bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒09‒08
forty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Cell Rep. 2019 Sep 03. pii: S2211-1247(19)31014-9. [Epub ahead of print]28(10): 2608-2619.e6
    Tompkins SC, Sheldon RD, Rauckhorst AJ, Noterman MF, Solst SR, Buchanan JL, Mapuskar KA, Pewa AD, Gray LR, Oonthonpan L, Sharma A, Scerbo DA, Dupuy AJ, Spitz DR, Taylor EB.
      Hepatocellular carcinoma (HCC) is a devastating cancer increasingly caused by non-alcoholic fatty liver disease (NAFLD). Disrupting the liver Mitochondrial Pyruvate Carrier (MPC) in mice attenuates NAFLD. Thus, we considered whether liver MPC disruption also prevents HCC. Here, we use the N-nitrosodiethylamine plus carbon tetrachloride model of HCC development to test how liver-specific MPC knock out affects hepatocellular tumorigenesis. Our data show that liver MPC ablation markedly decreases tumorigenesis and that MPC-deficient tumors transcriptomically downregulate glutathione metabolism. We observe that MPC disruption and glutathione depletion in cultured hepatomas are synthetically lethal. Stable isotope tracing shows that hepatocyte MPC disruption reroutes glutamine from glutathione synthesis into the tricarboxylic acid (TCA) cycle. These results support a model where inducing metabolic competition for glutamine by MPC disruption impairs hepatocellular tumorigenesis by limiting glutathione synthesis. These findings raise the possibility that combining MPC disruption and glutathione stress may be therapeutically useful in HCC and additional cancers.
    Keywords:  Mitochondrial Pyruvate Carrier; cancer; glutamine; glutathione; hepatocellular carcinoma; liver; metabolomics; stable isotope tracing; synthetic lethality
  2. J Physiol. 2019 Sep 06.
    Willingham TB, Zhang Y, Andreoni A, Knutson JR, Lee DY, Glancy B.
      KEY POINTS: We developed a novel metabolic imaging approach that provides direct measures of the rate of mitochondrial energy conversion with single-cell and subcellular resolution by evaluating NADH autofluorescence kinetics during the mitochondrial redox after cyanide experiment (mitoRACE). Measures of mitochondrial NADH flux by mitoRACE are sensitive to physiological and pharmacological perturbations in vivo. Metabolic imaging with mitoRACE provides a highly adaptable platform for evaluating mitochondrial function in vivo and in single cells with potential for broad applications in the study of energy metabolism.ABSTRACT: Mitochondria play a critical role in numerous cell types and diseases, and structure and function of mitochondria can vary greatly among cells or within different regions of the same cell. However, there are currently limited methodologies that provide direct assessments of mitochondrial function in vivo, and contemporary measures of mitochondrial energy conversion lack the spatial resolution necessary to address cellular and subcellular heterogeneity. Here, we describe a novel metabolic imaging approach that provides direct measures of mitochondrial energy conversion with single-cell and subcellular resolution by evaluating NADH autofluorescence kinetics during the mitochondrial redox after cyanide experiment (mitoRACE). mitoRACE measures the rate of NADH flux through the steady-state mitochondrial NADH pool by rapidly inhibiting mitochondrial energetic flux, resulting in an immediate, linear increase in NADH fluorescence proportional to the steady-state NADH flux rate, thereby providing a direct measure of mitochondrial NADH flux. The experiments presented here demonstrate the sensitivity of this technique to detect physiological and pharmacological changes in mitochondrial flux within tissues of living animals and reveal the unique capability of this technique to evaluate mitochondrial function with single-cell and subcellular resolution in different cell types in vivo and in cell culture. Furthermore, we highlight the potential applications of mitoRACE by showing that within single neurons, mitochondria in neurites have higher energetic flux rates than mitochondria in the cell body. Metabolic imaging with mitoRACE provides a highly adaptable platform for evaluating mitochondrial function in vivo and in single cells with potential for broad applications in the study of energy metabolism. This article is protected by copyright. All rights reserved.
  3. FASEB J. 2019 Sep 05. fj201901136R
    Kowaltowski AJ, Menezes-Filho SL, Assali EA, Gonçalves IG, Cabral-Costa JV, Abreu P, Miller N, Nolasco P, Laurindo FRM, Bruni-Cardoso A, Shirihai OS.
      Changes in mitochondrial size and shape have been implicated in several physiologic processes, but their role in mitochondrial Ca2+ uptake regulation and overall cellular Ca2+ homeostasis is largely unknown. Here we show that modulating mitochondrial dynamics toward increased fusion through expression of a dominant negative (DN) form of the fission protein [dynamin-related protein 1 (DRP1)] markedly increased both mitochondrial Ca2+ retention capacity and Ca2+ uptake rates in permeabilized C2C12 cells. Similar results were seen using the pharmacological fusion-promoting M1 molecule. Conversely, promoting a fission phenotype through the knockdown of the fusion protein mitofusin (MFN)-2 strongly reduced the mitochondrial Ca2+ uptake speed and capacity in these cells. These changes were not dependent on modifications in mitochondrial calcium uniporter expression, inner membrane potentials, or the mitochondrial permeability transition. Implications of mitochondrial morphology modulation on cellular calcium homeostasis were measured in intact cells; mitochondrial fission promoted lower basal cellular calcium levels and lower endoplasmic reticulum (ER) calcium stores, as indicated by depletion with thapsigargin. Indeed, mitochondrial fission was associated with ER stress. Additionally, the calcium-replenishing process of store-operated calcium entry was impaired in MFN2 knockdown cells, whereas DRP1-DN-promoted fusion resulted in faster cytosolic Ca2+ increase rates. Overall, our results show a novel role for mitochondrial morphology in the regulation of mitochondrial Ca2+ uptake, which impacts cellular Ca2+ homeostasis.-Kowaltowski, A. J., Menezes-Filho, S. L., Assali, E. A., Gonçalves, I. G., Cabral-Costa, J. V., Abreu, P., Miller, N., Nolasco, P., Laurindo, F. R. M., Bruni-Cardoso, A., Shirihai, O. Mitochondrial morphology regulates organellar Ca2+ uptake and changes cellular Ca2+ homeostasis.
    Keywords:  ER stress; bioenergetics; calcium; metabolism; mitochondria
  4. Cell Metab. 2019 Aug 27. pii: S1550-4131(19)30432-2. [Epub ahead of print]
    Chung KW, Dhillon P, Huang S, Sheng X, Shrestha R, Qiu C, Kaufman BA, Park J, Pei L, Baur J, Palmer M, Susztak K.
      Fibrosis is the final common pathway leading to end-stage renal failure. By analyzing the kidneys of patients and animal models with fibrosis, we observed a significant mitochondrial defect, including the loss of the mitochondrial transcription factor A (TFAM) in kidney tubule cells. Here, we generated mice with tubule-specific deletion of TFAM (Ksp-Cre/Tfamflox/flox). While these mice developed severe mitochondrial loss and energetic deficit by 6 weeks of age, kidney fibrosis, immune cell infiltration, and progressive azotemia causing death were only observed around 12 weeks of age. In renal cells of TFAM KO (knockout) mice, aberrant packaging of the mitochondrial DNA (mtDNA) resulted in its cytosolic translocation, activation of the cytosolic cGAS-stimulator of interferon genes (STING) DNA sensing pathway, and thus cytokine expression and immune cell recruitment. Ablation of STING ameliorated kidney fibrosis in mouse models of chronic kidney disease, demonstrating how TFAM sequesters mtDNA to limit the inflammation leading to fibrosis.
    Keywords:  TFAM; cGAS-STING pathway; chronic kidney disease; innate immunity; mitochondrial DNA; mitochondrial transcription factor A; renal fibrosis
  5. J Mol Cell Cardiol. 2019 Sep 03. pii: S0022-2828(19)30174-9. [Epub ahead of print]
    Lu X, Thai PN, Lu S, Pu J, Bers DM.
      Mitochondria are involved in multiple cellular functions, in addition to their core role in energy metabolism. Mitochondria localized in different cellular locations may have different morphology, Ca2+ handling and biochemical properties and may interact differently with other intracellular structures, causing functional specificity. However, most prior studies have utilized isolated mitochondria, removed from their intracellular environment. Mitochondria in cardiac ventricular myocytes are highly organized, with a majority squeezed between the myofilaments in longitudinal chains (intrafibrillar mitochondria, IFM). There is another population of perinuclear mitochondria (PNM) around and between the two nuclei typical in myocytes. Here, we take advantage of live myocyte imaging to test for quantitative morphological and functional differences between IFM and PNM with respect to calcium fluxes, membrane potential, sensitivity to oxidative stress, shape and dynamics. Our findings show higher mitochondrial Ca2+ uptake and oxidative stress sensitivity for IFM vs. PNM, which may relate to higher local energy demand supporting the contractile machinery. In contrast to IFM which are remarkably static, PNM are relatively mobile, appear to participate readily in fission/fusion dynamics and appear to play a central role in mitochondrial genesis and turnover. We conclude that while IFM may be physiologically tuned to support local myofilament energy demands, PNM may be more critical in mitochondrial turnover and regulation of nuclear function and import/export. Thus, important functional differences are present in intrafibrillar vs. perinuclear mitochondrial subpopulations.
    Keywords:  Mitochondrial Ca; Mitochondrial dynamic; Mitochondrial heterogeneity
  6. Biosci Rep. 2019 Sep 04. pii: BSR20192101. [Epub ahead of print]
    Ivanova IG, Perkins ND.
      The NF-kB family of transcription factors can directly or indirectly regulate many important areas of biology, including immunity, inflammation and cell survival. One intriguing aspect of NF-kB crosstalk with other cell signalling pathways is its regulation of mitochondrial biology, including biogenesis, metabolism and apoptosis. In addition to regulating the expression of mitochondrial genes encoded in the nucleus, NF-kB signalling components are also found within mitochondria themselves and associated with mitochondrial DNA. However, complete biochemical analysis of mitochondrial and sub-mitochondrial localisation of all NF-kB subunits has not been undertaken. Here we show that only the RelA NF-kB subunit and its inhibitor IkBa reside within mitochondria, while p50 is found in the endoplasmic reticulum (ER). Fractionation of mitochondria revealed that only RelA was found in the mitoplast, the location of the mtDNA. We demonstrate that hypoxia leads to a very rapid but transient accumulation of RelA and IkBa in mitochondria. This effect required reactive oxygen species (ROS) but was not dependent on the hypoxia sensing transcription factor subunit HIF1a or intracellular Ca2+ release. We also observed rapid mitochondrial localisation of transcription factor STAT3 following hypoxia. Inhibition of STAT3 blocked RelA and IkBa mitochondrial localisation revealing a previously unknown aspect of crosstalk between these key cellular regulators.
    Keywords:  hypoxia; mitochondria; nuclear factor kappaB; reactive oxygen species
  7. Arch Pharm Res. 2019 Sep 04.
    Cho HY, Kleeberger SR.
      A constant improvement in understanding of mitochondrial biology has provided new insights into mitochondrial dysfunction in human disease pathogenesis. Impaired mitochondrial dynamics caused by various stressors are characterized by structural abnormalities and leakage, compromised turnover, and reactive oxygen species overproduction in mitochondria as well as increased mitochondrial DNA mutation frequency, which leads to modified energy production and mitochondria-derived cell signaling. The mitochondrial dysfunction in airway epithelial, smooth muscle, and endothelial cells has been implicated in diseases including chronic obstructive lung diseases and acute lung injury. Increasing evidence indicates that the NRF2-antioxidant response element (ARE) pathway not only enhances redox defense but also facilitates mitochondrial homeostasis and bioenergetics. Identification of functional or potential AREs further supports the role for Nrf2 in mitochondrial dysfunction-associated airway disorders. While clinical reports indicate mixed efficacy, NRF2 agonists acting on respiratory mitochondrial dynamics are potentially beneficial. In lung cancer, growth advantage provided by sustained NRF2 activation is suggested to be through increased cellular antioxidant defense as well as mitochondria reinforcement and metabolic reprogramming to the preferred pathways to meet the increased energy demands of uncontrolled cell proliferation. Further studies are warranted to better understand NRF2 regulation of mitochondrial functions as therapeutic targets in airway disorders.
    Keywords:  Antioxidant response element; Lung; Metabolism; Mitochondria; NRF2; Sulforaphane
  8. J Clin Invest. 2019 Sep 04. pii: 127597. [Epub ahead of print]
    De Souza DP, Achuthan A, Lee MK, Binger KJ, Lee MC, Davidson S, Tull DL, McConville MJ, Cook AD, Murphy AJ, Hamilton JA, Fleetwood AJ.
      Macrophage activation in response to LPS is coupled to profound metabolic changes, typified by accumulation of the TCA cycle intermediates citrate, itaconate, and succinate. We have identified that endogenous type I IFN controls the cellular citrate/α-ketoglutarate ratio and inhibits expression and activity of isocitrate dehydrogenase (IDH); and, via 13C-labeling studies, demonstrated that autocrine type I IFN controls carbon flow through IDH in LPS-activated macrophages. We also found that type I IFN-driven IL-10 contributes to inhibition of IDH activity and itaconate synthesis in LPS-stimulated macrophages. Our findings have identified the autocrine type I IFN pathway as being responsible for the inhibition of IDH in LPS-stimulated macrophages.
    Keywords:  Cellular immune response; Inflammation; Macrophages; Metabolism; Mitochondria
  9. J Cell Physiol. 2019 Sep 06.
    Altinok O, Poggio JL, Stein DE, Bowne WB, Shieh AC, Snyder NW, Orynbayeva Z.
      Metabolism in cancer cells is rewired to generate sufficient energy equivalents and anabolic precursors to support high proliferative activity. Within the context of these competing drives aerobic glycolysis is inefficient for the cancer cellular energy economy. Therefore, many cancer types, including colon cancer, reprogram mitochondria-dependent processes to fulfill their elevated energy demands. Elevated glycolysis underlying the Warburg effect is an established signature of cancer metabolism. However, there are a growing number of studies that show that mitochondria remain highly oxidative under glycolytic conditions. We hypothesized that activities of glycolysis and oxidative phosphorylation are coordinated to maintain redox compartmentalization. We investigated the role of mitochondria-associated malate-aspartate and lactate shuttles in colon cancer cells as potential regulators that couple aerobic glycolysis and oxidative phosphorylation. We demonstrated that the malate-aspartate shuttle exerts control over NAD+ /NADH homeostasis to maintain activity of mitochondrial lactate dehydrogenase and to enable aerobic oxidation of glycolytic l-lactate in mitochondria. The elevated glycolysis in cancer cells is proposed to be one of the mechanisms acquired to accelerate oxidative phosphorylation.
    Keywords:  OxPhos; colon cancer; l-lactate; mLDH; malate-aspartate shuttle
  10. Redox Biol. 2019 Aug 25. pii: S2213-2317(19)30733-5. [Epub ahead of print]26 101307
    Gu L, Larson Casey JL, Andrabi SA, Lee JH, Meza-Perez S, Randall TD, Carter AB.
      Idiopathic pulmonary fibrosis (IPF) is a progressive disease with an increased mortality. Metabolic reprogramming has a critical role in multiple chronic diseases. Lung macrophages expressing the mitochondrial calcium uniporter (MCU) have a critical role in fibrotic repair, but the contribution of MCU in macrophage metabolism is not known. Here, we show that MCU regulates peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and metabolic reprogramming to fatty acid oxidation (FAO) in macrophages. MCU regulated PGC-1α expression by increasing the phosphorylation of ATF-2 by the p38 MAPK in a redox-dependent manner. The expression and activation of PGC-1α via the p38 MAPK was regulated by MCU-mediated mitochondrial calcium uptake, which is linked to increased mitochondrial ROS (mtROS) production. Mice harboring a conditional expression of dominant-negative MCU in macrophages had a marked reduction in mtROS and FAO and were protected from pulmonary fibrosis. Moreover, IPF lung macrophages had evidence of increased MCU and mitochondrial calcium, increased phosphorylation of ATF2 and p38, as well as increased expression of PGC-1α. These observations suggest that macrophage MCU-mediated metabolic reprogramming contributes to fibrotic repair after lung injury.
    Keywords:  Fatty acid oxidation (FAO); MCU; Metabolic reprogramming; Mitochondrial ROS; PGC-1α; Pulmonary fibrosis
  11. Mol Biol Cell. 2019 Sep 04. mbcE19030166
    Odendall F, Backes S, Tatsuta T, Weill U, Schuldiner M, Langer T, Herrmann JM, Rapaport D, Dimmer KS.
      Mitochondria are unique organelles harboring two distinct membranes, the mitochondrial inner and outer membrane (MIM and MOM, respectively). Mitochondria comprise only a subset of metabolic pathways for the synthesis of membrane lipids, therefore most lipid species and their precursors have to be imported from other cellular compartments. One of such import processes is mediated by the ER mitochondria encounter structure (ERMES) complex. Both mitochondrial membranes surround the hydrophilic intermembrane space (IMS). Therefore additional systems are required that shuttle lipids between MIM and MOM. Recently, we identified the IMS protein Mcp2 as a high-copy suppressor for cells that lack functional ERMES complex. To understand better, how mitochondria facilitate transport and biogenesis of lipids, we searched for genetic interactions of this suppressor. We found, that MCP2 has a negative genetic interaction with the gene TGL2 encoding a neutral lipid hydrolase. We show that this lipase is located in the intermembrane space of mitochondria and is imported via the Mia40 disulfide relay system. Furthermore, we show a positive genetic interaction of double deletion of MCP2 and PSD1, the gene encoding the enzyme that synthesizes the major amount of cellular phosphatidylethanolamine. Finally, we demonstrate that the nucleotide binding motifs of the predicted atypical kinase Mcp2 are required for its proper function. Taken together, our data suggest that Mcp2 is involved in mitochondrial lipid metabolism and a rise of this involvement by overexpression suppresses loss of ERMES.
  12. Nature. 2019 Sep 04.
    Padmanaban V, Krol I, Suhail Y, Szczerba BM, Aceto N, Bader JS, Ewald AJ.
      Metastasis is the major driver of death in patients with cancer. Invasion of surrounding tissues and metastasis have been proposed to initiate following loss of the intercellular adhesion protein, E-cadherin1,2, on the basis of inverse correlations between in vitro migration and E-cadherin levels3. However, this hypothesis is inconsistent with the observation that most breast cancers are invasive ductal carcinomas and express E-cadherin in primary tumours and metastases4. To resolve this discrepancy, we tested the genetic requirement for E-cadherin in metastasis using mouse and human models of both luminal and basal invasive ductal carcinomas. Here we show that E-cadherin promotes metastasis in diverse models of invasive ductal carcinomas. While loss of E-cadherin increased invasion, it also reduced cancer cell proliferation and survival, circulating tumour cell number, seeding of cancer cells in distant organs and metastasis outgrowth. Transcriptionally, loss of E-cadherin was associated with upregulation of genes involved in transforming growth factor-β (TGFβ), reactive oxygen species and apoptosis signalling pathways. At the cellular level, disseminating E-cadherin-negative cells exhibited nuclear enrichment of SMAD2/3, oxidative stress and increased apoptosis. Colony formation of E-cadherin-negative cells was rescued by inhibition of TGFβ-receptor signalling, reactive oxygen accumulation or apoptosis. Our results reveal that E-cadherin acts as a survival factor in invasive ductal carcinomas during the detachment, systemic dissemination and seeding phases of metastasis by limiting reactive oxygen-mediated apoptosis. Identifying molecular strategies to inhibit E-cadherin-mediated survival in metastatic breast cancer cells may have potential as a therapeutic approach for breast cancer.
  13. Int J Mol Sci. 2019 Sep 03. pii: E4311. [Epub ahead of print]20(17):
    Kondadi AK, Anand R, Reichert AS.
      Mitochondria are vital cellular organelles involved in a plethora of cellular processes such as energy conversion, calcium homeostasis, heme biogenesis, regulation of apoptosis and ROS reactive oxygen species (ROS) production. Although they are frequently depicted as static bean-shaped structures, our view has markedly changed over the past few decades as many studies have revealed a remarkable dynamicity of mitochondrial shapes and sizes both at the cellular and intra-mitochondrial levels. Aberrant changes in mitochondrial dynamics and cristae structure are associated with ageing and numerous human diseases (e.g., cancer, diabetes, various neurodegenerative diseases, types of neuro- and myopathies). Another unique feature of mitochondria is that they harbor their own genome, the mitochondrial DNA (mtDNA). MtDNA exists in several hundreds to thousands of copies per cell and is arranged and packaged in the mitochondrial matrix in structures termed mt-nucleoids. Many human diseases are mechanistically linked to mitochondrial dysfunction and alteration of the number and/or the integrity of mtDNA. In particular, several recent studies identified remarkable and partly unexpected links between mitochondrial structure, fusion and fission dynamics, and mtDNA. In this review, we will provide an overview about these recent insights and aim to clarify how mitochondrial dynamics, cristae ultrastructure and mtDNA structure influence each other and determine mitochondrial functions.
    Keywords:  cristae; fusion and fission; mitochondrial dynamics; mitochondriopathy; mtDNA
  14. Mol Cell. 2019 Aug 12. pii: S1097-2765(19)30551-9. [Epub ahead of print]
    Beaumatin F, O'Prey J, Barthet VJA, Zunino B, Parvy JP, Bachmann AM, O'Prey M, Kania E, Gonzalez PS, Macintosh R, Lao LY, Nixon C, Lopez J, Long JS, Tait SWG, Ryan KM.
      Sensing nutrient availability is essential for appropriate cellular growth, and mTORC1 is a major regulator of this process. Mechanisms causing mTORC1 activation are, however, complex and diverse. We report here an additional important step in the activation of mTORC1, which regulates the efflux of amino acids from lysosomes into the cytoplasm. This process requires DRAM-1, which binds the membrane carrier protein SCAMP3 and the amino acid transporters SLC1A5 and LAT1, directing them to lysosomes and permitting efficient mTORC1 activation. Consequently, we show that loss of DRAM-1 also impacts pathways regulated by mTORC1, including insulin signaling, glycemic balance, and adipocyte differentiation. Interestingly, although DRAM-1 can promote autophagy, this effect on mTORC1 is autophagy independent, and autophagy only becomes important for mTORC1 activation when DRAM-1 is deleted. These findings provide important insights into mTORC1 activation and highlight the importance of DRAM-1 in growth control, metabolic homeostasis, and differentiation.
    Keywords:  DRAM-1; SCAMP3; amino acid transporters; and adipocyte differentiation; autophagy; insulin signaling; mTOR
  15. Am J Physiol Cell Physiol. 2019 Sep 04.
    Turnbull PC, Hughes MC, Perry CGR.
      Previous evidence suggests that palmitoylcarnitine incubations trigger mitochondrial-mediated apoptosis in HT29 colorectal adenocarcinoma cells, yet non-transformed cells appear resistant. The mechanism by which palmitoylcarnitine induces cancer cell death is unclear. The purpose of this investigation was to examine the relationship between mitochondrial kinetics and glutathione buffering in determining the effect of palmitoylcarnitine on cell survival. HT29 and HCT 116 colorectal adenocarcinoma cells, CCD 841 non-transformed colon cells and MCF7 breast adenocarcinoma cells were exposed to 0μM, 50μM and 100μM palmitoylcarnitine for 24-48 hours. HCT 116 and HT29 cells showed decreased cell survival following palmitoylcarnitine compared to CCD 841 cells. Palmitoylcarnitine stimulated H2O2 emission in HT29 and CCD 841 cells but increased it to a greater level in HT29 cells due largely to a higher basal H2O2 emission. This greater H2O2 emission was associated with lower glutathione buffering capacity and caspase-3 activation in HT29 cells. The glutathione depleting agent, buthionine sulfoximine, sensitized CCD 841 cells and further sensitized HT29 cells to palmitoylcarnitine-induced decreases in cell survival. MCF7 cells did not produce H2O2 when exposed to palmitoylcarnitine and were able to maintain glutathione levels. Furthermore, HT29 cells demonstrated the lowest mitochondrial oxidative kinetics vs CCD 841 and MCF7 cells. The results demonstrate that colorectal cancer is sensitive to palmitoylcarnitine due in part to an inability to prevent oxidative stress through glutathione-redox coupling thereby rendering the cells sensitive to elevations in H2O2. These findings suggest that the relationship between inherent metabolic capacities and redox regulation is altered early in response to palmitoylcarnitine.
    Keywords:  Cancer; Warburg effect; glutathione; mitochondria; reactive oxygen species (ROS)
  16. Proc Natl Acad Sci U S A. 2019 Sep 06. pii: 201902397. [Epub ahead of print]
    He L, Fei DL, Nagiec MJ, Mutvei AP, Lamprakis A, Kim BY, Blenis J.
      The mTORC1 pathway regulates cell growth and proliferation by properly coupling critical processes such as gene expression, protein translation, and metabolism to the availability of growth factors and hormones, nutrients, cellular energetics, oxygen status, and cell stress. Although multiple cytoplasmic substrates of mTORC1 have been identified, how mTORC1 signals within the nucleus remains incompletely understood. Here, we report a mechanism by which mTORC1 modulates the phosphorylation of multiple nuclear events. We observed a significant nuclear enrichment of GSK3 when mTORC1 was suppressed, which promotes phosphorylation of several proteins such as GTF2F1 and FOXK1. Importantly, nuclear localization of GSK3 is sufficient to suppress cell proliferation. Additionally, expression of a nuclear exporter of GSK3, FRAT, restricts the nuclear localization of GSK3, represses nuclear protein phosphorylation, and prevents rapamycin-induced cytostasis. Finally, we observe a correlation between rapamycin resistance and FRAT expression in multiple-cancer cell lines. Resistance to Food and Drug Administration (FDA)-approved rapamycin analogs (rapalogs) is observed in many tumor settings, but the underling mechanisms remain incompletely understood. Given that FRAT expression levels are frequently elevated in various cancers, our observations provide a potential biomarker and strategy for overcoming rapamycin resistance.
    Keywords:  FRAT; GSK3; Resistance; mTOR
  17. Sci Rep. 2019 Sep 02. 9(1): 12651
    Grings M, Seminotti B, Karunanidhi A, Ghaloul-Gonzalez L, Mohsen AW, Wipf P, Palmfeldt J, Vockley J, Leipnitz G.
      Ethylmalonic encephalopathy protein 1 (ETHE1) and molybdenum cofactor (MoCo) deficiencies are hereditary disorders that affect the catabolism of sulfur-containing amino acids. ETHE1 deficiency is caused by mutations in the ETHE1 gene, while MoCo deficiency is due to mutations in one of three genes involved in MoCo biosynthesis (MOCS1, MOCS2 and GPHN). Patients with both disorders exhibit abnormalities of the mitochondrial respiratory chain, among other biochemical findings. However, the pathophysiology of the defects has not been elucidated. To characterize cellular derangements, mitochondrial bioenergetics, dynamics, endoplasmic reticulum (ER)-mitochondria communication, superoxide production and apoptosis were evaluated in fibroblasts from four patients with ETHE1 deficiency and one with MOCS1 deficiency. The effect of JP4-039, a promising mitochondrial-targeted antioxidant, was also tested on cells. Our data show that mitochondrial respiration was decreased in all patient cell lines. ATP depletion and increased mitochondrial mass was identified in the same cells, while variable alterations in mitochondrial fusion and fission were seen. High superoxide levels were found in all cells and were decreased by treatment with JP4-039, while the respiratory chain activity was increased by this antioxidant in cells in which it was impaired. The content of VDAC1 and IP3R, proteins involved in ER-mitochondria communication, was decreased, while DDIT3, a marker of ER stress, and apoptosis were increased in all cell lines. These data demonstrate that previously unrecognized broad disturbances of cellular function are involved in the pathophysiology of ETHE1 and MOCS1 deficiencies, and that reduction of mitochondrial superoxide by JP4-039 is a promising strategy for adjuvant therapy of these disorders.
  18. Proc Natl Acad Sci U S A. 2019 Sep 05. pii: 201904979. [Epub ahead of print]
    Li J, Wang PY, Long NA, Zhuang J, Springer DA, Zou J, Lin Y, Bleck CKE, Park JH, Kang JG, Hwang PM.
      Doxorubicin is a widely used chemotherapeutic agent that causes dose-dependent cardiotoxicity in a subset of treated patients, but the genetic determinants of this susceptibility are poorly understood. Here, we report that a noncanonical tumor suppressor activity of p53 prevents cardiac dysfunction in a mouse model induced by doxorubicin administered in divided low doses as in the clinics. While relatively preserved in wild-type (p53 +/+ ) state, mice deficient in p53 (p53 -/- ) developed left ventricular (LV) systolic dysfunction after doxorubicin treatment. This functional decline in p53 -/- mice was associated with decreases in cardiac oxidative metabolism, mitochondrial mass, and mitochondrial genomic DNA (mtDNA) homeostasis. Notably, mice with homozygous knockin of the p53 R172H (p53 172H/H ) mutation, which like p53 -/- state lacks the prototypical tumor suppressor activities of p53 such as apoptosis but retains its mitochondrial biogenesis capacity, showed preservation of LV function and mitochondria after doxorubicin treatment. In contrast to p53-null state, wild-type and mutant p53 displayed distinct mechanisms of transactivating mitochondrial transcription factor A (TFAM) and p53-inducible ribonucleotide reductase 2 (p53R2), which are involved in mtDNA transcription and maintenance. Importantly, supplementing mice with a precursor of NAD+ prevented the mtDNA depletion and cardiac dysfunction. These findings suggest that loss of mtDNA contributes to cardiomyopathy pathogenesis induced by doxorubicin administered on a schedule simulating that in the clinics. Given a similar mtDNA protection role of p53 in doxorubicin-treated human induced pluripotent stem cell (iPSC)-derived cardiomyocytes, the mitochondrial markers associated with cardiomyopathy development observed in blood and skeletal muscle cells may have prognostic utility.
    Keywords:  anthracycline; cardiomyopathy; mitochondria; mtDNA; p53
  19. Bone. 2019 Aug 31. pii: S8756-3282(19)30346-1. [Epub ahead of print]129 115056
    Lee SH, Lee SH, Lee JH, Park JW, Kim JE.
      Mitochondria are not only responsible for cellular energy production but are also involved in signaling, cellular differentiation, cell death, and aging. Mitochondrial NADP+-dependent isocitrate dehydrogenase (IDH2) catalyzes the decarboxylation of isocitrate to α-ketoglutarate, accompanied by NADPH production. IDH2 plays a central role in mitochondrial function in multiple cell types and various organs, including the heart, kidneys, and brain. However, the function of IDH2 in bone tissue is yet to be elucidated. Here, we report that disruption of IDH2 in mice results in high bone mass due to decreased osteoclast number and resorption activity. Although IDH2 played no cell-intrinsic role in osteoclasts, IDH2-deficient animals showed decreased serum markers of osteoclast activity and bone resorption. Bone marrow stromal cells/osteoblasts from Idh2 knockout mice were defective in promoting osteoclastogenesis due to a reduced expression of a key osteoclastogenic factor, receptor activator of nuclear factor-κB ligand (RANKL), in osteoblasts in vivo and in vitro through the attenuation of ATF4-NFATc1 signaling. Our findings suggest that IDH2 is a novel regulator of osteoblast-to-osteoclast communication and bone metabolism, acting via the ATF4-NFATc1-RANKL signaling axis in osteoblasts, and they provide a rationale for further study of IDH2 as a potential therapeutic target for the prevention of bone loss.
    Keywords:  High bone mass; IDH2; Osteoblast-to-osteoclast crosstalk; RANKL
  20. Cancer Res. 2019 Sep 05. pii: canres.0198.2019. [Epub ahead of print]
    Jung J, Zhang Y, Celiku O, Zhang W, Song H, Williams BJ, Giles AJ, Rich JN, Abounader R, Gilbert MR, Park DM.
      Cancer cells rely on mitochondrial functions to regulate key survival and death signals. How cancer cells regulate mitochondrial autophagy (mitophagy) in the tumor microenvironment as well as utilize mitophagy as a survival signal is still not well understood. Here we elucidate a key survival mechanism of mitochondrial NIX-mediated mitophagy within the hypoxic region of glioblastoma, the most malignant brain tumor. NIX was overexpressed in the pseudopalisading cells that envelop the hypoxic-necrotic regions, and mitochondrial NIX expression was robust in patient-derived glioblastoma tumor tissues and glioblastoma stem cells (GSC). NIX was required for hypoxia and oxidative stress-induced mitophagy through NFE2L2/NRF2 transactivation. Silencing NIX impaired mitochondrial reactive oxygen species (ROS) clearance, cancer stem cell maintenance, and HIF/mTOR/RHEB signaling pathways under hypoxia, resulting in suppression of glioblastoma survival in vitro and in vivo. Clinical significance of these findings was validated by the compelling association between NIX expression and poor outcome for glioblastoma patients. Taken together, our findings indicate that the NIX-mediated mitophagic pathway may represent a key therapeutic target for solid tumors including glioblastoma.
  21. Cell Metab. 2019 Sep 03. pii: S1550-4131(19)30442-5. [Epub ahead of print]30(3): 434-446
    Kim J, DeBerardinis RJ.
      Tumors display reprogrammed metabolic activities that promote cancer progression. We currently possess a limited understanding of the processes governing tumor metabolism in vivo and of the most efficient approaches to identify metabolic vulnerabilities susceptible to therapeutic targeting. While much of the literature focuses on stereotyped, cell-autonomous pathways like glycolysis, recent work emphasizes heterogeneity and flexibility of metabolism between tumors and even within distinct regions of solid tumors. Metabolic heterogeneity is important because it influences therapeutic vulnerabilities and may predict clinical outcomes. This Review describes current concepts about metabolic regulation in tumors, focusing on processes intrinsic to cancer cells and on factors imposed upon cancer cells by the tumor microenvironment. We discuss experimental approaches to identify subtype-selective metabolic vulnerabilities in preclinical cancer models. Finally, we describe efforts to characterize metabolism in primary human tumors, which should produce new insights into metabolic heterogeneity in the context of clinically relevant microenvironments.
  22. Cancer Discov. 2019 Sep;9(9): 1161-1163
    Affronti HC, Wellen KE.
      In this issue of Cancer Discovery, Gimple and colleagues examine superenhancers in glioblastoma and glioma stem cells (GSC), identifying one which promotes expression of ELOVL2, an enzyme in polyunsaturated fatty acid (PUFA) synthesis. They find that ELOVL2 products help maintain cell membrane organization and EGFR signaling in GSCs, and that targeting PUFA metabolism along with EGFR offers a potential novel therapeutic strategy for glioblastoma.See related article by Gimple et al., p. 1248.
  23. Trends Biochem Sci. 2019 Aug 28. pii: S0968-0004(19)30176-8. [Epub ahead of print]
    Bommer GT, Van Schaftingen E, Veiga-da-Cunha M.
      Hundreds of metabolic enzymes work together smoothly in a cell. These enzymes are highly specific. Nevertheless, under physiological conditions, many perform side-reactions at low rates, producing potentially toxic side-products. An increasing number of metabolite repair enzymes are being discovered that serve to eliminate these noncanonical metabolites. Some of these enzymes are extraordinarily conserved, and their deficiency can lead to diseases in humans or embryonic lethality in mice, indicating their central role in cellular metabolism. We discuss how metabolite repair enzymes eliminate glycolytic side-products and prevent negative interference within and beyond this core metabolic pathway. Extrapolating from the number of metabolite repair enzymes involved in glycolysis, hundreds more likely remain to be discovered that protect a wide range of metabolic pathways.
    Keywords:  enzyme specificity; inborn errors of metabolism, glycolysis; metabolite damage; spontaneous reaction
  24. Mol Cell. 2019 Aug 16. pii: S1097-2765(19)30552-0. [Epub ahead of print]
    Letts JA, Fiedorczuk K, Degliesposti G, Skehel M, Sazanov LA.
      The mitochondrial electron transport chain complexes are organized into supercomplexes (SCs) of defined stoichiometry, which have been proposed to regulate electron flux via substrate channeling. We demonstrate that CoQ trapping in the isolated SC I+III2 limits complex (C)I turnover, arguing against channeling. The SC structure, resolved at up to 3.8 Å in four distinct states, suggests that CoQ oxidation may be rate limiting because of unequal access of CoQ to the active sites of CIII2. CI shows a transition between "closed" and "open" conformations, accompanied by the striking rotation of a key transmembrane helix. Furthermore, the state of CI affects the conformational flexibility within CIII2, demonstrating crosstalk between the enzymes. CoQ was identified at only three of the four binding sites in CIII2, suggesting that interaction with CI disrupts CIII2 symmetry in a functionally relevant manner. Together, these observations indicate a more nuanced functional role for the SCs.
    Keywords:  bioenergetics; complex i; cryoEM; cytochrome bc1 complex; mitochondria; oxidative phosphorylation; oxidoreductas; protein structure; respiration; supercomplex
  25. J Membr Biol. 2019 Sep 04.
    De Vecchis D, Brandner A, Baaden M, Cohen MM, Taly A.
      Mitochondria are dynamic organelles characterized by an ultrastructural organization which is essential in maintaining their quality control and ensuring functional efficiency. The complex mitochondrial network is the result of the two ongoing forces of fusion and fission of inner and outer membranes. Understanding the functional details of mitochondrial dynamics is physiologically relevant as perturbations of this delicate equilibrium have critical consequences and involved in several neurological disorders. Molecular actors involved in this process are large GTPases from the dynamin-related protein family. They catalyze nucleotide-dependent membrane remodeling and are widely conserved from bacteria to higher eukaryotes. Although structural characterization of different family members has contributed in understanding molecular mechanisms of mitochondrial dynamics in more detail, the complete structure of some members as well as the precise assembly of functional oligomers remains largely unknown. As increasing structural data become available, the domain modularity across the dynamin superfamily emerged as a foundation for transfering the knowledge towards less characterized members. In this review, we will first provide an overview of the main actors involved in mitochondrial dynamics. We then discuss recent example of computational methodologies for the study of mitofusin oligomers, and present how the usage of integrative modeling in conjunction with biochemical data can be an asset in progressing the still challenging field of membrane dynamics.
    Keywords:  Dynamin-related proteins; Fzo1; Mitochondrial dynamics; Mitochondrial fission; Mitochondrial fusion; Mitofusin
  26. Nat Rev Nephrol. 2019 Sep 05.
    Menezes LF, Germino GG.
      Autosomal dominant polycystic kidney disease (ADPKD) affects an estimated 1 in 1,000 people and slowly progresses to end-stage renal disease (ESRD) in about half of these individuals. Tolvaptan, a vasopressin 2 receptor blocker, has been approved by regulatory authorities in many countries as a therapy to slow cyst growth, but additional treatments that target dysregulated signalling pathways in cystic kidney and liver are needed. Metabolic reprogramming is a prominent feature of cystic cells and a potentially important contributor to the pathophysiology of ADPKD. A number of pathways previously implicated in the pathogenesis of the disease, such as dysregulated mTOR and primary ciliary signalling, have roles in metabolic regulation and may exert their effects through this mechanism. Some of these pathways are amenable to manipulation through dietary modifications or drug therapies. Studies suggest that polycystin-1 and polycystin-2, which are encoded by PKD1 and PKD2, respectively (the genes that are mutated in >99% of patients with ADPKD), may in part affect cellular metabolism through direct effects on mitochondrial function. Mitochondrial dysfunction could alter the redox state and cellular levels of acetyl-CoA, resulting in altered histone acetylation, gene expression, cytoskeletal architecture and response to cellular stress, and in an immunological response that further promotes cyst growth and fibrosis.
  27. Proc Natl Acad Sci U S A. 2019 Sep 03. pii: 201911895. [Epub ahead of print]
    Panagaki T, Randi EB, Augsburger F, Szabo C.
      Down syndrome (DS) is associated with significant perturbances in mitochondrial function. Here we tested the hypothesis that the suppression of mitochondrial electron transport in DS cells is due to high expression of cystathionine-β-synthase (CBS) and subsequent overproduction of the gaseous transmitter hydrogen sulfide (H2S). Fibroblasts from DS individuals showed higher CBS expression than control cells; CBS localization was both cytosolic and mitochondrial. DS cells produced significantly more H2S and polysulfide and exhibited a profound suppression of mitochondrial electron transport, oxygen consumption, and ATP generation. DS cells also exhibited slower proliferation rates. In DS cells, pharmacological inhibition of CBS activity with aminooxyacetate or siRNA-mediated silencing of CBS normalized cellular H2S levels, restored Complex IV activity, improved mitochondrial electron transport and ATP synthesis, and restored cell proliferation. Thus, CBS-derived H2S is responsible for the suppression of mitochondrial function in DS cells. When H2S overproduction is corrected, the tonic suppression of Complex IV is lifted, and mitochondrial electron transport is restored. CBS inhibition offers a potential approach for the pharmacological correction of DS-associated mitochondrial dysfunction.
    Keywords:  H2S; bioenergetics; metabolism; mitochondria
  28. Aging Cell. 2019 Sep 06. e13029
    Ross JM, Coppotelli G, Branca RM, Kim KM, Lehtiö J, Sinclair DA, Olson L.
      The accumulation of mitochondrial DNA (mtDNA) mutations is a suspected driver of aging and age-related diseases, but forestalling these changes has been a major challenge. One of the best-studied models is the prematurely aging mtDNA mutator mouse, which carries a homozygous knock-in of a proofreading deficient version of the catalytic subunit of mtDNA polymerase-γ (PolgA). We investigated how voluntary exercise affects the progression of aging phenotypes in this mouse, focusing on mitochondrial and protein homeostasis in both brain and peripheral tissues. Voluntary exercise significantly ameliorated several aspects of the premature aging phenotype, including decreased locomotor activity, alopecia, and kyphosis, but did not have major effects on the decreased lifespan of mtDNA mutator mice. Exercise also decreased the mtDNA mutation load. In-depth tissue proteomics revealed that exercise normalized the levels of about half the proteins, with the majority involved in mitochondrial function and nuclear-mitochondrial crosstalk. There was also a specific increase in the nuclear-encoded proteins needed for the tricarboxylic acid cycle and complex II, but not in mitochondrial-encoded oxidative phosphorylation proteins, as well as normalization of enzymes involved in coenzyme Q biosynthesis. Furthermore, we found tissue-specific alterations, with brain coping better as compared to muscle and with motor cortex being better protected than striatum, in response to mitochondrial dysfunction. We conclude that voluntary exercise counteracts aging in mtDNA mutator mice by counteracting protein dysregulation in muscle and brain, decreasing the mtDNA mutation burden in muscle, and delaying overt aging phenotypes.
    Keywords:  PolG; aging; exercise; mitochondria; mtDNA; proteomics
  29. Trends Cancer. 2019 Sep;pii: S2405-8033(19)30143-8. [Epub ahead of print]5(9): 541-546
    Brosseau JP, Le LQ.
      Hereditary cancer syndromes are typically caused by mutations of a tumor suppressor gene that lead to the early development of multifocal benign neoplasms followed by their malignant progression. However, the term 'hereditary cancer syndrome' may be misleading, as a large subgroup of syndromes are characterized by highly penetrant benign tumors. The reason why these cardinal tumors rarely progress to malignancy has been an elusive question in cancer biology. In this opinion article, we propose a framework where a heterozygous tumor suppressor gene microenvironment has antagonistic roles in tumorigenesis, by accelerating development of benign tumors while restraining further progression to malignant cancers.
    Keywords:  MPNST; NF1; STK11; benign tumor; hereditary benign tumor syndromes; hereditary cancer; malignant peripheral nerve sheath tumor; neurofibroma; tumor microenvironment; tumor suppressor gene
  30. Cancer Res. 2019 Sep 04. pii: canres.1395.2019. [Epub ahead of print]
    Kenny TC, Gomez M, Germain D.
      The discovery of the Warburg effect - the preference of cancer cells to generate ATP via glycolysis rather than oxidative phosphorylation has fostered the misconception that cancer cells become independent of the electron transport chain (ETC) for survival. This is inconsistent with the need of ETC function for the generation of pyrimidines. Along with this misconception, a large body of literature has reported numerous mutations in mitochondrial DNA (mtDNA) further fueling the notion of non-functional ETC in cancer cells. More recent findings, however, suggest that cancers maintain oxidative phosphorylation capacity and that the role of mtDNA mutations in cancer is likely far more nuanced in light of the remarkable complexity of mitochondrial genetics. This review aims at describing the various model systems that were developed to dissect the role of mtDNA in cancer, including cybrids, and more recently mitochondria-nuclear exchange (MNX) and conplastic mice. Further, we put forward the notion of mtDNA landscapes, where the surrounding non-synonymous mutations and variants can enhance or repress the biological effect of specific mtDNA mutations. Notably, we review recent studies describing the ability of some mtDNA landscapes to activate the mitochondrial unfolded protein response (UPRmt), but not others. Further, the role of the UPRmt in maintaining cancer cells in the mitohormetic zone to provide selective adaptation to stress is discussed. Among the genes activated by the UPRmt, we suggest that the dismutases SOD2 and SOD1 may play key roles in the establishment of the mitohormetic zone. Finally, we propose that using a UPRmt nuclear gene expression signature may be a more reliable readout than mtDNA landscapes given their diversity and complexity.
  31. Mol Cell. 2019 Aug 22. pii: S1097-2765(19)30622-7. [Epub ahead of print]
    Qian X, Li X, Shi Z, Xia Y, Cai Q, Xu D, Tan L, Du L, Zheng Y, Zhao D, Zhang C, Lorenzi PL, You Y, Jiang BH, Jiang T, Li H, Lu Z.
      The PTEN tumor suppressor is frequently mutated or deleted in cancer and regulates glucose metabolism through the PI3K-AKT pathway. However, whether PTEN directly regulates glycolysis in tumor cells is unclear. We demonstrate here that PTEN directly interacts with phosphoglycerate kinase 1 (PGK1). PGK1 functions not only as a glycolytic enzyme but also as a protein kinase intermolecularly autophosphorylating itself at Y324 for activation. The protein phosphatase activity of PTEN dephosphorylates and inhibits autophosphorylated PGK1, thereby inhibiting glycolysis, ATP production, and brain tumor cell proliferation. In addition, knockin expression of a PGK1 Y324F mutant inhibits brain tumor formation. Analyses of human glioblastoma specimens reveals that PGK1 Y324 phosphorylation levels inversely correlate with PTEN expression status and are positively associated with poor prognosis in glioblastoma patients. This work highlights the instrumental role of PGK1 autophosphorylation in its activation and PTEN protein phosphatase activity in governing glycolysis and tumorigenesis.
    Keywords:  PGK1; PTEN; autophosphorylation; glycolysis; tumorigenesis
  32. Nat Commun. 2019 Sep 06. 10(1): 4052
    Wilinski D, Winzeler J, Duren W, Persons JL, Holme KJ, Mosquera J, Khabiri M, Kinchen JM, Freddolino PL, Karnovsky A, Dus M.
      Metabolites are active controllers of cellular physiology, but their role in complex behaviors is less clear. Here we report metabolic changes that occur during the transition between hunger and satiety in Drosophila melanogaster. To analyze these data in the context of fruit fly metabolic networks, we developed Flyscape, an open-access tool. We show that in response to eating, metabolic profiles change in quick, but distinct ways in the heads and bodies. Consumption of a high sugar diet dulls the metabolic and behavioral differences between the fasted and fed state, and reshapes the way nutrients are utilized upon eating. Specifically, we found that high dietary sugar increases TCA cycle activity, alters neurochemicals, and depletes 1-carbon metabolism and brain health metabolites N-acetyl-aspartate and kynurenine. Together, our work identifies the metabolic transitions that occur during hunger and satiation, and provides a platform to study the role of metabolites and diet in complex behavior.
  33. Cancer Res. 2019 Sep 03. pii: canres.0974.2019. [Epub ahead of print]
    Balic J, Garama DJ, Saad M, Yu L, West A, West AJ, Livis T, Bhathal PS, Gough DJ, Jenkins BJ.
      Deregulated activation of the latent oncogenic transcription factor signal transducer and activator of transcription (STAT)3 in many human epithelial malignancies, including gastric cancer (GC), has invariably been associated with its canonical tyrosine phosphorylation and enhanced transcriptional activity. By contrast, serine phosphorylation (pS) of STAT3 can augment its nuclear transcriptional activity and promote essential mitochondrial functions, yet the role of pS-STAT3 among epithelial cancers is ill-defined. Here, we reveal that genetic ablation of pS-STAT3 in the gp130F/F spontaneous GC mouse model and human GC cell line xenografts abrogated tumor growth that coincided with reduced proliferative potential of the tumor epithelium. Microarray gene expression profiling demonstrated that the suppressed gastric tumorigenesis in pS-STAT3-deficient gp130F/F mice associated with reduced transcriptional activity of STAT3-regulated gene networks implicated in cell proliferation and migration, inflammation and angiogenesis, but not mitochondrial function or metabolism. Notably, the pro-tumorigenic activity of pS-STAT3 aligned with its capacity to primarily augment RNA polymerase II-mediated transcriptional elongation, but not initiation, of STAT3 target genes. Furthermore, by employing a combinatorial in vitro and in vivo proteomics approach based on the rapid immunoprecipitation mass spectrometry of endogenous protein (RIME) assay, we identified RuvB-like AAA ATPase 1 (RUVBL1/Pontin) and enhancer of rudimentary homolog (ERH) as interacting partners of pS-STAT3 that are pivotal for its transcriptional activity on STAT3 target genes. Collectively, these findings uncover a hitherto unknown transcriptional role and obligate requirement for pS-STAT3 in GC that could be extrapolated to other STAT3-driven cancers.
  34. Nat Commun. 2019 Sep 02. 10(1): 3929
    Dieterich IA, Lawton AJ, Peng Y, Yu Q, Rhoads TW, Overmyer KA, Cui Y, Armstrong EA, Howell PR, Burhans MS, Li L, Denu JM, Coon JJ, Anderson RM, Puglielli L.
      AT-1/SLC33A1 is a key member of the endoplasmic reticulum (ER) acetylation machinery, transporting acetyl-CoA from the cytosol into the ER lumen where acetyl-CoA serves as the acetyl-group donor for Nε-lysine acetylation. Dysfunctional ER acetylation, as caused by heterozygous or homozygous mutations as well as gene duplication events of AT-1/SLC33A1, has been linked to both developmental and degenerative diseases. Here, we investigate two models of AT-1 dysregulation and altered acetyl-CoA flux: AT-1S113R/+ mice, a model of AT-1 haploinsufficiency, and AT-1 sTg mice, a model of AT-1 overexpression. The animals display distinct metabolic adaptation across intracellular compartments, including reprogramming of lipid metabolism and mitochondria bioenergetics. Mechanistically, the perturbations to AT-1-dependent acetyl-CoA flux result in global and specific changes in both the proteome and the acetyl-proteome (protein acetylation). Collectively, our results suggest that AT-1 acts as an important metabolic regulator that maintains acetyl-CoA homeostasis by promoting functional crosstalk between different intracellular organelles.
  35. Sci Adv. 2019 Aug;5(8): eaaw4597
    Karch J, Bround MJ, Khalil H, Sargent MA, Latchman N, Terada N, Peixoto PM, Molkentin JD.
      The mitochondrial permeability transition pore (MPTP) has resisted molecular identification. The original model of the MPTP that proposed the adenine nucleotide translocator (ANT) as the inner membrane pore-forming component was challenged when mitochondria from Ant1/2 double null mouse liver still had MPTP activity. Because mice express three Ant genes, we reinvestigated whether the ANTs comprise the MPTP. Liver mitochondria from Ant1, Ant2, and Ant4 deficient mice were highly refractory to Ca2+-induced MPTP formation, and when also given cyclosporine A (CsA), the MPTP was completely inhibited. Moreover, liver mitochondria from mice with quadruple deletion of Ant1, Ant2, Ant4, and Ppif (cyclophilin D, target of CsA) lacked Ca2+-induced MPTP formation. Inner-membrane patch clamping in mitochondria from Ant1, Ant2, and Ant4 triple null mouse embryonic fibroblasts showed a loss of MPTP activity. Our findings suggest a model for the MPTP consisting of two distinct molecular components: The ANTs and an unknown species requiring CypD.
  36. Mitochondrion. 2019 Aug 29. pii: S1567-7249(19)30183-7. [Epub ahead of print]
    George J, Jacobs HT.
      The PGC-1 transcriptional coactivators have been proposed as master regulators of mitochondrial biogenesis and energy metabolism. Here we show that the single member of the family in Drosophila, spargel (srl) has an essential role in early development. Female germline-specific RNAi knockdown resulted in embryonic semilethality. Embryos were small, with most suffering a catastrophic derangement of cellularization and gastrulation, although genes dependent on localized determinants were expressed normally. The abundance of mtDNA, representative mitochondrial proteins and mRNAs were not decreased in knockdown ovaries or embryos, indicating that srl has a more general role in early development than specifically promoting mitochondrial biogenesis.
    Keywords:  Drosophila; Embryogenesis; Mitochondrial biogenesis; Oogenesis; PGC-1α; Transcriptional coactivator
  37. Nat Commun. 2019 Sep 02. 10(1): 3925
    Matsuno Y, Atsumi Y, Shimizu A, Katayama K, Fujimori H, Hyodo M, Minakawa Y, Nakatsu Y, Kaneko S, Hamamoto R, Shimamura T, Miyano S, Tsuzuki T, Hanaoka F, Yoshioka KI.
      Mismatch repair (MMR)-deficient cancers are characterized by microsatellite instability (MSI) and hypermutation. However, it remains unclear how MSI and hypermutation arise and contribute to cancer development. Here, we show that MSI and hypermutation are triggered by replication stress in an MMR-deficient background, enabling clonal expansion of cells harboring ARF/p53-module mutations and cells that are resistant to the anti-cancer drug camptothecin. While replication stress-associated DNA double-strand breaks (DSBs) caused chromosomal instability (CIN) in an MMR-proficient background, they induced MSI with concomitant suppression of CIN via a PARP-mediated repair pathway in an MMR-deficient background. This was associated with the induction of mutations, including cancer-driver mutations in the ARF/p53 module, via chromosomal deletions and base substitutions. Immortalization of MMR-deficient mouse embryonic fibroblasts (MEFs) in association with ARF/p53-module mutations was ~60-fold more efficient than that of wild-type MEFs. Thus, replication stress-triggered MSI and hypermutation efficiently lead to clonal expansion of cells with abrogated defense systems.
  38. Cancers (Basel). 2019 Sep 03. pii: E1298. [Epub ahead of print]11(9):
    Al Ahmad A, Paffrath V, Clima R, Busch JF, Rabien A, Kilic E, Villegas S, Timmermann B, Attimonelli M, Jung K, Meierhofer D.
      Papillary renal cell carcinoma (pRCC) is a malignant kidney cancer with a prevalence of 7-20% of all renal tumors. Proteome and metabolome profiles of 19 pRCC and patient-matched healthy kidney controls were used to elucidate the regulation of metabolic pathways and the underlying molecular mechanisms. Glutathione (GSH), a main reactive oxygen species (ROS) scavenger, was highly increased and can be regarded as a new hallmark in this malignancy. Isotope tracing of pRCC derived cell lines revealed an increased de novo synthesis rate of GSH, based on glutamine consumption. Furthermore, profound downregulation of gluconeogenesis and oxidative phosphorylation was observed at the protein level. In contrast, analysis of the The Cancer Genome Atlas (TCGA) papillary RCC cohort revealed no significant change in transcripts encoding oxidative phosphorylation compared to normal kidney tissue, highlighting the importance of proteomic profiling. The molecular characteristics of pRCC are increased GSH synthesis to cope with ROS stress, deficient anabolic glucose synthesis, and compromised oxidative phosphorylation, which could potentially be exploited in innovative anti-cancer strategies.
    Keywords:  Papillary renal cell carcinoma (pRCC); glutathione metabolism; metabolic reprogramming; metabolome profiling; proteome profiling
  39. Nat Metab. 2019 Feb;1(2): 276-290
    Sousa-Victor P, Neves J, Cedron-Craft W, Ventura PB, Liao CY, Riley RR, Soifer I, van Bruggen N, Kolumam GA, Villeda SA, Lamba DA, Jasper H.
      Aging is accompanied by altered intercellular communication, deregulated metabolic function, and inflammation. Interventions that restore a youthful state delay or reverse these processes, prompting the search for systemic regulators of metabolic and immune homeostasis. Here we identify MANF, a secreted stress-response protein with immune modulatory properties, as an evolutionarily conserved regulator of systemic and in particular liver metabolic homeostasis. We show that MANF levels decline with age in flies, mice and humans, and MANF overexpression extends lifespan in flies. MANF deficient flies exhibit enhanced inflammation and shorter lifespans, and MANF heterozygous mice exhibit inflammatory phenotypes in various tissues, as well as progressive liver damage, fibrosis, and steatosis. We show that immune cell-derived MANF protects against liver inflammation and fibrosis, while hepatocyte-derived MANF prevents hepatosteatosis. Liver rejuvenation by heterochronic parabiosis in mice further depends on MANF, while MANF supplementation ameliorates several hallmarks of liver aging, prevents hepatosteatosis induced by diet, and improves age-related metabolic dysfunction. Our findings identify MANF as a systemic regulator of homeostasis in young animals, suggesting a therapeutic application for MANF in age-related metabolic diseases.
  40. Cell Metab. 2019 Sep 03. pii: S1550-4131(19)30435-8. [Epub ahead of print]30(3): 411-413
    Heilbronn LK, Panda S.
      Various forms of fasting improve health and longevity in preclinical models. However, safety, outcomes, and the molecular changes underpinning human fasting are unclear. Stekovic et al. (2019) report improved markers of health for up to 6 months and associated metabolic changes among healthy adults who followed alternate-day fasting.
  41. Cell Rep. 2019 Sep 03. pii: S2211-1247(19)31023-X. [Epub ahead of print]28(10): 2501-2508.e4
    Yang WH, Ding CC, Sun T, Rupprecht G, Lin CC, Hsu D, Chi JT.
      Despite recent advances, the poor outcomes in renal cell carcinoma (RCC) suggest novel therapeutics are needed. Ferroptosis is a form of regulated cell death, which may have therapeutic potential toward RCC; however, much remains unknown about the determinants of ferroptosis susceptibility. We found that ferroptosis susceptibility is highly influenced by cell density and confluency. Because cell density regulates the Hippo-YAP/TAZ pathway, we investigated the roles of the Hippo pathway effectors in ferroptosis. TAZ is abundantly expressed in RCC and undergoes density-dependent nuclear or cytosolic translocation. TAZ removal confers ferroptosis resistance, whereas overexpression of TAZS89A sensitizes cells to ferroptosis. Furthermore, TAZ regulates the expression of Epithelial Membrane Protein 1 (EMP1), which, in turn, induces the expression of nicotinamide adenine dinucleotide phosphate (NADPH) Oxidase 4 (NOX4), a renal-enriched reactive oxygen species (ROS)-generating enzyme essential for ferroptosis. These findings reveal that cell density-regulated ferroptosis is mediated by TAZ through the regulation of EMP1-NOX4, suggesting its therapeutic potential for RCC and other TAZ-activated tumors.
    Keywords:  EMP1; Epithelial Membrane Protein 1; Hippo pathway; NADPH Oxidase 4; NOX4; TAZ; WW Domain Containing Transcription Regulator 1; cell density; erastin; ferroptosis; renal cell carcinoma
  42. Cell Metab. 2019 Sep 03. pii: S1550-4131(19)30440-1. [Epub ahead of print]30(3): 414-433
    Li X, Sun X, Carmeliet P.
      In 2009, it was postulated that endothelial cells (ECs) would only be able to execute the orders of growth factors if these cells would accordingly adapt their metabolism. Ten years later, it has become clear that ECs, often differently from other cell types, rely on distinct metabolic pathways to survive and form new blood vessels; that manipulation of EC metabolic pathways alone (even without changing angiogenic signaling) suffices to alter vessel sprouting; and that perturbations of these metabolic pathways can underlie excess formation of new blood vessels (angiogenesis) in cancer and ocular diseases. Initial proof of evidence has been provided that targeting (normalizing) these metabolic perturbations in diseased ECs and delivery of metabolites deserve increasing attention as novel therapeutic approaches for inhibiting or stimulating vessel growth in multiple disorders.
    Keywords:  angiogenesis; cell metabolism; endothelium; ocular neovascularization; tumor endothelial cells
  43. Nat Commun. 2019 Sep 06. 10(1): 4072
    Walker RV, Keynton JL, Grimes DT, Sreekumar V, Williams DJ, Esapa C, Wu D, Knight MM, Norris DP.
      The human PKD2 locus encodes Polycystin-2 (PC2), a TRPP channel that localises to several distinct cellular compartments, including the cilium. PKD2 mutations cause Autosomal Dominant Polycystic Kidney Disease (ADPKD) and affect many cellular pathways. Data underlining the importance of ciliary PC2 localisation in preventing PKD are limited because PC2 function is ablated throughout the cell in existing model systems. Here, we dissect the ciliary role of PC2 by analysing mice carrying a non-ciliary localising, yet channel-functional, PC2 mutation. Mutants develop embryonic renal cysts that appear indistinguishable from mice completely lacking PC2. Despite not entering the cilium in mutant cells, mutant PC2 accumulates at the ciliary base, forming a ring pattern consistent with distal appendage localisation. This suggests a two-step model of ciliary entry; PC2 first traffics to the cilium base before TOP domain dependent entry. Our results suggest that PC2 localisation to the cilium is necessary to prevent PKD.
  44. Mol Cell. 2019 Aug 26. pii: S1097-2765(19)30621-5. [Epub ahead of print]
    Zhang H, Alsaleh G, Feltham J, Sun Y, Napolitano G, Riffelmacher T, Charles P, Frau L, Hublitz P, Yu Z, Mohammed S, Ballabio A, Balabanov S, Mellor J, Simon AK.
      Failure to make adaptive immune responses is a hallmark of aging. Reduced B cell function leads to poor vaccination efficacy and a high prevalence of infections in the elderly. Here we show that reduced autophagy is a central molecular mechanism underlying immune senescence. Autophagy levels are specifically reduced in mature lymphocytes, leading to compromised memory B cell responses in old individuals. Spermidine, an endogenous polyamine metabolite, induces autophagy in vivo and rejuvenates memory B cell responses. Mechanistically, spermidine post-translationally modifies the translation factor eIF5A, which is essential for the synthesis of the autophagy transcription factor TFEB. Spermidine is depleted in the elderly, leading to reduced TFEB expression and autophagy. Spermidine supplementation restored this pathway and improved the responses of old human B cells. Taken together, our results reveal an unexpected autophagy regulatory mechanism mediated by eIF5A at the translational level, which can be harnessed to reverse immune senescence in humans.
    Keywords:  B cell; TFEB; aging; autophagy; eIF5A; spermidine