bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2021‒01‒31
forty-six papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Nat Commun. 2021 Jan 29. 12(1): 707
      Mitochondrial complex I is central to the pathological reactive oxygen species (ROS) production that underlies cardiac ischemia-reperfusion (IR) injury. ND6-P25L mice are homoplasmic for a disease-causing mtDNA point mutation encoding the P25L substitution in the ND6 subunit of complex I. The cryo-EM structure of ND6-P25L complex I revealed subtle structural changes that facilitate rapid conversion to the "deactive" state, usually formed only after prolonged inactivity. Despite its tendency to adopt the "deactive" state, the mutant complex is fully active for NADH oxidation, but cannot generate ROS by reverse electron transfer (RET). ND6-P25L mitochondria function normally, except for their lack of RET ROS production, and ND6-P25L mice are protected against cardiac IR injury in vivo. Thus, this single point mutation in complex I, which does not affect oxidative phosphorylation but renders the complex unable to catalyse RET, demonstrates the pathological role of ROS production by RET during IR injury.
    DOI:  https://doi.org/10.1038/s41467-021-20942-w
  2. Nat Immunol. 2021 Jan 28.
      Mitochondrial abnormalities have been noted in lupus, but the causes and consequences remain obscure. Autophagy-related genes ATG5, ATG7 and IRGM have been previously implicated in autoimmune disease. We reasoned that failure to clear defective mitochondria via mitophagy might be a foundational driver in autoimmunity by licensing mitochondrial DNA-dependent induction of type I interferon. Here, we show that mice lacking the GTPase IRGM1 (IRGM homolog) exhibited a type I interferonopathy with autoimmune features. Irgm1 deletion impaired the execution of mitophagy with cell-specific consequences. In fibroblasts, mitochondrial DNA soiling of the cytosol induced cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING)-dependent type I interferon, whereas in macrophages, lysosomal Toll-like receptor 7 was activated. In vivo, Irgm1-/- tissues exhibited mosaic dependency upon nucleic acid receptors. Whereas salivary and lacrimal gland autoimmune pathology was abolished and lung pathology was attenuated by cGAS and STING deletion, pancreatic pathology remained unchanged. These findings reveal fundamental connections between mitochondrial quality control and tissue-selective autoimmune disease.
    DOI:  https://doi.org/10.1038/s41590-020-00859-0
  3. Int J Mol Sci. 2021 Jan 20. pii: E1006. [Epub ahead of print]22(3):
      Several genetic variants in the mitochondrial genome (mtDNA), including ancient polymorphisms, are associated with chronic inflammatory conditions, but investigating the functional consequences of such mtDNA polymorphisms in humans is challenging due to the influence of many other polymorphisms in both mtDNA and the nuclear genome (nDNA). Here, using the conplastic mouse strain B6-mtFVB, we show that in mice, a maternally inherited natural mutation (m.7778G > T) in the mitochondrially encoded gene ATP synthase 8 (mt-Atp8) of complex V impacts on the cellular metabolic profile and effector functions of CD4+ T cells and induces mild changes in oxidative phosphorylation (OXPHOS) complex activities. These changes culminated in significantly lower disease susceptibility in two models of inflammatory skin disease. Our findings provide experimental evidence that a natural variation in mtDNA influences chronic inflammatory conditions through alterations in cellular metabolism and the systemic metabolic profile without causing major dysfunction in the OXPHOS system.
    Keywords:  ATP8; autoimmune disease; complex V; conplastic mice; immunometabolism; metabolomics; mitochondria; mt-Atp8; mtDNA polymorphisms; propionate; short chain fatty acids; skin inflammation
    DOI:  https://doi.org/10.3390/ijms22031006
  4. Nat Commun. 2021 01 27. 12(1): 614
      Infiltrating gliomas are devastating and incurable tumors. Amongst all gliomas, those harboring a mutation in isocitrate dehydrogenase 1 mutation (IDH1mut) acquire a different tumor biology and clinical manifestation from those that are IDH1WT. Understanding the unique metabolic profile reprogrammed by IDH1 mutation has the potential to identify new molecular targets for glioma therapy. Herein, we uncover increased monounsaturated fatty acids (MUFA) and their phospholipids in endoplasmic reticulum (ER), generated by IDH1 mutation, that are responsible for Golgi and ER dilation. We demonstrate a direct link between the IDH1 mutation and this organelle morphology via D-2HG-induced stearyl-CoA desaturase (SCD) overexpression, the rate-limiting enzyme in MUFA biosynthesis. Inhibition of IDH1 mutation or SCD silencing restores ER and Golgi morphology, while D-2HG and oleic acid induces morphological defects in these organelles. Moreover, addition of oleic acid, which tilts the balance towards elevated levels of MUFA, produces IDH1mut-specific cellular apoptosis. Collectively, these results suggest that IDH1mut-induced SCD overexpression can rearrange the distribution of lipids in the organelles of glioma cells, providing new insight into the link between lipid metabolism and organelle morphology in these cells, with potential and unique therapeutic implications.
    DOI:  https://doi.org/10.1038/s41467-020-20752-6
  5. Front Cell Dev Biol. 2020 ;8 624216
      Cardiac tissue requires a persistent production of energy in order to exert its pumping function. Therefore, the maintenance of this function relies on mitochondria that represent the "powerhouse" of all cardiac activities. Mitochondria being one of the key players for the proper functioning of the mammalian heart suggests continual regulation and organization. Mitochondria adapt to cellular energy demands via fusion-fission events and, as a proof-reading ability, undergo mitophagy in cases of abnormalities. Ca2+ fluxes play a pivotal role in regulating all mitochondrial functions, including ATP production, metabolism, oxidative stress balance and apoptosis. Communication between mitochondria and others organelles, especially the sarcoplasmic reticulum is required for optimal function. Consequently, abnormal mitochondrial activity results in decreased energy production leading to pathological conditions. In this review, we will describe how mitochondrial function or dysfunction impacts cardiac activities and the development of dilated cardiomyopathy.
    Keywords:  Ca ATPase (SERCA) 2+; calcium; cardiomyocytes; cardiomyopathies; heart function; mitochondria; organoids model; sarcoplasmic reticulum
    DOI:  https://doi.org/10.3389/fcell.2020.624216
  6. Cell. 2021 Jan 18. pii: S0092-8674(20)31694-9. [Epub ahead of print]
      Ras GTPase-activating protein-binding proteins 1 and 2 (G3BP1 and G3BP2, respectively) are widely recognized as core components of stress granules (SGs). We report that G3BPs reside at the cytoplasmic surface of lysosomes. They act in a non-redundant manner to anchor the tuberous sclerosis complex (TSC) protein complex to lysosomes and suppress activation of the metabolic master regulator mechanistic target of rapamycin complex 1 (mTORC1) by amino acids and insulin. Like the TSC complex, G3BP1 deficiency elicits phenotypes related to mTORC1 hyperactivity. In the context of tumors, low G3BP1 levels enhance mTORC1-driven breast cancer cell motility and correlate with adverse outcomes in patients. Furthermore, G3bp1 inhibition in zebrafish disturbs neuronal development and function, leading to white matter heterotopia and neuronal hyperactivity. Thus, G3BPs are not only core components of SGs but also a key element of lysosomal TSC-mTORC1 signaling.
    Keywords:  G3BP1; G3BP2; TSC complex; cancer; lysosome; mTORC1; metabolism; neuronal function; stress granule
    DOI:  https://doi.org/10.1016/j.cell.2020.12.024
  7. Nat Rev Mol Cell Biol. 2021 Jan 25.
      The research field of ferroptosis has seen exponential growth over the past few years, since the term was coined in 2012. This unique modality of cell death, driven by iron-dependent phospholipid peroxidation, is regulated by multiple cellular metabolic pathways, including redox homeostasis, iron handling, mitochondrial activity and metabolism of amino acids, lipids and sugars, in addition to various signalling pathways relevant to disease. Numerous organ injuries and degenerative pathologies are driven by ferroptosis. Intriguingly, therapy-resistant cancer cells, particularly those in the mesenchymal state and prone to metastasis, are exquisitely vulnerable to ferroptosis. As such, pharmacological modulation of ferroptosis, via both its induction and its inhibition, holds great potential for the treatment of drug-resistant cancers, ischaemic organ injuries and other degenerative diseases linked to extensive lipid peroxidation. In this Review, we provide a critical analysis of the current molecular mechanisms and regulatory networks of ferroptosis, the potential physiological functions of ferroptosis in tumour suppression and immune surveillance, and its pathological roles, together with a potential for therapeutic targeting. Importantly, as in all rapidly evolving research areas, challenges exist due to misconceptions and inappropriate experimental methods. This Review also aims to address these issues and to provide practical guidelines for enhancing reproducibility and reliability in studies of ferroptosis. Finally, we discuss important concepts and pressing questions that should be the focus of future ferroptosis research.
    DOI:  https://doi.org/10.1038/s41580-020-00324-8
  8. BMC Biol. 2021 Jan 25. 19(1): 14
      BACKGROUND: Lipoylation of 2-ketoacid dehydrogenases is essential for mitochondrial function in eukaryotes. While the basic principles of the lipoylation processes have been worked out, we still lack a thorough understanding of the details of this important post-translational modification pathway. Here we used yeast as a model organism to characterize substrate usage by the highly conserved eukaryotic octanoyl/lipoyl transferases in vivo and queried how amenable the lipoylation system is to supplementation with exogenous substrate.RESULTS: We show that the requirement for mitochondrial fatty acid synthesis to provide substrates for lipoylation of the 2-ketoacid dehydrogenases can be bypassed by supplying the cells with free lipoic acid (LA) or octanoic acid (C8) and a mitochondrially targeted fatty acyl/lipoyl activating enzyme. We also provide evidence that the S. cerevisiae lipoyl transferase Lip3, in addition to transferring LA from the glycine cleavage system H protein to the pyruvate dehydrogenase (PDH) and α-ketoglutarate dehydrogenase (KGD) E2 subunits, can transfer this cofactor from the PDH complex to the KGD complex. In support of yeast as a model system for human metabolism, we demonstrate that the human octanoyl/lipoyl transferases can substitute for their counterparts in yeast to support respiratory growth and protein lipoylation. Like the wild-type yeast enzyme, the human lipoyl transferase LIPT1 responds to LA supplementation in the presence of the activating enzyme LplA.
    CONCLUSIONS: In the yeast model system, the eukaryotic lipoylation pathway can use free LA and C8 as substrates when fatty/lipoic acid activating enzymes are targeted to mitochondria. Lip3 LA transferase has a wider substrate specificity than previously recognized. We show that these features of the lipoylation mechanism in yeast are conserved in mammalian mitochondria. Our findings have important implications for the development of effective therapies for the treatment of LA or mtFAS deficiency-related disorders.
    Keywords:  Lip2/LIPT2; Lip3 substrate; Lip3/LIPT1; Lipoylation; Lipoylation disorders; Mitochondrial fatty acid synthesis (mtFAS); Octanoyl/lipoyl transferases; S. cerevisiae model; Supplementation studies
    DOI:  https://doi.org/10.1186/s12915-021-00951-3
  9. Free Radic Biol Med. 2021 Jan 20. pii: S0891-5849(21)00053-8. [Epub ahead of print]
      The heart is the most metabolically flexible organ with respect to the use of substrates available in different states of energy metabolism. Cardiac mitochondria sense substrate availability and ensure the efficiency of oxidative phosphorylation and heart function. Mitochondria also play a critical role in cardiac ischemia/reperfusion injury, during which they are directly involved in ROS-producing pathophysiological mechanisms. This review explores the mechanisms of ROS production within the energy metabolism pathways and focuses on the impact of different substrates. We describe the main metabolites accumulating during ischemia in the glucose, fatty acid, and Krebs cycle pathways. Hyperglycemia, often present in the acute stress condition of ischemia/reperfusion, increases cytosolic ROS concentrations through the activation of NADPH oxidase 2 and increases mitochondrial ROS through the metabolic overloading and decreased binding of hexokinase II to mitochondria. Fatty acid-linked ROS production is related to the increased fatty acid flux and corresponding accumulation of long-chain acylcarnitines. Succinate that accumulates during anoxia/ischemia is suggested to be the main source of ROS, and the role of itaconate as an inhibitor of succinate dehydrogenase is emerging. We discuss the strategies to modulate and counteract the accumulation of substrates that yield ROS and the therapeutic implications of this concept.
    Keywords:  Cardiac injury; Energy metabolism; Ischemia/reperfusion; Long-chain acylcarnitines; Mitochondria; Reactive oxygen species; Succinate
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2021.01.036
  10. Redox Biol. 2021 Jan 21. pii: S2213-2317(21)00018-5. [Epub ahead of print] 101870
      Cancer cells display abnormal metabolic activity as a result of activated oncogenes and loss of tumor suppressor genes. The Warburg Effect is a common metabolic feature of cancer that involves a preference for aerobic glycolysis over oxidative phosphorylation to generate ATP and building blocks for biosynthesis. However, emerging evidence indicates that mitochondrial metabolic pathways are also reprogrammed in cancer and play vital roles in bioenergetics, biosynthesis, and managing redox homeostasis. The mitochondria act a central hub for metabolic pathways that generate ATP and building blocks for lipid, nucleic acid and protein biosynthesis. However, mitochondrial respiration is also a leading source of reactive oxygen species that can damage cellular organelles and trigger cell death if levels become too high. In general, cancer cells are reported to have higher levels of reactive oxygen species than their non-cancerous cells of origin, and therefore must employ diverse metabolic strategies to prevent oxidative stress. However, mounting evidence indicates that the metabolic profiles between proliferative and disseminated cancer cells are not the same. In this review, we will examine mitochondrial metabolic pathways, such as glutaminolysis, that proliferative and disseminated cancer cells utilize to control their redox status.
    Keywords:  Cancer progression; Glutaminolysis; Mitochondria metabolism; Redox homeostasis
    DOI:  https://doi.org/10.1016/j.redox.2021.101870
  11. Arch Biochem Biophys. 2021 Jan 22. pii: S0003-9861(21)00025-4. [Epub ahead of print] 108775
      Ferroptosis is a type of iron-dependent, non-apoptotic cell death, which is typically induced by cysteine starvation or by the inhibition of glutathione peroxidase 4 (GPX4) activity with the accompanying elevation in lipid peroxidation product levels. Despite the central role of mitochondria in oxidative metabolism and hence, as main sources of superoxide, the issue of whether mitochondrial superoxide participates in the execution of ferroptosis remains unclear. To gain additional insights into this issue, we employed suppressors of the site IQ electron leak (S1QEL) and suppressors of the site IIIQo electron leak (S3QEL), small molecules that suppress mitochondrial superoxide production from complex I and III, respectively. The findings indicate that S3QEL, but not S1QEL, significantly protected mouse hepatoma Hepa 1-6 cells from lipid peroxidation and the subsequent ferroptosis induced by cysteine (Cys) starvation (cystine deprivation from culture media or xCT inhibition by erastin). The intracellular levels of Cys and GSH remained low irrespective of life or death. Moreover, S3QEL also suppressed ferroptosis in xCT-knockout mouse-derived embryonic fibroblasts, which usually die under conventional cultivating conditions due to the absence of intracellular Cys and GSH. Although it has been reported that erastin induces the hyperpolarization of the mitochondrial membrane potential, no correlation was observed between hyperpolarization and cell death in xCT-knockout cells. Collectively, these results indicate that superoxide production from complex III plays a pivotal role in the ferroptosis that is induced by Cys starvation, suggesting that protecting mitochondria is a promising therapeutic strategy for the treatment of multiple diseases featuring ferroptosis.
    Keywords:  Ferroptosis; Glutathione; Lipid peroxidation; Mitochondria; Superoxide
    DOI:  https://doi.org/10.1016/j.abb.2021.108775
  12. J Hepatol. 2021 Jan 20. pii: S0168-8278(21)00024-6. [Epub ahead of print]
      BACKGROUND AND AIMS: Little is known about the metabolic regulation of cancer stem cells (CSC) in cholangiocarcinoma (CCA). We analyzed whether mitochondrial-dependent metabolism and related signaling pathways contribute to stem state in CCA.METHODS: The stem-like subset was enriched by sphere culture (SPH) in human intrahepatic CCA cells (HUCCT1 and CCLP1) and compared to cells cultured in monolayer. Extracellular flux analysis was examined by Seahorse technology and high-resolution respirometry. In patients with CCA, expression of factors related to mitochondrial metabolism was analyzed for possible correlation with clinical parameters.
    RESULTS: Metabolic analyses revealed a more efficient respiratory phenotype in CCA-SPH than in monolayers, due to mitochondrial oxidative phosphorylation. CCA-SPH showed high mitochondrial membrane potential and elevated mitochondrial mass, and over-expressed peroxisome proliferator-activated receptor gamma coactivator (PGC)-1α, a master regulator of mitochondrial biogenesis. Targeting mitochondrial complex I in CCA-SPH by metformin, or PGC-1α silencing or pharmacologic inhibition (SR-18292) impaired spherogenicity and expression of markers related to the CSC phenotype, pluripotency, and epithelial-mesenchymal transition. In mice with tumor xenografts generated by injection of CCA-SPH, administration of metformin or SR-18292 significantly reduced tumor growth and determined a phenotype more similar to tumors originated from cells grown in monolayer. In CCA patients, expression of PGC-1α was correlated to expression of mitochondrial complex II and of stem-like genes. Patients with higher PGC-1α expression by immunostaining had lower overall survival (OS) and progression-free survival, higher angioinvasion and faster recurrence. In GSEA analysis, CCA patients with high levels of mitochondrial Complex II had shorter OS and time to recurrence.
    CONCLUSIONS: The CCA stem-subset has a more efficient respiratory phenotype and depends on mitochondrial oxidative metabolism and PGC-1α to maintain CSC features.
    LAY SUMMARY: The growth of many cancers is sustained by a specific type of cells with more embryonic characteristics, termed as 'cancer stem cells'. These cells have been described in cholangiocarcinoma, a type of liver cancer with poor prognosis and limited therapeutic approaches. We demonstrate that cancer stem cells in cholangiocarcinoma have different metabolic features, and use mitochondria, an organelle located within the cells, as the major source of energy. We also identify PGC-1α, a molecule which regulates the biology of mitochondria, as a possible new target to be explored for developing new treatments for cholangiocarcinoma.
    Keywords:  CCLP1; HUCCT1; OXPHOS; PGC-1α; SR-18292
    DOI:  https://doi.org/10.1016/j.jhep.2020.12.031
  13. Biology (Basel). 2021 Jan 22. pii: 83. [Epub ahead of print]10(2):
      Ferroptosis is a unique cell death mechanism that is executed by the excessive accumulation of lipid peroxidation in cells. The relevance of ferroptosis in multiple human diseases such as neurodegeneration, organ damage, and cancer is becoming increasingly evident. As ferroptosis is deeply intertwined with metabolic pathways such as iron, cyst(e)ine, glutathione, and lipid metabolism, a better understanding of how ferroptosis is regulated by these pathways will enable the precise utilization or prevention of ferroptosis for therapeutic uses. In this review, we present an update of the mechanisms underlying diverse metabolic pathways that can regulate ferroptosis in cancer.
    Keywords:  GPX4; SLC7A11; cyst(e)ine metabolism; ferroptosis; glutathione metabolism; iron metabolism; lipid peroxidation; reactive oxygen species
    DOI:  https://doi.org/10.3390/biology10020083
  14. Nat Cell Biol. 2021 Jan 25.
      Cell competition allows winner cells to eliminate less fit loser cells in tissues. In Minute cell competition, cells with a heterozygous mutation in ribosome genes, such as RpS3+/- cells, are eliminated by wild-type cells. How cells are primed as losers is partially understood and it has been proposed that reduced translation underpins the loser status of ribosome mutant, or Minute, cells. Here, using Drosophila, we show that reduced translation does not cause cell competition. Instead, we identify proteotoxic stress as the underlying cause of the loser status for Minute competition and competition induced by mahjong, an unrelated loser gene. RpS3+/- cells exhibit reduced autophagic and proteasomal flux, accumulate protein aggregates and can be rescued from competition by improving their proteostasis. Conversely, inducing proteotoxic stress is sufficient to turn otherwise wild-type cells into losers. Thus, we propose that tissues may preserve their health through a proteostasis-based mechanism of cell competition and cell selection.
    DOI:  https://doi.org/10.1038/s41556-020-00627-0
  15. J Biol Chem. 2020 Feb 07. pii: S0021-9258(17)49861-9. [Epub ahead of print]295(6): 1623-1636
      Permeabilization of the mitochondrial outer membrane is a key step in the intrinsic apoptosis pathway, triggered by the release of mitochondrial intermembrane space proteins into the cytoplasm. The BCL-2-associated X apoptosis regulator (BAX) protein critically contributes to this process by forming pores in the mitochondrial outer membrane. However, the relative roles of the mitochondrial residence of BAX and its oligomerization in promoting membrane permeabilization are unclear. To this end, using both cell-free and cellular experimental systems, including membrane permeabilization, size-exclusion chromatography-based oligomer, and retrotranslocation assays, along with confocal microscopy analysis, here we studied two BAX C-terminal variants, T182I and G179P. Neither variant formed large oligomers when activated in liposomes. Nevertheless, the G179P variant could permeabilize liposome membranes, suggesting that large BAX oligomers are not essential for the permeabilization. However, when G179P was transduced into BAX/BCL2 agonist killer (BAK) double-knockout mouse embryonic fibroblasts, its location was solely cytoplasmic, and it then failed to mediate cell death. In contrast, T182I was inefficient in both liposome insertion and permeabilization. Yet, when transduced into cells, BAXT182I resided predominantly on mitochondria, because of its slow retrotranslocation and mediated apoptosis as efficiently as WT BAX. We conclude that BAX's mitochondrial residence in vivo, regulated by both targeting and retrotranslocation, is more significant for its pro-apoptotic activity than its ability to insert and to form higher-order oligomers in model membranes. We propose that this finding should be taken into account when developing drugs that modulate BAX activity.
    Keywords:  Bax; anticancer drug; apoptosis; liposome; mitochondrial apoptosis; mitochondrial localization; mitochondrial outer membrane permeabilization (MOMP); molecular cell biology; protein oligomers; translocation
    DOI:  https://doi.org/10.1074/jbc.RA119.011635
  16. Biomaterials. 2021 Jan 09. pii: S0142-9612(20)30893-0. [Epub ahead of print]269 120646
      Historically, the field of regenerative medicine has aimed to heal damaged tissue through the use of biomaterials scaffolds or delivery of foreign progenitor cells. Despite 30 years of research, however, translation and commercialization of these techniques has been limited. To enable mammalian regeneration, a more practical approach may instead be to develop therapies that evoke endogenous processes reminiscent of those seen in innate regenerators. Recently, investigations into tadpole tail regrowth, zebrafish limb restoration, and the super-healing Murphy Roths Large (MRL) mouse strain, have identified ancient oxygen-sensing pathways as a possible target to achieve this goal. Specifically, upregulation of the transcription factor, hypoxia-inducible factor one alpha (HIF-1α) has been shown to modulate cell metabolism and plasticity, as well as inflammation and tissue remodeling, possibly priming injuries for regeneration. Since HIF-1α signaling is conserved across species, environmental or pharmacological manipulation of oxygen-dependent pathways may elicit a regenerative response in non-healing mammals. In this review, we will explore the emerging role of HIF-1α in mammalian healing and regeneration, as well as attempts to modulate protein stability through hyperbaric oxygen treatment, intermittent hypoxia therapy, and pharmacological targeting. We believe that these therapies could breathe new life into the field of regenerative medicine.
    Keywords:  Drug delivery; Hypoxia-inducible factor; Oxygen signaling; Tissue regeneration
    DOI:  https://doi.org/10.1016/j.biomaterials.2020.120646
  17. Trends Mol Med. 2021 Jan 21. pii: S1471-4914(20)30329-4. [Epub ahead of print]
      Genome editing holds great promise for treating a range of human genetic diseases. While emerging clustered regularly interspaced short-palindromic repeats (CRISPR) technologies allow editing of the nuclear genome, it is still not possible to precisely manipulate mitochondrial DNA (mtDNA). Here, we summarize past developments and recent advances in nuclear and mitochondrial genome editing.
    Keywords:  gene therapy; genome editing; mitochondria; translational medicine
    DOI:  https://doi.org/10.1016/j.molmed.2020.12.005
  18. Mol Metab. 2021 Jan 20. pii: S2212-8778(21)00009-0. [Epub ahead of print] 101169
      BACKGROUND: The global rise of metabolic disorders, such as obesity, diabetes type 2 and cardiovascular disease, demands a thorough molecular understanding of the cellular mechanisms that govern health or disease. The endoplasmic reticulum (ER) is a key organelle for cellular function and metabolic adaptation and, therefore, disturbed ER function, "ER stress", is a key feature of metabolic disorders.SCOPE OF REVIEW: As ER stress remains an ill-defined phenomenon, this review provides a general guide to understanding the nature, aetiology and consequences of ER stress in metabolic disorders. We define ER stress by its type of stressor, which is driven by proteotoxicity, lipotoxicity, and/or glucotoxicity. We discuss the implications of ER stress in metabolic disorders by reviewing evidence implicating ER phenotypes and organelle communication, protein quality control, calcium homeostasis, lipid and carbohydrate metabolism, and inflammation as key mechanisms in the development of ER stress and metabolic dysfunction.
    MAJOR CONCLUSIONS: In mammalian biology, ER is a phenotypically and functionally diverse platform for nutrient sensing, which is critical for cell-type specific metabolic control by e.g. hepatocytes, adipocytes, muscle cells, and neurons. In these cells, ER stress is a distinct, transient state of functional imbalance, which is usually resolved by the activation of adaptive programs such as the unfolded protein response (UPR), ER-associated protein degradation (ERAD), or autophagy. However, challenges to proteostasis also impact lipid and glucose metabolism and vice versa. In the ER, both sensing and adaptive measures are integrated and failure of the ER to adapt leads to aberrant metabolism, organelle dysfunction, insulin resistance, and inflammation. In conclusion, the ER is intricately linked to a wide spectrum of cellular functions and is a critical component in maintaining and restoring metabolic health.
    Keywords:  ERAD; NFE2L1; Obesity; UPR; UPS; autophagy; calcium homeostasis; diabetes; endoplasmic reticulum; glucotoxicity; inflammation; lipid metabolism; lipotoxicity; proteostasis; proteotoxicity
    DOI:  https://doi.org/10.1016/j.molmet.2021.101169
  19. Sci Rep. 2021 Jan 25. 11(1): 2157
      Bloom Syndrome (BS; OMIM #210900; ORPHA #125) is a rare genetic disorder that is associated with growth deficits, compromised immune system, insulin resistance, genome instability and extraordinary predisposition to cancer. Most efforts thus far have focused on understanding the role of the Bloom syndrome DNA helicase BLM as a recombination factor in maintaining genome stability and suppressing cancer. Here, we observed increased levels of reactive oxygen species (ROS) and DNA base damage in BLM-deficient cells, as well as oxidative-stress-dependent reduction in DNA replication speed. BLM-deficient cells exhibited increased mitochondrial mass, upregulation of mitochondrial transcription factor A (TFAM), higher ATP levels and increased respiratory reserve capacity. Cyclin B1, which acts in complex with cyclin-dependent kinase CDK1 to regulate mitotic entry and associated mitochondrial fission by phosphorylating mitochondrial fission protein Drp1, fails to be fully degraded in BLM-deficient cells and shows unscheduled expression in G1 phase cells. This failure to degrade cyclin B1 is accompanied by increased levels and persistent activation of Drp1 throughout mitosis and into G1 phase as well as mitochondrial fragmentation. This study identifies mitochondria-associated abnormalities in Bloom syndrome patient-derived and BLM-knockout cells and we discuss how these abnormalities may contribute to Bloom syndrome.
    DOI:  https://doi.org/10.1038/s41598-021-81075-0
  20. Nat Metab. 2021 Jan 28.
      Cancer cells reprogramme their metabolism to support unrestrained proliferation and survival in nutrient-poor conditions. Whereas non-transformed cells often have lower demands for serine and glycine, several cancer subtypes hyperactivate intracellular serine and glycine synthesis and become addicted to de novo production. Copy-number amplifications of serine- and glycine-synthesis genes and genetic alterations in common oncogenes and tumour-suppressor genes enhance serine and glycine synthesis, resulting in high production and secretion of these oncogenesis-supportive metabolites. In this Review, we discuss the contribution of serine and glycine synthesis to cancer progression. By relying on de novo synthesis pathways, cancer cells are able to enhance macromolecule synthesis, neutralize high levels of oxidative stress and regulate methylation and tRNA formylation. Furthermore, we discuss the immunosuppressive potential of serine and glycine, and the essentiality of both amino acids to promoting survival of non-transformed neighbouring cells. Finally, we point to the emerging data proposing moonlighting functions of serine- and glycine-synthesis enzymes and examine promising small molecules targeting serine and glycine synthesis.
    DOI:  https://doi.org/10.1038/s42255-020-00329-9
  21. Front Cell Dev Biol. 2020 ;8 613892
      Peroxisomes are membrane-bound organelles involved in many metabolic pathways and essential for human health. They harbor a large number of enzymes involved in the different pathways, thus requiring transport of substrates, products and cofactors involved across the peroxisomal membrane. Although much progress has been made in understanding the permeability properties of peroxisomes, there are still important gaps in our knowledge about the peroxisomal transport of metabolites and cofactors. In this review, we discuss the different modes of transport of metabolites and essential cofactors, including CoA, NAD+, NADP+, FAD, FMN, ATP, heme, pyridoxal phosphate, and thiamine pyrophosphate across the peroxisomal membrane. This transport can be mediated by non-selective pore-forming proteins, selective transport proteins, membrane contact sites between organelles, and co-import of cofactors with proteins. We also discuss modes of transport mediated by shuttle systems described for NAD+/NADH and NADP+/NADPH. We mainly focus on current knowledge on human peroxisomal metabolite and cofactor transport, but also include knowledge from studies in plants, yeast, fruit fly, zebrafish, and mice, which has been exemplary in understanding peroxisomal transport mechanisms in general.
    Keywords:  carrier; cofactor; exchanger; membrane contact sites; metabolism; peroxisomes; transporter
    DOI:  https://doi.org/10.3389/fcell.2020.613892
  22. Mol Syst Biol. 2021 Jan;17(1): e9730
      Multi-omics datasets can provide molecular insights beyond the sum of individual omics. Various tools have been recently developed to integrate such datasets, but there are limited strategies to systematically extract mechanistic hypotheses from them. Here, we present COSMOS (Causal Oriented Search of Multi-Omics Space), a method that integrates phosphoproteomics, transcriptomics, and metabolomics datasets. COSMOS combines extensive prior knowledge of signaling, metabolic, and gene regulatory networks with computational methods to estimate activities of transcription factors and kinases as well as network-level causal reasoning. COSMOS provides mechanistic hypotheses for experimental observations across multi-omics datasets. We applied COSMOS to a dataset comprising transcriptomics, phosphoproteomics, and metabolomics data from healthy and cancerous tissue from eleven clear cell renal cell carcinoma (ccRCC) patients. COSMOS was able to capture relevant crosstalks within and between multiple omics layers, such as known ccRCC drug targets. We expect that our freely available method will be broadly useful to extract mechanistic insights from multi-omics studies.
    Keywords:  causal reasoning; kidney cancer; metabolism; multi-omics; signaling
    DOI:  https://doi.org/10.15252/msb.20209730
  23. Redox Biol. 2021 Jan 16. pii: S2213-2317(21)00014-8. [Epub ahead of print]40 101866
      Autophagy and apoptosis are powerful regulators of multiple facets of cellular metabolism and homeostasis. Here, we uncover that galanin, a pleiotropic peptide, regulates cardiac autophagy and deactivates apoptotic cell death through the Forkhead box protein O1 (FoxO1) pathway. In hypertrophied heart, galanin promotes autophagy and metabolic shift from fatty acid (FA) to glucose oxidation and preserves mitochondrial integrity. In cardiomyoblasts, galanin triggers autophagosome formation and alleviates hypertrophy, apoptotic cell death, and mitochondrial stress. Mechanistically, galanin dictates cell autophagic and anti-apoptotic phenotypes through FoxO1 pathway. Together, these findings uncover a previously unknown role for galanin in the regulation of cardiac autophagy and provide new insights into the molecular mechanisms supporting cell survival in the hypertrophic reprogramming of the heart.
    Keywords:  Apoptosis; Autophagy; Cardiac remodeling; Galanin; Hypertrophy; Metabolism
    DOI:  https://doi.org/10.1016/j.redox.2021.101866
  24. Plant Commun. 2021 Jan 11. 2(1): 100081
      Metabolons are transient multi-protein complexes of sequential enzymes that mediate substrate channeling. They differ from multi-enzyme complexes in that they are dynamic, rather than permanent, and as such have considerably lower dissociation constants. Despite the fact that a huge number of metabolons have been suggested to exist in plants, most of these claims are erroneous as only a handful of these have been proven to channel metabolites. We believe that physical protein-protein interactions between consecutive enzymes of a pathway should rather be called enzyme-enzyme assemblies. In this review, we describe how metabolons are generally assembled by transient interactions and held together by both structural elements and non-covalent interactions. Experimental evidence for their existence comes from protein-protein interaction studies, which indicate that the enzymes physically interact, and direct substrate channeling measurements, which indicate that they functionally interact. Unfortunately, advances in cell biology and proteomics have far outstripped those in classical enzymology and flux measurements, rendering most reports reliant purely on interactome studies. Recent developments in co-fractionation mass spectrometry will likely further exacerbate this bias. Given this, only dynamic enzyme-enzyme assemblies in which both physical and functional interactions have been demonstrated should be termed metabolons. We discuss the level of evidence for the manifold plant pathways that have been postulated to contain metabolons and then list examples in both primary and secondary metabolism for which strong evidence has been provided to support these claims. In doing so, we pay particular attention to experimental and mathematical approaches to study metabolons as well as complexities that arise in attempting to follow them. Finally, we discuss perspectives for improving our understanding of these fascinating but enigmatic interactions.
    Keywords:  metabolon; protein–protein interaction; substrate channeling
    DOI:  https://doi.org/10.1016/j.xplc.2020.100081
  25. Front Cell Dev Biol. 2020 ;8 603837
      Metabolic reprogramming has been widely recognized as a hallmark of malignancy. The uptake and metabolism of amino acids are aberrantly upregulated in many cancers that display addiction to particular amino acids. Amino acids facilitate the survival and proliferation of cancer cells under genotoxic, oxidative, and nutritional stress. Thus, targeting amino acid metabolism is becoming a potential therapeutic strategy for cancer patients. In this review, we will systematically summarize the recent progress of amino acid metabolism in malignancy and discuss their interconnection with mammalian target of rapamycin complex 1 (mTORC1) signaling, epigenetic modification, tumor growth and immunity, and ferroptosis. Finally, we will highlight the potential therapeutic applications.
    Keywords:  amino acids (AAs); cancer; epigenetic; ferroptosis; mTORC (mammalian target of rapamycin kinase complex); metabolism; tumor growth; tumor immunity
    DOI:  https://doi.org/10.3389/fcell.2020.603837
  26. Cancers (Basel). 2021 Jan 22. pii: 401. [Epub ahead of print]13(3):
      Overcoming tumor immunosuppression still represents one ambitious achievement for cancer immunotherapy. Of note, the cytokine TGF-β contributes to immune evasion in multiple cancer types, by feeding the establishment of a tolerogenic environment in the host. Indeed, it fosters the expansion and accumulation of immunosuppressive regulatory cell populations within the tumor microenvironment (TME), where it also activates resident stromal cells and enhances angiogenesis programs. More recently, TGF-β has also turned out as a key metabolic adjuster in tumors orchestrating metabolic pathways in the TME. In this review, we will scrutinize TGF-β-mediated immune and stromal cell crosstalk within the TME, with a primary focus on metabolic programs.
    Keywords:  TGF-β; immune-metabolism; tumor microenvironment
    DOI:  https://doi.org/10.3390/cancers13030401
  27. Cancers (Basel). 2021 Jan 22. pii: 412. [Epub ahead of print]13(3):
      Amino acids are integral components of cancer metabolism. The non-essential amino acid asparagine supports the growth and survival of various cancer cell types. Here, different mass spectrometry approaches were employed to identify lower aspartate levels, higher aspartate/glutamine ratios and lower tricarboxylic acid (TCA) cycle metabolite levels in asparagine-deprived sarcoma cells. Reduced nicotinamide adenine dinucleotide (NAD+)/nicotinamide adenine dinucleotide hydride (NADH) ratios were consistent with redirection of TCA cycle flux and relative electron acceptor deficiency. Elevated lactate/pyruvate ratios may be due to compensatory NAD+ regeneration through increased pyruvate to lactate conversion by lactate dehydrogenase. Supplementation with exogenous pyruvate, which serves as an electron acceptor, restored aspartate levels, NAD+/NADH ratios, lactate/pyruvate ratios and cell growth in asparagine-deprived cells. Chemicals disrupting NAD+ regeneration in the electron transport chain further enhanced the anti-proliferative and pro-apoptotic effects of asparagine depletion. We speculate that reductive stress may be a major contributor to the growth arrest observed in asparagine-starved cells.
    Keywords:  asparagine starvation; metabolomics; reductive stress; sarcoma
    DOI:  https://doi.org/10.3390/cancers13030412
  28. Front Immunol. 2020 ;11 624556
      IFI16, hnRNPA2B1, and nuclear cGAS are nuclear-located DNA sensors that play important roles in initiating host antiviral immunity and modulating tumorigenesis. IFI16 triggers innate antiviral immunity, inflammasome, and suppresses tumorigenesis by recognizing double-stranded DNA (dsDNA), single-stranded DNA (ssDNA), damaged nuclear DNA, or cooperatively interacting with multiple tumor suppressors such as p53 and BRCA1. hnRNPA2B1 initiates interferon (IFN)-α/β production and enhances STING-dependent cytosolic antiviral signaling by directly binding viral dsDNA from invaded viruses and facilitating N6 -methyladenosine (m6A) modification of cGAS, IFI16, and STING mRNAs. Nuclear cGAS is recruited to double-stranded breaks (DSBs), suppresses DNA repair, and promotes tumorigenesis. This review briefly describes the nuclear functions of IFI16, hnRNPA2B1, and cGAS, and summarizes the transcriptional, post-transcriptional, and post-translational regulation of these nuclear DNA sensors.
    Keywords:  IFI16; cGAS; hnRNPA2B1; nuclear DNA sensor; p53; tumorigenesis; type I interferon
    DOI:  https://doi.org/10.3389/fimmu.2020.624556
  29. J Clin Invest. 2021 Jan 28. pii: 143861. [Epub ahead of print]
      Omega-3 fatty acids from fish oil reduce triglyceride levels in mammals, yet the mechanisms underlying this effect have not been fully clarified despite the clinical use of omega-3 ethyl esters to treat severe hypertriglyceridemia and reduce cardiovascular disease risk in humans. Here we identified in bile a class of hypotriglyceridemic omega-3 fatty acid-derived N-acyl taurines (NATs) that, after dietary omega-3 fatty acid supplementation, increased to concentrations similar to those of steroidal bile acids. The biliary docosahexaenoic acid (DHA) containing NAT, C22:6 NAT, was increased in human and mouse plasma after dietary omega-3 fatty acid supplementation and potently inhibited intestinal triacylglycerol hydrolysis and lipid absorption. Supporting this observation, genetic elevation of endogenous NAT levels in mice impaired lipid absorption, while selective augmentation of C22:6 NAT levels protected against hypertriglyceridemia and fatty liver. When administered pharmacologically, C22:6 NAT accumulated in bile and reduced high fat diet-induced, but not sucrose-induced, hepatic lipid accumulation in mice, suggesting that C22:6 NAT was a negative feedback mediator that limited excess intestinal lipid absorption. Thus, biliary omega-3 NATs may contribute to the hypotriglyceridemic mechanism of action of fish oil and could influence the design of more potent omega-3 fatty acid-based therapeutics.
    Keywords:  Endocrinology; Fatty acid oxidation; Gastroenterology; Lipoproteins
    DOI:  https://doi.org/10.1172/JCI143861
  30. Annu Rev Pathol. 2021 Jan 24. 16 323-349
      Unlike other cell types, B cells undergo multiple rounds of V(D)J recombination and hypermutation to evolve high-affinity antibodies. Reflecting high frequencies of DNA double-strand breaks, adaptive immune protection by B cells comes with an increased risk of malignant transformation. In addition, the vast majority of newly generated B cells express an autoreactive B cell receptor (BCR). Thus, B cells are under intense selective pressure to remove autoreactive and premalignant clones. Despite stringent negative selection, B cells frequently give rise to autoimmune disease and B cell malignancies. In this review, we discuss mechanisms that we term metabolic gatekeepers to eliminate pathogenic B cell clones on the basis of energy depletion. Chronic activation signals from autoreactive BCRs or transforming oncogenes increase energy demands in autoreactive and premalignant B cells. Thus, metabolic gatekeepers limit energy supply to levels that are insufficient to fuel either a transforming oncogene or hyperactive signaling from an autoreactive BCR.
    Keywords:  B cell; malignant transformation; metabolism; signaling; transcription
    DOI:  https://doi.org/10.1146/annurev-pathol-061020-050135
  31. Cancer Res. 2021 Jan 26. pii: canres.3020.2019. [Epub ahead of print]
      Cancer-specific metabolic phenotypes and their vulnerabilities represent a viable area of cancer research. In this study, we explored the association of breast cancer subtypes with different metabolic phenotypes and identified isocitrate dehydrogenase 2 (IDH2) as a key player in triple-negative breast cancer (TNBC) and HER2. Functional assays combined with mass spectrometry-based analyses revealed the oncogenic role of IDH2 in cell proliferation, anchorage-independent growth, glycolysis, mitochondrial respiration, and antioxidant defense. Genome-scale metabolic modeling identified PHGDH and PSAT1 as the synthetic dosage lethal (SDL) partners of IDH2. In agreement, CRISPR-Cas9 knockout of PHGDH and PSAT1 showed the essentiality of serine biosynthesis proteins in IDH2-high cells. The clinical significance of the SDL interaction was supported by patients with IDH2-high/PHGDH-low tumors, who exhibited longer survival than patients with IDH2-high/PHGDH-high tumors. Furthermore, PHGDH inhibitors were effective in treating IDH2-high cells in vitro and in vivo. Altogether, our study creates a new link between two known cancer regulators and emphasizes PHGDH as a promising target for TNBC with IDH2 overexpression.
    DOI:  https://doi.org/10.1158/0008-5472.CAN-19-3020
  32. Cancers (Basel). 2021 Jan 23. pii: 425. [Epub ahead of print]13(3):
      With most cancer-related deaths resulting from metastasis, the development of new therapeutic approaches against metastatic colorectal cancer (mCRC) is essential to increasing patient survival. The metabolic adaptations that support mCRC remain undefined and their elucidation is crucial to identify potential therapeutic targets. Here, we employed a strategy for the rational identification of targetable metabolic vulnerabilities. This strategy involved first a thorough metabolic characterisation of same-patient-derived cell lines from primary colon adenocarcinoma (SW480), its lymph node metastasis (SW620) and a liver metastatic derivative (SW620-LiM2), and second, using a novel multi-omics integration workflow, identification of metabolic vulnerabilities specific to the metastatic cell lines. We discovered that the metastatic cell lines are selectively vulnerable to the inhibition of cystine import and folate metabolism, two key pathways in redox homeostasis. Specifically, we identified the system xCT and MTHFD1 genes as potential therapeutic targets, both individually and combined, for combating mCRC.
    Keywords:  colorectal cancer; genome-scale metabolic models; metastasis; redox metabolism
    DOI:  https://doi.org/10.3390/cancers13030425
  33. Commun Biol. 2021 Jan 29. 4(1): 142
      The genetic and metabolic heterogeneity of RAS-driven cancers has confounded therapeutic strategies in the clinic. To address this, rapid and genetically tractable animal models are needed that recapitulate the heterogeneity of RAS-driven cancers in vivo. Here, we generate a Drosophila melanogaster model of Ras/Lkb1 mutant carcinoma. We show that low-level expression of oncogenic Ras (RasLow) promotes the survival of Lkb1 mutant tissue, but results in autonomous cell cycle arrest and non-autonomous overgrowth of wild-type tissue. In contrast, high-level expression of oncogenic Ras (RasHigh) transforms Lkb1 mutant tissue resulting in lethal malignant tumors. Using simultaneous multiview light-sheet microcopy, we have characterized invasion phenotypes of Ras/Lkb1 tumors in living larvae. Our molecular analysis reveals sustained activation of the AMPK pathway in malignant Ras/Lkb1 tumors, and demonstrate the genetic and pharmacologic dependence of these tumors on CaMK-activated Ampk. We further show that LKB1 mutant human lung adenocarcinoma patients with high levels of oncogenic KRAS exhibit worse overall survival and increased AMPK activation. Our results suggest that high levels of oncogenic KRAS is a driving event in the malignant transformation of LKB1 mutant tissue, and uncovers a vulnerability that may be used to target this aggressive genetic subset of RAS-driven tumors.
    DOI:  https://doi.org/10.1038/s42003-021-01663-8
  34. Trends Cancer. 2021 Jan 23. pii: S2405-8033(21)00016-9. [Epub ahead of print]
      The molecular elements that govern cellular transformation and tumorigenic competence remain poorly understood. Metabolic reprogramming has emerged as a hallmark of malignant transformation. Recently in Cell Metabolism, Zhang et al. showed that an increase of cellular antioxidant capacity and nucleotide availability is sufficient to induce oncogenic transformation and tumorigenesis.
    DOI:  https://doi.org/10.1016/j.trecan.2021.01.003
  35. Int J Mol Sci. 2021 Jan 24. pii: 1131. [Epub ahead of print]22(3):
      Coenzyme A (CoA) is an essential cofactor present in all living cells. Under physiological conditions, CoA mainly functions to generate metabolically active CoA thioesters, which are indispensable for cellular metabolism, the regulation of gene expression, and the biosynthesis of neurotransmitters. When cells are exposed to oxidative or metabolic stress, CoA acts as an important cellular antioxidant that protects protein thiols from overoxidation, and this function is mediated by protein CoAlation. CoA and its derivatives are strictly maintained at levels controlled by nutrients, hormones, metabolites, and cellular stresses. Dysregulation of their biosynthesis and homeostasis has deleterious consequences and has been noted in a range of pathological conditions, including cancer, diabetes, Reye's syndrome, cardiac hypertrophy, and neurodegeneration. The biochemistry of CoA biosynthesis, which involves five enzymatic steps, has been extensively studied. However, the existence of a CoA biosynthetic complex and the mode of its regulation in mammalian cells are unknown. In this study, we report the assembly of all five enzymes that drive CoA biosynthesis, in HEK293/Pank1β and A549 cells, using the in situ proximity ligation assay. Furthermore, we show that the association of CoA biosynthetic enzymes is strongly upregulated in response to serum starvation and oxidative stress, whereas insulin and growth factor signaling downregulate their assembly.
    Keywords:  coenzyme A; coenzyme A biosynthesis; extracellular stimuli; oxidative stress
    DOI:  https://doi.org/10.3390/ijms22031131
  36. Semin Cancer Biol. 2021 Jan 21. pii: S1044-579X(21)00010-9. [Epub ahead of print]
      Cellular senescence, a stable form of cell cycle arrest, accompanied by pronounced secretory activity, has functional roles in both physiological and pathological conditions. Although senescence has been linked for a long time with cancer and ageing, recent studies have revealed a functional role of senescence in development, regeneration and reprogramming. Notably, the transient presence of senescent cells may be beneficial, in contrast to the potential deleterious effects of persistent senescence in aged or chronically damaged tissues. We will discuss how senescence contributes to embryonic development, cell plasticity and tissue regeneration, as a highly coordinated and programmed cellular state.
    Keywords:  Cellular senescence; Embryonic development; Placenta; Regeneration
    DOI:  https://doi.org/10.1016/j.semcancer.2021.01.004
  37. Adv Protein Chem Struct Biol. 2021 ;pii: S1876-1623(20)30062-6. [Epub ahead of print]123 27-47
      Cancer represents a global health concern, imposing a severe burden both from a societal and clinical perspective. Despite the latest advancements and achievements in the treatment and management of malignancy, cancer still imposes a dramatically high burden worldwide. Different theories (biophysical or biochemical, genetic or epigenetic) related to the origin of tumor cells have been put forth. These theories can also be subdivided into reductionist and emergentist/holistic theories. In the current overview, we will focus only on the cancer metabolic theory, one of the emergentist/holistic theories: it is holistic in that maintains that pathways, cascades and networks controlling energy metabolism, as well as those devoted to cell growth, cell cycle, replication, division and other cellular processes are highly interwoven and interconnected, and cannot be understood if not assuming a systems biology perspective. Cells should be seen as metabolic factories, in which metabolic fluxes and circuits (anabolic and catabolic) are plastically re-wired on the basis of the internal/external stimuli (cell make-up and genetic determinants, micro-environment, etc.). Complex regulatory and meta-regulatory systems exist that finely tune the functioning of cell, cell-cell communication and its interaction with the surrounding environment. At the tissue level, not all tissues share the same degree of metabolic plasticity (metabolic rigidity vs. metabolic flexibility), even though some metabolic coupling systems exist in order to guarantee an overall minimum extent of metabolic plasticity. The same broad picture of molecular events is necessary when describing the impairment and dysregulation of these processes, leading to multi-stage phenomena, including carcinogenesis.
    Keywords:  Bioenergetics; Cancer theories; Metabolic fluxes; Metabolic plasticity; Transport proteins involved in metabolism
    DOI:  https://doi.org/10.1016/bs.apcsb.2020.09.001
  38. Immunity. 2021 Jan 20. pii: S1074-7613(21)00001-7. [Epub ahead of print]
      CRISPR-Cas9 genome engineering has increased the pace of discovery for immunology and cancer biology, revealing potential therapeutic targets and providing insight into mechanisms underlying resistance to immunotherapy. However, endogenous immune recognition of Cas9 has limited the applicability of CRISPR technologies in vivo. Here, we characterized immune responses against Cas9 and other expressed CRISPR vector components that cause antigen-specific tumor rejection in several mouse cancer models. To avoid unwanted immune recognition, we designed a lentiviral vector system that allowed selective CRISPR antigen removal (SCAR) from tumor cells. The SCAR system reversed immune-mediated rejection of CRISPR-modified tumor cells in vivo and enabled high-throughput genetic screens in previously intractable models. A pooled in vivo screen using SCAR in a CRISPR-antigen-sensitive renal cell carcinoma revealed resistance pathways associated with autophagy and major histocompatibility complex class I (MHC class I) expression. Thus, SCAR presents a resource that enables CRISPR-based studies of tumor-immune interactions and prevents unwanted immune recognition of genetically engineered cells, with implications for clinical applications.
    Keywords:  CRISPR; Natural Killer cells; antigen presentation; checkpoint blockade; immuno-oncology; immunotherapy; in vivo screen; lentiviral vectors; pooled screen; target discovery
    DOI:  https://doi.org/10.1016/j.immuni.2021.01.001
  39. Am J Physiol Renal Physiol. 2021 Jan 25.
      Nrf2 and HIF1αtranscription factors protect against ischemicacute kidney injury (AKI) by upregulating metabolic and cytoprotective gene expression. In this study, we tested the hypothesis that Nrf2 is required for HIF1α-mediated hypoxic responses using Nrf2-sufficient (WT) and Nrf2-deficient (Nrf2-/-) primary murine kidney tubular epithelial cells (RTECs) and human immortalized tubular epithelial cells (HK2 cells) with HIF1 inhibition and activation. HIF1 pathway inhibitor digoxin blocked hypoxia-stimulated HIF1α activation and heme oxygenase (HMOX1) expression in HK2 cells. Hypoxia mimicking CoCl2 stimulated HMOX1 expression was significantly lower in Nrf2-/- RTECs than in WT counterparts. Similarly, hypoxia-stimulated HIF1α-dependent metabolic gene expression was markedly impaired in Nrf2-/- RTECs. Nrf2 deficiency impaired hypoxia-induced HIF1α stabilization independent of increased prolyl 4-hydroxylase gene expression. We found decreased HIF1α mRNA levels in Nrf2-/- RTECs both in normoxia and hypoxia-reoxygenation conditions. In silico analysis and chromatin immunoprecipitation assays demonstrated Nrf2 binding to the HIF1α promoter in normoxia, but its binding decreased in hypoxia exposed HK2 cells. However, Nrf2 binding at the HIF1α promoter was enriched following reoxygenation demonstrating that Nrf2 maintains constitutive HIF1α expression. Consistent with this result, we found decreased levels of Nrf2 in hypoxia and that were restored following reoxygenation. Inhibition of mitochondrial complex I prevented hypoxia-induced Nrf2 downregulation and also increased basal Nrf2 levels. These results demonstrate a crucial role for Nrf2 in optimal HIF1α activation in hypoxia, that mitochondrial signaling downregulates Nrf2 levels in hypoxia whereas reoxygenation restores it. Nrf2 and HIF1α interact toprovide optimal metabolic and cytoprotective responses in ischemic AKI.
    Keywords:  Acute kidney injury; HIF1α; Nrf2; ischemic reperfusion; mitochondria
    DOI:  https://doi.org/10.1152/ajprenal.00501.2020
  40. Free Radic Biol Med. 2021 Jan 22. pii: S0891-5849(21)00043-5. [Epub ahead of print]
      Iron is an essential micronutrient metal for cellular functions but can generate highly reactive oxygen species resulting in oxidative damage. For these reasons its uptake and metabolism is highly regulated. A small but dynamic fraction of ferrous iron inside the cell, termed intracellular labile iron, is redox-reactive and ready to participate multiples reactions of intracellular enzymes. Due to its nature its determination and precise quantification has been a roadblock. However, recent progress in the development of intracellular labile iron probes are allowing the reevaluation of our current understanding and unmasking new functions. The role of intracellular labile iron in regulating the epigenome was recently discovered. This chapter examine how intracellular labile iron can modulate histone and DNA demethylation and how its pool can mediate a signaling pathway from cAMP serving as a sensor of the metabolic needs of the cells.
    Keywords:  DNA methylation; G-protein coupled receptor; Histone methylation; Intracellular labile Fe(II); Iron; JmjC domain-containing demethylases; RapGEF2; Reactive oxygen species; TET methylcytosine Dioxygenases; cAMP
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2021.01.026
  41. Philos Trans R Soc Lond B Biol Sci. 2021 Mar 15. 376(1820): 20190758
      All living cells interact dynamically with a constantly changing world. Eukaryotes, in particular, evolved radically new ways to sense and react to their environment. These advances enabled new and more complex forms of cellular behaviour in eukaryotes, including directional movement, active feeding, mating, and responses to predation. But what are the key events and innovations during eukaryogenesis that made all of this possible? Here we describe the ancestral repertoire of eukaryotic excitability and discuss five major cellular innovations that enabled its evolutionary origin. The innovations include a vastly expanded repertoire of ion channels, the emergence of cilia and pseudopodia, endomembranes as intracellular capacitors, a flexible plasma membrane and the relocation of chemiosmotic ATP synthesis to mitochondria, which liberated the plasma membrane for more complex electrical signalling involved in sensing and reacting. We conjecture that together with an increase in cell size, these new forms of excitability greatly amplified the degrees of freedom associated with cellular responses, allowing eukaryotes to vastly outperform prokaryotes in terms of both speed and accuracy. This comprehensive new perspective on the evolution of excitability enriches our view of eukaryogenesis and emphasizes behaviour and sensing as major contributors to the success of eukaryotes. This article is part of the theme issue 'Basal cognition: conceptual tools and the view from the single cell'.
    Keywords:  cilia; eukaryogenesis; excitability; membranes; motility; protists
    DOI:  https://doi.org/10.1098/rstb.2019.0758
  42. Autophagy. 2021 Jan 26. 1-3
      Lysosomes play an essential role in quality control mechanisms by functioning as the primary digestive system in mammalian cells. However, the quality control mechanisms governing healthy lysosomes are not fully understood. Using a method to study lysosome membrane turnover, we discovered that LC3-lipidation on the lysosome limiting membrane is involved in invagination and formation of intralumenal vesicles, an activity known as microautophagy. This activity occurs in response to metabolic stress, in the form of glucose starvation, or osmotic stress induced by treatment with lysosomotropic compounds. Cells rendered deficient in the ability to lipidate LC3 through knockout of ATG5 show reduced ability to regulate lysosome size and degradative function in response to stress. These findings demonstrate that cells can adapt to changing metabolic conditions by turning over selective portions of the lysosomal membrane, using a mechanism that involves lysosome-targeted LC3 lipidation and the induction of selective microautophagy.
    Keywords:  ATG5; LC3; autophagy; lysophagy; microautophagy
    DOI:  https://doi.org/10.1080/15548627.2021.1877935
  43. Cancer Cell. 2021 Jan 27. pii: S1535-6108(21)00054-4. [Epub ahead of print]
      Pathologists use histological features to classify tumors and assign site of origin for metastasis. How and why tumors organize the way they do and recreate their histological organization during metastasis is unknown. Here, I discuss the concept of "histostasis" conferring tumors a histological memory and hypothesize its implications for metastasis.
    DOI:  https://doi.org/10.1016/j.ccell.2021.01.010
  44. Cancer Drug Resist. 2020 ;3 762-774
      At the forefront of cancer research is the rapidly evolving understanding of metabolic reprogramming within cancer cells. The expeditious adaptation to metabolic inhibition allows cells to evolve and acquire resistance to targeted treatments, which makes therapeutic exploitation complex but achievable. 3-phosphoglycerate dehydrogenase (PHGDH) is the rate-limiting enzyme of de novo serine biosynthesis and is highly expressed in a variety of cancers, including breast cancer, melanoma, and Ewing's sarcoma. This review will investigate the role of PHGDH in normal biological processes, leading to the role of PHGDH in the progression of cancer. With an understanding of the molecular mechanisms by which PHGDH expression advances cancer growth, we will highlight the known mechanisms of resistance to cancer therapeutics facilitated by PHGDH biology and identify avenues for combatting PHGDH-driven resistance with inhibitors of PHGDH to allow for the development of effective metabolic therapies.
    Keywords:  PHGDH; cancer; drug resistance; folate cycle; metabolism; one-carbon metabolism; serine
    DOI:  https://doi.org/10.20517/cdr.2020.46
  45. Aging (Albany NY). 2021 Jan 20. 12
      Previous studies have reported the association between branched-chain amino acid trasaminase1 (BCAT1) and IDH1 wild-type gliomas. Nonetheless, as a promising target for treatment of primary glioblastoma, comprehensive reports on BCAT1 in gliomas are still lacking. In the present study, we accessed glioma patient cohorts and tissue microarray to evaluate the expression pattern of BCAT1 for determining its prognostic value and its relationship with IDH1 mutation status. Furthermore, we explored the potential regulatory mechanism of BCAT1 in gliomas by comparing the BCAT1 mRNA expression pattern with selected tumor biological signatures. The results showed that BCAT1 is highly expressed in GBM versus lower grade gliomas and could represent the poor survival of IDH1 wild-type gliomas. Moreover, BCAT1 is an independent prognostic factor for glioma patients, high BCAT1 expression is related to unfavorable clinical parameters including older age, IDH wildtype, no 1p/19q codeletion, ATRX wildtype and MGMT unmethylated. Additionally, BCAT1 correlated with apoptosis, hypoxia and angiogenesis processes in gliomas and high expression of BCAT1 revealed higher glycolysis level and increased immunosuppressive status in tumor progression. We concluded that BCAT1 is a strong prognostic factor for glioma patients and involved in the malignant progression of IDH1 wild-type gliomas.
    Keywords:  IDH1; branched chain amino acid transaminase 1; glioma; prognosis
    DOI:  https://doi.org/10.18632/aging.202328