bims-mibica 2021-04-11 papers

bims-mibica

Biomed News

on Mitochondrial bioenergetics in cancer

Issue of 2021‒04‒11
thirty-nine papers selected by
Kelsey Fisher-Wellman
East Carolina University

Respiratory complex and tissue lineage drive recurrent mutations in tumour mtDNA.
Mitochondrial-targeted methionine sulfoxide reductase overexpression increases the production of oxidative stress in mitochondria from skeletal muscle.
Mitochondrial NADP+ is essential for proline biosynthesis during cell growth.
Exploiting pyocyanin to treat mitochondrial disease due to respiratory complex III dysfunction.
The mitochondrial Ca2+ uptake regulator, MICU1, is involved in cold stress-induced ferroptosis.
Cell-programmed nutrient partitioning in the tumour microenvironment.
Genetic deletion of Nox4 enhances cancerogen-induced formation of solid tumors.
Kv1.3 voltage-gated potassium channels link cellular respiration to proliferation through a non-conducting mechanism.
A novel tumor suppressor CECR2 down regulation links glutamine metabolism contributes tumor growth in laryngeal squamous cell carcinoma.
Quantitative detection of circulating MT-ND1 as a potential biomarker for colorectal cancer.
Mitochondrial Pyruvate Carrier Subunits Are Essential for Pyruvate-Driven Respiration, Infectivity, and Intracellular Replication of Trypanosoma cruzi.
Avian red blood cell mitochondria produce more heat in winter than in autumn.
Membrane transporter dimerization driven by differential lipid solvation energetics of dissociated and associated states.
LDLR inhibition promotes hepatocellular carcinoma proliferation and metastasis by elevating intracellular cholesterol synthesis through MEK/ERK signaling pathway.
+PGC1A driven enhanced mitochondrial DNA copy number predicts outcome in pediatric acute myeloid leukemia.
Direct detection of coupled proton and electron transfers in human manganese superoxide dismutase.
Myofibril and mitochondria morphogenesis are coordinated by a mechanical feedback mechanism in muscle.
Targeting ACLY Attenuates Tumor Growth and Acquired Cisplatin Resistance in Ovarian Cancer by Inhibiting the PI3K-AKT Pathway and Activating the AMPK-ROS Pathway.
Cryo-EM structure and kinetics reveal electron transfer by 2D diffusion of cytochrome c in the yeast III-IV respiratory supercomplex.
Augmenter of Liver Regeneration regulates cellular iron homeostatis by modulating mitochondrial transport of ATP-binding cassette B8.
NDUFA4L2 promotes glioblastoma progression, is associated with poor survival, and can be effectively targeted by apatinib.
Discovery of AG-270, a First-in-Class Oral MAT2A Inhibitor for the Treatment of Tumors with Homozygous MTAP Deletion.
DNMT1 maintains metabolic fitness of adipocytes through acting as an epigenetic safeguard of mitochondrial dynamics.
Enhanced cytarabine-induced killing in OGG1-deficient acute myeloid leukemia cells.
Coding and non-coding roles of MOCCI (C15ORF48) coordinate to regulate host inflammation and immunity.
Cardiomyocyte-specific Srsf3 deletion reveals a mitochondrial regulatory role.
Intact TP53 function is essential for sustaining durable responses to BH3-mimetic drugs in leukemias.
Host Mitochondrial Requirements of Cytomegalovirus Replication.
Down-regulation of SLC25A20 promotes hepatocellular carcinoma growth and metastasis through suppression of fatty-acid oxidation.
Hexokinase 2 discerns a novel circulating tumor cell population associated with poor prognosis in lung cancer patients.
Restoration of fitness lost due to dysregulation of the pyruvate dehydrogenase complex is triggered by ribosomal binding site modifications.
Mitochondrial NADPH is a pro at Pro synthesis.
Mitochondrial Aurora kinase A induces mitophagy by interacting with MAP1LC3 and Prohibitin 2.
Pancreatic β cells put the glutamine engine in reverse.
Neural stem cells traffic functional mitochondria via extracellular vesicles.
Dual-process brain mitochondria isolation preserves function and clarifies protein composition.
The critical role of peroxiredoxin-2 in colon cancer stem cells.
Identification of Metabolic-Associated Genes for the Prediction of Colon and Rectal Adenocarcinoma.
Creatine promotes cancer metastasis through activation of Smad2/3.

Nat Metab. 2021 Apr 08.

Respiratory complex and tissue lineage drive recurrent mutations in tumour mtDNA.

Alexander N Gorelick, Minsoo Kim, Walid K Chatila, Konnor La, A Ari Hakimi, Michael F Berger, Barry S Taylor, Payam A Gammage, Ed Reznik.

Mitochondrial DNA (mtDNA) encodes protein subunits and translational machinery required for oxidative phosphorylation (OXPHOS). Using repurposed whole-exome sequencing data, in the present study we demonstrate that pathogenic mtDNA mutations arise in tumours at a rate comparable to those in the most common cancer driver genes. We identify OXPHOS complexes as critical determinants shaping somatic mtDNA mutation patterns across tumour lineages. Loss-of-function mutations accumulate at an elevated rate specifically in complex I and often arise at specific homopolymeric hotspots. In contrast, complex V is depleted of all non-synonymous mutations, suggesting that impairment of ATP synthesis and mitochondrial membrane potential dissipation are under negative selection. Common truncating mutations and rarer missense alleles are both associated with a pan-lineage transcriptional programme, even in cancer types where mtDNA mutations are comparatively rare. Pathogenic mutations of mtDNA are associated with substantial increases in overall survival of colorectal cancer patients, demonstrating a clear functional relationship between genotype and phenotype. The mitochondrial genome is therefore frequently and functionally disrupted across many cancers, with major implications for patient stratification, prognosis and therapeutic development.

DOI: https://doi.org/10.1038/s42255-021-00378-8
Aging Pathobiol Ther. 2020 ;2(1): 45-51

Mitochondrial-targeted methionine sulfoxide reductase overexpression increases the production of oxidative stress in mitochondria from skeletal muscle.

Arunabh Bhattacharya, Daniel Pulliam, Yuhong Liu, Adam B Salmon.

  Objective: Mitochondrial dysfunction comprises part of the etiology of myriad health issues, particularly those that occur with advancing age. Methionine sulfoxide reductase A (MsrA) is a ubiquitous protein oxidation repair enzyme that specifically and catalytically reduces a specific epimer of oxidized methionine: methionine sulfoxide. In this study, we tested the ways in which mitochondrial bioenergetic functions are affected by increasing MsrA expression in different cellular compartments.Methods: In this study, we tested the function of isolated mitochondria, including free radical generation, ATP production, and respiration, from the skeletal muscle of two lines of transgenic mice with increased MsrA expression: mitochondria-targeted MsrA overexpression or cytosol-targeted MsrA overexpression.
Results: Surprisingly, in the samples from mice with mitochondrial-targeted MsrA overexpression, we found dramatically increased free radical production though no specific defect in respiration, ATP production, or membrane potential. Among the electron transport chain complexes, we found the activity of complex I was specifically reduced in mitochondrial MsrA transgenic mice. In mice with cytosolic-targeted MsrA overexpression, we found no significant alteration made to any of these parameters of mitochondrial energetics.
Conclusions: There is also a growing amount of evidence that MsrA is a functional requirement for sustaining optimal mitochondrial respiration and free radical generation. MsrA is also known to play a partial role in maintaining normal protein homeostasis by specifically repairing oxidized proteins. Our studies highlight a potential novel role for MsrA in regulating the activity of mitochondrial function through its interaction with the mitochondrial proteome.

Keywords:  Superoxide; electron transport chain; mitochondria; oxidative stress; protein homeostasis

DOI:  https://doi.org/10.31491/apt.2020.03.012
Nat Metab. 2021 Apr 08.

Mitochondrial NADP+ is essential for proline biosynthesis during cell growth.

Diem H Tran, Rushendhiran Kesavan, Halie Rion, Mona Hoseini Soflaee, Ashley Solmonson, Divya Bezwada, Hieu S Vu, Feng Cai, John A Phillips, Ralph J DeBerardinis, Gerta Hoxhaj.

Nicotinamide adenine dinucleotide phosphate (NADP+) is vital to produce NADPH, a principal supplier of reducing power for biosynthesis of macromolecules and protection against oxidative stress. NADPH exists in separate pools, in both the cytosol and mitochondria; however, the cellular functions of mitochondrial NADPH are incompletely described. Here, we find that decreasing mitochondrial NADP(H) levels through depletion of NAD kinase 2 (NADK2), an enzyme responsible for production of mitochondrial NADP+, renders cells uniquely proline auxotrophic. Cells with NADK2 deletion fail to synthesize proline, due to mitochondrial NADPH deficiency. We uncover the requirement of mitochondrial NADPH and NADK2 activity for the generation of the pyrroline-5-carboxylate metabolite intermediate as the bottleneck step in the proline biosynthesis pathway. Notably, after NADK2 deletion, proline is required to support nucleotide and protein synthesis, making proline essential for the growth and proliferation of NADK2-deficient cells. Thus, we highlight proline auxotrophy in mammalian cells and discover that mitochondrial NADPH is essential to enable proline biosynthesis.

DOI: https://doi.org/10.1038/s42255-021-00374-y
Nat Commun. 2021 04 08. 12(1): 2103

Exploiting pyocyanin to treat mitochondrial disease due to respiratory complex III dysfunction.

Roberta Peruzzo, Samantha Corrà, Roberto Costa, Michele Brischigliaro, Tatiana Varanita, Lucia Biasutto, Chiara Rampazzo, Daniele Ghezzi, Luigi Leanza, Mario Zoratti, Massimo Zeviani, Cristiano De Pittà, Carlo Viscomi, Rodolfo Costa, Ildikò Szabò.

Mitochondrial diseases impair oxidative phosphorylation and ATP production, while effective treatment is still lacking. Defective complex III is associated with a highly variable clinical spectrum. We show that pyocyanin, a bacterial redox cycler, can replace the redox functions of complex III, acting as an electron shunt. Sub-μM pyocyanin was harmless, restored respiration and increased ATP production in fibroblasts from five patients harboring pathogenic mutations in TTC19, BCS1L or LYRM7, involved in assembly/stabilization of complex III. Pyocyanin normalized the mitochondrial membrane potential, and mildly increased ROS production and biogenesis. These in vitro effects were confirmed in both DrosophilaTTC19KO and in Danio rerioTTC19KD, as administration of low concentrations of pyocyanin significantly ameliorated movement proficiency. Importantly, daily administration of pyocyanin for two months was not toxic in control mice. Our results point to utilization of redox cyclers for therapy of complex III disorders.

DOI: https://doi.org/10.1038/s41467-021-22062-x
EMBO Rep. 2021 Apr 06. e51532

The mitochondrial Ca2+ uptake regulator, MICU1, is involved in cold stress-induced ferroptosis.

Toshitaka Nakamura, Motoyuki Ogawa, Kazuki Kojima, Saki Takayanagi, Shunya Ishihara, Kazuki Hattori, Isao Naguro, Hidenori Ichijo.

  Ferroptosis has recently attracted much interest because of its relevance to human diseases such as cancer and ischemia-reperfusion injury. We have reported that prolonged severe cold stress induces lipid peroxidation-dependent ferroptosis, but the upstream mechanism remains unknown. Here, using genome-wide CRISPR screening, we found that a mitochondrial Ca2+ uptake regulator, mitochondrial calcium uptake 1 (MICU1), is required for generating lipid peroxide and subsequent ferroptosis under cold stress. Furthermore, the gatekeeping activity of MICU1 through mitochondrial calcium uniporter (MCU) is suggested to be indispensable for cold stress-induced ferroptosis. MICU1 is required for mitochondrial Ca2+ increase, hyperpolarization of the mitochondrial membrane potential (MMP), and subsequent lipid peroxidation under cold stress. Collectively, these findings suggest that the MICU1-dependent mitochondrial Ca2+ homeostasis-MMP hyperpolarization axis is involved in cold stress-induced lipid peroxidation and ferroptosis.

Keywords:  CRISPR screening; Ca2+; MICU1; cold stress-induced ferroptosis; mitochondria

DOI:  https://doi.org/10.15252/embr.202051532
Nature. 2021 Apr 07.

Cell-programmed nutrient partitioning in the tumour microenvironment.

Bradley I Reinfeld, Matthew Z Madden, Melissa M Wolf, Anna Chytil, Jackie E Bader, Andrew R Patterson, Ayaka Sugiura, Allison S Cohen, Ahmed Ali, Brian T Do, Alexander Muir, Caroline A Lewis, Rachel A Hongo, Kirsten L Young, Rachel E Brown, Vera M Todd, Tessa Huffstater, Abin Abraham, Richard T O'Neil, Matthew H Wilson, Fuxue Xin, M Noor Tantawy, W David Merryman, Rachelle W Johnson, Christopher S Williams, Emily F Mason, Frank M Mason, Katherine E Beckermann, Matthew G Vander Heiden, H Charles Manning, Jeffrey C Rathmell, W Kimryn Rathmell.

Cancer cells characteristically consume glucose through Warburg metabolism1, a process that forms the basis of tumour imaging by positron emission tomography (PET). Tumour-infiltrating immune cells also rely on glucose, and impaired immune cell metabolism in the tumour microenvironment (TME) contributes to immune evasion by tumour cells2-4. However, whether the metabolism of immune cells is dysregulated in the TME by cell-intrinsic programs or by competition with cancer cells for limited nutrients remains unclear. Here we used PET tracers to measure the access to and uptake of glucose and glutamine by specific cell subsets in the TME. Notably, myeloid cells had the greatest capacity to take up intratumoral glucose, followed by T cells and cancer cells, across a range of cancer models. By contrast, cancer cells showed the highest uptake of glutamine. This distinct nutrient partitioning was programmed in a cell-intrinsic manner through mTORC1 signalling and the expression of genes related to the metabolism of glucose and glutamine. Inhibiting glutamine uptake enhanced glucose uptake across tumour-resident cell types, showing that glutamine metabolism suppresses glucose uptake without glucose being a limiting factor in the TME. Thus, cell-intrinsic programs drive the preferential acquisition of glucose and glutamine by immune and cancer cells, respectively. Cell-selective partitioning of these nutrients could be exploited to develop therapies and imaging strategies to enhance or monitor the metabolic programs and activities of specific cell populations in the TME.

DOI: https://doi.org/10.1038/s41586-021-03442-1
Proc Natl Acad Sci U S A. 2021 Mar 16. pii: e2020152118. [Epub ahead of print]118(11):

Genetic deletion of Nox4 enhances cancerogen-induced formation of solid tumors.

Valeska Helfinger, Florian Freiherr von Gall, Nina Henke, Michael M Kunze, Tobias Schmid, Flavia Rezende, Juliana Heidler, Ilka Wittig, Heinfried H Radeke, Viola Marschall, Karen Anderson, Ajay M Shah, Simone Fulda, Bernhard Brüne, Ralf P Brandes, Katrin Schröder.

  Reactive oxygen species (ROS) can cause cellular damage and promote cancer development. Besides such harmful consequences of overproduction of ROS, all cells utilize ROS for signaling purposes and stabilization of cell homeostasis. In particular, the latter is supported by the NADPH oxidase 4 (Nox4) that constitutively produces low amounts of H2O2 By that mechanism, Nox4 forces differentiation of cells and prevents inflammation. We hypothesize a constitutive low level of H2O2 maintains basal activity of cellular surveillance systems and is unlikely to be cancerogenic. Utilizing two different murine models of cancerogen-induced solid tumors, we found that deletion of Nox4 promotes tumor formation and lowers recognition of DNA damage. Nox4 supports phosphorylation of H2AX (γH2AX), a prerequisite of DNA damage recognition, by retaining a sufficiently low abundance of the phosphatase PP2A in the nucleus. The underlying mechanism is continuous oxidation of AKT by Nox4. Interaction of oxidized AKT and PP2A captures the phosphatase in the cytosol. Absence of Nox4 facilitates nuclear PP2A translocation and dephosphorylation of γH2AX. Simultaneously AKT is left phosphorylated. Thus, in the absence of Nox4, DNA damage is not recognized and the increased activity of AKT supports proliferation. The combination of both events results in genomic instability and promotes tumor formation. By identifying Nox4 as a protective source of ROS in cancerogen-induced cancer, we provide a piece of knowledge for understanding the role of moderate production of ROS in preventing the initiation of malignancies.

Keywords:  AKT; Nox4; genomic instability; solid tumors

DOI:  https://doi.org/10.1073/pnas.2020152118
Cell Death Dis. 2021 Apr 07. 12(4): 372

Kv1.3 voltage-gated potassium channels link cellular respiration to proliferation through a non-conducting mechanism.

Faye L Styles, Moza M Al-Owais, Jason L Scragg, Eulashini Chuntharpursat-Bon, Nishani T Hettiarachchi, Jonathan D Lippiat, Aisling Minard, Robin S Bon, Karen Porter, Piruthivi Sukumar, Chris Peers, Lee D Roberts.

Cellular energy metabolism is fundamental for all biological functions. Cellular proliferation requires extensive metabolic reprogramming and has a high energy demand. The Kv1.3 voltage-gated potassium channel drives cellular proliferation. Kv1.3 channels localise to mitochondria. Using high-resolution respirometry, we show Kv1.3 channels increase oxidative phosphorylation, independently of redox balance, mitochondrial membrane potential or calcium signalling. Kv1.3-induced respiration increased reactive oxygen species production. Reducing reactive oxygen concentrations inhibited Kv1.3-induced proliferation. Selective Kv1.3 mutation identified that channel-induced respiration required an intact voltage sensor and C-terminal ERK1/2 phosphorylation site, but is channel pore independent. We show Kv1.3 channels regulate respiration through a non-conducting mechanism to generate reactive oxygen species which drive proliferation. This study identifies a Kv1.3-mediated mechanism underlying the metabolic regulation of proliferation, which may provide a therapeutic target for diseases characterised by dysfunctional proliferation and cell growth.

DOI: https://doi.org/10.1038/s41419-021-03627-6
Clin Transl Oncol. 2021 Apr 07.

A novel tumor suppressor CECR2 down regulation links glutamine metabolism contributes tumor growth in laryngeal squamous cell carcinoma.

Xiaoting Wang, Chong Xu, Shengming Wang, Weijun Huang, Yuenan Liu, Xiaoxu Zhang, Niannian Li, Zhenfei Gao, Fan Wang, Nan Zhang, Jian Guan, Hongliang Yi, Feng Liu.

  PURPOSE: Glutamine plays an important role in tumor metabolism and progression. This research aimed to find out how Gln exert their effects on laryngeal squamous cell carcinoma (LSCC).METHODS: Cell proliferation was measured by CCK8 and EdU assay, mitochondrial bioenergetic activity was measured by mitochondrial stress tests. Gene expression profiling was revealed by RNA sequencing and validated by RT-qPCR. In LSCC patients, protein expression in tumor and adjacent tissues was examined and scored by IHC staining. RNAi was performed by stably expressed shRNA in TU177 cells. In vivo tumor growth analysis was performed using a nude mouse tumorigenicity model.
RESULTS: Gln deprivation suppressed TU177 cell proliferation, which was restored by αKG supplementation. By transcriptomic analysis, we identified CECR2, which encodes a histone acetyl-lysine reader, as the downstream target gene for Gln and αKG. In LSCC patients, the expression of CECR2 in tumors was lower than adjacent tissues. Furthermore, deficiency of CECR2 promoted tumor cell growth both in vitro and in vivo, suggesting it has tumor suppressor effects. Besides, cell proliferation inhibited by Gln withdrawal could be restored by CECR2 depletion, and the proliferation boosted by αKG supplementation could be magnified either, suggested that CECR2 feedback suppressed Gln and αKG's effect on tumor growth. Transcriptomic profiling revealed CECR2 regulated the expression of a series of genes involved in tumor progression.
CONCLUSION: We confirmed the Gln-αKG-CECR2 axis contributes to tumor growth in LSCC. This finding provided a potential therapeutic opportunity for the use of associated metabolites as a potential treatment for LSCC.

Keywords:  CECR2; Glutamine metabolism; Laryngeal squamous cell carcinoma; α-ketoglutarate

DOI:  https://doi.org/10.1007/s12094-021-02603-y
Bosn J Basic Med Sci. 2021 Mar 15.

Quantitative detection of circulating MT-ND1 as a potential biomarker for colorectal cancer.

Yichun Xu, Jiajing Zhou, Qing Yuan, Jun Su, Qian Li, Xiaoliang Lu, Liwen Zhang, Zhai Cai, Junsong Han.

Liquid biopsy represents a diagnostic and monitoring tool and the circulating cell-free mitochondrial DNA (mtDNA) plays a vital role in tumor diagnosis and dynamic assessment. Colorectal cancer (CRC) is one of the most common fatal cancers worldwide. Mitochondrially encoded NADH dehydrogenase subunit 1 (MT-ND1) encodes the biggest subunit of respiratory complex I of mtDNA, and mutations in the MT-ND1 are common in CRC. We sought to determine if mutations in circulating MT-ND1 could be a potential biomarker for colorectal cancer. In this study, twenty-two CRC patients at Zhujiang Hospital were included. We mainly used droplet digital PCR to determine the mutation status of MT-ND1, combined with clinical data. In the experiment in vivo, cell-free mtDNA generally presented high concordance with tumor tissues. By quantitative PCR, the MT-ND1 content of plasma in CRC patients was significantly higher than that in healthy individuals (58.01 vs. 0.64, p=0.027). The detection of circulating MT-ND1 content and variants (m.3606 A>G, m.3970 C>T, m.4071 C>T, m.4086 C>T) in cfDNA showed a good correlation with predicted tumor response and progression to chemotherapy. In conclusion, the content and variants of circulating MT-ND1 may become a versatile tool for the diagnosis and monitoring of colorectal cancer.

DOI: https://doi.org/10.17305/bjbms.2021.5576
mBio. 2021 04 06. pii: e00540-21. [Epub ahead of print]12(2):

Mitochondrial Pyruvate Carrier Subunits Are Essential for Pyruvate-Driven Respiration, Infectivity, and Intracellular Replication of Trypanosoma cruzi.

Raquel S Negreiros, Noelia Lander, Miguel A Chiurillo, Anibal E Vercesi, Roberto Docampo.

  Pyruvate is the final metabolite of glycolysis and can be converted into acetyl coenzyme A (acetyl-CoA) in mitochondria, where it is used as the substrate for the tricarboxylic acid cycle. Pyruvate availability in mitochondria depends on its active transport through the heterocomplex formed by the mitochondrial pyruvate carriers 1 and 2 (MPC1/MPC2). We report here studies on MPC1/MPC2 of Trypanosoma cruzi, the etiologic agent of Chagas disease. Endogenous tagging of T. cruzi MPC1 (TcMPC1) and TcMPC2 with 3×c-Myc showed that both encoded proteins colocalize with MitoTracker to the mitochondria of epimastigotes. Individual knockout (KO) of TcMPC1 and TcMPC2 genes using CRISPR/Cas9 was confirmed by PCR and Southern blot analyses. Digitonin-permeabilized TcMPC1-KO and TcMPC2-KO epimastigotes showed reduced O2 consumption rates when pyruvate, but not succinate, was used as the mitochondrial substrate, while α-ketoglutarate increased their O2 consumption rates due to an increase in α-ketoglutarate dehydrogenase activity. Defective mitochondrial pyruvate import resulted in decreased Ca2+ uptake. The inhibitors UK5099 and malonate impaired pyruvate-driven oxygen consumption in permeabilized control cells. Inhibition of succinate dehydrogenase by malonate indicated that pyruvate needs to be converted into succinate to increase respiration. TcMPC1-KO and TcMPC2-KO epimastigotes showed little growth differences in standard or low-glucose culture medium. However, the ability of trypomastigotes to infect tissue culture cells and replicate as intracellular amastigotes was decreased in TcMPC-KOs. Overall, T. cruzi MPC1 and MPC2 are essential for cellular respiration in the presence of pyruvate, invasion of host cells, and replication of amastigotes.IMPORTANCE Trypanosoma cruzi is the causative agent of Chagas disease. Pyruvate is the end product of glycolysis, and its transport into the mitochondrion is mediated by the mitochondrial pyruvate carrier (MPC) subunits. Using the CRISPR/Cas9 technique, we generated individual T. cruzi MPC1 (TcMPC1) and TcMPC2 knockouts and demonstrated that they are essential for pyruvate-driven respiration. Interestingly, although glycolysis was reported as not an important source of energy for the infective stages, MPC was essential for normal host cell invasion and intracellular replication.

Keywords:  Trypanosoma cruzi; mitochondria; oxygen consumption; pyruvate carrier

DOI:  https://doi.org/10.1128/mBio.00540-21
FASEB J. 2021 May;35(5): e21490

Avian red blood cell mitochondria produce more heat in winter than in autumn.

Andreas Nord, Neil B Metcalfe, Jennifer L Page, Anna Huxtable, Dominic J McCafferty, Neal J Dawson.

  Endotherms in cold regions improve heat-producing capacity when preparing for winter. We know comparatively little about how this change is fueled by seasonal adaptation in cellular respiration. Thus, we studied the changes of mitochondrial function in red blood cells in sympatric Coal (Periparus ater), Blue (Cyanistes caeruleus), and Great (Parus major) tits between autumn and winter. These species differ more than twofold in body mass and in several aspects of their foraging ecology and social dominance, which could require differential seasonal adaptation of energy expenditure. Coal and Great tits in particular upregulated the mitochondrial respiration rate and mitochondrial volume in winter. This was not directed toward ATP synthesis, instead reflecting increased uncoupling of electron transport from ATP production. Because uncoupling is exothermic, this increased heat-producing capacity at the sub-cellular level in winter. This previously unexplored the route of thermogenesis in birds should be addressed in future work.

Keywords:  cellular metabolism; erythrocyte; overwintering; oxygen consumption; thermal biology

DOI:  https://doi.org/10.1096/fj.202100107R
Elife. 2021 Apr 07. pii: e63288. [Epub ahead of print]10

Membrane transporter dimerization driven by differential lipid solvation energetics of dissociated and associated states.

Rahul Chadda, Nathan Bernhardt, Elizabeth G Kelley, Susana C M Teixeira, Kacie Griffith, Alejandro Gil-Ley, Tuğba N Öztürk, Lauren E Hughes, Ana Forsythe, Venkatramanan Krishnamani, José D Faraldo-Gómez, Janice L Robertson.

  Over two-thirds of integral membrane proteins of known structure assemble into oligomers. Yet, the forces that drive the association of these proteins remain to be delineated, as the lipid bilayer is a solvent environment that is both structurally and chemically complex. In this study we reveal how the lipid solvent defines the dimerization equilibrium of the CLC-ec1 Cl-/H+ antiporter. Integrating experimental and computational approaches, we show that monomers associate to avoid a thinned-membrane defect formed by hydrophobic mismatch at their exposed dimerization interfaces. In this defect, lipids are strongly tilted and less densely packed than in the bulk, with a larger degree of entanglement between opposing leaflets and greater water penetration into the bilayer interior. Dimerization restores the membrane to a near-native state and therefore, appears to be driven by the larger free-energy cost of lipid solvation of the dissociated protomers. Supporting this theory, we demonstrate that addition of short-chain lipids strongly shifts the dimerization equilibrium towards the monomeric state, and show that the cause of this effect is that these lipids preferentially solvate the defect. Importantly, we show that this shift requires only minimal quantities of short-chain lipids, with no measurable impact on either the macroscopic physical state of the membrane or the protein's biological function. Based on these observations, we posit that free-energy differentials for local lipid solvation define membrane-protein association equilibria. With this, we argue that preferential lipid solvation is a plausible cellular mechanism for lipid regulation of oligomerization processes, as it can occur at low concentrations and does not require global changes in membrane properties.

Keywords:  E. coli; molecular biophysics; structural biology

DOI:  https://doi.org/10.7554/eLife.63288
Mol Metab. 2021 Apr 03. pii: S2212-8778(21)00075-2. [Epub ahead of print] 101230

LDLR inhibition promotes hepatocellular carcinoma proliferation and metastasis by elevating intracellular cholesterol synthesis through MEK/ERK signaling pathway.

Ziye Chen, Lu Chen, Bo Sun, Dongming Liu, YuChao He, Lisha Qi, Guangtao Li, Zhiqiang Han, Linlin Zhan, Su Zhang, Keyun Zhu, Yi Luo, Liwei Chen, Ning Zhang, Hua Guo.

  OBJECTIVE: Adaptive rewiring of cancer energy metabolism has received more attention. By binding with LDLs, LDLRs make most of the circulating cholesterol available for cells to utilize. However, paucity still remains regarding how LDLR works in HCC development by affecting cholesterol metabolism.METHODS: Databases analyses and immunohistochemical staining were used to identify the clinical significance of LDLR in HCC. The transcriptome analysis was used to reveal the mechanism of LDLR aberration in HCC progression. The liver orthotopic transplantation model was used to evaluate the role of LDLR in HCC progression in vivo.
RESULTS: Downregulation of LDLR was identified as a negative prognostic factor in human HCC. Reduced expression of LDLR in HCC cell lines led to LDL uptake impairment but promoted proliferation and metastasis in vitro and in vivo. Mechanistically, increasing intracellular de novo cholesterol biosynthesis was the chief contributor to the malignant behaviors caused by LDLR inhibition, which could be rescued by simvastatin. Activation of the MEK/ERK pathway by LDLR downregulation partially contributed to intracellular cholesterol synthesis in HCC.
CONCLUSIONS: Downregulation of LDLR may elevate intracellular cholesterol synthesis to accelerate proliferation and motility via a mechanism partially attributed to stimulation of the MEK/ERK signaling pathway. Repression of intracellular cholesterol synthesis with statins may constitute a targetable liability in the context of lower LDLR expression in HCC.

Keywords:  Cholesterol biosynthesis; DHCR24; HCC; LDLR; MEK/ERK pathway; Simvastatin

DOI:  https://doi.org/10.1016/j.molmet.2021.101230
Mitochondrion. 2021 Mar 31. pii: S1567-7249(21)00045-3. [Epub ahead of print]

+PGC1A driven enhanced mitochondrial DNA copy number predicts outcome in pediatric acute myeloid leukemia.

Shilpi Chaudhary, Shuvadeep Ganguly, Jayanth Kumar Palanichamy, Archna Singh, Radhika Bakhshi, Ayushi Jain, Anita Chopra, Sameer Bakhshi.

  Mitochondrial DNA (mtDNA) copy number alterations occur in acute myeloid leukemia (AML). We evaluated regulation and biological significance of mtDNA copy number in pediatric AML patients (n=123) by qRT-PCR, and in-vitro studies. MtDNA copy number was significantly higher (p<0.001) and an independent predictor of aggressive disease (p=0.006), lower event free survival (p=0.033), and overall survival (p=0.007). Expression of TFAM, POLG, POLRMT, MYC and ND3 were significantly upregulated. In cell lines, PGC1A inhibition decreased mtDNA copy number (p=0.032) while MYC inhibition had no effect (p=0.229). PGC1A may contribute to enhanced mtDNA copy number, which predicts disease aggressiveness and inferior survival outcome.

Keywords:  Acute Myeloid Leukemia; Biogenesis; Child; MYC; Mitochondrial DNA copy number; PGC1A

DOI:  https://doi.org/10.1016/j.mito.2021.03.013
Nat Commun. 2021 04 06. 12(1): 2079

Direct detection of coupled proton and electron transfers in human manganese superoxide dismutase.

Jahaun Azadmanesh, William E Lutz, Leighton Coates, Kevin L Weiss, Gloria E O Borgstahl.

Human manganese superoxide dismutase is a critical oxidoreductase found in the mitochondrial matrix. Concerted proton and electron transfers are used by the enzyme to rid the mitochondria of O2•-. The mechanisms of concerted transfer enzymes are typically unknown due to the difficulties in detecting the protonation states of specific residues and solvent molecules at particular redox states. Here, neutron diffraction of two redox-controlled manganese superoxide dismutase crystals reveal the all-atom structures of Mn3+ and Mn2+ enzyme forms. The structures deliver direct data on protonation changes between oxidation states of the metal. Observations include glutamine deprotonation, the involvement of tyrosine and histidine with altered pKas, and four unusual strong-short hydrogen bonds, including a low barrier hydrogen bond. We report a concerted proton and electron transfer mechanism for human manganese superoxide dismutase from the direct visualization of active site protons in Mn3+ and Mn2+ redox states.

DOI: https://doi.org/10.1038/s41467-021-22290-1
Nat Commun. 2021 04 07. 12(1): 2091

Myofibril and mitochondria morphogenesis are coordinated by a mechanical feedback mechanism in muscle.

Jerome Avellaneda, Clement Rodier, Fabrice Daian, Nicolas Brouilly, Thomas Rival, Nuno Miguel Luis, Frank Schnorrer.

Complex animals build specialised muscles to match specific biomechanical and energetic needs. Hence, composition and architecture of sarcomeres and mitochondria are muscle type specific. However, mechanisms coordinating mitochondria with sarcomere morphogenesis are elusive. Here we use Drosophila muscles to demonstrate that myofibril and mitochondria morphogenesis are intimately linked. In flight muscles, the muscle selector spalt instructs mitochondria to intercalate between myofibrils, which in turn mechanically constrain mitochondria into elongated shapes. Conversely in cross-striated leg muscles, mitochondria networks surround myofibril bundles, contacting myofibrils only with thin extensions. To investigate the mechanism causing these differences, we manipulated mitochondrial dynamics and found that increased mitochondrial fusion during myofibril assembly prevents mitochondrial intercalation in flight muscles. Strikingly, this causes the expression of cross-striated muscle specific sarcomeric proteins. Consequently, flight muscle myofibrils convert towards a partially cross-striated architecture. Together, these data suggest a biomechanical feedback mechanism downstream of spalt synchronizing mitochondria with myofibril morphogenesis.

DOI: https://doi.org/10.1038/s41467-021-22058-7
Front Oncol. 2021 ;11 642229

Targeting ACLY Attenuates Tumor Growth and Acquired Cisplatin Resistance in Ovarian Cancer by Inhibiting the PI3K-AKT Pathway and Activating the AMPK-ROS Pathway.

Xuan Wei, Juanjuan Shi, Qianhan Lin, Xiaoxue Ma, Yingxin Pang, Hongluan Mao, Rui Li, Wei Lu, Yu Wang, Peishu Liu.

  Background: Ovarian cancer is the most lethal female genital malignancy. Although cisplatin is the first-line chemotherapy to treat ovarian cancer patients along with debulking surgeries, its efficacy is limited due to the high incidence of cisplatin resistance. ATP citrate lyase (ACLY) has been shown to be a key metabolic enzyme and is associated with poor prognosis in various cancers, including ovarian cancer. Nevertheless, no studies have probed the mechanistic relationship between ACLY and cisplatin resistance. Methods: Survival analysis was mainly carried out online. Bioinformatic analysis was performed in R/R studio. Proliferative activity was measured by MTT and colony formation assays. Cell cycle and apoptosis analysis were performed by flow cytometry. The acquired-cisplatin-resistant cell line A2780/CDDP was generated by exposing A2780 to cisplatin at gradually elevated concentrations. MTT assay was used to calculate IC50 values of cisplatin. A xenograft tumor assay was used test cell proliferation in vivo. Results: Higher expression of ACLY was found in ovarian cancer tissue and related to poor prognosis. Knockdown of ACLY in A2780, SKOV3, and HEY cells inhibited cell proliferation, caused cell-cycle arrest by modulating the P16-CDK4-CCND1 pathway, and induced apoptosis probably by inhibiting p-AKT activity. Bioinformatic analysis of the GSE15709 dataset revealed upregulation of ACLY and activation of PI3K-AKT pathway in cells with acquired cisplatin resistance, in line with observations on A2780/CDDP cells that we generated. Knockdown of ACLY alleviated cisplatin resistance, and works synergistically with cisplatin treatment to induce apoptosis in A2780/CDDP cells by inhibiting the PI3K-AKT pathway and activating AMPK-ROS pathway. The ACLY-specific inhibitor SB-204990 showed the same effect. In A2780/CDDP cells, AKT overexpression could attenuate cisplatin re-sensitization caused by ACLY knockdown. Conclusions: Knockdown of ACLY attenuated cisplatin resistance by inhibiting the PI3K-AKT pathway and activating the AMPK-ROS pathway. These findings suggest that a combination of ACLY inhibition and cisplatin might be an effective strategy for overcoming cisplatin resistance in ovarian cancer.

Keywords:  ACLY; AMPK-ROS pathway; PI3K-AKT pathway; cisplatin resistance; ovarian cancer

DOI:  https://doi.org/10.3389/fonc.2021.642229
Proc Natl Acad Sci U S A. 2021 Mar 16. pii: e2021157118. [Epub ahead of print]118(11):

Cryo-EM structure and kinetics reveal electron transfer by 2D diffusion of cytochrome c in the yeast III-IV respiratory supercomplex.

Agnes Moe, Justin Di Trani, John L Rubinstein, Peter Brzezinski.

  Energy conversion in aerobic organisms involves an electron current from low-potential donors, such as NADH and succinate, to dioxygen through the membrane-bound respiratory chain. Electron transfer is coupled to transmembrane proton transport, which maintains the electrochemical proton gradient used to produce ATP and drive other cellular processes. Electrons are transferred from respiratory complexes III to IV (CIII and CIV) by water-soluble cytochrome (cyt.) c In Saccharomyces cerevisiae and some other organisms, these complexes assemble into larger CIII2CIV1/2 supercomplexes, the functional significance of which has remained enigmatic. In this work, we measured the kinetics of the S. cerevisiae supercomplex cyt. c-mediated QH2:O2 oxidoreductase activity under various conditions. The data indicate that the electronic link between CIII and CIV is confined to the surface of the supercomplex. Single-particle electron cryomicroscopy (cryo-EM) structures of the supercomplex with cyt. c show the positively charged cyt. c bound to either CIII or CIV or along a continuum of intermediate positions. Collectively, the structural and kinetic data indicate that cyt. c travels along a negatively charged patch on the supercomplex surface. Thus, rather than enhancing electron transfer rates by decreasing the distance that cyt. c must diffuse in three dimensions, formation of the CIII2CIV1/2 supercomplex facilitates electron transfer by two-dimensional (2D) diffusion of cyt. c This mechanism enables the CIII2CIV1/2 supercomplex to increase QH2:O2 oxidoreductase activity and suggests a possible regulatory role for supercomplex formation in the respiratory chain.

Keywords:  bioenergetics; cytochrome bc1; cytochrome c oxidase; electron transfer; mitochondria

DOI:  https://doi.org/10.1073/pnas.2021157118
Elife. 2021 Apr 09. pii: e65158. [Epub ahead of print]10

Augmenter of Liver Regeneration regulates cellular iron homeostatis by modulating mitochondrial transport of ATP-binding cassette B8.

Hsiang-Chun Chang, Jason Solomon Shapiro, Xinghang Jiang, Grant Senyei, Teruki Sato, Justin Geier, Konrad T Sawicki, Hossein Ardehali.

  Chronic loss of Augmenter of Liver Regeneration (ALR) results in mitochondrial myopathy with cataracts, however, the mechanism for this disorder remains unclear. Here, we demonstrate that loss of ALR, a principal component of the MIA40/ALR protein import pathway, results in impaired cytosolic Fe/S cluster biogenesis in mammalian cells. Mechanistically, MIA40/ALR facilitates the mitochondrial import of ATP binding cassette (ABC)-B8, an inner mitochondrial membrane protein required for cytoplasmic Fe/S cluster maturation, through physical interaction with ABCB8. Downregulation of ALR impairs mitochondrial ABCB8 import, reduces cytoplasmic Fe/S cluster maturation, and increases cellular iron through the iron regulatory protein-iron response element system. Our finding provides a mechanistic link between MIA40/ALR import machinery and cytosolic Fe/S cluster maturation through the mitochondrial import of ABCB8, and offers a potential explanation for the pathology seen in patients with ALR mutations.

Keywords:  cell biology; human; medicine

DOI:  https://doi.org/10.7554/eLife.65158
Cell Death Dis. 2021 Apr 07. 12(4): 377

NDUFA4L2 promotes glioblastoma progression, is associated with poor survival, and can be effectively targeted by apatinib.

Zheng Chen, Xiangyu Wei, Xueyi Wang, Xuan Zheng, Bowen Chang, Lin Shen, Hanshuo Zhu, Min Yang, Shiting Li, Xuesheng Zheng.

NADH dehydrogenase [ubiquinone] 1 alpha subcomplex, 4-like 2 (NDUFA4L2) is a subunit of Complex I of the mitochondrial respiratory chain, which is important in metabolic reprogramming and oxidative stress in multiple cancers. However, the biological role and molecular regulation of NDUFA4L2 in glioblastoma (GBM) are poorly understood. Here, we found that NDUFA4L2 was significantly upregulated in GBM; the elevated levels were correlated with reduced patient survival. Gene knockdown of NDUFA4L2 inhibited tumor cell proliferation and enhanced apoptosis, while tumor cells initiated protective mitophagy in vitro and in vivo. We used lentivirus to reduce expression levels of NDUFA4L2 protein in GBM cells exposed to mitophagy blockers, which led to a significant enhancement of tumor cell apoptosis in vitro and inhibited the development of xenografted tumors in vivo. In contrast to other tumor types, NDUFA4L2 expression in GBM may not be directly regulated by hypoxia-inducible factor (HIF)-1α, because HIF-1α inhibitors failed to inhibit NDUFA4L2 in GBM. Apatinib was able to effectively target NDUFA4L2 in GBM, presenting an alternative to the use of lentiviruses, which currently cannot be used in humans. Taken together, our data suggest the use of NDUFA4L2 as a potential therapeutic target in GBM and demonstrate a practical treatment approach.

DOI: https://doi.org/10.1038/s41419-021-03646-3
J Med Chem. 2021 Apr 08.

Discovery of AG-270, a First-in-Class Oral MAT2A Inhibitor for the Treatment of Tumors with Homozygous MTAP Deletion.

Zenon Konteatis, Jeremy Travins, Stefan Gross, Katya Marjon, Amelia Barnett, Everton Mandley, Brandon Nicolay, Raj Nagaraja, Yue Chen, Yabo Sun, Zhixiao Liu, Jie Yu, Zhixiong Ye, Fan Jiang, Wentao Wei, Cheng Fang, Yi Gao, Peter Kalev, Marc L Hyer, Byron DeLaBarre, Lei Jin, Anil K Padyana, Lenny Dang, Joshua Murtie, Scott A Biller, Zhihua Sui, Kevin M Marks.

The metabolic enzyme methionine adenosyltransferase 2A (MAT2A) was recently implicated as a synthetic lethal target in cancers with deletion of the methylthioadenosine phosphorylase (MTAP) gene, which is adjacent to the CDKN2A tumor suppressor and codeleted with CDKN2A in approximately 15% of all cancers. Previous attempts to target MAT2A with small-molecule inhibitors identified cellular adaptations that blunted their efficacy. Here, we report the discovery of highly potent, selective, orally bioavailable MAT2A inhibitors that overcome these challenges. Fragment screening followed by iterative structure-guided design enabled >10 000-fold improvement in potency of a family of allosteric MAT2A inhibitors that are substrate noncompetitive and inhibit release of the product, S-adenosyl methionine (SAM), from the enzyme's active site. We demonstrate that potent MAT2A inhibitors substantially reduce SAM levels in cancer cells and selectively block proliferation of MTAP-null cells both in tissue culture and xenograft tumors. These data supported progressing AG-270 into current clinical studies (ClinicalTrials.gov NCT03435250).

DOI: https://doi.org/10.1021/acs.jmedchem.0c01895
Proc Natl Acad Sci U S A. 2021 Mar 16. pii: e2021073118. [Epub ahead of print]118(11):

DNMT1 maintains metabolic fitness of adipocytes through acting as an epigenetic safeguard of mitochondrial dynamics.

Yoon Jeong Park, Sangseon Lee, Sangsoo Lim, Hahn Nahmgoong, Yul Ji, Jin Young Huh, Assim A Alfadda, Sun Kim, Jae Bum Kim.

  White adipose tissue (WAT) is a key regulator of systemic energy metabolism, and impaired WAT plasticity characterized by enlargement of preexisting adipocytes associates with WAT dysfunction, obesity, and metabolic complications. However, the mechanisms that retain proper adipose tissue plasticity required for metabolic fitness are unclear. Here, we comprehensively showed that adipocyte-specific DNA methylation, manifested in enhancers and CTCF sites, directs distal enhancer-mediated transcriptomic features required to conserve metabolic functions of white adipocytes. Particularly, genetic ablation of adipocyte Dnmt1, the major methylation writer, led to increased adiposity characterized by increased adipocyte hypertrophy along with reduced expansion of adipocyte precursors (APs). These effects of Dnmt1 deficiency provoked systemic hyperlipidemia and impaired energy metabolism both in lean and obese mice. Mechanistically, Dnmt1 deficiency abrogated mitochondrial bioenergetics by inhibiting mitochondrial fission and promoted aberrant lipid metabolism in adipocytes, rendering adipocyte hypertrophy and WAT dysfunction. Dnmt1-dependent DNA methylation prevented aberrant CTCF binding and, in turn, sustained the proper chromosome architecture to permit interactions between enhancer and dynamin-1-like protein gene Dnm1l (Drp1) in adipocytes. Also, adipose DNMT1 expression inversely correlated with adiposity and markers of metabolic health but positively correlated with AP-specific markers in obese human subjects. Thus, these findings support strategies utilizing Dnmt1 action on mitochondrial bioenergetics in adipocytes to combat obesity and related metabolic pathology.

Keywords:  DNA methylation; adiposity; chromosome structure; metabolic disease; mitochondria

DOI:  https://doi.org/10.1073/pnas.2021073118
Proc Natl Acad Sci U S A. 2021 Mar 16. pii: e2016833118. [Epub ahead of print]118(11):

Enhanced cytarabine-induced killing in OGG1-deficient acute myeloid leukemia cells.

Nichole Owen, Irina G Minko, Samantha A Moellmer, Sydney K Cammann, R Stephen Lloyd, Amanda K McCullough.

  Human clinical trials suggest that inhibition of enzymes in the DNA base excision repair (BER) pathway, such as PARP1 and APE1, can be useful in anticancer strategies when combined with certain DNA-damaging agents or tumor-specific genetic deficiencies. There is also evidence suggesting that inhibition of the BER enzyme 8-oxoguanine DNA glycosylase-1 (OGG1), which initiates repair of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxo-dG) and 2,6-diamino-4-hydroxy-5-formamidopyrimidine (Fapy-dG), could be useful in treating certain cancers. Specifically, in acute myeloid leukemia (AML), both the RUNX1-RUNX1T1 fusion and the CBFB-MYH11 subtypes have lower levels of OGG1 expression, which correlate with increased therapeutic-induced cell cytotoxicity and good prognosis for improved, relapse-free survival compared with other AML patients. Here we present data demonstrating that AML cell lines deficient in OGG1 have enhanced sensitivity to cytarabine (cytosine arabinoside [Ara-C]) relative to OGG1-proficient cells. This enhanced cytotoxicity correlated with endogenous oxidatively-induced DNA damage and Ara-C-induced DNA strand breaks, with a large proportion of these breaks occurring at common fragile sites. This lethality was highly specific for Ara-C treatment of AML cells deficient in OGG1, with no other replication stress-inducing agents showing a correlation between cell killing and low OGG1 levels. The mechanism for this preferential toxicity was addressed using in vitro replication assays in which DNA polymerase δ was shown to insert Ara-C opposite 8-oxo-dG, resulting in termination of DNA synthesis. Overall, these data suggest that incorporation of Ara-C opposite unrepaired 8-oxo-dG may be the fundamental mechanism conferring selective toxicity and therapeutic effectiveness in OGG1-deficient AML cells.

Keywords:  AML therapy; DNA polymerase delta; DNA repair; DNA replication; fragile site

DOI:  https://doi.org/10.1073/pnas.2016833118
Nat Commun. 2021 Apr 09. 12(1): 2130

Coding and non-coding roles of MOCCI (C15ORF48) coordinate to regulate host inflammation and immunity.

Cheryl Q E Lee, Baptiste Kerouanton, Sonia Chothani, Shan Zhang, Ying Chen, Chinmay Kumar Mantri, Daniella Helena Hock, Radiance Lim, Rhea Nadkarni, Vinh Thang Huynh, Daryl Lim, Wei Leong Chew, Franklin L Zhong, David Arthur Stroud, Sebastian Schafer, Vinay Tergaonkar, Ashley L St John, Owen J L Rackham, Lena Ho.

Mito-SEPs are small open reading frame-encoded peptides that localize to the mitochondria to regulate metabolism. Motivated by an intriguing negative association between mito-SEPs and inflammation, here we screen for mito-SEPs that modify inflammatory outcomes and report a mito-SEP named "Modulator of cytochrome C oxidase during Inflammation" (MOCCI) that is upregulated during inflammation and infection to promote host-protective resolution. MOCCI, a paralog of the NDUFA4 subunit of cytochrome C oxidase (Complex IV), replaces NDUFA4 in Complex IV during inflammation to lower mitochondrial membrane potential and reduce ROS production, leading to cyto-protection and dampened immune response. The MOCCI transcript also generates miR-147b, which targets the NDUFA4 mRNA with similar immune dampening effects as MOCCI, but simultaneously enhances RIG-I/MDA-5-mediated viral immunity. Our work uncovers a dual-component pleiotropic regulation of host inflammation and immunity by MOCCI (C15ORF48) for safeguarding the host during infection and inflammation.

DOI: https://doi.org/10.1038/s41467-021-22397-5
FASEB J. 2021 May;35(5): e21544

Cardiomyocyte-specific Srsf3 deletion reveals a mitochondrial regulatory role.

Audrey-Ann Dumont, Lauralyne Dumont, Delong Zhou, Hugo Giguère, Chantal Pileggi, Mary-Ellen Harper, Denis P Blondin, Michelle S Scott, Mannix Auger-Messier.

  Serine-rich splicing factor 3 (SRSF3) was recently reported as being necessary to preserve RNA stability via an mTOR mechanism in a cardiac mouse model in adulthood. Here, we demonstrate the link between Srsf3 and mitochondrial integrity in an embryonic cardiomyocyte-specific Srsf3 conditional knockout (cKO) mouse model. Fifteen-day-old Srsf3 cKO mice showed dramatically reduced (below 50%) survival and reduced the left ventricular systolic performance, and histological analysis of these hearts revealed a significant increase in cardiomyocyte size, confirming the severe remodeling induced by Srsf3 deletion. RNA-seq analysis of the hearts of 5-day-old Srsf3 cKO mice revealed early changes in expression levels and alternative splicing of several transcripts related to mitochondrial integrity and oxidative phosphorylation. Likewise, the levels of several protein complexes of the electron transport chain decreased, and mitochondrial complex I-driven respiration of permeabilized cardiac muscle fibers from the left ventricle was impaired. Furthermore, transmission electron microscopy analysis showed disordered mitochondrial length and cristae structure. Together with its indispensable role in the physiological maintenance of mouse hearts, these results highlight the previously unrecognized function of Srsf3 in regulating the mitochondrial integrity.

Keywords:  Srsf3; cardiomyocyte; mitochondria; oxidative phosphorylation; respiratory chain complex I

DOI:  https://doi.org/10.1096/fj.202002293RR
Blood. 2021 Apr 06. pii: blood.2020010167. [Epub ahead of print]

Intact TP53 function is essential for sustaining durable responses to BH3-mimetic drugs in leukemias.

Rachel Thijssen, Sarah T Diepstraten, Donia M Moujalled, Edward Chew, Christoffer Flensburg, Melissa Xiaoqing Shi, Michael A Dengler, Veronique Litalien, Sarah MacRaild, Maoshan Chen, Natasha S Anstee, Boris Reljic, Sarah S Gabriel, Tirta M Djajawi, Chris D Riffkin, Brandon James Aubrey, Catherine Chang, Lin Tai, Zhen Xu, Thomas David Morley, Giovanna Pomilio, Claudia Bruedigam, Axel Kallies, David A Stroud, Ashish Bajel, Ruth M Kluck, Steven W Lane, Marie Schoumacher, Sébastien Banquet, Ian J Majewski, Andreas Strasser, Andrew W Roberts, David Ching Siang Huang, Fiona C Brown, Gemma Kelly, Andrew H Wei.

Selective targeting of BCL2 with the BH3-mimetic venetoclax is proving transformative for patients with various leukemias. TP53 controls apoptosis upstream from where BCL2 and its pro-survival relatives, such as MCL1, act. Therefore, targeting these pro-survival proteins could trigger apoptosis across diverse blood cancers, irrespective of TP53 mutation status. Indeed, targeting BCL2 has produced clinically relevant responses in blood cancers with aberrant TP53. However, we show that TP53 mutated or deficient myeloid and lymphoid leukemias outcompete isogenic controls with intact TP53, unless sufficient concentrations of BH3-mimetics targeting BCL2 or MCL1 are applied. Strikingly, tumor cells with TP53 dysfunction escape and thrive over time if inhibition of BCL2 or MCL1 is sub-lethal, in part because of an increased threshold for BAX/BAK activation in these cells. Our study reveals the key role of TP53 in shaping long-term responses to BH3-mimetic drugs and reconciles the disparate pattern of initial clinical response to venetoclax, followed by subsequent treatment failure among patients with TP53-mutant chronic lymphocytic leukemia (CLL) or acute myeloid leukemia (AML). In contrast to BH3-mimetics targeting just BCL2 or MCL1 at doses which are individually sub-lethal, we find that a combined BH3-mimetic approach targeting both pro-survival proteins enhances lethality and durably suppresses leukemic burden, regardless of TP53 mutation status. Our findings highlight the importance of employing sufficiently lethal treatment strategies to maximize outcomes for patients with TP53-mutant disease. In addition, our findings caution against use of sub-lethal BH3-mimetic drug regimens, which may enhance the risk of disease progression driven by emergent TP53 mutant clones.

DOI: https://doi.org/10.1182/blood.2020010167
Curr Clin Microbiol Rep. 2020 Dec;7(4): 115-123

Host Mitochondrial Requirements of Cytomegalovirus Replication.

Chandler H Monk, Kevin J Zwezdaryk.

  Purpose of Review: Metabolic rewiring of the host cell is required for optimal viral replication. Human cytomegalovirus (HCMV) has been observed to manipulate numerous mitochondrial functions. In this review, we describe the strategies and targets HCMV uses to control different aspects of mitochondrial function.Recent Findings: The mitochondria are instrumental in meeting the biosynthetic and bioenergetic needs of HCMV replication. This is achieved through altered metabolism and signaling pathways. Morphological changes mediated through biogenesis and fission/fusion dynamics contribute to strategies to avoid cell death, overcome oxidative stress, and maximize the biosynthetic and bioenergetic outputs of mitochondria.
Summary: Emerging data suggests that cytomegalovirus relies on intact, functional host mitochondria for optimal replication. HCMV large size and slow replication kinetics create a dependency on mitochondria during replication. Targeting the host mitochondria is an attractive antiviral target.

Keywords:  CMV; ETC; Membrane potential; Mitochondria; Oxidative phosphorylation; ROS

DOI:  https://doi.org/10.1007/s40588-020-00153-5
Cell Death Dis. 2021 Apr 06. 12(4): 361

Down-regulation of SLC25A20 promotes hepatocellular carcinoma growth and metastasis through suppression of fatty-acid oxidation.

Peng Yuan, Jiao Mu, Zijun Wang, Shuaijun Ma, Xiuwei Da, Jian Song, Hongxin Zhang, Le Yang, Jibin Li, Jingyue Yang.

Solute carrier family 25 member 20 (SLC25A20) is a mitochondrial-membrane-carrier protein involved in the transport of acylcarnitines into mitochondrial matrix for oxidation. A previous-integrated-proteogenomic study had identified SLC25A20 as one of the top-three prognostic biomarkers in HCC. However, the expression and the biological function of SLC25A20 have not yet been investigated in HCC. In the present study, we found that SLC25A20 expression is frequently down-regulated in HCC cells mainly due to the up-regulation of miR-132-3p. Down-regulation of SLC25A20 is associated with a poor prognosis in patients with HCC. SLC25A20 suppressed HCC growth and metastasis, both in vitro and in vivo, by suppression of G1-S cell transition, epithelial-to-mesenchymal transition (EMT), and induction of cell apoptosis. Mechanistically, SLC25A20 down-regulation promoted HCC growth and metastasis through suppression of fatty-acid oxidation. Altogether, SLC25A20 plays a critical tumor-suppressive role in carcinogenesis of HCC; SLC25A20 may serve as a novel prognostic factor and therapeutic target for patients with HCC.

DOI: https://doi.org/10.1038/s41419-021-03648-1
Proc Natl Acad Sci U S A. 2021 Mar 16. pii: e2012228118. [Epub ahead of print]118(11):

Hexokinase 2 discerns a novel circulating tumor cell population associated with poor prognosis in lung cancer patients.

Liu Yang, Xiaowei Yan, Jie Chen, Qiong Zhan, Yingqi Hua, Shili Xu, Ziming Li, Zhuo Wang, Yu Dong, Dongqing Zuo, Min Xue, Yin Tang, Harvey R Herschman, Shun Lu, Qihui Shi, Wei Wei.

  Unlike other epithelial cancer types, circulating tumor cells (CTCs) are less frequently detected in the peripheral blood of non-small cell lung cancer (NSCLC) patients using epithelial marker-based detection approaches despite the aggressive nature of NSCLC. Here, we demonstrate hexokinase-2 (HK2) as a metabolic function-associated marker for the detection of CTCs. In 59 NSCLC patients bearing cytokeratin-positive (CKpos) primary tumors, HK2 enables resolving cytokeratin-negative (HK2high/CKneg) CTCs as a prevalent population in about half of the peripheral blood samples with positive CTC counts. However, HK2high/CKneg tumor cells are a minority population in pleural effusions and cerebrospinal fluids. Single-cell analysis shows that HK2high/CKneg CTCs exhibit smaller sizes but consistent copy number variation profiles compared with CKpos counterparts. Single-cell transcriptome profiling reveals that CK expression levels of CTCs are independent of their epithelial-to-mesenchymal transition (EMT) status, challenging the long-standing association between CK expression and EMT. HK2high/CKneg CTCs display metastasis and EGFR inhibitor resistance-related molecular signatures and are selectively enriched in patients with EGFR L858R driver oncogene mutation as opposed to EGFR 19Del , which is more frequently found in patients with prevalent CKpos CTCs in the blood. Consistently, treatment-naïve patients with a larger number or proportion of HK2high/CKneg CTCs in the blood exhibit poor therapy response and shorter progression-free survival. Collectively, our approach resolves a more complete spectrum of CTCs in NSCLC that can potentially be exploited to identify patient prognosis before therapy.

Keywords:  circulating tumor cells; hexokinase-2; liquid biopsy; non–small cell lung cancer; single-cell sequencing

DOI:  https://doi.org/10.1073/pnas.2012228118
Cell Rep. 2021 Apr 06. pii: S2211-1247(21)00275-8. [Epub ahead of print]35(1): 108961

Restoration of fitness lost due to dysregulation of the pyruvate dehydrogenase complex is triggered by ribosomal binding site modifications.

Amitesh Anand, Connor A Olson, Anand V Sastry, Arjun Patel, Richard Szubin, Laurence Yang, Adam M Feist, Bernhard O Palsson.

  Pyruvate dehydrogenase complex (PDC) functions as the main determinant of the respiro-fermentative balance because it converts pyruvate to acetyl-coenzyme A (CoA), which then enters the TCA (tricarboxylic acid cycle). PDC is repressed by the pyruvate dehydrogenase complex regulator (PdhR) in Escherichia coli. The deletion of the pdhR gene compromises fitness in aerobic environments. We evolve the E. coli pdhR deletion strain to examine its achievable growth rate and the underlying adaptive strategies. We find that (1) optimal proteome allocation to PDC is critical in achieving optimal growth rate; (2) expression of PDC in evolved strains is reduced through mutations in the Shine-Dalgarno sequence; (3) rewiring of the TCA flux and increased reactive oxygen species (ROS) defense occur in the evolved strains; and (4) the evolved strains adapt to an efficient biomass yield. Together, these results show how adaptation can find alternative regulatory mechanisms for a key cellular process if the primary regulatory mode fails.

Keywords:  adaptive laboratory evolution; bioenergetics; proteome allocation; system biology; transcriptional regulatory network

DOI:  https://doi.org/10.1016/j.celrep.2021.108961
Nat Metab. 2021 Apr 08.

Mitochondrial NADPH is a pro at Pro synthesis.

Frances F Diehl, Matthew G Vander Heiden.

DOI: https://doi.org/10.1038/s42255-021-00381-z
Life Sci Alliance. 2021 Jun;pii: e202000806. [Epub ahead of print]4(6):

Mitochondrial Aurora kinase A induces mitophagy by interacting with MAP1LC3 and Prohibitin 2.

Giulia Bertolin, Marie-Clotilde Alves-Guerra, Angélique Cheron, Agnès Burel, Claude Prigent, Roland Le Borgne, Marc Tramier.

Epithelial and haematologic tumours often show the overexpression of the serine/threonine kinase AURKA. Recently, AURKA was shown to localise at mitochondria, where it regulates mitochondrial dynamics and ATP production. Here we define the molecular mechanisms of AURKA in regulating mitochondrial turnover by mitophagy. AURKA triggers the degradation of Inner Mitochondrial Membrane/matrix proteins by interacting with core components of the autophagy pathway. On the inner mitochondrial membrane, the kinase forms a tripartite complex with MAP1LC3 and the mitophagy receptor PHB2, which triggers mitophagy in a PARK2/Parkin-independent manner. The formation of the tripartite complex is induced by the phosphorylation of PHB2 on Ser39, which is required for MAP1LC3 to interact with PHB2. Last, treatment with the PHB2 ligand xanthohumol blocks AURKA-induced mitophagy by destabilising the tripartite complex and restores normal ATP production levels. Altogether, these data provide evidence for a role of AURKA in promoting mitophagy through the interaction with PHB2 and MAP1LC3. This work paves the way to the use of function-specific pharmacological inhibitors to counteract the effects of the overexpression of AURKA in cancer.

DOI: https://doi.org/10.26508/lsa.202000806
Cell Metab. 2021 Apr 06. pii: S1550-4131(21)00117-0. [Epub ahead of print]33(4): 702-704

Pancreatic β cells put the glutamine engine in reverse.

Evan C Lien, Matthew G Vander Heiden.

The metabolism of nutrients other than glucose influences insulin secretion by pancreatic β cells, but the mechanisms involved are incompletely understood. In this issue of Cell Metabolism, Zhang et al. (2020) report that reductive glutamine metabolism generates cytosolic NADPH to promote insulin secretion by β cells.

DOI: https://doi.org/10.1016/j.cmet.2021.03.010
PLoS Biol. 2021 Apr 07. 19(4): e3001166

Neural stem cells traffic functional mitochondria via extracellular vesicles.

Luca Peruzzotti-Jametti, Joshua D Bernstock, Cory M Willis, Giulia Manferrari, Rebecca Rogall, Erika Fernandez-Vizarra, James C Williamson, Alice Braga, Aletta van den Bosch, Tommaso Leonardi, Grzegorz Krzak, Ágnes Kittel, Cristiane Benincá, Nunzio Vicario, Sisareuth Tan, Carlos Bastos, Iacopo Bicci, Nunzio Iraci, Jayden A Smith, Ben Peacock, Karin H Muller, Paul J Lehner, Edit Iren Buzas, Nuno Faria, Massimo Zeviani, Christian Frezza, Alain Brisson, Nicholas J Matheson, Carlo Viscomi, Stefano Pluchino.

Neural stem cell (NSC) transplantation induces recovery in animal models of central nervous system (CNS) diseases. Although the replacement of lost endogenous cells was originally proposed as the primary healing mechanism of NSC grafts, it is now clear that transplanted NSCs operate via multiple mechanisms, including the horizontal exchange of therapeutic cargoes to host cells via extracellular vesicles (EVs). EVs are membrane particles trafficking nucleic acids, proteins, metabolites and metabolic enzymes, lipids, and entire organelles. However, the function and the contribution of these cargoes to the broad therapeutic effects of NSCs are yet to be fully understood. Mitochondrial dysfunction is an established feature of several inflammatory and degenerative CNS disorders, most of which are potentially treatable with exogenous stem cell therapeutics. Herein, we investigated the hypothesis that NSCs release and traffic functional mitochondria via EVs to restore mitochondrial function in target cells. Untargeted proteomics revealed a significant enrichment of mitochondrial proteins spontaneously released by NSCs in EVs. Morphological and functional analyses confirmed the presence of ultrastructurally intact mitochondria within EVs with conserved membrane potential and respiration. We found that the transfer of these mitochondria from EVs to mtDNA-deficient L929 Rho0 cells rescued mitochondrial function and increased Rho0 cell survival. Furthermore, the incorporation of mitochondria from EVs into inflammatory mononuclear phagocytes restored normal mitochondrial dynamics and cellular metabolism and reduced the expression of pro-inflammatory markers in target cells. When transplanted in an animal model of multiple sclerosis, exogenous NSCs actively transferred mitochondria to mononuclear phagocytes and induced a significant amelioration of clinical deficits. Our data provide the first evidence that NSCs deliver functional mitochondria to target cells via EVs, paving the way for the development of novel (a)cellular approaches aimed at restoring mitochondrial dysfunction not only in multiple sclerosis, but also in degenerative neurological diseases.

DOI: https://doi.org/10.1371/journal.pbio.3001166
Proc Natl Acad Sci U S A. 2021 Mar 16. pii: e2019046118. [Epub ahead of print]118(11):

Dual-process brain mitochondria isolation preserves function and clarifies protein composition.

Maria F Noterman, Kalyani Chaubey, Kristi Lin-Rahardja, Anjali M Rajadhyaksha, Andrew A Pieper, Eric B Taylor.

  The brain requires continuously high energy production to maintain ion gradients and normal function. Mitochondria critically undergird brain energetics, and mitochondrial abnormalities feature prominently in neuropsychiatric disease. However, many unique aspects of brain mitochondria composition and function are poorly understood. Developing improved neuroprotective therapeutics thus requires more comprehensively understanding brain mitochondria, including accurately delineating protein composition and channel-transporter functional networks. However, obtaining pure mitochondria from the brain is especially challenging due to its distinctive lipid and cell structure properties. As a result, conflicting reports on protein localization to brain mitochondria abound. Here we illustrate this problem with the neuropsychiatric disease-associated L-type calcium channel Cav1.2α1 subunit previously observed in crude mitochondria. We applied a dual-process approach to obtain functionally intact versus compositionally pure brain mitochondria. One branch utilizes discontinuous density gradient centrifugation to isolate semipure mitochondria suitable for functional assays but unsuitable for protein localization because of endoplasmic reticulum (ER) contamination. The other branch utilizes self-forming density gradient ultracentrifugation to remove ER and yield ultrapure mitochondria that are suitable for investigating protein localization but functionally compromised. Through this process, we evaluated brain mitochondria protein content and observed the absence of Cav1.2α1 and other previously reported mitochondrial proteins, including the NMDA receptor, ryanodine receptor 1, monocarboxylate transporter 1, excitatory amino acid transporter 1, and glyceraldehyde 3-phosphate dehydrogenase. Conversely, we confirmed mitochondrial localization of several plasma membrane proteins previously reported to also localize to mitochondria. We expect this dual-process isolation procedure will enhance understanding of brain mitochondria in both health and disease.

Keywords:  channel; mitochondria; neuropsychiatric disease; solute carrier; transporter

DOI:  https://doi.org/10.1073/pnas.2019046118
Aging (Albany NY). 2021 Mar 26. 13

The critical role of peroxiredoxin-2 in colon cancer stem cells.

Linglong Peng, Yongfu Xiong, Rong Wang, Ling Xiang, He Zhou, Zhongxue Fu.

  Colon cancer stem cells (CCSCs) play an important role in facilitating colon cancer occurrence, metastasis and drug resistance. The results of our previous studies confirmed that the well-studied antioxidant gene peroxiredoxin-2 (PRDX2) promotes colon cancer progression. However, the underlying function and mechanisms associated with PRDX2 remodeling in the context of CCSCs have remained poorly studied. In our present study, we demonstrated that PRDX2 is highly expressed in CD133/CD44-positive colon cancer tissues and spheroid CD133+CD44+ CCSCs. PRDX2 overexpression was shown to be closely correlated with CD133+CD44+ CCSCs in colon cancer. Furthermore, PRDX2 depletion markedly suppressed CD133+CD44+ CCSC stemness maintenance, tumor initiation, migration and invasion and liver metastasis. Furthermore, the expression of various EMT markers and Wnt/β-catenin signaling proteins was altered after PRDX2 inhibition. In addition, PRDX2 knockdown led to increased ROS production in CD133+CD44+ CCSCs, sensitizing CCSCs to oxidative stress and chemotherapy. These results suggest that PRDX2 could be a possible therapeutic target in CCSCs.

Keywords:  chemoresistance; colon cancer; colon cancer stem cells; metastasis; peroxiredoxin-2

DOI:  https://doi.org/10.18632/aging.202784
Onco Targets Ther. 2021 ;14 2259-2277

Identification of Metabolic-Associated Genes for the Prediction of Colon and Rectal Adenocarcinoma.

Yanfen Cui, Baoai Han, He Zhang, Hui Liu, Fei Zhang, Ruifang Niu.

  Background and Aim: Uncontrolled proliferation is the most prominent biological feature of tumors. In order to rapidly proliferate, tumor cells regulate their metabolic behavior by controlling the expression of metabolism-related genes (MRGs) to maximize the utilization of available nutrients. In this study, we aimed to construct prognosis models for colorectal adenocarcinoma (COAD) and rectum adenocarcinoma (READ) using MRGs to predict the prognoses of patients.Methods: We first acquired the gene expression profiles of COAD and READ from the TCGA database, and then utilized univariate Cox analysis, Lasso regression, and multivariable Cox analysis to identify the MRGs for risk models.
Results: Eight genes (CPT1C, PLCB2, PLA2G2D, GAMT, ENPP2, PIP4K2B, GPX3, and GSR) in the colon cancer risk model and six genes (TDO2, PKLR, GAMT, EARS2, ACO1, and WAS) in the rectal cancer risk model were identified successfully. Multivariate Cox analysis indicated that these two models could accurately and independently predict overall survival (OS) for patients with COAD or READ. Furthermore, functional enrichment analysis was used to identify the metabolism pathway of MRGs in the risk models and analyzed these genes comprehensively. Then, we verified the prognosis model in independent COAD cohorts (GSE17538) and detected the correlations of the protein expression levels of GSR and ENPP2 with prognosis for COAD or READ.
Conclusion: In this study, 14 MRGs were identified as potential prognostic biomarkers and therapeutic targets for colorectal cancer.

Keywords:  ENPP2; GSR; colon adenocarcinoma; metabolism-related gene; prognosis; rectum adenocarcinoma

DOI:  https://doi.org/10.2147/OTT.S297134
Cell Metab. 2021 Mar 27. pii: S1550-4131(21)00116-9. [Epub ahead of print]

Creatine promotes cancer metastasis through activation of Smad2/3.

Liwen Zhang, Zijing Zhu, Huiwen Yan, Wen Wang, Zhenzhen Wu, Fei Zhang, Qixiang Zhang, Guizhi Shi, Junfeng Du, Huiyun Cai, Xuanxuan Zhang, David Hsu, Pu Gao, Hai-Long Piao, Gang Chen, Pengcheng Bu.

  As one of the most popular nutrient supplements, creatine has been highly used to increase muscle mass and improve exercise performance. Here, we report an adverse effect of creatine using orthotopic mouse models, showing that creatine promotes colorectal and breast cancer metastasis and shortens mouse survival. We show that glycine amidinotransferase (GATM), the rate-limiting enzyme for creatine synthesis, is upregulated in liver metastases. Dietary uptake, or GATM-mediated de novo synthesis of creatine, enhances cancer metastasis and shortens mouse survival by upregulation of Snail and Slug expression via monopolar spindle 1 (MPS1)-activated Smad2 and Smad3 phosphorylation. GATM knockdown or MPS1 inhibition suppresses cancer metastasis and benefits mouse survival by downregulating Snail and Slug. Our findings call for using caution when considering dietary creatine to improve muscle mass or treat diseases and suggest that targeting GATM or MPS1 prevents cancer metastasis, especially metastasis of transforming growth factor beta receptor mutant colorectal cancers.

Keywords:  GATM; MPS1; SLC6A8; Smad2; Smad3; breast cancer; colorectal cancer; creatine; metastasis

DOI:  https://doi.org/10.1016/j.cmet.2021.03.009