bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2020‒09‒27
forty-eight papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. Cell Metab. 2020 Sep 16. pii: S1550-4131(20)30483-6. [Epub ahead of print]
      The nutritional source for catabolism in the tricarboxylic acid (TCA) cycle is a fundamental question in metabolic physiology. Limited by data and mathematical analysis, controversy exists. Using isotope-labeling data in vivo across several experimental conditions, we construct multiple models of central carbon metabolism and develop methods based on metabolic flux analysis (MFA) to solve for the preferences of glucose, lactate, and other nutrients used in the TCA cycle. We show that in nearly all circumstances, glucose contributes more than lactate as a substrate to the TCA cycle. This conclusion is verified in different animal strains from different studies and different administrations of 13C glucose, and is extended to multiple tissue types. Thus, this quantitative analysis of organismal metabolism defines the relative contributions of nutrient fluxes in physiology, provides a resource for analysis of in vivo isotope tracing data, and concludes that glucose is the major nutrient used in mammals.
    Keywords:  TCA cycle; glucose metabolism; isotope tracing; lactate; liver metabolism; metabolic flux analysis; mitochondrial metabolism; multi-tissue modeling; parameter sensitivity analysis; quantitative biology; systems biology
  2. EMBO Rep. 2020 Sep 23. e50635
      Nutrients are indispensable resources that provide the macromolecular building blocks and energy requirements for sustaining cell growth and survival. Cancer cells require several key nutrients to fulfill their changing metabolic needs as they progress through stages of development. Moreover, both cell-intrinsic and microenvironment-influenced factors determine nutrient dependencies throughout cancer progression-for which a comprehensive characterization remains incomplete. In addition to the widely studied role of genetic alterations driving cancer metabolism, nutrient use in cancer tissue may be affected by several factors including the following: (i) diet, the primary source of bodily nutrients which influences circulating metabolite levels; (ii) tissue of origin, which can influence the tumor's reliance on specific nutrients to support cell metabolism and growth; (iii) local microenvironment, which dictates the accessibility of nutrients to tumor cells; (iv) tumor heterogeneity, which promotes metabolic plasticity and adaptation to nutrient demands; and (v) functional demand, which intensifies metabolic reprogramming to fuel the phenotypic changes required for invasion, growth, or survival. Here, we discuss the influence of these factors on nutrient metabolism and dependence during various steps of tumor development and progression.
    Keywords:  cancer metabolism; diet; microenvironment; nutrients; tumor heterogeneity
  3. Open Biol. 2020 Sep;10(9): 200187
      Lysine lactoylation is a recently described protein post-translational modification (PTM). However, the biochemical pathways responsible for this acylation remain unclear. Two metabolite-dependent mechanisms have been proposed: enzymatic histone lysine lactoylation derived from lactoyl-coenzyme A (lactoyl-CoA, also termed lactyl-CoA), and non-enzymatic lysine lactoylation resulting from acyl-transfer via lactoyl-glutathione. While the former has precedent in the form of enzyme-catalysed lysine acylation, the lactoyl-CoA metabolite has not been previously quantified in mammalian systems. Here, we use liquid chromatography-high-resolution mass spectrometry (LC-HRMS) together with a synthetic standard to detect and validate the presence of lactoyl-CoA in cell and tissue samples. Conducting a retrospective analysis of data from previously analysed samples revealed the presence of lactoyl-CoA in diverse cell and tissue contexts. In addition, we describe a biosynthetic route to generate 13C315N1-isotopically labelled lactoyl-CoA, providing a co-eluting internal standard for analysis of this metabolite. We estimate lactoyl-CoA concentrations of 1.14 × 10-8 pmol per cell in cell culture and 0.0172 pmol mg-1 tissue wet weight in mouse heart. These levels are similar to crotonyl-CoA, but between 20 and 350 times lower than predominant acyl-CoAs such as acetyl-, propionyl- and succinyl-CoA. Overall our studies provide the first quantitative measurements of lactoyl-CoA in metazoans, and provide a methodological foundation for the interrogation of this novel metabolite in biology and disease.
    Keywords:  LC-HRMS; high resolution; lactoyl-CoA; lactyl-CoA; metabolism
  4. Nat Commun. 2020 Sep 25. 11(1): 4866
      Mitochondria house evolutionarily conserved pathways of carbon and nitrogen metabolism that drive cellular energy production. Mitochondrial bioenergetics is regulated by calcium uptake through the mitochondrial calcium uniporter (MCU), a multi-protein complex whose assembly in the inner mitochondrial membrane is facilitated by the scaffold factor MCUR1. Intriguingly, many fungi that lack MCU contain MCUR1 homologs, suggesting alternate functions. Herein, we characterize Saccharomyces cerevisiae homologs Put6 and Put7 of MCUR1 as regulators of mitochondrial proline metabolism. Put6 and Put7 are tethered to the inner mitochondrial membrane in a large hetero-oligomeric complex, whose abundance is regulated by proline. Loss of this complex perturbs mitochondrial proline homeostasis and cellular redox balance. Yeast cells lacking either Put6 or Put7 exhibit a pronounced defect in proline utilization, which can be corrected by the heterologous expression of human MCUR1. Our work uncovers an unexpected role of MCUR1 homologs in mitochondrial proline metabolism.
  5. Cell Calcium. 2020 Sep 11. pii: S0143-4160(20)30130-5. [Epub ahead of print]92 102288
      Calcium (Ca2+) is known to stimulate mitochondrial bioenergetics through the modulation of TCA cycle dehydrogenases and electron transport chain (ETC) complexes. This is hypothesized to be an essential pathway of energetic control to meet cellular ATP demand. While regulatory mechanisms of mitochondrial calcium uptake have been reported, it remains unknown if metabolite flux itself feedsback to regulate mitochondrial calcium (mCa2+) uptake. This hypothesis was recently tested by Nemani et al. (Sci. Signal. 2020) where the authors report that TCA cycle substrate flux regulates the mitochondrial calcium uniporter channel gatekeeper, mitochondrial calcium uptake 1 (MICU1), gene transcription in an early growth response protein 1 (EGR1) dependent fashion. They posit this is a regulatory feedback mechanism to control ionic homeostasis and mitochondrial bioenergetics with changing fuel availability. Here, we provide a historical overview of mitochondrial calcium exchange and comprehensive appraisal of these results in the context of recent literature and discuss possible regulatory pathways of mCa2+ uptake and mitochondrial bioenergetics.
    Keywords:  Calcium; Energetics; MCU; MICU1; MPC; Mitochondria; OXPHOS; TCA cycle; TCA substrates
  6. Cancer Metab. 2020 ;8 20
      Background: Mitochondrial serine catabolism to formate induces a metabolic switch to a hypermetabolic state with high rates of glycolysis, purine synthesis and pyrimidine synthesis. While formate is a purine precursor, it is not clear how formate induces pyrimidine synthesis.Methods: Here we combine phospho-proteome and metabolic profiling to determine how formate induces pyrimidine synthesis.
    Results: We discover that formate induces phosphorylation of carbamoyl phosphate synthetase (CAD), which is known to increase CAD enzymatic activity. Mechanistically, formate induces mechanistic target of rapamycin complex 1 (mTORC1) activity as quantified by phosphorylation of its targets S6, 4E-BP1, S6K1 and CAD. Treatment with the allosteric mTORC1 inhibitor rapamycin abrogates CAD phosphorylation and pyrimidine synthesis induced by formate. Furthermore, we show that the formate-dependent induction of mTOR signalling and CAD phosphorylation is dependent on an increase in purine synthesis.
    Conclusions: We conclude that formate activates mTORC1 and induces pyrimidine synthesis via the mTORC1-dependent phosphorylation of CAD.
  7. Redox Biol. 2020 Aug 07. pii: S2213-2317(20)30881-8. [Epub ahead of print]37 101676
      UCH-L1 is a deubiquitinating enzyme (DUB), highly abundant in neurons, with a sub-cellular localization dependent on its farnesylation state. Despite UCH-L1's association with familial Parkinson's Disease (PD), the effects on mitochondrial bioenergetics and quality control remain unexplored. Here we investigated the role of UCHL-1 in mitochondrial dynamics and bioenergetics. We demonstrate that knock-down (KD) of UCH-L1 in different cell lines reduces the levels of the mitochondrial fusion protein Mitofusin-2, but not Mitofusin-1, resulting in mitochondrial enlargement and disruption of the tubular network. This was associated with lower tethering between mitochondria and the endoplasmic reticulum, consequently altering mitochondrial calcium uptake. Respiratory function was also altered, as UCH-L1 KD cells displayed higher proton leak and maximum respiratory capacity. Conversely, overexpression of UCH-L1 increased Mfn2 levels, an effect dramatically enhanced by the mutation of the farnesylation site (C220S), which drives UCH-L1 binding to membranes. These data indicate that the soluble cytosolic form of UCH-L1 regulates Mitofusin-2 levels and mitochondrial function. These effects are biologically conserved, since knock-down of the corresponding UCH-L1 ortholog in D. melanogaster reduces levels of the mitofusin ortholog Marf and also increases mitochondrial respiratory capacity. We thus show that Mfn-2 levels are directly affected by UCH-L1, demonstrating that the mitochondrial roles of DUBs go beyond controlling mitophagy rates.
    Keywords:  Deubiquitinase; Mitochondria; Mitochondrial function; Parkinson's disease
  8. Cancer Res. 2020 Sep 21. pii: canres.1314.2020. [Epub ahead of print]
      Although lower-grade gliomas are driven by mutations in the isocitrate dehydrogenase 1 (IDH1) gene and are less aggressive than primary glioblastoma, they nonetheless generally recur. IDH1 mutant patients are increasingly being treated with temozolomide (TMZ), but early detection of response remains a challenge and there is a need for complementary imaging methods to assess response to therapy prior to tumor shrinkage. The goal of this study was to determine the value of magnetic resonance spectroscopy (MRS)-based metabolic changes for detection of response to TMZ in both genetically engineered and patient-derived mutant IDH1 models. Using 1H MRS in combination with chemometrics identified several metabolic alterations in TMZ-treated cells, including a significant increase in steady-state glutamate levels. This was confirmed in vivo, where the observed 1H MRS increase in glutamate/glutamine occurred prior to tumor shrinkage. Cells labeled with [1-13C]glucose and [3-13C]glutamine, the principal sources of cellular glutamate, showed that flux to glutamate both from glucose via the tricarboxylic acid cycle and from glutamine were increased following TMZ treatment. In line with these results, hyperpolarized [5-13C]glutamate produced from [2-13C]pyruvate and hyperpolarized [1-13C]glutamate produced from [1-13C]α-ketoglutarate were significantly higher in TMZ-treated cells compared to controls. Collectively, our findings identify 1H MRS-detectable elevation of glutamate and hyperpolarized 13C MRS-detectable glutamate production from either pyruvate or α-ketoglutarate as potential translatable metabolic biomarkers of response to TMZ treatment in mutant IDH1 glioma.
  9. Trends Mol Med. 2020 Sep 17. pii: S1471-4914(20)30190-8. [Epub ahead of print]
      Advances in surgical procedures, technology, and immune suppression have transformed organ transplantation. However, the metabolic changes that occur during organ retrieval, storage, and implantation have been relatively neglected since the developments many decades ago of cold storage organ preservation solutions. In this review we discuss how the metabolic changes that occur within the organ during transplantation, particularly those associated with mitochondria, may contribute to the outcome. We show how a better understanding of these processes can lead to changes in surgical practice and the development of new drug classes to improve the function and longevity of transplanted grafts, while increasing the pool of organs available for transplantation.
    Keywords:  ischemia–reperfusion injury; metabolism.; mitochondria; transplantation
  10. Nat Commun. 2020 09 24. 11(1): 4837
      ATP synthesis and thermogenesis are two critical outputs of mitochondrial respiration. How these outputs are regulated to balance the cellular requirement for energy and heat is largely unknown. Here we show that major facilitator superfamily domain containing 7C (MFSD7C) uncouples mitochondrial respiration to switch ATP synthesis to thermogenesis in response to heme. When heme levels are low, MSFD7C promotes ATP synthesis by interacting with components of the electron transport chain (ETC) complexes III, IV, and V, and destabilizing sarcoendoplasmic reticulum Ca2+-ATPase 2b (SERCA2b). Upon heme binding to the N-terminal domain, MFSD7C dissociates from ETC components and SERCA2b, resulting in SERCA2b stabilization and thermogenesis. The heme-regulated switch between ATP synthesis and thermogenesis enables cells to match outputs of mitochondrial respiration to their metabolic state and nutrient supply, and represents a cell intrinsic mechanism to regulate mitochondrial energy metabolism.
  11. Biochem Biophys Res Commun. 2020 Sep 21. pii: S0006-291X(20)31784-8. [Epub ahead of print]
      The interplay between nutrient scarcity and signal transduction circuits is an important aspect of tumorigenesis that regulates many aspects of cancer progression. Glutamine is a critical nutrient for cancer cells, as it contributes to biosynthetic reactions that sustain cancer proliferation and growth. In tumors, because nutrient utilization can often outpace supply, glutamine levels can become limiting and oncogene-mediated metabolic rewiring triggers signaling cascades that support nutrient stress survival. Recently, we identified that in pancreatic ductal adenocarcinoma (PDAC) cells, glutamine depletion can trigger p21-activated kinase (Pak) activation through EGFR signaling as a means to circumvent metabolic stress. Here, we elucidate that glutamine starvation, as well EGF stimulation, can enhance the presence of many different Pak phosphoforms, and that this activation only occurs in a subset of PDAC cells. Pak is a well-established effector of Rac1, and while Rac1 mutant variants can modulate the metabolic induction of Pak phosphorylation, Rac1 inhibition only partially attenuates Pak activation upon glutamine depletion. We decipher that in order to efficiently suppress metabolic activation of Pak, both EGFR and Rac1 signaling must be inhibited. These results provide a mechanistic understanding of how glutamine-regulated signal transduction can control Pak activation in PDAC cells.
    Keywords:  EGFR; Glutamine; Nutrient stress; Pak; Pancreatic; Rac
  12. Sci Rep. 2020 Sep 23. 10(1): 15513
      The insulin/IGF signalling pathway impacts lifespan across distant taxa, by controlling the activity of nodal transcription factors. In the nematode Caenorhabditis elegans, the transcription regulators DAF-16/FOXO and SKN-1/Nrf function to promote longevity under conditions of low insulin/IGF signalling and stress. The activity and subcellular localization of both DAF-16 and SKN-1 is further modulated by specific posttranslational modifications, such as phosphorylation and ubiquitination. Here, we show that ageing elicits a marked increase of SUMO levels in C. elegans. In turn, SUMO fine-tunes DAF-16 and SKN-1 activity in specific C. elegans somatic tissues, to enhance stress resistance. SUMOylation of DAF-16 modulates mitochondrial homeostasis by interfering with mitochondrial dynamics and mitophagy. Our findings reveal that SUMO is an important determinant of lifespan, and provide novel insight, relevant to the complexity of the signalling mechanisms that influence gene expression to govern organismal survival in metazoans.
  13. Biochem Biophys Res Commun. 2020 Sep 21. pii: S0006-291X(20)31770-8. [Epub ahead of print]
      Nutrient stress driven by glutamine deficiency activates EGFR signaling in a subset of KRAS-mutant pancreatic ductal adenocarcinoma (PDAC) cells. EGFR signaling in the context of glutamine starvation is thought to be instigated by the transcriptional upregulation of EGFR ligands and functions as an adaptation mechanism to allow PDAC cells to maintain metabolic fitness. Having a clear view of the intricate signaling cascades potentiated by the metabolic induction of EGFR is important in understanding how these effector pathways influence cancer progression. In this study, we examined the complex signaling that occurs in PDAC cells when EGFR is activated by glutamine deprivation. We elucidate that the metabolic activation of EGFR is principally mediated by HB-EGF, and that other members of the ErbB receptor tyrosine kinase family are not activated by glutamine starvation. Additionally, we determine that glutamine depletion-driven EGFR signaling is associated with a specific receptor phosphorylation known to participate in a feedback loop, a process that is dependent on Erk. Lastly, we determine that K-Ras is required for glutamine depletion-induced Erk activation, as well as EGFR feedback phosphorylation, but is dispensable for Akt activation. These data provide important insights into the regulation of EGFR signaling in the context of metabolic stresses.
    Keywords:  Akt; EGFR; Erk; Glutamine; Metabolism; Nutrient stress; Ras
  14. Front Oncol. 2020 ;10 1692
      Mitochondria as the cellular energy powerhouses provide a common site for multiple metabolic reactions in order to cover energy and biomolecule demands, thus integrating the diverse metabolic pathways to endow cells with metabolic adaptation. Mitochondrial plasticity is normally regulated by mitochondrial dynamics, mitochondrial metabolism and mitochondrial biogenesis. Given that tumor cells and T cells share the metabolic similarities of survival, proliferation, expansion as well as effector function, manipulation of mitochondrial plasticity would change the metabolic competition between "foe" and "friend" during tumor malignant progression. On the one hand, for "foe" tumor cells, mitochondrial plasticity provides the enhancement of tumor metastasis and the development of resistance to' diverse antitumor drugs. On the other hand, for "friend" T cells, mitochondrial plasticity promotes the generation of long-term memory T (TM) cells and alleviates the exhaustion of tumor-infiltrating lymphocytes (TILs). Therefore, downregulation of mitochondrial plasticity of tumor cells through engineering tumor-targeting nanoparticles may effectively potentiate metabolic vulnerability and re-sensitize tumor to relevant therapeutic treatment. On the contrary, upregulation of mitochondrial plasticity of T cells through optimizing adoptive cellular immunotherapy (ACI) or chimeric antigen receptor (CAR)-T cell therapy would provide T cells with the robust metabolic fitness and the persistent immune function, thus blocking tumor metastasis and reoccurrence.
    Keywords:  T cells exhaustion; memory T cells; mitochondrial plasticity; therapeutic resistance; tumor metastasis
  15. Trends Cell Biol. 2020 Sep 22. pii: S0962-8924(20)30169-0. [Epub ahead of print]
      Mitochondria are dynamic organelles that have essential metabolic and regulatory functions. Earlier studies using electron microscopy (EM) revealed an immense diversity in the architecture of cristae - infoldings of the mitochondrial inner membrane (IM) - in different cells, tissues, bioenergetic and metabolic conditions, and during apoptosis. However, cristae were considered to be largely static entities. Recently, advanced super-resolution techniques have revealed that cristae are independent bioenergetic units that are highly dynamic and remodel on a timescale of seconds. These advances, coupled with mechanistic and structural studies on key molecular players, such as the MICOS (mitochondrial contact site and cristae organizing system) complex and the dynamin-like GTPase OPA1, have changed our view on mitochondria in a fundamental way. We summarize these recent findings and discuss their functional implications.
    Keywords:  MICOS; OPA1; cristae dynamics; remodeling
  16. PLoS One. 2020 ;15(9): e0239625
      During alcohol consumption, the esophageal mucosa is directly exposed to high concentrations of ethanol (EtOH). We therefore investigated the response of normal human esophageal epithelial cell lines EPC1, EPC2 and EPC3 to acute EtOH exposure. While these cells were able to tolerate 2% EtOH for 8 h in both three-dimensional organoids and monolayer culture conditions, RNA sequencing suggested that EtOH induced mitochondrial dysfunction. With EtOH treatment, EPC1 and EPC2 cells also demonstrated decreased mitochondrial ATPB protein expression by immunofluorescence and swollen mitochondria lacking intact cristae by transmission electron microscopy. Mitochondrial membrane potential (ΔΨm) was decreased in a subset of EPC1 and EPC2 cells stained with ΔΨm-sensitive dye MitoTracker Deep Red. In EPC2, EtOH decreased ATP level while impairing mitochondrial respiration and electron transportation chain functions, as determined by ATP fluorometric assay, respirometry, and liquid chromatography-mass spectrometry. Additionally, EPC2 cells demonstrated enhanced oxidative stress by flow cytometry for mitochondrial superoxide (MitoSOX), which was antagonized by the mitochondria-specific antioxidant MitoCP. Concurrently, EPC1 and EPC2 cells underwent autophagy following EtOH exposure, as evidenced by flow cytometry for Cyto-ID, which detects autophagic vesicles, and immunoblots demonstrating induction of the lipidated and cleaved form of LC3B and downregulation of SQSTM1/p62. In EPC1 and EPC2, pharmacological inhibition of autophagy flux by chloroquine increased mitochondrial oxidative stress while decreasing cell viability. In EPC2, autophagy induction was coupled with phosphorylation of AMP activated protein kinase (AMPK), a cellular energy sensor responding to low ATP levels, and dephosphorylation of downstream substrates of mechanistic Target of Rapamycin Complex (mTORC)-1 signaling. Pharmacological AMPK activation by AICAR decreased EtOH-induced reduction of ΔΨm and ATP in EPC2. Taken together, acute EtOH exposure leads to mitochondrial dysfunction and oxidative stress in esophageal keratinocytes, where the AMPK-mTORC1 axis may serve as a regulatory mechanism to activate autophagy to provide cytoprotection against EtOH-induced cell injury.
  17. Diabetologia. 2020 Sep 22.
      AIMS/HYPOTHESIS: In islets from individuals with type 2 diabetes and in islets exposed to chronic elevated glucose, mitochondrial energy metabolism is impaired. Here, we studied early metabolic changes and mitochondrial adaptations in human beta cells during chronic glucose stress.METHODS: Respiration and cytosolic ATP changes were measured in human islet cell clusters after culture for 4 days in 11.1 mmol/l glucose. Metabolomics was applied to analyse intracellular metabolite changes as a result of glucose stress conditions. Alterations in beta cell function were followed using insulin secretion assays or cytosolic calcium signalling after expression of the calcium probe YC3.6 specifically in beta cells of islet clusters.
    RESULTS: At early stages of glucose stress, mitochondrial energy metabolism was augmented in contrast to the previously described mitochondrial dysfunction in beta cells from islets of diabetic donors. Following chronic glucose stress, mitochondrial respiration increased (by 52.4%, p < 0.001) and, as a consequence, the cytosolic ATP/ADP ratio in resting human pancreatic islet cells was elevated (by 27.8%, p < 0.05). Because of mitochondrial overactivation in the resting state, nutrient-induced beta cell activation was reduced. In addition, chronic glucose stress caused metabolic adaptations that resulted in the accumulation of intermediates of the glycolytic pathway, the pentose phosphate pathway and the TCA cycle; the most strongly augmented metabolite was glycerol 3-phosphate. The changes in metabolites observed are likely to be due to the inability of mitochondria to cope with continuous nutrient oversupply. To protect beta cells from chronic glucose stress, we inhibited mitochondrial pyruvate transport. Metabolite concentrations were partially normalised and the mitochondrial respiratory response to nutrients was markedly improved. Furthermore, stimulus-secretion coupling as assessed by cytosolic calcium signalling, was restored.
    CONCLUSION/INTERPRETATION: We propose that metabolic changes and associated mitochondrial overactivation are early adaptations to glucose stress, and may reflect what happens as a result of poor blood glucose control. Inhibition of mitochondrial pyruvate transport reduces mitochondrial nutrient overload and allows beta cells to recover from chronic glucose stress. Graphical abstract.
    Keywords:  Beta cells; Calcium; Human islets; Metabolomics; Mitochondria
  18. Nature. 2020 Sep 23.
      Cell death in human diseases is often a consequence of disrupted cellular homeostasis. If cell death is prevented without restoring cellular homeostasis, it may lead to a persistent dysfunctional and pathological state. Although mechanisms of cell death have been thoroughly investigated1-3, it remains unclear how homeostasis can be restored after inhibition of cell death. Here we identify TRADD4-6, an adaptor protein, as a direct regulator of both cellular homeostasis and apoptosis. TRADD modulates cellular homeostasis by inhibiting K63-linked ubiquitination of beclin 1 mediated by TRAF2, cIAP1 and cIAP2, thereby reducing autophagy. TRADD deficiency inhibits RIPK1-dependent extrinsic apoptosis and proteasomal stress-induced intrinsic apoptosis. We also show that the small molecules ICCB-19 and Apt-1 bind to a pocket on the N-terminal TRAF2-binding domain of TRADD (TRADD-N), which interacts with the C-terminal domain (TRADD-C) and TRAF2 to modulate the ubiquitination of RIPK1 and beclin 1. Inhibition of TRADD by ICCB-19 or Apt-1 blocks apoptosis and restores cellular homeostasis by activating autophagy in cells with accumulated mutant tau, α-synuclein, or huntingtin. Treatment with Apt-1 restored proteostasis and inhibited cell death in a mouse model of proteinopathy induced by mutant tau(P301S). We conclude that pharmacological targeting of TRADD may represent a promising strategy for inhibiting cell death and restoring homeostasis to treat human diseases.
  19. Nat Metab. 2020 Sep 21.
      Following activation, conventional T (Tconv) cells undergo an mTOR-driven glycolytic switch. Regulatory T (Treg) cells reportedly repress the mTOR pathway and avoid glycolysis. However, here we demonstrate that human thymus-derived Treg (tTreg) cells can become glycolytic in response to tumour necrosis factor receptor 2 (TNFR2) costimulation. This costimulus increases proliferation and induces a glycolytic switch in CD3-activated tTreg cells, but not in Tconv cells. Glycolysis in CD3-TNFR2-activated tTreg cells is driven by PI3-kinase-mTOR signalling and supports tTreg cell identity and suppressive function. In contrast to glycolytic Tconv cells, glycolytic tTreg cells do not show net lactate secretion and shuttle glucose-derived carbon into the tricarboxylic acid cycle. Ex vivo characterization of blood-derived TNFR2hiCD4+CD25hiCD127lo effector T cells, which were FOXP3+IKZF2+, revealed an increase in glucose consumption and intracellular lactate levels, thus identifying them as glycolytic tTreg cells. Our study links TNFR2 costimulation in human tTreg cells to metabolic remodelling, providing an additional avenue for drug targeting.
  20. Redox Biol. 2020 Aug 27. pii: S2213-2317(20)30901-0. [Epub ahead of print] 101696
      Reactive oxygen species (ROS) are critical for the progression of cardiovascular diseases, inflammations and tumors. However, the mechanisms of how ROS sense metabolic stress, regulate metabolic pathways and initiate proliferation, inflammation and cell death responses remain poorly characterized. In this analytic review, we concluded that: 1) Based on different features and functions, eleven types of ROS can be classified into seven functional groups: metabolic stress-sensing, chemical connecting, organelle communication, stress branch-out, inflammasome-activating, dual functions and triple functions ROS. 2) Among the ROS generation systems, mitochondria consume the most amount of oxygen; and nine types of ROS are generated; thus, mitochondrial ROS systems serve as the central hub for connecting ROS with inflammasome activation, trained immunity and immunometabolic pathways. 3) Increased nuclear ROS production significantly promotes cell death in comparison to that in other organelles. Nuclear ROS systems serve as a convergent hub and decision-makers to connect unbearable and alarming metabolic stresses to inflammation and cell death. 4) Balanced ROS levels indicate physiological homeostasis of various metabolic processes in subcellular organelles and cytosol, while imbalanced ROS levels present alarms for pathological organelle stresses in metabolic processes. Based on these analyses, we propose a working model that ROS systems are a new integrated network for sensing homeostasis and alarming stress in metabolic processes in various subcellular organelles. Our model provides novel insights on the roles of the ROS systems in bridging metabolic stress to inflammation, cell death and tumorigenesis; and provide novel therapeutic targets for treating those diseases. (Word count: 246).
    Keywords:  A sensing network for metabolic stress; Inflammation; Nuclear signaling; Reactive oxygen species (ROS); Trained immunity
  21. EMBO Rep. 2020 Sep 25. e50202
      Mitochondrial quality is controlled by the selective removal of damaged mitochondria through mitophagy. Mitophagy impairment is associated with aging and many pathological conditions. An iron loss induced by iron chelator triggers mitophagy by a yet unknown mechanism. This type of mitophagy may have therapeutic potential, since iron chelators are clinically used. Here, we aimed to clarify the mechanisms by which iron loss induces mitophagy. Deferiprone, an iron chelator, treatment resulted in the increased expression of mitochondrial ferritin (FTMT) and the localization of FTMT precursor on the mitochondrial outer membrane. Specific protein 1 and its regulator hypoxia-inducible factor 1α were necessary for deferiprone-induced increase in FTMT. FTMT specifically interacted with nuclear receptor coactivator 4, an autophagic cargo receptor. Deferiprone-induced mitophagy occurred selectively for depolarized mitochondria. Additionally, deferiprone suppressed the development of hepatocellular carcinoma (HCC) in mice by inducing mitophagy. Silencing FTMT abrogated deferiprone-induced mitophagy and suppression of HCC. These results demonstrate the mechanisms by which iron loss induces mitophagy and provide a rationale for targeting mitophagic activation as a therapeutic strategy.
    Keywords:  hepatocellular carcinoma; iron chelator; mitochondria; mitochondrial ferritin; mitophagy
  22. Cancer Sci. 2020 Sep 24.
      Protein Phosphatase 6 (PP6) is an essential serine/threonine protein phosphatase that acts as an important tumor suppressor. However, increased protein levels of PP6 have been observed in some cancer types, and correlate with poor prognosis in glioblastoma. This raises a question about how PP6 protein levels are regulated in normal and transformed cells. In this study, we show that PP6 protein levels increase in response to pharmacologic and genetic inhibition of autophagy. PP6 associates with autophagic adaptor protein p62/SQSTM1 and is degraded in a p62-dependent manner. Accordingly, protein levels of PP6 and p62 fluctuate in concert under different physiological and pathophysiological conditions. Our data reveal that PP6 is regulated by p62-dependent autophagy and suggest that accumulation of PP6 protein in tumor tissues is caused at least partially by deficiency in autophagy.
    Keywords:  autophagy; cell biology; p62/SQSTM1; protein phosphatase 2A; protein phosphatase 6
  23. Front Oncol. 2020 ;10 1561
      To adjust cell growth and proliferation to changing environmental conditions or developmental requirements, cells have evolved a remarkable network of signaling cascades that integrates cues from cellular metabolism, growth factor availability and a large variety of stresses. In these networks, cellular information flow is mostly mediated by posttranslational modifications, most notably phosphorylation, or signaling molecules such as GTPases. Yet, a large body of evidence also implicates cytosolic pH (pHc) as a highly conserved cellular signal driving cell growth and proliferation, suggesting that pH-dependent protonation of specific proteins also regulates cellular signaling. In mammalian cells, pHc is regulated by growth factor derived signals and responds to metabolic cues in response to glucose stimulation. Importantly, high pHc has also been identified as a hall mark of cancer, but mechanisms of pH regulation in cancer are only poorly understood. Here, we discuss potential mechanisms of pH regulation with emphasis on metabolic signals regulating pHc by Na+/H+-exchangers. We hypothesize that elevated NHE activity and pHc in cancer are a direct consequence of the metabolic adaptations in tumor cells including enhanced aerobic glycolysis, generally referred to as the Warburg effect. This hypothesis not only provides an explanation for the growth advantage conferred by a switch to aerobic glycolysis beyond providing precursors for accumulation of biomass, but also suggests that treatments targeting pH regulation as a potential anti-cancer therapy may effectively target the result of altered tumor cell metabolism.
    Keywords:  Na+/H+-exchanger; aerobic glycolysis; cytosolic pH; growth and proliferation; metabolism
  24. Curr Opin Cell Biol. 2020 Sep 19. pii: S0955-0674(20)30111-3. [Epub ahead of print]68 28-36
      Mitochondria form networks that continually remodel and adapt to carry out their cellular function. The mitochondrial network is remodeled through changes in mitochondrial morphology, number, and distribution within the cell. Mitochondrial dynamics depend directly on fission, fusion, shape transition, and transport or tethering along the cytoskeleton. Over the past several years, many of the mechanisms underlying these processes have been uncovered. It has become clear that each process is precisely and contextually regulated within the cell. Here, we discuss the mechanisms regulating each aspect of mitochondrial dynamics, which together shape the network as a whole.
    Keywords:  Cytoskeleton; Fission; Fusion; Mitochondria; Morphology; Transport
  25. Elife. 2020 Sep 22. pii: e56686. [Epub ahead of print]9
      Cooperation and cheating are widespread evolutionary strategies. While cheating confers an advantage to individual entities within a group, competition between groups favors cooperation. Selfish or cheater mitochondrial DNA (mtDNA) proliferates within hosts while being selected against at the level of host fitness. How does environment shape cheater dynamics across different selection levels? Focusing on food availability, we address this question using heteroplasmic Caenorhabditis elegans. We find that the proliferation of selfish mtDNA within hosts depends on nutrient status stimulating mtDNA biogenesis in the developing germline. Interestingly, mtDNA biogenesis is not sufficient for this proliferation, which also requires the stress-response transcription factor FoxO/DAF-16. At the level of host fitness, FoxO/DAF-16 also prevents food scarcity from accelerating the selection against selfish mtDNA. This suggests that the ability to cope with nutrient stress can promote host tolerance of cheaters. Our study delineates environmental effects on selfish mtDNA dynamics at different levels of selection.
    Keywords:  C. elegans; cheating; evolutionary biology; genetics; genomics; heteroplasmy; metabolism; mitochondria; multilevel selection; nutrient availability
  26. Autophagy. 2020 Sep 20. 1-2
      The kidney, similar to many other organs, has to face shear stress induced by biological fluids. How epithelial kidney cells respond to shear stress is poorly understood. Recently we showed in vitro and in vivo that proximal tubule epithelial cells use lipophagy to fuel mitochondria with fatty acids. Lipophagy is stimulated by a primary cilium-dependent signaling that converges at AMP kinase. AMP kinase is a central signaling hub to trigger lipophagy and also to stimulate mitochondrial biogenesis. These two pathways contribute to generate ATP needed to support energy-consuming cellular processes such as glucose reabsorption, gluconeogenesis. These findings demonstrate the role of the primary cilium and selective macroautophagy/autophagy to integrate shear stress and to sustain the execution of a specific cellular program.
    Keywords:  macroautophagy; metabolism; nephrology; oxidative phosphorylation
  27. Int J Mol Sci. 2020 Sep 22. pii: E6941. [Epub ahead of print]21(18):
      Heme oxygenase-1 is induced by many cellular stressors and catalyzes the breakdown of heme to generate carbon monoxide and bilirubin, which confer cytoprotection. The role of HO-1 likely extends beyond the simple production of antioxidants, for example HO-1 activity has also been implicated in metabolism, but this function remains unclear. Here we used an HO-1 knockout lung cell line to further define the contribution of HO-1 to cellular metabolism. We found that knockout cells exhibit reduced growth and mitochondrial respiration, measured by oxygen consumption rate. Specifically, we found that HO-1 contributed to electron transport chain activity and utilization of certain mitochondrial fuels. Loss of HO-1 had no effect on intracellular non-heme iron concentration or on proteins whose levels and activities depend on available iron. We show that HO-1 supports essential functions of mitochondria, which highlights the protective effects of HO-1 in diverse pathologies and tissue types. Our results suggest that regulation of heme may be an equally significant role of HO-1.
    Keywords:  heme; iron; metabolism; succinate dehydrogenase
  28. Hum Mol Genet. 2020 Sep 25. pii: ddaa214. [Epub ahead of print]
      Abnormalities of one carbon, glutathione and sulfide metabolisms have recently emerged as novel pathomechanisms in diseases with mitochondrial dysfunction. However, the mechanisms underlying these abnormalities are not clear. Also, we recently showed that sulfide oxidation is impaired in Coenzyme Q10 (CoQ10) deficiency. This finding leads us to hypothesize that the therapeutic effects of CoQ10, frequently administered to patients with primary or secondary mitochondrial dysfunction, might be due to its function as cofactor for sulfide:quinone oxidoreductase (SQOR), the first enzyme in the sulfide oxidation pathway. Here, using biased and unbiased approaches, we show that supraphysiological levels of CoQ10 induces an increase in the expression of SQOR in skin fibroblasts from control subjects and patients with mutations in Complex I subunits genes or CoQ biosynthetic genes. This increase of SQOR induces the downregulation of the cystathionine β-synthase and cystathionine γ-lyase, two enzymes of the transsulfuration pathway, the subsequent downregulation of serine biosynthesis and the adaptation of other sulfide linked pathways, such as folate cycle, nucleotides metabolism and glutathione system. These metabolic changes are independent of the presence of sulfur aminoacids, are confirmed in mouse models, and are recapitulated by overexpression of SQOR, further proving that the metabolic effects of CoQ10 supplementation are mediated by the overexpression of SQOR. Our results contribute to a better understanding of how sulfide metabolism is integrated in one carbon metabolism and may explain some of the benefits of CoQ10 supplementation observed in mitochondrial diseases.
  29. Cardiovasc Drugs Ther. 2020 Sep 26.
      PURPOSE: HFpEF (heart failure with preserved ejection fraction) is a major consequence of diabetic cardiomyopathy with no effective treatments. Here, we have characterized Akita mice as a preclinical model of HFpEF and used it to confirm the therapeutic efficacy of the mitochondria-targeted dicarbonyl scavenger, MitoGamide.METHODS AND RESULTS: A longitudinal echocardiographic analysis confirmed that Akita mice develop diastolic dysfunction with reduced E peak velocity, E/A ratio and extended isovolumetric relaxation time (IVRT), while the systolic function remains comparable with wild-type mice. The myocardium of Akita mice had a decreased ATP/ADP ratio, elevated mitochondrial oxidative stress and increased organelle density, compared with that of wild-type mice. MitoGamide, a mitochondria-targeted 1,2-dicarbonyl scavenger, exhibited good stability in vivo, uptake into cells and mitochondria and reactivity with dicarbonyls. Treatment of Akita mice with MitoGamide for 12 weeks significantly improved the E/A ratio compared with the vehicle-treated group.
    CONCLUSION: Our work confirms that the Akita mouse model of diabetes replicates key clinical features of diabetic HFpEF, including cardiac and mitochondrial dysfunction. Furthermore, in this independent study, MitoGamide treatment improved diastolic function in Akita mice.
    Keywords:  Advanced glycation endproducts (AGE); Akita mice; Diabetes; Heart failure with preserved ejection fraction (HFpEF); Mitochondria
  30. Crit Rev Biochem Mol Biol. 2020 Sep 24. 1-16
      Mammalian mitochondria contain multiple copies of a circular, double-stranded DNA genome (mtDNA) that codes for subunits of the oxidative phosphorylation machinery. Mutations in mtDNA cause a number of rare, human disorders and are also associated with more common conditions, such as neurodegeneration and biological aging. In this review, we discuss our current understanding of mtDNA replication in mammalian cells and how this process is regulated. We also discuss how deletions can be formed during mtDNA replication.
    Keywords:  DNA helicase; DNA polymerase; DNA replication; Mitochondrion; deletion
  31. Trends Cell Biol. 2020 Sep 23. pii: S0962-8924(20)30170-7. [Epub ahead of print]
      Cellular senescence is a state of permanent cell cycle arrest accompanied by unique secretory actions, which influences tissue formation, tumor suppression and aging in vivo. Recent evidences suggest that metabolic and epigenomic reprogram cooperatively creates phenotypic differences of senescent cells, which may provide new clues to control aging processes.
    Keywords:  cellular senescence; epigenome; gene regulation; metabolism; senescence-associated secretory phenotype
  32. Ann Transl Med. 2020 Aug;8(16): 1028
      Tumor associated macrophages (TAMs) are important components of the tumor microenvironment (TME). They are characterized by a remarkable functional plasticity, thereby mostly promoting cancer progression. Changes in immune cell metabolism are paramount for this functional adaptation. Here, we review the functional consequences of the metabolic programming of TAMs and the influence of local and systemic targeted therapies on the metabolic characteristics of the TME that shape the functional phenotype of the TAMs. Understanding these metabolic changes within the context of the cross-talk between the different components of the TME including the TAMs and the tumor cells is an essential step that can pave the way towards identifications of ways to improve responses to different treatments, to overcome resistance to treatments, tumor progression and reduce treatment-specific toxicity.
    Keywords:  Immunotherapy; metabolism; thyroid cancer; tumor associated macrophages; tumor microenvironment (TME)
  33. Cell Chem Biol. 2020 Sep 16. pii: S2451-9456(20)30342-1. [Epub ahead of print]
      MYC is a major oncogenic transcriptional driver of most human cancers that has remained intractable to direct targeting because much of MYC is intrinsically disordered. Here, we have performed a cysteine-reactive covalent ligand screen to identify compounds that could disrupt the binding of MYC to its DNA consensus sequence in vitro and also impair MYC transcriptional activity in situ in cells. We have identified a covalent ligand, EN4, that targets cysteine 171 of MYC within a predicted intrinsically disordered region of the protein. We show that EN4 directly targets MYC in cells, reduces MYC and MAX thermal stability, inhibits MYC transcriptional activity, downregulates multiple MYC transcriptional targets, and impairs tumorigenesis. We also show initial structure-activity relationships of EN4 and identify compounds that show improved potency. Overall, we identify a unique ligandable site within an intrinsically disordered region of MYC that leads to inhibition of MYC transcriptional activity.
    Keywords:  MYC; activity-based protein profiling; chemoproteomics; covalent ligand; cysteine; intrinsically disordered; transcription factor; undruggable
  34. Oncogene. 2020 Sep 25.
      Metabolic reprogramming fulfils increased nutrient demands and regulates numerous oncogenic processes in tumors, leading to tumor malignancy. Branched-chain amino acids (BCAAs, i.e., valine, leucine, and isoleucine) function as nitrogen donors to generate macromolecules such as nucleotides and are indispensable for human cancer cell growth. The cell-autonomous and non-autonomous roles of altered BCAA metabolism have been implicated in cancer progression and the key proteins in the BCAA metabolic pathway serve as possible prognostic and diagnostic biomarkers in human cancers. Here we summarize how BCAA metabolic reprogramming is regulated in cancer cells and how it influences cancer progression.
  35. Cancer Cell. 2020 Sep 14. pii: S1535-6108(20)30427-X. [Epub ahead of print]
      PIK3CA, encoding the PI3Kα isoform, is the most frequently mutated oncogene in estrogen receptor (ER)-positive breast cancer. Isoform-selective PI3K inhibitors are used clinically but intrinsic and acquired resistance limits their utility. Improved selection of patients that will benefit from these drugs requires predictive biomarkers. We show here that persistent FOXM1 expression following drug treatment is a biomarker of resistance to PI3Kα inhibition in ER+ breast cancer. FOXM1 drives expression of lactate dehydrogenase (LDH) but not hexokinase 2 (HK-II). The downstream metabolic changes can therefore be detected using MRI of LDH-catalyzed hyperpolarized 13C label exchange between pyruvate and lactate but not by positron emission tomography measurements of HK-II-mediated trapping of the glucose analog 2-deoxy-2-[18F]fluorodeoxyglucose. Rapid assessment of treatment response in breast cancer using this imaging method could help identify patients that benefit from PI3Kα inhibition and design drug combinations to counteract the emergence of resistance.
    Keywords:  FDG-PET; FOXM1; MRI; PI3K alpha inhibition; biomarker; breast cancer; hexokinase 2; hyperpolarized [1-(13)C]pyruvate; lactate dehydrogenase; treatment response
  36. Ann R Coll Surg Engl. 2020 Sep 24. e1-e3
      Succinate dehydrogenase (SDH)-deficient renal cell carcinoma (RCC) accounts for 0.05-2% of all RCCs. The majority of patients have germline mutations, most frequently in the SDHB gene. People with these mutations are predisposed to developing paragangliomas, phaeochromocytomas and gastrointestinal stromal tumours. Patients should be referred to genetic services for further workup and close surveillance imaging due to the risk of development of further tumours. We present a woman with SDH-deficient RCC and review the literature associated with this uncommon entity.
    Keywords:  Germline mutations; RCC; Renal cell cancer; SDH
  37. Nat Commun. 2020 09 24. 11(1): 4830
      Non-invasively probing metabolites within single live cells is highly desired but challenging. Here we utilize Raman spectro-microscopy for spatial mapping of metabolites within single cells, with the specific goal of identifying druggable metabolic susceptibilities from a series of patient-derived melanoma cell lines. Each cell line represents a different characteristic level of cancer cell de-differentiation. First, with Raman spectroscopy, followed by stimulated Raman scattering (SRS) microscopy and transcriptomics analysis, we identify the fatty acid synthesis pathway as a druggable susceptibility for differentiated melanocytic cells. We then utilize hyperspectral-SRS imaging of intracellular lipid droplets to identify a previously unknown susceptibility of lipid mono-unsaturation within de-differentiated mesenchymal cells with innate resistance to BRAF inhibition. Drugging this target leads to cellular apoptosis accompanied by the formation of phase-separated intracellular membrane domains. The integration of subcellular Raman spectro-microscopy with lipidomics and transcriptomics suggests possible lipid regulatory mechanisms underlying this pharmacological treatment. Our method should provide a general approach in spatially-resolved single cell metabolomics studies.
  38. Nat Metab. 2020 Sep 21.
      Current immunotherapies yield remarkable clinical outcomes by boosting the power of host immunity in cancer cell elimination and viral clearance. However, after prolonged antigen exposure, CD8+ T cells differentiate into a special differentiation state known as T-cell exhaustion, which poses one of the major hurdles to antiviral and antitumor immunity during chronic viral infection and tumour development. Growing evidence indicates that exhausted T cells undergo metabolic insufficiency with altered signalling cascades and epigenetic landscapes, which dampen effector immunity and cause poor responsiveness to immune-checkpoint-blockade therapies. How metabolic stress affects T-cell exhaustion remains unclear; therefore, in this Review, we summarize current knowledge of how T-cell exhaustion occurs, and discuss how metabolic insufficiency and prolonged stress responses may affect signalling cascades and epigenetic reprogramming, thus locking T cells into an exhausted state via specialized differentiation programming.
  39. Biochim Biophys Acta Rev Cancer. 2020 Sep 19. pii: S0304-419X(20)30146-3. [Epub ahead of print] 188427
      Macrophages are innate phagocytic leukocytes that are highly present in solid tumors, where they are referred to as tumor-associated macrophages (TAMs). In solid tumors, the microenvironment is often immunosuppressive and hypoxic regions are prevalent. These hypoxic conditions impose tumor cells to reprogram their metabolism, shifting from oxidative phosphorylation to anaerobic glycolysis. This so-called glycolytic switch enables hypoxic tumor cells to survive, proliferate, and eventually to outcompete untransformed cells. The hypoxia-induced change in tumor cell metabolism leads to the production of oncometabolites, among which are the glycolytic end-metabolite lactate and the tricarboxylic acid cycle intermediate succinate. TAMs can react to these oncometabolites, resulting in an altered maturation and the adoption of pro-angiogenic features. These angiogenesis-promoting TAMs have been reported to cooperate with tumor cells in the formation of new vessels, and even have been considered an important cause of resistance against anti-angiogenic therapies. For a long time, the mechanisms by which lactate and succinate activated pro-angiogenic TAMs were not understood. Researchers now start to unravel and understand some of the underlying mechanisms. Here, the importance of microenvironmental cues in inducing different macrophage activation states is discussed, as well as the role of hypoxia in the recruitment and activation of pro-angiogenic macrophages. In addition, the latest findings on the oncometabolites lactate and succinate in the activation of angiogenesis supporting macrophages are reviewed. Finally, various oncometabolite-targeting therapeutic strategies are proposed that could improve the response to anti-angiogenic therapies. SIGNIFICANCE STATEMENT: Tumor-associated macrophages (TAMs) are known promotors of tumor neovascularization, and significantly contribute to the emergence of resistance to anti-angiogenic therapies. Recent evidence suggests that the angiogenesis promoting phenotype of TAMs can be activated by hypoxic tumor cell-derived oncometabolites, including lactate and succinate. Here, the latest findings into the lactate- and succinate-mediated mechanistic activation of pro-angiogenic TAMs are reviewed, and therapeutic strategies that interfere with this mechanism and may delay or even prevent acquired resistance to anti-angiogenic agents are discussed.
    Keywords:  Angiogenesis; Cancer; Lactate; Macrophages; Oncometabolite; Succinate; TAM; Tumor; Tumor-associated macrophage
  40. Curr Opin Cell Biol. 2020 Sep 22. pii: S0955-0674(20)30109-5. [Epub ahead of print]68 37-44
      The Arp2/3 complex orchestrates the formation of branched actin networks at the interface between the cytoplasm and membranes. Although it is widely appreciated that these networks are useful for scaffolding, creating pushing forces and delineating zones at the membrane interface, it has only recently come to light that branched actin networks are mechanosensitive, giving them special properties. Here, we discuss recent advances in our understanding of how Arp2/3-generated actin networks respond to load forces and thus allow cells to create pushing forces in responsive and tuneable ways to effect cellular processes such as migration, invasion, phagocytosis, adhesion and even nuclear and DNA damage repair.
    Keywords:  Actin; Arp2/3 complex; Cell migration; Endocytosis; Mechanosensing; Metabolism
  41. Ann Transl Med. 2020 Aug;8(15): 937
      Background: Proline levels are significantly increased in tumor specimens and urine samples from gastric cancer (GC) patients, and we previously showed that intracellular proline levels significantly differ between human GC cell lines and normal gastric epithelial cells. Pyrroline-5-carboxylate reductase 1 (PYCR1) is the key enzyme in intracellular proline synthesis, but its role in GC remains largely unknown.Methods: Bioinformatic analysis and immunohistochemical (IHC) staining with a tissue microarray were conducted to assess the association between PYCR1 expression and clinical parameters. PYCR1 downregulation and overexpression were then established in two GC cell lines (AGS and MKN28 cells) to determine whether PYCR1 promotes malignant behavior in GC. Gene set enrichment analysis (GSEA) was further performed to investigate the pathway regulating PYCR1 in GC.
    Results: PYCR1 expression was up-regulated in different GC cohorts. High PYCR1 protein expression was correlated with advanced tumor stage, aggressive histological type and high Ki-67 index. High PYCR1 expression in GC tissues was an indicator of poor outcome in GC patients. In vitro, PYCR1 knockdown markedly attenuated GC cells growth and promoted apoptosis, while overexpression produced the opposite effects. GSEA analysis indicated PI3K/Akt axis was strongly correlated with PYCR1 expression and that PIK3CB and AKT1 mRNA expression was positively associated with PYCR1 in GC tissues. PI3K inhibition further significantly reduced PYCR1 mRNA and protein expression. Moreover, as PYCR1 is a mitochondrial endomembrane protein, nutrient stress induced by glucose deprivation also regulated PYCR1 expression.
    Conclusions: PYCR1 is highly expressed in GC and acts as a mitochondrial oncogene to induce cancer progression by enhancing tumor proliferation and responding to metabolic stress. PYCR1 is a novel prognostic marker and a potential therapeutic target in GC.
    Keywords:  Gastric cancer (GC); PI3K/Akt; Pyrroline-5-carboxylate reductase 1 (PYCR1); metabolic stress; proline metabolism
  42. Apoptosis. 2020 Sep 21.
      Small-molecule compound-based therapies have provided new insights into cancer treatment against mitochondrial impairment. N6-furfuryladenosine (kinetin riboside, KR) is a purine derivative and an anticancer agent that selectively affects the molecular pathways crucial for cell growth and apoptosis by interfering with mitochondrial functions and thus might be a potential mitotoxicant. Metabolism of cancer cells is predominantly based on the Crabtree effect that relies on glucose-induced inhibition of cell respiration and thus on oxidative phosphorylation (OXPHOS), which supports the survival of cancer cells in metabolic stress conditions. The simplest way to circumvent this phenomenon is to replace glucose with galactose in the culture environment. Consequently, cells become more sensitive to mitochondrial perturbations caused by mitotoxicants. In the present study, we evaluated several cellular parameters and investigated the effect of KR on mitochondrial functions in HepG2 cells forced to rely mainly on OXPHOS. We showed that KR in the galactose environment is a more potent apoptosis-inducing agent. KR decreases the mitochondrial membrane potential, reduces glutathione level, depletes cellular ATP, and induces reactive oxygen species (ROS) production in the OXPHOS state, leading to the loss of cell viability. Taken together, these results demonstrate that KR directly acts on the mitochondria to limit their function and that the sensitivity of cells is dependent on their ability to cope with energetic stress.
    Keywords:  Cancer cells; Crabtree effect; Kinetin riboside; Metabolism; Mitochondria; Purine derivative
  43. Nat Rev Endocrinol. 2020 Sep 22.
      Both the consumption of a diet rich in fatty acids and exercise training result in similar adaptations in several skeletal muscle proteins. These adaptations are involved in fatty acid uptake and activation within the myocyte, the mitochondrial import of fatty acids and further metabolism of fatty acids by β-oxidation. Fatty acid availability is repeatedly increased postprandially during the day, particularly during high dietary fat intake and also increases during, and after, aerobic exercise. As such, fatty acids are possible signalling candidates that regulate transcription of target genes encoding proteins involved in muscle lipid metabolism. The mechanism of signalling might be direct or indirect targeting of peroxisome proliferator-activated receptors by fatty acid ligands, by fatty acid-induced NAD+-stimulated activation of sirtuin 1 and/or fatty acid-mediated activation of AMP-activated protein kinase. Lactate might also have a role in lipid metabolic adaptations. Obesity is characterized by impairments in fatty acid oxidation capacity, and individuals with obesity show some rigidity in increasing fatty acid oxidation in response to high fat intake. However, individuals with obesity retain improvements in fatty acid oxidation capacity in response to exercise training, thereby highlighting exercise training as a potential method to improve lipid metabolic flexibility in obesity.
  44. Front Oncol. 2020 ;10 1333
      O. Warburg conducted one of the first studies on tumor energy metabolism. His early discoveries pointed out that cancer cells display a decreased respiration and an increased glycolysis proportional to the increase in their growth rate, suggesting that they mainly depend on fermentative metabolism for ATP generation. Warburg's results and hypothesis generated controversies that are persistent to this day. It is thus of great importance to understand the mechanisms by which cancer cells can reversibly regulate the two pathways of their energy metabolism as well as the functioning of this metabolism in cell proliferation. Here, we made use of yeast as a model to study the Warburg effect and its eventual function in allowing an increased ATP synthesis to support cell proliferation. The role of oxidative phosphorylation repression in this effect was investigated. We show that yeast is a good model to study the Warburg effect, where all parameters and their modulation in the presence of glucose can be reconstituted. Moreover, we show that in this model, mitochondria are not dysfunctional, but that there are fewer mitochondria respiratory chain units per cell. Identification of the molecular mechanisms involved in this process allowed us to dissociate the parameters involved in the Warburg effect and show that oxidative phosphorylation repression is not mandatory to promote cell growth. Last but not least, we were able to show that neither cellular ATP synthesis flux nor glucose consumption flux controls cellular growth rate.
    Keywords:  Hap4p; Warburg effect; mitochondria; mitochondrial biogenesis; oxidative phosphorylation; yeast
  45. Nat Commun. 2020 Sep 25. 11(1): 4880
      Through advanced mechanistic modeling and the generation of large high-quality datasets, machine learning is becoming an integral part of understanding and engineering living systems. Here we show that mechanistic and machine learning models can be combined to enable accurate genotype-to-phenotype predictions. We use a genome-scale model to pinpoint engineering targets, efficient library construction of metabolic pathway designs, and high-throughput biosensor-enabled screening for training diverse machine learning algorithms. From a single data-generation cycle, this enables successful forward engineering of complex aromatic amino acid metabolism in yeast, with the best machine learning-guided design recommendations improving tryptophan titer and productivity by up to 74 and 43%, respectively, compared to the best designs used for algorithm training. Thus, this study highlights the power of combining mechanistic and machine learning models to effectively direct metabolic engineering efforts.
  46. Front Immunol. 2020 ;11 1866
      Intracellular metabolic programs tightly regulate the functions of macrophages, and previous studies have shown that serine mainly shapes the macrophage function via one-carbon metabolism. However, it is unknown whether serine modulates the macrophage function independent of one-carbon metabolism. Here, we find that serine deprivation lowers interleukin (IL)-1β production and inflammasome activation, as well as reprograms the transcriptomic and metabolic profile in M1 macrophages. Intriguingly, supplementation of formate, glycine, dNTPs, and glucose cannot rescue the production of IL-1β from serine-deprived macrophages. Mechanistically, serine deprivation inhibits macrophage IL-1β production through inhibition of mechanistic target of rapamycin (mTOR) signaling. Of note, the macrophages from mice feeding serine-free diet have lower IL-1β production, and these mice also show less inflammation after LPS challenge. Collectively, our data highlight a new regulatory mechanism for serine to modulate the macrophage function.
    Keywords:  IL-1β; inflammation; mTOR; macrophage; serine
  47. Cancer Metab. 2020 ;8 19
      Pancreatic ductal adenocarcinoma (PDAC) is one of the most malignant forms of cancer. Lack of effective treatment options and drug resistance contributes to the low survival among PDAC patients. In this study, we investigated the metabolic alterations in pancreatic cancer cells that do not respond to the EGFR inhibitor erlotinib. We selected erlotinib-resistant pancreatic cancer cells from MiaPaCa2 and AsPC1 cell lines. Metabolic profiling of erlotinib-resistant cells revealed a significant downregulation of glycolytic activity and reduced level of glycolytic metabolites compared to the sensitive cells. The resistant cells displayed elevated expression of the pentose phosphate pathway (PPP) enzymes involved in ROS regulation and nucleotide biosynthesis. The enhanced PPP elevated cellular NADPH/NADP+ ratio and protected the cells from reactive oxygen species (ROS)-induced damage. Inhibition of PPP using 6-aminonicotinamide (6AN) elevated ROS levels, induced G1 cell cycle arrest, and sensitized resistant cells to erlotinib. Genetic studies identified elevated PPP enzyme glucose-6-phosphate dehydrogenase (G6PD) as an important contributor to erlotinib resistance. Mechanistically, our data showed that upregulation of inhibitor of differentiation (ID1) regulates G6PD expression in resistant cells thus contributing to altered metabolic phenotype and reduced response to erlotinib. Together, our results highlight an underlying role of tumor metabolism in PDAC drug response and identify G6PD as a target to overcome drug resistance.
    Keywords:  Erlotinib resistance; Metabolic reprogramming; Pancreatic cancer