bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2021‒10‒10
thirty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Cell Metab. 2021 Oct 05. pii: S1550-4131(21)00430-7. [Epub ahead of print]33(10): 1895
      
    DOI:  https://doi.org/10.1016/j.cmet.2021.09.011
  2. Cell Metab. 2021 Oct 05. pii: S1550-4131(21)00425-3. [Epub ahead of print]33(10): 1905-1907
      Leigh syndrome, a mitochondrial disease, can be modeled in mice with a deficiency in mitochondrial complex I that results in a decreased NAD+/NADH ratio. In this issue of Cell Metabolism, Liu et al. (2021) identify glycerol-3-phosphate (Gro3P) biosynthesis as a method for regenerating cytosolic NAD+ to ameliorate pathology in this mitochondrial disease model.
    DOI:  https://doi.org/10.1016/j.cmet.2021.09.006
  3. Cell Rep. 2021 Oct 05. pii: S2211-1247(21)01221-3. [Epub ahead of print]37(1): 109767
      Cardiac metabolism is a high-oxygen-consuming process, showing a preference for long-chain fatty acid (LCFA) as the fuel source under physiological conditions. However, a metabolic switch (favoring glucose instead of LCFA) is commonly reported in ischemic or late-stage failing hearts. The mechanism regulating this metabolic switch remains poorly understood. Here, we report that loss of PHD2/3, the cellular oxygen sensors, blocks LCFA mitochondria uptake and β-oxidation in cardiomyocytes. In high-fat-fed mice, PHD2/3 deficiency improves glucose metabolism but exacerbates the cardiac defects. Mechanistically, we find that PHD2/3 bind to CPT1B, a key enzyme of mitochondrial LCFA uptake, promoting CPT1B-P295 hydroxylation. Further, we show that CPT1B-P295 hydroxylation is indispensable for its interaction with VDAC1 and LCFA β-oxidation. Finally, we demonstrate that a CPT1B-P295A mutant constitutively binds to VDAC1 and rescues LCFA metabolism in PHD2/3-deficient cardiomyocytes. Together, our data identify an oxygen-sensitive regulatory axis involved in cardiac metabolism.
    Keywords:  cardiac metabolism switch; cardiomyocyte; carnitine O-palmitoyltransferase 1b; heart failure; hypoxia; long-chain fatty acid; myocardial infarction; prolyl hydroxylase domain protein; voltage-dependent anion channel
    DOI:  https://doi.org/10.1016/j.celrep.2021.109767
  4. Dev Cell. 2021 Sep 29. pii: S1534-5807(21)00731-0. [Epub ahead of print]
      The metabolic coupling of Schwann cells (SCs) and peripheral axons is poorly understood. Few molecules in SCs are known to regulate axon stability. Using SC-specific Rheb knockout mice, we demonstrate that Rheb-regulated mitochondrial pyruvate metabolism is critical for SC-mediated non-cell-autonomous regulation of peripheral axon stability. Rheb knockout suppresses pyruvate dehydrogenase (PDH) activity (independently of mTORC1) and shifts pyruvate metabolism toward lactate production in SCs. The increased lactate causes age-dependent peripheral axon degeneration, affecting peripheral nerve function. Lactate, as an energy substrate and a potential signaling molecule, enhanced neuronal mitochondrial metabolism and energy production of peripheral nerves. Albeit beneficial to injured peripheral axons in the short term, we show that persistently increased lactate metabolism of neurons enhances ROS production, eventually damaging mitochondria, neuroenergetics, and axon stability. This study highlights the complex roles of lactate metabolism to peripheral axons and the importance of lactate homeostasis in preserving peripheral nerves.
    Keywords:  ROS; Rheb; Schwann cells; axon degeneration; lactate shuttle; mTORC1; metabolic coupling; oxidative stress; peripheral axons; pyruvate metabolism
    DOI:  https://doi.org/10.1016/j.devcel.2021.09.013
  5. Immunometabolism. 2021 Sep 24. 3(4): e210030
      Immunotherapy has underscored a revolution in cancer treatment. Yet, many patients fail to respond due to T cell exhaustion. Here, an intervention that restores mitochondrial function reversed the exhausted T cell phenotype to promote cytotoxicity and durable anti-tumour responses in vivo.
    Keywords:  IL-10; T cell; exhaustion; immunotherapy; metabolism; mitochondria
    DOI:  https://doi.org/10.20900/immunometab20210030
  6. JCI Insight. 2021 Oct 05. pii: e148438. [Epub ahead of print]
      Mounting evidence points to alterations in mitochondrial metabolism in renal cell carcinoma (RCC). However, the mechanisms that regulate the TCA cycle in RCC remain uncharacterized. Here, we demonstrate that loss of TCA cycle enzyme expression is retained in RCC metastatic tissues. Moreover, proteomic analysis demonstrates that reduced TCA cycle enzyme expression is far more pronounced in RCC relative to other tumor types. Loss of TCA cycle enzyme expression is correlated with reduced expression of the transcription factor peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) which is also lost in RCC tissues. PGC-1α re-expression in RCC cells restores the expression of TCA cycle enzymes in vitro and in vivo and leads to enhanced glucose carbon incorporation into TCA cycle intermediates. Mechanistically, TGF-β signaling, in concert with histone deacetylase 7 (HDAC7), suppresses TCA cycle enzyme expression. Our studies show that pharmacologic inhibition of TGF-β restores the expression of TCA cycle enzymes and suppresses tumor growth in an orthotopic model of RCC. Taken together, this investigation reveals a novel role for the TGF-β/HDAC7 axis in global suppression of TCA cycle enzymes in RCC and provides new insight into the molecular basis of altered mitochondrial metabolism in this malignancy.
    Keywords:  Cancer; Cell Biology; Mitochondria; Molecular biology
    DOI:  https://doi.org/10.1172/jci.insight.148438
  7. J Cell Biol. 2021 Dec 06. pii: e202006049. [Epub ahead of print]220(12):
      The cystine-glutamate antiporter, xCT, supports a glutathione synthesis program enabling cancer cells to cope with metabolically stressful microenvironments. Up-regulated xCT, in combination with glutaminolysis, leads to increased extracellular glutamate, which promotes invasive behavior by activating metabotropic glutamate receptor 3 (mGluR3). Here we show that activation of mGluR3 in breast cancer cells activates Rab27-dependent release of extracellular vesicles (EVs), which can transfer invasive characteristics to "recipient" tumor cells. These EVs contain mitochondrial DNA (mtDNA), which is packaged via a PINK1-dependent mechanism. We highlight mtDNA as a key EV cargo necessary and sufficient for intercellular transfer of invasive behavior by activating Toll-like receptor 9 in recipient cells, and this involves increased endosomal trafficking of pro-invasive receptors. We propose that an EV-mediated mechanism, through which altered cellular metabolism in one cell influences endosomal trafficking in other cells, is key to generation and dissemination of pro-invasive microenvironments during mammary carcinoma progression.
    DOI:  https://doi.org/10.1083/jcb.202006049
  8. Blood. 2021 Oct 05. pii: blood.2021011563. [Epub ahead of print]
      Proton export is often considered a detoxifying process in animal cells with monocarboxylate symporters co-exporting excessive lactate and protons during glycolysis or the Warburg effect. Here we report a novel mechanism by which lactate/H+ export is sufficient to induce cell growth. Increased lactate/proton export induces intracellular alkalization that selectively activates catalysis by key metabolic gatekeeper enzymes, HK1/PKM2/G6PDH, thereby enhancing glycolytic and pentose phosphate pathway carbon flux. The result is increased nucleotide levels, NADPH/NADP+ ratio and cell proliferation. Simply increasing the lactate/proton symporter, MCT4, or sodium-proton antiporter, NHE1 was sufficient to increase intracellular-pH (pHi) and give normal hematopoietic cells a significant competitive growth advantage in vivo. This process does not require additional cytokine triggers and is exploited in malignancy where leukemogenic mutations epigenetically increase MCT4. Inhibiting MCT4 decreased intracellular pH, carbon flux and eliminated acute myeloid leukemia-initiating-cells without cytotoxic chemotherapy. Intracellular alkalization is a primitive mechanism by which proton partitioning can directly reprogram carbon metabolism for cell growth.
    DOI:  https://doi.org/10.1182/blood.2021011563
  9. Nat Rev Mol Cell Biol. 2021 Oct 07.
      The mitochondrial oxidative phosphorylation system is central to cellular metabolism. It comprises five enzymatic complexes and two mobile electron carriers that work in a mitochondrial respiratory chain. By coupling the oxidation of reducing equivalents coming into mitochondria to the generation and subsequent dissipation of a proton gradient across the inner mitochondrial membrane, this electron transport chain drives the production of ATP, which is then used as a primary energy carrier in virtually all cellular processes. Minimal perturbations of the respiratory chain activity are linked to diseases; therefore, it is necessary to understand how these complexes are assembled and regulated and how they function. In this Review, we outline the latest assembly models for each individual complex, and we also highlight the recent discoveries indicating that the formation of larger assemblies, known as respiratory supercomplexes, originates from the association of the intermediates of individual complexes. We then discuss how recent cryo-electron microscopy structures have been key to answering open questions on the function of the electron transport chain in mitochondrial respiration and how supercomplexes and other factors, including metabolites, can regulate the activity of the single complexes. When relevant, we discuss how these mechanisms contribute to physiology and outline their deregulation in human diseases.
    DOI:  https://doi.org/10.1038/s41580-021-00415-0
  10. Neurochem Res. 2021 Oct 08.
      Glucose and oxygen (O2) are vital to the brain. Glucose metabolism and mitochondria play a pivotal role in this process, culminating in the increase of reactive O2 species. Hexokinase (HK) is a key enzyme on glucose metabolism and is coupled to the brain mitochondrial redox modulation by recycling ADP for oxidative phosphorylation (OXPHOS). GABA shunt is an alternative pathway to GABA metabolism that increases succinate levels, a Krebs cycle intermediate. Although glucose and GABA metabolisms are intrinsically connected, their interplay coordinating mitochondrial function is poorly understood. Here, we hypothesize that the HK and the GABA shunt interact to control mitochondrial metabolism differently in the cortex and the hypothalamus. The GABA shunt stimulated mitochondrial O2 consumption and H2O2 production higher in hypothalamic synaptosomes (HSy) than cortical synaptosomes (CSy). The GABA shunt increased the HK coupled to OXPHOS activity in both population of synaptosomes, but the rate of activation was higher in HSy than CSy. Significantly, malonate and vigabatrin blocked the effects of the GABA shunt in the HK activity coupled to OXPHOS. It indicates that the glucose phosphorylation is linked to GABA and Krebs cycle reactions. Together, these data shed light on the HK and SDH role on the metabolism of each region fed by GABA turnover, which depends on the neurons' metabolic route.
    Keywords:  Bioenergetics; Brain; GABA shunt; Hexokinase; Mitochondria; Synaptosome
    DOI:  https://doi.org/10.1007/s11064-021-03463-2
  11. Trends Immunol. 2021 Oct 02. pii: S1471-4906(21)00178-2. [Epub ahead of print]
      The cancer-immunity cycle (CIC) comprises a series of events that are required for immune-mediated control of tumor growth. Interruption of one or more steps of the CIC enables tumors to evade immunosurveillance. However, attempts to restore antitumor immunity by reactivating the CIC have had limited success thus far. Recently, numerous studies have implicated metabolic reprogramming of tumor and immune cells within the tumor microenvironment (TME) as key contributors to immune evasion. In this opinion, we propose that alterations in cellular metabolism during tumorigenesis promote both initiation and disruption of the CIC. We also provide a rationale for metabolically targeting the TME, which may assist in improving tumor responsiveness to chimeric antigen receptor (CAR)-transduced T cells or immune checkpoint blockade (ICB) therapies.
    Keywords:  CAR-T cells; PD-1; glycolysis; immunotherapy; lactate; metabolism; tumor immunology
    DOI:  https://doi.org/10.1016/j.it.2021.09.002
  12. J Biol Chem. 2021 Oct 05. pii: S0021-9258(21)01082-6. [Epub ahead of print] 101279
      Mitochondria are essential organelles that carry out a number of pivotal metabolic processes and maintain cellular homeostasis. Mitochondrial dysfunction caused by various stresses is associated with many diseases such as type 2 diabetes, obesity, cancer, heart failure, neurodegenerative disorders, and aging. Therefore, it is important to understand the stimuli that induce mitochondrial stress. However, broad analysis of mitochondrial stress has not been carried out to date. Here, we present a set of fluorescent tools, called mito-Pain (mitochondrial PINK1 accumulation index), which enables the labeling of stressed mitochondria. Mito-Pain utilizes PINK1 stabilization on mitochondria and quantifies mitochondrial stress levels by comparison with PINK1-GFP, which is stabilized under mitochondrial stress, and RFP-Omp25, which is constitutively localized on mitochondria. To identify compounds that induce mitochondrial stress, we screened a library of 3374 compounds using mito-Pain and identified 57 compounds as mitochondrial stress inducers. Furthermore, we classified each compound into several categories based on mitochondrial response: depolarization, mitochondrial morphology, or Parkin recruitment. Parkin recruitment to mitochondria was often associated with mitochondrial depolarization and aggregation, suggesting that Parkin is recruited to heavily damaged mitochondria. In addition, many of the compounds led to various mitochondrial morphological changes, including fragmentation, aggregation, elongation, and swelling, with or without Parkin recruitment or mitochondrial depolarization. We also found that several compounds induced an ectopic response of Parkin, leading to the formation of cytosolic puncta dependent on PINK1. Thus, mito-Pain enables the detection of stressed mitochondria under a wide variety of conditions and provide insights into mitochondrial quality control systems.
    Keywords:  PTEN‐induced putative kinase 1 (PINK1); Parkin; mitochondria; mitochondrial membrane potential; mitochondrial sensor; mitochondrial stress
    DOI:  https://doi.org/10.1016/j.jbc.2021.101279
  13. Lab Invest. 2021 Oct 04.
      Mitochondrial homeostasis is crucial for the function of pancreatic β-cells. ATP synthase inhibitory factor subunit 1 (IF1) is a mitochondrial protein interacting with ATP synthase to inhibit its enzyme activity. IF1 may also play a role in maintaining ATP synthase oligomerization and mitochondrial inner membrane formation. A recent study confirmed IF1 expresses in β-cells. IF1 knockdown in cultured INS-1E β-cells enhances glucose-induced insulin release. However, the role of IF1 in islet β-cells remains little known. The present study investigates islets freshly isolated from mouse lines with global IF1 knockout (IF1-/-) and overexpression (OE). The glucose-stimulated insulin secretion was increased in islets from IF1-/- mice but decreased in islets from IF1 OE mice. Transmitted Electronic Microscopic assessment of isolated islets revealed that the number of matured insulin granules (with dense core) was relatively higher in IF1-/-, but fewer in IF1 OE islets than those of controlled islets. The mitochondrial ultrastructure within β-cells of IF1 overexpressed islets was comparable with those of wild-type mice, whereas those in IF1-/- β-cells showed increased mitochondrial mass. Mitochondrial network analysis in cultured INS-1 β-cells showed a similar pattern with an increased mitochondrial network in IF1 knockdown cells. IF1 overexpressed INS-1 β-cells showed a compromised rate of mitochondrial oxidative phosphorylation with attenuated cellular ATP content. In contrast, INS-1 cells with IF1 knockdown showed markedly increased cellular respiration with improved ATP production. These results support that IF1 is a negative regulator of insulin production and secretion via inhibiting mitochondrial mass and respiration in β-cells. Therefore, inhibiting IF1 to improve β-cell function in patients can be a novel therapeutic strategy to treat diabetes.
    DOI:  https://doi.org/10.1038/s41374-021-00670-x
  14. Plant Physiol. 2021 Oct 05. 187(2): 931-946
      Light is the ultimate source of energy for photosynthetic organisms, but respiration is fundamental for supporting metabolism during the night or in heterotrophic tissues. In this work, we isolated Physcomitrella (Physcomitrium patens) plants with altered respiration by inactivating Complex I (CI) of the mitochondrial electron transport chain by independently targeting on two essential subunits. Inactivation of CI caused a strong growth impairment even in fully autotrophic conditions in tissues where all cells are photosynthetically active, demonstrating that respiration is essential for photosynthesis. CI mutants showed alterations in the stoichiometry of respiratory complexes while the composition of photosynthetic apparatus was substantially unaffected. CI mutants showed altered photosynthesis with high activity of both Photosystems I and II, likely the result of high chloroplast ATPase activity that led to smaller ΔpH formation across thylakoid membranes, decreasing photosynthetic control on cytochrome b6f in CI mutants. These results demonstrate that alteration of respiratory activity directly impacts photosynthesis in P. patens and that metabolic interaction between organelles is essential in their ability to use light energy for growth.
    DOI:  https://doi.org/10.1093/plphys/kiab276
  15. Elife. 2021 10 05. pii: e69207. [Epub ahead of print]10
      The Connexin43 gap junction gene GJA1 has one coding exon, but its mRNA undergoes internal translation to generate N-terminal truncated isoforms of Connexin43 with the predominant isoform being only 20 kDa in size (GJA1-20k). Endogenous GJA1-20k protein is not membrane bound and has been found to increase in response to ischemic stress, localize to mitochondria, and mimic ischemic preconditioning protection in the heart. However, it is not known how GJA1-20k benefits mitochondria to provide this protection. Here, using human cells and mice, we identify that GJA1-20k polymerizes actin around mitochondria which induces focal constriction sites. Mitochondrial fission events occur within about 45 s of GJA1-20k recruitment of actin. Interestingly, GJA1-20k mediated fission is independent of canonical Dynamin-Related Protein 1 (DRP1). We find that GJA1-20k-induced smaller mitochondria have decreased reactive oxygen species (ROS) generation and, in hearts, provide potent protection against ischemia-reperfusion injury. The results indicate that stress responsive internally translated GJA1-20k stabilizes polymerized actin filaments to stimulate non-canonical mitochondrial fission which limits ischemic-reperfusion induced myocardial infarction.
    Keywords:  GJA1-20k; actin dynamics; cell biology; human; ischemia/reperfusion; mitochondria; mitochondria dynamics; mouse; organ protection
    DOI:  https://doi.org/10.7554/eLife.69207
  16. J Clin Invest. 2021 Sep 01. pii: e139933. [Epub ahead of print]131(17):
      Mitochondrial electron transport chain complex I (ETCC1) is the essential core of cancer metabolism, yet potent ETCC1 inhibitors capable of safely suppressing tumor growth and metastasis in vivo are limited. From a plant extract screening, we identified petasin (PT) as a highly potent ETCC1 inhibitor with a chemical structure distinct from conventional inhibitors. PT had at least 1700 times higher activity than that of metformin or phenformin and induced cytotoxicity against a broad spectrum of tumor types. PT administration also induced prominent growth inhibition in multiple syngeneic and xenograft mouse models in vivo. Despite its higher potency, it showed no apparent toxicity toward nontumor cells and normal organs. Also, treatment with PT attenuated cellular motility and focal adhesion in vitro as well as lung metastasis in vivo. Metabolome and proteome analyses revealed that PT severely depleted the level of aspartate, disrupted tumor-associated metabolism of nucleotide synthesis and glycosylation, and downregulated major oncoproteins associated with proliferation and metastasis. These findings indicate the promising potential of PT as a potent ETCC1 inhibitor to target the metabolic vulnerability of tumor cells.
    Keywords:  Amino acid metabolism; Cancer; Metabolism; Mitochondria; Oncology
    DOI:  https://doi.org/10.1172/JCI139933
  17. Cell Metab. 2021 Sep 28. pii: S1550-4131(21)00429-0. [Epub ahead of print]
      Excessive sugar consumption is increasingly considered as a contributor to the emerging epidemics of obesity and the associated cardiometabolic disease. Sugar is added to the diet in the form of sucrose or high-fructose corn syrup, both of which comprise nearly equal amounts of glucose and fructose. The unique aspects of fructose metabolism and properties of fructose-derived metabolites allow for fructose to serve as a physiological signal of normal dietary sugar consumption. However, when fructose is consumed in excess, these unique properties may contribute to the pathogenesis of cardiometabolic disease. Here, we review the biochemistry, genetics, and physiology of fructose metabolism and consider mechanisms by which excessive fructose consumption may contribute to metabolic disease. Lastly, we consider new therapeutic options for the treatment of metabolic disease based upon this knowledge.
    Keywords:  ALDOB; ChREBP; GLUT5; KHK; NAFLD; TKFC; cardiometabolic disease; fructose; insulin resistance; lipogenesis; steatosis; uric acid
    DOI:  https://doi.org/10.1016/j.cmet.2021.09.010
  18. Biochem Biophys Rep. 2021 Dec;28 101142
      The correct organization of mitochondrial DNA (mtDNA) in nucleoids and the contacts of mitochondria with the ER play an important role in maintaining the mitochondrial genome distribution within the cell. Mitochondria-associated ER membranes (MAMs) consist of interacting proteins and lipids located in the outer mitochondrial membrane and ER membrane, forming a platform for the mitochondrial inner membrane-associated genome replication factory as well as connecting the nucleoids with the mitochondrial division machinery. We show here that knockdown of a core component of mitochondrial nucleoids, TFAM, causes changes in the mitochondrial nucleoid populations, which subsequently impact ER-mitochondria membrane contacts. Knockdown of TFAM causes a significant decrease in the copy number of mtDNA as well as aggregation of mtDNA nucleoids. At the same time, it causes significant upregulation of the replicative TWNK helicase in the membrane-associated nucleoid fraction. This is accompanied by a transient elevation of MAM proteins, indicating a rearrangement of the linkage between ER and mitochondria triggered by changes in mitochondrial nucleoids. Reciprocal knockdown of the mitochondrial replicative helicase TWNK causes a decrease in mtDNA copy number and modifies mtDNA membrane association, however, it does not cause nucleoid aggregation and considerable alterations of MAM proteins in the membrane-associated fraction. Our explanation is that the aggregation of mitochondrial nucleoids resulting from TFAM knockdown triggers a compensatory mechanism involving the reorganization of both mitochondrial nucleoids and MAM. These results could provide an important insight into pathological conditions associated with impaired nucleoid organization or defects of mtDNA distribution.
    Keywords:  Mitochondrial DNA; Mitochondrial transcription factor A (TFAM); Nucleoids; Organellar membranes; TWNK helicase
    DOI:  https://doi.org/10.1016/j.bbrep.2021.101142
  19. FEBS J. 2021 Oct 04.
      Mitochondria act as key organelles in cellular bioenergetics and biosynthetic processes producing signals that regulate different molecular networks for proliferation and cell death. This ability is also preserved in pathologic contexts such as tumorigenesis, during which bioenergetic changes and metabolic reprogramming confer flexibility favoring cancer cells survival in a hostile microenvironment. Although different studies epitomize mitochondrial dysfunction as a pro-tumorigenic hit, genetic ablation or pharmacological inhibition of respiratory Complex I causing a severe impairment are associated with a low proliferative phenotype. In this scenario, it must be considered that despite the initial delay in growth, cancer cells may become able to resume proliferation exploiting molecular mechanisms to overcome growth arrest. Here we highlight the current knowledge on molecular responses activated by Complex I-defective cancer cells to bypass physiological control systems and to re-adapt their fitness during microenvironment changes. Such adaptive mechanisms could reveal possible novel molecular players in synthetic lethality with Complex I impairment, thus providing new synergistic strategies for mitochondria-based anti-cancer therapy.
    Keywords:  Respiratory complex I; adaptive responses; cancer metabolism; mitochondria; tumor microenvironment
    DOI:  https://doi.org/10.1111/febs.16218
  20. Nat Commun. 2021 Oct 07. 12(1): 5880
      The evolution of microorganisms often involves changes of unclear relevance, such as transient phenotypes and sequential development of multiple adaptive mutations in hotspot genes. Previously, we showed that ageing colonies of an E. coli mutant unable to produce cAMP when grown on maltose, accumulated mutations in the crp gene (encoding a global transcription factor) and in genes involved in pyrimidine metabolism such as cmk; combined mutations in both crp and cmk enabled fermentation of maltose (which usually requires cAMP-mediated Crp activation for catabolic pathway expression). Here, we study the sequential generation of hotspot mutations in those genes, and uncover a regulatory role of pyrimidine nucleosides in carbon catabolism. Cytidine binds to the cytidine regulator CytR, modifies the expression of sigma factor 32 (RpoH), and thereby impacts global gene expression. In addition, cytidine binds and activates a Crp mutant directly, thus modulating catabolic pathway expression, and could be the catabolite modulating factor whose existence was suggested by Jacques Monod and colleagues in 1976. Therefore, transcription factor Crp appears to work in concert with CytR and RpoH, serving a dual role in sensing both carbon availability and metabolic flux towards DNA and RNA. Our findings show how certain alterations in metabolite concentrations (associated with colony ageing and/or due to mutations in metabolic or regulatory genes) can drive the evolution in non-growing cells.
    DOI:  https://doi.org/10.1038/s41467-021-26098-x
  21. Nat Cell Biol. 2021 Oct 06.
      Cells respond to stress by blocking translation, rewiring metabolism and forming transient messenger ribonucleoprotein assemblies called stress granules (SGs). After stress release, re-establishing homeostasis and disassembling SGs requires ATP-consuming processes. However, the molecular mechanisms whereby cells restore ATP production and disassemble SGs after stress remain poorly understood. Here we show that upon stress, the ATP-producing enzyme Cdc19 forms inactive amyloids, and that their rapid re-solubilization is essential to restore ATP production and disassemble SGs in glucose-containing media. Cdc19 re-solubilization is initiated by the glycolytic metabolite fructose-1,6-bisphosphate, which directly binds Cdc19 amyloids, allowing Hsp104 and Ssa2 chaperone recruitment and aggregate re-solubilization. Fructose-1,6-bisphosphate then promotes Cdc19 tetramerization, which boosts its activity to further enhance ATP production and SG disassembly. Together, these results describe a molecular mechanism that is critical for stress recovery and directly couples cellular metabolism with SG dynamics via the regulation of reversible Cdc19 amyloids.
    DOI:  https://doi.org/10.1038/s41556-021-00760-4
  22. Mitochondrion. 2021 Oct 01. pii: S1567-7249(21)00140-9. [Epub ahead of print]
      Although alterations in cellular mitochondrial DNA (mtDNA) content have been linked to various pathological conditions, the mechanisms that govern mtDNA copy number (mtCN) control remain poorly understood. Moreover, techniques for mtDNA quantification do not allow for direct comparisons of absolute mtCNs between labs. Here we report the development of a direct droplet digital PCR technique for the determination of mtCNs in whole-cell lysates. Using this technique, we demonstrate that cellular mtDNA content can fluctuate in culture by as much as 50% and provide evidence for both cell proliferation-coupled and uncoupled mtDNA replication.
    Keywords:  Mitochondrial DNA; X-ray; cell cycle; cell proliferation; mtDNA copy number; mtDNA replication
    DOI:  https://doi.org/10.1016/j.mito.2021.09.014
  23. Cell Metab. 2021 Sep 30. pii: S1550-4131(21)00423-X. [Epub ahead of print]
      Glucose and fructose are closely related simple sugars, but fructose has been associated more closely with metabolic disease. Until the 1960s, the major dietary source of fructose was fruit, but subsequently, high-fructose corn syrup (HFCS) became a dominant component of the Western diet. The exponential increase in HFCS consumption correlates with the increased incidence of obesity and type 2 diabetes mellitus, but the mechanistic link between these metabolic diseases and fructose remains tenuous. Although dietary fructose was thought to be metabolized exclusively in the liver, evidence has emerged that it is also metabolized in the small intestine and leads to intestinal epithelial barrier deterioration. Along with the clinical manifestations of hereditary fructose intolerance, these findings suggest that, along with the direct effect of fructose on liver metabolism, the gut-liver axis plays a key role in fructose metabolism and pathology. Here, we summarize recent studies on fructose biology and pathology and discuss new opportunities for prevention and treatment of diseases associated with high-fructose consumption.
    Keywords:  NASH; cancer; fructos; gut inflammation; metabolic disease
    DOI:  https://doi.org/10.1016/j.cmet.2021.09.004
  24. Hum Cell. 2021 Oct 04.
      Lactate, as the product of glycolytic metabolism and the substrate of energy metabolism, is an intermediate link between cancer cell and tumor microenvironment metabolism. The exchange of lactate between the two cells via mono-carboxylate transporters (MCTs) is known as the lactate shuttle in cancer. Lactate shuttle is the core of cancer cell metabolic reprogramming between two cells such as aerobic cancer cells and hypoxic cancer cells, tumor cells and stromal cells, cancer cells and vascular endothelial cells. Cancer cells absorb lactate by mono-carboxylate transporter 1 (MCT1) and convert lactate to pyruvate via intracellular lactate dehydrogenase B (LDH-B) to maintain their growth and metabolism. Since lactate shuttle may play a critical role in energy metabolism of cancer cells, components related to lactate shuttle may be a crucial target for tumor antimetabolic therapy. In this review, we describe the lactate shuttle in terms of both substance exchange and regulatory mechanisms in cancer. Meanwhile, we summarize the difference of key proteins of lactate shuttle in common types of cancer.
    Keywords:  Glycolysis; LDH; Lactate shuttle; MCT; Metabolic reprogramming
    DOI:  https://doi.org/10.1007/s13577-021-00622-z
  25. Nature. 2021 Oct 06.
      Understanding cellular architecture is essential for understanding biology. Electron microscopy (EM) uniquely visualizes cellular structures with nanometre resolution. However, traditional methods, such as thin-section EM or EM tomography, have limitations in that they visualize only a single slice or a relatively small volume of the cell, respectively. Focused ion beam-scanning electron microscopy (FIB-SEM) has demonstrated the ability to image small volumes of cellular samples with 4-nm isotropic voxels1. Owing to advances in the precision and stability of FIB milling, together with enhanced signal detection and faster SEM scanning, we have increased the volume that can be imaged with 4-nm voxels by two orders of magnitude. Here we present a volume EM atlas at such resolution comprising ten three-dimensional datasets for whole cells and tissues, including cancer cells, immune cells, mouse pancreatic islets and Drosophila neural tissues. These open access data (via OpenOrganelle2) represent the foundation of a field of high-resolution whole-cell volume EM and subsequent analyses, and we invite researchers to explore this atlas and pose questions.
    DOI:  https://doi.org/10.1038/s41586-021-03992-4
  26. Biosci Rep. 2021 Oct 05. pii: BSR20211320. [Epub ahead of print]
      Mitochondria are highly specialised organelles required for cellular processes including ATP-production through cellular respiration and controlling apoptosis. Mitochondria contain their own DNA genome which encodes both protein and RNA required for cellular respiration. Each cell may contain hundreds to thousands of copies of the mitochondrial genome, which is essential for normal cellular function - deviation of mitochondrial DNA (mtDNA) copy number is associated with cellular aging and disease. Furthermore, mtDNA lesions can arise from both endogenous or exogenous sources and must either be tolerated or corrected to preserve mitochondrial function. Importantly, replication of damaged mtDNA can lead to stalling and introduction of mutations or genetic loss, mitochondria have adapted mechanisms to repair damaged DNA. These mechanisms rely on nuclear encoded DNA repair proteins that are translocated into the mitochondria. Despite the presence of many known nuclear DNA repair proteins being found in the mitochondrial proteome, it remains to be established which DNA repair mechanisms are functional in mammalian mitochondria. Here, we summarise the existing and emerging research, alongside examining proteomic evidence, demonstrating that mtDNA damage can be repaired using Base Excision Repair (BER), Homologous Recombination (HR) and Microhomology-mediated End Joining (MMEJ). Critically, these repair mechanisms do not operate in isolation and evidence for interplay between pathways and repair associated with replication is discussed. Importantly, characterising non-canonical functions of key proteins and understanding the bespoke pathways used to tolerate, repair or bypass DNA damage will be fundamental in fully understanding the causes of mitochondrial genome mutations and mitochondrial dysfunction.
    Keywords:  DNA replication and recombination; DNA synthesis and repair; genome integrity; mtDNA
    DOI:  https://doi.org/10.1042/BSR20211320
  27. Clin Sci (Lond). 2021 Oct 08. pii: CS20210821. [Epub ahead of print]
      AMP-activated protein kinase (AMPK) plays a key role in the cellular response to low energy stress and has emerged as an attractive therapeutic target for tackling metabolic diseases. Whilst significant progress has been made regarding the physiological role of AMPK, its function in the kidney remains only partially understood. We use a mouse model expressing a constitutively active mutant of AMPK to investigate the effect of AMPK activation on kidney function in vivo. Kidney morphology and changes in gene and protein expression were monitored and serum and urine markers were measured to assess kidney function in vivo. Global AMPK activation resulted in an early onset polycystic kidney phenotype, featuring collecting duct cysts and compromised renal function in adult mice. Mechanistically, the cystic kidneys had increased cAMP levels and ERK activation, increased hexokinase I expression, glycogen accumulation and altered expression of proteins associated with autophagy. Kidney tubule-specific activation of AMPK also resulted in a polycystic phenotype, demonstrating that renal tubular AMPK activation caused the cystogenesis. Importantly, human ADPKD kidney sections revealed similar protein localisation patterns to that observed in the murine cystic kidneys. Our findings show that early onset chronic AMPK activation leads to a polycystic kidney phenotype, suggesting dysregulated AMPK signalling is a contributing factor in cystogenesis.
    Keywords:  AMPK; chronic kidney disease; metabolic regulation
    DOI:  https://doi.org/10.1042/CS20210821
  28. Nature. 2021 Oct 06.
      The enzymes of the mitochondrial electron transport chain are key players of cell metabolism. Despite being active when isolated, in vivo they associate into supercomplexes1, whose precise role is debated. Supercomplexes CIII2CIV1-2 (refs. 2,3), CICIII2 (ref. 4) and CICIII2CIV (respirasome)5-10 exist in mammals, but in contrast to CICIII2 and the respirasome, to date the only known eukaryotic structures of CIII2CIV1-2 come from Saccharomyces cerevisiae11,12 and plants13, which have different organization. Here we present the first, to our knowledge, structures of mammalian (mouse and ovine) CIII2CIV and its assembly intermediates, in different conformations. We describe the assembly of CIII2CIV from the CIII2 precursor to the final CIII2CIV conformation, driven by the insertion of the N terminus of the assembly factor SCAF1 (ref. 14) deep into CIII2, while its C terminus is integrated into CIV. Our structures (which include CICIII2 and the respirasome) also confirm that SCAF1 is exclusively required for the assembly of CIII2CIV and has no role in the assembly of the respirasome. We show that CIII2 is asymmetric due to the presence of only one copy of subunit 9, which straddles both monomers and prevents the attachment of a second copy of SCAF1 to CIII2, explaining the presence of one copy of CIV in CIII2CIV in mammals. Finally, we show that CIII2 and CIV gain catalytic advantage when assembled into the supercomplex and propose a role for CIII2CIV in fine tuning the efficiency of electron transfer in the electron transport chain.
    DOI:  https://doi.org/10.1038/s41586-021-03927-z
  29. Trends Biochem Sci. 2021 Oct 01. pii: S0968-0004(21)00191-2. [Epub ahead of print]
      The recent discovery that collision of ribosomes triggers quality control and stress responses in eukaryotes has shifted the perspective of the field. Collided eukaryotic ribosomes adopt a unique structure, acting as a ubiquitin signaling platform for various response factors. While several of the signals that determine which downstream pathways are activated have been uncovered, we are only beginning to learn how the specificity for the activation of each process is achieved during collisions. This review will summarize those findings and how ribosome-associated factors act as molecular sentinels, linking aberrations in translation to the overall cellular state. Insights into how cells respond to ribosome collision events will provide greater understanding of the role of the ribosome in the maintenance of cellular homeostasis.
    Keywords:  collisions; integrated stress response; mRNA surveillance; quality control; ribosome; signaling
    DOI:  https://doi.org/10.1016/j.tibs.2021.09.001
  30. Nucleic Acids Res. 2021 Oct 04. pii: gkab871. [Epub ahead of print]
      KRAS-activating mutations are oncogenic drivers and are correlated with radioresistance of multiple cancers, including colorectal cancer, but the underlying precise molecular mechanisms remain elusive. Herein we model the radiosensitivity of isogenic HCT116 and SW48 colorectal cancer cell lines bearing wild-type or various mutant KRAS isoforms. We demonstrate that KRAS mutations indeed lead to radioresistance accompanied by reduced radiotherapy-induced mitotic catastrophe and an accelerated release from G2/M arrest. Moreover, KRAS mutations result in increased DNA damage response and upregulation of 53BP1 with associated increased non-homologous end-joining (NHEJ) repair. Remarkably, KRAS mutations lead to activation of NRF2 antioxidant signaling to increase 53BP1 gene transcription. Furthermore, genetic silencing or pharmacological inhibition of KRAS, NRF2 or 53BP1 attenuates KRAS mutation-induced radioresistance, especially in G1 phase cells. These findings reveal an important role for a KRAS-induced NRF2-53BP1 axis in the DNA repair and survival of KRAS-mutant tumor cells after radiotherapy, and indicate that targeting NRF2, 53BP1 or NHEJ may represent novel strategies to selectively abrogate KRAS mutation-mediated radioresistance.
    DOI:  https://doi.org/10.1093/nar/gkab871
  31. Endocrinology. 2021 Oct 06. pii: bqab212. [Epub ahead of print]
      Estrogen and estrogen receptor (ER) play a fundamental role in breast cancer. To adapt the rapid proliferation of ER+ breast cancer cells, estrogen increases glucose uptake and reprograms glucose metabolism. Meanwhile, estrogen/ER activates the anticipatory unfolded protein response (UPR) preparing cancer cells for the increased protein production required for subsequent cell proliferation. Here, we report that thioredoxin-interacting protein (TXNIP) is an important regulator of glucose metabolism in ER+ breast cancer cells, and estrogen/ER increases glucose uptake and reprograms glucose metabolism via activating anticipatory unfolded protein response (UPR) and subsequently repressing TXNIP expression. By using two widely used ER+ breast cancer cell lines MCF7 and T47D, we showed that MCF7 cells express high TXNIP levels and exhibit mitochondrial oxidative phosphorylation (OXPHOS) phenotype, while T47D cells express low TXNIP levels and display aerobic glycolysis (Warburg effect) phenotype. Knockdown of TXNIP promoted glucose uptake and Warburg effect, while forced overexpression of TXNIP inhibited glucose uptake and Warburg effect. We further showed that estrogen represses TXNIP expression and activates UPR sensor inositol-requiring enzyme 1 (IRE1) via ER in the breast cancer cells, and IRE1 activity is required for estrogen suppression of TXNIP expression and estrogen-induced cell proliferation. Together, our study suggests that TXNIP is involved in estrogen-induced glucose uptake and metabolic reprogramming in ER+ breast cancer cells, and links anticipatory UPR to estrogen reprogramming glucose metabolism.
    Keywords:  TXNIP; breast cancer; estrogen; glucose metabolism; unfolded protein response
    DOI:  https://doi.org/10.1210/endocr/bqab212
  32. Front Endocrinol (Lausanne). 2021 ;12 731096
      Carotid body paragangliomas (PGLs) are rare neuroendocrine tumors that develop within the adventitia of the medial aspect of the carotid bifurcation. Carotid body PGLs comprise about 65% of head and neck paragangliomas, however, their genetic background remains elusive. In the present study, we report one case of carotid body PGL with a somatic mutation in the gene encoding isocitrate dehydrogenase 2 (IDH2). The missense mutation in IDH2 resulted in R172G amino acid substitution, which exhibits neomorphic activity and production of D-2-hydroxyglutarate.
    Keywords:  D-2-hydroxyglutarate; IDH2; PET/CT; carotid body tumor; isocitrate dehydrogenase 2; paraganglioma
    DOI:  https://doi.org/10.3389/fendo.2021.731096
  33. FEBS J. 2021 Oct 05.
      Forkhead box O (FOXO) transcription factors are a subclass of the larger family of Forkhead transcription factors. Mammalians express four members FOXO1, FOXO3, FOXO4 and FOXO6. The interest in FOXO function stems mostly from their observed role in determining lifespan, where in model organisms increased FOXO activity results in extended lifespan. FOXOs act as downstream of several signaling pathway and are extensively regulated through posttranslational modifications. The transcriptional program activated by FOXOs in various cell types, organisms and under various conditions has been described and has shed some light on what the critical transcriptional targets are in mediating FOXO function. At the cellular level, these studies have revealed a role for FOXOs in cell metabolism, cellular redox, cell proliferation, DNA repair, autophagy and many more. The general picture that emerges hereof is that FOXOs act to preserve equilibrium, they are important for cellular homeostasis. Here we will first briefly summarize the general knowledge of FOXO regulation and possible functions. We will use genomic stability to illustrate how FOXOs ensure homeostasis. Genomic stability is critical for maintaining genetic integrity, and therefore preventing disease. However, genomic mutations need to occur during lifetime to enable evolution, yet their accumulation is believed to be causative to aging. Therefore, the role of FOXO in genomic stability may underlie its role in lifespan and ageing. Finally, we will come up with questions on some of the unknowns in FOXO function, the answer(s) to which we believe will further our understanding of FOXO function and ultimately may help to understand lifespan and its consequences.
    Keywords:  Ageing; DNA damage; Transcription; signal transduction
    DOI:  https://doi.org/10.1111/febs.16221