bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2022‒03‒27
27 papers selected by
Kelsey Fisher-Wellman
East Carolina University

  1. Sci Rep. 2022 Mar 24. 12(1): 5143
      Glycolytic and mitochondrial oxidative metabolism, which are two major energy sources in tumors, are potential targets in cancer treatment. Metabolic reprogramming from glycolysis to mitochondrial oxidative metabolism and vice versa is an adaptive strategy with which tumor cells obtain energy to survive and thrive under the compromised conditions of glycolysis and mitochondrial respiration. Developing highly potent, nontoxic, and tumor-selective oxidative phosphorylation (OXPHOS) inhibitors may help advance therapeutic targeting of mitochondrial drugs in cancer. The FDA-approved antimalarial drug atovaquone (ATO), a mitochondrial complex III inhibitor, was repurposed in cancer treatment. Here, we developed a new class of PEGylated mitochondria-targeted ATO (Mito-(PEG)n-ATO). Depending on the PEGylation chain length (n), Mito-PEG-ATO analogs inhibit both mitochondrial complex I- and complex III-induced oxygen consumption in human pancreatic (MiaPaCa-2) and brain (U87MG) cancer cells. Mito-PEG5-ATO is one of the most potent antiproliferative mitochondria-targeted compounds (IC50 = 38 nM) in MiaPaCa-2 cells, and is more effective than other inhibitors of OXPHOS in MiaPaCa-2 and U87MG cells. Furthermore, we show that the combined use of the most potent OXPHOS-targeted inhibitors (Mito-PEG5-ATO) and inhibitors of monocarboxylate transporters (MCT-1 and MCT-4), Krebs cycle redox metabolism, or glutaminolysis will synergistically abrogate tumor cell proliferation. Potential clinical benefits of these combinatorial therapies are discussed.
  2. Cell Death Differ. 2022 Mar 24.
      Cancer cells are known for their ability to adapt variable metabolic programs depending on the availability of specific nutrients. Our previous studies have shown that uptake of fatty acids alters cellular metabolic pathways in colon cancer cells to favor fatty acid oxidation. Here, we show that fatty acids activate Drp1 to promote metabolic plasticity in cancer cells. Uptake of fatty acids (FAs) induces mitochondrial fragmentation by promoting ERK-dependent phosphorylation of Drp1 at the S616 site. This increased phosphorylation of Drp1 enhances its dimerization and interaction with Mitochondrial Fission Factor (MFF) at the mitochondria. Consequently, knockdown of Drp1 or MFF attenuates fatty acid-induced mitochondrial fission. In addition, uptake of fatty acids triggers mitophagy via a Drp1- and p62-dependent mechanism to protect mitochondrial integrity. Moreover, results from metabolic profiling analysis reveal that silencing Drp1 disrupts cellular metabolism and blocks fatty acid-induced metabolic reprograming by inhibiting fatty acid utilization. Functionally, knockdown of Drp1 decreases Wnt/β-catenin signaling by preventing fatty acid oxidation-dependent acetylation of β-catenin. As a result, Drp1 depletion inhibits the formation of tumor organoids in vitro and xenograft tumor growth in vivo. Taken together, our study identifies Drp1 as a key mediator that connects mitochondrial dynamics with fatty acid metabolism and cancer cell signaling.
  3. EMBO J. 2022 Mar 23. e109049
      Cellular metabolism must adapt to changing demands to enable homeostasis. During immune responses or cancer metastasis, cells leading migration into challenging environments require an energy boost, but what controls this capacity is unclear. Here, we study a previously uncharacterized nuclear protein, Atossa (encoded by CG9005), which supports macrophage invasion into the germband of Drosophila by controlling cellular metabolism. First, nuclear Atossa increases mRNA levels of Porthos, a DEAD-box protein, and of two metabolic enzymes, lysine-α-ketoglutarate reductase (LKR/SDH) and NADPH glyoxylate reductase (GR/HPR), thus enhancing mitochondrial bioenergetics. Then Porthos supports ribosome assembly and thereby raises the translational efficiency of a subset of mRNAs, including those affecting mitochondrial functions, the electron transport chain, and metabolism. Mitochondrial respiration measurements, metabolomics, and live imaging indicate that Atossa and Porthos power up OxPhos and energy production to promote the forging of a path into tissues by leading macrophages. Since many crucial physiological responses require increases in mitochondrial energy output, this previously undescribed genetic program may modulate a wide range of cellular behaviors.
    Keywords:  immune cell infiltration; mitochondrial bioenergetics; oxidative phosphorylation; protein translation; transcription factor
  4. Function (Oxf). 2021 ;2(6): zqab050
      Mitochondrial reactive oxygen species (ROS) play important roles in cellular signaling; however, certain pathological conditions such as ischemia/reperfusion (I/R) injury disrupt ROS homeostasis and contribute to cell death. A major impediment to developing therapeutic measures against oxidative stress-induced cellular damage is the lack of a quantitative framework to identify the specific sources and regulatory mechanisms of mitochondrial ROS production. We developed a thermodynamically consistent, mass-and-charge balanced, kinetic model of mitochondrial ROS homeostasis focused on redox sites of electron transport chain complexes I, II, and III. The model was calibrated and corroborated using comprehensive data sets relevant to ROS homeostasis. The model predicts that complex I ROS production dominates other sources under conditions favoring a high membrane potential with elevated nicotinamide adenine dinucleotide (NADH) and ubiquinol (QH2) levels. In general, complex I contributes to significant levels of ROS production under pathological conditions, while complexes II and III are responsible for basal levels of ROS production, especially when QH2 levels are elevated. The model also reveals that hydrogen peroxide production by complex I underlies the non-linear relationship between ROS emission and O2 at low O2 concentrations. Lastly, the model highlights the need to quantify scavenging system activity under different conditions to establish a complete picture of mitochondrial ROS homeostasis. In summary, we describe the individual contributions of the electron transport system complex redox sites to total ROS emission in mitochondria respiring under various combinations of NADH- and Q-linked respiratory fuels under varying workloads.
    Keywords:  Electron transport system (ETS); computational biology; enzyme kinetics; forward electron transport; ischemia/reperfusion injury; mitochondria; oxidative stress; reactive oxygen species; reverse electron transport
  5. Biochim Biophys Acta Bioenerg. 2022 Mar 21. pii: S0005-2728(22)00013-5. [Epub ahead of print] 148544
      Proton-translocating FOF1 ATP synthase (F-ATPase) couples ATP synthesis or hydrolysis to transmembrane proton transport in bacteria, chloroplasts, and mitochondria. The primary function of the mitochondrial FOF1 is ATP synthesis driven by protonmotive force (pmf) generated by the respiratory chain. However, when pmf is low or absent (e.g. during anoxia), FOF1 consumes ATP and functions as a proton-pumping ATPase. Several regulatory mechanisms suppress the ATPase activity of FOF1 at low pmf. In yeast mitochondria they include special inhibitory proteins Inh1p and Stf1p, and non-competitive inhibition of ATP hydrolysis by MgADP (ADP-inhibition). Presumably, these mechanisms help the cell to preserve the ATP pool upon membrane de-energization. However, no direct evidence was presented to support this hypothesis so far. Here we report that a point mutation Q263L in subunit beta of Saccharomyces cerevisiae ATP synthase significantly attenuated ADP-inhibition of the enzyme without major effect on the rate of ATP production by mitochondria. The mutation also decreased the sensitivity of the enzyme ATPase activity to azide. Similar effects of the corresponding mutations were observed in earlier studies in bacterial enzymes. This observation indicates that the molecular mechanism of ADP-inhibition is probably the same in mitochondrial and in bacterial FOF1. The mutant yeast strain had lower growth rate and had a longer lag period preceding exponential growth phase when starved cells were transferred to fresh growth medium. However, upon the loss of mitochondrial DNA (ρ0) the Q263L mutation effect was reversed: the Q263L ρ0 mutant grew faster than the wild type ρ0 yeast. The results suggest that ADP-inhibition might play a role in prevention of wasteful ATP hydrolysis in the mitochondrial matrix.
  6. Biomolecules. 2022 Feb 28. pii: 379. [Epub ahead of print]12(3):
      Breast cancer (BC) is the most prevalent cancer and the one with the highest mortality among women worldwide. Although the molecular classification of BC has been a helpful tool for diagnosing and predicting the treatment of BC, developments are still being made to improve the diagnosis and find new therapeutic targets. Mitochondrial dysfunction is a crucial feature of cancer, which can be associated with cancer aggressiveness. Although the importance of mitochondrial dynamics in cancer is well recognized, its involvement in the mitochondrial function and bioenergetics context in BC molecular subtypes has been scantly explored. In this study, we combined mitochondrial function and bioenergetics experiments in MCF7 and MDA-MB-231 cell lines with statistical and bioinformatics analyses of the mitochondrial proteome of luminal A and basal-like tumors. We demonstrate that basal-like tumors exhibit a vicious cycle between mitochondrial fusion and fission; impaired but not completely inactive mitochondrial function; and the Warburg effect, associated with decreased oxidative phosphorylation (OXPHOS) complexes I and III. Together with the results obtained in the cell lines and the mitochondrial proteome analysis, two mitochondrial signatures were proposed: one signature reflecting alterations in mitochondrial functions and a second signature exclusively of OXPHOS, which allow us to distinguish between luminal A and basal-like tumors.
    Keywords:  MCF7 cell line; MDA-MB-231 cell line; basal-like breast cancer; luminal A breast cancer; mitochondria dynamics; mitochondrial biogenesis; mitochondrial proteome; reactive oxygen species (ROS)
  7. Nat Commun. 2022 Mar 21. 13(1): 1503
      Although reprogramming of cellular metabolism is a hallmark of cancer, little is known about how metabolic reprogramming contributes to early stages of transformation. Here, we show that the histone deacetylase SIRT6 regulates tumor initiation during intestinal cancer by controlling glucose metabolism. Loss of SIRT6 results in an increase in the number of intestinal stem cells (ISCs), which translates into enhanced tumor initiating potential in APCmin mice. By tracking down the connection between glucose metabolism and tumor initiation, we find a metabolic compartmentalization within the intestinal epithelium and adenomas, where a rare population of cells exhibit features of Warburg-like metabolism characterized by high pyruvate dehydrogenase kinase (PDK) activity. Our results show that these cells are quiescent cells expressing +4 ISCs and enteroendocrine markers. Active glycolysis in these cells suppresses ROS accumulation and enhances their stem cell and tumorigenic potential. Our studies reveal that aerobic glycolysis represents a heterogeneous feature of cancer, and indicate that this metabolic adaptation can occur in non-dividing cells, suggesting a role for the Warburg effect beyond biomass production in tumors.
  8. Biomolecules. 2022 Feb 24. pii: 361. [Epub ahead of print]12(3):
      The present article will not attempt to deal with sulfide per se as a signaling molecule but will aim to examine the consequences of sulfide oxidation by mitochondrial sulfide quinone reductase in mammalian cells. This oxidation appears first as a priority to avoid self-poisoning by endogenous sulfide and second to occur with the lowest ATP/O2 ratio when compared to other mitochondrial substrates. This is explained by the injection of electrons in the respiratory chain after complex I (as for succinate) and by a sulfur oxidation step implying a dioxygenase that consumes oxygen but does not contribute to mitochondrial bioenergetics. Both contribute to increase cellular oxygen consumption if sulfide is provided below its toxic level (low µM). Accordingly, if oxygen supply or respiratory chain activity becomes a limiting factor, small variations in sulfide release impact the cellular ATP/ADP ratio, a major metabolic sensor.
    Keywords:  ATP/ADP ratio; bioenergetics; dioxygenase; mitochondria; oxygen; oxygen-sensing; redox state; succinate
  9. Cancers (Basel). 2022 Mar 16. pii: 1516. [Epub ahead of print]14(6):
      To successfully generate distant metastases, metastatic progenitor cells must simultaneously possess mesenchymal characteristics, resist to anoïkis, migrate and invade directionally, resist to redox and shear stresses in the systemic circulation, and possess stem cell characteristics. These cells primarily originate from metabolically hostile areas of the primary tumor, where oxygen and nutrient deprivation, together with metabolic waste accumulation, exert a strong selection pressure promoting evasion. Here, we followed the hypothesis according to which metastasis as a whole implies the existence of metabolic sensors. Among others, mitochondria are singled out as a major source of superoxide that supports the metastatic phenotype. Molecularly, stressed cancer cells increase mitochondrial superoxide production, which activates the transforming growth factor-β pathway through src directly within mitochondria, ultimately activating focal adhesion kinase Pyk2. The existence of mitochondria-targeted antioxidants constitutes an opportunity to interfere with the metastatic process. Here, using aggressive triple-negative and HER2-positive human breast cancer cell lines as models, we report that MitoQ inhibits all the metastatic traits that we tested in vitro. Compared to other mitochondria-targeted antioxidants, MitoQ already successfully passed Phase I safety clinical trials, which provides an important incentive for future preclinical and clinical evaluations of this drug for the prevention of breast cancer metastasis.
    Keywords:  MitoQ; breast cancer; clonogenicity; invasion; metastasis; migration; mitochondria; mitochondria-targeted antioxidant; mitochondrial superoxide; spheroids
  10. Mitochondrion. 2022 Mar 17. pii: S1567-7249(22)00022-8. [Epub ahead of print]64 59-72
      Respiratory Complex I is the site of a large fraction of the mutations that appear to cause mitochondrial disease. Seven of its subunits are mitochondrially encoded, and therefore, such mutants are particularly difficult to construct in cell-culture model systems. We have selected 13 human clinical mutations found in ND2, ND3, ND4, ND4L, ND5 and ND6 that are generally found at subunit interfaces, and not in critical residues. These mutations have been modeled in E. coli subunits of Complex I, nuoN, nuoA, nuoM, nuoK, nuoL, and nuoJ, respectively. All mutants were expressed from a plasmid encoding the entire nuo operon, and membrane vesicles were analyzed for deamino-NADH oxidase activity, and proton translocation activity. ND5 mutants were also analyzed using a time-delayed expression system, recently described by this lab. Other mutants were analyzed for the ability to associate in subcomplexes, after expression of subsets of the genes. For most mutants there was a positive correlation between those that were previously determined to be pathogenic, or likely to be pathogenic, and those that we found with compromised Complex I activity or subunit interactions in E. coli. In conclusion, this approach provides another way to explore the deleterious effects of human mitochondrial mutations, and it can contribute to molecular understanding of such mutations.
    Keywords:  Bioenergetics; Complex I; LHON; Mitochondria; Mutations; NADH dehydrogenase
  11. J Hematol Oncol. 2022 Mar 21. 15(1): 30
      BACKGROUND: Isocitrate dehydrogenase-2 (IDH2) is a mitochondrial enzyme that catalyzes the metabolic conversion between isocitrate and alpha-ketoglutarate (α-KG) in the TCA cycle. IDH2 mutation is an oncogenic event in acute myeloid leukemia (AML) due to the generation of 2-hydroxyglutarate. However, the role of wild-type IDH2 in AML remains unknown, despite patients with it suffer worse clinical outcome than those harboring mutant type.METHODS: IDH2 expression in AML cell lines and patient samples was evaluated by RT-qPCR, western blotting and database analyses. The role of wild-type IDH2 in AML cell survival and proliferation was tested using genetic knockdown and pharmacological inhibition in AML cells and animal models. LC-MS, GC-MS, isotope metabolic tracing, and molecular analyses were performed to reveal the underlying mechanisms.
    RESULTS: We found that wild-type IDH2 was overexpressed in AML and played a major role in promoting leukemia cell survival and proliferation in vitro and in vivo. Metabolomic analyses revealed an active IDH2-mediated reductive TCA cycle that promoted the conversion of α-KG to isocitrate/citrate to facilitate glutamine utilization for lipid synthesis in AML cells. Suppression of wild-type IDH2 by shRNA resulted in elevated α-KG and decreased isocitrate/citrate, leading to reduced lipid synthesis, a significant decrease in c-Myc downregulated by α-KG, and an inhibition of AML viability and proliferation. Importantly, pharmacological inhibition of IDH2 showed significant therapeutic effect in mice inoculated with AML cells with wt-IDH2 and induced a downregulation of C-MYC in vivo.
    CONCLUSIONS: Wt-IDH2 is an essential molecule for AML cell survival and proliferation by promoting conversion of α-KG to isocitrate for lipid synthesis and by upregulating c-Myc expression and could be a potential therapeutic target in AML.
    Keywords:  Acute myeloid leukemia; Alpha-ketoglutarate; Lipid synthesis; TCA cycle; Wild-type IDH2; c-Myc
  12. Dev Cell. 2022 Mar 14. pii: S1534-5807(22)00121-6. [Epub ahead of print]
      Invasive cells use transient, energy-consuming protrusions to breach basement membrane (BM) barriers. Using the ATP sensor PercevalHR during anchor cell (AC) invasion in Caenorhabditis elegans, we show that BM invasion is accompanied by an ATP burst from mitochondria at the invasive front. RNAi screening and visualization of a glucose biosensor identified two glucose transporters, FGT-1 and FGT-2, which bathe invasive front mitochondria with glucose and facilitate the ATP burst to form protrusions. FGT-1 localizes at high levels along the invasive membrane, while FGT-2 is adaptive, enriching most strongly during BM breaching and when FGT-1 is absent. Cytosolic glycolytic enzymes that process glucose for mitochondrial ATP production cluster with invasive front mitochondria and promote higher mitochondrial membrane potential and ATP levels. Finally, we show that UNC-6 (netrin), which polarizes invasive protrusions, also orients FGT-1. These studies reveal a robust and integrated energy acquisition, processing, and delivery network that powers BM breaching.
    Keywords:  ATP; basement membrane; biosensor; cell invasion; glucose transporters; glycolytic enzyme clustering; invasive protrusions; live imaging; mitochondria
  13. Mol Cancer Ther. 2022 Mar 21. pii: molcanther.0623.2021. [Epub ahead of print]
      WNT signaling promotes pancreatic ductal adenocarcinoma (PDAC) through diverse effects on proliferation, differentiation, survival, and stemness. A subset of PDAC with inactivating mutations in ring finger protein 43 (RNF43) show growth dependency on autocrine WNT ligand signaling and are susceptible to agents that block WNT ligand acylation by Porcupine O-acyltransferase, which is required for proper WNT ligand processing and secretion. For this study, global transcriptomic, proteomic, and metabolomic analyses were performed to explore the therapeutic response of RNF43-mutant PDAC to the Porcupine inhibitor (PORCNi) LGK974. LGK974 disrupted cellular bioenergetics and mitochondrial function through actions that included rapid mitochondrial depolarization, reduced mitochondrial content, and inhibition of oxidative phosphorylation and tricarboxylic acid cycle. LGK974 also broadly altered transcriptional activity, downregulating genes involved in cell cycle, nucleotide metabolism, and ribosomal biogenesis and upregulating genes involved in epithelial-mesenchymal transition, hypoxia, endocytosis, and lysosomes. Autophagy and lysosomal activity were augmented in response to LGK974, which synergistically inhibited tumor cell viability in combination with chloroquine. Autocrine WNT ligand signaling dictates metabolic dependencies in RNF43-mutant PDAC through a combination of transcription dependent and independent effects linked to mitochondrial health and function. Metabolic adaptations to mitochondrial damage and bioenergetic stress represent potential targetable liabilities in combination with PORCNi for the treatment of WNT ligand-addicted PDAC.
  14. Antioxidants (Basel). 2022 Feb 25. pii: 461. [Epub ahead of print]11(3):
      Venetoclax (ABT199) is a selective B-cell lymphoma 2 (BCL-2) inhibitor. The US FDA recently approved it to be used in combination with low-dose cytarabine or hypomethylating agents in acute myeloid leukemia (AML) or elderly patients non-eligible for chemotherapy. However, acquiring resistance to venetoclax in AML patients is the primary cause of treatment failure. To understand the molecular mechanisms inherent in the resistance to BCL-2 inhibitors, we generated a venetoclax-resistant cell line model and assessed the consequences of this resistance on its metabolic pathways. Untargeted metabolomics data displayed a notable impact of resistance on the PI3K/AKT pathway, the Warburg effect, glycolysis, the TCA cycle, and redox metabolism. The resistant cells showed increased NADPH and reduced glutathione levels, switching their energy metabolism towards glycolysis. PI3K/AKT pathway inhibition shifted resistant cells towards oxidative phosphorylation (OXPHOS). Our results provide a metabolic map of resistant cells that can be used to design novel metabolic targets to challenge venetoclax resistance in AML.
    Keywords:  MV4-11; OXPHOS; PI3K/AKT pathway; acute myeloid leukemia; glycolysis; metabolomics; redox metabolism; venetoclax; venetoclax resistance model
  15. PLoS Biol. 2022 Mar;20(3): e3001576
      Mitochondria and the complex endomembrane system are hallmarks of eukaryotic cells. To date, it has been difficult to manipulate organelle structures within single live cells. We developed a FluidFM-based approach to extract, inject, and transplant organelles from and into living cells with subcellular spatial resolution. The technology combines atomic force microscopy, optical microscopy, and nanofluidics to achieve force and volume control with real-time inspection. We developed dedicated probes that allow minimally invasive entry into cells and optimized fluid flow to extract specific organelles. When extracting single or a defined number of mitochondria, their morphology transforms into a pearls-on-a-string phenotype due to locally applied fluidic forces. We show that the induced transition is calcium independent and results in isolated, intact mitochondria. Upon cell-to-cell transplantation, the transferred mitochondria fuse to the host cells mitochondrial network. Transplantation of healthy and drug-impaired mitochondria into primary keratinocytes allowed monitoring of mitochondrial subpopulation rescue. Fusion with the mitochondrial network of recipient cells occurred 20 minutes after transplantation and continued for over 16 hours. After transfer of mitochondria and cell propagation over generations, donor mitochondrial DNA (mtDNA) was replicated in recipient cells without the need for selection pressure. The approach opens new prospects for the study of organelle physiology and homeostasis, but also for therapy, mechanobiology, and synthetic biology.
  16. Nat Metab. 2022 Mar 21.
      Tumour cells utilize multiple strategies to evade the immune system, but the underlying metabolic mechanisms remain poorly understood. The pyruvate dehydrogenase (PDH) complex converts pyruvate to acetyl-coenzyme A in mitochondria, thereby linking glycolysis to the ricarboxylic acid cycle. Here we show that the PDH complex E1 subunit α (PDHE1α) is also located in the cytosol. Cytosolic PDHE1α interacts with IKKβ and protein phosphatase 1B, thereby facilitating the inhibition of the NF-κB pathway. Cytosolic PDHE1α can be phosphorylated at S327 by ERK2 and translocated into mitochondria. Decreased cytosolic PDHE1α levels restore NF-κB signalling, whereas increased mitochondrial PDHE1α levels drive α-ketoglutarate production and promote reactive oxygen species detoxification. Synergistic activation of NF-κB and reactive oxygen species detoxification promotes tumour cell survival and enhances resistance to cytotoxic lymphocytes. Consistently, low levels of PDHE1α phosphorylation are associated with poor prognosis of patients with lung cancer. Our findings show a mechanism through which phosphorylation-dependent subcellular translocation of PDHE1α promotes tumour immune evasion.
  17. Proc Natl Acad Sci U S A. 2022 Mar 29. 119(13): e2115566119
      SignificanceMitochondria are double-membraned eukaryotic organelles that house the proteins required for generation of ATP, the energy currency of cells. ATP generation within mitochondria is performed by five multisubunit complexes (complexes I to V), the assembly of which is an intricate process. Mutations in subunits of these complexes, or the suite of proteins that help them assemble, lead to a severe multisystem condition called mitochondrial disease. We show that SFXN4, a protein that causes mitochondrial disease when mutated, assists with the assembly of complex I. This finding explains why mutations in SFXN4 cause mitochondrial disease and is surprising because SFXN4 belongs to a family of amino acid transporter proteins, suggesting that it has undergone a dramatic shift in function through evolution.
    Keywords:  complex assembly; mitochondria; respiratory chain; sideroflexins
  18. Cancers (Basel). 2022 Mar 15. pii: 1488. [Epub ahead of print]14(6):
      In oncology, the occurrence of distant metastases often marks the transition from curative to palliative care. Such outcome is highly predictable for breast cancer patients, even if tumors are detected early, and there is no specific treatment to prevent metastasis. Previous observations indicated that cancer cell mitochondria are bioenergetic sensors of the tumor microenvironment that produce superoxide to promote evasion. Here, we tested whether mitochondria-targeted antioxidant MitoQ is capable to prevent metastasis in the MDA-MB-231 model of triple-negative human breast cancer in mice and in the MMTV-PyMT model of spontaneously metastatic mouse breast cancer. At clinically relevant doses, we report that MitoQ not only prevented metastatic take and dissemination, but also local recurrence after surgery. We further provide in vitro evidence that MitoQ does not interfere with conventional chemotherapies used to treat breast cancer patients. Since MitoQ already successfully passed Phase I safety clinical trials, our preclinical data collectively provide a strong incentive to test this drug for the prevention of cancer dissemination and relapse in clinical trials with breast cancer patients.
    Keywords:  MitoQ; breast cancer; cancer relapse; metastasis; metastasis prevention; mitochondria; mitochondria-targeted antioxidant; mitochondrial superoxide; translational research
  19. EMBO J. 2022 Mar 21. e110466
      Pancreatic ductal adenocarcinoma (PDA) tumor cells are deprived of oxygen and nutrients and therefore must adapt their metabolism to ensure proliferation. In some physiological states, cells rely on ketone bodies to satisfy their metabolic needs, especially during nutrient stress. Here, we show that PDA cells can activate ketone body metabolism and that β-hydroxybutyrate (βOHB) is an alternative cell-intrinsic or systemic fuel that can promote PDA growth and progression. PDA cells activate enzymes required for ketogenesis, utilizing various nutrients as carbon sources for ketone body formation. By assessing metabolic gene expression from spontaneously arising PDA tumors in mice, we find HMG-CoA lyase (HMGCL), involved in ketogenesis, to be among the most deregulated metabolic enzymes in PDA compared to normal pancreas. In vitro depletion of HMGCL impedes migration, tumor cell invasiveness, and anchorage-independent tumor sphere compaction. Moreover, disrupting HMGCL drastically decreases PDA tumor growth in vivo, while βOHB stimulates metastatic dissemination to the liver. These findings suggest that βOHB increases PDA aggressiveness and identify HMGCL and ketogenesis as metabolic targets for limiting PDA progression.
    Keywords:  HMGCL; ketone bodies; metastasis; pancreatic cancer; β-hydroxybutyrate
  20. Cell Death Differ. 2022 Mar 23.
      Mitochondrial ATP synthase is vital not only for cellular energy production but also for energy dissipation and cell death. ATP synthase c-ring was suggested to house the leak channel of mitochondrial permeability transition (mPT), which activates during excitotoxic ischemic insult. In this present study, we purified human c-ring from both eukaryotic and prokaryotic hosts to biophysically characterize its channel activity. We show that purified c-ring forms a large multi-conductance, voltage-gated ion channel that is inhibited by the addition of ATP synthase F1 subcomplex. In contrast, dissociation of F1 from FO occurs during excitotoxic neuronal death suggesting that the F1 constitutes the gate of the channel. mPT is known to dissipate the osmotic gradient across the inner membrane during cell death. We show that ATP synthase c-subunit knock down (KD) prevents the osmotic change in response to high calcium and eliminates large conductance, Ca2+ and CsA sensitive channel activity of mPT. These findings elucidate the gating mechanism of the ATP synthase c-subunit leak channel (ACLC) and suggest how ACLC opening is regulated by cell stress in a CypD-dependent manner.
  21. Sci Rep. 2022 Mar 25. 12(1): 5196
      Aging in mammals leads to reduction in genes encoding the 45-subunit mitochondrial electron transport chain complex I. It has been hypothesized that normal aging and age-related diseases such as Parkinson's disease are in part due to modest decrease in expression of mitochondrial complex I subunits. By contrast, diminishing expression of mitochondrial complex I genes in lower organisms increases lifespan. Furthermore, metformin, a putative complex I inhibitor, increases healthspan in mice and humans. In the present study, we investigated whether loss of one allele of Ndufs2, the catalytic subunit of mitochondrial complex I, impacts healthspan and lifespan in mice. Our results indicate that Ndufs2 hemizygous mice (Ndufs2+/-) show no overt impairment in aging-related motor function, learning, tissue histology, organismal metabolism, or sensitivity to metformin in a C57BL6/J background. Despite a significant reduction of Ndufs2 mRNA, the mice do not demonstrate a significant decrease in complex I function. However, there are detectable transcriptomic changes in individual cell types and tissues due to loss of one allele of Ndufs2. Our data indicate that a 50% decline in mRNA of the core mitochondrial complex I subunit Ndufs2 is neither beneficial nor detrimental to healthspan.
  22. Cells. 2022 Mar 14. pii: 992. [Epub ahead of print]11(6):
      This study addresses the eventual consequence of cytochrome c oxidase (CytOx) inhibition by ATP at high ATP/ADP ratio in isolated rat heart mitochondria. Earlier, it has been demonstrated that the mechanism of allosteric ATP inhibition of CytOx is one of the key regulations of mitochondrial functions. It is relevant that aiming to maintain a high ATP/ADP ratio for the measurement of CytOx activity effectuating the enzymatic inhibition as well as mitochondrial respiration, optimal concentration of mitochondria is critically important. Likewise, only at this concentration, were the differences in ΔΨm and ROS concentrations measured under various conditions significant. Moreover, when CytOx activity was inhibited in the presence of ATP, mitochondrial respiration and ΔΨm both remained static, while the ROS production was markedly decreased. Consubstantial results were found when the electron transport chain was inhibited by antimycin A, letting only CytOx remain functional to support the energy production. This seems to corroborate that the decrease in mitochondrial ROS production is solely the effect of ATP binding to CytOx which results in static respiration as well as membrane potential.
    Keywords:  ATP; ROS; cytochrome c oxidase; mitochondrial membrane potential
  23. Nat Commun. 2022 Mar 25. 13(1): 1606
      The cellular processes that govern tumor resistance to immunotherapy remain poorly understood. To gain insight into these processes, here we perform a genome-scale CRISPR activation screen for genes that enable human melanoma cells to evade cytotoxic T cell killing. Overexpression of four top candidate genes (CD274 (PD-L1), MCL1, JUNB, and B3GNT2) conferred resistance in diverse cancer cell types and mouse xenografts. By investigating the resistance mechanisms, we find that MCL1 and JUNB modulate the mitochondrial apoptosis pathway. JUNB encodes a transcription factor that downregulates FasL and TRAIL receptors, upregulates the MCL1 relative BCL2A1, and activates the NF-κB pathway. B3GNT2 encodes a poly-N-acetyllactosamine synthase that targets >10 ligands and receptors to disrupt interactions between tumor and T cells and reduce T cell activation. Inhibition of candidate genes sensitized tumor models to T cell cytotoxicity. Our results demonstrate that systematic gain-of-function screening can elucidate resistance pathways and identify potential targets for cancer immunotherapy.
  24. Cancer Lett. 2022 Mar 20. pii: S0304-3835(22)00142-2. [Epub ahead of print]535 215659
      Adenosine monophosphate activated protein kinase (AMPK) is a master regulator of cell metabolism and is involved in cancer as both a tumor suppressor and a source of resistance to metabolic stress. The role of AMPK in response to chemotherapy has been examined in solid tumor models but remains unclear in acute myeloid leukemia (AML). To determine the role of AMPK in chemotherapy response, AML cell lines were generated lacking AMPK activity. AMPK knock out cells demonstrated significant resistance to cytarabine and doxorubicin both in vitro and in vivo. Mitochondrial mass and function were unchanged in AMPK knockout cells. Mechanistically, AMPK knock out cells demonstrated a diminished DNA damage response with significantly lower γH2AX foci, p53 and p21 induction as well as decreased apoptosis following chemotherapy exposure. Most importantly, TCGA datasets revealed that patients expressing low levels of the PRKAA1 subunit of AMPK had significantly shorter survival. Finally, AML cells were sensitized to chemotherapy with the addition of the AMPK activator AICAR. These data demonstrate that AMPK sensitizes AML cells to chemotherapy and suggests a contribution of the cellular metabolic state to cell fate decisions ultimately affecting therapy response.
  25. Nat Commun. 2022 Mar 25. 13(1): 1624
      Patient-derived xenografts (PDX) are widely used as human cancer models. Previous studies demonstrated clonal discordance between PDX and primary cells. However, in acute myeloid leukemia (AML)-PDX models, the significance of the clonal dynamics occurring in PDX remains unclear. By evaluating changes in the variant allele frequencies (VAF) of somatic mutations in serial samples of paired primary AML and their PDX bone marrow cells, we identify the skewing engraftment of relapsed or refractory (R/R) AML clones in 57% of PDX models generated from multiclonal AML cells at diagnosis, even if R/R clones are minor at <5% of VAF in patients. The event-free survival rate of patients whose AML cells successfully engraft in PDX models is consistently lower than that of patients with engraftment failure. We herein demonstrate that primary AML cells including potentially chemotherapy-resistant clones dominantly engraft in AML-PDX models and they enrich pre-existing treatment-resistant subclones.
  26. J Biol Chem. 2022 Mar 22. pii: S0021-9258(22)00298-8. [Epub ahead of print] 101858
      The mitochondrial permeability transition pore (PTP) is a Ca2+-dependent megachannel that plays an important role in mitochondrial physiology and cell fate. Cyclophilin D (CyPD) is a well-characterized PTP regulator, and its binding to the PTP favors pore opening. It has previously been shown that p53 physically interacts with CyPD and opens the PTP during necrosis. Accumulating studies also suggest that the F-ATP synthase contributes to the regulation and formation of the PTP. F-ATP synthase inhibitory factor 1 (IF1) is a natural inhibitor of F-ATP synthase activity; however, whether IF1 participates in the modulation of PTP opening is basically unknown. Here, we demonstrate using calcium retention capacity assay that IF1 overexpression promotes mitochondrial permeability transition via opening of the PTP. Intriguingly, we show that IF1 can interact with the p53-CyPD complex and facilitate cell death. We also demonstrate that the presence of IF1 is necessary for the formation of p53-CyPD complex. Therefore, we suggest that IF1 regulates the PTP via interaction with the p53-CyPD complex, and that IF1 is necessary for the inducing effect of p53-CyPD complex on PTP opening.
    Keywords:  F-ATP synthase inhibitory factor 1; cyclophilin D; mitochondria; mitochondrial permeability transition; p53
  27. Curr Opin Struct Biol. 2022 Mar 19. pii: S0959-440X(22)00029-X. [Epub ahead of print]74 102350
      Complex I is one of the major respiratory complexes, conserved from bacteria to mammals. It oxidises NADH, reduces quinone and pumps protons across the membrane, thus playing a central role in the oxidative energy metabolism. In this review we discuss our current state of understanding the structure of complex I from various species of mammals, plants, fungi, and bacteria, as well as of several complex I-related proteins. By comparing the structural evidence from these systems in different redox states and data from mutagenesis and molecular simulations, we formulate the mechanisms of electron transfer and proton pumping and explain how they are conformationally and electrostatically coupled. Finally, we discuss the structural basis of the deactivation phenomenon in mammalian complex I.