bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2020‒08‒23
forty-four papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit

  1. EBioMedicine. 2020 Aug 17. pii: S2352-3964(20)30319-4. [Epub ahead of print]59 102943
    Missiroli S, Perrone M, Genovese I, Pinton P, Giorgi C.
      Mitochondria are dynamic organelles that have essential metabolic activity and are regarded as signalling hubs with biosynthetic, bioenergetics and signalling functions that orchestrate key biological pathways. However, mitochondria can influence all processes linked to oncogenesis, starting from malignant transformation to metastatic dissemination. In this review, we describe how alterations in the mitochondrial metabolic status contribute to the acquisition of typical malignant traits, discussing the most recent discoveries and the many unanswered questions. We also highlight that expanding our understanding of mitochondrial regulation and function mechanisms in the context of cancer cell metabolism could be an important task in biomedical research, thus offering the possibility of targeting mitochondria for the treatment of cancer.
    Keywords:  Calcium; Cancer; Metabolism; Mitochondria; ROS
  2. Proc Natl Acad Sci U S A. 2020 Aug 14. pii: 202005976. [Epub ahead of print]
    Vais H, Payne R, Paudel U, Li C, Foskett JK.
      Ca2+ uptake by mitochondria regulates bioenergetics, apoptosis, and Ca2+ signaling. The primary pathway for mitochondrial Ca2+ uptake is the mitochondrial calcium uniporter (MCU), a Ca2+-selective ion channel in the inner mitochondrial membrane. MCU-mediated Ca2+ uptake is driven by the sizable inner-membrane potential generated by the electron-transport chain. Despite the large thermodynamic driving force, mitochondrial Ca2+ uptake is tightly regulated to maintain low matrix [Ca2+] and prevent opening of the permeability transition pore and cell death, while meeting dynamic cellular energy demands. How this is accomplished is controversial. Here we define a regulatory mechanism of MCU-channel activity in which cytoplasmic Ca2+ regulation of intermembrane space-localized MICU1/2 is controlled by Ca2+-regulatory mechanisms localized across the membrane in the mitochondrial matrix. Ca2+ that permeates through the channel pore regulates Ca2+ affinities of coupled inhibitory and activating sensors in the matrix. Ca2+ binding to the inhibitory sensor within the MCU amino terminus closes the channel despite Ca2+ binding to MICU1/2. Conversely, disruption of the interaction of MICU1/2 with the MCU complex disables matrix Ca2+ regulation of channel activity. Our results demonstrate how Ca2+ influx into mitochondria is tuned by coupled Ca2+-regulatory mechanisms on both sides of the inner mitochondrial membrane.
    Keywords:  EMRE; MICU1; calcium; electrophysiology; mitochondria
  3. J Biol Chem. 2020 Aug 19. pii: jbc.AC120.014993. [Epub ahead of print]
    Perez M, Bak DW, Bergholtz SE, Crooks DR, Arimilli BS, Yang Y, Weerapana E, Linehan WM, Meier JL.
      An important context in which metabolism influences tumorigenesis is the genetic cancer syndrome hereditary leiomyomatosis and renal cell carcinoma (HLRCC), a disease in which mutation of the TCA cycle enzyme fumarate hydratase (FH) causes hyperaccumulation of fumarate. This electrophilic oncometabolite can alter gene activity at the level of transcription, via reversible inhibition of epigenetic dioxygenases, as well as posttranslationally, via covalent modification of cysteine residues. To better understand the potential for metabolites to influence posttranslational modifications important to tumorigenesis and cancer cell growth, here we report a chemoproteomic analysis of a kidney-derived HLRCC cell line. Using a general reactivity probe, we generated a dataset of proteomic cysteine residues sensitive to the reduction in fumarate levels caused by genetic re-introduction of active FH into HLRCC cell lines. This revealed a broad upregulation of cysteine reactivity upon FH rescue, which evidence suggests is caused by an approximately equal proportion of transcriptional and posttranslational modification-mediated regulation. Gene ontology analysis highlighted several new targets and pathways potentially modulated by FH mutation. Comparison of the new dataset to prior studies highlights considerable heterogeneity in the adaptive response of cysteine-containing proteins in different models of HLRCC. This is consistent with emerging studies indicating the existence of cell and tissue-specific cysteine-omes, further emphasizing the need for characterization of diverse models. Our analysis provides a resource for understanding the proteomic adaptation to fumarate accumulation, and a foundation for future efforts to exploit this knowledge for cancer therapy.
    Keywords:  chemical biology; inborn error of metabolism; metabolism; mitochondria; post-translational modification (PTM); proteomics; redox signaling; tricarboxylic acid cycle (TCA cycle) (Krebs cycle)
  4. Nature. 2020 Aug 19.
    Gomes AP, Ilter D, Low V, Endress JE, Fernández-García J, Rosenzweig A, Schild T, Broekaert D, Ahmed A, Planque M, Elia I, Han J, Kinzig C, Mullarky E, Mutvei AP, Asara J, de Cabo R, Cantley LC, Dephoure N, Fendt SM, Blenis J.
      The risk of cancer and associated mortality increases substantially in humans from the age of 65 years onwards1-6. Nonetheless, our understanding of the complex relationship between age and cancer is still in its infancy2,3,7,8. For decades, this link has largely been attributed to increased exposure time to mutagens in older individuals. However, this view does not account for the established role of diet, exercise and small molecules that target the pace of metabolic ageing9-12. Here we show that metabolic alterations that occur with age can produce a systemic environment that favours the progression and aggressiveness of tumours. Specifically, we show that methylmalonic acid (MMA), a by-product of propionate metabolism, is upregulated in the serum of older people and functions as a mediator of tumour progression. We traced this to the ability of MMA to induce SOX4 expression and consequently to elicit transcriptional reprogramming that can endow cancer cells with aggressive properties. Thus, the accumulation of MMA represents a link between ageing and cancer progression, suggesting that MMA is a promising therapeutic target for advanced carcinomas.
  5. Biochem Pharmacol. 2020 Aug 18. pii: S0006-2952(20)30438-X. [Epub ahead of print] 114202
    Ciccarone F, De Falco P, Rosa Ciriolo M.
      Aconitase 2 (ACO2) belongs to the tricarboxylic acid (TCA) cycle, which represents a key metabolic hub for cellular metabolism that is frequently altered in cancer for satisfying bioenergetic and biosynthetic requirements of proliferating cells. The promotion of ACO2 activity in breast cancer cell lines was shown to slow down proliferation imposing a switch from aerobic glycolysis to oxidative metabolism. The alteration of metabolic pathways in cancer also impinges on the sensitivity to chemotherapeutic interventions. In this work, we evidence that the presence of ACO2 sensitizes cells to the treatment with the genotoxic agents cisplatin (CDDP) and doxorubicin activating the apoptotic cell death mechanism. This response was driven by the accumulation of reactive oxygen species (ROS) following both ACO2 overexpression and CDDP exposure that permit the stabilization/activation of p53 in nuclear and mitochondrial compartments. Collectively, our results highlight that in ACO2 overexpressing cells the promotion of mitochondrial metabolism accounts for increased ROS production that was buffered by p53 mitochondrial recruitment and autophagy induction. However, these systems are not able to counteract the CDDP-mediated oxidative stress that becomes the Achilles heel for increasing susceptibility to apoptotic cell death.
    Keywords:  TCA cycle; autophagy; cisplatin; mitochondria; oxidative stress
  6. Elife. 2020 Aug 17. pii: e58041. [Epub ahead of print]9
    Nowinski SM, Solmonson A, Rusin SF, Maschek JA, Bensard CL, Fogarty S, Jeong MY, Lettlova S, Berg JA, Morgan JT, Ouyang Y, Naylor BC, Paulo JA, Funai K, Cox JE, Gygi SP, Winge DR, DeBerardinis RJ, Rutter J.
      Cells harbor two systems for fatty acid synthesis, one in the cytoplasm (catalyzed by fatty acid synthase, FASN) and one in the mitochondria (mtFAS). In contrast to FASN, mtFAS is poorly characterized, especially in higher eukaryotes, with the major product(s), metabolic roles, and cellular function(s) being essentially unknown. Here we show that hypomorphic mtFAS mutant mouse skeletal myoblast cell lines display a severe loss of electron transport chain (ETC) complexes and exhibit compensatory metabolic activities including reductive carboxylation. This effect on ETC complexes appears to be independent of protein lipoylation, the best characterized function of mtFAS, as mutants lacking lipoylation have an intact ETC. Finally, mtFAS impairment blocks the differentiation of skeletal myoblasts in vitro. Together, these data suggest that ETC activity in mammals is profoundly controlled by mtFAS function, thereby connecting anabolic fatty acid synthesis with the oxidation of carbon fuels.
    Keywords:  biochemistry; chemical biology; mouse
  7. Nat Commun. 2020 Aug 17. 11(1): 4111
    Hoefflin R, Harlander S, Schäfer S, Metzger P, Kuo F, Schönenberger D, Adlesic M, Peighambari A, Seidel P, Chen CY, Consenza-Contreras M, Jud A, Lahrmann B, Grabe N, Heide D, Uhl FM, Chan TA, Duyster J, Zeiser R, Schell C, Heikenwalder M, Schilling O, Hakimi AA, Boerries M, Frew IJ.
      Mutational inactivation of VHL is the earliest genetic event in the majority of clear cell renal cell carcinomas (ccRCC), leading to accumulation of the HIF-1α and HIF-2α transcription factors. While correlative studies of human ccRCC and functional studies using human ccRCC cell lines have implicated HIF-1α as an inhibitor and HIF-2α as a promoter of aggressive tumour behaviours, their roles in tumour onset have not been functionally addressed. Herein we show using an autochthonous ccRCC model that Hif1a is essential for tumour formation whereas Hif2a deletion has only minor effects on tumour initiation and growth. Both HIF-1α and HIF-2α are required for the clear cell phenotype. Transcriptomic and proteomic analyses reveal that HIF-1α regulates glycolysis while HIF-2α regulates genes associated with lipoprotein metabolism, ribosome biogenesis and E2F and MYC transcriptional activities. HIF-2α-deficient tumours are characterised by increased antigen presentation, interferon signalling and CD8+ T cell infiltration and activation. Single copy loss of HIF1A or high levels of HIF2A mRNA expression correlate with altered immune microenvironments in human ccRCC. These studies reveal an oncogenic role of HIF-1α in ccRCC initiation and suggest that alterations in the balance of HIF-1α and HIF-2α activities can affect different aspects of ccRCC biology and disease aggressiveness.
  8. Radiat Oncol. 2020 Aug 14. 15(1): 197
    Xiang K, Jendrossek V, Matschke J.
      Radiotherapy (RT) is applied in 45-60% of all cancer patients either alone or in multimodal therapy concepts comprising surgery, RT and chemotherapy. However, despite technical innovations approximately only 50% are cured, highlight a high medical need for innovation in RT practice. RT is a multidisciplinary treatment involving medicine and physics, but has always been successful in integrating emerging novel concepts from cancer and radiation biology for improving therapy outcome. Currently, substantial improvements are expected from integration of precision medicine approaches into RT concepts.Altered metabolism is an important feature of cancer cells and a driving force for malignant progression. Proper metabolic processes are essential to maintain and drive all energy-demanding cellular processes, e.g. repair of DNA double-strand breaks (DSBs). Consequently, metabolic bottlenecks might allow therapeutic intervention in cancer patients.Increasing evidence now indicates that oncogenic activation of metabolic enzymes, oncogenic activities of mutated metabolic enzymes, or adverse conditions in the tumor microenvironment can result in abnormal production of metabolites promoting cancer progression, e.g. 2-hyroxyglutarate (2-HG), succinate and fumarate, respectively. Interestingly, these so-called "oncometabolites" not only modulate cell signaling but also impact the response of cancer cells to chemotherapy and RT, presumably by epigenetic modulation of DNA repair.Here we aimed to introduce the biological basis of oncometabolite production and of their actions on epigenetic regulation of DNA repair. Furthermore, the review will highlight innovative therapeutic opportunities arising from the interaction of oncometabolites with DNA repair regulation for specifically enhancing the therapeutic effects of genotoxic treatments including RT in cancer patients.
    Keywords:  DNA repair; Epigenetic regulation; Ionizing radiation; Oncometabolites
  9. J Pathol. 2020 Aug 20.
    Nilsson H, Lindgren D, Axelson H, Brueffer C, Saal LH, Lundgren J, Johansson ME.
      Clear cell renal cell carcinoma (ccRCC) is the most common form of renal cancer. Due to inactivation of the von Hippel Lindau tumour suppressor, the hypoxia inducible transcription factors (HIFs) are constitutively activated in these tumours, resulting in a pseudo-hypoxic phenotype. The HIFs induce the expression of genes involved in angiogenesis and cell survival, but they also reset the cellular metabolism to protect cells from oxygen and nutrient deprivation. ccRCC tumours are highly vascularized and the cytoplasm of the cancer cells is filled with lipid droplets and glycogen resulting in the histologically distinctive pale (clear) cytoplasm. Intratumoural heterogeneity may occur, and in some tumours, areas with granular, eosinophilic cytoplasm are found. Little is known regarding these traits and how they relate to the coexistent clear cell component, yet eosinophilic ccRCC is associated with higher grade and clinically more aggressive tumours. In this study we have for the first time performed RNA sequencing comparing histologically verified clear cell and eosinophilic areas from ccRCC tissue, aiming to analyse the characteristics of these cell types. Findings from RNA sequencing were confirmed by immunohistochemical staining of biphasic ccRCC. We found that the eosinophilic phenotype displayed a higher proliferative drive and lower differentiation, and we confirmed a correlation to tumours of higher stage. We further identified mutations of the tumour suppressor p53 (TP53) exclusively in the eosinophilic ccRCC component, where mTORC1 activity was also elevated. Also, eosinophilic areas were less vascularized, yet harboured more abundant infiltrating immune cells. The cytoplasm of clear cell ccRCC cells was filled with lipids but had very low mitochondrial content while the reverse was found in eosinophilic tissue. We herein suggest possible transcriptional mechanisms behind these phenomena. This article is protected by copyright. All rights reserved.
    Keywords:  Renal cell carcinoma; VHL; clear cell; electron microscopy; eosinophilic; granular; kidney cancer; mTOR; mitochondria; p53; vasculature
  10. Biomedicines. 2020 Aug 20. pii: E294. [Epub ahead of print]8(9):
    Liu Y, Lang F, Chou FJ, Zaghloul KA, Yang C.
      Mutations in isocitrate dehydrogenase (IDH) are commonly observed in lower-grade glioma and secondary glioblastomas. IDH mutants confer a neomorphic enzyme activity that converts α-ketoglutarate to an oncometabolite D-2-hydroxyglutarate, which impacts cellular epigenetics and metabolism. IDH mutation establishes distinctive patterns in metabolism, cancer biology, and the therapeutic sensitivity of glioma. Thus, a deeper understanding of the roles of IDH mutations is of great value to improve the therapeutic efficacy of glioma and other malignancies that share similar genetic characteristics. In this review, we focused on the genetics, biochemistry, and clinical impacts of IDH mutations in glioma.
    Keywords:  IDH mutation; cancer; glioma; therapy resistance
  11. Nat Microbiol. 2020 Aug 17.
    Deo P, Chow SH, Han ML, Speir M, Huang C, Schittenhelm RB, Dhital S, Emery J, Li J, Kile BT, Vince JE, Lawlor KE, Naderer T.
      Sensing of microbes activates the innate immune system, depending on functional mitochondria. However, pathogenic bacteria inhibit mitochondrial activity by delivering toxins via outer membrane vesicles (OMVs). How macrophages respond to pathogenic microbes that target mitochondria remains unclear. Here, we show that macrophages exposed to OMVs from Neisseria gonorrhoeae, uropathogenic Escherichia coli and Pseudomonas aeruginosa induce mitochondrial apoptosis and NLRP3 inflammasome activation. OMVs and toxins that cause mitochondrial dysfunction trigger inhibition of host protein synthesis, which depletes the unstable BCL-2 family member MCL-1 and induces BAK-dependent mitochondrial apoptosis. In parallel with caspase-11-mediated pyroptosis, mitochondrial apoptosis and potassium ion efflux activate the NLRP3 inflammasome after OMV exposure in vitro. Importantly, in the in vivo setting, the activation and release of interleukin-1β in response to N. gonorrhoeae OMVs is regulated by mitochondrial apoptosis. Our data highlight how innate immune cells sense infections by monitoring mitochondrial health.
  12. JCI Insight. 2020 Aug 20. pii: 138729. [Epub ahead of print]5(16):
    Beckermann KE, Hongo R, Ye X, Young K, Carbonell K, Healey DCC, Siska PJ, Barone S, Roe CE, Smith CC, Vincent BG, Mason FM, Irish JM, Rathmell WK, Rathmell JC.
      Metabolic reprogramming dictates the fate and function of stimulated T cells, yet these pathways can be suppressed in T cells in tumor microenvironments. We previously showed that glycolytic and mitochondrial adaptations directly contribute to reducing the effector function of renal cell carcinoma (RCC) CD8+ tumor-infiltrating lymphocytes (TILs). Here we define the role of these metabolic pathways in the activation and effector functions of CD8+ RCC TILs. CD28 costimulation plays a key role in augmenting T cell activation and metabolism, and is antagonized by the inhibitory and checkpoint immunotherapy receptors CTLA4 and PD-1. While RCC CD8+ TILs were activated at a low level when stimulated through the T cell receptor alone, addition of CD28 costimulation greatly enhanced activation, function, and proliferation. CD28 costimulation reprogrammed RCC CD8+ TIL metabolism with increased glycolysis and mitochondrial oxidative metabolism, possibly through upregulation of GLUT3. Mitochondria also fused to a greater degree, with higher membrane potential and overall mass. These phenotypes were dependent on glucose metabolism, as the glycolytic inhibitor 2-deoxyglucose both prevented changes to mitochondria and suppressed RCC CD8+ TIL activation and function. These data show that CD28 costimulation can restore RCC CD8+ TIL metabolism and function through rescue of T cell glycolysis that supports mitochondrial mass and activity.
    Keywords:  Glucose metabolism; Immunology; Immunotherapy; Oncology; T cells
  13. Pharmacol Ther. 2020 Aug 15. pii: S0163-7258(20)30194-7. [Epub ahead of print] 107664
    Liu Y, Lang F, Yang C.
      Nuclear factor-erythroid 2-related factor 2 (NRF2) is a master regulator of a series of cytoprotective genes, which protects cells from stress conditions such as reactive oxygen species (ROS) and electrophiles. Besides its pivotal role in cellular physiology and stress response, several recent advances revealed that NRF2-governed pathways are extensively exploited in cancer cells, and play critical roles in granting growth advantage, supporting cancer metabolism, and promoting malignant transformation. In the present review, we focus on the regulatory mechanisms of NRF2 and its roles in cancer biology. We also discuss the value of targeting NRF2-associated pathways as a means of developing future cancer therapeutics.
    Keywords:  Antioxidant pathway; Cancer; Glutathione; KEAP1; NRF2; Therapy resistance
  14. J Biochem. 2020 Aug 20. pii: mvaa098. [Epub ahead of print]
    Kazuhito T, Wei FY.
      A fundamental aspect of mitochondria is that they possess DNA and protein translation machinery. Mitochondrial DNA encodes 22 tRNAs that translate mitochondrial mRNAs to 13 polypeptides of respiratory complexes. Various chemical modifications have been identified in mitochondrial tRNAs via complex enzymatic processes. A growing body of evidence has demonstrated that these modifications are essential for translation by regulating tRNA stability, structure, and mRNA binding, and can be dynamically regulated by the metabolic environment. Importantly, the hypomodification of mitochondrial tRNA due to pathogenic mutations in mitochondrial tRNA genes or nuclear genes encoding modifying enzymes can result in life-threatening mitochondrial diseases in humans. Thus, the mitochondrial tRNA modification is a fundamental mechanism underlying the tight regulation of mitochondrial translation and is essential for life. In this review, we focus on recent findings on the physiological roles of 5-taurinomethyl modification (herein referred as taurine modification) in mitochondrial tRNAs. We summarize the findings in human patients and animal models with a deficiency of taurine modifications and provide pathogenic links to mitochondrial diseases. We anticipate that this review will help understand the complexity of mitochondrial biology and disease.
  15. Sci Adv. 2020 Aug;6(32): eabc7288
    Ruan L, McNamara JT, Zhang X, Chang AC, Zhu J, Dong Y, Sun G, Peterson A, Na CH, Li R.
      Proteostasis declines with age, characterized by the accumulation of unfolded or damaged proteins. Recent studies suggest that proteins constituting pathological inclusions in neurodegenerative diseases also enter and accumulate in mitochondria. How unfolded proteins are managed within mitochondria remains unclear. Here, we found that excessive unfolded proteins in the mitochondrial matrix of yeast cells are consolidated into solid-phase inclusions, which we term deposits of unfolded mitochondrial proteins (DUMP). Formation of DUMP occurs in mitochondria near endoplasmic reticulum-mitochondria contact sites and is regulated by mitochondrial proteins controlling the production of cytidine 5'-diphosphate-diacylglycerol. DUMP formation is age dependent but accelerated by exogenous unfolded proteins. Many enzymes of the tricarboxylic acid cycle were enriched in DUMP. During yeast cell division, DUMP formation is necessary for asymmetric inheritance of damaged mitochondrial proteins between mother and daughter cells. We provide evidence that DUMP-like structures may be induced by excessive unfolded proteins in human cells.
  16. Nat Commun. 2020 Aug 18. 11(1): 4135
    Gutiérrez-Fernández J, Kaszuba K, Minhas GS, Baradaran R, Tambalo M, Gallagher DT, Sazanov LA.
      Complex I is the first and the largest enzyme of respiratory chains in bacteria and mitochondria. The mechanism which couples spatially separated transfer of electrons to proton translocation in complex I is not known. Here we report five crystal structures of T. thermophilus enzyme in complex with NADH or quinone-like compounds. We also determined cryo-EM structures of major and minor native states of the complex, differing in the position of the peripheral arm. Crystal structures show that binding of quinone-like compounds (but not of NADH) leads to a related global conformational change, accompanied by local re-arrangements propagating from the quinone site to the nearest proton channel. Normal mode and molecular dynamics analyses indicate that these are likely to represent the first steps in the proton translocation mechanism. Our results suggest that quinone binding and chemistry play a key role in the coupling mechanism of complex I.
  17. Methods Mol Biol. 2020 ;2184 185-196
    Wei HJ, Letterio JJ, Pareek TK.
      Dendritic cells (DCs) are the bridge between innate and T cell-dependent adaptive immunity, and are promising therapeutic targets for cancer and immune-mediated disorders. In the recent past, DCs have gained significant interest to manipulate them for the treatment of cancer and immune-mediated disorders. This can be achieved by differentiating them into either immunogenic or tolerogenic DCs (TolDCs), by modulating their metabolic pathways, including glycolysis, oxidative phosphorylation, and fatty acid metabolism, to orchestrate their desired function. For immunogenic DCs, this maturation shifts the metabolic profile to a glycolytic metabolic state and leads to the use of glucose as a carbon source, whereas TolDCs prefer oxidative phosphorylation (OXPHOS) and fatty acid oxidation for their energy resource.Understanding the metabolic regulation of DC subsets and functions at large not only will improve our understanding of DC biology and immune regulation, but can also open up opportunities for treating immune-mediated ailments and cancers by tweaking endogenous T-cell responses through DC-based immunotherapies. Here we describe a method to analyze this dichotomous metabolic reprogramming of the DCs for generating reliable and effective DC cell therapy products. We, hereby, report how to measure the OXPHOS and glycolysis level of DCs. We focus on the metabolic reprogramming of TolDCs using a pharmacological nuclear factor (erythroid-derived 2)-like-2 factor (Nrf2) activator as an example to illustrate the metabolic profile of TolDCs.
    Keywords:  Dendritic cells; Glycolysis; Immunometabolism; Oxidative phosphorylation
  18. Autophagy. 2020 Aug 19.
    Han S, Jeong YY, Sheshadri P, Cai Q.
      Mitochondria sustain various essential functions at synaptic terminals. Synaptic mitochondria deficits have been implicated in early Alzheimer disease (AD) pathophysiology. Mitophagy, a selective autophagy for removal of damaged mitochondria, plays a key role in mitochondrial quality control in neurons. However, fundamental questions remain unanswered as to whether mitophagy regulates synaptic mitochondrial integrity and whether AD-associated early deficits in synaptic mitochondria are attributed to mitophagy failure. We have recently revealed that the integrity of synaptic mitochondria is maintained by a coordination of RHEB-mediated mitophagy with dynein- and SNAPIN-driven retrograde transport. We demonstrate that increased mitophagy initiation, coupled with defective retrograde transport, triggers mitophagy stress at AD synapses. Excitingly, SNAPIN-enhanced retrograde transport reduces synaptic mitophagy stress and ameliorates mitochondrial deficits, thereby counteracting synaptic damage in AD mouse brains. Therefore, our study provides new mechanistic insights into how mitophagy facilitates synaptic mitochondrial maintenance and how mitophagy failure exacerbates AD-linked mitochondrial defects and synaptic degeneration.
    Keywords:  Alzheimer; Nix; PRKN; RHEB; SNAPIN; mitophagosome; retrograde transport; synaptic degeneration; synaptic mitochondrial deficits; synaptic mitophagy
  19. Cell Res. 2020 Aug 17.
    Gao K, Cheng M, Zuo X, Lin J, Hoogewijs K, Murphy MP, Fu XD, Zhang X.
      RNA interference (RNAi) has been thought to be a gene-silencing pathway present in most eukaryotic cells to safeguard the genome against retrotransposition. Small interfering RNAs (siRNAs) have also become a powerful tool for studying gene functions. Given the endosymbiotic hypothesis that mitochondria originated from prokaryotes, mitochondria have been generally assumed to lack active RNAi; however, certain bacteria have Argonaute homologs and various reports suggest the presence of specific microRNAs and nuclear genome (nDNA)-encoded Ago2 in the mitochondria. Here we report that transfected siRNAs are not only able to enter the matrix of mitochondria, but also function there to specifically silence targeted mitochondrial transcripts. The mitoRNAi effect is readily detectable at the mRNA level, but only recordable on relatively unstable proteins, such as the mtDNA-encoded complex IV subunits. We also apply mitoRNAi to directly determine the postulated crosstalk between individual respiratory chain complexes, and our result suggests that the controversial observations previously made in patient-derived cells might result from differential adaptation in different cell lines. Our findings bring a new tool to study mitochondrial biology.
  20. Int J Mol Sci. 2020 Aug 21. pii: E6014. [Epub ahead of print]21(17):
    Frattaruolo L, Brindisi M, Curcio R, Marra F, Dolce V, Cappello AR.
      Metabolic reprogramming is a hallmark of cancer, which implements a profound metabolic rewiring in order to support a high proliferation rate and to ensure cell survival in its complex microenvironment. Although initial studies considered glycolysis as a crucial metabolic pathway in tumor metabolism reprogramming (i.e., the Warburg effect), recently, the critical role of mitochondria in oncogenesis, tumor progression, and neoplastic dissemination has emerged. In this report, we examined the main mitochondrial metabolic pathways that are altered in cancer, which play key roles in the different stages of tumor progression. Furthermore, we reviewed the function of important molecules inhibiting the main mitochondrial metabolic processes, which have been proven to be promising anticancer candidates in recent years. In particular, inhibitors of oxidative phosphorylation (OXPHOS), heme flux, the tricarboxylic acid cycle (TCA), glutaminolysis, mitochondrial dynamics, and biogenesis are discussed. The examined mitochondrial metabolic network inhibitors have produced interesting results in both preclinical and clinical studies, advancing cancer research and emphasizing that mitochondrial targeting may represent an effective anticancer strategy.
    Keywords:  cancer therapy; metabolic network; metabolic rewiring; mitochondria; targeting mitochondria
  21. J Biomed Sci. 2020 Aug 17. 27(1): 87
    Takahara T, Amemiya Y, Sugiyama R, Maki M, Shibata H.
      The mechanistic target of rapamycin complex 1 (mTORC1) is an essential regulator of cell growth and metabolism through the modulation of protein and lipid synthesis, lysosome biogenesis, and autophagy. The activity of mTORC1 is dynamically regulated by several environmental cues, including amino acid availability, growth factors, energy levels, and stresses, to coordinate cellular status with environmental conditions. Dysregulation of mTORC1 activity is closely associated with various diseases, including diabetes, cancer, and neurodegenerative disorders. The discovery of Rag GTPases has greatly expanded our understanding of the regulation of mTORC1 activity by amino acids, especially leucine and arginine. In addition to Rag GTPases, other factors that also contribute to the modulation of mTORC1 activity have been identified. In this review, we discuss the mechanisms of regulation of mTORC1 activity by particular amino acids.
    Keywords:  Amino acids; Intracellular Ca2+ concentration; Rag GTPases; Rheb GTPase; mTOR; mTORC1
  22. Proc Natl Acad Sci U S A. 2020 Aug 18. pii: 202010275. [Epub ahead of print]
    Khatib A, Solaimuthu B, Ben Yosef M, Abu Rmaileh A, Tanna M, Oren G, Schlesinger Frisch M, Axelrod JH, Lichtenstein M, Shaul YD.
      One of the emerging hallmarks of cancer illustrates the importance of metabolic reprogramming, necessary to synthesize the building blocks required to fulfill the high demands of rapidly proliferating cells. However, the proliferation-independent instructive role of metabolic enzymes in tumor plasticity is still unclear. Here, we provide evidence that glutathione peroxidase 8 (GPX8), a poorly characterized enzyme that resides in the endoplasmic reticulum, is an essential regulator of tumor aggressiveness. We found that GPX8 expression was induced by the epithelial-mesenchymal transition (EMT) program. Moreover, in breast cancer patients, GPX8 expression significantly correlated with known mesenchymal markers and poor prognosis. Strikingly, GPX8 knockout in mesenchymal-like cells (MDA-MB-231) resulted in an epithelial-like morphology, down-regulation of EMT characteristics, and loss of cancer stemness features. In addition, GPX8 knockout significantly delayed tumor initiation and decreased its growth rate in mice. We found that these GPX8 loss-dependent phenotypes were accompanied by the repression of crucial autocrine factors, in particular, interleukin-6 (IL-6). In these cells, IL-6 bound to the soluble receptor (sIL6R), stimulating the JAK/STAT3 signaling pathway by IL-6 trans-signaling mechanisms, so promoting cancer aggressiveness. We observed that in GPX8 knockout cells, this signaling mechanism was impaired as sIL6R failed to activate the JAK/STAT3 signaling pathway. Altogether, we present the GPX8/IL-6/STAT3 axis as a metabolic-inflammatory pathway that acts as a robust regulator of cancer cell aggressiveness.
    Keywords:  GPX8; JAK/STAT3 signaling; cancer metabolism; epithelial–mesenchymal transition
  23. PLoS Biol. 2020 Aug 20. 18(8): e3000808
    Ma D, Zheng B, Liu HL, Zhao YB, Liu X, Zhang XH, Li Q, Shi WB, Suzuki T, Wen JK.
      Although dysregulation of mitochondrial dynamics has been linked to cellular senescence, which contributes to advanced age-related disorders, it is unclear how Krüppel-like factor 5 (Klf5), an essential transcriptional factor of cardiovascular remodeling, mediates the link between mitochondrial dynamics and vascular smooth muscle cell (VSMC) senescence. Here, we show that Klf5 down-regulation in VSMCs is correlated with rupture of abdominal aortic aneurysm (AAA), an age-related vascular disease. Mice lacking Klf5 in VSMCs exacerbate vascular senescence and progression of angiotensin II (Ang II)-induced AAA by facilitating reactive oxygen species (ROS) formation. Klf5 knockdown enhances, while Klf5 overexpression suppresses mitochondrial fission. Mechanistically, Klf5 activates eukaryotic translation initiation factor 5a (eIF5a) transcription through binding to the promoter of eIF5a, which in turn preserves mitochondrial integrity by interacting with mitofusin 1 (Mfn1). Accordingly, decreased expression of eIF5a elicited by Klf5 down-regulation leads to mitochondrial fission and excessive ROS production. Inhibition of mitochondrial fission decreases ROS production and VSMC senescence. Our studies provide a potential therapeutic target for age-related vascular disorders.
  24. F1000Res. 2020 ;pii: F1000 Faculty Rev-935. [Epub ahead of print]9
    Luo X, O'Neill KL, Huang K.
      Bax and Bak, two functionally similar, pro-apoptotic proteins of the Bcl-2 family, are known as the gateway to apoptosis because of their requisite roles as effectors of mitochondrial outer membrane permeabilization (MOMP), a major step during mitochondria-dependent apoptosis. The mechanism of how cells turn Bax/Bak from inert molecules into fully active and lethal effectors had long been the focal point of a major debate centered around two competing, but not mutually exclusive, models: direct activation and indirect activation. After intensive research efforts for over two decades, it is now widely accepted that to initiate apoptosis, some of the BH3-only proteins, a subclass of the Bcl-2 family, directly engage Bax/Bak to trigger their conformational transformation and activation. However, a series of recent discoveries, using previously unavailable CRISPR-engineered cell systems, challenge the basic premise that undergirds the consensus and provide evidence for a novel and surprisingly simple model of Bax/Bak activation: the membrane (lipids)-mediated spontaneous model. This review will discuss the evidence, rationale, significance, and implications of this new model.
    Keywords:  Activator; Apoptosis; BH3 mimetics; BH3-only proteins; Bad; Bak; Bax; Bcl-2 family; Bcl-xL; Bid; Bim; Direct activation; Indirect activation; Mcl-1; Membrane-mediated Spontaneous activation; Mitochondrial outer membrane; Sensitizer; auto-activation; de novo activation; retro-translocation
  25. Elife. 2020 Aug 19. pii: e59166. [Epub ahead of print]9
    Walls JF, Subleski JJ, Palmieri EM, Gonzalez Cotto M, Gardiner CM, McVicar DW, Finlay DK.
      Natural Killer (NK) cells have an important role in immune responses to viruses and tumours. Integrating changes in signal transduction pathways and cellular metabolism is essential for effective NK cells responses. The glycolytic enzyme Pyruvate Kinase Muscle 2 (PKM2) has described roles in regulating glycolytic flux and signal transduction, particularly gene transcription. While PKM2 expression is robustly induced in activated NK cells, mice lacking PKM2 in NK cells showed no defect in NK cell metabolism, transcription or anti-viral responses to MCMV infection. NK cell metabolism was maintained due to compensatory PKM1 expression in PKM2-null NK cells. To further investigate the role of PKM2 we used TEPP-46, which increases PKM2 catalytic activity while inhibiting any PKM2 signalling functions. NK cells activated with TEPP-46 had reduced effector function due to TEPP-46-induced increases in oxidative stress. Overall, PKM2-regulated glycolytic metabolism and redox status, not transcriptional control, facilitate optimal NK cells responses.
    Keywords:  cell biology; immunology; inflammation; mouse
  26. Nat Cell Biol. 2020 Aug 17.
    Liu J, Guan D, Dong M, Yang J, Wei H, Liang Q, Song L, Xu L, Bai J, Liu C, Mao J, Zhang Q, Zhou J, Wu X, Wang M, Cong YS.
      p53 is the most intensively studied tumour suppressor1. The regulation of p53 homeostasis is essential for its tumour-suppressive function2,3. Although p53 is regulated by an array of post-translational modifications, both during normal homeostasis and in stress-induced responses2-4, how p53 maintains its homeostasis remains unclear. UFMylation is a recently identified ubiquitin-like modification with essential biological functions5-7. Deficiency in this modification leads to embryonic lethality in mice and disease in humans8-12. Here, we report that p53 can be covalently modified by UFM1 and that this modification stabilizes p53 by antagonizing its ubiquitination and proteasome degradation. Mechanistically, UFL1, the UFM1 ligase6, competes with MDM2 to bind to p53 for its stabilization. Depletion of UFL1 or DDRGK1, the critical regulator of UFMylation6,13, decreases p53 stability and in turn promotes cell growth and tumour formation in vivo. Clinically, UFL1 and DDRGK1 expression are downregulated and positively correlated with levels of p53 in a high percentage of renal cell carcinomas. Our results identify UFMylation as a crucial post-translational modification for maintenance of p53 stability and tumour-suppressive function, and point to UFMylation as a promising therapeutic target in cancer.
  27. Autophagy. 2020 Aug 17.
    Chen X, Li J, Kang R, Klionsky DJ, Tang D.
      Ferroptosis is an iron-dependent, non-apoptotic form of regulated cell death caused by lipid peroxidation, which is controlled by integrated oxidation and antioxidant systems. The iron-containing enzyme lipoxygenase is the main promoter of ferroptosis by producing lipid hydroperoxides, and its function relies on the activation of ACSL4-dependent lipid biosynthesis. In contrast, the selenium-containing enzyme GPX4 is currently recognized as a central repressor of ferroptosis, and its activity depends on glutathione produced from the activation of the cystine-glutamate antiporter SLC7A11. Many metabolic (especially involving iron, lipids, and amino acids) and degradation pathways (macroautophagy/autophagy and the ubiquitin-proteasome system) orchestrate the complex ferroptotic response through direct or indirect regulation of iron accumulation or lipid peroxidation. Although the detailed mechanism of membrane injury during ferroptosis remains a mystery, ESCRT III-mediated plasma membrane repair can make cells resistant to ferroptosis. Here, we review the recent rapid progress in understanding the molecular mechanisms of ferroptosis and focus on the epigenetic, transcriptional, and posttranslational regulation of this process.
  28. Nat Commun. 2020 Aug 17. 11(1): 4113
    Wu H, Estrella V, Beatty M, Abrahams D, El-Kenawi A, Russell S, Ibrahim-Hashim A, Longo DL, Reshetnyak YK, Moshnikova A, Andreev OA, Luddy K, Damaghi M, Kodumudi K, Pillai SR, Enriquez-Navas P, Pilon-Thomas S, Swietach P, Gillies RJ.
      The acidic pH of tumors profoundly inhibits effector functions of activated CD8 + T-cells. We hypothesize that this is a physiological process in immune regulation, and that it occurs within lymph nodes (LNs), which are likely acidic because of low convective flow and high glucose metabolism. Here we show by in vivo fluorescence and MR imaging, that LN paracortical zones are profoundly acidic. These acidic niches are absent in athymic Nu/Nu and lymphodepleted mice, implicating T-cells in the acidifying process. T-cell glycolysis is inhibited at the low pH observed in LNs. We show that this is due to acid inhibition of monocarboxylate transporters (MCTs), resulting in a negative feedback on glycolytic rate. Importantly, we demonstrate that this acid pH does not hinder initial activation of naïve T-cells by dendritic cells. Thus, we describe an acidic niche within the immune system, and demonstrate its physiological role in regulating T-cell activation.
  29. Cold Spring Harb Perspect Med. 2020 Aug 17. pii: a035477. [Epub ahead of print]
    Stahl M, Epstein-Peterson ZD, Intlekofer AM.
      Leukemias and lymphomas acquire the capacity for unrestrained cell growth and proliferation in conjunction with loss of responsiveness to molecular programs that promote terminal differentiation. Malignant cells generate the building blocks required for rapid cell division through both increased acquisition of nutrients from the environment and reprogrammed intermediary metabolism to shunt these molecules into producing the protein, lipids, and nucleic acids that comprise cell biomass. These accelerated metabolic processes require energy in the form of ATP and reducing equivalents in the form of NADPH, which power biosynthetic reactions and buffer oxidative stress encountered by the metabolically active cancer cell. Cancer-associated metabolic alterations can also promote accumulation or depletion of specific metabolites that directly regulate cell fate and function, thereby coupling metabolic reprogramming to dedifferentiation and stemness. This review will focus on the mechanisms by which leukemia and lymphoma cells rewire cellular metabolism to support: (1) bioenergetics, (2) biomass accumulation, (3) redox balance, and (4) differentiation blockade. We will further highlight examples of how specific pathways of leukemia and lymphoma metabolism confer therapeutic vulnerabilities that can be targeted to inhibit growth or promote differentiation.
  30. Semin Cancer Biol. 2020 Aug 14. pii: S1044-579X(20)30172-3. [Epub ahead of print]
    Garcia-Ruiz C, de la Rosa LC, Ribas V, Fernandez-Checa JC.
      Cholesterol is a crucial component of membrane bilayers that determines their physical and functional properties. Cells largely satify their need for cholesterol through the novo synthesis from acetyl-CoA and this demand is particularly critical for cancer cells to sustain dysregulated cell proliferation. However, the association between serum or tissue cholesterol levels and cancer development is not well established as epidemiologic data do not consistently support this link. While most preclinical studies focused on the role of total celular cholesterol, the specific contribution of the mitochondrial cholesterol pool to alterations in cancer cell biology has been less explored. Although low compared to other bilayers, the mitochondrial cholesterol content plays an important physiological function in the synthesis of steroid hormones in steroidogenic tissues or bile acids in the liver and controls mitochondrial function. In addition, mitochondrial cholesterol metabolism generates oxysterols, which in turn, regulate multiple pathways, including cholesterol and lipid metabolism as well as cell proliferation. In the present review, we summarize the regulation of mitochondrial cholesterol, including its role in mitochondrial routine performance, cell death and chemotherapy resistance, highlighting its potential contribution to cancer. Of particular relevance is hepatocellular carcinoma, whose incidence in Western countries had tripled in the past decades due to the obesity and type II diabetes epidemic. A better understanding of the role of mitochondrial cholesterol in cancer development may open up novel opportunities for cancer therapy.
    Keywords:  Mevalonate pathway; StARD1; chemotherapy; free cholesterol; hepatocellular carcinoma; oxysterols
  31. Cancer Res. 2020 Aug 19. pii: canres.1255.2020. [Epub ahead of print]
    Rozeveld CN, Johnson KM, Zhang L, Razidlo GL.
      Oncogene-induced metabolic reprogramming is a hallmark of pancreatic cancer (PDAC), yet the metabolic drivers of metastasis are unclear. In PDAC, obesity and excess fatty acids accelerate tumor growth and increase metastasis. Here, we report that excess lipids, stored in organelles called lipid droplets (LD), are a key resource to fuel the energy-intensive process of metastasis. The oncogene KRAS controlled the storage and utilization of LD through regulation of hormone sensitive lipase (HSL), which was downregulated in human PDAC. Disruption of the KRAS-HSL axis reduced lipid storage, reprogrammed tumor cell metabolism, and inhibited invasive migration in vitro and metastasis in vivo. Finally, microscopy-based metabolic analysis revealed that migratory cells selectively utilize oxidative metabolism during the process of migration to metabolize stored lipids and fuel invasive migration. Taken together, these results reveal a mechanism that can be targeted to attenuate PDAC metastasis.
  32. Cell Rep. 2020 Aug 18. pii: S2211-1247(20)31017-2. [Epub ahead of print]32(7): 108032
    Pattanayak GK, Liao Y, Wallace EWJ, Budnik B, Drummond DA, Rust MJ.
      An emerging principle of cell biology is the regulated conversion of macromolecules between soluble and condensed states. To screen for such regulation of the cyanobacterial proteome, we use quantitative mass spectrometry to identify proteins that change solubility during the day-night cycle. We find a set of night-insoluble proteins that includes many enzymes in essential metabolic pathways. Using time-lapse microscopy and isotope labeling, we show that these proteins reversibly transition between punctate structures at night and a soluble state during the day without substantial degradation. We find that the cyanobacterial circadian clock regulates the kinetics of puncta formation during the night and that the appearance of puncta indicates the metabolic status of the cell. Reversible condensation of specific enzymes is thus a regulated response to the day-night cycle and may reflect a general bacterial strategy used in fluctuating growth conditions.
    Keywords:  circadian clock; cyanobacteria; metabolism; protein condensation
  33. Sci China Life Sci. 2020 Aug 17.
    Fan C, Zhang S, Gong Z, Li X, Xiang B, Deng H, Zhou M, Li G, Li Y, Xiong W, Zeng Z, Li X.
      Mounting evidence has revealed that the therapeutic efficacy of immunotherapies is restricted to a small portion of cancer patients. A deeper understanding of how metabolic reprogramming in the tumor microenvironment (TME) regulates immunity remains a major challenge to tumor eradication. It has been suggested that metabolic reprogramming in the TME may affect metabolism in immune cells and subsequently suppress immune function. Tumor cells compete with infiltrating immune cells for nutrients and metabolites. Notably, the immunosuppressive TME is characterized by catabolic and anabolic processes that are critical for immune cell function, and elevated inhibitory signals may favor cancer immune evasion. The major energy sources that supply different immune cell subtypes also undergo reprogramming. We herein summarize the metabolic remodeling in tumor cells and different immune cell subtypes and the latest advances underlying the use of metabolic checkpoints in antitumor immunotherapies. In this context, targeting both tumor and immune cell metabolic reprogramming may enhance therapeutic efficacy.
    Keywords:  antitumor immunotherapy; infiltrating immune cells; metabolic reprogramming; tumor immune evasion; tumor microenvironment
  34. Redox Biol. 2020 Aug 03. pii: S2213-2317(20)30875-2. [Epub ahead of print]36 101670
    Fuhrmann DC, Mondorf A, Beifuß J, Jung M, Brüne B.
      Cellular iron, at the physiological level, is essential to maintain several metabolic pathways, while an excess of free iron may cause oxidative damage and/or provoke cell death. Consequently, iron homeostasis has to be tightly controlled. Under hypoxia these regulatory mechanisms for human macrophages are not well understood. Hypoxic primary human macrophages reduced intracellular free iron and increased ferritin expression, including mitochondrial ferritin (FTMT), to store iron. In parallel, nuclear receptor coactivator 4 (NCOA4), a master regulator of ferritinophagy, decreased and was proven to directly regulate FTMT expression. Reduced NCOA4 expression resulted from a lower rate of hypoxic NCOA4 transcription combined with a micro RNA 6862-5p-dependent degradation of NCOA4 mRNA, the latter being regulated by c-jun N-terminal kinase (JNK). Pharmacological inhibition of JNK under hypoxia increased NCOA4 and prevented FTMT induction. FTMT and ferritin heavy chain (FTH) cooperated to protect macrophages from RSL-3-induced ferroptosis under hypoxia as this form of cell death is linked to iron metabolism. In contrast, in HT1080 fibrosarcome cells, which are sensitive to ferroptosis, NCOA4 and FTMT are not regulated. Our study helps to understand mechanisms of hypoxic FTMT regulation and to link ferritinophagy and macrophage sensitivity to ferroptosis.
    Keywords:  FTMT; Ferritinophagy; Ferroptosis; Hypoxia; Iron; JNK; Macrophages; NCOA4; miR-6862-5p
  35. Antioxid Redox Signal. 2020 Aug 14.
    Miller CG, Schmidt EE.
      Significance: In humans, imbalances in the reduction-oxidation (redox) status of cells are associated with many pathological states. In addition, many therapeutics and prophylactics used as interventions for diverse pathologies either directly modulate oxidant levels or otherwise influence endogenous cellular redox systems. Recent Advances: The cellular machineries that maintain redox homeostasis or that function within antioxidant defense systems rely heavily on the regulated reactivities of sulfur atoms either within or derived from the amino acids cysteine and methionine. Recent advances have substantially advanced our understanding of the complex and essential chemistry of biological sulfur-containing molecules. Critical Issues: The redox machineries that maintain cellular homeostasis under diverse stresses can consume large amounts of energy to generate reducing power and/or large amounts of sulfur-containing nutrients to replenish or sustain intracellular stores. By understanding the metabolic pathways underlying these responses, one can better predict how to protect cells from specific stresses. Future Directions: Here, we summarize the current state of knowledge about the impacts of different stresses on cellular metabolism of sulfur-containing molecules. This analysis suggests that there remains more to be learned about how cells use sulfur chemistry to respond to stresses, which could in turn lead to advances in therapeutic interventions for some exposures or conditions.
    Keywords:  disulfide reductase systems; drug metabolism; methionine cycle; oxidative stress; trans-sulfuration
  36. Nat Commun. 2020 Aug 17. 11(1): 4116
    Sharanek A, Burban A, Laaper M, Heckel E, Joyal JS, Soleimani VD, Jahani-Asl A.
      Glioblastoma contains a rare population of self-renewing brain tumor stem cells (BTSCs) which are endowed with properties to proliferate, spur the growth of new tumors, and at the same time, evade ionizing radiation (IR) and chemotherapy. However, the drivers of BTSC resistance to therapy remain unknown. The cytokine receptor for oncostatin M (OSMR) regulates BTSC proliferation and glioblastoma tumorigenesis. Here, we report our discovery of a mitochondrial OSMR that confers resistance to IR via regulation of oxidative phosphorylation, independent of its role in cell proliferation. Mechanistically, OSMR is targeted to the mitochondrial matrix via the presequence translocase-associated motor complex components, mtHSP70 and TIM44. OSMR interacts with NADH ubiquinone oxidoreductase 1/2 (NDUFS1/2) of complex I and promotes mitochondrial respiration. Deletion of OSMR impairs spare respiratory capacity, increases reactive oxygen species, and sensitizes BTSCs to IR-induced cell death. Importantly, suppression of OSMR improves glioblastoma response to IR and prolongs lifespan.
  37. Cell Death Dis. 2020 Aug 20. 11(8): 662
    Brashears CB, Barlin M, Ehrhardt WR, Rathore R, Schultze M, Tzeng SC, Van Tine BA, Held JM.
      Arginine auxotrophy due to the silencing of argininosuccinate synthetase 1 (ASS1) occurs in many carcinomas and in the majority of sarcomas. Arginine deiminase (ADI-PEG20) therapy exploits this metabolic vulnerability by depleting extracellular arginine, causing arginine starvation. ASS1-negative cells develop resistance to ADI-PEG20 through a metabolic adaptation that includes re-expressing ASS1. As arginine-based multiagent therapies are being developed, further characterization of the changes induced by arginine starvation is needed. In order to develop a systems-level understanding of these changes, activity-based proteomic profiling (ABPP) and phosphoproteomic profiling were performed before and after ADI-PEG20 treatment in ADI-PEG20-sensitive and resistant sarcoma cells. When integrated with metabolomic profiling, this multi-omic analysis reveals that cellular response to arginine starvation is mediated by adaptive ERK signaling and activation of the Myc-Max transcriptional network. Concomitantly, these data elucidate proteomic changes that facilitate oxaloacetate production by enhancing glutamine and pyruvate anaplerosis and altering lipid metabolism to recycle citrate for oxidative glutaminolysis. Based on the complexity of metabolic and cellular signaling interactions, these multi-omic approaches could provide valuable tools for evaluating response to metabolically targeted therapies.
  38. Commun Biol. 2020 Aug 18. 3(1): 451
    Wikström M, Springett R.
      The protonmotive mitochondrial respiratory chain, comprising complexes I, III and IV, transduces free energy of the electron transfer reactions to an electrochemical proton gradient across the inner mitochondrial membrane. This gradient is used to drive synthesis of ATP and ion and metabolite transport. The efficiency of energy conversion is of interest from a physiological point of view, since the energy transduction mechanisms differ fundamentally between the three complexes. Here, we have chosen actively phosphorylating mitochondria as the focus of analysis. For all three complexes we find that the thermodynamic efficiency is about 80-90% and that the degree of coupling between the redox and proton translocation reactions is very high during active ATP synthesis. However, when net ATP synthesis stops at a high ATP/ADP.Pi ratio, and mitochondria reach "State 4" with an elevated proton gradient, the degree of coupling drops substantially. The mechanistic cause and the physiological implications of this effect are discussed.
  39. Curr Biol. 2020 Aug 17. pii: S0960-9822(20)30933-7. [Epub ahead of print]30(16): R921-R925
    Anderson NM, Simon MC.
      A tumor is not simply a group of cancer cells, but rather a heterogeneous collection of infiltrating and resident host cells, secreted factors and extracellular matrix. Tumor cells stimulate significant molecular, cellular and physical changes within their host tissues to support tumor growth and progression. An emerging tumor microenvironment is a complex and continuously evolving entity. The composition of the tumor microenvironment varies between tumor types, but hallmark features include immune cells, stromal cells, blood vessels, and extracellular matrix. It is believed that the "tumor microenvironment is not just a silent bystander, but rather an active promoter of cancer progression" (Truffi et al., 2020). Early in tumor growth, a dynamic and reciprocal relationship develops between cancer cells and components of the tumor microenvironment that supports cancer cell survival, local invasion and metastatic dissemination. To overcome a hypoxic and acidic microenvironment, the tumor microenvironment coordinates a program that promotes angiogenesis to restore oxygen and nutrient supply and remove metabolic waste. Tumors become infiltrated with diverse adaptive and innate immune cells that can perform both pro- and anti- tumorigenic functions (Figure 1). An expanding literature on the tumor microenvironment has identified new targets within it for therapeutic intervention.
  40. Cell Death Dis. 2020 Aug 06. 11(8): 649
    Wan X, Wang C, Huang Z, Zhou D, Xiang S, Qi Q, Chen X, Arbely E, Liu CY, Du P, Yu W.
      The folate-coupled metabolic enzyme MTHFD2 (the mitochondrial methylenetetrahydrofolate dehydrogenase/cyclohydrolase) confers redox homeostasis and drives cancer cell proliferation and migration. Here, we show that MTHFD2 is hyperacetylated and lysine 88 is the critical acetylated site. SIRT3, the major deacetylase in mitochondria, is responsible for MTHFD2 deacetylation. Interestingly, chemotherapeutic agent cisplatin inhibits expression of SIRT3 to induce acetylation of MTHFD2 in colorectal cancer cells. Cisplatin-induced acetylated K88 MTHFD2 is sufficient to inhibit its enzymatic activity and downregulate NADPH levels in colorectal cancer cells. Ac-K88-MTHFD2 is significantly decreased in human colorectal cancer samples and is inversely correlated with the upregulated expression of SIRT3. Our findings reveal an unknown regulation axis of cisplatin-SIRT3-MTHFD2 in redox homeostasis and suggest a potential therapeutic strategy for cancer treatments by targeting MTHFD2.
  41. Life Sci. 2020 Aug 14. pii: S0024-3205(20)30999-1. [Epub ahead of print] 118247
    Wang N, Zhu P, Huang R, Wang C, Sun L, Lan B, He Y, Zhao H, Gao Y.
      PTEN-induced putative kinase 1 (PINK1) performs many important functions in cells and has been highlighted for its role in early-onset Parkinson's disease. In recent years, an increasing number of studies have revealed the involvement of PINK1 in regulation of a variety of cell physiological and pathophysiological processes, of which regulation of mitochondrial function remains the most prominent. As the "energy factory" of cells, mitochondria provide energy support for various cellular activities. Changes in mitochondrial function often have a fundamental and global impact on cellular activities. Moreover, mitochondrial dysfunction has been implicated in many diseases, especially those related to aging. Thus, a comprehensive study of PINK1 will help us better understand the various cell physiological and pathophysiological processes in which PINK1 is involved, including a variety of mitochondria-related diseases such as Parkinson's disease. This article will review the structural characteristics and expression regulation of PINK1, as well as its unique role in mitochondrial quality control (MQC) systems.
    Keywords:  MQC; Mitochondria; Mitochondrial dynamics; Mitochondrial function maintenance; Mitophagy; PINK1
  42. Nature. 2020 Aug 19.
    Grüner BM, Fendt SM.
    Keywords:  Cancer; Medical research; Metabolism
  43. Mech Ageing Dev. 2020 Aug 17. pii: S0047-6374(20)30130-5. [Epub ahead of print] 111334
    Wan Y, Finkel T.
      Mitochondrial dysfunction and stem cell exhaustion are among the nine separate hallmarks of aging. Emerging evidence however suggests that mitochondrial activity can have a profound influence on the self-renewal and function of stem cells, thus mechanistically linking mitochondrial function and stem cell decline. In this review, we discuss how accumulation of mtDNA mutations or alterations in mitochondrial dynamics, turnover, and signaling can modulate age-dependent stem cell function. Finally, we also describe how mitochondrial substrate utilization influences stem and progenitor activity. Together, this growing body of evidence suggests that modulation of mitochondrial activity might provide a strategy to slow or reverse age-dependent stem cell decline, and potentially, slow or reverse human aging.
  44. Nature. 2020 Aug 19.
    Ubellacker JM, Tasdogan A, Ramesh V, Shen B, Mitchell EC, Martin-Sandoval MS, Gu Z, McCormick ML, Durham AB, Spitz DR, Zhao Z, Mathews TP, Morrison SJ.
      Cancer cells, including melanoma cells, often metastasize regionally through the lymphatic system before metastasizing systemically through the blood1-4; however, the reason for this is unclear. Here we show that melanoma cells in lymph experience less oxidative stress and form more metastases than melanoma cells in blood. Immunocompromised mice with melanomas derived from patients, and immunocompetent mice with mouse melanomas, had more melanoma cells per microlitre in tumour-draining lymph than in tumour-draining blood. Cells that metastasized through blood, but not those that metastasized through lymph, became dependent on the ferroptosis inhibitor GPX4. Cells that were pretreated with chemical ferroptosis inhibitors formed more metastases than untreated cells after intravenous, but not intralymphatic, injection. We observed multiple differences between lymph fluid and blood plasma that may contribute to decreased oxidative stress and ferroptosis in lymph, including higher levels of glutathione and oleic acid and less free iron in lymph. Oleic acid protected melanoma cells from ferroptosis in an Acsl3-dependent manner and increased their capacity to form metastatic tumours. Melanoma cells from lymph nodes were more resistant to ferroptosis and formed more metastases after intravenous injection than did melanoma cells from subcutaneous tumours. Exposure to the lymphatic environment thus protects melanoma cells from ferroptosis and increases their ability to survive during subsequent metastasis through the blood.