bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2021‒05‒23
fifty-one papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Cell Metab. 2021 May 17. pii: S1550-4131(21)00183-2. [Epub ahead of print]
      Mitochondria control eukaryotic cell fate by producing the energy needed to support life and the signals required to execute programed cell death. The biochemical milieu is known to affect mitochondrial function and contribute to the dysfunctional mitochondrial phenotypes implicated in cancer and the morbidities of aging. However, the physical characteristics of the extracellular matrix are also altered in cancerous and aging tissues. Here, we demonstrate that cells sense the physical properties of the extracellular matrix and activate a mitochondrial stress response that adaptively tunes mitochondrial function via solute carrier family 9 member A1-dependent ion exchange and heat shock factor 1-dependent transcription. Overall, our data indicate that adhesion-mediated mechanosignaling may play an unappreciated role in the altered mitochondrial functions observed in aging and cancer.
    Keywords:  UPRmt; adhesion; aging; cancer; extracellular matrix; mechanical stress; mechanotabolism; metabolism; oxidative stress; tension
    DOI:  https://doi.org/10.1016/j.cmet.2021.04.017
  2. J Cell Sci. 2020 Jan 01. pii: jcs.247957. [Epub ahead of print]
      In response to environmental stimuli, macrophages change their nutrient consumption and undergo an early metabolic adaptation that progressively shapes their polarization state. During the transient, early phase of pro-inflammatory macrophage activation, an increase in tricarboxylic acid (TCA) cycle activity has been reported but the relative contribution of branched chain amino acid (BCAA) leucine remain to be determined. Here we show that glucose but not glutamine is a major contributor of the increase in TCA cycle metabolites during early macrophage activation in humans. We then show that, although BCAA uptake is not altered, their transamination by BCAT1 is increased following 8h lipopolysaccharide (LPS) stimulation. Of note, leucine is not metabolized to integrate the TCA cycle in neither basal nor stimulated human macrophages. Surprisingly, the pharmacological inhibition of BCAT1 reduced glucose-derived itaconate, α-ketoglutarate, and 2-hydroxyglutarate levels, without affecting succinate and citrate levels, indicating a partial inhibition of TCA cycle. This indirect effect is associated with NRF2 activation and anti-oxidant responses. These results suggest a moonlighting role of BCAT1 through redox-mediated control of mitochondrial function during early macrophage activation.
    Keywords:  BCAT1; Immunometabolism; Macrophages; Mitochondria; Redox biology; TCA cycle
    DOI:  https://doi.org/10.1242/jcs.247957
  3. Dis Model Mech. 2020 Jan 01. pii: dmm.045898. [Epub ahead of print]
      L-2-hydroxyglutarate (L-2HG) is an oncometabolite found elevated in renal tumors. However, this molecule may have physiologic roles that extend beyond its association with cancer as L-2HG levels are elevated in response to hypoxia and during Drosophila larval development. L-2HG is known to be metabolized by L-2HG dehydrogenase (L2HGDH), and loss of L2HGDH leads to elevated L-2HG levels. Despite being highly expressed in the kidney, L2HGDH's role in renal metabolism has not been explored. Here, we report our findings utilizing a novel CRISPR/Cas9 murine knockout model with a specific focus on the role of L2HGDH in the kidney. Histologically, L2hgdh KO kidneys have no demonstrable histologic abnormalities. However, GC/MS metabolomics demonstrates significantly reduced levels of the TCA cycle intermediate succinate in multiple tissues. Isotope labeling studies with [U-13C] glucose demonstrate that restoration of L2HGDH in renal cancer cells (which lowers L-2HG) leads to enhanced incorporation of label into TCA cycle intermediates. Subsequent biochemical studies demonstrate that L-2HG can inhibit the TCA cycle enzyme α-ketoglutarate dehydrogenase. Bioinformatic analysis of mRNA expression data from renal tumors demonstrates that L2HGDH is co-expressed with genes encoding TCA cycle enzymes as well as the gene encoding the transcription factor PGC-1α, which is known to regulate mitochondrial metabolism. Restoration of PGC-1α in renal tumor cells results in increased L2HGDH expression with a concomitant reduction if L-2HG levels. Collectively, our studies provide new insight into the physiologic role for L2HGDH as well as mechanisms that promote L-2HG accumulation in disease states.
    Keywords:  L-2-Hydroxyglutarate Dehydrogenase; L-2-hydroxyglutarate; PPARG coactivator 1-α; TCA cycle
    DOI:  https://doi.org/10.1242/dmm.045898
  4. J Biol Chem. 2021 May 14. pii: S0021-9258(21)00573-1. [Epub ahead of print] 100780
      Macroautophagy (hereafter, autophagy) is a process that directs the degradation of cytoplasmic material in lysosomes. In addition to its homeostatic roles, autophagy undergoes dynamic positive and negative regulation in response to multiple forms of cellular stress, thus enabling the survival of cells. However, the precise mechanisms of autophagy regulation are not fully understood. To identify potential negative regulators of autophagy, we performed a genome-wide CRISPR screen using the quantitative autophagic flux reporter GFP-LC3-RFP. We identified phosphoribosylformylglycinamidine synthase (PFAS), a component of the de novo purine synthesis pathway, as one such negative regulator of autophagy. Autophagy was activated in cells lacking PFAS or phosphoribosyl pyrophosphate amidotransferase (PPAT), another de novo purine synthesis enzyme, or treated with methotrexate when exogenous levels of purines were insufficient. Purine starvation-induced autophagy activation was concomitant with mTORC1 suppression, and was profoundly suppressed in cells deficient for TSC2, which negatively regulates mTORC1 through inhibition of RHEB, suggesting that purines regulate autophagy through the TSC-RHEB-mTORC1 signaling axis. Moreover, depletion of the pyrimidine synthesis enzymes carbamoyl-phosphate synthetase 2, aspartate transcarbamylase, and dihydroorotase (CAD) and dihydroorotate dehydrogenase (DHODH) activated autophagy as well, although mTORC1 activity was not altered by pyrimidine shortage. These results suggest a different mechanism of autophagy induction between purine and pyrimidine starvation. These findings provide novel insights into the regulation of autophagy by nucleotides and possibly the role of autophagy in nucleotide metabolism, leading to further developing anticancer strategies involving nucleotide synthesis and autophagy.
    Keywords:  CRISPR/Cas; mammalian target of rapamycin (mTOR); nucleoside/nucleotide biosynthesis; nucleoside/nucleotide metabolism; nucleotide; phosphoribosylformylglycinamidine synthase (PFAS); tuberous sclerosis complex (TSC)
    DOI:  https://doi.org/10.1016/j.jbc.2021.100780
  5. EMBO Mol Med. 2021 May 20. e13579
      Mutations in OPA1 cause autosomal dominant optic atrophy (DOA) as well as DOA+, a phenotype characterized by more severe neurological deficits. OPA1 deficiency causes mitochondrial fragmentation and also disrupts cristae, respiration, mitochondrial DNA (mtDNA) maintenance, and cell viability. It has not yet been established whether phenotypic severity can be modulated by genetic modifiers of OPA1. We screened the entire known mitochondrial proteome (1,531 genes) to identify genes that control mitochondrial morphology using a first-in-kind imaging pipeline. We identified 145 known and novel candidate genes whose depletion promoted elongation or fragmentation of the mitochondrial network in control fibroblasts and 91 in DOA+ patient fibroblasts that prevented mitochondrial fragmentation, including phosphatidyl glycerophosphate synthase (PGS1). PGS1 depletion reduces CL content in mitochondria and rebalances mitochondrial dynamics in OPA1-deficient fibroblasts by inhibiting mitochondrial fission, which improves defective respiration, but does not rescue mtDNA depletion, cristae dysmorphology, or apoptotic sensitivity. Our data reveal that the multifaceted roles of OPA1 in mitochondria can be functionally uncoupled by modulating mitochondrial lipid metabolism, providing novel insights into the cellular relevance of mitochondrial fragmentation.
    Keywords:  OPA1; genetic modifiers; high-throughput screening; mitochondrial dynamics; phospholipid metabolism
    DOI:  https://doi.org/10.15252/emmm.202013579
  6. Front Physiol. 2021 ;12 669497
      Aging is a process that can be accompanied by molecular and cellular alterations that compromise cardiac function. Although other metabolic disorders with increased prevalence in aged populations, such as diabetes mellitus, dyslipidemia, and hypertension, are associated with cardiovascular complications; aging-related cardiomyopathy has some unique features. Healthy hearts oxidize fatty acids, glucose, lactate, ketone bodies, and amino acids for producing energy. Under physiological conditions, cardiac mitochondria use fatty acids and carbohydrate mainly to generate ATP, 70% of which is derived from fatty acid oxidation (FAO). However, relative contribution of nutrients in ATP synthesis is altered in the aging heart with glucose oxidation increasing at the expense of FAO. Cardiac aging is also associated with impairment of mitochondrial abundance and function, resulting in accumulation of reactive oxygen species (ROS) and activation of oxidant signaling that eventually leads to further mitochondrial damage and aggravation of cardiac function. This review summarizes the main components of pathophysiology of cardiac aging, which pertain to cardiac metabolism, mitochondrial function, and systemic metabolic changes that affect cardiac function.
    Keywords:  autophagy; carbohydrate metabolism; cardiac aging; fatty acid oxidation; ketone bodies; mitochondria
    DOI:  https://doi.org/10.3389/fphys.2021.669497
  7. BMC Biol. 2021 May 17. 19(1): 102
      BACKGROUND: Environmental stimuli experienced by the parental generation influence the phenotype of subsequent generations (Demoinet et al., Proc Natl Acad Sci U S A 114:E2689-E2698, 2017; Burton et al., Nat Cell Biol 19:252-257, 2017; Agrawal et al., Nature 401:60-63, 1999). The effects of these stimuli on the parental generation may be passed through the germline, but the mechanisms at the basis of this non-Mendelian type of inheritance, their level of conservation, how they lead to adaptive vs non-adaptive, and intergenerational vs transgenerational inheritance are poorly understood. Here we show that modulation of nutrient-sensing pathways in the parental generation of the nematode Auanema freiburgensis regulates phenotypic plasticity of its offspring.RESULTS: In response to con-specific pheromones indicative of stress, AMP-activated protein kinase (AMPK), mechanistic target of rapamycin complex 1 (mTORC1), and insulin signaling regulate stress resistance and sex determination across one generation, and these effects can be mimicked by pathway modulators. The effectors of these pathways are closely associated with the chromatin, and their regulation affects the chromatin acetylation status in the germline.
    CONCLUSION: These results suggest that highly conserved metabolic sensors regulate phenotypic plasticity through regulation of subcellular localization of their effectors, leading to changes in chromatin acetylation and epigenetic status of the germline.
    Keywords:  AMPK; Auanema; C. elegans; Dauer; Histone acetylation; Intergenerational inheritance; Sex determination; Transgenerational inheritance; nematode
    DOI:  https://doi.org/10.1186/s12915-021-01032-1
  8. J Cell Physiol. 2021 May 18.
      Autophagy is primarily a homeostatic and catabolic process that is increasingly being recognized to have a pivotal role in the initiation and maintenance of cancer cells, as well as in the emergence of therapeutic resistance. Moreover, in the tumor microenvironment (TME) autophagy plays a crucial and sometimes dichotomous role in tumor progression. Recent studies show that during the early stages of tumor initiation, autophagy suppresses tumorigenesis. However, in the advanced stage of tumorigenesis, autophagy promotes cancer progression by protecting cancer cells against stressful conditions and therapeutic assault. Specifically, in cancer-associated fibroblasts (CAFs), autophagy promotes tumorigenesis not only by providing nutrients to the cancerous cells but also by inducing epithelial to mesenchymal transition, angiogenesis, stemness, and metastatic dissemination of the cancer cells, whereas in the immune cells, autophagy induces the tumor-localized immune response. In the TME, CAFs play a crucial role in cancer cell metabolism, immunoreaction, and growth. Therefore, targeting autophagy in CAFs by several pharmacological inducers like rapamycin or the inhibitor such as chloroquine has gained importance in preclinical and clinical trials. In the present review, we summarized the basic mechanism of autophagy in CAFs along with its role in driving tumorigenic progression through several emerging as well as classical hallmarks of cancer. We also addressed various autophagy inducers as well as inhibitors of autophagy for more efficient cancer management. Eventually, we prioritized some of the outstanding issues that must be addressed with utmost priority in the future to elucidate the role of autophagy in CAFs on tumor progression and therapeutic intervention.
    Keywords:  autophagy; cancer associated fibroblast; therapy resistance; tumor microenvironment; tumorigenesis
    DOI:  https://doi.org/10.1002/jcp.30419
  9. Cell Death Dis. 2021 May 19. 12(6): 511
      MYCN amplification is tightly associated with the poor prognosis of pediatric neuroblastoma (NB). The regulation of NB cell death by MYCN represents an important aspect, as it directly contributes to tumor progression and therapeutic resistance. However, the relationship between MYCN and cell death remains elusive. Ferroptosis is a newly identified cell death mode featured by lipid peroxide accumulation that can be attenuated by GPX4, yet whether and how MYCN regulates ferroptosis are not fully understood. Here, we report that MYCN-amplified NB cells are sensitive to GPX4-targeting ferroptosis inducers. Mechanically, MYCN expression reprograms the cellular iron metabolism by upregulating the expression of TFRC, which encodes transferrin receptor 1 as a key iron transporter on the cell membrane. Further, the increased iron uptake promotes the accumulation of labile iron pool, leading to enhanced lipid peroxide production. Consistently, TFRC overexpression in NB cells also induces selective sensitivity to GPX4 inhibition and ferroptosis. Moreover, we found that MYCN fails to alter the general lipid metabolism and the amount of cystine imported by System Xc(-) for glutathione synthesis, both of which contribute to ferroptosis in alternative contexts. In conclusion, NB cells harboring MYCN amplification are prone to undergo ferroptosis conferred by TFRC upregulation, suggesting that GPX4-targeting ferroptosis inducers or TFRC agonists can be potential strategies in treating MYCN-amplified NB.
    DOI:  https://doi.org/10.1038/s41419-021-03790-w
  10. J Cell Sci. 2020 Jan 01. pii: jcs.237917. [Epub ahead of print]
      Heme is a cofactor and signaling molecule that is essential for much of aerobic life. All heme-dependent processes in eukaryotes require that heme is trafficked from its site of synthesis in the mitochondria to hemoproteins located throughout the cell. However, the mechanisms governing the mobilization of heme out of the mitochondria, and the spatio-temporal dynamics of these processes, are poorly understood. Herein, using genetically encoded fluorescent heme sensors, we developed a live cell assay to monitor heme distribution dynamics between the mitochondrial inner-membrane, where heme is synthesized, and the mitochondrial matrix, cytosol, and nucleus. Surprisingly, heme trafficking to the nucleus is ∼25% faster than to the cytosol or mitochondrial matrix, which are nearly identical, potentially supporting a role for heme as a mitochondrial-nuclear retrograde signal. Moreover, we discovered that the heme synthetic enzyme, 5-aminolevulinic acid synthase (ALAS), and GTPases in control of the mitochondrial dynamics machinery, Mgm1 and Dnm1, and ER contact sites, Gem1, regulate the flow of heme between the mitochondria and nucleus. Overall, our results indicate that there are parallel pathways for the distribution of bioavailable heme.
    Keywords:  Heme; Heme transport; Mitochondrial dynamics; Yeast
    DOI:  https://doi.org/10.1242/jcs.237917
  11. Front Cell Dev Biol. 2021 ;9 606639
      Over the years, Drosophila has served as a wonderful genetically tractable model system to unravel various facets of tissue-resident stem cells in their microenvironment. Studies in different stem and progenitor cell types of Drosophila have led to the discovery of cell-intrinsic and extrinsic factors crucial for stem cell state and fate. Though initially touted as the ATP generating machines for carrying various cellular processes, it is now increasingly becoming clear that mitochondrial processes alone can override the cellular program of stem cells. The last few years have witnessed a surge in our understanding of mitochondria's contribution to governing different stem cell properties in their subtissular niches in Drosophila. Through this review, we intend to sum up and highlight the outcome of these in vivo studies that implicate mitochondria as a central regulator of stem cell fate decisions; to find the commonalities and uniqueness associated with these regulatory mechanisms.
    Keywords:  Drosophila; differentiation; maintenance; metabolism; mitochondria; regulation; stem cell
    DOI:  https://doi.org/10.3389/fcell.2021.606639
  12. Curr Biol. 2021 May 14. pii: S0960-9822(21)00609-6. [Epub ahead of print]
      Mutations in Vps13D cause defects in autophagy, clearance of mitochondria, and human movement disorders. Here, we discover that Vps13D functions in a pathway downstream of Vmp1 and upstream of Marf/Mfn2. Like vps13d, vmp1 mutant cells exhibit defects in autophagy, mitochondrial size, and clearance. Through the relationship between vmp1 and vps13d, we reveal a novel role for Vps13D in the regulation of mitochondria and endoplasmic reticulum (ER) contact. Significantly, the function of Vps13D in mitochondria and ER contact is conserved between fly and human cells, including fibroblasts derived from patients suffering from VPS13D mutation-associated neurological symptoms. vps13d mutants have increased levels of Marf/MFN2, a regulator of mitochondrial fusion. Importantly, loss of marf/MFN2 suppresses vps13d mutant phenotypes, including mitochondria and ER contact. These findings indicate that Vps13d functions at a regulatory point between mitochondria and ER contact, mitochondrial fusion and autophagy, and help to explain how Vps13D contributes to disease.
    Keywords:  Drosophila; Vmp1; Vps13D; autophagy; membrane contact; mitochondria
    DOI:  https://doi.org/10.1016/j.cub.2021.04.062
  13. Dis Model Mech. 2020 Jan 01. pii: dmm.044925. [Epub ahead of print]
      The conserved B-subunit of succinate dehydrogenase (SDH) participates in the TCA cycle and mitochondrial electron transport. The Arg230His mutation in SDHB causes heritable pheochromocytoma/paraganglioma (PPGL). In C. elegans, we generated an in vivo PPGL model (SDHB-1 Arg244His; equivalent to human Arg230His) which manifests delayed development, shortened lifespan, attenuated ATP production and reduced mitochondrial number. Although succinate is elevated in both missense and null sdhb-1(gk165) mutants, transcriptomic comparison suggests very different causal mechanisms that are supported by metabolic analysis where only Arg244His (not null) worms elevate lactate/pyruvate levels, pointing to a missense-induced, 'Warburg'-like aberrant glycolysis. In silico predictions of the SDHA-B dimer structure demonstrate that Arg230His modifies the catalytic cleft despite the latter's remoteness from the mutation site. We hypothesise that Arg230His SDHB mutation rewires metabolism, reminiscent of metabolic reprogramming in cancer. Our tractable model provides a novel tool to investigate the metastatic propensity of this familial cancer and our approach may illuminate wider SDH pathology.
    Keywords:  C. elegans; Cancer; Familial Paraganglioma Syndrome (FPS); Succinate dehydrogenase; TCA cycle; Warburg-like glycolysis
    DOI:  https://doi.org/10.1242/dmm.044925
  14. Cancer Metab. 2021 May 19. 9(1): 24
      BACKGROUND: Neuroblastoma accounts for 7% of paediatric malignancies but is responsible for 15% of all childhood cancer deaths. Despite rigorous treatment involving chemotherapy, surgery, radiotherapy and immunotherapy, the 5-year overall survival rate of high-risk disease remains < 40%, highlighting the need for improved therapy. Since neuroblastoma cells exhibit aberrant metabolism, we determined whether their sensitivity to radiotherapy could be enhanced by drugs affecting cancer cell metabolism.METHODS: Using a panel of neuroblastoma and glioma cells, we determined the radiosensitising effects of inhibitors of glycolysis (2-DG) and mitochondrial function (metformin). Mechanisms underlying radiosensitisation were determined by metabolomic and bioenergetic profiling, flow cytometry and live cell imaging and by evaluating different treatment schedules.
    RESULTS: The radiosensitising effects of 2-DG were greatly enhanced by combination with the antidiabetic biguanide, metformin. Metabolomic analysis and cellular bioenergetic profiling revealed this combination to elicit severe disruption of key glycolytic and mitochondrial metabolites, causing significant reductions in ATP generation and enhancing radiosensitivity. Combination treatment induced G2/M arrest that persisted for at least 24 h post-irradiation, promoting apoptotic cell death in a large proportion of cells.
    CONCLUSION: Our findings demonstrate that the radiosensitising effect of 2-DG was significantly enhanced by its combination with metformin. This clearly demonstrates that dual metabolic targeting has potential to improve clinical outcomes in children with high-risk neuroblastoma by overcoming radioresistance.
    Keywords:  131I-MIBG; 2-DG; Metabolism; Metformin; Neuroblastoma; Radiation
    DOI:  https://doi.org/10.1186/s40170-021-00258-5
  15. Sci Transl Med. 2021 May 19. pii: eabd1869. [Epub ahead of print]13(594):
      Although the role of hydrophilic antioxidants in the development of hepatic insulin resistance and nonalcoholic fatty liver disease has been well studied, the role of lipophilic antioxidants remains poorly characterized. A known lipophilic hydrogen peroxide scavenger is bilirubin, which can be oxidized to biliverdin and then reduced back to bilirubin by cytosolic biliverdin reductase. Oxidation of bilirubin to biliverdin inside mitochondria must be followed by the export of biliverdin to the cytosol, where biliverdin is reduced back to bilirubin. Thus, the putative mitochondrial exporter of biliverdin is expected to be a major determinant of bilirubin regeneration and intracellular hydrogen peroxide scavenging. Here, we identified ABCB10 as a mitochondrial biliverdin exporter. ABCB10 reconstituted into liposomes transported biliverdin, and ABCB10 deletion caused accumulation of biliverdin inside mitochondria. Obesity with insulin resistance up-regulated hepatic ABCB10 expression in mice and elevated cytosolic and mitochondrial bilirubin content in an ABCB10-dependent manner. Revealing a maladaptive role of ABCB10-driven bilirubin synthesis, hepatic ABCB10 deletion protected diet-induced obese mice from steatosis and hyperglycemia, improving insulin-mediated suppression of glucose production and decreasing lipogenic SREBP-1c expression. Protection was concurrent with enhanced mitochondrial function and increased inactivation of PTP1B, a phosphatase disrupting insulin signaling and elevating SREBP-1c expression. Restoration of cellular bilirubin content in ABCB10 KO hepatocytes reversed the improvements in mitochondrial function and PTP1B inactivation, demonstrating that bilirubin was the maladaptive effector linked to ABCB10 function. Thus, we identified a fundamental transport process that amplifies intracellular bilirubin redox actions, which can exacerbate insulin resistance and steatosis in obesity.
    DOI:  https://doi.org/10.1126/scitranslmed.abd1869
  16. Methods Mol Biol. 2021 ;2318 231-239
      The MYC gene regulates normal cell growth and is deregulated in many human cancers, contributing to tumor growth and progression. The MYC transcription factor activates RNA polymerases I, II, and III target genes that are considered housekeeping genes. These target genes are largely involved in ribosome biogenesis, fatty acid, protein and nucleotide synthesis, nutrient influx or metabolic waste efflux, glycolysis, and glutamine metabolism. MYC's function as a driver of cell growth has been revealed through RNA sequencing, genome-wide chromatin immunoprecipitation, proteomics, and importantly metabolomics, which is highlighted in this chapter.
    Keywords:  Cancer metabolism; MYC; Mass spectrometry; Metabolomics; Transcription
    DOI:  https://doi.org/10.1007/978-1-0716-1476-1_11
  17. Trends Pharmacol Sci. 2021 May 12. pii: S0165-6147(21)00072-9. [Epub ahead of print]
      TRAP1, the mitochondrial isoform of heat shock protein (Hsp)90 chaperones, is a key regulator of metabolism and organelle homeostasis in diverse pathological states. While selective TRAP1 targeting is an attractive goal, classical active-site-directed strategies have proved difficult, due to high active site conservation among Hsp90 paralogs. Here, we discuss advances in developing TRAP1-directed strategies, from lead modification with mitochondria delivery groups to the computational discovery of allosteric sites and ligands. Specifically, we address the unique opportunities that targeting TRAP1 opens up in tackling fundamental questions on its biology and in unveiling new therapeutic approaches. Finally, we show how crucial to this endeavor is our ability to predict the activities of TRAP1-selective allosteric ligands and to optimize target engagement to avoid side effects.
    Keywords:  drug design; mitochondrial proteostasis; molecular chaperones; molecular dynamics
    DOI:  https://doi.org/10.1016/j.tips.2021.04.003
  18. J Cell Sci. 2020 Jan 01. pii: jcs.237503. [Epub ahead of print]
      Glioblastoma (GBM) is one of the most malignant brain tumours, and despite advances in treatment modalities, it remains largely incurable. Calcium regulation and dynamics play crucial roles in different aspects of cancer, but they have never been investigated in detail in GBM. Here, we report that spontaneous calcium waves in GBM cells cause unusual [Ca2+]i elevations (>1 µM), often propagating through tumour microtubes (TMs) connecting adjacent cells. This unusual [Ca2+]i elevation is not associated with the induction of cell death and is concomitant with overexpression of mitochondrial calcium uniporter (MCU). Here, we show that MCU silencing decreases proliferation and alters [Ca2+]i dynamics in U87 GBM cells, while MCU overexpression increases [Ca2+]i elevation in human astrocytes (HA). These results suggest that changes in the expression level of MCU, a protein involved in intracellular calcium regulation, influences GBM cell proliferation, contributing to GBM malignancy.
    Keywords:  Calcium waves; Glioblastoma; MCU; Malignancy
    DOI:  https://doi.org/10.1242/jcs.237503
  19. Mol Oncol. 2021 May 18.
      Oncogenic KRAS mutations develop unique metabolic dependencies on nutrients to support tumor metabolism and cell proliferation. In particular, KRAS mutant cancer cells exploit amino acids (AAs) such as glutamine and leucine, to accelerate energy metabolism, redox balance through glutathione (GSH) synthesis and macromolecule biosynthesis. However, the identities of the amino acid transporters (AATs) that are prominently upregulated in KRAS mutant cancer cells, and the mechanism regulating their expression have not yet been systematically investigated. Here we report that the majority of the KRAS mutant colorectal cancer (CRC) cells upregulate selected AATs (SLC7A5/LAT1, SLC38A2/SNAT2 and SLC1A5/ASCT2), which correlates with enhanced uptake of AAs such as glutamine and leucine. Consistently, knockdown of oncogenic KRAS downregulated the expression of AATs, thereby decreasing the levels of amino acids taken up by CRC cells. Moreover, overexpression of mutant KRAS upregulated the expression of AATs (SLC7A5/LAT1, SLC38A2/SNAT2 and SLC1A5/ASCT2) in KRAS wild-type CRC cells and mouse embryonic fibroblasts (MEFs). In addition, we show that the YAP1 (Yes-associated protein 1) transcriptional coactivator accounts for increased expression of AATs and mTOR activation in KRAS mutant CRC cells. Specific knockdown of AATs by shRNAs or pharmacological blockage of AATs effectively inhibited AA uptake, mTOR activation and cell proliferation. Collectively, we conclude that oncogenic KRAS mutations enhance the expression of AATs via the hippo effector YAP1, leading to mTOR activation and CRC cell proliferation.
    Keywords:  Amino acid transporters; Oncogene; SLC1A5/ASCT2; SLC38A2/SNAT2; SLC7A5/LAT1; Solute carriers
    DOI:  https://doi.org/10.1002/1878-0261.12999
  20. Trends Endocrinol Metab. 2021 May 18. pii: S1043-2760(21)00113-2. [Epub ahead of print]
      We propose that fructose-1,6-bisphosphate (F-1,6-BP) promotes a feedback loop between phosphofructokinase-1 (PFK1), phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt), and PFK2/PFKFB3, which enhances aerobic glycolysis and sustains effector T (Teff) cell activation, while oxidative metabolism is concomitantly downregulated. This regulation, promoted by low citrate and mitochondrial ATP synthesis, also sustains the Warburg effect in cancer cells.
    Keywords:  T cell; Warburg effect; cancer cell; citrate; fructose-1,6-bisphosphate; metabolism
    DOI:  https://doi.org/10.1016/j.tem.2021.04.013
  21. Commun Biol. 2021 May 21. 4(1): 615
      Mitochondria are typically essential for the viability of eukaryotic cells, and utilize oxygen and nutrients (e.g. glucose) to perform key metabolic functions that maintain energetic homeostasis and support proliferation. Here we provide a comprehensive functional annotation of mitochondrial genes that are essential for the viability of a large panel (625) of tumour cell lines. We perform genome-wide CRISPR/Cas9 deletion screening in normoxia-glucose, hypoxia-glucose and normoxia-galactose conditions, and identify both unique and overlapping genes whose loss influences tumour cell viability under these different metabolic conditions. We discover that loss of certain oxidative phosphorylation (OXPHOS) genes (e.g. SDHC) improves tumour cell growth in hypoxia-glucose, but reduces growth in normoxia, indicating a metabolic switch in OXPHOS gene function. Moreover, compared to normoxia-glucose, loss of genes involved in energy-consuming processes that are energetically demanding, such as translation and actin polymerization, improve cell viability under both hypoxia-glucose and normoxia-galactose. Collectively, our study defines mitochondrial gene essentiality in tumour cells, highlighting that essentiality is dependent on the metabolic environment, and identifies routes for regulating tumour cell viability in hypoxia.
    DOI:  https://doi.org/10.1038/s42003-021-02098-x
  22. Oncogene. 2021 May 20.
      ING2 (Inhibitor of Growth 2) is a tumor suppressor gene that has been implicated in critical biological functions (cell-cycle regulation, replicative senescence, DNA repair and DNA replication), most of which are recognized hallmarks of tumorigenesis occurring in the cell nucleus. As its close homolog ING1 has been recently observed in the mitochondrial compartment, we hypothesized that ING2 could also translocate into the mitochondria and be involved in new biological functions. In the present study, we demonstrate that ING2 is imported in the inner mitochondrial fraction in a redox-sensitive manner in human cells and that this mechanism is modulated by 14-3-3η protein expression. Remarkably, ING2 is necessary to maintain mitochondrial ultrastructure integrity without interfering with mitochondrial networks or polarization. We observed an interaction between ING2 and mtDNA under basal conditions. This interaction appears to be mediated by TFAM, a critical regulator of mtDNA integrity. The loss of mitochondrial ING2 does not impair mtDNA repair, replication or transcription but leads to a decrease in mitochondrial ROS production, suggesting a detrimental impact on OXPHOS activity. We finally show using multiple models that ING2 is involved in mitochondrial respiration and that its loss confers a protection against mitochondrial respiratory chain inhibition in vitro. Consequently, we propose a new tumor suppressor role for ING2 protein in the mitochondria as a metabolic shift gatekeeper during tumorigenesis.
    DOI:  https://doi.org/10.1038/s41388-021-01832-3
  23. Mitochondrion. 2021 May 16. pii: S1567-7249(21)00072-6. [Epub ahead of print]
      Non-shivering thermogenesis takes place in brown and beige adipocytes and facilitates cold tolerance and acclimation. However, thermogenesis in adipose tissue also was found to be activated in metabolic overload states for fast utilization of nutrients excess. This observation spurred research interest in mechanisms of thermogenesis regulation for metabolic overload and obesity prevention. One of proposed regulators of thermogenic efficiency in adipocytes is the dynamics of mitochondria, where thermogenesis takes place. Indeed, brown and beige adipocytes exhibit fragmented round-shaped mitochondria, while white adipocytes have elongated organelles with high ATP synthesis. Mitochondrial morphology can determine uncoupling protein 1 (UCP1) content, efficiency of catabolic pathways and electron transport chain, supplying thermogenesis. This review will highlight the co-regulation of mitochondrial dynamics and thermogenesis and formulate hypothetical ways for excessive nutrients burning in response to mitochondrial morphology manipulation .
    Keywords:  Mitochondrial dynamics; beige fat; brown fat; metabolism; thermogenesis
    DOI:  https://doi.org/10.1016/j.mito.2021.05.001
  24. Immunity. 2021 May 11. pii: S1074-7613(21)00176-X. [Epub ahead of print]
      Human CD4+CD25hiFOXP3+ regulatory T (Treg) cells are key players in the control of immunological self-tolerance and homeostasis. Here, we report that signals of pseudo-starvation reversed human Treg cell in vitro anergy through an integrated transcriptional response, pertaining to proliferation, metabolism, and transmembrane solute carrier transport. At the molecular level, the Treg cell proliferative response was dependent on the induction of the cystine/glutamate antiporter solute carrier (SLC)7A11, whose expression was controlled by the nuclear factor erythroid 2-related factor 2 (NRF2). SLC7A11 induction in Treg cells was impaired in subjects with relapsing-remitting multiple sclerosis (RRMS), an autoimmune disorder associated with reduced Treg cell proliferative capacity. Treatment of RRMS subjects with dimethyl fumarate (DMF) rescued SLC7A11 induction and fully recovered Treg cell expansion. These results suggest a previously unrecognized mechanism that may account for the progressive loss of Treg cells in autoimmunity and unveil SLC7A11 as major target for the rescue of Treg cell proliferation.
    Keywords:  SLC7A11; Treg cells; autoimmunity; dimethyl fumarate; leptin; metabolism; multiple sclerosis; proliferation; starvation; xCT
    DOI:  https://doi.org/10.1016/j.immuni.2021.04.014
  25. J Cell Sci. 2020 Jan 01. pii: jcs.248880. [Epub ahead of print]
      Neutrophils rely on glycolysis for energy production. How mitochondria regulate neutrophil function is not fully understood. Here, we report that mitochondrial outer membrane protein Mitofusin 2 (Mfn2) regulates neutrophil homeostasis and chemotaxis in vivo. Mfn2-deficient neutrophils are released from the hematopoietic tissue, trapped in the vasculature in zebrafish embryos, and not capable of chemotaxis. Consistently, human neutrophil-like cells deficient with MFN2 fail to arrest on activated endothelium under sheer stress or perform chemotaxis on 2D surfaces. Deletion of Mfn2 results in a significant reduction of neutrophil infiltration to the inflamed peritoneal cavity in mice. Mechanistically, MFN2-deficient neutrophil-like cells display disrupted mitochondria-ER interaction, heightened intracellular calcium levels, and elevated Rac activation after chemokine stimulation. Restoring mitochondria-ER tether rescues the abnormal calcium levels, Rac hyperactivation, and chemotaxis defect resulted from MFN2 depletion. Finally, inhibition of Rac activation restores chemotaxis in MFN2-deficient neutrophils. Altogether, we identified that MFN2 regulates neutrophil migration via maintaining mitochondria-ER interaction to suppress Rac activation and uncovered a previously unrecognized role of MFN2 in regulating cell migration and the actin cytoskeleton.
    Keywords:  Actin; Chemotaxis; Leukocyte; Mitochondria; Rac; Zebrafish
    DOI:  https://doi.org/10.1242/jcs.248880
  26. J Cell Sci. 2020 Jan 01. pii: jcs.240374. [Epub ahead of print]
      The mitochondrial inner membrane contains a unique phospholipid known as cardiolipin (CL), which stabilises the protein complexes embedded in the membrane and supports its overall structure. Recent evidence indicates that the mitochondrial ribosome may associate with the inner membrane to facilitate co-translational insertion of the hydrophobic oxidative phosphorylation (OXPHOS) proteins into the inner membrane. We generated three mutant knockout cell lines for the cardiolipin biosynthesis gene Crls1 to investigate the effects of cardiolipin loss on mitochondrial protein synthesis. Reduced CL levels caused altered mitochondrial morphology and transcriptome-wide changes that were accompanied by reduced uncoordinated mitochondrial translation rates and impaired respiratory supercomplex formation. Aberrant protein synthesis was caused by impaired formation and distribution of mitochondrial ribosomes. Reduction or loss of cardiolipin resulted in divergent mitochondrial and endoplasmic reticulum stress responses. We show that cardiolipin is required to stabilise the interaction of the mitochondrial ribosome with the membrane via its association with OXA1 during active translation. This interaction facilitates insertion of newly synthesised mitochondrial proteins into the inner membrane and stabilises the respiratory supercomplexes.
    Keywords:  Mitochondrial membranes; Mitochondrial ribosomes; Protein synthesis
    DOI:  https://doi.org/10.1242/jcs.240374
  27. J Exp Biol. 2020 Jan 01. pii: jeb.223776. [Epub ahead of print]
      The association of complex I (CI), complex III (CIII) and complex IV (CIV) of the mitochondrial electron transport chain into stable high-molecular weight supercomplexes (SCs) has been observed in several prokaryotes and eukaryotes, but among vertebrates it has only been examined in mammals. The biological role of these SCs is unclear but suggestions so far include enhanced electron transfer between complexes, decreased production of the reactive oxygen species (ROS) O2·- and H2O2, or enhanced structural stability. Here, we provide the first overview on the stability, composition and activity of mitochondrial SCs in representative species of several vertebrate classes to determine patterns of SC variation across endotherms and ectotherms. We found that the stability of the CICIII2 SC and the inclusion of CIV within SC varied considerably. Specifically, when solubilized by the detergent DDM, mitochondrial CICIII2 SCs were unstable in endotherms (birds and mammals) and highly stable in reptiles. Using mass-spectrometric complexomics, we confirmed that the CICIII2 is the major SC in the turtle, and that 90% of CI is found in this highly stable SC. Interestingly, the presence of stable SCs did not prevent mitochondrial H2O2 production and was not associated with elevated respiration rates of mitochondria isolated from the examined species. Together, these data show that SC stability varies among vertebrates and is greatest in poikilothermic reptiles and weakest in endotherms. This pattern suggests an adaptive role of SCs to varying body temperature, but not necessarily a direct effect on electron transfer or in the prevention of ROS production.
    Keywords:  Bioenergetics; Complexomics; Mass spectrometry; Mitochondria; Oxidative phosphorylation; Reactive oxygen species
    DOI:  https://doi.org/10.1242/jeb.223776
  28. Oncologist. 2021 May 18.
      SDH (succinate dehydrogenase)- deficient renal cancer is a rare renal cancer (RCC) subtype recently accepted by WHO as an unique RCC subtype with only 59 cases described worldwide. Here we report a case of 17-year old man. The detailed evaluation indicated occurrence of the SDHB-deficient RCC. The genetic testing revealed no germline mutation in SDH genes. Immunohistochemistry showed SDHB deficiency, overexpression of PKM2 and dramatic downregulation of FBP1 metabolic enzymes, unaltered levels of pAMPK and mTOR. Furthermore, the strong upregulation of INI1, BRG1 and overexpression of BAF180 subunits of SWI/SNF ATP-dependent chromatin remodeling complex were found. The identified tumor pathologically did not resemble ccRCC (clear cell renal cell carcinoma) but some metabolic alterations are common for both cancer types. Thus, we postulate that the phenotypical differences between ccRCC and SDHB-deficient RCC may be related to distinct molecular and metabolic alterations. IMPLICATIONS FOR PRACTICE: SDH-deficient RCC is a rare renal tumor occurring also in young age. So far in all described and genetically tested cases the mutations/deletions in SDH genes were found [2]. Here we describe SDHB-deficient RCC without any germ line mutations in SDH genes. Therefore, the genetic analysis for germ line mutations in SDH genes in SDH-deficient RCC, especially in young individuals should be strongly recommended, although up to date is not obligatory. This knowledge will allow to improve the further patient monitoring including both disease recurrence and new cancer appearance.
    Keywords:  Fructose-1,6-Bisphosphatase; Pyruvate Kinase M2; SDHB-deficient renal cancer; SWI/SNF chromatin remodeling complex
    DOI:  https://doi.org/10.1002/onco.13825
  29. J Cell Sci. 2020 Jan 01. pii: jcs.241539. [Epub ahead of print]
      One major cause of endoplasmic reticulum (ER) stress is homeostatic imbalance between biosynthetic protein folding and protein folding capacity. Cells utilize mechanisms such as the unfolded protein response (UPR) to cope with ER stress. Nevertheless, when ER stress is prolonged or severe, cell death may occur, accompanied by production of mitochondrial reactive oxygen species (ROS). Using a yeast model, we describe an innate, adaptive response to ER stress to increase select mitochondrial proteins, O2 consumption, and cell survival. The mitochondrial response allows cells to resist additional ER stress. ER stress-induced mitochondrial response is mediated by activation of retrograde (RTG) signaling to enhance anapleurotic reactions of the TCA cycle. Mitochondrial response to ER stress is accompanied by inactivation of the conserved TORC1 pathway, and activation of Snf1/AMPK, the conserved energy sensor and regulator of metabolism. Our results provide new insight into the role of respiration in cell survival in the face of ER stress, and should help in developing therapeutic strategies to limit cell death in disorders linked to ER stress.
    Keywords:  ER stress; Endoplasmic reticulum; Mitochondria; Yeast
    DOI:  https://doi.org/10.1242/jcs.241539
  30. Plant Cell Physiol. 2021 May 21. pii: pcab061. [Epub ahead of print]
      Metabolism, auxin signalling and ROS all contribute to plant growth and each is linked to plant mitochondria and the process of respiration. Knockdown of mitochondrial Succinate Dehydrogenase Assembly Factor 2 (SDHAF2) in Arabidopsis thaliana, lowered succinate dehydrogenase activity and led to pH-inducible root inhibition when the growth medium pH was poised at different points between 7.0 and 5.0, but this phenomenon was not observed in WT. Roots of sdhaf2 mutants showed high accumulation of succinate, depletion of citrate and malate and up-regulation of ROS-related and stress-inducible genes at pH 5.5. A change of oxidative status in sdhaf2 roots at low pH was also evidenced by low ROS staining in root tips and altered root sensitivity to H2O2. sdhaf2 had low auxin activity in root tips via DR5-GUS staining, but displayed increased IAA (auxin) abundance and IAA hypersensitivity, which is most likely caused by the change in ROS levels. On this basis we conclude that knockdown of SDHAF2 induces pH-related root elongation and auxin hyperaccumulation and hypersensitivity, mediated by altered ROS homeostasis. This observation extends the existing evidence of associations between mitochondrial function and auxin by establishing a cascade of cellular events that link them through ROS formation, metabolism and root growth at different pH values.
    Keywords:  Auxin; Mitochondrial Metabolism; Oxidative Stress; Reactive Oxygen Species; Root Elongation; Soil Acidification
    DOI:  https://doi.org/10.1093/pcp/pcab061
  31. Proc Natl Acad Sci U S A. 2021 May 25. pii: e2002486118. [Epub ahead of print]118(21):
      Most human cancer cells harbor loss-of-function mutations in the p53 tumor suppressor gene. Genetic experiments have shown that phosphatidylinositol 5-phosphate 4-kinase α and β (PI5P4Kα and PI5P4Kβ) are essential for the development of late-onset tumors in mice with germline p53 deletion, but the mechanism underlying this acquired dependence remains unclear. PI5P4K has been previously implicated in metabolic regulation. Here, we show that inhibition of PI5P4Kα/β kinase activity by a potent and selective small-molecule probe disrupts cell energy homeostasis, causing AMPK activation and mTORC1 inhibition in a variety of cell types. Feedback through the S6K/insulin receptor substrate (IRS) loop contributes to insulin hypersensitivity and enhanced PI3K signaling in terminally differentiated myotubes. Most significantly, the energy stress induced by PI5P4Kαβ inhibition is selectively toxic toward p53-null tumor cells. The chemical probe, and the structural basis for its exquisite specificity, provide a promising platform for further development, which may lead to a novel class of diabetes and cancer drugs.
    Keywords:  chemical biology; lipid kinase; p53; pip4k; synthetic lethality
    DOI:  https://doi.org/10.1073/pnas.2002486118
  32. Nat Metab. 2021 May 17.
      Non-alcoholic fatty liver disease (NAFLD), the most prevalent liver pathology worldwide, is intimately linked with obesity and type 2 diabetes. Liver inflammation is a hallmark of NAFLD and is thought to contribute to tissue fibrosis and disease pathogenesis. Uncoupling protein 1 (UCP1) is exclusively expressed in brown and beige adipocytes, and has been extensively studied for its capacity to elevate thermogenesis and reverse obesity. Here we identify an endocrine pathway regulated by UCP1 that antagonizes liver inflammation and pathology, independent of effects on obesity. We show that, without UCP1, brown and beige fat exhibit a diminished capacity to clear succinate from the circulation. Moreover, UCP1KO mice exhibit elevated extracellular succinate in liver tissue that drives inflammation through ligation of its cognate receptor succinate receptor 1 (SUCNR1) in liver-resident stellate cell and macrophage populations. Conversely, increasing brown and beige adipocyte content in mice antagonizes SUCNR1-dependent inflammatory signalling in the liver. We show that this UCP1-succinate-SUCNR1 axis is necessary to regulate liver immune cell infiltration and pathology, and systemic glucose intolerance in an obesogenic environment. As such, the therapeutic use of brown and beige adipocytes and UCP1 extends beyond thermogenesis and may be leveraged to antagonize NAFLD and SUCNR1-dependent liver inflammation.
    DOI:  https://doi.org/10.1038/s42255-021-00389-5
  33. Front Immunol. 2021 ;12 673916
      Mitochondria are major energy-producing organelles that have central roles in cellular metabolism. They also act as important signalling hubs, and their dynamic regulation in response to stress signals helps to dictate the stress response of the cell. Rheumatoid arthritis is an inflammatory and autoimmune disease with high prevalence and complex aetiology. Mitochondrial activity affects differentiation, activation and survival of immune and non-immune cells that contribute to the pathogenesis of this disease. This review outlines what is known about the role of mitochondria in rheumatoid arthritis pathogenesis, and how current and future therapeutic strategies can function through modulation of mitochondrial activity. We also highlight areas of this topic that warrant further study. As producers of energy and of metabolites such as succinate and citrate, mitochondria help to shape the inflammatory phenotype of leukocytes during disease. Mitochondrial components can directly stimulate immune receptors by acting as damage-associated molecular patterns, which could represent an initiating factor for the development of sterile inflammation. Mitochondria are also an important source of intracellular reactive oxygen species, and facilitate the activation of the NLRP3 inflammasome, which produces cytokines linked to disease symptoms in rheumatoid arthritis. The fact that mitochondria contain their own genetic material renders them susceptible to mutation, which can propagate their dysfunction and immunostimulatory potential. Several drugs currently used for the treatment of rheumatoid arthritis regulate mitochondrial function either directly or indirectly. These actions contribute to their immunomodulatory functions, but can also lead to adverse effects. Metabolic and mitochondrial pathways are attractive targets for future anti-rheumatic drugs, however many questions still remain about the precise role of mitochondrial activity in different cell types in rheumatoid arthritis.
    Keywords:  DAMP; DMARD (disease modifying anti-rheumatic drug); NLRP3; metabolism; mitochondria; oxidative phosphorylation; rheumatoid arthritis
    DOI:  https://doi.org/10.3389/fimmu.2021.673916
  34. Dis Model Mech. 2020 Jan 01. pii: dmm.046706. [Epub ahead of print]
      Somatic models of tissue pathology commonly utilise induction of gene specific mutations in mice mediated by spatiotemporal regulation of Cre recombinase. Subsequent investigation of the onset and development of disease can be limited by the inability to track changing cellular behaviours over time. Here a lineage tracing approach based on ligand dependent activation of Dre recombinase that can be employed independently of Cre is described. The clonal biology of intestinal epithelium following Cre-mediated stabilisation of ß-catenin reveals that within tumours many new clones rapidly become extinct. Surviving clones show accelerated population of tumour glands compared to normal intestinal crypts but in a non-uniform manner indicating that intra-tumour glands follow heterogeneous dynamics. In tumour adjacent epithelium clone sizes are smaller than in the background epithelium as a whole. This suggests a zone of around 5 crypt diameters within which clone expansion is inhibited by tumours and that may facilitate their growth.
    Keywords:  Cancer; Epithelial; Intestine; Lineage tracing
    DOI:  https://doi.org/10.1242/dmm.046706
  35. Amino Acids. 2021 May 18.
      Proline metabolism features prominently in the unique metabolism of cancer cells. Proline biosynthetic genes are consistently upregulated in multiple cancers, while the proline catabolic enzyme proline dehydrogenase has dual, context-dependent pro-cancer and pro-apoptotic functions. Furthermore, the cycling of proline and Δ1-pyrroline-5-carboxylate through the proline cycle impacts cellular growth and death pathways by maintaining redox homeostasis between the cytosol and mitochondria. Here we focus on the last enzyme of proline biosynthesis, Δ1-pyrroline-5-carboxylate reductase, known as PYCR in humans. PYCR catalyzes the NAD(P)H-dependent reduction of Δ1-pyrroline-5-carboxylate to proline and forms the reductive half of the proline metabolic cycle. We review the research on the three-dimensional structure, biochemistry, inhibition, and cancer biology of PYCR. To provide a global view of PYCR gene upregulation in cancer, we mined RNA transcript databases to analyze differential gene expression in 28 cancer types. This analysis revealed strong, widespread upregulation of PYCR genes, especially PYCR1. Altogether, the research over the past 20 years makes a compelling case for PYCR as a cancer therapy target. We conclude with a discussion of some of the major challenges for the field, including developing isoform-specific inhibitors, elucidating the function of the long C-terminus of PYCR1/2, and characterizing the interactome of PYCR.
    Keywords:  Cancer; PYCR; Proline biosynthesis; Proline metabolism; Pyrroline-5-carboxylate reductase
    DOI:  https://doi.org/10.1007/s00726-021-02999-5
  36. J Exp Bot. 2021 May 16. pii: erab182. [Epub ahead of print]
      The adaptation of plant metabolism to abiotic stress involves profound changes in amino acid metabolism. Unfavorable environmental conditions often lead to an impairment of photosynthesis. In response to the resulting lack of energy, plants activate respiratory pathways that use amino acids as alternative substrates. This review highlights recent progress in understanding these amino acid oxidation pathways, their regulation during stress, and the role of amino acids as signaling molecules. We present an updated map of the degradation pathways for lysine and the branched-chain amino acids including the last missing step in plant lysine catabolism, which has recently been identified, and several new steps involved in the degradation of leucine, isoleucine, and valine. The adaptation of amino acid metabolism to energy deprivation is mediated by the balance between TOR and SnRK signaling. The coordinated induction of several catabolic pathways during starvation is achieved by SnRK1 kinase via formation of a ternary complex including bZIP transcription factors. Recent findings indicate that some amino acids might act as TOR activators and thus promote a shift from catabolic to anabolic pathways. The metabolism of the sulfur containing amino acid cysteine is highly interconnected with TOR and SnRK signaling. Mechanistic details have recently been elucidated for cysteine signaling during the abscisic acid dependent drought response. Local cysteine synthesis triggers abscisic acid production and in addition, cysteine degradation produces the gaseous messenger hydrogen sulfide, which promotes stomatal closure via protein persulfidation. Amino acid signaling in plants is still an emerging topic with potential for fundamental discoveries.
    Keywords:  Abiotic stress; SnRK; TOR; alternative respiration; amino acid metabolism; branched-chain amino acid degradation; energy deficiency; lysine degradation; signaling
    DOI:  https://doi.org/10.1093/jxb/erab182
  37. Adv Exp Med Biol. 2021 ;1311 205-214
      Although cancer has classically been regarded as a genetic disease of uncontrolled cell growth, the importance of the tumor microenvironment (TME) [1, 2] is continuously emphasized by the accumulating evidence that cancer growth is not simply dependent on the cancer cells themselves [3, 4] but also dependent on angiogenesis [5-8], inflammation [9, 10], and the supporting roles of cancer-associated fibroblasts (CAFs) [11-13]. After the discovery that CAFs are able to remodel the tumor matrix within the TME and provide the nutrients and chemicals to promote cancer cell growth [14], many studies have aimed to uncover the cross talk between cancer cells and CAFs. Moreover, a new paradigm in cancer metabolism shows how cancer cells act like "metabolic parasites" to take up the high-energy metabolites, such as lactate, ketone bodies, free fatty acids, and glutamine from supporting cells, including CAFs and cancer-associated adipocytes (CAAs) [15, 16]. This chapter provides an overview of the metabolic coupling between CAFs and cancer cells to further define the therapeutic options to disrupt the CAF-cancer cell interactions.
    Keywords:  Cancer therapy; Cancer-associated adipocytes; Cancer-associated fibroblasts; Metabolism; Metabolites; Tumor microenvironment
    DOI:  https://doi.org/10.1007/978-3-030-65768-0_15
  38. Biochim Biophys Acta Rev Cancer. 2021 May 13. pii: S0304-419X(21)00062-7. [Epub ahead of print]1876(1): 188565
      Autophagy is a highly conserved metabolic process involved in the degradation of intracellular components including proteins and organelles. Consequently, it plays a critical role in recycling metabolic energy for the maintenance of cellular homeostasis in response to various stressors. In cancer, autophagy either suppresses or promotes cancer progression depending on the stage and cancer type. Epithelial-mesenchymal transition (EMT) and cancer metastasis are directly mediated by oncogenic signal proteins including SNAI1, SLUG, ZEB1/2, and NOTCH1, which are functionally correlated with autophagy. In this report, we discuss the crosstalk between oncogenic signaling pathways and autophagy followed by possible strategies for cancer treatment via regulation of autophagy. Although autophagy affects EMT and cancer metastasis, the overall signaling pathways connecting cancer progression and autophagy are still illusive. In general, autophagy plays a critical role in cancer cell survival by providing a minimum level of energy via self-digestion. Thus, cancer cells face nutrient limitations and challenges under stress during EMT and metastasis. Conversely, autophagy acts as a potential cancer suppressor by degrading oncogenic proteins, which are essential for cancer progression, and by removing damaged components such as mitochondria to enhance genomic stability. Therefore, autophagy activators or inhibitors represent possible cancer therapeutics. We further discuss the regulation of autophagy-dependent degradation of oncogenic proteins and its functional correlation with oncogenic signaling pathways, with potential applications in cancer therapy.
    Keywords:  Anticancer therapy; Autophagy; Cancer metastasis; EMT; Oncogenic proteins
    DOI:  https://doi.org/10.1016/j.bbcan.2021.188565
  39. Cell Metab. 2021 May 17. pii: S1550-4131(21)00223-0. [Epub ahead of print]
      How amphipathic phospholipids are shuttled between the membrane bilayer remains an essential but elusive process, particularly at the endoplasmic reticulum (ER). One prominent phospholipid shuttling process concerns the biogenesis of APOB-containing lipoproteins within the ER lumen, which may require bulk trans-bilayer movement of phospholipids from the cytoplasmic leaflet of the ER bilayer. Here, we show that TMEM41B, present in the lipoprotein export machinery, encodes a previously conceptualized ER lipid scramblase mediating trans-bilayer shuttling of bulk phospholipids. Loss of hepatic TMEM41B eliminates plasma lipids, due to complete absence of mature lipoproteins within the ER, but paradoxically also activates lipid production. Mechanistically, scramblase deficiency triggers unique ER morphological changes and unsuppressed activation of SREBPs, which potently promotes lipid synthesis despite stalled secretion. Together, this response induces full-blown nonalcoholic hepatosteatosis in the TMEM41B-deficient mice within weeks. Collectively, our data uncovered a fundamental mechanism safe-guarding ER function and integrity, dysfunction of which disrupts lipid homeostasis.
    Keywords:  SREBP; endoplasmic reticulum; fatty liver disease; lipid scramblase; lipoprotein metabolism
    DOI:  https://doi.org/10.1016/j.cmet.2021.05.006
  40. Front Physiol. 2021 ;12 682467
      
    Keywords:  ATP synthase; channels; hypoxia; mitochondria; pathophysiology
    DOI:  https://doi.org/10.3389/fphys.2021.682467
  41. Adv Exp Med Biol. 2021 ;1311 39-56
      The study of cancer cell metabolism has traditionally focused on glycolysis and glutaminolysis. However, lipidomic technologies have matured considerably over the last decade and broadened our understanding of how lipid metabolism is relevant to cancer biology [1-3]. Studies now suggest that the reprogramming of cellular lipid metabolism contributes directly to malignant transformation and progression [4, 5]. For example, de novo lipid synthesis can supply proliferating tumor cells with phospholipid components that comprise the plasma and organelle membranes of new daughter cells [6, 7]. Moreover, the upregulation of mitochondrial β-oxidation can support tumor cell energetics and redox homeostasis [8], while lipid-derived messengers can regulate major signaling pathways or coordinate immunosuppressive mechanisms [9-11]. Lipid metabolism has, therefore, become implicated in a variety of oncogenic processes, including metastatic colonization, drug resistance, and cell differentiation [10, 12-16]. However, whether we can safely and effectively modulate the underlying mechanisms of lipid metabolism for cancer therapy is still an open question.
    Keywords:  Cancer metabolism; Fatty acid oxidation; Fatty acid uptake; Lipid synthesis; Lipidomics; Metastasis; Tumor heterogeneity
    DOI:  https://doi.org/10.1007/978-3-030-65768-0_3
  42. Proc Natl Acad Sci U S A. 2021 May 25. pii: e2016904118. [Epub ahead of print]118(21):
      Pancreatic ductal adenocarcinoma (PDAC) is a lethal malignancy with limited treatment options. Although activating mutations of the KRAS GTPase are the predominant dependency present in >90% of PDAC patients, targeting KRAS mutants directly has been challenging in PDAC. Similarly, strategies targeting known KRAS downstream effectors have had limited clinical success due to feedback mechanisms, alternate pathways, and dose-limiting toxicities in normal tissues. Therefore, identifying additional functionally relevant KRAS interactions in PDAC may allow for a better understanding of feedback mechanisms and unveil potential therapeutic targets. Here, we used proximity labeling to identify protein interactors of active KRAS in PDAC cells. We expressed fusions of wild-type (WT) (BirA-KRAS4B), mutant (BirA-KRAS4BG12D), and nontransforming cytosolic double mutant (BirA-KRAS4BG12D/C185S) KRAS with the BirA biotin ligase in murine PDAC cells. Mass spectrometry analysis revealed that RSK1 selectively interacts with membrane-bound KRASG12D, and we demonstrate that this interaction requires NF1 and SPRED2. We find that membrane RSK1 mediates negative feedback on WT RAS signaling and impedes the proliferation of pancreatic cancer cells upon the ablation of mutant KRAS. Our findings link NF1 to the membrane-localized functions of RSK1 and highlight a role for WT RAS signaling in promoting adaptive resistance to mutant KRAS-specific inhibitors in PDAC.
    Keywords:  BioID; KRAS; NF1; PDAC; RSK
    DOI:  https://doi.org/10.1073/pnas.2016904118
  43. Adv Exp Med Biol. 2021 ;1311 77-88
      Currently, approximately 95% of pancreatic cancers are pancreatic ductal adenocarcinomas (PDAC), which are the most aggressive form and the fourth leading cause of cancer death with extremely poor prognosis [1]. Poor prognosis is primarily attributed to the late diagnosis of the disease when patients are no longer candidates for surgical resection [2]. Cancer cells are dependent on the oncogenes that allow them to proliferate limitlessly. Thus, targeting the expression of known oncogenes in pancreatic cancer has been shown to lead to more effective treatment [3]. This chapter discusses the complexity of metabolic features in pancreatic cancers. In order to comprehend the heterogeneous nature of cancer metabolism fully, we need to take into account the close relationship between cancer metabolism and genetics. Gene expression varies tremendously, not only among different types of cancers but also within the same type of cancer among different patients. Cancer metabolism heterogeneity is often prompted and perpetuated not only by mutations in oncogenes and tumor-suppressor genes but also by the innate diversity of the tumor microenvironment. Much effort has been focused on elucidating the genetic alterations that correlate with disease progression and treatment response [4, 5]. However, the precise mechanisms by which tumor metabolism contributes to cancer growth, survival, mobility, and aggressiveness represent a functional readout of tumor progression (Fig. 1).
    Keywords:  Combined therapy; Glucose metabolism; Glutamine metabolism; KRAS mutation; Pancreatic ductal adenocarcinoma
    DOI:  https://doi.org/10.1007/978-3-030-65768-0_5
  44. Semin Cancer Biol. 2021 May 18. pii: S1044-579X(21)00146-2. [Epub ahead of print]
      The complex role of NRF2 in the context of cancer continues to evolve. As a transcription factor, NRF2 regulates various genes involved in redox homeostasis, protein degradation, DNA repair, and xenobiotic metabolism. As such, NRF2 is critical in preserving cell function and viability, particularly during stress. Importantly, NRF2 itself is regulated via a variety of mechanisms, and the mode of NRF2 activation often dictates the duration of NRF2 signaling and its role in either preventing cancer initiation or promoting cancer progression. Herein, different modes of NRF2 regulation, including oxidative stress, autophagy dysfunction, protein-protein interactions, and epigenetics, as well as pharmacological modulators targeting this cascade in cancer, are explored. Specifically, how the timing and duration of these different mechanisms of NRF2 induction affect tumor initiation, progression, and metastasis are discussed. Additionally, progress in the discovery and development of NRF2 inhibitors for the treatment of NRF2-addicted cancers is highlighted, including modulators that inhibit specific NRF2 downstream targets. Overall, a better understanding of the intricate nature of NRF2 regulation in specific cancer contexts should facilitate the generation of novel therapeutics designed to not only prevent tumor initiation, but also halt progression and ultimately improve patient wellbeing and survival.
    Keywords:  KEAP1; NRF2; carcinogenesis; chemoprevention; chemoresistance
    DOI:  https://doi.org/10.1016/j.semcancer.2021.05.016
  45. Nat Genet. 2021 May 17.
      Mitochondrial DNA (mtDNA) variation in common diseases has been underexplored, partly due to a lack of genotype calling and quality-control procedures. Developing an at-scale workflow for mtDNA variant analyses, we show correlations between nuclear and mitochondrial genomic structures within subpopulations of Great Britain and establish a UK Biobank reference atlas of mtDNA-phenotype associations. A total of 260 mtDNA-phenotype associations were new (P < 1 × 10-5), including rs2853822 /m.8655 C>T (MT-ATP6) with type 2 diabetes, rs878966690 /m.13117 A>G (MT-ND5) with multiple sclerosis, 6 mtDNA associations with adult height, 24 mtDNA associations with 2 liver biomarkers and 16 mtDNA associations with parameters of renal function. Rare-variant gene-based tests implicated complex I genes modulating mean corpuscular volume and mean corpuscular hemoglobin. Seven traits had both rare and common mtDNA associations, where rare variants tended to have larger effects than common variants. Our work illustrates the value of studying mtDNA variants in common complex diseases and lays foundations for future large-scale mtDNA association studies.
    DOI:  https://doi.org/10.1038/s41588-021-00868-1
  46. Cell Metab. 2021 May 12. pii: S1550-4131(21)00216-3. [Epub ahead of print]
      Emerging evidence suggests a key contribution to non-alcoholic fatty liver disease (NAFLD) pathogenesis by Th17 cells. The pathogenic characteristics and mechanisms of hepatic Th17 cells, however, remain unknown. Here, we uncover and characterize a distinct population of inflammatory hepatic CXCR3+Th17 (ihTh17) cells sufficient to exacerbate NAFLD pathogenesis. Hepatic ihTh17 cell accrual was dependent on the liver microenvironment and CXCR3 axis activation. Mechanistically, the pathogenic potential of ihTh17 cells correlated with increased chromatin accessibility, glycolytic output, and concomitant production of IL-17A, IFNγ, and TNFα. Modulation of glycolysis using 2-DG or cell-specific PKM2 deletion was sufficient to reverse ihTh17-centric inflammatory vigor and NAFLD severity. Importantly, ihTh17 cell characteristics, CXCR3 axis activation, and hepatic expression of glycolytic genes were conserved in human NAFLD. Together, our data show that the steatotic liver microenvironment regulates Th17 cell accrual, metabolism, and competence toward an ihTh17 fate. Modulation of these pathways holds potential for development of novel therapeutic strategies for NAFLD.
    Keywords:  CXCR3; IFNγ; NAFLD; PKM; T cell; TNF; cellular metabolism; glycolysis; liver; obesity
    DOI:  https://doi.org/10.1016/j.cmet.2021.04.018
  47. Bioessays. 2021 May 19. e2100069
      Recently, a review regarding the mechanics and evolution of mitochondrial fission appeared in Nature. Surprisingly, it stated authoritatively that the mitochondrial outer membrane, in contrast with the inner membrane of bacterial descent, was acquired from the host, presumably during uptake. However, it has been known for quite some time that this membrane was also derived from the Gram-negative, alpha-proteobacterium related precursor of present-day mitochondria. The zombie idea of the host membrane still surrounding the endosymbiont is not only wrong, but more importantly, might hamper the proper conception of possible scenarios of eukaryogenesis. Why? Because it steers the imagination not only with regard to possible uptake mechanisms, but also regarding what went on before. Here I critically discuss both the evidence for the continuity of the bacterial outer membrane, the reasons for the persistence of the erroneous host membrane hypothesis and the wider implications of these misconceptions for the ideas regarding events occurring during the first steps towards the evolution of the eukaryotes and later major eukaryotic differentiations. I will also highlight some of the latest insights regarding different instances of endosymbiont evolution.
    Keywords:  endosymbiont; eukaryogenesis; membrane replacement; serial endosymbiosis; symbiogenesis
    DOI:  https://doi.org/10.1002/bies.202100069
  48. Adv Exp Med Biol. 2021 ;1311 117-126
      According to data from the American Cancer Society, cancer is one of the deadliest health problems globally. Annually, renal cell carcinoma (RCC) causes more than 100,000 deaths worldwide [1-4], posing an urgent need to develop effective treatments to increase patient survival outcomes. New therapies are expected to address a major factor contributing to cancer's resistance to standard therapies: oncogenic heterogeneity. Gene expression can vary tremendously among different types of cancers, different patients of the same tumor type, and even within individual tumors; various metabolic phenotypes can emerge, making singletherapy approaches insufficient. Novel strategies targeting the diverse metabolism of cancers aim to overcome this obstacle. Though some have yielded positive results, it remains a challenge to uncover all of the distinct metabolic profiles of RCC. In the quest to overcome this obstacle, the metabolic oriented research focusing on these cancers has offered freshly new perspectives, which are expected to contribute heavily to the development of new treatments.
    Keywords:  Glucose metabolism; Glutamine metabolism; Metabolic phenotypes; Oncogenic heterogeneity—intratumoral heterogeneity; Renal cell carcinoma
    DOI:  https://doi.org/10.1007/978-3-030-65768-0_8
  49. Adv Exp Med Biol. 2021 ;1311 17-38
      Metabolism is a fundamental process for all cellular functions. For decades, there has been growing evidence of a relationship between metabolism and malignant cell proliferation. Unlike normal differentiated cells, cancer cells have reprogrammed metabolism in order to fulfill their energy requirements. These cells display crucial modifications in many metabolic pathways, such as glycolysis and glutaminolysis, which include the tricarboxylic acid (TCA) cycle, the electron transport chain (ETC), and the pentose phosphate pathway (PPP) [1]. Since the discovery of the Warburg effect, it has been shown that the metabolism of cancer cells plays a critical role in cancer survival and growth. More recent research suggests that the involvement of glutamine in cancer metabolism is more significant than previously thought. Glutamine, a nonessential amino acid with both amine and amide functional groups, is the most abundant amino acid circulating in the bloodstream [2]. This chapter discusses the characteristic features of glutamine metabolism in cancers and the therapeutic options to target glutamine metabolism for cancer treatment.
    Keywords:  Glutamine addiction; Glutamine metabolism; Targeting amino acid synthesis; Targeting glutamine metabolism; Transaminase upregulation
    DOI:  https://doi.org/10.1007/978-3-030-65768-0_2
  50. Dev Cell. 2021 May 17. pii: S1534-5807(21)00356-7. [Epub ahead of print]56(10): 1408-1416
      Brown and beige adipocytes, or thermogenic fat, were initially thought to be merely a thermogenic organ. However, emerging evidence suggests its multifaceted roles in the regulation of systemic glucose and lipid homeostasis that go beyond enhancing thermogenesis. One of the important functions of thermogenic fat is as a "metabolic sink" for glucose, fatty acids, and amino acids, which profoundly impacts metabolite clearance and oxidation. Importantly, lipids are not only the predominant fuel source used for thermogenesis but are also essential molecules for development, cellular signaling, and structural components. Here, we review the multifaceted role of lipids in thermogenic adipocytes.
    Keywords:  beige fat; brown adipose tissue; diabetes; lipid metabolism; obesity; thermogenesis
    DOI:  https://doi.org/10.1016/j.devcel.2021.04.018
  51. Mol Cell. 2021 May 08. pii: S1097-2765(21)00269-0. [Epub ahead of print]
      Glutaminase regulates glutaminolysis to promote cancer cell proliferation. However, the mechanism underlying glutaminase activity regulation is largely unknown. Here, we demonstrate that kidney-type glutaminase (GLS) is highly expressed in human pancreatic ductal adenocarcinoma (PDAC) specimens with correspondingly upregulated glutamine dependence for PDAC cell proliferation. Upon oxidative stress, the succinyl-coenzyme A (CoA) synthetase ADP-forming subunit β (SUCLA2) phosphorylated by p38 mitogen-activated protein kinase (MAPK) at S79 dissociates from GLS, resulting in enhanced GLS K311 succinylation, oligomerization, and activity. Activated GLS increases glutaminolysis and the production of nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione, thereby counteracting oxidative stress and promoting tumor cell survival and tumor growth in mice. In addition, the levels of SUCLA2 pS79 and GLS K311 succinylation, which were mutually correlated, were positively associated with advanced stages of PDAC and poor prognosis for patients. Our findings reveal critical regulation of GLS by SUCLA2-coupled GLS succinylation regulation and underscore the regulatory role of metabolites in glutaminolysis and PDAC development.
    Keywords:  GLS; GSH; NADPH; SUCLA2; glutaminolysis; p38; phosphorylation; succinyl-CoA; succinylation; tumorigenesis
    DOI:  https://doi.org/10.1016/j.molcel.2021.04.002