bims-unfpre Biomed News
on Unfolded protein response
Issue of 2020‒01‒12
eight papers selected by
Susan Logue
University of Manitoba

  1. Elife. 2020 Jan 06. pii: e52291. [Epub ahead of print]9
    Lam M, Marsters SA, Ashkenazi A, Walter P.
      Disruption of protein folding in the endoplasmic reticulum (ER) activates the unfolded protein response (UPR)-a signaling network that ultimately determines cell fate. Initially, UPR signaling aims at cytoprotection and restoration of ER homeostasis; that failing, it drives apoptotic cell death. ER stress initiates apoptosis through intracellular activation of death receptor 5 (DR5) independent of its canonical extracellular ligand TRAIL; however, the mechanism underlying DR5 activation is unknown. In cultured human cells, we find that misfolded proteins can directly engage with DR5 in the ER-Golgi intermediate compartment, where DR5 assembles pro-apoptotic caspase 8-activating complexes. Moreover, peptides used as a proxy for exposed misfolded protein chains selectively bind to the purified DR5 ectodomain and induce its oligomerization. These findings indicate that misfolded proteins can act as ligands to activate DR5 intracellularly and promote apoptosis. We propose a model in which cells use DR5 as a terminal protein-folding checkpoint before committing to a terminal apoptotic fate.
    Keywords:  biochemistry; cell biology; chemical biology; human
  2. Front Immunol. 2019 ;10 2900
    Studencka-Turski M, Çetin G, Junker H, Ebstein F, Krüger E.
      Proteostasis is critical for cells to maintain the balance between protein synthesis, quality control, and degradation. This is particularly important for myeloid cells of the central nervous system as their immunological function relies on proper intracellular protein turnover by the ubiquitin-proteasome system. Accordingly, disruption of proteasome activity due to, e.g., loss-of-function mutations within genes encoding proteasome subunits, results in systemic autoinflammation. On the molecular level, pharmacological inhibition of proteasome results in endoplasmic reticulum (ER) stress-activated unfolded protein response (UPR) as well as an induction of type I interferons (IFN). Nevertheless, our understanding as to whether and to which extent UPR signaling regulates type I IFN response is limited. To address this issue, we have tested the effects of proteasome dysfunction upon treatment with proteasome inhibitors in primary murine microglia and microglia-like cell line BV-2. Our data show that proteasome impairment by bortezomib is a stimulus that activates all three intracellular ER-stress transducers activation transcription factor 6, protein kinase R-like endoplasmic reticulum kinase and inositol-requiring protein 1 alpha (IRE1α), causing a full activation of the UPR. We further demonstrate that impaired proteasome activity in microglia cells triggers an induction of IFNβ1 in an IRE1-dependent manner. An inhibition of the IRE1 endoribonuclease activity significantly attenuates TANK-binding kinase 1-mediated activation of type I IFN. Moreover, interfering with TANK-binding kinase 1 activity also compromised the expression of C/EBP homologous protein 10, thereby emphasizing a multilayered interplay between UPR and type IFN response pathway. Interestingly, the induced protein kinase R-like endoplasmic reticulum kinase-activation transcription factor 4-C/EBP homologous protein 10 and IRE1-X-box-binding protein 1 axes caused a significant upregulation of proinflammatory cytokine interleukin 6 expression that exacerbates STAT1/STAT3 signaling in cells with dysfunctional proteasomes. Altogether, these findings indicate that proteasome impairment disrupts ER homeostasis and triggers a complex interchange between ER-stress sensors and type I IFN signaling, thus inducing in myeloid cells a state of chronic inflammation.
    Keywords:  CANDLE/PRAAS; ONX-0914; RIDD; UPR; bortezomib; microglia; proteasome; type I IFN response
  3. Curr Cancer Drug Targets. 2020 Jan 05.
    Rozpędek W, Pytel D, Wawrzynkiewicz A, Siwecka N, Dziki A, Dziki Ł, Diehl JA, Majsterek I.
      Hypoxia may directly evoke Endoplasmic Reticulum (ER) stress conditions within cancer cells and activate the Protein kinase RNA-like endoplasmic reticulum kinase (PERK)-mediated Unfolded Protein Response (UPR) signaling pathway. Currently used anti-cancer treatment strategies are still insufficient, but the newest data has demonstrated that modulation of the PERK-dependent UPR signaling pathway may constitute a novel, ground-breaking anti-cancer treatment. The main purpose of the study was to evaluate the effectiveness of the small-molecule PERK inhibitor 42215. The study was conducted on HT-29 and CCD 841 CoN cell lines. The cytotoxicity of the investigated compound was examined via resazurin-based and lactate dehydrogenase (LDH) assays. The effect of 42215 on apoptotic cell death activation was evaluated by flow cytometry and caspase-3 activity test, whereas an influence of 42215 on cell cycle progression by flow cytometry. The level of the phosphorylated form of the eukaryotic initiation factor 2 alpha (eIF2α) was measured by the Western blot technique. 42215 proved to be selective only for HT-29 cancer cells, since it significantly inhibited HT-29 cells' viability in a dose- and time-dependent manner, evoked their apoptosis and blocked cell cycle at G2/M phase at concentration of 50 µM. Moreover, Western blot analysis showed inhibition of eIF2α phosphorylation in HT-29 cells at concentrations of 25µM and 50µM. In conclusion, PERK inhibitor 42215 may provide an innovative treatment strategy against colorectal cancer (CRC) via the activation of the pro-apoptotic branch of the PERK-mediated UPR signaling pathway.
    Keywords:  Apoptosis; Endoplasmic Reticulum stress; PERK; PERK inhibitor; Unfolded Protein Response; cancer; eIF2α
  4. J Diabetes Investig. 2020 Jan 10.
    Ishibashi T, Morita S, Kishimoto S, Uraki S, Takeshima K, Furukawa Y, Inaba H, Ariyasu H, Iwakura H, Furuta H, Nishi M, Papa FR, Akamizu T.
      AIMS/INTRODUCTION: Under irremediable endoplasmic reticulum (ER) stress, hyperactivated inositol-requiring enzyme 1α (IRE1α) triggers the terminal unfolded protein response (T-UPR), causing crucial cell dysfunction and apoptosis. We hypothesized that nicotinic acetylcholine receptor (nAChR) signaling regulates IRE1α activation to protect β cells from the T-UPR under ER stress.MATERIALS AND METHODS: The effects of nicotine on IRE1α activation and key T-UPR markers, thioredoxin-interacting protein (TXNIP) and Insulin/proinsulin, were analyzed by real time PCR and Western blotting in rat INS-1 and human EndoC-βH1 β cell lines. Doxycycline-inducible IRE1α overexpression or ER stress agents were used to induce IRE1α activation. An α7 subunit-specific nAChR agonist (PNU-282987) and siRNA for α7 subunit-specific nAChR were used to modulate nAChR signaling.
    RESULTS: Nicotine inhibits the increase in TXNIP and the decrease in Insulin 1/proinsulin expression levels induced by either forced IRE1α hyperactivation or ER stress agents. Nicotine attenuated X-box-binding protein-1 mRNA site-specific splicing and IRE1α autophosphorylation induced by ER stress. Further, PNU-282987 attenuated T-UPR induction by either forced IRE1α activation or ER stress agents. The effects of nicotine on attenuating TXNIP and preserving Insulin 1 expression levels were attenuated by pharmacological and genetical inhibition of α7 nAChR. Finally, nicotine suppressed apoptosis induced by either forced IRE1α activation or ER stress agents.
    CONCLUSIONS: Our findings suggest that nAChR signaling regulates IRE1α activation to protect β cells from the T-UPR and apoptosis under ER stress partly through α7 nAChR. Targeting nAChR signaling to inhibit the T-UPR cascade may therefore hold therapeutic promise by thwarting β cell death in diabetes.
    Keywords:  Inositol-requiring enzyme 1α; Nicotinic acetylcholine receptor; pancreatic β cell
  5. Sci Adv. 2020 Jan;6(1): eaaz1441
    Daniele JR, Higuchi-Sanabria R, Durieux J, Monshietehadi S, Ramachandran V, Tronnes SU, Kelet N, Sanchez M, Metcalf MG, Garcia G, Frankino PA, Benitez C, Zeng M, Esping DJ, Joe L, Dillin A.
      Longevity is dictated by a combination of environmental and genetic factors. One of the key mechanisms to regulate life-span extension is the induction of protein chaperones for protein homeostasis. Ectopic activation of the unfolded protein response of the endoplasmic reticulum (UPRER) specifically in neurons is sufficient to enhance organismal stress resistance and extend life span. Here, we find that this activation not only promotes chaperones but also facilitates ER restructuring and ER function. This restructuring is concomitant with lipid depletion through lipophagy. Activation of lipophagy is distinct from chaperone induction and is required for the life-span extension found in this paradigm. Last, we find that overexpression of the lipophagy component, ehbp-1, is sufficient to deplete lipids, remodel ER, and promote life span. Therefore, UPR induction in neurons triggers two distinct programs in the periphery: the proteostasis arm through protein chaperones and metabolic changes through lipid depletion mediated by EH domain binding protein 1 (EHBP-1).
  6. Cell Death Dis. 2020 Jan 06. 11(1): 17
    Wang J, Hu B, Zhao Z, Zhang H, Zhang H, Zhao Z, Ma X, Shen B, Sun B, Huang X, Hou J, Xia Q.
      Endoplasmic reticulum (ER) stress-associated cell death is prevalent in various liver diseases. However, the determinant mechanism how hepatocytes survive unresolved stress was still unclear. Interleukin-24 (IL-24) was previously found to promote ER stress-mediated cell death, and yet its expression and function in the liver remained elusive. Here we identified an antiapoptotic role of IL-24, which transiently accumulated within ER-stressed hepatocytes in a X-box binding protein 1 (XBP1)-dependent manner. Disruption of IL-24 increased cell death in the CCL4- or APAP-challenged mouse liver or Tm-treated hepatocytes. In contrast, pharmaceutical blockade of eukaryotic initiation factor 2α (eIF2α) or genetical ablation of C/EBP homologous protein (CHOP) restored hepatocyte function in the absence of IL-24. In a clinical setting, patients with acute liver failure manifested a profound decrease of hepatic IL-24 expression, which was associated with disease progression. In conclusion, intrinsic hepatocyte IL-24 maintains ER homeostasis by restricting the eIF2α-CHOP pathway-mediated stress signal, which might be exploited as a bio-index for prognosis or therapeutic intervention in patients with liver injury.
  7. J Neuropathol Exp Neurol. 2020 Jan 08. pii: nlz129. [Epub ahead of print]
    Bond S, Lopez-Lloreda C, Gannon PJ, Akay-Espinoza C, Jordan-Sciutto KL.
      The proposed molecular mechanisms underlying neurodegenerative pathogenesis are varied, precluding the development of effective therapies for these increasingly prevalent disorders. One of the most consistent observations across neurodegenerative diseases is the phosphorylation of eukaryotic initiation factor 2α (eIF2α). eIF2α is a translation initiation factor, involved in cap-dependent protein translation, which when phosphorylated causes global translation attenuation. eIF2α phosphorylation is mediated by 4 kinases, which, together with their downstream signaling cascades, constitute the integrated stress response (ISR). While the ISR is activated by stresses commonly observed in neurodegeneration, such as oxidative stress, endoplasmic reticulum stress, and inflammation, it is a canonically adaptive signaling cascade. However, chronic activation of the ISR can contribute to neurodegenerative phenotypes such as neuronal death, memory impairments, and protein aggregation via apoptotic induction and other maladaptive outcomes downstream of phospho-eIF2α-mediated translation inhibition, including neuroinflammation and altered amyloidogenic processing, plausibly in a feed-forward manner. This review examines evidence that dysregulated eIF2a phosphorylation acts as a driver of neurodegeneration, including a survey of observations of ISR signaling in human disease, inspection of the overlap between ISR signaling and neurodegenerative phenomenon, and assessment of recent encouraging findings ameliorating neurodegeneration using developing pharmacological agents which target the ISR. In doing so, gaps in the field, including crosstalk of the ISR kinases and consideration of ISR signaling in nonneuronal central nervous system cell types, are highlighted.
    Keywords:  Cell fate; Integrated stress response (ISR); Neurodegeneration; Neurodegenerative disease pathogenesis; Stress signaling; eIF2α; phosphorylation (p-eIF2α)
  8. Neuron. 2020 Jan 02. pii: S0896-6273(19)31056-6. [Epub ahead of print]
    Smith HL, Freeman OJ, Butcher AJ, Holmqvist S, Humoud I, Schätzl T, Hughes DT, Verity NC, Swinden DP, Hayes J, de Weerd L, Rowitch DH, Franklin RJM, Mallucci GR.
      Recent interest in astrocyte activation states has raised the fundamental question of how these cells, normally essential for synapse and neuronal maintenance, become pathogenic. Here, we show that activation of the unfolded protein response (UPR), specifically phosphorylated protein kinase R-like endoplasmic reticulum (ER) kinase (PERK-P) signaling-a pathway that is widely dysregulated in neurodegenerative diseases-generates a distinct reactivity state in astrocytes that alters the astrocytic secretome, leading to loss of synaptogenic function in vitro. Further, we establish that the same PERK-P-dependent astrocyte reactivity state is harmful to neurons in vivo in mice with prion neurodegeneration. Critically, targeting this signaling exclusively in astrocytes during prion disease is alone sufficient to prevent neuronal loss and significantly prolongs survival. Thus, the astrocyte reactivity state resulting from UPR over-activation is a distinct pathogenic mechanism that can by itself be effectively targeted for neuroprotection.
    Keywords:  LCN2; PERK signalling; astrocyte reactivity state; astrocytes; neurodegeneration; neuroprotection; secretome; synapse; translational neuroscience; unfolded protein response