bims-mibica Biomed News
on Mitochondrial bioenergetics in cancer
Issue of 2021‒11‒14
forty-two papers selected by
Kelsey Fisher-Wellman
East Carolina University

  1. Int J Mol Sci. 2021 Nov 03. pii: 11938. [Epub ahead of print]22(21):
      Glioblastoma represents the highest grade of brain tumors. Despite maximal resection surgery associated with radiotherapy and concomitant followed by adjuvant chemotherapy with temozolomide (TMZ), patients have a very poor prognosis due to the rapid recurrence and the acquisition of resistance to TMZ. Here, initially considering that TMZ is a prodrug whose activation is pH-dependent, we explored the contribution of glioblastoma cell metabolism to TMZ resistance. Using isogenic TMZ-sensitive and TMZ-resistant human glioblastoma cells, we report that the expression of O6-methylguanine DNA methyltransferase (MGMT), which is known to repair TMZ-induced DNA methylation, does not primarily account for TMZ resistance. Rather, fitter mitochondria in TMZ-resistant glioblastoma cells are a direct cause of chemoresistance that can be targeted by inhibiting oxidative phosphorylation and/or autophagy/mitophagy. Unexpectedly, we found that PARP inhibitor olaparib, but not talazoparib, is also a mitochondrial Complex I inhibitor. Hence, we propose that the anticancer activities of olaparib in glioblastoma and other cancer types combine DNA repair inhibition and impairment of cancer cell respiration.
    Keywords:  PARP inhibitors; cancer metabolism; chemoresistance; glioblastoma; metformin; mitochondria; temozolomide (TMZ)
  2. Comp Biochem Physiol A Mol Integr Physiol. 2021 Nov 05. pii: S1095-6433(21)00219-1. [Epub ahead of print]264 111111
      Skeletal muscle mitochondria of the African pygmy mouse Mus mattheyi exhibit markedly reduced oxygen consumption and ATP synthesis rates but a higher mitochondrial efficiency than what would be expected from allometric trends. In the present study, we assessed whether such reduction of mitochondrial activity in M. mattheyi can limit the oxidative stress associated with an increased generation of mitochondrial reactive oxygen species. We conducted a comparative study of mitochondrial oxygen consumption, H2O2 release, and electron leak (%H2O2/O) in skeletal muscle mitochondria isolated from the extremely small African pygmy mouse (M. mattheyi, ~5 g) and Mus musculus, which is a larger Mus species (~25 g). Mitochondria were energized with pyruvate, malate, and succinate, after which fluxes were measured at different steady-state rates of oxidative phosphorylation. Overall, M. mattheyi exhibited lower oxidative activity and higher electron leak than M. musculus, while the H2O2 release did not differ significantly between these two Mus species. We further found that the high coupling efficiency of skeletal muscle mitochondria from M. mattheyi was associated with high electron leak. Nevertheless, data also show that, despite the higher electron leak, the lower mitochondrial respiratory capacity of M. mattheyi limits the cost of a net increase in H2O2 release, which is lower than that expected for a mammals of this size.
    Keywords:  Bioenergetics; Free electron leak; Mammals; Mitochondria; Oxidative phosphorylation; Reactive oxygen species; Skeletal muscle
  3. Cancers (Basel). 2021 Oct 31. pii: 5484. [Epub ahead of print]13(21):
      Although cancer cell metabolism was mainly considered to rely on glycolysis, with the concomitant impairment of mitochondrial metabolism, it has recently been demonstrated that several tumor types are sustained by oxidative phosphorylation (OXPHOS). In this context, endogenous fatty acids (FAs) deriving from lipolysis or lipophagy are oxidised into the mitochondrion, and are used as a source of energy through OXPHOS. Because the electron transport chain is the main source of ROS, cancer cells relying on fatty acid oxidation (FAO) need to be equipped with antioxidant systems that maintain the ROS levels under the death threshold. In those conditions, ROS can act as second messengers, favouring proliferation and survival. Herein, we highlight the different responses that tumor cells adopt when lipid catabolism is augmented, taking into account the different ROS fates. Many papers have demonstrated that the pro- or anti-tumoral roles of endogenous FA usage are hugely dependent on the tumor type, and on the capacity of cancer cells to maintain redox homeostasis. In light of this, clinical studies have taken advantage of the boosting of lipid catabolism to increase the efficacy of tumor therapy, whereas, in other contexts, antioxidant compounds are useful to reduce the pro-survival effects of ROS deriving from FAO.
    Keywords:  fatty acid oxidation; lipid catabolism; mitochondrial metabolism; reactive oxygen species
  4. BMC Biol. 2021 Nov 11. 19(1): 242
      BACKGROUND: Proteostasis unbalance and mitochondrial dysfunction are two hallmarks of aging. While the chaperone folds and activates its clients, it is the cochaperone that determines the specificity of the clients. Ids2 is an HSP90's cochaperone controlling mitochondrial functions, but no in vivo clients of Ids2 have been reported yet.RESULTS: We performed a screen of the databases of HSP90 physical interactors, mitochondrial components, and mutants with respiratory defect, and identified Atp3, a subunit of the complex V ATP synthase, as a client of Ids2. Deletion of IDS2 destabilizes Atp3, and an α-helix at the middle region of Ids2 recruits Atp3 to the folding system. Shortage of Ids2 or Atp3 leads to the loss of mitochondrial DNA. The intermembrane space protease Yme1 is critical to maintaining the Atp3 protein level. Moreover, Ids2 is highly induced when cells carry out oxidative respiration.
    CONCLUSIONS: These findings discover a cochaperone essentially for maintaining the stability of mitochondrial DNA and the proteostasis of the electron transport chain-crosstalk between two hallmarks of aging.
    Keywords:  ATP synthase; Aging; Ids2; Mitochondria; Proteostasis
  5. Int J Mol Sci. 2021 Oct 29. pii: 11786. [Epub ahead of print]22(21):
      Amiodarone is a potent antiarrhythmic drug and displays substantial liver toxicity in humans. It has previously been demonstrated that amiodarone and its metabolite (desethylamiodarone, DEA) can inhibit mitochondrial function, particularly complexes I (CI) and II (CII) of the electron transport system in various animal tissues and cell types. The present study, performed in human peripheral blood cells, and one liver-derived human cell line, is primarily aimed at assessing the concentration-dependent effects of these drugs on mitochondrial function (respiration and cellular ATP levels). Furthermore, we explore the efficacy of a novel cell-permeable succinate prodrug in alleviating the drug-induced acute mitochondrial dysfunction. Amiodarone and DEA elicit a concentration-dependent impairment of mitochondrial respiration in both intact and permeabilized platelets via the inhibition of both CI- and CII-supported respiration. The inhibitory effect seen in human platelets is also confirmed in mononuclear cells (PBMCs) and HepG2 cells. Additionally, amiodarone elicits a severe concentration-dependent ATP depletion in PBMCs, which cannot be explained solely by mitochondrial inhibition. The succinate prodrug NV118 alleviates the respiratory deficit in platelets and HepG2 cells acutely exposed to amiodarone. In conclusion, amiodarone severely inhibits metabolism in primary human mitochondria, which can be counteracted by increasing mitochondrial function using intracellular delivery of succinate.
    Keywords:  ATP; HepG2 cells; NV118; PBMCs; amiodarone; desethylamiodarone; mitochondria; platelets; respiration; sotalol
  6. Biochem Soc Trans. 2021 Nov 08. pii: BST20210460. [Epub ahead of print]
      Mitochondria are one of the most exhaustively investigated organelles in the cell and most attention has been paid to the components of the mitochondrial electron transport chain (ETC) in the last 100 years. The ETC collects electrons from NADH or FADH2 and transfers them through a series of electron carriers within multiprotein respiratory complexes (complex I to IV) to oxygen, therefore generating an electrochemical gradient that can be used by the F1-F0-ATP synthase (also named complex V) in the mitochondrial inner membrane to synthesize ATP. The organization and function of the ETC is a continuous source of surprises. One of the latest is the discovery that the respiratory complexes can assemble to form a variety of larger structures called super-complexes (SCs). This opened an unexpected level of complexity in this well-known and fundamental biological process. This review will focus on the current evidence for the formation of different SCs and will explore how they modulate the ETC organization according to the metabolic state. Since the field is rapidly growing, we also comment on the experimental techniques used to describe these SC and hope that this overview may inspire new technologies that will help to advance the field.
    Keywords:  N-respirasome; OXPHOS; Q-respirsome; electon transport chain; supercomplexes
  7. Cell Rep. 2021 Nov 09. pii: S2211-1247(21)01468-6. [Epub ahead of print]37(6): 109989
      Mutations in mitochondrial genes impairing energy production cause mitochondrial diseases (MDs), and clinical studies have shown that MD patients are prone to bacterial infections. However, the relationship between mitochondrial (dys)function and infection remains largely unexplored, especially in epithelial cells, the first barrier to many pathogens. Here, we generate an epithelial cell model for one of the most common mitochondrial diseases, Leigh syndrome, by deleting surfeit locus protein 1 (SURF1), an assembly factor for respiratory chain complex IV. We use this genetic model and a complementary, nutrient-based approach to modulate mitochondrial respiration rates and show that impaired mitochondrial respiration favors entry of the human pathogen Listeria monocytogenes, a well-established bacterial infection model. Reversely, enhanced mitochondrial energy metabolism decreases infection efficiency. We further demonstrate that endocytic recycling is reduced in mitochondrial respiration-dependent cells, dampening L. monocytogenes infection by slowing the recycling of its host cell receptor c-Met, highlighting a previously undescribed role of mitochondrial respiration during infection.
    Keywords:  (13)C isotopologue profiling; Listeria monocytogenes; Rab11; endocytic recycling; infection; metabolism; mitochondria; mitochondrial disease; respiration
  8. Sci Rep. 2021 Nov 11. 11(1): 22106
      O-GlcNAcylation is a prevalent form of glycosylation that regulates proteins within the cytosol, nucleus, and mitochondria. The O-GlcNAc modification can affect protein cellular localization, function, and signaling interactions. The specific impact of O-GlcNAcylation on mitochondrial morphology and function has been elusive. In this manuscript, the role of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and the activity of electron transport chain (ETC) complexes were evaluated. In a cellular environment with hyper O-GlcNAcylation due to the deletion of O-GlcNAcase (OGA), mitochondria showed a dramatic reduction in size and a corresponding increase in number and total mitochondrial mass. Because of the increased mitochondrial content, OGA knockout cells exhibited comparable coupled mitochondrial Oxphos and ATP levels when compared to WT cells. However, we observed reduced protein levels for complex I and II when comparing normalized mitochondrial content and reduced linked activity for complexes I and III when examining individual ETC complex activities. In assessing mitochondrial fission, we observed increased amounts of O-GlcNAcylated dynamin-related protein 1 (Drp1) in cells genetically null for OGA and in glioblastoma cells. Individual regions of Drp1 were evaluated for O-GlcNAc modifications, and we found that this post-translational modification (PTM) was not limited to the previously characterized residues in the variable domain (VD). Additional modification sites are predicted in the GTPase domain, which may influence enzyme activity. Collectively, these results highlight the impact of O-GlcNAcylation on mitochondrial dynamics and ETC function and mimic the changes that may occur during glucose toxicity from hyperglycemia.
  9. Cancers (Basel). 2021 Oct 24. pii: 5338. [Epub ahead of print]13(21):
      In pancreatic ductal adenocarcinoma (PDAC), the tumor stroma constitutes most of the cell mass and contributes to therapy resistance and progression. Here we show a hitherto unknown metabolic cooperation between pancreatic stellate cells (PSCs) and tumor cells through Interleukin 17B/Interleukin 17B receptor (IL-17B/IL-17RB) signaling. Tumor-derived IL-17B carrying extracellular vesicles (EVs) activated stromal PSCs and induced the expression of IL-17RB. PSCs increased oxidative phosphorylation while reducing mitochondrial turnover. PSCs activated tumor cells in a feedback loop. Tumor cells subsequently increased oxidative phosphorylation and decreased glycolysis partially via IL-6. In vivo, IL-17RB overexpression in PSCs accelerated tumor growth in a co-injection xenograft mouse model. Our results demonstrate a tumor-to-stroma feedback loop increasing tumor metabolism to accelerate tumor growth under optimal nutritional conditions.
    Keywords:  IL17B/RB; metabolism; pancreatic cancer; tumor microenvironment
  10. Oncogene. 2021 Nov 12.
      Reactive oxygen species (ROS) serve as critical signals in various cellular processes. Excessive ROS cause cell death or senescence and mediates the therapeutic effect of many cancer drugs. Recent studies showed that ROS increasingly accumulate during G2/M arrest, the underlying mechanism, however, has not been fully elucidated. Here, we show that in cancer cells treated with anticancer agent TH287 or paclitaxel that causes M arrest, mitochondria accumulate robustly and produce excessive mitochondrial superoxide, which causes oxidative DNA damage and undermines cell survival and proliferation. While mitochondrial mass is greatly increased in cells arrested at M phase, the mitochondrial function is compromised, as reflected by reduced mitochondrial membrane potential, increased SUMOylation and acetylation of mitochondrial proteins, as well as an increased metabolic reliance on glycolysis. CHK1 functional disruption decelerates cell cycle, spares the M arrest and attenuates mitochondrial oxidative stress. Induction of mitophagy and blockade of mitochondrial biogenesis, measures that reduce mitochondrial accumulation, also decelerate cell cycle and abrogate M arrest-coupled mitochondrial oxidative stress. These results suggest that cell cycle progression and mitochondrial homeostasis are interdependent and coordinated, and that impairment of mitochondrial homeostasis and the associated redox signaling may mediate the antineoplastic effect of the M arrest-inducing chemotherapeutics. Our findings provide insights into the fate of cells arrested at M phase and have implications in cancer therapy.
  11. J Biol Chem. 2021 Oct 28. pii: S0021-9258(21)01174-1. [Epub ahead of print] 101368
      The endoplasmic reticulum (ER) and mitochondria are structurally connected with each other at specific sites termed mitochondria-associated membranes (MAM). These physical links are composed of several tethering proteins and are important during varied cellular processes, such as calcium homeostasis, lipid metabolism and transport, membrane biogenesis and organelle remodeling. However, the attributes of specific tethering proteins in these cellular functions remain debatable. Here, we present data to show that one such tether protein, GRP75, is essential in increasing ER-mitochondria contact during palmitate-induced apoptosis in pancreatic insulinoma cells. We demonstrate that palmitate increased GRP75 levels in mouse and rat pancreatic insulinoma cells as well as in mouse primary islet cells. This was associated with increased mitochondrial Ca2+ transfer, impaired mitochondrial membrane potential, increased ROS production, and enhanced physical coupling between the ER and mitochondria. Interestingly, GRP75 inhibition prevented these palmitate-induced cellular aberrations. Additionally, GRP75 overexpression alone was sufficient to impair mitochondrial membrane potential, increase mitochondrial Ca2+ levels and ROS generation, augment ER-mitochondria contact, and induce apoptosis in these cells. In vivo injection of palmitate induced hyperglycemia and hypertriglyceridemia, as well as impaired glucose and insulin tolerance in mice. These animals also exhibited elevated GRP75 levels accompanied by enhanced apoptosis within the pancreatic islets. Our findings suggest that GRP75 is critical in mediating palmitate-induced ER-mitochondrial interaction leading to apoptosis in pancreatic islet cells.
    Keywords:  ER-mitochondria contact; GRP75; calcium apoptosis; palmitate
  12. FASEB J. 2021 Dec;35(12): e22031
      Loss of skeletal muscle mass and force is of critical importance in numerous pathologies, like age-related sarcopenia or cancer. It has been shown that the Akt-mTORC1 pathway is critical for stimulating adult muscle mass and function, however, it is unknown if mTORC1 is the only mediator downstream of Akt and which intracellular processes are required for functional muscle growth. Here, we show that loss of Raptor reduces muscle hypertrophy after Akt activation and completely prevents increases in muscle force. Interestingly, the residual hypertrophy after Raptor deletion can be completely prevented by administration of the mTORC1 inhibitor rapamycin. Using a quantitative proteomics approach we find that loss of Raptor affects the increases in mitochondrial proteins, while rapamycin mainly affects ribosomal proteins. Taken together, these results suggest that mTORC1 is the key mediator of Akt-dependent muscle growth and its regulation of the mitochondrial proteome is critical for increasing muscle force.
    Keywords:  Raptor; hypertrophy; mTOR; mitochondria; rapamycin; skeletal muscle
  13. Front Immunol. 2021 ;12 670338
      Proteins controlling mitochondrial fission have been recognized as essential regulators of mitochondrial functions, mitochondrial quality control and cell apoptosis. In the present study, we identified the critical B cell survival regulator TRAF3 as a novel binding partner of the key mitochondrial fission factor, MFF, in B lymphocytes. Elicited by our unexpected finding that the majority of cytoplasmic TRAF3 proteins were localized at the mitochondria in resting splenic B cells after ex vivo culture for 2 days, we found that TRAF3 specifically interacted with MFF as demonstrated by co-immunoprecipitation and GST pull-down assays. We further found that in the absence of stimulation, increased protein levels of mitochondrial TRAF3 were associated with altered mitochondrial morphology, decreased mitochondrial respiration, increased mitochondrial ROS production and membrane permeabilization, which eventually culminated in mitochondria-dependent apoptosis in resting B cells. Loss of TRAF3 had the opposite effects on the morphology and function of mitochondria as well as mitochondria-dependent apoptosis in resting B cells. Interestingly, co-expression of TRAF3 and MFF resulted in decreased phosphorylation and ubiquitination of MFF as well as decreased ubiquitination of TRAF3. Moreover, lentivirus-mediated overexpression of MFF restored mitochondria-dependent apoptosis in TRAF3-deficient malignant B cells. Taken together, our findings provide novel insights into the apoptosis-inducing mechanisms of TRAF3 in B cells: as a result of survival factor deprivation or under other types of stress, TRAF3 is mobilized to the mitochondria through its interaction with MFF, where it triggers mitochondria-dependent apoptosis. This new role of TRAF3 in controlling mitochondrial homeostasis might have key implications in TRAF3-mediated regulation of B cell transformation in different cellular contexts. Our findings also suggest that mitochondrial fission is an actionable therapeutic target in human B cell malignancies, including those with TRAF3 deletion or relevant mutations.
    Keywords:  B cell malignancies; B lymphocytes; MFF; TRAF3; apoptosis; mitochondria
  14. Dev Cell. 2021 Nov 08. pii: S1534-5807(21)00846-7. [Epub ahead of print]56(21): 2925-2927
      The significance of mitochondrial long-lived proteins (mitoLLPs) to tissue health has remained mysterious for over a decade. In this issue of Developmental Cell, Krishna et al. demonstrate that mitochondrial lifetimes are highly heterogeneous and that mitoLLPs promote respiratory capacity by facilitating supercomplex assembly within the electron transport chain.
  15. FASEB J. 2021 Dec;35(12): e22023
      B lymphocytes are responsible for humoral immunity and play a key role in the immune response. Optimal mitochondrial function is required to support B cell activity during activation. We examined how deficiency of tafazzin, a cardiolipin remodeling enzyme required for mitochondrial function, alters the metabolic activity of B cells and their response to activation by lipopolysaccharide in mice. B cells were isolated from 3-month-old wild type or tafazzin knockdown mice and incubated for up to 72 h with lipopolysaccharide and cell proliferation, expression of cell surface markers, secretion of antibodies and chemokines, proteasome and immunoproteasome activities, and metabolic function determined. In addition, proteomic analysis was performed to identify altered levels of proteins involved in survival, immunogenic, proteasomal and mitochondrial processes. Compared to wild type lipopolysaccharide activated B cells, lipopolysaccharide activated tafazzin knockdown B cells exhibited significantly reduced proliferation, lowered expression of cluster of differentiation 86 and cluster of differentiation 69 surface markers, reduced secretion of immunoglobulin M antibody, reduced secretion of keratinocytes-derived chemokine and macrophage-inflammatory protein-2, reduced proteasome and immunoproteasome activities, and reduced mitochondrial respiration and glycolysis. Proteomic analysis revealed significant alterations in key protein targets that regulate cell survival, immunogenicity, proteasomal processing and mitochondrial function consistent with the findings of the above functional studies. The results indicate that the cardiolipin transacylase enzyme tafazzin plays a key role in regulating mouse B cell function and metabolic activity during activation through modulation of mitochondrial function.
    Keywords:  B lymphocyte activation; cardiolipin; cell proliferation and survival; cytokines; immunoglobulin synthesis and secretion; immunoproteasome; lipopolysaccharide; mitochondria; proteasome; tafazzin
  16. iScience. 2021 Nov 19. 24(11): 103294
      Mitochondria are a hallmark of eukaryal cells and play an important role in cellular metabolism. There is a vast amount of knowledge available on mitochondrial metabolism and essential mitochondrial functions, such as protein import and iron-sulfur cluster biosynthesis, including multiple studies on the mitochondrial proteome. Therefore, there is a need for in silico approaches to facilitate the analysis of these data. Here, we present a detailed model of mitochondrial metabolism Saccharomyces cerevisiae, including protein import, iron-sulfur cluster biosynthesis, and a description of the coupling between charge translocation processes and ATP synthesis. Model analysis implied a dual dependence of absolute levels of proteins in protein import, iron-sulfur cluster biogenesis and cluster abundance on growth rate and respiratory activity. The model is instrumental in studying dynamics and perturbations in these processes and given the high conservation of mitochondrial metabolism in humans, it can provide insight into their role in human disease.
    Keywords:  Cell biology; Cellular physiology; In silico biology; Integrative aspects of cell biology; Systems biology
  17. J Biol Chem. 2021 Oct 28. pii: S0021-9258(21)01164-9. [Epub ahead of print] 101358
      Preserving optimal mitochondrial function is critical in the heart, which is the most ATP-avid organ in the body. Recently, we showed that global deficiency of the nuclear receptor RORα in the "staggerer" (RORαsg/sg) mouse exacerbates angiotensin II-induced cardiac hypertrophy and compromises cardiomyocyte mitochondrial function. However, the mechanisms underlying these observations have not been defined previously. Here we used pharmacological and genetic gain- and loss-of-function tools to demonstrate that RORα regulates cardiomyocyte mitophagy to preserve mitochondrial abundance and function. We found that RORαsg/sg cardiomyocyte mitochondria were less numerous and exhibited fewer mitophagy events than wild type (WT) controls. The hearts of our novel cardiomyocyte-specific RORα knockout (CMKO) mouse line demonstrated impaired contractile function, enhanced oxidative stress, increased apoptosis and reduced autophagic flux relative to Cre(-) littermates. We found that cardiomyocyte RORα was upregulated by hypoxia, a classical inducer of mitophagy. The loss of RORα blunted mitophagy and broadly compromised mitochondrial function in normoxic and hypoxic conditions in vivo and in vitro. We also show that RORα is a direct transcriptional regulator of the mitophagy mediator caveolin-3 in cardiomyocytes and that enhanced expression of RORα increases caveolin-3 abundance and enhances mitophagy. Finally, knockdown of RORα impairs cardiomyocyte mitophagy, compromises mitochondrial function, and induces apoptosis, but these defects could be rescued by caveolin-3 overexpression. Collectively, these findings reveal a novel role for RORα in regulating mitophagy through caveolin-3 and expand our currently limited understanding of the mechanisms underlying RORα-mediated cardioprotection.
  18. Mol Cancer Ther. 2021 Nov 08. pii: molcanther.MCT-21-0393-A.2021. [Epub ahead of print]
      Colorectal cancer (CRC) is one of the most frequent tumor entities, with an increasing incidence and mortality in younger adults in Europe and the US. 5-year survival rates for advanced CRC are still low, highlighting the need for novel targets in CRC therapy. Here, we investigated the therapeutic potential of the compound devimistat (CPI 613®) that targets altered mitochondrial cancer cell metabolism and its synergism with the antineoplastic drugs 5-fluorouracil (5-FU) and irinotecan (IT) in CRC. Devimistat exerted a comparable cytotoxicity in a panel of established CRC cell lines and patient-derived short-term culture independent of their genetic and epigenetic status, whereas human colonic epithelial cells were more resistant indicating tumor selectivity. These findings were corroborated in intestinal organoid and tumoroid models. Mechanistically, devimistat disrupted mitochondrial membrane potential and severely impaired mitochondrial respiration, resulting in CRC cell death induction independent of p53. Combination treatment of devimistat with 5-FU or IT demonstrated synergistic cell killing in CRC cells as shown by Combenefit modelling and Chou-Talalay analysis. Increased cell death induction was revealed as major mechanism involving downregulation of anti-apoptotic genes and accumulation of pro-apoptotic Bim, which was confirmed by its genetic knockdown. In human CRC xenograft mouse models, devimistat showed anti-tumor activity and synergized with IT, resulting in prolonged survival and enhanced therapeutic efficacy. In human tumor xenografts, devimistat prevented IT-triggered p53 stabilization and caused synergistic Bim induction. Taken together, our study revealed devimistat as a promising candidate in CRC therapy by synergizing with established antineoplastic drugs in vitro and in vivo.
  19. J Vis Exp. 2021 Oct 19.
      During activation, the metabolism of T cells adapts to changes that impact their fate. An increase in mitochondrial oxidative phosphorylation is indispensable for T cell activation, and the survival of memory T cells is dependent on mitochondrial remodeling. Consequently, this affects the long-term clinical outcome of cancer immunotherapies. Changes in T cell quality are often studied by flow cytometry using well-known surface markers and not directly by their metabolic state. This is an optimized protocol for measuring real-time mitochondrial respiration of primary human T cells using an Extracellular Flux Analyzer and the cytokines IL-2 and IL-15, which differently affect T cell metabolism. It is shown that the metabolic state of T cells can clearly be distinguished by measuring the oxygen consumption when inhibiting key complexes in the metabolic pathway and that the accuracy of these measurements is highly dependent on optimal inhibitor concentration and inhibitor injection strategy. This standardized protocol will help implement mitochondrial respiration as a standard for T cell fitness in monitoring and studying cancer immunotherapies.
  20. Cancers (Basel). 2021 Oct 29. pii: 5447. [Epub ahead of print]13(21):
      Metabolic reprogramming is a well-known hallmark of cancer, whereby the development of drugs that target cancer cell metabolism is gaining momentum. However, when establishing preclinical studies and clinical trials, it is often neglected that a tumor mass is a complex system in which cancer cells coexist and interact with several types of microenvironment populations, including endothelial cells, fibroblasts and immune cells. We are just starting to understand how such populations are affected by the metabolic changes occurring in a transformed cell and little is known about the impact of metabolism-targeting drugs on the non-malignant tumor components. Here we provide a general overview of the links between cancer cell metabolism and tumor microenvironment (TME), particularly focusing on the emerging literature reporting TME-specific effects of metabolic therapies.
    Keywords:  cancer metabolism; cancer-associated fibroblasts; metabolic reprogramming; tumor microenvironment; tumor-associated macrophages
  21. Cell Metab. 2021 Nov 06. pii: S1550-4131(21)00528-3. [Epub ahead of print]
      Nutrient sensing pathways influence metabolic health and aging, offering the possibility that diet might be used therapeutically, alone or with drugs targeting these pathways. We used the Geometric Framework for Nutrition to study interactive and comparative effects of diet and drugs on the hepatic proteome in mice across 40 dietary treatments differing in macronutrient ratios, energy density, and drug treatment (metformin, rapamycin, resveratrol). There was a strong negative correlation between dietary energy and the spliceosome and a strong positive correlation between dietary protein and mitochondria, generating oxidative stress at high protein intake. Metformin, rapamycin, and resveratrol had lesser effects than and dampened responses to diet. Rapamycin and metformin reduced mitochondrial responses to dietary protein while the effects of carbohydrates and fat were downregulated by resveratrol. Dietary composition has a powerful impact on the hepatic proteome, not just on metabolic pathways but fundamental processes such as mitochondrial function and RNA splicing.
    Keywords:  Geometric Framework; Nutrition; caloric restriction; liver; macronutrients; metformin; mitochondria; proteome; rapamycin; resveratrol; spliceosome
  22. Arch Pharm Res. 2021 Nov 09.
      Hepatocellular carcinoma (HCC) is one of the most common tumor types globally. Despite the progress made in surgical procedures and therapeutic options, HCC remains a considerable cause of cancer-related mortality. In this study, we investigated the antitumor effects of sanguinarine (Sang) on HCC and its potential mechanisms. Our findings showed that Sang impairs the acidic environment of lysosomes by inhibiting cathepsin D maturation. In addition, Sang inhibited the formation of autolysosomes in RFP-GFP-LC3 transfected cells, subsequently suppressing late mitophagy. Sang also induced reactive oxygen species (ROS)-dependent autophagy and apoptosis in HCC cells, which was significantly attenuated following treatment with a ROS scavenger. Further investigation using autophagy inhibitors revealed that sanguinarine-induced mitochondrial dysfunction and mitophagy led to mitochondrial apoptosis in HCC cells. Immunohistochemical staining of sanguinarine-treated xenograft samples revealed that it initiated and blocked autophagy. In summary, our findings suggest that in HCC cells, Sang impairs lysosomal function and induces ROS-dependent mitophagy and apoptosis.
    Keywords:  Apoptosis; Hepatocellular carcinoma; Lysosomal function; Mitophagy; Reactive oxygen species; Sanguinarine
  23. Annu Rev Physiol. 2021 Nov 10.
      Mitochondria of all tissues convert various metabolic substrates into two forms of energy: ATP and heat. Historically, the primary focus of research in mitochondrial bioenergetics was on the mechanisms of ATP production, while mitochondrial thermogenesis received significantly less attention. Nevertheless, mitochondrial heat production is crucial for the maintenance of body temperature, regulation of the pace of metabolism, and prevention of oxidative damage to mitochondria and the cell. In addition, mitochondrial thermogenesis has gained significance as a pharmacological target for treating metabolic disorders. Mitochondria produce heat as the result of H+ leak across their inner membrane. This review provides a critical assessment of the current field of mitochondrial H+ leak and thermogenesis, with a focus on the molecular mechanisms involved in the function and regulation of uncoupling protein 1 and the ADP/ATP carrier, the two proteins that mediate mitochondrial H+ leak. Expected final online publication date for the Annual Review of Physiology, Volume 84 is February 2022. Please see for revised estimates.
  24. Cancer Metab. 2021 Nov 08. 9(1): 39
      BACKGROUND: Pyruvate dehydrogenase complex (PDC) plays a central role in carbohydrate metabolism, linking cytoplasmic glycolysis to the mitochondrial tricarboxylic acid (TCA) cycle. PDC is a conserved E1-E2-E3 dehydrogenase with a PDHA1 and PDHB heterotetramer functioning as the E1 subunit. PDHA1 contains three serine residues that can be reversibly phosphorylated by a dedicated family of four inhibitory pyruvate dehydrogenase kinases (PDHK1-4) and two reactivating phosphatases (PDP1, 2). Hypoxia induces the expression of PDHK1 and PDHK3 and hyperphosphorylates PDHA1. The role of PDC in metabolic reprogramming and tumor progression appears to be for the integration of oncogenic and environmental signals which supports tumor growth.METHODS: To isolate the function of the serine-dependent regulation of PDC, we engineered MiaPaca2 cells to express PDHA1 protein with either intact serines at positions 232, 293, and 300 or all the combinations of non-phosphorylatable alanine substitution mutations. These lines were compared in vitro for biochemical response to hypoxia by western blot, metabolic activity by biochemical assay and Seahorse XF flux analysis, and growth in media with reduced exogenous metabolites. The lines were also tested for growth in vivo after orthotopic injection into the pancreata of immune-deficient mice.
    RESULTS: In this family of cells with non-phosphorylatable PDHA1, we found reduced hypoxic phosphorylation of PDHA1, decreased PDH enzymatic activity in normoxia and hypoxia, decreased mitochondrial function by Seahorse flux assay, reduced in vitro growth of cells in media depleted of lipids, and reduced growth of tumors after orthotopic transplantation of cells into the pancreata of immune-deficient mice.
    CONCLUSIONS: We found that any substitution of alanine for serine at regulatory sites generated a hypomorphic PDC. However, the reduced PDC activity was insensitive to further reduction in hypoxia. These cells had a very modest reduction of growth in vitro, but failed to grow as tumors indicating that dynamic PDC adaptation to microenvironmental conditions is necessary to support pancreatic cancer growth in vivo.
    Keywords:  Glucose metabolism; Hypoxia; Mitochondria; Orthotopic pancreatic tumors; Pyruvate dehydrogenase
  25. Cell Death Dis. 2021 Nov 12. 12(11): 1076
      Deregulated mitochondrial energetics is a metabolic hallmark of cancer cells. However, the causative mechanism of the bioenergetic deregulation is not clear. In this study, we show that somatic copy number alteration (SCNA) of mitoribosomal protein (MRP) genes is a key mechanism of bioenergetic deregulation in hepatocellular carcinoma (HCC). Association analysis between the genomic and transcriptomic profiles of 82 MRPs using The Cancer Genome Atlas-Liver HCC database identified eight key SCNA-dependent MRPs: MRPS31, MRPL10, MRPL21, MRPL15, MRPL13, MRPL55, and DAP3. MRPS31 was the only downregulated MRP harboring a DNA copy number (DCN) loss. MRPS31 loss was associated specifically with the DCN losses of many genes on chromosome 13q. Survival analysis revealed a unique dependency of HCC on the MRPS31 deficiency, showing poor clinical outcome. Subclass prediction analysis using several public classifiers indicated that MRPS31 loss is linked to aggressive HCC phenotypes. By employing hepatoma cell lines with SCNA-dependent MRPS31 expression (JHH5, HepG2, Hep3B, and SNU449), we demonstrated that MRPS31 deficiency is the key mechanism, disturbing the whole mitoribosome assembly. MRPS31 suppression enhanced hepatoma cell invasiveness by augmenting MMP7 and COL1A1 expression. Unlike the action of MMP7 on extracellular matrix destruction, COL1A1 modulated invasiveness via the ZEB1-mediated epithelial-to-mesenchymal transition. Finally, MRPS31 expression further stratified the high COL1A1/DDR1-expressing HCC groups into high and low overall survival, indicating that MRPS31 loss is a promising prognostic marker. SIGNIFICANCE: Our results provide new mechanistic insight for mitochondrial deregulation in HCC and present MRPS31 as a novel biomarker of HCC malignancy.
  26. Nat Commun. 2021 Nov 11. 12(1): 6506
      CRISPR knockout fitness screens in cancer cell lines reveal many genes whose loss of function causes cell death or loss of fitness or, more rarely, the opposite phenotype of faster proliferation. Here we demonstrate a systematic approach to identify these proliferation suppressors, which are highly enriched for tumor suppressor genes, and define a network of 145 such genes in 22 modules. One module contains several elements of the glycerolipid biosynthesis pathway and operates exclusively in a subset of acute myeloid leukemia cell lines. The proliferation suppressor activity of genes involved in the synthesis of saturated fatty acids, coupled with a more severe loss of fitness phenotype for genes in the desaturation pathway, suggests that these cells operate at the limit of their carrying capacity for saturated fatty acids, which we confirm biochemically. Overexpression of this module is associated with a survival advantage in juvenile leukemias, suggesting a clinically relevant subtype.
  27. J Biol Chem. 2021 Nov 08. pii: S0021-9258(21)01194-7. [Epub ahead of print] 101388
      Nicotinamide phosphoribosyltransferase (NAMPT) converts nicotinamide to nicotinamide adenine dinucleotide (NAD+). As low hepatic NAD+ levels have been linked to the development of nonalcoholic fatty liver disease (NAFLD), we hypothetized that ablation of hepatic Nampt would affect susceptibility to liver injury in response to diet-induced metabolic stress. Following 3 weeks on a low-methionine, choline-free 60% high-fat diet (MCD), hepatocyte-specific Nampt knockout mice (HNKO) accumulated less triglyceride than wild-type littermates, but had increased histological scores for liver inflammation, necrosis, and fibrosis. Surprisingly, liver injury was also observed in HNKO mice on the purified control diet (PD). This HNKO phenotype was also associated with decreased abundance of mitochondrial proteins, especially proteins involved in oxidoreductase activity. High-resolution respirometry revealed lower respiratory capacity in PD-fed HNKO liver. In addition, fibrotic area in HNKO liver sections negatively correlated with hepatic NAD+, and liver injury was prevented by supplementation with NAD+ precursors nicotinamide riboside (NR) and nicotinic acid. Mass spectrometry (MS)-based proteomic analysis revealed that NR supplementation rescued hepatic levels of oxidoreductase- and OXPHOS proteins. Finally, single nucleus RNAseq showed that transcriptional changes in the HNKO liver mainly occurred in hepatocytes, and changes in the hepatocyte transcriptome were associated with liver necrosis. In conclusion, HNKO livers have reduced respiratory capacity, decreased abundance of mitochondrial proteins, and are susceptible to fibrosis due to low NAD+ levels. Our data suggest a critical threshold level of hepatic NAD+ that determines the predisposition to liver injury and supports that NAD+ precursor supplementation can prevent liver injury and NAFLD progression.
    Keywords:  NAD(+) biosynthesis; NAMPT; fibrosis; hepatocyte; mitochondria; nicotinamide adenine dinucleotide (NAD)
  28. MethodsX. 2021 ;8 101520
      Mitochondria generate aerobic cellular energy (i.e., ATP) through the reduction of oxygen to water via oxidative phosphorylation. The efficiency of this pathway can be measured by the phosphate/oxygen (ATP/O) ratio, which is the amount of ATP produced per oxygen atom reduced. This ratio thus provides a measure of the efficiency of mitochondrial respiration that can be readily compared between species. The magnesium green (MgGr) fluorometric method permits easy measurement of ATP/O ratios from isolated mitochondria but the standard analysis approach employs an endpoint method to calculate ATP/O ratios. Here, we present a modified method of ATP/O calculation that permits dynamic observation of fluorescent measurements of the consumption of O2 (JO2) and the production of ATP (JATP). Specifically, by substituting the slope of a straight line within a given period of time (seconds to minutes) with the slope of a tangent to each time point (per second), it is possible to evaluate JO2, JATP and the ATP/O ratio in a dynamic manner.•Provides second-by-second visualization of ATP/O ratios throughout experiments vs. a single measurement.•Dynamic visualization allows for easy identification of outlying data and more accurate calculation of mean ATP/O ratios.
    Keywords:  ATP production; Fluorescence; Mitochondrial efficiency; Oxygen consumption
  29. EMBO Mol Med. 2021 Nov 09. e14072
      Adenine nucleotide translocase-1 (ANT1) is an ADP/ATP transporter protein located in the inner mitochondrial membrane. ANT1 is involved not only in the processes of ADP/ATP exchange but also in the composition of the mitochondrial membrane permeability transition pore (mPTP); and the function of ANT1 is closely related to its own conformational changes. Notably, various viral proteins can interact directly with ANT1 to influence mitochondrial membrane potential by regulating the opening of mPTP, thereby affecting tumor cell fate. The Epstein-Barr virus (EBV) encodes the key tumorigenic protein, latent membrane protein 1 (LMP1), which plays a pivotal role in promoting therapeutic resistance in related tumors. In our study, we identified a novel mechanism for EBV-LMP1-induced alteration of ANT1 conformation in cisplatin resistance in nasopharyngeal carcinoma. Here, we found that EBV-LMP1 localizes to the inner mitochondrial membrane and inhibits the opening of mPTP by binding to ANT1, thereby favoring tumor cell survival and drug resistance. The ANT1 conformational inhibitor carboxyatractyloside (CATR) in combination with cisplatin improved the chemosensitivity of EBV-LMP1-positive cells. This finding confirms that ANT1 is a novel therapeutic target for overcoming cisplatin resistance in the future.
    Keywords:  ANT1; LMP1; chemosensitivity; conformational change; mitochondrial membrane potential
  30. iScience. 2021 Nov 19. 24(11): 103244
      Acetylation coordinates many biological processes to ensure cells respond appropriately to nutrients. However, how acetylation regulates lipid surplus-induced inflammation remains poorly understood. Here, we found that a high-fat diet (HFD) enhanced mitochondrial fatty acid β-oxidation, which enhanced acetyl-CoA levels in the liver of the large yellow croaker. The HFD activated ACLY to govern the "citrate transport" to transfer acetyl-CoA from the mitochondria to the nucleus. Elevated acetyl-CoA activated CBP to increase p65 acetylation and then aggravated inflammation. SIRT1 was deactivated with a decline in NAD+/NADH, which further aggravated inflammation. Therefore, acetylation-dependent regulation of transcription factor activity is an adaptation to proinflammatory stimuli under nutrient stress, which was also confirmed in AML12 hepatocytes. In vitro octanoate stimulation further verified that acetyl-CoA derived from fatty acid β-oxidation mediated acetylation homeostasis in the nucleus. The broad therapeutic prospects of intermediate metabolites and acetyltransferases/deacetylases might provide critical insights for the treatment of metabolic diseases in vertebrates.
    Keywords:  Cellular physiology; Immunology; Pathophysiology
  31. Nat Metab. 2021 Nov 11.
      The aberrant production of collagen by fibroblasts is a hallmark of many solid tumours and can influence cancer progression. How the mesenchymal cells in the tumour microenvironment maintain their production of extracellular matrix proteins as the vascular delivery of glutamine and glucose becomes compromised remains unclear. Here we show that pyruvate carboxylase (PC)-mediated anaplerosis in tumour-associated fibroblasts contributes to tumour fibrosis and growth. Using cultured mesenchymal and cancer cells, as well as mouse allograft models, we provide evidence that extracellular lactate can be utilized by fibroblasts to maintain tricarboxylic acid (TCA) cycle anaplerosis and non-essential amino acid biosynthesis through PC activity. Furthermore, we show that fibroblast PC is required for collagen production in the tumour microenvironment. These results establish TCA cycle anaplerosis as a determinant of extracellular matrix collagen production, and identify PC as a potential target to inhibit tumour desmoplasia.
  32. FASEB J. 2021 Dec;35(12): e21991
      Mitochondria are intimately connected to cell fate and function. Here, we review how these intracellular organelles participate in the induction and maintenance of the senescent state. In particular, we discuss how alterations in mitochondrial metabolism, quality control and dynamics are all involved in various aspects of cellular senescence. Together, these observations suggest that mitochondria are active participants and are mechanistically linked to the unique biology of senescence. We further describe how these insights can be potentially exploited for therapeutic benefit.
    Keywords:  aging; metabolism; mitophagy; reactive oxygen species; senolytic
  33. Mol Metab. 2021 Nov 05. pii: S2212-8778(21)00240-4. [Epub ahead of print] 101389
      BACKGROUND: Aberrant metabolism is recognized as a hallmark of cancer, a pillar necessary for proliferation. Regarding bioenergetics (ATP-generation), most cancers display a preference towards aerobic glycolysis ("Warburg effect") and glutaminolysis (mitochondrial substrate level-phosphorylation), but also other metabolites such as lactate, pyruvate, and fat-derived sources. These secondary metabolites can assist in proliferation but cannot fully cover ATP demands.SCOPE OF REVIEW: The concept of a static metabolic profile is challenged by instances of heterogeneity and flexibility to meet fuel/anaplerotic demands. Although metabolic therapies are a promising tool to improve therapeutic outcomes, either via pharmacological targets or press-pulse interventions, metabolic plasticity is rarely considered. Lack of bioenergetic analysis in vitro and patient-derived models is hindering translational potential. Here, we review the bioenergetics of cancer and propose a simple analysis of major metabolic pathways, encompassing both affordable and advanced techniques. A comprehensive compendium of Seahorse XF bioenergetic measurements is presented for the first time.
    MAJOR CONCLUSIONS: Standardization of principal readouts might help researchers collect a complete metabolic picture of cancer using the most appropriate methods depending on the sample of interest.
    Keywords:  Cancer; Energy Metabolism; Glycolysis; Oxidative Phosphorylation; Research Design
  34. Cell Rep. 2021 Nov 09. pii: S2211-1247(21)01467-4. [Epub ahead of print]37(6): 109988
      The anti-apoptotic myeloid cell leukemia 1 (MCL1) protein belongs to the pro-survival BCL2 family and is frequently amplified or elevated in human cancers. MCL1 is highly unstable, with its stability being regulated by phosphorylation and ubiquitination. Here, we identify acetylation as another critical post-translational modification regulating MCL1 protein stability. We demonstrate that the lysine acetyltransferase p300 targets MCL1 at K40 for acetylation, which is counteracted by the deacetylase sirtuin 3 (SIRT3). Mechanistically, acetylation enhances MCL1 interaction with USP9X, resulting in deubiquitination and subsequent MCL1 stabilization. Therefore, ectopic expression of acetylation-mimetic MCL1 promotes apoptosis evasion of cancer cells, enhances colony formation potential, and facilitates xenografted tumor progression. We further demonstrate that elevated MCL1 acetylation sensitizes multiple cancer cells to pharmacological inhibition of USP9X. These findings reveal that acetylation of MCL1 is a critical post-translational modification enhancing its oncogenic function and provide a rationale for developing innovative therapeutic strategies for MCL1-dependent tumors.
    Keywords:  MCL1; USP9X; acetylation; chemoresistance; p300; protein degradation; protein stability; ubiquitination
  35. Elife. 2021 Nov 11. pii: e69621. [Epub ahead of print]10
      Iron-sulfur (Fe-S) clusters are cofactors essential for the activity of numerous enzymes including DNA polymerases, helicases, and glycosylases. They are synthesized in the mitochondria as Fe-S intermediates and are exported to the cytoplasm for maturation by the mitochondrial transporter ABCB7. Here, we demonstrate that ABCB7 is required for bone marrow B cell development, proliferation, and class switch recombination, but is dispensable for peripheral B cell homeostasis in mice. Conditional deletion of ABCB7 using Mb1-cre resulted in a severe block in bone marrow B cell development at the pro-B cell stage. The loss of ABCB7 did not alter expression of transcription factors required for B cell specification or commitment. While increased intracellular iron was observed in ABCB7-deficient pro-B cells, this did not lead to increased cellular or mitochondrial reactive oxygen species, ferroptosis, or apoptosis. Interestingly, loss of ABCB7 led to replication-induced DNA damage in pro-B cells, independent of VDJ recombination, and these cells had evidence of slowed DNA replication. Stimulated ABCB7-deficient splenic B cells from CD23-cre mice also had a striking loss of proliferation and a defect in class switching. Thus, ABCB7 is essential for early B cell development, proliferation, and class switch recombination.
    Keywords:  ABCB7; B cells; immunology; inflammation; iron; mouse
  36. Biophys J. 2021 Nov 05. pii: S0006-3495(21)00949-8. [Epub ahead of print]
      The mitochondrial ADP/ATP carrier (AAC) performs the first and last step in oxidative phosphorylation by exchanging, ADP and ATP across the mitochondrial inner membrane. Its optimal function has been shown to be dependent on cardiolipins (CLs), unique phospholipids located almost exclusively in the mitochondrial membrane. In addition, AAC exhibits an enthralling three-fold pseudo-symmetry, a unique feature of members of the SLC25 family. Recently, its conformation poised for binding of ATP was solved by X-ray crystallography, referred to as the matrix-state (m-state). Binding of the substrate leads to conformational changes that export of ATP to the mitochondrial intermembrane space. In this contribution, we investigate the influence of CLs on the structure, substrate-binding properties, and structural symmetry of the m-state, employing μs-scale molecular dynamics (MD) simulations. Our findings demonstrate that CLs play a minor stabilizing role on the AAC structure. The inter-domain salt-bridges and hydrogen bonds forming the cytoplasmic network and tyrosine braces, which ensure the integrity of the global AAC scaffold, highly benefit from the presence of CLs. Under these conditions, the carrier is found to be organized in a more compact structure in its interior, as revealed by analyses of the electrostatic potential, measure of the AAC cavity aperture, and the substrate-binding assays. Introducing a convenient structure-based symmetry metric, we quantified the structural three-fold pseudo-symmetry of AAC, not only for the crystallographic structure, but also for conformational states of the carrier explored in the MD simulations. Our results suggest that CLs moderately contribute to preserve the pseudo-symmetric structure of AAC. SIGNIFICANCE At both ends of oxidative phosphorylation, the mitochondrial ADP/ATP carrier (AAC) switches between two conformational states, the c- and m-states, to import and export nucleotides across the mitochondrial inner membrane. Its optimal function depends on cardiolipins, which stabilize the protein as it undergoes conformational transitions. Here, we assess how these lipids, ubiquitous to the mitochondrial membrane, modulate the structural stability, symmetry, and ATP-binding properties of the carrier in its m-state, and find that by strengthening inter-domain non-covalent interactions, they promote more compact conformations of the protein. In turn, the cardiolipin-induced structural rigidity of AAC regulates the number of conformations of ATP conducive for binding to the carrier. We also show that cardiolipins mildly preserve the three-fold pseudo-symmetry of the carrier.
  37. Adv Sci (Weinh). 2021 Nov 07. e2101553
      Metabolic disorder is one of the hallmarks of cancers, and reprogramming of metabolism is becoming a novel strategy for cancer treatment. Citrate is a key metabolite and critical metabolic regulator linking glycolysis and lipid metabolism in cellular energy homeostasis. Here it is reported that citrate treatment (both sodium citrate and citric acid) significantly suppresses tumor cell proliferation and growth in various tumor types. Mechanistically, citrate promotes excessive lipid biosynthesis and induces disruption of lipid metabolism in tumor cells, resulting in tumor cell senescence and growth inhibition. Furthermore, ATM-associated DNA damage response cooperates with MAPK and mTOR signaling pathways to control citrate-induced tumor cell growth arrest and senescence. In vivo studies further demonstrate that citrate administration dramatically inhibits tumor growth and progression in a colon cancer xenograft model. Importantly, citrate administration combined with the conventional chemotherapy drugs exhibits synergistic antitumor effects in vivo in the colon cancer models. These results clearly indicate that citrate can reprogram lipid metabolism and cell fate in cancer cells, and targeting citrate can be a promising therapeutic strategy for tumor treatment.
    Keywords:  DNA damage response; MAPK; apoptosis; cellular senescence; chemotherapy; citrate; lipid metabolism; mTOR
  38. J Am Chem Soc. 2021 Nov 10.
      Heat shock protein 90 (Hsp90) family proteins are molecular chaperones that modulate the functions of various substrate proteins (clients) implicated in pro-tumorigenic pathways. In this study, the mitochondria-targeted antioxidant mitoquinone (MitoQ) was identified as a potent inhibitor of mitochondrial Hsp90, known as a tumor necrosis factor receptor-associated protein 1 (TRAP1). Structural analyses revealed an asymmetric bipartite interaction between MitoQ and the previously unrecognized drug binding sites located in the middle domain of TRAP1, believed to be a client binding region. MitoQ effectively competed with TRAP1 clients, and MitoQ treatment facilitated the identification of 103 TRAP1-interacting mitochondrial proteins in cancer cells. MitoQ and its redox-crippled SB-U014/SB-U015 exhibited more potent anticancer activity in vitro and in vivo than previously reported mitochondria-targeted TRAP1 inhibitors. The findings indicate that targeting the client binding site of Hsp90 family proteins offers a novel strategy for the development of potent anticancer drugs.
  39. Cell. 2021 Nov 11. pii: S0092-8674(21)01235-6. [Epub ahead of print]184(23): 5693-5695
      The mitochondrial genome encodes proteins central to mitochondrial function; however, transcript-specific mechanistic studies of mitochondrial gene products have been difficult because of challenges in their experimental manipulation. Cruz-Zaragoza et al. provide a solution to this challenge, introducing an elegant system for efficient translational silencing of transcripts in human mitochondria.
  40. PLoS Comput Biol. 2021 Nov 11. 17(11): e1009594
    Regeneron Genetics Center
      The growing number of next-generation sequencing (NGS) data presents a unique opportunity to study the combined impact of mitochondrial and nuclear-encoded genetic variation in complex disease. Mitochondrial DNA variants and in particular, heteroplasmic variants, are critical for determining human disease severity. While there are approaches for obtaining mitochondrial DNA variants from NGS data, these software do not account for the unique characteristics of mitochondrial genetics and can be inaccurate even for homoplasmic variants. We introduce MitoScape, a novel, big-data, software for extracting mitochondrial DNA sequences from NGS. MitoScape adopts a novel departure from other algorithms by using machine learning to model the unique characteristics of mitochondrial genetics. We also employ a novel approach of using rho-zero (mitochondrial DNA-depleted) data to model nuclear-encoded mitochondrial sequences. We showed that MitoScape produces accurate heteroplasmy estimates using gold-standard mitochondrial DNA data. We provide a comprehensive comparison of the most common tools for obtaining mtDNA variants from NGS and showed that MitoScape had superior performance to compared tools in every statistically category we compared, including false positives and false negatives. By applying MitoScape to common disease examples, we illustrate how MitoScape facilitates important heteroplasmy-disease association discoveries by expanding upon a reported association between hypertrophic cardiomyopathy and mitochondrial haplogroup T in men (adjusted p-value = 0.003). The improved accuracy of mitochondrial DNA variants produced by MitoScape will be instrumental in diagnosing disease in the context of personalized medicine and clinical diagnostics.
  41. EMBO Mol Med. 2021 Nov 08. e14397
      Mitochondrial disorders are clinically and genetically diverse, with isolated complex III (CIII) deficiency being relatively rare. Here, we describe two affected cousins, presenting with recurrent episodes of severe lactic acidosis, hyperammonaemia, hypoglycaemia and encephalopathy. Genetic investigations in both cases identified a homozygous deletion of exons 2 and 3 of UQCRH, which encodes a structural complex III (CIII) subunit. We generated a mouse model with the equivalent homozygous Uqcrh deletion (Uqcrh-/- ), which also presented with lactic acidosis and hyperammonaemia, but had a more severe, non-episodic phenotype, resulting in failure to thrive and early death. The biochemical phenotypes observed in patient and Uqcrh-/- mouse tissues were remarkably similar, displaying impaired CIII activity, decreased molecular weight of fully assembled holoenzyme and an increase of an unexpected large supercomplex (SXL ), comprising mostly of one complex I (CI) dimer and one CIII dimer. This phenotypic similarity along with lentiviral rescue experiments in patient fibroblasts verifies the pathogenicity of the shared genetic defect, demonstrating that the Uqcrh-/- mouse is a valuable model for future studies of human CIII deficiency.
    Keywords:  OXPHOS; UQCRH; complex III; mitochondrial disease; mouse model
  42. Curr Biol. 2021 Nov 05. pii: S0960-9822(21)01495-0. [Epub ahead of print]
      Biological processes in all living cells are powered by ATP, a nearly universal molecule of energy transfer. ATP synthases produce ATP utilizing proton gradients that are usually generated by either respiration or photosynthesis. However, cyanobacteria are unique in combining photosynthetic and respiratory electron transport chains in the same membrane system, the thylakoids. How cyanobacteria prevent the futile reverse operation of ATP synthase under unfavorable conditions pumping protons while hydrolyzing ATP is mostly unclear. Here, we provide evidence that the small protein AtpΘ, which is widely conserved in cyanobacteria, is mainly fulfilling this task. The expression of AtpΘ becomes induced under conditions such as darkness or heat shock, which can lead to a weakening of the proton gradient. Translational fusions of AtpΘ to the green fluorescent protein revealed targeting to the thylakoid membrane. Immunoprecipitation assays followed by mass spectrometry and far western blots identified subunits of ATP synthase as interacting partners of AtpΘ. ATP hydrolysis assays with isolated membrane fractions, as well as purified ATP synthase complexes, demonstrated that AtpΘ inhibits ATPase activity in a dose-dependent manner similar to the F0F1-ATP synthase inhibitor N,N-dicyclohexylcarbodimide. The results show that, even in a well-investigated process, crucial new players can be discovered if small proteins are taken into consideration and indicate that ATP synthase activity can be controlled in surprisingly different ways.
    Keywords:  F(0)F(1) ATP synthase; Nostoc; Synechocystis; cyanobacteria; inhibitor; proton gradient; redox regulation; small proteins; thylakoid membranes