bims-mibica 2022-09-04 papers

bims-mibica

Biomed News

on Mitochondrial bioenergetics in cancer

Issue of 2022–09–04
24 papers selected by
Kelsey Fisher-Wellman, East Carolina University

In vivo isotope tracing reveals a requirement for the electron transport chain in glucose and glutamine metabolism by tumors.
Mitochondrial DNA is a major source of driver mutations in cancer.
Itaconate controls its own synthesis via feedback-inhibition of reverse TCA cycle activity at IDH2.
The human mitochondrial genome contains a second light strand promoter.
A novel splice variant of Elp3/Kat9 regulates mitochondrial tRNA modification and function.
Erythropoietin receptor regulates tumor mitochondrial biogenesis through iNOS and pAKT.
Phosphoregulation of the ATP synthase beta subunit stimulates mitochondrial activity for G2/M progression.
Cancer cell histone density links global histone acetylation, mitochondrial proteome and histone acetylase inhibitor sensitivity.
Protein import motor complex reacts to mitochondrial misfolding by reducing protein import and activating mitophagy.
The γ-Glutamylcyclotransferase Inhibitor Pro-GA Induces an Antiproliferative Effect Through the Generation of Mitochondrial Reactive Oxygen Species.
Functional characterization of two variants of mitochondrial topoisomerase TOP1MT that impact regulation of the mitochondrial genome.
Crosstalk between AML and stromal cells triggers acetate secretion through the metabolic rewiring of stromal cells.
The Warburg effect: Saturation of mitochondrial NADH shuttles triggers aerobic lactate fermentation.
Human acute leukemia utilizes branched-chain amino acid catabolism to maintain stemness through regulating PRC2 function.
FOXP3 expression diversifies the metabolic capacity and enhances the efficacy of CD8 T cells in adoptive immunotherapy of melanoma.
Maintenance of small molecule redox homeostasis in mitochondria.
Lisaftoclax (APG-2575) is a Novel BCL-2 Inhibitor with Robust Antitumor Activity in Preclinical Models of Hematologic Malignancy.
Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy.
Sublethal cytochrome c release generates drug-tolerant persister cells.
Operation of a TCA cycle subnetwork in the mammalian nucleus.
Decorin evokes reversible mitochondrial depolarization in carcinoma and vascular endothelial cells.
Pentamethinium salts suppress key metastatic processes by regulating mitochondrial function and inhibiting dihydroorotate dehydrogenase respiration.
Mitochondria in cancer: clean windmills or stressed tinkerers?
Low mitochondrial DNA copy number induces chemotherapy resistance via epithelial-mesenchymal transition by DNA methylation in esophageal squamous cancer cells.

Sci Adv. 2022 Sep 02. 8(35): eabn9550

In vivo isotope tracing reveals a requirement for the electron transport chain in glucose and glutamine metabolism by tumors.

Panayotis Pachnis, Zheng Wu, Brandon Faubert, Alpaslan Tasdogan, Wen Gu, Spencer Shelton, Ashley Solmonson, Aparna D Rao, Akash K Kaushik, Thomas J Rogers, Jessalyn M Ubellacker, Collette A LaVigne, Chendong Yang, Bookyung Ko, Vijayashree Ramesh, Jessica Sudderth, Lauren G Zacharias, Misty S Martin-Sandoval, Duyen Do, Thomas P Mathews, Zhiyu Zhao, Prashant Mishra, Sean J Morrison, Ralph J DeBerardinis.

In mice and humans with cancer, intravenous 13C-glucose infusion results in 13C labeling of tumor tricarboxylic acid (TCA) cycle intermediates, indicating that pyruvate oxidation in the TCA cycle occurs in tumors. The TCA cycle is usually coupled to the electron transport chain (ETC) because NADH generated by the cycle is reoxidized to NAD+ by the ETC. However, 13C labeling does not directly report ETC activity, and other pathways can oxidize NADH, so the ETC's role in these labeling patterns is unverified. We examined the impact of the ETC complex I inhibitor IACS-010759 on tumor 13C labeling. IACS-010759 suppresses TCA cycle labeling from glucose or lactate and increases labeling from glutamine. Cancer cells expressing yeast NADH dehydrogenase-1, which recycles NADH to NAD+ independently of complex I, display normalized labeling when complex I is inhibited, indicating that cancer cell ETC activity regulates TCA cycle metabolism and 13C labeling from multiple nutrients.

DOI: https://doi.org/10.1126/sciadv.abn9550
Trends Cancer. 2022 Aug 27. pii: S2405-8033(22)00172-8. [Epub ahead of print]

Mitochondrial DNA is a major source of driver mutations in cancer.

Minsoo Kim, Mahnoor Mahmood, Ed Reznik, Payam A Gammage.

  Mitochondrial DNA (mtDNA) mutations are among the most common genetic events in all tumors and directly impact metabolic homeostasis. Despite the central role mitochondria play in energy metabolism and cellular physiology, the role of mutations in the mitochondrial genomes of tumors has been contentious. Until recently, genomic and functional studies of mtDNA variants were impeded by a lack of adequate tumor mtDNA sequencing data and available methods for mitochondrial genome engineering. These barriers and a conceptual fog surrounding the functional impact of mtDNA mutations in tumors have begun to lift, revealing a path to understanding the role of this essential metabolic genome in cancer initiation and progression. Here we discuss the history, recent developments, and challenges that remain for mitochondrial oncogenetics as the impact of a major new class of cancer-associated mutations is unveiled.

Keywords:  cancer; genome editing; mitochondrial DNA; mutation selection

DOI:  https://doi.org/10.1016/j.trecan.2022.08.001
Biochim Biophys Acta Mol Basis Dis. 2022 Aug 26. pii: S0925-4439(22)00201-0. [Epub ahead of print] 166530

Itaconate controls its own synthesis via feedback-inhibition of reverse TCA cycle activity at IDH2.

Alexander Heinz, Yannic Nonnenmacher, Antonia Henne, Michelle-Amirah Khalil, Ketlin Bejkollari, Catherine Dostert, Shirin Hosseini, Oliver Goldmann, Wei He, Roberta Palorini, Charlène Verschueren, Martin Korte, Ferdinando Chiaradonna, Eva Medina, Dirk Brenner, Karsten Hiller.

  Macrophages undergo extensive metabolic reprogramming during classical pro-inflammatory polarization (M1-like). The accumulation of itaconate has been recognized as both a consequence and mediator of the inflammatory response. In this study we first examined the specific functions of itaconate inside fractionated mitochondria. We show that M1 macrophages produce itaconate de novo via aconitase decarboxylase 1 (ACOD1) inside mitochondria. The carbon for this reaction is not only supplied by oxidative TCA cycling, but also through the reductive carboxylation of α-ketoglutarate by isocitrate dehydrogenase (IDH). While macrophages are capable of sustaining a certain degree of itaconate production during hypoxia by augmenting the activity of IDH-dependent reductive carboxylation, we demonstrate that sufficient itaconate synthesis requires a balance of reductive and oxidative TCA cycle metabolism in mouse macrophages. In comparison, human macrophages increase itaconate accumulation under hypoxic conditions by augmenting reductive carboxylation activity. We further demonstrated that itaconate attenuates reductive carboxylation at IDH2, restricting its own production and the accumulation of the immunomodulatory metabolites citrate and 2-hydroxyglutarate. In line with this, reductive carboxylation is enhanced in ACOD1-depleted macrophages. Mechanistically, the inhibition of IDH2 by itaconate is linked to the alteration of the mitochondrial NADP+/NADPH ratio and competitive succinate dehydrogenase inhibition. Taken together, our findings extend the current model of TCA cycle reprogramming during pro-inflammatory macrophage activation and identified novel regulatory properties of itaconate.

Keywords:  2-hydroxyglutarate; Mitochondrial metabolism; Proinflammatory macrophage; Redox balance; Reductive carboxylation; TCA cycle

DOI:  https://doi.org/10.1016/j.bbadis.2022.166530
Mol Cell. 2022 Aug 23. pii: S1097-2765(22)00764-X. [Epub ahead of print]

The human mitochondrial genome contains a second light strand promoter.

Benedict G Tan, Christian D Mutti, Yonghong Shi, Xie Xie, Xuefeng Zhu, Pedro Silva-Pinheiro, Katja E Menger, Héctor Díaz-Maldonado, Wei Wei, Thomas J Nicholls, Patrick F Chinnery, Michal Minczuk, Maria Falkenberg, Claes M Gustafsson.

  The human mitochondrial genome must be replicated and expressed in a timely manner to maintain energy metabolism and supply cells with adequate levels of adenosine triphosphate. Central to this process is the idea that replication primers and gene products both arise via transcription from a single light strand promoter (LSP) such that primer formation can influence gene expression, with no consensus as to how this is regulated. Here, we report the discovery of a second light strand promoter (LSP2) in humans, with features characteristic of a bona fide mitochondrial promoter. We propose that the position of LSP2 on the mitochondrial genome allows replication and gene expression to be orchestrated from two distinct sites, which expands our long-held understanding of mitochondrial gene expression in humans.

Keywords:  DdCBE; LSP2; POLRMT; light strand promoter; mitochondria; mitochondrial DNA; mitochondrial gene expression; mitochondrial promoter; mtDNA; transcription

DOI:  https://doi.org/10.1016/j.molcel.2022.08.011
Sci Rep. 2022 Aug 31. 12(1): 14804

A novel splice variant of Elp3/Kat9 regulates mitochondrial tRNA modification and function.

Rachid Boutoual, Hyunsun Jo, Indra Heckenbach, Ritesh Tiwari, Herbert Kasler, Chad A Lerner, Samah Shah, Birgit Schilling, Vincenzo Calvanese, Matthew J Rardin, Morten Scheibye-Knudsen, Eric Verdin.

Post-translational modifications, such as lysine acetylation, regulate the activity of diverse proteins across many cellular compartments. Protein deacetylation in mitochondria is catalyzed by the enzymatic activity of the NAD+-dependent deacetylase sirtuin 3 (SIRT3), however it remains unclear whether corresponding mitochondrial acetyltransferases exist. We used a bioinformatics approach to search for mitochondrial proteins with an acetyltransferase catalytic domain, and identified a novel splice variant of ELP3 (mt-ELP3) of the elongator complex, which localizes to the mitochondrial matrix in mammalian cells. Unexpectedly, mt-ELP3 does not mediate mitochondrial protein acetylation but instead induces a post-transcriptional modification of mitochondrial-transfer RNAs (mt-tRNAs). Overexpression of mt-ELP3 leads to the protection of mt-tRNAs against the tRNA-specific RNase angiogenin, increases mitochondrial translation, and furthermore increases expression of OXPHOS complexes. This study thus identifies mt-ELP3 as a non-canonical mt-tRNA modifying enzyme.

DOI: https://doi.org/10.1038/s41598-022-18114-x
Front Oncol. 2022 ;12 976961

Erythropoietin receptor regulates tumor mitochondrial biogenesis through iNOS and pAKT.

Mostafa A Aboouf, Franco Guscetti, Nadine von Büren, Julia Armbruster, Hyrije Ademi, Maja Ruetten, Florinda Meléndez-Rodríguez, Thomas Rülicke, Alexander Seymer, Robert A Jacobs, Edith M Schneider Gasser, Julian Aragones, Drorit Neumann, Max Gassmann, Markus Thiersch.

  Erythropoietin receptor (EPOR) is widely expressed in healthy and malignant tissues. In certain malignancies, EPOR stimulates tumor growth. In healthy tissues, EPOR controls processes other than erythropoiesis, including mitochondrial metabolism. We hypothesized that EPOR also controls the mitochondrial metabolism in cancer cells. To test this hypothesis, we generated EPOR-knockdown cancer cells to grow tumor xenografts in mice and analyzed tumor cellular respiration via high-resolution respirometry. Furthermore, we analyzed cellular respiratory control, mitochondrial content, and regulators of mitochondrial biogenesis in vivo and in vitro in different cancer cell lines. Our results show that EPOR controls tumor growth and mitochondrial biogenesis in tumors by controlling the levels of both, pAKT and inducible NO synthase (iNOS). Furthermore, we observed that the expression of EPOR is associated with the expression of the mitochondrial marker VDAC1 in tissue arrays of lung cancer patients, suggesting that EPOR indeed helps to regulate mitochondrial biogenesis in tumors of cancer patients. Thus, our data imply that EPOR not only stimulates tumor growth but also regulates tumor metabolism and is a target for direct intervention against progression.

Keywords:  OXPHOS; VDAC1; erythropoietin receptor; mitochondrial biogenesis; nitric oxide (NO); respirometry; tumor metabolism

DOI:  https://doi.org/10.3389/fonc.2022.976961
Adv Biol Regul. 2022 Aug 19. pii: S2212-4926(22)00045-8. [Epub ahead of print]85 100905

Phosphoregulation of the ATP synthase beta subunit stimulates mitochondrial activity for G2/M progression.

Ana Cláudia Leite, Telma Silva Martins, Ana Campos, Vítor Costa, Clara Pereira.

  Mitochondrial ATP synthase is a multifunctional enzyme complex involved in ATP production. We previously reported that the ATP synthase catalytic beta subunit (Atp2p in yeast) is regulated by the 2A-like protein phosphatase Sit4p, which targets Atp2p at T124/T317 impacting on ATP synthase levels and mitochondrial respiration. Here we report that Atp2-T124/T317 is also potentially regulated by Cdc5p, a polo-like mitotic kinase. Since both Cdc5p and Sit4p have established roles in cell cycle regulation, we investigated whether Atp2-T124/T317 phosphorylation was cell cycle-related. We present evidence that Atp2p levels and phosphorylation vary during cell cycle progression, with an increase at G2/M phase. Atp2-T124/T317 phosphorylation stimulates mitochondrial membrane potential, respiration and ATP levels at G2/M phase, indicating that dynamic Atp2p phosphorylation contributes to mitochondrial activity at this specific cell cycle phase. Preventing Atp2p phosphorylation delays G2/M to G1 transition, suggesting that enhanced bioenergetics at G2/M may help meet the energetic demands of cell cycle progression. However, mimicking constitutive T124/T317 phosphorylation or overexpressing Atp2p leads to mitochondrial DNA instability, indicating that reversible Atp2p phosphorylation is critical for homeostasis. These results indicate that transient phosphorylation of Atp2p, a protein at the core of the ATP production machinery, impacts on mitochondrial bioenergetics and supports cell cycle progression at G2/M.

Keywords:  Atp2p phosphorylation; Bioenergetics; Cell cycle; Mitochondria; Yeast

DOI:  https://doi.org/10.1016/j.jbior.2022.100905
Commun Biol. 2022 Aug 27. 5(1): 882

Cancer cell histone density links global histone acetylation, mitochondrial proteome and histone acetylase inhibitor sensitivity.

Christopher Bruhn, Giulia Bastianello, Marco Foiani.

Chromatin metabolism is frequently altered in cancer cells and facilitates cancer development. While cancer cells produce large amounts of histones, the protein component of chromatin packaging, during replication, the potential impact of histone density on cancer biology has not been studied systematically. Here, we show that altered histone density affects global histone acetylation, histone deactylase inhibitor sensitivity and altered mitochondrial proteome composition. We present estimates of nuclear histone densities in 373 cancer cell lines, based on Cancer Cell Line Encyclopedia data, and we show that a known histone regulator, HMGB1, is linked to histone density aberrations in many cancer cell lines. We further identify an E3 ubiquitin ligase interactor, DCAF6, and a mitochondrial respiratory chain assembly factor, CHCHD4, as histone modulators. As systematic characterization of histone density aberrations in cancer cell lines, this study provides approaches and resources to investigate the impact of histone density on cancer biology.

DOI: https://doi.org/10.1038/s42003-022-03846-3
Nat Commun. 2022 Sep 02. 13(1): 5164

Protein import motor complex reacts to mitochondrial misfolding by reducing protein import and activating mitophagy.

Jonas Benjamin Michaelis, Melinda Elaine Brunstein, Süleyman Bozkurt, Ludovico Alves, Martin Wegner, Manuel Kaulich, Christian Pohl, Christian Münch.

Mitophagy is essential to maintain mitochondrial function and prevent diseases. It activates upon mitochondria depolarization, which causes PINK1 stabilization on the mitochondrial outer membrane. Strikingly, a number of conditions, including mitochondrial protein misfolding, can induce mitophagy without a loss in membrane potential. The underlying molecular details remain unclear. Here, we report that a loss of mitochondrial protein import, mediated by the pre-sequence translocase-associated motor complex PAM, is sufficient to induce mitophagy in polarized mitochondria. A genome-wide CRISPR/Cas9 screen for mitophagy inducers identifies components of the PAM complex. Protein import defects are able to induce mitophagy without a need for depolarization. Upon mitochondrial protein misfolding, PAM dissociates from the import machinery resulting in decreased protein import and mitophagy induction. Our findings extend the current mitophagy model to explain mitophagy induction upon conditions that do not affect membrane polarization, such as mitochondrial protein misfolding.

DOI: https://doi.org/10.1038/s41467-022-32564-x
Anticancer Res. 2022 Sep;42(9): 4311-4317

The γ-Glutamylcyclotransferase Inhibitor Pro-GA Induces an Antiproliferative Effect Through the Generation of Mitochondrial Reactive Oxygen Species.

Hiromi Ii, Keiko Taniguchi, Taku Yoshiya, Yukie Nohara, Susumu Kageyama, Akihiro Kawauchi, Susumu Nakata.

   BACKGROUND/AIM: γ-Glutamylcyclotransferase (GGCT) is up-regulated in a broad range of cancers, including breast cancer, and GGCT inhibition has been shown to be a promising strategy for therapy. Herein, we evaluated the efficacy and mechanism of action of pro-GA, a GGCT enzymatic inhibitor, in MCF7 breast cancer cells.
MATERIALS AND METHODS: Proliferation was evaluated by WST-8 and trypan blue dye exclusion assays. Western blot analysis was conducted to examine the expression of cyclin-dependent kinase inhibitors (CDKI), including p21, p27, and p16. Induction of senescence was assessed by senescence-associated β-galactosidase staining. Generation of mitochondrial superoxide reactive oxygen species (ROS) was assessed using flow cytometry. The effect of N-acetylcysteine (NAC) on pro-GA dependent inhibition of proliferation, ROS generation, and senescence was also studied. The efficacy of systemic administration of pro-GA was evaluated in a MCF7 xenograft mouse model.
RESULTS: Treatment with pro-GA inhibited proliferation of MCF7 cells, increased CDKI expression and mitochondrial ROS, and induced cellular senescence. We found that cotreatment with NAC restored proliferation in pro-GA treated cells. NAC similarly suppressed CDKI expression, mitochondrial ROS generation, and senescence induced by pro-GA. Furthermore, the systemic administration of pro-GA in an MCF7 xenograft model had significant antitumor effects without toxicity.
CONCLUSION: Pro-GA may be a promising therapeutic agent for the treatment of breast cancer.

Keywords:  N-acetylcysteine; breast cancer; cyclin-dependent kinase inhibitors; pro-GA; reactive oxygen species; γ-glutamylcyclotransferase

DOI:  https://doi.org/10.21873/anticanres.15931
J Biol Chem. 2022 Aug 24. pii: S0021-9258(22)00863-8. [Epub ahead of print] 102420

Functional characterization of two variants of mitochondrial topoisomerase TOP1MT that impact regulation of the mitochondrial genome.

Iman Al Khatib, Jingti Deng, Andrew Symes, Marina Kerr, Hongliang Zhang, Sharyin Huang, Yves Pommier, Aneal Khan, Timothy E Shutt.

  TOP1MT encodes a mitochondrial topoisomerase that is important for mtDNA regulation, and is involved in mitochondrial replication, transcription, and translation. Two variants predicted to affect TOP1MT function (V1 - R198C and V2 - V338L) were identified by exome sequencing of a newborn with hypertrophic cardiomyopathy. As no pathogenic TOP1MT variants had been confirmed previously, we characterized these variants for their ability to rescue several TOP1MT functions in knockout cells. Consistent with these TOP1MT variants contributing to the patient phenotype, our comprehensive characterization suggests that both variants had impaired activity. Critically, we determined neither variant was able to restore steady state levels of mitochondrial-encoded proteins, nor to rescue oxidative phosphorylation when re-expressed in TOP1MT knockout cells. However, we found the two variants behaved differently in some respects; while the V1 variant was more efficient in restoring transcript levels, the V2 variant showed better rescue of mtDNA copy number and replication. These findings suggest that the different TOP1MT variants affect distinct TOP1MT functions. Altogether, these findings begin to provide insight into the many roles that TOP1MT plays in the maintenance and expression of the mitochondrial genome, and how impairments in this important protein may lead to human pathology.

Keywords:  TOP1MT; mitochondria; mtDNA; replication; transcription; translation

DOI:  https://doi.org/10.1016/j.jbc.2022.102420
Elife. 2022 Sep 02. pii: e75908. [Epub ahead of print]11

Crosstalk between AML and stromal cells triggers acetate secretion through the metabolic rewiring of stromal cells.

Nuria Vilaplana-Lopera, Vincent Cuminetti, Ruba Almaghrabi, Grigorios Papatzikas, Ashok Kumar Rout, Mark Jeeves, Elena González, Yara Alyahyawi, Alan Cunnigham, Ayşegüll Erdem, Frank Schnütgen, Manoj Raghavan, Sandeep Potluri, Jean-Baptiste Cazier, Jan Jacob Schuringa, Michelle A C Reed, Lorena Arranz, Ulrich Günther, Paloma Garcia.

  Acute myeloid leukaemia (AML) cells interact and modulate components of their surrounding microenvironment into their own benefit. Stromal cells have been shown to support AML survival and progression through various mechanisms. Nonetheless, whether AML cells could establish beneficial metabolic interactions with stromal cells is underexplored. By using a combination of human AML cell lines and AML patient samples together with mouse stromal cells and a MLL-AF9 mouse model, here we identify a novel metabolic crosstalk between AML and stromal cells where AML cells prompt stromal cells to secrete acetate for their own consumption to feed the tricarboxylic acid cycle (TCA) and lipid biosynthesis. By performing transcriptome analysis and tracer-based metabolic NMR analysis, we observe that stromal cells present a higher rate of glycolysis when co-cultured with AML cells. We also find that acetate in stromal cells is derived from pyruvate via chemical conversion under the influence of reactive oxygen species (ROS) following ROS transfer from AML to stromal cells via gap junctions. Overall, we present a unique metabolic communication between AML and stromal cells and propose two different molecular targets, ACSS2 and gap junctions, that could potentially be exploited for adjuvant therapy.

Keywords:  biochemistry; cancer biology; chemical biology; human

DOI:  https://doi.org/10.7554/eLife.75908
Mol Cell. 2022 Sep 01. pii: S1097-2765(22)00757-2. [Epub ahead of print]82(17): 3119-3121

The Warburg effect: Saturation of mitochondrial NADH shuttles triggers aerobic lactate fermentation.

Hyllana C D Medeiros, Sophia Y Lunt.

In this issue of Molecular Cell, Wang et al. investigate the Warburg effect in proliferating cells and demonstrate that lactate fermentation is a secondary mechanism activated after mitochondrial shuttles exceed their capacity to oxidize cytosolic NADH.

DOI: https://doi.org/10.1016/j.molcel.2022.08.004
Blood Adv. 2022 Aug 31. pii: bloodadvances.2022008242. [Epub ahead of print]

Human acute leukemia utilizes branched-chain amino acid catabolism to maintain stemness through regulating PRC2 function.

Yoshikane Kikushige, Toshihiro Miyamoto, Yu Kochi, Yuichiro Semba, Maki Ohishi, Hidetoshi Irifune, Kiwamu Hatakeyama, Yuya Kunisaki, Takeshi Sugio, Teppei Sakoda, Kohta Miyawaki, Koji Kato, Tomoyoshi Soga, Koichi Akashi.

Cancer-specific metabolic activities play a crucial role in the pathogenesis of human malignancies. To investigate human acute leukemia-specific metabolic properties, we comprehensively measured the cellular metabolites within the CD34+ fraction of normal hematopoietic stem progenitor cells (HSPCs), and primary human acute myelogenous leukemia (AML) and lymphoblastic leukemia (ALL) cells. Here we show that human leukemia addicts to the branched-chain amino acid (BCAA) metabolism to maintain their stemness, irrespective of myeloid or lymphoid types. Human primary acute leukemias had BCAA transporters for BCAA uptake, cellular BCAA, α-ketoglutarate (α-KG) and cytoplasmic BCAA transaminase-1 (BCAT1) at significantly higher levels than control HSPCs. Isotope-tracing experiments showed that in primary leukemia cells, BCAT1 actively catabolizes BCAA using α-KG into branched-chain α-ketoacids (BCKAs), whose metabolic processes provide leukemia cells with critical substrates for the TCA cycle and the non-essential amino acids synthesis, both of which reproduce α-KG to maintain its cellular level. In xenogeneic transplantation experiments, deprivation of BCAA from daily diet strongly inhibited expansion, engraftment and self-renewal of human acute leukemia cells. Inhibition of BCAA catabolism in primary AML or ALL cells specifically inactivates polycomb repressive complex 2 (PRC2) function, an epigenetic regulator for stem cell signatures, through inhibiting transcription of PRC components, such as zeste homolog 2 (EZH2) and embryonic ectoderm development (EED). Accordingly, BCAA catabolism plays an important role in maintenance of stemness in primary human AML and ALL, and molecules related to the BCAA metabolism pathway should be critical targets for acute leukemia treatment.

DOI: https://doi.org/10.1182/bloodadvances.2022008242
Mol Ther. 2022 Aug 30. pii: S1525-0016(22)00505-6. [Epub ahead of print]

FOXP3 expression diversifies the metabolic capacity and enhances the efficacy of CD8 T cells in adoptive immunotherapy of melanoma.

Enrique Conde, Noelia Casares, Uxua Mancheño, Edurne Elizalde, Enric Vercher, Roberto Capozzi, Eva Santamaria, Juan R Rodriguez-Madoz, Felipe Prosper, Juan J Lasarte, Teresa Lozano, Sandra Hervas-Stubbs.

  Regulatory T cells overwhelm conventional T cells in the tumor microenvironment (TME) thanks to a FOXP3-driven metabolic program that allows them to engage different metabolic pathways. Using a melanoma model of adoptive T-cell therapy (ACT), we show that FOXP3 overexpression in mature CD8 T cells improved their antitumor efficacy, favoring their tumor recruitment, proliferation and cytotoxicity. FOXP3-overexpressing (Foxp3UP) CD8 T cells exhibited features of tissue-resident memory-like and effector T cells, but not suppressor activity. Transcriptomic analysis of tumor-infiltrating Foxp3UP CD8 T cells showed positive enrichment in a wide variety of metabolic pathways, such as glycolysis, fatty acid (FA) metabolism and oxidative phosphorylation (OXPHOS). Intratumoral Foxp3UP CD8 T cells exhibited an enhanced capacity for glucose and FA uptake, as well as accumulation of intracellular lipids. Interestingly, Foxp3UP CD8 T cells compensated for the loss of mitochondrial respiration-driven ATP production by activating aerobic glycolysis. Moreover, in limiting nutrient conditions these cells engaged FA oxidation to drive OXPHOS for their energy demands. Importantly, their ability to couple glycolysis and OXPHOS allowed them to sustain proliferation under glucose restriction. Our findings demonstrate a hitherto unknown role for FOXP3 in the adaptation of CD8 T cells to TME that may enhance their efficacy in ACT.

Keywords:  CD8 T cell response; FOXP3; T cell metabolism; T cell-based cancer immunotherapy

DOI:  https://doi.org/10.1016/j.ymthe.2022.08.017
FEBS Lett. 2022 Aug 27.

Maintenance of small molecule redox homeostasis in mitochondria.

Lianne Jhc Jacobs, Jan Riemer.

  Compartmentalization of eukaryotic cells enables fundamental otherwise often incompatible cellular processes. Establishment and maintenance of distinct compartments in the cell relies on proteins, lipids and metabolites but also on small redox molecules. In particular, small redox molecules such as glutathione, NAD(P)H, and hydrogen peroxide (H2 O2 ) cooperate with protein partners in dedicated machineries to establish specific subcellular redox compartments with conditions that enable oxidative protein folding and redox signalling. Dysregulated redox homeostasis has been directly linked with a number of diseases including cancer, neurological disorders, cardiovascular diseases, obesity, metabolic diseases, and aging. In this review, we will summarize mechanisms regulating establishment and maintenance of redox homeostasis in the mitochondrial subcompartments of mammalian cells.

Keywords:  compartmentalization; glutathione; hydrogen peroxide; mitochondria

DOI:  https://doi.org/10.1002/1873-3468.14485
Clin Cancer Res. 2022 Sep 01. pii: CCR-21-4037. [Epub ahead of print]

Lisaftoclax (APG-2575) is a Novel BCL-2 Inhibitor with Robust Antitumor Activity in Preclinical Models of Hematologic Malignancy.

Jing Deng, Aneel Paulus, Douglas D Fang, Alak Manna, Guangfeng Wang, Hengbang Wang, Saijie Zhu, Jianyong Chen, Ping Min, Yan Yin, Navnita Dutta, Nabanita Halder, Gina Ciccio, John A Copland, James Miller, Bing Han, Longchuan Bai, Liu Liu, Mi Wang, Donna McEachern, Sally Przybranowski, Chao-Yie Yang, Jeanne A Stuckey, Depei Wu, Caixia Li, Jeremy Ryan, Anthony Letai, Sikander Ailawadhi, Dajun Yang, Shaomeng Wang, Asher Chanan-Khan, Yifan Zhai.

PURPOSE: Development of BCL-2-specific inhibitors poses unique challenges in drug design because of BCL-2 homology domain 3 (BH3) shared homology between BCL-2 family members and the shallow surface of their protein-protein interactions. We report herein discovery and extensive preclinical investigation of lisaftoclax (APG-2575).
EXPERIMENTAL DESIGN: Computational modeling was used to design "lead" compounds. Biochemical binding, mitochondrial BH3 profiling, and cell-based viability or apoptosis assays were used to determine the selectivity and potency of BCL-2 inhibitor lisaftoclax. The antitumor effects of lisaftoclax were also evaluated in several xenograft models.
RESULTS: Lisaftoclax selectively binds BCL-2 (Ki < 0.1 nM), disrupts BCL-2:BIM complexes, and compromises mitochondrial outer membrane potential, culminating in BAX/BAK-dependent, caspase-mediated apoptosis. Lisaftoclax exerted strong antitumor activity in hematologic cancer cell lines and tumor cells from patients with chronic lymphocytic leukemia, multiple myeloma, or Waldenström macroglobulinemia. After lisaftoclax treatment, prodeath proteins BCL-2‒like protein 11 (BIM) and Noxa increased, and BIM translocated from cytosol to mitochondria. Consistent with these apoptotic activities, lisaftoclax entered malignant cells rapidly, reached plateau in 2 hours, and significantly downregulated mitochondrial respiratory function and ATP production. Furthermore, lisaftoclax inhibited tumor growth in xenograft models, correlating with caspase activation, poly (ADP-ribose) polymerase 1 (PARP-1) cleavage, and pharmacokinetics of the compound. Lisaftoclax combined with rituximab or bendamustine/rituximab enhanced antitumor activity in vivo.
CONCLUSIONS: These findings demonstrate that lisaftoclax is a novel, orally bioavailable BH3 mimetic BCL-2-selective inhibitor with considerable potential for the treatment of certain hematologic malignancies.

DOI: https://doi.org/10.1158/1078-0432.CCR-21-4037
Hum Mutat. 2022 Aug 28.

Biallelic pathogenic variants in COX11 are associated with an infantile-onset mitochondrial encephalopathy.

Rocio Rius, Neal K Bennett, Kaustuv Bhattacharya, Lisa G Riley, Zafer Yüksel, Luke E Formosa, Alison G Compton, Russell C Dale, Mark J Cowley, Velimir Gayevskiy, Saeed Al Tala, Abdulrahman A Almehery, Michael T Ryan, David R Thorburn, Ken Nakamura, John Christodoulou.

  Primary mitochondrial diseases are a group of genetically and clinically heterogeneous disorders resulting from oxidative phosphorylation (OXPHOS) defects. COX11 encodes a copper chaperone that participates in the assembly of complex IV (CIV) and has not been previously linked to human disease. In a previous study, we identified that COX11 knockdown decreased cellular ATP derived from respiration, and that ATP levels could be restored with CoQ10 supplementation. This finding is surprising since COX11 has no known role in CoQ10 biosynthesis. Here, we report a novel gene-disease association by identifying biallelic pathogenic variants in COX11 associated with infantile-onset mitochondrial encephalopathies in two unrelated families using trio genome and exome sequencing. Functional studies showed that mutant COX11 fibroblasts had decreased ATP levels which could be rescued by CoQ10 . These results not only suggest that COX11 variants cause defects in energy production but reveal a potential metabolic therapeutic strategy for patients with COX11 variants. This article is protected by copyright. All rights reserved.

Keywords:  COX11; Coenzyme Q; OXPHOS; mitochondrial disorders

DOI:  https://doi.org/10.1002/humu.24453
Cell. 2022 Sep 01. pii: S0092-8674(22)00978-3. [Epub ahead of print]185(18): 3356-3374.e22

Sublethal cytochrome c release generates drug-tolerant persister cells.

Halime Kalkavan, Mark J Chen, Jeremy C Crawford, Giovanni Quarato, Patrick Fitzgerald, Stephen W G Tait, Colin R Goding, Douglas R Green.

  Drug-tolerant persister cells (persisters) evade apoptosis upon targeted and conventional cancer therapies and represent a major non-genetic barrier to effective cancer treatment. Here, we show that cells that survive treatment with pro-apoptotic BH3 mimetics display a persister phenotype that includes colonization and metastasis in vivo and increased sensitivity toward ferroptosis by GPX4 inhibition. We found that sublethal mitochondrial outer membrane permeabilization (MOMP) and holocytochrome c release are key requirements for the generation of the persister phenotype. The generation of persisters is independent of apoptosome formation and caspase activation, but instead, cytosolic cytochrome c induces the activation of heme-regulated inhibitor (HRI) kinase and engagement of the integrated stress response (ISR) with the consequent synthesis of ATF4, all of which are required for the persister phenotype. Our results reveal that sublethal cytochrome c release couples sublethal MOMP to caspase-independent initiation of an ATF4-dependent, drug-tolerant persister phenotype.

Keywords:  ATF4; Bcl-2 family; GPX4; HRI; ferroptosis; persister integrated stress response

DOI:  https://doi.org/10.1016/j.cell.2022.07.025
Sci Adv. 2022 Sep 02. 8(35): eabq5206

Operation of a TCA cycle subnetwork in the mammalian nucleus.

Eleni Kafkia, Amparo Andres-Pons, Kerstin Ganter, Markus Seiler, Tom S Smith, Anna Andrejeva, Paula Jouhten, Filipa Pereira, Catarina Franco, Anna Kuroshchenkova, Sergio Leone, Ritwick Sawarkar, Rebecca Boston, James Thaventhiran, Judith B Zaugg, Kathryn S Lilley, Christophe Lancrin, Martin Beck, Kiran Raosaheb Patil.

Nucleic acid and histone modifications critically depend on the tricarboxylic acid (TCA) cycle for substrates and cofactors. Although a few TCA cycle enzymes have been reported in the nucleus, the corresponding pathways are considered to operate in mitochondria. Here, we show that a part of the TCA cycle is operational also in the nucleus. Using 13C-tracer analysis, we identified activity of glutamine-to-fumarate, citrate-to-succinate, and glutamine-to-aspartate routes in the nuclei of HeLa cells. Proximity labeling mass spectrometry revealed a spatial vicinity of the involved enzymes with core nuclear proteins. We further show nuclear localization of aconitase 2 and 2-oxoglutarate dehydrogenase in mouse embryonic stem cells. Nuclear localization of the latter enzyme, which produces succinyl-CoA, changed from pluripotency to a differentiated state with accompanying changes in the nuclear protein succinylation. Together, our results demonstrate operation of an extended metabolic pathway in the nucleus, warranting a revision of the canonical view on metabolic compartmentalization.

DOI: https://doi.org/10.1126/sciadv.abq5206
Am J Physiol Cell Physiol. 2022 Aug 29.

Decorin evokes reversible mitochondrial depolarization in carcinoma and vascular endothelial cells.

Thomas Neill, Christopher Xie, Renato V Iozzo.

  Decorin, a small leucine-rich proteoglycan with multiple biological functions, is known to evoke autophagy and mitophagy in both endothelial and cancer cells. Here, we investigated the effects of soluble decorin on mitochondrial homeostasis using live cell imaging and ex vivo angiogenic assays. We discovered that decorin triggers mitochondrial depolarization in triple-negative breast carcinoma, HeLa and endothelial cells. This bioactivity was mediated by the protein core in a time- and dose-dependent manner and was specific for decorin insofar as biglycan, the closest homolog, failed to trigger depolarization. Mechanistically, we found that the bioactivity of decorin to promote depolarization required the MET receptor and its tyrosine kinase. Moreover, two mitochondrial interacting proteins, mitostatin and mitofusin 2, were essential for downstream decorin effects. Finally, we found that decorin relied on the canonical mitochondrial permeability transition pore to trigger tumor cell mitochondrial depolarization. Collectively, our study implicates decorin as a soluble outside-in regulator of mitochondrial dynamics.

Keywords:  Met receptor; Proteoglycan; biglycan; breast carcinoma cells; endothelial cells

DOI:  https://doi.org/10.1152/ajpcell.00325.2022
Biomed Pharmacother. 2022 Aug 30. pii: S0753-3322(22)00971-4. [Epub ahead of print]154 113582

Pentamethinium salts suppress key metastatic processes by regulating mitochondrial function and inhibiting dihydroorotate dehydrogenase respiration.

Jindriska Leischner Fialova, Katerina Hönigova, Martina Raudenska, Lucie Miksatkova, Renata Zobalova, Jiri Navratil, Jana Šmigová, Taraka Ramji Moturu, Tomas Vicar, Jan Balvan, Katerina Vesela, Nikita Abramenko, Zdenek Kejik, Robert Kaplanek, Jaromir Gumulec, Daniel Rosel, Pavel Martasek, Jan Brábek, Milan Jakubek, Jiri Neuzil, Michal Masarik.

  Mitochondria generate energy and building blocks required for cellular growth and function. The notion that mitochondria are not involved in the cancer growth has been challenged in recent years together with the emerging idea of mitochondria as a promising therapeutic target for oncologic diseases. Pentamethinium salts, cyan dyes with positively charged nitrogen on the benzothiazole or indole part of the molecule, were originally designed as mitochondrial probes. In this study, we show that pentamethinium salts have a strong effect on mitochondria, suppressing cancer cell proliferation and migration. This is likely linked to the strong inhibitory effect of the salts on dihydroorotate dehydrogenase (DHODH)-dependent respiration that has a key role in the de novo pyrimidine synthesis pathway. We also show that pentamethinium salts cause oxidative stress, redistribution of mitochondria, and a decrease in mitochondria mass. In conclusion, pentamethinium salts present novel anti-cancer agents worthy of further studies.

Keywords:  Dihydroorotate dehydrogenase; Metastasis; Migration; Mitochondria; Pentamethinium salts

DOI:  https://doi.org/10.1016/j.biopha.2022.113582
Trends Cell Biol. 2022 Aug 18. pii: S0962-8924(22)00191-X. [Epub ahead of print]

Mitochondria in cancer: clean windmills or stressed tinkerers?

Dario C Altieri.

  There is now a consensus that mitochondria are important tumor drivers, sophisticated biological machines that can engender a panoply of key disease traits. How this happens, however, is still mostly elusive. The opinion presented here is that what cancer exploits are not the normal mitochondria of oxygenated and nutrient-replete tissues, but the unfit, damaged, and dysfunctional organelles generated by the hostile environment of tumor growth. These 'ghost' mitochondria survive quality control and thwart cell death to relay multiple comprehensive 'danger signals' of metabolic starvation, cellular stress, and reprogrammed gene expression. The result is a new, treacherous cellular phenotype, proliferatively quiescent but highly motile, that enables tumor cell escape from a threatening environment and colonization of distant, more favorable sites (metastasis).

Keywords:  Mic60; metabolism; metastasis; mitochondria; tumor plasticity

DOI:  https://doi.org/10.1016/j.tcb.2022.08.001
J Transl Med. 2022 Aug 29. 20(1): 383

Low mitochondrial DNA copy number induces chemotherapy resistance via epithelial-mesenchymal transition by DNA methylation in esophageal squamous cancer cells.

Yuto Kubo, Koji Tanaka, Yasunori Masuike, Tsuyoshi Takahashi, Kotaro Yamashita, Tomoki Makino, Takuro Saito, Kazuyoshi Yamamoto, Tomoyuki Tsujimoto, Takashi Harino, Yukinori Kurokawa, Makoto Yamasaki, Kiyokazu Nakajima, Hidetoshi Eguchi, Yuichiro Doki.

   BACKGROUND: Esophageal squamous cell carcinoma (ESCC) is one of the most severe cancers and is characterized by chemotherapy resistance and poor prognosis associated with epithelial-mesenchymal transition (EMT). In a previous study, a low mitochondrial DNA (mtDNA) copy number was associated with poorer prognosis and induced EMT in ESCC. However, the detailed mechanism related to mtDNA copy number and EMT is unclear. The aim of this study was to clarify the mechanism by which a change in mtDNA copy number contributes to EMT and to examine treatment of chemotherapy resistance in ESCC.
METHODS: The association between low mtDNA copy number and chemotherapy resistance was investigated using specimens from 88 patients who underwent surgery after neoadjuvant chemotherapy. Then, the mtDNA content of human ESCC cell lines, TE8 and TE11, was depleted by knockdown of mitochondrial transcription factor A expression. The present study focused on modulation of mitochondrial membrane potential (MMP) and DNA methylation as the mechanisms by which mtDNA copy number affects EMT. mRNA and protein expression, chemotherapy sensitivity, proliferation, MMP and DNA methylation were evaluated, and in vitro and in vivo assays were conducted to clarify these mechanisms.
RESULTS: ESCC patients with decreased mtDNA copy number who underwent R0 resection after neoadjuvant chemotherapy had significantly worse pathological response and recurrence-free survival. Additionally, low mtDNA copy number was associated with resistance to chemotherapy in vitro and in vivo. mtDNA controlled MMP, and MMP depolarization induced EMT. Depletion of mtDNA and low MMP induced DNA methylation via a DNA methylation transcription factor (DNMT), and a DNMT inhibitor suppressed EMT and improved chemotherapy sensitivity in mtDNA-depleted ESCC cells, as shown by in vitro and in vivo assays.
CONCLUSION: This study showed that decreased mtDNA copy number induced EMT via modulation of MMP and DNA methylation in ESCC. Therapeutic strategies increasing mtDNA copy number and DNMT inhibitors may be effective in preventing EMT and chemosensitivity resistance.

Keywords:  Chemotherapy; DNA methylation; Epithelial-mesenchymal transition; Esophageal cancer; Mitochondrial DNA; Mitochondrial membrane potential

DOI:  https://doi.org/10.1186/s12967-022-03594-2