bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒04‒21
forty-eight papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Autophagy. 2019 Apr 19. 1-17
    Tsakiri EN, Gumeni S, Vougas K, Pendin D, Papassideri I, Daga A, Gorgoulis V, Juhász G, Scorrano L, Trougakos IP.
      The ubiquitin-proteasome pathway (UPP) is central to proteostasis network (PN) functionality and proteome quality control. Yet, the functional implication of the UPP in tissue homeodynamics at the whole organism level and its potential cross-talk with other proteostatic or mitostatic modules are not well understood. We show here that knock down (KD) of proteasome subunits in Drosophila flies, induced, for most subunits, developmental lethality. Ubiquitous or tissue specific proteasome dysfunction triggered systemic proteome instability and activation of PN modules, including macroautophagy/autophagy, molecular chaperones and the antioxidant cncC (the fly ortholog of NFE2L2/Nrf2) pathway. Also, proteasome KD increased genomic instability, altered metabolic pathways and severely disrupted mitochondrial functionality, triggering a cncC-dependent upregulation of mitostatic genes and enhanced rates of mitophagy. Whereas, overexpression of key regulators of antioxidant responses (e.g., cncC or foxo) could not suppress the deleterious effects of proteasome dysfunction; these were alleviated in both larvae and adult flies by modulating mitochondrial dynamics towards increased fusion or by enhancing autophagy. Our findings reveal the extensive functional wiring of genomic, proteostatic and mitostatic modules in higher metazoans. Also, they support the notion that age-related increase of proteotoxic stress due to decreased UPP activity deregulates all aspects of cellular functionality being thus a driving force for most age-related diseases. Abbreviations: ALP: autophagy-lysosome pathway; ARE: antioxidant response element; Atg8a: autophagy-related 8a; ATPsynβ: ATP synthase, β subunit; C-L: caspase-like proteasomal activity; cncC: cap-n-collar isoform-C; CT-L: chymotrypsin-like proteasomal activity; Drp1: dynamin related protein 1; ER: endoplasmic reticulum; foxo: forkhead box, sub-group O; GLU: glucose; GFP: green fluorescent protein; GLY: glycogen; Hsf: heat shock factor; Hsp: Heat shock protein; Keap1: kelch-like ECH-associated protein 1; Marf: mitochondrial assembly regulatory factor; NFE2L2/Nrf2: nuclear factor, erythroid 2 like 2; Opa1: optic atrophy 1; PN: proteostasis network; RNAi: RNA interference; ROS: reactive oxygen species; ref(2)P: refractory to sigma P; SQSTM1: sequestosome 1; SdhA: succinate dehydrogenase, subunit A; T-L: trypsin-like proteasomal activity; TREH: trehalose; UAS: upstream activation sequence; Ub: ubiquitin; UPR: unfolded protein response; UPP: ubiquitin-proteasome pathway.
    Keywords:  ; Aging; autophagy; cncC; foxo; mitostasis; proteasome; proteostasis
  2. Mol Cell. 2019 Apr 03. pii: S1097-2765(19)30225-4. [Epub ahead of print]
    Wang G, Meyer JG, Cai W, Softic S, Li ME, Verdin E, Newgard C, Schilling B, Kahn CR.
      Brown adipose tissue (BAT) is rich in mitochondria and plays important roles in energy expenditure, thermogenesis, and glucose homeostasis. We find that levels of mitochondrial protein succinylation and malonylation are high in BAT and subject to physiological and genetic regulation. BAT-specific deletion of Sirt5, a mitochondrial desuccinylase and demalonylase, results in dramatic increases in global protein succinylation and malonylation. Mass spectrometry-based quantification of succinylation reveals that Sirt5 regulates the key thermogenic protein in BAT, UCP1. Mutation of the two succinylated lysines in UCP1 to acyl-mimetic glutamine and glutamic acid significantly decreases its stability and activity. The reduced function of UCP1 and other proteins in Sirt5KO BAT results in impaired mitochondria respiration, defective mitophagy, and metabolic inflexibility. Thus, succinylation of UCP1 and other mitochondrial proteins plays an important role in BAT and in regulation of energy homeostasis.
    Keywords:  UCP1; brown fat; mitochondria; succinylation; thermogenesis
  3. Nat Cell Biol. 2019 Apr 15.
    Yang C, Svitkina TM.
      Mitochondrial fission involves the preconstriction of an organelle followed by scission by dynamin-related protein Drp1. Preconstriction is facilitated by actin and non-muscle myosin II through a mechanism that remains unclear, largely due to the unknown cytoskeletal ultrastructure at mitochondrial constrictions. Here, using platinum replica electron microscopy, we show that mitochondria in cells are embedded in an interstitial cytoskeletal network that contains abundant unbranched actin filaments. Both spontaneous and induced mitochondrial constrictions typically associate with a criss-cross array of long actin filaments that comprise part of this interstitial network. Non-muscle myosin II is found adjacent to mitochondria but is not specifically enriched at the constriction sites. During ionomycin-induced mitochondrial fission, F-actin clouds colocalize with mitochondrial constriction sites, whereas dynamic myosin II clouds are present in the vicinity of constrictions. We propose that myosin II promotes mitochondrial constriction by inducing stochastic deformations of the interstitial actin network, which applies pressure on the mitochondrial surface and thus initiates curvature-sensing mechanisms that complete mitochondrial constriction.
  4. J Cell Mol Med. 2019 Apr 16.
    Jiang S, Wang Y, Luo L, Shi F, Zou J, Lin H, Ying Y, Luo Y, Zhan Z, Liu P, Zhu B, Huang D, Luo Z.
      Adenine monophosphate-activated protein kinase (AMPK) is a fuel sensing enzyme that is activated in shortage of energy and inhibited in its surplus. Cancer is a metabolic disease characteristic of aerobic glycolysis, namely Warburg effect, and possesses heterogeneity featured by spatiotemporal hypoxia and normoxia, where AMPK is deeply implicated. The present study delineates the regulation of mitochondrial functions by AMPK in cancer cells. On the one hand, AMPKα subunit binds to mitochondria independently of β subunit and targeting AMPK to mitochondria facilitates oxidative phosphorylation and fatty acid oxidation, and inhibits glycolysis. As such, mitochondrial AMPK inhibits the growth of cancer cells and tumorigenesis. On the other hand, ablation of the β subunits completely abolishes AMPK activity and simultaneously leads to decreases in mitochondria DNA and protein contents. The effect of the β deletion is rescued by overexpression of the active mutant of bulky AMPKα1 subunit. In conjunction, the transcriptional factors PGC1α and Nrf-1 are up-regulated by LKB1/AMPK, an event that is abolished in the absence of the β subunits. Intriguingly, the stimulation of mitochondria biogenesis is not achieved by mitochondria-targeted AMPK. Therefore, our study suggests that AMPK inhibits cancer cell growth and tumorigenesis via regulation of mitochondria-mediated metabolism.
    Keywords:  AMP-activated protein kinase; Warburg effect; cancer growth; glycolysis; mitochondrial function; oxidative phosphorylation
  5. FEBS J. 2019 Apr 16.
    Poliaková M, Felser A, Pierzchala K, Nuoffer JM, Aebersold DM, Zimmer Y, Zamboni N, Medová M.
      Genetic aberrations in the hepatocyte growth factor receptor tyrosine kinase MET induce oncogenic addiction in various types of human cancers, advocating MET as a viable anticancer target. Here, we report that MET signaling plays an important role in conferring a unique metabolic phenotype to cellular models expressing MET-activating mutated variants that are either sensitive or resistant towards MET small molecule inhibitors. MET phosphorylation downregulated by the specific MET inhibitor tepotinib resulted in markedly decreased viability and increased apoptosis in tepotinib-sensitive cells. Moreover, prior to the induction of MET inhibition-dependent cell death, tepotinib also led to an altered metabolic signature, characterized by a prominent reduction of metabolite ions related to amino sugar metabolism, gluconeogenesis, glycine and serine metabolism and of numerous TCA cycle-related metabolites such as succinate, malate and citrate. Functionally, a decrease in oxygen consumption rate, a reduced citrate synthase activity, a drop in membrane potential and an associated misbalanced mitochondrial function were observed exclusively in MET inhibitor-sensitive cells. These data imply that interference with metabolic state can be considered an early indicator of efficient MET inhibition and particular changes reported here could be explored in the future as markers of efficacy of anti-MET therapies. This article is protected by copyright. All rights reserved.
    Keywords:  MET receptor tyrosine kinase; metabolism; mitochondria; non-targeted mass spectrometry; small molecule inhibitor
  6. Biochim Biophys Acta Mol Cell Res. 2019 Jul;pii: S0167-4889(18)30479-8. [Epub ahead of print]1866(7): 1068-1078
    Rossi A, Pizzo P, Filadi R.
      The versatility of mitochondrial metabolism and its fine adjustments to specific physiological or pathological conditions regulate fundamental cell pathways, ranging from proliferation to apoptosis. In particular, Ca2+ signalling has emerged as a key player exploited by mitochondria to tune their activity according with cell demand. The functional interaction between mitochondria and endoplasmic reticulum (ER) deeply impacts on the correct mitochondrial Ca2+ signal, thus modulating cell bioenergetics and functionality. Indeed, Ca2+ released by the ER is taken up by mitochondria where, both in the intermembrane space and in the matrix, it regulates the activity of transporters, enzymes and proteins involved in organelles' metabolism. In this review, we will briefly summarize Ca2+-dependent mechanisms involved in the regulation of mitochondrial activity. Moreover, we will discuss some recent reports, in which alterations in mitochondrial Ca2+ signalling have been associated with specific pathological conditions, such as neurodegeneration and cancer.
    Keywords:  ATP; Bioenergetics; Ca(2+); Endoplasmic reticulum; MAM; Metabolism; Mitochondria
  7. Cell Metab. 2019 Apr 08. pii: S1550-4131(19)30139-1. [Epub ahead of print]
    Sanchez-Lopez E, Zhong Z, Stubelius A, Sweeney SR, Booshehri LM, Antonucci L, Liu-Bryan R, Lodi A, Terkeltaub R, Lacal JC, Murphy AN, Hoffman HM, Tiziani S, Guma M, Karin M.
      Choline is a vitamin-like nutrient that is taken up via specific transporters and metabolized by choline kinase, which converts it to phosphocholine needed for de novo synthesis of phosphatidylcholine (PC), the main phospholipid of cellular membranes. We found that Toll-like receptor (TLR) activation enhances choline uptake by macrophages and microglia through induction of the choline transporter CTL1. Inhibition of CTL1 expression or choline phosphorylation attenuated NLRP3 inflammasome activation and IL-1β and IL-18 production in stimulated macrophages. Mechanistically, reduced choline uptake altered mitochondrial lipid profile, attenuated mitochondrial ATP synthesis, and activated the energy sensor AMP-activated protein kinase (AMPK). By potentiating mitochondrial recruitment of DRP1, AMPK stimulates mitophagy, which contributes to termination of NLRP3 inflammasome activation. Correspondingly, choline kinase inhibitors ameliorated acute and chronic models of IL-1β-dependent inflammation.
    Keywords:  AMPK; CTL1; IL-18; IL-1β; NLRP3; choline; choline kinase; macrophages; mitochondrial lipids; mitophagy; phosphocholine
  8. Am J Hum Genet. 2019 Apr 02. pii: S0002-9297(19)30099-0. [Epub ahead of print]
    Radenkovic S, Bird MJ, Emmerzaal TL, Wong SY, Felgueira C, Stiers KM, Sabbagh L, Himmelreich N, Poschet G, Windmolders P, Verheijen J, Witters P, Altassan R, Honzik T, Eminoglu TF, James PM, Edmondson AC, Hertecant J, Kozicz T, Thiel C, Vermeersch P, Cassiman D, Beamer L, Morava E, Ghesquière B.
      Phosphoglucomutase 1 (PGM1) encodes the metabolic enzyme that interconverts glucose-6-P and glucose-1-P. Mutations in PGM1 cause impairment in glycogen metabolism and glycosylation, the latter manifesting as a congenital disorder of glycosylation (CDG). This unique metabolic defect leads to abnormal N-glycan synthesis in the endoplasmic reticulum (ER) and the Golgi apparatus (GA). On the basis of the decreased galactosylation in glycan chains, galactose was administered to individuals with PGM1-CDG and was shown to markedly reverse most disease-related laboratory abnormalities. The disease and treatment mechanisms, however, have remained largely elusive. Here, we confirm the clinical benefit of galactose supplementation in PGM1-CDG-affected individuals and obtain significant insights into the functional and biochemical regulation of glycosylation. We report here that, by using tracer-based metabolomics, we found that galactose treatment of PGM1-CDG fibroblasts metabolically re-wires their sugar metabolism, and as such replenishes the depleted levels of galactose-1-P, as well as the levels of UDP-glucose and UDP-galactose, the nucleotide sugars that are required for ER- and GA-linked glycosylation, respectively. To this end, we further show that the galactose in UDP-galactose is incorporated into mature, de novo glycans. Our results also allude to the potential of monosaccharide therapy for several other CDG.
    Keywords:  CDG; PGM1-CDG; central carbon metabolism; galactose; glycosylation; mitochondria; nucleotide sugars; tracer metabolomics
  9. Elife. 2019 Apr 16. pii: e44235. [Epub ahead of print]8
    Sullivan MR, Danai LV, Lewis CA, Chan SH, Gui DY, Kunchok T, Dennstedt EA, Vander Heiden MG, Muir A.
      Cancer cell metabolism is heavily influenced by microenvironmental factors, including nutrient availability. Therefore, knowledge of microenvironmental nutrient levels is essential to understand tumor metabolism. To measure the extracellular nutrient levels available to tumors, we utilized quantitative metabolomics methods to measure the absolute concentrations of >118 metabolites in plasma and tumor interstitial fluid, the extracellular fluid that perfuses tumors. Comparison of nutrient levels in tumor interstitial fluid and plasma revealed that the nutrients available to tumors differ from those present in circulation. Further, by comparing interstitial fluid nutrient levels between autochthonous and transplant models of murine pancreatic and lung adenocarcinoma, we found that tumor type, anatomical location and animal diet affect local nutrient availability. These data provide a comprehensive characterization of the nutrients present in the tumor microenvironment of widely used models of lung and pancreatic cancer and identify factors that influence metabolite levels in tumors.
    Keywords:  biochemistry; cancer biology; chemical biology; mouse
  10. Cell Rep. 2019 Apr 16. pii: S2211-1247(19)30382-1. [Epub ahead of print]27(3): 699-707.e4
    Pyaram K, Kumar A, Kim YH, Noel S, Reddy SP, Rabb H, Chang CH.
      Kelch-like ECH-associated protein 1 (Keap1) and nuclear factor (erythroid-derived 2)-like 2 (Nrf2) proteins work in concert to regulate the levels of reactive oxygen species (ROS). The Keap1-Nrf2 antioxidant system also participates in T cell differentiation and inflammation, but its role in innate T cell development and functions remains unclear. We report that T cell-specific deletion of Keap1 results in defective development and reduced numbers of invariant natural killer T (NKT) cells in the thymus and the peripheral organs in a cell-intrinsic manner. The frequency of NKT2 and NKT17 cells increases while NKT1 decreases in these mice. Keap1-deficient NKT cells show increased rates of proliferation and apoptosis, as well as increased glucose uptake and mitochondrial function, but reduced ROS, CD122, and Bcl2 expression. In NKT cells deficient in Nrf2 and Keap1, all these phenotypic and metabolic defects are corrected. Thus, the Keap1-Nrf2 system contributes to NKT cell development and homeostasis by regulating cell metabolism.
    Keywords:  NKT cells; antioxidant system; cell metabolism; innate T cells; reactive oxygen species
  11. Cell Rep. 2019 Apr 16. pii: S2211-1247(19)30388-2. [Epub ahead of print]27(3): 820-834.e9
    Sica V, Bravo-San Pedro JM, Izzo V, Pol J, Pierredon S, Enot D, Durand S, Bossut N, Chery A, Souquere S, Pierron G, Vartholomaiou E, Zamzami N, Soussi T, Sauvat A, Mondragón L, Kepp O, Galluzzi L, Martinou JC, Hess-Stumpp H, Ziegelbauer K, Kroemer G, Maiuri MC.
      Inhibition of oxidative phosphorylation (OXPHOS) by 1-cyclopropyl-4-(4-[(5-methyl-3-(3-[4-(trifluoromethoxy)phenyl]-1,2,4-oxadiazol-5-yl)-1H-pyrazol-1-yl)methyl]pyridin-2-yl)piperazine (BAY87-2243, abbreviated as B87), a complex I inhibitor, fails to kill human cancer cells in vitro. Driven by this consideration, we attempted to identify agents that engage in synthetically lethal interactions with B87. Here, we report that dimethyl α-ketoglutarate (DMKG), a cell-permeable precursor of α-ketoglutarate that lacks toxicity on its own, kills cancer cells when combined with B87 or other inhibitors of OXPHOS. DMKG improved the antineoplastic effect of B87, both in vitro and in vivo. This combination caused MDM2-dependent, tumor suppressor protein p53 (TP53)-independent transcriptional reprogramming and alternative exon usage affecting multiple glycolytic enzymes, completely blocking glycolysis. Simultaneous inhibition of OXPHOS and glycolysis provoked a bioenergetic catastrophe culminating in the activation of a cell death program that involved disruption of the mitochondrial network and activation of PARP1, AIFM1, and APEX1. These results unveil a metabolic liability of human cancer cells that may be harnessed for the development of therapeutic regimens.
    Keywords:  Krebs cycle; MDM2; cancer metabolism; glycolysis; mitochondrial fragmentation; parthanatos; regulated cell death
  12. Glia. 2019 Apr 16.
    Murru S, Hess S, Barth E, Almajan ER, Schatton D, Hermans S, Brodesser S, Langer T, Kloppenburg P, Rugarli EI.
      Mitochondrial dysfunction causes neurodegeneration but whether impairment of mitochondrial homeostasis in astrocytes contributes to this pathological process remains largely unknown. The m-AAA protease exerts quality control and regulatory functions crucial for mitochondrial homeostasis. AFG3L2, which encodes one of the subunits of the m-AAA protease, is mutated in spinocerebellar ataxia SCA28 and in infantile syndromes characterized by spastic-ataxia, epilepsy and premature death. Here, we investigate the role of Afg3l2 and its redundant homologue Afg3l1 in the Bergmann glia (BG), radial astrocytes of the cerebellum that have functional connections with Purkinje cells (PC) and regulate glutamate homeostasis. We show that astrocyte-specific deletion of Afg3l2 in the mouse leads to late-onset motor impairment and to degeneration of BG, which display aberrant morphology, altered expression of the glutamate transporter EAAT2, and a reactive inflammatory signature. The neurological and glial phenotypes are drastically exacerbated when astrocytes lack both Afg31l and Afg3l2, and therefore, are totally depleted of the m-AAA protease. Moreover, mitochondrial stress responses and necroptotic markers are induced in the cerebellum. In both mouse models, targeted BG show a fragmented mitochondrial network and loss of mitochondrial cristae, but no signs of respiratory dysfunction. Importantly, astrocyte-specific deficiency of Afg3l1 and Afg3l2 triggers secondary morphological degeneration and electrophysiological changes in PCs, thus demonstrating a non-cell-autonomous role of glia in neurodegeneration. We propose that astrocyte dysfunction amplifies both neuroinflammation and glutamate excitotoxicity in patients carrying mutations in AFG3L2, leading to a vicious circle that contributes to neuronal death.
    Keywords:  Bergmann glia; Purkinje neuron; glutamate transporter; mitochondrial disease; necroptosis; neuroinflammation; spinocerebellar ataxia
  13. Mitochondrion. 2019 Apr 11. pii: S1567-7249(18)30037-0. [Epub ahead of print]46 15-21
    Yoon YG, Koob MD.
      Mitochondrial genomes (mtDNA) depend on the nuclear genome with which they have evolved to provide essential replication functions and have been known to replicate as xenotransplants only in the cells of closely related species. We now report that complete mouse mitochondrial genomes can be stably transplanted into the mitochondrial network in yeast devoid of their own mtDNA. Our analyses of these xenomitochondrial yeast cells show that they are accurately replicating intact mouse mtDNA genomes without rearrangement and that these mtDNA genomes have the same overall topology as the mtDNA present in the mouse mitochondrial network (i.e., circular monomers). Moreover, non-mtDNA replication and selection sequences required for maintaining the mitochondrial genomes in bacterial hosts are dispensable in these yeast mitochondria and could be efficiently and seamlessly removed by targeted homologous recombination within the mitochondria. These findings demonstrate that the yeast mtDNA replication system is capable of accurately replicating intact mammalian mtDNA genomes without sequence loss or rearrangement and that yeast mitochondria are a highly versatile host system for engineering complete mammalian mitochondrial genomes.
    Keywords:  Mitochondrial genome; Mitochondrial host; Non-mtDNA sequence; Petite mutant; Xenomitochondrial yeast; mtDNA engineering
  14. Nature. 2019 Apr 17.
    Saito Y, Li L, Coyaud E, Luna A, Sander C, Raught B, Asara JM, Brown M, Muthuswamy SK.
      Drosophila Lgl and its mammalian homologues, LLGL1 and LLGL2, are scaffolding proteins that regulate the establishment of apical-basal polarity in epithelial cells1,2. Whereas Lgl functions as a tumour suppressor in Drosophila1, the roles of mammalian LLGL1 and LLGL2 in cancer are unclear. The majority (about 75%) of breast cancers express oestrogen receptors (ERs)3, and patients with these tumours receive endocrine treatment4. However, the development of resistance to endocrine therapy and metastatic progression are leading causes of death for patients with ER+ disease4. Here we report that, unlike LLGL1, LLGL2 is overexpressed in ER+ breast cancer and promotes cell proliferation under nutrient stress. LLGL2 regulates cell surface levels of a leucine transporter, SLC7A5, by forming a trimeric complex with SLC7A5 and a regulator of membrane fusion, YKT6, to promote leucine uptake and cell proliferation. The oestrogen receptor targets LLGL2 expression. Resistance to endocrine treatment in breast cancer cells was associated with SLC7A5- and LLGL2-dependent adaption to nutrient stress. SLC7A5 was necessary and sufficient to confer resistance to tamoxifen treatment, identifying SLC7A5 as a potential therapeutic target for overcoming resistance to endocrine treatments in breast cancer. Thus, LLGL2 functions as a promoter of tumour growth and not as a tumour suppressor in ER+ breast cancer. Beyond breast cancer, adaptation to nutrient stress is critically important5, and our findings identify an unexpected role for LLGL2 in this process.
  15. Life Sci Alliance. 2019 Apr;pii: e201900392. [Epub ahead of print]2(2):
    von Stockum S, Sanchez-Martinez A, Corrà S, Chakraborty J, Marchesan E, Locatello L, Da Rè C, Cusumano P, Caicci F, Ferrari V, Costa R, Bubacco L, Rasotto MB, Szabo I, Whitworth AJ, Scorrano L, Ziviani E.
      Aberrant mitochondrial dynamics disrupts mitochondrial function and contributes to disease conditions. A targeted RNA interference screen for deubiquitinating enzymes (DUBs) affecting protein levels of multifunctional mitochondrial fusion protein Mitofusin (MFN) identified USP8 prominently influencing MFN levels. Genetic and pharmacological inhibition of USP8 normalized the elevated MFN protein levels observed in PINK1 and Parkin-deficient models. This correlated with improved mitochondrial function, locomotor performance and life span, and prevented dopaminergic neurons loss in Drosophila PINK1 KO flies. We identified a novel target antagonizing pathologically elevated MFN levels, mitochondrial dysfunction, and dopaminergic neuron loss of a Drosophila model of mitochondrial dysfunction.
  16. JCI Insight. 2019 Apr 16. pii: 127713. [Epub ahead of print]5
    Woodall BP, Orogo AM, Najor RH, Cortez MQ, Moreno ER, Wang H, Divakaruni AS, Murphy AN, Gustafsson AB.
      The E3 ubiquitin ligase Parkin plays an important role in regulating clearance of dysfunctional or unwanted mitochondria in tissues, including the heart. However, whether Parkin also functions to prevent cardiac aging by maintaining a healthy population of mitochondria is still unclear. Here, we have examined the role of Parkin in the context of mtDNA damage and myocardial aging using a mouse model carrying a proofreading defective mitochondrial DNA polymerase gamma (POLG). We observed both decreased Parkin protein levels and development of cardiac hypertrophy in POLG hearts with age; however, cardiac hypertrophy in POLG mice was neither rescued, nor worsened by cardiac specific overexpression or global deletion of Parkin, respectively. Unexpectedly, mitochondrial fitness did not substantially decline with age in POLG mice when compared to WT. We found that baseline mitophagy receptor-mediated mitochondrial turnover and biogenesis were enhanced in aged POLG hearts. We also observed the presence of megamitochondria in aged POLG hearts. Thus, these processes may limit the accumulation of dysfunctional mitochondria as well as the degree of cardiac functional impairment in the aging POLG heart. Overall, our results demonstrate that Parkin is dispensable for constitutive mitochondrial quality control in a mtDNA mutation model of cardiac aging.
    Keywords:  Autophagy; Cardiology; Cell Biology; Mitochondria
  17. PLoS One. 2019 ;14(4): e0214764
    Pollock SR, Schinlever AR, Rohani A, Kashatus JA, Kashatus DF.
      Healthy mitochondria use an electrochemical gradient across the inner mitochondrial membrane (IMM) to generate energy in the form of ATP. A variety of endogenous and exogenous factors can lead to transient or sustained depolarization of the IMM, including mitochondrial fission events, expression of uncoupling proteins, electron transport chain (ETC) inhibitors, or chemical uncouplers. This depolarization in turn leads to a variety of physiological responses, ranging from selective mitochondrial clearance (mitophagy) to cell death. How cells recognize and ultimately respond to depolarized mitochondria remains incompletely understood. Here we show that the small GTPases RalA and RalB both relocalize to mitochondria following depolarization in a process dependent on clathrin-mediated endocytosis (CME). Furthermore, both genetic and pharmacologic inhibition of RalA and RalB leads to an increase in the activity of the atypical IκB kinase TBK1 both basally and in response to mitochondrial depolarization. This phenotype was also observed following inhibition of Ral relocalization. Collectively, these data suggest a model in which RalA and RalB inhibit TBK1 and that relocalization of Ral to depolarized mitochondria facilitates TBK1 activation through release of this inhibition.
  18. Nucleic Acids Res. 2019 Feb 14. pii: gkz083. [Epub ahead of print]
    Zheng J, Croteau DL, Bohr VA, Akbari M.
      Ataxia with oculomotor apraxia type 1 (AOA1) is an early onset progressive spinocerebellar ataxia caused by mutation in aprataxin (APTX). APTX removes 5'-AMP groups from DNA, a product of abortive ligation during DNA repair and replication. APTX deficiency has been suggested to compromise mitochondrial function; however, a detailed characterization of mitochondrial homeostasis in APTX-deficient cells is not available. Here, we show that cells lacking APTX undergo mitochondrial stress and display significant changes in the expression of the mitochondrial inner membrane fusion protein optic atrophy type 1, and components of the oxidative phosphorylation complexes. At the cellular level, APTX deficiency impairs mitochondrial morphology and network formation, and autophagic removal of damaged mitochondria by mitophagy. Thus, our results show that aberrant mitochondrial function is a key component of AOA1 pathology. This work corroborates the emerging evidence that impaired mitochondrial function is a characteristic of an increasing number of genetically diverse neurodegenerative disorders.
  19. Nat Commun. 2019 Apr 17. 10(1): 1796
    Sala D, Cunningham TJ, Stec MJ, Etxaniz U, Nicoletti C, Dall'Agnese A, Puri PL, Duester G, Latella L, Sacco A.
      Metabolic reprogramming is an active regulator of stem cell fate choices, and successful stem cell differentiation in different compartments requires the induction of oxidative phosphorylation. However, the mechanisms that promote mitochondrial respiration during stem cell differentiation are poorly understood. Here we demonstrate that Stat3 promotes muscle stem cell myogenic lineage progression by stimulating mitochondrial respiration in mice. We identify Fam3a, a cytokine-like protein, as a major Stat3 downstream effector in muscle stem cells. We demonstrate that Fam3a is required for muscle stem cell commitment and skeletal muscle development. We show that myogenic cells secrete Fam3a, and exposure of Stat3-ablated muscle stem cells to recombinant Fam3a in vitro and in vivo rescues their defects in mitochondrial respiration and myogenic commitment. Together, these findings indicate that Fam3a is a Stat3-regulated secreted factor that promotes muscle stem cell oxidative metabolism and differentiation, and suggests that Fam3a is a potential tool to modulate cell fate choices.
  20. Cell Rep. 2019 Apr 16. pii: S2211-1247(19)30384-5. [Epub ahead of print]27(3): 750-761.e7
    Fachi JL, Felipe JS, Pral LP, da Silva BK, Corrêa RO, de Andrade MCP, da Fonseca DM, Basso PJ, Câmara NOS, de Sales E Souza ÉL, Dos Santos Martins F, Guima SES, Thomas AM, Setubal JC, Magalhães YT, Forti FL, Candreva T, Rodrigues HG, de Jesus MB, Consonni SR, Farias ADS, Varga-Weisz P, Vinolo MAR.
      Antibiotic-induced dysbiosis is a key factor predisposing intestinal infection by Clostridium difficile. Here, we show that interventions that restore butyrate intestinal levels mitigate clinical and pathological features of C. difficile-induced colitis. Butyrate has no effect on C. difficile colonization or toxin production. However, it attenuates intestinal inflammation and improves intestinal barrier function in infected mice, as shown by reduced intestinal epithelial permeability and bacterial translocation, effects associated with the increased expression of components of intestinal epithelial cell tight junctions. Activation of the transcription factor HIF-1 in intestinal epithelial cells exerts a protective effect in C. difficile-induced colitis, and it is required for butyrate effects. We conclude that butyrate protects intestinal epithelial cells from damage caused by C. difficile toxins via the stabilization of HIF-1, mitigating local inflammatory response and systemic consequences of the infection.
    Keywords:  colitis; hypoxia; infection; intestinal epithelial cells; microbiota; short chain fatty acids
  21. FEBS Lett. 2019 Apr 19.
    Kerr EW, Shumar SA, Leonardi R.
      Coenzyme A (CoA) regulates energy metabolism and exists in separate pools in the cytosol, peroxisomes, and mitochondria. At the whole tissue level, the concentration of CoA changes with the nutritional state by balancing synthesis and degradation; however, it is currently unclear how individual subcellular CoA pools are regulated. Liver and kidney peroxisomes contain Nudt7 and Nudt19, respectively, enzymes that catalyze CoA degradation. We report that Nudt8 is a novel CoA-degrading enzyme that resides in the mitochondria. Nudt8 has a distinctive preference for manganese ions and exhibits a broader tissue distribution than Nudt7 and Nudt19. The existence of CoA-degrading enzymes in both peroxisomes and mitochondria suggests that degradation may be a key regulatory mechanism for modulating the intracellular CoA pools. This article is protected by copyright. All rights reserved.
    Keywords:  Coenzyme A; Nudix hydrolase; cell compartmentalization; metabolic regulation; mitochondria
  22. Integr Comp Biol. 2019 Apr 20. pii: icz025. [Epub ahead of print]
    Tobler M, Barts N, Greenway R.
      Mitochondria have been known to be involved in speciation through the generation of Dobzhansky-Muller incompatibilities, where functionally neutral co-evolution between mitochondrial and nuclear genomes can cause dysfunction when alleles are recombined in hybrids. We propose that adaptive mitochondrial divergence between populations can not only produce intrinsic (Dobzhansky-Muller) incompatibilities, but could also contribute to reproductive isolation through natural and sexual selection against migrants, post-mating prezygotic isolation, as well as by causing extrinsic reductions in hybrid fitness. We describe how these reproductive isolating barriers can potentially arise through adaptive divergence of mitochondrial function in the absence of mito-nuclear coevolution, a departure from more established views. While a role for mitochondria in the speciation process appears promising, we also highlight critical gaps of knowledge: (1) many systems with a potential for mitochondrially-mediated reproductive isolation lack crucial evidence directly linking reproductive isolation and mitochondrial function; (2) it often remains to be seen if mitochondrial barriers are a driver or a consequence of reproductive isolation; (3) the presence of substantial gene flow in the presence of mito-nuclear incompatibilities raises questions whether such incompatibilities are strong enough to drive speciation to completion; and (4) it remains to be tested how mitochondrial effects on reproductive isolation compare when multiple mechanisms of reproductive isolation coincide. We hope this perspective and the proposed research plans help to inform future studies of mitochondrial adaptation in a manner that links genotypic changes to phenotypic adaptations, fitness, and reproductive isolation in natural systems, helping to clarify the importance of mitochondria in the formation and maintenance of biological diversity.
    Keywords:  Dobzhansky-Muller incompatibilities; genetic incompatibilities; natural selection; physiological adaptation; reproductive isolation
  23. Thyroid. 2019 Apr 16.
    Strickaert A, Corbet C, Spinette SA, Craciun L, Dom G, Andry G, Larsimont D, Wattiez R, Dumont JE, Feron O, Maenhaut C.
      BACKGROUND: Energetic metabolism is described to be deregulated in cancer and the Warburg effect is presented as a major hallmark. Recently, cellular heterogeneity in tumors and tumor microenvironment have been recognized to play an important role in several metabolic pathways in cancer. However, their contribution to papillary thyroid cancer (PTC) development and metabolism is still poorly described.METHODS: We performed a proteomic analysis of 5 PTC and investigated the cellular distribution of several upregulated metabolic proteins in the cancer and in the stromal cells of PTC.
    RESULTS: MS/MS analysis revealed the upregulation of many metabolism-related proteins, among which pyruvate carboxylase. Pyruvate carboxylase knockdown in thyroid cell lines alters their proliferative and motility capacities, and measurements of oxygen consumption rates showed that this enzyme is involved in the replenishment of the TCA cycle. Immunostainings of several upregulated metabolic proteins showed that thyroid cancer cells have an increased mitochondrial oxidative metabolism compared to stromal cells.
    CONCLUSION: PTC have a very active TCA cycle, continuously replenished by a pyruvate carboxylase mediated anaplerosis. This is specifically observed in the tumor cells.
  24. Nature. 2019 Apr 17.
    Shi Y, Gao W, Lytle NK, Huang P, Yuan X, Dann AM, Ridinger-Saison M, DelGiorno KE, Antal CE, Liang G, Atkins AR, Erikson G, Sun H, Meisenhelder J, Terenziani E, Woo G, Fang L, Santisakultarm TP, Manor U, Xu R, Becerra CR, Borazanci E, Von Hoff DD, Grandgenett PM, Hollingsworth MA, Leblanc M, Umetsu SE, Collisson EA, Scadeng M, Lowy AM, Donahue TR, Reya T, Downes M, Evans RM, Wahl GM, Pawson T, Tian R, Hunter T.
      Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis largely owing to inefficient diagnosis and tenacious drug resistance. Activation of pancreatic stellate cells (PSCs) and consequent development of dense stroma are prominent features accounting for this aggressive biology1,2. The reciprocal interplay between PSCs and pancreatic cancer cells (PCCs) not only enhances tumour progression and metastasis but also sustains their own activation, facilitating a vicious cycle to exacerbate tumorigenesis and drug resistance3-7. Furthermore, PSC activation occurs very early during PDAC tumorigenesis8-10, and activated PSCs comprise a substantial fraction of the tumour mass, providing a rich source of readily detectable factors. Therefore, we hypothesized that the communication between PSCs and PCCs could be an exploitable target to develop effective strategies for PDAC therapy and diagnosis. Here, starting with a systematic proteomic investigation of secreted disease mediators and underlying molecular mechanisms, we reveal that leukaemia inhibitory factor (LIF) is a key paracrine factor from activated PSCs acting on cancer cells. Both pharmacologic LIF blockade and genetic Lifr deletion markedly slow tumour progression and augment the efficacy of chemotherapy to prolong survival of PDAC mouse models, mainly by modulating cancer cell differentiation and epithelial-mesenchymal transition status. Moreover, in both mouse models and human PDAC, aberrant production of LIF in the pancreas is restricted to pathological conditions and correlates with PDAC pathogenesis, and changes in the levels of circulating LIF correlate well with tumour response to therapy. Collectively, these findings reveal a function of LIF in PDAC tumorigenesis, and suggest its translational potential as an attractive therapeutic target and circulating marker. Our studies underscore how a better understanding of cell-cell communication within the tumour microenvironment can suggest novel strategies for cancer therapy.
  25. Mech Ageing Dev. 2019 Apr 16. pii: S0047-6374(18)30198-2. [Epub ahead of print]
    Patil P, Falabella M, Saeed A, Lee D, Kaufman B, Shiva S, Croix CS, Van Houten B, Neidernhofer LJ, Robbins PD, Lee J, Gwendolyn S, Vo N.
      Cellular senescence is a phenotype characterized by irreversible growth arrest, chronic elevated secretion of proinflammatory cytokines and matrix proteases, a phenomenon known as senescence associated secretory phenotype (SASP). Biomarkers of cellular senescence have been shown to increase with age and degeneration of human disc tissue. Senescent disc cells in culture recapitulate features associated with age-related disc degeneration, including increased secretion of proinflammatory cytokines, matrix proteases, and fragmentation of matrix proteins. However, little is known of the metabolic changes that underlie the senescence phenotype of disc cells. To assess the metabolic changes, we performed a bioenergetic analysis of in vitro oxidative stress induced senescent (SIS) human disc cells. SIS disc cells acquire SASP and exhibit significantly elevated mitochondrial content and mitochondrial ATP-linked respiration. The metabolic changes appear to be driven by the upregulated protein secretion in SIS cells as abrogation of protein synthesis using cycloheximide decreased mitochondrial ATP-linked respiration. Taken together, the results of the study suggest that the increased energy generation state supports the secretion of senescent associated proteins in SIS disc cells.
    Keywords:  Aging; Bioenergetics; Cellular senescence; Intervertebral disc degeneration; Matrix homeostasis; Mitochondria
  26. Chembiochem. 2019 Apr 16.
    Reed MA, Roberts J, Gierth P, Kupče Ē, Günther UL.
      Tracer-based metabolism is becoming increasingly important to study metabolic mechanisms in cells. NMR offers several approaches to measure label incorporation in metabolites, including 13C and 1H-detected spectra. The latter are generally more sensitive but quantification depends on the proton carbon 1JCH coupling constant which varies significantly between different metabolites. It is therefore not possible to have one experiment optimised for all metabolites and quantification of 1H-edited spectra such as HSQCs requires precise knowledge of coupling constants. Increasing interest in tracer-based and metabolic flux analysis requires robust analyses with reasonably small acquisition times. Here we compare 13C-filtered and 13C-edited methods for quantification and show the applicability of the method for real-time NMR of cancer cell metabolism where label incorporations are subject to constant flux. We find an approach using a double-filter most suitable and sufficiently robust to reliably obtain 13C-incorporations from difference spectra. This is demonstrated for JJN3 multiple myeloma cells processing glucose over 24h. The proposed method is equally well suited for calculating label incorporation levels in labelled cell extracts in the context of metabolic flux analysis.
    Keywords:  NMR, metabolism, metabolic fluxes
  27. Nature. 2019 Apr 17.
    Veglia F, Tyurin VA, Blasi M, De Leo A, Kossenkov AV, Donthireddy L, To TKJ, Schug Z, Basu S, Wang F, Ricciotti E, DiRusso C, Murphy ME, Vonderheide RH, Lieberman PM, Mulligan C, Nam B, Hockstein N, Masters G, Guarino M, Lin C, Nefedova Y, Black P, Kagan VE, Gabrilovich DI.
      Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are pathologically activated neutrophils that are crucial for the regulation of immune responses in cancer. These cells contribute to the failure of cancer therapies and are associated with poor clinical outcomes. Despite recent advances in the understanding of PMN-MDSC biology, the mechanisms responsible for the pathological activation of neutrophils are not well defined, and this limits the selective targeting of these cells. Here we report that mouse and human PMN-MDSCs exclusively upregulate fatty acid transport protein 2 (FATP2). Overexpression of FATP2 in PMN-MDSCs was controlled by granulocyte-macrophage colony-stimulating factor, through the activation of the STAT5 transcription factor. Deletion of FATP2 abrogated the suppressive activity of PMN-MDSCs. The main mechanism of FATP2-mediated suppressive activity involved the uptake of arachidonic acid and the synthesis of prostaglandin E2. The selective pharmacological inhibition of FATP2 abrogated the activity of PMN-MDSCs and substantially delayed tumour progression. In combination with checkpoint inhibitors, FATP2 inhibition blocked tumour progression in mice. Thus, FATP2 mediates the acquisition of immunosuppressive activity by PMN-MDSCs and represents a target to inhibit the functions of PMN-MDSCs selectively and to improve the efficiency of cancer therapy.
  28. Br J Dermatol. 2019 Apr 20.
    Lehmann SM, Leube RE, Schwarz N.
      BACKGROUND: Epidermal differentiation is a multi-level process in which keratinocytes need to lose their organelles including their mitochondria by autophagy. Disturbed autophagy leads to thickening of the epidermis as it is encountered in Pachyonychia congenita, a rare skin disease caused by mutations in keratins 6, 16, and 17.OBJECTIVES: We therefore asked if mitophagy is disturbed in Pachyonychia congenita and if so at which stage.
    METHODS: Immortalised keratinocytes derived from Pachyonychia congenita patients were used in fluorescence-based and biochemical assays to dissect the different steps of mitophagy.
    RESULTS: Pachyonychia congenita keratinocytes accumulate old mitochondria and display a disturbed clearance of mitochondria after mitochondrial uncoupling. Early mitophagy steps and autophagosome formation, however, are not affected. We find that autolysosomes accumulate in Pachyonychia congenita and are not sufficiently recycled.
    CONCLUSION: We propose an influence of keratins on autolysosomal degradation and recycling. This article is protected by copyright. All rights reserved.
  29. Cancer Metastasis Rev. 2019 Apr 17.
    Lu J.
      The Warburg effect is prevalent in human cancer. Accordingly, most cancer cells display highly elevated glycolysis without proportionally increasing pyruvate oxidation. The metastatic process imposes strong selective pressure on cancer cells, and metastasizing cancer cells experience heightened oxidative stress. By constraining mitochondrial oxidative metabolism, the Warburg effect helps cancer cells to minimize oxidative stress, thereby facilitating metastatic dissemination. The PGC1α transcriptional coactivator is a central coordinator of oxidative metabolism. While promoting oxidative metabolism and reversing the Warburg effect, PGC1α critically activates antioxidant genes and protects cells against oxidative damage. Therefore, depending on the context, PGC1α may promote or suppress tumor metastasis. Cancer cells generally retain metabolic flexibility and can resist antiglycolysis treatment by undergoing metabolic reprogramming. Synthetic lethal combination therapies are thus essential to attack the liabilities of the Warburg metabolism for therapeutic benefit.
    Keywords:  Cancer; Tumor metastasis; Warburg effect
  30. Front Neurosci. 2019 ;13 292
    de Oliveira Bristot VJ, de Bem Alves AC, Cardoso LR, da Luz Scheffer D, Aguiar AS.
      In understanding the pathology of neurological diseases, the role played by brain energy metabolism is gaining prominence. Animal models have demonstrated that regular physical exercise improves brain energy metabolism while also providing antidepressant, anxiolytic, antioxidant and neuroprotective functions. This review summarizes the latest evidence on the roles played by peroxisome proliferator-activated receptor gamma (PPAR-γ) coactivator 1-alpha (PGC-1α) and mitochondrial uncoupling protein (UCP) in this scenario. The beneficial effects of exercise seem to depend on crosstalk between muscles and nervous tissue through the increased release of muscle irisin during exercise.
    Keywords:  FNDC5; PGC-1α; UCP2; irisin; mitochondria; physical exercise
  31. Biochem Biophys Res Commun. 2019 Apr 16. pii: S0006-291X(19)30706-5. [Epub ahead of print]
    Wang JM, Liu BQ, Li C, Du ZX, Sun J, Yan J, Jiang JY, Wang HQ.
      Glucose limitation activates p53, which functions as an adaptive response to maintain cell survival. However, p53 is frequently deleted or mutated in a variety of tumors, while most cancer cells can acclimatize themselves to metabolically unfavorable surrounding, indicating that alternative mechanisms other than p53 transactivation underly adaptive response of cancer cells with p53 deletion or mutation to metabolically hostile environment. Sestrin 2 (SESN2) is a p53 downstream target, which plays a protective role against various stressful stimuli, such as genotoxic, energetic, and oxidative stress. In the current study, we demonstrated that SESN2 transcript was stabilized by glucose limitation at the posttranscriptional level irrespective of p53 status. Importantly, SESN2 also protected cells from metabolic stress triggered by glucose limitation in a p53-independent manner. Our data indicated that stabilization of SESN2 transcript might be an alternative adaptive response to metabolic stress other than p53 activation. Thereby, the current study highlights the significance of stabilization of SESN2 transcript in adaptation of cells with p53 deletion or mutation to metabolic stress.
    Keywords:  Metabolic stress; SESN2; p53
  32. Cell. 2019 Apr 18. pii: S0092-8674(19)30336-8. [Epub ahead of print]177(3): 737-750.e15
    Lehrbach NJ, Breen PC, Ruvkun G.
      The proteasome mediates selective protein degradation and is dynamically regulated in response to proteotoxic challenges. SKN-1A/Nrf1, an endoplasmic reticulum (ER)-associated transcription factor that undergoes N-linked glycosylation, serves as a sensor of proteasome dysfunction and triggers compensatory upregulation of proteasome subunit genes. Here, we show that the PNG-1/NGLY1 peptide:N-glycanase edits the sequence of SKN-1A protein by converting particular N-glycosylated asparagine residues to aspartic acid. Genetically introducing aspartates at these N-glycosylation sites bypasses the requirement for PNG-1/NGLY1, showing that protein sequence editing rather than deglycosylation is key to SKN-1A function. This pathway is required to maintain sufficient proteasome expression and activity, and SKN-1A hyperactivation confers resistance to the proteotoxicity of human amyloid beta peptide. Deglycosylation-dependent protein sequence editing explains how ER-associated and cytosolic isoforms of SKN-1 perform distinct cytoprotective functions corresponding to those of mammalian Nrf1 and Nrf2. Thus, we uncover an unexpected mechanism by which N-linked glycosylation regulates protein function and proteostasis.
    Keywords:  N-linked glycosylation; NFE2L1; NFE2L2; NGLY1; NGLY1 deficiency; Nrf1; Nrf2; PNG-1; PNGase; SKN-1; SKN-1A; bortezomib; deglycosylation; glycobiology; neurodegenerative diseases; peptide:N-glycanase; proteasome; protein quality control; protein sequence editing; proteostasis
  33. Cancer Immunol Res. 2019 Apr 15. pii: canimm.0513.2018. [Epub ahead of print]
    Santos PM, Menk AV, Shi J, Tsung A, Delgoffe GM, Butterfield LH.
      Cellular metabolism supports immune cell function. Here, we identify a reduction in fatty acid synthesis and mitochondrial metabolism in dendritic cells (DCs) due to α-fetoprotein (AFP), a protein secreted by hepatocellular cancer (HCC). DCs cultured in the presence of AFP show reduced expression of the metabolic regulatory molecules SREBP-1 and PGC1-α. The negative effect of AFP on mitochondrial metabolism and ATP production was confirmed with observation of reduction in basal oxygen consumption rate (OCR) in DCs exposed to AFP derived from cord blood. More severe reduction in basal OCR was observed in tumor-derived DCs exposed to AFP due to downregulation of cytochrome c oxidase. We also showed reduced expression of PGC1-α in circulating myeloid DCs of HCC patients and impaired capacity to stimulate antigen-specific effector functions. These data show the negative effects of AFP on DC metabolism. These findings elucidate a mechanism of immune suppression in HCC and may help generate therapeutic approaches to reverse such immunosuppression.
  34. Nat Chem Biol. 2019 May;15(5): 489-498
    Bolognini D, Barki N, Butcher AJ, Hudson BD, Sergeev E, Molloy C, Moss CE, Bradley SJ, Le Gouill C, Bouvier M, Tobin AB, Milligan G.
      Differentiating actions of short chain fatty acids (SCFAs) at free fatty acid receptor 2 (FFA2) from other free fatty acid-responsive receptors and from non-receptor-mediated effects has been challenging. Using a novel chemogenetic and knock-in strategy, whereby an engineered variant of FFA2 (FFA2-DREADD) that is unresponsive to natural SCFAs but is instead activated by sorbic acid replaced the wild-type receptor, we determined that activation of FFA2 in differentiated adipocytes and colonic crypt enteroendocrine cells of mouse accounts fully for SCFA-regulated lipolysis and release of the incretin glucagon-like peptide-1 (GLP-1), respectively. In vivo studies confirmed the specific role of FFA2 in GLP-1 release and also demonstrated a direct role for FFA2 in accelerating gut transit. Thereby, we establish the general principle that such a chemogenetic knock-in strategy can successfully define novel G-protein-coupled receptor (GPCR) biology and provide both target validation and establish therapeutic potential of a 'hard to target' GPCR.
  35. Cell Metab. 2019 Apr 03. pii: S1550-4131(19)30138-X. [Epub ahead of print]
    Molinaro A, Becattini B, Mazzoli A, Bleve A, Radici L, Maxvall I, Sopasakis VR, Molinaro A, Bäckhed F, Solinas G.
      Phosphatidylinositol-3-kinase (PI3K) activity is aberrant in tumors, and PI3K inhibitors are investigated as cancer therapeutics. PI3K signaling mediates insulin action in metabolism, but the role of PI3K isoforms in insulin signaling remains unresolved. Defining the role of PI3K isoforms in insulin signaling is necessary for a mechanistic understanding of insulin action and to develop PI3K inhibitors with optimal therapeutic index. We show that insulin-driven PI3K-AKT signaling depends on redundant PI3Kα and PI3Kβ activities, whereas PI3Kδ and PI3Kγ are largely dispensable. We have also found that RAS activity promotes AKT phosphorylation in insulin-stimulated hepatocytes and that promotion of insulin-driven AKT phosphorylation by RAS depends on PI3Kα. These findings reveal the detailed mechanism by which insulin activates AKT, providing an improved mechanistic understanding of insulin signaling. This improved model for insulin signaling predicts that isoform-selective PI3K inhibitors discriminating between PI3Kα and PI3Kβ should be dosed below their hyperglycemic threshold to achieve isoform selectivity.
    Keywords:  PROS; PTEN; diabetes; glycogen; hepatic glucose production; insulin resistance; obesity; phosphoinositide 3-kinase
  36. Nat Cell Biol. 2019 Apr 15.
    Esposito M, Mondal N, Greco TM, Wei Y, Spadazzi C, Lin SC, Zheng H, Cheung C, Magnani JL, Lin SH, Cristea IM, Sackstein R, Kang Y.
      How disseminated tumour cells engage specific stromal components in distant organs for survival and outgrowth is a critical but poorly understood step of the metastatic cascade. Previous studies have demonstrated the importance of the epithelial-mesenchymal transition in promoting the cancer stem cell properties needed for metastasis initiation, whereas the reverse process of mesenchymal-epithelial transition is required for metastatic outgrowth. Here we report that this paradoxical requirement for the simultaneous induction of both mesenchymal-epithelial transition and cancer stem cell traits in disseminated tumour cells is provided by bone vascular niche E-selectin, whose direct binding to cancer cells promotes bone metastasis by inducing mesenchymal-epithelial transition and activating Wnt signalling. E-selectin binding activity mediated by the α1-3 fucosyltransferases Fut3/Fut6 and Glg1 are instrumental to the formation of bone metastasis. These findings provide unique insights into the functional role of E-selectin as a component of the vascular niche critical for metastatic colonization in bone.
  37. Biochem Biophys Res Commun. 2019 Apr 12. pii: S0006-291X(19)30659-X. [Epub ahead of print]
    Mazaki Y, Takada S, Nio-Kobayashi J, Maekawa S, Higashi T, Onodera Y, Sabe H.
      Neutrophils rapidly migrate to infection sites after the recognition of invaders. During chemotaxis, neutrophils require energy supplied by mitochondria oxidative phosphorylation (OXPHOS), whereas neutrophils rely heavily on glycolysis under normal conditions. Mitochondrial OXPHOS correlates with mitochondrial morphology. Here, we examined the mitochondrial morphology of neutrophil-like differentiated HL-60 cells after chemoattractant N-formyl-Met-Leu-Phe (fMLP) stimulation. We found that mitochondrial morphology changes to a tubular form after fMLP stimulation. Mitochondrial OXPHOS activity and mitochondrial complex II significantly increased after fMLP stimulation. On the other hand, the silencing of mitochondrial fusion protein mitofusin 2 (MFN2) suppresses mitochondrial morphological changes. Furthermore, MFN2 silencing suppressed OXPHOS activation and chemotaxis after fMLP stimulation. These results suggest that MFN2 is involved in chemotaxis of differentiated HL-60 cells depending on mitochondria.
    Keywords:  Chemotaxis; Mitofusin 2; Neutrophil; Oxidative phosphorylation
  38. Sci Adv. 2019 Apr;5(4): eaaw0025
    Simic MS, Moehle EA, Schinzel RT, Lorbeer FK, Halloran JJ, Heydari K, Sanchez M, Jullié D, Hockemeyer D, Dillin A.
      Somatic cells can be reprogrammed into pluripotent stem cells using the Yamanaka transcription factors. Reprogramming requires both epigenetic landscape reshaping and global remodeling of cell identity, structure, basic metabolic processes, and organelle form and function. We hypothesize that variable regulation of the proteostasis network and its influence upon the protein-folding environment within cells and their organelles is responsible for the low efficiency and stochasticity of reprogramming. We find that the unfolded protein response of the endoplasmic reticulum (UPRER), the mitochondrial UPR, and the heat shock response, which ensure proteome quality during stress, are activated during reprogramming. The UPRER is particularly crucial, and its ectopic, transient activation, genetically or pharmacologically, enhances reprogramming. Last, stochastic activation of the UPRER predicts reprogramming efficiency in naïve cells. Thus, the low efficiency and stochasticity of cellular reprogramming are due partly to the inability to properly initiate the UPRER to remodel the ER and its proteome.
  39. Dev Cell. 2019 Apr 03. pii: S1534-5807(19)30224-2. [Epub ahead of print]
    Princely Abudu Y, Pankiv S, Mathai BJ, Håkon Lystad A, Bindesbøll C, Brenne HB, Yoke Wui Ng M, Thiede B, Yamamoto A, Mutugi Nthiga T, Lamark T, Esguerra CV, Johansen T, Simonsen A.
      The clearance of damaged or dysfunctional mitochondria by selective autophagy (mitophagy) is important for cellular homeostasis and prevention of disease. Our understanding of the mitochondrial signals that trigger their recognition and targeting by mitophagy is limited. Here, we show that the mitochondrial matrix proteins 4-Nitrophenylphosphatase domain and non-neuronal SNAP25-like protein homolog 1 (NIPSNAP1) and NIPSNAP2 accumulate on the mitochondria surface upon mitochondrial depolarization. There, they recruit proteins involved in selective autophagy, including autophagy receptors and ATG8 proteins, thereby functioning as an "eat me" signal for mitophagy. NIPSNAP1 and NIPSNAP2 have a redundant function in mitophagy and are predominantly expressed in different tissues. Zebrafish lacking a functional Nipsnap1 display reduced mitophagy in the brain and parkinsonian phenotypes, including loss of tyrosine hydroxylase (Th1)-positive dopaminergic (DA) neurons, reduced motor activity, and increased oxidative stress.
    Keywords:  ALFY; NDP52; NIPSNAP1; NIPSNAP2; Parkin; TAX1BP1; autophagy; mitophagy; optineurin; p62/SQSTM1
  40. Genes (Basel). 2019 Apr 02. pii: E264. [Epub ahead of print]10(4):
    Lameirinhas A, Miranda-Gonçalves V, Henrique R, Jerónimo C.
      Renal cell carcinoma (RCC) is the most common malignancy affecting the kidney. Current therapies are mostly curative for localized disease, but do not completely preclude recurrence and metastization. Thus, it is imperative to develop new therapeutic strategies based on RCC biological properties. Presently, metabolic reprograming and epigenetic alterations are recognized cancer hallmarks and their interactions are still in its infancy concerning RCC. In this review, we explore RCC biology, highlighting genetic and epigenetic alterations that contribute to metabolic deregulation of tumor cells, including high glycolytic phenotype (Warburg effect). Moreover, we critically discuss available data concerning epigenetic enzymes' regulation by aberrant metabolite accumulation and their consequences in RCC emergence and progression. Finally, we emphasize the clinical relevance of uncovering novel therapeutic targets based on epigenetic reprograming by metabolic features to improve treatment and survival of RCC patients.
    Keywords:  Warburg effect; epigenetic alterations; metabolic reprograming; renal cell carcinoma
  41. Proc Natl Acad Sci U S A. 2019 Apr 18. pii: 201821323. [Epub ahead of print]
    Lim JKM, Delaidelli A, Minaker SW, Zhang HF, Colovic M, Yang H, Negri GL, von Karstedt S, Lockwood WW, Schaffer P, Leprivier G, Sorensen PH.
      The RAS family of proto-oncogenes are among the most commonly mutated genes in human cancers and predict poor clinical outcome. Several mechanisms underlying oncogenic RAS transformation are well documented, including constitutive signaling through the RAF-MEK-ERK proproliferative pathway as well as the PI3K-AKT prosurvival pathway. Notably, control of redox balance has also been proposed to contribute to RAS transformation. However, how homeostasis between reactive oxygen species (ROS) and antioxidants, which have opposing effects in the cell, ultimately influence RAS-mediated transformation and tumor progression is still a matter of debate and the mechanisms involved have not been fully elucidated. Here, we show that oncogenic KRAS protects fibroblasts from oxidative stress by enhancing intracellular GSH levels. Using a whole transcriptome approach, we discovered that this is attributable to transcriptional up-regulation of xCT, the gene encoding the cystine/glutamate antiporter. This is in line with the function of xCT, which mediates the uptake of cystine, a precursor for GSH biosynthesis. Moreover, our results reveal that the ETS-1 transcription factor downstream of the RAS-RAF-MEK-ERK signaling cascade directly transactivates the xCT promoter in synergy with the ATF4 endoplasmic reticulum stress-associated transcription factor. Strikingly, xCT was found to be essential for oncogenic KRAS-mediated transformation in vitro and in vivo by mitigating oxidative stress, as knockdown of xCT strongly impaired growth of tumor xenografts established from KRAS-transformed cells. Overall, this study uncovers a mechanism by which oncogenic RAS preserves intracellular redox balance and identifies an unexpected role for xCT in supporting RAS-induced transformation and tumorigenicity.
    Keywords:  RAS; antioxidants; oncogene; xCT
  42. Cancer Res. 2019 Apr 15. 79(8): 1799-1809
    Shah R, Singh SJ, Eddy K, Filipp FV, Chen S.
      Aberrant glutamatergic signaling has been implicated in altered metabolic activity in many cancer types, including malignant melanoma. Previously, we have illustrated the role of metabotropic glutamate receptor 1 (GRM1) in neoplastic transformation of melanocytes in vitro and spontaneous metastatic melanoma in vivo. In this study, we showed that autocrine stimulation constitutively activates the GRM1 receptor and its downstream mitogenic signaling. GRM1-activated (GRM1+) melanomas exhibited significantly increased expression of glutaminase (GLS), which catalyzes the first step in the conversion of glutamine to glutamate. In cultured GRM1+ melanoma cell lines, CB-839, a potent, selective, and orally bioavailable inhibitor of GLS, suppressed cell proliferation, while riluzole, an inhibitor of glutamate release, promoted apoptotic cell death in vitro and in vivo. Combined treatment with CB-839 and riluzole treatment proved to be superior to single-agent treatment, restricting glutamate bioavailability and leading to effective suppression of tumor cell proliferation in vitro and tumor progression in vivo. Hyperactivation of GRM1 in malignant melanoma is an oncogenic driver, which acts independently of canonical melanoma proto-oncogenes, BRAF or NRAS. Overall, these results indicate that expression of GRM1 promotes a metabolic phenotype that supports increased glutamate production and autocrine glutamatergic signaling, which can be pharmacologically targeted by decreasing glutamate bioavailability and the GLS-dependent glutamine to glutamate conversion. SIGNIFICANCE: These findings demonstrate that targeting glutaminolytic glutamate bioavailability is an effective therapeutic strategy for GRM1-activated tumors.
  43. J Virol. 2019 Apr 17. pii: JVI.01834-18. [Epub ahead of print]
    Pant A, Cao S, Yang Z.
      Viruses actively interact with host metabolism because viral replication relies on host cells to provide nutrients and energy. Vaccinia virus (VACV; the prototype poxvirus) prefers glutamine to glucose for efficient replication to the extent that VACV replication is hindered in glutamine-free medium. Remarkably, our data show that VACV replication can be fully rescued from glutamine depletion by asparagine supplementation. By global metabolic profiling, as well as genetic and chemical manipulation of the asparagine supply we provide evidence demonstrating that the production of asparagine, which exclusively requires glutamine for biosynthesis, accounts for VACV's preference of glutamine to glucose rather than glutamine's superiority over glucose in feeding the tricarboxylic acid (TCA) cycle. Further, we show that sufficient asparagine supply is required for efficient VACV protein synthesis. Our study highlights that the asparagine supply, the regulation of which has been evolutionarily tailored in mammalian cells, presents a critical barrier to VACV replication due to a high asparagine content of viral proteins and a rapid demand of viral protein synthesis. The identification of asparagine availability as a critical limiting factor for efficient VACV replication suggests a new direction of anti-viral strategy development.IMPORTANCE Viruses rely on their infected host cells to provide nutrients and energy for replication. Vaccinia virus, the prototypic member of poxviruses that comprise many significant human and animal pathogens, prefers glutamine to glucose for efficient replication. Here we show that the preference is not because glutamine is superior to glucose as the carbon source to fuel the tricarboxylic acid cycle for vaccinia virus replication. Rather interestingly, the preference is because the asparagine supply for efficient viral protein synthesis becomes limited in the absence of glutamine that is necessary for asparagine biosynthesis. We provide further genetic and chemical evidence to demonstrate that asparagine availability plays a critical role in efficient vaccinia virus replication. This discovery identifies a weakness of vaccinia virus and suggests a possible direction to intervene poxvirus infection.
  44. Cell Rep. 2019 Apr 16. pii: S2211-1247(19)30397-3. [Epub ahead of print]27(3): 690-698.e4
    Vara-Ciruelos D, Dandapani M, Russell FM, Grzes KM, Atrih A, Foretz M, Viollet B, Lamont DJ, Cantrell DA, Hardie DG.
      AMPK acts downstream of the tumor suppressor LKB1, yet its role in cancer has been controversial. AMPK is activated by biguanides, such as metformin and phenformin, and metformin use in diabetics has been associated with reduced cancer risk. However, whether this is mediated by cell-autonomous AMPK activation within tumor progenitor cells has been unclear. We report that T-cell-specific loss of AMPK-α1 caused accelerated growth of T cell acute lymphoblastic leukemia/lymphoma (T-ALL) induced by PTEN loss in thymic T cell progenitors. Oral administration of phenformin, but not metformin, delayed onset and growth of lymphomas, but only when T cells expressed AMPK-α1. This differential effect of biguanides correlated with detection of phenformin, but not metformin, in thymus. Phenformin also enhanced apoptosis in T-ALL cells both in vivo and in vitro. Thus, AMPK-α1 can be a cell-autonomous tumor suppressor in the context of T-ALL, and phenformin may have potential for the prevention of some cancers.
    Keywords:  AMP-activated protein kinase; AMPK; T cell acute lymphoblastic leukemia/lymphoma; T-ALL; biguanides; metformin; phenformin
  45. J Pathol. 2019 Apr 14.
    Fontecha-Barriuso M, Martín-Sánchez D, Martinez-Moreno JM, Carrasco S, Ruiz-Andrés O, Monsalve M, Sanchez-Ramos C, Gómez MJ, Ruiz-Ortega M, Sánchez-Niño MD, Cannata-Ortiz P, Cabello R, Gonzalez-Enguita C, Ortiz A, Sanz AB.
      PGC-1α (peroxisome proliferator-activated receptor gamma coactivator-1α, PPARGC1A) regulates the expression of genes involved in energy homeostasis and mitochondrial biogenesis. Here we identify inactivation of the transcriptional regulator PGC-1α as a landmark for experimental nephrotoxic acute kidney injury (AKI) and describe the in vivo consequences of PGC-1α deficiency over inflammation and cell death in kidney injury. Kidney transcriptomic analyses of wild type (WT) mice with folic acid-induced AKI revealed 1398 up- and 1627 down-regulated genes. Upstream transcriptional regulator analyses pointed to PGC-1α as the transcription factor potentially driving the observed expression changes with the highest reduction in activity. Reduced PGC-1α expression was shared by human kidney injury. Ppargc1a-/- mice had spontaneous subclinical kidney injury characterized by tubulointerstitial inflammation and increased Ngal expression. Upon AKI, Ppargc1a-/- mice had lower survival and more severe loss of renal function, tubular injury and reduction in expression of mitochondrial PGC-1α-dependent genes in the kidney, and an earlier decrease in mitochondrial mass than WT mice. Additionally, surviving Ppargc1a-/- mice showed higher rates of tubular cell death, compensatory proliferation, expression of proinflammatory cytokines, NF-κB activation and interstitial inflammatory cell infiltration. Specifically, Ppargc1a-/- mice displayed increased M1 and decreased M2 responses and expression of the anti-inflammatory cytokine IL-10. In cultured renal tubular cells, PGC-1α targeting promoted spontaneous cell death and pro-inflammatory responses. In conclusion, PGC-1α inactivation is a key driver of the gene expression response in nephrotoxic AKI and PGC-1α deficiency promotes a spontaneous inflammatory kidney response that is magnified during AKI.
    Keywords:  PGC-1α; acute kidney injury; cell death; inflammation; mitochondria; proximal tubule
  46. Cancer Discov. 2019 Apr 16.
    Yuan S, Norgard RJ, Stanger BZ.
      During cancer progression, tumor cells undergo molecular and phenotypic changes collectively referred to as cellular plasticity. Such changes result from microenvironmental cues, stochastic genetic and epigenetic alterations, and/or treatment-imposed selective pressures, thereby contributing to tumor heterogeneity and therapy resistance. Epithelial-mesenchymal plasticity is the best-known case of tumor cell plasticity, but recent work has uncovered other examples, often with functional consequences. In this review, we explore the nature and role(s) of these diverse cellular plasticity programs in premalignant progression, tumor evolution, and adaptation to therapy and consider ways in which targeting plasticity could lead to novel anticancer treatments.Significance: Changes in cell identity, or cellular plasticity, are common at different stages of tumor progression, and it has become clear that cellular plasticity can be a potent mediator of tumor progression and chemoresistance. Understanding the mechanisms underlying the various forms of cell plasticity may deliver new strategies for targeting the most lethal aspects of cancer: metastasis and resistance to therapy.
  47. Biochem Biophys Res Commun. 2019 Apr 13. pii: S0006-291X(19)30622-9. [Epub ahead of print]
    Durairaj Pandian V, Giovannucci DR, Vazquez G, Kumarasamy S.
      Several independent genome-wide association studies (GWAS) have indicated that calcium (Ca2+) voltage-gated channel auxiliary subunit beta 2 (CACNB2) an L-type Ca2+ channel (LTCC) associated protein has strong association with hypertension. However, the molecular mechanism of CACNB2 and its role in the pathophysiology of hypertension is not clear. To address this knowledge gap, we utilized in vitro and in vivo approaches using HEK293 cells and genetically hypertensive, Dahl Salt-Sensitive (SS) rats. We demonstrated that CACNB2 over-expression in HEK293 cells triggers cell proliferation via an up-regulation of the RAS-MAPK pathway compared to non-transfected cells. These effects were likely independent of LTCC activity as treatment with nifedipine, a well-known LTCC blocker, in CACNB2 overexpressing cells failed to inhibit the RAS-MAPK pathway gene expressions or show an effect on apoptosis marker gene expression. Furthermore, the expression level of CACNB2 was up-regulated in the high salt (HS) diet fed SS rat kidneys compared to low salt diet (LS) fed group. Similar to our in vitro observation the RAS-MAPK mRNA levels were increased in HS fed SS rat kidneys, compared to LS fed group. Collectively, our data suggest that CACNB2 is associated with the increase in RAS-MAPK gene expressions and lead us to speculate that in addition to its role in regulating LTCC α1-subunit trafficking, CACNB2 might lead to aberrant RAS activation, which is one of the key cascade associated with hypertension.
    Keywords:  CACNB2; Dahl SS rat; L-type calcium channel; RAS–MAPK
  48. Cancer Metastasis Rev. 2019 Apr 13.
    White KA, Kisor K, Barber DL.
      An unresolved question critical for understanding cancer is how recurring somatic mutations are retained and how selective pressures drive retention. Increased intracellular pH (pHi) is common to most cancers and is an early event in cancer development. Recent work shows that recurrent somatic mutations can confer an adaptive gain in pH sensing to mutant proteins, enhancing tumorigenic phenotypes specifically at the increased pHi of cancer. Newly identified amino acid mutation signatures in cancer suggest charge-changing mutations define and shape the mutational landscape of cancer. Taken together, these results support a new perspective on the functional significance of somatic mutations in cancer. In this review, we explore existing data and new directions for better understanding how changes in dynamic pH sensing by somatic mutation might be conferring a fitness advantage to the high pH of cancer.
    Keywords:  Intracellular pH dynamics; Oncogenes; Somatic mutations; pH sensing