bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2021‒07‒18
fifty papers selected by
Kelsey Fisher-Wellman
East Carolina University

  1. Proc Natl Acad Sci U S A. 2021 Jul 20. pii: e2019498118. [Epub ahead of print]118(29):
      Cellular respiration is powered by membrane-bound redox enzymes that convert chemical energy into an electrochemical proton gradient and drive the energy metabolism. By combining large-scale classical and quantum mechanical simulations with cryo-electron microscopy data, we resolve here molecular details of conformational changes linked to proton pumping in the mammalian complex I. Our data suggest that complex I deactivation blocks water-mediated proton transfer between a membrane-bound quinone site and proton-pumping modules, decoupling the energy-transduction machinery. We identify a putative gating region at the interface between membrane domain subunits ND1 and ND3/ND4L/ND6 that modulates the proton transfer by conformational changes in transmembrane helices and bulky residues. The region is perturbed by mutations linked to human mitochondrial disorders and is suggested to also undergo conformational changes during catalysis of simpler complex I variants that lack the "active"-to-"deactive" transition. Our findings suggest that conformational changes in transmembrane helices modulate the proton transfer dynamics by wetting/dewetting transitions and provide important functional insight into the mammalian respiratory complex I.
    Keywords:  QM/MM; bioenergetics; cell respiration; cryoEM; molecular simulations
  2. Cell Metab. 2021 Jul 08. pii: S1550-4131(21)00283-7. [Epub ahead of print]
      Electron transport chain (ETC) dysfunction or hypoxia causes toxic NADH accumulation. How cells regenerate NAD+ under such conditions remains elusive. Here, integrating bioinformatic analysis and experimental validation, we identify glycerol-3-phosphate (Gro3P) biosynthesis as an endogenous NAD+-regeneration pathway. Under genetic or pharmacological ETC inhibition, disrupting Gro3P synthesis inhibits yeast proliferation, shortens lifespan of C. elegans, impairs growth of cancer cells in culture and in xenografts, and causes metabolic derangements in mouse liver. Moreover, the Gro3P shuttle selectively regenerates cytosolic NAD+ under mitochondrial complex I inhibition; enhancing Gro3P synthesis promotes shuttle activity to restore proliferation of complex I-impaired cells. Mouse brain has much lower levels of Gro3P synthesis enzymes as compared with other organs. Strikingly, enhancing Gro3P synthesis suppresses neuroinflammation and extends lifespan in the Ndufs4-/- mice. Collectively, our results reveal Gro3P biosynthesis as an evolutionarily conserved coordinator of NADH/NAD+ redox homeostasis and present a therapeutic target for mitochondrial complex I diseases.
    Keywords:  ETC dysfunction and hypoxia; NAD(+) regeneration; glycerol-3-phosphate biosynthesis; mitochondrial complex I disease
  3. Oncol Lett. 2021 Aug;22(2): 630
      Colorectal cancer (CRC) is the fourth most lethal cancer in the world. Heat shock protein 60 (HSP60), a mitochondrial chaperone that maintains mitochondrial proteostasis, is highly expressed in tumors compared with in paracancerous tissues, suggesting that high HSP60 expression benefits tumor growth. To determine the effects of HSP60 expression on tumor progression, stable HSP60-knockdown HCT116 cells were constructed in the present study, revealing that knockdown of HSP60 inhibited cell proliferation. Proteomic analysis demonstrated that mitochondrial proteins were downregulated, indicating that knockdown of HSP60 disrupted mitochondrial homeostasis. Metabolomic analysis demonstrated that cellular adenine levels were >30-fold higher in HSP60-knockdown cells than in control cells. It was further confirmed that elevated adenine activated the AMPK signaling pathway, which inhibited mTOR-regulated protein synthesis to slow down cell proliferation. Overall, the current results provide a valuable resource for understanding mitochondrial function in CRC, suggesting that HSP60 may be a potential target for CRC intervention.
    Keywords:  adenine; colorectal cancer; heat shock protein 60; mTOR pathway; metabolomics; quantitative proteomics
  4. Int Rev Cell Mol Biol. 2021 ;pii: S1937-6448(21)00020-4. [Epub ahead of print]362 171-207
      It has been demonstrated for more than 40 years that intracellular calcium (Ca2+) controls a variety of cellular functions, including mitochondrial metabolism and cell proliferation. Cytosolic Ca2+ fluctuation during key stages of the cell cycle can lead to mitochondrial Ca2+ uptake and subsequent activation of mitochondrial oxidative phosphorylation and a range of signaling. However, the relationship between mitochondrial Ca2+ and cell cycle progression has long been neglected because the molecule responsible for Ca2+ uptake has been unknown. Recently, the identification of the mitochondrial Ca2+ uniporter (MCU) has led to key advances. With improved Ca2+ imaging and detection, effects of MCU-mediated mitochondrial Ca2+ have been observed at different stages of the cell cycle. Elevated Ca2+ signaling boosts ATP and ROS production, remodels cytosolic Ca2+ pathways and reprograms cell fate-determining networks. These findings suggest that manipulating mitochondrial Ca2+ signaling may serve as a potential strategy in the control of many crucial biological events, such as tumor development and cell division in hematopoietic stem cells (HSCs). In this review, we summarize the current understanding of the role of mitochondrial Ca2+ signaling during different stages of the cell cycle and highlight the potential physiological and pathological significance of mitochondrial Ca2+ signaling.
    Keywords:  Cell cycle; MCU; Metabolism; Mitochondrial Ca(2+)
  5. Semin Cancer Biol. 2021 Jul 06. pii: S1044-579X(21)00196-6. [Epub ahead of print]
      TRAP1, the mitochondrial component of the Hsp90 family of molecular chaperones, displays important bioenergetic and proteostatic functions. In tumor cells, TRAP1 contributes to shape metabolism, dynamically tuning it with the changing environmental conditions, and to shield from noxious insults. Hence, TRAP1 activity has profound effects on the capability of neoplastic cells to evolve towards more malignant phenotypes. Here, we discuss our knowledge on the biochemical functions of TRAP1 in the context of a growing tumor mass, and we analyze the possibility of targeting its chaperone functions for developing novel anti-neoplastic approaches.
    Keywords:  Anti-tumor compounds; Mitochondria; Molecular chaperone; TRAP1; Tumor metabolism
  6. Curr Biol. 2021 Jul 12. pii: S0960-9822(21)00763-6. [Epub ahead of print]31(13): R859-R861
      Mechanical forces regulate metabolism in healthy and cancerous tissue. A new study reveals that extracellular matrix stiffness modulates mitochondrial shape and function. The mechanical reprogramming of mitochondria confers resistance to oxidative stress and promotes survival.
  7. J Biol Chem. 2021 Jul 09. pii: S0021-9258(21)00750-X. [Epub ahead of print] 100950
      Mammalian cells synthesize H2S from sulfur containing amino acids and are also exposed to exogenous sources of this signaling molecule, notably from gut microbes. As an inhibitor of complex IV in the electron transport chain, H2S can have a profound impact on metabolism, suggesting the hypothesis that metabolic reprogramming is a primary mechanism by which H2S signals. In this study, we report that H2S increases lipogenesis in many cell types, using carbon derived from glutamine rather than from glucose. H2S-stimulated lipid synthesis is sensitive to the mitochondrial NAD(P)H pools and is enabled by reductive carboxylation of α-ketoglutarate. Lipidomics analysis revealed that H2S elicits time-dependent changes across several lipid classes, e.g., upregulating triglycerides while down regulating phosphatidylcholine. Direct analysis of triglyceride concentration revealed that H2S induces a net increase in the size of this lipid pool. These results provide a mechanistic framework for understanding the effects of H2S on increasing lipid droplets in adipocytes and population studies that have pointed to a positive correlation between cysteine (a substrate for H2S synthesis) and fat mass.
  8. Cell Signal. 2021 Jul 13. pii: S0898-6568(21)00176-5. [Epub ahead of print] 110087
      NADPH is a cofactor used by reactive oxygen species (ROS) scavenging enzymes to block ROS produced in cells. Recently, it was shown that in cancer cells, ROS progressively increases in tune to cell cycle leading to a peak in mitosis. Loss of IDH2 is known to cause severe oxidative stress in cell and mouse models as ROS increases in mitochondria. Therefore, we hypothesized that IDH2, a major NADPH-producing enzyme in mitochondria is ubiquitinated for ROS to increase in mitosis. To test this hypothesis, in cancer cells we examined IDH2 ubiquitination in mitosis and measured the ROS produced. We found that IDH2 is ubiquitinated in mitosis and on inhibiting anaphase-promoting complex/Cyclosome (APC/C) IDH2 was stabilized. Further, we observed that overexpressing APC/C coactivator CDH1 decreased IDH2, whereas depleting CDH1 decreased IDH2 ubiquitination. To understand the link between IDH2 ubiquitination and ROS produced in mitosis, we show that overexpressing mitochondria-targeted-IDH1 decreased ROS by increasing NADPH in IDH2 ubiquitinated cells. We conclude that APC/C CDH1 ubiquitinates IDH2, a major NADPH-producing enzyme in mitochondria contributing to ROS increase in mitosis. Based on our results, we suggest that mitosis can be a therapeutic window in mutant IDH2-linked pathologies.
    Keywords:  APC/C; CDH1; IDH2; Mitosis; NADPH; ROS
  9. Nat Cell Biol. 2021 Jul;23(7): 684-691
      Members of the mammalian AlkB family are known to mediate nucleic acid demethylation1,2. ALKBH7, a mammalian AlkB homologue, localizes in mitochondria and affects metabolism3, but its function and mechanism of action are unknown. Here we report an approach to site-specifically detect N1-methyladenosine (m1A), N3-methylcytidine (m3C), N1-methylguanosine (m1G) and N2,N2-dimethylguanosine (m22G) modifications simultaneously within all cellular RNAs, and discovered that human ALKBH7 demethylates m22G and m1A within mitochondrial Ile and Leu1 pre-tRNA regions, respectively, in nascent polycistronic mitochondrial RNA4-6. We further show that ALKBH7 regulates the processing and structural dynamics of polycistronic mitochondrial RNAs. Depletion of ALKBH7 leads to increased polycistronic mitochondrial RNA processing, reduced steady-state mitochondria-encoded tRNA levels and protein translation, and notably decreased mitochondrial activity. Thus, we identify ALKBH7 as an RNA demethylase that controls nascent mitochondrial RNA processing and mitochondrial activity.
  10. J Cell Biol. 2021 Sep 06. pii: e202005193. [Epub ahead of print]220(9):
      Long-lived proteins (LLPs) have recently emerged as vital components of intracellular structures whose function is coupled to long-term stability. Mitochondria are multifaceted organelles, and their function hinges on efficient proteome renewal and replacement. Here, using metabolic stable isotope labeling of mice combined with mass spectrometry (MS)-based proteomic analysis, we demonstrate remarkable longevity for a subset of the mitochondrial proteome. We discovered that mitochondrial LLPs (mt-LLPs) can persist for months in tissues harboring long-lived cells, such as brain and heart. Our analysis revealed enrichment of mt-LLPs within the inner mitochondrial membrane, specifically in the cristae subcompartment, and demonstrates that the mitochondrial proteome is not turned over in bulk. Pioneering cross-linking experiments revealed that mt-LLPs are spatially restricted and copreserved within protein OXPHOS complexes, with limited subunit exchange throughout their lifetimes. This study provides an explanation for the exceptional mitochondrial protein lifetimes and supports the concept that LLPs provide key structural stability to multiple large and dynamic intracellular structures.
  11. Trends Biochem Sci. 2021 Jul 06. pii: S0968-0004(21)00121-3. [Epub ahead of print]
      Within cellular structures, compartmentalization is the concept of spatial segregation of macromolecules, metabolites, and biochemical pathways. Therefore, this concept bridges organellar structure and function. Mitochondria are morphologically complex, partitioned into several subcompartments by a topologically elaborate two-membrane system. They are also dynamically polymorphic, undergoing morphogenesis events with an extent and frequency that is only now being appreciated. Thus, mitochondrial compartmentalization is something that must be considered both spatially and temporally. Here, we review new developments in how mitochondrial structure is established and regulated, the factors that underpin the distribution of lipids and proteins, and how they spatially demarcate locations of myriad mitochondrial processes. Consistent with its pre-eminence, disturbed mitochondrial compartmentalization contributes to the dysfunction associated with heritable and aging-related diseases.
    Keywords:  bioenergetics; cristae; macromolecular trafficking; mitochondria; morphogenesis; ultrastructure
  12. Cancer Sci. 2021 Jul 12.
      Although the role of bromodomain-containing protein 4 (BRD4) in ovarian cancer, pancreatic cancer, multiple lymphoma and many other diseases is well known, its function in cutaneous melanoma is only partially understood. Here, our results show that the BRD4 inhibitor JQ1 promotes the apoptosis of B16 melanoma cells by altering mitochondrial dynamics, thereby inducing mitochondrial dysfunction and increasing oxidative stress. We found that treatment of B16 cells with different concentrations of JQ1 (125 nM or 250 nM), significantly downregulated the expression of protein subunits involved in mitochondrial respiratory chain complexes I, III, IV, and V, increased reactive oxygen species (ROS), induced energy metabolism dysfunction, significantly enhanced apoptosis and activated the mitochondrial apoptosis pathway. At the same time, JQ1 inhibited the activation of AMP-activated protein kinase (AMPK), a metabolic energy sensor. In addition, we found that the mRNA and protein levels of mitochondrial dynamin-related protein 1 (DRP1) increased, whereas the levels of mitochondrial fusion protein 1 (MFN1) and optic atrophy protein 1 (OPA1) decreased. Mechanistically, we determined that JQ1 inhibited the expression of c-Myc and altered mitochondrial dynamics, eventually leading to changes in the mitochondrial function, metabolism, and apoptosis of B16 melanoma cells.
    Keywords:  BRD4; apoptosis; energy metabolism; melanoma; mitochondrial dynamics
  13. Cell Oncol (Dordr). 2021 Jul 09.
      BACKGROUND: The ability of cancer cells to develop treatment resistance is one of the primary factors that prevent successful treatment. Although initially thought to be dysfunctional in cancer, mitochondria are significant players that mediate treatment resistance. Literature indicates that cancer cells reutilize their mitochondria to facilitate cancer progression and treatment resistance. However, the mechanisms by which the mitochondria promote treatment resistance have not yet been fully elucidated.CONCLUSIONS AND PERSPECTIVES: Here, we describe various means by which mitochondria can promote treatment resistance. For example, mutations in tricarboxylic acid (TCA) cycle enzymes, i.e., fumarate hydratase and isocitrate dehydrogenase, result in the accumulation of the oncometabolites fumarate and 2-hydroxyglutarate, respectively. These oncometabolites may promote treatment resistance by upregulating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway, inhibiting the anti-tumor immune response, or promoting angiogenesis. Furthermore, stromal cells can donate intact mitochondria to cancer cells after therapy to restore mitochondrial functionality and facilitate treatment resistance. Targeting mitochondria is, therefore, a feasible strategy that may dampen treatment resistance. Analysis of tumoral DNA may also be used to guide treatment choices. It will indicate whether enzymatic mutations are present in the TCA cycle and, if so, whether the mutations or their downstream signaling pathways can be targeted. This may improve treatment outcomes by inhibiting treatment resistance or promoting the effectiveness of anti-angiogenic agents or immunotherapy.
    Keywords:  2-Hydroxyglutarate; Fumarate; Mitochondria; Mitochondrial transfer; Treatment resistance
  14. Biochem Biophys Res Commun. 2021 Jul 07. pii: S0006-291X(21)01019-6. [Epub ahead of print]569 139-146
      Brown adipocytes (BA) are a specialized fat cell which possesses a high capacity for fuel oxidation combined with heat production. The maintenance of high metabolic activity in BA requires elevated oxidation of fuel through the tricarboxylic acid cycle. Pyruvate carboxylase (PC) was previously proposed to be essential for coordination between fuel oxidation and thermogenesis. By differentiating human pluripotent stem cells to mature BA in vitro, we showed that ablation of PC gene by CRISPR Cas9 genome engineering did not impair the ability of stem cells to generate mature BA. However, brown adipocytes deficient for PC expression displayed a 35% reduction in ATP-linked respiration, but not thermogenesis under both basal and isoproterenol-stimulated conditions. This relatively mild impairment of ATP-link respiration in PC knockout BA was protected by increased spare mitochondrial respiratory capacity. Taken together, this study highlights the role of PC in supporting fuel oxidation rather than thermogenesis in human BA.
    Keywords:  Metabolism; Pluripotent stem cell; Pyruvate carboxylase; Thermogenesis; brown adipocytes
  15. PLoS One. 2021 ;16(7): e0253849
      BACKGROUND: Loss of mitochondrial function contributes to fatigue, exercise intolerance and muscle weakness, and is a key factor in the disability that develops with age and a wide variety of chronic disorders. Here, we describe the impact of a first-in-class cardiolipin-binding compound that is targeted to mitochondria and improves oxidative phosphorylation capacity (Elamipretide, ELAM) in a randomized, double-blind, placebo-controlled clinical trial.METHODS: Non-invasive magnetic resonance and optical spectroscopy provided measures of mitochondrial capacity (ATPmax) with exercise and mitochondrial coupling (ATP supply per O2 uptake; P/O) at rest. The first dorsal interosseous (FDI) muscle was studied in 39 healthy older adult subjects (60 to 85 yrs of age; 46% female) who were enrolled based on the presence of poorly functioning mitochondria. We measured volitional fatigue resistance by force-time integral over repetitive muscle contractions.
    RESULTS: A single ELAM dose elevated mitochondrial energetic capacity in vivo relative to placebo (ΔATPmax; P = 0.055, %ΔATPmax; P = 0.045) immediately after a 2-hour infusion. No difference was found on day 7 after treatment, which is consistent with the half-life of ELAM in human blood. No significant changes were found in resting muscle mitochondrial coupling. Despite the increase in ATPmax there was no significant effect of treatment on fatigue resistance in the FDI.
    CONCLUSIONS: These results highlight that ELAM rapidly and reversibly elevates mitochondrial capacity after a single dose. This response represents the first demonstration of a pharmacological intervention that can reverse mitochondrial dysfunction in vivo immediately after treatment in aging human muscle.
  16. Proc Natl Acad Sci U S A. 2021 Jul 13. pii: e2019822118. [Epub ahead of print]118(28):
      Cancer cells acquire metabolic reprogramming to satisfy their high biogenetic demands, but little is known about how metabolic remodeling enables cancer cells to survive stress associated with genomic instability. Here, we show that the mitochondrial methylenetetrahydrofolate dehydrogenase (MTHFD2) is transcriptionally suppressed by p53, and its up-regulation by p53 inactivation leads to increased folate metabolism, de novo purine synthesis, and tumor growth in vivo and in vitro. Moreover, MTHFD2 unexpectedly promotes nonhomologous end joining in response to DNA damage by forming a complex with PARP3 to enhance its ribosylation, and the introduction of a PARP3-binding but enzymatically inactive MTHFD2 mutant (e.g., D155A) sufficiently prevents DNA damage. Notably, MTHFD2 depletion strongly restrains p53-deficient cell proliferation and sensitizes cells to chemotherapeutic agents, indicating a potential role for MTHFD2 depletion in the treatment of p53-deficient tumors.
    Keywords:  MTHFD2; NHEJ; cell proliferation; folate metabolism; p53
  17. Nat Commun. 2021 Jul 16. 12(1): 4371
      Metabolic programming and mitochondrial dynamics along with T cell differentiation affect T cell fate and memory development; however, how to control metabolic reprogramming and mitochondrial dynamics in T cell memory development is unclear. Here, we provide evidence that the SUMO protease SENP1 promotes T cell memory development via Sirt3 deSUMOylation. SENP1-Sirt3 signalling augments the deacetylase activity of Sirt3, promoting both OXPHOS and mitochondrial fusion. Mechanistically, SENP1 activates Sirt3 deacetylase activity in T cell mitochondria, leading to reduction of the acetylation of mitochondrial metalloprotease YME1L1. Consequently, deacetylation of YME1L1 suppresses its activity on OPA1 cleavage to facilitate mitochondrial fusion, which results in T cell survival and promotes T cell memory development. We also show that the glycolytic intermediate fructose-1,6-bisphosphate (FBP) as a negative regulator suppresses AMPK-mediated activation of the SENP1-Sirt3 axis and reduces memory development. Moreover, glucose limitation reduces FBP production and activates AMPK during T cell memory development. These data show that glucose limitation activates AMPK and the subsequent SENP1-Sirt3 signalling for T cell memory development.
  18. Am J Cancer Res. 2021 ;11(6): 2911-2927
      Acute myeloid leukemia (AML) is a highly heterogenous and aggressive disease with a poor prognosis, necessitating further improvements in treatment therapies. Recently, several targeted therapies have become available for specific AML populations. To identify potential new therapeutic targets for AML, we analyzed published genome wide CRISPR-based screens to generate a gene essentiality dataset across a panel of 14 human AML cell lines while eliminating common essential genes through integration analysis with core fitness genes among 324 human cancer cell lines and DepMap databases. The key glutathione metabolic enzyme, glutamate-cysteine ligase catalytic subunit (GCLC), met the selection threshold. Using CRISPR knockout, GCLC was confirmed to be essential for the cell growth, survival, clonogenicity, and leukemogenesis in AML cells but was comparatively dispensable for normal hematopoietic stem and progenitor cells (HSPCs), indicating that GCLC is a potential therapeutic target for AML. In addition, we evaluated the essentiality of GCLC in solid tumors and demonstrated that GCLC represents a synthetic lethal target for ARID1A-deficient ovarian and gastric cancers.
    Keywords:  Acute myeloid leukemia (AML); CRISPR; glutamate-cysteine ligase catalytic subunit (GCLC); glutathione metabolic enzyme; synthetic lethality
  19. Toxicol Appl Pharmacol. 2021 Jul 06. pii: S0041-008X(21)00246-5. [Epub ahead of print] 115642
      Disulfiram (DSF), a sulfur-containing compound, has been used to treat chronic alcoholism and cancer for decades by inactivating aldehyde dehydrogenase (ALDH). Hydrogen sulfide (H2S) is a new gasotransmitter and regulates various cellular functions by S-sulfhydrating cysteine in the target proteins. H2S exhibits similar properties to DSF in the sensitization of cancer cells. The interaction of DSF and H2S on ALDH activity and liver cancer cell survival are not clear. Here it was demonstrated that DSF facilitated H2S release from thiol-containing compounds, and DSF and H2S were both capable of regulating ALDH through inhibition of gene expression and enzymatic activity. The supplement of H2S sensitized human liver cancer cells (HepG2) to DSF-inhibited cell viability. The expression of cystathionine gamma-lyase (a major H2S-generating enzyme) was lower but ALDH was higher in mouse liver cancer stem cells (Dt81Hepa1-6) in comparison with their parental cells (Hepa1-6), and H2S was able to inhibit liver cancer stem cell adhesion. In conclusion, these data point to the potential of combining DSF and H2S for inhibition of cancer cell growth and tumor development by targeting ALDH.
    Keywords:  Aldehyde dehydrogenase; Cystathionine gamma-lyase; Disulfiram; H(2)S; Liver cancer stem cells
  20. Neuro Oncol. 2021 Jul 14. pii: noab175. [Epub ahead of print]
      BACKGROUND: Tumor-specific metabolic processes essential for cell survival are promising targets to potentially circumvent intratumoral heterogeneity, a major resistance factor in gliomas. Tumor cells preferentially using nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in the salvage pathway for synthesis of NAD, a critical cofactor for diverse biological processes including cellular redox reactions, energy metabolism and biosynthesis. NAMPT is overexpressed in most malignancies, including gliomas, and can serve as a tumor-specific target.METHODS: Effects of pharmacological inhibition of NAMPT on cellular oxygen consumption rate, extracellular acidification, mitochondrial respiration, cell proliferation, invasion and survival were assessed through in vitro and ex vivo studies on genetically heterogeneous glioma cell lines, glioma stem-like cells (GSCs) and mouse and human ex vivo organotypic glioma slice culture models.
    RESULTS: Pharmacological inhibition of the NAD salvage biosynthesis pathway using a highly specific inhibitor, KPT-9274, resulted in reduction of NAD levels and related downstream metabolites, inhibited proliferation, and induced apoptosis in vitro in cell lines and ex vivo in human glioma tissue. These effects were mediated by mitochondrial dysfunction, DNA damage and increased oxidative stress leading to apoptosis in GSCs independent of genotype, IDH status or MGMT promoter methylation status. Conversely, NAMPT inhibition had minimal in vitro effects on normal human astrocytes (NHA) and no apparent in vivo toxicity in non-tumor-bearing mice.
    CONCLUSIONS: Pharmacological NAMPT inhibition by KPT9274 potently targeted genetically heterogeneous gliomas by activating mitochondrial dysfunction. Our preclinical results provide a rationale for targeting the NAMPT-dependent alternative NAD biosynthesis pathway as a novel clinical strategy against gliomas.
    Keywords:  Gliomas; KPT-9274; NAD; NAMPT; metabolism
  21. J Cell Sci. 2021 Jul 01. pii: jcs252197. [Epub ahead of print]134(13):
      The mitochondrial inner membrane is a protein-rich environment containing large multimeric complexes, including complexes of the mitochondrial electron transport chain, mitochondrial translocases and quality control machineries. Although the inner membrane is highly proteinaceous, with 40-60% of all mitochondrial proteins localised to this compartment, little is known about the spatial distribution and organisation of complexes in this environment. We set out to survey the arrangement of inner membrane complexes using stochastic optical reconstruction microscopy (STORM). We reveal that subunits of the TIM23 complex, TIM23 and TIM44 (also known as TIMM23 and TIMM44, respectively), and the complex IV subunit COXIV, form organised clusters and show properties distinct from the outer membrane protein TOM20 (also known as TOMM20). Density based cluster analysis indicated a bimodal distribution of TIM44 that is distinct from TIM23, suggesting distinct TIM23 subcomplexes. COXIV is arranged in larger clusters that are disrupted upon disruption of complex IV assembly. Thus, STORM super-resolution microscopy is a powerful tool for examining the nanoscale distribution of mitochondrial inner membrane complexes, providing a 'visual' approach for obtaining pivotal information on how mitochondrial complexes exist in a cellular context.
    Keywords:  COXIV; Mitochondria; Mitochondrial complexes; Nanoscopy; Protein import; STORM; TIM23
  22. Bio Protoc. 2021 Jun 20. 11(12): e4057
      Mitochondria are essential organelles containing approximately 1,500 proteins. Only approximately 1% of these proteins are synthesized inside mitochondria, whereas the remaining 99% are synthesized as precursors on cytosolic ribosomes and imported into the organelle. Various tools and techniques to analyze the import process have been developed. Among them, in vitro reconstituted import systems are of importance to study these processes in detail. These experiments monitor the import reaction of mitochondrial precursors that were previously radiolabeled in a cell-free environment. However, the methods described have been mostly performed in mitochondria isolated from S. cerevisiae. Here, we describe the adaptation of this powerful assay to import proteins into crude mitochondria isolated from human tissue culture cells. Graphic abstract: Overview of the assay to monitor protein import into mitochondria isolated from human cells.
    Keywords:  Cell-free protein synthesis; Human tissue culture cells; In organello import ; Isolated mitochondria; Radiolabeled proteins
  23. Proc Natl Acad Sci U S A. 2021 Jul 20. pii: e2023079118. [Epub ahead of print]118(29):
      Mitochondria form tubular networks that undergo coordinated cycles of fission and fusion. Emerging evidence suggests that a direct yet unresolved interaction of the mechanoenzymatic GTPase dynamin-related protein 1 (Drp1) with mitochondrial outer membrane-localized cardiolipin (CL), externalized under stress conditions including mitophagy, catalyzes essential mitochondrial hyperfragmentation. Here, using a comprehensive set of structural, biophysical, and cell biological tools, we have uncovered a CL-binding motif (CBM) conserved between the Drp1 variable domain (VD) and the unrelated ADP/ATP carrier (AAC/ANT) that intercalates into the membrane core to effect specific CL interactions. CBM mutations that weaken VD-CL interactions manifestly impair Drp1-dependent fission under stress conditions and induce "donut" mitochondria formation. Importantly, VD membrane insertion and GTP-dependent conformational rearrangements mediate only transient CL nonbilayer topological forays and high local membrane constriction, indicating that Drp1-CL interactions alone are insufficient for fission. Our studies establish the structural and mechanistic bases of Drp1-CL interactions in stress-induced mitochondrial fission.
    Keywords:  NMR; cardiolipin; dynamin; intrinsically disordered; mitochondria
  24. Cancer Lett. 2021 Jul 13. pii: S0304-3835(21)00345-1. [Epub ahead of print]519 150-160
      Calcium channel TRPV6 upregulation is associated with poor prognosis of breast cancer by promoting invasion and metastasis, and TRPV6 is a potential target for breast cancer therapy. However, the mechanism by which TRPV6 promotes breast metastasis remains unclear. Here, we report that TRPV6 expression is upregulated in metastatic breast cancers and that TRPV6 overexpression or upregulation accelerates primary breast cancer cell migration. In contrast, TRPV6 suppression decreases cell migration. Mechanistically, TRPV6 activates NFATC2 by increasing NFATC2IP phosphorylation at Ser204, and CDK5 is a candidate kinase that may perform this phosphorylation. Consequently, activated NFATC2 increases breast cancer metastasis by upregulating ADAMTS6 expression. These observations suggest that TRPV6 increases NFATC2 transcriptional activity by increasing NFATC2IP phosphorylation, which consequently upregulates ADAMTS6 expression to promote breast cancer metastasis.
    Keywords:  Breast cancer; CDK5; Metastasis; NFATC2IP; TRPV6
  25. Cell Death Dis. 2021 Jul 15. 12(7): 705
      Pancreatic ductal adenocarcinoma (PDAC) is an extremely lethal cancer with limited treatment options. Cisplatin (DDP) is used as a mainstay of chemotherapeutic agents in combination with other drugs or radiotherapy for PDAC therapy. However, DDP exhibits severe side-effects that can lead to discontinuation of therapy, and the acquired drug resistance of tumor cells presents serious clinical obstacles. Therefore, it is imperative to develop a more effective and less toxic therapeutic strategy. We and others have previously discovered that dihydroartemisinin (DHA) represents a safe and promising therapeutic agent to preferentially induce cancer cell ferroptosis. In the present study, we find that DHA could intensively strengthen the cytotoxicity of DDP and significantly reduce its effective concentrations both in vitro and in vivo. Combination of DHA and DDP synergistically inhibits the proliferation and induces DNA damage of PDAC cells. Mechanically, the combinative treatment impairs mitochondrial homeostasis, characterized by destroyed mitochondrial morphology, decreased respiratory capacity, reduced ATP production, and accumulated mitochondria-derived ROS. Further studies show that ferroptosis contributes to the cytotoxic effects in PDAC cells under the challenge of DHA and DDP, together with catastrophic accumulation of free iron and unrestricted lipid peroxidation. Moreover, pharmacologic depleting of the free iron reservoir or reconstituted expression of FTH contributes to the tolerance of DHA/DDP-induced ferroptosis, while iron addition accelerates the ferroptotic cell death. In summary, these results provide experimental evidence that DHA acts synergistically with DDP and renders PDAC cells vulnerable to ferroptosis, which may act as a promising therapeutic strategy.
  26. Sci Rep. 2021 Jul 16. 11(1): 14575
      Transmembrane electrostatically localized protons (TELP) theory has been recently recognized as an important addition over the classic Mitchell's chemiosmosis; thus, the proton motive force (pmf) is largely contributed from TELP near the membrane. As an extension to this theory, a novel phenomenon of mitochondrial thermotrophic function is now characterized by biophysical analyses of pmf in relation to the TELP concentrations at the liquid-membrane interface. This leads to the conclusion that the oxidative phosphorylation also utilizes environmental heat energy associated with the thermal kinetic energy (kBT) of TELP in mitochondria. The local pmf is now calculated to be in a range from 300 to 340 mV while the classic pmf (which underestimates the total pmf) is in a range from 60 to 210 mV in relation to a range of membrane potentials from 50 to 200 mV. Depending on TELP concentrations in mitochondria, this thermotrophic function raises pmf significantly by a factor of 2.6 to sixfold over the classic pmf. Therefore, mitochondria are capable of effectively utilizing the environmental heat energy with TELP for the synthesis of ATP, i.e., it can lock heat energy into the chemical form of energy for cellular functions.
  27. Nat Metab. 2021 Jul 12.
      Cell competition is emerging as a quality-control mechanism that eliminates unfit cells in a wide range of settings from development to the adult. However, the nature of the cells normally eliminated by cell competition and what triggers their elimination remains poorly understood. In mice, 35% of epiblast cells are eliminated before gastrulation. Here we show that cells with mitochondrial defects are eliminated by cell competition during early mouse development. Using single-cell transcriptional profiling of eliminated mouse epiblast cells, we identify hallmarks of cell competition and mitochondrial defects. We demonstrate that mitochondrial defects are common to a range of different loser cell types and that manipulating mitochondrial function triggers cell competition. Moreover, we show that in the mouse embryo, cell competition eliminates cells with sequence changes in mt-Rnr1 and mt-Rnr2, and that even non-pathological changes in mitochondrial DNA sequences can induce cell competition. Our results suggest that cell competition is a purifying selection that optimizes mitochondrial performance before gastrulation.
  28. Am J Cancer Res. 2021 ;11(6): 2893-2910
      Mitochondria play leading roles in initiation and progression of colorectal cancer (CRC). Proteogenomic analyses of mitochondria of CRC tumor cells would likely enhance our understanding of CRC pathogenesis and reveal new independent prognostic factors and treatment targets. However, comprehensive investigations focused on mitochondria of CRC patients are lacking. Here, we investigated global profiles of structural variants, DNA methylation, chromatin accessibility, transcriptome, proteome, and phosphoproteome on human CRC. Proteomic investigations uncovered greatly diminished mitochondrial proteome size in CRC relative to that found in adjacent healthy tissues. Integrated with analysis of RNA-Seq datasets obtained from the public database containing mRNA data of 538 CRC patients, the proteomic analysis indicated that proteins encoded by 45.5% of identified prognostic CRC genes were located within mitochondria, highlighting the association between altered mitochondrial function and CRC. Subsequently, we compared structural variants, DNA methylation, and chromatin accessibility of differentially expressed genes and found that chromatin accessibility was an important factor underlying mitochondrial gene expression. Furthermore, phosphoproteomic profiling demonstrated decreased phosphorylation of most mitochondria-related kinases within CRC versus adjacent healthy tissues, while also highlighting MKK3/p38 as an essential mitochondrial regulatory pathway. Meanwhile, systems-based analyses revealed identities of key kinases, transcriptional factors, and their interconnections. This research uncovered a close relationship between mitochondrial dysfunction and poor CRC prognosis, improve our understanding of molecular mechanism underlying mitochondrial linked to human CRC, and facilitate identifies of clinically relevant CRC prognostic factors and drug targets.
    Keywords:  Mitochondria; colorectal cancer; drug targets; multi-omics; prognosis
  29. Cell Transplant. 2021 Jan-Dec;30:30 9636897211027524
      Energy metabolism programming is a hallmark of cancer, and serves as a potent target of cancer therapy. Valproic acid (VPA), a broad Class I histone deacetylases (HDACs) inhibitor, has been used as a therapeutic agent for cancer. However, the detail mechanism about the potential role of VPA on the Warburg effect in breast cancer remains unclear. In this study, we highlight that VPA significantly attenuates the Warburg effect by decreasing the expression of pyruvate kinase M2 isoform (PKM2), leading to inhibited cell proliferation and reduced colony formation in breast cancer MCF-7 and MDA-MB-231 cells. Mechanistically, Warburg effect suppression triggered by VPA was mediated by inactivation of ERK1/2 phosphorylation through reduced HDAC1 expression, resulting in suppressing breast cancer growth. In summary, we uncover a novel mechanism of VPA in regulating the Warburg effect which is essential for developing the effective approach in breast cancer therapy.
    Keywords:  Valproic acid; Warburg effect; breast cancer; cell proliferation; histone deacetylases; pyruvate kinase M2 isoform
  30. J Biol Chem. 2021 Jul 12. pii: S0021-9258(21)00760-2. [Epub ahead of print] 100960
      Mammalian mitochondrial tRNA (mt-tRNA) plays a central role in the synthesis of the 13 subunits of the oxidative phosphorylation complex system (OXPHOS). However, many aspects of the context-dependent expression of mt-tRNAs in mammals remains unknown. To investigate the tissue-specific effects of mt-tRNAs, we performed a comprehensive analysis of mitochondrial tRNA expression across 5 mice tissues (brain, heart, liver, skeletal muscle, and kidney) using Northern blot analysis. Striking differences in the tissue-specific expression of 22 mt-tRNAs were observed, in some cases differing by as much as ten-fold from lowest to highest expression levels among these 5 tissues. Overall, the heart exhibited the highest levels of mt-tRNAs, while the liver displayed markedly lower levels. Variations in the levels of mt-tRNAs showed significant correlations with total mitochondrial DNA (mtDNA) contents in these tissues. However, there were no significant differences observed in the 2-thiouridylation levels of tRNALys, tRNAGlu, and tRNAGln among these tissues. A wide range of aminoacylation levels for 15 mt-tRNAs occurred among these five tissues, with skeletal muscle and kidneys most notably displaying the highest and lowest tRNA aminoacylation levels, respectively. Among these tissues, there was a negative correlation between variations in mt-tRNA aminoacylation levels and corresponding variations in mitochondrial tRNA synthetases (mt-aaRS) expression levels. Furthermore, the variable levels of OXPHOS subunits, as encoded by mtDNA or nuclear genes may reflect differences in relative functional emphasis for mitochondria in each tissue. Our findings provide new insight into the mechanism of mt-tRNA tissue-specific effects on oxidative phosphorylation.
    Keywords:  Mitochondrial tRNA; murine; oxidative phosphorylation; tissue specific expression; translation
  31. Blood. 2021 Jul 13. pii: blood.2021011707. [Epub ahead of print]
      YTHDC1 has distinct functions as a nuclear N6-methyladenosine (m6A) reader in regulating RNA metabolism. Here we show that YTHDC1 is overexpressed in Acute Myeloid Leukemia (AML) and that it is required for proliferation and survival of human AML cells. Genetic deletion of Ythdc1 markedly blocks AML development and maintenance as well as self-renewal of leukemia stem cells (LSCs) in vivo in mice. We find that Ythdc1 is also required for normal hematopoiesis and hematopoietic stem/progenitor cell (HSPC) maintenance in vivo. Notably, Ythdc1 haploinsufficiency reduces self-renewal of LSCs, but not HSPCs in vivo. YTHDC1 knockdown has a strong inhibitory effect on proliferation of primary AML cells. Mechanistically, YTHDC1 regulates leukemogenesis through MCM4, which is a critical regulator of DNA replication. Our study provides the compelling evidence to show an oncogenic role and a distinct mechanism of YTHDC1 in AML.
  32. Am J Cancer Res. 2021 ;11(6): 3039-3054
      Colon cancer (CC) is a prevalent malignancy worldwide. Approaches to specifically induce tumor cell death have historically been a popular research topic. Honokiol (HNK), which exhibits highly efficient and specific anticancer effects, is a biphenolic compound found in Magnolia grandiflora. In the present study, we aim to study the effect of HNK on CC cells and elucidate the potential underlying mechanisms. Seven CC cell lines (RKO, HCT116, SW48, HT29, LS174T, HCT8, and SW480) were used. Cells were exposed to HNK and subjected to a series of assays to evaluate characteristics such as cellular activity, reactive oxygen species (ROS) levels and ferroptosis-related protein expression levels. Lentiviral transduction was also used to verify molecular mechanisms in vivo and in vitro. We here observed that HNK reduced the viability of CC cell lines by increasing ROS and Fe2+ levels. Transmission electron microscopy revealed HNK-induced changes in mitochondrial morphology. HNK decreased the activity of Glutathione Peroxidase 4 (GPX4) but did not affect system Xc-. Thus, our datas indicated that HNK can induce ferroptosis in CC cells by reducing the activity of GPX4. As a potential therapeutic drug, HNK showed good anticancer effects through diverse signal transduction mechanisms and multiple pathways.
    Keywords:  GPX4; Honokiol (HNK); colon cancer (CC); ferroptosis; reactive oxygen species (ROS)
  33. Cell Death Dis. 2021 Jul 15. 12(7): 706
      Ferroptosis, a newly defined mode of regulated cell death caused by unbalanced lipid redox metabolism, is implicated in various tissue injuries and tumorigenesis. However, the role of ferroptosis in stem cells has not yet been investigated. Glutathione peroxidase 4 (GPX4) is a critical suppressor of lipid peroxidation and ferroptosis. Here, we study the function of GPX4 and ferroptosis in hematopoietic stem and progenitor cells (HSPCs) in mice with Gpx4 deficiency in the hematopoietic system. We find that Gpx4 deletion solely in the hematopoietic system has no significant effect on the number and function of HSPCs in mice. Notably, hematopoietic stem cells (HSCs) and hematopoietic progenitor cells lacking Gpx4 accumulated lipid peroxidation and underwent ferroptosis in vitro. α-Tocopherol, the main component of vitamin E, was shown to rescue the Gpx4-deficient HSPCs from ferroptosis in vitro. When Gpx4 knockout mice were fed a vitamin E-depleted diet, a reduced number of HSPCs and impaired function of HSCs were found. Furthermore, increased levels of lipid peroxidation and cell death indicated that HSPCs undergo ferroptosis. Collectively, we demonstrate that GPX4 and vitamin E cooperatively maintain lipid redox balance and prevent ferroptosis in HSPCs.
  34. Nat Commun. 2021 07 09. 12(1): 4228
      Homozygous deletion of methylthioadenosine phosphorylase (MTAP) in cancers such as glioblastoma represents a potentially targetable vulnerability. Homozygous MTAP-deleted cell lines in culture show elevation of MTAP's substrate metabolite, methylthioadenosine (MTA). High levels of MTA inhibit protein arginine methyltransferase 5 (PRMT5), which sensitizes MTAP-deleted cells to PRMT5 and methionine adenosyltransferase 2A (MAT2A) inhibition. While this concept has been extensively corroborated in vitro, the clinical relevance relies on exhibiting significant MTA accumulation in human glioblastoma. In this work, using comprehensive metabolomic profiling, we show that MTA secreted by MTAP-deleted cells in vitro results in high levels of extracellular MTA. We further demonstrate that homozygous MTAP-deleted primary glioblastoma tumors do not significantly accumulate MTA in vivo due to metabolism of MTA by MTAP-expressing stroma. These findings highlight metabolic discrepancies between in vitro models and primary human tumors that must be considered when developing strategies for precision therapies targeting glioblastoma with homozygous MTAP deletion.
  35. Nat Rev Cancer. 2021 Jul 09.
      Oncogenic mutations in KRAS drive common metabolic programmes that facilitate tumour survival, growth and immune evasion in colorectal carcinoma, non-small-cell lung cancer and pancreatic ductal adenocarcinoma. However, the impacts of mutant KRAS signalling on malignant cell programmes and tumour properties are also dictated by tumour suppressor losses and physiological features specific to the cell and tissue of origin. Here we review convergent and disparate metabolic networks regulated by oncogenic mutant KRAS in colon, lung and pancreas tumours, with an emphasis on co-occurring mutations and the role of the tumour microenvironment. Furthermore, we explore how these networks can be exploited for therapeutic gain.
  36. Cell Death Dis. 2021 Jul 14. 12(7): 701
      The mitochondrial DNA m.3243A > G mutation is well-known to cause a variety of clinical phenotypes, including diabetes, deafness, and osteoporosis. Here, we report isolation and expansion of urine-derived stem cells (USCs) from patients carrying the m.3243A > G mutation, which demonstrate bimodal heteroplasmy. USCs with high levels of m.3243A > G mutation displayed abnormal mitochondrial morphology and function, as well as elevated ATF5-dependent mitochondrial unfolded protein response (UPRmt), together with reduced Wnt/β-catenin signaling and osteogenic potentials. Knockdown of ATF5 in mutant USCs suppressed UPRmt, improved mitochondrial function, restored expression of GSK3B and WNT7B, and rescued osteogenic potentials. These results suggest that ATF5-dependent UPRmt could be a core disease mechanism underlying mitochondrial dysfunction and osteoporosis related to the m.3243A > G mutation, and therefore could be a novel putative therapeutic target for this genetic disorder.
  37. Immunometabolism. 2021 ;3(3): e210025
      Following brief exposure to endogenous atherogenic particles, such as oxidized low-density lipoprotein (oxLDL), monocytes/macrophages can adopt a long-term pro-inflammatory phenotype, which is called trained immunity. This mechanism might contribute to the chronic low-grade inflammation that characterizes atherosclerosis. In this study, we aim to elucidate immunometabolic pathways that drive oxLDL-induced trained immunity. Primary isolated human monocytes were exposed to oxLDL for 24 h, and after five days stimulated with LPS to measure the cytokine production capacity. RNA-sequencing revealed broad increases in genes enriched in mitochondrial pathways after 24 h of oxLDL exposure. Further omics profiling of oxLDL-trained macrophages via intracellular metabolomics showed an enrichment for tricarboxylic acid (TCA) cycle metabolites. Single cell analysis revealed that oxLDL-trained macrophages contain larger mitochondria, potentially likely linked to increased oxidative phosphorylation (OXPHOS) activity. Co-incubation with pharmacological blockers of OXPHOS inhibited oxLDL-induced trained immunity. The relevance of OXPHOS was confirmed in a cohort of 243 healthy subjects showing that genetic variation in genes coding for enzymes relevant to OXPHOS correlated with the capacity of monocytes to be trained with oxLDL. Interestingly, OXPHOS appears to play an important role in the increased cytokine hyperresponsiveness by oxLDL-trained macrophages. The TCA-cycle can also be fuelled by glutamine and free fatty acids, and pharmacological blockade of these pathways could prevent oxLDL-induced trained immunity. This study demonstrates that the mitochondria of oxLDL-trained macrophages undergo changes to their function and form with OXPHOS being an important mechanism for trained immunity, which could unveil novel pharmacological targets to prevent atherogenesis.
    Keywords:  metabolic reprogramming; mitochondria; monocyte; oxidized low-density lipoprotein; trained immunity
  38. Mol Metab. 2021 Jul 10. pii: S2212-8778(21)00139-3. [Epub ahead of print] 101294
      BACKGROUND: There is growing interest in the analysis of tumor metabolism to identify cancer-specific metabolic vulnerabilities and therapeutic targets. The identification of such candidate metabolic pathways mainly relies on the highly sensitive identification and quantitation of numerous metabolites and metabolic fluxes using metabolomics and isotope tracing analyses. However, nutritional requirements and metabolic routes used by cancer cells cultivated in vitro do not always reflect the metabolic demands of malignant cells within the tumor milieu. Therefore, to be able to understand how the metabolism of a tumor cell in its physiological environment differs from that of normal cells, these analyses must be performed in vivo.SCOPE OF REVIEW: This review covers the physiological impact of the exogenous administration of a stable isotope tracer into cancer animal models. We discuss specific aspects of in vivo isotope tracing protocols based on discrete bolus injections of a labeled metabolite: the tracer administration per se and the fasting period prior to tracer administration. In addition, we illustrate the complex physiological scenarios that arise when studying tumor metabolism by isotopic labeling in animal models fed with a diet restricted in a specific amino acid. Finally, we provide strategies to minimize those limitations.
    MAJOR CONCLUSIONS: There is a growing evidence that metabolic dependencies in cancers are influenced by tissue environments, cancer lineage, and genetic events. More and more studies are describing discrepancies in tumor metabolic dependencies when studied in in vitro settings or in in vivo models, including cancer patients. Therefore, in depth in vivo profiling of tumor metabolic routes within the appropriate patho-physiological environment will be key to identifying relevant alterations that contribute to cancer onset and progression.
    Keywords:  Fasting; Inter-organ exchange; Stable isotope tracing; Tracer administration; Tumor metabolism
  39. Front Cell Dev Biol. 2021 ;9 610683
      Melanoma cells exhibit increased aerobic glycolysis, which represents a major biochemical alteration associated with malignant transformation; thus, glycolytic enzymes could be exploited to selectively target cancer cells in cancer therapy. Sperm-specific glyceraldehyde-3-phosphate dehydrogenase (GAPDHS) switches glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate by coupling with the reduction of NAD+ to NADH. Here, we demonstrated that GAPDHS displays significantly higher expression in uveal melanoma (UM) than in normal controls. Functionally, the knockdown of GAPDHS in UM cell lines hindered glycolysis by decreasing glucose uptake, lactate production, adenosine triphosphate (ATP) generation, cell growth and proliferation; conversely, overexpression of GAPDHS promoted glycolysis, cell growth and proliferation. Furthermore, we identified that SOX10 knockdown reduced the activation of GAPDHS, leading to an attenuated malignant phenotype, and that SOX10 overexpression promoted the activation of GAPDHS, leading to an enhanced malignant phenotype. Mechanistically, SOX10 exerted its function by binding to the promoter of GAPDHS to regulate its expression. Importantly, SOX10 abrogation suppressed in vivo tumor growth and proliferation. Collectively, the results reveal that GAPDHS, which is regulated by SOX10, controls glycolysis and contributes to UM tumorigenesis, highlighting its potential as a therapeutic target.
    Keywords:  SOX10; glycolysis; glycolytic enzyme; sperm-specific glyceraldehyde-3-phosphate dehydrogenase; uveal melanoma
  40. Nat Rev Cancer. 2021 Jul 16.
      Tumour initiation and progression requires the metabolic reprogramming of cancer cells. Cancer cells autonomously alter their flux through various metabolic pathways in order to meet the increased bioenergetic and biosynthetic demand as well as mitigate oxidative stress required for cancer cell proliferation and survival. Cancer driver mutations coupled with environmental nutrient availability control flux through these metabolic pathways. Metabolites, when aberrantly accumulated, can also promote tumorigenesis. The development and application of new technologies over the last few decades has not only revealed the heterogeneity and plasticity of tumours but also allowed us to uncover new metabolic pathways involved in supporting tumour growth. The tumour microenvironment (TME), which can be depleted of certain nutrients, forces cancer cells to adapt by inducing nutrient scavenging mechanisms to sustain cancer cell proliferation. There is growing appreciation that the metabolism of cell types other than cancer cells within the TME, including endothelial cells, fibroblasts and immune cells, can modulate tumour progression. Because metastases are a major cause of death of patients with cancer, efforts are underway to understand how metabolism is harnessed by metastatic cells. Additionally, there is a new interest in exploiting cancer genetic analysis for patient stratification and/or dietary interventions in combination with therapies that target metabolism. In this Perspective, we highlight these main themes that are currently under investigation in the context of in vivo tumour metabolism, specifically emphasizing questions that remain unanswered.
  41. Cell Rep. 2021 Jul 13. pii: S2211-1247(21)00721-X. [Epub ahead of print]36(2): 109345
      Upon nutrient stimulation, pre-adipocytes undergo differentiation to transform into mature adipocytes capable of storing nutrients as fat. We profiled cellular metabolite consumption to identify early metabolic drivers of adipocyte differentiation. We find that adipocyte differentiation raises the uptake and consumption of numerous amino acids. In particular, branched-chain amino acid (BCAA) catabolism precedes and promotes peroxisome proliferator-activated receptor gamma (PPARγ), a key regulator of adipogenesis. In early adipogenesis, the mitochondrial sirtuin SIRT4 elevates BCAA catabolism through the activation of methylcrotonyl-coenzyme A (CoA) carboxylase (MCCC). MCCC supports leucine oxidation by catalyzing the carboxylation of 3-methylcrotonyl-CoA to 3-methylglutaconyl-CoA. Sirtuin 4 (SIRT4) expression is decreased in adipose tissue of numerous diabetic mouse models, and its expression is most correlated with BCAA enzymes, suggesting a potential role for SIRT4 in adipose pathology through the alteration of BCAA metabolism. In summary, this work provides a temporal analysis of adipocyte differentiation and uncovers early metabolic events that stimulate transcriptional reprogramming.
    Keywords:  BCAA catabolism; MCCC; PPARg; SIRT4; adipogenesis; amino acids; differentiation; sirtuin
  42. J Biol Chem. 2021 Jul 13. pii: S0021-9258(21)00754-7. [Epub ahead of print] 100954
      PPARδ is a nuclear receptor transcription factor that plays an important role in the regulation of metabolism, inflammation, and cancer. In addition, the nutrient-sensing kinase AMPK is a critical regulator of cellular energy in coordination with PPARδ. However, the molecular mechanism of AMPK/PPARδ pathway on cancer progression is still unclear. Here we found that activated AMPK induced PPARδ-S50 phosphorylation in cancer cells, while the PPARδ/S50A (non-phosphorylation mimic) mutant reversed this event. Further analysis showed that the PPARδ/S50E (phosphorylation mimic) but not the PPARδ/S50A mutant increased PPARδ protein stability, which led to reduced p62/SQSTM1-mediated degradation of misfolded PPARδ. Furthermore, PPARδ-S50 phosphorylation decreased PPARδ transcription activity and alleviated PPARδ-mediated uptake of glucose and glutamine in cancer cells. Soft agar and xenograft tumor model analysis showed that the PPARδ/S50E mutant but not the PPARδ/S50A mutant inhibited colon cancer cell proliferation and tumor growth, which was associated with inhibition of Glut1 and SLC1A5 transporter protein expression. These findings reveal a new mechanism of AMPK-induced PPARδ-S50 phosphorylation, accumulation of misfolded PPARδ protein, and inhibition of PPARδ transcription activity contributing to the suppression of colon tumor formation.
    Keywords:  AMPK; PPARδ; cancer; misfolded protein; phosphorylation
  43. J Clin Invest. 2021 Jul 13. pii: 138276. [Epub ahead of print]
      Glioblastoma (GBM) remains among the deadliest of human malignancies, and the emergence of the cancer stem cell (CSC) phenotype represents a major challenge to durable treatment response. Because the environmental and lifestyle factors that impact CSC populations are not clear, we sought to understand the consequences of diet on CSC enrichment. We evaluated disease progression in mice fed an obesity-inducing high-fat diet (HFD) versus a low-fat, control diet. HFD resulted in hyper-aggressive disease accompanied by CSC enrichment and shortened survival. HFD drove intracerebral accumulation of saturated fats, which inhibited the production of the cysteine metabolite and gasotransmitter, hydrogen sulfide (H2S). H2S functions principally through protein S-sulfhydration and regulates multiple programs including bioenergetics and metabolism. Inhibition of H2S increased proliferation and chemotherapy resistance, whereas treatment with H2S donors led to death of cultured GBM cells and stasis of GBM tumors in vivo. Syngeneic GBM models and GBM patient specimens present an overall reduction in protein S-sulfhydration, primarily associated with proteins regulating cellular metabolism. These findings provide clear evidence that diet modifiable H2S signaling serves to suppress GBM by restricting metabolic fitness, while its loss triggers CSC enrichment and disease acceleration. Interventions augmenting H2S bioavailability concurrent with GBM standard of care may improve outcomes for GBM patients.
    Keywords:  Brain cancer; Oncology; Stem cells
  44. BMC Bioinformatics. 2021 Jul 15. 22(Suppl 10): 369
      BACKGROUND: Mitochondria play essential roles in regulating cellular functions. Some drug treatments and molecular interventions have been reported to have off-target effects damaging mitochondria and causing severe side effects. The development of a database for the management of mitochondrial toxicity-related molecules and their targets is important for further analyses.RESULTS: To correlate chemical, biological and mechanistic information on clinically relevant mitochondria-related toxicity, a comprehensive mitochondrial toxicity database (MitoTox) was developed. MitoTox is an electronic repository that integrates comprehensive information about mitochondria-related toxins and their targets. Information and data related to mitochondrial toxicity originate from various sources, including scientific journals and other electronic databases. These resources were manually verified and extracted into MitoTox. The database currently contains over 1400 small-molecule compounds, 870 mitochondrial targets, and more than 4100  mitochondrial toxin-target associations. Each MitoTox data record contains over 30 fields, including biochemical properties, therapeutic classification, target proteins, toxicological data, mechanistic information, clinical side effects, and references.
    CONCLUSIONS: MitoTox provides a fully searchable database with links to references and other databases. Potential applications of MitoTox include toxicity classification, prediction, reference and education. MitoTox is available online at .
    Keywords:  Database; Mitochondria; Mitochondrial toxicity; Toxin-target association
  45. FEBS J. 2021 Jul 16.
      Bacterial pathogens employ a variety of tactics to persist in their host and promote infection. Pathogens often target host organelles in order to benefit their survival, either through manipulation or subversion of their function. Mitochondria are regularly targeted by bacterial pathogens owing to their diverse cellular roles, including energy production and regulation of programmed cell death. However, disruption of normal mitochondrial function during infection can be detrimental to cell viability because of their essential nature. In response, cells use multiple quality control programs to mitigate mitochondrial dysfunction and promote recovery. In this review, we will provide an overview of mitochondrial recovery programs including mitochondrial dynamics, the mitochondrial unfolded protein response (UPRmt ), and mitophagy. We will then discuss the various approaches used by bacterial pathogens to target mitochondria which result in mitochondrial dysfunction. Lastly, we will discuss how cells leverage mitochondrial recovery programs beyond their role in organelle repair, to promote host defense against pathogen infection.
    Keywords:  UPRmt; defense; infection; mitochondria; mitochondrial dynamics; mitochondrial fission; mitochondrial fusion; mitophagy; pathogen
  46. EMBO J. 2021 Jul 16. e107480
      The mTORC1 pathway plays key roles in regulating various biological processes, including sensing amino acid deprivation and driving expression of ribosomal protein (RP)-coding genes. In this study, we observed that depletion of glutamate dehydrogenase 1 (GDH1), an enzyme that converts glutamate to α-ketoglutarate (αKG), confers resistance to amino acid deprivation on kidney renal clear cell carcinoma (KIRC) cells. Mechanistically, under conditions of adequate nutrition, GDH1 maintains RP gene expression in a manner dependent on its enzymatic activity. Following amino acid deprivation or mTORC1 inhibition, GDH1 translocates from mitochondria to the cytoplasm, where it becomes ubiquitinated and degraded via the E3 ligase RNF213. GDH1 degradation reduces intracellular αKG levels by more than half and decreases the activity of αKG-dependent lysine demethylases (KDMs). Reduced KDM activity in turn leads to increased histone H3 lysine 9 and 27 methylation, further suppressing RP gene expression and preserving nutrition to support cell survival. In summary, our study exemplifies an economical and efficient strategy of solid tumor cells for coping with amino acid deficiency, which might in the future be targeted to block renal carcinoma progression.
    Keywords:  GDH1; amino acid deprivation; kidney cancer; ribosomes; αKG
  47. Onco Targets Ther. 2021 ;14 4047-4060
      Introduction: Glutathione reductase (GSR) provides reduced glutathione (GSH) to maintain redox homeostasis. Inhibition of GSR disrupts this balance, resulting in cell damage, which benefits cancer therapy. However, the effect of GSR inhibition on the tumorigenicity of human cervical cancer is not fully understood.Materials and Methods: Tissue microarray analysis was employed to determine GSR expression in cervical cancer tissues by immunohistochemical staining. Cell death was measured with PI/FITC-annexin V staining. mRNA levels were measured via quantitative RT-PCR. Protein expression was measured by Western blotting and flow cytometry. STAT3 deletion was performed with CRISPR/Cas9 technology. GSR knockdown was achieved by RNA interference. Reactive oxygen species (ROS) levels were measured by DCF staining. GSR enzymatic activity was measured with a GSR assay kit. The effect of GSR inhibition on the growth of tumors formed by cervical cancer cells was investigated using a xenograft model.
    Results: The expression of GSR was increased in human cervical cancer tissues, as shown by immunohistochemical staining. GSR knockdown by RNA interference in human cervical cancer cell lines resulted in cell death, suggesting the ability of GSR to maintain cancer cell survival. The STAT3 inhibitor 6-nitrobenzo[b]thiophene 1,1-dioxide (Stattic) also inhibited the enzymatic activity of GSR and induced the death of cervical cancer cells. More importantly, Stattic decreased the growth of xenograft tumors formed by cervical cancer cells in nude mice. Mechanistically, tumor cell death induced by Stattic-mediated GSR inhibition was ROS-dependent, since the ROS scavengers GSH and N-acetyl cysteine (NAC) reversed the effect of Stattic. In contrast, pharmacological and molecular inhibition of STAT3 did not induce the death of cervical cancer cells, suggesting a STAT3-independent activity of Stattic.
    Conclusion: Stattic inhibits the enzymatic activity of GSR and induces STAT3-independent but ROS-dependent death of cervical cancer cells, suggesting its potential application as a therapeutic agent for human cervical cancers.
    Keywords:  Stattic; cell death; cervical cancer; glutathione reductase; reactive oxygen species; tumor growth
  48. PLoS Biol. 2021 Jul;19(7): e3001302
      Defects in mitochondrial function activate compensatory responses in the cell. Mitochondrial stress that is caused by unfolded proteins inside the organelle induces a transcriptional response (termed the "mitochondrial unfolded protein response" [UPRmt]) that is mediated by activating transcription factor associated with stress 1 (ATFS-1). The UPRmt increases mitochondrial protein quality control. Mitochondrial dysfunction frequently causes defects in the import of proteins, resulting in the accumulation of mitochondrial proteins outside the organelle. In yeast, cells respond to mistargeted mitochondrial proteins by increasing activity of the proteasome in the cytosol (termed the "unfolded protein response activated by mistargeting of proteins" [UPRam]). The presence and relevance of this response in higher eukaryotes is unclear. Here, we demonstrate that defects in mitochondrial protein import in Caenorhabditis elegans lead to proteasome activation and life span extension. Both proteasome activation and life span prolongation partially depend on ATFS-1, despite its lack of influence on proteasomal gene transcription. Importantly, life span prolongation depends on the fully assembled proteasome. Our data provide a link between mitochondrial dysfunction and proteasomal activity and demonstrate its direct relevance to mechanisms that promote longevity.
  49. Nat Commun. 2021 07 13. 12(1): 4284
      The translocase of the outer mitochondrial membrane TOM constitutes the organellar entry gate for nearly all precursor proteins synthesized on cytosolic ribosomes. Thus, TOM presents the ideal target to adjust the mitochondrial proteome upon changing cellular demands. Here, we identify that the import receptor TOM70 is targeted by the kinase DYRK1A and that this modification plays a critical role in the activation of the carrier import pathway. Phosphorylation of TOM70Ser91 by DYRK1A stimulates interaction of TOM70 with the core TOM translocase. This enables transfer of receptor-bound precursors to the translocation pore and initiates their import. Consequently, loss of TOM70Ser91 phosphorylation results in a strong decrease in import capacity of metabolite carriers. Inhibition of DYRK1A impairs mitochondrial structure and function and elicits a protective transcriptional response to maintain a functional import machinery. The DYRK1A-TOM70 axis will enable insights into disease mechanisms caused by dysfunctional DYRK1A, including autism spectrum disorder, microcephaly and Down syndrome.
  50. Transl Oncol. 2021 Jul 09. pii: S1936-5233(21)00151-0. [Epub ahead of print]14(9): 101159
      The persistence of leukemia stem cells (LSCs) is one of the leading causes of chemoresistance in acute myeloid leukemia (AML). To explore the factors important in LSC-mediated resistance, we use mass spectrometry to screen the factors related to LSC chemoresistance and defined IFN-γ-inducible lysosomal thiol reductase (GILT) as a candidate. We found that the GILT expression was upregulated in chemoresistant CD34+ AML cells. Loss of function studies demonstrated that silencing of GILT in AML cells sensitized them to Ara-C treatment both in vitro and in vivo. Further mechanistic findings revealed that the ROS-mediated mitochondrial damage plays a pivotal role in inducing apoptosis of GILT-inhibited AML cells after Ara-C treatment. The inactivation of PI3K/Akt/ nuclear factor erythroid 2-related factor 2 (NRF2) pathway, causing reduced generation of antioxidants such as SOD2 and leading to a shifted ratio of GSH/GSSG to the oxidized form, contributed to the over-physiological oxidative status in the absence of GILT. The prognostic value of GILT was also validated in AML patients. Taken together, our work demonstrated that the inhibition of GILT increases AML chemo-sensitivity through elevating ROS level and induce oxidative mitochondrial damage-mediated apoptosis, and inhibition of the PI3K/Akt/NRF2 pathway enhances the intracellular oxidative state by disrupting redox homeostasis, providing a potentially effective way to overcome chemoresistance of AML.
    Keywords:  AML; Chemoresistance; GILT; LSC; Oxidative stress