bims-auttor Biomed News
on Autophagy and mTOR
Issue of 2020‒05‒03
twenty-two papers selected by
Viktor Korolchuk, Newcastle University

  1. Biochem J. 2020 Apr 29. pii: BCJ20190958. [Epub ahead of print]
      The mammalian target of rapamycin (mTOR) is an evolutionarily conserved Ser/Thr kinase that comprises two complexes, termed mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). mTORC1 phosphorylates S6K1 at Thr 389, whereas mTORC2 phosphorylates AKT at Ser 473 to promote cell growth. As the mTOR name implies it is the target of natural product called rapamycin, a clinically approved drug used to treat human disease. Short-term rapamycin treatment inhibits the kinase activity of mTORC1 but not mTORC2. However, ATP-competitive catalytic mTOR inhibitor Torin1 was identified to inhibit the kinase activity of both mTORC1 and mTORC2. Here, we report that H89 (N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide), a well-characterized ATP-mimetic kinase inhibitor, renders the phosphorylation of S6K1 and AKT resistant to mTOR inhibitors across multiple cell lines. Moreover, H89 prevented the dephosphorylation of AKT and S6K1 under nutrient depleted conditions. PKA and other known H89-targeted kinases do not alter the phosphorylation status of S6K1 and AKT. Pharmacological inhibition of some phosphatases also enhanced S6K1 and AKT phosphorylation. These findings suggest a new target for H89 by which it sustains the phosphorylation status of S6K1 and AKT, resulting in mTOR signaling.
    Keywords:  kinase inhibitors; mechanistic target of rapamycin; nutrients
  2. EMBO Rep. 2020 Apr 26. e48192
      Autophagy is an essential cellular quality control process that has emerged as a critical one for vascular homeostasis. Here, we show that trichoplein (TCHP) links autophagy with endothelial cell (EC) function. TCHP localizes to centriolar satellites, where it binds and stabilizes PCM1. Loss of TCHP leads to delocalization and proteasome-dependent degradation of PCM1, further resulting in degradation of PCM1's binding partner GABARAP. Autophagic flux under basal conditions is impaired in THCP-depleted ECs, and SQSTM1/p62 (p62) accumulates. We further show that TCHP promotes autophagosome maturation and efficient clearance of p62 within lysosomes, without affecting their degradative capacity. Reduced TCHP and high p62 levels are detected in primary ECs from patients with coronary artery disease. This phenotype correlates with impaired EC function and can be ameliorated by NF-κB inhibition. Moreover, Tchp knock-out mice accumulate of p62 in the heart and cardiac vessels correlating with reduced cardiac vascularization. Taken together, our data reveal that TCHP regulates endothelial cell function via an autophagy-mediated mechanism.
    Keywords:   GABARAP ; SQSTM1/p62; autophagy; centriolar satellites; endothelial cells
  3. Cell Death Discov. 2020 ;6 27
      Glucose is a major requirement for biological life. Its concentration is constantly sensed at the cellular level, allowing for adequate responses to any changes of glucose availability. Such responses are mediated by key sensors and signaling pathway components that adapt cellular metabolism to glucose levels. One of the major hubs of these responses is mechanistic target of rapamycin (mTOR) kinase, which forms the mTORC1 and mTORC2 protein complexes. Under physiological glucose concentrations, mTORC1 is activated and stimulates a number of proteins and enzymes involved in anabolic processes, while restricting the autophagic process. Conversely, when glucose levels are low, mTORC1 is inhibited, in turn leading to the repression of numerous anabolic processes, sparing ATP and antioxidants. Understanding how mTORC1 activity is regulated by glucose is not only important to better delineate the biological function of mTOR, but also to highlight potential therapeutic strategies for treating diseases characterized by deregulated glucose availability, as is the case of cancer. In this perspective, we depict the different sensors and upstream proteins responsible of controlling mTORC1 activity in response to changes in glucose concentration. This includes the major energy sensor AMP-activated protein kinase (AMPK), as well as other independent players. The impact of such modes of regulation of mTORC1 on cellular processes is also discussed.
    Keywords:  Cell biology; Cell signalling
  4. Exp Ther Med. 2020 Jun;19(6): 3565-3570
      Tuberous sclerosis complex (TSC) is a relatively rare autosomal dominant disease which involves multiple organs, including the brain, kidney, lung, skin and heart. Renal angiomyolipomas (RAML) are the main causes of mortality in patients with TSC. The preferred treatment for RAML is the use of mTOR inhibitors, but the efficacy of these are not satisfactory. Therefore, an alternative treatment is urgently required. Autophagy levels decline in TSC associated cortical tubers, and the inhibition of autophagy in animal or cell models of TSC may suppress tumor development and cell proliferation. PTEN is a protein tyrosine phosphatase and can inhibit the activation of Akt. In the present study, it was indicated that the PTEN inhibitor, hydroxyl(oxo)vanadium 3-hydroxypiridine-2-carboxylic acid (VO-OHpic), suppressed proliferation and growth of TSC2- / - murine embryonic fibroblasts (MEFs) by further inhibiting autophagy of cells. The expression levels of human microtubule-associated protein 1 light chain 3-I (LC3-I) and LC3-II, which are autophagy associated proteins, were demonstrated to decline following VO-OHpic treatment. The expression levels of phosphorylated proline-rich Akt substrate 40 kDa (PRAS40) also decreased in TSC2- / - MEFs treated with VO-OHpic. The PTEN inhibitor may inhibit the proliferation of TSC2- / - MEFs through the PTEN-PRAS40 pathway by excessively inhibiting autophagy, without the dependence of the Ras homolog, mTORC1 binding/mTOR pathway. PTEN may be a potential therapeutic target for the treatment of TSC. Further in vivo studies are required to confirm these results.
    Keywords:  PTEN; autophagy; hydroxyl(oxo)vanadium 3-hydroxypiridine-2-carboxylic acid; tuberous sclerosis complex; tuberous sclerosis complex 2-/- murine embryonic fibroblasts
  5. Cell Rep. 2020 Apr 28. pii: S2211-1247(20)30520-9. [Epub ahead of print]31(4): 107571
      Mechanistic target of rapamycin complex 1 (mTORC1) is a master modulator of cellular growth, and its aberrant regulation is recurrently documented within breast cancer. While the small GTPase Rheb1 is the canonical activator of mTORC1, Rheb1-independent mechanisms of mTORC1 activation have also been reported but have not been fully understood. Employing multiple transgenic mouse models of breast cancer, we report that ablation of Rheb1 significantly impedes mammary tumorigenesis. In the absence of Rheb1, a block in tumor initiation can be overcome by multiple independent mutations in Mtor to allow Rheb1-independent reactivation of mTORC1. We further demonstrate that the mTOR kinase is indispensable for tumor initiation as the genetic ablation of mTOR abolishes mammary tumorigenesis. Collectively, our findings demonstrate that mTORC1 activation is indispensable for mammary tumor initiation and that tumors acquire alternative mechanisms of mTORC1 activation.
    Keywords:  Rheb; breast; cancer; mTOR; mutation; tumorigenesis
  6. iScience. 2020 Apr 11. pii: S2589-0042(20)30233-9. [Epub ahead of print]23(5): 101048
      Early-onset Parkinson's disease-associated PINK1-Parkin signaling maintains mitochondrial health. Therapeutic approaches for enhancing PINK1-Parkin signaling present a potential strategy for treating various diseases caused by mitochondrial dysfunction. We report two chemical enhancers of PINK1-Parkin signaling, identified using a robust cell-based high-throughput screening system. These small molecules, T0466 and T0467, activate Parkin mitochondrial translocation in dopaminergic neurons and myoblasts at low doses that do not induce mitochondrial accumulation of PINK1. Moreover, both compounds reduce unfolded mitochondrial protein levels, presumably through enhanced PINK1-Parkin signaling. These molecules also mitigate the locomotion defect, reduced ATP production, and disturbed mitochondrial Ca2+ response in the muscles along with the mitochondrial aggregation in dopaminergic neurons through reduced PINK1 activity in Drosophila. Our results suggested that T0466 and T0467 may hold promise as therapeutic reagents in Parkinson's disease and related disorders.
    Keywords:  Biological Sciences; Cell Biology; Neuroscience
  7. FEBS Lett. 2020 Apr 29.
      Ageing is driven by the inexorable and stochastic accumulation of damage in biomolecules vital for proper cellular function. Although this process is fundamentally haphazard and uncontrollable, genetic and extrinsic factors influence senescent decline and ageing. Numerous gene mutations and treatments have been shown to extend the lifespan of organisms ranging from the unicellular Saccharomyces cerevisiae to primates. Most such interventions ultimately interface with cellular stress response mechanisms, suggesting that longevity is intimately related to the ability of the organism to counter both intrinsic and extrinsic stress. Mitochondria, the main energy hub of the cell, are highly dynamic organelles, playing essential roles in cell physiology. Mitochondrial function impinges on several signalling pathways modulating cellular metabolism, survival and healthspan. Maintenance of mitochondrial function and energy homeostasis requires both generation of new healthy mitochondria and elimination of the dysfunctional ones. Here, we survey the mechanisms regulating mitochondrial number in cells, with particular emphasis on neurons. We, further, discuss recent findings implicating perturbation of mitochondrial homeostasis in cellular senescence and organismal ageing as well as in age-associated neurodegenerative diseases.
    Keywords:  Ageing; Energy homeostasis; Human disease; Mitochondria; Mitochondrial turnover; Mitophagy; Necrosis; Neurodegeneration; Neurons
  8. Biochim Biophys Acta Rev Cancer. 2020 Apr 24. pii: S0304-419X(20)30058-5. [Epub ahead of print] 188366
      Autophagy is an evolutionarily conserved self-cannibalization process commonly found in all eukaryotic cells. Through autophagy, long-lived or damaged organelles, superfluous proteins, and pathogens are sequestered and encapsulated into the double-membrane autophagosomes prior to fusion with lysosomes for ultimate degradation and recycling. Given that autophagy is deemed both protective and detrimental in malignancies, the clinical therapeutic utilization of autophagy modulators in cancer has attracted immense attentions over the past decades. Dependence of tumor cells on autophagy during amino acid insufficiency or deprivation has prompted us to explore the underlying autophagy regulatory mechanisms to inject amino acid degrading enzymes and enzyme-based strategies into therapeutic maneuvers of autophagy in cancer.
    Keywords:  Amino acids; Autophagy; Cancer; Cell death; Cytoprotective autophagy; Enzymes
  9. Am J Physiol Gastrointest Liver Physiol. 2020 Apr 27.
      Reduced ciliary expression is reported in several tumors, including cholangiocarcinoma (CCA). We previously showed primary cilia have tumor suppressor characteristics and HDAC6 is involved in ciliary loss. However, mechanisms of ciliary disassembly are unknown. Herein, we tested the hypothesis that HDAC6-dependent autophagy of primary cilia, i.e. ciliophagy, is the main mechanism driving ciliary disassembly in CCA. Utilizing the cancer genome atlas database, human CCA cells, and a rat orthotopic CCA model, we assessed basal and HDAC6-regulated autophagy levels. The effects of RNA-silencing or pharmacological manipulations of ciliophagy on ciliary expression were assessed. Interactions of ciliary proteins with autophagy machinery was assessed by immunoprecipitations. Cell proliferation was assessed by MTS and IncuCyte. A CCA rat model was used to assess the effects of pharmacological inhibition of ciliophagy in vivo. Autophagy is increased in human CCA as well as in a rat orthotopic CCA model and human CCA cell lines. Autophagic flux was decreased via inhibition of HDAC6, while increased by its overexpression. Inhibition of autophagy and HDAC6 restores cilia and decreases cell proliferation. LC3 interacts with HDAC6 and ciliary proteins, and the autophagy cargo receptor involved in targeting ciliary components to the autophagy machinery is primarily NBR1. Treatment with chloroquine, ACY1215 or its combination decreased tumor growth in vivo. Mice that overexpress the autophagy transcription factor TFEB show a decrease of ciliary number. These results suggest ciliary disassembly is mediated by HDAC6-regulated autophagy, i.e. ciliophagy. Inhibition of ciliophagy may decrease cholangiocarcinoma growth and warrant further investigations as a potential therapeutic approach.
    Keywords:  Autophagy Cargo Receptors; LC3; NBR1; Primary Cilia; ciliophagy
  10. J Cell Biol. 2020 Jun 01. pii: e202002085. [Epub ahead of print]219(6):
      Autophagosome biogenesis involves de novo formation of a membrane that elongates to sequester cytoplasmic cargo and closes to form a double-membrane vesicle (an autophagosome). This process has remained enigmatic since its initial discovery >50 yr ago, but our understanding of the mechanisms involved in autophagosome biogenesis has increased substantially during the last 20 yr. Several key questions do remain open, however, including, What determines the site of autophagosome nucleation? What is the origin and lipid composition of the autophagosome membrane? How is cargo sequestration regulated under nonselective and selective types of autophagy? This review provides key insight into the core molecular mechanisms underlying autophagosome biogenesis, with a specific emphasis on membrane modeling events, and highlights recent conceptual advances in the field.
  11. Brain. 2020 May 01. pii: awaa076. [Epub ahead of print]
      Many RNA-binding proteins, including TDP-43, FUS, and TIA1, are stress granule components, dysfunction of which causes amyotrophic lateral sclerosis (ALS). However, whether a mutant RNA-binding protein disrupts stress granule processing in vivo in pathogenesis is unknown. Here we establish a FUS ALS mutation, p.R521C, knock-in mouse model that carries impaired motor ability and late-onset motor neuron loss. In disease-susceptible neurons, stress induces mislocalization of mutant FUS into stress granules and upregulation of ubiquitin, two hallmarks of disease pathology. Additionally, stress aggravates motor performance decline in the mutant mouse. By using two-photon imaging in TIA1-EGFP transduced animals, we document more intensely TIA1-EGFP-positive granules formed hours but cleared weeks after stress challenge in neurons in the mutant cortex. Moreover, neurons with severe granule misprocessing die days after stress challenge. Therefore, we argue that stress granule misprocessing is pathogenic in ALS, and the model we provide here is sound for further disease mechanistic study.
    Keywords:  ALS; FUS-R521C; knock-in; mouse model; stress granule
  12. Cells. 2020 Apr 27. pii: E1082. [Epub ahead of print]9(5):
      Lipophilic weak base therapeutic agents, termed lysosomotropic drugs (LDs), undergo marked sequestration and concentration within lysosomes, hence altering lysosomal functions. This lysosomal drug entrapment has been described as luminal drug compartmentalization. Consistent with our recent finding that LDs inflict a pH-dependent membrane fluidization, we herein demonstrate that LDs undergo intercalation and concentration within lysosomal membranes. The latter was revealed experimentally and computationally by (a) confocal microscopy of fluorescent compounds and drugs within lysosomal membranes, and (b) molecular dynamics modeling of the pH-dependent membrane insertion and accumulation of an assortment of LDs, including anticancer drugs. Based on the multiple functions of the lysosome as a central nutrient sensory hub and a degradation center, we discuss the molecular mechanisms underlying the alteration of morphology and impairment of lysosomal functions as consequences of LDs' intercalation into lysosomes. Our findings bear important implications for drug design, drug induced lysosomal damage, diseases and pertaining therapeutics.
    Keywords:  drug sequestration; lysosomes; lysosomotropic drugs; membrane intercalation; molecular dynamics
  13. Cells. 2020 Apr 28. pii: E1090. [Epub ahead of print]9(5):
      Mammalian target of rapamycin complex 1 (mTORC1) is a master regulator of cellular proliferation and survival which controls cellular response to different stresses, including viral infection. HIV-1 interferes with the mTORC1 pathway at every stage of infection. At the same time, the host cells rely on the mTORC1 pathway and autophagy to fight against virus replication and transmission. In this review, we will provide the most up-to-date picture of the role of the mTORC1 pathway in the HIV-1 life cycle, latency and HIV-related diseases. We will also provide an overview of recent trends in the targeting of the mTORC1 pathway as a promising strategy for HIV-1 eradication.
    Keywords:  HIV-1; HIV-1 related diseases; autophagy; mTORC1 pathway
  14. Biochim Biophys Acta Gen Subj. 2020 Apr 23. pii: S0304-4165(20)30137-9. [Epub ahead of print] 129625
      BACKGROUND: N-myc downstream regulated gene 1 (NDRG1) is an established stress-response protein. This study investigated the effects of NDRG1 on autophagic degradation and how this can be therapeutically exploited.METHODS: Cell culture, western analysis, confocal microscopy, acridine orange staining, cholesterol determination, cellular proliferation assessment and combination index (CI) estimation.
    RESULTS: NDRG1 expression suppressed autophagic degradation and autolysosome formation, measured by increased p62 expression and reduced co-localization between the well-characterized, autophagosomal and lysosomal markers, LC3 and LAMP2, respectively. NDRG1 elicited autophagic suppression at the initiation stage of autophagy. The NDRG1-inducer and anti-cancer agent, di-2-pyridylketone 4,4,-dimethyl-3-thiosemicarbazone (Dp44mT), was able to induce lysosomal membrane permeabilization (LMP). Over-expression of NDRG1 further sensitized cells to LMP mediated by both Dp44mT, or the redox active Dp44mT‑copper complex. This sensitization may be mediated via a decrease in cholesterol levels upon NDRG1 expression, as cholesterol stabilizes lysosomal membranes. However, the effect of NDRG1 on cholesterol appeared independent of the key energy homeostasis sensor, 5' AMP-activated protein kinase (AMPK), whose activation was significantly (p < .001) reduced by NDRG1. Finally, Dp44mT synergistically potentiated the anti-proliferative activity of Gemcitabine that activates autophagy. In fact, Dp44mT and Gemcitabine (Combination Index (CI): 0.38 ± 0.07) demonstrated higher synergism versus the autophagy inhibitor, Bafilomycin A1 and Gemcitabine (CI: 0.64 ± 0.19).
    CONCLUSIONS AND GENERAL SIGNIFICANCE: Collectively, this study demonstrated a dual-inhibitory mechanism of NDRG1 on autophagic activity, and that NDRG1 expression sensitized cells to Dp44mT-induced LMP. Considering the ability of Dp44mT to inhibit autophagy, studies demonstrated the potential of combination therapy for cancer treatment of Dp44mT with Gemcitabine.
  15. Life Sci. 2020 Apr 23. pii: S0024-3205(20)30448-3. [Epub ahead of print]253 117700
      AIMS: Although previous studies elaborated that selective autophagy was involved in quality control of some organelles, including nucleus, mitochondria, the endoplasmic reticulum and peroxisomes, it remained unclear whether the selective autophagy of the Golgi apparatus (Golgiphagy) existed or not.MAIN METHODS: In this study, H9c2 cells, HUVECs, HA-VSMCs and HEK293T cells were treated with autophagy inducers, Golgi stress inducers and cardiomyocytes hypertrophy stimulators. The Golgiphagy was evaluated by analysing the co-localization of Golgi markers and LC3B. Furthermore, the transmission electron microscope was used to observe the occurrence of Golgiphagy. The co-immunoprecipitation assay was used to evaluate the interaction of GOLPH3 and LC3B.
    KEY FINDINGS: Results showed that starvation promoted the co-localization of both GM130-positive and TGN46-positive Golgi fragments with LC3B-positive autophagosomes in H9c2 cells, HUVECs, HA-VSMCs and HEK293T cells. Transmission electron microscopy images showed that Golgi apparatus was sequestered into the autophagosomes in the starvation group. Moreover, Golgi stress inducers also facilitated the co-localization of Golgi markers and LC3B in H9c2 cells, HUVECs, HA-VSMCs and HEK293T cells. Furthermore, cardiomyocyte hypertrophy stimulators also triggered the appearance of Golgiphagy in H9c2 cells. Importantly, the co-immunoprecipitation assay indicated endogenous GOLPH3 interacted with LC3B in H9c2 cells, HUVECs, HA-VSMCs. However, knocking down GOLPH3 inhibited the Golgiphagy.
    SIGNIFICANCE: This study unveiled a new selective autophagy of the Golgi apparatus (Golgiphagy). In addition, GOLPH3 might act as a novel cargo receptor to regulate Golgiphagy. Maintaining homeostasis of the Golgi apparatus via GOLPH3-mediated autophagy was indispensable for cell survival.
    Keywords:  Autophagy; Cardiomyocytes hypertrophy; GOLPH3; Golgi apparatus; Golgi stress
  16. Aging (Albany NY). 2020 Apr 26. 12
      Stress-induced α-synuclein aggregation, especially the most toxic species (oligomers), may precede synaptic and cognitive dysfunction. Under pathological conditions, α-synuclein is degraded primarily through the autophagic/lysosomal pathway. We assessed the involvement of autophagy in α-synuclein aggregation and cognitive impairment following general anesthesia and surgical stress. Autophagy was found to be suppressed in the aged rat hippocampus after either 4-h propofol anesthesia alone or 2-h propofol anesthesia during a laparotomy surgery. This inhibition of autophagy was accompanied by profound α-synuclein oligomer aggregation and neurotransmitter imbalances in the hippocampus, along with hippocampus-dependent cognitive deficits. These events were not observed 18 weeks after propofol exposure with or without surgical stress. The pharmacological induction of autophagy using rapamycin markedly suppressed α-synuclein oligomerization, restored neurotransmitter equilibrium, and improved cognitive behavior after prolonged anesthesia or anesthesia combined with surgery. Thus, both prolonged propofol anesthesia alone and propofol anesthesia during surgery impaired autophagy, which may have induced abnormal hippocampal α-synuclein aggregation and neurobehavioral deficits in aged rats. These findings suggest that the activation of autophagy and the clearance of pathological α-synuclein oligomers may be novel strategies to ameliorate the common occurrence of postoperative cognitive dysfunction.
    Keywords:  autophagy; hippocampus; oligomerization; postoperative cognitive dysfunction (POCD); α-synuclein
  17. Int Rev Cell Mol Biol. 2020 ;pii: S1937-6448(19)30123-6. [Epub ahead of print]352 159-187
      Autophagy, the process of macromolecular degradation through the lysosome, has been extensively studied for the past decade or two. Autophagy can regulate cell death, especially apoptosis, through selective degradation of both positive and negative apoptosis regulators. However, multiple other programmed cell death pathways exist. As knowledge of these other types of cell death expand, it has been suggested that they also interact with autophagy. In this review, we discuss the molecular mechanisms that comprise three non-apoptotic forms of cell death (necroptosis, pyroptosis and ferroptosis) focusing on how the autophagy machinery regulates these different cell death mechanisms through (i) its degradative functions, i.e., true autophagy, and (ii) other non-degradative functions of the autophagy machinery such as serving as a signaling scaffold or by participating in other autophagy-independent cellular processes.
    Keywords:  Autophagy; Cell death; Ferroptosis; Necroptosis; Pyroptosis
  18. Int Rev Cell Mol Biol. 2020 ;pii: S1937-6448(20)30025-3. [Epub ahead of print]352 189-214
      Aberrant cell death signaling and oxidative stress are implicated in myriad of human pathological states such as neurodegenerative, cardiovascular, metabolic and liver diseases, as well as drug-induced toxicities. While regulated cell death and mild oxidative stress are essential during normal tissue homeostasis, deregulated signaling can trigger massive depletion in a particular cell type and/or damage tissues and impair organ function with deleterious consequences that manifest as disease states. If regeneration cannot restore tissue homeostasis, the severity of the disease correlates with the extent of cell loss. Cell death can be executed via multiple modalities such as apoptosis, necrosis, pyroptosis, necroptosis and ferroptosis, depending on cell autonomous mechanisms (e.g., reactive oxygen species production, calcium overload and altered proteostasis) and/or non-cell autonomous processes (e.g., environmental stress, irradiation, chemotherapeutic agents, inflammation and pathogens). Accordingly, the inhibition of aberrant cell death and oxidative stress together with activation of autophagy, a regulated self-degradation process, are progressively emerging as relevant cytoprotective strategies to sustain homeostasis. In this review, we summarize the current literature on the crosstalk between cellular redox state and cell fate signaling, specifically from the standpoint of autophagy and its role in the maintenance of tissue/organ homeostasis via regulating oxidative stress and the potential implications for the design of novel therapeutic strategies.
    Keywords:  Apoptosis; Autophagy; Drug discovery; Metabolism; Necrosis
  19. Br J Cancer. 2020 Apr 27.
      BACKGOUND: The mechanistic target of rapamycin complex 1 (mTORC1) is important in the development and progression of many cancers. Targeted cancer therapy using mTORC1 inhibitors is used for treatment of cancers; however, their clinical efficacies are still limited.METHODS: We recently created a new mouse model for human lymphangiosarcoma by deleting Tsc1 in endothelial cells and consequent hyper-activation of mTORC1. Using Tsc1iΔEC tumour cells from this mouse model, we assessed the efficacies of histone deacetylase (HDAC) inhibitors as anti-tumour agents for mTORC1-driven tumours.
    RESULTS: Unlike the cytostatic effect of mTORC1 inhibitors, HDAC inhibitors induced Tsc1iΔEC tumour cell death in vitro and their growth in vivo. Analysis of several HDAC inhibitors suggested stronger anti-tumour activity of class I HDAC inhibitor than class IIa or class IIb inhibitors, but these or pan HDAC inhibitor SAHA did not affect mTORC1 activation in these cells. Moreover, HDAC inhibitor-induced cell death required elevated autophagy, but was not affected by disrupting caspase-dependent apoptosis pathways. We also observed increased reactive oxygen species and endoplasmic reticulum stress in SAHA-treated tumour cells, suggesting their contribution to autophagic cell death, which were dependent on mTORC1 hyper-activation.
    CONCLUSION: These studies suggest a potential new treatment strategy for mTORC1-driven cancers like lymphangiosarcoma through an alternative mechanism.
  20. Int J Mol Sci. 2020 Apr 24. pii: E3028. [Epub ahead of print]21(8):
      Alterations in autophagy and the ubiquitin proteasome system (UPS) are commonly implicated in protein aggregation and toxicity which manifest in a number of neurological disorders. In fact, both UPS and autophagy alterations are bound to the aggregation, spreading and toxicity of the so-called prionoid proteins, including alpha synuclein (α-syn), amyloid-beta (Aβ), tau, huntingtin, superoxide dismutase-1 (SOD-1), TAR-DNA-binding protein of 43 kDa (TDP-43) and fused in sarcoma (FUS). Recent biochemical and morphological studies add to this scenario, focusing on the coordinated, either synergistic or compensatory, interplay that occurs between autophagy and the UPS. In fact, a number of biochemical pathways such as mammalian target of rapamycin (mTOR), transcription factor EB (TFEB), Bcl2-associated athanogene 1/3 (BAG3/1) and glycogen synthase kinase beta (GSk3β), which are widely explored as potential targets in neurodegenerative proteinopathies, operate at the crossroad between autophagy and UPS. These biochemical steps are key in orchestrating the specificity and magnitude of the two degradation systems for effective protein homeostasis, while intermingling with intracellular secretory/trafficking and inflammatory pathways. The findings discussed in the present manuscript are supposed to add novel viewpoints which may further enrich our insight on the complex interactions occurring between cell-clearing systems, protein misfolding and propagation. Discovering novel mechanisms enabling a cross-talk between the UPS and autophagy is expected to provide novel potential molecular targets in proteinopathies.
    Keywords:  FUS; SOD-1; TDP-43; alpha-synuclein; amyloid-beta; cell-to-cell propagation; huntingtin; neuro-inflammation; prion-like; tau
  21. Biochim Biophys Acta Mol Cell Res. 2020 Apr 22. pii: S0167-4889(20)30087-2. [Epub ahead of print] 118729
      Cereblon (CRBN), a substrate receptor for Cullin-ring E3 ubiquitin ligase (CRL), is a major target protein of immunomodulatory drugs. An earlier study demonstrated that CRBN directly interacts with the catalytic α subunit of AMP-activated protein kinase (AMPK), a master regulator of energy homeostasis, down-regulating the enzymatic activity of AMPK. However, it is not clear how CRBN modulates AMPK activity. To investigate the mechanism of CRBN-dependent AMPK inhibition, we measured protein levels of each AMPK subunit in brains, livers, lungs, hearts, spleens, skeletal muscles, testes, kidneys, and embryonic fibroblasts from wild-type and Crbn-/- mice. Protein levels and stability of the regulatory AMPKγ subunit were increased in Crbn-/- mice. Increased stability of AMPKγ in Crbn-/- MEFs was dramatically reduced by exogenous expression of Crbn. In wild-type MEFs, the proteasomal inhibitor MG132 blocked degradation of AMPKγ. We also found that CRL4CRBN directly ubiquitinated AMPKγ. Taken together, these findings suggest that CRL4CRBN regulates AMPK through ubiquitin-dependent proteasomal degradation of AMPKγ.
    Keywords:  AMP-activated protein kinase γ; Cereblon; Proteasomal degradation; Ubiquitination