bims-camemi 2020-09-06 papers

bims-camemi

Biomed News

on Mitochondrial metabolism in cancer

Issue of 2020‒09‒06
thirty-one papers selected by
Christian Frezza,

Targeting succinate dehydrogenase with malonate ester prodrugs decreases renal ischemia reperfusion injury.
Low-protein/high-carbohydrate diet induces AMPK-dependent canonical and non-canonical thermogenesis in subcutaneous adipose tissue.
The Unique Cysteine of F-ATP Synthase OSCP Subunit Participates in Modulation of the Permeability Transition Pore.
Stable retention of chloramphenicol-resistant mtDNA to rescue metabolically impaired cells.
p53 deficiency triggers dysregulation of diverse cellular processes in physiological oxygen.
Inhibition of proteasome reveals basal mitochondrial ubiquitination.
Cellular metabolic reprogramming controls sugar appetite in Drosophila.
Alpha-Ketoglutarate, an Endogenous Metabolite, Extends Lifespan and Compresses Morbidity in Aging Mice.
Mitochondrial dysfunction in kidney injury, inflammation, and disease: Potential therapeutic approaches.
The effect of short-term methionine restriction on hydrogen peroxide metabolism in Fischer-344 rat skeletal muscle mitochondria.
Single-cell metabolic profiling of human cytotoxic T cells.
A Cell-Autonomous Signature of Dysregulated Protein Phosphorylation Underlies Muscle Insulin Resistance in Type 2 Diabetes.
Cancer SLC43A2 alters T cell methionine metabolism and histone methylation.
CRISPR-GEMM pooled mutagenic screening identifies KMT2D as a major modulator of immune checkpoint blockade.
Alpha-Ketoglutarate, the Metabolite that Regulates Aging in Mice.
Pervasive chromosomal instability and karyotype order in tumour evolution.
A High-Density Human Mitochondrial Proximity Interaction Network.
Structural mechanism for amino acid-dependent Rag GTPase nucleotide state switching by SLC38A9.
Electrophilic Nrf2 activators and itaconate inhibit inflammation at low dose and promote IL-1β production and inflammatory apoptosis at high dose.
Ferroptosis occurs through an osmotic mechanism and propagates independently of cell rupture.
Rescue of myocardial energetic dysfunction in diabetes through the correction of mitochondrial hyperacetylation by honokiol.
The role of α-ketoglutarate and the hypoxia sensing pathway in the regulation of pancreatic β-cell function.
Single-Cell Information Analysis Reveals That Skeletal Muscles Incorporate Cell-to-Cell Variability as Information Not Noise.
A Protocol to Study Mitochondrial Function in Human Neural Progenitors and iPSC-Derived Astrocytes.
Selective linkage of mitochondrial enzymes to intracellular calcium stores differs between human induced pluripotent stem cells, neural stem cells and neurons.
Metabolic reprogramming sustains cancer cell survival following extracellular matrix detachment.
Beclin 2 negatively regulates innate immune signaling and tumor development.
The roles of SDHAF2 and dicarboxylate in covalent flavinylation of SDHA, the human complex II flavoprotein.
Phase Separation in Cell Division.
An Antibody Attack against Body Wasting in Cancer.
Branched-chain ketoacid overload inhibits insulin action in the muscle.

Redox Biol. 2020 Jul 12. pii: S2213-2317(20)30845-4. [Epub ahead of print]36 101640

Targeting succinate dehydrogenase with malonate ester prodrugs decreases renal ischemia reperfusion injury.

Timothy E Beach, Hiran A Prag, Laura Pala, Angela Logan, Margaret M Huang, Anja V Gruszczyk, Jack L Martin, Krishnaa Mahbubani, Mazin O Hamed, Sarah A Hosgood, Michael L Nicholson, Andrew M James, Richard C Hartley, Michael P Murphy, Kourosh Saeb-Parsy.

  Renal ischemia reperfusion (IR) injury leads to significant patient morbidity and mortality, and its amelioration is an urgent unmet clinical need. Succinate accumulates during ischemia and its oxidation by the mitochondrial enzyme succinate dehydrogenase (SDH) drives the ROS production that underlies IR injury. Consequently, compounds that inhibit SDH may have therapeutic potential against renal IR injury. Among these, the competitive SDH inhibitor malonate, administered as a cell-permeable malonate ester prodrug, has shown promise in models of cardiac IR injury, but the efficacy of malonate ester prodrugs against renal IR injury have not been investigated. Here we show that succinate accumulates during ischemia in mouse, pig and human models of renal IR injury, and that its rapid oxidation by SDH upon reperfusion drives IR injury. We then show that the malonate ester prodrug, dimethyl malonate (DMM), can ameliorate renal IR injury when administered at reperfusion but not prior to ischemia in the mouse. Finally, we show that another malonate ester prodrug, diacetoxymethyl malonate (MAM), is more potent than DMM because of its faster esterase hydrolysis. Our data show that the mitochondrial mechanisms of renal IR injury are conserved in the mouse, pig and human and that inhibition of SDH by 'tuned' malonate ester prodrugs, such as MAM, is a promising therapeutic strategy in the treatment of clinical renal IR injury.

Keywords:  Ischemia reperfusion injury; Kidney; Malonate; Mitochondria; Succinate; Succinate dehydrogenase

DOI:  https://doi.org/10.1016/j.redox.2020.101640
Redox Biol. 2020 Jul 09. pii: S2213-2317(20)30838-7. [Epub ahead of print]36 101633

Low-protein/high-carbohydrate diet induces AMPK-dependent canonical and non-canonical thermogenesis in subcutaneous adipose tissue.

Katia Aquilano, Francesca Sciarretta, Riccardo Turchi, Bo-Han Li, Marco Rosina, Veronica Ceci, Giulio Guidobaldi, Simona Arena, Chiara D'Ambrosio, Matteo Audano, Illari Salvatori, Barbara Colella, Raffaella Faraonio, Concita Panebianco, Valerio Pazienza, Donatella Caruso, Nico Mitro, Sabrina Di Bartolomeo, Andrea Scaloni, Jing-Ya Li, Daniele Lettieri-Barbato.

  Low-protein/high-carbohydrate (LPHC) diet has been suggested to promote metabolic health and longevity in adult humans and animal models. However, the complex molecular underpinnings of how LPHC diet leads to metabolic benefits remain elusive. Through a multi-layered approach, here we observed that LPHC diet promotes an energy-dissipating response consisting in the parallel recruitment of canonical and non-canonical (muscular) thermogenic systems in subcutaneous white adipose tissue (sWAT). In particular, we measured Ucp1 induction in association with up-regulation of actomyosin components and several Serca (Serca1, Serca2a, Serca2b) ATPases. In beige adipocytes, we observed that AMPK activation is responsible for transducing the amino acid lowering in an enhanced fat catabolism, which sustains both Ucp1-and Serca-dependent energy dissipation. Limiting AMPK activation counteracts the expression of brown fat and muscular genes, including Ucp1 and Serca, as well as mitochondrial oxidative genes. We observed that mitochondrial reactive oxygen species are the upstream molecules controlling AMPK-mediated metabolic rewiring in amino acid-restricted beige adipocytes. Our findings delineate a novel metabolic phenotype of responses to amino acid shortage, which recapitulates some of the benefits of cool temperature in sWAT. In conclusion, this highlights LPHC diet as a valuable and practicable strategy to prevent metabolic diseases through the enhancement of mitochondrial oxidative metabolism and the recruitment of different energy dissipating routes in beige adipocytes.

Keywords:  Metabolism; Mitochondria; Serca; Systems physiology; Ucp1

DOI:  https://doi.org/10.1016/j.redox.2020.101633
Cell Rep. 2020 Sep 01. pii: S2211-1247(20)31084-6. [Epub ahead of print]32(9): 108095

The Unique Cysteine of F-ATP Synthase OSCP Subunit Participates in Modulation of the Permeability Transition Pore.

Michela Carraro, Kristen Jones, Geppo Sartori, Marco Schiavone, Salvatore Antonucci, Roza Kucharczyk, Jean-Paul di Rago, Cinzia Franchin, Giorgio Arrigoni, Michael Forte, Paolo Bernardi.

  The mitochondrial permeability transition pore (PTP) is a Ca2+-activated channel that plays a key role in cell death. Thiol oxidation facilitates PTP opening, yet the targets and molecular mechanisms still await a definition. Here, we investigate the role of C141 of F-ATP synthase oligomycin sensitivity conferral protein (OSCP) subunit in PTP modulation by oxidation. We find that the OSCP C141S mutation confers resistance to PTP opening and cell death by diamide and MitoParaquat only when cyclophilin D (CyPD) has been ablated, a protective role that can be explained by CyPD shielding C141 from oxidants. The mutation decreases apoptosis in zebrafish embryos, indicating that this OSCP residue is involved in development. Site-directed mutagenesis in yeast suggests that other conserved cysteines in the α, γ, and c subunits of F-ATP synthase are not involved in PTP modulation. Thus, OSCP provides a strategic site that regulates PTP opening by the interplay between CyPD (un)binding and thiol oxidation-reduction.

Keywords:  F-ATP synthase; OSCP; cyclophilin D; cysteine; mitochondria; oxidation; permeability transition pore

DOI:  https://doi.org/10.1016/j.celrep.2020.108095
Sci Rep. 2020 Aug 31. 10(1): 14328

Stable retention of chloramphenicol-resistant mtDNA to rescue metabolically impaired cells.

Emma R Dawson, Alexander N Patananan, Alexander J Sercel, Michael A Teitell.

The permanent transfer of specific mtDNA sequences into mammalian cells could generate improved models of mtDNA disease and support future cell-based therapies. Previous studies documented multiple biochemical changes in recipient cells shortly after mtDNA transfer, but the long-term retention and function of transferred mtDNA remains unknown. Here, we evaluate mtDNA retention in new host cells using 'MitoPunch', a device that transfers isolated mitochondria into mouse and human cells. We show that newly introduced mtDNA is stably retained in mtDNA-deficient (ρ0) recipient cells following uridine-free selection, although exogenous mtDNA is lost from metabolically impaired, mtDNA-intact (ρ+) cells. We then introduced a second selective pressure by transferring chloramphenicol-resistant mitochondria into chloramphenicol-sensitive, metabolically impaired ρ+ mouse cybrid cells. Following double selection, recipient cells with mismatched nuclear (nDNA) and mitochondrial (mtDNA) genomes retained transferred mtDNA, which replaced the endogenous mutant mtDNA and improved cell respiration. However, recipient cells with matched mtDNA-nDNA failed to retain transferred mtDNA and sustained impaired respiration. Our results suggest that exogenous mtDNA retention in metabolically impaired ρ+ recipients depends on the degree of recipient mtDNA-nDNA co-evolution. Uncovering factors that stabilize exogenous mtDNA integration will improve our understanding of in vivo mitochondrial transfer and the interplay between mitochondrial and nuclear genomes.

DOI: https://doi.org/10.1038/s41598-020-71199-0
J Cell Biol. 2020 Nov 02. pii: e201908212. [Epub ahead of print]219(11):

p53 deficiency triggers dysregulation of diverse cellular processes in physiological oxygen.

Liz J Valente, Amy Tarangelo, Albert Mao Li, Marwan Naciri, Nitin Raj, Anthony M Boutelle, Yang Li, Stephano Spano Mello, Kathryn Bieging-Rolett, Ralph J DeBerardinis, Jiangbin Ye, Scott J Dixon, Laura D Attardi.

The mechanisms by which TP53, the most frequently mutated gene in human cancer, suppresses tumorigenesis remain unclear. p53 modulates various cellular processes, such as apoptosis and proliferation, which has led to distinct cellular mechanisms being proposed for p53-mediated tumor suppression in different contexts. Here, we asked whether during tumor suppression p53 might instead regulate a wide range of cellular processes. Analysis of mouse and human oncogene-expressing wild-type and p53-deficient cells in physiological oxygen conditions revealed that p53 loss concurrently impacts numerous distinct cellular processes, including apoptosis, genome stabilization, DNA repair, metabolism, migration, and invasion. Notably, some phenotypes were uncovered only in physiological oxygen. Transcriptomic analysis in this setting highlighted underappreciated functions modulated by p53, including actin dynamics. Collectively, these results suggest that p53 simultaneously governs diverse cellular processes during transformation suppression, an aspect of p53 function that would provide a clear rationale for its frequent inactivation in human cancer.

DOI: https://doi.org/10.1083/jcb.201908212
J Proteomics. 2020 Aug 31. pii: S1874-3919(20)30317-1. [Epub ahead of print] 103949

Inhibition of proteasome reveals basal mitochondrial ubiquitination.

Prasad Sulkshane, Inbar Duek, Jonathan Ram, Anita Thakur, Noa Reis, Tamar Ziv, Michael H Glickman.

  Strict quality control for mitochondrial proteins is necessary to ensure cell homeostasis. Two cellular pathways-Ubiquitin Proteasome System (UPS) and autophagy-contribute to mitochondrial homeostasis under stressful conditions. Here, we investigate changes to the mitochondria proteome and to the ubiquitin landscape at mitochondria in response to proteasome inhibition. Treatment of HeLa cells devoid of Parkin, the primary E3 ligase responsible for mitophagy, with proteasome inhibitor MG132 for a few hours caused mitochondrial oxidative stress and fragmentation, reduced energy output, and increased mitochondrial ubiquitination without inducing mitophagy. Overexpression of Parkin did not show any induction of mitophagy in response to MG132 treatment. Analysis of ubiquitin chains on isolated mitochondria revealed predominance of K48, K29 and K63-linked polyubiquitin. Interestingly, of all ubiquitinated mitochondrial proteins detected in response to MG132 treatment, a majority (≥90%) were intramitochondrial irrespective of Parkin expression. However, overall levels of these ubiquitinated mitochondrial proteins did not change significantly upon proteasome inhibition when evaluated by quantitative proteomics (LFQ and SILAC), suggesting that only a small portion are ubiquitinated under basal conditions. Another aspect of proteasome inhibition is significant enrichment of UPS, lysosomal and phagosomal components, and other heat shock proteins associated with isolated mitochondria. Taken together, our study highlights a critical role of UPS for ubiquitinating and removing imported proteins as part of a basal mitochondrial quality control system independent of Parkin. SIGNIFICANCE: As centers of cellular bioenergetics, numerous metabolic pathways and signaling cascades, the health of mitochondria is of utmost importance for ensuring cell survival. Due to their unique physiology, mitochondria are constantly subjected to damaging oxidative radicals (ROS) and protein import-related stress due to buildup of unfolded aggregate-prone proteins. Thus, for quality control purposes, mitochondria are constantly under surveillance by Autophagy and the Ubiquitin Proteasome System (UPS), both of which share ubiquitin as a common signal. The ubiquitin landscape of mitochondria has been studied in detail under stressful conditions, however, little is known about basal mitochondrial ubiquitination. Our study reveals that the extent of ubiquitination at mitochondria greatly increases upon proteasome inhibition, pointing to a large number of potential substrates for proteasomal degradation. Interestingly, most of the ubiquitination occurs on intramitochondrial proteins, components of the electron transport chain (ETC) and matrix-resident metabolic enzymes in particular. Moreover, numerous cytosolic UPS components, chaperones and autophagy-lysosomal proteins were recruited to mitochondria upon proteasome inhibition. Taken together, this suggests that the levels and functions of mitochondrial proteins are constantly regulated through ubiquitin-dependent proteasomal degradation even under basal conditions. Unclogging mitochondrial import channels may provide a mechanism to alleviate stress associated with mitochondrial protein import or to adapt cells according to their metabolic needs. Therefore, targeting the mitochondrial ubiquitination/deubiquitination machinery, such as improving the therapeutic potency of proteasome inhibitors, may provide an additional therapeutic arsenal against tumors.

Keywords:  Mitochondria; Mitostasis; Proteasome; Quantitative proteomics; Ubiquitin

DOI:  https://doi.org/10.1016/j.jprot.2020.103949
Nat Metab. 2020 Aug 31.

Cellular metabolic reprogramming controls sugar appetite in Drosophila.

Zita Carvalho-Santos, Rita Cardoso-Figueiredo, Ana Paula Elias, Ibrahim Tastekin, Célia Baltazar, Carlos Ribeiro.

Cellular metabolic reprogramming is an important mechanism by which cells rewire their metabolism to promote proliferation and cell growth. This process has been mostly studied in the context of tumorigenesis, but less is known about its relevance for nonpathological processes and how it affects whole-animal physiology. Here, we show that metabolic reprogramming in Drosophila female germline cells affects nutrient preferences of animals. Egg production depends on the upregulation of the activity of the pentose phosphate pathway in the germline, which also specifically increases the animal's appetite for sugar, the key nutrient fuelling this metabolic pathway. We provide functional evidence that the germline alters sugar appetite by regulating the expression of the fat-body-secreted satiety factor Fit. Our findings demonstrate that the cellular metabolic program of a small set of cells is able to increase the animal's preference for specific nutrients through inter-organ communication to promote specific metabolic and cellular outcomes.

DOI: https://doi.org/10.1038/s42255-020-0266-x
Cell Metab. 2020 Sep 01. pii: S1550-4131(20)30417-4. [Epub ahead of print]32(3): 447-456.e6

Alpha-Ketoglutarate, an Endogenous Metabolite, Extends Lifespan and Compresses Morbidity in Aging Mice.

Azar Asadi Shahmirzadi, Daniel Edgar, Chen-Yu Liao, Yueh-Mei Hsu, Mark Lucanic, Arash Asadi Shahmirzadi, Christopher D Wiley, Garbo Gan, Dong Eun Kim, Herbert G Kasler, Chisaka Kuehnemann, Brian Kaplowitz, Dipa Bhaumik, Rebeccah R Riley, Brian K Kennedy, Gordon J Lithgow.

  Metabolism and aging are tightly connected. Alpha-ketoglutarate is a key metabolite in the tricarboxylic acid (TCA) cycle, and its levels change upon fasting, exercise, and aging. Here, we investigate the effect of alpha-ketoglutarate (delivered in the form of a calcium salt, CaAKG) on healthspan and lifespan in C57BL/6 mice. To probe the relationship between healthspan and lifespan extension in mammals, we performed a series of longitudinal, clinically relevant measurements. We find that CaAKG promotes a longer, healthier life associated with a decrease in levels of systemic inflammatory cytokines. We propose that induction of IL-10 by dietary AKG suppresses chronic inflammation, leading to health benefits. By simultaneously reducing frailty and enhancing longevity, AKG, at least in the murine model, results in a compression of morbidity.

Keywords:  IL-10; SASP; alpha-ketoglutarate; frailty; healthspan; inflammation; lifespan; longevity

DOI:  https://doi.org/10.1016/j.cmet.2020.08.004
Kidney Res Clin Pract. 2020 Sep 01.

Mitochondrial dysfunction in kidney injury, inflammation, and disease: Potential therapeutic approaches.

Divya Bhatia, Allyson Capili, Mary E Choi.

  Mitochondria are energy-producing organelles that not only satisfy the high metabolic demands of the kidney but sense and respond to kidney injury-induced oxidative stress and inflammation. Kidneys are rich in mitochondria. Mitochondrial dysfunction plays a critical role in the progression of acute kidney injury and chronic kidney disease. Mitochondrial responses to specific stimuli are highly regulated and synergistically modulated by tightly interconnected processes, including mitochondrial dynamics (fission, fusion) and mitophagy. The counterbalance between these processes is essential in maintaining a healthy network of mitochondria. Recent literature suggests that alterations in mitochondrial dynamics are implicated in kidney injury and the progression of kidney diseases. A decrease in mitochondrial fusion promotes fission-induced mitochondrial fragmentation, but a reduction in mitochondrial fission produces excessive mitochondrial elongation. The removal of dysfunctional mitochondria by mitophagy is crucial for their quality control. Defective mitochondrial function disrupts cellular redox potential and can cause cell death. Mitochondrial DNA derived from damaged cells also act as damage-associated molecular patterns to recruit immune cells and the inflammatory response can further exaggerate kidney injury. This review provides a comprehensive overview of the role of mitochondrial dysfunction in acute kidney injury and chronic kidney disease. We discuss the processes that control mitochondrial stress responses to kidney injury and review recent advances in understanding the role of mitochondrial dysfunction in inflammation and tissue damage through the use of different experimental models of kidney disease. We also describe potential mitochondria-targeted therapeutic approaches.

Keywords:  Acute kidney injury; Inflammation; Kidney diseases; Mitochondria; Oxidative stress

DOI:  https://doi.org/10.23876/j.krcp.20.082
Mitochondrion. 2020 Aug 31. pii: S1567-7249(20)30175-6. [Epub ahead of print]

The effect of short-term methionine restriction on hydrogen peroxide metabolism in Fischer-344 rat skeletal muscle mitochondria.

Nahid Tamanna, Daniel Munro, Kathryn Kroeker, Sheena Banh, Jason R Treberg.

  Skeletal muscle, a significant contributor to resting energy expenditure and reactive oxygen species, may play critical role in body-weight regulation and aging processes. Methionine restriction (MR) is a dietary intervention which extends lifespan, lowers body-weight and enhances energy expenditure in rodents, all of which has been linked to mitochondrial function in various tissues including liver, kidney, heart and brown adipose tissue; however, mitochondrial responses to MR in skeletal muscle is largely unknown. Given the importance of skeletal muscle on energy mobilization and aging-related processes, we investigated if there are changes in skeletal muscle mitochondrial energetics in response to MR. Although MR lowers body-weight in rats, neither respiration, proton leak nor hydrogen peroxide metabolism was altered in isolated skeletal muscle mitochondria. This suggests that the function of skeletal muscle remains conserved while MR alters metabolism in other tissues.

Keywords:  H(2)O(2); Skeletal muscle; antioxidants; methionine restriction; proton leak; respiration

DOI:  https://doi.org/10.1016/j.mito.2020.08.006
Nat Biotechnol. 2020 Aug 31.

Single-cell metabolic profiling of human cytotoxic T cells.

Felix J Hartmann, Dunja Mrdjen, Erin McCaffrey, David R Glass, Noah F Greenwald, Anusha Bharadwaj, Zumana Khair, Sanne G S Verberk, Alex Baranski, Reema Baskar, William Graf, David Van Valen, Jan Van den Bossche, Michael Angelo, Sean C Bendall.

Cellular metabolism regulates immune cell activation, differentiation and effector functions, but current metabolic approaches lack single-cell resolution and simultaneous characterization of cellular phenotype. In this study, we developed an approach to characterize the metabolic regulome of single cells together with their phenotypic identity. The method, termed single-cell metabolic regulome profiling (scMEP), quantifies proteins that regulate metabolic pathway activity using high-dimensional antibody-based technologies. We employed mass cytometry (cytometry by time of flight, CyTOF) to benchmark scMEP against bulk metabolic assays by reconstructing the metabolic remodeling of in vitro-activated naive and memory CD8+ T cells. We applied the approach to clinical samples and identified tissue-restricted, metabolically repressed cytotoxic T cells in human colorectal carcinoma. Combining our method with multiplexed ion beam imaging by time of flight (MIBI-TOF), we uncovered the spatial organization of metabolic programs in human tissues, which indicated exclusion of metabolically repressed immune cells from the tumor-immune boundary. Overall, our approach enables robust approximation of metabolic and functional states in individual cells.

DOI: https://doi.org/10.1038/s41587-020-0651-8
Cell Metab. 2020 Aug 31. pii: S1550-4131(20)30420-4. [Epub ahead of print]

A Cell-Autonomous Signature of Dysregulated Protein Phosphorylation Underlies Muscle Insulin Resistance in Type 2 Diabetes.

Thiago M Batista, Ashok Kumar Jayavelu, Nicolai J Wewer Albrechtsen, Salvatore Iovino, Jasmin Lebastchi, Hui Pan, Jonathan M Dreyfuss, Anna Krook, Juleen R Zierath, Matthias Mann, C Ronald Kahn.

  Skeletal muscle insulin resistance is the earliest defect in type 2 diabetes (T2D), preceding and predicting disease development. To what extent this reflects a primary defect or is secondary to tissue cross talk due to changes in hormones or circulating metabolites is unknown. To address this question, we have developed an in vitro disease-in-a-dish model using iPS cells from T2D patients differentiated into myoblasts (iMyos). We find that T2D iMyos in culture exhibit multiple defects mirroring human disease, including an altered insulin signaling, decreased insulin-stimulated glucose uptake, and reduced mitochondrial oxidation. More strikingly, global phosphoproteomic analysis reveals a multidimensional network of signaling defects in T2D iMyos going beyond the canonical insulin-signaling cascade, including proteins involved in regulation of Rho GTPases, mRNA splicing and/or processing, vesicular trafficking, gene transcription, and chromatin remodeling. These cell-autonomous defects and the dysregulated network of protein phosphorylation reveal a new dimension in the cellular mechanisms underlying the fundamental defects in T2D.

Keywords:  chromatin remodeling; glucose transport; iPSC; insulin resistance; mRNA splicing; mitochondrial oxidation; phosphoproteomics; skeletal muscle; type 2 diabetes; vesicle trafficking

DOI:  https://doi.org/10.1016/j.cmet.2020.08.007
Nature. 2020 Sep 02.

Cancer SLC43A2 alters T cell methionine metabolism and histone methylation.

Yingjie Bian, Wei Li, Daniel M Kremer, Peter Sajjakulnukit, Shasha Li, Joel Crespo, Zeribe C Nwosu, Li Zhang, Arkadiusz Czerwonka, Anna Pawłowska, Houjun Xia, Jing Li, Peng Liao, Jiali Yu, Linda Vatan, Wojciech Szeliga, Shuang Wei, Sara Grove, J Rebecca Liu, Karen McLean, Marcin Cieslik, Arul M Chinnaiyan, Witold Zgodziński, Grzegorz Wallner, Iwona Wertel, Karolina Okła, Ilona Kryczek, Costas A Lyssiotis, Weiping Zou.

Abnormal epigenetic patterns correlate with effector T cell malfunction in tumours1-4, but the cause of this link is unknown. Here we show that tumour cells disrupt methionine metabolism in CD8+ T cells, thereby lowering intracellular levels of methionine and the methyl donor S-adenosylmethionine (SAM) and resulting in loss of dimethylation at lysine 79 of histone H3 (H3K79me2). Loss of H3K79me2 led to low expression of STAT5 and impaired T cell immunity. Mechanistically, tumour cells avidly consumed methionine and outcompeted T cells for methionine by expressing high levels of the methionine transporter SLC43A2. Genetic and biochemical inhibition of tumour SLC43A2 restored H3K79me2 in T cells, thereby boosting spontaneous and checkpoint-induced tumour immunity. Moreover, methionine supplementation improved the expression of H3K79me2 and STAT5 in T cells, and this was accompanied by increased T cell immunity in tumour-bearing mice and patients with colon cancer. Clinically, tumour SLC43A2 correlated negatively with T cell histone methylation and functional gene signatures. Our results identify a mechanistic connection between methionine metabolism, histone patterns, and T cell immunity in the tumour microenvironment. Thus, cancer methionine consumption is an immune evasion mechanism, and targeting cancer methionine signalling may provide an immunotherapeutic approach.

DOI: https://doi.org/10.1038/s41586-020-2682-1
Cancer Discov. 2020 Sep 04. pii: CD-19-1448. [Epub ahead of print]

CRISPR-GEMM pooled mutagenic screening identifies KMT2D as a major modulator of immune checkpoint blockade.

Guangchuan Wang, Ryan D Chow, Lvyun Zhu, Zhigang Bai, Lupeng Ye, Feifei Zhang, Paul A Renauer, Matthew B Dong, Xiaoyun Dai, Xiaoya Zhang, Yaying Du, Yujing Cheng, Leilei Niu, Zhiyuan Chu, Kristin Kim, Cun Liao, Paul Clark, Youssef Errami, Sidi Chen.

Immune checkpoint blockade (ICB) has shown remarkable clinical efficacy in several cancer types. However, only a fraction of patients will respond to ICB. Here, we performed pooled mutagenic screening with CRISPR-mediated genetically engineered mouse models (CRISPR-GEMMs) in ICB settings, and identified KMT2D as a major modulator of ICB response across multiple cancer types. KMT2D encodes a histone H3K4 methyltransferase and is among the most frequently mutated genes in cancer patients. Kmt2d loss led to increased DNA damage and mutation burden, chromatin remodeling, intron retention, and activation of transposable elements. Additionally, Kmt2d-mutant cells exhibit increased protein turnover and IFN-γ-stimulated antigen presentation. In turn, Kmt2d-mutant tumors in both mouse and human are characterized by increased immune infiltration. These data demonstrate that Kmt2d deficiency sensitizes tumors to ICB by augmenting tumor immunogenicity, and also highlight the power of CRISPR-GEMMs for interrogating complex molecular landscapes in immunotherapeutic contexts that preserve the native tumor microenvironment.

DOI: https://doi.org/10.1158/2159-8290.CD-19-1448
Cell Metab. 2020 Sep 01. pii: S1550-4131(20)30422-8. [Epub ahead of print]32(3): 323-325

Alpha-Ketoglutarate, the Metabolite that Regulates Aging in Mice.

Timothy W Rhoads, Rozalyn M Anderson.

In this issue of Cell Metabolism, Asadi Shahmirzadi et al. (2020) demonstrate that late-onset dietary supplementation with calcium alpha-ketoglutarate results in increased survival, compressed morbidity, and reduced frailty in mice. The study provides further evidence for critical links between metabolism, inflammation, and aging.

DOI: https://doi.org/10.1016/j.cmet.2020.08.009
Nature. 2020 Sep 02.

Pervasive chromosomal instability and karyotype order in tumour evolution.

Thomas B K Watkins, Emilia L Lim, Marina Petkovic, Sergi Elizalde, Nicolai J Birkbak, Gareth A Wilson, David A Moore, Eva Grönroos, Andrew Rowan, Sally M Dewhurst, Jonas Demeulemeester, Stefan C Dentro, Stuart Horswell, Lewis Au, Kerstin Haase, Mickael Escudero, Rachel Rosenthal, Maise Al Bakir, Hang Xu, Kevin Litchfield, Wei Ting Lu, Thanos P Mourikis, Michelle Dietzen, Lavinia Spain, George D Cresswell, Dhruva Biswas, Philippe Lamy, Iver Nordentoft, Katja Harbst, Francesc Castro-Giner, Lucy R Yates, Franco Caramia, Fanny Jaulin, Cécile Vicier, Ian P M Tomlinson, Priscilla K Brastianos, Raymond J Cho, Boris C Bastian, Lars Dyrskjøt, Göran B Jönsson, Peter Savas, Sherene Loi, Peter J Campbell, Fabrice Andre, Nicholas M Luscombe, Neeltje Steeghs, Vivianne C G Tjan-Heijnen, Zoltan Szallasi, Samra Turajlic, Mariam Jamal-Hanjani, Peter Van Loo, Samuel F Bakhoum, Roland F Schwarz, Nicholas McGranahan, Charles Swanton.

Chromosomal instability in cancer consists of dynamic changes to the number and structure of chromosomes1,2. The resulting diversity in somatic copy number alterations (SCNAs) may provide the variation necessary for tumour evolution1,3,4. Here we use multi-sample phasing and SCNA analysis of 1,421 samples from 394 tumours across 22 tumour types to show that continuous chromosomal instability results in pervasive SCNA heterogeneity. Parallel evolutionary events, which cause disruption in the same genes (such as BCL9, MCL1, ARNT (also known as HIF1B), TERT and MYC) within separate subclones, were present in 37% of tumours. Most recurrent losses probably occurred before whole-genome doubling, that was found as a clonal event in 49% of tumours. However, loss of heterozygosity at the human leukocyte antigen (HLA) locus and loss of chromosome 8p to a single haploid copy recurred at substantial subclonal frequencies, even in tumours with whole-genome doubling, indicating ongoing karyotype remodelling. Focal amplifications that affected chromosomes 1q21 (which encompasses BCL9, MCL1 and ARNT), 5p15.33 (TERT), 11q13.3 (CCND1), 19q12 (CCNE1) and 8q24.1 (MYC) were frequently subclonal yet appeared to be clonal within single samples. Analysis of an independent series of 1,024 metastatic samples revealed that 13 focal SCNAs were enriched in metastatic samples, including gains in chromosome 8q24.1 (encompassing MYC) in clear cell renal cell carcinoma and chromosome 11q13.3 (encompassing CCND1) in HER2+ breast cancer. Chromosomal instability may enable the continuous selection of SCNAs, which are established as ordered events that often occur in parallel, throughout tumour evolution.

DOI: https://doi.org/10.1038/s41586-020-2698-6
Cell Metab. 2020 Sep 01. pii: S1550-4131(20)30412-5. [Epub ahead of print]32(3): 479-497.e9

A High-Density Human Mitochondrial Proximity Interaction Network.

Hana Antonicka, Zhen-Yuan Lin, Alexandre Janer, Mari J Aaltonen, Woranontee Weraarpachai, Anne-Claude Gingras, Eric A Shoubridge.

  We used BioID, a proximity-dependent biotinylation assay with 100 mitochondrial baits from all mitochondrial sub-compartments, to create a high-resolution human mitochondrial proximity interaction network. We identified 1,465 proteins, producing 15,626 unique high-confidence proximity interactions. Of these, 528 proteins were previously annotated as mitochondrial, nearly half of the mitochondrial proteome defined by Mitocarta 2.0. Bait-bait analysis showed a clear separation of mitochondrial compartments, and correlation analysis among preys across all baits allowed us to identify functional clusters involved in diverse mitochondrial functions and to assign uncharacterized proteins to specific modules. We demonstrate that this analysis can assign isoforms of the same mitochondrial protein to different mitochondrial sub-compartments and show that some proteins may have multiple cellular locations. Outer membrane baits showed specific proximity interactions with cytosolic proteins and proteins in other organellar membranes, suggesting specialization of proteins responsible for contact site formation between mitochondria and individual organelles.

Keywords:  BioID proximity interactions; functional modules; mitochondrial protein proximity map; mitochondrial translation initiation; organellar contact sites; sub-mitochondrial organization

DOI:  https://doi.org/10.1016/j.cmet.2020.07.017
Nat Struct Mol Biol. 2020 Aug 31.

Structural mechanism for amino acid-dependent Rag GTPase nucleotide state switching by SLC38A9.

Simon A Fromm, Rosalie E Lawrence, James H Hurley.

The Rag GTPases (Rags) recruit mTORC1 to the lysosomal membrane in response to nutrients, where it is then activated in response to energy and growth factor availability. The lysosomal folliculin (FLCN) complex (LFC) consists of the inactive Rag dimer, the pentameric scaffold Ragulator, and the FLCN:FNIP2 (FLCN-interacting protein 2) GTPase activating protein (GAP) complex, and prevents Rag dimer activation during amino acid starvation. How the LFC is disassembled upon amino acid refeeding is an outstanding question. Here we show that the cytoplasmic tail of the human lysosomal solute carrier family 38 member 9 (SLC38A9) destabilizes the LFC and thereby triggers GAP activity of FLCN:FNIP2 toward RagC. We present the cryo-EM structures of Rags in complex with their lysosomal anchor complex Ragulator and the cytoplasmic tail of SLC38A9 in the pre- and post-GTP hydrolysis state of RagC, which explain how SLC38A9 destabilizes the LFC and so promotes Rag dimer activation.

DOI: https://doi.org/10.1038/s41594-020-0490-9
Redox Biol. 2020 Jul 21. pii: S2213-2317(20)30852-1. [Epub ahead of print]36 101647

Electrophilic Nrf2 activators and itaconate inhibit inflammation at low dose and promote IL-1β production and inflammatory apoptosis at high dose.

Jonathan Muri, Helene Wolleb, Petr Broz, Erick M Carreira, Manfred Kopf.

  Controlling inflammation is critical for preventing many diseases including cancer, autoimmune disorders and hypersensitivity reactions. NF-E2-related factor 2 (Nrf2) is a key transcription factor that controls the cellular antioxidant and cytoprotective response. Moreover, Nrf2 has been implicated in the regulation of inflammatory processes, although the ultimate mechanism by which this is achieved is unknown. Here, we investigated mechanisms of inflammation and cell death pathways induced by a variety of Nrf2 activators including dimethyl fumarate (DMF) and the endogenous metabolite itaconate. We found that exposure of bone marrow-derived dendritic cells (BMDCs) to low concentrations of a variety of electrophilic Nrf2 activators including itaconate prior to Toll-like receptor (TLR) stimulation inhibits transcription of pro-inflammatory cytokines (such as interleukin [IL]-12 and IL-1β) by activation of Nrf2. By contrast, high doses of these electrophilic compounds after TLR activation promote inflammatory apoptosis and caspase-8-dependent IL-1β processing and release independently of Nrf2. Interestingly, tert-butylhydroquinone (tBHQ), a non-electrophilic Nrf2-activator, failed to induce IL-1β production. These results have important implications for clinical application of electrophilic compounds.

Keywords:  Caspase-8; IL-1β; Inflammatory apoptosis; Itaconate; Mitochondria; Nrf2 activators

DOI:  https://doi.org/10.1016/j.redox.2020.101647
Nat Cell Biol. 2020 Sep;22(9): 1042-1048

Ferroptosis occurs through an osmotic mechanism and propagates independently of cell rupture.

Michelle Riegman, Liran Sagie, Chen Galed, Tom Levin, Noah Steinberg, Scott J Dixon, Ulrich Wiesner, Michelle S Bradbury, Philipp Niethammer, Assaf Zaritsky, Michael Overholtzer.

Ferroptosis is a regulated form of necrotic cell death that is caused by the accumulation of oxidized phospholipids, leading to membrane damage and cell lysis1,2. Although other types of necrotic death such as pyroptosis and necroptosis are mediated by active mechanisms of execution3-6, ferroptosis is thought to result from the accumulation of unrepaired cell damage1. Previous studies have suggested that ferroptosis has the ability to spread through cell populations in a wave-like manner, resulting in a distinct spatiotemporal pattern of cell death7,8. Here we investigate the mechanism of ferroptosis execution and discover that ferroptotic cell rupture is mediated by plasma membrane pores, similarly to cell lysis in pyroptosis and necroptosis3,4. We further find that intercellular propagation of death occurs following treatment with some ferroptosis-inducing agents, including erastin2,9 and C' dot nanoparticles8, but not upon direct inhibition of the ferroptosis-inhibiting enzyme glutathione peroxidase 4 (GPX4)10. Propagation of a ferroptosis-inducing signal occurs upstream of cell rupture and involves the spreading of a cell swelling effect through cell populations in a lipid peroxide- and iron-dependent manner.

DOI: https://doi.org/10.1038/s41556-020-0565-1
JCI Insight. 2020 Sep 03. pii: 140326. [Epub ahead of print]5(17):

Rescue of myocardial energetic dysfunction in diabetes through the correction of mitochondrial hyperacetylation by honokiol.

Matthew Kerr, Jack J Miller, Dharendra Thapa, Sophie Stiewe, Kerstin N Timm, Claudia N Montes Aparicio, Iain Scott, Damian J Tyler, Lisa C Heather.

  Cardiac energetic dysfunction has been reported in patients with type 2 diabetes (T2D) and is an independent predictor of mortality. Identification of the mechanisms driving mitochondrial dysfunction, and therapeutic strategies to rescue these modifications, will improve myocardial energetics in T2D. We demonstrate using 31P-magnetic resonance spectroscopy (31P-MRS) that decreased cardiac ATP and phosphocreatine (PCr) concentrations occurred before contractile dysfunction or a reduction in PCr/ATP ratio in T2D. Real-time mitochondrial ATP synthesis rates and state 3 respiration rates were similarly depressed in T2D, implicating dysfunctional mitochondrial energy production. Driving this energetic dysfunction in T2D was an increase in mitochondrial protein acetylation, and increased ex vivo acetylation was shown to proportionally decrease mitochondrial respiration rates. Treating T2D rats in vivo with the mitochondrial deacetylase SIRT3 activator honokiol reversed the hyperacetylation of mitochondrial proteins and restored mitochondrial respiration rates to control levels. Using 13C-hyperpolarized MRS, respiration with different substrates, and enzyme assays, we localized this improvement to increased glutamate dehydrogenase activity. Finally, honokiol treatment increased ATP and PCr concentrations and increased total ATP synthesis flux in the T2D heart. In conclusion, hyperacetylation drives energetic dysfunction in T2D, and reversing acetylation with the SIRT3 activator honokiol rescued myocardial and mitochondrial energetics in T2D.

Keywords:  Cardiology; Metabolism; Mitochondria

DOI:  https://doi.org/10.1172/jci.insight.140326
Islets. 2020 Sep 02. 1-12

The role of α-ketoglutarate and the hypoxia sensing pathway in the regulation of pancreatic β-cell function.

M Hoang, J W Joseph.

  Anaplerosis and the associated mitochondrial metabolite transporters generate unique cytosolic metabolic signaling molecules that can regulate insulin release from pancreatic β-cells. It has been shown that mitochondrial metabolites, transported by the citrate carrier (CIC), dicarboxylate carrier (DIC), oxoglutarate carrier (OGC), and mitochondrial pyruvate carrier (MPC) play a vital role in the regulation of glucose-stimulated insulin secretion (GSIS). Metabolomic studies on static and biphasic insulin secretion, suggests that several anaplerotic derived metabolites, including α-ketoglutarate (αKG), are strongly associated with nutrient regulated insulin secretion. Support for a role of αKG in the regulation of insulin secretion comes from studies looking at αKG dependent enzymes, including hypoxia-inducible factor-prolyl hydroxylases (PHDs) in clonal β-cells, and rodent and human islets. This review will focus on the possible link between defective anaplerotic-derived αKG, PHDs, and the development of type 2 diabetes (T2D).

Keywords:  Insulin; alpha-ketoglutarate; hypoxia-inducible factor-prolyl hydroxylases; islets

DOI:  https://doi.org/10.1080/19382014.2020.1802183
Cell Rep. 2020 Sep 01. pii: S2211-1247(20)31036-6. [Epub ahead of print]32(9): 108051

Single-Cell Information Analysis Reveals That Skeletal Muscles Incorporate Cell-to-Cell Variability as Information Not Noise.

Takumi Wada, Ken-Ichi Hironaka, Mitsutaka Wataya, Masashi Fujii, Miki Eto, Shinsuke Uda, Daisuke Hoshino, Katsuyuki Kunida, Haruki Inoue, Hiroyuki Kubota, Tsuguto Takizawa, Yasuaki Karasawa, Hirofumi Nakatomi, Nobuhito Saito, Hiroki Hamaguchi, Yasuro Furuichi, Yasuko Manabe, Nobuharu L Fujii, Shinya Kuroda.

  Cell-to-cell variability in signal transduction in biological systems is often considered noise. However, intercellular variation (i.e., cell-to-cell variability) has the potential to enable individual cells to encode different information. Here, we show that intercellular variation increases information transmission of skeletal muscle. We analyze the responses of multiple cultured myotubes or isolated skeletal muscle fibers as a multiple-cell channel composed of single-cell channels. We find that the multiple-cell channel, which incorporates intercellular variation as information, not noise, transmitted more information in the presence of intercellular variation than in the absence according to the "response diversity effect," increasing in the gradualness of dose response by summing the cell-to-cell variable dose responses. We quantify the information transmission of human facial muscle contraction during intraoperative neurophysiological monitoring and find that information transmission of muscle contraction is comparable to that of a multiple-cell channel. Thus, our data indicate that intercellular variation can increase the information capacity of tissues.

Keywords:  cell-to-cell variability; information theory; signaling pathways; single-cell analysis

DOI:  https://doi.org/10.1016/j.celrep.2020.108051
Curr Protoc Toxicol. 2020 Sep;85(1): e97

A Protocol to Study Mitochondrial Function in Human Neural Progenitors and iPSC-Derived Astrocytes.

Gabriela Assis-de-Lemos, Pítia Flores Ledur, Karina Karmirian, Stevens Kastrup Rehen, Antonio Galina.

  Mitochondrial dysfunction is a central component in the pathophysiology of multiple neuropsychiatric and degenerative disorders. Evaluating mitochondrial function in human-derived neural cells can help characterize dysregulation in oxidative metabolism associated with the onset of brain disorders, and may also help define targeted therapies. Astrocytes play a number of different key roles in the brain, being implicated in neurogenesis, synaptogenesis, blood-brain-barrier permeability, and homeostasis, and, consequently, the malfunctioning of astrocytes is related to many neuropathologies. Here we describe protocols for generating induced pluripotent stem cell (iPSC)-derived astrocytes and evaluating multiple aspects of mitochondrial function. We use a high-resolution respirometry assay that measures real-time variations in mitochondrial oxygen flow, allowing the evaluation of cellular respiration in the context of an intact intracellular microenvironment, something not possible with permeabilized cells or isolated mitochondria, where the cellular microenvironment is disrupted. Given that an impairment in the mitochondrial regulation of intracellular calcium homeostasis is involved in many pathologic stresses, we also describe a protocol to evaluate mitochondrial calcium dynamics in human neural cells, by fluorimetry. Lastly, we outline a mitochondrial function assay that allows for the measurement of the enzymatic activity of mitochondrial hexokinase (mt-HK), an enzyme that is functionally coupled to oxidative phosphorylation and is involved in redox homeostasis, particularly in the brain. In all, these protocols allow a detailed characterization of mitochondrial function in human neural cells. High-resolution respirometry, calcium dynamics, and mt-HK activity assays provide data regarding the functional status of mitochondria, which may reflect mitochondrial stress or dysfunction. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Generation of iPSC-derived human astrocytes Basic Protocol 2: Measuring real-time oxygen flux in human iPSC-derived astrocytes using a high-resolution OROBOROS Oxygraph 2k (O2k) Basic Protocol 3: Measuring mitochondrial calcium dynamics fluorometrically in permeabilized human neural cells Basic Protocol 4: Measuring OXPHOS-dependent activity of mitochondrial hexokinase in permeabilized human neural cells using a spectrophotometer.

Keywords:  astrocytes; calcium dynamics; iPSC; mitochondrial stress; respirometry

DOI:  https://doi.org/10.1002/cptx.97
J Neurochem. 2020 Aug 31.

Selective linkage of mitochondrial enzymes to intracellular calcium stores differs between human induced pluripotent stem cells, neural stem cells and neurons.

Huanlian Chen, Abigail C Cross, Ankita Thakkar, Hui Xu, Aiqun Li, Dan Paull, Scott A Noggle, Laken Kruger, Travis T Denton, Gary E Gibson.

  Mitochondria and releasable endoplasmic reticulum (ER) calcium modulate neuronal calcium signaling, and both change in Alzheimer's disease (AD). The releasable calcium stores in the ER are exaggerated in fibroblasts from AD patients and in multiple models of AD. The activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key mitochondrial enzyme complex, is diminished in brains from AD patients, and can be plausibly linked to plaques and tangles. Our previous studies in cell lines and mouse neurons demonstrate that reductions in KGDHC increase the ER releasable calcium stores. The goal of these studies was to test whether the relationship was true in human iPSC-derived neurons. Inhibition of KGDHC for one or 24 hours increased the ER releasable calcium store in human neurons by 69% and 144%, respectively. The effect was mitochondrial enzyme specific because inhibiting the pyruvate dehydrogenase complex, another key mitochondrial enzyme complex, diminished the ER releasable calcium stores. The link of KGDHC to ER releasable calcium stores was cell type specific as the interaction was not present in iPSC or neural stem cells. Thus, these studies in human neurons verify a link between KGDHC and releasable ER calcium stores, and support the use of human neurons to examine mechanisms and potential therapies for AD.

Keywords:  Alzheimer’s disease; alpha-ketoglutarate dehydrogenase complex; calcium stores; development; endoplasmic reticulum; mitochondria; pyruvate dehydrogenase complex; stem cells; tricarboxylic acid cycle

DOI:  https://doi.org/10.1111/jnc.15160
Redox Biol. 2020 Jul 13. pii: S2213-2317(20)30848-X. [Epub ahead of print]36 101643

Metabolic reprogramming sustains cancer cell survival following extracellular matrix detachment.

Hitoshi Endo, Satoshi Owada, Yutaka Inagaki, Yukari Shida, Masayuki Tatemichi.

  Epithelial cells require attachment to a support, such as the extracellular matrix, for survival. During cancer progression and metastasis, cancerous epithelial cells must overcome their dependence on adhesion signals. Dependence on glucose metabolism is a hallmark of cancer cells, but the nutrient requirements of cancer cells under anchorage-deficient conditions remain uncharacterized. Here, we report that cancer cells prioritize glutamine-derived tricarboxylic acid cycle energy metabolism over glycolysis to sustain anchorage-independent survival. Moreover, glutamine-dependent metabolic reprogramming is required not only to maintain ATP levels but also to suppress excessive oxidative stress through interaction with cystine. Mechanistically, AMPK, a central regulator of cellular responses to metabolic stress, participates in the induction of the expression of ASCT2, a glutamine transporter, and enhances glutamine consumption. Most interestingly, AMPK activation induces Nrf2 and its target proteins, allowing cancer cells to maintain energy homeostasis and redox status through glutaminolysis. Treatment with an integrin inhibitor was used to mimic the alterations in cell morphology and metabolic reprogramming caused by detachment. Under these conditions, cells were vulnerable to glutamine starvation or glutamine metabolism inhibitors. The observed preference for glutamine over glucose was more pronounced in aggressive cancer cell lines, and treatment with the glutaminase inhibitor, CB839, and cystine transporter inhibitor, sulfasalazine, caused strong cytotoxicity. Our data clearly show that anchorage-independent survival of cancer cells is supported mainly by glutaminolysis via the AMPK-Nrf2 signal axis. The discovery of new vulnerabilities along this route could help slow or prevent cancer progression.

Keywords:  Anoikis; Extracellular matrix detachment; Glutaminolysis; Metabolic reprogramming; Metastasis

DOI:  https://doi.org/10.1016/j.redox.2020.101643
J Clin Invest. 2020 Aug 31. pii: 133283. [Epub ahead of print]

Beclin 2 negatively regulates innate immune signaling and tumor development.

Motao Zhu, Guangtong Deng, Peng Tan, Changsheng Xing, Cuiping Guan, Chongming Jiang, Yinlong Zhang, Bo Ning, Chaoran Li, Bingnan Yin, Kaifu Chen, Yuliang Zhao, Helen Y Wang, Beth Levine, Guangjun Nie, Rong-Fu Wang.

  Beclin 2 plays a critical role in metabolic regulation and obesity, but its functions in innate immune signaling and cancer development remain largely unknown. Here, we identified Beclin 2 as a critical negative regulator of inflammation and lymphoma development. Mice with homozygous ablation of BCL2-interacting protein 2 (Becn2) developed splenomegaly and lymphadenopathy and markedly increased ERK1/2 and NF-κB signaling for proinflammatory cytokine production. Beclin 2 targeted the key signaling kinases MEKK3 and TAK1 for degradation through an ATG9A-dependent, but ATG16L/Beclin 1/LC3-independent, autophagic pathway. Mechanistically, Beclin 2 recruited MEKK3 or TAK1 through ATG9A to form a complex (Beclin 2-ATG9A-MEKK3) on ATG9A+ vesicles upon ULK1 activation. Beclin 2 further interacted with STX5 and STX6 to promote the fusion of MEKK3- or TAK1-associated ATG9A+ vesicles to phagophores for subsequent degradation. Importantly, Becn2-deficient mice had a markedly increased incidence of lymphoma development, with persistent STAT3 activation. Myeloid-specific ablation of MEKK3 (Map3k3) completely rescued the phenotypes (splenomegaly, higher amounts of proinflammatory cytokines, and cancer incidence) of Becn2-deficient mice. Hence, our findings have identified an important role of Beclin 2 in the negative regulation of innate immune signaling and tumor development through an ATG9A-dependent, but ATG16L/Beclin 1/LC3-independent, autophagic pathway, thus providing a potential target for the treatment of inflammatory diseases and cancer.

Keywords:  Autophagy; Cell Biology; Inflammation; Innate immunity

DOI:  https://doi.org/10.1172/JCI133283
Proc Natl Acad Sci U S A. 2020 Sep 04. pii: 202007391. [Epub ahead of print]

The roles of SDHAF2 and dicarboxylate in covalent flavinylation of SDHA, the human complex II flavoprotein.

Pankaj Sharma, Elena Maklashina, Gary Cecchini, T M Iverson.

  Mitochondrial complex II, also known as succinate dehydrogenase (SDH), is an integral-membrane heterotetramer (SDHABCD) that links two essential energy-producing processes, the tricarboxylic acid (TCA) cycle and oxidative phosphorylation. A significant amount of information is available on the structure and function of mature complex II from a range of organisms. However, there is a gap in our understanding of how the enzyme assembles into a functional complex, and disease-associated complex II insufficiency may result from incorrect function of the mature enzyme or from assembly defects. Here, we investigate the assembly of human complex II by combining a biochemical reconstructionist approach with structural studies. We report an X-ray structure of human SDHA and its dedicated assembly factor SDHAF2. Importantly, we also identify a small molecule dicarboxylate that acts as an essential cofactor in this process and works in synergy with SDHAF2 to properly orient the flavin and capping domains of SDHA. This reorganizes the active site, which is located at the interface of these domains, and adjusts the pKa of SDHAR451 so that covalent attachment of the flavin adenine dinucleotide (FAD) cofactor is supported. We analyze the impact of disease-associated SDHA mutations on assembly and identify four distinct conformational forms of the complex II flavoprotein that we assign to roles in assembly and catalysis.

Keywords:  assembly; bioenergetics; complex II; flavinylation; protein folding

DOI:  https://doi.org/10.1073/pnas.2007391117
Mol Cell. 2020 Aug 19. pii: S1097-2765(20)30550-5. [Epub ahead of print]

Phase Separation in Cell Division.

Joseph Y Ong, Jorge Z Torres.

  Cell division requires the assembly and organization of a microtubule spindle for the proper separation of chromosomes in mitosis and meiosis. Phase separation is an emerging paradigm for understanding spatial and temporal regulation of a variety of cellular processes, including cell division. Phase-separated condensates have been recently discovered at many structures during cell division as a possible mechanism for properly localizing, organizing, and activating proteins involved in cell division. Here, we review how these condensates play roles in regulating microtubule density and organization and spindle assembly and function and in activating some of the key players in cell division. We conclude with perspectives on areas of future research for this exciting and rapidly advancing field.

Keywords:  cell division; membraneless compartments; microtubule-based spindle; phase separation; phase-separated condensates

DOI:  https://doi.org/10.1016/j.molcel.2020.08.007
Cell Metab. 2020 Sep 01. pii: S1550-4131(20)30416-2. [Epub ahead of print]32(3): 331-333

An Antibody Attack against Body Wasting in Cancer.

Maria Rohm, Stephan Herzig.

Cachexia is a devastating, non-curable condition in many cancer patients that is marked by severe wasting of the muscle and fat tissue. Its prevention has been hampered by an insufficient knowledge of the underlying molecular mechanism(s) that lead to its pathogenesis. Suriben et al. (2020) now report the development and characterization of an antagonistic antibody for the previously identified GDF15-GFRAL axis that efficiently blocks tumor-induced body wasting in experimental animals.

DOI: https://doi.org/10.1016/j.cmet.2020.08.003
J Biol Chem. 2020 Sep 02. pii: jbc.RA120.013121. [Epub ahead of print]

Branched-chain ketoacid overload inhibits insulin action in the muscle.

Dipsikha Biswas, Khoi T Dao, Angella Mercer, Andrew M Cowie, Luke Duffley, Yassine El Hiani, Petra C Kienesberger, Thomas Pulinilkunnil.

  Branched-chain α-keto acids (BCKAs) are catabolites of branched-chain amino acids (BCAAs). Intracellular BCKAs is cleared by branched-chain ketoacid dehydrogenase (BCKDH), which is sensitive to inhibitory phosphorylation by BCKD kinase (BCKDK). Accumulation of BCKAs is an indicator of defective BCAA catabolism and has been correlated with glucose intolerance and cardiac dysfunction. However, it is unclear whether BCKAs directly alter insulin signaling and function in the skeletal and cardiac muscle cell. Furthermore, the role of excess fatty acids (FA) in perturbing BCAA catabolism and BCKA availability merits investigation. By using immunoblot and UPLC MS/MS to analyze the hearts of fasted mice, we observed decreased BCAA catabolizing enzyme expression and increased circulating BCKAs, but not BCAAs. In mice subjected to diet-induced obesity (DIO), we observed similar increases in circulating BCKAs with concomitant changes in BCAA catabolizing enzyme expression only in the skeletal muscle. Effects of DIO were recapitulated by simulating lipotoxicity in skeletal muscle cells treated with saturated FA, palmitate. Exposure of muscle cells to high concentrations of BCKAs resulted in inhibition of insulin-induced AKT phosphorylation, decreased glucose uptake and mitochondrial oxygen consumption. Altering intracellular clearance of BCKAs by genetic modulation of BCKDK and BCKDHA expression showed similar effects on AKT phosphorylation. BCKAs increased protein translation and mTORC1 activation. Pretreating cells with mTORC1 inhibitor rapamycin restored BCKAs effect on insulin-induced AKT phosphorylation. This study provides evidence for FA mediated regulation of BCAA catabolizing enzymes, BCKA content and highlights the biological role of BCKAs in regulating muscle insulin signaling and function.

Keywords:  BCKA; Insulin signaling; amino acid; cardiomyocyte; cardiomyocytes; insulin resistance; protein translation; skeletal muscle; skeletal muscle metabolism; translation

DOI:  https://doi.org/10.1074/jbc.RA120.013121