bims-camemi Biomed News
on Mitochondrial metabolism in cancer
Issue of 2019‒09‒22
forty-nine papers selected by
Christian Frezza
University of Cambridge, MRC Cancer Unit


  1. Nature. 2019 Sep 18.
    Morris JP, Yashinskie JJ, Koche R, Chandwani R, Tian S, Chen CC, Baslan T, Marinkovic ZS, Sánchez-Rivera FJ, Leach SD, Carmona-Fontaine C, Thompson CB, Finley LWS, Lowe SW.
      The tumour suppressor TP53 is mutated in the majority of human cancers, and in over 70% of pancreatic ductal adenocarcinoma (PDAC)1,2. Wild-type p53 accumulates in response to cellular stress, and regulates gene expression to alter cell fate and prevent tumour development2. Wild-type p53 is also known to modulate cellular metabolic pathways3, although p53-dependent metabolic alterations that constrain cancer progression remain poorly understood. Here we find that p53 remodels cancer-cell metabolism to enforce changes in chromatin and gene expression that favour a premalignant cell fate. Restoring p53 function in cancer cells derived from KRAS-mutant mouse models of PDAC leads to the accumulation of α-ketoglutarate (αKG, also known as 2-oxoglutarate), a metabolite that also serves as an obligate substrate for a subset of chromatin-modifying enzymes. p53 induces transcriptional programs that are characteristic of premalignant differentiation, and this effect can be partially recapitulated by the addition of cell-permeable αKG. Increased levels of the αKG-dependent chromatin modification 5-hydroxymethylcytosine (5hmC) accompany the tumour-cell differentiation that is triggered by p53, whereas decreased 5hmC characterizes the transition from premalignant to de-differentiated malignant lesions that is associated with mutations in Trp53. Enforcing the accumulation of αKG in p53-deficient PDAC cells through the inhibition of oxoglutarate dehydrogenase-an enzyme of the tricarboxylic acid cycle-specifically results in increased 5hmC, tumour-cell differentiation and decreased tumour-cell fitness. Conversely, increasing the intracellular levels of succinate (a competitive inhibitor of αKG-dependent dioxygenases) blunts p53-driven tumour suppression. These data suggest that αKG is an effector of p53-mediated tumour suppression, and that the accumulation of αKG in p53-deficient tumours can drive tumour-cell differentiation and antagonize malignant progression.
    DOI:  https://doi.org/10.1038/s41586-019-1577-5
  2. Mol Cell Oncol. 2019 ;6(5): e1536843
    Alkan HF, Bogner-Strauss JG.
      Cancer cells rely on glutamine to fuel mitochondria, however it remains unclear whether this is needed for bioenergetic or biosynthetic pathways. Our study suggests that an essential function of mitochondrial glutamine metabolism is to provide aspartate to the cytosol where it can be used for nucleotide and protein synthesis.
    Keywords:  AGC1; Aralar; CB-839; Glutamine; Slc25a12; TCA cycle; aspartate; aspartate-glutamate carrier; cancer metabolism; mitochondrial transporters; targeting metabolism
    DOI:  https://doi.org/10.1080/23723556.2018.1536843
  3. Autophagy. 2019 Sep 19. 1-14
    Zheng L, Shu WJ, Li YM, Mari M, Yan C, Wang D, Yin ZH, Jiang W, Zhou Y, Okamoto K, Reggiori F, Klionsky DJ, Song Z, Du HN.
      Mitophagy is a critical process that safeguards mitochondrial quality control in order to maintain proper cellular homeostasis. Although the mitochondrial-anchored receptor Atg32-mediated cargo-recognition system has been well characterized to be essential for this process, the signaling pathway modulating its expression as a contribution of governing the mitophagy process remains largely unknown. Here, bioinformatics analyses of epigenetic or transcriptional regulators modulating gene expression allow us to identify the Paf1 complex (the polymerase-associated factor 1 complex, Paf1C) as a transcriptional repressor of ATG genes. We show that Paf1C suppresses glucose starvation-induced autophagy, but does not affect nitrogen starvation- or rapamycin-induced autophagy. Moreover, we show that Paf1C specifically regulates mitophagy through modulating ATG32 expression. Deletion of the genes encoding two core subunits of Paf1C, Paf1 and Ctr9, increases ATG32 and ATG11 expression and facilitates mitophagy activity. Although Paf1C is required for many histone modifications and gene activation, we show that Paf1C regulates mitophagy independent of its positive regulatory role in other processes. More importantly, we also demonstrate the mitophagic role of PAF1C in mammals. Overall, we conclude that Paf1C maintains mitophagy at a low level through binding the promoter of the ATG32 gene in glucose-rich conditions. Dissociation of Paf1C from ATG32 leads to the increased expression of this gene, and mitophagy induction upon glucose starvation. Thus, we uncover a new role of Paf1C in modulating the mitophagy process at the transcriptional level. Abbreviations: AMPK: AMP-activated protein kinase; ATP5F1A: ATP synthase F1 subunit alpha; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CCCP: chlorophenylhydrazone; DFP: chelator deferiprone; GFP: green fluorescent protein; H2B-Ub1: H2B monoubiquitination; HSPD1/HSP60: heat shock protein family D (Hsp60) member 1; KD: kinase dead; OPTN, optineurin; Paf1: polymerase-associated factor 1; PINK1: PTEN induced kinase 1; PRKN/Parkin: parkin RBR E3 ubiquitin protein ligase; RT-qPCR: real-time quantitative PCR; SD-N: synthetic dropout without nitrogen base; TIMM23: translocase of inner mitochondrial membrane 23; TOMM20: translocase of outer mitochondrial membrane 20; WT: wild-type; YPD: yeast extract peptone dextrose; YPL: yeast extract peptone lactate.
    Keywords:  Atg32; Paf1 complex; glucose starvation; mitophagy; transcription
    DOI:  https://doi.org/10.1080/15548627.2019.1668228
  4. Oncogene. 2019 Sep 20.
    Dias MM, Adamoski D, Dos Reis LM, Ascenção CFR, de Oliveira KRS, Mafra ACP, da Silva Bastos AC, Quintero M, de G Cassago C, Ferreira IM, Fidelis CHV, Rocco SA, Bajgelman MC, Stine Z, Berindan-Neagoe I, Calin GA, Ambrosio ALB, Dias SMG.
      Many types of cancers have a well-established dependence on glutamine metabolism to support survival and growth, a process linked to glutaminase 1 (GLS) isoforms. Conversely, GLS2 variants often have tumor-suppressing activity. Triple-negative (TN) breast cancer (testing negative for estrogen, progesterone, and Her2 receptors) has elevated GLS protein levels and reportedly depends on exogenous glutamine and GLS activity for survival. Despite having high GLS levels, we verified that several breast cancer cells (including TN cells) express endogenous GLS2, defying its role as a bona fide tumor suppressor. Moreover, ectopic GLS2 expression rescued cell proliferation, TCA anaplerosis, redox balance, and mitochondrial function after GLS inhibition by the small molecule currently in clinical trials CB-839 or GLS knockdown of GLS-dependent cell lines. In several cell lines, GLS2 knockdown decreased cell proliferation and glutamine-linked metabolic phenotypes. Strikingly, long-term treatment of TN cells with another GLS-exclusive inhibitor bis-2'-(5-phenylacetamide-1,3,4-thiadiazol-2-yl)ethyl sulfide (BPTES) selected for a drug-resistant population with increased endogenous GLS2 and restored proliferative capacity. GLS2 was linked to enhanced in vitro cell migration and invasion, mesenchymal markers (through the ERK-ZEB1-vimentin axis under certain conditions) and in vivo lung metastasis. Of concern, GLS2 amplification or overexpression is linked to an overall, disease-free and distant metastasis-free worse survival prognosis in breast cancer. Altogether, these data establish an unforeseen role of GLS2 in sustaining tumor proliferation and underlying metastasis in breast cancer and provide an initial framework for exploring GLS2 as a novel therapeutic target.
    DOI:  https://doi.org/10.1038/s41388-019-1007-z
  5. FASEB J. 2019 Sep 17. fj201901117RR
    Zhang R, Hou T, Cheng H, Wang X.
      Mitochondria are fundamental organelles for cellular and systemic metabolism, and their dysfunction has been implicated in the development of diverse metabolic diseases. Boosted mitochondrial metabolism might be able to protect against metabolic stress and prevent metabolic disorders. Here we show that NADH:ubiquinone oxidoreductase (NDU)-FAB1, also known as mitochondrial acyl carrier protein, acts as a novel enhancer of mitochondrial metabolism and protects against obesity and insulin resistance. Mechanistically, NDUFAB1 coordinately enhances lipoylation and activation of pyruvate dehydrogenase mediated by the mitochondrial fatty acid synthesis pathway and increases the assembly of respiratory complexes and supercomplexes. Skeletal muscle-specific ablation of NDUFAB1 causes systemic disruption of glucose homeostasis and defective insulin signaling, leading to growth arrest and early death within 5 postnatal days. In contrast, NDUFAB1 overexpression effectively protects mice against obesity and insulin resistance when the animals are challenged with a high-fat diet. Our findings indicate that NDUFAB1 could be a novel mitochondrial target to prevent obesity and insulin resistance by enhancing mitochondrial metabolism.-Zhang, R., Hou, T., Cheng, H., Wang, X. NDUFAB1 protects against obesity and insulin resistance by enhancing mitochondrial metabolism.
    Keywords:  metabolic disorder; mitochondrial respiratory complexes; pyruvate dehydrogenase; respiratory supercomplexes
    DOI:  https://doi.org/10.1096/fj.201901117RR
  6. Circulation. 2019 Sep 19.
    Lambert JP, Luongo TS, Tomar D, Jadiya P, Gao E, Zhang X, Lucchese AM, Kolmetzky DW, Shah NS, Elrod JW.
      Background: The mitochondrial calcium uniporter (mtCU) is a ~700 kD multi-subunit channel residing in the inner mitochondrial membrane (IMM) required for mitochondrial Ca2+ (mCa2+) uptake. Here we detail the contribution of MCUB, a paralog of the pore-forming subunit - MCU, in mtCU regulation and function and for the first time investigate MCUB's relevance to cardiac physiology. Methods: We created a stable MCUB knockout cell line (MCUB-/-) utilizing CRISPR-Cas9n technology and generated a cardiac-specific, tamoxifen-inducible MCUB mutant mouse (CAG-CAT-MCUB x MCM; MCUB-Tg) for in vivo assessment of cardiac physiology and response to ischemia-reperfusion (IR) injury. Live cell imaging and high-resolution spectrofluorometery were employed to determine intracellular Ca2+ exchange and size-exclusion chromatography, blue native page and immunoprecipitation studies were utilized to determine the molecular function and impact of MCUB on the high-molecular weight mtCU complex. Results: Using genetic gain- and loss-of-function approaches we show that MCUB expression displaces MCU from the functional mtCU complex and thereby decreases the association of MICU1 and MICU2 to alter channel gating. These molecular changes decrease MICU1/2-dependent cooperative activation of the mtCU thereby decreasing mCa2+ uptake. Further, we show that MCUB incorporation into the mtCU is a stress-responsive mechanism to limit mCa2+ overload during cardiac injury. Indeed, overexpression of MCUB is sufficient to decrease infarct size following IR injury. However, MCUB incorporation into the mtCU does come at a cost, as acute decreases in mCa2+ uptake impairs mitochondrial energetics and contractile function. Conclusions: In summary, we detail a new regulatory mechanism to modulate mtCU function and mCa2+ uptake. Our results suggest that MCUB-dependent changes in mtCU stoichiometry is a prominent regulatory mechanism to modulate mCa2+ uptake and cellular physiology.
    Keywords:  MCU; MCUB; MICU1; mitochondrial calcium uniporter channel; oxidative phosphorylation
    DOI:  https://doi.org/10.1161/CIRCULATIONAHA.118.037968
  7. Nat Rev Cancer. 2019 Sep 17.
    Lien EC, Vander Heiden MG.
      The way cancer cells utilize nutrients to support their growth and proliferation is determined by cancer cell-intrinsic and cancer cell-extrinsic factors, including interactions with the environment. These interactions can define therapeutic vulnerabilities and impact the effectiveness of cancer therapy. Diet-mediated changes in whole-body metabolism and systemic nutrient availability can affect the environment that cancer cells are exposed to within tumours, and a better understanding of how diet modulates nutrient availability and utilization by cancer cells is needed. How diet impacts cancer outcomes is also of great interest to patients, yet clear evidence for how diet interacts with therapy and impacts tumour growth is lacking. Here we propose an experimental framework to probe the connections between diet and cancer metabolism. We examine how dietary factors may affect tumour growth by altering the access to and utilization of nutrients by cancer cells. Our growing understanding of how certain cancer types respond to various diets, how diet impacts cancer cell metabolism to mediate these responses and whether dietary interventions may constitute new therapeutic opportunities will begin to provide guidance on how best to use diet and nutrition to manage cancer in patients.
    DOI:  https://doi.org/10.1038/s41568-019-0198-5
  8. Sci Signal. 2019 Sep 17. pii: eaav3334. [Epub ahead of print]12(599):
    Dimeloe S, Gubser P, Loeliger J, Frick C, Develioglu L, Fischer M, Marquardsen F, Bantug GR, Thommen D, Lecoultre Y, Zippelius A, Langenkamp A, Hess C.
      Transforming growth factor-β (TGF-β) is produced by tumors, and increased amounts of this cytokine in the tumor microenvironment and serum are associated with poor patient survival. TGF-β-mediated suppression of antitumor T cell responses contributes to tumor growth and survival. However, TGF-β also has tumor-suppressive activity; thus, dissecting cell type-specific molecular effects may inform therapeutic strategies targeting this cytokine. Here, using human peripheral and tumor-associated lymphocytes, we investigated how tumor-derived TGF-β suppresses a key antitumor function of CD4+ T cells, interferon-γ (IFN-γ) production. Suppression required the expression and phosphorylation of Smad proteins in the TGF-β signaling pathway, but not their nuclear translocation, and depended on oxygen availability, suggesting a metabolic basis for these effects. Smad proteins were detected in the mitochondria of CD4+ T cells, where they were phosphorylated upon treatment with TGF-β. Phosphorylated Smad proteins were also detected in the mitochondria of isolated tumor-associated lymphocytes. TGF-β substantially impaired the ATP-coupled respiration of CD4+ T cells and specifically inhibited mitochondrial complex V (ATP synthase) activity. Last, inhibition of ATP synthase alone was sufficient to impair IFN-γ production by CD4+ T cells. These results, which have implications for human antitumor immunity, suggest that TGF-β targets T cell metabolism directly, thus diminishing T cell function through metabolic paralysis.
    DOI:  https://doi.org/10.1126/scisignal.aav3334
  9. Sci Adv. 2019 Sep;5(9): eaax1978
    Oleinik N, Kim J, Roth BM, Selvam SP, Gooz M, Johnson RH, Lemasters JJ, Ogretmen B.
      How lipid metabolism is regulated at the outer mitochondrial membrane (OMM) for transducing stress signaling remains largely unknown. We show here that this process is controlled by trafficking of ceramide synthase 1 (CerS1) from the endoplasmic reticulum (ER) to the OMM by a previously uncharacterized p17, which is now renamed protein that mediates ER-mitochondria trafficking (PERMIT). Data revealed that p17/PERMIT associates with newly translated CerS1 on the ER surface to mediate its trafficking to the OMM. Cellular stress induces Drp1 nitrosylation/activation, releasing p17/PERMIT to retrieve CerS1 for its OMM trafficking, resulting in mitochondrial ceramide generation, mitophagy and cell death. In vivo, CRISPR-Cas9-dependent genetic ablation of p17/PERMIT prevents acute stress-mediated CerS1 trafficking to OMM, attenuating mitophagy in p17/PERMIT-/- mice, compared to controls, in various metabolically active tissues, including brain, muscle, and pancreas. Thus, these data have implications in diseases associated with accumulation of damaged mitochondria such as cancer and/or neurodegeneration.
    DOI:  https://doi.org/10.1126/sciadv.aax1978
  10. FASEB J. 2019 Sep 17. fj201901366R
    Wang Y, Agarwal E, Bertolini I, Ghosh JC, Seo JH, Altieri DC.
      The role of mitochondria in cancer continues to be debated and paradoxically implicated in opposing functions in tumor growth and tumor suppression. To understand this dichotomy, we explored the function of mitochondrial isocitrate dehydrogenase (IDH)2, a tricarboxylic acid cycle enzyme mutated in subsets of acute leukemias and gliomas, in cancer. Silencing of IDH2 in prostate cancer cells impaired oxidative bioenergetics, elevated reactive oxygen species (ROS) production, and promoted exaggerated mitochondrial dynamics. This was associated with increased subcellular mitochondrial trafficking, turnover of membrane focal adhesion complexes, and enhanced tumor cell migration and invasion, without changes in cell cycle progression. Mechanistically, loss of IDH2 caused ROS-dependent stabilization of hypoxia-inducible factor-1α in normoxia, which was required for increased mitochondrial trafficking and tumor cell movements. Therefore, IDH2 is a dual regulator of cancer bioenergetics and tumor cell motility. This pathway may reprogram mitochondrial dynamics to differentially adjust energy production or promote tumor cell invasion in response to microenvironment conditions.-Wang, Y., Agarwal, E., Bertolini, I., Ghosh, J. C., Seo, J. H., Altieri, D. C. IDH2 reprograms mitochondrial dynamics in cancer through a HIF-1α-regulated pseudohypoxic state.
    Keywords:  HIF-1α metastasis; ROS; mitochondria; tumor cell motility
    DOI:  https://doi.org/10.1096/fj.201901366R
  11. Cell Metab. 2019 Aug 29. pii: S1550-4131(19)30443-7. [Epub ahead of print]
    Sun RC, Dukhande VV, Zhou Z, Young LEA, Emanuelle S, Brainson CF, Gentry MS.
      Nuclear glycogen was first documented in the early 1940s, but its role in cellular physiology remained elusive. In this study, we utilized pure nuclei preparations and stable isotope tracers to define the origin and metabolic fate of nuclear glycogen. Herein, we describe a key function for nuclear glycogen in epigenetic regulation through compartmentalized pyruvate production and histone acetylation. This pathway is altered in human non-small cell lung cancers, as surgical specimens accumulate glycogen in the nucleus. We demonstrate that the decreased abundance of malin, an E3 ubiquitin ligase, impaired nuclear glycogenolysis by preventing the nuclear translocation of glycogen phosphorylase and causing nuclear glycogen accumulation. Re-introduction of malin in lung cancer cells restored nuclear glycogenolysis, increased histone acetylation, and decreased growth of cancer cells transplanted into mice. This study uncovers a previously unknown role for glycogen metabolism in the nucleus and elucidates another mechanism by which cellular metabolites control epigenetic regulation.
    Keywords:  E3 ubiquitin ligase; EPM2B; Lafora disease; NHLRC1; glycogen; glycogen phosphorylase; histone acetylation; malin; non-small cell lung cancer; nuclear metabolism
    DOI:  https://doi.org/10.1016/j.cmet.2019.08.014
  12. Sci Adv. 2019 Sep;5(9): eaax8352
    Heden TD, Johnson JM, Ferrara PJ, Eshima H, Verkerke ARP, Wentzler EJ, Siripoksup P, Narowski TM, Coleman CB, Lin CT, Ryan TE, Reidy PT, de Castro Brás LE, Karner CM, Burant CF, Maschek JA, Cox JE, Mashek DG, Kardon G, Boudina S, Zeczycki TN, Rutter J, Shaikh SR, Vance JE, Drummond MJ, Neufer PD, Funai K.
      Exercise capacity is a strong predictor of all-cause mortality. Skeletal muscle mitochondrial respiratory capacity, its biggest contributor, adapts robustly to changes in energy demands induced by contractile activity. While transcriptional regulation of mitochondrial enzymes has been extensively studied, there is limited information on how mitochondrial membrane lipids are regulated. Here, we show that exercise training or muscle disuse alters mitochondrial membrane phospholipids including phosphatidylethanolamine (PE). Addition of PE promoted, whereas removal of PE diminished, mitochondrial respiratory capacity. Unexpectedly, skeletal muscle-specific inhibition of mitochondria-autonomous synthesis of PE caused respiratory failure because of metabolic insults in the diaphragm muscle. While mitochondrial PE deficiency coincided with increased oxidative stress, neutralization of the latter did not rescue lethality. These findings highlight the previously underappreciated role of mitochondrial membrane phospholipids in dynamically controlling skeletal muscle energetics and function.
    DOI:  https://doi.org/10.1126/sciadv.aax8352
  13. Cell Rep. 2019 Sep 17. pii: S2211-1247(19)31074-5. [Epub ahead of print]28(12): 3011-3021.e4
    Ron-Harel N, Ghergurovich JM, Notarangelo G, LaFleur MW, Tsubosaka Y, Sharpe AH, Rabinowitz JD, Haigis MC.
      T cell stimulation is metabolically demanding. To exit quiescence, T cells rely on environmental nutrients, including glucose and the amino acids glutamine, leucine, serine, and arginine. The expression of transporters for these nutrients is tightly regulated and required for T cell activation. In contrast to these amino acids, which are essential or require multi-step biosynthesis, alanine can be made from pyruvate by a single transamination. Here, we show that extracellular alanine is nevertheless required for efficient exit from quiescence during naive T cell activation and memory T cell restimulation. Alanine deprivation leads to metabolic and functional impairments. Mechanistically, this vulnerability reflects the low expression of alanine aminotransferase, the enzyme required for interconverting pyruvate and alanine, whereas activated T cells instead induce alanine transporters. Stable isotope tracing reveals that alanine is not catabolized but instead supports protein synthesis. Thus, T cells depend on exogenous alanine for protein synthesis and normal activation.
    Keywords:  T cell activation; T cells; alanine; metabolism; protein synthesis
    DOI:  https://doi.org/10.1016/j.celrep.2019.08.034
  14. J Immunol. 2019 Sep 20. pii: ji1801604. [Epub ahead of print]
    Wedel J, Stack MP, Seto T, Sheehan MM, Flynn EA, Stillman IE, Kong SW, Liu K, Briscoe DM.
      The T cell-specific adaptor protein (TSAd), encoded by the SH2D2A gene, is an intracellular molecule that binds Lck to elicit signals that result in cytokine production in CD4+ T effector cells (Teff). Nevertheless, using Sh2d2a knockout (KO; also called TSAd-/-) mice, we find that alloimmune CD4+ Teff responses are fully competent in vivo. Furthermore, and contrary to expectations, we find that allograft rejection is accelerated in KO recipients of MHC class II-mismatched B6.C-H-2bm12 heart transplants versus wild-type (WT) recipients. Also, KO recipients of fully MHC-mismatched cardiac allografts are resistant to the graft-prolonging effects of costimulatory blockade. Using adoptive transfer models, we find that KO T regulatory cells (Tregs) are less efficient in suppressing Teff function and they produce IFN-γ following mitogenic activation. In addition, pyrosequencing demonstrated higher levels of methylation of CpG regions within the Treg-specific demethylated region of KO versus WT Tregs, suggesting that TSAd, in part, promotes Treg stability. By Western blot, Lck is absent in the mitochondria of KO Tregs, and reactive oxygen species production by mitochondria is reduced in KO versus WT Tregs. Full transcriptomic analysis demonstrated that the key mechanism of TSAd function in Tregs relates to its effects on cellular activation rather than intrinsic effects on mitochondria/metabolism. Nevertheless, KO Tregs compensate for a lack of activation by increasing the number of mitochondria per cell. Thus, TSAd serves as a critical cell-intrinsic molecule in CD4+Foxp3+ Tregs to regulate the translocation of Lck to mitochondria, cellular activation responses, and the development of immunoregulation following solid organ transplantation.
    DOI:  https://doi.org/10.4049/jimmunol.1801604
  15. Immunity. 2019 Sep 17. pii: S1074-7613(19)30364-4. [Epub ahead of print]51(3): 491-507.e7
    Li C, Zhu B, Son YM, Wang Z, Jiang L, Xiang M, Ye Z, Beckermann KE, Wu Y, Jenkins JW, Siska PJ, Vincent BG, Prakash YS, Peikert T, Edelson BT, Taneja R, Kaplan MH, Rathmell JC, Dong H, Hitosugi T, Sun J.
      Tissue-resident memory CD8+ T (Trm) cells share core residency gene programs with tumor-infiltrating lymphocytes (TILs). However, the transcriptional, metabolic, and epigenetic regulation of Trm cell and TIL development and function is largely undefined. Here, we found that the transcription factor Bhlhe40 was specifically required for Trm cell and TIL development and polyfunctionality. Local PD-1 signaling inhibited TIL Bhlhe40 expression, and Bhlhe40 was critical for TIL reinvigoration following anti-PD-L1 blockade. Mechanistically, Bhlhe40 sustained Trm cell and TIL mitochondrial fitness and a functional epigenetic state. Building on these findings, we identified an epigenetic and metabolic regimen that promoted Trm cell and TIL gene signatures associated with tissue residency and polyfunctionality. This regimen empowered the anti-tumor activity of CD8+ T cells and possessed therapeutic potential even at an advanced tumor stage in mouse models. Our results provide mechanistic insights into the local regulation of Trm cell and TIL function.
    Keywords:  Bhlhe40; PD-L1; Tubastatin A; acetate; epigenetic; metabolism; mitochondria; tissue resident memory T cell; tumor-infiltrating lymphocytes
    DOI:  https://doi.org/10.1016/j.immuni.2019.08.013
  16. Free Radic Biol Med. 2019 Sep 13. pii: S0891-5849(19)31247-X. [Epub ahead of print]
    Corrêa da Silva F, Favero de Aguiar C, Pereira JAS, de Brito Monteiro L, Davanzo GG, Codo AC, Pimentel de Freitas L, Berti AS, Ferruci D, Castelucci BG, Consonni SR, Carvalho HF, Moraes-Vieira PMM.
      Over the past years, systemic derived cues that regulate cellular metabolism have been implicated in the regulation of immune responses. Ghrelin is an orexigenic hormone produced by enteroendocrine cells in the gastric mucosa with known immunoregulatory roles. The mechanism behind the function of ghrelin in immune cells, such as macrophages, is still poorly understood. Here, we explored the hypothesis that ghrelin leads to alterations in macrophage metabolism thus modulating macrophage function. We demonstrated that ghrelin exerts an immunomodulatory effect over LPS-activated peritoneal macrophages, as evidenced by inhibition of TNF-α and IL-1β secretion and increased IL-12 production. Concomitantly, ghrelin increased mitochondrial membrane potential and increased respiratory rate. In agreement, ghrelin prevented LPS-induced ultrastructural damage in the mitochondria. Ghrelin also blunted LPS-induced glycolysis. In LPS-activated macrophages, glucose deprivation did not affect ghrelin-induced IL-12 secretion, whereas the inhibition of pyruvate transport and mitochondria-derived ATP abolished ghrelin-induced IL-12 secretion, indicating a dependence on mitochondrial function. Ghrelin pre-treatment of metabolic activated macrophages inhibited the secretion of TNF-α and enhanced IL-12 levels. Moreover, ghrelin effects on IL-12 are and not on TNF-α are dependent on mitochondria elongation, since ghrelin did not enhance IL-12 secretion in metabolic activated mitofusin-2 deficient macrophages. Thus, ghrelin affects macrophage mitochondrial metabolism and the subsequent macrophage function.
    DOI:  https://doi.org/10.1016/j.freeradbiomed.2019.09.012
  17. Mitochondrion. 2019 Sep 14. pii: S1567-7249(19)30151-5. [Epub ahead of print]
    Zhang Z, Sliter DA, Bleck CKE, Ding S.
      Mitochondrial dynamics and mitophagy are important aspects of mitochondrial quality control, and are linked to neurodegenerative diseases and muscular diseases. Fis1, a protein on the mitochondrial outer membrane, is thought to mediate mitochondrial fission. However, Fis1 null worms and mammalian cells only display mild fission defects but show aberrant mitophagy. To assess Fis1 function in vivo, we generated conditional knock-out Fis1 mice to allow for specific Fis1 deletion in adult skeletal muscle. In the absence of Fis1 in Type I muscle, mitochondrial hyperfusion, respiratory chain deficiency, and increased mitophagy were found. Moreover, abnormal mitophagy was aggravated by endurance exhaustive exercise stress (EEE), suggesting that Fis1 is involved in maintaining normal mitophagy in mitochondria-rich Type I muscle during exercise. Additionally, Fis1 loss induced delayed onset muscle ultrastructure change (DOMUC) in Type I muscle and strong inflammation in response to acute exhaustive exercise (EE). Thus, we identify a role for Fis1 in maintaining normal mitochondrial structure and function at rest and under exercise stress.
    Keywords:  Exhaustive exercise; Fis1; Inflammation response; Mitochondrial dynamics; Mitophagy
    DOI:  https://doi.org/10.1016/j.mito.2019.09.005
  18. J Biol Chem. 2019 Sep 18. pii: jbc.RA119.008202. [Epub ahead of print]
    Yu R, Liu T, Ning C, Tan F, Jin SB, Lendahl U, Zhao J, Nistér M.
      Recruitment of the GTPase dynamin-related protein 1 (Drp1) to mitochondria is a central step required for mitochondrial fission. Reversible Drp1 phosphorylation has been implicated in the regulation of this process, butwhether Drp1 phosphorylation at Ser-637 determines its subcellular localization and fission activity remains to be fully elucidated. Here, using HEK 293T cells and immunofluorescence, immunoblotting, RNA interference, subcellular fractionation, co-immunoprecipitation assays, and CRISPR/Cas9 genome editing,we show that Drp1 phosphorylated at Ser-637 (Drp1pS637) resides both in the cytosol and on mitochondria. We found that the receptorsmitochondrial fission factor (Mff) and mitochondrial elongation factor 1/2 (MIEF1/2) interact with and recruit Drp1pS637to mitochondria and that elevated Mff or MIEF levels promote Drp1pS637accumulation on mitochondria. We also noted that protein kinase A (PKA), which mediates phosphorylation of Drp1 on Ser-637, is partially present on mitochondria and interacts with both MIEFs and Mff. PKA knockdown did not affect the Drp1-Mff interaction, but slightly enhanced the interaction between Drp1 and MIEFs. In Drp1-deficient HEK 293T cells, both phosphomimetic Drp1-S637D and phospho-deficient Drp1-S637A variants, like wild-type Drp1, located to the cytosol and to mitochondria and rescued a Drp1 deficiency-induced mitochondrial hyperfusion phenotype. However, Drp1-S637D was less efficient than Drp1-WT and Drp1-S637A in inducing mitochondrial fission. In conclusion, the Ser-637 phosphorylation status in Drp1 is not a determinant that controls Drp1 recruitment to mitochondria.
    Keywords:  dynamin-related protein 1 (Drp1); membrane protein; membrane transport; mitochondria; mitochondrial dynamics; mitochondrial elongation factor 1/2 (MIEF1/2); mitochondrial fission factor (Mff); mitochondrial metabolism; molecular dynamics; phosphorylation; signal transduction
    DOI:  https://doi.org/10.1074/jbc.RA119.008202
  19. Cell Rep. 2019 Sep 17. pii: S2211-1247(19)31065-4. [Epub ahead of print]28(12): 3199-3211.e5
    Du C, Hansen LJ, Singh SX, Wang F, Sun R, Moure CJ, Roso K, Greer PK, Yan H, He Y.
      H2AX safeguards genomic stability in a dose-dependent manner; however, mechanisms governing its proteostasis are poorly understood. Here, we identify a PRMT5-RNF168-SMURF2 cascade that regulates H2AX proteostasis. We show that PRMT5 sustains the expression of RNF168, an E3 ubiquitin ligase essential for DNA damage response (DDR). Suppression of PRMT5 occurs in methylthioadenosine phosphorylase (MTAP)-deficient glioblastoma cells and attenuates the expression of RNF168, leading to destabilization of H2AX by E3 ubiquitin ligase SMURF2. RNF168 and SMURF2 serve as a stabilizer and destabilizer of H2AX, respectively, via their dynamic interactions with H2AX. In supporting an important role of this signaling cascade in regulating H2AX, MTAP-deficient glioblastoma cells display higher levels of DNA damage spontaneously or in response to genotoxic agents. These findings reveal a regulatory mechanism of H2AX proteostasis and define a signaling cascade that is essential to DDR and that is disrupted by the loss of a metabolic enzyme in tumor cells.
    Keywords:  H2AX; MTAP; PRMT5; RNF168; SMURF2; glioblastoma
    DOI:  https://doi.org/10.1016/j.celrep.2019.08.031
  20. Biochim Biophys Acta Biomembr. 2019 Sep 12. pii: S0005-2736(19)30210-X. [Epub ahead of print] 183064
    Camilleri A, Ghio S, Caruana M, Weckbecker D, Schmidt F, Kamp F, Leonov A, Ryazanov S, Griesinger C, Giese A, Cauchi RJ, Vassallo N.
      Misfolding and aggregate formation by the tau protein has been closely related with neurotoxicity in a large group of human neurodegenerative disorders, which includes Alzheimer's disease. Here, we investigate the membrane-active properties of tau oligomers on mitochondrial membranes, using minimalist in vitro model systems. Thus, exposure of isolated mitochondria to oligomeric tau evoked a disruption of mitochondrial membrane integrity, as evidenced by a combination of organelle swelling, efflux of cytochrome c and loss of the mitochondrial membrane potential. Tau-induced mitochondrial dysfunction occurred independently of the mitochondrial permeability transition (mPT) pore complex. Notably, mitochondria were rescued by pre-incubation with 10-N-nonyl acridine orange (NAO), a molecule that specifically binds cardiolipin (CL), the signature phospholipid of mitochondrial membranes. Additionally, NAO prevented direct binding of tau oligomers to isolated mitochondria. At the same time, tau proteins exhibited high affinity to CL-enriched membranes, whilst permeabilisation of lipid vesicles also strongly correlated with CL content. Intriguingly, using single-channel electrophysiology, we could demonstrate the formation of non-selective ion-conducting tau nanopores exhibiting multilevel conductances in mito-mimetic bilayers. Taken together, the data presented here advances a scenario in which toxic cytosolic entities of tau protein would target mitochondrial organelles by associating with their CL-rich membrane domains, leading to membrane poration and compromised mitochondrial structural integrity.
    Keywords:  Cardiolipin; Membrane permeabilisation; Mitochondria; Nanopores; Oligomers; Tau
    DOI:  https://doi.org/10.1016/j.bbamem.2019.183064
  21. Nat Commun. 2019 Sep 20. 10(1): 4320
    Stangl A, Elliott PR, Pinto-Fernandez A, Bonham S, Harrison L, Schaub A, Kutzner K, Keusekotten K, Pfluger PT, El Oualid F, Kessler BM, Komander D, Krappmann D.
      OTULIN (OTU Deubiquitinase With Linear Linkage Specificity) specifically hydrolyzes methionine1 (Met1)-linked ubiquitin chains conjugated by LUBAC (linear ubiquitin chain assembly complex). Here we report on the mass spectrometric identification of the OTULIN interactor SNX27 (sorting nexin 27), an adaptor of the endosomal retromer complex responsible for protein recycling to the cell surface. The C-terminal PDZ-binding motif (PDZbm) in OTULIN associates with the cargo-binding site in the PDZ domain of SNX27. By solving the structure of the OTU domain in complex with the PDZ domain, we demonstrate that a second interface contributes to the selective, high affinity interaction of OTULIN and SNX27. SNX27 does not affect OTULIN catalytic activity, OTULIN-LUBAC binding or Met1-linked ubiquitin chain homeostasis. However, via association, OTULIN antagonizes SNX27-dependent cargo loading, binding of SNX27 to the VPS26A-retromer subunit and endosome-to-plasma membrane trafficking. Thus, we define an additional, non-catalytic function of OTULIN in the regulation of SNX27-retromer assembly and recycling to the cell surface.
    DOI:  https://doi.org/10.1038/s41467-019-12309-z
  22. Proc Natl Acad Sci U S A. 2019 Sep 16. pii: 201908271. [Epub ahead of print]
    Lipper CH, Stofleth JT, Bai F, Sohn YS, Roy S, Mittler R, Nechushtai R, Onuchic JN, Jennings PA.
      MitoNEET is an outer mitochondrial membrane protein essential for sensing and regulation of iron and reactive oxygen species (ROS) homeostasis. It is a key player in multiple human maladies including diabetes, cancer, neurodegeneration, and Parkinson's diseases. In healthy cells, mitoNEET receives its clusters from the mitochondrion and transfers them to acceptor proteins in a process that could be altered by drugs or during illness. Here, we report that mitoNEET regulates the outer-mitochondrial membrane (OMM) protein voltage-dependent anion channel 1 (VDAC1). VDAC1 is a crucial player in the cross talk between the mitochondria and the cytosol. VDAC proteins function to regulate metabolites, ions, ROS, and fatty acid transport, as well as function as a "governator" sentry for the transport of metabolites and ions between the cytosol and the mitochondria. We find that the redox-sensitive [2Fe-2S] cluster protein mitoNEET gates VDAC1 when mitoNEET is oxidized. Addition of the VDAC inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS) prevents both mitoNEET binding in vitro and mitoNEET-dependent mitochondrial iron accumulation in situ. We find that the DIDS inhibitor does not alter the redox state of MitoNEET. Taken together, our data indicate that mitoNEET regulates VDAC in a redox-dependent manner in cells, closing the pore and likely disrupting VDAC's flow of metabolites.
    Keywords:  CISD1; VDAC1; direct coupling; ferroptosis; mitoNEET
    DOI:  https://doi.org/10.1073/pnas.1908271116
  23. Nat Metab. 2019 Apr;1(4): 460-474
    Zhang WC, Wells JM, Chow KH, Huang H, Yuan M, Saxena T, Melnick MA, Politi K, Asara JM, Costa DB, Bult CJ, Slack FJ.
      Drug-tolerance is an acute defense response prior to a fully drug-resistant state and tumor relapse, however there are few therapeutic agents targeting drug-tolerance in the clinic. Here we show that miR-147b initiates a reversible tolerant-state to the EGFR inhibitor osimertinib in non-small cell lung cancer. With miRNA-seq analysis we find that miR-147b is the most upregulated microRNA in osimertinib-tolerant and EGFR mutated lung cancer cells. Whole transcriptome analysis of single-cell derived clones reveals a link between osimertinib-tolerance and pseudohypoxia responses irrespective of oxygen levels. Further metabolomics and genetic studies demonstrate that osimertinib-tolerance is driven by miR-147b repression of VHL and succinate dehydrogenase linked to the tricarboxylic acid cycle and pseudohypoxia pathways. Finally, pretreatment with a miR-147b inhibitor delays osimertinib-associated drug tolerance in patient-derived three-dimensional (3D) structures. This link between miR-147b and tricarboxylic acid cycle may provide promising targets for preventing tumor relapse.
    DOI:  https://doi.org/10.1038/s42255-019-0052-9
  24. JCI Insight. 2019 Sep 19. pii: 130681. [Epub ahead of print]4(18):
    Ruegsegger GN, Vanderboom PM, Dasari S, Klaus KA, Kabiraj P, McCarthy CB, Lucchinetti CF, Nair KS.
      Insulin resistance associates with increased risk for cognitive decline and dementia; however, the underpinning mechanisms for this increased risk remain to be fully defined. As insulin resistance impairs mitochondrial oxidative metabolism and increases ROS in skeletal muscle, we considered whether similar events occur in the brain, which - like muscle - is rich in insulin receptors and mitochondria. We show that high-fat diet-induced (HFD-induced) brain insulin resistance in mice decreased mitochondrial ATP production rate and oxidative enzyme activities in brain regions rich in insulin receptors. HFD increased ROS emission and reduced antioxidant enzyme activities, with the concurrent accumulation of oxidatively damaged mitochondrial proteins and increased mitochondrial fission. Improvement of insulin sensitivity by both aerobic exercise and metformin ameliorated HFD-induced abnormalities. Moreover, insulin-induced enhancement of ATP production in primary cortical neurons and astrocytes was counteracted by the insulin receptor antagonist S961, demonstrating a direct effect of insulin resistance on brain mitochondria. Further, intranasal S961 administration prevented exercise-induced improvements in ATP production and ROS emission during HFD, supporting that exercise enhances brain mitochondrial function by improving insulin action. These results support that insulin sensitizing by exercise and metformin restores brain mitochondrial function in insulin-resistant states.
    Keywords:  Diabetes; Endocrinology; Metabolism
    DOI:  https://doi.org/10.1172/jci.insight.130681
  25. Eur J Pharmacol. 2019 Sep 17. pii: S0014-2999(19)30616-8. [Epub ahead of print] 172664
    Gou Q, Dong C, Jin J, Liu Q, Lu W, Shi J, Hou Y.
      As a nuclear receptor, peroxisome-proliferator-activated receptor α (PPARα) plays a critical role in regulation of metabolism and cancer, while the effect of PPARα agonist on cancer cell glucose metabolism-linked tumor growth is still unclear. Here we found that PPARα agonist (Wy14,643) decreased Glut1 (Glucose transporter 1) gene and protein expressions of colorectal cancer cell lines in response to normoxia or hypoxia. Dual-luciferase analysis showed that Wy14,643 inhibited Glut1 transcription activity. Importantly, ChIP-qPCR analysis showed that Wy14,643 increased the binding of PPARα to Glut1 promoter region. Wy14,643 suppressed Glut1 transcription activity resulting in reduced influx of glucose in cancer cells in response to normoxia or hypoxia. Further analysis showed that Wy14,643-mediated inhibition of tumor growth and chemo-resistance was associated with inhibition of mTOR pathway. Taken together, PPARα agonist Wy14,643 suppressed Glut1 transcription activity, glucose uptake and mTOR pathway in colorectal cancer cells, which was involved in reduced tumor growth and chemo-resistance. These findings provided a novel therapy strategy for cancer progression.
    Keywords:  Glut1; PPARα agonist; Transcription repression; Tumor growth; Wy14,643
    DOI:  https://doi.org/10.1016/j.ejphar.2019.172664
  26. Stem Cell Res. 2019 Sep 10. pii: S1873-5061(19)30203-X. [Epub ahead of print]40 101573
    Morganti C, Bonora M, Ito K, Ito K.
      The role of mitochondria in the fate determination of hematopoietic stem and progenitor cells (HSPCs) is not solely limited to the switch from glycolysis to oxidative phosphorylation, but also involves alterations in mitochondrial features and properties, including mitochondrial membrane potential (ΔΨmt). HSPCs have a high ΔΨmt even when the rates of respiration and phosphorylation are low, and we have previously shown that the minimum proton flow through ATP synthesis (or complex V) enables high ΔΨmt in HSPCs. Here we show that HSPCs sustain a unique equilibrium between electron transport chain (ETC) complexes and ATP production. HSPCs exhibit high expression of ETC complex II, which sustains complex III in proton pumping, although the expression levels of complex I or V are relatively low. Complex II inhibition by TTFA caused a substantial decrease of ΔΨmt, particularly in HSPCs, while the inhibition of complex I by Rotenone mainly affected mature populations. Functionally, pharmacological inhibition of complex II reduced in vitro colony-replating capacity but this was not observed when complex I was inhibited, which supports the distinct roles of complex I and II in HSPCs. Taken together, these data highlight complex II as a key regulator of ΔΨmt in HSPCs and open new and interesting questions regarding the precise mechanisms that regulate mitochondrial control to maintain hematopoietic stem cell self-renewal.
    Keywords:  ATP synthase; Electron transport chain; HSC; Mitochondrial membrane potential; SDHA; TMRM
    DOI:  https://doi.org/10.1016/j.scr.2019.101573
  27. J Exerc Rehabil. 2019 Aug;15(4): 512-517
    Yoo SZ, No MH, Heo JW, Chang E, Park DH, Kang JH, Seo DY, Han J, Jung SJ, Hwangbo K, Kwak HB.
      This study aimed to determine the effects of a single bout exercise on mitochondria-mediated apoptotic signaling in cardiac and skeletal muscles. Fischer 344 rats (4 months old) were randomly divided into the control or a single bout of exercise group (n=10 each). The rats performed a single bout of treadmill exercise for 60 min. Mitochondria-mediated apoptotic signaling (e.g., Bax, Bcl-2, mitochondrial permeability transition pore [mPTP] opening, cytochrome c, and cleaved caspase-3) was measured in cardiac (e.g., left ventricle) and skeletal (e.g., soleus and white gastrocnemius) muscles. A single bout of exercise significantly decreased mPTP opening sensitivity in all tissues. However, a single bout of exercise did not show any statistical differences in Bax, Bcl-2, cytochrome c, and cleaved caspase-3 in all tissues measured. A single bout of exercise did not show definite results on characteristics of mitochondria-mediated apoptotic signaling. Therefore, further research is necessary to provide a more mechanistic understanding of the apoptosis pathway.
    Keywords:  Apoptosis; Exercise; Heart; Mitochondria; Skeletal muscle
    DOI:  https://doi.org/10.12965/jer.1938380.190
  28. Proc Natl Acad Sci U S A. 2019 Sep 16. pii: 201903678. [Epub ahead of print]
    Binger KJ, Neukam M, Tattikota SG, Qadri F, Puchkov D, Willmes DM, Wurmsee S, Geisberger S, Dechend R, Raile K, Kurth T, Nguyen G, Poy MN, Solimena M, Muller DN, Birkenfeld AL.
      Pancreatic β cells store insulin within secretory granules which undergo exocytosis upon elevation of blood glucose levels. Crinophagy and autophagy are instead responsible to deliver damaged or old granules to acidic lysosomes for intracellular degradation. However, excessive consumption of insulin granules can impair β cell function and cause diabetes. Atp6ap2 is an essential accessory component of the vacuolar ATPase required for lysosomal degradative functions and autophagy. Here, we show that Cre recombinase-mediated conditional deletion of Atp6ap2 in mouse β cells causes a dramatic accumulation of large, multigranular vacuoles in the cytoplasm, with reduction of insulin content and compromised glucose homeostasis. Loss of insulin stores and gigantic vacuoles were also observed in cultured insulinoma INS-1 cells upon CRISPR/Cas9-mediated removal of Atp6ap2. Remarkably, these phenotypic alterations could not be attributed to a deficiency in autophagy or acidification of lysosomes. Together, these data indicate that Atp6ap2 is critical for regulating the stored insulin pool and that a balanced regulation of granule turnover is key to maintaining β cell function and diabetes prevention.
    Keywords:  (pro)renin receptor; autophagy; diabetes; vacuolar H+ ATPase
    DOI:  https://doi.org/10.1073/pnas.1903678116
  29. JCI Insight. 2019 Sep 19. pii: 128568. [Epub ahead of print]4(18):
    Shen J, Wang C, Ying J, Xu T, McAlinden A, O'Keefe RJ.
      Recently we demonstrated that ablation of the DNA methyltransferase enzyme, Dnmt3b, resulted in catabolism and progression of osteoarthritis (OA) in murine articular cartilage through a mechanism involving increased mitochondrial respiration. In this study, we identify 4-aminobutyrate aminotransferase (Abat) as a downstream target of Dnmt3b. Abat is an enzyme that metabolizes γ-aminobutyric acid to succinate, a key intermediate in the tricarboxylic acid cycle. We show that Dnmt3b binds to the Abat promoter, increases methylation of a conserved CpG sequence just upstream of the transcriptional start site, and inhibits Abat expression. Dnmt3b deletion in articular chondrocytes results in reduced methylation of the CpG sequence in the Abat promoter, which subsequently increases expression of Abat. Increased Abat expression in chondrocytes leads to enhanced mitochondrial respiration and elevated expression of catabolic genes. Overexpression of Abat in murine knee joints via lentiviral injection results in accelerated cartilage degradation following surgical induction of OA. In contrast, lentiviral-based knockdown of Abat attenuates the expression of IL-1β-induced catabolic genes in primary murine articular chondrocytes in vitro and also protects against murine articular cartilage degradation in vivo. Strikingly, treatment with the FDA-approved small-molecule Abat inhibitor, vigabatrin, significantly prevents the development of injury-induced OA in mice. In summary, these studies establish Abat as an important new target for therapies to prevent OA.
    Keywords:  Arthritis; Bone Biology; Cartilage; Homeostasis
    DOI:  https://doi.org/10.1172/jci.insight.128568
  30. Cell Metab. 2019 Sep 09. pii: S1550-4131(19)30448-6. [Epub ahead of print]
    Forsström S, Jackson CB, Carroll CJ, Kuronen M, Pirinen E, Pradhan S, Marmyleva A, Auranen M, Kleine IM, Khan NA, Roivainen A, Marjamäki P, Liljenbäck H, Wang L, Battersby BJ, Richter U, Velagapudi V, Nikkanen J, Euro L, Suomalainen A.
      Mitochondrial dysfunction elicits stress responses that safeguard cellular homeostasis against metabolic insults. Mitochondrial integrated stress response (ISRmt) is a major response to mitochondrial (mt)DNA expression stress (mtDNA maintenance, translation defects), but the knowledge of dynamics or interdependence of components is lacking. We report that in mitochondrial myopathy, ISRmt progresses in temporal stages and development from early to chronic and is regulated by autocrine and endocrine effects of FGF21, a metabolic hormone with pleiotropic effects. Initial disease signs induce transcriptional ISRmt (ATF5, mitochondrial one-carbon cycle, FGF21, and GDF15). The local progression to 2nd metabolic ISRmt stage (ATF3, ATF4, glucose uptake, serine biosynthesis, and transsulfuration) is FGF21 dependent. Mitochondrial unfolded protein response marks the 3rd ISRmt stage of failing tissue. Systemically, FGF21 drives weight loss and glucose preference, and modifies metabolism and respiratory chain deficiency in a specific hippocampal brain region. Our evidence indicates that FGF21 is a local and systemic messenger of mtDNA stress in mice and humans with mitochondrial disease.
    Keywords:  FGF21; de novo serine biosynthesis; endocrine signaling; mitochondrial disease; mitochondrial integrated stress response; mitochondrial unfolded protein response; one carbon cycle; stress response
    DOI:  https://doi.org/10.1016/j.cmet.2019.08.019
  31. Mol Microbiol. 2019 Sep 20.
    Eichenberger C, Oeljeklaus S, Bruggisser J, Mani J, Haenni B, Kaurov I, Niemann M, Zuber B, Lukeš J, Hashimi H, Warscheid B, Schimanski B, Schneider A.
      The mitochondrial contact site and cristae organization system (MICOS) mediates the formation of cristae, invaginations in the mitochondrial inner membrane. The highly diverged MICOS complex of the parasitic protist Trypanosoma brucei consists of 9 subunits. Except for two Mic10-like and a Mic60-like protein, all subunits are specific for kinetoplastids. Here we determined on a proteome-wide scale how ablation of individual MICOS subunits affects the levels of the other subunits. The results reveal co-regulation of TbMic10-1, TbMic10-2, TbMic16 and TbMic60, suggesting that these non-essential, integral inner membrane proteins form an interdependent network. Moreover, the ablation of TbMic34 and TbMic32 reveals another network consisting of the essential, intermembrane space-localized TbMic20, TbMic32, TbMic34 and TbMic40, all of which are peripherally associated with the inner membrane. The downregulation of TbMic20, TbMic32 and TbMic34 also interferes with mitochondrial protein import and reduces the size of the TbMic10-containing complexes. Thus, the diverged MICOS of trypanosomes contains two subcomplexes: a non-essential membrane-integrated one, organized around the conserved Mic10 and Mic60, that mediates cristae formation, and an essential membrane-peripheral one consisting of four kinetoplastid-specific subunits, that is required for import of intermembrane space proteins.
    Keywords:   Trypanosoma brucei ; cristae; intermembrane space; mitochondria; protein import
    DOI:  https://doi.org/10.1111/mmi.14389
  32. Nat Commun. 2019 Sep 19. 10(1): 4276
    Höglinger D, Burgoyne T, Sanchez-Heras E, Hartwig P, Colaco A, Newton J, Futter CE, Spiegel S, Platt FM, Eden ER.
      Transport of dietary cholesterol from endocytic organelles to the endoplasmic reticulum (ER) is essential for cholesterol homoeostasis, but the mechanism and regulation of this transport remains poorly defined. Membrane contact sites (MCS), microdomains of close membrane apposition, are gaining attention as important platforms for non-vesicular, inter-organellar communication. Here we investigate the impact of ER-endocytic organelle MCS on cholesterol transport. We report a role for Niemann-Pick type C protein 1 (NPC1) in tethering ER-endocytic organelle MCS where it interacts with the ER-localised sterol transport protein Gramd1b to regulate cholesterol egress. We show that artificially tethering MCS rescues the cholesterol accumulation that characterises NPC1-deficient cells, consistent with direct lysosome to ER cholesterol transport across MCS. Finally, we identify an expanded population of lysosome-mitochondria MCS in cells depleted of NPC1 or Gramd1b that is dependent on the late endosomal sterol-binding protein STARD3, likely underlying the mitochondrial cholesterol accumulation in NPC1-deficient cells.
    DOI:  https://doi.org/10.1038/s41467-019-12152-2
  33. Metab Eng. 2019 Sep 14. pii: S1096-7176(19)30220-4. [Epub ahead of print]
    Gatto F, Ferreira R, Nielsen J.
      Metabolic reprogramming is considered a hallmark of malignant transformation. However, it is not clear whether the network of metabolic reactions expressed by cancers of different origin differ from each other nor from normal human tissues. In this study, we reconstructed functional and connected genome-scale metabolic models for 917 primary tumor samples across 13 types based on the probability of expression for 3765 reference metabolic genes in the sample. This network-centric approach revealed that tumor metabolic networks are largely similar in terms of accounted reactions, despite diversity in the expression of the associated genes. On average, each network contained 4721 reactions, of which 74% were core reactions (present in >95% of all models). Whilst 99.3% of the core reactions were classified as housekeeping also in normal tissues, we identified reactions catalyzed by ARG2, RHAG, SLC6 and SLC16 family gene members, and PTGS1 and PTGS2 as core exclusively in cancer. These findings were subsequently replicated in an independent validation set of 3662 genome-scale metabolic models. The remaining 26% of the reactions were contextual reactions. Their inclusion was dependent in one case (GLS2) on the absence of TP53 mutations and in 94.6% of cases on differences in cancer types. This dependency largely resembled differences in expression patterns in the corresponding normal tissues, with some exceptions like the presence of the NANP-encoded reaction in tumors not from the female reproductive system or of the SLC5A9-encoded reaction in kidney-pancreatic-colorectal tumors. In conclusion, tumors expressed a metabolic network virtually overlapping the matched normal tissues, raising the possibility that metabolic reprogramming simply reflects cancer cell plasticity to adapt to varying conditions thanks to redundancy and complexity of the underlying metabolic networks. At the same time, the here uncovered exceptions represent a resource to identify selective liabilities of tumor metabolism.
    Keywords:  Cancer metabolism; Genome-scale metabolic modeling
    DOI:  https://doi.org/10.1016/j.ymben.2019.09.006
  34. Cell Chem Biol. 2019 Sep 19. pii: S2451-9456(19)30275-2. [Epub ahead of print]26(9): 1195-1196
    Zhang J, Bar-Peled L.
      In this issue of Cell Chemical Biology, Kang et al. (2019) describe the use of a high-throughput cell-based screen to identify chemical scaffolds that selectively inhibit mTORC1 nutrient sensing. Chemical proteomic-based target identification reveals class I glucose transporters as direct targets for these inhibitors, linking glucose sensing with mTORC1 regulation.
    DOI:  https://doi.org/10.1016/j.chembiol.2019.09.001
  35. Oncogene. 2019 Sep 18.
    Sung JS, Kang CW, Kang S, Jang Y, Chae YC, Kim BG, Cho NH.
      Integrin beta 4 (ITGB4) overexpression in cancer cells contributes to cancer progression. However, the role of stromal ITGB4 expression in cancer progression remains poorly understood, despite stromal ITGB4 overexpression in malignant cancers. In our study, ITGB4-overexpressing triple negative breast cancer (TNBC) cells provided cancer-associated fibroblasts (CAFs) with ITGB4 proteins via exosomes, which induced BNIP3L-dependent mitophagy and lactate production in CAFs. In coculture assays, the ITGB4-induced mitophagy and glycolysis were suppressed in CAFs by knocking down ITGB4 or inhibiting exosome generation in MDA-MB-231, or blocking c-Jun or AMPK phosphorylation in CAFs. ITGB4-overexpressing CAF-conditioned medium promoted the proliferation, epithelial-to-mesenchymal transition, and invasion of breast cancer cells. In a co-transplant mouse model, MDA-MB-231 made a bigger tumor mass with CAFs than ITGB4 knockdown MDA-MB-231. Herein, we presented how TNBC-derived ITGB4 protein triggers glycolysis in CAFs via BNIP3L-dependent mitophagy and suggested the possibility that ITGB4-induced mitophagy could be targeted as a cancer therapy.
    DOI:  https://doi.org/10.1038/s41388-019-1014-0
  36. Nat Commun. 2019 Sep 20. 10(1): 4291
    Sambeat A, Ratajczak J, Joffraud M, Sanchez-Garcia JL, Giner MP, Valsesia A, Giroud-Gerbetant J, Valera-Alberni M, Cercillieux A, Boutant M, Kulkarni SS, Moco S, Canto C.
      Supplementation with the NAD+ precursor nicotinamide riboside (NR) ameliorates and prevents a broad array of metabolic and aging disorders in mice. However, little is known about the physiological role of endogenous NR metabolism. We have previously shown that NR kinase 1 (NRK1) is rate-limiting and essential for NR-induced NAD+ synthesis in hepatic cells. To understand the relevance of hepatic NR metabolism, we generated whole body and liver-specific NRK1 knockout mice. Here, we show that NRK1 deficiency leads to decreased gluconeogenic potential and impaired mitochondrial function. Upon high-fat feeding, NRK1 deficient mice develop glucose intolerance, insulin resistance and hepatosteatosis. Furthermore, they are more susceptible to diet-induced liver DNA damage, due to compromised PARP1 activity. Our results demonstrate that endogenous NR metabolism is critical to sustain hepatic NAD+ levels and hinder diet-induced metabolic damage, highlighting the relevance of NRK1 as a therapeutic target for metabolic disorders.
    DOI:  https://doi.org/10.1038/s41467-019-12262-x
  37. Oncogene. 2019 Sep 16.
    Esteves P, Dard L, Brillac A, Hubert C, Sarlak S, Rousseau B, Dumon E, Izotte J, Bonneu M, Lacombe D, Dupuy JW, Amoedo N, Rossignol R.
      The basic understanding of the biological effects of eukaryotic translation initiation factors (EIFs) remains incomplete, notably for their roles independent of protein translation. Different EIFs exhibit nuclear localization and DNA-related functions have been proposed, but the understanding of EIFs novel functions beyond protein translation lacks of integrative analyses between the genomic and the proteomic levels. Here, the noncanonical function of EIF3F was studied in human lung adenocarcinoma by combining methods that revealed both the protein-protein and the protein-DNA interactions of this factor. We discovered that EIF3F promotes cell metastasis in vivo. The underpinning molecular mechanisms involved the regulation of a cluster of 34 metastasis-promoting genes including Snail2, as revealed by proteomics combined with immuno-affinity purification of EIF3F and ChIP-seq/Q-PCR analyses. The interaction between EIF3F and signal transducer and activator of transcription 3 (STAT3) controlled the EIF3F-mediated increase in Snail2 expression and cellular invasion, which were specifically abrogated using the STAT3 inhibitor Nifuroxazide or knockdown approaches. Furthermore, EIF3F overexpression reprogrammed energy metabolism through the activation of AMP-activated protein kinase and the stimulation of oxidative phosphorylation. Our findings demonstrate the role of EIF3F in the molecular control of cell migration, invasion, bioenergetics, and metastasis. The discovery of a role for EIF3F-STAT3 interaction in the genetic control of cell migration and metastasis in human lung adenocarcinoma could lead to the development of diagnosis and therapeutic strategies.
    DOI:  https://doi.org/10.1038/s41388-019-1009-x
  38. Nat Metab. 2019 Apr;1(4): 475-484
    Inoue F, Eckalbar WL, Wang Y, Murphy KK, Matharu N, Vaisse C, Ahituv N.
      Genome wide association studies (GWAS) in obesity have identified a large number of noncoding loci located near genes expressed in the central nervous system. However, due to the difficulties in isolating and characterizing specific neuronal subpopulations, few obesity-associated SNPs have been functionally characterized. Leptin responsive neurons in the hypothalamus are essential in controlling energy homeostasis and body weight. Here, we combine FACS-sorting of leptin-responsive hypothalamic neuron nuclei with genomic and epigenomic approaches (RNA-seq, ChIP-seq, ATAC-seq) to generate a comprehensive map of leptin-response specific regulatory elements, several of which overlap obesity-associated GWAS variants. We demonstrate the usefulness of our leptin-response neuron regulome, by functionally characterizing a novel enhancer near Socs3, a leptin response-associated transcription factor. We envision our data to serve as a useful resource and a blueprint for functionally characterizing obesity-associated SNPs in the hypothalamus.
    DOI:  https://doi.org/10.1038/s42255-019-0051-x
  39. Nat Immunol. 2019 Oct;20(10): 1311-1321
    Burgener AV, Bantug GR, Meyer BJ, Higgins R, Ghosh A, Bignucolo O, Ma EH, Loeliger J, Unterstab G, Geigges M, Steiner R, Enamorado M, Ivanek R, Hunziker D, Schmidt A, Müller-Durovic B, Grählert J, Epple R, Dimeloe S, Lötscher J, Sauder U, Ebnöther M, Burger B, Heijnen I, Martínez-Cano S, Cantoni N, Brücker R, Kahlert CR, Sancho D, Jones RG, Navarini A, Recher M, Hess C.
      Whether screening the metabolic activity of immune cells facilitates discovery of molecular pathology remains unknown. Here we prospectively screened the extracellular acidification rate as a measure of glycolysis and the oxygen consumption rate as a measure of mitochondrial respiration in B cells from patients with primary antibody deficiency. The highest oxygen consumption rate values were detected in three study participants with persistent polyclonal B cell lymphocytosis (PPBL). Exome sequencing identified germline mutations in SDHA, which encodes succinate dehydrogenase subunit A, in all three patients with PPBL. SDHA gain-of-function led to an accumulation of fumarate in PPBL B cells, which engaged the KEAP1-Nrf2 system to drive the transcription of genes encoding inflammatory cytokines. In a single patient trial, blocking the activity of the cytokine interleukin-6 in vivo prevented systemic inflammation and ameliorated clinical disease. Overall, our study has identified pathological mitochondrial retrograde signaling as a disease modifier in primary antibody deficiency.
    DOI:  https://doi.org/10.1038/s41590-019-0482-2
  40. Anal Biochem. 2019 Sep 17. pii: S0003-2697(19)30733-X. [Epub ahead of print] 113443
    Bauer TM, Giles AV, Sun J, Femnou A, Covian R, Murphy E, Balaban RS.
      Tissue transmission optical absorption spectroscopy provides dynamic information on metabolism and function. Murine genetic malleability makes it a major model for heart research. The diminutive size of the mouse heart makes optical transmission studies challenging. Using a perfused murine heart center mounted in an integrating sphere for light collection with a ventricular cavity optical catheter as an internal light source provided an effective method of optical data collection in this model. This approach provided high signal to noise optical spectra which when fit with model spectra provided information on tissue oxygenation and redox state. This technique was applied to the study of cardiac ischemia and ischemia reperfusion which generates extreme heart motion, especially during the ischemic contracture. The integrating sphere reduced motion artifacts associated with a fixed optical pickup and methods were developed to compensate for changes in tissue thickness. During ischemia, rapid decreases in myoglobin oxygenation occurred along with increases in cytochrome reduction levels. Surprisingly, when ischemic contracture occurred, myoglobin remained fully deoxygenated, while the cytochromes became more reduced consistent with a further, and critical, reduction of mitochondrial oxygen tension during ischemic contraction. This optical arrangement is an effective method of monitoring murine heart metabolism.
    Keywords:  Cytochromes; Linear least squares fitting; Mitochondria membrane potential; Myoglobin; Optical pathlength; Oxidative phosphorylation; Oxygen
    DOI:  https://doi.org/10.1016/j.ab.2019.113443
  41. Cell Chem Biol. 2019 Sep 19. pii: S2451-9456(19)30279-X. [Epub ahead of print]26(9): 1197-1199
    Katt WP, Lukey MJ, Cerione RA.
      Increased consumption of glucose and glutamine are metabolic hallmarks of tumorigenesis. In this issue of Cell Chemical Biology, Reckzeh et al. (2019) describe the discovery of Glutor, a potent inhibitor of cellular glucose uptake. Combining Glutor with the glutaminase inhibitor CB-839 creates a metabolic crisis in cancer cells, synergistically impeding proliferation.
    DOI:  https://doi.org/10.1016/j.chembiol.2019.09.005
  42. EMBO Rep. 2019 Sep 18. e47865
    Andréasson C, Ott M, Büttner S.
      The eukaryotic cell is morphologically and functionally organized as an interconnected network of organelles that responds to stress and aging. Organelles communicate via dedicated signal transduction pathways and the transfer of information in form of metabolites and energy levels. Recent data suggest that the communication between organellar proteostasis systems is a cornerstone of cellular stress responses in eukaryotic cells. Here, we discuss the integration of proteostasis and energy fluxes in the regulation of cellular stress and aging. We emphasize the molecular architecture of the regulatory transcriptional pathways that both sense and control metabolism and proteostasis. A special focus is placed on mechanistic insights gained from the model organism budding yeast in signaling from mitochondria to the nucleus and how this shapes cellular fitness.
    Keywords:  mitochondria-to-nucleus signaling; organellar connectivity; protein folding; proteostasis; stress response
    DOI:  https://doi.org/10.15252/embr.201947865
  43. Nat Metab. 2019 Jan;1(1): 86-97
    Seo JB, Riopel M, Cabrales P, Huh JY, Bandyopadhyay GK, Andreyev AY, Murphy AN, Beeman SC, Smith GI, Klein S, Lee YS, Olefsky JM.
      Decreased adipose tissue oxygen tension and increased HIF-1α expression can trigger adipose tissue inflammation and dysfunction in obesity. Our current understanding of obesity-associated decreased adipose tissue oxygen tension is mainly focused on changes in oxygen supply and angiogenesis. Here, we demonstrate that increased adipocyte O2 demand, mediated by ANT2 activity, is the dominant cause of adipocyte hypoxia. Deletion of adipocyte Ant2 improves obesity-induced intracellular adipocyte hypoxia by decreasing obesity-induced adipocyte oxygen demand, without effects on mitochondrial number or mass, or oligomycin-sensitive respiration. This led to decreased adipose tissue HIF-1α expression and inflammation with improved glucose tolerance and insulin resistance in both a preventative or therapeutic setting. Our results suggest that ANT2 may be a target for the development of insulin sensitizing drugs and that ANT2 inhibition might have clinical utility.
    Keywords:  ANT2; Adipose Tissue Hypoxia; HIF-1α; Inflammation; Insulin Resistance; Mitochondria; Obesity; Oxygen Consumption; Type 2 diabetes; Uncoupled Respiration
    DOI:  https://doi.org/10.1038/s42255-018-0003-x
  44. J Clin Invest. 2019 Sep 17. pii: 128287. [Epub ahead of print]
    Asrani K, Murali S, Lam B, Na CH, Phatak P, Sood A, Kaur H, Khan Z, Noë M, Anchoori RK, Talbot CC, Smith B, Skaro M, Lotan TL.
      The Microphthalmia family of transcription factors (MiT/TFE) controls lysosomal biogenesis and is negatively regulated by the nutrient sensor mTORC1. However, the mechanisms by which cells with constitutive mTORC1 signaling maintain lysosomal catabolism remain to be elucidated. Using the murine epidermis as a model system, we found that epidermal Tsc1 deletion resulted in a phenotype characterized by wavy hair and curly whiskers, and was associated with increased EGFR and HER2 degradation. Unexpectedly, constitutive mTORC1 activation with Tsc1 loss increased lysosomal content via up-regulated expression and activity of MiT/TFEs, while genetic deletion of Rheb or Rptor or prolonged pharmacologic mTORC1 inactivation had the reverse effect. This paradoxical increase in lysosomal biogenesis by mTORC1 was mediated by feedback inhibition of AKT, and a resulting suppression of AKT-induced MiT/TFE down-regulation. Thus, inhibiting hyperactive AKT signaling in the context of mTORC1 loss-of-function fully restored MiT/TFE expression and activity. These data suggest that signaling feedback loops work to restrain or maintain cellular lysosomal content during chronically inhibited or constitutively active mTORC1 signaling respectively, and reveal a mechanism by which mTORC1 regulates upstream receptor tyrosine kinase signaling.
    Keywords:  Genetic diseases; Lysosomes; Metabolism; Oncology
    DOI:  https://doi.org/10.1172/JCI128287
  45. Sci Rep. 2019 Sep 20. 9(1): 13658
    Okuno K, Naito Y, Yasumura S, Sawada H, Asakura M, Masuyama T, Ishihara M.
      Limb ischemia (LI) is a major consequence of peripheral artery disease (PAD) with a high mortality rate. Iron is an essential mineral to maintain physiological function of multiple organs. Intracellular iron transport is regulated by transferrin receptor 1 (TfR1). Although increase in serum ferritin levels has been reported in PAD patients, the mechanism of iron metabolism in LI is still unclear. The aim of this study is to investigate whether TfR1 deletion attenuates LI formation. To generate LI, the left femoral artery of 8-10 week-old C57BL6/J male mice was ligated. Adductor muscles were harvested at 28 days after surgery to investigate iron metabolism. The level of ferritin, intracellular iron storage protein, was higher in ischemic adductor muscles compared to non-ischemic adductor muscles. Level of intracellular iron transport protein, TfR1, was decreased in ischemic adductor muscles. LI was then generated in TfR1 heterozygous deleted mice (TfR1+/-) to examine whether TfR1 contributes to the pathophysiology of LI. Laser Doppler blood flowmetry revealed that blood flow recovery was attenuated in TfR1+/- mice compared to wild type (WT) littermates, along with decreased expression of ferritin and CD31 in ischemic adductor muscles. Since iron is used for energy production in mitochondria, we then assessed mitochondrial complexes in the ischemic adductor muscle. Of interest, expression of mitochondrial complex I, but not complexes II, III, and V in ischemic adductor muscles was significantly reduced in TfR1+/- mice compared to WT mice. Haploinsufficiency of TfR1 attenuated angiogenesis via reduction of mitochondrial complex I in LI in mice.
    DOI:  https://doi.org/10.1038/s41598-019-49983-4
  46. Cell. 2019 Sep 19. pii: S0092-8674(19)30951-1. [Epub ahead of print]179(1): 219-235.e21
    Wolf Y, Bartok O, Patkar S, Eli GB, Cohen S, Litchfield K, Levy R, Jiménez-Sánchez A, Trabish S, Lee JS, Karathia H, Barnea E, Day CP, Cinnamon E, Stein I, Solomon A, Bitton L, Pérez-Guijarro E, Dubovik T, Shen-Orr SS, Miller ML, Merlino G, Levin Y, Pikarsky E, Eisenbach L, Admon A, Swanton C, Ruppin E, Samuels Y.
      Although clonal neo-antigen burden is associated with improved response to immune therapy, the functional basis for this remains unclear. Here we study this question in a novel controlled mouse melanoma model that enables us to explore the effects of intra-tumor heterogeneity (ITH) on tumor aggressiveness and immunity independent of tumor mutational burden. Induction of UVB-derived mutations yields highly aggressive tumors with decreased anti-tumor activity. However, single-cell-derived tumors with reduced ITH are swiftly rejected. Their rejection is accompanied by increased T cell reactivity and a less suppressive microenvironment. Using phylogenetic analyses and mixing experiments of single-cell clones, we dissect two characteristics of ITH: the number of clones forming the tumor and their clonal diversity. Our analysis of melanoma patient tumor data recapitulates our results in terms of overall survival and response to immune checkpoint therapy. These findings highlight the importance of clonal mutations in robust immune surveillance and the need to quantify patient ITH to determine the response to checkpoint blockade.
    Keywords:  anti-tumor immunity; cancer neoantigens; checkpoint immunotherapy; intra-tumor heterogeneity; melanoma; mouse model; mutational load
    DOI:  https://doi.org/10.1016/j.cell.2019.08.032
  47. Cell Syst. 2019 Aug 23. pii: S2405-4712(19)30238-8. [Epub ahead of print]
    Brubaker DK, Paulo JA, Sheth S, Poulin EJ, Popow O, Joughin BA, Strasser SD, Starchenko A, Gygi SP, Lauffenburger DA, Haigis KM.
      The highest frequencies of KRAS mutations occur in colorectal carcinoma (CRC) and pancreatic ductal adenocarcinoma (PDAC). The ability to target downstream pathways mediating KRAS oncogenicity is limited by an incomplete understanding of the contextual cues modulating the signaling output of activated K-RAS. We performed mass spectrometry on mouse tissues expressing wild-type or mutant Kras to determine how tissue context and genetic background modulate oncogenic signaling. Mutant Kras dramatically altered the proteomes and phosphoproteomes of preneoplastic and neoplastic colons and pancreases in a context-specific manner. We developed an approach to statistically humanize the mouse networks with data from human cancer and identified genes within the humanized CRC and PDAC networks synthetically lethal with mutant KRAS. Our studies demonstrate the context-dependent plasticity of oncogenic signaling, identify non-canonical mediators of KRAS oncogenicity within the KRAS-regulated signaling network, and demonstrate how statistical integration of mouse and human datasets can reveal cross-species therapeutic insights.
    Keywords:  ASL; CDK2; KRAS; MET; SMAD3; cancer; colon; pancreas; phosphoproteomics; proteomics; species-translation
    DOI:  https://doi.org/10.1016/j.cels.2019.07.006
  48. Elife. 2019 Sep 17. pii: e48003. [Epub ahead of print]8
    Xin Y, Malick A, Hu M, Liu C, Batah H, Xu H, Duan C.
      Epithelial homeostasis and regeneration require a pool of quiescent cells. How the quiescent cells are established and maintained is poorly understood. Here we report that Trpv6, a cation channel responsible for epithelial Ca2+ absorption, functions as a key regulator of cellular quiescence. Genetic deletion and pharmacological blockade of Trpv6 promoted zebrafish epithelial cells to exit from quiescence and re-enter the cell cycle. Reintroducing Trpv6, but not its channel dead mutant, restored the quiescent state. Ca2+ imaging showed that Trpv6 is constitutively open in vivo. Mechanistically, Trpv6-mediated Ca2+ influx maintained the quiescent state by suppressing insulin-like growth factor (IGF)-mediated Akt-Tor and Erk signaling. In zebrafish epithelia and human colon carcinoma cells, Trpv6/TRPV6 elevated intracellular Ca2+ levels and activated PP2A, which down-regulated IGF signaling and promoted the quiescent state. Our findings suggest that Trpv6 mediates constitutive Ca2+ influx into epithelial cells to continuously suppress growth factor signaling and maintain the quiescent state.
    Keywords:  developmental biology; zebrafish
    DOI:  https://doi.org/10.7554/eLife.48003
  49. Mol Cell. 2019 Sep 19. pii: S1097-2765(19)30665-3. [Epub ahead of print]75(6): 1092-1101
    Cornett EM, Ferry L, Defossez PA, Rothbart SB.
      Landmark discoveries made nearly two decades ago identified known transcriptional regulators as histone lysine methyltransferases. Since then, the field of lysine methylation signaling has been dominated by studies of how this small chemical posttranslational modification regulates gene expression and other chromatin-based processes. However, recent advances in mass-spectrometry-based proteomics have revealed that histones are just a subset of the thousands of eukaryotic proteins marked by lysine methylation. As the writers, erasers, and readers of histone lysine methylation are emerging as a promising therapeutic target class for cancer and other diseases, a key challenge for the field is to define the full spectrum of activities for these proteins. Here we summarize recent discoveries implicating non-histone lysine methylation as a major regulator of diverse cellular processes. We further discuss recent technological innovations that are enabling the expanded study of lysine methylation signaling. Collectively, these findings are shaping our understanding of the fundamental mechanisms of non-histone protein regulation through this dynamic and multi-functional posttranslational modification.
    DOI:  https://doi.org/10.1016/j.molcel.2019.08.026