bims-unfpre Biomed News
on Unfolded protein response
Issue of 2021‒02‒21
twelve papers selected by
Susan Logue
University of Manitoba

  1. EMBO Rep. 2021 Feb 15. e49617
      The unfolded protein response (UPR) has emerged as a central regulator of immune cell responses in several pathologic contexts including infections. However, how intracellular residing pathogens modulate the UPR in dendritic cells (DCs) and thereby affect T cell-mediated immunity remains uncharacterized. Here, we demonstrate that infection of DCs with Toxoplasma gondii (T. gondii) triggers a unique UPR signature hallmarked by the MyD88-dependent activation of the IRE1α pathway and the inhibition of the ATF6 pathway. Induction of XBP1s controls pro-inflammatory cytokine secretion in infected DCs, while IRE1α promotes MHCI antigen presentation of secreted parasite antigens. In mice, infection leads to a specific activation of the IRE1α pathway, which is restricted to the cDC1 subset. Mice deficient for IRE1α and XBP1 in DCs display a severe susceptibility to T. gondii and succumb during the acute phase of the infection. This early mortality is correlated with increased parasite burden and a defect in splenic T-cell responses. Thus, we identify the IRE1α/XBP1s branch of the UPR as a key regulator of host defense upon T. gondii infection.
    Keywords:  Toxoplasma gondii; UPR; antigen presentation; cytokines; dendritic cells
  2. Cell Mol Life Sci. 2021 Feb 18.
      Under physiological and pathological conditions, cells activate the unfolded protein response (UPR) to deal with the accumulation of unfolded or misfolded proteins in the endoplasmic reticulum. Multiple myeloma (MM) is a hematological malignancy arising from immunoglobulin-secreting plasma cells. MM cells are subject to continual ER stress and highly dependent on the UPR signaling activation due to overproduction of paraproteins. Mounting evidence suggests the close linkage between ER stress and oxidative stress, demonstrated by overlapping signaling pathways and inter-organelle communication pivotal to cell fate decision. Imbalance of intracellular homeostasis can lead to deranged control of cellular functions and engage apoptosis due to mutual activation between ER stress and reactive oxygen species generation through a self-perpetuating cycle. Here, we present accumulating evidence showing the interactive roles of redox homeostasis and proteostasis in MM pathogenesis and drug resistance, which would be helpful in elucidating the still underdefined molecular pathways linking ER stress and oxidative stress in MM. Lastly, we highlight future research directions in the development of anti-myeloma therapy, focusing particularly on targeting redox signaling and ER stress responses.
    Keywords:  Endoplasmic reticulum stress; Multiple myeloma; Oxidative stress; Reactive oxygen species; Unfolded protein response
  3. Exp Neurol. 2021 Feb 15. pii: S0014-4886(21)00053-4. [Epub ahead of print] 113648
      Mounting evidence support that glia play a key role in organismal ageing. However, the mechanisms by which glia impact ageing are not understood. One of the processes that has significant impact on the rate of ageing is the unfolded protein response. The more robust the UPR, the more the organism can counteract the effect of environmental and genetic stressors. However, how decline of cellular UPR translates into organismal ageing and eventual death is not fully understood. Here we discuss recent findings highlighting that neuropeptides released by glia act long distance to regulate ageing in C. elegans. Taking advantage of the short life span and the genetic amenability of this organism, the endoplasmic reticulum unfolded protein responses (UPRER) can be activated in C. elegans glia. This leads to cell-nonautonomous activation of the UPRER in the intestine. Activation of intestinal UPRER requires the function of genes involved in neuropeptide processing and release, suggesting that neuropeptides signal from glia to the intestine to regulate ER stress response. Importantly, the cell-nonautonomous activation of UPRER leads to extension of life span. Taken together, these data suggest that environmental and genetic factors that impact the response of glia to stress have the potential to influence organismal ageing. Further research on the specific neuropeptides involved should cast new light on the mechanism of ageing and may suggest novel anti-ageing therapies.
    Keywords:  Ageing; C. elegans; Glia; Neuropeptides; Stress; Unfolded protein response
  4. Exp Ther Med. 2021 Mar;21(3): 248
      The mismatch of oxygen supply and demand during hemorrhagic shock disturbs endoplasmic reticulum (ER) homeostasis. The resulting accumulation of unfolded proteins in the ER lumen, which is a condition that is defined as ER stress, triggers the unfolded protein response (UPR). Since the UPR influences the extent of organ damage following hemorrhagic shock/reperfusion (HS/R) and mediates the protective effects of stress preconditioning before ischemia-reperfusion injury, the current study investigated the mechanisms of ER stress preconditioning and its impact on post-hemorrhagic liver damage. Male C56BL/6-mice were injected intraperitoneally with the ER stress inductor tunicamycin (TM) or its drug vehicle 48 h prior to being subjected to a 90 min pressure-controlled hemorrhagic shock (30±5 mmHg). A period of 14 h after hemorrhagic shock induction, mice were sacrificed. Hepatocellular damage was quantified by analyzing hepatic transaminases and hematoxylin-eosin stained liver tissue sections. Additionally, the topographic expression patterns of the ER stress marker binding immunoglobulin protein (BiP), UPR signaling pathways, and the autophagy marker Beclin1 were evaluated. TM injection significantly increased BiP expression and modified the topographic expression patterns of the UPR signaling proteins. In addition, immunohistochemical analysis of Beclin1 revealed an increased pericentral staining intensity following TM pretreatment. The histologic analysis of hepatocellular damage demonstrated a significant reduction in cell death areas in HS/R+TM (P=0.024). ER stress preconditioning influences the UPR and alleviates post-hemorrhagic liver damage. The beneficial effects were, at least partially, mediated by the upregulation of BiP and autophagy induction. These results underscore the importance of the UPR in the context of HS/R and may help identify novel therapeutic targets.
    Keywords:  binding immunoglobulin protein; hemorrhage; ischemia-reperfusion injury; tunicamycin; unfolded protein response
  5. Plant Cell. 2019 May 13. 31(5): 1127-1140
      Endoplasmic reticulum (ER) stress is caused by the stress-induced accumulation of unfolded proteins in the ER. Here, we identified proteins and lipids that function downstream of the ER stress sensor INOSITOL-REQUIRING ENZYME1 (CrIRE1) that contributes to ER stress tolerance in Chlamydomonas (Chlamydomonas reinhardtii). Treatment with the ER stress inducer tunicamycin resulted in the splicing of a 32-nucleotide fragment of a basic leucine zipper 1 (bZIP1) transcription factor (CrbZIP1) mRNA by CrIRE1 that, in turn, resulted in the loss of the transmembrane domain in CrbZIP1, and the translocation of CrbZIP1 from the ER to the nucleus. Mutants deficient in CrbZIP1 failed to induce the expression of the unfolded protein response genes and grew poorly under ER stress. Levels of diacylglyceryltrimethylhomoserine (DGTS) and pinolenic acid (18:3Δ5,9,12) increased in the parental strains but decreased in the crbzip1 mutants under ER stress. A yeast one-hybrid assay revealed that CrbZIP1 activated the expression of enzymes catalyzing the biosynthesis of DGTS and pinolenic acid. Moreover, two lines harboring independent mutant alleles of Chlamydomonas desaturase (CrDES) failed to synthesize pinolenic acid and were more sensitive to ER stress than were their parental lines. Together, these results indicate that CrbZIP1 is a critical component of the ER stress response mediated by CrIRE1 in Chlamydomonas that acts via lipid remodeling.
  6. Cell Microbiol. 2021 Feb 14. e13318
      Dictyostelium discoideum Sey1 is the single ortholog of mammalian atlastin 1-3 (ATL1-3), which are large homodimeric GTPases mediating homotypic fusion of endoplasmic reticulum (ER) tubules. In this study, we generated a D. discoideum mutant strain lacking the sey1 gene and found that amoebae deleted for sey1 are enlarged, but grow and develop similarly to the parental strain. The ∆sey1 mutant amoebae showed an altered ER architecture, and the tubular ER network was partially disrupted without any major consequences for other organelles or the architecture of the secretory and endocytic pathways. Macropinocytic and phagocytic functions were preserved; however, the mutant amoebae exhibited cumulative defects in lysosomal enzymes exocytosis, intracellular proteolysis, and cell motility, resulting in impaired growth on bacterial lawns. Moreover, ∆sey1 mutant cells showed a constitutive activation of the unfolded protein response pathway (UPR), but they still readily adapted to moderate levels of ER stress, while unable to cope with prolonged stress. In D. discoideum ∆sey1 the formation of the ER-associated compartment harboring the bacterial pathogen Legionella pneumophila was also impaired. In the mutant amoebae, the ER was less efficiently recruited to the "Legionella-containing vacuole" (LCV), the expansion of the pathogen vacuole was inhibited at early stages of infection and intracellular bacterial growth was reduced. In summary, our study establishes a role of D. discoideum Sey1 in ER architecture, proteolysis, cell motility and intracellular replication of L. pneumophila. This article is protected by copyright. All rights reserved.
    Keywords:  Amoeba; Dictyostelium discoideum; Legionella pneumophila; Legionnaires' disease; atlastin; endocytic pathway; host-pathogen interaction; large GTPase; pathogen vacuole; unfolded protein response
  7. J Cell Physiol. 2021 Feb 15.
      Abnormalities of the tumor vasculature result in insufficient blood supply and development of a tumor microenvironment that is characterized by low glucose concentrations, low extracellular pH, and low oxygen tensions. We previously reported that glucose-deprived conditions induce metabolic stress and promote tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cytotoxicity. In this study, we examined whether the metabolic stress-associated endoplasmic reticulum (ER) stress response pathway plays a pivotal role in the enhancement of TRAIL cytotoxicity. We observed no significant cytotoxicity when human colorectal cancer SW48 cells were treated with various doses of TRAIL (2-100 ng/ml) for 4 h or glucose (0-25 mM) for 24 h. However, a combination of TRAIL and low glucose-induced dose-dependent apoptosis through activation of caspases (-8, -9, and -3). Studies with activating transcription factor 4 (ATF4), C/EBP-homologous protein (CHOP), p53 upregulated modulator of apoptosis (PUMA), or death receptor 5 (DR5)-deficient mouse embryonic fibroblasts or HCT116 cells suggest that the ATF4-CHOP-PUMA axis and the ATF4-CHOP-DR5 axis are involved in the combined treatment-induced apoptosis. Moreover, the combined treatment-induced apoptosis was completely suppressed in BH3 interacting-domain death agonist (Bid)- or Bcl-2-associated X protein (Bax)-deficient HCT116 cells, but not Bak-deficient HCT116 cells. Interestingly, the combined treatment-induced Bax oligomerization was suppressed in PUMA-deficient HCT116 cells. These results suggest that glucose deprivation enhances TRAIL-induced apoptosis by integrating the ATF4-CHOP-PUMA axis and the ATF4-CHOP-DR5 axis, consequently amplifying the Bid-Bax-associated mitochondria-dependent pathway.
    Keywords:  TRAIL cytotoxicity; endoplasmic reticulum stress; glucose deprivation
  8. EMBO Rep. 2021 Feb 15. e50852
      Transition from proliferative-to-invasive phenotypes promotes metastasis and therapy resistance in melanoma. Reversion of the invasive phenotype, however, is challenged by the poor understanding of mechanisms underlying its maintenance. Here, we report that the lncRNA TINCR is down-regulated in metastatic melanoma and its silencing increases the expression levels of invasive markers, in vitro migration, in vivo tumor growth, and resistance to BRAF and MEK inhibitors. The critical mediator is ATF4, a central player of the integrated stress response (ISR), which is activated in TINCR-depleted cells in the absence of starvation and eIF2α phosphorylation. TINCR depletion increases global protein synthesis and induces translational reprogramming, leading to increased translation of mRNAs encoding ATF4 and other ISR proteins. Strikingly, re-expression of TINCR in metastatic melanoma suppresses the invasive phenotype, reduces numbers of tumor-initiating cells and metastasis formation, and increases drug sensitivity. Mechanistically, TINCR interacts with mRNAs associated with the invasive phenotype, including ATF4, preventing their binding to ribosomes. Thus, TINCR is a suppressor of the melanoma invasive phenotype, which functions in nutrient-rich conditions by repressing translation of selected ISR RNAs.
    Keywords:  ATF4; integrated stress response; lncRNAs; melanoma; translational reprogramming
  9. Cell Death Dis. 2021 Feb 19. 12(2): 198
      Ferroptosis is a newly described form of regulated cell death triggered by oxidative stresses and characterized by extensive lipid peroxidation and membrane damages. The name of ferroptosis indicates that the ferroptotic death process depends on iron, but not other metals, as one of its canonical features. Here, we reported that zinc is also essential for ferroptosis in breast and renal cancer cells. Zinc chelator suppressed ferroptosis, and zinc addition promoted ferroptosis, even during iron chelation. By interrogating zinc-related genes in a genome-wide RNAi screen of ferroptosis, we identified SLC39A7, encoding ZIP7 that controls zinc transport from endoplasmic reticulum (ER) to cytosol, as a novel genetic determinant of ferroptosis. Genetic and chemical inhibition of the ZIP7 protected cells against ferroptosis, and the ferroptosis protection upon ZIP7 knockdown can be abolished by zinc supplementation. We found that the genetic and chemical inhibition of ZIP7 triggered ER stresses, including the induction of the expression of HERPUD1 and ATF3. Importantly, the knockdown of HERPUD1 abolished the ferroptosis protection phenotypes of ZIP7 inhibition. Together, we have uncovered an unexpected role of ZIP7 in ferroptosis by maintaining ER homeostasis. These findings may have therapeutic implications for human diseases involving ferroptosis and zinc dysregulations.
  10. Cell Metab. 2021 Feb 09. pii: S1550-4131(21)00013-9. [Epub ahead of print]
      The architecture of cristae provides a spatial mitochondrial organization that contains functional respiratory complexes. Several protein components including OPA1 and MICOS complex subunits organize cristae structure, but upstream regulatory mechanisms are largely unknown. Here, in vivo and in vitro reconstitution experiments show that the endoplasmic reticulum (ER) kinase PERK promotes cristae formation by increasing TOM70-assisted mitochondrial import of MIC19, a critical subunit of the MICOS complex. Cold stress or β-adrenergic stimulation activates PERK that phosphorylates O-linked N-acetylglucosamine transferase (OGT). Phosphorylated OGT glycosylates TOM70 on Ser94, enhancing MIC19 protein import into mitochondria and promoting cristae formation and respiration. In addition, PERK-activated OGT O-GlcNAcylates and attenuates CK2α activity, which mediates TOM70 Ser94 phosphorylation and decreases MIC19 mitochondrial protein import. We have identified a cold-stress inter-organelle PERK-OGT-TOM70 axis that increases cell respiration through mitochondrial protein import and subsequent cristae formation. These studies have significant implications in cellular bioenergetics and adaptations to stress conditions.
    Keywords:  MIC19; PERK-OGT axis; TOM70; brown adipocytes; cold stress; cristae biogenesis; mitochondrial protein import; respiration
  11. J Cell Mol Med. 2021 Feb 16.
      The aim of this study was to investigate how mesenchymal stromal cells (MSCs) modulate metabolic balance and attenuate hepatic lipotoxicity in the context of non-alcoholic fatty liver disease (NAFLD). In vivo, male SD rats were fed with high-fat diet (HFD) to develop NAFLD; then, they were treated twice by intravenous injections of rat bone marrow MSCs. In vitro, HepG2 cells were cocultured with MSCs by transwell and exposed to palmitic acid (PA) for 24 hours. The endoplasmic reticulum (ER) stressor thapsigargin and sarco/ER Ca2+ -ATPase (SERCA2)-specific siRNA were used to explore the regulation of ER stress by MSCs. We found that MSC administration improved hepatic steatosis, restored systemic hepatic lipid and glucose homeostasis, and inhibited hepatic ER stress in HFD-fed rats. In hepatocytes, MSCs effectively alleviated the cellular lipotoxicity. Particularly, MSCs remarkably ameliorated the ER stress and intracellular calcium homeostasis induced by either PA or thapsigargin in HepG2 cells. Additionally, long-term HFD or PA stimulation would activate pyroptosis in hepatocytes, which may contribute to the cell death and liver dysfunction during the process of NAFLD, and MSC treatment effectively ameliorates these deleterious effects. SERCA2 silencing obviously abolished the ability of MSCs against the PA-induced lipotoxicity. Conclusively, our study demonstrated that MSCs were able to ameliorate liver lipotoxicity and metabolic disturbance in the context of NAFLD, in which the regulation of ER stress and the calcium homeostasis via SERCA has played a key role.
    Keywords:  SERCA; calcium homeostasis; hepatic steatosis; insulin resistance; mesenchymal stromal cells