe in EMT6 cells. Knockdown of Drp1 and Fis1, which are mitochondrial fission regulators, resulted in elongated mitochondria and significantly attenuated cellular radiosensitivity. Reduced mitochondrial fission mainly decreased mitotic catastrophe rather than necrosis and apoptosis after irradiation. Cellular ATP contents in Drp1 and Fis1 knockdown cells were similar to those in control cells. N-acetylcysteine and 2-glucopyranoside ascorbic acid have no effect on mitotic catastrophe after irradiation. The cellular [Ca2+]i level increased after irradiation, which was completely suppressed by Drp1 and Fis1 inhibition. Furthermore, BAPTA-AM significantly reduced radiation-induced mitotic catastrophe, indicating that cellular Ca2+ is a key mediator of mitotic catastrophe induction after irradiation. These results suggest that mitochondrial fission is associated with radiation-induced mitotic catastrophe via cytosolic Ca2+ regulation.
    Keywords:  Ca(2+); Calcium regulation; Fission; Mitochondria; Mitotic catastrophe; Radiation
    DOI:  https://doi.org/10.1016/j.bbrc.2019.11.027
  20. Nat Chem Biol. 2019 Dec;15(12): 1232-1240
    Cao Y, Qiu T, Kathayat RS, Azizi SA, Thorne AK, Ahn D, Fukata Y, Fukata M, Rice PA, Dickinson BC.
      S-Palmitoylation is a reversible lipid post-translational modification that has been observed on mitochondrial proteins, but both the regulation and functional consequences of mitochondrial S-palmitoylation are poorly understood. Here, we show that perturbing the 'erasers' of S-palmitoylation, acyl protein thioesterases (APTs), with either pan-active inhibitors or a mitochondrial-targeted APT inhibitor, diminishes the antioxidant buffering capacity of mitochondria. Surprisingly, this effect was not mediated by the only known mitochondrial APT, but rather by a resident mitochondrial protein with no known endogenous function, ABHD10. We show that ABHD10 is a member of the APT family of regulatory proteins and identify peroxiredoxin-5 (PRDX5), a key antioxidant protein, as a target of ABHD10 S-depalmitoylase activity. We then find that ABHD10 regulates the S-palmitoylation status of the nucleophilic active site residue of PRDX5, providing a direct mechanistic connection between ABHD10-mediated S-depalmitoylation of PRDX5 and its antioxidant capacity.
    DOI:  https://doi.org/10.1038/s41589-019-0399-y
  21. J Clin Invest. 2019 Nov 18. pii: 132532. [Epub ahead of print]
    Zelinger L, Swaroop A.
      Mitochondrial dysfunction or loss is evident in neurodegenerative diseases. Furthermore, mitochondrial DNA (mtDNA) mutations associated with NADH dehydrogenase subunits and nuclear gene mutations that affect mitochondrial function result in optic neuropathies. In this issue of the JCI, Del Dotto et al. and Piro-Mégy et al. identify heterozygous mutations in nuclear-encoded mitochondrial single-strand binding protein 1 (SSBP1) in patients with apparently dominant optic neuropathy with or without extraocular phenotypes. Both research groups reported similar mitochondrial findings in response to SSBP1 mutations. However, the specific SSBP1 mitochondria-associated function in retinal ganglion cells (RGCs) and the resulting optic nerve remains unclear. We suggest that high expression of SSBP1 during RGC differentiation is critical for mtDNA maintenance to produce appropriate optic nerve connectivity and that SSBP1 mutations in dominant optic atrophy patients do not permit stable binding to N6-methyldeoxyadenosine on the heavy strand involved with replication, leading to disruptions of mtDNA and, eventually, optic nerve dysfunction.
    DOI:  https://doi.org/10.1172/JCI132532
  22. Biochim Biophys Acta Gen Subj. 2019 Nov 14. pii: S0304-4165(19)30273-9. [Epub ahead of print] 129484
    Rumping L, Pras-Raves ML, Gerrits J, Tang YF, Willemsen MA, Houwen RHJ, van Haaften G, van Hasselt PM, Verhoeven-Duif NM, Jans JJM.
      BACKGROUND: High glutaminase (GLS;EC3.5.1.2) activity is an important pathophysiological phenomenon in tumorigenesis and metabolic disease. Insight into the metabolic consequences of high GLS activity contributes to the understanding of the pathophysiology of both oncogenic pathways and inborn errors of glutamate metabolism. Glutaminase catalyzes the conversion of glutamine into glutamate, thereby interconnecting many metabolic pathways.METHODS: We developed a HEK293-based cell-model that enables tuning of GLS activity by combining the expression of a hypermorphic GLS variant with incremental GLS inhibition. The metabolic consequences of increasing GLS activity were studied by metabolic profiling using Direct-Infusion High-Resolution Mass-Spectrometry (DI-HRMS).
    RESULTS AND CONCLUSIONS: Of 12,437 detected features [m/z], 109 features corresponding to endogenously relevant metabolites were significantly affected by high GLS activity. As expected, these included strongly decreased glutamine and increased glutamate levels. Additionally, increased levels of tricarboxylic acid (TCA) intermediates with a truncation of the TCA cycle at the level of citrate were detected as well as increased metabolites of transamination reactions, proline and ornithine synthesis and GABA metabolism. Levels of asparagine and nucleotide metabolites showed the same dependence on GLS activity as glutamine. Of the nucleotides, especially metabolites of the pyrimidine thymine metabolism were negatively impacted by high GLS activity, which is remarkable since their synthesis depend both on aspartate (product of glutamate) and glutamine levels. Metabolites of the glutathione synthesizing γ-glutamyl-cycle were either decreased or unaffected.
    GENERAL SIGNIFICANCE: By providing a metabolic fingerprint of increasing GLS activity, this study shows the large impact of high glutaminase activity on the cellular metabolome.
    Keywords:  DI-HRMS; Glutamate metabolism; Glutaminase activity; Metabolic profiling; Untargeted metabolomics
    DOI:  https://doi.org/10.1016/j.bbagen.2019.129484
  23. Trends Cell Biol. 2019 Nov 18. pii: S0962-8924(19)30195-3. [Epub ahead of print]
    Nesci S, Trombetti F, Pagliarani A.
      The enzyme nicotinamide nucleotide transhydrogenase (NNT) transfers hydride from NADH to NADP+ coupled to H+ translocation across the inner mitochondrial membrane. In a recent study, Kampjut and Sazanov reveal that the bifunctional NNT mechanism rules the NAD(P)+/NAD(P)H interconversion ratio, which in turn regulates antioxidant defense and sirtuin actions.
    Keywords:  NAD(P)(+)/NAD(P)H ratio; antioxidant defense; mitochondria; nicotinamide nucleotide transhydrogenase; sirtuins
    DOI:  https://doi.org/10.1016/j.tcb.2019.11.001
  24. Anal Chem. 2019 Nov 19.
    Zou X, Shi Y, Zhu R, Han J, Han S.
      Mitochondrial DNA (mtDNA) plays important roles in diverse physiological processes and myriad diseases. We herein report mtDNA imaging with a chameleon sensor containing a cationic rhodamine B (RB) entity for mitochondria targeting and a fluorogenic SYBR Green-I (SG) entity for DNA sensing. SG-RB selectively binds to mtDNA and gives green SG fluorescence in mitochondria of living cells but gives red RB fluorescence upon delivery of mitochondria into lysosomes in mitophagy. With the dual color imaging, mtDNA aggregation and elevated mitophagy were identified in HeLa cells stressed with anticancer doxorubicin. These results suggest the utility of organelle-redirected DNA sensors for live cell imaging of mtDNA involved in myriad pathological disorders.
    DOI:  https://doi.org/10.1021/acs.analchem.9b04364
  25. Cancer Lett. 2019 Nov 13. pii: S0304-3835(19)30568-3. [Epub ahead of print]
    Robinson AD, Eich ML, Varambally S.
      Cancer is a disease of uncontrolled cell growth and a major cause of death worldwide. Many molecular events characterize tumor initiation and progression. Global gene expression analyses using next-generation sequencing, proteomics and metabolomics show genomic, epigenetic, and metabolite concentration changes in various tumors. Molecular alterations identified include multiple cancer-driving mutations, gene fusions, amplifications, deletions, and post-translational modifications. Data integration from many high-throughput platforms unraveled dysregulation in many metabolic pathways in cancer. Since cancer cells are fast-growing, their metabolic needs are enhanced, hence the requirement for de novo synthesis of essential metabolites. One critical requirement of fast-growing cells and a historically important pathway in cancer is the nucleotide biosynthetic pathway and its enzymes are valuable targets for small molecule inhibition. Purines and pyrimidines are building blocks of DNA synthesis and due to their excessive growth, cancer cells extensively utilize de novo pathways for nucleotide biosynthesis. Methotrexate, one of the early chemotherapeutic agents, targets dihydrofolate reductase of the folate metabolic pathway that is involved in nucleotide biosynthesis. In this review, we discuss the nucleotide biosynthetic pathways in cancer and targeting opportunities.
    Keywords:  energetics; folate; one carbon metabolism; purine; pyrimidine
    DOI:  https://doi.org/10.1016/j.canlet.2019.11.013
  26. PLoS Pathog. 2019 Nov;15(11): e1008008
    Voleman L, Doležal P.
      The shape and number of mitochondria respond to the metabolic needs during the cell cycle of the eukaryotic cell. In the best-studied model systems of animals and fungi, the cells contain many mitochondria, each carrying its own nucleoid. The organelles, however, mostly exist as a dynamic network, which undergoes constant cycles of division and fusion. These mitochondrial dynamics are driven by intricate protein machineries centered around dynamin-related proteins (DRPs). Here, we review recent advances on the dynamics of mitochondria and mitochondrion-related organelles (MROs) of parasitic protists. In contrast to animals and fungi, many parasitic protists from groups of Apicomplexa or Kinetoplastida carry only a single mitochondrion with a single nucleoid. In these groups, mitochondrial division is strictly coupled to the cell cycle, and the morphology of the organelle responds to the cell differentiation during the parasite life cycle. On the other hand, anaerobic parasitic protists such as Giardia, Entamoeba, and Trichomonas contain multiple MROs that have lost their organellar genomes. We discuss the function of DRPs, the occurrence of mitochondrial fusion, and mitophagy in the parasitic protists from the perspective of eukaryote evolution.
    DOI:  https://doi.org/10.1371/journal.ppat.1008008
  27. J Allergy Clin Immunol. 2019 Nov 15. pii: S0091-6749(19)31520-9. [Epub ahead of print]
    Galle-Treger L, Hurrell BP, Lewis G, Howard E, Jahani PS, Banie H, Razani B, Soroosh P, Akbari O.
      BACKGROUND: Allergic asthma is a chronic inflammatory disorder that is characterized with airway hyperreactivity (AHR) and driven by Th2 cytokine production. Group 2 innate lymphoid cells (ILC2s) secrete high amount of Th2 cytokines and contribute to the development of AHR. Autophagy is a cellular degradation pathway that recycles cytoplasmic content. However, the role of autophagy in ILC2s remains to be fully elucidated.OBJECTIVE: We characterized the effects of autophagy deficiency on ILC2 effector functions and metabolic balance.
    METHODS: ILC2s from autophagy deficient mice were isolated to evaluate proliferation, apoptosis, cytokine secretion, gene expression and cell metabolism. Also, autophagy deficient ILC2s were adoptively transferred into Rag-/-GC-/- mice, which were them challenged with IL-33 and assessed for airway hyperreactivity and lung inflammation.
    RESULTS: We demonstrate that autophagy is extensively used by activated ILC2s to maintain their homeostasis and effector functions. Deletion of the critical autophagy gene Atg5 resulted in decreased cytokine secretion and increased apoptosis. Moreover, lack of autophagy among ILC2s impaired their ability to utilize fatty acid oxidation and strikingly promoted glycolysis as evidenced by our transcriptomic and metabolite analyses. This shift of fuel dependency led to impaired homeostasis and Th2 cytokine production, thus inhibiting the development of ILC2-mediated AHR. Notably, this metabolic reprogramming was also associated with an accumulation of dysfunctional mitochondria producing excessive reactive oxygen species.
    CONCLUSION: These findings provide new insights into the metabolic profile of ILC2s and suggest that modulation of fuel dependency by autophagy is a potentially new therapeutic approach to target ILC2 dependent inflammation.
    Keywords:  Airway hyperreactivity; Autophagy; ILC2; Immune metabolism
    DOI:  https://doi.org/10.1016/j.jaci.2019.10.035
  28. Aging Cell. 2019 Nov 18. e13072
    Kim DE, Dollé MET, Vermeij WP, Gyenis A, Vogel K, Hoeijmakers JHJ, Wiley CD, Davalos AR, Hasty P, Desprez PY, Campisi J.
      ERCC1 (excision repair cross complementing-group 1) is a mammalian endonuclease that incises the damaged strand of DNA during nucleotide excision repair and interstrand cross-link repair. Ercc1-/Δ mice, carrying one null and one hypomorphic Ercc1 allele, have been widely used to study aging due to accelerated aging phenotypes in numerous organs and their shortened lifespan. Ercc1-/Δ mice display combined features of human progeroid and cancer-prone syndromes. Although several studies report cellular senescence and apoptosis associated with the premature aging of Ercc1-/Δ mice, the link between these two processes and their physiological relevance in the phenotypes of Ercc1-/Δ mice are incompletely understood. Here, we show that ERCC1 depletion, both in cultured human fibroblasts and the skin of Ercc1-/Δ mice, initially induces cellular senescence and, importantly, increased expression of several SASP (senescence-associated secretory phenotype) factors. Cellular senescence induced by ERCC1 deficiency was dependent on activity of the p53 tumor-suppressor protein. In turn, TNFα secreted by senescent cells induced apoptosis, not only in neighboring ERCC1-deficient nonsenescent cells, but also cell autonomously in the senescent cells themselves. In addition, expression of the stem cell markers p63 and Lgr6 was significantly decreased in Ercc1-/Δ mouse skin, where the apoptotic cells are localized, compared to age-matched wild-type skin, possibly due to the apoptosis of stem cells. These data suggest that ERCC1-depleted cells become susceptible to apoptosis via TNFα secreted from neighboring senescent cells. We speculate that parts of the premature aging phenotypes and shortened health- or lifespan may be due to stem cell depletion through apoptosis promoted by senescent cells.
    Keywords:  DNA damage repair; aging; cell death; senescence-associated secretory phenotype; tumor necrosis factor α
    DOI:  https://doi.org/10.1111/acel.13072
  29. Prog Biophys Mol Biol. 2019 Nov 13. pii: S0079-6107(19)30211-1. [Epub ahead of print]
    Hards K, Adolph C, Harold LK, McNeil MB, Cheung CY, Jinich A, Rhee KY, Cook GM.
      Cellular bioenergetics is an area showing promise for the development of new antimicrobials, antimalarials and cancer therapy. Enzymes involved in central carbon metabolism and energy generation are essential mediators of bacterial physiology, persistence and pathogenicity, lending themselves natural interest for drug discovery. In particular, succinate and malate are two major focal points in both the central carbon metabolism and the respiratory chain of Mycobacterium tuberculosis. Both serve as direct links between the citric acid cycle and the respiratory chain due to the quinone-linked reactions of succinate dehydrogenase, fumarate reductase and malate:quinone oxidoreductase. Inhibitors against these enzymes therefore hold the promise of disrupting two distinct, but essential, cellular processes at the same time. In this review, we discuss the roles and unique adaptations of these enzymes and critically evaluate the role that future inhibitors of these complexes could play in the bioenergetics target space.
    Keywords:  Tuberculosis; fumarate reductase; malate:quinone oxidoreductase; mycobacteria; succinate dehydrogenase
    DOI:  https://doi.org/10.1016/j.pbiomolbio.2019.11.003
  30. Cell Metab. 2019 Nov 13. pii: S1550-4131(19)30561-3. [Epub ahead of print]
    Camell CD, Günther P, Lee A, Goldberg EL, Spadaro O, Youm YH, Bartke A, Hubbard GB, Ikeno Y, Ruddle NH, Schultze J, Dixit VD.
      During aging, visceral adiposity is often associated with alterations in adipose tissue (AT) leukocytes, inflammation, and metabolic dysfunction. However, the contribution of AT B cells in immunometabolism during aging is unexplored. Here, we show that aging is associated with an expansion of a unique population of resident non-senescent aged adipose B cells (AABs) found in fat-associated lymphoid clusters (FALCs). AABs are transcriptionally distinct from splenic age-associated B cells (ABCs) and show greater expansion in female mice. Functionally, whole-body B cell depletion restores proper lipolysis and core body temperature maintenance during cold stress. Mechanistically, the age-induced FALC formation, AAB, and splenic ABC expansion is dependent on the Nlrp3 inflammasome. Furthermore, AABs express IL-1R, and inhibition of IL-1 signaling reduces their proliferation and increases lipolysis in aging. These data reveal that inhibiting Nlrp3-dependent B cell accumulation can be targeted to reverse metabolic impairment in aging AT.
    Keywords:  B cell depletion; IL-1 signaling; Nlrp3 inflammasome; adipose tissue B cells; age-associated B cells; aging; fat-associated lymphoid cluster; growth hormone receptor; inflammaging; lipolysis
    DOI:  https://doi.org/10.1016/j.cmet.2019.10.006
  31. Curr Diab Rep. 2019 Nov 21. 19(12): 144
    Ducasa GM, Mitrofanova A, Fornoni A.
      PURPOSE OF REVIEW: The goal of this review is to review the role that renal parenchymal lipid accumulation plays in contributing to diabetic kidney disease (DKD), specifically contributing to the mitochondrial dysfunction observed in glomerular renal cells in the context of DKD development and progression.RECENT FINDINGS: Mitochondrial dysfunction has been observed in experimental and clinical DKD. Recently, Ayanga et al. demonstrate that podocyte-specific deletion of a protein involved in mitochondrial dynamics protects from DKD progression. Furthermore, our group has recently shown that ATP-binding cassette A1 (a protein involved in cholesterol and phospholipid efflux) is significantly reduced in clinical and experimental DKD and that genetic or pharmacological induction of ABCA1 is sufficient to protect from DKD. ABCA1 deficiency in podocytes leads to mitochondrial dysfunction observed with alterations of mitochondrial lipids, in particular, cardiolipin (a mitochondrial-specific phospholipid). However, through pharmacological reduction of cardiolipin peroxidation DKD progression is reverted. Lipid metabolism is significantly altered in the diabetic kidney and renders cellular components, such as the podocyte, susceptible to injury leading to worsened DKD progression. Dysfunction of the lipid metabolism pathway can also lead to mitochondrial dysfunction and mitochondrial lipid alteration. Future research aimed at targeting mitochondrial lipids content and function could prove to be beneficial for the treatment of DKD.
    Keywords:  ABCA1; Cardiolipin; Diabetic kidney disease; Lipid metabolism; Mitochondria; Podocyte
    DOI:  https://doi.org/10.1007/s11892-019-1263-x
  32. Trends Cancer. 2019 Nov;pii: S2405-8033(19)30190-6. [Epub ahead of print]5(11): 693-703
    Peck B, Schulze A.
      Obesity is a leading contributing factor to cancer development worldwide. Epidemiological evidence suggests that diet affects cancer risk and also substantially alters therapeutic outcome. Therefore, studying the impact of diet in the development and treatment of cancer should be a clinical priority. In this Review, we set out the evidence supporting the role of lipid metabolism in shaping the tumor microenvironment (TME) and cancer cell phenotype. We will discuss how dietary lipids can impact phenotype thereby affecting disease trajectory and treatment response. Finally, we will posit potential strategies on how this knowledge can be exploited to increase treatment efficacy and patient survival.
    Keywords:  cancer; cancer metabolism; diet; environmental heterogeneity; lipids; nutrient stress; obesity; tumor microenvironment
    DOI:  https://doi.org/10.1016/j.trecan.2019.09.007
  33. Curr Genet. 2019 Nov 22.
    Gupta R, Laxman S.
      Cells must appropriately sense available nutrients and accordingly regulate their metabolic outputs, to survive. This mini-review considers the idea that conserved chemical modifications of wobble (U34) position tRNA uridines enable cells to sense nutrients and regulate their metabolic state. tRNA wobble uridines are chemically modified at the 2- and 5- positions, with a thiol (s2), and (commonly) a methoxycarbonylmethyl (mcm5) modification, respectively. These modifications reflect sulfur amino acid (methionine and cysteine) availability. The loss of these modifications has minor translation defects. However, they result in striking phenotypes consistent with an altered metabolic state. Using yeast, we recently discovered that the s2 modification regulates overall carbon and nitrogen metabolism, dependent on methionine availability. The loss of this modification results in rewired carbon (glucose) metabolism. Cells have reduced carbon flux towards the pentose phosphate pathway and instead increased flux towards storage carbohydrates-primarily trehalose, along with reduced nucleotide synthesis, and perceived amino acid starvation signatures. Remarkably, this metabolic rewiring in the s2U mutants is caused by mechanisms leading to intracellular phosphate limitation. Thus this U34 tRNA modification responds to methionine availability and integratively regulates carbon and nitrogen homeostasis, wiring cells to a 'growth' state. We interpret the importance of U34 modifications in the context of metabolic sensing and anabolism, emphasizing their intimate coupling to methionine metabolism.
    Keywords:  Amino acid sensing; Metabolism; Methionine; Phosphate; S-adenosyl methionine; tRNA modification
    DOI:  https://doi.org/10.1007/s00294-019-01045-y
  34. Nucleic Acids Res. 2019 Nov 22. pii: gkz1101. [Epub ahead of print]
    Zheng L, Meng Y, Campbell JL, Shen B.
      DNA2 nuclease/helicase is a structure-specific nuclease, 5'-to-3' helicase, and DNA-dependent ATPase. It is involved in multiple DNA metabolic pathways, including Okazaki fragment maturation, replication of 'difficult-to-replicate' DNA regions, end resection, stalled replication fork processing, and mitochondrial genome maintenance. The participation of DNA2 in these different pathways is regulated by its interactions with distinct groups of DNA replication and repair proteins and by post-translational modifications. These regulatory mechanisms induce its recruitment to specific DNA replication or repair complexes, such as DNA replication and end resection machinery, and stimulate its efficient cleavage of various structures, for example, to remove RNA primers or to produce 3' overhangs at telomeres or double-strand breaks. Through these versatile activities at replication forks and DNA damage sites, DNA2 functions as both a tumor suppressor and promoter. In normal cells, it suppresses tumorigenesis by maintaining the genomic integrity. Thus, DNA2 mutations or functional deficiency may lead to cancer initiation. However, DNA2 may also function as a tumor promoter, supporting cancer cell survival by counteracting replication stress. Therefore, it may serve as an ideal target to sensitize advanced DNA2-overexpressing cancers to current chemo- and radiotherapy regimens.
    DOI:  https://doi.org/10.1093/nar/gkz1101
  35. Cell Metab. 2019 Nov 13. pii: S1550-4131(19)30562-5. [Epub ahead of print]
    Zivanovic J, Kouroussis E, Kohl JB, Adhikari B, Bursac B, Schott-Roux S, Petrovic D, Miljkovic JL, Thomas-Lopez D, Jung Y, Miler M, Mitchell S, Milosevic V, Gomes JE, Benhar M, Gonzales-Zorn B, Ivanovic-Burmazovic I, Torregrossa R, Mitchell JR, Whiteman M, Schwarz G, Snyder SH, Paul BD, Carroll KS, Filipovic MR.
      Life on Earth emerged in a hydrogen sulfide (H2S)-rich environment eons ago and with it protein persulfidation mediated by H2S evolved as a signaling mechanism. Protein persulfidation (S-sulfhydration) is a post-translational modification of reactive cysteine residues, which modulate protein structure and/or function. Persulfides are difficult to label and study due to their reactivity and similarity with cysteine. Here, we report a facile strategy for chemoselective persulfide bioconjugation using dimedone-based probes, to achieve highly selective, rapid, and robust persulfide labeling in biological samples with broad utility. Using this method, we show persulfidation is an evolutionarily conserved modification and waves of persulfidation are employed by cells to resolve sulfenylation and prevent irreversible cysteine overoxidation preserving protein function. We report an age-associated decline in persulfidation that is conserved across evolutionary boundaries. Accordingly, dietary or pharmacological interventions to increase persulfidation associate with increased longevity and improved capacity to cope with stress stimuli.
    Keywords:  aging; calorie restriction; hydrogen peroxide; hydrogen sulfide; protein persulfidation; redox signaling; sulfenylation; sulfinylation; sulfonylation
    DOI:  https://doi.org/10.1016/j.cmet.2019.10.007
  36. Cell Mol Life Sci. 2019 Nov 20.
    Singh D, Lercher MJ.
      Genome-scale metabolic models (GSMs) provide a comprehensive representation of cellular metabolism. GSMs provide a mechanistic link between cellular genotypes and metabolic phenotypes, and are thus widely used to analyze metabolism at the systems level. GSMs consist of hundreds or thousands of reactions. They have thus largely been analyzed with computationally efficient constraint-based methods such as flux-balance analysis, limiting their scope and phenotype prediction accuracy. Computationally more demanding but potentially more informative methods, such as kinetic and dynamic modeling, are currently limited to small or medium-sized models. Thus, it is desirable to achieve unbiased stoichiometric reductions of large-scale metabolic models to small, coarse-grained model representations that capture significant metabolic modules. Here, we review published automated and semiautomated methods used for large-scale metabolic model reduction. The top-down methods discussed provide minimal networks that retain a set of user-protected phenotypes, but may reduce the model's metabolic and phenotypic versatility. In contrast, the two bottom-up approaches reviewed retain a more unbiased set of phenotypes; at the same time, these methods require the partitioning of the GSM into metabolic subsystems by the user, and make strong assumptions on the subsystems' connections and their states, respectively.
    Keywords:  Elementary flux modes; Flux-balance analysis; Genome-scale metabolic models; Metabolic networks; Network reduction methods
    DOI:  https://doi.org/10.1007/s00018-019-03383-z
  37. Neuroscience. 2019 Nov 15. pii: S0306-4522(19)30740-7. [Epub ahead of print]
    Pagani F, Testi C, Grimaldi A, Corsi G, Cortese B, Basilico B, Baiocco P, De Panfilis S, Ragozzino D, Di Angelantonio S.
      Dimethyl fumarate (DMF) is the only available approved drug for first line treatment of multiple sclerosis (MS), a lethal condition impairing central nervous system (CNS). To date, however, little is known of its mechanisms of action. Only recently, it has been suggested that DMF exerts neuroprotective effects acting as an immunomodulator and that it may alter the activation state of microglia cells, crucial in MS pathogenesis. However, DMF effects on microglia functions are still not well determined. Here, we examine the effects of DMF treatment on microglia functional activities, as phenotype, morphology, processes motility and rearrangement, migration, ATP response and iron uptake in mouse primary microglia culture and acute hippocampal slices. We found that DMF treatment reduces microglia motility, downregulating functional response to ATP, increases ferritin uptake and pushes microglia towards an anti-inflammatory phenotype, thus reducing its proinflammatory reactivity in response to tissue damage. These results highlight the effects of this compound on microglia functions and provide new insights on the mechanism of action of DMF in MS treatment.
    Keywords:  dimethyl fumarate; ferritin; hippocampus; microglia; multiple sclerosis
    DOI:  https://doi.org/10.1016/j.neuroscience.2019.10.041
  38. Int J Biol Sci. 2019 ;15(12): 2707-2718
    Fu A, Hou Y, Yu Z, Zhao Z, Liu Z.
      Tumor mitochondria alter their functions to reprogram cell metabolism and then allow tumor cells to rapidly proliferate in the hypoxic and acidic microenvironment. However, roles of normal mitochondria played in tumor progression are still unclear. Here we investigate the normal mitochondrial effect on abnormal metabolism of tumors, and to clarify why the mitochondria have to undergo functional changes in the tumor growth. The mitochondria isolated from healthy mouse livers were intravenously injected into melanoma model mice with lung metastasis, then the tumor growth, animal survival and associated metabolic changes were studied. The results reveal that the mitochondria significantly retard tumor growth and increase survival days of animals. The anti-tumor effect of the mitochondria is related to interfering the tumor cell metabolisms, such as reducing glycolysis and producing an oxidative intracellular environment, all of which are not suitable for tumor cell proliferation. In addition, the mitochondria increases cell apoptosis, necrosis, and mitophagy. These effects are more efficient with the mitochondria isolated from young mouse livers than those from aged mice. Our study not only provides a valuable approach to invest mitochondrial function associated with tumor growth but also offer new insight into tumor therapy through interfering the tumor cell metabolism by healthy mitochondria.
    Keywords:  bioenergy; isolated mitochondria; melanoma; redox
    DOI:  https://doi.org/10.7150/ijbs.38104
  39. Immunity. 2019 Nov 19. pii: S1074-7613(19)30456-X. [Epub ahead of print]51(5): 783-785
    Varanasi SK, Ma S, Kaech SM.
      Our knowledge of T cell metabolism relies primarily on studies performed in vitro that may not fully recapitulate physiological conditions in vivo. In this issue of Immunity, Ma et al. find that the in vivo environment dictates the metabolic phenotype of effector CD8+ T cells-particularly their glucose utilization.
    DOI:  https://doi.org/10.1016/j.immuni.2019.10.012
  40. Commun Biol. 2019 ;2 414
    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.
    Keywords:  Biochemical reaction networks; Cancer genomics; Data integration; Tumour heterogeneity
    DOI:  https://doi.org/10.1038/s42003-019-0666-1
  41. J Biol Chem. 2019 Nov 19. pii: jbc.RA119.011695. [Epub ahead of print]
    Krycer JR, Elkington SD, Diaz-Vegas A, Cooke KC, Burchfield JG, Fisher-Wellman KH, Cooney GJ, Fazakerley DJ, James DE.
      Insulin action in adipose tissue is crucial for whole-body glucose homeostasis, with insulin resistance being a major risk factor for metabolic diseases such as type 2 diabetes. Recent studies have proposed mitochondrial oxidants as a unifying driver of adipose insulin resistance, serving as a signal of nutrient excess. However, neither the substrates for nor sites of oxidant production are known. Since insulin stimulates glucose utilisation, we hypothesised that glucose oxidation would fuel respiration, in turn generating mitochondrial oxidants. This would impair insulin action, limiting further glucose uptake in a negative feedback loop of 'glucose-dependent' insulin resistance. Using primary rat adipocytes and cultured 3T3-L1 adipocytes, we observed that insulin increased respiration, but notably this occurred independently of glucose supply. In contrast, glucose was required for insulin to increase mitochondrial oxidants. Despite rising to similar levels as when treated with other agents that cause insulin resistance, glucose-dependent mitochondrial oxidants failed to cause insulin resistance. Subsequent studies revealed a temporal relationship whereby mitochondrial oxidants needed to increase before the insulin stimulus to induce insulin resistance. Together, these data reveal that a) adipocyte respiration is principally fuelled from non-glucose sources, b) there is a disconnect between respiration and oxidative stress, whereby mitochondrial oxidant levels do not rise with increased respiration unless glucose is present, and c) mitochondrial oxidative stress must precede the insulin stimulus to cause insulin resistance, explaining why short-term insulin-dependent glucose utilisation does not promote insulin resistance. These data provide additional clues to mechanistically link nutrient excess to adipose insulin resistance.
    Keywords:  adipocyte; glucose; insulin; insulin resistance; mitochondria; oxidative stress; respiration
    DOI:  https://doi.org/10.1074/jbc.RA119.011695
  42. Nat Chem Biol. 2019 Dec;15(12): 1137-1147
    Conrad M, Pratt DA.
      Lipid peroxidation underlies the mechanism of oxidative cell death now known as ferroptosis. This modality, distinct from other forms of cell death, has been intensely researched in recent years owing to its relevance in both degenerative disease and cancer. The demonstration that it can be modulated by small molecules in multiple pathophysiological contexts offers exciting opportunities for novel pharmacological interventions. Herein, we introduce the salient features of lipid peroxidation, how it can be modulated by small molecules and what principal aspects require urgent investigation by researchers in the field. The central role of non-enzymatic reactions in the execution of ferroptosis will be emphasized, as these processes have hitherto not been generally considered 'druggable'. Moreover, we provide a critical perspective on the biochemical mechanisms that contribute to cell vulnerability to ferroptosis and discuss how they can be exploited in the design of novel therapeutics.
    DOI:  https://doi.org/10.1038/s41589-019-0408-1
  43. Mol Cell. 2019 Nov 05. pii: S1097-2765(19)30801-9. [Epub ahead of print]
    Wu JY, Huang TW, Hsieh YT, Wang YF, Yen CC, Lee GL, Yeh CC, Peng YJ, Kuo YY, Wen HT, Lin HC, Hsiao CW, Wu KK, Kung HJ, Hsu YJ, Kuo CC.
      Macrophages form a major cell population in the tumor microenvironment. They can be activated and polarized into tumor-associated macrophages (TAM) by the tumor-derived soluble molecules to promote tumor progression and metastasis. Here, we used comparative metabolomics coupled with biochemical and animal studies to show that cancer cells release succinate into their microenvironment and activate succinate receptor (SUCNR1) signaling to polarize macrophages into TAM. Furthermore, the results from in vitro and in vivo studies revealed that succinate promotes not only cancer cell migration and invasion but also cancer metastasis. These effects are mediated by SUCNR1-triggered PI3K-hypoxia-inducible factor 1α (HIF-1α) axis. Compared with healthy subjects and tumor-free lung tissues, serum succinate levels and lung cancer SUCNR1 expression were elevated in lung cancer patients, suggesting an important clinical relevance. Collectively, our findings indicate that the secreted tumor-derived succinate belongs to a novel class of cancer progression factors, controlling TAM polarization and promoting tumorigenic signaling.
    Keywords:  PI3K-HIF-1α axis; SUCNR1; cancer metastasis; metabolomics; succinate; tumor microenvironment; tumor-associated macrophages
    DOI:  https://doi.org/10.1016/j.molcel.2019.10.023